A study published in Applied Catalysis A: General intended to investigate the effect of different morphological configurations based on the modification of the concentration of molybdenum carbide quantum dots (MoC-QDs) on carbon film and the morphological characteristics of three-dimensional multi-pored g-C3N4.
Study: MoC quantum dots embedded in ultra-thin carbon film coupled with 3D porous g-C3N4 for enhanced visible-light-driven hydrogen evolution. Image Credit: mitchFOTO/Shutterstock.com
The primary goal of photocatalytic hydrogen evolution reactions is to effectively tackle the challenges of energy scarcity and pollution.
With bulk g-C3N4 (CN-B) as a baseline, solvothermal and chemical vapor deposition procedures were used to create tubular and honeycomb g-C3N4 (CN-T and CN-H, respectively).
CN-H and CN-T exhibit distinct slow photo-effect and direction-dependent electron transport capabilities. The many active areas provided by properly dispersed MoC-QDs and the fine carbon coating facilitates dye molecule adsorption and electron transmission.
Challenges with Hydrogen Evolution
Using solar power for splitting water molecules for hydrogen evolution, relying on semiconductors, offers a plethora of practical uses in addressing worldwide energy scarcity and environmental degradation.
The primary reasons existing photocatalytic agents for water breakdown cannot be used in commercial operations are their high cost, limited activity, and relative instability.
The graphite-based carbon nitride (g-C3N4), an organic semiconducting polymer constituted of sp2 hybridized carbon and nitrogen, is regarded as a highly prospective versatile material due to its easy manufacturing procedure, appropriate band-gap, and strong chemical stability.
However, the bulk g-C3N4 synthesized by traditional thermal polymerization procedures provides a small specific area while the lifespan of photo-carriers is shortened due to the impact of the coupled electrons, limiting its use in water breakdown.
Graphitic C3N4 can offer relatively high hydrogen precipitation action if it is combined with precious metals such as platinum or gold as co-catalysts. It would enhance the high work functionality and adequate available energy of hydrogen adsorption. However, their exorbitant cost and rarity hamper their practical usage.
Various efforts have been made, including the development of heterojunctions, heteroatom doping, and copolymerization with organic molecules, to impede the recombining of photoinduced carriers and thus increase the H2 production flow of g-C3N4, but none have entirely resolved the inherent limitations of g-C3N4. As a result, various types of g-C3N4 are devised and made, such as thin layers, hollow spheres, and hollow tubular structures.
The interior chamber of the hollow tubular g-C3N4 allows for multiple scatter and reflections of incoming light, and the photo-carriers produced by photoexcitation move directionally in a one-dimensional channel.
The honeycomb g-C3N4 developed by the team features a big cavity, a distinct slow photon action, and the ability to delay and store a particular incoming wavelength.
Overall, the 3D g-C3N4 structure features a high specific area, many active sites, short photo-carrier diffusion routes, and efficient channels that might help with reactant adsorption and diffusion.
Use of Molybdenum Carbide Quantum Dots
Molybdenum carbide (MoC) is a conventional transition-metal carbide (TMC) with a straightforward fabrication procedure, cheap cost, and excellent stability, as well as outstanding hydrogen adsorption characteristics. It has received a great deal of attention in the domains of hydrodesulfurization, hydrogen generation via photocatalysis, and water-gas transfer.
The approach of producing cubic MoC at a low temperature is considered to be safer. Despite the inability of the carbon layer to produce photo-carriers, its superb conductance enables electron transfer. Moreover, rational catalytic anchoring on the carbon sheet is a viable technique.
In this study, a significant number of widely scattered MoC quantum dots were produced on the carbon layer and linked with a minimal quantity of g-C3N4 with various morphological makeups. Researchers demonstrated that combining catalysts with diverse morphologies is a successful method for improving performance.
The clever pairing of nanoparticles with varied morphologies is crucial for enhancing performance. After nine rounds of sustained irradiation, the catalytic composites virtually retained their initial hydrogen evolution efficiency, suggesting their high stability and longevity.
The structural stability of the catalytic composites is largely responsible for this phenomenon. Both CN-H and CN-B have stable structures that are difficult to modify; the carbon film adsorbed in the internal cavity of CN-T can maintain the tubular morphology, successfully avoiding rupture and breakdown.
The nanostructures and behaviors of the catalysts were rigorously examined in this study, stressing the importance of the interior cavity of CN-T and the delayed photo-effect of CN-H.
MoC-QDs formed on the carbon layer improve the catalytic composite's photo-absorption capability, while the widely distributed MoC-QDs serve as the major active sites. Furthermore, even after 45 hours of continued reaction, the catalytic composites show great stability.
This work provides an in-depth examination of g-C3N4 and the synthesis of new photocatalysts, paving the path for future advances.
Continue reading: Perfecting Quantum Dots to Maximize Solar Panel Efficiency.
Yan, T., Wang, Y., Cao, Y., Liu, H., & Jin, Z. (2021) MoC quantum dots embedded in ultra-thin carbon film coupled with 3D porous g-C3N4 for enhanced visible-light-driven hydrogen evolution. Applied Catalysis A, General. Available at: https://www.sciencedirect.com/science/article/pii/S0926860X21004713?via%3Dihub