Defect-Mediated Slow Carrier Recombination and Broad Photoluminescence in Non-Metal-Doped ZnIn₂S₄ Nanosheets for Enhanced Photocatalytic Activity

Abstract

Elemental doping has already been established to be one of the most effective approaches for band-gap engineering and controlled material response for improved photocatalytic activity. Herein atomically thin ZnIn2S4 (ZIS) nanosheets were doped with O and N separately, and the effects of doping were spectroscopically investigated for photocatalytic H2 evolution. Steady-state photoluminescence studies revealed an enhanced charge-carrier population in the doped systems along with a defect-state-induced broad peak in the red region of the spectra. Transient absorption (TA) spectroscopy demonstrated that the conduction-band-edge electrons are transferred on an ultrafast time scale to the inter-band-gap defect states. TA analysis suggests that O and N doping contributes to the defect state concentration and ensures an enhanced photocatalytic activity of the system. This detailed spectroscopic analysis uncovers the role of inter-band-gap defect states in the photocatalytic activity of ZIS and will open new avenues for the construction of nanosheet-based optical devices.

Ultrafast Hot Electron Transfer and Trap-State Mediated Charge Carrier Separation toward Enhanced Photocatalytic Activity in g-C3N4/ZnIn2S4 Heterostructure

“…In Figure c-iv, the HRTEM image of CN displays the lattice fringes of 0.32 nm spacing, which matches with the interplanar distance of the (002) plane (Figure a). Figure c-ii shows the morphology of ZIS flakes which are in good agreement with earlier reports , Figure c-v represents the HRTEM image of pristine ZIS. The distance between lattice fringes are found to be 0.41 nm which matches with diffraction from the (006) planes of hexagonal ZIS.…”

“…This excitonic feature must be originating from the involvement of the higher order excited states in the conduction regime of CN. We observed similar observations in the TA study of ZIS earlier . Next, to understand the exciton relaxation mechanism, the HSE and BSE states are monitored by probing at 392 and 450 nm shown in Figure b, and the kinetics traces are fitted with multiexponential functions and are listed in the Supporting Information (Table S2).…”

“…The absorption peak maximum is the expression of the π–π* transition in the CN network . The ZIS absorption spectrum also displays a peak maxima around 400 nm which is assigned as a higher energy transition . Interestingly, the CN/ZIS spectrum strongly resembles that of ZIS, although the visible regime absorption is slightly enhanced.…”

“…The fabrication of a heterostructure by integrating another semiconductor is a plausible way to overcome such obstacles. Several permutations and combinations have already been applied to design an effective heterostructure based on CN. − Just like CN, hexagonal ZnIn 2 S 4 (ZIS) is also garnering enormous interest because of its two-dimensional properties and attracting photocatalytic activity. , The heterostructure made of both CN and ZIS will be very interesting considering the fact that both are photoactive materials and will go on to construct a 2D–2D van der Waal’s heterostructure and might have the ability to improve photocatalytic activity with respect to the pristine systems. There are a few reports of CN/ZIS heterostructures where the photocatalytic activity is improved following the formation of the heterojunction. − Although the improvement has not reached that expected level, what this particular heterojunction really deserves, considering its immense potential.…”

“…12−14 Just like CN, hexagonal ZnIn 2 S 4 (ZIS) is also garnering enormous interest because of its two-dimensional properties and attracting photocatalytic activity. 15,16 The heterostructure made of both CN and ZIS will be very interesting considering the fact that both are photoactive materials and will go on to construct a 2D−2D van der Waal's heterostructure and might have the ability to improve photocatalytic activity with respect to the pristine systems. There are a few reports of CN/ZIS heterostructures where the photocatalytic activity is improved following the formation of the heterojunction.…”