Modularization of Regional Electronic Structure over Defect-Rich CeO2 Rods for Enhancing Photogenerated Charge Transfer and CO2 Activation.

Oxygen vacancy (OV) engineering has been widely applied in different types of metal oxide-based photocatalytic reactions. Our study has shown that the redistributed OVs resulting from voids in CeO2 rods lead to significant differences in the band structure in space. The flat energy band within the highly crystallized bulk region hinders the recombination of photogenerated carrier pairs during the transfer process. The downward curved energy band in the surface region enhances the activation of the absorbents. Therefore, the localization of the band structure through crystal structure regionalization renders V-CeO2 capable of achieving efficient utilization of photogenerated carriers. Practically, the V-CeO2 rod shows a remarkable turnover number of 190.58 µmol g-1 h-1 in CO2 photoreduction, which is ∼9.4 times higher than that of D-CeO2 (20.46 µmol g-1 h-1). The designed modularization structure in our work is expected to provide important inspiration and guidance in coordinating the kinetic behavior of carriers in OV defect-rich photocatalysts.

Single-atom catalyst of TM@D-silicene-an effective way to reduce N2 into ammonia.

Nowadays, the electrocatalytic nitrogen reduction reaction (NRR) still faces great challenges. It's significant to design the electrocatalysts with excellent activity and high selectivity. Herein, the 28 single atom catalysts of transition metal atoms anchored on defective silicene (TM@D-silicene) are designed for electrocatalytic ammonia synthesis under ambient conditions. Two independent screening schemes are proposed to screen the potential SAC candidate. The criteria of Ebin < 0 eV, ΔG*N2< -0.1 eV, ΔG*H > ΔG*N2, and the lowest ΔG*NNH in scheme I, as well as ΔG*N2< -0.1 eV, smaller G*NNH and larger G*NH2 in scheme II are utilized in the screening procedure. Finally, Cr@D-silicene is picked out since it performs well in the aspects of N2 adsorption, selectivity and catalytic activity of NRR. Moreover, the electronic properties are systematically investigated to clarify why the Cr@D-silicene is qualified for NRR from the perspective of the strong interaction between N2 and Cr, the continuous activation of the N2 molecule, charge transfer and distribution. This work provides a new idea for electrocatalytic ammonia synthesis by using single-atom catalysts.

Nitrogen reduction reaction on single cluster catalysts of defective PC6-trimeric or tetrameric transition metal.

The traditional Haber-Bosch method of ammonia (NH3) synthesis has low production efficiency and can lead to greenhouse gas emission due to high temperature and pressure dependent reactions. Hence, the nitrogen reduction reaction (NRR) in a mild environment has been developed. However, the inert NN triple bond and the competition with the hydrogen evolution reaction (HER) limit its wide application. In order to find an effective way of reducing N2 into NH3, in this work, PC6 monolayers with good electro-optical properties and eight transition metals (V, Cr, Mn, Fe, Co, Ni, Cu, Zn) are chosen to construct PC6-TM3 and PC6-TM4 single cluster catalysts (SCCs), which are proved to have low overpotential, multiple active-sites and superior activity. The thermodynamic stability, N2 adsorption, reaction paths, selectivity for the NRR and catalytic mechanism are systematically investigated. (PC6-Co3, PC6-Fe4)/(PC6-V3, PC6-Cr3)/(PC6-V4, PC6-Mn4) prefer to adsorb N2 rather than H in the end-on/side-on I/side-on III mode. PC6-Fe4 and PC6-Cr3 are finally screened out which have excellent catalytic activity with an overpotential of -0.46 V and -0.26 V in the consecutive path of side-on III and I modes, respectively. Moreover, both of them have 100% faradaic efficiency and present high selectivity for the NRR. The catalytic mechanism is elucidated by discussing the electronic properties of PC6-Cr3, where the back-donation behaviors of Cr atoms play an important role during the formation of NH3. This research may provide theoretical guidance for finding potential NRR catalysts with excellent performance and high selectivity.

