A DFT Study for Eliminating a Water Pollutant by Using an Adsorbent

A pollutant on the water is an azoic dye molecule (adsorbate) within its corresponding ˉO3S active site, and it can be relieved from water using chitosan copolymer molecule (adsorbent) within its active site, which is an ion 3 NH + of ammonia from amino group protonated. After DFT geometry optimization, the reactivity between these two active sites in acidic aqueous solutions can become either neutral acid form or two products (sulfur dioxide SO2 and H2NOH). We infer the kind of adsorption established on the neutral acid form molecule. 345 Introduction Our primary goal in here is to apply DFT to the interaction between chitosan (adsorbent) and azoic dye (adsorbate), through their reaction sites 3 NH + (ion of ammonia from amino group protonated) and ˉO3S (sulfur trioxide ion of sulfonate group) respectively, just to infer possible existing adsorption. This is done first calculating its geometry optimization between 3 NH + and ˉO3S. The reaction among these molecular ions produces sulfamic acid which in zwitterion form 3 3 H NSO + − is more stable than the neutral acid form H2NSO2OH in solid state [1-5]. Physical properties (structural and spectroscopic) and chemical reactions of sulfamic acid have been extensively reviewed [6-8]. The structure of both the zwitterion and neutral form has theoretically been studied previously [9-13]. We study here the neutral acid case as an isomer HSO3NH2. Azo dyes are a class of synthetic dyes which when degraded in the bodies of water can cause the rupture of azo bond of amines, causing many harmful effects in some human organs such as the brain, liver, kidneys, central nervous system and reproductive system. Synthetic dyes also affect the photosynthetic activity of some aquifer’s plants due to the presence of aromatics, metals, chlorides, etc. [14]. The discovery of synthetic dyes has limited the role of natural dyes due to its characteristics such as low production cost, brighter colors, better resistance to environmental factors and easy application. However synthetic dyes can be often highly toxic and carcinogenic [15]. The dyes have become a major source of severe water pollution as a result of the rapid development of many industries that use them in order to colorize their products [16]. Effects described by the pollution of azoic dyes mean a problem that requires attention and treatment. Chitosan is a product of chitin, which is the second most abundant natural polysaccharide in nature. Chitosan can be obtained from partial deacetylation of chitin [17]. Among the many uses of chitosan products are nutraceuticals, food protectors, medical uses, agricultural uses, and many others. Application to water purification is in research. Chitosan is a polymer, its chemical structure as copolymer is drawn in (s 1a), which is the input for applying geometry optimization, and its output can be seen in (Figure 1b). This copolymer chitosan is made up two units: a. β-(1-4)-2-acetamide-2-deoxy-D-glucopyranose b. β-(1-4)-2-amino-2-deoxy-D-glucopyranose.


Introduction
Our primary goal in here is to apply DFT to the interaction between chitosan (adsorbent) and azoic dye (adsorbate), through their reaction sites 3 NH + (ion of ammonia from amino group protonated) and ˉO 3 S (sulfur trioxide ion of sulfonate group) respectively, just to infer possible existing adsorption. This is done first calculating its geometry optimization between 3 NH + and ˉO 3 S. The reaction among these molecular ions produces sulfamic acid which in zwitterion form 3 3 H NSO + − is more stable than the neutral acid form H 2 NSO 2 OH in solid state [1][2][3][4][5]. Physical properties (structural and spectroscopic) and chemical reactions of sulfamic acid have been extensively reviewed [6][7][8]. The structure of both the zwitterion and neutral form has theoretically been studied previously [9][10][11][12][13].
We study here the neutral acid case as an isomer HSO 3 NH 2 .
Azo dyes are a class of synthetic dyes which when degraded in the bodies of water can cause the rupture of azo bond of amines, causing many harmful effects in some human organs such as the brain, liver, kidneys, central nervous system and reproductive system. Synthetic dyes also affect the photosynthetic activity of some aquifer's plants due to the presence of aromatics, metals, chlorides, etc. [14]. The discovery of synthetic dyes has limited the role of natural dyes due to its characteristics such as low production cost, brighter colors, better resistance to environmental factors and easy application. However synthetic dyes can be often highly toxic and carcinogenic [15]. The dyes have become a major source of severe water pollution as a result of the rapid development of many industries that use them in order to colorize their products [16]. Effects described by the pollution of azoic dyes mean a problem that requires attention and treatment.
Chitosan is a product of chitin, which is the second most abundant natural polysaccharide in nature. Chitosan can be obtained from partial deacetylation of chitin [17]. Among the many uses of chitosan products are nutraceuticals, food protectors, medical uses, agricultural uses, and many others. Application to water purification is in research. Chitosan is a polymer, its chemical structure as copolymer is drawn in (s 1a), which is the input for applying geometry optimization, and its output can be seen in (Figure 1b).
This copolymer chitosan is made up two units: The former has a molecular weight of 203.2, 8 13 4 C H NO formula, composition: C 47.3%, H 6.4%, N 6.9% and O 39.4%; and the latter has a molecular weight of 161.1, 6 11 4 C H NO formula, composition: C 44.7%, H 6.9 %, N 8.7%, O 39.7%. When chitosan is dissolved in an acidic medium the amino group is protonated, this fact generates a positive charge, while the azo dyes with sulfonate groups dissolved in water have a negative charge. Therefore, there are groups 3 NH + and ˉO 3 S, which have attracted to each other, giving rise to adsorption of azo dyes with sulfonic groups in the chitosan. It is known the use of ammonia (NH 3 ) to remove sulfur dioxide (SO 2 ) [18,19]. Some researchers [20,21] have also worked with interactions and reactions of sulfur trioxide and ammonia not alone.
In our case, we recognize an ion of ammonia (

Methodology
To study some characteristics of this molecular system, density functional theory (DFT) is used. The main advantage of this technique is to predict the geometry, band structure and cohesive ener-    [29].
The importance of removing this pollutant is evident after these statements, one more reason is that it is a histamine liberator and may intensify symptoms of asthma.

Conclusion
Applying DFT geometry optimization first to 3 NH + ion, then to ˉO3S ion and finally to both molecular ions in a particular position take us to the isomer HSO3NH2 complex molecule which is neutral acid form NH2SO2OH of sulfamic acid, and it is chemisorption.
We present two possibilities of ˉO 3 S ion, one of them is because we found it in this way in literature, and the other because when applying DFT connectivity it is considered with a single double bond, and in this case the adsorption energy is more chemisorbed.
However, when this has two double bonds, the adsorption energy is less chemisorbed. These two adsorption energies remain in the threshold among physisorption and chemisorption, and we can say that the lowest adsorption energy is closer to physisorption than to chemisorption. s These two ions work as adsorbent and adsorbate active sites of chitosan and azoic dye molecules, respectively. Furthermore, chitosan has nutritious properties as food. Consequently, chitosan has the right properties to be used as natural food, favoring cleaning of pollutants in both water and the human body.