Degradação de antibióticos por processo foto-Fenton heterogêneo mediado por ferro imobilizado em argila sob irradiação LED UV e LED VIS
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Data
2019-04-18
Autores
Rojas-Mantilla, Hernán Dario
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Este trabalho descreve um estudo comparativo da atividade catalítica de material obtido com imobilização de ferro em vários suportes argilominerais: Argila natural modificada com amido (AN+A) Vermiculita (V) e Nontronita (N) para processo Fenton heterogêneo. A atividade catalítica foi avaliada pela degradação dos antibióticos sulfatiazol (STZ) e cefalexina (CFX) utilizando dispositivos LED-UV (360 nm) e LED-Vis (460 nm) como fonte de irradiação, bem como solar. Os materiais usados como suportes de ferro passaram previamente por processo de moagem, secagem e peneiragem (≤ 180 μm). Foram realizadas diversas impregnações de Fe em diferentes condições e com posterior tratamento térmico (450, 600 e 750 °C). Os materiais foram caracterizados pelas técnicas de Fluorescência de raios X, Difração de Raios- X, Espectroscopia de Reflectância Difusa, Espectrometria de absorção ultravioleta-visível e infravermelho próximo, área superficial específica, Microscopia Eletrônica de Varredura de Alta Resolução e Potencial Zeta. Foi observado que o aumento do pH natural da solução (pH < 1) para 5,0 proporcionou uma maior impregnação de Fe passando de 7,4% (m/m) para 49% Fe no caso AN+ A, e para 45% Fe para a N. Os materiais apresentaram em sua composição química SiO2, Al2O3, Fe2O3, K2O, TiO2, MgO como óxidos maioritários, e mostraram alta absorção na faixa UVA, UVB e Vis e energias de banda proibida de 1,9 eV. O Potencial Zeta em pH 3,0 mostrou comportamentos opostos para os dois materiais sendo de -12,7 mV para a AN + A 49% Fe e de 7,2 mV N 45% Fe, o que indicaria mecanismos de interação diferentes com STZ. A atividade catalítica dos materiais frente à degradação de STZ foi avaliada em diferentes valores de pH (3,0 e 6,0), concentrações de peróxido de hidrogênio (0,5 1,5 e 3,0 mmol L-1), concentrações de catalisador (0,5 e 1,0 g L-1) sob irradiação de dispositivos LED. Foi observado que o aumento na porcentagem de Fe impregnado é um fator muito importante na eficiência catalítica da degradação no processo, assim como o tratamento térmico, já que permite um reordenamento estrutural junto com a conversão de outras fases de óxidos de ferro para hematita (mais reativa). As condições que resultaram em maior degradação foram em pH 3,0, dosagem de catalisador 0,5 g L-1 e 1,5 mmol L-1 de H2O2 resultando em degradação de STZ >97% com o catalisador AN+A 49% e de 64% com N 45%Fe após 60 min sem ajuste de pH, com pequenas diferenças de acordo com o tipo de dispositivo LED usado. A AN+A 49% mostrou alta estabilidade devido à ausência de Fe em solução, porém a N 45% mesmo sem apresentar Fe em solução, lixiviou sílica amorfa para a solução, o que exigiu um controle de pH. Os dois catalisadores oferecem bons resultados de reuso resultando em 93% de degradação de STZ após três ciclos de 90 min. A identificação de intermediários de degradação de STZ indicam a hidroxilação como principal rota de degradação seguida da ruptura da ligação N- anel tiazol.
