Tuning Oxygen Vacancies in Ultrathin TiO2 Nanosheets to Boost Photocatalytic Nitrogen Fixation up to 700 nm

Electrocatalytic H2O2 production via two-electron O2 reduction by Mo-doped TiO2 nanocrystallines

Mo acts as an effective dopant to boost the catalytic activity of TiO2 for the 2e− O2 reduction reaction. Such Mo–TiO2 electrocatalyst achieves a high Faradaic efficiency of 92% and a large H2O2 yield of 395.3 mmol gcat−1 h−1 in alkaline medium.

Boosted photocatalytic nitrogen fixation by bismuth and oxygen vacancies in Bi2MoO6/BiOBr composite structures

Bi₂MoO₆/V_Bi+O–BiOBr composites with surface bismuth and oxygen vacancies were synthesized by an ion-exchange method, and exhibited boosted photocatalytic nitrogen fixation activity.

Sintering- and oxidation-resistant ultrasmall Cu(I)/(II) oxides supported on defect-rich mesoporous alumina microspheres boosting catalytic ozonation

Supported copper oxides with well-dispersed metal species, small size, tunable valence and high stability are highly desirable in catalysis. Herein, novel copper oxide (CuO_x) catalysts supported on defect-rich mesoporous alumina microspheres are developed using a spray-drying-assisted evaporation induced self-assembly method. The catalysts possess a special structure composed of a mesoporous outer layer, a mesoporous-nanosphere-stacked under layer and a hollow cavity. Because of this special structure and the defective nature of the alumina support, the CuO_x catalysts are ultrasmall in size (1 ~ 3 nm), bivalent with a very high Cu⁺/Cu²⁺ ratio (0.7), and highly stable against sintering and oxidation at high temperatures (up to 800 °C), while the wet impregnation method results in CuO_x catalysts with much larger sizes (~15 nm) and lower the Cu⁺/Cu²⁺ ratios (~0.29). The catalyst formation mechanism through the spray drying method is proposed and discussed. The catalysts show remarkable performance in catalytic ozonation of phenol wastewaters. With high-concentration phenol (250 ppm) as the model organic pollutant, the optimized catalyst delivers promising catalytic performance with 100% phenol removal and 53% TOC removal in 60 min, and a high cyclic stability. Superoxide anion free radicals (⋅O₂^-), singlet oxygen (¹O₂) and hydroxyl radicals (⋅OH) are the predominant reactive species. A detailed structure-performance study reveals the surface hydroxyl groups and Cu⁺/Cu²⁺ redox couples play cooperatively to accelerate O₃ decomposition generating reactive radicals. The plausible catalytic O₃ decomposition mechanism is proposed and discussed with supportive evidences.

Exploiting Co Defects in CoFe-Layered Double Hydroxide (CoFe-LDH) Derivatives for Highly Efficient Photothermal Cancer Therapy

Currently, two-dimensional materials are being actively pursued in catalysis and other fields due their abundance of defects, which results in enhanced performance relative to their bulk defect-free counterparts. To date, the exploitation of defects in two-dimensional materials to enhance photothermal therapies has received little attention, motivating a detailed investigation. Herein, we successfully fabricated a series of novel CoFe-based photothermal agents (CoFe-x) by heating CoFe-layered double hydroxide (CoFe-LDH) nanosheets at different temperatures (x) between 200-800 °C under a Ar atmosphere. The CoFe-x products differed in their particle size, cobalt defect concentration, and electronic structure, with the CoFe-500 product containing the highest concentration of Co²⁺ defects and most efficient photothermal performance under near-infrared (NIR, 808 nm) irradiation. Experiments and density functional theory (DFT) calculations revealed that Co²⁺ defects modify the electronic structure of CoFe-x, narrowing the band gap and thus increasing the nonradiative recombination rate, thereby improving the NIR-driven photothermal properties. In vitro and in vivo results demonstrated that CoFe-500 was an efficient agent for photothermal cancer treatment and also near-infrared (NIR) thermal imaging, magnetic resonance (MR) imaging, and photoacoustic (PA) imaging. This work provides valuable new insights about the role of defects in the rational design of nanoagents with optimized structures for improved cancer therapy.

