Abstract:
This article explores the synthesis, characterization, and application of bimetallic Ag/MgO/biochar nanocomposites for wastewater treatment.The article is focusing on the removal of organic pollutants like methylene blue (M.B.) and tetracycline (TCN). Using a solvent-free ball milling technique, biochar derived from rice straw is combined with silver and magnesium oxide nanoparticles. The research demonstrates how the synergy between adsorption and photocatalytic degradation can enhance the treatment of polluted water. Adsorption is described by both Langmuir and Freundlich models. Photocatalytic degradation achieved up to 80% removal efficiency under optimal conditions. The study highlights the potential for these nanocomposites in treating wastewater.
Introduction
The paper addresses the global challenge of wastewater pollution, highlighting the need for innovative and cost-effective technologies. Water scarcity, fluctuating rainfall, and environmental contamination necessitate new methods to reclaim wastewater for reuse. Organic pollutants such as dyes and pharmaceutical residues, including antibiotics like tetracycline (TCN). They are especially problematic due to their persistence and harm to the environment and human health. The study proposes using biochar in combination with metal oxides like silver (Ag) and magnesium oxide (MgO). It is to create a multifunctional nanocomposite. This material could simultaneously remove pollutants through adsorption and catalyze their breakdown via photocatalysis.
Materials and Methods
To synthesize the Ag/MgO/biochar nanocomposites, the authors employed a solvent-free ball milling technique. This method is environmentally friendly, scalable, and efficient, producing nanocomposites with improved surface characteristics. The synthesis process started with rice straw biochar, silver nitrate (AgNO3), and magnesium chloride hexahydrate (MgCl2.6H2O). The ball milling process, carried out for 12 hours at 400 rpm, improved the structural properties of the biochar. By increasing its surface area and introducing (Katiyar, 2024 #2470)g porosity, essential for both adsorption and catalytic activities. Characterization techniques such as X-ray photoelectron spectroscopy (XPS) confirmed the successful incorporation of Ag and MgO onto the biochar surface. It is crucial for enhancing its pollutant-removal properties (Rehan, 2024 #2471).
Adsorption Performance of Ag/MgO/Biochar Nanocomposites:
The study evaluated the ability of the nanocomposites to adsorb methylene blue (M.B.), a common dye pollutant. Adsorption tests showed that the Nanocomposites performed well in removing M.B. from water, especially within the first 20 minutes due to the large number of active adsorption sites. The kinetic analysis revealed that the adsorption process followed a pseudo-second-order model, indicating that chemisorption was the rate-limiting step. The adsorption process was enhanced by the mesopores and macrospores introduced during ball milling, which allowed for greater pollutant capture. The Langmuir and Freundlich adsorption isotherms were used to model the adsorption data, with both fitting well, confirming the nanocomposite’s high adsorption capacity (Kalsoom, 2024 #2472).
Photocatalytic Analysis:
In addition to adsorption, the study explored the photocatalytic degradation of tetracycline (T.C.), an antibiotic pollutant. The nanocomposite was subjected to light irradiation to evaluate its efficiency in breaking down T.C. into less harmful components. Under optimal conditions pH 6, a T.C. concentration of 50 ppm, and a nanocomposite dose of 0.01 g—the photocatalytic degradation efficiency reached 80.26%. The results showed that hydroxyl radicals (•OH) generated during the photocatalysis process played a crucial role in breaking down T.C. The study also examined the impact of pH, temperature, and the presence of hydrogen peroxide (H₂O₂), which further boosted the photocatalytic activity by generating additional radicals (James et al., 2012).
Adsorption Mechanism and Isothermal Models:
The article discusses the mechanisms behind the nanocomposites’ adsorption abilities. The adsorption of methylene blue was found to be influenced by both electrostatic interactions and the physical structure of the biochar, which included abundant mesopores and macro-pores. The Langmuir and Freundlich models were used to describe the adsorption behavior, showing that the process could involve both monolayer adsorption on a homogeneous surface (Langmuir) and multilayer adsorption on a heterogeneous surface (Freundlich). The high surface area created through ball milling and the presence of functional groups like C-O and C=C bonds allowed the nanocomposites to exhibit strong adsorptive properties (Manikandan, 2025 #2473).
Photocatalytic Degradation:
The study also highlights the photocatalytic degradation of tetracycline. Key factors influencing this process included pH, temperature, and catalyst dosage. Photocatalysis was most efficient at a pH of 6, where the surface of the nanocomposite was most reactive. When the amount of H₂O₂ was increased, the removal efficiency also improved, demonstrating that the presence of additional oxidizing agents could enhance the degradation process. The authors also investigated the effect of temperature, finding that an increase in temperature to 30°C significantly improved photocatalytic efficiency. However, the study noted a decline in performance after several reuse cycles, indicating some limitations in the material’s long-term stability (Mohamed, 2012 #2474).
Future Scope and Recommendations
The authors suggest several areas for future research. First, more work is needed to optimize the pyrolysis conditions used to create biochar, as this can greatly affect the material’s adsorption capacity. Second, the authors recommend exploring other metal oxides or combinations that could improve photocatalytic efficiency. Lastly, they suggest further investigation into the stability and recyclability of the Ag/MgO/biochar nanocomposites to ensure that they can be used in real-world applications over extended periods without significant loss of efficiency (Mohamed, 2012 #2474).
Conclusion
The study concludes that the bimetallic Ag/MgO/biochar nanocomposites synthesized via ball milling exhibit high potential for wastewater treatment. The combination of adsorption and photocatalytic properties allows for effective removal of both dyes and antibiotics, making the material versatile for treating a variety of pollutants. The study successfully demonstrates the benefits of integrating metal oxides into biochar to enhance its functionality, but also points out the need for further research into the long-term application and environmental impacts of these nanocomposites.
Key References
- Freundlich, H., & Langmuir, I. Adsorption models applied in the study.
- Kumar, M., Xiong, X., Wan, Z. (2020). “Ball milling as a mechanochemical technology for novel biochar nanomaterials,” Bioresource Technology.
- James, S. L., Adams, C. J., Bolm, C., et al. (2012). “Mechanochemistry Opportunities for new and cleaner synthesis,” Chemical Society Reviews.
