Engineering Commercial TiO₂ Powder into Tailored Beads for Efficient Water Purification

In this study, efficient commercial photocatalyst (Degussa P25) nanoparticles were effectively dispersed and stabilized in alginate, a metal binding biopolymer. Taking advantage of alginate’s superior metal chelating properties, copper nanoparticle-decorated photocatalysts were developed after a pyrolytic or calcination-sintering procedure, yielding ceramic beads with enhanced photocatalytic and mechanical properties, excellent resistance to attrition, and optimized handling compared to powdered photocatalysts. The morphological and structural characteristics were studied using LN2 porosimetry, SEM, and XRD. The abatement of an organic pollutant (Methyl Orange, MO) was explored in the dark and under UV irradiation via batch experiments. The final properties of the photocatalytic beads were defined by both the synthesis procedure and the heat treatment conditions, allowing for their further optimization. It was found that the pyrolytic carbon residuals enabled the adhesion of the TiO2 nanoparticles, acting as binder, and increased the MO adsorption capacity, leading to increased local concentration in the photocatalyst vicinity. Well dispersed Cu nanoparticles were also found to enhance photocatalytic activity. The prepared photocatalysts exhibited increased MO adsorption capacity (up to 3.0 mg/g) and also high photocatalytic efficiency of about 50% MO removal from water solutions, reaching an overall MO rejection of about 80%, at short contact times (3 h). Finally, the prepared photocatalysts kept their efficiency for at least four successive photocatalytic cycles

A Green Route to Copper Loaded Silica Nanoparticles Using Hyperbranched Poly(Ethylene Imine) as a Biomimetic Template: Application in Heterogeneous Catalysis

Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and neutral pH, through a biomimetic silicification process. Furthermore, the derived hybrid organic/inorganic materials dispersed in water can be easily loaded with various copper amounts, due to the presence of PEI, which, despite having been integrated in the silica network, retains its strong copper chelating ability. Following calcination, the obtained copper loaded nanopowders are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption, Temperature programmed reduction (TPR) and UV-Vis diffuse reflectance (UV-Vis-DR) techniques and evaluated for automotive exhaust purification under simulated conditions at the stoichiometric point. Effective control over final materials’ pore structural and morphological characteristics is provided by employing different buffer solutions, i.e., tris(hydroxymethyl)aminomethane (Tris) or phosphate buffer. It was found that the enhancement of the nanopowders textural features, obtained in the presence of Tris buffer, had a great impact on the material’s catalytic behavior, improving significantly its activity towards pollutants oxidation

A green route to copper loaded silica nanoparticles using hyperbranched poly(ethylene imine) as a biomimetic template : application in heterogeneous catalysis

Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and neutral pH, through a biomimetic silicification process. Furthermore, the derived hybrid organic/inorganic materials dispersed in water can be easily loaded with various copper amounts, due to the presence of PEI, which, despite having been integrated in the silica network, retains its strong copper chelating ability. Following calcination, the obtained copper loaded nanopowders are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption, Temperature programmed reduction (TPR) and UV-Vis diffuse reflectance (UV-Vis-DR) techniques and evaluated for automotive exhaust purification under simulated conditions at the stoichiometric point. Effective control over final materials’ pore structural and morphological characteristics is provided by employing different buffer solutions, i.e., tris(hydroxymethyl)aminomethane (Tris) or phosphate buffer. It was found that the enhancement of the nanopowders textural features, obtained in the presence of Tris buffer, had a great impact on the material’s catalytic behavior, improving significantly its activity towards pollutants oxidation

Towards highly loaded and finely dispersed CuO catalysts via ADP : effect of the alumina support

