Researchers Develop Novel Photocatalyst to Remove NO with High Selectivity--The Xinjiang Technical Institute of Physics & Chemistry.CAS

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Researchers Develop Novel Photocatalyst to Remove NO with High Selectivity

Editor: | Jun 07,2017

In recent years, the emission of NO_x is growing and the emitted NO_x may lead to photochemical smog, acid rain, haze, etc. NO_x mainly exists in the form of NO under high temperature conditions which accounts for about 95% of the initial released NO_x. Generally, chemical removal of NO is mainly achieved through reduction or oxidation by catalysis. Oxidation is less desirable as it produces NO₂and NO₃^？.

Conventional approaches such as selective catalytic reduction, three-way catalysis, and wet scrubbing are not economically feasible to treat air pollutants in urban environments. Therefore, it is critical to develop a strategy to remove NO by selective reduction at very low concentrations.

A research group led by Prof. WANG Chuanyi at Xinjiang Technical Institute of Physics & Chemistry（XTIPC）of the Chinese Academy of Sciences developed a plasmonic Ag-TiO_{2 ？ x}nanocomposite for the photocatalytic removal of NO with high selectivity under visible light. The study was published in Applied Catalysis B: Environmental.

Researchers used the commercial P25 (a mixture of anatase and rutile TiO₂) as the raw materials to synthesize the visible-light-driven plasmonic photocatalyst Ag-TiO_{2 ？ x} composite. The Ag loading amount was optimized at 2.5% (in mole ratio) based on former evaluation of the loading amount effects.

Results of electron paramagnanetic resonance (EPR) and Raman spectra prove that the post-annealing treatment of TiO₂ (under oxygen-depleted condition) leads to oxygen loss and the formation of oxygen vacancies (V_O).

High resolution transmission electron microscopy (HRTEM) results indicate that close Schottky contact was formed at Ag/TiO_{2 – x} interface after the post-annealing treatment, which favors the photogenerated electrons transfer and restrains the carriers recombination.

Besides, researchers found the photoactivity of Ag-TiO_{2 ？ x} composite was approximately twice higher than that of the commercial P25, and Ag-TiO_{2 ？ x} could significantly inhibit the production of NO₂.

Based on gas chromatography and Fourier transform infrared spectroscopy (FTIR) measurement, researchers deduced that the photo-oxidation of NO and selective photo-reduction of NO to N₂occur simultaneously during the process of NO removal by Ag-TiO_{2 ？ x}. The oxidation of NO was due to the synergic effect between superoxide radicals (^？O₂^？) and photogenerated holes (h⁺); while the selective photo-reduction was resulted from introduced V_O in TiO_{2 ？ x}.

This work provides a new insight into the different effects of photogenerated reactive species on NO photo-oxidation and V_O on NO photo-reduction, and can open a promising avenue to developing novel materials with effective light harvesting property and reactivity for photocatalytic removal of NO.

Figure: A plausible mechanism for visible light induced photocatalytic NO removal onAg-TiO_{2 ？ x} (Image by XTIPC)

Contact:

Prof. WANG Chuanyi

E-mail: cywang@ms.xjb.ac.cn

Xinjiang Technical Institute of Physics & Chemistry, CAS

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