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

摘要

In this study, nano-silica (Nano-SiO_2), 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-SiO_2, which was mainly attributed to surface complexation and cation-π interaction. The fraction of Pb~(2+) adsorbed in the inside channel of CNTs should not be ignored. In coexisting systems, the absolute sorption inhibition of the SMR (ΔQ_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-SiO_2 (ΔQ_e~(SMR) ＞ 0), but hardly affected SMR adsorption on CNTs (ΔQ_e~(SMR) ≈ 0) which was attributed to cation-n interaction. In addition, CAHB formed between SMR and Nano-SiO_2 (ΔpK_a ≈ 4.34) was weaker than that formed between SMR and O-CNTs (ΔpK_a ≈ 3.15), which also consequently resulted in stronger competition of Pb(Ⅱ) to SMR on Nano-SiO_2 than that on O-CNTs. Moreover, coexisting BA increased adsorption of SMR on Nano-SiO_2 and G-CNTs (ΔQ_e~(SMR) ＜ 0), but did not result in an apparent competition on SMR adsorption by O-CNTs (ΔQ_e~(SMR)≈ 0). These results emphasize that the environmental behaviors of a certain pollutant should be assessed carefully by considering the presence of other pollutants.