Removal of the Anionic Dye Congo Red from an Aqueous Solution Using a Crosslinked Poly(vinyl alcohol)-ZnO-Vitamin M Nanocomposite Film: A Study of the Recent Concerns about Nonlinear and Linear Forms of Isotherms and Kinetics

This paper deals with the preparation, characterization, and application of a crosslinked poly­(vinyl alcohol)/ZnO-vitamin M (PVA/ZnO-VM) nanocomposite film for the removal of Congo red (CR) from an aqueous solution. The characterization of a crosslinked PVA/ZnO-VM nanocomposite film showed that the structure became more regular and also the surface morphology appeared smooth in comparison with pure PVA. The obtained data from Brunauer–Emmett–Teller (BET) proved the mesoporous structure for this nanocomposite film. Several effective factors were examined for the adsorption ability of the nanocomposite film, including solution pH (2–10), sorbent amount (0.02–0.08 g), contact time (3–240 min), initial concentration of the adsorbate (30–300 mg·L^–1), and temperature (318–358 K). The optimal conditions are as follows: pH = 10, adsorbent amount = 0.06 g, and C₀ = 200 mg·L^–1. The removal efficiency of the nanocomposite film was 92% after 4 h at the ambient temperature. To interpret the adsorption process, nonlinear and linear forms of kinetic and isotherm models were considered. The obtained data followed nonlinear pseudo-second-order and linear Langmuir isotherm models, which indicated the monolayer formation of CR over the crosslinked PVA/ZnO-VM nanocomposite film with the maximum adsorption capacity of about 56.49 mg·g^–1. Also, the adsorption process of CR by the crosslinked PVA/ZnO-VM nanocomposite film is a spontaneous and exothermic reaction.