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Exploring the structural changes of the reduced Cu/ZnO catalyst deposited on an activated carbon support and the factors affecting CO2 hydrogenation.

CO2 hydrogenation to methanol was conducted using a set of activated carbon-supported Cu/ZnO/Al2O3 catalysts (CCZA) prepared by an incipient wetness impregnation approach. The effect of the Cu/Al ratio on the physicochemical properties of the catalysts, as well as their catalytic performance, were investigated. As Cu/Al ratio increased, the metallic Cu surface area displayed a reducing trend from 6.88 to 4.18 m2∙gcat−1, while the CO2 adsorption capacity exhibited an increasing trend. Meanwhile, aluminum content will have an important effect on the catalysts’ reducibility and, thus, on their catalytic performance. The CCZA-2.7-de catalyst demonstrated the highest selectivity to methanol at 83.75% due to the excellent distribution and synergistic effect of copper and zinc. Although the CO2 conversion of CCZA-2.2-de and CCZA-3.5-de exceeded 10%, the CH3OH selectivity was less than 60%, which may be attributed to the larger particle sizes of ZnO and poor interactions in Cu–Zn. The present study offers a novel approach to increase the number of active sites, optimize the activated carbon-aided Cu/ZnO/Al2O3 catalyst’s composition, and finally elucidate the mechanism for CO2 hydrogenation to methanol.

2D/2D BOB/CN is applied for NFA degradation for the first time with high efficiency and stability, and the charge separation mechanism is demonstrated by EPR, in situ XPS and theoretical calculations.

To achieve high photocatalytic efficiency of H2 evolution, promoting the utilization rate of photogenerated charge carriers by photocatalytic synergistic reaction is an efficient strategy.

Precise regulation and control solar-light-driven charges photoexcited on photocatalysts for separation-transfer and target redox reactions is an attractive and challenging pathway toward sustainability. Herein, 0D/2D-3D Pt/In2S3 Schottky junction was fabricated for simultaneous selective phenylcarbinol conversion into value-added aldehydes and production of clean energy H2 by directly utilizing photoexcited holes and electrons in one reaction system under mild reaction conditions. In contrast to pure water splitting and pure In2S3, the reaction thermodynamics and kinetics of H2 evolution on the Pt/In2S3 were significantly enhanced. The optimized 0.3% Pt/In2S3 exhibited the highest and most stable photocatalytic activity with 22.1 mmol g−1 h−1 of H2 production rate and almost 100% selectivity of benzaldehyde production. Notably, this dual-function photocatalysis also exhibited superiority in contrast to sacrificial-agent H2 evolution reactions such as lactic acid, Na2S, methanol and triethanolamine. The turnover frequency (TOF) could reach up to ~2394 h−1. The Pt clusters anchored at the electron location and strong metal-support interactions (SMSI) between Pt and In2S3 synergistically improved the spatial charge separation and directional transportation (~90.1% of the charge transport efficiency could be achieved over the Pt/In2S3 hybrid), and thus result in significant enhancement of photocatalytic H2 evolution with simultaneous benzaldehyde production.

With an improved charge separation efficiency, the heterojunction catalysts are widely used to enhance photocatalytic activity. However, the transfer mechanism of photoexcited charge carriers remains unclear and the researches about...

Photocatalytic H

Integrating ultra-low content precious metal and low-cost solid-state optical absorber for effective utilization of photogenerated charges has been a hopeful strategy for selective organic transformations (SOTs). Herein, series of novel Au/CdS nanocomposites with (ultra-) low-content Au were prepared via two-step solvothermal treatment for the selective oxidation (SO) of aromatic alcohols (AA) and selective reduction (SR) of nitroarenes (NA) in one coupling system. Taking the advantages of electron accumulator property of Au and virtues of formed tight heterojunction between 5 nm gold nanoparticle (Au NPs) and CdS nanorods (CdS NRs), the Au/CdS nanocomposites exhibited outstanding charge separation and transfer performance and durable stability compared with blank CdS. The activities corresponding to the oxidation of aromatic alcohols and reduction of nitroaromatic hydrocarbons on the optimal 0.0028% Au/CdS samples are about 2 and 4 times higher than those of blank CdS. This is mainly due to the introduction of Au NPs and the construction of reasonable coupling reaction system, thus realizing the synergistic utilization of photogenerated charges. Finally, the mechanism and photocatalytic reaction pathway for the coupling reaction system were also proposed.

