Photoreduction Process Research Articles

Corrosion Study of TiO2 Nanotubes Decorated with Ag Silver Nanoparticles Prepared by Photoreduction Process

Corrosion Study of TiO2 Nanotubes Decorated with Ag Silver Nanoparticles Prepared by Photoreduction Process

Snowflake-like In2S3/Cu2S heterojunction for simultaneous photocatalytic persulfate oxidation of tetracycline hydrochloride and CO2 photoreduction

To achieve tetracycline hydrochloride (TCH) elimination and CO2 photoconversion to CH4 and CO, snowflake-like In2S3/Cu2S heterojunctions were fabricated through the hydrothermal approach. Z-scheme junction generated between In2S3 and Cu2S was likely to separate and migrate the photoactivated e-/h+ pairs, boosting the photocatalytic-persulfate (photo-PS) activity and CO2 photoconversion capacity. The single photo-PS oxidation of TCH and CO2 photoreduction as well as their simultaneous photocatalytic behaviors over snowflake-like In2S3/Cu2S composites were comparatively investigated. For optimal 3-In2S3/Cu2S with a nominal In2S3 content of 5.0 wt%, the removal efficiency of unary photo-PS oxidation system was 99.90 %, CH4 and CO yield rates of single CO2 photoreduction process were respectively 177.67 and 94.42 μmol g-1h−1. In dual photo-PS oxidation and CO2 photoreduction system, the addition of CO2 leaded to the lower photo-PS activity, while the higher CH4 and CO yield rates of 3-In2S3/Cu2S. When added CO2 to dual photocatalytic system, the removal efficiency of TCH, CH4 and CO yield rates reached to 78.38 %, 106.80, and 73.84μmol g-1h−1, which were 0.94, 1.34, and 1.39 folds than those without CO2. This work provided the possibility of simultaneous photo-PS oxidation of pollutants and CO2 photoconversion to C1 compounds.

Efficient photocatalytic hydrogen production via single-atom Pt anchored hydrogen-bonded organic frameworks

Constructing single-atom catalysts (SACs) using organic porous framework materials as supports presents a promising approach for developing highly efficient photocatalysts for hydrogen evolution. However, the fabrication of SACs that are both highly stable and active poses a significant challenge, particularly in the precise anchoring of metal single atoms. In this study, we utilized 1,3,6,8-tetra (p-methyl benzoate) pyrene as a ligand to synthesize pyrene-based hydrogen-bonded organic frameworks (denoted as PFC-1) through a self-assembly approach. Subsequently, a liquid-phase photoreduction process was employed to deposit noble metal platinum (Pt) onto PFC-1, resulting in the fabrication of SACs (PFC-1@Pt). Characterization results confirmed that Pt existed in a monatomic state, anchored through PtC and PtO coordination bonds with PFC-1. Serving as electron capture and separation centers, the Pt single atoms effectively suppressed electron-hole recombination, thereby prolonging carrier lifetimes. Consequently, the PFC-1@Pt SAC exhibited efficient hydrogen evolution performance with a rate of 2202.5 μmol g−1 h−1 and maintained photocatalytic activity for over 40 h. Our findings provide a systematic approach for developing efficient and stable SACs based on HOFs, expanding the potential applications of HOF materials in photocatalysis.

Triggering Asymmetric Layer Displacement Polarization and Redox Dual-Sites Activation by Inside-Out Anion Substitution for Efficient CO2 Photoreduction.

Sluggish bulk charge transfer and barren catalytic sites severely hinder the CO2 photoreduction process. Seeking strategies for accelerating charge dynamics and activating reduction and oxidation sites synchronously presents a huge challenge. Herein, an inside-out chlorine (Cl) ions substitution strategy on the layered polar Bi4O5Br2 is proposed for achieving layer structure-dependent polarization effect and redox dual-sites activation. Cl ions in the bulk phase shrink the halogen layer interspace by 8‰, triggering asymmetric [Bi4O5]2+ layer displacement polarization, prolonging the average photocharge lifetime to 201.8ps. Meanwhile, surface substituted Cl ions enhance the electron-donating capability of neighboring Bi atoms, activating the intrinsic Bi reduction sites, and increasing H2O molecule adsorption on nearby intrinsic O oxidation site (cal. by 0.105eV), also self-donating as an alien oxidation site. Besides, Cl upshifts the p-band center closer to the Fermi level, facilitating the reactant adsorption. Therefore, the energy barrier for CO2 activation and rate-limiting *COOH intermediate formation steps are significantly decreased. Without cocatalysts and sacrificial reagents, inside-out Cl-substituted Bi4O5Br2 delivers a remarkable CO2-to-CO photoreduction rate of 50.18µmol g-1 h-1, being one of the state-of-the-art catalysts. This finding offers insights into exploiting polarization at the molecular-level and enhances understanding of catalytic site activation.

