Adsorption Properties of Calcium Alginate-Silica Dioxide Hybrid Adsorbent to Methylene Blue

Abstract

Sodium alginate (SA) was used as a raw material to react with the silica (SiO2) which was the alcoholysis product of tetraethyl orthosilicate (TEOS).The SiO2/CA hybrid adsorbent was prepared by ion exchange method. The chemical structure and microstructure of the adsorbent were tested by Fourier transform infrared spectroscopy and scanning electron microscopy. The effects of raw material ratio, Ca2+ concentration, pH value, adsorbent dosage, temperature, adsorption time and initial dye concentration on the adsorption of methylene blue (MB) were investigated. At the same time, this experiment also carried out multiple adsorption/desorption cycles on the adsorption of MB by SiO2/CA, and studied its reusability. The results showed that when the MB concentration was 100 mg/L, mass ratio of SA to TEOS was 1:3, Ca2+ was 2% (w/v), amount of adsorbent was 0.2 g, pH was 5, and temperature was 35 °C, the mixed adsorbent has the best adsorption capacity to MB and the removal rate reached 94.9%. At the same time, the adsorption kinetics study shows that the quasi-first-order kinetic model can be better fitting the experimental data. The Langmuir isotherm model has a good correlation with MB adsorption, and the maximum capacity obtained by simulation is 1158.332 mg/g. Thermodynamic studies show that the adsorption process of SiO2/CA on MB is a spontaneous endothermic process driven by entropy. In addition, after five adsorption/desorption cycles, the removal rate of the adsorbent was maintained at about 85%, indicating that it can be reused.