Method for the production of new nanomaterials
10960385 ยท 2021-03-30
Assignee
- Commissariat A L'energie Atomique Et Aux Energies Alternatives (Paris, FR)
- UNIVERSITE DE CERGY PONTOISE (Cergy Pontoise, FR)
Inventors
Cpc classification
B01J21/066
PERFORMING OPERATIONS; TRANSPORTING
C01G23/053
CHEMISTRY; METALLURGY
B01J21/063
PERFORMING OPERATIONS; TRANSPORTING
C01P2002/88
CHEMISTRY; METALLURGY
B01J37/0018
PERFORMING OPERATIONS; TRANSPORTING
International classification
C01G23/053
CHEMISTRY; METALLURGY
B01J37/00
PERFORMING OPERATIONS; TRANSPORTING
B01J35/00
PERFORMING OPERATIONS; TRANSPORTING
B01J21/06
PERFORMING OPERATIONS; TRANSPORTING
B01J37/03
PERFORMING OPERATIONS; TRANSPORTING
Abstract
A method for producing new nanomaterials, 80 to 100 mol % of which are composed of TiO.sub.2 and 0 to 20 mol % are composed of another metal or semi-metal oxide that has a specific surface of 100 to 300 m.sup.2.Math.g.sup.1 and 1 to 3 hydroxyl groups per nm.sup.2.
Claims
1. Method of preparing a nanomaterial containing 80 to 100 mole % of TiO.sub.2 and 0 to 20 mole % of another metal or semi-metal oxide chosen particularly from among SiO.sub.2, ZrO.sub.2, WO.sub.3, ZnO, Al.sub.2O.sub.3 and Fe.sub.2O.sub.3, with a specific surface area of between 100 and 300 m.sup.2.Math.g.sup.1 and from 1 to 3 hydroxyl groups per nm.sup.2, said method including the following steps: a) Synthesis of a material composed of 80 to 100 mole % of TiO.sub.2 and 0 to 20 mole % of another oxide starting from a titanium oxide precursor or a mix of a titanium oxide precursor and a precursor of another oxide, the synthesis being made in an aqueous medium with a pH between 0 and 1 and at a temperature varying from 40 to 95 C. in the presence of a non-ionic surfactant chosen from among ankenyl ethers of polyoxyethylene glycol and poloxamers; b) Elimination of the surfactant from the material synthesised in the previous step by the following steps: b1) Preparation of a metallised material by washing the material containing the surfactant with an aqueous solution of a bivalent metal salt and an aqueous solution of ammonia, b2) Recovery of firstly the metallised material and secondly a washing solution, b3) Treatment of the metallised material with an inorganic acid to remove the metal from the material, c) Recovery of firstly a nanomaterial with no surfactant and secondly a residual solution.
2. Method according to claim 1, in which the material synthesis step a) comprises the following steps: a1) preparing an acid aqueous solution of the non-ionic surfactant, a2) adding the titanium oxide precursor or the mixture of the titanium oxide precursor and the precursor of the other oxide to the acid aqueous solution of the non-ionic surfactant, and a precipitate then forms, a3) vigorously stiring the reaction medium so as to dissolve the precipitate formed in step a2) then polymerising the titanium oxide precursor or the mixture of the titanium oxide precursor and the precursor of the other oxide, a4) placing the reaction mixture from step a3) under static conditions for at least 24 h, and then a5) recovering firstly a material composed of 80 to 100 mole % TiO2 and 0 to 20 mole % of the other oxide, and secondly a residual solution.
3. Method according to claim 1, in which step b) is performed in situ.
4. Method according to claim 1, in which the bivalent metal salt is chosen from salts of copper (II), cobalt (II), nickel (II) and zinc (II).
5. Method according to claim 1, in which the other oxide is chosen from SiO.sub.2 and ZrO.sub.2.
6. Method according to claim 1, in which the nanomaterial is composed of 100 mole % of TiO.sub.2.
7. Nanomaterial obtainable by the method according to claim 1 composed of 80 to 100 mole % of TiO.sub.2 and 0 to 20 mole % of another metal or semi-metal oxide chosen from among SiO.sub.2, ZrO.sub.2, WO.sub.3, ZnO and Al.sub.2O.sub.3 and Fe.sub.2O.sub.3, particularly among SiO.sub.2 and ZrO.sub.2, with divalent metal cations adsorbed on the surface of the nanomaterial, surface acidity, coming from step b) of the method, nitrate ions, a specific surface area between 100 and 300 m.sup.2.Math.g.sup.1, from 1 to 3 hydroxyl groups per nm.sup.2, a pH equal to between 3 and 5 and having a rutile nanocrystalline structure when it composed of 100 mole % of TiO.sub.2.
8. Nanomaterial according to claim 7, characterised in that is composed of 80 to 95 mole % of TiO.sub.2 and 5 to 20 mole % of another metal or semi-metal oxide chosen from SiO.sub.2, ZrO.sub.2, WO.sub.3, ZnO and Al.sub.2O.sub.3 and Fe.sub.2O.sub.3, and particularly from SiO.sub.2 and ZrO.sub.2.
