The presence of sulfate-reducing bacteria (SRB) can reduce the bioavailability of toxic metal ions (e.g., Ag+) to plants via mediating the formation of metal sulfide precipitates; it remains largely elusive if SRB can also affect the phytouptake of metal nanoparticles (e.g., Ag0-NPs) however. In the current study, the bioavailability of Ag0-NPs to a model wetland plant, Scirpus triqueter, was investigated in the presence/absence of SRB. Comparative experiments were conducted using 0.01-10 mg/L Ag0-NPs and silver ions. In addition to quantifying the total dissolved Ag concentrations, we analyzed the average sizes and particle concentrations of Ag-containing NPs (Ag-NPs) in plant tissues, including both roots and stems, after the designated treatments. The results show that although the presence of SRB can reduce the uptake of total Ag by 37% during the exposure of the plant to Ag ions, it can significantly enhance the uptake of total Ag during exposure of the plant to Ag0-NPs, likely by transforming Ag0-NPs into Ag-sulfide NPs with smaller particle sizes. Transmission electron microscopy data revealed that biogenic secondary Ag-sulfide particles smaller than 10 nm in size form in the vicinity of pristine Ag0-NPs. These NPs are likely generated from the parent Ag0-NPs via a dissolution-diffusion-sulfidation process. Moreover, the phytouptake of Ag0-NPs of various sizes (i.e., 20, 40 and 80 nm) in the presence/absence of SRB also confirmed a size-dependent pattern, with more silver identified in the plants in exposure to smaller Ag-NPs. The combined results suggest that the enhanced bioavailability of Ag-NPs to Scirpus triqueter in the presence of SRB is mainly attributed to the formation of secondary biogenic NPs with minute size. This result points to the importance of the complex, coupled interactions between aqueous solutions, bacteria, plants, and labile NPs.

Capacitive deionization (CDI) is a forward-looking technology that removes ions from brine due to its low energy consumption, low cost and prevention of secondary pollution. Removal capacity is still an issue for the CDI technology. It is quite urgent to design high performance CDI electrode material with reasonable porous structure, excellent conductivity and hydrophilic surface. Herein, we originally designed nitrogen-doped rod-like porous carbon derived from dual-ligand metal-organic frameworks (MOFs), in which two ligands, namely 1, 4-benzenedicarbocylic acid and triethylenediamine, to coordinate with zinc (Zn), respectively. The 1, 4-benzenedicarbocylic acid can be used as a pore-forming agent to increase the specific surface area of carbon material, and the triethylenediamine is used as nitrogen doping source to increase the hydrophilicity and conductivity of carbon material. By adjusting the ratio of two ligands, the optimal specific surface area and nitrogen doping for carbon material is obtained, thereby achieving the highest removal capacity for capacitive deionization of brine. The obtained carbon materials possess a hierarchical porous structure with moderate nitrogen doping. The large specific surface area of the electrode materials delivers many adsorption sites for adsorption of salt ions. The hierarchically porous structure provides a rapid transport channel of salt ions, and high-level N doping enhances conductivity and hydrophilicity for carbon materials to some extent. More importantly, the salt removal capacity of the electrodes is as high as 24.17 mg g-1 at 1.2 V in 500 mg L-1 NaCl aqueous solution. Hence, the moderate nitrogen doping porous carbon materials derived from dual-ligand MOFs is potential electrode material for CDI application. Such results open up a new method for preparation high performance electrodes to remove ions from saline water.

Effective removal of toxic mercury (II) from aqueous media is a primary challenge for public health and environmental protection. In this work, dendritic mesoporous silica nanoparticles modified with thiol moieties (denoted as TDMSNs) are used as nanoadsorbents to trap mercury (II) ions. It is demonstrated that the exceptionally high density and accessibility of thiol moieties are both necessary to achieve efficient mercury (II) decontamination. TDMSNs with the highest surface thiol group density of 283.2 μmol g-1 exhibit a Hg (II) adsorption capacity of 1502.4 mg g-1, outperforming reported thiolated adsorbents. The large and well-exposed mesopores of TDMSNs enable a fast adsorption kinetics within 5 min to reduce the mercury (II) concentration from 10 ppm to below 2 ppb (US Environmental Protection Agency acceptable limit) which is faster than previous reports. Furthermore, TDMSNs show adsorption stability in a wide range of pH and promising reusability performance (89% adsorption capacity maintenance after 5 reuses). Our contribution paves the way for the rational design of nanoadsorbents for efficient environmental pollutant remediation.

