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•Novel direct Z-scheme AgI/Bi4V2O11 photocatalysts were prepared.•A superior photocatalytic activity for the degradation of SMZ refractory pollutants.•A plausible degradation pathway ...for SMZ was proposed.•The fabrication Z-scheme heterostructure play a central role in promoting charge separation and active radical generation.
Z-scheme heterojunction can not only promote the separation of photogenerated carriers, but also retain the strong redox potential of the system, which would greatly improve the photocatalytic performance of catalyst. Herein, a Z-scheme AgI/Bi4V2O11 heterojunction photocatalyst was prepared by a hydrothermal process combined with in situ coprecipitation process. Multiple techniques were employed to investigate the morphology, composition, chemical and electronic properties of the as-prepared samples. The obtained Z-scheme AgI/Bi4V2O11 heterojunction photocatalyst exhibited remarkably enhanced photocatalytic performance towards sulfamethazine (SMZ) degradation under visible light irradiation. Especially, the 20 wt% AgI/Bi4V2O11 composites exhibited the highest photocatalytic activity for sulfamethazine (SMZ) degradation and 91.47% SMZ would be eliminated within 60 min. In comparison with NO3− and SO42−, the presence of Cl− and HCO3− presented more obviously inhibition effects on SMZ degradation. The possible degradation pathways of SMZ were speculated by identifying degradation intermediates. O2−, h+ and OH all involved in the photocatalytic degradation SMZ. The highly enhanced photocatalytic performance might be attributed to form Z-scheme junction between AgI and BVO, which are conducive to the efficient charges separation and maintain high redox potential. This work enriches Bi4V2O11-based Z-scheme heterojunction photocatalytic system and provides a reference for the preparation of effective Z-scheme junction photocatalysts.
Synthetic nitrogen (N) fertilizer has played a key role in enhancing food production and keeping half of the world's population adequately fed. However, decades of N fertilizer overuse in many parts ...of the world have contributed to soil, water, and air pollution; reducing excessive N losses and emissions is a central environmental challenge in the 21st century. China's participation is essential to global efforts in reducing N-related greenhouse gas (GHG) emissions because China is the largest producer and consumer of fertilizer N. To evaluate the impact of China's use of N fertilizer, we quantify the carbon footprint of China's N fertilizer production and consumption chain using life cycle analysis. For every ton of N fertilizer manufactured and used, 13.5 tons of CO₂-equivalent (eq) (tCO₂-eq) is emitted, compared with 9.7 t CO₂-eq in Europe. Emissions in China tripled from 1980 131 terrogram (Tg) of CO₂-eq (Tg CO₂-eq) to 2010 (452 Tg CO₂-eq). N fertilizer-related emissions constitute about 7% of GHG emissions from the entire Chinese economy and exceed soil carbon gain resulting from N fertilizer use by several-fold. We identified potential emission reductions by comparing prevailing technologies and management practices in China with more advanced options worldwide. Mitigation opportunities indude improving methane recovery during coal mining, enhancing energy efficiency in fertilizer manufacture, and minimizing N overuse in field-level crop production. We find that use of advanced technologies could cut N fertilizer-related emissions by 20-63%, amounting to 102-357 Tg CO₂-eq annually. Such reduction would decrease China's total GHG emissions by 2-6%, which is significant on a global scale.
Multicompartment microcapsules, with each compartment protected by a distinct stimuli‐responsive shell for versatile controlled release, are highly desired for developing new‐generation ...microcarriers. Although many multicompartmental microcapsules have been created, most cannot combine different release styles to achieve flexible programmed sequential release. Here, one‐step template synthesis of controllable Trojan‐horse‐like stimuli‐responsive microcapsules is reported with capsule‐in‐capsule structures from microfluidic quadruple emulsions for diverse programmed sequential release. The nested inner and outer capsule compartments can separately encapsulate different contents, while their two stimuli‐responsive hydrogel shells can individually control the content release from each capsule compartment for versatile sequential release. This is demonstrated by using three types of Trojan‐horse‐like stimuli‐responsive microcapsules, with different combinations of release styles for flexible programmed sequential release. The proposed microcapsules provide novel advanced candidates for developing new‐generation microcarriers for diverse, efficient applications.
Trojan‐horse‐like stimuli‐responsive microcapsules with controllable capsule‐in‐capsule structures are created for diverse programmed sequential release. Different combinations of stimuli‐responsive hydrogel shells allow for flexible control of the content release from each capsule compartment for versatile sequential release. The proposed Trojan‐horse‐like stimuli‐responsive microcapsules provide novel advanced candidates for developing new‐generation microcarriers for diverse, efficient applications.
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•Novel OCN-24-550 photocatalyst was prepared by a green strategy.•OCN-24-550 exhibits outstanding photocatalytic performance for ROS generation.•Ultrathin porous structure and ...oxygen-substitution boost exciton dissociation.•This work provides guidance for the development of g-C3N4-based photocatalyst.
