Method for obtaining mesoporous silica particles with surface functionalization

Abstract

It is provided a method for obtaining mesoporous silica particles with surface functionalisation comprising the steps of a) providing solutions of at least three precursors; wherein the pH of the mixture is adjusted to a range between 2 and 8 in a buffered system; b) Mixing the precursor solutions thereby allowing a reaction to take place at a temperature between 20 and 60° C., whereby surface functionalized mesoporous silica particles as solid reaction product are formed; c) Separating the surface functionalized mesoporous silica particles from the reaction mixture by centrifugation or filtration; d) Removing any pore structure directing agent present in the pores of the formed surface functionalized mesoporous silica particles by ultrasonication; e) followed by separation by centrifugation or filtration, washing and drying of the surface functionalized mesoporous silica particles.

Claims

1. Method for obtaining mesoporous silica particles with surface functionalisation comprising the steps of a) providing solutions of at least three precursor agents, wherein the at least three precursor agents are selected from a group containing: at least one alkali silicate solution, at least one solution containing at least one pore structure directing agent (SDA), wherein the at least one pore structure directing agent is a non-ionic polymeric pore structure directing agent from the group of poly(alkylene oxide)triblock copolymer, wherein the at least one pore structuring agent is provided in a buffer solution with a pH between 2 and 8, wherein the buffer solution is selected from a sodium citrate/citric acid buffer, a Na.sub.2HPO.sub.4/citric acid buffer, a HCl/sodium citrate buffer or a Na.sub.2HPO/NaH.sub.2PO.sub.4 buffer, and at least one functionalising agent for surface functionalisation; wherein the at least one functionalising agent is of the following general structure:
Y.sub.3Si—(CH.sub.2).sub.n—X  (I) wherein Y is OR.sup.1, wherein R can be a H or an alkyl chain, optionally a C.sub.1-C.sub.20 alkyl chain, n is 1 to 20, X is selected from a group comprising H, a linear or branched substituted or non-substituted C.sub.1-C.sub.30-alkyl or a cyclic substituent in form of a substituted or non-substituted C.sub.5-C.sub.20-cycloalkyl, a substituted or non-substituted C.sub.5-C.sub.20-aryl, wherein in each case one or multiple carbon atoms can be substituted by one or multiple oxygen atoms, sulphur atoms, substituted nitrogen atoms, double bonds and/or by one or multiple groups of the type —C(O)O—, —OC(O)—, —C(O)—)—, —NHC(O)O—, —OC(O)NH— and/or —OC(O)O—, and/or can be functionalized by one or multiple hydroxyl groups, amino groups and/or mercapto groups, wherein the pH of the mixture is adjusted to a range between 2 and 8 in a buffered system; b) Mixing the precursor solutions thereby allowing a reaction to take place at a temperature between 20 and 60° C., optionally between 20° C. and 25° C., whereby surface functionalized mesoporous silica particles as solid reaction product are formed; c) Separating the surface functionalized mesoporous silica particles from the reaction mixture by centrifugation or filtration and optionally washing the surface functionalized mesoporous silica; d) Removing any pore structuring directing agent present in the pores of the formed surface functionalized mesoporous silica particles by ultrasonication in a C.sub.1-C.sub.3 alcohol at a temperature between 20° C. and 60° C., optionally between 20° C. and 35° C.; e) followed by separation by centrifugation or filtration, washing and drying of the surface functionalized mesoporous silica particles.

2. Method according to claim 1, wherein no organic solvent is used in the reaction.

3. Method according to claim 1, wherein the at least one alkali silica precursor solution comprises an aqueous sodium silicate solution.

4. Method according to claim 1, wherein the at least one alkali silicate solution comprises the alkali silicate in an amount between 20 and 40 wt % (based on the total solution) of SiO.sub.2, and 5-30 wt of NaOH.

5. Method according to claim 1, wherein the at least one pore structuring directing agent is HO(CH.sub.2CH.sub.2O).sub.20(CH.sub.2CH(CH.sub.3)O).sub.70(CH.sub.2CH.sub.2O).sub.20H (Pluronic P123).

6. Method according to claim 1, wherein the group X is selected from a group comprising H, substituted and non-substituted C.sub.1-C.sub.12-alkyl and substituted and non-substituted C.sub.3-C.sub.7-cycloalkyl.

7. Method according to claim 1, wherein the buffer system provides a pH between 2 and 8, optionally 5 to 7 and is a sodium citrate/citric acid buffer.

8. Method according to claim 1, wherein the at least three precursors are mixed and reacted at a temperature between 20 and 25° C. in a batch mode or in a continuous mode.

