Surface Of Palygorskite Research Articles

Synthesis of palygorskite based microspheres for efficient and recyclable simultaneous removal of radioactive iodine and iodide

The valence state of radioactive iodine is abundant and convertible. Therefore, it is crucial to synthesize a cost-effective, recyclable adsorbent that can effectively and simultaneously remove polyvalent radioactive iodine. Polymerized microsphere adsorbents (PMs) with pore size of 10 ∼ 20 μm and surface of palygorskite (PAL) were prepared by the Pickering emulsion template method using 2-(diethylamine)ethyl methacrylate (DEAEMA) as functional monomer and affordable PAL as matrix material. Under the synergistic effect of chemical adsorption of tertiary amine group in PDEAEMA and physical adsorption, the optimized PM-2 exhibits excellent adsorption activities for gaseous iodine (2.98 g/g), iodine in n-hexane (1.39 g/g), and iodide (1.48 mmol/g). After heating and soaking in NaOH solution, the high adsorption capacity and almost unchanged morphology and crystal structure of PM-2 after 5 cycles indicate that PMs have outstanding physical and chemical stability and reusability. Importantly, PMs also show astonishing adsorption activity for the simultaneous removal of iodine and iodide. Moreover, the ultra-fast adsorption rate and ultra-high adsorption efficiency of PMs provide promising results for the removal of polyvalent radioactive iodine in environmental remediation.

Adsorption of Cd(II) on mercapto-palygorskite functional materials with different proportions: Performance, mechanism and DFT study

Cd contamination has cosmopolitan harm and urgent needs to be addressed, the mercapto (-SH) modified materials are emerging in the Cd remediation field. In this study, three mercapto-palygorskite functional materials (0.2MP, 0.5MP, 1.0MP) were prepared by trimethoxysilane (MPTMS) and palygorskite (PAL) with different weight ratios (0.2:1, 0.5:1, 1:1), to investigate the effect of -SH proportions differences on material properties and combination configuration with Cd. The results indicated that mercapto groups grafting occurred on the PAL surface, retaining the original mineral structure. The adsorption capacity improved with the increase of -SH ratio, and 1.0 MP (30.06 mg g−1) was up to about 3 times of PAL (10.07 mg g−1). The Cd stabilization subjected to the pseudo-second-order kinetic, Redlich-Paterson and Langmuir isothermal model, belonging to monolayer homogeneous chemisorption. Multifaceted characterization revealed that MP utilized mercapto and hydroxyl groups to form complexation with Cd as the dominant action mechanism. The electron transfer that took place from -SH to Cd was confirmed by Bader net change. DFT calculation manifested that bidentate complex S-Cd-S (Ead = −1.089 eV) was the best configuration of -SH combined with Cd due to its lower binding energy than the monodentate complex (Ead = −0.579 eV). This study confirms that MP as a friendly functional material offers a bright application prospect in the treatment of Cd contamination.

First-principle calculations of sulfur dioxide adsorption on the palygorskite

This study uses the density functional theory (DFT) method of first-principle to provide theoretical guidance for a deeper understanding of the adsorption performance of palygorskite (PAL). An analysis was conducted to determine the optimal surface configurations and binding sites for SO2 on the PAL (100) surface. The results show that for the SO2/PAL adsorption system, the adsorption energies (-0.13 and -0.10 eV) and charge transfer amounts (0.017 and 0.029 e) at the top and bridge sites are greater than those at the hollow site (0.55 eV and 0.015 e), which determine the steadiest adsorption sites. Moreover, the fermi level is altered by orbitals in SO2, revealing interactions between SO2 and the (100) surface of PAL.