9. A method for the photocatalytic degradation of compounds, comprising bringing the nanomaterial according to claim 7 into contact with a solution containing the compounds and exposing the solution and nanomaterial to at least one of UV radiation and visible radiation thereby to degrade compounds adsorbed onto the surface of the nanomaterial.
10. The method according to claim 9, characterised in that the compounds are chosen from dyes, pharmaceutical active constituents, herbicides, pesticides, fungicides, hormones, saccharides, such as glucose, and/or hydrocarbons.
11. Nanomaterial according to claim 7, characterised in that the metal cations are chosen from Zn.sup.2+, Ni.sup.2+ or Cu.sup.2+.
Description
FIGURES
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EXAMPLES
(34) I. Preparation and Analysis of Nanomaterials
(35) Spectrometry analyses were made to identify the different significant bands of specific bonds using a Fourier Transform InfraRed (FTIR) Spectrometer (Shimadzu). In the following, this method is called FTIR spectrometry.
Example 1
Synthesis of Titanium Oxide Comprising a Surfactant
(36) At 50 C., 10 g of 37% v/v hydrochloric acid is mixed with 50 g of water. 1.6 g of Pluronic P123 surfactant is introduced while stirring vigorously. After two hours of stirring, 8.47 mL of titanium tetraisopropoxide (or titanium isopropoxide (TiPOT)) is added. Since this precursor is very reactive in an aqueous medium, precipitation takes place spontaneously. By vigorous stirring, the precipitate dissolves very quickly before the appearance of a new precipitation originating from the polymerisation between the three-dimensional structure derived from hydrolysis and polycondensation of the titanium oxide precursor and the micellar network. The reaction mix is then placed at 50 C. under static conditions for 24 h then at 90 C. for at least 24 h. The solution is then filtered. The solid obtained is rinsed several times with excess water and is dried at ambient temperature.
Example 2
Preparation of Nanomaterials Based on Surfactant-Free Titanium Oxide by Calcination
(37) The surfactant of the nanomaterial prepared according to example 1 was extracted using an extraction method based on calcination.
(38) According to this method, 1 g of the nanomaterial containing the surfactant was placed in a ceramic crucible deposited in a tubular furnace at a temperature of 550 C. for 10-15 minutes. The calcination lasted for 16 h. After 5 h of cooling to return to ambient temperature, the surfactant-free nanomaterial was recovered and weighed.
(39) The nanomaterial based on titanium oxide from which the surfactant was extracted according to this method is also called TiO.sub.2 C in the following.
Example 3
Preparation of Nanomaterials Based on Surfactant-Free Titanium Oxide According to the Invention
(40) The surfactant of the nanomaterial prepared according to example 1 was extracted in situ in the surfactant elimination step according to the invention.
(41) An aqueous solution of bivalent metal salt with a concentration of 0.05 mol/L was firstly prepared for this purpose. 200 ml of this solution was then added into a beaker. The pH of this solution was adjusted to the required value (10.5 for Cu.sup.2+ and Zn.sup.2+ and 11.5 pour Ni.sup.2+) by the addition of a 35% v/v solution of ammonia.
(42) Several aqueous solutions of different bivalent metal salts were tested: a solution of copper (II) nitrate trihydrate, nickel (II) nitrate and a solution of zinc (II) nitrate. An entire reaction medium (70.5 mL) was then added to each basic metal salt solution at the end of the synthesis of the nanomaterial containing the surfactant according to example 1, in other words before filtration, rinsing and drying, and the mixture was then stirred vigorously for 10 minutes at ambient temperature and then filtered. The solid obtained was rinsed with ultrapure excess water and dried at ambient temperature.
(43) In order to remove the metal previously grafted to the nanomaterial, and consequently in order to extract all of the surfactant remaining in the nanomaterial, chelated to metal ions, the metallised nanomaterial was immersed into a 60% v/v solution of nitric acid (100 mg of material for 5 mL of nitric acid solution). After 20 minutes of vigorous stirring, the reaction medium was centrifuged (5 minutes at 4500 rpm in a Hettich Universal 320 centrifuge). The nanomaterial obtained was washed with water then dried overnight in a drying oven at 50 C.
(44) Titanium dioxides from which the surfactants were extracted using this method are also referred to below as TiO.sub.2 L followed by the bivalent metal ion used, for example TiO.sub.2 L Zn.sup.2+ or TiO.sub.2 L Cu.sup.2+. The denomination TiO.sub.2 bis L Zn.sup.2+ is used for a second sample for which the synthesis according to examples 1 and 3 was repeated so as to demonstrate reproducibility of the method according to the invention.
Example 4
Preparation of Nanomaterials Based on Surfactant-Free Hybrid Titanium-Silicon Oxides According to the Invention
(45) This protocol is identical to that described for the TiO.sub.2 material. 1.6 g of Pluronic P123 is dissolved in a mixture of acid water (10 g of HCl (37% v/v) and 50 g of water) at 50 C. After 2 h of vigorous magnetic stirring, 15/85, 10/90 and 5/95 molar mixtures of TIPOT/TEOS are added. A precipitation takes place spontaneously but is dissolved very quickly. A new precipitation occurs after a few hours. The reaction mix is then placed still at 50 C. under static conditions for 24 h then at 90 C. for 24 h.
