Preparation And Properties Of TiO₂ Based Composite Semiconductor Materials

Recent years,titanium dioxide?TiO₂?materials have attracted extensive attention and research in the fields of photocatalytic degradation,photolysis of water to produce hydrogen and solar cells due to the low cost,non-toxicity,good chemical activity and high stability.Among them,TiO₂ nanomaterials with high energy{001}facet exposed exhibits superior photoelectrochemical?PEC?performance and more potential applications than the conventional TiO₂ nanomaterials due to the unique"surface heterostructure"and better surface chemical activity.However,how to obtain the uniformTiO₂ nanomaterials with the high exposure ratio of{001}facet has been an important problem for researchers.In addition,based on the energy band structure characteristics of TiO₂,TiO₂ materials have two inherent disadvantages of low solar light utilization rate?only 3-5%of sunlight?and high recombination probability of photogenerated electron-hole pairs.Therefore,how to achieve effective modification about TiO₂materials has become a key for its practical application.In this paper,based on the TiO₂ nanosheet?NS?with high energy{001}facet exposed,TiO₂ NSs array films and TiO₂ nanoflowers were obtained by regulating the experimental parameters.In addition,Fe₂O₃ composite,Sn doping and g-C₃N₄ composite were done for the modification.The specific research contents are as follows:?1?A regular TiO₂ NSs array was prepared by hydrothermal method using ammonium fluorotitanate as the crystal plane controlling agent and FTO as the substrate at 170°C for 12 h.On this basis,Fe₂O₃/TiO₂ composites were prepared by different water bath time and different concentrations of iron nitrate as Fe source.Then the samples were tested by XRD,SEM,TEM,UV-vis absorption spectroscopy,BET and PEC.The results show that Fe₂O₃/TiO₂ composites have pure phase,high crystallinity and good visible light response.Furthermore,Fe₂O₃nanomaterials preferentially grow on the{101}crystal plane of TiO₂ NSs.Fe₂O₃/TiO₂composites have better visible light photocatalysis and PEC performance than pure TiO₂ NSs arrays,which is mainly due to the introduction of narrow band gap Fe₂O₃ that significantly improves the visible light absorption properties of the material,increases the specific surface area of the material and promotes the transport and separation of photogenerated electrons and holes.Among Fe₂O₃/TiO₂ composites,the sample T3 obtained by 0.05 M nonferrous nitrate at 90°C reacting for 100 min has the best visible light catalytic activity and PEC performance.The photodegradation efficiency about methylene blue?MB?reached 89.3%in 120 min and the photocurrent density reached 2.39 mA cm^-2 at potential 0 V,which was 1.83 and 11.95 times of the pure TiO₂ NSs array,respectively.?2?TiO₂ nanoflowers were prepared by the hydrothermal method with diethylenetriamine and isopropanol as the crystal plane controlling agent at 200°C for different time.Then the sample were tested by XRD,SEM,TEM,UV-vis absorption spectroscopy,photocatalytic degradation to study its growth mechanism and photocatalytic properties.The result show that TiO₂ nanoflower is a three-dimensional hierarchical structure formed by self-assembly of many small TiO₂ NSs with high energy{001}facet exposed.With the increase of time,TiO₂nanoflowers have experienced the process of becoming larger,stable and falling off,respectively.Among them,the TiO₂ nanoflowers with hydrothermal time of 24 h have the best photocatalytic performance.Based on these conditions,the effects of Sn doping on the morphology,structure,optical properties and photocatalytic activity of the samples were investigated.The results show that Sn doping enhances the photocatalytic activity of TiO₂ nanoflowers.This is mainly due to the Sn doping forms appropriate lattice defects and effectively optimizes of the band structure in TiO₂ nanoflowers.Furthermore,5%Sn-doped TiO₂ nanoflowers showed the best photocatalytic degradation activity to MB,and the degradation rate reached 93%in 100 min,which was 1.84times than pure TiO₂ nanoflowers.?3?The g-C₃N₄/TiO₂ composites were prepared at 200°C for 24 h by the hydrothermal method with diethylenetriamine and isopropanol as the crystal plane controlling agent.The morphology and structure of samples were characterized by XRD,SEM,TEM and UV-vis absorption spectroscopy.The results show that all samples have a pure phase,high crystallinity and good visible light response.The prepared g-C₃N₄/TiO₂ composites were tested by degradation of MB,MO and RhB,respectively,to study the selectivity and stability about different organic pollutants.The g-C₃N₄/TiO₂ materials exhibit good degradation properties about MB and RhB,but the degradation properties of all samples are very stable.Among them,0.5%g-C₃N₄/TiO₂ nanoflower composite shows the best photocatalytic degradation effect within100 min,which was 1.34,1.47 and 1.52 times than pure TiO₂ nanoflowers,respectively.The g-C₃N₄/TiO₂ composites exhibit the enhanced photocatalytic activity,which should be mainly due to the narrow band gap of g-C₃N₄ that can effectively broaden the light absorption range and accelerate the transmission and separation of photogenerated charges.