9. Method according to claim 1, wherein the reaction mixture is allowed to age for 12 to 48 h, optionally 24 h at a temperature between 20° C. and 100° C.

10. Method according to claim 1, wherein the surface functionalized mesoporous silica particles are dried in air at a temperature between 50° C. and 70° C., optionally at 60° C.

11. Method according to claim 1, wherein any pore structure directing agent present in the pores of the formed mesoporous silica particles is removed in a C.sub.1-C.sub.3 alcohol by ultra-sonication at a frequency between 20 and 60 kHz for a time period of 5 to 20 min, optionally 5 to 10 min.

12. Method according to claim 11, wherein any pore structure directing agent present in the pores of the formed mesoporous silica particles is removed by ultra-sonication at a temperature between 20 and 30° C., optionally between 20 and 25° C., such as at room temperature in the presence of a alcohol.

13. Method according to claim 1, wherein after removal of any pore structuring directing agent the surface functionalized mesoporous silica particles are dried at 50 to 80° C., optionally at 60 to 80° C.

14. Method according to claim 1, wherein the group X is selected from the group comprising proton (H), amine (—NR.sup.2.sub.2, where R.sup.2 can be H or an alkyl chain), imino, urea ((—NH)CO(NH.sub.2)), amide (—CONH.sub.2)) carboxylic acid (—CO.sub.2H), carboxylic acid anion (—CO.sub.2), sulfonic acid (—SO.sub.3H), sulfonic acid anion (—SO.sub.3), methanedthionic acid (—CS.sub.2H), phosphonate (—PO.sub.3R.sup.3.sub.2 with R.sup.3 is an alkyl chain), phosphonic acid (—PO.sub.3H.sub.2), sulfide (—S—), phosphine (—PR.sup.4.sub.2, where R.sup.4 can be H or an alkyl chain), pyridine, pyrazine, halogens (Cl, Br or I).

15. Method according to claim 1, wherein group X is selected from: ##STR00003##

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The solution is explained in more detail by means of the following examples with references to the figures.

(2) FIG. 1 show a process flow diagram for the continuous production of surface functionalized mesoporous silica particles.

(3) FIG. 2 show a process flow diagram for the continuous production of surface functionalized mesoporous silica particles according to a first feed sequence.

(4) FIG. 3 show a process flow diagram for the continuous production of surface functionalized mesoporous silica particles according to a second feed sequence.

(5) FIG. 4 show a process flow diagram for the continuous production of surface functionalized mesoporous silica particles according to a third feed sequence.

DETAILED DESCRIPTION

(6) The scheme of FIG. 1 provides a conceptual process flow diagram for a continuous production of surface functionalized mesoporous silica particles. The set up comprise a synthesis section (left side) and a downstream section (right side).

(7) The synthesis section comprises one feed tank F-1 for the silica precursor solution, one feed tank F-2 for the solution containing the pore structure directing agent (SDA), and one feed tank F-3 for the functionalising agent for surface functionalisation.

(8) The synthesis section comprises furthermore several static mixers SM-1, SM-2, SM-3 for mixing the precursors.

(9) The downstream section comprises the devices and apparatus required for aging, separating and cleaning the functionalized mesoporous silica particles. Specifically, the downstream section comprises an aging tank A-1, one first filter unit FIL-1 for separating the surface functionalized mesoporous silica particles from the reaction mixture, one mixer unit M-1 for mixing the surface functionalized mesoporous silica particles with an extracting agent (such as methanol), one continuous ultrasonication unit US-1 for removing any pore structuring agent, and one second filter unit FIL-2 for separating the surface functionalized mesoporous silica particles from the extracting agent.

(10) The downstream section further comprises one washing liquid tank F-4 (for providing washing liquid such as water for washing the surface functionalized mesoporous silica particles filtered off the in the first filter unit FIL-1) and one wastewater tank W-1 for collecting the waste washing liquid leaving the first filter unit FIL-1.

(11) The downstream section further comprises one tank F-5 containing the extracting agent and one distillation unit DIS-1 for separating the extracting agent from the pore structure agent after their removal from the surface functionalized mesoporous silica particles in the second filter unit FIL-2.

(12) Pumps P-1, P-2, P-3, P-4, P-5 are used for transporting the feeds and suspensions in the synthesis section and downstream section.

