Spatial Separation Of Charge Carriers Research Articles

Bi3TiNbO9/Bi2S3 Heterojunction for Efficient Photosynthesis of H2O2 in Pure Water

AbstractHeterojunction engineering has been deemed one of the most promising strategies for promoting charge separation and improving solar‐to‐chemicals efficiency. Howbeit, constructing well‐defined nanoheterojunction with superior photocatalytic activity for H2O2 generation and a clear reaction mechanism remains a formidable challenge. Herein, an in situ vulcanization way to synthesize an intriguing 2D/1D Bi3TiNbO9/Bi2S3 heterojunction by growing Bi2S3 nanorods on Bi3TiNbO9 microsheet is used for the first time, where an S‐scheme charge transfer mechanism is formed that facilitates the spatial separation of charge carriers. Moreover, the in situ grown Bi2S3 on Bi3TiNbO9 can optimize the interfacial electronic structure and the reaction energy barriers. As a result, the H2O2 yield rate for Bi3TiNbO9/Bi2S3 can reach 810(2) µmol g−1 h−1 without any sacrificial agents and cocatalysts, ≈6.18 and ≈18.0 times of pristine Bi3TiNbO9 and Bi2S3, respectively. Importantly, the heterojunction unveiled unprecedented stability, remaining ≈95.46(2)% of the initial one after 13 continuous cycles. This work highlights an innovative in situ vulcanization strategy to engineer oxide perovskite/metal sulfide nanocomposite catalysts for artificial photosynthesis of H2O2, opening new opportunities for achieving highly efficient photocatalyst systems.

Efficient Charge Carriers Separation and Transfer Driven by Interface Electric Field in FeS2@ZnIn2S4 Heterojunction Boost Hydrogen Evolution.

Photocatalytic H2 evolution technology is regarded as a promising and green route for the urgent requirement of efficient H2 production. At present, low efficiency is a major bottleneck that limits the practical application of photocatalytic H2 evolution. The construction of high-activity photocatalysts is highly crucial for achieving advanced hydrogen generation. Herein, a new S-scheme FeS2@ZnIn2S4 (FeS2@ZIS) heterostructure as the photocatalyst was developed for enhanced photocatalytic H2 evolution. Density function theory (DFT) calculation results strongly demonstrated that FeS2@ZIS generates a giant interface electric field (IEF), thus promoting the separation efficiency of photogenerated charge carriers for efficient visible-light-driven hydrogen evolution. At optimal conditions, the H2 production rate of the 8%FeS2@ZIS is 5.3 and 3.6 times higher than that of the pure FeS2 and ZIS, respectively. The experimental results further indicate that the close contact between FeS2 and ZIS promotes the formation of the S-scheme heterojunction, where the interfacial charge transfer achieves spatial separation of charge carriers. This further broadens the light absorption range of the FeS2@ZIS and improves the utilization rate of photogenerated charge carriers. This work thus offers new insights that the FeS2-based co-catalyst can enrich the research on S-scheme heterojunction photocatalysts and improve the transfer and separation efficiency of photogenerated carriers for photocatalytic hydrogen production.

Insight into photocatalytic chlortetracycline degradation by WO3/AgI S-scheme heterojunction: DFT calculation, degradation pathway and electron transfer mechanism

