Kgotla Katlego Masibi

Zinc indium sulphide (ZIS) quantum dots (QDs) have attracted remarkable attention due to their non-toxicity and tuneable optical properties. However, little attention has been given to their optoelectronic properties for electrochemical sensor applications. This limitation is largely attributed to their defect-rich lattice, arising from In/Zn antisite defects that impede efficient charge transport. Herein, this study reports on the aqueous reflux synthesis of ZIS QDs under varying reaction times (0-135 min), pH values (2, 4, 7, 11), and precursor concentrations (sulfur and gelatin), followed by coating the core with zinc sulfide (ZnS) to form ZIS/ZnS QDs. The formation of ZIS/ZnS QDs resulted in a red-shifted emission maximum with enhanced peak intensity, indicating reduced surface defects and increased size following shell growth. Electrochemical characterization of the synthesized ZIS and ZIS/ZnS QDs using Cyclic Voltammetry (CV) and Square-Wave Voltammetry (SWV) showed comparable redox features for both systems. CV showed similar redox features for both ZIS QDs and ZIS/ZnS, with ZIS/ZnS exhibiting an enhanced current response, attributed to improved charge-transfer kinetics resulting from ZnS-induced defect passivation. Similarly, SWV showed an enhanced peak current for ZIS/ZnS QDs, with two additional peaks at +0.53V and +0.74V (vs Ag|AgCl), suggesting modified surface states and enhanced electrochemical responses following effective passivation. The findings in this paper reveal that defect passivation with ZnS shell is an effective strategy to improve charge transport in ZIS QDs, demonstrating their potential in optoelectronic devices and electrochemical sensor applications.

Bioengineering of bimetallic oxides is a significant requirement for both social and environmental applications. In this work, bimetal oxide nanomaterials, Zinc orthotitanate Zn₂TiO₄ was produced using a green process which utilizes natural extract of Hibiscus sabdariffa. More accurately, natural extract/phyto-compounds of Hibiscus sabdariffa was validated as an effective chelating agent at room temperature and atmospheric pressure. A variety of techniques were applied to analyse their physicochemical properties and verify the production of the Zn₂TiO₄ nanoparticles. The XRD analysis illustrated the crystalline structure of the Zn₂TiO₄ nanocomposites. The SEM analysis showed the morphology of the compounds Zn₂TiO₄ to be highly porous. The EDS analysis validated the presence of elements such as Ti, and Zn while FTIR analysis indicated the existence of multiple functional groups, including O-H, C-H, C=O, Ti-O, and Zn-O bonds in the compound. The PL peaks identified at 240 and 450 nm are attributed to the charge transfer characteristics present in the surface state of the resulting product. The single phase crystals of the bio-engineered Zn₂TiO₄ were found to be within the nanoscale while exhibiting a significantly elevated photocatalytic efficacy in decomposing Methylene Blue reaching a threshold of about 94.1% efficacy at about 120 min. From the electrochemistry viewpoint, the bioengineered Zn₂TiO₄ nanomaterial demonstrated enhanced redox activity and stability, exhibiting 94.2% current retention after 20 cycles. Cyclic voltammetry (CV) studies confirmed a diffusion-controlled process, while electrochemical impedance spectroscopy (EIS) revealed a 10-fold reduction in charge transfer resistance ®_ct), from 5.48 to 0.53 KΩ. This significant acceleration in electron transfer kinetics is corroborated by a nearly 2-fold increase in interfacial admittance (Y_o), indicating an expanded electroactive surface area. These results demonstrate the applicability and potential for Zn₂TiO₄ nanomaterial in advanced electrochemical applications. From the antibacterial perspective, Zn₂TiO₄ nanomaterial showed limited activity in the agar-disc diffusion assay, with no meaningful inhibition against most tested Gram-positive and Gram-negative strains and only a marginal response against K. pneumoniae. These results suggest that any antibacterial potential of the Zn₂TiO₄ nanomaterial may likely to be strongly dependent on assay format, nanoparticle dispersion, contact conditions, and possible light-driven ROS generation.

