Carbon nitride has attracted extensive attention because of its promising properties and great application potential in photocatalysis, electrocatalysis, bioimaging and biomedicine. In this work, carbon nitride with a novel morphology, i.e., tetragonal carbon nitride hollow tube (TCNT), was in-situ synthesized by a molten salt method at 450 degrees C using melamine as the starting precursor. As-prepared TCNTs were 2-20 mu m long and 50-2000 nm wide and possessed higher content of impurity nitrogen and larger specific surface area than conventional bulk g-C3N4 (B-CN). A possible salt-assisted self-assembly mechanism is believed to have dominated the formation of TCNTs. As-prepared TCNTs exhibited superior photocatalytic activities and adsorption performance for methylene blue and phenol degradation to B-CN, suggesting that they could be potentially used as a promising photocatalyst and adsorbent.