Showing papers in "Environmental science. Nano in 2020"

Recent advances in the design of colorimetric sensors for environmental monitoring

Abstract: Colorimetric sensors and biosensors exhibit promising potential toward the detection of metallic cations, anions, organic dyes, drugs, pesticides and other toxic pollutants due to their easy fabrication, quick detection, and high sensitivity and selectivity, as well as easy naked-eye sensing In this work, we present the recent advances (since 2014) made in the fabrication of colorimetric sensors for the environmental monitoring of toxic pollutants To understand the relationships between the type, structure, and functions of nanomaterials as building units and the sensing performance of the designed colorimetric sensors, the fabrication of several sensor platforms based on functional nanomaterials (such as metal nanoparticles, metal oxides, quantum dots, two-dimensional nanozymes, organic probes, and Schiff bases) are demonstrated and discussed The sensing mechanisms of the considered colorimetric sensors based on the aggregation of nanoparticles, decomposition of nanoparticles, nanozymes, fluorescence on–off, ligand–receptor interactions, and photonic structures are introduced and discussed in detail In addition, instrument-based colorimetric sensors and advanced colorimetric sensor products for high-performance environmental monitoring are presented Finally, the advantages and disadvantages of various colorimetric sensors in environmental monitoring are analyzed and compared It is expected that this work will be valuable for readers to understand the fabrication and sensing mechanisms of various colorimetric biosensors and promote their development in environmental science, materials science, nanotechnology, food science, and bioanalysis

Nitrogen-doped carbon nanotubes encapsulating Fe/Zn nanoparticles as a persulfate activator for sulfamethoxazole degradation: role of encapsulated bimetallic nanoparticles and nonradical reaction

Abstract: In this work, the carbon nanotubes (CNTs) encapsulating Zn and Fe bimetallic nanoparticles (FeZn@NC) were synthesized through a one-pot pyrolytic strategy. The persulfate (PS) activation ability of FeZn@NC with various ratios of Fe and Zn was determined by sulfamethoxazole (SMX) degradation. The results indicated that the iron played a key role in forming external CNTs and the catalytic activity of FeZn@NC was mainly based on the encapsulated FeZn nanoparticles. In addition, PS activation was greatly strengthened by the heterostructure of FeZn@NC. Free radical quenching experiments and electron paramagnetic resonance (EPR) spectra suggested that the singlet oxygen was the key reactive oxygen species for SMX degradation. The activity of pyridinic-N, pyrrolic-N and graphitic-N on external CNTs was analyzed by theoretical calculations, which showed the pyridinic-N possessed strong adsorptive ability to activate PS to degenerate sulfate radicals.

Nanoplastics as a potential environmental health factor: effects of polystyrene nanoparticles on human intestinal epithelial Caco-2 cells

Abstract: The ubiquitous and increasing presence of micro-/nanoplastics (MNPLs) in our environment demands an urgent hazard assessment, in order to determine the potential risk they pose to human beings. Given the scarce information found in the literature regarding MNPL's effects over human cells, the aim of our work is to evaluate MNPL's ability to penetrate the cells, and their potential toxic/genotoxic effects. To this aim, we used polystyrene MNPLs, as they are a widespread model of synthetic polymer, using nanoparticles with (y-nPS) or without (nPS) a fluorescent label. The human colon adenocarcinoma Caco-2 cell line was used as the cellular target, as ingestion is one of the main entry routes of MNPLs. Different endpoints were analyzed as indicators of nanotoxicity, including cytotoxicity, ROS increase, genotoxicity, DNA oxidative damage and increase in the expression of stress-related genes.

Nanoplastic ingestion induces behavioral disorders in terrestrial snails: trophic transfer effects via vascular plants

Abstract: This study investigated the transfer of plastic debris in a terrestrial environment from the soil to a plant (the mung bean, Vigna radiata), and then to a consumer (the African giant snail, Achatina fulica). Adverse effects of these plastic pollutants on the physiology of the plant and animal were investigated. The mung bean plants were directly exposed to nanoplastics (NPs) by adding NPs to the soil for 10 days. The snails were indirectly exposed by feeding them for 14 days the leaves of mung bean plants that had internalized NPs. We found that NPs decreased their root growth (82.9 and 83.3% of control growth at low and high concentrations, respectively) and led to particle accumulation in the leaves of the mung bean plants. Meanwhile, the growth rate (77.1 and 62.0% of the control rate at low and high concentrations, respectively) and feeding and foraging speeds (63.4 and 54.0% of control speeds at low and high concentrations, respectively) of the snails were decreased by dietary NP intake. This was associated with decreased gut microbiota viability and histological damage to the digestive organ tissues of the snails. Thus, NPs negatively affect the growth of plants and the animals that consume them in terrestrial ecosystems, which could have adverse effects at higher trophic levels.

