Layered double hydroxides (LDHs) show great potential as CO 2 adsorbent materials, but require improvements in stability and CO 2 adsorption capacity for commercial applications. In the current study, graphene oxide provides a light-weight, chargecomplementary, two-dimensional (2D) material that interacts effectively with the 2D LDHs, in turn enhancing the CO 2 uptake capacity and multicycle stability of the assembly. As a result, the absolute capacity of the LDH was increased by 62% using only 7 wt % graphene oxide (GO) as a support. The experimental procedure for the synthesis of the materials is based on a direct precipitation of the LDH nanoparticles onto GO followed by a structural and physical characterization by electron microscopy, X-ray diffraction, thermogravimetric analysis, and Brunauer−Emmett− Teller (BET) surface area measurements. Detailed titration confirmed the compatibility of the surface chemistry. After thermal decomposition, mixed metal oxides (MMOs) are obtained with the basic sites required for the CO 2 adsorption. A range of samples with different proportions of GO/MMO were prepared, fully characterized, and correlated with the CO 2 sorption capacity, established via TGA.
Layered double hydroxides (LDHs) are promising materials for CO 2 sorption, although improvements in performance are required for practical applications. In the current study, the CO 2 sorption capacity and multi-cycle stability were both increased by introducing an open supporting framework of multiwalled carbon nanotubes (MWNTs). This nanostructured inert network provides a high surface area, maximizing the gas accessibility and minimizing coarsening effects. Specifically, LDH nanoparticles were precipitated directly onto MWNTs, initially oxidised to ensure a favourable electrostatic interaction and hence a good dispersion. The dependence of the structural and physical properties of the Mg-Al LDH grown on MWNT supports has been studied, using electron microscopy, X-ray diffraction, thermogravimetric analysis (TGA), and BET surface area, and correlated with the CO 2 sorption capacity, established via TGA and temperature programmed desorption measurements. The use of a MWNT support was found to improve the absolute capacity and cycle stability of the hybrid adsorbent under dry conditions.
HIGHLIGHTS The adsorption of sulfur from liquid hydrocarbons using mixed metal oxides unsupported and supported on graphene oxide was studied for the first time Sulfur adsorption capacity and thermal stability of mixed metal oxides is enhanced by the presence of graphene oxide The GO supported adsorbents show good selectivity for organosulfur compounds over sulfur-free aromatic hydrocarbons KEYWORDSGraphene oxide, mixed metal oxide, dibenzothiophene, adsorption, desulfurization ABSTRACTA series of mixed metal oxides (MMOs) adsorbents (MgAl-, CuAl-and CoAl-MMOs) were supported on graphene oxide (GO) through in-situ precipitation of layered double hydroxides (LDHs) onto exfoliated GO, followed by thermal conversion. The study shows that GO is an excellent support for the LDH-derived MMOs due to matching geometry and charge complementarity, resulting in a strong hybrid effect, evidenced by significantly enhanced adsorption performance for the commercially important removal of heavy thiophenic compounds from hydrocarbons. Fundamental liquid-phase adsorption characteristics of the MMO/GO hybrids are quantified in terms of adsorption equilibrium isotherms, selectivity and adsorbent regenerability. Upon incorporation of as little as 5wt% GO into the MMO material, the organosulfur uptake was increased by up to 170%, the recycling stability was markedly improved and pronounced selectivity for thiophenic organosulfurs over sulfur-free aromatic hydrocarbons was observed.2
Reduced-graphene-oxide (rGO) aerogels provide highly stabilising, multifunctional, porous supports for hydrotalcite-derived nanoparticles, such as MgAl-mixed-metal-oxides (MgAl-MMO), in two commercially important sorption applications. Aerogel-supported MgAl-MMO nanoparticles show remarkable enhancements in adsorptive desulfurization performance compared to unsupported nanoparticle powders, including substantial increases in organosulfur uptake capacity (>100% increase), sorption kinetics (>30-fold), and nanoparticle regeneration stability (>3 times). Enhancements in organosulfur capacity are also observed for aerogelsupported NiAl-and CuAl-metal-nanoparticles. Importantly, the electrical conductivity of the rGO aerogel network adds completely new functionality by enabling accurate and stable nanoparticle temperature control via direct electrical heating of the graphitic support. Support-mediated resistive heating allows for thermal nanoparticle recycling at much faster heating rates (>700 °C•min −1) and substantially reduced energy consumption, compared to conventional, external heating. For the first time, the CO 2 adsorption performance of MgAl-MMO/rGO hybrid aerogels is assessed under elevated-temperature and high-CO 2-pressure conditions relevant for pre-combustion carbon capture and hydrogen generation technologies. The total CO 2 capacity of the aerogel-supported MgAl-MMO nanoparticles is more than double that of the unsupported nanoparticles and reaches 2.36 mmol•CO 2 g −1 ads (at p CO2 = 8 bar, T = 300 °C), outperforming other high-pressure CO 2 adsorbents.
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