**1. Introduction**

Poly ionic liquids (PILs) are a kind of functional polymer material that contain at least one ion center in a polymer chain and a repeating unit similar to a common ionic liquid (IL) structure; they combine the properties of polymers and ionic liquids, and show are in the foreground of applications for ionic conductors, adsorption and separation, dispersants, and catalysts [1–4]. Therefore, the research on the preparation and performance of PILs has aroused wide interest and concern in recent years [5,6].

The dicationic ionic liquids (DILs) are considered to be a combination of three structural moieties: (1) cationic head groups; (2) a linkage chain (also called a spacer); and (3) counter anions. DILs can be classified as either homoanionic or heteroanionic, which can further be categorized as symmetrical or

asymmetrical. Homoanionic dicationic ionic liquids are typical DILs that consist of a dication and two identical anions. Symmetrical or geminal dicationic ILs (GDILs) can be synthesized by joining two of the same cations, such as imidazolium or pyrrolidinium, and may contain a cyclic or aliphatic chain via either a rigid or a flexible spacer. A common spacer is an alkyl chain [7,8]. Armstrong et al. [9] studied the relationship between the structure and properties of DILs by synthesizing 39 imidazolium-based and pyrrolidinium-based DILs. The head groups were linked with an alkyl chain (from three to 12 carbons long), and hence reacted with four different traditional anions. The thermal stability of these ILs was found to be in the range of −4 to > 400 ◦C, which is greater than that of most traditional monocationic ILs. GDILs have more unique physical and chemical properties and solvation characteristics, and can be used as separation materials [10], surfactants [11], and catalyst candidates [12,13], although they have not yet been studied heavily [14,15]. The same is true of poly-GDILs (PGDILs).

As is known, nano-TiO<sup>2</sup> has better chemical properties and photon characteristics due to its good absorbability and lower electron/hole recombining rate, and can be used as a new kind of electrical catalyst material [16–18]. There have been many reports on the application of nano-TiO<sup>2</sup> composite polymers in the electrocatalysis of organic materials [19], including a study by the present research group [20]. Aniline is a kind of monomer that is easy to polymerize. Polyaniline is an important conductive polymer [21–23] that can be used as anode or cathode material with electrocatalytic function due to its excellent electrical and electrochemical properties [24]. The combination of polyaniline and nano-TiO<sup>2</sup> can not only effectively inhibit the agglomeration of TiO<sup>2</sup> nanoparticles, but also improve the physical and chemical properties of composites, and may be widely applied in the electrochemical catalysis field [20,25,26].

Hydroquinone (HQ) and catechol (CC) are important phenolic compounds that are widely used as basic raw materials in the organic chemical, agriculture, and medicine industries, among others [27]. They are typical and important electro-active molecules in fundamental electrochemical research. Therefore, it is of great significance to establish a high-sensitivity detection method for HQ and CC in the fields of environmental monitoring and food inspection. Moreover, the chemical structures and the physicochemical properties of HQ and CC are very similar, and they are, therefore, difficult to distinguish [28]. Current methods for the determination of HQ and CC include fluorescence [29], the electrochemical method [30], the photometric method [31], and high-performance liquid chromatography [32]. The electrochemical method is highly valued because of its versatility, simple operation, easy automation, and environmental compatibility. In electro-catalytic reactions, in which an electrode is an electrical catalyst, different electrode materials can change the electrochemical reaction rate by different magnitudes, so new and efficient catalytic electrode materials have always been a focus of related research.

The present research group previously successfully synthesized 1,4-bis(3-(m-aminobenzyl) imidazol-1-yl)butane bis(hexafluorinephosphate) ([C4(m-ABIM)2][PF6]2), which is a novel GDIL containing anilino groups, and poly-[C4(m-ABIM)2][PF6]<sup>2</sup> (PGDIL) with a polyaniline-like structure was prepared by electro-polymerization [33]. In this study, a novel PGDIL–TiO<sup>2</sup> composite was prepared via electrodeposition on an Au electrode surface, and the electrochemical redox behaviors of HQ and CC were respectively investigated via the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. It was expected that the PGDIL–TiO<sup>2</sup> composite film would have the advantages of both PGDIL and TiO2.

#### **2. Experimental**

#### *2.1. Main Reagents and Instrumentation*

The primary reagents used in the experiments, [C4(m-ABIM)2][PF6]<sup>2</sup> ([33]), sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium chloride, hydroquinone, and anatase nano-TiO<sup>2</sup> powder (10–25 nm), were of analytical grade, and were used as received. The water used in the experiment was double distilled water.

The instruments used in the experiments were an automatic double distilled water distillation apparatus D1810C (Shanghai Asia-Pacific Glass instrument Company, Shanghai, China); a heat-collecting, constant temperature magnetic heating stirrer CJJ 78-1 (Zhengzhou Greatwall Scientific Industrial and Trade Co., Ltd., Zhengzhou, China); a rotary evaporator R.1002 (Zhengzhou Greatwall Scientific Industrial and Trade Co., Ltd., Zhengzhou, China); an ultrasonic cleaner SK5200HP (Shanghai Kudos Ultrasonic instrument Co., Ltd., Shanghai, China); an infrared spectrophotometer TJ270-30 (A) (Tianjin Jinwei Electronic Instrument Co., Ltd., Tianjin, China ); and an electrochemical workstation IviumStat (Ivium Technologies BV, Eindhoven, Netherlands).
