sp2-Hybridized Carbon-Containing Block Copolymer Templated Synthesis of Mesoporous Semiconducting Metal Oxides with Excellent Gas Sensing Property
sp2-Hybridized Carbon-Containing Block Copolymer Templated Synthesis of Mesoporous Semiconducting Metal Oxides with Excellent Gas Sensing Property
复制标题
sp2杂化含碳嵌段共聚物模板化合成具有优异气敏性能的介孔半导体金属氧化物
DOI：
10.1021/acs.accounts.8b00598
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发表时间：
2019
影响因子：
18.3
通讯作者：
Yonghui Deng
中科院分区：
文献类型：
--
作者：
Yidong Zou;Xinran Zhou;Yongheng Zhu;Xiaowei Cheng;Dongyuan Zhao;Yonghui Deng
结论近年来，有序介孔金属氧化物，特别是具有可调孔结构和骨架组成的金属氧化物半导体材料，由于其独特的电子结构、长程有序的多孔骨架、均匀的介孔尺寸和高的比表面积，引起了人们的广泛研究兴趣。介孔材料的研究在过去的30年里得到了蓬勃发展，并发展了许多合成方法，如分别以两亲性共聚物为软模板或以介孔碳/二氧化硅为硬模板的模板法。软模板法是通过可控的界面诱导共组装过程设计有序介孔材料的最有效、最灵活的方法之一。然而，大多数商业化的两亲性共聚物，如基于聚（环氧乙烷）-b-聚（环氧丙烷）的Pluronic型共聚物，具有热稳定性差的缺点，因为它们即使在惰性气氛中也太容易分解。因此，它们在高煅烧温度（>400 °C）下难以支撑介孔金属氧化物的结构。为了解决这一挑战，我们设计了新的两亲性嵌段共聚物，其在疏水链段中具有高含量的sp2杂化碳，这些碳相对稳定，并且可以通过活性自由基聚合原位转化为残余碳以支撑介孔结构。我们发展了多种基于sp2杂化含碳嵌段共聚物的新型合成方法，如配体辅助组装和resol辅助组装策略，实现了具有优异气敏性能的介孔半导体金属氧化物的可控和通用合成。特别是它们在转化为残余碳时的热解行为。结合溶剂蒸发诱导的共组装和碳支撑的结晶策略，我们实现了各种有序介孔半导体金属氧化物（例如，WO 3，SnO 2，Co 3 O 4，In 2 O3，TiO 2，ZnO）及其结构特征的调控。为了克服金属前体的快速水解速率和嵌段共聚物与金属前体之间的弱相互作用，我们开发了有效的配体辅助（例如，乙酰丙酮和乙酸）共组装和甲阶酚醛树脂辅助的共组装方法来阻止水解行为并通过氢键、共价键、静电相互作用等增强相互作用。我们还重点介绍了这些有序介孔的n型和p型半导体金属氧化物在气敏领域中的应用，并且由于它们在电子耗尽层上的丰富活性位点和通过可接近的孔通道的快速气体扩散，它们显示出巨大的传感性能。最后，在经典的表面电子耗尽层模型的基础上，深入阐述了靶气体分子与活化物种之间的表面催化反应（例如，吸附的氧物种）在传感过程中的介孔金属氧化物的表面。这些新开发的基于sp2杂化含碳嵌段共聚物的软模板合成方法将为有序介孔半导体金属氧化物的设计和在各个领域的应用开辟新的途径。
ConspectusIn recent years, rational design of ordered mesoporous metal oxides, especially metal oxide semiconductors with adjustable pore architecture and framework compositions, has aroused extensive research interest owing to their unique electronic structures, long-range ordered porous framework, uniform mesopore size, and high specific surface area. Research on mesoporous materials has been booming in the past 30 years, and many synthesis methods have been developed, such as templating methods based on amphiphilic copolymers as soft templates or mesoporous carbon/silica as hard templates, respectively. Soft-templating synthesis has been considered as one of the most efficient and flexible methods in designing ordered mesoporous materials through the controllable interfacial induced coassembly process. However, most commercial amphiphilic copolymers, such as poly(ethylene oxide)-b-poly(propylene oxide) based Pluronic-type ones, suffer the drawback of poor thermal stability, because they are too easy to be decomposed even in inert atmosphere. Therefore, they are difficult to support the structures of mesoporous metal oxides under high calcination temperatures (>400 °C). To solve this challenge, we designed new amphiphilic block copolymers with high content of sp2-hybridized carbon in the hydrophobic segments that were relatively stable and could be in situ converted into residual carbon to support the mesoporous structure, via living free radical polymerization. We developed a variety of novel synthesis methods based on sp2-hybridized carbon-containing block copolymer, such as ligand-assisted assembly and resol-assisted assembly strategies, achieving a controllable and versatile synthesis of mesoporous semiconducting metal oxides with excellent gas sensing performance.In this Account, we first outline the features of sp2-hybridized carbon-containing block copolymers synthesized via living free radical polymerization, particularly their pyrolysis behavior in converting into residual carbon. Combining the solvent evaporation induced coassembly and the carbon-supported crystallization strategies, we realized the rational design of various ordered mesoporous semiconducting metal oxides (e.g., WO3, SnO2, Co3O4, In2O3, TiO2, ZnO) and the regulation of their architectural features. To overcome the fast hydrolysis rate of metal precursors and weak interaction between block copolymers and metal precursors, we developed efficient ligand-assisted (e.g., acetylacetone and acetic acid) coassembly and resol-assisted coassembly methods to retard hydrolysis behavior and enhance the interaction via hydrogen bonds, covalent bonds, electrostatic interactions, etc. We also highlight the applications of these ordered mesoporous semiconducting metal oxides of both n-type and p-type in gas sensing fields, and they show tremendous sensing performance due to their abundant active sites on electron depletion layer and rapid gas diffusion via accessible pore channels. Finally, on the basis of the classic surface-electron depletion layer model, we elucidated in depth the surface catalytic reactions between the target gas molecules and the activated species (e.g., the adsorbed oxygen species) in the surface of mesoporous metal oxides during sensing process. These newly developed soft-templating synthesis methods that rely on sp2-hybridized carbon-containing block copolymers will open a new avenue for the design and application of ordered mesoporous semiconducting metal oxides in various fields.