Amjad H. El-Sheikh

Characterization of activated carbon prepared from a single cultivar of Jordanian olive stones by chemical and physicochemical techniques

Abstract The yearly production of olives in Jordan is more than 100 kton of which a significant proportion is de-stoned prior to sale. In this work, olive stones from Jordan were used for the preparation of activated carbon with the aim of producing a water treatment product suitable for treatment of contaminated groundwater. The preparation conditions were varied to study their effects on the surface area, porosity, morphology, functionality and crystal structure. Variables studied included time of carbonization, time of activation, activating agent, particle size, sample pre-drying, hydrogen peroxide post treatment and the effect of the activation process itself. X-ray diffraction analysis showed that the prepared activated carbon is essentially amorphous and indicated the presence of traces of oxides of calcium and magnesium, while infrared spectroscopy showed peaks relating to hydroxyl, aliphatic, ether, aromatic and phenolic groups. These functional groups and crystals may have some effect(s), i.e. catalytic, if the products were to be used in any reaction for water treatment. Nitrogen adsorption was used for the determination of apparent surface area and pore size distribution. Results showed that the active carbon is of moderate surface area and micropore volume is over 80% of the total pore volume. Scanning electron microscopy showed the development of the pores during different treatments. The most noticeable effect on the texture was that when the sample was not pre-dried. The adsorption capacity and surface acidity/basicity of all the samples have been studied by methylene blue (MB) adsorption method and partial Boehm titrations, respectively. Results showed that the surface is mainly of basic nature, and also indicated that MB was adsorbed following the pore filling mechanism. Hydrogen peroxide post-treatment produced reduced surface area measurements.

Critical evaluation and comparison of enrichment efficiency of multi-walled carbon nanotubes, C18 silica and activated carbon towards some pesticides from environmental waters

In this work, optimization of multi-residue solid phase extraction (SPE) procedures coupled with high-performance liquid chromatography for the determination of Propoxur, Atrazine and Methidathion from environmental waters is reported. Three different sorbents were used in this work: multi-walled carbon nanotubes (MWCNTs), C18 silica and activated carbon (AC). The three optimized SPE procedures were compared in terms of analytical performance, application to environmental waters, cartridge re-use, adsorption capacity and cost of adsorbent. Although the adsorption capacity of MWCNT was larger than AC and C18, however, the analytical performance of AC could be made close to the other sorbents by appropriate optimization of the SPE procedures. A sample of AC was then oxidized with various oxidizing agents to show that ACs of various surface properties has different enrichment efficiencies. Thus researchers are advised to try AC of various surface properties in SPE of pollutants prior to using expensive sorbents (such as MWCNT and C18 silica).

Effect of oxidation of activated carbon on its enrichment efficiency of metal ions: comparison with oxidized and non-oxidized multi-walled carbon nanotubes.

The effect of oxidation of activated carbon (AC) with various oxidizing agents (nitric acid, hydrogen peroxide, ammonium persulfate) on preconcentration of metal ions (Cr3+, Mn2+, Pb2+, Cu2+, Cd2+ and Zn2+) from environmental waters prior to their flame atomic absorption spectroscopic analysis was investigated. The highest recoveries and adsorption capacities towards metal ions were achieved when using nitric acid-oxidized AC (sorbent AC-NA) as preconcentrating sorbent at pH 9. A preconcentration procedure was optimized using AC-NA as sorbent, which was then compared with non-oxidized AC in terms of analytical performance of the preconcentration method. Higher sensitivity, lower detection limits and wider linear ranges were achieved when AC-NA was used. The analytical performance of the method using AC-NA as preconcentrating sorbent was also compared with nitric acid-oxidized multi-walled carbon nanotubes (sorbent MWCNT-NA) and non-oxidized multi-walled carbon nanotubes (sorbent MWCNT). The analytical performance of the preconcentration method using AC-NA was close to MWCNT-NA, but AC-NA was better than non-oxidized MWCNT. Application of the optimized preconcentration method (using AC-NA sorbent) to environmental waters (tap water, reservoir water, stream water) gave spike recoveries of the metals in the range 63-104%.

Simultaneous determination of pesticides at trace levels in water using multiwalled carbon nanotubes as solid-phase extractant and multivariate calibration.

