Haopeng Feng

Treatment of arsenic in acid wastewater and river sediment by Fe@Fe2O3 nanobunches: The effect of environmental conditions and reaction mechanism

High concentration of arsenic in acid wastewater and polluted river sediment caused by metallurgical industry has presented a great environmental challenge for decades. Nanoscale zero valent iron (nZVI) can detoxify arsenic-bearing wastewater and groundwater, but the low adsorption capacity and rapid passivation restrict its large-scale application. This study proposed a highly efficient arsenic treatment nanotechnology, using the core-shell Fe@Fe2O3 nanobunches (NBZI) for removal of arsenic in acid wastewater with cyclic stability and transformation of arsenic speciation in sediment. The adsorption capacity of As(III) by NBZI was 60 times as high as that of nanoscale zero valent iron (nZVI) at neutral pH. Characterization of the prepared materials after reaction revealed that the contents of As(III) and As(V) were 65% and 35% under aerobic conditions, respectively, which is the evidence of oxidation included in the reaction process apart from adsorption and co-precipitation. The presence of oxygen was proved to improve the adsorption ability of the prepared NBZI towards As(III) with the removal efficiency increasing from 68% to 92%. In order to further enhance the performance of NBZI-2 in the absence of oxygen, a new Fenton-Like system of NBZI/H2O2 to remove arsenic under the anoxic condition was also proposed. Furthermore, the removal efficiency of arsenic in acid wastewater remained to be 78% after 9 times of cycling. Meanwhile, most of the mobile fraction of arsenic in river sediment was transformed into residues after NBZI treatment for 20 days. The reaction mechanism between NBZI and arsenic was discussed in detail at last, indicating great potential of NBZI for the treatment of arsenic in wastewater and sediment.

pH-dependent degradation of p-nitrophenol by sulfidated nanoscale zerovalent iron under aerobic or anoxic conditions.

Sulfidated nanoscale zerovalent iron (S-NZVI) is attracting considerable attention due to its easy production and high reactivity to pollutants. We studied the reactivity of optimized S-NZVI (Fe/S molar ratio 6.9), comparing with pristine nanoscale zerovalent iron (NZVI), at various pH solutions (6.77-9.11) towards p-nitrophenol (PNP) under aerobic and anoxic conditions. Studies showed that the optimized extent of sulfidation could utterly enhance PNP degradation compared to NZVI. Batch experiments indicated that in anoxic S-NZVI systems the degradation rate constant increased with increasing pH up to 7.60, and then declined. However, in aerobic S-NZVI, and in anoxic or aerobic NZVI systems, it decreased as pH increased. It was manifested that anoxic S-NZVI systems preferred to weaker alkaline solutions, whereas aerobic S-NZVI systems performed better in acidic solutions. The highest TOC removal efficiency of PNP (17.59%) was achieved in the aerobic S-NZVI system at pH 6.77, revealing that oxygen improved the degradation of PNP by excessive amounts of hydroxyl radicals in slightly acidic conditions, and the TOC removal efficiency was supposed to be further improved in moderate acidic solutions. Acetic acid, a nontoxic ring opening by-product, confirms that the S-NZVI system could be a promising process for industrial wastewater containing sulfide ions.

Plasmonic resonance excited dual Z-scheme BiVO4/Ag/Cu2O nanocomposite: synthesis and mechanism for enhanced photocatalytic performance in recalcitrant antibiotic degradation

