Makara Journal of Science Makara Journal of Science
Volume 27
Issue 3 September Article 4
9-25-2023
Synthesis, Characterization, Antibacterial Activity, and Potential Synthesis, Characterization, Antibacterial Activity, and Potential Water Filter Application of Copper Oxide/Zeolite Composite Water Filter Application of Copper Oxide/Zeolite Composite
Elfa Aida Kamila
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Institut Pertanian Bogor, Bogor 16680, Indonesia
Zaenal Abidin
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Institut Pertanian Bogor, Bogor 16680, Indonesia, [email protected]
Irma Isnafia Arief
Department of Animal Production and Technology, Faculty of Animal Sciences, Institut Pertanian Bogor, Bogor 16680, Indonesia
Trivadila Trivadila
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Institut Pertanian Bogor, Bogor 16680, Indonesia
Follow this and additional works at: https://scholarhub.ui.ac.id/science Part of the Chemistry Commons, and the Microbiology Commons Recommended Citation
Recommended Citation
Kamila, Elfa Aida; Abidin, Zaenal; Arief, Irma Isnafia; and Trivadila, Trivadila (2023) "Synthesis,
Characterization, Antibacterial Activity, and Potential Water Filter Application of Copper Oxide/Zeolite Composite," Makara Journal of Science: Vol. 27: Iss. 3, Article 4.
DOI: 10.7454/mss.v27i3.1555
Available at: https://scholarhub.ui.ac.id/science/vol27/iss3/4
This Article is brought to you for free and open access by the Universitas Indonesia at UI Scholars Hub. It has been accepted for inclusion in Makara Journal of Science by an authorized editor of UI Scholars Hub.
Synthesis, Characterization, Antibacterial Activity, and Potential Water Filter Application of Copper Oxide/Zeolite Composite
Elfa Aida Kamila
1, Zaenal Abidin
1*, Irma Isnafia Arief
2, and Trivadila
11. Department of Chemistry, Faculty of Mathematics and Natural Sciences, Institut Pertanian Bogor, Bogor 16680, Indonesia
2. Department of Animal Production and Technology, Faculty of Animal Sciences, Institut Pertanian Bogor, Bogor 16680, Indonesia
*E-mail: [email protected]
Received March 17, 2023 | Accepted July 1, 2023
Abstract
Detection of E. coli bacteria in water samples can indicate the presence of other bacterial contamination in feces. Bacterial contamination can be treated with antibiotics, but excessive use of antibiotics leads to the emergence of multiresistant bacteria. Therefore, alternative antibacterial agents must be explored. Copper ion/zeolite composite has been widely studied as an antibacterial agent. However, the released copper ions accumulate in water and are toxic to humans; this can be prevented by converting copper ions into copper oxides (CuO and Cu2O). In this study, copper oxide/zeolite composite is synthesized and characterized using the heating method, followed by evaluation of its effect, antibacterial activity, and potential application as a water filter. The results showed that heat treatment and combination of zeolite with copper did not change the composition of zeolite, rather impurities were reduced from natural zeolites. Antibacterial activity test against E. coli showed that the copper oxide/zeolite composite possessed good antibacterial activity and exhibited better potential as a water filter compared with copper/zeolite. The copper ion released from the synthesized materials was under 2 mg/L, indicating that it is safe for use provided the minimum contact between the sample and water for less than 20 min or 50–60 min.
Keywords: antibacterial activity, copper oxide, water filter, zeolite
Introduction
Good water quality is an important factor for life, especially drinking water as well as the water for household, agriculture, and industrial needs. Although water-quality requirements vary in different sectors and from one form of use to another, many of these activities have implications for public health because they can lead to the transmission of waterborne diseases [1]. E. coli is one of the common pathogenic bacterial contaminants in water; The presence of E. Coli in water samples can indicate the fecal contamination of other bacteria, such as Salmonella sp. or hepatitis A virus [2]. Antibiotics can be used for bacterial infection treatment; however, excessive antibiotic use causes the emergence of multiresistant bacteria. Therefore, alternative antibacterial agents must be explored.
