Abdul Rahman Al-Arfaj

Catalytic cracking of polyethylene over all-silica MCM-41 molecular sieve

Abstract The catalytic cracking of high-density polyethylene has been demonstrated over all-silica MCM-41 catalysts. The cracking activity increases with the degree of crystallinity of the catalysts. The pore diameter of the samples has an effect on the level of the catalytic activity, with catalysts having small pore diameters giving higher activity. A carbenium ion-mediated mechanism is proposed for the cracking reaction, as high levels of isobutene and isobutane and low levels of C 1 and C 2 were produced. The product distribution was compared with those obtained from thermal cracking tests. The surface acidity of the all-silica MCM-41 is attributed to the presence of silanol groups. It is proposed that the formation and stabilization of carbenium ions in the pores of the catalyst are due to the adsorption interaction between the polyethylinic fragments with the surface of the channels.

Chemical characterization of sediments from the Gulf area after the 1991 oil spill

Sediment samples were collected during leg (II) of Mt Mitchell cruise in the Abu Ali area of the Gulf. These samples were subjected to trace metal analysis to determine the 1991 Gulf War oil spill environmental impact on the inundated Abu Ali area. The concentrations of barium, cadmium, cobalt, chromium, copper, manganese, nickel, lead, titanium, vanadium, and zinc were determined using an Inductively Coupled Plasma (ICP). The results are compared to baseline data previously collected on the Western Coast of the Gulf with special emphasis on the Abu Ali area. Higher trace metals concentrations are observed in heavily oiled sites than moderately oiled areas. Lowest concentrations were observed in benthic samples in areas of high currents.

Application of electro-enhanced solid-phase microextraction for determination of phthalate esters and bisphenol A in blood and seawater samples.

The electro-enhanced solid-phase microextraction (EE-SPME) method was developed for the determination of endocrine disruptor compounds such as phthalate esters and bisphenol A in human blood and seawater samples. After EE-SPME, samples were analyzed by gas chromatography-mass spectrometry (GC-MS). In this approach, commercial SPME fiber was used in direct-immersion mode with an applied potential to extract di-ethyl phthalate, di-butyl phthalate, benzyl butyl phthalate and bisphenol A. The applied potential facilitates and enhances the extraction efficiency of the target analytes. Various experimental conditions influencing performance of the EE-SPME such as extraction time, applied potential and ionic strength were optimized. Under the optimum conditions, EE-SPME was more efficient than a conventional SPME approach. Very good linearity was observed for all analytes in a range between 1 and 100 µg L(-1) with correlation of determination (R(2)) between 0.963 and 0.996. The limits of a detection based signal-to-noise of 3 were from 0.004 to 0.15 µg L(-1). The reproducibility of EE-SPME was evaluated and the relative standard deviations were between 1.0% and 5.0% (n=9). The proposed method was applied to human blood samples stored in transfusion bags and seawater. Results showed that the proposed EE-SPME was simple and suitable for trace level analysis.

Mixed-ligand complexes of copper(I) with heterocyclic thiones

SummaryNovel mixed-ligand copper(I) complexes of general formula [TPP−Cu−(L)Cl] or [TPPhos−Cu−(L)Cl], where TPP=triphenylphosphine, TPPhos=triphenylphosphate and L=imidazolidine-2-thione [Imt],N-propylimidazolidice-2-thione [PrImt],N-i-propylimidazolidine-2-thione [iPrImt], and 1,3-diazinine-2-thione [Diaz] and bis coniplexes of formula [(L)2CuCl] where L=[PrImt] and [iPrImt] have been prepared and characterized by electronic, vibrational and n.m.r. spectroscopy. The spectral data are consistent with S-donation of thiones. The magnitude of upfield shift in13Cn.m.r. of the thionreide carbon on complexation has been interpreted in terms of coordination geometry around the metal stoms. X-ray structure analysis agrees with the conclusions from the spectroscopic measurements. The structure of [(PrImt)2CuCl] revealed three-coordinated copper(I) with crystal data:a=14.106(4),b=14.380(2),c=19.024(3) A, β=108.8(2)°,z=8 and space group P2/c.

Efficient removal of phenol from water using Fe2O3 semiconductor catalyst under UV laser irradiation.

Efficient removal of phenol was carried out using laser induced photocatalyis process in the presence of Fe2O3 semiconductor catalysts, and under UV laser irradiation. Parametric dependence of the removal process was investigated carefully by variation of laser irradiation time, laser energy, and concentration of the catalysts. pH measurements were also carried out to understand the photocatalytic process for removal of phenol. Maximum phenol removal achieved in this process was more than 90% during 1 hour of laser irradiation. This is considered highly efficient as compared to conventional setups using lamps. Reaction kinetics for the removal of phenol was also studied, and a reaction rate of 0.017 min− 1 was estimated, following first order kinetics.

