Ayad F. Alkaim

Enhancing the photocatalytic activity of TiO2 by pH control: a case study for the degradation of EDTA

The photocatalytic degradation of EDTA has been investigated in detail under pH-controlled conditions employing the pH-stat technique. The results indicate that by holding the pH constant (i.e., at pH 5) during the experiment, the photocatalytic degradation rate is enhanced by ca. 50% as compared with measurements carried out under “free-floating” pH conditions, i.e., with the pH being adjusted to 5 at the beginning of the reaction. The higher photocatalytic activity at a constant pH of 5 is explained by the higher adsorptivity of EDTA on TiO2 at this pH as evinced from the dark adsorption measurements. Investigations carried out at different light intensities indicate that the rate of the photocatalytic EDTA degradation is proportional to the square root of the light intensity at moderate values becoming independent from the light intensity at higher values. The activation energies for the photocatalytic EDTA degradation and for its complete mineralization, respectively, have been determined to be 21.54 ± 1.4 kJ mol−1 and 16.4 ± 0.5 kJ mol−1, respectively, employing the Arrhenius data treatment. This difference is explained by the fact that the intermediates formed upon the photocatalytic EDTA degradation are less resistant against their photocatalytic mineralization than the parent molecule.

Preparation, structure and adsorption properties of synthesized multiwall carbon nanotubes for highly effective removal of maxilon blue dye

Multiwall carbon nanotubes (MWCNTs) have been hydrothermally prepared using polyethylene glycol as the carbon source. Herein, new MWCNTs composites with high adsorption capacity were prepared and applied as efficient adsorbents for adsorption of maxilon blue dye (GRL) from aqueous solution. The morphologies of the MWCNTs were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform-infrared (FT-IR) spectroscopy. The adsorption property of maxilon blue (GRL) from aqueous solution onto MWCNTs was studied as a function of mass dosage, pH of solution, initial dye concentration and temperature. The adsorption of GRL depends on the initial pH of the solution with maximum uptake occurring at about pH 10. The maximum adsorption capacity of prepared MWCNTs was 260.7mg/g. Langmuir, Freundlich and Temkin isotherms were applied to fit the experimental data. The Freundlich equilibrium isotherm fitted well the experimental data indicating the homogeneity of the adsorbent surface sites. Thermodynamics parameters were studied the changes in free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) during adsorption. It is noticeable that the adsorption of GRL dye onto MWCNTs was a spontaneous and endothermic process and indicates that the adsorption is favored at high temperature.

Effect of polar and movable (OH or NH2 groups) on the photocatalytic H2 production of alkyl-alkanolamine: a comparative study

The photocatalytic production of molecular hydrogen (H2) from aqueous solutions of alkyl-alkanolamines (triethanolamine (tri-EOA), diethanolamine (di-EOA), ethanolamine (EOA), ethylamine (EA) and ethanol over Pt-loaded commercial (Sachtleben Hombikat UV100) nanoparticle titanium dioxide photocatalysts was studied. These photocatalysts were characterized using X-ray diffraction, Brunauer−Emmett−Teller, field-emission scanning electron microscopy, atomic force microscopy and UV–vis diffuse reflectance spectroscopy techniques. Effect of pH and temperature on photocatalytic hydrogen production of alkyl-alkanolamines was investigated. It was found for all molecules under study that the amount of hydrogen produced at a constant illumination time is a function of pH and temperature. At all temperatures investigated the rate of hydrogen production at pH 9 followed the order tri-EOAethanolamine >> di-EOA ≈ EOA > ethanol > EA. From the values of the photocatalytic rate constants at various temperatures, the apparent activation energies were determined for the hydrogen production. The observed dependence of the reaction rate on solution temperature cannot be related to light-driven reaction steps, because the band-gap energy of the semiconductor is too high for thermal excitation to become significant in the temperature range investigated.

