Interfacial nanobubbles can exist on various hydrophobic and hydrophilic material interfaces. There are diverse applications for oxygen nanobubbles, which are closely related to their content and ...long-term stability. However, it remains challenging to determine the amount of nanobubbles loaded in a porous material. In this study, a novel method was used to quantify the total amount of oxygen nanobubbles loaded onto irregular particulate materials. Different materials were evaluated and their oxygen-loading capacities were found to be as follows: activated carbon (AC) > zeolite > biochar > diatomite > coal ash > clay. Significant differences in oxygen-loading capacities were mainly ascribed to differences in the specific surface area and hydrophobic/hydrophilic properties of the materials. The total oxygen loading on AC achieved using the high pressure loading method was higher than that achieved by the temperature variation method. This new quantitative method provides the possibility for the manipulation of oxygen nanobubble materials in practical applications and it is anticipated to be an important supplement to the existing methods of characterizing interfacial oxygen nanobubbles. Our results demonstrate that materials containing oxygen nanobubbles can significantly increase the dissolved oxygen and oxidation reduction potential in anaerobic systems. With the addition of oxygen-loaded materials (such as AC), the survival time of zebrafish was prolonged up to 20 h in a deoxygenated water system, and the germination rate of Vallisneria spiralis was also increased from 27 to 73% in an anaerobic sediment.
A series of spinel-type Mg
0.25−
x
Al
2.57
O
3.79
N
0.21
:
x
Mn
2+
(MgAlON:
x
Mn
2+
) phosphors were synthesized by the solid-state reaction route. The transparent ceramic phosphors were fabricated ...by pressureless sintering followed by hot-isostatic pressing (HIP). The crystal structure, luminescence and mechanical properties of the samples were systematically investigated. The transparent ceramic phosphors with tetrahedrally coordinated Mn
2+
show strong green emission centered around 515 nm under blue light excitation. As the Mn
2+
concentration increases, the crystal lattice expands slightly, resulting in a variation of crystal field and a slight red-shift of green emission peak. Six weak absorption peaks in the transmittance spectra originate from the spin-forbidden
4
T
1
(
4
G)→
6
A
1
transition of Mn
2+
. The decay time was found to decrease from 5.66 to 5.16 ms with the Mn
2+
concentration. The present study contributes to the systematic understanding of crystal structure and properties of MgAlON:
x
Mn
2+
green-emitting transparent ceramic phosphor which has a potential application in high-power light-emitting diodes.
Harmful algal blooms (HABs), eutrophication, and internal pollutant sources from sediment, represent serious problems for public health, water quality, and ecological restoration worldwide. Previous ...studies have indicated that Modified Local Soil (MLS) technology is an efficient and cost-effective method to flocculate the HABs from water and settle them onto sediment. Additionally, MLS capping treatment can reduce the resuspension of algae flocs from the sediment, and convert the algal cells, along with any excessive nutrients in-situ into fertilisers for the restoration of submerged macrophytes in shallow water systems. Furthermore, the capping treatment using oxygen nanobubble-MLS materials can also mitigate sediment anoxia, causing a reduction in the release of internal pollutants, such as nutrients and greenhouse gases. This paper reviews and quantifies the main features of MLS by investigating the effect of MLS treatment in five pilot-scale whole-pond field experiments carried out in Lake Tai, South China, and in Cetian Reservoir in Datong city, North China. Data obtained from field monitoring showed that the algae-dominated waters transform into a macrophyte-dominated state within four months of MLS treatment in shallow water systems. The sediment-water nutrient fluxes were substantially reduced, whilst water quality (TN, TP, and transparency) and biodiversity were significantly improved in the treatment ponds, compared to the control ponds within a duration ranging from one day to three years. The sediment anoxia remediation effect by oxygen nanobubble-MLS treatment may further contribute to deep water hypoxia remediation and eutrophication control. Combined with the integrated management of external loads control, MLS technology can provide an environmentally friendly geo-engineering method to accelerate ecological restoration and control eutrophication.
Abstract
Copper-chromium (CuCr) alloys are widely used as electrical contact materials, and their arc erosion resistance can be improved by reducing the sizes of the Cu and Cr phases or by adding Mo. ...In this study, supersaturation solid solutions of CuCr and CuCrMo films were prepared via magnetron sputtering. After annealing at 773 K, the CuCr and CuCrMo films are composed of a small Cu-rich face-centred cubic phase and a Cr-rich body-centred cubic phase. Meanwhile, the addition of Mo reduces the diffusion rate during annealing. The lattice distortion of the CuCrMo thin film exceeds that of the CuCr film, and the elastic modulus and hardness increase. Compared with those of the CuCr film, the erosion area of the CuCrMo film is larger, and the depth of the erosion pit is lower. The arc erosion experiment proved that CuCrMo films exhibit satisfactory arc erosion resistance.
