The Control Of Nanostructure Of Carbon Materials And Their Research Of Adsorption Mechanism Of Dye Molecules

Activated carbon and activated carbon fiber, as the typical representative of thecarbon materials, had been widely used in various fields, especially the application ofdye wastewater adsorption, because of their developed pore size and a wealth ofsurface functional groups, the high adsorption capacity. With the continuousdevelopment of the dye industry, the number and types of composition of dyewastewater were more complex, which had become the main pollution sources ofwater bodies. To further enhance the adsorption properties of carbon materials, theresearch on the control of nanostructure of carbon materials had been more and moreconcern.Powdered activated carbon(PAC), granular activated carbon(GAC) and activatedcarbon fiber(ACF) were taken as adsorbents and neutral red(NR), methyleneblue(MB) and crystal violet(CV) were taken as the adsorbate, the study was dividedinto the morphology, the surface functional groups and pore size. The influence ofnanostructure, such as aperture, the surface area and surface functional groups, on thedyes adsorption and the control conditions of them were discussed:1. The effect of the morphology of activated carbon on the dyes adsorption wasconsidered, while the effect of the pH value of the solution and the temperature ondyes adsorption onto PAC and GAC were investigated. The adsorption data was fittedby the kinetic model. The results showed that the adsorption rate and saturationadsorption capacity of PAC was better than that of GAC; the temperature and the pHof the dyes solution have different influences on the adsorption with differentmorphology of activated carbon and different dyes. Owning to the correlationcoefficient of pseudo-second order kinetic model, R~2>0.990, it could better reflectthe adsorption mechanism.2. The impact of the surface structure of activated carbon on MB adsorption wasdiscussed. The surface structure of GAC was modified by NaOH, NH3·H2O, H2O2and different concentrations of HNO3solution, respectively. Nitrogen adsorptionisotherms, Boehm titration, and IR spectra were used to analyse the impact of structure and surface functional groups on MB adsorption onto modified activatedcarbon. The adsorption kinetic behavior of MB onto the modified activated carbonwas investigated by conducting a series of batch adsorption experiments andadsorption mechanism was discussed from kinetic model. The results showed that thecarboxyl quantity of the surface of activated carbon increased by Nitric acid modified,while phenolic hydroxyl content decreasing; the adsorption quantity of methyleneblue on modified activated carbon by40%nitric acid was better than that by65%concentrations of nitric acid; the increase of the groups containing oxygen and theenhancement of the surface polarity were beneficial to the adsorption of methyleneblue on hydrogen peroxide modified activated carbon; owing to sodium hydroxideand ammonia modified, the basic groups had a significant increase and the acidgroups and the surface polarity both subdued so that the saturation adsorptioncapacity decreased. The adsorption kinetics of methylene blue onto modifiedactivated carbon were more in line with pseudo-second-order model, R~2＞0.99.3. It was studied that different microporous structure of ACFs played the role in theadsorption of different dye molecules. Based on the relation between the aperture areaof ACFs and minimum cross-sectional area of dye molecules, activated carbon fiberswith different micropore size adsorbed dye molecules of neutral red, methylene blue,crystal violet, respectively. The structural features of ACFs were characterized bynitrogen adsorption isotherms, while the surface functional groups were described bythe X-ray photoelectron spectroscopy (XPS). The kinetic model and adsorptionisotherm model were used to simulate the data about dyes adsorbed on ACFs. Theresults showed that when the aperture area was1.3to6.2times the minimum crosssectional area, there was high adsorption capacity; the correlation coefficient (R~2) ofpseudo-second order model and the Dubinin-Radushkevich-Stoeckli model was morethan0.998, which were more appropriate for illustrating dyes adsorbed on ACFs.4. The control methods of microporous structure of ACF and the effect of fluorinationon the surface structure of ACF were considered. By regulating the activationtemperature, the flow of activation gas and the activation time to control thenanostructure of the activated carbon fiber, the effect of activation conditions on thecontrol of nanostructure of ACFs was investigated and nanostructure change of ACFs on different activation condions was improved by MB adsoption ability. Thestructural features of ACFs were characterized by nitrogen adsorption isotherms. Theresults showed that the activation yield of ACFs gradually decreased, the adsorptioncapacity of methylene blue first increased and then decreased with the activationtemperature increasing; with the flow of the activation gas increasing, it had the samesituation and tendency with the activation temperature; the activation yield ofactivated carbon fibers gradually reduced, the MB adsorption quantity was anincreasing trend with the extension of activation time. It was discussed thefluorination had impact on surface structure of ACF. The results showed the specificsurface area, pore volume and pore size decrease, the surface polarity enhances.