WO1996026004A1 - Colloidal metal preparation and method for producing it - Google Patents

Abstract

A liquid preparation contains micelles which consist of a block copolymer that has at least one polymer block solvating in the solvent and one polymer block bindable for the colloidal metal and which contain colloidal metal enclosed in metallic, oxidic or sulfidic semiconductor form in an organic or inorganic liquid solvent. To produce it, a salt of a metal that can be converted to a colloidal form is added to a solution of the block copolymer in a suitable solvent, forming metallic salt-containing micelles from the block copolymer; the salt is then reduced to form a colloid and the resulting colloidal metal is optionally converted with a sulfide or hydroxide donator to its sulfidic or oxidic semiconductor form or the salt is converted directly to its colloidal sulfidic or oxidic semiconductor form with a sulfide or hydroxide donator.

Description

Colloidal metal preparation and process for its preparation

description

The invention relates to a liquid preparation containing colloidal metal in metallic form or in the semiconducting form of a metal oxide or sulfide in a liquid solvent.

The use of inorganic colloids and clusters for the purpose of catalysis, the energetic conversion of sunlight and in nonlinear optical devices is known, for example from JN Lewis, Chem. Rev. 9J3 _. , 2693 (1993). The advantages of the known systems are very high reactivities and selectivities. Disadvantages result from the often complex synthesis and above all from the strong drop in activity under harsh reaction conditions. A typical description of a conventional synthesis and catalytic activity determinations can be found, for example, in H. Bonnemann, R. Brinkmann, P. Neiteler, Appl. Organo et. Chem. 8, 361 (1994).

To increase the stability of these colloids have been in the past, polymeric stabilizers (eg N. Tashima, T. Yonezawa, K. Kushihashi, J. Chem. Soc. Faraday _{Trans., 89th,} 2537 (1993)) inverse micelles (eg C. Petit, P. Lixon, MP Pileni, J. Phys. Chem. 9, 12974 (1993)) or microemulsion (e.g. R. Touroude, P. Girard, G. Maire, J. Kizling, M. Boutonnet-Kizling, P. Stenius, Coll. Surf. 6J7, 9 (1992)). These processes, which already use nano-structured reaction media, are very successful in academic research and have made access to the colloids described considerably easier. Nevertheless, there is still a need for easier access and better stability without impairing the activity. The invention is therefore based on the object of increasing the stability of these metal colloids, simplifying their production and thus substantially improving their industrial usability.

This object is achieved by a liquid preparation with a content of colloidal metal in metallic, oxidic or sulfidic semiconducting form in a liquid organic or inorganic solvent, which is characterized by a content of micelles which consist of a block copolymer, which has at least one polymer block which solvates in the solvent and a polymer block which is capable of binding to the colloidal metal and which contain the colloidal metal enclosed.

The invention makes it possible to provide metal colloids, in particular noble metal colloids and metal compounds having semiconductor properties, in the colloidal size range between 2 nm <d <20 nm, which have a substantially superior stability against aggregation, make such colloids accessible at comparatively high concentrations and the size to control the colloids by appropriate selection of the block polymer and the relative ratio of block polymer to metal. This improves their application for catalysis and optical and magnetic purposes.

An essential feature of the invention is the selection of the suitable block copolymer. As mentioned above, this contains at least one polymer block which mediates solvation in the selected solvent and at least one polymer block which is capable of binding to the colloidal metal. The block copolymer forms micelles in the solvent in which the block of the block copolymer which mediates the solvation is on the outside, ie facing the solvent, and on the inside is the polymer which mediates the bond with the metal. The solvating block therefore contains or consists of monomer units with affinity for the solvent. The block causing the metal bond, on the other hand, contains monomer units which can interact with the respective metal, for example basic or acidic groups such as amines, amides, basic heterocycles (for example pyridine) or carboxyl groups and hydroxyl groups. Block copolymers which are composed of the combination of the polymer blocks listed below are preferably used for this purpose:

solvating block binding block

Polystyrene poly (4) vinyl pyridine

Polyisoprene poly (2) vinyl pyridine

Polypropylene glycol polyethylene glycol

Polyalkylstyrenes polar modified polydienes, e.g. Polybutadiene

Polybutadiene polyacrylic acid / polymethacrylic acid

The block copolymers resulting from the blocks listed above by combination are particularly suitable for organic solvents, such as toluene, cyclohexane or tetrahydrofuran. If inorganic solvents are used, such as H ₂ O, liquid NH ₃ or liquid S0 ₂ , the block which mediates the solvation consists of a polymer soluble therein. The block copolymer can also contain more than two polymer blocks, it being possible for the third or further block with one of the first two blocks to have the same or different composition (block terpolymer, etc.)

