Solar powered metal free catalyst turns industrial sulfite waste into a powerful tool for cleaning polluted water
image: Boosting solar-driven metal-free activation of sulfites by biochar-based photocatalyst for organic pollutants degradation: in-situ precise regulation and the enhancement mechanism
Credit: Yani Zang, Jie Ding, Jiayi Wang, Chengxin Chen, Hanjun Sun, Jiwei Pang, Luyan Zhang, Nanqi Ren, Lan Ding & Shanshan Yang
A research team from Harbin Institute of Technology has developed a new solar driven photocatalyst that uses industrial sulfite waste to rapidly break down toxic dyes in wastewater. The study demonstrates a sustainable approach that improves water quality while transforming an abundant industrial by product into a valuable resource.
The work focuses on a new biochar based carbon nitride material called BVCN. It is precisely engineered with nitrogen vacancies, nitrogen doping and biochar to activate sulfites under solar light. In tests with the common dye Reactive Red 120, the new material achieved a degradation rate of 92 percent in only 90 minutes. This result is five times faster than unmodified carbon nitride and more than fifteen times faster than using the catalyst without sulfites.
Sulfites are widely generated in pulp and paper production and are often treated as pollutants. The team found that sulfites can be activated by light to form very reactive radicals that attack complex dye molecules. However, this activation requires an efficient photocatalyst. Traditional catalysts often contain metals that may introduce secondary contamination. The new BVCN material contains no metals, and its low cost and high environmental safety make it suitable for large scale water treatment.
According to the research team, the key lies in the structural design. Nitrogen vacancies act as traps that hold electrons. Nitrogen doping adjusts the electronic structure and creates mid gap states that enhance light absorption. Biochar, which is rich in pyridinic nitrogen, provides a channel for electron transfer and also acts as an electron storage medium. Biochar also allows strong interactions between the catalyst and sulfite ions. As a result, the material absorbs more visible light, separates photogenerated electrons more effectively and exhibits improved stability.
“We aimed to design a catalyst that is efficient, inexpensive and environmentally safe” said the research team. “By combining structural control with biochar, we created a system that uses waste to treat waste.”
Experiments showed that the main reactive species in the system are sulfite radicals, superoxide radicals and photogenerated holes. These species work together to break down the complex structure of azo dyes through a series of reactions that eventually lead to carbon dioxide, water and inorganic salts. The catalyst maintained strong performance across a wide pH range and could be reused multiple times with minimal loss of activity.
The researchers also performed theoretical calculations to understand why the material works so efficiently. The models confirmed that nitrogen doping and vacancies enhance the transfer of electrons from sulfites to the catalyst. Biochar further strengthens this interaction and increases the adsorption of sulfites. Together, these features significantly boost the catalytic reactions under solar light.
Azo dyes are widely used in textile, printing and paper industries, and their wastewater is often highly toxic and difficult to treat. This new technology provides a promising route for cleaner and more sustainable wastewater management. By turning industrial by products into active reagents, it offers a practical strategy for reducing both pollution and treatment costs.
The study highlights the potential of advanced carbon based materials in green environmental technologies. With further development, the solar driven BVCN system could be applied in real industrial wastewater treatment plants and contribute to safer water resources.
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Journal Reference: Zang, Y., Ding, J., Wang, J. et al. Boosting solar-driven metal-free activation of sulfites by biochar-based photocatalyst for organic pollutants degradation: in-situ precise regulation and the enhancement mechanism. Biochar 7, 76 (2025).
https://doi.org/10.1007/s42773-025-00468-w
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About Biochar
Biochar is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.