Chitosan/tannic acid/ZnFe layered double hydroxides and mixed metal oxides nanocomposite for the adsorption of reactive dyes.

The fabrication of the environmentally friendly nanocomposite beads containing chitosan (Chi), tannic acid (TA), layered double hydroxides (LDH), and mixed metal oxides (MMO) was carried out. The synthesized ZnFe LDH, ZnFe MMO, and fabricated beads (Chi/TA@LDH and Chi/TA@MMO) were characterized using FESEM, XRD, FTIR, BET, and TGA. The beads were applied for the simultaneous removal of three reactive dyes. The design of experiments was based on a full factorial design considering the effect of six independent variables (initial dye concentrations, adsorbent dosage, time, and adsorbent type) on the dye removal percentages (DR%) of each dye. Regression equations were extracted from the experimental results (R > 0.983) and high obtained F-values from analysis of variance (ANOVA) proved the significance of the models. The maximum adsorption capacity of the dyes onto, Chi/TA@LDH and Chi/TA@MMO beads were between 257 and 483 mg g. The spontaneity and exothermic nature of the adsorption processes were determined by thermodynamic studies (-8 < ΔH° (KJ mol) < -1, -22 < ΔG° (KJ mol) < -18). Reusability studies showed that the fabricated beads could be regenerated and applied several times.