Electronic Structure Optimization and Proton-Transfer Enhancement on Titanium Oxide-Supported Copper Nanoparticles for Enhanced Nitrogen Recycling from Nitrate-Contaminated Water.

Electrocatalytic reduction of nitrate to NH3 (NO3RR) on Cu offers sustainable NH3 production and nitrogen recycling from nitrate-contaminated water. However, Cu affords limited NO3RR activity owing to its unfavorable electronic state and the slow proton transfer on its surface, especially in neutral/alkaline media. Furthermore, although a synchronous "NO3RR and NH3 collection" system has been developed for nitrogen recycling from nitrate-laden water, no system is designed for natural water that generally contains low-concentration nitrate. Herein, we demonstrate that depositing Cu nanoparticles on a TiO2 support enables the formation of electron-deficient Cuδ+ species (0 < δ ≤ 2), which are more active than Cu0 in NO3RR. Furthermore, TiO2-Cu coupling induces local electric-field enhancement that intensifies water adsorption/dissociation at the interface, accelerating proton transfer for NO3RR on Cu. With the dual enhancements, TiO2-Cu delivers an NH3-N selectivity of 90.5%, mass activity of 41.4 mg-N h gCu-1, specific activity of 377.8 mg-N h-1 m-2, and minimal Cu leaching (<25.4 µg L-1) when treating 22.5 mg L-1 of NO3--N at -0.40 V, outperforming most of the reported Cu-based catalysts. A sequential NO3RR and NH3 collection system based on TiO2-Cu was then proposed, which could recycle nitrogen from nitrate-contaminated water under a wide concentration window of 22.5-112.5 mg L-1 at a rate of 209-630 mgN m-2 h-1. We also demonstrated this system could collect 83.9% of nitrogen from NO3--N (19.3 mg L-1) in natural lake water.

Electrocatalytic hydrodechlorination system with antiscaling and anti-chlorine poisoning features for salt-laden wastewater treatment.

The high salinity and coexistence of scaling ions (Ca2+, Mg2+, HCO3-) in wastewater challenge the efficacy and durability of palladium (Pd)-mediated electrocatalytic hydrodechlorination (EHDC) reaction for chlorinated organic pollutant detoxification, due to the accompanying Cl- poisoning at Pd sites and scaling on electrode. In a concentrated NaCl solution (5.8 g L - 1) with Ca2+ (80.0 mg L - 1), Mg2+ (30.0 mg L - 1) and HCO3- (180.0 mg L - 1), the EHDC efficiency of Pd towards 2,4-dichlorophenol decreases significantly from 67.8% to 33.1% in 72.0 h of reaction, and the electrode is covered with layers of fluffy aragonite precipitate. Herein we demonstrate the inclusion of a commercial antiscalant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) can prevent both scale formation and Cl- poisoning, leading to an efficient and steady EHDC process. A mechanistic study reveals that the unique dual function of PBTC primarily originates from the bearing phosphonate and carboxyl groups. With the large affinity of these groups (especially the phosphonate group) for scaling cations and Pd, the PBTC can chelate and stabilize the scaling cations in water and replace Cl- at Pd surface. It can also release protons, and trigger the formation of more electron-deficient Pdδ+ species via PBTC-Pd binding, leading to an enhanced EHDC. This work provides effective solutions to the scaling/poisoning issues that commonly encountered in real wastewater and paves a solid road for EHDC application in pollution abatement.

Dual-site electrocatalytic nitrate reduction to ammonia on oxygen vacancy-enriched and Pd-decorated MnO2 nanosheets.

