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.