Hole Recombination Research Articles

Improved performance of inorganic CsPbI3 perovskite solar cells with WO3/C60 UTL bilayer as an ETL structure: a computational study

CsPbI3, also known as cesium lead iodide, has garnered significant attention as a potential absorber in perovskite solar cells (PSCs). CsPbI3-PSCs have not matched the high performance of hybrid PSCs. This study aimed to identify an effective combination of charge transport layers. Six-hole transporting layers (HTLs) including Spiro-OMeTAD, Cu2O, CuO, CuAlO2, CuSbS2, and SrCu2O2, as well as five electron transporting layers (ETLs) such as TiO2, WO3, ZnO, IGZO, and CdZnS, were tested separately in 30 PSCs. The findings of this research indicate that CuAlO2 as the HTL and WO3 as the ETL that are the most appropriate materials among the options examined, so we use FTO/WO3/CsPbI3/CuAlO2/Au as a required PSC. In this research, we used SCAPS (Solar Cell Capacitance Simulator)−1D device modeling to investigate the bilayer ETL of inorganic CsPbI3-PSC and discover the methods to improve their efficiency. In planar PSCs, optimizing electron–hole pair extraction and recombination at the ETL/perovskite interface is crucial for achieving high performance. The key concept is to enhance the WO3/perovskite interface properties by adding a 5 nm ultra-thin layer (UTL) of C60. The bilayer structure WO3/C60 was found to have the advantage of high electron extraction and low interfacial recombination, primarily due to more effective energy level alignment and defect passivation. To achieve the superior efficiency of PSC, various factors such as defect and doping densities in all layers, the energy level alteration of ETL and HTL, interface defect densities on both ETL and HTL sides, back metal contact, operating temperature, and parasitic resistances were optimized. After optimizing these parameters, the efficiency of the system containing WO3/C60 bilayer ETL was found to be 29.39%. The current work proposes a straightforward and promising method to create photovoltaic devices, especially for many types of perovskites, with desirable charge transport layers and recombination properties.

Influence of deposition temperature on the defect mediated persistence photo-conducting behaviour of spray coated Zn0.96Nd0.04O thin films

The incorporation of Neodymium into ZnO lattice enhances the photo conducting property of the deposited films which are strongly dependent on preparation conditions. Hence, the comprehensive work carried out to understand the influence of deposition temperature (300 °C–500 °C) on the persistence photoconductivity of Zn0.96Nd0.04O films deposited on glass substrates using spray pyrolysis method. The maximum crystallite size of ∼16.3 nm with minimum dislocation density and strain values were noticed for the films deposited at 450 °C. The mixed fibrous -granular morphology was noticed in the deposited films. The maximum transparency above 90 % in the visible region and an increased bandgap of 3.42 eV was observed in the films deposited at 450 °C. The percentage of defects were calculated using the area under the curve of photoluminescence spectra. The charge carrier density of 1.7 × 1017 cm−3, mobility of 62.8 cm2/Vs and lesser resistivity of 1.3 × 102 Ω cm were noted for the films deposited at 450 °C. Under the illumination of UV light, the photocurrent of Zn0.96Nd0.04O films deposited at 450 °C increased by four orders. The persistence in the photo resistance was due to the presence of Zn and O related defects, which acts as trap centres. The variation of photo resistance with time indicates the films deposited at 450 °C has faster photo response due to the faster electron – hole recombination process. The maximum photocurrent at 360 nm was noted for the films synthesized at 450 °C due to improved crystallinity with stoichiometry nature of the films. Hence, the Zn0.96Nd0.04O films deposited at 450 °C suitable for light dependent resistor and fixed wavelength UV photodetector applications.

