Photocatalytic Reduction of CO2 with H2O Mediated by Ce-Tailored Bismuth Oxybromide Surface Frustrated Lewis Pairs

Optimizing photocatalytic hydrogen evolution performance by rationally constructing S-scheme heterojunction to modulate the D-band center

The research in the field of photocatalysis has progressed, with the development of heterojunctions being recognized as an effective method to improve carrier separation efficiency in light-induced processes. In this particular study, CuCo2S4 particles were attached to a new cubic CdS surface to create an S-scheme heterojunction, thus successfully addressing this issue. Specifically, owing to the higher conduction band and Fermi level of CuCo2S4 compared to CdS, they serve as the foundation and driving force for the formation of an S-scheme heterojunction. Through in-situ X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis, the direction of charge transfer in the composite photocatalyst under light exposure was determined, confirming the charge transfer mechanism of the S-scheme heterojunction. By effectively constructing the S-scheme heterojunction, the d-band center of the composite photocatalyst was adjusted, reducing the energy needed for electron filling in the anti-bonding energy band, promoting the transfer of photogenerated carriers, and ultimately enhancing the photocatalytic hydrogen production. performance. After optimization, the hydrogen evolution activity of the composite photocatalyst CdS-C/CuCo2S4-3 reached 5818.9 μmol g-1h-1, which is 2.6 times higher than that of cubic CdS (2272.3 μmol g-1h-1) and 327.4 times higher than that of CuCo2S4 (17.8 μmol g-1h-1), showcasing exceptional photocatalytic activity. Electron paramagnetic resonance and in situ X-ray photoelectron spectroscopy have established a theoretical basis for designing and constructing S-scheme heterojunctions, offering a viable method for adjusting the D-band center to enhance the performance of photocatalytic hydrogen evolution.

A Review on Bi2WO6-Based Materials for Photocatalytic CO2 Reduction

Photocatalytic reduction of CO2 (PCR) technology offers the capacity to transmute solar energy into chemical energy through an eco-friendly and efficacious process, concurrently facilitating energy storage and carbon diminution, this innovation harbors significant potential for mitigating energy shortages and ameliorating environmental degradation. Bismuth tungstate (Bi2WO6) is distinguished by its robust visible light absorption and distinctive perovskite-type crystal architecture, rendering it highly efficiency in PCR. In recent years, numerous systematic strategies have been investigated for the synthesis and modification of Bi2WO6 to enhance its photocatalytic performance, aiming to achieve superior applications. This review provides a comprehensive review of the latest research progress on Bi2WO6 based materials in the field of photocatalysis. Firstly, outlining the fundamental principles, associated reaction mechanisms and reduction pathways of PCR. Then, the synthesis strategy of Bi2WO6-based materials is introduced for the regulation of its photocatalytic properties. Furthermore, accentuating the extant applications in CO2 reduction, including metal-Bi2WO6, semiconductor-Bi2WO6 and carbon-based Bi2WO6 composites etc. while concludes with an examination of the future landscape and challenges faced. This review hopes to serve as an effective reference for the continuous improvement and implementation of Bi2WO6-based photocatalysts in PCR.

Leaf-like MSX/TiN heterojunction photocathodes mimicking plant cell - An effective strategy to enhance photoelectrocatalytic carbon dioxide reduction and systematic mechanism investigation

Semiconductors, such as metal oxides and metal sulfides (MSX), are widely investigated as effectively catalytic materials to convert carbon dioxide (CO2) and water into chemicals under simulated solar light. These valuable investigations might address both the energy crisis and climate change in our modern society. Herein, a novel strategy to construct leaf-like heterojunctions of VS-ZnIn2S4/TiN-x is reported. The new semiconductor heterojunctions were then applied to photoelectrocatalytic CO2 reduction, achieving excellent performance (formate formation rate of 1173.2 μM h-1 cm-2) attributed to the plant cell-like morphology and enhanced electron mobility from the heterojunction interfaces to the active sites on the surface. Our findings suggest that titanium nitride (TiN) with good conductivity can improve the photoelectrocatalytic ability of MSX through heterojunction construction. The photocathode VS-ZnIn2S4/TiN-3 exhibits 81.0 % selectivity toward C2 products by optimizing the material structure and reaction conditions. According to the systematic investigation of operando Fourier transform infrared (FTIR) spectra, common intermediates such as *COO-, *COOH, *CO, *CHO, *COCHO, and *COCH3 reported in the literature were carefully verified. Among these, the carbene specie serve as the key intermediate responsible for generating other intermediates and resulting in all products.