The construction of S-scheme heterojunction with excellent redox ability holds promising prospects for photocatalytic environment remediation. However, the rationally design of the heterojunction interface to achieve efficient charge transfer still faces challenges. In this study, we fabricated a tight-contacted S-scheme heterojunction by in situ anchoring AgI nanoparticles onto WO3 nanoplates. The significant difference in Fermi energy levels between WO3 and AgI results in the formation of a space charge region around the interface and bending of the energy band, facilitating directional migration and spatial separation of charge carriers. This contributes to enhanced generation of superoxide radicals (•O2−) and holes (h+) active species, leading to a significant increase in chlortetracycline (CTC) degradation rate. The apparent rate constant for CTC removal using the WO3/AgI (WA-2) is approximately 15 times higher than that observed for pure WO3. Furthermore, WA-2 exhibits universal degradation effects on tetracycline (TC) and oxytetracycline (OTC). Molecular dynamics (MD) simulation reveals the synergistic adsorption effect of WO3 and AgI on CTC and reactive oxygen species molecules. Based on Fukui function calculation of CTC molecules and degradation intermediates, liquid chromatography-mass spectrometry (LC-MS) analysis, photocatalytic degradation pathway over WO3/AgI was determined to be sequential demethylation followed by dechlorination and decarbonylation. These findings provide valuable insights into high-performance S-scheme heterojunctions interface design and elucidation of pollutant degradation mechanism.

Enhanced Photocatalytic Activity of Direct Z‐Scheme K4Nb6O17/Carbon‐Rich Melon Heterostructures

AbstractMelon (also known as graphitic carbon nitride, g‐C3N4) holds promise for photocatalysis, but challenges such as severe charge recombination, low oxidation potential, and sluggish exciton dissociation hinder its performance. Herein, a series of carbon‐rich, melon‐based photocatalysts are synthesized via one‐pot, temperature‐induced condensation of urea with the addition of a trace amount of citric acid. The addition of citric acid enhances crystallinity, extends melon chains, increases the C/N ratio, and improves π–π layer stacking of heptazine units, thereby enhancing charge transport properties and visible‐light harvesting capacity. These carbon nitride samples are then coupled with molten salt synthesized K4Nb6O17 crystals by a straightforward self‐assembly method to construct 2D/2D heterostructure photocatalysts. Z‐scheme electron transfer from K4Nb6O17 to the melon samples is established based on their work functions and band edge positions. This efficient charge transfer in the Z‐scheme heterostructure facilitates the spatial separation of charge carriers, resulting in a nearly fivefold enhancement in photocatalytic performance compared to the individual constituents.

Enhanced photocatalytic hydrogen evolution of an imine-linked covalent triazine framework through the assistance of Ti3C2Tx

Imine-linked covalent triazine frameworks (CTFs) with high crystallinity and nano-morphologies are synthesized more easily compared to the CTFs with irreversible bonds. Nevertheless, their photocatalytic hydrogen evolution is usually less efficient due to the low utilization of photogenerated charge carriers. Herein, ultrathin Ti3C2Tx nanosheets with high conductivity and a good deal of terminal -O groups are employed to improve the photocatalytic hydrogen evolution of CTF-TFB through the fabrication of composites CTF-TFB/Ti3C2Tx (TM-x). And the broad-spectrum light absorption and photothermal effect of Ti3C2Tx nanosheets significantly enhance the utilization of visible light for CTF-TFB. Typically, Ti3C2Tx absorbing photogenerated electrons from CTF-TFB to achieve spatial separation of charge carriers, thereby TM-20 exhibiting an about 0.5-fold increase in AQYs at 420 nm and 450 nm compared to CTF-TFB. Meanwhile, the great photothermal effect of Ti3C2Tx brings a higher surface temperature for TM-20, leading to an additional 67 % increase in the photocatalytic hydrogen evolution rate of TM-20.

Role of oxygen vacancy enriched m-BiVO4/t-BiVO4 isotype heterojunction for enhanced photocatalytic degradation of rhodamine B dye and in ferroelastic to paraelastic phase transition

