Fabrication of nitrogen doped TiO2/Fe2O3 nanostructures for photocatalytic oxidation of methanol based wastewater.

An important industrial process that often occurs on the surface of a heterogeneous catalyst using thermochemical or photochemical could help in the oxidation of methanol-based wastewater to formaldehyde. Titania-based photocatalysts have drawn a lot of interest from scientists because they are a reliable and affordable catalyst material for photocatalytic oxidation processes in the presence of light energy. In this study, a straight-forward hydrothermal method for producing n-TiO2@α-Fe2O3 composite photocatalysts and hematite (α-Fe2O3) nanocubes has been done. By adjusting the ratio of n-TiO2 in the prepared composite photocatalysts, the enhancing influence of the nitrogen-doped titania on the photocatalytic characteristics of the prepared materials was investigated. The prepared materials were thoroughly characterized using common physiochemical methods, such as transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), X-ray photoelectrons spectroscopy (XPS), physisorption (BET), and others, in order to learn more about the structure The results obtained showed that nitrogen-doped titania outperforms non-doped titania for methanol photooxidation. The addition of nitrogen-doped titania to their surfaces resulted in an even greater improvement in the photooxidation rates of the methanol coupled with hematite. The photooxidation of methanol in the aqueous solution to simulate its concentration in the wastewater has been occurred. After 3 h, the four weight percent of n-TiO2@α-Fe2O3 photocatalyst showed the highest rate of HCHO production.

Facile Microwave Synthesis of Hierarchical Porous Copper Oxide and Its Catalytic Activity and Kinetics for Carbon Monoxide Oxidation.

The synthesis of copper oxide (CuO)-based nanomaterials has received a tremendous deal of interest in recent years. Particularly, the design and development of novel CuO structures with improved physical and chemical properties have attracted immense attention, especially for catalysis applications. We report on a rational, rapid, and surfactant-free microwave synthesis (MWS) of hierarchical porous copper oxide (HP-CuO) with a three-dimensional (3D) sponge-like topology using an MWS reactor. The activity of the microwave (MW)-synthesized HP-CuO catalysts for carbon monoxide (CO) oxidation was studied and compared to CuO prepared by the conventional heating method (CHM). Results showed that HP-CuO catalysts prepared by MWS for 10 and 30 min surpassed the CuO catalyst prepared by CHM, exhibiting T 80 of 98 and 115 °C, respectively, as compared to 185 °C of CuO prepared by CHM (T80 is the temperature corresponding to 80% CO conversion). In addition, the MW-synthesized HP-CuO catalysts outperformed the CHM-synthesized CuO, achieving a 100% CO conversion at 150 °C compared to 240 °C in the case of CuO prepared by CHM. Interestingly, the HP-CuO catalyst expressed workable CO conversion kinetics with a reaction rate of c.a.35 µmol s-1 g-1 at 150 °C and apparent activation energy (E a) of 82 kJ mol-1. The HP-CuO catalyst showed excellent cycling and long-term stabilities for CO oxidation up to 4 cycles and 72 h on the stream, respectively. The enhanced catalytic activity and stability of the HP-CuO catalyst appear to result from the unique topological and structural features of HP-CuO, which were revealed by SEM, XRD, Raman, BET, TGA, XPS, and TPR techniques.

CO Oxidation at Near-Ambient Temperatures over TiO2-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO2 Morphology.

Significant improvement of the catalytic activity of palladium-based catalysts toward carbon monoxide (CO) oxidation reaction has been achieved through alloying and using different support materials. This work demonstrates the promoting effects of the nanointerface and the morphological features of the support on the CO oxidation reaction using a Pd-Cu/TiO2 catalyst. Pd-Cu catalysts supported on TiO2 were synthesized with wet chemical approaches and their catalytic activities for CO oxidation reaction were evaluated. The physicochemical properties of the prepared catalysts were studied using standard characterization tools including SEM, EDX, XRD, XPS, and Raman. The effects of the nanointerface between Pd and Cu and the morphology of the TiO2 support were investigated using three different-shaped TiO2 nanoparticles, namely spheres, nanotubes, and nanowires. The Pd catalysts that are modified through nanointerfacing with Cu and supported on TiO2 nanowires demonstrated the highest CO oxidation rates, reaching 100% CO conversion at temperature regime down to near-ambient temperatures of ~45 °C, compared to 70 °C and 150 °C in the case of pure Pd and pure Cu counterpart catalysts on the same support, respectively. The optimized Pd-Cu/TiO2 nanowires nanostructured system could serve as efficient and durable catalyst for CO oxidation at near-ambient temperature.

Spectroscopic and photostability study of water-soluble hypericin encapsulated with polyvinylpyrrolidone.

Hypericin has gained great attention as a powerful photosensitizing and fluorescent agent for photodynamic therapy (PDT) and fluorescence diagnosis (FD) of cancer. However, native hypericin is hydrophobic and nearly insoluble in aqueous media which hinders its photobiological activity. Herein, we demonstrate the encapsulation of hypericin and polyvinylpyrrolidone (hypericin@PVP) as an attractive class of water-soluble formula of hypericin with improved absorption and emission characteristics in water. The absorption and fluorescence properties of the water-soluble hypericin@PVP were studied at room temperature. Also, the photostability of the prepared hypericin@PVP was studied under visible light irradiation. The absorbance and emission measurements confirm the association and binding of hypericin and PVP with a binding constant (Kb) of 1.2 × 105 M-1. The interaction between hypericin and PVP in water could lead to the dissociation of aggregated hypericin into their monomeric state which is crucial for effective photobiological implementation in PDT and FD. Upon encapsulation with PVP, hypericin showed a significant increase in the fluorescence properties with an enhanced emission intensity of 300% at a PVP concentration of 1 × 10-4 M. Moreover, water-soluble hypericin@PVP demonstrated high photostability under visible light irradiation with an irradiance of 15 mW/cm2 and exposure time up to 150 min. This enhancement in the absorption, emission, and photostability of hypericin in water is related to the effects of encapsulation with PVP and the unique spectroscopic properties of the formulated hypericin@PVP.

