Preliminary Analysis studies of hazelnut shell and activated carbon
The main reason why we chose the chemical H3PO4 in chemical activation in our study is that it is frequently preferred due to its lower toxic effects on the environment, cheaper, more effective activation, and lowering carbonization temperature compared to other activating agents (such as ZnCl2, KOH or NaOH) in the literature research (Sych et al., 2012; Al Bahri et al., 2012).
Proximate and Ultimate analysis experiments of HS used in the production of AC and activated carbon impregnated with H3PO4 at a ratio of 1:1 were carried out. Analysis results are given in Table 1.
Table 1
Characteristics of the HS and AC
Characteristics | Methods | HS | AC |
Moisture content (wt.%) | ASTM D 2016 2.67 | 7.23 | 2.87 |
Proximate analysis (wt.%) | | 64.91 | 9.1 |
Volatile Matter | ASTM E 872 78.50 | 26.56 | 86.83 |
Ash | ASTM D1102 0.17 | 1.3 | 1.2 |
Fixed carbon | By difference | | |
%Yield | | - | 36 |
Ultimate analysis (wt.%) | | | |
Carbon | AR2092-0721 | 49.35 | 56.01 |
Hydrogen | | 6.10 | 3.44 |
Nitrogen | | 0.36 | 0.77 |
Sulphur | | 0.048 | 0.012 |
Oxygen | By difference | 44.142 | 39.768 |
* Fixed Carbon = 100-(Moisture + Ash + Volatile Matter) |
Table 1. Characteristics of the HS and AC
Table 1 presents the characteristic properties of HS and AC obtained from its activation with H3PO4.Raw materials with low ash, high volatile matter, and fixed carbon content are preferred in the production of AC. When the studies in the literature are examined; It has been observed that vegetable wastes with volatile matter content between 20.40-67.36%, fixed carbon content between 17.62–70.70%, and ash content between 0.3-5.0% are used in the production of activated carbon (Hadoun et al., 2013; Budinova et al., 2006). In this context, according to the results of the short analysis of the raw materials in our study; It was concluded that the HS activated with 1:1 H3PO4 has low ash content (1.3%), volatile matter (64.91%), and fixed carbon (26.56%), and it is a suitable raw material for the production of AC from HS.
When the preliminary analysis results of AC are evaluated in Table 1, it is seen that the amount of ash, moisture and volatile matter determined in the hazelnut shell decreased as expected in the AC, while the fixed carbon ratio increased.
The yield of hazelnut shell activated with H3PO4 at a ratio of 1:1 was found to be 36%. A similar trend has been reported in the literature (Hadoun et al., 2013; Yorgun et al., 2015; Prahas et al., 2008).
The contents of carbon, hydrogen, nitrogen and sulphur of the HS and AC were measured using a LECO CHNS 628 Elemental Analyzer with ± 0.4% accuracy (LECO Instruments, USA). The oxygen contents were calculated by difference. The elemental composition of AC and HS samples is given in Table 1. When the HS and AC elemental analysis results are compared, it is seen that the amount of carbon contained in AC increases with carbonization.
N Adsorption/desorption Analysis Of Ac And Silver Coated Acs
Based on the nitrogen gas (N2) adsorption method in a liquid nitrogen atmosphere, the results of the BET isotherms of activated carbon and silver coated ACs obtained by the activation of the HS with H3PO4 were measured.
The surface areas, Iodine number, MB number, t-Plot Micropore area, Total porosity area, Microporosity volume, Average pore size, pore-volume, and pore size properties of AC and silver-coated ACs are given in Table 2 comparatively.
Table 2
Textural properties of AC and Ag impregnated ACs,
Samples | SBET (m2/g) | t-Plot Micropore (m2/g) | t-Plot (m2/g) | V total (cm3/g) | Vmicro (cm3/g) | Average pore size (Ǻ) | Iodine number, mg/g |
AC | 1208 | 534.0068 | 674.0041 | 0.6104 | 0.254 | 20.211 | 1142 |
AC/Ag-0.5 | 1185 | 444.6077 | 740.311 | 0.6847 | 0.210 | 23.115 | - |
AC/Ag-1.0 | 899.933 | 301.8536 | 598.079 | 0.5576 | 0.155 | 24.787 | - |
Table 2. Textural properties of AC and Ag impregnated ACs,
According to a classification made by IUPAC, a pore size greater than 500Ǻ is called a macropore, between 500 and 20Ǻ is called a mesopore, and less than 2Ǻ is called a micropore (Saeed et al., 2003). In our study, the pore size of AC was found to be 20.211 Ǻ. This tells us that our AC is a mixture of micro and mezzo.
