Step-by-Step Mechanism Insights into the TiO2/Ce2S3 S-Scheme Photocatalyst for Enhanced Aniline Production with Water as a Proton Source

Polarised electric field induced efficient photocatalytic hydrogen production at NiCrO4/ZnCdS heterogeneous interface

Zinc-cadmium sulfide (ZnCdS) has garnered significant attention as a potential photocatalyst for hydrogen production under visible light. However, enhancing the hydrogen production rate and long-term stability of ZnCdS remains a considerable challenge in the field. In this research, ZnCdS/NiCrO4 nanocomposites were synthesized via the physical stirring method, forming a p-n heterojunction. This heterojunction induces a localized polarization electric field at the interface due to electron cloud redistribution. The resulting electric field effectively improves charge carrier separation and facilitates the rapid migration of electrons and holes, thereby markedly enhancing the photocatalytic performance of the material in various reaction systems. Notably, the hydrogen production efficiency of the ZnCdS/NiCrO4 nanocomposite is 6.5 times higher than that of pure ZnCdS when tested in a lactic acid solution. Additionally, in a Na2S/Na2SO3 solution, the nanocomposite achieves a hydrogen production yield of 760.89 μmol. This research underscores the critical role of the polarization electric field in enhancing charge separation and the overall catalytic performance, offering significant insights for the development and optimization of advanced photocatalytic materials.

Charge-transfer dynamics in S-scheme photocatalyst

Natural photosynthesis represents the pinnacle that green chemistry aims to achieve. Photocatalysis, inspired by natural photosynthesis and dating back to 1911, has been revitalized, offering promising solutions to critical energy and environmental challenges facing society today. As such, it represents an important research avenue in contemporary chemical science. However, single photocatalytic materials often suffer from the rapid recombination of photogenerated electrons and holes, resulting in poor performance. S-scheme heterojunctions have emerged as a general method to enhance charge transfer and separation, thereby greatly improving photocatalytic efficiencies. This Perspective delves into the electron transfer dynamics in S-scheme heterojunctions, providing a comprehensive overview of their development and key characterization techniques, such as femtosecond transient absorption spectroscopy, in situ irradiated X-ray photoelectron spectroscopy and Kelvin probe force microscopy. By addressing a critical research gap, this work aims to trigger further understanding and advances in photo-induced charge-transfer processes, thereby contributing to green chemistry and the United Nations sustainable development goals.

Electrochemical hydrogenative coupling of nitrobenzene into azobenzene over a mesoporous palladium-sulfur cathode

Azobenzene (AZO) and its derivatives are of great importance in the dyestuff and pharmaceutical industries; however, their sustainable synthesis is much slower than expected due to the lack of high-performance catalysts. In this work, we report a robust yet highly efficient catalyst of PdS mesoporous nanospheres (MNSs) with confined mesostructures and binary elemental composition that achieved sustainable electrosynthesis of value-added AZO by selective hydrogenative coupling of nitrobenzene (NB) feedstocks in H2O under ambient conditions. Using a renewable electricity source and H2O, binary PdS MNSs exhibited a remarkable NB conversion of 95.4%, impressive AZO selectivity of 93.4%, and good cycling stability in selective NB hydrogenation reaction (NBHR) electrocatalysis. Detailed mechanism studies revealed that the confined mesoporous microenvironment of PdS MNSs facilitated the hydrogenative coupling of key intermediates (nitrosobenzene and phenylhydroxylamine) into AZO and/or azoxybenzene (AOB), while their electron-deficient S sites stabilized the Pd-spillovered active H* and inhibited the over-hydrogenation of AZO/AOB into AN. By coupling with the anodic methanol oxidation reaction (MOR), the (-)NBHR‖MOR(+) two-electrode system exhibits much better NB-to-AZO performance in a sustainable and energy-efficient manner. This work thus paves the way for designing functional mesoporous metal alloy electrocatalysts applied in the sustainable electrosynthesis of industrial value-added chemicals.

Regulating the spin state of a single Fe atom in BiOBr to enhance photocatalytic nitrogen reduction: insights from theoretical studies

Herein, we investigated the effects of the spin state of a single Fe atom on the nitrogen reduction reaction (NRR) in BiOBr using density functional theory. Our simulations revealed that P doping can reduce the spin state of the single Fe atom. This leads to an overlap of orbitals between N2 and the Fe atom at the Fermi energy level, thereby promoting the activation of N2. The investigation of NRR mechanisms revealed that the enzymatic mechanism is more favorable compared to the distal and alternating mechanisms. The formation of NNH with an energy barrier of 2.32 eV is identified as the rate-determining step for the NRR process in the Fe-doped BiOBr system. Furthermore, P doping dramatically reduces the energy barrier of the rate-determining step, which involves releasing the second NH3 molecule, by a factor of 2.37. This study elucidates the influence mechanism of the Fe spin state on the performance of the NRR, providing valuable theoretical guidance for designing highly efficient photocatalysts.

In situ engineered Ce2O2S/CeO2 nanofibrous heterojunctions for photocatalytic H2O2 synthesis via S-scheme charge separation

Photocatalytic H2O2 synthesis offers an efficient and sustainable means to convert solar energy into chemical energy, representing a forefront and focal point in photocatalysis. S-scheme heterojunctions demonstrate the capability to effectively separate photogenerated electrons and holes while possessing strong oxidation and reduction abilities, rendering them potential catalysts for photocatalytic H2O2 synthesis. However, designing S-scheme heterojunction photocatalysts with band alignment and close contact remains challenging. Here we report Ce2O2S/CeO2 multiphase nanofibrous prepared via an in situ sulphuration/de-sulphuration strategy. This in situ process enables intimate contact between the two phases, thereby shortening the charge transfer distance and promoting charge separation. The interfacial electronic interaction and charge separation were investigated using in situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. The work function difference enables Ce2O2S to donate electrons to CeO2 upon combination, resulting in the formation of an internal electric field (IEF) at interfaces. This IEF, along with bent energy bands, facilitates the separation and transfer of photogenerated charge carriers via an S-scheme pathway across the Ce2O2S/CeO2 interfaces. The Ce2O2S as the reduction photocatalyst exhibits significant O2 adsorption and activation along with a low energy barrier for the H2O2 production. The optimal Ce2O2S/CeO2 nanofibers heterojunction demonstrate enhanced photocatalytic H2O2 production of 2.91 mmol g-1h-1, 58 times higher than that of pristine CeO2 nanofibers. This investigation provides valuable insights for the rational design and preparation of intimate contact nanofibrous heterojunctions with efficient solar H2O2 synthesis.

