Interfacial engineering of a chitosan-tannic acid layer on bacterial cellulose for a high performance forward osmosis membrane toward sustainable juice concentration and reduced microplastic release.

Bacterial cellulose (BC), a renewable biopolymer, has emerged as a promising substrate for membrane fabrication due to its biocompatibility and sustainability. However, the intrinsic heterogeneity in BC fiber distribution results in polydisperse inter-fiber voids, impeding its widespread application in membrane technologies. To mitigate the inherent surface roughness and microporosity of BC substrates, a chitosan-tannic acid interlayer with tunable hydrophilicity was engineered. This interfacial modification facilitated the subsequent formation of an ultrathin, highly cross-linked polyamide selective layer, minimizing defect density in the forward osmosis (FO) membrane. The fabricated FO membrane exhibited a sustained permeate flux (9.07 L·m-2·h-1) and superior draw solute rejection (>94%), alongside strong anti-fouling durability against bovine serum albumin (BSA) and sodium alginate (SA). Moreover, it demonstrated enhanced chemical stability under acidic and alkaline cleaning regimens. Quantitative assessment via Nile red fluorescence revealed a 63% reduction in microplastic release compared to conventional membranes. Particularly in the application to apple juice concentration, the BC-CS/TA3-PA FO membrane increased the contents of total phenols, total flavonoids, and vitamin C by factors of 5.81, 4.14, and 2.46, respectively, compared with thermal concentration, while effectively retaining antioxidant activity in the concentrate. This work provides a foundational framework for fabricating BC-based FO membranes, introduces an innovative approach to eco-friendly, sustainable membrane development, and demonstrates the high feasibility and industrial potential of this novel membrane for apple juice concentration.