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Carbon nanotubes (CNT) are a family of carbon nanomaterials that have uses in many technological and medical applications due to their unique properties. However, compared to other nanomaterials, CNT have a significantly lower specific surface areas (SSA), which is a critical limitation for applications. To overcome this limitation, here, we report a new protocol to synthesize a hybrid material composed of varying ratios of multiwalled carbon nanotubes (MWCNT) and ferrihydrite (FHY). Furthermore, through a series of physical and electrochemical characterization tests, we determined that 36% FHY and 64% MWCNT is the optimum ratio for a composite that maximizes both SSA and specific capacitance. The calculated SSA of the composite was 190 m²·g−1, 2.9 times higher than that of MWCNT alone. Moreover, the composite retained valuable electrochemical properties of CNT with an estimated specific capacitance of 100 F·g−1. This composite is a promising multifunctional nanomaterial for environmental and technological applications requiring electrochemical reactivity and high specific areas such as environmental biosensors, and capacitive deionization for wastewater remediation, and water softening. [ABSTRACT FROM AUTHOR]

Abstract: Bulk geochemistry of ~1.8Ma lacustrine claystone at Olduvai Gorge, Tanzania, is controlled principally by the geochemistry of ultrafine (<0.1μm), authigenic clay minerals. Authigenic clays have an average structural formula of (Si3.83Al0.17)(Al0.43Fe0.49Mg0.84)(Na0.99K0.22Ca0.16)O10(OH)2; octahedral composition varies, with Mg/(Al+Fe) ranging from 0.7 to 2.3. These clay minerals have a complex history of interaction with saline, alkaline water, followed by secondary diagenetic reactions that leached Mg in freshwater paleoenvironments. Lateral variations in whole-rock and clay geochemistry show westward enrichment in Mg, from Mgoct =0.6–1.6. This is consistent with persistence of saline, alkaline Paleolake Olduvai to the west, and the presence of groundwater wetlands and other freshwater paleoenvironments to the east. Stone artifact mass density also varies systematically across the basal Bed II deposits, ranging from 100.0 to 104.3 g of artifacts per cubic meter of excavated sediment. Significant correlation is found between clay geochemistry and the density of artifacts excavated from associated archeological trenches (r2 =0.59, p<0.01). This relationship supports models of hominin land use in which artifact use and discard is concentrated near freshwater paleoenvironments such as wetlands associated with surface and groundwater discharge. Independent paleoenvironmental proxies such as clay geochemistry allow quantitative hypothesis testing to improve our understanding of early hominin behavior and paleoecology. [Copyright &y& Elsevier]

Magnesium silicates such as chain clays and Mg-rich interstratifications commonly form in saline and alkaline soil and lake waters. Geochemical analyses of water and sediment from the Lake Eyasi and Ngorongoro Crater watersheds (northern Tanzania) were carried out to test the hypothesis that elevated aqueous CO2 due to biological activity strongly affects the stability of Mg-rich clay minerals. Field data and model calculations show that Pco2 is an important control on pH, thereby affecting mineral stability. Initial supersaturation of water with respect to magnesium clays generally requires elevated pH, and subsequent pH suppression due to biotic CO2 can prevent mineral precipitation. At Ngorongoro and Eyasi, solute Na+, SO42-, Cl-, and alkalinity follow generally conservative evaporative enrichment trajectories, whereas solute Ca2+ is lost to calcite, SiO2 to biogenic amorphous silica, and K+ to clay uptake. Mg2+ behavior is highly variable, and does not follow any simple trajectory. Minimal evaporative concentration is required for magnesium silicate supersaturation, and a strong correlation is found between Pco2 and magnesium silicate solubility (Ngorongoro r²=0.70, p<0.001; Eyasi r²=0.61, p<0.001), independent of evaporatively-driven brine evolution. Microbial decay in surface and groundwaters therefore likely plays an important role in the diagenesis of lacustrine clays. Associated ultrafine (<0.1µm) clays show significant Mg enrichment (Mg/(Al+Fe)=1.5-4.0) compared to <0.1µm detrital source clays (Mg/(Al+Fe)<0.1), and have an intermediate average chemistry between aluminous dioctahedral clays and end-member trioctahedral smectites or kerolite. The kinetics of magnesium clay precipitation remain poorly understood, but the preservation of such clays in ancient deposits may represent not only paleo-solution salinity and alkalinity, but also CO2 gas equilibrium status. These diagenetic processes should be considered in the use of lacustrine clay minerals as paleochemical indicators, because diagenetic pH suppression in sub-lacustrine pore waters can effectively remove indicators of high paleo-salinity [ABSTRACT FROM AUTHOR]