半导体等离激元增强型纳米催化剂的合成及性能研究

Coupling solar energy into heterogeneous catalytic reactions by the utilization of hybrid nanocatalysts containing both strong surface plasmon and abundant catalytic active sites is an effective way to improve the reaction efficiency and save traditional energy. Compared with those based on plasmonic noble metal which are under extensive research nowadays, hybrid nanocatalysts based on self-doping semiconductor possess not only lower costs, but also various plasmon types and tunable plasmon energy. However, the research on self-doping semiconductor/metal hybrid nanocatalysts is now limited by some serious problems, including the plasmons are easily destroyed during the deposition of metal catalysts and the high-efficient loading of metal catalyst on semiconductors is difficult. To overcome these problems, we propose a new synthetic strategy, in which the catalytic metal is first in situ grown on a template and the template is metallized subsequently, to prepare self-doping semiconductor/catalytic metal hybrid nanocatalysts which contain both strong semiconductor plasmon and abundant catalytic active sites, and control the energy of plasmon and the distribution, size, morphology of catalytic metal. Further, the influence of energy and hot carrier transfer between semiconductor plasmon and metal catalyst on the catalytic properties of different hybrid nanocatalysts will be also studied through electrochemical, spectroscopy methods and model reactions. Finally, the hybrid nanocatalysts will be optimized to couple more clean solar energy into chemical reactions and improve the reaction efficiency more effectively.

利用表面等离激元增强型复合催化剂将太阳能耦合进异相催化反应，是提高反应效率和节约传统能源的有效途径。与目前广泛研究的贵金属表面等离激元增强型催化剂相比，自掺杂半导体等离激元增强型催化剂不仅成本较低，而且等离激元类型多样、能量可调，但是其合成中面临着自掺杂半导体表面等离激元易被破坏、难实现催化活性材料的高效负载等问题。为此，本项目提出先在模板上原位还原沉积催化活性材料再将模板等离激元化的策略，来合成兼具强半导体等离激元和丰富金属催化活性位点的复合催化剂，并实现对复合催化剂中等离激元能量及贵金属分布、尺寸、形貌的控制。在此基础上，进一步通过电化学、光谱、模型反应等手段研究自掺杂半导体等离激元与金属催化剂之间的能量与载流子转移对催化性能的影响规律，实现对复合催化剂的优化，从而能够更有效地将太阳能引入到催化反应中，达到利用清洁的太阳能来提高化学反应效率的目的。

借助于由等离激元材料和催化剂材料组成的纳米复合催化剂，可以利用太阳能来提升催化反应的效率，从而节约传统能源。本项目主要研究了氧化物半导体等离激元/金属复合催化剂的合成，以及在电催化析氢、对硝基苯酚还原等模型反应中光照对复合催化剂性能的增强规律，在此基础上分析了复合催化剂中氧化物等离激元对金属催化中心的影响机制。首先，在二氧化硅牺牲层保护下通过还原PtOx/TiO2制备了Pt/Ti4O7复合催化剂，发现较小的TiO2颗粒尺寸和较高的还原温度有助于得到具有强等离激元特性的Ti4O7，而二氧化硅牺牲层的存在能够抑制高温下Pt的熟化长大，从而实现了Ti4O7与Pt的有效结合。催化反应结果表明光照(>420纳米)能够增强复合催化剂在碱性条件下的电催化析氢性能，反应过电势从250毫伏降为235毫伏，通过不同波长光照下的测试发现Ti4O7的带间吸收对增强起主要作用；其次，通过还原预先制备的镍钒双金属氢氧化物钼酸盐制备了不含贵金属元素的MoNi4/V2O3复合催化剂，发现光照能够增强复合催化剂在中性条件下的电催化析氢性能，反应过电势从292毫伏降为184毫伏，通过测试MoNi4/V2O3复合催化剂在非光照和光照下的阿伦尼乌斯曲线，发现反应活化能从非光照时的36.77千焦/摩尔降低为光照时的29.95千焦/摩尔，表明光照下V2O3等离激元不仅能够通过光热效应提高反应界面的温度，而且能够通过热电子转移效应改变MoNi4的电子结构，从而降低反应能垒；最后，通过还原预先制备的钼酸镍前驱体，制备了MoNi4/MoO2复合催化剂，发现光照下MoO2等离激元也能提升MoNi4催化硼氢化钠还原对硝基苯酚反应的效率，反应活化能从非光照时的28.03千焦/摩尔降低为23.59千焦/摩尔。本项目的研究拓展了半导体等离激元增强型催化剂的合成方法，对研究等离激元增强各类催化反应具有广泛的借鉴意义。