(46) Since the solid particles are so very fine, more than 70% of them pass through all filtration systems. Furthermore, these particles cannot be sedimented using a centrifuge. Thus, no solid containing the surfactant can be recovered, and therefore no calcination can be done. This very fine size of nanoparticles can be interpreted as a crystallinity index of the hybrid nanomaterials according to the invention.
(47) One solution to this problem s to agglomerate these particles by metallisation. To achieve this, the washing procedure must be used in situ after cooling the reaction medium from 90 C. to ambient temperature. A solution of a bivalent metal salt chosen from among copper(II) nitrate, nickel (II) nitrate and zinc (II) nitrate at 0.05 M and with a pH of between 10 and 12 is prepared.
(48) For each Ti/SiO hybrid material.sub.2 (85/15, 90/10 and 95/5), 150 mL of the metal salt solution at 0.05 M and with pH between 10 and 12 are introduced into a beaker. The reaction medium is incorporated. The pH of the solution then drops suddenly due to the presence of acid in the reaction medium. The addition of a few drops of ammonia raises the pH to the required value (10.5 for Cu.sup.2+ and Zn.sup.2+ and 11.5 for Ni.sup.2+).
(49) After 10 minutes of vigorous mechanical stirring, the materials obtained are filtered under a vacuum using a small pore frit, and then rinsed with water and dried. The presence of foam in the filtrate indicates that the surfactant has been eliminated. Since the particles are metallised and agglomerated to each other, none passes through the filtration system.
(50) The second washing step (demetallisation) is then done. Thus, for 1 g of solid (green with Cu.sup.2+, white with Zn.sup.2+ and light green with Ni.sup.2+), 50 mL of pure nitric acid is used for demetallisation. After 20-30 minutes of vigorous mechanical stirring, the reaction medium is separated equitably into two 50 mL tubes. These tubes are then placed in a centrifuge at 5000 rpm for 5 minutes (Hettich Universal 320 centrifuge). It will be seen that the solid has sedimented and that the solution has become clear. This solution is eliminated and replaced by the same volume of water. The tubes are stirred manually and then placed once again in the centrifuge at the same rotation speed and for the same time as before.
(51) This procedure is repeated until the centrifuged solution remains slightly cloudy, which means that particles of materials remain in suspension. At least 3 centrifuging operations are necessary for optimum rinsing.
(52) The solids obtained are dried.
(53) In the following, titanium-silicon hybrid dioxides according to the invention are also called x/y % TiO.sub.2 L Zn.sup.2+ followed by or x/y % TiO.sub.2 L where x/y is the molar ratio Ti/Si, for example 85/15% TiO.sub.2 L Zn.sup.2.
Example 5
Physiochemical Analyses of Nanomaterials
(54) The nanomaterials prepared according to examples 1 to 4 and from which the surfactant has been extracted using the method according to the invention using a copper (II) nitrate solution (see examples 3 and 4) or by calcination (see example 2), have been analysed in order to detect specific bonds present, and the specific surface area (A.sub.s).
(55) The different significant bands of specific bonds were determined by FTIR spectrometry.
(56) The specific surface area (A.sub.s) was determined by volumetric adsorption of nitrogen. The volumetric adsorption was measured with a Belsorp II Japan device. Before the measurements, the samples were degassed at 373K at 10 kPa for at least 20 h.
(57) The specific surface area was calculated using the Brunnauer-Emmet-Teller (BET) method.
(58) The volumetric adsorption isotherms of nitrogen, representing the adsorbed volume as a function of P/PO (pressure/saturating vapour pressure), are presented in
(59) TABLE-US-00001 TABLE 1 specific surface area Matrix (m.sup.2/g) TiO.sub.2 L 124 (Cu.sup.2+) TiO.sub.2 L 133 (Ni.sup.2+) TiO.sub.2 L 153 (Zn.sup.2+) TiO.sub.2 C 32 85/15% 207 Ti/SiO.sub.2 L 90/10% 195 Ti/SiO.sub.2 L 95/5% 249 Ti/SiO.sub.2 L
(60) Finally, the type of adsorption isotherm indicates that we are in the presence of isotherms characteristic of non-porous nanomaterials.
(61) Furthermore, the specific surface area and the number of hydroxyl groups per nm.sup.2 of the nanomaterial from which the surfactant was extracted by the method according to the invention are larger than those for the nanomaterial from which the surfactant was extracted by calcination (see
(62) Titanium oxide from which the surfactant was extracted using the method according to the invention (TiO.sub.2 L;
(63) The TEM images show a clear difference in the morphology that is in perfect agreement with the difference between the specific surface areas. Calcination at 550 C. agglomerates the crystals together to form larger crystalline assemblies reducing the specific surface area. The method according to the invention prevents assembly of crystals.
(64) The number of hydroxyl groups of the different nanomaterials was determined by thermogravimetric analysis (TGA), starting from the mass loss during heating. This analysis was made on a TA Q 50 device. The samples were heated up to 850 C. at a rate of 10 C./min. Two weeks before the TGA was used, the samples had been placed under the same humidity conditions. The graphs are presented in
(65) Concerning the thermogravitometric analysis, it is important to specify that the samples were placed under the same humidity conditions during 4 days before the analysis. This is done by placing each sample in a pillbox and each pillbox is placed in a large receptacle. A pillbox containing water is then added and the large receptacle is closed and put into a drying oven at 25 C.
