负载型二氧化钛纳米管/纳米晶复合光催化剂的制备及性能研究
摘要
由于全球工业化进程的发展,污染问题日益严重,环境保护和可持续发展成为了人们考虑的首要问题,光催化降解技术是指在光照射条件下,使污染物发生氧化-还原反应,生成二氧化碳、水及盐类等无害物质,属于绿色环保技术。纳米TiO2作为一种重要的半导体光催化材料,具有粒径小、比表面积高、催化活性高、化学稳定性好、价格低廉等优势,已成为当前研究的热点。其中一维管状二氧化钛纳米管2 nanotubes,简称为TNTs)具有开口、中空的特殊结构,本身具有很强的吸附性能,但是光催化活性很低。如何在保持TNTs强吸附性能的同时,又使其具有很高的光催化活性,是一个值得研究的重要课题。本论文通过表面负载TiO2、Pt、Au纳米晶来对TNTs进行复合改性,从而制备出具有高活性的负载型二氧化钛纳米管/纳米晶复合光催化剂。
首先以TiO2(P25)为原料,利用水热合成法制备了具有高长径比、均一形貌的TNTs。将其作为载体,分散在无水乙醇中,通过柠檬酸还原氯铂酸,一步法合成了表面负载贵金属Pt的二氧化钛纳米管/纳米晶复合光催化剂(简称为Pt/TNNs)。分析比较了在不同热蒸发温度、不同Pt负载量的条件下,复合光催化剂对模型污染物酸性红G(Acid Reg G)、亚甲基蓝(Methylene Blue)的光催化降解效果。研究结果表明：
采用水热法制备了直径为5-8nm,长度为200-400nm,比表面积为463m2/g的具有均一形貌、两端开口的中空二氧化钛纳米管。表面负载贵金属Pt后,直径约为4nm的贵金属Pt以单质的形态很好得分散在TNTs表面,纳米管部分转变为晶粒尺寸为8nm锐钛矿相Ti02纳米晶,并保留了高于216m2/g的比表面积,较未载铂的样品有着更高的比表面积。这说明了在TNTs表面负载Pt纳米晶,在促进Ti02纳米晶粒生长的同时,增强了TNTs的热稳定性。纯纳米管的光催化活性很低,在120℃蒸气处理并负载贵金属Pt后光催化活性有了显著的提高,但是当Pt的负载量大于2.5wt%时,由于负载量过大导致复合光催化剂的捕光效率下降,降低了光催化活性。
为了更好得了解贵金属负载对于提高TNTs光催化活性的机理,论文尝试了通过硼氢化钠还原氯金酸,一步法合成了表面负载贵金属Au的二氧化钛纳米管/纳米晶复合光催化剂(简称为Au/NTs),由XRD和TEM可以计算得出直径为10nm的Au单质吸附在了TNTs表面的同时,纳米管和贵金属单质都有良好的结晶性能。由于Au纳米晶粒尺寸较大,所以在120℃蒸气处理后,复合光催化剂的比表面积有大幅度降低。Au/NTs对于阳离子型染料亚甲基蓝具有良好的吸附性能,且较Pt/TNNs相比,光催化性能有所提高。
论文通过将TNTs分散在溶有钛酸四丁酯(TBOT)的乙醇溶液,利用热蒸发的方法制备了表面负载Ti02纳米晶的二氧化钛纳米管／纳米晶复合光催化剂(简称为NT/NC),结果表明,表面负载TiO2纳米晶是提高纳米管光催化活性的有效方法。
综上所述,本论文运用热蒸发的方法,将TiO2、Pt、Au等纳米晶负载在TNTs上,热蒸发的过程中TNTs部分转变为锐钛矿相TiO2,但依然保持着很高的比表面积。这种高比表面积的复合光催化剂具有很好的吸附性能和较高的光催化活性。
With the development of global industrialization, pollution has become increasingly seriously. Environmental protection and sustainable development are the primary problems facing mankind. Photocatalytic degradation technique is a kind of green environmental friendly technology, which refers to using the solar energy to decomposite contaminants into CO2, H2O and other harmless substance. TiO2 is an important semiconductor photocatalysis material due to its small diameter, large surface area, high photocatalytic activities, chemical stability and low cost. Among the various TiO2-based materials, the one-dimensional tubular TiO2 nanotubes (refers to TNTs) which present an end opened, middle hollow structure. It has strong adsorptive capacity but very low photocatalytic activity. Research has been focused on the composite photocatalysts combining the high adsorptive capacity with the enhanced photocatalytic efficiency. This thesis has prepared a kind of supported titania nanotubes/nanocrystals composite with high photocatalytic activity through surface modification.
