Eco-friendly grinding method transforms invasive weed into antibiotic sponge

A team of scientists from the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, has introduced an economical and environmentally friendly approach for cleaning antibiotic-contaminated water. The work, led by authors Jingqi Wu and Jiawei Chen, focuses on enhancing a carbon material called hydrochar, derived from the noxious invasive water hyacinth plant. By applying a simple mechanical grinding process, the team was able to nearly triple the material's capacity to adsorb the common antibiotic norfloxacin, presenting a promising new avenue for water remediation.

The presence of antibiotics like norfloxacin in surface and ground water poses significant risks to ecosystems and human health, potentially accelerating the development of antibiotic resistance. While hydrochar, a charcoal-like substance produced from biomass, is a known low-cost adsorbent, its performance can be limited. This team sought a green method to improve it without resorting to harsh chemicals or high energy consumption. They produced hydrochar from water hyacinth through hydrothermal carbonization and then subjected it to ball-milling, a physical process that grinds the material into finer particles.

A Mechanical Twist for Cleaner Water

The results of their aqueous batch adsorption experiments were striking. The ball-milled hydrochar (BMHC) prepared at 220°C exhibited a norfloxacin adsorption capacity of 68.53 mg per gram, a massive improvement over the 24.29 mg per gram capacity of the original, unmilled hydrochar. This superior performance was observed across a wide and environmentally relevant pH range of 5 to 9. The modified material also worked faster, reaching adsorption equilibrium in about 600 minutes compared to 1440 minutes for the untreated version.

Interestingly, the enhancement did not come from an increase in surface area, which is a common mechanism for adsorbents. The team’s analysis showed that ball-milling actually decreased the hydrochar's specific surface area. The true source of the improvement was a change in the material's surface chemistry. Characterization revealed that the ball-milling process increased the material's surface functional groups, aromaticity, and hydrophobicity. These alterations strengthened the forces of attraction between the hydrochar and the antibiotic molecules in the water.

Boosting Adhesion at the Molecular Level

The investigation into the underlying mechanisms confirmed that the improved performance stemmed from a combination of interactions. The increased number of functional groups on the hydrochar surface promoted the formation of hydrogen bonds with norfloxacin. Concurrently, the greater hydrophobicity of the ball-milled material amplified the hydrophobic interaction, a key driver for binding with the water-fearing portion of the antibiotic molecule. The process also appeared to enhance π-π electron-donor–acceptor interactions, further securing the pollutant to the hydrochar's surface. Thermodynamic analysis indicated the adsorption process was spontaneous and exothermic.

The corresponding author, Jiawei Chen from the China University of Geosciences, commented on the findings. "Our work demonstrates that a simple, mechanical modification like ball-milling can dramatically improve the performance of biomass-derived materials for water purification. We have effectively turned a problematic invasive plant into a highly effective tool for tackling pharmaceutical pollution, offering a sustainable, cost-effective solution that avoids additional chemical reagents."

From Nuisance Plant to Promising Pollutant Trap

This research offers a dual environmental benefit: it finds a valuable use for the invasive water hyacinth, a plant known for clogging waterways, while simultaneously creating a superior material for removing emerging contaminants from water. The ball-milled hydrochar proved to be robust and reusable over multiple cycles with minimal loss in adsorption capacity. An economic analysis suggests the production cost is highly competitive, making it a potentially viable option for large-scale applications.

While the study was conducted under controlled laboratory conditions, its findings pave the way for future investigations into real-world wastewater treatment scenarios. The success of this facile and green modification method suggests that ball-milling could be applied to other biomass-derived carbons to create a new class of powerful adsorbents for a variety of environmental pollutants, contributing to a more circular and sustainable economy.

Corresponding Author: Jiawei Chen

Original Source: https://doi.org/10.1007/s44246-024-00145-w

Contributions: All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Jingqi Wu, Tongshuai Wang, Shijia Li and Zilong Zhao. Wei Tang and Shuhan Yu revised the manuscript. Jiawei Chen acquired funding, supervised the study, and reviewed and edited the manuscript. The first draft of the manuscript was written by Jingqi Wu and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.