EP4313913A1

EP4313913A1 - Composition comprising carbon quantum dots (cqd´s)

Info

Publication number: EP4313913A1
Application number: EP22721273.5A
Authority: EP
Inventors: Wolfgang Schwarz
Original assignee: Cas Composite Applied Systems GmbH
Current assignee: Cas Composite Applied Systems GmbH
Priority date: 2021-03-29
Filing date: 2022-03-29
Publication date: 2024-02-07
Also published as: DE102021107867A1; WO2022207592A1

Abstract

The invention relates to a composition for building purposes, comprising 0.001 – 2 wt.% of carbon quantum dots. Furthermore, the use of the composition is provided in a paint composition, coating agent, binder, concrete or mortar.

Description

Composition with Carbon Quantum Dots (CQD's)

The invention relates to compositions containing carbon quantum dots (CQD's). The content of CQD's causes a targeted modification of the properties of the solid mixture, such as electrical conductivity, ion conductivity, polarization resistance, adhesion to solid substrates measured as tensile strength, galvanic currents from galvanic metal anodes, preferably zinc anodes, etc .

Changes in the material properties such as strength, tensile strength, electrical conductivity and changes in the electrochemical properties such as ionic conductivity, polarization resistance, galvanic activity of galvanic metal anodes, preferably zinc anodes, are advantageous.

According to the generally accepted definition, a quantum dot (QD) is a nanoscopic material structure. Charge carriers (electrons, holes) in a quantum dot are restricted in their mobility in all three spatial directions to such an extent that their energy no longer assumes continuous but only discrete values. Typically, their own atomic scale is about 10 ⁴ atoms. Several QD's can combine to form agglomerates - quantum dot molecules - [Somnath Koley, Jiabin Cui, Yossef E. Panfil, and Uri Banin, acc. Chem. Res. (2021), 54, 5, 1178 - 1188] Quantum dots are mini-crystals with edge lengths of around three nanometers that can be excited to fluoresce like a single atom with short-wave light. The color of a quantum dot depends on its size: a two-nanometer diameter crystal emits shorter-wavelength light than one composed of the same atoms with a diameter of eight nanometers [Qin Hu, Xiaojuan Gong, Lizhen Liu, and Martin MF Choi, Hindawi, Journal of Nanomaterials (2017), Volume 2017, Article ID 1804178]

Carbon Quantum Dots (CQD's) are a new class of fluorescent carbon nanomaterials that possess the attractive properties of high stability, good conductivity, low toxicity, environmental friendliness, simple synthesis routes, and comparable optical properties to quantum dots. Due to their strong and tunable fluorescence emission properties, CQDs are used in biomedicine, optronics, catalysis and sensors [Wang, Youfu; Hu, Aiguo (2014). Journal of Materials Chemistry C. 2 (34), 6921] CQDs can also be obtained from everyday materials such as polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), bovine albumin, ascorbic acid, citric acid, chitosan, carregan powder, etc. [Wang, Youfu; Hu, Aiguo (2014) Journal of Materials Chemistry C (2014), 2, 69213] [Raz Jelinek, Carbon Quantum Dots, Springer International Publishing Switzerland, April 22, 2018] Furthermore, CQD's are commercially available, e.g. at Sigma-Aldrich Co.

(a subsidiary of Merck KGaA) as a 0.2% aqueous colloid with a quantum efficiency of 5% and a fluorescence _em 450 - 550 nm.

Nothing is yet known about the use of CQDs to modify materials and material properties, in particular compositions for construction purposes of mixtures, in particular solids and/or electrolytes, for example their improvement in conductivity and polarization resistance, their strength or adhesion to solid substrates .

The object of the present invention is therefore to provide a composition whose conductivity and polarization resistance and whose adhesion to solid substrates is improved and which can be used in particular for construction purposes.

This object is achieved by a composition according to claim 1. Preferred configurations of the composition are specified in the dependent claims.

Surprisingly, it was found that low to very low levels of CQD's can be used to specifically modify material properties, in particular of solids, such as electrolytic and / or electrical conductivity, polarization resistance, adhesive strength, compressive strength, elasticity, ductility, activity of galvanic embedded in the solid according to the invention Metal anodes, preferably zinc anodes, etc.

The admixture of even small amounts of CQDs to mixtures causes significant changes in the material properties, for example of solid mixtures but also of electrochemical systems that contain CQD-containing electrolyte solutions and/or electrodes.

The compositions according to the invention preferably contain at least one chemical compound or a mixture of chemical compounds selected from inorganic chemical substances such as silicates, silicon dioxide, aluminates, aluminosilicates, carbonates, carbon, graphite, etc., from organic chemical substances such as polymers (e.g. polyamide, Polyurethanes, etc.), resins (acrylic resins, epoxy resins, etc.), cellulose, silicones, silicone rubber, etc. They can also contain metals in the form of powders, fibers, etc. The solid according to the invention has at least one property selected from hard, soft, brittle, elastic, plastic, deformable. The composition according to the invention for building purposes is preferably a building material, in particular an artificial building material. The composition according to the invention for building purposes is preferably a paint, coating material, binder,

concrete or mortar.

The composition according to the invention for building purposes is preferably liquid, in particular viscous. The composition preferably cures at room temperature within three weeks, more preferably within one week, most preferably within four days. The CQD's content can be achieved by impregnating the solid mixture, for example with a liquid in which the CQD's are suspended, preferably colloidally. Another method according to the invention is to admix the CQDs during the manufacture of the solid, e.g. to the raw material or raw materials from which the solid according to the invention is produced. The CQDs are preferably added to the raw material or raw materials as a suspension, preferably as a colloid, in a suitable liquid. A further preferred method is to admix suitable substances to the raw material or raw materials, so that the CQDs arise in situ during the production or formation of the mixture according to the invention.

