The Preparation Of Fish-Scale-Based Porous Carbon And Its Application For Chromium(Ⅵ) Adsorption

Hexavalent chromium is widely used in industrial wastewater, it has high toxicity, so hexavalent chromium must be removed before the discharge of industrial wasterwater. Porous carbon is a good adsorbent for Hexavalent chromium because of its excellent physical and chemical properties such as large specific surface area, high porosity and abundant groups etc. The problem of the industrial removal processes is the separation of the Cr-absorbed carbon materials. Traditional separation methods involved filtration or centrifugation, which is tedious, laborious, energy intensive and expensive. Based on these considerations above, we developed an economic in situ synthetic strategy to prepare zero-valent iron (nZVI) supported on fish-scale-bascd porous carbon (FHLC). Specific research is listed as follows:Firstly, Magnetic carbon materials that have nanoscale zero-valent iron (nZVI) supported on fish scale based hierarchical lamellar porous carbon (FHLC) is successfully synthesized in this study. X-ray diffraction (XRD) results showed that the magnetic porous carbon was composed of nano zero-valent iron and the amorphous carbon, the zero-valent iron crystal showed body centered cubic structure. SEM and TEM results showed that with the increase of iron contents, the pores of FHLC were blocked, when the iron contents were low, the abundant pore structure could still be maintained. The nitrogen absorption-desorption experiment results showed that the specific surface area (SBET), total pore volume (Vt) and micropore volume (Vm) of the FHLC decreased with the increase of Fe contents.Secondly, the effects of pH value, initial Cr(VI) concentration and time on Cr(VI) adsorption capacity for magnetic fish-scale carbon were studied. The experimental data was also fitted to the isotherm adsorption model and the kinetic model. The results showed that both Langmuir and Freundlich isotherm adsorption model could described the process well, based on Langmuir isotherm adsorption model, magnetic fish-scale carbon had a higher adsorption capacity (357.12 mg/g) compared with FHLC. Moreover, the pseudo-second kinetic model gave a better coefficient for both FHLC and magnetic fish-scale carbon. The adsorption rate of magnetic fish-scale carbon was 7.2 × 10-3 g/mg/h, significantly higher than FHLC (5.3 × 10-3 g/mg/h). The regeneration efficiency of magnetic porous carbon was also studied, after 3 times adsorption-desorption cycles magnetic porous carbon could reach 88.5% of its initial adsorption capacity, while the fish-scale porous carbon could only reach 66.1% of its initial adsorption capacity.Finally, The adsorption mechanism was further studied by X-ray photoelectron spectroscopy, suggesting that FHLC could adsorb Cr(Ⅵ) by electrostatic attraction as well as chemical adsorption, and the nZVI on FHLC provides new adsorption sites for Cr(Ⅵ). The magnetic hysteresis curve showed that this magnetic carbon material had high saturated magnetization (16.49 emu/g), higher than most of the magnetic carbon materials reported in other literatures. It is indicated that the as-prepared carbon material not only can be used to remove Cr(Ⅵ) efficiently but also shows excellent magnetic separation performance from wastewater.