【作者】 黄加乐；

【导师】 李清彪；

【作者基本信息】 厦门大学 ， 工业催化， 2009， 博士

【摘要】 贵金属纳米材料因其具有独特的催化和光学性能而得到广泛重视，其制备与应用已成为当今纳米技术领域中的一个研究热点。相对于传统的物理法和化学法，近年来出现的基于微生物或植物的生物还原法，具有成本低、绿色环保、纳米材料稳定性高等优点，成为贵金属纳米材料具有发展前景的新颖制备方法。在原材料方面，相比微生物繁琐的筛选与培养过程，植物及其提取液的获得和使用更加简便，得到了一定的关注。然而，目前有关植物及其提取液制备贵金属纳米材料的研究更多地集中在简单的条件实验和纳米材料的表征等，很多重要的基础问题还远未搞清楚，例如：贵金属纳米材料形貌和颗粒粒度的控制仍较为有限，植物及其提取液的工艺路线和还原反应器，以及还原工艺条件的优化均未见报道。这些基础问题的解决对于建立一种贵金属纳米材料形貌和粒度调控的新方法，以及建立实际可行的植物生物还原制备工艺过程与关键技术具有极为重要的意义。基于以上研究现状，本工作旨在利用植物干粉及其提取液来还原Ag⁺或[AuCl₄]^-获得相应的银和金纳米材料。通过对植物干粉的筛选，以及植物还原过程的工艺路线的优化和还原反应器的设计，建立了一套可调控银和金纳米材料的形貌及颗粒粒度的新方法，并初步探索了银纳米颗粒的抗菌应用和金纳米颗粒的催化应用。首先，本工作利用了芳樟叶干粉还原制备了银纳米颗粒和金纳米颗粒，并在芳樟叶提取液还原体系中引入纳米晶种，以调控纳米颗粒的形貌和粒度。通过改变芳樟叶干粉的用量，可以调控获得粒度在55-80 nm之间的近球形银纳米颗粒、边长在25-150 mm和厚度约为7 nm的三角金纳米片以及粒度在10-35 nm之间的近球形金纳米颗粒。在芳樟叶提取液还原Ag⁺体系中引入适量的银纳米晶种，促进了银纳米颗粒各向异性生长，而在芳樟叶提取液还原[AuCl₄]^-体系中引入适量的金纳米晶种，反应快速产生的金原子在金晶种上的快速累积，促进了金纳米颗粒各向同性生长。芳樟叶干粉的初步成分分析和红外光谱分析结果表明，多糖、还原糖、黄酮等多羟基化合物的羟基对Ag⁺和[AuCl₄]^-起还原作用。其次，本工作采用来源广泛而极易获得的中草药植物干粉，在30℃的条件下对银纳米颗粒和金纳米颗粒的形貌进行可控制备，并研究植物干粉还原制备银纳米颗粒和金纳米颗粒过程的共性规律。利用红花、菊花、淫羊藿、夏枯草、金钱草等五种植物干粉可用于制备近球形银纳米颗粒；栀子和金银花可用于制备单晶银纳米线，银纳米线的平均直径约为45 nm，长度可达10μm以上，银纳米线是由近球形银纳米颗粒串接并沿[110]方向生长的。金银花和厚朴花可用于制备银纳米片，银纳米片是由粒度较小的近球形银纳米颗粒逐渐转化而来的，纳米片重叠生长，易于形成树枝状银晶体。基于植物干粉红外光谱计算所得的各向异性生长指数（S）可作为植物干粉筛选的参考依据之一，S＞1．0的植物干粉可促进银纳米材料各向异性生长，而S＜1．0的植物干粉可促进银纳米材料的各向同性生长。植物干粉在还原制备金纳米颗粒方面是普遍适用的，利用不同的植物干粉来还原HAuCl₄，可获得不同粒度分布的球形金纳米颗粒和三角金纳米片，研究还发现雏形的“纳米片”是由许多10 nm以下的近球形金纳米颗粒团聚形成的。再次，研究了植物提取液还原连续制备银纳米颗粒工艺，并考察了主要工艺参数对纳米颗粒形貌和粒度的影响规律。管式微反应器适宜的加热温度为90℃，在该温度下，可以将银晶核的形成过程与银纳米颗粒的生长过程分开，不存在二次成核，因此能够获得粒度分布较窄的银纳米颗粒；原料液经过预热处理有利于获得粒度分布较窄的银纳米颗粒。三通的适宜夹角为60°或90°。获得粒度分布较窄的银纳米颗粒的适宜进料体积流率为0．5 mL·min^-1或0．8 mL·min^-1；在相同的进料体积流率下，反应管内径越小，流体温度越均匀，银晶核成核速度越快，所得的银纳米颗粒粒度分布也越窄，反应管的适宜内径为2 mm或3 mm。最后，通过液体培养基法和固体培养基法评价了银纳米颗粒对金黄色葡萄球菌和大肠杆菌的抗菌性能；采用了侧柏叶提取液还原制备了Au／TiO₂催化剂，并以4-硝基酚（4-NP）向4-氨基酚（4-AP）的催化转化反应作为模型反应，对所得的Au／TiO₂催化剂进行催化性能评价。采用侧柏叶提取液快速制备的银纳米颗粒对大肠杆菌的最小抑菌浓度（MIC）和最小杀菌浓度（MBC）分别为1．4 ppm和27 ppm，而银纳米颗粒对金黄色葡萄球菌的MIC为5．4 ppm。侧柏叶干粉所制得的金纳米颗粒较稳定，且对4-NP的催化转化反应有较好的催化活性。利用侧柏叶提取液制备的Au／TiO₂催化剂对4-NP的催化转化反应有较好的催化活性；在30℃下制备的Au／TiO₂催化剂的催化性能优于60℃和90℃下制备的催化剂；经过300℃焙烧处理之后的Au／TiO₂催化剂的催化性能较未焙烧的催化剂好。更多还原

【Abstract】 Noble metal nanomaterials have attracted extensive attention owing to their uniquecatalytic and optical properties.Therefore,their preparation and application have become oneof research highlights in the field of nanotechnology.Compared with the traditional physicaland chemical methods of synthesizing metal nanomaterials,the bioreduction methods basedon microorganisms or plants have emerged as cost-effective and environmentally benignapproaches to highly stable metal nanomaterials in recent years.Therefore,we envision thatthey will be used to produce commercial metal nanomaterials with promising