Novel ferrous disulfide loaded palygorskite composites as additives in lignocellulosic waste composting for improving humification

Improving the composting efficiency of lignocellulose wastes has been the focus in the field of aerobic fermentation. In this study, FeS2 was modified on the surface of palygorskite to regulate the straw composting. Material characterizations showed that FeS2/Pal composite exhibited glutathione oxidase and catalase activities, attributing to the fact that nano FeS2 filled the aggregation space of the original palygorskite, exposing more active sulfur vacancy defects. During the composting process, the addition of FeS2/Pal could adjust pH value and increase electrical conductivity, which was conducive to improving the efficiency of biological redox process. The total degradation ratio of cellulose was 52.54% with FeS2/Pal added. The repolymerization of small molecule intermediates was strengthened, and the final polymerization degree and maturity of composting products was improved. Since the sequence abundance of aromatic amino acids biosynthesis and carbon fixation pathways was higher revealed by PICRUSt. High-throughput sequencing results showed that bacterial community was more dominant than fungi, with community richness index increased by 2.3–3.7 times. The pathogenic bacteria such as Atopostipes and Corynebacterium were disappeared, and heat-resistant bacteria were dominant. The key bacteria and fungi in the group added with FeS2/Pal were Limnochordaceae and Melanocarpus genus, which were related to the cellulose enzymatic hydrolysis and humification degree.

Investigation on the Mechanism of PAL (100) Surface Modified by APTES.

The interfacial mechanism has always been a concern for 3-aminopropyltriethoxysilane (APTES)-grafted palygorskite (PAL). In this research, the mechanism of graft modification for grafting of APTES to the surface of PAL (100) was studied using density functional theory (DFT) calculation. The results illustrated that different grafting states of the APTES influence the inter- and intramolecular interactions between APTES/PAL (100), which are reflected in the electronic structures. For single-, double-, and three-toothed state APTES-PAL (100), the charge transfer rates from the PAL (100) surface to APTES were 0.68, 1.02, and 0.77 e, respectively. The binding energy results show that PAL (100) modification performance in the double-tooth state is the best compared to the other states, with the lowest value of -181.91 kJ/mol. The double-toothed state has lower barrier energy (94.69, 63.11, and 153.67 kJ/mol) during the modification process. This study offers theoretical insights into the chemical modification of the PAL (100) surface using APTES coupling agents, and can provide a guide for practical applications.

Evolution mechanism of SO2 adsorption on palygorskite (1 0 0) surface modified by APTES: Effect of different grafting modification

The effects of 3-aminopropyltriethoxysilane (APTES) with different grafting modifications on the (100) surface of palygorskite (PAL) have been examined in the current work using the first principles method. Our finding results show that the chemisorption is probably occurring because the adsorption energies of the single, double, and three-tooth APTES-PAL (100) surface systems are −66.45, −199.55, and −153.63 kJ/mol, respectively, all below −18.86 kJ/mol (or −0.2 eV). Moreover, the different grafting structures of the APTES-PAL (100) surface have different adsorption characteristics, showing that H2O was produced in the double and three-tooth APTES-PAL (100) surface systems and H2 was produced in the single-tooth APTES-PAL (100) surface system. Additionally, the rate-determining step to adjust the effectiveness of the adsorbent is the H atom broken from the NH2 group of APTES combining with the O atom of SO2. These insights will be used to develop clay composite materials in the future for gas adsorption.

Magnetic field assisted process for preparing anti-biofouling PVDF membranes incorporated by hydrophilic magnetic palygorskite

Membrane technology can realize wastewater recycling in industry, but its efficiency is threatened by fouling. In this study, magnetic palygorskite (m-Pal) nanofibers were obtained by anchoring Fe3O4 nanoparticles onto the surface of palygorskite. Then, composite membranes composed of poly(vinylidene fluoride) (PVDF) and m-Pal were prepared during a magnetic field assisted phase inversion process. The m-Pal can be elevated to the membrane surface due to magnetic force, thus adjusting membrane performance. The PVDF/m-Pal composite membrane prepared with magnetic field displayed higher water flux and better hydrophilicity than that of pristine PVDF membrane. The water flux can be increased to 343.2 L·m−2·h−1·bar−1, and water contact angle decreases to 71.8° with the addition of 7% m-Pal. Moreover, the anti-fouling and easy-cleaning performance of the composite membrane was demonstrated in bovine serum albumin (BSA) solution separation, with BSA flux and flux recovery ratio increased by 41.3% and 155.4%, respectively, compared with the control PVDF membrane.

