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.

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Photocatalytic dry reformation of methane (DRM) is an appealing alternative to transform CO2 into precious syngas for the Fischer–Tropsch synthesis while simultaneously reducing greenhouse gas emissions. However, the reaction mechanisms of DRM over photocatalysts have not been fully explored to date. In this work, two-dimensional graphitic carbon nitride (gC3N4) nanosheets are taken as a case study to shed light on their behaviors under the multistep reaction of DRM through first-principles calculations. The results show that gC3N4 is a promising candidate for DRM due to its suitable electronic band structure to drive the redox reaction and its ability to facilitate the adsorption of reactants (CO2 + CH4) and the desorption of products (CO + H2). The systematic Gibbs free energy calculations identified the possible reaction pathways for the reforming of CH4 to syngas using CO2. We observed that the H atoms from CH4 dissociation are more likely to form H2 since the Gibbs free pathway indicates that the main contributor of CO formation is the direct reduction of CO2 to CO rather than the oxidation of CH4 to CO due to the large activation barrier required for the formation of the CH2O intermediate. Overall, our work sheds light on the mechanism underlying the photocatalytic dry reforming of CH4 over gC3N4 nanosheets.

Resembling a distinctive stratum of chemical transformations, photocatalysis employs the energy from the Sun to drive thermodynamically uphill reactions by simply emulating what nature does bestphotosynthesis; photocatalysis therefore promises a sustainable solution to circumvent the increasingly tense environmental threats and energy crisis. In this contribution, we shed light on the opportune design and development of a dual Z-scheme photocatalytic system with homo–hetero junctions using mixed-phase red/black phosphorus (RP/BP) and tungsten oxide (WO3) in regulating charge steering for directional electron–hole transfer to drive efficient CO2 reduction. Fascinatingly, the ternary composite material (RP/BP@WO3) displayed a striking enhancement in optical absorption capacity, which extended from the ultraviolet up to the near-infrared region, rendering its capability of maximizing photon absorption to power efficacious photocatalytic reactions. With the endowment of two effective charge transport pathways that feature a cascade electron flow profile, the RP/BP@WO3 dual Z-scheme photocatalyst achieved a CH4 yield of 6.21 μmol g–1 over 6 h under visible light illumination, whereas the pristine counterparts, namely, RP, WO3, and RP/BP, did not produce any CH4 yield. The amalgamation of RP/BP homojunction as the reduction catalyst and WO3 as the oxidation catalyst intriguingly serve as a complement to provoke CO2 reduction to CH4. The phenomenon is explicated by the formation of an arrow-up dual Z-scheme system that is governed by an internal electric field from the homo–hetero junctions which bestows strong redox potentials and favors the separation and transfer of photoinduced charge carriers, leading to increased participation of electron–hole pairs in redox reactions for improved photoconversion performance.