Modification Of TiO₂Nanotube Arrays With Graphene Quantum Dots For Improving Visible-light Photoelectrocatic Activity

Titanium dioxide nanotube array synthetized by anodic oxidation method hasgreat application value in the field of photocatalytic degradation of organic pollutants.However, TiO₂has the activity only under UV wavelength condition because of itsfairly wide band gap, which largely limited its application. Therefore, doping somenon-toxic, harmless materials in titanium dioxide arrays and make it active in visiblelight condition has become an imperative research topics. In this papers, we mainlystudied using graphene quantum dot to modify titanium dioxide nanotube array.Preparing modified dioxide nanotube array which has photo-electricity catalyticactivity under visible light. Besides, we systematically discussed their photoelectriccatalysis performance and catalytic mechanism. The main contents are as follows:1) Vacuum assisted method was employed to modified the titanium dioxidenanotube arrays by graphene quantum dots and used methylene blue as degradationsubstance. The results reveal that the catalytic performance of assembling TiO₂nanotubes is superior than undoped.2) Taking advantage of negative charge of GQD, we assembled titanium dioxidenanotube array by graphene quantum dots through electrophoresis method andprepared TiO₂/graphene quantum dot compound with stable structure and make thecorresponding characterization. After comparison, we find that the light absorption ofassembled nanotube shift from385nm to425nm and the photocurrent intensityincreased about threefold. The methylene blue was used as degradation material andthe photocatalytic performance has dramatically improved under visible lightcondition. The photocatalysis kinetic constant increased ninefold. After react severaltimes, the modified titanium dioxide nanotube array still maintained great catalyticefficiency, which is far more than the CdS. The results proved that the GQD’s stabilityis very good and do not occur photooxidation. In addition, we used CV method toexplore and analyze the cause of improving of nanotube’s photocatalysis.3) Hydrothermal method was used to composite the graphene quantum dot with P25powder and synthtized P25/GQD compound, the UV-vis diffuse reflectionspectrum of the compound occurred red shift. With methyl orange as a degradablematerial, under the condition visible light catalytic performance is greatly improved inall adopt the method of twice anodic oxidation preparation of TiO₂nanotube arrays,and made with longer diameter larger specific surface area and stronger absorptionability of nanotube arrays.4) We utilized two-step anodization method to prepare TiO₂nanotube arrays, andgot the double layer nanotube arrays which have longer diameter, larger specificsurface area, stronger adsorption capacity and higher photoelectric catalytic activity.