First stage of experiment has been accomplished. The result was not satisfying. I used 50, 15 and 1 kD. In terms of flux and accumulated flux, TiO2-UV displayed lower result compare to just naked membrane. Although for 50 kD and 15 kD initial flux were higher than naked membrane, but after around 30-100 minutes, they showed severe decline for flux. This also applied for 1 kD TiO2-UV membrane. I do not think that permeability plays a big role on this, since the permeability of all membranes were similar, there were not significant difference. This also proves that TiO2 does not affect the structure of the membrane.
I put again the info of my previous post.
5 kD, no TiO2, just naked membrane, pH 7, HA 9 ppm, TMP 10 psi (G)
50 kD, naked membrane, pH 4, HA 9 ppm, TMP 10 psi (A)
50 kD, Coating TiO2+UV, pH 4, HA 9 ppm, TMP 10 psi (B)
50 kD, naked membrane, pH neutral, HA 9 ppm, TMP 10 psi (C)
50 kD, coated+UV, pH neutral, HA 9 ppm, TMP 10 psi (D)
15 kD, naked membrane, pH neutral, HA 9 ppm, TMP 10 psi (E)
15 kD, coated+UV, pH neutral, HA 9 ppm, TMP 10 psi (F)
A:B:C:D:E:F:G = 0.015 : 0.0145 : 0.0129 : 0.01 : 0.0131 : 0.0115 : 0.034
I only put C, D, E anf F into consideration. The permeability of TiO2-UV membrane for 50 kD indeed more than naked membrane, so the rejection is lower, but the problem is the flux of 50 kD was relatively lower, while in fact, higher permeability should have meant that more water can be screened. The reason is still under investigation. The same with 15 kD, TiO2-UV produce lower rejection and lower flux, and lower accumulated permeate as well. This is really interesting. 1 kD membrane also showed the same, TiO2-UV gave lowest flux, while for rejection, was also lower than naked membrane but higher than naked membrane combined with only UV or TiO2 coated on the surface of the membrane.
So, overall, temporary conclusion is bad.. TiO2-UV is worse than naked membrane. Several hypotheses:
1. Perhaps TiO2 coating affect the structure of the membrane, this will need confirmation by device such as SEM. Permeability will not be sufficient to determine it.
2. Perhaps NOM due to photocatalysis process become smaller thus give bad rejection rate, this will need confirmation by conducting TiO2-UV batch test to determine apparent molecular weight (AMW) distribution of NOM, in this case, is humic acid (HA).
3. Bigger HA molecule will attach on the surface of the TiO2 particle coated on the surface of the membrane, resulting sort of double deposition within the surface of the membrane.
I am still doing literature review, in short term I will repeat some experiments which I think need to done once again.