Highly Selective Photocatalytic CO2 Methanation with Water Vapor on Single-Atom Platinum-Decorated Defective Carbon Nitride.

Solar-driven CO2 methanation with water is an important route to simultaneously address carbon neutrality and produce fuels. It is challenging to achieve high selectivity in CO2 methanation due to competing reactions. Nonetheless, aspects of the catalyst design can be controlled with meaningful effects on the catalytic outcomes. We report highly selective CO2 methanation with water vapor using a photocatalyst that integrates polymeric carbon nitride (CN) with single Pt atoms. As revealed by experimental characterization and theoretical simulations, the widely explored Pt-CN catalyst is adapted for selective CO2 methanation with our rationally designed synthetic method. The synthesis creates defects in CN along with formation of hydroxyl groups proximal to the coordinated Pt atoms. The photocatalyst exhibits high activity and carbon selectivity (99 %) for CH4 production in photocatalytic CO2 reduction with pure water. This work provides atomic scale insight into the design of photocatalysts for selective CO2 methanation.

TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction with enhanced photocatalytic for NO removal.

A TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction (TNS/BOB) was fabricated via a hydrothermal and electrostatic self-assembly method. The photocatalytic activity for NO removal was evaluated under simulated solar light irradiation. Through optimizing the content of TNS nanosheets, the photo-oxidative NO removal rate of 15% TNS/BOB was increased by up to 54.3%. This value is much higher than that of the individual components TNS (31.1%) and BOB (37.7%). Through capturing experiments and electron spin resonance (ESR) measurements, the main active species in the photocatalytic process were identified as ·[Formula: see text] and ·OH. Discrete Fourier transform computation results and ESR tests revealed that the photo-induced electrons in TNS should recombine with the holes in BOB, leading to effectively promoted charge separation at the TNS/BOB interface through the Z-type charge transfer. This work showed that with appropriate facet control and heterojunction design TiO2 can be used as an effective visible-light photocatalyst material.

Synergetic Effects of Pd0 Metal Nanoparticles and Pd2+ Ions on Enhanced Photocatalytic Activity of ZnWO4 Nanorods for Nitric Oxide Removal.

Doping and novel metallic nanoparticles loading on the photocatalyst are two effective means to enhance its photocatalytic activity. In our study, Pd0/Pd2+-co-modified ZnWO4 nanorods were fabricated by a two-step hydrothermal process and room-temperature reduction method. The performance of the as-prepared samples was evaluated through the photocatalytic nitric oxide (NOx) removal under simulated solar and visible-light irradiation. Pd0/Pd2+-co-modified ZnWO4 nanorods present a significantly enhanced photocatalytic activity for NOx removal compared with Pd0-loaded or Pd2+-doped ZnWO4 under simulated sunlight irradiation owing to a narrower band gap of Pd2+ doping compared with that of pure ZnWO4. The role of Pd0 nanoparticles is to act as an electron reservoir to restrain the recombination of e-/h+ pairs. According to the trapping measurements, the photoinduced holes and electrons play critical roles during the photocatalytic process. In addition, electron spin resonance (ESR) results further confirm that •O2- and •OH radicals are present and assist in the photocatalysis under simulated solar light irradiation. Stability test demonstrated that 1.5% Pd0/0.5% Pd2+-co-modified ZnWO4 nanorods as photocatalyst have high photocatalytic stability in NOx removal. This work proved that Pd0/Pd2+-co-modified ZnWO4 nanorods can be considered as an efficient photocatalyst for NOx removal.

Highly visible-light-responsive photocatalytic AgCl/BiOCl hetero-nanostructures synthesized by a chemical coprecipitation method.

AgCl/BiOCl heteronanostructures were synthesized by a room-temperature chemical coprecipitation method. The as-obtained products were characterized by energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse spectra, which show the structures, morphologies, and optical properties. The results revealed that the absorption edge of AgCl/BiOCl shifted towards visible light regions. Meanwhile, the AgCl/BiOCl heteronanostructures showed better photocatalytic properties than the pure BiOCl to degrade rhodamine B and the 5% AgCl/BiOCl showed the best photocatalytic ability, which completely decomposed the target molecules in 17 minites with the visible-light illumination. The formation of heteronanostructures might improve the separation of photogenerated electrons and holes derived from the coupling effect of BiOCl and AgCl heteroarchitectures, which was regarded as the main reason for the high photocatalytic activity.

