We have carried out the effect of post annealing temperatures on the performance of solution-grown ZnO rods as photoanodes in dye-sensitized solar cells. Keeping our basic objective of exploring the effect of native defects on the performance of DSSC, we have synthesized ZnO rods having length in the range of 2-5 μm by a modified sonication-induced precipitation technique. We performed extensive characterization on the samples annealed at various temperatures and confirmed that annealing at 300 °C results in ZnO rods with minimum native defects that have been identified as doubly ionized oxygen vacancies. The electron paramagnetic resonance measurements on the samples, on the other hand, confirmed the presence of shallow donors in the low temperature annealed samples. We also carried out electrochemical impedance measurements to understand the transport properties at different interfaces in the solar cell assembly. We could conclude that solution-processed ZnO rods annealed at 300 °C are better suited for fabricating DSSC with improved efficiency (1.57%), current density (5.11 mA/cm(2)), and fill factor (45.29%). On the basis of our results, we were able to establish a close connection between the defects in the metal oxide electron transporting nano system and the DSSC performance.
A large scale synthesis of mesoporous
hematite (α-Fe2O3) nanorods with a high
surface area of 98 m2/g and an average pore size of ∼26
nm was used for
adsorption studies for pollutant dye removal. The nanorods exhibited
rapid, superior, and selective adsorption efficiency toward Congo
red, an organic dye present in wastewater. Highly selective adsorption
capability of the mesoporous α-Fe2O3 nanorods
has been attributed to the presence of abundant surface active sites
with porous networks which make it highly water dispersible facilitating
the formation of H-bonding and coordination effect between the -NH2 group of Congo red with its surface -OH groups and Fe3+, respectively. Adsorption studies concerning the effect
of contact time, initial dye concentration, dosage of adsorbent, and
effect of pH on adsorption kinetics were explored in addition to the
desorption process investigation regarding the effect of solution
pH from acidic to alkaline. To unravel the unresolved phenomenon toward
selective adsorption of Congo red by mesoporous α-Fe2O3 nanorods beyond conventional factors (viz., surface
area/porosity, electrostatic interaction, and so on), investigation
was also carried out by varying the nature of the different dye molecules
as well as the phase and morphology of the α-Fe2O3 nanomaterials.
ZnO/CdS heterostructured nanocomposites were fabricated with enhanced light harvesting capability and photostability using sequential sonochemical and hydrothermal methods from ZnO rods and particles. Interestingly, in the composite made up of CdS sensitized ZnO rods, both ZnO and CdS exist in the hexagonal wurtzite form with different morphologies. On the other hand, in the composite made up of CdS sensitized ZnO particles, ZnO exists in the hexagonal wurtzite form, whereas CdS in the cubic form but with a similar morphology. The synthesized photocatalysts under simulated solar irradiation exhibited hydrogen evolution rates of 870 and 1007 μmol h(-1) g(-1) for the ZnO rod/CdS and ZnO nanoparticle/CdS composites, respectively, compared to the native ZnO (40 μmol h(-1) g(-1) for rods and 154 μmol h(-1) g(-1) for particles) and CdS (208 μmol h(-1) g(-1)) structures. The apparent quantum yield of CdS was only 1.2%, whereas the composites exhibited much higher quantum yields of 4.9% and 5.7%. Our results confirmed that the morphology of the host matrix ZnO played a crucial role in forming ZnO/CdS heterostructures with improved interface for the direct Z-scheme mechanism with enhanced hydrogen evolution efficiency.
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