(66) Thus, looking at the results, it is observed that the washing procedure increases the number of hydroxyl groups on the surface. The sudden slope change that occurs between 200 and 400 C. is another characteristic. It corroborates the results of FTIR spectrometry and demonstrates the presence of nitrate ions. Cabo et al. confirm this hypothesis by studying the decomposition of cobalt and/or nickel nitrate by GTA [10]. Thus, NOx compounds are released in gas form between 200 and 400 C.
(67) Considering that within this temperature range, it is very difficult to separate mass losses due to condensation of silanols and mass losses due to NOx releases, in the table the percentage of nitrogen from the elementary analyses was used as a reference value to more precisely determine the number of silanols.
(68) TABLE-US-00002 TABLE 2 T 85/15% 90/10% 95/5% TiO.sub.2 L TiO.sub.2 TiO.sub.2 L TiO.sub.2 L ( C.) Ti/SiO.sub.2 L Ti/SiO.sub.2 L Ti/SiO.sub.2 L 100% Cu 100% C 100% Ni 100% Zn Number of 400-700 1.3 1.4 1.1 1.6 0.6 2.5 1.7 hydroxyls/nm.sup.2
(69) Considering the different curves, the mass loss of the washed material is greater. At between 100 and 200 C. a loss of water is observed around the nanomaterials, at between 200 and 400 C. a loss of nitrogenated materials is observed, and starting at 400 C. a loss of water is observed due to condensation of OH groups.
(70) TABLE-US-00003 TABLE 3 Elementary analysis for 100% TiO2 nanomaterials Matrix % N % C TiO.sub.2 L 1.1 absence or trace (Cu.sup.2+) TiO.sub.2 L 0.6 absence or trace (Ni.sup.2+) TiO.sub.2 L 0.8 absence or trace (Zn.sup.2+) TiO.sub.2 C nc absence or trace 85/15 3.2 absence or trace Ti/SiO2 L (Zn.sup.2+) 90/10 1.8 absence or trace Ti/SiO2 L (Zn.sup.2+) 95/5 0.9 absence or trace Ti/SiO2 L (Zn.sup.2+)
Example 6
Analysis by Electronic Diffraction of Titanium Dioxide Crystals (TiO.SUB.2 .C and TiO.SUB.2 .L Cu.SUP.2+.)
(71) Titanium oxide crystals (TiO.sub.2 C and L Cu.sup.2+) were analysed by electronic diffraction to determine their crystalline structure. Several diffraction measurements were made. The results are summarised in Tables 4 and 5 below. Some measurements could be used for the study of all planes.
(72) TABLE-US-00004 TABLE 4 electronic diffraction of TiO2 C Perimeter Max. Distance between Diffraction Area (nm.sup.2) (nm) outside dia. planes TiO.sub.2 C-4 4170.29 228.92 73.456 3.223 TiO.sub.2 C-4 9332.36 342.45 109.569 2.160 TiO.sub.2 C-4 15222.70 437.37 139.812 1.693 TiO.sub.2 C-4 20094.79 502.51 160.549 1.474 TiO.sub.2 C-4 6968.68 295.92 94.808 2.497 TiO.sub.2 C-4 24808.38 558.35 178.335 1.327 TiO.sub.2 C-4 37532.60 686.77 219.205 1.080 TiO.sub.2 C-5 4238.37 230.78 74.049 3.197 TiO.sub.2 C-5 7323.71 303.37 97.189 2.436 TiO.sub.2 C-5 9536.34 346.18 110.759 2.137 TiO.sub.2 C-5 15877.37 446.68 142.772 1.658 TiO.sub.2 C-5 20543.82 508.10 162.314 1.458 TiO.sub.2 C-5 25307.03 563.93 180.130 1.314 TiO.sub.2 C-6 4238.37 230.78 74.049 3.197 TiO.sub.2 C-6 7234.12 301.51 96.585 2.451 TiO.sub.2 C-6 9434.08 344.31 110.185 2.148 TiO.sub.2 C-6 16009.95 448.54 143.387 1.651 TiO.sub.2 C-6 20393.59 506.23 161.725 1.464 TiO.sub.2 C-6 25140.26 562.07 179.510 1.319 TiO.sub.2 C-19 4170.29 228.92 73.456 3.223 TiO.sub.2 C-19 7234.12 301.51 96.585 2.451 TiO.sub.2 C-19 15877.37 446.68 142.772 1.658 TiO.sub.2 C-19 9846.45 351.76 112.531 2.104 TiO.sub.2 C-19 21303.23 517.40 165.288 1.432
(73) TABLE-US-00005 TABLE 5 electronic diffraction of TiO.sub.2 L TiO.sub.2 L-3 4102.76 227.06 72.894 3.247 TiO.sub.2 L-3 6794.47 292.20 93.593 2.529 TiO.sub.2 L-3 8832.06 333.15 106.632 2.220 TiO.sub.2 L-3 15352.53 439.23 140.388 1.686 TiO.sub.2 L-3 19650.72 496.93 158.793 1.491 TiO.sub.2 L-3 23988.33 549.04 175.376 1.350 TiO.sub.2 L-3 33382.16 647.68 206.747 1.145 TiO.sub.2 L-3 36723.30 679.32 216.822 1.092 TiO.sub.2 L-5 6881.29 294.06 94.166 2.514 TiO.sub.2 L-5 4170.29 228.92 73.456 3.223 TiO.sub.2 L-5 10161.51 357.34 114.368 2.070 TiO.sub.2 L-5 15613.85 442.96 141.613 1.672 TiO.sub.2 L-5 19357.43 493.21 157.590 1.502 TiO.sub.2 L-5 23664.17 545.32 174.165 