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Room temperature detection is a crucial objective in semiconductor sensor research, given its inherent benefits including reduced energy consumption, extended sensor lifespan, and significant reduction of safety hazards. Herein, novel room temperature sensing materials, SnO 2 -modified In 2 O 3 porous microrods were synthesized, which exhibited exceptional sensing capability towards formaldehyde at room temperature. Specifically, the 5%-SnO 2 /In 2 O 3 porous microrods demonstrate an impressive sensing response across varying formaldehyde concentrations, even at sub-ppm levels (0.1 ppm, 5.22), with a theoretical detection limit of 5.47 ppb, thereby enabling the detection of trace amounts of formaldehyde. Moreover, the sensors exhibit superior formaldehyde selectivity, rapid response characteristic, as well as good stability and reproducibility. The exceptional formaldehyde sensing ability of the SnO 2 /In 2 O 3 sensor primarily arises from the creation of n-n heterojunctions at the SnO 2 /In 2 O 3 interface, effectively modulating the interfacial potential. Additionally, the presence of SnO 2 enhances the amount of surface-adsorbed oxygen species and active sites, thereby boosting sensing response. The porous rod-like structures further facilitate gas adsorption and diffusion, enhancing gas sensing capabilities. This work presents a novel strategy for constructing SnO 2 -In 2 O 3 heterojunctions to achieve room-temperature formaldehyde detection. [ABSTRACT FROM AUTHOR]

The accurate detection of hazardous gases and monitoring of ambient temperature are crucial for preserving the ecological environment, safeguarding human health, and fostering industrial advancement. In this research, a straightforward hydrothermal technique was employed to synthesize the heterogeneous nanocomposite structure of CsPbBr 3 /SnWO 4 , which facilitates the detection of ethanolamine gas at room temperature. The synthesized CsPbBr 3 /SnWO 4 heterostructures underwent further analysis using XRD, SEM, HRTEM, XPS, BET and Mott-Schottky techniques. The findings revealed that the CsPbBr 3 /SnWO 4 heterostructure exhibits a coarse cubic morphology, consisting of nano-cubic CsPbBr 3 and nano-sheet SnWO 4. Additionally, the integration of CsPbBr 3 markedly enhances the specific surface area of the pristine SnWO 4 nanosheets. Due to its coarse surface, expansive contact area, and n-n heterojunction, CsPbBr 3 –SnWO 4 demonstrates remarkable selectivity, superior long-term stability, and a sensitivity of 45.6 to ethanolamine at ambient temperature. In conclusion, the CsPbBr 3 /SnWO 4 heterostructure, constructed from a cube with a rough surface, is anticipated to serve as an effective room temperature sensor with heightened selectivity for ethanolamine. [ABSTRACT FROM AUTHOR]

Construction of heterostructure photocatalysts is an effective strategy to achieve charge separation and enhance photocatalytic activity. Herein, perovskite-based n-n heterostructure of BiFeO 3 –BaTiO 3 was prepared and applied for water splitting process with the aim of H 2 production. The slope of Mott-Schottky plots revealed that both BiFeO 3 and BaTiO 3 are n -type photocatalysts with flat band potentials of +0.67 and −0.03 eV, respectively. The flat band potential of BaTiO 3 meets the potential required for reducing H+ to H 2. However, the results of PL and EIS demonstrated the high recombination rate of charge carriers in pure BaTiO 3. By introducing BiFeO 3 and construction of n-n heterostructures, the charge separation and mobility were promoted as a result of charge transfer process. Based on the Fermi level positions, difference of the work function between the two photocatalysts, and the radical scavenger experiments results, the direct Z -scheme charge transfer mechanism is suggested in BiFeO 3 –BaTiO 3 heterojunction. The best photocatalytic H 2 evolution under UV–vis irradiation and without using sacrificial agent was obtained to be 328 μmol g−1 h−1 by a heterostructure composed of 70 wt % BFO. [Display omitted] • Perovskite n-n heterostructures of BiFeO 3 –BaTiO 3 were fabricated by a sol-precipitation process for photocatalytic H 2 evolution. • The n–n heterojunction effectively promoted charge transfer and separation. • The direct Z -scheme charge transfer is suggested in n-n heterojunction. • Best photocatalytic H 2 evolution was obtained to be 328 mol g−1 h−1 by a composed of 70 wt % BiFeO 3. [ABSTRACT FROM AUTHOR]

The development of a sensor capable of selectively detecting hydrogen levels in the environment holds immense importance for ensuring the safer utilization of hydrogen energy. In this study, a hydrogen sensor made of Ce-doped single-layer graphene (SLG)/SnO2 composite material was fabricated using a hydrothermal method. The study examined the impact of varying Ce doping concentrations on the hydrogen sensing capabilities of the SLG/SnO2 matrix. The results show that the SLG/SnO2 hydrogen sensor doped with 2 mol% Ce demonstrated optimal performance at a humidity of 20%. It operated most efficiently at 250 °C, with a response of 2.49, representing a 25.75% improvement over the undoped sample. The response/recovery times were 0.46/3.92 s, which are 54.9% shorter than those of the undoped sample. The enhancement in hydrogen sensitivity stems from the synergistic effect of Ce and SLG, which facilitates the coexistence of n–n and p–n heterojunctions, thereby increasing carrier mobility and refining grain structure. Analysis via X-ray photoelectron spectroscopy (XPS) reveals that Ce increases the material's oxygen vacancy concentration, enhancing its hydrogen sensitivity. Ce-doped SLG/SnO2, with its robust hydrogen sensitivity, represents one of the leading candidates for future hydrogen gas sensors. [ABSTRACT FROM AUTHOR]

This study reports the photoelectrocatalytic (PEC) activity of a n–n heterojunction comprising MoS2 and NiSe2. The synthesis of the composite was achieved through a facile solvothermal method, yielding an exfoliated MoS2 layered sheet loaded with NiSe2 nanoparticles. Under visible light radiation and an external electric field, the obtained composite NiSe2/MoS2 exhibited enhanced catalytic activity for ciprofloxacin (CIP) degradation. The NiSe2/MoS2 heterojunction achieved about 78 % degradation efficiency with a first‐order kinetic rate of 0.0111 min−1, compared to 38 % efficiency and a first‐order kinetic rate of 0.0044 min−1 observed for MoS2. The NiSe2/MoS2 heterojunction was more advantageous due to the synergy of charge carrier induction by visible light radiation and improved charge carrier separation induced by the external electric field. The formation of n–n heterojunction at the interface of the two materials resulted in charge redistribution in the materials, with a simultaneous realignment of the band structure to achieve Fermi energy equilibration. The primary reactive species responsible for CIP degradation was identified as the photo‐induced h+. Furthermore, the catalyst exhibited high stability and reusability, with no significant reduction in activity observed after five experimental cycles. This study reveals the potential of exploring the synergy between the photocatalytic and electrocatalytic processes in removing harmful pharmaceutical compounds from water. [ABSTRACT FROM AUTHOR]

In this study, a series of mesoporous TiO2 nanotablets implanted with uniformly distributed MoO3 were formed by the heat treatment of a titanium-based metal–organic framework (MIL-125) in the presence of Mo ions, and their hydrogen sensing properties were investigated for the first time. The TiO2 and MoO3/TiO2 composites present a typical tablet-like morphology. Compared with the bare TiO2, the MoO3/TiO2 (Mo6+/Ti4+ = 1:10) composite has a richer porous structure (3 times larger than pure TiO2) which can provide a larger surface area (2.1 times larger than pure TiO2). The sensing performance reveals that the MoO3/TiO2 composite (Mo6+: Ti4+ = 1:10) not only exhibits the highest response of 47.57 (5 times higher than pure TiO2) to 1000 ppm of H2 at room temperature but also shows good reproducibility, long-term stability, and selectivity, which is mainly due to the richer porous structures, the n–n heterojunction, and the catalytic effect between MoO3 and hydrogen. It is noteworthy that the response of the optimal MoO3/TiO2 composite has shown an exponential increase at higher hydrogen concentrations and reaches 1178 at 4000 ppm of hydrogen. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) sensing is crucial for environmental safety, necessitating the development of efficient NH3 sensors. In this study, an efficient NH3 sensor based on CdS quantum dots (QDs) decorated with ZnO (CdS/ZnO) covering optical fiber was successfully fabricated. The CdS/ZnO was first synthesized by a hydrothermal method, featuring an n-n heterojunction in the composite material. The optimal sensor with 10 wt% CdS QDs exhibits efficient performance, with a response sensitivity of 0.9 × 10−3 dB/ppm and R2 = 0.9858. Additionally, it demonstrates excellent selectivity and repeatability. Mechanistic insights for the NH3 sensor were elucidated through X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. These results confirm that the enhancement in NH3 sensing performance is attributed to the formation of well-defined n-n heterojunctions. This study contributes to the advancement of gas-sensing technology, particularly in the detection of harmful gases, such as NH3. [ABSTRACT FROM AUTHOR]

