Mokhtar Mohamed

Synthesis, characterization and catalytic properties of titania-silica catalysts

The preparation of titania doped (0.63–3.2 mmol g−1) silica (TiO2/SiO2) was described together with a mixed oxide sample (TiO2–SiO2) at a nominal molar ratio near to 1. These materials were thoroughly characterized by XRD, N2 adsorption at 76 K and ammonia adsorption measurements as well as FTIR spectroscopy. The activity of the materials towards 1-butene isomerization was also tested. FTIR results showed a band at 612 cm−1 attributed to bulk TiO2 phase, in the doped 3.2 mmol g−1 TiO2/SiO2 sample, that was paralleled to an exhibited perturbation for the SiO2 bands in the low frequency region, specifically those at 470 and 808 cm−1. The former band was similarly obtained in the TiO2–SiO2 sample, with a lower decrease in intensity, together with the appearance of a new band at 948 cm−1 attributed to Ti–O–Si linkages. This deed indicated the decrease in population of Ti–O–Ti bridges in the mixed oxide sample. FTIR spectra of adsorbed D2O established the presence of different types of titania hydroxyl groups (3615 and 3520 cm−1) that were composed during desorption of water from the titania surface. The activity towards 1-butene isomeriztion was found to increase gradually, in the doped samples, to achieve its maximum at the titania loading 3.2 mmol g−1, however, a tremendous decrease was obtained for the mixed oxide sample. This behavior was correlated with the acidity of the samples. The dependence of the reaction on either Ti–O–Ti or Ti–O–Si sites was evaluated and discussed.

Structural and acidic characteristics of Cu–Ni-modified acid-leached mordenites

Two series of dealuminated Na-mordenite zeolites (DML and DMH) were impregnated, in comparison with the parent nondealuminated NaMSP, in aqueous nitrate solutions of Cu and Ni to achieve varying loadings for both of the cations. These samples were characterized by N(2) adsorption, XRD, DSC of ammonia desorption, ammonia volumetric sorption, IR of ammonia adsorption, and FTIR-photoacoustic (FTIR-PAS) techniques. The FTIR-PAS spectrum of CuNi-loaded NaMSP shows a band at 935 cm(-1) ascribed to O(3)Siz.sbnd;Oz.sbnd;SiO(3) linkages produced as a result of dealumination caused by the synergistic effect of Cu and Ni cations under the preparation conditions. As a confirmation, this band was intensified upon acid dealumination (DML) where, at the extent of dealumination (DMH), collapsing of the zeolite structure was obtained subsequent to cation modification. In addition, the dealumination effect was markedly enhanced upon increasing the load of Cu in proportion to Ni. A total erosion of OH group characteristics of Siz.sbnd;(OH)z.sbnd;Al at 3610 cm(-1) was depicted when the Ni content exceed that of Cu where it did not show any change when the Cu content surpasses that of Ni. The amount of adsorbed ammonia measured volumetrically was enlarged after dealumination as well as after increasing the contents of the modificating cations. The IR study of ammonia adsorption revealed a band at 1428 cm(-1), in either nondealuminated or dealuminated-modified samples, assigned to stronger Bronsted acid sites than those at 1455 cm(-1). The band at 1428 cm(-1) was markedly enhanced in the latter samples than in the former. This was due in part to the replacement of the protons by cations, producing sufficiently mobile protons. In conformity, DeltaH values obtained for DSC effects via ammonia desorption were enhanced after dealumination. Other correlations with XRD and surface texturing on one hand and the structural variations following cations incorporation on the other hand are evaluated and discussed.