Enhancing d/p-2π* Orbitals Hybridization via Strain Engineering for Efficient CO2 Photoreduction.

The photoconversion of CO2 into valuable chemical products using solar energy is a promising strategy to address both energy and environmental challenges. However, the strongly adsorbed CO2 frequently impedes the seamless advancement of the subsequent reaction by significantly increasing the reaction activation energy. Here, we present a BiFeO3 material with lattice strain that collaboratively regulates the d/p-2π* orbitals hybridization between metal sites and *CO2 as well as *COOH intermediates to achieve rapid conversion of solidly adsorbed CO2 to critical *COOH intermediates, accelerating the overall CO2 reduction kinetics. Quasi in situ X-ray photoelectron spectroscopy and in situ Fourier Transform infrared spectroscopy combined with theoretical calculation reveals that the optimized Fe sites enhance the adsorption and activation effect of CO2, and continuous internal electrons are rapidly transferred to the reaction sites and injected into the surface *CO2 and *COOH under the condition of illumination, which promotes the rapid formation and stability of *COOH. Certainly, the performance of CO2 photoreduction to CO is improved by 12.81-fold compared with the base material. This work offers a new perspective for the rapid photoreduction process of strongly adsorbed CO2.

Enhancing d/p‐2π* Orbitals Hybridization via Strain Engineering for Efficient CO2 Photoreduction

AbstractThe photoconversion of CO2 into valuable chemical products using solar energy is a promising strategy to address both energy and environmental challenges. However, the strongly adsorbed CO2 frequently impedes the seamless advancement of the subsequent reaction by significantly increasing the reaction activation energy. Here, we present a BiFeO3 material with lattice strain that collaboratively regulates the d/p‐2π* orbitals hybridization between metal sites and *CO2 as well as *COOH intermediates to achieve rapid conversion of solidly adsorbed CO2 to critical *COOH intermediates, accelerating the overall CO2 reduction kinetics. Quasi in situ X‐ray photoelectron spectroscopy and in situ Fourier Transform infrared spectroscopy combined with theoretical calculation reveals that the optimized Fe sites enhance the adsorption and activation effect of CO2, and continuous internal electrons are rapidly transferred to the reaction sites and injected into the surface *CO2 and *COOH under the condition of illumination, which promotes the rapid formation and stability of *COOH. Certainly, the performance of CO2 photoreduction to CO is improved by 12.81‐fold compared with the base material. This work offers a new perspective for the rapid photoreduction process of strongly adsorbed CO2.

Research on 2D/2D Au/g-C3N4 electron donor/acceptor strategy for highly efficient CO2 photoreduction

Utilizing CO2 photoreduction technology to convert CO2 into carbon-based gaseous fuels represented an effective strategy for maintaining sustainable development on Earth. Addressing the issue of poor electron separation efficiency in pure g-C3N4, an innovative approach was taken to construct a two-dimensional/two-dimensional (2D/2D) structure using Au nanosheets (Au NSs) combined with g-C3N4 nanosheets (CN NSs) for CO2 photoreduction. The CO and CH4 yields converted by CO2 photoreduction over Au/CN composite (15AC) with optimized proportion were about 44.76 and 32.12 μmol g−1 h−1 under UV–Vis light irradiation, respectively. Photoelectrochemical experiments revealed that the modification of CN NSs with Au NSs significantly improved the separation efficiency of photogenerated carriers at the 2D/2D interface, while enhancing the CO2 adsorption ability of pure CN NSs. Density Functional Theory (DFT) calculations were employed to analyze the electron transfer pathways at the 15AC interface and the formation of a built-in electric field, which concurrently confirmed that the electron donor–acceptor relationship accelerated the transfer of photogenerated electrons from CN NSs to Au NSs. In-situ FTIR and 13CO2 isotope calibration experiment were utilized to probe the CO2 photoreduction process. Finally, the possible electron donor–acceptor enhanced mechanism at the 2D/2D Au/CN interface for enhancing the CO2 photoreduction reaction were discussed.

