Design and characterization of palladium nano-catalyst supported on chitosan/NiO mlcrospheres for catalytlc reduction of some environmental pollutants

Aromatic nitro compounds and organic dyes, which are highly dangerous for aquatic life, the environment, and human health, are one of the most significant environmental pollutants found in water/wastewater. Therefore, the removal of these pollutants from water/wastewater using effective, simple, and economical technologies has become a significant issue worldwide. The catalytic reduction method is considered one of the most effective procedures used for the removal of these environmental pollutants. In this study, a new heterogeneous catalyst system has been developed by stabilizing palladium nanoparticles on microspheres composed of chitosan-NiO particles. The structure of the developed Pd-KS-NiO nanocatalyst was illuminated using FT-IR/ATR, XRD, FE-SEM, EDS, TEM analyses, and the average particle size was found to be 10 nm. Subsequently, the catalytic power of the synthesized Pd-KS-NiO nanocatalyst was tested in the catalytic reduction of aromatic nitro compounds such as 4-nitro-o-phenylenediamine (4-NPDA), 4-nitrophenol (4-NP), 4-nitroaniline (4-NA), 2-nitroaniline (2-NA), and organic dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) using NaBH4. The catalytic tests were monitored using UV-Vis spectroscopy, and it was found that the Pd-KS-NiO nanocatalyst successfully reduced these pollutants within 0-145 seconds. The rate constants for Pd-KS-NiO catalyzed reductions of 2-NA, 4-NP, 4-NA, 4-NPDA, MO, and RhB were calculated as 0.017 s-1, 0.011 s-1, 0.006 s-1, 0.013 s-1, 0.023 s-1, and 0.03 s-1, respectively. More importantly, due to the microsphere structure and heterogeneous nature of the Pd-KS-NiO nanocatalyst, it was easily recovered from the reaction medium and consecutively used in seven runs without significant changes in its catalytic performance, surface morphology, and chemical structure.