Silica nanoparticles inhibit cadmium uptake by the protozoan Tetrahymena thermophila without the need for adsorption

The simultaneous presence of nanoparticles (NPs) and heavy metals in the environment may affect their mutual biological uptake. Although previous studies showed that NPs could alter the cellular uptake of heavy metals by their adsorption of heavy metals, whether they could affect metal uptake without the need for adsorption is unknown. This study examined the effects of silica (SiO2) NPs on the uptake of Cd ion by the protozoan Tetrahymena thermophila. We found that, even with negligible levels of adsorption, SiO2 NPs at concentrations of 3 to 100 mg/L inhibited Cd uptake. This inhibitory effect decreased as the ambient Cd concentration increased from 1 to 100 μg/L, suggesting the involvement of at least two transporters with different affinities for Cd. The transporters were subsequently identified by the specific protein inhibitors amiloride and tariquidar as NCX and ABCB1, which are responsible for the uptake of Cd at low and high Cd levels, respectively. RT-qPCR and molecular dynamics simulation further showed that the inhibitory effects of SiO2 NPs were attributable to the down-regulated expression of the genes Ncx and Abcb1, steric hindrance of Cd uptake by NCX and ABCB1, and the shrinkage of the central channel pore of the transporters in the presence of SiO2 NPs. SiO2 NPs more strongly inhibited Cd transport by NCX than by ABCB1, due to the higher binding affinity of SiO2 NPs with NCX. Overall, our study sheds new light on a previously overlooked influence of NPs on metal uptake and the responsible mechanism.

Investigation of Magnetic Electrodes in Conducting Polymeric Materials: Electrochemical Properties of a Fullerene[C60 ]-Pd Polymer and Iron Oxide Magnetic Nanocomposite

A composite of iron oxide magnetic nanoparticles and coordination fullerene polymer (C60 Pd3 )n is formed by chemical deposition of spherical polymer nanoparticles on iron oxide magnetic nanoparticles in benzene containing C60 and Pd(0) complex. The composition of the composite can be controlled by the amount of magnetite and concentration of polymerization precursors as well as the time of polymerization. The magnetic composite material Fe3 O4 -γFe2 O3 /(C60 Pd3 )n is used as a model system to investigate its deposition on a magnetic electrode and its electrochemical properties. The iron oxide magnetic nanoparticles ensure both the magnetic activity of the composite and its nanostructured morphology. Both of these factors are responsible for the enhancement of the electrochemical activity of the polymer phase forming the composite in comparison to the pure polymer material deposited on the same magnetic electrode. In the magnetic field of the electrode, the composite undergoes permanent and strong bonding with the surface of the electrode. The nanostructured morphology of the Fe3 O4 -γFe2 O3 /(C60 Pd3 )n composite also provides very good capacitive properties.

Preparation of N-doped cellulose-based hydrothermal carbon using a two-step hydrothermal induction assembly method for the efficient removal of Cr(VI) from wastewater

Cr(VI) pollution is a growing problem that causes the deterioration of the environment and human health. We report the development of an effective adsorbent for the removal of Cr(VI) from wastewater. N-doped cellulose-based hydrothermal carbon (N-CHC) was prepared via a two-step hydrothermal method. The morphology and structural properties of N-CHC were investigated by various techniques. N-CHC has many O and N groups, which are suitable for Cr(VI) adsorption and reduction. Intermittent adsorption experiments showed that N-CHC had an adsorption capacity of 151.05 mg/g for Cr(VI) at pH 2, indicating excellent adsorption performance. Kinetic and thermodynamic analyses indicates that the adsorption of Cr(VI) on N-CHC follows a monolayer uniform adsorption process, which is a spontaneous endothermic process dominated by chemical interaction and limited by diffusion within particles. In a multi-ion system (Pb²⁺, Cd²⁺, Mn⁷⁺, Cl^-, and SO₄^2-), the selectivity of N-CHC toward Cr(VI) was 82.62%. In addition, N-CHC demonstrated excellent reuse performance over seven adsorption-desorption cycles; the Cr(VI) removal rate of N-CHC in 5-20 mg/L wastewater was >99.87%, confirming the potential of N-CHC for large-scale applications. CN/C-OR, pyridinic-N, and pyrrolic-N were found to play a critical role in the adsorption process. This study provides a new technology for Cr(VI) pollution control that could be utilized in large-scale production and other environmental applications.

