As a semiconductor, zinc oxide (ZnO) has better UV absorbing properties compared to other semiconductor materials, and therefore, it has better dye degrading abilities. However, ZnO tends to agglomerate, which lead to poor degradation compared to the other semiconductors. In this study, to overcome the agglomeration of ZnO, silica (SiO2) was combined with ZnO. The composite was tested for its photocatalytic activity. The ZnO/SiO2 photocatalyst was fabricated on a glass plate. In order to investigate the addition of SiO2 on ZnO, X-ray diffraction (XRD) and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) was used. The result of the XRD analysis demonstrates similar peak results with ZnO XRD data from ICSD 157132 with a hexagonal structure. The results indicate that the ZnO structure did not change after the addition of SiO2, while SEM-EDS results showed that SiO2 was supported on ZnO with 8% composition. The optimal composition was found to be ZnO/SiO2 95/5, as indicated by high degradation activity, which can degrade up to 89% methylene blue.
Part of the book: Visible-Light Photocatalysis of Carbon-Based Materials
Cr(III) and Cr(VI) have significantly different toxicological properties, with the latter being toxic for human health. The anodic stripping voltammetry using pencil graphite electrode (PGE) was developed to determine Cr(III), and it can measure the ion within linear range 12.5–75 ppm with 0.31 ppm detection limit, while adsorptive striping voltammetry was used to determine very low level of Cr(VI) using PGE with the addition of diethylenetriaminepentaacetic acid (DTPA). The results indicate that Cr(VI) can give electrochemical response when adsorptive stripping voltammetry was used, and addition of DTPA gives a specific Cr(VI) peak at −0.65 V. A more advanced method was developed for the differentiation of Cr(VI) and Cr(III) using gold nanoparticle-modified glassy carbon electrode (AuNP-GCE). The AuNP-GCE was applied as electrochemical sensor for Cr(VI) and Cr(III) analysis. The electrode can differentiate Cr(VI) from Cr(III) using different conditions. Linear range for Cr(VI) determination using the method was between 0.050 and 0.250 μg/L, with detection limit of 2.38 ng/L, while for Cr(III), the linear range was between 0.500 and 75.000 ng/L, with detection limit of 0.010 ng/L. The study of other ions’ effects on the method showed that copper(II), cadmium(II), nickel(II), and iron(III) do not interfere the measurement.
Part of the book: Voltammetry