Facet-dependent in-situ formation of oxygen vacancy and plasmonic Bi in BiOBr nanosheets and resultant influence on the generation and separation of charge carriers

The development of advanced photoactive materials has aroused widespread interest, but is severely plagued by the inherent narrow photo-responsive range and rapid recombination of electrons and holes. In this study, the unconventional BiOBr nanosheets decorated with Bi0 and oxygen vacancies (OVs) are successfully synthesized through a facial one-pot hydrothermal method, followed by heat treatment. Cetyltrimethylammonium bromide and mannitol contribute to the selective exposure of (001) and (010) facets, respectively. The absence of the outermost Br atoms facilitates the simultaneous generation of OVs and Bi0 on the surface during heating, forming the Schottky junction. The synergy of SPR in the Bi0 metal, OVs and Schottky junction can effectively enhance the light absorption and charge separation. This work proposes and verifies a feasible approach to construct defects in-situ by regulating the crystal facets and manipulating the surface atomic arrangement and coordination.

A nano photocatalyst rGO/TiO2 modified by sol–gel‐irradiation and its degradation of deoxynivalenol in liquid products

SummaryThe rGO/TiO2 nanocomposite photocatalyst was synthesised using the sol–gel‐irradiation way to efficiently remove deoxynivalenol (DON) for the grains product's safety and quality. With the nanosize effect of irradiation, the photocatalyst has a smaller average grain size, preventing the recombination of electrons and holes. Moreover, based on UV–Vis DRS study, rGO/TiO2 could utilise visible light and have a broader response range to light. Furthermore, to the application, the photocatalyst rGO/TiO2 with 30 KGy irradiation dosage had an 80.32 ± 4.41% photocatalytic degradation rate of DON. Compared to the photocatalyst without irradiation, there was a 9.98% increase in the degradation rate. This result provided an excellent candidate photocatalyst for the removal of DON and also promoted the development of photocatalysis applications.

Visible-light-driven 2D carbonaceous-based SnSe nanohybrid soft materials: A photocatalyst for efficient photo reduction of malachite green dye

Preserving a healthy environment of air, land, and water requires the treatment of dangerous organic effluents. Efficiently degrading hazardous pollutants requires low-cost, high-absorption visible-light-driven photocatalysts. Furthermore, the tin selenide exhibited a tiny band gap that promotes the faster recombination of electrons and holes, and rGO shows restacking morphology that reduces the surface area of the materials. Both issues have been resolved by adding the rGO into SnSe to make an rGO/SnSe resolving the restacking issue and narrowing the band gap. In this research work, we report a hydrothermally synthesize tin selenide (SnSe) sustained on reduced graphene oxide (rGO) nanosheets as photocatalysts. Our research focuses on the degradation of hazardous industrial malachite green dye. Our analysis suggests that the rGO/SnSe nanocomposite effectively degrades malachite green (MG) dyes by 95.52% compared to pure SnSe (83.52%). The rGO sheets facilitate electron (e-) excitation from the valence band (V.B) to the conduction band (C.B), which significantly enhances the photocatalytic performance. We also investigated the reusability of the photocatalyst and the mineralization activity of a malachite green (MG) pollutant to check the photocatalytic mechanism and stability. The reusability test indicates that rGO/SnSe exhibited excellent 86.45% stability. The scavenger’s analysis suggests that electrons (e-) and holes (h+) play a significant part in the photocatalytic mineralization of MG dye. Our research explores that the rGO/SnSe nanohybrid is a significant material for wastewater treatment, solar energy conversion as well as environmental restoration.

Rapid synthesis of Cu2O/CeO2 p–n heterojunctions with enhanced photocatalytic properties by a sonochemical method

AbstractThe construction of p–n heterojunction is critical to reduce the electron–hole recombination rate and broaden the light absorption edge of photocatalysts. In this study, we successfully synthesize the Cu2O/CeO2 p–n heterojunctions through a rapid, simple, and environmentally friendly sonochemical method without any additional oxidants or elevation of the temperature and pressure. The prepared Cu2O/CeO2 heterojunction shows excellent adsorption of light, low electronic transfer resistance, and higher electron transfer efficiency. Under the irradiation of visible light, the as‐prepared Cu2O/CeO2 heterojunction exhibits exceptional capability for the degradation of methylene blue as well as outstanding reusability. The photo‐generated h+ is found to have a significant influence on the photocatalytic antibacterial of the as‐prepared Cu2O/CuO2 heterojunction under visible‐light irradiation and the sterilization rate toward Staphylococcus aureus and Escherichia coli of our samples can achieve up to 100%. Our work provides a green and rapid way to produce Cu2O/CeO2 p–n heterojunctions with enhanced photocatalysis.

