Selective Photocatalytic Reduction of CO2 to CH4 Modulated by Chloride Modification on Bi2WO6 Nanosheets

Oxygen-deficient AgIO3 for efficiently photodegrading organic contaminants under natural sunlight

Defect engineering is regarded as an effective strategy to boost the photo-activity of photocatalysts for organic contaminants removal. In this work, abundant surface oxygen vacancies (Ov) are created on AgIO3 microsheets (AgIO3-OV) by a facile and controllable hydrogen chemical reduction approach. The introduction of surface Ov on AgIO3 broadens the photo-absorption region from ultraviolet to visible light, accelerates the photoinduced charges separation and migration, and also activates the formation of superoxide radicals (•O2-). The AgIO3-OV possesses an outstanding degradation rate constant of 0.035 min-1, for photocatalytic degrading methyl orange (MO) under illumination of natural sunlight with a light intensity is 50 mW/cm2, which is 7 and 3.5 times that of the pristine AgIO3 and C-AgIO3 (AgIO3 is calcined in air without generating Ov). In addition, the AgIO3-OV also exhibit considerable photoactivity for degrading other diverse organic contaminants, including azo dye (rhodamine B (RhB)), antibiotics (sulflsoxazole (SOX), norfloxacin (NOR), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)), and even the mixture of organic contaminants (MO-RhB and CTC-OFX). After natural sunlight illumination for 50 min, 41.4% of total organic carbon (TOC) for MO-RhB mixed solution can be decreased over AgIO3-OV. In a broad range of solution pH from 3 to 11 or diverse water bodies of MO solution, AgIO3-OV exhibits attractive activity for decomposing MO. The MO photo-degradation process and mechanism over AgIO3-OV under natural sunlight irradiation has been systemically investigated and proposed. The toxicities of MO and its degradation intermediates over AgIO3-OV are compared using Toxicity Estimation Software (T.E.S.T.). Moreover, the non-toxicity of both AgIO3-OV catalyst and treated antibiotic solution (CTC-OFX mixture) are confirmed by E. coli DH5a cultivation test, supporting the feasibility of AgIO3-OV catalyst to treat organic contaminants in real water under natural sunlight illumination.

Defective Nb2C MXene Cocatalyst on TiO2 Microsphere for Enhanced Photocatalytic CO2 Conversion to Methane

Sustainable and scalable solar-energy-driven CO2 conversion into fuels requires earth-abundant and stable photocatalysts. In this work, a defective Nb2C MXene as a cocatalyst and TiO2 microspheres as photo-absorbers, constructed via a coulombic force-driven self-assembly, is synthesized. Such photocatalyst, at an optimized loading of defective Nb2C MXene (5% def-Nb2C/TiO2), exhibits a CH4 production rate of 7.23 µmol g-1 h-1, which is 3.8 times higher than that of TiO2. The Schottky junction at the interface improves charge transfer from TiO2 to defective Nb2C MXene and the electron-rich feature (nearly free electron states) enables multielectron reaction of CO2, which apparently leads to high activity and selectivity to CH4 (sel. 99.5%) production. Moreover, DFT calculation demonstrates that the Fermi level (EF) of defective Nb2C MXene (-0.3 V vs NHE) is more positive than that of Nb2C MXene (-1.0 V vs NHE), implying a strong capacity to accept photogenerated electrons and enhance carrier lifetime. This work gives a direction to modify the earth-abundant MXene family as cocatalysts to build high-performance photocatalysts for energy production.

Enabling N2 to Ammonia Conversion in Bi2 WO6 -Based Materials: A New Avenue in Photocatalytic Applications

The field of photocatalysis has been evolving since 1972 since Honda and Fujishima's initial push for using light as an energy source to accomplish redox reactions. Since then, many photocatalysts have been studied, semiconductors or otherwise. A new photocatalytic application to convert N2 gas to ammonia (N2 fixation or nitrogen reduction reaction; NRR) has emerged. Many researchers have steered their research in this direction due to developments in the ease of ammonia detection through UV-Vis spectroscopy. This concept will specifically discuss Bi2 WO6 -based materials, techniques to enhance their photocatalytic activity (CO2 reduction, H2 production, pollutant removal, etc.), and their current application in photocatalytic NRR. Initially, a brief introduction of Bi2 WO6 along with its VB and CB potentials will be compared to various redox potentials. A final topic of interest would be a brief description of photocatalytic nitrogen fixation with additional consideration to Bi2 WO6 -based materials in N2 fixation. A major problem with photocatalytic NRR is the false ammonia quantification in Bi-based materials, which will be discussed in detail and also ways to minimize them.

