Browsing by Author "Tan, K.-H."

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    Surface interaction of tetrabromobisphenol A, bisphenol A and phenol with graphene-based materials in water: Adsorption mechanism and thermodynamic effects
    (Elsevier B.V., 2023) Catherine, H.N.; Tan, K.-H.; Shih, Y.-H.; Doong, R.-A.; Manu, B.; Ding, J.-Y.
    Carbon-based materials, especially graphene nanocomposites (GNS) have attracted wide attention in recent years. In this study, graphene oxide (GO) and reduced graphene oxide (rGO) were prepared using the Improved Hummers method and were investigated for their adsorption behavior of emerging contaminants such as tetrabromobisphenol A (TBBPA), bisphenol A (BPA), and a conventional contaminant, phenol. The adsorption capacity seemed to slightly increase with increasing reduction degree of GO, highlighting its hydrophobic effect. The adsorption kinetics and isotherms were well delineated using pseudo-second-order and Langmuir equations respectively. At higher temperatures, the adsorption of these selected organic contaminants on GO and rGO slightly increased, also indicating the slight effect of temperature on the adsorption in the environment. From a thermodynamic analysis, the endothermic and spontaneous reaction was observed. The adsorption mechanisms included hydrophobicity, π- π interactions and π electron acceptor and donor ones. GNS can suspend in water even after adsorbing pollutants at the water interface. This would enhance the transport of these contaminants with nanomaterials in the environment. These findings are valuable to elucidate the interaction mechanism between phenol, BPA, and TBBPA on GNS while further understanding the physicochemical behavior of these organic contaminants in the environment. Summary: Adsorption capacities of emerging contaminants, BPA and TBBPA, as well as phenol on graphene oxide (GO) and reduced GO (rGO), were similar. Higher temperatures slightly increased the adsorption of these phenolic compounds on GO and rGO, which also indicated an endothermic and spontaneous process. © 2022
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    The degradation of tetrabromobisphenol A by metal-free graphene oxide in the dark
    (Elsevier Ltd, 2024) Catherine, H.N.; Tan, K.-H.; Lin, C.-Y.; Sahu, R.S.; Shih, Y.-H.
    Brominated flame retardants (BFRs) such as tetrabromobisphenol A (TBBPA) were widely detected in the environment. The ease of synthesis of graphene-based materials (GBMs) makes it an excellent metal-free carbon-based catalyst for the reductive debromination of TBBPA. Here we explore the complete debromination of TBBPA from the aqueous environment in the dark using metal-free graphene oxide (GO) and reduced GO (rGO). More importantly, radical scavenger experiments reveal the formation of superoxide radicals and singlet oxygen from the surface of GBMs leading to the debromination of TBBPA. GO shows an enhanced catalytic activity due to enriched O-functional groups on the surface than rGO, as observed by cyclic voltammetry and electrochemical impedance spectroscopy. In addition, the TBBPA degradation pathway was proposed with BPA as the end product and by-products were identified by mass spectroscopy. The complete TBBPA degradation was observed within 240 mins of reaction time (kobs = 8.6×10−3 min−1), which was significantly more efficient than the catalytic activity of other metal-based catalysts. Our study thus provides a new insight into the debromination mechanisms of TBBPA which would exhibit potential for future efficient catalyst development. © 2024 Elsevier Ltd