Optimized removal of phosphate and nitrate from aqueous media using zirconium functionalized nanochitosan-graphene oxide composite

The decontamination of excess nutrients by polysaccharide-graphene oxide composites has gained much research attention. However, the usage of synthetic polymers and toxic crosslinking agents affects the environment. This investigation is, therefore, aimed at achieving a simple, effective and nontoxic technique of fabricating nanocomposites by ionotropic gelation of chitosan and tripolyphosphate crosslinking agent. The nanochitosan-graphene oxide composite (NCS@GO) was synthesized and investigated for its potential to remove phosphate (P) and nitrate (N) from aqueous solutions. High and low amounts of zirconium (Zr) were loaded in NCT@GO composite to make it selective for the adsorbate anions. The developed nanocomposites were comparatively explored by N(2)isotherms, FTIR, XRD, TGA, DTA, FESEM, EDS with mapping analysis and water regain property. Experimental design was conducted by the five-factorial central composite design-as a branch of response surface methodology (RSM). According to the design of RSM, NCS@GO/H-Zr demonstrated an excellent P and N uptake of 172.41 mgP/g and 138.88 mgN/g, reasonable pH-compatibility from 3 to 11, suitable selectivity for both adsorbates among competitor anions, desired recyclability and desorption efficiency for P and N, and retained 76% and 85% for P and N adsorption ability after ten recycles. The removal capacity of P and N anions were also assessed in bi-component systems. Thermodynamic data were considered, in which it was found that the adsorptive removal of the both anions was endothermic and spontaneous in nature. The adsorption isotherm of P and N on the surface of the NCS@GO/H-Zr was suitable for the Freundlich isotherm model, suggesting the multilayer adsorption. On the basis of kinetic studies, specific rate constants involved in the processes were calculated and the obtained result indicates that the pseudo second order kinetics was found to be a better fit. Real samples analysis indicated that the NCS@GO/H-Zr works well for removal of P and N from contaminated waters.