ZnMn2O4 nanostructures: Synthesis via two different chemical methods, characterization, and photocatalytic applications for the degradation of new dyes

Abstract

Water pollution have become contentious among researchers. By increasing industrialization, the availability of clean water has been reduced. Industrial dyestuffs contribute to the escalation of environmental pollution and are the largest group of organic compounds. The aim of the present work is the synthesis of nanostructures that accelerate the removal of organic dyes from water. To reach this aim, first, ZnMn2O4 nanostructures were synthesized by hydrothermal and co-precipitation methods using maleic acid and phenylalanine as a capping agent. Second, the nanostructures were characterized. XRD analysis revealed the formation of ZnMn2O4 with diameters about 32.3 nm. SEM analysis showed the formation of the agglomerated spherical ZnMn2O4 nanostructures with diameters lower than 50 nm. EDX analysis confirmed the purity of the prepared samples with the presence of Zn, Mn, and O. FT-IR analysis confirmed the bonding between Mn and O at about 620 cm−1. ZnMn2O4 nanostructures showed antiferromagnetic behaviors due to the super-exchange interactions between manganese ions. Finally, the photocatalytic behavior of the nanostructures was investigated for degradation of the anionic and cationic dyes. The results of the photocatalytic tests of two as-prepared samples via different methods were similar. The results exhibit a promising photocatalytic activity in the presence of 0.03 g photocatalyst for degradation of a dye solution with 10 ppm concentration. We introduced these conditions as optimum conditions and achieved maximum decolorization (92.43 %) in the 10 ppm of MV solution after 90 min. Also, we repeated six consecutive reaction cycles and observed a little activity loss after six reactions. We related this result to the high stability of the photocatalyst. We performed scavenging experiments to evaluate the active species involved in the photocatalytic process and plausible mechanisms. The photocatalytic degradation of MV decreased in the presence of TBA and BQ, respectively. This decrease indicated that OH° and O2°− radicals are important active species in the MV degradation process.