Inner-sphere Complexes Research Articles

Facile synthesis of novel hexagonal strontium ferrites for promising adsorption of cadmium from aqueous solutions

Cadmium (Cd(II)) contamination in both the surface and ground water is threatening the lives of millions of people across the world. In this work, we have hydrothermally synthesized the novel multiphase (MP) and single phase (SP) M-type hexagonal strontium ferrites (SF, SrFe12O19) for removing Cd(II) from contaminated water. The as-synthesized materials were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectrometry (XPS). The MP-SF and SP-SF demonstrated excellent Cd(II) adsorption capacities over wide pH range. The pseudo-first and second-order kinetics models as well as the Langmuir and Freundlich isotherms models were used for fitting the experimental data for adsorption of Cd(II) on both the MP-SF and SP-SF. The maximum adsorption capacities reached to 57.5 and 78.9 mg/g for the MP-SF and SP-SF, respectively, at pH 7, which were better than many recently reported magnetic adsorbents. The effects of common co-existing ions on the adsorption capacities of both the MP-SF and SP-SF were also evaluated. FTIR and XPS spectroscopic analyses further confirmed that Cd(II) was adsorbed on to the surface of SP-SF through the formation of an inner-sphere complex between the Cd(II) and surface metal centers.Furthermore, the as-synthesized materials were employed for the treatment of simulated real Cd(II) contaminated water. The experimental results suggested that the SP-SF could be a strong candidate for practical applications of Cd(II) removal from aqueous solutions.

Unraveling pH-Dependent Changes in Adsorption Structure of Uranyl on Alumina (012).

Mitigating uranium transport in groundwater is imperative for ensuring access to clean water across the globe. Here, in situ resonant anomalous X-ray reflectivity is used to investigate the adsorption of uranyl on alumina (012) in acidic aqueous solutions, representing typical UVI concentrations of contaminated water near mining sites. The analyses reveal that UVI adsorbs at two distinct heights of 2.4-3.2 and 5-5.3 Å from the surface terminal oxygens. The former is interpreted as the mixture of inner-sphere and outer-sphere complexes that adsorb closest to the surface. The latter is interpreted as an outer-sphere complex that shares one equatorial H2O with the terminal surface oxygen. With increasing pH, we observe an increasing prevalence of these outer-sphere complexes, indicating the enhanced role of the hydrogen bond that stabilizes adsorbed uranyl species. The presented work provides a molecular-scale understanding of sorption of uranyl on Al-based-oxide surfaces that has implications for environmental chemistry and materials science.

Enhanced removal of phosphate from aqueous solutions by oxygen vacancy-rich MgO microspheres: Performance and mechanism

The efficient removal of phosphate from water environments was extremely significant to control eutrophication of water bodies and prevent further deterioration of water quality. In this study, oxygen vacancy-rich magnesium oxide (OV–MgO) microspheres were synthesized by a simple solvothermal method coupling high-temperature calcination. The effects of adsorbent dosage, contact time, initial pH and coexisting components on phosphate adsorption performance were examined. The physicochemical properties of OV-MgO microspheres and the phosphate removal mechanisms were analyzed by various characterization techniques. The maximum adsorption capacity predicted by the Sips isotherm model was 379.7 mg P/g for OV-MgO microspheres. The phosphate adsorption in this study had a fast adsorption kinetics and a high selectivity. OV-MgO microspheres had a good acid resistance for phosphate adsorption, but their adsorption capacity decreased under alkaline conditions. The electrostatic attraction, ligand exchange, surface precipitation, inner-sphere surface complexation and oxygen vacancy capture were mainly responsible for efficient removal of phosphate from aqueous solutions. This study probably promoted the development of oxygen vacancy-rich metal (hydr)oxides with potential application prospects.

Electrospinning Chitosan/Fe-Mn Nanofibrous Composite for Efficient and Rapid Removal of Arsenite from Water.

