| Activated carbons were prepared from biomass renewable source-Arundo donax L.was using H4P2O7as activator. First, the preparation conditions were optimized by conventional and microwave heating and the optimal preparation condition was obtained. The physicochemical properties and adsorption behavior of two optimal activated carbons were compared. Then, according the characteristics of adsorbate, the activated carbon was modified by inorganic and organic methods to regulate the pore textural and surface chemistry, enhancing the affinity between activated carbon and adsorbate and improving adsorption capacity. Analysis methods such as scanning electron microscopy (SEM), BET specific surface area analyzer, Fourier transformed infrared (FT-IR), X-Ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology, BET specific surface area, surface functional group and element speciation analysis of activated carbon. Batch experiments with variable pH, temperature, dosage, contact time and other coexisting ions were conducted to evaluate the sorption performance of pollutant by adsorbents from aqueous solutions. Combined with structural analysis and characterization results, the adsorption structure-activity relationship was established and the adsorption mechanism was discussed. This study provides theoretical basis for resource utilization of Arundo donax L. and the treatment of wastewater with different properties by activated carbon.Activated carbons were prepared from renewable source Arundo donax Linn using H4P2O7as activator with conventional heating method. Through single factor experiment, the influences of chemical impregnation ratio (mass of H4P2O7:Arundo donax Linn), activation temperature and soaking time on the properties (yield, BET surface area, pore volume and surface functional group) of activated carbon were investigated. The optimal activated carbon (ALAC) was characterized by SEM, N2adsorption/desorption isotherms, XPS and oxytetracycline (OTC) adsorption experiments. Results showed that the pore development was significant at temperatures>400℃, and reached maximum BET surface area (1463m2/g) at600℃and maximum total pore volume (1.24cm3/g) at500℃. At a low impregnation ratio of0.4, BET surface area and pore volume could reach as high as1150.69m2/g and0.59m3/g respectively. Both BET surface area and pore volume initial increase followed by decrease after reaching a maximum, with the maximal surface area was obtained at impregnation ratio of0.75and maximal pore volume at1.0. BET surface area and mesopore volume reached maximum after soaking for10h. compared with activated carbon prepared by H3PO4, activated carbon prepared by H3PO4had a higher portion of mesopore which was favorable for adsorption of large molecules. At temperature of20℃, the adsorption capacity for OTC534.8mg/g。Activated carbons were prepared with a microwave-induced activation process using H4P2O7as the activating agent. Through single factor experiment, the effects of various factors such as microwave radiation power, radiation time and impregnation ratio between H4P2O7and precursor on the specific surface area and pore volume were studied. Results showed that both the BET specific surface area and pore volume increased at the first stage and then decreased with the increase of radiation power. The highest value was obtained at700W. Lower temperature could not make raw materials be fully activated and higher temperature made the pore produced be ablated, thus resulting in the lower surface area and lower pore volume. As the radiation time increased, both the BET specific surface area and pore volume increased at the first stage and then decreased and the highest value was obtained at radiation of15min. The same trend was observed with the increase of impregnation ratio and the highest value was obtained at impregnation ratio of0.75. H4P2O7has a strong ability for microwave-absorbing. With the increase of impregnation ratio, the activated temperature was high and the raw material was fully activtated. In addtion, the raw material was impregnated fully by H4P2O7was advantage to pore development. When the impregnation ratio was higher than0.75, the pore was ablated because of the higer temperature. The optimal activation conditions were determined as:microwave power of700W, radiation time of10min and H4P2O7/precursor ratio of0.75:1, under which a carbon yield of56.1%, a surface area of1568m2/g, a micropore surface area of631m2/g, a external surface area of936m2/g, a total pore volume of1.08m3/g, a micropore of0.28m3/g and a external pore volume of0.80m3/g could be reached.The textural structure, chemical properties and adsorption behavior of activated carbons (ACs) derived from Arundo donax Linn using H4P2O7activation by conventional (AAC) and microwave heating methods (MAAC) were compared. Although