Controllable hierarchical Bi2MoO6 spheres with ferroelectric polarization enhanced photocatalytic efficiency

AbstractThe fast recombination of photogenerated electrons and holes remains a major issue in hindering photocatalytic efficiency. Apart from traditional methods, such as rare metal deposition and element doping, the introduction of a built‐in electric field has been proven an efficient way in recent years. Ferroelectrics, which possess spontaneous polarization and associated polarization electric fields, are attracting more attention as photocatalysts. In this study, Bi2MoO6 spheres with different hierarchical upper nanostructures are synthesized through a one‐pot hydrothermal method. With this porous structure and the intrinsic ferroelectricity, BMO spheres present excellent physisorption and photodegradation ability toward dye molecules. After corona poling treatment, the ferroelectric field of the BMO samples was enhanced, and the recombination of charges was suppressed, leading to an obvious increase in photocatalytic rate. The origin BMO‐5 can reach a total degradation of RhB in 20 min, and the polarized BMO‐5 (BMO‐5P) can remove all RhB molecules instantly through the physisorption process. Apart from BMO‐5, other samples also present excellent catalytic behavior. Origin BMO‐2 can fully degrade the RhB in 40 min, and the degradation time of polarized BMO‐2P is 30 min. The hierarchical structure and internal polarized electric field endow BMO spheres with outstanding adsorption purification and photodegradation ability and provide a new comprehensive strategy for the catalyst design.

Synthesis and characterization of bi-functional Cu and Ni co-doped ZnO photocatalysts for organic pollutant degradation and antimicrobial activity

The study of visible light active photocatalysts for organic pollutants degradation and antimicrobial activity has gained significant attention in recent years. Herein, we report the synthesis of pure ZnO, Ni-doped ZnO (Ni-ZnO), Cu-doped ZnO (Cu-ZnO), and Cu and Ni co-doped ZnO (CuNi-ZnO) photocatalysts via a facile coprecipitation method. These photocatalyst materials were characterized using various analytical techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscope (HR-TEM), Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), photoluminescence (PL), and total organic carbon (TOC) analysis. XRD patterns confirm the presence of a mixed phase in the CuNi-ZnO sample. The presence of Cu, Ni, and Zn in CuNi-ZnO was verified through the XPS spectra. The nanoparticle-like morphology of the CuNi-ZnO photocatalyst was confirmed using HRTEM analysis. The FTIR spectra reveal the chemical bonds present in the materials. UV–visible spectroscopy was employed to determine the band gap of the materials, revealing a value of 3.10 eV for CuNi-ZnO. The mitigation in recombination of excited electrons (e−) and holes (h+) in CuNi-ZnO is validated through photoluminescence (PL) studies. The synthesized materials were used for the degradation of Indigo carmine (IC) dye and antimicrobial activity. The results showed that the optimized CuNi-ZnO sample displayed a better visible light photocatalytic performance (93.32 % IC dye degradation efficiency in 60 min) than the other samples. A notable degree of mineralization was observed with a reduction in total organic carbon (TOC) reaching 65.91 %. Additionally, the photocatalyst showed antimicrobial activity against both S. aureus and E. coli. Furthermore, a plausible visible light photocatalytic mechanism was proposed for the degradation of IC dye using the CuNi-ZnO photocatalyst.

Hierarchical Hollow TiO2@Bi2WO6 with Light-Driven Excited Bi(3-x)+ Sites for Efficient Photothermal Catalytic CO2 Reduction.