Mn3O4/graphene nanocomposites: outstanding performances as highly efficient photocatalysts and microwave absorbers

Mn3O4 (M) incorporated graphenes (G) synthesized by a deposition–solvothermal process, formed at various nominal weight percentages (G1M1, G3M1 and G1M3), were efficiently used for the photodegradation of methylene blue dye (MB) under visible light illumination (λ > 420 nm, 88 W, 20 ppm, 298 K) and under microwave irradiation (800 W, 2.45 GHz, 373 K). These materials were characterized using XRD, TEM-SAED, UV-Vis diffuse reflectance, N2 sorptiometry, FTIR and Raman techniques. Amongst the nanocomposites, G3M1 of polyhedral structure and an average domain equal to 10–12 nm has presented unique photo-degradation performance (100% degradation, 60 min, 0.0791 min−1 and TOC of 60%) exceeding the rest of the materials. This was mainly due to the extraordinary optical properties and to the strong interaction between Mn3O4 and graphene through which charge recombination is hampered. Based on the conduction and valence band edges together with the studied reactive species, it has been shown that ˙OH was the dominant species responsible for the MB degradation. Interestingly, the G3M1 nanocomposite has shown fascinating microwave absorption properties and is capable of degrading MB at a faster rate (0.287 min−1) than the one conducted via photocatalysis. Scavenger studies have shown that ˙OH and electrons were responsible for the excellent performance of the MB microwave degradation. The microwave results were discussed in view of the marked increase in dielectric constant (e−) and dielectric loss (e′′) in the studied frequency range of 1.0 Hz to 100 kHz, in addition to the electronic conductivity measurements. This work offers an exceptional approach for exploring high-performance microwave absorption as well as distinctive visible light photocatalytic reaction for organics degradation.

Gold loaded titanium dioxide–carbon nanotube composites as active photocatalysts for cyclohexane oxidation at ambient conditions

Photocatalytic oxidation of neat cyclohexane (CHA) with H2O2 as an oxidant was carried out using gold modified versions of several types of materials, including titania nanotubes (Au/TNT), reduced graphene oxide (Au/RGO) as well as titania nanotubes–multiwalled carbon nanotubes composite (Au/TNT–MWCNT) under UV irradiation (125 W, λ > 296 nm). The synthesized nanoparticles were characterized using physical adsorption of nitrogen, X-ray diffraction, transmission electron microscopy and ultraviolet-visible diffuse reflectance spectroscopy, and the reaction products were analyzed by GC-MS. Both Au/RGO and Au/TNT–MWCNT catalysts promoted partial CHA oxidation with higher conversion (6–9.0%) and selectivity (60–75%) for cyclohexanone, exceeding Au/TNT, TNT–MWCNT and TNT catalysts (conv. 2.1–4%, sel. 32–55%). Au/TNT–MWCNT synthesized using hydrothermal deposition methods exhibited the highest catalytic activity. This was chiefly attributable to the high surface hydrophobicity of MWCNT that accelerated CHA adsorption, bonding of cyclohexanol and cyclohexanone to TNT as well as decomposition of H2O2 on gold nanoparticles. Increasing the surface area as well as decreasing the average particle size of Au0 to 15 nm of hexagonal shape contributed to the superior catalytic activity of Au/TNT–MWCNT, in achieving an average rate of 0.0035 mmol−1 g−1 min−1 and conversion was 9.0% after 12 h of reaction. The latter catalyst exceeded industrially synthesized Co based catalysts (3.6%) operated at high temperatures. For confirming the autoxidation process, a radical scavenger offered a proof that the oxidation follows a radical-chain mechanism. The differences in surface morphology, light absorption and surface properties of Au/TNT when incorporated with MWCNT were well investigated. The photocatalytic oxidation mechanism elucidated using active scavengers suggested that OH˙ and O2˙− play key roles in the oxidation of CHA.

Determination of zinc and calcium in multigrade crankcase oils

Abstract Atomic absorption spectroscopy is used for the determination of zinc and calcium in multigrade crankcase oils. It has been found that zinc and calcium concentrations are subjected to matrix interferences from polymers incorporated in the oil formulations as viscosity index (VI) improvers. Results indicate that the two most important factors are concentration and chemical structure type for the following VI improvers: styrene-isoprene, styrene-butadiene, poly(alkylmethacrylate) and ethylene-propylene. Correlations between the zinc or calcium concentrations and either the concentration or the type of each VI improver are established via a regression analysis statistical technique. Acceptable models have been found with confidence higher than 99.5%.

