Low-dosage viscosity breakdown and mechanistic insights into Cu-MOF-74/PMS degradation of high-concentration polyacrylamide

Abstract

The high viscosity of oilfield produced water caused by high-concentration polyacrylamide (PAM) readily leads to quartz sand filter clogging, necessitating efficient viscosity reduction during the sedimentation stage. This study employed hydrothermally synthesized Cu-MOF-74 to activate peroxymonosulfate (PMS) for efficient PAM degradation and viscosity breakdown. Characterization via SEM, XRD, and XPS confirmed the successful synthesis and stable structure of the catalyst. Under the conditions of a low dosage of 7 mg L⁻¹ Cu-MOF-74, 0.2 mmol L⁻¹ PMS, and 20 °C, a viscosity reduction rate of 91.59% was achieved after just one hour of reaction. Quenching tests and in situ EPR revealed that singlet oxygen and hydroxyl radicals were the primary reactive species, and superoxide radicals. Analyses including UV-vis, Zeta potential, and COD indicated that the viscosity reduction originated from the cleavage of PAM chains. GC/MS analysis of intermediate products elucidated a stepwise degradation pathway involving main-chain scission, side-chain transformation, and generation of small molecules.