Converting CO2 into valuable chemicals via sustainable energy sources is indispensable for human development. Photothermal catalysis combines the high selectivity of photocatalysis and the high yield of thermal catalysis, which is promising for CO2 reduction. However, the present photothermal catalysts suffer from low activity due to their poor light absorption ability and fast recombination of photogenerated electrons and holes. Here, a TiO2@Bi2WO6 heterojunction photocatalyst featuring a hierarchical hollow structure was prepared by an in situ growth method. The visible light absorption and photothermal effect of the TiO2@Bi2WO6 photocatalyst is promoted by a hierarchical hollow structure, while the recombination phenomenon is significantly mitigated due to the construction of the heterojunction interface and the existence of excited Bi(3-x)+ sites. Such a catalyst exhibits excellent photothermal performance with a CO yield of 43.7 μmol h-1 g-1, which is 15 and 4.7 times higher than that of pure Bi2WO6 and that of physically mixed TiO2/Bi2WO6, respectively. An in situ study shows that the pathway for the transformation of CO2 into CO over our TiO2@Bi2WO6 proceeds via two important intermediates, including COO- and COOH-. Our work provides a new idea of excited states for the design and synthesis of highly efficient photothermal catalysts for CO2 conversion.

Ideal Structures of Isolated BiVO4 Nanoparticles on WO3 Nanocorals to Enhance Photoelectrochemical Hydrogen Evolution

Metal oxide nanoparticles (NPs) of n-type semiconductors have recently garnered significant attention in the photoelectrochemical (PEC) field. In this study, isolated BiVO4 NPs on anodized WO3 nanocorals are investigated with respect to the formation mechanism of the NPs and the correlation between particle size and PEC efficiency. The sizes and distances of the BiVO4 NPs on the WO3 nanocorals are controlled via spin-coating and heat-treatment. The optimized BiVO4 NPs, with ideal sizes of 10 nm and distances of 100 nm between them, exhibit satisfactory electron and hole diffusion lengths, suppressing electron–hole recombination and promoting the exposure of WO3 to ultraviolet light. Furthermore, high-quality BiVO4, without the formation of by-products due to the optimized concentrations of Bi and V in the precursor solution, results in a 2.3-fold higher photocurrent density and H2 production, and a 6-fold higher incident photon-to-current conversion efficiency (IPCE) compared to those of pristine WO3 nanocorals.

First-principles study on the electronic and optical properties of pn-type SnO/MoS[formula omitted] heterojunction tuned by various intrinsic vacancy defects and layer thicknesses

The impact of various intrinsic point defects and layer thicknesses on the electronic structure and optical properties of pn-type SnO/MoS2 heterojunctions has been investigated using first-principles calculations in this study. SnO/MoS2 heterojunctions are indirect bandgap semiconductors, with a narrower bandgap compared to monolayer SnO and MoS2, which decreases with increasing thickness of SnO or MoS2 layers. Intrinsic vacancy defects with different valence states were introduced using the transfer to the real state model method, which ensures that ionized electrons or holes are placed in the real band edge states. The primary intrinsic vacancy defects in the SnO/MoS2 heterojunction are Sn vacancies, and the valence states of the defects significantly influence the defect formation energy. Under different growth conditions, the dominant defects transition between VSn2−, VSn−, VO, and VS as the Fermi level varies. The intrinsic monolayer (1/1) SnO/MoS2 heterojunction exhibits weak n-type doping characteristics, while the introduction of VSn− defects leads to a shift towards p-type doping. As the number of SnO layers increases, VSn2− and VS defects introduce defect levels of different degrees in the bandgap, acting as electron–hole recombination centers and facilitating the transition between p-type doping and metallic conductivity characteristics. Increasing the number of MoS2 layers introduces localized defect energy levels in the bandgap, leading to p-doping or n-doping characteristics. The intrinsic SnO/MoS2 heterojunction primarily absorbs in the near-ultraviolet region, while also exhibiting a certain absorption capacity in the visible and deep ultraviolet regions. The presence of Sn and S defects can enhance the response to visible light absorption.

