Rare-Earth Single-Atom La-N Charge-Transfer Bridge on Carbon Nitride for Highly Efficient and Selective Photocatalytic CO2 Reduction

Optimizing the semiconductor–metal-single-atom interaction for photocatalytic reactivity

Metal single-atom (MSA) catalysts with 100% metal atom utilization and unique electronic properties are attractive cocatalysts for efficient photocatalysis when coupled with semiconductors. Owing to the absence of a metal-metal bond, MSA sites are exclusively coordinated with the semiconductor photocatalyst, featuring a chemical-bond-driven tunable interaction between the semiconductor and the metal single atom. This semiconductor-MSA interaction is a platform that can facilitate the separation/transfer of photogenerated charge carriers and promote the subsequent catalytic reactions. In this Review, we first introduce the fundamental physicochemistry related to the semiconductor-MSA interaction. We highlight the ligand effect on the electronic structures, catalytic properties and functional mechanisms of the MSA cocatalyst through the semiconductor-MSA interaction. Then, we categorize the state-of-the-art experimental and theoretical strategies for the construction of the efficient semiconductor-MSA interaction at the atomic scale for a wide range of photocatalytic reactions. The examples described include photocatalytic water splitting, CO₂ reduction and organic synthesis. We end by outlining strategies on how to further advance the semiconductor-MSA interaction for complex photocatalytic reactions involving multiple elementary steps. We provide atomic and electronic-scale insights into the working mechanisms of the semiconductor-MSA interaction and guidance for the design of high-performance semiconductor-MSA interface photocatalytic systems.

Effect of Light and Heavy Rare Earth Doping on the Physical Structure of Bi2O2CO3 and Their Performance in Photocatalytic Degradation of Dimethyl Phthalate

In order to solve the problem of environmental health hazards caused by phthalate esters, a series of pure Bi2O2CO3 and light (La, Ce, Pr, Nd, Sm and Eu) and heavy (Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) rare earth-doped Bi2O2CO3 samples were prepared by hydrothermal method. The crystalline phase composition and physical structure of the samples calcined at 300 °C were studied, and we found that the rare earth ion doping promoted the transformation of Bi2O2CO3 to β-Bi2O3 crystalline phase, thus obtaining a mixed crystal phase photocatalyst constituted by rare earth-ion-doped Bi2O2CO3/β-Bi2O3. The Bi2O3/Bi2O2CO3 heterostructure had a lower band gap and more efficient charge transfer. The fabricated samples were applied to the photocatalytic degradation of dimethyl phthalate (DMP) under a 300 W tungsten lamp, and it was found that the rare earth ion doping enhanced the photocatalytic degradation activity of DMP, in which the heavy rare earth of Er-doped sample reached 78% degradation for DMP at 150 min of light illumination. In addition, the doping of rare earths resulted in a larger specific surface area and a stronger absorption of visible light. At the same time, the formation of Bi2O2CO3/β-Bi2O3 heterogeneous junction enhanced the separation efficiency of photogenerated electrons and holes.

Phosphorus Tailors the d-Band Center of Copper Atomic Sites for Efficient CO2 Photoreduction under Visible-Light Irradiation

Photoreduction of CO₂ into solar fuels has received great interest, but suffers from low catalytic efficiency and poor selectivity. Herein, two single-Cu-atom catalysts with unique Cu configurations in phosphorus-doped carbon nitride (PCN), namely, Cu₁ N₃ @PCN and Cu₁ P₃ @PCN were fabricated via selective phosphidation, and tested in visible light-driven CO₂ reduction by H₂ O without sacrificial agents. Cu₁ N₃ @PCN was exclusively active for CO production with a rate of 49.8 μmol_CO  g_cat ^-1  h^-1 , outperforming most polymeric carbon nitride (C₃ N₄ ) based catalysts, while Cu₁ P₃ @PCN preferably yielded H₂ . Experimental and theoretical analysis suggested that doping P in C₃ N₄ by replacing a corner C atom upshifted the d-band center of Cu in Cu₁ N₃ @PCN close to the Fermi level, which boosted the adsorption and activation of CO₂ on Cu₁ N₃ , making Cu₁ N₃ @PCN efficiently convert CO₂ to CO. In contrast, Cu₁ P₃ @PCN with a much lower Cu 3d electron energy exhibited negligible CO₂ adsorption, thereby preferring H₂ formation via photocatalytic H₂ O splitting.