Friction Reduction and Antiwear Mechanisms of Cerium Sulfide Nanosheets under Different Sliding Conditions

With the rapid development of modern industry, traditional lubricants often require a variety of additives to be used in conjunction with each other, which not only increases the cost but also causes a waste of resources. Therefore, the development of a lubricant additive with both a dyeing function and an antiwear and friction reduction performance can more effectively meet the industrial needs. Cerium sulfide (Ce2S3), with its excellent photostability, weather resistance, thermal stability, and nontoxicity, shows great potential as an environmentally friendly pigment. However, traditional methods for synthesizing Ce2S3 are typically hindered by high-temperature requirements and potential toxicity issues, which limits the broad application of Ce2S3 in lubricants. To overcome these limitations, this study employed a liquid-phase method under mild conditions to synthesize oleylamine-modified, wrinkle-free Ce2S3 nanosheets (OA-Ce2S3 NSs). The antiwear and friction-reducing properties of OA-Ce2S3 NSs in poly alpha-olefin-6 base oils were evaluated under various friction conditions with a four-ball tribometer. Experimental results indicate that OA-Ce2S3 NSs significantly enhance the friction-reducing and antiwear performance of lubricants by forming a physical adsorption film and an ultra thick tribochemical reaction film (with a typical thickness of 350 nm and a maximum thickness of up to 700 nm) on the friction surface. Furthermore, the study elucidates the lubrication mechanism of OA-Ce2S3 NSs and proposes their sliding mechanism on friction surfaces. This research highlights the potential of Ce2S3 nanosheets as lubricant additives and provides future directions for optimizing their synthesis and multifunctional applications, offering new insights into the field of lubrication science.

Highly efficient visible-light-driven S-scheme graphene bridged MoS2/Co3O4 nanohybrid for the photocatalytic performance of hazardous dye and antibacterial activity

A novel graphene-bridged MoS2/Co3O4 (MCG) nanohybrid was well fabricated by a hydrothermal route. The purpose of valuable and economical S-scheme systems with vigorous interface interactions is pressing to photocatalytic efficiency and efficient utilization. While mighty progress has been created with respect to charge carrier bridges, the charge transferring ability of the facility charge carrier bridges is far from capable owing to lower electrical conductivity. The photocatalytic antibacterial tests were performed with visible light activity, and the results exhibited that the as-prepared MCG nanohybrid with powerful interfacial coupling presented excellent photodegradation performance in comparison with bare MoS2 and Co3O4 samples for the removal of methylene blue (MB) and E-coli with visible light irradiation. In addition, a better photocatalytic MB capability and antibacterial activity of 99.5 % and 100 % are approached through MCG-4 nanohybrid, which is 2.76 and 8.32 folds higher than that of the pristine MoS2 sample. The PL measurements and EIS analysis also illustrated that MCG-4 nanohybrid possesses a great separation efficiency of photoinduced charge carriers. This work provides a new objective for high-potential S-scheme photocatalysts and their utilization in the field of environmental remediation.

Prolonging Charge Carrier Lifetime via Intraband Defect Levels in S-Scheme Heterojunctions for Artificial Photosynthesis

S-scheme heterostructure photocatalysts, distinguished by unique charge-transfer pathways and exceptional catalytic redox capabilities, have found widespread applications in addressing challenging chemical processes, including the photocatalytic reduction of CO2 with a high reaction barrier. Nevertheless, the influence of intraband defect levels within S-scheme heterojunctions on charge separation, carrier lifetime, and surface catalytic reactions has, for the most part, been overlooked. Herein, we develop a tunable defect-level-assisted strategy to construct an electron reservoir, effectively prolonging the lifetime of charge carriers through the rapid capture and gradual release of photoelectrons within WO3-x/In2S3 S-scheme heterojunctions, as authenticated by femtosecond transient absorption spectroscopy and theoretical simulations. The surface photoredox mechanism, unraveled by Gibbs free energy calculations, demonstrates that oxygen-vacancy-induced defect states in WO3-x/In2S3 heterojunctions unlock the rate-determining H2O oxidation into free oxygen molecules by forming metastable oxygen intermediates, contributing to the facilitation of H2O photooxidation. This distinct role, combined with the extended carrier lifetime, results in boosted CO2 photoreduction with nearly 100 % CO selectivity in the absence of any photosensitizer or scavenger. Our work sheds light on the role of controllable defect levels in governing charge transfer dynamics within S-scheme heterojunctions, thereby inspiring the development of more advanced photocatalysts for artificial photosynthesis.

Ternary Heteronanocrystals with Dual-Heterojunction for Boosting Near-Infrared-Triggered Photo-Chemodynamic Therapy

Strongly coupled interfaces in the epitaxial growth heteronanocrystals (HNCs) provide advanced functionalities regarding interface connection, electron transfer, and carrier separation. However, the majority of current nanocomposites primarily focus on a single heterojunction involving only two subunits, which hinders the achievement of optimized synergy energy transfer among more than two components. Herein, ternary NaGdF4:Yb,Tm-TiO2:F-Fe3O4 HNCs with dual-heterojunction were synthesized based on the crystal plane epitaxial growth strategy for boosting near-infrared (NIR)-triggered photo-chemodynamic therapy (PCDT). Fluorine is doped into TiO2 (TiO2:F), which not only enhances the exposure of the (001) facet of TiO2 for Fe3O4 subunit growth but also promotes the growth of the NaGdF4:Yb,Tm upconversion nanocrystal (UCNC) subunit, enabling an epitaxial combination of all three components. Upon NIR irradiation, the UCNC subunit transfers the light energy of the absorbed NIR light to the TiO2:F subunit, thereby facilitating the generation of electron-hole pairs within TiO2:F. Due to different work functions between TiO2:F and Fe3O4 in the ternary HNCs, electrons tend to transfer from TiO2:F into Fe3O4, resulting in a reduction of inactive Fe3+ into active Fe2+ and further enhancing the Fenton-catalysis performance. Simultaneously, the efficient separation of electrons and holes improves the photocatalytic oxidation property induced by TiO2:F. Based on ternary UCNC-TiO2:F-Fe3O4 HNCs boosting Fenton catalysis and photocatalysis at the single particle level, as a proof of concept, we propose a NIR light-triggered PCDT (NIR-PCDT) synergistically enhanced tumor treatment strategy. In vitro and in vivo experiments demonstrate that this NIR-PCDT agent exhibits a pronounced ability to generate reactive oxygen species, effectively inducing apoptosis in tumor cells.

Polarization-Induced Internal Electric Field-Dominated S-Scheme KNbO3-CuO Heterojunction for Photoreduction of CO2 with High CH4 Selectivity

The polarization-induced internal electric field (IEF) in ferroelectric materials could promote photogenerated charge transfer across the heterojunction interface, but the effect of polarization-induced IEF on the mechanism of photogenerated charge transfer is ambiguous. In this study, a KNbO3-CuO heterojunction was synthesized by depositing copper oxide (CuO) onto KNbO3. Incorporating CuO broadens the light absorption of KNbO3, thereby enhancing the dissociation of the photogenerated charges. The results show that the polarization-induced IEF in KNbO3 determines that the charge transport mechanism in the KNbO3-CuO heterojunction follows the S-scheme. Owing to the S-scheme heterojunctions and efficient CO2 capture and activation by CuO, the CH4 production rate of KNbO3-CuO increased by nearly 26 times compared to KNbO3. Additionally, the CH4 selectivity of KNbO3-CuO could reach up to 97.80%. This research offers valuable insights into enhancing the photogenerated charge separation and constructing heterojunctions.