Electrocatalytic nitrate reduction (NRR) represents one promising alternative to the Haber-Bosch process for NH3 production due to the lower reaction energy barrier compared to N2 reduction and the potential recycling of nitrogen source from nitrate wastewater. The metal oxides with oxygen vacancy (Ov) display high NH3 selectivities in NRR (NO2-/N2 as side products), but the complexity in Ov enrichment and the inferior hydrogen adsorption on oxides make NRR an inefficient process. Herein, one superior dual-site NRR electrocatalyst that is composed of Ov-enriched MnO2 nanosheets (MnO2-Ov) and Pd nanoparticles (deposited on MnO2) is constructed over the three-dimensional porous nickel foam (Pd-MnO2-Ov/Ni foam). In a continuous-flow reaction cell, this electrode delivers a NO3--N conversion rate of 642 mg N m-2electrode h-1 and a NH3 selectivity of 87.64% at -0.85 V vs. Ag/AgCl when feeding 22.5 mg L-1 of NO3--N (0.875 mL min-1), outperforming the Pd/Ni foam (369 mg N m-2electrode h-1, 85.02%) and MnO2-Ov/Ni foam (118 mg N m-2electrode h-1, 32.25%). Increasing the feeding NO3--N concentration and flow rate to 180.0 mg L-1 and 2.81 mL min-1 can further lift the conversion rate to 1933 and 1171 mg N m-2electrode h-1, respectively. The combination of experimental characterizations and theoretical calculations reveal that the MnO2-Ov adsorbs, immobilizes, and activates the NO3- and N-intermediates, while the Pd supplies the Ov sites with sufficient adsorbed hydrogen (H*) for both the NRR and Ov refreshment. Our work presents a good example of utilizing dual-site catalysis in the highly selective conversion of NO3- to NH3 that is important for nitrate pollution abatement, nitrogen resource recycling, as well as sustainable NH3 production.

Optimizing the metal-support interactions at the Pd-polymer carbon nitride Mott-Schottky heterojunction interface for an enhanced electrocatalytic hydrodechlorination reaction.

We reported one novel strategy via band engineering of the semiconductor support to optimize the metal-support interactions at a Mott-Schottky heterojunction interface and enhance the metal's electrocatalytic hydrodechlorination (EHDC) performance. Taking palladium-polymer carbon nitride (Pd/PCN) as a model, the band tuning of PCN by heteroatomic phosphorus (P) doping substantially boosted the EHDC of 2,4-dichlorophenol (2,4-DCP, one typical chlorinated organic pollutants (COPs)) on Pd, and a peak specific activity of 0.172 min-1 cmPd-2 was achieved by Pd/P-PCN-0.25 (0.25 reflected the P content, and denoted the mass ratio of the P source to PCN precursor used in P-PCN synthesis), quadrupling 0.041 min-1 cmPd-2 of Pd/C and outperforming most of the reported catalysts. The mechanism study revealed the P doping in PCN enabled the positive shift of its Fermi level, which weakened the Pd-PCN interactions and alleviated the electron excess of Pd in Pd/PCN. The P-PCN in Pd/P-PCN-0.25 with the ideal band structure evoked a Pd electronic state that maximized EHDC efficiency. Further investigation into the intermediate products of EHDC on Pd/P-PCN and the biological safety of the 2,4-DCP-contaminated water after EHDC treatment demonstrated the EHDC over our catalyst was environmental-benignity for COPs abatement.

Surface Ligand Environment Boosts the Electrocatalytic Hydrodechlorination Reaction on Palladium Nanoparticles.