Direct Z-scheme mediated SmVO4/UiO-66-NH2 heterojunction nanocomposite for the degradation of antibiotic tetracycline hydrochloride molecules under sunlight

The use of tetracycline hydrochloride (TCH) for veterinary, human therapy, and agriculture has risen in the past few decades, making it to become one of the most exploited antibiotics. However, TCH residue in the environment is causing issues related to the evolution of antibiotic-resistant bacteria. To address such a problem, photodegradation offers a potential solution to decompose these pollutants in wastewater and thereby mitigates negative environmental impacts. In this context, the research focuses on the use of the rare-earth metal oxide samarium orthovanadate (SmVO₄) with nanorod structure, coupled with UiO-66-NH₂ for the photocatalytic degradation. Their photocatalytic activity to degrade antibiotic TCH molecules is explored under simulated solar light irradiation. The integration of UiO-66-NH₂ with SmVO₄ enhanced the light absorption, recombination resistance, carrier lifetime (from 0.382 to 0.411 ns) and specific surface area (from 67.17 to 246 m²/g) of the composite system as confirmed from multiple analyses. The obtained results further indicated that SmVO₄/UiO-66-NH₂ nanocomposites could form a direct Z-scheme based heterojunction. Such mechanism of charge transfer leads to the effective degradation of TCH molecules up to 50% in 90 min under solar light, while it is degraded only 30% in the case of bare-SmVO₄ nanorods. In this work, the incorporation of UiO-66-NH₂ positively influences photoelectrochemical properties and improves the overall photoredox properties of SmVO₄ for the degradation of complex compounds like antibiotic TCH molecules. Therefore, UiO-66-NH₂ can be proposed as an effective material to sensitize the rare-earth based photocatalytic material.

Rare-Earth Single-Atom Catalysts: A New Frontier in Photo/Electrocatalysis

Single-atom catalysts (SACs) provide well-defined active sites with 100% atom utilization, and can be prepared using a wide range of support materials. Therefore, they are attracting global attention, especially in the fields of energy conversion and storage. To date, research has focused on transition-metal and precious-metal-based SACs. More recently, rare-earth (RE)-based SACs have emerged as a new frontier in photo/electrocatalysis owing to their unique electronic structure arising from the spin-orbit coupling of the 4f and valence orbitals, unsaturated coordination environment, and unique behavior as charge-transport bridges. However, a systematic review on the role of the RE active sites, catalytic mechanisms, and synthetic methods for RE SACs is lacking. Therefore, in this review, the latest developments in RE SACs having applications in photo/electrocatalysis are summarized and discussed. First, the theoretical advantages of RE SACs for photo/electrocatalysis are briefly introduced, focusing on the roles of the 4f orbitals and coupled energy levels. In addition, the most recent research progress on RE SACs is summarized for several important photo/electrocatalytic reactions and the corresponding catalytic mechanisms are discussed. Further, the synthetic strategies for the production of RE SACs are reported. Finally, challenges for the development of RE SACs are highlighted, along with future research directions and perspectives.

d-sp orbital hybridization: a strategy for activity improvement of transition metal catalysts

Orbital hybridization to regulate the electronic structures and surface chemisorption properties of transition metals has been extensively investigated for searching high-performance catalysts toward various reactions. Unlike conventional d-d hybridization, the d-sp hybridization interaction between transition metals and p-block elements could result in surprising electronic properties and catalytic activities. This feature article highlights the recent progress in the development of high-performance transition metal-based catalysts through the extraordinary d-sp hybridization strategy, particularly for energy-related electrocatalytic applications. We start by giving an introduction of fundamental concepts associated with electronic structures of transition metal catalysts, including the Sabatier principle, d-band theory, electronic descriptor, as well as the comparison of d-d hybridization and d-sp hybridization strategies. Then, we summarize the theoretical and experimental advances in d-sp hybridization catalysts, including p-block element-doped metal catalysts, intermetallic catalysts and supported metal catalysts, with emphasis on the important roles of d-sp hybridization in tuning catalytic performances. Finally, we present existing challenges and future development prospects for the rational design of advanced d-sp hybridization catalysts.