Molybdenum oxides and sulfides stand out as promising materials for chemiresistive gas sensors. In this study, we tailored MoS2/MoO2 heterostructures, adapting pyrolysis-assisted in situ sulfidation of hydrothermally grown MoO3 by tuning the concentration of the sulfur source. The MoS2 flakes adorning a MoO2 cuboid rod heterostructure represent the n-type semiconducting property, confirmed by Hall measurement. Notably, the sensor demonstrated dual selectivity toward NH3 and NOx at room temperature. To our knowledge, the dual selectivity of the MoS2/MoO2 heterostructure has not been reported previously. The heterostructure, characterized by a higher carrier concentration, displayed enhanced sensitivity, yielding responses of 10.3 and 8.4% to 10 ppm of NH3 and NOx, respectively. The lowest detection limits were 0.32 ppm for NH3 and 0.29 ppm for NOx. Furthermore, the heterostructure sensor exhibited commendable cyclic stability and device reproducibility. A long-term stability assessment over 50 days revealed that the response of the sensor remained at 98.6 and 98.4% toward NH3 and NOx, respectively. Our results show that the optimized n–n heterojunction between MoO2 and MoS2 offers superior sensitivity to NH3 and NOx at room temperature. The results could have potential for the development of dual gas sensors suitable for real-time applications. [ABSTRACT FROM AUTHOR]

The current study, accurately designed and created a two-dimensional (2D) structure of SnO 2 nano-flowers and In 2 O 3 nanoparticles using a simple hydrothermal technique and sol-gel method, respectively. On the outer surface of SnO 2 nanoflowers the In 2 O 3 nanoparticles were uniformly growing, clearly revealed by field emission scanning electron microscopic. Besides, crystal phase structure, surface area and elementals composition were characterized by XRD, BET, TEM, EDS, XPS and the gas sensing properties of In 2 O 3 @SnO 2 NFs. The results exhibited that 2 wt% In 2 O 3 @SnO 2 NFs sensor is highly sensitive to NO 2 , the response (R g /R a) to 30 ppm NO 2 is 94.5, and at 50 ppb the response measured 0.61 at 150 °C, the response time is 32 and 51s, respectively, along with good moisture resistance. Besides along with excellent selectivity, long-term stability, and relative humidity (RH) in high-humidity environment, the 2 wt% In 2 O 3 @SnO 2 NFs still maintain high response 91 at 30 ppm. More importantly, at room temperature the response was (Rg/Ra = 1.01) at detection limit 300 ppb towards NO 2 , which could use be for trace NO 2 gas detection. The large specific surface areas of SnO 2 , the abundance of oxygen species adsorbed on the surface, the distinctive electron transformation between heterojunction materials, and high electron transmission channel of SnO 2 and In 2 O 3 transition layer were all considered to have a synergistic effect thatin2 contributed to excellent sensing properties of In 2 O 3 @SnO 2 NFs. [ABSTRACT FROM AUTHOR]

Abstract This study reports the photoelectrocatalytic (PEC) activity of a n–n heterojunction comprising MoS2 and NiSe2. The synthesis of the composite was achieved through a facile solvothermal method, yielding an exfoliated MoS2 layered sheet loaded with NiSe2 nanoparticles. Under visible light radiation and an external electric field, the obtained composite NiSe2/MoS2 exhibited enhanced catalytic activity for ciprofloxacin (CIP) degradation. The NiSe2/MoS2 heterojunction achieved about 78 % degradation efficiency with a first‐order kinetic rate of 0.0111 min−1, compared to 38 % efficiency and a first‐order kinetic rate of 0.0044 min−1 observed for MoS2. The NiSe2/MoS2 heterojunction was more advantageous due to the synergy of charge carrier induction by visible light radiation and improved charge carrier separation induced by the external electric field. The formation of n–n heterojunction at the interface of the two materials resulted in charge redistribution in the materials, with a simultaneous realignment of the band structure to achieve Fermi energy equilibration. The primary reactive species responsible for CIP degradation was identified as the photo‐induced h+. Furthermore, the catalyst exhibited high stability and reusability, with no significant reduction in activity observed after five experimental cycles. This study reveals the potential of exploring the synergy between the photocatalytic and electrocatalytic processes in removing harmful pharmaceutical compounds from water.

The development of a sensor capable of selectively detecting hydrogen levels in the environment holds immense importance for ensuring the safer utilization of hydrogen energy. In this study, a hydrogen sensor made of Ce-doped single-layer graphene (SLG)/SnO2 composite material was fabricated using a hydrothermal method. The study examined the impact of varying Ce doping concentrations on the hydrogen sensing capabilities of the SLG/SnO2 matrix. The results show that the SLG/SnO2 hydrogen sensor doped with 2 mol% Ce demonstrated optimal performance at a humidity of 20%. It operated most efficiently at 250 °C, with a response of 2.49, representing a 25.75% improvement over the undoped sample. The response/recovery times were 0.46/3.92 s, which are 54.9% shorter than those of the undoped sample. The enhancement in hydrogen sensitivity stems from the synergistic effect of Ce and SLG, which facilitates the coexistence of n–n and p–n heterojunctions, thereby increasing carrier mobility and refining grain structure. Analysis via X-ray photoelectron spectroscopy (XPS) reveals that Ce increases the material’s oxygen vacancy concentration, enhancing its hydrogen sensitivity. Ce-doped SLG/SnO2, with its robust hydrogen sensitivity, represents one of the leading candidates for future hydrogen gas sensors.

Ammonia (NH3) sensing is crucial for environmental safety, necessitating the development of efficient NH3 sensors. In this study, an efficient NH3 sensor based on CdS quantum dots (QDs) decorated with ZnO (CdS/ZnO) covering optical fiber was successfully fabricated. The CdS/ZnO was first synthesized by a hydrothermal method, featuring an n-n heterojunction in the composite material. The optimal sensor with 10 wt% CdS QDs exhibits efficient performance, with a response sensitivity of 0.9 × 10−3 dB/ppm and R2 = 0.9858. Additionally, it demonstrates excellent selectivity and repeatability. Mechanistic insights for the NH3 sensor were elucidated through X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. These results confirm that the enhancement in NH3 sensing performance is attributed to the formation of well-defined n-n heterojunctions. This study contributes to the advancement of gas-sensing technology, particularly in the detection of harmful gases, such as NH3.

