Removal of Atrazine from Contaminated Water by Functionalized Graphene Quantum Dots

doi:10.21203/rs.3.rs-3454210/v1

The limitation of clean water supplies and the increment of water pollution resources, like industrial processes, oil pollution, and herbicides, are urgent reasons for introducing new techniques for treating contaminated water. Atrazine is heavily used as a herbicide due to its high effectiveness and low price. However, its environmental persistence causes water contamination, and human exposure to AAtrazine is linked to several health effects. This work presents a simulation study of the possibility of removing the Atrazine Atrazine from water by functionally activated carbon quantum dots (CQDs), using density functional theory (DFT)at a B3LYP level basis set. The activity of CQDs C46 with a total dipole moment of 0.9 is enhanced by the attachment of chemical groups; for instance, attaching CN and NO2 groups increases the total dipole moment to 8.744 and 9.123, respectively. The effect of the functionalized groups Carboxyl and cyanide was investigated, and confirmed that there was no structure deformation due to the functionalization process. Analysis of the obtained data shows the remarkable adsorption ability of CQDs activated by CN and NO2 groups toward the removal of atrazine herbicides due to positive adsorption energy 1.31, 128, and 1.3 eV obtained from pristine, Carboxyl, and cyanide Graphene respectively. According to the calculated total charge on the complexes Atrazine and CQD and Functionalized CQD, charge transfer mainly depends on the interaction pattern. The values of charges were -0.02, 0.004, and -0.004 for pristine, -Carboxyl, and cyanide graphene, respectively. Therefore, the observed results demonstrated the possibility of applying the chemically modified carbon quantum dots as a potential candidate for the treatment of contaminated water.

Wastewater

ZTRI

DFT

Atrazine

Pesticide is a descriptive word for many chemicals used in the agriculture sector. It can be classified but not limited to insecticides, herbicides, fungicides, rodenticides, nematicides, etc. Pesticides play an essential role in increasing world crop production. Nearly 45% of crop production is lost because of pest invasion, and this percentage tends to increase in tropical areas due to suitable conditions for pest enhancement multiplications [1]. Atrazine is a chlorotriazine herbicide. It consists of a ring structure called the triazine ring, five nitrogen atoms, and a chlorine atom(2-chloro-4-methylamino-6-isopropylamino-1,3,5-riazine). Atrazine is a member of an s-thiazine group of herbicides introduced in the market as an agrochemical since the 1970s; it continues to be applied to crops in the U.S., China, Australia, and elsewhere even though it has been banned in the European Union, from that time considered one of Public used herbicides because of its effectiveness to remove a wide range of undesirable weeds and algae with average use 70,000 to 90,000 tons applied per year [2–4]. Atrazine is almost non-volatile, and its half-life in neutral conditions is about 200 days but varies from 4–57 weeks depending on various environmental factors like pH, moisture content, temperature, and microbial activity [5–7]. As a result of their structure properties and water solubility, atrazine pesticides have persistent occurrence and are detectable in surface water bodies, causing degradation in their quality [8–9]. Fish and other aquatic animals consume such contaminated water, which bio-accumulates in their bodies, giving other reasons to increase these environmental pollutants through the food chain [10]. This herbicide can cause an endocrine disruptor genic effect and epidemiological connection to low sperm levels in men, it is recommended to be banned in the U.S. Exposure to AAtrazine can be harmful and in extreme cases, can cause health problems [11]. One of the most beneficial techniques is to employ nanotechnology applications to face environmental challenges. The latest material to capture the attention of researchers is Graphene and Graphene compounds. They can use to create a new class of sorbent materials that are efficient at adsorbing contaminants from polluted water. Graphene is a two-dimensional layer of carbon atoms organized on a honeycomb shape [12–16]. This class of compounds' importance comes from possessing some electronic properties that enable them to be utilized in many applications, including thermal mobility, mechanical strength, and tuneable band gap energy [17–19]. In addition to low cost, less and a high surface area theoretically estimated by 2630 m2 g-1. These options acquire the Graphene's unique adsorption option. The chemical and electronic properties of Graphene can be enhanced by functionalization. For instance, Hazem et al. (2018) demonstrate that Graphene functionalized with a carboxyl group (-COOH) significantly increases the total dipole moment to 4.033 (D), which reflects strong reactivity toward contact medium [20].

