金银合金纳米团簇合成光学性研究
摘
Au纳米团簇相尺寸Au纳米颗粒言具更表面积催化反应中表现出更催化活性总二者存收率较低选择性高等缺点Brust[7] 1994年开创金纳米颗粒双相制备方法金纳米团簇控制合成法快速发展断合成出原子数精确金纳米团簇通系列分析表征确定原子组成
文中首次报道表面掺杂AuAg合金纳米团簇该团簇目前止报道合金纳米团簇该团簇相活泼Ag原子中心说明活性金属构成合金纳米团簇中活泼金属作团簇中心时惰性金属存团簇表面该团簇电子数36（70322）具四重核壳结构分Ag2@Au18@Au20三层金属核外层6心型AgAu壳该团簇MOTIF结构中首次发现Ag4SR单元Ag2Au1SR单元该团簇解AuAg合金纳米颗粒原子层面精确结构结构相关催化研究提供
关键词：金纳米团簇巯基保护光学性
The Synthesization and the optical properties study of AgAu alloy nanocluster
Abstract
Considering that Au nanoclusters have relatively bigger surface area compared to Au nanoparticles they always perform much more active in some catalytic reactions But both Au nanoclusters and nanoparticles have some shortcomings such as the low yield and the low selectivity In 1994 Brust firstly created the biphasic method of the preparation for Au nanoparticles Since then the controlled synthesis method of Au nanoclusters made rapid progress Now in the process of synthetizing Au nanoclusters the number of the atoms of the nanoclusters can be controlled more and more precisely The atomic composition of the nanoclusters can be also determined by some systematic analyses
In this paper we reported the AuAg alloy nanocluster with some other atoms on its surface for the first time It is the biggest alloy nanocluster among the reported ones The relatively active atoms Ag are in the center of the nanocluster This suggests that among the alloy nanoclusters that consist of metal atoms with different chemical activities the relatively active metal atoms will be the center of the nanocluster while the inert mental atoms will be on the surfaceThat AuAg alloy nanocluster has 36 (70322) free electrons and its structure formed by three metal cores (Ag2@Au18@Au20) and one outermost layer (which consists of 6 heartshaped AgAu shells) In the MOTIF structure of that alloy nanocluster we found the Ag4SR Unit and the Ag2Au1SR Unit for the first timeWe probably have the possibility to learn about the accurate structure of AuAg alloy nanocluster at atomic level and to study the relationship between the structure and the activity of the catalyst by further research on that AuAg alloy nanocluster
Keywords
目 录
1引言4
11纳米材料概述4
12合金纳米团簇概述5
13巯基保护金纳米团簇6
2实验部分7
21实验材料7
22实验步骤7
221合成[Ag46Au24(StBu)32](BPh4)2 纳米团簇7
222单金属纳米团簇合金纳米团簇合成7
223催化剂制备7
23测试表征8
231苯乙烯氧化中选择性活性测试8
232晶体结构分析8
233光谱分析 8
234透射电镜成 8
3结果讨8
4结17
参考文献18
致谢22
1 引言
11 纳米材料概述
纳米材料世纪70年代出现已30年80年代中期实验室合成出纳米块状材料包括1984年德国Gleiter教授采惰性气体凝聚法制备金属纳米粒子1987年美国Siegel等制陶瓷TiO2晶材料等等研究成果纳米材料成纳米科学研究热点全球范围掀起科研界纳米热1990年7月美国巴尔摩召开世界第届纳米科技学术会议正式提出纳米材料学概念纳米科学作材料科学新分支纳米材料科学正式诞生纳米材料纳米科技发展重基础纳米科技重活跃研究领域十年中纳米材料作种新型机材料科学研究实际生活中越越引起重视基纳米科技发展起种分析方法技术解决传统分析方法遇难题提供强力手段显示出广阔应前景潜价值迅速发展成材料科学前新领域
宏观物体细分成超微颗粒（纳米颗粒）显示出许奇异特性光学热学电学磁学力学化学方面性质块固体时相会显著20世纪60年代开始分立纳米粒子进行研究1990年7月美国巴尔摩召开世界第届纳米科技学术会议正式提出纳米材料学概念纳米科学作材料科学新分支纳米材料科学正式诞生20世纪70年代纳米颗粒材料问世研究涵特点致划分三阶段：第阶段（1990年前）：实验室探索种方法制备种材料纳米颗粒粉体合成块体研究评估表征方法探索纳米材料普通材料特殊性研究象般局限单材料单相材料国际通常种材料称纳米晶纳米相材料第二阶段（1990~1994年）：关注热点利纳米材料已发掘物理化学特性设计纳米复合材料复合材料合成物性探索度成纳米材料研究导方第三阶段（1994年）：纳米组装体系工组装合成纳米结构材料体系正成纳米材料研究新热点国际类材料称纳米组装材料体系者纳米尺度图案材料基涵纳米颗粒组成纳米丝基单元维二维三维空间组装排列成具纳米结构体系纳米材料纳米科技发展重基础纳米科技重活跃研究领域十年中纳米材料作种新型机材料科学研究实际生活中越越引起重视基纳米科技发展起种分析方法技术解决传统分析方法遇难题提供强力手段显示出广阔应前景潜价值迅速发展成材料科学前新领域