[Display omitted] • BaSnO 3 nanosheets grown by solvothermal process with a surface area of 150 m2g−1. • Addition of 3.0–12.0 wt% CuMn 2 O 4 constructing n - n heterojunction. • CuMn 2 O 4 boosts light harvesting and reduce bandgap to 2.78 eV. • Photooxidation of TC enhanced by >5.5 times compared to bare BaSnO 3. • Complete mineralization of TC achieved within 90 min over 2.4 gL–1 of 9% CuMn 2 O 4 /BaSnO 3. Photocatalytic oxidation of antibiotic waste over semiconducting heterojunction photocatalysts is considered eco-friendly because it is simple and operates under light irradiation. In this work, we apply a solvothermal-based process for obtaining high surface area barium stannate (BaSnO 3) nanosheets followed by adding 3.0–12.0 wt% of spinel copper manganate (CuMn 2 O 4) nanoparticles to form n - n CuMn 2 O 4 /BaSnO 3 heterojunction photocatalyst after calcination process. The CuMn 2 O 4 -supported BaSnO 3 nanosheets exhibit mesostructure surfaces with a high surface area range of 133–150 m2 g−1. Moreover, introducing CuMn 2 O 4 to BaSnO 3 shows a significant broadening in visible light absorption range due to bandgap reduction down to 2.78 eV in 9.0% CuMn 2 O 4 /BaSnO 3 compared to 3.0 eV for pure BaSnO 3. The produced CuMn 2 O 4 /BaSnO 3 is used for photooxidation of tetracycline (TC) in water as emerging antibiotic waste under visible light. The photooxidation of TC exhibits the first-order reaction model. The specific dose of 9.0 wt% CuMn 2 O 4 /BaSnO 3 at 2.4 gL−1 displays the highest-performed and recyclable photocatalyst for total oxidation of TC after 90 min. This sustainable photoactivity is attributed to the improved light harvesting and charges migration upon coupling between CuMn 2 O 4 and BaSnO 3. [ABSTRACT FROM AUTHOR]

The nanometer size Cu2O@WO3·H2O composite material has been prepared by the direct hydrolysis of mesitylcopper (I) on WO3·2H2O nanoleaves. The synthesis has been performed in toluene without the addition of any ancillary ligands. The prepared nanocomposite has been deposited as a gas-sensitive layer on miniaturized silicon devices and heated up gradually to 500 °C in the ambient air. During the heating, the CuWO4 phase is formed upon the reaction of Cu2O with the WO3 support as revealed by the XRD analyses. The as-prepared CuWO4@WO3 sensors have been exposed to 10 ppm of CO or 0.4 ppm of NO2 (RH = 50%). At the operating temperature of 445 °C, a normalized response of 620% towards NO2 is obtained whereas the response to CO is significantly lower (S = 30%). Under these conditions, the sensors prepared either with pristine CuO or WO3 nanostructures are sensitive to only one of the two investigated gases, i.e., CO and NO2, respectively. Interestingly, when the CuWO4@WO3 sensitive layer is exposed to UV light emitted from a 365 nm Schottky diode, its sensitivity towards CO vanishes whereas the response towards NO2 remains high. Thus, the application of UV illumination allowed us to modify the selectivity of the device. This new nanocomposite sensor is a versatile sensitive layer that will be integrated into a gas sensor array dedicated to electronic nose platforms. [ABSTRACT FROM AUTHOR]

Mesoporous Li 2 MnO 3 /BaSnO 3 nanocomposites were constructed by sol-gel and impregnation approaches. The photocatalytic performance of Li 2 MnO 3 /BaSnO 3 nanocomposites was assessed by Atrazine degradation as a probe herbicide molecule under visible light illumination. The optimum 15%Li 2 MnO 3 /BaSnO 3 photocatalyst degraded the Atrazine completely (100%) after 50 min of illumination, which was enhanced two times larger than bare BaSnO 3 NPs. The apparent rate constant of 15%Li 2 MnO 3 /BaSnO 3 nanocomposite was about 3.11 times greater than bare BaSnO 3 NPs. The results revealed that incorporating Li 2 MnO 3 and BaSnO 3 efficiently strengthened the separation of photoinduced carriers and extended the absorption of visible light. Due to the obtained nanocomposites having a porous structure, the Atrazine molecules are easily moved to the active sites with a large •OH radical concentration and reduced light scattering. The photocatalytic ability of Li 2 MnO 3 /BaSnO 3 nanocomposite was a little minimized after five cycles of Atrazine degradation due to its high photocatalytic stability. The appropriate band bending of heterojunction Li 2 MnO 3 /BaSnO 3 nanocomposite could be promoted the transport of photoinduced electrons toward the heterogeneous interface through the S-scheme mechanism, thus significantly prohibiting recombination and promoting the separation efficiency of carriers. [ABSTRACT FROM AUTHOR]

Cerium dioxide (CeO2), especially doped cerium, is widely used as an electrolyte, while stannic oxide (SnO2) is known as a gas sensor material, but it is exceptionally new in solid-state ionics. In this work, a new semiconductor composite that consists of CeO2 and SnO2 was synthesized using a co-precipitation method and investigated for applications in solid oxide fuel cells (SOFCs). The as-prepared CeO2-SnO2 composite (n-n type) is employed as an electrolyte sandwiched between two Ni0.8Co0.15Al0.05LiO2-δ (NCAL) electrodes to fabricate fuel cells with a high power density of 1167 mW cm−2, accompanied by high open-circuit voltage (OCV) of 1.11 V at 550°C XRD, SEM, and HR-TEM analyses are employed to investigate the microstructure of the composites, illustrating that the as-prepared composite has particles of the nanometer size, without any other impurity phases. The electrical properties of the device are studied by EIS measurements. The results indicate that the synthesized CeO2-SnO2 composite exhibits higher ionic conductivity than that of the CeO2-SnO2 composite prepared by a dry grinding method. Considerable proton conductivity was also found for the CeO2-SnO2 composite. Interestingly, although two n-type semiconductor materials are composited for the electrolyte membrane, there is no short-circuit issue. Hence, the n-n heterojunction is proposed to explain the electron blocking mechanism. [ABSTRACT FROM AUTHOR]

Detecting volatile organic compounds is essential to improving the environment and human health. This study prepared a novel composite of hollow SnO 2 /ZnO cubes using a self-template hydrothermal method followed by a calcination process. The morphology and structure of the composites were characterized using a series of analysis techniques, and the formation mechanism of a hollow cube-like structure was explored. Compared to the hollow SnO 2 cube sensor, the hollow SnO 2 /ZnO cube sensor exhibited a strong response (148–100 ppm formaldehyde), fast response/recovery time (15 s/25 s), good linearity (R2 = 0.995), good repeatability, and excellent stability. The superior gas sensing property of the hollow SnO 2 /ZnO cubes was attributed to the combined advantages of hollow structures and heterojunctions. [ABSTRACT FROM AUTHOR]

Herein, a ratiometric fluorescent sensor based on CPB⊆Pb/Eu-MOF heterojunction has been designed for rapid, sensitive and visual detection of H 2 O and Cu2+ in extraction solution. The energy transfer from Pb2+ to Eu3+ in Pb/Eu-MOF has enhanced the luminescent emission of Eu3+, and the CPB⊆Pb/Eu-MOF n-n heterojunction with S-scheme charge transfer can stabilize CPB to activate the detecting for H 2 O and Cu2+. In-situ XPS and XRD have confirmed the phase transformation from cubic CPB to CsPb 2 Br 5 majorly contributes to color switch when being introduced by H 2 O. Moreover, the dynamic quenching and electron transfer are verified by the adsorption energy Br-Cu bonding according to DFT calculation and the shortened fluorescence lifetime. Typically, 0.2CPB⊆Pb/Eu-MOF composite exhibits a highly sensitive and selective ratiometric fluorescent sensing. The proper linear ranges from 10.80 % to 23.10 % and a low detection limit of 0.26 % for H 2 O, while 20–180 μM, R2 = 0.996, and 8.09 μM for Cu2+. More importantly, the paper-based sheet sensor has been manufactured practically in the real floral teas and different solvents for the visual detection of H 2 O and Cu2+ by naked eyes. • The CPB⊆Pb/Eu-MOF heterojunction was self-sacrificed from Eu-MOF doped with Pb2+. • The obtained ratiometric sensor exhibited good detection capability for H 2 O and Cu2+. • Paper-based sensor was used to detect H 2 O and Cu2+ in floral teas and solutions. • M-S, UPS, in-situ XPS and DFT proved the electron redistribution and charge transfer mode. [ABSTRACT FROM AUTHOR]

Developing fast, accurate and sensitive triethylamine gas sensors with low detection limits is paramount to ensure the safety of workers and the public. However, sensors based on single metal oxide materials still suffer from drawbacks such as low response sensitivity and long response and recovery times. To address these challenges, in this work, a series of mesoporous CdO/CdGa 2 O 4 microspheres were synthesized. We optimized the sensor's sensing performance to triethylamine by fine-tuning the ratio of CdO to CdGa 2 O 4. Among them, CdO:3CdGa 2 O 4 -based sensor demonstrates a rapid response time of 2 s to detect 100 ppm of triethylamine, with a high response value of 211 and exceptional selectivity. Furthermore, it exhibits a low detection limit of 20 ppb for triethylamine, making it suitable for practically testing fish freshness. Crucially, electron transfer between the heterojunctions increases the chemically adsorbed oxygen on the materials' surface, thereby enhancing the sensor's response sensitivity to triethylamine. This discovery provides new insights and methodologies for the design of highly efficient triethylamine gas sensors. [Display omitted] • A novel triethylamine gas sensor based on mesoporous CdO/CdGa 2 O 4 microspheres has been successfully synthesized. • The sensor based on this material has fast response and low detection limit. • Electron transfer between the heterojunctions increases chemically adsorbed oxygen on the material's surface. • The sensor shows excellent selectivity for triethylamine and can be used in complex environments. [ABSTRACT FROM AUTHOR]