ACs are generally solids with dense aromatic groups, large surface area, and pore volume. The pores in the carbon cause an increase in the surface area after activation (Mbark et al., 2022). Surface area is one of the important properties of activated carbon to be used for adsorption. The size of the surface area means that the pore volume that will perform the adsorbing is also large. This porosity is a requirement for the effective use of activated carbon. Although the surface area of activated carbons used commercially in the literature is in the range of 400–1000 m2 g− 1, this value can be exceeded in special-purpose productions (Lima et al., 2019; Spessato et al., 2019). Looking at Table 2, the BET surface area value of activated carbon obtained by chemical activation of H3PO4 was measured as 1208 m2 g− 1. This result shows us that the surface area of our activated carbon is large enough. 1142 mg g− 1, which we found because of iodine adsorption, is quite compatible with this result. The high iodine adsorption indicates that our AC is generally microporous.
When Table 2 is examined, it is seen that the surface area, micropore area, outer surface area, micropore volume, and average pore size decrease as the amount of silver added to the activated carbon increases. Chen et al., 2000, in their study on activated carbon fibers, showed that the antibacterial effect increased as the surface area decreased (Feng et al., 2000). Yang et al., 2009, showed that the surface area of silver nanocomposites prepared by adding silver to bamboo charcoal decreased as the amount of added silver increased (Yang et al., 2009)
While the macropores allow the molecule to be adsorbed and transferred to the AC, the meso and micropores perform the adsorption process. Mesopores are crucial for the absorption of organic compounds (Jiun-Horng et al., 2008; Fischer et al., 2017; Ng et al., 2018; Zhang et al., 2009). In our study, it is seen in Table 2 that the pore size increased after adding Ag to the AC. The increase in the amount of silver and the size of the mesopores can be explained by the increase in its antibacterial effect (Hadoun et al., 2013). The pore width is in the range of 20.211–24.787 Ǻ as seen in Table 2 of this study.
These results show us that the AC we have obtained can be used effectively in the removal of organic compounds such as MB.
Iodine number (IS) determination provides information about the surface area of activated carbons due to its ability to adsorb small molecules and is an indicator of porosity (Saka et al., 2021). In our study, the iodine number was calculated as 1142 mg g− 1 (Table 2). The iodine number we found showed parallelism with the surface area of the AC. The high iodine number given in the literature is generally between (500–1200 mg g− 1) (Benaddi et al., 2000; Saka et al., 2022). Our study is among these values This result shows that AC synthesized with H3PO4 activation has a high ability to adsorb impurities and a high microporosity of activated carbon.
Textural Characterization By Sem
SEM and EDS images of HS, AC, AC/Ag-0.5, and AC/Ag-0.1 samples are shown in Fig. 1 (a-d), respectively.
Figure 1 SEM and EDS a) HS b) AC c) of AC impregnated with 0.5 g Ag d) of AC impregnated with 1.0 g Ag
SEM photographs of hazelnut shells are shown in Fig. 1(a) HS has a fibrous appearance. These fibers are visible in SEM images. When SEM-EDS results are examined; C, O, Na, Ca, K, and Cu elements were found in the structure. It is thought that these elements come from the soil and hazelnut's structure.
SEM photographs of activated carbon are shown in Fig. 1(b) When this photograph was examined, significant differences were observed between the surface topography of the HS and ACs. While there are no pores on the surface of the raw HS, many large pores have developed on the surface of the ACs. Depending on the impregnation ratio, the outer surfaces of AC have pores of different sizes and shapes. Similar results have been reported in the literature (Hadoun et al., 2013; Wang et al., 2005). When the EDS analysis was examined, C, O, and P elements were found on the surface of the activated carbons. Although C and O are the elements that should be in the activated carbon, it has been determined that there is phosphorus on the surface. It has been determined that the phosphorus on the surface of the activated carbon comes from the phosphoric acid residues that remain in the activated carbon during the activation process and cannot be removed by washing.
