PHOTOCATALYTIC DEGRADATION OF TARTRAZINE WITH IMMOBILIZED TiO 2 IN ALGINATE BEADS. The potential of heterogeneous photocatalysis using TiO 2 immobilized in alginate beads was evaluated for the degradation of tartrazine yellow azo dye. The treatment was performed under the action of a high-pressure mercury vapor lamp of 125 W and the degradation performance was investigated with the absorbance supplied by a photocolorimeter. Alginate beads with TiO 2 were prepared and the catalyst was quantified by thermogravimetric analysis (TG) and characterized by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) and specific area analysis (BET). The immobilization was performed as a very simple and reproductible technique. The bead diameter was approximately 1 mm and its surface presented a homogeneous dispersion of catalytic sites containing about 1-2% (w/w) of TiO 2 . The TiO 2 /alginate beads presented low density and can be easier separated than the TiO 2 dispersed from the reacting medium, remaining available to be reused in another batch. The dye degradation reached 30% after 120 minutes of irradiation, for the following conditions: alcaline pH (pH=9.0), 3 g of TiO 2 /alginate beads and 20 mol L -1 dye concentration.Keywords: heterogeneous photocatalysis; calcium alginate; azo dye. INTRODUÇÃOO descarte de efluentes com alto índice de coloração leva a alterações na quantidade e qualidade da luz que penetra nas camadas mais profundas dos corpos hídricos, alterando as condições da biota aquática, diminuindo a transparência da água e a penetração da luz solar, o que pode afetar a atividade fotossintética e o regime de solubilidade dos gases, principalmente próximos às regiões de descarga.1,2 Devido ao alto grau de aromaticidade das moléculas de corantes e à sua alta estabilidade, os métodos de tratamento biológi-cos são ineficientes para a descoloração e degradação. Esta estrutura recalcitrante também inibe o metabolismo de certos microrganismos presentes no tratamento biológico.3,4 Logo, outras técnicas de tratamento físico-químico se fazem necessárias, tais como coagulação com agentes químicos, adsorção em carvão ativado, ultrafiltração, osmose reversa, remoção com uso de resinas de troca iônica, etc. Todavia, essas operações constituem técnicas não destrutivas, uma vez que transferem os compostos orgânicos da água para outra fase, causando então uma poluição secundária. 5Neste contexto, a fotocatálise heterogênea surge como uma tecnologia muito efetiva e limpa, e que tem se destacado para a eliminação definitiva de poluentes orgânicos tóxicos de efluentes, sendo capaz de promover a degradação total de inúmeros compostos orgânicos a dióxido de carbono, água e íons inorgânicos provenientes de heteroátomos.5-8 O dióxido de titânio está muito próximo de ser um catalisador ideal para o processo de fotooxidação, pois apresenta muitas vantagens: não é tóxico, tem baixo custo, é abundante, é de simples obtenção e é resistente a processos fotocorrosivos. 5,7 No processo da fotocatálise, o TiO 2 pr...
This study presents activated carbon-alginate(AC-alginate) utilized as adsorbent to remove a cationic and anionic dyes: methylene blue (MB) and tartrazine (TZ), from aqueous solution. The adsorbent, AC-alginate beads, were synthesized by ionotropic gelation. The textural characterization was performed by using N2 adsorption-desorption and the morphology was analyzed by SEM microscopy with EDX analysis. Batch experiments were conducted on two temperatures (30 and 50°C), different initial concentrations (20-100 mg.L -1 ), fixed volume of adsorbate (20 mL) and fixed amount of adsorbent (4g.L -1 )at pH 7.0 for MB and 3.0 for TZ. Equilibrium adsorption isotherms and kinetics were investigated. The equilibrium experimental data were analyzed by the Langmuir and Freundlich models. The best results were achieved with the Langmuir isotherm equilibrium model. The kinetic data obtained were better fitted by a pseudo-second order. The AC-alginate beads were found to be very effective low-cost adsorbent for MB and TZ from aqueous solutions.
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