Ni-C Materials From Ni-Pyridine Alcohol Clusters And Their Catalytic Properties

Recently,scientists show more interest in coordination complex precursors,which offer a number of advantages for the preparation of finely divided and evenly dispersed carbon-hosted nanoparticles(NPs/C)used as supercapacitors,gas absorbers and catalysts.And this approach is that the carbon matrix and impregnated metal formed by carbonization usually exhibit high uniformity and stability.Pyridyl alcohol ligands possess many kinds of coordination mode,and have great application on magnetism,catalytic and fluorescence.We employ one of the pyridyl alcohol complex[Ni4O4]as a precursor to prepare nanometer materials.Compared with other methods,this precursor method doesn’t necessarily to add extra carbon atom or heteroatom to enhance its efficiency,and the precursor can act as a well template.In this article,a pyridyl alcohol ligand(5-(4-(tert-butyl)phenyl)pyridine-2-yl)methanol was synthesized by two steps:a classical Suzuki-Miyaura Coupling reaction and selective reduction.Four cuboidal[Ni4O4]cluster compounds have been synthesized from the solvethermal reactions of Ni(Ⅱ)sources and HL,viz[Ni4L4(μ-HCOO)2(HCOO)2(H2O)2]H20(1),[Ni4L4(μ-OAc)2(OAc)2(H20)(MeOH)]·2H2O· 3CH3OH(2),[Ni4L4(EtOH)4Cl4](3)and[Ni4L4(MeOH)4Br4](4).They all own a[Ni4O4]cubane center,and among them,complex 1 not only owns highest yield,but also keeps good crystallinity upon separation from the mother liquor,while complex 2-4 cannot.So we select compound 1 as an example for subsequent studies.Carbonization of 1 at different temperatures gave rise to NiNPs/C of different uniformity.NiNPs/C-450 were well-dispersed,while particles in NiNPs/C-500 started to sinter.Further increase in temperature to 550 ℃ and 600 ℃ caused the Ni nanoparticles to aggregate,reaching around 50 nm in size.So we selected 450 ℃ as the optimized carbonization temperature and employed NiNPs/C-450 for subsequent characterizations and catalysis experiments.A preliminary catalytic study of NiNPs/C-450 for the reduction of 4-nitrophenol(4-NP)to 4-aminophenol(4-AP)suggests that the catalyst is remarkably effective,giving 98.2%conversion for 4-NP solution in the presence of NaBH4 in 210 seconds at room temperature.The catalyst can be readily concentrated using a magnet for the next reaction and remained equally active for at least 10 cycles.Meanwhile,we have performed further experiments by treating NiNPs/C-450 with HC1(10 M)solution to remove Ni nanoparticles,and the catalytic experiment showed that the metal-free host material itself is not effective.We further carried out the catalytic experiment under the same condition,and explored the Brunauer-Emmett-Teller(BET)surface areas of NiNPs/C-450,NiNPs/C-500,NiNPs/C-550 and NiNPs/C-600 to gain additional insight into the relations between the material morphology and their catalytic performances.The porosity of NiNPs/C-450,NiNPs/C-500 are marginally larger than those of NiNPs/C-550 and NiNPs/C-600.This observation pointed to a positive relationship between the material porosity and catalytic efficiency which is a subject of our future work.In addition,we synthesized a mononuclear compelex[Ni(mhmpH)2(NO3)2],dinuclear[Ni2(mhmpH)4Cl2],two[Ni404]cubane[Ni4(mhmp)4(μ-OAc)2(OAc)2(CH3OH)2)]·(CH3OH)2,[Ni4(mhmp)4(CH3OH)4Cl4].CH3OH,and two dipolymer[Fe2(mhmpH)2Cl4],[Fe2(2,5,4-hmbpp)2Cl4].Finally,we carried out simple characterization upon these compounds.In summary,we have successfully prepared catalytically active NiNPs/C-450 by direct carbonization of a simple[Ni4O4]cluster and demonstrated promising performance in the catalytic reduction of 4-NP to 4-AP.