In situ/operando XAFS investigation of the sorption/precipitation of Zn(II) on palygorskite surface at the molecular scale: Implications for Zn stable isotope fractionation

In aqueous geological environments, the fate and transport of Zn are controlled by geochemical reactions (e.g., sorption) occurring at the mineral/water interface. However, many of the underlying Zn fixation mechanisms, especially the kinetics of surface-induced precipitation, are still unclear. Additionally, Zn stable isotope fractionation during sorption has recently been shown to be an important process, but the relationship between Zn isotope fractionation and sorption mechanisms (e.g., surface complexation, precipitation) is also not well understood. To address these issues, we employed X-ray absorption fine structure (XAFS) spectroscopy, high-resolution transmission electron microscopy (HRTEM), and in situ/operando quick-scanning XAS (QXAS) spectroscopy to elucidate the sorption/precipitation mechanisms of Zn at palygorskite/solution interfaces. We also measured Zn isotope ratios during some sorption experiments to illustrate how Zn isotope fractionation behavior is affected by the evolution of coordination environments at different pH values, initial concentrations, and reaction times. Our results demonstrate that Zn sorption mechanisms vary as a function of pH, ionic strength, initial concentration, and reaction time. At low pH (pH < 7.0) and low ionic strength (I ≤ 0.01 M), Zn(II) predominantly forms an outer-sphere surface complex in octahedral coordination. At low pH (pH < 7.0) and high ionic strength (I = 0.1 M), Zn(II) is predominantly sorbed as an inner-sphere octahedral surface complex with insignificant isotopic fractionation (Δ66Znsorbed-aqueous = −0.02 ± 0.05‰). At high pH and high initial Zn concentration (pH 7.5, C0 ≥ 0.2 mM), the formation of octahedral Zn phyllosilicate precipitates is observed, yielding a small fractionation with an average Δ66Znsorbed-aqueous of 0.10 ± 0.07‰. In addition, in situ/operando QXAS of Zn sorption at pH 7.5 in a flow cell revealed that the predominant sorbed Zn species shifted from inner-sphere tetrahedral complexes during the initial stage (e.g., within minutes) to inner-sphere octahedral complexes during later stages (e.g., within hours), followed by the formation of Zn-phyllosilicate precipitates (e.g., within days). This molecular evidence coincides with the evolution of Zn isotope fractionation from a large Δ66Znsorbed-aqueous value (0.53 ± 0.05‰) to a small value of 0.05 ± 0.04‰ during the sorption process. The combination of QXAS and isotope fractionation results reveals a change in the Zn local environment from tetrahedral coordination to octahedral coordination. The findings in this study not only provide new insight into surface adsorption/precipitation mechanisms but also demonstrate that stable isotope fractionation is linked with the local molecular/bonding environments at mineral–water interfaces.

On the adsorption of neodymium species from aqueous solution by beneficiated palygorskite

Run-of-mine (ROM) palygorskite (PAL) from Guadalupes (Piauí/Brazil) was prepared, beneficiated and then properly characterized by physical–chemical analyses. Then, the removal of Nd3+ ions by PAL was evaluated as a function of solution pH, adsorbent concentration, and initial metal concentration. The results showed that the maximum sorption capacity was 18 mg/g, and more than 99 % of Nd was remove from the solution at pH 5. The sorption data were analysed by several isotherm models, but the better good of fitness (R2 ≥ 0.97; RMSE ≤ 0.98) was attributed to the Temkin model. It́s suggested that the adsorption process proceeds firstly by the introduction of the Nd ions into the interior and exterior pore of PAL, then the PAL surface acquires a negative charge by deprotonation of PAL actives sites (Me-OH), and then the capture of the Nd3+ ions on its inside and outside surface may take place through electrostatic interaction. Thermodynamic parameters indicated that the sorption process was favourable and endothermic. Thus, the present results pointed out that palygorskite has potential for removing Nd ions, and probable another rare earth elements from aqueous solutions, being a promisor adsorbent to the treatment of effluents containing neodymium, e.g. industry of permanent magnets.

