CdTe Quantum Dot-Functionalized P25 Titania Composite with Enhanced Photocatalytic NO₂ Storage Selectivity under UV and Vis Irradiation

Abstract

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 NO x oxidation and storage during NO(g) + O 2 (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 NO x storage in solid state (25% in UV-A and 35% in vis). Therefore, P25 could efficiently photooxidize NO(g) + O 2 (g) into NO 2 ; however, it failed to store photogenerated NO 2 and released toxic NO 2 (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 NO x abatement effect. Control experiments suggested that photocatalytic active sites responsible for the NO(g) + O 2 (g) photooxidation and formation of NO 2 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 NO 2 to the adsorbed NO x species, significantly boosting the selectivity toward solid-state NO x 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.

Cr3+ substituted Zn-Al layered double hydroxides as UV–Vis light photocatalysts for NO gas removal from the urban environment

“…The NO 2 gas appears as an intermediate during the NO photochemical oxidation (Balbuena et al, 2015) which must be avoided because it is much more dangerous than NO (Lewis and Sax, 2012). Taking into account the above values, the selectivity of the De-NOx process (S) is estimated at around 90% for all the photocata lysts here studied, an outstanding value in line with those reported for the last advanced De-NOx photocatalysts recently reported (Balci Leinen et al, 2019;Folli et al, 2011;Pastor et al, 2019;Shang et al, 2019;Tan et al, 2017).…”

Insight into the role of copper in the promoted photocatalytic removal of NO using Zn2-xCuxCr-CO3 layered double hydroxide

“…Therefore, the DeNOx selectivity exhibited by these LDHs is outstanding with values > 97 %. It is worth mentioning that such high selectivity values are difficult to attain only being reported for some DeNOx advanced photocatalysts (Balbuena et al, 2018b;Leinen et al, 2019;Pastor et al, 2020Pastor et al, , 2019Shang et al, 2019;Tan et al, 2017). Finally, the whole removal of nitrogen gases from the air is considered following the NOx concentration profile (Fig.…”

Core‐crown Quantum Nanoplatelets with Favorable Type‐II Heterojunctions Boost Charge Separation and Photocatalytic NO Oxidation on TiO2

“…[59] Figure 3b presents the corresponding C1s spectrum of fresh NPL without TiO 2 , where the shoulder visible at 288.1 eV can be ascribed to CÀ O and C=O functionalities of the oleic acid capping and the larger signal at 284.8 eV can be attributed to CÀ C linkages of oleic acid as well as the surface (adventitious) carbon species. Note that binding energy (B. E.) positions of the spectra in Figures 3a-3e for the fresh NPL without TiO 2 were calibrated using the adventitious of carbon signal at 284.8 eV while the spectra in Figures 3f-3g were calibrated using the Ti 4 + features of P25 (TiO 2 ) (i. e. Ti2p 3/2 and Ti2p 1/2 features at 458.5 eV and 464.1 eV, respectively [14,60] ). Figures S1 and S2 show that in the case of NPL/P25 composite system, O1s and C1s signal intensities diminish after PHONOS reaction under UV-A or VIS illumination due to decomposition of the oleic acid capping functionalities and possibly photo-desorption of CO x / H x C y O z species.…”

“…In this regard, photocatalytic oxidative NO x storage (PHONOS) [12][13][14][15][16][17][18] presents an appealing alternative as it can store airborne NO x in the solid state under ambient conditions after the point of NO x discharge to the atmosphere. This approach requires the presence of only sunlight, water and oxygen (all of which are abundantly present in the atmosphere) and a photocatalytically active material.…”

“…[56] Our hypothesis here is that in the proposed CdSe/ CdSeTe/TiO 2 composite system, photogenerated electrons from the CdSe/CdSeTe NPL can be injected to the conduction band of TiO 2 , whereas the corresponding holes in the valence band of TiO 2 can be transferred to the valence band of CdSe/CdSeTe NPL. [14,57,58] Such functionalization of TiO 2 with NPL is also expected to enhance the photon absorption in the VIS region of the solar spectrum. Hence, an improvement in the photocatalytic DeNO x performance of TiO 2 is anticipated upon incorporation of NPL.…”