Surface domain heterojunction on rutile TiO2 for highly efficient photocatalytic hydrogen evolution

Compared with the highly active anatase TiO2, rutile TiO2 usually presents poor photocatalytic performance due to high electron-hole recombination. Herein, we propose a surface domain heterojunction (SDH) structure between adjacent micro-domains with and without chemisorbed chlorine on rutile TiO2, which utilizes the potential difference between these domains to form a built-in field that promotes charge separation. Single-crystal rutile TiO2 nanorods assembled into radial microspheres with SDHs were fabricated, and these exhibited excellent solar-driven photocatalytic hydrogen evolution, ∼8-fold higher than that of the pristine one. Experimental results and density functional theory calculations reveal that the exceptional photocatalytic performance can be attributed to the in situ formation of chemisorbed chlorine, which forms SDHs that separate electrons and holes efficiently and results in surface reconfiguration, exposing the tri-active sites, increasing the O-site active centers and enhancing the catalytic activity of the 4-coordinated (Ti4c) and 5-coordinated Ti sites (Ti5c). This SDH strategy can extend to other halogen elements and thus provides an universal approach for the rational design of high-efficiency TiO2 photocatalysts toward sustainable solar-fuel evolution.

Photoexcited Electron Dynamics of Nitrogen Fixation Catalyzed by Ruthenium Single-Atom Catalysts

It is still a grand challenge to exploit efficient catalysts to achieve sustainable photocatalytic N₂ reduction under ambient conditions. Here, we developed a ruthenium-based single-atom catalyst anchored on defect-rich TiO₂ nanotubes (denoted Ru-SAs/Def-TNs) as a model system for N₂ fixation. The constructed Ru-SAs/Def-TNs exhibited a catalytic efficiency of 125.2 μmol g^-1 h^-1, roughly 6 and 13 times higher than those of the supported Ru nanoparticles and Def-TNs, respectively. Through ultrafast transient absorption and photoluminescence spectroscopy, we revealed the relationship between catalytic activity and photoexcited electron dynamics in such a model SA catalytic system. The unique ligand-to-metal charge-transfer state formed in Ru-SAs/Def-TNs was found to be responsible for its high catalytic activity because it can greatly promote the transfer of photoelectrons from Def-TNs to the Ru-SAs center and the subsequent capture by Ru-SAs. This work sheds light on the origin of the high performance of SA catalysts from the perspective of photoexcited electron dynamics and hence enriches the mechanistic understanding of SA catalysis.

Friction energy harvesting on bismuth tungstate catalyst for tribocatalytic degradation of organic pollutants

Mechanical energy as the green and sustainable energy source widely distributes in natural environment. In this paper, we successfully realize the conversion of mechanical energy through a friction route on the tribocatalyst of Bi₂WO₆. Under magnetic stirring, the friction between the PTFE-sealed magnetic bar and the catalyst particles resulted in the electron transfer crossing the contact interface, in which PTFE accepted the electrons and simultaneously the holes were left on the catalyst. The positively charged catalyst was demonstrated through electrostatic attraction and repulsion tests. Like photocatalytic process, the holes on the valence band of Bi₂WO₆ have strong oxidative ability that can efficiently oxidize organic pollutants. The tribocatalytic tests showed that the Bi₂WO₆ could eliminate organic dyes under magnetic stirring in dark, and we could further optimize the tribocatalytic performance via regulating the size of magnetic bar and reactor material. Finally, a high stability of tribocatalysis was revealed by the multiple tests. This work not only develops a green tribocatalysis strategy to oxidative purification of organic pollutants, but also provides a possible pathway to convert mechanical energy in environment to chemical energy, such as potential applications in environmental remediation and sustainable energy.