1.359 TiO.sub.2 L-5 35724.07 670.02 213.881 1.107 TiO.sub.2 L-9 4102.76 227.06 72.894 3.247 TiO.sub.2 L-9 7145.09 299.65 95.975 2.466 TiO.sub.2 L-9 16009.95 448.54 143.387 1.651 TiO.sub.2 L-9 36522.35 677.46 216.261 1.095 TiO.sub.2 L-9 30383.10 617.90 197.309 1.200 TiO.sub.2 L-12 3969.34 223.34 71.694 3.302 TiO.sub.2 L-12 7056.61 297.79 95.362 2.482 TiO.sub.2 L-12 9130.59 338.73 108.372 2.184 TiO.sub.2 L-12 10267.64 359.20 114.932 2.060 TiO.sub.2 L-12 15482.91 441.09 141.004 1.679 TiO.sub.2 L-12 20393.59 506.23 161.725 1.464 TiO.sub.2 L-12 23825.97 547.18 174.770 1.354 TiO.sub.2 L-24 4170.29 228.92 73.456 3.223 TiO.sub.2 L-24 6881.29 294.06 94.166 2.514 TiO.sub.2 L-24 8832.06 333.15 106.632 2.220 TiO.sub.2 L-24 10161.51 357.34 114.368 2.070 TiO.sub.2 L-24 15352.53 439.23 140.388 1.686 TiO.sub.2 L-24 19066.35 489.48 156.381 1.514 TiO.sub.2 L-24 23664.17 545.32 174.165 1.359 TiO.sub.2 L-29 4307.01 232.64 74.625 3.172 TiO.sub.2 L-29 7056.61 297.79 95.362 2.482 TiO.sub.2 L-29 8832.06 333.15 106.632 2.220 TiO.sub.2 L-29 10267.64 359.20 114.932 2.060 TiO.sub.2 L-29 15352.53 439.23 140.388 1.686 TiO.sub.2 L-29 20694.60 509.96 162.898 1.453 TiO.sub.2 L-29 23342.21 541.60 173.013 1.368 TiO.sub.2 L-29 34934.61 662.57 211.487 1.119
(74) Having seen the results, it is demonstrated that the crystalline structure is not modified regardless of the surfactant elimination technique (calcination or washing).
(75) Comparing the charts [11], the structure of the synthesised titanium oxides is seen to be 100% rutile.
Example 7
Analyses of Nanomaterials by Scanning Microscopy
(76) The nanomaterials in Examples 2 to 4 were analysed by scanning microscopy (SEM-FEG JEOL 7100F).
(77) Scanning microscopy images show different aspects between 100% TiO.sub.2 L crystals (
(78) It is also observed that the specific surface area of 95% TiO.sub.2 is much larger than the other hybrids and the 100% TiO.sub.2.
Example 8
Photocatalysis of Different Dyes
(79) a) Experimental Protocol
(80) Photocatalysis experiments were undertaken with different organic compounds. The protocol is identical in all cases and takes place as follows. A dye concentration of 0.03 mmol.Math.L.sup.1 is prepared. For each sample, a concentration by mass of TiO.sub.2 materials or Ti/SiO.sub.2 hybrids equal to 1 mg/ml was used. After 15 minutes under ultrasounds for maximum particle dispersion, the samples were placed under radiation from a halogen spotlight (visible, 300 W).
(81) The solutions were tested with a UV Visible spectrophotometer.
(82) For a better comparison, standard samples (dyes alone) and samples with commercially available TiO.sub.2 are prepared. The latter, called Millenium PC50 or Degussa P25 TiO.sub.2 are composed of 99% anatase and 1% rutile, and 80% anatase and 20% rutile respectively.
(83) Unless mentioned otherwise, the 100% TiO.sub.2 material used in the photocatalysis experiments is that treated with Zn.sup.2+ ions in example 3. The hybrid materials used are those in example 4.
(84) b) Results and Discussion
(85) Rhodamine B (RhB)
(86) ##STR00001##
(87) The absorption spectra (after 5 h of radiation) show that the increase in the percentage of titanium oxide in nanomaterials according to the invention accelerates the rate of degradation (
(88) Methyl Orange (MO)
(89) In this case also, the absorption spectra (after 5 h of radiation) show that an increase in the fraction of titanium oxide accelerates the rate of degradation (
(90) Tests were carried out using UV radiation (.sub.max=365 nm, 12 W) for 5 h. These tests also demonstrated the superiority of 100% TiO.sub.2 materials according to the invention (
(91) Bromophenol Blue (BPB)
(92) ##STR00002##
(93) There is no longer any doubt about the hypothesis of the acidity of the washed matrix, the BPB solution changes from blue to green in contact with the material according to the invention. The powder becomes blue, which is synonymous with adsorption of dye molecules on the surface. At the same time, none of these phenomena are observed for the commercial sample.
