Patent Application
20090263314
The present invention relates to a method for producing catalyst, especially to a method for producing catalyst for wastewater treatment.
Titania have been used widely in various industries fields including, for example, pigment, paper-making, paint, catalyst, sterilizing, cleaning, primer, wastewater treatment, decomposition of organic waste, etc. Recently, titania has been increasingly applied in high technology due to its unique semi-conductive properties. Titania is n-type semi-conductor and its molecular structure belongs to zinc blende lattice. According to crystal structure, titania can be classified into three major types, i.e. anatase, rutile and brookite.
Generally, the crystal structure of titania is in an amorphous state at ambient temperature, in anatase type when calcined at a temperature from 200° C. to 500° C., in rutile type when calcined at a temperature from 500° C. to 600° C., and in brookite type when calcined at a temperature above 700° C. Crystal structure of anatase and rutile would change with temperature changing so that they are usually used in photo-catalysis reaction. Among them, for stability rutile is the best and for photo-reactivity anatase is the best. Thus, in various industries applications, anatase is the popular starting material. Due to the excellent photo-catalytic activity of titania, its band gap for valence band and conduction band is up to 3.0 to 3.2 eV. When titania is irradiated by light having energy more than the band gap, it will result in separation of electron-hole pair, and the separated electron and hole will in turn recombine. The separation and recombination of the electron-hole pair are counter mechanisms each other, thus electron and hole can exhibit their photo-catalytic activity only in the case that the electron-hole pair is separated into electron and hole and each of themselves subjects to free radical reaction.
From the past investigation on titania, it knows that the surface properties including particle size, porosity, particle structure and morphology of titania will vary depending on its preparation. Such surface properties will affect the photo-catalytic activity of titania, which will in turn affect its catalytic efficiency directly. For example, when titania is applied in treating wastewater, such surface properties will affect its ability for decomposing organic ingredients when using in wastewater treatment and affect its electron transferring effect when using in film electrode of dye sensitized solar cell.
Recently, nanometer titania powder has been widely used in various industries and its demanded amount is increasing greatly. Therefore various processes for producing nanometer titania powder have been continuously developed so that the cost for obtaining nanometer titania powder from commercial source (for example P25 titania from Degussa) is greatly decreasing. However, since nanometer titania powder is very fine, if it is used for treating aqueous system to decompose the organics contained therein, the nanometer titania powder is difficultly separated from the aqueous system when the treatment is completed. To resolve this problem, a process comprising formulating a titania slurry, coating the slurry on a substrate to prepare a titania film is proposed.
The decomposition technology conventionally used in treating organic contaminates includes bio-treatment and incineration. However, the treating time for the bio-treatment is long and is difficult to treat high concentration contaminates. As to incineration, it is critically regulated not to generate toxic substances such as dioxins and furans during its operation. With advancing scientific technology, it is known that oxidation has a comparable decomposing ability on organic contaminates. For example, water quality can be purified by using air diffusing or various oxidizing agent to oxide the contaminants contained in water. However, addition of various chemicals will result in secondary environmental contamination. To resolve the existing problems, several chemical oxidizing technologies are developing. Among them, an advanced oxidation process (referred to AOP) is most popular. The mechanical of the AOP mainly uses the generated free radical OH. as the reaction substrate, since the oxidizing potential of the free radical OH. is 2.8 eV, which is the strongest oxidizing agent in addition to fluoride ion. The free radical OH. is the best choice for the oxidizing agent since fluoride ion is corrosive and thus its use is limited. When a solution contains free radical OH., it will subject to oxidization to decompose the organic contaminants contained therein. The free radical OH. not only withdraws chlorine atom from compounds but also destroy C—C double bond in the structure. The oxidization induced by free radical OH always decomposes organic contaminants into CO2, H2O, and other low molecular material (such as acid or simple hydrocarbon compounds). Based on the mechanism of the AOP, several combination processes have been developed including a combination of UV/H2O2/Fe2+, UV/O3, UV/H2O2, O3/H2O2, UV/H2O2/Fe2+/O3 and the like. Improving the reaction effect of AOP by using photo-catalyst is aggressively developing recently. Therefore, how to prepare high reactive photo-catalyst is the major project.