Directing Charge Transfer in a Chemical-Bonded BaTiO3 @ReS2 Schottky Heterojunction for Piezoelectric Enhanced Photocatalysis

The piezo-assisted photocatalysis system, which can utilize solar energy and mechanical energy simulteneously, is promising but still challenging in the environmental remediation field. In this work, a novel metal-semiconductor BaTiO₃ @ReS₂ Schottky heterostructure is designed and it shows high-efficiency on piezo-assisted photocatalytic molecular oxygen activation. By combining experiment and calculation results, the distorted metal-phase ReS₂ nanosheets are found to be closely anchored on the surface of the BaTiO₃ nanorods, through interfacial ReO covalent bonds. The Schottky heterostructure not only forms electron-transfer channels but also exhibits enhanced oxygen activation capacity, which are helpful to produce more superoxide radicals. The polarization field induced by the piezoelectric BaTiO₃ can lower the Schottky barrier and thus reduce the transfer resistance of photogenerated electrons directing to the ReS₂ . As a result of the synergy effect between the two components, the BaTiO₃ @ReS₂ exhibits untrahigh activity for degradation of pollutants with an apparent rate constant of 0.133 min^-1 for piezo-assisted photocatalysis, which is 16.6 and 2.44 times as that of piezocatalysis and photocatalysis, respectively. This performance is higher than most reported BaTiO₃ -based piezo-assisted photocatalysis systems. This work paves the way for the design of high-efficiency piezo-assisted photocatalytic materials for environmental remediation through using green energies in nature.

Single-Atom Catalysts (SACs) for Photocatalytic CO2 Reduction with H2 O: Activity, Product Selectivity, Stability, and Surface Chemistry

In recent years, single-atom catalysts (SACs) have attracted the interest of researchers owing to their suitability for various catalytic applications. For instance, their optoelectronic features, site-specific activity, and cost-effectiveness make SACs ideal for photocatalytic CO₂ reduction. The activity, product selectivity, and photostability of SACs depend on various factors such as the nature of the metal/support material, the interaction between the metal atoms and support, light-harvesting ability, charge separation behavior, CO₂ adsorption ability, active sites, and defects. Consequently, it is necessary to investigate these factors in depth to elucidate the working principle(s) of SACs for catalytic applications. Herein, the recent progress in the development of SACs for photocatalytic CO₂ reduction with H₂ O is reviewed. First, a brief overview of CO₂ photoreduction and SACs for CO₂ conversion is provided. Several synthesis strategies and useful techniques for characterizing SACs employed in heterogeneous catalysis are then described. Next, the challenges of SACs for photocatalytic CO₂ reduction and related optimization strategies, in terms of activity, product selectivity, and stability, are explored. The progress in the development of noble metal- and transition metal-based SACs and dual-SACs for photocatalytic CO₂ reduction is discussed. Finally, the prospects of SACs for CO₂ reduction are considered.

Considering single-atom catalysts as photocatalysts from synthesis to application

With the ever-increased greenhouse effect and energy crisis, developing novel photocatalysts to realize high-efficient solar-driven chemicals/fuel production is of great scientific and practical significance. Recently, single-atom photocatalysts (SAPs) are promising catalysts with maximized metal dispersion and tuneable coordination environments. SAPs exhibit boosted photocatalytic performance by enhancing optical response, facilitating charge carrier transfer behaviors or directly manipulating surface reaction processes. In this regard, this article systematically reviews the state-of-the-art progress in the development and application of SAPs, especially the mechanism and performance of SAPs on various reaction processes. Some future challenges and potential research directions over SAPs are outlined at the final stage.

Carbon vacancy-mediated exciton dissociation in Ti3C2Tx/g-C3N4 Schottky junctions for efficient photoreduction of CO2

Earth-abundant g-C₃N₄ is a promising photocatalyst for CO₂ reduction, but its practical application is severely limited by the excitonic effect of g-C₃N₄ derived from strong binding energy and lack of electron-enriched active sites. Herein, we design a novel 2D/2D Schottky junction photocatalysts comprising of Ti₃C₂T_x-modified defective g-C₃N₄ nanosheets with carbon vacancy (denoted as Ti₃C₂T_x/V_c-CN) by a self-assembly method. The carbon vacancies in g-C₃N₄ promote exciton dissociation into free charge, while the formed Schottky junctions between Ti₃C₂T_x and V_c-CN further enables a directional charge transfer, thus providing an electron-rich catalytic surface for the CO₂ reduction. Thanks to the synergy of promoted exciton dissociation and directional electron transfer, the optimal 20% Ti₃C₂T_x/V_c-CN display a high CO evolution rate of 20.54 µmol·g^-1·h^-1 under visible light irradiation, which is 7.4 times higher than that of bare CN. This work highlights the synergy of the promoted exciton dissociation and directional electron transfer in the activity enhancement of photocatalytic CO₂ reduction.

