FTIR spectrum was used to characterization the functional groups of synthesized nanocomposite materials. The results of FTIR for the synthesized samples are given in Fig.2. According to Fig.2.a, the peaks appearing for chitosan nanoparticles at positions 3434 cm-1, 1604 cm-1 and 1074 cm-1 correspond to the tensile vibrations of OH, C = C and C-O alkoxy, respectively. For SiO2 nanoparticles, the peaks appearing in positions 3432 cm-1, 1381 cm-1 and 1074 cm-1 are related to the tensile vibrations of OH, C = C and C-O alkoxy and the peak 572 cm-1 belongs to the SiO2 group (Fig.2.b). Also, the peaks observed in 3532 cm-1, 2898 cm-1 and 1658 cm-1 are related to OH, C = H and C = C tensile strength in agar, respectively (Fig.2.c). Peaks observed for Agar/Chitosan samples at positions 3740 cm-1 (correspond to the group N-H), 3444 cm-1 (correspond to the group O-H), 1617 cm-1 (correspond to the group C=O), 1058-1368 cm-1 (correspond to the group C-O) and 572 it is related to the presence of Si=O group on the nanocomposite (Fig.2.d). Observed peaks of Chitosan/SiO2 nanocomposites in positions 3737 (correspond to the group N-H), 3413 cm-1 (correspond to the group O-H), 16413740 cm-1 (C=C correspond to the group), 1068 cm-1 (C-O correspond to the group) and 687 cm-1 and 646 cm-1 correspond to the belong to the C-C group (Fig.2.e). For Agar/Chitosan/SiO2 nanocomposites, the peaks observed in 3435, 1640 cm-1 and 537 cm-1 belong to the tensile group OH, C=C and Si=O, respectively.
The crystal structures of Agar/Chitosan, Chitosan/SiO2 and Agar/Chitosan/SiO2 nanocomposites were investigated by X-ray diffraction (XRD). The results showed that they were consistent with previous reports (Fig.3). Sharp peaks at 2Ɵ for Chitosan/SiO2 nanocomposites at 26.41˚ and 11.99˚ and for SiO2 nanoparticles at 42.29˚, representing amorphous carbon in the structure (Fig .3.c). As shown in Fig. 3.d, the XRD spectrum for Agar/Chitosan nanocomposites is a peak sharpness at 2Ɵ at 12˚ and for agar at 28˚ and 42˚ representing amorphous carbon. According to Fig .3. e for Agar/Chitosan/SiO2 nanocomposites Sharp peaks observed at 2Ɵ at 8.92˚ for chitosan and peaks at 17˚, 19˚ and 20.74˚ for SiO2 as well as peaks at 26.47˚ And 42.52˚ indicates amorphous carbon in the structure[47–49].
3.1.3. TEM and FE-SEM
FE-SEM image was taken from synthesized Agar/Chitosan, Chitosan/SiO2 and Chitosan/Agar/SiO2 nanocomposites to investigate morphology and particle size (Fig.4). According to the FE-SEM image of Fig.4.a for Agar/Chitosan nanocomposites, the particle size varies from 22.33 - 35.73 nm. According to the fig.4.b The morphology of SiO2 nanoparticles and its presence in the final product is clearly confirmed and for Chitosan/SiO2 nanocomposites the size of nanoparticles is between 24.56 - 42.43 nm. The image of Chitosan/Agar/SiO2 nanoparticle nanocomposite is shown in Fig.4.c which shows the morphology of SiO2 nanoparticles and its presence in the final product. According to the image TEM fig.5 the morphology of SiO2 nanocomposites is hexagonal and the particle size varies from 30 to 300 nm.
EDX analysis was performed to evaluate elemental analysis of synthesized nanocomposite materials (Fig.6). According to Fig.6.a for Agar/Chitosan nanocomposites, there is about 51.6% by weight of carbon atoms, 28.9% by weight of oxygen and 19.4% by weight of nitrogen in the synthesized nanocomposite structure. According to the results of EDX analysis, about 52% by weight of carbon atom, 24.2% by weight of oxygen, 16.5% by weight of nitrogen and 7.2% of silicon oxide are present in the Chitosan/SiO2 nanocomposite, which clearly confirms the presence of silicon oxide (Fig.6.b). For Agar/Chitosan/SiO2 oxide nanocomposites, there is about 46.3% by weight of carbon atom, 35.3% by weight of oxygen, 12.7% by weight of nitrogen and 5.9% by weight of silicon oxide in the sample structure (Fig.6.c).
3.1.5. DLS (Dynamic light scattering)
The light scattering spectrum of Agar/Chitosan/SiO2 nanocomposites is shown in Fig.7. As it is known, the synthesized sample was in the size of 100 nm and less and its maximum amount was in the range of 100 nm based on its number.
