We demonstrate a facile and reproducible means of producing quasi-spherical, colloidally stable gold nanoparticles (AuNPs) on the basis of rapid room-temperature mixing of aqueous solutions of HAuCl 4 and a cyclic oxocarbon diacid (squaric acid, SA; croconic acid, CA; or rhodizonic acid, SR) or ascorbic acid (AA) as dual reducing and capping agent. Although these reducing agents generally produced larger particles than those derived from the classical Turkevich method (using citrate in boiling water) and achieved a lower nanoparticle size uniformity in our hands (i.e., 30.4 ± 8.6, 33.1 ± 9.3, 29.9 ± 6.3, and 29.7 ± 7.6 nm for SA, AA, CA, and SR, respectively, compared with 15.8 ± 3.7 nm for citrate), the method is versatile and exceptionally convenient as fairly monodisperse AuNPs can be made "on-demand" within seconds by simple mixing in the absence of heating. A preliminary investigation into the effects of reaction parameters, such as synthesis temperature and the molar ratio of reducing agent to HAuCl 4 , was carried out. The reagent molar ratio was found to play a pivotal role in the mean AuNP size and size distribution, whereas reaction temperature (e.g., 5, 20, or 100 °C) only played a very minor role. Interestingly, CA-and SRmediated reduction generated AuNPs displaying bimodal size distributions, with a large fraction of the total nanoparticle count being represented by small AuNPs in the 3.5 ± 1.9 nm (CA) and 5.1 ± 1.0 nm (SR) size regimes. Cyclic and differential pulse voltammetry procedures were conducted to gain insight into the redox chemistry of the cyclic oxocarbons as prospective reducing agents for general metal nanoparticle synthesis as well as to furnish additional evidence in support of a proposed mechanism for the overall oxidation process using squaric acid as a representative cyclic oxocarbon acid. Finally, the catalytic activities of the prepared AuNPs were evaluated using the borohydride-assisted reduction of 4-nitrophenol as a model reaction, exhibiting apparent rates of 2.0 × 10 −3 , 3.6 × 10 −3 , 1.9 × 10 −3 , and 13.8 × 10 −3 s −1 for SA-, AA-, CA-, and SR-derived AuNPs, respectively (5 mol % catalyst). Notably, AuNPs generated using SR boasted a catalytic rate twice as high as that of Turkevich (citrate)-derived AuNPs at the same Au catalyst loading, an outcome we attribute to the prevalence of ultrasmall (∼5 nm) AuNPs produced in that sample. Overall, these findings open the possibility for "on-the-fly" nanomanufacturing methods (e.g., "glow stick"-inspired preparation) that allow the expedient, reproducible, and low-cost synthesis of metal nanoparticles with minimal environmental impact.
The adsorptive stripping voltammetric detection of nickel and cobalt in water samples at metal film electrodes has been extensively studied. In this work, a novel, environmentally friendly, metal-free electrochemical probe was constructed for the ultra-trace determination of Ni2+ in water samples by Adsorptive Cathodic Stripping Voltammetry (AdCSV). The electrochemical platform is based on the adsorptive accumulation of Ni2+ ions directly onto a glassy carbon electrode (GCE) modified with dimethylglyoxime (DMG) as chelating agent and a Nafion-graphene (NGr) nanocomposite to enhance electrode sensitivity. The nafion-graphene dimethylglyoxime modified glassy carbon electrode (NGr-DMG-GCE) shows superior detection capabilities as a result of the improved surface-area-to-volume ratio and enhanced electron transfer kinetics following the incorporation of single layer graphene, while limiting the toxic effects of the sensor by removal of the more common mercury, bismuth and lead films. Furthermore, for the first time the NGr-DMG-GCE, in the presence of common interfering metal ions of Co2+ and Zn2+ demonstrates good selectivity and preferential binding towards the detection of Ni2+ in water samples. Structural and morphological characterisation of the synthesised single layer graphene sheets was conducted by Raman spectrometry, HRTEM and HRSEM analysis. The instrumental parameters associated with the electrochemical response, including accumulation potential and accumulation time were investigated and optimised in addition to the influence of DMG and graphene concentrations. The NGr-DMG-GCE demonstrated well resolved, reproducible peaks, with RSD (%) below 5% and a detection limit of 1.5 µg L−1 for Ni2+ reduction at an accumulation time of 120 s. The prepared electrochemical sensor exhibited good detection and quantitation towards Ni2+ detection in tap water samples, well below 0.1 mg L−1 set by the WHO and EPA standards. This is comparable to the South African drinking water guidelines of 0.15 mg L−1.
The development of low-cost, disposable electrode materials has been at the forefront of sensor technology in recent decades. Paper, offers possibilities for multi-functional, disposable and economically friendly sensing capabilities and has proved to be a suitable reagent storage and substrate material in paper-based analytical devices (PADs). In this work, we report a simple inkjet printing procedure on photographic paper for the fabrication of single analyte electrochemical sensors. A three-electrode system, consisting of a 3 mm diameter working electrode (WE), a counter electrode (CE) and a reference electrode (RE) were prepared by inkjet printing of silver conductive inks for comparison to common commercial screen printed electrode (SPE) brands. In a second step, carbon coating and modification of the working electrode surface with an electrochemically reduced graphene oxide, gold nanoparticle (ERGO-AuNP) film, to improve electrode sensitivity and selectivity was employed. Improved electron-transfer kinetics, increased active surface area and enhanced catalytic properties were achieved due to the ERGO-AuNP layer inclusion. Electrical and topographical characterization of the printed layers was performed in the fabrication process. Printing of AgÀ NP ink showed good resistivity (1.8-6.3 Ω) on photographic paper. The prepared printed paper-based electrodes (PPE) offer a quantitative analysis of Ni(II), based on the accumulation of Ni(dmgH) 2 complexes at the modified electrode surface by squarewave adsorptive cathodic stripping voltammetry (SW-AdCSV). This study offers the first investigation on the feasibility of adsorptive electrochemical sensing methods at porous cellulose paper-based substrates. Instrumental parameters including deposition potential and deposition time were optimized for both electrochemical sensors. Improved sensitivities were achieved at the modified integrated electrodes over the unmodified derivate with a limit of detection (LOD) of 32.19 μg L À 1 achieved for the ERGO-AuNPÀ CCÀ AgÀ PPE. This is well below the EPA and WHO standards of 0.1 mg L À 1 or 0.1 ppm for Ni 2 + in drinking water.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.