Photocatalysis without borders: Charting progress in metal-free hydrogen peroxide synthesis

The Hydrogen peroxide (H₂O₂) gained attention as a versatile mild oxidizing agent, finding extensive uses in several activities such as bleaching, wastewater treatment, medical applications, and chemical transformations. Besides this, it is also prominently considered as a potential candidate for new liquid fuel therefore, its production is garnering attention of scientific fraternity. However, the conventional method of producing H₂O₂ through anthraquinone oxidation is often viewed as inefficient and less environmentally friendly, as it is high energy process and generates a lot of harmful organic waste products. This review article highlights recent advancements in metal-free photocatalytic systems for sustainable production of H₂O₂. Over the last decade, significant advancement has been made in developing ecological benign protocols for the synthesis of H₂O₂ to meet UN Sustainable Development Goals (SDGs). This comprehensive review showcases key findings and refinements in metal-free light-mediated H₂O₂ production, offering promising strategies to acquire SDGs via more eco-friendly and cost-effective approach, utilizing only H₂O and gaseous O₂ as primary inputs and harnessing solar energy as its sustainable energy source. Nevertheless, practical applications of photocatalytic H₂O₂ production continue to face challenges such as high electron-hole (e^--h⁺) pair recombination rates, limited utilization of visible light, and suboptimal product selectivity. While progress has been achieved in improving the photocatalytic activity for generating H₂O₂, it remains primarily within the realm of laboratory research due to its currently unsatisfactory productivity levels. Given the significance of H₂O₂, we have also considered the prevailing hurdles and potential breakthroughs in photocatalytic production. The review is wrapped up with a concise summary and visionary viewpoint on the potential forthcoming developments in this burgeoning research domain.