Microstructure and carbon storage capacity of hydrated magnesium carbonates synthesized from different sources and conditions

Recently, the mineral carbonation via the reaction of CO2 with saline aquafers received much attention as one of the most promising ways for geologic CO2 storage. This paper reports microstructure and carbon storage capacity of hydrated magnesium carbonates (HMCs) synthesized from different sources, i.e., reject brine and commercial Mg(OH)2 slurry, and under different conditions, i.e., pH (8–14) and Mg(OH)2:CO2 molar ratio (1:1–1:7). Results show that dypingite (Mg5(CO3)4(OH)2·5H2O) is the main phase forming at lower Mg(OH)2:CO2 ratios. An increase in the Mg(OH)2:CO2 ratio and/or pH leads to the precipitation of nesquehonite (MgCO3·3H2O). A unique “house of cards” texture, involving formation of the rosette-like dypingite flakes on the surface of nesquehonite needles, is discovered under elevated pH and Mg(OH)2:CO2 ratios. HMCs synthesized from reject brine exhibit a much higher carbon storage capacity of 82.6% than that produced from the commercial Mg(OH)2 slurry (43.7%). Findings from this study advance understanding of mineral recovery from reject brine and the capture and long-term storage of CO2 in the form of HMCs

Investigation of the properties of MgO recovered from reject brine obtained from desalination plants

In addition to its use in various applications such as those in the agriculture, pharmaceutical and refractory industries, MgO is being investigated as a cement binder due to the low calcination temperatures used during its production and its ability to gain strength by absorbing CO2in construction products. Similar to the dry-route, the reactivity of MgO synthesized from waste water or reject brine via the calcination of the precipitated Mg(OH)2depends on the calcination conditions. This study investigated the influence of two bases, namely ammonia solution (NH4OH) and sodium hydroxide (NaOH), on the properties of Mg(OH)2precipitated and consequently the characteristics of MgO produced under different calcination conditions. The energy consumption of the production of reactive MgO from reject brine via the addition of NH4OH and NaOH was also reported and compared with the industrial production routes to assess the sustainability of the production procedure. The final products were characterized in terms of their specific surface area (SSA) and microstructure. Results indicated that Mg(OH)2synthesized via the addition of NH4OH into reject brine generated a more porous, flake-like morphology than those obtained via the use of NaOH. The SSA and reactivity of NH4OH-based MgO demonstrated a sharper decrease with increasing temperature and duration compared to NaOH-based MgO. Out of all samples, NH4OH-based MgO calcined at 500 °C for 2 h revealed the highest reactivity (SSA of 78.8 m2/g), which was higher than NaOH-based MgO (SSA of 51.4 m2/g)

Recovery of reactive MgO from reject brine via the addition of NaOH

© 2017 Elsevier B.V. Reject brine, generated as a waste at the end of the desalination process, presents a useful source for the extraction of valuable resources. This study investigated the recovery of reactive MgO from reject brine obtained from a local desalination plant. This was enabled via the reaction of Mg2 + present within reject brine with an alkali source (NaOH), which led to the precipitation of Mg(OH)2, along with a small amount of CaCO3. The determination of the optimum NaOH/Mg2 + ratio led to the production of the highest amount of yield. The synthesized Mg(OH)2 was further calcined under a range of temperatures (500–700 °C) and durations (2 − 12h) to produce reactive MgO. A detailed characterization of MgO obtained under these conditions was presented in terms of its reactivity, specific surface area (SSA), composition and microstructure. While an increase in the calcination temperature and duration decreased the reactivity and SSA of MgO, samples calcined at 500 °C for 2 h revealed the highest reactivity, which was reflected by their SSA of 51.4 m2/g.This project is funded by the National Research Foundation (NRF), Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program

Synthesis of reactive MgO from reject brine via the addition of NH4_{4}OH

Reactive magnesia (MgO) with a high purity and reactivity is used in several high-end applications. This study reports the feasibility of synthesizing high reactivity MgO from reject brine with the use of NH$_{4}$OH. The molar amount of NH$_{4}$OH was optimized at a NH$_{4}$OH/Mg$^{2 +}$ molar ratio of 6 to provide maximum magnesium oxide yield and purity. This led to the synthesis of Mg(OH)$_{2}$ with a purity of 93.5%, which was further calcined at 500 °C for 2 h to produce reactive MgO with a SSA of 78.8 m2/g. This study shed light on the significant potential of reject brine in the recovery of Mg$^{2 +}$ and the synthesis of reactive MgO with a wide range of potential applications.The authors would like to acknowledge research scholarship from Energy Research Institute at Nanyang Technological University

