Nanomaterials and Nanotechnology

Herein, we synthesized gold-coated ZnO/Fe₃O₄ nanocomposites. Initially, we prepared Fe₃O₄ magnetic nanoparticles based on the co-precipitation of Fe³⁺ and Fe²⁺ under aqueous ammonia as a precipitating agent. Thereafter, the ZnO/Fe₃O₄ composite was prepared by dispersing the synthesized magnetic nanoparticles into an alkaline zinc nitrate solution. After calcination of the precipitate, the formed ZnO/Fe₃O₄ composites were coated with gold nanostructures by dispersing the composites in auric acid/ethylene glycol solution in a water bath. The synthesized Au@ZnO/Fe₃O₄ hybrid material was able to catalyze the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). We demonstrate that this catalytic activity can be exploited for the detection of Hg²⁺ ions in a cosmetic product. In the presence of Hg²⁺ ions, the catalytic activity of Au@ZnO/Fe₃O₄ was greatly suppressed. This novel finding underlies a straightforward, sensitive, and highly selective detection probe for Hg²⁺. The material exhibited excellent analytical performance as marked by the very low limit of detection (LOD) of 2.34 nM, which was well below acceptable levels of 4.99 μM for mercury in cosmetics as set by the US Food and Drug Administration (FDA), and within the linear dynamic ranges of 0–10 nM. High recoveries ranging from 96.5 to 100.3% accompanied by excellent selectivities toward Hg²⁺ over potentially interfering species were obtained.

In this study, an all-optical multiplexer (Mux) based on elliptical insulator-metal-insulator (IMI) plasmonic waveguides is designed. The area of the proposed structure is very small (400 nm × 400 nm) which operates at a wavelength of 1,550 nm. The developed device utilizes constructive and destructive interferences between the input signals and the selector signal. This structure is less complex and has lower loss compared to the previous works. Transmission (T), contrast ratio (CR), modulation depth (MD), insertion loss (IL), and contrast loss (CL) are the five parameters that describe the performance of the plasmonic Mux. The transmission threshold between logic 0 and logic 1 is 0.5. Moreover, the maximum transmission efficiency of the device is 163%. Moreover, based on the MD value of 95.09%, the dimensions of the proposed structure are excellent and optimal. The proposed plasmonic Mux structure contributes substantially to developing an all-optical arithmetic logic unit (ALU) and all-optical signal processing nanocircuits. The finite element method (FEM) simulates the proposed plasmonic multiplexer with COMSOL Multiphysics 5.4 software.

This study synthesized carbon quantum dots (CQDs) with green photoluminescence through a hydrothermal method that utilized mulberry juice as the carbon source. The influence of fruit ripeness on the physical and chemical properties, focusing on the fluorescence spectra, has been explored. Fourier-transform infrared spectroscopy (FT-IR) and energy dispersive X-ray analysis (EDX) showed that there were oxygen-containing groups, and X-ray diffraction (XRD) showed that the carbon quantum dots (CQDs) were graphitic. The results revealed that the CQDs had an average size of around 7.4 nm and 9.7 nm for unripe and ripe mulberry juice, respectively. These CQDs emitted green light at 500 nm and 510 nm in unripe and ripe mulberry juice, respectively, when excited at a wavelength of 400 nm. The prepared CQDs exhibited excitation-dependent photoluminescence (PL) emission behavior, demonstrating their dependence on the excitation light. The impact of fruit ripeness on optical properties was explored by examining fluorescent spectra from different fruits (including tomato and blackberry), demonstrating comparable behaviors observed in mulberry fruit. In addition, the prepared CQDs were utilized as a fluorescent sensor with high specificity to detect Cu²⁺ ions. The detection limit (DL) for this sensor was determined to be 0.2687 µM, and the limit of qualification (LOQ) is 0.814 µM. The linear range for detection lies between 0.1 and 1 µM. The selectivity of the CQDs towards Cu²⁺ ions was confirmed by recording the PL response for Cu²⁺ ions compared to the weak response of other metal ions. According to these results, the CQDs can be applied in various cellular imaging and biology applications, bio-sensing, optoelectronics, and sensors.

