Degradation of organic dyes by water soluble iron(III) mononuclear complexes from bis-(2-pyridylmethyl)amine NNN-derivative ligands

Fe(III)-Complex-Imprinted Polymers for the Green Oxidative Degradation of the Methyl Orange Dye Pollutant

One of the biggest problems worldwide is the pollution of natural water bodies by dyes coming from effluents used in the textile industry. In the quest for novel effluent treatment alternatives, the aim of this work was to immobilize Fe(III) complexes in molecularly imprinted polymers (MIPs) to produce efficient Fenton-like heterogeneous catalysts for the green oxidative degradation of the methyl orange (MO) dye pollutant. Different metal complexes bearing commercial and low-cost ligands were assayed and their catalytic activity levels towards the discoloration of MO by H2O2 were assessed. The best candidates were Fe(III)-BMPA (BMPA = di-(2-picolyl)amine) and Fe(III)-NTP (NTP = 3,3',3″-nitrilotripropionic acid), displaying above 70% MO degradation in 3 h. Fe(III)-BMPA caused the oxidative degradation through two first-order stages, related to the formation of BMPA-Fe-OOH and the generation of reactive oxygen species. Only the first of these stages was detected for Fe(III)-NTP. Both complexes were then employed to imprint catalytic cavities into MIPs. The polymers showed catalytic profiles that were highly dependent on the crosslinking agent employed, with N,N-methylenebisacrylamide (MBAA) being the crosslinker that rendered polymers with optimal oxidative performance (>95% conversion). The obtained ion-imprinted polymers constitute cheap and robust solid matrices, with the potential to be coupled to dye-containing effluent treatment systems with synchronous H2O2 injection.

Formation of Single-Walled Carbon Nanotube-Ruthenium Nanoparticles in Ethanol upon Microwave Radiation

In this work, an environmentally friendly microwave method was employed to rapidly synthesize a single-walled carbon nanotube-Ru nanoparticle (SWCNT-Ru) catalyst utilizing ethanol as the reducing agent. In general, the SWCNT-Ru nanoparticle catalyst facilitated the degradation of Congo red dye solutions, of both low and high concentrations, within eight minutes at room temperature, and possessed great recoverability and reusability properties. High-resolution transmission electron microscopy (HR-TEM) analysis of the SWCNT-Ru nanoparticle catalyst, which was synthesized with 0.05 wt. % RuCl₃ in ethanol, revealed highly dispersed Ru nanoparticles of the averaged size of 2.0 nm ± 0.5 nm onto the single-walled carbon nanotube bundles. Raman spectroscopy analysis indicated that there was no alteration to the nanotube structural framework upon the formation of the Ru nanoparticles. UV-Visible spectroscopy analysis indicated that the electronic properties of both smaller and larger diameters of SWCNTs were altered upon the coordination of the Ru nanoparticles. In addition, studies showed that when using ethanol as a reducing agent, concentrations of the RuCl₃ salt must remain below 0.10 wt. % to facilitate the production of Ru nanoparticles with efficient catalytic properties.