INVESTIGATION OF INHIBITORY EFFECT OF THE RASPBERRY FRUIT EXTRACT (

The paper presents an examination of the possibility of applying raspberry fruit extract (Rubus idaeus L.) as a green inhibitor of general corrosion of copper in 3% NaCl. Raspberry fruits (Rubus idaeus L.) sort Polka was collected from the Starposle near Kakanj, Bosnia and Herzegovina. Raspberry fruit extracts in ethanol were obtained by the Soxhlet extraction and the ultrasonic method. By UV/VIS spectrophotometry analysis, a significant content of polyphenols was found in the raspberry fruit extracts. Due to the great importance of gallic acid, the concentration of gallic acid was also determined using liquid chromatography. Corrosion testing of copper by the DC techniques was performed on a measuring device consisting of an electrochemical cell and a potentiostat/galvanostat, and electrochemical impedance spectroscopy measurements were performed using a potentiostat/galvanostat. Results obtained by the DC technique (by the method of Tafel extrapolation) prove that the corrosion rate decreases in the presence of the raspberry fruit extract. Tests performed by the method of electrochemical impedance spectroscopy prove that the tested extracts slow down the kinetics of the corrosion process, which is visible through the increase in resistance. The results of the conducted tests prove that in an aggressive medium, such as a 3% NaCl solution, Polka raspberry fruit extract can be used as an inhibitor of copper’s corrosion.


INTRODUCTION
Copper is a metal that has extra application due to its good properties.It is used in electrical engineering to produce wires, sheets, pipes, and production of alloys.It is relatively resistant to the effects of the atmosphere and many chemicals.However, it is known to be subject to corrosion in aggressive environments.The use of copper corrosion inhibitors is necessary in these cases because the formation of a passive protective layer cannot be expected.The development of new environmentally-friendly corrosion inhibitors is directed towards natural biological, non-toxic, biodegradable molecules to preserve the environment.Therefore, intensive efforts are still being made to find new effective but non-toxic compounds.Plant extracts contain a large number of organic compounds, and one of many is phenolic compounds.
Phenols are aromatic compounds with one or more hydroxyl groups (-OH) that bind directly to the carbon atom of the benzene ring.Some of them have Journal of Sustainable Technologies and Materials been found to possess anticancer and antimutagenic properties as well as antioxidant properties.Some of them express the possibility of forming chelated complexes with metals [1].Gallic acid (3,4, is one of the bestknown representatives of phenolic compounds commonly used to express the mass fraction of total phenols or phenolic subgroups in plant extracts [2].Gallic acid participates in the formation of hydrolyzing gallotannins, and its condensation produces dimer-ellagic acid, which is also part of ellagitannin.According to most literature data, some of the most significant compounds from the class of polyphenols in raspberry fruit is ellagic acid and ellagitannins [3].According to previous research on the dissolution of copper in a chloride medium, the anodic reaction is reversible mainly due to the strong, thermodynamically more favorable complexation of copper ions with chloride ions [4,5,6].The cathodic response is dominated by oxygen reduction, which is considered to be irreversible.Copper with chloride ions can form several complexes [5]: CuCl, CuCl2 ˉ, CuCl3 2-or CuCl4 3-.The formation of the CuCl layer takes place according to the reaction: CuCl is poorly soluble in NaCl solution, resulting in the formation of an ion CuCl2 ˉ complex: It is generally accepted that the anodic dissolution of Cu depends on the concentration of Clˉ ions and does not depend on the pH of the solution.At concentrations of Clˉ ions greater than 1 mol dm -3, it is possible to form more complex compounds such as CuCl3 2-and CuCl4 During hydrolysis CuCl2 ˉions in NaCl solution can cause precipitation of copper (l) oxide: or by direct oxidation of copper [6,5]: When a passive film is created on a metal (e.g.Cu2O) that does not have good protective properties and pitting corrosion will occur [9] in the presence of aggressive ions which is very dangerous because it quickly penetrates deep into the metal mass, and can lead to cracking of the structure under stress.Pitting corrosion most often occurs during the transition from the active to the passive state.Cu2O stability depends on the concentration of chloride ions.The use of inhibitors and alloying reduces the possibility of pitting corrosion.Many studies have focused on natural organic compounds from plant material.Natural antioxidants are affordable, available, and renewable compounds obtained by extraction from plant material or synthesized.Studies have shown that many of these compounds can be used as effective inhibitors of copper corrosion [10,11,12,13].
Effective environmental corrosion inhibitors show a high tendency for adsorption.The adsorption mechanism of organic inhibitors on the metal/solution partitioning surface may consist of one or more steps.In the first step, the adsorption of the organic inhibitor on the metal surface usually involves the replacement of one or more water molecules initially adsorbed on the metal surface [15]: where: Inh(sol) -inhibitor in solution, Inh(ads) -adsorbed inhibitor, x -number of water molecules displaced by the inhibitor.
The inhibitor combined with the metal ion M 2+ formed on the metal surface as a result of the metal oxidation or dissolution process, creating a metal-inhibitor complex [14]: Depending on the relative solubility of the resulting complex, further dissolution of the metal can be further inhibited or catalyzed [14].Raspberry fruit extract is a relatively cheap, readily available, and renewable natural product rich in various organic compounds such as polyphenolic compounds, organic acids, vitamins, etc., which makes it a potential corrosion inhibitor.