Constructing Active Sites on Self-Supporting Ti3C2Tx (T = OH) Nanosheets for Enhanced Photocatalytic CO2 Reduction into Alcohols

Ti3C2Tx (T = OH) was first prepared from Ti3AlC2 by HF etching and applied into a photocatalytic CO2 reduction. Then, the Ti3C2Tx nanosheets present interbedded a self-supporting structure and extended interlayer spacing. Meanwhile, the Ti3C2Tx nanosheets are decorated with abundant oxygen-containing functional groups in the process of etching, which not only serve as active sites but also show efficient charge migration and separation. Among Ti3C2Tx materials prepared by etching for different times, Ti3C2Tx-36 (Etching time: 36 h) showed the best performance for photoreduction of CO2 into alcohols (methanol and ethanol), giving total yield of 61 μmol g catal.−1, which is 2.8 times than that of Ti3AlC2. Moreover, excellent cycling stability for CO2 reduction is beneficial from the stable morphology and crystalline structure. This work provided novel sights into constructing surface active sites controllably.

Accelerated Water Oxidation Kinetics Triggered by Supramolecular Porphyrin Nanosheet for Robust Visible-Light-Driven CO2 Reduction

Water oxidation is one of the most challenging steps in CO₂ photoreduction, but its influence on CO₂ photoreduction is still poorly understood. Herein, the concept of accelerating the water oxidation kinetics to promote the CO₂ photoreduction is realized by incorporating supramolecular porphyrin nanosheets (NS) into the C₃ N₄ catalyst. As a prototype, porphyrin-C₃ N₄ based van der Waals heterojunctions with efficient charge separation are elaborately designed, in which the porphyrin and C₃ N₄ NS serve as the water oxidation booster and CO₂ reduction center, respectively. Theoretical calculations and relevant experiments demonstrate that the added porphyrin NS reverses the rate-limiting step in the water oxidation while reducing its energy barrier, thus resulting in faster reaction kinetics. Therefore, the optimal sample shows excellent performance in visible-light-driven CO₂ reduction with a maximum CO evolution rate of 16.8 µmol g^-1 h^-1 , which is 6.8 times that of the C₃ N₄ NS and reaches the current state of the art for C₃ N₄ -based materials in CO₂ photoreduction. Overall, this work throws light that accelerating water oxidation kinetics can effectively improve the CO₂ photoreduction efficiency.

Recent review of BixMOy (M=V, Mo, W) for photocatalytic CO2 reduction into solar fuels

The utilization of solar energy for CO₂ conversion not only enables a green and low-carbon recycling of CO₂ with renewable energy, but also solves ecological problems. Bi_xMO_y (M = V, Mo, W) materials have typical layered structures and unique electronic properties that provide suitable band gaps and potential to meet the basic conditions for CO₂ reduction. However, pristine Bi_xMO_y faces with problems such as small specific surface area, insufficient active sites, low charge carriers' separation and utilization efficiency. This review comprehensively described the basic principles and reaction pathways of photocatalytic CO₂ reduction, and further presented the research progress of Bi_xMO_y catalysts in CO₂ conversion reactions. In this perspective, we further focus on the design concepts and modification strategies to improve the photocatalytic CO₂ reduction activity of Bi_xMO_y, such as morphology control, constructing surface vacancies and heterojunction fabrication. Finally, based on representative researches, the present review will be expected to provide updated information and insights for developing advanced Bi_xMO_y materials to further improve CO₂ reduction activity and selectivity.

Viscosity Simulation of Glass Microfiber and an Unusual Air Filter with High-Efficiency Antibacterial Functionality Enabled by ZnO/Graphene-Modified Glass Microfiber

The current global pandemic of new coronary pneumonia clearly reveals the importance of developing highly efficient filtration and fast germicidal performance of multifunctional air filters. In this study, a novel air filter with a controllable morphology based on the rod-like to flower-like zinc oxide/graphene-based photocatalytic composite particles loaded on glass microfiber was prepared by one-step microwave rapid synthesis. The multifunctional air filter shows the following special functions: the 10 mg·L^-1 organic pollutant solution RhB was completely degraded within 2 h under a 500 W xenon lamp, and also 99% of Escherichia coli and Staphylococcus aureus were inactivated under a 60 W light-emitting diode lamp. Furthermore, after introducing the controllable morphology zinc oxide/graphene-based photocatalytic composite particles, the filtration efficiency of the multifunctional air filter was also kept at the same level (99.8%) as the one without any addition, indicating no loss of high-efficiency filtration while obtaining the rapid bactericidal function. The rapid antibacterial principle of the multifunctional air filter has also been proposed through the UV-vis spectroscopies, photoluminescence, and electron-spin resonance spectrum. The zinc oxide/graphene-based photocatalytic composite particles tightly coated on the glass microfiber surface could increase the active sites by changing the morphology of zinc oxide and, in the meantime, promote the separation of zinc oxide photo-generated electron-hole pairs to improve the rapid sterilization ability of the multifunctional air filters. In addition, an empirical formula to evaluate the relationship between the composition, viscosity, and viscosity modulus of glass microfiber was proposed by testing the viscosity of glass microfiber composed of 14 different compositions at 1300 and 1400 °C, which can be used as a criterion to evaluate the production technology of glass microfiber filters.