Cocatalyst Embedded Ce-BDC-CeO2 S-Scheme Heterojunction Hollowed-Out Octahedrons With Rich Defects for Efficient CO2 Photoreduction.

Constructing heterojunction photocatalysts with optimized architecture and components is an effective strategy for enhancing CO2 photoreduction by promoting photogenerated carrier separation, visible light absorption, and CO2 adsorption. Herein, defect-rich photocatalysts (Ni2P@Ce-BDC-CeO2 HOOs) with S-scheme heterojunction and hollowed-out octahedral architecture are prepared by decomposing Ce-BDC octahedrons embedded with Ni2P nanoparticles and subsequent lactic acid etching for CO2 photoreduction. The hollowed-out octahedral architecture with multistage pores (micropores, mesopores, and macropores) and oxygen vacancy defects are simultaneously produced during the preparation process. The S-scheme heterojunction boosts the quick transfer and separation of photoinduced charges. The formed hollowed-out multi-stage pore structure is favorable for the adsorption and diffusion of CO2 molecules and gaseous products. As expected, the optimized photocatalyst exhibits excellent performance, producing CO with a yield of 61.6µmolh-1g-1, which is four times higher than that of the original Ce-BDC octahedrons. The X-ray photoelectron spectroscopy, scanning Kelvin probe, and electron spin resonance spectroscopy characterizations confirm the S-schematic charge-transfer route. The key intermediate species during the CO2 photoreduction process are detected by in situ Fourier transform infrared spectroscopy to support the proposed mechanism for CO2 photoreduction. This work presents a synthetic strategy for excellent catalysts with potential prospects in photocatalytic applications.

High-performance photocatalytic reduction of CO2 to CO by defective g-C3N4/CeO2 under sacrificial agent-free conditions☆

Solar energy can be used to convert CO2 into valuable chemical compounds. However, the low activity of photocatalysts has hindered their development. By using defective g-C3N4/CeO2 heterojunctions, CO2 was successfully photo-reduced with high performance under ambient water vapor conditions without adding additives. g-C3N4 in this system has a significant impact on CO2 conversion efficiency, with 5 wt% g-C3N4/CeO2 exhibiting competitive performance, achieving 45.66 μmol/g CO in 6 h with nearly 100% selectivity. Photoactivity is attributed to the formation of g-C3N4/CeO2 heterojunctions, which provide excellent electron transport and electron-hole separation. Additionally, light enhances the CO2 adsorption capacity of the catalyst, thereby improving reaction properties. The photogenerated electrons generated under light excitation can quickly gather at the surface and defective parts of the sample, facilitating effective CO2 adsorption and promoting the formation of *COOH, thus promoting the photoreduction process of CO2. Cycle tests also demonstrate long-term stability. Highly efficient charge separation and reduced free energy of CO2 reduction both promote CO2 conversion performance. This work can provide an important idea for designing CeO2-based CO2 photocatalysts.

0D/2D Schottky heterojunction of CsPbBr3 nanocrystals on MoN nanosheets for enhancing charge transfer and CO2 photoreduction

Solar-driven conversion of CO2 to value-added chemical fuels has been regarded as a promising strategy for solving the climate problem and energy crisis. To realize this goal, it is vital to design photocatalysts with abundant catalytic active sites and excellent charge separation efficiency. Here, perovskite nanocrystals (CsPbBr3) were anchored on two-dimensional molybdenum nitride (MoN) using an in-situ growth method, forming a new and effective 0D/2D CsPbBr3@MoN (CPB@MoN) nanoheterosturcture with close contact interface for CO2 photoreduction. The introduction of MoN, acting as a charge transfer channel, could quickly trap the photoinduced charge from CsPbBr3 and provide abundant catalytic sites for CO2 photocatalytic reactions. For optimized CsPbBr3@MoN composites, the CO yield was 13.86μmol/gh−1 without any sacrificial reagent, which was a 4.5-fold enhancement of the pure CsPbBr3. Further, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the catalytic mechanism for the CO2 photoreduction process. This work provides a new platform for constructing superior perovskite/MoN-based photocatalysts for photocatalytic CO2 reduction.

