Ali Bumajdad

Understanding the superior photocatalytic activity of noble metals modified titania under UV and visible light irradiation.

Although TiO2 is one of the most efficient photocatalysts, with the highest stability and the lowest cost, there are drawbacks that hinder its practical applications like its wide band gap and high recombination rate of the charge carriers. Consequently, many efforts were directed toward enhancing the photocatalytic activity of TiO2 and extending its response to the visible region. To head off these attempts, modification of TiO2 with noble metal nanoparticles (NMNPs) received considerable attention due to their role in accelerating the transfer of photoexcited electrons from TiO2 and also due to the surface plasmon resonance which induces the photocatalytic activity of TiO2 under visible light irradiation. This insightful perspective is devoted to the vital role of TiO2 photocatalysis and its drawbacks that urged researchers to find solutions such as modification with NMNPs. In a coherent context, we discussed here the characteristics which qualify NMNPs to possess a great enhancement effect for TiO2 photocatalysis. Also we tried to understand the reasons behind this effect by means of photoluminescence (PL) and electron paramagnetic resonance (EPR) spectra, and Density Functional Theory (DFT) calculations. Then the mechanism of action of NMNPs upon deposition on TiO2 is presented. Finally we introduced a survey of the behaviour of these noble metal NPs on TiO2 based on the particle size and the loading amount.

Cerium oxide nanoparticles prepared in self-assembled systems

This review concerns recent research on the synthesis of cerium oxide (also known as ceria, CeO(2)) in colloidal dispersions media for obtaining high surface area catalyst materials. Nanoparticles as small as 5 nm and surface area as high as 250 m(2)/g can be readily prepared by this method. Both normal micelles and water-in-oil microemulsions have been employed to directly precipitate nanoceria or other cerium precursors which can be converted into ceria by calcination.

Preparation and characterization of Pd doped ceria-ZnO nanocomposite catalyst for methyl tert-butyl ether (MTBE) photodegradation.

A series of binary oxide catalysts (ceria-ZnO) were prepared and doped with different amounts of palladium in the range of 0.5%-1.5%. The prepared catalysts were characterized by SEM, TEM, XRD and XPS, as well as by N2 sorptiometry study. The XPS results confirmed the structure of the Pd CeO2-x-ZnO. The photocatalytic activity of these catalysts was evaluated for degradation of MTBE in water. These photocatalyst efficiently degrade a 100ppm aqueous solution of MTBE upon UV irradiation for 5h in the presence of 100mg of each of these photocatalysts. The removal of 99.6% of the MTBE was achieved with the ceria-ZnO catalyst doped with 1% Pd. In addition to the Pd loading, the N2 sorptiometry study introduced other factors that might affect the catalytic efficiency is the catalyst average pore sizes. The photoreaction was determined to be a first order reaction.

Mixing in cationic surfactant films studied by small-angle neutron scattering

Structure and composition of cationic surfactant films surrounding water nano-droplets in water-in-oil microemulsions has been studied by contrast variation small-angle neutron scattering (SANS). To arrive at a robust fit, and yield reliable values for structural parameters, the I(Q) curves for complementary contrasts were fitted simultaneously by a core–shell particle scattering law, as described before (J. Chem. Soc., FaradayTrans., 1996, 92, 65). The mass densities of solvents, and the surfactant layers in the microemulsions, were measured and used to calculate the scattering length densities ρ. Given known concentrations and scattering length densities, the fitted parameters were the water core radius Rc, the polydispersity p, the effective film thickness t and its scattering length density ρfilm. This latter value was used to probe the film compositions with two specific aims: (a) to ascertain the extent of alkane penetration into the curved monolayers, and (b) to measure the composition of a mixed surfactant layer. In the first case the surfactants were di-chain n-alkyl-n-dodecyldimethylammonium bromides (Cn–C12), with the first chain n C12 to C18. The effect of alkane structure, and molecular volume Vm, on the oil penetration was investigated with n-heptane (n-C7, Vm ≈ 240 A3 and cyclohexane (c-C6, Vm ≈ 180 A3). Apparently, heptane is essentially absent from the layers, but cyclohexane has a greater penetration, especially as the surfactant chain lengths become more unequal. The maximum mixing was for C18–C12, where the film contained approximately 8% by volume of cyclohexane. These results suggest that oil penetration is a subtle effect, which clearly depends on the chemical structures of both surfactant and oil. The findings for microemulsions are compared with related experiments on single chain cationic surfactants and n-dodecane at air/water interfaces (J. Phys. Chem., 1992, 96, 10971). This SANS contrast method was also applied to determine compositions of mixed surfactant films, containing blends of deuteriated di-dodecyldimethylammonium bromide (d-DDAB) and protonated n-dodecyltrimethylammonium bromide (h-DTAB). The fraction of h-DTAB in the layers, obtained either by model fitting for ρfilm, or using a model independent approximation based on the absolute SANS intensities, was consistent with ideal mixing in the interface. These results demonstrate the utility of SANS for investigating complex films at oil/water interfaces.