In this paper, we study different scenarios of the adsorption of Atrazine on Graphene quantum dots functionalized by many groups, including the carboxylic, cyanide, and nitrogen oxide groups. Many active sites were suggested for adsorption, and all these probabilities are studied using Density functional theory (DFT) calculations.

The unparalleled success of density functional theory (DFT) in explaining materials phenomena has led to the concept of 'materials by design—the idea that for any given set of properties, we can predict novel materials that outperform any known 'usual suspects. [21]. In this study, we use a powerful calculation tool of DFT [22–23] to estimate the most proper sites on ZTRI Graphene functionalized by different activation groups to adsorb Atrazine. The DFT is implemented in Gaussian 09 [24], which utilizes a basis set of Gaussian-type orbital functions. The Becke-three-parameters-Lee-Yang-Parr hybrid functional (B3LYP) [25] is implemented in our calculations because it provides an accurate illustration of the electronic structure of graphene-derivatives Atrazine and adsorption process state [26]. Different ways were studied for the adsorption of Atrazine on functionalized graphene quantum dots: (a) adsorption on the edges of the pristine ZTRI (b) adsorption on the edges of the ZTRI functionalized by carboxylic group, and (c) adsorption on the edges of the ZTRI functionalized by cyanide group interacting with functionalized. The adsorption energy, charge transfer, and band gap energy are calculated to demonstrate the effect of different functionalization groups in the atrazine adsorption process.

3.1. Stability of optimized structures

Triangular graphene quantum dots (ZTRI) are optimized using B3LYP/3-21G level of calculation without symmetry constraint using Gaussian 09. The optimization showed little increase of about 1.5% overall in the C-H bond in ZTRI to be 1.086 Å compared to 1.07 Å bond length before optimization. All C-C bonds adjusted after optimization to be in the range of 1.39–1.45 Å compared to 1.4 Å in the unoptimized one. The bond angle between (C-C-C) was 120o fixed overall unoptimized structure, but it is slightly changed in the optimized structure to range from 118.6o-122.0o where the most open angles were in the edge outside, as demonstrated in Fig. 1.

ZTRI has been studied by adding different functionalized groups. The capability of ZTRI to adsorb AAtrazine is estimated by activation either using a carboxylic group or cyanide group on one edge of the triangle of ZTRI. The optimized structure of carboxylate Graphene and cyno–graphene compared to ZTRI, in C-C bond length dcc, C-H bond length d_CH, and C-C-C bond angles shown in Fig. 2 and table − 1.

Table 1

The C-H bond length and C-C bond lengths and C-C-C bond angles
Structure	d_C-H(Å)	d_C-C(Å)	C-C-C(⁰c)
ZTRI pristine	1.07	1.4	119.99–120
ZTRI optimized	1.084	1.39–1.45	118.6–122
ZTRI-COOH	1.081–1.085	1.39–1.44	118.7-122.5
ZTRI-CN	1.083–1.085	1.39–1.43	118.5-122.5

Figure 2 indicates that there is no significant change in graphene structure by adding any functionalizing groups, and the geometric shape of ZTRI is not deformed. The optimized structure demonstrated in Fig. 3 of AAtrazine at B3LYP3-21G showed total energy was − 1041.84 Hartree's, whereas band gap energy which was calculated as a difference between HOMO-LUMO was 5.99 eV this outcome validated and agree with Atrazine optimized outcomes data from Luis Humberto et al. (2010) [27] using B3LYP/6-311 + + G (2d, 2p) level which recorded − 1047.50 Hartree and 5.91 eV respectively.

