Department of Chemistry

4,4'-(4,4'-Isopropylidenediphenoxy)bis(N-hydroxyphthalimide), which is a new lipophilic analogue of N-hydroxyphthalimide, can act as an effective catalyst in the aerobic oxidation of alkylaromatics under reduced amounts of polar cosolvent. The catalyst was selected on the basis of an in-depth study of the influence that substituents on the aromatic ring of N-hydroxyphthalimide exert on determining the NO-H bond dissociation energy (BDE). BDE values for a range of model molecules are calculated by DFT and measured by EPR spectroscopy. The new catalyst can be successfully employed in the aerobic oxidation of cumene, ethylbenzene, and cyclohexylbenzene, affording, in all cases, good conversions and high selectivity for the corresponding hydroperoxide. The effect of solvent, catalyst, and temperature has also been investigated.

A new class of lipophilic N-hydroxyphthalimides catalysts
designed for the aerobic oxidation of cumene in solvent-free
conditions were synthesized and tested. The specific strategy
proposed for the introduction of lipophilic tails on the NHPI moiety
leads to lipophilic catalysts which, while completely preserving the
activity of the precursor, allow to conduct the catalytic oxidation in
neat cumene for the very first time. The corresponding cumyl
hydroperoxide is obtained in good yields (28-52%) and high
selectivity (95-97%), under mild conditions. Importantly, the
presence of a polar solvent is no longer required to guarantee the
complete solubilization of the catalyst. On the other hand, the
oxidation conducted in neat cumene unearths the unexpected
necessity of using small amounts of acetonitrile in order to fully
promote the hydrogen atom transfer process and prevent the
catalyst from detrimental hydrogen bond (HB) driven aggregation.

N-hydroxyphthalimide (NHPI) is an organocatalyst for free-radical processes able to promote the aerobic oxidation of a wide range of organic substrates. In particular, NHPI can catalyze the hydroperoxidation of polyunsaturated fatty acids (PUFA). This property could be of interest for biological applications. This work reports the synthesis of two β-cyclodextrin derivatives (CD5 and CD6) having a different degree of methylation and bearing a NHPI moiety. These compounds, having different solubility in water, have been successfully tested for the hydroperoxidation of methyl linoleate, chosen as the PUFA model molecule.

N-hydroxyphthalimide (NHPI) is an organocatalyst for free-radical processes able to promote the aerobic oxidation of a wide range of organic substrates. In particular, NHPI can catalyze the hydroperoxidation of polyunsaturated fatty acids (PUFA). This property could be of interest for biological applications. This work reports the synthesis of two β-cyclodextrin derivatives (CD5 and CD6) having a different degree of methylation and bearing a NHPI moiety. These compounds, having different solubility in water, have been successfully tested for the hydroperoxidation of methyl linoleate, chosen as the PUFA model molecule.

The nanocomposite with polypyrrole (PPy) confined in ordered mesoporous silica SBA-15 channels was synthesized by in situ electropolymerization. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N 2 adsorption/desorption, and FT-IR studies indicated that the nanocomposite has the well-ordered hexagonal structures and PPy was in situ polymerized into the channels instead of the outer surface of SBA-15. Furthermore, the PPy/SBA-15 nanocomposite was used as an electrode modifier. We found that the nanocomposite-modified electrode exhibited good electrocatalytic activities for hydroquinone oxidation where PPy chains could facilitate the electron transfer between molecular sieves and electrode surface. Three dihydroxybenzene isomers (hydroquinone, catechol and resorcinol) have been successfully detected at PPy/SBA-15 modified electrode by preconcentration of the analyte.

The nanometer-size In 2 O 3 was synthesized via a reverse microemulsion. A new catalytic combustion-type In 2 O 3 -based H 2 gas sensor was developed based on the technology for fabricating the direct-heating-type sensor and a surface-modifying process. A dense SiO 2 layer near the surface of the sensor was formed by chemical vapor deposition (CVD) of hexamethyldisiloxane (HMDS). The SiO 2 layer, which acted as a molecular sieve, reduced the penetration of large molecular, such as C 2 H 5 OH, CH 4 , i-C 4 H 10 , into the sensing layer, resulting in the improvement of selectivity to H 2 . The sensitive properties and the working mechanism of the sensor were presented. The In 2 O 3 nanoparticles prepared by microemulsion were characterized by transmission electron microscopy and X-ray diffraction.

Hierarchical porous wood-templated ZnO has been successfully synthesized using Lauan and Fir woods as template through a simple hydrothermal bioinspired approach. The template type and calcination temperature in the preparation process have a large effect on the morphologies and porous structures of ZnO according to FESEM, TEM, mercury porosimetry and N 2 adsorption investigations. The gas sensing performances of wood-templated and non-templated ZnO were investigated using H 2 , CO, H 2 S, NH 3 , Formaldehyde, Methanol, Ethanol, Acetone, and Isobutene. The article studies the effects of wood template, calcination temperature, and working temperature of gas flow on the gas sensitivity and selectivity in detail. It is revealed that wood-templated ZnO has excellent sensitivity and selectivity to H 2 S due to inheritance of wood's hierarchical porous structure. The sensing response to H 2 S of Fir-templated ZnO is about 5.1 times higher than that of non-templated ZnO. Fir-templated ZnO calcined at 600 • C, has the best sensing properties including the highest gas sensing response, the highest selectivity coefficients of H 2 S and the shortest response and recovery time. The selective sensing mechanism has been discussed from some key aspects, such as gas properties, gas-solid reactions, grain size and hierarchical porous microstructures.

Nanosized ZnO powder was synthesized by using a chemical precipitation method, and loaded with different dopants through impregnation. The as-prepared ZnO powder was characterized by XRD and TEM. The characterization results show that the as-prepared sample is wurtzite polycrystalline ZnO, the mean grain size is 30-40 nm, and there are three types of adsorbed oxygen (O 2 − , O 2 2− , and O 2− ) on the surface of the sample. The as-prepared ZnO powder shows excellent gas responses to alcohol and acetaldehyde, but no response to ethene. The sensing mechanism of ZnO was further studied with the help of gas chromatography (GC) associated with a fixed-bed reactor. The studies show that acetaldehyde, carbon dioxide and water are the only oxidation products of C 2 H 5 OH over ZnO. The gas response to C 2 H 5 OH is strongly dependent on the conversion ratio of C 2 H 5 OH to acetaldehyde. In addition, among all the dopants tested, Ru is the optimal dopant which can increase the response to C 2 H 5 OH, but cannot increase the conversion ratio of C 2 H 5 OH to acetaldehyde. Thus we suggest that the gas sensing mechanism of ZnO to C 2 H 5 OH is the mode controlled by chemisorption of negatively charged oxygen, and the sensitizing role of Ru in the ZnO sensor belongs to the electronic sensitization mechanism.

Mesoporous SnO 2 is obtained through a simple hydrothermal process by using tin chloride as a raw material, urea as a pore-forming agent and pH regulator. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption measurements are employed to characterize the obtained mesoporous structures. The results show that the as synthesized material after calcination can be well indexed to tetragonal phase SnO 2 with a mesoporous structure. The sensing properties of the sensor based on mesoporous SnO 2 are investigated. The results reveal that the response to dilute Cl 2 gas of the materials is very high and fast. The short recovery time mainly attributes to the bigger pore size of mesoporous SnO 2 . Finally, the reaction mechanism is proposed.