Nafion/SiO2@TiO2‐palygorskite membranes with improved proton conductivity

AbstractThis work deals with the synthesis of SiO2@TiO2 supported palygorskite fibers and their use as a filler for proton exchange membrane fuel cells in order to improve their performance. SiO2@TiO2‐palygorskite nanostructured particles were synthesized separately with original route to ensure the growth of TiO2 and then of SiO2 on the surface of the clay. Accordingly, the introduction of the synthetic filler (SiO2@TiO2‐paly) into the electrolyte membrane (Nafion) aims to improve mechanical, thermal, and proton conductivity properties. The TiO2 nanoparticles were generated via a sol–gel process on the external surface of palygorskite. Then, SiO2 nanoparticles were synthetized using a similar sol–gel process, onto the TiO2‐palygorskite particles to produce the final SiO2@TiO2‐palygorskite particles. The physico‐chemical properties of the nanostructured particles were studied by X‐ray diffractometry, Fourier transform infrared, scanning electron microscopy, and transmission electron microscopy. Nafion based composite membranes were prepared using SiO2@TiO2‐palygorskite and TiO2‐palygorskite as a control standard. The composite membranes show improved mechanical properties, thermal stability, water retention, and proton conductivity compared to the neat Nafion membrane. Proton conductivities (at 100°C and 100% relative humidity) increased from 65.0 mS/cm for neat Nafion to 70.4 mS/cm and to 128.6 mS/cm when incorporated TiO2‐Paly (6% in weight) and SiO2@TiO2‐Paly (6% in weight), respectively.

Evidence of lead ions on palygorskite surface after adsorptive process: kinetic and isotherms studies

Our previous work reported that palygorskite has potential for application as metal cations adsorbent due to its chemical and mineralogical properties. In this work, kinetic study and adsorption isotherms were performed in order to evaluate Pb (II) ions adsorption rate, maximum capacity and type of adsorption by using palygorskite as adsorbent. Adsorption tests were performed in batch, using pH of 5, 2 g of palygorskite, 40 mL of synthetic effluent solution and stirring for 1 hour. Kinetic experiments were performed using 34 mg L-1 of a lead synthetic effluent at same mass and pH conditions. Furthermore, after adsorption studies, the sample was characterized by X-ray fluorecence (XRF), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) coupled with Energy-dispersive X-ray spectroscopy (EDS) analysis, in order to verify and understand the interaction of lead ions in palygorskite. The results demonstrated that palygorskite presented an equilibrium time of 10 min with 99.14% of removal, following pseudo-second order kinetic. The maximum adsorption capacity was 21.65 mg g-1 and Gibbs’ adsorption-free energy was -21.39 KJ mol-1, with Langmuir model being the most suitable for adjustment of the data. Thus, its presence was confirmed by characterization techniques, indicating that the metal is distributed homogeneously on palygorskite surface, proving its efficiency as lead ions adsorbent.

Smectite, sepiolite, and palygorskite for inactivation of pyocyanin, a biotoxin produced by drug-resistant Pseudomonas aeruginosa

