Rapid Synthesis of Fibrous Phosphorus for Ammonia Sensing at Room Temperature

Abstract

Ammonia (NH3) is a representative reducing toxic gas whose rapid, low-concentration detection is important in constant-temperature, constant-humidity environments such as semiconductor cleanrooms, yet existing NH3 sensors often suffer from high operating temperatures or slow response/recovery kinetics. Fibrous phosphorus (FP), a layered allotrope of elemental phosphorus with a parallel tubular structure, is an appealing sensing candidate, but its efficient preparation and gas-sensing potential remain underexplored. Here, we report an iodine-assisted chemical vapor transport method that enables gram-scale synthesis of FP within 5 h with a yield exceeding 99%, without the need for precise temperature-gradient control. The key is the iodine-mediated cleavage of P4 cages and the directed assembly of active phosphorus fragments into tubular FP. Taking advantage of the weak interlayer van der Waals interactions, high-quality FP nanoribbons (FP-NRs) with an average width of ∼50 nm, an average length of ∼6 μm, and aspect ratios exceeding 150 for ∼60% of the ribbons are obtained by 60 min of ice-bath exfoliation. The FP-NRs sensor exhibits a high response of 826% toward 100 ppm NH3 at room temperature, with response/recovery times of 31/7 s under the 90% criterion, and remains responsive at 2 ppm NH3 (response 69.8%). When all tested gases are compared at the same concentration, the response to NH3 is significantly higher than that to the interfering gases. Combined DFT calculations and in situ FTIR/Raman measurements reveal that NH3 adsorption on FP is dominated by physical adsorption (adsorption energy −0.26 eV; Bader charge transfer ∼0.02 e), which accounts for the high sensitivity, selectivity, and fast recovery. This work provides a scalable route to FP nanoribbons and demonstrates their potential for practical room-temperature NH3 sensing.