(94) After radiation with a halogen lamp for 6 h, the absorbance of the different elements at 610 nm was measured. The results are summarised in Table 6 below.
(95) TABLE-US-00006 TABLE 6 Absorbance after 6 h Sample Absorbance BPB alone 1.917 TiO.sub.2 L Cu.sup.2+ 0.060 TiO.sub.2 L Ni.sup.2+ 0.030 TiO.sub.2 L (Zn.sup.2+) 0.012 TiO.sub.2 com (PC50) 0.220 TiO.sub.2 C 1.820
(96) Having seen the results in the table, it can be seen that calcination annihilates the photocatalysis, there is no doubt that this is due to the reduction in the specific surface area and the number of hydroxyl groups. The efficiency of the materials according to the invention compared with the commercial material is confirmed.
(97) Thus, two properties of the washed TiO.sub.2 material were observed: trapping of organic compounds by adsorption of organic compounds on the surface and then their destruction by photocatalysis.
(98) For the latter, an acceleration of photodegradation was also observed with Ni.sup.2+ ions and even more with Zn.sup.2+ ions in comparison with Cu.sup.2+ ions used in the first washing step. It can be seen that despite the change in the metal salt, discolouration of the BPB solution still occurs on contact with the materials.
(99) Carminic Acid
(100) ##STR00003##
(101) Photocatalysis tests with a halogen lamp were made for the following materials: TiO.sub.2 L Zn.sup.2+, 85/15% Ti/SiO.sub.2 L, 90/10% Ti/SiO.sub.2 L, 95/5% Ti/SiO.sub.2 L and PC50. A discolouration of each solution is observed after 1 h 10.
(102) The solutions were analysed with a UV-visible spectrophotometer after 5 h of radiation, in each case the absorbance is null, no peak is detected at the maximum wavelength of carminic acid (527 nm). The solution containing the 100% TiO.sub.2 material according to the invention has a higher absorbance curve than the dye alone due to the diffusion of TiO.sub.2 particles that passed through the filter-syringe, but no plateau is observed. The only difference between all the samples is in the colour of the powder after filtration: very coloured for the commercial material and becoming less coloured as the quantity of TiO.sub.2 is increased for samples according to the invention until being absent from the matrix containing 100% of titanium oxide. Therefore it would appear that photocatalysis is complete for the latter material.
(103) A discolouration of each solution is observed after 1 h 10.
(104) The solutions were analysed with a UV-visible spectrophotometer after 5 h of radiation (
(105) Therefore it would appear that photocatalysis is complete for the latter material.
(106) Fuchsin Acid
(107) ##STR00004##
(108) A discolouration was observed for the solutions containing materials according to the invention. It is much more visible for the sample containing 90% of TiO.sub.2. At t=6 h, all the solutions are completely discoloured, the only solution that had not changed is the solution containing the PC50 material.
(109) The solutions are analysed with the UV-visible spectrophotometer after 6 h of radiation (halogen lamp), and the spectra obtained confirm the trend (
(110) Direct Red 75:
(111) ##STR00005##
(112) All solutions were discoloured after 3 h. However, all materials according to the invention are better than PC50.
(113) The solutions are analysed with the UV-visible spectrophotometer after 3 h of radiation (halogen lamp). The observed spectra confirm the trend (
(114) Calcomine Orange
(115) ##STR00006##
(116) A discolouration was observed for the solutions containing materials according to the invention. However, the best results are obtained with TiO.sub.2 L Zn.sup.2+ in example 3.
(117) The solutions are analysed with the UV-visible spectrophotometer after 3 h30 of radiation (halogen lamp), and the spectra obtained confirm the trend (
(118) During exposure to radiation (halogen lamp), the solution of calcomine orange with TiO.sub.2 L Zn.sup.2+ is the first to become clear but the powder recovered after filtration and rinsing only has very slight colouring. All the powders are coloured for the other materials, which means that dye molecules are adsorbed on the surface. The 85/15% Ti/Si hybrid material demonstrates the higher adsorption capacity of all the hybrid materials. Strong sedimentation is observed in the pillbox making the solution clear. It would also appear that the commercial material does not degrade the molecules, but simply adsorbs them.
(119) In conclusion, the combined action of the synthesis method and the washing process produces a highly reactive type of crystalline rutile titanium oxide that can either destroy the polluting compounds, or adsorb them (possibly with rerelease).
Example 9
Other Organic Compounds
(120) Glyphosate:
(121) A few laboratory tests were carried out using TiO.sub.2 L Zn.sup.2+ from example 3 to trap a glyphosate solution in water with a concentration of 0.1 mg/mL (herbicide known throughout the world as Round-Up) without any radiation. These compounds are apparently adsorbed on the surface. In an aqueous solution, the TiO.sub.2 remain in suspension even during centrifuging. However, sedimentation of particles is observed in contact with organic compounds, showing that the particles are agglomerated or their weight is increased. The hypothesis is confirmed by the study of the FTIR spectrum (
(122) Ampicillin:
(123) In the same way, molecules of ampicillin (antibiotic in the penicillins family) at a concentration by mass in water equal to 0.1 mg/ml were destroyed by photocatalysis by the TiO.sub.2 L Zn.sup.2+ from example 3 (see HPLC results:
(124) Hydrocarbons:
(125) A test was carried out using TiO.sub.2 L Ni.sup.2+ from example 3 to degrade a solution composed of 50% (v/v) of hydrocarbons (octane/1,3,5 trimethylbenzene) and 50% (v/v) of salty sea water.