CQDs usually have a size of 1 - 10 nm, they can agglomerate into CQD molecules with particle sizes up to 100 nm. For the sake of simplicity, both singular and CQD agglomerates such as CQD molecules are referred to as CQDs in the following.

The CQDs preferably have a particle size of >1 nm, preferably >3 nm. They contain carbon and when excited with electromagnetic radiation, e.g. UV light, they emit fluorescent light in the wavelength range from 380 nm to 700 nm, preferably in the wavelength range from 400 nm to 600 nm. Agglomerates of CQDs - so-called quantum dot molecules - behave as CQDs and are referred to as such, but as quantum dot molecules can have particle sizes> 10 nm.

In the context of the invention, UV light is understood to mean light with a wavelength of <400 nm, in particular light with a wavelength of 100-380 nm.

The invention is characterized in a preferred embodiment in that the content of CQD's material properties selected from strength, tensile strength, electrolytic conductivity, polarization resistance, galvanic activity of embedded metal electrodes, electrical conductivity are modified in a targeted manner, with the selection given being exemplary and not conclusive. CQD ^'s within the meaning of the invention are CQD's according to the prior art as already described and described, for example, in Raz Jelinek, Carbon Quantum Dots, Springer International Publishing Switzerland, April 22, 2018.

The CQD's are preferably produced in the medium in which the CQD's are mixed with the raw material(s) or with which the solid is impregnated. One of several methods according to the invention for producing a CQD suspension according to the invention comprises the step of synthesizing the CQDs from the medium in which they are subsequently suspended. The medium is thus both the liquid in which the CQDs are suspended and at least one of the raw materials from which the CQDs are made. Such a medium are, for example, polyethers, from which CQDs are produced by oxidative polycondensation, as is generally known. For this purpose, for example, polyethylene glycols (PEG) are mixed with alkali metal hydroxides. The PEGs condense around the alkali ion to form polycyclic aromatics and subsequently to CQDs. Details are described, for example, in Ji Chen, S.K. Spear, J.G., Huddleston and RD Rogers, "Polyethylene glycol and Solutions of polyethylene glycol as green reaction media", Green Chem., 2005, 7, 64-82.

Good results were achieved when using polyethylene glycol as the polyether, whereby the properties of the CQDs formed could be controlled via the cation (e.g. Li, Na, K, Rb, Cs) and the concentration of the alkali hydroxide added. CQD colloids produced in this way showed fluorescence in the range from 380 to 600 nm, in particular 400-600 nm, preferably with a peak in the range from 450 nm to 550 nm.

CQD suspensions or colloids produced in this way had a CQD content of 0.1% by weight. up to 10% by weight, approximately determined using the known molar extinction coefficient of 1.2 x 10 ⁶ M ¹ cnr ¹ at 265 nm.

When entering an electrically conductive coating according to EP 1 068 164 A1 (Example 1), it was surprisingly found that a content of CQD's significantly increases both the electrical conductivity and the tensile strength of the coating on concrete and also the electrolytic conductivity of the concrete covering on which the conductive coating was applied not only increases but also stabilizes the electrolytic conductivity in a dry environment (45% relative humidity), so that it decreases far less than in the absence of CQD's (Examples 1 - 7).

Surprisingly, even low to very low CQD contents have an effect on the material properties. Even just 0.5% of a 0.5% CQD suspension in polyethylene glycol caused a significant increase in adhesive strength (from 0.4 to 1.2 MPa), a decrease in the surface electrical resistance of the coating (100 ohms/square to 25 ohms/square) (Example 1). Contents of 0.08% also have an advantageous effect both on the polarization resistance (DC resistance) and on the tensile strength (Example 6).

The composition for building purposes according to the invention comprises 0.001-2% by weight of carbon quantum dots, based on the total weight of the composition. The composition according to the invention preferably contains 0.005-0.5% by weight, more preferably 0.01-0.3% by weight, particularly preferably 0.015-0.25% by weight, in particular 0.02-0.2% by weight of carbon -Quantum dots based on the total weight of the composition.

Electrically conductive coatings on concrete that are permeable to water vapor and gas, especially if they can be anodically polarized, are used to protect the steel reinforcement from corrosion. Ambient humidity of < 65% relative humidity causes an increase in the electrolytic resistance in the surface area of the concrete to which the electrically conductive coating is applied. The cause lies in the drying out of the surface area of the concrete as a result of water vapor diffusion, possibly enhanced by electro-osmosis. The drying out of the concrete/paint interface also causes an increase in the polarization resistance, which can be measured as part of the DC resistance. Part of the polarization resistance is also the transfer resistance from the electrode to the electrolyte. The increase in the electrolytic resistance of the concrete cover and the polarization resistance decreases the effectiveness of the corrosion protection of the steel reinforcement by reducing the current flow between the conductive coating and the steel reinforcement. In addition, this can lead to concrete damage at the electrically conductive coating/concrete interface as a result of acid attack on the concrete by anodically formed acid.

For the electrochemical application of electrically conductive coatings on concrete, such as for the corrosion protection of steel in concrete, not only the electrolytic resistance of the concrete is important, but also the polarization resistance of the electrodes - anode and cathode. Total resistance includes polarization resistance and electrolytic resistance. The electrolytic resistance can be determined by means of impedance measurements, usually at 1 kHz in concrete. The polarization resistance is measured as direct current resistance by applying a direct voltage of, for example, 2-3 volts between the two electrodes and calculating the specific resistance from the measured direct current according to Ohm's law (Example 2). The resistance thus determined includes the polarization resistance and the electrolytic resistance. In the following, the at The DC resistance measured when applying a DC voltage is referred to as polarization resistance and in the examples as DC resistance. The electrolytic concrete resistance measured at 1 kHz and 120 Hz is called impedance.

Surprisingly, it was found that even a low content of CQD's, for example a CQD content of 0.005% by weight, based on the total weight of the composition that was used as a coating agent for a concrete test specimen, led to a significant reduction in the polarization resistance and an increase in the adhesive strength when storing the coated and polarized concrete specimens at 50% relative humidity (Example 1 & 2).