12 合金纳米团簇概述
合金纳米颗粒年出现种新纳米材料[1]迅速应催化传感生物标记等领域 [212]研究显示：合金纳米团簇催化活性选择性[1317]电化学[18]光学性质[19]均高度赖结构合金纳米颗粒结构分析受越越关注
通发展合金纳米团簇直接合成法合成目前止合金纳米团簇(Ag46Au24)纳米团簇该团簇具反常结构例中心金属活泼Ag原子外围壳时相活泼金属Ag相惰性金属Au构成该团簇首次实现AuAg纳米团簇表面掺杂时进步催化研究显示表面掺杂时发挥Au高催化活性Ag高选择性
非精确结构合金纳米团簇方面量研究证明合金效提高催化性质[95]精确结构方面Tsukuda等报道通掺杂单PdPd1Au24纳米团簇效提高团簇催化氧化性[97]Jin组发现掺杂单PtPt1Au24提高团簇催化苯乙烯氧化活性[38]组报道单Cd掺杂Cd1Au24纳米团簇仅稳定性较提升时催化性质明显提高[98]炔基保护表面掺杂Ag28Au34纳米团簇中配体失团簇结构发生变化作者通配体保护脱保护Ag28Au34纳米团簇催化硅烷硅醇程中展示配体团簇催化促进作[87]
现工作指明掺杂位置掺杂原子种类团簇催化性质着明显影响着掺杂团簇发展更实验研究结合理计算原子层面解金属协作
13巯基保护金纳米团簇
巯基保护精确原子结构单金属（Au者Ag）纳米颗粒（<2nm时称纳米团簇）纳米颗粒中重分支年里通X射线晶体结构分析类团簇结构研究长足进步[20]基确定结构团簇催化磁性荧光等性质明确阐述 [2033]然相单金属团簇巯基保护合金纳米团簇结构然知甚少结构已报道Au纳米团簇具相框架（例Au25AgxAu25x）[3440]研究中发现相活泼金属更容易较高价态存团簇表面惰性金属更容易金属态处团簇中心导致问题否合成表面存AuAuAg合金纳米团簇果相核壳结构合金纳米团簇否会性质差异？问题答案更加深入解合金纳米团簇结构性质间关系
已发表巯基保护金基合金纳米团簇晶体结构分成两类：
1）单金属具相框架例基Au25框架AgxAu25x[36][37][81]Pd1Au24[82]纳米团簇基Ag25框架Pd1Ag24Pt1Ag24纳米团簇[44][83]基Au38框架AgxAu38x纳米团簇[84]基Ag44框架Ag32Au12纳米团簇[85][86]合金团簇单金属团簇保持着相框架（单子变量）更适合研究金属间协作
2）框架掺杂团簇例Ag28Au34Au24Ag20纳米团簇[87][88]炔基保护团簇中发现趣现象炔基加热离团簇结构未破坏该类团簇应分析结构合金纳米团簇催化性质研究中
Fishiness合作者通Au核掺杂Ag原子成功改变团簇HOMOLUMO跃迁需量 [36]Ag掺杂AgxAu38x[89]AgxAu144x[90]Cu掺杂CuxAu25x[37][91]Pd掺杂Pd1Au24[83]Pd2Au36[92]PdxAu144x[93]Pt掺杂Pt1Au24[38]等纳米团簇相继合成团簇电子结构明显区单Au纳米团簇遗憾受激发光方面没明显变化
Bakr合作者Ag25纳米团簇中心Ag原子换成Au原子发现增强发光效率通瞬态吸收光谱荧光增强机理做出解释[94]
研究表明金属身出发位置掺杂种类数量异种金属较程度改变团簇电子结构现结果显示电子结构变化受激发光方面然没质突破掺杂实现性质突破然需解决问题
2 实验部分
21 实验材料
非特殊说明实验材料均购ACROS者SigmaAldrich未特处理四氯金酸（>9999 metal basis）硼氢化钠（>98）购买ACROS色谱纯甲苯（≥9999）色谱纯乙醇（≥999）色谱纯甲醇（≥999）色谱纯二氯甲烷（≥999）购买SigmaAldrich公司纯净水购买杭州娃哈哈公司
22 实验步骤
221 合成 [Ag46Au24(StBu)32](BPh4)2 纳米团簇
硝酸银 (20 mg 0078 mmol) 搅拌溶解10 mL甲醇中加入四氯金酸(HAuCl4×3H2O 197mg 0050 mmol) 加入四氯金酸溶液颜色色变黄色悬浊液加入100ml叔丁基硫醇悬浊液颜色黄色变白色搅拌20分钟快速加入1mL NaBH4 水溶液 (140 mgmL)溶液颜色立变黑色说明价金属配合物原沉淀溶液中析出反应继续搅拌6时离心取沉淀黑色沉淀正烷洗涤数次余硫醇配体目标产物甲苯中溶副产物溶解甲苯中甲苯粗产物中杂质目标团簇溶解二氯甲烷中加入溶解10 mg NaBPh45 mL甲醇溶液团簇中Cl阴离子换易结晶BPh4阴离子换目标产物会迅速溶液中析出通离心收集甲醇洗涤次黑色固体溶解二氯甲烷正烷混合溶剂中通挥发二氯甲烷块状晶体总收率80 (Ag计算)
222 单金属纳米团簇合金纳米团簇合成
Au25(SR)18 Ag32Au12(SR)304 and Ag44(SR)304纳米团簇合成结晶参考文献报道未做改动
223 催化剂制备
壁碳纳米 (CNT) (10 mg) 溶解10 mL甲苯中加入02 mL团簇溶液（1 mgmL）制备成质量分数2 wt负载催化剂搅拌夜团簇吸附碳纳米表面通离心真空干燥余溶剂催化剂放置石英中真空状态200摄氏度煅烧配体
23 测试表征
231 苯乙烯氧化中选择性活性测试
10 mL圆底烧瓶中分加入15 mL乙醇负载型团簇催化剂20 mg 57ul (05mmol)苯乙烯加热65oC加入15mmoltbutylhydrogenperoxide (TBHP)24时停止反应通气相色谱产物进行分析
232 晶体结构分析
晶体通Bruker Smart APEX II CCD 晶体衍射仪进行收集光源CuKa (λ 154178 Å)数原吸收校正分通 SAINT SADABS 程序完成结构通直接法解析通SHELXTL软件二法精修非氢原子通异性精修氢原子通计算加入
233 光谱分析
文章出现紫外见光谱非特说明否均安捷伦8453二极阵列紫外见光谱仪进行测量溶剂二氯甲烷温度室温核磁谱图 Bruker Avance™ II 400 NMR 仪器进行测量样品制备条件5 mg团簇溶解08 mL氘代二氯甲烷中
234 透射电镜成
透射电镜 (TEM) 成实验仪器型号 JEM 2100电压200 kV
3 结果讨
[Ag46Au24(SR)32](BPh4)4纳米团簇单斜相空间群P2(1)c晶体尺寸024x022x020 mm3具体参数表示：
表31 [Ag46Au24(StBu)32](BPh4)2 纳米团簇晶体数结构精修参数
Table31 Crystal data and structure refinement for [Ag46Au24(StBu)32](BPh4)2 nanoclusters
Identification code
20141126a