Figures 1 (c) and (d) show SEM photographs after silver bonding to activated carbon. It is seen that the surface morphology of the AC and silver coated ACs changed. As the amount of silver increases, the whiteness on the surface increases. It is seen from the images that activated carbon with a 24 h impregnation time adsorbs silver. It is seen that the AC we obtained has a porous structure and due to its high surface area, it binds silver at a high rate (Altintig et al., 2016; Yang et al., 2009). When the amount of Ag added increases from 0.5 to 1.0 g, it is seen that the amount of silver increases. Moreover, according to the SEM results, as the silver ratio increases from 0.5 to 1.0 g, the amount of silver added to the surface also increases.
When the EDS analyzes are examined (Fig. 1a), it is seen that the hazelnut shell mainly contains C (42.828) and O (39.565). This ratio revealed that AC consists of C (76.428%) and O (15.378%) elements. C ratio increased in activated carbon. This shows us that there is activation. However, in the EDS analysis of 0.5 g Ag-ACs (Fig. 1c), the element ratios for C, O, and Ag were 38.73%, 12.48%, and 41.64%, respectively. In Fig. 1, the amount of Ag increased to 51.87% in 1.0 g of Ag-impregnated activated carbon. This result shows that the silver nanoparticles are successfully attached to the AC surface.
Powder Xrd Study
With XRD, important data are obtained about the composition of the inorganic substance in the structure. Figure 2 (a-d) gives a comparative XRD plot of hazelnut shell, activated carbon, AC/Ag-0.5, and AC/1.0 samples, respectively.
Figure 2 XRD pattern of a) HS b) AC c) of AC impregnated with 0.5 g Ag d) of AC impregnated with 1.0 g Ag
With XRD, important data are obtained about the composition of the inorganic substance in the structure. Figure 2 (a-d) gives a comparative XRD graph of the samples of HS, AC, AC/Ag-0.5, and AC/1.0 materials, respectively.
Figure 2(a-b) shows the XRD spectrum of the HS and AC sample, respectively. Weak peaks of 22° and 44° were observed in these spectra. These weak peaks prove to us HS and AC have an amorphous structure. This indicates that there is no characteristic peak after activation. Similar results have been reported in the literature (Altintig et al., 2013, Altintig et al., 2015; Saka and Balbay 2021).
In Fig. 2(c-d), the XRD spectra of AC/Ag-0.5 and AC/Ag-1.0 samples prepared from AC obtained by impregnation with H3PO4 for 24 h (1/1) are shown. When the images are examined, the peaks supporting the presence of silver in the mixtures are seen. It is clear from the sharpness of the peaks that after the addition of silver, the amorphous structure of activated carbons turns into a crystalline structure. As a result of XRD analysis of AC with the silver nanoparticle, 38.28°; 44.46°; 64.54°; Sharp peaks were obtained at 77.22° and 81.66°. These peaks obtained because of the analysis belong to surface-centered metallic silver in the coordinates (111), (200), (220), (311), (222). No silver oxide peaks were found in the structure in XRD results (Karadirek et al., 2019; Sang et al., 2016; Singh et al., 2014). This result leads us to the conclusion that silver is attached to activated carbon in the metallic form (Altintig et al., 2013). It is seen that the intensity of the characteristic peaks of silver increases as the amount of AgNO3 added to the ACs increases. This suggests that silver pieces with larger crystals were formed. These results show parallelism with SEM results.
Ftir Analysis
FTIR spectra were taken to determine the functional groups of HS, AC obtained by chemical activation of HS, and silver-coated activated carbon produced in two different ratios.
