Construction Of TiO2 Nanosheet-based Ternary Composite Heterostructures And Their Visible Light Photocatalytic Performance

Photocatalysis technology is considered to be a promising technology to deal with energy and environmental issues.TiO2 nano-photocatalytic materials have been widely concerned by researchers because of their advantages such as high efficiency,nontoxicity,good stability and low cost.However,due to the wide band gap and low photogenerated carrier separation efficiency,its application is subject to many restrictions.Macroscopically,the photocatalyst has poor visible light absorption and low photocatalytic efficiency.This makes its application limited.This thesis is based on a thorough investigation of the relevant literature,with nickel oxide/titanium dioxide nanosheets(Ni-TNSs)heterojunctions as the main body,and on the basis of binary heterojunctions,through the synergistic effect of ternary compounding,improve the visible light catalytic performance of the heterojunction.The structure and photoelectric properties of the materials were characterized and tested.The related applications of different ternary composite heterojunctions in the fields of photocatalytic decomposition of water to produce hydrogen,adsorption and photocatalytic degradation,photoelectrochemical sensing and piezoelectric catalysis are analyzed.The research of this article is mainly divided into the following parts:(1)Preparation and photocatalytic performance of nickel oxide/titanium dioxide nanosheet binary heterojunction(Ni-TNSs).The nano-nickel oxide(NixOy)supported titanium dioxide nanosheet-based heterojunction Ni-TNSs was prepared by hydrothermal method.The constructed heterojunction is surface-dispersed and has a high specific surface area(270?350 m2/g).The constructed NixOy/TNSs heterojunction can effectively improve the photoelectric performance of TNSs and improve the separation efficiency of photogenerated electron-hole pairs.The surface photocurrent value of 3.0%-Ni-TNSs reaches 0.296 ?A,which is 7.79 times that of TNSs(0.038 ?A).The effect of different compound ratios on photocatalytic activity was discussed.When the compound ratio is 3.0 at.%,the heterojunction has the highest photocatalytic activity.The catalytic efficiency of the target pollutants Rhodamine B(RhB)and Methylene Blue(MB)has been significantly improved.The reaction rate constant(Kapp)for the degradation of Rhodamine B is 34.856×10-3·min-1,which is 7.07 times(4.933×10-3 min-1)of TNSs,and 12.09 times of P25(2.882×l0-3·min-1).However,subject to the factors such as light absorption capacity and carrier recombination rate,there is still some restriction of binary heterojunctions.(2)Synthesis of ternary heterojunction NiS/Ni-TNSs supported by metallic co-catalyst NiS and the research on the performance of photocatalytic water splitting to produce hydrogen.The ternary heterojunction NiS/Ni-TNSs was synthesized using the hydrothermal method with the binary heterojunction Ni-TNSs as the matrix.NiS can effectively improve the photoelectric performance of Ni-TNSs.DRS results show that the absorption edge of the ternary heterojunction light appears red-shifted,and the absorption capacity of visible light is improved compared with the binary heterojunction.NiS recombination can reduce the interface polarization resistance and promote carrier transport and migration.The NiS compound ratio will affect the photoelectric performance of the material.By characterizing and testing ternary heterojunctions with different recombination ratios,it was found that 20%NiS/Ni-TNSs had the most negative flat band potential(-1.33 V),the highest carrier concentration and the largest open-circuit photoelectricity(5.8 mV).NiS/Ni-TNSs can produce hydrogen by photocatalytic decomposition of water using triethanolamine as a sacrificial reagent under the visible light irradiation.Compared with binary heterojunctions Ni-TNSs and metalloid NiS which have almost no photolysis ability,the performance of ternary heterojunctions has been improved,reflecting the synergistic effect of ternary heterojunctions.When the NiS loading ratio is 20 at.%,NiS/Ni-TNSs exhibits the best hydrogen evolution performance,and the hydrogen production rate reaches 345.04 ?molh-1g-1.(3)Preparation,visible light catalysis and photoelectrochemical sensing performance of ternary composite catalyst POSS/Ni-TNSs supported by polyhedral oligomeric silsesquioxane(POSS).The compounded material can maintain the morphology of the layer without destroying the original crystal structure,and can also maintain a large specific surface area(254.25 m2/g).The adsorption of POSS/Ni-TNSs to the organic dye crystal violet complies with the Langmuir adsorption model and has a higher maximum theoretical adsorption capacity(943.39 mg/g),which is 6.98 times that of the binary heterojunction Ni-TNSs.Adsorption kinetics studies show that the adsorption process of POSS/Ni-TNSs to CV conforms to a quasi-second-order model,which is mainly controlled by chemical adsorption.POSS/Ni-TNSs shows excellent activity for both photocatalytic degradation of RhB and photocatalytic reduction of Cr(VI),of which the degradation rate of rhodamine B is 2.40 times that of binary heterojunction Ni-TNSs.In addition,POSS/Ni-TNSs showed a synergistic effect on the catalytic degradation of RhB-Cr(VI)coexistence system.For the degradation of RhB,the degradation rate of the coexisting system is 4.81 times that of the single system.For Cr(VI),the degradation rate of the coexisting system is 2.04 times that of the single system.POSS/Ni-TNSs can be used for enzyme-free photoelectrochemical sensing under visible light,and it has a wide linear range(1.0-6.0 mM)for the detection of glucose solutions.(4)The structure,photocatalysis,piezoelectric catalysis and electrochemical energy storage performance of the ternary heterojunction MoS2/Ni-TNSs(MNT).The ternary heterojunction MoS2/Ni-TNSs(MNT)was prepared by hydrothermal method,using the binary heterojunction Ni-TNSs as the matrix.The ternary heterojunction exhibits the piezoelectric catalytic performance that the binary heterojunction does not have,and the MoS2 compound ratio will affect the piezoelectric catalytic activity of the material.The MNT-0.2 sample has the strongest piezoelectric catalytic activity,and can achieve the piezoelectric catalytic decomposition of 20 ppm MB solution(decomposition rate of 98%)within 6 min by ultrasound under dark conditions.The decomposition rate of MNT-0.2 to 20 ppm RhB solution was 78%in 6 min.There is a synergistic effect between the piezoelectric catalysis and photocatalysis of the ternary heterojunction.The MNT-0.2 sample can rely on piezoelectric/photocatalysis to provide efficient degradation of the 20 ppm RhB solution when the mechanical stress is provided by the high-speed stirring water flow.The degradation rate was 73%within 30 minutes.Based on the interaction between the built-in electric field of the heterojunction and the piezoelectric electric field,a possible piezoelectric/photocatalysis synergy mechanism is proposed.The ternary heterojunction MNT-0.2 can be used as the active material of supercapacitors.The charge storage mechanism is the EDLC electric double layer capacitor energy storage mechanism,and the specific capacitance is 39.7 F/g at a scan rate of 1 A/g.