Photothermal Synergistic Enhancement Of CO₂ Conversion Efficiency By Two-dimensional Ti₃C₂-based Materials

To cope with the environmental problems caused by the yearly increase in CO2 emissions in the atmosphere,China has developed the goals of "peak carbon dioxide emissions" and"carbon neutrality" The use of photothermal synergistic catalytic conversion technology for CO2 reduction and utilization is a promising strategy.However,the development of high-efficiency photothermal catalytic CO2 conversion materials remains a challenge in the field of energy and the environment.Among many photothermal catalytic CO2 materials,MXene has obvious advantages.Ti3C2-MXene is a graphene-like material with good electrical conductivity,photothermal properties,and the generation of plasmonic transverse electric(TE)and plasmonic transverse magnetic(TM)waves upon photoexcitation.Therefore,the use of Ti3C2-MXene as a substrate is promising for efficient photothermal catalytic conversion of CO2.However,the conversion of CO2 by Ti3C2-MXene photothermal catalytic materials suffers from low conversion efficiency.Therefore,by modifying the semiconductor/metal and doping rare earth ions into the semiconductor,an interfacial electric field is constructed to drive the reduction electrons to be replenished to Ti3C2-MXene,thus improving the efficiency of CO2 conversion.In this work,an electron transport medium and an interfacial electric field were constructed to promote charge transfer to Ti3C2-MXene,metal-activated reactants were used to promote the conversion of CO2 to CH4,and semiconductor oxides and hydroxides were used to modulate product selectivity.The Landau damping effect was applied to explain the photogenerated electron conversion process of hydroxides to high-energy hot electrons and the mechanism of hydroxide modification of Ti3C2-MXene to increase its total yield of photothermal catalytic conversion of CO2.Using the rare earth ion up-conversion effect to increase the number of photogenerated electrons in the semiconductor,which ultimately increases the number of high-energy electrons supplemented to Ti3C2-MXene to further enhance the selectivity of photothermal conversion of CO2 to CO over Ti3C2-MXene material.Mechanisms of interfacial electric field to promote charge transfer,Landau damping effect to empower charge,and the up-conversion effect to enhance the Landau damping and their influence on the photothermal conversion CO2 performance of Ti3C2-MXene materials are proposed,and the relationship between different modification strategies and CO2 conversion performance is established.The main research works are as follows:(1)Multilayer Ti3C2 was obtained by etching pretreatment process with acid and alkali successively.Ni-Cu-Ti3C2 photothermal catalysts with Ni and Cu bimetallic loading of Ti3C2 were prepared by chemical reduction.An interfacial electric field is established between NiTi3C2 to drive charge transfer,while metallic Cu acts as an electron transfer medium.The interaction of metal Ni,Cu,and Ti3C2 enhanced the Local Surface Plasmon Resonance(LSPR)effect as well as the light-absorbing property of Ti3C2.When Ni-Cu-Ti3C2 was exposed to light,the metal Ni underwent the LSPR effect to generate hot electrons,which were subsequently transferred to Ti3C2 through the conductive medium Cu driven by the interfacial electric field,which significantly prolonged the hot-electron lifetime of the metal Ni as well as enhanced the efficiency of the reactants activated by Ni-Cu-Ti3C2.The assisted heat further enhanced the migration of hot electrons at the interface of Ni,Cu,and Ti3C2.The bimetallic activation reactant and the addition of hot electrons from Ni to Ti3C2 via metallic Cu promoted the photothermal conversion of CO2 to CH4.The photothermal conversion of CO2 to CH4 in Ni-Cu-Ti3C2 reached a yield of 54.5 μmol·g-1·h-1,which is a 5.2-fold increase compared to the Cu-Ti3C2 material.