Metal-organic frameworks as solid-phase microextraction adsorbents for the determination of triacetone triperoxide by gas chromatography-mass spectrometry.

Triacetone triperoxide (TATP) is a high-power explosive which is often used by criminals. The detection of TATP is of great significance for solving the explosion cases. However, the preconcentration and analysis of trace levels of TATP still pose challenges for analytical researchers. In this study, metal-organic frameworks (MOFs), including IRMOF-8, MOF-5, UIO-66, ZIF-8, and MIL-101(Cr), were immobilized on a stainless steel wire using a physical adhesive method as a solid-phase microextraction (SPME) fiber coating. The prepared fibers with a controllable thickness were used for the extraction of TATP followed by gas chromatography-mass spectrometry (GC-MS) analysis. Under the identical experimental conditions, the IRMOF-8-coated fiber exhibited higher extraction efficiency for TATP than the other fibers. The IRMOF-8-coated fiber was then characterized using scanning electron microscopy and thermogravimetric analysis. The results indicated that the IRMOF-8-coated fiber not only had good thermal and chemical stabilities but also afforded a high TATP extraction efficiency. Under the same extraction conditions, the extraction efficiency of the IRMOF-8-coated fiber was 2-8 times higher than those of commercial fibers. The limit of detection was 13 ng/mL, and linearity was observed in the range of 50-5000 ng/mL with a correlation coefficient greater than 0.998. The intraday repeatability (n = 6), interday repeatability (n = 3), and fiber-to-fiber reproducibility (n = 3), were 4.1 %, 4.8 %, and 8.0 %, respectively. The recoveries of TATP from the simulated tap water and soil samples were 87.32-90.57 % and 88.76-100.93 %, respectively, with relative standard deviations lower than 11.11 % (n = 3). The above method was successfully applied for the detection of TATP transferred from a finger to a paper surface, demonstrating its good application prospects in the analysis of trace TATP.

Preparation of double-yolk egg-like nanoreactor: Enhanced catalytic activity in Fenton-like reaction and insight on confinement effect.

Peroxymonosulfate (PMS)-based Fenton-like reaction is an effective technique for the pollutant degradation, and the Co-based metal organic frameworks displayed the excellent activity for the PMS activation. Nevertheless, how to further improve the catalytic activity, suppress the leaching of toxic cobalt ions, and realize the rapid separation were still challenges for practical application. In this work, a novel solution was proposed: encapsulating Fe3O4 and Prussian blue analogue (PBA) into the polypyrrole (PPy) shell and constructing a "double-yolk egg-like" Fe3O4/PBA@PPy as a nanoreactor. In Fe3O4/PBA@PPy-10, the catalytic performance was remarkably enhanced with the help of confinement effect, and the degradation rate (0.38 L·min·mol-1) was 5.1 times than that of reference Fe3O4/PBA-10 (0.074 L·min·mol-1). In addition, the concentration of leached cobalt ions was reduced to only 0.174 mg/L by the protective function from the PPy shell. Moreover, the nanoreactor could be magnetically separated from the reaction solution due to the encapsulation of Fe3O4 nanospheres, and 84.5% of activity still preserved after the 4th cycle. The main active species involved in Fe3O4/PBA@PPy-10 system was 1O2, while that in reference Fe3O4/PBA-10 system was OH. Electron spin resonance analysis and radical trapping experiment revealed that the different catalytic mechanisms were attributed to the confinement effect inside the hollow cavity. This work not only presents a feasible way to prepare rarely-reported double-yolk egg-like nanoreactor, but also provides a new insight to solve the bottlenecks in Fenton-like reaction.

Partially oxidized MXenes-derived C-TiO2/Ti3C2 coupled with Fe-C3N4 as a ternary Z-scheme heterojunction: Enhanced photothermal and photo-Fenton performance.

Photo-Fenton reaction combining the photocatalytic reaction and Fenton reaction showed excellent degradation performance. However, it highly demanded the catalysts to display outstanding activity in these two reactions. Herein, Fe-doped carbon nitride/MXenes-derived C-TiO2/Ti3C2 (Fe-C3N4/Ti3C2/C-TiO2) was prepared via two steps: Fe-C3N4 and Ti3C2 were assembled via face-to-face attachment, following by in-situ partial oxidation of Ti3C2 to C-TiO2. DFT predicted a Z-scheme charge transfer routine via metallic Ti3C2 as bridge, which was verified by EPR and radical trapping experiments. Additionally, PDOS calculation revealed the charge density around the doped-Fe atoms was remarkably increased, leading to better H2O2 activation, which was experimentally confirmed by high yield of •OH. Moreover, Fe-C3N4/Ti3C2/C-TiO2 possessed the high photothermal effect to accelerate the surface reaction. By taking advantage of these merits, the degradation rate of Fe-C3N4/Ti3C2/C-TiO2 was at least 4.2 times higher than the reference catalysts. Our work provided an insight toward the g-C3N4/TiO2-based photo-Fenton catalysts with high performance.

