Metal-Organic Framework-Templated Deconstruction-Reconstruction Enables One-Dimensional to Two-Dimensional Self-Assembly of Transition Metal Phosphates for High-Performance Ammonia Sensing.

Self-assembled nanomaterials formed through the spontaneous organisation of nanoscale building blocks are attractive because of their high surface areas, strong interparticle connectivity, and ease of processing. However, programming the assembly of one-dimensional (1D) transition-metal nanostructures into two-dimensional (2D) architectures remains challenging because of dimensional mismatch and kinetic or thermodynamic barriers. Here, we report a general metal-organic framework (MOF)-templating strategy that enables the 1D-to-2D self-assembly of nickel phosphate into nanofibre-assembled quasi-nanosheets (QNSs). The conversion proceeds through an acid-driven deconstruction-reconstruction (ADR) mechanism, in which Ni-MOFs act as dissolution-programmable metal reservoirs that regulate local Ni2+ release and phosphate nucleation. This process first generates nickel phosphate nanofibres and subsequently drives their secondary assembly into QNSs. By changing the parent Ni-MOF, the porosity and specific surface area of the resulting nanofibre-assembled nickel phosphate QNSs can be readily tuned, and the strategy can be extended to bimetallic phosphate analogues. As a proof-of-concept sensing platform, the Ni-BPDC-derived nickel phosphate QNSs exhibit a high response to ammonia (NH3), with a frequency shift of 897.9 ± 24.8 Hz µg-1 at 69.5 ppm, a limit of detection (LoD) of 480 ppb, and excellent long-term stability, retaining 97% of the initial response after 6 months.