The C$_3$N$_4$/ZnO composite photocatalysts were synthesized by mechanical milling combined with a calcination process. Various ratios of melamine and ZnO powders were milled by a planetary ball mill for 10 h. Afterheating at 540$^{\circ}$C for 3 h in air, melamine was converted to C3N4 but the formation of C$_3$N$_4$ depended on the ratios of the melamine and ZnO (M/Z) powders. From the experimental results, the conversion of melamine to C$_3$N$_4$ could be inhibited by ZnO particles; as there was no detectable C$_3$N$_4$ in the sample at low M/Z values or high ZnO contents. The photocatalytic activities of prepared samples were investigated under the illumination of blacklight and fluorescent lamps as the low wattage light source. The C$_3$N$_4$/ZnO showed a better photocatalytic activity than ZnO to degrade a methylene blue (MB) dye solution using blacklight lamps, but there is no significant difference in photocatalytic activities between ZnO and prepared C$_3$N$_4$/ZnO under visible light by the fluorescent lamps. However, the prepared C$_3$N$_4$/ZnO can well function under illumination by Xe lamp as the high power light source. Ecotoxicities of MB solutions before and after photocatalytic process were also studied through growth inhibition of the alga Chlorella vulgaris.

In this study, the effect of water extract of wood ash (WEWA) as a reagent from waste was studied on the formation of Ti-O-based photocatalysts. The pH of the reaction solution was controlled by varying the volume of WEWA. In an acidic condition, the products were identified as TiO$_2$, but the K$_2$Ti$_6$O$_{13}$/TiO$_2$ was formed when pH of the solution was ${\ge}$6. Photocatalytic activities of calcined products were investigated through the degradation of methylene blue (MB,cationic dye) and reactive orange (RO, anionic dye) solutions. The TiO$_2$ prepared from acid condition degraded MB and RO under blacklight irradiation but not under visible-light irradiation, while the K$_2$Ti$_6$O$_{13}$/TiO$_2$ degraded MB undervisible-light irradiation through a dye-sensitized photocatalytic mechanism but could not degrade RO. Addition of MB into RO solution improved the photocatalytic degradation of RO by K$_2$Ti$_6$O$_{13}$/TiO$_2$ because MB could be adsorbed on thesurface of K$_2$Ti$_6$O$_{13}$/TiO$_2$ and promoted the MB-sensitized photocatalytic process.