Characterization of iron hydroxide/oxide nanoparticles prepared in microemulsions stabilized with cationic/non-ionic surfactant mixtures

Iron oxide-hydroxide (α-Fe(2)O(3); Fe(OH)(3)) nanoparticles have been prepared by a microemulsion route using ammonia (NH(3)) solution or tetrabutylammonium hydroxide (TBAH) as precipitants. The iron oxide-hydroxide nanoparticles obtained were characterized by TGA, N(2) sorptiometry, XRD, IR, SEM, HR-TEM, and DLS techniques. Properties such as specific surface area (S(BET)), pore sizes and shapes, average particle size and distribution, crystallite structure, and thermal stability were determined. The properties of nanoparticles prepared using NH(3) and TBAH were compared after drying at 100°C and after being calcined in the temperature range 250-1100°C. It was found that the suspensions prepared using TBAH suffered immediate separation while those prepared using NH(3) resulted in very stable suspensions. Also, it was found that TBAH did not offer any advantage over NH(3) either in terms of specific surface area or in particle size of the prepared nanoparticles. Hence, the later part of the study was concentrated on the NH(3)-precipitated nanoparticles with particular emphasis on finding the most favorable, W (water-to-surfactant ratio) and/or surfactant concentration, S, to obtain the best conditions in terms of higher surface areas and narrower particle size distribution. It was found that the prepared suspension consisted of monodisperse nanoparticles (standard deviations <10%) and after separation and drying, high surface area powders were obtained. The highest surface area (315 m(2) g(-1)) was obtained when the smallest W (=20) and highest S (=0.20 mol L(-1)) were employed.

Sonochemical Synthesis and Properties of Nanoparticles of FeSbO4

A sonochemical method was employed to prepare reactive nanoparticles of FeSbO(4) at 300 °C, which is the lowest calcination temperature reported so far for preparing FeSbO(4). A systematic evolution of the FeSbO(4) phase formation as a function of temperature was monitored by in situ synchrotron X-ray measurements. The 300 and 450 °C calcined powders exhibited specific surface areas of 116 and 75 m(2)/g, respectively. The X-ray photoelectron spectra analysis confirmed the presence of mainly Fe(3+) and Sb(5+) in the calcined powder. The response of the fabricated sensors (using both 300 and 450 °C calcined powders) toward 1000 ppm and 1, 2, 4, and 8% hydrogen, respectively, has been monitored at various operating temperatures. The sensors fabricated using 300 °C calcined powder exhibited a response of 76% toward 4% H(2) gas at an operating temperature of 300 °C, while those fabricated using 450 °C calcined powder exhibited a higher response of 91% with a quick recovery toward 4% H(2) gas at 300 °C. The results confirmed that a higher calcination temperature was preferred to achieve better sensitivity and selectivity toward hydrogen in comparison to other reducing gases such as butane and methane. The experimental results confirmed that the sonochemical process can be easily used to prepare FeSbO(4) nanoparticles for various catalytic applications as demonstrated. Here, we project FeSbO(4) as a new class of material exhibiting high sensitivity toward a wide range of hydrogen gas. Such sensors that could detect high concentrations of hydrogen may find application in nuclear reactors where there will be a leakage of hydrogen.

