Preparation of functionalized Pd/Fe-Fe3O4@MWCNTs nanomaterials for aqueous 2,4-dichlorophenol removal: Interactions, influence factors, and kinetics

Recent advances in bimetallic nanoscale zero-valent iron composite for water decontamination: Synthesis, modification and mechanisms

The environmental pollution of water is one of the problems that have plagued human society. The bimetallic nanoscale zero-valent iron (BnZVI) technology has increased wide attention owing to its high performance for water treatment and soil remediation. In recent years, the BnZVI technology based on the development of nZVI has been further developed. The material chemistry, synthesis methods, and immobilization or surface stabilization of bimetals are discussed. Further, the data of BnZVI (Fe/Ni, Fe/Cu, Fe/Pd) articles that have been studied more frequently in the last decade are summarized in terms of the types of contaminants and the number of research literatures on the same contaminants. Five contaminants including trichloroethylene (TCE), Decabromodi-phenyl Ether (BDE209), chromium (Cr(VI)), nitrate and 2,4-dichlorophenol (2,4-DCP) were selected for in-depth discussion on their influencing factors and removal or degradation mechanisms. Herein, comprehensive views towards mechanisms of BnZVI applications including adsorption, hydrodehalogenation and reduction are provided. Particularly, some ambiguous concepts about formation of micro progenitor cell, production of hydrogen radicals (H·) and H2 and the electron transfer are highlighted. Besides, in-depth discussion of selectivity for N2 from nitrates and co-precipitation of chromium are emphasized. The difference of BnZVI is also discussed.

Constructing Ni4/Fe@Fe3O4-g-C3N4 nanocomposites for highly efficient degradation of carbon tetrachloride from aqueous solution

Catalytic hydrodechlorination is one of the most potential remediation methods for chlorinated organic pollutants. In this study, Ni₄/Fe@Fe₃O₄-g-C₃N₄ (NFFOCN) nanocomposites were synthesized for carbon tetrachloride (CT) removal and characterized by SEM, XPS and FTIR. The characterization results demonstrated that the special functional groups of g-C₃N₄, especially NH groups, effectively alleviated the aggregation of nanoparticles. In addition, the C and N groups of g-C₃N₄ enhanced the catalytic dechlorination of CT by providing binding sites. The experimental results showed that NFFOCN could effectively remove CT over a wide initial pH range of 3-9, and the CT removal efficiency reached 94.7% after 35 min with only 0.15 g/L of NFFOCN at pH 5.5. The Cl^-, SO₄^2-, and HCO₃^- promoted the removal of CT, while HA and NO₃^- had the opposite effect. Furthermore, good sequential CT removal by NFFOCN nanocomposites was observed, and the CT removal efficiency reached 77.3% after four cycles. Based on the identification of products, a possible degradation pathway of CT was proposed. Moreover, the main mechanisms regarding CT removal included the direct reduction of nZVI (about 40.51%), adsorption (around 34.79%), and hydrodechlorination of CT by Ni⁰ using H₂ (about 19.40%).

Experimental Identification of the Roles of Fe, Ni and Attapulgite in Nitroreduction and Dechlorination of p-Chloronitrobenzene by Attapulgite-Supported Fe/Ni Nanoparticles

The porous-material loading and noble-metal doping of nanoscale zero-valent iron (nFe) have been widely used as countermeasures to overcome its limitations. However, few studies focused on the experimental identification of the roles of Fe, the carrier and the doped metal in the application of nFe. In this study, the nitroreduction and dechlorination of p-chloronitrobenzene (p-CNB) by attapulgite-supported Fe/Ni nanoparticles (ATP-nFe/Ni) were investigated and the roles of Fe, Ni and attapulgite were examined. The contributions of Ni are alleviating the oxidization of Fe, acting as a catalyst to trigger the conversion of H₂ to H*(active hydrogen atom) and promoting electron transfer of Fe. The action mechanisms of Fe in reduction of -NO₂ to -NH₂ were confirmed to be electron transfer and to produce H₂ via corrosion. When H₂ is catalyzed to H* by Ni, the production H* leads to the nitroreduction. In additon, H* is also responsible for the dechlorination of p-CNB and its nitro-reduced product, p-chloroaniline. Another corrosion product of Fe, Fe²⁺, is incapable of acting in the nitroreduction and dechlorination of p-CNB. The roles of attapulgite includes providing an anoxic environment for nFe, decreasing nFe agglomeration and increasing reaction sites. The results indicate that the roles of Fe, Ni and attapulgite in nitroreduction and dechlorination of p-CNB by ATP-nFe/Ni are crucial to the application of iron-based technology.