Adsorption of heavy metals by natural polymeric composites has attracted extensive attention due to their abundance, low cost, and eco-friendliness, but these composites tend to have low adsorption capacity, long response time and poor selectivity. Therefore, it is critically desired to develop an ecofriendly adsorbent that can remove heavy metal ions efficiently and quickly from aqueous solution. Here, a novel polyethyleneimine functionalized chitosan-lignin (PEI-CS-L) composite sponge adsorbent with nanowall-network structures is synthesized by cross-linking and lyophilization. Notably, the as-prepared adsorbent could remove Hg(II) ions selectively from aqueous solution with high efficiency at a very quick response time, reaching > 83.5% of the ultimate adsorption within just 1 min. This is attributed to the evenly interconnected porous structure of composite sponge with nanoscale-wall structures which increase the distribution of functional groups, and leading to the quick complexation of heavy metal ions with surface functional groups. It is worth noting that PEI-CS-L sponge has excellent reusability, and the adsorption capacity only decreased by 4.09% after 5 cycles of adsorption and desorption. Considering its eco-friendliness, high efficiency and low cost, the developed PEI-CS-L sponge holds great promise in removing Hg(II) ions from wastewater.

We successfully prepared a ternary Z-scheme photocatalyst, g-C3N4/Au/ZnIn2S4 (CN/Au/ZIS), for visible-light-driven NO removal and CO2 reduction by selecting Au NPs as the electron transfer mediator. The prepared photocatalysts demonstrated enhanced light absorption and a high surface area, which significantly improved the photocatalytic efficiency. The optimized CN/Au/ZIS photocatalyst achieved the highest NO removal efficiency of 59.7% and an excellent CO production rate of 242.3 μmol h−1 g−1 with a high selectivity of 94.1%, which were higher than those for pure g-C3N4 and ZnIn2S4. The improved photocatalytic activity could be ascribed to the Au NPs, which acted as an electron transfer mediator and enhanced the separation efficiency of the photogenerated electron–hole pairs. Additionally, the Z-scheme heterostructure affords the photocatalysts with a strong redox ability during the catalytic process. Finally, a possible Z-scheme mechanism for the CN/Au/ZIS photocatalytic system is detailed. This work sheds light on the design of high performance Z-scheme photocatalysts to advance photocatalytic redox capability.

Previous work has shown that spherical CuO nanomaterials show negative effects on cell and animal physiology. The biological effects of Cu2O materials, which posess unique chemical features compared to CuO nanomaterials and can be synthesized in a similarly large variety of shapes and sizes, are comparatively less studied. Here, we synthesized truncated octahedral Cu2O particles and characterized their structure, stability, and physiological effects in the nematode worm animal model, Caenorhabditis elegans. Cu2O particles were found to be generally stable in aqueous media, although the particles did show signs of oxidation and leaching of Cu2+ within hours in worm growth media. The particles were found to be especially sensitive to inorganic phosphate (PO43-) found in standard NGM nematode growth medium. Cu2O particles were observed being taken up into the nematode pharynx and detected in the lumen of the gut. Toxicity experiments revealed that treatment with Cu2O particles caused a significant reduction in animal size and lifespan. These toxic effects resembled treatment with Cu2+, but measurements of Cu leaching, worm size, and long-term behavior experiments show the particles are more toxic than expected from Cu ion leaching alone. These results suggest worm ingestion of intact Cu2O particles enhances their toxicity and behavior effects while particle exposure to environmental phosphate precipitates leached Cu2+ into biounavailable phosphate salts. Interestingly, the worms showed an acute avoidance of bacterial food with Cu2O particles, suggesting that animals can detect chemical features of the particles and/or their breakdown products and actively avoid areas with them. These results will help to understand how specific, chemically-defined particles proposed for use in polluted soil and wastewater remediation affect animal toxicity and behaviors in their natural environment.

