Green synthesis of copper oxide nanoparticles using extracts of Solanum macrocarpon fruit and their redox responses on SPAu electrode

Enyioma C Okpara; Oluwasayo E Ogunjinmi; Opeyemi A Oyewo; Omolola E Fayemi; Damian C Onwudiwe

doi:10.1016/j.heliyon.2021.e08571

Green synthesis of copper oxide nanoparticles using extracts of Solanum macrocarpon fruit and their redox responses on SPAu electrode

Heliyon. 2021 Dec 8;7(12):e08571. doi: 10.1016/j.heliyon.2021.e08571. eCollection 2021 Dec.

Authors

Enyioma C Okpara^{1

2}, Oluwasayo E Ogunjinmi³, Opeyemi A Oyewo⁴, Omolola E Fayemi^{1

2}, Damian C Onwudiwe^{1

2}

Affiliations

¹ Material Science Innovation and Modelling (MaSIM) Research Focus Area, Faculty of Natural and Agricultural Sciences, North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho, South Africa.
² Department of Chemistry, School of Physical and Chemical Sciences, Faculty of Natural and Agricultural Science, North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho, South Africa.
³ Industrial Chemistry Unit, Department of Physical Sciences, First Technical University, Ibadan, Oyo State, Nigeria.
⁴ Department of Science and Technology Education, Faculty of Education, University of Johannesburg, Johannesburg, South Africa.

Abstract

In this work, CuO nanoparticles (NPs) were prepared from the aqueous extracts of Solanum macrocarpon fruit by using the conventional heating (CuO(h) NPs) and microwave irradiation (CuO(m) NPs) methods. The synthesized nanoparticles were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The SEM analysis revealed that the CuO NPs from both routes contained essentially smooth surfaces, and displayed some degree of agglomeration. The TEM analysis confirmed some spherical morphology with mean particle sizes of 35.60 ± 6.24 nm and 47.14 ± 6.18 nm for the CuO(h) and CuO(m) NPs respectively. While the CuO(m) NPs possessed a single-phase consistent with the face cantered cubic structure of copper oxide, the CuO(h) NPs showed some extra peaks attributed to Cu₂O NPs as secondary phase. Electrochemical studies were conducted in order to evaluate the electrochemical properties of the NPs. The responses of a gold screen-printed electrode surface treated with both NPs showed that their redox behaviours on (Fe(CN)₆)^3-/4- probe and KCl electrolytes vary significantly. In (Fe(CN)₆)^3-/4- probe, the SPAuE/CuO(h) showed enhanced electrochemical response relative to the bare, while the SPAuE/CuO(m) showed a lower current response than the bare. However, in the KCl electrolye, the SPAuE/CuO(h) and SPAuE/CuO(m) were highly electroactive and demonstrated peak current magnitude that was about 26.5 and 83.38 times higher than that of the bare. In this KCl medium, the magnitude of the oxidation peak current of Cu²⁺ for SPAuE/CuO(m) was about 3 times higher than that of SPAuE/CuO(h). The percentage contraction in redox coordinates between the 1^st and 10^th scans in both electrodes were 3.88 and 19.28% for SPAuE/CuO(h) and SPAuE/CuO(m) respectively. Thus, the choice of green synthesis route could be exploited in different fields where green NPs is desired.

Keywords: Copper oxides; Green synthesis; Microwave irradiation; Redox behaviour; Solanum macrocarpon.