Direct ink writing of geopolymer-based membranes with anisotropic structures for water treatment

In the present work, direct ink writing (DIW) technology was utilized to fabricate geopolymer-based anisotropic membranes from metakaolin precursors. For evaluation of filtration performance in water treatment, the 3D -printed membranes were characterized, tested systematically, compared with a molded membrane and bench -marked against other geopolymer and ceramic membranes reported in the literature. With a novel approach, geopolymer-yttria stabilized zirconia (YSZ) ultrafiltration (UF) membrane with configuration of relatively dense rejection layer and gradient macroporous support was obtained via a one-step process of alkaline activation, DIW and curing, starting from a computer aided design (CAD) figure of an isotropic solid plate. The achievement of such structure resulted from the printing procedure leveraging both rheological properties of geopolymer ink and printing principle of DIW. The printed membrane displayed very high permeances (1453 L/(m2hbar) for pure water and 1311 L/(m2hbar) for suspension of 80-nm alumina particles), high rejection efficiency (98.4% for suspension of 80-nm alumina particles) and good chemical stability in alkaline solution. The present work provided the first-time report on additive manufacturing of geopolymer-based asymmetric UF membranes with superb performance for water treatment.