4.1 X-ray diffraction (XRD): Structural studies
The crystalline structural phase and purity of the synthesized ZnS @ ZnO nanocomposite were investigated by XRD analysis. The XRD peaks of the synthesized materials are shown in Fig. 1. Some of the peaks in the XRD pattern are very sharp and intense, indicating that the samples are good crystalline. The XRD pattern of ZnO showed diffraction peaks at 2θ values 23.80ᵒ, 34.51ᵒ, 36.21ᵒ, 47.52ᵒ, 56.61ᵒ, 62.90ᵒ, 67.91ᵒ, and 69.92ᵒ, with the corresponding Miller indices (hkl) of (100), (002), (101), (102), (110), (103), (112) and (201) respectively indicating the formation of hexagonal structure and single phase formation of nano ZnO, which is in agreement with the Joint Committee on Powder Diffraction Standards (JCPDS) card no. 36–1451, in addition to green synthesized ZnS peaks position at 2θ values at 28.64ᵒ, 47.68ᵒ, 42.13ᵒ, 56.70ᵒ which corresponds to (hkl) values (111), (220), (101), (311) corresponding to the cubic structure with a = 5.36 Å is in agreement with the JCPDS card no. 00-001-07292 reflection planes, respectively [36–42] and both set of peaks corresponds to the formation of ZnO-ZnS nanocomposite. The observed peaks are in good agreement with green synthesized ZnO-ZnS nanocomposite (JCPDS Card no. 89-1397 & 05-0566), which confirms that ZnO crystallizes in the hexagonal wurtzite form with a = 3.2 Å, c = 5.2 Å and ZnS in cubic structure with a = 5.368 Å. Some additional peaks are observed in ZnS, which may be due to the oxidation of ZnS at higher temperatures. The average crystalline size of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite was found to be 30 nm, 24 nm, and 71.19 nm, respectively.
The crystallite size of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite was calculated using the Debye-Scherrer formula D = kλ/βcosθ. In this equation, D is the crystallite size, λ is the wavelength of the X-ray source, which is 1.5418 Å and θ is the Bragg's diffraction angle in degree, k is constant equal to 0.9 and β is the full width at half maximum (FWHM) value in radians. The crystallite sizes were calculated from all three broad peaks, and the final crystallite size was obtained by averaging them. The average crystalline size for green synthesized ZnS @ ZnO nanocomposite and the average crystalline size calculated for the most intense green synthesized nano ZnO peak plane is (101). It has been observed that the crystalline size has decreased; the lattice parameters which correspond to hexagonal ZnO structure increased from 3.2 Å to 8.6 Å; and c = 5.6 Å fell to 4.7 Å.
4.2. Scanning electron microscopy (SEM) and EDAX
The surface morphology analysis of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite revealed the formation of irregular nanospheres, octahedral, cubic, and disc shapes for ZnO nanoparticles, nano pellets shapes were observed in the ZnS; while in ZnO-ZnS nanoclusters formed by the collection of Nano discs and nanoflowers with a good agglomeration of nanoparticles which may be due to the existence of interfacial surface tension phenomena. EDAX spectrum confirmed the purity of green synthesized ZnO, ZnS nanoparticles, and ZnO-ZnS nanocomposite and the presence of Zn, O, and S only. The atomic % is mentioned in Fig. 2.
TEM and HRTEM analysis studied the morphology of ZnS @ ZnO nanocomposites. As shown in Fig. 3a, ZnO nanoflakes with sparsely incorporated puff-like ZnS were found in ZnS @ ZnO nanocomposites. The high-resolution (HR) TEM images (Fig. 3b) show a crystalline structure of heterojunction composites, typically two sets of 0.18 and 0.14 nm, corresponding to the (111) plane of ZnO and the (101) plane of ZnS, respectively. The selected area electron diffraction (SAED) pattern of ZnS @ ZnO nanocomposite is shown in Fig. 3c; the diffraction rings centered around the transition point are observed, demonstrating the polycrystalline nature of the sample. These observations indicate that the heterojunction between ZnO, and ZnS is generated directly, suggesting that the combination mode facilitates the separation and transfer of photogenic charge carriers and enhances the photocatalytic activity. To sum up, these results from TEM confirmed the successful construction of ZnS @ ZnO nanocomposites with the nanosphere and puff-like structures.
