In this review, for a variety of metals and semiconductors, an attempt is made to generalize observations in the literature on the effect of process conditions applied during photodeposition on (i) particle size distributions, (ii) oxidation states of the metals obtained, and (iii) consequences for photocatalytic activities. Process parameters include presence or absence of (organic) sacrificial agents, applied pH, presence or absence of an air/inert atmosphere, metal precursor type and concentration, and temperature. Most intensively reviewed are studies concerning (i) TiO2; (ii) ZnO, focusing on Ag deposition; (iii) WO3, with a strong emphasis on the photodeposition of Pt; and (iv) CdS, again with a focus on deposition of Pt. Furthermore, a detailed overview is given of achievements in structure-directed photodeposition, which could ultimately be employed to obtain highly effective photocatalytic materials. Finally, we provide suggestions for improvements in description of the photodeposition methods applied when included in scientific papers.

Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review.

Metal sulphide semiconductors for photocatalytic hydrogen production

The development of novel highly efficient noble metal-free co-catalysts for enhanced photocatalytic hydrogen production is of great importance. Herein, we report the synthesis of novel and highly efficient noble metal-free ultra-thin MoS 2 (UM) layers on exfoliated reduced graphene oxide (ERGO) nanosheets as a cocatalyst for CdS nanorods (ERGO/UM/CdS). A simple method different from the usual preparation techniques is used to convert MoS 2 to UM layers, graphene oxide (GO) to ERGO nanosheets, based on ultrasonication in the absence of any external reducing agents. The structure, optical properties, chemical states, and dispersion of MoS 2 and CdS on ERGO are determined using diverse analytical techniques. The photocatalytic activity of as-synthesized ERGO/UM/CdS composites is assessed by the splitting of water to generate H 2 under simulated solar light irradiation in the presence of lactic acid as a hole ( h + ) scavenger. The observed extraordinary hydrogen production rate of ∼234 mmol h −1  g −1 is due to the synergetic effect of the ultrathin MoS 2 layers and ERGO, which leads to the effective separation of photogenerated charge carriers and improves the surface shuttling properties for efficient H 2 production. Furthermore, the observed H 2 evolution rate is much higher than that for individual noble metal (Pt), ERGO and MoS 2 -assisted CdS photocatalysts. Moreover, to the best of our knowledge, this is the highest H 2 production rate achieved by a RGO and MoS 2 based CdS photocatalyst for water splitting under solar light irradiation. Considering its low cost and high efficiency, this system has great potential for the development of highly efficient photocatalysts used in various fields

Ultrathin MoS2 layers anchored exfoliated reduced graphene oxide nanosheet hybrid as a highly efficient cocatalyst for CdS nanorods towards enhanced photocatalytic hydrogen production

Visible light sensitive and highly active Cu-doped ZnS hollow photocatalyst particles “Cu-ZnS-shell” were successfully developed. These particles could generate H2 through photocatalytic decomposition of HS− ion in Na2S solution. The photoactivity under xenon lamp irradiation was 6 and 130 times higher than that of copper-free “ZnS-shell” and coprecipitated ZnS particles, respectively. “Cu-ZnS-shell” particles were prepared by doping the “ZnS-shell” particles synthesized using zinc oxide as precursor with Cu, utilizing the difference in ionization tendency between zinc and copper. Though the photoactivity of “ZnS-shell” was higher than that of coprecipitated ZnS, their photoactivity under visible light conditions was low. However, the “Cu-ZnS-shell” was active to light of wavelengths higher than 440 nm and is preferred over CdS, which requires an expensive support metal catalyst such as platinum to decompose HS− ion.

Cu-Doped ZnS Hollow Particle with High Activity for Hydrogen Generation from Alkaline Sulfide Solution under Visible Light

Semiconductor-based photocatalytic hydrogen (H2) production from water has recently received considerable attention because of its enormous potential for solving worldwide ever-increasing energy crises and environmental issues. Among various semiconductors, cadmium chalcogenides (CdX, X = S, Se, Te), with a variety of superior properties including appropriate bandgaps for visible-light absorption, proper conduction band edge potentials for water reduction and abundant reserves on the earth, have fuelled great interest in exploring their photocatalytic properties for solar-driven H2 production from water. This review article summarizes the recent progress in developing CdX-based photocatalyst systems for the production of H2 from solar water splitting. The basic mechanistic fundamentals of CdX photocatalysts and various strategies to enhance the activity and stability of this class of photocatalysts are introduced in detail. Finally, some key scientific issues and prospective directions in this area of research are also discussed.

