Mesoporous Carbons from Polysaccharides and Their Use in Li-O2 Batteries

Polysaccharide Modified Cathodes for High-Capacity Rechargeable Nonaqueous Li-O2 Batteries

Nonaqueous rechargeable Li-O₂ batteries are recognized as possible alternatives to the currently established Li-ion battery technology for next-generation traction by virtue of their high specific energy. However, the technology is still far from commercial realization mainly due to the performance-limiting reactions at the cathode. The insulating discharge product, Li₂O₂, can passivate the cathode leading to issues such as low specific capacity and early cell death. Herein, the -OH functionalities at the cathode, incorporated by polysaccharide addition, are shown to enhance the discharge capacity and cyclability. The -OH functional group (high pK_a) at the cathode helps to stabilize the intermediate, LiO₂, via an energetically favorable pathway and delays the precipitation to Li₂O₂, without any parasitic reaction, unlike the other reported low pK_a additives. The role of the functionalities is studied using various experimental techniques and first principles density functional theory based studies. This approach provides a rational design route for the cathodes that provide high capacities for the emergent Li-O₂ batteries.

Template-Free Preparation of a Mesopore-Rich Hierarchically Porous Carbon Monolith from a Thermally Rearrangeable Polyurea Network

A mesopore-rich, hierarchically porous carbon monolith was prepared by carbonizing a polyisocyanurate network derived by thermal rearrangement of a polyurea network. The initial polyurea network was synthesized by the cross-linking polymerization of tetrakis(4-aminophenyl)methane (TAPM) and hexamethylene diisocyanate (HDI) in the sol-forming condition, followed by precipitation into nanoparticulate solids in a nonsolvent. The powder was molded into a shape and then heated at 200–400 °C to obtain the porous carbon precursor composed of the rearranged network. The thermolysis of urea bonds to amine and isocyanate groups, the subsequent cyclization of isocyanates to isocyanurates, and the vaporization of volatiles caused sintering of the nanoparticles into a monolithic network with micro-, meso-, and macropores. The rearranged network was carbonized to obtain a carbon monolith. It was found that the rearranged network, with a high isocyanurate ratio, led to a porous carbon with a high mesopore ratio. The electrical conductivity of the resulting carbon monoliths exhibited a rapid response to carbon dioxide adsorption, indicating efficient gas transport through the hierarchical pore structure.

Use of a Hybrid Porous Carbon Material Derived from Expired Polysaccharides Snack/Iron Salt Exhibiting Magnetic Properties, for Hexavalent Chromium Removal

Nowadays, the scientific interest is focused more and more on the development of new strategies in recycling of waste products as well as on the development of clean technologies due to the increased environmental pollution. In this work we studied the valorization of an expired cheese-tomato flavor corn snack, which is polysaccharide food product, by producing advanced hybrid magnetic materials for environmental remediation purposes. The carbonization-chemical activation of this snack using potassium hydroxide leads to a microporous activated carbon with high surface area (SgBET ~800 m2/g). The magnetic hybrid material was synthesized via an in-situ technique using iron acetate complex as the precursor to produce iron based magnetic nanoparticles. The resulting material retains a fraction of the microporous structure with surface area SgBET ~500 m2/g. Such material consists, of homogenously dispersed magnetic isolated zero valent iron nanoparticles and of iron carbides (Fe3C), into the carbon matrix. The magnetic carbon exhibited high adsorption capacity in Cr(VI) removal applications following a pseudosecond order kinetic model. The maximum adsorption capacity was 88.382 mgCr(VI)/gAC at pH = 3. Finally, oxidation experiments, in combination with FT-IR, Mössbauer, and VSM measurements indicated that the possible Cr6+ removal mechanism involves oxidation of iron phases and reduction of Cr6+ to Cr3+.