Enhancing the separation efficiency of photogenerated carriers is propitious for the promotion of photocatalytic hydrogen production from formic acid decomposition. Herein, MoS2/Zn3In2S6 (MoS2/ZIS6) composite photocatalysts containing varying mass percentages of MoS2 were obtained by a straightforward synthetic method. The results confirmed that MoS2, as a cocatalyst, markedly promoted the photogenerated charge separation efficiency and visible light-driven hydrogen production activity of ZIS6 (λ > 400 nm). Specifically, the as-prepared 0.5% MoS2/ZIS6 photocatalyst exhibited the highest photocatalytic hydrogen production rate (74.25 µmol·h−1), which was approximately 4.3 times higher than that of ZIS6 (17.47 µmol·h−1). The excellent performance of the 0.5% MoS2/ZIS6 photocatalyst may be due to the fact that MoS2 has a low Fermi energy level and can thus enrich photogenerated electrons from ZIS6, and furthermore reduce H+ derived from formic acid, to form hydrogen. The structure and morphology of the MoS2/ZIS6 photocatalysts and the reactive species were determined by X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy, among others; a plausible mechanistic rationale is discussed based on the results.

The transfer mechanism of photogenerated charges (e– and h+) has always been a research hotspot of the photocatalysis field. Here, a series of WO3/ZnO composite photocatalysts with different ratios...

Photocatalytic nitrogen fixation is considered as a very promising technology to solve the high-energy consumption problem in industrial ammonia synthesis. Because of the mildness of reaction condi...

Ni-based phosphides (NiPx) composed of earth-abundant elements are promising cocatalysts to replace noble metals for photocatalytic H2 evolution reaction (HER). A safe, energy-saving, and composition-controllable synthesis of NiPx is still highly desired. A facile and mild solvothermal process was developed for the first time for selective synthesis of a series of NiPx, including Ni, Ni12P5, Ni2P/Ni12P5, Ni/Ni2P and Ni2P, through controlling the dosage of NaBH4 and NaH2PO2. The phosphidation process was mainly composed of (1) a sequential reduction of Ni2+ to Ni0 and (H2PO2)− to P (around the formed Ni0) triggered by NaBH4, and (2) a final phosphidation between Ni0 and the in situ generated P atoms. The photocatalytic HER performance of g-C3N4 can be substantially improved with the decoration of NiPx (3 wt%) as the separation of photoinduced charge carriers can be promoted and some active sites with low over-potential for HER can be introduced. The cocatalytic efficiency of NiPx is mainly determined by P content. Ni2P with a high ratio of P consequently exhibits the highest HER performance (215.1 µmol g−1 h−1), which is almost six times higher than that of the pristine g-C3N4 (35.6 µmol g−1 h−1). Thus, as for the cocatalyst based on Ni phosphides, Ni2P is the preferable crystal phase and more efforts should be devoted to Ni2P to further optimize its structure, texture, and morphology in future works.

Construction of heterojunctions between semiconductors is a significant way to promote the photocatalytic performance by improving the photogenerated charge separation. Herein, CdS with multistage ...

Investigation of photoexcited charge transfer mechanism has always been one of the hotspots of photocatalysis field. In our recent studies, the relative p-n junction was proposed as a new concept, ...

