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A p-n heterojunction composite catalyst MoS 2 /Ni@NiO/g-C 3 N 4 was synthesized by hydrothermal method to produce H 2. The catalyst was characterized by X-ray diffraction, scanning electron microscopy, ultraviolet visible spectroscopy, photoluminescence spectrum, etc. The catalytic effect and mechanism of MoS 2 /Ni@NiO/g-C 3 N 4 were investigated. The hydrogen production rate of the composite catalyst could reach 7.98 mmol g−1 h−1, which was 5 times higher than g-C 3 N 4. It could be seen from the characterization that the specific surface area of the composite increased to 66.39 m2/g, the active sites on the surface increased. The formation of p-n heterojunction reduced the electron-hole recombination rate and improved the hydrogen production rate of the catalyst. Finally, the apparent quantum yield of MoS 2 /Ni@NiO/g-C 3 N 4 was calculated, which was 67.25%. It provided a new strategy for the preparation of highly efficient hydrogen-producing composite catalysts. • MoS 2 , Ni@NiO and g-C 3 N 4 were combined for photocatalytic hydrogen evolution for the first time. • Influence of adding ratio of substrate material toward photocatalytic hydrogen generation. • The hydrogen production rate of MoS 2 /Ni@NiO/g-C 3 N 4 composite catalyst was 7.98 mmol g−1 h−1. [ABSTRACT FROM AUTHOR]

Semiconductor-based heterostructure composites with high ionic conductivity have gained considerable attentions as potential electrolytes for low temperature solid oxide fuel cells (LT-SOFCs). Thereinto, the p-n junction is designed for the built-in electric field, thus avoiding short-circuiting occurrence and implementing fuel cell functionality. Herein, a novel strategy to construct the dual-layer electrolyte using p-type CuFeO 2 (CFO) and n-type ZnO respectively as individual layer is proposed. Electrochemical studies find that the fuel cell performance is significantly correlated with the weight ratios of CFO and ZnO phases. The device based on 3CFO-7ZnO (CFO in 30 wt% and ZnO in 70 wt%) electrolyte exhibits an open circuit voltage (OCV) of 1.06 V and a peak power density (PPD) of 557 mW cm−2 at 550 °C, apparently superior to both of the direct mixture of CFO-ZnO nanocomposite (468 mW cm−2) and single-phase ZnO electrolytes (300 mW cm−2) at the same operating temperature. Further investigations on energy band structure and rectifying characteristics related to the CFO and n-type ZnO indicate the existence of p-n junction. This work proposed a new method to design effective dual-layer semiconductor-based electrolytes for LT-SOFC. [Display omitted] • Design of dual-layer CuFeO 2 –ZnO electrolyte based on p-n heterojunction. • Energy band alignment to eliminate electronic conduction through electrolyte. • Electron blocking of ZnO layer to avoid internal short-circuiting occurrence. • Verification of p-n junction via rectifying characteristics for functionalization. [ABSTRACT FROM AUTHOR]

Development of protonic ceramic fuel cells (PCFCs) electrolyte with fast ionic conduction and high electrochemical performance at low temperature is highly desirable for the hydrogen suitable application. In this regard, semiconductor heterostructure of LSCF-CeO 2 is designed by introducing n-type CeO 2 into p-type semiconductor material La 0.8 Sr 0.2 Co 0.8 Fe 0.2 O 3-δ (LSCF) to construct a p-n heterojunction structure. This work discusses the role of semiconductor charge separation in fuel cell device on electrochemical performance by interesting physical and electrochemical characterizations in terms of energy band alignment, oxygen vacancies formation and Schottky junction. Further, the constructed LSCF-CeO 2 heterojunction composites by combining CeO 2 and LSCF with different concentrations tested the electrochemical performance as electrolyte to assemble fuel cell devices with significant power densities and high ionic conductivity of 0.11 S/cm. By comparison, it is found that the LSCF-CeO 2 heterojunction composite constructed with 20% molar ratio of CeO 2 play a better role in preventing electron transport, reflecting ionic conductivity and a pretty power output. The heterostructure electrolyte with ideal modulated energy band structure to enhance the fuel cell performance with fast ions transport. LSCF is a promising mixed ionic-electronic material, which is usually applied as cathode for its ultra-high electronic conductivity and excellent oxygen reduction reaction ability. So, pure LSCF cannot be used as electrolyte because of the possibility of short-circuiting. In this research, the seemingly "impossible" electronic conductor LSCF was applied for electrolyte material resulted from constructing a p-n heterojunction, which exhibits improved cell performance with the formation of a p-n heterojunction. The LSCF-CeO 2 interface significantly enhances the functionality as an electrolyte resulted into the formation of built-in electric field (BIEF) between p -LSCF and n-CeO 2. [Display omitted] • Modifying the properties of typical LSCF electrode by interacting via CeO 2. • Interaction of CeO 2 at LSCF can integrate the high ionic conductivity to induce considerable electrolytic functionality. • Introduction of CeO 2 into the LSCF to modulate the energy band structure. • Experimental evidence of formation of built-in electric field through the Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

Facet-specific NiCo 2 O 4 /Fe 2 O 3 p-n heterojunction with {1 1 1}-faceted NiCo 2 O 4 octahedral nanocrystals as the core and {0 0 1}-faceted Fe 2 O 3 nanorods as the shell were prepared and their triethylamine sensing performance/mechanism were systematically studied. [Display omitted] • NiCo 2 O 4 octahedral nanocrystals with {1 1 1} crystal facets were prepared. • Fe 2 O 3 nanorods with {0 0 1} crystal facets exposure were decorated on their surface. • The facet-specific NiCo 2 O 4 /Fe 2 O 3 p-n heterojunction were constructed. • The p-n heterojunction showed enhanced triethylamine sensing performance. • Sensing mechanism was systematically studied at the atomic and electronic scales. Semiconductor gas sensing materials with specific crystal facets exposure have attracted researchers' attention recently. However, related research mainly focuses on single metal oxide semiconductor. The research on crystal facets designing of semiconductor p-n heterojunction is still highly challenging. Herein, based on NiCo 2 O 4 octahedral nanocrystals with high-energy {1 1 1} crystal facets as substrate, Fe 2 O 3 nanorods with {0 0 1} crystal facets were decorated to obtain a facet-specific NiCo 2 O 4 /Fe 2 O 3 p-n heterojunction. The p-n heterojunction showed promising triethylamine sensing properties with a high response of 70 (R a /R g , 100 ppm) at 300 °C, which was about 57 and 10 times higher than that of pristine NiCo 2 O 4 and Fe 2 O 3 , respectively. Theoretical calculation suggested that the electronic coupling effect formed by d-orbitals of Co-Fe in heterojunction strengthened the influence on the orbitals of N site in triethylamine, which improved the triethylamine adsorption and interface charge transfer. The results indicate that crystal facets designing of NiCo 2 O 4 and Fe 2 O 3 can achieve synergistic optimization of surface/interface characteristics of p-n heterojunction, thereby achieving a comprehensive improvement in gas sensing performance. This study not only provides a high performance triethylamine sensing material, but also greatly enriches the gas sensing mechanism of p-n heterojunction at the atomic and electronic levels. [ABSTRACT FROM AUTHOR]

Herein, NiO cubes with {100} facets or NiO trapezohedrons with {311} facets modified graphite carbon nitride (g-C3N4) nanoparticles acidified by HCl (HCN) were fabricated to form a p-n heterojunction (NiO/HCN) for the first time. These were further used for the degradation of rhodamine B (RhB) in water. 8-{100}NiO/HCN exhibited the highest degradation efficiency of 98.56% in just 60 min within peroxymonosulfate (PMS) under visible light. It was 2.51% higher than that of 8-{311} NiO/HCN. A series of characterization and experimental results showed that introducing {100} NiO could improve both the photocatalysis and PMS activation efficiency of the g-C3N4 compared with {311} NiO. The influence of environmental parameters on RhB degradation was systematically studied as well. Stability experiments demonstrated that 8-{100}NiO/HCN maintained high catalytic performance over a period of 10 h. The degradation mechanism behind PMS activation under visible light involved several factors: the unique micron-nano interface structure, electron (e-) transfer between NiO and g-C3N4, as well as effective facilitation of PMS activation by Ni2+. These factors led to the formation of singlet oxygen (1O2), which contributed significantly to RhB degradation. Overall, this work highlights how facet design can be utilized in metal oxide cocatalysts to improve photocatalytic degradation performance. [ABSTRACT FROM AUTHOR]