We present an enhanced catalytic efficiency of palladium (Pd) nanoparticles (NPs) for the electrocatalytic hydrodechlorination (EHDC) reaction by incorporating the tetraethylammonium chloride (TEAC) ligand into the surface of NPs. Both experimental and theoretical analyses reveal that the surface-adsorbed TEAC is converted to molecular amine (primarily triethylamine) under reductive potentials, forming a strong ligand-Pd interaction that is beneficial to the EHDC kinetics. Using the EHDC of 2,4-dichlorophenol (2,4-DCP), a dominant persistent pollutant identified by the U.S. Environmental Protection Agency, as an example, the Pd/amine composite delivers a mass activity of 2.32 min-1 gPd-1 and a specific activity of 0.16 min-1 cm-2 at -0.75 V versus Ag/AgCl, outperforming Pd and most of the previously reported catalysts. The mechanistic study reveals that the amine ligand offers three functions: the H+-pumping effect, the electronic effect, and the steric effect, providing a favorable environment for the generation of reactive hydrogen radicals (H*) for hydrogenolysis of the C-Cl bond. It also weakens the adsorption strength of EHDC products, alleviating their poisoning on Pd. Investigation into the intermediate products of EHDC on Pd/amine and the biological safety of the 2,4-DCP-contaminated water after EHDC treatment demonstrates that EHDC on Pd/amine is environmentally benign for halogenated organic pollutant abatement. This work suggests that the tuning of NP catalysis using facile ligand post-treatment may lead to new strategies to improve EHDC for environmental remediation applications.

Analysis of Blimp-1 and PD-1/PD-L1 Immune Checkpoint in an Autoimmune Thyroiditis Animal Model.

OBJECTIVE: B lymphocyte-induced maturation protein 1 (Blimp-1) and programmed cell death protein 1 (PD-1) have opposing roles in the development of T cells; however, the mechanism of autoimmune thyroiditis- (AIT-) associated abortion is unclear. The present study investigated the expression of Blimp-1 and PD-1/PD-ligand 1 (PD-L1) in AIT-associated pregnancy loss and elucidated the related signaling pathway involving in the inflammatory response. METHODS: An experimental fetal loss model with autoimmune thyroiditis was established after murine thyroglobulin- (mTg-) immunized CBA/J female mice mating with Balb/c males. ELISA was employed to investigate the TgAb level in the serum of CBA/J female mice. The expression of Blimp-1, PD-1/PD-L1, mammalian target protein rapamycin (mTOR), and Foxp3 proteins in the placenta and spleen was detected through immunofluorescence staining and western blotting. RESULTS: ELISA indicated that the serum TgAb level in the mTg group was higher than that in the control group (P < 0.001). Fetal resorption rates increased in the mTg group compared with those in the control group (45.63% vs. 3.1%, P < 0.05). Blimp-1 levels in the placenta and spleen were higher in the AIT-related miscarriage group than in the control group. However, the expression of PD-1/PD-L1 and Foxp3 was significantly decreased in the placenta and spleen in the AIT-related miscarriage group. CONCLUSION: Blimp-1 participates in the pathogenesis of autoimmune thyroid disease-associated pregnancy loss through the inflammatory immune response, which is potentially mediated through the PD-1/PD-L1 signaling pathway.

Strong pyrrolic-N-Pd interactions boost the electrocatalytic hydrodechlorination reaction on palladium nanoparticles.

We demonstrated that heteroatomic nitrogen (N) doping of graphene can significantly enhance the performance of the graphene-palladium nanoparticle composite catalyst (N/G-Pd) in the electrocatalytic hydrodechlorination (EHDC) reaction. Specifically at -0.80 V (vs. Ag/AgCl), the N/G-430-Pd (prepared at 430 °C, pyridinic/pyrrolic-N-rich) and N/G-900-Pd (prepared at 900 °C, pyridinic/graphitic-N-rich) with equivalent total N content delivered the apparent rate constants (kobs) of 0.28 and 0.20 min-1 molPd-1 in removing 2,4-dichlorophenol, much higher than the 0.13 min-1 molPd-1 of the C-Pd. Additionally, we identified the determinant role of pyrrolic-N in boosting EHDC from the linear relationship between kobs-N and the pyrrolic-N content in the catalyst. Combined experimental and DFT analyses revealed that the positive effect of N doping originated from the strong N-Pd interactions, which modulated the Pd electronic structure and its interactions with the reactant and EHDC products (phenol and Cl-). The pyrrolic N-Pd bond was favorable as it could balance the reactant adsorption and the product desorption.