Enhanced selective adsorption of lead(II) from complex wastewater by DTPA functionalized chitosan-coated magnetic silica nanoparticles based on anion-synergism

Simultaneously removing heavy metal and dye from complex wastewater is of great significance to industrial wastewater treatment. Herein, a novel magnetic adsorbent, DTPA-modified chitosan-coated magnetic silica nanoparticle (FFO@Sil@Chi-DTPA), was successfully prepared and used to enhance the Pb(II) selective adsorption from multi-metal wastewater based on anion-synergism. In the competitive experiment conducted in a multi-ion solution, the type of selective adsorption of metals was changed by the adsorbents before and after amidation, in which FFO@Sil@Chi-DTPA exhibited an excellent selectively for capturing Pb(II), while FFO@Sil@Chi demonstrated highly selective adsorption of silver. More importantly, the selective adsorption of Pb(II)S by FFO@Sil@Chi-DTPA was enhanced from 111.71 to 268.01 mg g^-1 when the coexisting MB concentrations ranged from 0 to 100 mg L^-1 at pH 6.0. In the Pb(II)-MB binary system, Pb(II) and MB exhibited a synergistic effect, in which the presence of MB strengthened the adsorption effect of Pb(II) due to the sulfonic acid groups in MB molecules that create new specific sites for Pb(II) adsorption, while MB adsorption was also enhanced by the presence of Pb(II). This work provides a new strategy for exploring novel adsorbents that can enhance the selective removal of heavy metal in complex wastewater based on anion-synergism.

Tailored functional materials as robust candidates to mitigate pesticides in aqueous matrices-a review

Pesticides are among the top-priority contaminants, which significantly contribute to environmental deterioration. Conventional techniques are not efficient enough to remove pollutants from environmental matrices. The development of functional materials has emerged as promising candidates to remove and degrade pesticides and related hazardous compounds. Furthermore, the nanohybrid materials with unique structural and functional characteristics, such as better material anchorage, mass transfer, electron-hole separation, and charged interaction make them a versatile option to treat and reduce pollutants from aqueous matrices. Herein, we present the current progress in the development of functional materials for the abatement of toxic pesticides. The physicochemical characteristics and pesticide-removal functionalities of various metallic functional materials (e.g., zirconium, zinc, titanium, tungsten, and iron), polymer, and carbon-based materials are critically discussed with suitable examples. Finally, the industrial-scale applications of the functional materials, concluding remarks, and future directions in this important arena are given.

Anaerobic Corrosion of Zero-Valent Iron at Elevated Temperatures

Increasing groundwater temperatures caused by global warming, subsurface infrastructure, or heat storage projects may interfere with groundwater remediation techniques using zero-valent iron (ZVI) technology by accelerating anaerobic corrosion. The corrosion behavior of three ZVIs widely used in permeable reactive barriers (PRBs), Peerless cast iron (PL), Gotthart-Maier cast iron (GM), and an ISPAT iron sponge (IS), was investigated at temperatures between 25 and 70 °C in half-open batch reactors by measuring the volume of hydrogen gas generated. Initially, the corrosion rates of all tested ZVIs increased with temperature; at temperatures ≤40 °C, a material-specific steady state is reached, and at temperatures >40 °C, passivation causes a decrease in long-term corrosion rates. The observed corrosion behavior was therefore assumed to be superimposed by accelerating and inhibiting effects, caused by surface precipitates where the fitting of measured corrosion rates by a modeling approach, using the corroded amount of Fe⁰ to account for passivating minerals, yields intrinsic activation energies (E_a, _ZVI) of 81, 90, and 107 kJ mol^-1 for IS, GM, and PL, respectively. An increase in H₂ production might not be directly transferable to an increase in general ZVI reactivity; however, the results suggest that an increase in chlorinated hydrocarbon degradation rates can be expected for ZVI-PRBs in the immediate vicinity of low-temperature underground thermal energy storages (UTESs) or in the impact areas of high-temperature UTES with temperatures of ≤40 °C.

