Synergistic nitrate removal: Enhanced efficiency with zinc-immobilized calcium cross-linked polyvinyl alcohol film

Nitrate is a major water contaminant causing eutrophication and poses health risks. Controlling its levels is essential. In this study, zinc powder immobilized calcium cross-linked polyvinyl alcohol (Zn-Ca-PVA) film was synthesized for the removal of nitrate from water samples. The results demonstrated an enhanced removal efficiency, increasing from 47.82% ± 1.14% for the film without zinc powder to 78.47% ± 5.20% with a maximum adsorption capacity of 9.56 mg g −1 when using Zn-Ca-PVA with synthetic water samples. This enhancement suggests a synergistic mechanism in which nitrate is adsorbed onto the calcium cross-linked PVA film via electrostatic interaction, and then catalytically reduced by the zinc powder within the film, converting it into nitrogen-containing gas and removing it from the sample. Moreover, this synergistic approach resulted in high removal efficiencies for real water samples, ranging from 82.95% ± 0.98% to 96.19% ± 0.62%. The adsorption of nitrate aligned well with the Freundlich model, while the kinetic process aligned well with the pseudo-second-order model (R 2 > 0.99). Thermodynamic studies revealed ΔG° values ranging from -2.71 to -3.76 kJ mol −1 , ΔH° of 6.22 kJ mol −1 , and ΔS° of 29.98 J mol –1 K –1 , indicating spontaneous adsorption, an endothermic nature, and increased randomness at the solid/solution interfaces during nitrate adsorption. Furthermore, Zn-Ca-PVA exhibited tolerance to coexisting ions, with the removal efficiency of nitrate remaining largely unchanged (< 5%) even in the presence of mixed coexisting ions at five times higher concentrations. These findings highlight the promising potential of Zn-Ca-PVA films for practical applications in nitrate removal. • Zinc-immobilized calcium cross-linked PVA film was developed for nitrate removal. • Synergistic mechanism based on film adsorption and Zn reduction was proposed. • Removal efficiency increased from 47.82% to 78.47% with the addition of Zn reduction. • An excellent removal efficiency of 96.19% was achieved in real sample applications. • It remained effective against coexisting ions, even at concentrations 5 times higher.