Thin Amorphous TiO₂ Shell on CdSe Nanocrystal Quantum Dots Enhances Photocatalysis of Hydrogen Evolution from Water

Abstract

In this study, we designed and synthesized photocatalysts for hydrogen evolution from water by coating a thin layer of amorphous TiO2 (a-TiO2) on CdSe nanocrystals (NCs). The thin shell of a-TiO2 serves as a channel for charge carriers otherwise unutilized. Albeit a previous notion that a-TiO2 is a poor photocatalyst, the enhanced photocatalytic activity in the presence of a-TiO2 suggests that the material helps utilize the photogenerated charge carriers when it is in a form of thin shell on CdSe NCs. Type II band offset in CdSe/a-TiO2 appears to allow the electron in the conduction band of CdSe NCs to migrate over to that of a-TiO2, and the electron participates in the hydrogen production from water. Size of CdSe NCs influences the photocatalytic hydrogen evolution rate as the energy difference between the conduction bands of semiconductors becomes larger. Electron transfer from CdSe NCs to a-TiO2 layer is influenced by the level of the conduction-band edge of CdSe NCs: the size dependence indicates that electron injection to TiO2 is facilitated with energy level offset between CdSe and TiO2, while smaller NCs have larger band gap and thus narrower spectral range of absorption. The interplay between charge-transfer rate and absorption cross-section should be considered in designing heterostructure NC-based photocatalysts for water splitting.

Exploring the effect of boron and tantalum codoping on the enhanced photocatalytic activity of TiO2

“…This is mostly attributed to the fast recombination of electron-hole pairs and a relatively large energy gap of TiO 2 (E g = 3.2 eV for anatase phase and E g = 3.0 eV for rutile phase), limiting its light absorption to the ultraviolet fraction of the solar energy spectrum [1,2,5]. Numerous efforts have been devoted to extending the optical response regime of TiO 2 toward visible region, and/or suppress the charge carrier recombination [1,2,[6][7][8][9][10][11][12][13][14][15].…”

Enhancing the photocatalytic activity of CdS nanorods for selective oxidation of benzyl alcohol by coating amorphous TiO2 shell layer

“…However, most researches are focused on coupling CdS with crystalline TiO 2 , the studies on combining with amorphous TiO 2 (a-TiO 2 ) are infrequent. However, compared with TiO 2 crystallites, a-TiO 2 has some distinct advantages: Firstly, it can be easily prepared without calcination [10,11]. Secondly, it has a porous structure, thus leading to a higher adsorptive property [10,11].…”

Preparation and Photocatalytic Activities of Fe/BiVO4 by Low-Temperature Solid State Method

“…Recently the semiconductors as photocatalysis were widely applied in splitting water to produce hydrogen [1], degradation of organic pollutants [2], carbon capture and sequestration [3] and photoelectrochemical cell research [4]. Titanium dioxide (TiO 2 ) is an industrially important product, for example P25, however wide-band gap semiconductor always suffers from higher energy excited by UV-light [1][2][3][4], not adequately use sunlight.…”

“…Titanium dioxide (TiO 2 ) is an industrially important product, for example P25, however wide-band gap semiconductor always suffers from higher energy excited by UV-light [1][2][3][4], not adequately use sunlight. So face this trouble, except use of nanometer-structures and element doping [5], some new types photocatalyst had been utilized and investigated as BiVO 4 [6], BiFeO 3 [7], Bi 2 WO 6 [8], ZnWO 4 [9] and Cu 2 O [10].…”