A critical review on TiO2 based photocatalytic CO2 reduction system: Strategies to improve efficiency

Temperature-dependent CO2 sorption and thermal-reduction without reactant gases on BaTiO3 nanocatalysts at low temperatures in the range of 300-1000 K

Carbon utilization techniques to mitigate the impact on global warming are an important field in environmental science. CO₂ reduction is a significant step for carbon utilization. However, CO₂ reduction with less energy consumption has major challenges. In this study, CO₂ thermal reduction was demonstrated using nanocatalysts at temperatures lower than 1000 K, and the CO₂ sorption and reduction mechanisms within the temperature range of 300-1000 K were evaluated. The physical adsorption on nanocatalysts with a crystal size of 7.4 ± 0.4 nm (10 nm-nanocatalysts) majorly occurred at 300 K and was considerably decreased beyond that temperature. CO₂ chemisorption occurred above 450 K and subsequent CO₂ reduction occurred above 500 K, which was expected based on the temperature-programmed reaction. CO₂ reduction decreased above 900 K by the deactivation of the 10-nm nanocatalyst as a result of its crystal growth. The transmission electron microscopy images also indicated the complete reduction of CO₂ into carbon products at 600 and 800 K. Therefore, an optimal condition of CO₂ reduction in the temperature range of 500-800 K. The highly active thermocatalyst achieved CO₂ reduction into CO and carbon products without any reducing agents even at an extremely low temperature (500 K). In summary, temperature-dependent CO₂ sorption and reduction were observed on the 10-nm nanocatalyst; CO₂ physical adsorption at 300-500 K, CO₂ chemisorption above 450 K, CO₂ reduction at 500-850 K, and CO₂ and CO releases above 800 K.

Shape-Dependent Performance of Cu/Cu2 O for Photocatalytic Reduction of CO2

The photocatalytic conversion of CO₂ into solar fuels or chemicals is a sustainable approach to relieve the immediate problems related to global warming and the energy crisis. This study concerns the effects of morphological control on a Cu/Cu₂ O-based photocatalyst for CO₂ reduction. The as-synthesized spherical Cu/Cu₂ O photocatalyst exhibits higher activity than the octahedral one under visible light irradiation. The difference in photocatalytic performance between these two catalysts could be attributed to the following two factors: (1) The multifaceted structure of spherical Cu/Cu₂ O favors charge separation; (2) octahedral Cu/Cu₂ O only contains more positively charged (111) facets, which are unfavorable for CO₂ photoreduction. The results further highlight the importance of utilizing crystal facet engineering to further improve the performance of CO₂ reduction photocatalysts.

Synthesis, modification and application of titanium dioxide nanoparticles: a review

Titanium dioxide (TiO₂) has been heavily investigated owing to its low cost, benign nature and strong photocatalytic ability. Thus, TiO₂ has broad applications including photocatalysts, Li-ion batteries, solar cells, medical research and so on. However, the performance of TiO₂ is not satisfactory due to many factors such as the broad band gap (3.01 to 3.2 eV) and fast recombination of electron-hole pairs (10^-12 to 10^-11 s). Plenty of work has been undertaken to improve the properties, such as structural and dopant modifications, which broaden the applications of TiO₂. This review mainly discusses the aspects of TiO₂-modified nanoparticles including synthetic methods, modifications and applications.

Broadening the Action Spectrum of TiO2-Based Photocatalysts to Visible Region by Substituting Platinum with Copper

In this study, TiO₂-based photocatalysts modified with Pt and Cu/CuO_x were synthesized and studied in the photocatalytic reduction of CO₂. The morphology and chemical states of synthesized photocatalysts were studied using UV-Vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. A series of light-emitting diodes (LEDs) with maximum intensity in the range of 365–450 nm was used to determine the action spectrum of photocatalysts. It is shown for, the first time, that the pre-calcination of TiO₂ at 700 °C and the use of Cu/CuO_x instead of Pt allow one to design a highly efficient photocatalyst for CO₂ transformation shifting the working range to the visible light (425 nm). Cu/CuO_x/TiO₂ (calcined at 700 °C) shows a rate of CH₄ formation of 1.2 ± 0.1 µmol h⁻¹ g⁻¹ and an overall CO₂ reduction rate of 11 ± 1 µmol h⁻¹ g⁻¹ (at 425 nm).

