Co-adsorption and competitive adsorption of sulfamethoxazole by carboxyl-rich functionalized corn stalk cellulose in the presence of heavy metals

Diethylenetriamine pentaacetic acid (DTPA) functionalized modified corn stalk cellulose (DCS) was successfully prepared and applied to the adsorption of sulfamethoxazole (SMZ) wastewater in the presence of copper (Cu). Compared with the raw corn stalk cellulose (RCS), DCS has the characteristics of more hydrophilic groups, larger contact space and lower steric hindrance. The adsorption amount for Cu and SMZ in binary system were 4.41 mg/g and 29.7 mg/g, respectively. Additionally, DCS has good pH buffering capability, resistance to potentially interfering ions (NaCl and HA) and great regeneration performance after 5 cycles. More importantly, the experimental results demonstrated competitive adsorption and complexation synergy occurred between Cu, SMZ and DCS. Cu inhibited the adsorption of SMZ while SMZ promoted the adsorption of Cu, which was attributed to the fact that SMZ provided additional adsorption sites or complexation reduced the surface charge of Cu. Based on this situation, density functional theory (DFT) calculations were carried out for the further explanation of adsorption mechanism. The molecular electrostatic potential maps showed that DCS possessed more SMZ adsorption sites than Cu, and the adsorbed Cu or SMZ on DCS would provide additional adsorption sites. The equilibrium configurations and binding energy indicated that the competitive adsorption, bridge effect adsorption and co-adsorption would occur simultaneously. The total electron density and differential charge confirmed that SMZ was more likely to overlap electron clouds and transfer electrons with DCS, while the adsorption process of Cu was conformed the complexation adsorption dynamic equilibrium. This paper provided a new perspective on the co-adsorption and competitive adsorption processes by multisystem experiments and abundant DFT calculations and indicated the good adsorption performance of DCS on SMZ in the presence of Cu.