Low‐Energy Facets on CdS Allomorph Junctions with Optimal Phase Ratio to Boost Charge Directional Transfer for Photocatalytic H2 Fuel Evolution

Low‐energy facets on CdS allomorph junctions with optimal phase ratio are designed to boost charge directional transfer for photocatalytic H₂ fuel evolution. Fermi energy level difference between low‐energy facets as driving force promotes electrons directional transfer to hexagonal CdS(102) facet and holes to cubic CdS(111) facet. The optimal allomorphs CdS presents superior photocatalytic H₂ evolution rate of 32.95 mmol g^?1 h^?1 with release in a large amount of visible H₂ bubbles, which is much higher than single‐phase CdS with high‐energy facets and even supports noble metal photocatalysts. This scientific perspective on low‐energy facets of allomorph junctions with optimal phase ratio breaks the long‐held view of pursuing high‐energy crystal surfaces, which will break the understanding on surface structure crystal facet engineering of photocatalytic materials.     

2D g-C3N4 for advancement of photo-generated carrier dynamics: Status and challenges

2D organic g-C₃N₄ photocatalysts are low cost materials with facile fabrication, suitable bandgap, tunable functionalization, excellent thermal/chemical-physical stability and exceptional photocatalytic behavior, raising considerable interest in photocatalytic and redox research areas. The photocatalytic performance of g-C₃N₄ mostly relies on the separation/transfer of photo-generated carriers. The mobility properties of the carrier largely determine the formation of reactive species, which have a high impact on surface reactions in the photocatalytic systems based on g-C₃N₄. This review paper outlines the works carried out so far on the optimization of the carrier mobility dynamics of 2D g-C₃N₄ materials via the internal and external modification strategies. The peculiar layered planar structure of g-C₃N₄ allows charge carrier mobility at the interface, in-plane and interlayer, and mechanisms of the charge separation/transfer will also be discussed. Comprehensive conclusions and perspectives on the modification of g-C₃N₄ leading to satisfactory carrier mobility will be given as well.     

Preparation, characterization and application of TiO2 nanoparticles surface-modified by DDAT

DDAT(S-1-Dodecyl-S′-(α, α′-dimethyl-α″-acetic acid) trithiocarbonate) modified TiO₂ photocatalysts were prepared by hydrothermal treatment before TiO₂ crystallization. The adsorption of DDAT onto the surface of titania nanoparticles led the shifting of the onset wavelength of the optical absorption in the visible range corresponding to ligand-to-metal charge transfer transition within the surface-modified complex. The interaction of TiO₂ nanoparticles with DDAT was investigated by infrared spectra. The XRD indicated that the modification process could not influence the crystallite phase of TiO₂. The photocatalytic studies suggested that the DDAT modified TiO₂ photocatalysts showed enhanced photocatalytic efficiency of photodegradation of 2,4-dichlorophenol compared with the as-prepared TiO₂ under visible-light irradiation.     

Fabrication of Ag-doped MoO3 and its nanohybrid with a two-dimensional carbonaceous material to enhance photocatalytic activity

Recently, two-dimensional (2D) carbon-based materials and their nanocomposites have gained considerable fascination as a photocatalysts due to their remarkable contribution towards photocatalytic water splitting and remediation. Herein, a novel 2D reduced graphene oxide (rGO) based silver doped molybdenum trioxide (Ag/MoO₃) photocatalyst was synthesized successfully via hydrothermal and ultra-sonication methods. The surface structure, morphology, functional group characterization, and bandgap of the synthesized photocatalysts were analyzed using advanced physicochemical techniques. The photocatalytic performance of the prepared materials was scrutinized for Methylene blue (MB) dye degradation under solar light illumination. Because of its lower charge transfer resistance (19.54 Ω) and higher electrical conductivity (12.74 × 10² Sm^?1) the rGO/Ag/MoO₃ photocatalyst demonstrated significantly higher photocatalytic activity for dye removal than pure MoO₃ and Ag/MoO₃ photocatalysts. In particular, the rGO/Ag/MoO₃ photocatalyst illustrated about 98% dye degradation at a rate constant (0.0571 min^?1) greater than MoO₃ (0.0097 min^?1) and Ag/MoO₃ (0.0184 min^?1). Ag doping and the addition of rGO sheets led to enhanced optical absorbance and effectual separation of photo-induced electron-hole pairs, causing major progress in the photocatalytic behavior of MoO₃. Transient photocurrent results revealed longstanding photo-excited charge carriers in the graphene-based material.     