Defect-Induced Atomical Zn-O/N-C Bonding Promotes Efficient Charge Transfer in S-Scheme Interface for Bubble Level Solar Hydrogen Production

Establishing efficient and clear atomic-level charge transfer channels presents a significant challenge in the design of effective photocatalysts. A sound strategy has been developed herein involving the construction of defect-induced heterostructures that create chemical bonds serving as charge transfer channels at the heterojunction interface. In situ XPS, alongside theoretical calculations, demonstrates the successful construction of Zn-O/N-C as atomic charge transfer channels. Our findings reveal that the introduction of zinc vacancies (VZn) reduces the carrier transport activation energy (CTAE) from 155.2 meV for ZIS/CN to 128.7 meV for VZn-ZIS/CN. Consequently, the optimal VZn-ZIS/CN achieves a high hydrogen evolution rate of 22.26 mmol g-1 h-1 without Pt as a cocatalyst, which is approximately 57 times greater compared to that of ZIS/CN. Notably, hydrogen is generated at bubble levels under natural sunlight. This work provides insights into the mechanisms by which defect-induced heterostructure building strategies can introduce chemical bonds at the heterojunction interface.

Visible-Light-Promoted Reduction of Nitroarenes with Formate Salts as Reductants

A visible-light-promoted reduction of nitrobenzenes using formate salts as the reductant was developed. A wide range of nitrobenzenes can be converted into aniline products in a transition metal free fashion. Mechanistic studies revealed that radical species (carbon dioxide radical anion and thiol radical) are key intermediates for the transformation. We anticipate that this method will provide a valuable and green strategy for the reduction of nitrobenzenes.

Cocatalyst Embedded Ce-BDC-CeO2 S-Scheme Heterojunction Hollowed-Out Octahedrons With Rich Defects for Efficient CO2 Photoreduction

Constructing heterojunction photocatalysts with optimized architecture and components is an effective strategy for enhancing CO2 photoreduction by promoting photogenerated carrier separation, visible light absorption, and CO2 adsorption. Herein, defect-rich photocatalysts (Ni2P@Ce-BDC-CeO2 HOOs) with S-scheme heterojunction and hollowed-out octahedral architecture are prepared by decomposing Ce-BDC octahedrons embedded with Ni2P nanoparticles and subsequent lactic acid etching for CO2 photoreduction. The hollowed-out octahedral architecture with multistage pores (micropores, mesopores, and macropores) and oxygen vacancy defects are simultaneously produced during the preparation process. The S-scheme heterojunction boosts the quick transfer and separation of photoinduced charges. The formed hollowed-out multi-stage pore structure is favorable for the adsorption and diffusion of CO2 molecules and gaseous products. As expected, the optimized photocatalyst exhibits excellent performance, producing CO with a yield of 61.6 µmol h-1 g-1, which is four times higher than that of the original Ce-BDC octahedrons. The X-ray photoelectron spectroscopy, scanning Kelvin probe, and electron spin resonance spectroscopy characterizations confirm the S-schematic charge-transfer route. The key intermediate species during the CO2 photoreduction process are detected by in situ Fourier transform infrared spectroscopy to support the proposed mechanism for CO2 photoreduction. This work presents a synthetic strategy for excellent catalysts with potential prospects in photocatalytic applications.

Merging semi-crystallization and multispecies iodine intercalation at photo-redox interfaces for dual high-value synthesis

The artificial photocatalytic synthesis based on graphitic carbon nitride (g-C3N4) for H2O2 production is evolving rapidly. However, the simultaneous production of high-value products at electron and hole sites remains a great challenge. Here, we use transformable potassium iodide to obtain semi-crystalline g-C3N4 integrated with the I-/I3- redox shuttle mediators for efficient generation of H2O2 and benzaldehyde. The system demonstrates a prominent catalytic efficiency, with a benzaldehyde yield of 0.78 mol g-1 h-1 and an H2O2 yield of 62.52 mmol g-1 h-1. Such a constructed system can achieve an impressive 96.25% catalytic selectivity for 2e- oxygen reduction, surpassing previously reported systems. The mechanism study reveals that the strong crystal electric field from iodized salt enhances photo-generated charge carrier separation. The I-/I3- redox mediators significantly boost charge migration and continuous electron and proton supply for dual-channel catalytic synthesis. This groundbreaking work in photocatalytic co-production opens neoteric avenues for high-value synthesis.

Step-scheme CsPbBr3/BiOBr photocatalyst with oxygen vacancies for efficient CO2 photoreduction

Metal halide perovskites with suitable energy band structures and excellent visible-light responses have emerged as promising photocatalysts for CO2 reduction to valuable chemicals and fuels. However, the efficiency of CO2 photocatalytic reduction often suffers from inefficient separation and sluggish transfer. Herein, a step-scheme (S-scheme) CsPbBr3/BiOBr photocatalyst with oxygen vacancies possessing intimate interfacial contact was fabricated by anchoring CsPbBr3 QDs on BiOBr-Ov nanosheets using a mild anti-precipitation method. The results showed that CsPbBr3/BiOBr-Ov-2 with an internal electric field (IEF) heterojunction exhibited a boosted evolution rate of 27.4 μmol g-1 h-1 (CO: 23.8 μmol g-1 h-1 and CH4: 3.6 μmol g-1 h-1) with an electron consumption rate (Relectron) of 76.4 μmol g-1 h-1, which was 5.9 and 3.2 times that of single CsPbBr3 and BiOBr-Ov, respectively. Density functional theory (DFT) calculations revealed that BiOBr with oxygen vacancies can effectively enhance the adsorption and activation of CO2 molecules. More importantly, in situ infrared Fourier transform spectroscopy (DRIFTS) spectra show the transformation process of the surface species, while the femtosecond transient absorption spectrum (fs-TA) reveals the charge transfer kinetics of the CsPbBr3/BiOBr-Ov. Overall, this work provides some guidance for the rational design of S-scheme heterojunctions and vacancy-engineered photocatalysts, which are expected to have potential applications in the fields of photocatalysis and solar energy conversion.

Efficient reduction-oxidation coupling degradation of nitroaromatic compounds in continuous flow processes

Nitroaromatic compounds (NACs) with electron-withdrawing nitro (-NO2) groups are typical refractory pollutants. Despite advanced oxidation processes (AOPs) being appealing degradation technologies, inefficient ring-opening oxidation of NACs and practical large-scale applications remain challenges. Here we tackle these challenges by designing a reduction-oxidation coupling (ROC) degradation process in LaFe0.95Cu0.05O3@carbon fiber cloth (LFCO@CFC)/PMS/Vis continuous flow system. Cu doping enhances the photoelectron transfer, thus triggering the -NO2 photoreduction and breaking the barriers in the ring opening. Also, it modulates surface electronic configuration to generate radicals and non-radicals for subsequent oxidation of reduction products. Based on this, the ROC process can effectively remove and mineralize NACs under the environmental background. More importantly, the LFCO catalyst outperformed most of the recently reported catalysts with lower cost (13.72 CNY/ton) and higher processing capacity (3600 t/month). Furthermore, the high scalability, material durability, and catalytic activity of LFCO@CFC under various realistic environmental conditions prove the potential ability for large-scale applications.