Collaborative role of co-doping and surface modifying for adjusting surface state of hematite to release the photoelectrochemical activity

Inhibition of bulk and interfacial charge carrier recombination is an urgent solution to release furthest the photoelectrochemical potential abilities of hematite photoelectrode. Herein, the Zr-Y dual metal co-doping engineering and Co/Fe dual metal-organic frameworks cocatalyst layer were employed for modifying hematite photoanode. The novel CoFe-MOF/Zr-Y:Fe2O3 nanoarray composite photoanode exhibits higher PEC activity, the photocurrent density at 1.23 V vs.RHE is increased by 4.7 times than that of the pristine α-Fe2O3. The gain in bulk charge separation efficiency was mainly attributed to the synergistic effect between the two doping ions to improve the electrical conductivity. Wherein, Zr4+ doping endows more free electrons in the bulk α-Fe2O3 and Y3+ introduction causes polaron mobility enhancement. For another, co-doping could reduce the recombination surface state, but form the intermediate surface state to promote hole transfer, thus effectively inhibiting the severe recombination of photogenerated electrons and holes. Furthermore, the CoFe-MOF cocatalyst coating with abundant active sites not only expedites the oxygen evolution reaction kinetics process, but also passivates the surface hole trapping state more thoroughly, resulting in efficient interfacial hole transfer and utilization. This work affords a new collaborative role of co-doping and surface modifying effective avenue for adjusting surface state of hematite to release the photoelectrochemical activity.

High activity and CH4 selectivity for photocatalytic CO2 reduction by Cu modified C3N4 nanotubes

The photocatalytic CO2 reduction has the problems of low selectivity of single product. Here, the preparation of Cu modified tubular C3N4 (CTN) was studied. The increase of the active site inhibits the recombination of electrons (e-) and holes (h + ) and improves the selectivity of CO2 reduction products. Finally, the CO and CH4 yields of 1.5 % CTN photocatalyst are 11.55 μmol·g−1 and 4.72 μmol·g−1, respectively, which are 5 times higher than that of tubular C3N4 photocatalyst. The selectivity of 2 % CTN to CH4 is up to 68 %, indicating that the prepared CTN photocatalyst has high CO2 reduction activity and CH4 selectivity.

Carbon based cobalt titanate perovskite nanocomposite: Synthesis, characterization, and excellent visible light driven photocatalytic performance

Titanium-based perovskite oxides are the promising photocatalysts for an efficient degradation of organic pollutants. However, charge carriers recombination and wide band gap energy are still the main challenges in their visible-light-driven photocatalytic applications of Titanate perovskites, ATiO3. The immobilization of Titanium-based perovskites on a carbonaceous substrate such as nitrogen-rich carbon nitride, can be considered as an excellent option for enhancing photocatalytic performance. Here, the CoTiO3/C3N5 nanocomposite was synthesized by simple reflux method and used for photocatalytic degradation of three organic pollutants including methylene blue (MB), tetracycline hydrochloride (TC), and bisphenol A (BPA). The results indicated that the photocatalytic activity of the CoTiO3 perovskite was considerably improved by introducing C3N5 nanosheets and fabricating CoTP/C3N5 nanocomposite. The crystalline structure of CoTiO3/C3N5 (CoTP/C3N5) nanocomposites was confirmed successfully by XRD analysis. The specific surface area of the synthesized CoTP/C3N5 nanocomposite was 8.15 m2/g calculated by N2 adsorption–desorption technology. In the 60th minute of the photocatalytic process, the degradation efficiency of MB, TC, and BPA by CoTP/C3N5 were obtained as 98.70, 60.33, and 92.90 %, respectively, which were higher than pristine CoTiO3 nanorods and C3N5 nanosheets. Electrochemical impedance analysis shows that the CoTP/C3N5 nanocomposite has good electrochemical performance. The improvement photocatalytic activity CoTP/C3N5 can be attributed to the suppressing the recombination of photogenerated electrons and holes and good electrochemical performance with high electron transfer capability. The results achieved from UV–Visible Diffused Reflectance Spectroscopy (DRS), mott-schottky measurements and the photocatalytic degradation experiments in the presence of scavengers confirmed the significantly accelerating the Z-scheme charge transfer mechanism where photoexcited carriers can migrate between CoTiO3 perovskite and C3N5 nanosheets.

