Abstract
In this work, mesoporous TiO2-modified ZnO quantum dots (QDs) were immobilised on a linear low-density polyethylene (LLDPE) polymer using a solution casting method for the photodegradation of tetracycline (TC) antibiotics under fluorescent light irradiation. Various spectroscopic and microscopic techniques were used to investigate the physicochemical properties of the floating hybrid polymer film catalyst (8%-ZT@LLDPE). The highest removal (89.5%) of TC (40 mg/L) was achieved within 90 min at pH 9 due to enhanced water uptake by the LDDPE film and the surface roughness of the hybrid film. The formation of heterojunctions increased the separation of photogenerated electron-hole pairs. The QDs size-dependent quantum confinement effect leads to the displacement of the conduction band potential of ZnO QDs to more negative energy values than TiO2. The displacement generates more reactive species with higher oxidation ability. The highly stable film photocatalyst can be separated easily and can be repeatedly used up to 8 cycles without significant loss in the photocatalytic ability. The scavenging test indicates that the main species responsible for the photodegradation was O2●−. The proposed photodegradation mechanism of TC was demonstrated in further detail based on the intermediates detected by LC-time-of-flight/mass spectrometry (LC/TOF-MS).
Highlights
The efficiency of conventional wastewater treatment plants in removing antibiotics lies in the range of 12% to 80%
The X-ray Diffraction (XRD) profiles of ZnO quantum dots (QDs), ZT, bare linear low-density polyethylene (LLDPE), and the 8%-ZT@LLDPE are presented in Figure 1a–d, respectively
It has been reported that a lower degree of crystallinity allows a polymer to absorb more water [31], which is beneficial for the photocatalytic activity
Summary
The efficiency of conventional wastewater treatment plants in removing antibiotics lies in the range of 12% to 80%. The photocatalysts’ main drawback is the difficult separation from the water system for their reusability This relates to the common use of a powdered form of the photocatalysts, where they function as suspended colloidal particles in wastewater to degrade the organic contaminants. Other drawbacks include low light utilisation efficiency of the suspended photocatalyst; aggregation of catalytic particles, especially at higher concentrations, and potential human health problems associated with the fate and transport of dispersed powder and its mobility [10,11]. These drawbacks limit their application in large-scale commercial production. Polymer supports have relatively low density, allowing for the design of floating photocatalysts, especially in aqueous media [11,17,18,19]
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