Pullulan based zinc oxide and polyaniline nanocomposites for photodegradation of Rhodamine B

Abstract

Water pollution has been plaguing the world ever since the industrial revolution. One of the main water pollutants is dyes and they pose adverse effect on mankind and aquatic life. This pollutant can be removed through an emerging alternative technique; the advanced oxidation process (AOPs). Photocatalysis, one of popular AOPs, utilizes semiconductor catalyst to degrade the dyes. Zinc oxide (ZnO) is a promising material for this process. In this study, pullulan-based zinc oxide nanoparticles (ZnO NPs), polyaniline/pullulan composites (PANI/Pul Cs) and zinc oxide-polyaniline/pullulan nanocomposites (nZPP NCs) were synthesized. The catalysts were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectrophotometer (UV-Vis), transmission electron microscopy (TEM), surface area and pore analyser and thermogravimetric analysis (TGA). In this study pullulan served as capping agent for the production of ZnO NPs and PANI/Pul Cs. For the synthesis of ZnO NPs, the effects of calcination conditions, temperature and time, on the properties of ZnO NPs were studied. The crystallinity and particle size of ZnO NPs increased proportionally with calcination temperature. Concerning calcination time, significant increase of particle size was observed when the time was increased to two hours. TEM results showed that the particles size of synthesized ZnO NPs ranged from 28 to 127 nm. All the catalysts were subjected to photodegradation of rhodamine B (RhB) dye. ZnO NPs produced with calcination conditions of 400 °C for 1 hour showed the best activity with degradation rate of 0.0801 min-1. Then, composites PANI/Pul were synthesized with variation of aniline to pullulan mass ratio. The impact of mass ratio variation on the properties PANI/Pul Cs was compared. In the presence of pullulan, the crystallinity of PANI/Pul Cs improved. Besides, the particle morphology also became more consistent rod-like shape in the presence of pullulan with aniline to pullulan mass ratio of 1:3. All the synthesized PANI/Pul Cs were subjected to photodegradation of RhB and the results showed that the best activity was exhibited by the PANI/Pul C synthesized with 1:3 aniline to pullulan mass ratio with degradation rate of 0.0086 min-1. Then nZPP NCs were synthesized using ZnO NPs produced with calcination conditions of 400 °C for 1 hour and PANI/Pul C with 1:3 aniline to pullulan mass ratio. The weight per cent of PANI/Pul C in nZPP NCs were varied as two, six and 10 per cent. With the addition of PANI/Pul C on ZnO NPs, the crystallinity of ZnO NPs was not disturbed. The nZPP NCs catalyst activity was optimized by using response surface methodology (RSM) with the variable being weight per cent of PANI/Pul C, catalyst dosage and pH with the response being degradation rate. The results showed that the most suitable model was quadratic with the optimum degradation rate obtained was 0.2319 min-1 with six weight per cent of PANI/Pul C, catalyst dose of 0.7 g/L and initial pH of 8. Lastly, the optimized catalyst was tested with simulated dye wastewater which was created by mixing five dyes together. The results showed that complete decolourization was achieved in 180 minutes.