- Efficient photodegradation of 2-chloro-4-nitrophenol over Fe-doped BiOCl nanosheets with oxygen vacancy
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Photodegradation of organic pollutants emerged as a promising route for environmental remediation. Due to abundant localized electrons, oxygen vacancies (OVs) over BiOCl could promote the adsorption of organic pollutants and activation of oxygen to produce more reactive oxygen species (ROS) during the photocatalytic reaction. Considering the high oxidation potential (E0 = 1.8-2.7 V vs. NHE) of the hydroxyl radicals (OH), we introduced Fe dopant in the OV-associated BiOCl system (Fe-BOC) to build Fenton-like catalysts, which converted the H2O2 generated in the photoreaction to produce more OH for the photodegradation of 2-chloro-4-nitrophenol. Experimental results revealed that the concentration of H2O2 in the undoped BiOCl (BOC) photoreaction system was higher, while much more OH was detected in Fe-BOC, indicating that the Fenton-like reaction occurred for the conversion of H2O2 into OH over Fe-BOC. In addition, the better charge separation of Fe-BOC could motivate more surface e- for O2 activation into O2-. Thus, the more reactive oxygen species (OH and O2-) produced over Fe-BOC resulted in 3.1 times higher photocatalytic activity in contrast to that of BOC.
- Liu, Xiangming,Wu, Haoyuan,Xu, Hua,Yang, Xinmin,Ye, Jinhua
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p. 5119 - 5124
(2021/08/16)
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- Manifesto for the routine use of NMR for the liquid product analysis of aqueous CO2 reduction: From comprehensive chemical shift data to formaldehyde quantification in water
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CO2 reduction research is at a critical turnaround since it has the potential to partially or even substantially fulfil future clean energy needs. CO2-to-CO electrochemical conversion is getting closer from industrial implementation requirements. Efforts are now more and more directed to obtain highly reduced products such as methanol, methane, ethylene, ethanol, etc., most of them being liquids. Gas-phase products (e.g., CO, CH4) are typically detected and quantified by well-defined gas chromatography (GC and GC/MS) protocols. On the other hand, NMR, GC-MS, HPLC have been used for the liquid phase characterization, but no routine technique has yet been established, mainly due to lack of versatility of a single technique. Additionally, except NMR and GC-MS, classical techniques cannot distinguish 13C from 12C products, although it is a mandatory step to assess products origin. Herein, we show the efficiency and applicability of 1H NMR as routine technique for liquid phase products analysis and we address two previous shortcomings. We first established a comprehensive 1H and 13C NMR chemical shifts list for all 12CO2 and 13CO2 reduction products in water ranging from C1 to C3. Then we overcame the difficulty of identifying aqueous formaldehyde intermediate by 1H NMR through an efficient chemical trapping step, along with isotopic signature study. Formaldehyde can be reliably quantified in water with a concentration as low as 50 μM.
- Boutin, Etienne,Chatterjee, Tamal,Robert, Marc
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supporting information
p. 4257 - 4265
(2020/04/17)
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- Etude de la composition de solutions aqueuses d'acide glyoxylique en RMN de 13C
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In order to determine the composition of aqueous solutions of glyoxylic acid, we studied the 13C nmr spectra of variously concentrated solutions (20 to 60 percent).The two well-separated regions (acids and esters on one side, acetals, hemiacetals and hydrates on the other) display not directly related intensities owing to the relaxation times of carbonyl carbons.Nevertheless, by plotting the relative intensity of each line in its own region, we were able to associate signals coming from the same species.Aside from the two prominent lines of monomeric hydrate, we identified two other pairs with intensity increasing with total concentration.Apart from a small line due to glyoxal and some other very small lines, we observed four lines of equal and slightly increasing intensity, three of acetal type and one of acid or ester type.In order to establish the structures of the species present, we determined the chemical shifts of a series of related molecules to be used as models (reported on table 2): first esters, acids, acetals, hemiacetals and hydrates of monomeric strukture, then dimers and trimers of acetaldehyde, ethyl glyoxylate and glyoxal.We were thus able to establish increments and correlations which allowed us to estimate the values of chemical shifts for possible dimers and trimers of glyoxylic acid: it was easy to see that two of the entities present in the solution are dimeric hemiacetals-acids, the erythro and threo isomers (figure 3).The fourth species is necessarily a combination of acid with glyoxal and the inspection of models led us to identify it as dihydroxy-4,5 dioxolan-1,3 carboxylic acid (figure 4).Its concentration was shown to increase with that of glyoxal in glyoxylic acid, and furthermore, some of its derivatives could be isolated.The acetalization and esterification of glyoxylic acid by ethanol in acidic medium, effected with remowal of water, provided a mixture of esters-acetals which was analysed by coupled VPC-mass spectrometry and VPC-chemical ionization (with ammonia).The analysis confirmed the existence of the above monomer and dimers in proportions related to the composition of the aqueous solution; moreover a small amount of a cyclic dimer is observed.No more than 5 percent of higher oligomers was evidenced.As for the combinations between glyoxal and glyoxylic acid, the principal one can be accompanied by many others, of various stoechiometries, when more glyoxal is initially present in the glyoxylic acid solution.Thus it is shown that glyoxylic acid in aqueous solution is mostly in the form of monomeric hydrate (69 to 88 percent)) and dimeric hemiacetals-acids (2,5 to 12 percent).Higher oligomers never exceed 5 percent in concentrated solutions, but glyoxal, if present, easily combines with glyoxylic acid, to form various compounds, the major one accounting for up to 12 percent of the material in some concentrated mixture of glyoxal and glyoxylic acid.
- Chastrette, Francine,Bracoud, Corinne,Chastrette, Maurice,Mattioda, Georges,Christidis, Yani
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