Removal of Humic Acids in Water by Carbon Nanotubes

摘要

This study used multi-walled carbon nanotubes (MWCNTs) to remove humic acids (HA) in water. Experimental results showed the adsorption data fit pseudo-second order model well. The adsorption capacity of CNTs increased with increasing initial concentration of HA until reaching a stable capacity at 80 mgl~(-1) of HA. The capacity also increased with decreasing pH values in solution. Statistical paired T test showed the adsorption capacity at 40°C was significantly larger than those at 10°C and 25°C. The adsorption capacities after 24 h contact time at 10, 25, and 40°C were 58.6, 60.5, and 84.7 mgg~(-1), respectively. Three common sorption isotherm models, including the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) models, were employed to fit the isotherm data. Results showed the theoretical saturation capacity (Q_(max)) in the Langmuir model increased with increasing temperature and the capacity constant (K_f) in the Freundlich model also increased with increasing temperature. The intensity constants (n) implied HA is favorably adsorbed onto CNTs. The maximum HA adsorption capacity (q_(max)) in the D-R model increased with increasing temperature. All the three models suggested the adsorption process is endothermic. The extremely low values (0.4-0.5 kJ mol~(-1)) of mean sorption energies (E) calculated from the D-R model suggested the adsorption of HA by MWCNTs is physical nature.