RO132703A2 - Process for preparing polymeric cryogels based on 2-hydroxyethyl methacrylate and graphene oxide - Google Patents

Abstract

The invention relates to a process for preparing polymeric cryogels based on 2-hydroxyethyl methacrylate and graphene oxide, meant to be used for purification of water with high organic substance content. According to the invention, the process consists in photopolymerizing 2-hydroxyethyl methacrylate in the presence of N,N'-methylene bis-acryl amide as a cross-linking agent and 1-hydroxycyclohexyl-phenyl ketone with double role, of photopolymerization initiator and ligand, in a polymerization medium consisting of an aqueous solution with graphene oxide content, at a temperature below the mixture freezing point and in the presence of UV radiation, to result in a composite with controlled morphological characteristics.

Description

DESCRIPTION OF THE INVENTION

PROCESS FOR PREPARATION OF POLYMERIC CRYSTALS BASED ON 2-HYDROXYETHYL METACRYLATE AND GRAPHIDE OXIDE

The invention relates to a high-porosity polymeric cryogel, based on 2-hydroxyethyl methacrylate and graphene oxide, and to a process for its preparation. The cryogel is prepared by introducing graphene oxide dispersed in water, in which 2-hydroxyethyl polymerization takes place. of methacrylate (HEMA), in the presence of additions of N, N'methylene bis-acrylamide (MBAAM) as crosslinker and 1-Hydroxycyclohexyl-phenyl ketone (HCFC) with dual role, polymerization photoinitiator and ligand. The prepared composite can be used in applications aimed at photocatalytic purification of water and wastewater or, after a further step of thermal reduction of graphene oxide, in applications where the use of electrically conductive porous materials is required.

The polymeric cryogels with macroporous structure based on HEMA and MBAAM known by radical polymerization initiated by Ν, Ν, Ν ', Ν'-tetramethylene diamine (TEMED) [1] are known for selective recognition and protein purification. In another approach, HEMA-based cryogels having DNA inserted into the structure are used to remove anti-cDNA antibodies from blood plasma [2]. Cryogels obtained by radical polymerization (TEMED polymerization initiators and ammonium persulfate) from HEMA, glycidyl ether and MBAAM were studied in support of controlled-release drugs [3], The porous structure of HEMA-based cryogels allowed new approaches for elimination cholesterol in the coronary arteries. The cryogels studied are also obtained by radical polymerization initiated by TEMED [4]. Another application in the medical field, intended for the treatment of epidermal and transdermal wounds, involves the use of polymeric composites prepared by introducing polyuronic acid into polyHEMA macroporous matrices cross-linked with diacrylated polyethylene glycol) [5], Other applications in the medical field use HEMA-based cryogels and N-methacryloyl- (L) -histidine methyl ester obtained by mass polymerization. The obtained cryogel is complexed with Fe (III) ions and the resulting material is used for the absorption of enzymes [6], in a similar approach is presented a method of obtaining cryogels with controlled porosity based on HEMA and MBAAM which, then , are loaded with iron oxides leading to the production of composites that have potential interest for the purification of water and waste water [7],

to 2017 00036

25/01/2017

The main disadvantages of HEMA and MBAAM-based cryogels reported so far are:

- does not use HCFC with the dual role of polymerization photoinitiator and cation complexing agent.

- do not contain GO attached to the polymeric matrix of P-HEMA cross-linked with MBAAM.

The most similar cryogels prepared from HEMA and MBAAM that can be used to purify water and wastewater are made by thermal initiation of the polymerization process, the cryogel being subsequently loaded with nanoparticles of approx. 20 nm of α-Fe2O3 or activated carbon microparticles with dimensions of approx. 250-500 pm [7],

The technical problem that the invention aims to solve is to obtain a high porosity HEMA and MBAAM cryogel having introduced into the GO structure, which, due to the functional groups, can physically and chemically bind various organic compounds or cations present in water, and HCFC with the dual role of polymerization and complexing photoinitiator, and by subsequent thermal exposure will lead to the reduction of GO to graphene and obtaining cryogels with high electrical conductivity.

The solution of the technical problem consists in obtaining high porosity cryogels based on HEMA using MBAAM as crosslinker, excess HCPC, double role, photoinitiator and complexing agent, and an aqueous solution of GO as a polymerization medium for the monomers used.

The main advantages of the proposed invention are:

- process of photochemical polymerization that allows both precise control of the morphological characteristics of the cryogel (porosity, size, shape) and the elimination of some chemical compounds (initiators of type TEMED, ammonium persulfate) that, retained in the final structure, can interfere with the processes specific to water purification.

- The use of HCFC allows both the photoinitiation of the polymerization and the process steering at the low temperatures required to obtain the cryogels and the complexation of some cations or the chemical bonding of organic compounds present in water due to the existence of hydroxy (OH) and carbonyl (CO) groups in the HCFC structure.