Determination of polycyclic aromatic hydrocarbons in water using nanoporous material prepared from waste avian egg shell

For the first time a biocompatible calcium carbonate vateritic polymorph was recrystallized from eggshell waste and its application for the extraction of polycyclic aromatic hydrocarbons in water samples was demonstrated. This nanoporous calcium carbonate was used as sorbent in dispersive micro-solid-phase extraction method. In this approach 50 mg of the calcium carbonate material having about 25 nm pores was placed in a 5mL of water sample and ultrasonicated for 30min. The cloudy sample was centrifuged at 13500 rpm for 2 min. The aqueous layer was then discarded and the CaCO3 material was dabbed dry with a lint-free tissue. The analytes were then desorbed with 100 µL of dichloromethane by ultrasonication for 5 min. Finally, the extract was analyzed by gas chromatography flame ionization detector. Experimental parameters affecting the extraction recoveries were optimized. Using optimum extraction conditions, calibration curves were linear with correlation coefficients of 0.9853 to 0.9973 over the concentration range of 0.05 to 30 ng/mL. This method showed a detection limit as low as 0.004 ng/mL (at signal-to-noise ratio of 3). Performance of the dispersive micro-solid-phase extraction was compared with a previously optimized solid-phase extraction technique. The developed method displayed good extraction recoveries (85 ± 8-110 ± 4%) with high enhancement factors (388- 1433-fold) and good repeatability (% RSD < 13) and involved the use of minimal solvents. Analysis of seawater from Dammam Port revealed the presence of the analytes at concentrations between 0.15 ± 0.01 and 13.43 ± 1.54 ng/mL.

Synthesis of multiwalled carbon nanotubes-titania nanomaterial for desulfurization of model fuel

This work reported on the development of novel nanomaterials of multiwalled carbon nanotubes doped with titania (CNT/TiO2) for the adsorptive desulfurization of model fuel oils. Various analytical techniques such as field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of the nanomaterials. The initial results indicated the effectiveness of the prepared CNT/TiO2 nanomaterials in removing sulfur compounds from model fuel oil. The adsorption of DBT, BT, and thiophene from model fuel onto the derived sorbents was performed using batch mode system. These CNT/TiO2 nanomaterials initially afforded approximately 45% removal of DBT, 55% BT, and more than 65% thiophene compounds from model fuels. The CNT/TiO2 nanomaterials provided an excellent activity towards interaction with organosulfur compounds. More experiments are underway to optimize the parameters for the adsorptive desulfurization processes. We believe that these nanomaterials as adsorbents will find useful applications in petroleum industry because of their operational simplicity, high efficiency, and high capacity.

Determination of phenoxy herbicides in water samples using phase transfer microextraction with simultaneous derivatization followed by GC-MS analysis.

A sensitive and accurate method for the determination of two model phenoxy herbicides, 4-chloro-2-methylphenoxy acetic acid and 4-chloro-2-methylphenoxy propanoic acid, in water is explained. This method utilizes a simple phase transfer catalyst-assisted microextraction with simultaneous derivatization. Factors affecting the performance of this method including pH of the aqueous matrix, temperature, extraction duration, type and amount of derivatization reagents, and type and amount of the phase transfer catalyst are examined. Derivatization and the use of phase transfer catalyst have proven to be especially vital for the resolution of the analytes and their sensitive determination, with an enrichment factor of 288-fold for catalyzed over noncatalyzed procedure. Good linearity ranging from 0.1 to 80 μg L(-1) with correlation of determination (r(2) ) between 0.9890 and 0.9945 were obtained. Previous reported detection limits are compared with our new current method. The low LOD for the two analytes (0.80 ng L(-1) for 4-chloro-2-methylphenoxy propanoic acid and 3.04 ng L(-1) for 4-chloro-2-methylphenoxy acetic acid) allow for the determination of low concentrations of these analytes in real samples. The absence of matrix effect was confirmed through relative recovery calculations. Application of the method to seawater and tap water samples was tested, but only 4-chloro-2-methylphenoxy propanoic acid at concentrations between 0.27 ± 0.01 and 0.84 ± 0.06 μg L(-1) was detected in seawater samples.

Acidity of All-Silica MCM-41—Studied by Laser Spectroscopy of Adsorbed Fluorescent Probe Compounds

The polarity within the channel environment of all-silica MCM-41 and the surface acidity were probed by the adsorption of rhodamine-B lactone (RhB-L) and 1-naphthylamine (NA) respectively. The photochemical properties of these probe compounds were studied by laser-induced fluorescence spectroscopy and compared with their properties in solution. The environment within the channels was found to be as polar as methanol. The fluorescence wavelength and decay rate have shown that when adsorbed on all-silica MCM-41, the lactone ring in RhB-L was opened to form the zwitterion (RhB-Z). It was not possible to assess whether RhB-L was protonated by the surface of MCM-41 because the fluorescence of both the RhB-Z and the cationic form RhB-C are almost identical. NA was protonated at the ground state on the surface of all-silica MCM-41. The proton, however, was donated back to the surface upon excitation with laser. From the pKa of the conjugate acid of NA and the fluorescence decay time of the excited state of NA (NA*), the acidity of the surface of the all-silica MCM-41 was estimated to be equivalent to an aqueous perchloric acid with pH 1.8–2.5, depending on the level of loading of NA. The origin of the acid surface was concluded to be the silanol groups known to be present on the surface. The nature of these groups and the influence of the polarity and the solvation effect of the framework on the acidity were discussed.

THE REDOX REACTION OF GOLD(I)-THIOMALATE IN THE PRESENCE OF SELENOUREA

Abstract The interaction of thiourea (TU) and selenourea (SeU) with aurothiomalate (Autm) has been studied by 13C NMR spectroscopy. At a 1:1 ratio of TU:Autm, TU binds to Autm forming a ternary TU-Au-tm complex. However, in the presence of SeU at various mol ratios, some of the thiomalate (Htm) was ejected from Autm as a free ligand, oxidized to tm2, and gold(I) was reduced to metallic gold. This redox reaction is observed only in the presence of SeU which may be acting as a catalyst.