The colloidal metal is located in the micelles consisting of the block copolymer. It can be in metallic form or in the form of its semiconductor properties, in particular the corresponding oxides or sulfides. As already mentioned above, the size of the colloid particles is generally between 2 nm and 20 nm. A certain regulation of the size of the colloid particles can be achieved by regulating the size of the micelles, which in turn can be achieved by The length and type of the outer polymer block can be varied in relation to the given solvent. The size of the colloids is limited to the size of the core of the block copolymer micelle as well as to the number of metal ions per micelle.

The colloidal preparation according to the invention is preferably prepared by preparing a solution of the block copolymer in a suitable solvent, adding a salt of the selected metal to be converted into the colloidal form, micelles containing metal salt forming and then a) the Salt is reduced to form the colloid and, if appropriate, the colloidal metal thus obtained is converted into the semiconductor form, preferably using sulfide or hydroxide donors to form the sulfidic or oxidic semiconductor form of the metal, or b) the salt directly with a sulfide or hydroxide donor converted into its colloidal sulfidic or oxidic semiconductor form.

The formation of the micelles of the block copolymer in the respective solvent normally does not require any special measures. It is sufficient to dissolve the copolymer in the respective solvent, if necessary with stirring. The solvent is chosen so that it can dissolve the solvating block (in the micelle the outer block). For example, aromatic, cyclic and / or chlorinated hydrocarbons and ethers are particularly suitable for polystyrene as the solvating block, and aromatic, aliphatic or / and chlorinated hydrocarbons and ethers are suitable for polycarbonates as the solvating block.

Precious metals, other metals having other catalytic properties and metals suitable for semiconductor formation are preferably used as metals. In addition to the platinum group metals, this includes gold, silver, copper, cadmium, zinc, titanium, iron, cobalt and nickel. Since the person skilled in the art is well aware of the metals with the properties indicated above, they are not listed here any further. Particularly preferred metal salts are the chlorides and chlorates or the perchloric complexes of the metal ions intended for the reaction, such as HAuCl ₄ , Na ₂ PdCl ₆ , CuCl, CdCl0 ₄ , AgN0 ₃ . The acetates, nitrites, nitrates, the other halides and halogen oxides are also preferred. The metal salts are advantageously added to the solution of the block copolymer in solid form, but a corresponding solution can also be added. It has been found that the salt used does not necessarily have to be soluble in the solvent in the amount to be used. Even if the solubility of the salt is insufficient, there is nevertheless a slow uptake of the salt into the micelles mediated by the block copolymer.

After the micelle-containing micelles have been formed, the corresponding metal colloid is produced by reduction. Those skilled in the art are familiar with the agents suitable for the reduction. Typical examples of suitable reducing agents are hydrazine, NaBH ₄ , butyllithium, superhydride and the like.

If the metal salt is to be converted into semiconductor form, appropriate reagents, in particular sulfide or hydroxide donors, which lead to the formation of the corresponding sulfidic and oxidic semiconductor form, are added either after adding the metal salt or after reducing it beforehand to the metal colloid , too. Suitable sulfide donors are, for example, H ₂ S, NaHS or Na ₂ S, and oxide donors H ₂ 0, NaOH (in H ₂ 0 / tetrahydrofuran systems) or quaternary organic ammonium (NR ₄ OH). Each R here denotes a straight-chain or branched, saturated or unsaturated alkyl group having 1 to 12 C atoms.

In the production of the colloids, a molar ratio between metal and the binding groups in the binding block copolymer of 1:10 to 1: 1, particularly preferably from 1: 6 to 1: 2, is preferably maintained. For example, particularly molar ratios between methacrylic acid units in the binding block polymer to Pd ²⁺ of 1: 8, from vinyl pyridine units to Cu (I) from 1: 4, from Cd to vinyl pyridine from 1: 6, from Au ^{3 *} to pyridine from 1: 3.

