Biochar-Supported Magnesium-, Copper-, and Zinc Ammonium Carbonate Fertilizer Materials: Single-Pot Synthesis, Thermal Stability, Water Adsorption, Nitrogen Release, and Antifungal Activity

Abstract

Sustainable agricultural development requires novel composite materials to achieve nitrogen (N) storage, controlled release for effective plant uptake, and decreased volatilization and loss. Biochar is considered an emerging substrate that can be combined with nutrient-rich, waste-derived nitrogenous materials, as well as minerals, to serve not only as a sustainable source of carbon to enhance physical soil properties, but also as a host for complex, multinutrient fertilizers. While biochar has been shown to adsorb ammonium ions from diluted wastewater solutions, scalable solid-state synthesis methods, such as mechanochemistry for producing nutrient-rich fertilizer materials from waste-derived N sources and mineral nutrients, remain largely unexplored. In this work, double ammonium carbonate salts, including magnesium- (BC-MAC), copper- (BC-CAC), and zinc (BC-ZAC) ammonium carbonates, have been combined with biochar using the mechanochemical method in a single-pot reaction. The crystalline structure and temporal evolution of the particles were confirmed using X-ray diffraction and scanning electron microscopy, respectively, while thermogravimetric analysis revealed the complex thermal behavior of the resulting materials that evolved with storage time. The dynamic vapor sorption showed that while MAC lost 47% of its initial mass after one day of drying, 10BC-MAC lost about 37% under the same conditions. Nitrogen emissions measured showed that 10% biochar containing BC-MAC emitted ∼20% less N, compared to ammonium carbonate. This decrease in antifungal activity was tested and CAC properties were shown to be modulated by the biochar matrix. The significant effect of biochar on the structural and adsorption behavior of double salt ammonium carbonate materials highlights the potential of this composite design for agricultural applications, particularly in high nutrient content but low negative environmental impact fertilizer systems.