Comparison kinetics studies of Cu(II) adsorption by multi-walled carbon nanotubes in homo and heterogeneous systems: Effect of nano-SiO2

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2014-08, Vol.250, p.119-127
• Main Authors: Sun, Wei-Ling, Xia, Jing, Shan, Ying-Chun
• Format: Article
• Language: English
• Subjects: Adsorption kinetics; Cu(II); Multi-walled carbon nanotubes; Nano-SiO2
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2014.03.094

•Cu(II) adsorption kinetics by CNTs and CNTs–SiO2 mixture were investigated.•Cu(II) adsorption kinetic data were well described by pseudo-second-order kinetics.•Hydroxy CNTs, with higher k2, adsorb Cu(II) ion much faster than carboxyl CNTs.•The addition of nano-SiO2 accelerates the Cu(II) adsorption.•This effect is related to adsorption mechanisms of Cu(II) by CNTs and SiO2. The adsorption kinetics of Cu(II) in homogeneous systems of CNTs and heterogeneous systems of CNTs and nano-SiO2 were investigated using ion selective electrode potentiometry. Particular attention was paid on the role of nano-SiO2 in the adsorption kinetics of Cu(II) by CNTs. It was found that the Cu(II) adsorption by CNTs and CNTs–SiO2 mixture was well described by pseudo-second-order kinetics. In homogeneous systems, the equilibrium time of Cu(II) adsorption decreases and the pseudo-second-order rate constant (k2) increases with increasing CNTs concentrations. Comparing the different types of CNTs, hydroxy CNTs (CNTs-OH), with higher k2 values, adsorb Cu(II) ion much faster than carboxyl CNTs (CNTs-COOH). This may be ascribed to their different adsorption mechanisms. The electrostatic attraction is the primary mechanism of Cu(II) adsorption by CNTs-OH, while Cu(II) adsorbed on CNT-COOH through complexing with the carboxyl groups on the surface of CNTs besides electrostatic attraction. In heterogeneous systems of CNTs and nano-SiO2, the Cu(II) adsorption reaches equilibrium much faster than in homogeneous systems of CNTs, indicating nano-SiO2 accelerates the Cu(II) adsorption. This acceleration effect is possibly related to the adsorption mechanism (electrostatic attraction) and higher BET surface area of nano-SiO2. FTIR and XPS spectra demonstrate the binding of nano-SiO2 and CNTs, and CNTs and Cu(II). The present results highlight the significant influence of nano-SiO2 on the Cu(II) adsorption by CNTs. Hence, it is critical to consider these effects in modeling and predicting the adsorption kinetics of metals by CNTs in heterogeneous systems.