Zeolite is a porous alumina–silica material found in nature or synthesized in the laboratory and is composed of an alumina tetrahedron and a silica tetrahedron, which act as a negative charge and a positive charge, respectively. Zeolites have many applications, especially
as ion exchangers, and can contain metal ions or nanoparticles. Loading metal ions with antibacterial properties in zeolite provides the composite with antibacterial activity [3]. Copper is one of the metal ions widely used as an antibacterial agent. Zeolites, either natural or synthetic, containing copper ions or copper oxide, have been extensively studied and proven to have antibacterial activity. An example is zeolite X composited with Cu2+ and Zn2+ ions; the antibacterial activity of the composite was tested on S. aureus and E. coli [4]. Y zeolite was also composited with Cu2+ and then tested for antibacterial activity using S. aureus and E. coli [5]. The results of these two studies indicated that both types of composites were able to reduce the growth activity of S.
aureus and E. coli. Natural zeolite composites containing Ag+, Cu2+, and Zn2+ have also shown antibacterial activity against S. aureus, E. coli, Candida albicans, and Aspergillus niger [6]. In addition, a copper composite with natural zeolite can be applied as a rainwater filter to inhibit E. coli [7].
Copper and copper oxide nanoparticles exhibit multitoxicity against a broad spectrum of bacterial
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species by reactive oxygen species (ROS) and copper-ion release mechanisms. These reactive species, including hydroxide ions and hydroxyl radicals, chemically damage the cell wall of bacteria [8]. Copper oxide is more abundant and cheaper than other precious metals, such as gold and silver, and is widely used due to its nontoxic nature [9].
The conversion of copper ions into CuO or Cu2O nanoparticles generally utilizes reducing/reductant agents, such as hydrazine [10], NaBH4 [9], or NaOH [11].
Another way to convert copper ions into copper oxide is by heating in a furnace [7, 12] but this process still needs fuel to facilitate copper reduction. However, heating copper/zeolite composites at temperatures above 400 °C can cause autoreduction from Cu(II) to Cu(I) [13]. In this study, copper oxide (CuO and Cu2O)/zeolite composites were synthesized from granules of natural zeolite to investigate the effect of CuSO4 addition and heating on the shape and structure of the zeolite. In addition, an antibacterial activity test was carried out on E. coli to determine the potential of the composite as an antibacterial filter.
Materials and Methods
Materials and chemicals. Local commercial natural zeolite (0.1–1 mm), obtained from Cikembar area, West Java, Indonesia, was washed with distilled water and dried at 60 °C overnight before use. Technical grade CuSO4⋅5H2O was used for the synthesis of the composite.
Synthesis of composites. The natural zeolites were soaked in CuSO4⋅5H2O 0.5 M solution for 2 days and then dried at 60 °C overnight. Half of the samples were heated under ~500 °C for 2 h to obtain CuO and Cu2O/zeolite composite. Analysis of the initial samples and composites was performed using X-ray diffraction (XRD), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), and Fourier transform infrared (FTIR) spectroscopy to determine their morphology, crystallography, and mineralogy.
Diffusion method for antibacterial test. Mueller–
Hinton agar (MHA), commonly used for bacterial tests, was applied as a medium to incubate the bacteria. Pure bacterial cultures of E. coli (Gram-negative bacteria) were prepared at a concentration of 106 CFU. In brief, 0.1 mL of bacterial culture was spread evenly on the surface of the medium. Paper disks with a diameter of 6 mm were dripped with 17 μL of sterile distilled water, and 10 mg of zeolite was added as a sample. The paper disk containing the sample was placed on the surface of the medium at a certain distance. This procedure was done in two replication. The plates were incubated at 37 °C for 24 h. The diameter of the inhibition zone for each sample was measured. Sterile distilled water was used as blank for comparison.
Minimum Inhibitory Concentration. Minimum Inhibitory Concentration (MIC) is the shortest contact time that can inhibit bacterial growth. A container consisting of 27 mL sterile distilled water, 3 mL cultured E. coli, and 3 g sample was incubated for 60 min at 37
°C. Approximately 1 mL of the solution was used to measure the turbidity using a spectrophotometer at a wavelength of 600 nm and time points of 0, 5, 10, 15, 20, 25, 30, 40, 50, and 60 min.
Results and Discussion
Synthesis and characterization. Sample A was untreated natural zeolite sample (blank) with a gray color and different surface shapes, such as fiber, cube, and ball, which are the shapes of natural zeolite (Figure 1). Fibers or needle-like shape indicated the shape of mordenite, and a tabular shape indicated clinoptilolite [14]. XRD data (Figure 2) showed that all samples had similar values for the peaks of mordenite and clinoptilolite at 9.71°, 13.46°, 19.64°, 20.48°, 22.27°, 26.62°, and 27.74°.