Activating palladium nanoparticles via a Mott-Schottky heterojunction in electrocatalytic hydrodechlorination reaction.

This work exploited one novel power of the Mott-Schottky heterojunction interface in activating the palladium (Pd) in electrocatalytic hydrodechlorination reaction (EHDC, one reaction targeted for the abatement of chlorinated organic pollutants from water). By forming a Mott-Schottky contact with polymer carbon nitride (Pd-PCN), the Pd nanoparticles enable a relatively complete and pseudo-first-order conversion of 2,4-dichlorophenol (2,4-DCP) to phenol and Cl- with the reaction rate constant (kobs) triple that of the conventional Pd-C (0.68 vs. 0.26 min-1 molPd-1). Further comparison in kobs of Pd-PCN and the Pd catalysts reported in literatures revealed that our Pd-PCN was among the top active catalysts for EHDC. The robust performance of Pd-PCN was attributed to the strong metal-support interactions at the Mott-Schottky heterojunction interface, which enriched the electron on Pd and improved its anti-poisoning ability against phenol. The strong support-metal interactions also endowed Pd-PCN with high activity/structure stability in EHDC. The presence of some anions in water body including NO3-, NO2- and Cl- exerted little effect on EHDC, while the reduced sulfur compounds (S2- and SO32-), even in a very low concentration (1 mM), could significantly deactivate the catalyst. This work provides a facile and efficient strategy to activate noble metals in catalytic reactions.

Identifying the rate-determining step of the electrocatalytic hydrodechlorination reaction on palladium nanoparticles.

Identifying the rate-determining step over the catalysts and clarifying the underlying mechanisms are crucial for maximizing the electrocatalytic hydrodechlorination (EHDC) efficiency for detoxification of the chlorophenol pollutants in water. Here, monodisperse palladium nanoparticles (Pd NPs) separately supported on carbon (C) and titanium nitride (TiN) were synthesized as two model catalysts. The support effects on EHDC efficiency, kinetics and current efficiency towards 2,4-dichlorophenol (2,4-DCP), and the electronic structure of Pd and its binding strengths with 2,4-DCP, phenol and Cl- (the primary EHDC product) were investigated by experimental and density functional theory (DFT) analyses. The low current efficiency (<30%) of both catalysts and the good description of EHDC kinetics by the Langmuir-Hinshelwood model suggest that the 2,4-DCP coverage on Pd, rather than the well-known adsorbed hydrogen generation, determines EHDC efficiency. Furthermore, the superior EHDC efficiency on TiN-Pd (96.4% vs. 80.9% on C-Pd), coupled with the weakened adsorption of 2,4-DCP and phenol on TiN-supported Pd, demonstrates that the 2,4-DCP coverage is largely influenced by phenol due to its poisoning effect by blocking active sites, and phenol desorption is the rate-determining step of EHDC on the catalyst. The support TiN enables alleviation of the phenol poisoning by modulating the electronic structure of Pd. The d band center of Pd can serve as a potential descriptor of EHDC efficiency, and its optimization for balancing 2,4-DCP and phenol adsorption should be an effective strategy to enhance EHDC.

Nanoscale zero valent iron supported on MgAl-LDH-decorated reduced graphene oxide: Enhanced performance in Cr(VI) removal, mechanism and regeneration.

