Investigations On The Electronic And Optic Properties Of New Carbon-based Materials

In most recent years,carbon-based materials become a research hot spot due to their abundant morphology as well as remarkable mechanical,electrical and thermal dynamic properties.In a broad sense,carbon-based materials consist of all the substances of carbon atom skeleton,including pure carbon systems like graphite and other hybrid systems like g-C₃N₄ polymers.As the heating up of low-dimensional-system-related research,tremendous attention have been paid to those carbon-based materials owning to the low cost,profusion and high modulation freedom.In particular,graphic carbon nitrides come to be the focus at the outset since it is artificially designed and synthesized carbon-based products.Lately,a lot of theoretical and experimental studies focused on photo-catalyzed organic pollutant degradation,CO₂ and NO reduction,hydrogen production and fuel cells have been carried out on account of its unique chemical or physical characters.Nonetheless,most of previous works focus on introducing external factors such as doping,heterojunctions,electric or magnetic field and so forth,while ignoring the complexity of pristine g-C₃N₄ as well as simple modification such as protonation.Thus,the following studies have been carried out to tackle with such issues:1.For the very first time,We propose that the stacking-dependent spatial?SDS? charge separation could be realized through controlling the stacking patterns in layered semiconductor materials and relevant theory is subtly expounded in g-C₃N₄ system.As spatial charge separation naturally suppresses the electron-hole re-combination,that makes g-C₃N₄ layers with proper stacking much more efficient for harvesting solar energy in photovoltaic or photocatalytic applications.The SDS charge separation has been understood as a result of the inter-layer quantum entanglement from those g-C3N4 band electrons,whose unique chirality and phases in corner-atom-shared C₆N₁₀ units are relatively isolated and in tune only through the corner N atoms.The SDS charge separation in g-C₃N₄ may lead to an intrinsic way without alien dopings,interfaces or electrical fields,to manipulate charge carriers in semiconducting materials.That may lead to new physics in the future optoelectronics or electronics of two-dimensional?2D?materials,such as realizing the layer-selected charge transport through the bilayer or multi-layer 2D materials.Besides,two different pristine stacking schemes are built according to which we figured out all the possible stacking configurations.Based on DFT calculations,the energy diagram with respect to translational stacking manners is obtained for the comprehension of the relations between various motifs.And also the result could be an aid for the improvement of bulk crystallization quality.Furthermore,we calculate the influence of stacking on motif band structures.We ascertain the fact that stacking effect could largely modify the band gap and the energy level,which could be play a guiding role in experimental works.2.Experimentally we report a simple,facile and effective method to simultaneously hydrogenate and exfoliate g-C₃N₄ based on which we set up five relevant possible hydrogenated g-C₃N₄ super-cells.The hydrogenation mechanism of g-C₃N₄ is explained experimentally and it is further revealed in detail by first principle calculation as well as the corresponding electronic structure evolutions.Five different atomic sites in unit cell of g-C₃N₄ are structurally available to be hydrogenated,and four of them are energetically favored to form hydrogenated structures.The hydrogenated g-C₃N₄ structures also present blue-shifted UV–vis absorption and photoluminesce?PL?peaks compared to that of pristine g-C₃N₄,and it is well explained by theoretical calculation results that the bandgap becomes larger due to hydrogenation.Finally,it is found that the photocatalytic performance of g-C₃N₄ is dramatically enhanced once the crystal structure is hydrogenated,which is mainly attributed to the hydrogenation caused spatial charge separation due to the redistribution of charge density in both valence band maximum and conduction band minimum.The revealing of spatial charge separation provides insight into the deep understanding of hydrogenation mechanism of g-C₃N₄,which is critically significant for designing light-efficient photo-catalysis further on.3.We have designed a new energy system of microporous graphite/Ag/phosphomolybdic acid?PMA?as efficient hybrid material for supercapacitors,in which microporous graphite serves as skeleton?contribution of EDLCs?,PMA as redox additive?contribution of pseudo-capacitance?,Ag as conducting agent?promotion of electrical conductivity?.The energy density has reached up to 22.8 Wh kg–1 at the power density of 500 W kg–1,which is almost1.91 fold of pristine microporous graphite.Our work has provided an alternative material for high performance supercapacitors and paved the way for similar applications of g-C₃N₄ in the future.