| Summary: | Guar gum–nano zinc oxide (GG/nZnO) biocomposite was used as an adsorbent for enhanced removal of Cr(VI) from aqueous solution. The maximum adsorption was achieved at 50 min contact time, 25 mg/L Cr(VI) conc., 1.0 g/L adsorbent dose and 7.0 pH. Langmuir, Freundlich, Dubinin–Kaganer–Radushkevich and Temkin isotherm models were used to interpret the experimental data. The data obeyed both Langmuir and Freundlich models (R2 = 0.99) indicating a multilayer adsorption of Cr(VI) onto the heterogeneous surface. The linear plots of Temkin isotherm showed adsorbent-adsorbate interactions. Moreover, the energy obtained from DKR isotherm (1.58–2.24 kJ/mol) indicated a physical adsorption of the metal ions onto the adsorbent surface, which implies more feasibility of the regeneration of the adsorbent. GG/nZnO biocomposite adsorbent showed an improved adsorption capacity for Cr(VI) (qm = 55.56 mg/g) as compared to other adsorbents reported in the literature. Adsorption process followed pseudo-second order kinetics; controlled by both liquid-film and intra-particle diffusion mechanisms. Thermodynamic parameters (ΔGo, ΔHo and ΔSo) reflected the feasibility, spontaneity and exothermic nature of adsorption. The results suggested that GG/nZnO biocomposite is economical, eco-friendly and capable to remove Cr(VI) from natural water resources.
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