Ultrafast electron transfer at the In2O3/Nb2O5 S-scheme interface for CO2 photoreduction

Constructing S-scheme heterojunctions proves proficient in achieving the spatial separation of potent photogenerated charge carriers for their participation in photoreactions. Nonetheless, the restricted contact areas between two phases within S-scheme heterostructures lead to inefficient interfacial charge transport, resulting in low photocatalytic efficiency from a kinetic perspective. Here, In2O3/Nb2O5 S-scheme heterojunctions are fabricated through a straightforward one-step electrospinning technique, enabling intimate contact between the two phases and thereby fostering ultrafast interfacial electron transfer (<10 ps), as analyzed via femtosecond transient absorption spectroscopy. As a result, powerful photo-electrons and holes accumulate in the Nb2O5 conduction band and In2O3 valence band, respectively, exhibiting extended long lifetimes and facilitating their involvement in subsequent photoreactions. Combined with the efficient chemisorption and activation of stable CO2 on the Nb2O5, the resulting In2O3/Nb2O5 hybrid nanofibers demonstrate improved photocatalytic performance for CO2 conversion.

COF/In2S3 S-Scheme Photocatalyst with Enhanced Light Absorption and H2O2-Production Activity and fs-TA Investigation

Photocatalytic hydrogen peroxide (H2O2) synthesis from water and O2 is an economical, eco-friendly, and sustainable route for H2O2 production. However, single-component photocatalysts are subjected to limited light-harvesting range, fast carrier recombination, and weak redox power. To promote photogenerated carrier separation and enhance redox abilities, an organic/inorganic S-scheme photocatalyst is fabricated by in situ growing In2S3 nanosheets on a covalent organic framwork (COF) substrate for efficient H2O2 production in pure water. Interestingly, compared to unitary COF and In2S3, the COF/In2S3 S-scheme photocatalysts exhibit significantly larger light-harvesting range and stronger visible-light absorption. Partial density of state calculation, X-ray photoelectron spectroscopy, and femtosecond transient absorption spectroscopy reveal that the coordination between In2S3 and COF induces the formation of mid-gap hybrid energy levels, leading to smaller energy gaps and broadened absorption. Combining electron spin resonance spectroscopy, radical-trapping experiments, and isotope labeling experiments, three pathways for H2O2 formation are identified. Benefited from expanded light-absorption range, enhanced carrier separation, strong redox power, and multichannel H2O2 formation, the optimal composite shows an impressive H2O2-production rate of 5713.2 µmol g-1 h-1 in pure water. This work exemplifies an effective strategy to ameliorate COF-based photocatalysts by building S-scheme heterojunctions and provides molecular-level insights into their impact on energy level modulation.

A Solar to Chemical Strategy: Green Hydrogen as a Means, Not an End

Green hydrogen is the key to the chemical industry achieving net zero emissions. The chemical industry is responsible for almost 2% of all CO2 emissions, with half of it coming from the production of simple commodity chemicals, such as NH3, H2O2, methanol, and aniline. Despite electrolysis driven by renewable power sources emerging as the most promising way to supply all the green hydrogen required in the production chain of these chemicals, in this review, it is worth noting that the photocatalytic route may be underestimated and can hold a bright future for this topic. In fact, the production of H2 by photocatalysis still faces important challenges in terms of activity, engineering, and economic feasibility. However, photocatalytic systems can be tailored to directly convert sunlight and water (or other renewable proton sources) directly into chemicals, enabling a solar-to-chemical strategy. Here, a series of recent examples are presented, demonstrating that photocatalysis can be successfully employed to produce the most important commodity chemicals, especially on NH3, H2O2, and chemicals produced by reduction reactions. The replacement of fossil-derived H2 in the synthesis of these chemicals can be disruptive, essentially safeguarding the transition of the chemical industry to a low-carbon economy.

Engineering of Ultra-Thin Layer of MIL-125(Ti) Nanosheet\Zn-Tetracarboxy-Phthalocyanine S-Scheme Heterojunction as Photocatalytic CO2 Reduction Catalyst

Metal-organic frameworks (MOFs) with ultrathin 2D structure have attracted remarkable attention in photocatalytic application owing to the accessibility of abundant active sites on the surface. But high charge recombination results in poor photocatalytic activity. Herein, the synthesis of ultrathin MIL-125(Ti) nanosheets is reported with a thickness of 1.3 nm through a simple chemical reaction route of precursor solution aging and subsequent solvothermal process for photocatalytic CO2 production. The maximal CO evolution rate achieves 200.8 µmol g-1 h-1, which is prominently higher than that (78.6 µmol g-1 h-1) of the bulk MIL-125(Ti) counterpart. Furthermore, the structurally stable Zn (II) tetracarboxy phthalocyanine (ZnTcPc) molecules assembly on ultrathin MIL-125(Ti) nanosheet (NS) to form MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction through the strong interaction between the Ti3+ in MIL-125(Ti) and the COOH in ZnTcPc. The introduction of ZnTcPc greatly extends light absorption range and increases charge separation rate. The experimental and density functional theory calculation results validate that the MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction can favor CO2 adsorption and effectively depress the formation energy of the intermediates, achieving a high CO evolution rate of 450.8 µmol g-1 h-1. This work provides a strategy of engineering 2D MOF-based heterostructure systems for photocatalytic application.

Dynamic Hydroxylation Enhances Hydrogen Atom Abstraction from Water for Nitrogen Fixation Revealed by Isotope Labeling in Situ Fourier-Transform Infrared Spectroscopy

Employing water as a hydrogen source to participate in the hydrogen atom transfer (HAT) process is a low-cost and carbon-free process demonstrating great economic and environmental potential in catalysis. However, the low efficiency of hydrogen atom abstraction from water leads to slow kinetics of HAT for most hydrogenative reactions. Here, we prepared ultrathin Bi4O5Cl2 nanosheets where the surface can be in situ reconstructed via hydroxylation under light illumination to facilitate the abstraction of hydrogen atoms from pure water for efficient nitrogen fixation. Consequently, the isotope labeling in situ Fourier-transform infrared spectroscopy (FT-IR) involving H2O and D2O has clearly revealed that the hydroxyl groups tend to be adsorbed on the chloride vacancy sites on the Bi4O5Cl2 surface to form hydroxylated surfaces, where the hydroxylated photocatalyst surface enables partial dehydrogenation of water into H2O2, allowing the utilization of H atoms for efficient of N2 hydrogenation via HAT steps. This work elucidates the in-depth reaction mechanism of hydrogen atom extraction from H2O molecules via the light-generated chloride vacancy to promote photocatalytic nitrogen fixation, ultimately enabling the inspiration and providing crucial rules for the design of important functional materials that can efficiently deliver active hydrogen for chemical synthesis.

