【作者】 刘新亮；

【导师】 王双飞；

【作者基本信息】 广西大学 ， 制糖工程， 2012， 博士

【摘要】 重金属污染形势越来越严峻。据调查统计,目前我国五分之一的耕地面积不同程度上受到镉、砷、铅、铬等重金属的污染。有些重金属通过植物吸收富集,然后进入食物链,导致动物致残、致疾、致畸,甚至死亡,直接影响人类或其他动物的健康安全。目前,重金属的处理方法有很多,如膜分离法、化学沉淀法、离子交换法等,比较各种重金属处理方法,其中吸附法更方便有效,尤其是可再生的生物资源吸附材料有更大的发展前景。此外,甘蔗是我国主要的糖料作物之一,广西蔗糖产量占我国糖产量的60%以上。甘蔗渣已经成为广西制浆造纸工业的重要原料。然而,占甘蔗质量30%-35%的蔗髓,成为制糖、造纸工业的废弃物,且产生量巨大。目前,蔗髓的利用率极低,大多被焚烧掉。因此,蔗髓生物质资源的合理有效利用,可以大大提高制糖、造纸工业废弃物的附加值,使其具有更大的发展空间。本研究采用化学方法对蔗髓进行改性,制备重金属离子的吸附材料,从蔗髓的主要成分纤维素、木素两方面对蔗髓在改性过程中的化学反应机理进行探讨,并对改性蔗髓的吸附重金属离子的机理进行研究。主要研究内容和结果如下：经过环氧氯丙烷对碱预处理、高碘酸钠氧化处理的蔗髓进行交联醚化,然后利用二乙烯三胺、甲醛在碱性条件下胺化改性,并探讨了改性后蔗髓对重金属的吸附性能。利用傅立叶红外光谱仪、扫描电子显微镜对改性前后蔗髓进行表征分析。结果发现,蔗髓改性的最佳工艺为：环氧化改性的反应温度为30℃,环氧氯丙烷加入量为20mL,反应时间为3.5h。胺化改性反应时间为3h,反应温度为30℃,甲醛和二乙烯三胺的加入量为7ml和5ml。红外分析表明,改性后的蔗髓出现C-N、C-N、N-H的特征振动峰。SEM对改性前后的表面结构分析,发现改性后的纤维表面存在许多卷曲、碎片。利用改性后的蔗髓对重金属离子Cu(Ⅱ)、Pb(Ⅱ)进行吸附研究,在pH=6.5,离子浓度为150mg/L,吸附时间为60min,对Cu、Pb的吸附量分别可以达到62.75mg/g和46.32mg/g,高于改性前蔗髓对Cu、Pb的吸附量8.25mg/g和17.85mg/g。经过分离蔗髓中的纤维素、木素,探讨蔗髓纤维素、木素的改性工艺和吸附效果,并利用傅立叶红外分析仪、X射线衍射仪、扫描电子显微镜等分析手段,寻找蔗髓中纤维、木素在蔗髓改性及重金属吸附中的作用。实验结果表明,蔗髓纤维改性的环氧化和胺化最佳工艺与蔗髓改性的相近,说明蔗髓的改性与蔗髓中的纤维有很大的关系。木素环氧化改性和胺化改性,其最佳工艺与蔗髓改性的最优条件有所差异。改性后木素的傅立叶红外光谱分析表明,在改性过程中,木素中引入了环氧基、胺基和羰基。因此,说明蔗髓中木素参与蔗髓改性,但对蔗髓改性起到辅助作用。改性后的纤维、木素对Cu(Ⅱ)、Pb(Ⅱ)的吸附表明,蔗髓中纤维素的改性对Pb(Ⅱ)的吸附有很大的贡献,而蔗髓中的木素对Cu(Ⅱ)的吸附有贡献。此外,基于纤维素的氧化和降解反应,建立了高碘酸钠氧化纤维氧化降解动力学方程,并引入损失单位纤维产生的醛基量的参数R对氧化程度进行评价。其中高碘酸钠氧化纤维的醛基产生动力学方程为[DGlc]=Co(C1-exp(-α1K1t))-α3K3t,高碘酸钠氧化降解纤维的动力学方程为[L]=(a2K2+α3K3)t,其中K1、K2、K3均为动力学参数。引入参数R来评价氧化反应,其表达式为R=[DGlc]/[L]=MbmDGlc/MamL=MB/Aa·F/L·(1-L)。用建立的模型对实验结果进行拟合分析,结果表明,实验数据与动力学模型间有很好的拟合效果,因此利用其对高碘酸钠氧化纤维进行描述。分析表明高碘酸钠浓度的变化对纤维的降解速率影响较小,而升高温度在加快纤维上醛基的产生的同时,也加速了纤维的降解。运用量子化学理论,对纤维素、木素的结构单元进行计算,探讨其反应活性和在改性中反应历程。在DFT B3LYP/6-31G基组下,对环氧氯丙烷、纤维素的葡萄糖三糖单元、木素的结构单元进行量子化优化计算,分别对其电荷分布、电子能级轨道进行分析,并利用核磁共振对其结构进行分析推测。结果表明,纤维素的反应活性基团主要分布在分子链中的葡萄糖基单元上的C2、C3和C6位的羟基上。木素的结构单元的酚羟基具有很高的反应活性,容易受到亲核试剂进攻,且反应活性顺序为：紫丁香基苯丙烷的酚羟基>愈创木酚基丙烷酚羟基。对羟苯基丙烷和愈创木酚基丙烷的酚羟基邻位C上分布的电荷在-0.15eV和-0.16eV之间,对H的束缚较弱,因此,在甲醛的质子化作用下,使木素单元上活泼氢脱除。改性蔗髓吸附机理的研究,主要从吸附动力学模型的拟合、吸附控制模型的拟合及吸附前后傅立叶红外光谱分析三方面进行探讨。结果发现,准一级模型和准二级吸附模型都可以较好的描述对改性后的蔗髓、蔗髓纤维素和木素对重金属Cu(Ⅱ)、Pb(Ⅱ)吸附过程。Webber扩散控制模型可以分两个阶段描述吸附过程；粒子外扩散模型可以较好描述吸附初始阶段,粒子内扩散控制模型对实验结果的拟合效果较差。为了探讨改性蔗髓对重金属离子吸附的活性位点,实验对改性纤维和木素吸附重金属离子前后的红外光谱变化进行了分析,考察吸附重金属前后各官能团振动变化。实验结果表明：改性后的纤维中的NH2与0H或醚键中的C-0-C参与了重金属离子的吸附；改性木素中的酚羟基、胺基对重金属离子吸附也有一定的贡献。更多还原

【Abstract】 Nowadays, heavy metal ions pollution is a serious problem in China. It was investigated that1/5of farmland were polluted by Cd, As, Pb and Cr, et. al. Some heavy metal moved into the food chain, which would lead the disease, disability and deformity, or even death of animals or human beings. There are several methods for heavy metal ions removal, such as membrane separation, chemical precipitation, ion-exchange and so on. However, adsorption