Drug delivery system using porous silica-mannan nanocomposites

Electrochemical CO2 reduction reaction (CO2RR) constitutes an essential technology for utilizing CO2 as chemical feedstocks. In this work, a nickel(II) complex containing N4-Schiff base ligand (NiL) was prepared by a nickel-templated [1+1] imine condensation of diphenylamine-2,2’-dicarboxaldehyde and diethylenetriamine (DETA). The complex NiL showed the catalytic current enhancement for the CO2RR in a homogeneous MeCN solution. This result encourages us to further immobilize NiL onto multi-walled carbon nanotube (MWCNT) and graphene oxide (GO) support by non-covalent strategy to achieve a CO2RR conversion in aqueous NaHCO3 solutions. The hybrid materials, NiL/CNT and NiL/GO, were obtained as black solid and then characterized by scanning electron microscope with energy dispersive X-ray spectrometer (SEM-EDS) and Inductively coupled plasma - optical emission spectrometry (ICP-OES). The results indicated NiL was immobilized onto the carbon supports to some extent, although small amount of Ni contents were detected in the materials. In cyclic voltammetry (CV) studies, both materials showed no significant catalytic current enhancement in CO2-saturated solution compared to the same condition under N2 atmosphere. NiL/CNT was not active toward CO2 reduction as no CO was detected. Likewise, NiL/GO also performed poorly, affording CO with Faradaic efficiency (FE) of only 16%. In additionLow NiL, active species, on the supports due to the weak interactions between them encouraged a concomitant hydrogen evolution reaction (HER) which easily occurred in the aqueous electrolytes resulting in H2 as a major product in both cases with FE of 72% in NiL/CNT and 57% in NiL/GO, H2 was found to be the major product in both NiL/CNT and NiL/GO with FE(H2) of 72% and 57%, respectively. This is possibly due to low amount of NiL (active species for CO2RR) immobilized on the supports because of the weak interaction between them. As a result, hydrogen evolution reaction (HER) which is a competitive reaction can easily occurred, especially in aqueous electrolyte.. The present study suggests that using a non-covalent immobilization strategy, CNT and GO are not suitable carbon substrates to further develop heterogeneous NiL catalysts for CO2RR. Thus, the better condition and other carbon supports for immobilizing the complex should be further studied.