Biowaste valorization: multifunctional hybrid lignin/TiO2 nanostructures for bacterial-biocide disinfection and dye removal

Abstract

An urgent goal is to enhance the economic and environmental value of biowaste via recycling and conversion techniques. Lignin, a plentiful plant polymer, holds significant potential for the development of sustainable multifunctional materials. Despite its advantages in terms of red-ox and pollutant adsorption properties, challenges in lignin valorization must address its chemical complexity and tendency to aggregate in water. We demonstrate that lignin and TiO₂ can be intimately combined through a versatile in situ hydrothermal strategy to obtain hybrid multifunctional nanostructures with tunable functionalities. An in-depth physicochemical analysis elucidates the structure–property–function correlations. The synergistic combination of lignin and TiO₂ in hybrid nanoparticles enhances ROS-scavenging/generating properties. Indeed, a lignin content of 20% wt/wt within nanostructures (TiO₂_DL200 sample) resulted in nanoparticles with improved antibacterial/antimycotic properties (15 mm increase in the diameter of bacterial growth inhibition (DDK) and 3-fold decrease in the minimum inhibitory concentration (MIC) against fungi compared to neat TiO₂ nanoparticles and around 1.3 mm DDK increase and 3-fold MIC decrease against fungi compared to neat lignin) and 90% radical scavenging activity in only 2 minutes. In addition, TiO₂_DL200 nanoparticles achieved nearly 80% and 90% removal of methylene blue (MB) and fuchsin (F) dyes, respectively, by adsorption within 5 minutes. Conversely, by tuning the lignin content within the hybrid nanomaterial, a trade-off between the adsorption capacity and the photocatalytic activity is achieved, with MB and F removal efficiencies exceeding 80% in 120 minutes under UV-A conditions for TiO₂_DL50. These outcomes prove the potential uses of the obtained hybrid nanoparticles as antioxidant, antibacterial and antifungal additives and for the decontamination of dyes in water remediation.