Empirical formula
C176 H328 Ag46 Au24 B2 S32
Formula weight
1318114
Temperature
150(2) K
Wavelength
071073 Å
Crystal system
Monoclinic
Space group
P2(1)c
Unit cell dimensions
a 30009(3) Å
α90
b 23247(2) Å
β92630(3)
c 42895(3) Å
γ90
Volume
29893(5) Å3
Z
4
Density (calculated)
2929 Mgm3
Absorption coefficient
14910 mm1
F(000)
23856
Crystal size
024 x 022 x 020 mm3
Theta range for data collection
068 to 2650°
Index ranges
37
Reflections collected
295735
Independent reflections
61987 [R(int) 00597]
Completeness to theta 2650
1000
Absorption correction
Semiempirical from equivalents
Max and min transmission
01544 and 01242
Refinement method
Fullmatrixblock leastsquares on F2
Data restraints parameters
61987 0 2617
Goodnessoffit on F2
1077
Final R indices [I>2sigma(I)]
R1 00584 wR2 01434
R indices (all data)
R1 00596 wR2 01437
Largest diff peak and hole
2068 and 2585 e3
[Ag46Au24(SR)32]2+ 纳米团簇结构见图31该结构中发现两BPh4离子证明团簇价态+2价70金属原子具三层结构中心2银原子18Au原子包裹 （图32A32B）形成Ag2@Au18结构该结构20银原子保护（图32C32D）18Au原子总3层层6Au原子形成正六边形结构围成桶状结构均AuAu键距离27764 Å20银原子分5层两端两层分1位Au18桶状结构端位层6Ag原子分成3层金原子外延伸形成Ag2@Au18@Ag20结构该结构中金属金属间成键均距离28821 Å图32D中出该结构7层层原子数1121121121该重复结构接密六方堆积形式(hcp)注：Teo报道[Au39(PPh3)14Cl6]Cl2 纳米团簇中中心919结构Ag46Au24(SR)32中找[41]
图31 [Ag46Au24(SR)32](PPh4)2纳米团簇通X射线晶体衍射全结构图（显示手性中种映体）灰色碳红色硫绿色银黄色金粉色硼氢未添加
Fig 31 Total structure of bimetallic chiral [Ag46Au24(SR)32](PPh4)2 nanocluster (one of enantiomer) by xray crystallography Gray carbon red sulfur green silver yellow gold pink boron
Ag22Au18核AgAu双金属手性壳保护该壳结构中基单元Ag7Au1(SR)8组成心型MOTIF结构两基础单元Ag3(SR)3结构MOTIF结构中四种键合形式（32G）：1）巯基配体连接三Ag原子形成Ag3SR结构该结构银纳米团簇中较常见[404243]2）巯基配体时连接四Ag原子形成Ag4SR结构AgS键键长该单元中差距较短2330 Å明显短般团簇中AgS键长（~26 Å）证明AgRS具非常强相互作该单元中时存键长2911 ÅAgS键说明该AgS键结合力弱种极端键长变化时首次团簇中发现3）RS基团时连接两Ag原子Au原子形成Ag2Au1SR结构该结构首次发现该结构说明巯基力形成双金属表面结构4）直线型Au1(SR)2结构种线性结构巯基保护Au纳米团簇中较常见[4450]
图32 [Ag46Au24(SR)32]2+纳米团簇分层结构图(AB) Ag2Au18金属核顶部侧面视角该金属核未巯基连接(CD) Ag2@Au18@Ag20核顶部侧面视角AB相该结构中出20Ag原子(EF) Ag2@Au18@Ag20外围Ag24Au6(SR)32双金属壳保护顶部侧面视角(G)中显示外层壳中发现四种金属巯基配体键合形式图中黄色金绿色蓝色灰色银巯基红色
Fig 32 The threeshell structure of [Ag46Au24(SR)32]2+ (A and B) Top and side views of Ag2Au18 core (which is not connected with any thiolate ligands) (C and D) Top and side views of the Ag2@Au18@Ag20 core (E and F) Top and side views of Ag2@Au18@Ag20 core protected by Ag24Au6(SR)32 bimetallicshell (G) Four bonding modes in the motif structure Light greenbulelight grey silver yellow gold red sulfur
前报道巯基保护合金纳米团簇框架结构均相金属数量AuAg纳米团簇相例Ag32Au12(SR)32 Ag44(SR)30[3440] AgxAu38x(SR)24 Au38(SR)24[3639] AgxAu25x(SR)18 Au25(SR)18[353738]时计算显示AgxAu144x(SR)60纳米团簇Au144(SR)60具相结构[51]团簇中Ag掺杂位置中心核掺杂表面结构中[Ag46Au24(SR)32]2+纳米团簇首发现Ag表面掺杂AuAg合金纳米团簇时首Ag掺杂中心AuAg纳米团簇表面结构出巯基时连接两AgAu原子时RSAuRS角度接180度遵循规律发现团簇表面金属原子外种类金属原子换
该纳米团簇中金属核具手性整体结构具手性结构进行分解助解团簇手性源图33A中显示移金属核AuRS两端RS基团AgRS壳点群D3d说明该壳非手性壳加入AuSR（图33B）失3称面称性降低团簇然具C3轴称中心两端巯基加入图33C33D示团簇失C3轴称中心成手性结构种手性构成相前报道单金属纳米团簇中手性源般种情况：1）通手性配体诱导非手性团簇具手性[52]2）外围RSAuRS基团手性排列团簇具手性[3948495053][Ag46Au24(SR)32]2+结构中手性源仅仅两巯基基团非称排列
