Construction of Shallow Surface States through Light Ni Doping for High‐Efficiency Photocatalytic Hydrogen Production of CdS Nanocrystals

Abstract

Ni-doped CdS nanowires were synthesized by a simple one-step method. X-ray diffraction, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy confirmed that light Ni doping can form shallow surface states due to the presence of substitutional Ni ions, and heavy Ni doping can form deep surface states due to the presence of interstitial Ni ions. Surface photovoltage spectroscopy and transient photovoltage measurements revealed that the shallow surface states can prolong the lifetime of the photogenerated charge carriers, whereas the deep surface states lead to recombination of the photogenerated charge carriers. The relationship between different surface states and the photocatalytic performance of CdS nanocrystals are discussed. The enhanced density of shallow surface states due to light Ni doping significantly promotes photocatalytic H2 production.

Role of aliovalent cation doping in the activity of nanocrystalline CdS for visible-light-driven H2 production from water

“…The PL spectra shown in these figures illustrated three distinct emission mechanisms: direct recombination of the photogenerated electrons and holes, recombination of the excitons bound to certain shallow trapping states, and transitions involving sub-band gap energy states due to the defects in the lattice. As reported [11,34]; the PL bands at~530 nm (2.36 eV) and 547 nm (2.28 eV) were ascribed to band edge emission, i.e. the direct recombination of the photogenerated electrons and holes from the i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 0 ( 2 0 1 5 ) 8 6 9 5 e8 7 0 5 conduction and valence bands.…”

“…However, we demonstrated that the dopingenhanced activity may in fact have its origin in certain bulk properties of CdS instead of the charge transfer processes mentioned above [23]. Moreover, shallow surface states or inter-bandgap charge trapping sites, which arose from the doping of an impurity, were found to be important [11,13]. We point out that not many studies have investigated how the preparation-conditionedependent morphology and structural properties contribute to the water splitting activity of a semiconductor such as CdS.…”

“…However, doping with Ag þ would lead to anion vacancies, and hence, trapping states in the vicinity of the valence band of CdS [40]. Li et al [11] reported that the energy level of these trapping states would depend upon the dopant concentration and its location, either at the cation sites or at the interstitial positions of the CdS lattice. Accordingly, the photoluminescence emission band at 2.17 eV in Fig.…”

“…The emission bands at 500 nm (~2.54 eV), which appear at a wavelength shorter than the onset of edge position (Fig. 8a), are normally ascribed to a recombination of the excitons bound to certain shallow trapping states [11]. The PL emission at energies lower than the band gap of CdS (the 2.17 and 2.0 eV bands in Fig.…”

ZnCr Layered Double Hydroxide (LDH) Nanosheets Assisted Formation of Hierarchical Flower‐Like CdZnS@LDH Microstructures with Improved Visible‐Light‐Driven H2 Production

“…[3][4][5] It has been known that the control over the synthesis of CdS with certain morphologies plays a key role in their photocatalytic properties. [6][7][8] In addition, it was reported that the incorporation of Zn element into CdS to form CdZnS solid solution can result in enhanced photocatalytic activity for H 2 production relative to pure CdS via tuning the CdS bandgap width and band-edge position. [9][10][11] In addition, the combination of a suitable semiconductor with CdZnS can also result in a high photocatalytic activity.…”