In the absence of CQD's suspended in the polyether, a three times higher polarization resistance of the concrete was measured after 60 days of storage at 50% relative humidity compared to the polarization resistance of the concrete in the presence of 0.01% CQD's.

Further tests showed that the results described above can generally be achieved with conductive coatings, preferably with conductive coatings containing carbon, for example selected from graphite, carbon black, graphene.

In a preferred embodiment, the composition for building purposes according to the invention contains one or more compounds selected from the group consisting of silicate, silicon dioxide, aluminate, aluminosilicate, graphite, carbonate, resin, silicone, cellulose and organic polymer. Preferably, the composition of said one or more compounds contains at least 5% by weight, more preferably >20% by weight, particularly preferably 30-95% by weight and most preferably 35-80% by weight of the one or several compounds composed of silicate, silicon dioxide, aluminate, aluminosilicate, graphite, carbonate, resin, silicone, cellulose and organic polymer.

In a preferred embodiment of the invention, the composition contains one or more aluminosilicates with the formula aM ₂ O _* bAl ₂ O _{3 *} cSiO ₂ , where the molar ratio c/b=0.1-15 and the molar ratio a/b=0. is 2-10, with M=Li, Na, K. The molar ratios c/b are preferably 1-11 and/or a/b 0.5-3, with M=Li, Na, K. It is also preferred that the composition contains one or more aluminosilicates comprising calcium, the molar ratio S1O2/AI2O3 preferably being <25, particularly preferably <20, the molar ratio Si0 ₂ /(Ca0+Al ₂ O ₃ ) being <10, particularly preferably < 5 and preferably the molar ratio Ca/Si is <2, particularly preferably <1. The ratio for Mg-containing aluminosilicates, the molar ratio SiCVCCaO+MgO+AhCh) is preferably <10, preferably <5.

Good results were achieved with conductive coatings containing aluminosilicate based on EP 1 068 164 A1, with a molar ratio S1O2/Al2O3 of the aluminosilicates of greater than 0.1, preferably >1, and an aluminosilicate content of greater than 1% by weight, preferably greater 3% by weight.

Advantageous results could also be achieved if, before the conductive coating was applied to the concrete, an aqueous suspension was applied to the concrete surface, in particular with a CQD content of 0.01-2% by weight, preferably 0.05-1% by weight. -%, analogous to a “primer” or a “primer” as described in Examples 3-5: After impregnation with an aqueous suspension containing 0.05% of CQD's, the polarization resistance was after 60 days of storage at 50% relative humidity by a factor of 3 lower than in the comparison sample without CQD suspension (Example 3).

The properties of the solid mixture, in particular the polarization resistance, can thus also be specifically modified by impregnating the solid mixture, e.g. concrete.

Surprisingly, it turned out that the CQD impregnation has a particular effect on the polarization resistance (DC resistance) and much less on the electrolyte resistance (impedance) (example 4):

Compared to the reference sample (sample 1), the polarization resistance (DC resistance) decreases by a factor of 1.8 when the concrete surface is impregnated with a primer containing 0.05% of CQDs and the direct current increases accordingly, which flows by the same factor with an applied voltage of 2 volts. However, the impedance is only reduced by a factor of 1.2. If the concrete substrate is only impregnated with polyether as in sample 4, adding CQD's to the same amount of polyether (sample 3) causes a decrease in polarization resistance (DC resistance) by a factor of 2 while the impedance only decreases by a factor of 1 .3 decreases.

The influence of the amount of CQD's with which the concrete substrate is impregnated affects the extent of the reduction in polarization resistance, as shown by the measurement results presented in example 5:

In sample 2 in example 5, compared to sample 2 in example 4 (as described above), four times the amount of CQD's (0.2% CQD) was mixed into the primer. Compared to the reference sample (sample 1), the polarization resistance (DC resistance) is reduced by a factor of 2.8, ie 1.6 times more than in Example 4. In addition, the decrease in the polarization resistance follows the amount of CQDs admixed—Sample 2-4: the polarization resistance decreases approximately proportionally to the amount of CQDs admixed to the primer. Surprisingly, with the higher amounts of CQD's added, the impedance practically no longer changes. The absolute values of the measured resistances and impedances, measured on different concrete test slabs, cannot be compared because the electrolyte resistances of the different concrete slabs differ significantly.

Surprisingly, it was also possible to establish a correlation between the amount of CQDs added and their effects on the polarization resistance (Example 5): In general, the polarization resistance decreases when CQDs are added - compare sample 1 with sample 2 - 4. The increase in polarization resistance correlates with the amount of CQD's and decreases with increasing concentration of CQD's - comparison samples 2, 3 and 4). Surprisingly, the addition of the CQDs has no significant influence on the impedances - this indicates that the CQDs are active with regard to the polarization resistance, especially at the electrode/electrolyte interface (Example 6).

This interpretation is supported by the results of determining the effectiveness of the CQD's on the type of polarization of the electrode - anodic or cathodic - as presented in Example 7: In the absence of CQD's, no significant difference in polarization resistance is expected depending on whether anodic or cathodically polarized is found (pos. 1 & 2). In the presence of 0.08% CQD's, the polarization resistance decreases significantly from approx. 20 MOhm.cm to 6 - 8 MOhm.cm. However, it is surprising that the polarization resistance depends on the type of polarization - the CQD's have a significantly stronger effect on the cathode (5.9 MOhm.cm) than on the anode (8.2 MOhm.cm).