图33 手性[Ag46Au24(SR)32]2+ 纳米团簇结构分解 (A)AuSR单元两端巯基单元顶部视图（B）加入AuSR单元顶部视图（CD）加入两端巯基两种构型顶部视图（EF）全结构图（未含CH）
Fig 33 Chiral structure of [Ag46Au24(SR)32]2+ nanocluster (A and B) Top view of the shell structure without the AuSR unit and the topbottom RS group (A) and with the addition of three AuSR groups (B) (C and D) Top views of twoenantiomer shell (E and F) Top views of twoenantiomer nanoclusters without H and C atoms
通核磁振氢谱团簇价态进行进步确认核磁振氢谱中（图34）苯环区(6575 ppm)处40H应BPh4中芳基氢高场位置(0545ppm)处2887H应叔丁基烷基氢该结果显示BPh4叔丁基氢数目402887换算成两者摩尔2：32团簇中团簇分子拥32叔丁基BPh4团簇摩尔21该结果晶体结果相互验证进步证明团簇+2价
图34 [Ag46Au24(StBu)32](BPh4)2纳米团簇核磁振氢谱
Fig 34 1H NMR spectrum of [Ag46Au24(StBu)32](BPh4)2 nanoclusters (single crystal dissolved in CD2Cl2)
[Ag46Au24(SR)32]2+纳米团簇精确结构表征结构相关性质研究提供通已报道合金纳米团簇揭示掺杂结构催化性质影响里合成具核壳结构Au12@Ag32纳米团簇时作合成单金属Au25纳米团簇Ag44纳米团簇选壁碳纳米作载体选原：1）团簇该纳米效吸附2）碳纳米效避免团簇煅烧聚集[54]TEM图中出（图35图36）团簇热处理前尺寸范围均12 nm证明团簇煅烧没发生团聚[9]
图35 纳米团簇负载碳纳米反应前透射电镜图片(a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT嵌图尺寸分布图
Fig35 Typical TEM images and cluster size distributions of (a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT before reaction
图36 纳米团簇负载碳纳米反应透射电镜图片(a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT嵌图尺寸分布图
Fig 36 Typical TEM images and cluster size distributions of (a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT after reaction
表32结果进行汇总环氧化合物苯甲醛苯乙烯氧化产物空白试验证明未负载碳纳米催化活性较低Au25@CNT表现出高转化效率（728）然苯甲醛选择性664单Ag44@CNT催化活性较低（436）苯甲醛选择性高达926表面掺杂Ag46Au24纳米团簇效苯甲醛选择性提高926时保持着较高催化活性（~70）然核壳结构Au12@Ag32纳米团簇苯甲醛选择性376数出表面掺杂合金纳米催化剂结合单Au纳米团簇高活性单Ag纳米团簇高选择性(图36)该发现首次明确揭示团簇表面结构催化影响金属协作表面掺杂AuAg纳米团簇中作
表32 纳米团簇负载碳纳米催化效率催化选择性
Tab 42 The catalytic performance of CNT supported metal nanoclustersaSelectivity ()c
Entry
catalyst
Conversion ()b
Epoxide
Benzaldehyde
Other products
1
Au25CNT
728
203
664
133
2
Ag44CNT
436
61
926
13
3
Ag46Au24CNT
682
12
963
25
4
Ag32Au12CNT
697
576
376
48
5
CNT
317
305
5562
1388
aReaction conditions 20 mg catalysis 2 wt nanocluster loading 57 ml (05 mmol) styrene 144 ml (15 mmol) TBHP 15 ml ethanol 65 oC 24h bConversion (styrene converted)(initial amount of styrene) x 100 cDetermined by GC
图 37 两种结构合金纳米团簇催化苯乙烯中选择性差异表面掺杂产物苯甲醛核壳结构产物环氧化合物
Fig 37 Two different kinds of nanocluster catalysts in the styrene oxidization Thesurfacedoped nanocluster shows high selectivity for benzaldehyde while the coreshell structured nanocluster shows high selectively for epoxide
Figure S2 The spacefill mode of the metal core of (a) Ag12Au13(SR)18 (b) Ag32Au12(SR)304 and (c) Ag46Au24(SR)322+ NCs
Figure S3 Typical TEM images and cluster size distributions of (a)Au25CNT (b) Ag~7Au~18CNT (c) Ag44CNT (d) Ag32Au12CNT (e) Ag46Au24CNT
Figure S4 The UVVis spectra of (a) Au25(SC2H4Ph)18 (b) Ag~7Au~18(SC2H4Ph)18 (c) Ag44(SPhF2)304 (d) Ag32Au12(SPhF2)4 (e) Ag46Au24(StBu)322+ NCs dissolved in DCM solution
4 结
文中报道Ag46Au24(SR)32(BPh4)2纳米团簇合成通核磁振氢谱X射线衍射团簇结构进行精确表征该团簇首报道具表面掺杂活性金属中心AuAg合金纳米团簇研究催化苯乙烯氧化程中发现表面参杂合金纳米团簇结合单Au纳米团簇活性单Ag纳米团簇选择性该工作中展示特异性结构扩展合金团簇认识时基结构相关催化性质研究解团簇性质起源高效催化剂合成提供理实验
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金银合金纳米团簇合成光学性研究