The scaled application of nanoscale zero-valent iron nanoparticles (nZVI or Fe° NPs) in environmental remediation is challenged by easy surface passivation and particle aggregation. To improve this situation and enhance their performance in Cr(VI) removal from water phase, we present one novel strategy to hybridize nZVI with layered double hydroxide (LDH) decorated reduced graphene oxide (rGO). The as-prepared ternary (Fe@LDH/rGO) composites possess better dispersibility, improved hydrophilicity and more positive surfaces that allows higher removal efficiency and capacity for Cr(VI) oxyanions. Composition proportion are optimized and influences of surroundings (solution pH, Cr(VI) concentration and temperature) are evaluated. Also, we demonstrate that Fe@LDH/rGO can be reused with suitable post-treatments, which combines alkaline solution desorption and NaBH4 revivification possess. Cr desorption and Fe leaching ratio during regeneration should be critical indicators that determine the recovery efficiency. Synergistic effect within this ternary system not only contributes to its superiorities in stability, but also continuous iron corrosion via the formation of micro Fe-C batteries, where rGO acts as cathode and alternative electron conductor. The present work suggests great potentials of Fe@LDH/rGO composites in groundwater remediation.

MgAl layered double oxide: One powerful sweeper of emulsified water and acid for oil purification.

We exploit a novel role of MgAl-layered double oxide (LDO) as a powerful sweeper to remove trace emulsified water and organic acids from contaminated oil. Notably, 0.4 g of LDO enable to purify 20 mL of contaminated oil with 0.2 g of water and 0.1 mL of octanoic acid, and the separation efficiency reaches 94.6 and 28.2%, respectively. The separation process is initiated with the immobilization of water droplets at the crystalline matrix of LDO (driven by the unique water memory effect), accompanied by the LDO converted to MgAl-layered double hydroxide (LDH). LDH possesses a high point of zero charge and abundant OH- and Mg2+/Al3+ on its layered surface, which enables it to remove the acids via neutralization and complexing reactions. The immobilized water and adsorbed acids are eventually swept by collecting the solids. The collected solids, mainly composed of LDH, can be regenerated to LDO for recycle through a calcination process. Economy evaluation reveals it takes $6.7 for LDO to purify every cubic meters of emulsion, much more cost-effective than the reported CaSO4•0.5H2O and Fe3O4-based adsorbents. The robust performance with the competitive economy points to the high potential of LDO for oil regeneration.

Curcumin potentiates the potent antitumor activity of ACNU against glioblastoma by suppressing the PI3K/AKT and NF-κB/COX-2 signaling pathways.

Glioblastoma (GBM) is a highly invasive and challenging primary tumor of the central nervous system (CNS), and currently available treatments provide limited benefits to patients with this disease. Therefore, the development of novel therapeutic targets and effective treatment strategies is essential. Nimustine hydrochloride (ACNU) is widely used as the standard chemotherapeutic agent and is frequently administered together with other chemotherapeutic agents in clinical studies. Curcumin, a natural polyphenolic compound, could potentially be combined with chemotherapeutics for cancer treatment; however, there are no reports of studies where ACNU and curcumin were combined for GBM treatment, and the mechanisms underlying their activity remain poorly understood. In the present study, we investigated the effects of combined treatment with curcumin and ACNU on GBM cells and found that it significantly enhanced the inhibition of cell proliferation, colony formation, migration, and invasion. In addition, co-treatment with curcumin increased ACNU-induced apoptosis through enhancing the release of cytochrome c from the mitochondrial intermembrane space into the cytosol. Further, curcumin and ACNU acted synergistically in their antitumor effects by targeting N-cadherin/MMP2/9, PI3K/AKT, and NF-κB/COX-2 signaling. These results indicate that curcumin can enhance the anti-proliferation, anti-migration, and proapoptotic activities of ACNU against GBM, and provide strong evidence that combined treatment with curcumin and ACNU has the potential to be an effective therapeutic option for GBM.

Calcium Sulfate Hemihydrate Nanowires: One Robust Material in Separation of Water from Water-in-Oil Emulsion.

