**The Electrochemical Oxidation of Hydroquinone and Catechol through a Novel Poly-geminal Dicationic Ionic Liquid (PGDIL)–TiO<sup>2</sup> Composite Film Electrode**

#### **Yanni Guo <sup>1</sup> , Deliang He 1,\*, Aomei Xie <sup>2</sup> , Wei Qu <sup>1</sup> , Yining Tang <sup>1</sup> , Lei Zhou <sup>1</sup> and Rilong Zhu 1,\***


Received: 17 October 2019; Accepted: 15 November 2019; Published: 19 November 2019

**Abstract:** A novel poly-geminal dicationic ionic liquid (PGDIL)-TiO2/Au composite film electrode was successfully prepared by electrochemical polymerization of 1,4-bis(3-(m-aminobenzyl) imidazol-1-yl)butane bis(hexafluorinephosphate) containing polymerizable anilino groups in the electrolyte containing nano-TiO2. The basic properties of PGDIL–TiO2/Au composite films were studied by SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry. The SEM results revealed that the PGDIL–TiO<sup>2</sup> powder has a more uniform and smaller particle size than the PGDIL. The cyclic voltammetry results showed that the catalytic effect on electrochemical oxidation of hydroquinone and catechol of the PGDIL–TiO<sup>2</sup> electrode is the best, yet the *R*ct of PGDIL–TiO<sup>2</sup> electrode is higher than that of PGDIL and TiO<sup>2</sup> electrode, which is caused by the synergistic effect between TiO<sup>2</sup> and PGDIL. The PGDIL–TiO2/Au composite electrode presents a good enhancement effect on the reversible electrochemical oxidation of hydroquinone and catechol, and differential pulse voltammetry tests of the hydroquinone and catechol in a certain concentration range revealed that the PGDIL–TiO2/Au electrode enables a high sensitivity to the differentiation and detection of hydroquinone and catechol. Furthermore, the electrochemical catalytic mechanism of the PGDIL–TiO2/Au electrode was studied. It was found that the recombination of TiO<sup>2</sup> improved the reversibility and activity of the PGDIL–TiO2/Au electrode for the electrocatalytic reaction of HQ and CC. The PGDIL–TiO2/Au electrode is also expected to be used for catalytic oxidation and detection of other organic pollutants containing –OH groups.

**Keywords:** nano-TiO2; poly-geminal dicationic ionic liquid; hydroquinone; catechol