There are usually two processes for making nanometer titania powder. The first one is a liquid phase synthesis and the second one is a gas phase synthesis. The liquid phase synthesis is further classified into the following four subclasses: (1) sol-gel which comprises dissolving high purity metal alkoxide (M(OR)n) or metal salt in a solvent such as water or alcohol and carrying out hydrolysis and condensation to form a gel having some spatial structure; (2) hydrolysis which comprises forcing hydrolysis of metal salt in solvents of different pH value to obtain a homogeneous dispersion of nanometer titania particles; (3) hydrothermal process which comprises reacting titania precursor in a sealed stainless container at a specified temperature and a specified pressure to obtain nanometer titania particles; (4) micro-emulsion process which comprises adding titania precursor into micro emulsion consisting of water and surfactant and reacting to form mono-dispersion of nanometer micell and then drying and calcining the resultant mono-dispersion.
The gas phase synthesis for preparing titania powder can be classified into the following subclasses: (1) chemical vapor deposition which comprises subjecting a titania precursor and oxygen to chemical vapor deposition in a low pressure chemical vapor deposition device to form a titania film or powder; (2) flame synthesis which comprises stream-heating metal compound by hydrogen-oxygen flame or acetylene-oxygen flame to induce chemical reaction and form nanometer particles; (3) vapor condensation which comprises vaporizing the starting material through vaporization under vacuum, heating or high frequency induction into gaseous or fine particles and then quickly chilling to collect the resultant nanometer powder; (4) laser ablation which comprises vaporizing a metal or non-metal target by using high energy laser beam and condensing the stream to obtain stable atom clusters from the gaseous phase.
The present invention provides a method for producing catalyst used in wastewater treatment, which is characterized by using a solution of titanate salts such as tetra-isopropyl orthotitanate in acetylacetone as titanium ion source, using hydroxyamines compounds such as hydroxylamine hydrochloride as a reducing agent, and using polymer as both a dispersing agent and stabilizer such as polyvinyl alcohol to prevent from the aggregation among particles and to generate porosity on particle surface. The present method is further characterized by adding suitable thiol compound such as 1-thioglycerol as a complexing agent for complexing metal and as a catalyst for enhancing efficiency of hydrolysis-condensation and thus shorten the synthesis time for synthesizing nanometer titania photo-catalyst. The nanometer titania photo-catalyst prepared by the present method has a high porosity, high specific surface area, and excellent light-absorbance and is suitable as photo-catalyst so that it can effectively enhance the degradation of organic substance when using in water treatment.
The present invention provides a method for producing catalyst used in wastewater treatment, which is characterized by using a solution of titanate salts such as tetra-isopropyl orthotitanate in acetylacetone as titanium ion source, using hydroxyamines compounds such as hydroxylamine hydrochloride as a reducing agent, and using polymer as both dispersing agent and stabilizer to prepare a titania slurry. Then the titania slurry is coated on a substrate to form a fine and transparent nanometer titania film. The film-coated substrate is suitable used for treating wastewater to decompose the organic substance contained therein. Moreover, since the photo-catalyst is formed as a film coated on a substrate, it is easily recovered from wastewater and recycled to use in next treatment so that the cost for wastewater treatment will be decreased.
The present invention provides a method for producing catalyst used in wastewater treatment, which is characterized by using a solution of titanate salts such as tetra-isopropyl orthotitanate in acetylacetone as titanium ion source, using hydroxyamines compounds such as hydroxylamine hydrochloride as reducing agent, and using polymer as both dispersing agent and stabilizer to prepare a titania slurry. Then the titania slurry is mixed with commercial available titania powder and added with proper amount metal oxide (such as Nb2O5, Ta2O5 etc.) to formulate a mixture slurry and the resultant mixture slurry is coated on a substrate to form a fine and transparent nanometer titania film.
In one embodiment, the present invention provides a method for producing catalyst used in wastewater treatment, which comprises the following steps: a) preparing a solution containing a polymer and a hydroxylamine compound; b) preparing a titanate solution; c) mixing the solution in step a) and the titanate solution in step b) to form a first mixture; d) adding a thiol compound into the first mixture in step c) to form a second mixture; and e) allowing the second mixture to react to form a viscose catalyst slurry.
The method for producing catalyst used in wastewater treatment according to the present invention preferably further comprises steps of: drying the viscose catalyst slurry; grinding it into powder; and calcining the resultant powder to form titania powder in crystal form.
In one embodiment, the present invention further provides a method for producing catalyst used in wastewater treatment, which comprises the following steps: a) preparing a solution containing a polymer and a hydroxylamine compound; b) preparing a titanate solution; c) mixing the solution in step a) and the titanate solution in step b) to form a first mixture; d) adding a thiol compound into the first mixture in step c) to form a second mixture; e) allowing the second mixture to react to form a first viscose catalyst slurry; f) dissolving the first viscose catalyst slurry in an alcohol solvent to formulate a second catalyst slurry; and g) coating the second catalyst slurry on a substrate and heating the slurry to form a catalyst film on the substrate.