Templated synthesis of microparticles with carbonaceous skeletal structures using polymer cubosomes as templates

Polymer cubosomes (PCs) are bicontinuous mesoporous colloidal particles that feature high surface areas and an extremely ordered crystalline pore network. PCs have attracted tremendous attention because of their potential applications in many fields. Herein, we obtained new microparticles with carbonaceous reticulated networks via templated synthesis using PCs as templates. The water-channel networks of the PCs were translated into a carbonaceous skeletal cubic structure. Carbon precursors were polymerized inside the water-channel networks of the PCs under acidic conditions without collapsing the internal crystalline mesophases. The carbonaceous interconnected networks created by the templated synthesis exhibited cubic crystalline skeletal networks similar to those of the PCs. These cubic-ordered mesoporous carbon (cOMC) microparticles exhibited several properties in electrochemical experiments. In addition, the nanoscopic structures and surfaces of these microparticles sustain electrochemically perturbing environments, and thus retain more than 90% capacitance after 1000 charge-discharge cycles.

Water treatment using stimuli-responsive polymers

Stimuli-responsive polymers are a new category of smart materials used in water treatment via a stimuli-induced purification process and subsequent regeneration processes.

Investigation of kinetics and adsorption isotherm for fluoride removal from aqueous solutions using mesoporous cerium-aluminum binary oxide nanomaterials

Herein, we report the synthesis of Ce–Al (1 : 1, 1 : 3, 1 : 6, and 1 : 9) binary oxide nanoparticles by a simple co-precipitation method at room temperature to be applied for defluoridation of an aqueous solution. The characterization of the synthesized nanomaterial was performed by XRD (X-ray diffraction), FTIR (Fourier transform infrared) spectroscopy, TGA/DTA (thermogravimetric analysis/differential thermal analysis), BET (Brunauer–Emmett–Teller) surface analysis, and SEM (scanning electron microscopy). Ce–Al binary oxides in 1 : 6 molar concentration were found to have the highest surface area of 110.32 m² g⁻¹ with an average crystallite size of 4.7 nm, which showed excellent defluoridation capacity. The adsorptive capacity of the prepared material towards fluoride removal was investigated under a range of experimental conditions such as dosage of adsorbents, pH, and initial fluoride concentration along with adsorption isotherms and adsorption kinetics. The results indicated that fluoride adsorption on cerium–aluminum binary metal oxide nanoparticles occurred within one hour, with maximum adsorption occurring at pH 2.4. The experimental data obtained were studied using Langmuir, Freundlich, and Temkin adsorption isotherm models. The nanomaterial showed an exceptionally high adsorbent capacity of 384.6 mg g⁻¹. Time-dependent kinetic studies were carried out to establish the mechanism of the adsorption process by pseudo-first-order kinetics, pseudo-second-order kinetics, and Weber–Morris intraparticle diffusion kinetic models. The results indicated that adsorption processes followed pseudo-second-order kinetics. This study suggests that cerium–aluminum binary oxide nanoparticles have good potential for fluoride removal from highly contaminated aqueous solutions.

Mesoporous Ce–Al binary oxide nanomaterials prepared with a surface area of 110.32 m² g⁻¹ showed defluoridation capacity at pH 2.4, exhibited maximum adsorption capacity of 384.6 mg g⁻¹ and a removal efficiency of 91.5% at a small dose of nanoadsorbent.

Mesoporous Carbon: A Versatile Material for Scientific Applications

Mesoporous carbon is a promising material having multiple applications. It can act as a catalytic support and can be used in energy storage devices. Moreover, mesoporous carbon controls body’s oral drug delivery system and adsorb poisonous metal from water and various other molecules from an aqueous solution. The accuracy and improved activity of the carbon materials depend on some parameters. The recent breakthrough in the synthesis of mesoporous carbon, with high surface area, large pore-volume, and good thermostability, improves its activity manifold in performing functions. Considering the promising application of mesoporous carbon, it should be broadly illustrated in the literature. This review summarizes the potential application of mesoporous carbon in many scientific disciplines. Moreover, the outlook for further improvement of mesoporous carbon has been demonstrated in detail. Hopefully, it would act as a reference guidebook for researchers about the putative application of mesoporous carbon in multidimensional fields.

Synthesis of Magnetite Nanorods from the Reduction of Iron Oxy-Hydroxide with Hydrazine

Nanowires and nanorods of magnetite (Fe3O4) are of interest due to their varied biological applications but most importantly for their use as magnetic resonance imaging contrast agents. One-dimensional (1D) structures of magnetite, however, are more challenging to synthesize because the surface energy favors the formation of isotropic structures. Synthetic protocols can be dichotomous, producing either the 1D structure or the magnetite phase but not both. Here, superparamagnetic Fe3O4 nanorods were prepared in solution by the reduction of iron oxy-hydroxide (β-FeOOH) nanoneedles with hydrazine (N2H4). The amount of hydrazine and the reaction time affected the phase and morphology of the resulting iron oxide nanoparticles. One-dimensional nanostructures of Fe3O4 could be produced consistently from various aspect ratios of β-FeOOH nanoneedles, although the length of the template was not retained. Fe3O4 nanorods were characterized by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and SQUID magnetometry.