EKSPERIMENTAL PART
Polka variety raspberry (Rubus idaeus L.) fruits were collected at the Starposle-Kakanj site, Bosnia and Herzegovina.The Starposle site near Kakanj is far from industrial plants.

2.1.
Obtaining extracts and samples of raspberry fruit for HPLC analysis Defrosted raspberry fruits were ground in a blender, and as such, used in the Soxhlet apparatus.Ethanol was used as the solvent.The extraction lasted for six hours, after which the obtained extract was evaporated to dryness.The extracts obtained in this way were stored in dark bottles in a refrigerator at a temperature of +4 ºC.The obtained extract samples were of resinous consistency and well-soluble in ethanol.Extractions were also performed in the ultrasonic bath under defined conditions: frequency (20-40 kHz), power (250-500 W), temperature (40ºC), and extraction time (30 min) [15].The fact that plants contain several thousand secondary metabolites creates a need to develop fast and precise extraction methods.Dry fruit extracts (about 0.5 g), obtained by Soxhlet extraction and ultrasonic method, were dissolved in 50% methanol in an ultrasonic bath.Then filtered to remove impurities and transferred to vials.The content of total phenols was determined spectrophotometrically, on the PerkinElmer, Lambda 650, UV -VIS spectrophotometer device, by the Folin-Ciocalteu method.

Galic acid analysis using RP-HPLC-
UV/Vis technique Many scientists are showing great interest in gallic acid, which has contributed to its analysis in raspberry fruit extracts.Gallic acid analysis of Polka raspberry fruit extracts was performed by highperformance liquid chromatography on reversed phases on Shimadzu Prominence Modular HPLC with UV/Vis detector, mobile phase degasser, pump, autosampler, and column oven.Analysis of gallic acid was performed on a Nucleosil C18 column (250 mm x 4.6 mm, particle size 5 μm; Macherey-Nagel).As the mobile phase, a solvent system was used: A (1% formic acid) and B (acetonitrile) at a flow rate of 1 ml/min and using the following linear gradient: 0-10 min from 10 to 25% A; 10-20 min linear rise to 60% A, 20-30 min linear rise to 70% A. The column was balanced to initial conditions, 10% A, 10 min with an additional 5 min for stabilization [3].The gallic acid standard was dissolved in 50% methanol.Chromatograms were recorded at 280 nm for hydroxybenzoic acid derivatives (gallic).

Journal of Sustainable Technologies and Materials
Based on the obtained chromatograms and the calibration diagram of the standard gallic acid solution, the gallic acid concentrations in the extracts were calculated (g/l) [3].The gallic acid standard of different concentrations is shown in Table 1 [3,15].and PowerCORR® software package.The electrochemical cell contains three electrodes.A carbon electrode is used as an auxiliary electrode, and a saturated calomel electrode (SCE) with a potential of 0.2415 V is used as a reference electrode.The working electrode is a cylindrical body (disk) and is located inside a space made of glass and metal.Sample preparation and care were done according to the ASTM G5 standard [16].The electrochemical impedance spectroscopy method (EIS) was used to determine the kinetic parameters of the electrochemical reaction of copper corrosion in a 3 % NaCl solution without and in the presence of raspberry fruit extracts.Measurements were performed using the IviumSoft software package on IVIUM ® Vertex Onepotentiostat/galvanostat.

