Enhancement of bisphenol a removal from wastewater via the covalent functionalization of graphene oxide with short amine molecules

Abstract

Water pollution is a serious environmental problem worldwide. This problem is augmented by the shortages in fresh water supplies in several parts of the world. Thus, the effective treatment and reuse of polluted water is an inevitable necessity. One of the highly toxic water pollutants with potentially mutagenic and carcinogenic effects is bisphenol A (BPA). Accordingly, the adsorptive removal of BPA from wastewater samples using novel graphene-based materials has been investigated in this study. The results showed the ineffectiveness of the unmodified graphene oxide (GO) in removing BPA from the wastewater samples. The functionalization of GO with short organic amines (i.e., hexamethylenetetramine (HTMA), diethylenetriamine (DETA), and diethylamine (DEA)) boosted the BPA removal by several folds relative to GO and hydrazine-reduced GO. Additionally, the amine structure affected the performance of the amine-modified GO adsorbents. The most effective adsorbent was found to be the one modified with DEA (GO-DEA) followed by GO-DETA. The maximum adsorption capacity (qmax) of BPA on GO-DETA and GO-DEA were 258.6 and 334.4 mg/g respectively, relative to 16.2 and 87.0 mg/g in the case of the unmodified GO and the hydrazine-reduced GO (i.e., rGO), respectively. The results of the adsorption kinetics revealed that BPA adsorption on GO-DETA is much faster than its adsorption on GO-DEA. The adsorption kinetics for both adsorbents were best fitted using the Avrami model with adsorption rate constant of 0.0149 (GO-DETA) and 0.0033 min−0.47 (GO-DEA). Although variations in BPA adsorption capacity were observed with changing the pH of the wastewater, the lowest BPA adsorption was encountered at pH 10 for all the graphene-based materials synthesized in this study. The characterization of the synthesized adsorbents revealed that BPA adsorption is not correlated with the surface area/porosity of the adsorbents. It is also not correlated with the degree of GO deoxygenation or nitrogen content alone. The most plausible adsorption mechanisms are π−π stacking interaction and hydrogen bonding. The findings reported in this study reveal the potential of GO functionalization with short organic amines in significantly boosting the adsorptive removal of phenolic pollutants from wastewater.