Preparation of Colloidal Silica Nanoparticles for Analytical Applications

Abstract

Colloidal silica or silicon dioxide nanoparticles (SiO2 NPs) can be obtained in different size ranges and they are recognized by their wide applications. In this work, the synthesis of highly stable SiO2 NPs in small size range was carried out. Accordingly, the preparation of these nanoparticles was done based on a simple synthesis route, that consist of the hydrolysis of silica colloidal in ethanol medium using ultrasonication by sol-gel process. The size of the NPs and their stability will be controlled by varying the reaction parameters and taking into consideration the silica precursor used and the best concentration of sodium hydroxide. Furthermore, the formed silica powder will be characterized by using microscopic and spectroscopic techniques such as XRD, TGA and SEM. The purpose of this study is the formation of the most suitable, highly stable, small and uniform silica nanoparticles that will be used in various applications. Firstly, the prepared SiO2 NPs played an outstanding role as nanoprobe for the detection of silver ion in an easy, fast, cheap, selective and sensitive method using Resonance Rayleigh scattering technique. As the concentration of silver ion increased (5-300 μM) the RRS intensity was seen to decrease. The LOD obtained was equal to 130 nM. The recovery range was between 98.4-100.4%. Secondly, the adsorption of benzo(ghi)perylene onto the surface of SiO2 NPs was established with kinetic and isothermal studies. In the first step, a complete study of the adsorption of benzo(ghi)perylene using SiO2 NPs as adsorbent was verified. The impact of the adsorbent dose, the concentration of the PAH, the pH and the temperature of the solution were varied and regulated in a certain assortment. It was found that the adsorption was improved when increasing the dosage of the nanoparticles and with subsiding the concentration of the PAH. Hence, the numerous adsorption sites will extend to fullness. Additionally, a basic medium improved the adsorption process of benzo(ghi)perylene. Then the kinetics study was investigated, and it was found that the adsorption process followed the 1st order kinetic model which indicated that it was a physisorption. Afterwards the isothermal study was also carried out and showed that the adsorption process followed Langmuir isotherm model. Finally, thermodynamics parameters were calculated, and a negative standard free energy change was acquired in a range of -20 < ΔGo< 0 kJ/mol indicating that indeed the adsorption process taking place was a physisorption.