Effects Of Temperature And Light Intensity On Photocatalytic Properties Of Co-catalyst Modified TiO₂

The frequent air pollution events have facilitated the process of catalytic degradation of volatile organic compounds?VOCs?.Due to its significant advantages in safety,stability,and cost,TiO₂ has great potential for application in energy generation and air purification.In order to reduce the cost for eliminating VOCs,it is needed to explore the catalytic performance.As a matter of fact,photocatalysis relies on temperature and light intensity,so the photocatalysis not only belongs to a photochemical process,but also relates to heat processes.However,it is still unclear that the dominant role of photocatalysis and thermal catalysis and how light and heat work during the photocatalytic reaction.In this research,P25?TiO₂?is used as the substrate material and Au was loaded on the TiO2 by deposition precipitation method.The TiO2 and Au/TiO2 samples were studied by the TEM,XPS,and UV-Vis diffusion absorption to characterize the morphologies.The samples were used to study the catalytic performances of some volatile organics componds,including acetone,formaldehyde,and formic acid at different temperatures and light intensity.The dominant role of photocatalysis and thermal catalysis and how light and heat work during the photocatalytic reaction are discussed.The main conclusions are as follows:?1?The effect of temperature on the catalytic activities of TiO₂:Under dark conditions,formic acid has a significant thermal catalytic effect at temperatures higher than 155°C and acetone at 125°C except formaldehyde.Under UV light illuminations,the photocatalytic oxidation of formaldehyde and formic acid by TiO₂reaches a maximum at¹25°C.In photocatalytic oxidation of acetone by TiO₂,photocatalysis plays a dominant role when the temperature is less than 135°C,and thermal catalysis becomes important when the temperature is higher than 135°C.?2?The effect of light intensity on the catalytic activity of TiO₂:The photocatalytic reaction rate is positively correlated with the nth power of the light intensity?rate?intensityⁿ,with n?1?,thus indicating that when temperature is fixed and the light intensity are in the range of 1 to 5 mW cm^-2,the increased photocatalytic reaction rate is due to a photochemical process.In the photocatalytic reaction,the photochemical process?light?and the heat activation process?heat?have no synergistic effect.?3?The effect of temperature on the catalytic activity of Au/TiO₂:There is a significant thermal catalytic oxidation effect at 110°C in dark condition to catalyze acetone with Au/TiO2?trace?.The Au/TiO2?0.3%?is the same as TiO2.Under the UV light illumination,the photocatalytic oxidation rate reaches a maximum at¹55°C with Au/TiO₂?trace?.The photocatalysis plays a dominant role when the temperature is less than 170°C,and thermal catalysis plays a dominant role when the temperature is higher than 170°C.In photocatalytic oxidation of acetone with Au/TiO₂?0.3%?,the photocatalysis plays a dominant role when the temperature is less than 140°C,and photocatalysis and thermal catalysis work together when the temperature is higher than 140°C.?4?Comparative study of TiO₂ and Au/TiO₂ samples:Under dark conditions,Au/TiO₂?trace?has the best effect on the thermal catalysis of acetone.Under UV light conditions,the photocatalytic rate of TiO₂ is the highest from 20°C to 75°C.From72°C to 102°C,the photocatalytic rate of Au/TiO₂?0.3%?is the highest,while the photocatalytic rate of Au/TiO₂?trace?is the highest at 102°C to 215°C.?5?For the photocatalytic reaction of TiO₂ and Au/TiO₂ with temperature,after ruling out the effect of thermal degradation,the activation energy of photocatalytic reaction can be observed as a constant.No significant activation energy temperature transition point was observed.Therefore,when the light intensity is fixed and the temperature rises within a certain range,the increased photocatalytic reaction rate due to the temperature activity process,and the photochemical process?light?and the heat activation process?heat?in the photocatalytic reaction process have no synergistic effect.