The Effect of Recycled Solvent on the Structure of Photonic Crystal

Minimizing or avoiding the creation of waste solvents can be most effective in protecting environment and managing the cost. Since fabrication of silica spheres (approximately 1.0 g of silica spheres with diameter of approximately 300 nm) for photonic crystal requires relatively large amount of solvents (100 ml 2-propanol and 100 ml NH4OH solution), it will be ideal to use recycled solvents for reducing waste solvents. Monodisperse silica spheres were synthesized with Stober synthetic process. The diameter of the spheres was uniform when the ratio of 2-propanol and NH4OH was 1:1. To investigate the effect of recycled solvents, the ratio of 2-propanol:NH4OH maintained 1:1. The spheres were separated by filtration or centrifuge. The mixture of solvents was recycled repeatedly after separating the spheres. The spheres became irregular shape when the mixture of solvents recycled by filtration more than twice. The solvent was completely dried and collected the residual compound in the mixture of solvents, which was comprised of mainly –OH and Si-O-Si. However, there was no irregular shape and residual solid in the mixture of solvents after 4 times recycling by centrifuge. These results imply that the filtering process removes NH4OH due to the low pressure during the filtering process, but the centrifuge method requires no low pressure process and maintains similar NH4OH concentration after repeated recycling process. Therefore, the recycled solvent mixture can be repeatedly used as long as similar NH4OH concentration maintains.