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Highfield J.,Institute of Chemical and Engineering Sciences, Singapore | Lim H.,National Junior College | Fagerlund J.,Abo Akademi University | Zevenhoven R.,Abo Akademi University
RSC Advances | Year: 2012

This paper concerns the growing role of cheap and potentially recyclable ammonium salts in CO 2 mineralization. The powerful hyphenated technique TG-FTIR, along with XRD and ICP-AES, were used to shed light on the underlying chemistry and measure the efficiency of magnesium ion extraction from a Finnish serpentinite in contact with molten ammonium sulfate above 300 °C. From micro- and gram-scale tests, flux extraction as epsomite [MgSO 4·7H 2O] proceeds via the intermediacy of Tutton salts, NH 4/Mg double sulfates increasingly rich in Mg. Extraction is effected through the agency of acidic derivatives, principally ammonium bisulfate and sulfamic acid, which are created sequentially from ammonium sulfate in situ. However, sulfamic acid volatilizes and/or decomposes at a significant rate by 400 °C. This loss mechanism is primarily responsible for the modest recovery of Mg (50-60%). An improved process would operate below 400 °C where Mg extraction as efremovite [(NH 4) 2Mg 2(SO 4) 3] is effective. Future experiments evaluating the use of humid air to stabilize the bisulfate and impede the loss of flux are recommended. This journal is © 2012 The Royal Society of Chemistry. Source

Highfield J.,Institute of Chemical and Engineering Sciences, Singapore | Lim H.,National Junior College | Fagerlund J.,Abo Akademi University | Zevenhoven R.,Abo Akademi University
RSC Advances | Year: 2012

This paper assesses the suitability of mechanochemistry as a convenient low-energy processing option in CO 2 mineralization. Whereas some success has been reported in milling alkaline earth-containing minerals under gaseous CO 2, this work focuses instead on a purely solid-state approach towards two key objectives: (a) Mg extraction from serpentine using ammonium bisulfate; and (b) direct or indirect CO 2 sequestration using ammonium bicarbonate in a natural extension of its role as "CO 2 carrier" in the chilled ammonia scrubbing process. In Mg extraction work, dry milling of serpentine with ammonium bisulfate gave respectable yields (>60% Mg) as boussingaultite [(NH 4) 2Mg(SO 4) 2·6H 2O] in 2 to 4 h. In CO 2 sequestration, dry milling anhydrous magnesium sulfate with ammonium bicarbonate yielded only mixed sulfate products. Carbonation of the heptahydrate, epsomite, was found to proceed via ammonium magnesium carbonate hydrate [(NH 4) 2Mg(CO 3) 2· 4H 2O], which dissolves incongruently to yield nesquehonite [MgCO 3·3H 2O]. The modest conversion (∼30%) is probably due to equipartition of Mg into the double sulfate co-product. A similar route is followed in magnesia and brucite, in which the existence of an amorphous native carbonate precursor to nesquehonite in the same molar ratio (Mg:CO 2 = 1) was inferred from inconsistency in the XRD intensities. This was largely responsible for the high carbonation yields in the unwashed products, ∼70% and ∼85% in MgO and Mg(OH) 2, respectively, as confirmed by TG-FTIR. The same intermediate is probably formed in serpentine, but it is apparently soluble in the aqueous mineral environment. When the unwashed product is subjected to mild thermal consolidation, stable hydromagnesite [Mg 5(CO 3) 4(OH) 2·4H 2O] is formed in ∼20% yield after milling for 16 h. Possible identities for the amorphous precursor are briefly considered. This journal is © 2012 The Royal Society of Chemistry. Source

Koh E.Y.,Victoria University of Wellington | Koh E.Y.,National University of Singapore | Phua W.,Victoria University of Wellington | Phua W.,National Junior College | Ryan K.G.,Victoria University of Wellington
Environmental Microbiology Reports | Year: 2011

Aerobic anoxygenic phototrophs are obligate aerobes with unusually high concentrations of carotenoids, low cellular contents of bacteriochlorophyll-a and they lack light-harvesting complex II. In this study, sea ice and seawater samples were collected from six different sites in the Ross Sea, Antarctica. Using a combination of primers for pufM (which encodes a pigment-binding protein subunit of the reaction centre complex), clone libraries of DNA and cDNA were created and a total of 63 positive clones were obtained from three sites, all clustering within the α-Proteobacteria. Fifty-three of these clones were from seawater. The remaining clones were from sea ice and all were found in the middle and bottom sections of the ice. These sea ice bacteria may favour the lower part of the ice matrix where irradiance is low. This report highlights the first findings of AAnPs in antarctic sea ice and seawater within the Ross Sea Region. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd. Source

This paper presents the customization of Easy Java Simulation models, used with actual laboratory instruments, to create active experiential learning for measurements. The laboratory instruments are the vernier caliper and the micrometer. Three computer model design ideas that complement real equipment are discussed. These ideas involve (1) a simple two-dimensional view for learning from pen and paper questions and the real world; (2) hints, answers, different scale options and the inclusion of zero error; (3) assessment for learning feedback. The initial positive feedback from Singaporean students and educators indicates that these tools could be successfully shared and implemented in learning communities. Educators are encouraged to change the source code for these computer models to suit their own purposes; they have creative commons attribution licenses for the benefit of all. © 2014 IOP Publishing Ltd. Source

Janczewski D.,Institute of Materials Research and Engineering of Singapore | Tomczak N.,Institute of Materials Research and Engineering of Singapore | Song J.,Institute of Materials Research and Engineering of Singapore | Long H.,National Junior College | And 4 more authors.
Journal of Materials Chemistry | Year: 2011

A facile method for the fabrication of Quantum Dot/poly(N- isopropylacrylamide) (QD/PNIPAM) micropatterns on glass is presented. Water-soluble QDs functionalized with polymerizable methacrylic groups effectively copolymerize with N-isopropylacrylamide monomer resulting in stable hybrid organic-inorganic networks. The patterns display temperature and pH responsive luminescence behaviour. © 2011 The Royal Society of Chemistry. Source

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