Integrated p-n/Schottky junctions for efficient photocatalytic hydrogen evolution upon Cu@TiO2-Cu2O ternary hybrids with steering charge transfer

Photocatalytic reduction of carbon dioxide by BiTeX (X = Cl, Br, I) under visible-light irradiation

In this study, a series of BiTeX (X = Cl, Br, I) photocatalysts were successfully synthesized via a simple hydrothermal method. The synthesis process involved dissolving BiX3 and Te powder in toluene to identify the most efficient material for photocatalytic activity. The main objective of this approach is to facilitate the conversion of carbon dioxide into sustainable solar fuels, such as alcohols and hydrocarbons, offering an appealing solution to address environmental concerns and energy crises. The BiTeX photocatalysts demonstrated significant proficiency in converting CO2 into CH4, particularly BiTeCl exhibited a notable photocatalytic conversion rate of up to 0.51 μmolg-1h-1. The optimized BiTeX photocatalysts displayed a gradual and selective transition from CO2 to CH4, ultimately producing valuable hydrocarbons (C2+). Furthermore, owing to their ability to reduce CO2, these photocatalysts show promise as materials for mitigating environmental pollution.

Self-healing of oxygen vacancies and phase transition-induced built-in electric field regulate H2 and H2O2 production

Oxygen vacancies in photocatalysts are an important parameter for improving their catalytic activities. However, this study found that oxygen vacancies do not always help with photocatalytic properties. MXene nanosheets were annealed at different temperatures to prepare nanosheets of titanium dioxide (TiO2) with anatase or rutile phase. Photo-induced self-healing of oxygen vacancies in MXene nanosheets annealed at 400 °C promoted the efficient photocatalytic evolution of hydrogen (H2) with a ∼ 6.8 mmol/g optimized yield. In contrast, the photo-induced increase of oxygen vacancies in MXene nanosheets annealed at 500 °C corresponded to an optimized ∼ 1.8 mmol/g/h yield of hydrogen peroxide (H2O2). Spectroscopic and electrochemical methods revealed that the built-in electric field between the anatase and rutile TiO2 facilitated the fast charge separation from the anatase to rutile TiO2. The photo-induced self-healing of oxygen vacancies and the phase transition-induced built-in electric field regulated the photocatalytic selectivity of H2 and H2O2 production.

The construction of S-scheme heterostructure in ultrathin WS2/Zn3In2S6 nanosheets for enhanced photocatalytic hydrogen evolution

Metal sulfide based photocatalysts are considered to be economic, environmentally benign and renewable. The rapid recombination of photogenerated electrons and holes and low solar energy utilization efficiency, however, remain a huge bottleneck. Herein, two-dimensional/two-dimensional (2D/2D) S-scheme WS2/Zn3In2S6 heterostructure with ultrathin nanosheets intervening between neighboring component has been designed. The large and intimate S-scheme heterojunctions facilitate interfacial charge separation/transfer and optimize the available redox potential. Besides, the ultrathin 2D/2D heterostructure ensures large specific surface area, maximized interface synergistic interaction, and effective exposure of surface active sites. As a result, 2 wt% WS2/Zn3In2S6 exhibits a high photocatalytic hydrogen production rate of 30.21 mmol·g-1·h-1 under simulated solar light illumination with an apparent quantum efficiency of 56.1% at 370 nm monochromatic light, far exceeding pristine Zn3In2S6 (6.65 mmol·g-1·h-1). Our work underscores the significance of integrating morphology engineering and S-scheme heterojunctions design for high-efficient and low-cost photocatalysts.

Tailoring Interfacial Physicochemical Properties in Cu2O-TiO2@rGO Heterojunction: Insights from EXAFS and Electron Trap Distribution Analysis

