**4. Conclusions**

Zn-doped α-Fe2O<sup>3</sup> nanoparticles were synthesized by sol-gel method to investigate the effect of Zn doping on structural, optical and dielectric behavior of hematite. XRD reveals the rhombohedral structure of as-prepared samples with average crystallite size lying between 14–21 nm and other various parameters like lattice parameter, strain, stress, dislocation density also has been discussed. Raman spectroscopy confirms defects in the host lattice exist that are consistent with XRD results. FTIR spectra reveals the metal oxygen vibrations and shifting in the spectra with doping ion concentration. The optical band gap obtained from Tauc plot decreases from 2.66 eV for pure Fe2O<sup>3</sup> to 2.31 eV for 4% Zn doping and then increases for Zn 6%, which is in accordance with structural parameters. Photodegradation analysis shows that 4% Zn doped α–Fe2O<sup>3</sup> is a good catalyst for degradation of RB dye under the illumination of UV light and almost 87% of RB dye has been degraded in 90 min in the presence of catalyst. In future, Zn doped α-Fe2O<sup>3</sup> have been used as a very good photocatalyst to remove organic pollutants from waste water. AC conductivity increases with the increase in frequency for all the samples, due to the conduction hopping mechanism, revealing a small polaron hopping mechanism involved in conduction. The dispersion in dielectric constant spectra with frequency can be understood based on Koop and Maxwell-Wagner's models and also on basis of space charge polarization. Higher value of dielectric constant of synthesized samples at room temperature makes them suitable for high energy storage applications.

**Author Contributions:** Conceptualization, S. & S.C.; investigation, S.; resources, P.K.; writing—original draft preparation, S.; writing—review and editing, A.K. & P.K.; visualization, A.K.; supervision, P.K.; project administration, P.K.; funding acquisition, P.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The present work was financially supported by DST, New Delhi for providing research grant under DST-INSPIRE faculty award (No. DST/INSPIRE/04/2015/003149) to Parmod Kumar. Also, Suman acknowledges University Grant Commission, India (UGC-JRF) for providing research fellowship (UGC-Ref. No.: 1320/ (OBC) (CSIR-UGC NET DEC. 2016)).

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