Antibacterial Properties of Scallop Shell Derived Calcium Hydroxide Powders

Globally increased bivalve aquaculture production results in a vast amount of by-product discharges such as scallop shells. Utilization of these wastes to produce new products such as antibacterial agents can cooperate to reduce environmental problems and provide a high value-added product at a lower cost. In this study, scallop shells are heat-treated at 800°, 900°, 1000°, and 1100°C for 4 hours at atmospheric conditions. X-ray diffraction analysis revealed that calcium carbonate is the only inorganic phase in the powdered scallop shells. Ten weeks after the thermal treatment of the scallop shells, the calcium hydroxide phase was the only crystalline phase determined by X-ray diffraction analysis for the samples calcined at 1000° and 1100°C. At lower calcination temperatures, calcium carbonate and calcium hydroxide phases were co-existing in the samples. Scanning electron microscopy investigations depicted that using scallop shells as a starting material to synthesize nanometer-sized calcium hydroxide is achieved. It was determined that applied calcination temperature has a significant effect on the particle size of the obtained calcium hydroxide phase. Antimicrobial activity of calcined and uncalcined shell powders were tested against Escherichia coli and Staphylococcus aureus. No antibacterial activity was detected for the uncalcined scallop shell powders. However strong antibacterial activity was determined for the powders after subjection to calcination. Calcination of scallop shells is an environmentally friendly, readily applied, and low- cost approach to achieve nanometer-size calcium hydroxide that can be used as an inorganic antibacterial material in various composite systems.

Quantitative microscale Fe redox imaging by multiple energy X-ray fluorescence mapping at the Fe K pre-edge peak

Fe oxidation/reduction reactions play a fundamental role in a wide variety of geological processes. In natural materials, Fe redox state commonly varies across small spatial scales at reaction interfaces, yet the approaches available for quantitatively mapping the Fe redox state at the microscale are limited. We have designed an optimized synchrotron-based X-ray spectroscopic approach that allows microscale quantitative mapping of Fe valence state by extending the Fe XANES pre-edge technique. An area of interest is mapped at nine energies between 7109–7118 eV and at 7200 eV, allowing reconstruction, baseline subtraction, and integration of the pre-edge feature to determine Fe(III)/ΣFe with 2 μm spatial resolution. By combining the Fe redox mapping approach with hyperspectral Raman mineralogy mapping, the Fe oxidation state distributions of the major mineral phases are revealed. In this work, the method is applied to a partially serpentinized peridotite with various Fe-bearing secondary mineral phases to trace the Fe transformations and redox changes that occurred during its alteration. Analysis with the Fe redox mapping technique revealed that the peridotite contained relict olivine with abundant Fe(II), while serpentine, pyroaurite, and another hydroxide phase are secondary mineral reservoirs of Fe(III). Although serpentine is not Fe-rich, it contained approximately 74% ± 14% Fe(III)/ΣFe. These analytical results are integral to interpreting the sequence of alteration reactions; serpentinization of primary olivine formed Fe(II)-rich brucite and oxidized serpentine, which could have contributed to H2 production during serpentinization. Subsequent weathering by oxidizing, CO2-bearing fluids led to the partial carbonation and oxidation of brucite, forming pyroaurite and a hydroxide phase containing dominantly Fe(III). This Fe redox imaging approach is applicable to standard petrographic thin sections or grain mounts and can be applied to various geologic and biogeochemical systems.

CAPTURING GREENHOUSE GAS CARBON DIOXIDE TO FORM CARBONATE COMPOUNDS

The application of CuO and MgO nanoparticles in CO2 capture was evaluated experimentally using 5% CO2 in nitrogen via physisorption and chemisorption instrumentation. The structural and surface micrograph of the CuO and MgO nanoparticles were characterized by XRD and TEM, respectively. After CO2 capture by the CuO nanoparticles, the amounts of oxide, hydroxide, and carbonate phases in the adsorbents were determined by XPS measurements. No hydroxide phase was detected in the MgO nanoparticles because of the efficient transformation of MgO into MgCO3. Monolayer adsorptions of CO2 were shown to occur in the MgO nanoparticles with a total chemisorption of 5.0 mmol/g. After the fifth cycle, only 3% reduction of the CO2 chemisorption was reported because of some agglomeration by sintering during desorption.

Enhancement of CO2 Capture Using CuO Nanoparticles Supported on Green Activated Carbon

At room temperature, dehydrating agent, concentrated sulfuric acid (H2SO4) was used to form porous carbon (BAC) from bamboo waste shows good properties as CO2 adsorbent. Selection of nano-CuO supported BAC produce composite materials with high total surface area and smaller pores size composite of 660.8 cm2/g and 2.7 nm. XRD data showed the support data to confirm the hydroxide phase formation as intermediate for carbonate and accelerate the CO2 chemisorption reaction. Besides, the presence of BAC together with metal oxide can improve the CO2 interaction physically on the surface and pores resulting the higher adsorption capability of 32.2 cm3 of CO2 per gram adsorbent. The combination of nano-CuO on BAC become a good adsorbent which can stimulate the CO2 reduction programme as well as reduce the CO2 emissions during BAC production.