Method of controlling nano titanium dioxide crystal form and obtained nano titanium dioxide using said method

Method for controlling crystal form of nano titanium dioxide and nano titanium dioxide obtained thereby

FIELD OF THE INVENTION The present invention relates to a method for controlling the crystal form of nanometer titania, more specifically, the present invention relates to a method for controlling the crystal form of nanometer titania through oxygen vacancy catalytic phase transformation. The invention also relates to nano titanium dioxide of different crystal types obtainable by the above-mentioned method.

Titanium dioxide can be divided into rutile-type titanium dioxide, anatase-type titanium dioxide and brookite-type titanium dioxide according to the different lattice structure. Their crystal structure is different, and their properties are also different. Among them, brookite-type titanium dioxide is very unstable, and it is rarely prepared and used due to lack of application performance. Anatase nano-titanium dioxide has a good photocatalytic function and is therefore widely used in fields such as environmental purification, food packaging, household appliances, textile fibers, and building materials. Rutile nano-titanium dioxide is widely used in photosensitive and gas-sensitive components, weather-resistant and aging-resistant materials, reinforced and toughened materials, automotive topcoats, cosmetics, cultural relic coatings and other fields. Especially rutile nano-titanium dioxide has excellent chemical stability, thermal stability, optical effect, photosensitivity effect, photoelectric effect and other properties, which is the most precious and valuable functional material. However, it is difficult to prepare rutile nano-titanium dioxide. When the rutile phase transformation is completed, the grain size is difficult to control within the nanometer scale. At present, there is a technology for preparing rutile nano-titanium dioxide by using expensive butyl titanate in China. The ratio of rutile-type crystals obtained is not high enough, and the grain size distribution is also wide. A considerable proportion of titanium dioxide grains exceed 100nm in size. However, using titanium tetrachloride as a raw material, it is easy to prepare micron and sub-micron rutile titanium dioxide, and it is difficult to control the nanometer particle size.

Therefore, an object of the present invention is to provide a method for controlling the crystal form of nanometer titanium dioxide, which can produce the desired crystal form of nanometer titanium dioxide by using compounds with oxidizing and/or reducing properties, alone or in combination, and The grain size is controlled within 100nm.

Another object of the present invention is to provide nano titanium dioxide with a weight ratio of anatase crystal form to a rutile crystal form of 0:100-100:0 and a crystal grain size within 100 nm.

One aspect of the present invention provides a method for controlling the crystal form of nano-titanium dioxide. The method includes the following steps: 1) hydrolysis reaction: hydrolyzing the titanium tetrachloride raw material to obtain a mixed liquid containing white precipitate; 2) sol-gel reaction: Add compounds with oxidizing and/or reducing properties to the mixed liquid obtained in step 1) alone or in combination to dissolve the white precipitate to form a uniform reaction solution, and then heat at a temperature of 50-150°C to slowly evaporate the liquid to form Sol-gel; 3) Filtration and washing: filter and repeatedly wash the product obtained in step 2) with water until the pH is 6-8; 4) dry: the product obtained in step 3) is heated at a temperature of -30°C to 30°C and 5- Drying under a vacuum of 15 mmHg to obtain a metastable titanium dioxide precursor of self-formed particle system; and 5) high-temperature calcination: the precursor obtained in step 4) is calcined at a temperature of 200-1000° C. for 0.5-6 hours.

Another aspect of the present invention provides nano titanium dioxide obtainable by the method of the present invention, the grain size of which is within 100 nm and the weight ratio of anatase crystal form to rutile crystal form is 0:100-100:0.

These and other objects, features and advantages of the present invention will become more clear after reading the entire specification in conjunction with the accompanying drawings.

