Sulfur Vacancy-Mediated Electron–Hole Separation at MoS₂/CdS Heterojunctions for Boosting Photocatalytic N₂ Reduction

Abstract

Defect engineering is considered as an efficient method for improving the photocatalytic activity of semiconductor photocatalysis because defects can not only serve as trapping centers for electrons and holes but also work as active sites for reaction. Herein, we synthesized a series of MoS2/CdS heterojunctions with abundant sulfur vacancies and used for photocatalytic N2 reduction. The sulfur vacancies at MoS2/CdS heterojunctions were confirmed by UV–vis diffuse-reflectance spectroscopy (UV-DRS) and electron paramagnetic resonance. The charge transfer behaviors of the photocatalysts were characterized by X-ray photoelectron spectroscopy, transient photocurrent, steady and transient photoluminescence spectroscopy, and so forth. Under visible light irradiation for 4 h, the production of NH3 at 3% MoS2/CdS heterojunctions (249.7 mg L–1 g–1) was about 5.4 and 3.9 times higher than that of pure MoS2 (45.9 mg L–1 g–1) and pristine CdS (64.5 mg L–1 g–1), respectively. The reaction mechanisms and pathways were further studied by in situ diffuse reflection infrared Fourier transform spectroscopy.

Recent Progress of Metal Sulfide Photocatalysts for Solar Energy Conversion

“…[ 151 ] Sulfur vacancies as active sites for N 2 adsorption were constructed by Zheng et al. [ 151 ] and electrons trapped by the defects could be transferred to the π orbitals of adsorbed N 2 , resulting in the weakening of the N≡N bond and the subsequent formation of N 2 *. Simultaneously, H* released from the surface of the metal sulfides permits the sequential hydrogenation of N 2 and the formation of *NNH.…”

“…In addition, defect engineering enables coordinatively unsaturated metal sites on metal sulfides for N 2 chemisorption, thus reducing the energy barriers for N 2 reduction. [151] Sulfur vacancies as active sites for N 2 adsorption were constructed by Zheng et al [151] and electrons trapped by the defects could be transferred to the π orbitals of adsorbed N 2 , resulting in the weakening of the N≡N bond and the subsequent formation of N 2 *. Simultaneously, H* released from the surface of the metal sulfides permits the sequential hydrogenation of N 2 and the formation of *NNH.…”

Fabrication of Z-Scheme TiO2/Au/CdS Nanostructured Coating with Enhanced Photocathodic Protection Performance for Carbon Steel

“…The peak at 303 cm −1 belongs to the characteristic peak of the 1-Longitudinal optical (LO) phonon vibration modes of CdS. 41,42 In Figures 3d and S4b and TiO 2 /Au30/CdS may lead to the reduction of the Raman intensity compared to that of TiO 2 /Au10/CdS. XPS analysis has been used for investigating the valence states of the obtained coatings.…”

MOF-Derived Hollow Tubular In2O3/MIIIn2S4 (MII: Ca, Mn, and Zn) Heterostructures: Synergetic Charge-Transfer Mechanism and Excellent Photocatalytic Performance to Boost Activation of Small Atmospheric Molecules

“… Here, A i and τ i represent the intensity and individual lifetime values obtained from the exponential equation. The τ 1 corresponds to radiative emission due to direct interband photoexcited charge carrier recombination, and the decay time τ 2 is ascribed to the indirect recombination of trapped charge carriers . The longer decay time (τ 2 ) of hierarchical HT-In 2 O 3 /M II In 2 S 4 composites as compared to pure HT-In 2 O 3 is attributed to slow recombination of photogenerated electron–hole pairs.…”

“…The τ 1 corresponds to radiative emission due to direct interband photoexcited charge carrier recombination, and the decay time τ 2 is ascribed to the indirect recombination of trapped charge carriers. 50 The longer decay time (τ 2 ) of hierarchical HT-In 2 O 3 /M II In 2 S 4 composites as compared to pure HT-In 2 O 3 is attributed to slow recombination of photogenerated electron− hole pairs. The calculated average emission lifetime of the HT-In 2 O 3 /ZIS (1:1) nanocomposite (5.0 ns) is higher than that of HT-In 2 O 3 /MIS (1:1) (4.5 ns) and HT-In 2 O 3 /CIS (1:1) (4.4 ns) as well as pure In 2 O 3 (3.4 ns) materials.…”