Hydroxymethyl Lignin‐Capped Silver Nanoparticles: Antimicrobial and Hydrogen Peroxide‐Sensing Ability

Abstract Lignin (Lg) fractionation overcomes the limitations of its heterogeneous nature. In this study, the effect of methanol fractionation on the thermal degradation, crystallinity, morphology, and chemical structure of lignin and its application in hydrogen peroxide sensing are investigated. Pristine Lg was separated into low‐molecular‐weight (LMwLg) and high‐molecular‐weight fractions (HMwLg), followed by modification to hydroxymethyl lignin (HmLg), which reduced silver ions in solution to silver nanoparticles (AgNPs). The functional groups, crystallinity, thermal profile, and morphology were then investigated using Fourier transform infrared spectroscopy, powder diffraction, thermal gravimetry, and scanning electron microscopy. LMwLg was found to be crystalline, highly hygroscopic, and had four thermal degradation stages, while HMwLg had several degradation stages and was amorphous. The sharp peaks in the LMwLg diffractogram were characteristic of sodium ions, while those in AgNPs‐HmLg were characteristic of AgNPs, as evidenced by the SPR peak at 428 nm whose intensity decreased in the presence of hydrogen peroxide. Moreover, AgNPs‐HmLg exhibited higher inhibitory activity toward Escherichia coli , Staphylococcus aureus , Pseudomonas aeruginosa , and Bacillus subtilis with inhibition zones of 10.67 ± 0.58, 11.50 ± 0.00, 10.33 ± 0.58, and 8.33 ± 0.57 cm as compared to pristine lignin. In conclusion, AgNPs‐HmLg detected the presence of hydrogen peroxide in solution and inhibited the growth of selected Gram‐positive and Gram‐negative bacteria.