摘
Au纳米团簇相尺寸Au纳米颗粒言具更表面积催化反应中表现出更催化活性总二者存收率较低选择性高等缺点Brust[7] 1994年开创金纳米颗粒双相制备方法金纳米团簇控制合成法快速发展断合成出原子数精确金纳米团簇通系列分析表征确定原子组成
文中首次报道表面掺杂AuAg合金纳米团簇该团簇目前止报道合金纳米团簇该团簇相活泼Ag原子中心说明活性金属构成合金纳米团簇中活泼金属作团簇中心时惰性金属存团簇表面该团簇电子数36（70322）具四重核壳结构分Ag2@Au18@Au20三层金属核外层6心型AgAu壳该团簇MOTIF结构中首次发现Ag4SR单元Ag2Au1SR单元该团簇解AuAg合金纳米颗粒原子层面精确结构结构相关催化研究提供
关键词：金纳米团簇巯基保护光学性
The Synthesization and the optical properties study of AgAu alloy nanocluster
Abstract
Considering that Au nanoclusters have relatively bigger surface area compared to Au nanoparticles they always perform much more active in some catalytic reactions But both Au nanoclusters and nanoparticles have some shortcomings such as the low yield and the low selectivity In 1994 Brust firstly created the biphasic method of the preparation for Au nanoparticles Since then the controlled synthesis method of Au nanoclusters made rapid progress Now in the process of synthetizing Au nanoclusters the number of the atoms of the nanoclusters can be controlled more and more precisely The atomic composition of the nanoclusters can be also determined by some systematic analyses
In this paper we reported the AuAg alloy nanocluster with some other atoms on its surface for the first time It is the biggest alloy nanocluster among the reported ones The relatively active atoms Ag are in the center of the nanocluster This suggests that among the alloy nanoclusters that consist of metal atoms with different chemical activities the relatively active metal atoms will be the center of the nanocluster while the inert mental atoms will be on the surfaceThat AuAg alloy nanocluster has 36 (70322) free electrons and its structure formed by three metal cores (Ag2@Au18@Au20) and one outermost layer (which consists of 6 heartshaped AgAu shells) In the MOTIF structure of that alloy nanocluster we found the Ag4SR Unit and the Ag2Au1SR Unit for the first timeWe probably have the possibility to learn about the accurate structure of AuAg alloy nanocluster at atomic level and to study the relationship between the structure and the activity of the catalyst by further research on that AuAg alloy nanocluster
Keywords
目 录
1引言4
11纳米材料概述4
12合金纳米团簇概述5
13巯基保护金纳米团簇6
2实验部分7
21实验材料7
22实验步骤7
221合成[Ag46Au24(StBu)32](BPh4)2 纳米团簇7
222单金属纳米团簇合金纳米团簇合成7
223催化剂制备7
23测试表征8
231苯乙烯氧化中选择性活性测试8
232晶体结构分析8
233光谱分析 8
234透射电镜成 8
3结果讨8
4结17
参考文献18
致谢22
1 引言
11 纳米材料概述
纳米材料世纪70年代出现已30年80年代中期实验室合成出纳米块状材料包括1984年德国Gleiter教授采惰性气体凝聚法制备金属纳米粒子1987年美国Siegel等制陶瓷TiO2晶材料等等研究成果纳米材料成纳米科学研究热点全球范围掀起科研界纳米热1990年7月美国巴尔摩召开世界第届纳米科技学术会议正式提出纳米材料学概念纳米科学作材料科学新分支纳米材料科学正式诞生纳米材料纳米科技发展重基础纳米科技重活跃研究领域十年中纳米材料作种新型机材料科学研究实际生活中越越引起重视基纳米科技发展起种分析方法技术解决传统分析方法遇难题提供强力手段显示出广阔应前景潜价值迅速发展成材料科学前新领域
宏观物体细分成超微颗粒（纳米颗粒）显示出许奇异特性光学热学电学磁学力学化学方面性质块固体时相会显著20世纪60年代开始分立纳米粒子进行研究1990年7月美国巴尔摩召开世界第届纳米科技学术会议正式提出纳米材料学概念纳米科学作材料科学新分支纳米材料科学正式诞生20世纪70年代纳米颗粒材料问世研究涵特点致划分三阶段：第阶段（1990年前）：实验室探索种方法制备种材料纳米颗粒粉体合成块体研究评估表征方法探索纳米材料普通材料特殊性研究象般局限单材料单相材料国际通常种材料称纳米晶纳米相材料第二阶段（1990~1994年）：关注热点利纳米材料已发掘物理化学特性设计纳米复合材料复合材料合成物性探索度成纳米材料研究导方第三阶段（1994年）：纳米组装体系工组装合成纳米结构材料体系正成纳米材料研究新热点国际类材料称纳米组装材料体系者纳米尺度图案材料基涵纳米颗粒组成纳米丝基单元维二维三维空间组装排列成具纳米结构体系纳米材料纳米科技发展重基础纳米科技重活跃研究领域十年中纳米材料作种新型机材料科学研究实际生活中越越引起重视基纳米科技发展起种分析方法技术解决传统分析方法遇难题提供强力手段显示出广阔应前景潜价值迅速发展成材料科学前新领域
