Preparation and application of a novel electrochemical sensing material based on surface chemistry of polyhydroquinone

New insight for simultaneous determination of hazardous di-hydroxybenzene isomers at crown ether modified polymer/carbon nanotubes composite sensor

A new insight is presented in the fabrication of a reliable electrochemical sensor for di-hydroxybenzene isomers; hydroquinone (HQ), catechol (CC), and resorcinol (RC) which have been considered as common pollutants in environment and water samples. The sensor is based on modifying the glassy carbon electrode (GC) with successive layers, multi-walled carbon nanotubes (CNT), poly-hydroquinone (PHQ) and benzo-12-crown-4 (CE); GC/CNT/PHQ/CE. CE is introduced for the first time as a receptor for the di-hydroxybenzene isomers based on host-guest size matching. Other cycling compound with different cavity diameter as β-cyclodextrin (β-CD) (6.0-6.5 Å) was examined displaying lower current responses. CE exhibited "fit" cavity size (1.20-1.50 Å). Thus, the inclusion complexes formed between β-CD and di-hydroxybenzene isomers are less stable. The layered sensor showed highly electro-catalytic activity for simultaneous determination of isomers; HQ, CC and RC in the concentration ranges of 0.03-100 μM, 0.01-100 μM and 0.05-100 μM with low detection limit values of 0.156 nM, 0.118 nM and 0.427 nM, respectively. The practical impact of the sensor was illustrated for determination of di-hydroxybenzene isomers in real water matrices from two different sources. Moreover, anti-interference ability of the layered sensor for determination of di-hydroxybenzene isomers was successfully achieved in presence of common interfering ions and organic pollutants.

High-Energy Flexible Supercapacitor-Synergistic Effects of Polyhydroquinone and RuO2· xH2O with Microsized, Few-Layered, Self-Supportive Exfoliated-Graphite Sheets

An effective and straightforward route for tailoring the self-supporting, exfoliated flexible graphite substrate (E-FGS) using electrochemical anodization is proposed. E-FGS has essential features of highly exfoliated, few-layered, two-dimensional graphite sheets with the size of several tens of micrometers, interconnected along the axis of the substrate surface. The novel hierarchical porous structural morphology of E-FGS enables large active sites for efficient electrolyte ion and charge transport when used as electrode material for a supercapacitor. In order to effectively utilize this promising E-FGS electrode for energy storage purpose, a ternary composite is further synthesized with pseudocapacitive polyhydroquinone (PHQ) and hydrous RuO₂ (hRO). hRO is synthesized via a sol-gel route, while electropolymerization is utilized for the electrodeposition of PHQ over E-FGS. Ultimately, the fabricated self-supporting E-FGS-based flexible supercapacitor is capable of delivering areal specific capacitance values as high as 378 mF cm^-2 at a current density of 1 mA cm^-2. Addition of the pseudocapacitive component to the E-FGS texture leads to ∼10 times increase of the electrochemical charge storage capability. The imposition of mechanical forces to this flexible supercapacitor device results in trivial changes in electrochemical properties and is still capable of retaining 91% of the initial specific capacitance after 10 000 cycles. Alongside, the fabricated symmetrical solid-state flexible device exhibited a high energy density of 8.4 μWh cm^-2. The excellent performance along with the ease of synthesis and fabrication process of the flexible solid-state supercapacitor device using PHQ/hRO/E-FGS holds promise for large-scale production.