CsPbBr_(3)rhombic dodecahedra,octahedra,and nanocubes have been synthesized using typical reagents but by adjusting the amounts of organic capping molecules used and the reaction temperature.Although some Cs_(4)PbBr_(...CsPbBr_(3)rhombic dodecahedra,octahedra,and nanocubes have been synthesized using typical reagents but by adjusting the amounts of organic capping molecules used and the reaction temperature.Although some Cs_(4)PbBr_(6)has been identified,its presence was found not to affect optical property examination.With increasing sizes of CsPbBr_(3)rhombic dodecahedra from 59 to 168 nm,their band gaps decrease gradually.Remarkably,the much larger octahedra and{110}-bound rhombic dodecahedra show more blue-shifted absorption wavelengths than the{100}-bound nanocubes do,demonstrating the presence of optical facet effects.10 nm CsPbI_(3)nanocubes were also prepared and anion-exchanged to CsPbBr_(3)nanocubes.Similarly,CsPbBr_(3)rhombic dodecahedra were converted to rhombic dodecahedral CsPbI_(3).For both compositions,the much larger rhombic dodecahedra still display more blue-shifted absorption and emission bands than those of the nanocubes,indicating very large optical band shifts are possible by tuning the crystal morphology or exposed surfaces.展开更多
The thermolysis of metal-organic frameworks(MOFs)opens a new window for the fabrication of oxide semiconductors due to its simplicity,low cost and large-area uniformity of the resulting material.However,this approach ...The thermolysis of metal-organic frameworks(MOFs)opens a new window for the fabrication of oxide semiconductors due to its simplicity,low cost and large-area uniformity of the resulting material.However,this approach usually requires high annealing temperatures over 350°C.In this work,sub-micro hierarchical porous Co_(3)O_(4)dodecahedra were synthesized by the thermolysis of zeolitic imidazolate frameworks 67(ZIF-67)at a low temperature of 268°C assisted by ammonium perchlorate(AP),in which ZIF-67 was employed as a metal source and a sacrificial template.The formation mechanism was probably attributable to the generation of Co-O bonds between the Co atom of ZIF-67 and the O atom of AP at lower temperatures which can accelerate the weakening of Co-N bonds of ZIF-67 and thus lead to an abrupt decomposition of ZIF-67 at 268°C.More importantly,the generation of the Co-O bond and the weakening of the Co-N bond were identified using the FTIR,Raman and XPS results.As confirmed by DFT results,ZIF-67 can be decomposed into Co_(3)O_(4)at lower temperatures assisted by AP than that in air.In addition,the obtained sub-micro hierarchical porous Co_(3)O_(4)dodecahedra showed a very large specific surface area of 106.11 m^(2)g^(-1),much larger than that in previous reports.Therefore,this work can provide a novel atomic insight into the formation mechanism of Co_(3)O_(4)hierarchical porous structures derived from ZIF-67 with AP at lower temperatures and also an energy-efficient method to synthesize porous metal oxide structures.展开更多
文摘CsPbBr_(3)rhombic dodecahedra,octahedra,and nanocubes have been synthesized using typical reagents but by adjusting the amounts of organic capping molecules used and the reaction temperature.Although some Cs_(4)PbBr_(6)has been identified,its presence was found not to affect optical property examination.With increasing sizes of CsPbBr_(3)rhombic dodecahedra from 59 to 168 nm,their band gaps decrease gradually.Remarkably,the much larger octahedra and{110}-bound rhombic dodecahedra show more blue-shifted absorption wavelengths than the{100}-bound nanocubes do,demonstrating the presence of optical facet effects.10 nm CsPbI_(3)nanocubes were also prepared and anion-exchanged to CsPbBr_(3)nanocubes.Similarly,CsPbBr_(3)rhombic dodecahedra were converted to rhombic dodecahedral CsPbI_(3).For both compositions,the much larger rhombic dodecahedra still display more blue-shifted absorption and emission bands than those of the nanocubes,indicating very large optical band shifts are possible by tuning the crystal morphology or exposed surfaces.
基金Nature Science Foundation of China(No.51572075)Open Foundation of the State Key Laboratory of Silicate Materials for Architectures at WUT(No.SYSJJ2018-05)。
文摘The thermolysis of metal-organic frameworks(MOFs)opens a new window for the fabrication of oxide semiconductors due to its simplicity,low cost and large-area uniformity of the resulting material.However,this approach usually requires high annealing temperatures over 350°C.In this work,sub-micro hierarchical porous Co_(3)O_(4)dodecahedra were synthesized by the thermolysis of zeolitic imidazolate frameworks 67(ZIF-67)at a low temperature of 268°C assisted by ammonium perchlorate(AP),in which ZIF-67 was employed as a metal source and a sacrificial template.The formation mechanism was probably attributable to the generation of Co-O bonds between the Co atom of ZIF-67 and the O atom of AP at lower temperatures which can accelerate the weakening of Co-N bonds of ZIF-67 and thus lead to an abrupt decomposition of ZIF-67 at 268°C.More importantly,the generation of the Co-O bond and the weakening of the Co-N bond were identified using the FTIR,Raman and XPS results.As confirmed by DFT results,ZIF-67 can be decomposed into Co_(3)O_(4)at lower temperatures assisted by AP than that in air.In addition,the obtained sub-micro hierarchical porous Co_(3)O_(4)dodecahedra showed a very large specific surface area of 106.11 m^(2)g^(-1),much larger than that in previous reports.Therefore,this work can provide a novel atomic insight into the formation mechanism of Co_(3)O_(4)hierarchical porous structures derived from ZIF-67 with AP at lower temperatures and also an energy-efficient method to synthesize porous metal oxide structures.
