Insight into the Overlooked Photochemical Decomposition of Atmospheric Surface Nitrates Triggered by Visible Light

Abstract

The nitrogen oxides (NOx) formed by photochemical reaction of surface nitrates raise significant concerns. However, little is known about the effect of visible light (>380 nm) on nitrate decomposition and the reaction mechanism. Herein, the decomposition of surface nitrates is investigated under visible light. The results indicate that visible light photocatalysis contributes significantly to nitrate decomposition. Monodentate nitrate (m‐NO3−) can be decomposed into NOx by photogenerated electrons starting from the weakly coordinated N−O bond. Water vapor promotes NOx generation because more stable bidentate nitrate (b‐NO3−) will be converted into m‐NO3− by surface hydroxyl groups through hydrogen bonding interactions. Alternatively, b‐NO3− can be directly decomposed to NO2− by NO attack, but this process is subject to photocatalytic oxidation. This work brings a new focus on the atmospheric NOx sources and provides a more nuanced understanding of nitrates decomposition processes.

Recent Advances in Electrocatalytic Nitrate Reduction to Ammonia: Mechanism Insight and Catalyst Design

“…However, electrocatalysts, electrolytes, and the electrolytic cell can be sources of nitrogen in the ammonia. Therefore, the 15 N isotope labeling experiment using Na 15 NO 3 as the feedstock is commonly used to confirm the source of nitrogen in ammonia. The typical double peaks of 15 NH 4 + and triple peaks of 14 NH 4 + can be seen via the 1 H nuclear magnetic resonance (NMR) spectroscopy (Figure 4a).…”

“…Therefore, the 15 N isotope labeling experiment using Na 15 NO 3 as the feedstock is commonly used to confirm the source of nitrogen in ammonia. The typical double peaks of 15 NH 4 + and triple peaks of 14 NH 4 + can be seen via the 1 H nuclear magnetic resonance (NMR) spectroscopy (Figure 4a). 49 This result shows that the nitrogen in the ammonia comes entirely from nitrates.…”

“…So far, solar and wind power generation technologies are very mature, which can be used as the driving force for nitrate reduction to achieve the efficient utilization of clean energy. Photocatalytic nitrate reduction by direct use of light energy as the driving force and a semiconductor as a photocatalyst has also been reported as an effective method. − However, this method faces many problems, for instance, the additional sacrificial reagents and low utilization rate of light energy. Over the past decade, electrocatalytic nitrate reduction has been widely studied according to incomplete statistical data, as shown in Figure .…”

Effects of SO2 on NH4NO3 Photolysis: The Role of Reducibility and Acidic Products

“…Mineral dust, accounting for 4% of atmospheric particulate matter by mass, , provides important active reaction surfaces for atmospheric heterogeneous reactions. ,, Mineral dust is composed of many metallic oxides, including approximately 10–15% Al 2 O 3 , small fractions of Fe 2 O 3 , MgO, and tiny amounts of TiO 2 . ,, The uptake and oxidation of NOx on the surface of mineral oxides results in the formation of surface nitrate . Nitrate is usually mixed with mineral oxides in the atmosphere. , Therefore, the surface of mineral oxides is an essential and considerable interface for nitrate photolysis. ,, The properties of mineral oxides and the coordination of nitrate with mineral oxides play significant roles in the photochemical reactivity of adsorbed nitrate. ,,, For example, several studies suggest that remarkable NOx production and nitrate consumption takes place on the surface of alumina under irradiation, , while TiO 2 , a kind of semiconductor metal oxide, can provide photogenerated holes and electrons to activate the photolysis of absorbed nitrate, producing more NOx than the nonphotoactive metal oxides. , Besides, the different binding modes of nitrate absorbed on mineral oxides lead to differences in the photolysis rate and the distribution of photolysis products . Wang et al reported that monodentate nitrate (m-NO 3 – ) can be more easily decomposed into NOx than bidentate nitrate (b-NO 3 – ) on the surface of TiO 2 .…”

“…24,30,44 The properties of mineral oxides and the coordination of nitrate with mineral oxides play significant roles in the photochemical reactivity of adsorbed nitrate. 24,29,30,44 For example, several studies suggest that remarkable NOx production and nitrate consumption takes place on the surface of alumina under irradiation, 30,45 while TiO 2 , a kind of semiconductor metal oxide, can provide photogenerated holes and electrons to activate the photolysis of absorbed nitrate, producing more NOx than the nonphotoactive metal oxides. 17,30 Besides, the different binding modes of nitrate absorbed on mineral oxides lead to differences in the photolysis rate and the distribution of photolysis products.…”