Copper(II) phosphate as a promising catalyst for the degradation of ciprofloxacin via photo-assisted Fenton-like process.

This work aims to unravel the potential of copper(II) phosphate as a new promising heterogenous catalyst for the degradation of ciprofloxacin (CIP) in the presence of H2O2 and/or visible light (λ > 400 nm). For this purpose, copper(II) phosphate was prepared by a facile precipitation method and fully characterized. Of our particular interest was the elucidation of the kinetics of CIP degradation on the surface of this heterogeneous catalyst, identification of the main reactive oxygen species responsible for the oxidative degradation of CIP, and the evaluation of the degradation pathways of this model antibiotic pollutant. It was found that the degradation of the antibiotic proceeded according to the pseudo-first-order kinetics. Copper(II) phosphate exhibited ca. 7 times higher CIP degradation rate in a Fenton-like process than commercial CuO (0.00155 vs. 0.00023 min-1, respectively). Furthermore, the activity of this metal phosphate could be significantly improved upon exposure of the reaction medium to visible light (reaction rate = 0.00445 min-1). In a photo-assisted Fenton-like process, copper(II) phosphate exhibited the highest activity in CIP degradation from among all reference samples used in this study, including CuO, Fe2O3, CeO2 and other metal phosphates. The main active species responsible for the degradation of CIP were hydroxyl radicals.

The influence of ferrocene anchoring method on the reactivity and stability of SBA-15-based catalysts in the degradation of ciprofloxacin via photo-Fenton process.

The study is aimed at evaluation of the impact of ferrocene (Fc) anchoring method on the efficiency of its incorporation on the surface of mesoporous silica SBA-15, as well as the reactivity and stability of these hybrid organic-inorganic materials in degradation of ciprofloxacin (CIP) via photocatalytic, Fenton and photo-Fenton processes. For this purpose, Fc was anchored on SBA-15 supports via three different methods: (i) Schiff base formation, (ii) Friedel-Crafts alkylation, and (iii) click reaction (azide-alkyne cycloaddition). The as-prepared materials were characterized by powder X-ray diffraction, nitrogen physisorption, infrared spectroscopy and inductively coupled plasma optical emission spectrometry, as well as UV-visible and X-ray photoelectron spectroscopies. The highest efficiency of Fc anchoring was obtained when applying the Friedel-Crafts alkylation, while the least effective was the Schiff base formation. As concerns the catalysts activity, all materials exhibited negligible reactivity in the photocatalytic process, but were capable of degrading CIP in the presence of H2O2 (Fenton process). For all materials, the highest efficiency of CIP removal was observed for the photo-Fenton reaction. When expressed as the activity of a single Fc site, the most reactive were Fc species from the catalyst prepared by the click reaction. All materials, irrespectively of the ferrocene anchoring method, were deactivating over the reaction time because of Fc leaching. The highest stability in three subsequent reaction cycles was observed for the catalyst prepared by the azide-alkyne cycloaddition. Thus, the click reaction was found to be the best method for the preparation of Fc-containing catalysts for CIP degradation.

Modification of Gold Zeolitic Supports for Catalytic Oxidation of Glucose to Gluconic Acid.

Activity of gold supported catalysts strongly depends on the type and composition of support, which determine the size of Au nanoparticles (Au NPs), gold-support interaction influencing gold properties, interaction with the reactants and, in this way, the reaction pathway. The aim of this study was to use two types of zeolites: the three dimensional HBeta and the layered two-dimensional MCM-36 as supports for gold, and modification of their properties towards the achievement of different properties in oxidation of glucose to gluconic acid with molecular oxygen and hydrogen peroxide. Such an approach allowed establishment of relationships between the activity of gold catalysts and different parameters such as Au NPs size, electronic properties of gold, structure and acidity of the supports. The zeolites were modified with (3-aminopropyl)-trimethoxysilane (APMS), which affected the support features and Au NPs properties. Moreover, the modification of the zeolite lattice with boron was applied to change the strength of the zeolite acidity. All modifications resulted in changes in glucose conversion, while maintaining high selectivity to gluconic acid. The most important findings include the differences in the reaction steps limiting the reaction rate depending on the nature of the oxidant applied (oxygen vs. H2O2), the important role of porosity of the zeolite supports, and accumulation of negative charge on Au NPs in catalytic oxidation of glucose.

Enhanced adsorption and degradation of methylene blue over mixed niobium-cerium oxide - Unraveling the synergy between Nb and Ce in advanced oxidation processes.

Formation of reactive oxygen species (ROS) via H2O2 activation is of vital importance in catalytic environmental chemistry, especially in degradation of organic pollutants. A new mixed niobium-cerium oxide (NbCeOx) was tailored for this purpose. A thorough structural and chemical characterization of NbCeOx along with CeO2 and Nb2O5 reference materials was carried out using TEM/STEM/EDS, SEM, XRD, XPS, EPR, UV-vis and N2 physisorption. The ability of the catalysts to activate H2O2 towards ROS formation was assessed on the basis of EPR and Raman measurements. Catalytic activity of the oxides was evaluated in degradation of methylene blue (MB) as a model pollutant. Very high activity of NbCeOx was attributed to the mixed redox-acidic nature of its surface, which originated from the synergy between Nb and Ce species. These two properties (redox activity and acidity) ensured convenient conditions for efficient activation of H2O2 and degradation of MB. The activity of NbCeOx in MB degradation was found 3 times higher than that of the commercial Nb2O5 CBMM catalyst and 240 times higher than that of CeO2. The mechanism of the degradation reaction was found to be an adsorption-triggered process initiated by hydroxyl radicals, generated on the surface via the transformation of O2-•/O22-.

Lights and Shadows of Gold Introduction into Beta Zeolite.

Four different methods for gold deposition on Beta zeolite, namely impregnation, ion-exchange, deposition-reduction, and grafting on (3-aminopropyl)trimethoxysilane functionalized support, were applied to investigate their influence on textural/structural changes in the zeolite support and its surface acidity. The as-prepared materials were fully characterized by XRD, N2 physisorption, ICP-OES, XPS, TEM, and pyridine adsorption. The obtained results indicated that bifunctional redox-acidic materials prepared within this work were characterized not only by different gold loading and gold particle size, but also different textural parameters and acidity. All these features were strongly affected by the procedure applied for gold deposition. The introduction of Au into Beta zeolite by ion exchange caused a significant decrease in the Si/Al ratio in the zeolite framework. The size of Au particles determined the textural parameters of the zeolite and the number of Lewis acid sites (LAS). The Brønsted acid sites (BAS) number was decreased if (3-aminopropyl)trimethoxysilane or NaBH4 were used in the procedure of gold deposition. The highest BAS/LAS ratio was achieved for the sample prepared by ion exchange in the ammonium form of Beta zeolite. The presented results permit making a proper choice of the gold modification procedure for the preparation of bifunctional (redox-acidic) materials, addressed to a desired application.