Efficient removal of extremely mobile and toxic As(III) from water is a challenging but critical task. Herein, we developed a functionalized sorbent of chitosan nanofiber with iron-manganese (Fe-Mn@CS NF) using a one-step hybrid electrospinning approach to remove trace As(III) from water. Batch adsorption studies were performed to determine the adsorption efficiency under a variety of conditions, including contact time, starting concentration of As(III), ionic strength, and the presence of competing anions. The experimental results demonstrated that the concentration of As(III) dropped from 550 to less than 1.2 µg/L when using 0.5 g/L Fe-Mn@CS NF. This demonstrates the exceptional adsorption efficiency (99.8%) of Fe-Mn@CS NF for removing As(III) at pH 6.5. The kinetic tests revealed that the adsorption equilibrium was reached in 2.6 h, indicating a quick uptake of As(III). The ionic strength effect analysis showed that the adsorbed As(III) formed inner-sphere surface complexes with Fe-Mn@CS NF. The presence of SO42- or F- had a negligible impact on As(III) uptake, while the presence of PO43- impeded As(III) absorption by competing for adsorption sites. The exhausted sorbent could be effectively regenerated with a dilute NaOH solution. Even after 10 cycles of regenerating Fe-Mn@CS NF, the adsorption efficiency of As(III) in natural groundwater was maintained over 65%. XPS and FTIR analyses show that the presence of M-OH and C-O groups on the sorbent surface is essential for removing As(III) from water. Overall, our study highlights the significant potential of Fe-Mn@CS NF for the efficient and quick elimination of As(III) from water.

Goethite and Hematite Nucleation and Growth from Ferrihydrite: Effects of Oxyanion Surface Complexes.

The presence of oxyanions, such as nitrate (NO3-) and phosphate (PO43-), regulates the nucleation and growth of goethite (Gt) and hematite (Hm) during the transformation of ferrihydrite (Fh). Our previous studies showed that oxyanion surface complexes control the rate and pathway of Fh transformation to Gt and Hm. However, how oxyanion surface complexes control the mechanism of Gt and Hm nucleation and growth during the Fh transformation is still unclear. We used synchrotron scattering methods and cryogenic transmission electron microscopy to investigate the effects of NO3- outer-sphere complexes and PO43- inner-sphere complexes on the mechanism of Gt and Hm formation from Fh. Our TEM results indicated that Gt particles form through a two-step model in which Fh particles first transform to Gt nanoparticles and then crystallographically align and grow to larger particles by oriented attachment (OA). In contrast, for the formation of Hm, imaging shows that Fh particles first aggregate and then transform to Hm through interface nucleation. This is consistent with our X-ray scattering results, which demonstrate that NO3- outer-sphere and PO43- inner-sphere complexes promote the formation of Gt and Hm, respectively. These results have implications for understanding the coupled interactions of oxyanions and iron oxy-hydroxides in Earth-surface environments.

Efficient removal of radioactive Th(IV) from nuclear wastewater using phosphate-functionalized Ti3C2Tx

In this study, Ti3C2Tx was synthesized from Ti3AlC2 by HF 40% and 12 M LiF + 9 M HCL in 24 hr at temperatures of 313.15 and 333.15 K. Morphology, structure, and functional groups were investigated by the XRD, SEM, EDS, and BET analyses. Under the conditions of thorium (IV) concentration of 150 mg.l−1, pH ∼ 3, temperature of 298.15 K, and contact time of 540 min, the adsorption uptake of thorium (IV) with Ti3C2Tx-HF and Ti3C2Tx-HF in situ was 148 and 346 mg.g−1, respectively. The 3-fold adsorption of Ti3C2Tx-HF in situ was because of the larger interlayer spacing, the larger number of hydroxyl functional groups, and the larger surface area due to the synthesis with 12 M LiF + 9 M HCL. Modification of Ti3C2Tx with phosphate groups was done to increase the adsorption capacity of thorium (IV). The results showed that the adsorption process of thorium (IV) with pristine and modified Ti3C2Tx followed pseudo-second-order kinetics and Freundlich model heterogeneous isotherm. Thermodynamic data revealed that the adsorption process was endothermic. Examining the adsorption mechanism indicated that electrostatic reactions and inner-sphere complexation were the dominant mechanisms of the process.