In Situ UV-Vis-NIR Absorption Spectroscopy and Catalysis

This review highlights in situ UV-vis-NIR range absorption spectroscopy in catalysis. A variety of experimental techniques identifying reaction mechanisms, kinetics, and structural properties are discussed. Stopped flow techniques, use of laser pulses, and use of experimental perturbations are demonstrated for in situ studies of enzymatic, homogeneous, heterogeneous, and photocatalysis. They access different time scales and are applicable to different reaction systems and catalyst types. In photocatalysis, femto- and nanosecond resolved measurements through transient absorption are discussed for tracking excited states. UV-vis-NIR absorption spectroscopies for structural characterization are demonstrated especially for Cu and Fe exchanged zeolites and metalloenzymes. This requires combining different spectroscopies. Combining magnetic circular dichroism and resonance Raman spectroscopy is especially powerful. A multitude of phenomena can be tracked on transition metal catalysts on various supports, including changes in oxidation state, adsorptions, reactions, support interactions, surface plasmon resonances, and band gaps. Measurements of oxidation states, oxygen vacancies, and band gaps are shown on heterogeneous catalysts, especially for electrocatalysis. UV-vis-NIR absorption is burdened by broad absorption bands. Advanced analysis techniques enable the tracking of coking reactions on acid zeolites despite convoluted spectra. The value of UV-vis-NIR absorption spectroscopy to catalyst characterization and mechanistic investigation is clear but could be expanded.

Progress of disinfection catalysts in advanced oxidation processes, mechanisms and synergistic antibiotic degradation

Human diseases caused by pathogenic microorganisms make people pay more attention to disinfection. Meanwhile, antibiotics can cause microbial resistance and increase the difficulty of disease treatment, resulting in risk of triggering a vicious circle. Advanced oxidation process (AOPs) has been widely studied in the field of synergistic treatment of the two contaminates. This paper reviews the application of catalytic materials and their modification strategies in the context of AOPs for disinfection and antibiotic degradation. It also delves into the mechanisms of disinfection such as the pathways for microbial inactivation and the related influencing factors, which are essential for understanding the pivotal role of catalytic materials in disinfection principles by AOPs. More importantly, the exploratory research on the combined use of AOPs for disinfection and antibiotic degradation is discussed, and the potential and prospects in this field is highlighted. Finally, the limitations and challenges associated with the application of AOPs in disinfection and antibiotic degradation are summarized. It aims to provide a starting point for future research efforts to facilitate the widespread use of advanced oxidation processes in the field of public health.

Decoration of 0D Bi3NbO7 nanoparticles onto 2D BiOIO3 nanosheets as visible-light responsive S-scheme photocatalyst for photo-oxidation of antibiotics in wastewater

In this work, a new S-type hybrid composed of 2D BiOIO3 and 0D Bi3NbO7 was proposed and hybridized by a facile self-assembly strategy. The developed nanomaterials were characterized and identified by a series of sophisticated analyses, like XRD, SEM, EIS, XPS, PL, UPS, EDS, BET, M-S, TEM, HRTEM, and DRS. The photocatalytic behavior of BiOIO3/Bi3NbO7 was examined and optimized against amoxicillin (AMX) and other types of antibiotics under a variety of environmental conditions, such as visible light (150 W LED), direct sunlight, pH (3-11), catalyst dosages (20-80 mg), humic acid (0-24 mg/L), AMX concentration (10-40 mg/L), and different inorganic ions (0.05 M). The optimized BiOIO3/Bi3NbO7 hybrid attained exceptional AMX degradation activity (96.5%) under visible light (60 min), with a reaction constant of up to 0.04559 min-1, exceeding bare BiOIO3 and Bi3NbO7 by 5.57 and 5.3 folds, respectively. The obtained BiOIO3/Bi3NbO7 hybrid unclosed expanded light utilization behavior compared with neat catalysts, which originates from the powerful incorporation between BiOIO3 and Bi3NbO7 in the S-type system. The radical investigations confirmed the superiority of BiOIO3/Bi3NbO7 in generating both •OH and •O2- during the photoreaction. The novel Bi3NbO7-based heterojunction afforded robust photostability in five treatment cycles and simple charge transfer activity in the S-type route, boosting the photo-mechanism for antibiotic degradation in an efficient manner. The building of the S-scheme heterojunction between BiOIO3 and Bi3NbO7 stimulates the utilization of holes by the recombination process and promotes the overall stability of the composite. Our study introduces a new class of semiconductor heterojunctions that may contribute to the development potential of the photocatalysis sector in wastewater treatment.

Grain Engineering of Sb2 S3 Thin Films to Enable Efficient Planar Solar Cells with High Open-Circuit Voltage

Sb2 S3 is a promising environmentally friendly semiconductor for high performance solar cells. But, like many other polycrystalline materials, Sb2 S3 is limited by nonradiative recombination and carrier scattering by grain boundaries (GBs). This work shows how the GB density in Sb2 S3 films can be significantly reduced from 1068 ± 40 to 327 ± 23 nm µm-2 by incorporating an appropriate amount of Ce3+ into the precursor solution for Sb2 S3 deposition. Through extensive characterization of structural, morphological, and optoelectronic properties, complemented with computations, it is revealed that a critical factor is the formation of an ultrathin Ce2 S3 layer at the CdS/Sb2 S3 interface, which can reduce the interfacial energy and increase the adhesion work between Sb2 S3 and the substrate to encourage heterogeneous nucleation of Sb2 S3 , as well as promote lateral grain growth. Through reductions in nonradiative recombination at GBs and/or the CdS/Sb2 S3 heterointerface, as well as improved charge-carrier transport properties at the heterojunction, this work achieves high performance Sb2 S3 solar cells with a power conversion efficiency reaching 7.66%. An impressive open-circuit voltage (VOC ) of 796 mV is achieved, which is the highest reported thus far for Sb2 S3 solar cells. This work provides a strategy to simultaneously regulate the nucleation and growth of Sb2 S3 absorber films for enhanced device performance.

Efficient Exciton Dissociation on Ceria Chelated Cerium-Based MOF Isogenous S-Scheme Photocatalyst for Acetaldehyde Purification

Long-term exposure to low concentration indoor VOCs of acetaldehyde (CH3 CHO) is harmful to human health. Thus, a novel isogenous heterojunction CeO2 /Ce-MOF photocatalyst is synthesized via a one-step hydrothermal method for the effective elimination of CH3 CHO in this work. This CeO2 /Ce-MOF photocatalyst performs well in CH3 CHO removal and achieves an apparent quantum efficiency of 7.15% at 420 nm, which presents ≈6.7 and 3.4 times superior to those generated by CeO2 and Ce-MOF, respectively. The enhanced efficiency is due to two main aspects including i) an effective photocarrier separation ability and the prolonged reaction lifetime of excitons play crucial roles and ii) the formation of an internal electric field (IEF) is sufficient to overcome the considerable exciton binding energy, and increases the exciton dissociation efficiency by up to 50.4%. Moreover, the reasonable pathways and mechanisms of CH3 CHO degradation are determined by in situ DRIFTS analysis and simulated DFT calculations. Those results demonstrated that S-scheme heterojunction successfully increases the efficiency of harmful volatile organic compounds elimination, and it offers essential guidance for designing rare earth-based MOF photocatalysts.

