Phenothiazine functionalized reduced graphene oxide aerogel for adsorption and charge storage / Lee Soon Poh

Faculty of Industrial Science and Technology

Thesis (Doctor of Philosophy (Biotechnology)) -- Universiti Malaysia Pahang – 2023

Bibliography : p. 134-159

The development of recent technology escalates the massive demand for charge storage devices in maintaining the function of electronic devices and industrial machines. Such a scenario increases industrial operations and indirectly increases water pollution issues. Reduced graphene oxide (rGO) is an emerging carbon material discovered to be the potential material that can overcome the limitations of activated carbon in adsorption and charge storage. Performance enhancement on both applications via rGO functionalization often involved a complex synthesis approach or relatively high-cost process. In this study, the different graphene oxide (GO) sheet size precursors were obtained via sonication and the physicochemical properties of the rGO xerogel upon reduction were examined. The one-step functionalized phenothiazine-rGO (PTZ-rGO) aerogel was synthesis via photoreduction using PTZ as a reductant and functionalization precursor. The optimized sheet size precursor (4h GO) renders excellent pore strength through optimal parallel sheet stacking that prevents pore deformation during xerogel formation. Such an effect allows the 4h rGO to have a high surface area (190.40 m2 g−1) and pore volume (0.261 cm3 g−1). The functionalized PTZ-rGO aerogel reflects the important role of PTZ in preventing restacking of rGO layers and thus, generates a high surface area (539.67 m2 g−1) material. The synergistic effect of high porosity and excellent surface properties of rGO xerogel and PTZ-rGO aerogel structured them to be well-performed in electrochemical analysis. The optimal remaining oxygen in rGO xerogel and optimal PTZ loaded on PTZ-rGO aerogel contribute to the diffusive charge storage mechanism allowing it to obtain 182 F g−1 and 193.4 F g−1 at 0.75 A g−1 for 4h rGO and P8G1 sample, respectively. The excellent physicochemical properties of 4h rGO and P8G1 also build up a high-performing adsorbent for organic and heavy metal ions removal. The adsorption kinetic obeys the pseudo-second-order kinetic model, which indicates chemisorption as a pollutant removal mechanism for entire rGO xerogel and PTZ-rGO aerogel samples. Langmuir adsorption isotherms well describe the adsorption behavior of rGO xerogel and PTZ-rGO aerogel for all the adsorbates except Fe3+ which fits better in Freundlich isotherm. Hence, the extraordinary performance of the optimized PTZ-rGO aerogel in electrochemical and pollutant removal renders it a suitable candidate to be implemented as a supercapacitor electrode material and excellent adsorbent material. Therefore, PTZ-rGO aerogel contributes to the solution for increasing charge storage demand and wastewater remediation.