is the most convenient and effective method. Especially, the biomass absorbents, as environment friendly and renewable resources, have great potential.Sugar cane is one of the main sugar crops,60%of sucrose output in China was produced from sugar cane in Guangxi. Thus, bagasse is the most abundant raw material for pulping and papermaking industry in Guangxi. However,30%-35%(w/w) of bagasse is pith, which is the main waste with high-volume from papermaking and sugaring industry. Therefore, the reasonable and effective utilization of pith, improving its added value, would have more development.The study is on the preparation of absorbent by chemical modifing bagasse pith and its adsorption property for heavy metal ions removal from aqueous solution. The mechanism of the reaction was discussed based on the main components of pith, cellulose and lignin. The adsorption dynamics models were also used to description the heavy metal adsorption process. The main contents and results were shown as followings.The bagasse pith, after being pretreated by alkali and periodate, was reacted with epoxy chloropropane, and then with diethylenetriamine and formaldehyde. The products were used to remove the heavy metal ions from aqueous sigle metal solution. Fourier transform infrared spectroscopy (FTIR) and scanning electronic microscope (SEM) were used to characterize the modified pith. The optimal conditions were30℃, epoxy chloropropane20ml, reaction time3.5h for epoxyl modification and30℃, formaldehyde7ml, diethylenetriamine5ml, reaction time3h for aminated modification. FTIR spectra showed that the stretching peaks of C=N、 C-N、N-H exist in the modified bagasse pith, and some curled fragments adhered on the surface of modified pith charactorized by SEM. The adsorption capbility of metal ions Cu(II) and Pb(Ⅱ) was62.75mg/g and46.32mg/g for modified pith, respectively, compared to8.25mg/g and17.85mg/g for pith, at the pH6.5, ion concentration150mg/L and contact60min.To study the actions of bagasse pith in the processes of modification and adsorption, the main components, cellulose and lignin, were seperated. They were modified by the method for pith modification, and their adsorption properties were investigated, by FTIR, X-ray and SEM were the main analysis approaches for their characterization. As the results shown, the cellulose in pith played an important role in modification of pith under the similar optimal coditions. However, the lignin in the pith may play a supporting role, as the differences existed in the optimal factors for modification, though the epoxy group, amido group and carbonyl group were introduced. The study on their heavy metal adsorption capbility