Typical peaks of mordenite are at 9.76°, 19.67°, and 25.66°, and those of clinoptilolite are at 11.16°, 17.26°, and 22.39° [14]. FTIR results (Figure 3) demonstrate that
Figure 1. Morphology of Samples Under SEM/EDX A) Zeolite B) Zeolite + Heat Treatment C) Zeolite + CuSO4 D) Zeolite + CuSO4 + Heat Treatment
all the samples show peaks at ~780, 902, 1215, 1659, and 3400–3600 cm−1, which indicated the characteristic of zeolite, and peaks at ~3440 and ~1640 cm−1, which corresponded to the O–H stretching vibration and the signal stretching and angular deformation of the hydroxyl molecules of water from the hydration of zeolites, respectively. The symmetric stretch vibrational modes of Si−O−Si and Si–O–Al groups, were localized in low frequencies (400–700 cm−1) [15].
Zeolite soaked in CuSO4 solution (sample C) showed a color change compared with sample A. This immersion caused the sample to turn bluish, indicating the adsorption of Cu2+ ions into the zeolite surface. The presence of copper (as much as 3.02%) in the sample was confirmed by SEM–EDX (Figure 1). However, the color was not stable during immersion in water. The water turned bluish (Figure 4), indicating that the adsorbed copper was eventually desorbed. The XRD and FTIR peaks of sample C did not remarkably differ from those of sample A. Nevertheless, the XRD of sample C showed higher and sharper peaks compared with that of sample A. This finding indicated that the properties and characteristics of zeolite become apparent after immersion in the CuSO4 solution.
CuSO4 has a pH 4, making it an acidic solution that could damage the zeolite structure. In theory, the H+ in the solution will form hydrogen bonds with the negative charge of zeolite through the connecting oxygen from the Al−O−Si bond in zeolite, thus forming Al−OH−Si and then dissolving aluminum and silicon in the zeolite surface [16]. Natural zeolite is composed of the zeolite mineral itself. Negative ions from these structures are counterbalanced with positive ions or oxide compounds in nature. In this study, immersion in the CuSO4 solution caused the zeolite peaks of the sample to become apparent in the XRD spectrum, indicating that the contact
Figure 2. XRD Patterns of Samples A) Zeolite B) Zeolite + Heat Treatment C) Zeolite + CuSO4 D) Zeolite + CuSO4 + Heat Treatment. CLI Represents to Clinoptilolite, MOR Represents to Mordenite
between the zeolite and copper solution caused the natural impurification of natural zeolite. Copper replaced surface H+ and other counterbalanced surface cations through ion exchange reactions [17].
Apart from acid addition, the heating treatment also affected the structure and purity of natural zeolite.
Heating treatment for natural zeolite was performed on sample B which caused a color change from gray to black. This color appeared stable as evidenced by the unchanged color of the water soaked in sample B. SEM results showed that the heat treatment damaged the shape of natural zeolite fibers (Figure 1). However, no significant difference in XRD and FTIR spectra was observed between samples A and B, indicating that the heating damaged the outer surface of the natural zeolite but did not change its crystallinity. A previous study suggested that heating treatment removes impurities;
enhances sorption properties, surface area, and porosity;
and induces important crystallinity loss [18].
Figure 3. FTIR Spectrum of the Samples A) Zeolite B)Zeolite + Heat Treatment C) Zeolite + CuSO4
D) Zeolite + CuSO4 + Heat Treatment
Figure 4. Sample Soaked in the Water a) Sample+Water after Soaked b) Soaked Water after Separated with Sample, A) Zeolite B) Zeolite + Heat Treatment C) Zeolite + CuSO4 D) Zeolite + CuSO4 + Heat Treatment
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Sample D had the smoothest surface shape among the samples and maintained a long-lasting black color even after being immersed in water (Figure 4). A previous study proved that adding acid and heating natural zeolite can increase the ratio of Si/Al in zeolite and reduce zeolite impurities [19]. Heating can cause the dehydration of zeolite, thus damaging its structure. In addition, dehydration due to heating can trap some exchangeable cations in the channels to [18]. In sample D, heating prompted the copper ions to undergo autoredox, resulting in Cu2+ ions that were adsorbed inside and on the surface of the zeolite, resulting into a mixture of CuO and Cu2O.
