A facile protocol to greatly increase the amplitude of surface-enhanced Raman scattering and harvest significant photoinduced-enhanced Raman scattering by exploiting the synergy of 2D ZnO nanoflakes.
The techniques we describe herein are straightforward yet incredibly efficient in providing a favorable environment for two-dimensional (2D) zinc oxide nanoflakes (ZnONFs) to greatly increase the intensity of surfaceenhanced Raman scattering (SERS) and produce significant photoinduced-enhanced Raman scattering (PIERS). Rhodamine 6G (R6G) was used as a Raman probe, and silver nanoparticles (AgNPs) as the SERS mediator. Two types of heterostructure composites, ZnONFs-R6G-AgNPs and ZnONFs-AgNPs-R6G, were fabricated onto four different base substrates (aluminum, copper, , stainless steel, and silicon-wafer) by a simple sequential drop deposition technique. Intriguingly, ZnONFs-R6G-AgNPs could yield a ~3.2-fold larger SERS enhancement factor (EF) than ZnONFs-AgNPs-R6G, which rendered the ZnONFs-R6G-AgNPs heterostructure a good choice for comprehensive investigations. For inducing PIERS, ZnONFs-R6G-AgNPs stacks were photoirradiated with a 365 nm UV light having energy just above the bandgap of ZnO (band edge ~400 nm). Remarkably, ZnONFs-R6GAgNPs could produce gigantic SERS and PIERS intensities of R6G compared to AgNPs alone, yielding 8.2- and 12.0-fold larger magnitudes of the EF, respectively. The observed enormous magnitudes of SERS and PIERS intensities are attributed to the synergistic interplay of ZnONFs evolved with AgNPs. Of the four base substrates, aluminum was found to be the best for observing a remarkable synergy of ZnONFs on SERS, while silicon wafer was the best for PIERS, presumably due to the contributions of additional charge carriers photogenerated by the 785 nm (≈1.6 eV) laser excitation. Thanks to the synergy that ZnONFs conferred, we were able to discriminate the Raman signal of R6G and aldicarb (AlC) pesticide at concentrations as low as 10 14 M on both aluminum and silicon-wafer substrates. Furthermore, our observation demonstrates that the particular heterostructure composite offers the unique opportunity to study the two seemingly opposing functions of ZnONFs (synergy on SERS/PIERS intensity enhancement and triggering the photocatalytic activity) through a single experimental platform.
Unveiling the Role of Sintering Temperatures in the Physical Properties of Cu-Mg Ferrite Nanoparticles for Photocatalytic Application
This research presents an explicit analysis of the effects of sintering temperature (Ts) on the structural, morphological, magnetic, and optical properties of Cu0.5Mg0.5Fe2O4 nanoferrites synthesized via the sol-gel method. To accomplish it, Cu-Mg ferrite NPs were sintered at temperatures ranging from 300 to 800 ºC in increments of 100 with a constant holding duration of 5 hours. Thermogravimetric analysis was used to observe the degradation of organic components and the thermally stable zone of the material. XRD analysis and SAED patterns revealed the formation of a single face-centred cubic (fcc) spinel structure with an Fd–3m space group. The particle's crystallite sizes have grown from 4.54 to 102.54 nm as Ts have increased, consistent with TEM results. Further evidence for the creation of spinel structure was provided by two prominent absorption bands in FTIR spectroscopy below 1000 cm-1. The particles were found to have a densely packed, nearly spherical morphology, as confirmed by TEM images. The EDS was utilized to identify the chemical species that were present in the sample. A significant correlation was observed between particle size and magnetic properties. The field-dependent magnetization investigations revealed that particles with crystallite sizes of 4.54 and 5.10 nm were superparamagnetic, while those measuring 11.68, 23.81, 42.95, and 102.54 nm exhibited ferrimagnetic characteristics. Furthermore, it was revealed that an increase in sintering temperature results in a concurrent amplification of crystallites, which subsequently heightens the saturation magnetization of the prepared NPs from 9.49 to 33.04 emu/g. The coercivity value clarifies the sintering effect of transforming the particle from a single-domain to a multi-domain magnetic state. The finite-size scaling formula precisely characterizes the changes in Curie temperature. In addition, the semiconducting characteristics of Cu-Mg ferrite NPs were confirmed through DRS, which unfolded an optical band gap within the range of 1.84-2.26 eV. The Mulliken electronegativity approach unveiled the prospective efficacy of these NPs in photocatalytically generating O2 from water. Cu-Mg nanoferrites exhibit a favourable bandgap and potential as a photocatalyst, rendering them a potentially fruitful addition to the family of ferrite materials utilized in photocatalytic and associated solar energy applications.
Enhanced photocatalytic activity in RhB dye degradation by Mn and B co-doped mixed phase TiO2 photocatalyst under visible light irradiation.
Here, we report synthesis of undoped, manganese (Mn) doped, boron (B) doped and Mn-B co-doped TiO2 nanoparticles (NPs) by a cost-effective sol-gel method. The structural properties, phase, micro-morphology and particle size of the synthesized nanoparticles have been characterized by X-ray diffraction, Raman spectroscopy, Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) techniques. These studies revealed that undoped and mono (Mn/B) doped TiO2 NPs exhibit only anatase phase, whereas (Mn and B) co-doped TiO2 NPs exhibit anatase and rutile mixed phase structure. Furthermore, co-doping reduces the particle size, agglomeration in aqueous medium and the sample possesses crystal defects. UV–Visible diffusive reflectance spectroscopy (DRS) revealed that the co-doped sample demonstrates extended optical response in the visible wavelength range of the solar spectrum and is red shifted when compared to undoped and mono doped TiO2 NPs. The obtained optical band gap (2.11 eV) and the Urbach energy (1.12 eV) for the Mn and B co-doped TiO2 NPs suggest the formation of mid-gap energy states, which might make this NPs a suitable candidate for photocatalysis in the visible light spectrum. We investigated the photocatalytic degradation of rhodamine B (RhB) dye by the synthesized NPs under visible light irradiation. Our studies revealed that co-doped TiO2 photocatalyst can degrade 99% of RhB dye within 90 min of visible light irradiation and can retain 95% degradation efficiency up to the third consecutive cycles. Finally, we provide a plausible explanation for such enhanced visible light assisted photocatalytic performance.