Light-driven reactive oxygen species (ROS) generation from molecular oxygen activation is normally recognized as an effective route for environmental pollutants removal. Herein, oxygen-substituted ultrathin porous graphitic carbon nitride (g-C3N4) nanosheets are prepared through a two-step hydrothermal-recalcination treatment of bulk g-C3N4 (BCN), and it is found that the obtained samples display enhanced ROS generation, as reflected by the removal of oxytetracycline hydrochloride (OTC). When stimulated by visible light, about 85.76% of OTC can be removed by the optimal sample (OCN-24-550) within 120 min, which is obviously higher than that of bulk g-C3N4 by a factor of 4.99. Meanwhile, nitroblue tetrazolium (NBT) transformation and H2O2 generation also indicate that the OCN-24-550 possess the highest reactivity, which can produce 47.25 μM of H2O2 and 9.07 × 10−10 M of the steady-state O2− during the reaction. The enhanced photocatalytic performance of OCN-24-550 is attributed to the synergistic effect of ultrathin porous structure and heteroatom O substitution. Specifically, the ultrathin porous structure can enlarge the surface area and then facilitate the diffusion of reactant, while the O substitution can optimize the electronic structure by creating a local electronic polarization effect, as confirmed by density functional theory (DFT) calculations, and thus result in a boosted exciton dissociation and accelerated charge migration. This work not only presents a comprehensive insight into g-C3N4-based reaction system from exciton and charge carrier, but also provides a meaningful guidance for exploring novel photocatalytic wastewater treatment devices from a more environment-friendly perspective.
We combine field observations, microcosm, stoichiometry, and molecular and stable isotope techniques to quantify N2O generation processes in an intensively managed low carbon calcareous fluvo-aquic ...soil. All the evidence points to ammonia oxidation and linked nitrifier denitrification (ND) being the major processes generating N2O. When NH4(+)-based fertilizers are applied the soil will produce high N2O peaks which are inhibited almost completely by adding nitrification inhibitors. During ammonia oxidation with high NH4(+) concentrations (>80 mg N kg(-1)) the soil matrix will actively consume oxygen and accumulate high concentrations of NO2(-), leading to suboxic conditions inducing ND. Calculated N2O isotopomer data show that nitrification and ND accounted for 35-53% and 44-58% of total N2O emissions, respectively. We propose that slowing down nitrification and avoiding high ammonium concentrations in the soil matrix are important measures to reduce N2O emissions per unit of NH4(+)-based N input from this type of intensively managed soil globally.
In this paper, chitosan microcapsules with stable nano-membranes for controlled release of drugs are prepared by a simple one-step microfluidic strategy from oil-in-water (O/W) single emulsion ...templates. The ultrathin membranes of microcapsules are formed at the interface of the O/W emulsion droplets via the interfacial reaction between chitosan in aqueous phase and terephthalaldehyde in oil core. The membrane thickness can be effectively controlled within 10 nm and accurately regulated at nanoscale from 2.8 nm to 8.0 nm by adjusting the crosslinking time, concentrations of reactant and viscosity of aqueous solution. Among these factors, the membrane thickness is more susceptible to the viscosity of aqueous phase. The stability of the nano-membranes is quite good, which makes the microcapsules exhibit excellent structure integrity during 150 days. Using tea tree oil (TTO) as the model drug, the prepared chitosan microcapsules with nano-membranes show low mass transfer resistance and rapid drug release. The cumulative release rate of TTO from chitosan microcapsules with membrane thickness of 3.1 nm and 4.3 nm reach to 76.1% and 56.6% within 10 h, respectively. The drug release behaviors from the chitosan microcapsules are directly related to the thickness of the capsule membranes, and therefore can also be finely controlled. The thinner the capsule membrane is, the faster the drug release. The initial TTO release rate doubles as the membrane thickness decreases from 4.3 nm to 3.1 nm. In addition, because no surfactant is used in the whole preparation process, the prepared chitosan microcapsules present satisfactory biocompatibility. The results provide valuable guidance for designing and fabricating polymeric microcapsule membranes with controllable nanoscale thickness to enhance their performances in biological and medical applications.
•Chitosan microcapsule membranes with controllable nanoscale thickness are developed by a simple microfluidic strategy.•The thickness of capsule membranes can be controlled within 10 nm and accurately regulated at nanoscale.•Drug release behaviors from chitosan microcapsules with nano-membranes can be finely controlled.•The nano-membranes of chitosan microcapsules present both stability and good biocompatibility.
In this paper, a new 'turn-on' fluorescence probe for the rapid, sensitive, and visual detection of hypochlorite is reported. The push-pull type trianiline-tricyanofuran-based fluorescent probe was ...prepared using a condensation reaction between tricyanofuran and the thiophene-trianiline derivative that had high quantum yields and showed aggregation-induced emission enhanced properties. Upon exposure to hypochlorite, prominent fluorescence enhancement of the probe was observed via the release of the fluorophore from the probe. The probe showed a ratiometric absorption change at 315 nm and 575 nm. Importantly, the probe showed an excellent detection limit for hypochlorite at 1.2 × 10
M in solution and it was successfully applied for monitoring hypochlorite in waste water by test strip. This work reports a new fluorescence analytical sensing method for hypochlorite that has potential practical value in environmental monitoring and biological discrimination.
