Adel A. Ismail

Mesoporous titania photocatalysts: preparation, characterization and reaction mechanisms

Titanium dioxide is a very important semiconductor with a high potential for applications in photocatalysis, solar cells, photochromism, sensoring, and various other areas of nanotechnology. Increasing attention has recently been focused on the simultaneous achievement of high bulk crystallinity and the formation of ordered mesoporous TiO2 frameworks with high thermal stability. Mesoporous TiO2 has continued to be highly active in photocatalytic applications because it is beneficial for promoting the diffusion of reactants and products, as well as for enhancing the photocatalytic activity by facilitating access to the reactive sites on the surface of photocatalyst. This steady progress has demonstrated that mesoporous TiO2 nanoparticles are playing and will continue to play an important role in the protection of the environment and in the search for renewable and clean energy technologies. This review focuses on the preparation and characterisation of mesoporous titania, noble metals nanoparticles, transition metal ions, non-metal/doped mesoporous titania networks. The photocatalytic activity of mesoporous titania materials upon visible and UV illumination will be reviewed, summarized and discussed, in particular, concerning the influence of preparation and solid-state properties of the materials. Reaction mechanisms that are being discussed to explain these effects will be presented and critically evaluated.

Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue)

Lanthanide ions (La(3+), Nd(3+), Sm(3+), Eu(3+), Gd(3+), and Yb(3+))/doped TiO2 nanoparticles were successfully synthesized by sol-gel method. Their photocatalytic activities were evaluated using Direct Blue dye (DB53) as a decomposition objective. The structural features of TiO2 and lanthanide ions/TiO2 were investigated by XRD, SEM, UV-diffuse reflectance, and nitrogen adsorption measurements. Our findings indicated that XRD data characteristic anatase phase reflections and also XRD analysis showed that lanthanides phase was not observed on Lanthanide ions/TiO2. The results indicated that Gd(3+)/TiO2 has the lowest bandgap and particle size and also the highest surface area and pore volume (V(p)) as well. Lanthanide ions can enhance the photocatalytic activity of TiO2 to some extent as compared with pure TiO2 and it was found that Gd(3+)/TiO2 is the most effective photocatalyst. The photocatalytic tests indicate that at the optimum conditions; illumination time 40 min, pH approximately 4, 0.3g/L photocatalyst loading and 100 ppm DB53; the dye removal efficiency was 100%. Details of the synthesis procedure and results of the characterization studies of the produced lanthanide ions/TiO2 are presented in this paper.

Catalytic reduction of p-nitrophenol over precious metals/highly ordered mesoporous silica

Precious metals, Au, Pt, and Pd, were successfully deposited on highly ordered mesoporous SBA-15. Two different reduction routes were employed to deposit precious metals: (1) under H2 and (2) using sodium citrate. Samples prepared using sodium citrate exhibit a uniform particle size of 10 nm while samples synthesized under H2 show high dispersion with a particle size of 8 and 20 nm for Pt and Pd, respectively. The surface area and pore volume of the mesoporous SBA-15 were significantly reduced due to the impregnation of the precious metals. Detailed TEM and XPS analyses reveal a uniform distribution of particles with a metallic valence state and no evidence of metallic oxides. The prepared catalysts were used to reduce p-nitrophenol (PNP) into p-aminophenol (PAP) where two trends were observed. The catalytic reduction efficiency for PNP reduction using the catalyst prepared with sodium citrate as a reducing agent is in the order of Au > Pt > Pd with a rate constant of 3.24 × 10−1 s−1 for Au/SBA-15. On the other hand, the catalyst prepared with H2 as a reducing agent showed a reverse trend Pd > Pt > Au with a rate constant of 7.15 × 10−1 s−1 for Pd/SBA-15. The highest catalyst efficiency was observed for the case of Pd/SBA-15 synthesized via the H2 route with a rate constant of 7.15 × 10−1 s−1. Also the reaction rate of Pd/SBA-15 synthesized via the H2 route was 2.2 times higher than that of Au/SBA-15 prepared using the sodium citrate route.

