Metwally Madkour

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.

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.

Au/ZnS and Ag/ZnS nanoheterostructures as regenerated nanophotocatalysts for photocatalytic degradation of organic dyes

Although several groups have reported the synthesis of ZnS quantum dots, only a few have developed methods to prepare potentially nontoxic, noble metal loaded ZnS QDs. In this study, we devised a gram scale, environmentally benign, room temperature, aqueous solution based method for the synthesis of renewable and eco-friendly, well dispersed ZnS quantum dots along with noble metal loaded ZnS QDs (loading amount 4 wt%). The properties of the nanophotocatalysts were determined by using XRD, XPS, TEM and SEM techniques. The ZnS QDs were found to have small sizes of ca. 4.5 nm and to display quantum effects in terms of blue shifts in their absorption maxima associated with an optical band gap, Eg, of 4.63 eV. The photocatalytic activities of ZnS QDs, Au/ZnS and Ag/ZnS were assessed using photodegradation of methylene blue. The results demonstrate that a significant increase in the photocatalytic efficiency takes place upon the loading of Ag and Au nanoparticles on ZnS QDs. An in-depth investigation was carried out to uncover information about the effects of noble metals on band gap energies and surface charges of the QDs. Finally, a new surface reactivation procedure was developed for the reactivation of nanophotocatalysts. Consequently, the newly synthesized photocatalysts are renewable, a property that should make their use in practical applications cost effective.

Hydrothermally modified PVA/ZnS-NCQD nanocoating for stainless steel corrosion protection in saline water

Herein, we report a facile method for the fabrication of a hydrothermally modified well shaped nanocubed ZnS quantum dot (NCQD)/polyvinyl alcohol nanocomposite. The prepared nanocomposite via this method was characterized using various techniques such as field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and atomic force microscopy (AFM). For the first time, a thin film of the fabricated nanocomposite was coated on 316L stainless steel alloy by heat treatment. The corrosion protection efficiency of the PVA/ZnS-NCQD nanocomposite coating on stainless steel was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques in 3.5% NaCl solution. The corrosion protection of stainless steel was enhanced in the presence of the PVA/ZnS-NCQD nanocomposite coating which exhibited better corrosion resistance in saline water. The presence of ZnS-NCQDs increases the inhibition efficiency of PVA against the corrosion of stainless steel in chloride solution from 67.0% to 94.0%. The electrochemical corrosion parameters obtained from potentiodynamic polarization and EIS are in good agreement.

The effect of surface charge on photocatalytic degradation of methylene blue dye using chargeable titania nanoparticles

Herein, a simple approach based on tailoring the surface charge of nanoparticles, NPs, during the preparation to boost the electrostatic attraction between NPs and the organic pollutant was investigated. In this study, chargeable titania nanoparticles (TiΟ2 NPs) were synthesized via a hydrothermal route under different pH conditions (pH = 1.6, 7.0 and 10). The prepared TiΟ2 NPs were fully characterized via various techniques including; transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible spectroscopy (UV-Vis) and dynamic light scattering (DLS). The influence of the preparation pH on the particle size, surface area and band gap was investigated and showed pH-dependent behavior. The results revealed that upon increasing the pH value, the particle size decreases and lead to larger surface area with less particles agglomeration. Additionally, the effect of pH on the surface charge was monitored by XPS to determine the amount of hydroxyl groups on the TiO2 NPs surface. Furthermore, the photocatalytic activity of the prepared TiΟ2 NPs towards methylene blue (MB) photodegradation was manifested. The variation in the preparation pH affected the point of zero charge (pHPZC) of TiO2 NPs, subsequently, different photocatalytic activities based on electrostatic interactions were observed. The optimum efficiency obtained was 97% at a degradation rate of 0.018 min−1 using TiO2 NPs prepared at pH 10.

Non-noble, efficient catalyst of unsupported α-Cr 2 O 3 nanoparticles for low temperature CO Oxidation

Herein, we report the synthesis of chromium oxide nanoparticles, α -Cr2O3 NPs, followed by full characterization via XRD, SEM, XPS, and N2 sorptiometry. The synthesized nanoparticles were tested as catalysts toward the oxidation of CO. The impact of calcination temperature on the catalytic activity was also investigated. CO conversion (%), light-off temperature, T50, data were determined. The results revealed that chromia obtained at low calcination temperature (400 °C) is more active than those obtained at high calcination temperatures (600° or 800 °C) and this is ascribed to the smaller particle size and higher surface area of this sample. The results revealed a superior catalytic activity of Cr2O3 NPs at lower temperature as we reached a complete conversion at 200 °C which is high value in the forefront of the published results of other non-noble catalysts. The high activity of Cr2O3 nanoparticles (T50 as low as 98 °C) where found to be dependent on a careful selection of the calcination temperature. These results may provide effective and economic solutions to overcome one of the major environmental threats.

