Interfacial thermodynamics of gallic acid adsorption on a chargeable hydrophobic surface

Preparation and characterization of magnetic chitosan-modified diatomite for the removal of gallic acid and caffeic acid from sugar solution

The phenolic substances in sugar cane juice affect the color value of white sugar. A magnetic chitosan-modified-diatomite (MCMD), as a new type of clarifying agent for sugar, prepared via a co-precipitation method combined with cross-linking treatment was firstly used to adsorb two primary phenolic acids of sugarcane juice: gallic acid (GA) and caffeic acid (CA). The maximum adsorption capacities for GA and CA by MCMD were 31.949 mg g^-1 and 27.640 mg g^-1, respectively. Additionally, our results showed that adsorption of GA and CA on MCMD fitted well with the pseudo-second-order model and Langmuir equation, respectively. The adsorption, a physical spontaneous endothermic process, might have involved electrostatic attraction and micropore filling. Importantly, MCMD has good regenerability and achieves better sulfur-free clarification of sugar cane juice and improves more significantly the food safety of white sugar than the traditional decolorization method.

Recovery of phenolic compounds from multi-component solution by a synthesized activated carbon using resorcinol and formaldehyde

The adsorption of four phenolic compounds (gallic acid, protocatechuic acid, vanillic acid and syringic acid) is investigated using a synthesized mesoporous carbon on both single and multi-component synthetic solutions. Some correlation of the adsorption capacity of the carbon and the nature of adsorbate could be made, except for gallic acid whose concentration decrease seems to be not exclusively due to adsorption but also to polymerization reaction. In the multi-component mixture, negative effects in the adsorption capacity are observed probably due to competition for the active centers of the adsorbent surface. In desorption studies, ethanol presents better performance than water and acetonitrile. Vanillic acid is the compound with the higher adsorption and interestingly it is then possible to desorb a relatively high amount of it from the adsorbent, which may represent a possibility for a selective recovery of vanillic acid. These results present a potential way to treat the wastewater from the cork industry.

Oxidation of municipal wastewater by free radicals mechanism. A UV/Vis spectroscopy study

This study investigates the oxidation of municipal wastewater (WW) by complexation with natural polyphenols having radical scavenging activity, such as (3,4,5 tri-hydroxy-benzoic acid) gallic acid (GA) in alkaline pH (>7), under ambient O₂ and temperature. Physicochemical and structural characteristics of GA-WW complex-forming are evaluated by UV/Vis spectroscopy. The comparative analysis among UV/Vis spectra of GA monomer, GA-GA polymer, WW compounds, and GA-WW complex reveals significant differences within 350-450 and 500-900 nm. According to attenuated total reflectance (ATR) spectroscopy and thermogravimetric analysis (TGA), these spectra differences correspond to distinct complexes formed. This study suggests a novel role of natural polyphenols on the degradation and humification of wastes.