Polymeric graphitic carbon nitride (g-C 3 N 4) shares a structural similarity to graphene, yet it possesses a distinctive electronic band structure, rendering it promising for photoelectric applications. However, g-C 3 N 4 faces inherent limitations such as inadequate crystalline quality, limited conductivity, and a short lifespan of photogenerated charge carriers, all of which impede the photoelectric conversion efficiency. In this work, we introduce a two-step thermal vapor condensation method for depositing compact, crack-free sulfur-doped g-C 3 N 4 thin films. The doped thin films exhibit reduced interlayer spacing, which leads to improved conductivity and charge transfer capabilities. These processes culminate in the creation of sulfur-doped g-C 3 N 4 /GaN thin film heterojunction blue-ultraviolet photodetectors with remarkable photodetection performance, including an ultrahigh on/off ratio of 7.3 × 107 and specific detectivity of 2.06 × 1014 Jones under a low bias of −0.4 V. Moreover, it is found that the n-n heterojunction undergoes a transition from photodiode to photoconduction behavior, attributed to the photoinduced electron trapping effects by sulfur-doped sites, which outcomes a notable gain with the responsivity as high as 581 mA/W. These findings underscore the vast potential of high-quality sulfur-doped g-C 3 N 4 thin films for photoelectric applications. Pre-pyrolyzing melamine as precursors and thiourea as the dopant have been employed to produce high-quality sulfur-doped g-C 3 N 4 thin film, resulting in the creation of sulfur-doped g-C 3 N 4 /GaN thin film n-n heterojunction blue-ultraviolet photodetectors with exceptional attributes, including an ultrahigh on/off ratio of 7.3 × 107 and detectivity of 2.06 × 1014 Jones at 0.4 V. [Display omitted] [ABSTRACT FROM AUTHOR]

The nanometer size Cu2O@WO3·H2O composite material has been prepared by the direct hydrolysis of mesitylcopper (I) on WO3·2H2O nanoleaves. The synthesis has been performed in toluene without the addition of any ancillary ligands. The prepared nanocomposite has been deposited as a gas-sensitive layer on miniaturized silicon devices and heated up gradually to 500 °C in the ambient air. During the heating, the CuWO4 phase is formed upon the reaction of Cu2O with the WO3 support as revealed by the XRD analyses. The as-prepared CuWO4@WO3 sensors have been exposed to 10 ppm of CO or 0.4 ppm of NO2 (RH = 50%). At the operating temperature of 445 °C, a normalized response of 620% towards NO2 is obtained whereas the response to CO is significantly lower (S = 30%). Under these conditions, the sensors prepared either with pristine CuO or WO3 nanostructures are sensitive to only one of the two investigated gases, i.e., CO and NO2, respectively. Interestingly, when the CuWO4@WO3 sensitive layer is exposed to UV light emitted from a 365 nm Schottky diode, its sensitivity towards CO vanishes whereas the response towards NO2 remains high. Thus, the application of UV illumination allowed us to modify the selectivity of the device. This new nanocomposite sensor is a versatile sensitive layer that will be integrated into a gas sensor array dedicated to electronic nose platforms.

This work reports the synthesis of a Fe 2 P/NiCoP n-n heterojunction with well-designed built-in electric field, which can accelerate electron transfer and induce the charge redistribution, thus significantly promoting the kinetics of OER in water/seawater solution. [Display omitted] • The Fe 2 P/NiCoP n-n heterojunction with a 1D/2D core/shell structure is constructed. • The obtained n-n heterojunction has strong electronic interactions. • A built-in electric field is also constructed at the heterointerfaces. • The Fe 2 P/NiCoP n-n heterojunction exhibits superior OER performance and long-term stability. Optimizing the electron cloud density on the catalyst surface is the key to achieving fast kinetics for oxygen evolution reaction (OER). Here, a n-n Fe 2 P/NiCoP core/shell with strong built-in electric field (BEF) is successfully constructed to enable efficient local charge redistribution at heterointerface and contribute to extraordinary OER performance. Remarkably, the optimized Fe 2 P/NiCoP catalyst only requires the overpotentials of 272 and 291 mV to achieve a current density of 10 mA·cm−2 in 1 M KOH and alkaline seawater solutions, along with superb electrochemical stability over 140 h and 120 h, respectively. Detailed experimental and theoretical studies demonstrate that the well-designed BEF at the heterointerface of Fe 2 P/NiCoP n-n heterojunction can accelerate the charge transfer and enhance the conductivity. In addition, the self-propelled electron transfer across the n-n interface can prompt localized charge redistribution at the interface region, leading to enhanced adsorption of OH– and thus significantly boosting the kinetics of OER. This research paves a new avenue for the fabrication of heterostructured catalysts with BEF and optimized interfacial electron cloud for the enhanced OER. [ABSTRACT FROM AUTHOR]

In order to achieve high response, excellent selectivity and stable detection of ethanol vapor, CeO 2 nanodot-decorated ZnSnO 3 hollow microspheres with heterostructures that could meet the requirements of ethanol detection were obtained through a convenient hydrothermal method. The prepared uniform nanodot-decorated hollow microspheres were observed by SEM and TEM, it is noticeable that CeO 2 nanodots of about 10 nm were uniformly anchored on the surface of ZnSnO 3 hollow microspheres with a diameter of 0.8–1.4 μm. Compared with the pure ZnSnO 3 , the 15% CeO 2 /ZnSnO 3 hollow microspheres exhibited higher response (219.2) to 100 ppm ethanol, superior selectivity (ethanol) and rapid response recovery. In addition, a scientific and effective method was used to calculate the ultra-low theoretical gas detection limit (11.3 ppb) of the CeO 2 nanodot-decorated ZnSnO 3 hollow microspheres. The outstanding gas sensing properties were attributed to the existence of large amounts of dissociative oxygen and the n-n heterojunction between ZnSnO 3 and CeO 2. Meanwhile, our work confirmed that CeO 2 nanodot-decorated ZnSnO 3 hollow microspheres have satisfied the application needs of ethanol detection. [ABSTRACT FROM AUTHOR]

Complicated oxygen evolution reaction (OER) poses the bottleneck in improving the efficiency of hydrogen production through water electrolysis. Herein, an integrated strategy to modulate the electronic structure of NiFe layered double hydroxide (NiFe-LDH) is reported by constructing Ag-incorporated NiCo-PBA@NiFe-LDH heterojunction with a hierarchical hollow structure. This "double heterojunction" facilitates local charge polarization at the interface, thereby promoting electron transfer and reducing the adsorption energy of intermediates, ultimately enhancing the intrinsic activity of the catalyst. It is noteworthy that an exchange bias field is observed between NiCo-PBA and NiFe-LDH, which will be conducive to regulating the electron spin states of metals and facilitating the production of triplet oxygen. Additionally, the unique hierarchical nanoboxes provide a large specific surface area that ensures adequate exposure to adsorption sites and active sites. Profiting from the synergistic advantages, the overpotential is as low as 190 mV at a current density of 10 mA cm -2 , with a low Tafel slope of 21 mV dec -1 . Moreover, density functional theory (DFT) calculation further substantiated that the incorporation of Ag in the heterojunction can effectively reduce the adsorption energy of reactant intermediates and enhance the conductivity., (© 2023 Wiley‐VCH GmbH.)

