Hernandez-Aldave Sandra, Tarat Afshin, McGettrick James D, Bertoncello Paolo
Systems and Process Engineering Centre, College of Engineering, Swansea University, Bay Campus, Crwmlyn Burrows, Swansea SA1 8EN, UK.
Perpetuus Advanced Materials, Unit B1, Olympus Court, Millstream Way, Swansea Vale, Llansamlet, SA7 0AQ, UK.
Nanomaterials (Basel). 2019 Feb 7;9(2):221. doi: 10.3390/nano9020221.
We report for the first time a procedure in which Nafion/Graphite nanoplatelets (GNPs) thin films are fabricated using a modified layer-by-layer (LbL) method. The method consists of dipping a substrate (quartz and/or glassy carbon electrodes) into a composite solution made of Nafion and GNPs dissolved together in ethanol, followed by washing steps in water. This procedure allowed the fabrication of multilayer films of (Nafion/GNPs) by means of hydrogen bonding and hydrophobic‒hydrophobic interactions between Nafion, GNPs, and the corresponding solid substrate. The average thickness of each layer evaluated using profilometer corresponds to ca. 50 nm. The as-prepared Nafion/GNPs LbL films were characterized using various spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), FTIR, and optical microscopy. This characterization highlights the presence of oxygen functionalities that support a mechanism of self-assembly via hydrogen bonding interactions, along with hydrophobic interactions between the carbon groups of GNPs and the Teflon-like (carbon‒fluorine backbone) of Nafion. We showed that Nafion/GNPs LbL films can be deposited onto glassy carbon electrodes and utilized for the voltammetric detection of caffeine in beverages. The results showed that Nafion/GNPs LbL films can achieve a limit of detection for caffeine (LoD) of 0.032 μM and linear range between 20‒250 μM using differential pulse voltammetry, whereas, using cyclic voltammetry LoD and linear range were found to be 24 μM and 50‒5000 μM, respectively. Voltammetric detection of caffeine in beverages showed good agreement between the values found experimentally and those reported by the beverage producers. The values found are also in agreement with those obtained using a standard spectrophotometric method. The proposed method is appealing because it allows the fabrication of Nafion/GNPs thin films in a simple fashion using a single-step procedure, rather than using composite solutions with opposite electrostatic charge, and also allows the detection of caffeine in beverages without any pre-treatment or dilution of the real samples. The proposed method is characterized by a fast response time without apparent interference, and the results were competitive with those obtained with other materials reported in the literature.
我们首次报道了一种使用改进的层层（LbL）方法制备Nafion/石墨纳米片（GNP）薄膜的工艺。该方法包括将基底（石英和/或玻碳电极）浸入由Nafion和GNP溶解在乙醇中制成的复合溶液中，然后进行水洗步骤。此工艺通过Nafion、GNP与相应固体基底之间的氢键和疏水-疏水相互作用，实现了（Nafion/GNP）多层膜的制备。使用轮廓仪评估的每层平均厚度约为50 nm。使用各种光谱技术，如X射线光电子能谱（XPS）、能量色散X射线能谱（EDS）、傅里叶变换红外光谱（FTIR）和光学显微镜，对制备好的Nafion/GNP LbL薄膜进行了表征。该表征突出了氧官能团的存在，这些官能团支持通过氢键相互作用的自组装机制，以及GNP的碳基团与Nafion的类聚四氟乙烯（碳-氟主链）之间的疏水相互作用。我们表明，Nafion/GNP LbL薄膜可以沉积在玻碳电极上，并用于饮料中咖啡因的伏安检测。结果表明，使用差分脉冲伏安法，Nafion/GNP LbL薄膜对咖啡因的检测限（LoD）可达0.032 μM，线性范围为20-250 μM；而使用循环伏安法，LoD和线性范围分别为24 μM和50-5000 μM。饮料中咖啡因的伏安检测结果表明，实验测得的值与饮料生产商报告的值吻合良好。测得的值也与使用标准分光光度法获得的值一致。所提出的方法具有吸引力，因为它允许通过单步程序以简单的方式制备Nafion/GNP薄膜，而不是使用带相反静电荷的复合溶液，并且还允许在不进行任何预处理或稀释实际样品的情况下检测饮料中的咖啡因。所提出的方法具有快速响应时间且无明显干扰的特点，其结果与文献中报道的其他材料所获得的结果具有竞争力。
