| As a two-dimensional group IV graphene analog,germanene has become a hot spot in the research area of new materials due to its extremely high theoretical carrier mobility,distinctive sp2-sp3 hybrid bond and low buckled honeycomb structure.Therefore,it has been widely explored in various application fileds including electronic,photoelectric,energy storage and conversion,quantum field,etc.However,the difficulties in the synthesis of germanene and its zero bandgap characteristics limit the wide application and in-depth study of germanene.An effective way to realize the preparation and functionalization of germanene is the direct synthesis of germanene derivatives,and thus the bandgap regulation of germanene can be realized.The exploration of germanene's physical and chemical properties and potential applications therefore can be achieved through the study of the relationship between the structure and electronic properties.In this thesis,the organic functionalized germanene(germanane)was synthesized by the topological chemical reaction of the Zintl phase crystal CaGe2 in which there existed the graphene-like structure for germanium.The relationship between the structure and electronic properties of germanane was studied by theoretical calculation and experimental results,and the band gap regulation of germanane was achieved in the range of 1.60-2.04 e V.Starting from the alloying of CaGe2 crystal,the Ca(Ge1-xSix)2(x=0.1-0.9)alloys were synthesized by doping Si atom,and the siligenes(gersiloxenes)terminated by-H/-OH group were synthesized through the topological intercalation reaction of Ca(Ge1-xSix)2.The structural characteristics and electronic properties of gersiloxenes were studied by theoretical calculation and experimental results for the first time.By adjusting the ratio of Si atoms,the bandgap of gersiloxenes can be tailored in the range of 1.80-2.57 e V.On this basis,we explored the band structure feature and application potential of gersiloxenes in the field of photocatalysis.The results showed that the bandgap and band structure of gersiloxenes are suitable for light driven water reduction into H2 and CO2 reduction to CO.The gersiloxene with x=0.5(HGe Si OH)is most suitable for photocatalytic hydrogen production and reduction of CO2 to CO than other gersiloxenes,due to its moderate band edge levels and bandgap,hybridized orbital composition of the valence band(VB)and conduction band(CB),wide spectral response range,high specific surface area,and oxygen vacancies in gersiloxenes,therefore exhibited the best photocatalytic performance.When used as a photocatalyst in water reduction to produce H2,it has a hydrogen production rate of 1.58 mmol g-1 h-1 and good cycle stability.When applied to photoreduction of CO2 under mild conditions(25°C,1 atm CO2),it achieves high conversion efficiency to produce CO with a production rate of 6.91 mmol g-1 h-1 and has a high AQE of 5.95%at 420 nm,which is better than the majority of recently reported photocatalysts.The electrochemical performance of organic functionalized germanane was studied.The potential of few layer methyl functionalized germanane(Ge CH3)nanosheets as anode materials for Li-ion batteries was explored.By compounding with graphene and forming sandwich structure composite,the discharge capacity,cycle stability and rate performance of Ge CH3 nanosheets can be improved significantly.The Ge CH3/r GO-2 composite with 30 wt%r GO content showed the best performance.Testing at 0.2 A g-1 for 100 cycles,the specific capacities of the Ge CH3/r GO-2maintained 1058 m Ah g-1,which presents a better performance than many other recently reported Ge-based 2D material systems.Additionally,it had high rate and long cycle stability,and could be cycled for 500 cycles at 0.5 and 1 A g-1 with retained capacity of 439 and 288 m Ah g-1,respectively.This makes the organic functionalized germanane a promising cathode material for lithium-ion batteries. |
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