The mechanism used to estimate the interaction between ZTRI and different functionalized ZTRI with AAtrazine is by approaching Terminal H (H17) atom from three carbon side of AAtrazine to (Edge H atom of un-functionalized ZTRI, H atom of the hydroxyl group of carboxylate Z.T.R. and finally Nitrogen atom of cyanide group in ZTR C46 functionalized by cyanide group ) Edge-to-edge with distance 1.8, 2.27 and 2.49 Å respectively, to show the effect of different functionalized group in the adsorption process as shown in Fig. 4.

3.2 Chemical reactivity and adsorption process

The total dipole moment of ZTRI has a non-zero value of approx. 0.9 Debye. This is a result of the slight electronegativity difference between carbon and hydrogen atoms. 0.35 Pauling [28] in outer frame combined with the effect of geometrical shape because an odd number of sides three heads in ZTRI triangles shape which can't cancel each other causing constant slight partial polarity [29] dipole moments provide information about a molecule's polarity, anisotropy, and reactivity in addition to its polarity [32]. A dramatic increase in total dipole moment (T.D.M.) has been observed in functionalized ZTRI by adding either a carboxylic or cyanide group on the head side. The T.D.M. was calculated to be 2.75 and 7.99 Debye respectively as shown in Table 2 which is expected to increase the interactivity of carboxylated and cyanide ZTRI toward adsorb Atrazine.

The chemical properties of the adsorbent/adsorbate systems are highly dependent on the chosen surface plane, surface atomic termination, and molecular orientation, Adsorption energy is a decreasing of energy while two materials are combined under the adsorption process in which an atom, ion, or molecule (adsorbate) is attached to the surface of a solid (adsorbent). so, in our work, different functionalization to estimate the adsorption process, The adsorption energy was calculated as:

\({E}_{ads}=(\left({E}_{G}+{E}_{Atz}\right)-{E}_{Sys}\) ) / N atoms)

Where:

\({E}_{G}\) : is the total energy of isolated ZTRI C46H18-COOH

\({E}_{Atz}\) : is the total energy of isolated Optimized Atrazine

\({ E}_{Sys}\) : is the total energy of isolated Optimized Resultant

\(\) N: Number of complex atoms

Table 2 and Fig. 5 show the predicted positive adsorption energy (Ea). The calculated values validate the stability of the adsorption process of AAtrazine on ZTRI and its derivatives. Chemically functionalized ZTRI was observed to have an increase in adsorption energy considerably. The adsorption energies of non-functionalized ZTRI toward Atrazine were 1.31 eV and increased to 1.28 and 1.3 eV in functionalized ZTRI by the carboxylic group and cyanide group, respectively. The calculation of adsorption energy allows us to confirm the adsorption process and compare the adsorption strength of each functionalized group.

3.3 Charge transfer

The charge density differences have been calculated as the difference between the electron density of Atrazine in the complex after adsorption and before adsorption, The charge on AAtrazine was after adsorption and calculated from (Q = Q total- Qin), where Q total is a charge of AAtrazine and Qin is a charge of Atrazine before adsorption

A negative Q (-0.04) value in AAtrazine adsorbed in ZTRI-CN verifies that partially electron charge from ZTRI functionalized by cyanide group to Atrazine which acts as electron acceptor and graphene flakes act as electron donner.

In ZTRI functionalized by the cyanide group the nitrogen atom has five valence electrons, three of which are unpaired, and the other two form a lone pair. Usually, nitrogen forms three covalent bonds, by employing its unpaired electrons. Sometimes, by employing its lone pair, it can form a fourth covalent bond, which is dative (or coordinate), inasmuch the source of the bonding pair of electrons is only one of the two participants in the bond. In these cases, sometimes a positive charge is drawn on nitrogen (and a negative one on the other participant in the coordinate bond), as if nitrogen had nominally given an electron of its lone pair to the other atom, so that nominally now nitrogen has four unpaired electrons. On the contrary, in the case of AAtrazine adsorbed on ZTRI functionalized by the carboxylic group, it has a positive value of 0.004 which may come back to the hydroxyl group in the carboxylic group; oxygen is more electronegative than Hydrogen atom develops a partial positive charge (δ+) and the oxygen atom develops a partial negative charge (δ-) causing the atrazine molecule positive charge when adsorbing with ZTRI-COOH at this side.

