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The magnetic composite BiOCl-SrFe12O19, a novel p-n type heterojunction was synthesized by hydrolysis with a medium temperature sintering method. The microstructure and magnetic properties of the prepared material were characterized by FTIR, XRD, SEM, TEM, HRTEM, SAED, and VSM. The results showed the [001] facet of BiOCl with high photocatalytic activity was exposed in the BiOCl-SrFe12O19. The heterostructured BiOCl-SrFe12O19 had better magnetic properties, contributing to its reuse and improvement in photocatalysis. Moreover, the composite was blessed with excellent photocatalytic activity and stability. In the BiOCl-SrFe12O19 system, SrFe12O19 not only inhibited the growth of BiOCl along the [001] direction to enhance the exposure of the [001] wafer, but also acted as a sensitizer absorbing light irradiation. The magnetic field generated from SrFe12O19 made BiOCl, under light irradiation, produce more photo-induced electrons and holes and simultaneously hampered their recombination. For the first time we propose the possible mechanism of how to enhance photocatalytic activity by a magnetic field effect originating from the magnetic photocatalyst itself.

Magnetic composite photocatalyst Bi2O3/SrFe12O19 was synthesized by hydrolysis with medium temperature sintering method. X-ray diffraction (XRD) investigation revealed that introduction of SrFe12O19 did not change the favorite growth direction of Bi2O3, [121] orientation. Micromorphology study indicated that SrFe12O19 was distributed on the surface of Bi2O3 to possess the best possibility of forming some heterojunction structures. Vibrating sample magnetometer (VSM) measurements manifested the composite possessed better magnetic properties, which was conducive to its separation, recycling, and reuse. Three main reasons for the increase in photocatalytic activity of Bi2O3/SrFe12O19 were (1) the formation of p–n-type heterojunction between p-type Bi2O3 and n-type SrFe12O19 semiconductors, (2) magnetic field effect stemming from magnetic composite itself generated a shunt effect for photoexcited electrons, and (3) as a sensitizer absorbing visible light, SrFe12O19 could help Bi2O3 absorb more incident photons and then produce more photoexcited electron–hole pairs. In addition, this work was expected to provide a simple preparation method for various functional materials, especially magnetic functional materials.

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The selective crystal facet growth of BiOX (X = Cl, Br, I) is very significant since each facet possesses different physicochemical properties.