Template-free hydrothermal synthesis different morphologies of visible-light-driven BiVO4 photocatalysts.

Monoclinic BiVO4 nano- and microstructures with a diversity of well-defined morphologies, such as nanoplates, dendrite leaves-like structures, sub-microrods, and microflowers were synthesized via a template-free hydrothermal process with bismuth nitrate and ammonium metavanadate as metal source. The crystal structures, morphologies and optical properties of the as-prepared samples were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV-visible absorption spectra (UV-vis). Results showed that the pH value of the solution and the volume of ethylenediamine have great effect on the formation of these unique structures. The photocatalytic activity of these as-prepared samples had been tested by degradation of methylene blue under visible light, indicating that showed good photocatalytic performance.

Sustainable all-weather CO2 utilization by mimicking natural photosynthesis in a single material.

Solar-driven CO2 conversion into hydrocarbon fuels is a sustainable approach to synchronously alleviating the energy crisis and achieving net CO2 emissions. However, the dependence of the conversion process on solar illumination hinders its practical application due to the intermittent availability of sunlight at night and on cloudy or rainy days. Here, we report a model material of Pt-loaded hexagonal tungsten trioxide (Pt/h-WO3) for decoupling light and dark reaction processes, demonstrating the sustainable CO2 conversion under dark conditions for the first time. In such a material system, hydrogen atoms can be produced by photocatalytic water splitting under solar illumination, stored together with electrons in the h-WO3 through the transition of W6+ to W5+ and spontaneously released to trigger catalytic CO2 reduction under dark conditions. Furthermore, we demonstrate using natural light that CH4 production can persist at night and on rainy days, proving the accomplishment of all-weather CO2 conversion via a sustainable way.

Induced dipole moments in amorphous ZnCdS catalysts facilitate photocatalytic H2 evolution.

Amorphous semiconductors without perfect crystalline lattice structures are usually considered to be unfavorable for photocatalysis due to the presence of enriched trap states and defects. Here we demonstrate that breaking long-range atomic order in an amorphous ZnCdS photocatalyst can induce dipole moments and generate strong electric fields within the particles which facilitates charge separation and transfer. Loading 1 wt.% of low-cost Co-MoSx cocatalysts to the ZnCdS material increases the H2 evolution rate to 70.13 mmol g-1 h-1, which is over 5 times higher than its crystalline counterpart and is stable over the long-term up to 160 h. A flexible 20 cm × 20 cm Co-MoSx/ZnCdS film is prepared by a facile blade-coating technique and can generate numerous observable H2 bubbles under natural sunlight, exhibiting potential for scale-up solar H2 production.

Achieving Molecular-Level Selective Detection of Volatile Organic Compounds through a Strong Coupling Effect of Ultrathin Nanosheets and Au Nanoparticles.

The high density of surface active sites, high efficiency of interfacial carrier transport, and molecular diffusion path determine the efficiency of the electrochemical sensors. The ultrathin structures have atomic-level thickness, carrier migration and heat diffusion are limited in the two-dimensional plane, resulting in excellent conductivity and high carrier concentration. A one-step chemical method is applied to synthesize defect-rich Au-SnO2 in an ultrathin nanosheet form (thickness of 2-3 nm). The strong interaction between Au and SnO2 via the Au-O-Sn bonding and the catalytic effect of Au can prolong the service life via decreasing the optimal operating temperature (55 °C) and promote the Au-SnO2 sensor to exclusively detect formaldehyde at the ppb level (300 ppb). The experimental findings along with theoretical study reveal that Au nanoparticles have a different effect on the competitive adsorption and chemical reaction over the surface of the Au-SnO2 with formaldehyde and other interfering VOC gases, such as methanol, ethanol, and acetone. This study provides mechanistic insights into the correlation between operating temperature and the performance of the Au-SnO2 chemiresistive sensor. This work allows the development of highly efficient and stable electrochemical sensors to detect VOC gases at room temperature in the future.

