Measuring zeta potential of ceramic TiO2 NF membrane for different salts by filtration potential technique using innovated silver electrodes

Abstract

Nanofiltration (NF) and zeta potential are being increasingly used in water, wastewater, and pharmaceutical applications. In this study, the zeta potential behaviors of eight different 0.01 M salts (NaCl, KCl, NaHCO 3 , MgCl 2 , CaCl 2 , Na 2 CO 3 , Na 2 SO 4, and MgSO 4) for 0.9 nm tubular ceramic titanium dioxide NF membrane were measured for the first time using a filtration potential technique by conducting in-situ two electrodes made from a composite material that consisted of pure silver and 4% gauge 21 gold. The measurements were conducted under pH 3-9 at an applied transmembrane pressure (TMP) of 0.25-1.5 bar. Experimental results showed that the membranes of the salts were negatively charged at neutral pH and had an isoelectric point (IEP) of pH 3.4−3.8. Membrane zeta potential results were compared and justified using the electrophoresis method for the same membrane. The powder dispersions of the pulverized membrane in this measuring technique were a suspension at a certain salt concentration. Experimental results from the electrophoresis method agreed with those of the filtration potential method, whose IEP was at pH 3.3−3.5. The rejection experiments of the reference solutions (0.1 and 0.01 M NaCl) were conducted at a constant applied TMP of 12 bar. Rejections results showed that both NaCl concentrations were a function of pH. The low rejections were 17% and 21% at pH 3.8 for 0.01 and 0.001 M NaCl, respectively, and the high rejections were 34.2% and 38% at pH 9. This work also investigated the effects of the measured membrane zeta potential on the ion rejection of the standard solution of NaCl (0.01 and 0.001 M) using a similar pH range.

Effect of Solution Conditions and Applied Potential on Ion Transport in TiO2 Nanopores

“…The increase of PZC for the MgCl 2 electrolyte relative to the NaCl electrolyte was attributed to the specific adsorption of Mg 2+ on TiO 2 under basic conditions. The observed effects of Mg 2+ and SO 4 2– on zeta potential measurements were consistent with those reported in the literature. ,,− The adsorption of these ions on TiO 2 caused a change in σ, which influenced ion rejection and is discussed in further detail in Section .…”

“…The specific adsorption of Mg 2+ and SO 4 2– on TiO 2 and polymeric membranes has also been reported in the literature. ,,,− The Mg 2+ ion exhibited a strong affinity for TiO 2 , showing quasi-irreversible adsorption . Moreover, Mg 2+ complexed with two adjacent Ti–O – sites and SO 4 2– complexed with two adjacent Ti–OH 2 + sites. , While the model did not directly incorporate these complexation reactions, their effect on σ was indirectly accounted for in the modeling process.…”

“…27 Moreover, Mg 2+ complexed with two adjacent Ti−O − sites and SO 4 2− complexed with two adjacent Ti−OH 2 + sites. 27,60 While the model did not directly incorporate these complexation reactions, their effect on σ was indirectly accounted for in the modeling process.…”