Mixed-phase isotype heterojunction oxide materials with superior photocatalytic activities have recently revealed a significant coupling between individual phases with controlled optical properties. Therefore, we focus on synthesizing a mixed-phase monoclinic-tetragonal (m-t) BiVO4 photocatalyst using hydrothermal method. The increased recombination rate of electron-hole (e−-h+) pairs limits the photocatalytic performance of monoclinic (m) BiVO4 photocatalysts. Therefore, effective spatial charge carrier separation can be improved by creating an isotype heterojunction between the phases m-BiVO4 and t-BiVO4. The precursor pH, mechanical grinding, and calcination temperature regulate the formation of m-t BiVO4. The phase fractions of the two phases in m-t BiVO4 sample are 85% monoclinic and 15% tetragonal. Herein, we demonstrate the optical properties and photocatalytic activity based on the crystal chemistry of m-BiVO4 and m-t BiVO4. Temperature-dependent Raman measurements suggest a second order ferroelastic monoclinic to paraelastic tetragonal phase transition above 530 K owing to optical phonon anharmonic coupling interactions. The small increase (5 °C) in Tc in m-t BiVO4 compared to m-BiVO4 is due to the coexistence of tetragonal and monoclinic phases. The optical band gap of m-t BiVO4 is larger than that of m-BiVO4. Additionally, the evaluation of BiVO4 photocatalytic activity over rhodamine-B (Rh-B) dye suggests that the m-t BiVO4 with 97.5% degradation efficiency is superior compared to m-BiVO4 with 89% degradation efficiency. This is because, the two phases (m and t) of BiVO4 form an isotype heterojunction interface, which results in a high charge separation efficiency, as demonstrated by photocurrent studies and electrochemical impedance spectroscopy. Moreover, oxygen vacancies tune the charge carrier dynamics through the modification of band edges. These findings regarding the isotype phase-junction mechanism provide possibilities for innovative ideas for highly efficient mixed-phase isotype heterojunction photocatalysts for wastewater remediation.

Enhanced piezocatalytic and piezo-photocatalytic dye degradation via S-scheme mechanism with photodeposited nickel oxide nanoparticles on PbBiO2Br nanosheets

The fabrication of an S-scheme heterojunction demonstrates as an efficient strategy for achieving efficient charge separation and enhancing catalytic activity of piezocatalysts. In this study, a new S-scheme heterojunction was fabricated on the PbBiO2Br surface through the photo-deposition of NiO nanoparticles. It was then employed in the piezoelectric catalytic degradation of Rhodamine B (RhB). The results demonstrate that the NiO/PbBiO2Br composite exhibits efficient performance in piezocatalytic RhB degradation. The optimal sample is the NiO/PbBiO2Br synthesized after 2 h of irradiation, achieving a RhB degradation rate of 3.11 h−1, which is 12.4 times higher than that of pure PbBiO2Br. Simultaneous exposure to visible light and ultrasound further increases in the RhB degradation rate, reaching 4.60 h−1, highlighting the synergistic effect of light and piezoelectricity in the NiO/PbBiO2Br composite. A comprehensive exploration of the charge migration mechanism at the NiO/PbBiO2Br heterojunction was undertaken through electrochemical analyses, theoretical calculations, and in-situ X-ray photoelectron spectroscopy analysis. The outcomes reveal that p-type semiconductor NiO and n-type semiconductor PbBiO2Br possess matching band structures, establishing an S-scheme heterojunction structure at their interface. Under the combined effects of band bending, interface electric fields, and Coulomb attraction, electrons and holes migrate and accumulate on the conduction band of PbBiO2Br and valence band of NiO, respectively, thereby achieving effective spatial separation of charge carriers. The catalyst’s synergistic photo-piezoelectric catalysis effect can be ascribed to its role in promoting the generation and separation of charge carriers under both light irradiation and the piezoelectric field. The results of this investigation offer valuable insights into the development and production of catalytic materials that exhibit outstanding performance through the synergy of piezocatalysis and photocatalysis.