4.3. UV-Visible diffused reflection spectroscopy (DRS) analysis.
The optical properties of the green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite were analyzed using UV-Visible diffuse reflectance spectroscopy, as shown in Fig. 4. a. The absorption peak at 378 nm is due to the higher potential energies of O 2p orbitals. The band gap values were calculated from the Kubeka-Munk plot[43]. The Kubeka-Munk function E(hν) is generally applied to convert the diffused reflectance and to calculate the optical reflectance according to the equation Α = E= (1-R)2/2R, where α is the absorption coefficient, R is the reflectance, E is Kubeka-Munk function. The plotted graph is between (Ehν)2 against hν. Extrapolation of the linear equation in the plots to (Ehν)2 = 0 gives the direct band gap values. The band gap energy of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite was found to be 3.4 eV, 3.5 eV, and 3.2 eV, respectively, as shown in Fig. 4. b. Further results indicate the decreased band gap values for the composition suitable for photocatalysis.
4.4. FT-IR Spectral Analysis
FT-IR spectra of the synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite were recorded in the 400 cm− 1 to 1500 cm− 1, as shown in Fig. 5, which further confirms the crystalline hexagonal wurtzite and cubic structures. The characteristic absorption peaks at 425 cm− 1 and 665 cm− 1 are attributed to the ZnS @ ZnO nanocomposite. The 423 cm− 1 and 670 cm− 1 bands are associated with stretching vibrations of nano ZnS. The bands at 423 cm− 1 and 840 cm− 1 are due to stretching vibrations of nano ZnO.
Figure 5. IR spectra of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite.
4.5. photoluminescence Analysis
As per the theory, the rate of separation and migration of photogenerated electron-hole pairs significantly affects the photocatalytic activity of the catalyst. Using the PL technique, the migration and recombination of the charge carriers in ZnS @ ZnO nanocomposites were studied, resulting in higher photodegradation efficiency. The emission spectra of synthesized ZnO, ZnS, and ZnS @ ZnO nanocomposites are shown in Fig. 6 at 410 nm for excitation. ZnO and ZnS exhibit an intense emission peak at 430 and 440 nm, respectively. While ZnO -ZnS exhibits an intense emission peak at 450 nm, consistent with the previous findings [44]. As the emission peaks decreased drastically in ZnS @ ZnO nanocomposites, this suggests that the recombination rate of photogenerated charge carriers is lower in ZnS @ ZnO, resulting in faster charge transfer and separation rates. These results agree well with the enhanced photocatalytic degradation of dyes.
4.6 Photo electrochemical measurement
Photocurrent and electrochemical impedance were measured in a three-electrode setup using the prepared samples as working electrodes, a platinum plate as a counter electrode, and a saturated Ag/AgCl electrode as a reference electrode. An aqueous 0.5 M Na2SO4 solution was used as the electrolyte. The working electrodes were prepared: 0.8 mg samples were ground, 2 mg carbon black, 20 µL Nafion, and 200 µL 2-propanol were added. Sonicate them in an Ultra-Sonicator for 60 minutes. The ink is dropped on a glassy carbon electrode (0.5 cm in diameter) and dried at room temperature. The loaded active material on the glassy carbon electrode is about 2 mg. Before spotting the ink on the glassy carbon electrode, it was polished with 0.05µ alumina powder and cleaned with acetone.
