Many studies have reported significant improvements in the photocatalytic degradation capacity of TiO 2 immobilized in carbonaceous materials, mainly due to a well-characterized synergistic effect. The photocatalytic degradation of the estrogens 17β-estradiol and 17α-ethynylestradiol was evaluated using 1 mg L -1 aqueous solutions, employing a nanocomposite containing TiO 2 and activated carbon (TiO 2 -AC) prepared by sol-gel technique. The synthesized materials were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). These techniques allowed to estimate the carbon proportion (11.4 wt.%), the phase composition (anatase: 80.2%, brookite: 14.0%, and rutile: 5.8%) and the superficial morphology. Using UV-A radiation provided by a high pressure mercury vapor lamp (125 W) and the synthesized photocatalysts, it was observed the almost complete removal of both estrogens in times shorter than 10 minutes. Considering the similarity between the degradation percentage of nanocomposites (TiO 2 and TiO 2 -AC), no synergistic effects between AC and TiO 2 could be assumed. Keywords: titanium dioxide/activated carbon, nanocomposite, photocatalysis, estrogens IntroductionOver the last two decades, many studies have demonstrated the high degradation capacity of advanced oxidation processes (AOPs). In general, homogeneous 1 and heterogeneous systems 2 promote fast degradation of resistant substrates, mainly due to the high oxidizing capacity of the in situ generated hydroxyl radical. 3 In the context of the AOPs, heterogeneous photocatalysis occupies a prominent place, particularly when assisted by titanium dioxide. 4 Many recalcitrant organic pollutants have been efficiently degraded by TiO 2 -photocatalysis, including azo dyes, 5 pharmaceuticals 6 and estrogens. 7 Typically, the process is applied as slurry systems, consisting in a suspension of fine powdered TiO 2 . Because of these characteristics, the separation of the catalyst is expensive and time demanding, which often causes a significant reduction in the benefits of the usual mineralization of the organic substrates. Combinations between TiO 2 and carbonaceous materials have been widely explored since the 1990s, with results that demonstrate significant synergistic effects that increase the catalytic activity.14 In this context, the use of activated carbon (AC) is particularly attractive, because of providing a high surface area for distribution and immobilization of TiO 2 .14 According to the current literature, the synergistically enhanced photocatalytic activity observed with the use of TiO 2 -AC composites may be explained by the high adsorption capacity of AC and by the consequent enrichment of target molecules around the catalyst.14-17 Although the positive effect of AC on the photocatalytic efficiency of TiO 2 is observed with simple mechanical mixtures, 18 it is admitted that the synergetic effect can be maximized by a more intimate contact between the components, which can normall...

PHOTOCATALYTIC DEGRADATION OF DYE OVER GRAPHENE-TiO 2 NANOCOMPOSITE. In this work the sol-gel method was used to synthesize a nanocomposite containing TiO 2 and graphene oxide (GO). The photocatalytic activity of the TiO 2 /GO nanocomposite was evaluated regarding the degradation of a reactive dye (reactive black 5) in aqueous solution using processes assisted by UV-A radiation. Under these conditions the nanocomposite showed higher degradation efficiency than the reference photocatalyst (Degussa P25 TiO 2 ), mainly due to the high degradation capacity of the synthesized TiO 2 nanoparticles. Although contradictory to several reports in the specialized literature, no synergistic effect was observed between the nanocomposite components.Keywords: photocatalysis; nanocomposite; TiO 2 ; graphene oxide INTRODUÇÃODe maneira geral, grande parte do potencial poluente associado às atividades antrópicas está relacionado com a emissão de resíduos domésticos e industriais, os quais apresentam espécies químicas resistentes e tóxicas. Dentro do contexto industrial é possível destacar atividades de tingimento de fibras têxteis, 1 processo que é responsável pela geração de grandes volumes de resíduos contendo corantes não-fixados, alguns dos quais, mostrando resistência frente a rotinas convencionais de tratamento, contaminam o meio hídrico. 2Em função desta realidade, muitos esforços têm sido dedicados ao desenvolvimento de tecnologias alternativas, com claro destaque para os processos avançados de oxidação (POAs), 3 que permitem a degradação de substratos orgânicos de diversa natureza, eventualmente até completa mineralização.A degradação de corantes por POAs tem sido abundantemente relatada desde inícios da década de 1990, principalmente recorrendo-se a processos de fotocatálise heterogênea mediados por óxido de titânio.4 Para contornar alguns inconvenientes de ordem prática, principalmente representados pelas dificuldades encontradas na separação dos fotocatalisadores, usualmente em escala nanométrica, formas imobilizadas de TiO 2 tem sido propostas também desde a década de 1990, 5 utilizando-se suportes de diversa natureza.6 Particularmente interessante se mostra o uso de suportes constituídos por materiais carbonáceos, os quais, além de facilitar a separação e o reuso dos catalisadores, favorecem o processo de degradação, principalmente em função da sua elevada capacidade de adsorção facilitar a aproximação entre o radical hidroxila e as moléculas de poluente. Nos últimos anos numerosos trabalhos tem relatado um efeito sinérgico entre TiO 2 e grafeno, não apenas em função do efeito acima salientado, mas também em razão do favorecimento do processo de separação de cargas. No grafeno, a hibridização sp 2 dos átomos de carbono resulta em um orbital p vazio, que permite o transporte balístico dos elétrons fotogerados, o que, evitando o processo de recombinação do par e -/h + , favorece a geração de radical hidroxila e aumenta a capacidade de degradação do processo fotocatalítico. 8Em função desta constatação, muitos trabalhos ...