Three-layered nanoplates and amorphous/crystalline interface synergism boost CO2 photoreduction on bismuth oxychloride nanospheres

Structural features like 3D nano-size, ultrathin thickness and amorphous/crystalline interfaces play crucial roles in regulating charge separation and active sites of photocatalysts. However, their co-occurrence in a single catalyst and exploitation in photocatalytic CO2 reduction (PCR) remains challenging. Herein, nano-sized bismuth oxychloride spheres (BiOCl-NS) confining three-layered nanoplates (∼2.2 nm ultrathin) and an amorphous/crystalline interface are exclusively developed via intrinsic engineering for an enhanced sacrificial-reagent-free PCR system. The results uncover a unique synergism wherein the three-layered nanoplates accelerate electron-hole separation, and the amorphous/crystalline interface exposes electron-localized active sites (Bi-Ovac-Bi). Consequently, BiOCl-NS exhibit efficient CO2 adsorption and activation with the lowering of rate-determining-step energy barriers, leading to remarkable CO production (102.72 μmol g-1 h-1) with high selectivity (>99%), stability (>30 h), and apparent quantum efficiency (0.51%), outperforming conventional counterparts. Our work provides a facile structural engineering approach for boosting PCR and offers distinct synergism for advancing diverse materials.

Polyoxometalates tailoring of frustrated Lewis pairs on Ce-doped Bi2O3 for boosting photocatalytic CO2 reduction

Constructing frustrated Lewis pairs (FLPs) on catalysts will provide catalytic sites to activate CO2 and boost photocatalytic CO2 reduction. Herein, a Ce-doped bismuth oxide (CeBiOX) with FLPs was designed by loading [(α-SbW9O33)2Cu3(H2O)3]12- (Cu3) via strong electrostatic interactions to create oxygen vacancies (OVs). Detailed experiments and measurements showed that Cu3 could regulate the FLPs and optimize the band structure of CeBiOX to boost photocatalytic CO2 reduction. In particular, the Cu3/CeBiOX composite exhibited the highest yields of CO (42.85 μmoL g-1) and CH4 (13.23 μmoL g-1), being 6.6 and 3.3 times, and 4.9 and 6.3 times higher than those of pristine Bi2O3 and CeBiOX, respectively. This work provides a significant and mild approach to obtaining advanced catalysts with tuneable FLPs for more fields.

Role of Facets and Morphologies of Different Bismuth-Based Materials for CO2 Reduction to Fuels

Carbon dioxide (CO2) emission has been a global concern over the past few decades due to the increase in the demand of energy, a major source of which is fossil fuels. To mitigate the emission issues, as well as to find a solution for the energy needs, an ample load of research has been carried out over the past few years in CO2 reduction by catalysis. Bismuth, being an active catalyst both photocatalytically and electrocatalytically, is an interesting material that can be formed into oxides, sulphides, oxyhalides, etc. Numerous works have been published based on bismuth-based materials as active catalysts for the reduction of CO2. However, a proper understanding of the behavior of the active facets and the dependence of morphology of the different bismuth-based catalysts is an interesting notion. In this review, various bismuth-based materials will be discussed regarding their activity and charge transfer properties, based on the active facets present in them. With regard to the available literature, a summarization, including photocatalysis, electrocatalysis as well as photoelectrocatalysis, will be detailed, considering various materials with different facets and morphologies. Product selectivity, varying on morphological difference, will also be realized photoelectrochemically.

