Title : Reduction of graphene oxide supported on paper by CO2 laser and its application as electrochemical sensing of phosphate ions
Nowadays, the development of new analytical devices able to carry out chemical analysis in situ and in real time with fast and cheap protocols is a theme of great importance. Indeed, chemical sensors are very important in many fields, from sanity to the environmental one. Actually, many of these analysis are carried out using ICP-MS, titration, HPLC or spectrophotometric analysis that, even if very accurate and sensitive, lack of portability, simplicity and cheapness. On the other hand, electrochemical cells can be used to make chemical sensors that quantify the concentration of an analyte by monitoring its oxidation or reduction. During last years, different electrochemical sensors were developed for different analyte, such as hydrogen peroxide, glucose, nitrate, nitrite ions among others. The properties of these sensors highly depend on the electrode material and morphology. Graphene based sensors have been studied for this kind of application showing excellent results. In this work, we show the fabrication of graphene based electrochemical cells composed of reduced graphene oxide working and counter electrodes and a printed Ag/AgCl reference electrode. The as obtained cell was deposited on different substrates, ranging from paper, textile, plastic and bandaid demonstrating the flexibility of the electrode synthesis. Particularly, a solution of graphene oxide was deposited by filtering (for paper) or by drop casting (on other substrates) on top of the substrates and then it was reduced to graphene using a programmable CO2 laser. The speed and laser power were optimized for each substrate and electrode conductivity was measured using four-point probe method. After the reduction, the electrode conductivity increased from 10 -5 S m-1 to 300 S m-1 demostrating the reduction of graphene oxide. The electrode was then characterized using RAMAN, XRD, XPS, EDS and SEM demostrating again the effective reduction of the graphene oxide layer. This protocol thus demostrate the possibility to obtain a full electrochemical cell made of reduced graphene oxide on different substrate for different applications. Particularly, in this work, the paper based electrode was used to quantify phosphate ions in water samples. Indeed, this quantification is currently carried out using a long and difficult spectroscopy method that doesn’t allow a in situ analysis. Here, we have used the phosphomolybdenum blue method that requries the addition of sulphuric acid and ammonium molybdate to the testing solution. Using this approach, adding these chemicals manually, the proposed sensor is able to quantify phosphate ions with a limit of detection of 0.4 µM. By the way, using this approach, the sample must still be manipulted in order to add sulphuric acid and ammonium molybdate. For this reason we have choose to use paper as substrate: paper was soaked with those two chemicals and, after drying, phosphate ions were quantified without adding any reagents to the solution. Results showed that the substrate released the chemicals to the solution allowing the quantification without any pre-treatment and thus enabling a in situ and real time analysis of phosphate ions in water.
Audience Take Away:
- Synthesis and fabrication of planar electrochemical cell composed of reference, counter and working electrodes made of reduced graphene oxide on different substrate
- Characterization of graphene/graphene oxide and reduced graphene oxide films
- Electrochemical sensing as analytical tool for in situ and fast analysis
- Electrochemical quantification of phosphate ions using the molybden blu method
- Advantages of paper based sensors