Hollow Nanostructures for Photocatalysis: Advantages and Challenges

Photocatalysis for solar‐driven reactions promises a bright future in addressing energy and environmental challenges. The performance of photocatalysis is highly dependent on the design of photocatalysts, which can be rationally tailored to achieve efficient light harvesting, promoted charge separation and transport, and accelerated surface reactions. Due to its unique feature, semiconductors with hollow structure offer many advantages in photocatalyst design including improved light scattering and harvesting, reduced distance for charge migration and directed charge separation, and abundant surface reactive sites of the shells. Herein, the relationship between hollow nanostructures and their photocatalytic performance are discussed. The advantages of hollow nanostructures are summarized as: 1) enhancement in the light harvesting through light scattering and slow photon effects; 2) suppression of charge recombination by reducing charge transfer distance and directing separation of charge carriers; and 3) acceleration of the surface reactions by increasing accessible surface areas for separating the redox reactions spatially. Toward the end of the review, some insights into the key challenges and perspectives of hollow structured photocatalysts are also discussed, with a good hope to shed light on further promoting the rapid progress of this dynamic research field.     

The effect of support on the structure and photocatalytic activity of ternary ZnO-ZnFe2O4/palygorskite composite photocatalysts

The ternary ZnO-ZnFe₂O₄/palygorskite composite photocatalysts were fabricated via a solvothermal method followed by thermal treatment. The structure, morphology and photoelectric performances of samples were characterized, and the results indicated that ZnO/ZnFe₂O₄ nanoparticles with size of 25–30 nm were adequately anchored on the palygorskite fibers surface. Compared with ZnO, ZnFe₂O₄, ZnO/ZnFe₂O₄ and ZnO/palygorskite, the ZnO-ZnFe₂O₄/palygorskite composite photocatalysts exhibited significantly improved photocatalytic activity in degradation of methylene blue (MB). Especially, the optimal photocatalyst (ZF1.5) displayed the highest photocatalytic activity, achieving 99.68% and 99.48% degradation efficiency after 90 min of UV–vis (350 ≤ λ ≤ 780 nm) and 100 min of visible-light (λ ≥ 420 nm) irradiation, respectively. The photocatalysis degradation process matched well with the Langmuir-Hinshelwood kinetics. The obtained improvement of photocatalytic activity was ascribed to the synergetic effect of superior visible-light utilization; effective charge carrier separation and palygorskite support effect (optimize nanoparticles dispersibility, developed mesoporous structure, enlarge specific surface area and increase adsorption capacity).     

Dual Cocatalysts in TiO2 Photocatalysis

Semiconductor photocatalysis is recognized as a promising strategy to simultaneously address energy needs and environmental pollution. Titanium dioxide (TiO₂) has been investigated for such applications due to its low cost, nontoxicity, and high chemical stability. However, pristine TiO₂ still suffers from low utilization of visible light and high photogenerated‐charge‐carrier recombination rate. Recently, TiO₂ photocatalysts modified by dual cocatalysts with different functions have attracted much attention due to the extended light absorption, enhanced reactant adsorption, and promoted charge‐carrier‐separation efficiency granted by various cocatalysts. Recent progress on the component and structural design of dual cocatalysts in TiO₂ photocatalysts is summarized. Depending on their components, dual cocatalysts decorated on TiO₂ photocatalysts can be divided into the following categories: bimetallic cocatalysts, metal–metal oxide/sulfide cocatalysts, metal–graphene cocatalysts, and metal oxide/sulfide–graphene cocatalysts. Depending on their architecture, they can be categorized into randomly deposited binary cocatalysts, facet‐dependent selective‐deposition binary cocatalysts, and core–shell structural binary cocatalysts. Concluding perspectives on the challenges and opportunities for the further exploration of dual cocatalyst–modified TiO₂ photocatalysts are presented.     