Here we report a facile and cost-effective wet-chemical approach to the synthesis of calcium sulfate hemihydrate nanowires (HH NWs, CaSO4·0.5H2O), and their robust performance in immobilizing water molecules to the crystal lattice of CaSO4 and then separating them from a surfactant-stabilized water-in-oil emulsion (mean droplet size of around 1.2 µm). Every gram of HH NWs are capable of treating 20 mL emulsion (water content: 10.00 mg mL-1) with a separation efficiency of 99.23% at room temperature, and this efficiency can be further improved by tuning the surface charge density of HH. Along with the water immobilization, HH NWs are converted to large cubic-like calcium sulfate dihydrate microparticles (DH, CaSO4·2H2O, mean size: 50 µm), and the accompanied size increment enables efficient collection of the solid phase from oil. DH microparticles can be regenerated into HH NWs, which retain the high performance of the original NWs. Such a unique renewable feature improves the economics of our method and simultaneously prevents the secondary pollution. Further economic evaluation finds that purification of every cubic meters of emulsion (water content: 10.00 mg mL-1) will cost about $34.18 for HH NWs, much lower than the $490.78 for the previously reported HH NPs, and $11 052.05-$23 420.32 Fe3O4 NP-based adsorbents, respectively. With the high efficiency, easy collection, low cost, and renewable feature, HH NWs show highly promising applications in the field of oil purification and recycle.

Zero-valent iron nanoparticles embedded into reduced graphene oxide-alginate beads for efficient chromium (VI) removal.

Zero-valent iron nanoparticles (Fe0 NPs) technologies are often challenged by poor dispersibility, chemical instability to oxidation, and mobility during processing, storage and use. This work reports a facile approach to synthesize Fe0 NPs embedded reduced graphene oxide-alginate beads (Fe@GA beads) via the immobilization of pre-synthesized Fe0 NPs into graphene oxide modified alginate gel followed by a modelling and in-situ reduction process. The structure/composition characterization of the beads finds that the graphene sheets and the Fe0 NPs (a shape of ellipsoid and a size of <100nm) are uniformly dispersed within the alginate beads. We demonstrate that these Fe@GA beads show a robust performance in aqueous Cr(VI) removal. With a optimized Fe and alginate content, Fe@GA bead can achieve a high Cr(VI) removal efficiency and an excellent mechanical strength. The initial Cr(VI) concentration, ionic strength, temperature and especially solution pH are all critical factors to control the Fe@GA beads performance in Cr(VI) removal. Fitness of the pseudo second-order adsorption model with data suggests adsorption is the rate-controlling step, and both Langmuir and Freundlich adsorption isotherm are suitable to describe the removal behavior. The possible Cr(VI) removal path by Fe@GA beads is put forward, and the synergistic effect in this ternary system implies the potentials of Fe@GA beads in pollutant removal from water body.

Identification of Active Hydrogen Species on Palladium Nanoparticles for an Enhanced Electrocatalytic Hydrodechlorination of 2,4-Dichlorophenol in Water.

Clarifying hydrogen evolution and identifying the active hydrogen species are crucial to the understanding of the electrocatalytic hydrodechlorination (EHDC) mechanism. Here, monodisperse palladium nanoparticles (Pd NPs) are used as a model catalyst to demonstrate the potential-dependent evolutions of three hydrogen species, including adsorbed atomic hydrogen (H*ads), absorbed atomic hydrogen (H*abs), and molecular hydrogen (H2) on Pd NPs, and then their effect on EHDC of 2,4-dichlorophenol (2,4-DCP). Our results show that H*ads, H*abs, and H2 all emerge at -0.65 V (vs Ag/AgCl) and have increased amounts at more negative potentials, except for H*ads that exhibits a reversed trend with the potential varying from -0.85 to -0.95 V. Overall, the concentrations of these three species evolve in an order of H*abs < H*ads < H2 in the potential range of -0.65 to -0.85 V, H*ads < H*abs < H2 in -0.85 to -1.00 V, and H*ads < H2 < H*abs in -1.00 to -1.10 V. By correlating the evolution of each hydrogen species with 2,4-DCP EHDC kinetics and efficiency, we find that H*ads is the active species, H*abs is inert, while H2 bubbles are detrimental to the EHDC reaction. Accordingly, for an efficient EHDC reaction, a moderate potential is desired to yield sufficient H*ads and limit H2 negative effect. Our work presents a systematic investigation on the reaction mechanism of EHDC on Pd catalysts, which should advance the application of EHDC technology in practical environmental remediation.

