Nauman Ali

Micellar structures of poly(styrene-b-4-vinylpyridine)s in THF/toluene mixtures and their functionalization with gold.

The effects of the block copolymer composition and the solvent selectivity on the micellar morphologies of poly(styrene- b-4-vinylpyridine)s (PS- b-P4VPs) and their functionalizations with gold were studied in 10 mg/mL solutions using small-angle X-ray scattering and transmission electron microscopy (TEM). The solvent selectivity for the PS block was controlled by toluene/tetrahydrofuran (THF) mixtures in which toluene and THF are selective for PS and nonselective, respectively. The micellar structure was strongly dependent on phi (wt % toluene in toluene/THF mixture) and the composition of the block copolymers. PS(12K)- b-P4VP(11.8K) (symmetric) showed spherical micelles in the entire range of phi except phi = 0 (THF, nonselective solvent). PS(3.3K)- b-P4VP(18.7K) (asymmetric, longer P4VP) showed multiple morphologies with transitions from spheres to cylinders and finally to vesicles with an increase in phi. PS(19.6K)- b-P4VP(5.1K) (asymmetric, longer PS) showed spherical micelles only at the narrow ranges of 90 wt % <or= phi <or= 100 wt % and an isotropic state at the other ranges. The micelles formed a complex with HAuCl 4 and were reduced with hydrazine in the solvent mixtures. The morphologies of micelles, hybrid micelles, and gold nanoparticles were investigated by using TEM and UV/vis spectroscopy. The possible mechanisms leading to these morphological changes and the formation of the nanosized gold particles were also discussed.

Polymer Nanocomposite Membranes for Antifouling Nanofiltration

Fouling refers to the unwanted and undesirable attachment of biological macromolecules, inorganic, organic matter, and microorganisms on water contact surfaces. Fouling reduces the performance of devices involving these submerged surfaces and is considered the bottle-neck issue for various applications in the biomedical industry, food processing, and water treatment, especially in reverse osmosis (RO) desalination. Investigations have proven that nanocomposite membranes can exhibit enhanced antifouling performances and can be used for longer life times. The nanocomposite means addition of nanomaterials to main matrix at low loadings, exhibiting better properties compared to virgin matrix. In this review, a summarized description about related methods and their mechanisms for the fabrication of nanocomposite membranes with antifouling properties has been documented. Around 87 manuscripts including 10 patents were used to demonstrate the antifouling applications of of various nanocomposite membranes.

Photocatalytic degradation of bromophenol blue in aqueous medium using chitosan conjugated magnetic nanoparticles

Three different chitosan conjugated magnetic nanoparticles (CCMN) of Co, Ni and Fe were prepared using co-precipitation method. The prepared CCMN were characterized by scanning electron microscopy (SEM), Xray diffraction (XRD) and Fourier transform infra-red (FT-IR) spectroscopic techniques. The SEM results showed a smooth surface morphology with almost uniform particle size and irregular shape structure for all CCMN. The XRD study revealed the crystalline structure in case of Co-CCMN and Ni-CCMN, while amorphous nature of Fe-CCMN was observed. The particle size of the prepared CCMN was found to be <95 nm, as confirmed from SEM and XRD analyses. Similarly, FT-IR analysis showed the incorporation and conjugation of Co, Ni and Fe magnetic nanoparticles into the chitosan polymer matrix. The point of zero charge (PZC) was found to be 7.41 for Co-CCMN and Ni-CCMN and 7.70 for Fe-CCMN. The photocatalytic activity of the prepared CCMN was investigated under UV light irradiation (254 nm and 15 W) in the aqueous medium using bromophenol blue (BPB). The photocatalytic process was monitored by UV-visible spectrophotometer for different irradiation times (0 to 10 h). The results showed that all the prepared CCMN displayed good to excellent photocatalytic property where the highest degradation was exhibited by Fe-CCMN (94.5%), followed by Co-CCMN (85.1%) and Ni-CCMN (83.0%). The prepared catalysts were recycled and reused, maintaining good photocatalytic activity for four consecutive batches.

