Salasiah Endud

29Si MAS NMR, XRD and FESEM studies of rice husk silica for the synthesis of zeolites

We have used rice husk ash as a silica source for the synthesis of zeolites. Amorphous silica is a highly reactive silicon source, but not all silica which is amorphous to XRD is equally suitable. The local structure of amorphous silica was investigated by 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) and field emission scanning electron microscopy (FESEM) in order to optimize the process. The results show that amorphous silica extracted by physical combustion with controlled temperature contains only ∗Si(OSi)4 tetrahedral units and is the most reactive silica source in the synthesis of zeolite Y, compared to other silica samples prepared by chemical extraction and uncontrolled burning. The presence of crystalline cristobalite and trydimite phases and SiOH groups render the silica less active.

Alumination of the purely siliceous mesoporous molecular sieve MCM-41 and its hydrothermal conversion into zeolite Na-A

Purely siliceous mesoporous [Si]-MCM-41 has been aluminated using an aqueous solution of sodium aluminate, NaAlO2, to form [Si,Al]-MCM-41 with the framework Si/Al ratio as low as 1.9. 27Al and 29Si magic-angel-spinning (MAS) NMR show that all aluminium is incorporated in the framework. The well resolved X-ray diffraction (XRD) pattern of calcined [Si,Al]-MCM-41 indicates that the mesopore system is stable and that the channel diameter decreases with the increased degree of incorporation of Al. The intensity of lines corresponding to Si(nAl) building blocks in the 29Si MAS NMR spectra reflect changes in the local atomic arrangement upon alumination. Increased reaction temperature at a constant concentration of NaAlO2 enhances the efficiency of the alumination, but increased concentration at constant temperature disrupts the framework structure. Upon treatment with a concentrated (>1 mol 1–1) solution of NaAlO2 at moderate temperatures (100 ± 20 °C), [Si]-MCM-41 is transformed into crystalline zeolite Na-A.

MCM-41 solid phase membrane tip extraction combined with liquid chromatography for the determination of non-steroidal anti-inflammatory drugs in human urine

Mesoporous silica material, MCM-41, was utilized for the first time as an adsorbent in solid phase membrane tip extraction (SPMTE) of non-steroidal anti-inflammatory drugs (NSAIDs) in urine prior to high performance liquid chromatography-ultraviolet (HPLC-UV) analysis. The prepared MCM-41 material was enclosed in a polypropylene membrane tip and used as an adsorbent in SPMTE. Four NSAIDs namely ketoprofen, diclofenac, mefenamic acid and naproxen were selected as model analytes. Several important parameters, such as conditioning solvent, sample pH, salting-out effect, sample volume, extraction time, desorption solvent and desorption time were optimized. Under the optimum extraction conditions, the MCM-41-SPMTE method showed good linearity in the range of 0.01-10μg/mL with excellent correlation coefficients (r=0.9977-0.9995), acceptable RSDs (0.4-9.4%, n=3), good limits of detection (5.7-10.6μg/L) and relative recoveries (81.4-108.1%). The developed method showed a good tolerance to biological sample matrices.

Structural and luminescence studies of europium ions in lithium aluminium borophosphate glasses

Abstract Eu3+ doped borophosphate glasses with the chemical composition 20Li2O-30Al2O3-10B2O3-40P2O5-xEu2O3 (where x=0.05 mol.%, 0.1 mol.%, 1.0 mol.%, 1.5 mol.% and 2.0 mol.%) were prepared by conventional melt quenching technique. The structural and luminescence properties of the prepared Eu3+ doped borophosphate glasses were studied and compared with reported results. The XRD pattern showed the amorphous nature of the prepared glasses. Whereas, the FTIR spectra revealed the vibrational modes in the prepared glasses. The bonding parameters ( β ¯ and δ) were calculated through the excitation spectra. Judd–Ofelt (J–O) intensity parameters were calculated from the emission spectra and were used to determine transition probability (A), stimulated emission cross-section (σEP), radiative lifetime (τR) and branching ratios (βexp) for the transition 5D0→7Fj (j=1, 2, 3 and 4) of Eu3+ ions. Furthermore, the luminescence intensity ratio (R) of 5D0→7F2 to 5D0→7F1 transition was also calculated. Transition 5D0→7F2 had the highest value of stimulated emission cross-section and branching ratios and the results were comparable with the reported values. This indicated that the present glass is promising host material for Eu3+ doped fiber amplifiers.