In one embodiment, the present invention also provides a method for producing catalyst used in wastewater treatment, which comprises the following steps: a) preparing a solution containing a polymer and a hydroxylamine compound; b) preparing a titanate solution; c) mixing the solution in step a) and the titanate solution in step b) to form a first mixture; d) adding a thiol compound into the first mixture in step c) to form a second mixture; e) allowing the second mixture to react to form a first viscose catalyst slurry; f) mixing the first viscose catalyst mixture and titania powder at a certain ratio to form a second catalyst slurry; g) mixing the second catalyst slurry with at least one metal oxide to form a third catalyst slurry; and h) coating the third catalyst slurry on a substrate and heating the slurry to form a catalyst film on the substrate.
The present invention is illustrated in detail by the following Examples by reference to the accompanied drawings. But the present invention is not limited to the Examples.
Step 21: prepare a titanate solution. In this step, the titanate solution is a solution of tetra-isopropyl orthotitanate in acetylacetone as titanium source. Step 22: mix the titanate solution from Step 21 with the hydroxylamine solution from Step 20 to form a first mixture. After mixing thoroughly, subject to step 23: add a thiol compound into the first mixture and stir evenly to form a second mixture. In Step 23, the thiol compound is used as both complexing agent and catalyst, which can enhance the stability and prevent the metal ion from being oxidized so that it facilitates hydrolysis and condensation and shorten reaction time. In this embodiment, the thiol compound is 1-thioglycerol but is not limited thereto.
Step 24: subject the second mixture to a reaction to form a viscose titania catalyst slurry. Please refer to
Next, the method for preparing catalyst slurry is illustrated by an Example.
2.2 Grams of hydroxyamines such as hydroxylamine hydrochloride were dissolved in distilled water completely and 1 gram polymer such as polyvinylpyrrolidone was added into the hydroxylamine solution and stirred to dissolve the polymer completely. Then distilled water was added to make the volume to be 100 ml. 10 ml tetra-isopropyl orthotitanate and 3.5 ml were mixed and added into 85 ml of the hydrxyamine hydrochoride/polyvinylpyrrolidine solution. After stirring, 0.5 ml thiol compound such as 1-thioglycerol was added therein and stirred for 30 minutes. The resultant solution was placed in a water bath at a constant temperature of 40° C. for 24 hours. The resultant solution was transferred into a 100 ml sealable flask and the flask was sealed and placed into an oven at a temperature of 80° C. for 2-6 days, preferably for 3-4 days. Then the flask was taken out from the oven and cooled to room temperature, in that time, the solution contained in the flask was converted into white flowable slurry from yellow solution. The slurry was washed with isopropanol for several times to remove un-reacted substance and obtain a titania slurry. The particle size of the titania contained in the slurry was measured as from 10 to 50 nm, its average particle size was 20 nm, crystal structure was anatase, and specific surface area was 40 to 60 m2/g.
Next, the method for preparing titania powder is illustrated by the following Example.
The titania slurry prepared from Example 1 was washed with isopropanol to remove un-reacted substances and dried in air (or in an oven at a temperature of 40 to 80° C.). After drying, the titania was placed in a mortar to be ground into powder. Then the ground powder was placed in a furnace at a temperature of 400° C. and calcined for 2 hours and cooled to room temperature. The average particle size of the titania powder was measured as from 50 to 250 nm. 0.05 g of the titania powder was added with 50 ml of 0.2M aqueous potassium iodide (KI) solution and shaken by ultra sonicator in dark for 5 minutes to disperse the titania powder in the aqueous solution evenly. At that time, the resultant titania dispersion was sampled and measured the concentration as a standard concentration before reaction. The titania dispersion was stirred for 5 minutes and then subjected to photo-chemical reaction by irradiating with mercury lamp at a light power of 500 W in a distance of 11 cm above the dispersion while the reaction was shield with a stainless housing to prevent from interfering with external light. The reaction solution was sampled at 15, 30, 60, 90, and 120 minutes, respectively, and filtered by syringe filter or high speed centrifuge to remove titania powder dispersed therein. The upper layer was measured its absorbance variation at 288 nm by using Ultraviolet Absorption Spectrophotometer. In the titania/KI dispersion, titania was irradiated to oxide I− ion in the solution and the I− ion was further reacted to form I3−. The absorbance intensity change of I3− at wavelength 288 nm in UV absorption spectrum was measured to determine the photo-catalytic activity of titania.