Molecular Heptazine-Triazine Junction over Carbon Nitride Frameworks for Artificial Photosynthesis of Hydrogen Peroxide

Revealing the photocatalytic mechanism between various junctions and catalytic activities has become a hotspot in photocatalytic systems. Herein, an internal molecular heptazine/triazine (H/T) junction in crystalline carbon nitride (HTCN) is constructed and devoted to selective two-electron oxygen reduction reaction (2e- ORR) for efficient hydrogen peroxide (H2 O2 ) production. In-situ X-ray diffraction spectra under various temperatures authenticate the successful formation of molecular H/T junction in HTCN during the calcining process rather than physically mixing. The increased surface photovoltage and transient photovoltage signals, and the decreased exciton binding energy undoubtably elucidate that an obvious increasement of carrier density and diffusion capability of photogenerated electrons are realized over HTCN. Additionally, the analyses of in situ photoirradiated Kelvin probe force microscopy and femto-second transient absorption spectra reveal the successful construction of the strong internal built-in-electric field and the existence of the majority of long-lived shallow trapped electrons associated with molecular H/T junction over HTCN, respectively. Benefiting from these, the photocatalytic results exhibit an incredible improvement (96.5-fold) for H2 O2 production. This novel work provides a comprehensive understanding of the long-lived reactive charges in molecular H/T junctions for strengthening the driving-force for photocatalytic H2 O2 production, which opens potential applications for enhancing PCN-based photocatalytic redox reactions.

Self-assembled micro and nano rod-shaped porphyrin@Bi12O17Cl2 composite as an efficient photocatalyst for degradation of organic contaminants

Bi12O17Cl2 is a potential photocatalyst in practical applications due to its excellent photostability, visible light activity, and competitive bandgap energy. However, the fast recombination of photogenerated charge carriers makes it impractical for pollution mitigation. Recently, aggregated porphyrins have emerged as photosensitizers in light-dependent applications such as photocatalysis. Although Bi12O17Cl2 and porphyrin can function as separate photocatalysts, their photocatalytic properties in terms of visible light adsorption, charge separation and transport, can be improved when they are combined to form heterostructure. In this study, rod-shaped aggregated 5,10,15, 20-Tetrakis (4-carboxyphenyl) porphyrin was synthesized by CTAB-assisted, self-assembly strategy and Bi12O17Cl2 by a facile microwave method. The porphyrin and Bi12O17Cl2 were combined to generate a series of x%Porphyrin@Bi12O17Cl2 having 0.02% wt., 0.1% wt., 0.4% wt., 1% wt. and 10% wt. as compositions of porphyrin. The materials' photocatalytic degradation efficiency was tested on Rhodamine B dye as a representative pollutant. The best and worst performances were reported for 1%Porphyrin@Bi12O17Cl2 and 10%Porphyrin@Bi12O17Cl2, respectively, which are 3.1 and 0.5 times increases in efficiency compared to pure Bi12O17Cl2. From the radical trapping experiment, electrons and superoxide were the dominant reactive species in the degradation process. The enhanced photocatalytic capability of the materials was attributed to the photosensitizing property of porphyrin and the heterojunction formation, which promotes the separation of photogenerated charge carriers. A plausible step-scheme (S-scheme) was proposed for the photocatalytic degradation mechanism. The S-scheme provided the high redox potential of the photogenerated charge carriers. The findings herein offer a new option for improving the photocatalytic performance of Bi12O17Cl2 for environmental applications through the photosensitization strategy.

Enhanced and synergistic catalytic activation by photoexcitation driven S-scheme heterojunction hydrogel interface electric field

The regulation of heterogeneous material properties to enhance the peroxymonosulfate (PMS) activation to degrade emerging organic pollutants remains a challenge. To solve this problem, we synthesize S-scheme heterojunction PBA/MoS2@chitosan hydrogel to achieve photoexcitation synergistic PMS activation. The constructed heterojunction photoexcited carriers undergo redox conversion with PMS through S-scheme transfer pathway driven by the directional interface electric field. Multiple synergistic pathways greatly enhance the reactive oxygen species generation, leading to a significant increase in doxycycline degradation rate. Meanwhile, the 3D polymer chain spatial structure of chitosan hydrogel is conducive to rapid PMS capture and electron transport in advanced oxidation process, reducing the use of transition metal activator and limiting the leaching of metal ions. There is reason to believe that the synergistic activation of PMS by S-scheme heterojunction regulated by photoexcitation will provide a new perspective for future material design and research on enhancing heterologous catalysis oxidation process.

Recent advancements in the fabrication and photocatalytic applications of graphitic carbon nitride-tungsten oxide nanocomposites

The present review focuses on the widely used graphitic carbon nitride (g-C3N4)-tungsten oxide (WO3) nanocomposite in photocatalytic applications. These catalysts are widely employed due to their easy preparation, high physicochemical stability, nontoxicity, electron-rich properties, electronic band structure, chemical stability, low cost, earth-abundance, high surface area, and strong absorption capacity in the visible range. These sustainable properties make them predominantly attractive and unique from other photocatalysts. In addition, graphitic carbon nitride (g-C3N4) is synthesized from nitrogen-rich precursors; therefore, it is stable in strong acid solutions and has good thermal stability up to 600 °C. This review covers the historical background, crystalline phases, density-functional theory (DFT) study, synthesis method, 0-D, 1-D, 2-D, and 3-D materials, oxides/transition/nontransition metal-doped, characterization, and photocatalytic applications of WO3/g-C3N4. Enhancing the catalytic performance strategies such as composite formation, element-doping, heterojunction construction, and nanostructure design are also summarized. Finally, the future perspectives and challenges for WO3/g-C3N4 composite materials are discussed to motivate young researchers and scientists interested in developing environment-friendly and efficient catalysts.

Constructing Spatially Separated Cage-Like Z-scheme Heterojunction Photocatalyst for Enhancing Photocatalytic H2 Evolution

Heterojunctions coupled into micro-mesoscopic structures is an attractive strategy to optimize the light harvesting and carrier separation of semiconductor photocatalysts. A self-templating method of ion exchange is reported to synthesize an exquisite hollow cage-structured Ag₂ S@CdS/ZnS that direct Z-scheme heterojunction photocatalyst. On the ultrathin shell of the cage, Ag₂ S, CdS, and ZnS with Zn-vacancies (V_Zn ) are arranged sequentially from outside to inside. Among them, the photogenerated electrons are excited by ZnS to the V_Zn energy level and then recombine with the photogenerated holes that are generated by CdS, while the electrons remained in the CdS conduction band are further transferred to Ag₂ S. The ingenious cooperation of the Z-scheme heterojunction with the hollow structure optimizes the photogenerated charges transport channel, spatially separated the oxidation and reduction half-reactions, decreases the charge recombination probability, and simultaneously improves the light harvesting efficiency. As a result, the photocatalytic hydrogen evolution activity of the optimal sample is 136.6 and 17.3 times higher than that of cage-like ZnS with V_Zn and CdS by, respectively. This unique strategy demonstrates the tremendous potential of the incorporation of heterojunction construction to morphology design of photocatalytic materials, and also provided a reasonable route for designing other efficient synergistic photocatalytic reactions.

