Size-controlled synthesis of BiPO4 nanocrystals for enhanced photocatalytic performance

Well dispersed BiPO4 nanocrystals with a diameter of ∼9 nm are synthesized in oleic acid (OA) and bis(2-ethylhexyl) phosphate (BEHP) media by a high-temperature hydrolysis reaction. OA absorbed on the surface of the nanocrystals helps make a monodispersion. In this reaction, the diameters of the as prepared BiPO4 nanocrystals can be controlled from 9 nm to 250 nm by changing the OA/BEHP ratio (v/v). The roles of BEHP and OA during the formation of the nanocrystals and for tuning the grain size of the particles have been discussed, and a possible formation mechanism of the nanocrystals is proposed. BiPO4 nanocrystals with a diameter of ∼9 nm after OA removal show the highest activity for degradation of methylene blue solution in the UV region, which is also nearly twice the reported activity of BiPO4, and 2.6 times higher than that of P25. The high Brunauer–Emmett–Teller (BET) surface, large band gap, surface effect, and short mobility distance for carriers to the surface are recognized as the key factors for the high photocatalytic activity of nanocrystals.