Visible light photocatalysis with c-WO(3-x)/WO3×H2O nanoheterostructures in situ formed in mesoporous polycarbosilane-siloxane polymer.

In recent years, there have been significant efforts to find novel photocatalytic materials with improved properties. Thus, there is an active ongoing search for new materials that can operate at a broad range of wavelengths for photocatalytic reactions. Among photocatalytically active semiconductors, considerable attention has been given to tungsten oxide with a band gap of E(g) ≈ 2.6 eV, which provides the opportunity to harvest visible light. In the present work, we report on a one-step synthesis of c-WO(3-x)/WO3×H2O nanowhiskers dispersed in a hydrolytically stable mesoporous polycarbosilane-siloxane ([-Si(O)CH2-]n) matrix. The as-synthesized nanocomposites possess high photocatalytic activity for the degradation of methylene blue (MB) under visible light irradiation. The enhanced photocatalytic activity is due to (i) the reduction in the electron-hole recombination rate because of the reduced dimensions of nanowhiskers, (ii) more efficient consumption of photogenerated electrons and holes as a result of the high surface-to-bulk-ratio of the nanowhiskers, and (iii) better electron-hole pair separation due to the formation of c-WO(3-x)/WO3×H2O nanoheterostructures.

Jointly augmented photocatalytic NO removal by S-scheme Bi12SiO20/Ag2MoO4 heterojunctions with surface oxygen vacancies.

The deep oxidation of NO molecules to NO3- species with the avoidance of toxic NO2 generation is a big and challengeable concern, which can be solved by the rational design and construction of catalytic systems with satisfactory structural and optical features. For such, in this investigation binary composites Bi12SiO20/Ag2MoO4 (BSO-XAM) were fabricated through a facile mechanical ball-milling route. From microstructural and morphological analyses, heterojunction structures with surface oxygen vacancies (OVs) were simultaneously created, contributing to the enhanced visible-light absorption, reinforced migration and separation of charge carries, and further boosted generation of reactive species such as superoxide radicals and singlet oxygen. Based on the density-functional theory (DFT) calculations, surface OVs induced the strengthened adsorption and activation of O2, H2O, and NO molecules and oxidation of NO to NO2, while heterojunction structures were beneficial for the continuous oxidation of NO2 to NO3- species. Thus, the heterojunction structures with surface OVs synergistically guaranteed the augmented photocatalytic NO removal and constrained NO2 generation of BSO-XAM through a typical S-scheme model. This study may provide scientific guidances for the photocatalytic control and removal of NO at ppb level by Bi12SiO20-based composites through the mechanical ball-milling protocol.

Hydrothermal synthesis of perovskite bismuth ferrite crystallites with the help of NH4Cl.

Bismuth ferrite nanopowders were hydrothermally synthesized with and without NH4Cl for comparison. The effects of NaOH concentration, reaction temperature and reaction time on the product phases and morphologies were studied in detail. Pure BiFeO3 was synthesized in a wide hydrothermal condition with the help of NH4Cl. Especially, it can be synthesized at low temperature of 140 degrees C. X-ray diffraction and Fourier transform infrared spectra revealed the BiFeO3 products had a perovskite structure. Scanning electron microscopy images showed that different BiFeO3 morphologies were formed under different hydrothermal conditions. NH4Cl played a key role in the BiFeO3 formation and BiFeO3 morphologies. Part BiFeO3 samples exhibited weak magnetic properties.

Rational design of n-Bi12TiO20@p-BiOI core-shell heterojunction for boosting photocatalytic NO removal.