Novel Cerium-Based Sulfide Nano-Photocatalyst for Highly Efficient CO2 Reduction

To address the environmental crisis caused by excessive emissions of CO₂ , the development of effective photocatalysts for the conversion of CO₂ into chemicals has emerged as one of the most promising strategies. Herein, beyond those well-studied materials, a rare-earth sulfide-based nanocrystal NaCeS₂ is fabricated and investigated for efficient and selective conversion of CO₂ into CO, where the role of Ce ions is crucial. Firstly, the hybridization of Ce 4f and Ce 5d orbitals contributes to the photoresponsive band structure of NaCeS₂ . Secondly, due to the charge rearrangement supplied by the incompletely filled 4f orbitals of Ce ions, NaCeS₂ exhibits excellent charge separation efficiency and CO₂ adsorption affinity, reducing the energy barrier for the conversion from CO₂ to CO. Moreover, a NaCeS₂ -MoS₂ heterostructure is also designed to further boost the electron transfer from the Mo site to the Ce site, which results in an improvement of the catalytic reduction yield from 7.24 to 23.42 µmol g^-1 within 9 h (both better than TiO₂ controls). This work offers a platform for the development of rare-earth-based photocatalysts for CO₂ conversion.

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.

Ultrathin Nanosheet Assembled Multishelled Superstructures for Photocatalytic CO2 Reduction

Solar-driven conversion of CO₂ is considered an efficient way to tackle the energy and environmental crisis. However, the photocatalytic performance is severely restricted due to the insufficient accessible active sites and inhibited electron transfer efficiency. This work demonstrates a general in situ topological transformation strategy for the integration of uniform Co-based species to fabricate a series of multishelled superstructures (MSSs) for CO₂ photocatalytic conversion. Thorough characterizations reveal the obtained MSSs feature ultrathin Co-based nanosheet assembled polyhedral structures with tunable shell numbers, inner cavity sizes, and compositions. The superstructures increase the spatial density of Co-based active sites while maintaining their high accessibility. Further, the ultrathin nanosheets also facilitate the transfer of photogenerated electrons. As a result, the ZnCo bimetallic hydroxide featuring an ultrathin nanosheet assembled quadruple-shell hollow structure (ZnCo-OH QUNH) exhibits high photocatalytic efficiency toward CO₂ reduction with a CO evolution rate of 134.2 μmol h^-1 and an apparent quantum yield of 6.76% at 450 nm. The quasi in situ spectra and theoretical calculations disclose that Co sites in ZnCo-OH QUNH act as highly active centers to stabilize the COOH* intermediate, while Zn species play the role of adsorption sites for the [Ru(bpy)₃]²⁺ molecules.

Anchoring Copper Single Atoms on Porous Boron Nitride Nanofiber to Boost Selective Reduction of Nitroaromatics

Single-atom catalysts have received widespread attention for their fascinating performance in terms of metal atom efficiency as well as their special catalysis mechanisms compared to conventional catalysts. Here, we prepared a high-performance catalyst of single-Cu-atom-decorated boron nitride nanofibers (BNNF-Cu) via a facile calcination method. The as-prepared catalyst shows high catalytic activity and good stability for converting different nitro compounds into their corresponding amines both with and without photoexcitation. By combined studies of synchrotron radiation analysis, high-resolution high-angle annular dark-field transmission electron microscopy studies, and DFT calculations, dispersion and coordination of Cu atoms as well as their catalytic mechanisms are explored. The BNNF-Cu catalyst is found to have a record high turnover frequency compared to previously reported non-precious-metal-based catalysts. While the performance of the BNNF-Cu catalyst is only of the middle range level among the state-of-the-art precious-metal-based catalysts, due to the much lower cost of the BNNF-Cu catalyst, its cost efficiency is the highest among these catalysts. This work provides a choice of support material that can promote the development of single-atom catalysts.

Visible Light-Driven Highly Selective CO2 Reduction to CH4 Using Potassium-Doped g-C3N5

Establishment of an efficient and robust artificial photocatalytic system to convert solar energy into chemical fuels through CO₂ conversion is a cherished goal in the fields of clean energy and environmental protection. In this work, we have explored an emergent low-Z nitrogen-rich carbon nitride material g-C₃N₅ (analogue of g-C₃N₄) for CO₂ conversion under visible light illumination. A significant enhancement of the CH₄ production rate was detected for g-C₃N₅ in comparison to that of g-C₃N₄. Notably, g-C₃N₅ also showed a very impressive selectivity of 100% toward CH₄ as compared to 21% for g-C₃N₄. The photocatalytic CO₂ conversion was performed without using sacrificial reagents. We found that 1% K doping in g-C₃N₅ enhanced its performance even further without compromising the selectivity. Moreover, 1% K-doped g-C₃N₅ also exhibited better photostability than undoped g-C₃N_5. We have also employed density functional theory calculation-based analyses to understand and elucidate the possible reasons for the better photocatalytic performance of K-doped g-C₃N₅.

