3.1. TEM anaylsis of PtNPs and CoNPs
Figure 2 (a) and (b) shows the TEM images and particle size distribution corresponding to TEM analysis of PtNPs obtained under different ablation liquids, respectively. Figure 1 shows that PtNPs have a spherical shape, with little aggregation observe in the as-prepared DDDW and DMEM liquids. It was determined that the grain sizes of PtNPs3 produced in DMEM have smaller than PtNPs2 produced in water. PtNPs2 produced in DDDW have a more heterogeneous structure compared to the others. Because of this, the particles clustered together and the PtNPs2 are more opaque. This case also affected the absorption of the PtNPs2 nanoparticles (Fig. 4 (a)).
Figure 2 (b) shows PtNPs2 and PtNPs3 nanoparticles the particle size distribution histogram. The particle sizes of PtNPs2 nanoparticles ranged from 5 to 40 nm while the particle sizes of PtNPs3 nanoparticles were about 5 to 50 nm.
Spherical PtNPs2 and PtNPs3 nanoparticles of average particle size varies are obtained as 12–20 nm, respectively. The particle size of PtNPs produced in water was obtained smaller than the others.
Figure 2
Figure 3 (a) and (b) shows the TEM images and particle size distribution corresponding to TEM analysis of CoNPs obtained under different ablation liquids, respectively. The CoNPs showed a rod and spherical shape with few aggregations that were observed in the medium of double distilled water and DMEM nanoparticles (Fig. 3). The particle sizes ranged from 15 to 55 nm, with an average of 38 nm.
Figure 3
3.2 Optical absorption analysis
Figure 4 shows absorbance spectra of PtNPs and CoNPs nanoparticles. According to Fig. 4 (a), the absorption edge of PtNPs2 nanoparticles produced in water was observed at long wavelengths while that of PtNPs3 nanoparticles produced in DMEM was observed at shorter wavelengths. In addition, the band edge structure nad absorsbans values changed depending on the type of liquid used. PtNPs2 nanoparticles have higher absorbance value than PtNPs3 while PtNPs3 nanoparticles have shaper band edge than PtNPs2. This depends on the particle size and distribution of the nanoparticles. TEM analysis also support this results. When Fig. 4 (b) is examined, it is seen that there is much variation between the absorption spectra of CoNPs nanoparticles.
Figure 4
The band values of CoNPs and PtNPs were calculated by the following relation [32]:
(αhν) = A(hν − Eg) n (1)
where A is a constant that depends on refractive index of the material, Eg is the optical band gap, hν is the photon energy. Figures (5) shows the value of (Eg) obtained for the direct energy transition from plotting between the linear part of (αhν)² versus (hν). Likewise from the Figure (5), one can extract the band gap as 2.3 and 2.7 eV for the PtNPs2,and PtNPs3 nanoparticles the band gap as 4.4 and 4 eV for the CoNPs0 and CoNPs1.
Table 3
The radius of CoNPs and PtNPs nanoparticles
Nanoparticles
|
Absorbance peak point
|
Particle r (nm)
|
CoNPs0
|
355
|
1.342
|
CoNPs1
|
350
|
2.406
|
PtNPs2
|
471
|
1.050
|
PtNPs3
|
466
|
653.9
|
In addition, the average particle size was calculated using the absorption spectra of NPs. First of all, inflection points in the absorption spectra were determined. In the particle size calculations, it was determined using the effective mass model, which describes the particle size (r, radius) of the nanoparticles as a function of the peak absorption wavelength (λp) [33] .
$$\text{r} \left(\text{n}\text{m}\right)=\frac{{\left[\frac{\text{1020,72}}{{}_{\text{p}}}\right]}^{1/2}-\left(\text{0,3049}\right)}{\frac{\text{2483,2}}{{}_{\text{p}}}-\text{6,3829}}$$
2
During the derivation of Eq. (2), me = 0.26 mo, mh = 0.59mo, mo is the free electron mass, ε = 8.5, and bulk Eg = 3.3 eV [34]. Particle sizes of CoNPs and PtNPs are given in Table 3 The lowest particle size was PtNPs3, while the highest particle size was formed in CoNPs1 material. The size values of CoNPs0 and PtNPs2 particles are close to each other. It was found that the particle size of both CoNPs and PtNPs materials decreased in the DMEM liquid. It was determined that water did not have a significant effect on the sizes of CoNPs and PtNPs nanoparticles.