Characteristic and mechanism of efficient phosphate removal by Portland cement/slag powder/coal ash-hydrate (PC/SP/CA-H)

The excessive presence of phosphate in water leads to eutrophication, prompting us to develop a novel material named PC/SP/CA-H (Portland cement/slag powder/coal ash-hydrate). The experimental data accorded with the pseudo-second-order kinetics and Langmuir model, suggesting that chemical interactions predominated in the adsorption process. Within 4 hours, PC/SP/CA-H rapidly removed phosphate at a rate of 65%, which exceeded 90% after 12 hours with a material dosage of 30 g/L and a phosphate concentration of 30 mg/L. The maximum phosphate adsorption capacity of PC/SP/CA-H was 8.84 mg/g. The material exhibited effective phosphate removal capabilities across a wide pH range of 3.0–11.0. It demonstrated remarkable selectivity to phosphate in the presence of competitive anions, such as CO32-, HCO3-, NO3-, SO42-, and Cl-. Characterization analyses including SEM, BET, XRD, XRF, FTIR, and XPS were conducted to investigate the performance of PC/SP/CA-H and mechanisms of phosphate removal. The findings indicated that phosphate replaced hydroxyl groups on the material to form inner-sphere complexes through ligand exchange. Besides, phosphate was adsorbed onto the positively charged material via electrostatic attraction with protonated hydroxyl groups (-OH2+). It also reacted with metal cations (Ca2+) released by the material to form insoluble crystalline substances (Ca-P) through surface precipitation. This material holds promising prospects for efficiently removing phosphate from water or wastewater, while simultaneously enhancing the resource utilization of coal ash and slag powder.

Sorption of U(VI) on MX-80 Bentonite and Granite in Ca-Na-Cl Saline Solutions

Uranium has been identified as an element of interest for the safety assessment of a deep geological repository for used nuclear fuel. This paper examines the sorption behavior of U(VI) onto MX-80 bentonite and granite in Ca-Na-Cl solutions of varying ionic strengths [0.05 to 3 mol/kgw (m)] and across a pH range of 4 to 10. U(VI) sorption on MX-80 showed that U(VI) sorption gradually increased with pHm until pHm = 6, where it reached its maximum, and decreased slightly with pHm until pHm = 8, and then became constant. U(VI) sorption on granite increased along with pHm, reached the maximum around pHm = 7 to 8, and then slightly decreased with pHm. Both MX-80 and granite showed essentially no ionic strength dependence for sorption of U(VI). A nonelectrostatic surface complexation model successfully predicted sorption of U(VI) onto MX-80 and granite using the formation of an inner-sphere surface complex. Optimized values of surface complexation reaction constants (log K0) for the formation reactions of these surface species are proposed.

Functionalized cellulose nanocrystals extracted from date pits as agricultural waste for the efficient remediation of molybdenum from groundwater: Performance and mechanistic studies

The adsorption technique has proven to be an excellent option for treating contaminated water. This work was designed to investigate the efficient remediation of molybdenum (Mo(VI)) from groundwater by using a novel adsorbent composed of date pits (DP) modified by manganese oxide/cellulose nanocrystal (CNC) composite (MnO2/CNC@DP). The physicochemical properties of the adsorbent were examined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope with energy-dispersive X-ray spectroscopy techniques (SEM/EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to study the functional group on the adsorbent surface, surface morphology and chemical composition, and the crystallinity behavior. The performance of prepared (MnO2/CNC@DP) toward Mo(VI) was studied using synthetic solutions and real groundwater samples. Also, the effect of pH, temperature, and initial Mo concentration on the adsorption process was investigated. Moreover, various adsorption isotherm models were calculated, and the thermodynamics of adsorption was studied. The recovery experiments for Mo(VI) saturated MnO2/CNC@DP were conducted by using acidic and alkaline solutions. At the optimum pH of 2, the adsorption capacity increased with increasing the initial concentration of Mo(VI), and Qmax was 30 mg/g at 35 °C. The removal of Mo(VI) from real groundwater was 88.42% The negative values of Gibbs energy (ΔG°) demonstrated that the adsorption is spontaneous, and the experimental data followed the Langmuir isotherm model. Moreover, Mo(VI) can be desorbed from the MnO2/CNC@DP surface by using 1.0M HCl. The proposed mechanisms for the adsorption of Mo(VI) by MnO2/CNC@DP were dominated by electrostatic attraction and inner-sphere complexation. As a result of the research, MnO2/CNC@DP is a promising adsorbent with a high potential for removing Mo(VI) from groundwater. Furthermore, This research provides new knowledge into the modification of date pits using different metal oxides/cellulose nanocrystal particles. Furthermore, the results suggest an excellent chance of employing the efficiently produced adsorbent MnO2/CNC@DP for sustainable groundwater treatment from additional contaminants.