N2adsorption/desorption isotherms showed that MAAC had larger surface area than AAC, AAC acted as a better adsorbent for the removal of CIP with maximum monolayer adsorption capacities of418.410mg/g for AAC and395.257mg/g for MAAC at20℃. It was related to the less acidic functionalities of MAAC. The initial pH from2.1to2.8corresponding to a lower CIP adsorption capacity was probably related to the electrostatic repulsion between cation and positive surface charge of the sorbents. When the pH was higher than the pKa2of the CIP, the anionic form would predominate and thus induce evident repulsion to negatively charged carbon surfaces. Such behaviors would lead to a significant reduction of CIP uptake on both adsorbents. Thus, the optimum operation pH for AAC and MAAC adsorption were both in the range of3.2-8.2, suggesting that both cationic and zwitterionic forms of CIP could adsorb significantly onto carbons. Compared with pseudo-first-order kinetic, pseudo-second-order kinetic model was considered more appropriate to represent the kinetic data. The negative AG values for both carbons indicated spontaneous nature and feasibility of the adsorption process. The negative AH indicated exothermic nature of the adsorption process. Higher temperature is not favorable for CIP adsorption.FeCl3, AICl3and MnCl2were used as the assisted activation agent in activated carbon preparation by H3PO4activation using microwave heating method. The results suggested that carbon with MnCl2as assisted activation agent displayed the highest BET surface area (1332m2/g) and the highest pore volume (1.060cm3/g). Doping with MnCl2was favorable for the enlargement of activated carbon, especially for micropore, whereas, the addition of AICl3decreased the specific surface area of activated carbon. The addition of FeCl3, MnCl2and AICl3increased the yield of carbons, but hindered the creation of acidic functional groups on carbons. FeCl3, AICl3and MnCl2had successfully improved Cr(VI) adsorption and activated carbon with FeCl3as assisted activation agent exhibited the best uptake capacity. The adsorption of Cr(VI) onto activated carbons was not only due to the large surface area but the interactions between charged chromium ions and carbon surface. After interaction with electron on carbon surface, Cr(VI) was reduced to Cr(III), which was adsorbed by carbons or partly released into solution. The XPS analysis indicated the acidic surface functional was beneficial for the conversion of Cr(VI) to Cr(III).To study the transformation of Cr(VI) in adsorption process, total chromium in the aqueous solution was also recorded. The ratio of the amount of Cr(VI) to Cr(III) on each adsorbent was explained by XPS analysis results. Both the co-existing salts (Na2SO4and NaNO3) demonstrated promoted effects on Cr(VI) removal by four carbons. The pseudo-second-order model and Freundlich equation displayed a good correlation with adsorption data.AC-EDT, which contained amino groups, was an effective adsorbent for Cr(VI) adsorption from aqueous solution. The amino groups-grafted activated carbon demonstrated a better adsorption capacity for Cr(VI) compared to the original carbon. The adsorption of Cr(VI) was highly pH-dependent and the best results were obtained at a wide pH range. In addition, the rate of Cr(VI) adsorption onto AC-EDT was rapid,10min was sufficient. However, in the case of AC, equilibrium time was obtained with10h. The results proposed that AC adsorbed adsorbate involved in three steps:the external surface adsorption, the intraparticle diffusion stage and the final equilibrium stage. After reaction with electron, Cr(VI) was reduced to Cr(III), which was adsorbed by carbon or partly released into solution. In the case of AC-EDT, Cr(VI) was adsorbed via an electrostatic attraction and was subsequently reduced from toxic Cr(VI) to Cr(III) on the adsorbent surface. These results were confirmed by the XPS analysis. Moreover, The reduced Cr(VI) on the AC-EDT was bound to C-O or carbonyl groups (C=O). The results of this study showed that the AC-EDT was a efficient adsorbent for the removal of Cr(VI) in wastewater.Compared with previous study, renewable source Arundo donax L. was employed as raw material for activated carbon. On one hand, the coal resource was saved. On the other hand, a reasonable way was found to realize the use of Arundo donax L.. The properties such as pore distribution and surface chemistry of activated carbon were regulated to make it had the ability of selectivity. According the characteristic of adsorbate, the preparation condition and the modification method could be adjusted. Arundo donax Linn was used as raw material to prepare activated carbon with excellent properties. This study has a certain environmental, economic and social benefits... |
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