Core-shell TiO2-x-CuyO microspheres for photogeneration of cyclic carbonates under simulated sunlight

Propylene carbonates are important organic solvents and feedstocks for different applications, including synthesis of polymers and Li-batteries. The generation of propylene carbonate utilising anthropogenic CO₂ and renewable solar energy offers an alternative sustainable process with a closed loop carbon cycle. The development of microstructured photocatalysts with desired properties, including high degree of product selectivity, wide range of optical properties, and maximised conversion yield, plays an important role for effective production of propylene carbonate from CO₂. A hierachical hollow core with a double shell of TiO_2-x-Cu₂O-CuO was fabricated using the versatile solvothermal-microwave synthesis method. The fabricated sample revealed effective cascading of photogenerated electrons and holes that promoted the conversion of propylene carbonate (i.e., 1.6 wt%) under 1 Sun irradiation.

Research Progress in Semiconductor Materials with Application in the Photocatalytic Reduction of CO2

The large-scale burning of non-renewable fossil fuels leads to the gradual increase of the CO2 concentration in the atmosphere, which is associated with negative impacts on the environment. The consequent need to reduce the emission of CO2 resulting from fossil fuel combustion has led to a serious energy crisis. Research reports indicate that the photocatalytic reduction of CO2 is one of the most effective methods to control CO2 pollution. Therefore, the development of novel high-efficiency semiconductor materials has become an important research field. Semiconductor materials need to have a structure with abundant catalytic sites, among other conditions, which is of great significance for the practical application of highly active catalysts for CO2 reduction. This review systematically describes various types of semiconductor materials, as well as adjustments to the physical, chemical and electronic characteristics of semiconductor catalysts to improve the performance of photocatalytic reduction of CO2. The principle of photocatalytic CO2 reduction is also provided in this review. The reaction types and conditions of photocatalytic CO2 reduction are further discussed. We believe that this review will provide a good basis and reference point for future design and development in this field.

Photocatalytic CO2 Reduction Using TiO2-Based Photocatalysts and TiO2 Z-Scheme Heterojunction Composites: A Review

Photocatalytic CO₂ reduction is a most promising technique to capture CO₂ and reduce it to non-fossil fuel and other valuable compounds. Today, we are facing serious environmental issues due to the usage of excessive amounts of non-renewable energy resources. In this aspect, photocatalytic CO₂ reduction will provide us with energy-enriched compounds and help to keep our environment clean and healthy. For this purpose, various photocatalysts have been designed to obtain selective products and improve efficiency of the system. Semiconductor materials have received great attention and have showed good performances for CO₂ reduction. Titanium dioxide has been widely explored as a photocatalyst for CO₂ reduction among the semiconductors due to its suitable electronic/optical properties, availability at low cost, thermal stability, low toxicity, and high photoactivity. Inspired by natural photosynthesis, the artificial Z-scheme of photocatalyst is constructed to provide an easy method to enhance efficiency of CO₂ reduction. This review covers literature in this field, particularly the studies about the photocatalytic system, TiO₂ Z-scheme heterojunction composites, and use of transition metals for CO₂ photoreduction. Lastly, challenges and opportunities are described to open a new era in engineering and attain good performances with semiconductor materials for photocatalytic CO₂ reduction.

