REPOSITORY > RESULTS

Abstract

Water is one of the most important natural resources on Earth. Despite its abundant
resources, the water pollution is present due to ever growing human population and
accompanying industrial development. Even though there are many ecological actions
targeted to preserve this precious natural resource it is quite impossible to eliminate or
reduce water pollution completely. This is why there will always be a need for various
technologies for water purification either following industrial processes (wastewaters) or
even for conditioning of drinking water. This may be done by conventional available
treatment technologies; however they may be ineffective for removal of hazardous organic
compounds. This is why new advanced oxidation processes (AOP) are needed to eliminate
pollutants from wastewaters as well as from drinking water in order to improve the quality
of our life. In view of t his, m y R&D work within my thesis was focused on the use of
photoelectrocatalytic technology for degradation of hazardous organic pollutants. Within
my thesis, I have designed, assembled and characterized photoelectrocatalytic reactors with
an immobilized photocatalyst. The goal of my studies was to develop novel designs of
photoelectrocatalytic reactors and to investigate the influence of reactor design and
operational parameters on the efficiency of such systems.
The first part of my thesis was dedicated to the synthesis and characterization of active
photocatalyst in the form of ordered TiO2 nanotubes arrays that were obtained by the
anodic oxidation process of various metallic titanium forms (coils, foil, mesh). The influence
of the anodization parameters and annealing conditions on the nanotubes morphology and
their photocatalytic activity was investigated. It was found out that the most
photocatalytically active TiO2 nanotube arrays films (tested on caffeine degradation) were
obtained after anodization of metallic titanium forms at 60 V for 6 hours and after
subsequent annealing at 450 °C for 1 hour. The resulting polycrystalline TiO 2 nanotubes
had length of app 40 µm, grain size of app 5 to 10 nm and anatase crystal structure.
The second part of my thesis was focused on design and characterization of two types
of photoelectrocatalytic reactors, namely coil type microreactor and foil type reactor. The
photoelectrocatalytic activity of microreactors was investigated by measuring the
degradation of caffeine and phenol at different flow rates, UV light intensities, applied
external electrical potentials and supporting electrolyte conductivities. Four different
configurations of the photoanode and cathode were used. When an applied anodic bias
potential of 4 V w as used in the most efficient microreactor configuration, 1 mL of the 40
mg L 1 caffeine was fully decomposed in 55 min. It was found out that the most influential
parameters contributing to the microreactor efficiency are the position and surface area of
cathode coils placed inside the microreactor adjacent to photocatalytically active anode
coils. Cathode coils enable the photoelectrocatalytic process, which is far more efficient
compared to only photocatalytic oxidation. The scaled up version of the coil type
microreactor was used for the photocatalytic, electrocatalytic and photoelectrocatalytic
degradation of phenol. The highest initial phenol concentration of app 45.7 mg L 1 was
completely degraded at an applied potential of 16 V, a UV light intensity of app 2.8 mW
cm 2 , and a flow rate of 50 µL min 1 . In my study, the mechanisms of photocatalysis and
photoelectrocatalysis were proposed and validated with a three dimensional mathematical
model describing the governing processes occurring during the microreactor s operation.
Afterwards, a larger photoelectrocatalytic device, made of perforated anodized titanium
foils, was assembled. This reactor enabled degradation of organic compounds with larger
flow rates as compared to the coil type microreactor.