MoSMoS22 and ZnO nano-heterojunctions with enhanced photo and ZnO nano-heterojunctions with enhanced photo catalysiscatalysis

Amir Khalid School of Chemical And Materials Engineering, NUST

INTRODUCTION

RESULTS OF SOLAR CELL

RESULTS OF MOLIBDENUM OXIDE (MoS2)

ABSTRACT

EXPERIMENTS

The molybdenum disulfide (MoS2) and ZnO nano-heterojunctions were successfully fabricated through a three step synthetic process: prefabrication of the ZnO nanoparticles, the synthesis of MoS2 nanoflowers, and the fabrication of MoS2@ZnO heterojunctions, in which ZnO nanoparticles were uniformly self-assembled on the MoS2 nanoflowers by utilizing polyethyleneimine as a binding agent. The photocatalytic activities of the composite samples were evaluated by monitoring the photodegradation of methylene blue (MB). Compared with pure MoS2 nanoflowers, the composites show higher adsorption capability in dark and better photocatalytic efficiency due to the increased specific surface area and improved electron-hole pair separation. After irradiation for 100min, the remaining MB in solution is about 7.3%. Moreover, the MoS2-ZnO heterojunctions possess enhanced field emission properties with lower turn-on field of 3.08V lm-1and lower threshold field of 6.9V lm-1 relative to pure MoS2 with turn-on field of 3.65V lm1 and threshold field of 9.03V lm-1.

Molibdenum diSulphide (MoS2)

Fig.4. (a) The dependence of the FE current density (J) on the applied electric field strength (E) of MoS2 nanoflowers and MoS2@ZnO heterojunctions. The inset is the schematic illustration for FE measurement. (b The inset is the field emission photos for the MoS2 nanoflowers (left) and MoS2 nanoflowers (right).

MoS2@ZnO nano-heterojunctions were successfully fabricated via low-temperature hydrothermal method and thermal annealing process.

Compared with pure MoS2 nanoflowers, the composite samples demonstrate stronger adsorption capabilities in dark and enhanced photocatalytic activities.

The high photodegradation activity is attributed to the increased specific surface area and improved electron-hole pair separations.

The field emission properties of MoS2@ZnO heterojunctions were measured.

The results indicate the significantly enhanced field emission properties than those of pure MoS2, because of more emission sites on the surface of the composites and the decrease in potential energy barrier. It can be demonstrated that the ZnO nanoparticles play important roles.

ZnO nanoparticles fabricated via hydrothermal route from urea solution and zinc chloride solution. MoS2 nanoflowers were also synthesized through hydrothermal method by sodium molybdate, thiocarbamide and citric acid.MoS2-PEI-ZnO a hybrid is prepared and annealed to remove PEI (Polyimmineethylene).

The combination of MoS2 nanoflowers, a narrow band gap p-type semiconductor, and ZnO nanoparticles, a n-type semiconductor with a wide band gap and small sizes will enhance light absorption from UV to visible, increase the separation and lifetime of charge carriers, which can provide potential applications in photocatalytic and field emission fields.

CONCLUSION

Formation of ZnO nanoparticles and ZnO/MoS2 composite

Fig.2. c) & d) TEM Images of ZnO/MoS2 Composite

Fig.3. a) UV-Vis absorption spectra of MoS2 ZnO nanocomposite b) the photo degradation rates of Methyl blue MB with phoocatalyst

FIG. 7. Schematic diagram of the charge generation and transfer process under the UV-vis light in MOS2@ZnO nano-heterojunctions.

RESULTS OF ZnO/MoS2 JUNCTION

Fig.1. a) Low Magnification b) High Magnification