Pyocyanin is an important virulence factor in the resistance of Pseudomonas aeruginosa to antibiotics. This study evaluated the potential of three clay minerals (smectite, sepiolite, and palygorskite) in binding and degrading pyocyanin. A combination of adsorption experiments, in-situ variable-temperature x-ray diffraction (VTXRD), energy dispersive x-ray spectrometry (EDS), and UV spectroscopy were employed to investigate the (1) adsorption affinity (K) and capacity (Q max ) of clay minerals for pyocyanin, (2) binding sites for adsorption on clay minerals and (3) the degradation/transformation of pyocyanin on clay surfaces. Adsorption experiments were performed at pH3, 4.9, and 7 at which pyocyanin occurred as ∼100% protonated, ∼50% protonated and zwitterionic, and ∼100% zwitterionic species, respectively. Overall, the estimated Q max was 0.23-0.53 mol/kg for sepiolite, 0.21-0.43 mol/kg for palygorskite, and 0.43-0.68 mol/kg for montmorillonite. The Q max and K were pH dependent: pH3 < pH7 for sepiolite, pH3 > pH7 for palygorskite, and pH3≈pH4.9>pH7 for montmorillonite. Pyocyanin was mainly adsorbed in the tunnels of sepiolite, external surface of palygorskite, and the interlayer of montmorillonite. The clays did not degrade pyocyanin, instead the structure was slightly transformed on the surfaces of sepiolite and montmorillonite. These results demonstrated the potentials of clay minerals in disarming P. aeruginosa through adsorbing the virulence factor pyocyanin. • Adsorption of pyocyanin by sepiolite, palygorskite and montmorillonite was investigated. • Adsorption (mol/kg) ranged from 0.23 to 0.53 (sepiolite), 0.21 to 0.43 (palygorskite), and 0.43 to 0.68 (montmorillonite). • The surfaces of sepiolite have higher affinity for zwitterionic pyocyanin. • Palygorskite and montmorillonite surfaces have higher affinity for protonated pyocyanin. • Adsorption occurred mainly in the tunnels of sepiolite, external surface of palygorskite and interlayer of montmorillonite.

The Removal of Cd2+, Cu2+ and Pb2+ from Aqueous Solution with Palygorskite: The Effects of Humic Acid

To investigate the impact of Humic acid (HA) on Palygorskite (PAL) as the adsorbent for heavy metal ions, this study was carried out to solve the existing dispute in the effects of HA on PAL sorption capacity. The sorption properties of PAL and HA-loaded PAL (HA/PAL) for Cd2+, Cu2+, Pb2+ in batch experiments were evaluated. PAL and HA/PAL effects on metal ion elimination were examined under various test settings (time, dosage and starting concentration) were compared. The sorption efficiency of PAL was significantly higher than that of HA/PAL. The N2 sorption-desorption and FTIR results showed that HA successfully adhered to the PAL surface without changing its crystal structure but reducing its specific surface area. Cd2+, Cu2+, and Pb2+ for PAL and Cd2+ and Cu2+ for HA/PAL were modelled by pseudo-first-order kinetics; the pseudo-second-order rate conformed to Cu2+ for PAL and Pb2+ for HA/PAL. the Langmuir linear fitting was consistent with Cd2+, Cu2+ and Pb2+ for PAL and HA/PAL. Pb2+ for PAL and Cd2+, Pb2+ for HA/PAL were consistent with the Freundlich isotherm. The results proved that HA was not conducive to improving the adsorption performance of PAL.

Degradation of bisphenol S by peroxymonosulfate activation through monodispersed CoFe2O4 nanoparticles anchored on natural palygorskite

