Design of Two-step Isotherms for Enhancement Sorption Efficiency of C-type Fly Ash for Acid and Basic Dyes and Prediction of their Chemical Reactivities using DFT Calculations
摘要
The process parameters have been adjusted to obtain two-step isotherm profile for increment sorptive removal efficiency of natural calcium-rich (C-type) fly ash for dyes from water. Sorption of the anionic acid–dye Brillant-Blue N-GL and cationic basic-dye Methylene-Blue onto calcium-rich fly-ash is examined via batch-method. The sorbent properties are characterized by X-ray-diffraction, diffuse-reflectance-infrared-Fourier-transform spectroscopy, atomic-force and scanning-electron microscopy techniques. The predicted molecular chemical reactivity of the dye molecules based on density-functional-theory was well correlated with the sorption results. The Langmuir capacity for Brillant-Blue N-GL increases nearly four times in the second step of isotherm with an enhancement from 0.242 to 1.500 mmol/g. Amount of the dye removed at 318 K is higher than the weight of the sorbent itself (1.26 g/g) which surpasses all modified sorbents reported for acid–dye removal. The capacities for both acid and basic-dyes increase nearly 6 times in the second step at 298 K. The curves calculated from the Liu isotherm model fit both the L-shaped first-step and the S-shaped second-step of isotherms. The diffusion-coefficients calculated using the homogeneous-surface-diffusion model are 8.0 and 13.0 × 10–13 m2 s−1 for Brillant-Blue N-GL and Methylene-Blue respectively. They are higher than those of the two-resistance-diffusion model in ~ 10–14 m2 s−1 magnitude.