H. Mohamed

Screening of oil sands naphthenic acids by UV-Vis absorption and fluorescence emission spectrophotometry

Oil sands extracted naphthenic acids fractions are known to contain impurities with various levels of unsaturation and aromaticity. These constituents contain functional groups that absorb ultraviolet-visible wavelength (UV-Vis) radiation and give intense florescence emission in contrast to the fully saturated alicyclic naphthenic acids. UV-Vis absorption and fluorescence emission spectrophotometry are presented here as inexpensive and quick screening methods that the detection of chromophoric surrogate compounds that serve as an internal standard for the indirect analysis of oil sands naphthenic acids. The method detection limit for the screening techniques was approximately 1 mg/L with an observed linear range of 1–100 mg/L. The precision of measurements was generally within 10% r.s.d. There was generally good agreement (within 20% r.s.d) for isotherm parameters from non-linear fitting of Langmuir, BET and Freundlich models for sorption of Athabasca oil sands naphthenic acid mixtures to activated carbon samples determined by UV-Vis absorption, fluorescence emission spectroscopy, and conventional direct injection electrospray ionization mass spectrometry.

Investigation of the sorption properties of β-cyclodextrin-based polyurethanes with phenolic dyes and naphthenates.

The sorption of p-nitrophenol (PNP), phenolphthalein (phth) and naphthenates (NAs) with β-cyclodextrin (β-CD) based polyurethane sorbents from aqueous solutions are reported. The copolymer sorbents were synthesized at various β-CD/diisocyanate monomer mole ratios (e.g., 1:1, 1:2, and 1:3) with diisocyanates of variable molecular size and hydrogen deficiency. The copolymer sorbents were characterized in the solid state using (13)C CP-MAS NMR spectroscopy, IR spectroscopy and elemental (C,H,N) analysis. The equilibrium sorption properties of the copolymer sorbents in aqueous solution were characterized using isotherm models at pH 4.6 and 9.0 for PNP, pH 9.0 for naphthenates and pH 10.5 for phth. UV-Vis spectroscopy was used to monitor the unbound fraction of the phenolic dyes in the aqueous phase, whereas, electrospray ionization mass spectrometry was used to monitor the unbound fraction of naphthenates. The sorption results of the copolymer sorbents were compared with a commercially available carbonaceous standard; granular activated carbon (GAC). The sorption properties and capacities of the copolymer sorbents (Q(m)) were estimated using the Sips isotherm. The sorption capacity for GAC was 2.15 mmol PNP/g, 0.0698 mmol phth/g, and 142 mg NAs/g, respectively, whereas the polymeric materials ranged from 0.471 to 1.60 mmol/g (PNP), 0.114 to 0.937 mmol/g (phth), and 0 to 75.5 mg/g (naphthenates), respectively, for the experimental conditions investigated. The observed differences in the sorption properties were attributed to the accessible surface areas and pore structure characteristics of the copolymer sorbents. The binding constant, K(eq), for copolymer materials for each sorbate is of similar magnitude to the binding affinity observed for native β-CD. PNP showed significant binding onto the copolymer framework containing diisocyanate domains, whereas, negligible sorption to the sites was observed for phth and naphthenates. The β-CD inclusion sites in the copolymer framework are concluded to be the main sorption site for phth and naphthenates through the formation of well-defined inclusion complexes.

Porous Copolymer Resins: Tuning Pore Structure and Surface Area with Non Reactive Porogens

In this review, the preparation of porous copolymer resin (PCR) materials via suspension polymerization with variable properties are described by tuning the polymerization reaction, using solvents which act as porogens, to yield microporous, mesoporous, and macroporous materials. The porogenic properties of solvents are related to traditional solubility parameters which yield significant changes in the surface area, porosity, pore volume, and morphology of the polymeric materials. The mutual solubility characteristics of the solvents, monomer units, and the polymeric resins contribute to the formation of porous materials with tunable pore structures and surface areas. The importance of the initiator solubility, surface effects, the temporal variation of solvent composition during polymerization, and temperature effects contribute to the variable physicochemical properties of the PCR materials. An improved understanding of the factors governing the mechanism of formation for PCR materials will contribute to the development and design of versatile materials with tunable properties for a wide range of technical applications.

