Theoretical and experimental estimation of structural, electronic and optoelectronic properties of alkali metals absorbed monolayer of g-C3N4

Abstract

Carbon nitride of layered structure, bulk form, and its state of nano-particles bear separate characteristics. Adsorbing alkali metal in it modifies its geometrical structure. The intercalation property of C3N4allows it to adsorb ions of varied sizes, even in greater quantity. From the various allotropes of g-C3N4, the trigonal structure is the most popular as well as readily fabricable. In this work,electrical and optoelectrical properties of Li, Na, and K adsorbedg-C3N4was investigated using DFT simulation and several other properties are observed by experiment.DFT based simulation was carried out based on 3×3×1 supercell. Several different DFT functionals on Quantum Espresso and CASTEP codes were tested to choose the best option. It was found that the BLYP_US_VDW functional yielded the best performance. Simulation shows that the layers of graphitic carbon nitride mandatorily distort after ion adsorption. Angle of contact between the ions and the C3N4 layer was lowest (44.9°) for Li+ and the highest (58.2°) for K+.Simulation shows the band gap energy to benearly indirect after all the ion adsorptions. Density of states is almost identical for Li and Na doping. But it is noticeably different for K doping. Graphitic carbon nitride can find its application in various pressure and vibration sensing devices. Therefore, piezoelectric constant measurement is very important. This work estimated the values of piezoelectric constant (d33) from the simulated piezoelectric tensor data. The estimated and experimental values are comparable. In experiment it is found that the piezo-electric constant differs very slightly upon doping. The highest value is for K doping and it is 3.8 × 10-11 C/N (Pure g-C3N4shows3.3 × 10-11 C/N). So, the dopants are not a well contributor to the improvement of piezoelectricity.In this thesis, UV-vis spectroscopy was carried out for pure g-C3N4, K and Na adsorbed samples. All of them have shown notable absorbance peaks at around 200 nm wavelength (more or less) and the band gap decreased from 2.74 eV to 2.65 eV. So, the band gap suggests thatgraphitic carbon nitride can be a promising candidate in photodegradation-relatedapplications, though the effectiveness has not been justified in this work.At the end of this thesis paper, the concluding remarks are included and perspectives are made for further study.