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Doctoral Thesis
DOI
Document
Author
Full name
Carolina Ferreira Torres
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2019
Supervisor
Committee
Freire, Renato Sanches (President)
Constantino, Vera Regina Leopoldo
Martins, Tereza da Silva
Silva, Cecília de Carvalho Castro e
Title in Portuguese
Síntese, modificação, caracterização e mecanismos de formação de semicondutores fotoativos a base de bismuto
Keywords in Portuguese
Fotocatálise
Óxidos de bismuto
Óxidos de ferro
Oxihaletos de bismuto
Semicondutores
Abstract in Portuguese
Este trabalho descreve a síntese de semicondutores a base de bismuto [Bi2O3, BiOX (X= Cl, Br ou I)] e óxidos de ferro (FexOy), a modificação por tratamento hidrotérmico e a formação de compostos híbridos de BiOX e Bi2O2CO3 ou Fe3O4 e a aplicação destes na degradação fotocatalítica de soluções de rodamina B e de fenol. A formação de vacâncias de oxigênio (VO) em estruturas de BiOCl e Bi2O2CO3 foi promovida por processo de sonicação. Os diferentes oxihaletos de bismuto, polimorfos de óxidos de bismuto e de óxidos de ferro foram precipitados pela elevação de pH do meio precursor utilizando soluções aquosas de monoisopropanolamina (MIPA), diisopropanolamina (DIPA), triisopropanolamina (TIPA), hidróxidos de sódio, potássio ou de amônio. Por meio de caracterização das propriedades físico-químicas, estruturais e morfológicas foram propostos mecanismos atentando-se a participação da base utilizada para formação e atividade catalítica dos compostos. Foram obtidas as fases α-Bi2O3 quando utilizado bases minerais e MIPA e γ-Bi2O3 utilizando-se TIPA, fases amorfas ou mistas foram obtidas com as demais bases. Os oxihaletos de bismuto se formaram independente da base utilizada na precipitação, apresentando diferenças estruturais. O processo de sonicação levou a formação de VO em estruturas de BiOCl e Bi2O2CO3 que foi verificado por Raman e espectroscopia de fotoelétrons excitados por raios X. Na precipitação de íons Fe2+ a utilização de MIPA levou à formação de magnetita, enquanto as demais bases levou a formação de misturas de óxidos de ferro. O tratamento hidrotérmico levou a híbridos de BiOX e magnetita, que apresentaram comportamento magnético, e de BiOCl e Bi2O2CO3, além de oxibrometos ricos em bismuto. Todos os materiais apresentaram atividade fotocatalítica na degradação de soluções de fenol e/ou rodamina B, as caracterizações de espectroscópicas, área superficial e potencial Zeta foram utilizadas para explicar as diferenças nestas atividades.
Title in English
Synthesis, modification, characterization and mechanisms of formation of bismuth-based photo semiconductors
Keywords in English
Bismuth oxides
Bismuth oxyhalides
Iron oxide
Photocatalysis
Semiconductors
Abstract in English
This study describes the synthesis of semiconductors based on bismuth [Bi2O3, BiOX (X = Cl, Br or I)] and iron oxides (FexOy), the modification by hydrothermal treatment and the formation of hybrids of BiOX and Bi2O2CO3 or Fe3O4, and the application of the materials to the photocatalytic degradation of rhodamine B and phenol solutions. The formation of oxygen vacancies (VO) in the structures of BiOCl and Bi2O2CO3 was promoted by a sonication process. The different bismuth oxyhalides, polymorphs of bismuth oxides and iron oxides were precipitated by raising the precursor pH level using aqueous solutions of monoisopropanolamine (MIPA), diisopropanolamine (DIPA), triisopropanolamine (TIPA), sodium, potassium or ammonium hydroxides. By performing the characterization of physico-chemical, structural and morphological properties, mechanisms were proposed considering the participation of the base on the formation of the compounds and their catalytic activity. The α- Bi2O3 phase was obtained when mineral bases and MIPA were used; the γ- Bi2O3 was formed when using TIPA; amorphous or mixed phases were obtained when using the other bases. Bismuth oxyhalides were formed independently of the base used for precipitation, showing structural differences. The sonication process led to the formation of VO in structures of BiOCl and Bi2O2CO3which was verified by Raman and X-ray excited photoelectron spectroscopies. For Fe2+ ion precipitation, the use of MIPA led to the formation of magnetite, while the other bases led to the formation of mixtures of iron oxides. The hydrothermal treatment led to hybrids of BiOX and magnetite, which presented magnetic behavior, and BiOCl and Bi2O2CO3, in addition to bismuth-rich oxybromides. All the materials showed photocatalytic activity in the degradation of phenol and / or rhodamine B solutions. Characterization techniques such as spectroscopy, surface and Zeta potential were used to explain as the different photocatalytic activities.
 
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Publishing Date
2019-08-20
 
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