Honeycomb-like structure-tunable chitosan-based porous carbon microspheres for methylene blue efficient removal

Chitosan (CS) can be used for the preparation of carbon materials with different morphologies due to its excellent properties, but there are no reports on its spherical morphology. In this study, a feasible step-by-step strategy was proposed to fabricate nitrogen-containing chitosan-based porous carbon microspheres (CPCM) in HCl and KOH. The unique spherical morphology and honeycomb-like porous structure of CPCM were accurately regulated. A great quantity of micro/mesopores endowed CPCM an ultra-high specific surface area up to 2463.9 m² g^-1. Moreover, CPCM exhibited an ultra-high maximum adsorption capacity up to 1599.03 mg g^-1 for methylene blue (MB), meanwhile the adsorption process was in well agreement with the Langmuir isotherm and pseudo-second-order kinetic models. It was simultaneously a favorable reusable adsorbent with high regenerative capacity. The high dye adsorption properties suggest that chitosan can be a promising candidate for sewage treatment in the form of carbon microspheres.

Pristine Graphene Microspheres by the Spreading and Trapping of Graphene at an Interface

The interfacial spreading and exfoliation of graphene was used to create low-density, hollow microspheres defined by a thin shell of graphene. The spheres were templated by a thermodynamically driven self-assembly process in which graphite spontaneously exfoliated and spread at the high-energy interfaces of a water-in-oil emulsion. Graphene thus acted as a 2D surfactant to stabilize the dispersed water droplets utilized as polymerization templates. Using a mixture of organic solvent and monomer as the emulsion oil phase, polystyrene-coated hollow graphene microspheres were created. These spheres were characterized by optical and electron microscopy, thermo-gravimetric analysis, nanoindentation, and particle sizing. The mechanism leading to the microsphere surface morphology and shape is discussed, with the oil phase composition shown to play a critical role.

Supramolecular Nanopumps with Chiral Recognition for Moving Organic Pollutants from Water

Since organic pollutants in water resources have raised concerns on aquatic ecosystems and human health, mechanical machines such as a nanopump for rapid and efficient removal of pollutants from water with regeneration properties remains a challenge. Here, a pH-responsive artificial pump from left-handed porous tubules into right-handed solid fibers was presented by the self-assembly of bent-shaped aromatic amphiphiles. The bent-shaped amphiphile with a pH-sensitive segment was demonstrated in aromatic hexameric macrocycles, which could contract into dimeric disks. Such a switchable aromatic pore with superhydrophobicity was well-suited for an efficient removal and controlled release of organic pollutants from water through pulsating motion. The removal efficiency is found to be 78% for ethinyloestradiol and 82% for bisphenol. Additionally, the pumping accompanied by chiral inversion was endowed with a rapid removal and convenient regenerable ability. The inflation from right-handed solid fibers into left-handed tubules for efficient removal pollutants was remarkably promoted by (-)-acidic enantiomer of malic acid, whereas the contraction with full desorption of pollutants was incisively responsive to alkaline with (+)-conformation. The kinetically regulable porous device with a chiral recognition will provide a promising platform for the construction of rapid responsible machine for sewage treatment.

In-situ prepared ZnO-ZnFe2O4 with 1-D nanofiber network structure: An effective adsorbent for toxic dye effluent treatment

Current research on ZnFe₂O₄-based adsorbents rely mainly on its surface charge to remove Congo red (CR). However, the weak charge of ZnFe₂O₄ due its normal spinel structure makes this approach inefficient as evident from its low activity. Considering the potential of ZnFe₂O₄ as a low cost nontoxic adsorbent, it is important to improve its activity. Herein, we present an in-situ prepared 1-D ZnO-ZnFe₂O₄ with a heterojunction which adsorbs CR chemically instead of the generic physisorption. While its 1-D structure allows very low adsorbent loading to be employed. Together, these two unique properties make 1-D ZnO-ZnFe₂O₄ ˜3.3x more effective at treating CR effluent than reported ZnFe₂O₄-based adsorbents. The chemisorption reaction involves chelating/bridging bidentate bonding between sulfonic groups on CR and ZnO-ZnFe₂O₄ heterojunction. Its potency is regulated by the ZnO content of the composite which suggest a synergistic effect between the metal oxides phases. Interestingly, spent 1-D ZnO-ZnFe₂O₄ can be regenerated in NaOH solution and retains ˜75% of its adsorption capacity even after repeated use. These findings provide key insights into how interfacial interactions in mixed metal oxide composites and their morphology affect dye adsorption. This information may be useful to develop high performing adsorbents from metal oxides in general.

