KENTECH Institute for Environmental and Climate Technology, Korea Institute of Energy Technology (KENTECH), Naju 58330, Korea.
Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea.
Acc Chem Res. 2023 Apr 4;56(7):867-877. doi: 10.1021/acs.accounts.3c00002. Epub 2023 Mar 22.
ConspectusEmploying semiconductor materials is a popular engineering method to harvest solar energy, which is widely investigated for photocatalysis (PC) and photoelectrocatalysis (PEC) that convert solar light to chemical energy. In particular, environmental photo(electro)catalysis has been extensively studied as a sustainable method for water treatment, air purification, and resource recovery. Environmental PC/PEC processes working in ambient conditions are initiated mainly through hole transfer to water (water oxidation) and electron transfer to dioxygen (O reduction) and the subsequent photoredox transformation of water and dioxygen serves as a base of various PC/PEC systems. Through the redox transformations, different products can be generated depending on the number of transferred electrons and holes. The single electron/hole transfer generates radical species and reactive oxygen species (ROS) which initiate the degradation/transformation of various pollutants in water and air, while the multicharge transfer can generate energy-rich chemicals (e.g., H, HO). Therefore, understanding the characteristics of the photoredox reactions of water and dioxygen on the semiconductor surface is critically important in controlling the selectivity and efficiency of photoconversion processes.In this Account, we describe various environmental PC/PEC conversions with a particular focus on how the phototransformation of dioxygen and water is related to the overall processes occurring on diverse semiconductor materials. The activation of water or dioxygen can be controlled by modifying the properties of semiconductors, changing the kind of counterpart half-reaction and the experimental conditions. If water can be used as a ubiquitous reductant under solar irradiation, many kinds of reductive transformations can be carried out under ambient environmental conditions. For example, various toxic oxyanions (or metal ions) can be reductively transformed to harmless or less harmful species or useful chemicals/fuels can be synthesized under ambient conditions if water can provide electrons and protons via solar water oxidation. On the other hand, dioxygen can turn into reactive oxygen species (ROS) as a versatile oxidant or to a chemical like HO. There should be many more possibilities of utilizing the photoconversion of water and dioxygen for environmentally significant purposes, which are yet to be further developed and demonstrated. In this Account, we highlight the recent strategies and the novel functional materials for effective activation of water and dioxygen in environmental PC/PEC systems. Design of environmentally functional PC/PEC systems should be based on better understanding of water and dioxygen activation.
采用半导体材料是一种从太阳能中获取能量的常用工程方法，这种方法广泛应用于光催化（PC）和光电催化（PEC）中，用于将太阳能转化为化学能。特别是，环境光（电）催化作为一种可持续的水净化、空气净化和资源回收方法得到了广泛的研究。在环境条件下工作的环境 PC/PEC 工艺主要通过空穴转移到水中（水氧化）和电子转移到氧气中（O 还原）来引发，随后水和氧气的光还原转化作为各种 PC/PEC 体系的基础。通过氧化还原转化，可以根据转移的电子和空穴的数量生成不同的产物。单电子/空穴转移会产生自由基和活性氧物种（ROS），从而引发水中和空气中各种污染物的降解/转化，而多电荷转移可以生成富含能量的化学物质（例如 H、HO）。因此，了解半导体表面上水和氧气的光氧化还原反应的特征对于控制光转化过程的选择性和效率至关重要。
在本述评中，我们描述了各种环境 PC/PEC 转化，特别关注氧气和水的光转化如何与不同半导体材料上发生的整体过程相关。通过改变半导体的性质、改变对应半反应的种类和实验条件，可以控制水或氧气的活化。如果在太阳辐射下可以使用水作为普遍存在的还原剂，那么在环境条件下可以进行多种还原转化。例如，如果水可以通过太阳能水氧化提供电子和质子，可以将各种有毒含氧阴离子（或金属离子）还原转化为无毒或毒性较小的物质，或者可以在环境条件下合成有用的化学品/燃料。另一方面，氧气可以作为一种多功能氧化剂或 HO 等化学物质转化为活性氧物种（ROS）。利用水和氧气的光转化来实现环境意义上的目标还有更多的可能性，这些可能性有待进一步开发和验证。在本述评中，我们强调了最近用于环境 PC/PEC 系统中有效激活水和氧气的策略和新型功能材料。环境功能 PC/PEC 系统的设计应基于对水和氧气激活的更好理解。