A simple and green method to prepare non-typical yolk/shell nanoreactor with dual-shells and multiple-cores: Enhanced catalytic activity and stability in Fenton-like reaction.

Nowadays, non-typical yolk/shell structure has drawn much attentions due to the better catalytic performance than traditional counterparts (one yolk/one shell). In this study, ZIF-67 @Co2SiO4/SiO2 yolk/shell structure was prepared in one-step at room temperature, in which ZIF-67 was served as the hard-template, H2O was served as etchant and tetraethyl orthosilicat was served as the raw material for Co2SiO4/SiO2. After calcination, the non-typical CoxOy @Co2SiO4/SiO2 yolk/shell nanoreactor with Co2SiO4/SiO2 dual-shells and CoxOy multiple-cores was obtained. On the one hand, more active sites were exposed on multiple-cores surface and better protection were provided by dual-shells. On the other hand, the sheet-like Co2SiO4 inner shell not only extended the travel path and retention time of pollutants trapped in cavity, but also separated the multiple-cores from aggregation. Therefore, the nanoreactor displayed the outstanding catalytic activity and recyclability in Fenton-like reaction. Metronidazole (20 mg/L) was completely degraded after 30 min, rhodamine B (50 mg/L) and methyl orange (20 mg/L) were removed even within 5.0 min. Catalytic mechanism indicated that 1O2 greatly contributed to the pollutant degradation. This paper presented a simple, versatile, green and energy-saving method for non-typical yolk/shell nanoreactor, and it could inspire to prepare other catalysts with high activity and stability for environmental remediation.

Enhancing the heterojunction component-interaction by in-situ hydrothermal growth toward photocatalytic hydrogen evolution.

The in-situ synthesis method to construct a heterostructure with a tight binding interface can promote the separation and transfer of charges, which is particularly crucial for improving photocatalytic efficiency. Herein, we have successfully synthesized a high-efficiency photoreduction catalyst by in situ growing a layer of flaky nickel chromium layered double hydroxides nanosheets (LDH) on carbon nitride hexagonal tube (CN) in hydrothermal. The tube-flakes like CN-LDH heterostructures have enhanced hydrogen evolution efficiency (14.5 mmol h-1 g-1), which is about 4.7 times that of pure CN (2.7 mmol h-1 g-1) and much higher than that of LDH (0.06 mmol h-1 g-1). We attribute this performance improvement mainly to the close-knit heterostructure formed between LDH and CN. This tight combination strengthens the diffusion of self-charge between the two semiconductors to form a strong built-in electric field and band bending. Under the action of the built-in electric field (BIEF), the photogenerated charge can be efficiently separated and oriented fast transfer, thereby greatly improving the photocatalytic efficiency. This work constructs a tightly connected heterostructure photocatalyst through hydrothermal method, and uses the catalyst to convert high-efficiency solar energy into renewable energy.

SO2 enhanced desorption from basic aluminum sulfate desulphurization-regeneration solution by falling-film evaporation.

To find the optimal structure of the converging-diverging tube and develop a high-efficiency falling-film evaporator, the heat and mass transfer performances of falling-film evaporation with converging-diverging tubes of different dimensions were studied. The optimal converging-diverging tube was used in falling-film evaporation desorption of the basic aluminum sulfate desulphurization-regeneration solution, and different influential factors on the desorption effect were analyzed. It was found that converging-diverging tubes with large falling-film flow rate performed well in the heat and mass transfer of falling-film evaporation, and their rib height largely affected the heat and mass transfer performances. At the same rib height and rib pitch, the longer the converging segment of the converging-diverging tube was, the better the heat transfer performance was. The evaporation heat transfer coefficient and evaporation mass transfer rate in the optimal converging-diverging tube were 1.6 and 1.38 times larger than the smooth tube, respectively. The optimal converging-diverging tube was used in falling-film evaporation desorption of basic aluminum sulfate desulphurization-regeneration solution, at a perimeter flow rate of 0.114-0.222 kg m-1 s-1, the desorption efficiency inside the tube was up to 94.2%, which was 10.3-10.5% higher than that of the smooth tube. At the inlet sulfur concentration of 0.02-0.1 kmol m-3, the desorption efficiency was up to 94.1%, which was 12.0-16.3% larger than that of the smooth tube. At the heating temperature of 371.15-386.15 K, the desorption efficiency was up to 93.4%, which was 6.7-11.5% larger than that of the smooth tube. Smaller falling-film flow rate, higher sulfur concentration, or higher heating temperature was more constructive to SO2 desorption. Correlations were obtained to predict the mass transfer coefficient and SO2 desorption efficiency. This study develops a new type of falling-film evaporator for SO2 desorption from basic aluminum sulfate desulphurization-regeneration solution and provides a basis for process design and industrial application.

