Biochar derived from different biomass feedstocks exhibits varying capabilities in removing heavy metals from aqueous solutions, with the effectiveness largely dependent on both the source material and the pyrolysis conditions. In this study, biochars were produced from two abundant waste materials—paper mill sludge (PMS) and rice straw (RS)—using nitrogen (N₂) or carbon dioxide (CO₂) as purging gases during pyrolysis at 600 °C. The resulting biochars demonstrated significant differences in surface properties and adsorption performance for cadmium(II), copper(II), nickel(II), and lead(II). The Langmuir model revealed that lead(II) had the highest adsorption capacity among all tested metals, reaching up to 256.4 mg g⁻¹ for PMS-N₂ biochar and 133.3 mg g⁻¹ for RS-N₂ biochar. In contrast, nickel(II), cadmium(II), and copper(II) showed lower capacities, ranging between 40.MMP9 Antibody Epigenetic Reader Domain 2–64.C20orf30 Antibody Autophagy 1 mg g⁻¹, 29.5–42.7 mg g⁻¹, and 18.5–39.4 mg g⁻¹, respectively. These findings highlight a clear trend: lead(II) is preferentially adsorbed due to its smaller hydrated radius and stronger interaction with functional groups on the biochar surface.
The type of feedstock was the dominant factor influencing adsorption capacity, outweighing the effect of the purging gas. PMS-derived biochars consistently outperformed RS-based ones, particularly in lead(II) removal. This superior performance is attributed to the higher mineral content—especially calcium and iron—in PMS, which enhances cation exchange capacity and promotes metal binding through electrostatic interactions. Additionally, PMS biochars exhibited greater surface area (up to 31.PMID:35178611 6 m² g⁻¹) and pore volume compared to RS biochars (1.8–10.9 m² g⁻¹), facilitating increased access to active adsorption sites. Notably, while CO₂ purging slightly reduced surface area and porosity in RS biochars, it had minimal impact on PMS biochars, suggesting that the catalytic role of Fe and Ca minerals in PMS mitigates the degrading effects of CO₂.
Adsorption kinetics followed a pseudo-second-order model, indicating chemisorption as the primary mechanism. Intraparticle diffusion analysis revealed that film diffusion dominated the initial phase, accounting for 30–62% of total adsorption within the first hour, while pore diffusion acted as the rate-limiting step. Surface functional groups such as hydroxyl and carbonyl played crucial roles in metal complexation and ion exchange, especially for Pb(II) and Cu(II). The presence of oxygen-containing species, confirmed by XPS and Raman spectroscopy, further supports these mechanisms. Despite the higher surface area of some RS biochars, their overall adsorption capacity remained lower than PMS counterparts, likely due to competitive inhibition by silicon-rich compounds and diminished functional group abundance under CO₂ atmosphere.
In conclusion, the design of effective biochar sorbents for heavy metal remediation must prioritize feedstock selection over pyrolysis gas choice. PMS biochars, particularly those produced under N₂, offer exceptional potential for treating industrial wastewater contaminated with toxic metals like lead and copper. Their high surface area, rich mineral content, and favorable surface chemistry make them ideal candidates for scalable, low-cost environmental applications. Future research should focus on optimizing real-world conditions, including pH variation, co-existing ions, and long-term stability, to fully realize the practical utility of these biochars in water treatment systems.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
