Copolymerization of transition metal salen complexes and conversion into metal nanoparticles supported on hierarchically porous carbon monoliths: a one pot synthesis

Described is the synthesis of metal (Ni, Cr, and Mn) doped macro/mesoporous carbon monoliths by co-polymerization of transition metal complexes with resorcinol/formaldehyde and subsequent pyrolysis. Two salen ligands were synthesized via reaction of ethylene diamine (EDA) and 1,6-diaminohexane (DAH) with 2,4-dihydroxybenzaldehyde to give 4,4′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(benzene-1,3-diol) (=E-salen) and 4,4′-((1E,1′E)-(hexane-1,6-diylbis(azanylylidene))bis(methanylylidene))bis(benzene-1,3-diol) (=D-salen). Their metal salen complexes were prepared. All the samples pyrolyzed at 500 °C had macro and mesopores with a specific surface area ranging from 250–500 m²/g. However, the surface area and porosity of the samples decreased dramatically for the metal containing samples pyrolyzed at 800 °C. This is suggested to result from incomplete co-polymerization of the metal salen complexes. The extent of graphitization determined from Raman increased with the pyrolysis temperature. The electrical conductivity was found to increase with the pyrolysis temperature, and followed the trend Ni > Mn > Cr. The M-E-salen containing samples had significantly lower conductivity than their D-salen counterparts.