Using the electron spin resonance to detect the functional centers in materials for sensor devices

AbstractThe paper reports and comments the results of several electron spin resonance investigations, performed on semiconductor oxides for gas sensing. The main aspects, related to the comparison between spectroscopic and electric data, are concerning on (i) the role of the oxide defects in interacting with the gas atmosphere; (ii) the origin of the sensing enhancement, which follows the doping of the oxide by transition metal ions; and (iii) the effects of different particle morphology and of the controlled particle shape on the sensing functionality. The electron spin resonance results have been associated, when possible, to those deriving from X-ray photoelectron spectroscopy, in order to investigate the electronic configuration of the transition metal centers. Special emphasis has been deserved to the oxide synthesis procedures, in several cases well related to the electrical response. The data have been drawn from several studies, performed in different time periods, and have been compared to suggest a possible common interpretation of the sensing mechanism, based on either electronic or morphological properties

Structure of Starch-Sepiolite Bio-Nanocomposites: Effect of Processing and Matrix-Filler Interactions

Sepiolite clay is a natural filler particularly suitable to be used with polysaccharide matrices (e.g., in starch-based bio-nanocomposites), increasing their attractiveness for a wide range of applications, such as packaging. Herein, the effect of the processing (i.e., starch gelatinization, addition of glycerol as plasticizer, casting to obtain films) and of the sepiolite filler amount on the microstructure of starch-based nanocomposites was investigated by SS-NMR (solid-state nuclear magnetic resonance), XRD (X-ray diffraction) and FTIR (Fourier-transform infrared) spectroscopy. Morphology, transparency and thermal stability were then assessed by SEM (scanning electron microscope), TGA (thermogravimetric analysis) and UV-visible spectroscopy. It was demonstrated that the processing method allowed to disrupt the rigid lattice structure of semicrystalline starch and thus obtain amorphous flexible films, with high transparency and good thermal resistance. Moreover, the microstructure of the bio-nanocomposites was found to intrinsically depend on complex interactions among sepiolite, glycerol and starch chains, which are also supposed to affect the final properties of the starch-sepiolite composite materials

Nonlinear Modelling of Kinetic Data Obtained from Photocatalytic Mineralisation of 2,4-Dichlorophenol on a Titanium Dioxide Membrane

Photomineralisation of 2,4-dichlorophenol (DCP) in aqueous solutions (10.0–100.0 mg/L of C) was systematically studied at 318±3 K, in an annular laboratory-scale reactor, by photocatalytic membranes immobilizing titanium dioxide, as a function of substrate concentration, and absorbed power per unit length of membrane. Kinetics of both substrate disappearance, to yield intermediates, and total organic carbon (TOC) disappearance, to yield carbon dioxide, were followed (first series of experiments). At a fixed value of irradiance (1.50 W⋅cm−1), other series of mineralization experiments were repeated (second series of experiments) by carrying out only analyses of chemical oxygen demand (COD), in order to compare modelling results of the two sets of experiments. In both sets of experiments, stoichiometric hydrogen peroxide was used as oxygen donor. For the first series of experiments, a kinetic model was employed, already validated in previous work, from which, by a set of differential equations, four final optimised parameters, k1 and K1, k2 and K2, were calculated. By these parameters, the whole kinetic profile could be fitted adequately. The influence of irradiance on k1 and k2 could be rationalised very well by this four-parameter kinetic model. Modelling of quantum yields, as a function of irradiance, could also be carried out satisfactorily. As has been found previously for other kinds of substrates, modelling of quantum yields for DCP mineralization is consistent with kinetics of hydroxyl radicals reacting between themselves, leading to hydrogen peroxide, other than with substrate or intermediates leading finally to carbon dioxide, paralleled by a second competition kinetics involving superoxide radical anion. For the second series of experiments, on the contrary, the Langmuir-Hinshelwood model was employed. Uncertainties of COD analyses, coupled with discrepancies of this model and with its inability to reproduce kinetics up to complete mineralization, are underlined