Development of high-efficiency photocatalysts for photocatalysis research has been a hotspot in recent years. Herein, the phosphate-based MOF/P-TiO2 hybrid composites (MOFx/P-TiO2) were first synthesized by phosphonate-based MOF [Cd(H2L)]n (H4L = 2,5-dimethylbenzene-1,4-diylbis(methylene) diphosphonic acid) and phosphated mesoporous TiO2 beads (P-TiO2) using a versatile step-by-step self-assembly strategy for the environment remediation. Results showed that the Cd-MOF loading content in the MOFx/P-TiO2 displays important influence on the pollutants degradation, and the hybrid materials could significantly enhance photocatalytic activity for the photo-oxidative degradation of RhB (97.6% in 25 min over MOF1.5/P-TiO2) and reduction of Cr(VI) (96.1% in 60 min over MOF0.5/P-TiO2) in comparison with the single-component Cd-MOF or P-TiO2. The enhancement of photocatalytic activity of MOFx/P-TiO2 could be mainly attributed to (i) strong light absorption capacity, and (ii) effective photogenerated charge separation and transfer through the coupled heterojunction interfaces of P-TiO2 and Cd-MOF. What's more, the results verified that matched band structure of P-TiO2 and Cd-MOF could induce a superfast Z-scheme interfacial charge transfer path. Therefore, a reasonable Z-scheme charge transfer mechanism was proposed based on the active species trapping experiments and ESR. More importantly, MOF0.5/P-TiO2 and MOF1.0/P-TiO2 possess good stability and reusability after recycling 5 times due to the high chemical stability of the Cd-MOF, P-TiO2 and heterojunctions. The present work provides a promising approach to construct the direct Z-scheme porous heterojunctions for elimination of environmental pollutants.

Nano-scale zero-valent iron (nZVI) is highly-attractive material that is widely studied and used for pollution abatement, and thus it is one of the most abundant types of engineered nanoparticles introduced into the environment. Nevertheless, there is still a lack of information about the extent of nZVI migration and fate in real groundwater conditions and associated environmental impact and risks related to its introduction into the groundwater/soil. The present paper proposes a new analytical approach based on a multi-elemental signatures (ICP-MS analyses of trace elements in particular nZVI type and soil/groundwater samples) enabling easy tracing of nZVI and their transformation products, as well as their distinguishing from background colloids. A multi-elemental signatures approach was verified under laboratory conditions (in a large-scale sand-filled tank) and subsequently verified at three contaminated sites remediated with nZVI. Multivariate data analysis on 39 elements, such as principle component analysis (PCA), demonstrates that the method can be used to observe changes in signatures over time and it enabled us to confirm the presence of nZVI in monitoring wells. PCA analysis indicated that lanthanides are particularly suitable for tracing nZVI particles.

Carbon-based materials have been used in water engineering to provide more effective and efficient methods to deliver clean water. Recent research efforts have focused on the implementation of nanoarchitectured carbon molecular sieves in membranes. In this study, a hierarchical carbon membrane (HCM), fully-constituted by elemental carbon structures from the carbon fiber mechanical support to the graphene oxide selective layer, was fabricated. The assembled HCM were characterized by a combination of surface science tools, capillary flow porometry, thermogravimetric analysis, and membrane performance evaluation. The HCM were resistant to harsh cleaning by hypochlorite solutions and annealing cycles (similar to ceramic membranes). The HCM permeability and rejection performance were evaluated in a cross-flow setup and indicate the membrane operates in the nanofiltration regime, with 85% rejection of sulfate ions and 1.3 LMH-bar permeability. In summary, the results here support the emerging research direction of hierarchal fully elemental carbon membrane materials to enhance the membrane technology toolbox for sustainable water resource reuse and wastewater reclamation.

Carbon nanodots (CDs), as a kind of fluorescent nanomaterials, have attracted widespread attention for biomedical application. Since different cells possess different membrane potential, the influence of trans-membrane potential on the adsorption behaviour is required to be explored extensively. It is found that less amount of CDs can be adsorbed by depolarized cells with decreased membrane potential while hyperpolarized cells with enhanced membrane potential promoted the adsorption of CDs. Similar adsorption trend is observed for two cell lines, namely NIH3T3 and MCF-7. Since phosphocholine is the primary component of the cellular membrane, the adsorption behaviour of CDs is further complemented with the interactions between CDs and three kinds of liposome with different surface charge via the thermodynamic and kinetic perspective. The adsorption constants between negative charged CDs and liposome are positive related with their membrane potential, which is similar to the adsorption rate constants. It was further found that adsorption of CDs onto liposome is initiated by electrostatic attraction forces. Finally, the membrane integrity and fluidity of liposome exposed to CDs have also been characterized. So the membrane potential of cells is especially important, when prediciting the relative cytotoxicity of CDs and developing CDs based nanomaterial for biomedical application.

