REVERSIBLY DETECTS DISSOLVED CARBON DIOXIDE IN THE

ENVIRONMENT FOR USE IN FOOD AND ENVIRONMENTAL PRODUCTS

Technical Field of the Invention

The invention relates to a colorimetric indicator solution that instantly and reversibly detects dissolved carbon dioxide in the environment for use in food and environmental products.

State of the Art of the Invention (Prior Art)

There are many studies on indicator solutions developed to detect dissolved CO2 in the state of the art. Some of these are listed below.

In the study conducted by Yanan Zhang et al., a colorimetric indicator was developed for the detection of NH3 and CO2 using pH-sensitive dyes encapsulated in ethylcellulose matrices (dimethyl yellow, methyl red, chlorophenol red, methyl orange, phenol red, thymol blue, m- cresol purple). pH-sensitive dyes were added with either hydrochloric acid or tetrabutylammonium hydroxide to manipulate colorimetric responses (Y. Zhang, L. Lim, Colorimetric array indicator for NH3 and CO2 detection, Sensors and Actuators B: Chemical,2018, 255, 3216-3226). Here, many chemical additions are needed for the colorimetric indicator.

In the study conducted by Dr. Tamim A. Darwish et al., a sensitive reversible colorimetric CO2 consisting of an algae-amide complex substituted with an amide group was prepared as the probe. The aqueous alcohol solutions of this complex are purple, and yellow color formation is observed by adding low concentrations of CO2 gas to the component. Here, in the recovery of the purple color, CO2 is slowly recovered by removing it from the solution with inert gas or air sprinkling, or leaving it uncovered. (T.A. Darwish, R.A. Evans, M. James, T.L. Hanley, Spiropyran- Amidine: A Molecular Canary for Visual Detection of Carbon Dioxide Gas, Chemistry A European Journal, 2011,17, 11399-11404). In this study, the indicator solution undergoes a process to return to its initial color.

In the study conducted by Li Qun Xu et al., a fluorophore-polymer conjugate, PBL PDMAEMA, consisting of two arms of CCb-sensitive N,N-dimethylaminoethyl methacrylate polymer (PDMAEMA) and a central perylene-3,4,9,10-tetracarboxylic acid bisimide (PBI) fluorophore was synthesized by atomic transfer radical polymerization of N,N- dimethylaminoethyl methacrylate from N,N'-bis{2-[2-(2-bromo-2- methylpropanoyl)oxy]ethyl]ethyl}perylene-3,4. This fluorophore-polymer conjugate exhibits a colorimetric change in the presence of CO2 in aqueous solutions. By removing the adsorbed CO2 from the environment using N2 gas, this CO2 chemosensor can be fully recovered (L.Q. Xu, B. Zhang, M. Sun, L. Hong, K. Neoh, E. Kang and G. Fub, CCh-triggered fluorescence “turn-on” response of perylene diimide-containing poly(N,N-dimethylaminoethyl methacrylate, Journal of Materials Chemistry A, 2013, 4). In this study, the indicator substance must be treated with nitrogen gas to be reused.

In the study conducted by Xin Zhang et al., NAP-chol 1, a chemosensor system developed to be activated with anion, also serves as a super gelling agent for DMSO. The gel obtained is converted into a homogeneous solution when exposed to fluoride anions. Repeated washing with N2 or heating allows CO2 to be released and the sol form to be regenerated. This conversion sequence is reversible. As can be understood from this, additional treatment is mandatory in ensuring the reversible effect (X. Zhang, S. Lee, Y. Liu, M. Lee, J. Yin, J. L. Sessler & J. Yoon, Anion-activated, therm oreversible gelation system for the capture, release and visual monitoring of CO2, Scientific Reports, 2014).

