Enhancing photocatalytic CO2 reduction with TiO2-based materials: Strategies, mechanisms, challenges, and perspectives

Photo-assisted thermal catalytic CO2 reduction over Ru-TiO2 catalysts

Photothermal catalysis is a promising technology to convert CO2 into high value-added products. Here, we show that loading Ru NPs on TiO2 achieved a remarkable photothermal synergistic effect and the Ru-TiO2 demonstrated a high efficiency for the photothermal conversion of low CO2 concentration to CH4 at the gas-solid interface. The photothermal activity of the Ru-TiO2 (217.9 µmol/(g·h)) was nearly 6 times higher than pure thermal activity (38.08 µmol/(g·h)), and nearly 20 times than the photocatalytic activity (10.9 µmol/(g·h)). We revealed that the light excitation could drive the generated electrons from TiO2 to Ru particles, beneficial to CO2 reduction, while external heating showed no influence on the charge separation of the Ru-TiO2. Hence, the photothermal synergy is not a heat-assisted photocatalytic process, but a photo-assisted thermal catalytic process. We finally demonstrated that the CO2 was firstly converted to CO, and the CO was further hydrogenated to CH4. The introduction of light could promote the activation of intermediate CO species at the Ru-Ti interface sites, thus greatly accelerating CO hydrogenation to CH4. This work contributes to further understanding of the mechanism of photothermal catalytic CO2 reduction.

Engineering cycling of Cu2+/Cu+ pairs in Bi2WO6 nanoflowers for boosting photocatalytic CO2 reduction

The photocatalytic reduction of CO2 represents an effective method for addressing environmental and energy crises. However, the slow migration and rapid recombination of photogenerated carriers have been identified as significant limitations on the efficiency of this process. Herein, we developed the cycling of Cu2+/Cu+ pairs in Bi2WO6 nanoflowers for boosting photocatalytic CO2 reduction. Cu2+ is an electron trap that captures electrons to generate Cu+, and Cu+ is unstable and prone to losing electrons to generate Cu2+ in Bi2WO6. The two processes are in concert to realize Cu2+/Cu+ cycling, which alters the charge transfer pathway and enhances the effective separation of photogenerated carriers for CO2 photoreduction reaction. Consequently, Cu2+-modified Bi2WO6 exhibited remarkable photocatalytic performance with the rate of CO and C2H4 production reaching 165.28 and 16.49 μL·g-1 in 3 h, which are 3.34 and 11.53 times that of the pristine Bi2WO6. And the *COOH is the key to triggering the conversion of CO2 to CO, and *OC-CHOH is the key to forming C2H4 by CC coupling. This work elucidates a dynamic copper valence cycling mechanism, establishing a paradigm for rational design of Cu-modified photocatalysts in solar-driven CO2 conversion.

Mechanism Decoding of an S-Scheme ZnIn2S4/H2WO4 Heterojunction with Favorable Surface Electronic Potential for Enhanced and Anti-Corrosion Photocatalytic Hydrogen Evolution

The rational construction of heterojunction interfaces plays a critical role in enhancing the carrier separation efficiency for photocatalytic hydrogen evolution. In this study, a ZnIn2S4/H2WO4 S-scheme heterojunction was successfully synthesized via a self-assembly strategy. Compared with conventional WO3, the H2WO4 component exhibits a lower work function, which significantly promotes surface electron overflow and establishes an optimized S-scheme charge transfer pathway. Structural characterization reveals that the intimate integration of H2WO4 nanosheets within ZnIn2S4 nanoflowers provides enhanced interfacial contact, thereby facilitating efficient charge separation and migration. As a result, the optimized ZnIn2S4/H2WO4 composite demonstrates a hydrogen evolution rate of 138 mmol/g/h, achieving a 4.7-fold enhancement over pristine ZnIn2S4 and a 1.9-fold improvement compared to the ZnIn2S4/WO3. This work highlights the dual requirements for oxidation photocatalysts in S-scheme systems: precise band gap alignment and favorable surface electronic properties, both essential for enabling efficient electron overflow and ensuring effective S-scheme charge migration channels.