Highly efficient and 100 % selectivity of CO generation via CO2 Photoreduction over a novel CsBr@CuBr2 Heterojunction

To address the global challenge posed by excessive carbon dioxide emissions, our research pioneers the transformation of CO2 into valuable hydrocarbon fuels. Central to this approach is the innovation of photocatalysts, engineered to exhibit exceptional photoresponse characteristics. In this research, the CsBr@CuBr2 photocatalyst was innovatively synthesized through a straightforward and effective one-pot method. The catalyst displayed remarkable efficacy, achieving a CO2 photoreduction rate of 201.47 μmol g−1 within just 4 h. The incorporation of CsBr into CuBr2 effectively captures excited-state electrons, thereby significantly enhancing charge separation efficiency. Utilizing in situ DRIFTS and DFT theoretical analysis, the experiment reveals the complex process of CO2 photoreduction to CO. The results of this experiment provide breakthrough insights for the systematic design of metal bromide heterostructures, which possess robust CO2 adsorption/activation potential and notable stability.

Using Mercury Stable Isotopes to Quantify Directional Soil-Atmosphere Hg(0) Exchanges in Rice Paddy Ecosystems: Implications for Hg(0) Emissions to the Atmosphere from Land Surfaces.

Gaseous elemental mercury [Hg(0)] emissions from soils constitute a large fraction of global total Hg(0) emissions. Existing studies do not distinguish biotic- and abiotic-mediated emissions and focus only on photoreduction mediated emissions, resulting in an underestimation of soil Hg(0) emissions into the atmosphere. In this study, directional mercury (Hg) reduction pathways in paddy soils were identified using Hg isotopes. Results showed significantly different isotopic compositions of Hg(0) between those produced from photoreduction (δ202Hg = -0.80 ± 0.67‰, Δ199Hg = -0.38 ± 0.18‰), microbial reduction (δ202Hg = -2.18 ± 0.25‰, Δ199Hg = 0.29 ± 0.38‰), and abiotic dark reduction (δ202Hg = -2.31 ± 0.25‰, Δ199Hg = 0.50 ± 0.22‰). Hg(0) exchange fluxes between the atmosphere and the paddy soils were dominated by emissions, with the average flux ranging from 2.2 ± 5.7 to 16.8 ± 21.7 ng m-2 h-1 during different sampling periods. Using an isotopic signature-based ternary mixing model, we revealed that photoreduction is the most important contributor to Hg(0) emissions from paddy soils. Albeit lower, microbial and abiotic dark reduction contributed up to 36 ± 22 and 25 ± 15%, respectively, to Hg(0) emissions on the 110th day. These novel findings can help improve future estimation of soil Hg(0) emissions from rice paddy ecosystems, which involve complex biotic-, abiotic-, and photoreduction processes.

Mott–Schottky heterostructural TiO2@Ag@AgBr nanohybrids for efficient photocatalytic degradation of Cr (VI) and enhanced on-site SERS detection

