Metal and metal oxide particles are abundant in various ash-based wastes. Utilising these as catalyst sources for the fabrication of carbon nanomaterials could present a valuable approach to reduce our reliance on non-renewable and costly catalyst sources, thereby facilitating large-scale nanomaterial production. In this context, secondary waste materials (SWMs) are by-products resulting from the (complete or partial) combustion of carbon-rich sources or other industrial processes and their disposal poses a serious environmental problem. In this study, we demonstrate a novel strategy to upcycle SWMs as catalysts, as received, for the growth of carbon nanoarchitectured electrodes through microwave plasma-enhanced chemical vapour deposition (MPECVD), without the need for functionalisation. Firstly, 10 SWMs were selected to fabricate porous hierarchical nanocarbon (PHN) electrodes by phase-inversion and subsequent catalytic MPECVD growth. Secondly, distinct growth conditions, both in the presence and absence of CH as an external carbon source were applied, resulting in conductive electrodes, on which acetaminophen oxidation was performed. Results show that not all SWMs, despite originating from similar processes, work as a catalyst. In particular, principal component analysis suggests the presence of calcium oxosilicate and calcium‑magnesium‑iron carbonate as potential catalysts, which are present in two SWMs. Contrary to what might be expected, the occurrence of metals, such as Fe, Ni, is not a sufficient factor for the catalytic growth of carbon nanostructures. Interestingly, water vapour adsorption isotherms suggest the formation of different porous networks according to the specific SWMs. Finally, the development of waste-derived catalysts fosters the concept of upcycling, converting waste into higher-value products, thus closing the loop on resource utilisation and minimising waste generation.

中文翻译：

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从灰烬到多孔分级纳米碳电极：通过自催化化学气相沉积升级回收二次废料

各种灰基废物中富含金属和金属氧化物颗粒。利用这些作为制造碳纳米材料的催化剂源可以提供一种有价值的方法来减少我们对不可再生和昂贵的催化剂源的依赖，从而促进大规模纳米材料的生产。在这种情况下，二次废料（SWM）是富碳源（完全或部分）燃烧或其他工业过程产生的副产品，其处置造成了严重的环境问题。在这项研究中，我们展示了一种新颖的策略，将SWM作为催化剂进行升级改造，通过微波等离子体增强化学气相沉积（MPECVD）来生长碳纳米结构电极，而无需功能化。首先，选择 10 个 SWM 通过相转化和随后的催化 MPECVD 生长来制造多孔分级纳米碳 (PHN) 电极。其次，应用不同的生长条件，在存在和不存在CH作为外部碳源的情况下，产生导电电极，在其上进行对乙酰氨基酚的氧化。结果表明，尽管源自相似的过程，但并非所有 SWM 都能起到催化剂的作用。特别是，主成分分析表明，硅酸钙和碳酸钙镁铁作为潜在催化剂存在于两种 SWM 中。与预期相反，金属（例如 Fe、Ni）的出现并不是碳纳米结构催化生长的充分因素。有趣的是，水蒸气吸附等温线表明根据特定的 SWM 形成了不同的多孔网络。最后，废物衍生催化剂的开发培育了升级循环的概念，将废物转化为更高价值的产品，从而形成资源利用的闭环并最大限度地减少废物的产生。