TWI421229B - Environmental friendly process of sensitizers for dye sensitized solar cells - Google Patents

Description

Environmentally friendly process for dye-sensitized solar cell sensitizer

The present invention relates to the purification of sensitizing dyes for dye-sensitized solar cells. In particular, the present invention provides a process for purifying 4,4'-dicarboxy-2,2'-bipyridine.

The dye-sensitized solar cell is mainly a new type of solar cell developed by imitating the principle of photosynthesis. Its main advantages are abundant raw materials, low cost, relatively simple manufacturing technology, and great advantages in large-scale industrial production, and all raw materials. And manufacturing technology is non-toxic, non-polluting, and some materials can be fully recovered, which is of great significance for the protection of the human environment. In summary, dye-sensitized solar cell dye-sensitized solar cells have the following advantages compared to conventional solar cells: (1) the service life can be as long as 15-20 years; (2) the structure is simple, easy to manufacture and production technology Simple, easy to large-scale industrial production; (3) low production cost, only 1/5 to 1/10 of solar cells; (4) less energy consumption in the manufacturing process; (5) non-toxic and non-polluting in the manufacturing process.

The dye-sensitized solar cell is mainly composed of a nanoporous semiconductor film, a dye sensitizer, a redox electrolyte, a counter electrode, and a conductive substrate. The nanoporous semiconductor thin film is usually a metal oxide (TiO ₂ , SnO ₂ , ZnO, etc.), which is collected on a glass plate having a transparent conductive film as a negative electrode of a dye-sensitized solar cell, and the counter electrode is used as a reduction catalyst, usually with The glass of the transparent conductive film is plated with platinum. The sensitizing dye is adsorbed on the surface of the nanoporous titanium dioxide film, and the electrolyte containing the redox couple is filled between the positive and negative electrodes.

Dye sensitizers for dye-sensitized solar cells can be divided into two categories: metal complex pigments, including bismuth series pigments and other metal series pigments (such as Os, Fe, Cu, Pt), and organic pigments. Classes, including methyl dyes and other organic pigments (such as phthalocyanine, azo, coumarin). At present, in the field of dye-sensitized solar cells, a series of dyes based on base metals are the mainstream. US20050139257A1 provides a photosensitized transition metal complex of the formula MLX2 wherein M is a transition metal selected from the group consisting of Ru(II), Os(II), Fe(II), Re(I) and Tc(I); ligand groups, H ₂ O and consisting of pyridyl ^- and X is selected from ^{NCS -, Cl -, Br -} , I -, CN -, NCO; polypyridine ligands. US7321037 discloses a photosensitizing dye for a cerium-containing composite applied to a dye-sensitized solar cell.

4,4'-dicarboxylic acid-2,2'-bipyridine (4,4'-dicarboxy), a key material for the preparation of photosensitizing dyes (eg N3, Z907, N719, N854, K8, K19, K73, Z910, Z955) -2,2'-bipyridine) is a very important ligand whose main function is to bond the dye to TiO ₂ . This kind of ligand base is quite expensive, and most of them are mainly self-synthesis. However, the crude product synthesized must be further purified to be a raw material for the dye-sensitized solar cell sensitizer. Conventional techniques for the purification of 4,4'-dicarboxylic acid-2,2'-bipyridine require boiling with 50% nitric acid for four hours (Adremi R. Oki and Robert J. Morgan, Syn. Comm., 1995, 25(24), 4093-4097; Martin Lang, Susanne Lang-Fugmann, and Wolfgang Steglich, org. Syn., 2004, 10, 432). However, the purity of the product after the purification process is still not satisfactory, and the waste acid liquid generated in the process is seriously polluted, and the treatment cost is not competitive in the market, and the economic benefit of the dye-sensitized solar cell is also affected. In summary, the above-mentioned nitric acid boiling purification method has the following disadvantages:

(1) Nitric acid is a volatile, strong acid that is highly corrosive to boilers in industrial production and releases toxic NO ₂ gas.

(2) Nitric acid has a risk of explosion in boiling state.

(3) This method needs to be heated to boiling for 4 hours to increase energy consumption.

