Comparative study of uncoated and tetraethylorthosilicate-coated magnetic chitosan beads in the adsorption of two textile dyes

Abstract

Textile dyes are harmful to human health and aquatic ecosystems. To tackle this issue, an environmentally friendly alternative should be addressed. In this research, magnetic chitosan beads, uncoated (MCB) and coated (CMCB) with tetraethylorthosilicate (TEOS), were fabricated. The beads were synthesized using magnetite and TEOS-coated magnetite as starting materials and glutaraldehyde as a crosslinker through an ionotropic gelation method that includes the dropwise addition of a ferrofluid into a basic solution. The magnetic beads were characterized by several techniques, such as FT-IR, VSM, XRD, and SEM–EDX. In addition, the beads loaded with the adsorbed dye were also characterized to assess the stability of the materials after the adsorption process. MCB and CMCB were evaluated as adsorbents for textile dyes Synozol Red HF-6BN (SR) and Synozol Yellow HF-2GR (SY). For both dyes, the maximum removal efficiencies were obtained at pH 2 with 20 mg of adsorbent and 180 r min−1. Adsorption of both dyes followed the Freundlich model, and the maximum adsorption capacities were SR dye: 88.12 (MCB) and 192.02 (CMCB) mg g−1, SY dye: (MCB) and 70.5 (CMCB) mg g−1. The adsorption kinetics fitted well with the pseudo-second-order kinetic model. Reusability of the materials was also demonstrated. The modeling of the data gathered by the Box–Behnken design experiments helped corroborate the obtained experimental data and find the optimal pH, dye concentration, and adsorbent dose for dyes removal.