Optical transitions between the valence and conduction band in a material, defect states, conduction mechanisms and defects caused by disproportionate charge depend on the material's bandwidth. Detection of these changes and defects in the structure is made by detecting the Urbach tails formed in the band structure. The energy associated with these imperfect Urbach tails in the band structure is defined as the Urbach energy. Therefore, it is an important parameter for the detection of changes in the band structure of the materials. The Urbach energy were calculated by taking inverse of the slope of equetion [35].
$$\alpha ={\alpha }_{0}{exp}^{h-E/{E}_{u}}$$
3
where E and α0 are a constant and Eu is the Urbach energy interpreted as the width of the tails of localized states, in the band gap. Figure 6 shows lnα-hν graphs.
Figure 6
Another important parameter showing the change in the band structure is the stepness parameter. This parameter is a perpendicularity parameter that indicates the band broadening in the material. Futhermore, the stepness parameter determines the electron-phonon interaction. These two important parameters can be calculated with the following equations [34, 35].
$$=\frac{{k}_{B}T}{{E}_{u}}$$
4
$${ E}_{e-p}=\frac{2}{3}$$
5
where σ is steepness parameter, kB is Boltzmann constant, T is absolute temperature and Ee−p is electron-phonon interaction. Also, we calculated the refractive index of CoNPs and PtNPs using Ravindra relation [36] .This relation related to tne band gap of material. This equation is given below:
$$n=\text{4,084}-\text{0,62}{E}_{g }$$
6
where Eg is optical band gap energy calculated from Tauc plot and n is refractive index.
In additon to, Fig. 7 and Fig. 8 shows varitions of optical band gap-Urbach energy and stepness parameter-electron phonon interaction, respectively. The porosity values of CoNPs and PtNPs were calculated using Eq. (6), a quantitative analysis on porosity based on refractive index [37].
$$Porosity \left(\%\right)=\left[1-\frac{{n}^{2}-1}{{n}_{d}^{2}-1}\right]\times 100$$
7
where, n is the refractive index of the CoNPs and PtNPs and nd is the refractive index values of the pore-free CoNPs and PtNPs known in the literature. These calculated refractive index and prosity values has also been given in Table 4. In this study, while the refractive index values of PtNPs were consistent with the literature in both DDDW and DMEM fluids, the refractive index values of CoNPs were low in both water and DMEM fluids. It was determined that PtNPs produced in water had the lowest porosity value and CoNPs had the highest value. Also, the porosity values are lower when produced in DDDW while it is lower in DMEM fluid for CoNPs.
Table 4
The some optical parametres of CoNPs and PtNPs obtained under different ablation liquids
Nanoparticles | Eg (eV) | Eu (eV) | Stepness Parameter (σ) | Refractive index (n) | Porosity (%) | Ee-p |
---|
CoNPs0 | 4.0 | 4.70 | 8.02⋅1022 | 1.60 | 62.9 | 5.34⋅10− 22 |
CoNPs1 | 4.4 | 1.76 | 2.14⋅1021 | 1.32 | 55.0 | 1.42⋅10− 22 |
PtNPs2 | 2.7 | 0.20 | 1.88⋅1020 | 2.41 | 32.6 | 3.54⋅10− 21 |
PtNPs3 | 2.3 | 0.44 | 8.56⋅1021 | 2.65 | 37.4 | 7.78⋅10–23 |
Figure 7
Figure 8
3.3. FTIR Analysis
The PtNPs and CoNPs nanoparticles were analyzed using FTIR to determine the biomolecules involved in nanoparticle stabilization in solution. Figure 9 shows transmittance spectra of PtNPs and CoNPs nanoparticles obtained under different ablation liquids. In Fig. 9, PtNPs-S2 generated by laser ablation with DDDW and DMEM, the spectrum PtNP-S3 was recreded in range (500–5000 cmˉ¹) this shows the peaks at [3319.46 cmˉ¹, 1637.14cmˉ¹ and 598.45cmˉ¹] The peak at 1637.14 cmˉ¹ belongs to the C-H bending aromatic compound, whereas the peak at 3319.46 cm ˉ¹ relates to the O-H stretching bond. The C-I vibration was linked to the band at about 598.45cmˉ¹. The spectrum PtNPs2 was recrded in range [3324.98 cmˉ¹,1636.54 cmˉ¹ and 577.60 cmˉ1] correspond to an whereas the peak at 3324.98 cmˉ¹ medium, N-H stretching bond and 636.54 cmˉ¹ belongs to the C = C stretching band. and 577.60 cmˉ¹ C = C strong band.