Terahertz frequency quantum cascade lasers for use as waveguide-integrated local oscillators

Since their first demonstration in 2002, the performance of terahertz frequency quantum cascade lasers has developed extremely rapidly. We consider the potential use of terahertz frequency quantum cascade lasers as local oscillators in satellite-borne instrumentation for future Earth observation and planetary science missions. A specific focus will be on the development of compact, waveguide-integrated, heterodyne detection systems for the supra-terahertz range

Feedhorn-integrated THz QCL local oscillators for the LOCUS atmospheric sounder

The LOCUS atmospheric sounder is a satellite-borne THz radiometer concept, for studying molecular species in the mesosphere and lower thermosphere. We report waveguide-integrated THz quantum-cascade lasers for use as 3.5 THz local oscillators. A waveguide-integration scheme, using an integrated diagonal feedhorn significantly improves power outcoupling. 1.3 mW THz emission is demonstrated in a space-qualified Stirling cryocooler at 57 K, with ∼15° beam divergence

Phase Locking Of A 2.5 THz Quantum Cascade Laser To A Microwave Reference Using THz Schottky Mixer

The frequency of a 2.5 THz QCL are stabilized to sub-hertz accuracy by phase-locking to a stable 100 MHz microwave reference, using a 2.3–3.2 THz room temperature Schottky diode based harmonic mixer. The down-converted phase locked beat note is stable over a long term test

The promoter polymorphism -232C/G of the PCK1 gene is associated with type 2 diabetes in a UK-resident South Asian population

Background: The PCK1 gene, encoding cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), has previously been implicated as a candidate gene for type 2 diabetes (T2D) susceptibility. Rodent models demonstrate that over-expression of Pck1 can result in T2D development and a single nucleotide polymorphism (SNP) in the promoter region of human PCK1 (-232C/G) has exhibited significant association with the disease in several cohorts. Within the UK-resident South Asian population, T2D is 4 to 6 times more common than in indigenous white Caucasians. Despite this, few studies have reported on the genetic susceptibility to T2D in this ethnic group and none of these has investigated the possible effect of PCK1 variants. We therefore aimed to investigate the association between common variants of the PCK1 gene and T2D in a UK-resident South Asian population of Punjabi ancestry, originating predominantly from the Mirpur area of Azad Kashmir, Pakistan. \ud \ud Methods: We used TaqMan assays to genotype five tagSNPs covering the PCK1 gene, including the -232C/G variant, in 903 subjects with T2D and 471 normoglycaemic controls. \ud \ud Results: Of the variants studied, only the minor allele (G) of the -232C/G SNP demonstrated a significant association with T2D, displaying an OR of 1.21 (95% CI: 1.03 - 1.42, p = 0.019). \ud \ud Conclusion: This study is the first to investigate the association between variants of the PCK1 gene and T2D in South Asians. Our results suggest that the -232C/G promoter polymorphism confers susceptibility to T2D in this ethnic group. \ud \ud Trial registration: UKADS Trial Registration: ISRCTN38297969

In vitro assembly of Ebola virus nucleocapsid-like complex expressed in E. coli

Ebola virus (EBOV) harbors an RNA genome encapsidated by nucleoprotein (NP) along with other viral proteins to form a nucleocapsid complex. Previous Cryo-eletron tomography and biochemical studies have shown the helical structure of EBOV nucleocapsid at nanometer resolution and the first 450 amino-acid of NP (NPΔ451–739) alone is capable of forming a helical nucleocapsid-like complex (NLC). However, the structural basis for NP-NP interaction and the dynamic procedure of the nucleocapsid assembly is yet poorly understood. In this work, we, by using an E. coli expression system, captured a series of images of NPΔ451–739 conformers at different stages of NLC assembly by negative-stain electron microscopy, which allowed us to picture the dynamic procedure of EBOV nucleocapsid assembly. Along with further biochemical studies, we showed the assembly of NLC is salt-sensitive, and also established an indispensible role of RNA in this process. We propose the diverse modes of NLC elongation might be the key determinants shaping the plasticity of EBOV virions. Our findings provide a new model for characterizing the self-oligomerization of viral nucleoproteins and studying the dynamic assembly process of viral nucleocapsid in vitro