TiO2-based photocatalysts for controllable hydrogen evolution from ammonia borane

Synthesis of Ilmenite Nickel Titanite-Supported Carbon Nanofibers Derived from Polyvinylpyrrolidone as Photocatalyst for H2 Production from Ammonia Borane Photohydrolysis

The present study involves the synthesis of photocatalytic composite nanofibers (NFs) comprising ilmenite nickel titanite-supported carbon nanofibers (NiTiO3/TiO2@CNFs) using an electrospinning process. The photocatalytic composite NFs obtained were utilized in hydrogen (H2) production from the photohydrolysis of ammonia borane (AB). The experimental findings show that the photocatalytic composite NFs with a loading of 25 mg had a good catalytic performance for H2 generation, producing the stoichiometric H2 in 11 min using 1 mmol AB under visible light at 25 °C and 1000 rpm. The increase in catalyst load to 50, 75, and 100 mg leads to a corresponding reduction in the reaction time to 7, 5, and 4 min. The findings from the kinetics investigations suggest that the rate of the photohydrolysis reaction is directly proportional to the amount of catalyst in the reaction system, adhering to a first-order reaction rate. Furthermore, it was observed that the reaction rate remains unaffected by the concentration of AB, thereby suggesting a reaction of zero order. Increasing the reaction temperature results in a decrease in the duration of the photohydrolysis reaction. Furthermore, an estimated activation energy value of 35.19 kJ mol-1 was obtained. The composite nanofibers demonstrated remarkable and consistent effectiveness throughout five consecutive cycles. The results suggest that composite NFs possess the capacity to function as a feasible substitute for costly catalysts in the process of H2 generation from AB.

Plasmonic Metal/Semiconductor Heterostructure for Visible Light-Enhanced H2 Production

A plasmonic Ag/Bi₂WO₆ heterostructure, having Ag NPs deposited on Bi₂WO₆, is obtained by a hydrothermal and photodeposition method. The synthesized Ag/Bi₂WO₆ composite exhibits strong visible light absorption with a localized surface plasmon resonance (LSPR) and shows an enhanced photoabsorption property. It is demonstrated that such a Ag/Bi₂WO₆ heterostructure shows excellent plasmon-enhanced photocatalytic activity in the dehydrogenation of ammonia borane (NH₃BH₃) solution under visible light irradiation, which is due to the results from the synergetic effect between Ag NPs and emerging W⁵⁺ ions. More importantly, the performance of a Ag/Bi₂WO₆ hybrid is almost eight times higher than that of sole Bi₂WO₆ nanosheets. The introduction of LSPR of Ag in Bi₂WO₆ improves the electrical conductivity of the composite and lowers the recombination rate of charge carriers. This study opens up the opportunity of rationally fabricating plasmonic metal/semiconductor heterostructures for highly efficient photocatalysis.

A Photocatalytic Hydrolysis and Degradation of Toxic Dyes by Using Plasmonic Metal–Semiconductor Heterostructures: A Review

Converting solar energy to chemical energy through a photocatalytic reaction is an efficient technique for obtaining a clean and affordable source of energy. The main problem with solar photocatalysts is the recombination of charge carriers and the large band gap of the photocatalysts. The plasmonic noble metal coupled with a semiconductor can give a unique synergetic effect and has emerged as the leading material for the photocatalytic reaction. The LSPR generation by these kinds of materials has proved to be very efficient in the photocatalytic hydrolysis of the hydrogen-rich compound, photocatalytic water splitting, and photocatalytic degradation of organic dyes. A noble metal coupled with a low bandgap semiconductor result in an ideal photocatalyst. Here, both the noble metal and semiconductor can absorb visible light. They tend to produce an electron–hole pair and prevent the recombination of the generated electron–hole pair, which ultimately reacts with the chemicals in the surrounding area, resulting in an enhanced photocatalytic reaction. The enhanced photocatalytic activity credit could be given to the shared effect of the strong SPR and the effective separation of photogenerated electrons and holes supported by noble metal particles. The study of plasmonic metal nanoparticles onto semiconductors has recently accelerated. It has emerged as a favourable technique to master the constraint of traditional photocatalysts and stimulate photocatalytic activity. This review work focuses on three main objectives: providing a brief explanation of plasmonic dynamics, understanding the synthesis procedure and examining the main features of the plasmonic metal nanostructure that dominate its photocatalytic activity, comparing the reported literature of some plasmonic photocatalysts on the hydrolysis of ammonia borane and dye water treatment, providing a detailed description of the four primary operations of the plasmonic energy transfer, and the study of prospects and future of plasmonic nanostructures.