【作者】 张欢；

【导师】 王锐；

【作者基本信息】 郑州大学 ， 无机化学， 2024， 硕士

【摘要】 金属纳米团簇是一类具有明确结构的亚纳米尺度材料,其原子级精确的结构为光/电催化反应的研究提供了理想的结构模型,有助于对反应机理和构效关系的深入探索。目前对Au、Ag等贵金属纳米团簇研究颇多,相对于金和银,铜具有更丰富的含量和更低廉的价格,在实际的应用中更具优势,然而目前对铜簇相关研究相对较少,这是因为铜纳米团簇通常稳定性较差,因此开发合成稳定的铜团簇具有很大的挑战性。含有平面型氮硫多齿配位点(N=C-SH或NH-C=S)的有机配体具有很好的螯合锚定作用,有助于提升簇分子的结构稳定性,形成稳定的铜簇材料。因此,本文首先设计合成了具有多齿螯合配位点的4-吡啶基嘧啶-2-硫醇分子作为有机保护配体,然后通过不同的合成方法制备得到了两例结构稳定的铜纳米团簇材料,并分别对其催化析氢和CO2还原性能进行了系统的研究。具体研究内容主要如下:一、利用4-吡啶基嘧啶-2-硫醇配体(简称:PPSH)和叔丁硫铜(tBuSCu)通过溶剂挥发法构筑得到了一例具有氮硫三齿配位的稳定的Cu6团簇。结构分析表明,该团簇是由6个Cu+、4个PPS-和两个tBuS-构成,呈扁平八面体构型,每个配体与3个Cu(Ⅰ)离子配位,由配体上的N、S组成的三齿配位爪牢牢地锚定在铜簇单元的表面。由于PPSH配体本身具有较好的光吸收(吸收光谱边缘为900 nm),因此我们得到的Cu6团簇也具有很宽的光吸收范围。基于Cu6良好的稳定性和光吸收能力,我们对其光催化产氢性能进行了研究,发现在不添加光敏剂的条件下,Cu6自身就具有较好的光催化析氢性能,通过优化牺牲剂的种类、反应体系的溶剂、比例以及催化剂的质量,获得了该催化体系的最佳条件。在最佳体系中经过可见光照6小时后的产氢效率可达48.84 mmol g-1,在近红外光下反应6小时后的产氢效率可以达到40.5 mmol g-1,并且经过6轮循环测试以后还保持着较好的性能。该部分工作首次研究了原子级结构精确的铜团簇在无光敏剂的情况下,利用近红外光催化析氢反应的性能。二、利用PPSH配体和乙酸铜(Cu(OAc)2)成功合成了一例全部由PPSH配体保护的Cu4团簇。单晶结构分析表明,该团簇结构是由4个Cu+、4个PPS-配体构成,呈四面体构型。有意思的是,4个PPS-配体与铜离子之间存在两种配位模式,其中3个PPS-配体以氮硫三齿配位的模式横向锚定在Cu4簇表面,而另一个配体通过氮硫双齿配位的模式竖立在铜簇单元的表面。同时,结合上一章节的工作,对Cu6团簇进行精确热处理可以选择性地去除叔丁基配体得到也是4个PPS-配体保护的Cu6-T团簇。我们从金属内核,外围保护配体两个方面对Cu4、Cu6和Cu6-T三种铜簇进行了系统的性能对比。将这三种团簇作为CO2还原催化剂,系统探究了相同配体不同金属内核以及相同金属内核不同配体配位对催化性能的影响。其中相同配体不同金属内核的Cu4和Cu6-T相比,Cu4纳米团簇的FEcH4可以达到50.93%,是Cu6-T的2倍;而相同金属内核不同配体的Cu6和Cu6-T相比,其FEH2发生了较大的变化,且Cu6-T更加倾向于向C2产物转化。本部分研究表明,可以通过多层级调控原子级结构精确的金属团簇来优化CO2还原的催化活性和选择性。更多还原

