LETTER pubs.acs.org/JPCL Sequestering High-Energy Electrons to Facilitate Photocatalytic Hydrogen Generation in CdSe/CdS Nanocrystals (original) (raw)
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Recent developments and perspectives in CdSbased photocatalysts for water splitting
Journal of Materials Chemistry A, 2020
Over the past few years, many approaches have been developed progressively to produce hydrogen (H 2) from water under solar light irradiation. This process of fuel production is clean, potentially costeffective, and environment-friendly. At present, however, current technologies are unable to meet the industrial requirements because of high cost, low photoresponse, and insufficient catalytic performance. Among water splitting photocatalysts, CdS is considered to be an interesting and important material owing to its low cost, prominent catalytic activity, high absorption in the visible spectrum, and the suitable positions of its conduction (CB) and valence (VB) bands. There are, however, some associated problems such as the rapid recombination of photogenerated electron-hole pairs and photocorrosion that have severely hampered its practical usage. The efficient conversion of water to H 2 depends on the extent to which the charge carriers, especially the electrons, are first generated and then have sufficient lifetime for their effective utilization. This review highlights work over the past several years to improve the photocatalytic efficiency and stability of CdS for H 2 production from water.
Proceedings of the National Academy of Sciences, 2013
Significance Conversion of solar energy into chemically stored energy via artificial photosynthesis (AP) represents a key strategy in renewable energy. Systems for AP that split water reduce aqueous protons to H 2 fuel and oxidize water to make O 2 . The present study on the light-driven generation of H 2 describes a new, highly active, and durable system with components made solely of earth-abundant elements. The light absorber in this system consists of quantum-confined CdSe nanocrystals that are made water soluble through surface binding agents. Realization of the effects of surface ligand exchange on system activity stimulated the new compounds reported here that bind more strongly to the nanocrystals through tridentate coordination and allow assessment of catalyst activity for H 2 generation.
Advanced Functional Materials, 2016
of the electrochemical watersplitting on a TiO 2 electrode by Fujishima and Honda, [3] semiconductor photocatalysis has become an intriguing approach for the economical and eco-friendly production of hydrogen by using solar energy. This process involves generation of electron-hole pairs in a semiconductor material upon light irradiation and successful separation and transportation of these charge carriers to the surface active sites, where they can participate in chemical reactions. Over the last few years, numerous efforts have been devoted to the development of highly active catalysts for the photocatalytic splitting of water by the hydrogen evolution reaction (HER). [4] However, most of these catalysts are composed of wide bandgap semiconductors (like SrTiO 3 , ZnO, K 4 Nb 6 O 17 , and Ta 2 O 5) that take advantage of UV light, which constitutes only 4% of the solar spectrum. This is a limitation that restricts their practical application for solar hydrogen production. [4b] Recently, metal chalcogenides have garnered special attention as electro-or photocatalysts for water splitting owing to their remarkable optical and electronic properties. To this end, a variety of transition-metal sulfides (MoS 2 , EMoS x (E = Fe, Co), Cu x Zn 1-x S, etc.) have been rapidly investigated, [5] and among all, CdS is the most extensively used for the photocatalytic reduction of water to hydrogen. [6] The interest in CdS stems from its narrow bandgap (E g ≈ 2.4 eV), which enables the absorption of visible light, high electron mobility (>350 cm 2 V −1 s −1) and a favorable conduction band (CB) edge position well above the thermodynamic threshold for water reduction reaction (−0.41 V vs NHE at pH = 7). [6a] However, its hydrogen evolution activity is often plagued by the slow transfer of surface-reaching holes to electrolytes and poor electron-hole separation yield. Therefore, the main challenge in designing effective CdS-based photocatalysts is to eliminate the competitive process of charge carrier recombination. [7] Previous efforts to increase the lifetime of photogenerated carriers in CdS materials mainly focused on the deposition of metal nanoparticles, especially noble metals such as Au, Pt, Rd, and Ag as co-catalysts. [8] These metal nanoparticles have been considered as effective electron acceptors,