The application of solid-phase extraction with multivariate calibration for simultaneous determination of three toxic pesticides in tap and reservoir waters was presented. The proposed analytical method was used for the determination of atrazine, methidathion, and propoxur in complex water samples without the need for chromatographic separation. Among the applied multivariate calibration methods, partial least squares (PLS-1) method was found the most effective for pesticides quantification. Multiwalled carbon nanotubes (MWCNTs) adsorbent showed a perfect extraction/preconcentration of pesticides present at trace levels. The experimental factors that affect pesticides extraction by MWCNTs adsorbent such as sample volume, eluent volume, solution pH, and extraction flow rate were studied and optimized. The figures of merit of the proposed method were: limits of detection 3, 2, and 3 microg l(-1) and linear ranges 5-30, 3-60, and 5-40 microg l(-1) for atrazine, methidathion, and propoxur, respectively. A good precision was reported for the method, R.S.D. values were always less than 5.0%. Satisfactory results were reported for simultaneous determination of trace levels of pesticides in complex matrices. In tap water, the percent recoveries for pesticides were extended from 95 to 104% and R.S.D. from 1 to 3%, while lower recoveries were observed in reservoir water: 84-93% (R.S.D.: 1-3). Although the pesticides can be accurately quantified by SPE and liquid chromatography, SPE-PLS-1 method was found simpler and operated at lower running costs.

Solid-phase extraction and simultaneous determination of trace amounts of sulphonated and azo sulphonated dyes using microemulsion-modified-zeolite and multivariate calibration.

A simple and rapid analytical method for the determination of trace levels of five sulphonated and azo sulphonated reactive dyes: Cibacron Reactive Blue 2 (C-Blue, trisulphonated dye), Cibacron Reactive Red 4 (C-Red, tetrasulphonated azo dye), Cibacron Reactive Yellow 2 (C-Yellow, trisulphonated azo dye), Levafix Brilliant Red E-4BA (L-Red, trisulphonated dye), and Levafix Brilliant Blue E-4BA (L-Blue, disulphonated dye) in water is presented. Initially, the dyes were preconcentrated from 250 ml of water samples with solid-phase extraction using natural zeolite sample previously modified with a microemulsion. The modified zeolite exhibited an excellent extraction for the dyes from solution. The parameters that influence quantitative recovery of reactive dyes like amount of extractant, volume of dye solution, pH, ionic strength, and extraction-elution flow rate were varied and optimized. After elution of the adsorbed dyes, the concentration of dyes was determined spectrophotometrically with the aid of principle component regression (PCR) method without separation of dyes. The results obtained from PCR method were comparable to those obtained from HPLC method confirming the effectiveness of the proposed method. With the aid of SPE by M-zeolite, the concentration of dyes could be reproducibly detected over the range 25-200 ppb for C-Yellow and L-Blue and from 50 to 250 ppb for C-Blue, C-Red, and L-Red. The multivariate detection limits of dyes were found to be 15 ppb for C-Yellow and L-Blue and 25 ppb for C-Blue, C-Red, and L-Red dyes. The proposed chemometric method gave recoveries from 85.4 to 115.3% and R.S.D. from 1.0 to 14.5% for determination of the five dyes without any prior separation for solutes.

Derivatization of 2-chlorophenol with 4-amino-anti-pyrine: A novel method for improving the selectivity of molecularly imprinted solid phase extraction of 2-chlorophenol from water

Molecularly imprinted polymer (MIP) may not selectively recognize small template of limited number of functional groups, such as 2-chlorophenol (2-CP). In this work, a novel method was proposed to improve the recognition ability of the molecularly imprinted solid phase extraction (MISPE) of 2-CP from environmental waters. This was achieved by derivatization of 2-CP with 4-amino-anti-pyrine (4-AAP) to enlarge its molecular size and add more binding sites. For that purpose, two MISPE methods of 2-CP were developed. In method 1, a polymer imprinted with 2-CP was used as the extracting sorbent but it suffered from low selectivity and high detection limit of 2-CP (7.10 ng L(-1)). In method 2, a polymer imprinted with 4-AAP derivatized 2-CP (2-CP-4-AAP) was used as the extracting sorbent. Prior to loading the water sample it was subjected to a simple derivatization procedure with 4-AAP. Method 2 showed high recognition ability/selectivity towards 2-CP-4-AAP with lower detection limit of 0.05 ng L(-1) for 2-CP-4-AAP. Method 2 was able to detect the presence of 2-CP-4-AAP in unspiked real water samples and almost full spike recovery was achieved.