- The use of GO dispersed in water as a polymerization medium leads to its retention in the final structure of the polymeric cryogel, thus allowing the chemical bonding of some organic compounds present in the water due to the existence of various functional groups in the GO structure.

to 2017 00036

25/01/2017 Extended domain of use due to the possibility of obtaining an electroconductive polymeric cryogel by reducing GO, retained in the structure, to graphene, realized in a later, simple stage, of short term thermal exposure (2-3 min., 110 -130 ° C).

According to the invention, obtaining the cryogel involves in the first stage the preparation of an aqueous solution containing GO, HEMA and MBAAM. After stirring the MBAAM and stirring the mixture, add HCFC. The dissolution of the photoinitiator (HCFC) is carried out under energetic stirring at a temperature of approx. 35 ° C, the reaction mass having a homogeneous appearance after approx. 120-180 min. The aqueous solution containing the dissolved reactants is transferred into a transparent container with UV radiation having the shape and dimensions specific to the application concerned. The container containing the reagent mixture is placed in a cooling bath at a temperature of 260 K. At the same time, the container is exposed to UV radiation with a wavelength of 310-330 nm. The process of polymerization and formation of the cryogel lasts 36-48 hours, with cooling and UV exposure being ensured continuously. After completion of the polymerization step, the obtained cryogel is lyophilized to remove the solvent (water) and obtain the cryogel in the dry state. The cryogel thus obtained has a porous and homogeneous appearance having a yellowish color due to the presence of GO in the structure. If an electroconductive cryogel is to be obtained, to the method of obtaining detailed above, a graphene reduction step of GO retained in the polymeric structure is added. This is achieved either by exposure for 2-3 min. to a hot air source with a temperature of 110-130 ° C or by exposure to a combined UV-IR power source for a period of 60-120 min. After thermal or UV-IR exposure, the cryogel takes on a gray-metallic appearance.

The following is an example of an embodiment of the invention for obtaining photoluminescent composites:

In a typical experimental procedure, the initial step involves the preparation of an aqueous solution of GO with a concentration of 5 mg / mL. before use, the GO solution is ultrasound for 10 min. to ensure high homogeneity. In the second step, 1 mL HEMA and 0.2 g MBAAM are dissolved in 8 mL GO solution followed by vigorous stirring for approx. 60 min. After complete dissolution and obtaining a homogeneous solution, 0.05 g HCFC is added followed by the resumption of energetic stirring for approx. 90 min. at a temperature of 35 ° C. After the addition of the photoinitiator (HCFC) the stirring proceeds without exposure to sunlight / artificial light sources to avoid premature initiation of the polymerization process. meanwhile, the cooling bath starts and waits until it reaches a temperature of 260-261 K. The vessel in which the cryogel formation process takes place is

to 2017 00036

01/25/2017 Pre-cools to process temperature (260-261K). In the third step, the solution containing the aforementioned reactants is transferred to the immersed container in the cooling bath. To initiate the photopolymerization process, a UV-B (310-330 nm) radiation source is used, having dimensions that allow the solution to be exposed evenly. The process is carried out under cooling conditions (360-361 K) and continuous UV exposure, its duration being between 36 - 48 hours depending on the amount of cryogel to be prepared. After the process is completed, the cryogel is immediately transferred to a lyophilizer. Depending on the equipment used, the freeze-drying process lasts 40-48 hours, finally obtaining a high-porosity, yellow-brown cryolel having the shape and dimensions of the container in which the polymerization process takes place. The cryogel thus obtained can be used for the photocatalytic purification of waters with a high content of organic substances.

In order to obtain the electroconductive cryogel, the preparation process proceeds identically and a subsequent stage of thermal or UV / IR exposure is required. Thus, after freeze-drying and obtaining the dry cryogel, it is exposed on all external surfaces for 2-3 min. at a hot air flow of 110-130 ° C or at a UV-IR power source for a period of 60-120 min.

Claims (2)

1. High-porosity polymeric cryogel based on 2-Hydroxyethyl methacrylate (HEMA), N, N'methylene bis-acrylamide (MBAAM), 1-Hydroxycyclohexyl-phenyl ketone (HCFC), graphene oxide (GO) with a physical configuration - chemistry favorable both for the use in photocatalytic processes of water purification and for obtaining electroconductive cryogels, characterized in that: it is obtained by UV photopolymerization at temperatures of 260-261 K, initiated by HCPC, of a mixture of HEMA and MBAAM monomers in - an aqueous environment in which GO is dispersed, followed by obtaining the dry cryogel by lyophilization and its thermal exposure to reduce GO to graphene and to obtain an electroconductive cryogel. 2. Process for the preparation of a high porosity polymeric cryogel based on 2 Hydroxyethyl methacrylate and graphene oxide, characterized in that it involves the preparation of an aqueous solution of graphene oxide (GO) in which 2-Hydroxyethyl methacrylate (HEMA) is dissolved, Ν , Ν'-methylene bis-acrylamide (MBAAM) and 1-Hydroxycyclohexyl-phenyl ketone (HCFC) which is further cooled to 260-261 K and concomitantly photopolymerized by exposure to UV radiation, the cryogel thus prepared being freeze dried and thermally exposed. for the reduction of graphene oxide to graphene for obtaining electroconductive properties.