To meet current economic demands enforcing the replacement of platinum-group metals, extensively used in three-way-catalytic converters (TWC), research is driven towards low-cost and widely available base metals. However, to cope with their lower activity, high metal loadings must be coupled with increased dispersion. Herein, a series of CuO/Al2O3 samples is produced and the effect of different alumina supports’ properties on CuO dispersion, speciation and eventually on the TWC performance is studied. The alumina samples are synthesized via different methods, including soft-templating routes and flame spray pyrolysis, and compared with a commercial one, while CuO used as the catalytic active phase is added through ammonia-driven deposition–precipitation. As found, the large surface area and low crystallinity of the aluminas produced by soft-templating routes favor strong metal–support interaction, generating highly dispersed and strongly bonded CuO species at low loading and copper-aluminate phases at high loading. Notably, the use of amorphous mesoporous alumina completely prevents the formation of crystalline CuO even at 15 wt% Cu. Such high metal loading and dispersion capacity without the application of elevated calcination temperatures is one of the best reported for nonreducible supports. Catalytic evaluation of this material reveals a pronounced enhancement of oxidation activity with metal loading increase

Towards Highly Loaded and Finely Dispersed CuO Catalysts via ADP: Effect of the Alumina Support

To meet current economic demands enforcing the replacement of platinum-group metals, extensively used in three-way-catalytic converters (TWC), research is driven towards low-cost and widely available base metals. However, to cope with their lower activity, high metal loadings must be coupled with increased dispersion. Herein, a series of CuO/Al2O3 samples is produced and the effect of different alumina supports’ properties on CuO dispersion, speciation and eventually on the TWC performance is studied. The alumina samples are synthesized via different methods, including soft-templating routes and flame spray pyrolysis, and compared with a commercial one, while CuO used as the catalytic active phase is added through ammonia-driven deposition–precipitation. As found, the large surface area and low crystallinity of the aluminas produced by soft-templating routes favor strong metal–support interaction, generating highly dispersed and strongly bonded CuO species at low loading and copper-aluminate phases at high loading. Notably, the use of amorphous mesoporous alumina completely prevents the formation of crystalline CuO even at 15 wt% Cu. Such high metal loading and dispersion capacity without the application of elevated calcination temperatures is one of the best reported for nonreducible supports. Catalytic evaluation of this material reveals a pronounced enhancement of oxidation activity with metal loading increase

Pore structure, interface properties and photocatalytic efficiency of hydration/dehydration derived TiO2/CNT composites

Manifold advantages are foreseen by using carbon nanotubes (CNTs) as support for inorganic TiO2 nanoparticles due to the unique texture/morphology and adsorption capacity of CNTs. Synergistic effects might also result from interfacial charge transfer between the CNTs and TiO2. Effective charge transfer has the potentiality to limit electron/hole recombination and shift the TiO2 photocatalytic response to the visible range. Homogeneous mixing and intimate contact between the graphitic and TiO2 surfaces are of high importance in order to trigger synergistic effects. Thus, the existence of complementary methods to shed light on both these features is of high importance when developing TiO2/CNT composite photocatalysts. In this work, a wide variety of TiO2/CNT composites was prepared by a simple hydration/dehydration procedure, using single-wall (SWCNTs) and multi-wall (MWCNTs) carbon nanotubes, either functionalized or not, and TiO2 nanoparticles of different size. To evaluate the degree of homogeneity between the graphitic and inorganic phases, a new methodology which was based on a complex interpretation of the liquid nitrogen porosimetry (LN2) isotherms of the composites and of each phase in the composite separately was developed. Furthermore, interface interaction characteristics were elucidated by micro-Raman spectroscopy while small-angle X-ray scattering (SAXS) measurements provided insight on the surface roughness and micropore structure of the TiO2/SWCNT samples. The Raman analysis concluded to the absence of any interfacial interaction. In this context the efficiency of the prepared composites to photocatalytically oxidize caffeine was evaluated in regard to their homogeneity, as derived by the LN2 method. As expected, in the absence of synergetic effects the photbcatalytic efficiency correlated well with the extent of mixing between the CNTs and TiO2 phases. The discrepancy observed for one of the samples was attributed to the existence of large micropores, a feature that was distinguishable solely by SAXS measurements