Detailed Description of the Invention In the method for controlling the crystal form of nano-titanium dioxide of the present invention, step 1) involves the hydrolysis of the raw material titanium tetrachloride. The raw material used in this step can be technical grade titanium tetrachloride or reagent-pure titanium tetrachloride. From a cost point of view, technical grade titanium tetrachloride is preferred. The concentration of titanium tetrachloride is not particularly limited, but the molar concentration is preferably controlled within the range of 0.01-30 mol/l, preferably 0.05-10 mol/l, and more preferably 0.09-5 mol/l. The hydrolysis reaction of step 1) can be carried out at any pH value, for example, the pH value can be about 0-11, preferably 0-8, more preferably 0-5, and most preferably 1-3. It is preferable to use an alkali in the hydrolysis step to perform a certain degree of neutralization, wherein the alkali that can be used includes, for example, ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), potassium hydroxide (KOH), etc., preferably ammonium hydroxide. There is also no limitation on the amount of the base, for example, the amount may be 0.1-10 moles per mole of titanium tetrachloride, preferably 0.5-5 moles, more preferably 1-3 moles. The temperature at which the hydrolysis reaction is carried out is not particularly limited, and it can be carried out at room temperature (about 30°C) or low temperature, but it is preferably carried out at room temperature. Since the hydrolysis reaction of titanium tetrachloride exotherms violently, it is necessary to use conventional cooling methods such as liquid nitrogen cooling, chilled water bath, etc. for cooling. After the hydrolysis reaction is completed, a mixed liquid containing white precipitate is obtained.

In the method for controlling the crystal form of nano titanium dioxide of the present invention, step 2) involves the formation of sol-gel. Specifically, a compound with oxidizing properties and/or reducing properties is added to the hydrolysate obtained in step 1) individually or in combination at a temperature of 10-180°C, preferably 30-100°C, and the white precipitate is dissolved to form a uniform reaction Then, the reaction solution is heated at a temperature of 50-150°C, preferably 70-100°C for 1-10 hours to slowly evaporate the liquid to form a sol-gel. The oxidizing and/or reducing compound used in this step includes, for example, hydrochloric acid, ammonium sulfide, sulfuric acid, nitric acid, perchloric acid, and the like. The amount of the oxidizing and/or reducing compound used in this step is 0-01-5 moles per mole of titanium tetrachloride, preferably 0.05-3 moles, more preferably 0.1-2 moles. The treatment with oxidizing and/or reducing compounds in step 2) is very important to the method for controlling the crystal form of nanometer titanium dioxide of the present invention. For example, in order to obtain 100% anatase nano titanium dioxide, compounds with strong oxidizing properties such as nitric acid and perchloric acid must be used; in order to obtain 100% rutile nano titanium dioxide, compounds with strong reducing properties such as ammonium sulfide or Hydrochloric acid; in order to obtain 50% anatase/50% rutile nano titanium dioxide, a compound with both redox properties such as sulfuric acid should be used; and in order to obtain other anatase/rutile nano titanium dioxide, the above oxidation can be adjusted The amount of sexual and/or reducing compounds. The terms "oxidation performance" and "reduction performance" as used herein are a relative concept, that is, when the element oxidation number of the compound used is the smallest, it is easy to lose electrons and is defined as a reducing agent; and when the element oxidation number of the compound used is the largest, It is easy to get electrons and is defined as an oxidant.

In the method for controlling the crystal form of nano titanium dioxide of the present invention, step 3) involves filtration and water washing of the sol-gel obtained in step 2). The purpose of washing is to remove acid radicals and other impurities. Washing should be repeated until the pH of the sol-gel is about 6-8, preferably 6.5-7.5.

In the method for controlling the crystal form of nano titanium dioxide of the present invention, step 4) involves drying the washed sol-gel obtained in step 3). This step is preferably carried out as follows: the washed sol-gel is dried at a temperature of -30°C to 30°C and a vacuum degree of 5-15 mmHg for 3-6 hours, thereby removing the water and possible solvents in the sol to obtain Metastable titanium dioxide precursor of self-contained particulate system.

In the method for controlling the crystal form of nanometer titanium dioxide of the present invention, step 5) involves high-temperature calcination of the metastable titanium dioxide precursor obtained in step 4). This step is preferably carried out at a temperature of 200-1000°C, more preferably 500-980°C, in a calcination device commonly used in the art. There is no restriction on the calcination atmosphere. The calcination can be performed in an oxygen or oxygen-containing air atmosphere, or in the presence of an inert gas such as nitrogen, helium, and argon. Although calcination in an oxygen atmosphere is the most ideal, considering production safety, production cost, and production satisfaction, the calcination step is performed in an air atmosphere. The calcination time can be 0.5-6 hours.

