Trace Alcohol Adsorption by Metal Hexacyanocobaltate Nanoparticles and the Adsorption Mechanism

Adsorption of alkyl chain alcohols, ranging from methanol to <i>n</i>-hexanol, on manganese hexacyanocobaltate (MnHCCo) and copper hexacyanocobaltate (CuHCCo) nanoparticles was evaluated. The equilibrium adsorption capacity at low pressure was found to be larger than previously published results using other kinds of adsorbents, metal organic frameworks, zeolites, and activated carbons. For example, MnHCCo adsorbed 5 mmol/g of methanol at only 8.9 Pa, less than 1/10 of the lowest pressures used in previous studies. The adsorption can be understood using a two-step process: initial adsorption into the crystal (intra-nanoparticle adsorption) followed by that among the nanoparticles (inter-nanoparticle adsorption). The suggested mechanism was supported by the analysis of the adsorption isotherm with the dual-site Langmuir equation, and the entropy loss in the adsorption process. The highest adsorption amount at low pressure was caused by a combination of coordination bonding between alcohol molecules at the high-density open metal sites in the adsorbent and by the intermolecular interaction between the framework of the adsorbent and the alkyl chain of alcohols