Structural insight into [Fe-S2-Mo] motif in electrochemical reduction of N2 over Fe1-supported molecular MoS2

The catalytic synthesis of NH₃ from the thermodynamically challenging N₂ reduction reaction under mild conditions is currently a significant problem for scientists. Accordingly, herein, we report the development of a nitrogenase-inspired inorganic-based chalcogenide system for the efficient electrochemical conversion of N₂ to NH₃, which is comprised of the basic structure of [Fe-S₂-Mo]. This material showed high activity of 8.7 mg_NH3 mg_Fe ^-1 h^-1 (24 μg_NH3 cm^-2 h^-1) with an excellent faradaic efficiency of 27% for the conversion of N₂ to NH₃ in aqueous medium. It was demonstrated that the Fe₁ single atom on [Fe-S₂-Mo] under the optimal negative potential favors the reduction of N₂ to NH₃ over the competitive proton reduction to H₂. Operando X-ray absorption and simulations combined with theoretical DFT calculations provided the first and important insights on the particular electron-mediating and catalytic roles of the [Fe-S₂-Mo] motifs and Fe₁, respectively, on this two-dimensional (2D) molecular layer slab.

The role of oxygen defects in metal oxides for CO2 reduction

The abuse of fossil fuels release large amount of CO2, causing intense global warming. Using photoreduction and electroreduction to convert CO2 into highly valuable fuels such as CO and CH4 can effectively solve this problem. However, due to the limited activity and selectivity, pristine catalyst materials cannot meet the requirements of practical applications, which means that some modifications to these catalysts are necessary. In this review, a series of research reports on oxygen defect engineering have been introduced. First, the methods of preparing oxygen defects by heat treatment, doping, and photoinduction combined with influencing factors in the preparation are introduced. Subsequently, common characterization methods of oxygen defects including EPR, Raman, XPS, EXAFS, and HRTEM are summarized. Finally, the mechanisms of introducing oxygen defects to improve CO2 reduction are discussed, and include enhancing light absorption, improving CO2 adsorption and activation, as well as promoting stability of the reaction intermediates. The summary of research on oxygen defects provides guidance for researchers who focus on CO2 reduction and accelerate the realization of its industrial applications in the future.

Enhanced active oxidative species generation over Fe-doped defective TiO2 nanosheets for boosted photodegradation

Semiconductor photocatalysis is widely proposed for decomposing multiple pollutants via photo-generated oxidative species. However, the photocatalytic degradation performance in practical settings still remains unsatisfactory due to the limited production of active oxidative species (AOS). In this work, a defect engineering strategy was developed to explore the superiority of oxygen vacancies (Vo) and their structural regulation to enhance AOS production for boosting photodegradation. Taking anatase TiO₂ as a model photocatalyst, ultrathin TiO₂ nanosheets containing abundant Vo and appropriate Fe doping exhibited an unprecedented 134 times higher activity in the degradation of Rhodamine B (RhB) (rate as high as 0.3073 min⁻¹) than bulk anatase and were superior to most reported photocatalysts. The defect-rich ultrathin TiO₂ nanosheets could be further applied in high-efficiency degradation of tetracycline hydrochloride (TC-HCl) with the degradation rate of 0.0423 min⁻¹. The in situ electron paramagnetic resonance, advanced spectroscopic characterization and electrochemical measurement revealed the key role of Vo and Fe doping in facilitating the production of photo-generated holes and superoxide radicals (˙O₂⁻) that were identified to be effective to decompose both RhB and TC-HCl. This research provides insight into defect engineering promoting AOS generation and gives inspiration for the design of efficient photocatalysts for photooxidation applications.

Defect-rich ultrathin TiO₂ nanosheets with tunable Fe doping realize the efficient generation of active oxidative species for boosted dye/antibiotic photodegradation.

In situ preparation of g-C3N4 nanosheet/FeOCl: Achievement and promoted photocatalytic nitrogen fixation activity

Climate change, global warming, and population growth have led researchers to use eco-sociable procedures for the N₂ reduction reaction. It has discovered that N₂ molecule can be transformed into NH₃ in ambient circumstances with nanocomposites upon visible irradiation. In this research paper, a new visible-light-driven photocatalyst was constructed, with various weight percents of FeOCl particles (10, 20, 30, and 40%) that have adhered on NS-CN. Subsequently, multiple features of the nanocomposites were assayed in detail. The results illustrated that the NS-CN/FeOCl (20%) system has remarkable photoactivity in the NH₄⁺ production reaction in comparison with the NS-CN and CN, which showed 2.5 and 8.6 higher activity, respectively. The durability of NS-CN/FeOCl (20%) system, as a substantial factor, was assayed for 5 recycles. Moreover, the effect of electron quenchers, pH of media, and solvent was studied. At last, a feasible Z-scheme mechanism for the remarkable improvement of N₂ fixation efficiency was offered.

