3-1 Fourier transform infrared spectroscopy (FTIR)
CA, anatase, and their blend membranes were tested. The FTIR spectra are illustrated in Fig. 4. The blank CA membrane shows the presence of three important acetyl group vibrations at 3521 (νO-H), 2965 (alkane νC-H), 1771 (νC=O), 1382 & 1450 cm-1 (ν–CH bending), 1251 (esters νC–O) and 1032 cm-1 (anhydroglucose unit νC–O–C) [28]. Peaks of anatase TiO2 are visible at 3485 (vO-H), 3055 and 1697 cm-1(vTi-OH). The biosynthesis of polymorphs of TiO2 nanoparticles is similar to be like the shield protecting B. thuringiensis from the harmful effects of Ultra Violet). The peaks in the blended films are the same but have varying intensities. When compared to blank CA, the OH and C = O intensities rose, demonstrating anatase incorporation. Ti-O-Ti and Ti-O-C bonds are responsible for the blended films peak about 600 cm-1.
3-2 X-ray diffraction (XRD)
Table 2
The crystallinity index of membrane compositions.
Sample | Total area of crystalline peaks | Total area of crystalline and amorphous peaks | Crystallinity index in % |
M0 | 537.54 | 1719.89 | 31% |
M1 | 401.68 | 1677.822 | 24% |
M2 | 381.93 | 1680.12 | 23% |
M3 | 283.89 | 1386.294 | 20% |
M4 | 255.46 | 1662.74 | 15% |
M5 | 145.09 | 1344.929 | 11% |
M6 | 43.25 | 1002.3 | 4% |
The crystallinity was analyzed using X-ray diffraction (Table 2 and Fig. 2). CA displayed an amorphous signal at 2θ = 7.73 and 18.57° correlated to the plane, which showed a characteristic signal for CA (Development of Magnetite/Graphene Oxide Hydrogels from Agricultural Wastes for Water Treatment). The calculated crystallinity showed that the crystallinity of the blended membrane decreased compared to the blank CA, crystallinity disagrees with thermal analysis may be due to the difference in the type of H bond (intra- and inter-molecular) [22].
3-3 Thermogravimetric analysis (TGA)
Figure (6) showed the decomposition curves of M0, M1, M2, M3, M4, and M5 revealed three decomposition steps with a weight loss of 68.9, 55.1, 67.4, 68.2, 67.5, 57.6, and 66.3%, respectively, at 800°C, which indicated a fractional existence of non-volatile contents. The first weight loss was in the range of 30–125, 30–120, 30–130, 30–100, 30–130, 35–80, and 35–80°C with a maximum temperature of 60, 80, 45, 60, 40, 59, and 60°C and an average weight loss of 0.2, 0.3, 0.2, 0.4, 0.3, 0.7, and 0.7%, which is most likely attributed to the loss of moisture content. The second endothermic stage is between 150–280, 120–180, 130–170, 150–250, 120–270, 130–280, and 130–270°C, with a maximum temperature of 213, 148, 220, 215, 220, 209, and 218°C and an average weight loss of 7.5, 0.1, 6.8, 4.6, 6.8, 8.8, and 7.6% respectively. This step is attributed to dehydroxylation reaction in combination with pyrolytic degradation. The third decomposition step was between 310–430, 290–430, 280–430, 280–430, 280–430, 270–430, and 280–430°C with maximum temperature values at 372, 368, 370, 370, 370, 356, and 366°C and an average weight loss of 61.2, 54.7, 60.4, 63.2, 60.4, 48.1, and 58.0%. The degradation of the remaining carbonaceous, which produces low molecular mass volatile compounds, was linked to the third decomposition process. M5 has the greatest second step decomposition, which expressed as greater thermal stability compared with the blank. [29].
3-4 Scanning & EDX electron microscopy
SEM images were prepared to recognize swelling and porosity scattering in the membrane. Cross-section and top surface images were reported in Fig. 7 (A-H). SEM of CA membranes in (Fig. 7A and B) was observed with a top dense skin layer. It was evident from the SEM that the existence of nanosheets, which has an impact on the structure of membrane-forming in the phase inversion process, is primarily responsible for the variable pore size distribution of the created membranes. By adding anatase, the porosity in the membrane decreased, the appearance of this phenomenon may be attributed to the higher chance of agglomeration for anatase. On the whole, for all the prepared membranes revealed in (Fig. 7), the top surfaces (7B, 7D, 7F) are dense structure, meanwhile in the cross sections the top surface was supported in the intermediate by a spongy like structure in (7A, 7C), while followed by a macrovoids/finger like structure in (7E), at end by the last bottom surface layers shown in EDX investigations (Fig. 7G and H). The revealed peak at about 3 keV corresponds to Titanium [30].
3-5 Mechanical properties
The mechanical properties of membranes are shown in Fig. 8. Anatase was added to improve the characteristics of the membrane, and Young's modulus steadily rose as anatase content rose. With the addition of anatase, the load at break initially rose. It peaked when the anatase ratio was between two and three percent, and after adding a lot of anatase, it started to decline. The maximum load measurements of membranes showed a similar fluctuation tendency. The maximal load increased with anatase addition reaching its peak value at 2%, then declined with anatase ratio increase. Moreover, stress levels during the break followed a similar pattern, reaching their peak with 2% anatase. These patterns could be brought on by the anatase addition increasing the viscosities of CA solutions [25].
