The Evolution from a Typical Type-I CdS/ZnS to Type-II and Z-Scheme Hybrid Structure for Efficient and Stable Hydrogen Production under Visible Light

Abstract

An incompletely covered CdS/ZnS core/shell is synthesized via a simple hydrothermal method. Due to the defect energy levels introduced by zinc vacancies, the typical type-I heterojunction of CdS/ZnS evolves to a type-II heterojunction and Z-scheme hybrid structure so that the ZnS shell can timely transfer and capture the photogenerated holes from the CdS core. The surface photovoltage (SPV) distribution caused by photogenerated charges on the surface of catalyst is visually presented by Kelvin probe force microscopy with synchronous illumination (microscope SPV). It intuitively proves the effective spatial separation of photogenerated holes from the CdS core to the ZnS shell, for the first time. Under optimal conditions, the highest hydrogen production rate of CdS/ZnS reached 24.1 mmol g–1 h–1 under visible light illumination. The average apparent quantum yield of 9.3% can be achieved for 9 h of illumination (λ = 420 ± 5 nm). It exhibits highly efficient photocatalytic H2 evolution with well stability.

Surface defect engineering of mesoporous Cu/ZnS nanocrystal-linked networks for improved visible-light photocatalytic hydrogen production

“…In particular, the light excitation of CZS′-5 generates more surface-reaching electrons for hydrogen evolution, instead of losing a portion to electron-hole recombination at the structure or surface defects. The AQY of the CZS′-5 NCAs is also higher than or comparable to those of other noble-metal-free ZnS-based photocatalysts, such as CdS/ZnS core-shell microparticles (9.3% AQY at 420 nm), 29 36 CuS/ZnS porous nanosheets (20% AQY at 420 nm), 37 (CuAgZnSnS 4 ) 0.9 (ZnS) 0.4 mixed crystals (0.25% AQY at 400 nm), 38 Bi (0.3%)-doped ZnS hollow spheres (0.99% AQY at 420 nm) 39 and Ga(0.1%), Cu(0.01%)-co-doped ZnS nanospheres (0.14% AQY at 425 nm). 40 Interestingly, when sulfidation was performed on the starting ZnS NCs or mesoporous network of the cross-linked ZnS NCs to form the sulfurated products (denoted as C/ZS-S′-5 and C/ZS′-5 NCAs, respectively, details in the Experimental section), the resulting catalytic activity was significantly lower; namely, C/ZS-S′-5 and C/ZS′-5 catalysts gave a H 2 production rate of 3.9 and 22.5 μmol h −1 over a 3 h reaction period, respectively (Fig.…”

Interfacial chemical bond and internal electric field modulated Z-scheme Sv-ZnIn2S4/MoSe2 photocatalyst for efficient hydrogen evolution

“…It is noted that the pristine MoSe 2 presents no SPV signals in the whole wavelength, suggesting the poor photocarriers separation efficiency inside the MoSe 2 , that's why MoSe 2 performed very poor hydrogen evolution. In comparison, a significant positive photovoltage response can be observed in the SPV spectra of S v -ZIS, suggesting that the holes migrate to the surface of S v -ZIS, which is the typical trait of n-type semiconductor 49 . Meanwhile, the SPV response of S v -ZIS/MoSe 2 is significantly lower than that of S v -ZIS, which means that fewer photogenerated holes migrate to the surface of S v -ZIS/MoSe 2 .…”

Novel n‐p‐n heterojunction of AgI/BiOI/UiO‐66 composites with boosting visible light photocatalytic activities

“…Type II heterojunction has been considered as the optimal structure for high separation rate of photogenerated electron holes. [ 65 ] After being decorated with AgI, degradation rate constant k of the 1‐ABU can highly improve compared with the pristine and 1‐BU composites via facilitating the separation of electron–hole pairs. [ 66 ] In any event, UiO‐66 plays an important role on boosting the photocatalytic activities for two reasons.…”