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Influence of ultraviolet wavelengths on kinetics and selectivity for N-gases during TiO2 photocatalytic reduction of nitrate
Applied Catalysis B: Environment and Energy ( IF 22.1 ) Pub Date : 2017-08-30 , DOI: 10.1016/j.apcatb.2017.08.078
Heather O’Neal Tugaoen , Pierre Herckes , Kiril Hristovski , Paul Westerhoff

For drinking water applications, photocatalytic reduction processes beneficially transform aqueous nitrate to innocuous nitrogen gases (N-gases) but can produce nitrite and ammonia as undesirable aqueous by-products. We hypothesize that by-product selectivity is a function of light source and photon fluence dose, such that discrete wavelengths can increase yield of desirable N-gases. Experiments performed under different wavelength irradiation (ultraviolet- [UV] A, B, C) reduced nitrate in water to differing extents based on pH over the range of 1–8 or the presence of soluble organic electron donors. At an equivalent photon fluence dose, the most rapid nitrate loss in acidic solutions occurred using a combination of three UV-light emitting diodes (285 nm, 300 nm, 365 nm) closely followed by a polychromatic medium pressure UV lamp. A polychromatic xenon light source was least effective in reducing nitrate. Nitrite is an important intermediate during photocatalytic reduction of nitrate. Nitrite absorbs 330–380 nm light with high quantum efficiency. Thus, polychromatic or monochromatic light sources with strong UV-A emission more rapidly convert nitrite to by-products than UV-C monochromatic light sources. Nitrous acid (HONO) has a higher molar absorptivity (ε) and quantum efficiency than nitrite ion (pKa = 3.39) around 350–370 nm. Selectivity towards N-gases is bifurcated at the nitrite intermediate and is strongly influenced by direct photolysis instead of photocatalytic reduction. Thus, the selectivity of by-products can be controlled by delivering light in the 350–370 nm wavelength range, where it enables photocatalytic processes to rapidly initiate NO3 reduction and delivers photons for direct photolysis of HONO.



中文翻译:

紫外线波长对TiO 2光催化还原硝酸盐过程中N气动力学和选择性的影响

对于饮用水应用,光催化还原过程可将硝酸水溶液有益地转化为无害的氮气(N气),但会产生亚硝酸盐和氨,这是不希望的水溶液副产物。我们假设副产物的选择性是光源和光子注量剂量的函数,因此离散的波长可以增加所需N气体的产率。在1–8范围内的pH值或存在可溶性有机电子给体的情况下,在不同波长的辐射(紫外线[UV] A,B,C)下进行的实验会将水中的硝酸盐还原到不同程度。在等效的光子注量剂量下,在酸性溶液中硝酸盐损失最迅速的是使用三个紫外发光二极管(285 nm,300 nm,365 nm)紧接着是多色中压UV灯的组合。多色氙气光源在还原硝酸盐方面效果最低。亚硝酸盐是光催化还原硝酸盐过程中的重要中间体。亚硝酸盐以高量子效率吸收330-380 nm的光。因此,具有强UV-A发射的多色或单色光源比UV-C单色光源更快速地将亚硝酸盐转化为副产物。亚硝酸(HONO)的摩尔吸收率(ε)和量子效率比亚硝酸根离子(pK)高a  = 3.39)大约在350-370 nm之间。在亚硝酸盐中间体上,对N气的选择性分叉,并且受直接光解而不是光催化还原的强烈影响。因此,副产物的选择性可以通过在350-370纳米的波长范围内,在那里它使光催化过程来迅速地递送光来控制发起NO 3 -还原并提供对光子的HONO直接光解。

更新日期:2017-08-30
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