Mn-doped CeO2-CNT nanohybrid for removal of water soluble organic dyes

In spite of the efficient redox properties of CeO2 originating from the easy inter-conversion of the Ce4+/Ce3+ couple, its large band gap (similar to 3 eV) limits its photocatalytic application. Herein, we report a novel one-pot method to synthesize phase-pure Mn-doped CeO2 nanoparticles (average size similar to 7 nm) well dispersed in a network of carbon nanotubes (CNT) and also attached onto the CNT surface, as confirmed by transmission electron micrographs. The Mn and CNT content in ceria were optimised based on ability for synergistic sorptive-photocatalytic removal of a model cationic dye under UV-visible light. Diffuse reflectance spectra revealed narrowed optical band gap (only similar to 1.8 eV) in the optimised visible light active Mn-CeO2/CNT nanohybrid resulting from increased defect states due to multivalent Mn dopants (confirmed by X-ray photoelectron spectroscopy). N-2 adsorption-desorption data confirmed large increase in the specific surface area compared to ceria nanoparticles leading to improved dye adsorption. The arrest of recombination of photogenerated carriers (suggested by photoluminescence quenching) due to conductive CNT support further contribute to enhancing photocatalytic activity. Thus, the findings presented in this article are relevant to materials research for environmental remediation from a surface and band gap engineering point of view.