Oxidative Dimerization of o-Aminophenol by Heterogeneous Mesoporous Material Modified with Biomimetic Salen-Type Copper(II) Complex

Copper(II) N,N′-bis[4-(N,N-diethylamino)salicylidene]ethylenediamine (CAS) complex, which has the metal–ligand coordination “CuN2O2” that mimics the galactose enzyme active site, was synthesised and incorporated onto the organo-modified MCM-48. The supported CAS catalyst successfully catalysed the conversion of o-aminophenol to 2-amino-3H-phenoxazon-3-one in the presence of aqueous peroxide as oxidant. The catalytic performance of the CAS supported on organo-modified MCM-48 was found highly affected by the temperature, the type of aqueous peroxide and reaction solvent used.Graphical AbstractA salen-type copper complex of N2O2 donor ligand was synthesised and incorporated onto the modified MCM-48. The corresponding supported catalysts are active in the oxidation of o-aminophenol to 2-amino-3H-phenoxazin-3-one in the presence of peroxide as an oxidant.

A simple microextraction and preconcentration approach based on a mixed matrix membrane

A simple adsorption/desorption procedure using a mixed matrix membrane (MMM) as extraction medium is demonstrated as a new miniaturized sample pretreatment and preconcentration technique. Reversed-phase particles namely polymeric bonded octadecyl (C18) was incorporated through dispersion in a cellulose triacetate (CTA) polymer matrix to form a C18-MMM. Non-steroidal anti-inflammatory drugs (NSAIDs) namely diclofenac, mefenamic acid and ibuprofen present in the environmental water samples were selected as targeted model analytes. The extraction setup is simple by dipping a small piece of C18-MMM (7 mm × 7 mm) in a stirred 10 mL sample solution for analyte adsorption process. The entrapped analyte within the membrane was then desorbed into 100 μL of methanol by ultrasonication prior to high performance liquid chromatography (HPLC) analysis. Each membrane was discarded after single use to avoid any analyte carry-over effect. Several important parameters, such as effect of sample pH, salting-out effect, sample volume, extraction time, desorption solvent and desorption time were comprehensively optimized. The C18-MMM demonstrated high affinity for NSAIDs spiked in tap and river water with relative recoveries ranging from 92 to 100% and good reproducibility with relative standard deviations between 1.1 and 5.5% (n=9). The overall results obtained were found comparable against conventional solid phase extraction (SPE) using cartridge packed with identical C18 adsorbent.

Portable micro-solid phase extraction for the determination of polycyclic aromatic hydrocarbons in water samples

This work describes for the first time the application of portable micro-solid phase extraction (μ-SPE) for the determination of polycyclic aromatic hydrocarbons (PAHs). In this technique, a battery-operated electric whisk stirrer combined with a μ-SPE device was employed to provide agitation of the sample solution and facilitate the pre-concentration of the target analytes. The μ-SPE device consisted of multi-walled carbon nanotubes (MWCNTs) packed in a polypropylene (PP) membrane. The performance of μ-SPE sampling coupled with high performance liquid chromatography-ultraviolet detection (HPLC-UV) was evaluated for the analysis of five target PAHs (fluorene, anthracene, fluoranthene, pyrene and benzo[a]pyrene) in water. Important μ-SPE parameters were studied and the optimal extraction conditions were 30 min extraction time, 10 min desorption time, isopropanol as the conditioning and desorption solvent and no addition of a salt. The developed portable μ-SPE method provided good linearity in the concentration range of 0.1–100 μg L−1 for fluorene, anthracene, fluoranthene and pyrene, and 1–100 μg L−1 for benzo[a]pyrene, with good coefficients of determination (r2, 0.9975–0.9989), low limits of detection (0.01–0.59 μg L−1), acceptable intra-day precisions (3.5–6.2% for on-site analysis) and acceptable relative recoveries (77.3–107.2%). Portable μ-SPE combined with HPLC-UV was successfully applied to the determination of target PAHs in selected water samples. The proposed sample preparation technique proved to be simple, cost effective, easy-to-operate and feasible for both off-site and on-site analyses.

