الفهرس 
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Abstract
The present work is concerned with the preparation and characterization of silica composites from natural silica sand available locally at the Abu Zenima area, South Sinai, Egypt. This research is divided into two parts; the first part is concerned with removing Acid blue 92 dye (AB92) by adsorption on the modified milled silica sand (MMSS) surface. The second part deals with the kinetics of the catalytic degradation of Methylene Blue (MB) with hydrogen peroxide in the presence of SiO2-NH2-Cu(II)@SiO2 nanocomposite. Thus, the thesis consists of four main chapters: Chapter I embraces an introduction to industrial dyes and wastewater treatment methods (physical and chemical), the importance of nanotechnology, synthesis of silica nanoparticles from natural silica sand, and functionalization. It also contains a literature survey on silica and modified silica nanocomposites, also core-shell nanoparticles and silica-etching chemistry besides using various compounds from silica in wastewater treatment and ended by some aspects of the concerned dyes Chapter II: includes the experimental part, which describes the materials, the synthesis of composites, organic dyes used, and instruments that have been used. The batch adsorption studies and kinetic measurements were also included. Chapter III: comprises the results and discussion. It contains the characterization of composites and displays results in a systematic manner. It is divided into two main parts: Part 1: shows the adsorption activity of the modified milled silica sand (MMSS) as an effective adsorbent toward the removal of Acid blue 92 dye. The adsorbent was characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Thermogravimetric (TGA), Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) techniques. The reaction was followed xv by measuring the decrease in absorbance of AB92 dye (λmax =570 nm) with time. The reaction follows second-order kinetics with respect to the concentration of the dye. The adsorption process fitted well with the Langmuir isotherm. The effect of MMSS composite characterization was studied under optimum conditions for maximum adsorption. The efficiency of MMSS was largely dependent on the APTES loaded on its surfaces; the dye removal efficiency was optimized at acidic medium at pH 2, low dye concentration, increasing the dose of adsorbent and high temperature. It decreased with increasing the pH from 2 to 12, increasing the concentration of dye and the presence of NaCl. The removal percentage has reached up to 99 %. Part 2: Shows catalytic activity of SiO2-NH2-Cu(II)@SiO2 nanoparticles as catalyst towards the degradation of MB in the presence of H2O2. In this sections, synthesis of silica nanoparticles were successfully derived from Egyptian natural quartz sand via alkali melting reaction and acid precipitation processes followed by calcination at 400 oC with particles size 20 1 nm. The catalyst was characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), X-ray photo -electron spectroscopy (XPS), Thermogravimetric (TGA), Brunauer-Emmett-Teller (BET), Inductively coupled plasma (ICP-OES), Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) techniques. The reaction was followed by measuring the decrease in absorbance with the time of MB at (max= 664 nm). The reaction followed first-order kinetics with respect to the concentration of the dye. The effect of medium variables such as the amount of composite, substrate concentration, temperature, and pH on the reaction rate was also investigated. The rate of reaction was greatly affected by the initial concentrations of H2O2, MB, and the amount of catalyst. The rise in temperature, alkaline solution at pH 12 and the increase in the concentration of NaCl induced the reaction rate. The chemical stability of SiO2-NH2-Cu(II)@SiO2 as catalyst and its reusability within four cycles. xvi Chapter IV: provides a general discussion with the deep interpretation of the results obtained. Plausible mechanisms for adsorption of AB92 on the surface of MMSS and the catalytic degradation of MB with SiO2-NH2-Cu(II)@SiO2 nanoparticles were proposed. The present study may be considered as a good technique for the disposal of pollutant dyes from wastewater streams with high efficiency and cost-effectiveness.