Electronic characteristics of the two-dimensional van der Waals ferroelectric α-In2Se3/Cs3Bi2I9 heterostructures

Two-dimensional (2D) van der Waals (vdWs) ferroelectric heterostructures provide a platform to design multifunctional electronic devices. In this Letter, the 2D vdWs ferroelectric α-In2Se3/Cs3Bi2I9 heterostructures were constructed to investigate the appropriate band alignment, effective masses, charge transfer, and polarization switching barriers by employing first-principle calculation. The results show that the polarization reversal of α-In2Se3 engineers band alignment transition from type-II (α-In2Se3-P↑/Cs3Bi2I9) to type-I (α-In2Se3-P↓/Cs3Bi2I9), resulting in an indirect bandgap changing from 0.09 to 0.75 eV. Calculated electron effective masses are isotropic, which is smaller than those of anisotropic hole effective masses. Interfacial charges transfer from Cs3Bi2I9 to α-In2Se3, which can be ascribed to work function difference. By combining non-equilibrium Green's functions, the current–voltage characteristics of α-In2Se3/Cs3Bi2I9 based ferroelectric tunnel junction were investigated, and the current on/off ratio of 103 is resulted by spatial charge carrier separation and recombination. The proposed electron–hole separation transport design strategy provides a comprehensive theoretical support for the development of microelectronic storage devices.

Superior visible-light absorbing Ag@ZnO nanorods hybrid photocatalyst for efficient decomposition of commercial pharmaceuticals tetracycline and amoxicillin

This work assesses the role of the noble metal silver in the visible-light sensitization of UV-active ZnO by introducing a localized plasmonic resonance effect and enhancing the spatial charge carrier separation. We herein synthesize ZnO nanorods via a solvothermal approach, yielding nanorods of length and diameter 1.356 ± 0.619 μm and 120.56 ± 25.09 nm, respectively. Silver nanoparticles are reduced on the surface of ZnO nanorods via the photodeposition route. XRD spectra reveal a high crystallinity and wurtzite-type structure for ZnO with new peaks for cubic phase Ag upon Ag-loading. The diffraction peaks shift upon Ag modification, indicating partial incorporation of Ag into the ZnO lattice. Further, upon Ag-decoration, a slight increase in dislocation density and micro strain is obtained, which could suppress the recombination rate of charge carriers. The DRS spectra reveal a band gap contraction of materials from 3.19 to 2.98 eV with increasing Ag density. The PL spectra confirmed that the optimum Ag concentration of 3 wt% is proficient in harvesting visible light towards high photocatalytic degradation efficiencies of tetracycline (92.1 %) and amoxicillin (76.4 %) in 90 min as compared to 49.4 % and 38 % over pristine ZnO nanorods. TOC studies reveal only partial mineralization of ∼42.7 % (tetracycline) and ∼31.3 % (amoxicillin) due to the formation of reaction intermediates identified by HR-MS chromatograms. In addition, degradation pathways are proposed through the fragments at different m/z ratios.

Efficient spatial separation of charge carriers over Sv-ZnIn2S4/NH2-MIL-88B(Fe) S-scheme heterojunctions for enhanced photocatalytic H2 evolution and antibiotics removal performance

The exploration of highly efficient sunlight-assisted photocatalyst for photodegradation of organic contaminants or energy conversion is strongly encouraged. In this work, we designed a novel three-dimensional spindle-like Sv-ZIS@NMFe heterojunction made of amino functionalized NH2-MIL-88B(Fe) (NMFe) and ZnIn2S4 nanosheets with abundant sulfur vacancies (Sv-ZIS). The structural properties of NMFe materials, such as a clearly defined system of pores and cavities, were retained by the Sv-ZIS@NMFe composites. Additionally, the incorporation of sulfur vacancies, –NH2 functional groups, and well-matched energy level positions led to various synergistic effects that considerably enhanced internal electron transformation and migration, as well as improved adsorption performance. Consequently, under visible light irradiation, the optimized sample exhibited superior hydrogen production activity and tetracycline hydrochloride photodegradation performance. At last, density functional theory calculations was used to further elucidated the possible photoreactivity mechanism. This study demonstrates that the Sv-ZIS@NMFe heterojunction materials formed by ZnIn2S4 with suitable sulfur vacancies and amino functionalized Fe-MOFs have promising applications in photocatalysis.