[Display omitted] It is imperative to seek for novel materials with pronounced gas sensing performance towards triethylamine for the sake of human health. Herein, we successfully fabricate an outstanding triethylamine sensor based on CdS/ZnO composite with 0D/2D structure, which are prepared by in-situ growth of CdS quantum dots on ultra-thin ZnO nanosheets. The ratios between the two ingredients are adjusted and their effect is evaluated. The optimal sample exhibits the lowest operating temperature of 200 °C, the highest response value of ~20 and the fastest response time of 2 s. Besides, it also has the virtues of durable stability, excellent selectivity and superior anti-interference ability. The mechanism behind the aforementioned intriguing performance is investigated by X-ray photoelectron spectroscopy, Kelvin probe and density function theory (DFT) simulation. All the results verify that the enhanced gas sensing properties are derived from splendid 0D/2D structure, n - n heterojunction and large specific surface area. Additionally, this study opens an avenue for designing sensors with 0D/2D structure. [ABSTRACT FROM AUTHOR]

• A novel g-C 3 N 4 nanosheet/Cu 3 V 2 O 8 nanocomposite constructed by calcination- method. • The prepared nanocomposite exhibited improved activity on photocatalytic N 2 fixation under visible light irradiation. • The photocatalytic efficiency of g-C 3 N 4 nanosheet/Cu 3 V 2 O 8 nanocomposite was 7.7, 2.6, and 4.3 times higher than that of g-C 3 N 4 , g-C 3 N 4 nanosheet, and Cu 3 V 2 O 8. • Electron-hole pair separation and transfer pathways for g-C 3 N 4 nanosheet/Cu 3 V 2 O 8 nanocomposite based n-n heterojunction formation were discussed. • Stability and reusability of photocatalyst were confirmed in consecutive cycles The production of ammonia in the nitrogen cycle plays an essential role in sustaining life. Recently, clean and efficient photocatalytic processes for the synthesis of ammonia from nitrogen under mild conditions have been considered. However, progress in the design of efficient photocatalysts operating in the visible region for the nitrogen fixation reaction remains a challenge. For the first time, a novel visible-light-driven g-C 3 N 4 nanosheet/Cu 3 V 2 O 8 photocatalyst with prominent photocatalytic nitrogen fixation ability was synthesized by a facile calcination synthetic method. The purity, morphology, crystallinity, optical property, and chemical composition of prepared samples were investigated by XRD, FT-IR, DRS, PL, FESEM, TEM, HRTEM, EDX, XPS, and photoelectrochemical techniques. The g-C 3 N 4 nanosheet/Cu 3 V 2 O 8 nanocomposite exhibited an outstanding improved photocatalytic ammonium generation of 3850 μmol L−1 g−1, which was 2.6 and 4.3 times higher than that of g-C 3 N 4 nanosheet and Cu 3 V 2 O 8. The positive effect of n-n-heterojunction formation increased photocatalytic activity through the built-in electric field between g-C 3 N 4 nanosheet and Cu 3 V 2 O 8 , transferring electron-hole pairs and extending the life of charge carriers. High efficiency and reusability of the photocatalyst after 5 consecutive tests show the prepared nanocomposite potential for large-scale photocatalytic processes. [Display omitted] [ABSTRACT FROM AUTHOR]

Sensors of volatile organic compounds (VOCs) play a vital role in environmental monitoring. Although much progress has been made to develop new sensing materials, it remains challenging to detect a particular VOC selectively and without the interference of humidity. Herein, we report the effect of In2O3 nanoparticles on the VOC-sensing performance of ZnO twin-rods. The VOC-sensing tests were carried out in dry air and at a relative humidity (RH) of 26, 59, and 98%. The results indicated that the In2O3/ZnO heterostructure exhibited an improved sensing performance to triethylamine (TEA) compared to ZnO. In dry air, the responses to 100 ppm of TEA at 350 °C were 60.2 for the In2O3/ZnO heterostructure and 39.2 for pure ZnO. In2O3/ZnO even exhibited a high response of 6.2 to 1 ppm of TEA. Moreover, In2O3/ZnO exhibited a response to TEA up to 46.2 times higher than those of the other VOCs, indicating excellent selectivity. At 98% RH, the In2O3/ZnO heterostructure still had a high sensitivity to TEA, showing a response of 21.2 to 100 ppm of TEA with a response time of 1 s. The improved TEA-sensing performance of the In2O3/ZnO heterostructure can be attributed to the formation of the n-n heterojunction.

[Display omitted] • In 2 O 3 and SnO 2 form an n-n heterojunction, which improves the gas-sensitive properties of SnO 2. • In 2 O 3 grows in situ on SnO 2 , and the composite has a unique hedgehog-like nanoflower morphology with abundant oxygen vacancies. • Improved gas-sensitizing properties attributed to the change in charge density. • Formation of heterojunction leads to In 2 O 3 -SnO 2 composites with higher electron transfer capacity and accelerated charge transfer kinetics. The In 2 O 3 -SnO 2 heterojunction nanostructures resembling hedgehogs were synthesized through hydrothermal method and physical stirring for acetone detection. SEM and TEM characterization showed that the composites were SnO 2 nanosheets (NSs) assembled into a flower-like morphology with In 2 O 3 particles grown in situ on the NSs. The In 2 O 3 -SnO 2 sensor has excellent vapor sensitivity compared to pure SnO 2. At an optimal temperature of 260 ℃, the In 2 O 3 -SnO 2 sensor achieves a response value of 19.4 for acetone vapors at a concentration of 100 ppm. The composites still exhibit excellent gas-sensitized performance at low concentration (100 ppb). The improved gas-sensitized performance of In 2 O 3 -SnO 2 composites is attributed to the sea urchin-like nanoflower morphology enriched with oxygen vacancies and the formation of n-n heterojunctions. To further substantiate its enhancing mechanism, the adsorption behavior of acetone molecules on the fabricated composite material was investigated through the utilization of density functional theory (DFT). This study confirms the enhanced gas sensing performance of In 2 O 3 -SnO 2 heterojunction composites towards acetone and elucidates the enhancement mechanism by DFT calculations. [ABSTRACT FROM AUTHOR]

Increasing requirements for environmental protection have led to the need for the development of control systems for exhaust gases monitored directly at high temperatures in the range of 300–800 °C. The development of high-temperature gas sensors requires the creation of new materials that are stable under these conditions. The stability of nanostructured semiconductor oxides at high temperature can be enhanced by creating composites with highly dispersed silicon carbide (SiC). In this work, ZnO and SiC nanofibers were synthesized by electrospinning of polymer solutions followed by heat treatment, which is necessary for polymer removal and crystallization of semiconductor materials. ZnO/SiC nanocomposites (15–45 mol % SiC) were obtained by mixing the components in a single homogeneous paste with subsequent thermal annealing. The composition and microstructure of the materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The electrophysical and gas sensing properties of the materials were investigated by in situ conductivity measurements in the presence of the reducing gases CO and NH3 (20 ppm), in dry conditions (relative humidity at 25 °C RH25 = 0) and in humid air (RH25 = 30%) in the temperature range 400–550 °C. The ZnO/SiC nanocomposites were characterized by a higher concentration of chemisorbed oxygen, higher activation energy of conductivity, and higher sensor response towards CO and NH3 as compared with ZnO nanofibers. The obtained experimental results were interpreted in terms of the formation of an n–n heterojunction at the ZnO/SiC interface.

• TiO 2 -OVs/Bi 4 O 5 Br 2 nanocomposites as efficient visible-light-active photocatalysts are reported. • The nanocomposite with 30% of Bi 4 O 5 Br 2 displayed the highest activity in RhB degradation. • The activity TiO 2 -OVs/Bi 4 O 5 Br 2 (30%) was almost 23.2 times higher than the TiO 2 sample. • The photocatalyst displayed impressively improved activity in degradations of various pollutants. Despite significant advancements in the improvement of heterogeneous photocatalysis towards water treatment, these processes still have some bottlenecks. In this research paper, oxygen vacancy rich-TiO 2 was combined with Bi 4 O 5 Br 2 nanoparticles (denoted as TiO 2 -OVs/Bi 4 O 5 Br 2) by eco-friendly hydrothermal approach. The outcomes demonstrated that the photoactivity strongly depends on plenteous active sites, reinforced charge segregation, as well as striking visible-light absorption ability in TiO 2 -OVs/Bi 4 O 5 Br 2 nanocomposite with n-n heterojunction. The photoactivity was found to follow the trend: TiO 2 -OVs/Bi 4 O 5 Br 2 (30%) > TiO 2 -OVs > TiO 2. Briefly, the removal efficiencies of RhB, MB, and fuchsine were 100%, 96.2%, and 84.7% using TiO 2 -OVs/Bi 4 O 5 Br 2 (30%) in 120 min, while they were 25.1%, 20.0%, and 15.3% over the TiO 2 , respectively. Further, the boosted rate constant was observed for the photoreduction of Cr (VI) on the TiO 2 -OVs/Bi 4 O 5 Br 2 (30%) nanocomposite, which was 19.4 and 7.8-folds more than the TiO 2 and TiO 2 -OVs photocatalysts, respectively. The radical scavenging tests with different quenchers demonstrated that holes and superoxide anion radicals take part in the degradation reaction. Finally, by investigating the electrochemical properties, a mechanism was offered to describe the improved e–/h+ pairs separation and migration. This research displayed that the design of n-n heterojunction using TiO 2 -OVs could be suitable for severely improving photocatalytic performance of TiO 2 under visible light. [ABSTRACT FROM AUTHOR]