Dispersed Ag2O/Ag on CNT-Graphene Composite: An Implication for Magnificent Photoreduction and Energy Storage Applications

A simple hydrothermal route assisted by a triblock copolymer was used to synthesize Ag2O/Ag nanoparticles on a robotic support consists of functionalized MWCNTs and graphene composite (Ag2O/Ag/CNT-graphene). The composites together with the individual analog of Ag/CNT and Ag/graphene were characterized by means of XRD, TEM-SAED, N2 sorptiometry, Raman, FTIR, UV-Vis, and photoluminescence spectroscopy. These nanomaterials were then tested for the catalytic reduction of 4-nitrophenol (4-NP) to the technologically beneficial 4-aminophenol (4-AP). The Ag2O@Ag@CNT-graphene composite calcined at 400°C has shown fascinating reduction performances for 4-NP either in the dark (k = 0.014 s−1) or under visible light illumination (k = 0.039 s−1) in the presence of 5 mM NaBH4 compared to Ag/CNT (0.0112 s−1) and Ag/graphene (0.010 s−1) catalysts. This was chiefly because Ag2O@Ag@CNT-graphene comprises the highest pore volume (0.49 cm3/g) and involves three types of pores in the margin from 1.8 to 4.0 nm in front of only one modal type of pores for the rest of the catalysts and thus maximizes the adsorptive capacity of the reactants (4-NP and NaBH4). Moreover, the former composite exhibits the highest concentration of the Ag2O component as established by numerous techniques in addition to the cyclic voltammetry, proposing its facile reaction with 4-NP along with the simultaneous transfer of surface hydrogen and electrons from NaBH4 ions to produce 4-AP. The promotion of the p-n junction evaluated using the Mott-schottky equation on Ag2O@Ag@CNT-graphene assisted by charges separation and surface plasmon resonance bands of Ag and Ag2O are found to be advantageous for 4-NP reduction. The latter composite delivers a specific capacitance of 355 F g−1 at 1.0 A g−1 exceeding those of Ag/CNT (230 F g−1) and Ag/graphene (185 F g−1). The EIS study establishes the high electronic conductivity of the metallic Ag and Ag2O moieties, low internal resistance of CNT-graphene as well as the marked ionic transfer facilitated by the composite porous nature.

Nitrogen Graphene: A New and Exciting Generation of Visible Light Driven Photocatalyst and Energy Storage Application

The synthesis of nitrogen, boron, and nitrogen–boron-codoped graphenes was attained via mixing solutions of GO with urea, boric acid, and a mixture of both, respectively, followed by drying in vacuum and annealing at 900 °C for 10 h. These materials were thoroughly characterized employing XRD, TEM, FTIR, Raman, UV–vis, XPS, IPCE%, and electrical conductivity measurements. The nitrogen-doped graphene (NG) showed an excellent supercapacitor performance with a higher specific capacitance (388 F·g–1 at 1 A·g–1), superior stability, and a higher power density of 0.260 kW kg–1. This was mainly due to the designated N types of doping and most importantly N–O bonds and to lowering charge transfer and equivalent series resistances. The NG also indicated the highest photocatalytic performance for methylene blue (MB 20 ppm, power = 160 W, λ > 420 nm) and phenol (5 ppm) degradation under visible light illumination with rate constants equal 0.013 min–1 and 0.04 min–1, respectively. The photodegradation mechanism was proposed via determining the energy band potentials using the Mott–Schottky measurements. This determined that photoactivity enhancement of the NG is accounted for by acquisition of nitrogen-oxy-carbide phases that shared in inducing a higher IPCE% (60%) and a lower band gap value (1.68 eV) compared to boron and nitrogen–boron-codoped graphenes. The achieved photodegradation mechanism relied on scavengers performance suggesting that •OH and electrons were the main reactive species responsible for the MB photodegradation.