Abstract Chemical tracers, both artificial and natural, are the established tools for providing information on groundwater flow characteristics such as groundwater flow velocity and flow direction. Chemicals namely chloride, bromide, iodide, dye tracers (Rhodamine-WT) and radioactive elements (Tritium) are artificial tracers that have been used as injected tracers for hydrogeological studies. However, the use of conventional tracers are often limited due to high diffusion rates and difficulties in estimating very low water flow velocities of the order 0.00001 to 0.001 m/s. Herein, we report the first ever large scale synthesis and testing of carbon quantum dots (CQDs) as hydrogeological tracers. CQDs, as they are now popularly termed, are a new class of environmentally friendly and highly fluorescent nanomaterial mainly used for bio-imaging and catalytic applications. In this manuscript, we have used fluorescence emission and surface functionalization of the CQDs as parameters to study flow of water in simulated laboratory columns and in field. The robustness of the CQDs towards environmental factors has been tested. Comparative tracer results suggested that CQDs may be envisaged as nano-tracers for future hydrogeological investigations.

中文翻译：

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稳健的碳量子点作为地下水研究的纳米示踪剂的出现

摘要 人工和天然化学示踪剂是提供地下水流动特征（如地下水流速和流动方向）信息的既定工具。化学品，即氯化物、溴化物、碘化物、染料示踪剂 (罗丹明-WT) 和放射性元素 (氚) 是人工示踪剂，已被用作水文地质研究的注入示踪剂。然而，由于高扩散率和难以估计 0.00001 到 0.001 m/s 的极低水流速度，传统示踪剂的使用通常受到限制。在此，我们报告了作为水文地质示踪剂的碳量子点（CQD）的首次大规模合成和测试。CQD，正如现在普遍所说的那样，是一类新型的环境友好型高荧光纳米材料，主要用于生物成像和催化应用。在这份手稿中，我们使用 CQD 的荧光发射和表面功能化作为参数来研究模拟实验室柱子和现场的水流。CQDs 对环境因素的鲁棒性已经过测试。比较示踪剂结果表明，CQDs 可能被设想为未来水文地质调查的纳米示踪剂。