In this study, a solution-based synthesis technique was utilized to produce Cu2O nanoparticles (NPs) on TiO2 nanofibers (TNF), which were then subsequently coated with reduced graphene oxide (rGO) nanosheets. In the absence of any cocatalyst, CTNF@rGO-3% composite displayed an ideal photocatalytic H2 evolution rate of 96 μmol g-1 h-1 under visible light irradiation, this was 10 times higher than that of pure TNF. At 420 nm, the apparent quantum efficiency of this composite reached a maximum of 7.18%. Kelvin probe force microscopy demonstrated the formation of an interfacial electric field that was oriented from CTNF to rGO and served as the driving force for interfacial electron transfer. The successful establishment of an intimate interface between CTNF@rGO facilitated the efficient transfer of charges and suppressed the rate of recombination of photogenerated electron-hole pairs, leading to a substantial enhancement in photocatalytic performance. X-ray photoelectron spectroscopy, photoluminescence spectra, and electrochemical characterization provide further confirmation that formation of a heterojunction between CTNF@rGO leads to an extension in the lifetimes of the photogenerated charge carriers. The experimental evidence suggests that a p-n heterojunction is the mechanism responsible for the significant photocatalytic activity observed in the CTNF@rGO composite during H2 evolution.

Synergistic effect of excellent carriers separation and efficient high level energy electron utilization on Bi3+-Ce2Ti2O7/ZnIn2S4 heterostructure for photocatalytic hydrogen production

The separation of photogenerated carriers and the efficient utilization of high-level energy electrons (HLEEs) are the key processes for improving the performance of photocatalysts. Herein, Ce2Ti2O7/ZnIn2S4 (CTOZIS) and Bi3+-doped Ce2Ti2O7/ZnIn2S4 (BCTOZIS) photocatalyst were successfully synthesized through hydrothermal method. The photocatalytic hydrogen production of CTOZIS and BCTOZIS was 1233.7 μmol g-1 and 4168.5 μmol g-1 under visible light irradiation (λ ≥ 420 nm) within 5 h, which was 2.3 and 7.6 times than that of pure ZnIn2S4, respectively. X-ray photoelectron spectroscopy, photoluminescence spectroscopy and electrochemical characterization demonstrated that after Bi3+ doping, the electron-hole pairs recombination of BCTOZIS was inhibited, which may be ascribed to the establishment of a Z-scheme heterojunction and the presence of oxygen vacancy and Ce4+/Ce3+ redox center. The doping of Bi3+ resulted in the adjustment of the valence band position of Ce2Ti2O7 from 1.98 V to 1.92 V. This adjustment enabled direct transfer of HLEEs generated in Ce2Ti2O7 to the conduction band of ZnIn2S4 for hydrogen production with a wavelength below 423 nm. The synergistic effect of conventional Z-scheme electron transfer and the unique utilization of HLEEs boosted the photocatalytic performance of BCTOZIS. This study affords an innovative insight for designing visible-light-driven photocatalysts with high photocatalytic activity.

A Review on Cu2O-Based Composites in Photocatalysis: Synthesis, Modification, and Applications

Photocatalysis technology has the advantages of being green, clean, and environmentally friendly, and has been widely used in CO₂ reduction, hydrolytic hydrogen production, and the degradation of pollutants in water. Cu₂O has the advantages of abundant reserves, a low cost, and environmental friendliness. Based on the narrow bandgap and strong visible light absorption ability of Cu₂O, Cu₂O-based composite materials show infinite development potential in photocatalysis. However, in practical large-scale applications, Cu₂O-based composites still pose some urgent problems that need to be solved, such as the high composite rate of photogenerated carriers, and poor photocatalytic activity. This paper introduces a series of Cu₂O-based composites, based on recent reports, including pure Cu₂O and Cu₂O hybrid materials. The modification strategies of photocatalysts, critical physical and chemical parameters of photocatalytic reactions, and the mechanism for the synergistic improvement of photocatalytic performance are investigated and explored. In addition, the application and photocatalytic performance of Cu₂O-based photocatalysts in CO₂ photoreduction, hydrogen production, and water pollution treatment are discussed and evaluated. Finally, the current challenges and development prospects are pointed out, to provide guidance in applying Cu₂O-based catalysts in renewable energy utilization and environmental protection.