Nanoparticles of antimony doped tin dioxide as a liquid petroleum gas sensor: effect of size on sensitivity

The gas sensitivity exhibited by nanoparticles of 1 wt% Pd catalysed antimony doped tin dioxide (ATO) prepared by a citrate-nitrate process is reported here. The reduction of particle size to <3 nm, a dimension smaller than double the thickness of the charge depletion layer, has resulted in an exceptionally high butane sensitivity and selectivity. The sensitivity and selectivity of ATO particles of different sizes unequivocally proved that reducing the size of particles to below twice the Debye length dimension produces materials with exceptionally high sensitivity and selectivity for sensor applications. The sensitivity of the samples towards 1000 ppm butane varied in the order 98%>55%>47%, for CNP>SP>CP samples having crystallite sizes of the order of 2.4 nm to 18 nm to 25 nm, respectively. The ATO nanoparticles exhibited not only a remarkable increase in gas sensitivity of around 98% towards 1000 ppm butane at 350 °C, but also a preferential selectivity to butane compared to other gases such as CO, CO2, SO2, CH4 and H2. In addition to the exceptionally high sensitivity and selectivity, the developed sensors also exhibited an improved response time and long term stability, which are of paramount importance for practical device development.

Inducing solid-state isolation of the phthalocyanine macrocycle by its incorporation within rigid, randomly shaped oligomers

The synthesis and properties of two non-planar and highly rigid pentamers containing four phthalocyanine units linked, via a spirocyclic fused ring system, to a central phthalocyanine or porphyrin core is described. It is shown that the rigidity of these novel oligomers, together with the large number of structural isomers of irregular shape induced by the presence of the four spiro-centres, inhibits efficient packing of the macrocycles in the solid state. Therefore, the UV–visible absorption spectrum of spin-coated films of these materials is almost identical to that obtained from the non-aggregated oligomers in dilute solution. Nitrogen adsorption measurements indicate a high surface area for one of the pentamers, which is consistent with some degree of microporosity.

The Efficient Photocatalytic Degradation of Methyl Tert-butyl Ether Under Pd/ZnO and Visible Light Irradiation

Methyl tert‐butyl ether is a commonly used fuel oxygenate that is present in gasoline. It was introduced to eliminate the use of leaded gasoline and to improve the octane quality because it aids in the complete combustion of fuel by supplying oxygen during the combustion process. Over the past decade, the use of MTBE has increased tremendously worldwide. For obvious reasons relating to accidental spillage, MTBE started to appear as an environmental and human health threat because of its nonbiodegradable nature and carcinogenic potential, respectively. In this work, MTBE was degraded with the help of an advanced oxidation process through the use of zinc oxide as a photocatalyst in the presence of visible light. A mixture of 200 mg of zinc oxide in 350 mL of 50 ppm MTBE aqueous solution was irradiated with visible light for a given time. The complete degradation of MTBE was recorded, and approximately 99% photocatalytic degradation of 100 ppm MTBE solution was observed. Additionally, the photoactivity of 1% Pd‐doped ZnO was tested under similar conditions to understand the effect of Pd doping on ZnO. Our results obtained under visible light irradiation are very promising, and they could be further explored for the degradation of several nondegradable environmental pollutants.

FT-IR and 1H NMR studies of the state of solubilized water in water-in-oil microemulsions stabilized by mixtures of single- and double-tailed cationic surfactants.

The structure of solubilized water in water-in-n-heptane aggregates stabilized by mixtures of single- and double-tail quaternary ammonium surfactants, namely didodecyldimethylammonium chloride/dodecyltrimethylammonium chloride (DDAC/DTAC) or didodecyldimethylammonium bromide/dodecyltrimethylammonium bromide (DDAB/DTAB) was studied by two noninvasive techniques, (1)H NMR and FT-IR. In the former, the chemical shift data, δ(obs), were used to calculate the so-called deuterium/protium fractionation factor, φ(M), of the aggregate-solubilized water and were found to be unity. In the FT-IR study, upon increasing water/surfactant molar ratio, W, the frequency, ν(OD), of the HOD species decreases, while its full width at half height and its area increase. The results obtained from both techniques indicate that the water appears to be present as a single nano-phase and the structure varies continuously as a result of increasing W. In addition, the effect of changing the counter-ion (Br(-) or Cl(-)) on (1)H NMR and FT-IR results was investigated. In spite of the known difference in the dissociation of these counter-ions from micellar aggregates, this was found not to affect the state of solubilized water. This report gives further insight into the contradictory scientific debates on the structure of water in the polar nano-cores of microemulsions.