Tetracycline adsorption on the composite magnetite-bentonite

In this research, magnetite-bentonite composites were synthesized as a unique sorbent for the delivery of tetracycline. The introduction of magnetite particles into bentonite structure is based on X-ray phase analysis. Adsorption of tetracycline on bentonite surface and magnetite-bentonite composite was studied. It is shown that maximum adsorption of tetracycline on the surface of bentonite and composite magnetite-bentonite is 84.2 and 71.1 mg/g, respectively. The dependence of adsorption on pH and time was established. The increase in the adsorption value on the surface of the composite magnetite-bentonite with increasing pH is due to the dissociation in alkaline medium of bentonite silicate groups in the composite content. Electrostatic interaction occurs between the amino acids of tetracycline and negatively charged silicate groups in bentonite, oxygen atoms and OH groups form hydrogen bonds with SiOH groups of bentonite and Fe-O groups of magnetite. Electrostatic interactions and H-bonds were determined as the main forces providing adsorption.

Enhanced photocatalytic performance of magnetic multi-walled carbon nanotubes/cerium dioxide nanocomposite

An easily separated photocatalyst, magnetic multi-walled carbon nanotubes/cerium dioxide (MMWCNTs-CeO₂) nanocomposite, has been successfully prepared by hydrothermal synthesis and subsequent loading of magnetic nanoparticles. The synthesized nanocomposite was characterized by scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, and vibrating sample magnetometer. The characterization results indicated the successful synthesis of MMWCNTs-CeO₂ nanocomposite. Photocatalytic degradation experiments were conducted to evaluate photocatalytic properties of MMWCNTs-CeO₂ by using methylene blue (MB) as a model pollutant. After a light irradiation of two hours, relatively high degradation efficiency (97.5%) of MB was achieved by using MMWCNTs-CeO₂ nanocomposite as photocatalyst in the presence of H₂O₂. The incorporation of magnetic nanoparticles could not only facilitate the separation of photocatalyst from the solution after treatment, but also enhance the photocatalytic degradation efficiency. The results of this study suggested that the synthesized MMWCNTs-CeO₂ nanocomposite showed an attractive prospect for application in the treatment of organic wastewater.

Synthesis of C@Ni-Al LDH HSS for efficient U-entrapment from seawater

In this paper, a double hollow spherical shell composite modified with layered double hydroxide (C@Ni-Al LDH HSS) was fabricated for uranium(VI) (U(VI)) adsorption. Various batch experiments were carried out to investigate the influence of pH, concentration, time and coexistence ion on extraction. The results showed that the adsorption processes of U(VI) onto C@Ni-Al LDH HSS were spontaneous and endothermic and closely followed pseudo-second-order and Langmuir isotherm models. The equilibrium time and maximum adsorption capacity of C@Ni-Al LDH HSS was 360 min and 545.9 mg g^-1. FT-IR and XPS analyses proved that the adsorption behavior was primarily attributed to the strong interaction between oxygen-containing functional groups and U(VI). Moreover, the extraction of trace U(VI) (μg L^-1) in artificial and natural seawater was also studied. The results showed that C@Ni-Al LDH HSS provided a promising application for the efficient extraction of U(VI) from seawater.

Magnetically Navigated Core-Shell Polymer Capsules as Nanoreactors Loadable at the Oil/Water Interface

Polymer core-shell nanocapsules with magnetic nanoparticles embedded in their oil cores were fabricated and applied as nano(photo)reactors. Superparamagnetic iron oxide nanoparticles (SPIONs) coated with oleic acid were first synthesized and characterized structurally, and their magnetic properties were determined. The capsules with chitosan-based shells were then formed in a one-step process by sonication-assisted mixing of (1) an aqueous solution of the hydrophobically derived chitosan and (2) oleic acid containing the dispersed SPIONs. In this way, magnetic capsules with a diameter of approximately 500-600 nm containing encapsulated SPIONs with an average diameter of approximately 20-30 nm were formed as revealed by dynamic light scattering and scanning transmission electron microscopy measurements. The composition and magnetic properties of the formed capsules were also followed using dynamic light scattering, electron microscopies, and magnetic force microscopy. The water-dispersible capsules, thanks to their magnetic properties, were then navigated in a static magnetic field gradient and transferred between the water and oil phases, as evidenced by fluorescence microscopy. In this way, the capsules could be loaded in a controlled way with a hydrophobic reactant, perylene, which was later photooxidized upon transferring the capsules to the aqueous phase. The capsules were shown to serve as robust reloadable nanoreactors/nanocontainers that via magnetic navigation can be transferred between immiscible phases without disruption. These features make them promising reusable systems not only for loading and carrying lipophilic actives, conducting useful reactions in the confined environment of the capsules, but also for magnetically separating and guiding the encapsulated active molecules to the site of action.