Journal of Alloys and Compounds, 2020
The heterogeneous structure of Cu 2 O quantum dots (QDs) sensitized CdS nanorods (NRs) was synthesized by an easy and cost-effective technique. The morphology, structure and optical properties of asprepared photocatalysts are thoroughly investigated by field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (UVDRS) and photoluminescence (PL) spectroscopic techniques. The different weight percentages (10, 20, and 30) of Cu 2 O QDs deposited on the CdS NRs structures and their photocatalytic hydrogen (H 2) evolution (PCHE) performance are systematically investigated. The Cu 2 O QDs deposition on CdS NRs shows an increase in the rate of hydrogen (H 2) evolution due to the formation of type II heterojunction in between Cu 2 O QDs and CdS NRs. The 20% loading of Cu 2 O QDs on CdS exhibits the highest photocatalytic H 2 generation than other ratios as well as pure Cu 2 O QDs and CdS NRs. The photocatalytic rate of H 2 evolution of 26060 mmolg-1 h-1 was obtained for 20 % Cu 2 O-CdS, which is18 times more than pure Cu 2 O QDs and 5.1 times than CdS NRs. Photoelectrochemical (PEC) measurements, electrochemical impedance spectroscopy, and photoluminescence measurements suggest that the Cu 2 O QDs deposition on CdS NRs reduces interfacial recombination of photogenerated charge carrier owing to the formation of the p-n junction between the components. The apparent quantum yield (AQY) obtained for 20 % Cu 2 O QDs modified CdS NRs photocatalysts is exceptionally high i.e. 20.67%. This convenient and cost-effective strategy will pave the way for large-scale synthesis of type II heterogeneous photocatalyst for efficient H 2 evolution.
The Journal of Physical Chemistry C, 2007
We describe a simple cadmium-thiourea complex thermolysis route for the formation of CdS nanocrystals with controlled dispersity, crystalline phase, composition, average grain size, and band gap. Visible-lightdriven photocatalytic activities for hydrogen production over the different CdS products have been compared. Phase structure and composition of the obtained CdS nanocrystals has been optimized either by changing the ratio of thiourea to Cd or by changing the annealing temperature. Over a broad annealing temperature range of 150-500°C, either cubic, a mixture of cubic and hexagonal, or hexagonal CdS nanocrystals are obtained at thiourea/Cd molar ratios of <1.0, 1.5-2.5, and 3.0-4.5, respectively. Nanocrystalline cubic CdS is stable at temperatures as high as 500°C for 0.5 h, and is converted to hexagonal CdS for annealing time longer than 1 h. The phase transition from cubic to hexagonal CdS occurs at temperatures of 200-300°C, and pure hexagonal CdS is formed at annealing temperatures higher than 600°C. The dispersity, crystallinity, and average grain size of the CdS nanocrystals has been determined as a function of annealing temperature and time. Increased photocatalytic activity is observed from the mixture of cubic and hexagonal CdS as compared to pure cubic or hexagonal CdS. Nearly monodisperse hexagonal CdS with good crystallinity and very fine particle size is expected to offer the highest photocatalytic activity for hydrogen production under visible light.
An Overview of the Photocatalytic H2 Evolution by Semiconductor-Based Materials for Nonspecialists
Journal of the Brazilian Chemical Society, 2020
The solar-to-chemical energy conversion is promising to tackle sustainability challenges toward a global future. The production of H 2 from sunlight represents an attractive alternative to the use of carboniferous fossil fuels to meet our energy demands. In this context, the water splitting reaction photocatalyzed by semiconductors that can be excited under visible or near-infrared light excitation represents an attractive route to the clean generation of H 2. In this review, we present an overview of the most important concepts behind the H 2 generation, from water splitting, promoted by semiconductor-based systems for readers that were recently introduced to the water splitting topic. Then, we present the main classes of photocatalysts based on semiconductors. For each class of semiconductors, we focused on the examples that lead to the highest activities towards the H 2 production and discuss the operation principles, advantages, performances, limitations, and challenges. We cover metal oxides, sulfides, and nitrides. We also discuss strategies in which these materials are combined, including hybridization with metal nanoparticles, other semiconductors, and carbon dots, to achieve improved performances and circumvent the limitations of the individual counterparts.