Magnetic phosphorylated chitosan composite as a novel adsorbent for highly effective and selective capture of lead from aqueous solution

Separating and recovering lead from heavy metal contaminated wastewater is crucial for the environment remediation and reutilization of lead resources. Herein, a novel adsorbent, the phosphorylated chitosan-coated magnetic silica nanoparticles (Fe₃O₄@SiO₂@CS-P), was successfully fabricated and applied to highly selective adsorption of lead. Competitive experiments were conducted in a multi-ion solution (7 metal ions coexist) at pH 6.0, Fe₃O₄@SiO₂@CS-P exhibited an excellent selectively for capturing lead with the distribution coefficient (0.75 L g^-1) more ten times than other metal, while Fe₃O₄@SiO₂@CS demonstrated a highly selective adsorption of silver. These implied that phosphorylation of adsorbent not only improves the sorption performance of lead, but also changes the selective adsorption of metal types. Acidity experiments can draw conclusions that Fe₃O₄@SiO₂@CS-P exhibited better acid resistance (with barely any iron leaching) than silica-uncoated adsorbent (Fe₃O₄@CS-P) at pH 1.0. Furthermore, the FTIR and XPS spectra after adsorption suggested that the high adsorption performance and selective capture lead were predominantly controlled by the coordination of the phosphate groups on the surface of the adsorbent. This work shows a broad prospect of developing a series of novel, acid-resistant, good reusable and rapidly separable magnetic materials that can be used to efficiently and selectively capture lead from aqueous solutions.

Unveiling the Role of Sulfur in Rapid Defluorination of Florfenicol by Sulfidized Nanoscale Zero-Valent Iron in Water under Ambient Conditions

Groundwater contamination by halogenated organic compounds, especially fluorinated ones, threatens freshwater sources globally. Sulfidized nanoscale zero-valent iron (SNZVI), which is demonstrably effective for dechlorination of groundwater contaminants, has not been well explored for defluorination. Here, we show that SNZVI nanoparticles synthesized via a modified post-sulfidation method provide rapid dechlorination (∼1100 μmol m^-2 day^-1) and relatively fast defluorination (∼6 μmol m^-2 day^-1) of a halogenated emerging contaminant (florfenicol) under ambient conditions, the fastest rates that have ever been reported for Fe⁰-based technologies. Batch reactivity experiments, material characterizations, and theoretical calculations indicate that coating S onto the metallic Fe surface provides a highly chemically reactive surface and changes the primary dechlorination pathway from atomic H for nanoscale zero-valent iron (NZVI) to electron transfer for SNZVI. S and Fe sites are responsible for the direct electron transfer and atomic H-mediated reaction, respectively, and β-elimination is the primary defluorination pathway. Notably, the Cl atoms in florfenicol make the surface more chemically reactive for defluorination, either by increasing florfenicol adsorption or by electronic effects. The defluorination rate by SNZVI is ∼132-222 times higher with chlorine attached compared to the absence of chlorine in the molecule. These mechanistic insights could lead to new SNZVI materials for in situ groundwater remediation of fluorinated contaminants.

Dechlorination of 2,4-dichlorophenol in a hydrogen-based membrane palladium-film reactor: Performance, mechanisms, and model development

We created a hydrogen-based membrane palladium-film reactor (MPfR) by depositing palladium nanoparticles (PdNPs) on hollow-fiber membranes via autocatalytic hydrogenation to form a Pd-film. The MPfR was used for hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP). HDC performances and mechanisms were systematically evaluated, and a continuous-flow dechlorination model was established. Approximately 87% of the input 2,4-DCP was reduced to the end-product phenol (P), while 2-chlorophenol (2-CP) was an intermediate, but only at 2%. Selective adsorption of the 2,4-DCP onto the Pd-film and fast desorption of P facilitated efficient dechlorination. Modeling results represented well the concentrations of 2,4-DCP and its intermediates. It demonstrated three dechlorination pathways: The majority of 2,4-DCP was completely dechlorinated to P in an adsorbed state without release of monochlorphenol, some 2,4-DCP was degraded to 2-CP that was released and subsequently adsorbed and reduced to P, and a small amount was reduced to 4-CP that was released and subsequently adsorbed and reduced to P. Analysis based on Density Functional Theory suggests that the pathway of full dechlorination was dominant due to its thermodynamically favorable adsorption configuration, with both Cl atoms bonded to Pd. This study documents full dechlorination of 2,4-DCP in the MPfR and the interacting roles of adsorption and HDC.

