Latest ArticlesIt is generally recognized that the formation and accumulation of iron oxides on the surface of zero-valent iron (Fe0) resulting in significant decrease of contaminant degradation rates during the long-term reactions. However, in this study, we found that the removal efficiencies of p-nitrophenol (PNP) by micro zero-valent iron (mFe0) could maintain at the satisfactory level in the process of continuous reactions (20 cycles). The removal rate constant (0.1779 min-1) of the 5th cycle was 6.74 times higher than that of the 1st reaction (0.0264 min-1), even the 20th cycle (0.0371 min-1) was higher than that of the 1st reaction. Interestingly, almost no dissolved iron was detected in the solution, and the total iron concentrations decreased dramatically with the process of continuous reactions. The results of scanning electron microscope and energy dispersive spectrometry (SEM-EDS) and X-ray diffraction (XRD) revealed that the structure and composition of corrosion products change from amorphous to highly crystal with the increase of the number of cycles. The corrosion products were mainly magnetite (Fe3O4) and a small part of maghemite (γ-Fe2O3), which were in the form of microspheres on the surface of mFe0. The formation of surface oxidation shell hindered the release of Fe2+. X-ray photoelectron spectroscopy (XPS) results illustrated that partial Fe3O4 could be converted into γ-Fe2O3. Electrochemical analysis proved that the electron transfer rate of mFe0 increased with the formation of the oxides shell. However, the consumption of iron core and thicker oxide film weakened the electron transfer rate. Besides, the quenching experiments indicated that the reaction activity of mFe0 could be enhanced with the addition of scavengers. This study deepened the understanding of the structural transformation and radical production of mFe0 in continuous reactions.
In this study, Fe2O3/Mn2O3 composite was synthesized by a facile two-step technique, and several methods were carried out to characterize it. Then, the decomposition experiments of tartrazine (TTZ), a kind of refractory organic pollutant, were conducted under various environmental condition to detect the catalyst performance, such as reaction system, the dosage of catalyst, peroxymonosulfate (PMS) concentration, initial pH, different natural water substances. The results exhibited that Fe2O3/Mn2O3 composite with the mole rate 2:3 had the best PMS activation performance and the removal efficiency was 97.3% within 30 min. Besides, the optimum degradation conditions of TTZ were also discussed, that is catalyst dosage (0.6 g/L), PMS concentration (0.8 g/L) and the initial pH 11. In addition, proved by the natural water substances adding experiments, HPO42-, HCO3-, NO3- and NOM (nature organic matter) could slow down the experiments progressing, but Cl- could boost it. Then inhibitor experiments indicated both the HO· and SO4·- played a vital role in the experiments. Reusability and ions leaching experiments as well as the used catalyst physical characterization images exhibited the excellent stability and cyclicity of the Fe2O3/Mn2O3 composite. Finally, based on the XPS (X-ray photoelectron spectroscopy) and the experiments results, the possible mechanism of TTZ degradation was proposed. This system might provide a novel thought for the decomposition of refractory organic pollutant and had potential in promotion of actual sewage treatment technology.
Activated persulfate oxidation is an emerging advanced oxidation process for organic pollutant degradation. Own to different molecular structures and oxidation potentials, persulfate (PDS) and peroxymonosulfate (PMS) may show different degradation performances due to various catalytic mechanisms even by the same catalysts. In this study, the nitrogen-doped mesoporous carbon (N-OMC) was applied to activate PDS and PMS for degrading a model organic pollutant phenol to reveal their activation mechanisms. Results show that both PDS and PMS could be efficiently activated by N-OMC. The degradation of phenol fitted well with pseudo-first-order kinetics, whose kinetic constants increased with the increase of pH, PDS/PMS dosage, and N-OMC dosage. Based on quenching experiments and electron spin resonance spin-trapping technique, the N-OMC was found to activate PDS and PMS via non-radical process of electron transfer and singlet oxygen formation, respectively, instead of the commonly observed radical process. This work will be useful to understand the activation processes of PDS and PMS, and benefit for the development of catalysts for pollutant degradation.
One of the core issues in the photocatalytic oxidation of nitric oxide is the effective conversion of NO into the final product (nitrate). More than just improving the visible light photocatalytic performance of BiOCl, we aim to inhibit the generation of toxic by-product NO2 during this process. In this study, we demonstrate that the oxygen vacancies (OVs) modulate its surface photogenerated carrier transfer to inflect the NO conversion pathway by a facile mixed solvent method to induce OVs on the surface of BiOCl. The photocatalytic NO removal efficiency under visible light increased from 5.6% to 36.4%. In addition, the production rate of NO2 is effectively controlled. The effects of OVs on the generation of reactive oxygen species, electronic transfer, optical properties, and photocatalytic NO oxidation are investigated by combining density functional theory (DFT) theoretical calculations, the in situ FTIR spectra and experimental characterization. The OVs on the surface of BiOCl speed the trapping and transfer of localized electrons to activate the O2, producing O2·-, which avoid NO2 formation, resulting in complete oxidation of NO (NO + O2·- → NO3-). These findings can serve as the basis for controlling and blocking the generation of highly toxic intermediates through regulating the reactive species during the NO oxidation. It also can help us to understand the role of OV on the BiOCl surface and application of photocatalytic technology for safe air purification.
Antibiotic resistance genes (ARGs) in aquatic environments, which seriously endanger human health and ecological safety, have become a worldwide concern due to their easy diffusion and proliferation. Wastewater treatment plants (WWTPs), which receive resistant bacteria and ARGs from a wide variety of sources (i.e., livestock farms, hospitals, antibiotic manufactures, and households), are regarded as important emission sources of aquatic ARGs. This review presents a quantitative profile of the majority sources of ARGs in the influent of WWTPs and discusses the potential factors that affect the concentration distribution of ARGs. Specifically, a noteworthy existence of ARGs, which ranged from 1E + 05 to 1E + 11 copies/mL, was detected in livestock breeding wastewater, and household wastewater (caused by the unlimited utilization of antibiotics) was determined to be the predominant contributor of ARGs in WWTPs. We summarized the selective pressure on ARGs and determined the positive correlation of the concentration of ARGs and the existence of many containments, including antibiotics, heavy metals (Zn and Cu were frequently reported), quaternary ammonium compounds, etc. In the last section, physical, chemical, and biological treatments for the removal of ARGs and their effluent in WWTPs are discussed and prospective future studies are summarized.
In this study, α-Bi2O3/g-C3N4 nanocomposite with direct Z-scheme was successfully prepared through calcination of BiOCOOH/g-C3N4 precursor at different temperature. Meanwhile, the effect of calcination temperature on the physicochemical properties of α-Bi2O3/g-C3N4 was studied. All results confirmed that calcination temperature greatly influences structural, morphology, surface states, photoelectrochemical property and photocatalytic (PC) performance of α-Bi2O3/g-C3N4 composite. Furthermore, the α-Bi2O3/g-C3N4 composite was applied as photocatalyst to degrade amido black 10B dye under visible light irradiation. It was found that the composite synthesized at 400 ℃ exhibited the highest PC performance due to the intense visible light absorbance and high separation efficiency of electron and hole pairs. Besides, the possible PC mechanism was proposed that the photo-generated charge carrier migration in α-Bi2O3/g-C3N4 photocatalyst followed a Z-scheme structure. Finally, the stability test also manifest that the α-Bi2O3/g-C3N4 composite photocatalyst has good stability and reusability, which was a promising candidate for wastewater treatment.
In recent decades, the properties and behaviors of nanofluidic devices have been widely explored in varied subjects such as engineering, physics, chemistry, and biology. Among the rich properties of nanofluidics, ionic current rectification (ICR) is a unique phenomenon arising from asymmetric nanofluidic devices with electric double layer (EDL) overlapped. The ICR property is especially useful in applications including energy conversion, mass separation, sea water purification and bioanalysis. In this review, the ICR property in nanofluidics as well as the underlying mechanism is demonstrated. The influencing factors concerning to the ICR property are systematically summarized. The asymmetric geometry as well as the charge distribution is in charge of the ICR behavior occurring in nanofluidic devices. This review is aimed at readers who are interested in the fundamentals of mass transport in nanofluidics in general, as well as those who are willing to apply nanofluidics in various research fields.
Tailored design and synthesis of high-quality electrocatalysts is vital for the advancement of oxygen evolution reaction (OER). Herein, we report a powerful puffing method to fabricate hierarchical porous N-doped carbon with numerous embedded Ni nanoparticles. Interestingly, during the puffing and annealing process, rice precursor with N and Ni sources can be in-situ converted into Niembedded N-doped porous carbon (N-PC/Ni) composite. The obtained N-PC/Ni composite possesses a cross-linked porous architecture containing conductive carbon backbone and active Ni nanoparticles electrocatalysts for OER. The pore formation in N-PC/Ni composite is also proposed because of carbothermic reduction. The N-PC/Ni composite is fully studied as electrocatalysts for OER. Due to increased active surface area, enhanced electronic conductivity and reactivity, the designed N-PC/Ni composite exhibits superior OER performance with a low Tafel slope (~88 mV/dec) and a low overpotential as well as excellent long-term stability in alkaline solution. Our proposed rational design strategy may provide a new way to construct other advanced metal/heteroatom-doped composites for widespread application in electrocatalysis.
In the past few years, the increasing energy consumption of traditional fossil fuels has posed a huge threat to human health. It is very imperious to develop the sustainable and renewable energy storage and conversion devices with low cost and environment friendly features. Hybrid supercapacitors are emerging as one of the promising energy devices with high power density, fast charge-discharge process and excellent cycle stability. However, morphology and structure of the electrode materials exert serious effect on their electrochemical performances. In this review, we summarized recent progresses in transition metal oxide based electrode materials for supercapacitors. Different synthesis routes and electrochemical performances of electrode materials and storage mechanisms of supercapacitor devices have been presented in details. The future developing trends of supercapacitor based on metal oxide electrode materials are also proposed.
Access to safe drinking water has become an extremely urgent research topic worldwide. In recent years, the technology of solar vapor generation has been extensively explored as a potential and effective strategy of transforming elements content in seawater. In this review, the basic concepts and theories of metal-based photothermal vapor generation device (PVGD) with excellent optical and thermal regulatory are introduced. In the view of optical regulation, how to achieve high-efficiency localized evaporation in different evaporation system (i.e., volumetric solar heating and interface solar heating) is discussed; from the aspect of thermal regulation, the importance of selective absorption surface for interfacial PVGD is analyzed. Based on the above discussion and analysis, we summarize the challenges of metal-based desalination device.
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