Antonio Aronne

Origin and Electronic Features of Reactive Oxygen Species at Hybrid Zirconia-Acetylacetonate Interfaces

The hybrid sol-gel zirconia-acetylacetonate amorphous material (HSGZ) shows high catalytic activity in oxidative degradation reactions without light or thermal pretreatment. This peculiar HSGZ ability derives from the generation of highly reactive oxygen radical species (ROS) upon exposure to air at room conditions. We disclose the origin of such unique feature by combining EPR and DRUV measurements with first-principles calculations. The organic ligand acetylacetonate (acac) plays a pivotal role in generating and stabilizing the superoxide radical species at the HSGZ-air interfaces. Our results lead the path toward further development of HSGZ and related hybrid materials for ROS-based energy and environmental applications.

Electronic properties of TiO2-based materials characterized by high Ti3+ self-doping and low recombination rate of electron–hole pairs

Factors tuning the functional performances of the various TiO2-based materials in the wide range of their possible applications are poorly understood. Here the electronic structure of TiO2-based materials characterized by Ti3+ self-doping, obtained by a sol–gel route wholly performed in air at room temperature, is reported. In the amorphous hybrid TiO2–acetylacetonate (HSGT) material the formation of the Ti(IV)–acac complex makes it photoresponsive to visible light and allows us to obtain by means of a simple annealing in air at 400 °C a very stable black Ti3+ self-doped anatase TiO2 nanomaterial (HSGT-400), characterized by an extraordinary high concentration of Ti atoms with oxidation states lower than IV (about 26%), which absorbs light in the entire visible range. The very high stability of HSGT-400 is mainly related to the process, which does not require the use of harsh conditions nor external reducing agents. The electronic structure of HSGT, owing to the presence of the Ti(IV)–acac complex, allows the stabilization of superoxide anion radicals on its surface for a very long time (months) at room temperature. The extraordinary low recombination rate of electron–hole pairs gives to HSGT unusual catalytic performances at room temperature allowing the complete removal of 2,4-dichlorophenol from water in about one hour without any light irradiation. Our results clearly highlight the connection among the production process of TiO2-based materials, their electronic structure and, finally, their functional behaviour.

Hybrid TiO2–acetylacetonate amorphous gel-derived material with stably adsorbed superoxide radical active in oxidative degradation of organic pollutants

Hybrid sol–gel TiO2–acetylacetonate (HSGT) material has been synthesized via a sol–gel route. The as dried HSGT can be described as an amorphous polymeric network of titanium oxo-clusters on which surface part of Ti4+ ions are involved in strong complexation with acetylacetonate (acac) ligands. In this material a ligand-to-metal charge transfer (LMCT) is active giving light absorption in the visible region indicating a band gap of 2.5 eV, lower than crystalline TiO2. In the HSGT gel derived material the LMCT mechanism results much more active respect to ligands on crystalline nanoparticles. In presence of air, the acac ligands on the HSGT surface are able to generate and stabilize superoxide radical as resulting by EPR measurements. The ˙O2− radicals were stably adsorbed on the HSGT at room temperature for very long time. The presence of these free radicals makes HSGT material a useful catalyst in degradation of organic pollutants. Its catalytic activity has been tested in the oxidative degradation of phenanthrene resulting in a fast degradation rate in absence of any light irradiation.

Phosphorus stably bonded to a silica gel matrix through niobium bridges

For the first time niobium–phosphorus–silicon mixed oxide gels xNb2O5·xP2O5·(100 − 2x)SiO2, with x = 2.5 (2.5PNb), 5 (5PNb), 7.5 (7.5PNb) and 10 (10PNb), were synthesized at room temperature by an innovative sol–gel route from phosphoryl chloride, niobium chloride and tetraethoxysilane. Thermogravimetry/differential thermal analysis, X-ray diffraction, solid state 29Si and 31P NMR, Raman and Fourier transform infrared spectroscopy were used to examine the structure of dried and heat-treated (1 h at 500 °C) gels. The synthesis procedure developed in this work allowed obtaining, for each studied composition, transparent chemical gels by means of careful control of the precursor reactivity. Amorphous dried gels were obtained which were characterized by a very high degree of silicon cross-linking. Moreover, Si–O–Nb bridges were formed which allowed phosphorus to be anchored stably through Nb–O–P bonds within the gel. All heat-treated gels retain their amorphous nature with a high content of OH groups that are mainly linked to phosphorus, making them strong acidic solids.

Oxidative Degradation of Different Chlorinated Phenoxyalkanoic Acid Herbicides by a Hybrid ZrO2 Gel-Derived Catalyst without Light Irradiation

The oxidative degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA), 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB), 4-chlorophenoxyacetic acid (4-CPA) and 2,4-dichlorophenoxyacetic acid (2,4 D) by ZrO2-acetylacetonate hybrid catalyst (HSGZ) without light irradiation was assessed. The thermal stability of the catalyst was investigated by thermogravimetry, differential thermal analysis, and Fourier transform infrared spectroscopy. For each herbicide, a virtually complete removal in about 3 days without light irradiation at room temperature was achieved. The removal kinetics of the herbicides has been satisfactorily characterized by a double-stage physico-mathematical model, in the hypothesis that a first-order adsorption on HSGZ surface is followed by the herbicide degradation, catalytically driven by HSGZ surface groups. The long-term use of the HSGZ catalyst was assessed by repeated-batch tests. The specific cost for unit-volume removal of herbicide was evaluated by a detailed cost analysis showing that it is comparable with those pertaining to alternative methods.

Frozen Microemulsions for MAPLE Immobilization of Lipase

Candida rugosa lipase (CRL) was deposited by matrix assisted pulsed laser evaporation (MAPLE) in order to immobilize the enzyme with a preserved native conformation, which ensures its catalytic functionality. For this purpose, the composition of the MAPLE target was optimized by adding the oil phase pentane to a water solution of the amino acid 3-(3,4-dihydroxyphenyl)-2-methyl-l-alanine (m-DOPA), giving a target formed by a frozen water-lipase-pentane microemulsion. Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used to investigate the structure of MAPLE deposited lipase films. FTIR deconvolution of amide I band indicated a reduction of unfolding and aggregation, i.e., a better preserved lipase secondary structure in the sample deposited from the frozen microemulsion target. AFM images highlighted the absence of big aggregates on the surface of the sample. The functionality of the immobilized enzyme to promote transesterification was determined by thin layer chromatography, resulting in a modified specificity.