Isotype Heterojunction-Boosted CO2 Photoreduction to CO

Photocatalytic conversion of CO₂ to high-value products plays a crucial role in the global pursuit of carbon-neutral economy. Junction photocatalysts, such as the isotype heterojunctions, offer an ideal paradigm to navigate the photocatalytic CO₂ reduction reaction (CRR). Herein, we elucidate the behaviors of isotype heterojunctions toward photocatalytic CRR over a representative photocatalyst, g-C₃N₄. Impressively, the isotype heterojunctions possess a significantly higher efficiency for the spatial separation and transfer of photogenerated carriers than the single components. Along with the intrinsically outstanding stability, the isotype heterojunctions exhibit an exceptional and stable activity toward the CO₂ photoreduction to CO. More importantly, by combining quantitative in situ technique with the first-principles modeling, we elucidate that the enhanced photoinduced charge dynamics promotes the production of key intermediates and thus the whole reaction kinetics.

Highly Efficient Photocatalytic Reduction of CO2 to CO by In Situ Formation of a Hybrid Catalytic System Based on Molecular Iron Quaterpyridine Covalently Linked to Carbon Nitride

Efficient and selective photocatalytic CO₂ reduction was obtained within a hybrid system that is formed in situ via a Schiff base condensation between a molecular iron quaterpyridine complex bearing an aldehyde function and carbon nitride. Irradiation (blue LED) of an CH₃ CN solution containing 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), triethylamine (TEA), Feqpy-BA (qpy-BA=4-([2,2':6',2'':6'',2'''-quaterpyridin]-4-yl)benzaldehyde) and C₃ N₄ resulted in CO evolution with a turnover number of 2554 and 95 % selectivity. This hybrid catalytic system unlocks covalent linkage of molecular catalysts with semiconductor photosensitizers via Schiff base reaction for high-efficiency photocatalytic reduction of CO₂ , opening a pathway for diverse photocatalysis.

Recent Progress in the Synthesis and Applications of Composite Photocatalysts: A Critical Review

Photocatalysis is an advanced technique that transforms solar energy into sustainable fuels and oxidizes pollutants via the aid of semiconductor photocatalysts. The main scientific and technological challenges for effective photocatalysis are the stability, robustness, and efficiency of semiconductor photocatalysts. For practical applications, researchers are trying to develop highly efficient and stable photocatalysts. Since the literature is highly scattered, it is urgent to write a critical review that summarizes the state-of-the-art progress in the design of a variety of semiconductor composite photocatalysts for energy and environmental applications. Herein, a comprehensive review is presented that summarizes an overview, history, mechanism, advantages, and challenges of semiconductor photocatalysis. Further, the recent advancements in the design of heterostructure photocatalysts including alloy quantum dots based composites, carbon based composites including carbon nanotubes, carbon quantum dots, graphitic carbon nitride, and graphene, covalent-organic frameworks based composites, metal based composites including metal carbides, metal halide perovskites, metal nitrides, metal oxides, metal phosphides, and metal sulfides, metal-organic frameworks based composites, plasmonic materials based composites and single atom based composites for CO₂ conversion, H₂ evolution, and pollutants oxidation are discussed elaborately. Finally, perspectives for further improvement in the design of composite materials for efficient photocatalysis are provided.

Atomically Dispersed Cu Nanozyme with Intensive Ascorbate Peroxidase Mimic Activity Capable of Alleviating ROS-Mediated Oxidation Damage