Oxygen-Deficient Bimetallic Oxide FeWOX Nanosheets as Peroxidase-Like Nanozyme for Sensing Cancer via Photoacoustic Imaging

Nanozymes with high catalytic activity and great stability have attracted increasing interests as the promising alternative to natural enzymes for applications in various fields. In this study, a new type of highly efficient peroxidase-like nanozymes based on FeWO_X nanosheets (NSs) synthesized by a thermal-decomposition method is reported. Owing to the sheet-structure with maximized utilization of catalytic sites (Fe atoms and oxygen vacancies), such FeWO_X NSs exert efficient enzyme activity to trigger catalytic decomposition of hydrogen peroxide (H₂ O₂ ) into hydroxyl radicals (•OH). A nanozyme-based ratio-metric nanoprobe is then fabricated by co-loading of 3,3,5,5-tetramethylbenzidine (TMB) and IR780 dye on FeWO_X NSs to enable ratio-metric photoacoustic (PA) imaging of endogenous H₂ O₂ , as verified by imaging of the subcutaneous 4T1 xenograft tumor model and lipopolysaccharide (LPS)-induced inflammation model. Moreover, FeWO_X NSs could also be employed as promising nanoagents for multimodal computed tomography (CT) and magnetic resonance (MR) imaging of tumors, due to the strong X-ray attenuation ability of W element and high MR contrast ability of Fe element, respectively. Importantly, FeWO_X NSs with good biodegradability could be cleared out from the body without any significant biotoxicity. This work highlights bimetallic oxide FeWO_X NSs as an enzyme-mimetic nanoplatform for imaging of the tumor microenvironment.

Enhancement of Titania Photoanode Performance by Sandwiching Copper between Two Titania Layers

Vacancies in semiconductors can play a versatile role in boosting their photocatalytic activity. In this work, a novel TiO2/Cu/TiO2 sandwich structure is designed and constructed. Abundant vacancies were introduced in TiO2 lattice by Cu reduction under heat treatment. Meanwhile, Cu atom could diffuse into TiO2 to form Cu-doped TiO2. The synergistic effect between oxygen vacancies and Cu atoms achieved about 2.4 times improved photocurrent of TiO2/Cu/TiO2 sandwich structure compared to bare TiO2 thin film. The enhanced photoactivity may be attributed to regulated electron structure of TiO2 by oxygen vacancies and Cu dopant from experimental results and density functional theory calculations. Oxygen vacancies and Cu dopant in TiO2 formed through copper metal reduction can introduce impurity levels and narrow the band gap of TiO2, thus improve the visible light response. More importantly, the Cu2+ and oxygen vacancies in TiO2 lattice can dramatically increase the charge density around conduction band and promote separation of photo-induced charge carriers. Furthermore, the oxygen vacancies on the surface may serve as active site for sufficient chemical reaction. This work presents a novel method to prepare doped metal oxides catalysts with abundant vacancies for improving photocatalytic activity.

Fe doped SrWO4 with tunable band structure for photocatalytic nitrogen fixation

Transition metal element doping into semiconducting materials has been a promising method for the preparation of active photocatalysts for the efficient use of solar energy. In this study, we report the facile synthesis of Fe doped SrWO₄ nanoparticles by a solvothermal method for photocatalytic nitrogen reduction. The intrinsic bandgap of SrWO₄ is greatly narrowed by the Fe-dopant which not only extends the light absorption from UV to visible light range, but also reduces the charge recombination. The narrowed band structure still fulfils the thermodynamic requirements of nitrogen reduction reaction. At optimal doping concentration, Fe doped SrWO₄ shows much higher photocatalytic nitrogen fixation performance. The present study provides a route toward the development of active photocatalysts for nitrogen fixation.