Development of a UPLC-MS/MS method for pesticide analysis in paddy water and evaluation of anodic TiO2 nanostructured films for pesticide photodegradation and antimicrobial applications

Pesticide contamination in agricultural water poses serious environmental and public health risks, particularly due to the accumulation of harmful residues that threaten aquatic ecosystems and human health. This study investigated the levels of five pesticides-carbaryl (CBR), methiocarb (MTC), diazinon (DZN), chlorpyrifos (CLO), and cypermethrin (CYPER)-in agricultural water samples from Can Tho City and Hau Giang Province, Vietnam. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was employed for their detection and quantification. Chlorpyrifos was the most frequently detected pesticide (32.5%), with concentrations ranging from 1.7 to 10.9 ng mL-1. The concentrations of cypermethrin, carbaryl, methiocarb, and diazinon were 2.6-9.4 ng mL-1, 1.3-14.3 ng mL-1, 4.1-7.7 ng mL-1, and 2.8-10.5 ng mL-1, respectively. The persistence of pesticide residues in the water samples highlights the significant contamination concerns in the region. To address this issue, two types of TiO2 nanophotocatalysts-TiO2 nanotube arrays (TNAs) and TiO2 nanowires on nanotube arrays (TNWs/TNAs)-were synthesized for the photocatalytic degradation of the identified pesticides. Under UV-vis irradiation (∼96 mW cm-2), both nanostructures achieved rapid pesticide degradation, with removal efficiencies of up to 99% within 25 minutes. TNWs/TNAs exhibited superior photocatalytic performance, attributed to their increased surface area compared to TNAs. In addition to pesticide degradation, their antibacterial activity was assessed. Under weak UV-vis light (6.3 mW cm-2), both TNAs and TNWs/TNAs achieved 100% antibacterial efficacy against Escherichia coli, significantly higher than the 68% efficacy of UV light treatment alone. Even under dark conditions, TNWs/TNAs demonstrated enhanced antibacterial activity, achieving 63% efficacy compared to 12% for TNAs. These results underscore the dual functionality of TNWs/TNAs as effective photocatalysts for both pesticide degradation and bacterial inactivation, presenting a promising approach for agricultural water treatment.

g-C3N4 S-Scheme Homojunction through Van der Waals Interface Regulation by Intrinsic Polymerization Tailoring for Enhanced Photocatalytic H2 Evolution and CO2 Reduction

The effective S-scheme homojunction relies on the precise regulation of band structure and construction of advantaged charge migration interfaces. Here, the electronic structural properties of g-C3N4 were modulated through meticulous polymerization of self-assembled supramolecular precursors. Experimental and DFT results indicate that both the intrinsic bandgap and surface electronic characteristics were adjusted, leading to the formation of an in-situ reconstructed homojunction interface facilitated by intrinsic van der Waals forces. The homojunction catalyst, composed of g-C3N4 nanodots and ultra-thin g-C3N4 nanoflakes, exhibited a significant S-scheme carrier separation mechanism, which enhances the utilization of electrons and holes. Consequently, under AM 1.5 light irradiation (~100 mW/cm2), the g-C3N4 homojunction photocatalyst achieved a remarkable hydrogen evolution rate of 580 μmol h-1. Furthermore, a reversed CH4 selectivity in CO2 reduction was observed, yielding 80.30 μmol g-1 h-1 with a selectivity of 96.86 %, in contrast to the performance of bulk g-C3N4, which produced only 2.22 μmol g-1 h-1 with the 15.69 % CH4 selectivity. These findings not only highlight the significant potential of the g-C3N4 homojunction photocatalyst for hydrogen production and CO2 reduction but also propose a superior and effective strategy for optimizing the structural properties of g-C3N4, which are crucial for the design of photocatalytic reactions.