Polystyrene nano- and microplastic accumulation at Arabidopsis and wheat root cap cells, but no evidence for uptake into roots

Abstract: Association of plastic particles with plant roots could represent a pathway for human consumption of plastic and plastic-associated organic contaminants. Here, we investigated the uptake of spherical, negatively-charged, polystyrene nano- and microparticles by plant roots. We used negatively-charged, 40 nm and 1 μm fluorescently-labeled polystyrene spheres and two plant species: Arabidopsis (Arabidopsis thaliana) and wheat (Triticum aestivum). Plants were grown from seeds to 5 days for wheat and 12 days for Arabidopsis, in agar growth media containing plastic spheres (0.029 g L−1), and plant uptake of spheres was investigated by laser scanning confocal microscopy and pyrolysis gas chromatography-mass spectrometry (GC-MS). The confocal images of both plant species showed no evidence for active uptake of nano- and microsized polystyrene spheres during plant growth up to the 1 to 2 leaf growth stage. Pyrolysis GC-MS was unsuccessful because of the occurrence of natural styrene monomers in plant roots and insufficient detection limits. Both 40 nm and 1 μm polystyrene spheres accumulated at the root surface of each species, particularly at the root tip, and were still found attached to the root surface after washing. However, there was no evidence of plastic particles in the internal root structure. Our results demonstrate the association and accumulation of plastics at root surface and cap cells.

Silica nanoparticles inhibit arsenic uptake into rice suspension cells via improving pectin synthesis and the mechanical force of the cell wall

Abstract: Our previous studies indicated that the foliar application of silica nanoparticles (SiO2 NPs) could obviously reduce arsenic (As) accumulation in rice. However, the mechanism underlying this effect at the single-cell level has not been reported. In this study, we investigated for the first time the effects of SiO2 NPs on inhibiting As uptake into rice using individual rice cells. The results indicated that the addition of SiO2 NPs could enhance the proportion of live cells by weakening oxidative stress upon As exposure. Compared to the treatment of cells with As only, treatment with SiO2 NPs could maintain the integrity of the cell, increase the thickness of the cell wall (77.4%) and the ratio of As in the pectin (19.6%). In addition, the pectin content, cation exchange capacity (CEC) and pectin methylesterase (PME) activity were also increased in the SiO2 NPs-pretreated cells, leading to a decreased degree of pectin methylesterification and an improved mechanical force of the cell walls. Furthermore, in the SiO2 NPs-pretreated rice cells, the expression of the OsLis1 and OsLis2 genes was lower, whereas the expression of the OsNIP1;1 and OsNIP3;3 genes was higher than that of the As-only group. This finding provides new insights into the mechanism of how the addition of SiO2 NPs inhibits As uptake into rice at the single-cell level and lays the foundation for its application in As-contaminated paddy soil.

The fabrication of 3D hierarchical flower-like δ-MnO2@COF nanocomposites for the efficient and ultra-fast removal of UO22+ ions from aqueous solution

Abstract: Herein, interpenetrating 3D flower-like δ-MnO2@TpPa-1 composites were suitably constructed though the integration of δ-crystal manganese dioxide (δ-MnO2) nano-flowers with a covalent organic framework (COF, TpPa-1) via adopting a simple ultrasonication process. The physicochemical properties of δ-MnO2@TpPa-1 were characterized via SEM, TEM-EDX, XRD, FT-IR, pHpzc, XPS, and N2 adsorption–desorption studies. The kinetics of UO22+-ion adsorption onto δ-MnO2 and δ-MnO2@TpPa-1 confirmed the existence of a pseudo-second-order model. The results of isothermal experiments showed that the Langmuir model provided a better fit, illustrating a spontaneous, endothermic, and monolayer chemisorption process for UO22+ ions onto δ-MnO2 and δ-MnO2@TpPa-1. The maximum adsorption levels of UO22+ ions onto δ-MnO2 and δ-MnO2@TpPa-1 were 499.41 mg g−1 and 1147.773 mg g−1, respectively, at pH 6.5 and 298 K, owing to electrostatic attraction and inner-sphere surface complexation. Oxygen-containing groups played essential roles in the formation of U–O bonds and covalent Mn–O–U bonds, making δ-MnO2@TpPa-1 an excellent adsorbent for radionuclide elimination from solution.

