Abstract Copper oxide nanoparticles were successfully synthesised via cost effective approach using aqueous extracts obtained from red flowers of Euphorbia pulcherrima. Green precipitates were obtained post-drying which were thermally oxidised to pure single phase monoclinic CuO at 500 °C as per the XRD analysis. Further characterization of un-annealed and annealed samples was carried out using Scanning Electron Microscope (SEM), Optical Microscope (OPM), High Resolution Transmission Electron Microscope (HRTEM), Energy-Dispersive X-ray spectroscopy (EDS), Fourier Transform Infrared spectroscopy (FTIR/ATR), Thermogravimetric analysis (TGA). Zeta potential, X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance (DR), UV–Vis and Photoluminescence measurements (PL). Electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). SEM and OPM analysis on un-annealed and annealed samples reveal elongate and dense cubic agglomerate nanoparticles respectively. EDS spectra confirmed high purity phase composition of CuO. HRTEM analysis of annealed samples revealed a densed cubic nanoparticles, while selected electron area diffraction (SAED) and XRD patterns shows well-crystalline nanoparticles. FTIR/ATR spectra display peaks at 480 and 525 cm−1, which are characteristic peaks of CuO. Zeta potential measurement of annealed samples recorded a value of −6.58 mV. TGA analysis indicated the thermal stability of CuO while XPS analysis confirmed synthesis of pure single phase CuO. Value of energy band gap obtained from diffuse reflectance spectrum was 1.3 eV. From electrochemical study, maximum areal capacitance achieved was 39.45 mF/cm2 at a scan rate of 20 mV/s. This shows that Euphorbia pulcherrima mediated copper oxide nanoparticles is promising material for electrochemical energy storage application.

中文翻译：

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大戟介导的氧化铜纳米粒子的电化学性质

摘要 使用从大戟红花中提取的水提取物，通过具有成本效益的方法成功合成了氧化铜纳米颗粒。根据 XRD 分析，干燥后获得绿色沉淀物，在 500°C 下将其热氧化为纯单相单斜 CuO。使用扫描电子显微镜 (SEM)、光学显微镜 (OPM)、高分辨率透射电子显微镜 (HRTEM)、能量色散 X 射线光谱 (EDS)、傅立叶变换红外光谱对未退火和退火样品进行进一步表征(FTIR/ATR)、热重分析 (TGA)。Zeta 电位、X 射线光电子能谱 (XPS)、漫反射 (DR)、UV-Vis 和光致发光测量 (PL)。通过循环伏安法（CV）和电化学阻抗谱（EIS）研究电化学性质。未退火和退火样品的 SEM 和 OPM 分析分别显示细长和致密的立方团聚纳米颗粒。EDS 光谱证实了 CuO 的高纯度相组成。退火样品的 HRTEM 分析显示出致密的立方纳米颗粒，而选择电子面积衍射 (SAED) 和 XRD 图案显示出结晶良好的纳米颗粒。FTIR/ATR 光谱在 480 和 525 cm-1 处显示峰，这是 CuO 的特征峰。退火样品的 Zeta 电位测量值记录为 -6.58 mV。TGA 分析表明 CuO 的热稳定性，而 XPS 分析证实纯单相 CuO 的合成。从漫反射光谱获得的能带隙值为1.3 eV。根据电化学研究，在 20 mV/s 的扫描速率下实现的最大面积电容为 39.45 mF/cm2。这表明大戟介导的氧化铜纳米粒子是电化学储能应用的有前途的材料。