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In this study, we demonstrate the emergence of NO2 gas sensing capabilities in the typically non-active NiWO4, a strongly correlated electron system (SCES), by introducing substitutional Fe at the Ni site. NiWO4 typically exhibits strong Coulombic repulsion between Ni atoms, resulting in a large band gap of over 3.0 eV and insulating behavior. This correlated behavior is clearly reflected in the significant increase of band gap when considering the Hubbard U correction for the cations, bringing the theoretical value closer to the observed value. The single-phase Fe0.5Ni0.5WO4 displays a notable shift in the [NiO6] symmetric vibration mode and an increase in magnetization. Additionally, theoretical calculations confirm the preservation of the wide band gap, with the Fe and O levels generated within the band gap. These findings indicate that Fe located in the Ni sites modulate Coulombic repulsion in NiWO4 SCES insulators. Unlike the poor gas-sensing performance of intrinsic NiWO4, Fe0.5Ni0.5WO4 exhibits a significant NO2 response (Rg/Ra) of 11 at 200°C than other gases and a limit of detection (LOD) of 46.4 ppb. This study provides a pathway for realizing gas-sensing performance in strongly correlated electron insulators with large band gaps through the introduction of dopant levels at the cation sites.

The demand for gas-sensing operations with lower electrical power and guaranteed sensitivity has increased over the decades due to worsening indoor air pollution. In this report, we develop room-temperature operational NH3 gas-sensing materials, which are activated through electron doping and crystal structure distortion effect in Fe0.2Ni0.8WO4. The base material, synthesized through solid-state synthesis, involves Fe cations substitutionally located at the Ni sites of the NiWO4 crystal structure and shows no gas-sensing response at room temperature. However, doping Na into the interstitial sites of Fe0.2Ni0.8WO4 activates gas adsorption on the surface via electron donation to the cations. Additionally, the hydrothermal method used to achieve a more than 70-fold increase in the surface area of structure-distorted Na-doped Fe0.2Ni0.8WO4 powder significantly enhances gas sensitivity, resulting in a 4-times increase in NH3 gas response (Rg/Ra). Photoluminescence and XPS results indicate negligible oxygen vacancies, demonstrating that cation contributions are crucial for gas-sensing activities in Na-doped Fe0.2Ni0.8WO4. This suggests the potential for modulating gas sensitivity through carrier concentration and crystal structure distortion. These findings can be applied to the development of room-temperature operational gas-sensing materials based on the cations.

Recent years have seen a great deal of interest in the exceptional biological activities such as antioxidant, antimicrobial, antiinflammation, antidiabetic and anticancer activity of various biosynthesized Metal Oxide nanoparticles. Among these metal oxide nanoparticle ZnO NPs is gaining its important in various biological applications is increasingly gain prominence. Thus, the green production of ZnO NPs using plant extract has been demonstrated as a one step, environmentally friendly and cost-effective process. This paper describes the utilization of an aqueous extract of Brassica juncea (L.) Czern seed as a reducing agent in the creation of ZnO NPs from Zinc Sulfate using a green synthesis approach. UV–visible spectroscopic peak at around 363 nm verifies the production of ZnO NPs. FE-SEM was confirmed the spherical forms of produced ZnO NPs. The average particle size of produced ZnO NPs was found to be 13.35 nm from TEM analysis. On screening the ZnO NPs for antioxidant activity it showed scavenging activity with 62.40 %, with IC50 value of 68.30 µg/mL through DPPH assay. The antidiabetic activity was found to be 72 %, with IC50 value of 71.76 μg/mL, using alpha amylase assay. In anti-inflammatory activity, the activity was recorded as 68.50 % and IC50 value as 64.67 µg/mL, using BSA denaturation assay. The synthesized nanoparticles exhibited anticancer activity against the MCF-7 and A549 cell lines. The determined IC50 value of produced ZnO NPs for these two cell lines was found to be 43.83 µg/mL and 41.48 µg/mL respectively. Additionally, a hyperchromic shift in the absorbance was noted when CT-DNA interacted with biosynthesized ZnO NPs. These findings confirm that the ZnO NPs synthesized from Brassica juncea (L.) Czern seed exhibit significant biological properties namely antioxidant, antidiabetic and cytotoxic activity. Among all these activities, the biosynthesized ZnO NPs showed excellent cytotoxic activity with the IC50 values, thus proving its effectiveness.

Thermo-electrochemical cells (TECs) are able to convert heat into electricity. They are formed by two electrodes (typically Pt) separated by a redox electrolyte (usually 0.4 M aqueous ferro/ferricyanide). The widely adopted architecture of TECs consists of the two electrodes separated by an electrolyte channel. To our knowledge, no studies have been reported exploring a different architecture. Here, we evaluate an alternative configuration, which comprises a substrate with the two electrodes at its ends and with the electrolyte added on the top contacting both electrodes, forming a planar configuration. We explore first the use of the standard Pt electrodes deposited on top of a conductive glass substrate. Then, we replace the Pt by nanostructured and porous Sb-doped SnO2. The planar configurations are compared with their corresponding typical architectures using the common ferro/ferricyanide electrolyte. It was found that the planar TEC with Sb:SnO2 reached a temperature coefficient of 1.76 mV/K, higher than the value obtained in the standard configuration with Sb:SnO2 (1.21 mV/K), and also higher than the planar architecture with Pt electrodes, which showed the typical value for the ferro/ferricyanide electrolyte (1.45 mV/K). As a consequence of this significantly larger value, a 29.7 % higher maximum power output than the planar TEC with Pt was observed. Our study identifies for the first time interesting new features when a planar architecture is employed, opening the door to explore in more detail this alternative configuration in TECs.

To meet today’s requirements, new active catalysts with reduced noble metal content are needed for hydrogen sensing. A palladium-functionalized nanostructured Ni0.5Co2.5O4 catalyst with a total Pd content of 4.2 wt% was synthesized by coprecipitation to obtain catalysts with an advantageous sheet-like morphology and surface defects. Due to the synthesis method and the reducible nature of Ni0.5Co2.5O4 enabling strong metal-metal oxide interactions, the palladium was highly distributed over the metal oxide surface, as determined using scanning transmission electron microscopy and energy-dispersive X-ray investigations. The catalyst tested in planar pellistor sensors showed high sensitivity to hydrogen in the concentration range below the lower flammability limit (LFL). At 400 °C and in dry air, a sensor response of 109 mV/10,000 ppm hydrogen (25% of LFL) was achieved. The sensor signal was 4.6-times higher than the signal of pristine Ni0.5Co2.5O4 (24.6 mV/10,000 ppm). Under humid conditions, the sensor responses were reduced by ~10% for Pd-functionalized Ni0.5Co2.5O4 and by ~27% for Ni0.5Co2.5O4. The different cross-sensitivities of both catalysts to water are attributed to different activation mechanisms of hydrogen. The combination of high sensor sensitivity to hydrogen and high signal stability over time, as well as low cross-sensitivity to humidity, make the catalyst promising for further development steps.