Surprising results were obtained from the tensile bond strength measurements 77 days after application of the conductive paint to the concrete impregnated with a CQD-containing primer (Example 6): on concrete impregnated with a CQD-containing primer, the bond strengths were 5.2 MPa compared to 4.5 MPa significantly higher on concrete impregnated with a CQD-free primer. During these measurements, the demolition took place exclusively in the concrete - pieces of concrete up to 1 cm deep were torn out of the concrete slab. Surprisingly, this indicates that the impregnation of concrete with CQD's leads to an increase in concrete strength. Surprisingly, it was also shown that even low levels of CQD's significantly increase the activity of anodes, especially embedded zinc anodes (EZA's):

Galvanic anode systems as described, for example, in EP 2 313352 A1 consist of a galvanic metal anode, preferably zinc, embedded in a binder containing aluminosilicate (Example 8). The metal anode is preferably embedded in the binder as a grid. The binder contains additives that are intended to prevent or at least minimize the passivation of the zinc anode. Current densities in the range of up to 20 mA/m ² are usually measured shortly after the galvanic zinc anode has been put into operation. After 3 - 6 months, approx. 3 - 6 mA/m ² of active zinc surface at 70% relative humidity usually flow.

Surprisingly, it was found that even a content of 0.03 to 0.04% by weight of CQDs in a coating composition, based on the total weight of the coating composition, added for example as 0.5% CQD colloid in polyalkyl ether, results in a significant increase the galvanic activity of a zinc anode applied to a steel-reinforced test panel with a chloride content of 3% by weight (Example 8,

Sample 8.2. and 8.3. compared to sample 1.4.). The initial galvanic currents increased from 35.8 mA/m2 to approx. 42 mA/m2, after 1 month at 75% relative humidity from 10 mA/m2 to 12 mA/m2. Higher addition amounts of CQD's increase both the initial galvanic currents and the galvanic currents after 1 month of operation:

With 0.1% CQD's in the encapsulant, compared to an encapsulant containing 0.035% CQD's, galvanic currents are 11% higher initially and 21% higher after one month. Compared to reference sample 8.4. the initial current is 35% higher and the galvanic current is 48% higher after 1 month of operation.

The effect of the CQD's is maintained even during a longer period of operation, at least up to 14 months. As the results presented in Example 9 show, the addition of 0.018% by weight of CQDs increases the galvanic activity by at least 65% after six months of operation.

A blank test in which only the medium - polyether, without CQD's - was added showed a slight reduction in the galvanic activity of the zinc anodes. Thus, adding as little as 0.03% by weight of CQDs has a clear and significant effect: As the results presented in Example 8 show, the effect of admixing CQDs in the concentration range from 0.03 to 0.1% is comparable - it leads to a "boost" of the galvanic current over a period of approx. 3 weeks. After that, the concentration of the CQD's starts to play a role in the activity of the EZ anode. the Results indicate that a concentration of at least 0.05% by weight CQD, preferably 0.1% by weight CQD, is advantageous for a permanent increase in the galvanic activity of the zinc anode (EZ anode). At concentrations of < 0.03% by weight, the galvanic activity equals that of the EZ anode without the addition of CQD after approx. 3 months. This result is confirmed by the results shown in Example 10: An EZ anode with a CQD content of 0.010% based on the binder shows an almost doubling of the galvanic currents after 1 day, but after 2 weeks the currents are still approx. 50% higher than in the CQD-free EZ anode, but only 20% after 3 months.

The admixture of CQD's to the potting binder also causes an increase in galvanic currents in the absence of chloride, as shown by the results presented in Example 11. The addition of 0.05% CQD to the embedding adhesive increases the galvanic currents of an EZ anode stored at 75% relative humidity by 40% after 3 days and by 44% after 7 days of operation.

As is generally known, chloride has an activating effect on the galvanic activity of zinc anodes. In the absence of chloride, CQD's activate the EZ anode twice as much (example 11) as in the presence of chloride (example 8 - 10). This is of particular importance for the application of the EZ-Anode on concrete components repaired with repair mortar: State-of-the-art zinc anodes lose their effectiveness over time in the absence of chloride, this means that the concrete contaminated with chloride also removes behind the steel reinforcement must be repaired, usually by high-pressure water jets, and replaced with repair mortar - a significant additional expense in terms of time and expense.

Activating the EZ anode with CQD's allows for a very simplified repair of corrosion damaged components - only the cracked and spalled concrete needs to be removed and replaced with repair mortar, not the chloride contaminated concrete behind the steel rebar - this means a high savings in costs and especially time.

Another benefit of the CQD content is the increase in galvanic activity associated with a decrease in auto-corrosion of the zinc anode. Autocorrosion was determined by comparing the loss due to galvanic current, expressed in coulombs, with the actual weight loss. Furthermore, the auto-corrosion can be determined via the measured "open circuit" potential of the zinc anode against a reference electrode placed on the surface from the outside - eg an Ag/AgCl, 3M KCl electrode (example 12). In the case of autocorrosion, the values are in the range from -400 mV to - 500 mV Ag/AgCl, in the absence of autocorrosion the values are close to the theoretical value of - 900 mV against Ag/AgCl, in any case more negative than - 600 mV. Values between -800 and -600 mV vs. Ag/AgCl were measured. It was found that the admixture of CQDs does not cause increased auto-corrosion of the zinc anode, as the results presented in example 12 show.

A further advantage of admixing CQD's lies in a significantly lower sensitivity of the currents to the relative humidity of the ambient air, as shown by the influence of the storage humidity of concrete slabs provided with a conductive coating as described in example 2 on a constant applied voltage (2 - 4 volts) measured currents shows (Example 13): Storage of the concrete slabs with a CQD content of 0.018% by weight at 45% - 54% relative humidity resulted in currents of approx. 0.5 - 1.5 mA/m2 after 6 months of operation , in the absence of CQD's in the conductive composite paint, these were about 0.3-0.7 mA/m ² at an applied voltage of 4 volts (Example 13).

With storage humidity of RH > 70% and thus lower concrete resistance, the effect of the CQD's is significantly lower: 2 - 19% compared to 71 - 102% at RH. 45-54%.