Encapsulated green magnetic nanoparticles for the removal of toxic Pb2+ and Cd2+ from water: Development, characterization and application

Current research is based on an innovative approach of the fabrication of encapsulated sustainable, green, phytogenic magnetic nanoparticles (PMNPs), to inhibit the generation of secondary pollutants (Iron/Fe^o) during water treatment applications. These novel bio-magnetic membrane capsules (BMMCs) were prepared using two-step titration gel crosslink method, with polyvinyl alcohol and sodium alginate matrix as the model encapsulating materials to eliminate potentially toxic metals (Pb²⁺ and Cd²⁺) from water. The development of BMMCs was characterized by FTIR, XRD, XPS, SEM, VSM, TGA and EDX techniques. The effects of various operating parameters, adsorbent dose, contact time, solution pH, temperature, initial concentration of metals cations and co-existing ions were studied. The hysteresis loops have illustrated an excellent super-paramagnetic nature, demonstrating the smooth encapsulation of PMNPs without losing their magnetic properties. The maximum monolayer adsorptive capacities estimated at pH 6.5 by the Langmuir isotherm model were 548 and 610.67 mg/g for Pb²⁺ and Cd²⁺, respectively. The novel BMMCs did not only control oxidation of PMNPs but also sustained the adsorptive removal over a wide range of pH (3-8), and the electrostatic interaction and ion-exchange were the core adsorption mechanisms. The BMMCs could easily be regenerated using 25% HNO₃ as an eluent for successful usage in seven repeated cycles. Therefore, the BMMCs as a material can be used as an excellent sorbent or composite material to remove toxic metals Pb²⁺ and Cd²⁺, showing strong potential for improving water and wastewater treatment technologies.

Synthesis and Characterization of Flower-like Carbon-encapsulated Fe-C Nanoparticles for Application as Adsorbing Material

Carbon-encapsulated Fe-C (Fe-C@C) nanoparticles with a divergently flower-like morphology were successfully synthesized for application as an adsorbing material by using freeze-drying and chemical vapor deposition (CVD) methods. The Fe metallic source was first loaded onto a sodium chloride (NaCl) supporter via freeze-drying to obtain the Fe/NaCl composite powder. Then, Fe-C@C nanoparticles were synthesized in the temperature range of 300–450 °C via CVD of acetylene in the Fe/NaCl composite powder using Fe nanoparticles as catalysts and NaCl as supporters. Because the NaCl supporter is water-soluble, the synthesized Fe-C@C nanoparticles were easy to purify, and a high purity was obtained by simple washing and centrifugation. The optimal Fe-C@C nanoparticles, synthesized at 400 °C, possessed a unique divergently flower-like structure and a high specific surface area of 169.4 m²/g that can provide more adsorption sites for contaminants. Adsorption experiments showed that the flower-like Fe-C@C adsorbent exhibited high adsorption capacity (90.14 mg/g) and fast removal of methylene blue (MB). Moreover, the magnetic properties of the nanoparticles, with saturation magnetization of 36.544 emu/g, facilitated their magnetic separation from wastewater. Therefore, the novel flower-like Fe-C@C nanoparticles with integrated adsorptive and magnetic properties have the potential to be an effective adsorbent in dye wastewater treatment.

Space-Confined Synthesis of ZIF-67 Nanoparticles in Hollow Carbon Nanospheres for CO2 Adsorption

Herein, the design and synthesis of ZIF-67 nanoparticles (NPs) with tunable size grown inside hollow carbon nanospheres (ZIF-67@HCSs) via a space-confined strategy is reported. HCSs are first prepared via pyrolysis of polystyrene@polypyrrole (PS@PPy) composite nanospheres. Further infiltration of 2-methylimidazole (MI) into the HCSs (MI@HCSs) using a melting-diffusion strategy, followed by immersing MI@HCSs into Co(NO₃ )₂ solution through the pores and channels of HCSs results in the formation of ZIF-67@HCSs. The as-synthesized ZIF-67@HCSs with tunable ZIF-67 size is achieved by changing the amount of MI. Due to the high pore volume provided by nanoscale ZIF-67 NPs, the as-prepared core-shell ZIF-67@HCSs exhibit outstanding adsorption capacity for CO₂ .

Development and application of novel bio-magnetic membrane capsules for the removal of the cationic dye malachite green in wastewater treatment