(13) The continuous process in the synthesis section and downstream section is carried out applying the following steps: 1. The feed solutions are prepared in tanks F-1, F-2 and F-3. 2. Mixing of feed solutions is done in one of three possible ways: a. Solutions from F-2(SDA) and F-3 (functionalising agent) are mixed in static mixer SM-1, and this is then mixed with solution from F-1 (sodium silicate) (first feed sequence as shown in FIG. 2) b. Solutions from F-1 (sodium silicate) and F-3 (functionalising agent) are first mixed in static mixer SM-3, and this is then mixed with solution from F-2 (SDA) in static mixer SM-4 (second feed sequence as shown FIG. 3) c. Solutions form F-1 (sodium silicate), F-2 (SDA) and F-3 (functionalising agent) are mixed in SM-5 (third feed sequence as shown FIG. 4) 3. The slurry consisting of surface functionalized ordered mesoporous silica (SF-OMS)-SDA composite in water (streams coming from SM-1, SM-4 and SM-5) are treated in one of two possible ways: a. Slurry is aged for a period of time and then filtered, washed and dried in FIL-1 b. Slurry is filtered, washed and dried in FIL-1 without aging 4. The filtered solid is mixed in mixer M-1 with the extracting agent (methanol) and ultrasonicated in US-1 to remove the SDA 5. The slurry consisting of surface functionalized ordered mesoporous silica (SF-OMS) suspended in a solution of methanol and SDA is filtered, washed and dried in FIL-2 6. The final solid product is collected (SF-OMS) 7. Recycling of extracting agent and SDA takes place as follows: a. The filtrate (extracting agent and SDA solution) from FIL-2 is mixed with water in SM-4 and the methanol is separated from the water and SDA via distillation b. The extracting agent is condensed and recycled into R-1 to be used again in FIL-2 c. The water-SDA solution is recycled into R-2 to be used again in F-2

Example 1: Batch Synthesis

(14) Material Synthesis

(15) 1. Dissolve 4 g P123 in 107.5 ml DIW (SDA) 2. Add 3.684 g citric acid and 2.540 g sodium citrate (buffer) 3. Stir for 24 h at 25° C. 4. Add (3-Aminopropyl)triethoxysilane (APTES) to buffered P123 solution (calculated based on an SiO.sub.2:APTES molar ratio of ˜7) 5. Prepare sodium silicate solution with 10.4 g sodium silicate (27% SiO.sub.2) and 30 g DIW 6. Add sodium silicate solution to buffered P123/APTES solution and stir for 5 min at 25° C.
OR 1. Dissolve 4 g P123 in 107.5 ml DIW (SDA) 2. Add 3.684 g citric acid and 2.540 g sodium citrate (buffer) 3. Stir for 24 h at 25° C. 4. Prepare sodium silicate solution with 10.4 g sodium silicate (27% SiO.sub.2) and 30 g DIW 5. Add (3-Aminopropyl)triethoxysilane (APTES) to sodium silicate solution (calculated based on an SiO.sub.2:APTES molar ratio of ˜7) 6. Add sodium silicate/APTES solution to buffered P123 solution and stir for 5 min at 25° C.
OR 1. Dissolve 4 g P123 in 107.5 ml DIW (SDA) 2. Add 3.684 g citric acid and 2.540 g sodium citrate (buffer) 3. Stir for 24 h at 25° C. 4. Prepare sodium silicate solution with 10.4 g sodium silicate (27% SiO.sub.2) and 30 g DIW 5. Mix both solutions with (3-Aminopropyl)triethoxysilane (APTES, calculated based on an SiO.sub.2:APTES molar ratio of ˜7) and stir for 5 min at 25° C.
Aging and Filtration 1. Age for 24 h at 25° C. (optional) 2. Filter the slurry under vacuum 3. Wash the solid with 500 ml DIW 4. Filter again 5. Dry at 60° C. overnight
Template Removal 1. Suspend 100 mg in 100-500 ml methanol and immerse in an ultrasound bath at 25° C. and 50 kHz for 5 min 2. Filter under vacuum 3. Wash with 500 ml ethanol 4. Dry at 80° C. overnight

Example 2: Continuous Process

(16) Material Synthesis (Synthesis Section)

