CHANGE OF FUNCTIONAL GROUPS AND STRUCTURE IN THE CONTENT OF PLUM SEED, CARBONIZATION, AND ACTIVATED CARBON, DEPENDING ON TEMPERATURE

ABSTRACT

The article analyzes the IR indicators of plum fruit seed coat, carbonization, and physically activated carbon. These analyses studied changes in the functional groups in the samples depending on the temperature. According to the results, the release of functional groups in the composition of plum kernels and carbonatite after processing in water vapor at 800⁰C explained the effect of temperature and pressure. In conclusion, it can be said that during the carbonization process and water vapor treatment, the release of various functional groups, tars, some elements, and volatile substances in the grains led to an increase in the number of C and, as a result, the appearance of micro-, meso-, and macropores. This causes the adsorption properties of the obtained activated carbon to be high.

АННОТАЦИЯ

В статье проанализированы ИК-показатели семенной кожуры плодов сливы, карбонизации и физически активированного угля. С помощью этих анализов были изучены изменения функциональных групп в образцах в зависимости от температуры. Согласно результатам, выделение функциональных групп в составе ядер сливы и карбонатита после обработки в присутствии водяного пара при температуре 800 ⁰С объяснило влияние температуры и давления. В заключение можно сказать, что процесс карбонизации и обработки водяным паром привел к выделению в зерне различных функциональных групп, смол, некоторых элементов и летучих веществ, что привело к увеличению количества C и, как следствие, увеличению в результате появляются микро-, мезо- и макропоры. Это обуславливает высокие адсорбционные свойства полученного активированного угля.

Keywords: adsorption, SEM, functional group, plum kernel waste, activation.

Ключевые слова: адсорбция, СЭМ, функциональная группа, отходы косточек сливы, активация.

Introduction. The fact that the production and use of activated carbons are increasing today can be seen from the fact that it is difficult to find an area of ​​human activity in which they are not involved. The use of activated carbons in particular to achieve a clean extraction mass determines the high competitiveness of adsorption. The use of these activated carbons in wastewater treatment processes is particularly effective.

In addition to being an important factor for chemical technological processes, and environmental protection [1], active carbons are an integral part of food, medicine, and healthcare [2 - 7] and modern cosmetology [8].

The increasing consumption of active carbons from year to year is known from the growing trends of this product in the world markets. The price of these adsorbents is estimated to increase from 6.53 billion US dollars to 14.67 billion US dollars from 2023 to 2032, with a compound annual growth rate of 9.4% [9].

Methods. Determining the original composition of plum kernel skin was carried out using SEM analysis (EVOMA 10 brand scanning electron microscope) and high-efficiency energy dispersive X-ray fluorescence spectrometer - Japan, Rigaku NEX CG EDXRF Analyzer with Polarization in set - 9022 19 000 0. Also, functional groups and structural changes of plum kernel bark and carbon activated by heat and water vapor at 300°C, 400°C, 500°C, 600°C, 700°C, and 800°C infrared IRSpirit-T brand A22416103442 were analyzed by spectroscopy.

Results and discussion. According to the results, the composition of the plum kernel shell is C 61.1%, O2 38% [10], and was examined by SEM analysis (EVOMA 10 brand scanning electron microscope) to study their elemental composition.

Figure 1. SEM images of plum seed coat

Besides C and O2, the grain contains Cl 0.0086%, Mg 0.0592%, Al 0.0805%, Si 0.0959%, ​​S 0.0222%, K 0.0933%, Ca 0.250%, Ti 0.0009%, Cr 0.0005%, Mn 0.0019%, Fe 0.0353%, Cu 0.0023%, Zn 0.0011%, Sr 0.0013%, Zr 0.0446%, Ag 0.0004%, Hf (0.0008)%, Dy (0.0013)% high-efficiency energy dispersive X-ray fluorescence spectrometer - Japan, Rigaku NEX CG EDXRF Analyzer with Polarization in set - 9022 19 000 0 was checked to determine the initial composition. Table 1 shows the percentage of components in the grain.

Figure 2. X-ray fluorescence spectrometry of the constituents of plum kernels

Experiment part. Carbon adsorbents were obtained from the husks of plum seeds of certain sizes by the method of thermal activation up to 300 - 800°С in a pyrolysis device designed for laboratory conditions. The charring process was carried out for 2 hours for each sample in an inert environment - in the presence of argon gas. Temperature-dependent heating rate was changed: heating up to 200°C was 5°C/min, 200 - 700°C was 10°C/min, and subsequent heating was reduced to the previous rate. Activated with steam for 30 minutes at a temperature of 800⁰C with a pressure of 2.5 kgs/cm2 (196,133 kPa). This leads to an increase in the porosity of the adsorbent and its sorption properties. Figure 3 shows the IR spectra of the original plum kernel bark before heat treatment.

