Significantly enhancement of sunlight photocatalytic performance of ZnO by doping with transition metal oxides.

In this study we report, the synthesis of ZnO and its doping with Transition Metal Oxides -TMO-, such as Cr2O3, MnO2, FeO, CoO, NiO, Cu2O and CuO. Various characterization techniques were employed to investigate the structural properties. The X-ray diffraction (XRD) data and Rietveld refinement confirmed the presence of TMO phases and that the ZnO structure was not affected by the doping with TMO which was corroborated using transmission Electron microscopy (TEM). Surface areas were low due to blockage of adsorption sites by particle aggregation. TMO doping concentration in the range of 3.7-5.1% was important to calculate the catalytic activity. The UV-Visible spectra showed the variation in the band gap of TMO/ZnO ranging from 3.45 to 2.46 eV. The surface catalyzed decomposition of H2O2 was used as the model reaction to examine the photocatalytic activity following the oxygen production and the systems were compared to bulk ZnO and commercial TiO2-degussa (Aeroxyde-P25). The results indicate that the introduction of TMO species increase significantly the photocatalytic activity. The sunlight photocatalytic performance in ZnO-doped was greater than bulk-ZnO and in the case of MnO2, CoO, Cu2O and CuO surpasses TiO2 (P25-Degussa). This report opens up a new pathway to the design of high-performance materials used in photocatalytic degradation under visible light irradiation.

Heterogeneous singlet oxygen generation: in-operando visible light EPR spectroscopy.

The use of photosensitizers immobilized on mesoporous materials to produce singlet oxygen (1O2) has opened a new way to synthetic and environmental applications due to the fast development of flow photochemistry and continuous-flow microreactors. 1O2-based photosensitized processes can be employed for the degradation of organic pollutants in an aqueous medium and the photosensitizer can be covalently attached to the support and separated from the effluent reducing the environmental impact. The aim of the present paper is to evaluate the 1O2 generation of Rose Bengal (RB) in homogeneous and heterogeneous systems using in-operando evaluation. Mesoporous SiO2 nanoparticles (MSNs) were successfully conjugated with RB (MSN-RB) and electron paramagnetic resonance (EPR) spectroscopy in combination with the spin trap TEMP was employed to obtain paramagnetic TEMPO via generated 1O2 when RB or MSN-RB are exposed to visible light. Additionally, EPR/DMPO was used to exclude the possible generation of other reactive oxygen species (ROS) by the functionalized nanoparticles. We found that in situ 1O2 generation was enhanced when the same amount of RB is immobilized inside of mesoporous SiO2.

Protoporphyrin IX-Functionalized AgSiO2 Core-Shell Nanoparticles: Plasmonic Enhancement of Fluorescence and Singlet Oxygen Production.

Metal-enhanced processes arising from the coupling of a dye with metallic nanoparticles (NPs) have been widely reported. However, few studies have simultaneously investigated these mechanisms from the viewpoint of dye fluorescence and photoactivity. Herein, protoporphyrin IX (PpIX) is grafted onto the surface of silver core silica shell NPs in order to investigate the effect of silver (Ag) localized surface plasmon resonance (LSPR) on PpIX fluorescence and PpIX singlet oxygen (1 O2 ) production. Using two Ag core sizes, we report a systematic study of these photophysical processes as a function of silica (SiO2 ) spacer thickness, LSPR band position and excitation wavelength. The excitation of Ag NP LSPR, which overlaps the PpIX absorption band, leads to the concomitant enhancement of PpIX fluorescence and 1 O2 production independently of the Ag core size, but in a more pronounced way for larger Ag cores. These enhancements result from the increase in the PpIX excitation rate through the LSPR excitation and decrease when the distance between PpIX and Ag NPs increases. A maximum fluorescence enhancement of up to 14-fold, together with an increase in photogenerated 1 O2 production of up to five times are obtained using 100 nm Ag cores coated with a 5 nm thick silica coating.

The range of validity of sorption kinetic models.

Several hundred papers are published yearly reporting liquid-phase adsorption kinetics data. In general the data is analyzed using a variety of standard models such as the pseudo first- and second-order models and the Intraparticle-Diffusion model. The validity of these models is often assessed empirically via their ability to fit the data, independently of their physicochemical soundness. The aim of the present paper is to rationalize the analysis of liquid-phase adsorption kinetics data, and to investigate experimental factors that influence the adsorption kinetics, in addition to the characteristics of the adsorbent material itself. For that purpose we use a simple Langmuir adsorption-diffusion model, which enables us to identify three dimensionless numbers that characterize the working regime of any batch adsorption experiment: an adsorption Thiele modulus, a saturation modulus, and a loading modulus. The standard models are found to be particular cases of the general adsorption-diffusion model for specific values of the dimensionless numbers. This provides sound physicochemical criteria for the validity of the models. Based on our modeling, we also propose a general yet simple data analysis procedure to practically estimate the diffusion coefficient in adsorbent pellets starting from adsorption half-times.

A one-step short-time synthesis of Ag@SiO2 core-shell nanoparticles.

A performance of shell-thickness precise control in silver-silica coating core-shell nanoparticles is presented. 60nm sized citrate-stabilized silver nanoparticles are directly silica coated using a modified Stöber process. Tetraethyl orthosilicate is used as a silica precursor and ammonium hydroxide as catalyst in an alcoholic solvent to promote the seeded silica growth. By simply varying the synthesis reaction time from 4 to 60min, the silica shell thickness is increased from 5.1nm to 76.4nm. This well-controlled synthesis is then transposed to 40, 80 and 100nm sized silver cores in order to show the independence of the silica shell growth on the nanoparticle core size. Optical properties, i.e. localized surface plasmon resonance, of the produced silver-silica core-shell are also investigated.