Novel bio-magnetic membrane capsules (BMMCs) were prepared by a simple two-step titration-gel cross-linking method using a polyvinyl alcohol (PVA) and sodium alginate (SA) matrix to control the disintegration of phytogenic magnetic nanoparticles (PMNPs) in an aqueous environment, and their performance was investigated for adsorbing cationic malachite green (MG) dye from water. The prepared BMMCs were characterized by FTIR, powder XRD, SEM, EDX, XPS, VSM and TGA techniques. The findings revealed that the hysteresis loops had an excellent superparamagnetic nature with saturation magnetization values of 11.02 emu g⁻¹. The prepared BMMCs not only controlled the oxidation of PMNPs but also improved the adsorptive performance with respect to MG dye (500 mg g⁻¹ at 298.15 K and pH 6.5) due to the presence of a large amount of hydrophilic functional groups (hydroxyl/–OH and carboxyl/–COOH) on/in the BMMCs. The smooth encapsulation of PMNPs into the PVA–SA matrix established additional hydrogen bonding among polymer molecular chains, with improved stability, and adsorptive performance was maintained over a wide range of pH values (3–12). Importantly, the prepared BMMCs were easily regenerated just by washing with water, and they could be re-utilized for up to four (4) consecutive treatment cycles without observing any apparent dissolution of iron/Fe⁰ or damage to the morphology. According to the mass balance approach, an estimated amount of 100 mL of treated effluent can be obtained from 160 mL of MG dye solution (25 mg L⁻¹) just by employing a 0.02 g L⁻¹ adsorbent dosage. Finally, a model of BMMCs based on zero-effluent discharge was also proposed for commercial or industrial applications. The prepared BMMCs are greatly needed for improving the water/wastewater treatment process and they can be utilized as an excellent adsorbent to remove cationic pollutants for various environmental applications.

Novel bio-magnetic membrane capsules were prepared by a simple two-step titration-gel cross-linking method using a polyvinyl alcohol and sodium alginate matrix to control the disintegration of phytogenic magnetic nanoparticles in aqueous media.

DLVO Interaction Energies for Hollow Particles: The Filling Matters

A thorough knowledge of the interaction energy between a hollow particle (HP) and a surface or between two HPs is critical to the optimization of HP-based products and assessing the environmental risks of HPs and HP-associated pollutants. The van der Waals (vdW) energy between a HP and a surface is often calculated by subtracting the vdW energies of the inner and outer HP geometries. In this study, we show that this subtraction method is only valid when the interior and exterior fluids are the same, for example, for water-filled HPs (WHPs) dispersed in an aqueous solution. Expressions were developed to calculate the vdW energies for HPs whose interiors were filled with air (AHPs). The vdW energies were then calculated between a planar surface and a spherical or cylindrical WHP and AHP, and between WHPs or AHPs. The vdW attraction between a surface and a WHP was decreased at large separation distances compared to solid particles, and this reduced the depth of the secondary minimum. In contrast, the vdW attraction for AHPs and a surface was significantly reduced at all separation distances, and even became repulsive for thin shells, and this inhibited both primary and secondary minimum interactions. The vdW attraction between WHPs decreased with increasing shell thicknesses, and this reduced aggregation in both primary and secondary minima. In contrast, aggregation of AHPs was increased in both minima with decreasing shell thicknesses because of an increase in vdW attraction. Our theoretical calculations show the evolution of vdW and total interaction energies for HPs with different interior fluids and shell thicknesses. These results help explain various experimental observations such as inhibited attachment and favorable aggregation for AHPs (e.g., carbon nanotubes) and favorable bubble coalescence.

Intelligent Mesoporous Materials for Selective Adsorption and Mechanical Release of Organic Pollutants from Water

Despite recent advances in the porous materials for efficient removal of dissolved organic pollutants from water, the regeneration of porous characteristics for reuse with preventing secondary contamination remains a challenge. Here, novel supramolecular absorbents with hydrophobic pore are prepared by the self-assembly of propeller-shaped aromatic amphiphiles. The assembly of folded propeller provides a mesoporous environment within aromatic segments, which is suitable for the removal of organic pollutants from waste water. The removal efficiency is found to be 92% and 90% for ethinyl oestradiol (Eo) and bisphenol A (BPA). Notably, the folded architecture of propeller is observed to be flattened by the salt addition, which results in the strong π-π interaction driving the porous materials closed and forms solid fibers. It is found that most of the removed pollutants are spontaneously released by the dynamic porous assembly, and subsequent dialysis triggers the porous materials to be recovered.

Silica-Coated Magnetite Nanoparticles Carrying a High-Density Polymer Brush Shell of Hydrophilic Polymer

Integrating the properties of magnetite nanoparticles (MNPs) and high-density polymer brushes in one structure requires sophisticated synthetic designs and effective chemical approaches. A simple and versatile strategy for the fabrication of hydrophilic-polymer-capped magnetite-core-silica-shell nanohybrids with well-defined structure employing reverse microemulsion technique and reversible addition-fragmentation chain transfer (RAFT) polymerization is presented. The high-density polymer brush allows precise patterning of the magnetic nanohybrids with a tunable interparticle distance ranging from 20 nm to 80 nm by controlling the polymer size. The high structural precision provides a near stand-alone state of the MNPs in the nanohybrids with effectively inhibited magnetic interaction, as shown by superconducting quantum interference device (SQUID) measurements.

