Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Electrochemıcal Behavıor Of Some Nıckel Complexes And Theır

Adsorptıon On Zınc-Oxıde
Colored complexes of transition elements have been utilized for improving photocatalytic activity of ZnO which is extensively used as photo-anode in dye sensitized solar cells. Electrochemical equilibria of nickel (II) complexes with the N-donor ligands 2,2’-bipyridyl-1,3,5-tripyridyl-s-triazine (TPTZ) and 2,2’-Bipyridyl (Bpy) were investigated in aqueous solutions in deaerated solutions to elucidate their electron and proton transfer mechanisms.
The electrochemical response of colored nickel complexes was studied using square-wave voltammetry (SWV) and cyclic voltammetry (CV) techniques. A conventional three-electrode system, consisting of glassy carbon (GCE), carbon paste (CPE) and ZnO modified carbon paste (ZnOCPE) working electrodes, saturated calomel (SCE) or Ag/AgCl reference electrodes and a platinum wire auxiliary electrode, was employed.
The mechanisms of the electrode processes were elucidated by examining effects of pH, frequency and scan rate on voltammograms of the complexes. Acetate, phosphate and borate buffers were used for pH adjustments in the range of 4-10 for 1.0 mM Ni(II) complexes. pH values for optimum working conditions were found as 7.8 for Ni-TPTZ and Ni₂(Bpy)(TPTZ)₂. The numbers of proton (p), electron (n) and transfer coefficient (a) in electrode process were estimated from the change of peak potentials (Ep) depending on pH and frequency (25–200 Hz). The reversibility of the processes was determined from the ratio of cathodic and anodic peak on CV voltammograms. The rate constants of electrode processes were calculated by changing Ep with scan rate.
The electrochemical mechanisms on GCE, CPE and ZnOMCPE have been proposed by using transferred proton and electron numbers. Results showed that both central Ni(II) ion and ligands can be protonated and reduced on the GCE and CPE whereas only ZnOMCPE behaved as an anode for oxidation of complexes.
Adsorption isotherms obtained from the results of equilibrium study and the adsorption kinetics onto ZnO were investigated for TPTZ and TPTZ-Bpy complexes. Adsorption isotherms evaluated from equilibrium results gave S shaped isotherm profile for TPTZ and TPTZ-Bpy complexes. The Freundlich models were applied to analyze equilibrium data.