Photochemical Kinetics Of Small Molecules On Titanium Dioxide

Titanium dioxide has been extensively investigated as a catalyst, particularly in applications involving photodegradation of organic molecules and water splitting, which have important implications in environmental remediation and clean energy.In this thesis, a surface photochemical apparatus based on high sensitivity mass spectrometry has been constructed, the combination of laser-induced photocatalysis with a mass spectrometer having extremely low background provides a tool to probe photocatalytic chemistry with detecting methods of temperature programmed desorption (TPD) and time-of-flight (TOF).The experimental results show that dissociation of CD3OH on Rutile (110) occurs in a stepwise manner in which the O桯dissociation proceed first and is then followed by C-D dissociation by irradiating a CD3OH adsorbed Rutile (110) surface with400nm light. Through the detection of volatile products after irradiation by TPD, we have found that HCOOCH3is formed by the cross-coupling reaction of CH3O and CH2O, which are products of the first and second dissociation step, respectively, in the stepwise photocatalysis of CH3OH on Rutile (110). And we have also investigated deuterium formation from photocatalysis of the fully deuterated methanol (CD3OD) on Rutile (110) at400nm. Photocatalytic dissociation products formaldehyde (CD2O) and D-atoms on BBO sites (via D2O TPD product) have been detected. In addition to D2O formation by heating the photocatalyzed methanol/Rutile (110) surface, we have also observed D2product formation. D2is clearly formed via thermal recombination of the D-atoms on the BBO sites from photocatalysis of methanol. Photoinduced decomposition of formaldehyde and acetaldehyde on a Rutile (110) surface need be assisted by bridge-bonded oxygen atoms.Photocatalysis of CH3OH on Anatase (101) has been investigated using TPD method with266nm light at low surface temperatures. Experimental results show that CH3OH adsorbs on the Anatase (101) surface predominantly in molecular form, with only a small amount of CH3OH in dissociated form. Photocatalytic products, formaldehyde (CH2O) and methyl format (HCOOCH3), have been detected under266nm light irradiation. In addition to H2O formation, H2product is also observed using TPD spectroscopy. Experimental results indicate that H2product is formed via thermal recombination of H-atoms on the BBO sites from photocatalysis of CH3OH on the Anatase (101) surface, and H2production on the Anatase (101) surface is significantly more efficient than that on the Rutile (110) surface. Photocatalytic water splitting on Rutile (110) at two UV wavelengths (266and400nm) has been investigated using the laser surface photolysis method, in combination with the TPD and TOF techniques. Gas phase OH radical dissociated from H2O on Tisc sites has been clearly detected at266nm, while no evidence of H2O photocatalytic dissociation was found at400nm. Experimental results show that the dissociation probability of0.25ML H2O covered Rutile (110) surface is larger than16%. With increasing coverage, the dissociation probability of H2O on Rutile (110) is strongly depressed. This is attributed to the formation of hydrogen bond networks at high water coverage surface.