Solar-CO2-to-Syngas Conversion Enabled by Precise Charge Transport Modulation

The rational design of the directional charge transfer channel represents an important strategy to finely tune the charge migration and separation in photocatalytic CO₂-to-fuel conversion. Despite the progress made in crafting high-performance photocatalysts, developing elegant photosystems with precisely modulated interfacial charge transfer feature remains a grand challenge. Here, a facile one-pot method is developed to achieve in situ self-assembly of Pd nanocrystals (NYs) on the transition metal chalcogenide (TMC) substrate with the aid of a non-conjugated insulating polymer, i.e., branched polyethylenimine (bPEI), for photoreduction of CO₂ to syngas (CO/H₂). The generic reducing capability of the abundant amine groups grafted on the molecular backbone of bPEI fosters the homogeneous growth of Pd NYs on the TMC framework. Intriguingly, the self-assembled TMCs@bPEI@Pd heterostructure with bi-directional spatial charge transport pathways exhibit significantly boosted photoactivity toward CO₂-to-syngas conversion under visible light irradiation, wherein bPEI serves as an efficient hole transfer mediator, and simultaneously Pd NYs act as an electron-withdrawing modulator for accelerating spatially vectorial charge separation. Furthermore, in-depth understanding of the in situ formed intermediates during the CO₂ photoreduction process are exquisitely probed. This work provides a quintessential paradigm for in situ construction of multi-component heterojunction photosystem for solar-to-fuel energy conversion.     

Defect‐Tailoring Mediated Electron–Hole Separation in Single‐Unit‐Cell Bi3O4Br Nanosheets for Boosting Photocatalytic Hydrogen Evolution and Nitrogen Fixation

Solar photocatalysis is a potential solution to satisfying energy demand and its resulting environmental impact. However, the low electron–hole separation efficiency in semiconductors has slowed the development of this technology. The effect of defects on electron–hole separation is not always clear. A model atomically thin structure of single‐unit‐cell Bi₃O₄Br nanosheets with surface defects is proposed to boost photocatalytic efficiency by simultaneously promoting bulk‐ and surface‐charge separation. Defect‐rich single‐unit‐cell Bi₃O₄Br displays 4.9 and 30.9 times enhanced photocatalytic hydrogen evolution and nitrogen fixation activity, respectively, than bulk Bi₃O₄Br. After the preparation of single‐unit‐cell structure, the bismuth defects are controlled to tune the oxygen defects. Benefiting from the unique single‐unit‐cell architecture and defects, the local atomic arrangement and electronic structure are tuned so as to greatly increase the charge separation efficiency and subsequently boost photocatalytic activity. This strategy provides an accessible pathway for next‐generation photocatalysts.     

Multichannel Charge Transfer and Mechanistic Insight in Metal Decorated 2D–2D Bi2WO6–TiO2 Cascade with Enhanced Photocatalytic Performance

Promising semiconductor‐based photocatalysis toward achieving efficient solar‐to‐chemical energy conversion is an ideal strategy in response to the growing worldwide energy crisis, which however is often practically limited by the insufficient photoinduced charge‐carrier separation. Here, a rational cascade engineering of Au nanoparticles (NPs) decorated 2D/2D Bi₂WO₆–TiO₂ (B–T) binanosheets to foster the photocatalytic efficiency through the manipulated flow of multichannel‐enhanced charge‐carrier separation and transfer is reported. Mechanistic characterizations and control experiments, in combination with comparative studies over plasmonic Au/Ag NPs and nonplasmonic Pt NPs decorated 2D/2D B–T composites, together demonstrate the cooperative synergy effect of multiple charge‐carrier transfer channels in such binanosheets‐based ternary composites, including Z‐scheme charge transfer, “electron sink,” and surface plasmon resonance effect, which integratively leads to the boosted photocatalytic performance.     

