A novel Co–CoAl2O4/exfoliated montmorillonite composite with improved nanoparticle dispersion for methyl orange removal via coupling peroxydisulfate

Abstract

The degradation of refractory pollutants via the activation of peroxydisulfate (PDS) by Co-based nanostructures as catalysts has been gaining significant attention. However, most cobalt-based catalysts suffer from severe aggregation and metal ion leakage, resulting in a loss of activity and potential environmental threats. In this study, exfoliated montmorillonite (EMMT) loaded Co–CoAl2O4 composites were elaborately constructed through a facile coprecipitation-reduction method. The effects of the calcination temperature, the EMMT addition content, the pH of the precursor, and the reduction temperature on the microstructure of the Co–CoAl2O4/EMMT composites were investigated, and the optimum synthesis conditions were determined. In the optimal sample, well-crystallized CoAl2O4 nanoparticles were uniformly deposited onto the EMMT nanosheets with a considerably large specific surface area, while ultrafine metallic Co nanoparticles were homogeneously immobilized on the CoAl2O4 surface. This sample exhibited a superior activity (90% within 70 min) and reusability during methyl orange (MO) degradation. In the catalytic reaction, the superior adsorption property of EMMT facilitated the rapid transfer of MO molecules to the catalytically active sites. Moreover, CoAl2O4 acted as a transition layer which provided a cobalt source for the subsequent reduction process and regulated the growth of metallic Co nanoparticles, which increased the number of active sites for catalysis. Simultaneously, the metallic Co can not only activate PDS by being an electron donor, but also initiate the formation of Co-based redox pairs. This study offers new insights into the synthesis of efficient and cost-effective supported Co-based catalysts.