Polyamidoamine-Functionalized Graphene Oxide-SBA-15 Mesoporous Composite: Adsorbent for Aqueous Arsenite, Cadmium, Ciprofloxacin, Ivermectin, and Tetracycline

Polyamidoamine functionalized graphene oxide-SBA-15 mesoporous composite (PGOSBA) was synthesized, characterized, and examined for aqueous adsorption of metals (As(III) and Cd(II)) and emerging pollutants (ciprofloxacin, ivermectin, and tetracycline). The adsorption data were explained with kinetics and adsorption isotherm models. PGOSBA is mesoporous, but has lower Brunauer-Emmett-Teller (BET) surface area and pore dimensions in comparison to the amine-functionalized SBA-15 (SBA-15-NH2). Infrared spectra peaks peculiar to the individual constituents were observed in the PGOSBA, which exhibited thermal stability in-between those of its SBA-15-NH2 and graphene oxide (GO) constituents. The basic structural lattices of individual constituents were unaffected in the PGOSBA morphology, which was covered by GO sheet-like structures. The adsorption of Cd(II), As(III), ciprofloxacin, and ivermectin attained equilibrium at 240, 20, 180, and 720 min, respectively. The adsorption rate data for Cd(II) fitted the pseudo-second-order kinetics model, while As(III), ciprofloxacin, and ivermectin adsorption fitted the fractal pseudo-second-order kinetics model better. PGOSBA exhibited one optimum adsorption pH for Cd(II) (pH 5), while two pH points were recorded for ivermectin (a lower peak at pH 3 and a higher one at pH 9). The Cd(II) and ivermectin adsorption processes were spontaneous and endothermic; an increase in temperature up to approximate to 30 degrees C slightly enhanced Cd(II) adsorption (<= 5%), as well as ivermectin (>= 15%), but to an extent; a higher temperature increase (approximate to 40 degrees C) may result in lower adsorption (<= 2%) than at approximate to 30 degrees C. Multiple sorption phenomena including electrostatic interactions, multilayer adsorption due to pi-pi interactions, as well as pore filling were involved in the pollutants removal processes. The PGOSBA adsorption capacities for Cd(II), As(III), tetracycline, and ciprofloxacin are 92.4, 22.3, 29.2, and 24.6 mg/g, respectively, while it is 291.8 mu g/g for ivermectin. The adsorbent could lower ivermectin in low-concentration ivermectin solutions (<80 mu g/L) to less than 8.5 mu g/L. The PGOSBA reusability for ivermectin adsorption over three consecutive cycles of adsorption, desorption, and reuse was >= 95%. These results imply that the PGOSBA adsorbent would be economically viable for potential use in water treatment processes.

Automated summary

PGOSBA, a polyamidoamine functionalized graphene oxide-SBA-15 mesoporous composite, showed mesoporous structure and different adsorption properties for Cd(II), As(III), ciprofloxacin, and ivermectin. The adsorption processes involved multiple phenomena such as electrostatic interactions, pi-pi interactions, and pore filling. The material has potential for use in water treatment due to its high adsorption capacities and reusability.