In situ growth of Fe3O4 on montmorillonite surface and its removal of anionic pollutants

An environmentally functional material for the efficient removal of anionic pollutants in water was prepared for our study. Montmorillonite (M) was modified by hydrochloric acid (HCl) and cetyltrimethylammonium bromide (CTAB). Fe₃O₄ was grown in situ to prepare modified Fe₃O₄/montmorillonite (AC Fe₃O₄–Mt) composites. The number of hydroxyl sites on the surface of Mt and the surface tension were increased by HCl and CTAB modification, respectively, which enabled higher Fe₃O₄ surface growth, promoting the multi-directional crystallisation of Fe₃O₄ and improving reactivity. The XRD results show that Fe₃O₄ grows on the surface of Mt and has good crystallinity and high purity, meaning that AC Fe₃O₄–Mt is more reactive than Fe₃O₄. When AC Fe₃O₄–Mt is used to remove anionic pollutants in water, the removal effect under the synergistic action of adsorption-redox is significantly improved, and the maximum removable quantities of Cr(vi) and 2-4-dichlorophenol can reach 41.57 mg g⁻¹ and 239.33 mg g⁻¹, respectively. AC Fe₃O₄–Mt is a high efficiency and environmentally functional material with green environmental protection, which can be used in the field of sewage treatment.

An environmentally functional material for the efficient removal of anionic pollutants in water, was prepared for our study.

Stabilization of Soil Arsenic with Iron and Nano-Iron Materials: A Review

Soil arsenic (As) contamination is an important environmental problem, and chemical stabilization is one of the major techniques used to remediate soil As contamination. Iron and iron nanoparticle materials are widely used for soil As stabilization because they have one or more of the following advantages: high adsorption capacity, high reduction capacity, cost effectiveness and environmental friendliness. Therefore, this review introduces the stabilization of soil As with iron and iron nanoparticles, including zero-valent iron, iron oxides/hydroxides, some iron salts and Fe-based binary oxides and the nanoparticles of these iron materials. The mechanism of chemical soil As stabilization, which involves adsorption and the coprecipitation process, is discussed. The factors affecting the chemical stabilization process are presented, and challenges to overcome in the future are also discussed in this review.

Iron and Sulfur Precursors Affect Crystalline Structure, Speciation, and Reactivity of Sulfidized Nanoscale Zerovalent Iron

The reactivity of sulfidized nanoscale zerovalent iron (SNZVI) is affected by the amount and species of sulfur in the materials. Here, we assess the impact of the Fe (Fe²⁺ and Fe³⁺) and S (S₂O₄^2-, S^2-, and S₆^2-) precursors used to synthesize both NZVI and SNZVI on the resulting physicochemical properties and reactivity and selectivity with water and trichloroethene (TCE). X-ray diffraction indicated that the Fe precursors altered the crystalline structure of both NZVI and SNZVI. The materials made from the Fe³⁺ precursor had an expanded lattice in the Fe⁰ body-centered-cubic (BCC) structure and lower electron-transfer resistance, providing higher reactivity with water (∼2-3 fold) and TCE (∼5-13 fold) than those made from an Fe²⁺ precursor. The choice of the S precursor controlled the S speciation in the SNZVI particles, as indicated by X-ray absorption spectroscopy. Iron disulfide (FeS₂) was the main S species of SNZVI made from S₂O₄^2-, whereas iron sulfide (FeS) was the main S species of SNZVI made from S^2-/S₆^2-. The former SNZVI was more hydrophobic, reactive with, and selective for TCE compared to the latter SNZVI. These results suggest that the Fe and S precursors can be used to select the conditions of the synthesis process and provide selected physicochemical properties (e.g., S speciation, hydrophobicity, and crystalline structure), reactivity, and selectivity of the SNZVI materials.

Nanocomposites of zero-valent Iron@Activated carbon derived from corn stalk for adsorptive removal of tetracycline antibiotics

The hybrid nanocomposites of zero-valent iron loaded the activated carbon derived from the corn stalk (ZVI@ACCS) was prepared and used to remove the antibiotics of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) from aqueous solution. The adsorption amounts of three antibiotics (103.1 mg g^-1 for CTC, 72.9 mg g^-1 for OTC and 81.5 mg g^-1 for TC) were sensitive to the temperature and independent of pH in the range of 4.2-7.1 at 298 K through the synergistic interactions of the electrostatic attraction, the bridging complexation and the surface complexation. The equilibrium was performed within 20 min at 298 K. The spontaneous (ΔG^o<0) and endothermic (ΔH^o>0) adsorption of three antibiotics onto the ZVI@ACCS nanocomposites gave a better matching (r² > 0.99) with Langmuir and pseudo-second-order models.

