Resolidified Chalcogen Precursors for High-Quality 2D Semiconductor Growth

Two-dimensional (2D) semiconductors including transition metal dichalcogenides (TMDCs) have gained attention in optoelectronics for their extraordinary properties. However, the large amount and locally distributed lattice defects affect the optical properties of 2D TMDCs, and the defects originate from unstable factors in the synthesis process. In this work, we develop a method of pre-melting and resolidification of chalcogen precursors (sulfur and selenium), namely resolidified chalcogen, as precursor for the chemical vapor deposition growth of TMDCs with ultrahigh quality and uniformity. Taking WS₂ as an example, the monolayer WS₂ shows uniform fluorescence intensity and a small full-width at half-maximum of photoluminescence peak at low temperatures with an average value of 13.6±1.9 meV. The defect densities at the interior and edge region are both low and comparable, i.e., (9±3)×10¹² cm⁻² and (10±4)×10¹² cm⁻², indicating its high structural quality and uniformity. This method is universal in growing high quality monolayer MoS₂, WSe₂, MoSe₂, and will benefit their applications.     

Hydrothermal synthesis of TiO2 nanorods: formation chemistry,growth mechanism,and tailoring of surface properties for photocatalytic activities

Titanium dioxide (TiO₂) is one of the best semiconductor photocatalysts with optical band gap of 3.2 eV. The optical band gap and photocatalytic properties could be further tuned by tailoring shape, size, composition, and morphology of the nanostructures. Hydrothermal synthesis methods have been applied to produce well-controlled nanostructured TiO₂ materials with different morphologies and improved optoelectronic properties. Among various morphologies, one-dimensional (1D) TiO₂ nanostructures are of great importance in the field of energy, environmental, and biomedical because of the directional transmission properties resulting from their 1D geometry. Particularly, TiO₂ nanorods (NRs) have gained special attention because of their densely packed structure, quantum confinement effect, high aspect ratio, and large specific surface area that could specially improve the directional charge transmission efficiency. This results in the effective photogenerated charge separation and light absorption, which are really important for potential applications of TiO₂-based materials for photocatalytic and other important applications. In this review, hydrothermal syntheses of TiO₂ NRs including the formation chemistry and the growth mechanism of NRs under different chemical environments and effects of various synthesis parameters (pH, reaction temperature, reaction time, precursors, solvents etc.) on morphology and optoelectronic properties have been discussed. Recent developments in the hydrothermal synthesis of TiO₂ NRs and tailoring of their surface properties through various modification strategies such as defect creation, doping, sensitization, surface coating, and heterojunction formation with various functional nanomaterials (plasmonic, oxide, quantum dots, graphene-based nanomaterials, etc.) have been reported to improve the photocatalytic activities. Furthermore, applications of TiO₂ NRs/tailored TiO₂ NRs as superior photocatalysts in degradation of organic pollutants and bacterial disinfection have been discussed with emphasis on mechanisms of action and recent advances in the fields.     

Tailored indium sulfide-based materials for solar-energy conversion and utilization

To relieve the growing pressure originated from the energy shortage and environmental issues, solar-energy conversion into chemical or electrical energy has undergone an unprecedented development as a promising strategy in recent years. Indium sulfide (In₂S₃), an efficient visible-light harvester, has been extensively investigated in the field of photoconversion, owing to the fascinating merits including superior photo-absorption coefficient, photoelectric sensitivity, favorable carrier mobility, moderate band gap, excellent stability, and low toxicity. To take full advantage of these properties and further expand beyond the existing short board like low quantum efficiency, various In₂S₃-based functional nanostructures like nanoparticles, nanotubes, atomic two-dimensional sheets, and nanosheets-assembled complexes have been developed. Meanwhile, pleasurable characters of In₂S₃ have been modulated via defective engineering, doping, and hybridization (with inorganic materials or bio-molecules). Gratifyingly, In₂S₃-based photocatalytic, photoelectrocatalytic and photovoltaic systems have made significant impact on the field of energy and environmental issues. Therefore, this review provides an overview of crystal and morphologic structures of pristine In₂S₃ as well as many outstanding properties. Moreover, the pristine In₂S₃ and its derivatives with diverse synthesis routes are systematically summarized. Further, the advancement of In₂S₃-based photocatalytic, photoelectrocatalytic and photovoltaic systems, especially in environmental decontamination, artificial photosynthesis for renewable fuels and solar cells, are highlighted in detail. Ultimately, we conclude with a summary and propose some invigorating perspectives on the challenges from atomic (or macroscopical) structure modulation in material nature, photochemical behavior understanding to solar photovoltaic applications at the forefront of this research platform.     

