Simultaneous oxidation and absorption of nitric oxide and sulfur dioxide by peroxymonosulfate activated by bimetallic metal-organic frameworks

SO2 and NO from coal combustion are the main precursors of acid rain, regional haze, and photochemical smog. Advanced oxidation strategies can be used to simultaneously remove SO2 and NO from flue gas under a low temperature. Two metal-organic frameworks (MOFs), FeBDC and CuFeBDC, were synthesized and used to activate peroxymonosulfate (PMS) for the oxidation and absorption of flue pollutants. The characterization re-sults revealed that MOFs contained the redox pairs Fe(II)/Cu(I) and Fe(III)/Cu(II). Fe(II)/Cu(I) initiated firstly the PMS activation. Then, the Fe(II-III-II) and Cu(I-II-I) redox cycles continuously activated PMS and generated reactive species. MOFs-PMS removed 76.6 % and 86.5 % of NO in the presence of FeBDC and CuFeBDC catalysts, respectively. 100 % of SO2 was removed. CuFeBDC exhibited the efficient catalytic properties for the removal of NO and SO2 in PMS solution, and could be recycled and regenerated. After five cycles, the removal efficiencies of NO and SO2 were 71.2 % and 100 %, respectively, and NO and SO2 emissions in the outlet were lower than the emission limit when using CuFeBDC-PMS. During the oxidation and absorption process, NO and SO2 were first oxidized to NO2- and SO32-as intermediates, then formed the final products of NO3- and SO42-. Radical scavenging experiments and electron paramagnetic resonance measurements revealed that both radical (SO4-center dot, center dot OH) and non-radical pathways (1O2) contributed to the efficient oxidation of NO/ SO2. 1O2 was the predominant reactive oxygen species for the removal of NO, while SO4-center dot and center dot OH were responsible for the removal of SO2.