Preparation of TiO2 Anatase Nanocrystals by TiCl4 Hydrolysis with Additive H2SO4:
Abstract
A new methodology was developed to synthesize uniform titania anatase nanocrystals by the hydrolysis of titanium chloride in sulfuric acid aqueous solutions at 0–90°C. The samples were characterized by Raman spectroscopy, UV-visible spectroscopy, transmission electron microscopy (TEM), electron diffraction (ED), and an Energy dispersive X-ray spectroscopy (EDS). The effects of the reaction temperature, mole ratio of SO42− to Ti4+, and the calcinations temperature on the particle size and crystal phase were investigated. Depending on the acidity, the hydrolysis temperature, and the calcination temperature, rhombic anatase nanocrystals sizes in the range of 10 nm to 50 nm were obtained. In the additive of sulfuric acid, Raman spectra and electron diffraction confirmed that the nanoparticles are composed of anatase TiO2. No other titania phases, such as rutile or brookite, were detected.
Introduction
It is well known that TiO2 occurs in nature in three distinct crystallographic phases: anatase, rutile, and brookite. While anatase TiO2 are the most widely used photocatalysts for oxidative decomposition of organic compounds, and an excellent photocatalyst for photodecomposition and solar-energy conversion due to its high photoactivity.It has the advantages of both cheapness and nontoxicity, in addition to its excellent functionality and long-term stability. The configurations of titanium oxide researched and reported have mainly been powders or films based on materials.A notable problem connected with these traditional preparations is that the growth of TiO2 nanocrystallites take a long time. Therefore it is highly desirable to find some new ways that are capable of overcoming the above problems to prepare crystal structure TiO2. Many attempts have been made in this field over the past few years.At the same time, recent photocatalytic studies have demonstrated that the photoactivity of anatase nanoparticles is strongly particle size dependent.The applications for TiO2 are also strongly dependent on the crystalline structure and morphology.Thus, it is very important to develop synthetic methods in which the crystalline form. It is also important that the TiO2 sizes and shapes be controlled.Anatase nanoparticles have been synthesized primarily by solution chemistries involving titanium sulfates and organic titanium.These methods have shortcomings since chemical impurities or minor accessory phases are always present in the final products. In the case of organic hydrolytic reactions, TiO2 nanoparticles obtained are crystallized primarily in the anatase phase but a minor phase of brookite couldn't be eliminated by tuning the reaction conditions.The presence of trace amounts of brookite might have side effects on the application of anatase nanoparticles in photocatalytic reactions and many other chemical processes. Hydrolysis of TiCl4 has extensively been reported for the synthesis of anatase nanocrystals, however, the preparation of titania anatase nanocrystals directly in sulfuric acid solution is seldom reported.
In this study, the preparation of titania anatase nanocrystals by hydrolysis of TiCl4 with diluted sulfuric acid solution was studied. With the precisely control of reaction parameters, we could get titania anatase nanocrystals and achieve high phase purity anatase. To the best of our knowledge, such works have not yet been reported. The effects of the reaction temperature, sulfuric acid concentration, and the calcination temperature on the particle size and crystal phase were investigated.
Materials and Methods
1). Materials
All chemicals were obtained commercially and used without further purification. Titanium chloride (TiCl4, 99.90%) and Concentrated Sulfuric acid (98%) were obtained from Fisher. Concentrated NH3.H2O was purchased from Sigma-Aldrich. All chemicals, unless specified, were of reagent grade. Deionized (DI) water, with a resistivity greater than 18.0 MΩ·cm (Millipore Milli-Q system), was used in preparing the aqueous solutions. All glassware used in the experiments was washed with freshly prepared aqua regia and rinsed thoroughly in tap water first and then DI water before using.
