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

Sulfone-Modified Covalent Organic Frameworks Enabling Efficient Photocatalytic Hydrogen Peroxide Generation via One-Step Two-Electron O2 Reduction

Photocatalytic oxygen reduction reaction (ORR) offers a promising hydrogen peroxide (H2 O2 ) synthetic strategy, especially the one-step two-electron (2e- ) ORR route holds great potential in achieving highly efficient and selectivity. However, efficient one-step 2e- ORR is rarely harvested and the underlying mechanism for regulating the ORR pathways remains greatly obscure. Here, by loading sulfone units into covalent organic frameworks (FS-COFs), we present an efficient photocatalyst for H2 O2 generation via one-step 2e- ORR from pure water and air. Under visible light irradiation, FS-COFs exert a superb H2 O2 yield of 3904.2 μmol h-1  g-1 , outperforming most reported metal-free catalysts under similar conditions. Experimental and theoretical investigation reveals that the sulfone units accelerate the separation of photoinduced electron-hole (e- -h+ ) pairs, enhance the protonation of COFs, and promote O2 adsorption in the Yeager-type, which jointly alters the reaction process from two-step 2e- ORR to the one-step one, thereby achieving efficient H2 O2 generation with high selectivity.

Carbonaceous Material Modified MoO2 Nanospheres with Oxygen Vacancies for Enhanced Visible-Light Photocatalytic Oxidative Coupling of Benzylamine

Surface oxygen vacancy (OV) plays a pivotal role in the activation of molecular oxygen and separation of electrons and holes in photocatalysis. Herein, carbonaceous materials-modified MoO₂ nanospheres with abundant surface OVs (MoO₂/C-OV) were successfully synthesized via glucose hydrothermal processes. In situ introduction of carbonaceous materials triggered a reconstruction of the MoO₂ surface, which introduced abundant surface OVs on the MoO₂/C composites. The surface oxygen vacancies on the obtained MoO₂/C-OV were confirmed via electron spin resonance spectroscopy (ESR) and X-ray photoelectron spectroscopy (XPS). The surface OVs and carbonaceous materials boosted the activation of molecular oxygen to singlet oxygen (¹O₂) and superoxide anion radical (•O₂^-) in selectively photocatalytic oxidation of benzylamine to imine. The conversion of benzylamine was 10 times that of pristine MoO₂ nanospheres with a high selectivity under visible light irradiation at 1 atm air pressure. These results open an avenue to modify Mo-based materials for visible light-driven photocatalysis.

Sodium alginate/chitosan-coated TiO2NPs hybrid fiber with photocatalytic self-cleaning property, UV resistance and enhanced tensile strength

SA/CS-coated TiO₂NPs hybrid fibers with photocatalytic self-cleaning properties, UV resistance and enhanced tensile strength were successfully prepared by adding CS-coated TiO₂NPs to SA matrix. The FTIR and TEM results demonstrate the successful preparation of CS-coated TiO₂NPs core-shell structured composite particles. SEM and Tyndall effect results showed that the core-shell particles were uniformly dispersed in the SA matrix. When the content of Core-shell particles increased from 0.1 to 0.3 wt%, the tensile strength of SA/CS-coated TiO₂NPs hybrid fibers increased from 26.89 to 64.45 % compared with SA/TiO₂NPs hybrid fibers. The SA/CS-coated TiO₂NPs hybrid fiber (0.3 wt%) exhibits excellent photocatalytic degradation performance, achieving a 90 % degradation rate for the RhB solution. And the fibers also exhibit outstanding photocatalytic degradation performance towards various dyes and stains commonly encountered in daily life, including methyl orange, malachite green, Congo red, coffee and mulberry juice. The UV transmittance of the SA/CS-coated TiO₂NPs hybrid fibers decreased significantly from 90 % to 75 % with the increase in core-shell particle addition, and correspondingly, the UV absorption capacity increased. The SA/CS-coated TiO₂NPs hybrid fibers prepared lay the groundwork for potential applications in various fields, including textiles, automotive engineering, electronics and medicine.

S-Scheme Heterojunction Photocatalysts for H2O2 Production

Photocatalysis opens a new door to H₂O₂ formation via a low-cost, clean, mild, and sustainable process, which holds great promise for the next generation of massive H₂O₂ production. However, fast photogenerated electron-hole recombination and slow reaction kinetics are the main obstacles for its practical application. An effective solution is to construct the step-scheme (S-scheme) heterojunction, which remarkably promotes carrier separation and boosts the redox power for efficient photocatalytic H₂O₂ production. Considering the superiority of S-scheme heterojunctions, this Perspective summarizes the recent advances of S-scheme photocatalysts for H₂O₂ production, including photocatalysts for building S-scheme heterojunctions, H₂O₂-production performance, and S-scheme photocatalytic mechanisms. Lastly, some prospects are given to motivate future research in this promising field, other promising strategies are provided to further improve H₂O₂ yields, and future research directions are suggested.