Adsorption behavior of anionic reactive dyes on H-type activated carbon: Competitive adsorption and desorption studies

Abstract A microporous H‐type activated carbon was shown to be effective for removing anionic reactive dyes from single and binary component solutions. The extent of the dye adsorption from a single‐solute solution was high (0.25–0.42 mmol/g). From the binary dye solutions, the experimental data indicated a high degree of competition for active sites and the obtained adsorption capacities were reduced to 0.10–0.26 mmol/g. Adsorption data from single dye solutions were correlated using the Langmuir, Ferundlich, and Redlich‐Peterson models. Hydrophobic, hydrophobic mechanisms were significant in the adsorption process. Furthermore, the system showed a low extent of desorption.

Preparation of an efficient sorbent by washing then pyrolysis of olive wood for simultaneous solid phase extraction of chloro-phenols and nitro-phenols from water

Simultaneous preconcentration of phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol was improved by using olive wood (OW) washed with ethanol then pyrolyzed at 200°C as preconcentrating sorbent. Various OW sorbents were prepared by either washing OW (with ethanol, ether, dichloromethane, tetrahydrofuran or n-hexane); or by pyrolysis (at 100, 150, 200, 250 or 300°C); or by combined pyrolysis/washing. The adsorbents were characterized by elemental analysis, total acidity/basicity, methylene blue relative surface area, point of zero charge, distribution coefficients of the phenols, and sample loading flow rate. It seems that washing and pyrolysis have removed compounds covering the OW pores, which improved the OW porosity and exposed more acidic groups on the OW surface. The pores and the surface acidic groups seem to play major role in phenols sorption. Ethanol-washed OW then pyrolyzed at 200°C gave the best preconcentration performance towards phenols (300 mg sorbent, 150 mL of the sample (pH 7), and elution with 3 mL of acetonitrile). The method was linear up to 100 μg L(-1); limit of quantification: 0.20-0.48 μg L(-1). The method could detect phenol and 2,4-dinitrophenol in industrial wastewater with spiked recovery range from 80.2% to 91.4% (± 1.1 to 5.5%RSD) for all the phenols.

A rapid and simple microwave-assisted digestion procedure for spectrophotometric determination of titanium dioxide photocatalyst on activated carbon

Deposition of titanium dioxide (TiO(2)) on activated carbon (AC) surface has been widely utilized for the production of TiO(2)/AC photocatalyst, which can be used in photo-degradation of pollutants. In this work, a fast and simple digestion procedure has been developed for the spectrophotometric quantitative analysis of TiO(2) in TiO(2)/AC photocatalyst. Microwave-assisted digestion was used in the procedure. The microwave-digestion procedure was optimized using the single-variable method. Variables optimized included time of ashing, effective digestion time, volume and concentration of sulfuric acid, effect of adding a digestion catalyst, effect of sample pulverizing and on-off time cycle of the microwave. The analysis was completed spectrophotometrically after addition of hydrogen peroxide to the digested solution. Procedure precision and accuracy was tested by application to photocatalyst samples containing known amounts of TiO(2), and compared with previously published spectrophotometric procedures. The proposed microwave procedure was capable of recovering 98.4-101.1% of TiO(2) in the catalyst in less than 10min, without the need for sample ashing. Analytical precision is 1.42-2.39% relative standard deviation (R.S.D.). In terms of accuracy and precision, the proposed microwave procedure was comparable with other procedures, but the proposed microwave procedure was superior in terms of shorter procedure duration.

Bio-separation, speciation and determination of chromium in water using partially pyrolyzed olive pomace sorbent.

Speciation of Cr(III)/Cr(VI) from water using olive pomace (OP) was improved by partial pyrolysis of OP. The sorbents were characterized by physicochemical techniques. Sorption of Cr(III) on raw and partially pyrolyzed OP sorbents followed Freundlich isotherm and second-order rate kinetics. OP pyrolyzed at 150°C (sorbent OP-150) exhibited maximum sorption capacity, favorability and the lowest sorption energy. Sorption was exothermic and spontaneous for the raw-OP and OP pyrolyzed at 100 or 150°C; but endothermic and non-spontaneous for OP pyrolyzed at 200, 250, 300 or 400°C. A speciation method of chromium was proposed, in which Cr(III) was selectively retained at pH 3 on sorbent OP-150; while total Cr was determined after reduction of Cr(VI). The method was selective with a detection limit for Cr(III) of 1.58 μg L(-1). The method was applied on natural and industrial waters (recoveries >97.7%, RSDs <9%) and on tobacco leaves certified reference material (INCT-PVTL-6).