Cocatalysts in Semiconductor‐based Photocatalytic CO2 Reduction: Achievements,Challenges, and Opportunities

Ever‐increasing fossil‐fuel combustion along with massive CO₂ emissions has aroused a global energy crisis and climate change. Photocatalytic CO₂ reduction represents a promising strategy for clean, cost‐effective, and environmentally friendly conversion of CO₂ into hydrocarbon fuels by utilizing solar energy. This strategy combines the reductive half‐reaction of CO₂ conversion with an oxidative half reaction, e.g., H₂O oxidation, to create a carbon‐neutral cycle, presenting a viable solution to global energy and environmental problems. There are three pivotal processes in photocatalytic CO₂ conversion: (i) solar‐light absorption, (ii) charge separation/migration, and (iii) catalytic CO₂ reduction and H₂O oxidation. While significant progress is made in optimizing the first two processes, much less research is conducted toward enhancing the efficiency of the third step, which requires the presence of cocatalysts. In general, cocatalysts play four important roles: (i) boosting charge separation/transfer, (ii) improving the activity and selectivity of CO₂ reduction, (iii) enhancing the stability of photocatalysts, and (iv) suppressing side or back reactions. Herein, for the first time, all the developed CO₂‐reduction cocatalysts for semiconductor‐based photocatalytic CO₂ conversion are summarized, and their functions and mechanisms are discussed. Finally, perspectives in this emerging area are provided.     

Visible-light-driven photocatalysis with dopamine-derivatized titanium dioxide/<Emphasis Type="Italic">N</Emphasis>-doped carbon core/shell nanoparticles

Titanium dioxide/N-doped carbon core/shell nanoparticles enabling efficient visible-light-driven photocatalytic degradation of rhodamine B, considered a model compound for water-soluble environmental pollutants, were successfully prepared by the carbonization of dopamine-grafted TiO₂ nanoparticles. These precursor nanoparticles were prepared via simple ligand-to-metal charge transfer (LMCT) between TiO₂ nanoparticles and dopamine. Owing to the incorporation of Ti–O–C chelating bonds and the subsequent narrowing of the optical band gap, the dopamine-derivatized photocatalyst demonstrated enhanced activity compared with that of commercial photocatalysts and promoted the photocatalytic degradation of rhodamine B under both UV light and visible light. This LMCT-mediated incorporation of thin amorphous N-doped carbon shells onto the surface of semiconducting photocatalysts may be widely applicable for the generation of novel and robust hybrid materials with enhanced photocatalytic activities for many applications.     

Ligand-Assistant Iced Photocatalytic Reduction to Synthesize Atomically Dispersed Cu Implanted Metal-Organic Frameworks for Photo-Enhanced Uranium Extraction from Seawater

Uranium extraction from natural seawater is one of the most promising routes to address the shortage of uranium resources. By combination of ligand complexation and photocatalytic reduction, porous framework-based photocatalysts have been widely applied to uranium enrichment. However, their practical applicability is limited by poor photocatalytic activity and low adsorption capacity. Herein, atomically dispersed Cu implanted UiO-66-NH₂ (Cu SA@UiO-66-NH₂) photocatalysts are prepared via ligand-assistant iced photocatalytic reduction route. N—Cu–N moiety acts as an effective electron acceptor to potentially facilitate charge transfer kinetics. By contrast, there exist Cu sub-nanometer clusters by the typical liquid phase photoreduction, resulting in a relatively low photocatalytic activity. Cu SA@UiO-66-NH₂ adsorbents exhibit superior antibacterial ability and improved photoreduction conversion of the adsorbed U(VI) to insoluble U(IV), leading to a high uranium sorption capacity of 9.16 mg-U/g-Ads from natural seawater. This study provides new insight for enhancing uranium uptake by designing SA-mediated MOF photocatalysts.     

