We prepared cadmium sulfide (CdS) nanoparticles of a specific size via chemical precipitation at room temperature and characterized them using high-resolution transmission electron microscopy, x-ray powder diffraction, ultraviolet-visible spectroscopy, and Fourier-transform infrared (FTIR) measurements. The results showed that the samples were grown with a cubic phase; the particle size could be changed from 2 nm to 4 nm by varying the molar ratios of the precursors (cadmium chloride and sodium sulfide) in the presence of poly(ethylene glycol) (PEG) as an effective capping agent. The optical bandgap of the synthesized nanoparticles was calculated and ranged from 2.73 eV to 2.92 eV depending on the particle size. A large blue-shift from the bulk bandgap (2.42 eV) was observed owing to the quantum size effect. Surface passivation and adsorption of PEG on the CdS nanoparticles was explained on the basis of FTIR measurements; two bands were observed at 476 cm À1 and 622 cm À1 , corresponding to cadmium and sulfide stretching vibrations. We conclude that particle size can be controlled by varying the molar ratios of the precursors. Owing to the PEG encapsulation, the as-prepared samples were extremely stable over time.

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Solar energy is a good solution for energy-deficiency problems, especially in regions such as rural areas in the Middle East that have not been electrified yet or are under electrification. In this paper, with the aid of a Computational Fluid Dynamics simulation, we propose a system that comprises a trough solar concentrator and a pipe-with flowing water-that is set in the concentrator focus. The aim of this work is to investigate the feasibility of generating steam from such a system as well as analyzing the generated steam quantitatively and qualitatively. Effects of variation of solar radiation intensity, ambient temperature, water flow rate and pipe diameter on the quantity and quality of the generated steam have been investigated. The results show that a quantity of about 130 kg of steam could be generated per day with a 0.01 m diameter with 0.0042 kg/s flowing water, although qualitatively, a narrower pipe achieves better performance than a wider one. About 74 kg of daily accumulated steam mass with a temperature >423 K could be achieved for a 0.005 m diameter tube compared to about 50 kg for the 0.01 m diameter tube. Steam quality factor is higher at all flow rates for the 0.005 m diameter tube compared to that of 0.01 m.

Zinc sulfide nanoparticles were synthesized with controllable size via chemical precipitation. highresolution transmission electron microscopy (HRTEM) and X-ray powder diffraction (XRD) showed that the samples were grown with the cubic phase; the particle size was varied by varying the molar ratios of zinc chloride and sodium sulfide in the presence of poly(ethylene glycol). The optical band gap was calculated on the basis of ultraviolet-visible spectroscopy (UV-VIS) and ranged from 4.13 eV to 4.31 eV depending on the particle size. Surface passivation and adsorption of poly(ethylene glycol) on the nanoparticles was explained on the basis of Fourier transform infrared measurements (FTIR).