Figure 3. IR spectral parameters of plum kernel bark

The following characteristic absorption lines can be observed in the IR spectrum of plum kernel peel: a broad peak at 3344.37 cm⁻¹ indicates the presence of hydroxyl groups (-OH) and hydrogen bonds, possibly water or cellulose. Peaks at 2901.47 cm⁻¹ indicate C-H stretching vibrations of methyl and methylene groups, and sharp peaks at 1731.41 cm⁻¹ and 1592.86 cm⁻¹ indicate the presence of carbonyl (C=O) and aromatic (C=C) groups, respectively show. Other absorption lines at 1503.85 cm⁻¹, 1418.43 cm⁻¹, 1370.34 cm⁻¹, and 1320.09 cm⁻¹ are attributed to bending vibrations of aromatic rings and methyl groups. The peaks at 1227.49 cm⁻¹ and 1027.21 cm⁻¹ can be attributed to C–O vibrations in alcohols and ethers, while the peak at 895.85 cm⁻¹ can be attributed to C–H bending vibrations in aromatic compounds.

After obtaining information about the functional groups in the original plum seed coat, the next analysis was conducted for samples thermally pyrolyzed at 300°C. Figure 4 shows the IR spectra of the sample thermally pyrolyzed at 300°C.

Figure 4. IR spectrum values of the sample thermally pyrolyzed at 300°C

According to it, the IR spectrum of the sample activated at 300°C shows weak peaks at 3350, 3050, 2900, 2600, 2100, 1414, and 1050 cm-¹ and stronger peaks at 1590, 1193, and 787 cm-¹. The peak at 3350 cm⁻¹ is due to stretching vibrations of -ON groups, possibly indicating the presence of hydroxyl groups or water. The peak at 3050 cm⁻¹ can be attributed to =C–H stretching vibrations in alkenes. Peaks at 2900 cm⁻¹ and 2600 cm⁻¹ indicate -C-H vibrations in alkanes. The peak at 2100 cm⁻¹ can be attributed to the presence of C≡C or C≡N triple bonds. The intense peak at 1590 cm⁻¹ is associated with aromatic C=C vibrations, the peak at 1414 cm⁻¹ with C-H bending vibrations, and the peak at 1193 cm⁻¹ with CO vibrations in ethers or phenols. The peak at 1050 cm⁻¹ can also be attributed to C–O vibrations. The peak at 787 cm⁻¹ is analyzed to be due to C-H vibrations in aromatic compounds.

For the sample activated at 400°C, weak peaks at 3350, 3050, 2100, and 1050 cm⁻¹ are observed as in the previous sample. However, compared to the first sample, the intensity of the 1559, 1177, and 1414 cm⁻¹ peaks decreased and the intensity of the 750 cm⁻¹ peak increased. This indicates a decrease in aromatic C=C, C-H, and C-O bending vibrations, as well as an increase in C-H bending vibrations in aromatic compounds. Figure 5 shows the IR spectrum of the sample thermally pyrolyzed at 500°C.

Figure 5. IR spectrum readings of the sample thermally pyrolyzed at 500⁰C

After heat treatment at 500⁰C, the following changes were observed in the IR spectrum: the peak at 1579.23 cm⁻¹ indicates the presence of residual carbonate or aromatic compounds. The broad peaks at 1007.55 cm⁻¹ (73.5%) and 801.95 cm⁻¹ may result from changes in the structure of cellulose or other polysaccharides, as well as the presence of C–H bending vibrations in alkenes. Peaks at 872.16 cm⁻¹ and 745.11 cm⁻¹ indicate the presence of C–H bending vibrations in aromatic compounds and substituted benzenes.

Figure 6. IR spectrum readings of a sample thermally pyrolyzed at 700⁰C

The peaks at 3350 and 2900 cm⁻¹ disappeared in the IR spectra of samples activated at 600°C and 700°C. The intensity of 1578-1559, 1450-1400, and 1180-1160 cm⁻¹ peaks also decreased. Also, the intensity of peaks at 873-871, 747-745 cm⁻¹ increased. This may indicate the withdrawal of -OH and C-H groups, further reduction of aromatic C=C vibrations, reduction of C-H bending vibrations and C-O vibrations, and the formation of more condensed aromatic structures.

In the next figure, the release of all the functional groups, volatile components, and compounds identified above at 800°C is concluded by the absence of any peaks in the sample composition.

Figure 7. IR spectrum values ​​of the sample thermally pyrolyzed at 800⁰C

Conclusions. IR-spectroscopic analysis revealed significant structural changes in activated carbon obtained from plum seeds at different activation temperatures. An increase in the activation temperature leads to the formation of more stable and condensed aromatic structures, which indicate the removal of functional groups such as -OH and C-H the decomposition of organic matter, and the formation of new structures. This indicates the profound chemical changes that occur in the material at high temperatures, such as the decomposition of cellulose, the release of volatile components, and the formation of stable aromatic structures. These changes help to improve the adsorptive properties of activated carbon and make it more effective for applications in various fields.

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