New insights into MnOOH/peroxymonosulfate system for catalytic oxidation of 2,4-dichlorophenol: Morphology dependence and mechanisms

Sulfate radical-based advanced oxidation processes (SR-AOPs) have received increasing attention as viable technology for recalcitrant organics removal from polluted waters. As for heterogeneous catalyst, it is crucial to reveal the effect of morphology on its catalytic activity and mechanism, providing guidelines for rational design of morphology-dependent catalysts. Hence, in this study, we selected manganese oxyhydroxide (MnOOH) as the peroxymonosulfate (PMS) activator and synthesized different morphological MnOOH with the same crystal structure. The catalytic activity of MnOOH follows: nanowires > multi-branches > nanorods. Different morphological MnOOH had different physical and chemical characterization such as specific surface area, Lewis sites, ζ-potential and redox potential, which played positive roles in catalytic activity of MnOOH as PMS activator. Unexpectedly, it was found that ζ-potential was more crucial than specific surface area, redox potential and Lewis sites. Notably, nanowires exhibited higher positive zeta potential, which was favor of promoting interfacial reactivity between HSO₅^- and surface of MnOOH. Furthermore, •OH, SO₄•^-, O₂•^- and ¹O₂, were involved in the MnOOH/PMS system. Moreover, the cycle of Mn (III)/Mn (II) accelerated MnOH⁺ formation. This study provided a new understanding of manganese-catalyzed peroxymonosulfate activation and elucidated the relationships between morphology of catalyst and its catalytic activity.

Cationic metal-organic frameworks as an efficient adsorbent for the removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions

Metal-organic frameworks (MOFs) material with high surface area, good chemical stability and multi-functionality, has become an emerging adsorbent for water treatment. A novel kind of quaternary amine anionic-exchange MOFs UiO-66 namely UiO-66-NMe₃⁺ was firstly synthesized for adsorptive removal of a widely used toxic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solutions. The well-prepared UiO-66-NMe₃⁺ MOFs were fully characterized, and then the main parameters affecting the adsorption process including solution pH, adsorbent dosage and coexisting anions were systematically investigated. The maximum adsorption capacity of UiO-66-NMe₃⁺ toward 2,4-D reached as high as 279 mg g^-1, much higher than that of pristine UiO-66 and aminated UiO-66. The adsorption mechanism could be attributed to the electrostatic interactions efficiently enhanced by the functionalization of quaternary amine groups, combining with the π-π conjugations between the linkers in MOFs and 2,4-D molecules, leading to the better adsorption performance of UiO-66-NMe₃⁺. Additionally, the UiO-66-NMe₃⁺ could be well regenerated by simple solvent washing and exhibited a slight decline of adsorption capacity after seven successive recycle. Furthermore, satisfactory adsorption capacity and reusability of the MOFs in environmental water samples were attained. Comparing with reported activated carbon and resin materials, the UiO-66-NMe₃⁺ MOFs possessed higher adsorption capacity and shorter equilibrium time, as well as good reusability and practicality. The developed ion-exchange functionalized MOFs provided an ideal alternative for efficient adsorptive-removal of 2,4-D from complicated aqueous environment.

Efficient degradation of sodium diclofenac via heterogeneous Fenton reaction boosted by Pd/Fe@Fe3O4 nanoparticles derived from bio-recovered palladium