S doping induces to promoted spatial separation of charge carriers on carbon nitride for efficiently photocatalytic degradation of atrazine

Atrazine (ATZ), as one of the most extensively employed organochlorine-based herbicides, exhibits persistence and environmental toxicity. Photocatalytic technology based on polymer carbon nitride is regarded as a sustainable and promising approach for the degradation of emerging organic pollutants. Regrettably, the inherent shortcomings of pure carbon nitride greatly limit its practical application. Herein, S-doped carbon nitride was elaborately constructed for efficient degradation of ATZ. The removal efficiency of ATZ by the optimal sample (0.052 min−1) is 3.25 times as that of pure carbon nitride (0.016 min−1). Experiments and DFT calculations show that S doping optimizes electronic structure of carbon nitride, which significantly enhances the spatial separation and transfer efficiency of photogenerated electrons and holes. Moreover, the reactive sites and degradation paths of ATZ were predicted by Fukui function and LC-MS determination. Our work provides an effective approach for the design of efficient photocatalysts to achieve efficient environmental remediation.

S-Scheme WO3/SnIn4S8 Heterojunction for Water Purification: Enhanced Photocatalytic Performance and Mechanism

Photocatalysis is a promising technology for removing micropollutants in water. However, developing efficient and stable catalysts remains a challenge. In this work, a novel step-scheme (S-scheme) heterojunction of WO3/SnIn4S8 (WSI) was constructed through the combined process of in situ precipitation with hydrothermal synthesis to simultaneously realize photocatalytic degradation of bisphenol A(BPA) and reduction of Cr(VI) in contaminated water. Results showed that the WSI S-scheme heterojuction has a synergistic effect for the removal of BPA and Cr(VI). An optimum case of the WSI-12% heterojunction exhibited the highest photocatalytic efficiency in the degradation of BPA under visible light, which is ca. 2.5 and 3.8 times more than the pure WO3 and SIS, respectively. The enhanced photocatalytic activity is attributed to the formation of the WSI S-scheme heterojunctions which facilitate the spatial separation of charge carriers and preserve strong photoredox ability. Further, the S-scheme mechanism of enhanced photocatalysis was examined by the radical-trapping experiment and ESR, and superoxide and hydroxyl radicals were determined to be the major reactive oxygen species responsible for BPA degradation and Cr(VI) reduction by WSI. This work provides a novel strategy for tailoring high-performance S-scheme heterojunctions and shows the promising application in purifying wastewater with complex pollutants.

A novel chemical reaction between P25 and γ-Bi2O3 in CaTiO3 preparation constructing two new transfer channels of charge carriers to boost photocatalytic degradation activity

For the current design of heterojunction, only one new transfer channel of charge carriers was generated. In this paper, a novel chemical reaction between P25 and γ-Bi2O3 generated Bi4Ti3O12 to construct two new transfer channels in the preparation process of CaTiO3. The optimal sample CaTiO3/Bi4Ti3O12/γ-Bi2O3-12 could degrade 94 % of bisphenol A and 99 % of bisphenol AF, which was much higher than those of the pure phases and the two-phase junction samples. The photocatalytic efficiency of these two pollutants remained 94 % and 99 % in the five cycle tests to indicate that the above new channels were not destroyed after continuous utilization. The main active substances were hole, electron and superoxide radical O2–• in process of degradation. Different wastewater environments held a slight impact on photocatalytic efficiency to reveal a good applicability in real-world environments. After 90 min, the TOC and COD removal efficiencies of bisphenol A also attained 43 % and 44 % while those of bisphenol AF reached to 77 % and 83 %. The excellent photodegradation activity came from the formation of two new channels to accelerate the spatial separation of charge carriers. The colony numbers of Escherichia coli were 0.87 × 10-6 CFU/mL and 0.88 × 10-6 CFU/mL in the solution degraded by bisphenol A and bisphenol AF to show the non-toxicity of the final product. Thus two new transfer channels were obtained via P25 reacting with γ-Bi2O3 to enhance the catalyst activity, opening up a unique idea for heterojunction preparation.

