Hollow carbon spheres for diclofenac and venlafaxine adsorption

Abstract

Silica@polymer spheres with a core@shell structure were synthesized and thermally annealed at 800 ºC to obtain silica@carbon spheres (SiO2@CSs). The silica core was removed by etching with NaOH, hollow carbon spheres (CSs) being obtained. The particle size of SiO2@CSs and CSs increased with the ethanol/water (E/W) volumetric ratio (2, 4.5, and 7) employed in the first synthesis step (i.e., the Stöber's method to obtain silica particles). Moreover, the average diameter of the materials prepared with E/W ratio of 2 was affected by the etching of the SiO2 core (from 168 to 109 nm), in contrast with those synthesized at higher E/W ratios of 4.5 and 7 (251-245 and 270-284 nm, respectively). The specific surface area (SBET) of the CSs ranged from 271 to 602 m2 g-1, which are more porous than SiO2@CSs (SBET in the range 115-144 m2 g-1). Adsorption kinetic and equilibrium studies were carried out with diclofenac and venlafaxine as model organic micropollutants (OMPs). Despite the silica removal was not effective for all the CSs (TGA residue ranging from 3 to 46 wt%), the kinetic studies and the ATR-FTIR spectra confirmed the positive effect of having a hollow core (i.e., removing the silica core). Equilibrium studies demonstrated that CSs prepared with an E/W ratio of 7 were the best performing material when considering both OMPs. Moreover, these CSs performed well to remove a set of 24 OMPs from wastewater effluents and thus, they are an interesting option for water or wastewater treatment. (c) 2022 Elsevier Ltd.