Enhanced phytoremediation in the removal of metal(loid)s from contaminated soils using a titanium dioxide/activated carbon nanocomposite as catalyst: Integrative physiological, biochemical, and proteomic insights

This study evaluates the effectiveness of titanium dioxide/activated carbon (TiO₂/AC) nanocomposites in enhancing the phytoremediation performance of vetiver (<i>Chrysopogon zizanioides</i>) grown in soil contaminated with potentially toxic elements (PTEs), including lead (Pb), cadmium (Cd), and arsenic (As). Incorporation of TiO₂/AC increased the pseudo-total accumulation of PTEs in roots and shoots, with combined uptake reaching 529.98 mg kg^-1 compared with 401.31 mg kg^-1 in untreated plants. Shoot concentrations reached 277.85 mg kg^-1 (Pb), 181.75 mg kg^-1 (Cd), and 70.38 mg kg^-1 (As). The adsorption behavior of TiO₂/AC followed Langmuir and Freundlich isotherms, with the Langmuir model showing superior fitting (<i>R</i>² > 0.99), indicating monolayer adsorption onto homogeneous surfaces. Soil concentrations of Pb, Cd, and As decreased by 92%, 59%, and 70%, respectively, over four months of treatment. Biochemical analyses indicated that TiO₂/AC enhanced antioxidant defense responses, increasing SOD, CAT, and POD activities while reducing malondialdehyde (MDA) and reactive oxygen species (ROS), indicating effective mitigation of oxidative stress. Metabolomic and proteomic analyses demonstrated enrichment of stress-related metabolites and differential expression of over 2,400 proteins associated with detoxification pathways. These results show that TiO₂/AC nanocomposites improve PTE bioavailability and uptake while strengthening plant physiological responses, supporting their potential application in controlled phytoremediation systems.