| In recent years, the advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) have been attracted extensive attentions of many scientific research institutes.Using carbon materials as catalyst or catalyst carrier, catalytic PMS to generate sulfate free radicals (SO4-) that can degradation of organic pollutants in water, has became the focus of recent research direction.However, most recent researches were using granule active carbon (GAC) or active carbon fiber (ACF) as the carriers of some transition metals, such as Fe and Co.The studies about carbon material directly activated-PMS oxidation for pollutant degradation were rare. Furthermore, the targeted pollutants in the scarce papers are mainly the organics which can be easily adsorbed.In this paper, the Reactive Black 5 (RB5)was selected as targeted pollutants.As it is a macromolecule that can hardly be adsorbed by ACF, the interference of the adsorption can be eliminated when we investigate the mechanism of degradation. However, for the commercial ACF, the degradation capacity of RB5 is feeble.In order to promoting the performance of ACF, we have attempted to modify its surface physical and chemical properties.On the other hand,we would like to analyze the effect of surface physical and chemical properties on the degradation of RB5.Specific studies are as follows:(1)The three kinds of ACF:ACF-N (treated ACF-0 by 3M nitric acid),ACF-H (treated ACF-0 in 900℃ in nitrogen), ACF-NH (treated ACF-N in 900℃ in nitrogen) were obtained by modifying the original ACF (ACF-0) in three different processes. BET, Boehm titration,FT-IR,SEM-EDS.XPS were used to characterise the surface physical and chemical properties of these four kinds of ACF samples.It found that nitric acid could corrode the surface of ACF and promote the amount of carboxyl, keto and-NO2 in the surface.While vast acid functional groups such as carboxyl, ketone and aldehyde were pyrolysed in high temperature treatment process,part of nitrogen functional groups would also be decomposed in the process.At last, we found that after a serial of treatment a considerable amount of alkaline nitrogen functional groups were generated on the ACF-NH.(2)The ACF-0,ACF-N,ACF-H and ACF-NH was used to activate PS,PMS and H2O2 to degrade Acid Orange 7 (AO7) and RB5.For the degradation of AO7, the rank of activity of the ACFs:ACF-NH>ACF-0>ACF-H>ACF-N.As to RB5 the rank changed to ACF-NH>ACF-0>ACF-N>ACF-H.After a comparison, for the degradation of RB5 the ACF-NH/PMS is the optimal combination.Moreover, increasing the amount of the dosage of ACF-NH and PMS could promote the degradation ability. After all,the cost effective dosage of ACF-NH and ratio of PMS to RB5 were 0.4 g/L and 50:1 respectively.(3)Since we want to expound the effect of element state of C,N and O of ACF on the catalytic oxidation capacity,XPS full spectrum of above three elements and the degradation efficiency of the four kinds of ACFs were taken advantage.Firstly, π-π bonds could promote the catalytic ability. Besides, the other carbon and oxygen functional groups could change the surface acid-base properties of ACF. Then the degradation efficiency would effect by the change of contact rate of ACF and RB5. Eventually, the chemical state of nitrogen was vita to the catalytic activity of ACF. We reinforce that the pyridine, imine/amide/amine have promoting effect while the-NO2 have inhibitory effect in our system.(4) Qualitative analysis of RB5 degradation mechanism of ACF-NH/PMS system was proceeded.The decomposition of RB5 is mainly by the reactions of breaking of azo linkage and opening of benzene and naphthalene rings.The primary oxidizing species were SO4- and HO-. We also found that the activation site is the surface of ACF. And the reaction site is close to the surface.The adsorption capacity does not affect the degradation efficiency of RB5 but the contact rate dose.In a word, the treatment of heat after nitric acid is not only a process of modification but also a way of regeneration. |
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