Excitons with Reverse Rectifying Characteristics for Superior Solar Photocatalysis

Abstract

This study demonstrates an inverted energy‐gradient hybrid nanoparticle architecture that supports the formation of 2D excitons in the nanoshell domain. The developed geometry places a wide‐gap semiconductor quantum dot (ZnS, Eg= 3.68 eV) at the core of the nanocomposite particle in order to funnel the photoinduced energy into the low‐gap (CdS, Eg= 2.42 eV) shell layer. This inverted band regime helps to extract the photogenerated excitons into the shell and hence increases the exciton transport quantum efficiency, hereby leading to the superior photocatalytic efficiency for photoredox reactions over the nanohybrid. To demonstrate bandgap engineering and photoinduced charge carrier delocalization, we employed steady‐state and time‐resolved emission and absorption techniques in the presence and absence of an electron quencher (4‐nitrophenol) and hole quencher (4‐methoxyphenol). The significant suppression of band‐edge emissions and the decrement of the fluorescence lifetimes demonstrated the key role of nanoshell on the transfer of photogenerated charge carriers from core to the surface of the photocatalyst. Detailed investigations of the photocatalytic activity of ZnS@CdS and kinetic study of the reactions were also carried out under solar radiation. The contribution of O2•− and •OH to photocatalytic reactions revealed respectively via luminol chemiluminescence and terephthalic acid photoluminescence techniques.

Magnetically Separable Fe3O4@CdS Type‐II Nanohybrids with Excellent Photocatalytic Activity and Antibacterial Properties

“…The complete absence of core (magnetite) peaks and the presence of shell (CdS) peaks indicate the core–shell structure of the magnetite@CdS NHs. This is in good agreement with previous reports on core–shell systems, for which, as the shell diameter increases, the diffraction pattern of the shell material prevails . Additionally, the observed shift in the 2 θ position of the XRD reflection peaks of Fe 3 O 4 @CdS NHs to higher reflection angles can be correlated with the decrease in interplanar separation of the crystal lattice and formation of compressive strain in the samples, owing to the Miller mismatch between Fe 3 O 4 and CdS.…”

“…This is in good agreement with previousr eports on core-shell systems, for which,a st he shell diameter increases, the diffraction pattern of the shell material prevails. [29,30] Additionally,t he observed shift in the 2 q position of the XRD reflection peaks of Fe 3 O 4 @CdS NHs to higher reflection anglesc an be correlated with the decrease in interplanar separation of the crystal lattice and formation of compressive strain in the samples, owing to the Miller mismatch between Fe 3 O 4 and CdS. In the proposed core-shell NHs, ac ompressive strain is inducedo nt he CdS crystal planes by the Fe 3 O 4 crystal with smaller d spacing.…”