Recent advances in three-dimensional nanoflower-based membrane engineering for water and wastewater treatment: from fundamental mechanisms to scale-up.

Three-dimensional (3D) nanoflower (NF)-based membranes have recently emerged as a promising platform for advanced water and wastewater treatment owing to their hierarchical architectures, high surface-to-volume ratio, tunable physicochemical properties, and multifunctional performance. Unlike conventional nanomaterials, NF structures provide abundant exposed reactive sites, interconnected transport pathways, and enhanced interfacial interactions, enabling simultaneous improvements in adsorption, separation, catalytic activity, hydrophilicity, antifouling behavior, and contaminant selectivity. These distinctive features have accelerated their integration into polymeric, ceramic, and thin-film composite membranes for the efficient removal of heavy metals, dyes, pharmaceuticals, nutrients, pathogens, and emerging contaminants. This review critically examines recent advances in engineering 3D NF-based membranes for sustainable water and wastewater treatment, with emphasis on the mechanistic principles governing membrane performance and material functionality. Fundamental transport and removal mechanisms, including adsorption, separation, pore-filling effects, adsorption kinetics, surface charge regulation, wettability modulation, and band-gap engineering for enhanced photocatalytic activity, are comprehensively discussed. Particular attention is given to how NF morphology, composition, and membrane integration strategies influence local membrane properties, transport behavior, permeability-selectivity trade-offs, and long-term operational performance. Recent advances in hybrid NF-incorporated membrane architectures, including metal oxide, metal phosphate as well as nanoflowers integrated with functional materials such as biochar, covalent organic frameworks (COFs), and other functional materials, are systematically evaluated through application-based studies and comparative performance analysis. Critical barriers hindering industrial implementation, including fabrication complexity, structural instability, nanoparticle leaching, membrane fouling, interfacial incompatibility, scalability limitations, and economic constraints, are also discussed under realistic operational conditions. Emerging opportunities in scalable manufacturing, hybrid membrane engineering, computational modeling, and artificial intelligence-assisted materials design are highlighted as pathways toward commercialization. By integrating mechanistic understanding with application-oriented analysis, this review establishes a comprehensive framework for the rational design and large-scale deployment of NF-based membranes, positioning them as promising next-generation technologies for sustainable, energy-efficient, and high-performance water purification systems.