Template synthesis of nitrogen-doped carbon nanocages–encapsulated carbon nanobubbles as catalyst for activation of peroxymonosulfate

Abstract

Nitrogen-doped carbon nanocages–encapsulated carbon nanobubbles (CBs@NCCs) were feasibly fabricated by the in situ thermal conversion of Co–Fe Prussian blue analogues (Co–Fe PBAs) coated with polydopamine (PDA) shells. Interestingly, PBA cores can act as a self-sacrificing template and decompose during high-temperature treatment. PDA shells play a crucial role in stabilizing the steric architecture, supplementing nitrogen-doping of CBs@NCCs under high-temperature treatments. When compared with carbon nanobubbles (CBs) without the protection of carbon nanocages, CBs@NCCs possess higher specific surface area and pore volume. The contributions of a unique configuration and proper nitrogen modification are significant for improving the peroxymonosulfate (PMS) activation performance of CBs@NCCs, which is expected to be a promising alternative to other conventional carbocatalysts and metal oxides. Moreover, the applicability of the as-synthesized carbocatalysts was systematically investigated by adjusting several operating parameters, and some ubiquitous anions and natural organic matters (NOMs) were also taken into account in methylene blue (MB) degradation. The radical evolution and PMS activation mechanism are investigated by radical quenching and electron paramagnetic resonance (EPR) tests, which revealed that sulfate radicals (SO₄˙⁻) and singlet oxygen (¹O₂) are simultaneously responsible for the overall MB removal in a CBs@NCCs-800/PMS system. This study may provide a broader perspective for upgrading the catalytic efficiency of various green heterogeneous carbocatalysts.