Ion sieving is of great importance in a variety of applications, such as water desalination/purification, biomedical engineering and so on. The currently available techniques, based on ion size ...sieving by constructing membranes with nanochannels and nanopores, are still not able to achieve precise sieving of mono-/multi-valent metal ions. Here, we report on the fabrication of graphene-based membranes by constructing uniform two-dimensional (2D) nanochannels with effective channel heights of ~ 8Å for precise and efficient sieving of mono-/multi-valent metal ions. Our membranes with uniform 2D nanochannels are built using facilely reduced graphene oxide (FRGO) nanosheets, which are controllably fabricated by avoiding the corrugation of graphene oxide (GO) nanosheets and controlling the content of oxidation groups during the reduction process. We illustrate the ability of precise sieving of mono-/multi-valent metal ions afforded by this technique by fabricating FRGO membranes with uniform 2D nanochannels, and demonstrate the excellent repeatability and long-term stability of FRGO membranes for sieving of mono-/multi-valent metal ions.
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•Graphene-based membranes are fabricated with uniform 2D nanochannels.•The uniform 2D nanochannels are constructed with facilely reduced graphene oxide nanosheets.•The effective channel heights of uniform 2D nanochannels can be controllably adjusted.•The membranes show efficient sieving performance of mono-/multi-valent metal ions.
This work reports on a simple and general strategy for continuous fabrication of self-propelled micromotors with photocatalytic metal–organic frameworks (MOFs) for enhanced synergistic degradation of ...organic contaminants. With emulsion microdroplets from microfluidics as templates, uniform porous micromotors decorated with Fe3O4@Ag nanoparticles (Fe3O4@AgNPs) at the bottom and zeolitic imidazolate framework-8@ZnO nanoparticles (ZIF-8@ZnONPs) on the surface can be synthesized. The spatial location of ZIF-8@ZnONPs and Fe3O4@AgNPs in micromotors is accurately controlled in one step via their directional migration in the confined microspace of emulsion droplets driven by interfacial energy and magnetic field. The nanoengines Fe3O4@AgNPs enable asymmetric decomposition of H2O2 for bubble-propelled motion and easy magnetic recycling of the micromotor. The porous structures of micromotors provide a large surface area, benefiting decoration of Fe3O4@AgNPs and their contact with H2O2 for promoting bubble generation and reduced micromotor weight for promoting bubble-propelled motion. The nanophotocatalysts ZIF-8@ZnONPs allow enrichment of organic contaminant molecules via adsorption for efficient photocatalytic degradation. With synergistic coupling of the photocatalysis of ZIF-8@ZnONPs and advanced oxidation of the H2O2/UV system, the micromotors with bubble-propelled motion for improved mixing can achieve enhanced degradation of organic contaminants via dual synergistic degradation mechanisms. As highlighted by degradation of rhodamine B, the micromotors exhibit the highest degradation performance as compared to control groups with a single degradation mechanism and with dual degradation mechanisms but without self-propelled motion. This simple fabrication strategy is general and can be flexibly extended to other MOF materials, which may open up new avenues for developing advanced MOF-integrated micromotors for myriad applications.
Graphene oxide (GO) membranes have shown enormous promise in desalination and molecular/ionic sieving. However, the instability of GO membranes in aqueous solutions seriously hinders their practical ...applications. Herein, we report a novel and simple strategy to fabricate stable GO membranes in water-based environments through the insertion of various metal cations from metal foils (e.g., copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) foils) and natural deposition. Based on the cation-π, coordination, and electrostatic interaction between metal cations and GO nanosheets, the aqueous stability and mechanical strength of the membranes are significantly improved. The permeation rates for acetone, toluene, and p-xylene molecules across the GO membrane cross-linked by copper ions with a deposition time of 24 h are 0.966, 0.074, and 0.100 mol m–2 h–1, respectively. Moreover, this membrane displays excellent separation performance, and the separation factor of K+/Mg2+ is up to 68.8 in mono-/multivalent metal cation sieving, which indicate the effective molecular/ionic sieving performance. Meanwhile, the ionic sieving of the GO membrane cross-linked by copper ions has excellent repeatability and long-term stability. The versatility of this natural deposition strategy to fabricate GO membranes cross-linked by metal cations is investigated by using Fe foil, Zn foil, and Ni foil as well as other porous substrates such as polyvinylidene fluoride (PVDF), polyethersulfone (PES), and nylon membranes and filter paper. This fabrication strategy also enables low-cost preparation of large-area GO membranes. Therefore, GO membranes cross-linked by metal cations and prepared by this simple metal cation incorporation strategy have large potential application for molecular/ionic sieving in various solution systems.
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