The XRD and FTIR spectra of sample D did not significantly differ from those of samples A and C, but the XRD peaks of sample D showed more apparent peaks than those of samples A and B (Figures 2 and 3).
According to JCPDS card number 05-0667, the typical peaks of Cu2O nanocrystals are at 29.61°, 36.48°, 42.38°, 61.46°, 73.56°, and 77.52°; however, CuO showed peaks at 35° and 38° (JCPDS-41-254). According to the data, no peak indicated CuO or Cu2O, which might happen because the amount of copper oxide in the composite is too small (around 3%) (Figure 1). In addition to the small amount of CuO and Cu2O, no peaks of copper oxide were detected because the formed copper oxide is amorphous.
CuO and Cu2O practically do not have functional groups, so they do not participate in any chemical interaction that will be detected in FTIR [20]. However, the black color of the zeolite after the treatment indicated the formation of copper oxide.
Antibacterial activity. Antibacterial analysis was performed via disk diffusion. This method utilizes a sample that diffuses into the surrounding area so that the growth of surrounding bacteria can be inhibited. This phenomenon is indicated by the presence of a clear zone around the sample called the inhibition zone. The results showed that natural zeolite alone (A and B) did not exhibit antibacterial activity. However, granular natural zeolite samples with 0.5-M CuSO4 (C and D) showed good antibacterial activity against E. coli (Figure 5) with diameters of 13.81 and 10.69 mm, respectively (Table 1).
Davis and Stout [21] grouped the antibacterial strength based on the clear zone into very strong (>20 mm), strong (10–20 mm), medium (5–10 mm), and no response (<5 mm). ANOVA test showed that the antibacterial activities of samples C and D were not significantly different from each other. According to the grouping in [21], samples C and D were classified as strong antibacterials. Meanwhile, zeolite itself had no antibacterial activity.
Figure 5. Antibacterial Activity from Samples using Disk Diffusion Method A) zeolite B) Zeolite + Heat Treatment C) Zeolite + CuSO4 D) Zeolite + CuSO4 + Heat Treatment
Table 1. Sample Antibacterial Test Against E. coli.
Sample code Type of sample Heat treatment
(450 °C)
Mean diameter of inhibition zone (mm)
A Natural zeolite + water - 0.00 ± 0.00b
B Natural zeolite + water heated 0.00 ± 0.00b
C Natural zeolite + CuSO4 0.5 M - 13.81 ± 3.20a
D Natural zeolite + CuSO4 0.5 M heated 10.69 ± 3.50a
Numbers in the same row followed by different letters indicate that the results are significantly different (P < 0.05).
E. coli belongs to Gram-negative bacteria. The difference between Gram-positive and Gram-negative bacteria is that the former have a thick peptidoglycan layer on their cell membrane, and the latter have an outer membrane that makes them less susceptible to antibacterial agents.
In general, bacteria grow by producing their own polysaccharides, proteins, and nucleic acids from their exopolymer matrix [21]. Antibacterial agents kill bacteria by inhibiting the formation of the bacterial membrane through the accumulation and dissolution of antibacterial particles in the bacterial membrane and then changing its permeability and damaging cellular structures by ROS and uptake of metallic ions derived from antibacterial particles [22].
Figure 4 shows that sample C had antibacterial activity due to the release of Cu2+ ions as evidenced by the desorption of copper ions into the water, causing the water to turn blue. The MHA medium contains several types of minerals that have positive ions, which interact with bacteria in two ways. One is the adsorption of bacterial cells on the surface of the Cu2+ carriers, and the other is the dissociation of Cu2+ ions from the composite that directly interact with bacterial cells. Cu2+ ions can bind to lipopolysaccharides or peptidoglycans or carboxylic groups in the cell wall of Gram-positive and Gram-negative bacteria and affect the stability of bacterial cell envelope [10, 23–25]. Cu2+ shows an antibacterial mechanism by interacting with bacteria and disrupting their cell walls and membranes, causing cell membrane depolarization, replacing or binding the native cofactor in metalloproteins by inhibiting metal binding sites in iron–sulfur protein, and damaging intracellular component [25]. The ROS mechanism occurs through copper oxide on the surface of the zeolite in contact with bacteria. The reactive species formed can be superoxide anion (O2− ), hydrogen peroxide (H2O2), hydroxyl radicals (HO･), and organic hydroperoxides, all of which damage bacterial cell wall components, including lipids,
peptidoglycan, proteins, and DNA [19, 20, 28]. ROS can be generated through two types of mechanisms, namely, Fenton type and Haber–Weiss type [22, 26, 27]:
Haber–Weiss Reaction
H2O2 + O2−→ ･OH + OH− + O2
Fenton Reaction
Cu+ ＋ H2O2 → ･OH ＋ OH−+ Cu2+
Sample D showed antibacterial activity through the Cu2+
ion release mechanism and ROS from the formed copper oxide. According to the results, the copper oxide formed is a mixture of CuO and Cu2O, with different antibacterial abilities [25]. Cu2O exhibits stronger antibacterial abilities compared with that of CuO.