This study used an NH4Cl-induced low temperatures second-calcination approach to create a nitrogen-rich g-C3N4 sheet that was then used to support heterometallic spinel ZnCo2O4 nanoparticles. The as-prepared p–n heterojunction ZnCo2O4/nitrogen-rich g-C3N4 sheet was used as visible light-induced photocatalysts for the photodegradation of p-Nitrophenol. The photocatalysts were analyzed using a variety of methods, including XRD, FTIR, FE-SEM, TEM, PL, BET, and UV–Vis DRS. The combination of the ZnCo2O4 nanoparticles and the nitrogen-rich g-C3N4 sheet produces a large number of active sites that increase the absorption of visible light and further improve the photocatalytic activity. The ZnCo2O4/nitrogen-rich g-C3N4 sheet that was produced showed more photocatalytic activity under UV–Visible light than ZnCo2O4/g-C3N4, whereas the usage of nitrogen-rich g-C3N4 sheet considerably increases the reaction to visible light and accelerates carrier transfer. This study could offer a fresh method for creating artificial photocatalytic devices with excellent charge transfer efficiency. [ABSTRACT FROM AUTHOR]

A highly sensitive ammonia-gas sensor based on a tungsten trioxide and polypyrrole (WO3/PPy) nanocomposite synthesized using pulsed-laser deposition (PLD) and matrix-assisted pulsed-laser evaporation (MAPLE) is presented in this study. The WO3/PPy nanocomposite is prepared through a layer-by-layer alternate deposition of the PPy thin layer on the WO3 mesoporous layer. Extensive characterization using X-ray diffraction, FTIR and Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle are carried out on the as-prepared layers. The gas-sensing properties of the WO3/PPy nanocomposite layers are systematically investigated upon exposure to ammonia gas. The results demonstrate that the WO3/PPy nanocomposite sensor exhibits a lower detection limit, higher response, faster response/recovery time, and exceptional repeatability compared to the pure PPy and WO3 counterparts. The significant improvement in gas-sensing properties observed in the WO3/PPy nanocomposite layer can be attributed to the distinctive interactions occurring at the p–n heterojunction established between the n-type WO3 and p-type PPy. Additionally, the enhanced surface area of the WO3/PPy nanocomposite, achieved through the PLD and MAPLE synthesis techniques, contributes to its exceptional gas-sensing performance. [ABSTRACT FROM AUTHOR]

Addressing the challenges associated with the highly exothermic nature of CO2 methanation, there is considerable interest in innovative catalyst designs on structural metallic supports. One promising solution in this regard involves thin films containing cobalt oxide within a carbon matrix, fabricated using the cold plasma deposition method (PECVD). The objective of this study was to search for a relationship between the molecular structure, nanostructure, and electronic structure of such films and their catalytic activity. The investigations employed various techniques, including X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), X-ray diffraction (XRD), UV-VIS absorption, and catalytic tests in the CO2 methanation process. Three types of films were tested: untreated as-deposited (ad-CoO), thermally post-treated (TT-CoO), and argon plasma post-treated (PT-CoO) films. Among these, TT-CoO exhibited the most favorable catalytic properties, demonstrating a CO2 conversion rate of 83%, CH4 selectivity of 98% at 400 °C, and stability during the catalytic process. This superior performance was attributed to the formation of nanoscale heterojunctions in the TT-CoO film, where p-type CoO nanocrystallites interacted with the n-type carbon matrix. This work provides compelling evidence highlighting the key role of nanoscale heterojunctions in shaping the properties of nanocatalysts in thermal catalysis. These findings suggest promising prospects for designing new catalytic systems by manipulating interactions at the nanoscale. [ABSTRACT FROM AUTHOR]

Constructing heterostructures is a promising strategy to improve the photoelectrochemical (PEC) performance of photoanodes in PEC water‐splitting systems. The effect on PEC performance is dependent on the deposition conditions of the overlayer in the heterostructured photoanode. Herein, the deposition condition of the antimony selenide (Sb2Se3) overlayer by adjusting the duty cycle and cycle number during pulse‐reverse electrodeposition. This aims to assess its impact on the PEC characteristics of the Sb2Se3 overlayered titanium dioxide (Sb2Se3/TiO2) nanotube photoanode. Adequate pulse‐off time in the duty cycle ensures sufficient permeation of deposition electrolyte into the inner wall of TiO2 nanotube, leading to uniform Sb2Se3 deposition. On the other hand, an excessive cycle number negatively affects PEC performance, as Sb2Se3 agglomeration blocks the pores of the TiO2 nanotube. Consequently, the Sb2Se3/TiO2 nanotube photoanode, when fabricated with the optimal pulse‐off time and cycle number, exhibits enhanced PEC performance. This is due to efficient charge transfer/separation facilitated by the p–n heterojunction and improved light absorption. These insights offer valuable guidance in choosing the appropriate fabrication processes for heterostructured photoanodes in efficient PEC water‐splitting systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Type-II p-n heterojunction of Cu 2 O/g-C 3 N 4 as bifunctional electro and photo catalyst. • Exhibits lower overpotential of 47 and 72 mVdec-1 for the HER and OER reactions, with 81% of faradaic efficiency. • Photocatalytic H 2 evolution of 3492 µmol g cat - 1 with TEOA as sacrificial agent, with AQY of 18%. • Water splitting is induced by the transfer of photogenerated electrons from p-type Cu 2 O to n -type g-C 3 N 4. One of the most efficient ways for the photogenerated charge carriers is by the development of heterojunction between p-type and n -type semiconductors, which creates an interfacial charge transfer between two semiconductors. By enhancing the bifunctional characteristics for hydrogen generation via photocatalytic and electrocatalytic water splitting reaction, we report the type-II Cu 2 O/g-C 3 N 4 heterostructure in this article. Due to significantly increased catalytically active sites for the hydrogen evolution reaction (HER) reaction during electrocatalysis and decreased charge transfer resistance, the as-prepared heterostructure exhibits a lower overpotential of 47 and 72 mVdec-1 for the HER and oxygen evolution reactions (OER), respectively, when compared to alone g-C 3 N 4. In addition, Cu 2 O/g-C 3 N 4 heterostructures have a higher photocatalytic hydrogen evolution of 3492 µmol g cat - 1 in the presence of Triethanolamine as a sacrificial agent, which is nearly 2-fold times greater than g-C 3 N 4 (1818 µmol g cat - 1 ) after 5 h of continuous light-irradiation. Moreover, produced heterostructure exhibits 81% of Faradaic efficiency and 18% of apparent quantum yield. This work successfully explains how the rise in water splitting is induced by the transfer of photogenerated electrons in a cascade way from p-type Cu 2 O to the n -type g-C 3 N 4 using density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

By substituting Zn1-xMgxO (ZMO) for the conventional CdS buffer layer, the CZTSSe solar cells with the efficiency of 11.2% are obtained herein, which can be attributed to the conduction band regulation in the heterojunction. An appropriate conduction band offset (CBO) value can effectively reduce nonradiative recombination loss of charge carriers at the interface, thereby improving the open-circuit voltage (Voc). Herein, ZMO buffer layer with the optical bandgap ranging from 3.34 to 3.90 eV is applied to enhance the CBO in the heterojunction from 0.14 to 0.72 eV. The ZMO-buffered solar cells exhibit higher Voc and shortcurrent density (Jsc) compared to CdS-buffered cells. The optimal efficiency of 11.2% is obtained in CZTSSe solar cell with the CBO of 0.27 eV, Jsc of 39.0 mA cm-2, fill factor of 69.6%, and Voc of 412 mV. [ABSTRACT FROM AUTHOR]

