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.