Photocatalytic active silver organic framework: Ag(I)-MOF and its hybrids with silver cyanamide

Probing into the new heterostructure based on metal–organic frameworks (MOFs) and optimizing their photocatalytic efficiency under solar energy irradiation are one of hot topics in extending applications of MOFs in photocatalytic technology. Inspired by the excellent visible-light responses and photocatalytic activities of inorganic silver salts, in this work, we focused on the construction of hybrid photocatalysts involving Ag-MOF and silver cyanamide (Ag₂NCN). Two opposite in situ synthesis routes were adopted, which are hydrothermally producing Ag-MOF in the presence of Ag₂NCN (route A) or precipitating Ag₂NCN in the existence of Ag-MOF (route B), and the mass ratio of Ag₂NCN vs. Ag-MOF was optimized. The morphology and structure character show that the synthetic routes have no obvious influences on the crystal structure, but change the morphology and size of final hybrid photocatalysts. The photocatalytic degradation of Rhodamine B under simulated solar energy has been tested to evaluate the photocatalytic activities for resulting hybrids. Compared to single Ag-MOF and Ag₂NCN, the enhanced photocatalytic rates are represented by the hybrids. The electrochemical analyses and the active species trapping experiments were conducted to clarify the photocatalytic mechanism for resulting hybrids. The good recycling photocatalytic results indicate the prospect applications of Ag-MOF based hybrid photocatalysts.     

Rational Design and Application of Covalent Organic Frameworks for Solar Fuel Production

Harnessing solar energy and converting it into renewable fuels by chemical processes, such as water splitting and carbon dioxide (CO₂) reduction, is a highly promising yet challenging strategy to mitigate the effects arising from the global energy crisis and serious environmental concerns. In recent years, covalent organic framework (COF)-based materials have gained substantial research interest because of their diversified architecture, tunable composition, large surface area, and high thermal and chemical stability. Their tunable band structure and significant light absorption with higher charge separation efficiency of photoinduced carriers make them suitable candidates for photocatalytic applications in hydrogen (H₂) generation, CO₂ conversion, and various organic transformation reactions. In this article, we describe the recent progress in the topology design and synthesis method of COF-based nanomaterials by elucidating the structure-property correlations for photocatalytic hydrogen generation and CO₂ reduction applications. The effect of using various kinds of 2D and 3D COFs and strategies to control the morphology and enhance the photocatalytic activity is also summarized. Finally, the key challenges and perspectives in the field are highlighted for the future development of highly efficient COF-based photocatalysts.     

Recent advances in kaolinite-based material for photocatalysts

The composite catalytic materials based on the mineral kaolinite are considered to be a potential approach for solving global energy scarcity and environmental pollution, which have excellent catalytic performance, low cost and excellent chemical stability. However, pure kaolinite does not have visible light absorption ability and cannot be used as a potential photocatalytic material. Fortunately, the unique physical and chemical properties of kaolinite can be acted as a good semiconductor carrier. Herein, this paper firstly presents the mineralogical characteristics of kaolinite. Next, kaolinite-based photocatalysts (such as TiO₂/kaolinite, g-C₃N₄/kaolinite, g-C₃N₄/TiO₂/kaolinite, ZnO) are discussed in detail from the formation of heterostructures, synthesis-modification methods, photocatalytic mechanisms, and electron transfer pathways. Furthermore, the specific role of kaolinite in photocatalytic materials is summarized and discussed. In addition, the photocatalytic applications of kaolinite-based photocatalysts in the fields of water decomposition, pollutant degradation, bacterial disinfection are reviewed. However, the modification of kaolinite is hard, the manufacture of a large number of kaolinite-based photocatalysts is difficult, the cost of doping noble metals is expensive, and the utilization rate of visible light is low, which limits its application in industrial practice. Finally, this paper presents some perspectives on the future development of kaolinite-based photocatalysts.     