Emerging investigator series: molecular mechanisms of plant salinity stress tolerance improvement by seed priming with cerium oxide nanoparticles

Abstract: Engineered nanomaterials interfaced with plant seeds can improve stress tolerance during the vulnerable seedling stage Herein, we investigated how priming seeds with antioxidant poly(acrylic acid)-coated cerium oxide nanoparticles (PNC) impacts cotton (Gossypium hirsutum L) seedling morphological, physiological, biochemical, and transcriptomic traits under salinity stress Seeds primed with 500 mg L−1 PNC in water (24 h) and germinated under salinity stress (200 mM NaCl) retained nanoparticles in the seed coat inner tegmen, cotyledon, and root apical meristem Seed priming with PNC significantly (P < 005) increased seedling root length (56%), fresh weight (41%), and dry weight (38%), modified root anatomical structure, and increased root vitality (114%) under salt stress compared with controls (water) PNC seed priming led to a decrease in reactive oxygen species (ROS) accumulation in seedling roots (46%) and alleviated root morphological and physiological changes induced by salinity stress Roots from exposed seeds exhibited similar Na content, significantly decreased K (6%), greater Ca (22%) and Mg content (60%) compared to controls A total of 4779 root transcripts were differentially expressed by PNC seed priming alone relative to controls with no nanoparticles under non-saline conditions Under salinity stress, differentially expressed genes (DEGs) in PNC seed priming treatments relative to non-nanoparticle controls were associated with ROS pathways (13) and ion homeostasis (10), indicating that ROS and conserved Ca2+ plant signaling pathways likely play pivotal roles in PNC-induced improvement of salinity tolerance These results provide potential unifying molecular mechanisms of nanoparticle-seed priming enhancement of plant salinity tolerance

Applications of nanozymes in the environment

Abstract: Nanozymes are inorganic nanoparticles that mimic the enzyme-like properties in redox reactions, processing both unique properties of nanomaterials and a catalytic function. Because of high catalytic activity, stability and multifunctionality, nanozyme are of increasingly wide interest in the fields of environmental science and technology. In this article, we review the most recent advances of nanozyme research for environmental pollutant detection and treatment. Nanozymes can be used to detect ions, molecules and organic compounds both qualitatively and quantitatively. They have also been applied for destruction multi-drug resistant bacteria and the degradation of various organic pollutants. Despite the apparent potential of nanozymes in environmental science and technology, current research and application is still limited, and so future challenges and research prospects have been highlighted.

Hierarchical Z-scheme g-C3N4/Au/ZnIn2S4 photocatalyst for highly enhanced visible-light photocatalytic nitric oxide removal and carbon dioxide conversion

Abstract: 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.

A review on graphene quantum dots and their nanocomposites: from laboratory synthesis towards agricultural and environmental applications

Abstract: Graphene quantum dots (GQDs) are 0D materials belonging to the carbon-based family that present some interesting characteristics of graphene combined with a tunable bandgap emerging from their reduced size, which gives them final outstanding physical–chemical properties. Furthermore, GQDs can be combined with other materials to produce nanocomposites with remarkable properties and superior performance. In this review, we present a timely survey on how the structural characteristics and physical–chemical properties of GQDs enable their use in advanced composite materials for agricultural and environmental applications. Specifically, emphasis is given to GQD-based composites in the form of films, nanofibers, aerogels, and molecularly imprinted polymers. The unique properties of GQD nanocomposites are suitable for designing devices employed in: i) filtration membranes and adsorbent materials for contaminant removal; ii) optical devices and (bio)sensors with different transduction modes for detecting hazardous analytes including pesticides, heavy metals, antibiotics, and food contaminants; iii) and novel catalyst systems for degrading pollutants. Finally, current challenges and future prospects on industrial applications of GQD-based composites are also discussed.

An MXene-based membrane for molecular separation

Abstract: Two-dimensional (2D) materials with a nanoscale thickness are promising candidates for advanced molecular separations. MXenes are cutting-edge 2D materials, which have been extensively explored and applied in high performance molecular separations. Due to their remarkable flexibility, hydrophilic surface, high mechanical strength, and good electrical conductivity, the MXene family of materials has unique advantages in a wide range of membrane-based separation processes, such as gas separation, pervaporation, desalination, and solvent/water separation. In this review, recent advances in the design of MXene-based membranes and their applications in molecular separations are highlighted. The current synthetic strategies and structures of MXenes are described; based on these, the key parameters that affect the MXene properties are identified. Then, the fabrication methods of MXene-based membranes and their ground-breaking separation applications are reviewed. Despite the remaining challenges, the vigorous development of MXene materials offers a new avenue for the design of novel membranes for precise and effective separation.

Nanosilicon-based recovery of barley (Hordeum vulgare) plants subjected to drought stress