High performance sulfur, nitrogen and carbon doped mesoporous anatase–brookite TiO2 photocatalyst for the removal of microcystin-LR under visible light irradiation

Carbon, nitrogen and sulfur (C, N and S) doped mesoporous anatase-brookite nano-heterojunction titania photocatalysts have been synthesized through a simple sol-gel method in the presence of triblock copolymer Pluronic P123. XRD and Raman spectra revealed the formation of anatase and brookite mixed phases. XPS spectra indicated the presence of C, N and S dopants. The TEM images demonstrated the formation of almost monodisperse titania nanoparticles with particle sizes of approximately 10nm. N2 isotherm measurements confirmed that both doped and undoped titania anatase-brookite materials have mesoporous structure. The photocatalytic degradation of the cyanotoxin microcystin-LR (MC-LR) has been investigated using these novel nanomaterials under visible light illumination. The photocatalytic efficiency of the mesoporous titania anatase-brookite photocatalyst dramatically increased with the addition of the C, N and S non-metal, achieving complete degradation (∼ 100 %) of MC-LR. The results demonstrate the advantages of the synthetic approach and the great potential of the visible light activated C, N, and S doped titania photocatalysts for the treatment of organic micropollutants in contaminated waters under visible light.

Mesoporous TiO2 nanostructures: a route to minimize Pt loading on titania photocatalysts for hydrogen production

Mesostructured TiO(2) nanocrystals have been prepared using Pluronic F127 as the structure-directing agent. Platinum nanoparticles at different contents (0.1-1.0 wt%) have been photochemically deposited onto the mesoporous TiO(2). TEM investigation of 0.2 wt% Pt/TiO(2) calcined at 450 °C reveals that the TiO(2) particles are quite uniform in size and shape with the particle sizes of TiO(2) and Pt being 10 and 3 nm, respectively. The photocatalytic activities of the Pt loaded TiO(2) have been assessed and compared with those of nonporous commercial Pt/TiO(2)-P25 by determining the rates and the photonic efficiencies of molecular hydrogen production from aqueous methanol solutions. The results show that the amount of hydrogen evolved on Pt/TiO(2)-450 at low Pt loading (0.2 wt%) is three times higher than that evolved on Pt/TiO(2)-P25 and twelve times higher than that evolved on Pt/TiO(2)-350. Despite the BET surface area of the TiO(2)-450 photocatalyst being 3.5 times higher than that of TiO(2)-P25, a 60% smaller amount of the Pt co-catalyst is required to obtain the optimum photocatalytic hydrogen production activity. The reduced Pt loading on the mesoporous TiO(2) will be important both from a commercial and an ecological point of view.

Highly sensitive and stable phenyl hydrazine chemical sensors based on CuO flower shapes and hollow spheres

Chemical sensors are needed to develop efficient sensing systems with high flexibility, and low capital cost for controlled recognition of analytes. Herein, we report a highly sensitive, low cost, simple chemical sensor based on flower shape and hollow sphere CuO. Following the precipitation process, FESEM images revealed that CuO nanosheets are grown in high density and organized in a proper manner to give a flower shape structure; however, following the hydrothermal method in the presence of urea, the cage like micro structures CuO hollow spheres have been discovered. XRD revealed that the grown CuO has a single-crystalline phase of a monoclinic system. The resistivity of CuO hollow spheres (1.93 × 106 Ω m) is ∼100 times higher than flower shape CuO (2.2 × 104 Ω m). The prepared CuO flower shapes and hollow spheres have been evaluated for the detection and quantification of phenyl hydrazine. The findings indicate that CuO hollow spheres and flowers exhibited good sensitivity (0.578 and 7.145 μA cm−2 mM−1) and a lower limit of detection (LOD = 2.4 mM) with a linear dynamic range (LDR) of 5.0 μM to 10.0 mM and rapid assessment of the reaction kinetics (in the order of seconds). The designed flower shape CuO sensing system is 12 times more sensitive than CuO hollow spheres. To the best of our knowledge, the measured sensitivity ∼ 7.145 μA cm−2 mM−1 of CuO flower shapes is found to be among the highest sensitivity values reported for phenyl hydrazine up to now.

Metal-Free Porphyrin-Sensitized Mesoporous Titania Films For Visible-Light Indoor Air Oxidation