(17) 1. Dissolve 1000 g P123 in 26875 ml DIW (this is the template) in F-2 2. Add 921 g citric acid and 653 g sodium citrate (buffer) in F-2 3. Mix this solution with 250 ml APTES to buffered P123 solution (calculated based on an SiO.sub.2:APTES molar ratio of ˜7) in SM-1 4. Stir for 24 h at 25° C. in F-2 5. Prepare sodium silicate solution with 2600 g sodium silicate (27% SiO.sub.2) and 7500 g DIW in F-1 6. Mix both solutions in static mixer SM-2 (see feed sequence 1, FIG. 2)
OR 1. Dissolve 1000 g P123 in 26875 ml DIW (this is the template) in F-2 2. Add 921 g citric acid and 653 g sodium citrate (buffer) in F-2 3. Stir for 24 h at 25° C. in F-2 4. Prepare sodium silicate solution with 2600 g sodium silicate (27% SiO.sub.2) and 7500 g DIW in F-1 5. Mix this solution with 250 ml APTES to sodium silicate solution (calculated based on an SiO.sub.2:APTES molar ratio of ˜7) in SM-3 6. Mix both solutions in static mixer SM-4 (see feed sequence 2, FIG. 3)
OR 1. Dissolve 1000 g P123 in 26875 ml DIW (this is the template) in F-2 2. Add 921 g citric acid and 653 g sodium citrate (buffer) in F-2 3. Stir for 24 h at 25° C. in F-2 4. Prepare sodium silicate solution with 2600 g sodium silicate (27% SiO.sub.2) and 7500 g DIW in F-1 5. Mix the three solutions in static mixer SM-5 (see feed sequence 3, FIG. 4)
Template Removal (Downstreaming Section) 1. Age for 24 h at 25° C. in aging tank A-1 (optional) 2. Filter the slurry/wash with water in rotary vacuum drum filter FIL-1 3. Suspend slurry in the equivalent of 100-500 ml methanol/100 mg slurry and ultrasonicate at 25° C. and 50 kHz in continuous ultrasound bath US-1 4. Filter the slurry/wash with ethanol in rotary vacuum drum filter FIL-2 5. Collect the dried solid material in SF-OMS
Recycling of Extracting Agent (in this Case Ethanol) and Pore Templating Agent (in this Case P123) (Downstreaming Section) 1. Pump filtrate consisting of a solution of P123 and ethanol to static mixer SM-4 2. Mix P123-ethanol with water from F-6 for separation 3. Pump P123-ethanol-water solution to distillation unit DIS-1 to separate P123-water and ethanol 4. Condense ethanol in CON-1 and recycle to FIL-2 5. Recycle P123-water solution to F-2

(18) TABLE-US-00001 Reference signs Equipment number Description F-1 Jacketed silica source solution feed tank F-2 Jacketed templating agent solution feed tank F-3 Jacketed functionalising agent solution feed tank F-4 Washing liquid feed tank (water) F-5 Extracting agent feed tank F-6 Dilution water tank R-1 Recycled washing liquid feed tank (extracting agent) R-2 Recycled structure-directing agent solution tank A-1 Jacketed aging tank P-1 Silica source solution rotary pump P-2 Structure-directing agent solution rotary pump P-3 Functionalising agent solution rotary pump P-4 SurFOMS/structure-directing agent composite suspension screw pump P-5 Extracting agent rotary pump P-6 SF-OMS slurry screw pump P-7 SF-OMS slurry screw pump P-8 Filtrate rotary pump P-9 Dilution water rotary pump P-10 Structure-directing agent/extracting agent solution rotary pump P-11 Extracting agent condensate rotary pump P-12 Structure-directing agent solution rotary pump P-13 Recycled structure-directing agent solution rotary pump V-1 to V-35 Valves SM-1 to, SM-6 Static mixers FIL-1, FIL-2 Continuous drum filters/driers W-1 Wastewater tank M-1 Mixer US-1 Continuous ultrasonication unit DIS-1 Distillation column for extracting agent/structure-directing agent separation CON-1 Condenser to condense extracting agent Stream number Stream description 1-9 Silica source feed 10-18 Structure directing agent (SDA) feed 19-27 Functionalizing agent feed 28 Templating agent and functionalizing agent mixture (feed sequence #1) 29-33 Slurry: surface functionalized ordered mesoporous silica (SF-OMS)- templating agent composite in water (feed sequence #1) 34 Silica source and functionalizing agent mixture (feed sequence #2) 35-39 Slurry: surface functionalized ordered mesoporous silica (SF-OMS)- templating agent composite in water (feed sequence #2) 40-44 Slurry: surface functionalized ordered mesoporous silica (SF-OMS)- templating agent composite in water (feed sequence #3) 45-47 Aged slurry 48-50 Washing liquid feed (water) 51 Filtrate: wastewater 52 Solid: SF-OMS/templating agent composite 53-55 Extracting agent feed (methanol) 56-58 Suspension: SF-OMS/templating agent composite suspended in extracting agent 59-61 Slurry: SF-OMS in extracting agent/templating agent solution 62 SF-OMS (final product) 63-65 Filtrate: extracting agent/templating agent solution 66-68 Water feed (for dilution and separation of extracting agent and templating agent) 69-71 Solution containing templating agent, extracting agent and water 72 Vaporized extracting agent  73-765 Condensed extracting agent for recycling 76-78 Recycled washing liquid feed (extracting agent) 79-84 Recycled templating agent solution in water