Copper indium sulfide quantum dots in photocatalysis

Since the advent of photocatalytic technology, scientists have been searching for semiconductor materials with high efficiency in solar energy utilization and conversion to chemical energy. Recently, the development of quantum dot (QD) photocatalysts has attracted much attention because of their unique characteristics: small size, quantum effects, strong surface activity, and wide photoresponse range. Among ternary chalcogenide semiconductors, CuInS₂ QDs are increasingly examined in the field of photocatalysis due to their high absorption coefficients, good matching of the absorption range with sunlight spectrum, long lifetimes of photogenerated electron-hole pairs and environmental sustainability. In this review paper, the structural and electronic properties, synthesis methods and various photocatalytic applications of CuInS₂ QDs are systematically expounded. The current research status on the photocatalytic properties of materials based on CuInS₂ QD is discussed combined with the existing modification approaches for the enhancement of their performances. Future challenges and new development opportunities of CuInS₂ QDs in the field of photocatalysis are then prospected.

Strain-Engineering of Mesoporous Cs3 Bi2 Br9 /BiVO4 S-Scheme Heterojunction for Efficient CO2 Photoreduction

Slow charge kinetics and unfavorable CO₂ adsorption/activation strongly inhibit CO₂ photoreduction. In this study, a strain-engineered Cs₃ Bi₂ Br₉ /hierarchically porous BiVO₄ (s-CBB/HP-BVO) heterojunction with improved charge separation and tailored CO₂ adsorption/activation capability is developed. Density functional theory calculations suggest that the presence of tensile strain in Cs₃ Bi₂ Br₉ can significantly downshift the p-band center of the active Bi atoms, which enhances the adsorption/activation of inert CO₂ . Meanwhile, in situ irradiation X-ray photoelectron spectroscopy and electron spin resonance confirm that efficient charge transfer occurs in s-CBB/HP-BVO following an S-scheme with built-in electric field acceleration. Therefore, the well-designed s-CBB/HP-BVO heterojunction exhibits a boosted photocatalytic activity, with a total electron consumption rate of 70.63 µmol g^-1 h^-1 , and 79.66% selectivity of CO production. Additionally, in situ diffuse reflectance infrared Fourier transform spectroscopy reveals that CO₂ photoreduction undergoes a formaldehyde-mediated reaction process. This work provides insight into strain engineering to improve the photocatalytic performance of halide perovskite.

Revisiting the roles of dopants in g-C3N4 nanostructures for piezo-photocatalytic production of H2O2: a case study of selenium and sulfur

The sustainable production of hydrogen peroxide (H₂O₂) from oxygen and water has become an exciting research hotspot in the scientific community due to the importance of this fine chemical in various fields. Besides, piezo-photocatalysis is an emerging star for generating H₂O₂ from these green reagents. For developing catalysts for this specific application, doping heteroatoms into carbon-based materials such as graphitic carbon nitrides (g-C₃N₄) is a growing fascination among worldwide scientists. However, systematic study on the effects of doping precursors on the catalytic results is still rare. Herein, we fabricated sulfur (S) and selenium (Se) doped g-C₃N₄ with various doping precursors to evaluate the effects of these agents on the production of H₂O₂ under light and ultrasound irradiation. Based on the results, Se-doped g-C₃N₄ gave an outstanding catalytic performance compared to S-doped g-C₃N₄, even in a significantly low quantity of Se. In order to fully understand the chemical, physical, optical, and electronic properties of pristine g-C₃N₄ and its derivatives, the as-prepared materials were thoroughly analyzed with various tools. Thus, this study would give more profound insights into doping techniques for carbon-based materials and encourage further research on the design and development of piezo-photocatalysts for practical applications.

Spatial Specific Janus S-Scheme Photocatalyst with Enhanced H2 O2 Production Performance

Photocatalytic oxygen reduction reaction (ORR) for H₂ O₂ production in the absence of sacrificing agents is a green approach and of great significance, where the design of photocatalysts with high performance is the central task. Herein, a spatial specific S-scheme heterojunction design by introducing a novel semiconducting pair with a S-scheme mechanism in a purpose-designed Janus core-shell-structured hollow morphology is reported. In this design, TiO₂ nanocrystals are grown inside the inner wall of resorcinol-formaldehyde (RF) resin hollow nanocakes with a reverse bumpy ball morphology (TiO₂ @RF). The S-scheme heterojunction preserves the high redox ability of the TiO₂ and RF pair, the spatial specific Janus design enhances the charge separation, promotes active site exposure, and reduces the H₂ O₂ decomposition to a large extent. The TiO₂ @RF photocatalyst shows a high H₂ O₂ yield of 66.6 mM g^-1  h^-1 and solar-to-chemical conversion efficiency of 1.11%, superior to another Janus structure (RF@TiO₂ ) with the same heterojunction but a reversed Janus spatial arrangement, and most reported photocatalysts under similar reaction conditions. The work has paved the way toward the design of next-generation photocatalysts for green synthesis of H₂ O₂ production.

