Oxidation Of Black Carbon And Its Sorption Behavior Of Contaminants

Black carbon （BC）, derived from incompletely combustion ofbiomass and fossil fuels, shows strong sorption capacity toward thecontaminants in the environment. It was reported that the oxidation ofblack carbon could strongly influence its surface structure properties andchemical characteristics, thus changing its sorption to pollutants. In thisstudy, The oxidized BC was obtained by immersing with nitric acid ofdifferent concentrations, and then characterized with FTIR, Boehmtitration, elemental analysis. The surface area of oxidized BC wascharacterized by N₂and CO₂adsorption. Four kinds of contaminants（benzene, nitrobenzene, anisole and cumene） with different polaritieswere selected as the representatives of benzene series compounds, whilephenol and Cd（Ⅱ） were selected as the representative contaminants ofcombined pollution. The aims of this paper were to study the influence ofthe oxidation on the surface properties of BC and its sorption towardcontaminants. First, the influence of surface modification on the composition andthe physical/chemistry properties of black carbon was investigated. Thesurface area of black carbon was characterized by N₂（77K） andCO₂（273K） adsorption, respectively. Both results indicated that thesurface area shrinked greatly after modification. And the method ofadsorption and desorption of CO₂was more suitable for reflecting themicroporous surface structure of BC. Boehm titrations demonstrated thatthe oxidation caused the acid surface functional groups on BC increasedgreatly, the result was consistent with the results of FT-IR result andelemental analyses.Second, the sorption of benzene series compounds on modified BCwas determined. It was found that the available adsorption sites forbenzene series compounds were greatly decreased because themicroporous structures of BC were damaged during the oxidationreaction, which played the primary role in decreasing adsorption of them.The introduction of more acid surface functional groups on BC mayimprove their hydrophilicity and polarity because of which the watermolecules were more likely to be adsorbed via hydrogen bonding andthen in turn blocked the micropores on BC. The adsorption affinity to BCdecreased following the order of nitrobenzene> anisole> benzene>cumene, which was attributed to the effect of the substituent in aromaticring as well as the hydrogen bonding. Third, a series of batch equilibrium experiments were carried out toinvestigate the the single-component and competitive sorption of phenoland cadmium on modified BC. In single system, it showed that sorptionof phenol decreased with the increase of the oxidization degree of BC,whereas the sorption Cd（Ⅱ） increased by enhancing the coordinationability of BC. In binary system, the sorption of phenol on BC hardlyinfluenced by the coexisting Cd（Ⅱ） ions. However, a slight decrease ofsorption was observed in the higher Cd（Ⅱ） concentration because of thesteric effect of the hydrated Cd（Ⅱ）. Similarly, the phenol molecules didnot exhibit impact significantly to the sorption of Cd（Ⅱ） dues to thesmaller radius of phenol.