Improved Three-Channel Capillary Composite Nanofiltration Membrane Using UiO-66-NH2 and Interface Polymerization

Literature Overview

The study by Sun Jingying and colleagues from the State Key Laboratory of Chemical Engineering at East China University of Science and Technology, published in Membrane Science and Technology in 2020, addresses the fabrication and performance evaluation of a positively charged three-channel capillary composite nanofiltration membrane. The research employs a novel approach by incorporating UiO-66-NH2 metal-organic framework (MOF) nanoparticles into the aqueous phase of an interfacial polymerization process, using piperazine (PIP) and polyethyleneimine (PEI) as amine sources and trimesoyl chloride (TMC) as the acyl chloride reactant in the organic phase. The work was supported by the Ministry of Education Basic Research Fund and the National Science and Technology Support Program, reflecting its significance in advanced membrane technology development.

Core Technical Approach and Membrane Fabrication

The interfacial polymerization method is a well-established technique for creating thin-film composite (TFC) membranes, but the introduction of UiO-66-NH2 MOF nanoparticles represents an innovative modification. The MOF nanoparticles serve as a structural additive that alters the morphology of the polyamide selective layer formed at the interface between the aqueous and organic phases. The key process parameter examined is the mass fraction of UiO-66-NH2 in the aqueous phase, with the optimal concentration identified at 0.005 wt%. At this concentration, the pure water flux reached 111 L/(m²·h·MPa), demonstrating significant improvement over conventional membranes without MOF addition.

The characterization methodology employed in this study is comprehensive and well-suited for membrane analysis. Attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) was used to confirm the chemical bonding between the MOF and the polyamide layer. Scanning electron microscopy (SEM) revealed the surface topography changes, while atomic force microscopy (AFM) provided nanoscale roughness data. Water contact angle measurements quantified the hydrophilicity enhancement, and zeta potential measurements confirmed the positive surface charge of the resulting membrane. The combination of these techniques provides a thorough understanding of both the chemical structure and physical properties of the fabricated membrane.

Performance Evaluation and Surface Morphology Analysis

The most striking morphological finding is the formation of abundant wrinkles on the membrane surface upon UiO-66-NH2 incorporation. These wrinkles significantly increase the effective surface area, which in turn enhances hydrophilicity and permeability. This wrinkle formation is attributed to the interaction between the MOF nanoparticles and the polymerization reaction kinetics at the interface. The nanoparticles likely disrupt the uniform reaction front, creating localized variations in polymerization rate that manifest as surface undulations.

The separation performance was evaluated using cetyltrimethylammonium bromide (CTAB) as a model cationic surfactant pollutant. The membrane achieved a rejection rate exceeding 95% for CTAB, demonstrating excellent capability for removing cationic surfactants from wastewater. This high selectivity is attributed to the combined effects of size exclusion, electrostatic repulsion (due to the positively charged membrane surface repelling cationic species), and the enhanced hydrophilicity that reduces fouling tendency. The three-channel capillary configuration offers advantages in terms of flux distribution and mechanical stability compared to flat-sheet membranes, making it suitable for industrial-scale applications.

Engineering Implications and Study Insights

From a materials engineering perspective, this research demonstrates the potential of incorporating MOF nanoparticles into membrane fabrication processes to achieve simultaneous improvements in permeability and selectivity. The 0.005 wt% optimal concentration suggests that even trace amounts of MOF can significantly influence membrane morphology, which has important implications for cost-effective scale-up. The positively charged nature of the membrane opens applications in treating industrial effluents containing cationic surfactants, dyes, and pharmaceuticals. However, long-term stability of the MOF-polyamide interface under operating conditions, including chemical resistance to chlorine and mechanical durability during compaction, remains a critical consideration for practical deployment. The research represents a meaningful contribution to the field of membrane separation technology and provides a foundation for further development of MOF-enhanced composite membranes for water treatment applications.