【作者】 孙媛媛；

【导师】 岳钦艳；

【作者基本信息】 山东大学 ， 环境工程， 2014， 博士

【摘要】 本研究以生物质资源-芦竹为原料,焦磷酸为活化剂制备活性炭。首先优化了常规加热和微波加热下活性炭的制备条件,明确了两种加热方式下制备活性炭的最佳参数,对比研究了常规加热和微波加热下两种活性炭的物理结构、化学性质和吸附行为,然后结合吸附质的特点,对活性炭进行无机和有机改性,调控其孔径结构和表面化学性质,增加对目标污染物的亲和性,提高吸附效果。采用扫描电子显微镜(SEM)、比表面测定仪、傅里叶红外光谱仪(FT-IR).X-射线衍射仪(XRD)和X-射线光电子能谱(XPS)分析等现代分析手段对芦竹活性炭的结构形貌、比表面积和孔径、表面官能团和元素含量等性质进行分析表征,采用静态实验方法,在不同的pH、温度、投加量、时间和其它共存离子条件下,考察芦竹活性炭对水体中污染物的吸附性能,结合上述性质分析和表征结果,研究芦竹活性炭与吸附质之间的构效关系,并明确吸附机理。本研究对于芦竹的资源化利用及芦竹活性炭应用于不同性质废水的处理提供理论指导。选择芦竹为原料,焦磷酸为活化剂,普通加热法制备活性炭。通过单因素实验考察了剂料比、浸渍时间和活化温度对活性炭产品得率、比表面积和孔容的影响,筛选出制备活性炭的最优条件,通过SEM、氮气吸附脱附实验和XPS分析对最优活性炭进行表征,通过土霉素(OTC)吸附试验考察最优条件下制备的活性炭的吸附性能。结果表明当温度大于400℃时,活性炭比表面积开始大幅度增加,最大比表面积在600℃时取得,最大孔容在500℃时取得；在剂料比为0.4时,比表面积可达到1150.69m2/g,孔容可达0.59m3/g,随着剂料比的增加,比表面积和孔容也逐渐增加,在剂料比为0.75时,比表面积达到最大,在剂料比为1.0时,孔容达到最大值；随着浸渍时间的延长,比表面积和孔容均呈现先增加后降低的趋势,在浸溃时间为5h时,比表面积达到最大值,在浸渍时间为10h时,总孔容达到最大值。与磷酸作为活化剂时相比,焦磷酸的使用量较少,得到的活性炭介孔含量更多,更加适合于对大分子污染物的去除,在20℃,对OTC的最大吸附量为534.8mg/g。采用微波加热法制备了芦竹活性炭。通过单因素实验考察辐射功率、辐射时间和剂料比对活性炭得率、比表面积和孔容的影响。通过表面形态分析、氮气吸附脱附实验和吸附试验对最优活性炭性质进行表征。结果表明随着辐射功率的增加,芦竹活性炭的比表面积和孔容均呈现先上升后趋于下降的趋势,在700w时达到最大值,当辐射功率过低时,所达到的温度不足以使芦竹原料完全活化,当辐射功率增加到一定值时,芦竹原料能够活化完全,形成发达的孔隙结构,比表面积增加,当辐射功率过高时,导致反应过快,反应温度过高,部分孔被烧蚀,造成比表面积降低。活性炭的比表面积和孔容均随着剂料比的增加而增加,当剂料比达到0.75时,比表面积达到最大值,当剂料比超过0.75时,造成比表面积的降低。随着辐射时间的增长,芦竹活性炭的比表面积和总孔容呈现先上升后下降的趋势,在辐射时间为15min时达到最大值。综上,微波加热法制备芦竹活性炭的最佳制备条件为：辐射功率700w,辐射时间为10min,剂料比为0.75。此时,活性炭得率为56.1%,比表面积高达1568m2/g,微孔比表面积为631m2/g,外比表面积为936m2/g,孔容为1.08m3/g,微孔孔容为0.28m3/g,外孔容为0.80m3/g。在前两章节的基础上,采用氮气吸附/脱附试验、傅里叶红外光谱分析和贝姆滴定等多种手段对比研究了两种加热方式下活性炭的物理化学性质和对环丙沙星的吸附性能。氮气吸附/脱附试验表明微波炭具有较大的比表面积；傅里叶红外光谱分析和贝姆滴定结果表明普通炭表面的酸性含氧官能团含量明显高于微波炭,微波加热减少了活性炭表面的酸性官能团含量,增加了pHpzc。吸附实验结果表明,在20℃时,普通炭和微波炭对环丙沙星吸附量分别为321.07mg/g和300.35mg/g,虽然微波炭具有较大的比表面积,但对环丙沙星(CIP)吸附量却较低,这主要是由于微波炭表面含氧官能团较少,负电性较弱,对CIP静电吸引较弱导致的。由于存在静电斥力的作用,初始溶液pH太高或者太低对环丙沙星的吸附都不利,在3.2-8.2范围内,吸附量最大。两种活性炭对CIP的吸附均符合伪二级动力学模型和Langumuir吸附等温模型。吸附等温线拟合结果表明该吸附为单分子层吸附,吸附过程以物理吸附为主,热力学参数表明该吸附过程是一个放热自发的过程,温度升高不利于吸附的进行。采用磷酸为活化剂,FeCl3、MnCl2和AICl3作为辅助活化剂制备了芦竹活性炭,并考察其对溶液中Cr(VI)的去除效果。结果表明FeCl3、AICl3和MnCl2作为辅助活化剂制备的活性炭均可提高对溶液中Cr(VI)的吸附效果,MnCl2作为辅助活化剂制备的活性炭具有最大的比表面积(1332m2/g)和最大的孔容(1.060cm3/g);AlC13的加入不利于活性炭孔的生成,此时活性炭比表面积和孔容分别为992m2/g和0.688cm3/g, FeCl3的加入对活性炭的比表面积影响很小,但增加了活性炭的介孔含量,降低了活性炭的微孔含量,增加了活性炭的孔容。溶液中三价铬和六价铬的比值及XPS分析结果了证实Cr(Ⅵ)在吸附过程中的转化过程。共存离子吸附结果显示溶液中的正电荷极易被吸附到表面带负电的活性炭吸附后,中和了活性炭表面的负电性,因此,有利于对带负电荷的铬酸根的吸附。采用环氧氯丙烷、N,N-二甲基甲酰胺、二乙烯三胺以及三乙胺对活性炭进行了改性(AC-EDT)研究,重点考察了改性对活性炭性质及吸附性能所产生的影响。XPS分析结果表明氨基成功的接枝到活性炭表面,对带负电的铬酸根具有更好的亲和作用。与改性前吸附平衡时间为10h相比,AC-EDT对Cr(VI)的吸附速度更快,10min即可达到平衡,且AC-EDT对铬酸根具有更好的吸附效果。AC对铬酸根的吸附以孔吸附为主,当强氧化性的Cr(VI)吸附到活性炭表面后,与活性炭表面能提供电子的C=C、C=O反应,自身还原为Cr(Ⅲ);而对于AC-EDT,吸附机理以静电吸引为主,当Cr(VI)快速吸附到表面后,同样发生氧化还原反应。本研究利用资源丰富的芦竹为原料制备出了优质活性炭,并通过辅助活化和改性,从孔径分布和表面性质两个方面对活性炭性质进行调控,提高了活性炭的选择性,拓宽了芦竹活性炭的应用范围。该研究不仅节约了煤炭资源,也为芦竹的利用寻找到一个合理的出路,实现了其资源化、高值化和商品化。该研究具有一定的环境、经济和社会效益。更多还原

【Abstract】 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更多还原