A large decrease in permeability is often observed during the filtration of nano-sized colloids, while fouling is widely regarded as the main explanation for this phenomenon. The osmotic pressure or concentration polarization (CP) of colloids can also contribute to the flux decline. However, the contribution of CP to flux loss cannot be determined by the traditional CP model. In this study, the effect of fouling and CP/osmotic pressure on flux was distinguished. The CP values of polyethylene glycol (PEG) and silica-colloids were determined by the osmotic pressures near the membrane surface and in the feed. The CP induced by colloids accounted for 43–95% of the flux loss in our experiments. Silica exhibited higher CP values (127–460), compared to 7–71 for PEG. This was attributed to the slower back diffusion caused by the larger colloids, as evidenced by the diffusion coefficients of 4.30 × 10⁻¹¹ m²/s for silica (10 nm) and 1.45 × 10⁻¹⁰ m²/s for PEG (2.9 nm). Although the CP was mitigated by increasing the cross-flow velocity, CP values of 31 and 250 were observed for PEG and silica at high Reynolds number of 7317, respectively. The experimentally obtained CP values were also compared with those calculated by the film diffusion model.

This work focuses on the photocatalytic removal of recalcitrant organic pollutants in water treatment. Based on facile precipitation reaction, we fabricated a photocatalyst (PbCrO₄) in single crystals that present evident response to visible light and employed the catalyst in the photocatalytic decomposition of microcystin-LR (MC-LR). In the degradation test using the nanorods with prepared PbCrO₄ photocatalyst, a 100% removal efficiency (27 min reaction) and a kinetics constant of 0.1356 min⁻¹ were achieved. Such a high performance of PbCrO₄ in photocatalytic conversion of MC-LR was ascribed to its high carrier separation efficiency, positive valence band (VB) position, and good delocalization of VB and conduction band (CB). The test of electron spin-resonance resonance (ESR) demonstrated that excessive free [rad]OH radicals were produced during the PbCrO₄ photocatalysis of MC-LR. The density functional theory (DFT) and LC/MS/MS technology were employed to ascertain the intermediates during the MC-LR photocatalytic degradation. The major intermediates were resulted from the attack of hydroxyl radicals to the ADDA side chains of MC-LR structure. This study provides a proof-of-concept strategy to develop effective photocatalysts to efficiently produce [rad]OH radicals for the visible-light induced photocatalytic degradation of MC-LR in water.