Dehalogenation of emerging pollutants has attracted worldwide attention. In this study, novel bio-Pd/Fe@Fe₃O₄ nanoparticles (NPs) were proposed to boost the heterogeneous Fenton reaction for degradation of sodium diclofenac (DCF). Specifically, Enterococcus faecalis (E. faecalis) was employed to achieve bio-recovered palladium (bio-Pd). Results showed that expected preparation of bio-Pd/Fe@Fe₃O₄ NPs was confirmed by various characterization techniques. The prepared bio-Pd/Fe@Fe₃O₄ NPs were spherical morphology with average size of 9 nm. Under the optimum conditions, the removal efficiency of 10 mg/L DCF in 20 min and 40 min reached as high as 94.69% and 99.65%, respectively. The dechlorination and mineralization efficiencies of DCF were 85.16% and 59.21% in 120 min, respectively. The main degradation pathway of DCF was complete mineralization with the final products CO₂, chloride ions and H₂O. The improvement of dechlorination efficiency was ascribed to the accelerated corrosion of nano zero valent iron (nZVI) by Pd/Fe galvanic effect and the rise of active hydrogen. Meanwhile, more ferrous ions were released into this solution, resulting in the higher heterogeneous Fenton reaction rate driven by bio-Pd/Fe@Fe₃O₄ NPs. Therefore, the findings suggested that bio-Pd/Fe@Fe₃O₄ NPs were effective catalysts for DCF dechlorination and mineralization. The work provided a novel strategy for degradation of halogen-containing environmental pollutants.

Facile synthesis of graphene-based hyper-cross-linked porous carbon composite with superior adsorption capability for chlorophenols

In this work, we proposed a green and cost-effective method to prepare a graphene-based hyper-cross-linked porous carbon composite (GN/HCPC) by one-pot carbonization of hyper-cross-linked polymer (HCP) and glucose. The composite combined the advantages of graphene (GN) and hyper-cross-linked porous carbon (HCPC), leading to high specific surface area (396.93 m²/g) and large total pore volume (0.413 cm³/g). The resulting GN/HCPC composite was applied as an adsorbent to remove 2,4-dichlorophenol (2,4-DCP) from aqueous solutions. The influence of different solution conditions including pH, ionic strength, contact time, system temperature and concentration of humic acid was determined. The maximum adsorption capacity of GN/HCPC composite (calculated by the Langmuir model) could reach 348.43 mg/g, which represented increases of 43.6% and 13.6% over those of the as-prepared pure GN and HCPC, respectively. The Langmuir model and pseudo-second-order kinetic model were found to fit well with the adsorption process. Thermodynamic experiments suggested that the adsorption proceeded spontaneously and endothermically. In addition, the GN/HCPC composite showed high adsorption performance toward other organic contaminants including tetracycline, bisphenol A and phenol. Measurement of the adsorption capability of GN/HCPC in secondary effluent revealed a slight decrease over that in pure water solution. This study demonstrated that the GN/HCPC composite can be utilized as a practical and efficient adsorbent for the removal of organic contaminants in wastewater.

Fast degradation, large capacity, and high electron efficiency of chloramphenicol removal by different carbon-supported nanoscale zerovalent iron

It remains unclear that which kind of carbon support is better for improving the reactivity of nanoscale zerovalent iron (nZVI) without the adsorption effects of carbon. Finding appropriate contaminants that could be degraded by nZVI with high capacity and electron utilization is crucial for exploring the applications of nZVI. High degradation rate (up to 3.70 min^-1) and high capacity (up to 3000 mg g^-1) of antibiotic chloramphenicol (C₁₁H₁₂Cl₂N₂O₅, CAP) removal with high electron utilization (>97%) was achieved by different carbon supported nZVI in this study. Carbon powder (CP) was found to be the best support, possessing good distribution and reactivity of nZVI. 99% of CAP was removed by CP-nZVI after 3 min, without the electron consumption via the side reaction between nZVI and water, suggesting that CAP could outcompete with water for the electrons from nZVI. The entire pathway of CAP removal was elucidated based on UPLC-MS/MS analysis. Partial degradation of CAP (denitration and dechlorination) was enough to take away the antimicrobial properties. These results suggest a promising application scenario of carbon supported nZVI for the remediation of CAP-contaminated water to reduce the antibiotic selection pressure of the environment.

The highly efficient and selective dicarbonylation of acetylene catalysed by palladium nanosheets supported on activated carbon

An ultrathin Pd nanosheet-supported heterogeneous catalyst, Pd_CO/AC, with exposed (111) crystal plane was synthesized, and it shows superior catalytic reactivity (∼43.8%) and selectivity (∼99.0%) for the dicarbonylation of acetylene and CO.

