Hiroshi Takehira

Graphene oxide and reduced graphene oxide hybrids with spin crossover iron(III) complexes

Graphene (rGO) based hybrid materials exhibiting electrical conductivity and spin crossover (SCO) behavior are reported. The non-conductive [Fe(qnal)2]nGO (1·GO) and [Fe(qsal)2]nGO (2·GO) hybrids have been prepared by employing the electrostatic interaction between the negatively charged graphene oxide (GO) nanosheet and the respective iron(III) complex cations in [Fe(qnal)2]+Cl− and [Fe(qsal)2]+Cl−. The conductive [Fe(qnal)2]nrGO (1·rGO) and [Fe(qsal)2]nrGO (2·rGO) hybrids were obtained by thermal reduction of 1·GO and 2·GO. 1·GO and 1·rGO exhibit SCO behavior, and 1·rGO also shows a light-induced excited spin state trapping (LIESST) effect. Thus, in 1·rGO the electrical conductivity of rGO and the SCO behavior of [Fe(qnal)2]+ coexist in a single structure. We propose that the observed cooperativity for the rGO nanosheet-bound iron(III) [Fe(qnal)2]+ SCO material occurs through formation of large domains via π–π stacking between the graphene skeleton and the [Fe(qnal)2]+ cations.

Synthesis of mesoporous materials as nano-carriers for an antimalarial drug

An antimalarial drug artesunate (ATS) was encapsulated in both functionalized MCM-41 and ordinary MCM-41 with an excellent loading capacity and sustained release behavior for possible biomedical applications.

Reduced graphene oxide–transition metal hybrids as p-type semiconductors for acetaldehyde sensing

Acetaldehyde gas sensing using hybrids of reduced graphene oxide (rGO) and transition metal elements, rGO–M (M = oxide/hydroxide of Mn, Fe, Co and Ni) has been investigated. Thin films of GO, rGO and rGO–M on conductive glass were deposited through simple and affordable techniques and characterized using Raman spectroscopy, powder X-ray diffraction patterns, field emission scanning electron microscopy and electrical conductivity measurements. Concentration dependent resistances during the oxidation of acetaldehyde gas in air (10 to 50%) were investigated by using a sensing probe devised from rGO, GO–M and the rGO–M hybrids, of which rGO–Ni exhibited the maximum sensitivity. In rGO–Ni, in combination with rGO the NiOOH precursor can capture electrons (generated from acetaldehyde oxidation) through the holes, while indicating rGO–Ni to be a p-type semiconductor. This report implies the possibility of developing inexpensive graphene based p-type semiconductors for sensing other gases as well.