The synergism of multi-electric field modulation and interfacial chemical bond bridging expedites the vectorial charge separation and migration kinetic for efficient photocatalysis over S O bonded 0D Ag 2 S/2D Bi 4 TaO 8 Cl p-n oriented heterojunction. [Display omitted] • S O bonded 0D Ag 2 S/2D Bi 4 TaO 8 Cl p-n oriented heterostructure is constructed. • Double inner electric fields deliver powerful driving forces for charge separation. • Interfacial S O bond serves as atomic-level channel for promoting charge transfer. • Oriented heterojunction shows brilliant redox activity for TC and Cr(VI) removal. • Detailed photocatalytic mechanisms, degradation pathway and toxicity were proposed. Heterojunctions have been proved to be the promising photocatalysts for hazardous contaminants removal, but the inferior interfacial contact, low carrier mobility and random carrier diffusion seriously hamper the photoactivity improvement of the conventional heterojunctions. Herein, S O chemically bonded p-n oriented heterostructure is fabricated via selectively anchoring of p-type Ag 2 S nanoparticles on the lateral facet of n -type Bi 4 TaO 8 Cl nanosheet. Such a p-n heterojunction engineering on specific facet of Bi 4 TaO 8 Cl semiconductor derives ingenious double internal electric field (IEF), which not only effectively creates the spatially separated oxidation and reduction sites, but also delivers the powerful driving forces for impactful spatial directed photocarrier transfer along the cascade path. Additionally, our experimental and theoretical analyses jointly signify that the interfacial S O bond could serve as an efficient atomic-level interfacial channel, which is conducive to encouraging the vectorial charge separation and migration kinetic. As a result, the Ag 2 S/Bi 4 TaO 8 Cl oriented heterojunction exhibits significantly enhanced visible light driven photocatalytic redox ability for tetracycline oxidation and hexavalent chromium reduction than those of single component and the traditional random/mixed heterojunctions. This study could provide a deeper insight into the synergistic effects of multi-IEF modulation and interfacial chemical bond bridging on optimizing the photogenerated carrier behaviors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The BEF created by the charge transfer facilitates the transfer of the charge. • Regions with opposite charges play different roles. • The transformation of active center in CoP-Nb 2 O 5 is observed. • The hierarchical structure of the catalysts promotes the diffusion of electrolyte. Studying interfacial charge transfer is of great significance for the preparation of electrocatalysts with high activity for the hydrogen evolution reaction (HER). Particularly, exploring the in-depth catalytic mechanisms and facile fabrication methods of narrow bandgap metal phosphides remains worthwhile. This work successfully combined catalytically inert n-type Nb 2 O 5 with p-type CoP to prepare a p-n heterojunction (CoP-Nb 2 O 5). The self-supporting heterojunction was fabricated by gas-phase phosphorization of the Co(OH) 2 -Nb 2 O 5 precursor obtained through hydrothermal-electrodeposition strategy. By analyzing the electronic and band structures of CoP and Nb 2 O 5 , it was found that there exists a built-in electric field (BEF) in the heterojunction. This BEF can modulate the electronic structure of CoP at the interface, enhance its intrinsic activity and accelerate charge migration. The subsequent experimental results also demonstrate that Nb 2 O 5 can significantly enhance the activity and stability of CoP. Our findings can serve as a novel perspective on the application of p-n heterojunction in the field of energy storage and conversion. [ABSTRACT FROM AUTHOR]

Semiconductor p‐n heterojunctions are important building blocks for modern electronic and photonic devices. Further combining semiconductor p‐n heterojunctions with light and electrolyte environment, interesting photoelectrochemical (PEC) phenomena can occur, which enriches the design principles of multifunctional devices. In fact, recent years have witnessed the emergence of PEC‐type photonic devices. For PEC‐type photonic devices, a key to realize multifunctionality is to control the photocurrent polarity of the photoelectrode. In this study, an abnormal photocurrent is reported from p‐InGaN/n‐GaN nanowire heterojunctions under a blue light illumination: although n‐GaN is transparent to the blue light (and thus optical absorption mainly occurs in p‐InGaN) and p‐InGaN in principle can only give negative PEC photocurrent, the detailed experiments show that positive PEC photocurrent can be generated from the p‐InGaN segment due to the existence of the built‐in electric field at the p‐n junction. This study shows a new route to control the photocurrent polarity in a semiconductor p‐n heterojunction photoelectrode. This unveiled role of the built‐in electric field is expected to impact the design of emerging PEC‐type photonic devices, as well as other novel photonic and electronic devices based on semiconductor nanowire p‐n heterojunctions. [ABSTRACT FROM AUTHOR]

Abstract In recent years, metal compound‐based heterojunctions have received increasing attention from researchers as a candidate anode for lithium/sodium‐ion batteries, because heterojunction anodes possess unique interfaces, robust architectures, and synergistic effects, thus promoting Li/Na ions storage and accelerating ions/electrons transport. Exhilaratingly, the development of heterostructures has made rapid progress in the field of energy storage, greatly encouraging the industrialization of high energy and power density Li/Na ion batteries. However, there are few in‐detail and in‐depth reviews on the energy storage mechanism, synthesis routes, characterization methods and electrochemical performance of metal compound‐based heterojunction anodes. Herein, a deeper understanding of the correlation between the building blocks of heterojunctions and their enhanced electrochemical behaviors are summarized. Furthermore, various synthesis routes and characterization methods for heterostructure anodes are roundly reviewed. Finally, challenges and perspectives of heterojunction anodes in energy storage are presented in this work.

This review critically examines the progress and challenges in the field of nanostructured tungsten oxide (WO3) gas sensors. It delves into the significant advancements achieved through nanostructuring and composite formation of WO3, which have markedly improved sensor sensitivity for gases like NO2, NH3, and VOCs, achieving detection limits in the ppb range. The review systematically explores various innovative approaches, such as doping WO3 with transition metals, creating heterojunctions with materials like CuO and graphene, and employing machine learning models to optimize sensor configurations. The challenges facing WO3 sensors are also thoroughly examined. Key issues include cross-sensitivity to different gases, particularly at higher temperatures, and long-term stability affected by factors like grain growth and volatility of dopants. The review assesses potential solutions to these challenges, including statistical analysis of sensor arrays, surface functionalization, and the use of novel nanostructures for enhanced performance and selectivity. In addition, the review discusses the impact of ambient humidity on sensor performance and the current strategies to mitigate it, such as composite materials with humidity shielding effects and surface functionalization with hydrophobic groups. The need for high operating temperatures, leading to higher power consumption, is also addressed, along with possible solutions like the use of advanced materials and new transduction principles to lower temperature requirements. The review concludes by highlighting the necessity for a multidisciplinary approach in future research. This approach should combine materials synthesis, device engineering, and data science to develop the next generation of WO3 sensors with enhanced sensitivity, ultrafast response rates, and improved portability. The integration of machine learning and IoT connectivity is posited as a key driver for new applications in areas like personal exposure monitoring, wearable diagnostics, and smart city networks, underlining WO3's potential as a robust gas sensing material in future technological advancements.

Abstract Semiconductor p‐n heterojunctions are important building blocks for modern electronic and photonic devices. Further combining semiconductor p‐n heterojunctions with light and electrolyte environment, interesting photoelectrochemical (PEC) phenomena can occur, which enriches the design principles of multifunctional devices. In fact, recent years have witnessed the emergence of PEC‐type photonic devices. For PEC‐type photonic devices, a key to realize multifunctionality is to control the photocurrent polarity of the photoelectrode. In this study, an abnormal photocurrent is reported from p‐InGaN/n‐GaN nanowire heterojunctions under a blue light illumination: although n‐GaN is transparent to the blue light (and thus optical absorption mainly occurs in p‐InGaN) and p‐InGaN in principle can only give negative PEC photocurrent, the detailed experiments show that positive PEC photocurrent can be generated from the p‐InGaN segment due to the existence of the built‐in electric field at the p‐n junction. This study shows a new route to control the photocurrent polarity in a semiconductor p‐n heterojunction photoelectrode. This unveiled role of the built‐in electric field is expected to impact the design of emerging PEC‐type photonic devices, as well as other novel photonic and electronic devices based on semiconductor nanowire p‐n heterojunctions.

