Cerâmicas porosas de TiO2 preparadas a partir da integração do método sol-gel com moldes moles para aplicações em catálise e fotocatálise
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Data
2019-10-18
Autores
Moraes, Paula Glazielli Paulino
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Universidade Estadual Paulista (Unesp)
Resumo
Este trabalho envolve a síntese, caracterização e avaliação do potencial fotocatalítico de pós e espumas cerâmicas de titânia e titânia sulfatada. Os materiais na forma de pós foram sintetizados pelo método sol-gel para formação de suspensões coloidais de TiO2 e TiO2/SO42-, enquanto as espumas foram obtidas a partir destas suspensões associadas a emulsões como molde de poros. As emulsões foram preparadas pela adição do surfactante aniônico dodecil sulfato de sódio (SDS) e a fase apolar miristato de isopropila às suspensões de titânia e titânia sulfatada. O ácido p-tolueno sulfônico (PTSH) foi empregado como catalisador da síntese sol-gel e agente sulfatante. Foi investigada a influência da adição de grupos sulfato nas propriedades estruturais e porosas, bem como na acidez como catalisador na desidratação do isopropanol e na fotodegradação do corante rodamina B. Os parâmetros de síntese como razão de PTSH/Ti e a quantidade de surfactante também foram avaliados nas propriedades das espumas cerâmicas por diferentes técnicas de caracterização. Os resultados mostraram um efeito benéfico da adição de espécies sulfato nas propriedades da titânia, como a estabilização da fase anatase em temperaturas de calcinação de 600 °C e 700 °C, controle do tamanho (~22 e 16 nm) e agregação das partículas, maiores volume de poros (~ 0,56 cm3g-1) e aumento de até 10 vezes no valor da área específica do pó de TiO2. O molde de emulsões possibilitou a obtenção de materiais macro-mesoporos com maiores valores de área específica (até 80 m2g-1). O aumento da razão PTSH/Ti (razão SO42-/Ti) de 0,1 para 1 permitiu a preservação das mesofases nas emulsões em temperaturas próximas a 400 °C. Maiores quantidades de SDS favorecem a estabilização das mesofases, com formação de um material macroporoso com 51 m2g-1 de área específica. As amostras sulfatadas apresentaram maiores atividades na conversão do isopropanol a propeno, indicando maior acidez relativa dos materiais. As espumas cerâmicas exibiram maiores eficiências fotocatalíticas na degradação da rodamina B e os dados cinéticos indicaram que a reação segue um mecanismo de pseudo-primeira ordem.
This work involves the synthesis, characterization and evaluation of the photocatalytic activity of titania and sulfated titania ceramic powders and foams. The powders were synthesized by sol-gel process for producing TiO2 and TiO2/SO42- colloidal suspensions, while the foams were obtained by these suspensions associated to emulsion as pores template. The emulsions were prepared by addition of the anionic surfactant sodium dodecyl sulfate (SDS) and the apolar phase isopropyl myristate to the titania suspensions. The p-toluene sulfonic acid (PTSH) was employed as a catalyst for sol-gel synthesis and sulfating agent. The influence of the addition of sulfate groups on the structural and porous properties, as well as on the acidity as catalyst in the isopropanol dehydration and photocatalytic activity in the photodegradation of the rhodamine B dye of titania was investigated. PTSH/Ti ratio and surfactant amount synthesis parameters were evaluated in the ceramic foams properties by different characterization techniques. The results showed a beneficial effect of the sulfate addition on the titania properties, such as the stabilization of the anatase phase at calcination temperatures of 600 °C and 700 °C, particle size (~22 and 16 nm) and aggregation control, higher pore volume (~ 0.56 cm3g-1) and leading to values up to 10 times higher than for TiO2 powder surface area. The emulsion allowed the obtaining of macro-mesoporous materials with surface areas up to 80 m2g-1. Mesophases in emulsions were preserved by increasing the PTSH/Ti ratio (SO42-/Ti ratio) from 0.1 to 1 at temperatures around 400 °C. Increasing the amount of SDS favors the mesophase stabilization with formation of a macroporous material of surface area ~ 51 m2g-1. The sulfated samples showed higher conversion of isopropanol to propene, indicating high relative acidity of these materials. The ceramic foams exhibited higher photocatalytic efficiency in the degradation of rhodamine B and kinetic data indicated that the reaction follows a pseudo-first order mechanism.
This work involves the synthesis, characterization and evaluation of the photocatalytic activity of titania and sulfated titania ceramic powders and foams. The powders were synthesized by sol-gel process for producing TiO2 and TiO2/SO42- colloidal suspensions, while the foams were obtained by these suspensions associated to emulsion as pores template. The emulsions were prepared by addition of the anionic surfactant sodium dodecyl sulfate (SDS) and the apolar phase isopropyl myristate to the titania suspensions. The p-toluene sulfonic acid (PTSH) was employed as a catalyst for sol-gel synthesis and sulfating agent. The influence of the addition of sulfate groups on the structural and porous properties, as well as on the acidity as catalyst in the isopropanol dehydration and photocatalytic activity in the photodegradation of the rhodamine B dye of titania was investigated. PTSH/Ti ratio and surfactant amount synthesis parameters were evaluated in the ceramic foams properties by different characterization techniques. The results showed a beneficial effect of the sulfate addition on the titania properties, such as the stabilization of the anatase phase at calcination temperatures of 600 °C and 700 °C, particle size (~22 and 16 nm) and aggregation control, higher pore volume (~ 0.56 cm3g-1) and leading to values up to 10 times higher than for TiO2 powder surface area. The emulsion allowed the obtaining of macro-mesoporous materials with surface areas up to 80 m2g-1. Mesophases in emulsions were preserved by increasing the PTSH/Ti ratio (SO42-/Ti ratio) from 0.1 to 1 at temperatures around 400 °C. Increasing the amount of SDS favors the mesophase stabilization with formation of a macroporous material of surface area ~ 51 m2g-1. The sulfated samples showed higher conversion of isopropanol to propene, indicating high relative acidity of these materials. The ceramic foams exhibited higher photocatalytic efficiency in the degradation of rhodamine B and kinetic data indicated that the reaction follows a pseudo-first order mechanism.
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Palavras-chave
Processo sol-gel, Cerâmicas porosas, Titânia sulfatada, Fotocatálise heterogênea