Electrospun PVDF/ZnO- Based Composite Fibers for Oil Absorption and Photocatalytic Degradation of Organic Dyes from Waste Water

Abstract

The one-dimensional PVDF/ZnO composite nanofibers exhibit a large specific area, which is beneficial for the absorption of pollutants in wastewater. Moreover, the uniformly distributed ZnO nanoparticles provide a large number of reaction sites for the degradation of the organic contaminants in wastewater. The prepared multifunctional nanofiber membranes have been exploited to both dye degradation and oil absorption. This multifunctional composite nanofiber membrane are characterized and studied the photocatalytic degradation of organic pollutants. In addition, the oil absorption capacity of PVDF/ZnO composite fibers is examined using engine oil.In this work, a hydrophobic membrane was successfully prepared by incorporating ZnO nanofiller into polyvinylidene fluoride (PVDF) using an electrospinning method (Figure-1) for organic dye degradation and oil absorption applications. The hydrothermal method was used to prepare pure ZnO. The structural properties of PVDF/ZnO composite fibers and pure ZnO were studied using the X-ray diffraction technique (XRD). The crystallite size value for ZnO is calculated using Scherrer’s formula. The calculated crystallite size is 20 nm. The TEM image of pure ZnO shows a flower-like structure. The EDX spectrum shows that the ZnO sample consists of Zn and O elements. SEM images of pure PVDF and PVDF/ZnO composite electrospun mat shows uniformly oriented, interconnected structure with bead free fibers. Finally, the prepared fibers were tested for oil absorption and the photocatalytic degradation of organic dyes. Comparing the oil absorption capacity results of both pure PVDF and PVDF/ZnO, shows that the oil absorption capacity is higher for the composites with the addition of ZnO nanofiller. This is due to the addition of ZnO filler increase the hydrophobicity of the fibers. The superhydrophobic materials can allows oil to flow through and repel water. The photocatalytic activity of PVDF/ZnO was evaluated by the degradation of Azocarmine G (AZG) and Malachite green (MG) dye under sunlight irradiation. The absorption spectra shows the decrease in intensities of the absorption peak of AZG and MG dye upon the increasing of irradiation time. The results showed that 85% of AZG and 90% of MG dye could be degraded within 120 min and 240 min. When the time increases, the photodegradation efficiency also increases for the PVDF/ZnO composite fibers. The results indicate that the PVDF/ZnO composite play an vital role in AZG and MG dye degradation. The smaller crystallite size of ZnO catalyst play a key role in photocatalytic activity. As particle size decreases, the number of active surface sites increases. This in tern enhances the photocatalytic activity. The photocatalytic degradation mechanism of the PVDF/ZnO composite fiber can be explained as follows; When photon energy is irradiated on a ZnO surface, holes and electrons are formed. Superoxide radicals are formed when excited electrons in the conduction band react with adsorbed oxygen, whereas hydroxyl radicals are formed when holes in the valence band react with surface bound water molecules. Both hydroxyl and superoxide radicals have the ability to directly oxidize dye molecules. Good oil absorption efficiency (115 %) was achieved using PVDF/ZnO membrane. The results show that the prepared composite fibers can be used to absorb oil and degrade organic contaminants. This cost-effective, easy operation, reusability, and efficiency of the PVDF/ZnO fiber mats could be potentially useful for water treatment and oil recovery. Figure 1