Z-Scheme photocatalysts as a research focus perform strong redox capability and high photocatalytic performance. WO3/KNbO3 photocatalysts were fabricated by ball milling method, and performed higher photocatalytic activity in liquid degradation(rhodamine B, methylene blue and bisphenol A), compared with WO3 or KNbO3 monomer. This is due to that Z-scheme heterojunction is formed between WO3 and KNbO3, and the holes photoexcited in valence band of KNbO3 are quickly combined with the electrons in conduction band of WO3. The electrons accumulated in conduction band of KNbO3 show high reducibility, thereby reducing O2 to •O2−, and the holes in valence band of WO3 show high oxidative to oxidize H2O to •OH, respectively. Furthermore, it is proved by means of electron spin resonance(ESR) spectra, terephthalic acid photoluminescence probing technique(TA-PL), and UV-Vis absorption spectra of nitroblue tetrazolium. This work indicates that the fabrication of Z-scheme structure can improve the photocatalytic activity by efficiently separating the photogenerated electrons and holes in the photocatalytic reaction system, which is helpful to deeply understand the migration mechanism of photoexcited carrier(band-band transfer and Z-scheme transfer) in heterojunction photocatalysts.

Photocatalytic H2 production and CO2 reduction have attracted considerable attention for clean energy development. In this work, we designed an efficient photocatalyst by integrating lamellar oxygen-doped carbon nitride (CNO) nanosheets into ZnIn2S4 (ZIS) microflowers by a one-step hydrothermal method. A well-fitted 2D hierarchical hybrid heterostructure was fabricated. Under visible light irradiation, the ZIS@CNO composite with 40 wt% CNO (ZC 40%) showed the highest hydrogen evolution rate from water (188.4 μmol·h−1), which was approximately 2.1 times higher than those of CNO and ZIS (88.6 and 90.2 μmol·h−1, respectively). Furthermore, the selective CO production rates of ZC 40% (12.69 μmol·h−1) were 2.2 and 14.0 times higher than those of ZIS (5.85 μmol·h−1) and CNO (0.91 μmol·h−1), respectively, and the CH4 production rate of ZC 40% was 1.18 μmol·h−1. This enhanced photocatalytic activity of CNO@ZIS is due mainly to the formation of a heterostructure that can promote the transfer of photoinduced electrons and holes between CNO and ZIS, thereby efficiently avoiding recombination of electron-hole pairs.

Selective transformation of alcohols to corresponding aldehydes has a crucial significance under mild conditions in industrial manufacturing. Herein, a novel photothermal catalyst (Cr2O3-Al2O3)/CdS...

Developing an efficient, stable and low-cost photocatalytic hydrogen production from formic acid is a daunting challenge and has attracted the intense interest of many of researchers. In this paper, we report the synthesis of novel composite photocatalysts (Ni2P/Zn3In2S6 (ZIS6) and MoP/ZIS6) and their catalytic performance for H2 production reaction from formic acid under visible light irradiation, in which Ni2P and MoP were used as cocatalysts to enhance hydrogen generation activity of ZIS6. The photocatalytic hydrogen production rates of the optimized 1.5 wt% Ni2P/ZIS6 (45.73 μmol·h−1) and 0.25 wt% MoP/ZIS6 (92.69 μmol·h−1) were 3.5 times and 7.2 times higher than that of the pure ZIS6 (12.88 μmol·h−1), respectively. The apparent quantum efficiency at wavelength λ = 400 ± 10 nm for the two photocatalysts was about 1.8% and 6.4%, respectively. Significantly, it was found that the remarkable improvement of hydrogen production performance is attributed to the introduction of the phosphide cocatalysts, which can serve as a charge separation center and an active site for photocatalytic hydrogen production from the decomposition of formic acid. The reaction mechanism of photocatalytic hydrogen production from formic acid was also proposed.

Semiconductor photocatalysis has received tremendous attention as a promising way for solving the worldwide energy and environment issues. Many efforts have been devoted to developing distinctive morphology and various semiconductor-based composite photocatalysts for enhancing photocatalytic activity in recent years. However, it is still a great challenge and imperative to profoundly understand the transfer mechanisms and to realize complete utilization of photoexcited charge carriers. This perspective for the first time highlights the inner impetus of the photogenerated charge carrier migration (band-band and Z-scheme transfers) over composite photocatalytsts. The notion of relative p-n junction for photocatalysis and the corresponding design principle of Z-scheme photocatalysts are introduced first. Then, simultaneous utilization of photogenerated electrons and holes for photocatalytic selective redox syntheses in one reaction system is recommended. The proposed reaction systems have characteristics of the environmentally friendly, atom economy, synergistic effect and high efficiency. Finally, the challenges and opportunities of photocatalysis are outlined and a perspective is given. We hope that the perspective review could give an inspiration for the fundamental research and guide the research direction of photocatalysis.