In the study, ZIF-8@BIOI composites were synthesized by the hydrothermal method and then calcined to acquire the ZnO@Bi5O7I composite as a novel composite for the photocatalytic deterioration of the antibiotic tetracycline (TC). The prepared ZnO@Bi5O7I composites were physically and chemically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmet–Teller (BET) surface area, UV–Vis diffuse reflectance spectroscopy (DRS), emission fluorescence spectra, transient photocurrent response, electrochemical impedance spectra and Mott–Schottky. Among the composites formed an n–n heterojunction, which increased the separation efficiency of electrons and holes and the efficiency of charge transfer. After the photocatalytic degradation test of TC, it showed that ZnO@Bi5O7I (2:1) had the best photodegradation effect with an 86.2% removal rate, which provides a new approach to the treatment of antibiotics such as TC in wastewater.

In this work, a novel heterojunction based on ZnSnO3/ZnO nanofibers was prepared by a simple electrospinning method. The crystal, structural, and surface compositional properties of ZnSnO3 and ZnSnO3/ZnO composite nanofibers were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectrometer (XPS), and Brunauer–Emmett–Teller (BET). Compared to pure ZnSnO3 nanofibers, the ZnSnO3/ZnO heterostructure nanofibers had high sensitivity and selectivity response with the fast response toward ethanol gas at low operational temperature. The sensing response of the sensor based on ZnSnO3/ZnO composite nanofibers was 19.6 toward 50 ppm ethanol gas at 225 °C, which was about 1.5 times superior to that of pure ZnSnO3 nanofibers. It can be owed mainly to the oxygen vacancies and the synergistic effect between ZnSnO3 and ZnO.

The Ag-Pi/BiVO 4 heterojunction shows mechanism of PEC water oxidation. • Ag-Pi/BiVO 4 n - n heterojunction were successfully prepared by SILAR method. • The built-in field of Ag-Pi/BiVO 4 promotes the charge separation efficiency. • The desirable stability endows Ag-Pi/BiVO 4 with a great potential in PEC system. • The photocurrent density of optimal Ag-Pi/BiVO 4 has been enhanced to 2.32 mA/cm2. The limitation of pristine BiVO 4 photoanode severely causes the high carrier recombination efficiency and low energy conversion efficiency in the photoelectrochemical (PEC) system. In this work, the Ag-Pi/BiVO 4 n - n heterojunction has been rationally designed and fabricated for efficient PEC water splitting, through successive ionic layer adsorption reaction method. The built-in field of Ag-Pi/BiVO 4 significantly promotes the separation efficiency of photogenerated carriers, benefiting for the participation of abundant holes in water oxidation. The photocurrent density of 40-Ag-Pi/BiVO 4 has been enhanced to 2.32 mA/cm2, which is 4.5 times than that of the pristine BiVO 4. Compared with the pristine BiVO 4 (6.5%), the IPCE value of 40-Ag-Pi/BiVO 4 achieves 22% (410 nm, 1.23V RHE). In addition, the charge injection efficiency (η injection) and charge separation efficiency (η separation) of 40-Ag-Pi/BiVO 4 have been achieved to 74.36% (1.23 V RHE) and 31.57% (1.23 V RHE), respectively, revealing the excellent carriers' transfer behavior in the both bulk and interface. The desirable stability endows Ag-Pi/BiVO 4 system with a great potential in the practical application in PEC water splitting, and the corresponding mechanism for in-depth understanding the process of carriers' transfer in Ag-Pi/BiVO 4 structure has been also proposed. Therefore, the construction of Ag-Pi/BiVO 4 heterojunction will provide a new insight for the configuration of efficient PEC system. [ABSTRACT FROM AUTHOR]

A semiconductor photocatalyst was prepared in facile, standard conditions by integrating 1% metal-free, sulphur-doped graphene oxide (sGO) as cocatalyst and Ag3VO4 as photocatalyst and characterised via spectroscopic, microscopic and voltammetric techniques. The catalytic activity was performed on notable water pollutants like textile dyes and fungicide employing various techniques. Cationic dyes such as methylene blue and rhodamine B were degraded > 99% with above 90% organic carbon content removal indicating total mineralisation while anionic dyes were degraded 75–80% in 1 h. For the first time, a dithiocarbamate fungicide thiram is degraded to give thiourea as a product in 1 h. Photocatalysis follows pseudo-first order kinetics with rate 3.67, 49.50 and 3.19 times higher than Ag3VO4, sGO and GO-Ag3VO4 respectively with excellent stability and recyclability. One percent sGO aided excellent carrier separation boosted by electrons and surface defects from sGO, morphology and n-n heterojunction formation. The catalyst efficiently removed 82.8% of the total organic carbon content of a real water sample from the textile mill under 2-h sunlight irradiation. [ABSTRACT FROM AUTHOR]

In this work, perovskite structure of BaTiO3 was coupled with Fe2O3 in different molar ratios achieving the best photocatalytic performance of CO2 reduction in the presence of CH4 as reducing agent; both of them are main greenhouse gases. The photocatalysts were synthesized by facile hydrothermal method. The samples were characterized by XRD, FTIR, FESEM, EDX, UV–Vis DRS, and photoluminescence (PL) analyses. The BaTiO3 synthesized in this research showed a weak PL signal which is due to the intrinsic ferroelectric property as has been observed in previous reports. Compared to the pure BaTiO3 and Fe2O3, the heterojunctions exhibited enhanced photocatalytic activity. The maximum CO2 reduction under visible light irradiation was obtained to be 22% during 60 min process time. The enhanced photocatalytic activity could be attributed to the increased optical absorption, the good separation, and immigration of photogenerated charge carriers that decreased the recombination rate of charge carriers in the n–n heterojunction. [ABSTRACT FROM AUTHOR]

The health of people and the environmental ecosystem are severely threatened by pollutants. Photocatalysis a desirable and effective method for pollutants removal that is associated with the adsorption phenomenon. The CoMoO 4 /ZnO photocatalysts were fabricated by facile template free methods. 1D-0D of CoMoO 4 /ZnO was fully characterized by different techniques for investigation of Pb+2, Cd+2 and Zn+2 removal in aqueous medium. Although the support photocatalyst did not show proper activity, the formation of the heterostructure led to the significant removal of Pb+2 ion. Adequate adsorption of Pb+2 ion was accompanied by photocatalytic process of visible-light-driven n-n CoMoO 4 /ZnO heterojunction, caused to high performance. Effect of different parameters on photoactivity, and kinetics and thermodynamic were considered. The synergistic effect induced by formation of 1D CoMoO 4 containing 0D ZnO particles drastically improve the charge carrier generation, transfer and separation. Consequently, the prepared CoMoO 4 /ZnO composites are considered good candidates for wastewater treatment. [Display omitted] • The 1D-0D CoMoO 4 /ZnO composite was studied for synergistic effects of adsorption and photocatalysis. • Enhanced removal of heavy metal ion from water was observed. • Mechanism, kinetics and thermodynamic of process were investigated. [ABSTRACT FROM AUTHOR]

A TiO2@Cu2O semiconductor heterostructure with better photochemical response compared to TiO2 was obtained using an electrochemical deposition method of Cu2O on the surface of TiO2 nanotubes. The choice of 1D nanotubes was motivated by the possibility of achieving fast charge transfer, which is considered best suited for photochemical applications. The morphology and structural properties of the obtained heterojunction were determined using standard methods —SEM and Raman spectroscopy. Analysis of photoelectrochemical properties showed that TiO2@Cu2O heterostructures exhibit better properties resulting from an interaction with sunlight than TiO2. A close relationship between the morphology of the heterostructures and their photoproperties was also demonstrated. Investigations representing a combination of photoelectrochemical cells for hydrogen production and photocatalysis—photoelectrocatalysis—were also carried out and confirmed the observations on the photoproperties of heterostructures. Analysis of the Mott–Schottky plots as well as photoelectrochemical measurements (Iph-V, Iph-t) showed that TiO2 as well as, unusually, Cu2O exhibit n-type conductivity. On this basis, a new energy diagram of the TiO2@Cu2O system was proposed. It was found that TiO2@Cu2O n-n type heterostructure prevents the processes of photocorrosion of copper(I) oxide contained in a TiO2-based heterostructure.

