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Photocatalysis is a perennial solution that promises to resolve deep-rooted challenges related to environmental pollution and energy deficit through harvesting the inexhaustible and renewable solar energy. To date, a cornucopia of photocatalytic materials has been investigated with the research wave presently steered by the development of novel, affordable, and effective metal-free semiconductors with fascinating physicochemical and semiconducting characteristics. Coincidentally, the recently emerged red phosphorus (RP) semiconductor finds itself fitting perfectly into this category ascribed to its earth abundant, low-cost, and metal-free nature. More notably, the renowned red allotrope of the phosphorus family is spectacularly bestowed with strengthened optical absorption features, propitious electronic band configuration, and ease of functionalization and modification as well as high stability. Comprehensively detailing RP's roles and implications in photocatalysis, this review article will first include information on different RP allotropes and their chemical structures, followed by the meticulous scrutiny of their physicochemical and semiconducting properties such as electronic band structure, optical absorption features, and charge carrier dynamics. Besides that, state-of-the-art synthesis strategies for developing various RP allotropes and RP-based photocatalytic systems will also be outlined. In addition, modification or functionalization of RP with other semiconductors for promoting effective photocatalytic applications will be discussed to assess its versatility and feasibility as a high-performing photocatalytic system. Lastly, the challenges facing RP photocatalysts and future research directions will be included to propel the feasible development of RP-based systems with considerably augmented photocatalytic efficiency. This review article aspires to facilitate the rational development of multifunctional RP-based photocatalytic systems by widening the cognizance of rational engineering as well as to fine-tune the electronic, optical, and charge carrier properties of RP.

Photocatalysts with atomic dimensions exhibit superior performance in photocatalytic applications owing to their large surface-to-volume ratio, enormous surface active sites, and superior light-harvesting ability. The single-unit-cell thickness reduces interlayer charge transfer resistance, facilitating the rapid transfer of electrons and holes from the interior to the surface. This review aims to provide a comprehensive discussion on the fundamentals of photocatalysis and the advancements achieved from the evolution of photocatalysts from their bulk-counterpart to atomic dimensions. State-of-the-art techniques in designing and modifying atomically thin photocatalysts, such as defect engineering, impurity doping, facet engineering, and atomic-scale heterojunction construction, for diverse photocatalytic applications will be comprehensively elucidated.

Photocatalysis, a renewable, bountiful, and viable technology, has been widely regarded as a promising method to alleviate environmental challenges and circumvent the increasingly tensed energy crisis. Specifically, substantial carbon dioxide (CO2) emission reduction can be achieved by using CO2 as the starting carbon source to generate renewable solar fuels such as methanol, methane, and formic acid. The fabrication and development of highly efficient photocatalysts are crucial determinants of this approach. The recently emerged two-dimensional (2D) materials have taken the research and energy scene by storm owing to their distinctive features of tunable bandgap, large surface-to-volume ratio, ultrathin characteristic, extraordinary electrical and optical absorption properties, copious active centers, and abundant coordinated unsaturated surface sites. These unique physicochemical properties render 2D materials as promising candidates for photocatalytic CO2 conversion into carbon-based fuels. In this article, an overview of the recent developments summarizing the CO2 photoreduction over 2D materials, namely, graphene-based photocatalysts, transition metal dichalcogenide–based photocatalysts and graphitic carbon nitride–based photocatalysts, are highlighted. In detail, the emerging strategies and recent advances for tailoring highly functional 2D material–based photocatalytic semiconductors comprising heterostructure fabrication, functionalization with advanced nanostructures, surface defect engineering, and elemental doping are discussed.