【作者】 赵玲；

【导师】 邵长路；

【作者基本信息】 东北师范大学 ， 凝聚态物理， 2018， 硕士

【摘要】 多孔二氧化硅作为一种常用的载体材料在催化领域具有广泛的应用。根据孔径的不同,多孔二氧化硅可以分为微孔（孔径≤2 nm）、介孔（2 nm<孔径<50 nm）以及大孔（孔径≥50 nm）二氧化硅。微孔和介孔二氧化硅具有较高的比表面积,是催化剂的理想载体。但是由于其较小孔径,严重影响反应物在其中的输运能力。相比之下,大孔二氧化硅具有优异的传质能力,能够为反应物提供有效的输运通道,但是由于其自身比表面积较低,催化剂的催化效果同样会受到严重影响。鉴于此,制备兼具微孔、介孔以及大孔结构的多级多孔二氧化硅（HPS）是提高催化剂催化能力的关键,也是目前获得优异载体材料的重要策略之一。本论文首先利用真空冷冻干燥技术结合高温煅烧的方法制备出了多种HPS,然后结合原位还原法在HPS表面负载了小尺寸的银纳米粒子（AgNPs）,得到了多孔纳米复合材料AgNPs/HPS,并深入研究了该多孔纳米复合物的催化性能。具体研究结果如下:（1）利用正硅酸乙酯（TEOS）水解溶液与聚乙烯醇（PVA）水溶液的混合液体作为前躯体,通过真空冷冻干燥和高温煅烧相结合的方法进行HPS的制备。并利用SEM、EDAX、XRD、FTIR、TG-DTA以及N₂吸附脱附等测试手段对HPS的形貌以及结构进行表征。结果表明,实验中合成的HPS不仅具有较高的比表面积,而且具有丰富的相互连通孔和独特的自支撑结构。相比于不加PVA的二氧化硅产物,高分子PVA的引入可以使二氧化硅的比表面积提高229余倍。而且随着PVA添加量的增加,HPS的比表面积呈现先增加后降低的趋势。（2）以上述HPS为载体,通过原位还原法进一步制备了AgNPs/HPS复合材料。并再次利用SEM、EDAX、TEM、以及N₂吸附脱附等测试手段对多孔纳米复合材料的形貌以及结构进行表征,研究结果表明,通过改变制备过程中加入的氨水（NH₃·H₂O）的浓度可以有效调控AgNPs的尺寸。随着NH₃·H₂O含量的增加,AgNPs的尺寸逐渐减小。最后,为了研究上述AgNPs/HPS复合材料的催化能力,我们进一步研究了该多孔复合材料对对硝基酚的催化还原效果。研究发现,AgNPs/HPS纳米复合材料可在30 s内将对硝基酚催化还原成对氨基酚,其优异的催化活性可能是由于HPS较高的比表面积以及相互连通的大孔结构对AgNPs/HPS的催化性能产生了积极的影响。此外,由于AgNPs/HPS纳米复合材料独特的自支撑结构使其同时表现出优异的回收利用性。更多还原

【Abstract】 As a common carrier material,porous silica has a wide range of applications in the field of catalysis.According to different pore sizes,porous silica can be classified into micropores（pore diameter≤2 nm）,mesopores（2 nm<pore diameter<50 nm）and macropores（pore diameter≥50 nm）silica.Microporous or mesoporous silica has a high specific surface area and is ideal carrier for catalysts.However,due to its small pore size,the transportability of reactants is seriously affected.In contrast,macroporous silica has excellent mass transfer ability and can provide effective transport channels for reactants.However,due to its low specific surface area,the catalytic effect of the catalyst is also seriously affected.Hence,the preparation of hierarchically porous silica（HPS）with micropores,mesopores and macropores is the key to improve the catalytic ability of the catalyst,and it is also one of the important strategies for obtaining excellent carrier materials.In this dissertation,a variety of HPS was prepared by vacuum freeze-drying combined with high-temperature calcination.Then,small size of silver nanoparticles（AgNPs）were loaded on the surface of HPS by in-situ reduction method,and porous nanocomposites AgNPs/HPS were obtained.Further,the catalytic properties of the porous nanocomposites were studied.The specific findings are as follows:（1）Using a mixed liquid of tetraethyl orthosilicate（TEOS）hydrolysis solution and polyvinyl alcohol（PVA）aqueous solution as a precursor,the preparation of HPS was performed by a combination of vacuum freeze drying and high temperature calcination.The morphology and structure of HPS were characterized by SEM,EDAX,XRD,FTIR,TG-DTA and N₂ adsorption and desorption.The results show that the synthesized HPS in the experiment not only has a high specific surface area,but also has rich interconnecting pores and a unique self-supporting structure.Compared to silica products without PVA,the introduction of polymer PVA can increase the specific surface area of silica by more than 229times.With the increase of PVA addition,the specific surface area of HPS increases first and then decreases.（2）Using the HPS as the carrier,AgNPs/HPS composites were further prepared by the in-situ reduction method.The morphology and structure of porous nanocomposites were characterized by SEM,EDAX,TEM,and N₂ adsorption and desorption.The results showed that the concentration of ammonia（NH₃·H₂O）added during the preparation process can effectively regulate the size of AgNPs.With the increase of NH₃·H₂O content,the size of AgNPs gradually decreases.Finally,in order to study the catalytic ability of the above AgNPs/HPS composites,we further studied the catalytic reduction effect of the porous composites on p-nitrophenol.The study found that AgNPs/HPS nanocomposites could be used as a catalyst to reduce p-nitrophenol to p-aminophenol in 30 s,and its excellent catalytic activity may be due to the high specific surface area and the interconnected macroporous structure of HPS which had a positive effect on the catalytic performance of AgNPs/HPS.In addition,due to the unique self-supporting structure,AgNPs/HPS nanocomposites also exhibited excellent recyclability.更多还原