Enhanced Solar Photothermal Catalysis over Solution Plasma Activated TiO2

Colored wide-bandgap semiconductor oxides with abundant mid-gap states have long been regarded as promising visible light responsive photocatalysts. However, their catalytic activities are hampered by charge recombination at deep level defects, which constitutes the critical challenge to practical applications of these oxide photocatalysts. To address the challenge, a strategy is proposed here that includes creating shallow-level defects above the deep-level defects and thermal activating the migration of trapped electrons out of the deep-level defects via these shallow defects. A simple and scalable solution plasma processing (SPP) technique is developed to process the presynthesized yellow TiO2 with numerous oxygen vacancies (Ov), which incorporates hydrogen dopants into the TiO2 lattice and creates shallow-level defects above deep level of Ov, meanwhile retaining the original visible absorption of the colored TiO2. At elevated temperature, the SPP-treated TiO2 exhibits a 300 times higher conversion rate for CO2 reduction under solar light irradiation and a 7.5 times higher removal rate of acetaldehyde under UV light irradiation, suggesting the effectiveness of the proposed strategy to enhance the photoactivity of colored wide-bandgap oxides for energy and environmental applications.

Modified Nano-TiO2 Based Composites for Environmental Photocatalytic Applications

TiO2 probably plays the most important role in photocatalysis due to its excellent chemical and physical properties. However, the band gap of TiO2 corresponds to the Ultraviolet (UV) region, which is inactive under visible irradiation. At present, TiO2 has become activated in the visible light region by metal and nonmetal doping and the fabrication of composites. Recently, nano-TiO2 has attracted much attention due to its characteristics of larger specific surface area and more exposed surface active sites. nano-TiO2 has been obtained in many morphologies such as ultrathin nanosheets, nanotubes, and hollow nanospheres. This work focuses on the application of nano-TiO2 in efficient environmental photocatalysis such as hydrogen production, dye degradation, CO2 degradation, and nitrogen fixation, and discusses the methods to improve the activity of nano-TiO2 in the future.

Synergistic Effect of Surface-Terminated Oxygen Vacancy and Single-Atom Catalysts on Defective MXenes for Efficient Nitrogen Fixation

The production of ammonia (NH₃) from molecular dinitrogen (N₂) under ambient conditions is of great significance but remains as a great challenge. Using first-principles calculations, we have investigated the potential of using a transition metal (TM) atom embedded on defective MXene nanosheets (Ti_3-xC₂O_y and Ti_2-xCO_y with a Ti vacancy) as a single-atom electrocatalyst (SAC) for the nitrogen reduction reaction (NRR). The Ti_3-xC₂O_y nanosheet with Mo and W embedded, and the Ti_2-xC₂O_y nanosheet with Cr, Mo, and W embedded, can significantly promote the NRR while suppressing the competitive hydrogen evolution reaction, with the low limiting potential of -0.11 V for W/Ti_2-xC₂O_y. The outstanding performance is attributed to the synergistic effect of the exposed Ti atom and the TM atom around an extra oxygen vacancy. The polarization charges of the active center are reasonably tuned by the embedded TM atoms, which can optimize the binding strength of key intermediate *N₂H. The good feasibility of preparing such TM SACs on defective MXenes and the high NRR selectivity with regard to the competitive HER suggest new opportunities for driving NH₃ production by MXene-based SAC electrocatalysts under ambient conditions.

Efficient Nitrate Synthesis via Ambient Nitrogen Oxidation with Ru-Doped TiO2 /RuO2 Electrocatalysts

A facile pathway of the electrocatalytic nitrogen oxidation reaction (NOR) to nitrate is proposed, and Ru-doped TiO₂ /RuO₂ (abbreviated as Ru/TiO₂ ) as a proof-of-concept catalyst is employed accordingly. Density functional theory (DFT) calculations suggest that Ru^{δ +} can function as the main active center for the NOR process. Remarkably doping Ru into the TiO₂ lattice can induce an upshift of the d-band center of the Ru site, resulting in enhanced activity for accelerating electrochemical conversion of inert N₂ to active NO*. Overdoping of Ru ions will lead to the formation of additional RuO₂ on the TiO₂ surface, which provides oxygen evolution reaction (OER) active sites for promoting the redox transformation of the NO* intermediate to nitrate. However, too much RuO₂ in the catalyst is detrimental to both the selectivity of the NOR and the Faradaic efficiency due to the dominant OER process. Experimentally, a considerable nitrate yield rate of 161.9 µmol h^-1 g_cat ^-1 (besides, a total nitrate yield of 47.9 µg during 50 h) and a highest nitrate Faradaic efficiency of 26.1% are achieved by the Ru/TiO₂ catalyst (with the hybrid composition of Ru_x Ti_y O₂ and extra RuO₂ by 2.79 wt% Ru addition amount) in 0.1 m Na₂ SO₄ electrolyte.