Fluorescence Emission of Disperse Red 1 in PS-b-P4VP Micelles Controlled by a Toluene/Ethanol Solvent Mixture

The effects of Disperse Red 1 (DR1) in the poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) micelle on micellar morphology and fluorescence emission were studied using small-angle X-ray scattering (SAXS), generalized indirect Fourier transform (GIFT), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and photoluminescence (PL). PS-b-P4VP was coupled with DR1 in 10 mg/mL toluene/ethanol mixture solutions where ethanol and toluene were P4VP and PS selective, respectively. Hydrogen bonds were formed between the -OH group of DR1 and the pyridine ring in PS-b-P4VP. DR1 (which was coupled with P4VP) was confined in the core or corona of the micelle depending on the location of P4VP. The micellar structure was strongly dependent on varphi (weight percentage of toluene in a toluene/ethanol mixture). The PS-b-P4VP-DR1 complex in the mixture solutions showed the spherical micelle with the cores of P4VP and PS in ethanol-rich and toluene-rich solvents, respectively. The quenching phenomenon was observed for DR1 in the corona of PS-b-P4VP micelles [at varphi = 0 (ethanol)], while the fluorescence quantum yield decreased. However, significant increases in the fluorescence quantum yields at varphi = 100 were observed when DR1 was confined in the core of the PS-b-P4VP micelles. The confinement of DR1 in the hard core was more effective in fluorescence emission than that in the soft corona due to the slow trans-to-cis transition of DR1.

Chitosan-coated cotton cloth supported copper nanoparticles for toxic dye reduction

A new route to fabricate cotton cloth (CC) as easily removable substrate for the synthesis of copper nanoparticles on its surface and its utilization in a toxic dye reduction is reported herein. A 1 wt% chitosan (Chi) aqueous solution was prepared and coated onto CC surface to prepare the ions affinity Chi-CC material. The Chi-CC was then kept in copper sulphate solution with three different concentrations (0.05 M, 0.1 M and 0.2 M) to interact with Cu2+ ions through -NH and -OH functional groups of the Chi chain. After sufficient time of the Cu2+ uptake, the Chi-CC was treated with 0.1 M NaBH4 solution which turned its color indicating well organization of the adsorbed ions into Cu-nanoparticles. The bare CC, Chi-CC and Cu/Chi-CC were spectroscopically examined via scanning electron microscopy, X-ray diffractometry, energy dispersive X-ray spectroscopy and thermo-gravimetric analysis. Afterward, Cu/Chi-CC was used in the Congo red (CR) dye reduction by NaBH4 as catalyst. The performance of the amount of the catalyst and its usage in a series of similar dye reduction was evaluated.

Structures of the Cylindrical and Vesicular Micelles of an P4VP-longer Asymmetric PS-b-P4VP

