Azaindole grafted titanium dioxide for the photodegradation of pharmaceuticals under solar irradiation.

The application of metal-free organic molecules grafted titanium dioxide (TiO2) as photocatalysts for the degradation of pharmaceuticals under solar light has been scarcely studied. Herein, a novel photocatalyst was synthesized anchoring a bipolar electron-donor and -acceptor molecule based on azaindole derivative (AZA4) onto TiO2 aiming to improve the photoactivity under simulated solar irradiation. The TiO2-azaindole (TiO2-AZA4) was fully characterized, confirming that AZA4 was successfully grafted onto TiO2 and improving the light absorption. The grafted TiO2 was applied in the photodegradation of acetaminophen in water, showing a significantly better photocatalytic performance compared to that of pure TiO2 under both solar and visible irradiations. AZA4 grafting leads to the TiO2 band gap narrowing and favors the charge separation, thus improving the TiO2 photoactivity. The photocatalytic performance of TiO2-AZA4 was evaluated using different conditions such as photocatalyst dose or initial pH of the solution, and the radical species involved in the process were investigated. The high activity of TiO2-AZA4 was confirmed in the photodegradation of a mixture of pharmaceuticals, namely acetaminophen, ibuprofen, and antipyrine, further demonstrating its stability and catalytic performance in a novel continuous flow test under simulated solar irradiation, thus finding a new strategy to design solar-light driven photocatalysts for the degradation of pollutants in water.

Effect of Activating Agent on the Properties of TiO2/Activated Carbon Heterostructures for Solar Photocatalytic Degradation of Acetaminophen.

Several activated carbons (ACs) were prepared by chemical activation of lignin with different activating agents (FeCl3, ZnCl2, H3PO4 and KOH) and used for synthesizing TiO2/activated carbon heterostructures. These heterostructures were obtained by the combination of the activated carbons with a titania precursor using a solvothermal treatment. The synthesized materials were fully characterized (Wavelength-dispersive X-ray fluorescence (WDXRF), X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption-desorption, Fourier transform infrared (FTIR) and UV-visible diffuse reflectance spectra (UV-Vis DRS) and further used in the photodegradation of a target pharmaceutical compound (acetaminophen). All heterostructures were composed of anatase phase regardless of the activated carbon used, while the porous texture and surface chemistry depended on the chemical compound used to activate the lignin. Among all heterostructures studied, that obtained by FeCl3-activation yielded complete conversion of acetaminophen after 6 h of reaction under solar-simulated irradiation, also showing high conversion after successive cycles. Although the reaction rate was lower than the observed with bare TiO2, the heterostructure showed higher settling velocity, thus being considerably easier to recover from the reaction medium.

Silica-sepiolite nanoarchitectures.

Silica-sepiolite heterostructured materials have been prepared as novel nanoarchitectures by generation of SiO2 nanoparticles (NPs) on the surface of the sepiolite fibrous clay mineral. The synthetic approach implies the use of organo-sepiolites dispersed in isopropanol to which is incorporated a selected silicon alcoxysilane, such as tetramethoxysilane (TMOS), that then is slowly hydrolyzed to procure the formation of a viscous gel under ultrasound irradiation. Once the sol-gel reaction is achieved the intermediate silica-sepiolite organo-heterostructures can be submitted to a thermal treatment for the removal of the organic matter, which finally gives rise to the silica-sepiolite nanoarchitectures. Influence of different experimental variables, such as nature of both alkoxysilane precursor and organo-sepiolite as well as their relative ratio in the reaction media, in the characteristics of both intermediate silica-sepiolite organo-heterostructures and final nanoarchitectures has been explored. Both type of heterostructured materials have been characterized by means of diverse experimental techniques such as CHN chemical analysis, TG-DTA, XRD, FTIR, 29Si NMR, FE-SEM and TEM. Special attention has been devoted to the analysis of changes in the morphological and textural features of the SiO2-sepiolite samples before and after the thermal treatment carried out for removing the organic matter and consolidation of the silica network. This study describes the resulting nanoarchitectures as sepiolite microfibers covalently assembled to silica nanoparticles exhibiting specific surface areas ca. to 350 m2/g, practically without microporous contribution. Preliminary tests regarding the use of the SiO2-sepiolite nanoarchitectures as nanofillers in polymer nanocomposites have been also investigated in order to show one of their potential fields of application. Mechanical properties of epoxy resin nanocomposites have been determined and discussed considering the different nature of the external surface of the intermediate organo-heterostructures and the final inorganic nanoarchitectures.

Polymer-clay nanocomposites as precursors of nanostructured carbon materials for electrochemical devices: templating effect of clays.

The present work introduces a comparative study on the use of polymer nanocomposites containing clay minerals of different structure, such as montmorillonite and sepiolite as host solids for the templating synthesis of carbon-like materials from different organic precursors. Carbon-clay nanocomposites were obtained by polymerization of either acrylonitrile or sucrose previously inserted in the pores of the clay minerals, followed by their further thermal transformation in carbon-like compounds. Acid treatment of the resulting carbon-clay nanocomposites removes the inorganic templates giving carbon-like materials with different textural features. Polymer-clay, carbon-clay and carbon-like materials have been characterized by applying spectroscopic techniques as FTIR and in situ EIS (electrochemical impedance spectroscopy) and other structural, textural and analytical tools (chemical analysis, XRD, SEM-EDX, TEM-EDX, N2 adsorption isotherms,...). Electrochemical properties of these carbon-clay nanocomposites, as well as their templated carbonaceous materials and their use as electrode materials of different electrochemical devices such as rechargeable Li-batteries, supercapacitors and electrochemical sensors, are also discussed.