Thermo-electrochemical cells (or thermogalvanic cells or thermocells, TECs) have gained attention as devices able to convert low temperature heat into electricity. Within TECs, Pt is one of the most employed electrodes, since it exhibits a fast transfer of electrons with the redox couple in the electrolyte. However, its high price represents a serious drawback. Here, we analyze the use of nanostructured and porous antimony-doped tin oxide (Sb:SnO2) as electrode material. Electrodes of different thickness (320, 550 and 1550 nm) were fabricated by spin coating to study the effect of the electrode area in contact with the electrolyte. F:SnO2 (FTO) glass was used as a substrate and the typical 0.4 M potassium ferro/ferricyanide aqueous solution served as electrolyte. An impedance spectroscopy analysis under operating conditions (10 K temperature difference) showed that the Sb:SnO2 electrodes exhibit the same excellent kinetics as Pt for all the different thickness. On the other hand, the power output density was thickness independent, since the temperature coefficients and the series and mass-transport resistances were similar, leading to no performance improvements when the electrode area in contact with the electrolyte was significantly increased. Finally, the Carnot-related efficiencies estimated for the Sb:SnO2 cells were in the same order of magnitude as for Pt electrodes. These results open the possibility to use Sb:SnO2 as a suitable electrode in TECs at low cost.

Dyes are the most widely employed materials for coloring applications, especially for industrial purposes; thus, dyes are applied in the textile, cosmetics and foodstuffs. Dyes are very important owing to their applications in all aspects of human life. Accordingly, the production volume of dyes around the world is increasing. In this study, a new type of multifunctional material: polyaniline/Nb2O5/MnO2 and polyaniline/Nb2O5/Cr2O3 nanocomposites, was prepared by chemical polymerization from aniline monomer in the presence of metal oxides (Nb2O5, Cr2O3, and MnO2) and an oxidant (ammonium persulfate) in acidic aqueous solution for the elimination of dye from water. Herein, the nanocomposite was found to be a favorable adsorbent for wastewater treatment due to its high adsorption and efficiency, self-regeneration quality, low cost and easy synthesis. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and UV-visible spectroscopy were used to assess the synthesized nanocomposites' characteristics. From the results, we discovered that polyaniline nanocomposites doped with Nb2O5 and MnO2 nanoparticles had a higher adsorption efficiency (~97.37%) than those found in polyaniline with Cr2O3 and MnO2 (~94.3%). We looked at the adsorption conditions, including the medium's pH, the initial dye concentration, the dosage of the adsorbent, and the adsorption time.

A typical study has been performed for synthesizing Ag2O and ZnO nanoparticles. In our case, aloe vera extract was used as a reducing agent for synthesizing Ag2O. This green synthesis of silver oxide used silver nitrate (AgNO3) as a precursor material. On the other hand, the direct precipitation method was used for synthesizing zinc oxide nanoparticles, in which the precursor materials used were zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and potassium hydroxide (KOH). Afterward, the characterization of these synthesized nanoparticles was done by the X-ray diffraction (XRD) method. Then, the crystal size, lattice strain, stress, and energy density of synthesized ZnO and Ag2O were determined by using XRD peak profile analysis. Among the various available models for determining these microstructural parameters, we explored the Scherrer model, the linear straight-line method of the Scherrer equation, the Monshi-Scherrer model, the Sahadat-Scherrer model, the Williamson-Hall model (including the uniform deformation model, the uniform stress deformation model, the uniform deformation energy density model), the size-strain plot method, the Halder-Wagner model, etc. By employing the crystal size values from these models, the accuracy and validity of crystals were also performed. The synthesized products were also characterized by the exploration of functional groups (by FTIR) and optical band gaps (by UV technique).

In this study, we fabricated a divergent strategy to enhance the electrochemical capacitive properties of electrodes via the cost-effective multistep green and facile electrodeposition and brush coating technique of PEDOT-TiO2/GO/PEDOT-TiO2 composite. The synthesised composite showed both EDLCs and pseudocapacitive behaviour with a good specific capacitance of 501 Fg−1 for sandwiched structure at 1 Ag−1. From the results, synthesized composite has a better ion transportation mechanism which leads to a fast charge–discharge cycle as well as a very high value of power density (500 kW/ kg) suitable for supercapacitor applications. The substance demonstrated excellent electrochemical stability, retaining 94 % of capacitance after 2000 cycles. The obtained nanocomposites were examined by FTIR, XRD, Raman, SEM-EDX and electrochemical analyses such as CV, GCD and EIS analyses. We consider that the highly stable PEDOT-TiO2/GO/PEDOT-TiO2 nanocomposite with super-capacitive behaviours is a very promising material for high-performance electrochemical storage.

Cuprous oxide is a potential photocatalyst for the reduction of CO2. However, its high rate of charge recombination and low ability to adsorb CO2 limit its activity, particularly when gaseous CO2 was used. Herein, a Cu-based metal-organic framework (Cu-MOF-74) with high CO2 adsorption is coated onto Cu2O nanowires by a topotactic transformation method. The optimized Cu2O@Cu-MOF-74 composite thin film showed a CH4 evolution rate 4.5 times higher than that of bare Cu2O under visible light illumination (>420 nm), with water vapor as the electron donor. Analysis results of electrochemical impedance spectroscopy, transient photocurrent measurements, and fluorescence spectroscopy collectively suggest that the decoration of Cu2O with Cu-MOF-74 facilitates electron extraction from excited Cu2O, thereby inducing long-lived photocharges for the reduction of CO2. This study provides insights into the modification of transition metal oxides for application in photocatalysis by coating the surface with metal-organic frameworks.

Production of butadiene from biomass-based tetrahydrofuran (THF) is explored as an alternative to the existing petroleum-based processes. Metal oxide catalysts have been shown to exhibit varying product selectivities when reacted with THF. Among those oxides, ZrO2 showed the highest selectivity for butadiene. In contrast, Al2O3 showed the highest selectivity for the competing retro-Prins products, C3H6 and HCHO. The reasons behind the varying selectivity across oxides are unclear. In this work, we employ periodic density functional theory and mean-field microkinetic modeling to investigate the mechanism of the reaction of THF to butadiene and retro-Prins products on t-ZrO2 (101) (dry and hydrous) and on γ-Al2O3 (110). Our simulations reproduce the experimental selectivity trends. High selectivity for butadiene is promoted by the presence of neighboring Lewis acid metal sites that facilitate E1cB hydroxyl elimination from a 3-butenoxide intermediate; on hydrous Al2O3; where such neighboring Lewis acid centers are not available, the butenoxide undergoes E2 elimination and retro-Prins products ensue. The THF ring opening is rate-determining on ZrO2, whereas the γ-proton elimination that yields the 3-butenoxide intermediate is rate controlling on hydroxylated Al2O3. We conclude that the local topology around the active site greatly influences the mechanism and selectivity.