Heterogeneous Photocatalytic Systems Formed by Compound [Zr6O4(OH)4(C6H5COO)8(H2O)8][SiW12O40] in Combination with Inorganic Cocatalysts for the CO2 Reduction to Alcohols in Water

The photoreduction of CO2 to methanol and ethanol is a highly sought-after reaction due to the economic and environmental implications of these products. Both methanol and ethanol are versatile chemical feedstock and renewable fuels. The ionic hybrid compound [Zr6O4(OH)4(C6H5COO)8(H2O)8][SiW12O40] (Zr6W12) provides effective separation of the generated electron-hole pair during exposure to UV radiation through a Z-scheme disposition of the HOMO-LUMO levels of each discrete ionic entity. However, this compound does not promote the CO2 reduction. In contrast, the incorporation of selected inorganic cocatalysts, such as AgI, Bi2O3, CeO2, CuI, CuO, Cu2O, In2O3, PbO, Sb2O3, SnO, TiO2 or ZnO, to the photocatalytic system can enable the activation and reduction of CO2, leveraging their electronic properties and interactions with Zr6W12. Some of these heterogeneous photocatalytic systems perform well for the photoreduction of CO2 into methanol and/or ethanol in water and without the need of any sacrificial chemical reagent, achieving maximum production levels of 163 μg g-1 h-1 and 144 μg g-1 h-1 for methanol and ethanol, respectively, for the Zr6W12/CuI photocatalytic mixture. Theoretical calculations have been conducted to determine how the relative disposition of the HOMO/LUMO energy levels of Zr6W12 and the band structure of the inorganic cocatalysts impact on the CO2 photocatalytic reduction to alcohols.

Recent Advances of Indium-Based Sulfides in Photocatalytic CO2 Reduction

Urgent and significant, the mitigation of greenhouse effects and the preservation of the Earth's ecological environment are paramount concerns. Photocatalytic carbon dioxide (CO2) reduction technology holds immense promise as it directly harnesses renewable solar energy to convert CO2 into hydrocarbon fuels and valuable chemical products. Indium (In)-based sulfides have garnered significant attention in the realm of fundamental research on CO2 photocatalytic conversion. The photocatalytic performance exhibited by In-based materials is attributed to the appropriate bandgap (E g), unique electronic states, tunable atomic structure, and superior optoelectronic properties. Notably, In-based metal sulfides also show excellent potential for addressing challenges related to photocorrosion and carrier recombination. This paper highlighted the key structural features and commonly employed synthesis techniques of In-based metal sulfides. Furthermore, it summarized effective modification strategies aimed at optimizing the photocatalytic performance of these materials. A particular focus was placed on exploring the intricate structure-activity relationships, encompassing the influence of heterostructure construction, element doping, defect engineering, and co-catalyst modification on enhancing photocatalytic efficiency. Finally, the article identified the current challenges and outlined the promising future directions for In-based photocatalysts, hoping to provide valuable references for researchers.

First-principles study of CO2 and H2O adsorption on the anatase TiO2(101) surface: effect of Au doping

Photocatalytic reduction of CO2 will play a major role in future energy and environmental crisis. To investigate the adsorption mechanisms of CO2 and H2O molecules involved in the catalytic process on the surface of anatase titanium dioxide 101 (TiO2(101)) and the influence of Au atom doping on their adsorption, first-principles density functional theory calculations were used. The results show that 1. Au atom doping stabilizes the structure of the catalyst system and reduces the band gap, facilitating the reaction of CO2 and H2O molecules. 2. The O site is the most stable adsorption site for the CO2 molecule on the surface, and chemical adsorption occurs, leading to structural deformation during the adsorption process. The adsorption energy is the highest when the H2O molecule is adsorbed parallel to the surface, and there is a bonding trend between H2O and the surface. 3. The adsorption performances of CO2 and H2O molecules improve after Au atom doping. 4. Au atom doping creates stronger adsorption sites on the catalyst surface, with the two-coordinated O atoms near the Au atom becoming the preferred adsorption sites for both molecules. The revealed microscopic mechanism provides theoretical support for the design and manufacture of photocatalytic CO2 reduction catalysts.

