Modification of coal-based activated carbon with nitric acid using microwave radiation for adsorption of phenanthrene and naphthalene

摘要

In order to obtain directional structure and characteristics of coal-based activated carbon (CAC), it was modified with nitric acid using microwave radiation. The effects of various factors on this modification were analyzed. The adsorption capacities of the modified CAC (MCAC) were evaluated by determining the adsorbed amounts of methylene blue and iodine. The results showed that MCAC-16h (oxidation time 16 h, nitric acid concentration 20 %; microwave time 8 min, and microwave power 500 W) possess excellent adsorption capacities. CAC and MCAC-16h were characterized by performing scanning electron microscopy, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, Boehm method, point of zero charge determination, and X-ray photoelectron spectroscopy, as well as by determining the adsorption capacities of phenanthrene and naphthalene. SEM results showed that the surface of MCAC-16h became clean and smooth. The BET surface area, pore volume and average pore diameter of the modified sample slightly increased; meanwhile, the acidic functional groups significantly decreased, resulting in an increased pH(pzc) value. XPS results showed that the content of elements ratio of C/O increased from 2.25 to 3.68. Adsorption isotherms revealed that Langmuir model was applicable for CAC and MCAC-16h. Furthermore, kinetic studies indicated that the pseudo-second-order fitted well for phenanthrene and naphthalene. The modified sample exhibited superior performance over CAC for naphthalene and phenanthrene. In addition, the adsorption capacity for phenanthrene was larger than that for naphthalene. The results suggest that microwave radiation is an efficient and rapid method for the modification of activated carbons and which achieved the effective removal for the polycyclic aromatic hydrocarbons.