TiO2 photocatalysis: Design and applications

TiO₂ photocatalysis is widely used in a variety of applications and products in the environmental and energy fields, including self-cleaning surfaces, air and water purification systems, sterilization, hydrogen evolution, and photoelectrochemical conversion. The development of new materials, however, is strongly required to provide enhanced performances with respect to the photocatalytic properties and to find new uses for TiO₂ photocatalysis. In this review, recent developments in the area of TiO₂ photocatalysis research, in terms of new materials from a structural design perspective, have been summarized. The dimensionality associated with the structure of a TiO₂ material can affect its properties and functions, including its photocatalytic performance, and also more specifically its surface area, adsorption, reflectance, adhesion, and carrier transportation properties. We provide a brief introduction to the current situation in TiO₂ photocatalysis, and describe structurally controlled TiO₂ photocatalysts which can be classified into zero-, one-, two-, and three-dimensional structures. Furthermore, novel applications of TiO₂ surfaces for the fabrication of wettability patterns and for printing are discussed.     

Solar Light Responsive Graphitic Carbon Nitride Coupled Porphyrin Photocatalyst that Uses for Solar Fine Chemical Production

Photocatalysis is a defendable manner for production of several organic chemicals, energy and its storage from solar energy. For the evolution of metal free, cost-effective catalyst a 2D composite has been appear as a photocatalyst. Here, we had reported the synthesis of a light harvesting composite as a photocatalyst which was assembled by a poly-condensation mechanism between graphitic carbon nitride and tetrakis(4-nitrophenyl) porphyrin and the resulting composite manifest the excellent light harvesting properties, suitable energy band and low charge recombination. The photocatalyst [(NO₂)₄TPP@g-C₃N₄] enables the efficient photocatalytic production of nicotinamide adenine dinucleotide (NADH) from consumed NAD⁺ also the production of organic chemicals like 4-methoxybenzylimines from 4-methoxybenzylamines. The photocatalytic efficiency of the photocatalyst was estimated by the percentage of NADH regeneration and the percentage yield of organic transformations. It shows the tetrakis(4-nitrophenyl) porphyrin could enhance the charge transfer capacity of graphitic carbon nitride which shows excellent photocatalysis activities and organic transformations.     

Template‐Free Synthesis of Core–Shell TiO2 Microspheres Covered with High‐Energy {116}‐Facet‐Exposed N‐Doped Nanosheets and Enhanced Photocatalytic Activity under Visible Light

Core–shell TiO₂ microspheres possess a unique structure and interesting properties, and therefore, they have received much attention. The high‐energy facets of TiO₂ also are being widely studied for the high photocatalytic activities they are associated with. However, the synthesis of the core–shell structure is difficult to achieve and requires multiple‐steps and/or is expensive. Hydrofluoric acid (HF), which is highly corrosive, is usually used in the controlling high‐energy facet production. Therefore, it is still a significant challenge to develop low‐temperature, template‐free, shape‐controlled, and relative green self‐assembly routes for the formation of core–shell‐structured TiO₂ microspheres with high‐energy facets. Here, we report a template‐ and hydrofluoric acid free solvothermal self‐assembly approach to synthesize core–shell TiO₂ microspheres covered with high‐energy {116}‐facet‐exposed nanosheets, an approach in which 1,4‐butanediamine plays a key role in the formation of nanosheets with exposed {116} facets and the doping of nitrogen in situ. In the structure, nanoparticle aggregates and nanosheets with {116} high‐energy facets exposed act as core and shell, respectively. The photocatalytic activity for degradation of 2,4,6‐tribromophenol and Rhodamine B under visible irradiation and UV/Vis irradiation has been examined, and improved photocatalytic activity under visible light owing to the hierarchical core–shell structure, {116}‐plane‐oriented nanosheets, in situ N doping, and large surface areas has been found.     

