Hydrogen-bonded organic frameworks for environmental applications: a review on design, performance and prospects

Hydrogen-bonded organic frameworks (HOFs) are an emerging class of crystalline porous materials assembled through intermolecular hydrogen-bonding interactions between organic building units. Distinguished from metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), HOFs are entirely metal-free, exhibit excellent solution processability, and can be regenerated through simple recrystallization, making them highly attractive for sustainable environmental applications. This review systematically surveys the environmental applications of HOFs, encompassing (i) selective gas adsorption and separation of industrially relevant gas pairs (C 2 H 2 /CO 2 , C 2 H 6 /C 2 H 4 , CH 4 /C 2 H x , Xe/Kr, NH 3 ), (ii) CO 2 capture, sensing, and photocatalytic reduction, (iii) proton conduction for clean energy fuel cells, (iv) photocatalytic hydrogen evolution via band-gap-engineered is reticular HOFs, (v) enzyme encapsulation for biocatalytic remediation of toxic organophosphorus compounds, (vi) luminescence- and electrochemical-based sensing of heavy metal ions and antibiotic contaminants, (vii) oil/water separation using superhydrophobic metal-mediated HOFs, and (viii) antimicrobial membranes exploiting ionic HOF architectures. The interplay between molecular design, pore chemistry, and environmental performance is critically analyzed, and key challenges including scalability, long-term water stability, and mechanistic understanding are discussed alongside future research directions.