Enhanced photodegradation of Congo red dye under sunlight irradiation by p-n NiFe2O4/TiO2 heterostructure

This work is dedicated to the investigation of NiFe2O4, prepared by sol gel auto-combustion method using glycine as fuel, to degrade a hazardous dye (Congo red) under sunlight irradiation. TiO2-NiFe2O4 Z-scheme has constructed via solid dispersion technique to improve the photoactivity by decreasing the recombination of electron/ hole (e -/h+) pairs. The photocatalysts are characterized by X-ray diffraction, Fourier Transform infrared spectroscopy and Scanning electronic microscopy with integrated EDX. The optical characterization indicates a direct transition of NiFe2O4 with the band gap (Eg) of 1.64 eV, and an indirect transition for TiO2 (Eg = 3.21 eV). Electrochemical characterization is used to determine the flat band potential (Efb) using the Mott-Schottky plot of the interfacial capacitance, which confirmed the p and n type behavior of NiFe2O4 (Efb = +0.05 VSCE) and TiO2 (Efb = +0.31 VSCE), respectively. Electrochemical impedance spectroscopy (EIS) shows that NiFe2O4 has a low charge transfer resistance (950 & omega; cm2) smaller than that of TiO2. The kinetics of Congo red adsorption is well fitted by a pseudo-second order model. The photodegradation tests confirm that p-NiFe2O4/n-TiO2 heterostructure facilitates the charge separation of photogenerated electrons and holes by reducing the recombination of (e -/h+) pairs. This increases the overall efficiency of the photocatalytic process, which reaches 97 % of Congo red oxidation after 180 min for the composition (p-NiFe2O4/n-TiO2 (0.75/0.25)).