A minireview on catalysts for photocatalytic N2 fixation to synthesize ammonia

Ammonia (NH3) is an important feedstock in chemical industry. Nowadays NH3 is mainly produced via the industrialized Haber-Bosch process, which requires substantial energy input, since it operates at high temperatures (400-650 °C) and high pressures (20-40 Mpa). From the energy conservation point of view, it is of great significance to explore an alternative avenue to synthesize NH3, which is in line with the concept of sustainable development. Very recently, photocatalytic N2 fixation (PNF) has been discovered as a safe and green approach to synthesize NH3, as it utilizes the inexhaustible solar energy and the abundant N2 in nature to synthesize NH3 under mild conditions. A highly efficient catalyst is the core of PNF. Up to now, extensive studies have been conducted to design efficient catalysts for PNF. Summarizing the catalysts reported for PNF and unraveling their reaction mechanisms could provide guidance for the design of better catalysts. In this review, we will illustrate the development of catalysts for PNF, including semiconductors, plasmonic metal-based catalysts, iron-based catalysts, ruthenium-based catalysts and several other catalysts, point out the remaining challenges and outline the future opportunities, with the aim to contribute to the development of PNF.

Heterojunction-based photocatalytic nitrogen fixation: principles and current progress

Nitrogen fixation is considered one of the grand challenges of the 21st century for achieving the ultimate vision of a green and sustainable future. It is crucial to develop and design sustainable nitrogen fixation techniques with minimal environmental impact as an alternative to the energy-cost intensive Haber-Bosch process. Heterojunction-based photocatalysis has recently emerged as a viable solution for the various environmental and energy issues, including nitrogen fixation. The primary advantages of heterojunction photocatalysts are spatially separated photogenerated charge carriers while retaining high oxidation and reduction potentials of the individual components, enabling visible light-harvesting. This review summarises the fundamental principles of photocatalytic heterostructures, the reaction mechanism of the nitrogen reduction reaction, ammonia detection methods, and the current progress of heterostructured photocatalysts for nitrogen fixation. Finally, future challenges and prospects are briefly discussed for the emerging field of heterostructured photocatalytic nitrogen fixation.

Heterojunction photocatalysts for artificial nitrogen fixation: fundamentals, latest advances and future perspectives

As an indispensable energy source, ammonia plays an essential role in agriculture and various industries. Given that the current ammonia production is still dominated by the energy-intensive and high carbon footprint Haber-Bosch process, photocatalytic nitrogen fixation represents a low-energy consuming and sustainable approach to generate ammonia. Heterostructured photocatalysts are hybrid materials composed of semiconductor materials containing interfaces that make full use of the unique superiorities of the constituents and synergistic effects between them. These promising photocatalysts have superior performances and substantial potential in photocatalytic reduction of nitrogen. In this review, a wide spectrum of recently developed heterostructured photocatalysts for nitrogen fixation to ammonia are evaluated. The fundamentals of solar-to-ammonia conversion, basic principles of various heterojunction photocatalysts and modification strategies are systematically reviewed. Finally, a brief summary and perspectives on the ongoing challenges and directions for future development of nitrogen photofixation catalysts are also provided.

Photocatalytic nitrogen fixation on transition metal modified TiO2 nanosheets under simulated sunlight

Transition metal modified TiO₂ was synthesized using a microwave assisted hydrothermal method for efficient photocatalytic nitrogen fixation under simulated sunlight.