In a recent study published in BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, Yani Zang and colleagues from institutions including the Harbin Institute of Technology, Harbin Corner Science & Technology Inc., Yancheng Institute of Technology, and Jilin University, have unveiled a groundbreaking approach to tackle industrial wastewater pollution. Their research focuses on developing a high-performance, metal-free photocatalyst by precisely regulating the structure of graphitic carbon nitride (CN) and combining it with biochar (BC) to activate sulfites for the degradation of organic pollutants. This innovative material, termed BVCN, shows significant promise for treating refractory pollutants under solar light, presenting a sustainable solution for industries like paper, printing, and dyeing.

Industrial activities, particularly the paper industry, generate vast amounts of highly polluted wastewater containing difficult-to-degrade and toxic substances like azo dyes. While advanced oxidation processes (AOPs) are effective, many common reagents are expensive or toxic. Sulfites, often industrial byproducts, offer a more environmentally friendly alternative, as they can be activated by photocatalysts to produce highly reactive radicals for pollutant degradation. However, traditional photocatalysts often contain transition metals, leading to secondary pollution. This highlights the need for metal-free, non-toxic, and highly efficient photocatalysts.

Graphitic carbon nitride (CN) is an attractive metal-free semiconductor that can be excited by visible light. However, its practical application has been limited by a high recombination rate of photogenerated carriers and a small specific surface area. To overcome these limitations, the researchers engineered CN by introducing nitrogen vacancies and nitrogen doping. These modifications were found to trap electrons, regulate the electronic structure, and form mid-gap states, all contributing to enhancing the separation of photogenerated carriers.

The integration of biochar proved to be a critical component of the BVCN photocatalyst. Biochar, with its abundant and inexpensive raw materials and simple preparation, serves multiple functions. It acts as both an electron transfer channel and an electron storage medium, facilitating electron delocalization through π-π interaction with the structurally regulated CN (VCN). This effectively inhibits the recombination of photogenerated carriers, thereby boosting the photocatalytic efficiency. Furthermore, biochar’s large specific surface area provides more active sites for pollutant adsorptionBiochar has a remarkable ability to attract and hold onto pollutants, like heavy metals and organic chemicals. This makes it a valuable tool for cleaning up contaminated soil and water.   More and degradation.

The performance of the synthesized BVCN was rigorously evaluated using Reactive Red 120 (RR120) dye as a model pollutant. The photocatalyst with 5wt% biochar (5BVCN) demonstrated exceptional performance. In a sulfite-containing solution, the reaction rate constant for RR120 degradation reached 0.0247 min⁻¹. This rate was 5.49 times higher than that of CN and an impressive 15.43 times higher than 5BVCN in a sulfite-free solution. The system also achieved a remarkable 92.0% degradation of RR120 within 90 minutes, with a total organic carbon (TOC) mineralization rate of 52.1%.

Further analysis revealed that in the sulfite-containing system, the primary active species responsible for degradation were sulfite radicals (SO3⋅−​), superoxide radicals (∙O2−​), and holes (h+). The researchers also found that 5BVCN exhibited excellent stability and recyclability, maintaining 70.49% RR120 degradation efficiency after five cycles. This reusability is crucial for practical, large-scale wastewater treatment applications. The study provides a strong theoretical foundation for a “treating waste with waste” strategy for industrial wastewater through photocatalysis.

Source: Zang, Y., Ding, J., Wang, J., Chen, C., Sun, H., Pang, J., Zhang, L., Ren, N., Ding, L., & Yang, S. (2025). 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(1), 76.