In the study, a novel ternary composite TiO2@Ag@AgBr was successfully prepared by surface modification of complete Ag layer and AgBr particles for photocatalytic degradation of representative heavy metal ions Cr (VI) and on-site Surface-enhanced Raman spectroscopy (SERS) detection of the Cr (VI) reduction process. The Mott–Schottky heterojunction contained structure exhibited remarkable photocatalytic ability for heavy metal ions Cr (VI) by tuning the ratio of Ag and AgBr, which could reduce Cr (VI) ions within 30 min and the reaction rate constant is 0.12 min−1. The remarkable photo-reduction performance is attributed to synergistic effect among the various components: the AgBr decorated on the surface of TiO2@Ag could significantly enhance the absorption of visible light and generate numerous photoexcited electrons and holes. Furthermore, the complete Ag layer was constructed on the TiO2 microspheres surface to form heterojunctions in the photocatalytic system by in-situ deposition of AgNO3. Mott–Schottky junctions formed between AgBr/Ag and Ag/TiO2 interface which could extend the charge transfer pathway and facilitate separation of photoexcited electrons and holes. The plasmonic metal layer of nano Ag could generate significant surface plasmon resonance (SPR) effect which not only enhanced the absorption of visible light but also exhibited remarkable SERS effect for probe molecules. And an amazing detection limit of 1 × 10–10 M could be obtained when using crystal violet (CV) as probe molecules. In addition, the SERS substrates exhibited significant linear relationship between concentration and SERS signal intensity which ensures the accuracy of quantitative analysis and monitoring photoreduction process. The substrates have good cycling stability, enabling it to be reused for SERS detection many times. Thus, the excellent photocatalytic and SERS performance of Mott–Schottky hetero-structural TiO2@Ag@AgBr substrates shows great potential toward rapidly photocatalytic removal Cr (VI) ions and SERS on-site detection reduction process of Cr (VI) in waste water, which is of great significance to environmental protection and ecological restoration.

Photocatalytic Deposition of Au Nanoparticles on Ti3C2Tx MXene Substrates for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman scattering (SERS) is a promising technique for sensitive detection. The design and optimization of plasma-enhanced structures for SERS applications is an interesting challenge. In this study, we found that the SERS activity of MXene (Ti3C2Tx) can be improved by adding Au nanoparticles (NPs) in a simple photoreduction process. Fluoride-salt-etched MXene was deposited by drop-casting on a glass slide, and Au NPs were formed by the photocatalytic growth of gold(III) chloride trihydrate solutions under ultraviolet (UV) irradiation. The Au-MXene substrate formed by Au NPs anchored on the Ti3C2Tx sheet produced significant SERS through the synergistic effect of chemical and electromagnetic mechanisms. The structure and size of the Au-decorated MXene depended on the reaction time. When the MXene films were irradiated with a large number of UV photons, the size of the Au NPs increased. Hot spots were formed in the nanoscale gaps between the Au NPs, and the abundant surface functional groups of the MXene effectively adsorbed and interacted with the probe molecules. Simultaneously, as a SERS substrate, the proposed Au-MXene composite exhibited a wider linear range of 10-4-10-9 mol/L for detecting carbendazim. In addition, the enhancement factor of the optimized SERS substrate Au-MXene was 1.39 × 106, and its relative standard deviation was less than 13%. This study provides a new concept for extending experimental strategies to further improve the performance of SERS.

Effect of the Photoreduction Process on the Self-Cleaning and Antibacterial Activity of Au-Doped TiO2 Colloids on Cotton Fabric.

This study aims at understanding the effect of the photoreduction process during the synthesis of gold (Au)-doped TiO2 colloids on the conferred functionalities on cotton fabrics. TiO2/Au and TiO2/Au/SiO2 colloids were synthesized through the sol-gel method with and without undergoing the photoreduction step based on different molar ratios of Au:Ti (0.001 and 0.01) and TiO2/SiO2 (1:1 and 1:2.3). The colloids were applied to cotton fabrics, and the obtained photocatalytic self-cleaning, wet photocatalytic activity, UV protection, and antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria were investigated. The obtained results demonstrated that the photoreduction of Au weakened the self-cleaning effect and reduced the photocatalytic activity of coated fabrics. Also, an excess amount of Au deteriorated the photocatalytic activity under both UV and visible light. The most efficient self-cleaning effect was obtained on fabrics coated with a ternary TiO2/Au/SiO2 colloid containing ionic Au, where it decomposed coffee and red-wine stains after 3 h of illumination. Adding silica (SiO2) made the fabrics superhydrophilic and led to greater methylene blue (MB) dye adsorption, a faster dye degradation pace, and more efficient stain removal. Moreover, the photoreduction process affected the size of Au nanoparticles (NPs), weakened the antibacterial activity of fabrics against both types of tested bacteria, and modestly increased the UV protection. In general, the photoactivity of Au-doped colloids was influenced by the synthesis method, the ionic and metallic states of the Au dopant, the concentration of the Au dopant, and the presence and concentration of silica.