Cu2ZnSn(S,Se)4 (CZTSSe) solar cells, composed of earth‐abundant materials, face challenges in achieving high power conversion efficiency (PCE) due to non‐radiative recombination. The limitations primarily stem from the prevalence of CuZn‐related and SnZn‐related defects in the bulk of the absorber and at the heterojunction interface region. To overcome these challenges, a dual treatment approach is proposed that involves Ag‐alloying in the bulk and Al2O3 atomic layer deposition (ALD) process at the p–n interface. Comprehensive characterizations of the fabricated devices reveal that Ag‐alloying leads to a substantial reduction in deep defects within the bulk, while Al2O3 ALD process facilitates the formation of a well‐defined p–n interface region, along with the defect passivation. This synergetic effect enables PCE enhancement accompanied by the improvements of all device parameters. Notably, devices subjected to the additional Al2O3 ALD process exhibit a substantial improvement in fill factor, which is found to be consistent with a reduced element intermixing width at the p–n heterojunction region. Due to improvements in both the bulk absorber and the heterojunction, the highest PCE of 13.33% is achieved without an anti‐reflection coating. [ABSTRACT FROM AUTHOR]

Nanostructured hematite (α-Fe2O3) shows promise as a semiconductor for photoelectrochemical (PEC) water oxidation. However, it suffers from inadequate charge separation, limited hole-collection efficiency and sluggish kinetics. Herein, a nanotubular Fe2O3/Fe3O4 p–n heterojunction is prepared via electrochemical anodization to in situ construct an internal electric field (IEF) that facilitates charge separation from photoactive hematite. Additionally, In2O3 clusters are introduced to form a second IEF with dual-phase iron oxides, exploiting their Fermi level difference. The unique configuration of the dual IEFs in a novel tandem way synergistically promotes charge carrier separation/migration, enhancing PEC performance. Specifically, the 1st IEF between Fe2O3 and Fe3O4 accelerates electron migration from Fe3O4 to Fe2O3 (with holes transporting in the opposite direction), while the 2nd IEF at the In2O3 and Fe2O3/Fe3O4 interface drives holes towards the In2O3 surface, enhancing the hole-collection efficiency. The composite photoanode achieves a state-of-the-art current density of 11.5 mA cm−2 at 1.55 VRHE and a superior applied bias photon-to-current efficiency of 0.44% at 0.95 V. DFT calculations reveal that In2O3 induces an electron-deficient surface, creating favorable adsorption sites for oppositely charged key intermediates (*OOH). This work presents a novel approach for modulating reaction kinetics via the construction of tandem IEFs and holds great significance for the rational design of efficient PEC catalysts. [ABSTRACT FROM AUTHOR]

Industrial effluents are a leading major threat for water contamination, subsequently which results in severe health associated risks. Hence, purifying wastewater before releasing into the water resources is essential to avoid contamination. In this study, ZnO/Cu-DPA nano-composites were prepared by altering the percentage of Cu-DPA (20%, 30%, 40%, and 50% which are denoted to be ZnO/20%Cu-DPA, ZnO/30%Cu-DPA, ZnO/40%Cu-DPA and ZnO/50%Cu-DPA) using a simple mechanical grinding process. Several spectroscopic studies were employed such as electron paramagnetic analysis (EPR), powdered X-ray diffractometer (PXRD), UV–Vis absorbance spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscope to characterize these nano-composites. The photo-catalytic activities of the prepared nano-composites were studied by degrading MB under visible light irradiation. ZnO, ZnO/20%Cu-DPA, ZnO/30%Cu-DPA, ZnO/40%Cu-DPA and ZnO/50%Cu-DPA degradation efficiencies were determined to be 71.8, 78.5, 77.1, and 66.1%, respectively. Among the composite catalysts, the ZnO/20%Cu-DPA coupled system are demonstrated the best efficiency (87%) for photo-degradation of MB within 80 min when exposed to visible light. The ZnO/Cu-DPA nano-composites had a greater MB photodegradation efficiency than pristine ZnO owing to p-n heterojunction in the linked system. Under visible light irradiation, the ZnO/20%Cu-DPA catalysed the conversion of dissolved O2 to hydroxyl radicals (OH·), triggering the reduction of MB. This suggests that ·OH is the primary specific active radical involved in the photo-catalytic decomposition of MB. Furthermore, EPR analysis indicates the existence of ·OH in the photo-catalytic system. The proposed nano-composites (ZnO/20%Cu-DPA) reusability was investigated across three cycles as the most efficient photo-catalyst. The results show that, the ZnO/Cu-DPA nano-catalyst is a potential candidate for the remediation of dirty water. [ABSTRACT FROM AUTHOR]

[Display omitted] Hollow structure hybrids have gained considerable attention for their ability to reduce CO 2 owing to their rich active sites, high gas adsorption ability, and excellent light utilization capacity. Herein, a template-engaged strategy was provided to fabricate copper sulphide@cerium dioxide (CuS@CeO 2) p-n heterojunction hollow cube photocatalysts using Cu 2 O cubes as a sacrificial template. The sequential steps of loading of CeO 2 nanolayer, sulfidation, and etching reaction facilitate the formation of CuS@CeO 2 p-n heterojunction hollow cubes. Compared with the single CuS, CeO 2 , and their physical mixture, the CuS@CeO 2 p-n heterojunction hollow cube photocatalyst expresses a higher performance toward photocatalytic CO 2 reduction under solid–gas reaction conditions due to the faster separation of photogenerated charges. The further enhanced performance of CuS@CeO 2 p-n heterojunction hollow cubes was achieved by decorating pt nanoparticles due to the fact that Pt nanoparticles had a high electron affinity and CO 2 adsorption capacity, and the highest CO and CH 4 yields of the optimized hybrid reached 195.8 μmol g-1 h−1 and 19.96 μmol g-1 h−1, respectively. This work might provide a strategy for designing and synthesizing efficient hollow heterostructured photocatalysts for solar energy conversion and utilization. [ABSTRACT FROM AUTHOR]

Herein, a p–n GaN/AlN heterojunction in a piezoelectric semiconductor (PSC) composite fiber driven by dynamic magnetic loads is studied. The numerical results of nonlinear dynamic responses of a composite p–n heterojunction subjected to a time‐harmonic magnetic load and a pulse magnetic load are obtained by the finite‐element method, respectively. The effects of different magnetic loads on the I–V curve and piezoelectric behavior of a composite p–n heterojunction are investigated. Numerical results show that when driven by uniformly dynamic magnetic loads, the electromechanical fields show significant asymmetry due to electric nonlinearity. The time‐harmonic magnetic loads drive the round‐trip motion of electrons and holes, and the dynamic electric behaviors driven by pulsed magnetic loads are nonlinear pulse motions. Further analysis of the p–n heterojunction subjected to the bias voltage shows that positive magnetic loads increase the depletion layer's width but decrease the carrier concentration. The results presented in this study have a referential significance to contactless performance tuning of a PSC heterojunction structure and new‐generation piezotronic devices. [ABSTRACT FROM AUTHOR]

This study reports a novel Ni(OH)2/Co3O4 heterostructured nanomaterial synthesized through a simple two-step hydrothermal method combined with subsequent heat treatment. The Ni(OH)2/Co3O4 heterostructured nanomaterial showed excellent performance in the detection of xylene gas. XRD, SEM, and EDS characterized the crystal structure, microstructure, and composition elements of Co3O4 and Ni(OH)2/Co3O4, and the gas sensing properties of the Co3O4 sensor and Ni(OH)2/Co3O4 sensor were systematically tested. The test results indicate the Ni(OH)2/Co3O4 sensor has an optimal operating temperature of 175 °C, which is 10 °C lower than that of the Co3O4 sensor; has a response of 14.1 to 100 ppm xylene, which is 7-fold higher than that of the Co3O4 sensor; reduces the detection limit of xylene from 2 ppm to 100 ppb; and has at least a 4-fold higher response to xylene than other gases. The Ni(OH)2/Co3O4 nanocomposite exerts the excellent catalytic performance of two-dimensional nanomaterial Ni(OH)2, solves the deficiency in the electrical conductivity of Ni(OH)2 materials, and realizes the outstanding sensing performance of xylene, while the construction of the p–n heterojunction between Ni(OH)2 and Co3O4 also improves the sensing performance of the material. This study provides a strategy for designing high-performance xylene gas sensors using two-dimensional Ni(OH)2 materials. [ABSTRACT FROM AUTHOR]

