Thorn-like polycrystalline Ca₂B₂O₅.H₂O microspheres with nano-sized slices were synthesized using boric acid and calcium hydroxide as reactants by a facile catalyst-free hydrothermal method at low temperature. The products were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern reveals that the Ca₂B₂O₅.H₂O is a monoclinic phase polycrystalline with cell parameters 𝑎 = 0.6702, 𝑏 = 0.5419 and 𝑐 = 0.3558 nm. SEM also reveals that the monoclinic phase polycrystalline are thornlike microspheres composed of many flakes with an average thickness of <100 nm. Possible reaction and growth mechanism were also discussed.

Brookite TiO$_2$ was synthesized and BiOBr was supported on the surface of brookite TiO$_2$ by a hydrothermal method. X-ray diffraction and X-ray photoelectron spectroscopy analyses of the composites confirmed the formation of brookite TiO$_2$/BiOBr. Transmission electron microscopy results confirmed the as-prepared composites were nano-sized.The optimum loading amount of BiOBr was 30%. The photocatalytic results show that the degradation efficiency of rhodamine B by titanite TiO$_2$/BiOBr (30%) under visible-light irradiation for 2 h is close to 100%. ${\bullet}$O$_2$$^–$ and h$^+$ are themain active species during the photocatalytic process. The improvement of photocatalytic activity might be because theformation of p–n hetero-junction enhanced the separation efficiency of photogenerated electron–hole pairs. The photocurrentdensity of the brookite/BiOBr (30%) was about 2 times higher than that of pure brookite.