The utilization of solar energy based on semiconductor photocatalysts for pollutant removal and environmental remediation has become a research hot spot and attracted great attention. In this study, a novel ternary BiVO4/Ag/Cu2O nanocomposite has been successfully synthesized via simple wet impregnation of Cu2O particles coupled with a subsequent photo-reduction pathway for the deposition of metallic Ag on the surface of BiVO4. The resulting BiVO4/Ag/Cu2O photocatalyst was used for the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). Results showed that the coating contents of the Cu2O and Ag particles presented a great effect on the eventual photocatalytic activity of the photocatalysts, and the optimum coating contents of Cu2O and Ag were obtained with their mass ratios of 3% and 2%, respectively. Under optimum conditions, nearly 91.22% TC removal efficiency was obtained based on ternary BiVO4/Ag/Cu2O nanocomposites, higher than that of pure BiVO4 (42.9%) and binary BiVO4/Cu2O (65.17%) and BiVO4/Ag (72.63%) nanocomposites. Meanwhile, the enhanced total organic carbon (TOC) removal efficiency also indicated the excellent photocatalytic degradation ability of the BiVO4/Ag/Cu2O nanocomposites. As for their practical application, the effects of initial TC concentration, various supporting electrolytes and different irradiation conditions were investigated in detail. Three-dimensional excitation–emission matrix fluorescence spectroscopy (3D EEMs) was used to show the by-products of TC molecule degradation. Cycling experiments indicated the high stability of the as-prepared photocatalysts. Furthermore, the results obtained from radical trapping experiments and ESR measurements suggested that the photocatalytic degradation of TC in the BiVO4/Ag/Cu2O based photocatalytic system was the joint action of the photogenerated holes (h+), superoxide radical (˙O2−) and hydroxyl radical (˙OH). The enhanced photocatalytic activity of BiVO4/Ag/Cu2O was attributed to the synergistic effect of Cu2O, Ag and BiVO4, especially the surface plasmon resonance effect and the established local electric field brought about by metallic Ag. Additionally, to deeply understand the reaction mechanism, a dual Z-scheme charge transfer pathway has been proposed.

Construction of plasmonic Ag modified phosphorous-doped ultrathin g-C 3 N 4 nanosheets/BiVO 4 photocatalyst with enhanced visible-near-infrared response ability for ciprofloxacin degradation

To realize the full utilization of solar energy, the design of highly efficient photocatalyst with improved visible-near-infrared photocatalysis performance has attracted great attentions for environment pollutant removal. In this work, we rationally employed the surface plasmon resonance effect of metallic Ag in the phosphorus doped ultrathin g-C3N4 nanosheets (PCNS) and BiVO4 composites to construct a ternary Ag@PCNS/BiVO4 photocatalyst. It was applied for the photodegradation of ciprofloxacin (CIP), exhibiting 92.6% removal efficiency under visible light irradiation (λ>420nm) for 10mg/L CIP, and presenting enhanced photocatalytic ability than that of single component or binary nanocomposites under near-infrared light irradiation (λ>760nm). The improved photocatalytic activity of the prepared Ag@PCNS/BiVO4 nanocomposite can be attributed to the synergistic effect among the PCNS, BiVO4 and Ag, which not only improves the visible light response ability and hinders the recombination efficiency of the photogenerated electrons and holes, but also retains the strong the redox ability of the photogenerated charges. According to the trapping experiment and ESR measurements results, OH, h+ and O2- all participated in the photocatalytic degradation process. Considering the SPR effect of metallic Ag and the established local electric field around the interfaces, a dual Z-scheme electrons transfer mechanism was proposed.

Cu-Doped Fe@Fe2O3 core–shell nanoparticle shifted oxygen reduction pathway for high-efficiency arsenic removal in smelting wastewater

