Removal of the antibiotic sulfamethoxazole from environmental water by mesoporous silica-magnetic graphene oxide nanocomposite technology: Adsorption characteristics, coadsorption and uptake mechanism

In this study, the mesoporous silica-magnetic graphene oxide nanocomposite material (mGO-Si) was prepared. The surfactant cetyltrimethyl ammonium bromide (CTAB) was utilized as the mesoporous template while the tetraethyl orthosilicate (TEOS) was used as the silica source. The synthesized nanocomposite was characterized through different analyses, namely XRD, XPS, TEM, FT-IR, VSM, BET, and acid-base titration. Various factors like the effects of the initial concentration, contact time, influence of the pH and the coexistence of other antibiotics on the sulfamethoxazole (SMX) uptake, were investigated. Adsorption results exhibited that the mGO-Si adsorbed the SMX molecules more effectively than the pristine magnetic graphene oxide (mGO). Kinetic data showed good correlation on the basis of the pseudo-second-order model. The equilibrium adsorption data fitted well to the Langmuir model, and a maximum SMX adsorption capacity of 15.46 mg/g was obtained. At high pH, the solution had significantly impaired then declined capacity of SMX adsorption. Electrostatic repulsion occurred between the dissociated SMX and the more negatively charged mGO-Si at basic pH. Adsorption mechanisms between SMX and mGO-Si were plausibly activated by hydrogen bonding, π–π EDA interactions, and solution pH-based electrostatic interactions dependent upon the status of SMX and the pH ,PZC of mGO-Si. Moreover, the CIP and OTC competitors in the mixed solute system managed to improve the SMX adsorption by acting as a bridge to form CIP−SMX−mGO-Si/ OTC−SMX−mGO-Si surface complex. At low aqueous phase concentration of SMX, CIP was likely to form a stronger electrostatic interaction system with the adsorbent, thereby resulting in an adsorption level which was more competitive in the process opposing CIP to SMX than in that opposing OTC to SMX.