In the study conducted by Xin Zhang et al., several aroylhydrazone-derived organogel ators were developed as CO2 sensors by activation with anion. Fluoride anion-triggered solutions of organogel ators may allow the detection of CO2 in the air with the naked eye through the passage from the solution to the gel. The developed gelling system ensures the convertibility of these sensing systems in the flow of CO2 through fluorescence enhancement caused by regelling (X. Zhang, H. Mu, H. Li, Y. Zhang, M. An, X. Zhang, J. Yoon, H. Yu, Dual-channel sensing of CO2: Reversible solution-gel transition and gelation-induced fluorescence enhancement, Sensors and Actuators B: Chemical, 2018,255, 2764-2778). In this study, the fluorescence enhancement method is used to reuse the solution used as a CO2 sensor.

In the indicator solutions used in the colorimetric detection of dissolved carbon dioxide gas in the previous technical applications detailed above, toxic chemicals that may be hazardous to the environment and human health are used. Furthermore, additional processes such as heat treatment, fluorescence, and nitrogen gas application are needed to obtain the reversible reaction, which is important in indicator solutions used in the colorimetric detection of dissolved carbon dioxide gas. In this case, it aggravates the conversion and applicability of the indicator to the product and increases the product cost. In current applications, the CO2 detection rate is slow, and the amount of perceived CO2 is high. Therefore, there is a need for fast, cheap, and nanotechnology-based colorimetric products that do not contain toxic chemicals that may be hazardous to human and environmental health, are environmentally friendly and can detect low levels of CO2 gas.

Brief Description and Objects of the Invention

With the invention, a colorimetric indicator detecting dissolved carbon dioxide in the environment was obtained.

The indicator obtained by the invention, which reacts with carbon dioxide gas, naturally carries out the reaction reversibly. There is no need for chemical and physical processes for repeated use of the indicator due to the reversible reaction with the indicator CO2 gas obtained by the invention.

Since non-toxic/low-toxic chemical agents were used in obtaining the colorimetric indicator of the invention, an environmentally and human health-friendly product was obtained. The obtained colorimetric indicator is safe in contact with important components such as food and water.

Edible materials are used as the sources in the production of colorimetric indicators of the invention. There is no emission of pollutant/hazardous waste material or gas in production. Since organic waste vegetable resources are used, a simple, easy-to-apply, low-cost product is obtained.

With the invention, no additional energy consumption such as pressure, temperature, fluorescence, nitrogen, etc. is required in ambient conditions. Dissolved carbon dioxide gas is instantly detected. It reacts to 3200 ppm carbon dioxide gas concentration with color change in 3 seconds. As soon as the gas is cut off, it immediately returns to the initial color of the indicator solution. Since the sensor is reversible, it can be used repeatedly.

Definitions of Figures Describing the Invention

The figures prepared to better explain the method of obtaining the colorimetric indicator developed by this invention that detects carbon dioxide and the instantaneous and reversible detection of the dissolved carbon dioxide in the environment are explained below.

Figure 1: It shows the reaction (1) caused by the dissolution of the CO2 gas in the indicator and then the reversible reaction (2) caused by the reduction of the CO2 gas in the environment. Molecular structures belong to anthocyanin.

Figure 2: UV-Vis spectrum of anthocyanin in the extract obtained from red cabbage

Figure 3: UV-Vis spectra of PVA/FeO Nanoparticle/PVA coated FeO Nanoparticle/Indicator Figure 4: Decrease in pH due to CO2 gas dissolved in different concentrations in the indicator (different concentrations of CO2 gas were dissolved in the indicator at the places indicated by *.)

Figure 5: UV-Vis spectra of the indicator at pH 4 and pH 3

Figure 6: FTIR spectra of PVA-coated FeO and FeO Nanoparticles

Detailed Description of the Invention

The invention relates to a colorimetric indicator solution that instantly and reversibly detects dissolved carbon dioxide in the environment for use in food and environmental products and the method of obtaining it. The colorimetric indicator solution of the invention comprises polyvinyl alcohol (PVA) coated iron oxide nanoparticles and anthocyanin which gives colorimetric color change with dissolved CO2 attached to polyvinyl alcohol coated iron oxide nanoparticles. The invention can instantly and reversibly detect the dissolved carbon dioxide in the environment with the test kit comprising the colorimetric indicator solution.

