Photokatalyse

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Photocatalysis is the induc­tion and accel­er­a­tion of reac­tions by the action of light. Photocatalysis involves absorp­tion of light in a semi­con­ductor with a suit­able distri­bu­tion of energy states. Upon irra­di­ation of the semi­con­ductor with light of energy exceed­ing the bandgap energy, an elec­tron is promoted to the valence band and leaves a hole in the valence band. These photo­gen­er­ated charge carri­ers can drive redox reac­tions either with molecules adsorbed on or close to the surface of the photocata­lyst: for self-clean­ing prop­er­ties, dissolved or adsorbed contam­in­ants are oxid­ized to yield ulti­mately CO2, mineral salts and mineral acids.

This phenomenon was first detec­ted on single crys­tals of TiO2 in the rutile modi­fic­a­tion, but research has shown that nano­struc­tured anatase TiO2 is the better cata­lyst.

TiO2 remains the most widely invest­ig­ated photocata­lyst so far.

 Applications of photocatalysis
  • Self clean­ing surfaces
  • Waste water treat­ment
  • Superhydrophilic surfaces

Photocatalysis has been used in archi­tec­ture and in water treat­ment mainly. In archi­tec­ture self-clean­ing windows and facades are among the main applic­a­tions. Attempts have also been made with indoor photocata­lysis. However, due to severely lower indoor UV levels, photocata­lysis is signi­fic­antly less effect­ive. Efforts have been made to shift the bandgap energy of TiO2 into the visible light region by doping with e.g. W.

Another poten­tial applic­a­tion of photocata­lysis is waste water treat­ment by water oxid­iz­ing contam­in­ants on a sunlight illu­min­ated photocata­lyst.

To quantify differ­ent photocata­lysts, AAC has developed a test setup, where cata­lysts can be exposed to a model analyte.

AAC Photocatalysis Test Reactor

AAC has developed a flow through reactor to meas­ure the photocata­lytic activ­ity of a photocata­lyst. The reactor consists of a flow through cell where the photocata­lyst is brought into close contact with dye solu­tion. Through a quartz window the cata­lyst is illu­min­ated with a Hg lamp. The dye solu­tion is cycled through the system and the dye concen­tra­tion is meas­ured photo­met­ric­ally in a second flow cell.

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