Ascorbate peroxidase (APX) as a crucial antioxidant enzyme has drawn attentions for its utilization in preventing cells from oxidative stress responses by efficiently scavenging H2 O2 in plants. For eliminating the specific inactivation of natural APXs and regulating the catalytic activity, single-atom nanozymes are considered as promising classes of alternatives with similar active sites and maximal atomic utilization efficiency to natural APXs. Herein, graphitic carbon nitride (g-C3 N4 ) anchored with isolated single copper atoms (Cu SAs/CN) is designed as an efficient nanozyme with intrinsic APX mimetic behavior. The engineered Cu SAs/CN exhibits comparable specific activity and kinetics to the natural APXs. Based on the density functional theory (DFT), Cu-N4 moieties in the active center of Cu SAs/CN are determined to exert such favorable APX catalytic performance, in which the electron transfer between Cu and coordinated N atoms facilitates the activation and cleavage of the adsorbed H2 O2 molecules and results in fast kinetics. The constructed Cu SAs/CN nanozyme with superior APX-like performance and high biocompatibility can be applied for effectively protecting the H2 O2 -treated cells against oxidative injury in vitro. These findings report the single-atom nanozymes as a successful paradigm for guiding nanozymes to implement APX mimetic performance for reactive oxygen species-related biotherapeutic.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Construction of brown mesoporous carbon nitride with a wide spectral response for high performance photocatalytic H2 evolution

A novel brown mesoporous carbon nitride photocatalyst is synthesized by a doping strategy. The excellent visible light response and stable mesoporous structure lead to an efficient hydrogen evolution activity.

Rational Design of Dot-on-Rod Nano-Heterostructure for Photocatalytic CO2 Reduction: Pivotal Role of Hole Transfer and Utilization

Inspired by green plants, artificial photosynthesis has become one of the most attractive approaches toward carbon dioxide (CO₂ ) valorization. Semiconductor quantum dots (QDs) or dot-in-rod (DIR) nano-heterostructures have gained substantial research interest in multielectron photoredox reactions. However, fast electron-hole recombination or sluggish hole transfer and utilization remains unsatisfactory for their potential applications. Here, the first application of a well-designed ZnSe/CdS dot-on-rods (DORs) nano-heterostructure for efficient and selective CO₂ photoreduction with H₂ O as an electron donor is presented. In-depth spectroscopic studies reveal that surface-anchored ZnSe QDs not only assist ultrafast (≈2 ps) electron and hole separation, but also promote interfacial hole transfer participating in oxidative half-reactions. Surface photovoltage (SPV) spectroscopy provides a direct image of spatially separated electrons in CdS and holes in ZnSe. Therefore, ZnSe/CdS DORs photocatalyze CO₂ to CO with a rate of ≈11.3 µmol g^-1 h^-1 and ≥85% selectivity, much higher than that of ZnSe/CdS DIRs or pristine CdS nanorods under identical conditions. Obviously, favored energy-level alignment and unique morphology balance the utilization of electrons and holes in this nano-heterostructure, thus enhancing the performance of artificial photosynthetic solar-to-chemical conversion.

Biotemplated g-C3N4/Au Periodic Hierarchical Structures for the Enhancement of Photocatalytic CO2 Reduction with Localized Surface Plasmon Resonance

Graphitic carbon nitride (g-C₃N₄) is a promising photocatalyst for CO₂ reduction to alleviate the greenhouse effect. However, the low light absorption, small specific surface area, and rapid charge recombination limit the photocatalytic efficiency of g-C₃N₄. Herein, we demonstrate a bioinspired nanoarchitecturing strategy to significantly improve the light harvesting and charge separation of the g-C₃N₄/Au composite, as proven by the remarkable photocatalytic CO₂ reduction. Specifically, a biotemplating approach is employed to transfer the sophisticated hierarchical structures and the related light-harvesting functionality of Troides helena butterfly wings to the g-C₃N₄/Au composite. The resulting g-C₃N₄/Au composite shows high photocatalytic efficiency under UV-visible excitation with triethanolamine as the sacrificial agent. The yields of CO and CH₄ are 331.57 and 39.71 μmol/g/h, respectively, which are ∼36 times and ∼88 times that of pure g-C₃N₄ under the same conditions. Detailed experiments and the finite-difference time-domain method suggest that the superb photocatalytic activity should be ascribed to the unique periodic hierarchical structure which assists the light absorption and the localized surface plasmon resonance for promoted charge separation in addition to the more effective CO₂ diffusion and larger specific surface area. Our work provides a new path for the design and optimization of photocatalysts based on biological structures that are usually unattainable artificially.

Rare earth element based single-atom catalysts: synthesis, characterization and applications in photo/electro-catalytic reactions

Rare earth elements play an important role in various fields, which has attracted increasing interest from the scientific community. Meanwhile, single-atom catalysts show huge advantages in many aspects compared with traditional nanomaterials due to their 100% atomic utilization efficiency. Thus, the combination of the two concepts has yielded an efficient way to realize the high-value utilization of rare earth elements. In this mini-review, rare earth-based single-atom catalysts including their synthesis methods, characterization means and corresponding applications are constructively summarized and discussed. In particular, the important roles of rare earth elements as active centers in photo/electrocatalytic reactions are focused on. Finally, future prospects are also provided.