New insights into the sensing mechanism of shape controlled ZnO particles

The sensing behavior of pyramidal (PY), prismatic hexagonal (EP) and hexagonal rod-like (ER) ZnO micro and sub-microparticles, has been compared with that of commercial ZnO (ZnO®) particles having nanometric size and uneven shape. The performances have been firstly related to the predominance of specific crystal surfaces and then, more in depth, to the paramagnetic defects in ZnO (and), detected by Electron Spin Resonance (ESR), in order to associate the particles morphology with the defects amount and reactivity and, in turn, with a particular sensing mechanism. The results showed that the sensing behavior of ZnO® containing irregular nanoparticles is essentially related to the alternate formation and filling of oxygen vacancies during the gas pulse (oxygen vacancy mechanism), while that of ER and EP crystals does not seem to directly involve the defects. In particular, the sensing properties of shape controlled ZnO particles are mainly attributed to the ability of (0001) exposed surfaces in favoring a far better chemisorption of negatively charged oxygen species, then available for the reactions with the reducing gas (i.e. ionosorption mechanism). The outcomes and the approach adopted in this study may positively contribute to the debate still existing between the oxygen vacancy and ionosorption models by giving indications on the predominance of a specific sensing mechanism in shape controlled ZnO

Cooperative assembly synthesis of mesoporous SrTiO3 with enhanced photocatalytic properties

The synthesis of mesoporous SrTiO3 by using the cooperative assembly of metal chelate complexes and alkoxysilanes is here presented. The high affinity and intimate mixing between the two precursors fostered the formation, via polycondensation, of interpentrating organic and inorganic polymers. Hence, after calcination and removal of the siliceous phase, aggregates of mesoporous, polycrystalline SrTiO3 with interconnected pores of ca. 10 nm and surface areas as high as 240 m2 g 121 were obtained. Systems using different SrTiO3\u2006:\u2006SiO2 molar ratios were prepared to vary the porosity and microstructure. The templating action of the silica and its effect on the physicochemical properties of the final porous materials were addressed by a multi-technique approach. Finally, the activity of the bulk mesoporous SrTiO3 systems was exemplarily demonstrated by photodegradation tests of methylene blue under UV light. The dye conversion progressively increased with the content of silica template, proving the higher activity of the proposed mesoporous materials

Clavicle aseptic nonunion: is there a place for cortical allogenic strut graft?

: We investigated functional and radiological outcome in 57 cases of midshaft clavicle nonunion treated with open reduction and internal fixation with plate and screws over a 13 year-period. Intercalary bone graft was used in 42 patients; opposite autologous strut graft was used in 31 cases to provide mechanical support to the host bone. Patients were analysed using chart and radiological review and assessed with DASH questionnaire obtained at the latest follow-up. 37 patients were male while 20 were females, with a mean age of 35 years (63-17). All cases were of nonunion, 35 atrophic and 22 hypertrophic. The dominant side was injured in 32 cases and the non dominant in 25 cases. Primarily, 43 cases were treated conservatively with a figure of eight bandage. Time between fracture and our operative treatment was on average 44 months (13-72 months). Only those patients who were symptomatic were included in this study. We used straight reconstruction LCP and low profile precontoured plates. By reviewing patients charts all the cases but one of nonunion progressed to osseous healing at a mean time of 14 weeks (range 12-16). The patient with non-union refused further surgery. 49 patients were available for a final follow up. DASH score was 16.7 at an average of 42 months. Open surgery and internal fixation, using plate and screws in a compression construct is the treatment of choice for symptomatic clavicular non-unions. Intercalary autologous or allograft bone graft should be used especially in patient with significant bone loss; autologous cortical strut graft provides optimum mechanical stability, thus assuring optimal screw purchase and allowing immediate limb movement.We investigated functional and radiological outcome in 57 cases of midshaft clavicle nonunion treated with open reduction and internal fixation with plate and screws over a 13 year-period. Intercalary bone graft was used in 42 patients; opposite autologous strut graft was used in 31 cases to provide mechanical support to the host bone. Patients were analysed using chart and radiological review and assessed with DASH questionnaire obtained at the latest follow-up. 37 patients were male while 20 were females, with a mean age of 35 years (63–17). All cases were of nonunion, 35 atrophic and 22 hypertrophic. The dominant side was injured in 32 cases and the non dominant in 25 cases. Primarily, 43 cases were treated conservatively with a figure of eight bandage. Time between fracture and our operative treatment was on average 44 months (13–72 months). Only those patients who were symptomatic were included in this study. We used straight reconstruction LCP and low profile precontoured plates. By reviewing patients charts all the cases but one of nonunion progressed to osseous healing at a mean time of 14 weeks (range 12–16). The patient with non-union refused further surgery. 49 patients were available for a final follow up. DASH score was 16.7 at an average of 42 months. Open surgery and internal fixation, using plate and screws in a compression construct is the treatment of choice for symptomatic clavicular non-unions. Intercalary autologous or allograft bone graft should be used especially in patient with significant bone loss; autologous cortical strut graft provides optimum mechanical stability, thus assuring optimal screw purchase and allowing immediate limb movement