• Monodispersed CoFe 2 O 4 nanoparticles anchored on palygorskite to activate PMS. • 16%-CFO@PAL/PMS oxidation system can effectively degrade BPS in water. • 16%-CFO@PAL composite exhibits high activity and low metal leaching property. • SO 4 · - and 1 O 2 mainly contributed degradation of BPS in 16%-CFO@PAL/PMS system. • Fe-O-Al bond between CoFe 2 O 4 and PAL improved the stability of 16%-CFO@PAL. Bisphenol S (BPS) has been detected frequently in water bodies, which poses a serious threat to human health and the environment. The sulfate radical-based advanced oxidation process is considered as a promising water purification technology by activating peroxymonosulfate (PMS). However, a catalyst with low metal leaching rate and high effective catalytic ability is needed to activate PMS. In this study, natural clay of palygorskite (PAL) was used to mediate monodispersed CoFe 2 O 4 nanoparticles to degrade BPS by PMS activation. The monodispersed CoFe 2 O 4 nanoparticles were distributed and anchored on the surface of PAL, which caused the 16%-CoFe 2 O 4 @PAL (16%-CFO@PAL) composite expose more reaction sites, thus exhibiting excellent catalytic performance. A satisfactory BPS removal rate (> 99%) was obtained by introducing 50 mg L -1 16%-CFO@PAL and 0.16 mM PMS. The interaction mechanism between CoFe 2 O 4 nanoparticles and PAL was discussed. The Al-O-Fe bond between CoFe 2 O 4 nanoparticles and PAL endowed the 16%-CFO@PAL composite with low metal leaching property, high stability and reusability. SO 4 ·- and 1 O 2 played a dominant role in the degradation of BPS. The generation mechanism of reactive species was proposed. The influences of various degradation parameters (e.g., catalyst dosage, PMS concentration, initial solution pH, and BPS concentration) and water constituents (e.g., inorganic anions and NOM) on the degradation of BPS were investigated. Based on the identified intermediates and density functional theory (DFT) calculations, the possible degradation pathways of BPS were discussed. This study provides a new idea for the preparation of high-efficiency natural clay-based PMS catalysts for water purification.

EXAFS investigation of Ni(Ⅱ) sorption at the palygorskite-solution interface: New insights into surface-induced precipitation phenomena

Sorption reactions at the mineral/water interface control the fate and transport of trace metals in aqueous geochemical environments. While surface complexation theory is well established, understanding of surface induced precipitation at mineral/water interfaces is still limited. In this research, we employed a combination of macroscopic batch sorption studies, transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), and extended X-ray absorption fine structure (EXAFS) spectroscopy to elucidate the sorption mechanisms of nickel (Ni) at palygorskite/solution interfaces. Compared to extensive studies focused on oxides and layer-structured clay minerals, research on chain-type clay minerals (e.g., palygorskite and sepiolite) is sparse. Thus, novel investigations using chain-type clay minerals can provide new insights into the metal sequestration mechanisms and improve equilibrium modeling. In this work, temperature-dependent kinetic experiments demonstrated that the activation reaction energy (Ea) for Ni sorption on palygorskite at pH 6.0 is 35.1 kJ mol−1, significantly lower than that of pH 7.5 (Ea = 102.1 kJ mol−1). These values indicated an adsorption reaction at low pH and a precipitation reaction at high pH. EXAFS analysis confirmed that below pH 6, Ni sorption was dominated by outer-sphere surface complexes at low ionic strength (I = 0.01 M) and inner-sphere surface complexation at high ionic strength (I = 0.1 M). Above pH 7.5, EXAFS data suggested the formation of Ni phyllosilicate precipitates, in agreement with its linear sorption isotherm. An important finding is that the precipitates can form at very low Ni concentrations (∼0.07 mM), with the sorption density of Γ = 0.09 μmol m−2, which corresponds to a 0.3% monolayer coverage for palygorskite. In contrast, at this low level of Ni concentration, surface precipitates did not form on γ-Al2O3. We propose that Ni can be directly induced to precipitate on the palygorskite surface in a process we term “continuous nucleation”. This is mechanistically different from the traditional adsorption-to-polymerization process on the γ-Al2O3 surface, which we term “staged nucleation”. Further testing revealed that a linear-shaped isotherm was also observed for Ni sorption on sepiolite, a clay mineral with similar structure and chemical composition to palygorskite, indicating a similar reactivity for both chain-structure phyllosilicates. This is distinct from the Langmuir-type sorption isotherm observed for Ni reaction with Al oxides and montmorillonite. The findings presented in this study improve not only the current understanding of metal sequestration and surface precipitation at mineral/water interfaces but also shed light on the large differences in the surface reactivities of clay minerals with chain structure versus layered structure.

