纳米ZnO/纤维素气凝胶复合材料及表征毕业论文_化学工程与工艺毕业论文

纳米ZnO/纤维素气凝胶复合材料及表征毕业论文

2021-04-27更新

摘 要

随着石化资源的短缺以及环境污染的日益严重,可再生资源的开发利用越来越受到人们的重视。纤维素作为自然界储藏量最大,可再生且可生物降解的生物高分子,其本身及衍生物在化工、医药、建筑、油田化学和生物化学等领域得到了广泛的应用。由于天然纤维素一般以纤维状为主,孔结构不理想,水分散性差,难以在实际处理中大规模使用,因此,再生纤维素及衍生物,尤其是纳米无机质/纤维素复合材料的利用是近几年研究的热点,其中纳米ZnO/纤维素复合材料引起人们极大的兴趣。目前,纳米ZnO/纤维素复合材料多是将锌源与天然纤维或醋酸纤维结合,所制备的纳米ZnO/纤维素复合材料具有较好的光催化性能和抗菌性能等。本文重点考察纤维素催化剂载体的性质以及水热条件对其产生的影响,为制备纳米ZnO/纤维素催化材料作前期探索。

本文将木浆溶解在65% ZnCl2水溶液中,用水或醇再生出纤维素凝胶,制备了颗粒状纤维素气凝胶。考察溶解温度、析出剂、水热pH以及水热温度对纤维素凝胶性质的影响,并对孔结构、晶型、热稳定性和形貌等进行了表征。

考察颗粒状纤维素凝胶的性质及水热条件下的变化,本文得出结论:(1)溶解温度为70 ℃时,纤维素凝胶的孔多且密,比表面积很大,含有的ZnO量很少,且热稳定性较好,热分解温度高,分解速度快;溶解温度高于80 ℃后,纤维素降解厉害,暴露的-OH较多,与Zn2 结合后经干燥仍残留较多的ZnO,且纤维素凝胶的孔结构和热稳定性均不理想。(2)以水作为析出剂时,纤维素凝胶的孔结构理想, ZnO的含量少;醇类作析出剂时,由于醇的极性较弱,更有利于-OH与Zn2 的结合,因此纤维素凝胶中含有的ZnO较多,孔结构不够理想。(3)水热pH为8时,纤维素凝胶的孔结构较好,晶型也理想;水热pH超过8后,水热使得纤维素凝胶的颜色变深,量变少,说明水热pH过高会对纤维素凝胶的性质产生很大的变化,利用价值不大。(4)水热温度为160 ℃时,纤维素凝胶的孔结构和热稳定性较好,含有的ZnO也少。

考察pH值对纳米ZnO/纤维素光催化剂晶型的影响,实验发现,pH为8和10时,所制得的纳米ZnO/纤维素中ZnO的衍射峰明显,但当pH为10时,纤维素凝胶性质不够稳定,经过高温水热过程,颜色很容易变黑,得率也明显下降,对研究的意义不大。因此,认为pH为8时制得的纳米ZnO/纤维素更适于作光催化剂。

关键字:纤维素;纤维素气凝胶;催化载体;水热法

Abstract

With the shortage of petroleum resources and the increasingly serious environmental pollution, people have paid more and more attention to the development and utilization of renewable resources. As the largest reserves and renewable and biodegradable biopolymer in nature, cellulose, its derivatives products and cellulosic materials have been widely used in the fields of chemical, pharmaceutical, construction, oilfield chemistry and biochemistry. Since natural cellulose is generally in the shape of powder or fibrous, its porous structure is not ideal, its dispersibility in water is poor, so it is difficult to scale in actual use, therefore, the use of cellulose derivative, especially the use of nano inorganic qualitative/cellulose composites, has become a research hotspot in recent years, nano zinc oxide/cellulose composites aroused great interest. Predecessors tried to combine zinc to cotton fibers or acetate fibers, the nano zinc oxide/cellulose composite material has good photocatalytic properties and antimicrobial resistance. In this paper, we made efforts to investigate the nature of cellulose catalyst carrier and the impact of hydrothermal conditions on its nature, it can be a preliminary exploration for the preparation of nanometer zinc oxide/fiber composites.

In this experiment, the pulp was dissolved in 65% zinc chloride solution, use water or alcohol to regenerate cellulose gel, the cellulose gel was prepared in the shape of granular or strip. Examine the impact of dissolution temperature, precipitation agents, hydrothermal pH, hydrothermal temperature and other factors on the thermal properties of cellulose gel, and characterize the pore structure, crystalline, thermal stability and morphology.

Investigate the properties of granular cellulose gel and the changes in the conditions of hydrothermal synthesis, we draw the conclusions: (1) when the dissolution temperature is 70 ℃, the amount of cellulose gel pore is big, the pore is dense, the specific surface area is big, the cellulose gel contains a small amount of zinc oxide, and its thermal stability is better, its thermal decomposition temperature is high, and it decomposites very fast; when the dissolution temperature is higher than 80 ℃, the degradation of cellulose is severe, the hydroxyl are more exposed, there is still much residue zinc oxide after binding to zinc ion and drying, is not ideal. (2) when use water as precipitation agent, the pore structure of the cellulose gel is ideal, the content of zinc oxide is less; when use alcohol as the precipitating agent, the cellulose gel contains more zinc oxide for the alcohol polarity is weak and it is more conducive to union zinc ion and hydroxyl. (3) when the hydrothermal pH is 8, the pore structure of cellulose gel is better, crystal is also ideal; when the hydrothermal pH is over 8, hydrothermal made the color of cellulose gel darker and quantitative change less, this indicated that high hydrothermal pH would produce great changes on the nature of cellulose gel, the value is less. (4) when the hydrothermal temperature is 160 ℃, the pore structure and thermal stability of the cellulose gel is good, it contained less zinc oxide.

Considering pH value on the influence of the photocatalyst nano zinc oxide /cellulose crystal, it was found that the preparation of nano zinc oxide /zinc oxide diffraction peak is obvious in cellulose when pH is 8 and 10 .Ellulose gel properties is not stablebut when the pH is 10.After high temperature hydrothermal process, color is very easy to turn black, also significantly lower yield, the significance of the research is useless. So that it is suitable for nano zinc oxide /cellulose to be made as photocatalyst when the pH of 8 .

Key Words: cellulose; cellulose gel; catalytic carrier; hydrothermal synthesis

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