Mechanism insight into double S-scheme heterojunctions and atomic vacancies with tunable band structures for notably enhanced light-driven enrofloxacin decomposition

Building narrow band gap semiconductors and fast separation of photogenerated electron-hole (e--h+) structures are of great significance for photocatalytic process. In this contribution, the CeO2-x/C3-yN4/Ce(CO3)(OH) double S-scheme heterojunctions with atomic vacancies tunable band gap (2.54 eV) have been designed and fabricated as a boost photocatalyst for enrofloxacin (ENR) photodegradation. Compared with the control samples, the experimental results indicate that the typical sample (CeO2-x/C3-yN4/Ce(CO3)(OH)-2) achieves the highest ENR photodegradation efficiency (93.6 %) in 240 min under a pH of 6, and the possible photodegradation pathways are also proposed. The superior performance is ascribed to the CeO2-x/C3-yN4/Ce(CO3)(OH) double S-scheme heterojunctions for selective recombination of photogenerated electrons with weak-reduction ability in conduction band (CB) of CeO2-x, C3-yN4 and the photogenerated holes with weak-oxidation nature in valance band (VB) of C3-yN4, Ce(CO3)(OH), which increase the retention rate of photogenerated electrons in CB of Ce(CO3)(OH) and photogenerated holes in VB of CeO2-x to degrade ENR. This is the first systematic study of CeO2-x/C3-yN4/Ce(CO3)(OH) double S-scheme heterojunctions for ENR photodegradation.

Frustrated Lewis pairs created by Ce-doped Bi2MoO6: A universal strategy to promote efficient utilization of H2O2 for Fenton-like photodegradation

Photo-Fenton-like technology based on H2O2 is considered as an ideal strategy to generate reactive oxygen species (ROS) for antibiotic degradation, but O2 overflow in the process severely limits the utilization efficiency of H2O2. Herein, we fabricate Bi2MoO6 (BMO) photocatalyst modified with Frustrated Lewis pairs (FLPs) as a Fenton catalyst model for enhancing reuse of spilled O2. The FLPs created by the introduction of cerium and oxygen vacancy were found to contribute to regulate the electronic structure of BMO and further improve the acidic and basic properties of photocatalyst surface. More importantly, the frustrated acid and base sites can enhance the H2O2 and O2 interfacial adsorption process and provide an Ce4+-Ov-O2- active site on the surface of Ce-BMO nanosheets, which can promote O2/•O2-/1O2/H2O2 redox cycles to achieve high H2O2 utilization efficiency. Specifically, in the experiment using tetracycline as a photocatalytic degradation object, the degradation activity of Ce-BMO was 2.15 times higher than that of BMO pure phase. Quenching experiments and EPR assays also confirmed that 1O2 and •O2- were the dominant oxidative species. This study systematically reveals the design of Fenton photocatalytic active sites at the atomic scale and provides new insights into constructing FLPs photocatalysts with high H2O2 utilization efficiency.

Preparation of highly dispersed Ni single-atom doped ultrathin g-C3N4 nanosheets by metal vapor exfoliation for efficient photocatalytic CO2 reduction

Single-atom photocatalysts can modulate the utilization of photons and facilitate the migration of photogenerated carriers. However, the preparation of single-atom uniformly doped photocatalysts is still a challenging topic. Herein, we propose the preparation of Ni single-atom doped g-C3N4 photocatalysts by metal vapor exfoliation. The Ni vapor produced by calcining nickel foam at high temperature accumulates in between g-C3N4 layers and poses a certain vapor pressure to destroy the interlayer van der Waals forces of g-C3N4. Individual metal atoms are doped into the structure while exfoliating g-C3N4 into nanosheets by metal vapor. Upon optimization of Ni content, the Ni single atom doped g-C3N4 nanosheets with 2.81 wt% Ni exhibits the highest CO2 reduction performance in the absence of sacrificial agents. The generation rates of CO and CH4 are 19.85 and 1.73 μmol g-1h-1, respectively. The improved photocatalytic performance is attributed to the anchoring Ni of single atoms on g-C3N4 nanosheets, which increases both carrier separation efficiency and reaction sites. This work provides insight into the design of photocatalysts with highly dispersed single-atom.

