Preparation Of Bamboo Based Activated Carbon And Its Application In Chromium Waste Water Treatment

Activated carbon(AC) is an excellent adsorbent with big specific surface area and well-developed pore structure, widely used in chemical industry, environmental protection, pharmaceutical,food and other industries. With the development of society, AC with ordered pore size distribution and specific surface chemistry is required in modern science and industry, therefore, it has been the core of preparation technology to regulate pore structure and surface chemistry of activated carbon. There are relatively abundant sources of bamboo in our country. Currently, bamboo industry has a low utilization of bamboo, which generates a lot of bamboo waste. In this paper, we prepared AC with bamboo by steam activation, and studied the evolution of surface area and porosity of AC produced from bamboo waste with varying steam activation parameters as well as changes in surface chemistry. Besides, the removal of chromium from waste water by bamboo based AC was also investigated.(1) Bamboo based AC was prepared by carbonization and steam activation, and the evolution of pore structure with varying steam activation parameters was studied. The results showed that higher steam activation temperature and/or times facilitated the formation of new micropores but widened existing micropores. Considering the evident pore-widening effect caused by steam activation, prolonged activation eventually led to reductions in BET surface area and total pore volume. Optimum conditions for preparing AC include carbonization temperature of 450 oC, carbonization time of 60 min, activation temperature of 850 oC, activation time of 120 min, steam flush of 0.2 cm3/min, and heating rate of 5 oC/min. The scanning electron microscope(SEM) photographs demonstrated that considerable porosity is present in AC in the form of interconnected network.(2) A series of analysis method were adopt to study the changes in surface chemistry during AC preparation systematically. The results of elemental analysis、Boehm titration and pH measurement revealed that pyrolyzed char and AC mainly consist of C and O, and basic groups present on their surface. The content of total acidic groups decreased while that of total basic groups increased after activation when compared with pyrolyzed char. Noticeable differences, which mainly concern band intensities, can be observed from the Fourier infrared transform spectrum(FTIR) between the pyrolyzed char and activated carbon. The surface functional groups present on the AC surface including hydroxy, methyl, methylene, aromatic ring, carbonyl,ether bond etc. The results of X-ray photoelectron spectroscopy(XPS) indicated that activation does not affect the species of oxygen-containing groups but changes the amount of these species. X-ray diffraction analysis showed that high-temperature activation increased the degree of graphitization of AC and made the crystal structure more regular.(3) Bamboo bark based AC prepared by steam activation was used for the remediation of Cr(VI) polluted water. The characterization of adsorbent showed that the textural property and surface chemistry of bamboo bark based AC are suitable for the adsorption of Cr(VI) anion from aqueous solution. Adsorption experiments demonstrated that the removal efficiency of Cr(VI) and total chromium declined with the increased of solution pH, and increased with the increase of AC dosage. The adsorption isotherms were fitted well with Langmiur. The maximum adsorption capacity at 303 K was 193 mg/g. The adsorption of Cr(VI) is spontaneous and endothermic. The kinetics adsorption data was fitted by pseudo-second-order model, and intraparticle diffusion was not the only control steps during adsorption process. Adsorption mechanisms was speculated to include four steps: protonation of AC surface functional groups; Cr(VI) anion was absorbed by the protonated surface functional groups through electrostatic attraction; the adsorbed Cr(VI) was reduced by AC; Cr(III) was absorbed by AC or released into solution.