(68a) Influence of Different Catalysts Upon the Efficiency of the Photo CREC Water – II Reactor During the Photocatalytic Degradation of Phenol

This study reports the efficiency profiles for the reactor so called Photo CREC Water II, during the photo catalytic degradation   of phenol,  using the following catalysts, based on titanium dioxide (TiO₂): DP25, Anatase 1, Hombikat UV – 100, Anatase 2 (home prepared with Sol – Gel method), DP25+Fe, Anatase 2 + Fe. Each experiment was performed just with one catalyst.

The criteria to measure the reactor efficiency are the quantum yield (QY) and the Photochemical and Thermodynamic Efficiency Factor (PTEF). In order to calculate the efficiencies with PTEF, the main parameters are the total rate of reaction of the free radical OH^• (r_OH^•_,T),  enthalpy of OH^• radical formation (), the absorbed photons by the catalyst (Q_abs) and fraction of the absorbed energy contributed by photons with λ<380 nm (γ).

To calculate the total rate of reaction of the free radicals OH, the model compound and the majority of the intermediates were detected. It is shown that phenol yields hydroquinone, catechol, benzoquinone, acetic and formic acids as main intermediate species. A phenomenological unified kinetic model (UKM) based in a “series-parallel” reaction network is proposed, which further indicates to be useful and suitable for predicting the photodegradation of compounds in water and air. According to the stoichiometry of each reaction step, the reaction rate of OH radical consumption is related with the measurable and detected compounds. Then the sum of reaction rates for OH in each step is done to evaluate the total reaction rate of consumption of OH radicals for all the process degradation. The UKM follows a Langmuir-Hinshelwood kinetics with this being applicable to the various TiO₂ photocatalysts studied. The UKM requires a number of significant assumptions in order to be used effectively avoiding overparametization. This approach also requires that the adsorption constants be obtained independently. As a result, the UKM is adapted for each specific TiO₂ photocatalyst to describe the experimental photoconversion data. It is concluded that this approach provides good and objective parameter estimates with low to moderate cross-correlation among kinetic parameters and acceptable 95% CIs.

The method for the preparation of the catalyst is reported, and the results of the characterization for each catalyst are presented. A discussion of their relationship with the catalytic activity is performed. It is shown that the iron ions have an important effect and enhance the efficiency of the reactor during the experiments, and also it is shown that the maximum quantum yields obtained are above 60 %, indicating the suitability of the reactor Photo CREC Water II to achieve the photodegradation.