No particle aggregation and no crystal growth beyond the block copolymer micelle was observed in the colloidal preparations produced according to the invention. However, chemical conversion does not necessarily result in a single colloid particle per micelle nucleus. With a suitable selection of the reaction conditions, several particles can be generated per micelle.

The liquid preparation according to the invention containing colloidal metal is particularly suitable for catalysis or for optical and magnetic applications. Many specialist applications for this are already known to the person skilled in the art for corresponding colloidal metal systems with different stabilization. The following may be mentioned as further applications: selective hydrogenations, i.e. Serve in addition to enen, triple in addition to double bonds, double bonds in addition to carbonyls or carbonyls in addition to double bonds; Carbonylation such as homologations, nitrates → isocyanates; Hydroformulations; Isomerizations of C – C frameworks; Cyclooligomerizations; Photooxidation or photo reduction. A particular advantage of the colloids according to the invention is that they have only a very small size distribution.

The following examples further illustrate the invention in conjunction with the accompanying drawing. In this represent:

Figure 1 shows the analytical result of a block copolymer cell with gold core according to the invention, i.e. the entire composite of polymer and metal colloid is described;

FIG. 2 shows a UV spectrogram of the red color of gold colloids according to the invention; FIG. 3 shows a graphic representation of the small-angle X-ray scattering for a gold colloid according to the invention and for a Bonnemann et al. manufactured known gold colloid.

Examples

example 1

A block copolymer of styrene and 4-vinylpyridine is produced by means of anionic polymerization in accordance with ref. (6) (not according to the invention). The total molecular weight is M _w = 135,000, the molar 4-vinylpyridine content is 21.5%. A corresponding amount of HAuCl _{4 is} added to a solution of 1 g of this block copolymer in 50 ml of toluene, for example in a molar ratio of 1: 3 (Au ^{3 *} to pyridine units). The gold acid crystals, insoluble in toluene, are dissolved micellarly in the block copolymer. The addition of hydrazine as a reducing agent results in a spontaneous red coloring of colloidal gold.

Example 2

The block copolymer micelles of the system obtained according to Example 1 are measured with a Nicomp C370 particle size analyzer. The result is a micelle diameter of 138.9 nm with a width of the distribution of 10.4%, as can be seen in the enclosed analysis result (FIG. 1). This micelle size changes only insignificantly when loaded with salt (HAuCl ₄ ) and during the subsequent reduction.

Example 3

The plasmon band (red color) that is usual for gold colloids is detected with UV spectrometry. The result is a spectrum which is typical of a finely divided, narrowly distributed gold coloid (FIG. 2). Example 4

A block copolymer of styrene and butadiene (M _w = 60,000) with 25 mol% butadiene content is epoxidized and the epoxy formed is opened in a known manner at room temperature with diethylamine or methylethanolamine with Lewis acid catalysis. The block copolymer thus partially hydrophilized is dissolved in toluene and mixed with crystalline silver nitrate. As in Example 1, a homogeneous micellar solution is obtained after stirring. The subsequent reduction with hydrazine gives a yellow solution which consists of narrowly distributed micelles containing silver colloids with a very sharp plasmon band which is customary for silver colloids.

Example 5

A block copolymer of isoprene and + -butyl methacrylate (M _w = 50,000, proportion of + -BMA 18%) is produced by means of anionic polymerization and hydrolyzed acidic to polyisoprene (b) polymethacrylic acid. The polymer is dissolved in cyclohexane and filled with Na ₂ PdCl ₄ (molar ratio Pd ²⁺ to methacrylic acid 1: 8). The subsequent reduction with H ₂ N ₂ results in a stable, deep black Pd colloid which is stabilized by block copolymers.

Example 6

The polystyrene (b) -poly (4) vinylpyridine block copolymer described in Example 1 is quaternized with methyl bromide. A solution of this block copolymer in THF is filled with copper (I) chloride (molar ratio Cu (I) to vinylpyridine units 1: 4) and reduced with butyllithium to a stable, rust-brown copper colloid.

Example 7

The quaternized block copolymer described in Example 6 is in a toluene / THF mixture (97: 3 wt .-%) with cadmium perm chlorate added (molar ratio Cd: vinyl pyridine 1: 6). After the salt has completely dissolved, H ₂ S is fumigated. A yellow colloidal CdS solution results, from the UV spectrum of which one can deduce narrowly distributed, approximately 8 nm large CdS semiconductor particles.

