Morphology-Controlled Synthesis of Hierarchical Copper Hydroxyphosphate Microcrystals in Alkaline Buffer Solution and their Optical Properties

A series of copper hydroxyphosphate (Cu₂(OH)PO₄) microcrystals with different shapes, including straw sheaf-like microcrystals, microrods-assembled microflowers, four-edged arrow-like microcrystals, and four-pointed star-like dendrites, are prepared by a hydrothermal method in Na₂HPO₄-NaOH buffer solutions. The buffer solutions serve as both reactant and solvent. More importantly, the pH values of the alkaline buffer solutions significantly affect the morphologies of Cu₂(OH)PO₄ microcrystals. Four samples have absorption bands in the near-ultraviolet, visible, and near-infrared regions; furthermore, four Cu₂(OH)PO₄ microcrystals exhibit different band gap energies (3.06, 2.78, 2.68, and 2.39 eV) owing to their different structures. This strategy can be scaled up for the simple, green, and low-cost production of Cu₂(OH)PO₄ microcrystals.