بررسي جزئيات مولكولي حذف آلاينده آرسنيك از آب توسط ساختارهاي MIL-88B با استفاده ازشبيه سازي ديناميك مولكولي

Drinking water is the most important source of arsenic entry into living systems. Continuous exposure to arsenic has a detrimental effect on the central nervous system, kidneys, skin, liver, an‎d lungs. Severe arsenic poisoning causes heart disease, increased blood pressure, an‎d affects the bodyʹs vessels. Long-term contact with arsenic-contaminated water leads to the accumulation of pigments in the skin an‎d the development of hard calluses on the palms of the han‎ds. In this study, iron-containing metal-organic frameworks have been used to remove arsenic contaminants from water. With the help of molecular dynamics simulation, Lamps software, an‎d the Dredging force field, the details of the adsorption of sodium dihydrogen arsenate on three types of MIL-88B structures were investigated. The effect of different concentrations of sodium dihydrogen arsenate, temperature, an‎d interfering ions on the adsorption of arsenate was studied, an‎d the maximum adsorption by each of the adsorbents was determined using adsorption isotherms. Finally, the adsorption capacity of all three adsorbents was compared with each other. The adsorption capacity of dihydrogen arsenate was simulated an‎d compared by three types of MIL-88B, namely MIL-88B(Fe) (Absorbent A), MIL-88B-tpt (Absorbent B), an‎d Fe-MIL-88B (Absorbent C) under the same conditions. For this purpose, the effect of changes in the concentration of dihydrogen arsenate on the adsorption was investigated, an‎d the maximum adsorption values by each of the adsorbents were obtained. The results of the radial distribution function data, the mean square displacement an‎d the root mean square deviation of the dihydrogen arsenate ions, the distance, energy an‎d force data between the pairs of atoms of interest showed that the percentage of arsenate ion adsorption by nanoparticles in the simulation box increases up to a certain amount of arsenate ion, but beyond that, the percentage of surface adsorption an‎d the adsorption efficiency of nanoparticles decrease. As a result, the maximum value for the direct adsorption of dihydrogen arsenate by 8 formula units of adsorbent A is equal to 5, for 8 formula units of adsorbent B, it is equal to 6, an‎d for 9 formula units of adsorbent C, it is equal to 8 dihydrogen arsenate ions. In other words, the maximum amount of sodium dihydrogen arsenate absorbed per gram of adsorbent A is 0.1410, adsorbent B is 0.1515, an‎d adsorbent C is 0.1205. This value was consistent with experimental evidence for adsorbent A. However, the experimental investigation was only conducted for adsorbent A. The adsorption mechanism of some arsenate ions was through the formation of As-O-Fe bridges to the surface of nanoparticles, an‎d some others formed hydrogen bonds with previously attached arsenate ions an‎d were attached to the nanoparticles. It was shown that all three adsorbents follow the Langmuir adsorption isotherm an‎d pseudo-second-order adsorption kinetics. Also, the effect of interfering ions of lead(II), phosphate, an‎d nitrate on the adsorption process was investigated, an‎d it was found that lead an‎d phosphate ions can reduce the adsorption efficiency, an‎d nitrate ions did not show any effect on the adsorption rate. The adsorption rate of arsenate was investigated by changing the temperature from 288 to 338 K, an‎d the amounts of adsorbed arsenate did not show much difference, although at ambient temperature, 298 K, the adsorption rate was slightly higher, an‎d the coordination number diagrams showed a higher value. Finally, it was found that nanoparticle B has a better performance in the adsorption of arsenate ions than the other two nanoparticles.

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