Nanoplastics in the environment lead to the human exposure to these particles. However, the consequences of this exposure are not yet fully understood. Here, the cytotoxicity of polystyrene ...nanoparticles (PS-NPs) with a uniform size (50 nm) but distinct surface functionalization (pristine polystyrene, PS; carboxy and amino functionalized, PS-COOH and PS-NH2, respectively), and at an exposure dosage of 10, 50 and 100 μg/mL, were assessed in the human hepatocellular carcinoma (HepG2) cell line. Although all PS-NPs could be internalized by the HepG2 cells, according to the fluorescent intensities, more of PS-COOH and PS-NH2 than PS, accumulated in the cells. The cell viability was significantly affected in a positively dose-related manner. Functionalized PS-NPs exhibited greater inhibition of cell viability than PS, and the viability inhibition peaked (46%) at 100 μg/mL of PS-NH2 exposure. Superoxide dismutase (SOD) activity was maximum when HepG2 cells were exposed to 10 μg/mL of PS-COOH (1.8 folds higher than that without PS-COOH exposure). The glutathione (GSH) content was maximum when the cells were treated with 50 μg/mL of PS (3.75 fold increase compared to untreated cells). Although the difference in inhibition of cell viability was not significant between PS-NH2 and PS-COOH exposure, 100 μg/mL of PS-NH2 exposure caused the most severe oxidative stress due to dramatically increased accumulation of malondialdehyde (MDA); however, a decrease in the antioxidants levels as the SOD activity and GSH content were also found. The results demonstrated that the cellular oxidative damage occurred and that the antioxidation enzymes may not be able to maintain the balance between the generation of oxidant species and the antioxidant defense. Consequently, 100 μg/mL of PS-NH2 exposure triggered the destruction of antioxidant structures. This study defines the cytotoxic effects of PS-NPs on HepG2 cells and emphasizes the significance of investigating the cytotoxic outcomes of nanoplastics in humans.
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•PS-NPs reduced the cell viability of HepG2 cells.•Reduced of cell viability showed positively dosage-related trend.•PS-NPs with size of 50 nm can be rapidly internalized by HepG2 cells.•Functionalized PS-NPs exhibited higher negative impact on cell viability than PS.•PS-NH2 of 100 μg/mL caused the destruction of antioxidant capabilities.
A new method for generating nanobubbles via microwave irradiation was verified and quantified. AFM measurement showed that nanobubbles with diameters ranging from 200 to 600 nm were generated at a ...water-HOPG surface by applying microwave radiation to aqueous solutions with 9.0–30.0 mg/L dissolved oxygen. Graphite displays strong microwave absorption and transmits high thermal energy to the surface. Because of the high dielectric constant (20 °C, 80 F/m) and dielectric loss factor, water molecules have a strong ability to absorb microwave radiation. The thermal and nonthermal effects of microwave radiation made contributions to decreasing the gas solubility, thus facilitating nanobubble nucleation. The yield of nanobubbles increased about 10-fold when the irradiation time increased from 60 to 120 s at 200 W of microwave radiation. The nanobubble density increased from 0.8 to 15 μm–2 by improving the working power from 200 to 600 W. An apparent improvement in nanobubbles yield was obtained between 300 and 400 W, and the resulting temperature was 34–52 °C. When the initial dissolved oxygen increased from 11.3 to 30.0 mg/L, the density of nanobubbles increased from 1.2 to 13 μm–2. The generation of nanobubbles could be well controlled by adjusting the gas concentration, microwave power, or irradiation time. The method may be valuable in preparing surface nanobubbles quickly and conveniently for various applications, such as catalysis, hypoxia/anoxia remediation, and templates for preparing nanoscale materials.
The prevalence of hypoxia in surface sediment inhibits the growth of aerobic denitrifiers in natural waters. A novel oxygen micro/nanobubble-loaded microporous biochar (OMB) was developed to activate ...indigenous aerobic denitrifiers in this study. The results indicate a thin-layer OMB capping mitigates hypoxia effectively. Following a 30-day microcosm-based incubation, a 60 % decrease in total nitrogen concentration was observed, and the oxygen penetration depth in the sediment was increased from <4.0 mm to 38.4 mm. High-throughput sequencing revealed the stimulation of indigenous mixotrophic aerobic denitrifiers, including autotrophic denitrifiers such as Hydrogenophaga and Thiobacillus, heterotrophic denitrifiers like Limnobacter and unclassified_f_Methylophilaceae, and heterotrophic nitrification aerobic denitrification bacteria, including Shinella and Acidovorax, with total relative abundance reaching up to 38.1 %. Further analysis showed OMB enhanced the overall collaborative relationships among microorganisms and promoted the expression of nitrification- and denitrification-related genes. This study introduces an innovative strategy for stimulating indigenous aerobic denitrifiers in aquatic ecosystems.