Visible-light responsive BiNbO4 nanosheet photoanodes for stable and efficient solar-driven water oxidation

Herein, we report bismuth niobate (BiNbO4), which is regarded as an emerging photoanode material for sustainable photoelectrochemical (PEC) solar energy conversion. BiNbO4 possesses a direct bandgap (Eg) of ∼2.6 eV, and shows an appropriate band alignment for the water oxidation/reduction reaction. In this study, a simple sol-gel route followed by a spin coating method was applied to develop BiNbO4 nanosheets under the optimum annealing conditions. It is known that the annealing temperatures of 500 and 550 °C influence the crystallinity and PEC properties of BiNbO4 films. In particular, the 550 °C annealed film exhibited sharply improved crystalline properties, and rapidly enhanced PEC performance, which were accompanied by a photocurrent density of 0.45 mA cm-2 at 1.23 V vs. the reversible hydrogen electrode (RHE) (briefly abbreviated as 1.23 VRHE) in a strong alkaline solution of 1 M NaOH, compared with 0.26 mA cm-2 at 1.23 VRHE of the 500 °C annealed film. This may be attributed to the main increase of the crystallinity, as well as the improvement of the electronic properties. In addition, the BiNbO4 (550 °C) film showed an incident photon-to-current efficiency of 20% at 425 nm, and produced a stable photoresponse under light illumination in a strong alkaline solution over 5 h, compared with a BiVO4 electrode.

Photogenerated Oxygen Vacancies in Hierarchical Ag/TiO2 Nanoflowers for Enhanced Photocatalytic Reactions

Oxygen vacancy (V_o) creation and morphology controlling make significant contributions to the electronic and structural regulation of metal oxide semiconductors, yet an investigation about convenient approaches for fabricating hierarchical catalyst with abundant oxygen vacancies still has significant challenges. Here, we report a unique method to create abundant oxygen vacancies in hierarchical Ag/TiO₂ nanoflowers during photocatalytic reaction, which is accompanied by light absorption variation and surface plasmon resonance (SPR) enhancement. Its high efficiency of photocatalytic H₂ evolution (the highest apparent quantum yield reaches 3.2% at 365 nm) and rhodamine B degradation can be considered as benefits from the synergistic effects of the well-arranged hierarchical structure, the photogenerated oxygen vacancies, and the SPR of cocatalyst Ag. This work proposes an effective strategy to optimize the synthesis of regular hierarchical structures and enriches the research on the vital function of oxygen vacancies in photocatalytic reactions.

MXene-Derived Defect-Rich TiO2@rGO as High-Rate Anodes for Full Na Ion Batteries and Capacitors

Sodium ion batteries and capacitors have demonstrated their potential applications for next-generation low-cost energy storage devices. These devices's rate ability is determined by the fast sodium ion storage behavior in electrode materials. Herein, a defective TiO2@reduced graphene oxide (M-TiO2@rGO) self-supporting foam electrode is constructed via a facile MXene decomposition and graphene oxide self-assembling process. The employment of the MXene parent phase exhibits distinctive advantages, enabling defect engineering, nanoengineering, and fluorine-doped metal oxides. As a result, the M-TiO2@rGO electrode shows a pseudocapacitance-dominated hybrid sodium storage mechanism. The pseudocapacitance-dominated process leads to high capacity, remarkable rate ability, and superior cycling performance. Significantly, an M-TiO2@rGO//Na3V2(PO4)3 sodium full cell and an M-TiO2@rGO//HPAC sodium ion capacitor are fabricated to demonstrate the promising application of M-TiO2@rGO. The sodium ion battery presents a capacity of 177.1 mAh g-1 at 500 mA g-1 and capacity retention of 74% after 200 cycles. The sodium ion capacitor delivers a maximum energy density of 101.2 Wh kg-1 and a maximum power density of 10,103.7 W kg-1. At 1.0 A g-1, it displays an energy retention of 84.7% after 10,000 cycles.