Example 8

A Pd colloid stabilized with polystyrene (b) poly (4) vinylpyridine is used to hydrogenate cyclohexadiene at room temperature and under 1 atm hydrogen pressure in toluene solution. The reaction is stopped after the calculated amount of hydrogen has been taken up . This results in a reactivity comparable to other Pd colloids (2) with a full selectivity for the reduction of cyclohexadiene to cyclohexene (> 98%) within the measurement accuracy.

Example 9

A conventionally produced gold colloid (stabilized with NR ₄ , analogous to Bonnemann loc. Cit.) And a colloid stabilized with polystyrene (b) - poly (4) vinylpyridine are characterized by small-angle X-ray scattering (FIG. 3). The conventionally produced colloid particle shows an unstructured diffractogram (Δ), which in this case can be inferred from particle aggregates, while the block-copolymerized product can be described with a spherical geometry with a radius of 5.2 nm and a very small distribution width.

Claims

claims 1. Liquid preparation with a content of colloidal metal in metallic, oxidic or sulfidic semiconducting form in a liquid organic or inorganic solvent, characterized by a content of micelles which consist of a block copolymer which contains at least one solva in the solvent ¬ tisierendem polymer block and a polymer block bindable for the colloidal metal and which contain the colloidal metal included. 2. Preparation according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the bindable polymer block contains basic or acidic groups. 3. Preparation according to claim 2, that the binding polymer block contains amine groups, amide groups or basic heterocyclic units. 4. Preparation according to claim 2, d a d u r c h g e k e n n z e i c h n e t that the bindable polymer block carboxyl groups or / and Contains hydroxyl groups. 5. Preparation according to one of the preceding claims, characterized in that the block copolymer at least one solvatisieren¬ the polymer block, selected from polystyrene, polyisoprene, polypropylene glycol, polyalkylstyrene and polybutadiene and at least one binding block selected from poly (4) vinylpyridine, poly ( 2) contains vinyl pyridine, polyethylene glycol, polar modified polydienes and polyacrylic acid / poly methacrylic acid. 6. Preparation according to one of the preceding claims, that the colloidal metal is a noble metal or a semi-conductive oxide or sulfide-forming metal. 7. Preparation according to one of the preceding claims, that the size of the colloidal particles lies between 2 nm and 20 nm. 8. A process for the preparation of the liquid colloid preparation according to one of claims 1 to 7, characterized in that a salt of a metal which can be converted into colloidal form is added to a solution of the block copolymer in a suitable solvent, with the formation of metal salt-containing micelles the block copolymer, then a) the salt is reduced to form the colloid and, if appropriate, the colloidal metal thus obtained is converted into its sulfide or oxide semiconductor form using a sulfide or hydroxide donor, or b) the salt is transferred directly using a sulfide or hydroxide donor converted into its colloidal sulfidic or oxidic semiconductor form. 9. The method according to claim 8, d a d u r c h g e k e n n z e i c h n e t that one uses a salt of a metal from the group platinum group metals, gold, silver, copper, cadmium, zinc, titanium, iron, nickel and cobalt, in particular as chloride or perchlorate. 10. The method according to claim 8 or 9, characterized in that the reducing agent used is hydrazine, NaBH ₄ , butyllithium hydride or superhydride. 11. The method according to any one of claims 8 to 10, characterized in that H ₂ S, NaHS or Na ₂ S is used as the sulfide donor. 12. The method according to any one of claims 8 to 10, characterized in that the oxide donor H ₂ 0, NaOH (in H ₂ 0 / THF systems) or NR ₄ OH, wherein each R is a straight-chain, branched, saturated or unsaturated Alkyl group with 1 to 12 carbon atoms means used. 13. The method according to any one of claims 8 to 12, so that the metal salt is added in such a quantity that a molar ratio between metal and the binding groups in the binding block of the copolymer is from 1:10 to 1: 1. 14. The method according to any one of claims 8 to 13, so that the metal salt is added to the solution of the block copolymer in solid form. 15. Use of a liquid preparation according to one of claims 1 to 7 as a catalyst. 16. Use of a preparation according to one of claims 1 to 7 for optical applications. 17. Use of a preparation according to one of claims 1 to 7 for magnetic applications.