Selective Surfaces: Quaternary Co(Ni)MoS-Based Chalcogels with Divalent (Pb²⁺, Cd²⁺, Pd²⁺) and Trivalent (Cr³⁺, Bi³⁺) Metals for Gas Separation

Porous chalcogels with tunable compositions of Co x M 1 –x MoS 4 and Ni x M 1– x MoS 4, where M = Pd 2+, Pb 2+, Cd 2+, Bi 3+, or Cr 3+ and x = 0.3–0.7, were synthesized by metathesis reactions between the metal ions and MoS 4 2– . Solvent exchange, counterion removal and CO 2 supercritical drying led to the formation of aerogels. All chalcogels exhibited high surface areas (170–510 m 2 /g) and pore volumes in the 0.56–1.50 cm 3 /g range. Electron microscopy coupled with nitrogen adsorption measurements suggest the presence of both mesoporosity (2 nm < d < 50 nm) and macroporosity ( d > 50 nm, where d is the average pore size). Pyridine adsorption corroborated for the acid character of the aerogels. We present X-ray photoelectron spectroscopic and X-ray scattering evidence that the [MoS 4 ] 2– unit does not stay intact when bound to the metals in the chalcogel structure. The Mo 6+ species undergoes redox reactions during network assembly, giving rise to Mo 4+/5+ -containing species where the Mo is bound to sulfide and polysulfide ligands. The chalcogels exhibit high adsorption selectivities for CO 2 and C 2 H 6 over H 2, N 2, and CH 4 whereas specific compositions exhibited among the highest CO 2 enthalpy of adsorption reported so far for a porous material (up to 47 kJ/mol). The Co-Pb-MoS 4 and Co-Cr-MoS 4 chalcogels exhibited a 2-fold to 4-fold increase in CO 2 /H 2 selectivity compared to ternary CoMoS 4 chalcogels.