A p-n Junction by Coupling Amine-Enriched Brookite-TiO2 Nanorods with CuxS Nanoparticles for Improved Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction is a promising technology for reaching the aim of "carbon peaking and carbon neutrality", and it is crucial to design efficient photocatalysts with a rational surface and interface tailoring. Considering that amine modification on the surface of the photocatalyst could offer a favorable impact on the adsorption and activation of CO₂, in this work, amine-modified brookite TiO₂ nanorods (NH₂-B-TiO₂) coupled with Cu_xS (NH₂-B-TiO₂-Cu_xS) were effectively fabricated via a facile refluxing method. The formation of a p-n junction at the interface between the NH₂-B-TiO₂ and the Cu_xS could facilitate the separation and transfer of photogenerated carriers. Consequently, under light irradiation for 4 h, when the Cu_xS content is 16%, the maximum performance for conversion of CO₂ to CH₄ reaches at a rate of 3.34 μmol g^-1 h^-1 in the NH₂-B-TiO₂-Cu_xS composite, which is approximately 4 times greater than that of pure NH₂-B-TiO₂. It is hoped that this work could deliver an approach to construct an amine-enriched p-n junction for efficient CO₂ photoreduction.

Co-embedding oxygen vacancy and copper particles into titanium-based oxides (TiO2, BaTiO3, and SrTiO3) nanoassembly for enhanced CO2 photoreduction through surface/interface synergy

Photocatalytic CO₂ reduction into valuable fuel and chemical production has been regarded as a prospective strategy for tackling with the issues of the increasing of greenhouse gases and shortage of sustainable energy. A composite photocatalysis system employing a semiconductor enriched with oxygen vacancy and coupled with metallic cocatalyst can facilitate charge separation and transfer electrons. In this work, mesoporous TiO₂ and titanium-based perovskite oxides (BaTiO₃ and SrTiO₃) nanoparticle assembly incorporated with abundant oxygen vacancy and copper particles have been successfully synthesized for CO₂ photoreduction. As an example, the TiO₂ decorated with different amounts of Cu particles has an impact on photocatalytic CO₂ reduction into CH₄ and CO. Particularly, the optimal TiO₂/Cu-0.1 exhibits nearly 13.5 times higher CH₄ yield (22.27 μmol g^-1 h^-1) than that of pristine TiO₂ (1.65 μmol g^-1 h^-1). The as-obtained BaTiO₃/Cu-0.1 and SrTiO₃/Cu-0.1 also show enhanced CH₄ yields towards photocatalytic CO₂ reduction compared with pristine ones. Based on the temperature programmed desorption (TPD) and photo/electrochemical measurements, the co-embedding of Cu particles and abundant oxygen vacancy into the titanium-based oxides could promote CO₂ adsorption capacity as well as separation and transfer of photoinduced electron-hole pairs, and finally result in efficient CO₂ photoreduction upon the TiO₂/Cu, SrTiO₃/Cu, and BaTiO₃/Cu composites.

Multifunctional magnetic Fe3O4/Cu2O-Ag nanocomposites with high sensitivity for SERS detection and efficient visible light-driven photocatalytic degradation of polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) with carcinogenic, teratogenic and mutagenic properties are persistent organic pollutants in the environment. Herein, the novel multifunctional Fe₃O₄/Cu₂O-Ag nanocomposites (NCs) have been established for ultra-sensitive surface-enhanced Raman scattering (SERS) detection and visible light-driven photocatalytic degradation of PAHs. Fe₃O₄/Cu₂O-Ag NCs with different amounts of Ag nanocrystals were synthesized, and the effect of Ag contents on SERS performance was studied by finite-difference time-domain (FDTD) algorithm. The synergistic interplay of electromagnetic and chemical enhancement was responsible for excellent SERS sensitivity of Fe₃O₄/Cu₂O-Ag NCs. The limit of detection (LOD) of optimal SERS substrates (FCA-2 NCs) for Nap, BaP, Pyr and Ant was as low as 10^-9, 10^-9, 10^-9 and 10^-10 M, respectively. The SERS detection of PAHs in actual soil environment was also studied. Moreover, a simple SERS method was used to monitor the photocatalytic process of PAHs. The recovery and reuse of Fe₃O₄/Cu₂O-Ag NCs were achieved through magnetic field, and the outstanding SERS and photocatalytic performance were still maintained even after eight cycles. This magnetic multifunctional NCs provide a unique idea for the integration of ultra-sensitive SERS detection and efficient photocatalytic degradation of PAHs, and thus will have more hopeful prospects in the field of environmental protection.