Layered double hydroxides-derived materials: synthesis, characterization and application in adsorption and advanced oxidation processes

Author(s)

Rodrigo Morais Menezes dos Santos

• Document type: Master's Dissertation
• Press: Araraquara. 2016-01-27.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2016-01-15
• Advisor: Celso Valentim Santilli; Jairo Tronto

Abstract

The contamination of water resources by several organic pollutants, including textile dyes, which have caused serious environmental problems. Solid materials for adsorption with appropriate features to be employed in industrial scale, such as high efficiency and low cost have been used in some decontamination processes. The Advanced Oxidation Processes (AOP) including heterogeneous photocatalysis, have also been used in water treatment, converting the organic pollutants into easily degradable, inert or harmless substances. Multifunctional materials, such as the Layered Double Hydroxides (LDH) and their derivatives, show potential in both adsorptive and photocatalytic processes. In this work the textile azo dye adsorption process using a ZnAl-CO3 LDH and the mixed oxide obtained from thermal treatment at 450 °C were focused. The materials presented interesting features and high removal capacity for the dye. The adsorption isotherms showed good correlation with the Langmuir isotherm model and the calculated parameters revealed that the maximum adsorption capacity of the calcined material was about 6 times higher than the non-calcined material, 1587.1 mg⋅g-1 and 261.8 mg⋅g-1, respectively. The higher adsorption capacity was assigned to the improvement of the textural properties and to the LDH-structure recovery from the calcined precursor. The results showed kinetic control of the process is a chemical adsorption step, and the calculated thermodynamic parameters showed the adsorption process is spontaneous and endothermic. The dye photocatalytic conversion experiments presented that the derivatives of the LDH calcination are promising materials to be used in the AOP. The formation of a ZnAl2O/ZnO nanocomposite from calcination at 850 °C showed the best conversion results from the coupling semiconductors for charge separation strategy that diminish some problems associated with charge carrier recombination and its higher UV absorbance. Thus, the results show the multi-functionality of these materials, giving some light to the discussion about LDH recovery by "memory effect" that remains a topic of intense debate in the literature. (AU)

• FAPESP's process: 13/25043-4 - Layered double hydroxides-derived materials: synthesis, characterization and application in adsorption and advanced oxidation processes
• Grantee: Rodrigo Morais Menezes dos Santos
• Support Opportunities: Scholarships in Brazil - Master