The control of the self-assembled micellar morphology of amphiphilic block copolymers in a selective solvent has engrossed substantial interests in the theoretical and applied research fields. The micellar morphology of the block copolymers can be controlled by solvent selectivity and block copolymer composition. There are three main factors for controlling these morphologies, i.e., the stretching of core blocks, the repulsive interaction among corona chains, and the surface tension of the core/corona interface at the onset of micellization. The block copolymer can selfassemble into spherical, cylindrical, and vesicular micelles in a given solution. Among those micelles, the vesicle has fascinated scientists because of its diverse applications such as drug delivery diagnostics, electronics (chip nanopatterning), and catalysis (enzyme entrapment). Vesicles (generally kinetically trapped and non-equilibrium) are usually formed by low molecular materials such as surfactants or lipids. Wittmann et al. for the first time reported the polymeric vesicles of poly(styrene-b-isoprene) (PS-b-PI) and poly(styrene-b-ethylene oxide) (PS-b-PEO) in a mixture of ethyl benzene (a selective solvent for both blocks) and n-decane (a PI and PEO selective solvent). Schrage et al. investigated vesicular morphologies of quaternized poly(1-methyl-4vinyl pyridine-b-styrene) and poly(1,2-butadiene-b-(cesium methacrylate)) which were self-assembled in THF (nonselective for PS and poly(1,2-butadiene) but selective for charged blocks). Kesselman et al. also studied the change in the vesicular morphologies of PS-b-PI by controlling solvent selectivity in diethyl phthalate (less PS-selective) and dimethyl phthalate (highly PS-selective) mixtures. Putaux et al. investigated the vesicular morphologies of PS-b-PI in n-heptane and n-decane, both of which are selective solvents for PI. The PS-b-P4VP vesicles have been observed when the P4VP blocks were complexed with other small molecules. The vesicles of PS-b-P4VP in chloroform were observed when perfluorooctanoic acid (PFOA) was added to be complexed with P4VP. Peng et al. also reported another interesting research on the vesicular morphology of PS-b-P4VP in a complex form with low molecular-weight aliphatic acids (stearic acid, decanoate, acetic acid, and formic acid) in chloroform (non-selective for PS-b-P4VP and aliphatic acids but selective in a complex form). But, PS-bP4VP vesicles without complexation were rarely observed. The cylindrical morphology of an asymmetric PS(19600)b-P4VP(5100) (PS longer) in P4VP selective solvents was reported. However, the vesicles with asymmetric PS-b-P4VPs (P4VP longer) in PS selective solvents have not been reported. The block length of P4VP of the PS-b-P4VP is of prime importance because a number of valuable metals or small molecules could be complexed with the P4VP core of micelles (in the PS selective solvents) which is utilized as a nanoreactor. The screening of the solvent selectivity is necessary to check the possible micellar morphologies of the given block copolymer. Recently the micellar structures and their ordered structures of PS(12K)-b-P4VP(11.8K) and PS(19.6K)-b-P4VP (5.1 K) in the toluene/ethanol solvent system were reported. However, we believe that solvent selection for PS-b-P4VP is important in this study. We used the toluene/ethanol solvent system where toluene and ethanol are selective solvents for PS and P4VP, respectively. The toluene/ethanol system covers from PS-selective, to neutral, and to P4VPselective solvents although our previous THF/toluene system covers only from neutral to PS-selective solvents. Thus, we expected that a wider range of the micellar morphologies can be formed in the toluene/ethanol solvent system. The solvent selectivity was narrowly screened by changing the mixing ratio of the two solvents. But the vesicular structure was not found probably due to the less-asymmetric composition of the block copolymer and/or the less selectivity of the used solvent mixtures. The research in this article used a more-asymmetric block copolymer of PS (3.3K)-b-P4VP(18.7 K) (P4VP longer) in the toluene/ethanol mixtures to screen the solvent selectivity.

Single-step modification of chitosan for toxic cations remediation from aqueous solution

AbstractChitosan was chemically modified with 4-acryloylmorpholine in order to enhance Lewis basic centres in polymeric chain for cations removal. The new material was characterized using elemental analysis, infrared and 13C NMR in solid state and was applied for sorption of copper, lead and cadmium from aqueous solutions. The kinetic parameters were evaluated using pseudo-first- and second-order reaction. Kinetic results showed that the sorption process was best described by the pseudo-second-order model. The experimental data were adjusted to the Langmuir, the Freundlich and the Temkin sorption isotherms using both linear and nonlinear regression methods. The material showed the maximum sorption capacity for copper (3.35 mmol g−1), than lead (1.60 mmol g−1) and cadmium (0.74 mmol g−1), obtained through the Langmuir sorption isotherm. The Langmuir model provided the lowest error values and fit better to the experimental data compared with other models.

