Synthesis of Nickel Sulfide Particles by Solvothermal Process

Chinese Chemical Letters Vol. 15, No. 1, pp 79- 82 , 200479htp://ww.imm.ac. cn/journal/ccl.htmlSynthesis of Nickel Sulfide Particles by Solvothermal ProcessDun Qing WANG.2 , Dai Rong CHEN' *, Xiu Ling JIAO'Department of Chemistry, Shandong University, Jinan 250100Department of Chemistry, Dezhou College, Dezhou 253000A bstract: Pyrite nickel disulfide and millerite nickel monosulfide have been successfully preparedby solvothermal method based on the reaction of Ni(NO3)26H2O and H2NC(S)NH2 in benzene andethylenediamine (EDA). The final products were characterized by X-ray powder diffraction(XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM). Theeffects of the solvent, reaction temperature and time on the morphology and phase of the productshave been discussed.Keywords: Chalcogenides, solvothermnal synthesis, X-ray diffaction analysis.Sulfides of many transition metals show electronic and optical properties such assemiconductivity and photoconductivity 12 For example, nickel sulfide is a potentialtransformation toughening agent for semiconductor materials 3, while nickel disulfideadopts the pyrite structure and exhibits semiconducting properties . Thus, the synthesisof the 3d transition metal sulfides has attracted great interests for several decades.Normally, these sulfides are prepared through stoichiometric amount of the metal andsulfur heated in evacuated and sealed quartz ampoules at 500-1000°C 5. However, thelow melting point and volatilization of sulfur in some cases may make the control ofcomposition difficult， and then several low temperature routes to group VIIItransition-metal disulfides were recently reportedFor the preparation of sulfides ofnickel, several techniques, such as solid-state reaction 8, chemical vapor transport 39.10,and liquid phase technique 35,9-12， have been developed.t is reported thatwell-crystallized nickel sulfides could be obtained through the solvothermal technique,but the Na+ was easily adsorbed on the nanocrystallite to contaminate the product. Inthis work, pyrite nickel disulfide nanoparticles and millerite nickel monosulfide withmicrometer size have been obtained through solvothermal process based on the reactionof Ni(NO3)26H2O and H2NC(S)NH2. The novel pathway effectively prevents thproduct from the contaminating of the Nat ions.Analytical grade solvents and reagents were applied as raw materials. In a typicalreaction, stoichiometric Ni(NO3)2 6H2O and thiourea were added into 11 mL benzene orEDA and then poured into a 15 mL Teflon- lined autoclave. Maintaining at 160-200°Cfor 12-30 h, the autoclave was cooled to room temperature. A black powder wasE-mail: cdr@ sdu.edu.cn.中国煤化工MHCNMH G.80Dun Qing WANG et al.collected by filtration, washed several times with absolute ethanol and distilled water andair-dried at ambient temperature.XRD patterns were recorded on a Rigaku D/MAX2200PC diffractometer with Cu-Ka radiation (n=0.15418 nm) and graphitemonochromator. JEM- 100 transmission electron microscopy and Hitachi S-520scanning electron microscopy were used to observe the morphology and size of theparticles.Because the interaction between the different solvents and N4 + is different, varioussulfides of nickel were obtained in different solvents. When benzene was selected assolvent, pure NiS2 was obtained, while pure NiS formed in EDA.Figure 1 a shows the XRD pattern of pure NS2 sample. All the peaks can beindexed as the pyrite nickel disulfide (JCPDS: 11-99). The crystalline size of thesample was about 29 nm from the full-width at half maximum (FWHM) of the strongestdiffraction peaks. The reaction time and temperature have an important effect on thephase composition of products during the solvothermal synthesis of NiS2 powders. Theoptimal condition is 180-200°C for 16-30 h. Lower temperature or shorter time leads toan incomplete reaction and other phases, such as tetrahedral Nis or polydymite NisS4(Figure 1b), millerite Nis and nickel