Table 2

Calculated T.D.M., energy gap, and charge
Compound	Dipole moment Debye	Adsorption E eV	Adsorption E /atom eV	Band gap eV	Q charge
ZTRI C46 pristine	0.9	-	-	0.31	-
Atrazine	5.7	-	-	5.71	-
ZTRI C46-ATR	7.1	120.4	1.31	0.30	-0.02
ZTRI C46-COOH	2.8	-	-	0.29	-
ZTRI C46-COOH atrazine	3.3	121.5	1.28	0.30	0.00
ZTRI C46-CN	8.0	-	-	0.30	-
ZTRI C46-CN atrazine	16.8	121.0	1.30	0.31	-0.04

3.4 HOMO-LUMO and Energy Gap Analysis.

HOMO and LUMO are the most essential parameters in quantum chemistry [29]. In chemistry, HOMO and LUMO are types of molecular orbitals. The acronyms stand for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively, and the difference between them is called the HOMO–LUMO gap. The calculation of HOMO and LUMO gives information on the transfer of charge within the molecule [30] Fig. 6 presents the distribution of HOMO and LUMO. In of HOMO and LUMO, the red color denotes the positive phase while green colour denotes the negative phase from the analysis, it is clear that HOMO in ZTRI is located over the center but LUMO has edge effect But in ZTRI the HOMO is localized at the zigzag edges, and the LUMO distributes over the surface of the cluster, with a relatively small band gap energy of ~ 0.31 eV, the low energy gap is due to ZTRI containing 18 hydrogen atoms the band gap decreasing first with increasing hydrogen atoms [31]. This is caused by the splitting of energy levels of HOMO and LUMO This splitting is caused by broken symmetry in the hydrogenation to the surface [32]. Adding the COOH group and C ≡ N to ZTRI slightly decreases the band gap from 0.31 eV in pristine Graphene to 0.29 and 0.3 eV in CCarboxyl and cyanide functionalized ZTRI respectively and this agreed with (Hao Li et al 2018) and Hazim et al. 2018 [33, 29] .figure 7 and 8 (a and b) show HOMO and LUMO of functionalized ZTRI with carboxyl and cyanide groups it seems that redistribution of orbitals without change in band gap energy values as shown in Table 2 from pristine ZTRI. There are no significant changes in band gap energy overall ZTRI, ZTRI functionalized nor adsorbed system and this is because of physical adsorption and no chemical reaction has been done to change orbital arrangements.

Electron density is central to density functional theory (DFT). The first Hohenberg-Kohn theorem states that the electron density distribution of a system in its ground state contains all its information [34].

The MESP contour is a physical description of the surface of each investigated structure. This might be accomplished by mapping the locations of electrophilic and nucleophilic assaults. This mapping is shown by a contour that uses colours to describe the charge distributions for the examined structure. Mapping the colours defines the site since each hue represents a different charge, thus, as the charge changes from negative to positive, the colors shift from red to blue. The color scheme red > orange represents the electronegativity > yellow > green > blue, with red indicating the highest electronegativity (highest electron density) and blue representing the lowest electronegativity (lowest electron density).

MESP is a useful concept in molecular modelling calculations because it can provide very accurate information on the active sites of various chemical entities [35]. Therefore, the MESP describes the reactivity of reactants by defining the active sites on its surface and its interaction with other molecules.

