ZnO–ZnS Heterojunctions: A Potential Candidate for Optoelectronics Applications and Mineralization of Endocrine Disruptors in Direct Sunlight

Abstract

Simple solution combustion synthesis was adopted to synthesize ZnO–ZnS (ZSx) nanocomposites using zinc nitrate as an oxidant and a mixture of urea and thiourea as a fuel. A large thiourea/urea ratio leads to more ZnS in ZSx with heterojunctions between ZnS and ZnO and throughout the bulk; tunable ZnS crystallite size and textural properties are an added advantage. The amount of ZnS in ZSx can be varied by simply changing the thiourea content. Although ZnO and ZnS are wide band gap semiconductors, ZSx exhibits visible light absorption, at least up to 525 nm. This demonstrates an effective reduction of the optical band gap and substantial changes in its electronic structure. Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and secondary-ion mass spectrometry results show features due to ZnO and ZnS and confirm the composite nature with heterojunctions. The above mentioned observations demonstrate the multifunctional nature of ZSx. Bare ZSx exhibits a promising sunlight-driven photocatalytic activity for complete mineralization of endocrine disruptors such as 2,4-dichlorophenol and endosulphan. ZSx also exhibits photocurrent generation at no applied bias. Dye-sensitized solar cell performance evaluation with ZSx shows up to 4% efficiency and 48% incident photon conversion efficiency. Heterojunctions observed between ZnO and ZnS nanocrystallites in high-resolution transmission electron microscopy suggest the reason for effective separation of electron–hole pairs and their utilization.

Rationally Designed, Efficient, and Earth-Abundant Ni–Fe Cocatalysts for Solar Hydrogen Generation

“…While the bare presence of three features could be seen for NFT11 and NFT13, no feature could be observed for NFT31. However, overall broadening indicates a strong electronic integration among the catalyst particles and more disordered surface structure of titania which facilitates generation of more oxygen vacancies impacting catalytic activity …”

“…However, overall broadening indicates a strong electronic integration among the catalyst particles and more disordered surface structure of titania which facilitates generation of more oxygen vacancies impacting catalytic activity. 45 Since the maximum changes were observed with NFT31 from the earlier characterizations and the highest SWS activity was observed with it (given in the next section; Table 1), it was decided to explore the NFT31 catalyst in more detail. To know about NFT31's surface elemental composition, oxidation state (Ni and Fe), and any other electronic state changes, XPS analysis was carried out.…”

ZnS Covering of ZnO Nanorods for Enhancing UV Emission from ZnO

“…In addition, the ZnS-covered ZnO NRs also show a scattering peak near 425 cm −1 which is the second-order nonpolar E 2 mode of ZnS. 58 As a representative of the ZnS-covered ZnO NRs, Figure 7 also illustrates the Raman backscattering spectra recorded from ZnS/ZnO-3 and ZnS/ZnO-5. In addition, it is obvious that the scatterings from ZnS get stronger as the thickness of the ZnS coating increases, whereas those from ZnO become weaker.…”

Construction of 2D‐ZnS@ZnO Z‐Scheme Heterostructured Nanosheets with a Highly Ordered ZnO Core and Disordered ZnS Shell for Enhancing Photocatalytic Hydrogen Evolution

“…[1][2]3] However the photocatalytic efficiency of TiO 2 is low due to its low quantum efficiency. ZnO is a promising candidate to TiO 2 with similar physical and chemical properties, [4][5]6] and ZnO exhibits a higher quantum efficiency compared to TiO 2 . [7,8] However, the direct band gap ZnO with a large band gap of 3.2 eV and the conduction position of À 0.31 eV at pH = 7, compared with that of standard hydrogen electrode (SHE, À 0.41 eV), hinder the production of photocatalytic H 2 .…”