Construction and Photocatalytic Performance of Quantum Dots Self-decorated TiO2 p-n Homojunction

Quantum dots ( QDs ) self-decorated TiO2 p-n homojunction ( PNT-x ) samples were fabricated by in-situ depositing p-type TiO2 QDs on the surface of n-type TiO2 nanosheets. The composition and structure of the samples were characterized by transmission electron microscopy ( TEM ) , X-ray diffraction ( XRD ) , Fourier transform infrared spectroscopy ( FTIR ) , X-ray photoelectron spectroscopy ( XPS ) , photoluminescence spectrometry ( PL ) , Raman spectrometry, UV visible diffuse reflectance spectrometry ( UV-Vis DRS ) , photoelectrochemical test and electrochemical impedance spectroscopy ( EIS ) analyses. The results indicate that PNT-x exhibits TiO2 QDs self-decorated structure. Meanwhile, there exist metal and oxygen vacancies in QDs and nanosheets , respectively , and the content of vacancies can be modulated by the composition. Therefore , the as-prepared PNT-x show typical characteristics of p-n homojunction, and the difference of Fermi level and internal electrical field is stronger than that in n-n type II homojunction and bulk p-n homojunction, thus leading to a significantly high charge separation and transfer efficiency. Under illumination, the order of photocatalytic activity is PNT-400>p-25>PNT-600>PNT-200>p-TiO2 >n-TiO2 , and PNT-400 display the photocatalytic hydrogen evolution rate as high as 41.7 mmol . g(-1) . h(-1) , which is 4.3 , 3.6 and 2.3 times that of n-TiO2 nanosheets , type II homojunction and bulk p-n homojunction , respectively , as well as a good catalytic stability.