Fabrication of an efficient system for Zn ions removal from industrial wastewater based on graphene oxide nanosheets decorated with highly crystalline polyaniline nanofibers (GO-PANI): Experimental and ab initio quantum mechanics approaches

The metal surface treatment by conversion coatings, i.e., zinc phosphate, anodizing-cleaning, and electroplating processes, especially in automotive, oil and gas industries, produces large amount of industrial wastewaters containing high level of heavy and toxic zinc ions. This research introduces the graphene oxide nanosheets modified by Polyaniline nanfibers (GO-PANI Nfs) as an effective adsorbent for water treatment and Zn ions removal. Different techniques including Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) analysis, Field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), thermal gravimetric analysis (TGA) and ultraviolet-visible spectrophotometry (UV-Vis) were utilized for studying the morphology and structural properties of GO-PANI Nfs. The effect of various parameters such as pH, time, temperature, Zn ions concentration and the adsorbent dosage on the Zn (II) ions removal efficiency were studied. Results depicted that the highest Zn (II) ions removal by GO and GO-PANI was obtained at pH 7 and within 20 min. The adsorption efficiency decreased with increasing the amount of adsorbent and decreasing the initial concentration of zinc ions. In order to describe the adsorption isotherms for GO and GO-PANI, the Langmuir and Freundlich isotherm models were used and the results showed that the GO and GO-PANI nanosheets followed Langmuir and Freundlich isotherm models, respectively. In overall the GO-PANI showed higher adsorption efficiency than GO nanosheets. Furthermore, the computational results derived from electronic-scale ab initio quantum mechanics (QM) studies of zinc-GO and zinc-PANI clusters proved the adsorption tendency of zinc cations over both GO and PANI.