market prospect.In contrast to microorganisms,the use of readily available plants and their extracts cancircumvent laborious biological screening and cultivation.Hence,plants and their extractswill be better options for synthesis of metal nanomaterials than microorganisms.However,atpresent,the researches on plant-based bioreduction have been focused on simple synthesisand characterization of nanomaterials.Many fundamental problems are far from clear.Forinstance,shape and size control of noble metal nanomaterials have met very limited success.Moreover,process design of plant-based biosynthesis and optimization of operation conditionhave not been reported yet.Sloving such problems are of great significance for establishing anew protocol on shape and size control of noble metal nanomaterials,and practicaltechnology.Silver and gold nanomaterials were fabricated via reduction of Ag⁺ and[AuCl₄]^- by driedplant biomass and their extract in this work.Concerning the above status of plant-basedbiosynthesis,through screening of plant biomass,process design and optimization ofplant-based biosynthesis,and design of reactors,this work aimed at establishing a newprotocol on shape and size control of Ag and Au nanomaterials.Furthermore,application ofthe Ag nanoparticles （AgNPs） as antimicrobials and Au nanoparticles （AuNPs） as catalystswas preliminarily explored,respectively.Firstly,AgNPs and AuNPs were synthesized by sundried C.camphora leaf.Ag or Auseeds were added to the mixture of the precursors and C.camphora leaf extract to tune theshape and size of AgNPs or AuNPs.Not only could silver nanoparticles ranging from 55 to 80nm in size be fabricated,but also gold nanotriangles with edge length range of 25-150 nm orspherical gold nanoparticles with size range of 10-35 nm could be easily modulated byadjusting the amount of C.camphora leaf biomass.The presence of Ag seeds promotedanisotropic growth of AgNPs while that of Au seeds improved the monodispersity of AuNPs.The polyol components such as polysaccharide,reducing sugar,flavones,etc were mainlyresponsible for the reduction of silver ions or chloroaurate ions.Secondly,richful and readily available plant biomass of traditional Chinese medicines（TCMs） were used to tune the shape of Ag and Au nanomaterials and particle size of AgNPsand AuNPs at 30℃.And general knowledge based on the biosynthesis by TCMs was proposed.AgNPs and AuNPs could be synthesized by dried powder of F.Carthami,F.Chrysanthemi,H.Epimedii Brevicornus,S.Prunellae Vulgaris and H.Lysimachiae.AgNWswith mean diameter of 45 nm and length of at least 10μm could be fabricated by driedpowder of F.Gardeniae and F.Lonicerae.The nanowires grew along