Photoactive Hybrid Film Photocatalyst of Polyethersulfone-ZnO for the Degradation of Methyl Orange Dye: Kinetic Study and Operational Parameters
A facile and effective technique to immobilize photocatalyst nanoparticles by incorporating zinc oxide (ZnO) into polyethersulfone polymeric films by means of a phase inversion technique is reported. The degradation study of methyl orange (MO) dye was performed using a series of ZnO-embedded polymer hybrid systems. The photoactivity of the films increased in parallel with increased ZnO loading up to 17 wt%. The photodegradation process followed a pseudo first-order kinetics with an achievement
... ith an achievement of almost 100% MO removal in original conditions. The PZ-17 film demonstrated an excellent and comparable degradation performance up to five cycles, signifying the reliability of the film photocatalyst against ultraviolet irradiation and degradation. Catalysts 2017, 7, 313 2 of 16 demonstrated that the use of a polymer resin such as polyethersulfone (PES) as a support allowed more stability under ultraviolet exposure, where the resin was not simply degraded by hydroxyl radicals formed during the process and was marked as the right candidate for support materials in photocatalysis [17, 18] . The incorporation of nanoparticles inside the PES matrix simultaneously improved its physicochemical properties such as surface hydrophilicity, as well as thermal and mechanical durability. Recently, researchers successfully prepared PES/TiO 2 film photocatalysts that exhibited good photocatalytic performance in degrading methyl orange dye solution  . Several studies reported that ZnO exhibited better photocatalytic activity than TiO 2 in the degradation of some organic compounds. The biggest advantage of using ZnO is that it absorbs over a larger fraction of the solar/UV spectrum than TiO 2 . Theoretically, the large band gap of ZnO of 3.37 eV has a high exciton binding energy of 60 meV at room temperature, which can exhibit semiconducting and piezoelectric dual properties. When ZnO is illuminated with UV radiation, electron-hole pairs are simultaneously generated within the metal oxide semiconductor. The valence band hole has an intensive reduction potential and it leads to the generation of more •OH radicals (as compared to TiO 2 ) that are known to be powerful and non-selective oxidizing agents, responsible for superior photocatalytic degradation activity [2, 20, 21] . Therefore it was hypothesized that the incorporation of the appropriate amount of ZnO into PES could yield a better performance than PES/TiO 2 film photocatalyst. However, a detailed study exploring the preparation of hybrid film photocatalyst incorporating high ZnO nanoparticles into PES has not been studied to the best of our knowledge, especially in the field of the photocatalysis process. Therefore, the purpose of the current work was to develop PES/ZnO hybrid film photocatalysts and to examine the effect of formulation on the physicochemical properties of the ZnO blended PES. Emphasis was placed on the photoactivity of PES/ZnO film photocatalysts in degrading methyl orange dyes in various operational parameters which include initial pH, initial concentration, and quantity of film. Moreover, the recyclibility study was also systematically elucidated by using the best PES/ZnO film photocatalyst in the photocatalytic degradation process. Results and Discussion X-ray Diffraction Analysis The crystallinity and phase formation of pristine PES and certain PES/ZnO film photocatalysts are shown in Figure 1 . The samples were labelled as per Table 5 in Section 3.2 below. No peaks were identified in the X-ray diffraction (XRD) spectrums for pristine PES indicating the amorphous nature of the film (Figure 1a ). For the PES/ZnO films, several peaks characteristic of the ZnO hexagonal structure according to the Joint Committee on Powder Diffraction Standard (JCPDS) card no. 36-1451 were observed (Figure 1b-d) , indicating the successful immobilization of ZnO into the PES matrix. The crystallinity of the ZnO peaks on diffraction plane (100, 002, and 101) increased in parallel with the increase in the amount of ZnO deposited into PES. Furthermore, there were no substantial changes of the peaks' intensities signifying that the PES had not experienced modifications in term of the crystallographic structure of ZnO nanoparticles after their incorporation into the PES matrix. Particularly, the diffracted peak at (101) is more intense than the peak at (002) and (101) orientation. This specifies that the nanocrystals formation has a preferred crystallographic at (101) orientation  . Thus, the crystallite size was estimated from the average peak width of (101) using the Scherrer equation and was equal to 55 nm for all prepared samples.