Metal-Organic Framework-Derived Hollow Carbon Nanocubes for Fast Solid-Phase Microextraction of Polycyclic Aromatic Hydrocarbons

Developing novel coating materials for fast and sensitive solid-phase microextraction (SPME) is highly desired but few are achieved. In this work, a new material of metal-organic framework (MOF)-derived hollow carbon nanocubes (HCNCs) was prepared as a fiber coating material for SPME. The HCNC-coated fiber (denoted as HCNCs-F) exhibited a better enrichment performance than solid carbon nanocube (SCNC)-coated fiber (denoted as SCNCs-F) and commercial fibers based on the abundant active sites of the hollow structure, hydrophobic interactions, and π-π interactions. Moreover, because of the reduced mass-transport lengths of the hollow mesoporous structure, the HCNCs-F demonstrated a faster mass transfer compared with the SCNCs-F. The HCNCs-F was used to determine the six hydrophobic polycyclic aromatic hydrocarbons (PAHs) with wide linear ranges (10-2000 ng L^-1 for naphthalene and 5-2000 ng L^-1 for the other five analytes), good reproducibility (relative standard deviation < 8.8%), and low detection limits (0.03-0.70 ng L^-1). Finally, the HCNCs-F was successfully applied for the determination of PAHs from the real water samples. It can be concluded from the results that MOF-derived hollow carbon materials are promising candidates for the fast SPME and can be used for practical applications in analytical chemistry.

Enhanced Congo red dye removal from aqueous solutions using iron nanoparticles: adsorption, kinetics, and equilibrium studies

We report on the Congo red dye removal properties of body centred cubic and amorphous iron nanoparticles, synthesized by a facile borohydride reduction method under ambient conditions. We have analyzed the adsorption of Congo red as a function of dye concentration, time, and temperature and measured a Congo red adsorption capacity of 1735 mg g^-1 for the amorphous iron nanoparticles. To our knowledge, this is the highest value reported so far for Congo red adsorption. The acquired data have been evaluated applying various models for adsorption kinetics and thermodynamic studies. The isotherm models as well as acquired Fourier transform infrared spectra suggest that both chemi- and physisorption occur for Congo red adsorption on iron nanoparticles, where chemisorption appears to be dominant. The kinetics of adsorption of Congo red on both bcc-structured and amorphous iron follow a pseudo-second order equation and are characterized by high initial adsorption rates. Diffusion studies indicate that adsorption occurs in two stages, namely film diffusion followed by intraparticle diffusion. Our studies show that amorphous iron nanoparticles are highly promising for dye adsorption and wastewater treatment applications.

Hierarchically porous SiO2/C hollow microspheres: a highly efficient adsorbent for Congo Red removal

Hierarchically porous SiO₂/C hollow microspheres (HPSCHMs) were synthesized by a hydrothermal and NaOH-etching combined route. The adsorption performance of the prepared HPSCHMs was investigated to remove Congo Red (CR) in aqueous solution. The results show that the synthesized composite possesses a hollow microspherical structure with hierarchical pores and a diameter of about 100–200 nm, and its surface area is up to 1154 m² g⁻¹. This material exhibits a remarkable adsorption performance for CR in solution, and its maximum adsorption amount for CR can reach up to 2512 mg g⁻¹. It shows faster adsorption and much higher adsorption capacity than the commercial AC and γ-Al₂O₃ samples under the same conditions. The studies of the kinetics and thermodynamics indicate that the adsorption of CR on the PHSCHM sample obeys the pseudo-second order model well and belongs to physisorption. The adsorption activation energy is about 7.72 kJ mol⁻¹. In view of the hierarchically meso–macroporous structure, large surface area and pore volume, the HPSCHM material could be a promising adsorbent for removal of pollutants, and it could also be used as a catalyst support.

Hierarchically porous SiO₂/C hollow microspheres (HPSCHMs) were synthesized. Its surface area is up to 1154 m² g^–1. Hierarchically porous structure facilitates diffusion of adsorbate. Its maximum adsorption amount for Congo Red is up to 2512 mg g^–1.

Fe-based hybrid electrocatalysts for nonaqueous lithium-oxygen batteries

Lithium–oxygen batteries promise high energy densities, but are confronted with challenges, such as high overpotentials and sudden death during discharge–charge cycling, because the oxygen electrode is covered with the insulating discharge product, Li₂O₂. Here, we synthesized low–cost Fe–based nanocomposites via an electrical wire pulse process, as a hybrid electrocatalyst for the oxygen electrode of Li–O₂ batteries. Fe₃O₄-Fe nanohybrids–containing electrodes exhibited a high discharge capacity (13,890 mA h g_c⁻¹ at a current density of 500 mA g_c⁻¹), long cycle stability (100 cycles at a current rate of 500 mA g_c⁻¹ and fixed capacity regime of 1,000 mA h g_c⁻¹), and low overpotential (1.39 V at 40 cycles). This superior performance resulted from the good electrical conductivity of the Fe metal nanoparticles during discharge–charge cycling, which could enhance the oxygen reduction reaction and oxygen evolution reaction activities. We have demonstrated the increased electrical conductivity of the Fe₃O₄-Fe nanohybrids using electrochemical impedance spectroscopy.