Z‐Scheme 2D/2D Heterojunction of Black Phosphorus/Monolayer Bi2WO6 Nanosheets with Enhanced Photocatalytic Activities

Black phosphorus (BP), a star‐shaped two‐dimensional material, has attracted considerable attention owing to its unique chemical and physical properties. BP shows great potential in photocatalysis area because of its excellent optical properties; however, its applications in this field have been limited to date. Now, a Z‐scheme heterojunction of 2D/2D BP/monolayer Bi₂WO₆ (MBWO) is fabricated by a simple and effective method. The BP/MBWO heterojunction exhibits enhanced photocatalytic performance in photocatalytic water splitting to produce H₂ and NO removal to purify air; the highest H₂ evolution rate of BP/MBWO is 21042 μmol g^?1, is 9.15 times that of pristine MBWO and the NO removal ratio was as high as 67 %. A Z‐scheme photocatalytic mechanism is proposed based on monitoring of ^.O₂^?, ^.OH, NO₂, and NO₃^? species in the reaction. This work broadens applications of BP and highlights its promise in the treatment of environmental pollution and renewable energy issues.     

Graphene/inorganic nanocomposites: Evolving photocatalysts for solar energy conversion for environmental remediation

Current energy crisis and environmental issues, including depletion of fossil fuels, rapid industrialization, and undesired CO₂ emission resulting in global warming has created havoc for the global population and significantly affected the quality of life. In this scenario the environmental problems in the forefront of research priorities. Development of renewable energy resources particularly the efficient conversion of solar light to sustainable energy is crucial in addressing environmental problems. In this regard, the synthesis of semiconductors-based photocatalysts has emerged as an effective tool for different photocatalytic applications and environmental remediation. Among different photocatalyst options available, graphene and graphene derivatives such as, graphene oxide (GO), highly reduced graphene oxide (HRG), and doped graphene (N, S, P, B-HRG) have become rising stars on the horizon of semiconductors-based photocatalytic applications. Graphene is a single layer of graphite consisting of a unique planar structure, high conductivity, greater electron mobility, and significantly very high specific surface area. Besides, the recent advancements in synthetic approaches have led to the cost-effective production of graphene-based materials on a large-scale. Therefore, graphene-based materials have gained considerable recognition for the production of semiconducting photocatalysts involving other semiconducting materials. The graphene-based semiconductors photocatalysts surpasses electron-holes pairs recombination rate and lowers the energy band gap by tailoring the valence band (VB) and conduction band (CB) leading to the enhanced photocatalytic performance of hybrid photocatalysts. Herein, we have summarized the latest developments in designing and fabrication of graphene-based semiconducting photocatalysts using a variety of commonly applied methods such as, post-deposition methods, in-situ binding methods, hydrothermal and/or solvothermal approaches. In addition, we will discuss the photocatalytic properties of the resulting graphene-based hybrid materials for various environmental remediation processes such as; (i) clean H₂ fuel production, photocatalytic (ii) pollutants degradation, (iii) photo-redox organic transformation and (iv) photo-induced CO₂ reduction. On the whole, by the inclusion of more than 300 references, this review possibly covered in detail the aspects of graphene-based semiconductor photocatalysts for environmental remediation processes. Finally, the review will conclude a short summary and discussion about future perspectives, challenges and new directions in these emerging areas of research.     

Pure and modified TiO2 photocatalysts and their environmental applications

Semiconductor photocatalysis is a process that harnesses light energy in chemical conversions. In particular, its applications to environmental remediation have been intensively investigated. The characteristics of TiO₂, the most popular photocatalyst, is briefly described and selected studies on the degradation/conversion of various recalcitrant pollutants using pure and modified TiO₂ photocatalysts, which were carried out in this group, are reviewed. Photocatalytic reactions are multi-phasic and take place at interfaces of not only water/TiO₂ and air/TiO₂ but also solid/TiO₂. Examples of photocatalytic reactions of various organic and inorganic substrates that are converted through the photocatalytic oxidation or reduction are introduced. TiO₂ has been modified in various ways to improve its photocatalytic activity. Surface modifications of TiO₂ that include surface platinization, surface fluorination, and surface charge alteration are discussed and their applications to pollutants degradation are also described in detail.     

