Graphene quantum dots (GQDs) are environmentally friendly fluorescent carbon-based nanomaterials. However, there is no report on the massive synthesis of GQDs with narrow-band fluorescence and a high photoluminescence quantum yield (PLQY) using a simple liquid-phase method under atmospheric conditions. In this study, GQDs were successfully synthesized in ∼100% product yield by heating phloroglucinol (PG) with Na₃PO₄·12H₂O in 1,2-pentanediol at 180 °C for 6 h in an open system with air flow, followed by dialysis purification. The high product yield was attributed to the addition of Na₃PO₄·12H₂O as a base catalyst, which promoted the dehydration–condensation reaction between PG molecules. The dispersion of PG derived GQDs (PG-GQDs) in ethanol resulted in blue fluorescence with a full width at half maximum of 32 nm and a PLQY of 54%. Further purification of PG-GQDs by silica gel column chromatography improved the PLQY to 75%. Fourier-transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy confirmed that dehydration–condensation reactions occurred not only between PGs but also between GQDs and 1,2-pentanediol. The binding of 1,2-pentanediol to the edges of GQDs suppressed the stacking of GQDs and prevented concentration quenching, resulting in a high PLQY. PG-GQDs exhibited negative fluorescence solvatochromism, i.e., the fluorescence wavelength blue-shifted with increasing solvent polarity. Dispersion of PG-GQDs in N-methyl-2-pyrrolidone (MP) resulted in green fluorescence with a PLQY of 96%. Dispersion of PG-GQDs in water resulted in blue fluorescence and a low PLQY of 6% at pH 7, while the PLQY was more than 50% at pH ≥ 11. Using these properties, the sensing of water (pH 13) in MP was investigated. The results showed that as the water content was increased from 0% to 100%, the fluorescence color gradually changed from green to blue and the fluorescence wavelength continuously shifted from 514 nm to 466 nm, indicating their applicability in water sensing.

中文翻译：

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窄带蓝绿荧光石墨烯量子点的开放系统大规模合成及其在水传感中的应用

石墨烯量子点（GQD）是环保型荧光碳基纳米材料。然而，目前还没有在大气条件下使用简单的液相方法大规模合成具有窄带荧光和高光致发光量子产率（PLQY）的GQD的报道。在这项研究中，通过将间苯三酚（PG）与Na ₃ PO ₄ ·12H ₂ O在1,2-戊二醇中在开放系统中于180℃加热6小时，成功合成了GQD，产物收率约为100%，然后进行透析纯化。高产率归因于添加Na ₃ PO ₄ ·12H ₂ O作为碱催化剂，促进了PG分子之间的脱水缩合反应。 PG 衍生的 GQD (PG-GQD) 在乙醇中的分散导致蓝色荧光，半峰全宽为 32 nm，PLQY 为 54%。通过硅胶柱色谱进一步纯化 PG-GQD，将 PLQY 提高至 75%。傅里叶变换红外光谱、^1H核磁共振光谱和X射线光电子能谱证实，脱水缩合反应不仅发生在PG之间，而且发生在GQD和1,2-戊二醇之间。 1,2-戊二醇与 GQD 边缘的结合抑制了 GQD 的堆积并防止浓度猝灭，从而产生高 PLQY。 PG-GQD表现出负荧光溶剂致变色现象，即荧光波长随着溶剂极性的增加而蓝移。 PG-GQD 在N-甲基-2-吡咯烷酮 (MP)中的分散产生绿色荧光，PLQY 为 96%。 PG-GQD 在水中的分散会产生蓝色荧光，并且在 pH 7 时 PLQY 为 6%，而在 pH ≥ 11 时 PLQY 超过 50%。利用这些特性，可以对 MP 中的水 (pH 13) 进行传感调查了。结果表明，随着含水量从0%增加到100%，荧光颜色逐渐从绿色变为蓝色，荧光波长不断从514 nm转变到466 nm，表明其在水传感方面的适用性。