In the current study, the researchers have explored the influence of doped Mg ions on the optical, morphological, and structural properties of zinc sulfide (ZnS) nanoparticles (NPs). The green technique was employed to prepare pure and 2% and 5% Mg-doped ZnS NPs using the Plectranthus barbatus leaf extract as a capping agent. XRD, SEM, FTIR, and UV-visible were used in the investigation process. The XRD results showed that all the synthesized materials have a cubic structure with space group F-43m. The D_av was nearly in the range of 2.02–2.20 nm. The SEM images illustrated that NPs were agglomerated. The UV-visible results showed that the optical bandgap increased as Mg²⁺ ions increased, which was in the range of 3.81–4.42 eV. The absorption shoulder of the prepared NPs is blue-shifted with increasing dopant concentration. The FTIR spectrum gives characteristic peaks for Zn-S bonds and asserts NPs’ formation. The antibacterial check against E. coli and S. aureus bacterial strains revealed that pure and Mg-doped ZnS NPs have higher activity for both bacterial strains. The results have shown that the prepared materials can be used for antibacterial activities and optoelectronic applications.

Bismuth (Bi) is a highly reactive catalyst for the generation of hydroxyl (∙OH) radicals. Cathodes constructed from composites of Bi and carbon nanotube (CNT) exhibit high stability and low resistance, which enhance their electron transfer capability. In this work, a titanium substrate was coated with multi-walled carbon nanotube (MWCNT/Ti) using electrophoretic deposition process, followed by electrodeposition of Bi onto the MWCNT-coated Ti (Bi/MWCNT/Ti). The effects of Bi electrodeposition time on the surface morphology of Bi/MWCNT/Ti cathodes were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy, and the electrochemical characteristics of each cathode were identified via a series of electrochemical analyses further. The results demonstrated that electrodeposition at −0.85 V vs. Ag/AgCl for 5 min revealed uniform distribution of dense Bi across the surface of cathode, which provides better hydrophilicity for cathode and promotes highest electron transfer rates, respectively; when the Bi/MWCNT/Ti cathode was used as an electro-Fenton (EF) cathode, the EF system achieved a rhodamine B degradation rate of 80.8% after 30 min, which is a significant increase (83.63%) than the unmodified Ti cathode. The use of Bi in EF cathodes improves the efficiency of the EF process.

Silver nanoparticles (AgNPs) were produced by green synthesis using Raphanus sativus (RsAgNPs), Beta vulgaris (BvAgNPs), and Ocimum basilicum (ObAgNPs) leaf extracts as reducing agents. Plant phytochemical composition analysis indicated that they contain phenolic compounds that can participate in the synthesis reaction as flavonoids. Synthesized AgNPs presented maximal absorption peak at 430 nm (RsAgNP), 440 nm (BvAgNP), and 420 nm (ObAgNP) in ultraviolet-visible spectrophotometry analysis. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis showed that RsAgNPs are 76 nm diameter spheres made of up to 54.1% silver, the BvAgNPs are 78 nm diameter spheres with 39.76% silver, and the ObAgNPs are cubes of 99 nm edges with 69.74% silver. The found Z potential values indicate that all the obtained AgNPs are stable in phosphate buffer. A disinfection of 100% and 90% was achieved for the in vitro culture of Arabidopsis thaliana and Psidium guajava (guava) seeds, respectively, with all AgNPs synthesized. Treatment with these AgNPs showed no negative effects on germination, and on the contrary, in guava, a higher germination percentage was observed when the seeds were exposed to RsAgNPs. Only at high concentration (10 mg/mL) of AgNPs, the growth of A. thaliana was decreased, while at low concentration (0.01 mg/mL) of ObAgNP and BvAgNPs, higher growth was showed, specifically 60 and 40% more than the control, respectively. All AgNPs showed antimicrobial activity against Escherichia coli and Klebsiella oxytoca which are bacteria of clinical interest, and against Agrobacterium tumefaciens, a bacterium used in the genetic transformation of plants.