Desenvolvimento de novos materiais lignocelulósicos e quitinosos com potencial aplicação em química ambiental

• Ano de defesa: 2015
• Autor(a) principal: Bruno Christiano Silva Ferreira
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Quitosana; Celulose; Lignocelulósicos; Adsorção; Funcionalização; Lignocelulose; Química Orgânica; Síntese orgânica
• Link de acesso: http://hdl.handle.net/1843/SFSA-9W3RE8

This work describes the preparation of new chelating materials derived from cellulose and chitosan. The first part describes the chemical modification of sugarcane bagasse (B) and cellulose (C) using Meldrum's acid as modifying agent in order to introduce carboxylicfunctional groups via a solvent-free synthesis. The optimized conditions provided sugarcane bagasse modified with Meldrums acid (BAM) and cellulose modified with Meldrums acid (CM) with a percent weight gain of 86,0 % and 80,0 %, respectively. The number of introducedcarboxylic acid groups was 4,69 ± 0,20 mmol/g for BAM and 4,21 mmol/g for CM. The capacity of BAM to adsorb crystal violet (CV) from aqueous solutions was evaluated at different contact times, pHs, temperature and initial dye concentrations. Kinetic experiments showed that the amount of crystal violet adsorbed increased with increasing temperature andequilibrium was reached at 12 h. Adsorption kinetics followed a pseudo-second-order model. The Arrhenius and Eyring models were used to obtain the activation energy and changes in freeenergy, enthalpy, and entropy of activation for the adsorption process. The calculated activation energy (14,14 kJ/mol) suggested physical adsorption of CV onto BAM. The equilibrium data were well fitted to the Langmuir and Sips isotherms. Maximum adsorption capacity was692,1 mg/g at 45 °C. Thermodynamic parameters such as changes in free energy, enthalpy and entropy were also determined. The second part of this work describes the chemical modification of chitosan (Q). Firstly, the amine groups present in chitosan were used to obtain quaternaryammonium salts. The alkylation of amino groups produced a methylated material (QM1). The chemical modification of QM1 using different cyclic anhydrides produced novel polyfunctionalized materials through an original strategy. Such materials may promote the adsorption of both cationic contaminants from aqueous medium (from carboxylate functions) and anionic contaminants (from quaternary ammonium groups), being a universal adsorbent. The new materials prepared from chitosan have a great versatility and applicability in chemicaltechnology due to their zwitterion characteristics. Another innovation of this work is the preparation of crosslinked chitosan derivatives by 1,3-dipolar cycloaddition reaction (Huisgenreaction). Chitosan-azide and chitosan-alkyne moieties were prepared and subjected to copperalkine-azide cicloadition reaction (click reaction). This reation produced new crosslinked materials with promising applications in the area of biomaterials, pharmaceutical industry and technological chemistry