Hexavalent chromium (Cr(VI)) is a highly toxic industrial pollutant that poses severe risks to human health and aquatic ecosystems. Effective and sustainable methods for its removal from water are urgently needed. A new study published in Scientific Reports, conducted by Rajesh Juturu, Ramesh Vinayagam, Gokulakrishnan Murugesan, and Raja Selvaraj, introduces a novel magnetic 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 (MBC) synthesized from Acacia falcata leaves for efficient Cr(VI) adsorption. This research highlights the development and characterization of a low-cost, reusable adsorbent with high removal efficiency, addressing the critical need for sustainable wastewater treatment solutions.

The researchers prepared the magnetic biochar by chemically treating Acacia falcata leaves with ZnCl2​ and incorporating Fe3​O4​ nanoparticles using FeCl3​⋅6H2​O as a precursor. The choice of A. falcata leaves is strategic due to their abundance and rich phytochemical content, which contributes to both carbon yield and favorable surface functionalities for adsorption. The resulting MBC exhibited a high specific surface area of 248.11 m2/g, as determined by BET analysis, indicating ample binding sites for pollutants. Field Emission Scanning Electron Microscopy (FESEM) images revealed a highly porous structure with uniformly embedded Fe3​O4​ nanoparticles, which became smoother and more compact after Cr(VI) removal, suggesting effective pore blockage by chromium ions.

Further characterization confirmed the successful synthesis and properties of the MBC. X-ray Diffraction (XRD) spectra verified the incorporation of Fe3​O4​ with distinct peaks matching its cubic spinel structure and an average crystallite diameter of 40.74 nm. X-ray Photoelectron Spectroscopy (XPS) analysis indicated the active participation of various functional groups—including carboxyl, hydroxyl, carbonyl, and Fe3​O4​ groups—in the reduction and adsorption of Cr(VI). Specifically, XPS showed that 62.63% of the adsorbed Cr(VI) was converted to less toxic Cr(III), highlighting a redox-coupled removal mechanism. Vibrating Sample Magnetometry (VSM) data confirmed the superparamagnetic nature of the MBC, with a magnetic saturation of 5.44 emu/g, enabling easy separation and recovery from treated water using an external magnetic field. Thermogravimetric analysis (TGA) demonstrated the MBC’s thermal stability, retaining approximately 53% of its original mass even after heating to 800∘C.

Batch adsorption experiments were conducted to optimize Cr(VI) removal. An optimum pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More of 2 was identified, at which the MBC achieved a maximum Cr(VI) uptake of 41.72% with a corresponding adsorption capacity of 10.43 mg/g. This high efficiency at low pH is attributed to the predominant Cr(VI) species (HCrO4−​ and Cr2​O72−​ ) forming strong electrostatic interactions with the protonated surface of the MBC, as well as the enhanced reduction of Cr(VI) to Cr(III) under acidic conditions. The optimal MBC dose was determined to be 0.4 g/L, and a contact time of 3 hours was found to be sufficient for efficient removal. The maximum adsorption capacity obtained was 25.62 mg/g at 303 K.

The adsorption data best fit the Freundlich isotherm, indicating heterogeneous multilayer adsorption on diverse binding sites, and followed pseudo-second-order kinetics, suggesting that chemisorption (involving electron sharing and valence forces) is the primary mechanism. Thermodynamic studies confirmed that Cr(VI) removal was a spontaneous and endothermic process, favored by increasing temperature, with enthalpy and entropy values of 17.71 kJ/mol and 53.22 J/mol·K, respectively.

Crucially, the MBC demonstrated excellent reusability, maintaining over 76% removal efficiency for up to five cycles at the optimum pH of 2 and an MBC dose of 1.4 g/L, which is vital for cost-effectiveness and sustainability in practical applications. Furthermore, the MBC proved highly effective in real-world scenarios, successfully removing over 97.80% of Cr(VI) from various water sources including river water, lake water, groundwater, and tap water, confirming its practical potential for environmental remediation. This research provides a promising and sustainable solution for mitigating Cr(VI) pollution using a biochar derived from readily available 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.

Source: Juturu, R., Vinayagam, R., Murugesan, G., & Selvaraj, R. (2025). Synthesis and characterization of Zn and Fe doped magnetic biochar from Acacia falcata leaves for Cr(VI) adsorption. Scientific Reports, 15(1), 22146.