The Photocatalytic And Gas-sensing Properties Of TiO₂-based Nanosheets With Exposed {001} Crystal Planes

{001} facets exposed TiO2[TiO2(001)]nanosheets are used as a research object in this thesis.MoS2-TiO2(001)and A-TiO2@R-TiO2(R:rutile,A:anatase)nano materials were fabricated by a simple photodeposition method and hydrothermal method,respectively.The best preparation conditions of the two kinds of nanomaterials were explored,and eventually MoS2-TiO2(001)nanomaterials with high photocatalytic performance and A-TiO2@R-TiO2 nanomaterials with high sensing properties were obtained.The photocatalytic performance of TiO2(001)nanosheets was enhanced by surface deposition of MoS2 nanoparticles,which overcame the disadvantages of high charge carrier recombination rate and low visible light absorption of TiO2(001)nanosheets.Surface rutilization of anatase TiO2(001)nanosheets was also performed to improve the low sensitivity,poor selectivity and high working temperature of pure phase TiO2(001)nanomaterials.The main points of this thesis can be summarized as follows:Firstly,TiO2 nanosheets with a high percentage(72%)of exposed {001} facets were fabricated by a hydrothermal approach in the presence of HF.Then,MoS2-TiO2(001)nanomaterials with different Mo/Ti ratios were prepared by loading few-layered MoS2 nanoparticles on the surfaces of TiO2(001)nanosheets through a simple photodeposition method using(NH4)2MOS4 as Mo source.The structure,morphology,composition,specific surface area,and light absorption properties of MoS2-TiO2(001)composites were characterized by XRD,TEM,XPS,BET,and UV-Vis diffuse spectra,respectively.The photocatalytic activities of the MoS2,TiO2(001)and MoS2-TiO2(001)nanomaterials for the degradation of rhodamine B(RhB)solution were investigated.The experimental results showed that MoS2-TiO2(001)nanomaterials exhibited higher photocatalytic activity in the degradation of RhB,compared with pure MoS2 and TiO2(001).At an optimal Mo/Ti molar ratio of 25%,the MoS2-TiO2(001)nanocomposites displayed the highest photocatalytic activity,which took only 30 min to degrade 50 mL of RhB(50 mg/L).The active species in the degradation reaction were determined to be h+and ·OH according to the free radical trapping experiments.The reduced charge carrier recombination rate due to the formation of dual heterojunctions and hybridized MoS2 phases,enhanced visible light utilization and increased surface areas contributed to the enhanced photocatalytic performances of the 25%MoS2-TiO2(001)nanocomposites.Secondly,A-TiO2@R-TiO2 core-shell nanosheets were prepared by simple hydrothermal treatment of the prefabricated TiO2(001).The influences of experimental parameters including the concentration of hydrochloric acid and growth time on the thickness of rutile TiO2 layer were explored.The morphology,structure,composition,specific surface area,and work function of A-TiO2@R-TiO2 nanomaterials were analyzed by means of SEM,TEM,XPS,BET,and UPS,respectively.The sensing results showed that the ethanol sensing performances of the A-TiO2@R-TiO2 nano materials were significantly improved compared with TiO2(001)nanosheets.The A-TiO2@R-TiO2 nanomaterials prepared with 0.8 M of HCL and 12 h of hydrothermal time displayed the highest ethanol sensing performances,including reduced working temperature by 50℃,increased response by 2 times,improved detection limit,and increased ethanol selectivity.The enhanced ethanol sensing performances of A-TiO2@R-TiO2 nanomaterials can be mainly ascribed to the formation of core-shell n-n type heterostructure between A-TiO2 and R-TiO2,increased surface oxygen species absorbing capability,and increased specific surface area.