Research Progress and Reaction Mechanism of CO2 Methanation over Ni-Based Catalysts at Low Temperature: A Review

The combustion of fossil fuels has led to a large amount of carbon dioxide emissions and increased greenhouse effect. Methanation of carbon dioxide can not only mitigate the greenhouse effect, but also utilize the hydrogen generated by renewable electricity such as wind, solar, tidal energy, and others, which could ameliorate the energy crisis to some extent. Highly efficient catalysts and processes are important to make CO2 methanation practical. Although noble metal catalysts exhibit higher catalytic activity and CH4 selectivity at low temperature, their large-scale industrial applications are limited by the high costs. Ni-based catalysts have attracted extensive attention due to their high activity, low cost, and abundance. At the same time, it is of great importance to study the mechanism of CO2 methanation on Ni-based catalysts in designing high-activity and stability catalysts. Herein, the present review focused on the recent progress of CO2 methanation and the key parameters of catalysts including the essential nature of nickel active sites, supports, promoters, and preparation methods, and elucidated the reaction mechanism on Ni-based catalysts. The design and preparation of catalysts with high activity and stability at low temperature as well as the investigation of the reaction mechanism are important areas that deserve further study.

Construction of WO3/CsPbBr3 S-scheme heterojunction via electrostatic Self-assembly for efficient and Long-Period photocatalytic CO2 reduction

Owing to the severe photogenerated carriers recombination and low oxidation ability, the photocatalytic performance of pristine CsPbBr₃ is still unsatisfactory. Herein, melamine foam supported S-scheme WO₃/CsPbBr₃ heterojunction is successfully synthesized by electrostatic self-assembly. Because of the appropriate energy level positions, an S-scheme charge migration route between CsPbBr₃ and WO₃ is constructed. Under solar light irradiation, melamine foam assisted WO₃/CsPbBr₃ exhibits significantly enhanced photocatalytic CO₂ reduction performance under liquid H₂O medium, and the electron consumption rate (R_electron) reaches to 1225.50 μmol^.g^-1.h^-1, which is 1.49- and 13.7-fold of CsPbBr₃ and WO₃, respectively, ascribing to the boosted charges transfer and the strengthened redox ability. Furthermore, S-scheme WO₃/CsPbBr₃ heterojunction also exhibits strong durability, with no noticeable reduction of product yields after four 8-h cycles.

Promoting photocatalytic CO2 reduction to CH4 via a combined strategy of defects and tunable hydroxyl radicals

A well-designed photocatalyst with excellent activity and selectivity is crucial for photocatalytic CO₂ conversion and utilization. TiO₂ is one of the most promising photocatalysts. However, its excessive surface oxidation potential and insufficient surface active sites inhibit its activity and photocatalytic CO₂ reduction selectivity. In this work, highly dispersed Bi₂Ti₂O₇ was introduced into defective TiO₂ to adjust its oxidation potential and the generation of radicals, further inhibiting reverse reactions during the photocatalytic conversion of CO₂. Moreover, an in situ topochemical reaction etching route was designed, which achieved defective surfaces, a contacted heterophase interface, and an efficient electron transfer path. The optimized heterophase photocatalyst exhibited 93.9% CH₄ selectivity at a photocatalytic rate of 6.8 μmol·g^-1·h^-1, which was 7.9 times higher than that of P25. This work proposes a feasible approach to fabricating photocatalysts with well-designed band structures, highly dispersed heterophase interfaces, and sufficient surface active sites to effectively modulate the selectivity and activity of CO₂ photoreduction by manipulating the reaction pathways.

Bi2S3-decorated three-dimensional BiOCl as a Z-scheme heterojunction with highly exposed {001} facets of BiOCl for enhanced visible-light photocatalytic performance

In BOC-BS-x, the highly exposed {001} facets of BiOCl have more oxygen vacancies, which can facilitate the migration of carriers.

