Adsorption Performance and Mechanisms of Copper by Soil Glycoprotein-Modified Straw Biochar

Abstract

Biochar is one of the most promising crop straw utilization pathways. However, its capacity for adsorbing heavy metals is limited, and there is a potential risk of secondary pollution, highlighting the importance of developing efficient and environmentally friendly bio-modification methods. Here, we utilized glomalin-related soil protein (GRSP), a byproduct from arbuscular mycorrhizal fungi, to modify straw biochar, developing a novel composite material and systematically evaluating its performance in removing copper ion (Cu2+) from aqueous solutions. Biochar samples derived from maize, wheat, and rice straw were prepared at three pyrolysis temperatures (300 °C, 500 °C, and 700 °C), followed by surface functionalization with GRSP to produce GRSP-modified straw biochar for Cu2+ adsorption experiments. The results demonstrated that the abundant functional groups (e.g., amino and carboxyl groups) in GRSP and the porous structure of the straw biochar exhibited a significant synergistic effect, enhancing the adsorption capacity for Cu2+. Notably, the GRSP-modified wheat straw biochar prepared at 700 °C achieved an adsorption capacity of 193.2 mg g−1 for Cu2+, representing a 76% improvement over the unmodified material. Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy revealed that hydroxyl, carboxyl, and ether groups served as key adsorption sites for Cu2+, while the hydrophobic-acid precipitation characteristics of GRSP further enhanced the material’s recoverability. By systematically characterizing the material’s microstructure and its adsorption behavior toward Cu2+, this study elucidated the role of critical functional groups in the adsorption mechanism. This work not only offers a low-carbon and efficient strategy for agricultural waste valorization and heavy metal pollution control, but also advances the mechanistic understanding of “bio-abiotic” synergy in environmental remediation.