Strong Spin Polarization Effect of Atomically Dispersed Metal Site Boosts the Selective Photocatalytic Nitrobenzene Hydrogenation to Aniline over Graphitic Carbon Nitride

Atomically dispersed catalysts (ADCs) with a well-defined structure are theoretically desirable for a high-selectivity photocatalytic reaction. However, achieving high product selectivity remains a practical challenge for ADCs-based photocatalysts. Herein, we reveal a spin polarization effect on achieving high product selectivity (95.0%) toward the photocatalytic nitrobenzene (PhNO₂) hydrogenation to aniline (PhNH₂) on atomically dispersed Fe site-loaded graphitic carbon nitride (Fe/g-C₃N₄). In combination with the Gibbs free energy diagram and electronic structure analysis, the origin of the photocatalytic performance is attributed not only to the strong metal-support interaction between the Fe site and g-C₃N₄, but more importantly to the strong spin polarization effect that promotes the potential-determining step (PDS) of *PhNO to *PhNOH. This work could be helpful for the design of ADCs-based photocatalysts in view of the spin polarization effect.

Recent advances on catalysts for photocatalytic selective hydrogenation of nitrobenzene to aniline

Selective hydrogenation of nitrobenzene (SHN) is an important approach to synthesize aniline, an essential intermediate with extremely high research significance and value in the fields of textiles, pharmaceuticals and dyes. SHN reaction requires high temperature and high hydrogen pressure via the conventional thermal-driven catalytic process. On the contrary, photocatalysis provides an avenue to achieve high nitrobenzene conversion and high selectivity towards aniline at room temperature and low hydrogen pressure, which is in line with the sustainable development strategies. Designing efficient photocatalysts is a crucial step in SHN. Up to now, several photocatalysts have been explored for photocatalytic SHN, such as TiO2, CdS, Cu/graphene and Eosin Y. In this review, we divide the photocatalysts into three categories based on the characteristics of the light harvesting units, including semiconductors, plasmonic metal-based catalysts and dyes. The recent progress of the three categories of photocatalysts is summarized, the challenges and opportunities are pointed out and the future development prospects are described. It aims to give a clear picture to the catalysis community and stimulate more efforts in this research area.

Femtosecond transient absorption spectroscopy investigation into the electron transfer mechanism in photocatalysis

Femtosecond transient absorption spectroscopy (fs-TAS) is a powerful technique for monitoring the electron transfer kinetics in photocatalysis. Several important works have successfully elucidated the electron transfer mechanism in heterojunction photocatalysts (HPs) using fs-TAS measurements, and thus a timely summary of recent advances is essential. This feature article starts with a thorough interpretation of the operating principle of fs-TAS equipment, and the fundamentals of the fs-TAS spectra. Subsequently, the applications of fs-TAS in analyzing the dynamics of photogenerated carriers in semiconductor/metal HPs, semiconductor/carbon HPs, semiconductor/semiconductor HPs, and multicomponent HPs are discussed in sequence. Finally, the significance of fs-TAS in revealing the ultrafast interfacial electron transfer process in HPs is summarized, and further research on the applications of fs-TAS in photocatalysis is proposed. This feature article will provide deep insight into the mechanism of the enhanced photocatalytic performance of HPs from the perspective of electron transfer kinetics.

Constructing Z-scheme NiMoO4@Co3O4 core-shell heterogeneous architectures with prominent photoelectrocatalytic performance toward water purification

Photoelectrocatalysis (PEC) oxidation is an efficient and eco-friendly advanced oxidation process (AOP), which is a hot research topic in the treatment of organic wastewater. The selection of superior photoelectrode materials is the critical factor affecting PEC efficiency and the main challenge in practical application. In this work, novel NiMoO₄@Co₃O₄ hierarchical core-shell heterogeneous photoanodes were prepared through a two-step hydrothermal method and exhibited superior catalytic performance in the degradation of reactive brilliant blue KN-R. The wrapping of NiMoO₄ nanosheets on Co₃O₄ nanowires electrode can enlarge its contact area with electrolyte, enable fast redox reaction and improve the long-term durability. The unique Z-scheme heterojunction structure between the two components ensured the effective separation of photo-generated carriers, facilitating the generation of OH and O^2- during the PEC degradation process. The optimal NiMoO₄@Co₃O₄-1.25 hierarchical architecture anode catalyst exhibited the highest removal rate of 83.65% of reactive brilliant blue KN-R in 120 min with long-term stability (∼12000 s) in 1.0 mol·L^-1 H₂SO₄ solution. This report may inspire the design and fabrication of heterostructure photoanode in water purification.

2D/1D MoS2 /TiO2 Heterostructure Photocatalyst with a Switchable CO2 Reduction Product

Regulating the transfer pathway of charge carriers in heterostructure photocatalysts is of great importance for selective CO₂ photoreduction. Herein, the charge transfer pathway and in turn the redox potential succeeded to regulate in 2D MoS₂ /1D TiO₂ heterostructure by varying the light wavelength range. Several in situ measurements and experiments confirm that charge transfer follows either an S-scheme mechanism under simulated solar irradiation or a heterojunction approach under visible light illumination, elucidating the switchable property of the MoS₂ /TiO₂ heterostructure. Replacing the simulated sunlight irradiation with the visible light illumination switches the photocatalytic CO₂ reduction product from CO to CH_4. ¹³ CO₂ isotope labeling confirms that CO₂ is the source of carbon for CH₄ and CO products. The photoelectrochemical H₂ generation further supports the switching property of MoS₂ /TiO₂ . Unlike previous studies, density functional theory calculations are used to investigate the band structure of Van der Waals MoS₂ /TiO₂ S scheme after contact, allowing to propose accurate charge transfer pathways, in which the theoretical results are well matched with the experimental results. This work opens the opportunity to develop photocatalysts with switchable charge transport and tunable redox potential for selective artificial photosynthesis.

Rational design of S-scheme AgI/ZrTiO4-x heterojunctions for remarkably boosted norfloxacin degradation

Emerging S-scheme heterojunction photocatalysts endowed with efficient charge separation and strong redox capacity have stimulated wide interests in dealing with environmental issues nowadays. In this work, we firstly fabricated the oxygen vacancy modified ZrTiO_4-x nanocrystals, which was further combined with AgI to build the defective S-scheme AgI/ZrTiO_4-x heterojunctions for visible-light photocatalytic norfloxacin degradation. The synthesized ZrTiO_4-x nanocrystals and AgI/ZrTiO_4-x heterojunctions displayed remarkably boosted norfloxacin degradation performance under visible-light irradiation. The reaction rate constant of the optimized AgI/ZrTiO_4-x-5% heterojunction is as high as 0.01419 min^-1, which is approximately 43.35 times that of AgI and 7.93 times that of ZrTiO_4-x nanocrystals, and far superior to those of commercial TiO₂ and commercial ZrO₂. The high-performance photocatalytic norfloxacin degradation could be mainly attributed to the formation of S-scheme charge transfer pathways and oxygen vacancy defects. More significantly, AgI/ZrTiO_4-x could also realize the effective photo-decomposition of other emerging pollutants. Finally, the visible-light photocatalytic performance and photocatalysis mechanism were investigated.

