Browsing by Subject "Photocatalytic NOx abatement"

Now showing 1 - 4 of 4

Open Access
CdTe quantum dot-functionalized P25 titania composite with enhanced photocatalytic NO2 storage selectivity under UV and vis irradiation
(American Chemical Society, 2019) Balcı-Leinen, Merve; Dede, Didem; Khan, Münir Ullah; Çağlayan, Mustafa; Koçak, Yusuf; Demir, Hilmi Volkan; Özensoy, Emrah
Composite systems of P25 (titania) functionalized with thioglycolic acid (TGA)-capped CdTe colloidal quantum dots (QDs) were synthesized, structurally characterized, and photocatalytically tested in the photocatalytic NOx oxidation and storage during NO(g) + O2(g) reaction. Pure P25 yielded moderate-to-high NO conversion (31% in UV-A and 40% in visible (vis)) but exhibited extremely poor selectivity toward NOx storage in solid state (25% in UV-A and 35% in vis). Therefore, P25 could efficiently photooxidize NO(g) + O2(g) into NO2; however, it failed to store photogenerated NO2 and released toxic NO2(g) to the atmosphere. CdTe QD-functionalized P25 revealed a major boost in photocatalytic performance with respect to pure P25, where NO conversion reached 42% under UV-A and 43% under vis illumination, while the respective selectivity climbed up to 92 and 97%, rendering the CdTe/P25 composite system an efficient broad-band photocatalyst, which can harvest both UV-A and vis light efficiently and display a strong NOx abatement effect. Control experiments suggested that photocatalytic active sites responsible for the NO(g) + O2(g) photooxidation and formation of NO2 reside mostly on titania, while the main functions of the TGA capping agent and the CdTe QDs are associated with the photocatalytic conversion of the generated NO2 to the adsorbed NOx species, significantly boosting the selectivity toward solid-state NOx storage. Reuse experiments showed that photocatalytic performance of the CdTe/P25 system can be preserved to a reasonable extent with only a moderate decrease in the photocatalytic performance. Although some decrease in the photocatalytic activity was observed after aging, CdTe/P25 could still outperform P25 benchmark photocatalyst. Increasing CdTe QDs loading from the currently optimized minuscule concentrations could be a useful strategy to increase further the catalytic lifetime/stability of the CdTe/P25 system with only a minor penalty in catalytic activity.
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
Quantum dot functionalized Titania systems for photocatalytic oxidative NOx storage
(2018-03) Balcı, Merve
Increasing activities of industrial combustion systems, volcanic eruptions, agriculture activities and utilization of stationary and mobile fossil and biomass combustion systems are known to be the major causes of toxic nitrogen oxides (NOx) pollution. These pollutants are not only highly hazardous for the ecosystem but also can trigger the formation of secondary pollutants such as acid rain and tropospheric ozone. Abatement of toxic NOx gases can be achieved by thermal catalytic processes or physical/chemical adsorption systems. However, environmentally friendly, cost-efficient and sustainable alternative photocatalytic systems can also be designed which can exploit readily abundant solar radiation. One of the most well-known benchmarks for environmental photocatalysts is titanium dioxide with a wide band gap typically varying within 3.0-3.2 eV that can be activated via UV photons. This wide band gap prevents efficient absorption of visible light, which corresponds to around 5 times higher intensity compared to UV light. In order to increase the photocatalytic efficiency of the titanium dioxide, its visible-light exploitation capability should be enhanced. Although, this can be done by doping of TiO2 with nonmetal main group elements, recently the research focus has shifted towards utilization of semiconductor quantum dots (QDs) for this purpose. Visible response of the QDs can be modified by tuning their particle size. Furthermore, QDs provide additional advantages such as the generation of hot electrons or multiple charge carriers with a single high-energy photon. In the present work, CdTe QDs were employed as a direct band gap semiconductor (1.44 eV) compatible with the visible window of the solar spectrum to promote titania based photocatalysts. Due to its higher conduction band, CdTe can transfer its conduction band electrons to the conduction band of TiO2 and the hole that is created on the valence band of TiO2 can be transferred to the valence band of CdTe; leading to efficient electron-hole separation. Thus, visible light exploitation capacity of TiO2 can be enhanced along with its photocatalytic activity. Current photocatalytic activity results on QD functionalized titania systems exhibited much higher NOx storage in solid state and an enhancement of NO conversion values as compared to that of P25 titania benchmark photocatalyst. In addition, various reference materials were prepared and photocatalytically tested in order to shed light on the mechanism of this photocatalytic enhancement. These results provided insight regarding the functionality of the different structural components of the photocatalytic architecture in the photocatalytic NOx oxidative storage process. The influence of each structural component in this catalytic architecture was studied. Control experiments were conducted with the dispersant water and the capping agent thioglycolic acid. The results revealed that NO conversion and selectivity can be enhanced by the adsorbed water on titania surface. By adding thioglycolic acid on titania, the NO conversion is suppressed but the selectivity of the system increased. Finally, by replacing titania with a photocatalytically inactive material alumina, it was shown that only in the presence of CdTe quantum dots, there can be NO oxidation/conversion. In overall, utilizing CdTe quantum dots are advantageous for exploiting more of the solar irradiation; however, they suffer from low stability and short catalytic life time.