Structural, optical, dielectric and magnetic behaviour of Cu1-xCoxO (x = 0.2-0.10) nano-composites and their applications in efficient removal of Cr (VI) ion from water

Abstract

Hexavalent Chromium (VI) is one of the main pollutants coming from industrial waste, dyes, paints, and plastics. It is one of the major concerns due to the adverse effects associated with Cr (VI) including respiratory cancer, skin irritation, kidney damage, liver damage and perforated eardrums. Many physico-chemical techniques used for the removal of Cr (VI) are not environment-friendly and cost-effective because of the large number of chemicals used. In the present study polyvinylpyrrolidone (PVP) capped Pure and Cu1−xCoxO (x = 2, 4, 6, 8 and 10) nanocomposites synthesized by the chemical co-precipitation method were investigated for their structural, optical, magnetic, and dielectric and for the effective removal of Cr (VI) ions from contaminated water. The monoclinic structure of synthesized materials was confirmed from detailed X-ray powder diffraction (XRD) analysis and Fourier transfer infrared (FTIR) measurements. High-resolution transmission electron microscope (HRTEM) analysis confirmed the synthesis of elongated nanoparticles with an average crystalline size of ∼12–30 nm. The optical properties were determined from the analysis of diffused reflectance spectroscopy (DRS) and results showed a decreasing trend in bandgap values from 2.56 to 2.03 eV with an increase in Co2+ ion content. The presence of Cr (III) ions resulting from reduction of Cr (VI) to Cr (III) was confirmed by high-resolution X-ray photoelectron spectroscopy (XPS) analysis. The vibrating sample magnetometer (VSM) measurements revealed weak room temperature ferromagnetism in all synthesized nanocomposites tailored by Co2+ ion substitutions. The dielectric constants and dielectric losses of synthesized nanocomposites exhibit significant variation with frequency (∼1 kHz–5 MHz) and temperature (∼25 °C–300 °C) due to inter-granular activities and grain boundary effects. The adsorption capacity of the synthesized materials for the removal of Cr (VI) ions was evaluated for different initial Cr (VI) ion concentrations and adsorbent doses at room temperature. The fitted adsorption data were found to be in good agreement with the Langmuir isotherm model relative to the Freundlich and Temkin models.