In order to evaluate the effectiveness of charge transfer and separation at the interface, photocurrent response and electrochemical impedance spectroscopy (EIS) were utilized (Fig. 7). As shown in Fig. 7b, ZnS @ ZnO composites is a higher photocurrent response as compared to the ZnS (1.8-fold), ZnO (2.4-fold) revealing the formation of the p-n heterojunction in hetero and binary composites contribute to the generation and transfer of the photogenic charge carriers. In addition, an electrochemical impedance test was conducted, and the results are depicted in Fig. 7b. In general, the magnitude of the arc dictates the rate at which the catalyst can transport electrons. The rate increases as the arc radius decreases [45]. The ESI Nyquist plots (Fig. 7a) demonstrate that the ZnS @ ZnO nanocomposites can improve the separation efficiency and free electrons transfer rate because the ZnS @ ZnO sample has the smallest arc radius compared to the ZnS and ZnO samples. The charge transfer and recombination process can be depicted by the equivalent circuits RS and CPE, which represent the resistance of the solution and the constant phase element, which can be viewed as a double-layered capacitor (Fig. 7a inset). Rct, which means the electron transfer resistance, can be calculated using the arc radius in the EIS Nyquist diagram. The values of these electrical parameters are summarized in Table 1. Compared to pure ZnO, ZnS, the Rct values were reduced from 21.2 ohms to 3.9 ohms, which is responsible for the improved photocatalytic performance of the ZnS @ ZnO nanocomposite.
Table 1
Fitting results for equivalent circuits of prepared samples
sample | Rs(Ώ) | Rct(kΏ) | CPE(µf) |
ZnO | 12.8 | 21.2 | 0.36 |
ZnS | 18.2 | 15.2 | 0.47 |
ZnS @ ZnO | 24.4 | 3.9 | 1.34 |
4.7. Analysis of photocatalytic activity
The photocatalytic performance of the synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite was evaluated by using photodegradation of 50 ppm aqueous solutions of Methylene blue [MB], Rhodamine B[RhB], and Congo red [CR] dye under visible light. Visually, the blue, pink, and red colors of the MB, RhB, and CR solutions also fade with increasing irradiation time. MB, RhB, and CR were initially degraded, and no degradation was observed. The maximum absorption peaks of MB, RhB, and CR appeared at 580 nm, 546 nm, and 497 nm, respectively. Fall of intensities with the irradiation time for ZnO, ZnS nanoparticles, and ZnS @ ZnO composite are shown in Fig. 8. Further, the photocatalytic activity of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite samples were analyzed with an increasing irradiation time of 70, 60, 60 min for MB, RhB and CR dyes. The maximum absorption peaks gradually decreased with an increase in time. The degradation efficiency(C/C0) values were found to be 1 to 0.34 - nano ZnO, 0.25 - nano ZnS, and 0.027 - ( ZnS @ ZnO) nanocomposite for [MB]; 1 to 0.24 - nano ZnO, 0.19 - nano ZnS, 0.015 - ( ZnS @ ZnO) nanocomposite for [RhB] and 1 to 0.186 - nano ZnO, 0.23-nano ZnS, 0.098 - ( ZnS @ ZnO) nanocomposite for [CR], and for blank with the respective catalyst under visible light for 70, 60, 60 min respectively and these results are presented in Fig. 8 (a, b, c).
The photocatalytic efficiencies of green synthesized ZnO, ZnS nanoparticles, and ZnS@ZnO nanocomposite were calculated by measuring the degradation of the MB, RhB, and CR dyes using the following equation.
$$\left(\eta \right) Dye removal efficiency \left(\%\right)=\frac{\text{C}\text{i} - \text{C}\text{f}}{Ci}\times 100 \left(1\right)$$
Where η is the photocatalytic efficiency, Ci is the initial absorbance intensity of MB, RhB, and CR, and Cf is the absorbance intensity of MB, RhB, and CR at the time t. The degradation percentage was calculated at 65.2% (ZnO), 75% (ZnS), and 92% (ZnS @ ZnO) for [MB]; 70.3% (ZnO), 80.4% (ZnS), and 98.4% (ZnS @ ZnO) for [RhB] and 70.36% (ZnO), 81.36% (ZnS),90.9% (ZnS @ ZnO) for [CR] as shown in Fig. 10 (a2, b2, c2). Kinetic values are mentioned in Table 2. The photodegradation of MB, RhB, and CR with ZnS @ ZnO nanocomposite was found to be higher in photocatalytic efficiency when compared with ZnO and ZnS nanoparticles.
Table 2
kinetic data of photocatalytic degradation of MB, CR, and RhB dyes by ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite.