Abstract: The present study explores the potential impact of silicon nanoparticles (Si NPs), in comparison with their bulk counterpart (silicate), on post-stress recovery performance of barley (Hordeum vulgare) seedlings under different drought stress intensities during vegetative growth. Barley plants were grown under 100% field capacity (FC), or mild (75% FC), moderate (50% FC) and severe (25% FC) drought stress levels, and were subsequently recovered by different treatments including soil application of 150 mL of Si NPs and silicate (at 125 and 250 mg Si L−1), and water. Si NPs application at 250 mg L−1 led to formation of Si NP aggregates in plant tissues, large pores in roots, and also rapid stomata closure in leaves. However, the lower Si NPs dose (125 mg Si L−1) was accompanied by a wider distribution of Si NPs in cells, and formation of a regular porosity pattern in roots i.e. more frequent pores of a smaller size. Upon recovery from all the drought stress levels, shoot biomass increased significantly in recovered plants compared to the respective non-recovered controls, and the maximum shoot biomass increase (27.3%) belonged to the moderate-stressed plants treated with Si NPs at 125 mg L−1. Exposure to Si NPs and silicate (at both doses) after all drought stress intensities caused a significant increase in total chlorophyll (up to 17.1%) and carotenoid (up to 24.1%) content of leaves except for the carotenoid content under severe drought stress. Post-drought recovery with Si NPs and silicate was linked to alterations in the plant osmolyte and metabolite profile, cellular injury and membrane stability indices, and the activity of antioxidant enzymes. Soil application of Si NPs (at a low dose of 125 mg Si L−1) showed a promising potential for post-drought recovery of barley plants via modifying plant morpho-physiological and antioxidative attributes and synthesis of specific metabolites.

Opportunities for nanotechnology to enhance electrochemical treatment of pollutants in potable water and industrial wastewater – a perspective

Abstract: Based upon an international workshop, this perspective evaluates how nano-scale pore structures and unique properties that emerge at nano- and sub-nano-size domains could improve the energy efficiency and selectivity of electroseparation or electrocatalytic processes for treating potable or waste waters An Eisenhower matrix prioritizes the urgency or impact of addressing potential barriers or opportunities There has been little optimization of electrochemical reactors to increase mass transport rates of pollutants to, from, and within electrode surfaces, which become important as nano-porous structures are engineered into electrodes A “trap-and-zap” strategy is discussed wherein nanostructures (pores, sieves, and crystal facets) are employed to allow localized concentration of target pollutants relative to background solutes (ie, localized pollutant trapping) The trapping is followed by localized production of tailored reactive oxygen species to selectively degrade the target pollutant (ie, localized zapping) Frequently overlooked in much of the electrode-material development literature, nano-scale structures touted to be highly “reactive” towards target pollutants may also be the most susceptible to material degradation (ie, aging) or fouling by mineral scales that form due to localized pH changes A need exists to study localized pH and electric-field related aging or fouling mechanisms and strategies to limit or reverse adverse outcomes from aging or fouling This perspective provides examples of the trends and identifies promising directions to advance nano-materials and engineering principles to exploit the growing need for near chemical-free, advanced oxidation/reduction or separation processes enabled through electrochemistry

Novel polyethyleneimine functionalized chitosan–lignin composite sponge with nanowall-network structures for fast and efficient removal of Hg(II) ions from aqueous solution

Abstract: 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 eco-friendly 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 an 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 the composite sponge with nanoscale-wall structures which increase the distribution of functional groups, leading to the fast complexation of heavy metal ions with surface functional groups. It is worth noting that the PEI-CS-L sponge has excellent reusability, and its 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 hold great promise in removing Hg(II) ions from wastewater.

Criteria of active sites in nonradical persulfate activation process from integrated experimental and theoretical investigations: boron–nitrogen-co-doped nanocarbon-mediated peroxydisulfate activation as an example

Abstract: Carbon-catalyzed persulfate activation is a metal-free advanced oxidation process for abating aqueous organic micropollutants. Recently, the electron-transfer mechanism in the activation of peroxydisulfate (PDS) has attracted tremendous interest due to its unknown nonradical reaction pathways. The conventionally used atomic-scale descriptors of adsorption energy (Eads), O–O bond length (lO–O) and S–O bond length (lS–O) cannot accurately reflect the ability of the functionalities of PDS in its activation. In this work, a new descriptor, local electrophilicity index (ω), which represents the oxidative capacity of adsorbed S2O82−, was included to identify the intrinsic active sites in carbocatalysts via density functional theory calculations. To verify the reliability of the proposed criteria, the catalytic performances of a series of highly boronated and nitrogenated carbon nanotube/nanosheet composites (BCN-NT/NS) with tailored physicochemical properties were comparatively studied for activating PDS to degrade phenol. By integrating the computational and experimental results, the catalytic activity of BCN-NT/NS was determined to not only be related to the contents of heteroatom dopants (B and N), but also the positions of B and N in the co-doping configurations. This study offers reliable criteria for determining the intrinsic catalytic sites in carbocatalysts for the activation of PDS based on an electron-transfer mechanism, which assists the rational design of nanocarbons as advanced catalysts for metal-free oxidation and water remediation.