Solid-Phase Synthesis of Titanium Dioxide Micro-Nanostructures

Titanium dioxide (TiO₂) micro-nanostructures are widely utilized in photochemical applications due to their unique band gaps and are of huge demand in scientific research and industrial manufacture. Herein, this work reports a controllable, facile, economical, and green solid-phase synthesis strategy to prepare TiO₂ with governable morphologies containing 1D nanorods, 3D microbulks, and irregular thick plates. Specifically, Ti powders are transformed into TiO₂ micro-nanostructures through dispersing them into a solid NaOH/KOH mixture with a low eutectic point, followed by grinding, heating, ion exchange, and calcination. As no solvents are utilized in the alkali treatment process, the usage of solvents is decreased and high vapor pressure is avoided. Moreover, the band gaps of TiO₂ micro-nanostructures can be regulated from 3.02 to 3.34 eV through altering the synthetic parameters. Notably, the as-prepared TiO₂ micro-nanostructures exhibit high photocatalytic activities in the degradation of rhodamine B and methylene blue under simulated solar light illumination. It is believed that the solid-phase synthesis strategy will be of huge demand for the synthesis of TiO₂ micro-nanostructures.

In Situ Irradiated X-ray Photoelectron Spectroscopy Investigation on Electron Transfer Mechanism in S-Scheme Photocatalyst

S-scheme photocatalysts have demonstrated great potential in solar fuel production. To study the electron transfer pathways in S-scheme heterojunctions, in situ irradiated X-ray photoelectron spectroscopy (ISIXPS) is an effective and widely used technology. However, the mechanism of ISIXPS in identifying the electron transfer pathways in S-scheme heterojunction has not yet been elucidated. In this Perspective, the development process and the formation mechanism of S-scheme photocatalysts are first introduced. Afterward, the principles of XPS and ISIXPS measurements are thoroughly explained, and the applications of XPS and ISIXPS in confirming the interfacial electron transfer in S-scheme heterojunctions are discussed. Finally, suggestions for future research on the utilization of ISIXPS in S-scheme heterojunctions are proposed. This Perspective will provide deep insight into the electron transfer mechanism in S-scheme photocatalysts through ISIXPS.

In-situ constructed 2D/2D ZnIn2S4/Bi4Ti3O12 S-scheme heterojunction for degradation of tetracycline: Performance and mechanism insights

Semiconductor materials dominated photocatalytic technology is one of the most efficient approaches to degrade organic pollutants. However, the limited light absorption range and rapid recombination of photogenerated carriers greatly restrict the application of photocatalysts. Rational design of photocatalysts to achieve high catalytic activity and stability is of great importance. Herein, ZnIn₂S₄/Bi₄Ti₃O₁₂ S-scheme heterojunction is synthesized by growing the ZnIn₂S₄ nanosheets on the sheet-like Bi₄Ti₃O₁₂ surface via a low-temperature solvothermal method. The TC removal efficiency of optimized heterojunction reaches 82.1% within 60 min under visible light, and the rate constant is nearly 6.8 times than that of pristine ZnIn₂S₄. The favorable photocatalytic performance of heterojunction is attributed to the tight contact interface and efficient separation of photogenerated carriers. Besides, the difference in work function between ZnIn₂S₄ and Bi₄Ti₃O₁₂ leads to band bending and the establishment of built-in electric field on the contact interface of heterojunction, which facilitates the migration and separation of photogenerated carriers. Furthermore, the cycling test demonstrates the attractive stability of heterojunction. The possible TC photodegradation pathways and toxicity assessment of the intermediates are also analyzed. In conclusion, this work provides an effective strategy to prepare S-scheme heterojunction photocatalysts with favorable photocatalytic activity, which can enhance wastewater purification efficiency.

Synthesis of adjustable {312}/{004} facet heterojunction MWCNTs/Bi5O7I photocatalyst for ofloxacin degradation: Novel insights into the charge carriers transport

Multi-wall carbon nanotubes (MWCNTs) with high electrical conductivity are commonly accounted as the ideal additives to enhance the charge surface migration efficiency in photocatalysis. Theoretically, the MWCNTs-modified binary photocatalysts have potential for the change of nanocrystal structure. Herein, we reports an adjustable {312}/{004}facet heterojunction MWCNTs/Bi₅O₇I nanocomposite. Interestingly, the synergistic effect of {312}/{004}facet heterojunction and MWCNTs can effectively accelerate the spatial charge carriers transport. A novel {312}/{004}facet "S-scheme" pathway was proven to be the dominated pathway for the enhancement of spatial charge carriers. As a result, the MWCNTs-{312}/{004}Bi₅O₇I composites exhibited superior photocatalytic oxidation efficiency for a representative antibiotics ofloxacin photodegradation. Density functional theory (DFT) calculation and LC-MS/MS analysis confirmed that the possible dealkylation and oxidation pathways could be found in OFL degradation. This work provides novel insights for the relationship between charge carrier transport and facet structure-property.

Cooperative Coupling of H2 O2 Production and Organic Synthesis over a Floatable Polystyrene-Sphere-Supported TiO2 /Bi2 O3 S-Scheme Photocatalyst

Cooperative coupling of photocatalytic H₂ O₂ production with organic synthesis has an expansive perspective in converting solar energy into storable chemical energy. However, traditional powder photocatalysts suffer from severe agglomeration, limited light absorption, poor gas reactant accessibility, and reusable difficulty, which greatly hinders their large-scale application. Herein, floatable composite photocatalysts are synthesized by immobilizing hydrophobic TiO₂ and Bi₂ O₃ on lightweight polystyrene (PS) spheres via hydrothermal and photodeposition methods. The floatable photocatalysts are not only solar transparent, but also upgrade the contact between reactants and photocatalysts. Thus, the floatable step-scheme (S-scheme) TiO₂ /Bi₂ O₃ photocatalyst exhibits a drastically enhanced H₂ O₂ yield of 1.15 mm h^-1 and decent furfuryl alcohol conversion to furoic acid synchronously. Furthermore, the S-scheme mechanism and dynamics are systematically investigated by in situ irradiated X-ray photoelectron spectroscopy and femtosecond transient absorption spectrum analyses. In situ Fourier transform infrared spectroscopy and density functional theory calculations reveal the mechanism of furoic acid evolution. The ingenious design of floatable photocatalysts not only furnishes insight into maximizing photocatalytic reaction kinetics but also provides a new route for highly efficient heterogeneous catalysis.

Dynamics of Photogenerated Charge Carriers in Inorganic/Organic S-Scheme Heterojunctions

Step-scheme heterojunctions formed between two firmly bound photocatalysts facilitate charge separation due to interfacial charge transfer, which is usually illustrated by the gain or loss of electrons in the constituent photocatalysts characterized by in situ irradiated X-ray photoelectron spectroscopy. This technique provides a steady-state view of charge distribution but overlooks the transient and complex dynamics of charge transfer, trapping, and recombination. To provide a molecular-level and dynamic view of these processes, we investigated the behaviors of photogenerated charge carriers within an inorganic/organic TiO₂/polydopamine S-scheme heterojunction using ultrafast transient absorption spectroscopy and time-resolved photoluminescence spectroscopy. We found the interfacial charge transfer within the step-scheme heterojunction occurred at a smaller shorter time scale than recombination, leading to efficient charge separation. Moreover, the charge-discharge property of polydopamine induces electron backflow, which should be avoided in practical photocatalytic applications. The composite showed higher photocatalytic H₂O₂-production activities due to faster H₂O₂ formation and suppressed H₂O₂ decomposition.