Facile Cd−Thiourea Complex Thermolysis Synthesis of Phase-Controlled CdS Nanocrystals for Photocatalytic Hydrogen Production under Visible Light

Abstract

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.

Nanostructured Materials Preparation via Condensation Ways

“…The transition of the cubic phase to the hexagonal one occurred at 473-573 K, whereas a pure hexagonal phase of CdS appeared at thermolysis over 873 K. These factors including the time of sintering affect dispersity, crystallinity, and average sizes of CdS nanoparticles. It is interesting that a photocatalytic activity in the synthesis of hydrogen is optimal for a mixture of cubic and hexagonal CdS apart from its pure phases [430]. Decomposition of Sb(n-C 12 H 25 S) 3 in polystyrene at 623 K affords Sb and Sb 2 S 3 nanoclusters (15-30 nm) evenly distributed in the amorphous polymeric phase [431].…”

On the role of metal particle size and surface coverage for photo-catalytic hydrogen production: A case study of the Au/CdS system

“…Other catalyst fabrication methods, have shown improved CdS based catalysts, especially core shell structures with other stable semiconductors, with the objective to overcome the inherent photo-corrosion of CdS [27]. CdS has usually been coupled with noble metals such as Au, Pt, Rh, Ru and Pd acting as co-catalyst [28][29][30][31].…”

Facile synthesis of uniform ZnxCd1−xS alloyed hollow nanospheres for improved photocatalytic activities

“…Cadmium sulfide (CdS), a kind of important II-VI semiconductors with a direct band gap energy of 2.42 eV, is of great significance in photocatalysis, owing to absorbing most of the visible light in the solar spectrum [10,11]. However, its further application as photocatalyst is limited by the weak oxidization of photogenerated holes and inevitable photocorrosion under the irradiation [12]. Whereas, ZnS with a band gap of 3.7 eV has strong redox ability and good photocorrosion resistance but cannot efficiently utilize the visible light [13].…”