Preparation of bio-silica/chitosan nanocomposite for adsorption of a textile dye in aqueous solutions

•The adsorption of a textile dye bio-silica/chitosan nanocomposite was evaluated.•The effect of operational conditions on the dye removal efficiency was studied.•The spontaneous and exothermic nature of the process was confirmed.•The isotherm data were well fitted to the Langmuir isotherm.•Pseudo-second order kinetic was obtained as the most suitable model.

The aim of this study was to evaluate the efficiency of immobilized nanosized bio-silica (average crystalline size of 20 nm) within chitosan as a nanocomposite adsorbent for removing Acid Red 88 (AR88) in aqueous phase. As result, the amount of adsorbed AR88 (mg g−1) was increased with increasing reaction time and adsorbate concentration and decreasing temperature and initial pH. A rapid increment in the adsorption was happened with increasing adsorbent dosage from 1 to 3 g l−1, while further increment in the adsorbent dosage resulted in an insignificant increase in the adsorption (1.66 mg g−1). The kinetic study was performed and the results indicated the suitability of pseudo-second order kinetic model (R2 = 0.994). Besides, the correlation coefficient of Elovich model confirmed chemical nature of the adsorption (R2 = 0.9756). The fitness of experimental data to the intra-particle diffusion model demonstrated that the adsorption process occurred via a multi-step mechanism. But, the intra-particle diffusion was not the sole rate-limiting stage. According to the Langmuir isotherm model (R2 = 0.9962), the maximum adsorption capacity of bio-silica/chitosan nanocomposite for sequestering AR88 was about 25.84 mg g−1. In addition, negative ΔG° and ΔH° values obtained through thermodynamic study indicated that the adsorption of AR88 onto nanocomposite was simultaneous and exothermic in nature, respectively.