The IR spectra of the manufactured CoNPs revealed that laser ablation with double-distilled water and DMEM produced a sequence of absorption peaks ranging from 500 to 5000 cm1 (Fig. 4 red and black) CoNPs-S0 this shows the peaks at [3330.76, 2973.38, 1379.74, 1087.21, 1045.07 ,879.67, 634.84]cmˉ¹ and CoNPs-S1 this shows the peaks at [3319.23 ,2973.37, 1380.10, 1087.12, 1045.09, 879.74, 635.09]cmˉ¹. The powerful and broad peak located at 3330.76 cmˉ¹,3319.23 cmˉ¹ assigned to N-H stretching bond. and the peak at 2973.38 cmˉ¹, 2973.37 cm ˉ¹ corresponds to the C-H stretching bending mode bond, and broad peak lacated at 1380.10 cmˉ¹, 1379.74 cmˉ¹ assigned to S = O stretching bond, the peak at 1087.2,11087.12 cm ˉ¹ and 1087.12, 1045.09 cmˉ¹ corresponds to the C-O stretching bond, the peak at 879.67 and 879.74 cmˉ¹ corresponds to the C = C bending mode bond, and the peak at [634.84, 635.09]cmˉ¹ assigned to C-I stretching halo compound.
Figure 9
3.4. Antibacterial activity of PtNPs and CoNPs
Figure 10 (a) and (b) show antibacterial effect of PtNPs and CoNPs nanoparticles obtained under different ablation liquids (double-distilied water and DMEM) on two different types of bacteria. Figure 10 (c) and (d) the zone of inhibition measurements against E. coli and B. subtilis. These CoNPs showed no toxicity against E. coli and B.subtilis but it showed significant toxicity toward PtNPs-S2 represent generated by laser ablation with double-distilled water and PtNPs-S3 generated by laser ablation with DMEM toxicity against E. coli and B.subtilis show more toxicity. Zone of inhibition measurements against E. coli and B. subtilis are shown graphically as shown Fig. 10 (c) and (d).
Figure 10
High purity platinum nanoparticles (PtNPs) with two particle sizes (platinum nanoparticles generated in double-distilled water and DMEM). The particle size was seen to range from 5 to 40 nm, with an average size of 12 nm, whereas the particles generated in DMEM medium ranged from 5 to 50 nm, with an average particle size of 20 nm.) The laser ablation approach was used to effectively synthesize it. PtNPs' antimicrobial action has long been of particular interest. Using the laser ablation process, it was effectively synthesized. The Pt nanoparticles were spherical in form, and their diameters shrank as the number of pulses increased. These qualities are controllable and are determined by laser parameters such as pulse rate, pulse energy, irradiation period, target material type, and the nature of the liquid in which the material is submerged [16, 7, 17]. PtNPs have been studied for their antibacterial properties. Akther and his colleagues show that PtNPs reduce biofilm development. They discovered that attaching these particles to bacterial surfaces can cause cell wall rupture or membrane lysis. These effects are connected to the production of intracellular ROS, which results in the production of cytokines associated with ROS [26–28]. This study evaluated the antibacterial resistance of Co NPs against two widespread pathogens, including E. coli and B. subtilis. The in vitro examination results showed that the Co NPs had weak antibacterial activity, suggesting that they might not be able to eradicate germs that are resistant to many drugs or be used to cure disease [14]. The theory put out by the authors was that once the nanoparticles accumulated past a certain point, they would eventually lose their capacity to enter the bacteria cell. According to a report, the surface-to-volume ratio rises as nanoparticle size decreases, suggesting that the nanoparticles' size may have a significant impact on the antibacterial activity [7, 30]. Cobalt nanoparticles (CoNPs) were created by laser ablation and were proven to be so by TEM and FTIR studies (s0 represent generated with double-distilled water and s1 generated by DMEM with a size ranging from (20nm to 70 nm). Nanorods with a rounded form and smooth surface were visible in the nanoparticles. This study evaluated the antibacterial resistance of CoNPs against Escherichia coli and B. subtilis, two common microorganisms. The outcomes of the in vitro test showed that the CoNPs had marginal antibacterial activity.Further studies are required to explore the antibacterial effect beyond this in the size of the nanoparticles.