1D/0D heterostructured ZnIn2S4@ZnO S-scheme photocatalysts for improved H2O2 preparation

Solar photocatalysis is a promising, green, and sustainable technique for the synthesis of H2O2. In this study, low-dimensional ZnO/ZnIn2S4 S-scheme heterojunction photocatalysts are fabricated using electrostatic spinning and chemical bath deposition methods for the efficient photocatalytic production of H2O2. ZnO nanofibers loaded with 20 wt% ZnIn2S4 exhibit a superior H2O2 production rate of 928 μmol g−1 h−1, which is more than four times higher than that seen in pristine hexagonal phase ZnO and ZnIn2S4. First-principles calculations and in-situ X-ray photoelectron spectroscopy reveal the charge separation and transfer mechanisms in the S-scheme heterojunction. The construction of the S-scheme heterojunction facilitates the spatial separation of charge carriers, and electrons and holes with higher redox abilities are retained. Photoelectrochemical and photoluminescence tests further show that the formation of an S-scheme heterojunction is beneficial for the separation of photoinduced charge carriers. Electrochemical tests and electron paramagnetic resonance measurements indicate that H2O2 production is primarily via a two-step single-electron O2 reduction path. This study provides a new approach for the construction of S-scheme heterojunction materials that can efficiently produce H2O2 under solar irradiation.

Composite photocatalyst C3N4/BiVO4 for adsorption/photocatalytic degradation of drugs in water

C3N4/BiVO4 composites as co-photocatalyst were successfully synthesized via hydrothermal method by varying the weight ratio of g-C3N4/BiVO4. The prepared samples were characterized using X-ray diffraction instrument, scanning electron microscopy, and UV-Vis diffuse reflectance spectroscopy. The morphological properties of composites show that g-C3N4 particles is deposited on the surface of BiVO4 while the crystal structure study shows that co-catalysts are existed by X-ray diffraction pattern. The photocatalytic degradation shows improvement by the composite with a ratio of 5% g-C3N4/BiVO4, the adsorption/photodegradation of Rhodamine B and Methyl Orange were about 97% and 88%, respectively within 40 min. The result indicates that g-C3N4/BiVO4 are paired their properties which are adsorption/photocatalyst, consequently, efficient spatial charge carrier separation. This finding was applied to remove ciprofloxacin and paracetamol in water. about 65% of paracetamol was removed from water compared with 15% of ciprofloxacin, this result revealing that excellent photodegradation of paracetamol by 5% g-C3N4/BiVO4 composite.

Facet-dependent CuO/{010}BiVO4 S-scheme photocatalyst enhanced peroxymonosulfate activation for efficient norfloxacin removal

Rapid recombination of charge carriers and sluggish Cu2+/Cu+ conversion rate in Cu-based photocatalysts hinder the improvement of the peroxymonosulfate (PMS) activation efficiency. Herein, a novel S-scheme system was successfully built through hydrothermal and in-situ calcination methods to activate PMS for norfloxacin (NOR) degradation, which combined CuO with BiVO4 (BVO) containing surface heterojunction. The UV–vis spectra manifested that BVO displayed excellent visible light absorption performance after compounding with CuO, and the light absorption threshold of CuO/BVO was about 600 nm. Thanks to the existence of surface heterojunction in BVO, the photoinduced electrons, and holes would transfer to {010} and {110} facets, respectively. The construction of S-scheme heterojunction further facilitated the accumulation of electrons on CuO, thus realizing the spatial separation of charge carriers. In addition, the electrons gathered on the CuO expedited the Cu2+/Cu+ cycle, thereby improving the activation efficiency of PMS. On this basis, the NOR removal capacity of 5CuO/BVO composites was obviously enhanced, which was 3.65 and 2.45 times that of CuO and BVO. Moreover, the influence of ambient pH and PMS dosage on the photocatalytic performance of CuO/BVO was investigated. Through the analysis of NOR degradation pathways and degradation products, it was found that the toxicity threat of NOR to the environment was reduced during the degradation process. According to the XPS results, forming the S-scheme heterojunction accelerated the Cu2+/Cu+ redox cycle during the PMS activating process. Meanwhile, photoluminescence (PL) and time-resolved photoluminescence (TRPL) analysis demonstrated that the CuO/BVO composites exhibited eminent ability for charge separation. The possible mechanism of charge transfer was assumed by exploring reactive species and the energy band structure of catalysts. To sum up, this research provides a new perspective on boosting PMS activation to purify antibiotics in water.