Preparation of crosslinked chitosan magnetic membrane for cations sorption from aqueous solution.

A chitosan magnetic membrane was prepared in order to confer magnetic properties to the membrane, which could be used for the removal of cations from aqueous solution. The crosslinked magnetic membrane was compared with pristine chitosan membrane in term of stability, morphology and cation adsorption capacity. The fabricated magnetic materials are thermally stable as shown by thermogravimetric curves. The membrane containing nickel magnetic particles (CHNiF-G) shows high thermal stability compared to the other membranes. The Fourier transform infrared spectroscopy showed successful preparation of chitosan magnetic membrane. Scanning electron microscopy micrographs showed the rough surface of the membrane with increased porosity. The prepared chitosan membranes were applied to cations of copper, nickel and lead in dilute aqueous solution. The chitosan membrane showed the following adsorption order for metallic cations: Cu2+ > Ni2+ > Pb2+, while CHNiF-G showed higher capacity, 3.51 mmol g-1 for copper, reflecting the improvement in adsorption capacity, since the amount of copper on pristine chitosan gave 1.40 mmol g-1. The time required for adsorption to reach to the equilibrium was 6 h for the selected cations using different chitosan membranes. The kinetic study showed that adsorption followed pseudo-second order kinetics. The most commonly used isotherm models, Freundlich, Langmuir and Temkin, were applied to experimental data using linear regression technique. However, The Temkin model fits better to experimental data.

Removal of Chromium(VI) from Industrial Effluents Through Supported Liquid Membrane Using Trioctylphosphine Oxide as a Carrier

The present study describes extraction of chromium(VI) through supported liquid membrane (SLM), Celgard 2400, which was impregnated with trioctylphosphine oxide (TOPO) dissolved in toluene. The stripping phase was comprised of diphenylcarbazide (DPC) in sulfuric acid (H2SO4) whereas the feed phase consists of potassium dichromate (K2Cr2O7) and hydrogen peroxide (H2O2). The effects of concentrations of chromium, TOPO, DPC, and H2SO4 have been studied in order to evaluate the transport efficiency of chromium(VI) ion. The optimum experimental conditions for the chromium(VI) extraction were established as follows: 19.2 × 10−4 mol L-1 chromium ion, 1.5 mol L-1 H2O2 concentration in the feed phase, 0.1 mol L-1 TOPO concentration in the membrane phase and 0.001 mol L-1 DPC and 1.5 mol L-1 H2SO4 as stripping phase. The measurements of percent recovery, distribution coefficient, flux and permeability were made at the given optimized conditions. The extraction time and membrane stability were also investigated. Extraction efficiency of 80% was recorded in 180 min and the SLM system was found stable up to 10 days. The optimized SLM system was then applied on the paint industry wastewater; about 80% of chromium(VI) was successfully removed from the wastewater.

Spectrophotometric methods for the determination of urea in real samples using silver nanoparticles by standard addition and 2nd order derivative methods

In this work, we have developed simple, sensitive and inexpensive methods for the spectrophotometric determination of urea in urine samples using silver nanoparticles (AgNPs). The standard addition and 2nd order derivative methods were adopted for this purpose. AgNPs were prepared by chemical reduction of AgNO3 with hydrazine using 1,3-di-(1H-imidazol-1-yl)-2-propanol (DIPO) as a stabilizing agent in aqueous medium. The proposed methods were based on the complexation of AgNPs with urea. Using this concept, urea in the urine samples was successfully determined spectrophotometric methods. The results showed high percent recovery with ±RSD. The recoveries of urea in the three urine samples by spectrophotometric standard addition were 99.2%±5.37, 96.3%±4.49, 104.88%±4.99 and that of spectrophotometric 2nd order derivative method were 115.3%±5.2, 103.4%±2.6, 105.93%±0.76. The results show that these methods can open doors for a potential role of AgNPs in the clinical determination of urea in urine, blood, biological, non-biological fluids.