Biomimetic Synthesis, Characterization, and Evaluation of Fluorescence Resonance Energy Transfer, Photoluminescence, and Photocatalytic Activity of Zinc Oxide Nanoparticles

Abstract

Owing to the development of nanotechnology, biosynthesis of nanoparticles (NPs) is gaining considerable attention as a cost-effective and eco-friendly approach that minimizes the effects of toxic chemicals used in NP fabrication. The present work reports low-cost phytofabrication of zinc oxide (ZnO) NPs employing aqueous extracts of various parts (leaves, stems, and inflorescences) of Tephrosia purpurea (T. purpurea). The formation, structure, morphology, and other physicochemical properties of ZnO NPs were characterized by ultraviolet–visible (UV–Vis) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS). UV–Vis spectral analysis revealed sharp surface plasmon resonance (SPR) at around 250–280 nm, while the XRD patterns confirmed distinctive peaks indices to the crystalline planes of hexagonal wurtzite ZnO NPs. TEM analysis confirmed the presence of spherical-shaped ZnO NPs with average particle sizes (PS) between 25–35 nm, which was in agreement with the XRD results. FTIR analysis revealed that phenolics, flavonoids, amides, alkaloids, and amines present in the plant extract are responsible for the stabilization of the ZnO NPs. Further, the hydrodynamic diameter in the range of 85–150 nm was measured using the DLS technique. The fluorescence resonance energy transfer (FRET) ability of biogenic ZnO NPs was evaluated, and the highest efficiency was found in ZnO NPssynthesized via T. purpurea inflorescences extract. Photoluminescence (PL) spectra of biogenic ZnO NPs showed three emission peaks consisting of a UV–Vis region with high-intensity compared to that of chemically synthesized ZnO NPs. The biosynthesized ZnO NPs showed photocatalytic activity under solar irradiation by enhancing the degradation rate of methylene blue (MB). Among the prepared biogenic ZnO NPs, T. purpurea leaves mediated with NPs acted as the most effective photocatalyst, with a maximum degradation efficiency of 98.86% and a half-life of 84.7 min. This is the first report related to the synthesis of multifunctional ZnO NPs using T. purpurea, with interesting characteristics for various potential applications in the future.

Green Synthesis, Structural Characterization and Photocatalytic Applications of ZnO Nanoconjugates Using Heliotropium indicum

“…Luminescence is one of the fastest-growing, and most sensitive, nondestructive techniques that help to understand point defects including extrinsic and intrinsic defects of semiconductor materials like ZnO, and TiO 2 [13,16,27,28]. ZnO with a wurtzite structure is one of the most promising n-type semiconductors for short-wavelength optoelectronic applications, displaying excellent chemical and thermal properties with a wide bandgap of 3.37 eV and high excitation binding energy of 60 meV at room temperature (RT) [12,[14][15][16]. It has attractive and novel optoelectronic properties such as high physical and chemical stability, luminescence, and superior UV emission characteristics at RT than TiO 2 [9,15,29,30].…”

“…Hence, nanosized semiconductors can act as effective photocatalysts for the degradation of various environmental pollutants (e.g., pesticides, detergents, dyes, and volatile organic compounds) in the presence of UV light and Sunlight irradiation [2,14,23,31]. To date, several methods, such as bio-treatment, incineration, ozonation, and adsorption processes based on solid adsorbents, have been utilized to treat wastewater containing pigments or dyes [15,24,32]. However, these methods are quite expensive and produce toxic non-biodegradable side products.…”

“…Moreover, ZnO NPs are being applied as bright fluorescent markers with enhanced photostability in fluorescence microscopy, sensor technology, and microarrays due to the interaction of fluorophores with MONPs, displaying various spectral changes such as enhancement in luminescence intensity, photostability, and quantum yield [33][34][35]. Fluorescence resonance energy transfer (FRET), a non-radiative quantum mechanical process that relies on the distance and energy transfer from an excited state donor to a ground state acceptor through dipole-dipole interactions [33,[35][36][37], is being widely used in polymer science, biochemistry, and structural biology [15,35]. The energy transfer between quantum dots has been investigated broadly to design FRET sensors [38][39][40].…”

“…To the best of our experience, the present study remains the first endeavor that used biogenic ZnO NPs synthesized from Heliotropium indicum (H. indicum) to investigate the efficacy of FRET. In FRET, when NPs are in close proximity to fluorophores, quenching of the luminescence occurs because the non-radiative decay of the excited molecules will increase due to energy transfer from the dyes to the NPs; conversely, when NPs are located at a greater distance, enhancement of the luminescence is observed due to a decrease in non-radiative decay [15,33,[35][36][37]. These effects have been explained by interactions with surface plasmon resonance in the NPs and fluorophore [15,41].…”

“…Metal and metal oxide NPs (MONPs) (e.g., gold, silver, nickel, copper, magnesium oxide, titanium dioxide (TiO 2 ), copper oxide, and zinc oxide (ZnO)) play a crucial role in many areas of chemistry, biomedical, and material science due to their unique physical properties, chemical reactivity, and potential applications [6][7][8][9][10][11]. Among MONPs, ZnO NPs are prominent in almost all their applicable fields, being commonly used in ceramics, electronics, cosmetics, piezoelectric transducers, chemical sensors, anti-UV additives, and photocatalysts due to their unique optical and chemical behaviors which can be simply tuned by changing their morphology [3,[12][13][14][15][16].…”