Efficient and rapid electrocatalytic degradation of polyethylene glycol by ammonium jarosite

Polyethylene glycol (PEG) in an aqueous environment is a potential problem for water pollution treatment because of its high thermal stability, difficult hydrolysis, and high biocompatibility. This study achieved the efficient and rapid degradation of PEG with a high polymerization degree of PEG (Mn = 20,000 g/mol) in simulated wastewater by a heterogeneous electro-Fenton process using ammonium jarosite as a catalyst. The results showed that the COD removal rate of simulated wastewater and the removal rate of PEG reached 85.85% and 92.29% within 60 min, respectively, and the number average molecular weight (Mn) of PEG was reduced by 79.18% at 180 min under the conditions of 80 mg/L PEG, pH = 3, current density of 5 mA/cm2, ammonium jarosite dosing amount of 0.8 g/L and aeration rate of 1 L/min. The catalytic mechanism of ammonium jarosite was proved that highly oxidative hydroxyl radicals (·OH) in the heterogeneous electro-Fenton process were the most critical active species, which can efficiently and rapidly oxidize PEG molecules. The oxygen atom in the ether bond of PEG molecules has lone pairs of electrons, which interact with the hydroxyl groups on the surface of ammonium jarosite to weaken the ether bonds in the PEG molecules. Then the ether bond is easily to be broken under the attack of the hydroxyl radical. The breakage of the polymer chains during PEG degradation leads to a continuous decrease in the average relative molecular mass of PEG, accompanied by the formation of aldehyde and carboxylic acid intermediates, which are eventually oxidized to form CO2 and H2O as the degradation time increases.