(4) The wastewater produced by this purification method is strongly acidic and causes serious pollution to the environment.

(5) Even after purification by this method, the purity of the product is not satisfactory, and the purification process needs to be repeated one more time.

Therefore, there is still a need in the art for a method for purifying 4,4'-dicarboxylic acid-2,2'-bipyridine which is safer, less expensive, less polluting and of increased purity.

The invention utilizes an alkaline solution and an acidic solution to treat 4,4'-dicarboxylic acid-2,2'-bipyridine to obtain 4,4'-dicarboxylic acid-2,2'-bipyridine having improved purity. The purification process of the present invention is safer, more polluting, less expensive, and yields a higher purity product than conventional techniques. The purification method of the present invention processes the impure 4,4'-dicarboxylic acid-2,2'-bipyridine using a relatively inexpensive alkali and an acidic solution, and can be carried out at room temperature, compared with the method of the prior art. It is more convenient, safe and cheap, and the pH value of the produced wastewater is neutral, which not only meets the emission standards, but also has the advantages of wastewater reuse.

The invention provides a method for purifying 4,4'-dicarboxylic acid-2,2'-bipyridine, which comprises the following steps:

(a) stirring and dissolving the impure 4,4'-dicarboxylic acid-2,2'-bipyridine using an alkaline solution;

(b) adding an acidic solution to the resulting mixture by titration to obtain a precipitated product, ie, purified 4,4'-dicarboxylic acid-2,2'-bipyridine;

(c) The suspension is filtered and the filtrate is combined with the precipitated product to obtain a high purity 4,4'-dicarboxylic acid-2,2'-bipyridine.

According to the invention, the alkaline solution in step (a) may be an alkali gold hydroxide solution or aqueous ammonia. Preferably, the alkaline solution is an alkali gold hydroxide or ammonia water; more preferably, the alkaline solution is sodium hydroxide, potassium hydroxide, lithium hydroxide or ammonia water. Most preferably, the alkaline solution is a sodium hydroxide solution.

According to the invention, the acidic solution in step (b) can be any acidic solution. Preferably, the acidic solution is hydrochloric acid, nitric acid, sulfuric acid and acetic acid. More preferably, the acidic solution is hydrochloric acid. The product precipitated by the acidic solution in the step (b) is purified 4,4'-dicarboxylic acid-2,2'-bipyridine.

According to the present invention, the alkaline solution in the step (a) and the acidic solution in the step (b) may be in any concentration. According to the present invention, the concentration of the alkaline solution in the step (a) and the acidic solution in the step (b) may be adjusted according to the type of the base to be used and the acid type, so that the pH of the solution after the acidic solution titration step is medium. Sex. The solution is a neutral waste liquid, meets emission standards, does not pollute the environment, and has the advantages of wastewater reuse. Preferably, the concentration of the acidic solution in step (b) is at least the same as the concentration of the alkaline solution in step (a). More preferably, the concentration of the acidic solution in step (b) is greater than the concentration of the alkaline solution in step (a).

According to the present invention, the filtrate obtained by filtering the suspension in the step (c) is combined with the precipitated product to obtain a high-purity 4,4'-dicarboxylic acid-2,2'-bipyridine.

According to the present invention, the method for purifying 4,4'-dicarboxylic acid-2,2'-bipyridine can be carried out at room temperature, without heating, saving energy and being more environmentally friendly.

The purification method of the present invention can obtain 4,4'-dicarboxylic acid-2,2'-bipyridine having a purity of up to 90% or more. Preferably, the purity of the 4,4'-dicarboxylic acid-2,2'-bipyridine is above 95%; more preferably, the purity of the 4,4'-dicarboxylic acid-2,2'-bipyridine is achieved. 98%, even 99%, above.

The purification of conventional techniques requires the use of boiling nitric acid, which is inconvenient and at risk of public safety. The purity of the product after one purification process is still not ideal, even after the second and third purification, the purity has reached the limit (about 85%) can not be improved. However, the purification method of the present invention treats the acidified crude product 4,4'-dicarboxylic acid-2,2'-bipyridine using an alkali and an acidic solution, and can obtain not only 4,4'-di with a purity of more than 90%. Carboxylic acid-2,2'-bipyridine, and the entire purification process is safe, inexpensive and free of contamination. In summary, the purification method of the present invention has the following advantages:

(1) The raw materials are general alkali and acidic solutions, which are cheap and easy to obtain.