Transparent cubic mesoporous TiO2 films coated on soda-lime glass have been developed. A metal free meso-tetrakis(4-sulfonatophenyl) porphyrin (TPPS) has been adsorbed on these TiO2 films from aqueous solutions. The results indicated that the obtained mesoporous TiO2 and 3D TPPS/TiO2 films are optically transparent and crack free (thickness ca. 200±20 nm). The introduction of the TPPS molecules has only a very small influence on the pore system and some limited pore blocking seems to occur. Transmission electron microscopy (TEM) images revealed that the adsorption of TPPS does not disrupt the meso order of TPPS/TiO2. The particle size of these TiO2 nanocrystals has been measured to be approximately 5-8 nm. TPPS/TiO2 photocatalysts, exhibiting regularly ordered mesopores, large surface area (ca. 102.5 cm(2) cm(-2)), and specific pore volume of about 0.1 mm(3) cm(-2), show improved light-harvesting efficiency as compared with other transparent TiO2 films. Employing the 3D TPPS/TiO2 photocatalyst, a quantum efficiency of 0.059 % has been obtained for the photodegradation of CH3CHO in the gas phase under visible-light illumination. Recycling tests demonstrated that the newly synthesized photocatalyst was quite stable during this gas-solid heterogeneous photocatalytic process because no significant decrease in photocatalytic activity was observed even after being used repetitively up to five times. Therefore, the newly synthesized transparent 3D TPPS/TiO2 photocatalysts can potentially be applied for low-cost air purification and self-cleaning applications.

Study of the Efficiency of UV and Visible-Light Photocatalytic Oxidation of Methanol on Mesoporous RuO2–TiO2 Nanocomposites

Mesoporous RuO(2)-TiO(2) nanocomposites at different RuO(2) concentrations (0-10 wt%) are prepared through a simple one-step sol-gel reaction of tetrabutyl orthotitanate with ruthenium(III) acetylacetonate in the presence of an F127 triblock copolymer as structure-directing agent. The thus-formed RuO(2)-TiO(2) network gels are calcined at 450 °C for 4 h leading to mesoporous RuO(2)-TiO(2) nanocomposites. The photocatalytic CH(3)OH oxidation to HCHO is chosen as the test reaction to examine the photocatalytic activity of the mesoporous RuO(2)-TiO(2) nanocomposites under UV and visible light. The photooxidation of CH(3)OH is substantially affected by the loading amount and the degree of dispersion of RuO(2) particles onto the TiO(2), which indicates the exclusive effect of the RuO(2) nanoparticles on this photocatalytic reaction under visible light. The measured photonic efficiency ξ=0.53% of 0.5 wt% RuO(2)-TiO(2) nanocomposite for CH(3)OH oxidation is maximal and the further increase of RuO(2) loading up to 10 wt% gradually decreases this value. The cause of the visible-light photocatalytic behavior is the incorporation of small amounts of Ru(4+) into the anatase lattice. On the other hand, under UV light, undoped TiO(2) shows a very good photonic efficiency, which is more than three times that for commercial photocatalyst, P-25 (Evonik-Degussa); however, addition of RuO(2) suppresses the photonic efficiency of TiO(2). The proposed reaction mechanism based on the observed behavior of RuO(2)-TiO(2) photocatalysts under UV and visible light is explored.

Ease synthesis of mesoporous WO3-TiO2 nanocomposites with enhanced photocatalytic performance for photodegradation of herbicide imazapyr under visible light and UV illumination.

Herein, we report the ease synthesis of mesoporous WO3-TiO2 nanocomposites at different WO3 contents (0-5wt%) together with their photocatalytic performance for the degradation of the imazapyr herbicide under visible light and UV illumination. XRD and Raman spectra indicated that the highly crystalline anatase TiO2 phase and monoclinic and triclinic of WO3 were formed. The mesoporous TiO2 exhibits large pore volumes of 0.267cm(3)g-1 and high surface areas of 180m(2)g(-1) but they become reduced to 0.221cm(3)g(-1) and 113m(2)g(-1), respectively upon WO3 incorporation, with tunable mesopore diameter in the range of 5-6.5nm. TEM images show WO3-TiO2 nanocomposites are quite uniform with 10-15nm of TiO2 and 5-10nm of WO3 sizes. Under UV illumination, the overall photocatalytic efficiency of the 3% WO3-TiO2 nanocomposite is 3.5 and 6.6 times higher than that of mesoporous TiO2 and commercial UV-100 photocatalyst, respectively. The 3% WO3-TiO2 nanocomposite is considered to be the optimum photocatalyst which is able to degrade completely (100% conversion) of imazapyr herbicide along 120min with high photonic efficiency ∼8%. While under visible light illumination, the 0.5% WO3-TiO2 nanocomposite is the optimum photocatalyst which achieves 46% photocatalytic efficiency.

A multi-pH-dependent, single optical mesosensor/captor design for toxic metals

The fabrication of low-cost, simple nanodesigns with sensing/capture functionality has been called into question by the toxicity and non-degradability of toxic metals, as well as the persistent threat they pose to human lives. In this study, a single, pH-dependent, mesocaptor/sensor was developed for the optical and selective removal of toxic ions from drinking water and physiological systems such as blood.