Plataformas de nanotubos de TiO2 usadas para depósitos de compostos de níquel e fosforeno aplicados na oxidação fotoeletrocatalítica da Penicilina G, na geração de H2 e conversão de CO2 em metanol
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Data
2020-10-19
Autores
Sayão, Fabiana Avolio
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Universidade Estadual Paulista (Unesp)
Resumo
A técnica de fotoeletrocatálise é largamente aplicada na área ambiental, seja para remoção de poluentes em águas, ou na produção de energia limpa. Os eletrodos de TiO2 tem sido largamente empregados na fotoeletrocatálise, no entanto a sua heterojunção com outros semicondutores possibilita o melhor desempenho, ampliando a absorção na região visível. No presente trabalho foi estudado as modificações da superfície de nanotubos de TiO2 com compostos de níquel e fosforeno para avaliar a fotoatividade no processo de oxidação e de redução, respectivamente. No caso específico da oxidação, os nanotubos de TiO2 foram modificados com Ni0, NiO e NiS e caracterizados por microscopia eletrônica de varredura, reflectância difusa e avaliou o comportamento eletroquímico, no qual a melhor resposta fotoeletrocatalítica apresentada foi com o NiS. O eletrodo Ti/TiO2/NiS, quando irradiado com luz UV-vis, apresentou melhor absorção na região do visível, menor valor de energia de band gap (2,91 eV) e maior densidade de fotocorrente (5,39 mA cm-2). A heterojunção n-p formada pelos semicondutores TiO2 e NiS favorece a diminuição da energia de band gap e a dispersão das cargas fotogeradas (e-/h+), diminuindo o processo de recombinação. Tendo em vista que antibiótico Penicilina G é considerado um poluente emergente por não possuir monitoramento e os tratamentos de efluentes tradicionais não são adequados para sua remediação. Dessa forma, foi investigado o emprego da fotoeletrocatálise utilizando o eletrodo Ti/TiO2/NiS, no qual resultou na remoção de 93 % de 10 mg L-1 Penicilina G e 59 % de carbono orgânico total (COT), em 0,1 mol L-1 Na2SO4 (pH 7) aplicando potencial externo de +1,0 V (vs Ag|AgCl) sob irradiação solar. No eletrodo Ti/TiO2 modificado com algumas monocamadas de fosforeno foi avaliado o seu emprego na quebra da água (water splitting) para geração de H2 e na reciclagem de CO2 em produtos de maior valor agregado. O eletrodo Ti/TiO2 foi coberto com um fino filme de polidopamina, que atua como agente ancorante para as monocamadas de fosforeno. O eletrodo Ti/TiO2/PDA/fosforeno foi caracterizado por microscopia eletrônica de varredura, difração de raio X, reflectância difusa e comportamento eletroquímico. A modificação sobre o eletrodo Ti/TiO2 com o filme de polidopamina e fosforeno, melhora a absorção na região do visível e permite a geração de H2 em potenciais menos negativos em relação ao eletrodo Ti/TiO2 puro. Sob a incidência de luz visível, a water splitting fotoeletrocatalítica sobre o eletrodo Ti/TiO2/PDA/fosforeno atingiu a geração de 2,01 μmol L-1 de H2, em 0,1 mol L-1 NaCl (pH 6) sob potencial aplicado de -0,2 V (vs Ag|AgCl) durante 1 hora de experimento. Para a redução de CO2, a melhor condição para a sua conversão em metanol foi em 0,1 mol L-1 Na2SO4 (pH 7) com potencial externo aplicado de -0,8 V (vs Ag|AgCl) sob irradiação solar simulada, alcançando a formação de 238,1 μmol L-1 de metanol, sem a geração de H2. Dentro desse contexto, a formação de heterojunção com eletrodo de Ti/TiO2 tanto com NiS e quanto com o fosforeno permitem um melhor desempenho fotocatalítico sob irradiação visível, ampliando a eficiência do processo fotoeletrocatalítico na remoção de poluentes e geração de energia limpa.