Figure 3 FTIR spectrums of a) HS b)AC c) of AC impregnated with 0.5 g Ag d) of AC impregnated with 1.0 g Ag
FTIR spectra were taken to determine the functional groups contained in the HS, the AC obtained by the chemical activation of the hazelnut shell, and the silver-coated activated carbon in two different ratios. FTIR spectra of HS are shown in Fig. 3a. Strong peaks at 3400 cm− 1, were attributed to the OH stretching vibration of hydroxyl functional groups. The peaks at 2800 cm− 1 were assigned to the stretching vibration of C-H bonds, and the peak at 1160 cm− 1 represented the stretching vibration of the C = C bonds in the benzene ring. Bands in the region of 1104 − 998 cm− 1 showed the presence of C-O, which was ascribed to alcohols, phenols, acids, or esters. The peak around 1050 cm− 1 is due to R-OH groups (Hadoun et al.,2013). In addition, the band around 1690 cm− 1 indicates C = O carbonyl groups. Peaks around 1500 cm− 1 indicate –CH2 = vibrations. Similar peaks were also observed in the literature (Mbarki et al., 2019; (Jawad et al., 2019). As seen in Fig. 3, OH and other peaks disappeared because of high-temperature activation and carbonization in ACs.
Figure 3c and d show the comparative FT-IR spectrum of ACS with 0.5 and 1.0 g of silver added, respectively. When silver is added to activated carbon, peaks of, 1618 cm− 1 and 1005 cm− 1 and 2907 cm− 1 appear. As the amount of silver increases, the sharpness of the peaks decreases. These peaks became apparent when silver was added, and, the peaks 2907 cm− 1, 1618 cm− 1 1005 cm− 1 show us that the Ag+ ion combines activated carbons by reduction (Singh et al., 2008; Altintig et al., 2016).
Adsorption Isotherm Studies
The adsorption isotherm determines were carried out to evaluate the adsorption capacity of AC and Ag/AC for MB. A certain amount of AC and Ag/AC was added to 100 mL MB solution with the initial concentration ranging from 50 mg L− 1 to 300 mg L− 1. The mixture was stirred at 250 rpm for 24 h at 298 K temperatures for adsorption. The adsorption properties of the samples were investigated by fitting isotherm models including Langmuir and Freundlich models. The Langmuir and Freundlich isotherms were widely used to study the relationship between the adsorption capacity and the equilibrium concentration of adsorbate under a certain temperature (Wu et al., 2006, Dinu et al., 2010). The linear correlation of the Langmuir isotherm is given in Eq. (3).
$$\frac{{C}_{e}}{{q}_{e}}=\frac{1}{{q}_{m}{K}_{L}}+\frac{1}{{q}_{m}}Ce$$
3
Ce is the adsorbate concentration in the solution following the adsorption (mg L− 1), qe is adsorbed amount onto adsorbent (mg g− 1), and KL is the isotherm coefficient (L mg− 1), qmax is the maximum adsorption capacity of adsorbent (mg g− 1).
Figure 4 Langmuir isotherm plots obtained for the adsorption of MB onto (a) AC b) of AC impregnated with 0.5 g Ag C) of AC impregnated with 1.0 g Ag
Equilibrium data calculated qmax as 277.77, 357.14, and 454.54 mg g− 1 for AC, AC impregnated with 0.5 g Ag and AC impregnated with 1.0 g Ag, respectively.
Freundlich isotherm model assumes the multi-layer coating of the adsorbent surface by adsorbent molecules (Karadirek et al., 2019). This linear formulation has been submitted in formula (4) as follows.
$${lnq}_{e}={lnK}_{f}+\frac{1}{n}{C}_{e}$$
4
where qe refers to the equilibrium concentration (mg g− 1) of adsorbate on the surface of the adsorbent, Ce refers to adsorbate (mg L− 1) in solution, Kf and n refer to Freundlich’s constants.
Figure 5 Freundlich isotherm plots obtained for the adsorption of MB onto (a) AC (b) of AC impregnated with 0.5 g Ag (c) of AC impregnated with 1.0 g Ag
Isotherm parameters calculated by linear Langmuir and Freundlich isotherm models are given in Table 3.
