Preparation And Characterizations Of Amorphous TiO₂ Nanoparticles

TiO2 is a semiconductor material with applications in many fields such as photocatalysis, cosmetics, solar cells, chemical sensors, and anode materials for lithium ion batteries. Compared with crystalline TiO2, amorphous TiO2 exhibits novel properties due to the lack of long range order in atomic structure and the meta-stability in thermodynamics and find potential applications as electrodes in solar batteries, in semiconductors and in nanoglasses. First of all, amorphous TiO2 nanoparticles are synthesized using titanium alkoxide [tetrabutyl titanate(TBOT) and titanium tetraisopropoxide(TTIP)] as starting materials via a facile sol-gel method and subsequent calcination. The influence of acetic acid serving as pH regulator and the surfactants on the morphology, size, phase transformation and agglomeration degree was investigated. Then Ti O2 particles are synthesized using inorganic titanium salt as starting material via precipitator method, and the samples synthesized were characterized by XRD, TG-DTA, FTIR and TEM. And then the photocatalytic properties of amorphous TiO2 nanoparticles were studied. The influence of the particle size and structure on the photocatalytic properties of TiO2 was investigated. At last, the effect of water and ethanol washing on the structure of TiO2 particles was studied, and the mechanism was investigated. The effect of water and ethanol washing on structure drawn from TiO2 also works well on ZrO2, FeO(OH) and Al(OH)3. Therefore, water and ethanol washing may be a common method to control the structure of metal oxide or hydroxide particles at low temperature.In this work, dispersed equiaxed amorphous TiO2 nanoparticles were synthesized via hydrolysis of titanium alkoxides TBOT and TTIP and calcination. Polyethylene glycol(PEG) was used as surfactant to improve the dispersity of nanoparticles. To control the particle size, acetic acid was used as the pH regulator. When acetic acid was added to the solution of TBOT, the pH value of the mixed solution decreased from 6.0 to 3.8 and the average particle size of amorphous TiO2 nanoparticles obtained from TBOT decreased from 52 to 38 nm. By replacing TBOT as the titanium alkoxide starting material with TTIP and adding acetic acid as the pH regulator, the average particle size of amorphous TiO2 nanoparticles was decreased to 21 nm. Consequently, dispersed equiaxed amorphous TiO2 nanoparticles with controllable average sizes ranging from 21 to 52 nm can be synthesized.Using TiCl4 as the starting material, 3 mol/L as the precipitant, amorphous TiO2 nanoparticles were synthesized by direct precipitation method. The XRD and DTA results show that the samples synthesized should be calcined at 300?C for 2 h, the FTIR result indicates that the samples are pure, the TEM images show that the amorphous TiO2 nanoparticles are dispersed and small in particle size, using the BET surface area measurement method, the average particle size of the precursor synthesized is 3.57 nm, and the average particle size of the sample after calcination is 3.64 nm. Using the homogeneous precipitation method to synthesize TiO2. The influence of titanium sources and precipitants on the morphology was investigated. The morphology of the samples synthesized from TiCl4 and TBOT are disorderly, while the morphology of the samples synthesized from Ti(SO4)2 are equiaxed. And the particle sizes of the samples synthesize changed greatly with using different precipitants.The photocatalytic properties of TiO2 nanoparticles were studied. The influence of the particle size and structure on the photocatalytic properties of TiO2 was investigated. First of all, the samples with average particle sizes of 52, 38, 21 and 3.64 nm were chosen to take photocatalytic experiments. The UV-vis results show that the bandgap energy decreases with the decrease of particle size. The UV decomposition of methyl orange results show that the catalytic properties of the samples increased with the decrease of particle size. The sample with the average particle size of 3.64 nm can keep 85% of the decomposition efficiency after 5 cycles. Then the influence of the structure on the photocatalytic properties of TiO2 was studied. The UV-vis results show that amorphous TiO2 has a high visible light absorption rate as well as a lower bandgap energy. The decomposition of methyl orange results show that crystalline TiO2 has a higher catalytic properties under UV light, whereas amorphous TiO2 has a higher catalytic properties under visible light.Water and ethanol washing is found to affect the structure of TiO2 particles. The water-washed TiO2 particles are crystalline whereas the ethanol-washed TiO2 particles are amorphous even after calcination at 320?C. This may be due to an cover layer(Ti(RCH2O)2xO2-x) covering the TiO2 particles which is oxidised to Ti(RCOO)2xO2-x upon calcination. Both these two types of organic cover layers may prevent the crystallisation of the TiO2 particles and stabilize the amorphous structure of the TiO2 particles. So the structure of TiO2 particles, amorphous or crystalline(anatase), can be easily controlled by washing medium, water or ethanol. The effect of water and ethanol washing on(crystalline or amorphous) structure drawn from TiO2 also works well on ZrO2, FeO(OH) and Al(OH)3. Water and ethanol washing may be a useful simple method to control the(crystalline or amorphous) structure of metal oxide and hydroxide particles at low temperature.