G Marcì

A survey of photocatalytic materials for environmental remediation

Heterogeneous photocatalysis is an advanced oxidation process which has been the subject of a huge amount of studies related to air cleaning and water purification. All these processes have been carried out mainly by using TiO(2)-based materials as the photocatalysts and ca. 75% of the articles published in the last 3 years is related to them. This review illustrates the efforts in the search of alternative photocatalysts that are not based on TiO(2), with some exceptions concerning particularly innovative modifications as nanoassembled TiO(2) or TiO(2) composites with active carbon, graphite and fullerene. Papers reporting preparation, characterization and testing of binary, ternary and quaternary compounds, have been reviewed. Despite many of these photocatalysts being effective for the photodecomposition of many pollutants, most of them do not allow a complete mineralization of the starting compounds, differently from TiO(2).

Environmentally sustainable production of cellulose-based superabsorbent hydrogels

The development of new products and materials, especially those which are non-petrolchemical reserves and based on renewable organic resources, using innovative sustainable processes is nowadays of increasing interest and deserves the attention of both academic and industrial research. Cellulose and its derivatives, as renewable organic resources, have been used to synthesize novel superabsorbent hydrogels. Although the production of cellulose is one of the causes connected to deforestation, the production of suitably engineered cellulose superabsorbent hydrogel materials has been proposed to preserve water in typically arid areas in the world. Paradoxically, divinylsulfone (DVS), a small di-functional highly toxic molecule, was used as a crosslinker for the preparation of the hydrogel. An environmentally sustainable heterogeneous TiO2 photo-catalysed process has been performed in order to achieve the detoxification (and a possible re-use) of washing waters deriving from the purification process carried out after the synthesis of a bio-degradable cellulose based superabsorbent hydrogel. The main species present in the washing water was DVS. DVS is a well known toxic agent and it was efficiently removed along with the unreacted polymers and oligomers by irradiating the washing waters in the presence of suspended polycrystalline TiO2. The photoprocess was studied not only by monitoring the total organic carbon (TOC) present in the solution but also by following the evolution of sulfate anions.

Photodegradation of lincomycin in aqueous solution

Aqueous solutions of lincomycin were irradiated with UV light in homogeneous and heterogeneous systems. Lincomycin disappeared in both systems but the presence of TiO2 noticeably accelerated the degradation of the antibiotic in comparison with direct photolysis. The rate of decomposition was dependent on the concentration of lincomycin and followed a pseudo-first-order kinetics. Photolysis involved only the oxidation of lincomycin without mineralization. Differently, the treatment with TiO2 and UV light resulted in a complete mineralization of the antibiotic. The degradation pathways involved S- and N-demethylation and propyldealkylation. The mineralization of the molecule led to the formation of sulfate, ammonium, and nitrate ions.

Ceria-zirconia nanostructured materials for catalytic applications: Textural characteristics and redox properties

Highly dispersed solid solutions of ceria-zirconia with nominal composition Ce0.6Zr0.4O2 were prepared by sol-gel technique and the influence of the gel aging time (1 day–3 weeks) on the morphological and textural properties of the materials was investigated. The samples were calcined at 923 K for 8 h, then characterized by XRD, BET surface area and pore size measurements by gas adsorption and by mercury porosimetry. DTA, TEM and SEM analyses were also carried out. The aging of the gel seems to have a remarkable influence on the morphology of the materials, whose surface area and porosity increase by increasing aging time. The phase composition of the solid solutions of ceria-zirconia, as determined by XRD analysis, seems to be independent from the synthetic procedure; in any case a cubic phase (space group Fm-3m) was identified as the main component. XRD and TEM characterizations show the presence of highly dispersed crystallites, with diameters in the range 60–80 Å. The redox properties and hydrogen chemisorption capacity have been studied by TPR/TPD/TPO experiments. Oxygen storage capacity measurements were carried out by a pulse technique, to determine the overall reducibility of the solid, OSCC (Oxygen storage capacity complete). OBC (Oxygen buffering capacity) measurement were also performed to determine the ability of the ceria-zirconia oxides to attenuate fast oscillations (0.1 Hz) of oxygen partial pressure. The correlation between textural, structural and redox properties of the oxides is discussed.

Synthesis of High-surface area CeO2 through silica xerogel template: influence of cerium salt precursor

Abstract Ceria nanosized oxides with high surface area were synthesized by means of a templating approach, using a porous silica xerogel with surface area as high as 718xa0m2/g. After impregnation of the silica template with the cerium salt solution and further calcination at 600xa0°C, the final ceria oxide was recovered by dissolving the silica framework in NaOH solution. The effect of cerium counteranion, nitrate or chloride, on the textural and reduction properties of the ceria oxide was examined. Characterizations by BET and pore size distribution, XRD, TPR and SEM/EDX techniques were performed. The silica xerogel templated approach resulted in the preparation of ceria with surface area of 205xa0m2/g and very small particle size (∼5xa0nm), when cerium chloride precursor was used. An enhanced reducibility, at temperature