چكيده لاتين
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.