Optimizing the Performance of the Meso-Scale Continuous-Flow Photoreactor for Efficient Photocatalytic CO2 Reduction with Water Over Pt/TiO2/RGO Composites

Tuning the reaction parameters to maximize products yield is one of the major needs for any process. The goal of this research is to increase the reduction of CO2 with water by examining the operating parameters of a meso-scale continuous-flow type photochemical reactor over hydrothermally synthesized photocatalysts such as Pt/TiO2 and Pt/TiO2/RGO. Effects of catalyst type, weight of catalyst utilized, photochemical reactor temperature, retention time by variating the liquid water flow rate, and cocatalyst loading were investigated to increase the concentration of total organic carbon compounds including HCHO and CH3OH. The effect of titanium dioxide phase ratio (anatase: rutile) presence at the Pt/TiO2/RGO photocatalysts was also studied. The results revealed that the 0.3 wt.% Pt/TiO2/RGO5% photocatalyst which includes a phase ratio of 81:19 for anatase: rutile respectively has the superior photocatalytic activity to other studied photocatalysts. The physciochemical properties of different prepared photocatalytic samples were determined using various characterization techniques. Analyzing the liquid products on gas chromatography, it was found that CH3OH represents the major product whereas HCHO was the minor one. This reactor exhibits a great performance towards CO2 photocatalytic reduction under the optimized conditions.

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Recent Advances in Plasmonic Photocatalysis Based on TiO2 and Noble Metal Nanoparticles for Energy Conversion, Environmental Remediation, and Organic Synthesis

Plasmonic photocatalysis has emerged as a prominent and growing field. It enables the efficient use of sunlight as an abundant and renewable energy source to drive a myriad of chemical reactions. For instance, plasmonic photocatalysis in materials comprising TiO₂ and plasmonic nanoparticles (NPs) enables effective charge carrier separation and the tuning of optical response to longer wavelength regions (visible and near infrared). In fact, TiO₂ -based materials and plasmonic effects are at the forefront of heterogeneous photocatalysis, having applications in energy conversion, production of liquid fuels, wastewater treatment, nitrogen fixation, and organic synthesis. This review aims to comprehensively summarize the fundamentals and to provide the guidelines for future work in the field of TiO₂ -based plasmonic photocatalysis comprising the above-mentioned applications. The concepts and state-of-the-art description of important parameters including the formation of Schottky junctions, hot electron generation and transfer, near field electromagnetic enhancement, plasmon resonance energy transfer, scattering, and photothermal heating effects have been covered in this review. Synthetic approaches and the effect of various physicochemical parameters in plasmon-mediated TiO₂ -based materials on performances are discussed. It is envisioned that this review may inspire and provide insights into the rational development of the next generation of TiO₂ -based plasmonic photocatalysts with target performances and enhanced selectivities.

Application of Porous Materials for CO2 Reutilization: A Review

CO2 reutilization processes contribute to the mitigation of CO2 as a potent greenhouse gas (GHG) through reusing and converting it into economically valuable chemical products including methanol, dimethyl ether, and methane. Solar thermochemical conversion and photochemical and electrochemical CO2 reduction processes are emerging technologies in which solar energy is utilized to provide the energy required for the endothermic dissociation of CO2. Owing to the surface-dependent nature of these technologies, their performance is significantly reliant on the solid reactant/catalyst accessible surface area. Solid porous structures either entirely made from the catalyst or used as a support for coating the catalyst/solid reactants can increase the number of active reaction sites and, thus, the kinetics of CO2 reutilization reactions. This paper reviews the principles and application of porous materials for CO2 reutilization pathways in solar thermochemical, photochemical, and electrochemical reduction technologies. Then, the state of the development of each technology is critically reviewed and evaluated with the focus on the use of porous materials. Finally, the research needs and challenges are presented to further advance the implementation of porous materials in the CO2 reutilization processes and the commercialization of the aforementioned technologies.

Solar-driven conversion of carbon dioxide over nanostructured metal-based catalysts in alternative approaches: Fundamental mechanisms and recent progress

Solar-driven carbon dioxide (CO₂) conversion has gained tremendous attention as a prominent strategy to simultaneously reduce the atmospheric CO₂ concentration and convert solar energy into solar fuels in the form of chemical bonds. Numerous efforts have been devoted to diverse photo-driven processes for CO₂ conversion, which utilized a multidisciplinary strategy. Among them, the architecture of nanostructured metal-based catalysts is emerging as an eminent solution for the design of catalysts of this field. In this work, we first provide fundamental mechanisms of photochemical, photoelectrochemical, photothermal, and photobio(electro)chemical CO₂ reduction processes to achieve an in-deep understanding of vital aspects. Importantly, the recent progress in the catalyst design for each reaction system is discussed and highlighted. Based on these analyses, an overview of photo-driven CO₂ reduction on metal-based catalysts for solar fuel production is also spotlighted. Finally, we analyze challenges and prospects for the strategic direction of developments in the field.

