超细金属纳米团簇在金属有机骨架的限域调控合成及其光催化产氢研究

Converting water into hydrogen via photocatalysts is an important way to solve the energy crisis and environmental pollution. As a new type of photocatalysts, metal-organic frameworks (MOFs) have achieved some progress in the field of photocatalytic hydrogen production via supporting platinum nanoparticles (Pt NPs) or platinum single atoms (Pt SAs), but their performance still unsatisfied (only hundreds μmol/g/h for most MOFs based photocatalysts). It is highly desirable yet remaining challenging to improve the photocatalytic hydrogen evolution activity of MOFs. Herein, we intend to synthesize ultrafine Pt nanoclusters (Pt NCs) and PtM nanoclusters (Pt NCs, M = Fe, Co, Ni, etc.) confined in MOFs via precise pore environmental modification strategy. Both introduction of porphyrin ligands with strong post-transition metal chelating ability on the wall of the MOF pores and post modification of the coordination unsaturated metal nodes of MOFs with monodentate ligands (formic acid, acetic acid, benzoic acid, p-toluic acid, etc.) are intended to be utilized as pore environmental modification methods for the ultrafine Pt NCs and PtM NCs formation in MOFs. The relationship between the pore environment and the resulting metal NCs size will be systematically studied. At the same time, combing with various characterization methods and theoretical calculations, in-depth study of the effect of nanoparticle size on photocatalytic hydrogen production activity will be conducted. Furthermore, the effect of M on the electronic structures and photocatalytic hydrogen production performance of alloy PtM NCs will also be studied.

利用太阳能将水转化为氢气是解决人类能源危机和环境污染的一种重要手段。MOF作为一种新型光催化剂，通过负载铂纳米颗粒和单原子，在光催化产氢领域已经取得一些成绩，但催化活性仍然较低（大多在几百μmol/g/h级别），难以达到实际应用的要求。调研发现，尺寸适中的铂纳米团簇具有最为适中的电子捕获能力和氢气脱附能，可能具有最好的光催化产氢活性。基于此，本课题拟首次采用MOF孔环境修饰的策略，在MOF孔壁上引入强金属螯合能力的卟啉限制纳米团簇迁移，并在MOF的配位不饱和金属节点上引入尺寸可调节的单齿配体进一步限制纳米团簇生长，合成负载铂和PtM（M = Fe、Co、Ni等）合金纳米团簇的MOF光催化剂。同时，通过对比MOF负载单原子、纳米团簇和纳米颗粒的光催化剂的产氢活性，结合多种表征手段深入研究纳米粒子尺寸对光催化产氢活性的影响以及贱金属M的引入对Pt的电子结构和光催化产氢性能的影响。

针对化石燃料的不足和环境污染问题，本项目设计合成了多种MOF基产氢光催化剂，包括PtSAs@PCN-224-BA、PtNCs@PCN-224-BA、PtNCs@PCN-224-AA、PtNCs@PCN-224-OH、PtNPs/H2TCPP、PtNPs@PCN-224-BA-PD、PtNPs@PCN-224-BA-NaBH4、PtNPs@PCN-224-BA、PtNPs/PCN-224-BA、PtNPs@PCN-222、PtNPs@PCN-223、Pt@NH2-ZSTU-2、Pt@ZSTU-2等。本项目首次提出了螯合和隔间辅助空间限域的策略（Chelation and Compartment assisted Spatial Confining strategy，CCSC），在该策略中，载体PCN-224中内同时有螯合位点和分子隔室来协同控制铂生长。用于构建分子隔室的分子栅栏的高度可以通过嫁接分子的大小调控。其中，苯甲酸作为最合适的分子栅栏，促进Pt在MOF的孔内形成超细纳米团簇。高分辨透射电镜、暗场电镜、X射线吸收光谱等证明了超细铂纳米团簇在PCN-224内均匀分散。活性实验表明，具有0.9nm铂团簇的PtNCs@PCN-224-BA的活性远高于负载铂单原子的PtSAs@PCN-224-BA和4.2nm铂纳米颗粒的PtNPs@PCN-224-BA。同时，该策略制备的催化剂也远高于其它方法制备的催化剂，如光沉积法、硼氢化钠还原法等。本项目致力于超细铂团簇@MOF材料的设计和构筑，实现了在光催化产氢等应用方面的突破，并且取得了一系列具有较高学术价值的研究成果，高质量、超额完成了既定目标。研究成果在国内外期刊上发表论文9篇，包括Appl. Catal. B: Environ.(3篇)，Chem. Eng. J.,Solar RRL, Inorg. Chem.等；申请发明专利2项，已授权1项。