Hierarchical porous spinel nickel cobaltite nanoflakes anchored reduced graphene oxide nano-photocatalyst for efficient degradation of organic pollutants under natural sunlight

Hierarchical spinel NiCo₂O₄ anchored with reduced graphene oxide (NiCO₂O₄-rGO) nanoflake composites was prepared by using a chemical route for a high-performance photocatalyst. X-ray diffractometry, field emission scanning electron microscopy and Fourier transform infrared spectroscopy were employed to study the structure, morphology and functional groups of the as-prepared NiCO₂O₄-rGO nanoflake composites. The UV–vis diffusive reflectance spectroscopy revealed the reduction of optical bandgap from 1.32 to 1.20 eV compared with pristine spinel NiCo₂O₄ nanoflakes. NiCO₂O₄-rGO nanoflake composites exhibited improved photocatalytic efficiency when compared with that of pristine NiCo₂O₄ nanoflakes. We verified that 100% degradation of MB in 40 min was observed under natural sunlight irradiation. The photocatalytic degradation efficiency was found to retain 97% of its original value after 6 cycles. The superior photocatalytic efficiency of NiCO₂O₄-rGO nanoflake composites over pristine NiCo₂O₄ nanoflakes is attributed to not only its enhanced surface area providing more active sites for light adsorption but also a heterojunction created between rGO and NiCo₂O₄. Addition of rGO greatly improves charge separation efficiency hence decreasing electron hole pair recombination. Overall, this work revealed that synthesis of NiCo₂O₄-rGO nanoflake composites may be a promising candidate for the removal of inorganic pollutant from waste water at industrial level under natural sunlight irradiation.