Please refer to
Then Step 32 is carried out for coating the catalyst slurry from Step 31 onto a substrate and subjecting to heating treatment to form a catalyst film. The substrate can be in a regular shape such as substrate in a plate, a sphere, a strand shape; or in un-regular shape. As to the method coating the slurry on the substrate, it includes a doctor coating method for coating the slurry on a plate substrate to form a catalyst film; or a dipping coating method for dipping a sphere, a strand, or un-regular substrate in the slurry. In other words, shape of substrate can be selected based on the final use and the coating method can also be selected based on the shape of substrate used, which is easily determined by those skilled in the art by reference to the disclosure of the present embodiments.
Next, the method for preparing titania powder is illustrated by the following Example.
The titania catalyst slurry prepared from Example 1 was coated on a FTO conductive glass substrate with a doctor coating method and then the substrate was placed in room temperature and dried in the air for at least 3 to 8 hours, preferable 5 hours. The substrate was then placed into a furnace at a temperature of 450˜500° C. for 0.5 to 1 hour and then cooled to room temperature to form a fine transparent titania film on the FTO conductive glass substrate. The titania film exhibited excellent adhesion to the substrate and the titania film had a thickness of from 1 to 5 μm, preferably 2 to 3 μm. In this embodiment, the polymer could be, for example, polyethylene oxide, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, carboxymethyl cellulose, polyethylene glycol, and the like. Moreover, in this embodiment, the hydroxylamine compound could also include laurylamine hydrochloride (LAHC) in addition to hydroxylamine hydrochloride. Also, the alcohol solvent used in this embodiment could be an alkanol solvent having 3 to 6 carbon atoms, preferably isopropanol.
Please refer to
In Step 41, the first titania catalyst mixture is mixed in an amount of 30 to 95% by weight, preferably from 60 to 90% by weight, with the available commercial titania powder to form a second titania catalyst mixture. Moreover, in Step 41, a minor binder can be added. Kinds of the binder and its amount are not limited and can be determined by those skilled in the art depending on the kinds of available commercial titania powder and the titania slurry prepared by the present method and their amounts. Examples of the binder include acetylacetone, polyethylene glycol having a molecular weight of from 400 to 50,000, Triton X-100, polyvinylalcohol (PVA), arabic gum powder, gelatin powder, polyvinylpyrrolidine (PVP), and styrene and the like. Among them, acetylacetone, polyethylene glycol having a molecular weight of from 400 to 50,000, and Triton X-100 are preferable.
Next Step 42 is carried out which comprises mixing the second titania catalyst mixture with at least one metal oxide to formulate a third titania catalyst mixture with a moderately viscosity. The metal oxide is selected from Nb2O5, Ta2O5, or a combination thereof. Finally, Step 43 is carried out which comprises coating the third titania catalyst mixture on a substrate and subjecting to a heating treatment to form a catalyst film. The substrate used in Step 43 is not limited, and can be a conductive substrate or others. Examples of the substrate include a ITO conduction glass, a FTO conductive glass, a fiber, a metal substrate and the like. The substrate can be in any shape, such as in form of plate, circular, or strand. The method for coating the mixture on the substrate can use any coating method as long as it can obtain a film having a desired thickness. For example, the coating can be wet coating process such as spin coating, doctor coating, dipping coating, and the like. The heating treatment comprises calcining the film at a temperature of from 450 to 500° C. for 0.5 to 1 hour, but it is not limited thereto. The heating conditions are easily determined by those skilled in the art based on the subject to be treated. The titania catalyst film prepared by the method of present invention has a thickness of from 5 to 40 μm, preferably from 10 to 20 μm; and a hardness of 2B to 6H determined by Pencil Test; and particle size of the particle contained in the film is in a range of from 5 to 100 nm, preferably from 15 to 50 nm.
Next, the method for preparing titania catalyst film is illustrated by the following Example.