The novelty of the invention is that the indicator is reversible and that conditions such as high pressure or high temperature and chemical substances are not needed to gain this feature.

The reason for the reversibility of the inventive indicator is the polyvinyl alcohol (PVA) substance and its reaction.

The reason there is no need for high pressure or high-temperature conditions or no need for additional chemicals in the reversibility of the indicator is the reaction order formed by Anthocyanin and PVA-FeONP in the structure of the indicator. With dissolved CO2, anthocyanin reacts quickly in the first place to create a color change. PVA, on the other hand, reverses the reaction that occurs in the first place spontaneously and quickly in the second place.

Since the reaction occurs spontaneously, there is no need for pressure, temperature, or a different chemical substance. The reason for this is the desire of the indicator consisting of the combination of Anthocyanin-PVA-FeO NP to react chemically with the H ⁺ ions formed in the dissolved CCh-induced environment.

In this indicator consisting of anthocyanin-PVA-FeO nanoparticle substances, the PVA substance reacts spontaneously in the second place and provides reversibility. Different polymers did not provide the same property. A reversible reaction was observed with the PVA substance. There were no effects on different polymers.

The invention provides a method of instantly and reversibly detecting dissolved carbon dioxide with a colorimetric indicator solution and comprises the following process steps: a) H ⁺ ion is formed in the environment by dissolving the carbon dioxide gas in the indicator solution, b) H ⁺ ion reacts with the anionic quinoidal base material, which is the chemical type of anthocyanin substance, to obtain the neutral quinoidal base chemical type of anthocyanin substance, c) As the amount of dissolved carbon dioxide gas in the environment decreases, the polyvinyl alcohol substance takes up the H ⁺ ions of the acyl group in the neutral quinoidal base and the OH" ions and H ⁺ ions surrounding the iron oxide nanoparticles (FeO NP) are reacted, d) Hence, the polyvinyl alcohol substance reverses the reaction, and the indicator returns to its initial pH value, PH 4-4.5, and thus to its first color.

The process steps for obtaining the colorimetric indicator solution of the invention are described in detail below:

Obtaining PVA-coated FeO Nanoparticle (PVA-FeO NP) Solution a) 10 g of horse chestnut tree fruit is peeled and cut into pieces. b) It is extracted in 150 mL distilled water at 100°C for 1 hour. c) The extract is filtered with Whatman Nol filter paper. d) 3 g of PVA is dissolved in 100 mL of the extract by stirring at 400 rpm for 30 minutes. e) 3.8 g of FeC13.6H ₂ O is dissolved in 100 mL distilled water for 15 minutes at 400 rpm and the iron solution is obtained. f) The PVA-horse chestnut extract obtained in step d and the iron solution obtained in step e is mixed in a 1 : 1 ratio in a sealed container at 600 rpm for 3 hours.

Here, horse chestnut is used as a reducing agent. In the reaction of the plant-based synthesis that provides iron nanoparticle formation, iron ions are brought into the form of iron nanoparticles. Carob, acacia, soybean, and pea plant extracts can also be used instead of horse chestnut as a reducing agent.

PVA (polyvinyl alcohol) is used as a chelator, that is, in the interaction of H ⁺ ions formed in the indicator with iron nanoparticles.

Preparation of Chitosan-Red Cabbage Solution 1.1. 50 g of red cabbage is divided into small pieces and kept in 30 mL ethanol: 70 mL distilled water mixture in a sealed container for 12 hours.

1.2. It is filtered by the Whatman Nol filter paper and the red cabbage extract is separated.

1.3. 1 g of chitosan is stirred in 100 mL of distilled water at 40°C for 3 hours at 400 rpm and 1% solution is prepared.

1.4. 2 mL of 1% chitosan solution is added to 20 mL of red cabbage extract and stirred at 400 rpm for 25 minutes.

The red cabbage was used to obtain anthocyanin. Black carrot and beetroot root can also be used instead of red cabbage to obtain anthocyanin.

Preparation of Indicator Solution

1.5. The PVA-FeO NP solution prepared in step 1 and the chitosan-red cabbage prepared in step 2 are mixed at 400 rpm for 30 minutes in a ratio of 1 : 10 by volume.

