Thermo-visible-absorption spectroscopy study of the protonated Congo-red montmorillonite complex

Hybrid Materials Based on Smectite Clays and Nutraceutical Anthocyanins from the Açaí Fruit

“…Among the inorganic structures, clay minerals (layered silicates) are good candidates for the stabilization of nutraceutical species, as they are common excipients or active principles in pharmaceutical products for topical and oral applications. [23] Some examples of synthetic dyes that were already intercalated in clays are Rhodamine 6G, [24] methylene blue, [25] Congo Red, [26] cyanines, [27,28] and cationic porphyrin. [17] Clay minerals (such as kaolin, talc, palygorskite, and smectites) have advantageous properties for utilization in pharmaceutical and cosmetic formulations: high surface area and adsorptive ability, and appropriate rheological characteristics.…”

“…The process of dye adsorption and interaction with clays is a matter of continuous study 23. Some examples of synthetic dyes that were already intercalated in clays are Rhodamine 6G,24 methylene blue,25 Congo Red,26 cyanines,27,28 and cationic porphyrin 29,30. Very little work has been reported on the intercalation of natural dyes (or nutraceuticals) in layered silicates.…”

Evaluation of the supramolecular interaction of Congo red with cucurbiturils using mass spectrometry and spectroscopic methods

“…33,34 Protonation of CR in water occurs below a pH of 5.3 and has been proposed to give an ammonium form (II) and a resonance-stabilised azonium form (III), which are in tautomeric equilibrium (Scheme 1). 33,53 The colour transition from red to blue has been associated with the formation of resonant quinoid structures. In the synthesis of CR@CB [7](RT), the mother liquor had a final pH of 5-6 and therefore the exclusive presence of the anionic form (I) in the isolated adduct is not surprising.…”

Preparation of Graphene Oxide/Chitosan Pellets and Their Adsorption Properties for Congo Red

“…Congo red is a kind of zwitterion molecule due to the amine group (-NH þ 3 ) and sulfonated group (-SO À 3 Þ. 41 The amine group (-NH þ 3 ) is easily attracted by the negatively charged GO. At lower pH value, the H þ ion concentration in the solution is high, and surface of GOP acquires positive charge by absorbing H þ ions, 41 it is amiable to negatively charged sulfonated group (-SO À 3 ) of congo red.…”

“…41 The amine group (-NH þ 3 ) is easily attracted by the negatively charged GO. At lower pH value, the H þ ion concentration in the solution is high, and surface of GOP acquires positive charge by absorbing H þ ions, 41 it is amiable to negatively charged sulfonated group (-SO À 3 ) of congo red. The high electrostatic attraction exists between the positively charged surface of GOP and congo red leading to the higher dye adsorption.…”