Combustion Synthesis of Non-Precious CuO-CeO2 Nanocrystalline Catalysts with Enhanced Catalytic Activity for Methane Oxidation.

In this study, xCuO-CeO2 mixed oxide catalysts (Cu weight ratio x = 1.5, 3, 4.5, 6 and 15 wt.%) were prepared using solution combustion synthesis (SCS) and their catalytic activities towards the methane (CH4) oxidation reaction were studied. The combustion synthesis of the pure CeO2 and the CuO-CeO2 solid solution catalysts was performed using copper and/or cerium nitrate salt as an oxidizer and citric acid as a fuel. A variety of standard techniques, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were employed to reveal the microstructural, crystal, thermal and electronic properties that may affect the performance of CH4 oxidation. The CuO subphase was detected in the prepared solid solution and confirmed with XRD and Raman spectroscopy, as indicated by the XRD peaks at diffraction angles of 35.3° and 38.5° and the Ag Raman mode at 289 cm-1, which are characteristics of tenorite CuO. A profound influence of Cu content was evident, not only affecting the structural and electronic properties of the catalysts, but also the performance of catalysts in the CH4 oxidation. The presence of Cu in the CeO2 lattice obviously promoted its catalytic activity for CH4 catalytic oxidation. Among the prepared catalysts, the 6% CuO-CeO2 catalyst demonstrated the highest performance, with T50 = 502 °C and T80 = 556 °C, an activity that is associated with the availability of a fine porous structure and the enhanced surface area of this catalyst. The results demonstrate that nanocrystalline copper-ceria mixed oxide catalysts could serve as an inexpensive and active material for CH4 combustion.

Tailoring the reducibility and catalytic activity of CuO nanoparticles for low temperature CO oxidation.

Copper oxide (CuO) nanoparticles have received considerable interest as active and inexpensive catalysts for various gas-solid reactions. The CuO reducibility and surface reactivity are of crucial importance for the high catalytic activity. Herein, we demonstrate that the reducibility and stability of CuO nanoparticles can be controlled and tailored for the high catalytic activity of CO oxidation. The synthesized CuO nanoparticles possessed enhanced reducibility in CO atmosphere at lower reduction temperature of 126 °C compared to 284 °C for that of reference CuO particles. Moreover, the CuO catalysts with tailored reducibility demonstrated a reaction rate of 35 µmol s-1 g-1 and an apparent activation energy of 75 kJ mol-1. Furthermore, the tailored catalysts exhibited excellent long-term stability for CO oxidation for up to 48 h on stream. These readily-reducible CuO nanoparticles could serve as efficient, inexpensive and durable catalysts for CO oxidation at low temperatures.

Silver Nanoparticles-Decorated Titanium Oxynitride Nanotube Arrays for Enhanced Solar Fuel Generation.

We demonstrate, for the first time, the synthesis of highly ordered titanium oxynitride nanotube arrays sensitized with Ag nanoparticles (Ag/TiON) as an attractive class of materials for visible-light-driven water splitting. The nanostructure topology of TiO2, TiON and Ag/TiON was investigated using FESEM and TEM. The X-ray photoelectron spectroscopy (XPS) and the energy dispersive X-ray spectroscopy (EDS) analyses confirm the formation of the oxynitride structure. Upon their use to split water photoelectrochemically under AM 1.5 G illumination (100 mW/cm2, 0.1 M KOH), the titanium oxynitride nanotube array films showed significant increase in the photocurrent (6 mA/cm2) compared to the TiO2 nanotubes counterpart (0.15 mA/cm2). Moreover, decorating the TiON nanotubes with Ag nanoparticles (13 ± 2 nm in size) resulted in exceptionally high photocurrent reaching 14 mA/cm2 at 1.0 VSCE. This enhancement in the photocurrent is related to the synergistic effects of Ag decoration, nitrogen doping, and the unique structural properties of the fabricated nanotube arrays.

Ultrasmall gold nanoparticles anchored to graphene and enhanced photothermal effects by laser irradiation of gold nanostructures in graphene oxide solutions.

In this work we demonstrate the coupling of the photothermal effects of gold nanostructures of controlled size and shape with graphene oxide nanosheets dispersed in water. The enhanced photothermal effects can be tuned by controlling the shape and size of the gold nanostructures, which result in a remarkable increase in the heating efficiency of the laser-induced size reduction of gold nanostructures. The Raman spectra of the Au-graphene nanosheets provide direct evidence for the presence of more structural defects in the graphene lattice induced by laser irradiation of graphene oxide nanosheets in the presence of Au nanostructures. The large surface areas of the laser-reduced graphene oxide nanosheets with multiple defect sites and vacancies provide efficient nucleation sites for the ultrasmall gold nanoparticles with diameters of 2-4 nm to be anchored to the graphene surface. This defect filling mechanism decreases the mobility of the ultrasmall gold nanoparticles and, thus, stabilizes the particles against the Ostwald ripening process, which leads to a broad size distribution of the laser-size-reduced gold nanoparticles. The Au nanostructures/graphene oxide solutions and the ultrasmall gold-graphene nanocomposites are proposed as promising materials for photothermal therapy and for the efficient conversion of solar energy into usable heat for a variety of thermal, thermochemical, and thermomechanical applications.