Gas-phase fluorination of boron nitride nanotubes

• BNNTs with tunable degrees of fluorination were prepared using molecular fluorine. • Different fluorination temperature, gas ratio, and exposure time were studied. • Fluorination mainly occurred on the outermost layer with the formation of B–F bonds. • F-BNNTs underwent thermal degradation through the desorption of fluorine. • DFT calculations suggested a strong preference for fluorine to bind with boron. Theoretical and experimental studies have highlighted the potential of surface-modified hexagonal boron nitride (hBN) flakes or boron nitride nanotubes (BNNTs) for achieving tunable electrical and magnetic properties. Here, we investigate the fluorination of BNNTs via a gas–solid phase reaction using molecular fluorine, focusing on controlling the degree of fluorination through varying reaction temperatures, gas mixing ratios, and reaction times. Effective fluorination is evident at elevated temperatures, with the degree of fluorination increasing with reaction time and temperature. Characterizations of the fluorinated BNNTs revealed fluorine incorporation, primarily on the outer nanotube layers, where fluorine preferentially binds to boron rather than nitrogen. Density functional theory calculations further indicate that fluorination becomes more thermodynamically favorable with increasing BNNT diameter and occurs preferentially at electron-deficient boron sites.