Key Takeaways & Executive Findings
- •• Carbon materials (CNTs, graphene, CQDs, etc.) enhance photocatalytic efficiency when integrated into Z-scheme and S-scheme heterojunctions. • These heterojunctions promote charge separation, reduce recombination losses, and extend spectral response for solar energy conversion. • The review summarizes recent advances in carbon-based heterojunctions for photocatalytic H2 generation and CO2 reduction. • Current challenges and future directions for carbon-based photocatalysts are critically discussed.
Abstract
Carbon materials, including carbon nanotubes/nanofibers, graphene, graphene oxide, reduced graphene oxide, graphyne, graphdiyne, carbon quantum dots and fullerenes, have received considerable attention in recent years because of their unique properties such as high conductivity, excellent stability and biocompatibility. The integration of these materials into Z-scheme and S-scheme heterojunctions has emerged as a transformative strategy to increase their photocatalytic efficiency for energy conversion applications. We first consider the fundamental principles of clean energy generation such as photocatalytic H2 generation and CO2 reduction, elucidating their respective mechanisms and advantages. Various types of carbon materials, their synthesis and construction of Z-scheme and S-scheme heterojunctions are then discussed, emphasizing their role in promoting charge separation, reducing recombination losses and extending the spectral response range. With a focus on solar energy production, recent advances in carbon-based Z-scheme and S-scheme heterojunctions are discussed and summarized for photocatalytic H2 generation and CO2 reduction. Lastly, the current problems in the field of carbon-based photocatalysts are discussed with insights for the future development of this field.
1. Introduction
One of the most pressing problems facing humanity today is the worldwide shortage of energy. Because of the overuse and exploitation of readily available fossil fuels, non-renewable energy supplies like coal and petroleum may eventually run out, raising concerns about the use and exploitation of clean, viable sources of energy. For near and foreseeable future, solar energy remains the most plausible source of renewable power[1]. One of the most promising approaches is the establishment of new energy systems that transform sunlight into photoelectrical and chemical energy. Examples of these systems include the production of hydrogen (H2) through water splitting and the photocatalytic reduction of carbon dioxide (CO2) to chemical fuels[2,3]. Under ambient settings, converting atmospheric CO2 and H2O into fuels like methanol, methane and carbon monoxide has proven to be a sustainable option without further harming the environment[4].
Photocatalysis is a green technique for transforming solar energy into chemical energy, which accelerate any chemical reaction by lowering the activation energy required for the reaction to proceed by direct or catalytic photon illumination[5]. It is an advanced oxidation process that uses photons’ active and passive involvement to split water and reduce carbon dioxide amidst the UV-visible radiation to produce hydrogen and solar fuels respectively[6]. This process is important because the process has low secondary pollution, gentle reaction conditions, excellent efficiency, fast speed and no selectivity. Actually, photocatalysis is seen to be among the best strategies available to help solve the world’s energy and environmental problems. Through the application of this technology, we can lessen our reliance on non-renewable energy sources and enhance the environment for coming generations[7].
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Sahil Rana, Amit Kumar, Wang Tong-tong, Gaurav Sharma, Pooja Dhiman, Alberto García-Peñas (2024). A review of carbon material-based Z-scheme and S-scheme heterojunctions for photocatalytic clean energy generation. New Carbon Materials. https://doi.org/10.1016/S1872-5805_N
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Frequently Asked Questions
What are Z-scheme and S-scheme heterojunctions?
Z-scheme and S-scheme heterojunctions are types of photocatalytic systems that mimic natural photosynthesis to achieve efficient charge separation. Z-scheme uses two semiconductors with a mediator to transfer electrons, while S-scheme (step-scheme) combines an oxidation and a reduction photocatalyst to enhance redox ability and suppress recombination.
How do carbon materials improve photocatalytic performance?
Carbon materials like graphene, CNTs, and carbon quantum dots offer high electrical conductivity, large surface area, and excellent stability. When integrated into heterojunctions, they facilitate charge transfer, reduce electron-hole recombination, and extend light absorption, thereby boosting photocatalytic efficiency.
What are the main applications of carbon-based heterojunctions?
The primary applications are photocatalytic hydrogen (H2) generation from water splitting and CO2 reduction to solar fuels such as methanol, methane, and carbon monoxide, contributing to clean energy production.
What are the current challenges in carbon-based photocatalysts?
Challenges include achieving high stability, optimizing charge transfer kinetics, scaling up synthesis, and improving selectivity for desired products. Future research focuses on designing novel carbon-based heterojunctions with enhanced performance and durability.
Why is this review important?
This review provides a comprehensive overview of carbon-based Z-scheme and S-scheme heterojunctions, highlighting recent advances and offering insights for future development. It serves as a valuable resource for researchers in photocatalysis and clean energy.
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