Immobilizing Water into Crystal Lattice of Calcium Sulfate for its Separation from Water-in-Oil Emulsion.

This work report a facile approach to efficiently separate surfactant-stabilized water (droplet diameter of around 2.0 µm) from water-in-oil emulsion via converting liquid water into solid crystal water followed by removal with centrifugation. The liquid-solid conversion is achieved through the solid-to-solid phase transition of calcium sulfate hemihydrate (CaSO4. 0.5H2O, HH) to dihydrate (CaSO4·2H2O, DH), which could immobilize the water into crystal lattice of DH. For emulsion of 10 mg mL(-1) water, the immobilization-separation process using polycrystalline HH nanoellipsoids could remove 95.87 wt % water at room temperature. The separation efficiency can be further improved to 99.85 wt % by optimizing the HH dosage, temperature, HH size and crystalline structure. Property examination of the recycled oil confirms that our method has neglectable side-effect on oil quality. The byproduct DH was recycled to alpha-HH (a valuable cemetitious material widely used in construction and binding field), which minimizes the risk of secondary pollution and promotes the practicality of our method. With the high separation efficiency, the "green" feature and the recyclability of DH byproduct, the HH-based immobilization-separation approach is highly promising in purifying oil with undesired water contamination.

Crumpled graphene nanoreactors.

Nanoreactors are material structures that provide engineered internal cavities that create unique confined nanoscale environments for chemical reactions. Crumpled graphene nanoparticles or "nanosacks" may serve as nanoreactors when filled with reactive or catalytic particles and engineered for a specific chemical function. This article explores the behavior of crumpled graphene nanoreactors containing nanoscale ZnO, Ag, Ni, Cu, Fe, or TiO2 particles, either alone or in combination, in a series of case studies designed to reveal their fundamental behaviors. The first case study shows that ZnO nanoparticles undergo rapid dissolution inside the nanoreactor cavity accompanied by diffusive release of soluble products to surrounding aqueous media through the irregular folded shell. This behavior demonstrates the open nature of the sack structure, which facilitates rapid small-molecule exchange between inside and outside that is a requirement for nanoreactor function. In a case study on copper and silver nanoparticles, encapsulation in graphene nanoreactors is shown in some cases to enhance their oxidation rate in aqueous media, which is attributed to electron transfer from the metal core to graphene that bypasses surface oxides and allows reduction of molecular oxygen on the high-area graphene shell. Nanoreactors also allow particle-particle electron transfer interactions that are mediated by the connecting conductive graphene, which give rise to novel behaviors such as galvanic protection of Ag nanoparticles in Ag/Ni-filled nanoreactors, and the photochemical control of Ag-ion release in Ag/TiO2-filled nanoreactors. It is also shown that internal graphene structures within the sacks provide pockets that reduce particle mobility and inhibit particle sintering during thermal treatment. Finally, these novel behaviors are used to suggest and demonstrate several potential applications for graphene nanoreactors in catalysts, controlled release, and environmental remediation.

Nanoscale zero-valent iron (nZVI) assembled on magnetic Fe3O4/graphene for chromium (VI) removal from aqueous solution.