Adsorption of Hg(II) in solution by mercaptofunctionalized palygorskite.

In the past 10 years, the treatment and restoration of soil and water bodies contaminated by mercury and other heavy metals have received unprecedented attention and support from China's environmental protection authorities. The search for low-cost and high-efficiency adsorbents has become one of the research hotspots in this field. In this paper, a simple and environment-friendly method was used to graft 3-mercaptopropyl trimethoxysilane on the surface of palygorskite. The synthesized mercaptofunctionalized palygorskite (M-PAL) was characterized by XRD, FT-IR, BET and SEM-EDS, respectively, and its adsorption conditions, adsorption models and thermodynamic parameters for Hg2+ were systematically investigated. The experimental results indicated that the saturated adsorption capacity of Hg2+ on the M-PAL could reach 203.4 mg·g-1, within 120 min at pH 4 and 298 K. By analyzing the experimental data of adsorption kinetics and thermodynamics, it was found that the adsorption process of Hg2+ conformed to the pseudo-second-order kinetic model, which belonged to chemical adsorption of the rate-controlled step; the Langmuir model better described the adsorption isotherm. The thermodynamic parameters obtained (ΔH=29.95 kJ·mol-1, ΔS=103.09 J·mol-1·K-1 and ΔG<0) show that the whole process is a spontaneous endothermic process. When the concentration of Na+, K+, Ca2+, Mg2+, Cl-, NO3-, H2C2O4 and C6H8O7 was 200 times that of Hg2+, although these organic acids had a slightly greater effect on the adsorption of Hg2+ on mercaptofunctionalized palygorskite than inorganic ions, the adsorption capacity remained above 185 mg·g-1. The adsorption products could be still stable in simulated acid rain with pH 3, 4, 5, 6, 7 and oxalic acid solution with concentration of 1, 2, 3, 4 and 5 mmol·L-1, and the desorption rates were about 3%. Through XPS analysis, the specific coordination of Hg2+ with the S atom on the surface of M-PAL was confirmed.

Preparation of one-dimensional magnetic nanocomposites with palygorskites as temples after inorganic modification

The hydrochloric acid (HCl), sodium hydroxide (NaOH) and hydrogen peroxide (H2O2) were used as inorganic modifiers for the surface modification of palygorskite (Pal). The Fe3O4 was attached on modified-palygorskite surface uniformly via coprecipitation in order to prepare magnetically oriented Pal@Fe3O4 one-dimensional nanocomposites. The effect of modifier kinds and concentration for Fe3O4 grow on palygorskite surface was evaluated carefully in this study. It was found that the acid modification and H2O2 modification of palygorskite could really help Fe3O4 nanoparticles grow on the nanorods, but the alkali treatment (after acid modification) gave the opposite effect. Especially the Fe3O4 nanoparticles could attached to modified-palygorskite uniformly when the modifier was HCl and the concentration was 2.0 mol/L. The Pal@Fe3O4 nanocomposites were superparamagnetic at room temperature without any coercivity, which could rapidly respond and orient to an external magnetic field. The brightness variation of magnetically oriented Pal@Fe3O4 under polarizing optical microscope (POM) in the direction of external magnetic fields, which provided a novel approach for the application of palygorskite as one-dimensional nanomaterials and optical active materials. Finally, a possible mechanism of inorganic modification was suggested. An appropriate concentration of HCl could not only improve the surface properties of palygorskite but also make palygorskite surface occupied by more H+ cations, which cause more Fe3+/Fe2+ cations absorbed on modified-Pal surface, leading to the Fe3O4 nanoparticles grow uniformly on palygorskite surface.