Space charge transfer is an effective strategy to regulate the electron density of narrow bandgap semiconductors for enhancing electrocatalytic activity. Herein, the CoNiLDH/FeOOH n-n heterojunction hollow nanocages structure is constructed. The hollow structure provides abundant catalytic active sites and enhances mass transfer. The space charge region in the n-n heterojunction significantly promotes the adsorption of OH - and electron transfer; and the built-in electric field accelerates the electron transport, optimizes the electronic structure during the catalytic reaction process, and ensures the stability of surface charged active center sites in the heterojunction. Thus, CoNiLDH/FeOOH delivers an excellent oxygen evolution reaction (OER) overpotential of 250 mV to achieve a current density of 10 mA cm -2 with a small Tafel slope of 60 mV dec -1 , and superior electrocatalytic durability for 210 h at a high current density. Density functional theory calculations further verify that the space charge effect and built-in electric field in the n-n heterojunction of CoNiLDH/FeOOH can improve the electron transfer and lower the adsorption energy of OH - and the reaction energy barrier of the rate-determining step. This work provides a new fundamental understanding of the space charge effect of semiconductor heterojunction during the electrocatalytic process for developing more efficient OER electrocatalysts., (© 2023 Wiley-VCH GmbH.)

Graphical abstract Highlights • A Type II n-n staggered heterojunction photoanode of V 2 O 5 /BiVO 4 was synthesized. • A high photocurrent density of 1.53 mA/cm2 at 1.5 V vs Ag/AgCl was measured. • This was due to lower charge resistance and faster transit time showed by EIS/IMPS. • Photo-excitons transfer in V 2 O 5 /BiVO 4 was validated by theoretical band diagram. Abstract Conventional photoanode using a singular semiconductor material is not technically viable for photoelectrochemical (PEC) water oxidation owing to the properties relating to its wide band gap, sluggish charge mobility, as well as poor separation and rapid recombination of photogenerated charge carriers. The main aim of this study was to fabricate an n-n heterojunction photoanode of V 2 O 5 /BiVO 4 via a facile electrodeposition synthesis method in order to overcome the technical bottlenecks encountered in conventional singular photoanode structures. Additionally, the synergistic effect of band potentials matching and conductivity difference between BiVO 4 and V 2 O 5 were studied using LSV, IMPS, EIS, HR-TEM, XRD, XPS, Raman and ultraviolet-visible spectroscopies. This was followed by the performance evaluation of the light-induced water splitting using a standard three-electrode assembly PEC cell under 1.5 AM solar simulator. Results showed that the V 2 O 5 /BiVO 4 heterojunction photoanode achieved a significantly improved photocurrent density of 1.53 mA/cm2 at 1.5 V vs Ag/AgCl, which was a 6.9-fold and a 7.3-fold improvement over the individual pristine BiVO 4 (0.22 mA/cm2) and V 2 O 5 (0.21 mA/cm2), respectively. The improvement was attributed to the lower charge resistances at the FTO/semiconductor, semiconductor/FTO and semiconductor/electrolyte interfaces as well as the fast transit time (τ) of 6.4 ms for photo-injected electrons in the V 2 O 5 /BiVO 4 heterojunction photoanode. Finally, the experimental results were used to reconstruct a theoretical band diagram in validating the heterojunction alignment between V 2 O 5 and BiVO 4 as well as in elucidating the photogenerated charge carriers transfer mechanism in the V 2 O 5 /BiVO 4 heterojunction photoanode. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Activated graphitic carbon nitride was combined with Fe 3 O 4 and Bi 2 S 3. • Activity of the nanocomposite in degradation of RhB is 16.6 times superior than g-C 3 N 4. • The nanocomposite displayed exceptional activity in removal of MB, MO, and Cr (VI). • The utilized nanocomposite was magnetically separated from the treated system. Abstract Herein, hydrogen peroxide activated graphitic carbon nitride (agCN) was combined with Fe 3 O 4 and Bi 2 S 3 to fabricate agCN/Fe 3 O 4 /Bi 2 S 3 nanocomposites via facile refluxing method, as visible-light-induced photocatalysts for photodegradations of anionic and cationic dyes such as MO, RhB, MB, and photoreduction of Cr(VI). The fabricated samples were explored by XRD, EDX, XPS, TGA, SEM, TEM, HRTEM, VSM, PL, FT-IR, BET, and UV-vis DRS. Photocatalytic activity of the nanocomposite with 20% of Bi 2 S 3 was 16.6, 40.4, 19.5, and 12.5 times more than that of the pristine gCN in removal of RhB, MB, MO, and Cr(VI), respectively. A plausible photocatalytic mechanism on the agCN/Fe 3 O 4 /Bi 2 S 3 nanocomposites was proposed by construction of n-n heterojunction between gCN and Bi 2 S 3. Also, stability of the magnetic hybrid was characterized through cyclic photocatalytic tests. [ABSTRACT FROM AUTHOR]

Photocatalytic reduction of heavy metal ions utilizing nanostructured semiconductor photocatalysts is a promising ecological way, thanks to its simplicity and feasibility. In this article, the improved photoreduction of mercury (II) ions (Hg2+) is achieved over wrinkled barium stannate (BaSnO 3) nanosheets modified by manganese cobaltate (MnCo 2 O 4) nanoparticles. The MnCo 2 O 4 was coupled to solvothermally-produced BaSnO 3 at 4.0–16.0 wt% by impregnation. The MnCo 2 O 4 /BaSnO 3 heterojunctions showed mesoporous surfaces with 133–150 m2 g 1 of surface areas. The visible light harvesting is improved owing to bandgap reduction down to 2.31 eV for 9.0 wt% MnCo 2 O 4 -impregnated BaSnO 3 compared to 2.99 eV for the bare BaSnO 3. The complete photoreduction of 368.30 µM Hg2+ utilizing 9.0% MnCo 2 O 4 /BaSnO 3 is achieved at a dosage of 2.4 gLẌ with a rate of 69.54 µM min–1 in 30 min. This optimized photocatalyst is also recyclable five times with 97% of its initial performance. The magnificent activity of MnCo 2 O 4 /BaSnO 3 is accredited to the improved visible-light harvesting and efficient charge separation by the controllable impregnation of MnCo 2 O 4. [Display omitted] • 159 m2g–1 wrinkled nano BaSnO 3 sheets were synthesized by solvothermal route. • Impregnation of 4.0–16.0 wt% MnCo 2 O 4 nanoparticles forming n-n heterojunctions. • MnCo 2 O 4 induced visible light harvesting and bandgap reduction to 2.31 eV. • Photoreduction of Hg2+ enhanced by > 13.1 times at 69.54 µM min–1 compared to BaSnO 3. • Stable heterojunction photocatalyst for five runs. [ABSTRACT FROM AUTHOR]