F- Serve as Surface Trapping Sites to Promote the Charge Separation and Transfer of TiO2

Finding an effective strategy to promote the charge transfer and separation of TiO₂ is urgently needed. Herein, a surface fluorination (F^-)-modified TiO₂ (denoted as TO-xF, where x represents the volume of HF added in the solution) catalyst has been prepared by a mild and facile post-treatment method. The changes induced by surface F^- on the morphological, structural, and surface electronic features and the charge separation and transfer efficiency of TiO₂ were specifically examined. Compared with pristine TO, TO-0.4F exhibits enhanced photocatalytic degradation of methyl orange and phenol, production of hydroxyl radicals, and photocurrent response. The enhanced photocatalytic activities of TO-0.4F can be attributed to the role of surface F^- as surface trapping sites in effectively boosting the charge transfer and separation processes, which is verified by the steady-state and time-resolved fluorescence spectroscopy, electrochemical impedance spectroscopy, Bode plot, transient photocurrent response, and open-circuit voltage measurements. This study emphasizes the role of surface F^- in promoting the charge transfer and separation and improving the photocatalytic activity of TiO₂.

Janus silver/ternary silver halide nanostructures as plasmonic photocatalysts boost the conversion of CO2 to acetaldehyde

Photocatalytic conversion of carbon dioxide (CO₂) to liquid product acetaldehyde (CH₃CHO) remains a great challenge due to the involvement of a complex 10-electron reduction process and a sluggish C-C coupling reaction. Herein, we report the synthesis of Janus silver/ternary silver halide (Ag/AgClBr) nanostructures through precisely manipulating the growth kinetics and its function as a plasmonic photocatalyst to boost the conversion of CO₂ to CH₃CHO. The obtained Janus nanostructures featuring both spatially separated architecture and broad light-harvesting capability facilitate the photocatalytic reduction of CO₂ under solar illumination. The photocatalytic CO₂ reduction with the characteristics of high activity and good selectivity can generate a 10-electron reduction product CH₃CHO with a generation rate of 209.3 ± 9.5 μmol h^-1 g^-1 and a selectivity of 96.9%, which are rarely achieved in previously reported photocatalytic CO₂ reduction systems. The excellent photocatalytic performance can be ascribed to the plasmonic effect of Ag nanocrystals and the favorable active sites on the catalyst surface. This research demonstrates for the first time the utilization of the Janus Ag/AgClBr nanostructures to generate the value-added C₂ liquid product through photocatalytic CO₂ reduction, paving the way for the design and construction of novel plasmonic photocatalysts.

Selectively triggering photoelectromacro for CO2to CH4reduction over SrTiO3{110} facet with dual-metal sites

In this article, the roles of surface-active sites in dominating photoelectron selectivity for CO₂reduction products are well demonstrated over photocatalyst models of SrTiO₃{100} and {110} facets. On the easily exposed {100} facets terminated with Sr-O atoms, photoelectrons are of 8 mol % for CH₄and 92 mol % for CO generation. The Sr-O-Ti configuration in the {110} facets could enrich the surface charge density due to the lower interface resistance for higher photocatalytic efficiency (1.6 fold). The dual sites of Ti and adjacent Sr atoms are active for strong adsorption and activation of the generated CO* species from primary CO₂reduction on the surface, thus kinetically favoring the activity of photoelectrons (73 mol %) in hydrogenation for CH₂* species and hence CH₄product. Inversely, the poor CH₄selectivity is due to difficulty in the subsequent photoelectron reduction reaction by the weak adsorption of CO* at the single-Sr site on the {100} facets, independent of the electron and proton concentration. Our results may offer some illuminating insights into the design of a highly efficient photocatalyst for selective CO₂reduction.

2D Bismuthene Metal Electron Mediator Engineering Super Interfacial Charge Transfer for Efficient Photocatalytic Reduction of Carbon Dioxide

The interfacial charge transfer still limits the photoactivity of artificial Z-scheme photocatalysts although they showed complementary light absorption and a strong photoredox ability. In this study, layered metallene is designed as an efficient electron mediator for constructing a C₃N₄/bismuthene/BiOCl 2D/2D/2D Z-scheme system. This bismuthene serves as a bridge processing superior charge conductibility, abundant metal-semiconductor contact sites, and the shortened charge diffusion distance, enhancing the photocatalytic CO₂ reduction reaction activity and stability. Density functional theory calculations show that the bismuthene creates a built-in electric field and congregates interfacial electrons, which is confirmed by the stable and consistent emission of the ultrafast transient absorption spectra. This work gives new insight into the interface design of Z-scheme photocatalysts by selecting a novel metallene electron mediator.