TNTs were synthesized via hydrothermal method using P25 as the raw material. The Pt-supported titania nanotubes/nanocrystals composite photocatalysts (refers to Pt/TNNs) were prepared via one-step method involved the vapor phase hydrolysis setup, where TNTs were added into the ethanol solution containing H2PtCl6·6H2O and C6H8O7 (as the reductant). The photocatalytic activities of the as-prepared catalysts were investigated by the degradation of acid red G (ARG) and methylene blue (MB). The following conclusions were obtained:
The as-prepared TNTs were 5-8nm in diameter,200-400nm in length and had a specific surface area as high as 463m2/g. The Pt nanoparticles in crystallite size of 4nm were uniformly dispersed onto the surface of remaining TNTs and anatase TiO2 nanocrystals with the crystallite size of 8nm derived from the transformation of TNTs, and the composite photocatalysts kept a specific surface area of more than 216m2/g. During the water vapor treatment, some of the nanotubes were transformed into anatase TiO2 nanocrystals and a small amount of TNTs were kept as the tubular morphologies, thus the composite had a higher adsorptive capacity. The photocatalytic activity of Pt/TNNs was evaluated by the degradation rate of ARG and MB under UV irradiation. The results showed that Pt/TNNs obtained via water vapor treatment at 120℃exhibited much higher photocatalytic efficiency compared to the pristine TNTs. But the photocatalytic efficiency dropped after the loading amount was higher than 2.5wt%.
The thesis prepared Au supported titania nanotubes/nanocrystals composite (refers to Au/NTs), where TNTs were added into the ethanol solution containing HAuCl4·4H2O and NaBH4 (as the reductant). The XRD and TEM results showed that Au nanoparticles in crystallite size of 10nm were uniformly dispersed onto the surface of TNTs and the composite had good crystallization as well. The specific surface area of Au/NTs dropped greatly after water vapor treatment at 120℃. It exhibited good adsorption to dyes MB and improved photocatalytic efficiency compared to Pt/TNNs.
We synthesized TiO2 supported titania nanotubes/nanocrystals composite (refers to NT/NC) using TBOT as the procuser via vapor hydrolysis method. It exhibited high photocatalytic activity compared to the pristine TNTs. The thesis prepared Pt, Au, TiO2 supported titania nanotubes/nanocrystals composites via vapor hydrolysis method. TNTs were partly transformed into anatase TiO2 nanocrystals during the process and the composite remained a high specific surface area. This kind of compound photocatalysts exhibited good adsorptive capacity and high photocatalytic activities.
首先以TiO2(P25)为原料,利用水热合成法制备了具有高长径比、均一形貌的TNTs。将其作为载体,分散在无水乙醇中,通过柠檬酸还原氯铂酸,一步法合成了表面负载贵金属Pt的二氧化钛纳米管/纳米晶复合光催化剂(简称为Pt/TNNs)。分析比较了在不同热蒸发温度、不同Pt负载量的条件下,复合光催化剂对模型污染物酸性红G(Acid Reg G)、亚甲基蓝(Methylene Blue)的光催化降解效果。研究结果表明：
采用水热法制备了直径为5-8nm,长度为200-400nm,比表面积为463m2/g的具有均一形貌、两端开口的中空二氧化钛纳米管。表面负载贵金属Pt后,直径约为4nm的贵金属Pt以单质的形态很好得分散在TNTs表面,纳米管部分转变为晶粒尺寸为8nm锐钛矿相Ti02纳米晶,并保留了高于216m2/g的比表面积,较未载铂的样品有着更高的比表面积。这说明了在TNTs表面负载Pt纳米晶,在促进Ti02纳米晶粒生长的同时,增强了TNTs的热稳定性。纯纳米管的光催化活性很低,在120℃蒸气处理并负载贵金属Pt后光催化活性有了显著的提高,但是当Pt的负载量大于2.5wt%时,由于负载量过大导致复合光催化剂的捕光效率下降,降低了光催化活性。
为了更好得了解贵金属负载对于提高TNTs光催化活性的机理,论文尝试了通过硼氢化钠还原氯金酸,一步法合成了表面负载贵金属Au的二氧化钛纳米管/纳米晶复合光催化剂(简称为Au/NTs),由XRD和TEM可以计算得出直径为10nm的Au单质吸附在了TNTs表面的同时,纳米管和贵金属单质都有良好的结晶性能。由于Au纳米晶粒尺寸较大,所以在120℃蒸气处理后,复合光催化剂的比表面积有大幅度降低。Au/NTs对于阳离子型染料亚甲基蓝具有良好的吸附性能,且较Pt/TNNs相比,光催化性能有所提高。
论文通过将TNTs分散在溶有钛酸四丁酯(TBOT)的乙醇溶液,利用热蒸发的方法制备了表面负载Ti02纳米晶的二氧化钛纳米管／纳米晶复合光催化剂(简称为NT/NC),结果表明,表面负载TiO2纳米晶是提高纳米管光催化活性的有效方法。
综上所述,本论文运用热蒸发的方法,将TiO2、Pt、Au等纳米晶负载在TNTs上,热蒸发的过程中TNTs部分转变为锐钛矿相TiO2,但依然保持着很高的比表面积。这种高比表面积的复合光催化剂具有很好的吸附性能和较高的光催化活性。
