Tunable porous silica nanoparticles as a universal dye adsorbent.

Here, we report selective adsorption of cationic dyes methylene blue (MB) and rhodamine B (RB) and anionic dyes methyl orange (MO) and bromo cresol green (BCG) by modifying the surface of cetyl trimethyl ammonium bromide (CTAB) coated porous silica nanoparticles (PSN). We used a top down approach to synthesize PSN (porous silica nanoparticles) without high temperature calcination. X-ray diffraction study confirms the formation of pure phase silica nanoparticles. SEM analysis reveals that the particle morphology is spherical and the size range lies in-between 150-200 nm. We have studied the dye adsorption properties for three cases of PSN at varying calcination temperatures of 100 °C, 250 °C and 500 °C, respectively. Thermal study has been performed in the temperature range of 50-800 °C to check the calcination temperature. In this report, we have tuned the surface properties for selective adsorption of cationic and anionic dyes in water. In the first case, 100 °C calcined PSN selectively adsorb only anionic dyes, whereas in the second case, 500 °C calcined PSN adsorb only cationic dyes and finally, an optimized calcination temperature ≈250 °C could be used for all types of dye to be adsorbed irrespective of charges on the dyes. The mode of interaction of dyes with PSN has been explained with a proper mechanism in all three cases. The adsorptions of dyes are confirmed by UV-Vis spectroscopy. Adsorption capacity and regenerable performance of adsorbents have also been studied.