2 ml nanometer titania slurry prepared in Example 1 was added with 5 to 30 wt %, preferably 7 to 15 wt % of titania powder Degussa P25 and the resultant mixture was ground in a mortar for 10 to 20 minutes to form an evenly slurry solution. The slurry solution was then added with 1 to 10 wt %, preferably 2 to 6 wt % of Nb2O5 or Ta2O5 powder and ground for 10 to 20 minutes to form an evenly titania slurry mixture. The resultant titania slurry mixture was coated on a FTO conductive glass substrate by doctor coating method and dried in the air for at least 3 to 8 hours, preferably 5 hours, and then calcined in a furnace at a temperature of from 450 to 500□ for 0.5 to 1 hour and cooled to room temperature to form a titania film on the FTO conductive glass. The titania film exhibited excellent adhesion to the substrate and its particle size was measured to be found an average particle size of from 50 to 250 nm and its thickness was in a range of from 5 to 15 μm, preferably from 8 to 12 μm. Moreover, in this embodiment, the titania slurry mixture can be further added with a binder, such as acetylacetone, polyethylene glycol having a molecular weight of from 400 to 50000, Triton X-100, and the like, in an amount of from 0 to 3 wt %.
The comparison between the titania powder prepared in the present invention and the commercial available titania powder is illustrated by the following Example.
A titania powder was prepared by the procedures mentioned in Example 1 except that LAHC (laurylamine hydrochloride) was used instead of hydroxylamine hydrochloride as the hydroxyamines compound and no polymers such as polyvinylpyrrolidone and 1-thioglycerol were added. The preparation was as follows: (a) 2.2 g LAHC was dissolved in 100 ml water; (b) 10 ml tetra-isopropyl orthotitanate was mixed with 3.52 ml acetylacetone and stirred thoroughly; (c) 85 ml solution prepared in the step (a) was added into the solution prepared in the step (b) and stirred for 30 minutes to form an evenly mixture solution; (d) the mixture solution prepared in the step (c) was placed in a water bath at a temperature of 40□ and reacted for at least 24 hours; (e) the solution prepared in the step (d) was transferred into a flask and sealed and then placed in an oven at a temperature of 80□ for further reacting for at least 5 days to form a light yellow flowable slurry. The flowable slurry was cooled and washed with isopropanol for several times to remove un-reacted material and then the isopropanol was evaporated. The residual slurry was dried in the air or in an oven at a temperature of from 40 to 80□ and ground into powder in a mortar. The resultant powder was calcined in a furnace at a temperature of 400□ for 2 hours and then cooled to room temperature to obtain a titania powder (referred to Powder A). The commercial available titania powder Degussa P 25 was referred to Powder B. The titania powder prepared from Examples 1 and 2 was referred to Powder C. Each 0.05 g of the Powder A, Powder B, and Powder C was added with 50 ml of 0.2M aqueous KI solution and subjected to the reactions and irradiation the same as in Example 2. The reaction was sampled to analysis its I3− concentration. The result was summarized in Table 1. The ability of Powder A, Powder B and powder for forming I3− was (C)>(B)>(A). In other words, the Powder C prepared by the present method exhibited the best photo-catalytic activity, which is higher than commercial available titania powder Degussa P25.
The first titania mixture slurry was prepared as the same as Example 4 in which the titania powder Degussa P25 was in an amount of 7 wt % (Slurry A). Separately, a commercial available titania slurry Solaronic TiO2 was mixed with 7 wt % of titania powder Degussa P25 to prepare a second mixture slurry (Slurry B). Separately, 2 g of titania powder Degussa P25 was added with 10 μl acetylacetone, 50 μl Triton X-100, 4 ml distilled water and 0.8 g polyethylene glycol and ground in a mortar to form a slurry (Slurry C). Each of Slurry A, Slurry B, and Slurry C was evenly coated on a FTO conductive glass substrate and dried in the air for at least 3 to 8 hours, preferably 5 hours, and then placed in a furnace at a temperature of 450 to 500□ and calcined 0.5 to 1 hour to form a titania film on the FTO conductive glass substrate. After the resultant substrate was cooled to 80□, the substrate was immersed in 0.3 mM Ruthenium 533 dye solution for 2 hours and then dried to obtain a working electrode. The resultant working electrode was used as the anode, a platinum-plated FTO conductive glass substrate was used as the cathod, and an iodine-containing solution was used as electrolyte to constitute a cell. The cell was tested its light-power conversion efficiency (η) by using AM1.5 Solar simulator. The results are shown in Table 2. From Table 2, it clearly shows that the light-power conversion efficiency (η) of the working electrode prepared from the Slurry A was 5.30%, and Slurry B was 3.02%, and Slurry C was 4.27%. It demonstrated that the titania film prepared by the present invention exhibited the best light-power conversion efficiency.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 097114577 | Apr 2008 | TW | national |
