Mesoporous silica SBA-15 and SBA-16 as working electrode for electrochemical determination of ascorbic acid and uric acid in water / Hashazirah Mohamad Hassan

Mesoporous silica SBA-15 and SBA-16 were synthesized via the surfactant templating technique. Two important components in synthesizing mesoporous silica are the silica source and surfactant. The silica source used was tetraorthosilicate (TEOS). The surfactant used were Pluronic P123 for SBA-15 and Pluronic F127 for SBA-16. SBA-15 and SBA-16 have been proposed as modifiers in carbon paste electrodes for ascorbic acid (AA) and uric acid (UA) detection in water. The physical and chemical characterization of SBA-15 and SBA-16 were carried out using Field Emission Scanning Electron Microscope (FESEM), X-Ray Diffractometer (XRD), Thermogravimetric analysis (TGA), Fourier Transform Infrared (FTIR), and Nitrogen Adsorption. Cyclic voltammetric (CV) method was used for AA and UA electrochemical determination. FESEM analysis showed that the SBA-15 synthesized possessing the rod-like shaped particles. While the SBA-16, exhibits spherical structure. XRD analysis was performed using lower angle which were in between 0.5° to 2.5°. XRD patterns of SBA-15 and SBA-16 showed that the corresponding peaks were indexed at (100),(110),(200) and (110),(200),(211). The surface area isotherms obtained in nitrogen adsorption analysis were both type IV for SBA-15 and SBA-16. Hysteresis loops were observed within the relative pressure range (P/Po) of 0.45 to 0.70. The average pore diameter for SBA-15 and SBA-16 were 6.01 nm and 6.05 nm. With the application of BJH and BET method, the surface area and pore volume calculated were 531.6 m2/g and 0.69 cm3/g for SBA-15. While for SBA-16, it was 626.72 m2/g and 0.52 cm3/g. The silica materials became porous after calcination process due to the removal of surfactant. Surfactant in general contains alkyl groups (C-H bonds). Hence, the elimination of C-H stretch band was observed in IR spectrums of calcined SBA-15 and SBA-16, in between the wavelength of 2858 cm-1 to 2934 cm-1 and 3000cm-1. A curve observed from the dTG graph of as-synthesized SBA-15 in between the temperature of 192°C and 329°C with 30% of mass loss. Together with two separate curves shown between 245°C and 445°C in as-synthesized SBA-16 dTG graphs with approximately 20% mass loss, showing that P123 and F127 was successfully removed during calcination and 550°C was a suitable temperature. SBA-15 and SBA-16 were utilized in the fabrication of carbon paste electrodes; MCPE/SBA-15 and MCPE/SBA-16. The detection limit of MCPE/SBA-15 and MCPE/SBA-16 on AA and UA were successfully identified which are 3.0x10-3 M and 5.0x10-4 M, and -1.0x10-4 M; 1.0x10-5 M. The results achieved showed SBA-16 able to promote better enhancement towards AA detection.