Defect engineering of photocatalysts for solar-driven conversion of CO2 into valuable fuels

Photoreduction of CO₂ into valuable fuels is a clean and sustainable way to mitigate the energy crisis and environmental problems. Factors limiting the efficiency of CO₂ photoreduction include narrow-band light absorption, poor charge carrier separation and transport, and sluggish activation/reaction of CO₂ on the surface of photocatalyst. In recent years, defect engineering of photocatalysts emerges as an effective method to improve their efficiency in the photocatalytic conversion of CO₂ into useful fuels. This review is focused on discussing how structural defects can be used to modulate the electronic structure of the photocatalysts and activate the inert CO₂ molecules. Special emphasis is placed on the important impact of defects on the charge carrier dynamics of the photocatalysts. Our discussions cover a variety of defective semiconductors, including metal oxides, metal sulfides, and two dimensional materials. In addition, the challenges and prospects of defect engineering in photoreduction of CO₂ are also analyzed. This review aims to provide useful information about the fundamental principles of photoreduction of CO₂ and guidance on the design and preparation of defective photocatalysts.     

Advanced Catalyst for CO2 Photo-Reduction: From Controllable Product Selectivity by Architecture Engineering to Improving Charge Transfer Using Stabilized Au Clusters

Despite enormous progress and improvement in photocatalytic CO₂ reduction reaction (CO₂RR), the development of photocatalysts that suppress H₂ evolution reaction (HER), during CO₂RR, remains still a challenge. Here, new insight is presented for controllable CO₂RR selectivity by tuning the architecture of the photocatalyst. Au/carbon nitride with planar structure (p Au/CN) showed high activity for HER with 87% selectivity. In contrast, the same composition with a yolk@shell structure (Y@S Au@CN) exhibited high selectivity of carbon products by suppressing the HER to 26% under visible light irradiation. Further improvement for CO₂RR activity was achieved by a surface decoration of the yolk@shell structure with Au₂₅(PET)₁₈ clusters as favorable electron acceptors, resulting in longer charge separation in Au@CN/Au_c Y@S structure. Finally, by covering the structure with graphene layers, the designed catalyst maintained high photostability during light illumination and showed high photocatalytic efficiency. The optimized Au@CN/Au_c/G Y@S structure displays high photocatalytic CO₂RR selectivity of 88%, where the CO and CH₄ generations during 8 h are 494 and 198 µmol/gcat., respectively. This approach combining architecture engineering and composition modification provides a new strategy with improved activity and controllable selectivity toward targeting applications in energy conversion catalysis.     

New insight for enhancing photocatalytic activity of MWCNT/TiO2 by decorating palladium nanoparticles as charge-transfer channel

A surface bond-grafted multi-walled carbon nanotube (MWCNT)/TiO₂ as supporter, palladium nanoparticles, approximately 3 nm in diameter, are uniformly deposited on the functional MWCNT surface in first, constructing a novel Pd-MWCNT/TiO₂ photocatalyst for photocatalytic solar conversion. The characterization of photocatalysts by a series of joint techniques, including BET surface area, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), Raman spectroscopy and ultraviolet/visible (UV/vis) diffuse reflectance spectra, discloses that palladium nanoparticles has a crucial role in enhancement of photocatalytic activity of MWCNT/TiO₂, that is to act as a charge transfer channel, which helps to trap electrons from MWCNT to TiO₂.     

Surface‐Halogenation‐Induced Atomic‐Site Activation and Local Charge Separation for Superb CO2 Photoreduction

Solar‐energy‐driven CO₂ conversion into value‐added chemical fuels holds great potential in renewable energy generation. However, the rapid recombination of charge carriers and deficient reactive sites, as two major obstacles, severely hampers the photocatalytic CO₂ reduction activity. Herein, a desirable surface halogenation strategy to address the aforementioned concerns over a Sillén‐related layer‐structured photocatalyst Bi₂O₂(OH)(NO₃) (BON) is demonstrated. The surface halogen ions that are anchored on the Bi atoms by replacing surface hydroxyls on the one hand facilitate the local charge separation, and, on the other hand, activate the hydroxyls that profoundly boost the adsorption of CO₂ molecules and protons and facilitate the CO₂ conversion process, as evidenced by experimental and theoretical results collectively. Among the three series of BON‐X (X = Cl, Br, and I) catalysts, BON‐Br shows the most substantially enhanced CO production rate (8.12 µmol g^?1 h^?1) without any sacrificial agents or cocatalysts, ≈73 times higher than that of pristine Bi₂O₂(OH)(NO₃), also exceeding that of the state‐of‐the‐art photocatalysts reported to date. This work presents a surface polarization protocol for engineering charge behavior and reactive sites to promote photocatalysis, which shows great promise to the future design of high‐performance materials for clean energy production.     