Photocatalytic conversion of H2O and CO2 into solar fuels is considered to be a green and renewable technology while photocatalytic performance is hampered by the severe recombination of photogenerated electron–hole pairs. Drawing inspiration from the concepts of the electrons transfer layer (ETL) and the holes transfer layer (HTL) in perovskite solar cells, a multicomponent photocatalyst SrTiO3/NiO/NiS that incorporates p–n heterojunction and Schottky junction is constructed for converting solar energy into easily storable solar fuels. The NiS and NiO play the roles analogy to the ETL and the HTL which accomplishes the reverse migration of electrons and holes, accordingly, SrTiO3/NiO/NiS exhibits a noticeable enhancement in photocatalytic performance. However, the lack of direct observation of charge transfer pathways in complex multicomponent photocatalysts makes it challenging to thoroughly investigate their catalytic mechanisms. Herein, the in situ irradiation X‐ray photoelectron spectroscopy (ISI–XPS) is employed to track photogenerated charges migration pathways between microscopic heterogeneous interfaces, thereby providing a comprehensive elucidation of the catalytic mechanism and heterojunction formation process by integrating the photoelectrochemical tests. This study not only serves as compelling evidence for the capability of ISI–XPS in directly and accurately tracking charge transfer pathways but also as an intriguing highlight within the catalyst design strategy. [ABSTRACT FROM AUTHOR]

Emerging semiconducting materials show considerable promise for application in the development of next‐generation optoelectronic devices. In particular, broadband light detection is crucial in various applications, including multispectral imaging and cognition. Therefore, tuning the physical properties of semiconductors and thereby building an efficient heterojunction are important for achieving a high‐performance photodetection device. In this study, a heavy p‐type colloidal quantum dot (CQD) is synthesized through solution‐based sulfurization. The resulting cubic‐shaped CQD exhibits broadband and strong absorption, which enable its broadband absorption. Further, a multidimensional 0D‐2D heterojunction is developed using p‐type CQD and n‐type tungsten disulfide (WS2). This efficient p‐n junction is operated as a fully self‐powered optical sensor and phototransistor under various light illumination conditions. Under the self‐powered condition, the CQD/WS2 heterojunction device exhibits 440‐ and 200‐fold‐higher responsivity and detectivity, respectively, than pristine WS2. [ABSTRACT FROM AUTHOR]

β‐Ga2O3‐based semiconductor devices are expected to have significantly improved high‐power and high‐temperature performance due to its ultrawide bandgap of close to 5 eV. However, the high‐temperature operation of these ultrawide‐bandgap devices is usually limited by the relatively low 1–2 eV built‐in potential at the Schottky barrier with most high‐work‐function metals. Herein, heterojunction p‐NiO/n‐β‐Ga2O3 diodes fabrication and optimization for high‐temperature device applications are reported, demonstrating a current rectification ratio (ION/IOFF) of more than 106 at 410 °C. The NiO heterojunction diode can achieve higher turn‐on (VON) voltage and lower reverse leakage current compared to the Ni‐based Schottky diode fabricated on the same single‐crystal β‐Ga2O3 substrate, despite charge transport dominated by interfacial recombination. Electrical characterization and device modeling show that these advantages are due to a higher built‐in potential and additional band offset. These results suggest that heterojunction p–n diodes based on β‐Ga2O3 can significantly improve high‐temperature electronic device and sensor performance. [ABSTRACT FROM AUTHOR]

Herein, a cobalt oxide/tungsten oxide (Co3O4/WO3) p–n heterojunction for NOx detection is developed and optimized. Field‐emission scanning electron microscopy shows that the WO3 nanorods are embellished with Co3O4 nanostructure. X‐ray photoelectron spectroscopy reveals the presence of oxygen vacancy on the Co3O4 coupled with WO3 heterojunction. Compared to bare WO3 and pure Co3O4, the Co3O4/WO3 heterojunction sensor shows significant sensitivity to NOx at 200 °C. The sensor exhibits higher linearity from 0.4 to 10 ppm of NOx, with a sensing response of 4.4–93%. The NOx sensitivity of the Co3O4/WO3 heterojunction sensor is ninefold higher than that of the pure WO3 sensor. Even in a high humidity (84%) environment, the Co3O4/WO3 heterojunction sensor demonstrates high NOx sensitivity. The sensor maintains remarkable stability measured for up to 4 weeks. The possible NOx sensing mechanism of the Co3O4/WO3 heterojunction is additionally discussed. [ABSTRACT FROM AUTHOR]

Over a decade, the application of p–n heterojunction-based sensing garnered tremendous interest in the domain of gas sensors. This interest is mainly attributed to the exceptional electronic band alignment of the constituent materials and their unparalleled features. This includes the provision of a greater number of gas interaction sites with the analyte gas molecules, superior charge transport, and decreased operational temperature of the sensor. Herein, we synthesized p-type cobalt oxide/n-type tin oxide (p-Co3O4/n-SnO2) heterojunction by a simple hydrothermal method. The molar ratios of Sn were varied with three different concentrations (10, 20, and 30%). The structural, morphological, chemical compositions, and specific surface area of the as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), Brunauer–Emmett–Teller (BET), and X-ray photoelectron spectroscopy (XPS) analyses. The formation of the nanostructured heterojunction between Co3O4 and SnO2 was confirmed with XPS and HR-TEM results. The high surface area and oxygen vacancy of the prepared Co3O4/SnO2 samples were evident from the BET and XPS analyses. The gas selectivity of the prepared samples was evaluated against nitrogen dioxide, hydrogen sulfide, ammonia, sulfur dioxide, nitrous oxide, and carbon dioxide. The prepared 10% Co3O4/SnO2 nanostructured sensor exhibited the maximum response toward 100 ppm of NO2 at a low operating temperature of 150 °C. Moreover, the proposed sensor exhibited a higher band bending of about 0.15 eV. The enhanced gas-sensing performance of the 10% Co3O4/SnO2 sensor with a low operating temperature is the result of the depletion region formed at the interface of Co3O4/SnO2, high surface area, and a large number of oxygen vacancies of the heterojunction samples. This approach paves the way for a plausible application of the Co3O4/SnO2 heterojunction for monitoring the NO2 gas in atmospheric air. [ABSTRACT FROM AUTHOR]

In this paper, the development of a conductometric ethanol sensor based on Fe2O3/Co3O4 nano-heterostructures, synthesized by sol–gel auto combustion reaction method, is reported. The as-synthesized composite nanoparticles with different Fe2O3/Co3O4 molar ratio were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectra (EDX), and diffuse reflectance spectroscopy (DRS). The electrical and ethanol sensing properties of the Fe2O3/Co3O4 nano-heterostructures were investigated. The results reveal that, when operated at the optimal working temperature of 250 ℃, the Fe2O3/Co3O4 (0.6:1 molar ratio) based sensor displays significantly improved ethanol sensing ability compared to pristine Co3O4. Good sensitivity, short response/recovery time, repeatability, and selectivity are the distinctive characteristics of the sensor developed. The improved ethanol sensing performances are attributed to the presence of p-n heterojunction in the Fe2O3/Co3O4 nano-heterostructures synthesized. [ABSTRACT FROM AUTHOR]

In this work, p-type cuprous oxide (Cu2O) films grown on beta gallium oxide (β-Ga2O3) substrates by magnetron sputtering were reported. The resulting vertical Cu2O/β-Ga2O3 heterojunction p–n diodes demonstrated superior performance compared to devices fabricated with polycrystalline Cu2O thin films. Meanwhile, analysis of the discrepancies between the built-in potential and turn-on voltage revealed diverse carrier transport mechanisms in the fabricated devices. Numerical fitting of the forward J–V characteristics further discerned that distinct carrier transport mechanisms dominated under various bias voltages or temperature conditions. At 300 K, trap-assisted tunneling dominates the regime because of the presence of defects in β-Ga2O3 or Cu2O. While the bias voltage is low, the polycrystalline nature of the films formed at room temperature leads to the prevalence of grain boundaries as the primary source of interface-type defects at the Cu2O/β-Ga2O3 interface. Consequently, the dominant mechanism governing carrier transport is interface recombination. As the temperature increases, however, thermionic emission becomes more important. This study presents an opportunity for further investigation into the epitaxial growth of Cu2O and provides insights into the carrier transport mechanism of β-Ga2O3-based heterojunctions. [ABSTRACT FROM AUTHOR]