Construction of Mn-Defective S/Mn0.4Cd0.6S for Promoting Photocatalytic N2 Reduction

Improving catalytic performance by controlling the microstructure of materials has become a hot topic in the field of photocatalysis, such as the surface defect site, multistage layered morphology, and exposed crystal surface. Due to the differences in the metal atomic radius (Mn and Cd) and solubility product constant (MnS and CdS), Mn defect easily occurred in the S/Mn0.4Cd0.6S (S/0.4MCS) composite. To optimize the photocatalytic performance in N2 fixation, the effects of the synthesis conditions and reaction conditions for S/0.4MCS were explored and systematically studied. Combined with the experimental characterization and theoretical calculation, not only the photocatalytic reaction pathway but also the key steps of N2 reduction were explored. Moreover, the transfer mechanism of photogenerated charge carriers (PCCs) formed between S and 0.4MCS was studied, which enhanced the utilization rate of photogenerated electrons (e-) and holes (h+). This work detailedly discusses the relationship between microstructure and photocatalytic performance, which is beneficial for the design of efficient photocatalyst.

Site-Specific for CO2 Photoreduction with Single-Atom Ni on Strained TiO2-x Derived from Bimetallic Metal-Organic Frameworks

The photocatalytic reduction of CO2 in water to produce fuels and chemicals is promising while challenging. However, many photocatalysts for accomplishing such challenging task usually suffer from unspecific catalytic active sites and the inefficient charge carrier's separation. Here, a site-specific single-atom Ni/TiO2-x catalyst is reported by in situ topological transformation of Ni-Ti-EG bimetallic metal-organic frameworks. The loading of nickel nanoparticles or individual atoms, which act as specific active sites, can be precisely regulated by chelating agents through the partial removal of nickel and adjacent oxygen atoms. Furthermore, the degree of lattice strain in Ni/TiO2-x catalysts, which improves the separation efficiency of charge carriers, can be modulated by fine-tuning the transformation process. By leveraging the anchored nickel atoms and the strained TiO2, the optimized NiSA0.27/TiO2-x shows a CO generation rate of 86.3 µmol g-1 h-1 (288 times higher than that of NiNPs/TiO2-x) and CO selectivity of up to 92.5% for CO2 reduction in a pure-water system. This work underscores the importance of tailoring lattice strain and creating specific single-atom active sites to facilitate the efficient and selective reduction of CO2.

Recent Advances of Electrode Materials Applied in an Electrochromic Supercapacitor Device

An electrochromic supercapacitor device (ESD) is an advanced energy storage device that combines the energy storage capability of a supercapacitor with the optical modulation properties of electrochromic materials. The electrode materials used to construct an ESD need to have both rich color variations and energy storage properties. Recent advances in ESDs have focused on the preparation of novel electrochromic supercapacitor electrode materials and improving their energy storage capacity, cycling stability, and electrochromic performance. In this review, the research significance and application value of ESDs are discussed. The device structure and working principle of electrochromic devices and supercapacitors are analyzed in detail. The research progress of inorganic materials, organic materials, and inorganic/organic nanocomposite materials used for the construction of ESDs is discussed. The advantages and disadvantages of various types of materials in ESD applications are summarized. The preparation and application of ESD electrode materials in recent years are reviewed in detail. Importantly, the challenges existing in the current research and recommendations for future perspectives are suggested. This review will provide a useful reference for researchers in the field of ESD electrode material preparation and application.

Photothermal Catalytic Degradation of VOCs: Mode, System and Application

Human production and living processes emit excessive VOCs into the atmosphere, posing significant threats to both human health and the environment. The photothermal catalytic oxidation process is an organic combination of photocatalysis and thermocatalysis. Utilizing photothermal catalytic degradation of VOCs can achieve better catalytic activity at lower temperatures, resulting in more rapid and thorough degradation of these compounds. Photothermal catalysis has been increasingly applied in the treatment of atmospheric VOCs due to its many advantages. A brief introduction on the three modes of photothermal catalysis is presented. Depending on the main driving force of the reactions, they can be categorized into thermal-assisted photocatalysis (TAPC), photo-assisted thermal catalysis (PATC) and photo-driven thermal catalysis (PDTC). The commonly used catalyst design methods and reactor types for photothermal catalysis are also briefly introduced. This paper then focuses on recent developments in specific applications for photothermal catalytic oxidation of different types of VOCs and their corresponding principles. Finally, the problems and challenges facing VOC degradation through this method are summarized, along with prospects for future research.