Boosting the piezo-photocatalytic performance of Na0.5Bi0.5TiO3 by modulating the oxygen vacancy concentration

The emergence of piezo-photocatalysis inaugurates a nascent approach aimed at mitigating the rapid recombination of electrons and holes, thus augmenting catalytic efficacy. This work endeavors to fabricate Na0.5Bi0.5TiO3 (BNT) nanosphere powders through a simplified hydrothermal method, whereby precise control over the quantity of tetrabutyl titanate, a titanium source, is employed. The piezo-photocatalytic performance of BNT nanospheres is meticulously scrutinized through the degradation of Rhodamine B (RhB) at a concentration of 5 mg/L, utilizing ultrasonic vibration and UV–visible light irradiation. Remarkably, the appropriate oxygen vacancies exerts a profound impact on the efficiency of piezoelectric photocatalytic degradation. Among the investigated catalysts, The material with the best performance exhibits the highest rate of piezo-photocatalytic degradation, boasting a rate constant (k value) of 0.052 min−1. Furthermore, the BNT nanospheres exhibit commendable stability and reusability in the context of piezo-photocatalytic degradation. Elucidation of the piezo-photocatalytic mechanism of BNT nanospheres is attained through the identification of radicals and intermediates present in the degradation process. This research imparts invaluable guidance for the design and development of state-of-the-art and high-performance piezo-photocatalytic catalysts.

P-Type DSSCs by sensitizing a benzofuran[b]-fused BODIPY with cyanoacrylic acid

We found that a benzofuran[b]-fused 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) with cyanoacrylic acid (1) served as a photosensitizer for p-type dye-sensitized solar cells (DSSCs). The photovoltaic parameters (short circuit current density = 3.57 mA cm2, open circuit voltage = 0.12 V, fill factor = 0.33, and power conversion efficiency = 0.14%) were obtained with a 1-loaded NiO photocathode under AM 1.5 conditions. The incident photon-to-current efficiency spectrum showed excellent photo-harvesting capability, with a significant band at approximately 600 nm. Time-dependent density functional theory (TD-DFT)/DFT calculations indicated that electron distributions of both the HOMO and LUMO levels spread over the benzofuran-fused BODIPY core, mainly owing to π-π* transition. It is noteworthy that 1 served as a photosensitizer for p-type DSSC, despite almost no push-pull sensitizers. The hole transport and recombination processes were investigated by using intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. This study demonstrates that the local excitation (LE) character of dye is significantly workable for p-type sensitization, which may contribute to surpass recombination.

Photoexcitation assisted oxygen vacancy for enhancing nitrogen fixation with Fe-CeO2

Photoexcitation assisted oxygen vacancy for enhancing N2 fixation was investigated with Fe-CeO2 as photocatalysts. Fe substituted doping of CeO2 promoted the formation of oxygen vacancies (Vo). 5 % Fe-CeO2 exhibited the highest Vo concentration with photocatalytic nitrogen fixation efficiency of 176 μmol·g−1·h−1. The oxygen vacancy could induce the formation of the oxygen vacancy level, which could reduce the band gap energy, attract electrons, and hinder the electron hole recombination. More importantly, the oxygen vacancy level could be used as a springboard to reduce the energy required for N2 activation. In addition, calcination and acid-wash were used to regulate the concentration of surface oxygen vacancies (Vo-s) and bulk oxygen vacancies (Vo-b), respectively. The results showed that acid-wash only reduced the Vo-s concentration, while calcination reduced both the Vo-s and the Vo-b concentration, and the high concentration of Vo and Vo-s was beneficial for photocatalytic nitrogen fixation. The regulation strategy of Vo had guiding significance for improving the photocatalytic performance of metal oxide photocatalysts.