2). Preparation of TiO2 anatase nanocrystals
In the procedure, TiCl4 was used as a main starting material. The detail process is shown in Figure 1. In brief, 1ml TiCl4 was slowly added to different amounts of diluted sulfuric acid (10%) solution at 0°C in an ice-water bath with vigorously stirring. During the mixing process, white fume, presumably HCl, was released as a consequence of the hydrolysis of TiCl4 with water. After about half an hour, a grey solution was formed with continuous stirring. Then when the solution was heated to above 60°C, it became clear solution. And then the solution was kept at room temperature or heated at different temperatures for one hour. Later, concentrated NH3.H2O was added drop by drop to the solution until the pH value reached about 7. During the process of adding concentrated NH3.H2O, the color of solution changed to white. At last, the white solution was cooled to room temperature and gelled 12 hours. The hydrous TiO2 powders were filtered out and washed with DI water until there was no white sediment with 0.1 M AgNO3 solution, and then dried at room temperature in a vacuum oven. In some cases, the dried TiO2 powders were calcinated at 400°C and 600°C for two hours separately, both producing an off-white powders.
Process of TiO2 anatase nanocrystals preparation.
3). Raman spectroscopy
Raman spectrometer was used for crystal phase identification. Raman spectroscopy is a form of vibrational spectroscopy, much like infrared (IR) spectroscopy. It exhibits high specificity and is compatible with aqueous and solid systems. No special preparation of the sample is needed, and the timescale of the experiment is short. Raman spectrum analysis was conducted using a Raman System's R-3000 spectrometer with a solid-state diode laser operating at 532 nm. The Raman system's incident power is 25 mW, which has a wavelength range of ∼200–4000 cm−1.
4). Extinction spectra
The extinction spectra were recorded on a Shimadzu UV-2101 Spectrophotometer (Shimadzu Corporation Japan) using a 1-cm path length quartz cuvette at room temperature and the spectra were recorded in the range 200–800 nm.
5). TEM and ED measurements
A drop of well-sonicated solution containing the nanoparticles was deposited onto a 400 mesh Cu grids with supporting carbon film. (Electron Microscopy Sciences, PA). The samples were allowed to dry at room temperature overnight. A JEOL 100CX electron microscope operated at 100 KV was used to obtain the TEM images and ED spectra.
6). Energy dispersive X-ray spectroscopy (EDS)
EDS is an analytical technique used for the elemental analysis or chemical characterization of a sample. The chemical compositions of the ultrafine nanoparticles were determined by using a JEOL 5400LV equipped with Sigma Microanalyzer Level LPX1 Energy Dispersive X-ray Spectrometer (EDS).
Results
When TiCl4 hydrolyses in diluted sulfuric acid solution, because of the presence of a certain amount of hydrogen ions, the reaction rate may be slower than in pure water.
Then the adding of concentrated NH3.H2O made the solution becoming white precipitate, and it could lead to the reaction. After the filtering, washing and heating, here is the decomposition of H2TiO3.
Conclusions
In conclusion, we report that titania nanocrystals in anatase phase have been synthesized from hydrolysis of TiCl4 with sulfuric acid solution. The presence of a certain amount of H2SO4 promotes occurrence of anatase phase and inhibits the anatase-rutile transformation even at 600°C. After the powders calcinated at 600°C for 2 hours, some samples became completely anatase. Both the calcinations temperature and hydrolysis temperature have important effects on the primary particle size. The compositions of samples are pure anatase, without other elements. A new methodology is reported for preparing uniformly sized nanocrystals of the pure anatase phase that have a well-controlled particle size at controlled temperatures and compositions. The new process should have great potential in preparation of large amount of pure antase nanocrystals.
TiO2 Nanoparticles Features & Application:
Nano TiO2 is excellent photo catalyst used in antiseptic which can not only inhibit reproduction ability of bacterium, but also decompose its structure of cell membrane which will degrade microorganisms completely and thus avoid a second time pollution caused by creatoxin. Titanium Oxide Nanoparticle is a non-dissolved material which does not dissolve itself when degrades organic contaminant and kills germs. It has a lasting effect on killing germs and degrading organic contaminants. TiO2 Nanoparticle is widely used as UV-resistant material and in the field of producing chemical fiber, plastics, printing ink, coating, self-cleaning glass, self-cleaning ceramics, antibacterial material, air purification, sewage treatment, chemical industry,cosmetics, sunscreen cream, natural white moisture protection cream, beauty and whitening cream, morning and night cream, moistening refresher, vanishing cream, skin protecting cream, face washing milk, skin milk, powder make-up, foods packing material, coating for paper-making industry: used for improving the impressionability and opacity of the paper and used for producing titanium, ferrotitanium alloy, carbide alloy etc in the metallurgical industry, astronautics industry, conducting material, gas sensor, and moisture sensor.