Rh/Al Nanoantenna Photothermal Catalyst for Wide-Spectrum Solar-Driven CO2 Methanation with Nearly 100% Selectivity

Solar-powered CO₂ conversion represents a promising green and sustainable approach for achieving a carbon-neutral economy. However, the rational design of a wide-spectrum sunlight-driven catalysis system for effective CO₂ reduction is an ongoing challenge. Herein, we report the preparation of a rhodium/aluminum (Rh/Al) nanoantenna photothermal catalyst that can utilize a broad range of sunlight (from ultraviolet to the near-infrared region) for highly efficient CO₂ methanation, achieving a high CH₄ selectivity of nearly 100% and an unprecedented CH₄ productivity of 550 mmol·g^-1·h^-1 under concentrated simulated solar irradiation (11.3 W·cm^-2). Detailed control experiment results verified that the CO₂ methanation process was facilitated by the localized surface plasmonic resonance and nanoantenna effects of the Rh/Al nanostructure under light irradiation. In operando temperature-programmed Fourier transform infrared spectroscopy confirmed that CO₂ methanation on the Rh/Al nanoantenna catalyst was a multistep reaction with CO as a key intermediate. The design of a wide-spectrum solar-driven photothermal catalyst provides a feasible strategy for boosting CO₂-to-fuel conversion.

Titania-Clay Mineral Composites for Environmental Catalysis and Photocatalysis

The use of titania-based composite materials in the field of heterogeneous catalysis and photocatalysis has a long and rich history. Hybrid structures combining titania nanoparticles with clay minerals have been extensively investigated for nearly four decades. The attractiveness of clay minerals as components of functional materials stems primarily from their compositional versatility and the possibility of using silicate lamellae as prefabricated building blocks ready to be fitted into the desired nanoconstruction. This review focuses on the evolution over the years of synthetic strategies employed for the manufacturing of titania–clay mineral composites with particular attention to the role of the adopted preparative approach in shaping the physical and chemical characteristics of the materials and enabling, ultimately, tuning of their catalytic and/or photocatalytic performance.

HKUST-1-derived highly ordered Cu nanosheets with enriched edge sites, stepped (211) surfaces and (200) facets for effective electrochemical CO2 reduction

A novel electrode composed of Cu nanosheets constructed from nanoparticles was synthesized by in situ electrochemical derivation from the metal-organic framework (MOF) HKUST-1. The prepared derivative electrode (HE-Cu) exhibited higher Faradaic efficiency (FE, 56.0%) of electrochemical CO₂ reduction (CO₂R) compared with that of pristine Cu foil (p-Cu, 32.3%) at an overpotential of -1.03 V vs. a reversible hydrogen electrode (RHE). HE-Cu also exhibited lower onset potential of CO₂R as well as inhibiting the H₂ evolution reaction. Electrochemical measurements revealed that HE-Cu exhibited higher CO₂ adsorption (1.58-fold) and a larger electrochemical active surface area (1.24-fold) compared with p-Cu. Physicochemical characterization and Tafel analysis showed that stepped Cu (211) surfaces, (200) facets and Cu edge atoms on HE-Cu contributed significantly to the enhanced CO₂R activity and/or HCOOH and/or C2 product selectivity. The FEs of HCOOH and C2 products for HE-Cu increased 1.57-fold and 10.6-fold at an overpotential of -1.19 V vs. RHE compared with p-Cu. Although CH₄ was produced on p-Cu, its formation was totally suppressed on HE-Cu due to the increase of edge sites and (200) facets. Our study demonstrates that electroreduction of MOFs is a promising method to prepare novel and stable electrochemical catalysts with unique surface structures. The fabricated derivative electrode not only promoted electrochemical CO₂R activity but also exhibited high C2 product selectivity.