The wording "metastable state" used in the terms "metastable chlorination method" and "metastable titanium dioxide precursor" in the present invention means that during the sol-gel preparation process of the method of the present invention, the gel is not homogeneous It is formed in a non-equilibrium and unstable system of phases. After filtration, washing, and vacuum drying, a metastable titanium dioxide precursor that is thermodynamically unstable and self-contained in a particulate system is formed. The phase transition temperature of the precursor from anatase type to rutile type is less than 1000°C, which is significantly lower than the phase transition temperature of conventional stable titanium dioxide (the rutile phase transition temperature range of conventional stable titanium dioxide is about 1100-1400°C) , This is the physical characteristics of metastable state. In addition, the X-ray diffraction spectrum exhibits a phenomenon of broadening of diffraction peaks, a large proportion of surface atoms, and rich surface unsaturated bonds, etc., which all indicate that the nano titanium dioxide precursor of the present invention is a metastable substance. Therefore, the term "metastable chlorination" is used in this specification to distinguish it from conventional chlorination.

Although not wishing to be bound by any theory, the inventor believes that the method for controlling the crystal form of nanometer titanium dioxide of the present invention can be explained as follows. When the titanium dioxide precursor is treated with a compound having oxidizing properties and/or reducing properties, oxygen saturation or oxygen vacancies are formed in the titanium dioxide precursor, respectively. The higher the degree of oxygen saturation in the crystal, the less oxygen vacancies are formed, the easier it is to stabilize the anatase type; if the oxygen is depleted in the crystal, the corresponding oxygen vacancies are more, and it is easy to promote the rutile phase transition. Specifically, when a strong oxidizing compound is used for treatment, the oxygen in the titanium dioxide crystal is enriched, and it is not easy to cause oxygen vacancies. During calcination, the corresponding ion diffusion, orientation and positioning of titanium ions and lattice transformation are difficult, and it is sharp in a wide temperature range. The titanium ore type exists stably; when there is no phase change, the grain size grows slowly with the increase of temperature, and the grain size can be kept small. When a strong reducing compound is used for processing, the oxygen in the titanium dioxide crystal is depleted, which is easy to cause oxygen vacancies. The corresponding ion diffusion, titanium ion orientation and lattice transformation are easier, and the anatase type orientation is completed in a narrow temperature range. Rutile phase transition; during phase transition, although the grain size grows faster with temperature increase, the phase transition temperature range can be controlled within a limited range by treatment with reducing compounds, so that the grain growth can be controlled.

By using the nano-titanium dioxide crystal type control method of the present invention, it is possible to obtain nano-titanium dioxide with a completely controllable crystal type according to the needs, and overcomes the large growth of the crystal grain size of the titanium dioxide when the phase transition temperature spans a large range, which is difficult to meet the nanometer The question of scale.

Table 1: X-ray diffraction peak results of nano titanium dioxide obtained in Example 1 Peak number 2θ intensity width d I/I01 13.000 518 *** 6.8045 132 25.380 3870 0.840 3.5065 1003 37.960 1182 0.660 2.3684 314 38.140 1019 0.300 2.3576 265 47.920 1065 0.330 1.8968 286 48.180 1280 0.330 1.8871 337 48.440 1069 0.360 1.8776 288 54.100 1086 0.360 1.6938 289 55.280 915 0.330 1.6604 2410 62.020 485 0.330 1.4951 1311 62.440 690 0.300 1.4861 1812 62.960 710 0.300 1.4751 1813 68.580 432 0.330 1.3672 1114 70.200 451 0.330 1.3396 1215 70.500 386 0.300 1.3346 1016 70.940 353 0.300 1.3274 917 74.960 553 0.300 1.2659 1418 75.460 392 0.5392 1419. *** 1.1625 1020 94.540 299 *** 1.0486 8

Table 2: X-ray diffraction peak results of nano titanium dioxide obtained in Example 2 Peak number 2θ intensity width d I/I01 13.600 421 0.300 6.5056 102 13.880 433 0.240 6.3750 113 27.540 4059 0.600 3.2362 1004 36.220 1987 0.540 2.478 1495 39.440 291 0.570 2.2828 76 41.420 1080 0.690 2.1782 277 44.200 385 0.780 2.0474 98 54.520 2253 0.780 1.6817 569 56.840 711 0.720 1.6185 1810 62.980 484 0.390 1.4746 1211 63.960 269 0.330 1.4544 712 64.260 326 0.390 1.4483 813 69.220 699 0.780 1.3561 1714 69.940 532 0.450 1.3439 1315 76.700 146 *** 1.2414 416 82.500 180 0.750 1.1682 *** 417 1.1469 84.380 117 318 89.620 243 0.360 1.0929 619 89.860 267 0.360 1.0907 720 90.500 194 0.270 1.0846 521 90.820 200 0.240 1.0816 522 91.100 177 0.300 1.0790 423 95.020 187 0.270 1.0446 524 95.520 268 0.660 1.0404 725 95.920 257 0.270 1.0371 626 96.259 245 0.330 1.0344 429 264 0.3428 161 0.240 1.0 264 0.328 106.380 106 *** 0.9621 3