the direction of[110]through chain connection of spheriodal AgNPs.Furthermore,Ag nanoplates could beprepared by dried powder of F.Lonicerae and F.Magnoliae Officinalis.The overlappinggrowth of Ag nanoplates led to dentritic Ag crystal.Anisotropic growth index （S） of plantbiomass based on their FTIR analyses could be used as one of referred indexes of screeningplant biomass.Anisotropic Ag nanostructures were promoted when S was more than 1.0,while isotropic Ag nanostructures were promoted when S was less than 1.0.This workexemplified the universal application of plant bioresources for the synthesis of AuNPs.Thesize,shape and associated optical properties of the AuNPs could be tuned by different TCMs.The nascent gold nanoplates were formed by aggregation of small AuNPs less than 10 nm.Thirdly,continuous-flow biosynthesis of Ag nanoparticles （AgNPs） by C.camphora leafextract in tubular microreactors was investigated.At the proper glycerin bath temperature 90℃,nucleation of silver nuclei and growth of AgNPs could be separated and secondarynucleation could be avoided to attain AgNPs with narrow size distribution.The proper angleof Y junction is 60°or 90°.And the proper volumetric flow rate is 0.5 or 0.8 mL.min^-1.At thesame volumetric flow rate,the nucleating rate of silver nuclei could be increased bydecreasing the inner diameter to produce AgNPs with narrow size distribution.The properinner diameters of the tubes were 2 or 3 mm.Lastly,on one hand,the antibacterial properties of AgNPs by the methods of liquidculture medium and solid culture medium were evaluated and the representative E.coli（gram-positive bacteria） and S.aureus （gram-negative bacteria） were used as tested strains.On the other hand,supported Au/TiO₂ catalysts were fabricated by in-situ bioreduction withthe extract of C.Platycladi and their catalytic activities were tested by catalytic reduction of4-nitrophenol （4-NP） into 4-acetaminophenol （4-AP） as model reaction.The results showedthat AgNPs have a good antibacterial property against these two strains;the minimuminhibitory concentration （MIC） and the minimum bactericidal concentration （MBC） of AgNPstowards E.coli is 1.4 ppm and 27 ppm,respectively,whilst the MIC of AgNPs towards S.aureus is 5.4 ppm.The AuNPs produced by dried powder of C.Platycladi were highly stableand exhibited excellent catalytic activity towards reduction of 4-NP to 4-AP.Furthermore,theAu/TiO₂ catalysts also showed good catalytic activity towards reduction of 4-NP to 4-AP.Generally,the Au/TiO₂ catalysts fabricated at 30℃possessed better catalytic activity thanthose at 60 or 90℃.And their catalytic performance could be enhanced by calcination at 300℃.更多还原