The goal of the current research was to develop CuO-ZnO heterojunction capable of detecting NO2 gas at room temperature. Pure CuO and CuO-ZnO composite samples were developed by changing the weight percentage of CuO and ZnO using a simple precipitation method and nominated as CZ0, CZ1, CZ2 and CZ3. Structural, optical and morphological properties of pristine CuO and heterojunctions were studied using XRD, FE-SEM, BET, XPS, FTIR and PL. Investigation of gas sensing properties revealed that the CZ2 sample (20 wt% ZnO) exhibited maximum response of 36.7% to 100 ppm of NO2 gas at room temperature. The mechanism behind the response of pristine material and CuO-ZnO was explained in detail. The development of p-n heterojunction due to the combination of p-type CuO and n-type ZnO was responsible for the increase in the gas detecting capabilities of the synthesized composite material for detecting NO2 gas at ambient temperature. Hence, the proposed approach focuses on the design of a cost-effective and sensitive gas sensor that can sense NO2 gas even at room temperature. [ABSTRACT FROM AUTHOR]

NiO-TiO 2 may be deemed as the preeminent resilient and cost-effective photocatalyst for the co-generated generation of hydrogen and value-added commodities via glycerol photoreforming. This assertion is founded on the fact that this composite catalyst possesses photochemical qualities, which enable it to effectively convert water & glycerol solution into hydrogen and other high-value added chemicals, which can be reliable option for industrial-scale glycerol photoreforming applications. [Display omitted] Selective photocatalysis to simultaneously produce sustainable hydrogen and value-added chemicals from biomass or biomass derivates is attracting extensive investigations. However, the lack of bifunctional photocatalyst greatly limits the possibility to realize the "one stone kills two birds" scenario. Herein, anatase titanium dioxide (TiO 2) nanosheets are rationally designed as the n-type semiconductor, combining with nickel oxide (NiO) nanoparticles, the p-type semiconductor, resulting in the formation of a p-n heterojunction structure. The shorten charge transfer path and the spontaneous formation of p-n heterojunction endow the photocatalyst with efficient spatial separation of photogenerated electrons and holes. As a result, TiO 2 accumulates electrons for efficient hydrogen generation while NiO collects holes to selectively oxidize glycerol into value-added chemicals. The results showed that by loading 5% nickel into the heterojunction caused a remarkable rise in the generation of hydrogen (H 2). The combination of NiO-TiO 2 created 4000 µmolh−1g−1 of H 2 , which is 50% greater than the H 2 production from pure nanosheet TiO 2 and 63 times more than the H 2 production from commercial nanopowder TiO 2. Then, by changing loading amount of Ni, it is found that when 7.5 % of Ni is loaded the highest amount of hydrogen production achieved, 8000 µmolh−1g−1. By employing best sample (S3), 20 % of glycerol converted to value added products, glyceraldehyde and dihydroxyacetone. The feasibility study revealed that glyceraldehyde generates the largest portion of yearly earnings at 89%, while dihydroxyacetone and H 2 account for 11% and 0.03% of the annual revenue, respectively. This work provides a good example to simultaneously produce green hydrogen and valuable chemicals with the rational design of dually functional photocatalyst. [ABSTRACT FROM AUTHOR]

This research aims to develop flexible semiconductors for triboelectric nanogenerator (TENG) applications. The sample powders of graphitic carbon nitride (g-C3N4) and copper (I) oxide (Cu2O) as N-type and P-type semiconductors, respectively, were synthesized. The semiconductors were prepared to be a composite film with alginate. The structure, morphology, and purity of the N- and P-type semiconductors were characterized using X-Ray diffraction and scanning electron microscopy techniques. Through the optical characterization, the N-type semiconductor showed the calculated energy band gap of 2.80 eV, while the P-type semiconductor was 1.90 eV. The P–N junction property of prepared samples was confirmed using a nonlinear current–voltage characteristic. After that, two flexible semiconductors were frictional paired for TENG. Through a vertical contact-separation mode, the P–N junction-based TENG produced a maximum output voltage and current of 3.90 V and 0.44 µA, respectively, with a maximum output power of 0.35 µW at 10 MΩ. In summary, the present work achieved the preparation of flexible P- and N-type semiconductors. The feasibility to harvest the mechanical energy was demonstrated in the TENG configuration. This idea is crucial for the future development of flexible harvesting/sensing devices using a novel concept. [ABSTRACT FROM AUTHOR]

Owing to the confinement of ZnO in the photocatalytic application: the wide bandgap, the rapid photogenerated carriers recombination, and the expensive cost for the catalyst separation from the wastewater, the p-n heterojunction of NiFe2O4 magnetic phase and ZnO is considered to improve the photocatalytic efficiency and the catalyst separation by the external magnetic. The NiFe2O4/ZnO composites with 0–12 wt% of NiFe2O4 were prepared by an ordinary process and characterized using XRD, Raman, SEM, EDS, TEM, HRTEM, UV–Vis spectroscopy, and PL techniques. The Raman spectra confirm the crystallinity of ZnO and NiFe2O4, including their defects. As increasing NiFe2O4 incorporation, the crystallite size of ZnO phase depicts a lower value with changing from 53.14 to 40.49 nm, whereas NiFe2O4 phase reveals a greater value of 60.61–141.55 nm. The dislocation density, lattice constants, and atomic coordinates are also discussed in terms of ion diffusion. The morphology analysis reveals ZnO particles on the surface of NiFe2O4 microcrystals, confirming the p-n heterojunction formation. The energy bandgap of the as-synthesized samples is in the range of 1.52–2.85 eV, suggesting to the visible light photocatalysis. The prominent PL spectrum indices the forming of Zn interstitial defect state. Under the visible light irradiation, the dye degradation was investigated as a result of the photoreduction percentage and catalyst dosage. With prepared by a facile process, 12 wt% NiFe2O4-loaded ZnO displayed the high methylene blue degradation of 96.96 % within 150 min under visible light irradiation, confirming an excellent photocatalyst. Due to the microstructural composite, the active surface site and the p-n heterojunction were elucidated as the principal mechanism for the difference in reaction time. The dye degradation was discussed in association with the structural constants, morphology, and defects. [ABSTRACT FROM AUTHOR]

An integrated patterned wettability surface was simply prepared for real-time detection of conductive/non-conductive liquids based on anisotropic wettability, while the signal from conductive liquids could be selectively output as a binary sequence signal. In addition, the p–n heterojunction formed by the hybridized photocatalytic particles significantly improved the photodegradation ability, and efficient degradation of a variety of water-soluble dyes (10 mg L−1) could be achieved after 3 h of UV irradiation (MB, 93.8%; R6G, 89.6%). [ABSTRACT FROM AUTHOR]

This paper proposes the study of a solar-based photocatalytic ozonation process for the degradation of salicylic acid (SA) using a novel S-scheme ZnO/Cu2O/CuO/carbon xerogel photocatalyst. The incorporation of CuO and Cu2O aims to enhance charge mobility through the formation of p-n heterojunctions with ZnO, whereas the carbon xerogel (XC) was selected due to its eco-friendly nature, capacity to stabilize S-scheme heterojunctions as a solid-state electron mediator, and ability to function as a reducing agent under high temperatures. The characterization of the composites demonstrates that the presence of the XC during the calcination step led to the reduction of a fraction of the CuO into Cu2O, forming a ternary semiconductor heterojunction system. In terms of photocatalysis, the XC/ZnO-CuxO 5% composite achieved the best efficiency for salicylic acid degradation, mainly due to the stabilization of the S-scheme charge transfer pathway between the ZnO/CuO/Cu2O semiconductors by the XC. The total organic carbon (TOC) removal during heterogeneous photocatalysis was 80% for the solar-based process and 68% for the visible light process, after 300 min. The solar-based photocatalytic ozonation process was highly successful regarding the degradation of SA, achieving a 75% increase in the apparent reaction rate constant when compared to heterogeneous photocatalysis. Furthermore, a 78% TOC removal was achieved after 150 min, which is half the time required by the heterogeneous photocatalysis to obtain the same result. Temperature, salinity, and turbidity had major effects on the efficiency of the photocatalytic ozonation process; the system's pH did not cause any major performance variation, which holds relevance for industrial applications. [ABSTRACT FROM AUTHOR]