Nanoscale Zero-Valent Iron (nZVI) assembled on magnetic Fe3O4/graphene (nZVI@MG) nanocomposites was synthesized for Cr(VI) removal from aqueous solution. nZVI particles were perfectly dispersed either among Fe3O4 nanoparticles (Fe3O4 NPs) or above the basal plane of graphene. This material shows Cr(VI) removal efficiency of 83.8%, much higher than those of individuals (18.0% for nZVI, 21.6% for Fe3O4 NPs and 23.7% for graphene) and even their sum of 63.3%. The removal process obeys pseudo-second-order adsorption model, suggesting that adsorption is rate-controlling step. Maximum Cr(VI) adsorption capacity varies from 66.2 to 101.0 mg g(-1) with decreasing pH from 8.0 to 3.0 at 30°C. Negative ΔG and ΔH indicate spontaneous tendency and exothermic nature. Robust performance of nZVI@MG arises from the formation of micro-nZVI-graphene/nZVI-Fe3O4 batteries and strong adsorption capability of broad graphene sheet/Fe3O4 surfaces. Electrons released by nZVI spread all over the surfaces of graphene and Fe3O4, and the adsorbed Cr(VI) ions on them capture these floating electrons and reduce to Cr(III). Fe3O4 NPs also served as protection shell to prevent nZVI from agglomeration and passivation.

Fe(0)-Fe3O4 nanocomposites embedded polyvinyl alcohol/sodium alginate beads for chromium (VI) removal.

In this study, Fe(0)-Fe3O4 nanocomposites embedded polyvinyl alcohol (PVA)/sodium alginate (SA) beads were synthesized, which exhibited an excellent physical properties and catalytic reactivity, and a robust performance of post-separation (complete separation using a simple grille) and reusability (efficiency of 69.8% after four runs) in Cr(VI) removal. 5.0 wt% PVA with 1.5 wt% SA was the optimal proportion for beads molding, and the followed acidification and reduction treatments were critical to ensure high mechanical strength and high Cr(VI) removal ability of beads. Effects of Fe(0) and Fe3O4 mass fraction, initial pH and Cr(VI) concentration on final removal efficiency were also evaluated. Merely 0.075 wt% Fe(0) together with 0.30 wt% Fe3O4 was sufficient to deal with 20 mg L(-1) Cr(VI) solution. The efficiency decreased from 100 to 79.5% as initial Cr(VI) increased from 5 to 40 mg L(-1), while from 99.3 to 76.3% with increasing pH from 3.0 to 11.0. This work provides a practical and high-efficient method for heavy metal removal from water body, and simultaneously solves the problems in stabilization, separation and regeneration of Fe(0) nanoparticles.

Enhanced dechlorination of 2,4-dichlorophenol by Pd/FeFe3O4 nanocomposites.

The Pd/FeFe(3)O(4) nanocomposites showed higher dechlorination efficiency of 2,4-dichlorophenol (2,4-DCP) rather than bare Pd/Fe nanoparticles in the batch dechlorination experiments. nFe(3)O(4) provided a convenient way to recycle the nanocomposites with an external magnetic field and significantly enhanced 2,4-DCP dechlorination. 2.0 g L(-1) nFe(3)O(4) was the optimal dosage in the presence of 3 g L(-1) Pd/Fe nanoparticles in our system, removing 76.4% 2,4-DCP within 5h in the aqueous environment. This was much higher than bare Pd/Fe nanoparticles (35.8%), 1.0 g L(-1) nFe(3)O(4) (58.0%) and 2.5 g L(-1) nFe(3)O(4) (66.3%) employed under the same conditions. However, excessive nFe(3)O(4) (3.0 g L(-1)) partially overlapped on Pd/Fe nanoparticles to obstruct their contact with 2,4-DCP, and then 2,4-DCP removal efficiency was dropped to 7.4%. Efficiencies of dechlorination and phenol formations were increased significantly when the amount of Pd increased, whereas the highest 2,4-DCP removal efficiency was observed 98.2% at 0.20 wt% Pd loading. Moreover, SO(4)(2-) would also inhibit the dechlorination while Cu(2+), Ni(2+) and Fe(2+) enhanced the dechlorination of 2,4-DCP by Pd/FeFe(3)O(4) nanocomposites. The nanocomposites showed stable catalytic activity, fairly good mechanic stability, and promising to recycle during the process.