Title

Synthesis of novel solid materials from carbon dioxide and carbon monoxide

Author

Yan Huo, Michigan Technological University

Date of Award

2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering (PhD)

College, School or Department Name

Department of Materials Science and Engineering

First Advisor

Yun Hang Hu

Abstract

The increase of atmospheric CO₂ has been identified as the primary cause for the observed global warming over the past century. The geological and oceanic sequestration of CO₂ has issues, such as cost and leakage as well as effects on sea biota. The ideal solution should be the conversion of CO₂ into useful materials. However, most processes require high energy input. Therefore, it is necessary to explore novel processes with low energy demands to convert CO₂ to useful solid materials.

Amorphous carbon nitride and graphone received much attention due to their unusual structures and properties as well as their potential applications. However, to date there has been no attempt to synthesize those solid materials from CO₂.

Lithium nitride (Li₃N) and lithium imide (Li₂NH) are important hydrogen storage materials. However, their optical properties and reactivity has not yet studied.

This dissertation research is aimed at the synthesis of carbon nitrides and graphone from CO₂ and CO via their reaction with Li₃N and Li₂NH. The research was focused on (1) the evaluation of Li₃N and Li₂NH properties, (2) thermodynamic analysis of conversion of carbon dioxide and carbon monoxide into carbon nitride and other solid materials, (3) synthesis of carbon nitride from carbon dioxide, and (4) synthesis of graphone from carbon monoxide.

First, the properties of Li₃N, Li₂NH, and LiNH₂ were investigated. The X-ray diffraction measurements revealed that heat-treatment at 500°C introduce a phase transformation of β-Li₃N to α-Li₃N. Furthermore, the UV-visible absorption evaluation showed that the energy gaps of α-Li₃N and β-Li₃N are 1.81 and 2.14 eV, respectively. The UV-visible absorption measurements also revealed that energy gaps are 3.92 eV for Li₂NH and 3.93 eV for LiNH₂.

This thermodynamic analysis was performed to predict the reactions. It was demonstrated that the reaction between carbon dioxide and lithium nitride is thermodynamically favorable and exothermic, which can generate carbon nitride and lithium cyanamide. Furthermore, the thermodynamic calculation indicated that the reaction between carbon monoxide and lithium imide can produce graphone and lithium cyanamide along with releasing heat.

Based on the above thermodynamic analysis, the experiment of CO₂ and Li₃N reaction and CO and Li₂NH were carried out. It was found that the reaction between CO₂ and Li₃N is very fast and exothermic. The XRD and element analysis revealed that the products are crystal lithium cyanamide and amorphous carbon nitrides with Li₂O and Li₂CO₃. Furthermore, TEM images showed that carbon nitrides possess layer-structure, namely, it is graphene-structured carbon nitride.

It was found that the reaction between Li₂NH and CO was also exothermic, which produced graphone instead of carbon nitride. The composition and structures of graphone were evaluated by XRD, element analysis, TEM observation, and Raman spectra.

Recommended Citation

Huo, Yan, "Synthesis of novel solid materials from carbon dioxide and carbon monoxide", Dissertation, Michigan Technological University, 2012.

https://doi.org/10.37099/mtu.dc.etd-restricted/43