Preparation And Modification Of Cobalt-based Hydrotalcite For Photocatalytic Reduction Of Carbon Dioxide

In recent decades,the problems of energy shortage and greenhouse effect caused by the rapid consumption of traditional fossil energy have become increasingly serious,and clean energy is in urgent need of in-depth development and utilization.Carbon dioxide（CO₂）is an important product of fossil fuel combustion,and also accounts for the largest number among the greenhouse gases,therefore people have done a lot of work on the capture,storage and conversion of CO₂.Inspired by plant photosynthesis,people have successfully achieved the conversion of CO₂ into higher value carbon-based fuels through artificial simulation of photocatalytic reduction,which has become an important research topic in the world today.In this paper,cobalt-based hydrotalcite catalysts were investigated for the optimal preparation conditions and were furthur modified for enhancing the photocatalytic activity,and the catalytic activity was evaluated by photocatalytic reduction of CO₂ to methanol（CH₃OH）,methane（CH₄）and carbon monoxide（CO）in isopropanol system.Main research contents were as follows:1.New ternary hydrocalcite Co Al In_x-LDHs were successfully prepared by simple steady co-precipitation method.The co-existence of ternary metal Co/Al/In in the main laminates was confirmed by XRD,TEM,XPS,etc.In the final experiment,photocatalytic reduction of CO₂ activity of LDHs with different Al/In mole ratios was explored.Photocatalytic activity of Co Al In₆-LDHs sample is the best,and its methanol yield reached at 233.71μmol·g^-1·h^-1.And the mechanism of Co Al In-LDHs photocatalytic reduction of CO₂ was deduced in detail.2.Cu O quantum dots（QDs）and ultrathin Co Al-LDHs（Co Al-u）were prepared by phase transfer method and one-step co-precipitation method,respectively.Then the compositions x%Cu O/Co Al-u with Z-scheme heterojunction was successfully prepared.TEM,XRD,XPS,etc were used to analyzes the structure and photoelectrical properties of ultrathin Co Al-u and the compositions.Finally,we carried on the photoreduction CO₂ active exploration of composite catalysts with the different Cu O loading and pure Co Al-LDHs,and tested the yield of liquid product（CH₃OH）and gaseous products（CH₄,CO）.Experiments results showed that the photocatalytic activity of 4.5%Cu O/Co Al-u compositions was the best,and the CH₃OH production rate was 283.26μmol·g^-1·h^-1,and further analysed the photocatalytic reduction CO₂ mechanism of Z-scheme heterojunction formed by Cu O/Co Al-u compositions,which proved that the migration direction of photogenerated electrons was from Cu O conduction band（CB）to Co Al-u valence band（VB）and the reduction reaction proceeded on the CB of Co Al-u while the oxidation reaction on the VB of Cu O.