稻壳基磁性介孔二氧化硅材料的改性及镉吸附效果研究

发布时间：2018-05-30 00:21

本文选题：稻壳 + 巯基改性磁性介孔二氧化硅　；参考：《江南大学》2017年硕士论文

【摘要】：水生环境中的重金属污染正威胁着生态系统平衡和公众健康,其中镉污染尤为突出。研发高吸附率、可再生、低成本的重金属吸附材料,已成为废水中重金属消减的重要研究方向。本论文在以稻壳灰为硅源和Fe3O4为磁性材料制备磁性介孔二氧化硅(Magnetic Mesoporous Silica,MMS)的基础上,以高效吸附镉为目的,研究MMS的改性工艺,优化MMS和巯基改性磁性介孔二氧化硅(Thiol-modified Magnetic Mesoporous Silica,TMMS)的吸附工艺,建立吸附动力学模型和等温吸附模型,探讨两种材料对Cd~(2+)的吸附和解吸机制,初步探索TMMS在镉大米除镉废水中的应用。本研究对稻壳灰的高效利用以及工业废水中Cd~(2+)的富集脱除具有重要意义。经初探,MMS巯基改性后对Cd~(2+)的吸附效果要优于氨基改性。据此,本研究对MMS的巯基改性工艺条件进行优化,结果表明,以巯丙基三甲氧基硅烷为硅烷偶联剂,在反应时间8 h、反应温度80oC、氨水添加量750μL时,制备的TMMS具有最好的Cd~(2+)吸附性能,其表面巯基浓度为0.131 mmol/L。采用磁铁分离、静态氮吸附、X衍射、红外光谱、Zeta电位等方法,分析MMS和TMMS的结构与性质。结果表明,在施加外磁场后,MMS和TMMS材料均可以和水相很好的分离;MMS和TMMS材料孔径分布均较为集中,MMS的平均孔径和比表面积分别为4.58 nm和581.77 m2/g,而TMMS分别为4.86 nm和367.67 m2/g,巯基接枝后材料的比表面积减小;X衍射结果表明,MMS与TMMS材料均为孔道有序的六方结构,Fe3O4均为标准的尖晶石结构;在MMS及TMMS的红外光谱图中均有SiO2、Fe3O4的特征吸收峰,TMMS的光谱图中有-CH2-CH2-CH2-SH的特征碳氢键伸缩振动吸收峰,说明巯基成功接枝到MMS表面;Zeta电位测定结果显示,MMS与TMMS的等电点分别为3.4和3.2。在镉标准溶液(初始浓度为1.50 mg/L)体系中,MMS的最佳吸附条件为pH 5、温度30oC、吸附时间5 h,在此条件下,MMS对Cd~(2+)的单位吸附量和吸附率分别为2.71 mg/g和79.46%;MMS对Cd~(2+)的吸附过程同时符合准二级动力学模型和颗粒内扩散模型,拟合得到的平衡吸附量值为2.81 mg/g;MMS对Cd~(2+)的等温吸附同时符合Langmuir模型和Freundlich模型,推测吸附过程可能同时存在化学作用力和物理作用力,30oC时,MMS对Cd~(2+)的饱和吸附量为17.86 mg/g。在初始浓度为1.50 mg/L的镉标准溶液体系中,TMMS的最佳吸附条件为pH 5、吸附时间4 h、吸附温度30oC,在此条件下,其单位吸附量和吸附率分别为2.88 mg/g和95.12%。TMMS对Cd~(2+)的吸附过程符合准二级动力学模型,推测以化学吸附为主,拟合得到TMMS的平衡吸附量为2.91 mg/g;TMMS的吸附反应速率常数k2是MMS的3倍,说明TMMS吸附Cd~(2+)的速率较快。TMMS对Cd~(2+)的等温吸附符合Langmuir模型,为单分子层吸附,30oC时的饱和吸附量为33.33 mg/g,约是MMS的2倍,说明改性在一定程度上提高了材料的吸附效果。MMS和TMMS的解吸行为研究表明,MMS吸附Cd~(2+)后,在0.1 mol/L HCl中解吸4 h即可达到解吸平衡,此时的解吸率为96.58%,重复吸附/解吸4次后,第5次的吸附率仅为29.18%;TMMS吸附Cd~(2+)后,解吸速率稍慢,在相同浓度的盐酸中需要解吸5 h才可达到解吸平衡,此时的解吸率为96.10%,与MMS相比,TMMS具有较好的重复利用性能,其重复吸附/解吸4次后,第5次的吸附率仍在70%以上。MMS与TMMS的解吸过程均符合准二级解吸动力学方程,推测解吸可能是一个化学反应的过程,TMMS的解吸速率常数比MMS小,说明MMS对Cd~(2+)的解吸速率较快,而TMMS与Cd~(2+)结合的作用力较强,不易被解吸,解吸速率慢。以TMMS为吸附剂,在最佳吸附条件下对镉大米除镉废水(Cd~(2+)浓度为1.36 mg/L)中的Cd~(2+)进行富集脱除,Cd~(2+)吸附率为78.80%。
[Abstract]:Heavy metal pollution in the aquatic environment is threatening the balance of the ecosystem and public health, especially the cadmium pollution. The development of heavy metal adsorption materials with high adsorption rate, renewable and low cost has become an important research direction for the reduction of heavy metals in wastewater. In this paper, the magnetic mesopore was prepared by using rice husk ash as a silicon source and Fe3O4 as magnetic material. On the basis of silica (Magnetic Mesoporous Silica, MMS), in order to efficiently adsorb cadmium, the modified process of MMS was studied, the adsorption process of MMS and Mercapto modified magnetic mesoporous silica (Thiol-modified Magnetic Mesoporous Silica, TMMS) was optimized. The adsorption kinetics model and isothermal adsorption model were established, and two kinds of materials were discussed. The mechanism of adsorption and desorption was used to preliminarily explore the application of TMMS in cadmium removal from cadmium rice. This study is of great significance to the efficient utilization of rice husk ash and the enrichment and removal of Cd~ (2+) in industrial wastewater. The adsorption effect of MMS mercapto on Cd~ (2+) is better than that of ammonia based modification. Accordingly, the sulfhydryl modified process bar of MMS is studied in this study. The results show that with mercapto trimethoxy silane as silane coupling agent, the TMMS has the best Cd~ (2+) adsorption properties when the reaction time is 8 h, the reaction temperature is 80oC and the amount of ammonia is added to 750 u L. The surface sulfhydryl concentration is 0.131 mmol/L. by magnetite separation, static nitrogen adsorption, X diffraction, infrared spectrum, Zeta potential and so on. The structure and properties of MMS and TMMS are analyzed. The results show that