Engineering of graphitic carbon nitride with simultaneous potassium doping sites and nitrogen defects for notably enhanced photocatalytic oxidation performance

Graphitic carbon nitride (g-C₃N₄) offers exciting opportunities for sustainable photocatalytic oxidation of organic pollutants but suffers from drawbacks of insufficient oxidation driving force and low quantum efficiency. To over the drawbacks, here a simple and effective strategy was developed to engineer g-C₃N₄ with simultaneous interstitially embedded potassium dopant and nitrogen defects, and the process included supramolecular preorganization followed by KOH-assisted thermal polycondensation. In the prepared D_N-K-CN catalysts, potassium doping level and the amount of nitrogen defects were both controllable. With the increment of potassium doping level, the bandgap of the D_N-K-CN became narrow, along with continuously downshifted valence band position. The D_N-K-CN showed greatly enhanced visible-light photocatalytic oxidation performance with respect to g-C₃N₄ in the degradation of emerging phenolic pollutants, acetaminophen and methylparaben; meanwhile, the oxidation performance of D_N-K-CN depended on potassium doping level and the amount of nitrogen defects. Combination of experimental findings and theory calculations it is confirmed that the enhanced photocatalytic oxidation performance of D_N-K-CN was attributed to the synergistic effect of potassium dopant and nitrogen defects, which resulted in the generation of plentiful active oxygen species and the improvement of oxidation driving force of valence holes. The influence of potassium dopant and nitrogen defects on the electronic and band structures of g-C₃N₄ was revealed; simultaneously, mechanism of the enhanced photocatalytic oxidation performance of g-C₃N₄ after the introduction of potassium dopant and nitrogen defects was studied. The present work provided new insights into the electronic and band structure tuning for the improvement of the photocatalytic oxidation performance of g-C₃N₄.

Tunable CO/H2 ratios of electrochemical reduction of CO2 through the Zn-Ln dual atomic catalysts

Electrochemical reduction of CO₂ (CO₂RR) to value-added liquid fuels is a highly appealing solution for carbon-neutral recycling, especially to syngas (CO/H₂). Current strategies suffer from poor faradaic efficiency (FE), selectivity, and controllability to the ratio of products. In this work, we have synthesized a series of single and dual atomic catalysts on the carbon nitride nanosheets. Adjusting the ratio of La and Zn atomic sites produces syngas with a wide range of CO/H₂ ratios. Moreover, the ZnLa-1/CN electrocatalyst generates the syngas with a ratio of CO/H₂ = 0.5 at a wide potential range, and the total FE of CO2RR reaches 80% with good stability. Density functional theory calculations have confirmed that the Zn and La affect electronic structures and determine the formation of CO and H₂, respectively. This work indicates a promising strategy in the development of atomic catalysts for more controllable CO₂RR.

Reticular-Chemistry-Inspired Supramolecule Design as a Tool to Achieve Efficient Photocatalysts for CO2 Reduction

Photocatalytic CO₂ reduction into C1 products is one of the most trending research subjects of current times as sustainable energy generation is the utmost need of the hour. In this review, we have tried to comprehensively summarize the potential of supramolecule-based photocatalysts for CO₂ reduction into C1 compounds. At the outset, we have thrown light on the inert nature of gaseous CO₂ and the various challenges researchers are facing in its reduction. The evolution of photocatalysts used for CO₂ reduction, from heterogeneous catalysis to supramolecule-based molecular catalysis, and subsequent semiconductor-supramolecule hybrid catalysis has been thoroughly discussed. Since CO₂ is thermodynamically a very stable molecule, a huge reduction potential is required to undergo its one- or multielectron reduction. For this reason, various supramolecule photocatalysts were designed involving a photosensitizer unit and a catalyst unit connected by a linker. Later on, solid semiconductor support was also introduced in this supramolecule system to achieve enhanced durability, structural compactness, enhanced charge mobility, and extra overpotential for CO₂ reduction. Reticular chemistry is seen to play a pivotal role as it allows bringing all of the positive features together from various components of this hybrid semiconductor-supramolecule photocatalyst system. Thus, here in this review, we have discussed the selection and role of various components, viz. the photosensitizer component, the catalyst component, the linker, the semiconductor support, the anchoring ligands, and the peripheral ligands for the design of highly performing CO₂ reduction photocatalysts. The selection and role of various sacrificial electron donors have also been highlighted. This review is aimed to help researchers reach an understanding that may translate into the development of excellent CO₂ reduction photocatalysts that are operational under visible light and possess superior activity, efficiency, and selectivity.

