Calcium oxide nanoparticles from eggshell waste: A green nanotechnological strategy for microwave-assisted environmental clean up

Jannatun Zia , Amit Kumar Shringi , Ufana Riaz
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Abstract

This study presents a sustainable and innovative strategy for waste reutilization and environmental remediation through the green synthesis of calcium oxide (CaO) nanoparticles (NPs) derived from waste eggshells, predominantly composed of calcium carbonate. The CaO NPs were synthesized via a straight forward calcination process and characterized using X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and UV–visible diffuse reflectance spectroscopy (UV–Vis DRS). XRD confirmed high crystallinity with an average crystallite size of 32 nm, while TEM revealed cubic nanoparticles in the range of 30–50 nm. TGA analysis demonstrated notable thermal stability up to 800 °C.The catalytic performance of the synthesized CaO NPs was evaluated via microwave-assisted degradation of Malachite Green (MG), a model organic pollutant. Under microwave irradiation, CaO NPs achieved 86 % degradation within 30 min, significantly outperforming raw eggshells (72 %). The degradation followed pseudo-first-order kinetics. Optimization studies revealed enhanced degradation efficiency (up to 93.40 %) at 900 W microwave powers and 94.59 % efficiency with a catalyst dose of 250 mg/L. However, increasing MG concentration from 20 to 50 mg/L resulted in a decline in degradation efficiency from 86 % to 60.2 %. Recyclability assessments showed 77 % degradation efficiency after four consecutive cycles, indicating the catalyst’s stability and reusability. Scavenger experiments identified the involvement of reactive species, including hydroxyl radicals (•OH), superoxide anions (•O₂⁻), and photo-generated holes (h⁺), in the degradation mechanism. Furthermore, LC-MS analysis proposed a plausible degradation pathway based on intermediate m/z values. Compared to conventional thermal or chemical degradation methods, the microwave-assisted catalytic process using CaO NPs demonstrated superior efficiency, rapid reaction kinetics, and reduced energy consumption. This work highlights the potential of converting bio-waste into high-value nanomaterials for scalable, eco-friendly, and cost-effective wastewater treatment applications.
蛋壳废弃物中的氧化钙纳米颗粒:微波辅助环境清理的绿色纳米技术策略
本研究提出了一种可持续和创新的废物再利用和环境修复策略,即通过从废蛋壳中提取主要由碳酸钙组成的氧化钙纳米颗粒(NPs)的绿色合成。通过直接煅烧工艺合成了CaO NPs,并使用x射线衍射(XRD)、扫描电子显微镜(SEM-EDX)、傅里叶变换红外光谱(FT-IR)、透射电子显微镜(TEM)、热重分析(TGA)和uv -可见漫反射光谱(UV-Vis DRS)对其进行了表征。XRD证实了高结晶度,平均晶粒尺寸为32 nm,而TEM显示了30-50 nm范围内的立方纳米颗粒。TGA分析表明,高达800°C的热稳定性显著。通过微波辅助降解孔雀石绿(Malachite Green, MG)这一典型有机污染物,考察了合成的CaO NPs的催化性能。在微波照射下,CaO NPs在30分钟内降解率达到86%,明显优于生蛋壳(72%)。降解遵循准一级动力学。优化研究表明,当微波功率为900 W时,降解效率可达93.40%,催化剂剂量为250 mg/L时,降解效率可达94.59%。当MG浓度从20 MG /L增加到50 MG /L时,降解率从86%下降到60.2%。可回收性评估表明,连续4次循环后,催化剂的降解效率为77%,表明催化剂的稳定性和可重复使用性。清道夫实验确定了活性物质,包括羟基自由基(•OH)、超氧阴离子(•O₂⁻)和光生空穴(h⁺)在降解机制中的作用。此外,LC-MS分析提出了基于中间m/z值的合理降解途径。与传统的热降解或化学降解方法相比,使用CaO NPs的微波辅助催化工艺表现出更高的效率、快速的反应动力学和更低的能耗。这项工作强调了将生物废物转化为高价值纳米材料的潜力,可用于可扩展、环保和经济有效的废水处理应用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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