(001)-TiO2/BiOI photocatalysts with microsphere morphology were synthesized by a solvothermal method. The (001)-TiO2/BiOI demonstrated highest photocatalytic performance for the RhB degradation rate of 0.049 min−1 under visible light, which is 5 and 7 times that of (001)-TiO2 and BiOI, respectively. The increased photocatalytic efficiency is due to the construction of heterojunctions, which promote the transportation of photo-generated carriers. The good photochemical stability of the prepared photocatalysts was demonstrated by cycling experiments. The radical quenching experiments show that ˙O2− and ˙OH are the principal active species in the photocatalytic reaction mechanism. Finally, a possible mechanism of p–n heterojunctions in the photocatalytic reaction process was proposed. [ABSTRACT FROM AUTHOR]

In the present contribution, p-n type heterojunction α-Fe 2 O 3 /Cr 2 O 3 S-scheme system photocatalyst has been fabricated utilizing a sol-gel approach with assisted nonionic surfactant for a highly effective H 2 evolution rate under visible illumination. Pt NPs have been reduced by photodeposition during the photocatalytic reaction to collect Pt@α-Fe2O3/Cr2O3 finally. XRD analysis of Fe 2 O 3 /Cr 2 O 3 nanocomposites verified the construction of Fe 2 O 3 and Cr 2 O 3 with rhombohedral phases. TEM images of Cr 2 O 3 NPs were almost spherical and uniform in shape and size (20 ± 5 nm), and very small Fe 2 O 3 NPs (3-5 nm) were distributed on the mesoporous Cr 2 O 3 networks. The obtained α-Fe 2 O 3 /Cr 2 O 3 photocatalyst exhibited noteworthy photocatalytic H 2 evolution with high efficiency and stability for 45 h. Interestingly, the photocatalytic H 2 evolution rate gradually boosted with the extent of Fe 2 O 3 percentage up to 15% and its rate of 2215.4 μmol g-1h-1, which was fostered 7.25 folds larger than that of Cr 2 O 3 NPs (305.7 μmol g-1h-1). The enhancement H 2 evolution rate of Fe 2 O 3 /Cr 2 O 3 photocatalyst in comparison with bare Cr 2 O 3 NPs was ascribed to facilitate the separation of photocarriers and existing considerable reactive sites. In addition, constructing n-type Fe 2 O 3 and p-type Cr 2 O 3 with close contact is essential in improving the H 2 evolution rate. The possible photocatalytic mechanism over Fe 2 O 3 /Cr 2 O 3 nanocomposite was addressed based on electrochemical measurements. The construction of the S-scheme system of Fe 2 O 3 /Cr 2 O 3 nanocomposite could be suggested to improve the separation of photocarriers through optimal transfer channels owing to the formation of synergistic characteristics. Our results provide avenues for constructing stable photocatalysts with high efficiency for H 2 evolution through visible exposure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanoporous titanium (Ti)-vanadium (V) oxides were fabricated by sputtering and anodization. • V incorporation at high contents leads to cluster formation by coalescing grains. • Substitution of V ions with Ti4+ in the composite induces chemical state of Ti3+. • V deposition decreases band gap values with absorption extensions to longer wavelengths. • A photocatalyst with the lowest V loading shows the highest degradation efficiency. This study addressed the separation problem of colloidal catalytic powder from its solution and pore blockage of traditional metallic oxides by fabricating nanoporous composites of titanium (Ti)-vanadium (V) oxide via magnetron sputtering, electrochemical anodization, and annealing processes. The effect of V-deposited loading on the composite semiconductors was investigated by varying V sputtering power (20–250 W) to correlate their physicochemical properties to the photodegradation performance of methylene blue. The obtained semiconductors revealed circular and elliptical pores (14–23 nm) and formed different metallic and metallic oxide crystalline phases. Within the nanoporous composite layer, V ions substituted Ti4+, leading to Ti3+ formation accompanied by decreased band gap values and higher visible-light absorption. Thus, the band gap of TiO 2 was 3.15 eV, while that of Ti-V oxide with the maximum V content (at 250 W) was 2.47 eV. The interfacial separators between clusters in the mentioned composite created traps disrupting the charge carrier movements between crystallites, thereby decreasing the photoactivity. In contrast, the composite prepared with the minimum V content showed approximately 90% degradation efficiency under solar-simulated irradiation resulting from the homogeneous V dispersion and the lower recombination possibility, owing to its p-n heterojunction constituent. The nanoporous photocatalyst layers with their novel synthesis approach and outstanding performance can be applied in other environmental remediation applications. [ABSTRACT FROM AUTHOR]

The construction of semiconductor-coupled heterojunctions can effectively enhance the transport efficiency of photogenerated electrons and holes and the photocatalytic hydrogen-producing performance of catalysts. SnS2 and Co9S8 were prepared by applying the hydrothermal method, and the composite catalyst Co9S8/SnS2 was prepared by applying the electrostatic self-assembly method. Both SnS2 and Co9S8 were amorphous monometallic sulfides, and the n-type semiconductor SnS2 and p-type semiconductor Co9S8 were constructed into Co9S8/SnS2 p–n type heterojunctions. Co9S8 irregular spheres around 400 nm were attached to SnS2 smooth balls around 800 nm, thereby providing more reactive sites. The doping of Co9S8 promoted the separation of hole–electron pairs and increased the photogenerated electron and hole transfer rate, thereby effectively improving the visible photocatalytic hydrogen-producing activity of SnS2. The 5 h hydrogen-producing amount of Co9S8/SnS2 reached 120.91 μmol, which was 4.5 times that of Co9S8. The morphology and structure of the catalyst were explored by XRD, SEM and TEM characterization tests. The catalyst was spectrally analyzed by XPS, PL and UV-vis characterization tests, and the electrochemical aspects of the catalyst were characterized by an electrochemical test and zeta potential test. The construction of Co9S8/SnS2 p–n heterojunction changes the transfer pathway of photogenerated carrier electrons, thereby promoting the hydrogen-producing performance of Co9S8/SnS2, and its construction mechanism provides certain theoretical support for photocatalytic and efficient hydrogen-producing technology. [ABSTRACT FROM AUTHOR]

α-Fe2O3/Bi2O3 nanocomposites with a p–n heterojunction were synthesized via an anodization strategy and the hydrothermal method for photocatalytic applications. By changing the hydrothermal treatment time, Bi2O3 nanosheets were deposited on the surface of α-Fe2O3 nanotube arrays (NTAs). The morphologies and photochemical performance of the as-prepared α-Fe2O3/Bi2O3 nanocomposites were investigated in detail. The presence of Bi2O3 nanosheets resulted in an obvious red-shift in the UV-Vis diffuse reflectance spectrum, indicating that the α-Fe2O3/Bi2O3 nanocomposites had an expanded visible light photo-response range. The α-Fe2O3/Bi2O3 nanocomposites displayed excellent photocatalytic activity, stability and recyclability toward the decomposition of methylene blue under visible light illumination. The photocurrent and electrochemical impedance spectra also testified efficient electron transport and charge separation in the α-Fe2O3/Bi2O3 nanocomposites. The enhanced photocatalytic performance can be ascribed to a high light harvesting ability, fast separation of photogenerated electron–hole pairs and the presence of an efficient interfacial electric field from the p–n heterojunction. The photogenerated holes and superoxide radicals played crucial roles in the photocatalytic process. The photocatalytic mechanism was discussed. [ABSTRACT FROM AUTHOR]

