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

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-pi 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 (Delta Q(e)(SMR)) 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 (Delta Q(e)(SMR) > 0), but hardly affected SMR adsorption on CNTs (Delta Q(e)(SMR) approximate to 0) which was attributed to cation-pi interaction. In addition, CAHB formed between SMR and Nano-SiO2 (Delta pK(a) approximate to 4.34) was weaker than that formed between SMR and O-CNTs (Delta pK(a) approximate to 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 (Delta Q(e)(SMR) < 0), but did not result in an apparent competition on SMR adsorption by O-CNTs (Delta Q(e)(SMR) approximate to 0). These results emphasize that the environmental behaviors of a certain pollutant should be assessed carefully by considering the presence of other pollutants. (C) 2020 Elsevier B.V. All rights reserved.