光催化固氮:人工光合成的新途径（英文）

氨不仅是一种广泛使用的化工原料,还可用作重要的能源载体.哈伯法合成氨被认为是20世纪最伟大的发明之一,为人类社会的发展做出了巨大贡献.同时,氨合成过程每年需要消耗世界总能源的1%–2%.因此,开发绿色清洁的氨合成方法一直是世界范围内工业界和学术界关注的热点.随着人工光合成太阳燃料研究的蓬勃发展,利用太阳能光催化的方式实现在温和条件下合成氨吸引了越来越多研究者的兴趣,因为这是一条最为理想的能源利用途径,即直接利用太阳能将氮气和水转化为氨.近期,该研究领域涌现了一系列有代表性的研究工作,报道了利用半导体光催化剂实现太阳能到氨的转化,虽然整体效率仍很低,但是已经证明了利用太阳能直接将氮气转化为氨的可能性.光催化合成氨过程中,最具挑战的是氮气分子在半导体光催化剂表面的吸附和活化.研究表明,通过在半导体光催化剂表面引入空位或者缺陷可有效地增加氮气的吸附,且很可能成为氮气分子活化并参与反应的活性中心.此外,借鉴自然界豆类植物固氮酶的独特结构,利用其对于氮气分子高效活化的独特优势,构建自然-人工杂化体系也是提升氮气吸附与活化的有效策略之一.本综述将从合成氨过程中氮气的吸附与活化问题入手,分别从缺陷与空位调控和固氮酶两个方面的策略考虑,结合几个典型的光催化剂体系(如卤氧化铋,二氧化钛及水滑石等)作为示例,介绍空位调控与模拟固氮酶策略对太阳能光催化固氮的影响并分析其可能的机理.虽然人工光合成固氮研究取得了一些进展,但是目前效率太低,亟需从基础科学问题的认识和理解上有新的突破,如氮气分子的吸附与活化微观过程、空位可控调变策略、新型光催化剂的开发与表界面修饰、氨氧化逆反应的抑制策略及精确的理论模拟指导人工光合成固氮体系的构建等.最后,对人工光合成固氮研究方向面临的挑战和未来的发展方向进行了总结与展望.

Photocatalytic nitrogen fixation:An attractive approach for artificial photocatalysis

Ammonia synthesis via the Haber-Bosch process, which has been heralded as the most important invention of the 20th century, consumes massive amounts of energy, around ～1%–2% of the world's annual energy consumption. Developing green and sustainable strategies for NH3synthesis under ambient conditions, using renewable energy, is strongly desired, by both industrial and sci-entific researchers. Artificial photosynthesis for ammonia synthesis, which has recently attracted significant attention, directly produces NH3from sunlight, and N2and H2O via photocatalysis. This has been regarded as an ideal, energy-saving and environmentally-benign process for NH3produc-tion because it can be performed under normal temperature and atmospheric pressure using re-newable solar energy. Although sustainable developments have been achieved since the pioneering work in 1977, many challenging issues (e.g., adsorption and activation of nitrogen molecules on the surface of photocatalysts under mild conditions) have still not been well solved and the photocata-lytic activities are generally low. In this miniature review, I summarize the most recent progress of photocatalytic N2fixation for ammonia synthesis, focusing specifically on two attractive aspects for adsorption and activation of nitrogen molecules: one is engineering of oxygen vacancies, and the other is mimicking natural nitrogenase for constructing artificial systems for N2fixation. Several representative works focusing on these aspects in artificial systems have been reported recently, and it has been demonstrated that both factors play more significant roles in photocatalytic N2re-duction and fixation under ambient conditions. At the end of the review, I also give some remarks and perspective on the existing challenges and future directions in this field.