Chitosan–sodium alginate encapsulated Co-doped ZrO₂–MWCNTs nanocomposites for photocatalytic decolorization of organic dyes

Photocatalytic decolorization properties of cobalt doped-ZrO₂-multiwalled carbon nanotubes (Co–ZrO₂–MWCNTs) and chitosan–sodium alginate encapsulated Co–ZrO₂–MWCNTs (CS/Alg–Co–ZrO₂–MWCNTs) with varying weight percentage of Co–ZrO₂–MWCNTs are presented in this research paper. The Co–ZrO₂–MWCNTs was first synthesized through homogenous co-precipitation method and introduced into the chitosan–sodium sodium alginate (CS/Alg) biopolymer matrix. The bio-nanocomposites were characterized using X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, (UV–Vis)-spectroscopy and energy dispersive spectroscopy to obtain information on their structure, formation, morphology, size and elemental analysis. The photodecolorization efficiency of the samples was determined through their decolorization of trypan blue dye aqueous solution in 180 min. Recyclability of the catalysts was also assessed. The bio-nanocomposites experienced reduced band gap values with subsequent improvement in visible light activity compared to the uncapped Co–ZrO₂–MWCNTs. All the CS/Alg–Co–ZrO₂–MWCNTs exhibited higher photodecolorization activities than the uncapped Co–ZrO₂–MWCNTs. The most efficient catalyst (CS/Alg–40 % Co–ZrO₂–MWCNTs) with a band gap of 2.56 eV displayed 94 % decolorization efficiency of the dye. Though reusability of the catalyst is significant, its efficiency diminished consistently after each cycle.