The low sensitivity of the galvanic currents to the external humidity has enormous advantages: In most concrete components, not only the steel reinforcement near the surface has to be protected against corrosion, but also the deeper steel reinforcement, which is in a humid environment even when the outside air is dry, especially if it contains chloride contaminated concrete. Reliable corrosion protection for the low-lying steel reinforcement, even in dry outdoor conditions, is therefore a very big advantage.

Surprisingly, the admixing of CQDs also had an effect on the strengths, in particular on the tensile adhesive strengths, of the embedding binder used in Examples 8-13: as the results presented in Examples 14 and 15 show. Good results were achieved with binders based on EP 2 313352 A1 (see example 8), with a molar ratio of S1O ₂ /Al ₂ O ₃ <20, preferably <15, a weight ratio Si0 ₂ /(Ca0+Mg0+Al ₂ 0 ₃ ) <10, preferably <5, a Ca/Si molar ratio of <2, preferably <1, and galvanic metal anodes made of zinc alloys. The effect of even very low CQD contents not only on the properties of the composition according to the invention itself but also on solids embedded in the solids mixture, such as metal anodes or on solids in contact with the CQD-containing mixture, such as CQD-containing conductive coatings applied to concrete suggests that the CQD's are primarily interfacial, both at interfaces within the solid Mixture, such as pores, grain boundaries and at the interfaces of mixtures in contact with the CQD-containing solid, especially at interfaces of electrodes / electrolyte.

Suitable CQD's are described for example in Shouvik Mitra, Sourov Chandra, Shaheen H. Pathan, Narattam Sikdar, Panchanan Pramanik and Arunava Goswami in RSC Advances (2013), 3, 3189-3193. Suitable CQD's are, for example, CQD's produced by polycondensation of polyethers, carbohydrates, chitosan as already mentioned above and as in Persia Ada N. de Yro,a, Beejay T. Salon, Blessie A. Basilia, Mark Daniel de Luna and Peerasak Paoprasert, MATEC Web of Conferences (2016) 43, 4002; Hui Peng and Jadranka Travas-Sejdic, Chem. Mater. (2009), 21, 5563-5565; Youfu Wang, Aiguo Hu, Journal of Materials Chemistry C, (2014), 2, 6921, described by way of example but not conclusively. Material properties can be modified particularly advantageously with surface-modified CQDs, such as with N-doped CQDs [Xin Liu, Jinhui Pang, Feng Xu &

Xueming Zhang, www.nature.com/scientificreports (2016) | 6:31100 | DOI:

10.1038/srep31100]

A preferred preparation of CQD's that can be used in the compositions of the invention is based on the description in Ji Chen, S.K. Spear, J.G. Hauddleston and R.D. Rogers, "Polyethylene glycol and solutions of polyethylene glycol as green reaction medis", Green Chem. (2005) 7, 64 - 82: Polyethylene glycol (PEG) is mixed with alkali hydroxide, e.g. B. KOH or LiOH. The PEGs condense around the alkali ion to form polycyclic aromatics and subsequently to CQDs. This allows CQD colloids with concentrations of up to 10% by weight to be produced directly; further concentration and purification can be carried out by dialysis.

CQDs can be characterized by their optical properties, UV-VIS absorption spectrum and/or fluorescence spectrum, as for example in [Qin Hu, Xiaojuan Gong, Lizhen Liu, and Martin MF Choi, Characterization and Analytical Separation of Fluorescent Carbon Nanodots, Hindawi Journal of Nanomaterials , (2017) Volume 2017, Article ID 1804178, 1 - 23]. Usually, CQD's show an absorption shoulder at about 260 nm with a molar extinction coefficient of about 1 x 10 ⁶ M ¹ cnr ¹ and a photoluminescence in the range of 350 - 700 nm with an emission maximum in the range of 400 - 600 nm, depending on the particle size . The particle size of the CQD's can vary between 1 and 10 nm, that of CQD molecules between 3 and 100 nm with an average molecular weight of 100 to 100,000 daltons, preferably from 500 to 50,000 daltons. Due to the particle size show CQD's and CQD molecules characteristic quantum effects. As defined above, CQD's and CQD molecules are referred to here as CQD's.

With their characteristic photoluminescence spectra, CQDs allow the detection of, for example, iron (III) (rust), the determination of the pH value, nitrite, silver, mercury and copper. Solids according to the invention with CQD contents thus allow the substances and values listed above to be detected and determined on their surface or via suitable embedded optical sensors in the interior of the solids according to the invention.

A further application according to the invention is the imparting of fluorescent properties by a content of QDs, preferably by a content of CQDs.

The change in the solid properties due to the content of CQDs is based on the specific properties of the CQDs as QDs, in particular their quantum-specific properties. CQD's are easy and cheap to produce, so the same or similar changes in solid properties can be achieved by QD's in general. The change according to the invention in the properties of mixtures, in particular of solid mixtures, through a content of CQDs can generally be applied according to the invention to solid mixtures, such as their production and/or by impregnating them with CQDs, e.g. a CQD colloid.

Material properties such as strength, adhesive strength, electrical conductivity and electrochemical properties such as electrolytic conductivity, polarization resistance, galvanic activity of embedded metal electrodes can be specifically modified by mixing and adding CQDs.

The invention also relates to the use of the composition according to the invention for building purposes, preferably the use in a building material, particularly preferably in an artificial building material. Most preferred among the uses is the use of the composition of the present invention in a paint, coating agent, binder, concrete or mortar.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention.

The invention is explained in more detail in the examples below, but without restricting the invention thereto. examples

Example 1:

An electrically conductive composite anode was manufactured as follows:

A concrete slab 40×40×4 cm was coated on one half 40×19.5 cm with an electrically conductive coating containing aluminosilicate according to EP 1 068 164 A2 (850 g/m 2 ) containing 0.5% by weight of a CQD Polyoxyethylene colloid with a CQD content of 1% by weight had been admixed.

