Synthesis and photoelectrochemical characterization of KZn2(HPO4)PO4: application to rhodamine B photodegradation under solar light

This work reports for the first time the study of the physical and photoelectrochemical properties of KZn2 (HPO4) PO4 nanopowder, prepared by hydrothermal route at 453K. The as-synthesized compound crystallizes in a triclinic system (space group: P1) with the lattice constants: a=5.2060(2)angstrom, b=8.8524(3)angstrom, c=9.4039(3)angstrom, =96.9810(10)degrees, =101.7410(10)degrees, =106.8130(10)degrees and a crystallite size of 90nm. The observed direct optical transition of 2.88eV is due to O2-: 2pZn(2+): 4s charge transfer; a further indirect transition at 5.80eV is noticed. The electrical conductivity follows an exponential type law: sigma=sigma(o) exp (-0.08eV/kT) in the temperature range (385-500K), with an electronic hopping through mixed valences, while the negative thermo-power indicates n-type behavior. The capacitance measurement at pH7 gives a flat band potential of -0.13 V-SCE for the conduction band, which derives from Zn2+: 4s orbital and a donor density of 3.18x10(19)cm(-3). The electrochemical impedance spectroscopy shows the predominance of the faradic charge transfer. In order to support the photoelectrochemical results, the photocatalytic degradation of rhodamine B (RhB) in the presence of KZn2(HPO4)PO4, under solar light, is conducted. The results indicate 40% conversion after 300min of irradiation time. A degradation mechanism is proposed to explain the mineralization. The photocatalytic RhB degradation obeys to a second-order kinetic model with a rate constant of 1.48x10(-3)mol(-1)Lmin(-1).