1.6. The dissolved carbon dioxide colorimetric indicator containing Anthocyanin-PVA- FeO NP at pH 4 is stored at +4°C in a sealed form.

The color of the indicator obtained with the use of PVA-FeO NP solution and chitosan-red cabbage in a 1 : 10 volumetric ratio changes. This enables the color change in the indicator to be detected visibly with the naked eye when the CO2 gas dissolves.

Principle for detecting dissolved carbon dioxide:

The complete reaction of the indicator with dissolved carbon dioxide is provided in Figure 1.

The pH of the indicator obtained as a result of the synthesis is in the range of 4-4.5. At pH 4- 4.5, the chemical type of the anthocyanin substance originating from the red cabbage in the indicator is the 'anionic quinoidal base'. In Figure 1, when carbon dioxide gas is dissolved in the indicator, H ⁺ ion is formed in the environment according to the reaction shown in number 1. The H ⁺ ion also reacts with the 'anionic quinoidal base', the chemical type of the anthocyanin substance from the red cabbage. As a result of the reaction of the H ⁺ ion with the anionic quinoidal base, which is the anthocyanin form, the pH drops to 3-4, and the chemical type of the ‘neutral quinoidal base’ anthocyanin substance is formed. The color change is also observed due to the reaction of anthocyanin substances. When the amount of dissolved carbon dioxide gas in the environment decreases, the PVA material removes the H ⁺ ions in the 'neutral quinoidal base' and reacts rapidly and spontaneously with the OH" ions and H ⁺ ions around the iron oxide nanoparticles (FeO NP). The PVA substance reverses the reaction, and the indicator returns to its initial pH value and hence to its initial color, i.e., blue tones.

In the indicator of the invention, anthocyanin substance from red cabbage extract was used. This substance provides a colorimetric color change in the indicator. The presence of this substance was detected by analysis with a UV-Vis spectrophotometer (Figure 2). It was mixed with chitosan for the stable preservation of anthocyanin. PVA-coated FeO (PVA+FeO NP) nanoparticles are used to ensure that the reaction of the indicator with CO2 gas is reversible. PVA+FeO NP synthesis was detected by UV-Vis spectrophotometer (Figure 3). FeO nanoparticles obtained at 294 nm in UV-Vis spectrophotometer gave a signal at 310 nm after coating with PVA. The PVA+FeO nanoparticles are bound with anthocyanin from red cabbage and form the indicator at pH 4. In Figure 3, a wide visible band is observed in the spectrum of the indicator at pH 4 in the range of 450 - 700 nm as a result of this binding. The peak at 614 nm is indicative of the anionic quinoidal base, which is the form of anthocyanin.

When the carbon dioxide gas dissolves in the indicator, it transforms into carbonate forms as in reaction 1, while giving H ⁺ ions to the environment. In Figure 4, the places where CO2 gas enters the environment are shown with an asterisk (*). With the dissolution of the CO2 gas, the pH decreases.

CO2 + H2O H2CO3 HCCU + H ⁺ CO ₃ ² ' + 2H ⁺ (1)

The chemical type changes as a result of the reaction of the anionic quinoidal base type of anthocyanin from the red cabbage extract with the H ⁺ ions formed in the environment. Figure 5 shows this change. There is a peak at 380 nm belonging to the neutral quinoidal base type of the newly formed anthocyanin in the spectrum of the indicator at pH 3. This shows the formation of new forms. After the reduction of the carbon dioxide gas in the environment, the acyl group belonging to the PVA polymer takes back the H ⁺ ion in the anthocyanin and reverses the reaction, and returns the indicator to its original state, that is, to its anionic quinoidal base. Figure 6 shows the presence of the acyl group on the surface of PVA-coated FeO nanoparticles with the signal at 1300 cm' ¹ .

In this way, a reversible colorimetric indicator that occurs spontaneously depending on the chemical reaction sequence of carbon dioxide gas dissolved at room temperature was obtained.