The binary metal oxide mesoporous interfacial layers (bi-MO meso IF layer) templated by a graft copolymer are synthesized between a fluorine-doped tin oxide (FTO) substrate and nanocrystalline TiO2 (nc-TiO2). Amphiphilic graft copolymers, Poly(epichlorohydrin)-graft-poly(styrene), PECH-g-PS, were used as a structure-directing agent, and the fabricated bi-MO meso IF layer exhibits good interconnectivity and high porosity. Even if the amount of ZnO in bi-MO meso IF layer increased, it was confirmed that the morphology and porosity of the bi-MO meso IF layer were well-maintained. In addtion, the bi-MO meso IF layer coated onto FTO substrates shows higher transmittance compared with a pristine FTO substrate and dense-TiO2/FTO, due to the reduced surface roughness of FTO. The overall conversion efficiency (η) of solid-state photovoltaic cells, dye-sensitized solar cells (DSSCs) fabricated with nc-TiO2 layer/bi-MO meso IF layer TZ1 used as a photoanode, reaches 5.0% at 100 mW cm−2, which is higher than that of DSSCs with an nc-TiO2 layer/dense-TiO2 layer (4.2%), resulting from enhanced light harvesting, good interconnectivity, and reduced interfacial resistance. The cell efficiency of the device did not change after 15 days, indicating that the bi-MO meso IF layer with solid-state electrolyte has improved electrode/electrolyte interface and electrochemical stability. Additionally, commercial scattering layer/nc-TiO2 layer/bi-MO meso IF layer TZ1 photoanode-fabricated solid-state photovoltaic cells (DSSCs) achieved an overall conversion efficiency (η) of 6.4% at 100 mW cm−2.

The contamination of lead in wastewater causes water quality problems, which is toxic to aquatic organisms and environment, so wastewater treatment is required before discharging to receiving water. Chicken eggshell powder (CP) and chicken eggshell powder-doped iron (III) oxide-hydroxide (CPF) were synthesized, characterized, and investigated lead removal efficiencies by batch experiments, adsorption isotherms, kinetics, and desorption experiments. The specific surface area and pore volume of CPF were higher than CP, whereas the pore diameter size of CPF was smaller than CP. The phase structures of both materials demonstrated semi-crystalline phases with presenting peaks of calcium carbonate. Their surface morphologies were irregular, rough, and uneven surfaces. In both materials, they detected carbon, calcium, oxygen, OH, NH, CO, CO, and CH. The point of zero charges (pHpzc) of CP and CPF were 4.47 and 4.83. For batch experiments, CPF demonstrated a higher lead removal efficiency than CP because of spending less material dosage and contact time than CP, and both materials had high lead removals at a lead concentration of 50 mg/L by more than 95 %. Thus, the addition of iron (III) oxide-hydroxide helped to increase material efficiency for lead adsorption. CP corresponded to the Langmuir model while CPF corresponded to the Freundlich model. In addition, both materials corresponded to a pseudo-second-order kinetic model relating to a chemisorption process. Moreover, both materials could be reusable for more than 5 cycles for lead adsorption of more than 77 %. Therefore, CPF was a potential material to apply for lead removals in industrial applications.

We synthesized zinc oxide nanoparticles (ZnO NPs) by meticulously controlling both temperature and reaction times, allowing us to fine-tune their crystalline properties, morphology, and particle dimensions. This analysis confirmed the existence of a mixture of rod and sphere shapes (ZnO-I), including rod-shaped NPs with an average size of 14.8 nm × 5.2 nm and spherical NPs with an average diameter of 5.27 nm. We subsequently incorporated these synthesized ZnO NPs into organic light-emitting diode (OLED) devices for red, green, and blue colors, utilizing them as the electron injection layer through a solution-based process. The green OLED device using ZnO-I exhibited a promising current efficiency of 4.02 cd/A and an external quantum efficiency of 1.47%.

The contamination of water by organic substances poses a significant global challenge. To address these pressing environmental and energy concerns, this study emphasizes the importance of developing effective photocatalysts powered by sunlight. In this research, we achieved the successful synthesis of a novel photocatalyst comprised of polymeric carbon nitride (CN) nanosheets embedded with Co3O4 material, denoted as CN-CO. The synthesis process involved subjecting the mixture to 500 °C for 10 h in a muffle furnace. Structural and morphological analyses confirmed the formation of CN-CO nanostructures, which exhibited remarkable enhancements in photocatalytic activity for the removal of methylene blue (MB) pollutants under replicated sunlight. After 90 min of exposure, the degradation rate reached an impressive 98.9%, surpassing the degradation rates of 62.3% for pure CN and 89.32% for pure Co3O4 during the same time period. This significant improvement can be attributed to the exceptional light captivation capabilities and efficient charge separation abilities of the CN-CO nanostructures. Furthermore, the CN-CO nanostructures demonstrated impressive photocurrent density-time (j-t) activity under sunlight, with a photocurrent density of 2.51 μA/cm2 at 0.5 V. The CN-CO nanostructure exhibited excellent methanol oxidation reaction (MOR) activity with the highest current density of 83.71 mA/cm2 at an optimal 2 M methanol concentration, benefiting from the synergy effects of CN and CO in the nanostructure. Overall, this study presents a straightforward and effective method for producing CN-based photocatalysts decorated with semiconductor nanosized materials. The outcomes of this research shed light on the design of nanostructures for energy-related applications, while also providing insights into the development of efficient photocatalytic materials for addressing environmental challenges.

Mesoporous nanocapsules originated from silica encapsulated ZnS doped with metal oxide (Cu or Mn) were assembled and characterized. The morphological characterization was performed using Fourier-transform infrared spectroscopy (FTIR), UV–visible absorption spectra, and transmission electron microscopy (TEM). The analyses findings proved the structures of the synthesized metal oxide nanoparticles. It was verified that those metal nanoparticles are doped in the silica mesopores with an average particle size of 10–50, 30, 40, and 200 nm for ZnS, Zn doped Cu+2, Zn doped Mn+2, and silica, respectively. The morphological characterization of the cotton fabrics treated with the prepared mesoporous nanocapsules has been carried out by scanning electron microscopy (SEM). The mechanical and physical properties, antibacterial activity, and UPF measurements were also explored. The analyses results confirmed that the silica-encapsulated ZnS doped with metal ions imparts excellent antibacterial activity and ultraviolet protection to the cotton fabric that is distracted by physical or mechanical properties.

Releasing contaminated dyes into water bodies might create environmental problems for water quality and toxic aquatic organisms. The toxicity of dyes might affect human health throughout the food chain, so it is necessary to treat contaminated dye in wastewater before discharging it into the water body. Chicken eggshell beads (CB), duck eggshell beads (DB), chicken eggshell beads mixed iron (III) oxide-hydroxide (CBF), duck eggshell beads mixed iron (III) oxide-hydroxide (DBF), chicken eggshell beads mixed zinc oxide (CBZ), and duck eggshell beads mixed zinc oxide (DBZ) were synthesized, and several characterized techniques of XRD, FESEM-FIB, EDX, and FTIR were used to identify the crystalline structure, surface morphology, and chemical composition and functional groups. Reactive blue 4 (RB4) dye removal efficiencies on dye adsorbent materials were investigated through batch experiments with varying doses, contact time, temperature, pH, and concentration. Their adsorption patterns and mechanisms also were studied by adsorption isotherm and kinetics. All dye adsorbent materials demonstrated semi-crystalline structures, and their surface morphologies had a spherical shape with coarse surfaces. Oxygen, carbon, calcium, chlorine, and sodium and four main function groups of OH, NH, CO, and COC were detected in all dye adsorbent materials. For batch tests, they could remove RB4 dye by more than 56%, and CBF represented the highest RB4 dye removal efficiency at 84.44%. Moreover, the addition of iron (III) oxide-hydroxide and zinc oxide helped to improve RB4 dye adsorbent efficiencies which an iron (III) oxide-hydroxide increased RB4 removal efficiency of chicken and duck eggshell beads more than zinc oxide. Their adsorption patterns and mechanisms were well explained by Freundlich and pseudo-second-order kinetic models. Therefore, all dye adsorbent materials especially CBF are potential dye adsorbent materials for further industrial applications.

