Adsorption, desorption and coadsorption behaviors of sulfamerazine, Pb(II) and benzoic acid on carbon nanotubes and nano-silica

Abstract In this study, nano-silica (Nano-SiO2), oxidized (O-CNTs) and graphitized multi-walled carbon nanotubes (G-CNTs) were applied as model adsorbents to study the adsorption, desorption and coadsorption behaviors of sulfamerazine (SMR), Pb(II) and benzoic acid (BA). The results showed that charge assisted H-bond (CAHB) formation played an important role in adsorption of SMR and BA on O-riched nanomaterials. The adsorption capacities of Pb(II) on CNTs were 21.46– 26.77 times higher than that on Nano-SiO2, which was mainly attributed to surface complexation and cation-π interaction. The fraction of Pb2+ adsorbed in the inside channel of CNTs should not be ignored. In coexisting systems, the absolute sorption inhibition of the SMR (ΔQeSMR) was compared with the amount of competitor adsorbed. Competitive sorption was observed as indicated by adding Pb(II) decreased adsorption of SMR on Nano-SiO2 (ΔQeSMR > 0), but hardly affected SMR adsorption on CNTs (ΔQeSMR ≈ 0) which was attributed to cation-π interaction. In addition, CAHB formed between SMR and Nano-SiO2 (ΔpKa ≈ 4.34) was weaker than that formed between SMR and O-CNTs (ΔpKa ≈ 3.15), which also consequently resulted in stronger competition of Pb(II) to SMR on Nano-SiO2 than that on O-CNTs. Moreover, coexisting BA increased adsorption of SMR on Nano-SiO2 and G-CNTs (ΔQeSMR