Table 3: X-ray diffraction peak results of nano titanium dioxide obtained in Example 3 Peak number 2θ intensity width DI/I01 10.860 547 0.390 8.14016 142 17.100 504 0.300 5.18119 133 17.760 493 0.360 4.99010 134 19.080 519 0.510 4.64775 145 25.220 3776 0.750 3.52841 1006 25.440 3186 0.330 3.49839 847 27.360 1388 0.600 3.25710 378 36.000 932 0.450 2.49274 259 37.400 948 0.300 2.40259 2510 37.640 1173 0.720 2.38782 3111 41.160 484 0.570 2.19137 1312 46.840 334 0.300 1.93802 913 47.880 1270 0.360 1.89832 3414 48.100 1126 0.390 1.89015 3015 52.400 328 0.420 1.74471 916 53.100 500 1.6967340 1.72335 1317 54.65 1.68692 3419 54.960 950 0.450 1.66934 2520 56.320 441 0.330 1.63221 1221 62.040 560 0.300 1.49475 1522 62.560 765 0.360 1.48357 2023 68.740 556 0.420 1.36449 1524 69.940 453 0.300 1.34398 1225 74.260 280 0.327 75.595 101.25 389 363 0.360 1.17084 1029 94.240 276 0.330 1.05120 730 96.200 256 0.360 1.03492 731 107.480 265 0.300 0.95530 7

Table 4: X-ray diffraction peak results of the nano titanium dioxide obtained in Example 4 Peak number 2θ intensity width DI/I01 11.800 262 0.660 7.49373 112 12.800 353 0.900 6.91045 153 17.000 262 0.600 5.21144 114 18.960 249 1.020 4.67689 105 20.320 231 0.660 4.36684 106 21.960 190 1.200 4.04428 87 25.280 2431 0.780 3.52017 1008 27.440 1816 1.020 3.24778 759 30.600 170 1.020 2.91921 710 31.640 181 0.660 2.82559 711 36.080 1179 0.780 2.48740 4812 37.760 626 0.780 2.38050 2613 38.520 327 0.600 2.33527 1314 39.040 234 0.600 2.30535 1015 41.240 651 0.840 2.18731 2716 43.960 261 0.780 2.05807 1117 1.890. 1.62691 2020 62.720 660 0.840 1.48017 2721 64.200 256 0.660 1.44957 1122 68.840 598 0.960 1.36275 2523 69.800 463 0.600 1.34634 1924 70.160 380 0.600 1.34031 1625 75.040 305 0.900 1.26478 1326 76.040 189 0.780 1.25062 827 82.400 216 1.20 1.16342 1.0924 1.0924 1.0924 1.16342 830 90.240 161 0.600 1.08709 731 95.400 248 0.780 1.04147 10

Table 5: X-ray diffraction peak results of nano titanium dioxide obtained in Example 5 Peak number 2θ Intensity width d I/I01 12.560 274 *** 7.0419 92 13.720 296 *** 6.4490 103 25.360 1184 0.840 3.5092 394 27.520 3030 0.840 3.2385 1005 36.160 1745 0.720 2.4820 586 37.880 340 0.780 2.3732 117 39.160 267 1.380 2.2985 98 41.320 879 0.780 2.1832 299 44.120 328 0.780 2.0509 1110 48.120 376 0.780 1.8894 1211 54.360 2016 0.960 1.6863 6712 56.640 613 0.840 1.6237 2013 62.840 533 0.780 1.4776 1814 64.120 308 0.900 1.4511 1015 69.120 638 0.840 1.3579 2116 69.800 530 0.720 1.3463 1717 75.160 166 1.140 1.2630 82 0.6520 76.560 145. 1.1680 720 89.439 195 0.480 1.0947 621 89.800 247 0.660 1.0912 822 95.360 266 0.600 1.0417 923 95.880 273 0.720 1.0375 9