The rapid recombination of photogenerated carriers of photocatalysts greatly limits their actual application in CO2 conversion into valuable chemicals. Herein, dual CuOx and MnOx cocatalysts are decorated on g-C3N4 nanosheets via a one-step photodeposition strategy. Benefiting from the repulsion between Cu2+ and Mn2+ cations, a novel g-C3N4-based heterostructure loaded with spatially separated CuOx and MnOx nanoparticle dual cocatalysts has been successfully fabricated. Cu favors the trapping of electrons, while MnOx tends to collect holes. Moreover, the Cu2O/g-C3N4 p–n heterojunction also accelerates the charge separation. As a result, the photogenerated holes and electrons flow into and out of the photocatalyst, respectively, resulting in enhanced charge separation for achieving efficient CO2 photoreduction over CuOx/g-C3N4/MnOx. Accordingly, the optimized CuOx/g-C3N4/MnOx exhibits an improved CO production rate of 5.49 μmol g−1 h−1, which is 27.5 times higher than that of bare g-C3N4. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2) production in water-splitting could be significantly increased by designing cost-effective photocatalysts with remarkable performance. The main objective of this study is to recognize the behavior of soot carbon-based metal nitrides nanocomposites on its photocatalytic activity when exposed to solar lights. This study synthesized a p-n heterojunction Ta 3 N 5 /PANI composite photocatalyst modified by eco-friendly and low-cost biomass soot carbon (BSC) using hydrothermal and chemisorption methods. BSC materials are photoactive when exposed to UV light because of their band gap (E g < 4 eV), indicating they behave as semiconductors. Compared to pure Ta 3 N 5 , the hydrogen production rate of a photocatalyst containing polyaniline (PANI) can reach up to 76.9 μmol g−1 h−1, equivalent to 3.42 times superior to pristine Ta 3 N 5. The formation of a p-n heterojunction at the interface of PANI and Ta 3 N 5 was primarily responsible for improving the H 2 evolution activity. This successfully prevents the self-photocorrosion of Ta 3 N 5 by providing a rapid route for the migration and separation of photogenerated charges. It also confirms the long-term stability of the materials by repeating the experiments up to 6 cycles with more than 95 %. [Display omitted] • Ta 3 N 5 /BSC@PANI have been successfully prepared via mechanical and chemisorption techniques. • Various characterization methods were used to reveal the structural and morphological of materials. • Light-driven water splitting via Ta 3 N 5 /BSC@PANI composite was favorably demonstrated. [ABSTRACT FROM AUTHOR]

In this study, Zinc stannate-silver (ZTO-Ag) nanoparticles are produced using the customary hydrothermal technique, followed by in-situ chemical oxidative polymerization, resulted in varied weight percentages (0, 5, 10, and 15 wt%) of ZTO-Ag@PPy nano-composites. The prepared composites are characterized for powder XRD, FTIR, FESEM and BET analysis. The I–V response of interdigitated electrode (IDE) composite films are studied at room temperature and the band gap for composites was determined using UV–visible. The 10% ZTO-Ag@PPy composite showed the highest dc electrical conductivity and the largest surface area among all the composites. Furthermore, the composites are exposed to H2S, NH3, CO, CO2, NO2, and Cl2 gases. The 10% ZTO-Ag@PPy composite demonstrated the highest selective response for H2S gas because there is a significant interaction between the nanoparticles and the polymer chain which results in an effective incorporation of ZTO-Ag nanoparticles in the macromolecular chain. For 15% ZTO-Ag@PPy the agglomeration effect offers more resistance in the path of ions hence composite showed less sensitivity. After being exposed to H2S gas, the gas sensing characteristics are properly examined. A composite sensor has a higher sensing range (2–120 ppm), a quicker response, and recovery time, good long-term stability and repeatability towards the H2S gas. At room temperature, protonation/deprotonation at the PPy surface, efficient charge carrier interaction at the p-n heterojunction, and a large surface area available for gas adsorption together played a vital role in enhancing the gas sensing capabilities of the wt % ZTO-Ag@PPy composite sensors. [ABSTRACT FROM AUTHOR]

2-butanone has been certified to cause potential harm to the human body, environment, etc. Therefore, achieving a method for the high sensitivity and low limit detection of 2-butanone is of great significance. To achieve this goal, this article uses ZIF-67 prepared by a precipitation method as a cobalt source, and then prepares cobalt-modified zinc oxide nanosheets through a hydrothermal method. The microstructure of the materials was observed by SEM, EDS, TEM, HRTEM, XPS and XRD. The test data display that the sensor ZC2 can produce a high response (2540) to 100 ppm 2-butanone at 270 °C, which is 21 times higher than that of pure ZnO materials. Its detection limit is also optimized to 24 ppb. The sensor (ZC2) also excels in these properties: selectivity, repeatability and stability over 30 days. Further analysis indicates that the synergistic and catalytic effects of p-n heterojunction are the key sources for optimizing the performance of sensors for detecting 2-butanone. [ABSTRACT FROM AUTHOR]

Ammonia monitoring in our daily life is significant. In this work, Ti3C2Tx/ZnO materials were prepared by hydrothermal method. The results of XRD, SEM, TEM, and XPS analyses demonstrated the successful preparation of the Ti3C2Tx/ZnO composite. Ti3C2Tx/ZnO (3:1) material exhibited the best morphology as ZnO grows evenly on it as ultrathin nanosheets. The gas sensing performance of Ti3C2Tx, ZnO, and Ti3C2Tx/ZnO (1:1, 2:1, 3:1, and 5:1) materials were studied. The Ti3C2Tx/ZnO (3:1) sensor has an excellent response to 50 ppm ammonia at a low operating temperature (∼28 °C), and the value of response is 196%, which is the highest response in this work. Furthermore, it was found that Ti3C2Tx/ZnO (3:1) detects ammonia selectively against other volatile organic compounds at a low operating temperature (∼28 °C). The actual lowest detection ability was measured at 1 ppm, and the corresponding response is 14%. The ultra-thin ZnO nanosheets on the Ti3C2Tx MXene and the p–n heterojunctions in Ti3C2Tx/ZnO (3:1) are designed to achieve better ammonia sensing performance. This paper provided a route to enhance the p-type characteristic of Ti3C2Tx MXene, which is meaningful to Ti3C2Tx MXene application at a low operating temperature in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal organic framework (MOF) is currently-one of the key catalysts for oxygen evolution reaction (OER), but its catalytic performance is severely limited by electronic configuration. In this study, cobalt oxide (CoO) on nickel foam (NF) was first prepared, which then wrapped it with FeBTC synthesized by ligating isophthalic acid (BTC) with iron ions by electrodeposition to obtain CoO@FeBTC/NF p-n heterojunction structure. The catalyst requires only 255 mV overpotential to reach a current density of 100 mA cm−2, and can maintain 100 h long time stability at 500 mA cm−2 high current density. The catalytic properties are mainly related to the strong induced modulation of electrons in FeBTC by holes in the p-type CoO, which results in stronger bonding and faster electron transfer between FeBTC and hydroxide. At the same time, the uncoordinated BTC at the solid–liquid interface ionizes acidic radicals which form hydrogen bonds with the hydroxyl radicals in solution, capturing them onto the catalyst surface for the catalytic reaction. In addition, CoO@FeBTC/NF also has strong application prospects in alkaline electrolyzers, which only needs 1.78 V to reach a current density of 1 A cm−2, and it can maintain long-term stability for 12 h at this current. This study provides a new convenient and efficient approach for the control design of the electronic structure of MOF, leading to a more efficient electrocatalytic process. [ABSTRACT FROM AUTHOR]

Here, we designed a flexible, highly adaptive, self-Standing photoelectrochemical (PEC) aptasensor for Aflatoxin B1 (AFB1) detection based on BiOBr/TiO 2 hierarchical nanofiber membranes (NFM) with a 3D pinecone-like structure by integrating sol-gel electrospinning with the successive ionic layer adsorption and reaction (SILAR) method. The uniformly deposited BiOBr nanosheets could not only enlarge the surface area but also expand the light absorption range of TiO 2 NFM. Owing to the pinecone-like and hierarchical structure, the photo-generated carriers of BiOBr/TiO 2 NFM could be separated quickly and efficiently, which was contributed to obtain a larger and more stable photocurrent intensity. The photocurrent intensity of 6-BiOBr/TiO 2 NFM was 12.1 times of pristine TiO 2 NFM and 3.4 times of pure BiOBr, respectively. The constructed flexible and self-Standing PEC aptasensor has achieved AFB1 detection in tomato samples with good repeatability, specificity and sensitivity. Under the optimized conditions, a wide linear range (0.001–400 ng mL−1) and a detection limit of 0.12 pg mL−1 (S/N = 3) were obtained for AFB1 determination. This design principle provided a neo-idea for development of flexible and self-Standing PEC aptasensor. [ABSTRACT FROM AUTHOR]