Green synthesis of bromine by TiO2 heterogeneous photocatalysis and/or ozone: A kinetic study

Understanding of TiO2 catalysis mechanism in underwater pulsed discharge system: Charge carrier generation and interfacial charge-transfer processes

Compared with traditional photocatalysis system, TiO₂ charge carrier generation and interfacial charge-transfer process may be influenced by various chemical and physical effects in underwater pulsed discharge plasma system. Here, the role of high-energy electron, ozone in TiO₂ charge carrier generation and transfer process has been investigated using phenol as the probe molecule. The introduction of electron-trapping agent (KH₂PO₄) have an inhibiting effect on TiO₂ catalytic activity, indicating high-energy electrons played a significant role in TiO₂ catalytic process. EPR analysis showed that TiO₂ could be activated to initiate pairs of electron-hole by high-energy electrons from plasma, and the electrons on the conduction band (CB) could be trapped on the oxygen vacancies. XPS analysis showed that the Ti³⁺OH species formed during discharge process due to the capture of CB electrons by Ti⁴⁺OH groups located at the TiO₂ surface. The CB electrons transfer processes on TiO₂ surface was strongly dependent on the redox potential of electron acceptors, which adsorbed on the TiO₂ surface. The CB electrons can be transferred to dissolved O₃, resulting in more OH production. Meanwhile, the CB electron also transferred to benzoquinone adsorbed on TiO₂, resulting in accumulation of hydroquinone.

Three-Dimensional Calibration for Routine Analyses of Bromide and Nitrate Ions as Indicators of Groundwater Quality in Coastal Territories

Nitrate and bromide ions are generally considered indicators of anthropogenic pollution and seawater intrusion, respectively, in the groundwater of coastal territories. The analysis of these species is generally carried out with routine chromatographic analyses which generally afford partially merged or poorly resolved peaks. In the present paper a simple method for the correct evaluation of their concentration in water is reported. This method does not imply utilization of other instruments or technologies, only the mathematical elaboration of the data obtained from routine analysis of standard solutions containing the two species. Standard binary solutions of nitrate and bromide ions at different concentrations, ranging between 0.1 and 2 mM, were analyzed by means of ion chromatography. Splitting two partially merged chromatographic peaks and considering each resulting area as originating from a single species produces "measured" concentration values which differ from the nominal ones. Such a procedure generates errors (one per species) which can be written as a function of the above mentioned "measured" concentrations and which can be graphically represented by means of a surface in a three-dimensional (3D) space. In this way, "measured" concentrations of bromide and nitrate ions can be corrected by calculating the errors generated under the experimental conditions at which the chromatographic separation is performed. Notably, this is analogous with the two-dimensional (2D) calibration normally carried out for analytical purposes. Indeed, both methods allow estimation of the unknown concentration of species in solution by correlating the instrumental response with the concentration of standard solutions.