Stabilisation of heavy metals in soil using nanoscale zero-valent iron coated with palygorskite

ABSTRACT The nanoscale zero-valent iron (nZVI) coated with palygorskite (PAL) was synthesised and used to remediate the soil contaminated by heavy metals. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated that a large number of nanoscale particles (had a grain size of 40–60 nm approximately) were distributed on the surface or pores of PAL homogeneously. The CaCl2 extraction and TCLP test were carried out to evaluate the bioavailability and mobility of four metals in soil amended by PAL-nZVI. The loading mass ratio of 2:1 between PAL and nZVI showed the optimised effect during the heavy metals’ stabilisation. BCR sequential extraction was employed to measure the change of metal fractions in soil. The residual fraction concentration increased significantly, indicating that the fraction of heavy metals tended to stabilise after amended with PAL-nZVI. The result of pot experience showed that the corn’s biomass increased, and the uptake of heavy metals was reduced significantly, which suggested the PAL-nZVI could stimulate the growth of corn by increasing the stabilisation of heavy metals in soil. Thus, PAL-nZVI as a novel and high-efficiency amendment could be applied to remediate the heavy metals-contaminated soil.

Hg0 removal by palygorskite (PG) supported MnOx catalyst

The MnOx/PG catalysts were prepared by supporting Mn oxides to palygorskite (PG) and used to remove Hg0 in simulated flue gas, which were analyzed and characterized by the specific surface area analysis (BET), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the co-effect of MnOx and PG significantly enhances the Hg0 removal performance; the MnOx/PG catalyst with 8% MnOx loading has the highest Hg0 removal activity. The Hg0 removal efficiency can maintain above 95% at 210°C with a space velocity of 6000 h−1 and an inlet Hg0 concentration of 80 μg/m3 for 400 min. O2 can promote the Hg0 removal by MnOx/PG catalysts, while SO2 and H2O have inhibitory effects. In the presence of O2, the inhibitory effect of SO2 can be obviously weakened. The results of XRD, XPS and temperature programmed desorption experiments (TPD) indicate that the active components MnOx disperse well on the surface of PG. The removal process of Hg0 on the MnOx/PG catalyst includes the steps of adsorption, oxidation and reaction, and HgO and HgSO4 are generated and adsorbed on the catalyst.

Stabilization of cadmium in polluted soil using palygorskite-coated nanoscale zero-valent iron

The palygorskite-coated nanoscale zero-valent iron (PAL-nZVI) was synthesized and used in the remediation of Cd-contaminated soils. The function of PAL-nZVI on fraction of Cd in soils, the growth, Cd translocation, and accumulation in corn (Zea mays L.) were investigated using a pot experiment. Cd-contaminated soils were amended with palygorskite, nanoscale zero-valent iron (nZVI), and PAL-nZVI (with varying mass ratios between PAL and nZVI) and with no amendment as control. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the changes in both the surface and the structure of stabilizers. CaCl2-extractable and toxicity characteristic leaching procedure (TCLP)-extractable Cd were measured in order to estimate the bioavailability and the stabilization efficiency. The Community Bureau of Reference (BCR) sequential extraction method was applied to evaluate the speciation change of Cd in soils stabilized by nZVI, PAL, and PAL-nZVI with different coating mass ratios of PAL to nZVI. The Cd accumulation in root and shoot fresh weight was measured to assess the stabilization efficiency. SEM and XRD indicated that nZVI particles were distributed uniformly and well fixed on the surface of palygorskite. After adding PAL-nZVI, the pH value of soil increased by 1 pH unit; CaCl2-extractable Cd decreased from 2.24 to 0.95 mg/kg; the residual Cd increased by 23.06% after 30-day incubation. The fresh weight of corn reached 43.02 g/plant, and the Cd contents in roots and shoots achieved minimum values of 1.50 and 0.73 mg/kg, respectively, when applying PAL-nZVI composite with a coating mass ratio of 2:1. The application of PAL-nZVI decreased the bioavailability and mobility of Cd in soils effectively. The stabilization showed a better effect when applying PAL-nZVI in Cd-contaminated soils than applying nZVI alone. Hence, it was a feasible and potential material that could be applied to amend the Cd-contaminated soil effectively, which would have a high and valuable utilization in field applications.