3.2. Pollutant removal
3.2.1. Initial concentration pollutant
Effect of initial concentration on naproxen and amoxicillin pharmaceutical with synthesized adsorbents in different concentrations (10, 30, 20 and 40 mg/l) in 25 ml of pharmaceutical solution with optimal adsorbent amount (0.05 g) and with optimal pH adjustment (8) was investigated at specified intervals (40 min) on a magnetic stirrer at room temperature (25 °C). According to Fig.8. (a, b), the maximum amount of adsorption for naproxen with Agar/Chitosan and Agar/Chitosan/SiO2 nanocomposite adsorbents occurred at a concentration of 10 mg/l, which is equal to 99%, which with increasing initial concentration to 40 mg/l, the removal efficiency reached its maximum value and its value remains constant and more active adsorption sites are used and filled, so that after a certain concentration the removal efficiency does not change and remains constant. The maximum adsorption for amoxicillin with Agar/Chitosan and Agar/Chitosan/SiO2 nanocomposite adsorbents occurred at initial concentrations of 20 mg/l, with removal efficiencies of 97.85% and 87.9%, respectively, and with increasing concentration to 40 mg/l more than The active adsorption sites are used and filled so that the removal efficiency is independent of the concentration and its value remains constant (Fig.8. (c, d))[50–54].
3.2.2. Effect pH
The pH of the solution is one of the most important factors in the adsorption process that can change the surface charge of adsorbents as well as the separation of functional groups in the active sites of adsorbent adsorption. Therefore, it is very important and necessary to study the effect of pH on the removal process. Effect of solution pH on naproxen and amoxicillin with Agar/Chitosan and Agar/Chitosan/SiO2 at different pHs in 25 ml of pharmaceutical solution with optimal concentration (20 mg/l), optimal adsorbent (0.05 g) and was tested for 40 min on a stirrer at room temperature (25 °C). The results of this study are shown in Fig.9. As shown in Fig.9. (a, b), the removal efficiency of naproxen with Agar/Chitosan and Agar/Chitosan/SiO2 adsorbents did not increase significantly with increasing the pH of the solution from 6 to 10, and the removal efficiency at pH=6 was at its max 99%. It can be said that slight competition between pharmaceutical ions increases the pH due to decreasing the concentration of H+ ions to bind to the adsorbent surface causing a slight change, so pH=6 was considered effective. The removal efficiency of amoxicillin with Agar/Chitosan and Agar/Chitosan/SiO2 adsorbents reaches its max value of 68% and 84% by increasing the pH of the solution from 4.6 to 8.6, respectively, at pH 7.6, 8.6. From Fig.9. (c, d) * it can be seen that by increasing the pH of the solution, the removal efficiency increases and increasing the pH of the solution increases the number of hydroxyl groups, which increases the number of active sites with a negative charge between the pharmaceutical and the adsorbent surface[55,56].
3.2.3. Adsorption contact time
Effect of contact time on absorption of naproxen and amoxicillin with synthesized Agar/chitosan and Agar/chitosan/SiO2 adsorbents in the time range of 5-240 min and by keeping other parameters constant (initial concentration 20 mg/l, the amount of adsorbent was 0.05 g and pH = 8) at room temperature. The results of this study are shown in Fig.10. As shown in Fig.10 (a-d), the uptake of these pharmaceutical with Agar/chitosan and Agar/chitosan/SiO2 adsorbents did not change much over time and reached equilibrium in the early times. Rapid pharmaceutical uptake in the early stages of the uptake process can be attributed to multiple voids and active sites of the adsorbent surface[57,58]. The results showed that the optimal values of contact time for removal of naproxen and amoxicillin with Agar/chitosan and Agar/chitosan/SiO2 adsorbents were 99%, 90%, 80% and 90% in the first 10 min, respectively.
3.2.4. Impact temperature
The effect of temperature on the adsorption of naproxen and amoxicillin with nanocomposite adsorbents of Agar/chitosan and Agar/chitosan/SiO2 at specified intervals (5-30 min) and by keeping other parameters constant (initial concentration 20 mg/l, the amount of adsorbent (0.05 g and pH = 8) was evaluated at different temperatures (10, 15, 20, 25 and 30 ˚C). The results of this study are presented in Fig.11. According to Fig.11. (a, b), with increasing temperature from 10 to 30˚C, the removal efficiency for naproxen for both adsorbents is 99% and is temperature independent. Also, for amoxicillin with increasing temperature from 10 to 30˚C, the removal efficiency for Agar/chitosan adsorbent at 20 °C is 67.35% and for Agar/chitosan/SiO2 adsorbent at 30 ° C is 87.75%. Because the velocity of pharmaceutical molecules is controlled by temperature, the rate of removal does not change with temperature. In other words, with increasing temperature due to greater resistance of viscous forces, reduces the molecules of the pharmaceutical in the outer boundary layer and the inner pores of the adsorbent particles. On the other hand, the small size of the particle pores causes more resistance to particle emission[59,60].