(126) In the same way as for glyphosate, it was observed that even if TiO.sub.2 L Ni.sup.2+ particles remain in suspension in the aqueous phase (milky appearance), a large quantity of particles settles at the interface between the aqueous phase and the organic phase after contact between the nanomaterial and the solution of hydrocarbons and sea water. Therefore hydrocarbon molecules are adsorbed at the surface of the nanomaterial. This was confirmed after filtration of the sample: 2.5 ml of hydrocarbons were thus trapped per 10 mg of nanomaterial.
(127) Glucose:
(128) For this experiment, the concentration of glucose is 0.5 mg/mL and the material concentration is identical 1 mg/mL (solvent: water).
(129) A range of glucose concentrations was prepared. These concentrations are determined by UV Visible spectrometry after the addition of 1 mL of Fehling's solution. When hot, in the presence of a reducing substance (in this case glucose), Fehling's solution gives a red precipitate of copper oxide Cu.sub.2O (copper I). Thus, the absorbance band of Zn.sup.2+ at about 660 nm reduces as the concentration of glucose increases.
(130) Thus, the TiO.sub.2 L Zn.sup.2+ material reduces the concentration of glucose in solution by half
(131) Perfluorooctanoic Acid:
(132) Perfluorooctanoic acid (PFOA) is a synthetic fluorinated surfactant (not found in nature). It is very stable and is consequently extremely persistent (quasi-indefinitely) in the environment. Due to its cumulation, its toxicity and its persistence, it is classified in Europe in the Reach regulation as a substance of very high concern.
(133) The experimental protocol is as follows: concentration of organic compound 0.1 mg/mL, concentration of TiO.sub.2 L Zn.sup.2+1 mg/mL (water solvent), 15 minutes in an ultrasound bath to disperse particles in solution, 3 hours of halogen radiation. The sample is then filtered to separate the material from the solution. The retained solid is rinsed with water then dried at ambient temperature and analysed by Fourier Transform InfraRed (FTIR) spectrometry.
(134) The FTIR spectrum of the TiO.sub.2 L Zn.sup.2+ recovered at the end of the experiment is very different from the FTIR spectrum for the TiO.sub.2 L Zn.sup.2+ material (
(135) It is thus demonstrated that PFOA molecules are adsorbed.
(136) In conclusion, and as demonstrated particularly in examples 8 and 9, the combined action of the synthesis method and the washing process produces a highly reactive type of crystalline rutile titanium oxide that can either destroy the polluting compounds, or adsorb them (possibly with rerelease).
(137) This characteristic is discussed fairly broadly in current literature. It would seem that adsorption is facilitated by the use of functionalised commercial titanium oxides (carbon, polymer) [12,13]. Adsorption of non-functionalised TiO.sub.2 materials would depend on the pH.
(138) In this respect, the best adsorption results would be obtained by moderately acidifying the adsorbent solution (pH=3) [14].
(139) Nevertheless, titanium oxide synthesised at the present time is still competitive in terms of its synthesis and environmental cost, and appears to have better adsorption properties.
Example 10
Synthesis of a Ti/ZrO.SUB.2 .Hybrid Material According to the Invention
(140) A Ti/ZrO.sub.2 hybrid nanomaterial was synthesised using the procedure according to example 4, replacing the silicon precursor (TEOS) by zirconium propoxide in 70% of propanol (the propanol is evaporated before the precursor is added into the reaction medium) and using a solution of zinc nitrate for the first washing step. This material is composed of 95% of TiO.sub.2 moles and 5% of ZrO.sub.2 moles and is called 95/5 Ti/ZrO.sub.2 (Zn) in the following.
Example 11
Physiochemical Analysis of 95/5 Ti/ZrO.SUB.2 .(Zn)
(141) The specific surface area (A.sub.s) was determined by volumetric adsorption of nitrogen as was described in example 5 for the following materials: TiO.sub.2 L Zn.sup.2+, ZrO.sub.2 L Zn.sup.2+, 95/5 Ti/ZrO.sub.2 (Zn). The ZrO.sub.2 L Zn.sup.2+ was prepared in a manner similar to the TiO.sub.2 L Zn.sup.2+ with zirconium propoxide in 70% of propanol as zirconium precursor (the propanol is evaporated before the precursor is added into the reaction medium).
(142) As shown by the adsorption isotherms, the specific surface area of ZrO.sub.2 is smaller than that of TiO.sub.2 but 5% of ZrO.sub.2 added to 95% of TiO.sub.2 gives a material (95/5 Ti/ZrO.sub.2 (Zn)) with a much larger specific surface area than the 100% TiO.sub.2 L Zn.sup.2+ material (
(143) The same phenomenon on the surface is observed on the FTIR spectra (
(144) As a reminder, the bands between 1300 and 1400 cm.sup.1 are characteristic of the NO bond of adsorbed NO.sub.3.sup.1 ions responsible for acidification of the surface. As mentioned above, this acidification would improve photocatalytic properties of materials.