Enhanced Photocatalytic Activity of Hybrid rGO@TiO2/CN Nanocomposite for Organic Pollutant Degradation under Solar Light Irradiation

The three-component hybrid (rGO/TiO2/CN) nanocomposite was prepared in order to enhance the photocatalytic properties of anatase TiO2 nanoparticles (NPs) under solar-like irradiation. The rGO/TiO2/CN was prepared in a mixture of the reduced graphene oxide (rGO, 8 wt%), anatase TiO2 nanoparticles (NPs), and graphitic carbon nitride (g-C3N4, 16 wt%). It was self-assembled through the one-step hydrothermal method, followed by an annealing process. The photocatalyst was thoroughly characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique and UV-Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the TiO2, TiO2/rGO, TiO2/CN and hybrid rGO/TiO2/CN nanocomposite was studied through the degradation of a rhodamine B (RhB) aqueous solution under solar-like irradiation. The results showed that the highest photocatalytic activity was achieved by the rGO/TiO2/CN mixture, which can be attributed to the synergistic effect of the incorporation of both rGO and g-C3N4 with TiO2. Further, the influence of the pH value of the RhB dye aqueous solution and different water matrix (Milli-Q, tap, and alkaline water) on the photocatalytic efficiency of the rGO/TiO2/CN nanocomposite was examined. In addition, a recycle test was performed for hybrid rGO@TiO2/CN to investigate the effectiveness of the photodegradation of RhB dye in three successive cycles. The conducted results indicate that the pH value of RhB dye aqueous solution and water matrices play an important role in the photocatalytic degradation rate.

Energy Transport of Photocatalytic Carbon Dioxide Reduction in Optical Fiber Honeycomb Reactor Coupled with Trough Concentrated Solar Power

Thanks to the high photon efficiency and reaction density, the optical fiber monolith reactor (OFMR) for InTaO4-based CO2 photoreduction is regarded as a promising photoreactor. In this work, the OFMR coupling with parabolic trough concentrator (PTC) is proposed to enlarge the daylighting area by several times without increasing the cost of photocatalysts. Based on the Monte Carlo ray-tracing (MCRT) approach and the finite volume method (FVM), a computational model of the reaction module considering the light, heat, and mass transfer is developed to optimize the fiber honeycomb reactor coupled with the PTC. As a result, the volume-averaged concentration of production reaches 1.85 × 10−4 mol·m−3, which is much higher than the traditional OFMR with the production concentration of 9.61 × 10−6 mol·m−3 under the same condition. The optimized structure of the monolith for better photocatalytic performance is obtained. It shows that the diameters of gas channels ranging from 1.5 to 2 mm are beneficial to the reaction efficiency. Finally, the results suggested that the even number of the gas channel should be avoided due to the pseudo-steady zone in the middle of the monolith. The reaction element with the high serial number along the flow direction has the reduced reaction density and endangers the organic optical fibers especially when the serial number exceeds 5.

The CO2 photoconversion over reduced graphene oxide based on Ag/TiO2 photocatalyst in an advanced meso-scale continuous-flow photochemical reactor

This study aims at examining the use of an advanced meso-scale continuous-flow photochemical reactor for the photocatalytic conversion of CO₂ with water into fuel over TiO₂ (P25), Ag/TiO₂, and Ag/TiO₂/RGO catalysts. The silver loaded photocatalysts were prepared by one-step process via hydrothermal method. The prepared photocatalysts were characterized by various characterization techniques in order to identify the morphological, chemical, physical, and optical properties. The photocatalytic activity of the as-prepared catalysts was firstly examined by the photoelectrochemical (PEC) measurements and secondly by the photocatalytic reduction of CO₂ in the proposed setup. Liquid products were analyzed using gas chromatography-mass spectrometry (GC-MS) and total organic carbon (TOC) techniques. It was found that the ternary composite revealed an outstanding performance towards CO₂ photocatalytic reduction, where its selectivity was directed towards methanol production. The incorporation of graphene nanosheets enhanced the photocatalytic reduction of CO₂ by 3.3 and 9.4 times compared with Ag/TiO₂ and bare TiO₂, respectively, using the proposed photochemical reactor in a continuous mode. This study sheds the light on a novel type of a photocatalytic reactor where CO₂ conversion over Ag/TiO₂/RGO ternary composite was evaluated. A meso-scale continuous-flow photochemical reactor.

