[Show abstract][Hide abstract] ABSTRACT: This work presents a soft templating approach for mesoporous carbon using the polyphenolic heterogeneous biomass, chestnut tannin, as the carbon precursor. By varying synthesis parameters such as tannin:surfactant ratio, cross-linker, reaction time and acid catalyst, the pore structure could be controllably modulated from lamellar to a more ordered hexagonal array. Carbonization at 600 °C under nitrogen produced a bimodal micro-mesoporous carbonaceous material exhibiting enhanced hydrogen bonding with the soft template, similar to that shown by soft-templating of phenolic-formaldehyde resins, allowing for a tailorable pore size. By utilizing the acidic nature of chestnut tannin (i.e. gallic and ellagic acid), hexagonal-type mesostructures were formed without the use of an acid catalyst. The porous carbon materials were activated with ammonia to increase the available surface area and incorporate nitrogen-containing functionality which led to a maximum CO2 adsorption capacity at 1 bar of 3.44 mmol/g and 2.27 mmol/g at 0 °C and 25 °C, respectively. The ammonia-activated carbon exhibited multiple peaks in the adsorption energy distribution which indicates heterogeneity of adsorption sites for CO2 capture.
[Show abstract][Hide abstract] ABSTRACT: Poly(acrylamidoxime)-based fibers bearing random mixtures of carboxylate and amidoxime groups are the most widely utilized materials for extracting uranium from seawater. However, the competition between uranyl (UO2(2+)) and vanadium ions poses a significant challenge to the industrial mining of uranium from seawater using the current generation of adsorbents. To design more selective adsorbents, a detailed understanding of how major competing ions interact with carboxylate and amidoxime ligands is required. In this work, we employ density functional theory (DFT) and wave-function methods to investigate potential binding motifs of the dioxovanadium ion, VO2(+), with water, formate, and formamidoximate ligands. Employing higher level of theory calculations (CCSD(T)) resolve the existing controversy between the experimental results and previous DFT calculations for the structure of the hydrated VO2(+) ion. Consistent with the EXAFS data, CCSD(T) calculations predict higher stability of the distorted octahedral geometry of VO2(+)(H2O)4 compared to the five-coordinate complex with a single water molecule in the second hydration shell, while all seven tested DFT methods yield the reverse stability of the two conformations. Analysis of the relative stabilities of formate-VO2(+) complexes indicates that both monodentate and bidentate forms may coexist in thermodynamic equilibrium in solution. Investigations of VO2(+) coordination with the formamidoximate anion has revealed the existence of seven possible binding motifs, four of which are within ∼4.0 kcal mol(-1) of each other. Calculations establish that the most stable binding motif entails the coordination of oxime oxygen and amide nitrogen atoms via a tautomeric rearrangement of amidoxime to imino hydroxylamine. The difference in the most stable VO2(+) and UO2(2+) binding conformation has important implications for the design of more selective UO2(2+) ligands.
Physical Chemistry Chemical Physics 11/2015; DOI:10.1039/C5CP06165B · 4.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A polymer gel electrolyte using AlCl3 complexed acrylamide as a functional monomer and acidic ionic liquid based on a mixture of 1-ethyl-3-methylimidazolium chloride (EMImCl) and AlCl3 (EMImCl-AlCl3, 1-1.5, in molar ratio) as a plasticizer has been successfully prepared for the first time via free radical polymerization. Aluminum deposition is successfully achieved using a polymer gel electrolyte containing 80 wt% ionic liquid. The polymer gel electrolytes are also good candidates for rechargeable aluminum ion batteries.
Chemical Communications 10/2015; DOI:10.1039/c5cc06643c · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hexagonal boron nitride nanosheets (h-BNNs) with rather high specific surface area (SSA) are important two-dimensional layer-structured materials. Here, a solvent-mediated synthesis of h-BNNs revealed a template-free lattice plane control strategy that induced high SSA nanoporous structured h-BNNs with outstanding aerobic oxidative desulfurization performance.
Chemical Communications 10/2015; DOI:10.1039/C5CC07830J · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Conventional methods for nitrogen-doping of nanostructured carbon materials involve either a high-temperature and low-yield activation of the carbons using toxic NH3, or a pyrolysis/carbonization of costly N-rich compounds as the carbon precursors. We have developed an innovative strategy for post-synthesis nitrogen-doping of mesoporous carbons (MCs) with high yields (>90%) at low temperatures (230–380˚C) by using a strong base, sodium amide (NaNH2). The excellent nucleophilicity of NaNH2 seems to facilitate the incorporation of nitrogen by substitution of residual oxygen species in the parent MCs. A considerable amount of micropores are created in the framework of MCs along with the nitrogen doping. The as-prepared N-doped MCs exhibit a significantly enhanced CO2 adsorption performance in terms of capacity and selectivity when compared to their parent MCs. This facile method can be easily extended to the synthesis of other N-doped carbon nanostructures.
Chemical Communications 10/2015; DOI:10.1039/C5CC05619E · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Knowledge of the relationship between gas solubility and enthalpy change of chemical absorption of CO2 is very important for exploring energy-efficient absorbents for CO2 capture. To this end, equations that can directly correlate gas solubility with absorption enthalpy were derived through combining the van’t Hoff Equation with the Reaction Equilibrium Thermodynamic Model (RETM). Two typical reaction mechanisms for chemical absorption of CO2 (1:1 and 1:2) were considered for RETM. The variations of gas solubility with enthalpy change were found to be distinctively sigmoid functions, regardless of the investigated temperature and pressure or assumed reaction forms between CO2 and the absorbent molecule. Theoretically calculated variation curves of gas solubility vs. enthalpy change agreed well with experimental results reported in literature. Based on the trade-off relationship between gas solubility and enthalpy change, criterions for evaluating energy-efficient chemical absorbents for CO2 capture were proposed.
[Show abstract][Hide abstract] ABSTRACT: High-surface-area nanosized CeO2 and M-doped CeO2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO2 adsorption. Cu, La, and Zr are doped into the lattice of CeO2 , whereas Mg is dispersed on the CeO2 surface. The doping of Cu and La into CeO2 leads to an increase of the CO2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO2 adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO2 adsorption capacity follows the sequence Cu-CeO2 >La-CeO2 >Zr-CeO2 ≈CeO2 >Mg-CeO2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO2 , modified by the dopants that play the vital role in CO2 chemisorption. The role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO2 adsorption on the doped CeO2 .
[Show abstract][Hide abstract] ABSTRACT: There is a need to reduce the use of noble metal elements—especially in the field of catalysis, where noble metals are ubiquitously applied. To this end, perovskite oxides, an important class of mixed oxide, have been attracting increasing attention for decades as potential replacements. Benefiting from the extraordinary tunability of their compositions and structures, perovskite oxides can be rationally tailored and equipped with targeted physical and chemical properties—for example, redox behavior, oxygen mobility, and ionic conductivity—for enhanced catalysis. Recently, the development of highly efficient perovskite oxide catalysts has been extensively studied. This perspective article summarizes the recent development of lanthanum-based perovskite oxides as advanced catalysts for both energy conversion applications and traditional heterogeneous reactions.