The photoelectrocatalysis technique is widely applied in the environment, removing pollutants in water, and producing clean energy. TiO2 electrodes have been extensively used on photoelectrocatalysis, however their heterojunction with other semiconductors can improve performance increasing absorption on visible light. In the present work, the surface modification of TiO2 nanotubes with nickel compounds and phosphorene was studied in order to evaluate photoactivity in oxidation and reduction, respectively. In the case of oxidation, TiO2 nanotubes were modified with Ni0, NiO, and NiS. They were characterized by scanning electronic microscopy, reflectance diffuse, and electrochemistry. The best performance was Ti/TiO2/NiS electrode that demonstrated better absorption on visible light, lower value of band gap energy (2.91 eV), and higher current density (5.39 mA cm-2) when irradiated with UV-vis light. The heterojunction n-p formed by semiconductors TiO2 and NiS favors the reduction of band gap energy and the dispersion of photogenerated charges (e-/h+), decreasing the recombination processes. Inside that antibiotic Penicillin G is considered emergent pollutants because it doesn`t have any monitoring and traditional effluent treatments are not suitable for its remediation. It was investigated the use of photoelectrocatalysis utilizing Ti/TiO2/NiS electrodes for Penicillin G degradation. Resulting in the removal of 93 % of 10 mg L-1 Penicillin G, and 59 % of total organic carbon. In the conditions of 0.1 mol L-1 Na2SO4 (pH 7) applying potential of +1.0 V (vs Ag|AgCl 3 mol L-1 KCl) under solar irradiation. On the other hand, Ti/TiO2 electrode modified with some layers of phosphorene had its use evaluated on water splitting, for H2 generation, and CO2 recycling to products with higher value added. First, Ti/TiO2 electrode was covered with thin poly dopamine film, as an adherent agent for phosphorene layers. The Ti/TiO2/PDA/fosforeno electrode was characterized by scanning electronic microscopy, X ray diffraction, reflectance diffuse, and electrochemistry. The modification over the Ti/TiO2 electrode with poly dopamine film and phosphorene increases absorption on visible light and allows generation of H2 in a lower negative potential compared to pure Ti/TiO2 electrode. Under visible light, photoelectrocalytic water splitting over Ti/TiO2/PDA/phosphorene reached generation of 2.0 μmol L-1 H2, in 0.1 NaCl (pH 6) under applied potential of -0.2 V (vs Ag|AgCl 4 mol L-1 KCl) during 1 hour of experiment. For CO2 reduction, the best condition for CO2 conversion on methanol was in 0.1 mol L-1 Na2SO4 (pH 7) applying potention of -0.8 V (vs Ag|AgCl 3 mol L-1) under solar irradiation. In this condition, it was formed 238,1 μmol L-1 methanol, without H2 generation. Within this context, heterojunction formation between TiO2 with both NiS and phosphorene allowed better photocatalytic performance under visible light, increasing the photoelectrocatalytic process efficiency on the pollutant remotion and generation of clean energy.
The photoelectrocatalysis technique is widely applied in the environment, removing pollutants in water, and producing clean energy. TiO2 electrodes have been extensively used on photoelectrocatalysis, however their heterojunction with other semiconductors can improve performance increasing absorption on visible light. In the present work, the surface modification of TiO2 nanotubes with nickel compounds and phosphorene was studied in order to evaluate photoactivity in oxidation and reduction, respectively. In the case of oxidation, TiO2 nanotubes were modified with Ni0, NiO, and NiS. They were characterized by scanning electronic microscopy, reflectance diffuse, and electrochemistry. The best performance was Ti/TiO2/NiS electrode that demonstrated better absorption on visible light, lower value of band gap energy (2.91 eV), and higher current density (5.39 mA cm-2) when irradiated with UV-vis light. The heterojunction n-p formed by semiconductors TiO2 and NiS favors the reduction of band gap energy and the dispersion of photogenerated charges (e-/h+), decreasing the recombination processes. Inside that antibiotic Penicillin G is considered emergent pollutants because it doesn`t have any monitoring and traditional effluent treatments are not suitable for its remediation. It was investigated the use of photoelectrocatalysis utilizing Ti/TiO2/NiS electrodes for Penicillin G degradation. Resulting in the removal of 93 % of 10 mg L-1 Penicillin G, and 59 % of total organic carbon. In the conditions of 0.1 mol L-1 Na2SO4 (pH 7) applying potential of +1.0 V (vs Ag|AgCl 3 mol L-1 KCl) under solar irradiation. On the other hand, Ti/TiO2 electrode modified with some layers of phosphorene had its use evaluated on water splitting, for H2 generation, and CO2 recycling to products with higher value added. First, Ti/TiO2 electrode was covered with thin poly dopamine film, as an adherent agent for phosphorene layers. The Ti/TiO2/PDA/fosforeno electrode was characterized by scanning electronic microscopy, X ray diffraction, reflectance diffuse, and electrochemistry. The modification over the Ti/TiO2 electrode with poly dopamine film and phosphorene increases absorption on visible light and allows generation of H2 in a lower negative potential compared to pure Ti/TiO2 electrode. Under visible light, photoelectrocalytic water splitting over Ti/TiO2/PDA/phosphorene reached generation of 2.0 μmol L-1 H2, in 0.1 NaCl (pH 6) under applied potential of -0.2 V (vs Ag|AgCl 4 mol L-1 KCl) during 1 hour of experiment. For CO2 reduction, the best condition for CO2 conversion on methanol was in 0.1 mol L-1 Na2SO4 (pH 7) applying potention of -0.8 V (vs Ag|AgCl 3 mol L-1) under solar irradiation. In this condition, it was formed 238,1 μmol L-1 methanol, without H2 generation. Within this context, heterojunction formation between TiO2 with both NiS and phosphorene allowed better photocatalytic performance under visible light, increasing the photoelectrocatalytic process efficiency on the pollutant remotion and generation of clean energy.
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Palavras-chave
Dióxido de titânio, Nanotubos, Fotodegradação, Redução (Química), Penicilina