Novel materials for efficient photocatalytic hydrogen production and gas sensing

Due to the depletion of fossil fuels and serious concern of environmental issues induced by fossil fuels, sustainable, clean, and renewable energy is urgently needed to replace the current situation using fossil fuel as the main energy resource. Hydrogen is considered one of the cleanest energies due to the final water product after combustion. Among the ways to fabricate hydrogen, photocatalysis has been considered the most sustainable and renewable way since it employs solar energy. Considering the low fabrication cost, abundance on earth, appropriate bandgap, and high performance, carbon nitride has attracted extensive attention as the catalyst for hydrogen production for the last two decades. Graphitic carbon nitride has attracted much attention as a photocatalyst due to its wide bandgap, high chemical stability, and visible light response. However, a challenge is synthesizing highly crystalline g-C₃N₄ that favours the separation of photogenerated electron-hole pairs and promotes improved photocatalytic activity. Herein, a highly crystalline carbon nitride with an optimum band structure that benefits enhanced light absorption and charges separation efficiency by a simple and economical thermal treatment using NaCl is reported. The new highly crystalline carbon nitride significantly showed a drastic improvement in the photocatalytic performance. The photocurrent response of the highly crystalline material under visible light irradiation is about 5 times higher than bulk material. As a photocatalyst, the material demonstrated a hydrogen production rate of 29 μmol h^-1. This work paves a new path to design novel carbon nitrides for enhanced photoelectrochemical and photocatalytic performance. In photocatalytic experiments, platinum is the primary co-catalyst for water reduction. Although platinum is an efficient hydrogen revolution reaction catalyst, the cost and limited reservation greatly hinder the development of photocatalytic technologies. Researchers are focusing on developing low-cost hydrogen evolution reaction agents for photocatalysis, and many candidates have been investigated. MoS₂ is one of the most promising efficient catalysts for hydrogen evolution reaction and a potential substitution for platinum in electrochemical hydrogen evolution in both acidic and basic environments and can also be used as a co-catalyst with carbon nitride for photocatalytic hydrogen evolution. Herein, in this work, MoS₂ quantum dots were integrated with sodium chloride-modified carbon nitride to reach a superior performance in photocatalytic hydrogen evolution compared with the combination of normal carbon nitride and 3 wt% platinum. The photocatalytic hydrogen evolution rate of the prepared sample was 2.1 folds to that of 3wt% Pt + g-CN, and this work has demonstrated that MoS₂ could be used as an efficient and low-cost photocatalyst for photocatalytic hydrogen evolution. In addition, an effort has been made to use single atom doped carbon nitride for acid and water sensing. Due to the enhanced active sites, the single copper atoms doped carbon nitride exhibit much better performance for acid and water sensing.