[Effects of pH and Ni2+ on sorption behavior of phenanthrene on engineered nano-silica]

In order to reveal the sorption behavior of phenanthrene (PHE) on engineered nano-silica, batch equilibriums were conducted to study the effects of heating, solution pH, and heavy metal ion (Ni2+) on PHE sorption, and a site energy distribution model was used to analyze the changes of sorption behavior. The results demonstrated that the sorption isotherm of PHE could be fitted well by the Freundlich model. The sorption capacity of the original nano-silica (PNS) was enhanced by heating (heated nano-silica, HNS), with the Freundlich adsorption coefficient (lgK(F)) increasing from 1.48 to 2.43. The nonlinearity of sorption isotherm increased after heating. The sorption characteristics together with pore distribution and surface area analysis suggested that PHE sorption on nano-silica was a combination of pore-filing and surface sorption, with the microspores and mesopores of nano-silica playing a major role. While changes in solution pH did not show a significant effect on the sorption of PHE on PNS, the sorption of PHE on HNS decreased significantly with increasing pH, with IgK(F) reducing by 73.7% when pH increased from 4.0 to pH 8.0. The pH caused differences in sorption capacity could be mainly explained by zeta potentials of nanoparticles. High pH enhanced the charge of nanoparticles, and reduced the pore accessibility. The effect of Ni2+ on PHE sorption on HNS varied with its concentration. At low concentration (<5 mmol x L(-1)), Ni2+ suppressed PHE sorption, while at a higher concentration, NiZ2 enhanced the sorption of PHE at a lower concentration (50 microg x L(-1)), and the inhibition on the sorption of PHE at a higher concentration (500 microg x L(-1)) did not increase further. This complex pattern was a result of concurrence of multiple processes.