The Preparation And Photoelectric Performance Of N/rGO-TiO₂ Composites

Recently,the crisis of environmental and energy have gradually attracted the attention of the society.To alleviate this problem,researchers have been exploring clean and efficient materials.TiO₂ is an environment-friendly semiconductor with low price,stability,chemical resistance and high photocatalytic activity,which has been determined as a promising photoelectric material.However,the development of TiO₂ is limited because of its unfavorable large band gap,poor conductivity and high electron-hole recombination rate,etc.Besides,the photoelectric performances are affected by many other factors,such as surface morphology and crystallinity.Fortunately,studies have found that both carbon materials and non-metals doping can enhance the performances.According to the above considerations,we utilize a facile alkaline-hydrothermal method to controllably synthesize Anatase TiO₂ at low temperature,and to simply modify it with N and rGO because of their advantages and positive synergistic effect.In this paper,the main work is as follows:（1）TBT as titanium source,EG/H₂O as mixed solvent,NaOH（5 M）as pH regulator,respectively.Different Anatase TiO₂ samples were synthesized by alkaline-hydrothermal method at 180°C.Experiment mainly discusses the effects of precursor’s pH values on the structure,morphology and photoelectric performances of TiO₂.Results show that the TiO₂samples have uniform surface distribution and good crystallinity when the precursor’s pH is large.In addition,the rod-shaped Anatase TiO₂ sample reveals the best photocatalytic activity（69.6%）when the value of precursor’s pH reaches 9.In the CV and EIS tests,it reflects a large charge-transfer and ion-diffusion impedance,and the specific capacitance is 119.94 F/g.（2）Controlling the pH to 9,then dispersing different contents of GO into TiO₂ precursor before oxidation reduction to prepare composites.The influences of rGO on structure and morphology of TiO₂ are investigated in the experiment.It turns out that GO is rapidly reduced to a flake-like rGO in alkaline environment.Besides,appropriate amount of rGO doping is conducive to the generation of composites with a high crystallinity,large surface area,small particle size and fast charge transfer.By photocatalytic tests,it suggests that appropriate rGO can improve the photocatalytic activity of TiO₂,and the sample can exhibit the best photocatalytic activity（86.3%）while rGO’s content is 5%.Moreover,the CV and EIS measurements demonstrate that a suitable amount of rGO can accelerate electron diffusion and make electrode contact with electrolyte fully.It leads to the composite with 5%of rGO own decreased impedance,the specific capacitance increases to 166.94 F/g,which shows reversible redox electrochemical performance.（3）The composite samples with different N content are synthesized by adjusting the pH=9 and using urea as the nitrogen source.Similarly,the impacts of N content on the structure,morphology and photoelectrical properties of TiO₂ are analyzed experimentally.It indicates that the morphology,crystallinity and surface distribution of the composite samples are different when the content of N has a distinction.What’s more,an appropriate doping of N makes the particle size decrease and the surface area increases for composites.It can form the Ti-N bond with TiO₂,so that the strong interaction helps to improve the photoelectric properties of TiO₂.When the content of N attains 10%,the photocatalytic activity of N-doped TiO₂ composite is the best（82.9%）.Compared with pure TiO₂,the composite impedance is decreased,the specific capacitance is increased to 166.75 F/g,and the reversible redox electrochemical performance is improved.（4）To control the pH=9,ensure the rGO is the best proportion of 5%,and constantly change the addition of urea.The composite samples of N and rGO co-modified TiO₂ are prepared by alkaline hydrothermal method.By contrast with pure TiO₂ and single-doped composites（rGO or N）,the research of N and rGO co-modified TiO₂ is carried out in the experiment.The results prove that N and rGO participate in the formation of a composite structure with thinner rod-like TiO₂ loaded on the surface of smaller flake-like N/rGO.Furthermore,a suitable amount of N and rGO can result in the production of composites,which have the decreased particle size and increased specific surface.Most of all,the highest photocatalytic activity of N and rGO co-modified TiO₂ sample is boosted significantly（90.5%）,if the mass percentage of N reaches 10%.It manifests excellent electrochemical performances in the CV and EIS tests,including the lowest charge-transfer and ion diffusion impedance,the raised specific capacitance of 235.31 F/g.This is mainly because the composites not only take advantages of N and rGO,but seize the characteristic of p-PI conjugated system between them.These synergistically give rise to the rapid separation of electron-holes,the increase of contact areas,the shortening of ion-diffusion distances and the enhancement of photoelectric activities.One-step alkaline hydrothermal method is simple,which facilitates the rapid reduction of GO and the formation·OH oxidative radicals.It will help to improve the conductivity and the oxidative degradation capacity of composites.Above all,the experiment not only takes advantages of N and rGO,but seizes the characteristic of p-PI conjugated system between them,so as to enhance the photoelectric activities of TiO₂.This work may offer a reliable insight for constructing efficient photoelectric composites.