Photoelectrochemical (PEC) water splitting can directly convert solar energy into hydrogen energy for storage, effectively ending the energy crisis and solving environmental problems. With their modification by many researchers, photoanodes have rapidly improved in PEC performance. Nevertheless, the poor stability of PEC water-splitting devices has not been effectively corrected, seriously hindering their practical application and large-scale commercialization. In this review, we provide a detailed introduction to the photocorrosion mechanism of photoanodes and characterizations of stability, summarizing the current research progress on the stability of metal oxide/sulfide photoanode materials. According to the specificity of each semiconductor, the corrosion mechanism and modification strategy of each photoanode are discussed in detail. Finally, we summarize the deficiencies in the current stability research and propose influencing factors and possible solutions that need to be considered in the photocorrosion research field of photoanodes. This review can provide a reference for the stability research of photoanodes based on metal oxides and sulfides, especially for the design of efficient and stable metal sulfide-based photoanodes.

The work presented in this paper describes the preparation and the electrochemical application of functionalized chitosan-entrapped carbon paste electrodes (CH/CPE) for lead ions (Pb2+) detection in industrial wastewater. The chitosan was first functionalized using TiO2 and CuO, which were both metal oxides that were obtained by extracting it from waste products derived from shrimp shells. The analytical performance of the as-prepared electrodes, CH/CPE, TiO2-CH/CPE, and NiO-CH/CPE, for the detection of lead (II) was examined using electrochemical impedance spectroscopy (EIS) technique in the 0.1 M KNO3 electrolyte solution. The effect of experimental conditions, including polarization potential, frequency, and pH, are optimized to maximize the sensitivity of the measurements. The developed impedimetric sensors provided a linear response over a concentration range of 10−6 to 10−4 M with a detection limit of 3.10−7 M based on S/N = 3. The DFT computational analysis demonstrated that chitosan biopolymer possesses the ability to adsorb Pb (II) ions that are present in wastewater. Chitosan and the derivatives of chitosan, have the potential to remove heavy metals from industrial effluent in a manner that is both economical and eco-friendly to the environment. Chitosan is a biopolymer that is abundantly renewable.

Cryogels from noble metal NPs have proven to be highly efficient catalysts due to their high specific surface area which increases the mass transfer channels and catalytic active sites. By using metal oxides as co-catalysts, the costs of the material can be significantly reduced, while the catalytic activity can remain the same or even improve due to synergetic effects. In this work, we synthesize different cryogel thin films supported on modified ITO substrates from Pt, Pd nanoparticles (NPs), and mixtures of these noble metals with γ-Fe2O3 NPs in a very low concentration (1 wt% of the noble metal). Structural and elemental analysis of the samples are performed, along with the measurement and analysis of their catalytic activity. The electrocatalytic activity of the cryogels towards ethanol oxidation reaction (EOR) in alkaline media was evaluated by means of cyclic voltammetry. By mixing γ-Fe2O3 NPs with Pt or Pd NPs in the cryogel structure, we observe increased tolerance against poisonous surface intermediates produced during the EOR. Moreover, we observe an increase in the catalytic activity towards EOR in the case of the 1 wt% Pd/γ-Fe2O3 cryogel, making them promising materials for the development of direct ethanol fuel cells.

Converting and storing solar energy directly as chemical energy through photoelectrochemical devices are promising strategies to replace fossil fuels. Metal oxides are commonly used as photoanode materials, but they still encounter challenges such as limited light absorption, inefficient charge separation, sluggish surface reactions, and insufficient stability. The regulation of surface oxygen species on metal oxide photoanodes has emerged as a critical strategy to modulate molecular and charge dynamics at the reaction interface. However, the precise role of surface oxygen species in metal oxide photoanodes remains ambiguous. The review focuses on elucidating the formation and regulation mechanisms of various surface oxygen species in metal oxides, their advantages and disadvantages in photoelectrochemical reactions, and the characterization methods employed to investigate them. Additionally, the article discusses emerging opportunities and potential hurdles in the regulation of surface oxygen species. By shedding light on the significance of surface oxygen species, this review aims to advance our understanding of their impact on metal oxide photoanodes, paving the way for the design of more efficient and stable photoelectrochemical devices.

The search for inexpensive, environmentally friendly, and highly effective catalysts to activate C-H bonds in propane dehydrogenation (PDH) reactions is still a major challenge. Co-based catalysts have gained significant attention in recent years due to their excellent ability to activate C-H bonds and their high selectivity towards olefins, despite being a non-noble and environmentally unfriendly metal. However, further improvements are necessary for practical utilization, particularly in terms of activity and anti-carbon deposition capacity. In this study, we synthesized Al2O3 nanorods with abundant pentacoordinated Al3+ (Al3+penta) sites. The supported Co on the Al2O3 nanorod (Co/Al2O3-NR) exhibited higher selectivity (>96% propylene selectivity) and stability (deactivation rate 0.15 h−1) compared to Co supported on an Al2O3 nanosheet with fewer pentacoordinated Al3+ sites. Various characterizations confirmed that Co(II) mainly exists as CoAl2O4 rather than Co3O4 in the form of Co/Al2O3-NR, which inhibits the reduction of Co(II) to Co0 and accordingly improves catalyst stability.

The catalytic hydrogenolysis of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) is a promising route towards sustainable liquid fuels with a high energy density. Herein, a novel CuCoNiAl-containing mixed metal oxide catalyst (CuCoNiAl-MMO) was prepared by calcination a layered double hydroxide (LDH) precursor in N2 at 500 °C, then applied for the catalytic hydrogenolysis of HMF to DMF. The effects of reaction time, reaction temperature and hydrogen pressure on DMF selectivity were investigated. Under relatively mild reaction conditions (180°C, 1.0 MPa H2, 6.0 h), CuCoNiAl-MMO showed both a high initial activity and selectivity for hydrogenolysis of HMF to DMF, with HMF conversion rate of 99.8% and DMF selectivity of 95.3%. Catalysts characterization studies using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed the presence of various metal oxides and metallic copper on the surface of the CuCoNiAl-MMO catalyst, with the presence of mixed metal-oxide-supported metallic Cu nanoparticles being responsible good hydrogenolysis activity of the catalyst for selective DMF synthesis.

