Measurement principle
The photocatalytic method is based on the semiconductor
(such as TiO2) acting as a photocatalyst for the redox process
due to its electronic structure, characterized by a filled
valence band and an empty conduction band. When it accepts
a photon with an energy equal to or greater than the
band gap, an electron is promoted to the conduction band,
leaving behind a positive hole in the valence band [20]. The
valence band holes are powerful oxidants, and can oxidatively
degrade organic compounds in aqueous solution. If
K2Cr2O7 is also present in the solution, it acts as an acceptor
of photogenerated electrons and is reduced [21,22]. The
whole reaction is shown as follows: