Yukun Qin

Influence of a reagents addition strategy on the Fenton oxidation of rhodamine B: control of the competitive reaction of ·OH

The Fenton system (Fe2+/H2O2) generates ·OH with a high oxidation potential. However, as reactants themselves, H2O2 and Fe2+ can act as ·OH initiators as well as ·OH scavengers, leading to the need for a high dosage of reactants and increased costs. As a mixing-sensitive reaction, the ·OH-related reaction kinetics (·OH with Fe2+, H2O2, and RhB) was determined from the reaction rates (which were a constant in this work) and stoichiometry, in which the latter could be regulated by an addition strategy of Fenton reagents. This suggests that ·OH competitive reactions could be controlled by applying a macrolevel addition strategy. Herein, the effects of different addition approaches of Fe2+ and H2O2 on ·OH competitive reactions were quantitatively and systematically studied by analyzing the removal of the model pollutant RhB. We found that without stirring, and compared with a one-time addition, once H2O2 or Fe2+ was added in a step-wise pattern (e.g., one drop by one drop, 2 times, or 4 times), a high concentration of H2O2 or Fe2+ existed in a localized place for a longer period, resulting in a lower proportion of ·OH reacting with RhB, which we ascribed to an enhanced reaction between Fe2+, H2O2, and ·OH. However, when H2O2 and Fe2+ were added from two close points without stirring, a larger proportion of ·OH was scavenged by H2O2 and Fe2+; while under stirring, even a one-time addition of H2O2 or Fe2+ could cause severe scavenging of ·OH. The results also revealed a linear relationship between the RhB removal percentage and wavelength blue-shifts. This study showed that microlevel ·OH competitive reactions could be controlled by applying a macrolevel addition strategy of Fenton reagents without the addition of external chemicals. The results suggest this methodology can also offer an approach to lower ·OH invalid consumption by regulating the addition strategy in bigger reactors.

Highlighting the role of nitrogen doping in enhancing CO2 uptake onto carbon surfaces: a combined experimental and computational analysis

N-doped carbons with a gradient N content and consistent pore structure were prepared to independently determine the N doping effect on CO2 adsorption. Density functional theory calculations combined with noncovalent interaction analysis further highlight the importance of dispersion and electrostatic interactions for explaining the CO2 adsorption mechanism on N-doped carbon surfaces.

In situ DRIFTS study of the NO + CO reaction on Fe–Co binary metal oxides over activated semi-coke supports

Activated semi-coke loaded with Fe and Co species by a hydrothermal method exhibited excellent CO-deNOx performance. In this study, the reaction mechanism and the evolution of surface-adsorbed species were investigated by CO-TPR, NO-TPO, and in situ DRIFTS. The results demonstrated that in the temperature range of 100–350 °C, the adsorbed CO coordinated to Fe species, inducing an electron migration that influenced the valence state of Fe. Furthermore, the Fe3+ species were found to be the active sites for the transformation of adsorbed CO, whereas the Co3+ species provided the sites for NO evolution. In the catalytic reaction, the Fe–Co interaction could also promote the transformation of adsorbed NO and CO. The DRIFTS spectra revealed that at relatively low temperatures, the transformation of NO species occurred in the following order: NO → NO2− → NO–NO3− → N2O; at higher temperatures, the NO species evolved in the order: NO → NO2− → bidentate NO3− → chelate NO3− + N2. However, the CO transformation process was the same at both low and high temperatures: CO → COO− → CO32− → CO2. NO2− proved to be an important intermediate in the NO + CO reaction.

Effect of char structures caused by varying the amount of FeCl3 on the pore development during activation

A series of Fe-loaded coal chars is obtained by varying the load amount of FeCl3 additives (0, 6, 15 and 30 wt%). The effect of FeCl3 on the char structure during pyrolysis is presented; furthermore, the chars with different typical structures are activated under different burn-offs to study the pore development during activation. The results show that the mesopore size distribution is related to the amount of FeCl3. A small amount of FeCl3 additive (6 and 15 wt%) can promote depolymerization of the aromatic structure and formation of well-developed spatial crosslinks, and a greater amount of FeCl3 additive (30 wt%) can accelerate the graphitization tendency. The pore formation of 0Fe-900 without initial mesopores follows a hierarchical development from the surface to the core. The chars 15Fe-900H, 15Fe-900H and 30Fe-900H with some initial mesopores follows a non-hierarchical development from the external and internal particles simultaneously; however, the difference in microstructure can affect the penetration of the activated agent into the particle, resulting in different burn-offs and external carbon losses when the hierarchical porous structure has been produced.