The synthesis of amides by the direct reaction of carboxylic acids with amines is an industrially relevant reaction in fine chemistry and drug synthesis, as well as a fundamental process for the construction of proteins in living organisms. To promote this process, the use of heterogeneous catalysts is preferred over their homogeneous counterparts, due to their advantages related to simple isolation, recovery and recycling. In addition, peptide bond formation over solid surfaces is interesting not only from the point of view of industrial organic synthesis but also from their implications in the understanding of prebiotic chemistry. For all this, we have highlighted some of the most relevant reported heterogeneous catalysts for the direct amide bond formation, focusing not only on the physicochemical properties of the solid catalyst –such as porosity and acidity- and its catalytic performance but also on the current understanding of the reaction mechanism. Different types of active sites incorporated at the surface (and bulk) of the solid are reviewed here: inorganic, organic and hybrid organic-inorganic. Besides the nature of the active sites, their interplay with the support in which they are embedded is thoroughly described, where surface area and pore size are key properties of the solid catalyst.

In this study, we introduce cobalt (Co)-doped zinc oxide (ZnO) spherical beads (SBs), synthesized using a sonochemical process, and their utilization for an acetone sensor that can be applied to an exhalation diagnostic device. The sonochemically synthezied Co-doped ZnO SBs were polycrystalline phases with sizes of several hundred nanometers formed by the aggregation of ZnO nanocrystals. As the Co doping concentration increased, the amount of substitutionally doped Co2+ in the ZnO nanocrystals increased, and we observed that the fraction of Co3+ in the Co-doped ZnO SBs increased while the fraction of oxygen vacancies decreased. At an optimal Co-doping concentration of 2 wt%, the sensor operating temperature decreased from 300 to 250 °C, response to 1 ppm acetone improved from 3.3 to 7.9, and minimum acetone detection concentration was measured at 43 ppb (response, 1.75). These enhancements are attributed to the catalytic role of Co3+ in acetone oxidation. Finally, a sensor fabricated using 2 wt% Co-doped ZnO SBs was installed in a commercially available exhalation diagnostic device to successfully measure the concentration of acetone in 1 ml of exhaled air from a healthy adult, returning a value of 0.44 ppm.

The increasing concentration of anthropogenic CO2 in the air is one of the main causes of global warming. The Paris Agreement at COP 21 aims to reach the global peak of greenhouse gas emissions in the second half of this century, with CO2 conversion towards valuable added compounds being one of the main strategies, especially in the field of heterogeneous catalysis. In the current search for new catalysts, the deposition of metallic nanoparticles (NPs) supported on metal oxides and metal carbide surfaces paves the way to new catalytic solutions. This review provides a comprehensive description and analysis of the relevant literature on the utilization of metal-supported NPs as catalysts for CO2 conversion to useful chemicals and propose that the next catalysts generation can be led by single-metal-atom deposition, since in general, small metal particles enhance the catalytic activity. Among the range of potential indicators of catalytic activity and selectivity, the relevance of NPs’ size, the strong metal–support interactions, and the formation of vacancies on the support are exhaustively discussed from experimental and computational perspective.

In this paper, we present a simple and inexpensive method for synthesizing conductive polyaniline and magnetite composites. Firstly, the magnetite was synthesized by precipitation in basic medium from FeCl3, and the Rietveld refinement confirmed the spinel structure. Different amounts of magnetite were used in the in situ synthesis of Pani-Fe3O4 composites to determine the influence, resulting in the following materials: Pani-Fe3O4 (1) with 0.06 g and Pani-Fe3O4 (2) with 0.24 g. The x-ray diffractogram demonstrates that interaction occurs between the polyaniline chains and the magnetite particles in the composites. Infrared and ultraviolet-visible vibrational spectra indicate that the composites are in the state of oxidation polyaniline salt emerald, which is the conductive form of greatest interest. Scanning electron microscopy images show that composites have particles with no definite geometry in the form of clusters, and the best homogeneity was achieved in the composite with the highest amount of magnetite. Evidence indicates that Pani-Fe3O4 (2) material with 0.24 g of magnetite to be incorporated in polyaniline synthesis may have more technologically interesting properties, but further studies will be needed for confirmation. DOI: http://dx.doi.org/10.17807/orbital.v11i7.1403

Magnetic activated carbon particles (Fe3O4/active carbon composites) as auxiliary electrodes (AEs) were fixed on the surface of Ti/Sb-SnO2 foil by a NdFeB magnet to form a new magnetically assembled electrode (MAE). Characterizations including cyclic voltammetry, Tafel analysis, and electrochemical impedance spectroscopy were carried out. The electrochemical oxidation performances of the new MAE towards different simulated wastewaters (azo dye acid red G, phenol, and lignosulfonate) were also studied. Series of the electrochemical properties of MAE were found to be varied with the loading amounts of AEs. The electrochemical area as well as the number of active sites increased significantly with the AEs loading, and the charge transfer was also facilitated by these AEs. Target pollutants’ removal of all simulated wastewaters were found to be enhanced when loading appropriate amounts of AEs. The accumulation of intermediate products was also determined by the AEs loading amount. This new MAE may provide a landscape of a more cost-effective and flexible electrochemical oxidation wastewater treatment (EOWT).

Sustainable water processing techniques have been extensively investigated and are capable of improving water quality. Among the techniques, photocatalytic technology has shown great potential in recent years as a low cost, environmentally friendly and sustainable technology. However, the major challenge in the industrial development of photocatalyst technology is to develop an ideal photocatalyst which must have high photocatalytic activity, a large specific surface area, harvest sunlight and shows recyclability. Keeping these views, the present review highlighted the synthesis approaches of graphene/metal oxide nanocomposite, characterization techniques and their prominent applications in photocatalysis. Various parameters such as photocatalyst loading, structure of photocatalyst, temperature, pH, effect of oxidizing species and wavelength of light were addressed which could affect the rate of degradation. Moreover, the formation of intermediates during photo-oxidation of organic pollutants using these photocatalysts is also discussed. The analysis concluded with a synopsis of the importance of graphene-based materials in pollutant removal. Finally, a brief overview of the problems and future approaches in the field is also presented.

In the last decades, the removal of benzene, toluene, ethylbenzene, and xylene (BTEX) has been considered a major environmental crisis. In this study, two novel nanocomposite materials (Fe2O3/SiO2 and Fe2O3-Mn2O3/SiO2) that have regeneration ability by UV irradiation have been fabricated to remove BTEX at ambient temperature. This research revealed that both nanocomposites could remove more than 85% of the BTEX in the first cycle. The adsorption capacities followed the order of ethylbenzene > m-xylene > toluene > benzene as in the molecular weight order. The reusability test using UV irradiation showed that the performance of Fe2O3/SiO2 decreased drastically after the fifth cycle for benzene. On the other hand, when Mn is located in the nanocomposite structure, Fe2O3-Mn2O3/SiO2 could maintain its adsorption performance with more than 80% removal efficiency for all the BTEX for ten consecutive cycles. The difference in the reusability of the two nanocomposites is that the electron energy (from the valence band to the conduction band) for BTEX decomposition is changed due to the presence of manganese. This study provides a promising approach for designing an economical reusable nanomaterial, which can be used for VOC-contaminated indoor air.

