Agricultural soils worldwide face increasing pressure from chemical pesticide buildup, which threatens long-term food security, soil microbial health, and ecosystem stability. Among the widely used agricultural chemicals, the herbicide 2,4-dichlorophenoxyacetic acid remains popular due to its low cost and effectiveness against broadleaf weeds. However, its persistence in soil poses serious environmental hazards and chronic health risks to humans. Traditional physical and chemical remediation techniques often disrupt native soil structures, kill vital microbial communities, or risk introducing secondary environmental pollutants. To address these limits, researchers in Scientific Reports investigated an innovative green remediation technique using a dual-action nanocomposite.

The research team, led by Weldmichael Solomon Tibebu, synthesized a composite material by combining plant-derived biochar from Rumex abyssinicus with metal-free graphitic carbon nitride through a ball-milling process. This material design combines two complementary mechanisms: physical adsorption and light-driven photocatalysis. The stable biochar backbone provides an extensive porous network with high surface area and alkaline mineral oxides that readily capture herbicide molecules. Concurrently, the graphitic carbon nitride component acts as a visible-light-harvesting semiconductor. By integrating the biochar core with the polymeric carbon nitride sheets, the team narrowed the overall electronic bandgap to 2.30 electron-volts, allowing the material to efficiently harness visible light rather than relying on energy-intensive ultraviolet radiation.

To systematically evaluate the performance of this system, the scientists conducted controlled soil microcosm experiments optimized through a response surface methodology known as central composite design. The team evaluated three key operational parameters: initial pesticide concentration, nanocomposite dosage, and total incubation time. Experimental results confirmed that increasing the catalyst dose significantly improved herbicide destruction by expanding available active surface sites and boosting radical generation. Under optimal conditions, the nanocomposite achieved near-complete soil detoxification, removing up to 94.84% of residual herbicide at low initial contamination levels and maintaining high degradation rates even under heavy pollutant loads.

Kinetic analyses revealed that the soil remediation reaction followed a pseudo-first-order rate law, confirming that degradation speed depends directly on pollutant availability at the catalyst interface. Furthermore, radical quenching experiments provided crucial mechanistic insights into the degradation process. While photogenerated holes and hydroxyl radicals contributed to pollutant breakdown, superoxide radicals emerged as the dominant reactive oxygen species responsible for breaking down the herbicide molecule. Periodic soil surface mixing and controlled moisture levels ensured continuous mass transfer and light absorption across the active soil-air boundary, overcoming common light-attenuation barriers inherent to solid soil matrices.

Compared to conventional treatment strategies such as clay sorption, thermal treatment, or metal-based photocatalysis, this metal-free nanocomposite offers superior environmental safety, high efficiency, and operational simplicity. By utilizing low-cost agricultural biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More and non-toxic carbon networks, this dual-action technology establishes a sustainable path forward for large-scale agricultural soil detoxification and environmental restoration.

Source: Tibebu, W. S., Worku, A., Aschale, M., & Weldmichael, T. G. (2026). Enhanced photocatalytic removal of 2,4-dichlorophenoxyacetic acid in soil using biochar and graphitic carbon nitride nanocomposites optimized by central composite design. Scientific Reports, 16, Article 69178.