Facile synthesis of surface-etched functionalized porous nanosilica microspheres for the simultaneous removal of cadmium and malachite green: Experimental and DFT studies

Co-contamination of wastewater with toxic metals and dyes pose a severe threat to ecosystems and human health. In the present study, a novel surface-etched mercapto-functionalized porous nanosilica microsphere (E-MPNS) was prepared for the simultaneous removal of Cd(II) and malachite green (MG) from wastewater. The effects of various environmental factors on Cd(II) and MG adsorption and their adsorption mechanisms are elucidated in detail. The results showed that the E-MPNS exhibited a relatively higher specific surface area (272.06 m²/g). The maximum adsorption capacities of E-MPNS for Cd(II) and MG were 436.68 and 3831.08 mg/g in the single system and 433.66 and 1932.18 mg/g in the binary system, respectively. The adsorption mechanisms of E-MPNS were surface complexation and ion exchange for Cd(II) and hydrogen bonding and electrostatic attraction for MG. Density functional theory calculation revealed that the E-MPNS-Cd(II) complex had a higher molecular stability and lower reactivity compared with that of E-MPNS-MG, and the energy gaps of the E-MPNS-Cd(II) (1.15 eV for SH and 0.71 eV for OH) were markedly larger than those of the E-MPNS-MG (0.69 eV for SH and 0.52 eV for OH). Moreover, the E-MPNS exhibited good biocompatibility with bacteria and plants. These results indicate that the E-MPNS is a promising adsorbent for remediating of Cd(II) and MG co-contaminated wastewater.