Preparation Of Nano-TiO₂-based Composites And Their Optical/electrical Properties Testing

With the rapid development of global economy and industry,energy and environment are two important problems that hinder the progress of human society.Titanium dioxide has many advantages,such as low cost,good stability,negligible volume expansion,small volume expansion,high light absorption characteristics,green environmental protection and so on.It has a very broad application prospect in photocatalytic decomposition of water for hydrogen production and lithium-ion battery(Li Bs)negative electrode direction.However,titanium dioxide composite materials need to be used to improve the photocatalysis capacity due to its poor photocatalytic properties.In this paper,a simple,convenient and environmentally friendly method is proposed to prepare layered protonated titanate,and its derivative anatase titanium dioxide(A-TiO₂)is prepared by high temperature calcination,so that A-TiO₂ has a layared structure.Different anatase rutile(A-R)ratios of heterojunction TiO₂ were synthesized by adjusting the ratio of carbon to titanium,and the photocatalytic properties of the above-mentioned layared A-TiO₂ and heterojunction TiO₂ for hydrogen production from water decomposition were systematically studied.In addition,commercial silicon was coated with protonated titanate and carbon to alleviate the volume expansion of silicon and improve the conductivity of the composite,and the performance of lithium-ion battery was discussed.The main research work of this paper is as follows.(1)In order to improve the agglomeration and fewer photocatalytic active sites of TiO₂ nanoparticles,it is an effective way to improve the photocatalytic performance of water decomposition for hydrogen production by adjusting the morphology of TiO₂nanoparticles.We propose a one-step solvothermal method using hydrazine hydrate and butyl titanate as raw materials to prepare a series of protonated titanates with controllable spherical sheet morphology.Finally,A-TiO₂ derivative is obtained by calcination.XRD,XPS,SEM,TEM and other characterization methods were used to explore the formation reason of layered protonated titanate and its derivative A-TiO₂.It was found that with the increasing amount of hydrazine hydrate,the continuous modulation process from spherical to layered was completed.After calcination at high temperature,its layared structure can still be maintained,and its crystal form remains anatase when calcined at 500?;with the temperature increasing to 800?,its crystal form transforms into rutile type,and its layared structure is also destroyed.It was found that the hydrogen production performance of A-TiO₂ was related to the content of layared structure.With the increase of hydrazine hydrate,the content of layared structure increased,and the hydrogen production increased accordingly.The photocatalytic activity of layared A-TiO₂ with 20 ml hydrazine hydrate is the highest,reaching 3.4412 mmol/g^-1h^-1,which is equivalent to P25(3.5707 mmol/g^-1h^-1),and 5.6times of spherical TiO₂(0.6147 mmol/g^-1h^-1);after five cycles,it can still reach3.0723 mmol/g^-1h^-1,which performs good cycle stability.This work provides theoretical basis and technical support for the preparation of layared TiO₂ and high performance photocatalytic decomposition of water for hydrogen production.(2)In order to improve the performance of TiO₂ photocatalytic decomposition of water for hydrogen production,the construction of phase junction is also a solution.In this paper,a series of heterojunction TiO₂ with adjustable A/R ratio can be obtained by one-step solvothermal method.The formation mechanism of heterojunction TiO₂was revealed by XRD,SEM and XPS.With the increase of glucose dosage,a series of heterojunction TiO₂ samples were obtained by calcining in nitrogen atmosphere at450?and then in air atmosphere,and the proportion of rutile phase increased gradually.The results show that the photocatalytic hydrogen production performance of heterojunction TiO₂ is related to the ratio of carbon and titanium,A:R=83.8:16.2 is the best,which is close to the ratio of A/R in P25.The hydrogen production of heterojunction TiO₂ is 0.3435 mmol/g^-1h^-1,which is 1.77 times of pure A-TiO₂(0.1939 mmol/g^-1h^-1)and 2.19 times of pure R-TiO₂(0.1564 mmol/g^-1h^-1).The hydrogen production rate of the sample reaches 0.4019 mmol/g^-1h^-1 after 20 h cycling,and the sample has excellent cycling stability.The lower hydrogen production data of the first cycle is due to the incomplete deposition of Pt in the initial cocatalyst.In this work,a method of adjusting the A/R phase ratio of TiO₂ by changing the ratio of carbon to titanium was proposed to guide the synthesis of heterogeneous junction TiO₂ and enhance the separation effect of photogenerated electron hole pairs.(3)Although LPT has the characteristics of"zero deformation"of lithium intercalation,it still has the problems of low theoretical capacity and poor conductivity.In order to optimize these two problems,this paper uses LPT to coat commercial silicon,which not only improves its specific capacity,but also alleviates the huge volume effect of silicon,and then uses glucose for secondary coating to improve its conductivity and maintain the stability of the battery.Using commercial silicon spheres,TBT and hydrazine hydrate as raw materials,the protonated titanate was coated on commercial silicon by a simple solvothermal method,and the Si@LPT composite was obtained.Then the Si@LPT composite was impregnated with glucose solution to form Si@LPT@C composite.According to the test results,the formation mechanism of Si@LPT@C composite was discussed.After solvothermal treatment,the well dispersed Si@LPT composite was obtained,and then the LPT and C double coated Si@LPT@C composite was obtained by impregnation method.It was found that the composite can effectively inhibit the volume effect of silicon.The composite not only reduces the specific capacity loss caused by silicon expansion,but also greatly improves the conductivity of the composite.When Si@Ti@C composite was used as anode material of Li ion battery,the initial discharge capacity was2006.8m Ahg^-1,the initial coulomb efficiency was 84.5%,and the specific capacity of1271.6 m Ahg^-1 was retained after 65 cycles;moreover,the specific capacity of 988.47m Ahg^-1 could be maintained under the current density of 1 Ag^-1,indicating that Si@Ti@C composite has excellent rate performance.This shows that the Si@Ti@C composite coated with Ti and C can effectively alleviate the huge volume effect of commercial silicon anode and improve the battery performance of nano-silicon anode.