In conclusion, the composite membranes with 3% anatasehad the best mechanical properties. Maximum load increased from 11.75 N of pure CA membrane to 15.64 MPa of CA loaded with 2% anatase. Stress at the break of the optimal membranes could reach 84.13 MPa, compared with 58.45 MPa of the pure CA membrane.
3-6 Porosity determination & swelling ratio of membrane
The effect of anatase on the CA membranes porosity and swelling are described in Fig. 9. Both porosity and swelling were decreased with increasing anatasecontent in the membrane. The porosity of membranes decreased from 12.12% of anatase-free CA to 1.21% of 0.6% anatase-loaded CA membranes. A similar variation trend was also exhibited with swelling that decreased from 8–1.01% by increasing anatasefrom 0 to 0.6%. These trends may be explained as follows; due to the hydrophobic nature of CA, it contains a lower number of active groups that can form hydrogen bonds with water molecules. By adding anatase, the matrix will be bounded by crosslinking, limiting water penetration inside the matrix.
3-7 Stability of anatase-containing CA membranes
The stability of the anatase-containing CA membrane was studied (Table 3) for seven days to evaluate the release of Ti-NPs from the membrane samples. The sample with dimensions of (L×W) 1×1 cm was soaked in a tube with 10 mL deionized (DI) water and Shacked at room temperature. TiO2 is an inert and safe material and has been used in many applications for decades because of its photocatalyst and non-toxicity property. The results showed that TiO2 is attractive for water treatment. The release rate of Ti-NPs from the CA-loaded anatasemembranes would control the duration of the effectiveness of membranes; consequently, the CA-loaded anatase was clearly more stable for industrial applications in desalination.
Table 3
Release of Ti from CA loaded anatasemembranes from 1 cm2 area membrane
Days | M1 | M2 | M3 | M4 | M5 | M6 |
1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
DI H2O | < 0.000 | < 0.000 | < 0.000 | < 0.000 | < 0.000 | < 0.000 |
3-8 Evaluating the membrane performance
The membrane performance was evaluated in this part by measuring permeate flux (J) and salt rejection (R) of the prepared CA/TiO2 membranes, as displayed in Figs. 10 and 11. It was clear from Fig. 10 that the permeate flux is increased with the increasing operating pressure for all tested membranes following Darcy’s law [31]. It was evident from Fig. 10 that the permeate flux of prepared CA/TiO2 membranes (M1:M6) was decreased with the addition of nanomaterial following this sequence; M0 > M1 > M2 > M3 > M4 > M5 > M6. With the addition of nanomaterial, the permeate flux of the prepared CA/TiO2 membranes is changed significantly, decreasing from 150: 90 kg/ m2 h with M0: M6 at operating condition 10 bar and feed concentration 5 g/l NaCl. This effect could be attributed to the change in prepared membrane morphology with the addition of the nanomaterial. Meanwhile, high TiO2 nanoparticle content shows lower porosity than blank membrane, this result is proved by the porosity and swelling results which have the same result; the TiO2 content is uniformly embedded in the polymer matrix resulting in the decrease of membrane flux. This result could be attributable to the hydrophobic nature of CA; it contains a lower number of active groups that can form hydrogen bonds with water molecules. By adding nanoparticle, the polymer matrix will be bounded by crosslinking, which decrease the permeate flux inside the prepared CA/TiO2 membrane.
It apparent from Fig. 11 that the salt rejection of prepared CA/TiO2 membranes (M1:M6) was improved with the addition of nanomaterial following this sequence; M6 > M5 > M4 > M3 > M2 > M1 > M0. With the addition of nanomaterial, the salt rejection of prepared CA/TiO2 membranes is changed significantly, increasing from 46 to 92% with M0: M6 at operating condition 10 bar and feed concentration 5 g/l NaCl. This result can be ascribed to the modification of prepared membrane morphology by adding the nanomaterial. In the meantime, high TiO2 nanoparticle content shows lower porosity than blank membrane; the TiO2 content is uniformly embedded in the polymer matrix resulting in increased membrane salt rejection [20].
3-9 Antimicrobial studies
The antimicrobial potential of composite film (CA and CA/ anatase) membrane was investigated against different Gram-positive and Gram-negative bacterial strains (Table 4). Overall, blank CA film has no inhibition zone. However, the composite film (CA and CA/ anatase) membrane displayed a broad inhibition zone against Gram-positive and Gram-negative strains. For instance, the composite film displayed an inhibition zone with a diameter of 25 and 20 mm against Escherichia coli and Salmonella Typhimrium (Gram-negative bacterial strains), respectively while, the diameter of the inhibition zone was 25 and 15 mm in the case of Staphylococcus aureus and Enterococcus fecalis (Gram-positive bacterial strains), respectively (Fig. 12) these findings indicated that the developed composite film possesses significance antibacterial potential due to the presence of Ti-NPs that oxidized onto titanium ions and interacts with the thiol group of protein and enzymes found on the cellular surface leading protein deactivation and bacterial death. These results agree with those of APHA [32].
Table 4
Inhibition zone of CA and CA/ anatase film and blank CA against bacterial strains after incubation at 37° C for 24 h.
Bacteria Strains | CA | CA/ anatase |
G-Ve | E.coli | No Zone | 15 |
Salmonella Typhimrium | No Zone | 20 |
Enterobacter aerogenes | No Zone | 15 |
G + Ve | Staphylococcus aureus | No Zone | 25 |
Enterococcus fecalis | No Zone | 15 |