Sulfur Dose and Sulfidation Time Affect Reactivity and Selectivity of Post-Sulfidized Nanoscale Zerovalent Iron

Exposing nanoscale zerovalent iron (NZVI) to dissolved sulfide species improves its performance as a remediation agent. However, the impacts of sulfur dose and sulfidation time on morphology, sulfur content, reactivity, and selectivity of the resulting sulfidized NZVI (SNZVI) have not been systematically evaluated. We synthesized SNZVI using different sulfur doses and sulfidation times and measured their properties. The measured S/Fe molar ratio in the particles ([S/Fe]_particle) was 10-500 times lower than [S/Fe]_dosed but was predictable based on [S/Fe]_dosed × t_sulfidation. The low sulfur content (0.02-0.65 mol % S/Fe) inhibited the reaction of SNZVI with water (up to 13-fold) and increased its reactivity with trichloroethene (TCE) (up to 14-fold) and its electron efficiency (up to 20-fold). A higher [S/Fe]_particle (0.86-1.13 mol % S/Fe) led to complex particle structures and lowered the resistance to electron transfer but did not improve the benefits realized at the lower S/Fe ratios. Adding small amounts of sulfur into NZVI led to more accumulation of acetylene, especially for low Fe/TCE conditions, suggesting that sulfur lowers the rate of hydrogenation of acetylene to ethene. These results show that [S/Fe]_dosed × t_sulfidation can be used to predict the measured S content in the particles and that affects reactivity, longevity, and electron selectivity, for post-SNZVI.

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.

Mechanism and influence factors of chromium(VI) removal by sulfide-modified nanoscale zerovalent iron

Sulfidation of nanoscale zerovalent iron (nZVI) has attracted increasing interest for improving the reactivity and selectivity of nZVI towards various contaminants, such as aqueous Cr(VI) removal. However, the benefits derived from sulfide modification that govern the removal of Cr(VI) remains unclear, which was studied in this work. S-nZVI with higher S/Fe molar ratio showed higher surface area, the discrepancy between the surface-area-normalized removal capacity of Cr(VI) by S-nZVI with different S/Fe indicated that the removal of Cr(VI) was also affected by other factors, such as electron transfer ability, surface-bounded Fe(II) species, and surface charges. High specific surface area would provide more active site for Cr(VI) removal, and as an efficient electron conductor, acicular-like FeS_x phase would also favor electron transfer from Fe⁰ core to Cr(VI). Low initial pH also enhanced the Cr(VI) removal, and the Cr(VI) removal capacity by S-nZVI and nZVI was not affected by aging process, these results confirmed that the Fe(II) species also played an important role in the Cr(VI) removal. Other influence factors were also investigated for potential application, including temperature, initial Cr(VI) concentration, ionic strength, and co-existed ions. The removal mechanism of Cr(VI) by S-nZVI involved the sulfide modification to increase the specific surface area and provide more active sites, the corrosion of Fe⁰ to produce surface-bounded Fe(II) species to adsorb Cr(VI) species, followed by the favored reduction of Cr(VI) to Cr(III) due to the electron transfer ability of FeS_x, then the formation of Cr(III)/Fe(III) hydroxides precipitates.

Reactivity, Selectivity, and Long-Term Performance of Sulfidized Nanoscale Zerovalent Iron with Different Properties

Sulfidized nanoscale zerovalent iron (SNZVI) has desirable properties for in situ groundwater remediation. However, there is limited understanding of how the sulfidation type and particle properties affect the reactivity and selectivity of SNZVI toward groundwater contaminants, or how reactivity changes as the particles age. Here, SNZVI synthesized by either a one-step (SNZVI-1) or two-step (SNZVI-2) process were characterized, and the reactivity of both fresh and aged (1d to 60 d) nanoparticles was assessed. The measured S/Fe ratio was 5.4 ± 0.5 mol % for SNZVI-1 and 0.8 ± 0.1 mol % for SNZVI-2. XPS analysis indicates S^2-, S₂^2-, and S _n^2- species on the surface of both SNZVI-1 and SNZVI-2, while S₂^2- is the dominant species inside of the SNZVI nanoparticles. SNZVI-1 particles were hydrophobic (contact angle = 103 ± 3°), while the other materials were hydrophilic (contact angles were 18 ± 2° and 36 ± 3° for NZVI and SNZVI-2, respectively). SNZVI-1, with greater S content and hydrophobicity, was less reactive with water than either NZVI or SNZVI-2 over a 60 d period, resulting in less H₂ evolution. It also had the highest reactivity with TCE and the lowest reactivity with nitrate, consistent with its higher hydrophobicity. In contrast, both NZVI and SNZVI-2 were reactive with both TCE and nitrate. Both types of SNZVI remained more reactive after aging in water over 60 d than NZVI. These data suggest that the properties of the SNZVI made from a one-step synthesis procedure may provide better reactivity, selectivity, and longevity than that made from a two-step process.