Deciphering the Superior Electronic Transmission Induced by the Li–N Ligand Pairs Boosted Photocatalytic Hydrogen Evolution

Atomic level decoration route is designated as one of the attractive methods to regulate both the charge density and band structure of photocatalysts. Moreover, to enable more efficient separation and transport of photocarriers, the construction of novel active sites can enhance both the reactivity and electrical conductivity of the crystal. Herein, an Li–N ligand is constructed via co-doping lithium and nitrogen atoms into ZnIn₂S₄ lattice, which achieves a promoted photocatalytic H₂ evolution at 9737 µmol g⁻¹ h⁻¹. The existence of Li–N ligand pairs and the behaviors of photocarriers on L₄₀N₅ZIS are determined systematically, which also provides a unique insight into the mechanism of the improved photocarrier migration rate. With the introduction of Li–N dual sites, the vacancy form of ZnIn₂S₄ has changed and the photocatalytic stability is significantly improved. Interestingly, the change of charge density around Li–N ligand in ZnIn₂S₄ is determined by theoretical simulations, as well as the regulated energy barrier of photocatalytic water splitting caused by Li–N dual sites, which act as both adsorption site for H₂O and stronger reactive sites. This work helps to extend the understanding of ZnIn₂S₄ and offers a fresh perspective for the creation of a Li–N co-doped photocatalyst.     

A Hierarchical Z‑Scheme α‐Fe2O3/g‐C3N4 Hybrid for Enhanced Photocatalytic CO2 Reduction

The challenge in the artificial photosynthesis of fossil resources from CO₂ by utilizing solar energy is to achieve stable photocatalysts with effective CO₂ adsorption capacity and high charge‐separation efficiency. A hierarchical direct Z‐scheme system consisting of urchin‐like hematite and carbon nitride provides an enhanced photocatalytic activity of reduction of CO₂ to CO, yielding a CO evolution rate of 27.2 µmol g^?1 h^?1 without cocatalyst and sacrifice reagent, which is >2.2 times higher than that produced by g‐C₃N₄ alone (10.3 µmol g^?1 h^?1). The enhanced photocatalytic activity of the Z‐scheme hybrid material can be ascribed to its unique characteristics to accelerate the reduction process, including: (i) 3D hierarchical structure of urchin‐like hematite and preferable basic sites which promotes the CO₂ adsorption, and (ii) the unique Z‐scheme feature efficiently promotes the separation of the electron–hole pairs and enhances the reducibility of electrons in the conduction band of the g‐C₃N₄. The origin of such an obvious advantage of the hierarchical Z‐scheme is not only explained based on the experimental data but also investigated by modeling CO₂ adsorption and CO adsorption on the three different atomic‐scale surfaces via density functional theory calculation. The study creates new opportunities for hierarchical hematite and other metal‐oxide‐based Z‐scheme system for solar fuel generation.     

含钛高炉渣催化剂的光催化活性

以攀钢含钛高炉废渣为原料,在不同温度下煅烧合成了钙钛矿型硫酸掺杂的含钛高炉渣催化剂(sulfuric acid-modified titanium-bearing blast furnace slag,STBBFS),研究了混晶结构和硫掺杂对含钛高炉渣光催化活性的影响,结果表明,含钛高炉渣催化剂具有钙钛矿/锐钛矿混晶结构,粉体的颗粒形状不规则,煅烧后粒径变大;在紫外区域具有很强的光吸收能力,STBBFS催化剂的光催化活性由Cr(Ⅵ)的还原率评价.煅烧温度为400℃时,STBBFS催化剂的表面存在含量较高的SO2-4和较高的CaTiO3/TiO2晶相比,具有较高的光催化活性,用500 W中压汞灯照射10 h,可将浓度为20 mg·L-1的六价铬废水完全降解.