With the development of global industrialization, pollution has become increasingly seriously. Environmental protection and sustainable development are the primary problems facing mankind. Photocatalytic degradation technique is a kind of green environmental friendly technology, which refers to using the solar energy to decomposite contaminants into CO2, H2O and other harmless substance. TiO2 is an important semiconductor photocatalysis material due to its small diameter, large surface area, high photocatalytic activities, chemical stability and low cost. Among the various TiO2-based materials, the one-dimensional tubular TiO2 nanotubes (refers to TNTs) which present an end opened, middle hollow structure. It has strong adsorptive capacity but very low photocatalytic activity. Research has been focused on the composite photocatalysts combining the high adsorptive capacity with the enhanced photocatalytic efficiency. This thesis has prepared a kind of supported titania nanotubes/nanocrystals composite with high photocatalytic activity through surface modification.
TNTs were synthesized via hydrothermal method using P25 as the raw material. The Pt-supported titania nanotubes/nanocrystals composite photocatalysts (refers to Pt/TNNs) were prepared via one-step method involved the vapor phase hydrolysis setup, where TNTs were added into the ethanol solution containing H2PtCl6·6H2O and C6H8O7 (as the reductant). The photocatalytic activities of the as-prepared catalysts were investigated by the degradation of acid red G (ARG) and methylene blue (MB). The following conclusions were obtained:
The as-prepared TNTs were 5-8nm in diameter,200-400nm in length and had a specific surface area as high as 463m2/g. The Pt nanoparticles in crystallite size of 4nm were uniformly dispersed onto the surface of remaining TNTs and anatase TiO2 nanocrystals with the crystallite size of 8nm derived from the transformation of TNTs, and the composite photocatalysts kept a specific surface area of more than 216m2/g. During the water vapor treatment, some of the nanotubes were transformed into anatase TiO2 nanocrystals and a small amount of TNTs were kept as the tubular morphologies, thus the composite had a higher adsorptive capacity. The photocatalytic activity of Pt/TNNs was evaluated by the degradation rate of ARG and MB under UV irradiation. The results showed that Pt/TNNs obtained via water vapor treatment at 120℃exhibited much higher photocatalytic efficiency compared to the pristine TNTs. But the photocatalytic efficiency dropped after the loading amount was higher than 2.5wt%.
The thesis prepared Au supported titania nanotubes/nanocrystals composite (refers to Au/NTs), where TNTs were added into the ethanol solution containing HAuCl4·4H2O and NaBH4 (as the reductant). The XRD and TEM results showed that Au nanoparticles in crystallite size of 10nm were uniformly dispersed onto the surface of TNTs and the composite had good crystallization as well. The specific surface area of Au/NTs dropped greatly after water vapor treatment at 120℃. It exhibited good adsorption to dyes MB and improved photocatalytic efficiency compared to Pt/TNNs.
We synthesized TiO2 supported titania nanotubes/nanocrystals composite (refers to NT/NC) using TBOT as the procuser via vapor hydrolysis method. It exhibited high photocatalytic activity compared to the pristine TNTs. The thesis prepared Pt, Au, TiO2 supported titania nanotubes/nanocrystals composites via vapor hydrolysis method. TNTs were partly transformed into anatase TiO2 nanocrystals during the process and the composite remained a high specific surface area. This kind of compound photocatalysts exhibited good adsorptive capacity and high photocatalytic activities.
引文
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