Photocatalytic Dissociation Of CH₃OH On The ZnO?0001? Surface

In recent years,with the increasing environmental pollution and energy shortage,it is of great interest for scientists to solve these problems by using semiconductor materials as photocatalysts.Zinc oxide?ZnO?is an important semiconductor material with wide band gap,which has good photocatalytic properties.In addition,it is one of the photocatalysts that have been widely studied and used to date.ZnO can degrade various types of organic pollutants under ultraviolet?UV?light irradiation.It plays an important role in wastewater treatment and green energy.Simple alcohol molecules are often chosen as model systems to study the catalytic and photocatalytic processes of organic pollutants on the surface of semiconductor metal oxide.ZnO-based catalysts are often used in the synthesis of methanol?CH₃OH?.Furthermore,CH₃OH is often used as a probe molecule to study the active sites and catalytic activity of the catalyst surface.The structure and morphology of semiconductor materials are closely related to photocatalytic activity.The Zn0?0041?surface has the highest photocatalytic activity in the low-Miller-index surfaces of ZnO.In order to better understand the photocatalytic performance of ZnO,the temperature-programmed desorption?TPD?and time-of-flight?TOF?methods based on high sensitivity mass spectrometry were used in this experiment.The photocatalytic reaction mechanism of CH₃OH on Zn0?0001?surface was studied under the irradiation of 266 nm femtosecond laser.The experimental results showed that there are molecular adsorption and dissociation adsorption of CH₃OH molecules on ZnO?OOOl?surface.The products of thermochemical reaction are hydrogen?H₂?,water?H₂O?,formaldehyde?CH₂O?,carbon monoxide?CO?and carbon dioxide?CO₂?.The surface of ZnO?OOOl?has high catalytic activity for the dissociation of CH₃OH.Illumination can promote the dissociation of methoxy(CH₃O· to form CH₂O,which could be further oxidized to formate?HCOO'?.The H₂O at low temperature is due to the exchange reaction between the CH₃OH molecule adsorbed on the Zn site and H atom adsorbed on the O step edge atom,leading to the desorption of methyl group?CH₃-?from the surface during the TPD process.In addition,light may also promote the dissociation of CH₃OH into CH₂O and the cleavage of C-O bond in CH₃OH and CH₃O·.