Preparation Of TiO₂/graphene （carbon Nanotubes） Composites By Using Nanotube Titanic Acid As The Precursor And Their Visible-light Photocatalytic Activities

Of the well-known photocatalysts, titanium dioxide (TiO2) has well applied in the elimination ofenvironmental contaminant and the solar enery conversion. However, TiO2is a wide band gap energysemiconductor, active only under the UV light irradiation, which is only a small fraction (ca.4%) of solarradiation. Combining TiO2with carbonaceous materials is being increasingly investigated as a means toincrease photocatalytic activity, and demonstrations of enhancement are plentiful.Carbon has many forms, such as fullerenes, carbon nanotubes(CNT), graphene (Gr), etc. Thecomposites of TiO2and carbonalso have been widely reported. However, up to date, few reports arecurrently available about the preparation and photocatalysis of carbon nanomaterials-TiO2nanocompositesby using titanic acid nanotubes (NTA) as the TiO2precursor.There are three advantages of combining NTAderived TiO2with carbon nanomaterials (i) Combined carbon nanomaterials can transfer electrons to TiO2by acting as a photosensitizer or inhibit the recombination of electron-hole pairs;(ii) Not only carbonnano-materials but also NTA have high BET specific surface areas, which facilitate the adsorption ofcontaminations on the catalysts;(iii) The NTA derived TiO2have shown capabilities of improving visiblelight photocatalytic properties. Therefore, we proposed to explore in this field. In this work, NTA/Gr,NTA/CNT, and the derived TiO2/Gr and TiO2/CNT composites were prepared by using the hydrothermalmethod. Their visible light photocatalytic activities for the degradation of methyl orange (MO) ormethylene blue (MB) were evaluated.The detailed contents and results are as follows:1. Firstly, graphene oxide (GO) and NTA were prepared. Then, nanotube titanic acid/graphene (NTA/Gr) composites were prepared by an easy hydrothermal treatment of graphene oxide (GO) and NTAin a mixed solution of ethanol–water. As-prepared NTA/Gr composites and GO were characterized bymeans of X-ray diffraction(XRD), transmission electron microscopy(TEM), thermal analysis(TA), UV-Visdiffuse-reflection spectrometry(UV-Vis DRS), and fourier transform infrared spectrometry(FTIR). Thephotocatalytic activities of as-prepared NTA/Gr composites were evaluated by monitoring the degradationof MO under visible lightirradiation. The results show that after the hydrothermal reaction, GO wasreduced to Gr and NTA/Gr composites were formed. Extending hydrothermal reaction time (24h instead of3h) leads to the formation of TiO2/Gr composites. Compared with NTA, the NTA/Gr composites and theTiO2/Gr composites have higher photocatalytic activities. With increasing the Gr content, the photocatalyticactivities increase. Pure GO only has adsorption effect but it has no photocatalytic activity in the visiblelight region.2. Carbon nanotube/TiO2(CNT/TiO2) composites were synthesized by hydrothermal method usingtitanic acid nanotubes as the TiO2precursor and CNT as the carbon precursor. The crystalline structures,morphologies, light absorption properties, specific surface areas of the prepared powders were investigatedwith XRD, TEM, UV-Vis absorption spectra and N2adsorption-desorption. The photocatalytic activities ofthe composites were evaluated by monitoring the degradation rate of MB under the visible light irradiation.The mechanism of the improved photocatalytic activity of the photocatalyst was discussed. It was foundthat all of the composites upon24h of hydrothermal reaction show the diffraction peaks indexed to anataseTiO2and the critical reaction time for anatase TiO2nanoparticles to form is3h. The visible lightphotocatalytic activities of the catalysts in this experiment were affected by a combination of BET specificsurface area, MWCNT content and hydrothermal reaction time.3. A TiO2/nanotube titanic acid (TiO2/NTA) heterostructure was prepared by a twice heat-treating method and characterized by TEM, SEM, XRD, IR, DRS and XPS. The results show that TiO2nanoparticles have been integrated with the NTA to form a heterostructure. Compared with NTA, theas-prepared heterostructure shows improved visible-light photocatalytic activities for the degradation ofMO. The sample of10%-TiO2/NTA-400-400exhibits the highest visible-light photocatalytic activity.