Dose–volume analysis of locoregional recurrences in head and neck IMRT, as determined by deformable registration: A prospective multi-institutional trial

BACKGROUND AND PURPOSE Although IMRT for head and neck cancer is widely accepted, the implications of sparing normal tissue immediately adjacent to target volumes are not well known. MATERIALS AND METHODS Between 2002 and 2007, 124 patients with head and neck cancer were treated with surgery and postoperative IMRT (n=79) or definitive RT (n=45). Locoregional recurrences were analyzed for location relative to target volumes, and dosimetry. RESULTS With a median follow-up of 26.1months, a total of 16 locoregional recurrences were observed. The five-year actuarial locoregional disease-free survival was 82% [95% CI, 72-90%]. Analysis of 18 distinct sites of locoregional failure revealed that five of these failures were within the high dose clinical target volume (CTV), nine failures were at the margin of the CTV, and four recurrences were outside the CTV. The mean dose delivered to these recurrent volumes was 63.1 Gy [range: 57-68 Gy], while the mean dose to the coolest 1cc within each recurrence was 60.0 Gy [range: 51-67 Gy]. There were two periparotid recurrences observed. CONCLUSIONS We observed excellent locoregional control rates overall. The majority of recurrences occur within high dose regions of the neck and not near the spared parotid glands.

Sorption of Aromatic Compounds with Copolymer Sorbent Materials Containing β-Cyclodextrin

Urethane copolymer sorbent materials that incorporate β-cyclodextrin (CD) have been prepared and their sorption properties with chlorinated aromatic compounds (i.e., pentachlorophenol, 2,4-dichlorophenol and 2,4-dichlorophenoxy acetic acid) have been evaluated. The sorption properties of granular activated carbon (GAC) were similarly compared in aqueous solution at variable pH conditions. The sorbents displayed variable BET surface areas as follows: MDI-X copolymers (< 101 m2/g), CDI-X copolymers (< 101 m2/g), and granular activated carbon (GAC ~103 m2/g). The sorption capacities for the copolymers sorbents are listed in descending order, as follows: GAC > CDI-3 copolymer ≈ MDI-3 copolymer. The sorption capacity for the aromatic adsorbates with each sorbent are listed in descending order, as follows: 2,4-dichlorophenol > 2,4-dichlorophenoxy acetic acid > pentachlorophenol. In general, the differences in the sorption properties of the copolymer sorbents with the chlorinated organics were related to the following factors: (i) surface area of the sorbent; (ii) CD content and accessibility; and (iii) and the chemical nature of the sorbent material.

A spectral displacement study of cyclodextrin/naphthenic acids inclusion complexes

The spectral displacement technique has been used to obtain 1:1 β-cyclodextrin (β-CD)/carboxylate anion equilibrium binding constants (K2) for some complex mixtures of naphthenic acids (NAs) and so...

Fractionation of carboxylate anions from aqueous solution using chitosan cross-linked sorbent materials

The sorptive uptake properties are reported for chitosan and cross-linked chitosan-glutaraldehyde (CG) polymers with single component carboxylic acids (surrogates; Si, i = 1–4). The single component surrogates are treated as model compounds to represent traditional naphthenic acids (NAs) with variable hydrogen deficiency (z) and carbon number (C), as follows: 2-hexyldecanoic acid (z = 0 and C = 16; S1), trans-4-pentylcyclohexanecarboxylic acid (z = −2 and C = 12; S2), dicyclohexylacetic acid (z = −4; C = 14; S3) and 2-ethyl hexanoic acid (z = 0 and C = 8; S4). Cross-linked polymers were synthesized at variable C : G mole ratios (i.e. 1 : 400, 1 : 700, and 1 : 1000) and characterized using FTIR and TGA. The uptake studies were evaluated at pH 6.00 and 9.00 in aqueous solution. Corresponding equilibrium uptake parameters were evaluated by several isotherm models (Sips, Freundlich, and Langmuir). The Freundlich model provided the “best-fit” for S1, S2 and S3. The Sips isotherm model gave the “best-fit” results for S4. The Freundlich sorption affinity constant (KF; L mg g−1) and the Sips monolayer adsorption capacity (Qm; mg g−1) for the sorbent systems was estimated. The parameters for each Si vary as the C : G mole ratio increases (KF, S1: 0.00800–6.65, S2: 1.41–2.45, S3: 1.29–2.93 and Qm, S4: 28.4–33.5). Differences in the uptake of Si species by the sorbents were attributed to steric effects between Si with ring systems (z S2 (4–10) > S3 (3–9). The fractionation efficacy of Si species is attributed to molecular sieving effects due to the tunable micropore sites of the cross-linked polymer, in accordance with the variable cross-linker content of the chitosan framework. Regeneration studies revealed the utility of these materials in cyclic adsorption–desorption processes.