Highly Efficient Magnetic Nitrogen-Doped Porous Carbon Prepared by One-Step Carbonization Strategy for Hg2+ Removal from Water

Hydrophilic magnetic N-doped porous carbon composites (MNPCs) with high special surface areas and rich nitrogen content was prepared via simple one-step carbonization of zinc oxide nanoparticles (ZnO NPs), 2-methylimidazole (HmIm), and Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) mixture directly. During the carbonization process, ZnO NPs directly reacts with HmIm to yield porous ZIF-8 while the MNPs are incorporated into the frameworks to generate magnetic metal-organic frameworks (MFCs), and the MFCs acts as a self-sacrificing template to prepare MNPC. The obtained MNPCs via simple one-step carbonization strategy display higher adsorption capacity (429 mg g^-1) for Hg²⁺ ions than MNPC-T700-M3-T (382 mg g^-1) which was obtained by two-step synthesis strategy for comparison. It also exhibits very fast adsorption dynamics (adsorption rate constant (K₂) = 2.45 g mg^-1 min^-1) for Hg²⁺ and could efficiently remove 95% Hg²⁺ in 2 min for 20 mg L^-1 Hg²⁺ solution. Furthermore, the prepared MNPC exhibits good chemical stability and the adsorption capacity is still more than 95% even after 10 adsorption-elution cycles. The proposed method is easy-processing and economic, which not only provides highly efficient MNPCs for metal ions capture but also paves the ways toward various MFCs with different ligands through solvent/additive-free synthesis approaches.

A facile sacrificial template method to synthesize one-dimensional porous CdO/CdFe2O4 hybrid nanoneedles with superior adsorption performance

A novel adsorbent based on 1D porous CdO/CdFe₂O₄ hybrid nanoneedles has been firstly synthesized via a facile sacrificial template (solid Cd₂Fe(CN)₆) method, which exhibit an superior adsorption capacity of 1491 mg g⁻¹ for CR from aqueous solution.

Rattle-type magnetic mesoporous hollow carbon as a high-performance and reusable adsorbent for water treatment

Rattle-type magnetic mesoporous hollow carbon (RMMHC) materials have shown great promise as adsorbents for water treatment. In this work, we report a surfactant-free synthesis of RMMHC nanoparticles (NPs) using magnetite NPs as the core, tetrapropyl orthosilicate, resorcinol and formaldehyde to form the shell followed by carbonization and selective silica etching. The pore size, specific surface area and pore volume of RMMHC NPs can be tuned by varying the carbonization temperature (500, 700 and 900 °C). At the optimized temperature of 700 °C, the RMMHC NPs possess the highest specific surface area of 579 m² g^-1, the largest pore volume of 0.795 cm³ g^-1, and the largest pore size of 7.6 nm among all three samples. The adsorption capacity of optimized RMMHC NPs towards di (2-ethylhexyl) phthalate (a model organic pollutant) reaches as high as 783.1 mg g^-1. Taking advantage of the magnetic property, the adsorbents retain more than 87% of their initial adsorption capacity over five times' reuse.

Carbon-cryogel hierarchical composites as effective and scalable filters for removal of trace organic pollutants from water

Effective technologies are required to remove organic micropollutants from large fluid volumes to overcome present and future challenges in water and effluent treatment. A novel hierarchical composite filter material for rapid and effective removal of polar organic contaminants from water was developed. The composite is fabricated from phenolic resin-derived carbon microbeads with controllable porous structure and specific surface area embedded in a monolithic, flow permeable, poly(vinyl alcohol) cryogel. The bead-embedded monolithic composite filter retains the bulk of the high adsorptive capacity of the carbon microbeads while improving pore diffusion rates of organic pollutants. Water spiked with organic contaminants, both at environmentally relevant concentrations and at high levels of contamination, was used to determine the purification limits of the filter. Flow through tests using water spiked with the pesticides atrazine (32 mg/L) and malathion (16 mg/L) indicated maximum adsorptive capacities of 641 and 591 mg pollutant/g carbon, respectively. Over 400 bed volumes of water contaminated with 32 mg atrazine/L, and over 27,400 bed volumes of water contaminated with 2 μg atrazine/L, were treated before pesticide guideline values of 0.1 μg/L were exceeded. High adsorptive capacity was maintained when using water with high total organic carbon (TOC) levels and high salinity. The toxicity of water filtrates was tested in vitro with human epithelial cells with no evidence of cytotoxicity after initial washing.