Bismuth titanate (Bi12TiO20) with unique sillenite structure has been shown to be an excellent photocatalyst for environmental remediation. However, the narrow light-responsive range and rapid recombination of photoinduced electrons-holes limit the photocatalytic performance of Bi12TiO20. To overcome the limitations, a practical and feasibleway is to fabricate heterojunctions by combining Bi12TiO20 with suitable photocatalysts. Here, using a facile chemical precipitation method, a novel and hierarchical core-shell structure of n-Bi12TiO20@p-BiOI (BTO@BiOI) heterojunction was rationally designed and synthesized by loading BiOI nanosheets on BTO nanofibers. The constructed BTO@BiOI composites exhibited significant charge transfer ability due to the synergistic effects of the built-in electric field between BTO and BiOI as well as close interfacial contacts. In addition, the narrow bandgapcharacteristics of the BiOI led to wide light absorption ranges. Therefore, the BTO@BiOI heterojunction exhibited an improved photocatalytic performance under visible light irradiation. The NO removal efficiency of optimal BTO@BiOI was 45.7%, which was significantly higher compared tothat of pure BTO (3.6%) or BiOI (23.1%). Moreover, the cycling experiment revealed that BTO@BiOI composite has a good stability and reusability. The possible mechanism of photocatalytic NO oxidation over BTO@BiOI was investigated in detail.

2D/2D Schottky heterojunction of in-situ growth FAPbBr3/Ti3C2 composites for enhancing photocatalytic CO2 reduction.

Mimicking the natural photosynthesis process to convert carbon dioxide into value-added chemicals is vital to solving both the climate crisis worldwide and the depletion of fossil fuels. Herein, we explore the synthesis of 2D FAPbBr3 nanoplate combined with 2D Ti3C2 nanosheet to form a 2D/2D FAPbBr3/Ti3C2 Schottky heterojunction using facile hot-injection and in-situ growth approaches. The Schottky heterojunction of FAPbBr3/Ti3C2 over large interfacial contact provides abundant channels for transferring photogenerated carriers from FAPbBr3 nanoplate to Ti3C2 nanosheet. The experimental results showed a CO yield of 93.82 µmol·g-1·h-1 with ethyl acetate/deionization water as a sacrificial reagent for FAPbBr3/Ti3C2 composite, which was 1.25-fold enhancement that on pristine FAPbBr3 nanoplates. The large 2D heterointerface can efficiently accelerate the spatial separation and transfer of photogenerated carriers and result in the superior photocatalytic activity and favorable stability of FAPbBr3/Ti3C2 photocatalysts, which are proved by in-situ X-ray photoelectron spectroscopy, photoluminescence, transient absorption spectra, and Mott-Schottky measurement. Thus, this work unveils that 2D/2D Schottky heterostructures would significantly improve the reaction activities of halide perovskite-based photocatalysts.

Recent advancement in Bi5O7I-based nanocomposites for high performance photocatalysts.

Bi5O7I belongs to the family of bismuth oxyhalides (BiOX, X = Cl, Br, I), having a unique layered structure with an internal electrostatic field that promotes the separation and transfer of photo-generated charge carriers. Interestingly, Bi5O7I exhibits higher thermal stability compared to its other BiOX member compounds and absorption spectrum extended to the visible region. Bi5O7I has demonstrated applications in diverse fields such as photocatalytic degradation of various organic pollutants, marine antifouling, etc. Unfortunately, owing to its wide band gap of ∼2.9 eV, its absorption lies mainly in the ultraviolet region, and a tiny portion of absorption lies in the visible region. Due to limited absorption, the photocatalytic performance of pure Bi5O7I is still facing challenges. In order to reduce the band gap and increase the light absorption capability of Bi5O7I, doping and formation of heterostructure strategies have been employed, which showed promising results in the photocatalytic performance. In addition, the plasmonic heterostructures of Bi5O7I were also developed to further boost the efficiency of Bi5O7I as a photocatalyst. Here, in this review article, we present such recent efforts made for the advanced development of Bi5O7I regarding its synthesis, properties and applications. The strategies for photocatalytic performance enhancement have been discussed in detail. Moreover, in the conclusion section, we have presented the current challenges and discussed possible prospective developments in this field.