Kinetic Uptake Studies of Powdered Materials in Solution

Challenges exist for the study of time dependent sorption processes for heterogeneous systems, especially in the case of dispersed nanomaterials in solvents or solutions because they are not well suited to conventional batch kinetic experiments. In this study, a comparison of batch versus a one-pot setup in two variable configurations was evaluated for the study of uptake kinetics in heterogeneous (solid/solution) systems: (i) conventional batch method; (ii) one-pot system with dispersed adsorbent in solution with a semi-permeable barrier (filter paper or dialysis tubing) for in situ sampling; and (iii) one-pot system with an adsorbent confined in a semi-permeable barrier (dialysis tubing or filter paper barrier) with ex situ sampling. The sorbent systems evaluated herein include several cyclodextrin-based polyurethane materials with two types of phenolic dyes: p-nitrophenol and phenolphthalein. The one-pot kinetics method with in situ (Method ii) or ex situ (Method iii) sampling described herein offers significant advantages for the study of heterogeneous sorption kinetics of highly dispersed sorbent materials with particles sizes across a range of dimensions from the micron to nanometer scale. The method described herein will contribute positively to the development of advanced studies for heterogeneous sorption processes where an assessment of the relative uptake properties is required at different experimental conditions. The results of this study will be advantageous for the study of nanomaterials with significant benefits over batch kinetic studies for a wide range of heterogeneous sorption processes.

Novel materials for environmental remediation of oil sands contaminants

Abstract The incorporation of β-cyclodextrin (β-CD) within the framework structure of copolymer sorbent materials, represents a novel modular design approach with significant potential for controlled tuning of the textural mesoporosity of such sorbent frameworks. β-CD copolymers represent an innovative design strategy for the development of “smart” or “functional” porous materials with improved solid phase extraction (SPE) and molecular recognition properties because of the porogen characteristics and their unique host-guest properties. Carbohydrate-based copolymers containing cyclodextrins (CDs) are of interest, in part, because of their ability to form stable inclusion complexes in aqueous solution. The inclusion properties of β-CD copolymers are determined by the surface area, pore structure, and site accessibility of inclusion sites within the copolymer framework. A mini-review of recent research in our group concerning the use of copolymers containing β-CD as sorbent materials for naphthenic acids is presented herein.

A novel solid-state fractionation of naphthenic acid fraction components from oil sands process-affected water

Various sorbent materials were evaluated for the fractionation of naphthenic acid fraction components (NAFCs) from oil sand process-affected water (OSPW). The solid phase materials include activated carbon (AC), cellulose, iron oxides (magnetite and goethite), polyaniline (PANI) and three types of biochar derived from biomass (BC-1; rice husks, BC-2; acacia low temperature and BC-3; acacia high temperature). NAFCs were semi-quantified using electrospray ionization high resolution Orbitrap mass spectrometry (ESI-MS) and the metals were assessed by inductively coupled plasma optical emission spectrometry (ICP-OES). The average removal efficacy of NAFCs by AC was 95%. The removal efficacy decreased in the following order: AC, BC-1>BC-2, BC-3, goethite>PANI>cellulose, magnetite. The removal of metals did not follow a clear trend; however, there was notable leaching of potassium by AC and biochar samples. The bound NAFCs by AC were desorbed efficiently with methanol. Methanol regeneration and recycling of AC revealed 88% removal on the fourth cycle; a 4.4% decrease from the first cycle. This fractionation method represents a rapid, cost-effective, efficient, and green strategy for NAFCs from OSPW, as compared with conventional solvent extraction.