Performance Analysis of TiO2-Modified Co/MgAl2O4 Catalyst for Dry Reforming of Methane in a Fixed Bed Reactor for Syngas (H2, CO) Production

Co/TiO2–MgAl2O4 was investigated in a fixed bed reactor for the dry reforming of methane (DRM) process. Co/TiO2–MgAl2O4 was prepared by modified co-precipitation, followed by the hydrothermal method. The active metal Co was loaded via the wetness impregnation method. The prepared catalyst was characterized by XRD, SEM, TGA, and FTIR. The performance of Co/TiO2–MgAl2O4 for the DRM process was investigated in a reactor with a temperature of 750 °C, a feed ratio (CO2/CH4) of 1, a catalyst loading of 0.5 g, and a feed flow rate of 20 mL min−1. The effect of support interaction with metal and the composite were studied for catalytic activity, the composite showing significantly improved results. Moreover, among the tested Co loadings, 5 wt% Co over the TiO2–MgAl2O4 composite shows the best catalytic performance. The 5%Co/TiO2–MgAl2O4 improved the CH4 and CO2 conversion by up to 70% and 80%, respectively, while the selectivity of H2 and CO improved to 43% and 46.5%, respectively. The achieved H2/CO ratio of 0.9 was due to the excess amount of CO produced because of the higher conversion rate of CO2 and the surface carbon reaction with oxygen species. Furthermore, in a time on stream (TOS) test, the catalyst exhibited 75 h of stability with significant catalytic activity. Catalyst potential lies in catalyst stability and performance results, thus encouraging the further investigation and use of the catalyst for the long-run DRM process.

Review of MXene-based nanocomposites for photocatalysis

Since multilayered MXenes (Ti₃C₂T_x, a new family of two-dimensional materials) were initially introduced by researchers at Drexel University in 2011, various MXene-based nanocomposites have received increased attention as photocatalysts owing to their exceptional properties (e.g., rich surface chemistry, adjustable bandgap structures, high electrical conductivity, hydrophilicity, thermal stability, and large specific surface area). Therefore, we present a comprehensive review of recent studies on fabrication methods for MXene-based photocatalysts and photocatalytic performance for contaminant degradation, CO₂ reduction, H₂ evolution, and N₂ fixation with various MXene-based nanocomposites. In addition, this review briefly discusses the stability of MXene-based nanophotocatalysts, current limitations, and future research needs, along with the various corresponding challenges, in an effort to reveal the unique properties of MXene-based nanocomposites.

Recent Advances in TiO2-Based Heterojunctions for Photocatalytic CO2 Reduction With Water Oxidation: A Review

