A microwave assisted ionic liquid route to prepare bivalent Mn5O8 nanoplates for 5-hydroxymethylfurfural oxidation

In order to develop highly active non-precious metal catalysts for the selective oxidation of the platform compound 5-hydroxymethylfurfural (HMF) to the value-added bio-chemical 2,5-diformylfuran (DFF), we prepared high purity bivalent Mn₅O₈ nanoplates by a microwave-assisted ionic liquid route. The precursor of bivalent Mn₅O₈ nanoplates was formed through π-π stacking between imidazolium rings of the ionic liquid 1-butyl-3-methyl-imidazolium chloride and extending hydrogen bonds between Cl anions and hydrohausmannite. An oriented aggregation growth occurred on the basis of the Ostwald ripening under microwave heating. The high purity bivalent Mn₅O₈ nanoplates obtained through calcination at 550 °C for 2 h exhibited high HMF conversion (51%) and DFF selectivity (94%) at 5 bar of oxygen pressure in 2 h. The high concentration of Mn⁴⁺ on the exterior surfaces of Mn₅O₈ nanoplates as active sites coupled with good crystallinity played key roles for desirable mass and heat transfer, and for fast desorption avoiding over-oxidation. The reaction process over the Mn₅O₈ nanoplates was proposed based on the understanding of Mn⁴⁺ active centers and lattice oxygen via a Mn⁴⁺/Mn²⁺ two-electron cycle to enhance their catalytic performance. Furthermore, the Mn₅O₈ nanoplates could be readily recovered and reused without loss of catalytic activity. Thus, the high purity Mn₅O₈ nanoplates with good catalytic performance raises the prospect of using the type of sole metal oxide for practical applications.

A Fast Strategy for Determination of Vitamin B₉ in Food and Pharmaceutical Samples Using an Ionic Liquid-Modified Nanostructure Voltammetric Sensor

Vitamin B₉ or folic acid is an important food supplement with wide clinical applications. Due to its importance and its side effects in pregnant women, fast determination of this vitamin is very important. In this study we present a new fast and sensitive voltammetric sensor for the analysis of trace levels of vitamin B₉ using a carbon paste electrode (CPE) modified with 1,3-dipropylimidazolium bromide (1,3-DIBr) as a binder and ZnO/CNTs nanocomposite as a mediator. The electro-oxidation signal of vitamin B₉ at the surface of the 1,3-DIBr/ZnO/CNTs/CPE electrode appeared at 800 mV, which was about 95 mV less positive compared to the corresponding unmodified CPE. The oxidation current of vitamin B₉ by square wave voltammetry (SWV) increased linearly with its concentration in the range of 0.08-650 μM. The detection limit for vitamin B₉ was 0.05 μM. Finally, the utility of the new 1,3-DIBr/ZnO/CNTs/CPE electrode was tested in the determination of vitamin B₉ in food and pharmaceutical samples.