The potential for bio-inspired conversion of CO ₂ to single phase Hydrozincite Zn ₅ (CO ₃ ) ₂ (OH) ₆ was confirmed for the first time in this contribution utilising aqueous extracts of Zea Mays var. saccharata (ZMS). The latter has been a successful chelating/reduction agent. Under ambient circumstances (room temperature & atmospheric pressure), this novel method produced single phase crystalline Hydrozincite Zn ₅ (CO ₃ ) ₂ (OH) ₆ with an average crystallite size of 38.5 nm. Furthermore, by including carbonate, this process provides a possible route for CO ₂ capture. The UV-VIS-DRS, PL, FT-IR, XRD, and SEM-EDS studies sustained the potential of the bio-engineered nanoscaled Hydrozincite Zn ₅ (CO ₃ ) ₂ (OH) ₆ as a high reflecting material (Diffuse reflectance > 85%) & an effective blue luminescence (λ ^Max _Emission ≈ 457.3 nm). Electrochemical properties were investigated in 1 M NaOH electrolyte using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV studies demonstrated a significant increase in current response with distinct Faradaic peaks at + 0.07 V, + 0.18 V, and − 0.16 V (vs Ag|AgCl), confirming electrocatalytic activity of the nanoparticles. This was further corroborated by EIS, which showed a substantial reduction in charge transfer resistance (R _ct ) from 845.84 kΩ for the bare glassy carbon electrode (GCE) to 94.30 kΩ for the Zn ₅ (CO ₃ ) ₂ (OH) ₆ modified GCE, indicating significantly improved charge transfer kinetics. These results demonstrate a scalable bio-engineering route for synthesizing single phase crystalline hydrozincite Zn ₅ (CO ₃ ) ₂ (OH) ₆ nanoparticles with favorable opto-electrochemical properties, positioning them as promising candidates for applications in CO ₂ conversion, optoelectronics & catalysis.

This report narrates the successful application of a fabricated novel sensor for the trace detection of endosulfan (EDS). The sensor was made by modifying a glassy-carbon electrode (GCE) with polyaniline (PANI), chemically synthesized antimony oxide nanoparticles (AONPs), acid-functionalized, single-walled carbon nanotubes (fSWCNTs), and finally, the AONP-PANI-SWCNT nanocomposite. The electrochemical properties of the modified electrodes regarding endosulfan detection were investigated via cyclic voltammetry (CV) and square-wave voltammetry. The current response of the electrodes to EDS followed the trend GCE-AONP-PANI-SWCNT (−510 µA) > GCE-PANI (−59 µA) > GCE-AONPs (−11.4 µA) > GCE (−5.52 µA) > GCE-fSWCNTs (−0.168 µA). The obtained results indicated that the current response obtained at the AONP-PANI-SWCNT/GCE was higher with relatively low overpotential compared to those from the other electrodes investigated. This demonstrated the superiority of the AONP-PANI-SWCNT-modified GCE. The AONP-PANI-SWCNT/GCE demonstrated good electrocatalytic activities for the electrochemical reduction of EDS. The results obtained in this study are comparable with those in other reports. The sensitivity, limit of detection (LoD), and limit of quantification (LoQ) of AONP-PANI-SWCNT/GCE towards EDS was estimated to be 0.0623 µA/µM, 6.8 µM, and 20.6 µM, respectively. Selectivity, as well as the practical application of the fabricated sensor, were explored, and the results indicated that the EDS-reduction current was reduced by only 2.0% when interfering species were present, whilst average recoveries of EDS in real samples were above 97%.

This work describes the chemical synthesis of antimony oxide nanoparticles (AONPs), polyaniline (PANI), acid functionalized single-walled carbon nanotubes (fSWCNTs), and the nanocomposite (AONP-PANI-SWCNT) as catalyst for the trace detection of lindane. Successful synthesis of the nanomaterials was confirmed by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, x-ray diffraction (XRD) spectroscopy, and scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for investigating the electrochemical behavior of the modified electrodes in the ferrocyanide/ferricyanide ([Fe(CN)₆]⁴⁻/[Fe(CN)₆]³⁻) redox probe. GCE-AONP-PANI-SWCNT exhibited faster electron transport properties as well as higher electroactivity as compared to bare-GCE, GCE-AONPs, GCE-PANI, and GCE-SWCNT electrodes. Electrocatalytic studies further showed that GCE-AONP-PANI-SWCNT modified electrode was stable (after 20 scans) with only a small current drop in lindane (0.57%). The GCE-AONP-PANI-SWCNT electrode with low detection limit of 2.01 nM performed better toward the detection of lindane as compared to other studies in literature. The GCE-AONP-PANI-SWCNT electrode is highly selective toward the detection of lindane in the presence of various organic and inorganic interfering species. Real sample analysis of river water and tap water samples using the developed sensor gave satisfactory percentage recoveries therefore confirming the potential of the proposed sensor for practical application.