This work aimed at constructing defective heterojunction to optimize the electronic structure and exploring the intrinsic mechanism of its excellent electrocatalytic performance. Specifically, Feδ+ is introduced through the cation exchange method using hexagonal interpenetrating twin Zn/Co-ZIFs as precursors. Then, the n-n heterojunction featuring oxygen vacancies at the biphasic interface of Fe 2 O 3 and ZnCo 2 O 4 is constructed through calcination. The obtained electrode for oxygen evolution reaction (OER) only requires 261 mV overpotential to achieve a current density of 10 mA cm−2, and shows exceptional stability at high current density, lasting for 50 h. Density functional theory calculations confirm that the construction of heterojunction can effectively optimize the d‐band center and improve the adsorption of the active center on oxygen-containing intermediates, thus optimizing the Gibbs free energy of the OER. This study provides inspiration and interface engineering strategy for the design of highly active catalysts, and enhances our understanding of the OER mechanism. [Display omitted] • The novel hexagonal hollow structures increased specific surface area and facilitated exposure of active sites. • More oxygen vacancies are introduced by Feδ+ exchange which improves the intrinsic activity of the active site. • N-n heterojunction interface induces spontaneous charge transfer and effectively optimizes the surface electronic state. • DFT calculations confirmed that heterojunctions with defects can effectively optimize the Gibbs free energy of the OER. [ABSTRACT FROM AUTHOR]

An n-n type heterojunction comprising with CuN and BN dual active sites is synthesized via in situ growth of a conductive metal-organic framework (MOF) [Cu 3 (HITP) 2 ] (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) on hexagonal boron nitride (h-BN) nanosheets (hereafter denoted as Cu 3 (HITP) 2 @h-BN) for the electrocatalytic nitrogen reduction reaction (eNRR). The optimized Cu 3 (HITP) 2 @h-BN shows the outstanding eNRR performance with the NH 3 production of 146.2 µg h -1 mg cat and the Faraday efficiency of 42.5% due to high porosity, abundant oxygen vacancies, and CuN/BN dual active sites. The construction of the n-n heterojunction efficiently modulates the state density of active metal sites toward the Fermi level, facilitating the charge transfer at the interface between the catalyst and reactant intermediates. Additionally, the pathway of NH -1 and the Faraday efficiency of 42.5% due to high porosity, abundant oxygen vacancies, and CuN/BN dual active sites. The construction of the n-n heterojunction efficiently modulates the state density of active metal sites toward the Fermi level, facilitating the charge transfer at the interface between the catalyst and reactant intermediates. Additionally, the pathway of NH 3 production catalyzed by the Cu 3 (HITP) 2 @h-BN heterojunction is illustrated by in situ FT-IR spectroscopy and density functional theory calculation. This work presents an alternative approach to design advanced electrocatalysts based on conductive MOFs., (© 2023 Wiley-VCH GmbH.)

It is essential to develop a high activity and stability photoanode for enhancing PEC water splitting performance. According to energy band matching principle the Fe 2 O 3 /BiVO 4 heterojunction based photoanode is constructed by electrodeposition and metal organic decomposition, following by electrodeposited NiFe-LDH on heterojunction to structure a trinary integrating photoanode. The structure of material and PEC properties of the photoanode are systemically studied, the results show that the photoanode achieves the highest photocurrent density that is about 4.25 times and 2 times higher than that of pristine α-Fe 2 O 3 and BiVO 4 photoanodes. The IPCE value is 3.7 times higher than α-Fe 2 O 3 and the onset potential has a significant cathodic shift of 400 mV compared to the pristine α-Fe 2 O 3 for the ternary integrating photoanode. These results are higher than or are comparable to other α-Fe 2 O 3 composites reported in literatures, which is attributed to the efficient separation of the photoexcited electron-hole pairs and alleviates holes accumulation at the surface of electrode due to the double action of semiconductor junction and co-catalyst of NiFe-LDH. [ABSTRACT FROM AUTHOR]

We report a novel composite of α-Fe 2 O 3 /BiVO 4 with n-n heterojunctions for the first time and application in detecting low concentration NO 2 gas. The flower-like α-Fe 2 O 3 hierarchical nanostructures were prepared by the solvothermal method followed by BiVO 4 nanoparticles decorated on α-Fe 2 O 3 surface by metal-organic decomposition to structure the heterojunctions of α-Fe 2 O 3 /BiVO 4 . The structure and morphology of material were characterized and the sensing properties to NO 2 were examined. The results show that the α-Fe 2 O 3 /BiVO 4 composite (atomic ratio of 8:1:1 for Fe: Bi: V) to 2 ppm NO 2 exhibits a four times higher response than pristine α-Fe 2 O 3 at 110 °C, excellent selectivity, and long-term stability. The enhanced sensing properties can be attributed to the porous hierarchical structure of composite and the formation of inner electronic field (IEF) caused by n-n heterojunction at interface between α-Fe 2 O 3 and BiVO 4. [ABSTRACT FROM AUTHOR]

Efficient visible-light active ZnO/Bi 2 MoO 6 /AgBr nanocomposites were fabricated using ultrasonic-assisted method. Crystallinity, structural, morphological, optical, and textural features of the photocatalysts were investigated by XRD, SEM, TEM, EDX, FT-IR, UV–Vis DRS, PL, and BET techniques. Photocatalytic performance of the ZnO sample was remarkably increased by combining with Bi 2 MoO 6 and AgBr, due to formation of tandem n-n heterojunctions. The as-prepared ZnO/Bi 2 MoO 6 /AgBr nanocomposites exhibited excellent photocatalytic activity and stability under visible light in comparison with the ZnO, ZnO/Bi 2 MoO 6, and ZnO/AgBr samples. About ∼97% of RhB was removed in 70 min by the optimized ZnO/Bi 2 MoO 6 /AgBr (20%) nanocomposite, which is 76.4, 4.75, and 17.3 times as fast as the ZnO, ZnO/Bi 2 MoO 6 (20%) and ZnO/AgBr (20%) photocatalysts, respectively. It was confirmed that due to improved utilization of visible light, considerable separation of the charge carriers, and enlarged surface area, the ZnO/Bi 2 MoO 6 /AgBr (20%) nanocomposite exhibited greatly improved photocatalytic activity in degradations of various dye contaminants under visible-light illumination. In addition, plausible photocatalytic degradation mechanism for the highly enhanced performances were also proposed. [ABSTRACT FROM AUTHOR]

α-Fe 2 O 3 nanoneedles were directly grown on the surface of Al 2 O 3 tubes by a cost-effective hydrothermal method. In addition, the construction of Au nanoparticle-loaded SnO 2 /α-Fe 2 O 3 core/shell heterostructure was fabricated by employing pulsed laser deposition (PLD) and DC-sputtering methods Gas sensors were fabricated from Au@SnO 2 /α-Fe 2 O 3 core-shell nanoneedles on Al 2 O 3 tubes, and their sensing properties have investigated for response to various target gases. The results indicated that the sensor based on Au@SnO 2 /α-Fe 2 O 3 core-shell nanoneedles showed superior selectivity toward triethylamine (TEA) gas, giving a response of 39–100 ppm, which was higher than that of α-Fe 2 O 3 nanoneedles and SnO 2 /α-Fe 2 O 3 core-shell nanoneedles. Moreover, the sensor based on Au@SnO 2 /α-Fe 2 O 3 core-shell nanoneedles showed an obvious better linearity ( R  = 0.9975) of sensing characteristics than of two other sensors. The enhanced sensing properties are discussed with the semiconductor depletion layer model along with the Schottky contact and N–N heterojunction theory. [ABSTRACT FROM AUTHOR]

Two dimensional semiconductors are promising gas sensing materials due to their large surface-to-volume ratio. However, some drawbacks just like low response, long recovery time, and insufficient selectivity limits the development of two dimensional semiconductors gas sensors. In order to optimize the gas sensing properties of MoS 2 sensors, tri-material compound nanostructure of sensing materials is designed and synthesized by depositing Au and SnO 2 nanoparticles on the surface of MoS 2 nanoflowers. Comparing with the pristine MoS 2 sensor, the Au@SnO 2 /MoS 2 sensor exhibits better sensing properties to triethylamine, such as higher sensitivity and faster response/recovery speed. The enhanced sensing properties of Au@SnO 2 /MoS 2 sensor are discussed from the points of Au@SnO 2 Schottky contact and SnO 2 /MoS 2 N-N heterojunction on the basic of depletion layer model. Moreover, MoS 2 nanoflowers are directly grew on Al 2 O 3 tubes via a facile and cost-effective hydrothermal method. And the construction of Au nanoparticles decorated SnO 2 /MoS 2 nanoflowers heterostructure were built by employing the pulsed laser deposition and DC-sputtering methods. [ABSTRACT FROM AUTHOR]