Tungsten oxide (WOx) thin films were synthesized through the RF magnetron sputtering method by varying the sputtering power from 30 W to 80 W. Different investigations have been conducted to evaluate the variation in different morphological, optical, and dielectric properties with the sputtering power and prove the possibility of using WOx in optoelectronic applications. An Energy Dispersive X-ray (EDX), stylus profilometer, and atomic force microscope (AFM) have been used to investigate the dependency of morphological properties on sputtering power. Transmittance, absorbance, and reflectance of the films, investigated by Ultraviolet-Visible (UV-Vis) spectroscopy, have allowed for further determination of some necessary parameters, such as absorption coefficient, penetration depth, optical band energy gap, refractive index, extinction coefficient, dielectric parameters, a few types of loss parameters, etc. Variations in these parameters with the incident light spectrum have been closely analyzed. Some important parameters such as transmittance (above 80%), optical band energy gap (~3.7 eV), and refractive index (~2) ensure that as-grown WOx films can be used in some optoelectronic applications, mainly in photovoltaic research. Furthermore, strong dependencies of all evaluated parameters on the sputtering power were found, which are to be of great use for developing the films with the required properties.

In order to synthesize the zinc-titanium (Zn-Ti) oxide nanocomposites using an atmospheric soft plasma jet, in this study mixtures of Zn and Ti precursors such as zinc nitrate and titanium butoxide were first prepared with different molar ratios; the mixed precursors then stirred at 700 rpm for two hours with atmospheric plasma, while maintaining a temperature of 25 °C. All the synthesized Zn-Ti oxide nanocomposites were post-heat-treated at 600 °C for six hours in an electrical furnace. The morphology, particle shape and size, crystal structure, oxidation state, and composition ratio were analyzed using FE-SEM, XRD, SEM-EDS, and Raman spectroscopy. BET was measured to calculate the specific surface area of the Zn-Ti oxide nanocomposites. Photocatalytic activity tests were performed for an application study, with 10 mL of 10 ppm methylene blue dye. UV-visible spectroscopy was performed on five different samples in order to analyze the changes of photocatalytic reactions. When the composition ratio of Zn/Ti was 2/1, maximum photocatalytic efficiency was obtained. We also carried out a theoretical kinetic study.

Metal oxide nanoporous materials and nanoparticles have main potential uses in several different fields such as nanoelectronics, biomedical science, renewable solar energy, drug-gene delivery, thermal insulation, and so on. On the other hand, it is vital for scientists to understand that agricultural waste biomass-assisted synthesis is less costly, environmentally friendly and renewable strategy, and therefore, agricultural wastes are ideal renewable resources for production of nanostructures as a substitute for toxic chemicals. This present review includes significant recent improvements concerning the synthesis of agricultural waste biomass-assisted metal oxide nanostructures and their application. The goal is to provide a vision for the use of non-extracted agricultural waste, especially lignocellulosic biomass an inexpensive, green, differentiated resource and policy for the synthesis of valuable nanoporous materials and nanoparticles.

Perovskite solar cells (PSCs) are a promising area of research among different new generations of photovoltaic technologies. Their manufacturing costs make them appealing in the PV industry compared to their alternatives. Although PSCs offer high efficiency in thin layers, they are still in the development phase. Hence, optimizing the thickness of each of their layers is a challenging research area. In this paper, we investigate the effect of the thickness of each layer on the photoelectric parameters of n-ZnO/p-CH3NH3PbI3/p-NiOx solar cell through various simulations. Using the Sol–Gel method, PSC structure can be formed in different thicknesses. Our aim is to identify a functional connection between those thicknesses and the optimum open-circuit voltage and short-circuit current. Simulation results show that the maximum efficiency is obtained using a perovskite layer thickness of 200 nm, an electronic transport layer (ETL) thickness of 60 nm, and a hole transport layer (HTL) thickness of 20 nm. Furthermore, the output power, fill factor, open-circuit voltage, and short-circuit current of this structure are 18.9 mW/cm2, 76.94%, 1.188 V, and 20.677 mA/cm2, respectively. The maximum open-circuit voltage achieved by a solar cell with perovskite, ETL and HTL layer thicknesses of (200 nm, 60 nm, and 60 nm) is 1.2 V. On the other hand, solar cells with the following thicknesses, 800 nm, 80 nm, and 40 nm, and 600 nm, 80 nm, and 80 nm, achieved a maximum short-circuit current density of 21.46 mA/cm2 and a fill factor of 83.35%. As a result, the maximum value of each of the photoelectric parameters is found in structures of different thicknesses. These encouraging results are another step further in the design and manufacturing journey of PSCs as a promising alternative to silicon PV.

Monitoring environmental hazards and pollution control is vital for the detection of harmful toxic gases from industrial activities and natural processes in the environment, such as nitrogen dioxide (NO2), ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), carbon dioxide (CO2), and sulfur dioxide (SO2). This is to ensure the preservation of public health and promote workplace safety. Graphene and its derivatives, especially reduced graphene oxide (rGO), have been designated as ideal materials in gas-sensing devices as their electronic properties highly influence the potential to adsorb specified toxic gas molecules. Despite its exceptional sensitivity at low gas concentrations, the sensor selectivity of pristine graphene is relatively weak, which limits its utility in many practical gas sensor applications. In view of this, the hybridization technique through heterojunction configurations of rGO with metal oxides has been explored, which showed promising improvement and a synergistic effect on the gas-sensing capacity, particularly at room temperature sensitivity and selectivity, even at low concentrations of the target gas. The unique features of graphene as a preferential gas sensor material are first highlighted, followed by a brief discussion on the basic working mechanism, fabrication, and performance of hybridized rGO/metal oxide-based gas sensors for various toxic gases, including NO2, NH3, H2, H2S, CO2, and SO2. The challenges and prospects of the graphene/metal oxide-based based gas sensors are presented at the end of the review.

Biomineralization is an elaborate process that controls the deposition of inorganic materials in living organisms with the aid of associated proteins. Magnetotactic bacteria mineralize magnetite (Fe3O4) nanoparticles with finely tuned morphologies in their cells. Mms6, a magnetosome membrane specific (Mms) protein isolated from the surfaces of bacterial magnetite nanoparticles, plays an important role in regulating the magnetite crystal morphology. Although the binding ability of Mms6 to magnetite nanoparticles has been speculated, the interactions between Mms6 and magnetite crystals have not been elucidated thus far. Here, we show a direct adsorption ability of Mms6 on magnetite nanoparticles in vitro. An adsorption isotherm indicates that Mms6 has a high adsorption affinity (Kd = 9.52 µM) to magnetite nanoparticles. In addition, Mms6 also demonstrated adsorption on other inorganic nanoparticles such as titanium oxide, zinc oxide, and hydroxyapatite. Therefore, Mms6 can potentially be utilized for the bioconjugation of functional proteins to inorganic material surfaces to modulate inorganic nanoparticles for biomedical and medicinal applications.