Deciphering the Superior Electronic Transmission Induced by the Li-N Ligand Pairs Boosted Photocatalytic Hydrogen Evolution

Atomic level decoration route is designated as one of the attractive methods to regulate both the charge density and band structure of photocatalysts. Moreover, to enable more efficient separation and transport of photocarriers, the construction of novel active sites can enhance both the reactivity and electrical conductivity of the crystal. Herein, an Li-N ligand is constructed via co-doping lithium and nitrogen atoms into ZnIn₂ S₄ lattice, which achieves a promoted photocatalytic H₂ evolution at 9737 µmol g^-1 h^-1 . The existence of Li-N ligand pairs and the behaviors of photocarriers on L₄₀ N₅ ZIS are determined systematically, which also provides a unique insight into the mechanism of the improved photocarrier migration rate. With the introduction of Li-N dual sites, the vacancy form of ZnIn₂ S₄ has changed and the photocatalytic stability is significantly improved. Interestingly, the change of charge density around Li-N ligand in ZnIn₂ S₄ is determined by theoretical simulations, as well as the regulated energy barrier of photocatalytic water splitting caused by Li-N dual sites, which act as both adsorption site for H₂ O and stronger reactive sites. This work helps to extend the understanding of ZnIn₂ S₄ and offers a fresh perspective for the creation of a Li-N co-doped photocatalyst.

Photoredox-Promoted Co-Production of Dihydroisoquinoline and H2 O2 over Defective Zn3 In2 S6

One of the most sustainable and promising approaches for hydrogen peroxide (H₂ O₂ ) production in a low-cost and environment-friendly way is photosynthesis, which, however, suffers from poor carrier utilization and low H₂ O₂ productivity. The addition of proton donors such as isopropanol or ethanol can increase H₂ O₂ production, which, unfortunately, will inevitably elevate the entire cost while wasting the oxidizing power of holes (h⁺ ). Herein, the tetrahydroisoquinolines (THIQs) is employed as a distinctive proton donor for the thermodynamically feasible and selective semi-dehydrogenation reaction to highly valuable dihydroisoquinolines (DHIQs), and meanwhile, to couple with and promote H₂ O₂ generation in one photoredox reaction under the photocatalysis by dual-functional Zn₃ In₂ S₆ photocatalyst. Surprisingly, the suitably defective Zn₃ In₂ S₆ offers an excellent and near-stoichiometric co-production performance of H₂ O₂ and DHIQs at unprecedentedly high rates of 66.4 and 62.1 mmol h^-1 g^-1 under visible light (λ ≥ 400 nm), respectively, which outperforms all the previously available reports even though sacrificial agents were employed in those reports. Additionally, photocatalytic redox reaction mechanism demonstrates that H₂ O₂ can be generated through multiple pathways, highlighting the synergistic effect among ROS (·O₂ ^- and ¹ O₂ ), h⁺ and proton donor, which has been ignored in previous studies.

Detecting and Quantifying Wavelength-Dependent Electrons Transfer in Heterostructure Catalyst via In Situ Irradiation XPS

The identity of charge transfer process at the heterogeneous interface plays an important role in improving the stability, activity, and selectivity of heterojunction catalysts. And, in situ irradiation X-ray photoelectron spectroscopy (XPS) coupled with UV light optical fiber measurement setup is developed to monitor and observe the photoelectron transfer process between heterojunction. However, the in-depth relationship of binding energy and irradiation light wavelength is missing based on the fact that the incident light is formed by coupling light with different wavelengths. Furthermore, a quantitative understanding of the charge transfer numbers and binding energy remains elusive. Herein, based on the g-C₃ N₄ /SnO₂ model catalyst, a wavelength-dependent Boltzmann function to describe the changes of binding energy and wavelength through utilizing a continuously adjustable monochromatic light irradiation XPS technique is established. Using this method, this study further reveals that the electrons transfer number can be readily calculated forming an asymptotic model. This methodology provides a blueprint for deep understanding of the charge-transfer rules in heterojunction and facilitates the future development of highly active advanced catalysts.

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.

Low-Temperature-Processed Monolayer Inverse Opal SnO2 Scaffold for Efficient Perovskite Solar Cells

Organic-inorganic halide perovskite solar cells (PSCs) have attracted tremendous attention in the photovoltaic field due to their excellent optical properties and simple fabrication process. However, the recombination of photogenerated electron-hole pairs at the interface severely affects the power conversion efficiency (PCE) of the PSCs. Herein, a monolayer of inverse opal SnO₂ (IO-SnO₂ ) is synthesized via a template-assisted method and used as a scaffold for perovskite layer (PSK). The porous IO-SnO₂ scaffold increases the contact area and shortens the transport distance between the electron transport layer (ETL) and PSK. Ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy results indicate that the built-in electric field is enhanced with IO-SnO₂ scaffold, strengthening the driving force for charge separation. Femtosecond transient absorption spectroscopy measurements reveal that the IO-SnO₂ scaffold facilitates interfacial electron transfer from PSK to ETL. Based on the above superiorities, the IO-SnO₂ -based PSCs exhibit boosted PCE and device stability compared with the pristine PSCs. This work provides insights into the development of novel scaffold layers for high-performance PSCs.