Role of pH on photocatalytic degradation of phenol derivatives using metal supported on mesoporous materials

Abstract

Photocatalysis is a promising advanced oxidation process (AOPs). It is often used in the degradation of phenolic derivatives due to their simplicity and easy handling, by converting organic molecules with total mineralisation into nontoxic H2O and CO2. In this study, a combination of microwave-assisted (MW) and facile electrochemical method was applied in the synthesis of catalysts (Fe-MTN and Cu-MZN). The characterisation of catalysts was tested using XRD, UV–Vis DRS and FTIR. It was found that there was no new bonding formed when Fe was introduced onto MTN, while the introduction of Cu onto MZN formed a new Zn-O-Cu. The introduction of Fe and Cu onto MTN and MZN also decreased the bandgap energy from 3.15 to 2.35 eV and 2.92 to 2.63 eV, respectively. The pH of the solution is one of the essential parameters that need to be measured in the photocatalytic process due to the amphoteric properties of semiconductor, which influenced the surface-charged properties of the catalysts. Fe-MTN and Cu-MZN were used in photocatalytic degradation of 2-chlorophenol (2-CP) and 2,4-diclorophenol (2,4-DCP), respectively. After the effect of pH over 2-CP and 2,4-DCP was tested in the range of 3 to 11, the greatest degradation of 2-CP using Fe-MTN was at pH 5 with 99% while 100% degradation of 2,4-DCP at pH 3 for Cu-MZN. These results are probably due to the amphoteric characteristic of catalyst, where it can be tested using point zero charged (pHZPC). The pHZPC value of Fe-MTN and Cu-MZN was 6.1 and 5.5, respectively illustrated that the photoactivity of both catalysts better in acidic condition compared to an alkaline condition.