The electrically conductive coating containing aluminosilicate according to EP 1 068 164 A2 was produced as follows: Component A:

Ingredient parts by weight

Water 12.00

Potassium silicate solution (24.5% Si0 ₂ , 24.8% K ₂ 0) 200.00 50% aqueous dispersion of a polystyrene-acrylic ether copolymer 290.00

Methyl Hydroxycellulose, M 6000 3.00

30% solution of a polyacrylate-based dispersing agent 10.00

butyl glycol 15.00

Graphite powder 300.00 deionized water 182.00

Component B: Ingredient parts by weight sodium aluminate 6.28 sodium hydroxide 1.05 demineralized water 17.36

Component A and Component B were mixed in a ratio of 45:1 with stirring. On the second half of the concrete slab, the same conductive coating mixed with 0.5% of the same polyoxyethylene (POE) was applied as a reference. In each case 800 g/m2 of conductive coating was applied. The coatings were cured at 75% relative humidity for 2 weeks.

After curing, the electrical surface conductivity was measured at 1 kHz with an impedance measuring device by pressing test tips into the conductive coating with a test tip distance of 5 cm.

After measuring the sheet resistance, the tensile strength was determined based on EN 13892-8.

Example 2:

An electrically conductive composite anode was produced as follows:

A concrete slab 40 x 20 x 4 cm was coated on one side with an electrically conductive coating containing aluminosilicate according to EP 1 068 164 A2, on the opposite side the same conductive coating with a CQD content of approx. 0.01% by weight was applied. applied. The CQD's were added as a polyoxyethylene colloid with a CQD content of 2% by weight. As a reference, the same test specimen was produced with the same conductive coating on both sides - i.e. a conductive coating without CQDs. In each case 800 g/m2 of conductive coating was applied.

A lead strip (width×thickness=1.5 cm×0.1 cm), which was provided with an adhesive layer on the underside, was embedded in each of the coatings for electrical contacting. The coatings were cured at 75% relative humidity for 2 weeks and the coated concrete slabs were then stored at 50% relative humidity for 2 months.

A DC voltage of 2.0 volts was applied between the two coatings via the two lead strips and the current flow via a "shunt" resistor measured at 100 ohms. From the current flow and the geometry of the concrete body, the specific resistance was calculated according to Ohm's law:

Resistivity (Ohm. cm) = (2 Volts x A)/Current x L)

A = surface area = 20 x 40 = 800 cm2 L = concrete slab thickness = 4 cm

current in amperes

The admixture of CQD's to the conductive coating caused a significant reduction in the DC resistance between the anodically and cathodically polarized electrodes consisting of the conductive coating. This is equivalent to a significant reduction in the polarization resistance under dry conditions (50% relative humidity) by adding small amounts of CQD's.

After completing the resistance measurements, the tensile bond strengths (MTS) of the conductive coating were measured: The tensile mix of CQD's acted to increase the adhesion of the conductive coating to the concrete.

Example 3:

Analogously to Example 2, concrete slabs L×W×H=40×20×4 cm were coated with composite anodes.

Before applying the conductive coating, however, a so-called primer, also known as a primer, was applied. As is known to those skilled in the art, when concrete surfaces are coated with mortar, organic coatings, foils, etc., a primer, also referred to as a primer, is applied to increase adhesion. The primer does not form a coating, but is absorbed by the concrete cover capillary - the concrete surface is impregnated with the primer. An alkaline aqueous potassium silicate solution (24.5% SiO 2 , 24.8% K 2 O) diluted with water 1:6 was used as a primer.

In each case 200 g of primer/m2 of concrete surface were applied. The conductive coating was applied as described in Example 2 24 hours after application of the primer. The underside of the concrete slab was coated with the electrically conductive paint without the application of a primer. Analogously to example 2, the DC resistances were determined at 2.0 volts:

This example also shows that adding 0.02% by weight of CQDs leads to a significant reduction in the polarization resistance.

Example 4:

Analogously to Example 2, concrete slabs L×W×H=40×20×4 cm were coated with the composite paint. A primer was applied as in Example 3 prior to application of the conductive coating. As described in Example 3, a primer was used alkaline aqueous solution of potassium silicate used. In each case 200 g of primer/m2 of concrete surface were applied. The conductive coating was applied as described in Example 4 24 hours after application of the primer. The underside of the concrete slab was coated with the electrically conductive paint without the application of a primer.

Analogously to example 2, the DC resistances were determined at 2.0 volts, and the impedances at 120 Hz and 1 KHz were also determined:

Comparing sample 1 (composite paint only) to sample 2 (primer + 0.05% CQD/polyether + composite paint) shows a significant reduction in

DC resistance. Also, comparing sample 3 (0.05% CQD/polyether as primer + composite paint) to sample 4 (polyether as primer + composite paint) shows a reduction in DC resistance by half. The influence of the CQD's on the AC resistance is significantly lower. Example 5:

Analogously to Example 4, concrete slabs L×W×H=40×20×4 cm were coated with composite anodes.

A primer was applied as in Example 3 prior to application of the conductive coating. As described in Example 3, an alkaline aqueous solution of potassium silicate was used as the primer. In each case 200 g of primer/m2 of concrete surface were applied. The conductive coating was dried as described in example 4 for 24 hours applied after applying the primer. The underside of the concrete slab was coated with the electrically conductive paint without the application of a primer.

Analogously to example 2, the DC resistances at 2.0 volts and the adhesive strengths were also determined, and the impedances were also determined: The results show a clear correlation of the amount of CQD's added and the measured DC resistance. The influence of the CQD's on the AC resistance is significantly lower.