Synthesis, characterization, and photocatalytic activity of sonochemical/hydration–dehydration prepared ZnO rod-like architecture nano/microstructures assisted by a biotemplate

ABSTRACT ZnO nanoparticles of rod-like architecture have excellent potential to be used in wastewater treatment as a photocatalyst. They were synthesized by utilizing sonochemical/hydration- dehydration techniques using glutamine as a biotemplate. The effects of calcination temperatures, that is, 300°C, 500°C, and 700°C, on the crystallinity, optical properties, and photocatalytic activity of synthesized zinc oxide nanoparticles were investigated. X-ray diffraction (XRD) results indicated that all calcinated samples have a crystalline hexagonal wurtzite structure. Morphology and elemental compositions were investigated using field emission-scanning electron microscopy with energy-dispersive X-ray spectroscopy. The XRD and Fourier transform infrared (FTIR) spectra revealed that the samples were amorphous at 100°C; however, it changed into a crystalline structure amid the calcination process. Optical properties were determined using a UV-visible reflection spectrophotometer and showed abatement in the band gap with increasing annealing temperature. The progress of the photocatalytic degradation was monitored by a UV-visible spectrophotometer, while the mineralization ability was estimated by total organic carbon tests of ZnO-calcinated samples. The effect of various operational parameters the photocatalytic efficiency and rate of dye degradation was studied. High photocatalytic degradation of maxilon blue dye (GRL) was found at pH 6.3.

Sonochemical/hydration–dehydration synthesis of Pt–TiO2 NPs/decorated carbon nanotubes with enhanced photocatalytic hydrogen production activity

Modified Pt-TiO2 NPs/decorated carbon nanotubes were synthesized utilizing sonochemical/hydration-dehydration techniques. Pt was loaded on TiO2 by a photodeposition method keeping in mind the end goal to achieve electron-hole pair separation and promote the surface reaction. The morphological and basic properties of Pt-TiO2/fCNTs were investigated by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) and Raman spectroscopy. The selected area electron diffraction (SAED) patterns of Pt-TiO2/fCNTs were obtained utilizing TEM-based energy dispersive X-ray spectroscopy (EDXS) analysis. It was found that the TiO2 nanoparticles were uniformly distributed on the fCNTs, and the Pt particles were decorated on the surface of TiO2/fCNTs. The photocatalytic hydrogen production activity of the Pt(0.5%)-TiO2/fCNTs(0.5%) nanoparticle composites was investigated using a sacrificial agent methanol solution. Pt-loaded TiO2 demonstrated a hydrogen evolution rate around 20 times that of TiO2/fCNTs(0.5%) (fSWCNTs, fMWCNTs). When compared with platinized TiO2 in methanol, which was utilized as a control material, Pt-TiO2/fCNTs demonstrated an almost 2-fold increment in hydrogen generation.

Photocatalytic hydrogen production from biomass-derived compounds: a case study of citric acid

ABSTRACT Highly crystalline anatase TiO2 nanoparticles with high BET surface area have been synthesized by thermal hydrolysis of titanium(IV) bis(ammoniumlactato) dihydroxide aqueous solutions. The photocatalytic H2 production from aqueous citric acid (CA) solutions over Pt-loaded TiO2 has been investigated under different experimental conditions, that is, different CA concentration, temperature, light intensity, and pH of Pt/TiO2 suspension. For comparison, the photocatalytic dehydrogenation of triethanolamine (TEA) has also been investigated. The highest H2 production rates were obtained at pH 3 and 9 for CA and TEA, respectively. This behavior is readily explained by the adsorption characteristic of the employed reagent on the surface of the charged TiO2. The effect of the photocatalyst loading and the light intensity on the H2 production rate showed the same behavior in the case of CA and TEA evincing that these parameters are catalyst dependent. The apparent activation energies have been determined to be 13.5 ± 1.8 and 14.7 ± 1.6 kJ mol−1 for CA and TEA, respectively, indicating the existence of an activation energy barrier in a photocatalytic process which can be attributed to the desorption of adsorbed products.

Investigation of photocatalytic removal and photonic efficiency of maxilon blue dye GRL in the presence of TiO2 nanoparticles

ABSTRACT TiO2 nanoparticles have been synthesized by solvent-free hydrothermal process. TiO2 nanoparticles were annealed at 500°C for enhancing the characterization and the photocatalytic activity. The synthesized TiO2 was characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), BET, and diffuse reflectance spectroscopy (UV-DR) techniques to study the morphology and structural configuration. The effects of different parameters such as the initial dye concentration, catalyst concentration, pH of the solution, light intensity, and reactive oxygen species (ROS) on relative photonic efficiencies and photocatalytic degradation kinetics of GRL were investigated, and the degradation of GRL follows pseudo-first order kinetics according to the Langmuir–Hinshelwood model. The ROS studies indicate that hydroxyl radicals and holes are the predominant reactive species within the same step, contributing up to 92.64%, hydroxyl radicals participate for about 55%, and holes share for about 37.64% in the photocatalytic degradation of GRL.