Efficient self-cleaning treatments for built heritage based on highly photo-active and well-dispersible TiO 2 nanocrystals

The present study reports on the preparation and characterization of innovative “self-cleaning” nano-TiO2 treatments to be used in cultural heritage, based on dispersion of solar-light activated TiO2 nanocrystals. The semiconductor has been prepared by an easy and low-cost non-aqueous procedure, providing anatase (NA_TiO2) nanoparticles photo-active not only under UV-light but also under solar irradiation. NA_TiO2 allows obtaining very stable dispersions either in water or in ethylene glycol used to produce homogeneous nano-TiO2 treatments on Noto stone and Carrara marble, which display excellent aesthetic compatibility, do not remarkably affect the capillary water absorption of the stones and slightly increase their wettability. The new treatment exhibits higher photocatalytic activity compared to that based on commercial TiO2 (P25_TiO2). This behavior has been attributed not only to the morphological properties of the treatments and of the stones, but also to the presence of residual benzyl alcohol molecules anchored on the anatase NP surfaces. This provides solar light absorption and partially improves the charge trapping, thus increasing the photoefficiency. The overall results suggest that the positive combination of high dispersion, solar-light absorption and reduced recombination effects in NPs plays a key role in the development of efficient photocatalytic treatments for stone restoration

Periprosthetic femoral re-fractures pathogenesis, classification, and surgical implications

Periprosthetic femoral re-fractures (PFRFs) represent an emerging challenge for orthopaedic surgeons, since their incidence is growing in the last years, but very few experiences about their management have been currently published. The present study aims to (1) introduce, for the first time, an etiologic classification for PRFRs and (2) to provide surgical and pharmacological tips for the correct management of these injuries. Periprosthetic femoral re-fractures (PFRFs) could be classified into traumatic-PFRFs (T-PFRFs) and pathological-PFRFs (P-PFRFs). T-PFRFs, i.e. the “true” periprosthetic re-fractures, present as new fracture lines occurring proximally or distally to a previous periprosthetic fracture, that has correctly healed. They are generally unpredictable injuries but, in selected cases, it is possible to predict them by analyzing the construct used in the treatment of the previous periprosthetic fracture. P-PFRFs, on the other hand, define re-fractures occurring on a previous periprosthetic non-union or delayed union: the new fracture line appears in the same district of the old one. According to the etiologic factors influencing the P-PFRFs pathogenesis, it is possible to define re-fractures caused by mechanical failures, biological failures, septic failures and multifactorial failures, i.e., a combination of the previously mentioned concerns. A successful postoperative outcome, following the surgical management of PFRFs, requires the correct identification of all the underlying causes, which should be promptly and appropriately managed

Elastomeric Compositions Comprising Silicate Fibres With Needle-Shaped Morphology Of Nanometric Size And Tyres For Vehicles That Comprise Them

The present invention regards a solid master elastomeric composition (masterbatch, MB) comprising silicate fibres with needle-shaped morphology of nanometric size, characterised by high fibre content and uniformity, a process advantageous for the preparation thereof and its use in manufacturing tyres for vehicles. Advantageously the present elastomeric composition allows minimising the drawbacks associated with the handling of the powdery fibres in the manufacturing of compounds for tyres, without altering the final performances thereof