Band-Gap Modulation for Enhancing NO Photocatalytic Oxidation over Hollow ZnCdS: A Combined Experimental and Theoretical Investigation

Abstract

The photocatalytic treatment of NO at ppm-level concentrations for the environment and human health protection has attracted ever-increasing interest in academia and industry. Here, hollow ZnCdS nanocage catalysts with different Cd dopings were prepared and used to remove NO under visible light, and a high removal rate of 85% was achieved. Density functional theory (DFT) theoretical calculations and experiments showed that Cd ions could effectively modulate the band gap of ZnS into the visible-light-absorbing range (2.69 eV). Zn 0.5 Cd 0.5 S with a cavity structure has an excellent photoelectric response and low electron− hole recombination probability. A relaxation signal of up to 2.33 μs was detected in the transient absorption spectrum, indicating the long lifetime of the photoexcited carriers. Furthermore, the photocatalytic oxidation process of NO was dynamically monitored by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It is found that NO adsorbed on the surface of Zn 0.5 Cd 0.5 S rapidly transformed into dimers (N 2 O 2 ) under dark and facilitated NO conversion to nitrate via intermediates such as nitrite after illumination (N 2 O 2 → NO → NO 3 − ). The high activity and stability of Zn 0.5 Cd 0.5 S present a high potential for scale-up application of the catalyst for NO oxidation under visible light.

Induced dipole moments in amorphous ZnCdS catalysts facilitate photocatalytic H2 evolution

“…As shown in Supplementary Fig. S3 , the HOMO charge densities are strongly localized at the S atoms, and the LUMO charge densities are strongly localized at the Zn, Cd, and S atoms, which is consistent to the literature that the valence band (VB) maximum of ZnCdS is mainly dominated by the 3 p orbital of the S atom, while the conduction band (CB) minimum of ZnCdS is mainly contributed by the hybridization of the 4 s orbital of the Zn atom, the 5 s orbital of the Cd atom and the 3 p orbital of the S atom 24 . In addition, the bandgap of AZCS is narrower than its CZCS counterpart, suggesting that AZCS can absorb a broader range of light.…”

Rational Design of Electron Transfer Kineties of CdS/Zn(impim) Dots-on-Rods for Efficient Visible-Light Reduced C-X Bond

“…These XPS results fully demonstrate the existence of CdS in CdS/Zn­(impim). In the high-resolution XPS spectrum of Zn, the Zn 2p 1 and Zn 2p 3 peaks are located at 1044.45 and 1021.31 eV, − respectively, suggesting the presence of Zn 2+ in CdS/Zn­(impim). Compared with the Cd 3d and S 2p peaks of the original CdS microspheres, the corresponding peaks of CdS/Zn­(impim) are shifted by 0.15 and 0.22 eV to the lower binding energy, respectively.…”

Ag/Cr-TiO2 and Pd/Cr-TiO2 for Organic Dyes Elimination and Treatment of Polluted River Water in Presence of Visible Light

“…As an alternative to overcome these problems, different researchers worldwide have studied the doping of TiO 2 with metallic species such as Ag, Au, Co, Cu, Cr, Fe, Ni, Mn, Pt, and Ru [ 3 ], among many others. The modification of titania and other semiconductors with different metals led to improve photochemical properties by acting as electron traps, thus, avoiding the electron–hole pair recombination, reducing the bandwidth, or adding new energy levels to efficiently absorb visible light from the electromagnetic spectrum [ 4 , 5 , 6 ].…”