Study of Structural and Optical Properties of Electrodeposited Silicon Films on Graphite Substrates.

Silicon (Si) films were deposited on low-cost graphite substrates by the electrochemical reduction of silicon dioxide nanoparticles (nano-SiO2) in calcium chloride (CaCl2), melted at 855 °C. Cyclic voltammetry (CV) was used to analyze the electrochemical reduction mechanism of SiO2 to form Si deposits on the graphite substrate. X-ray diffraction (XRD) along with Raman and photoluminescence (PL) results show that the crystallinity of the electrodeposited Si-films was improved with an increase of the applied reduction potential during the electrochemical process. Scanning electron microscopy (SEM) reveals that the size, shape, and morphology of the Si-layers can be controlled from Si nanowires to the microcrystalline Si particles by controlling the reduction potentials. In addition, the morphology of the obtained Si-layers seems to be correlated with both the substrate materials and particle size of the feed materials. Thus, the difference in the electron transfer rate at substrate/nano-SiO2 interface due to different applied reduction potentials along with the dissolution rate of SiO2 particles during the electrochemical reduction process were found to be crucial in determining the microstructural properties of the Si-films.

Aloe sp. leaf gel and water glass for municipal wastewater sludge treatment and odour removal.

Aloe gel (Alg), which is a natural extract from the Aloe sp. plant, was evaluated in this study for its potential use as a bioflocculant to treat urban wastewater sewage sludge. The gel was used alone and combined with water glass (WG) under controlled conditions in laboratory experiments. Alg was found effective to settle the flocculated sludge rapidly and remove distinctive unpleasant odours of the sludge as highlighted by gas chromatography-mass spectrometry (GC/MS) analysis. Furthermore, Alg was pH tolerant and had no effect in changing the pH of the wastewater. The optimum dose of Alg was 3% at which a sludge volume index (SVI) of 45.4 mL/g was obtained within 30 min settling time. To enhance the treatment performances of Alg, WG was also evaluated as an alkali agent to further reduce the chemical oxygen demand (COD) and ammonia (NH4-N) in the wastewater. At equal doses of 3% of WG and Alg each, the combined treatment outcomes showed high turbidity and NH4-N removals of 83 and 89%, respectively, but the overall COD removal was at best 25%. The settling rate of treated sludge with combined Alg/WG was very rapid giving an SVI of 25.4 mL/g within only 5 min.