Broad Spectral Response FeOOH/BiO2-x Photocatalyst with Efficient Charge Transfer for Enhanced Photo-Fenton Synergistic Catalytic Activity

In this work, to promote the separation of photogenerated carriers, prevent the catalyst from photo-corrosion, and improve the photo-Fenton synergistic degradation of organic pollutants, the coating structure of FeOOH/BiO2-x rich in oxygen vacancies was successfully synthesized by a facile and environmentally friendly two-step process of hydrothermal and chemical deposition. Through a series of degradation activity tests of synthesized materials under different conditions, it was found that FeOOH/BiO2-x demonstrated outstanding organic pollutant degradation activity under visible and near-infrared light when hydrogen peroxide was added. After 90 min of reaction under photo-Fenton conditions, the degradation rate of Methylene Blue by FeOOH/BiO2-x was 87.4%, significantly higher than the degradation efficiency under photocatalysis (60.3%) and Fenton (49.0%) conditions. The apparent rate constants of FeOOH/BiO2-x under photo-Fenton conditions were 2.33 times and 3.32 times higher than photocatalysis and Fenton catalysis, respectively. The amorphous FeOOH was tightly coated on the layered BiO2-x, which significantly increased the specific surface area and the number of active sites of the composites, and facilitated the improvement of the separation efficiency of the photogenerated carriers and the prevention of photo-corrosion of BiO2-x. The analysis of the mechanism of photo-Fenton synergistic degradation clarified that ·OH, h+, and ·O2- are the main active substances involved in the degradation of pollutants. The optimal degradation conditions were the addition of the FeOOH/BiO2-x composite catalyst loaded with 20% Fe at a concentration of 0.5 g/L, the addition of hydrogen peroxide at a concentration of 8 mM, and an initial pH of 4. This outstanding catalytic system offers a fresh approach to the creation and processing of iron-based photo-Fenton catalysts by quickly and efficiently degrading various organic contaminants.

Surface and interface engineering of BiOCl nanomaterials and their photocatalytic applications

BiOCl materials have received much attention because of their unique optical and electrical properties. Still, their unsatisfactory catalytic performance has been troubling researchers, limiting the application of BiOCl-based photocatalysts. Therefore, many researchers have studied the adjustment of BiOCl-based materials to enhance photocatalytic efficiency. This review focuses on surface and interface engineering strategies for boosting the photocatalytic performance of BiOCl-based nanomaterials, including forming oxygen vacancy defects, constructing metal/BiOCl, and the fabrication of semiconductor/BiOCl nanocomposites. The photocatalytic applications of the above composites are also concluded in photodegradation of aqueous pollutants, photocatalytic NO removal, photo-induced H2 production, and CO2 reduction. Special emphasis has been given to the modification methods of BiOCl and photocatalytic mechanisms to provide a more detailed understanding for researchers in the fields of energy conversion and materials sciences.

Post transition metal substituted Keggin-type POMs as thin film chemiresistive sensors for H2O and CO2 detection

Chemiresitive sensing allows the affordable and facile detection of small molecules such as H2O and CO2. Herein, we report a novel class of Earth-abundant post transition metal substituted Keggin polyoxometalates (POMs) for chemiresistive sensing applications, with conductivities up to 0.01 S cm-1 under 100% CO2 and 65% Relative Humidity (RH).