Dye | MB | RhB | CR |
Catalyst | ZnO | ZnS | ZnS@ZnO | ZnO | ZnS | ZnS@ZnO | ZnO | ZnS | ZnS@ZnO |
k (min − 1) | 0.023 | 0.025 | 0.037 | 0.016 | 0.019 | 0.031 | 0.214 | 0.026 | 0.065 |
R2 | 0.98 | 0.95 | 0.97 | 0.98 | 0.98 | 0.86 | 0.98 | 0.96 | 0.94 |
% Of dye degradation | 65.2 | 75 | 92 | 70.3 | 80.4 | 98.4 | 70.36 | 81.36 | 90.9 |
Time(min) | 70 | 60 | 60 |
4.8. Kinetics study
Photocatalysis of dye follows the pseudo-1st -order reaction. The kinetic values are estimated with the help of the following equation [14,15].
$$\text{ln}\left(\frac{\text{C}0}{\text{C}\text{t}}\right)=\text{k}\text{t} \left(2\right)$$
Where C0 is the concentration of MB, RhB, and CR before irradiation, Ct is the concentration of the MB, RhB, and CR dyes after irradiation at t (min), and k is the rate constant. The rate constant for MB, RhB, and CR dyes in the presence of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite was calculated by plotting the ln(C/C0) against the time as shown in Fig. 9 (a1, b1, c1). The rate constant for each sample was found to be 0.023, 0.020, 0.037 for [MB]; 0.016, 0.019, 0.031for [RhB] and 0.0212, 0.026, 0.065 for [CR] for ZnO, ZnS nanoparticles and ZnS @ ZnO respectively, these results are summarised in Table 3. Green synthesized ZnS @ ZnO nanocomposite is a better photocatalyst than green synthesized ZnO, ZnS nanoparticles and for MB, RhB, and CR dyes (50ppm) in terms of degradation efficiency and rate constant due to the smaller crystalline size, lower charge transfer, lower bandgap, absorption of light in the visible region and lower recombination of charge carriers.
Figure 9. (a, b & c) plot of [Ct/C0] vs time due to RhB, MB&CR dyes degradation of green synthesized ZnO, ZnS nanoparticles and ZnS @ ZnO nanocomposite; (a1, b1, c1), the corresponding rate constant of RhB, MB & CR dyes of green synthesized ZnO, ZnS, ZnS @ ZnO nanocomposite.
4.10. Stability of the green synthesized ZnO-ZnS nanocomposite
Important parameters that decide the promising photocatalyst for commercial and industrial applications are stability and reusability. The reusability of ZnS @ ZnO nanocomposite as a catalyst was analyzed by using MB, RhB, and CR dyes under visible light. The used catalyst was collected by centrifuging and washed multiple times with ethanol and DI water. Further, the cleaned catalyst was dried at 75℃ for five h. The photocatalytic activity is studied for four cycles, and only slight changes occurred during every process of reuse after exposure to visible light for 70, 60, and 60 min for MB, RhB, and CR dyes, respectively. Degradation efficiency and kinetic parameters are shown in Fig. 10(a1, b1, c1). After the photocatalytic test, the catalyst, ZnS @ ZnO nanocomposite, was collected and examined using XRD, as shown in Fig. 11.
The XRD pattern showed the same structure with small decreased peak intensities. The reusability test proves that green synthesized ZnS @ ZnO nanocomposite is a promising photocatalyst. The photocatalytic efficiency of MB, RhB, and CR dyes with four cycles is tabulated in Table 3.
Table 3
Summary of kinetic values of reused ZnS @ ZnO nanocomposite for photocatalytic degradation of MB, RhB, and CR dyes.
Dye | MB | RhB | CR |
Cycles | 1 | 2 | 3 | 4 | 1 | 2 | 3 | | 1 | 2 | 3 | |
k (min-1) | 0.051 | 0.034 | 0.027 | 0.019 | 0.065 | 0.059 | 0.048 | 0.036 | 0.037 | 0.054 | 0.048 | 0.036 |
R2 | 0.86 | 0.93 | 0.91 | 0.93 | 0.96 | 0.92 | 0.98 | 0.98 | 0.97 | 0.98 | 0.99 | 0.94 |
Dye degradation (%) | 97.82 | 90.21 | 86.95 | 77.17 | 98.44 | 97.44 | 94.94 | 89.94 | 90.9 | 87.83 | 83.83 | 80.45 |
Figure 10.: (a, b, c): Reusability study of ZnS @ ZnO nanocomposite towards the degradation of RhB, CR and MB dyes; (a1, b1, c1): corresponding rate constant study of ZnS @ ZnO nanocomposite for RhB, CR and MB; (a2, b2, c2): degradation of RhB, CR and MB by ZnO, ZnS nanoparticles and ZnS @ ZnO nanocomposite.