Preparation of magnetic polyimide@ Mg-Fe layered double hydroxides core-shell composite for effective removal of various organic contaminants from aqueous solution

In this work, a novel core-shell structured magnetic polyimide@layered double oxides (LDO) composites coating a porous polyimide (PI)-coated Fe3O4 magnetic core and layered double hydroxide (LDH) has been successfully synthesized by solve-thermal synthesis and co-precipitation process. The magnetic PI@LDO composites were characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), thermogravimetry analysis (TGA) and magnetic properties analysis. The composite materials displayed core-shell structure with flower-like morphology. The magnetic PI@LDO composites were applied to remove tetracycline (TC), 2,4-dichlorophenol (2,4-DCP) and glyphosate (GP) from aqueous solution. The action pH value was ranged from 5 to 9 for TC and GP and 3 to 7 for 2,4-DCP, respectively. Cl- showed a weak competitive adsorption effect to TC, 2, 4-DCP and GP. In addition, the presence of humic acid (HA) could slightly reduce the adsorption capacity of magnetic PI@LDO composites. The adsorption process could be well described by pseudo-second-order model for TC and GP, while pseudo-first-order model for 2,4-DCP. The experimental data of TC and 2,4-DCP could be fitted better with Freundlich model, while that of GP were fitted better with Langmuir model. The adsorptions of TC, 2,4-DCP and GP were both spontaneous and endothermic. The adsorption capacity decreased slightly after adsorption-desorption cycles repeated five times. This study demonstrated that magnetic PI@LDO exhibited great potential to be a mild and cost-effective adsorbent for the removal of various organic contaminants from wastewater.

Aqueous Hg(II) immobilization by chitosan stabilized magnetic iron sulfide nanoparticles

Stabilized iron sulfide (FeS) nanoparticles have been proven effective in the adsorption of Hg from the water environment. However, previous work with these nanoparticles determined that the separation from the treated water was difficult and time-consuming. In this study, nanoscale FeS-Fe₃O₄ nanocomposites were firstly synthesized with chitosan as the stabilizer (CTO-MFeS). Then, the Hg adsorption capacity and mechanism were studied. Results showed that the size of the prepared nanoparticles was about 20nm and the specific surface area was 21.3m²/g. Hg removal by the CTO-MFeS nanoparticles involved both adsorption and precipitation. Further investigation with XPS showed that Hg²⁺ was adsorbed on the surface of the CTO-MFeS nanoparticles and reacted with CTO-MFeS to form HgS and [Fe_(1-x)Hg_x]S. It was also found as pH decreased below 4, the adsorption capacity of CTO-MFeS was significantly reduced that might be due to the dissolving of Fe. Additionally, the presence of Cl^- resulted in the transformation of Hg²⁺ to HgClx^2-x (x=1, 2, 3, 4) that competed with OH in solution for Hg²⁺ and therefore inhibited the adsorption of Hg. Our findings provide additional information that may be useful for a theoretical basis for Hg treatment in water environment.

A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism

Carbon-based nanomaterials, especially carbon nanotubes and graphene, have drawn wide attention in recent years as novel materials for environmental applications. Notably, the functionalized derivatives of carbon nanotubes and graphene with high surface area and adsorption sites are proposed to remove heavy metals via adsorption, addressing the pressing pollution of heavy metal. This critical revies assesses the recent development of various functionalized carbon nanotubes and graphene that are used to remove heavy metals from contaminated water, including the preparation and characterization methods of functionalized carbon nanotubes and graphene, their applications for heavy metal adsorption, effects of water chemistry on the adsorption capacity, and decontamination mechanism. Future research directions have also been proposed with the goal of further improving their adsorption performance, the feasibility of industrial applications, and better simulating adsorption mechanisms.

Synthesis and characterization of magnetic mesoporous Fe3O4@mSiO2–DODGA nanoparticles for adsorption of 16 rare earth elements

The high selectivity magnetic mesoporous Fe₃O₄@mSiO₂–DODGA nanomaterials were prepared for adsorption of 16 rare earth elements.