No abstract

In nature, kaolin clay is referred to a readily available cheap source of silicon and used in various fields such as the paper, ceramic, paint, plastic, rubber, and cracking catalyst industries. This paper introduces utilization of natural kaolin clay for a new application. In particular, the kaolin clay is used as a new raw material for synthesis of ordered mesoporous carbon (OMC) materials, which serve as electrode active materials for supercapacitors. Kaoline used in the present work is originated from Yen Bai province (Vietnam). After subjected several steps of the treatment process, silica present in the kaolin clay is converted to sodium silicate and used directly as a source of silicon for the synthesis process of mesoporous porous silica (SBA-15). The synthesized SBA-15 mesoporous silicas exhibit rod-like nanostructure with the specific area of 432.7 m2 g-1 and the mean pore size of 7-8 nm. Subsequently, SBA-15 silica serves as hard template for preparation of OMCs by using nanocasting method. The OMCs carbonized at different temperatures in the absence and presence of boric acid reveal highly ordered mesoporous structure with the highest specific area of 1039.2 m2 g-1 and the mean pore size ranging from 6 to 7 nm. As used as electrode active material in 6 M KOH aqueous solution, the resultant OMCs exhibit excellent capacitive performance with a specific capacitance higher than 80 F g-1 at a scan rate of 5 mV s-1. The obtained results show that, in addition to the high specific area, the electrical conductivity also plays an important role in enhancing energy storage ability of the OMC electrodes. At the same carbonization temperature, the high surface area plays crucial role. However, at the higher carbonization temperatures, effect of the electrical conductivity of the materials prevails over the high surface area. This study illustrates highly application feasibility of Vietnam natural kaolin clay as available and cheap raw material source for synthesis of electrode active materials with the high supercapacitive performance for electrochemical double layer capacitors.

Porous MnO2 microflowers with a hexagonal crystalline structure were facilely prepared at a low hydrothermal temperature of 90°C, without using any template or capping agent. The as-prepared MnO2 only presented an excellent detection ability for copper (II) by a square wave anodic stripping voltammetry in the presence of super P carbon black as conducting agent, and Nafion as binder. In the present work, to evaluate the detection ability of copper (II) in the MnO2 microflowers, chips of screen-printed electrodes (SPEs) having a polyurethane substrate, a silver working electrode, a carbon counter electrode, and a silver pseudoelectrode, were designed. Then, the SPEs chips were modified with MnO2 microflowers and/or super P carbon and used as electrochemical sensors for the detection of copper (II) present in water sources. From the measured results, the fabricated sensors with excellent copper detection in a linear range from 0.625 nM to 15 nM (R2 = 0.9737), and a low detection limit (0.5 nM), high sensitivity (214.05 μA/cm2 nM), and rapid response (180 s) demonstrated high application potential for electrochemical sensors in the detection of copper in water resources.