Surface Modifications of Layered Perovskite Oxysulfide Photocatalyst Y2Ti2O5S2 to Enhance Visible-Light-Driven Water Splitting

Increasing the efficiency of visible-light-driven water splitting systems will require improvements in the charge separation characteristics and redox reaction kinetics associated with narrow-bandgap photocatalysts. Although the traditional approach of loading a single cocatalyst on selective facets provides reaction sites and reduces the reaction overpotential, pronounced surface charge carrier recombination still results in limited efficiency increases. The present study demonstrates a significant improvement in the hydrogen evolution activity of the layered single-crystal photocatalyst Y2Ti2O5S2. Increased performance is obtained through sequential loading of Pt cocatalysts using a two-step process followed by photodeposition of Cr2O3 nanolayers. The stepwise deposition of Pt involved an impregnation-reduction pretreatment with subsequent photodeposition and produced numerous hydrogen production sites while promoting electron capture. The Cr2O3 shells formed on Pt nanoparticles further promoted electron transfer from the Pt to the water and inhibited surface carrier recombination. Importantly, it is also possible to construct a Z-scheme overall water splitting system using the optimized Y2Ti2O5S2 in combination with surface-modified BiVO4 in the presence of [Fe(CN)6]3-/4-, yielding a solar-to-hydrogen energy conversion efficiency of 0.19%. This work provides insights into precise surface modifications of narrow-bandgap photocatalysts as a means of improving the solar water splitting process.

Novel Single Perovskite Material for Visible-Light Photocatalytic CO2 Reduction via Joint Experimental and DFT Study

Developing advanced and economically viable technologies for the capture and utilization of carbon dioxide (CO2) is crucial for sustainable energy production from fossil fuels. Converting CO2 into valuable chemicals and fuels is a promising approach to mitigate atmospheric CO2 levels. Among various methods, photocatalytic reduction stands out for its potential to reduce emissions and produce useful products. Here, novel perovskite ZnMoFeO3 (ZMFO) nanosheets are presented as promising semiconductor photocatalysts for CO2 reduction. Experimental results show that ZMFO has a narrow bandgap, exceptional visible light response, large specific surface area, high crystallinity, and various surface-active sites, leading to an impressive photocatalytic CO2 reduction activity of 24.87 µmolg-1h-1 and strong stability. Theoretical calculations reveal that CO2 conversion into CO and CH4 on the ZMFO surface follows formaldehyde and carbine pathways. This study provides significant insights into designing innovative perovskite oxide-based photocatalysts for economical and efficient CO2 reduction systems.

Strategies for Achieving Carbon Neutrality: Dual-Atom Catalysts in Focus

Carbon neutrality is a fundamental strategy for achieving the sustainable development of human society. Catalyzing CO2 reduction into various high-value-added fuels serves as an effective pathway to achieve this strategic objective. Atom-dispersed catalysts have received extensive attention due to their maximum atomic utilization, high catalytic selectivity, and exceptional catalytic performance. Dual-atom catalysts (DACs), as an extension of single-atom catalysts (SACs), not only retain the advantages of SACs, but also produce many new properties. This review initiates its exploration by elucidating the mechanism of CO2 reduction reaction (CO2RR) from CO2 adsorption and CO2 activation. Then, a comprehensive summary of recently developed preparation methods of DACs is presented. Importantly, the mechanisms underlying the promoted catalytic performance of DACs in comparison to SACs are subjected to a comprehensive analysis from adjustable adsorption capacity, tunable electronic structure, strong synergistic effect, and enhanced spacing effect, elucidating their respective superiorities in CO2RR. Subsequently, the application of DACs in CO2RR is discussed in detail. Conclusively, the prospective trajectories and inherent challenges of CO2RR are expounded upon concerning the continued advancement of DACs. This thorough review not only enhances the comprehension of DACs within CO2RR but also accentuates the prospective developments in the design of sophisticated catalytic materials.