Photocatalytic conversion of CO₂ into solar fuels has gained increasing attention due to its great potential for alleviating the energy and environmental crisis at the same time. The low-cost TiO₂ with suitable band structure and high resistibility to light corrosion has proven to be very promising for photoreduction of CO₂ using water as the source of electrons and protons. However, the narrow spectral response range (ultraviolet region only) as well as the rapid recombination of photo-induced electron-hole pairs within pristine TiO₂ results in the low utilization of solar energy and limited photocatalytic efficiency. Besides, its low selectivity toward photoreduction products of CO₂ should also be improved. Combination of TiO₂ with other photoelectric active materials, such as metal oxide/sulfide semiconductors, metal nanoparticles and carbon-based nanostructures, for the construction of well-defined heterostructures can enhance the quantum efficiency significantly by promoting visible light adsorption, facilitating charge transfer and suppressing the recombination of charge carriers, resulting in the enhanced photocatalytic performance of the composite photocatalytic system. In addition, the adsorption and activation of CO₂ on these heterojunctions are also promoted, therefore enhancing the turnover frequency (TOF) of CO₂ molecules, so as to the improved selectivity of photoreduction products. This review focus on the recent advances of photocatalytic CO₂ reduction via TiO₂-based heterojunctions with water oxidation. The rational design, fabrication, photocatalytic performance and CO₂ photoreduction mechanisms of typical TiO₂-based heterojunctions, including semiconductor-semiconductor (S-S), semiconductor-metal (S-M), semiconductor-carbon group (S-C) and multicomponent heterojunction are reviewed and discussed. Moreover, the TiO₂-based phase heterojunction and facet heterojunction are also summarized and analyzed. In the end, the current challenges and future prospects of the TiO₂-based heterostructures for photoreduction of CO₂ with high efficiency, even for practical application are discussed.

Photocatalytic CO2 Reduction Enabled by Interfacial S-Scheme Heterojunction between Ultrasmall Copper Phosphosulfide and g-C3N4

Transition metal phosphosulfides (TMPSs) have gained much interest due to their highly enhanced photocatalytic activities compared to their corresponding phosphides and sulfides. However, the application of TMPSs on photocatalytic CO₂ reduction remains a challenge due to their inappropriate band positions and rapid recombination of photogenerated electron-hole pairs. Herein, we report ultrasmall copper phosphosulfide (us-Cu₃P|S) nanocrystals anchored on 2D g-C₃N₄ nanosheets. Systematic studies on the interaction between us-Cu₃P|S and g-C₃N₄ indicate the formation of an S-scheme heterojunction via interfacial P-N chemical bonds, which acts as an electron transfer channel and facilitates the separation and migration of photogenerated charge carriers. Upon the composite formation, the band structures of us-Cu₃P|S and g-C₃N₄ are altered to enable the enhanced photocatalytic CO generation rate of 137 μmol g^-1 h^-1, which is eight times higher than that of pristine g-C₃N₄. The unique phosphosulfide structure is also beneficial for the enhanced electron transfer rate and provides abundant active sites. This first application of Cu₃P|S to photocatalytic CO₂ reduction marks an important step toward the development of TMPSs for photocatalytic applications.

Impact of structure, doping and defect-engineering in 2D materials on CO2 capture and conversion

2D material based strategies for adsorption and conversion of CO2 to value-added products.

Metal halide perovskites as an emergent catalyst for CO2 photoreduction: a minireview

The present minireview summarizes recent advances in the application of metal halide perovskite for CO₂ photoreduction.

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

Solar-driven photocatalytic CO₂ reduction into CH₄ with H₂O is considered to be a promising way to alleviate the energy crisis and greenhouse effect. However, current CO₂ photoreduction technologies tend to overlook the role of photooxidation half reaction as well as the effect of the protons produced by water oxidation on CH₄ generation, resulting in low CO₂ conversion efficiency and poor CH₄ selectivity. In the present study, a series of chloride-modified Bi₂WO₆ nanosheets were constructed in view of chloride-assisted photocatalytic water oxidation. The results show that the CH₄ yield of the synthesized sample can be enhanced up to about 10 times compared to that with no Cl^- modification. Besides, the selectivity of CH₄ can be regulated by the loading amount of chloride, varying from 51.29% for Bi₂WO₆ to 94.98% for the maximum. The increase of product yield is attributed to chloride modification, which not only changed the morphology of the catalyst, but also modified the pathway of water oxidation. Further studies on intermediate products and the density functional theory calculation confirm that the Cl^- ions on Bi₂WO₆ nanosheets not only promote H₂O oxidation, but also lower the energy barrier for intermediate *CHO generation, thus facilitating CH₄ production. The results gained herein may provide some illuminating insights into the design of a highly selective photocatalyst for efficient CO₂ reduction.