Biochar has been widely applied in soil and water. However, the fate and transport of biochar are not yet fully understood. Here, biochar's disintegration, transport, and the effect of temperature on ...biochar transport in soil (purple soil)-water systems were investigated. The results showed that the potentially transportable components (PTC) of biochar for corn straw, wheat straw, rice straw, rice husk and wood biochar reached 6.22–7.60%, 5.96–12.29%, 11.77–12.45%, 5.34–6.26% and 5.08–6.14% by mass, respectively. An external force (ultrasound exposure) intensified the physical disintegration, including colloidal and nanoparticles from larger particles, thereby increasing the transport potential. The mass recovery rates of PTC for rice straw biochar after penetrating through soil at 5, 20 and 35 °C reached 44.25%, 32.97% and 10.98%, respectively, which was supported by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory results. Elevated temperatures increased the hydrodynamic average diameter of PTC, and the Zeta potential of PTC and soil at 35 °C were less negative than those at 5 and 20 °C. As a result, biochar's transportability decreases with increasing temperature in the soil-water system, during which the enhanced PTC aggregation and the decreased electrostatic repulsion between biochar and soil particles played a crucial role. The increase in electrical conductivity in the soil-water system may be the main reason for the decrease in electrostatic repulsion at higher temperatures. The findings are helpful for an in-depth understanding of the environmental fate and managing the transport risk of biochar.
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•Biochar disintegration and transport in soil-water environment was evaluated.•Biochar showed transport potential due to its disintegration.•External forces intensified biochar disintegration.•Biochar transport in the soil-water system is reduced at higher temperatures.•Particle aggregation and reduced electrostatic repulsion inhibit biochar transport.
CuCr alloys with high contact performance for medium and high voltage vacuum circuit breakers are becoming increasingly urgent. In this work, WC/CuCr30 composites were prepared by SPS process, and ...nanometer-sized precipitated Cr phases were obtained by subsequent heat treatment. The microstructure and arc erosion behavior were investigated. The results show that nano-Cr phase precipitated in copper matrix can effectively improve the interfacial bonding strength between the Cu matrix and WC particles, and part of the precipitated nano-Cr phase is combined with the C element in WC to form nano-Cr23C6. Both nanophases can improve the resistance to dislocation and sub-grain boundary movement in the deformation process of WC/CuCr30 composite, thus improving the hardness of the copper matrix with a slight decrease in electrical conductivity. The results of electrical contact show that the addition of WC particles and nano-Cr precipitates can not only extend contact life of CuCr material, but also help to disperse the arc to avoid concentrated erosion. The presence of Cr23C6 phase around WC particles effectively improves the interfacial bonding between Cu phase and WC phase and reduces the probability of pore existence at the interface, which is beneficial to vacuum breaking performance.
•The WC/CuCr30 composites were prepared by SPS, and the precipitated nanometer Cr phases were obtained by heat treatment of solid solution and aging.•Nano-Cr phase precipitated in copper matrix can effectively improve the interfacial bonding strength between the Cu matrix and WC particles, and part of the nano-Cr phase is combined with the C element in WC to form nano-Cr23C6.•The addition of WC particles and nano-Cr precipitates can not only extend contact life of CuCr material, but also help to disperse the arc.
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•Modified zeolites that enable O2 loading and N and P adsorption was developed.•Application of the LOZ totally reversed N and P releasing from the sediment.•LOZ addition triggered ...adsorption and immobilization of internal P.•LOZ addition enhanced adsorption and biological approach towards N removal.•The O2 delivery generates anaerobic and aerobic environment across the sediment.
Nutrients released from lake sediments contribute to the total nutrient load of an aquatic ecosystem. In this study, we used the oxygen-loaded lanthanum modified zeolites (LOZ) for absorbing internal phosphorus (P) and nitrogen (N) meanwhile with potential to trigger biological transformation of the nutrients. The results showed that the lanthanum modification of the zeolites manifested both the P and N adsorption in comparison to the pristine zeolites (enhanced by 129.13 % for PO43−-P and 27.53% for NH4+−N, respectively). In addition, lanthanum modified zeolites also exhibited the excellent oxygen-loading capability (0.73 mmol/g) than the pristine one. Apart from the blocking of P and N, the LOZ application over surface sediment substantially improved the benthic and aquatic DO level as the DO concentration in overlying water was 3–5 mg/L and diffused to 12 mm depth of sediment. The increased oxygen level in sediment favored the phosphate and Fe oxy(hydr)oxides combination and reduced FeS formation with subsequent decline in PO43−-P release from sediments. The improvement of water DO level also induced the microbial community shifts and promoted the abundance of nitrifiers in the surface sediment while denitrifiers in the deeper layer. Consequently, the release of total phosphorus and total nitrogen from the sediment to overlying water was reduced by 80% and 92%, respectively. Thus, the application of LOZ to sediment was beneficial to not only the anaerobic and aerobic processes that involved in nitrogen removal, but also the inactivation of phosphate. The study delivered positive outcomes regarding the control of internal nutrients release with a quick, efficient and sustainable remediation approach to rehabilitate polluted water systems.
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