Facet-Dependent Photocatalytic CO2 Reduction on TiO2 Crystals in the Presence of SO2: Role of Surface Hydroxyl

Photocatalytic CO2 reduction to solar energy makes great sense to mitigate the greenhouse effect caused by CO2, and great efforts have been made to promote CO2 conversion efficiency. However, the effect of impurities in the photoreduction of CO2 has received relatively little attention. Here, the different CO2 photoreduction behaviors of TiO2 exposed (101) facet (TiO2-101) and (001) facet (TiO2-001) with an SO2 impurity were investigated. On TiO2-101, SO2 accelerates the deactivation of the catalyst for CO2 photoreduction activity, since SO2 mainly binds to the OHb site of TiO2-101. This site is highly susceptible to the transfer of photogenerated holes, resulting in the rapid generation of SO42-, which occupies the active site and poisons the catalyst. For TiO2-001, SO2 has relatively little negative effect on stability, as SO2 mainly binds to the weak binding site (OHt) of TiO2-001, preventing it from being oxidized to SO42-, which alleviates catalyst deactivation and ensures the continuity of CO2 reduction. This paper provides further insights into the role of SO2 in CO2 photoreduction over distinct TiO2 facets and reveals the importance of facet engineering in the photocatalytic reduction of CO2 from industrial flue gas.

Molecular Heterogeneous Photocatalysts for Visible-Light-Driven CO2 Reduction

Photoreduction of CO2 to high-value chemical fuels presents an effective strategy to reduce reliance on fossil fuels and mitigate climate change. The development of a photocatalyst characterized by superior activity, high selectivity, and good stability is a critical issue for PCR. Molecular heterogeneous photocatalytic systems integrate the advantages of both homogeneous and heterogeneous catalysts, creating a synergistic enhancement effect that increases photocatalytic performance. This review summarizes recent advancements in molecular heterogeneous photocatalysts for CO2 reduction. Much of the discussion focuses on the types of molecular heterogeneous photocatalysts, and their photocatalytic performance in CO2 reduction is summarized. The synthesis strategies for molecular heterogeneous photocatalysts are thoroughly discussed. Finally, the challenges and future prospects of molecular heterogeneous photocatalysts for PCR are addressed.

Band Diagram Insights into the Kinetic and Thermodynamic Engineering of Tandem Photocatalytic Cells

In this work, we theoretically investigate the impact of kinetic and thermodynamic properties on the performance of photocatalytic cells operating in an unassisted tandem configuration, including electron affinity and ionization energies, recombination rates, and reaction rates. To this end, we present general rules and metrics for identifying and isolating the origin of an observed shift in the onset potential at either the photoanode or the photocathode of these devices. The correlation between kinetic and thermodynamic shifts in the onset potential is demonstrated through the use of band diagrams and key comparable features within readily accessible characterization tools: current-voltage plots are taken both under illumination and in the dark and further coupled with Mott-Schottky plots. To illustrate this conceptual framework, a model system comprised of a p-type doped BiVO4 photocathode and an n-type doped BiVO4 photoanode is employed. By varying each of the aforementioned kinetic and thermodynamic parameters in isolation, the manner in which these various mechanisms shift the onset potential is demonstrated. This work intends to showcase how kinetic and thermodynamic effects are distinctly manifested in these commonly used characterization tools and further proposes thermodynamic band-edge engineering as a potentially useful and largely unexplored avenue for possibly improving tandem cell performance, in addition to the conventional approach of optimizing kinetics.

Recent Progress of Three-Dimensional Graphene-Based Composites for Photocatalysis

Converting solar energy into fuels/chemicals through photochemical approaches holds significant promise for addressing global energy demands. Currently, semiconductor photocatalysis combined with redox techniques has been intensively researched in pollutant degradation and secondary energy generation owing to its dual advantages of oxidizability and reducibility; however, challenges remain, particularly with improving conversion efficiency. Since graphene's initial introduction in 2004, three-dimensional (3D) graphene-based photocatalysts have garnered considerable attention due to their exceptional properties, such as their large specific surface area, abundant pore structure, diverse surface chemistry, adjustable band gap, and high electrical conductivity. Herein, this review provides an in-depth analysis of the commonly used photocatalysts based on 3D graphene, outlining their construction strategies and recent applications in photocatalytic degradation of organic pollutants, H2 evolution, and CO2 reduction. Additionally, the paper explores the multifaceted roles that 3D graphene plays in enhancing photocatalytic performance. By offering a comprehensive overview, we hope to highlight the potential of 3D graphene as an environmentally beneficial material and to inspire the development of more efficient, versatile graphene-based aerogel photocatalysts for future applications.

