文献名： Calcium-enhanced retention of humic substances by carbon nanotube membranes: Mechanisms and implication

作者 ： Yankun He ， Lanlan Qin ， Haiou Huang

State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Beijing Normal University, No. 19, Xinjiekouwai Street, Beijing, 100875, China

摘要： Efficient removal of humic substances (HS) in natural water is of importance to drinking water  treatment. In this study, the adsorption and retention of HS by multi-walled carbon nanotube (MWCNT) membranes were systematically investigated by dynamic filtration of synthetic and natural surface water. In the absence of Ca(II), HS were dominated by small, dissolved species albeit the varying pH. Accordingly, HS retention by the MWCNT layers only ranged from 15%-65% at the end of the filtration. In contrast, the presence of Ca(II) in the feed water partially transformed HS molecules into colloidal aggregates as found by light scattering analyses. Furthermore, molecular dynamics (MD) simulation results reveal that Ca(II) complexation with -COO ^-  on MWCNT and humic acid (HA) not only leads to HA aggregation in the feed solution, but also promotes HA adsorption onto carboxylated MWCNT. The modeling results are consistent with the high retention of HS by the carboxylated MWCNT membrane, i.e., >90% for the synthetic model water and >85% for the natural water, at a moderate calcium concentration range of 0.5–2.0 mM. Considering the widespread presence of calcium in natural water, these findings suggested that carboxylated MWCNT has a potential for effective adsorptive filtration of HS in drinking water.

关键词： Carbon nanotubes ； Functional groups ； Humic substances ； Adsorption ； Retention