198 research outputs found
Chitosan -A Natural Adsorbent for Copper Ions
Abstract -As a result of industrial activities and technological changes, a high and continuously increasing amount of heavy metals and heavy metal containing effluents are released into the environment by different industrial nations. These metals cannot be degraded. Furthermore, because of their toxicity, they are highly detrimental to the environment and human health. Heavy metals accumulate in the food chain and become permanent pollutants in the environment. In the human body they accumulate in different organs causing serious damage. To overcome this problem, the adsorption behaviour of heavy metal ions, in particular copper ions was investigated by apply chitosan flakes, powder, and beads as a natural adsorbent. Metal removal was studied using adsorbance measurements, SEM-EDX, and size measurements. The adsorption capacity of chitosan was determined at different concentration and times. The received adsorption capacities for copper ions were very promising, with a maximum value of 150 mg/g on chitosan powder
Unlocking CO Depletion in Protoplanetary Disks II. Primordial C/H Predictions Inside the CO Snowline
CO is thought to be the main reservoir of volatile carbon in protoplanetary
disks, and thus the primary initial source of carbon in the atmospheres of
forming giant planets. However, recent observations of protoplanetary disks
point towards low volatile carbon abundances in many systems, including at
radii interior to the CO snowline. One potential explanation is that gas phase
carbon is chemically reprocessed into less volatile species, which are frozen
on dust grain surfaces as ice. This mechanism has the potential to change the
primordial C/H ratio in the gas. However, current observations primarily probe
the upper layers of the disk. It is not clear if the low volatile carbon
abundances extend to the midplane, where planets form. We have run a grid of
198 chemical models, exploring how the chemical reprocessing of CO depends on
disk mass, dust grain size distribution, temperature, cosmic ray and X-ray
ionization rate, and initial water abundance. Building on our previous work
focusing on the warm molecular layer, here we analyze the results for our grid
of models in the disk midplane at 12 au. We find that either an ISM level
cosmic ray ionization rate or the presence of UV photons due to a low dust
surface density are needed to chemically reduce the midplane CO gas abundance
by at least an order of magnitude within 1 Myr. In the majority of our models
CO does not undergo substantial reprocessing by in situ chemistry and there is
little change in the gas phase C/H and C/O ratios over the lifetime of the
typical disk. However, in the small sub-set of disks where the disk midplane is
subject to a source of ionization or photolysis, the gas phase C/O ratio
increases by up to nearly 9 orders of magnitude due to conversion of CO into
volatile hydrocarbons.Comment: Accepted for publication in ApJ, 15 pages, 10 figures, 3 table
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Solubility and selectivity effects of the anion on the adsorption of different heavy metal ions onto chitosan
The biopolymer chitosan is a very efficient adsorber material for the removal of heavy metal ions from aqueous solutions. Due to the solubility properties of chitosan it can be used as both a liquid adsorber and a solid flocculant for water treatment reaching outstanding adsorption capacities for a number of heavy metal ions. However, the type of anion corresponding to the investigated heavy metal ions has a strong influence on the adsorption capacity and sorption mechanism on chitosan. In this work, the adsorption capacity of the heavy metal ions manganese, iron, cobalt, nickel, copper, and zinc were investigated in dependence on their corresponding anions sulfate, chloride, and nitrate by batch experiments. The selectivity of the different heavy metal ions was analyzed by column experiments. © 2020 by the authors
A Complementary and Revised View on the N-Acylation of Chitosan with Hexanoyl Chloride
The modification of the biobased polymer chitosan is a broad and widely studied field. Herein, an insight into the hydrophobization of low-molecular-weight chitosan by substitution of amino functionalities with hexanoyl chloride is reported. Thereby, the influence of the pH of the reaction media was investigated. Further, methods for the determination of the degree of substitution based on 1H-NMR, FTIR, and potentiometric titration were compared and discussed regarding their accuracy and precision. 1H-NMR was the most accurate method, while FTIR and the potentiometric titration, though precise and reproducible, underlie the influence of complete protonation and solubility issues. Additionally, the impact of the pH variation during the synthesis on the properties of the samples was investigated by Cd2+ sorption experiments. The adjusted pH values during the synthesis and, therefore, the obtained degrees of substitution possessed a strong impact on the adsorption properties of the final material
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Waterborne phenolic, triazine-based porous polymer particles for the removal of toxic metal ions
