EPR ENDOR STUDY OF THE DECAY OF TRAPPED RADICALS IN PHOTOPOLYMERIZED BUTANE-1,4-DIOL DIACRYLATE

Long-lived trapped radicals produced during the photopolymerization of butane-1,4-diol diacrylate (BDDA) were studied by EPR and ENDOR spectroscopy and their thermal decay was followed by EPR measurements at different temperatures (40-120-degrees-C) for kinetic study. The EPR signal showed the superimposition of two different patterns, a three-line and a single-line spectrum. Both EPR patterns decayed following first-order kinetics in the investigated temperature range. Activation parameters of the decay were obtained. The EPR patterns were attributed to the same radical species situated in fluid and in cross-linked regions of the photopolymerized BDDA. Radicals of the latter kind undergo electron spin exchange strong enough to wash out the hyperfine splitting. The single-line width is mainly determined by electron spin dipole-dipole interactions. The ENDOR response is only of the matrix kind, typical of radicals in a solid phase. The present model was also compared with recent literature reports

Membrane-Assisted Charge Separation and Photocatalytic Activity in Embedded TiO2: A Kinetic and Mechanistic Study

TiO2 dispersed in polyester acrylate membranes was tested as a photocatalyst in the phenol mineralization reaction assisted by molecular oxygen. Kinetics experiments revealed that, although embedded, the oxide maintains significant catalytic activity. This result was first attributed to the homogeneous dispersion inside the polymeric host of TiO2 nanocrystals, which can be easily irradiated and interact with the reactants. Furthermore, the investigation of the photogenerated charge carriers in the photocatalyst demonstrated that electrons are trapped on Ti3+ centers, while holes are trapped on C-centered species of the polymer matrix. In the presence of O-2, the C-centered radicals of the polymer transform into peroxy radicals, reinforcing the charge separation in the polymer-embedded oxide with respect to the powder. The positive interference of the polymer matrix in reinforcing the electron hole separation is responsible for the relevant photoactivity of the embedded TiO2

Efficacy of the Reactive Oxygen Species Generated by Immobilized TiO2 in the Photocatalytic Degradation of Diclofenac

We report on the photodegradation of diclofenac (DCF) by hydrothermal anatase nanocrystals either free or immobilized in porous silica matrix (TS) in connection to the type and amount of reactive oxygen species (ROS), in order to have deeper insight into their role in the photocatalysis and to provide an effective tool to implement the DCF mineralization. TiO2 and TS exhibit a remarkable efficiency in the DCF abatement, supporting that the utilization of anatase nanoparticles with the highly reactive {001}, {010}, and {101} exposed surfaces can be an effective way for enhancing the photooxidation even of the persistent pollutants. Furthermore, the hydrothermal TiO2, when immobilized in silica matrix, preserves its functional properties, combining high photoactivity with an easy technical use and recovery of the catalyst. The catalysts performances have been related to the presence of OH•, O21, and O2-• species by electron paramagnetic resonance spin-trap technique. The results demonstrated that the ROS concentration increases with the increase of photoactivity and indicated a significant involvement of O21 in the DCF degradation. The efficacy of TiO2 when immobilized on a silica matrix was associated with the high ROS life time and with the presence of singlet oxygen, which contributes to the complete photomineralization of DCF