Example 6:

Analogously to Example 4, concrete slabs L×W×H=40×20×4 cm were coated with primer+composite anodes and with primer+composite anode containing 0.04% and CQDs. The primer being an alumino-silicate primer which was prepared by mixing the alkali silicate primer according to example 3 with component B according to example 1 in a mixing ratio of 30:1. Approx. 200 g alumino-silicate primer/m ² concrete surface was applied. After a curing time of 14 days, a voltage of 2 volts was applied first and then 3 volts after the measured current had stabilized. From the measured shunt voltage, the direct current that flowed between the anode and cathode (composite coating on the opposite side of the concrete slab) was calculated, and from this the specific resistance was calculated. The impedances were measured after switching off the direct current or interrupting the applied voltage. Bond strengths were measured using a PROCEQ Dyna Z16 and 3M DP 100 epoxy adhesive.

Influence of current and voltage on specific resistance and adhesive strength, relative humidity: 45%, 20.0 °C temperature

The admixture of the CQD's causes a significant reduction in the DC resistance while the impedance increases - this indicates that the CQD's primarily lower the polarization resistance. The CQD's cause a significant increase in bond strength 77 days after application of the composite paint.

Example 7:

In order to investigate the selective influence of CQD's on the anodic and cathodic polarization, test plates were produced and measured as in example 4. The results show that the CQD's have a much stronger effect on the polarization resistance at the cathode than on the polarization resistance at the anode:

Relative humidity: 45%, 20.0 °C temperature, duration of polarization: 10 days Example 8:

A laboratory-scale galvanic zinc anode was produced as follows: A concrete test specimen (L x W x H = 27 x 19 x 5 cm) made of standard concrete (w/c = 0.47, cement content 350 kg/m ³ ) with a chloride content of 3 Wt.% chloride/cement weight in which a reinforcing steel grid (24 x 15 cm, consisting of 5 longitudinal parallel steel bars with a diameter of 10 mm and 2 transverse steel bars with a diameter of 6 mm, all steel bars were connected to each other by means of electric welding) with a concrete cover embedded by 2 cm. A 6 mm steel rod protruded from the steel grid from the concrete test specimen for the production of an electrical connection to the reinforced steel grid. The concrete specimens were 1 month at 99% rel. Humidity and then stored dry for 2 months in the laboratory (RT, relative humidity approx. 45%).

The concrete test specimen was coated with a binder according to the invention, consisting of 2 components and a filler (crushed marble sand 0.2-0.5 mm).

The binder was made as follows:

Mixing ratio A : B : F = 1 : 0.5 : 1

A zinc grid anode (99.9% zinc, mesh size 7 mm, wire thickness 1.1 mm) was installed on the concrete test specimen by first applying the binder according to the invention with a layer thickness of 2 mm and then placing the zinc grid (26×19 cm). was and then the zinc grid was embedded by applying another 4 mm of the binder according to the invention. An electrical connection was made by soldering on a 1.5 mm2 copper wire with a length of approx. 2 m. An electrical connection to the reinforced steel grid was also established. A binder according to EP 2313352 A1 with an SiO 2 /(CaO+MgO+Al 2 O 3 ) ratio of 1.7 and a molar SiO 2 /Al 2 O 3 ratio of 12 was used for embedding the zinc lattice. The binder was created by mixing 2 liquid components (component A and component B), where component B was mixed with different amounts of CQD's according to the invention, and adding a filler (marble sand 0.2 - 0.5 mm) with the following mixing ratio: A / B / Filler = 1 / 0.5 / 1 manufactured. The CQD's were added as a colloid - suspended in polyoxyethylene - to Component B in the following amounts:

The concentration of the CQD's was determined spectrophotometrically using UV/VIS spectroscopy. The CQD's have an absorption peak at 260 nm with an extinction coefficient of 1.3*10 ⁶ mol ¹ cnr ¹ .

The embedded zinc anode according to the invention (EZ anode) produced in this way and applied to the concrete test specimen was stored at 99% relative humidity for 1 week. After the EZ anode had hardened, a one meter long copper wire with a wire cross section of 1.5 mm2 was soldered on with an Sn/Zn solder.

The concrete specimen fitted with the EZ anode was stored at 75% relative humidity. Before commissioning, the electrochemical potentials of the reinforcing steel and the zinc anode were measured. The EZ anode was powered up by connecting the EZ anode and the rebar as the cathode via the copper strands with a 0.1 ohm shunt resistor in between. The galvanic current flowing between the EZ anode and the reinforcement steel was measured using an operational amplifier and recorded using a data logger. The following results were achieved:

The data clearly show that galvanic currents increase with increasing concentration of CQD's, with the concentration/galvanic current relationship being consistent. Even very low concentrations of CQD's cause a significant increase in the galvanic current - an addition of 0.1% by weight causes an increase in the galvanic current by 48%. The results - low concentration of CQD's with significant effect and consistent correlation with addition level - suggest that the CQD's surprisingly act as "interface" catalysts - by facilitating charge transfer at the anode surface.

Example 9:

In another example, the influence of CQD's on the galvanic current was measured between a zinc anode embedded in an alumino-silicate binder (SEZAC from CAS Composite Anode Systems GmbH) and reinforcing steel embedded in concrete as described in example 8 over a period of 14 months : The results show that the admixture of 0.018% by weight of CQDs to the embedding binder matrix increases the galvanic currents significantly with increasing service life and with decreasing current densities. The increase in galvanic activity and thus the increase in galvanic currents is a great advantage, especially with low galvanic currents. In addition, the results show that the activity of the CQD's does not decrease with the operating time.

Example 10:

As in Example 9, an EZ anode was applied to a concrete test panel having a chloride content of 3% wt/cement wt.

A binder as in example 9 with a SiO 2 /(CaO + MgO + Al 2 O 3 ) ratio of 1.5 and a SiO 2 /Al 2 O 3 molar ratio of 15 was used. The mixing ratio of component A to component B and to the filler (marble sand 0.2-0.5 mm) was 1.0/0.5/1.0, as in Example 8. Sample 10.1. was obtained by coating with a binder to which a 1.9% CQD colloid was added.

The EZ anode was started up as described in example 8 and the galvanic currents were recorded every 30 minutes. The following results were achieved:

As in examples 8 and 9, the addition of CQDs causes a significant increase in the galvanic currents.

