The role of process parameters on photooxidative degradation of 2,4-D herbicide using TiO2 nanoparticles: Kinetic and mechanistic study

Abstract

This systematic study investigates the effect of a wide range of TiO₂ nanoparticles on the kinetics and mechanism of photocatalytic degradation of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). Changes in degradation rate, mineralization, and transformation pathways of 2,4-D correlated with nanoparticle physicochemical properties such as phase composition, size, and total pore volume. Primary intermediates, including hydroxylated chlorophenoxyacetic acids and 2,4-dichlorochlorophenoxy derivatives, were identified and their formation yields linked to the acid-base behaviour of 2,4-D. A comparison with homogeneous UV/H₂O₂-assisted degradation showed similar distribution of hydroxylated aromatic degradation intermediates as with large anatase nanoparticles (70 nm), while smaller particles facilitated pathways leading to the direct 2,4-D mineralization. DFT calculations supported experimental findings, and a scheme of the oxidative degradation of 2,4-D was proposed. Our results demonstrate that monitoring not only pollutant degradation but also overall mineralization is essential for evaluating photocatalysis efficiency and potential for practical applications.