Highly Stable and Reusable 3D Graphene-Quinizarin Voltammetric pH Sensor

A simple pH sensor has been developed employing a 3D porous graphene framework blended with quinizarin. The performance of the fabricated sensor is tested via the square wave voltammetry technique by applying different buffer solutions and real samples. The peak potential of the designed electrode varies with the change in pH of solutions due to 2e(-)/2H(+) transfer process of pH-dependent quinone/hydroquinone redox couple. For varying pH (1-13), the designed sensor has a sensitivity of 65.6 +/- 0.4 mV/pH at 25 degrees C. Soil pH sensing is performed for different types of soil samples prepared using 1M KCl and 0.01M CaCl2 solutions with a potential shift of 63.5 +/- 0.9 mV/pH and 57.9 +/- 0.3 mV/pH, respectively. The 3D graphene-quinizarin pH sensing probe demonstrates negligible hysteresis (+/- 0.3 pH) and long-term stability (six months and more). In comparison to the commercial pH meter, the fabricated sensor shows a relative inaccuracy of less than 5%. Moreover, a single electrode could be used to detect the pH of multiple environments by mild rinsing with deionized water and is reusable for more than 500 cycles without significant potential drift. These low-cost and reusable pH-sensitive electrodes with linear Nernstian response are promising candidates for diverse pH-sensing applications.