Design and Optimization of Nanoporous Materials as Catalysts for Oxygen Evolution Reaction-A Review

With the growing demand for new energy sources, electrochemical water splitting for hydrogen production is a technology that must be vigorously promoted. Therefore, to improve the efficiency of the oxygen evolution reaction (OER) at the anode, high-performance OER catalysts are essential. Given their advantages in electrocatalysis, nanoporous materials have garnered considerable attention in previous studies for OER applications. This review provides a comprehensive overview of various strategies to optimize active site utilization in nanoporous materials. These strategies include regulating pore size and porosity, constructing hierarchical nanoporous structures, and enhancing material conductivity. Additionally, it covers approaches to boost the intrinsic OER activity of nanoporous materials, such as tuning the composition of anions and cations, creating vacancies, constructing interfaces, and forming boundary active sites. While nanoporous materials offer significant potential for advancing OER, challenges remain, including difficulties in quantifying activity within nanopores, the unclear impact of nanoporous material morphology, challenges in accessing nanopore interiors with in situ techniques, and a lack of theoretical calculations on pore structure. However, these challenges also present opportunities, and we hope this review provides a fresh perspective to inspire future research.

Applications of Ni-Based Catalysts in Photothermal CO2 Hydrogenation Reaction

Heterogeneous CO2 hydrogenation catalytic reactions, as the strategies for CO2 emission reduction and green carbon resource recycling, play important roles in alleviating global warming and energy shortages. Among these strategies, photothermal CO2 hydrogenation technology has become one of the hot catalytic technologies by virtue of the synergistic advantages of thermal catalysis and photocatalysis. And it has attracted more and more researchers' attentions. Various kinds of effective photothermal catalysts have been gradually discovered, and nickel-based catalysts have been widely studied for their advantages of low cost, high catalytic activity, abundant reserves and thermal stability. In this review, the applications of nickel-based catalysts in photothermal CO2 hydrogenation are summarized. Finally, through a good understanding of the above applications, future modification strategies and design directions of nickel-based catalysts for improving their photothermal CO2 hydrogenation activities are proposed.

Thermal and/or Microwave Treatment: Insight into the Preparation of Titania-Based Materials for CO2 Photoreduction to Green Chemicals

Titanium dioxide was synthesized via hydrolysis of titanium (IV) isopropoxide using a sol-gel method, under neutral or basic conditions, and heated in the microwave-assisted solvothermal reactor and/or high-temperature furnace. The phase composition of the prepared samples was determined using the X-ray diffraction method. The specific surface area and pore volumes were determined through low-temperature nitrogen adsorption/desorption studies. The photoactivity of the samples was tested through photocatalytic reduction of carbon dioxide. The composition of the gas phase was analyzed using gas chromatography, and hydrogen, carbon oxide, and methane were identified. The influence of pH and heat treatment on the physicochemical properties of titania-based materials during photoreduction of carbon dioxide have been studied. It was found that the photocatalysts prepared in neutral environment were shown to result in a higher content of hydrogen, carbon monoxide, and methane in the gas phase compared to photocatalysts obtained under basic conditions. The highest amounts of hydrogen were detected in the processes using photocatalysts heated in the microwave reactor, and double-heated photocatalysts.

Recent Progress of Ion-Modified TiO2 for Enhanced Photocatalytic Hydrogen Production