4.11. TOC analysis
To assess the degree of CR, MB, RhB mineralization, TOC analysis was performed for the samples catalyzed by ZnO, ZnS, and ZnS @ ZnO nanocomposites under optimized conditions [48]. The degree of RhB mineralization is defined based on TOC measurements from Eq. (3).
$$\% Mineralization=\frac{\left[\left(TOC\right)f-\left(TOC\right)i\right] }{\left(TOC\right)f} \left(3\right)$$
Where TOCi and TOCf are initial and residual total organic carbon concentrations, respectively. Figure 12 (a & b) compares the mineralization of CR, MB, and RhB in the photocatalytic process as a function of reaction time. The difference between the photodegradation and mineralization efficiencies is ascribed to the decomposition of RhB dye molecules into intermediates, which might have partially remained in the solution. It can be wholly mineralized by continuing the reaction for a little longer. The PFO reaction rate (R2) constant of CR, MB, and RhB mineralization is tabulated in Table 4.
Table 4
Comparison of the % mineralization from TOC analysis with theoretical data and corresponding kinetic results.
| CR | MB | RhB |
| ZnO | ZnS | ZnS@ZnO | ZnO | ZnS | ZnS@ZnO | ZnO | ZnS | ZnS@ZnO |
% Dye degradation | 65.2 | 75 | 92 | 70.3 | 80.4 | 98.4 | 70.36 | 81.36 | 90.9 |
% Mineralization | 52.2 | 64.4 | 78 | 56.4 | 68.3 | 81.2 | 51.4 | 63.4 | 79.4 |
R2 | 0.98 | 0.95 | 0.96 | 0.99 | 0.99 | 0.99 | 0.92 | 0.96 | 0.95 |
Rate constant | 0.009 | 0.0095 | 0.011 | 0.008 | 0.0087 | 0.010 | 0.00917 | 0.00967 | 0.0093 |
4.12. Photocatalysis mechanism
The mechanism of MB, RhB, and CR degradation by the green synthesized ZnS @ ZnO nanocomposite is depicted in Fig. 13. The UV photons excite the electrons from the valence band, while the visible light photons excite the electrons from the defect energy levels of nano ZnO to the conduction band. The photogenerated electrons subsequently react with O2 to produce superoxide radical anions (O2−) and hydrogen peroxide (H2O2), and the holes from the nano ZnO valence bands react with water (H2O) to produce hydroxyl radicals (OH*). Subsequently, hydrogen peroxide reacts with the electrons to form hydroxyl radicals, which in turn react with the MB, RhB, and CR, respectively, to produce harmless compounds such as CO2. NH3 and H2O. Both UV and visible light photons excite the electrons of nano ZnO and nano ZnS to the conduction band. Using the KM Plot, the band gap values for ZnO and ZnS nanoparticles are 3.4 and 3.6 eV, respectively. Due to the different work functions of the nano ZnO (3.4 eV) and ZnS (3.5 eV), after reaching the same Fermi level, the conduction band (CB) of ZnO-ZnS (3.02 eV) nanocomposite was situated above the CB of nano ZnO and ZnS. The valence band (VB) of ZnO -ZnS was positioned below the VB of nano ZnO and ZnS. The photoexcited electrons of nano ZnO were then transferred to nano ZnS, while the holes from the nano ZnO valence band were transferred to the valence band of nano ZnS. The major reason nano ZnO becomes less effective may be the hindered transfer of holes from reacting with water to produce hydroxyl radicals (OH*).
