Role of different dimensional carbon nanoparticles in catalytic oxidation of organic pollutants and alleviating membrane fouling during ultrafiltration of surface water

Abstract

Abstract In this study, carbon nanoparticles (CNPs) in different structural dimensions, including carbon nanotubes (CNTs), carbon nanofibers (CNFs), hexagonally (CMK-3) and cubically (CMK-8) ordered mesoporous carbons were proposed for peroxymonosulfate (PMS) activation. The performance for catalytic oxidation of organic pollutants and alleviating ultrafiltration membrane fouling was systematically investigated and compared. The results showed that CMK-3 performed best for PMS activation in the reduction of typical micropollutants and natural organic matter, whereas the efficiency of CNFs was relatively limited. The CNPs/PMS processes were efficient alternatives for alleviating membrane fouling, whereas discrepancies existed in the performance for different CNPs. Both the decomposition of macromolecular biopolymers and the degradation of fluorescent components reduced the foulants directly contacting with membranes, thus contributing to the fouling mitigation. The characterization of fouled membranes (i.e., surface morphologies and functional groups) further verified the fouling alleviation. From a comparison view, the decomposition of PMS by CMK-3 was more effective compared to the other CNPs, with the catalytic capacity of CMK-3 > CNTs > CMK-8 > CNFs. The discrepancy was likely ascribed to the microstructure differences of carbonaceous materials. To be specific, CNTs exhibited a curled-like shape with smaller diameter and larger specific surface area than CNFs, while CMK-3 showed long straight and parallel channels with decreased internal resistances than CMK-8. The electron paramagnetic resonance analyses revealed that SO4•−, •OH, O2•− and 1O2 were the main reactive oxygen species generated in the systems. The CNPs/PMS processes significantly changed the fouling mechanisms by delaying the formation of cake layers and prolonging the transition volumes. These findings possess a guiding significance for the application of carbon-based catalytic oxidation in membrane water treatment processes.