(2)Cu and TiO2 particles were grown in situ on surface of Ti3C2 by using hydrothermal method.A Schottky junction was formed at the TiO2-Ti3C2 interface,generating a built-in electric field of TiO2 that points to Ti3C2,while the metal Cu acted as an electron transfer medium at the Schottky junction interface.The light absorption property of TiO2-Cu-Ti3C2 is significantly enhanced compared to TiO2-Ti3C2,demonstrating that the interaction between Cu and Ti3C2 enhances the LSPR effect of Ti3C2.Characterization and test results indicate that after the separation of the photogenerated electron-hole pairs of TiO2,the conduction band electrons are driven by the Schottky junction at the TiO2-Ti2C2 interface to be transferred to Ti3C2 through the conductive medium Cu.During this period,the enhanced LSPR effect of Ti2C2 generated more hot electrons.Transfer of photogenerated electrons to Ti3C2 and its hot electrons improved reactant activation and further improved the photothermal conversion efficiency of CO2.Product selectivity was modulated by modifying TiO2 and metal Cu on the surface of Ti3C2.The highest yields of photothermal reduction of CO2 to CH4 and CO on TiO2-Cu-Ti3C2 catalysts were 16.2 and 5.4 μmol·g-1·h-1,respectively,with the highest selectivity of 35.4%for CO.(3)Ni(OH)2/Ti3C2 photothermal catalysts were prepared using an acid-base etching hydrothermal method.β-Ni(OH)2 was loaded onto the Ti3C2 surface and embedded in the layers,and Schottky junctions and built-in electric fields were established at the interface of Ni(OH)2 and Ti3C2.Visible-near-infrared light absorption from the intraband transitions of Ni(OH)2 is utilized,leading to spectral overlap of Ti3C2 and Ni(OH)2 to produce strong interfacial coupling.As a result,Ni(OH)2/Ti3C2 exhibits enhanced full-spectrum absorption and vibrational peaks TE and TM in the visible and near-infrared ranges,respectively.Landau damping of Ni(OH)2"pumps" its low-energy photogenerated electrons into hot electrons,and the photogenerated and hot electrons are supplemented in Ti3C2 by the built-in electric field.Photogenerated and hot electrons were added to Ti3C2 driven by the built-in electric field.More hot electrons were generated to enhance the photothermal CO2 conversion activity of Ti3C2.The total conversion of photothermally reduced CO2(total CO and CH4 production)on Ni(OH)2/Ti3C2 reached 891.9μmol·g-1·h-1 at 250℃,which was 14 times higher than that of Ti3C2,with CO and CH4 yields of 458.4 and 433.5 μmol·g-1·h-1,respectively,and selectivities of 51.4%and 48.6%.(4)Ni1-xNdx(OH)2/Ti3C2 photothermal catalyst was obtained by hydrothermally doping Nd3+into Ni(OH)2,and a built-in electric field was established at the interface of Ni1-xNdx(OH)2 and Ti3C2.The effect of introducing the up-conversion effect of Nd3+was to increase the concentration of photogenerated electrons and the surface temperature of the catalyst.The upconversion effect of Nd3+led to an enhancement of visible and near-infrared light absorption in the composites and therefore an increase in the concentration of photogenerated electrons.The catalyst surface temperature is increased due to enhanced light absorption by Ni1xNdx(OH)2/Ti3C2.The increase in the concentration of photogenerated electrons leads to the enhancement of the Landau damping effect,which increase the number of high-energy hot electrons replenished to Ti3C2.Furthermore,the Nd3+doping of Ni1-xNdx(OH)2 resulted in an upward shift of the valence band,which weakens the ability of Ni1-xNdx(OH)2/Ti3C2 to dissociate H2.The increase in catalyst surface temperature and the decrease in H2 dissociation capacity jointly promoted the photothermal catalytic conversion of CO2 to CO.The conversion of photothermally reduced CO2 to CO by Ni1-xNdx(OH)2/Ti3C2 was 532.9 μmol·g-1·h-1 with a selectivity of 82.5%in a photothermal environment of 250 ℃.