Simultaneous absorption of NO and SO2 by combined urea and FeIIEDTA reaction systems.

SO2 and NO emitted from coal-fired power plants have caused serious air pollution in China. In this work, a novel mixed absorbent, FeIIEDTA/urea, was employed for simultaneous removal of SO2 and NO in a packed tower, with a corresponding optimal ratio of 0.014 mol L-1 : 5%. The effects of various factors, such as mixed absorbent constitutions, reaction temperature, pH, O2 concentration, as well as concentrations of SO2 and NO, on simultaneous removal were investigated. The desulfurization efficiency was 95-99% in all tests, whereas denitrification was affected significantly by various conditions. NO removal efficiency decreased increasing oxygen concentration as well as increasing NO concentration. With an increase in temperature, pH, or SO2 concentration, NO removal efficiency increased first and then decreased. Under optimal conditions, SO2 removal efficiency was 100% and NO removal efficiency could exceed 91% within 80 min. The reaction mechanism was speculated according to relevant literature.

Nitric oxide removal by combined urea and FeIIEDTA reaction systems.

(NH2)2CO as well as FeIIEDTA is an absorbent for simultaneous desulfurization and denitrification. However, they have their own drawbacks, like the oxidation of FeIIEDTA and the low solubility of NO in urea solution. To overcome these defects, A mixed absorbent containing both (NH2)2CO and FeIIEDTA was employed. The effects of various operating parameters (urea and FeIIEDTA concentration, temperature, inlet oxygen concentration, pH value) on NO removal were examined in the packed tower. The results indicated that the NO removal efficiency increased with the decrease of oxygen concentration as well as the increase of FeIIEDTA concentration. The NO removal efficiency had little change with a range of 25-45 °C, and sharply decreased at the temperature of above 55 °C. The NO removal efficiency initially increases up to the maximum value and then decreases with the increase of pH value as well as the raise of urea concentration. In addition, the synergistic mechanism of (NH2)2CO and FeIIEDTA on NO removal was investigated. Results showed that urea could react with FeIIEDTA-NO to produce FeIIEDTA, N2, and CO2, and hinder oxidation of FeIIEDTA. Finally, to evaluate the effect of SO32- on NO removal, a mixed absorbent containing FeIIEDTA, urea, and Na2SO3 was employed to absorb NO. The mixed absorbent could maintain more than 78% for 80 min at 25 °C, pH = 7.0, (NH2)2CO concentration of 5 wt%, FeIIEDTA concentration of 0.02 M, O2 concentration of 7% (v/v), and Na2SO3 concentration of 0.2 M.

Simultaneous removing SO2 and NO by a new system containing cobalt complex.

Absorption and catalytic oxidation of nitric oxide can be achieved by using cobalt(III) ethylenediamine (Co(en)2(3+)). When simultaneous absorbing SO2 and NO, the precipitation of Co2(SO3)3 will be yielded and the NO removal will be decreased. A new catalyst system using Co(en)3(3+) coupled with urea has been developed to simultaneous remove NO and SO2 in the flue gas. NO is absorbed and catalytically oxidized to nitrite and nitrate by Co(en)3(3+). The dissolved oxygen in scrubbing solution from the feed stream acts as oxidant. Urea restrains the precipitation of Co2(SO3)3 by oxidizing SO3(2-) to SO4(-) as CoSO4 is more soluble in water. The experimental results proved that nearly all SO3(2-) can be oxidized to SO4(-2) and the high NO and SO2 removal could be obtained with the new system. The NO removal is influenced by gas flow rate, the concentration of Co(en)3(3+) and urea in the absorption solution, the temperature of the scrubbing solution and the content of oxygen in the flue gas. The low gas flow rate is favorable to increase the NO removal. The experiments proved that the NO removal could be maintained at more than 95% by the system of 0.02 mol/L Co(en)3(3+) and 1% urea at 50 degrees C with 10% O2 in the flue gas.