In Situ Constructed Perovskite-Chalcogenide Heterojunction for Photocatalytic CO2 Reduction.

Perovskite nanocrystals (PNCs) are promising candidates for solar-to-fuel conversions yet exhibit low photocatalytic activities mainly due to serious recombination of photogenerated charge carriers. Constructing heterojunction is regarded as an effective method to promote the separation of charge carriers in PNCs. However, the low interfacial quality and non-directional charge transfer in heterojunction lead to low charge transfer efficiency. Herein, a CsPbBr3 -CdZnS heterojunction is designed and prepared via an in situ hot-injection method for photocatalytic CO2 reduction. It is found that the high-quality interface in heterojunction and anisotropic charge transfer of CdZnS nanorods (NRs) enable efficient spatial separation of charge carriers in CsPbBr3 -CdZnS heterojunction. The CsPbBr3 -CdZnS heterojunction achieves a higher CO yield (55.8µmolg-1 h-1 ) than that of the pristine CsPbBr3 NCs (13.9µmolg-1 h-1 ). Furthermore, spectroscopic experiments and density functional theory (DFT) simulations further confirm that the suppressed recombination of charge carriers and lowered energy barrier for CO2 reduction contribute to the improved photocatalytic activity of the CsPbBr3 -CdZnS heterojunction. This work demonstrates a valid method to construct high-quality heterojunction with directional charge transfer for photocatalytic CO2 reduction. This study is expected to pave a new avenue to design perovskite-chalcogenide heterojunction.

Plasmonic silver nanoparticle-deposited n-Bi2S3/p-MnOS diode-type catalyst for enhanced photocatalytic nitrogen fixation: Introducing the defective p-MnOS

Photocatalytic nitrogen reduction reaction (PNRR) is clean and sustainable, considered an ideal synthesis technology for ammonia (NH3). In this study, we in situ developed the n-Bi2S3 nanorod/p-MnOS cubic composite catalyst for the first time using a one-step hydrothermal method, as MnOS, listed in the X-ray diffraction standard data file as an uncharacterized compound, has not been reported since 1965. Then, using a photodeposition technique, Ag nanoparticles (NPs) were added to the surface of the Bi2S3/MnOS to enhance PNRR via the surface plasmon resonance. After different characterization techniques for evaluation, Ag-Bi2S3/MnOS is found to be highly effective in the spatial separation of photogenerated electron-hole pairs due to the charge transfer at the composite interface. Photodeposited Ag is applied as an electron trapper to enhance the spatial separation of charge carriers. Based on their ability to reduce nitrogen under simulated solar light irradiation, the PNRR activities of Bi2S3, MnOS, Bi2S3/MnOS, and 0.5 to 2 % Ag-Bi2S3/MnOS were evaluated. After two hours, the PNRR activity of 1 % Ag-Bi2S3/MnOS produced ammonia 5.9 mmol/g, double the amount of Bi2S3/MnOS composite and approximately 5 times the amounts of Bi2S3 and MnOS materials. PNRR enhancement involves the internal static electron field created at the n-type Bi2S3/p-type MnOS interface and the improved electron conductivity with the photodeposition of Ag NPs, to speed up the reaction of reactive species. The importance of solid solution engineering in material design is demonstrated in this work.