However, CuO can induce greater ROS than Cu2O because CuO produces ROS through Harber–Weiss and Fenton-type reactions, whereas Cu2O can produce ROS only through the Fenton type. The combination of CuO and Cu2O in the heated samples in this study can optimize the antibacterial activity. E. coli specimens were found inside the periplasmic space with superoxide dismutase, which may act on superoxide anion, resulting in the formation of H2O2 that easily permeates the cell and thus oxidizes the cellular active systems [28, 29].
Antibacterial testing on samples was done using contact method and determination of minimum contact time to evaluate the further use of the composite as a water filter (Figure 6). MIC was defined as the lowest concentration of samples that inhibits the growth of a microorganism.
The results showed that samples C and D had better antibacterial activity than the zeolite samples alone.
Sample C had excellent antibacterial activity until the 20th min; after which its antibacterial inhibition decreased. This phenomenon occurred because the Cu2+
ion released from the zeolite have been used up to inhibit
Figure 6. Antibacterial Activity of Samples based on Minimum Contact Time between Sample and E. coli A) Zeolite B) Zeolite + Heat Treatment C) Zeolite + CuSO4 D) Zeolite + CuSO4 + Heat Treatment
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Figure 7. Levels of Copper Ions Released from the Water Soaked in Samples for 1 and 3 Days with Different Ratios Sample (g): Water (mL) A) Zeolite B) Zeolite + Heat Treatment C) Zeolite + CuSO4 D) Zeolite + CuSO4 + Heat Treatment
the growth of bacteria at the beginning. As a result, the amount of remaining Cu2+ ions is low for the following growing bacteria. By contrast, sample D, which utilizes the interaction between copper oxide and bacteria, showed a stable antibacterial activity. This experiment revealed that when the composite is applied as a filter, treated water can be used after the water has been treated for less than 20 min or 50–60 min.
Levels of released copper ions. Atomic absorption spectroscopy (AAS) test was carried out to measure Cu2+
ion levels separated from the water that has been soaked with samples for 1 and 3 days with different ratios (Figure 4). The results showed that the samples soaked for 3 days released a large amount of Cu2+ ions. In samples A and B, Cu2+ ions were detected in small quantities, indicating that the natural zeolite contains Cu2+ ions. Sample C released quite a large amount of Cu2+ ions (up to 49 ppm) after being soaked for 3 days, and sample D only released up to 2 ppm Cu2+ ions into the water (Figure 7). This finding showed that heating reduces the release of Cu2+ ions into the water. According to WHO standards, the threshold for Cu2+ ion content in the water that can be used as drinking water is as much as 2 mg/L. Sample D can still be used as a drinking water filter when soaked for less than 1 day, and the filtered water from the filter containing sample D can still be used when the filter was soaked for up to 2 days. Comparison of Cu2+ ion release and antibacterial diameters between samples C and D showed that the copper oxide compounds had the same strong antibacterial power as Cu2+ ions.
Conclusion
The characterization of the samples showed that heating and adding copper ions damages the zeolite surface but did not affect the composition of the zeolite. CuO and
Cu2O/zeolite (sample D) were successfully synthesized with strong antibacterial activity without any quality loss.
Sample D could be applied as water filter with low tox- icity and high antibacterial activity with minimum con- tact between the sample and water for less than 20 min or 50–60 min.
Acknowledgment
The authors acknowledge financial support from the Re- search and Innovation Program for Advanced Indonesia (RIIM) schema under contract 82/H.7/HK/2022 orga- nized by the Indonesian National Research and Innova- tion Agency.
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