Browsing by Author "Ebrahimi, Elnaz"

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Open Access
Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2
(Wiley, 2020-09) Ebrahimi, Elnaz; İrfan, Muhammad; Shabani, Farzan; Koçak, Yusuf; Karakurt, Bartu; Erdem, E.; Demir, Hilmi Volkan; Özensoy, Emrah
Functionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.
Open Access
Core-crown quantum-well nanoplatelet functionalized TIO2 for photocatalytic NOx abatement
(2020-07) Ebrahimi, Elnaz
Oleic acid capped core/crown CdSe/CdSeTe quantum-well nanoplatelets (NPL) were used in the surface functionalization of TiO2. Structural characterization of the synthesized photocatalytic architecture was carried out to shed light on its surface chemistry, electronic, and crystallographic structure. NPL/TiO2 composites were tested in NO photo-oxidation under ultraviolet-A (UVA) and visible (VIS) light, showing a remarkable activity in NOx abatement and high selectivity for nitrate storage as compared to standard benchmark TiO2 photocatalyst (i.e. P25). Improved photocatalytic behavior can be attributed to the decrease in the bandgap and enhanced photogenerated electron-hole pair separation as a result of the incorporation of CdSe/CdSeTe NPL onto TiO2. Stability of composites was also investigated in durability tests. Even though some decrease in photocatalytic activity and selectivity of NPL/TiO2 composites was observed, performance of the NPL/TiO2 composites was found to be significantly better than pure TiO2.
Open Access
Origins of the photocatalytic NOx oxidation and storage selectivity of mixed metal oxide photocatalysts: prevalence of electron-mediated routes, surface area, and basicity
(American Chemical Society, 2024-01-23) Ebrahimi, Elnaz; Irfan, Muhammad; Koçak, Yusuf; Rostas, A. M.; Erdem, E.; Özensoy, Emrah
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 sites.