Critical role of water stability in metal–organic frameworks and advanced modification strategies for the extension of their applicability

Abstract: Metal–organic frameworks (MOFs) are well known for their versatile applications in diverse fields (e.g., gas adsorption, water purification, sensing, drug delivery, and catalysis). The basic properties of most MOFs (e.g., morphology and structure) are, however, known to be affected sensitively if exposed to moisture/water. Consequently, it is necessary to conduct a comprehensive assessment on the stability of MOFs in relation to variables associated with such property changes (e.g., reduction in the surface area and structural collapse). In this article, factors and processes affecting the aqueous stability of diverse MOFs (e.g., imidazolate and carboxylate frameworks) are discussed. This article will thus help researchers properly assess the influence of water on the stability of MOFs so that suitable strategies can be established for the development of water-stable MOFs and for their efficient applications toward diverse fields (e.g., separation/storage of gases and adsorption/photocatalysis/sensing of pollutants in aqueous systems).

Nanostructured manganese oxides: natural/artificial formation and their induced catalysis for wastewater remediation

Abstract: Manganese oxides, with low toxicity and wide adaptability, have been demonstrated as promising catalysts for substituting noble metals/oxides in a diversity of chemical reactions. In environmental remediation, manganese oxides can catalyze peroxides to produce reactive oxygen species (ROS) in an aqueous phase for in situ chemical oxidation (ISCO) and advanced oxidation processes (AOPs). The manganese oxides stand out among the transition metal oxides due to their inherent dissimilarity in redox properties, crystal structure, and surface nano-architectures. In this paper, a comprehensive review is presented on the formation of nanostructured manganese oxides in nature (abiotic oxidation and biogenic evolution) as well as their artificial synthesis with rationally controlled tunnels and layers, crystal structures, exposed facet orientations, dimensional architecture and oxidation states. We further overview the applications of nanostructured manganese oxides in activation of various peroxides for catalytic oxidation to destroy organic contaminants during water purification. The roles of manganese oxides are emphasized in catalytic activation of hydrogen peroxide (H2O2), ozone (O3), and persulfates (peroxymonosulfate and peroxydisulfate). The mechanisms of the interactions between manganese oxides with the diverse peroxides and structure-dependent ROS production will be illustrated. The regulating rules of compositional alien-metal doping, formation of mixed metal oxides and hybrid materials are further discussed regarding the promoted catalytic activity. More importantly, both radical oxidation and nonradical pathways involved in manganese-based AOPs will be illustrated. Lastly, we will propose several prospects for future development of manganese oxides in practical applications.

UV-induced aggregation of polystyrene nanoplastics: effects of radicals, surface functional groups and electrolyte

Abstract: Aggregation behavior determines the fate and bioavailability of nanoparticles in aquatic environments. This study investigated the effect of UV irradiation and salts (NaCl, Na2SO4, CaCl2, and Na3PO4) on the aggregation of three polystyrene nanoparticles (PSNPs) with various surface functional groups. UV irradiation promoted the aggregation of pristine PSNPs in NaCl (>100 mM) and amino-modified PSNPs (PSNPs-NH2) in NaCl (≥100 mM) or Na2SO4 (≥100 mM) solutions. Under UV irradiation, hydroxyl radicals (˙OH) degraded the sulfate groups of PSNPs and amino groups of PSNPs-NH2 and decreased electrostatic repulsion forces among particles. Carboxyl-modified PSNPs (PSNPs-COOH) were relatively stable in NaCl and Na2SO4 solutions because of their high negative surface charge and hydrophilicity even after UV irradiation. Similarly, because the negative surface charge of PSNPs and PSNPs-NH2 in CaCl2 (1–50 mM) remained high under UV exposure, the strong electrostatic forces retarded the UV effect on the aggregation of PSNPs and PSNPs-NH2. However, UV irradiation accelerated PSNPs-COOH aggregation in CaCl2 (≥20 mM), probably because UV irradiation generated more carboxyl groups, which bind with Ca2+ and increase aggregation via a bridging effect. PO43− inhibited ˙OH photogeneration and stabilized the three types of PSNPs. Our study reveals the intriguing effects of light irradiation and salts on the aggregation behavior of emerging plastic nanoparticles in aquatic environments.

Nanobiochar: production, properties, and multifunctional applications

Abstract: Nanobiochar has received much attention recently among engineered biochar types owing to its useful chemical and physical properties. Research efforts have attempted to discover novel methods for nanobiochar preparation and applications. In this review, we summarize the literature on various aspects of nanobiochar preparation, production and use. Often, the bulk parent biochar is obtained from biomass pyrolysis, and mechanically ground using different milling processes to fabricate nanobiochar. Apart from mechanical means, direct fabrication of nanobiochar through flash heating resulting in graphitic nanosheets has been reported. Process conditions applied to the parent biochar directly influence the properties of the resulting nanobiochar. For instance, over 70% of 33 nanobiochar samples derived from biomass pyrolyzed above 450 °C demonstrated 32 times greater BET specific surface areas than nanobiochar produced at <450 °C. Nanobiochar has diverse applications, such as in wastewater treatment, health care applications, use as an electrode material, and in supercapacitors and sensors, owing to its wide range of physical and chemical properties. However, the toxicity of nanobiochar to human and ecosystem health has not received sufficient research attention. More research should be performed to elucidate the drawbacks, such as the high agglomeration potential and low yield, of nanobiochar for practical uses. Furthermore, reported data are insufficient to obtain a clear idea of the nature and behavior of nanobiochar, despite the growing interest in the research topic. Hence, future research should be driven towards exploring techniques to improve the yield of nanobiochar, reduce agglomeration, upscale it for electrode supercapacitor production and understand toxicological aspects.