Development of AgFeO2/rGO/TiO2 Ternary Composite Photocatalysts for Enhanced Photocatalytic Dye Decolorization

Dyestuff is one of the most widely released pollutants into the environment. Many approaches have been considered to deal with the dye removal from polluted water such as adsorption, ultrafiltration, osmosis, solvent extraction and photocatalytic degradation. The photocatalytic degradation process is one of the most beneficial, economical and environmentally friendly ways to degrade the organic pollutants from wastewater. In this study, an efficient ferrite-based photocatalyst, AgFeO2/rGO/TiO2 was successfully developed using simple deposition and reflux method. Physical, chemical and structural properties were analyzed by using XRD, FTIR Raman and PL spectroscopy. The efficiency of photocatalyst was investigated for the decolorization of methyl blue (MB) dye and activity was measured through UV-vis spectroscopy. The effect of parameters like pH, concentrations of MB dye, and loading of silver ferrite (AgFeO2) was investigated. The study depicted that the properties of TiO2 were improved due to addition of silver ferrite and reduced graphene oxide (rGO). The 2.5% AgFeO2/rGO/TiO2 exhibited the highest efficiency and completely degraded the 50 ppm of MB dye in 30 min. The parametric study revealed that dye decolorization is faster in a neutral solution than in basic and acidic medium. The higher performance of the photocatalyst was attributed to the reduced charge recombination and improved optical properties. Thus, AgFeO2/rGO/TiO2 can be a potential composite for photocatalytic dye degradation and other photocatalytic applications under UV-Visible light irradiations.

Photocatalytic H2 Evolution, CO2 Reduction, and NOx Oxidation by Highly Exfoliated g-C3N4

g-C3N4, with specific surface area up to 513 m2/g, was prepared via three successive thermal treatments at 550 °C in air with gradual precursor mass decrease. The obtained bulk and exfoliated (1ex, 2ex and 3ex) g-C3N4 were characterized and tested as photocatalysts for H2 production, CO2 reduction and NOx oxidation. The exfoliated samples demonstrated graphene-like morphology with detached (2ex) and sponge-like framework (3ex) of layers. The surface area increased drastically from 20 m2/g (bulk) to 513 m2/g (3ex). The band gap (Eg) increased gradually from 2.70 to 3.04 eV. Superoxide radicals (·O2−) were mainly formed under UV and visible light. In comparison to the bulk, the exfoliated g-C3N4 demonstrated significant increase in H2 evolution (~6 times), CO2 reduction (~3 times) and NOx oxidation (~4 times) under UV light. Despite the Eg widening, the photocatalytic performance of the exfoliated g-C3N4 under visible light was improved too. The results were related to the large surface area and low e−-h+ recombination. The highly exfoliated g-C3N4 demonstrated selectivity towards H2 evolution reactions.

Unique S-scheme heterojunctions in self-assembled TiO2/CsPbBr3 hybrids for CO2 photoreduction

Exploring photocatalysts to promote CO2 photoreduction into solar fuels is of great significance. We develop TiO2/perovskite (CsPbBr3) S-scheme heterojunctions synthesized by a facile electrostatic-driven self-assembling approach. Density functional theory calculation combined with experimental studies proves the electron transfer from CsPbBr3 quantum dots (QDs) to TiO2, resulting in the construction of internal electric field (IEF) directing from CsPbBr3 to TiO2 upon hybridization. The IEF drives the photoexcited electrons in TiO2 to CsPbBr3 upon light irradiation as revealed by in-situ X-ray photoelectron spectroscopy analysis, suggesting the formation of an S-scheme heterojunction in the TiO2/CsPbBr3 nanohybrids which greatly promotes the separation of electron-hole pairs to foster efficient CO2 photoreduction. The hybrid nanofibers unveil a higher CO2-reduction rate (9.02 μmol g-1 h-1) comparing with pristine TiO2 nanofibers (4.68 μmol g-1 h-1). Isotope (13CO2) tracer results confirm that the reduction products originate from CO2 source.