Table 3
Adsorption isotherm parameters for MB on AC and Ag impregnated ACs
Sample | Langmuir isotherm | Freundlich isotherm |
| qm (mg/g) KL (L/mg) R2 | KFn (l/mg) R2 |
AC | 277.77 | 0.38 | 0.99 | 84.17 | 2.84 | 0.88 | |
AC/Ag-0.5 | 454.54 | 0.08 | 0.99 | 37.12 | 1.69 | 0.93 | |
AC/ Ag-1.0 | 303.03 | 0.05 | 0.99 | 27.80 | 1.45 | 0.98 | |
Table 3. Adsorption isotherm parameters for MB on AC and Ag impregnated ACs
When Table 3, where the Langmuir and Freundlich isotherm constants are given together, is evaluated, it shows that the correlation coefficient of the Langmuir isotherm is in the range (R2 = 0.99) and the correlation coefficient of the Freundlich isotherm is between (R2 = 0.877–0.979). Comparing the correlation coefficients, the Langmuir isotherm is best fitted to the adsorption model which proves that the MB was adsorbed by AC, AC impregnated with 0.5 g Ag and AC impregnated with 1.0 g Ag in a homogenous monolayer. The maximum adsorption capacities (qmax) of AC calculated from the linear Langmuir isotherm equation, AC impregnated with 0.5 g Ag and AC impregnated with 1.0 g Ag are 277.77, 357.14, and 454.54 mg g-1, respectively. It can be seen from Fig. 5 that the experimental MB adsorption capacities (qmax) of silver-impregnated Activated carbons are higher than the adsorption capacity of AC. According to the Freundlich isotherm, the value of n between 1 and 10 is known as adsorption fitness (Mishra et al., 2009). This value is between 1.45 and 2.84 in our study in all our samples. Our study shows that it is suitable for MB adsorption. In addition, a high Kf value indicates high adsorption affinity. The qmax value is calculated for the highest 1.0 g Ag impregnated AC. This tells us that the highest adsorption capacity is 1.0 g Ag impregnated AC. It is an indication that it is suitable for adsorption for MB removal from aqueous solutions.
Determination Of Antibacterial Properties Of Silver-coated Activated Carbons
The disk diffusion method was used to determine the qualitative antibacterial properties of silver nanoparticle-bound AC (Xin et al., 2005). The study was conducted with two types of bacteria, gram-negative E. coli, and gram-positive S. aureus. The antibacterial properties of AC and silver nanoparticle bonded activated carbon were compared. As can be seen in Fig. 6, there was no inhibition area against E. coli and S. aureus bacterial cultures around the activated carbon, but the activated carbon with silver nanoparticles showed an antibacterial effect against both bacterial species.
Figure 6 Antibacterial activity of activated carbon and silver-coated activated carbons against E. coli and S. aureus bacteria.
The strength of the antibacterial property of AgNPs differs in Gram-positive and -negative bacteria. This is because these species differ in their cell walls' architecture, thickness, and composition (Tamayo et al., 2014). It is known that E. coli, a Gram-negative bacterium, is more sensitive to Ag+ ions than Gram-positive S. aureus. The reason for the different sensitivity lies in peptidoglycan, an important component of the bacterial cell membrane. In Gram-positive bacteria, the cell wall consists of a negatively charged peptidoglycan layer about 30 nm thick whereas in Gram-negative bacteria there is only a 3 to 4 nm peptidoglycan layer. These structural differences, including the thickness and composition of the cell wall, explain why Gram-positive S aureus is less sensitive to AgNPs and Gram-negative E.coli (Fayaz et al., 2010; Espinosa-Cristobal et al., 2009).