Bi selectively doped SrTiO3-x nanosheets enhance photocatalytic CO2 reduction under visible light.

Converting CO2 into chemical energy by using solar energy is an environmental strategy to achieve carbon neutrality. In this paper, two dimensionality (2D) SrTiO3-x nanosheets with oxygen vacancies were synthesized successfully. Oxygen vacancies will generate defect levels in the band structure of SrTiO3-x. So, SrTiO3-x nanosheets have good photocatalytic CO2 reduction performance under visible light. In order to further improve its photocatalytic efficiency, Bi was used to dope Sr site and Ti site in SrTiO3-x nanosheets respectively. It is found that Sr site is the adsorption site of CO2 molecules. When Bi replaced Sr, CO2 adsorption on the surface of SrTiO3-x nanosheets was weakened. When Bi replaced Ti, there has no effect on CO2 adsorption. Due to the synergistic effect of Bi doping, oxygen vacancies, and Sr active site, the 1.0% Bi-doped Ti site in SrTiO3-x (1.0% Bi-Ti-STO) had the best photocatalytic performance under visible light (λ ≥ 420 nm). CO and CH4 yields were 5.58 umol/g/h and 0.36 umol/g/h. Photocatalytic CO2 reduction path has always been the focus of exploration. The in-situ FTIR spectrum proved the step of photocatalytic CO2 reduction and COO- and COOH are important intermediates in the photocatalytic CO2 reaction.

Anchoring Platinum Clusters onto Oxygen Vacancy-Modified In2O3 for Ultraefficient, Low-Temperature, Highly Sensitive, and Stable Detection of Formaldehyde.

To avoid carcinogenicity, formaldehyde gas, currently being only detected at higher operating temperatures, should be selectively detected in time with ppb concentration sensitivity in a room-temperature indoor environment. This is achieved in this work through introducing oxygen vacancies and Pt clusters on the surface of In2O3 to reduce the optimal operating temperature from 120 to 40 °C. Previous studies have shown that only water participates in the competitive adsorption on the sensor surface. Here, we experimentally confirm that the adsorbed water on the fabricated sensor surface is consumed via a chemical reaction due to the strong interaction between the oxygen vacancies and Pt clusters. Therefore, the long-term stability of formaldehyde gas detection is improved. The results of theoretical calculations in this work reveal that the excellent formaldehyde gas detection of Pt/In2O3-x originates from the electron enrichment due to the surface oxygen vacancies and the molecular adsorption and activation ability of Pt clusters on the surface. The developed Pt/In2O3-x sensor has potential use in the ultraefficient, low-temperature, highly sensitive, and stable detection of indoor formaldehyde at an operating temperature as low as room temperature.

Anchoring of Formamidinium Lead Bromide Quantum Dots on Ti3C2 Nanosheets for Efficient Photocatalytic Reduction of CO2.

Metal halide perovskite with a suitable energy band structure and excellent visible-light response is a prospective photocatalyst for CO2 reduction. However, the reported inorganic halide perovskites have undesirable catalytic performances due to phase-sensitive and severe charge carrier recombination. Herein, we anchor the FAPbBr3 quantum dots (QDs) on Ti3C2 nanosheets to form a FAPbBr3/Ti3C2 composite within a Schottky heterojunction for photocatalytic CO2 reduction. Upon visible-light illumination, the FAPbBr3/Ti3C2 composite photocatalyst exhibits an appealing photocatalytic performance in the presence of deionized water. The Ti3C2 nanosheet acts as an electron acceptor to promote the rapid separation of excitons and supply specific catalytic sites. An optimal electron consumption rate of 717.18 µmol/g·h is obtained by the FAPbBr3/0.2-Ti3C2 composite, which has a 2.08-fold improvement over the pristine FAPbBr3 QDs (343.90 µmol/g·h). Meanwhile, the FAPbBr3/Ti3C2 photocatalyst also displays a superior stability during photocatalytic reaction. This work expands a new insight and platform for designing superb perovskite/MXene-based photocatalysts for CO2 reduction.