MoS2 Based Nanomaterials for Solar Energy Utilization

Abstract

Snowballing energy demands and environmental problems are the main concerns of this epoch. Depleting energy resources has urged us to find new renewable energy sources and methods to deal with environmental problems. SE has a great potential to be utilized as an energy resource and for environmental remediation applications by capturing the energy from the Sun and converting it to other forms of energy i.e., CE. Research interest in transition metal chalcogenides (TMC) has been increased in the past few years. Molybdenum sulfide is a member of the TMC group with an indirect band gap of 1.23 eV in the bulk form and a direct bandgap of 1.9 eV in few and monolayer MoS2. It is the most widely studied catalyst due to its distinctive electrical, optical, chemical, and mechanic a l properties. In this research project, we have focused on the synthesis of different binary and ternary heterostructures with MoS2, to utilize its full potential as photoactive material. In the beginning, the efforts were dedicated to producing a few-layered MoS2 by hydrotherma l method with a bandgap of 1.9 eV. After achieving the desired morphology, a heterojunct ion with CoTe was established by a simple ultrasonication method. This junction worked well for photoelectrochemical water splitting, which is a promising technique for hydrogen generation. A maximum photocurrent density of 2.791 mA/cm2 was observed for the heterojunction which is about 11 times higher than the pristine MoS2. This current density was obtained at an applied bias of 0.62 V vs. Ag/AgCl (1.23 V vs. RHE) under the light intensity of 100 mW/cm2 of AM 1.5G illumination. The enhanced photocurrent density may be attributed to the efficie nt electron-hole pair separation. The solar to hydrogen conversion efficiency was found to be 0.84% for 1:1 MoS2/CoTe, signifying the efficient formation of the heterojunction. This study offers a novel heterojunction photocatalyst, for PEC water splitting. Graphitic carbon nitride (g-C3N4) is restricted in use for application in photocatalytic domain because of high electron/hole recombination rate and poor charge transfer. Heterostructure series of ZnSe/g-C3N4 binary and ZnSe/GCN/MoS2 ternary was prepared by using a simple ultrasonication procedure to overcome these shortcomings. The successful formation of ZnSe/g-C3N4 and ZnSe/GCN/MoS2 was confirmed by phase, morphological and optical analysis. The prepared heterostructures were then tested for PEC water splitting for the first time. Linear sweep voltammograms of 0.05ZG and 1ZGM heterostructure showed a six- fold higher photocurrent density of 500μA and 7 folds higher at 1.7mA than pure g-C3N4. These results were supported by the Tafel slopes and PL studies by showing the smallest slope and lesser electron-hole recombination for 0.05ZG and 1ZGM. The EIS studies also showed the smallest semicircle for 0.05ZG and 1ZGM, implying the lowered charge transfer resistance. All the results comply with each other showing the successful formation of binary and a ternary heterojunction for enhanced PEC water splitting. we prepared MoS2/ZnSe binary heterostructures by a simple ultrasonication method. The results show that an efficient interface was formed to harness the visible light and degrade levofloxacin, which was monitored by gradual decreases in the UV-vis absorbance signal of levofloxacin. The prepared heterostructures, MoS2/ZnSe showed a better degradation activit y of 73.2% as compared to pure MoS2 (29%) and ZnSe (17.1%) in the presence of visible light in a time span of two hours. The reusability studies showed that the catalytic performance of 3:1 MZ did not decrease significantly after three cycles. Moreover, the morphology and the crystal structure also remained unchanged. In summary, this thesis presents studies on binary and ternary heterojunctions of MoS2 with CoTe, ZnSe, and g-C3N4. The prepared heterostructures display excellent PEC water splitting and degradation activity for Levofloxacin.