Rational synthesis of photocatalytic materials is an effective way to improve their performance. In this work, to optimize the S precursors, a series of MnxCd1−xS (MCS) were first hydrothermally synthesized with the prevalent thiourea (TA), thioacetamide (TAA) and L-cysteine (L-Cys) as the S sources. The optimum feed ratio of Mn/Cd was then determined based on the optimized S precursor. The effects of S precursors and the feed ratio of Mn/Cd on the phase structure, absorption, morphology, band structure, and the photocatalytic hydrogen evolution reaction (HER) performance of MCS were investigated systematically. The hexagonal phase structures of MnS, CdS, and MCS are favored by TA and L-Cys as the S sources, while their cubic phases are benefited by TAA. TAA is the preferred S source for the preparation of highly active MCS and the solid solution is formed through the consolidation of cubic α-MnS into cubic CdS. The activity of MCS can be improved with the increase of Mn content from x = 0–0.6. The sample with x = 0.6 shows the highest HER activity (2253 μmol·h−1·g−1) and the performance is almost 6 times higher than CdS (416 μmol·h−1·g−1). The enhanced activity can be attributed to the improved separation efficiency of photo-induced charge carriers and the negative-shifts of Ecb, which are induced by the introduction of Mn. A segregation of inert α−MnS from MCS is occurred when Mn content is >0.6, resulting in a decay of the HER activity. A change of the semiconductivity from n-type to bipolar type is occurred in MCS due to the uneven sulfidation of Mn in MCS.

Environmental photocatlytsis has been considered as a promising alternative strategy to address the current environmental threats and pressures. Fabrication of the photocatalysts with high efficiency, stability and bio-safety is the core of photocatalytic applications. Herein, we report a facile approach to synthesize monazite BiPO

Effective utilization of photogenerated electrons and holes in a system is always a research hotspot. Photocatalysis has been identified as a promising solution to tackle the current environmental and energy issues. However, photogenerated holes or electrons were wasted in the traditional photocatalytic process. In the paper, a dual-function photocatalytic reaction system was constructed using dispersed Ptx-modified 2D-3D Zn3In2S6 hierarchical structures (x = 1–4). In the system, aromatic alcohols were photocatalytically selectively oxidated into aldehydes and protons were reduced to hydrogen by photogenerated holes and electrons, respectively. In the reaction process, one aromatic alcohol is first dehydrogenated into aromatic aldehyde and two H+ via the corresponding carbon-centered radical by consuming of two holes, and then two H+ ions dehydrogenated from OH group and α C H of alcohol are evolved into H2 by depleting of two electrons. Atomically dispersed Ptx could offer the maximum atom efficiency and significantly promote visible light absorption and separation of photogenerated electron-hole pairs. The cooperative photoredox system exhibits remarkable photocatalytic activity for visible light-driven splitting of aromatic alcohols. Under visible light irradiation for 6 h, The H2 output over 2.14% Pt/Zn3In2S6 reaches up to 950 μmol, which is around 7.5, 5.3 and 3.8 times higher than that over Zn3In2S6, Pt-nanoparticle/Zn3In2S6 and MoS2/Zn3In2S6, respectively. The apparent quantum efficiency (AQE) of 2.14% Pt/Zn3In2S6 at 400 nm is about 4.6%. The utilization rate of photogenerated electrons to holes could be achieved 98.2%. Moreover, Pt/Zn3In2S6 hybrid shows high stability even when Zn3In2S6 was stored for 12 months. Compared with two half-reactions: the photocatalytic selective organics transformation under O2 atmosphere and the water splitting with sacrificial reagents, such designed dual-purpose photocatalytic reaction not only could effective use of photogenerated electrons and holes for organics transformation and hydrogen production simultaneously but also shows much higher photocatalytic activity than two half-reactions. At the same time, the work also expands the research field of photocatalysis, such as N2 fixation and CO2 reduction by using of the as-produced H+.