12 合金纳米团簇概述
合金纳米颗粒年出现种新纳米材料[1]迅速应催化传感生物标记等领域 [212]研究显示：合金纳米团簇催化活性选择性[1317]电化学[18]光学性质[19]均高度赖结构合金纳米颗粒结构分析受越越关注
通发展合金纳米团簇直接合成法合成目前止合金纳米团簇(Ag46Au24)纳米团簇该团簇具反常结构例中心金属活泼Ag原子外围壳时相活泼金属Ag相惰性金属Au构成该团簇首次实现AuAg纳米团簇表面掺杂时进步催化研究显示表面掺杂时发挥Au高催化活性Ag高选择性
非精确结构合金纳米团簇方面量研究证明合金效提高催化性质[95]精确结构方面Tsukuda等报道通掺杂单PdPd1Au24纳米团簇效提高团簇催化氧化性[97]Jin组发现掺杂单PtPt1Au24提高团簇催化苯乙烯氧化活性[38]组报道单Cd掺杂Cd1Au24纳米团簇仅稳定性较提升时催化性质明显提高[98]炔基保护表面掺杂Ag28Au34纳米团簇中配体失团簇结构发生变化作者通配体保护脱保护Ag28Au34纳米团簇催化硅烷硅醇程中展示配体团簇催化促进作[87]
现工作指明掺杂位置掺杂原子种类团簇催化性质着明显影响着掺杂团簇发展更实验研究结合理计算原子层面解金属协作
13巯基保护金纳米团簇
巯基保护精确原子结构单金属（Au者Ag）纳米颗粒（<2nm时称纳米团簇）纳米颗粒中重分支年里通X射线晶体结构分析类团簇结构研究长足进步[20]基确定结构团簇催化磁性荧光等性质明确阐述 [2033]然相单金属团簇巯基保护合金纳米团簇结构然知甚少结构已报道Au纳米团簇具相框架（例Au25AgxAu25x）[3440]研究中发现相活泼金属更容易较高价态存团簇表面惰性金属更容易金属态处团簇中心导致问题否合成表面存AuAuAg合金纳米团簇果相核壳结构合金纳米团簇否会性质差异？问题答案更加深入解合金纳米团簇结构性质间关系
已发表巯基保护金基合金纳米团簇晶体结构分成两类：
1）单金属具相框架例基Au25框架AgxAu25x[36][37][81]Pd1Au24[82]纳米团簇基Ag25框架Pd1Ag24Pt1Ag24纳米团簇[44][83]基Au38框架AgxAu38x纳米团簇[84]基Ag44框架Ag32Au12纳米团簇[85][86]合金团簇单金属团簇保持着相框架（单子变量）更适合研究金属间协作
2）框架掺杂团簇例Ag28Au34Au24Ag20纳米团簇[87][88]炔基保护团簇中发现趣现象炔基加热离团簇结构未破坏该类团簇应分析结构合金纳米团簇催化性质研究中
Fishiness合作者通Au核掺杂Ag原子成功改变团簇HOMOLUMO跃迁需量 [36]Ag掺杂AgxAu38x[89]AgxAu144x[90]Cu掺杂CuxAu25x[37][91]Pd掺杂Pd1Au24[83]Pd2Au36[92]PdxAu144x[93]Pt掺杂Pt1Au24[38]等纳米团簇相继合成团簇电子结构明显区单Au纳米团簇遗憾受激发光方面没明显变化
Bakr合作者Ag25纳米团簇中心Ag原子换成Au原子发现增强发光效率通瞬态吸收光谱荧光增强机理做出解释[94]
研究表明金属身出发位置掺杂种类数量异种金属较程度改变团簇电子结构现结果显示电子结构变化受激发光方面然没质突破掺杂实现性质突破然需解决问题
2 实验部分
21 实验材料
非特殊说明实验材料均购ACROS者SigmaAldrich未特处理四氯金酸（>9999 metal basis）硼氢化钠（>98）购买ACROS色谱纯甲苯（≥9999）色谱纯乙醇（≥999）色谱纯甲醇（≥999）色谱纯二氯甲烷（≥999）购买SigmaAldrich公司纯净水购买杭州娃哈哈公司
22 实验步骤
221 合成 [Ag46Au24(StBu)32](BPh4)2 纳米团簇
硝酸银 (20 mg 0078 mmol) 搅拌溶解10 mL甲醇中加入四氯金酸(HAuCl4×3H2O 197mg 0050 mmol) 加入四氯金酸溶液颜色色变黄色悬浊液加入100ml叔丁基硫醇悬浊液颜色黄色变白色搅拌20分钟快速加入1mL NaBH4 水溶液 (140 mgmL)溶液颜色立变黑色说明价金属配合物原沉淀溶液中析出反应继续搅拌6时离心取沉淀黑色沉淀正烷洗涤数次余硫醇配体目标产物甲苯中溶副产物溶解甲苯中甲苯粗产物中杂质目标团簇溶解二氯甲烷中加入溶解10 mg NaBPh45 mL甲醇溶液团簇中Cl阴离子换易结晶BPh4阴离子换目标产物会迅速溶液中析出通离心收集甲醇洗涤次黑色固体溶解二氯甲烷正烷混合溶剂中通挥发二氯甲烷块状晶体总收率80 (Ag计算)
222 单金属纳米团簇合金纳米团簇合成
Au25(SR)18 Ag32Au12(SR)304 and Ag44(SR)304纳米团簇合成结晶参考文献报道未做改动
223 催化剂制备
壁碳纳米 (CNT) (10 mg) 溶解10 mL甲苯中加入02 mL团簇溶液（1 mgmL）制备成质量分数2 wt负载催化剂搅拌夜团簇吸附碳纳米表面通离心真空干燥余溶剂催化剂放置石英中真空状态200摄氏度煅烧配体
23 测试表征
231 苯乙烯氧化中选择性活性测试
10 mL圆底烧瓶中分加入15 mL乙醇负载型团簇催化剂20 mg 57ul (05mmol)苯乙烯加热65oC加入15mmoltbutylhydrogenperoxide (TBHP)24时停止反应通气相色谱产物进行分析
232 晶体结构分析
晶体通Bruker Smart APEX II CCD 晶体衍射仪进行收集光源CuKa (λ 154178 Å)数原吸收校正分通 SAINT SADABS 程序完成结构通直接法解析通SHELXTL软件二法精修非氢原子通异性精修氢原子通计算加入
233 光谱分析
文章出现紫外见光谱非特说明否均安捷伦8453二极阵列紫外见光谱仪进行测量溶剂二氯甲烷温度室温核磁谱图 Bruker Avance™ II 400 NMR 仪器进行测量样品制备条件5 mg团簇溶解08 mL氘代二氯甲烷中
234 透射电镜成
透射电镜 (TEM) 成实验仪器型号 JEM 2100电压200 kV
3 结果讨
[Ag46Au24(SR)32](BPh4)4纳米团簇单斜相空间群P2(1)c晶体尺寸024x022x020 mm3具体参数表示：
表31 [Ag46Au24(StBu)32](BPh4)2 纳米团簇晶体数结构精修参数
Table31 Crystal data and structure refinement for [Ag46Au24(StBu)32](BPh4)2 nanoclusters
Identification code
20141126a