Morphology-Controlled Synthesis and Applications of Silver Halide Photocatalytic Materials

Semiconductor photocatalysis is considered to be one of the most promising technologies to solve the worldwide environmental and energy issues. In recent years, silver halide (AgX)-based photocatalytic materials have received increasing research attention owing to its excellent visible light-driven photocatalytic performances in the applications of organic pollutant degradation, H₂/O₂ generation, and disinfection. AgX-based materials used in photocatalytic fields can be classified into three categories: AgX (Ag/AgX), AgX composites, and supported AgX materials. For the AgX (Ag/AgX) photocatalysts, it has been widely accepted that the final photocatalytic performances of photocatalysts are severely dependent on their morphological structures as well as exposed crystal facets. As a result, considerable efforts have been devoted to fabricating different morphological AgX photocatalysts as well as exploring the relationship between the morphological structures and photocatalytic performances. In this review, we mainly introduce the recent developments made in fabricating morphology and facet-controllable AgX (Ag/AgX) photocatalytic materials. Moreover, this review also deals with the photocatalytic mechanism and applications of AgX (Ag/AgX) and supported AgX materials.     

Recent developments in the use of metal oxides for photocatalytic degradation of pharmaceutical pollutants in water—a review

In recent years, metal oxide semiconductors have been explored as photocatalysts for the degradation of organic contaminants in water/wastewater. The uniqueness of these oxide materials is in their ability to harness energy in the UV/Vis range, their relative ease of synthesis, low cost, and their general high surface ratio to mass, etc. Thus, these materials have consequently drawn much profound interest in environment applications, particularly pharmaceutical drugs for photocatalytic degradation. Furthermore, the non-toxic nature of most metal oxide semiconductors means they are convenient for water treatment works, resulting in safe drinking water for humans and safe environments for aquatic mammals. Pharmaceuticals are emerging pollutants that are increasingly being found in water systems. They have been detrimental to the human and animal health. In this article, pharmaceutical drugs abatement from water via photocatalysis process using oxide-based advanced metals such as TiO₂, ZnO, Fe₂O₃,WO₃, and Bi₂WO₆ is discussed. Degradation of various drugs at laboratory scale have been assessed and examples cited. Various approaches to metal oxides modifications and synthesis methods to improve degradation efficiency have also been discussed. Effects of experimental/operational parameters in the degradation process have been compiled and compared. Finally, a short preview of degradation of pharmaceuticals pilot scales is also highlighted.     

From Synthesis to Applications: Copper Calcium Titanate (CCTO) and its Magnetic and Photocatalytic Properties

Investigations focusing on electrical energy storage capacitors especially the dielectric ceramic capacitors for high energy storage density are attracting more and more attention in the recent years. Ceramic capacitors possess a faster charge-discharge rate and improved mechanical and thermal properties compared with other energy storage devices such as batteries. The challenge is to obtain ceramic capacitors with outstanding mechanical, thermal and storage properties over large temperature and frequencies ranges. ABO₃ as a type of perovskites showed a strong piezoelectric, dielectric, pyroelectric, and electro-optic properties useful as energy storage and environmental devices. CaCu₃Ti₄O₁₂ (CCTO) perovskite with cubic lattice (Im3 symmetry) was discovered to have a colossal dielectric constant (10⁴) that is stable over a wide range of frequencies (10 Hz–1 MHz) and temperature independence (100–300 K). The origin of this high dielectric constant is not fully established, specially because it is the same for single crystal and thin films. In this review, the history of CCTO will be introduced. The synthesis and the sintering approaches, the dopant elements used as well as the applications of CCTO will be reported. In addition to dielectrical properties useful to energy storage devices; CCTO could serve as photocatalytic materials with a very good performance in visible light.     

