Design, Synthesis And Properties Of Novel Intercalation Compounds Based On MnPS₃ And MoS₂

Recently, much interest has been focused on inorganic-organic nanocomposite materials due to their promising applications in many fields. Plentiful intercalates with some novel properties have been investigated by sandwiched multifarious organic species into layered inorganic hosts. Intercalation represents a useful approach to design and synthesize some functional and multifunctional materials including optical, electric and magnetic materials.The thesis contains four parts of the research work. The first part (Chapter 2) studies the synthesis, structural characterization and properties of two new intercalation compounds obtained by inserting a nitronyl-nitroxide radical MPYNN(2-(4-N-methyl-pyridinium)-4,4,5,5-tetrametyl-4,5-dihydro-1 H-imidazol-1 -o xyl-3-N-oxide iodide), into layered inorganic hosts MnPS3 and MoS2. The second part (Chapter 3 and 4) mainly describes the synthesis, structural characterization and magnetic, electrical properties of two series of amino acids intercalation compounds based on MnPS3 and MoS2. The third part (Chapter 5) studies the synthesis, structural characterization and magnetic, electrical properties of compounds obtained by intercalating N-substituted pyrrole (N-ethyl-pyrrole-trimethyl ammonium iodide), into inorganic hosts MnPS3 and MoS2. The fourth part (Chapter 6) investigates the mechanism of the reaction of DMSO with MnPS3, and synthesis a series of intercalation compounds directly based on MnPS3 in DMSO solvent.Chapter 1 briefly reviews the recent advances on the intercalation compounds and their promising applications in many fields, especially about the synthetic methods, structures, properties and potential applications of the intercalates based on layered MnPS3 and MoS2. Furthermore, the design strategies and the contents of the thesis are outlined at the end of this chapter.In Chapter 2, two new intercalation compounds (MPYNN)₀.14Mn₀.93PS₃ and (MPYNN)₀.13MoS2 have been synthesized through the reaction of the layered MnPS3 and MoS2 with a nitronyl-nitroxide radical MPYNN respectively. Compared with pure hosts, the lattice spacing of two compounds are both increased about 5.63 A, which means that the molecular plane (pyrrole ring or imidazol ring) of the guest is almost perpendicular to the layer of the hosts. From the IR spectra, the absorption peak of the radical N-O stretch at 1377 cm^-1 are observed at 1383 cm^-1, 1381 cm^-1, respectively. Their magnetic properties are studied with SQUID. For the intercalate(MPYNN)₀.14Mn₀.93PS₃, a magnetic transition from paramagnetism to ferrimagnetism was observed at around 7 K, maybe resulting from the guest-host interaction. (MPYNN)o.i3MoS2 only exhibits paramagnetism. The electrical property of (MPYNN)o.i3MoS2 was determined by four-probe technique. Above 120 K, it exhibited semiconductivity with Ea = 0.16 eV, a semiconductor to insulator transition occurs at 120 K. Its room temperature electrical conductivity is 2.5 X 10*3 S/cm, which is better than the pristine host M0S2.In Chapter 3, three intercalation compounds Mno.88PS3(Arg)o.25, Mno.84PS3(His)o.34 and Mno.83PS3(Lys)o.35, have been synthesized by the ion-exchange procedure. Compared with pure MnPS3, the lattice expansion of 4.47 A, 4.07 A and 3.76 A, respectively, indicate that amino acids are mono-molecule arranged in the layer of the host, with their straight carbon chain paralleled. And the carbamidine group plane of arginine is perpendicular, imidazol ring plane of histidine is a little incline, straight carbon chain of lysine is parallel, to the layer of the host, respectively. The results of SQUID measurement of these three intercalates indicate they show bulk spontaneous magnetization below 40 K.In Chapter 4, a new series of amino acids intercalation compounds (Arg)o.2oMoS2- (H2O)0.53, (His)0.i4MoS2- (H2O)0.38 and (Lys)o.23MoS2- (H2O)0.55, have been synthesized by exfoliation-restacked technique. Their structures are characterized with X-ray powder diffraction, IR, element analysis and TGA analysis. The lattice expansion of 5.86 A, 4.24 A and 4.85 A, compared with pure M0S2, suggest that the spatial arrangement of amino acids are similar to their relative intercalates based on MnPS3. The extra expansions probably come from the water molecules in the M0S2 layers. All of these three intercalates have a transition from semiconductor to insulator at 100 K. The values of their Ea are in the range of 6.65 X10 "2⁷.59X 10"2 eV, with room temperature electrical conductivities between lO'MO"3 S/cm. Their electrical properties are a little better than the pristine host M0S2.In Chapter 5, two intercalation compounds (C9Hi7N2)o.28Mno.86PS3, (C9Hi7N2)o.i8MoS2 were obtained by inserting N-ethyl-pyrrole-trimethyl ammonium iodide into inorganic hosts M11PS3 and M0S2, and the polymer intercalate (C9Hi5N2)o.i6MoS2 was prepared by oxidizing an aqueous solution of single layers and the N-substituted pyrrole monomer with FeCb. The lattice expansion of these intercalates is in the range of 5.23-5.74 A, indicating the spatial arrangement of guests are almost the same, with the pyrrole ring plane a little inclining to the layer of the hosts. For the intercalate (C9Hi7N2)o.28Mno.86PS3, a magnetic transition from paramagnetism to weak ferrimagnetism was observed at around 40 K. While (C9Hi7N2)o.i8MoS2 and (C9Hi5N2)o.i6MoS2 are both semiconductor, with Ea of 7.70X10'2 eV and 1.22 X 10"1 eV. Their room temperature electrical conductivities are 7.81 X 10' S/cm, 1.95 X 10' S/cm respectively, showing much enhancement in electrical conductivity over pristine M0S2.In Chapter 6, the mechanism of the reaction of DMSO with M11PS3 has been investigated by designing a series of compounds reacting at different reactive time. Their structures have been characterized with XRD (X-ray powder diffraction), IR, and TGA. Analyzing from the experimental data, the possible mechanism has been proposed as followed: at the beginning of the reaction, DMSO inserted and coordinated with Mn2+, which came out from the layers of M11PS3. A partial intercalate was obtained. As the period of the reaction prolonged, the lamellar structure of M11PS3 was destroyed and turned into a suspension, since so many DMSO molecules invaded layers of host to form a complex cation Mn(DMSO)n2+. The final product may be a new compound [Mn(DMSO)n]2P2S6, however, it needs further work to be confirmed. In the parallel experiments, we have found that DMSO should be a good solvent for the intercalation reaction based on M11PS3, though more work on reaction conditions is still needed.