Preparation and properties of α-Co(OH)2/SA nanofiltration membranes with a “brick and mortar” biomimetic structure

Combining novel two-dimensional (2D) and polymeric materials can construct high-performance membranes for nanofiltration (NF) applications. In this study, 2D α-Co(OH)2 nanosheets and sodium alginate (SA) were assembled to fabricate a serial of α-Co(OH)2/SA NF membranes with a "brick and mortar" biomimetic structure for dye removal. The prepared α-Co(OH)2 nanosheets were characterized with a typical 2D structure, and the α-Co(OH)2/SA membranes exhibited dense selective layers with hydrophilic negatively charged surfaces. Furthermore, the membrane thickness and NF performance both varied depending on the mass ratios of α-Co(OH)2 to SA, giving the tunability of the membrane structure and NF performance of α-Co(OH)2/SA membranes. The prepared α-Co(OH)2/SA membranes exhibited superior separation performance compared to pure SA membranes, with the α-Co(OH)2/SA(5/5) membrane demonstrating exceptional dye rejection of 99.92% for Rose Bengal (RB) and long-term stability lasting 48 h. They were effective against both gram-positive and gram-negative bacteria. In addition, the α-Co(OH)2/SA(5/5) membrane exhibited low rejection towards salt solutions (6.05% for NaCl, 9.63% for Na2SO4). The α-Co(OH)2/SA(5/5) membrane offers a promising application for separating dye/salt solutions, which provides potential in designing and fabricating novel composite membranes with 2D materials.