In the study in which we investigated the antimicrobial properties of AgNPAC, the findings showed that it inhibited S.aureus and E.coli in different zone ranges, as seen in Table 4. Results were evaluated concerning EUCAST disc diffusion results (2019). For Ampicillin (10 mg) and Cefotaxime (30 mg)
Table 4
Inhibition Zone Diameters of S.aureus (ATCC 25923) and E.coli (ATCC 25922)
Nano composites | Dose(mg) | Zon inhibasyon (mm) | Referance |
| | S. aureus | E.coli | |
AgAC(SA) | | 8.2 | 9.1 | Saravanan et al., 2016 |
AgAC(UA) | | 12.0 | 8.0 | Saravanan et al., 2016 |
AgNPs | | 13.3 | 15.5 | Njue et al., 2020 |
BCAg-0.5g | | 11.4 | 12.6 | Yang et al., 2009 |
BCA-1g | | 11.5 | 12.6 | Yang et al., 2009 |
AgNP-AC | | 17–18 | | Karthik and Radha 2016 |
ACNP | | 20 | | Varghese et al.,2013 |
ACF-Ag30 | | | 11.8 | Yoon et al., 2008 |
Ag-AC NC | | 15 | 15 | Devi et al., 2019 |
AgNPs/AC-CNF | | 6 | 5.8 | Sobhan et al., 2020 |
AgNPAC | | 13.38 | 10.60 | Karadirek and Okkay 2019 |
AC/Ag | | | 2.8 | Aravind et al., 2022 |
AgNP/AC | | 6–19 | 6 | Taha et al., 2020 |
AC | 10mg | 0 | 0 | This study |
0.5gAgNPAC | 10mg | 23.2 | 18.3 | This study |
1g AgNPAC | 10mg | 34.1 | 24.1 | This study |
Ampicillin | 10mg | 43.1 | 15.2 | This study |
Sefotaksim | 30mg | 22.8 | 31.3 | This study |
Note
Most coagulase-negative staphylococci are penicillinase producers and many are resistant to ampicillin and methicillin (EUCAST, 2019).
Due to its reactive electronic structure, the silver ion joins the donor groups containing sulfur, oxygen, and nitrogen. These three compounds, in which the silver ion is added, are found in biological molecules as amino, imidazole, carboxylate, and phosphate groups (Duran et al., 2007). Thus, silver ion reacts with thiol groups and causes the inactivation of bacteria. The silver ion also causes the formation of hydrogen peroxide, which catalyzes the destructive oxidation of microorganisms. Silver ions and hydrogen peroxide destroy protein cells. Since the antibacterial effect of silver ions is directly proportional to Ag+ concentration, silver ions are likely to dominate more than one target, such as DNA or cellular proteins (Prakash et al., 2013). Our study also observed that the antibacterial effect of the materials increased as the silver ion concentration increased.
The Time Optimization Of The Antibacterial Treatment
Optimization of the antibacterial effect of E Coli bacteria against time is shown in Fig. 7. It shows that the antibacterial effect changes with the increase in the bacteriostatic time on the AC/Ag composite. While AC/Ag composite bacteriostatic time was 30 min, its antibacterial rate was over 90%. It showed that the optimal bacteriostatic time was 30 min.
Figure 7 The antibacterial effect changes with the increase in the bacteriostatic time on the AC/Ag composite
As seen in Fig. 7, it was not taken into account because more than 300 colonies grew in the zeroth and tenth-min sowings, and less than thirty min in the fortieth min. By the 20th min, significant colony reduction was observed, and only one colony was observed at the fortieth min. In this study, 105 CFU/mL of E. coli was completely inhibited in 30 min. The same protocol was performed for 105 CFU/mL of E. coli with AC only (without Ag) and no reduction was observed within 40 min. While Zhao et al. (2013) removed E. coli from drinking water in 120 min in a similar study with AgAC, Yoon et al. (2008) reported the time taken for E. coli to be destroyed by AgAC as 60 min. Biswas and Bandyopadhyaya (2016), on the other hand, reported that all E. coli of 104 CFU/mL in drinking water were destroyed within 25 min of contact with the filter made with AgAC (Yoon et al., 2008; Zhao et al., 2013; Biswas and Bandyopadhyaya 2016).
Calculation of the number of colonies is carried out by taking into account the dilution carried out before sowing. In this case, while our initial colony count was 108 CFU/mL, this number was also taken into account in the counting, since the first treatment was started with 105 CFU/mL colonies at the end of three dilutions. CFU was calculated using Eq. 5 (Gamazo 2005).\(\frac{ \left(CFU\right)}{\text{m}\text{L}}=\frac{(No.ofcolonies)x \left(dilutionfactor \right)}{volumeofcultureplate}\) (5)
In drinking water with an initial concentration of 105 CFU/ml, all cells were killed within 30 min at the end of the treatment. As a result, 105 CFU/mL of E. coli bacteria was destroyed with 5 logarithmic reductions by using AgNPAC 30 min after drinking