Highly functional and also highly porous materials are presenting great advantages for applications in energy storage, catalysis and separation processes, which is why a continuous development of new materials can be seen. To create a material combining the promising potential interactions of triazine groups with the electrostatic or hydrogen bonding interactions of phenolic groups, a completely new polymeric resin was synthesized. From an eco-friendly dispersion polymerization in water, a copolymer network was obtained, which includes nine hydroxyl groups and one s-triazine ring per repetition unit. The polymer forms highly porous particles with specific surface areas up to 531 ​m2/g and a negative streaming potential over a great pH range. The adsorption isotherms of Ni2+, Cd2+, and Pb2+ were studied in more detail achieving very good adsorption capacities (16 mg Ni2+/g, 24 mg Cd2+/g, and 90 mg Pb2+/g). Demonstrating excellent properties for adsorption applications. The adsorbent exhibited selectivity for the adsorption of Pb2+ over more commonly occurring but non-toxic metal ions such as Fe2+, Ca2+, Mg2+, and K+. Furthermore, reusability of the material was demonstrated by facile, quantitative desorption of adsorbed Pb2+ with a small amount of diluted HCl, circumventing organic chelators. Subsequently, adsorption was carried out without decrease in adsorption performance
Probing the Gas Content of Late-stage Protoplanetary Disks with N_2H^+
The lifetime of gas in circumstellar disks is a fundamental quantity that informs our understanding of planet formation. Studying disk gas evolution requires measurements of disk masses around stars of various ages. Because H_2 gas is unobservable under most disk conditions, total disk masses are based on indirect tracers such as sub-mm dust and CO emission. The uncertainty in the relation between these tracers and the disk mass increases as the disk evolves. In a few well-studied disks, CO exhibits depletions of up to 100× below the assumed interstellar value. Thus, additional tracers are required to accurately determine the total gas mass. The relative lack of nitrogen found in solid solar system bodies may indicate that it persists in volatile form, making nitrogen-bearing species more robust tracers of gas in more evolved disks. Here we present Atacama Large Millimeter/submillimeter Array detections of N_2H^+ in two mature, ~5–11 Myr old disks in the Upper Scorpius OB Association. Such detections imply the presence of H_2-rich gas and sources of ionization, both required for N_2H^+ formation. The Upper Sco disks also show elevated N_2H^+/CO flux ratios when compared to previously observed disks with ≳10× higher CO fluxes. Based on line ratio predictions from a grid of thermochemical disk models, a significantly reduced CO/H_2 abundance of <10^(−6) for a gas-to-dust ratio of ≳100 is required to produce the observed N_2H^+ fluxes. These systems appear to maintain H_2 gas reservoirs and indicate that carbon- and nitrogen-bearing species follow distinct physical or chemical pathways as disks evolve
Erratum:Randomized double-blind placebo-controlled trial of perhexiline in heart failure with preserved ejection fraction syndrome (Future Cardiology (2014) 10:6 (693-698))
Following publication of the Clinical Trial Protocol by Satnam Singh, Roger Beadle, Donnie Cameron, Amelia Rudd, Maggie Bruce, Baljit Jagpal, Konstantin Schwarz, Gemma Brindley, Fergus McKiddie, Chim Lang, Dana Dawson and Michael Frenneaux, titled ‘Randomized double-blind placebo-controlled trial of perhexiline in heart failure with preserved ejection fraction syndrome’, which appeared in the December 2014 issue of Future Cardiology (Future Oncol. 10[6], 693–698 [2014]), it has been brought to our attention that the author names were presented incorrectly as:Satnam Singh, Roger Beadle, Donnie Cameron, Amelia Rudd, Maggie Bruce, Baljit Jagpal, Konstantin Schwarz, Gemma Brindley, Fergus Mckiddie, Peter Nightingale, Chim Lang, Dana Dawson and Michael Frenneaux.The correct presentation should be:Satnam Singh, Roger Beadle, Donnie Cameron, Amelia Rudd, Maggie Bruce, Baljit Jagpal, Konstantin Schwarz, Gemma Brindley, Fergus Mckiddie, Chim Lang, Dana Dawson and Michael Frenneaux.The authors and editors of Future Cardiology would like to sincerely apologize for any inconvenience or confusion this may have caused our readers.<br/
Erratum:Randomized double-blind placebo-controlled trial of perhexiline in heart failure with preserved ejection fraction syndrome (Future Cardiology (2014) 10:6 (693-698))
Following publication of the Clinical Trial Protocol by Satnam Singh, Roger Beadle, Donnie Cameron, Amelia Rudd, Maggie Bruce, Baljit Jagpal, Konstantin Schwarz, Gemma Brindley, Fergus McKiddie, Chim Lang, Dana Dawson and Michael Frenneaux, titled ‘Randomized double-blind placebo-controlled trial of perhexiline in heart failure with preserved ejection fraction syndrome’, which appeared in the December 2014 issue of Future Cardiology (Future Oncol. 10[6], 693–698 [2014]), it has been brought to our attention that the author names were presented incorrectly as:Satnam Singh, Roger Beadle, Donnie Cameron, Amelia Rudd, Maggie Bruce, Baljit Jagpal, Konstantin Schwarz, Gemma Brindley, Fergus Mckiddie, Peter Nightingale, Chim Lang, Dana Dawson and Michael Frenneaux.The correct presentation should be:Satnam Singh, Roger Beadle, Donnie Cameron, Amelia Rudd, Maggie Bruce, Baljit Jagpal, Konstantin Schwarz, Gemma Brindley, Fergus Mckiddie, Chim Lang, Dana Dawson and Michael Frenneaux.The authors and editors of Future Cardiology would like to sincerely apologize for any inconvenience or confusion this may have caused our readers.<br/
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