(2) The waste liquid produced by the purification process can be neutral and less likely to cause environmental pollution.

(3) The purification process can be carried out at room temperature without heating, which is safer and reduces energy consumption.

(4) The obtained 4,4'-dicarboxylic acid-2,2'-bipyridine has high purity.

Comparative Example 4,4'-Dicarboxylic acid-2,2'-bipyridine conventional purification process

After 5 g of the unpurified crude product 4,4'-dicarboxylic acid-2,2'-bipyridine was mixed with 170 ml of 50% nitric acid, it was stirred and heated to boiling for 4 hours. After the reaction apparatus was cooled, the solution was poured into a beaker containing ice cubes and diluted with water to 1000 ml. The precipitated solid was filtered and washed with water (5 x 50 mL) until neutral, and then dried, with a purity of 85%.

Example 1 Purification Process of 4,4'-Dicarboxylic Acid-2,2'-Bipyridine of the Invention

5 g of the unpurified crude product 4,4'-dicarboxylic acid-2,2'-bipyridine was slowly added to a 2 M NaOH 50 ml solution, and rapidly stirred at room temperature to completely dissolve the solid. The mixture was then added to the mixture by titration with 50 ml of the same concentration of HCl to precipitate the product. After filtration, the filtrate is dried to obtain a purified product. The above process is shown in the following process:

After the above purification process, 4,4'-dicarboxylic acid-2,2'-bipyridine is obtained with a purity of more than 99%. The purity test of 4,4'-dicarboxylic acid-2,2'-bipyridine was tested by the National Instruments Valuable Instrument Center using a gas chromatography mass spectrometer (Finnigan TSQ-700 GC/LC/MS), electronics. Free method (EI) and ionization voltage of 20 eV. Figure 1 shows the results of analysis by gas chromatography mass spectrometry. The signal of 243.9 m/z in the spectrum is the main molecular ion peak:

The 199.9 m/z signal is the molecular ion peak from which a carboxylic acid molecule is removed:

The 155.1 m/z signal is the molecular ion peak of the two carboxylic acid molecules removed:

1 is a gas chromatographic mass spectrometer analysis diagram of 4,4'-dicarboxylic acid-2,2'-bipyridine purified by the purification process of the present invention.

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Claims (8)

The present invention provides a method for purifying 4,4'-dicarboxylic acid-2,2'-bipyridine, which comprises the steps of: (a) using an alkaline solution to impure 4,4'-dicarboxylic acid-2, 2'-bipyridine is dissolved and dissolved; (b) an acidic solution is added to the resulting mixture by titration to obtain a precipitated product, ie, purified 4,4'-dicarboxylic acid-2,2'-bipyridine; (c) filtering the suspension and combining the filtrate with the precipitated product, and drying to obtain high-purity 4,4'-dicarboxylic acid-2,2'-bipyridine; wherein the alkali in the step (a) The solution is an alkali gold hydroxide solution or ammonia water; and the purity of the obtained 4,4'-dicarboxylic acid-2,2'-bipyridine is as high as 95% or more. The method of claim 1, wherein the alkaline solution in the step (a) is sodium hydroxide, potassium hydroxide, lithium hydroxide or aqueous ammonia. The method of claim 1, wherein the alkaline solution in the step (a) is sodium hydroxide. The method of claim 1, wherein the acidic solution in the step (b) is hydrochloric acid, nitric acid, sulfuric acid and acetic acid. The method of claim 1, wherein the acidic solution in the step (b) is hydrochloric acid. The method of claim 1, wherein the pH of the solution after the acidic solution titration step of step (b) is neutral. The method of claim 1, wherein the purity of the obtained 4,4'-dicarboxylic acid-2,2'-bipyridine is as high as 98% or more. The method of claim 1, wherein the purity of the obtained 4,4'-dicarboxylic acid-2,2'-bipyridine is as high as 99% or more.