Green electrochemical modification of RVC foam electrode and improved H2O2 electrogeneration by applying pulsed current for pollutant removal

AbstractThe performance of cathode on H2O2 electrogeneration is a critical factor that limits the practical application of electro-Fenton (EF) process. Herein, we report a simple but effective electrochemical modification of reticulated vitreous carbon foam (RVC foam) electrode for enhanced H2O2 electrogeneration. Cyclic voltammetry, chronoamperometry, and X-ray photoelectron spectrum were used to characterize the modified electrode. Oxygen-containing groups (72.5–184.0xa0μmol/g) were introduced to RVC foam surface, thus resulting in a 59.8–258.2% higher H2O2 yield. The modified electrodes showed much higher electrocatalytic activity toward O2 reduction and good stability. Moreover, aimed at weakening the extent of electroreduction of H2O2 in porous RVC foam, the strategy of pulsed current was proposed. H2O2 concentration was 582.3 and 114.0% higher than the unmodified and modified electrodes, respectively. To test the feasibility of modification, as well as pulsed current, EF process was operated for removal of Reactive Blue 19 (RB19). The fluorescence intensity of hydroxybenzoic acid in EF with modified electrode is 3.2 times higher than EF with unmodified electrode, illustrating more hydroxyl radicals were generated. The removal efficiency of RB 19 in EF with unmodified electrode, modified electrode, and unmodified electrode assisted by pulsed current was 53.9, 68.9, and 81.1%, respectively, demonstrating that the green modification approach, as well as pulsed current, is applicable in EF system for pollutant removal.n Graphical abstractᅟ

Development of highly effective CaO@Al2O3 with hierarchical architecture CO2 sorbents via a scalable limited-space chemical vapor deposition technique

High-temperature sorption of CO2via calcium looping is a promising technology for the implementation of carbon capture and storage (CCS). However, the major drawback of this technology is the rapid deactivation of CaO sorbents due to sintering. Here, a facile and cost-effective limited-space metal organic chemical vapor deposition approach is proposed to develop CaO-based sorbents exhibiting a very high and cyclically stable CO2 uptake. The TEM results show that Al2O3 nanoparticles (4–8 nm) are uniformly coated onto CaO crystalline grains, thus effectively inhibiting the sintering of sorbents. After 20 severe cycles, the synthetic sorbent, stabilized by 10 mol% Al2O3, exceeded the CO2 uptake of the benchmark CaO by more than 300%. Furthermore, the influence of Ca-based precursors on the synthetic sorbents cyclic CO2 uptake was established. The result shows that the sorbents synthesized from different Ca-based precursors all demonstrate high cycling stability, which means that low-cost and high-performance sorbents can be synthesized through selecting a low-cost Ca precursor, such as CaCO3.

Effects of oxygen functional groups and FeCl3 on the evolution of physico-chemical structure in activated carbon obtained from Jixi bituminous coal

It is crucial to increase the values of SBET/burn-off ratio to achieve activated carbon (AC) with a higher SO2 adsorption capacity at a low cost from flue gas. In this study, at first, Jixi bituminous coal was used as a raw material to prepare a series of pre-treated samples by oxidation treatment and adding different amounts of the FeCl3 catalyst. Then, the AC samples were prepared by pyrolysis under a N2 atmosphere and physical activation with CO2. Finally, the change in the physico-chemical structure of different samples was determined to study the effects of oxygen functional groups and FeCl3. The results show that the rapid growth of mesopores is mainly influenced by the evolution of oxygen functional groups, whereas the micropores are mainly influenced by the FeCl3 catalyst during pyrolysis. These effects can also further improve the size and the carbon type of the aromatic structure from a different perspective to promote the disordered microstructure of treated chars (1FeJXO15-800H, 3FeJXO15-800H and 6FeJXO15-800H) as compared to the ordered microstructure and less pores of the un-pretreated char (JX-800). Then, the active sites can no longer be consumed preferentially in the presence of the catalyst; this results in the continuous disordered conversion of the microstructure as compared to the ordered conversion of JX-800 char during activation. On the one hand, the developed initial pores of 1FeJXO15-800H, 3FeJXO15-800H, and 6FeJXO15-800H chars promote the favorable diffusion of activated gas, following the non-hierarchical development. On the other hand, the presence of Fe-based catalysts facilitates the etching of carbon structure and the rapid and continuous development of the micropores, hindering the severe carbon losses on the particle surface. Finally, the 3FeJXO15-800H char with a high value of SBET (1274.64 m2 g−1) at a low burn-off value (22.5%) has the highest SBET/burn-off ratio value of 56.65 m2 g−1/%, whereas the JX-800 char with a low value of SBET (564.19 m2 g−1) at a burn-off value of 58.2% has the lowest SBET/burn-off ratio value of 9.69 m2 g−1/%. Therefore, the presence of oxygen functional groups and FeCl3 has obviously changed the evolution of the physico-chemical structure in activated carbon to effectively enhance the values of SBET/burn-off.

“Floating” cathode for efficient H2O2 electrogeneration applied to degradation of ibuprofen as a model pollutant

The performance of the Electro-Fenton (EF) process for contaminant degradation depends on the rate of H2O2 production at the cathode via 2-electron dissolved O2 reduction. However, the low solubility of O2 (≈1×10-3 mol dm-3) limits H2O2 production. Herein, a novel and practical strategy that enables the synergistic utilization of O2 from the bulk electrolyte and ambient air for efficient H2O2 production is proposed. Compared with a conventional submerged cathode, the H2O2 concentration obtained using the floating cathode is 4.3 and 1.5 times higher using porous graphite felt (GF) and reticulated vitreous carbon (RVC) foam electrodes, respectively. This surprising enhancement results from the formation of a three-phase interface inside the porous cathode, where the O2 from ambient air is also utilized for H2O2 production. The contribution of O2 from ambient air varies depending on the cathode material and is calculated to be 76.7% for the GF cathode and 35.6% for the RVC foam cathode. The effects of pH, current, and mixing on H2O2 production are evaluated. Finally, the EF process enhanced by the floating cathode degraded 78.3% of the anti-inflammatory drug ibuprofen after 120 min compared to only 25.4% using a conventional submerged electrode, without any increase in the cost.

Investigation of SO2 tolerance of Ce-modified activated semi-coke based catalysts for the NO + CO reaction

Activated semi-coke was loaded with Fe–Co mixed oxides and doped with an optimized amount of cerium oxides. This prepared catalyst exhibited excellent NO removal (deNO) activity, and also showed outstanding SO2 resistance at 250 °C. To understand the SO2 tolerance mechanism, the catalysts were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, in situ Fourier-transform infrared spectroscopy, H2-temperature-programmed reduction, and SO2-temperature-programmed desorption, as well as CO–deNO activity testing under different conditions. The results indicate that the Ce (molar ratio = 0.1) doped onto the Fe–Co binary oxide catalysts would promote the generation of Ce2(SO4)3. This generation could prevent the active metal oxides from being poisoned by SO2. Furthermore, this kind of sulfate would weaken the interaction between SO2 and NO, so that the adsorbed NO will have a better opportunity to react with CO.

Trace Na2CO3 addition to limestone inducing high-capacity SO2 capture

Although the literature has reported enhanced indirect sulfation of limestone by adding Na2CO3, the amount of Na2CO3 additive required to achieve high CaO conversion is typically high (∼4.0 mol %), which commonly results in adverse effects in fluidized-bed combustion boiler systems and increased cost of sorbents. In this work, we demonstrate for the first time that trace Na2CO3 (0.1 mol %) can significantly enhance the sulfate conversion of limestone. This enhanced sulfation is attributed to the increased surface area and optimized pore size distribution. The trace Na2CO3 additive splits the pores of the original sorbents peaking at ∼70 nm into pores peaking at ∼4 nm and ∼140 nm due to the slight promotion of sintering. This well-developed pore structure results in a relatively high reactivity for sulfation. Thus, the Na2CO3 additive influences the sorbent reactivity in two ways: (1) at less than 0.5 mol %, tuning its pore structure; (2) at more than 0.5 mol %, promoting the product layer diffusion. We also find that trace amount of other metal salts, such as CaCl2 and NaCl, clearly enhance the sulfation of limestone. The strategy of enhancing limestone sulfation by the addition of trace amount of metal salts offers evident engineering and economic advantage.