CeO 2 -CB nanocomposite as a novel SALDI substrate for enhancing the detection sensitivity of pharmaceutical drug molecules in beverage samples

SALDI-MS analysis of pharmaceutical drug molecules (amitriptyline, imipramine and promazine) using carbon-based substrates, namely, activated charcoal (AC), carbon nanotubes (CNTs), carbon black (CB), graphene (rGO), graphene oxide (GO) and graphite, was explored and compared with the conventional organic matrix of MALDI. CB exhibited superior performance with respect to the other substrates in terms of detection sensitivity. Despite the effectiveness of CB to detect all drug molecules, it demonstrated a number of background signals, which may be an issue for the analysis of other molecules in the future. Therefore, for the first time, a CeO2-CB nanocomposite was synthesized and applied as a novel SALDI substrate to minimize the background signals and stabilize CB when exposed to high laser power. The nanocomposite was characterized using XRD, TEM, FTIR, UV-Vis and N2 sorpometry. The spectrum obtained using the novel nanocomposite in the absence of the drug molecules showed minimal background signals compared to CB. Additionally, the CeO2-CB nanocomposite enhanced the detection sensitivity of the drug molecules with a limit of detection (LOD) of 100 ng/mL. This active substrate nanocomposite was further applied for the analysis of drug-spiked beverages without sample pretreatment or extraction, mimicking cases encountered by forensic toxicologists. All of the drugs and/or their adducts were detected in the drug-spiked beverage samples.

Organic nanoparticles of acetohydrazides as novel inhibitors for mild steel corrosion

Novel organic nanoparticles (ONPs) of (E)-2-(4-(hydrazonomethyl)phenoxyl) acetohydrazide (H2) and N′((E)-benzylidene)-2-(4-((E)hydrazonomethyl)phenoxyl)acetohydrazide (H3) were prepared by the re-precipitation method. The ONPs were characterized using MS, 1H-NMR, 13C-NMR, FT-IR, DLS, TEM and XRD. Both nanoparticles revealed a hemispherical shape with a particle size of 3.0 nm and 2.0 nm for H2 and H3 nanoparticles, respectively. The protective effect of the ONPs on mild steel in 1.0 M HCl was monitored by polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The obtained results revealed that the inhibition efficiency increased with an increase in inhibitor concentration. The maximum inhibition efficiencies at a constant concentration of 1 × 10−3 M were 88.2% and 96.7% for H2 and H3, respectively. The inhibition mechanism depended on the physical adsorption of the nanoparticles on the steel surface, which was confirmed by SEM, AFM and impedance results. These novel nanomaterials showed great anti-corrosion behavior and thus can be potentially used in industrial applications such as cooling water systems, pipes, and oil production units.

Nano-heterostructured photo-stable Cd x Zn 1−x S heterojunction as a non-photocorrosive visible light active photocatalyst

A novel hydrothermal approach for synthesizing CdS quantum dots (QDs) and nano-heterostructured CdS/ZnS QDs has been reported. This innovative approach proved to reproduce nanoparticles with extraordinary electronic and optical properties. The as-synthesized CdS and CdS/ZnS nano-heterostructured QDs were characterized by X-ray diffraction (XRD), UV-visible spectroscopy (UV-Vis), Transmission electron scanning (TEM), high resolution transmission electron scanning (HR-TEM), X-ray photoelectron scanning (XPS), and photoluminescence (PL) emission spectra. The average particle sizes of CdS and CdS/ZnS QDs as shown by XRD and TEM, were 4~6 nm. The optical band gap of CdS and ZnS/CdS nanoparticles was calculated from Tauc plot using UV-vis spectra. The estimated band gaps are measured to be 2.8 and 3.3 eV for CdS and CdS/ZnS QDs, respectively. The blue shift of the absorption edge compared to that of bulk clearly explained the quantum confinement effect. Such nano-hetrostructures of CdS/ZnS provided enhanced physical properties compared to individual CdS nanoparticles. The photocatalytic activity of the photo-stable CdS/ZnS was found to be superior towards the photodegradation of Methylene Blue, MB, dye than that of CdS QDs under visible light irradiation. The enhanced photodegradation mechanism of the nano-heterostructure was investigated and correlated with the optoelectronic properties.