Photocatalytic water splitting is considered a promising route for producing green hydrogen because it can directly convert solar energy into chemical energy. CdS is particularly attractive because its relatively narrow bandgap allows it to absorb visible light, unlike many metal-oxide photocatalysts that primarily respond to ultraviolet radiation. However, its practical use remains constrained by photocorrosion, incomplete utilization of visible light, and rapid electron-hole recombination. CQDs can act as photosensitizers and electron acceptors, but many are produced from costly chemical precursors under harsh conditions involving hazardous reagents. Although biomass-derived CQDs offer a greener alternative, the use of structurally uniform cellulose-derived CQDs to regulate charge transfer in CdS photocatalysts has remained insufficiently explored.
A study (DOI: 10.48130/scm-0026-0020) published in Sustainable Carbon Materials on 08 June 2026 by Quan Sophia He's team, Dalhousie University, reports that cellulose-derived CQDs substantially improve the light absorption, charge separation, and hydrogen-production performance of CdS nanoparticles.
The researchers first prepared CQDs by heating corn-core-derived microcrystalline cellulose in water at 200 °C for 12 hours, followed by centrifugation, filtration, and dialysis. CdS nanoparticles were separately synthesized through a hydrothermal reaction involving cadmium chloride and thiourea. Different volumes of the CQD solution—6, 12, or 18 mL—were then combined with CdS to produce three composite catalysts. Electron microscopy, elemental mapping, X-ray diffraction, infrared spectroscopy, and X-ray photoelectron spectroscopy confirmed that CQDs averaging 3.5 nm in diameter were successfully anchored on the CdS surface without substantially changing its crystal structure. Optical measurements showed that CQD incorporation extended visible-light absorption and reduced the CdS bandgap from 2.05 eV to as low as 2.01 eV. The team evaluated hydrogen evolution using 20 mg of catalyst in 100 mL of water containing sodium sulfite and sodium sulfide as sacrificial agents. Under visible-light irradiation from a xenon lamp, all CQD-modified catalysts outperformed pristine CdS. After five hours, unmodified CdS generated 4,633.5 µmol/g of hydrogen, whereas composites prepared with 6, 12, and 18 mL of CQD solution produced 6,062.6, 7,812.5, and 6,855.6 µmol/g, respectively. The intermediate CQD loading therefore delivered the best performance. Excessive CQD coverage may obstruct active sites, reduce light penetration, or create additional charge-trapping centers. Photoelectrochemical measurements helped explain the improvement. The optimized composite reached a photocurrent density of 49.9 µA/cm², nearly 20 times the 2.63 µA/cm² recorded for pure CdS. Its interfacial charge-transfer resistance also decreased from 17.81 to 12.65 kΩ. Photoluminescence tests indicated reduced electron-hole recombination and longer carrier lifetimes. Together, the results suggest that CQDs perform two complementary functions: they broaden light absorption as photosensitizers and capture electrons from CdS to promote their transfer toward proton-reduction sites. Reuse experiments nevertheless revealed declining hydrogen output over three cycles, showing that CdS photocorrosion remains a durability challenge.
Overall, the study demonstrates that cellulose-derived CQDs can provide a simple, biomass-based means of improving CdS photocatalysts without noble metals or complicated architectures. The approach links renewable carbon feedstocks with solar-driven hydrogen production while revealing how CQD loading controls light absorption, charge transport, and surface reactions. Further work on protective coatings, cocatalysts, heterostructures, and CQD surface chemistry will be needed to suppress photocorrosion and improve long-term stability before the material can be considered for practical hydrogen-generation systems.
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References
DOI
10.48130/scm-0026-0020
Original Source URL
https://doi.org/10.48130/scm-0026-0020
Funding information
The authors are grateful for the financial support from the Discovery Grant, National Science and Engineering Research Council (NSERC), Canada, awarded to Dr. Quan Sophia He (Grant No. RGPIN-2026-06983).
About Sustainable Carbon Materials
Sustainable Carbon Materials (e-ISSN 3070-3557) is a multidisciplinary platform for communicating advances in fundamental and applied research on carbon-based materials. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon materials around the world to deliver findings from this rapidly expanding field of science. It is a peer-reviewed, open-access journal that publishes review, original research, invited review, rapid report, perspective, commentary and correspondence papers.