As a typical pollutant, methylene blue poses a serious threat to the environment and human health. Oily sludge pyrolysis residue loaded with metal oxides could be used to prepare composite materials, which is not only an effective way to treat oily sludge, but also a possible method to treat methylene blue pollutants. In this paper, composite materials (AC-CuO, AC-ZnO, and AC-TiO2) were prepared by oily sludge pyrolysis residue-loaded CuO, ZnO, and TiO2 directly, and characterized by XRD, SEM, EDS, BET, FT-IR, and XPS, and it was shown that the metal oxides were successfully supported on the pyrolysis residue. Then, the composite materials were applied to the removal of methylene blue solution. The removal effect of composite materials on methylene blue with respect to the impregnation time, impregnation ratio and dosage, and the contact time and number of regenerations were investigated, and the removal parameters were optimized by response surface methodology. The removal process for methylene blue was described by applying Lagergren, McKay, Langmuir isotherm, Freundlish isotherm and intraparticle diffusion models. According to the response surface methodology and the main factors affecting the removal effect of methylene blue, the results indicate that the removal effect of 5 mg/L methylene blue could reach 95.28%, 94.95%, and 96.96%, respectively, and the corresponding removal capacities were 4.76, 4.75, and 4.85 mg/g. In addition, kinetic studies showed that the removal process of methylene blue was mainly constituted by chemical adsorption. The intraparticle diffusion showed that the removal of methylene blue may be controlled by both liquid film diffusion and intraparticle diffusion. The isotherms showed that the adsorption sites of composites for methylene blue were uniformly distributed and had the same affinity. Furthermore, regeneration experiments showed that the composite materials were stable and had relatively reusability.

In recent times, metal oxide nanoparticles (NPs) have been regarded as having important commercial utility. However, the potential toxicity of these nanomaterials has also been a crucial research concern. In this regard, an important solution for ensuring lower toxicity levels and thereby facilitating an unhindered application in human consumer products is the green synthesis of these particles. Although a naïve approach, the biological synthesis of metal oxide NPs using microorganisms and plant extracts opens up immense prospects for the production of biocompatible and cost-effective particles with potential applications in the healthcare sector. An important area that calls for attention is cancer therapy and the intervention of nanotechnology to improve existing therapeutic practices. Metal oxide NPs have been identified as therapeutic agents with an extended half-life and therapeutic index and have also been reported to have lesser immunogenic properties. Currently, biosynthesized metal oxide NPs are the subject of considerable research and analysis for the early detection and treatment of tumors, but their performance in clinical experiments is yet to be determined. The present review provides a comprehensive account of recent research on the biosynthesis of metal oxide NPs, including mechanistic insights into biological production machinery, the latest reports on biogenesis, the properties of biosynthesized NPs, and directions for further improvement. In particular, scientific reports on the properties and applications of nanoparticles of the oxides of titanium, cerium, selenium, zinc, iron, and copper have been highlighted. This review discusses the significance of the green synthesis of metal oxide nanoparticles, with respect to therapeutically based pharmaceutical applications as well as energy and environmental applications, using various novel approaches including one-minute sonochemical synthesis that are capable of responding to various stimuli such as radiation, heat, and pH. This study will provide new insight into novel methods that are cost-effective and pollution free, assisted by the biodegradation of biomass.

Recently, hierarchical hybrid structures based on the combination of semiconductor micro/nanostructures and noble metal nanoparticles have become a hot research topic in the area of surface-enhanced Raman scattering (SERS). In this work, two core-satellite nanostructures of metal oxide/metal nanoparticles were successfully introduced into SERS substrates, assembling monodispersed small silver nanoparticles (Ag NPs) on large polydispersed ZnO nanospheres (p-ZnO NSs) or monodispersed ZnO nanospheres (m-ZnO NSs) core. The p-ZnO NSs and m-ZnO NSs were synthesized by the pyrolysis method without any template. The Ag NPs were prepared by the thermal evaporation method without any annealing process. An ultralow limit of detection (LOD) of 1 × 10−13 M was achieved in the two core-satellite nanostructures with Rhodamine 6G (R6G) as the probe molecule. Compared with the silicon (Si)/Ag NPs substrate, the two core-satellite nanostructures of Si/p-ZnO NSs/Ag NPs and Si/m-ZnO NSs/Ag NPs substrates have higher enhancement factors (EF) of 2.6 × 108 and 2.5 × 108 for R6G as the probe molecule due to the enhanced electromagnetic field. The two core-satellite nanostructures have great application potential in the low-cost massive production of large-area SERS substrates due to their excellent SERS effect and simple preparation process without any template.

CuO/ZnO nanocomposites were greenly prepared and tested for the catalytic degradation of methyl orange. The XRD analysis confirmed the existence of CuO and ZnO with crystallite sizes within the range of 15–30 nm. TEM and SEM images showed different morphological properties. The TGA analysis revealed a good thermal stability of the nanocomposite, with a total loss of less than 18% at a temperature of 700 °C. The nanocomposites were tested for the catalytic degradation of methyl orange under mild conditions with a catalyst mass/wastewater volume of 10 g/3 L, an initial dye concentration of 40 ppm, a pH of 4.5, and a degradation time of 3 h. The best efficiency of 49.1% was achieved by CuO nanoparticles (C), followed by 47.6%, which was obtained by 1C1Z. The degradation efficiency of ZnO (Z) was 16.4%, and it was increased by increasing the CuO precursor in the synthesis mixture, while adding ZnO to the CuO, resulting in a decrease in its catalytic performance.

Various carbon dioxide (CO2) capture materials and processes have been developed in recent years. The absorption-based capturing process is the most significant among other processes, which is widely recognized because of its effectiveness. CO2 can be used as a feedstock for the production of valuable chemicals, which will assist in alleviating the issues caused by excessive CO2 levels in the atmosphere. However, the interaction of carbon dioxide with other substances is laborious because carbon dioxide is dynamically relatively stable. Therefore, there is a need to develop types of catalysts that can break the bond in CO2 and thus be used as feedstock to produce materials of economic value. Metal oxide-based processes that convert carbon dioxide into other compounds have recently attracted attention. Metal oxides play a pivotal role in CO2 hydrogenation, as they provide additional advantages, such as selectivity and energy efficiency. This review provides an overview of the types of metal oxides and their use for carbon dioxide adsorption and conversion applications, allowing researchers to take advantage of this information in order to develop new catalysts or methods for preparing catalysts to obtain materials of economic value.

Metal oxide nanoparticles have been widely utilized for the fabrication of functional gas sensors to determine various flammable, explosive, toxic, and harmful gases due to their advantages of low cost, fast response, and high sensitivity. However, metal oxide-based gas sensors reveal the shortcomings of high operating temperature, high power requirement, and low selectivity, which limited their rapid development in the fabrication of high-performance gas sensors. The combination of metal oxides with two-dimensional (2D) nanomaterials to construct a heterostructure can hybridize the advantages of each other and overcome their respective shortcomings, thereby improving the sensing performance of the fabricated gas sensors. In this review, we present recent advances in the fabrication of metal oxide-, 2D nanomaterials-, as well as 2D material/metal oxide composite-based gas sensors with highly sensitive and selective functions. To achieve this aim, we firstly introduce the working principles of various gas sensors, and then discuss the factors that could affect the sensitivity of gas sensors. After that, a lot of cases on the fabrication of gas sensors by using metal oxides, 2D materials, and 2D material/metal oxide composites are demonstrated. Finally, we summarize the current development and discuss potential research directions in this promising topic. We believe in this work is helpful for the readers in multidiscipline research fields like materials science, nanotechnology, chemical engineering, environmental science, and other related aspects.

