Synthesis, characterization, and application of pristine and clay-templated carbon xerogel microspheres for removing diclofenac and heavy metals from water solution.

ABSTRACT

Organic xerogel microspheres (SX) were synthesized by inverse emulsion sol-gel polymerization and carbonized to obtain carbon xerogel spheres (SXCs). The catalyst was K2CO3 or Fe(C2H3O2)2, and the clay sodium sepiolite (SNa) or exfoliated vermiculite (Vexf) was added during the synthesis. Depending on the catalyst and clays, the SXCs were designated SXC-K, SXC-Fe, Vexf-K, Vexf-Fe, SNa-Fe, and SNa-K. At pH = 7 and T = 25 °C, the SXCs' adsorption capacities towards diclofenac (DCF) in water increased as follows SXC-K < Vexf-Fe < SXC-Fe < SNa-Fe < SNa-K < Vexf-K and this order is associated with the SXCs' surface area and mesopore volume. The Vexf-K displayed the highest capacity for DCF due to its optimal textural and chemical properties, and the DCF maximum uptake was 560 mg/g at pH = 6 and T = 35 °C. The adsorption capacity towards Cd2+ and Pb2+ decreased as SX-K > SX-Fe > SXC-K > SXC-Fe, indicating that the non-carbonized materials (SX) presented higher adsorption capacity than the SXCs because the SXs had a higher acidic site content. Adding SNa or Vexf to SXs enhanced the adsorption capacity towards Cd(II), and SNa-SX-K presented an exceptionally high capacity of 182.7 mg/g. This synergistic effect revealed that the Cd2+ was adsorbed on the SX-K acidic sites and by cation exchange on the SNa.