The document summarizes research on creating molybdenum disulfide (MoS2) and zinc oxide (ZnO) nano-heterojunctions through a hydrothermal process and investigating their photocatalytic and field emission properties. The MoS2-ZnO composites showed enhanced photocatalytic activity for degrading methylene blue due to increased surface area and improved electron-hole separation. Measurement of field emission properties revealed the composites have significantly lower turn-on and threshold fields than pure MoS2, demonstrating the ZnO nanoparticles increase emission sites and decrease the potential barrier. The combination of MoS2 and ZnO utilizes the materials' band gap structures to enhance light absorption and charge carrier separation

1. MoSMoS22 and ZnO nano-heterojunctions with enhanced photo catalysisand ZnO nano-heterojunctions with enhanced photo catalysis
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