Plasma electrolytic oxidation (PEO) is a novel surface treatment process to produce thick, dense metal oxide coatings, especially on light metals, primarily to improve their wear and corrosion resistance. The coating manufactured from the PEO process is relatively superior to normal anodic oxidation. It is widely employed in the fields of mechanical, petrochemical, and biomedical industries, to name a few. Several investigations have been carried out to study the coating performance developed through the PEO process in the past. This review attempts to summarize and explain some of the fundamental aspects of the PEO process, mechanism of coating formation, the processing conditions that impact the process, the main characteristics of the process, the microstructures evolved in the coating, the mechanical and tribological properties of the coating, and the influence of environmental conditions on the coating process. Recently, the PEO process has also been employed to produce nanocomposite coatings by incorporating nanoparticles in the electrolyte. This review also narrates some of the recent developments in the field of nanocomposite coatings with examples and their applications. Additionally, some of the applications of the PEO coatings have been demonstrated. Moreover, the significance of the PEO process, its current trends, and its scope of future work are highlighted.

Graphitic carbon nitride ($g$-C${}_{3}$N${}_{4}$) has recently triggered extensive investigations due to its potential applications, such as in direct photochemical water splitting, CO${}_{2}$ activation, and transition-metal-free spintronics. However, electronic, and particularly the optical properties of $g$-C${}_{3}$N${}_{4}$ still have not been well established. Based on one of the state-of-the-art approaches\char22{}many-body Green's function theory (i.e., $GW$ $+$ BSE)\char22{}absorption of ultraviolet light by $g$-C${}_{3}$N${}_{4}$ is found to be determined by strong excitonic effects with a significantly large binding energy assigned to the bound excitons. Dark states have also been found in $g$-C${}_{3}$N${}_{4}$, which can affect the photoluminescence yield of $g$-C${}_{3}$N${}_{4}$. We find that the band gap of $g$-C${}_{3}$N${}_{4}$ probably can be tuned by adjusting the condensation (dimensionality) to initiate excitonic absorption in the visible light region, which might help improve the solar energy conversion efficiency.

Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H₂O₂ production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity.

Silicene, which is the silicon equivalent of carbon-based graphene and shares some of the unique properties with graphene, has been attracting more and more attention since its synthesis and represents a breakthrough in current silicon-based technology. In this work, many-body effects in silicene, silicane, germanene and germanane have been demonstrated based on the Green's function perturbation theory, i.e., GW + Bethe–Salpeter equation. Due to confinement, many-body effects play a pivotal role in quasi-particle excitations and optical absorption spectra, which leads to excitonic resonance (π → π* excitation) in silicene and germanene, and strongly bound excitons in silicane and germanane with considerable binding energies.