Kinetics of Adsorption of the Cobalt Ions on the “Electrolytic Solution/γ-Alumina” Interface

Degradation of 4-Tert-Butylphenol in Water Using Mono-Doped (M1: Mo, W) and Co-Doped (M2-M1: Cu, Co, Zn) Titania Catalysts

Mono-doped (Mo-TiO₂ and W-TiO₂) and co-doped TiO₂ (Co-Mo-TiO₂, Co-W-TiO₂, Cu-Mo-TiO₂, Cu-W-TiO₂, Zn-Mo-TiO₂, and Zn-W-TiO₂) catalysts were synthesized by simple impregnation methods and tested for the photocatalytic degradation of 4-tert-butylphenol in water under UV (365 nm) light irradiation. The catalysts were characterized with various analytical methods. X-ray diffraction (XRD), Raman, Diffuse reflectance (DR) spectroscopies, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Energy dispersive spectroscopy (EDS) were applied to investigate the structure, optical properties, morphology, and elemental composition of the prepared catalysts. The XRD patterns revealed the presence of peaks corresponding to the WO₃ in W-TiO₂, Co-W-TiO₂, Cu-W-TiO₂, and Zn-W-TiO₂. The co-doping of Cu and Mo to the TiO₂ lattice was evidenced by the shift of XRD planes towards higher 2θ values, confirming the lattice distortion. Elemental mapping images confirmed the successful impregnation and uniform distribution of metal particles on the TiO₂ surface. Compared to undoped TiO₂, Mo-TiO₂ and W-TiO₂ exhibited a lower energy gap. Further incorporation of Mo-TiO₂ with Co or Cu introduced slight changes in energy gap and light absorption characteristics, particularly visible light absorption. In addition, photoluminescence (PL) showed that Cu-Mo-TiO₂ has a weaker PL intensity than undoped TiO₂. Thus, Cu-Mo-TiO₂ showed better catalytic activity than pure TiO₂, achieving complete degradation of 4-tert-butylphenol under UV light irradiation after 60 min. The application of Cu-Mo-TiO₂ under solar light conditions was also tested, and 70% of 4-tert-butylphenol degradation was achieved within 150 min.

Oxidation of Sulfamethoxazole by Rice Husk Biochar-Activated Persulfate

In the present study, biochars from rice husk were synthesized via pyrolysis at 400, 550, 700 and 850 °C for 1 h under a limited O2 atmosphere, characterized with a various techniques of and used as catalysts to activate persulfate and to degrade sulfamethoxazole (SMX). After physicochemical characterization of biochars. SMX degradation tests were performed using different water matrices, persulfate biochar and SMX concentrations and different initial pH solutions. Also, spiked solutions with bicarbonate, chloride, calcium nitrate, humic acid or alcohols were tested. It was found that catalytic reactivity rises with the pyrolysis temperature. Biochar is crucial for the oxidation of SMX and it can be described with a pseudo first–order kinetic model. Real matrices hinder the oxidation process, in waste water the SMX removal is 41% in 90 min, comparable with the inhibition obtained with spiked with bicarbonates solution (52% removal within 90 min) while complete removal can be achieved in ultrapure water matrices. The presence of alcohol slightly inhibits degradation contrary to the addition of sodium azide which causes significant inhibition, this is an evidence that degradation either under electron transfer/singlet oxygen control or dominated by surface-bound radicals.

The Influence of Preparation Method on the Physicochemical Characteristics and Catalytic Activity of Co/TiO2 Catalysts

Two Co/TiO2 catalysts with 7% CoO/g loading were prepared using equilibrium deposition filtration and the dry impregnation method. The two catalysts were characterized with various physicochemical techniques and tested for the degradation of sulfamethaxazole (SMX) using sodium persulfate (SPS) as the oxidant. It was found that the two catalysts exhibit different physicochemical characteristics. The equilibrium deposition filtration (EDF) catalyst had a higher dispersion of cobalt phase, more easily reduced Co(III) species, and a higher ratio of Co(III)/Co(II) species. The interactions between Co-deposited species and the titania surface were monitored with diffuse reflectance spectroscopy in all the preparation steps, and it was found that they increased during drying and calcination, while EDF favored the formation of surface species with strong interactions with the support. Finally, the EDF catalyst was more active for the degradation of sulfamethaxazole due to its better physicochemical characteristics.