Construction of 0D/1D CdS/g-C3N4 Z-scheme heterojunction for highly selective photocatalytic benzylamine oxidative coupling

The efficient solar-to-chemical energy conversion system is a green and cost-effective approach for producing high-value-added chemicals in chemical industry, which is highly demanded to develop. Photocatalytic C–N coupling of benzylamine into economic N-benzylidenebenzylamine is a great potential method for alternative conventional organic synthesis. In this work, a zero-dimensional/one-dimensional CdS/g-C3N4 Z-scheme heterojunction was constructed via in situ growing CdS quantum dot onto g-C3N4 nanorod surface for enhancing the spatial separation of charge carriers and maintaining the strong redox ability of the photogenerated charges and applied simultaneously in photocatalytic C–N coupling of benzylamine. This enables 20 wt% CdS/g-C3N4 to exhibit a remarkable photocatalytic performance enhancement for the production of C–N coupled product of benzylamine with the optimal yield of 199.79 μmol which is approximately 4.3 folds than those of pristine g-C3N4 under 2 h visible irradiation. Moreover, benzylamine conversion of approximately 90% within 100 h can be obtained in a gram scale-up reaction. By means of controlled photoelectric chemistry and in situ electron spin resonance spectroscopy experiments, possible spatial photogenerated charges separation and benzylamine conversion mechanisms on the Z-scheme junction were investigated in detail. This work paves a promising strategy for constructing zero-dimensional/one-dimensional Z-scheme heterojunction for the photocatalytic synthesis of high-value-added products.

Recent advances in designing ZnIn2S4-based heterostructured photocatalysts for hydrogen evolution

• This review mainly introduced various ZnIn 2 S 4 -based heterojunctions and their PHE application. • In-depth discussion on the mechanisms of various ZnIn 2 S 4 -based heterojunction systems for boosting PHE efficiency is provided. • We expressly introduced overall water splitting, dual-functional and photothermal effect-assisted PHE systems. • Some identification methods are presented for confirming heterojunction types. • The current states, challenges and perspectives of ZnIn 2 S 4 -based heterostructured photocatalysts for PHE are discussed. Water and solar energy are inexhaustible on Earth, and thus hydrogen evolution through photocatalytic water splitting taking sunlight as the input energy is an ideal green energy generation technology. As a typical visible-light-responsive photocatalyst, ZnIn 2 S 4 attracted worldwide research attention because of its many advantages for photocatalytic hydrogen evolution (PHE), such as layered structure, simple syntheses, structural stability, environmental friendliness, and suitable electronic band structure. In recent years, constructing ZnIn 2 S 4 -based heterostructured photocatalysts has become a research focus for their significantly improved spatial charge carrier separation efficiency and PHE performances. According to the charge carrier transfer/separation mechanisms, heterostructured ZnIn 2 S 4 -based photocatalysts are divided into five categories, conventional heterojunctions (type-I and type-II), p-n heterojunction, Z-scheme heterojunction, S-scheme (or Step-scheme) heterojunction, and co-catalyst deposition based heterojunction systems. This article reviews the recent advances in ZnIn 2 S 4 -based heterostructured photocatalysts for PHE. Firstly, the central part of this review introduced various ZnIn 2 S 4 -based heterojunctions and their PHE application. Secondly, apart from common half-reaction of water-splitting, we expressly introduced overall water splitting, dual-functional and photothermal effect-assisted PHE systems. Then, we briefly presented some identification methods for confirming heterojunction types. Finally, the current states, challenges and perspectives of ZnIn 2 S 4 -based heterostructured photocatalysts for PHE are also discussed. This review aims to explore the advantages of diverse ZnIn 2 S 4 -based heterostructures, and can provide an insight into designing high-efficiency heterostructured photocatalysts for PHE application.