Metallic oxide nanoparticles (NPs) have received great importance due to their unique properties and valuable applications in various fields. The release of nanoparticles into the environment at large scale has become serious threat to ecosystem specially the plants. Various reports have illustrated the toxicity of CuO NPs on plants, but the hypothesis underlying ethylene mediated CuO NPs toxicity is still unknown. The present study was conducted to investigate the response of ethylene insensitive mutants (ein2-1, ein4 and etr1-3) and WT under CuO NPs exposure. The results of present study showed that CuO NPs adversely affected the biomass, chlorophyll contents, guard cells, stomatal aperture and other cell organelles, with consequent decline in plant biomass. Moreover, CuO NPs significantly increased the ROS accumulation, and induced toxicity in leaves of all four genotypes. However, ethylene insensitive mutants markedly showed less sensitivity to this damage as compared to WT seedlings. More importantly, higher level of CuO NPs significantly increased the activity of ethylene reporter EBS::GUS lines and transcript level of ethylene signaling and biosynthesis genes. Furthermore, the expression levels of antioxidant enzymes related genes were slightly enhanced by exogenous application of ethylene biosynthesis and perception antagonist cobalt (Co2+) and silver (Ag+) respectively than the treatment with CuO NPs stress alone. In contrary, it is significantly suppressed by ethylene biosynthesis precursor (ACC), which further provided the evidence that ethylene participates in CuO NPs induced oxidative damage and growth reduction in Arabidopsis thaliana leaves.

Designing novel nanostructured materials is very significant to enhance the desalination capacity enabled by capacitive deionization (CDI). In this work, the vertical-aligned CuAl-layered double oxide grown on reduced graphene oxide (CuAl-LDO/rGO) is proposed as high-performance anode for hybrid CDI (HCDI). It is found that the morphology of CuAl-LDO is ultimately dependent on the loading mass of urea. As a result, the optimized CuAl-LDO/rGO exhibits relatively high specific surface area, 3D porous structure and electrochemical behavior. When employed as anode for HCDI, it demonstrated high salt removal capacity of 64.0 mg/g at cell voltage of 1.2 V in NaCl solution with an initial concentration of 1000 mg/L. After 20 cycles, the capacity still remains at 58.0 mg/g which is ～90% of initial value, suggesting the superior cycling ability. Moreover, the phase transformation of CuAl-LDO/rGO at various stages indicates that the formation of Cu(OH,Cl)2•2H2O may responsible for the capacity decay upon the cycling. However, the morphology characterization realizes that the aggregation of Cu(OH,Cl)2•2H2O nanoparticles can be effectively inhibited within CuAl-LDO/rGO by compared to that of random oriented CuAl-LDO nanoflakes, which is accounted for superior salt removal capacity retention. Besides, a comparison is performed on HCDI performance among different anodes, highlighting the advances of CuAl-LDO/rGO. It is attributed to the unique structure of CuAl-LDO/rGO which is beneficial to provide as much as tunnels for diffusion of salty ions and active sites for intercalation.

Droplet-based microfluidics is used to fabricate thin shell hydrogel microcapsules for the removal of methylene blue (MB) from aqueous solutions. The microcapsules composed of a poly(methacrylic acid) hydrogel shell exhibit unique properties, including permeation, separation, purification, and reaction of molecular species. Photocatalytic TiO2 and ZnO nanoparticles encapsulated in the microcapsules, i.e. photocatalyst in capsule (PIC), are used to remove organic pollutants using an adsorption-oxidation mechanism. A prototype flow microreactor is assembled to demonstrate a controllable water purification approach in short time using photocatalysts. Our studies of aqueous and homogeneous hydrogel environments for the photocatalysts provide important insights into understanding the effectiveness of MB removal. Hydrogel capsules have MB removal rate comparable to homogeneous particles. Further reduction of both capsule and photocatalyst sizes can potentially aid in quicker water purification.

