Enhancement of gaseous BTEX adsorption on RH-MCM-41 by chlorosilanes

In this research, the surface hydrophobicity of a mesoporous molecular sieve synthesized from rice husk silica, called RH-MCM41 was improved via silylation techniqueto enhance the adsorption efficiency of non-polar volatile organic compound. The effect of chlorosilane leaving on was analyzed with three silanes containing different numbers of chloride leaving group; trimethylchlorosilane (TMCS), dimethyldichlorosilane (DMDCS) and methyltrichlorosilane (MTCS). The unmodified RH-MCM-41 was soaked in 100 mL of 5% v/v of silane reagent at 30ºC for 24 h. The results showed that the silane loading on the RH-MCM-41 was in the order of increasing number of leaving groups as MTCS > DMDCS > TMCS. The crystallinity results studied by X-ray diffractometry indicated that the silylation did not affect the hexagonal pattern of RH-MCM-41. However, the porosity of the silylated RH-MCM-41 was significantly decreased after silylation, especially by MTCS, due to pore blocking. After silylation, the adsorption performance of gaseous BTEX (benzene, toluene, ethylbenzene and xylene) on the silylated RH-MCM-41 was determined by gas chromatography equipped with flame ionization detector (GC-FID). From the results of humidity effect on adsorbability, the BTEX adsorption capacity of the unsilylated RH-MCM-41 was dropped a half, conversely the BTEX adsorption capacity of all silylated RH-MCM-41 was decreased in range of 20-30% when the relative humidity increased from 25 to 99%. This was indicated that the influence of humidity on the BTEX adsorption was relieved after silylation. In additions, the maximum BTEX adsorption capacity belonged to RH-MCM-41 silylated by TMCS which was recommended for the enhancement of non-polar volatile organic compounds adsorption

Optimization for UV-photocatalytic degradation of paraquat over titanium dioxide supported on rice husk silica using Box-Behnken design

363-371The optimum conditions for UV-photocatalytic degradation of paraquat over titanium dioxide supported on rice husk silica (TiO2/RH-SiO2) catalyst, which is effected by four independent variables, namely initial paraquat concentration, pH of solution, titanium dioxide content (% TiO2) and catalyst loading,  have been evaluated. The TiO2/RH-SiO2 catalyst has been synthesized by colloidal impregnation method and calcined at 550 °C for 6 h. The Box-Behnken design, based on response surface methodology has been applied to design the experiment and analyze the data. Characterization of the catalysts is investigated by XRD, SEM, BET surface area and UV-DRS for explanation of reaction behaviour. The XRD patterns show a pure anatase crystalline phase at all TiO2 percentages, and the BET surface area of the catalysts is vastly decreased as the percentage of TiO2 is increased. The highest paraquat removal efficiency of 90.04% is obtained at 10 ppm initial paraquat concentration, 5.91 pH, 30 wt % TiO2 and 2.0 g/L catalyst loading

Removal of manganese ions from synthetic groundwater by oxidation using KMnO4 and the characterization of produced MnO2 particles

The aim of this study is to investigate the conditions for the removal of manganese ions from synthetic groundwater by oxidation using KMnO4 to keep the concentration below the allowed level (0.05 mg/L) The process includes low-level aeration and addition of KMnO4 in a Jar test system with Mn2+ concentration of 0.50 mg/L, similar to that of natural groundwater in Taiwan Different parameters such us aeration-pH, oxidant dose, and stirring speed were studied Aeration alone was not sufficient to remove Mn2+ ions completely even when the pH was increased When a stoichiometric amount of KMnO4 (0 96 mg/L) was used, a complete Mn2+ removal was achieved within 15 min at an optimum pH of 80 As the amount of KMnO4 was doubled, lower removal efficiency was obtained because the oxidant also generated manganese ions The removal of Mn2+ ions could be completed at pH 9 0 using an oxidant dose of 0 48 mg/L because Mn2+ could be sorbed onto the MnO2 particles Finally, The MnO2 particles were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX