Energy funneling and charge separation in CdS modified with dual cocatalysts for enhanced H2 generation

P-doped Mn0.5Cd0.5S coupled with cobalt porphyrin as co-catalyst for the photocatalytic water splitting without using sacrificial agents

Photocatalytic water splitting over semiconductors is an important approach to solve the energy demand of human beings. Most photocatalytic H2 generation reactions are conducted in the presence of sacrificial agent. However, the use of sacrificial reagents increases the cost of hydrogen generation. Realizing photocatalytic water splitting for hydrogen production without the addition of sacrificial agents is a major challenge for photocatalysts. The porphyrin MTCPPOMe and P doped MnxCd1-xS make a significant contribution in facilitating the MnxCd1-xS photocatalytic pure water splitting to H2 reaction. Herein, a novel MTCPPOMe/P-MnxCd1-xS (M = 2H, Fe, Co, Ni) composite catalyst which can efficiently split pure water without using sacrificial agents is developed. As a result, the H2 generation rate of CoTCPPOMe/P-Mn0.5Cd0.5S is as high as 2.10 μmol h-1, which is 9.1 and 4.2 times higher than that of Mn0.5Cd0.5S (MCS) and P-Mn0.5Cd0.5S (P-MCS), respectively. P doped MnxCd1-xS inhibits the recombination of photogenerated carriers, and introduction of MTCPPOMe as co-catalyst enhances the reduction capacity. In summary, an efficient and economical photocatalystis prepared for pure water splitting to prepare hydrogen.

Mononuclear ruthenium (II) complex covalently anchored on melem and g-C3N4 as efficient heterogeneous catalysts for chemical water oxidation

Ru-melem and Ru-C₃N₄ were synthesized by a simple and facile strategy to construct a novel covalently anchoring by introducing easily synthesized amide bond as a bridge connecting the Ru-terpy and melem or g-C₃N₄, respectively. The covalent anchoring of Ru complex on melem or C₃N₄ not only makes these materials exhibit water oxidation activity under Ce^IV-driven (Ce^IV = Ce(NH₄)₂(NO₃)₆) reaction condition, but also makes the obtained heterogeneous catalysts show higher catalytic activity than the corresponding homogeneous catalysts, which reveals that the covalent anchoring strategy of Ru complex is beneficial to improve the catalytic activity of homogeneous Ru catalysts. The synthetic method of hybrid catalysts offers an insightful strategy for enhancing water oxidation activity of molecular catalysts.

In situ self-exsolved ultrasmall Fe2P quantum dots from attapulgite nanofibers as superior cocatalysts for solar hydrogen evolution

Developing highly active, stable, and cost-efficient cocatalysts for photocatalytic H₂ evolution is pivotal in the area of renewable energy conversion. Herein, we present a straightforward, low-temperature phosphidation strategy for in situ exsolving doped Fe ions from natural attapulgite (ATP) nanofibers into a supported Fe₂P cocatalyst for the photocatalytic H₂ evolution reaction (HER). The resulting Fe₂P QDs/ATP features highly dispersed Fe₂P QDs with an average size of <2 nm and a strong interfacial interaction between self-exsolved Fe₂P QDs and the ATP substrate, thus providing ample and stable active sites for the photocatalytic HER. When employed as a cocatalyst, Fe₂P QDs/ATP exhibits superior catalytic activity and notable stability in a molecular system with low-cost xanthene dyes as the photosensitizer under visible light irradiation. More importantly, Fe₂P QDs/ATP can also efficiently and stably catalyze the photocatalytic HER when simply combined with various semiconductor photocatalysts (g-C₃N₄, TiO₂, and CdS). This strategy of exsolving transition metal ions from substrates is an effective yet simple approach for the development of highly active supported HER cocatalysts for renewable and clean energy conversion.

Co-catalyst and heterojunction dual strategies to induce photogenerated charge separation for efficient hydrogen evolution of CdS

The construction of heterojunctions is considered to be an important means to promote efficient electron-hole separation in photocatalysts. However, photocatalysts have poor light absorption ability and a relatively small chance of capturing H⁺, and the stability needs to be improved. In this work, a non-precious metal co-catalyst Cu₃P was introduced for the successful construction of p-n heterojunctions from NiO and CdS to promote charge separation while expanding the light absorption capacity and increasing the chance of H⁺ capture, thus enhancing the photocatalytic hydrogen precipitation activity and stability. The overall photocatalytic performance was improved by continuously optimizing the loading of NiO and Cu₃P. Satisfyingly, using a 5 W LED lamp as the light source, the hydrogen evolution rate of the composite photocatalyst 15NC@Cu-10 in 10 vol% lactic acid solution is 15 612.0 μmol h^-1 g^-1, and the AQE reaches 10.4%. XPS analysis confirmed the direction and path of electron transfer. This synergistic strategy of co-catalyst modification of p-n heterojunctions provides a unique insight into the preparation of efficient and stable photocatalysts and also expands the applications of MOFs and their derivatives in the field of photocatalysis.