sulfide NiS at higher temperature (Figure 1 c,d).It is likely that NisS4 decomposes to millerite NiS and tetrahedral Nis at 200°C sinceNisS4 is metastable'. Prolonging the reaction time to 16h at 180°C or 18 h at 200°C,only the pyrite NiS2 particles formed indicated by XRD patterns. It can be seen fromFigure 3a that the prepared NiS2 are spherical particles with the size of ca. 20 nm. Butthe particles tend to aggregate.The reaction was significantly influenced by the coordinating ability of the solvent.If the solvent is EDA at the same condition, pure phase of NiS was obtained asdemonstrated in Figure 2. All the peaks are indexed to millerite nickel sulfide (JCPDS:12-41). This is different from the results of reference 12, in which spherical and cubicshape NiS2 were obtained using the same precursor (NiSO4 6H2O with Na2S3) in benzeneor EDA at 130°C for 8-12 h. In their experiments EDA was supposed as template forinorganic ion self-assembling and growth, while benzene operated as the solvent. EDA,with strong N-chelation ability and basicity acts as a bidentate ligand to form a relativelystable Ni2+ complex cation just like [Ni(EDA);]2+13, which is a purple solution at roomtemperature. The complex cation formed usually acts as a template which possiblyincreases the reactivity of Ni (I), promoting the reactions 14. Although there wasthiourea in the solution, the coordination ability of thiourea is much smaller than that ofEDA 15. The preparation process of NiS may be proposed as a liquid reaction: Firstly,H2NC(S)NH2 is soluble in EDA at room temperature and decomposed to produce S- inthe base environment 16. Then [Ni(EDA)3] 2+ and S- were reacted to produce NiSpowder.The whole process may be expressed as follows:H2NC(S)NH2→s2Ni2+ + 3EDA→[Ni(EDA)3]2+[Ni(EDA)3]2++S2-NiS↓+ 3EDAIn our experiment, the optimal condition to prepare NiS was reacting at 200°C formore than 6 h. When the temperature was lower than 160°C, the reaction could notinitiate even the heating time was 30 h. Heating time shorter than6 h at 200°C led to中国煤化工MHCNMH G.Synthesis of Nickel Sulfide Particles by Solvothermal Process31Figure 1 XRD patterns of obtained powdersFigure2 XRD patterns of Nis powdersin benzeneobtained in EDANiS, (Polydymite)Nis (Nickel Sulfide)ilieneileLsleee.de3C4026203040。。 50507oa. at180C for24h;b. at 160°C for24 h;at 200°C fora. 6h;b. 12h;c. 18 h;d.30 hc. at 180C for 12h;d. at 200C for 12hFigure 3 TEM and SEM graphs of the as- prepared products .50mm .b，61520KVX860k087 20KY H5.um(a) TEM graph of the prepared NiS 2 particles at 180°C for 24 h;(b) SEM photograph of Nis particles at 200°C for 12 h;(c) SEM photograph of NiS particles at 200°C for 30 hincomplete reaction with decreased yield and a small amount of unknown impurity.Prolonging the time has no effect on the phase composition of the products. TEMphotograph (Figure 3b) indicated that the Nis particles have a rod-like morphology withdiameter of about 0.5-1.5 im. The rod broadened with the time prolonging (Figure 3c)and the crystallinity increased from the intensity of the XRD peaks (Figure 2).In conclusion, pyrite NiS2 nanocrystallites and millerite Nis rod-like particles havebeen successfully prepared through a simple solvothermal route using different solvents.The difference of the formation mechanism of NiS2 and NiS particles in benzene or EDAwas owing to the different polarity and coordination ability to Ni2+ of these solvents.中国煤化工YHCNMH G ..82Dun Qing WANG et al.The reaction temperature and time significantly affected the phase composition of NiS2powders, while that only affected the particle size of the NiS particles with theprolongation of the reaction time.References1. Q.Y. Lu, J.Q. Hu, K.B. Tang, et al, J. Solid State Chem, 1999, 146, 484.Y.U. Jeong, A. Manthiram, Inorg. Chem, 2001, 40, 73.， J. Grau, M. Akinc, J. Am. Ceram. Soc., 1997, 80, 941.4. A. Manthiram, Y. U. Jeong, J. Solid State Chem, 1999, 147, 679.5. X. M. Zhang, X. F. 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