Characterization of a copper phosphate triazole metal organic framework material (Cu3PO4(C2N3H2)2OH) and oxygen evolution studies

The metal organic framework (MOF) Cu3PO4(C2N3H2)(2)OH, synthesized by hydrothermal route, is characterized physically and photoelectrochemically. The compound crystallizes in a monoclinic symmetry with a layered structure. UV-visible spectroscopy shows an optical transition of 2.58 eV. The thermal variation of the electrical conductivity indicates a semiconducting behavior with a conduction mechanism dominated by small polaron hopping: sigma=sigma(0) exp {0.44 eV/kT} and electron mobility (mu(300) (K)=0.3 cm(2) V-1 s(-1)) thermally activated. The interfacial capacitance at pH similar to 7 is characteristic of n type behavior with a flat band potential of +0.40 V-SCE, an electrons density of 2 x 10(15) cm(-3) and a space charge region of 10 pm. The semicircle at high frequencies in the Nyquist plot is not centered on the real axis and the depletion angle (17 degrees) is due to a constant phase element. The impedance data at low frequencies indicate a diffusion-controlled process. As application, the photochemical oxygen evolution is successfully achieved under visible light with a liberation rate of 0.70 cm(3) min(-1) g(-1) and a quantum yield of 0.13%. The reaction (2 SO32-+H2O -> S2O32-+O-2+2OH, Delta G(0) = 90.68 kcal mol(-1)) can be evaluated for the chemical storage. (C) 2014 Elsevier Ltd. All rights reserved.