Ultrafast Removal of Cationic Dye Using Agrowaste-Derived Mesoporous Adsorbent

High-purity amorphous silica extracted from rice husk ash (RHA) was utilized for synthesizing a low cost, novel mesoporous adsorbent (RHS-MCM-41) for removal of the cationic dye Brilliant Green (BG) from water. Transformation of the silica to a mesoporous aluminosilicate structure resulted in similar to 9 fold enhancement of surface area generating negatively charged surface active sites. Adsorbent was characterized with small angle X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, nitrogen adsorptiondesorption analysis, and Fourier transform infrared spectroscopy. An equilibrium state was achieved very quickly (within 15 min) following pseudo-second-order kinetics (k(s) = 315 x 10(4) g/(mg min)) with a very high adsorption capacity of 250 mg/g. Variation in adsorbent surface functionality revealed that the presence of negative charge centers favor BG adsorption. The Elovich model fitting the system explicated involvement of the chemisorption process. Intraparticle diffusion model elucidates a two-step diffusion and saturation stage. Equilibrium batch adsorption data are best explained with LangmuirFreundlich isotherm model.