A new insight into the thermodynamical criterion for the preparation of semiconductor and metal nanocrystals using a polymerized complexing method.

Pingyun Li,Guodong Deng,Xiaode Guo,Wei Jiang,Hongying Liu,Fengsheng Li,Nguyen Thi Kim Thanh,Qingqing Wang

doi:10.1039/c7cp04097k

Abstract

This work reports the intrinsic thermodynamical criterion for the preparation of metal and semiconductor nanocrystals using a polymerized complexing method. The basic principle of this method is the formation of a polymerized complexing structure between mono-, binary-, or ternary-metallic ions and bonding agents in aqueous or ethylene glycol solutions by evaporation of the solvents. Heat treatment of the complexing structure under N2 atmosphere produces H2 and CH4 gases, which can reduce the oxide crystalline nuclei to semiconductor and metallic nanocrystals. Experimental results show that Te, CdTe, Ag2Te, CuTe, NiTe1.5, CoTe1.5, Bi2Te3, Sb2Te3, Bi-Sb, In2Te3, Ni2.9SnTe2, CuGaTe2, and CuInS2 semiconductors and Bi, Sb, Ag, Cu, and Ni metallic nanocrystals can be prepared by this method. Transmission electron microscopy observations show that the obtained Bi, Ag2Te, Bi2Te3, Sb2Te3, CdTe, and NiTe1.5 nanocrystals have grain sizes in the nanometer range. The types of metallic and semiconductor phase that can be obtained by this method are explained by the thermodynamical criterion based on calculations of the Gibbs free energy and electrode potential. It is proposed that the crystalline phase of the final product is controlled by the change of the Gibbs free energies of the reactions of the metal oxide with reducing gases and the metal oxide redox electrode potentials, not the metal redox standard electrode potentials and electronegativities of the elements. Furthermore, a prediction is presented for the preparation of other kinds of binary and ternary compound based on the thermodynamical criterion. Our results provide new insight into facile and green preparation of semiconductor and metal nanocrystals.

Highlights

NCs is the hot-injection process where Cd(CH3)[2] and trioctylphosphine selenide (TOPSe) or trioctylphosphine telluride (TOPTe) are treated in organic solutions,[9,10] which are detrimental to the environment.[11]
The standard electrode potential of a reducing agent should be lower than that of metallic ions so that the metallic ions can be reduced in solution directly,[18] and it seems that metallic NCs can not be prepared when the standard electrode potential of the reducing agent is higher than the metal redox potential
Since much attention has been paid to semiconductor NCs because of their potential applications in various fields, we extended the polymerized complexing method from the preparation of metallic NCs to fabricate semiconductor NCs for the first time

Summary

Introduction

NCs is the hot-injection process where Cd(CH3)[2] and trioctylphosphine selenide (TOPSe) or trioctylphosphine telluride (TOPTe) are treated in organic solutions,[9,10] which are detrimental to the environment.[11]. NCs is the reduction reaction of oxide by reducing gases during the heat treatment, not the electronegativities of the elements or the metal redox standard electrode potentials.

Results

Conclusion