Characterization and Catalytic Performance of Niobic Acid Dispersed over Titanium Silicalite

Niobic acid, , has been supported on the titanium silicalite by impregnation method. The obtained materials were characterized by X-ray diffraction, infrared, and ultra-violet—visible diffuse reflectance spectroscopy, temperature programmed reduction, pyridine adsorption, and field emission scanning electron microscopy techniques. It was demonstrated that the tetrahedral titanium species still retained after impregnation of niobic acid. The results revealed that niobium species interacted with hydroxyl groups on the surface of TS-1. The niobium species in the catalysts are predominantly polymerized niobium oxides species or bulk niobium oxide with the octahedral structure. All catalysts showed both Brønsted and Lewis acid sites. The catalysts have been tested for epoxidation of 1-octene with aqueous hydrogen peroxide. It was found that the presence of niobic acid in the catalysts enhanced the rate of the formation of epoxide at the initial reaction time. Diol as a side product was also observed due to the acidic properties of the catalysts.

Improved interfacial charge transfer and visible light activity of reduced graphene oxide–graphitic carbon nitride photocatalysts

Development of efficient visible light-driven photocatalysts is an important approach towards sustainability. Herein, reduced graphene oxide–graphitic carbon nitride (rGO–gCN) photocatalysts were successfully prepared by in situ photocatalytic reduction of graphene oxide (GO) in the presence of gCN as the photocatalyst. The XPS spectra revealed the presence of N-graphene, which confirmed the interaction between the rGO and the gCN. The rGO–gCN with GO loading amount of 0.1 wt% exhibited almost three times higher photocatalytic activity than gCN for degradation of phenol under visible light irradiation. Fluorescence spectroscopy, EIS, and photocurrent response studies indicated that the presence of rGO significantly promoted the electron–hole separation and improved the interfacial charge transfer on the gCN. These factors played a crucial role in enhancing the photocatalytic activity of the gCN under visible light irradiation.

Probing the active sites of aluminated mesoporous molecular sieve MCM-41 by secondary synthesis in the conversion of cyclohexanol

The active sites of H-AI-MCM-41 aluminated by secondary synthesis have been probed by the conversion of cyclohexanol and compared with those of HAI-MCM-41 prepared by direct synthesis, purely siliceous MCM-41, AIP04-5 and H-ZSM-5. Conversion of cyclohexanol produces cyclohexene, cyclohexanone and 3-methylpentane in the presence of Bronsted, basic and Lewis acid sites respectively. Whereas cyclohexanol is converted to polyaromatic compounds in the presence of very strong acid sites as those found in H-ZSM-5. The formation of cyclohexene as the only product of conversion over H-AI-MCM-41 prepared by direct and secondary synthesis indicates the presence of Bronsted acid sites in both systems, which is not observed in the purely siliceous MCM-41 and AIP04-5 samples. The larger amount of cyclohexene formed over H-AI-MCM-41 by secondary synthesis suggests that there is a higher degree of Bronsted acidity in this system than that of H-AI-MCM-41 by direct synthesis. However, the strength of acidity in HAI-MCM-41 by secondary synthesis is weaker than that of H-ZSM-5. In addition, the results of this reaction, supported by IR spectroscopy study, do not indicate the presence of Lewis acidity in H-AI-MCM-41 prepared by secondary synthesis.