3 research outputs found
Origins of the Photocatalytic NO<sub><i>x</i></sub> Oxidation and Storage Selectivity of Mixed Metal Oxide Photocatalysts: Prevalence of Electron-Mediated Routes, Surface Area, and Basicity
MgO, CaO, SrO, or BaO-promoted TiO2/Al2O3 was utilized in the photocatalytic
NOx oxidation and storage reaction. Photocatalytic
performance
was investigated as a function of catalyst formulation, calcination
temperature, and relative humidity. Onset of the photocatalytic activity
in TiO2/Al2O3 coincides with the
transition from the anatase to rutile phase and increasing number
of paramagnetic active centers and oxygen vacancies. Disordered AlOx domains enable the formation of oxygen vacancies
and paramagnetic centers on titania domains, hindering the nucleation
and growth of titania particles, as well as increasing specific surface
area (SSA) to store oxidized NOx species
away from titania active sites. Both e–- and h+-mediated pathways contribute to photocatalytic NO conversion.
Experiments performed using an e– scavenger (i.e., H2O2), suppressing
the e–-mediated route, attenuated the photocatalytic selectivity
by triggering NO2(g) release. Superior NOx storage selectivity of 7.0Ti/Al-700 as compared to other TiO2/Al2O3 systems in the literature was
attributed to an interplay between the presence of electrons trapped
at oxygen vacancies and superoxide species allowing a direct pathway
for the complete NO oxidation to HNO3/NO3– species, and the relatively large SSA of the photocatalyst
prevents the rapid saturation of the photocatalyst with oxidation
products. Longevity of the 7.0Ti/Al-700 was improved by the incorporation
of CaO, emphasizing the importance of the surface basicity of the
NOx storage site
Impact on the Photocatalytic Dye Degradation of Morphology and Annealing-Induced Defects in Zinc Oxide Nanostructures
In this study, three
different morphologies, nanoflower (NF), nano
sponge (NS), and nano urchin (NU), of zinc oxide (ZnO) nanostructures
were synthesized successfully via a mild hydrothermal method. After
synthesis, the samples were annealed in the atmosphere at 300, 600,
and 800 °C. Although annealing provides different degradation
kinetics for different morphologies, ZnO NS performed significantly
better than other morphologies for all annealing temperatures we used
in the study. When the photoluminescence, electron paramagnetic resonance
spectroscopy, BET surface, and X-ray diffraction analysis results
are examined, it is revealed that the defect structure, pore diameter,
and crystallinity cumulatively affect the photocatalytic activity
of ZnO nanocatalysts. As a result, to obtain high photocatalytic activity
in rhodamine B (RhB) degradation, it is necessary to develop a ZnO
catalyst with fewer core defects, more oxygen vacancies, near band
emission, large crystallite size, and large pore diameter. The ZnO
NS-800 °C nanocatalyst studied here had a 35.6 × 10–3 min–1 rate constant and excellent
stability after a 5-cycle photocatalytic degradation of RhB
Nitrogen-Doped WO<sub>3</sub> Nanoparticles as Electrode Materials in All-in-One Supercapacitor Devices
The
effect of the annealing temperature on 1% nitrogen-doped WO3 materials was studied, which were then used as electrode
materials for high-performance supercapacitor (SC) devices. The supercapacitive
performance of the proposed materials was strongly influenced by the
doping element and the annealing temperature by directly changing
the defect structure of the host material. The 1% N-doped WO3 materials annealed at different temperatures were thoroughly characterized
through various characterization techniques, including electron paramagnetic
resonance and photoluminescence spectroscopy, giving insight into
the effect of N-doping on the defect structure and optical properties
of WO3. When the WO3:N materials were used as
electrode material in symmetric SCs, the doping element and the annealing
temperature improved the electrochemical performance. No booster materials
(such as carbon black) were used in the symmetric SC designs, showing
increased specific capacitance (102 F/g) and energy density (14.6
W h/kg) values