Fabrication of 2D TiO2/α-Fe2O3/Fe-g-C3N4 heterogeneous from metallurgical solid waste for Photo-Fenton catalysis of levofloxacin/Cr(VI): Electron transfer pathway and DFT calculation

Herein, the 2D Nano α-Fe2O3 were prepared by solvent-free method from rolling iron scale (RIS) - a by-product of metallurgical industry. 2D TiO2/α-Fe2O3 nanostructures were prepared using the obtained nanocrystals. Fe-doped g-C3N4 (Fe-g-C3N4) was synthesized using RIS as the raw material. A Composite of TiO2/α-Fe2O3 and Fe-g-C3N4 was combined to prepare a TiO2/α-Fe2O3/Fe-g-C3N4 heterojunction with high catalytic performance. This heterojunction was employed as a photo-Fenton catalyst to synergistically remove Cr(VI) and levofloxacin (LEV). The TiO2/α-Fe2O3/Fe-g-C3N4 heterojunction enhanced the intensity of the visible light response and suppressed the recombination of photogenerated electrons and holes. The N-Fe-O bridge, formed by synergistic coordination effects, enhanced the charge lifetime by decreasing the impedance of the catalyst and increasing the electron transfer rate. Additionally, the Fermi level and work function of the sample were calculated, providing further evidence for the electron transfer. Direct electron transfer between TiO2/α-Fe2O3/Fe-g-C3N4 and LEV/Cr(VI) was observed, indicating its importance in the removal of pollutants. To determine the potential degradation pathways, the energy orbitals of LEV derived from DFT calculations were analyzed. Overall, the study presents an excellent strategy for the sustainable use of RIS and the preparation of highly active catalysts. In conclusion, TiO2/α-Fe2O3/Fe-g-C3N4 is predicted to considerably contribute to studies on treating heavy metal and organic pollutant-contaminated wastewater.

Unveiling the synergistic role of nitrogen vacancies and Z-scheme heterojunction in g-C3N4/β-Bi2O3 hybrids for enhanced CO2 photoreduction

Rational design of highly efficient photocatalysts for CO2 conversion into carbonaceous fuels is of great significance to mitigate the global greenhouse effect and energy shortage problem. Among numerous materials studied for this purpose, the carbon nitride (g-C3N4) has been widely used in photocatalytic CO2 reduction (PCR) due to its decent optical properties, low cost and environment friendliness. However, its wide use still remains a substantial challenge due to inefficiency of the active site and rapid recombination of photogenerated electrons and holes. Herein, we suggest a Z-scheme system of nitrogen vacancies g-C3N4/β-Bi2O3 heterojunction photocatalyst based on self-assembly of nitrogen vacancies in g-C3N4 nanosheets and β-Bi2O3 micro-flowers, yielding an enhanced CO evolution rate of 30.56 μmol·g−1·h−1 under the simulated solar light without any cocatalysts and sacrificial agents. Our detailed studies indicate that the promoted PCR performance originates from the stronger adsorption capability of the *COOH intermediates due to the cleavage of the C-C bond in nitrogen vacancies g-C3N4 (NV-C3N4), turning the most endothermic step from the formation of *COOH intermediates to *CO. Moreover, the unique Z-scheme feature can efficiently facilitate the separation of photoelectron-hole pairs and enhance redox capability by optimizing the energy band structure. To sum up, this work provides deep insights and guidelines for rational design of highly efficient Z-scheme heterojunctions catalysts for CO2 photoreduction to solar fuels.

First polyoxometalate-modified SnS2 composite nanostructure gas sensor toward enhanced sensitivity and high selectivity for NO2 detection

In this work, the first polyoxometalate modified SnS2 gas sensor are synthesized by convenient hydrothermal method and applied for detecting NO2 gas in the air. Under optimal test condition, the SnS2-3%PW12 sensor delivered a gas sensing response of 3.9 to 50 ppm NO2 gas, which is 2.3 times higher than pure SnS2 sensor. Fast response/recovery time (24/30 s) and low limit-of-detection (53 ppb) were also exhibited. Repeatability, long-term stability and humidity resistance were both good. The mechanism analysis shows that PW12, as an electron-transport mediator, can trap electrons in the conduction band of SnS2, generate shallow electron traps, and effectively inhibit the recombination of electrons and holes in SnS2, thereby enhancing gas sensing performance for NO2 detection. This paper introduces a new way of developing high sensitivity SnS2-based gas sensors by introducing polyoxometalates as electron acceptors.