Danish J. Malik

Characterisation of the surface of oxidised carbon adsorbents

The surface reactivity and functional group content of a series of oxidised active carbons has been assessed by elemental analysis, electrophoretic mobility measurements and potentiometric titrations. Oxidation of carbons with hot air resulted in a greater proportion of relatively weak acidic surface functional groups (i.e., phenolic), whereas nitric acid modification produced a greater amount of carboxylic groups. Electrophoretic mobility measurements suggest that the carbon surface is negatively charged within the range of the pH values studied. pH titration results indicate that the surface acidity of active carbons is stronger than that of a commercial polymeric carboxylic acid ion exchange resin. Possible mechanisms of carbon surface oxidation are discussed.

Characterisation of novel modified active carbons and marine algal biomass for the selective adsorption of lead

This paper discusses the sorption performance of novel materials for the removal of lead(II) and copper(II) from near-neutral aqueous solutions. Active carbons with surface heteroatoms of oxygen and phosphorus have been prepared. The surface functional groups display weakly acidic ion exchange characteristics. The optimum solution pH for maximum metal sorption is related to the pK values of the surface functional groups. In oxygenated active carbons, pK values are not distinct but can be obtained by describing proton binding to the heterogeneous adsorbent surface as a continuous proton affinity distribution. Information derived from zeta-potential measurements combined with knowledge of the pK distribution function and concentration of surface functional groups has been used to explain the selectivity of oxidised active carbons towards lead(lI) in the presence of copper(II) from multi-metal bearing solutions. Marine algal-based biosorbents have been challenged with lead(II) and copper(II)-bearing wastewater. The weakly acidic carboxyl groups of structural polysaccharides present within the algal matrix display high sorption capacity for both metals. The negative surface charge of algal particles results in electrostatic interactions as well as coordination between metal species and the adsorbent surface. Proton affinity for the algal surface lowers the negative surface potential at pH values around 2. The surface functional groups in algae unlike those in oxidised active carbons may be represented by discrete acid-dissociation constant values. The influence of conformational differences in uronic-acid segments upon metal ion selectivity is discussed.

The uses and abuses of rapid bioluminescence-based ATP assays.

Bioluminescence-based ATP testing of solid surfaces has become well established in the food processing industry as part of general hazard analysis and critical control points (HACCP) measures. The rise in healthcare associated infections (HAIs) at the turn of the century focussed attention on the environment as a potential reservoir of the agents responsible for such infections. In response to the need for objective methods of assessing the efficiency of cleaning in healthcare establishments and for rapid methods for detecting the presence of the pathogens responsible for HAIs, it was proposed that ATP testing of environmental surfaces be introduced. We examine the basis behind the assumptions inherent in these proposals. Intracellular ATP levels are shown to vary between microbial taxa and according to environmental conditions. Good correlations between microbial numbers and ATP levels have been obtained under certain specific conditions, but never within healthcare settings. Notwithstanding, ATP testing may still have a role in providing reassurance that cleaning regimes are being carried out satisfactorily. However, ATP results should not be interpreted as surrogate indicators for the presence of microbial pathogens.

Interpretation of Transition Metal Sorption Behavior by Oxidized Active Carbons and Other Adsorbents

Abstract Several active carbons derived from different precursors and oxidized by different techniques have been characterized by N2 porosimetry and various titration methods. The adsorption of Cu2+, Ni2+, Co2+, Zn2+ and Mn2+ from aqueous solutions was studied using these carbons and carboxylic resin Purolite C104. The affinity series Mn2+ < Co2+ < Ni2+ < Cu2+ > Zn2+ established in adsorption experiments coincides with the Irving–Williams order and is independent of the method and extent of adsorbent oxidation, carbon precursor, porous structure, and type of adsorbent. Enhanced selectivity of adsorbents towards Cu2+ is related to the electronic structure of this ion.

Estimating bacterial surface contamination by means of ATP determinations: 20 pence short of a pound

This Letter to the Editor was published in the Journal of Hospital Infection [© The Healthcare Infection Society. Published by Elsevier Ltd.] The definitive version is available at: http://dx.doi.org/10.1016/j.jhin.2011.12.021

Characterization and evaluation of seaweed-based sorbents for treating toxic metal-bearing solutions

Marine algal varieties Ascophyllum nodosum, Lessonia flavicans, Laminaria hyperborea and Durvillea potatorum as well as processed seaweed residues arising from the algin extraction industry have been evaluated for toxic metal sorption. Biosorption isotherms have been obtained for copper, cadmium and nickel at controlled solution pH 4. Potentiometric titrations and esterification of algal biomass indicate that carboxylate groups are primarily responsible for metal sorption. Proton/metal interactions play an important role in the biosorption process. Swelling of biosorbents is discussed in the context of potential large-scale fixed-bed column applications.

