Porphyrin controlled anisotropic and dendritic growth of thallium chloride crystals

Abstract

In this work, the morphology of TlCl crystals grown at the liquid-liquid interface between Tl2SO4 and HCl solutions was investigated in the presence of various porphyrin molecules. The addition of the tetrakis(4-sulfonatophenyl)porphyrin (TPPS2) molecules changed the TlCl morphology from spherical shape to single-crystalline strips with a diameter of 100-3,000 nm. The addition of meso-tetra(4-pyridyl)porphine (TPPyP) changed morphology of TlCl crystals into branching dendrites. The presence of the different porphyrins molecules in the crystallisation medium significantly influenced the morphology of the crystals. Crystals of TlCl with elongated rod-type or branching superstructures were nucleated with high aspect ratios depending on porphyrin type that was used. The composition and microstructure of dendrites was investigated by X-ray technique, SEM and atomic force microscopy (AFM). The wires were produced by elongation and stacking of planar TlCl crystals exhibiting (100) faces. The anisotropic growth behaviour causing the wire formation is tentatively ascribed to stepwise capping of the specific surfaces of TlCl crystals by porphyrin molecules.