The MESP map of ZTRI in Fig. 13a and b, shows the main colors in the map: red, blue, and dark blue. Red is in the centres of ZTRI in benzene-like rings in which all the ring atoms are sp²-hybridized allowing the π electrons to be delocalized in molecular orbitals that extend around the ring, above and below the plane of the ring, forming the effect of electron delocalization phenomenon within the rings making graphene core is most probable to undergo nucleophilic interactions. Less electronegative H atoms are present in the terminals, which is why light and dark blue colors distinguish them. As a result, electrophilic reactions might take place there more frequently. While ZTRI is functionalized by a carboxyl group Map characterized by two primary intense dark color active sites due to the presence of carboxyl groups. At carbonyl, part C = O is colored dark red which can be a good electrophilic active site and suitable for nucleophilic attack. since oxygen is more electronegative than carbon and pulls the electron density towards itself. As a result, the carbon atom develops a partial positive charge (δ+) and the oxygen atom develops a partial negative charge (δ-), leaving the centre part of Graphene almost neutral, and this charge active site concentration was the aim from functionalization of ZTRI. On the other side, the terminal H atom of the hydroxyl group region is colored dark blue color, which can be an excellent nucleophilic active site and suitable for electrophilic attack due to the exact reason for oxygen atom electronegativity.

ZTRI functionalized by a cyanide group Map characterized by only one red active site on the nitrogen atom as shown in Figs. 13f and g. The atrazine MESP map shows that the nitrogen atom within the benzene ring is red but terminal H atoms linked with nitrogen outside the benzene ring show blue color.

3.5 Infrared spectra

The B3LYB/3-21G estimated I.R. spectra for ZTRI, after adding carboxyl groups and cyanide to the edges, are shown in Figures. 14a, b and, c. The and isvibrational spectra is to verify that the electronic properties previously computed are calculated on optimum structures. Figures 14, 15, and 16 show no negative frequencies, hence the information from the earlier sections is supported by the recorded positive frequencies.

The Graphene triangle shape ZTRI was studied its capability to adsorb Atrazine from water. The chemical reactivity of ZTRI was improved by adding activated groups like carboxyl and cyanide groups. Carboxyl and cyanide groups were added to increase the selectivity, sensitivity, and adsorption capacity of ZTRI toward atrazine pollutants. This modification allows the electrochemical reaction to occur at a lower potential range. The electrical properties of the proposed models and their interactions were studied in terms of T.D.M., ΔE, and MESP, and results indicated that the electrical properties have improved since T.D.M. has increased, ΔE has slightly decreased, and electronegativity has significantly improved. At the interaction of ZTRI with Carboxyl and cyanide groups, the T.D.M. increased from 0.9 Debye in pristine ZTRI to 2.8 and 8 Debye, respectively, and ΔE decreased from 0.31 to 0.3 eV by 0.01 eV, with high electronegativity demonstrated in MESP maps. Successful adsorption of Atrazine on functionalized ZTRI by obtained positive adsorption energy ranging from 1.28–1.31 eV. The positive frequencies from drawing the I.R. spectrum indicate that all calculations were done in optimum structures.

Ethical Approval

This work does not applyto both human and/or animal studies.

Competing interests

I declare that the authors have no competing interests as defined by Springer or other interests that might be perceived to influence the results and/or discussion reported in this paper.

Conflicts of Interest

The authors declare no conflict of interest.

Authors' contributions: The authors contribute equally to the manuscript.

Funding

This research received no external funding.

Acknowledgments

The authors would like to the Molecular Spectroscopy and Modeling Unit at the Spectroscopy Department, National Research Centre, Egypt, for the computational facilities provided in this work.

Availability of data and materials

The data will be available upon request; contact Medhat A. Ibrahim [email protected]

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No competing interests reported.

Removal of Atrazine from Contaminated Water by Functionalized Graphene Quantum Dots

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Calculation Details

3. Results and Discussion

3.1. Stability of optimized structures

3.2 Chemical reactivity and adsorption process

3.3 Charge transfer

3.4 HOMO-LUMO and Energy Gap Analysis.

3.5 Infrared spectra

4. Conclusion

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1