Crystal-Structure-Dependent Photocatalytic Redox Activity and Reaction Pathways over Ga2O3 Polymorphs

Differentiated crystal structures generally affect the surface physicochemical properties of catalysts, causing variety in catalytic activity between polymorphs. However, the underlying mechanism has not been completely revealed, especially the influence of surface physicochemical properties on photocatalytic redox activity and the reaction mechanism. In this work, we reveal the mechanism of surface redox properties on different crystal forms of gallium oxide from a molecular level. α-Ga₂O₃ and β-Ga₂O₃ exhibit a slight difference in catalytic oxidation of organic pollutants due to comprehensive influencing factors, including their valence band position, reactive oxygen species, and pore structure properties related to the adsorption-reaction-desorption process. But the catalytic reduction ability of CO₂ is obviously different due to the large differences of interaction between the surface of crystal structures and CO₂ molecules, which are critical to determine the catalytic performance and reaction pathways. The enhanced adsorption and activation of CO₂ on the α-Ga₂O₃ surface could promote the reduction reaction efficiency. Moreover, the large energy barrier of CH₂* formation on β-Ga₂O₃ makes the formation of methane (CH₄) relatively difficult compared to that on α-Ga₂O₃. The yield rate of CH₄ (1.8 μmol·g^-1·h^-1) on α-Ga₂O₃ is three times better than that on β-Ga₂O₃ (CH₄: 0.6 μmol·g^-1·h^-1). The current findings can offer novel insights into the understanding of crystal-structure-dependent photocatalytic performances and the design of new catalysts applied in energy conversion and environmental purification by crystal structure-tuning.

Hierarchical Double-Shelled CoP Nanocages for Efficient Visible-Light-Driven CO2 Reduction

Visible-light-driven photocatalytic CO₂ reduction is considered an appealing strategy to mitigate the energy crisis and environmental issues, whereas the reactivity is limited due to the difficulties in activation of inert CO₂ molecule and efficient transportation of photoinduced carriers. Herein, we report the design of novel Fe doped CoP hierarchical double-shelled nanocages (Fe-CoP HDSNC) via a MOF-templated approach for highly efficient visible-light-driven CO₂ reduction. The unique hierarchical double-shelled hollow architectures can greatly shorten the charge transfer distances and also expose abundant reactive sites. Moreover, Fe atoms doping is able to reduce the CO₂ activation energy barrier through stabilizing the *COOH intermediates and promote the CO desorption by destabilizing the CO* adduct. As expected, the Fe-CoP HDSNC achieves an unprecedented catalytic efficiency in visible-light-driven CO₂ reduction with an up to 3.25% apparent quantum yield and 90.3% CO selectivity, superior to most of the state-of-the-art photocatalysts under comparable conditions. More importantly, the Fe-CoP HDSNC is also highly effective under diluted CO₂ atmosphere, suggesting the practicability of the present photocatalytic system.

Molecular-functionalized engineering of porous carbon nitride nanosheets for wide-spectrum responsive solar fuel generation

Carbon nitride (C₃N₄) is a promising metal-free photocatalyst for solar-to-energy conversion, but bulk carbon nitride (BCN) shows insufficient light absorption, sluggish photocarrier transfer and moderate activity for photocatalysis. Herein, a facile strategy to significantly increase solar spectrum absorption of the functionalized porous carbon nitride nanosheets (MFPCN) via molecule self-assembly engineering coupled thermal polymerization is reported. This strategy can greatly enhance the wide-solar-spectrum absorption of MFPCN up to 1000 nm than most reported carbon nitride-based photocatalysts. Experimental characterizations and theoretical calculations together display that this strategy could introduce hydroxyl groups into the structure of MFPCN as well as the rich pores and active sites at the edges of framework, which can narrow the bandgap and accelerate the transfer and separation of photoinduced carries. As a result, the optimal MFPCN photocatalyst exhibit the excellent photocatalytic hydrogen evolution rate of 7.745 mmol g^-1h^-1 under simulated solar irradiation, which is ≈13 times that of BCN with remarkable durable CO₂ reduction activities. New findings in this work will provide an approach to extend solar spectrum absorption of metal-free catalysts for solar fuel cascades.