This work describes a comparative study of the catalytic activity of material obtained with iron immobilization in several clay minerals: Natural clay modified with starch (AN + A) Vermiculite (V) and Nontronite (N) for heterogeneous Fenton process. The catalytic activity was evaluated by the degradation of the antibiotics sulfathiazole (STZ) and cefalexin (CFX) using LED-UV (360 nm) and LED-Vis (460 nm) devices as irradiation source as well as solar. The clay minerals used as iron supports were previously crushed, dried and sieved (≤ 180 μm). Several iron impregnations were carried out under different conditions and with subsequent thermal treatment (450, 600 and 750 °C). The materials were characterized by the techniques of X-ray Fluorescence, X-ray Diffraction, Diffuse Reflectance Spectroscopy, Ultraviolet-Visible and Near Infrared Absorption Spectrometry, specific surface area, High Resolution Scanning Electron Microscopy couple to Energy dispersive X-ray spectroscopy. It was observed that the increase inthe natural pH of the solution (pH <1)to 5.0 provided an improved Fe impregnation from 7.4% (m / m) to 49% Fe in the AN + A case, and to 45% Fe in the case of N. The materials presented in the chemical composition SiO2, Al2O3, Fe2O3, K2O, TiO2, MgO as major oxides, and showed high absorption in the UVA, UVB and Vis range, and bandgap energies of 1.9 eV. The Zeta Potential at pH 3.0 showed opposite behaviors for the two materials with -12.7 mV for AN + A 49% Fe and 7.2 mV for N 45% Fe, which indicate different interaction mechanisms with STZ. The catalytic activity of the materials for STZ degradation was evaluated at different pH values (3.0 and 6.0), concentrations of hydrogen peroxide (0.5 1.5 and 3.0 mmol L-1), concentrations of catalyst (0.5 and 1.0 g L-1) under irradiation of LED devices. It was observed that the increase in the impregnated Fe percentage is a very important factor in the catalytic efficiency of the degradation process, as well as the thermal treatment, since it allows a structural rearrangement along with the conversion of other phases of iron oxides to hematite (more reactive). The conditions that resulted in highest photo-Fenton degradation were pH 3.0, 0.5 g L-1catalyst dosage and 1.5 mmol L-1 of H2O2resulting in STZ degradation > 97% with AN + A 49% Fe and 64% with N 45% Fe after 60 min without pH adjustment, with small differences according to the type of LED device used. The AN + A 49% showed high stability due to the absence of Fe in solution, but the N 45% Fe even without Fe in solution, leached amorphous silica to the solution that required a pH control. The two catalysts offer good reuse results resulting in 93% STZ degradation after three 90 min cycles. Identification of STZ degradation intermediates indicates hydroxylationas the major route of degradation followed by cleavage of the bond N-tiazol ring.
This work describes a comparative study of the catalytic activity of material obtained with iron immobilization in several clay minerals: Natural clay modified with starch (AN + A) Vermiculite (V) and Nontronite (N) for heterogeneous Fenton process. The catalytic activity was evaluated by the degradation of the antibiotics sulfathiazole (STZ) and cefalexin (CFX) using LED-UV (360 nm) and LED-Vis (460 nm) devices as irradiation source as well as solar. The clay minerals used as iron supports were previously crushed, dried and sieved (≤ 180 μm). Several iron impregnations were carried out under different conditions and with subsequent thermal treatment (450, 600 and 750 °C). The materials were characterized by the techniques of X-ray Fluorescence, X-ray Diffraction, Diffuse Reflectance Spectroscopy, Ultraviolet-Visible and Near Infrared Absorption Spectrometry, specific surface area, High Resolution Scanning Electron Microscopy couple to Energy dispersive X-ray spectroscopy. It was observed that the increase inthe natural pH of the solution (pH <1)to 5.0 provided an improved Fe impregnation from 7.4% (m / m) to 49% Fe in the AN + A case, and to 45% Fe in the case of N. The materials presented in the chemical composition SiO2, Al2O3, Fe2O3, K2O, TiO2, MgO as major oxides, and showed high absorption in the UVA, UVB and Vis range, and bandgap energies of 1.9 eV. The Zeta Potential at pH 3.0 showed opposite behaviors for the two materials with -12.7 mV for AN + A 49% Fe and 7.2 mV for N 45% Fe, which indicate different interaction mechanisms with STZ. The catalytic activity of the materials for STZ degradation was evaluated at different pH values (3.0 and 6.0), concentrations of hydrogen peroxide (0.5 1.5 and 3.0 mmol L-1), concentrations of catalyst (0.5 and 1.0 g L-1) under irradiation of LED devices. It was observed that the increase in the impregnated Fe percentage is a very important factor in the catalytic efficiency of the degradation process, as well as the thermal treatment, since it allows a structural rearrangement along with the conversion of other phases of iron oxides to hematite (more reactive). The conditions that resulted in highest photo-Fenton degradation were pH 3.0, 0.5 g L-1catalyst dosage and 1.5 mmol L-1 of H2O2resulting in STZ degradation > 97% with AN + A 49% Fe and 64% with N 45% Fe after 60 min without pH adjustment, with small differences according to the type of LED device used. The AN + A 49% showed high stability due to the absence of Fe in solution, but the N 45% Fe even without Fe in solution, leached amorphous silica to the solution that required a pH control. The two catalysts offer good reuse results resulting in 93% STZ degradation after three 90 min cycles. Identification of STZ degradation intermediates indicates hydroxylationas the major route of degradation followed by cleavage of the bond N-tiazol ring.
Descrição
Palavras-chave
Argila natural, Nontronita, Fotoreator, Sulfatiazol