Fast photodegradation of Orange II azo dye under visible light irradiation using a semiconducting n-p heterojunction of ZnO nanoparticles/polypyrrole as catalyst

ALONDRA G. ESCOBAR-VILLANUEVA; M. PAULA MILITELLO; VÍCTOR M. OVANDO-MEDINA; HUGO MARTÍNEZ-GUTIÉRREZ

JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS

SPRINGER

Lugar: Berlin; Año: 2020 vol. 31 p. 1317 - 1327

0957-4522

Preparation of innovative nano and microstructured heterojunctions consisting of two semiconductors for highly efficient p-n photocatalysts has been of growing interest due to their advanced applications. n-type ZnO nanoparticles were synthesized by a simple precipitation method from ZnCl2 and NaOH and coated with semiconducting p-type polypyrrole (PPy) nanospheres by chemical oxidation in the presence of sodium dodecyl sulfate (SDS) as surfactant, obtaining a n-p type ZnO/PPy composite. The composite was characterized by scanning electron microscopy (SEM), FTIR and UV/Vis-NIR spectroscopies and thermogravimetric analysis (TGA). It was observed that composite consisted of ZnO nanoparticles with rice-like morphology of sizes in the range of 200 to 500 nm in length and between 70 and 150 nm wide, which were well dispersed into a matrix made of agglomerated spherical nanoparticles of PPy. The composite was tested as photocatalyst in the degradation of Orange II azo dye using visible light irradiation at different initial dye concentrations, catalyst loading, initial pH and in the presence of hole and radical scavengers. Photodegradation efficiencies after 30 min of reaction in the range 90.9 to 100% and fast photodegradation rates depending on the initial dye concentration and catalyst load were observed. The best photodegradation efficiency was observed at acidic pH, which was ascribed to an improved electrostatic interaction of dissociated dye molecules with the positively charged surface of photocatalyst. It was demonstrated that ?O-2 and other ROS are the main reactive species formed via reaction between O2 and photogenerated electrons, following a pseudo-first order of reaction.