Abstract
A new methodology was developed to synthesize uniform titania anatase nanocrystals by the hydrolysis of titanium chloride in sulfuric acid aqueous solutions at 0–90°C. The samples were characterized by Raman spectroscopy, UV-visible spectroscopy, transmission electron microscopy (TEM), electron diffraction (ED), and an Energy dispersive X-ray spectroscopy (EDS). The effects of the reaction temperature, mole ratio of SO42− to Ti4+, and the calcinations temperature on the particle size and crystal phase were investigated. Depending on the acidity, the hydrolysis temperature, and the calcination temperature, rhombic anatase nanocrystals sizes in the range of 10 nm to 50 nm were obtained. In the additive of sulfuric acid, Raman spectra and electron diffraction confirmed that the nanoparticles are composed of anatase TiO2. No other titania phases, such as rutile or brookite, were detected.
Introduction
It is well known that TiO2 occurs in nature in three distinct crystallographic phases: anatase, rutile, and brookite. While anatase TiO2 are the most widely used photocatalysts for oxidative decomposition of organic compounds, and an excellent photocatalyst for photodecomposition and solar-energy conversion due to its high photoactivity.It has the advantages of both cheapness and nontoxicity, in addition to its excellent functionality and long-term stability. The configurations of titanium oxide researched and reported have mainly been powders or films based on materials.A notable problem connected with these traditional preparations is that the growth of TiO2 nanocrystallites take a long time. Therefore it is highly desirable to find some new ways that are capable of overcoming the above problems to prepare crystal structure TiO2. Many attempts have been made in this field over the past few years.At the same time, recent photocatalytic studies have demonstrated that the photoactivity of anatase nanoparticles is strongly particle size dependent.The applications for TiO2 are also strongly dependent on the crystalline structure and morphology.Thus, it is very important to develop synthetic methods in which the crystalline form. It is also important that the TiO2 sizes and shapes be controlled.Anatase nanoparticles have been synthesized primarily by solution chemistries involving titanium sulfates and organic titanium.These methods have shortcomings since chemical impurities or minor accessory phases are always present in the final products. In the case of organic hydrolytic reactions, TiO2 nanoparticles obtained are crystallized primarily in the anatase phase but a minor phase of brookite couldn't be eliminated by tuning the reaction conditions.The presence of trace amounts of brookite might have side effects on the application of anatase nanoparticles in photocatalytic reactions and many other chemical processes. Hydrolysis of TiCl4 has extensively been reported for the synthesis of anatase nanocrystals, however, the preparation of titania anatase nanocrystals directly in sulfuric acid solution is seldom reported.
In this study, the preparation of titania anatase nanocrystals by hydrolysis of TiCl4 with diluted sulfuric acid solution was studied. With the precisely control of reaction parameters, we could get titania anatase nanocrystals and achieve high phase purity anatase. To the best of our knowledge, such works have not yet been reported. The effects of the reaction temperature, sulfuric acid concentration, and the calcination temperature on the particle size and crystal phase were investigated.
Materials and Methods
1). Materials
All chemicals were obtained commercially and used without further purification. Titanium chloride (TiCl4, 99.90%) and Concentrated Sulfuric acid (98%) were obtained from Fisher. Concentrated NH3.H2O was purchased from Sigma-Aldrich. All chemicals, unless specified, were of reagent grade. Deionized (DI) water, with a resistivity greater than 18.0 MΩ·cm (Millipore Milli-Q system), was used in preparing the aqueous solutions. All glassware used in the experiments was washed with freshly prepared aqua regia and rinsed thoroughly in tap water first and then DI water before using.
2). Preparation of TiO2 anatase nanocrystals
In the procedure, TiCl4 was used as a main starting material. The detail process is shown in Figure 1. In brief, 1ml TiCl4 was slowly added to different amounts of diluted sulfuric acid (10%) solution at 0°C in an ice-water bath with vigorously stirring. During the mixing process, white fume, presumably HCl, was released as a consequence of the hydrolysis of TiCl4 with water. After about half an hour, a grey solution was formed with continuous stirring. Then when the solution was heated to above 60°C, it became clear solution. And then the solution was kept at room temperature or heated at different temperatures for one hour. Later, concentrated NH3.H2O was added drop by drop to the solution until the pH value reached about 7. During the process of adding concentrated NH3.H2O, the color of solution changed to white. At last, the white solution was cooled to room temperature and gelled 12 hours. The hydrous TiO2 powders were filtered out and washed with DI water until there was no white sediment with 0.1 M AgNO3 solution, and then dried at room temperature in a vacuum oven. In some cases, the dried TiO2 powders were calcinated at 400°C and 600°C for two hours separately, both producing an off-white powders.
