A spectrophotometric study of the acid-base equilibria of o-methyl red in aqueous solutions

Tawarah, Khalid M.; Abu-Shamleh, Hakam M.

doi:10.1016/0143-7208(91)80027-7

Cited by 33 publications

(16 citation statements)

References 6 publications

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“…However, the UV-vis-NIR spectra of the PMRPy films in PBS showed reversible pH-dependent behaviour, similar to that described in the literature for MR solution [56,57], as illustrated in Fig. 7.…”

Section: Influence Of the Ph In The Pmrpy Chromatic Changessupporting

confidence: 75%

“…According to the literature [56,57], the absorption spectrum of the monoprotonated form of MR (HMR, structures A and B in Scheme 3) presents an absorption band at l max = 525 nm. As the pH increases (> 4.9), the intensity of the band at 525 nm decreases and a new band centred at about 430 nm starts to develop, indicating the presence of the yellow basic form MR À (structure C in Scheme 3).…”

Section: Influence Of the Ph In The Pmrpy Chromatic Changesmentioning

confidence: 99%

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A magenta polypyrrole derivatised with Methyl Red azo dye: synthesis and spectroelectrochemical characterisation

Almeida

Dias

Santos

et al. 2017

Electrochimica Acta

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Section: Influence Of the Ph In The Pmrpy Chromatic Changessupporting

confidence: 75%

Section: Influence Of the Ph In The Pmrpy Chromatic Changesmentioning

confidence: 99%

A magenta polypyrrole derivatised with Methyl Red azo dye: synthesis and spectroelectrochemical characterisation

Almeida

Dias

Santos

et al. 2017

Electrochimica Acta

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“…MR is a well-known indicator dye that has complex acid-base equilibria in the pH range 28 [21]. It changes the color from red (below pH 3.1) to yellow (over pH 6.2), between these values of pH MR is colored in orange (Scheme 2).…”

Section: Resultsmentioning

confidence: 99%

“…Protolytic equilibria of methyl red[21] Transmittance UV-Vis spectra of MR: a  in phosphate buffer solutions (C MR =0.0334 mmol/l); b  in benzene (C MR = 0.0171 mmol/l)…”

mentioning

confidence: 99%

pH-sensitive materials based on silica with chemically immobilized methyl red: synthesis and protolytic properties

Roik¹,

Belyakova²,

Dziazko³

2018

Him. Fiz. Tehnol. Poverhni

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The purpose of this work is to study the possibility of creating hydrolytically and chemically stable pH-sensitive materials using silica as a carrier and an acid-base indicator that changes color when the pH of medium is varied. Synthesis of pH-sensitive materials was carried out by covalent binding of methyl red dye with aminopropylsilica in the presence of 1,1'-carbonyldiimidazole as a coupling agent. The porous structure, the chemical composition of the surface, and the protolytic properties of the synthesized silica materials were characterized by low-temperature adsorption-desorption of nitrogen, quantitative chemical analysis, thermogravimetry, diffuse reflectance electron spectroscopy, pH-metry. It was proved that chemical immobilization of methyl red on the silica surface does not have a significant effect on the porous structure of initial silica: the isotherms of nitrogen adsorption-desorption and pore size distribution curves confirm retention of wide pore size distribution after chemical modification of silica. The content of the acid-base indicator chemically immobilized on the silica surface was determined by quantitative chemical analysis of synthesized materials, as well as by thermogravimetry and diffuse reflectance electron spectroscopy in the ultraviolet and visible regions. It was demonstrated that diffuse reflectance electron spectroscopy can be a reliable method of quantitatively determining an indicator dye chemically grafted to the silica surface. It was proved that chemically grafted dye retains the ability to protonation of tertiary amino group and formation of resonance azonium ion, which is responsible for changing the color of methyl red. It was found that the protonation of methyl red chemically fixed on the silica surface occurs at higher pH values than for individual indicator dye. Therefore, the color change of grafted dye takes place in less acidic solutions. The proposed synthetic approach can be used to produce regenerable and eco-friendly pH-sensitive materials.

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“…This shift suggests that when the Pec-Ca network is formed as described by Braccini and Pérez [27], the intermolecular ionic interactions and the existing hydrogen bonding between MO and Pec mentioned above are reinforced, promoting the formation of more stable J aggregates. On the other hand, Tawara and Abu-Shamleh have obtained the electronic absorption spectrum of MR at different pH values [79], and they found that MR has distinct UVvisible spectra when the pH value of its aqueous solution is changed. These researchers reported that in the pH range from 4 to 6, the visible spectra of MR show considerable changes.…”

Section: Visible Studiesmentioning

confidence: 99%

Application of the Zimm-Bragg Model to the Removal of Azo Dyes with Pectin

Lozano-Álvarez

Jáuregui-Rincón

Medina-Ramírez

et al. 2021

Adsorption Science & Technology

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In this work, the ability of pectin (Pec) to remove direct red 80 (DR80), Congo red (CR), methyl orange (MO), and methyl red (MR) was studied. The removal percentages under adequate pH and ionic strength conditions were as follows: DR80 (99.5%), CR (99.8%), MO (88.6%), and MR (68%), showing that this methodology is efficient to remove azo dyes. The proposed method included the addition of native Pec to the dye aqueous solution and the formation of a gel that occurred when a calcium salt solution was added. This gel retains the molecules adsorbed onto the molecular surface of Pec through hydrogen bonds and electrostatic and hydrophobic interactions. To our knowledge, it is the first time that the Zimm-Bragg model is used to describe the removal of azo dyes with native Pec. This model includes two parameters: K u (nucleation constant), which is related to the tendency exerted by a dye molecule attached to the Pec to bind to other molecules present in the aqueous phase, and U (cooperativity parameter), which determines the aggregation capacity of the dye molecules already attached to the Pec. This model fits the experimental isotherms very well, suggesting that Pec binds single molecules and dye aggregates. The obtained results in the values of K u ranged from 922 mol/kg (MR) to 1,157,462 mol/kg (CR), and U varied from 2.51 (MR) to 169.19 (MO). These results suggest that the use of Pec is a viable option to remove azo dyes from aqueous effluents and that the Zimm-Bragg model fits adequately the isotherms of dyes that have a high tendency to form aggregates.

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A spectrophotometric study of the acid-base equilibria of o-methyl red in aqueous solutions

Cited by 33 publications

References 6 publications

A magenta polypyrrole derivatised with Methyl Red azo dye: synthesis and spectroelectrochemical characterisation

A magenta polypyrrole derivatised with Methyl Red azo dye: synthesis and spectroelectrochemical characterisation

pH-sensitive materials based on silica with chemically immobilized methyl red: synthesis and protolytic properties

Application of the Zimm-Bragg Model to the Removal of Azo Dyes with Pectin

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