Mechanochemical Modification of Biochar Yields Durable Water-Repellent Coatings and Efficient Oil Adsorbents

In a groundbreaking advancement for sustainable materials science, researchers have developed an innovative, eco-friendly technique that transforms biochar into a highly hydrophobic, water-repellent material capable of absorbing substantial quantities of oil. This novel development opens new avenues for environmental cleanup technologies and green coating applications, promising enhanced sustainability and efficiency in addressing pollution challenges.

The study, recently published in the journal Biochar, showcases a solvent-free mechanochemical process that functionalizes biochar using octadecylamine, a long-chain amine molecule. Unlike traditional chemical modification methods, this approach replaces solvent-intensive reactions with a greener planetary ball milling technique, fundamentally altering the biochar’s surface properties under solvent-free conditions. The resultant hydrophobic material can be used as a coating on natural hemp fibers, endowing them with remarkable water repellency and exceptional oil absorption capabilities.

Biochar, a carbon-enriched substance produced through the pyrolysis of biomass, is prized for its porous architecture and expansive surface area. These properties have underpinned its wide exploration in fields such as soil amelioration, pollutant immobilization, and carbon sequestration. However, tailoring biochar’s surface chemistry conventionally demands wet chemical methods reliant on large volumes of solvents, which often entail significant environmental and economic costs. The new mechanochemical method circumvents these limitations, ensuring a more sustainable modification process.

In this innovative approach, the research team employed planetary ball milling to physically and chemically activate biochar. This technique forces intimate contact between biochar particles and octadecylamine molecules, facilitating covalent interactions without requiring solvents or elevated temperatures. This effective mechanochemical functionalization strategy generates hydrophobic coatings by grafting long alkyl chains directly onto the carbon-rich surface, significantly reducing polarity and enhancing microstructural roughness—both critical parameters for strong water repellency.

The researchers emphasize that this mechanochemical process represents a paradigm shift, enabling the synthesis of functionalized carbon materials without harsh reagents or environmentally damaging solvents. The synthesis takes place rapidly and under ambient conditions, underscoring its potential for scalable industrial applications. Moreover, this solvent-free method aligns with green chemistry principles, drastically cutting down chemical waste and energy consumption.

Once functionalized, the biochar can be dispersed in bio-derived solvents and applied via dip coating onto hemp fibers—a renewable, agricultural biomaterial. Contact angle measurements revealed that a single coating layer conferred a water contact angle of approximately 126°, indicative of pronounced hydrophobicity. In stark contrast, untreated hemp fibers absorbed water rapidly, highlighting the transformative effect of the biochar coating on surface characteristics.

Microscopic and morphological studies further substantiated these findings by illustrating increased surface roughness following coating. This roughness amplifies the hydrophobic effect by creating air pockets that hinder water adhesion. Such dual mechanisms—a chemically altered low-polarity surface coupled with enhanced topography—synergistically optimize water repellency, crucial for applications where moisture resistance is paramount.

Beyond water resistance, the coated hemp fibers excelled in oil absorption experiments, demonstrating the capacity to uptake up to fourteen times their own weight across various oil types, including sunflower, frying, motor, and pump oils. This extraordinary adsorption capacity, nearing 1400% of the fiber’s inherent mass, positions these materials as highly effective sorbents for oil spill remediation and wastewater treatment, where selective oil affinity combined with water repellence is essential.

The environmental implications of this innovation are profound. Both biochar and hemp originate from renewable biomass sources, while the processing solvent is derived sustainably from citrus waste byproducts. This integration of biodegradable materials and green processing techniques culminates in an oil sorbent technology that markedly diminishes the environmental footprint compared to conventional synthetic alternatives, aligning with circular economy principles.

Researchers project that this study not only introduces a practical route for eco-sustainable biochar functionalization but also exemplifies how mechanochemistry can unlock new functional material designs. The solvent-free strategy paves the way for scalable production of advanced carbon-based materials applicable in multiple sectors, including environmental remediation, composite manufacture, and water filtration technologies.

The team is currently exploring the upscaling potential of their process and investigating further functionalization possibilities to extend the utility of hydrophobic biochar coatings. These upcoming efforts may lead to deployable technologies for large-scale environmental cleanup and materials engineering, reinforcing the role of sustainable chemistry in addressing global ecological challenges.

This pioneering research underscores the synergistic power of combining renewable feedstocks, solvent-free mechanochemistry, and functional material science. It exemplifies a transformative approach that could revolutionize the development of hydrophobic coatings and oil sorbents, fostering a new generation of green materials tailored for environmental protection.

News Publication Date: 24-Feb-2026.

Web References: Biochar Journal, DOI 10.1007/s42773-025-00532-5.

References: Sozio, N., Kiani, A., Viscusi, G. et al. Mechanochemical functionalization of biochar for providing new eco-sustainable hydrophobic coating. Biochar 8, 32 (2026).

Keywords

Hydrophobic coatings, biochar functionalization, mechanochemistry, solvent-free synthesis, renewable materials, oil sorbents, environmental remediation, green chemistry, carbon materials, hemp fibers, sustainable coatings, water repellency.