Modified metal oxides supported on polyvinyl chloride catalysts for the photodegradation of paraquat dichloride

Abstract

The use of heterogeneous photocatalyst based on titanium dioxide has been proven as an effective treatment method for polluted water. In this research, titanium dioxide (TiO2), zinc oxide (ZnO) and tungsten trioxide (WO3) were used to prepare monometallic, bimetallic and trimetallic oxide photocatalysts using simple sonication and ball milling techniques with different weight percents of metal oxide. These metal oxides were then used to prepare metal oxides supported on polyvinyl chloride (MO/PVC). Multiwalled carbon nanotubes (MWCNT) was added in MO/PVC to give MO/PVC-MWCNT photocatalyst and was applied for photodegradation of paraquat dichloride. The treated paraquat dichloride solution was measured using ultraviolet-visible spectrophotometric technique. The best loading of metal oxides on PVC support was achieved at 80 weight percent which showed the total amount of catalyst is 4.0 g. This loading was used throughout the research. The effect of pH, H2O2 addition and sonication treatment time were also studied to determine the optimum reaction condition. Comparison using different preparation techniques between simple sonication and ball milling showed that simple sonication was preferred to prepare bimetallic and trimetallic oxide photocatalysts. The photocatalytic activity increased with the introduction of MWCNT for monometallic oxide but decreased for bimetallic and trimetallic oxide photocatalysts. The optimization of MWCNT loading for TiO2/PVC-MWCNT photocatalyst was successfully achieved when the ratio of MWCNT:TiO2 was at 1.19:98.81 which gave 73.55% degradation of paraquat dichloride. The activity of TiO2/PVC with 20 ppm H2O2 addition was the best which gave 76.57% paraquat dichloride degradation, followed by the activity of TiO2/PVC-MWCNT with the aid of 30 minutes sonication treatment which gave 74.37% paraquat degradation. The activity of TiO2/PVC-MWCNT and WT/PVC-MWCNT both gave 73.55% paraquat dichloride degradation. FESEM micrograph of MO/PVC-MWCNT photocatalysts showed that the MWCNT were covered by the metal oxides. EDX analysis confirmed the presence of Ti, Zn, W and O elements in the prepared photocatalysts. XRD patterns showed the degree of crystallinity of TiO2 powder was higher than TiO2 supported on PVC.