The widespread application of TiO2 NPs will lead to their increasing release into the aquatic environment and thus influence the ecosystem function of aquatic life. As a microbial community, responses of periphytic biofilm to toxicity of TiO2 NPs are largely unknown, in particular with respect to dynamic shifts of community structure and microbial functions of periphytic biofilms. Therefore, this study investigated the relationship between microbial functions and community composition of periphytic biofilms after chronic exposure (21 days) to 50 μg/L and 500 μg/L of TiO2 NPs. The increase of DOC in surface water was inhibited during the first 11 days (49.55%) by 500 μg/L of TiO2 NPs and then recovered. Distinct responses were observed between community structure and microbial functions of biofilms after exposure to TiO2 NPs. Specifically, both 50 μg/L and 500 μg/L of TiO2 NPs promoted the growth of microalgae (78.85-134.86%) and altered the bacterial community composition at day 7, and these trends lasted at day 21. In terms of the microbial functions determined using BiologTM ECO Microplates, biofilms maintained their total carbon metabolic activities under the stress of 50 μg/L of TiO2 NPs. However, the carbon metabolic activities were significantly inhibited (24.63%) by the exposure to 500 μg/L of TiO2 NPs at day 7 and then recovered to the control level at day 21. Although inhibition still existed in metabolic activity for carbohydrate (17.00%) after long-term exposure, periphytic biofilms exhibited resistance to TiO2 NPs and continuous decrease in nanotoxicity was observed.

The effects of model proteins (OVA: ovalbumin, and BSA: bovine serum albumin) on the colloidal stability of graphene oxide (GO) with different lateral sizes (around 1000, 500, 350 and 200 nm, respectively) were investigated. At low salt concentrations, aggregation rate (k) of GO displayed a parabolic relationship: increased until kfast (regime I), maintained at kfast (regime II), and then decreased gradually to zero (regime III), with the protein concentrations increasing at environmental pH (4, 6 and 9). Compared to BSA, much higher concentrations of OVA were needed to achieve similar effects on GO stability induced by BSA, since OVA has smaller molecular size and fewer positively charged groups. In regime I, k of the GO increased with the lateral size increasing at the same concentration of proteins, and higher dosage of proteins was needed to drive k to kfast for smaller sized GO. However, there was not such lateral size dependent effect in regime III, which was attributed to the predominance of steric repulsion caused by the large amount of proteins. In regime I, the GO displayed higher stability at higher pH, and thus more proteins were required to drive the k to kfast. In regime III, the proteins were more effective to stabilize GO at higher pH conditions due to the enhanced electrostatic and steric repulsion. This study highlights the crucial effects of GO lateral size, protein properties and concentrations, as well as solution chemistry on GO stability in aquatic environment.

Moist CO2-bearing air flowing in terrestrial environments of Earth’s, and now warming, cryosphere can be captured by thin nanometric water films supported by mineral nanoparticles. Molecular-level mechanisms driving the fate of CO2 by these water films at 25, -10 and -50 °C were resolved by vibration spectroscopy of mineral nanoparticles of well-known crystal habits and surface structures. This work shows that mineral-supported water films cooled below the freezing point of water do not freeze to ice and host hydrated carbonate species of comparable properties to those formed at 25 °C. CO2 uptake by water films is driven by nucleophilic attack of surface hydroxo groups. Conversion to carbonate species is, in turn, stabilised by hydrogen bonding with neighboring hydroxo groups and water molecules. The lower CO2 uptake under extremely cold conditions (-50 °C) is, as such, explained by the reduced mobility of water needed to hydrate carbonate ions. However, carbonate species were initially entrapped by cooling of warmer films to -50 °C are nonetheless resilient to outgassing, even under vacuum. This implies that CO2 initially entrapped by cooling of warm CO2-bearing water can have prolonged lifetimes under extremely cold conditions. Our findings shine new light on how nanominerals and the nanofilms they host alter the fate of CO2 in cold terrestrial environments under Earth’s changing climate. This chemistry is even strongly relevant to nanominerals in Earth’s atmosphere and on planet Mars.