Femtosecond transient absorption spectroscopy investigation into the electron transfer mechanism in photocatalysis

Femtosecond transient absorption spectroscopy (fs-TAS) is a powerful technique for monitoring the electron transfer kinetics in photocatalysis. Several important works have successfully elucidated the electron transfer mechanism in heterojunction photocatalysts (HPs) using fs-TAS measurements, and thus a timely summary of recent advances is essential. This feature article starts with a thorough interpretation of the operating principle of fs-TAS equipment, and the fundamentals of the fs-TAS spectra. Subsequently, the applications of fs-TAS in analyzing the dynamics of photogenerated carriers in semiconductor/metal HPs, semiconductor/carbon HPs, semiconductor/semiconductor HPs, and multicomponent HPs are discussed in sequence. Finally, the significance of fs-TAS in revealing the ultrafast interfacial electron transfer process in HPs is summarized, and further research on the applications of fs-TAS in photocatalysis is proposed. This feature article will provide deep insight into the mechanism of the enhanced photocatalytic performance of HPs from the perspective of electron transfer kinetics.

Mixing Characteristic and High-Throughput Synthesis of Cadmium Sulfide Nanoparticles with Cubic Hexagonal Phase Junctions in a Chaotic Millireactor

A four-stage oscillating feedback millireactor with splitters (S-OFM) was designed to improve the mixing performance based on chaotic advection. Three-dimensional CFD simulations were used to investigate its flow characteristics and mixing performance, and the generation mechanisms of secondary flows were examined. The results show that the mixing index (MI_cup) increased with the increase in the Reynolds number (Re), and MI_cup could reach 99.8% at Re = 663. Poincaré mapping and Kolmogorov entropy were adopted to characterize the chaotic advection intensity, which indicates that there is a intensity increase with the increase in Re. In addition, the results of Villermaux-Dushman experiments demonstrate that S-OFM performs excellently, and the mixing time could reach 1.04 ms at Re = 2764. Finally, S-OFM was successfully used to synthesize CdS nanoparticles with cubic hexagonal phase junctions. At a flow rate of 180 mL/min, the average particle size was 10.5 nm and the particle size distribution was narrow (with a coefficient of variation of 0.14).

Precise regulation of defect concentration in MOF and its influence on photocatalytic overall water splitting

In this work, the defective Cu-BDC with different defect concentration and Cu¹⁺/Cu²⁺ coordinatively unsaturated sites (CUS) content were designed and synthesized by introducing defective linkers with different pK_a values. The low-concentration defects in Metal-organic frameworks (MOFs) structure act as the active sites to enhance their photocatalytic activity. In contrast, the high concentration defects serve as the recombination centers of photogenerated electrons and holes to decrease the transfer efficiency of charge carriers. Cu-BDC-FBA shows an excellent bifunctional photocatalytic performance for overall water splitting due to the suitable defect concentration, which gives an oxygen production rate of 3114 μmol g^-1 h^-1 and hydrogen production rate of 16 829 μmol g^-1 h^-1, respectively. It is expected that this study can deepen the understanding of the relationship between defects and photocatalytic activity, and provide a new idea for the design and synthesis of defective MOFs photocatalysts with excellent performance.

Surface-Induced Engineering: P-Induced Formation of Surface Bonding States Based on the ZIF Synthesis Strategy for Photocatalytic Hydrogen Evolution

The development of clean energy is one of the effective strategies to solve carbon peak and carbon neutrality. The severe recombination of photogenerated carriers is one of the fundamental reasons that hinder the development of photocatalysis. In this work, NiCo-MOF/ZIF was obtained by the "ZIF on MOF" strategy for the first time, and a stable bonding state of surface P(δ^-)-Co/Ni(δ⁺)-O(δ^-) was formed on the surface of the catalyst by a one-step oxidation-phosphorus doping strategy. The X-ray photoelectron spectroscopy technique proves that phosphorus doping forms a unique bonding state on the surface of CoO-NiO. The novel surface bonding state can effectively inhibit the recombination of photogenerated carriers and can increase the migration rate of photogenerated electrons, which accelerates the process of photocatalytic hydrogen evolution. Photocatalytic hydrogen evolution kinetics verifies that the formation of P(δ^-)-Co/Ni(δ⁺)-O(δ^-) bonding states can accelerate the process of photocatalytic hydrogen evolution, and the durability of the catalyst is verified by cycling experiments. This work provides a new strategy for catalyst synthesis, new horizons, and effective strategies for the surface design of catalysts and the development of photocatalytic hydrogen evolution.

Ultrathin Bi2Se3/CdS composite for efficient photocatalytic hydrogen evolution via high interfacial charge separation and photothermal effect

Ultrathin Bi2Se3 nanosheets/CdS nanoparticles were prepared, which display excellent photocatalytic H2 activity, ascribed to the synergistic mechanism of the unusual transfer process of high-energy electrons and the photothermal effect.