Abstract
Membrane fouling has been a major issue in the development of more efficient water treatment processes. Specifically in surface waters filtration, organic matter, such as humic-like substances, can cause irreversible fouling. Therefore, this study evaluates the activity of a photocatalytic layer composed of Ce-doped zirconia nanoparticles in improving the fouling resistance during filtration of an aqueous solution of humic acid (HA). These nanoparticles were prepared by hydrothermal and sol–gel processes and then characterized. Before the filtration experiments, the photodegradation of HA catalyzed by Ce-doped zirconia nanoparticles in dispersion was studied. It was observed that the sol–gel prepared Ce-ZrO2 exhibited higher HA removal in practically neutral pH, achieving 93% efficiency in 180 min of adsorption in the dark followed by 180 min under visible-light irradiation using light-emitting diodes (LEDs). Changes in spectral properties and in total organic carbon confirmed HA degradation and contributed to the proposal of a mechanism for HA photodegradation. Finally, in HA filtration tests, Ce-ZrO2 photocatalytic membranes were able to recover the flux in a fouled membrane using visible-light by degrading HA. The present findings point to the further development of anti-fouling membranes, in which solar light can be used to degrade fouling compounds and possibly contaminants of emerging concern, which will have important environmental implications.
Highlights
As water scarcity becomes more severe and the emission of contaminants of emerging concern (CEC) increases, it is critical to develop more effective and less energy-consuming treatments for drinking and wastewaters [1,2]
Ce-doped ZrO2 nanoparticles with photocatalytic activity under visible light were synthesized in this study by hydrothermal and sol–gel processes
Ce-ZrO2 was applied in the photodegradation of humic acid, a good model molecule for membrane fouling tests
Summary
As water scarcity becomes more severe and the emission of contaminants of emerging concern (CEC) increases, it is critical to develop more effective and less energy-consuming treatments for drinking and wastewaters [1,2]. Despite TiO2’s unique photocatalytic activity and stability [22], this material requires photons in the UV frequencies to create the electron-hole photo-induced separation (i.e., excitation from the valence band (VB) to the conduction band (CB), separated by about 3.2 eV) This fact practically excludes the use of sunlight as an energy source for TiO2. In recent works from our group [33,34], doping ZrO2 with cerium has introduced intra band gap states between zirconia VB and CB, allowing the new catalyst to absorb visible light through a double jump mechanism These findings were relevant since they indicated that solar light could be used as a light source for the Ce-ZrO2 photocatalytic degradation of organic compounds. Ce-doped zirconia nanoparticles were supported in filter papers to produce prototypes of a photocatalytic membrane with improved anti-fouling resistance
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