Spatially Separated Bifunctional Cocatalysts Decorated on Hollow-Structured TiO2 for Enhanced Photocatalytic Hydrogen Generation

Efficient charge separation can promote photocatalysis of semiconductors. Herein, a hollow-structured TiO₂ sphere decorated with spatially separated bifunctional cocatalysts was designed, which exhibited enhanced photocatalytic hydrogen generation. Ultrasmall-sized MO_x (M = Pd, Co, Ni, or Cu) nanoparticles (NPs) were first introduced into a zeolite via confinement synthesis, and then, hollow TiO₂ was fabricated by using the zeolite as a sacrificial template forming MO_x@TiO₂. Finally, Pt NPs were decorated on the outer shell, giving rise to MO_x@TiO₂@Pt, in which the MO_x NPs and Pt NPs acted as hole capturers and electron sinks, respectively. Thanks to the enhanced light harvesting of the hollow structure and improved charge separation induced by the smaller-sized cocatalysts as well as spatially separated bifunctional cocatalysts, the as-prepared PdO_x@TiO₂@Pt catalyst exhibited a superior photocatalytic hydrogen-generation property (0.45 mmol h^-1). This work demonstrates the advantage of the spatially separated bifunctional cocatalysts in enhancing the photocatalytic properties of semiconductors.

Surface-Regulated Rhodium-Antimony Nanorods for Nitrogen Fixation

Surface regulation is an effective strategy to improve the performance of catalysts, but it has been rarely demonstrated for nitrogen reduction reaction (NRR) to date. Now, surface-rough Rh₂ Sb nanorod (RNR) and surface-smooth Rh₂ Sb NR (SNR) were selectively created, and their performance for NRR was investigated. The high-index-facet bounded Rh₂ Sb RNRs/C exhibit a high NH₃ yield rate of 228.85±12.96 μg h^-1  mg^-1 _Rh at -0.45 V versus reversible hydrogen electrode (RHE), outperforming the Rh₂ Sb SNRs/C (63.07±4.45 μg h^-1  mg^-1 _Rh ) and Rh nanoparticles/C (22.82±1.49 μg h^-1  mg^-1 _Rh ), owing to the enhanced adsorption and activation of N₂ on high-index facets. Rh₂ Sb RNRs/C also show durable stability with negligible activity decay after 10 h of successive electrolysis. The present work demonstrates that surface regulation plays an important role in promoting NRR activity and provides a new strategy for creating efficient NRR electrocatalysts.

Photocatalytic and Photoelectrochemical Systems: Similarities and Differences

Photocatalytic and photoelectrochemical processes are two key systems in harvesting sunlight for energy and environmental applications. As both systems are employing photoactive semiconductors as the major active component, strategies have been formulated to improve the properties of the semiconductors for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Although there are universal strategies applicable to improve the performance of photoactive semiconductors, similarities and differences exist when the semiconductors are to be used differently. Here, considerations on selected typical factors governing the performances in photocatalytic and photoelectrochemical systems, even though the same type of semiconductor is used, are provided. Understanding of the underlying mechanisms in relation to their photoactivities is of fundamental importance for rational design of high-performing photoactive materials, which may serve as a general guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuel generation.

Metastable oxygen vacancy ordering state and improved memristive behavior in TiO2 crystals

Oxygen vacancy is one of the pivotal factors for tuning/creating various oxide properties. Understanding the behavior of oxygen vacancies is of paramount importance. In this study, we identify a metastable oxygen vacancy ordering state other than the well-known Magnéli phases in TiO₂ crystals from both experimental and theoretical studies. The oxygen vacancy ordering is found to be a zigzag chain along the [0 0 1] direction in the (1 1 0) plane occurring in a wide temperature range of 200-500 °C. This metastable ordering state leads to a first-order phase transition accompanied by significant enhancement of dielectric permittivity and a memristive effect featuring a low driving electric field. Our results can improve oxide properties by engineering oxygen vacancies.