The transfer mechanism of photoexcited charge carriers is always a hot topic in the photocatalysis research field. Coupling a photocatalyst with other photocatalysts is one of the most widely used ...

Photocatalytic selective organic transformations (SOTs) with sunlight offer a “green” route for synthesis of fine chemicals. In this work, a bare ternary chalcogenide CdLa2S4 photocatalyst was fabricated to couple the selective oxidation (SO) of aromatic alcohols to aldehydes and selective reduction (SR) of nitroarenes to anilines in one reaction system. The photocatalyst showed a high stability and a good generality for the conversions due to the well–matched band structure and the high separation efficiency of photoinduced electrons (e–) and holes (h+). For p–substituted aromatic alcohols, the selectivities to the corresponding aldehydes are as high as ca. 90%. The electro–donating substituent in the para position benefits the SO reactions, which are triggered by h+ via a successive deprotonation; while for p–substituted nitroarenes, the SR to the corresponding anilines is vulnerable to the electro–withdrawing groups and the steric hindrance of the substituent and the selectivities to anilines are substantially lower than that of the SO conversions. H+ deprotonated in the SO of aromatic alcohols is indispensable for the SR of nitroarenes as they are achieved by a H+–coupled six e– reduction process, which leads to the low conversion efficiencies. The half conversions not only be coupled by the photoinduced e– and h+, but also collaborate with each other through H+. Our results clearly demonstrate the emerging concept of a coupled reaction system for sunlight–driven synthesis of fine chemicals and reveal the underlying mechanism.

CdIn2S4, CdS and In2S3 photocatalysts were fabricated via a facile solvothermal method using indium chloride, cadmium nitrate and thiacetamide as precursors. The physicochemical and optical properties of the as-prepared samples were characterized by a series of techniques. The photocatalytic activities of the as-prepared samples were evaluated by selective aerobic oxidation of aromatic alcohols to corresponding aldehydes under visible light illumination. Compared with pure In2S3 and CdS samples, CdIn2S4 photocatalyst shows superior photocatalytic performance for selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). Under the optimal conditions, the conversion and selectivity for photocatalytic selective oxidation of BA to BAD are 80.1 and 98.8% under visible light irradiation for 2 h, respectively. The excellent photocatalytic performance of CdIn2S4 photocatalyst should be ascribed to its unique structure with a favorable absorptivity, appropriate conduction band and valence band positions and longer lifetime of photogenerated charge carriers. A possible reaction mechanism for selective oxidation of BA to BAD over CdIn2S4 photocatalyst with O2 and visible light is proposed. It is hoped that the current work could offer an avenue to prepare high-performance chalcogenide photocatalysts used in the field of photocatalytic selective organic transformations.

In the paper, the synthesis of ZnO/TiO2 nanocomposites with different main parts (TiO2 or ZnO) is studied. When TiO2 is the main part of the ZnO/TiO2 heterojunction photocatalysts (ZnO/TiO2), the photocatalytic activity is decreased rapidly with the increase of the amount of ZnO. The reason may be attributed to the relative p–n junction (p-ZnO/n-TiO2) produced between ZnO and TiO2. The migration directions of the electrons and holes in the relative p–n junction are opposite to the transfer directions of the photogenerated electrons and holes in the valence band (VB) and conduction band (CB). However, when ZnO is the primary part of the heterojunction photocatalysts (TiO2/ZnO), the photocatalytic activity of the samples increases with the increase of the TiO2 amount up to 5% (95% ZnO/TiO2). The reason may be that the migration directions of the electrons and holes in the relative p–n junction (p-TiO2/n-ZnO) are the same as the transfer directions of the photoexcited electrons and holes in VB and CB between...