Emerging investigator series: polymeric nanocarriers for agricultural applications: synthesis, characterization, and environmental and biological interactions

Abstract: Polymeric nanoparticles represent one major class of nanomaterials that has been proposed to improve the sustainability of agricultural operations by delivering organic agrochemicals such as pesticides more efficiently. Polymeric nanoparticles can improve efficiency through improved targeting and uptake, slow release, and lower losses of the chemicals, while also conferring the benefits of biodegradability and biocompatibility. This review provides a tutorial to environmental nanotechnology researchers interested in initiating research on the development and application of polymeric nanocarriers for delivery of agrochemicals, including pesticides and growth promoters for crops and antibiotics for livestock. In particular, this review covers the wider suite of methods that will be required beyond those typically used for inorganic metal or metal oxide nanoparticles, including synthesis of custom polymeric nanocarriers and characterization and tuning of agrochemical loading and release profiles. Benefits of polymeric nanocarriers are then discussed in terms of the physicochemical properties and fate and transport behaviors that contribute to higher efficiency and lesser environmental impacts compared to traditional (non-nano) formulations. Finally, opportunities for environmental nanotechnology researchers to collaborate with material scientists, microbiologists, and agricultural scientists to optimize the development of polymeric nanocarriers for agriculture are discussed.

Efficient removal of metal ions by capacitive deionization with straw waste derived graphitic porous carbon nanosheets

Abstract: Capacitive deionization (CDI) is considered to be an energy-efficient and cost-effective technology for ion removal from saline or waste water. However, its implementation remains challenging due to low ion adsorption capacity of the commonly used electrode materials. It is thus desirable to develop highly efficient CDI electrode materials for ion removal. Herein, graphitic porous carbon nanosheets (GPCSs) were originally prepared from straw waste via a combined activation and graphitization process. Being composed of graphitic carbon sheets with abundant pores in the framework, the obtained GPCSs had a large specific surface area and good conductivity and wettability, which can provide sufficient adsorption sites and promote efficient ion transport. The GPCS electrodes presented a higher specific capacitance, good stability and low inner resistance in electrochemical tests. Moreover, the GPCSs showed a high deionization capacity of 19.3 mg g−1 at 1.2 V in a 500 mg L−1 NaCl solution. Repeated adsorption–desorption experiments demonstrated the good regeneration performance of the GPCS electrodes. Furthermore, the removal efficiency towards Cd2+, Ni2+ and Cu2+ of the GPCS electrodes is 91.5%, 97.0% and 100% at 1.2 V in a 100 mg L−1 CdCl2 , NiCl2 or CuCl2 solution, respectively. This work offers a promising solution to efficient removal of ions from saline or waste water and a new route to the utilization of straw waste.

Nano)microplastics promote the propagation of antibiotic resistance genes in landfill leachate

Abstract: Municipal landfill leachate is a huge reservoir of (nano)microplastics (N/MPs) and antibiotic resistance genes (ARGs). N/MPs have a proven ability to affect the growth of bacteria and composition of bacterial communities, which may further influence the spread of ARGs in the environment. To extrapolate the interactions between these two emerging contaminants, we investigated the variations of the ARG levels in leachate with exposures to different sizes of N/MPs. The results showed that ARGs were enriched in the N/MPs-exposed groups, especially in the 200–500 nm MP group. Notably, the enrichment became more pronounced in the long-term exposure samples than the short-term ones. Together with this process, the total abundance of bacteria, as well as the potential ARG-carrying bacteria, also increased in the N/MP-exposed groups, and the long-term N/MP exposure led more bacteria genera, such as Pseudomonas, Syntrophomonas, and Desulfotomaculum, to become closely associated with ARG variations. Meanwhile, the production of reactive oxygen species (ROS) induced by exposure to the 50–100 nm NPs and the 200–500 nm MPs was observed to increase bacterial membrane permeability, which might result in more bacteria becoming potential receptors of ARGs via the intra-bacterial community transfer of mobile genetic elements. Overall, the current study demonstrated that the presence of N/MPs in leachate promoted the propagation of ARGs due to their impacts on the bacterial community and cellular membrane permeability. These findings have important implications for understanding the environmental risks of the combined pollution of N/MPs and ARGs.