Ce-regulating defect and morphology engineering for efficiently enhancing the piezocatalytic performances of BiOBr

Cerium-doped bismuth oxybromide (1%, 5% and 10% Ce-BiOBr) piezocatalysts were synthesized. The piezocatalytic activity was efficiently regulated by defect and morphology engineering. Among them, the 5% Ce-BiOBr exhibits the highest piezocatalytic hydrogen production property with an evolution rate of 1147.6 μmol g-1 h-1, nearly twice that of the original BiOBr. Additionally, the MO dye degradation efficiency of 5% Ce-BiOBr reaches 91.9% within 60 min, with a higher reaction kinetic constant (0.0376 min-1) that was 6.1 times larger than that of pure BiOBr. These outstanding performances of 5% Ce-BiOBr surpass those of most other piezocatalytic material systems.

Efficient Removal of Antibiotic Resistance Genes through 4f-2p-3d Gradient Orbital Coupling Mediated Fenton-Like Redox Processes

Peroxymonosulfate (PMS) mediated radical and nonradical active substances can synergistically achieve the efficient elimination of antibiotic resistance genes (ARGs). However, enhancing interface electron cycling and optimizing the coupling of the oxygen-containing intermediates to improve PMS activation kinetics remains a major challenge. Here, Co doped CeVO4 catalyst (Co-CVO) with asymmetric sites was constructed based on Ce 4f-O 2p-Co 3d gradient orbital coupling. The catalyst achieved approximately 2.51×105 copies/mL of extracellular ARGs (eARGs) removal within 15 minutes, exhibited ultrahigh degradation rate (k=1.24 min-1 ). The effective gradient 4f-2p-3d orbital coupling precisely regulates the electron distribution of Ce-O-Co active center microenvironment, while optimizing the electronic structure of Co 3d states (especially the occupancy of eg ), promoting the adsorption of oxygen-containing intermediates. The generated radical and nonradical generated by interfacial electron cycling enhanced by the reduction reaction of PMS at the Ce site and the oxidation reaction at the Co site achieved a significant mineralization rate of ARGs (83.4 %). The efficient removal of ARGs by a continuous flow reactor for 10 hours significantly reduces the ecological risk of ARGs in actual wastewater treatment.

Co engineered CoP catalyst for photochemical CO2 reduction with accelerated electron transfer endowed by the space-charge region

Photocatalytic CO₂ reduction has been regarded as an ideal method to simulate photosynthesis for achieving carbon neutralization. However, poor charge transfer efficiency limits its development. Herein, an efficient Co/CoP@C catalyst was prepared with compact contact of Co and CoP layer by using MOF as precursor. At the interface of Co/CoP, the difference in functionality between the two phases may result in uneven distribution of electrons, thus forming a self-driven space-chare region. In this region, spontaneous electron transfer is guaranteed, thus facilitating the effective separation of photogenerated carriers as well as boosting the utilization of solar energy. Furthermore, the electron density of active site Co in CoP is increased and more active sites are exposed, which promotes the adsorption and activation of CO₂ molecules. Together with suitable redox potential, low energy barrier for *COOH formation and easy desorption of CO, the reduction rate of CO₂ catalyzed by Co/CoP@C is 4 times higher than that of CoP@C.

Applications of BiOX in the Photocatalytic Reactions

BiOX (X = Cl, Br, I) families are a kind of new type of photocatalysts, which have attracted the attention of more and more researchers. The suitable band gaps and their convenient tunability via the change of X elements enable BiOX to adapt to many photocatalytic reactions. In addition, because of their characteristics of the unique layered structure and indirect bandgap semiconductor, BiOX exhibits excellent separation efficiency of photogenerated electrons and holes. Therefore, BiOX could usually demonstrate fine activity in many photocatalytic reactions. In this review, we will present the various applications and modification strategies of BiOX in photocatalytic reactions. Finally, based on a good understanding of the above issues, we will propose the future directions and feasibilities of the reasonable design of modification strategies of BiOX to obtain better photocatalytic activity toward various photocatalytic applications.

