Templating agent-mediated Cobalt oxide encapsulated in Mesoporous silica as an efficient oxone activator for elimination of toxic anionic azo dye in water: Mechanistic and DFT-assisted investigations

While Azorubin S (AZRS) is extensively used as a reddish anionic azo dye for textiles and an alimentary colorant in food, AZRS is mutagenic/carcinogenic, and it shall be removed from dye-containing wastewaters. In view of advantages of SO4 center dot--related chemical oxidation technology, oxone (KHSO5) would an ideal source of SO4 center dot- for degrading AZRS, and heterogeneous Co3O4-based catalysts is required and shall be developed for activating oxone. Herein, a facile protocol is proposed for fabricating mesoporous silica (MS)-confined Co3O4 by a tem-plating agent-mediated dry-grinding procedure. As the templating agent retained inside the ordered pores of MS (before calcination) would facilitate insertion and dispersion of Co ions into pores, the resulting Co3O4 nanoparticles (NPs) would be grown and confined within the pores of MS after calcination, affording Co@MS. On the contrary, another analogue, Co/MS, is also prepared using the similar protocol without the templating agent-mediated introduction of Co, but Co3O4 NPs seriously aggregate as clusters on MS. Therefore, Co@MS out-performs Co/MS for activating oxone to eliminate AZRS. Co@MS shows a noticeably lower activation energy of AZRS elimination than the existing catalysts, revealing its advantage over the reported catalysts. Moreover, the mechanistic investigation of AZRS elimination by Co@MS-activated oxone has been also elucidated for identi-fying the presence of SO4 center dot-, center dot OH, and O-1(2) in AZRS degradation using scavengers, electron paramagnetic reso-nance spectroscopy, and semi-quantification. The AZRS decomposition pathway is also investigated and unveiled in details via the DFT calculation. These results validate that Co@MS appears as a superior catalyst of oxone activation for AZRS degradation.

Automated summary

In order to degrade AZRS, a highly oxidizing agent needs to be developed and Co3O4 nanoparticles with ordered pores need to be synthesized using a templating agent. This allows for the stable dispersion and activation of the oxidizing agent within the pores, improving the degradation efficiency.