1. Master Thesis

- Thesis topic: The Application of TiO2@g-C3N4 Core-shell and Ag/g-C3N4 Composites for Photodegradation on Pollutant Removal

- Doi: https://doi.org/10.6840/cycu202000611

- Abstract: 

        In this study, the both composites TiO2@g-C3N4 and Ag/g-C3N4 were used for the degradation of acid red dye, methylene blue dye, and methylene red dye from wastewater and NO gas from air pollutant. The TiO2@g-C3N4 catalysts were prepared by the heating method using different percentages weight of TiO2 and Urea, TiO2 (P25), the ratio of TiO2 and NH4N2O (Urea) are 1:2, 1:3, 1:4, 1:6, and 1:10. The Ag/g-C3N4 composites were synthesized by the deposition method with the change of the percentage amount of AgNO3 were 1%, 5%, 10%, 12.5%, 20%, and 30% per amount of g-C3N4. In the first part, the TiO2@g-C3N4 and Ag/g-C3N4 investigated the effect of NO gas standard, the affection of the absorption ability of the surface was determined and become a part of removal efficiency. The highest removal efficiency of the sample 1:6 TiO2@g-C3N4 was 62,2% and 20%Ag/g-C3N4 was 42%, respectively, this result higher than 3 times with the pure g-C3N4 is 32% and TiO2( P25) is 42% within 30 minutes under visible-light. In the second part, the best composite for NO photo-degradation of those samples was tested with commercial dye to determine the application not only for air pollutant but also can apply for water pollutants. In addition, the reusability and trapping investigation on photo-degradation efficiency for NO gas were calculated for future applications. The composite fabricated with 1:6 TiO2@g-C3N4 was observed to be more stable for 5 cycles. On the other hand, photocatalytic degradation of TiO2@g-C3N4 composites showed that the different percentage composite catalysts were more efficient and stable than the pure TiO2, g-C3N4 and Ag/g-C3N4 catalysts for NO gas. In contrast, the photo-degradation of Ag/g-C3N4 is better than the other samples, it was explained that the photocatalytic mechanism for each pollutant catalysts. The morphological structure and morphological face of the obtained composites were analyzed using X-ray diffraction (XRD), Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR). Diffuse reflectance spectroscopy (DRS) and Electron spin resonance (ESR) was used to determine the optical properties of the composite.

Keywords: TiO2, g-C3N4, Photocatalytic, Nitrogen oxides, Methylene Blue, Methylene Red

2. PhD Thesis 

- Thesis topic: Removal of Nitric Oxide from through the single photocatalysts, photocatalytic composites, and photocatalytic membranes: Discussion on Toxicity, Stability, and Mechanism

- Doi: https://doi.org/10.6840/cycu202301358

- ORCID or ResearchGate: orcid.org/0000-0002-6069-445X

- Abstract: 

        NOx air pollutants, with NO as a prominent component, present a significant environmental challenge due to their detrimental effects on both human health and the environment. NO is a highly reactive gas that contributes to the formation of nitrogen dioxide (NO2), a key component of smog and a precursor to harmful secondary pollutants such as ozone and particulate matter. Exposure to NOx has been linked to respiratory problems, cardiovascular diseases, and impaired lung development in children. How to control NOx effectively is an issue.
        When it comes to the removal of NOx pollutants, various methods exist, including chemical scrubbing, catalytic reduction, and adsorption. However, photocatalytic method stands out as a promising and environmentally friendly approach because of operating under mild conditions, and minimizing energy consumption and operational costs; it is a sustainable and green approach. However, most photocatalysts have a high bandgap and are inactive under visible or solar light, and have fast electron-hole (e– – h+) recombination rates. Both g-C3N4 and ZnSn(OH)6 (cZHS) are potential photocatalysts but still have the drawbacks mentioned above. This research focuses on modifying g-C3N4 and ZnSn(OH)6 (ZHS) to enhance their photocatalytic performance under visible or solar light, while examining the toxicity associated with these photocatalysts. The heterojunction structures were constructed by combining g-C3N4 with commercial MgO and TiO2 to improve the photocatalytic removal of NO under visible light. Additionally, noble metals (Au and Ag nanoparticles) were employed to enhance the photocatalytic NO removal capabilities of perovskite ZHS through surface plasmon resonance (SPR) under solar light. By integrating a novel apparent DeNOx index equation, the calculation and comparison of byproduct toxicity for both single catalysts (TiO2, MgO, g-C3N4, cZHS, Bi2S3) and composite photocatalysts (TiO2@g-C3N4, MgO@g-C3N4, Ag@Bi2S3, Au:cZHS, Ag:cZHS) were facilitated. In addition, this research also involved the construction of photocatalytic membranes by employing cold plasma and PAA grafting on PES membranes for future practice applications. The results demonstrated that under visible light, the photocatalytic efficiency of MgO/g-C3N4, TiO2/g-C3N4, Au:ZHS, and Ag:ZHS samples all reached 75% - 90% with low byproduct toxicity. In contrast, single photocatalysts revealed that NO removal efficiency under visible light ranged from 62%-72%; besides, they generated more toxic byproducts. On the other hand, cZHS, Au:cZHS, and Ag:cZHS achieved photocatalytic NO removal efficiencies in the range of 57%-87% under solar light while displaying low toxicity. Furthermore, the DeNOx index analysis indicated that the by-product toxicity of single photocatalysts was higher than that of composite photocatalysts, with TiO2@g-C3N4 and MgO@g-C3N4 showing promising performance. The TiO2@g-C3N4/PAA/PES membrane (83%) outperformed the MgO@g-C3N4/PAA/PES membrane (73%). Notably, the TiO2@g-C3N4/PAA/PES membrane exhibited high reusability, with only a 2.4% decrease in performance after five recycling cycles. The characterization of photocatalysts and photocatalytic membranes involving various advanced techniques such as XRD, FTIR, SEM-EDS, TEM, XPS, BET, UV-Vis DRS, ESR, etc showed that they were successfully prepared with excellent properties. It also showed that the preparation methods did not affect much the characteristic of the photocatalysts. The DRS spectra indicated that the heterojunctions and SPR reduce the bandgap and e– – h+ recombination rates of the photocatalysts and the BET results confirm that the charge carrier separation is the main effective factor on the photocatalytic performances. Given the low preparation cost and excellent photocatalytic activity, the fabrication and application of TiO2@g-C3N4/PAA/PES membranes have significant potential for scaling up in the photocatalytic reactors. These findings contribute crucial insights into the development of high-performance photocatalysts for air pollution removal, along with an accurate evaluation of their overall toxicity.

Keywords: Visible light/Solar light photocatalysis, Photocatalytic membranes, NOx removal, DeNOx byproduct toxicity index, Graphitic carbon nitride, ZnSn(OH)6 composite photocatalysts, Heterojunction mechanisms, Surface Plasmon resonances