ABSTRACT
Iron ion is widely present in the environment and in biological systems, and are indispensable trace elements in living organisms, so development of an efficient and simple sensor for sensing Fe(III) ions has attracted much attention. Here, six heterometallic AE-Ln coordination polymers (CPs) [Ln2 (pda)4(Hnda)2Ca2(H2O)2]·MeOH (Ln = Eu (1), Tb (2); H2pda = 2,6-pyridinedicarboxylic acid, H2nda = 2,3-naphthalenedicarboxylic acid), [Ln (pda)2 (nda)AE2(HCOO)(H2O)] (AE = Sr, Ln = Eu (3), Tb (4); AE = Ba, Ln = Eu (5), Tb (6)) with two-dimensional (2D) layer structures were synthesized by hydrothermal method. All of them were characterized by elemental analysis, XRD, IR, TG, as well as single crystal X-ray diffraction. They all show infinite 2D network structure, where complexes 1 and 2 are triclinic with space group of P 1 ¯ , while 3-6 belong to the monoclinic system, space group P21/n . The solid-state fluorescence lifetimes of complexes 1, 3 and 5 are τobs1 = 1930.94, 2049.48 and 2,413.04 µs, respectively, and the quantum yields Ф total are 63.01, 60.61, 87.39%, respectively, which are higher than those of complexes 2, 4 and 6. Complexes 1-6 all exhibited efficient fluorescence quenching response to Fe3+ ions in water, and were not interfered by the following metal ions: Cu2+, Cd2+, Mg2+, Ni2+, Co2+, Ca2+, Ba2+, Sr2+, Li+, Na+, K+, Al3+, Fe2+, Pb2+, Cr3+, Mn2+ and Zn2+. The quenching coefficient K SV for complexes 1-6 is 1.41 × 105 M-1, 7.10 × 104 M-1, 1.70 × 105 M-1, 1.57 × 105 M-1, 9.37 × 104 M-1, 1.27 × 105 M-1, respectively. The fluorescence quenching mechanism of these complexes towards Fe3+ ions was also investigated. It is possible that the weak interaction formed between the complexes and the Fe3+ ions reduce the energy transfer from the ligand to the Ln3+ ion, producing the emission burst effect. This suggests that complexes 1-6 can be candidate for efficient luminescent sensor of Fe3+.
ABSTRACT
Doped-polypyrrole/Fe3O4 (D-PPy/Fe3O4) nanospheres were successfully synthesized via a onepot process. In this process, polyvinyl alcohol (PVA) plays an important role in the construction of polypyrrole nanoparticles, and Fe3+ ions were the oxidant and the only raw resource of Fe3O4. The morphology, magnetic properties, and electromagnetic microwave absorption properties of D-PPy/Fe3O4 composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), a vibrating sample magnetometer (VSM) and a vector network analyser (VNA). The results indicate that D-PPy/Fe3O4 nanospheres become more disperse and regular due to the addition of PVA. The influence of the mass ratio of PVA to pyrrole on the microwave absorption performance of the D-PPy/Fe3O4 composites was also investigated. When the mass ratio of PVA/pyrrole was 0.75:1, the minimum reflection loss (RLmin) value of the D-PPy/Fe3O4 composites reached -41.3 dB at 7.7 GHz with a thickness of 3.0 mm. The microwave interference cancellation of interface reflection, nature resonance loss and current loss are the main reasons for the loss of electromagnetic microwaves for the as-prepared D-PPy/Fe3O4 composites.