Empirical formula
C176 H328 Ag46 Au24 B2 S32
Formula weight
1318114
Temperature
150(2) K
Wavelength
071073 Å
Crystal system
Monoclinic
Space group
P2(1)c
Unit cell dimensions
a 30009(3) Å
α90
b 23247(2) Å
β92630(3)
c 42895(3) Å
γ90
Volume
29893(5) Å3
Z
4
Density (calculated)
2929 Mgm3
Absorption coefficient
14910 mm1
F(000)
23856
Crystal size
024 x 022 x 020 mm3
Theta range for data collection
068 to 2650°
Index ranges
37
Reflections collected
295735
Independent reflections
61987 [R(int) 00597]
Completeness to theta 2650
1000
Absorption correction
Semiempirical from equivalents
Max and min transmission
01544 and 01242
Refinement method
Fullmatrixblock leastsquares on F2
Data restraints parameters
61987 0 2617
Goodnessoffit on F2
1077
Final R indices [I>2sigma(I)]
R1 00584 wR2 01434
R indices (all data)
R1 00596 wR2 01437
Largest diff peak and hole
2068 and 2585 e3
[Ag46Au24(SR)32]2+ 纳米团簇结构见图31该结构中发现两BPh4离子证明团簇价态+2价70金属原子具三层结构中心2银原子18Au原子包裹 （图32A32B）形成Ag2@Au18结构该结构20银原子保护（图32C32D）18Au原子总3层层6Au原子形成正六边形结构围成桶状结构均AuAu键距离27764 Å20银原子分5层两端两层分1位Au18桶状结构端位层6Ag原子分成3层金原子外延伸形成Ag2@Au18@Ag20结构该结构中金属金属间成键均距离28821 Å图32D中出该结构7层层原子数1121121121该重复结构接密六方堆积形式(hcp)注：Teo报道[Au39(PPh3)14Cl6]Cl2 纳米团簇中中心919结构Ag46Au24(SR)32中找[41]
图31 [Ag46Au24(SR)32](PPh4)2纳米团簇通X射线晶体衍射全结构图（显示手性中种映体）灰色碳红色硫绿色银黄色金粉色硼氢未添加
Fig 31 Total structure of bimetallic chiral [Ag46Au24(SR)32](PPh4)2 nanocluster (one of enantiomer) by xray crystallography Gray carbon red sulfur green silver yellow gold pink boron
Ag22Au18核AgAu双金属手性壳保护该壳结构中基单元Ag7Au1(SR)8组成心型MOTIF结构两基础单元Ag3(SR)3结构MOTIF结构中四种键合形式（32G）：1）巯基配体连接三Ag原子形成Ag3SR结构该结构银纳米团簇中较常见[404243]2）巯基配体时连接四Ag原子形成Ag4SR结构AgS键键长该单元中差距较短2330 Å明显短般团簇中AgS键长（~26 Å）证明AgRS具非常强相互作该单元中时存键长2911 ÅAgS键说明该AgS键结合力弱种极端键长变化时首次团簇中发现3）RS基团时连接两Ag原子Au原子形成Ag2Au1SR结构该结构首次发现该结构说明巯基力形成双金属表面结构4）直线型Au1(SR)2结构种线性结构巯基保护Au纳米团簇中较常见[4450]
图32 [Ag46Au24(SR)32]2+纳米团簇分层结构图(AB) Ag2Au18金属核顶部侧面视角该金属核未巯基连接(CD) Ag2@Au18@Ag20核顶部侧面视角AB相该结构中出20Ag原子(EF) Ag2@Au18@Ag20外围Ag24Au6(SR)32双金属壳保护顶部侧面视角(G)中显示外层壳中发现四种金属巯基配体键合形式图中黄色金绿色蓝色灰色银巯基红色
Fig 32 The threeshell structure of [Ag46Au24(SR)32]2+ (A and B) Top and side views of Ag2Au18 core (which is not connected with any thiolate ligands) (C and D) Top and side views of the Ag2@Au18@Ag20 core (E and F) Top and side views of Ag2@Au18@Ag20 core protected by Ag24Au6(SR)32 bimetallicshell (G) Four bonding modes in the motif structure Light greenbulelight grey silver yellow gold red sulfur
前报道巯基保护合金纳米团簇框架结构均相金属数量AuAg纳米团簇相例Ag32Au12(SR)32 Ag44(SR)30[3440] AgxAu38x(SR)24 Au38(SR)24[3639] AgxAu25x(SR)18 Au25(SR)18[353738]时计算显示AgxAu144x(SR)60纳米团簇Au144(SR)60具相结构[51]团簇中Ag掺杂位置中心核掺杂表面结构中[Ag46Au24(SR)32]2+纳米团簇首发现Ag表面掺杂AuAg合金纳米团簇时首Ag掺杂中心AuAg纳米团簇表面结构出巯基时连接两AgAu原子时RSAuRS角度接180度遵循规律发现团簇表面金属原子外种类金属原子换
该纳米团簇中金属核具手性整体结构具手性结构进行分解助解团簇手性源图33A中显示移金属核AuRS两端RS基团AgRS壳点群D3d说明该壳非手性壳加入AuSR（图33B）失3称面称性降低团簇然具C3轴称中心两端巯基加入图33C33D示团簇失C3轴称中心成手性结构种手性构成相前报道单金属纳米团簇中手性源般种情况：1）通手性配体诱导非手性团簇具手性[52]2）外围RSAuRS基团手性排列团簇具手性[3948495053][Ag46Au24(SR)32]2+结构中手性源仅仅两巯基基团非称排列