The effect of chelating anions on the retention of Co(II) by γ-alumina from aqueous solutions under the unadjusted pH condition of supported catalyst preparation

This study analyzes the effect of the addition of acetate, citrate, and nitrilotriacetate anions on the retention of Co(II) cations by the γ-alumina surface in view of the preparation of alumina supported cobalt catalysts. The emphasis was placed on the way the Co(II) species attach to the solid surface when adsorbed from aqueous solutions under the unadjusted pH condition. The individual adsorption isotherms onto γ-Al₂O₃ support for cobalt and a given ligand were determined by following the solution depletion method in single-solute and bi-solute systems. These adsorption data were supplemented by the results of potentiometric titrations. In the case of bi-solute systems, the adsorption procedures allowed either co-impregnation of γ-alumina with equimolar solutions of cobalt and ligand salts or pre-impregnation of γ-alumina with the ligand anions and the subsequent adsorption of cobalt. Changes in the pH of the equilibrium solid-liquid suspension were also monitored along the adsorption isotherms. The adsorption of Co(II) onto γ-Al₂O₃ in the presence of acetate and nitrilotriacetate led to the formation of the type A (i.e., solid-metal-ligand) ternary complexes. The use of citrate anions together with Co(II) cations was shown to improve the impregnation process through the formation of ternary complexes of type B (i.e., solid-ligand-metal). The comparison with a system containing tricarballylate anions allowed concluding that the presence of the hydroxyl group in the citrate anion enhanced its affinity for the alumina surface by contributing to the inner-sphere character of its surface-bound complexes.

Eigen kinetics in surface complexation of aqueous metal ions

The mechanism of chemisorption of aqueous metal ions at surfaces has long been a topical issue in such fields as soil chemistry and bioenvironmental science. Here it is quantitatively demonstrated for the first time that release of water from the inner hydration shell is the rate-limiting step in inner-sphere surface complexation. The reactive intermediate is an outer-sphere complex between metal ion and surface site, with an electrostatically controlled stability defined by Boltzmann statistics. Using tabulated dehydration rate constants for metal ions, the resulting scheme allows for prediction of rates of sorption of aqueous metal ions at any type of complexing surface.

The influence of the preparation method and the Co loading on the structure and activity of cobalt oxide/γ-alumina catalysts for NO reduction by propene

In the present work we studied the influence of the preparation method and the Co loading on the physicochemical properties and the catalytic activity of the cobalt oxide/gamma-alumina catalysts for the reduction of NO by propene under net oxidizing conditions. Two series of catalysts containing 1 and 5% w/w Co, respectively, were prepared using three preparation methods, namely, the equilibrium deposition filtration (EDF), the conventional incipient wetness impregnation (IWI) and the IWI adding nitrilotriacetic acid (nta) in the impregnating solution (IWInta). The catalysts were tested at various temperatures in the range 300-550 degrees C using a fixed-bed microreactor for the NO reduction by propene under lean burn conditions. The evolution of the Co species on the alumina surface was followed after each preparation step by diffuse reflectance spectroscopy (DRS). It was found that the catalysts of the first series were more active for the title reaction than those of the second one. The EDF sample of the first series was proved to be the most active and selective one followed by the IWI and then the IWInta sample of the same series. The DRS results indicated that the enhanced activity and selectivity of the EDF sample could be attributed to the increased concentration of isolated Co(II) inner sphere complexes of octahedral coordination, which are formed on the support surface by adsorption of the corresponding aqueous complexes, [Co(H2O)6]2+, being in the impregnating solution. These inner sphere complexes are transformed upon thermal treatment into a CoAl2O4 like phase with high dispersion. On the other hand, the [Co(H2O)6]2+(NO3)2- and [Co-nta]-.NH4+(or H+) and/or [Co-2nta]4+.4NH4+(or 4H+) complex salts, precipitated on the alumina surface upon drying in the cases of the IWI and IWInta samples, are transformed upon calcination into CoAl2O4 like phases with lower dispersion. All the samples of the second series promoted the propene combustion as well as the oxidation of NO and N2, used as carrier gas, to NO2. DRS results revealed that in all these samples cobalt(III) oxo species are formed in addition to the CoAl2O4 phase. These species are considered to be responsible for the enhancement of the rates of the oxidation reactions mentioned above.