Microencapsulation of Clostridium difficile specific bacteriophages using microfluidic glass capillary devices for colon delivery using pH triggered release

The prevalence of pathogenic bacteria acquiring multidrug antibiotic resistance is a global health threat to mankind. This has motivated a renewed interest in developing alternatives to conventional antibiotics including bacteriophages (viruses) as therapeutic agents. The bacterium Clostridium difficile causes colon infection and is particularly difficult to treat with existing antibiotics; phage therapy may offer a viable alternative. The punitive environment within the gastrointestinal tract can inactivate orally delivered phages. C. difficile specific bacteriophage, myovirus CDKM9 was encapsulated in a pH responsive polymer (Eudragit® S100 with and without alginate) using a flow focussing glass microcapillary device. Highly monodispersed core-shell microparticles containing phages trapped within the particle core were produced by in situ polymer curing using 4-aminobenzoic acid dissolved in the oil phase. The size of the generated microparticles could be precisely controlled in the range 80 μm to 160 μm through design of the microfluidic device geometry and by varying flow rates of the dispersed and continuous phase. In contrast to free ‘naked’ phages, those encapsulated within the microparticles could withstand a 3 h exposure to simulated gastric fluid at pH 2 and then underwent a subsequent pH triggered burst release at pH 7. The significance of our research is in demonstrating that C. difficile specific phage can be formulated and encapsulated in highly uniform pH responsive microparticles using a microfluidic system. The microparticles were shown to afford significant protection to the encapsulated phage upon prolonged exposure to an acid solution mimicking the human stomach environment. Phage encapsulation and subsequent release kinetics revealed that the microparticles prepared using Eudragit® S100 formulations possess pH responsive characteristics with phage release triggered in an intestinal pH range suitable for therapeutic purposes. The results reported here provide proof-of-concept data supporting the suitability of our approach for colon targeted delivery of phages for therapeutic purposes.

On the difficulties of isolating Clostridium difficile from hospital environments

Spores of Clostridium difficile were deposited on to a stainless steel surface and subsequently exposed to a chlorine-releasing disinfectant (dichloroisocyanurate). Recovery of the spores was carried out using RODAC plates containing a variety of selective and non-selective agars. The non-selective agar media yielded higher recoveries of both control and chlorine-stressed spores. Our results show that the antibiotics used in selective media imposed an additional stress on both disinfectant-treated and untreated spores resulting in considerably reduced recoveries. This could lead to a serious underestimate of the extent of environmental contamination by this organism.

Sorption of Pesticides and Herbicides on Highly Polar Polymeric Sorbents

Six porous copolymers of acrylonitrile (AN)/divinylbenzene (DVB) and methacrylonitrile (MAN)/DVB have been synthesized by the suspension polymerization in the presence of inert diluents. The resulting adsorbents are found to have slightly different specific surface areas (460–720 m2/g for AN/DVB and 560–730 m2/g for MAN/DVB) and contain various amounts of strongly polar nitrile groups. The influence of surface polarity has been studied for the sorption of selected pesticides and herbicides from water. In addition, a series of styrene-divinylbezene resins, namely Hypersol-Macronet™ MN-100 (weakly basic), MN-400 (strongly basic), and MN-200 (unfunctionalized) have been tested for the removal of selected pesticides and herbicides. The sorption of atrazine on all studied sorbents is significantly higher than sorption of imazapyr or 2,4-dichlorophenoxyacetic acid. Atrazine sorption on AN/DVB and MAN/DVB resins is in the range of 30–66 mg/g (0.055–0.092 mg/m2) at an equilibrium concentration of 1 mg/L in solution.

Influence of activated carbon oxidation treatments on the selective removalof copper and lead

Air, acid, and electrochemical oxidation treatments have been employed to carefully control the amount and distribution of acidic surface groups in a series of activated carbons prepared from apricot stones. The surface reactivity and functional group distribution of oxidized active carbons have been assessed using numerous analytical and surface measurement techniques including nitrogen sorption, elemental analysis, potentiometric titrations, zeta potential measurements, and Boehms titrations. Preliminary electrochemical oxidation results suggest that this treatment provides better control of the resultant surface acidity of the prepared carbons. Lead and copper sorption studies indicate that it is possible to alter the selectivity of the oxidized active carbons towards heavy metals by changing the quantity and/or relative proportion of the individual oxygenated surface functional groups.