An indirect Z-scheme heterostructure of nano-gold layer immobilized Cu-Al-doped SrTiO3 and CoOx-WO3 for photocatalytic CO2 reduction

Perovskite oxides have emerged as promising photocatalysts for CO2 reduction to valuable chemicals and fuels. However, conventional perovskite oxide photocatalysts often suffer from inefficient charge separation and bulk charge recombination, negatively impacting overall photoactivity. In this work, we present a novel immobilized perovskite oxide-based photocatalyst sheet featuring an indirect Z-scheme heterostructure composed of Cu-loaded Al-doped SrTiO3 (Cu-ASTO) and CoOx-loaded WO3 (CoOx-WO3) with an ultrathin (20 nm) gold interlayer serving as a conductive bridge. We tested this photocatalyst sheet in a sealed reactor containing a CO2-saturated aqueous solution of 0.1 M NaHCO3 and a side window to allow irradiation. Under irradiation with a 300 W Xe lamp, the Cu-ASTO/Au/CoOx-WO3 immobilized photocatalyst sheet produced methane (CH4) at a rate of 2.676 µmol cm-2 h−1 and methanol (CH3OH) at 0.517 µmol cm-2 h−1. We attribute the superior activity of this catalyst to the all-solid-state indirect Z-scheme heterostructure that greatly extends the lifespan of photoinduced charge carriers and enhances the CO2 photoconversion reaction. In experiments conducted outside, we demonstrated the immobilized photocatalyst's performance under natural sunlight, producing CH4 at 0.307 µmol cm-2 h−1 and CH3OH at 0.069 µmol cm-2 h−1. This work provides design ideas for developing robust immobilized photocatalyst systems for the scalable operation of the CO2 photoreduction process and broadening the scope of applications for perovskite heterostructure photocatalysts.

Dissolved black carbon mediated photo-reductive formation of colloidal-stable gold nanoparticles

Gold nanoparticles (AuNPs) have garnered attention as an emerging class of nanomaterials due to their wide range of applications across various sectors. This study reported that the dissolved black carbon (DBC) can mediate Au(III) photoreduction and form uniform and colloidal-stable AuNPs in aqueous solutions at room temperature under sunlight irradiation. Transmission electron microscopy images revealed that the average diameter of the photo-formed AuNPs was approximately 16 nm, and these nanoparticles maintained considerable colloidal-stability over time. Notably, no change in average size was observed following a 23-day storage period at 4°C in a light-free environment. The photo-formed superoxide (O2·-) is the crucial reductant in this reaction. O2·-, generated by DBC, reduces Au(III) to Au(I), which is then further reduced to Au(0), culminating in the formation of AuNPs. Furthermore, our findings illustrate that an increase in reaction pH shifts the predominant species of Au(III) in the solution toward forms with a lower redox potential, thereby decreasing the oxidizability of Au(III) and consequently decelerating the photoreduction process. A mildly acidic environment is more favorable for the DBC-mediated photoformation of AuNPs. This study elucidates that DBC can be observed as a novel reductant to complete the photo-reductive formation of AuNPs under low-cost conditions, opening up a new possibility for the green synthesis of AuNPs.

CdS/ZnS core–shell nanorod heterostructures co-deposited with ultrathin MoS2 cocatalyst for competent hydrogen evolution under visible-light irradiation

Hydrogen generation via semiconductor photocatalysts has gained significant attention as a sustainable fuel generation process. To demonstrate the performance of nanoscale core–shell heterostructure in photocatalytic hydrogen production, we have fabricated CdS nanorods coated with ZnS photocatalyst via wet-chemical reaction followed by deposition of ultrathin MoS2 nanosheets by photo reduction process. The effect of ZnS content and suitable amount of MoS2 loading over the visible-light induced photocatalytic hydrogen evolution was examined in Na2S and Na2SO3 aqueous solutions. Interestingly, it is apparent that a close connection (or heterojunction) between CdS and ZnS is believed to easily tunnel the charge carriers to the surplus surface states, making its electrons and holes energetically favourable to transfer from ZnS to MoS2 for photocatalytic reactions and subsequently, enhances the H2 evolution activity in CdS/ZnS type I core–shell heterostructures. The optimal MoS2 concentration is resolved to be 7 mol% and the subsequent visible-light induced H2 generation rate was 13589 μmol h−1g−1, which is 19 and 158 fold higher than pristine CdS and ZnS respectively. The probable photocatalytic mechanism of CdS/ZnS type I core–shell heterostructure with MoS2 cocatalyst is proposed. Our inexpensive and convenient preparation strategy may offer novel prospects in the engineering of desirable nanoheterostructures with better performance.