Cellulose nanocrystal/silver (CNC/Ag) thin-film nanocomposite nanofiltration membranes with multifunctional properties

Abstract: The trade-off between membrane permeability and selectivity and membrane fouling, including both physical and bio-fouling, are major challenges that limit the practical application of nanofiltration (NF) membranes. In order to address these issues simultaneously, multifunctional membranes with maximized water permeability/salt selectivity and enhanced antifouling and antibacterial properties are desired. In this work, we prepare a novel multifunctional thin film nanocomposite (TFN) NF membrane by embedding cellulose nanocrystal/silver (CNC/Ag) nanocomposites into a polyamide layer. The CNC/Ag TFN NF membranes exhibit excellent properties by taking advantage of both CNCs, a highly hydrophilic, low-cost, bio-renewable, and environmentally friendly nanomaterial, and Ag nanoparticles, one of the most effective bactericidal materials. With the incorporation of only 0.01 wt% CNC/Ag nanocomposites, a high pure water permeability (25.4 L m−2 h−1 bar−) and a high rejection rate of Na2SO4 (99.1%) of the CNC/Ag TFN NF membrane can be achieved, respectively. Besides, the membrane also exhibits exceptional antifouling (flux recovery ratio reaches 92.6% for humic acid) and antibacterial performance (99.4% reduction of Escherichia coli viability). Ag+ leaching tests also demonstrate the good stability of Ag nanoparticles in the active thin-film layer of the CNC/Ag NF membranes. These findings have strong positive implications for the development of next-generation high performance NF membranes for water treatment.

Physiological, transcriptomic, and metabolomic analyses reveal zinc oxide nanoparticles modulate plant growth in tomato

Abstract: With the increasing use of zinc oxide nanoparticles (ZnO NPs) in industry, there is an increased release of these NPs into ecosystem, with potential impact on the ecological environment. Herein, we investigated the physiological and molecular mechanisms underlying ZnO NP-mediated plant growth in tomato plants. Foliar spraying with ZnO NPs (20 and 100 mg L−1) improved tomato growth by increasing the chlorophyll content and photosystem II activity. Comparative transcriptomic analysis revealed that ZnO NPs upregulated the expression of a set of genes involved in nutrient element transport, carbon/nitrogen metabolism, and the secondary metabolism in tomato, with the metabolome analysis further supporting this result. Foliar spraying with ZnO NPs increased iron (Fe) accumulation by 12.2% in tomato leaves; we thus examined the effects of ZnO NPs in tomato plants in response to Fe deficiency. Interestingly, foliar spraying with ZnO NPs markedly improved Fe deficiency tolerance in tomato. Physiological analysis indicated that ZnO NPs reduced Fe deficiency-induced oxidative damage and improved the metal nutrient element contents in tomato. Further, transcriptomic and metabolomic analyses indicated that foliar spraying with ZnO NPs increased the expression of genes encoding antioxidative enzymes, transporters, and the enzymes or regulators involved in carbon/nitrogen metabolism and secondary metabolism, thereby improving the levels of antioxidation, sugars, and amino acids in Fe-deficient tomato plants. Taken together, these results contribute to our understanding of the ecological effects of ZnO NPs.

Response of intestinal signaling communication between the nucleus and peroxisome to nanopolystyrene at a predicted environmental concentration

Abstract: The molecular responses of organisms to environmental toxicants at environmentally relevant concentrations are still largely unknown. Nematode Caenorhabditis elegans is a sensitive animal model used for environmental exposure assessment. We here determined the role of canonical Wnt/β-catenin signaling, a conserved molecular signaling among different organisms, in regulating the response of nematodes to nanopolystyrene (100 nm) at a predicted environmental concentration (1 μg L−1) and the underlying mechanism. Among the components of the canonical Wnt/β-catenin signaling pathway, nanopolystyrene (1 μg L−1) only decreased GSK-3 expression and increased β-catenin BAR-1 expression. GSK-3 acted upstream of BAR-1 to regulate the response to nanopolystyrene, and the intestine-specific activity of the GSK-3-BAR-1 signaling cascade in regulating the response to nanopolystyrene was observed. Transcriptional factor DAF-16 and peroxisomal protein PRX-5 were identified as downstream targets of both BAR-1 and Wnt effector POP-1 in regulating the response to nanopolystyrene. During the control of the response to nanopolystyrene, DAF-16 and PRX-5 functioned synergistically, suggesting that the intestinal canonical Wnt/β-catenin signaling mediates two different molecular signals to regulate the response to nanopolystyrene. In the peroxisome, KAT-1 and ACOX-1.6 were further identified as downstream targets of PRX-5 to regulate the response to nanopolystyrene. Therefore, exposure to nanopolystyrene could activate the canonical Wnt/β-catenin-mediated signaling communication between the nucleus and peroxisome. Our results suggest the crucial function of intestinal canonical Wnt/β-catenin-mediated nucleus–peroxisome signaling communication in response to nanopolystyrene exposure at a predicted environmental concentration.