【Abstract】 Metal nanoclusters are a class of subnanoscale materials with definite structure,and their atomically precise structure provides an ideal structural model for the study of photocatalytic and electrocatalytic reactions,which is helpful for further exploration of reaction mechanism and structure-activity relationship.At present,there are a lot of researches on Au,Ag and other precious metal nanoclusters.Compared with gold and silver,copper has a richer content and lower price,which is more advantageous in practical applications.However,there are relatively few researches on copper clusters at present,because copper nanoclusters are usually poor in stability,so it is a great challenge to develop and synthesis stable copper clusters.The organic ligands containing plane-type nitrogen and sulfur polycoordinate sites(N=C-SH or NH-C=S)have good chelation anchoring effect,which helps to improve the structural stability of cluster molecules and form stable copper cluster materials.Therefore,in this paper,4pyridyl pyrimidine-2-mercaptan molecules with multi-dentate chelating coordination sites were first designed and synthesized as organic protection ligands,and then two cases of structurally stable copper nanoclusters were prepared by different synthesis methods,and their catalytic hydrogen evolution and CO2 reduction properties were systematically studied.The specific research contents are as follows:1.A stable Cu6 cluster with nitrogen and sulfur tridentate coordination was constructed by solvent volatilization with 4-pyridyl pyrimidine-2-mercaptan ligand(PPSH)and tert-butylcupric sulfide(tBuSCu).The structure analysis shows that the cluster is composed of 6 Cu+,4 PPS-and 2 tBuS-in a flat octahedral configuration,each ligand is coordinated with 3 Cu(I)ions,and the three-tooth coordination clawed by N and S on the ligand is firmly anchored to the surface of the copper cluster unit.Since the PPSH ligand itself has a good light absorption(absorption spectrum edge of 900 nm),the Cu6 clusters we obtained also have a wide light absorption range.Based on the excellent stability and light absorption capacity of Cu6,we studied its photocatalytic hydrogen production performance,and found that Cu6 itself has a good photocatalytic hydrogen evolution performance under the condition of no photosensitizer.By optimizing the type of sacrifice agent,the solvent of the reaction system,the proportion of the reaction system and the quality of the catalyst,the optimal conditions of the catalytic system were obtained.In the optimal system,the hydrogen production efficiency can reach 48.84 mmol g-1 after 6 hours of visible light,and the hydrogen production efficiency can reach 40.5 mmol g-1 after 6 hours of near-infrared light reaction,and the performance is still good after 6 rounds of cyclic testing.In this part of work,the properties of atomically accurate copper clusters catalyzed by nearinfrared light in the absence of photosensitizers were studied for the first time.2.A case of Cu4 cluster protected by PPSH ligand was successfully synthesized by PPSH ligand and copper acetate(Cu(OAc)2).The single crystal structure analysis shows that the cluster structure is tetrahedral,consisting of 4 Cu+and 4 PPS-ligands.Interestingly,there are two coordination modes between the four PPS-ligands and copper ions,in which three PPS-ligands are transversely anchored to the surface of the Cu4 cluster in a nitrogen-sulfur tridentate coordination mode,while the other ligand is mounted on the surface of the copper cluster unit through a nitrogen-sulfur binodentate coordination mode.At the same time,combined with the work in the previous chapter,precise heat treatment of Cu6 clusters can selectively remove tert-butyl ligands and obtain Cu6-T clusters protected by 4 PPS-ligands.We have systematically compared the properties of Cu4、Cu6 and Cu6-T copper clusters from two aspects of metal core and peripheral protective ligand.Using these three clusters as catalysts for CO2 reduction,the effects of different metal cores with the same ligand and different ligands in the same metal core on catalytic performance were systematically investigated.The FECH4 of Cu4 nanoclusters with the same ligand and different metal cores can reach 50.93%compared with Cu6-T,which is twice that of Cu6-T.The FEH2 of Cu6 and Cu6T with different ligands in the same metal core changes greatly,and Cu6-T is more inclined to transform into C2 products.This part of the study shows that the catalytic activity and selectivity of CO2 reduction can be optimized by multi-level regulation of atomically precise metal clusters.更多还原