In this review, we focus on analysing the fundamental electronic, optical and chemical properties of 2D phosphorene to assess its suitability as a metal-free water splitting photocatalyst.

Rhenium disulfide (ReS2) is a two dimensional (2D) group VII transition metal dichalcogenide (TMD). It is attributed with structural and vibrational anisotropy, layer independent electrical and optical properties, and metal-free magnetism properties. These properties are unusual compared with more widely used group VI-TMDs e.g. MoS2, MoSe2, WS2 and WSe2. Consequently, it has attracted significant interest in recent years and is now being used for a variety of applications including solid state electronics, catalysis, and, energy harvesting and energy storage. It is anticipated that ReS2 has the potential to be equally used in parallel with isotropic TMDs from group VI for all known applications and beyond.Therefore, a review on ReS2 is very timely. In this first review on ReS2, we critically analyze the available synthesis procedures and their pros-cons, atomic structure and lattice symmetry, crystal structure and growth mechanisms with an insight to the orientation and architecture of domain and grain boundaries, decoupling of structural and vibrational properties, anisotropic electrical, optical and magnetic properties impacted by crystal imperfections, doping and adatoms adsorptions, and the contemporary applications in different areas.

This article provides a comprehensive review of the latest progress, challenges and recommended future research related to metal-free photocatalysts for hydrogen production via water-splitting.

This article critically reviews the progress and challenges in using metal-free photocatalysts made from carbon, nitrogen and phosphorus used for hydrogen production.