Adsorption of diclofenac on MIL-96 and MIL-100: modeling of adsorption process
Abstract
In recent years, the consumption of diclofenac, a non-steroidal anti-inflammatory drug with strong analgesic and antipyretic effects, has increased significantly. However, it is a man-made pollutant due to its high resistance to biological treatment systems. One of the actively developing methods for wastewater treatment for various organic pollutants, including diclofenac, are adsorption methods, allowing reducing the residual concentration of a substance in a solution to the level of sensitivity of physical methods.
The adsorption of diclofenac from neutral aqueous solutions using as adsorbents metal-organic frameworks (MOFs), MIL-96 and MIL-100, formed by aluminium (III) ions and 1,3,5-benzene tricarboxylic acid was investigated in this study. The adsorption was studied at 20oС from solutions with pH = 6.0-6.2. The initial concentration of DCF was 40-800 mg/l and an adsorbent concentration was 1 mg/4 ml. A high adsorption capacity of 473-541 mg/g of the studied metal-organic MOFs was shown. The high adsorption capacity of MOFs allowed reducing the residual concentration of sodium diclofenac in solution to the level of sensitivity of UV spectroscopy. The maximal adsorption values of diclofenac on MIL-96 and MIL-100 were found to be 475 and 480 mg/g, respectively.
All adsorption isotherms were of L-type. Experimental adsorption isotherms were analysed using the Langmuir, Freundlich, and Temkin models to describe the distribution of diclofenac molecules between the adsorbent and liquid. The constants and parameters of adsorption models were determined. The obtained data indicated that the adsorption of diclofenac is proceeded by the mechanism of physical sorption. According to the Freundlich model, the surface of MIL-96 has energetically nonequivalent adsorption centres in comparison with MIL-100. The high microporosity of MIL-96 compared to MIL-100 is facilitated the diclofenac multilayer adsorption on the MIL-96 surface. By comparing the standard deviations (R2), it was concluded that the Freundlich model is better than others at describing the adsorption of diclofenac on MIL-96, and Langmuir's model better describes the adsorption of diclofenac on MIL-100. This conclusion was also consistent with the difference in their structural and textural properties.
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References
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