(145) The peak at about 1600 cm.sup.1 is characteristic of vibrations of water molecules.
Example 12
Recycling of TiO.SUB.2 .L (Zn.SUP.2+.)
(146) A good photocatalyst must be effective in eliminating organic compounds, as was demonstrated above. But it also needs to be recyclable and reusable several times without reducing its efficiency.
(147) To demonstrate the capability of TiO.sub.2 L Zn.sup.2+ to be recycled and reused, the powder recovered at the end of photocatalysis (Example 8: bromophenol blue) is rinsed by excess absolute ethanol. After centrifuging, the float is eliminated. The powder is then placed in a 10% solution of nitric acid to destroy molecules of residual dye but especially to restore the surface acidity that would appear to be reduced at the end of the previous photocatalysis. Centrifuging is very difficult at this time. A part of the recycled material remains in suspension. The float is eliminated and the other part of the material settles and is dried at ambient temperature.
(148)
Example 13
Photocatalysis with Recycled TiO.SUB.2 .L Zn.SUP.2+ and Ti/ZrO.SUB.2 .L Zn.SUP.2+
(149) a) Experimental Protocol
(150) The recycled TiO.sub.2 L Zn.sup.2+ and 95/5 Ti/ZrO.sub.2 L Zn.sup.2+ materials were tested in photocatalysis to degrade the dyes. The TiO.sub.2 L Zn.sup.2+ and commercial titanium oxide (PC50 and P25) materials were also used with the washing procedure, to compare their efficiency. It is important to note that commercial titanium oxides used up to now were pure. In recent years, very small quantities of metal ions are added within these materials to increase their photocatalytic reactivity. Therefore the washing procedure was used on these materials since metal elements in particular (in ionic form) remain adsorbed residually.
(151) The protocol is identical to previous experiments on dyes (concentration of material 1 mg/mL, concentration of dye 310.sup.5 mol/L). Two types of dyes were used (Bromophenol and methyl orange) in two types of radiation (visible light and UV lamp).
(152) c) Results and Discussion
(153) Bromophenol Blue
(154) All solutions changed colour in contact with the materials. Acidification of the surface is still applicable. In this case the source of radiation is the halogen spotlight (visible light equivalent to sunlight). Concentrations are monitored by visible spectrophotometry and the results after 3 h of radiation are given in
(155) The commercial oxide only partially destroys dye molecules, even when doped. This means that doping did not significantly improve its photocatalytic reactivity. All other materials have fairly good efficiency. No more peaks are observed, the spectra are flat. This means that there are no longer any more molecules in solution.
(156) Thus, recycling did not change the photocatalytic reactivity of the material. The recycled 95/5 Ti/ZrO.sub.2 hybrid and TiO.sub.2 L Zn.sup.2+ appear to be efficient.
(157) Methyl Orange
(158) The protocol is identical to that used for the test with bromophenol blue. A UV source is also used. The commercial material in this case is P25 that was also doped. Concentrations are monitored using spectrophotometry and the results after 5 h of radiation are given in
(159) Regardless of the source of radiation used, the doped commercial material has the lowest photocatalytic reactivity. Reactivity seems slightly better under UV radiation than under halogen radiation. Therefore doping could not reverse the trend even in UV, the most efficient material is still synthesised and washed 100% titanium oxide materials.
(160) The reactivity of the recycled TiO.sub.2 L Zn material is not as good as that of the TiO.sub.2 material. It is found that under UV radiation, the recycled TiO.sub.2 L Zn material is even better, undoubtedly related to the recycling procedure (use of nitric acid).
(161) Finally, the Ti/ZrO.sub.2 material is also just as efficient.
(162) The shape of its curve derived from the experiment with the halogen spotlight is due to the presence of particles in solution diffusing in the tank at the time of the measurement. But the dye molecules were entirely eliminated.
Example 14
Preparation of TiO.SUB.2 .with an Alkenyl Ether of Polyoxyethylene Glycol
(163) A TiO.sub.2 L Zn.sup.2+ material was synthesised using the procedure given in examples 1 and 3, replacing the surfactant by Brij 97 (C.sub.18H.sub.35(EO).sub.10OH, marketed for example by BASF). This material is called TiO.sub.2 Brij L Zn.sup.2+ in the following.
Example 15
Physiochemical Analysis of TiO.SUB.2 .Brij L Zn.SUP.2+
(164) The FTIR spectra of TiO.sub.2 Brij L Zn2.sup.+ and TiO.sub.2 L Zn.sup.2+ in example 3 (TiO.sub.2 Pluronic L Zn.sup.2+) were compared (
(165) Residual nitrate ions are present for the two materials. The spectra are similar. This means that replacement of the surfactant does not seem to have modified the material.
(166) The surfactant has been well eliminated by washing, no peak can be seen characteristic of the presence of surfactant molecules.
(167) The two materials were then analysed by N.sub.2 volumetric adsorption (
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