Few-Layer Black Phosphorus Nanosheets: A Metal-Free Cocatalyst for Photocatalytic Nitrogen Fixation

Exploiting an appropriate strategy to prepare fine crystal quality black phosphorus nanosheet (BPNS) catalyst is a major challenge for its practical application in catalysis. Herein, we address this challenge by developing a rapid electrochemical expansion strategy for scale preparation of fine crystal quality BPNSs from bulk black phosphorus, which was demonstrated to be an active cocatalyst for photocatalytic nitrogen fixation in the presence of CdS as a photocatalyst. The transient photocurrent and charge density studies show that the BPNSs can efficiently accelerate charge separation of CdS, leading to the enhanced photocatalytic activities of BPNS/CdS nanocomposites for nitrogen fixation. The 1.5% BPNS/CdS photocatalyst exhibits the highest photocatalytic activity for nitrogen fixation with an NH₃ evolution rate of 57.64 μmol·L^-1·h^-1. This study not only affords a rapid and simple strategy for scale synthesis of fine crystal quality BPNSs but also provides new insights into the design and development of black phosphorus-based materials as low-cost metal-free cocatalysts for photocatalytic nitrogen fixation.

Revisiting Pt/TiO2 photocatalysts for thermally assisted photocatalytic reduction of CO2

Artificial photosynthesis by a semiconductor-oxide-based photocatalysis is presently challenging due to low CO2 conversion rates and poor product selectivity. To promote CO2 reduction, Pt/TiO2 has been deemed as a classic photocatalyst. In this study, we restudy Pt/TiO2 for the thermally assisted photocatalytic reduction of CO2 and reveal a different story between photocatalysis and photothermal catalysis. For example, when using disordered Pt/TiO2-x, the CO2 conversion via photocatalysis at 298 K is not impressive. However, when the system temperature is increased to 393 K, the CO2 conversion rate is significantly enhanced by a factor of 155 as compared to that obtainable from pristine TiO2; further, surprisingly high selectivity of CH4 (87.5%) could be achieved. Thermally coupled photocatalysis yields the enhanced evolution of H2 side products over Pt (4.06 nm)/TiO2 and promoted H2 splitting over Pt (2.33 nm)/TiO2, which is seldom observed in conventional Pt/TiO2 photocatalysis. The synergy of improved charge separation at the Pt/TiO2-x interface induced by surface disordering and accelerated H2 consumption near smaller Pt nanoparticles by thermal assistance are believed to be critically important for the simultaneous enhancement of CO2 conversion rates and CH4 product selectivity. This study inspires revisiting not only Pt/TiO2 but also reactivating other semiconductor-oxide-based photocatalysts for use in thermally assisted photocatalysis.

Embedded carbon in a carbon nitride hollow sphere for enhanced charge separation and photocatalytic water splitting

Surface modification and morphological engineering are two important approaches to improve photocatalysis through enhancing photoabsorption and retarding charge recombination. Herein, a graphitic carbon integrated graphitic carbon nitride (C3N4) hollow sphere has been prepared via the modified shape-selective templating method in order to enchance light absorption and promote charge seperation under visible-light irradiation. MCM-41 that underwent carbonization at different temperatures in an inert atmosphere but not the conventional soft-template elimination was utilized as the sacrificial template. The resultant materials achieved an excellent photocatalytic performance with their hydrogen evolution rate reaching 718.1 μmol g-1 h-1, approximately 15 times higher than that of the bulk graphitic C3N4, resulting in 1.54% apparent quantum yield at 420 nm. The efficient photocatalysis was mainly attributed to the synergy of the vesicle morphology and carbon modification. The advantageous vesicle structure enhanced photoabsorption via the light scattering effect, while further carbon modification provided an efficient pathway to promote charge speration and transfer, which demonstrated that the carbon derived from the organic template residues (hexadecyl trimethyl ammonium bromide) was a facile yet effective medium to optimize the photocatalysis of C3N4.