The process of selective oxy-functionalization of hydrocarbons using peroxide, O3, H2O2, O2, and transition metals can be carried out by the reactive oxygen species such as hydroxyl/hydroperoxyl radical and/or metal oxygenated species generated in the catalytic reaction. Thus, a variety of mechanisms have been proposed for the selective catalytic oxidation of various hydrocarbons including light alkanes, olefins, and simple aromatics by the biological metalloproteins and their biomimetics either in their homogeneous or heterogeneous platforms. Most studies involving these metalloproteins are Fe or Cu monooxygenases. The pathways carried out by these metalloenzymes in the oxidation of C–H bonds invoke either radical reaction mechanisms including Fenton's chemistry and hydrogen atom transfer followed by radical rebound reaction mechanism or electrophilic oxygenation/O-atom transfer by metal-oxygen species. In this review, we discuss the metal oxide nano-catalysts obtained from metal salts/molecular precursors (M = Cu, Fe, and V) that can easily form in situ through the oxidation of substrates using H2O2(aq) in CH3CN, and be facilely separated from the reaction mixtures as well as recycled for several times with comparable catalytic efficiency for the highly selective conversion from hydrocarbons including aromatics to oxygenates. The mechanistic insights revealed from the oxy-functionalization of simple aromatics mediated by the novel biomimetic metal oxide materials can pave the way toward developing facile, cost-effective, and highly efficient nano-catalysts for the selective partial oxidation of simple aromatics.

Nanoparticles (nanoparticles) have received much attention in biological application because of their unique physicochemical properties. The metal- and metal oxide–supported nanomaterials have shown significant therapeutic effect in medical science. The mechanisms related to the interaction of nanoparticles with animal and plant cells can be used to establish its significant role and to improve their activity in health and medical applications. Various attempts have been made to discuss the antibiotic resistance and antimicrobial activity of metal-supported nanoparticles. Despite all these developments, there is still a need to investigate their performance to overcome modern challenges. In this regard, the present review examines the role of various types of metal-supported nanomaterials in different areas such as antibacterial, antifungal, anticancer, and so on. Based on the significant ongoing research and applications, it is expected that metal-supported nanomaterials play an outstanding role not only in medical but also in other important areas.

Tin oxide (SnO2) nanomaterials are of great interest in many fields such as catalytic, electrochemical, and biomedical applications, due to their low cost, suitable stability characteristics, high photosensitivity, etc. In this contribution, SnO2 NPs were facilely fabricated by calcination of tin (II) oxalate in air, followed by a liquid-phase exfoliation (LPE) method. Size-selected SnO2 NPs were easily obtained using a liquid cascade centrifugation (LCC) technique. The as-obtained SnO2 NPs displayed strong absorption in the UV region (~300 nm) and exhibited narrower absorption characteristics with a decrease in NP size. The as-fabricated SnO2 NPs were, for the first time, directly deposited onto a poly(ethylene terephthalate) (PET) film with a regular Ag lattice to fabricate a flexible working electrode for a photoelectrochemical (PEC)-type photodetector. The results demonstrated that the SnO2-NP-based electrode showed the strongest photoresponse signal in an alkaline electrolyte compared with those in neutral and acidic electrolytes. The maximum photocurrent density reached 14.0 μA cm−2, significantly outperforming black phosphorus nanosheets and black phosphorus analogue nanomaterials such as tin (II) sulfide nanosheets and tellurene. The as-fabricated SnO2 NPs with relatively larger size had better self-powered photoresponse performance. In addition, the as-fabricated SnO2-NP-based PEC photodetector exhibited strong cycling stability for on/off switching behavior under ambient conditions. It is anticipated that SnO2 nanostructures, as building blocks, can offer diverse availabilities for high-performance self-powered optoelectronic devices to realize a carbon-neutral or carbon-free environment.

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4–metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4–metal-oxide-based heterojunctions.

In recent times, an increasing number of applications in different fields need gas sensors that are miniaturized but also capable of distinguishing different gases and volatiles. Thermal electronic noses are new devices that meet this need, but their performance is still under study. In this work, we compare the performance of two thermal electronic noses based on SnO2 and ZnO nanowires. Using five different target gases (acetone, ammonia, ethanol, hydrogen and nitrogen dioxide), we investigated the ability of the systems to distinguish individual gases and estimate their concentration. SnO2 nanowires proved to be more suitable for this purpose with a detection limit of 32 parts per billion, an always correct classification (100%) and a mean absolute error of 7 parts per million.

It was developed a new technique to assess micro- and mesopores with sizes below a few nanometers. The porous materials with hierarchical fractal-percolation structure were obtained with the sol-gel method. The tetraethoxysilane hydrolysis and polycondensation reactions were performed in the presence of salts as the sources of metal oxides. The porous materials were obtained under spinodal decomposition conditions during application of the polymer sol to the substrate surface and thermal treatment of the structures. The model is based on an enhanced Kepler net of the 4612 type with hexagonal cells filled with a quasi-two-dimensional projection of the Jullien fractal after the 2nd iteration. The materials obtained with the sol-gel method were studied using the atomic force microscopy, electron microscopy, thermal desorption, as well as an AutoCAD 2022 computer simulation of the percolation transition in a two-component system using the proposed multimodal model. Based on the results obtained, a new method was suggested to assess micro- and mesopores with sizes below a few nanometrs, which cannot be analyzed using the atomic force microscopy and electron microscopy.

In this short review (Perspective), we identify key features of the performance of biocatalysts developed by the immobilization of enzymes on the supports containing magnetic nanoparticles (NPs), analyzing the scientific literature for the last five years. A clear advantage of magnetic supports is their easy separation due to the magnetic attraction between magnetic NPs and an external magnetic field, facilitating the biocatalyst reuse. This allows for savings of materials and energy in the biocatalytic process. Commonly, magnetic NPs are isolated from enzymes either by polymers, silica, or some other protective layer. However, in those cases when iron oxide NPs are in close proximity to the enzyme, the biocatalyst may display a fascinating behavior, allowing for synergy of the performance due to the enzyme-like properties shown in iron oxides. Another important parameter which is discussed in this review is the magnetic support porosity, especially in hierarchical porous supports. In the case of comparatively large pores, which can freely accommodate enzyme molecules without jeopardizing their conformation, the enzyme surface ordering may create an optimal crowding on the support, enhancing the biocatalytic performance. Other factors such as surface-modifying agents or special enzyme reactor designs can be also influential in the performance of magnetic NP based immobilized enzymes.