Example 11:

As described in Example 9, an EZ anode was installed on a concrete test panel. The same concrete was used, but without the addition of sodium chloride, i.e. chloride-free.

A binder as in example 8 with a SiO 2 /(CaO + MgO + Al 2 O 3 ) ratio of 2 and a SiO 2 /Al 2 O 3 molar ratio of 9 was used. The mixing ratio of component A to component B and to the filler (marble sand 0.2-0.5 mm) was 1.0/0.5/1.0, as in example 9.

The addition of 0.05% by weight of CQDs to the binder increases the galvanic current by 40%.

Example 12:

A significant limiting factor in the operation of galvanic anodes for the corrosion protection of steel is the auto-corrosion of the anode. A simple indicator of

Auto-corrosion is the electrochemical potential of the galvanic anode - the effect of QND's (CQD's) on the auto-corrosion of a zinc anode is shown using a zinc anode embedded in an alumino-silicate-containing binder:

As described in Example 8, a zinc grid is embedded as a zinc anode in the alumino-silicate binder described in Example 8, doped with different QND contents. After the binder had hardened, the electrochemical potential was measured against a standard Ag/AgCl reference electrode, which was placed on the embedded zinc anode using a moistened sponge. The measurement was made with a FLUKE 287 multimeter with a measuring impedance of 10 MegaOhm.

The results show that an admixture of CQD's does not cause increased auto-corrosion of the galvanic zinc anode.

Example 13: A composite anode as described in Example 2 was applied to the top of a concrete slab (20×10×2 cm), and a composite anode to which 0.018% by weight of CQDs had been mixed was applied to another identical concrete slab. The same conductive composite paint was applied to the underside of the concrete slabs as to the top of the concrete slab, without the admixture of CQD's. The conductive paint applied on the top was polarized as anode, the conductive paint applied on the bottom was polarized as cathodic. The current was supplied via 1 cm wide and 0.25 mm thick lead strips embedded in the composite anode, which were connected to a digitally controllable DC power supply unit via soldered 1.5 mm ² copper strands. Currents were recorded by a Grant 2020 Series data logger.

Current anode/cathode [mA/m2]

Time [d] rf % Voltage [V] 0% CQD 0.018% CQD Diff %

10 80 2.00 5.70 6.80 19%

20 80 2.00 3.90 4.40 13%

30 75 2.00 3.13 3.20 2%

60 70 4.00 8.17 12.90 58%

110 60 4.00 4.10 8.80 115%

122 54 4.00 1.69 2.99 77%

188 47 4.00 0.51 0.96 89%

212 54 4.00 0.73 1.48 102%

240 48 4.00 0.39 0.69 79%

248 45 4.00 0.31 0.53 71% The results show that the addition of CQDs causes a significant increase in the measured currents and thus in the ohmic resistance between anode and cathode. The effect of the CQD's increases significantly (70 - 115%) with decreasing humidity, while with increased current densities and normal ambient humidity (RH70 - 80%) the effect is noticeably lower (2 - 19%).

Example 14:

One half of a standard concrete slab 40 cm x 40 cm x 4 cm was coated with the binder described in Example 8 according to EP 2313352 A1 with a layer thickness of 6 mm: one half (19 cm x 40 cm) was coated with the binder without CQD - Additive applied, on the second half (19 cm x 40 cm) the binder was applied with an additive of 0.04% CQD's.

After 15 days, the tensile strengths were measured:

Even a very small addition of CQD's causes a significant increase in the adhesion of the hardened binder to the concrete substrate.

Example 15:

Half of a standard concrete slab 40 cm x 40 cm x 4 cm was coated as described in example 14 with the binder described in example 8 according to EP 2313352 A1 with a layer thickness of 6 mm: on one half (19 cm x 40 cm) was applied with the binder without CQD additive, but with a polyalkyl ether additive of 1.33% by weight. The binder with polyalkyl ether additive and additional was applied to the second half (19 cm×40 cm). applied with an addition of 0.03% CQD's.

After 15 days, the tensile strengths were measured: The following tensile strengths were measured after 28 days:

Claims

patent claims

Claims 1. A composition for building purposes, comprising 0.001-2% by weight of carbon quantum dots, based on the total weight of the composition.

2. Composition according to claim 1, characterized in that the composition is a paint, coating material, binder, concrete or mortar.

3. Composition according to claim 1 or 2, characterized in that the composition comprises 0.005-0.5% by weight, preferably 0.01-0.3% by weight, of carbon quantum dots, based on the total weight of the composition .

4. Composition according to any one of claims 1-3, characterized in that the composition is liquid and hardens at room temperature within a week.

5. Composition according to any one of claims 1-4, characterized in that the composition contains one or more compounds selected from the group consisting of silicate, silicon dioxide, aluminate, aluminosilicate, graphite, carbonate, resin, silicone, cellulose and organic polymer.

6. Composition according to claim 5, characterized in that the composition contains at least 30% by weight of the one or more compounds, based on the total weight of the composition.

7. Composition according to one of Claims 1 - 6, characterized in that the composition comprises one or more aluminosilicates with the formula aM 2 O bAl ₂ O _{3 cSiO 2} _, the molar ratio c/b being 0.1-15 and the molar ratio a/b is 0.2 - 10, with M=Li, Na, K and/or characterized in that the composition contains one or more aluminosilicates comprising calcium, the molar ratio S1O2/Al2O3 < 25 and the molar ratio SiO 2 /(CaO+Al 2 O 3 )<10.

8. The composition as claimed in any of claims 1-7, characterized in that the carbon quantum dots fluoresce when excited with UV light in the wavelength range from 400 to 600 nm.

9. Use of a composition according to any one of claims 1-8 in a building material.

10. Use of a composition according to any one of claims 1-8 in a paint, coating material, binder, concrete or mortar.