Controlled synthesis of monodisperse sub-100 nm hollow SnO2 nanospheres: a template- and surfactant-free solution-phase route, the growth mechanism, optical properties, and application as a photocatalyst

Controlled synthesis of low‐dimensional materials, such as nanoparticles, nanorods, and hollow nanospheres, is vitally important for achieving desired properties and fabricating functional devices. We report a systematic investigation of the growth of low‐dimensional sub‐100 nm SnO₂ hollow nanostructures by a mild template‐ and surfactant‐free hydrothermal route, aiming to achieve precise control of morphology and size. The starting materials are potassium stannate and urea in an ethylene glycol (EG)/H₂O system. We found the size of the SnO₂ hollow nanospheres can be controlled by simply adjusting the urea concentration. Investigation of the mechanism of formation of the SnO₂ hollow nanospheres revealed that reaction time, urea concentration, and reaction temperature make significant contributions to the growth of hollow nanospheres. On switching the solvent from EG/H₂O to H₂O or ethanol, the SnO₂ nanostructures changed from nanospheres to ultrafine nanorods and nanoparticles. On the basis of reaction parameter dependent experiments, oriented self‐assembly and subsequent evacuation through Ostwald ripening are proposed to explain the formation of hollow nanostructures. Their size‐dependent optical properties, including UV/Vis absorption spectra and room‐temperature fluorescence spectra, were also studied. Moreover, the studies on the photocatalytic property demonstrate that the fabricated hollow structures have slightly enhanced photocatalytic degradation activity for rhodamine B when exposed to mercury light irradiation compared to solid SnO₂ nanospheres under the same conditions. The synthesized tin oxide nanoparticles display high photocatalytic efficiency and have potential applications for cleaning polluted water in the textile industry.     

石墨相氮化碳量子点的制备及应用的研究进展

近年来,石墨相氮化碳(g-C3N4)因其稳定的物理化学性能和良好的生物相容性而受到研究者关注。与块体g-C3N4相比,石墨相氮化碳量子点(g-CNQDs)尺寸更小、荧光效率更高,且具有量子限域效应,因此拥有特殊的理化性质与更好的光催化性能。本文主要从g-CNQDs的制备策略和应用展开讨论,着重综述了微波辅助法、低温固相法、热化学腐蚀法和电化学刻蚀法制备g-CNQDs,以及g-CNQDs在催化剂、离子检测、生物传感与诊疗等领域的最新应用研究进展;指出了目前g-CNQDs在性质、制备和应用等研究方面的重点和难点;最后对g-CNQDs存在的问题和未来的发展方向作出了展望。     

Recent advances in 1D nanostructured catalysts for photothermal and photocatalytic reduction of CO2

The development of photocatalysts that can efficiently convert CO₂ into other valuable chemicals via photocatalytic and photothermal processes is critical to the current energy and climate change problems. However, low separation of charge carriers, short light absorption, and low activation of CO₂ molecules in photocatalysis limit the catalysts’ performance. Designing 1D heterostructures containing multiple materials can be a viable solution as their unique properties, such as high surface area, short diffusion paths of charge carriers, and enhanced light absorption properties, can potentially promote the reaction rate and product selectivity. In this review, we summarize the general features of heterostructures involving nanotubes, nanowires, nanorods, and nanobelts. Next, the main synthesis strategies are briefly highlighted, followed by the most important findings concerning their catalytic activity in the photothermal and photocatalytic CO₂ reduction processes. The article concludes with some of the current challenges and potential solutions.     

石墨相氮化碳的化学合成及应用

石墨相氮化碳(g-C₃N₄)具有独特的电子结构和优异的化学稳定性, 近年来不仅被作为不含金属组分的催化剂和催化剂载体, 广泛地应用于有机官能团的选择性转换、光催化分解水、氧还原和Au、Pd、Ag、Pt等贵金属的负载, 还被作为绿色储能材料和硬模板剂用于H₂、CO₂的存储和纳米金属氮(氧)化物的制备等, 在能源和材料相关领域逐渐引起人们的关注. 本文将从材料的制备和应用角度,综述国内外同行近年来在g-C₃N₄研究中所取得的一些重要进展, 并对其未来发展趋势,特别是在能源和环境领域中的应用进行了展望.     

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.