Harnessing solar energy to produce hydrogen through semiconductor-mediated photocatalytic water splitting is a promising avenue to address the challenges of energy scarcity and environmental degradation. Ever since Fujishima and Honda's groundbreaking work in photocatalytic water splitting, titanium dioxide (TiO2) has garnered significant interest as a semiconductor photocatalyst, prized for its non-toxicity, affordability, superior photocatalytic activity, and robust chemical stability. Nonetheless, the efficacy of solar energy conversion is hampered by TiO2's wide bandgap and the swift recombination of photogenerated carriers. In pursuit of enhancing TiO2's photocatalytic prowess, a panoply of modification techniques has been explored over recent years. This work provides an extensive review of the strategies employed to augment TiO2's performance in photocatalytic hydrogen production, with a special emphasis on foreign dopant incorporation. Firstly, we delve into metal doping as a key tactic to boost TiO2's capacity for efficient hydrogen generation via water splitting. We elaborate on the premise that metal doping introduces discrete energy states within TiO2's bandgap, thereby elevating its visible light photocatalytic activity. Following that, we evaluate the role of metal nanoparticles in modifying TiO2, hailed as one of the most effective strategies. Metal nanoparticles, serving as both photosensitizers and co-catalysts, display a pronounced affinity for visible light absorption and enhance the segregation and conveyance of photogenerated charge carriers, leading to remarkable photocatalytic outcomes. Furthermore, we consolidate perspectives on the nonmetal doping of TiO2, which tailors the material to harness visible light more efficiently and bolsters the separation and transfer of photogenerated carriers. The incorporation of various anions is summarized for their potential to propel TiO2's photocatalytic capabilities. This review aspires to compile contemporary insights on ion-doped TiO2, propelling the efficacy of photocatalytic hydrogen evolution and anticipating forthcoming advancements. Our work aims to furnish an informative scaffold for crafting advanced TiO2-based photocatalysts tailored for water-splitting applications.

Z-scheme heterojunction g-C3N4-TiO2 reinforced chitosan/poly(vinyl alcohol) film: Efficient and recyclable for fruit packaging

Nanoparticles-loaded bio-based polymers have emerged as a sustainable substitute to traditional oil-based packaging materials, addressing the challenges of limited recyclability and significant environmental impact. However, the functionality and efficiency of nanoparticles have a significant impact on the application of bio-based composite films. Herein, graphitic carbon nitride (g-C3N4) and titanium dioxide (TiO2) coupled photocatalyst (g-C3N4-TiO2) was prepared by one-step calcination and introduced into chitosan (CS) and polyvinyl alcohol (PVA) solution to fabricate g-C3N4-TiO2/CS/PVA green renewable composite film via solution casting method. The results demonstrated the successful preparation of a Z-scheme heterojunction g-C3N4-TiO2 with exceptional photocatalytic activity. Furthermore, the incorporation of heterojunction enhanced mechanical properties, water barrier, and ultraviolet (UV) resistance properties of the fresh-keeping film. The g-C3N4-TiO2/CS/PVA composite film exhibited superior photocatalytic antibacterial preservation efficacy on strawberries under LED light, with a prolonged preservation time of up to 120 h, when compared to other films such as polyethylene (PE), CS/PVA, g-C3N4/CS/PVA, and TiO2/CS/PVA. In addition, the composite film has good recyclability and renewability. This work is expected to have great potential for low-cost fruit preservation and sustainable packaging, which also contributes to environmental protection.

Sc-Modified C3N4 Nanotubes for High-Capacity Hydrogen Storage: A Theoretical Prediction

Utilizing hydrogen as a viable substitute for fossil fuels requires the exploration of hydrogen storage materials with high capacity, high quality, and effective reversibility at room temperature. In this study, the stability and capacity for hydrogen storage in the Sc-modified C3N4 nanotube are thoroughly examined through the application of density functional theory (DFT). Our finding indicates that a strong coupling between the Sc-3d orbitals and N-2p orbitals stabilizes the Sc-modified C3N4 nanotube at a high temperature (500 K), and the high migration barrier (5.10 eV) between adjacent Sc atoms prevents the creation of metal clusters. Particularly, it has been found that each Sc-modified C3N4 nanotube is capable of adsorbing up to nine H2 molecules, and the gravimetric hydrogen storage density is calculated to be 7.29 wt%. It reveals an average adsorption energy of -0.20 eV, with an estimated average desorption temperature of 258 K. This shows that a Sc-modified C3N4 nanotube can store hydrogen at low temperatures and harness it at room temperature, which will reduce energy consumption and protect the system from high desorption temperatures. Moreover, charge donation and reverse transfer from the Sc-3d orbital to the H-1s orbital suggest the presence of the Kubas effect between the Sc-modified C3N4 nanotube and H2 molecules. We draw the conclusion that a Sc-modified C3N4 nanotube exhibits exceptional potential as a stable and efficient hydrogen storage substrate.