after the external magnetic field is applied, both MMS and TMMS materials can be well separated from the aqueous phase; the pore size distribution of MMS and TMMS materials are all concentrated, the average pore size and specific surface area of MMS are 4.58 nm and 581.77 m2/g respectively, while TMMS are 4.86 nm and 367.67 m2/g, and the ratio of the sulfhydryl graft materials X diffraction results show that both MMS and TMMS are six square structures with orderly channel, Fe3O4 is the standard spinel structure, and the characteristic absorption peaks of SiO2, Fe3O4 in the infrared spectra of MMS and TMMS, and the characteristic hydrocarbon expansion vibration absorption peaks of -CH2-CH2-CH2-SH in the spectrum of TMMS, indicate that the sulfhydryl group is successfully grafted to the MMS table. The Zeta potential determination results show that the isoelectric points of MMS and TMMS are 3.4 and 3.2. in the cadmium standard solution (initial concentration of 1.50 mg/L), and the best adsorption conditions for MMS are pH 5, temperature 30oC, and adsorption time 5 h. Under this condition, the unit adsorption and adsorption rate of MMS to Cd~ (2+) are 2.71 and 79.46% respectively. The process conforms to the quasi two stage dynamic model and the internal particle diffusion model. The equilibrium adsorption amount is 2.81 mg/g, and the isothermal adsorption of Cd~ (2+) to Cd~ (2+) conforms to the Langmuir model and the Freundlich model. It is presumed that the adsorption process may have both chemical and physical forces. 30oC, MMS to Cd~ (2+) saturated adsorption capacity is 17.. 86 mg/g. in the cadmium standard solution system with an initial concentration of 1.50 mg/L, the optimum adsorption condition for TMMS is pH 5, the adsorption time is 4 h, and the adsorption temperature is 30oC. Under this condition, the adsorption capacity and adsorption rate of the unit are 2.88 mg/g and 95.12%.TMMS to Cd~ (2+), respectively, which conforms to the quasi two order kinetic model. The equilibrium adsorption capacity of TMMS is 2.91 mg/g, and the rate constant K2 of TMMS is 3 times of MMS, indicating that TMMS adsorption Cd~ (2+) is faster than.TMMS on Cd~ (2+). The adsorption of Cd~ (2+) is consistent with the single molecular layer, and the saturated adsorption amount is 33.33 times, which is about 2 times, indicating that the modification has been improved to a certain extent. The desorption behavior of.MMS and TMMS shows that after MMS adsorption Cd~ (2+), desorption of 4 h in 0.1 mol/L HCl can achieve the desorption equilibrium, and the desorption rate is 96.58%, and the adsorption rate is only 29.18% after repeated adsorption / desorption for 4 times, and the desorption rate is slightly slow after TMMS adsorption Cd~ (2+), and 5 h in the same concentration of hydrochloric acid needs to desorption 5 h. The desorption equilibrium can be achieved. The desorption rate at this time is 96.10%. Compared with MMS, TMMS has better reutilization performance. After 4 times of repeated adsorption / desorption, the adsorption rate of fifth times more than 70%.MMS and TMMS is consistent with the quasi two desorption kinetics equation. It is presumed that the desorption may be a chemical reaction process and the desorption speed of TMMS. The rate constant is smaller than MMS, indicating that the desorption rate of MMS to Cd~ (2+) is faster, while TMMS and Cd~ (2+) are stronger, not easily desorption, and the desorption rate is slow. With TMMS as an adsorbent, the enrichment and removal of the cadmium removal of cadmium waste water (Cd~ (2+) concentration is 1.36 mg/L) under the optimum adsorption conditions
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ424;X703

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