Al-coordination polymer-derived nanoporous nitrogen-doped carbon microfibers as metal-free catalysts for oxygen electroreduction and acetalization reactions

Abstract

Nanoporous nitrogen-doped carbon microfibers were facilely synthesized by the pyrolysis of coordination polymer microfibers of aluminium-diethylenetriamine pentaacetic acid (Al-DTPA). Al-DTPA microfibers could be easily produced at a scale of over 0.25 kilograms by a homogeneous precipitation reaction of DTPA and aluminium nitrate in aqueous solution. After undergoing thermal conversion of Al-DTPA at the optimized temperatures and acid-leaching, the well-defined nitrogen-doped carbon microfibers were obtained at a scale of over 10 g in the laboratory. The interconnected nanoporous textures and plentiful nitrogen-doped functional sites endow such microfibers with not only efficient catalytic activity for the oxygen reduction reaction (ORR) in 0.1 M KOH electrolyte, but also superior durability and methanol-tolerance during ORR. Moreover, Al-DTPA microfibers could be also transferred into carbon-based nanoporous solid acids by the sulfuric acid-solvothermal treatment. Plentiful –SO₃H functional groups were grafted on the surfaces of nanoporous nitrogen-dopped carbon microfibers (protonic acid amount, 1.8 mmol g⁻¹). They served as a highly efficient and recyclable solid acid catalyst for the acetalization of benzaldehyde and ethylene glycol in a yield of about 99.0 at%. The thermal conversion of Al-coordination polymers might be a new practically feasible technique for the preparation of functional nanoporous nitrogen-doped carbon microfibers.