Construction And Performance Of Novel Photoelectric Conversion Materials Based On MOFs

Metal-organic frameworks (MOFs) are crystalline materials constructed from metal ions or clusters bridged by organic ligands to form one-, two-, or three-dimensional infinite networks. Compared with conventional inorganic porous material, MOFs have greater porosity and specific surface area, especially adjustable aperture and variable functional groups and were studied in gas adsorptions, separations and storages. In order to expand their applications, composite materials based on MOFs, especially photoelectric conversion materials, through introducing functional molecules into MOFs holes or onto their frameworks have attracted more interests. In this work, some photoelectric conversion composite materials based on MOFs through introducing ruthenium complexes and graphene oxide were designed and prepared.Firstly, a new bio-MOF named LNU-1, formulated as Zn6(ad)4(BPDC)4O-2Me2 .NH2+,3DMF,8H2O(ad=adeninate;BPDC=biphenyldicarboxylate), was prepared through introducing biphenyldicarbolylic acid to reactions between adenine and zinc acetate dehydrate in dimethylformamide. Its structure was characterized by X-ray crystal diffraction, XRPD, nitrogen adsorption measurement and TG et. al. Its BET value was determined to be about 1300 m2/g and the size of holes was about 11.26 A. This material also showed excelled thermostability below 360℃.Composite materials B3@LNU-l(B3=Ru(bpy)3(PF6)2) and N3@LNU-1 (N3=Ru(bpy)2(SCN)2) were prepared successfully through introducing two ruthenium complex molecules into the holes of LNU-1 by cationic exchange and hydrothermal synthetic method respectively. Their structures were characterized by IR, X-ray crystal diffraction, XRPD, XPS, nitrogen adsorption measurement and TG et al. After it was entrapped in the holes of LNU-1, the emission intensity of complex B3 was enhanced obviously and the lifetime of its molecule excited state became 2.5 times long. In the photocurrent response measurements, the two composite materials B3@LNU-1 and N3@LNU-1 all showed relative higher photocurrents than LNU-1, which were 0.76 μA/cm and 1.03 μA/cm2 respectively.In order to improve the electron transfer ability of the composite materials, two ternary composite materials Ru(II)/MOF/GO and one binary composite materials LUN-1@GO were prepared successfully through hydrothermal synthetic method. Their structures were characterized by IR, X-ray crystal diffraction, XRPD, XPS, SEM, nitrogen adsorption measurement and TG et al. The effects of the quantity of GO in the composites on their image and photoelectric conversion properties were also studied. In the photocurrent response measurements, the two ternary composite materials Ru(II)/MOF/GO all gave a photocurrent density of about 12μA/cm2, which was much higher than the Ru(Ⅱ)/MOF composite materials. But it was surprising that the binary LUN-1@GO composite material exhibited a large photocurrent density of 21 uA/cm2, which was 1.8 times as high as that of the ternary composites. Therefore, the binary LUN-1@GO composite material has the potential application as photoelectric conversion materials.