Defect-synergetic effect enhanced CO2 photoreduction efficiency of TiO2 nanostructures with Fe dopants

TiO2 nanostructures (NSs) doped with varying Fe concentrations are synthesized using the sol-gel process, followed by annealing in 1 atm environment at 470 ℃ for 3 h. Anatase TiO2 crystal structure and defect levels are characterized using XRD, HRTEM, SEM-EDS, XPS, Raman, EPR, PL, and TR-PL techniques. Remarkably, the addition of approximately 4 wt% Fe dopant had no discernible impact on the crystal structure of the anatase TiO2. Furthermore, energy levels including VO, Tii∙∙∙, Fe3+/Fe2+, Fe3+/Fe4+, and Ti3+/Ti4+ are identified. The optical band-gap of TiO2 is reduced from 3.077 to 2.352 eV and its carrier lifetime is extended from 6.53 ns to 9.12 ns with Fe contents ranging from 0 to approximately 2 wt%. The CO2 photoreduction results demonstrate that Fe-doped TiO2 outperforms commercial TiO2 (P25) in terms of the photoreduction rate. Particularly, TiO2 NSs doped with 2 wt% Fe exhibit the highest CO2 photoreduction rates, yielding approximately 35.19×102 and 66.84×102 μmol‧g1‧min1of CO and CH4, respectively; thereby surpassing P25 by factors of 1.26 and 3.1, respectively. Therefore, Fe-doping can reduce the optical band-gap and extend the carrier lifetime of TiO2 photocatalysts, resulting in superior CO2 photoreduction capabilities. Moreover, the significance of electrons in the CO2 photoreduction process, as evidenced by the findings from the EPR spectrum and CO2 photoreduction, underscores the importance of an appropriate Fe content, such as 2 wt% used in this study, for enhancing the photoreduction abilities and potential applications of TiO2 in CO2 photoreduction.

MOF-on-MOF-derived CuO@In2O3 s-scheme heterojunction with core–shell structure for efficient photocatalytic CO2 reduction

Herein, a MOF-on-MOF-derived In2O3 nanosheets encapsulating CuO ortho-octahedral core–shell structure CuO@In2O3 S-Scheme heterojunction composite was designed and prepared by a new strategy of interfacial engineering integrating optical and catalytic activity centers, which endowed with the catalyst's dual properties of both highly efficient light absorption and charge separation. The In2O3 shell wraps around the CuO core in a tight coaxial contact, allowing them have the largest contact surface thus effectively promoting the transport of electrons and holes separated at the interface. More importantly, CuO@In2O3 formed a binuclear center could enhance the CO2 adsorption to facilitate the subsequent catalytic reaction and promote the charge transfer through Cu-O-In bonds. The successful construction of S-scheme heterojunction not only promotes the spatial separation of electron-hole pairs, but also maintains the strongest redox potentials of CuO and In2O3 at the conduction and valence band positions. Notably, the intermediates in the CO2 photoreduction process were probed by in situ infrared spectroscopy and a possible photocatalytic mechanism was hypothesized. Under visible light irradiation, the CuO@In2O3 rates of photocatalytic reduction of CO2 to produce CH4 and CO were 190.32 μmol g−1h−1 and 500.46 μmol g−1h−1, which are 2.1, 10.3 times and 2.4, 7.9 times higher than pristine CuO and In2O3, respectively. This work provides a feasible strategy for the design and synthesis of binuclear-centered photocatalysts with interfacial engineered modulation and application to the photocatalytic reduction of CO2.