Yield determination of Soxhlet and ultrasonic extractions
Extraction yields, Y, expressed as a percentage are calculated using the following formula [15]: where mE -extract mass, mS -plant mass.
Extraction yields of Soxhlet and ultrasonic extractions are shown in Table 2. Based on the results shown in Table 2, it is safe to say that ultrasonic extraction leads to higher yields.Results are expressed as mean ± SD (n = 3).
Based on the results of spectrometric and HPLC analyses, it can be concluded that the content of total phenols and gallic acid is much higher in all samples obtained using ultrasound extraction about Soxhlet extraction.Therefore, the extract obtained by ultrasonic extraction, which proved to be a better and more cost-effective technique than Soxhlet extraction for the extraction of Polka raspberry fruit, was further used to test copper corrosion.Figure 4 shows the polarization curves of copper in 3% NaCl without and with the addition of fruit extract in different concentrations, obtained by the Tafel extrapolation method.0.01612 g/l; 0.03221g/l; 0.04828 g/l; 0.06432 g/l; 0.08033g/l Table 5 shows the corrosion parameters of copper in 3% NaCl without and with the addition of fruit extract in different concentrations, determined by the Tafel extrapolation method.HPLC chromatograms showed the presence of gallic acid in extracts of Polka raspberry fruit The results shown in figure 4 and table 5 showed that the corrosion rate decreases in the presence of raspberry fruit extract, and that the fruit extract of concentration 0.04828 g/l provides the greatest protection of copper against corrosion in 3% NaCl because it shows the lowest corrosion current density, table 5.
The results of testing the inhibitory effect of raspberry fruit extract on copper in 3% NaCl by electrochemical impedance spectroscopy are shown in the Nyquist diagram, Figure 5.The results were later analyzed using an equivalent electrical circuit, and the obtained corrosion parameters are shown in Table 6.From Figure 5 it can be seen how the addition of the tested concentrations of raspberry fruit extract increases the diameter of the impedance curves copper in 3% NaCl compared to the one obtained without the addition of said extract.From this, it can be concluded that the addition of this extract reduces the corrosion rate.EIS parameters for raspberry fruit extract as well as without it obtained using the proposed model are shown in Table 6.Based on results from Table 6 it is observed that the highest corrosion resistance of copper is given by the extract concentration of 0.04828 g/l.
The concentration of gallic acid (201.66±6.44 μg/ml) in raspberry fruit extract was tested, so to conclude that gallic acid in the extract led to a decrease in copper corrosion, the effect of standard gallic acid solution at 0.03221 g/l on corrosion copper was examined.This lower concentration was taken into account because the same concentration of fruit extract showed a decrease in copper corrosion, and it is known that corrosion inhibitors are substances added in small quantities to aggressive media to reduce the rate of metal corrosion.
Figure 6 shows the polarization curves of copper in 3% NaCl without and with the addition of standard gallic acid solution, obtained by the Tafel extrapolation method.Table 7 shows the corrosion parameters of copper in 3% NaCl without and with the addition of standard gallic acid solution, determined by the Tafel extrapolation method.The results shown in figure 6 and table 7 showed that the corrosion rate decreases in the presence of standard gallic acid solution, so it can be concluded that the gallic acid contained in the tested extract led to a decrease in the corrosion rate of copper.

CONCLUSION
The results carried out in this paper show that the extract from raspberry fruit (Rubus idaeus L.) of Polka variety, obtained by the Ultrasonic method, contains significant amounts of total phenols (28.51±0.91 mg GA/g extract) then extract obtained using Soxhlet extraction (14.92±0.87mgGA/g extract) making it a potential corrosion inhibitor.HPLC chromatograms showed the presence of higher concconcentrationlic acid (201.66±6.44 μg/ml) in extrthe act obtained by the Ultrasonic method.
The results of testing the inhibitory effect of raspberry fruit extract, obtained by the Ultrasonic method, of general corrosion of copper obtained by DC techniques, showed that the corrosion rate decreases in the presence of almost all tested extract concentrations.Using the Tafel extrapolation method, it has been proven that raspberry fruit extract with a concentration of 0.04828 g/l provides the greatest protection copper against corrosion in 3% NaCl.Studies conducted by the electrochemical impedance spectroscopy method, show that almost all tested extract concentrations slow down the corrosion process kinetics, which is visible through the increase in resistance, and that a concentration of 0.04828 g/l provides the greatest protection copper against corrosion in 3% NaCl.The results of the conducted

Figure 4 .
Figure 4. Polarization curves of copper in 3% NaCl without and with the addition of fruit extract in different concentrations obtained by the Tafel extrapolation method 0 g/l;0.01612g/l; 0.03221g/l; 0.04828 g/l; 0.06432 g/l; 0.08033g/l

Figure 5 .Table 6 .
Figure 5. Nyquist copper curves in 3% NaCl without and with the addition of raspberry fruit extract

Figure 6 .Table 7 .
Figure 6.Anode and cathode curves of copper polarization in 3% NaCl without and with the addition of a standard solution of gallic acid 0 g/l; 0.03221g/l

Table 2 .
Extraction yields of Soxhlet and ultrasonic extractions

Table 3 .
Content of total phenols in Polka raspberry fruit extracts obtained by methods of Soxhlet and ultrasonic extractions

Table 4 .
Results of HPLC analysis of gallic acid in Polka raspberry fruit extract obtained by Soxhlet and ultrasonic extractions

Table 5 .
Corrosion parameters of copper in 3% NaCl without and with the addition of fruit extract in different determined by the Tafel extrapolation method