**4. Conclusions**

A novel poly-geminal dicationic ionic liquid-TiO<sup>2</sup> (PGDIL)-TiO2/Au composite electrode was synthesized via the electrochemical polymerization of 1,4-bis(3-(m-aminobenzyl)imidazol-1-yl)butane bis(hexafluorinephosphate) in an electrolyte containing nano-TiO2. The SEM results showed that the morphologies of the PGDIL and PGDIL–TiO<sup>2</sup> powder are similar. Additionally, the PGDIL–TiO<sup>2</sup> powder has a more uniform and smaller particle size than the PGDIL because the O-vacancies of TiO<sup>2</sup> can adsorb GDIL molecules to form the core of polymerization, and thus, the polymerization process can be carried out smoothly and slowly. EIS results revealed that the *R*ct value of the PGDIL–TiO<sup>2</sup> electrode is higher than those of the PGDIL and TiO<sup>2</sup> electrodes, but its catalytic effect on HQ and CC is the best due to the synergistic effect between TiO<sup>2</sup> and PGDIL. Furthermore, the DPV method was used to study the simultaneous qualitative and quantitative determination of HQ and CC at the PGDIL–TiO2/Au electrode. The results showed that the peak current of each component in the mixture had almost non-interference during electrochemical selectivity determination, and the peak current values were linearly related to their concentrations. The equation for HQ is *I*p, HQ (µA) = 3.413 + 0.008152 *C*HQ (µmol/L), and that for CC is *I*p, CC (µA) = 2.368 + 0.02179 *C*CC (µmol/L). The PGDIL–TiO2/Au electrode can be used for simultaneous qualitative and quantitative electrochemical determination of HQ and CC in wastewater by the DPV tests. The PGDIL–TiO2/Au electrode is also expected to be used for catalytic oxidation and detection of other organic pollutants containing –OH groups. Further experiments and studies are required to determine whether there are other synergistic effects between TiO<sup>2</sup> and PGDIL.

**Author Contributions:** Y.G., D.H., and R.Z. conceived and designed the experiments; A.X. performed the experiments; Y.G. and W.Q. analyzed the data; Y.G. wrote the paper. Y.T. and L.Z. revised the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**


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