Studies on the removal of As(III) by Fe-based materials have been carried out for decades, but the time-consuming process and low removal capacity are obstacles for large-scale practical applications. Here, a rapid and efficient technique was proposed for the removal of As(III) using Cu-doped Fe@Fe2O3 core–shell nanoparticles (CFF) synthesized by a facile two-step reduction method and aging process, which realized a thorough removal of As(III) from smelting wastewater at neutral pH within 30 min. The copper doped in CFF not only provided two extra oxygen reduction pathways to enhance the molecular oxygen activation, but also improved the electron transfer ability and removal efficiency of As(III). The existence of copper contributed to the rapid oxidization and adsorption of As(III), and the removal rate increased nearly 10-times in the aerobic system. Meanwhile, the proposed Cu-doped Fe@Fe2O3 core–shell nanoparticles and shifted oxygen reduction pathway could be easily scaled up for other transition metals, such as Ni. Molecular dynamics (MD) simulations based on the large-scale atomic/molecular massively parallel simulator (LAMMPS) were also employed to investigate the formation process of CFF. Furthermore, the removal efficiency of arsenic in smelting wastewater remained to be 90% after 6 times of cycling. Therefore, the distinctive oxidation activities of CFF hold great promise for applications in arsenic removal.

Antibiotic removal from water: A highly efficient silver phosphate-based Z-scheme photocatalytic system under natural solar light

Photocatalytic degradation is an alternative method to remove pharmaceutical compounds from water, however it is hard to achieve efficient rate because of the low efficiency of photocatalysts. In this study, an efficient Z-Scheme photocatalyst was constructed by integrating graphitic carbon nitride (CN) and reduced graphene oxide (rGO) with AP via a simple facile precipitation method. Excitedly, ternary AP/rGO/CN composite showed superior photocatalytic and anti-photocorrosion performances under both intense sunlight and weak indoor light irradiation. NOF can be completely degraded in only 30 min and about 85% of NOF can be mineralized after 2 h irradiation under intensive sunlight irradiation. rGO could work not only as a sheltering layer to protect AP from photocorrosion but also as a mediator for Z-Scheme electron transport, which can protect AP from the photoreduction. This strategy could be a promising method to construct photocatalytic system with high efficiency for the removal of antibiotics under natural light irradiation.

Carbon nanotube-based environmental technologies: the adopted properties, primary mechanisms, and challenges

Carbon nanotubes (CNTs) show great potential and bright prospect in the field of environment. It is believed that this new kind of material will bring opportunities and benefits to the environmental protection and pollution control. In recent years, a lot of CNT-based environmental technologies have been developed and applied with successful results, but the adequate understanding and large-scale industrial applications of these technologies are lacking. This paper systematically reviews current environmental applications of CNTs, including pollution treatment and environmental remediation, environmental sample analysis, environmental monitoring and sensing, and design of environment-friendly products. The adopted properties of CNTs are introduced. The main roles of CNTs in these technologies are illustrated. Additionally, the main current challenges to realizing their practical applications are analyzed and discussed, involving toxicity and ecological risks, production costs, general applicability, long-term effect, and public acceptance. Further studies should give priority to the toxicity and environmental risk of CNTs when developing new CNT-based technologies. Research on standardizing toxicity testing and risk assessment of CNTs is highly recommended and a large number of toxicity data of CNTs are needed.

Enhancement of Fenton processes at initial circumneutral pH for the degradation of norfloxacin with Fe@Fe2O3 core-shell nanomaterials

ABSTRACT The degradation of norfloxacin by Fenton reagent with core-shell Fe@Fe2O3 nanomaterials was studied under neutral conditions in a closed batch system. Norfloxacin was significantly degraded (90%) in the Fenton system with Fe@Fe2O3 in 30 min at the initial pH 7.0, but slightly degraded in Fenton system without Fe@Fe2O3 under the same experimental conditions. The intermediate products were investigated by gas chromatography-mass spectrometry, and the possible Fenton oxidation pathway of norfloxacin in the presence of Fe@Fe2O3 nanowires was proposed. Electron spin resonance spectroscopy was used to identify and characterize the free radicals generated, and the mechanism for norfloxacin degradation was also revealed. Finally, the reusability and the stability of Fe@Fe2O3 nanomaterials were studied using x-ray diffraction and scanning electron microscope, which indicated that Fe@Fe2O3 is a stable catalyst and can be used repetitively in environmental pollution control. GRAPHICAL ABSTRACT