Process of TiO2 anatase nanocrystals preparation.
3). Raman spectroscopy
Raman spectrometer was used for crystal phase identification. Raman spectroscopy is a form of vibrational spectroscopy, much like infrared (IR) spectroscopy. It exhibits high specificity and is compatible with aqueous and solid systems. No special preparation of the sample is needed, and the timescale of the experiment is short. Raman spectrum analysis was conducted using a Raman System's R-3000 spectrometer with a solid-state diode laser operating at 532 nm. The Raman system's incident power is 25 mW, which has a wavelength range of ∼200–4000 cm−1.
4). Extinction spectra
The extinction spectra were recorded on a Shimadzu UV-2101 Spectrophotometer (Shimadzu Corporation Japan) using a 1-cm path length quartz cuvette at room temperature and the spectra were recorded in the range 200–800 nm.
5). TEM and ED measurements
A drop of well-sonicated solution containing the nanoparticles was deposited onto a 400 mesh Cu grids with supporting carbon film. (Electron Microscopy Sciences, PA). The samples were allowed to dry at room temperature overnight. A JEOL 100CX electron microscope operated at 100 KV was used to obtain the TEM images and ED spectra.
6). Energy dispersive X-ray spectroscopy (EDS)
EDS is an analytical technique used for the elemental analysis or chemical characterization of a sample. The chemical compositions of the ultrafine nanoparticles were determined by using a JEOL 5400LV equipped with Sigma Microanalyzer Level LPX1 Energy Dispersive X-ray Spectrometer (EDS).
Results
When TiCl4 hydrolyses in diluted sulfuric acid solution, because of the presence of a certain amount of hydrogen ions, the reaction rate may be slower than in pure water.
Then the adding of concentrated NH3.H2O made the solution becoming white precipitate, and it could lead to the reaction. After the filtering, washing and heating, here is the decomposition of H2TiO3.
Conclusions
In conclusion, we report that titania nanocrystals in anatase phase have been synthesized from hydrolysis of TiCl4 with sulfuric acid solution. The presence of a certain amount of H2SO4 promotes occurrence of anatase phase and inhibits the anatase-rutile transformation even at 600°C. After the powders calcinated at 600°C for 2 hours, some samples became completely anatase. Both the calcinations temperature and hydrolysis temperature have important effects on the primary particle size. The compositions of samples are pure anatase, without other elements. A new methodology is reported for preparing uniformly sized nanocrystals of the pure anatase phase that have a well-controlled particle size at controlled temperatures and compositions. The new process should have great potential in preparation of large amount of pure antase nanocrystals.
TiO2 Nanoparticles Features & Application:
Nano TiO2 is excellent photo catalyst used in antiseptic which can not only inhibit reproduction ability of bacterium, but also decompose its structure of cell membrane which will degrade microorganisms completely and thus avoid a second time pollution caused by creatoxin. Titanium Oxide Nanoparticle is a non-dissolved material which does not dissolve itself when degrades organic contaminant and kills germs. It has a lasting effect on killing germs and degrading organic contaminants. TiO2 Nanoparticle is widely used as UV-resistant material and in the field of producing chemical fiber, plastics, printing ink, coating, self-cleaning glass, self-cleaning ceramics, antibacterial material, air purification, sewage treatment, chemical industry,cosmetics, sunscreen cream, natural white moisture protection cream, beauty and whitening cream, morning and night cream, moistening refresher, vanishing cream, skin protecting cream, face washing milk, skin milk, powder make-up, foods packing material, coating for paper-making industry: used for improving the impressionability and opacity of the paper and used for producing titanium, ferrotitanium alloy, carbide alloy etc in the metallurgical industry, astronautics industry, conducting material, gas sensor, and moisture sensor.