MOLECULAR VALIDATED MODEL FOR ADSORPTION OF PROTONATED DYE ON LDH

Braga, B. M.; Gonçalves, D. V.; Paiva, M. A. G.; Lucena, S. M. P.

doi:10.1590/0104-6632.20160331s00003451

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Brazilian Journal of Chemical Engineering

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THERMODYNAMICS • Braz. J. Chem. Eng. 33 (1) • Jan-Mar 2016 • https://doi.org/10.1590/0104-6632.20160331s00003451 copy

MOLECULAR VALIDATED MODEL FOR ADSORPTION OF PROTONATED DYE ON LDH

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Hydrotalcite-like compounds are anionic clays of scientific and technological interest for their use as ion exchange materials, catalysts and modified electrodes. Surface phenomenon are important for all these applications. Although conventional analytical methods have enabled progress in understanding the behavior of anionic clays in solution, an evaluation at the atomic scale of the dynamics of their ionic interactions has never been performed. Molecular simulation has become an extremely useful tool to provide this perspective. Our purpose is to validate a simplified model for the adsorption of 5-benzoyl-4-hydroxy-2-methoxy-benzenesulfonic acid (MBSA), a prototype molecule of anionic dyes, onto a hydrotalcite surface. Monte Carlo simulations were performed in the canonical ensemble with MBSA ions and a pore model of hydrotalcite using UFF and ClayFF force fields. The proposed molecular model has allowed us to reproduce experimental data of atomic force microscopy. Influences of protonation during the adsorption process are also presented.

Keywords:
Adsorption; Hydrotalcite; Dye; Molecular simulation

Atom	Charges (e)			Atom	Charges (e)
	MBSA^1-	MBSA^2-		MBSA^1-	MBSA^2-
C1	-0.198	-0.221	H1	0.127	0.104
C2	0.042	0.019	H2	0.127	0.104
C3	-0.127	-0.15	H3	0.127	0.104
C4	0.042	-0.023	H4	0.127	0.104
C5	0.052	0.029	H5	0.127	0.104
C6	-0.127	-0.15	H6	0.127	0.104
C7	0.315	0.292	H7	0.41	-
C8	0.052	0.029	H8	0.127	0.104
C9	-0.127	-0.15	H9	0.053	0.03
C10	-0.127	-0.15	H10	0.053	0.03
C11	-0.127	-0.15	H11	0.053	0.03
C12	-0.127	-0.15
C13	-0.127	-0.15
C14	0.001	-0.022	S	1.318	1.295

O1	-0.706	-0.729	O4	-0.419	-0.442
O2	-0.706	-0.729	O5	-0.452	-0.305
O3	-0.706	-0.729	O6	-0.202	-0.225

Atom	r₀ (Å)	ε_ij (kcal/mol)	Charges (C)
Magnesium^a a Cygan et al., 2004 (LDH);	5.909	1.3298.10^-6	1.36
Aluminium^a a Cygan et al., 2004 (LDH);	4.7943	9.0298.10^-7	1.575
Hydrogen^a a Cygan et al., 2004 (LDH);	-	-	0.425
Oxygen^a a Cygan et al., 2004 (LDH);	3.5532	0.1554	-0.95
Nitrogen^b b UFF-Rappe et al., 1992 (MBSA);	3.660	0.069	^c c See Table 1 and Figure 4
Carbon^b b UFF-Rappe et al., 1992 (MBSA);	3.851	0.105	^c c See Table 1 and Figure 4
Oxygen^b b UFF-Rappe et al., 1992 (MBSA);	3.500	0.060	^c c See Table 1 and Figure 4
Sulfur^b b UFF-Rappe et al., 1992 (MBSA);	4.035	0.274	^c c See Table 1 and Figure 4
Hydrogen^b b UFF-Rappe et al., 1992 (MBSA);	2.886	0.044	^c c See Table 1 and Figure 4

Number of MBSA anions	MBSA^-1 Interaction Energy (kcal/mol)	MBSA^-2 Interaction Energy (kcal/mol)
1	-585.77	-1026.77
2	-595.22	-1121.70
4	-597.25	-981.47
6	-505.95	-784.59
8	-465.74	-582.83
10	-416.43	-399.20

Number of H⁺ cations	MBSA^1- Interaction Energy (kcal/mol)	Number of H+ cations	MBSA^2- Interaction Energy (kcal/mol)
1	-78.77	2	-177.69
2	-129.76	4	-268.99
4	-161.63	8	-365.88
6	-204.07	12	-505.68
8	-261.61	16	-661.85
10	-324.66	20	-849.54

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[1] * E-mail: lucena@ufc.br; smlucena@uol.com.br