Antimicrobial and Antioxidant Activity of Zinc-Modified Coconut Husk Biochar

This study aimed to develop a low-cost, multifunctional material with both antimicrobial and antioxidant properties by modifying zinc-derived biochar (BC) from coconut husks. The coconut husk BC was produced through oxygen-limited pyrolysis at 450°C and was subsequently modified using a zinc nitrate ion-exchange treatment to create zinc-modified biochar (Zn-BC). Characterization techniques such as X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy demonstrated the retention of the carbonaceous BC matrix along with zinc-containing crystalline domains identified as ZnO. While unmodified BC showed no detectable antimicrobial activity within the tested range (minimum inhibitory concentration [MIC] > 1 mg·mL^-1), Zn-BC inhibited all tested bacterial and fungal strains at an MIC of 0.5 mg·mL^-1. Zn-BC exhibited enhanced radical-scavenging activity compared to BC, achieving 67.0 ± 1.5% inhibition of DPPH radicals at 5 mg·mL^-1 and 57.6 ± 5.2% inhibition of ABTS radicals at 25 mg·mL^-1. Integration of waste-derived coconut husk BC with zinc modification results in a material that combines broad-spectrum antimicrobial activity with measurable antioxidant properties. These findings indicate the need for further evaluation of Zn-BC in water treatment, environmental applications, and the development of antimicrobial surfaces.