suggested that the cellulose and lignin made some contribution to adsorption of Pb(II) and Cu(II) for modified pith.Furthermore, based on the generation of aldehyde generation and cellulose degradation in periodate oxidizing cellulose, the selectly oxidation kinetics model was constructed, and a variable factor R (the ratio of aldehyde content to the degradation of cellulose fiber) was introduced to evalue the oxidation levels. The kinetics model was as [DGic]=C0(C1-exp(-a,K,t)-a3K3t for oxidation and [L]=(a2K2+asK3)t for degradation. In the equations, K1, K2and K3were the parameters. The equation for evaluation index R was as R=[DGlc]/[L]=MbmDGlc/MamL=Mb/Ma·F/L·(1-L).The experimental data were fitted by the models, and the results shown that there was a better correlation between the dynamic model and the experimental data. Thus, the oxidation degree of bagasse fiber oxidized by periodate can be quantitative evaluated based on this model. The interpretation of results suggested that the yield and aldehyde content of the2,3-dialdehyde cellulose fiber could be controled by the reaction time and temperature at the same concentration level of periodate. In order to study the modification mechanism of pith, the quantized structures of cellulose unit and lignin unit were calculate by quantum chemistry software based on DFT B3LYP/6-31G, and the nuclear magnetic resonance (13C-NMR) of possible structures were discussed. The results showed that the hydroxyl groups on C2, C3and C6of cellulose unit were the sites with high reaction activity. Lignin could be attacked by nucleophile, and the syringyl lignin unit is easier than guajacyl lignin unit. The charges on the hydroxy-ortho carbon of hydroxy-phenyl lignin unit and guajacyl lignin unit were between-0.15eV and-0.16eV, which meant weak chemical bonding between hydrogens and carbons. Therefore, the active hydrogen would be easly removed under the protonation of formaldehyde.The adsorption dynamics models and control models were also used to describe the heavy metal adsorption process, and FTIR spectroscopy was used to study the active sites for heavy-metal adsorption. The results showed that the Pb(Ⅱ) and Cu(Ⅱ) ions adsorption can be well described by both Pseudo-first-order model and Pseudo-second-order model. Webber model could describe the adsoption process by two stages, and diffusion was found to be the rate-limiting step atinitial stage, but the approach equilibrium point the diffusion model could not fitted well.Aimed to discusse the active site, the FTIR spectroscopy of lignin and cellulose before and after adsorption. The results suggested that the sites for adsorption were related to hydroxyl and amido groups.更多还原