In addition, another possible tentative mechanism has been proposed. Because the Fermi level of ZnO is distinctly higher than that of ZnS, an internal electric field oriented from ZnO to ZnS between their interfaces and band bending is produced. Once the two materials are both excited by proper incident light, the excited electrons on the CB of ZnS will spontaneously slide into the VB of ZnO forced by the electric field and band bending and recombine with the holes in ZnO. Thus, the CB electron on ZnO with a more vital reduction ability acts as the main active species for proton generation, and the holes on the VB of ZnS act as the oxidation species. The transfer route of the charge carriers follows a slide path complying with the proposed S-scheme heterojunction, which can effectively suppress charge recombination while retaining the strong redox abilities of the heterojunction [47–50]. This mechanism is further supported by PL spectrometry of OH (Figs. 14). The green synthesized ZnS @ ZnO nanocomposite shows higher photocatalytic efficacy as compared to the individual green synthesized ZnO and ZnS nanoparticles due to the agglomerated morphology, decreased band gap and size, contuses cross transfer of electrons from O to S atoms in the composite, to support the above-proposed mechanism, we also performed PL spectroscopy to confirm the formation of •OH radicals (Fig. 14). It was examined using coumarin as a probe molecule. Coumarin is a poor fluorescent molecule, the reaction of •OH with coumarin gives rise to 7-hydroxyl coumarin (7HC) in aqueous solutions, which is fluorescence in the visible region. Dissolved oxygen plays a vital role in forming 7HC, hydroxylation of coumarin is not possible via one - e− oxidation, but it requires the intervention of •HO. In this process, 15 mg of ZnS @ ZnO nanocomposite was dispersed in 100 mL of 0.5 mM aqueous coumarin solution. The solution was bubbled for 30 min before irradiation. The reaction was carried out under the visible light lamp. For every time interval, two mL solution was taken out, and PL intensity was measured using a spectrophotometer shown at 450 and 500 nm, which shows the formation of 7HC. From all these supporting proofs, we conclude that ZnS @ ZnO nanocomposite is a promising photocatalyst for dye degradation.
5. Antibacterial properties of ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite
The antibacterial property of green synthesized ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite was studied using Gram-negative bacteria, Pseudomonas aeruginosa, klebsiella and Gram-positive bacteria, Staphylococcus aureus, and Streptococcus pneumonia. ZnS @ ZnO nanocomposite has shown good antibacterial activity against these pathogenic strains. ZnS @ ZnO nanocomposite showed profound activity towards Staphylococcus aureus, Streptococcus pneumonia, and Pseudomonas aeruginosa. But significantly less activity towards Klebsiella as compared to the individual nanoparticles; nanocomposite shows good activity, as shown in Fig. 15.
During the incubation time (24 h), the free radicals produced by the nanoparticles can interact with the bacterial cells causing death or inhibition of growth. ZnS @ ZnO nanocomposite exhibited higher activity than ZnO and ZnS nanoparticles. As the concentration of nanoparticles increases, the antibacterial activity increases due to an increase in the number of free radicals produced. These free radicals will oxidize the cellular components of the microorganism, causing its death. Maximum antibacterial activity was observed for 600 µg/ concentration of ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite for both types of strains; the results are tabulated in Table 5. Antibacterial activity of commercial ZnO and ZnS was found to be less than ZnO, ZnS nanoparticles, and ZnS @ ZnO nanocomposite against both types of bacterial strains under identical conditions.
Table 5
Inhibitory activity of test compounds against test organisms, where A = ZnO, B = ZnS.
Test Organisms | Test Compounds | Conc. per well (µg / well) | Zone of inhibition (mm) | Figure ref |
Streptococcus aureus | | | | Figure 11(a) |
Ciprofloxacin (Standard) | 10 | 24 |
A | 100 | 6 |
B | 100 | 5 |
A + B | 100 | 12 |
Streptococcus pneumoniae | Ciprofloxacin (Standard) | 10 | - | Figure 11(b) |
A | 100 | 21 |
B | 100 | 5 |
A + B | 100 | 6 |
Pseudomonas aeruginosa | Ciprofloxacin (Standard) | 10 | 12 | Figure 11(c) |
A | 100 | 22 |
B | 100 | 12 |
A + B | 100 | 9 |
Klebsiella | Ciprofloxacin (Standard) | 10 | 18 | Figure 11(d) |
A | 100 | - |
B | 100 | - |
A + B | 100 | 8 |