Shaping covalent triazine frameworks into films and membranes: A review of bottom-up strategies

Covalent Triazine Frameworks (CTFs) are among the most compelling subclasses of Covalent Organic Frameworks (COFs), combining intrinsic porosity, exceptional thermal and chemical robustness, high densities of catalytic active sites, and tunable electronic properties. These features position CTFs at the forefront of advanced materials research for applications in photocatalysis, molecular separations, optoelectronics, and energy storage. Despite remarkable advances in molecular design, the field has remained largely confined to bulk powders—predominantly amorphous—due to the challenges associated with the synthesis of crystalline CTFs. This powder-centric paradigm represents a critical bottleneck: next-generation technologies demand structurally defined and substrate-integrated materials. In this context, CTF films and membranes are not merely an alternative morphology, but a technological necessity. Emerging evidence demonstrates that CTF film architectures can outperform their powder counterparts in electronic transport, catalytic efficiency, and molecular sieving, unlocking functionalities inaccessible to bulk materials. However, the rational synthesis of continuous, defect-controlled CTF films remains highly challenging, hindered by the intrinsic rigidity of triazine networks and harsh polymerization conditions. Addressing this gap is pivotal for translating CTFs from laboratory curiosities to functional devices. In this Review, we provide the first comprehensive and critical analysis of bottom-up strategies for the direct synthesis of CTF films and membranes. Unlike top-down approaches based on post-synthetic processing, bottom-up methodologies enable the in situ construction of CTF films during network formation, offering unprecedented control over thickness, interface, and structural integrity. For the first time, we classify these methodologies into two main categories: sol–gel polymerization and interfacial polymerization. While the sol–gel polymerization approach has thus far been limited to the preparation of amorphous CTF membranes with poorly controlled thickness and limited reproducibility, interfacial polymerization has enabled improved control over film thickness, lateral dimensions, crystallinity, and morphology. In this Review, we provide a comprehensive analysis of both approaches, highlighting key advantages and limitations, as well as future perspectives and research needs. By consolidating the current state of this rapidly evolving field, this Review establishes a conceptual framework for the rational design of CTF films and aims to accelerate their integration into next-generation catalytic, separation, and electronic technologies.