Rational design of semiconductor-based photocatalysts for advanced photocatalytic hydrogen production: the case of cadmium chalcogenides

Among CdS, Rh/CdS, Rh{sub 2}S{sub 3}/CdS, and Rh{sub 2}S{sub 3}/Rh/CdS, the ternary material, viz., Rh{sub 2}S{sub 3}/Rh/CdS, is found to be the most active photocatalyst for the decomposition of aqueous sulfide. X-ray photoelectron spectroscopic studies show that Rh as it is photodeposited on CdS is in the zero oxidation state but is prone to aerial oxidation.

Rhodium and rhodium sulfide coated cadmium sulfide as a photocatalyst for photochemical decomposition of aqueous sulfide

I. B. RUFUS*,V. RAMAKRISHNAN, B. VISWANATHAN, J. C. KURIACOSE Department of Chemistry, Indian Institute of Technology, Madras 600036, India Metallized CdS is used as a photocatalyst for many reactions and as a photoanode in photoelectrochem- ical (PEC) cells [1-4]. Conversion and storage of solar energy can be achieved by means of photocata- lysis as well as by PEC cells. The photocatalytic and photoelectrochemical properties of metallized CdS depend on its surface properties. Pd/CdS is a better photocatalyst and photoanode than CdS [3]. However, a detailed surface study of Pd/CdS is lacking. X-ray photoelectron spectroscopy (XPS) is a versatile tool to probe the surface of materials. XPS investigation of Pd/CdS will yield useful infor- mation such as the oxidation state of Pd, the contact between Pd and CdS, and other species present on the surface. Metallized CdS is mostly prepared by the photodeposition of noble metals [1, 3, 4]. There- fore, in the present investigation Pd, one of the representatives of noble metals, was photodeposited on CdS and the Pd/CdS obtained was analysed by XPS. Pd, Pt, Rh, Ru and Ni/CdS were prepared by the simultaneous photodeposition (illuminating for 15 min with a 1000 W tungsten-halogen lamp) of these metals on a sintered (4 h at 873 K in nitrogen) CdS (Fluka, 99.999% purity) pellet from an equi- molar (1 x 10 -4 M) solution (acetic acid, pH 4.5) of the corresponding metal chlorides. Following a similar procedure, Pd was photodeposited from a solution of PdC12 (Arora Mathey Ltd, India). After photodeposition the pellets were washed with triply distilled water and dried in air at room temperature (303 K). The sides of the pellets that were exposed to visible light during the photodeposition were subjected to XPS analysis. The XPS studies were made with an ESCA Lab Mk II (VG Scientific Co., UK) at room temperature and at a pressure of 1 x 10 -7 Pa before and after sputtering with argon ions. The X-ray source used was MgKo~ with an energy of 1253.6 eV. The C ls peak at 285.0 eV was used as the internal standard. In the cases of Pd, Pt, Rh, Ru and Ni/CdS prepared by the simultaneous photodeposition of these metals, the Pd 3d and 3p binding energies (Figs 1 and 2) are higher than those reported for Pd metal, viz. 344.7, 340.0 and 531.5 eV [5], indicating that Pd which is on the surface of CdS is not in the zero oxidation state. The several Pd-O species identified are shown in Table I. Hence, in the case of Pd/CdS the XPS spectra were recorded only after argon-ion sputtering, in order to study the surface free of oxide

J. C. Kuriacose

Papers

Rhodium and rhodium sulfide coated cadmium sulfide as a photocatalyst for photochemical decomposition of aqueous sulfide

X-ray photoelectron spectroscopic studies on Pd/CdS

X-ray p hotoelectron s pectroscopic studies on Pd/CdS

Surface characterization of CdS0.62Se0.38 by X-ray photoelectron spectroscopy

Surface analysis of Rh/CdS