Strategies for determining heteroaggregation attachment efficiencies of engineered nanoparticles in aquatic environments

Abstract: Heteroaggregation of engineered nanoparticles (ENPs) with suspended particulate matter (SPM) ubiquitous in natural waters often dominates the transport behaviour and overall fate of ENPs in aquatic environments. In order to provide meaningful exposure predictions and support risk assessment for ENPs, environmental fate and transport models require quantitative information about this process, typically in the form of the so-called attachment efficiency for heteroaggregation αhetero. The inherent complexity of heteroaggregation—encompassing at least two different particle populations, various aggregation pathways and several possible attachment efficiencies (α values)—makes its theoretical and experimental determination challenging. In this frontier review we assess the current state of knowledge on heteroaggregation of ENPs with a focus on natural surface waters. A theoretical analysis presents relevant equations, outlines the possible aggregation pathways and highlights different types of α. In a second part, experimental approaches to study heteroaggregation and derive α values are reviewed and three possible strategies are identified: i) monitoring changes in size, ii) monitoring number or mass distribution and iii) studying indirect effects, such as sedimentation. It becomes apparent that the complexity of heteroaggregation creates various challenges and no single best method for its assessment has been developed yet. Nevertheless, many promising strategies have been identified and meaningful data can be derived from carefully designed experiments when accounting for the different concurrent aggregation pathways and clearly stating the type of α reported. For future method development a closer connection between experiments and models is encouraged.

Enhanced capacitive deionization of saline water using N-doped rod-like porous carbon derived from dual-ligand metal–organic frameworks

Abstract: Capacitive deionization (CDI) removes ions from brine, and is forward-looking technology due to its low energy consumption, low cost and prevention of secondary pollution. Removal capacity is still an issue for CDI technology. It is quite urgent to design a high-performance CDI electrode material with a 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, coordinate with zinc (Zn). 1,4-Benzenedicarbocylic acid can be used as a pore-forming agent to increase the specific surface area of the carbon material, and triethylenediamine is used as a nitrogen doping source to increase the hydrophilicity and conductivity of the carbon material. By adjusting the ratio of the two ligands, the optimal specific surface area and nitrogen doping for the 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 rapid transport channels for salt ions, and high-level N doping enhances the conductivity and hydrophilicity of the 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 material derived from dual-ligand MOFs is a potential electrode material for CDI application. Such results provide a new method for the preparation of high-performance electrodes to remove ions from saline water.

Nanomaterials for radioactive wastewater decontamination

Abstract: Radioactive waste is a byproduct of nuclear power generation and applications of various radioactive materials in many commercial sectors. This waste has been strictly regulated as a highly hazardous material to all forms of life as well as the environment. The technologies currently adopted for managing radioactive waste are mainly based on segregation and storage. Ideally, radioactive waste should be isolated from entering the environment, but there has been slow progress toward sustainable waste management. Nanomaterials, with unique physical and chemical properties, such as the nanosize effect, large specific surface area, and high reactivity and selectivity, have become new materials for radioactive wastewater decontamination. Therefore, this review aims to provide a comprehensive overview and analysis of a newer generation of nanomaterials that have been demonstrated to be effective for radioactive wastewater decontamination, such as carbon-based nanomaterials, metal nanoparticles, nanosized metal oxides, metal sulfides, nanosized natural materials, layered double hydroxides, hydroxyapatite nanoparticles, metal–organic frameworks, cellulose nanomaterials, and biogenic nanocomposites. Although many different types of nanomaterials have been developed, their engineering feasibility toward radioactive wastewater decontamination has not yet been demonstrated for real-world large-scale applications. Lastly, the challenges associated with the applications of nanomaterials for radioactive wastewater decontamination have been discussed in detail while shedding light on future research directions.

Room-temperature formaldehyde catalytic decomposition

Abstract: Formaldehyde (HCHO) is considered as a major indoor air pollutant, and may cause serious health problems for humans. Therefore, HCHO needs to be removed from indoor air. Several techniques have been developed for indoor HCHO removal, among which room-temperature HCHO oxidation is the most promising method. To obtain excellent catalytic performance, various well-designed hierarchical catalysts have been fabricated in recent years. In this review, we first summarize the strategies for gaseous HCHO removal with special regard to thermal catalytic oxidation. Then, the major influencing factors affecting the catalytic activities of supported noble metal catalysts are raised and discussed. Finally, we emphasize on hierarchical porous catalysts for room-temperature HCHO oxidation and propose the feasible mechanisms for supported noble metal catalysts. A comprehensive impression of catalysts for HCHO removal may bring a new understanding and opportunity for the design and fabrication of highly efficient and practical hierarchical catalysts for indoor HCHO oxidation.