Photocatalytic degradation of methylene blue by cqds based composite derived from watermelon rinds

• Main Author: Umi Rabiatul Ramzilah, P. Remli
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: T Technology (General); TA Engineering (General). Civil engineering (General)
• Online Access: http://umpir.ump.edu.my/id/eprint/34968/1/Photocatalytic%20degradation%20of%20methylene%20blue%20by%20cqds%20based%20composite.ir.pdf; http://umpir.ump.edu.my/id/eprint/34968/
• Institution: Universiti Malaysia Pahang

Dyes comprise of toxic and complex components and has slow degradation rate. The presence of dyes components altered the colour of the water and bring negative effects not only from aesthetics value but also reducing the sunlight penetration into the waterbody. It also harmful to aquatic organism and human health if discharge directly to environment. The effort to remove the methylene blue (MB) from wastewater were reported using numerous methods such as Fenton treatment, ozonation, membrane filtration, coagulation, adsorption, and advanced oxidation process. Recently, photocatalysis has been conducted in several studies to treat dye wastewater because of the complete mineralization of organic compounds. Despite of that, the current photocatalysis method is still limited due to the high cost and limited source. On the contrary, watermelon rinds (WMR) have been discarded as waste and left untreated in the environment. Therefore, to tackle both environmental issues, this study employed the WMR as the carbon precursor in the synthesize of carbon quantum dots (CQDs) that can be used as photocatalyst to treat the MB solution. Unlike many other carbon nanomaterials such as carbon nanotubes, graphene oxide and graphene quantum dots, CQDs are easily and inexpensively synthesized using a cheap and sustainable source of biomass. Hence, the main objective of this study is to evaluate the feasibility of WMR used in the synthesize of CQDs to act as a photocatalyst in degrading the MB solution. CQDs was incorporated with titanium dioxide TiO2 to enhance the chemical, physical and optical properties of TiO2 for evaluation of photocatalytic degradation under artificial light irradiation. All photocatalysts powder were characterized using powder X-ray diffractometer (XRD), high resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), Brunauer-Emmett-Teller (BET) surface area analyzer, X-ray photoelectron spectroscope (XPS), UV-visible light spectrophotometer (UV-Vis) and Photoluminescence (PL) spectra. Next, photocatalytic activity of the prepared photocatalysts was evaluated by degrading MB under visible light from xenon lamp (500W). Based on the results, it is feasible to synthesize CQDs derived from WMR which can be used as solely photocatalyst in photocatalytic degradation of MB. In the results, it is found that CQDs with 0.1 g/L catalyst loading at 5 ppm has the highest photocatalytic activity with 73% of MB removal compared to TiO2 and CQDs- TiO2 due to its small surface area. In terms of the percentage, the MB degradation are as follows: CQD >CQD-TiO2>TiO2 with 73%, 55% and 27% respectively. The result for pH of concentration showing that the degradation efficiency increases with increasing of pH. The catalysts work better in pH 9 due to the cationic property of MB. The kinetic data of MB degradation were fitted with Langmuir- Hinshelwood kinetic model and kinetic parameters were obtained. In conclusion, this study suggested that the concentration of MB can be reduced by utilizing CQDs derived from WMR.