Pine Dendritic Bi/BiOBr Photocatalyst for Efficient Degradation of Antibiotics

Constructing Bi/BiOX (X = Cl, Br) heterostructures with unique electron transfer channels enables charge carriers to transfer unidirectionally at the metal/semiconductor junction and inhibits the backflow of photogenerated carriers. Herein, novel pine dendritic Bi/BiOX (X = Cl, Br) nanoassemblies with multiple electron transfer channels have been successfully synthesized with the assistance of l-cysteine (l-Cys) through a one-step solvothermal method. Such a pine dendritic Bi/BiOBr photocatalyst shows excellent activity toward the degradation of many antibiotics such as tetracycline (TC), norfloxacin, and ciprofloxacin. In particular, its photocatalytic degradation activity of TC is higher than those of reference spherical Bi/BiOBr, lamellar BiOBr, and BiOBr/Bi/BiOBr double-sided nanosheet arrays. Comprehensive characterizations demonstrate that the pine dendritic structure can construct multiple electron transfer channels from BiOBr to metallic Bi, resulting in an obviously promoted separation efficiency of photogenerated carriers. The synthesis method that uses l-Cys to control the morphology provides a guidance to prepare special metal/semiconductor photocatalysts and would be helpful to design a highly efficient photocatalytic process.

Co-Dissolved Isostructural Polyoxovanadates to Construct Single-Atom-Site Catalysts for Efficient CO2 Photoreduction

We explored a co-dissolved strategy to embed mono-dispersed Pt center into V₂ O₅ support via dissolving [PtV₉ O₂₈ ]^7- into [V₁₀ O₂₈ ]^6- aqueous solution. The uniform dispersion of [PtV₉ O₂₈ ]^7- in [V₁₀ O₂₈ ]^6- solution allows [PtV₉ O₂₈ ]^7- to be surrounded by [V₁₀ O₂₈ ]^6- clusters via a freeze-drying process. The V centers in both [PtV₉ O₂₈ ]^7- and [V₁₀ O₂₈ ]^6- were converted into V₂ O₅ via a calcination process to stabilize Pt center. These double separations can effectively prevent the Pt center agglomeration during the high-temperature conversion process, and achieve 100 % utilization of Pt in [PtV₉ O₂₈ ]^7- . The resulting Pt-V₂ O₅ single-atom-site catalysts exhibit a CH₄ yield of 247.6 μmol g^-1  h^-1 , 25 times higher than that of Pt nanoparticle on the V₂ O₅ support, which was accompanied by the lactic acid photooxidation to form pyruvic acid. Systematical investigations on this unambiguous structure demonstrate an important role of Pt-O atomic pair synergy for highly efficient CO₂ photoreduction.

Zn3Sb4O6F6 and KI-Doped Zn3Sb4O6F6: A Metal Oxyfluoride System for Photocatalytic Activity, Knoevenagel Condensation, and Bacterial Disinfection

Zn₃Sb₄O₆F₆ crystallites were synthesized by a pH-regulated hydrothermal synthetic approach, while doping on Zn₃Sb₄O₆F₆ by KI was performed by the "incipient wetness impregnation technique." The effect of KI in Zn₃Sb₄O₆F₆ is found with the changes in morphology in the doped compound, i.e., needle-shaped particles with respect to the irregular cuboid and granular shaped in the pure compound. Closer inspection of the powder diffraction pattern of doped compounds also reveals the shifting of Braggs' peaks toward a lower angle and the difference in cell parameters compared to the pure compound. Both metal oxyfluoride comprising lone pair elements and their doped compounds have been successfully applied as photocatalysts for methylene blue dye degradation. Knoevenagel condensation reactions were performed using Zn₃Sb₄O₆F₆ as the catalyst and confirmed 99% yield even at 60 °C temperature under solvent-free conditions. Both pure and KI-doped compounds were tested against several standard bacterial strains, i.e., Enterobacter sp., Escherichia coli, Staphylococcus sp., Salmonella sp., Bacillus sp., Proteous sp., Pseudomonas sp., and Klebsiella sp. by the "disk diffusion method" and their antimicrobial activities were confirmed.