图33 手性[Ag46Au24(SR)32]2+ 纳米团簇结构分解 (A)AuSR单元两端巯基单元顶部视图（B）加入AuSR单元顶部视图（CD）加入两端巯基两种构型顶部视图（EF）全结构图（未含CH）
Fig 33 Chiral structure of [Ag46Au24(SR)32]2+ nanocluster (A and B) Top view of the shell structure without the AuSR unit and the topbottom RS group (A) and with the addition of three AuSR groups (B) (C and D) Top views of twoenantiomer shell (E and F) Top views of twoenantiomer nanoclusters without H and C atoms
通核磁振氢谱团簇价态进行进步确认核磁振氢谱中（图34）苯环区(6575 ppm)处40H应BPh4中芳基氢高场位置(0545ppm)处2887H应叔丁基烷基氢该结果显示BPh4叔丁基氢数目402887换算成两者摩尔2：32团簇中团簇分子拥32叔丁基BPh4团簇摩尔21该结果晶体结果相互验证进步证明团簇+2价
图34 [Ag46Au24(StBu)32](BPh4)2纳米团簇核磁振氢谱
Fig 34 1H NMR spectrum of [Ag46Au24(StBu)32](BPh4)2 nanoclusters (single crystal dissolved in CD2Cl2)
[Ag46Au24(SR)32]2+纳米团簇精确结构表征结构相关性质研究提供通已报道合金纳米团簇揭示掺杂结构催化性质影响里合成具核壳结构Au12@Ag32纳米团簇时作合成单金属Au25纳米团簇Ag44纳米团簇选壁碳纳米作载体选原：1）团簇该纳米效吸附2）碳纳米效避免团簇煅烧聚集[54]TEM图中出（图35图36）团簇热处理前尺寸范围均12 nm证明团簇煅烧没发生团聚[9]
图35 纳米团簇负载碳纳米反应前透射电镜图片(a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT嵌图尺寸分布图
Fig35 Typical TEM images and cluster size distributions of (a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT before reaction
图36 纳米团簇负载碳纳米反应透射电镜图片(a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT嵌图尺寸分布图
Fig 36 Typical TEM images and cluster size distributions of (a) Au25CNT (b) Ag44CNT (c) Ag32Au12CNT (d) Ag46Au24CNT after reaction
表32结果进行汇总环氧化合物苯甲醛苯乙烯氧化产物空白试验证明未负载碳纳米催化活性较低Au25@CNT表现出高转化效率（728）然苯甲醛选择性664单Ag44@CNT催化活性较低（436）苯甲醛选择性高达926表面掺杂Ag46Au24纳米团簇效苯甲醛选择性提高926时保持着较高催化活性（~70）然核壳结构Au12@Ag32纳米团簇苯甲醛选择性376数出表面掺杂合金纳米催化剂结合单Au纳米团簇高活性单Ag纳米团簇高选择性(图36)该发现首次明确揭示团簇表面结构催化影响金属协作表面掺杂AuAg纳米团簇中作
表32 纳米团簇负载碳纳米催化效率催化选择性
Tab 42 The catalytic performance of CNT supported metal nanoclustersaSelectivity ()c
Entry
catalyst
Conversion ()b
Epoxide
Benzaldehyde
Other products
1
Au25CNT
728
203
664
133
2
Ag44CNT
436
61
926
13
3
Ag46Au24CNT
682
12
963
25
4
Ag32Au12CNT
697
576
376
48
5
CNT
317
305
5562
1388
aReaction conditions 20 mg catalysis 2 wt nanocluster loading 57 ml (05 mmol) styrene 144 ml (15 mmol) TBHP 15 ml ethanol 65 oC 24h bConversion (styrene converted)(initial amount of styrene) x 100 cDetermined by GC
图 37 两种结构合金纳米团簇催化苯乙烯中选择性差异表面掺杂产物苯甲醛核壳结构产物环氧化合物
Fig 37 Two different kinds of nanocluster catalysts in the styrene oxidization Thesurfacedoped nanocluster shows high selectivity for benzaldehyde while the coreshell structured nanocluster shows high selectively for epoxide
Figure S2 The spacefill mode of the metal core of (a) Ag12Au13(SR)18 (b) Ag32Au12(SR)304 and (c) Ag46Au24(SR)322+ NCs
Figure S3 Typical TEM images and cluster size distributions of (a)Au25CNT (b) Ag~7Au~18CNT (c) Ag44CNT (d) Ag32Au12CNT (e) Ag46Au24CNT
Figure S4 The UVVis spectra of (a) Au25(SC2H4Ph)18 (b) Ag~7Au~18(SC2H4Ph)18 (c) Ag44(SPhF2)304 (d) Ag32Au12(SPhF2)4 (e) Ag46Au24(StBu)322+ NCs dissolved in DCM solution
4 结
文中报道Ag46Au24(SR)32(BPh4)2纳米团簇合成通核磁振氢谱X射线衍射团簇结构进行精确表征该团簇首报道具表面掺杂活性金属中心AuAg合金纳米团簇研究催化苯乙烯氧化程中发现表面参杂合金纳米团簇结合单Au纳米团簇活性单Ag纳米团簇选择性该工作中展示特异性结构扩展合金团簇认识时基结构相关催化性质研究解团簇性质起源高效催化剂合成提供理实验
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