Effect of the Mg/Al Ratio on Activated Sol-Gel Hydrotalcites for Photocatalytic Degradation of 2,4,6-Trichlorophenol

Abstract

Currently, interest has grown in finding effective solutions for the treatment of water pollution by toxic compounds. Some of the latter that have acquired importance are phenols and chlorophenols, due to their employment in the manufacture of pesticides, insecticides, cords of wood, paper industry, among others. The problem is rooted in that these compounds are very persistent in the environment because they are partially biodegradable and cannot be photodegraded directly by sunlight. Chlorophenols are extremely toxic, especially 2,4,6-trichlorophenol, which is potentially carcinogenic. In this work, Mg/Al-mixed oxide catalysts were obtained from the thermal treatment of hydrotalcite-type materials, synthesized by sol-gel method with different Mg/Al ratios. Hydrotalcites and Mg/Al-mixed oxides were physicochemically characterized by X-ray diffraction, thermal analysis (DTA and TGA), and N 2 physisorption. The results were obtained on having proven the photocatalytic degradation of 2,4,6-trichlorophenol as a pollutant model by water. The catalysts obtained present the hydrotalcite phase with thermal evolution until achieving Mg/Al-mixed oxides at 500°C. The catalysts are of mesoporous materials and exhibiting large surface areas. The catalysts demonstrated good photocatalytic activity with good efficiency, reaching degradation percentages with Mg/Al = 1, 2, 4, 5, and 7 ratios of 94.2, 92.5, 86.2, 84.2, and 63.9%, respectively, until achieving mineralization.

Enhanced Adsorption, Photocatalytic Degradation Efficiency of Phenol Red Using CuZnAl Hydrotalcite Synthesized by Co-Precipitation Technique

“…Therefore, similarly to MO (methyl orange), PR also acts as an anionic dye. LDHs materials have a good anion adsorption capacity due to their ability to exchange anions between CO 3 2 ions with MO anions or due to the electrostatic interaction of SO 3 2 ions of colorants with metal ions in the interlayered of brucite [2,10,26,27]. In addition, the structural memory effect of LDHs plays an important role in the adsorption process of the anion dyes [27].…”

“…In recent years, layered double hydroxide materials (LDHs) and hydrotalcites have been of great scientific interest as they are able to memorize structures (memory effect) [1][2][3], are easily synthesized by the co-precipitation method, and exhibit adsorption and catalytic properties, hence a wide range of applications such as wastewater treatment, catalysis, photocatalysis, pharmaceuticals, organic synthesis and antibacterial agents [4][5][6]. Hydrotalcite materials have the formula of Mg 0.667 Al 0.333 (OH) 2 (CO 3 ) 0.167 (H 2 O) 0.5 in the natural minerals.…”

“…The results showed that these synthesized materials are capable of effectively decomposing sustainable organic compounds and dyes in water. However, some limitations remained, including (the first) the poor adsorption capacity of these materials for dyes, especially cationic dyes, (the second) the high processing costs due to the use of expensive and power-consuming equipment such as UV [3,9], Xenon [5,10,15], and halogen [16] lamps as irradiation lights, and (the third) only survey on the low concentration of dyes.…”

ISOMORPHIC SUBSTITUTION OF Mg2+ BY Al3+ ON MgO: EFFECTS ON BASICITY, TEXTURAL PROPERTIES AND MICROSTRUCTURE

“…The MgO-Al 2 O 3 mixed oxides have been used as humidity sensors, catalysts, photocatalysts, gas adsorbents, in anionic exchange, as a drug carrier systems, among others (Klym et al, 2015;Gomes et al, 2016;Lee et al, 2016;Ramos-Ramirez et al, 2017). The MgO-Al 2 O 3 binary oxides usually were used as catalysts by themselves or as a supports in diverse reactions, i.e., alcohols decomposition (Corma et al, 1994), biodiesel synthesis (Xie et al, 2006;Stewart et al, 2015), or fossil fuels hydrotreatment (Zhao et al, 2003;Coelho et al, 2015).…”