Photocatalysis is an environmental protection method that can utilize solar energy for energy conversion and environmental governance. Among them, catalysts play a crucial role as an important part of photocatalysis. At present, the most commonly used catalysts are still traditional semiconductor catalysts, which have good environmental adaptability and stability, the large specific surface area and excellent photocatalytic intrinsic activity to ensure their excellent catalytic activity. Meanwhile, semiconductor photocatalysts have lower production costs and abundant reserves of raw materials on Earth, which also ensures their larger production volume and lower production costs. However, the bandgap of semiconductor catalysts is generally wide, which leads to high carrier recombination rate and insufficient visible light response, thereby limiting the efficient photocatalytic reaction. Rare earth elements, as dopants, have unique charge control mechanisms and optical modification mechanisms in photocatalysis, which can effectively enhance the photocatalytic activity of traditional semiconductors. Rare earth elements are a collective term for a total of 17 elements, including 15 lanthanide elements and scandium (Sc) and yttrium (Y), which have similar chemical properties to lanthanide elements. China is a major country in rare earth resources, with reserves of around 44 million tons, accounting for approximately 34% of the global rare earth reserves and ranking first in the world. Nowadays, rare earth elements have been widely used in metallurgy, chemical industry, aerospace transportation, and military fields, demonstrating their significant application value. They also have profound research significance in the field of photocatalysis industry, such as photocatalytic degradation of industrial printing and dyeing wastewater, reduction of CO2, preparation of hydrogen and oxygen from photocatalytic water splitting, etc. This article mainly introduces the regulation of rare earth element doping on the performance of semiconductor photocatalysts from the aspects of improving the photoelectric performance of semiconductor photocatalysts and reducing the recombination rate of charge carriers. Based on the classification of rare earth elements and the different number of doping components, the research progress and corresponding photocatalytic kinetic mechanisms of rare earth modified semiconductor photocatalysts are reviewed from the perspectives of single element rare earth doping, co doping of two rare earth elements, and multi element and high entropy rare earth doping. Through summary, it can be concluded that the larger atomic radius of rare earth elements can effectively cause lattice distortion of semiconductor photocatalysts, thereby increasing semiconductor defects, achieving the effect of refining particle size and exposing catalyst active sites; meanwhile, the unique band structure of rare earth elements can effectively adjust the photoelectric performance of semiconductor photocatalysts, promote efficient separation of charge carriers, and broaden their corresponding range of visible light. In addition, the up-conversion effect of some rare earth elements can also greatly improve the utilization of sunlight, compensate for the weak visible light absorption of semiconductor catalysts, and then promote the efficient progress of photocatalytic reactions. There are also studies indicating that doping with binary or more rare earth elements can also produce synergistic effects, jointly promoting the progress of specific photocatalytic reactions, such as the adsorption of reaction intermediates in photocatalytic reduction of CO2. In addition, when the doping type of rare earth elements reaches a high entropy level of five or more, it not only has excellent visible light response ability and large specific surface area, but also has stability and high entropy effect similar to high entropy alloys. These new advantages effectively enhance its photocatalytic activity and also saves a lot of consumption. Rare earth elements, as emerging dopants, have unique photocatalytic advantages. At the end of this article, the importance of rare earth element modification in improving the activity of semiconductor photocatalysts is elaborated and summarized, and corresponding prospects are made.