Nanosized lanthanum peroxide–loaded biochar composites for simple and effective glyphosate removal from wastewater: Behavior and mechanisms

The extensive use of glyphosate-based herbicides and its high solubility in water have led to its accumulation in aquatic environments, posing a risk to the ecological environment and human health. Therefore, an effective method for removing glyphosate from wastewater is urgently needed. Herein, a novel nanosized lanthanum peroxide–loaded biochar composite (n-LBC) was prepared using a simple precipitation method, in which biochar served as a dispersant and catalyst to improve the oxidation ability of nanosized lanthanum peroxide. Compared with other common metal peroxide systems, n-LBC exhibited better oxidation ability and achieved a glyphosate removal efficiency of 99.6%. Moreover, n-LBC retained the self-buffering effect of lanthanum peroxide and thus remained effective over a wide pH range, overcoming the problem of pH elevation observed in other metal peroxide systems. The mechanism for glyphosate removal was found to be a combined process of electrostatic attraction, oxidation, and inner-sphere complex formation. Most glyphosate could be oxidized to H2PO 4− by breaking the C–N bonds, and H2PO4− could be attracted to the material surface simultaneously by electrostatic attraction, forming La–O–P inner-sphere complexes. Thus, n-LBC is a simple and highly effective material for glyphosate removal.

Potentials of emergent plant residue derived biochar to be alternative carbon-based phosphorus fertilizer by Fe(II)/Fe(III) magnetic modification

Emergent plants have been remarkably effective in reducing phosphorus (P) discharge from ecological ditches; however, the treatment and recycling of these residues is a great challenge. In this study, magnetic biochars (MBs, i.e., MB-A, MB-C, and MB-T) were fabricated from three emergent plant residues (Acorus calamus L., Canna indica L., and Thalia dealbata Fraser, respectively) and modified with Fe(II)/Fe(III). Scanning electron microscopy-energy dispersive spectroscopy and X-ray diffraction spectra confirmed the successful loading of Fe3O4 and FeO(OH) onto the surfaces of the MBs. Batch adsorption experiments showed that MBs exhibited a higher P adsorption capacity than that of the raw biochars. Within the range of 0.8–43.0 mg L−1 in solution, the adsorption capacities of P by MB-A, MB-C, and MB-T were 304.6–5658.8, 314.9–6845.6, and 292.8–5590.0 mg kg−1, with adsorption efficiencies of 95.2–32.9%, 98.4–39.8%, and 91.5–32.5%, respectively. The primary mechanisms that caused P to adsorb onto the MBs were inner-sphere complexation and electrostatic attraction. Low pH conditions were more beneficial for the P adsorption of the MBs, while co-existing anions had a negative impact with the following order: HCO3− > SO42− > Cl−≈NO3−. The P-31 nuclear magnetic resonance results further demonstrated that the main adsorbed P species on the MBs was orthophosphate, followed by orthophosphate monoesters and DNA. Overall, MBs offer a resource utilization strategy for emergent plant residues and P-laden MBs are promising alternative P fertilizers.Graphical

Natural and synthetic plagioclases: Surface charge characterization and sorption of trivalent lanthanides (Eu) and actinides (Am, Cm)

The environmental fate of radiotoxic actinides may be controlled by their interactions with feldspars. Here, the sorption of trivalent minor actinides (Am, Cm) and their rare earth analog Eu onto synthetic pure Ca-feldspar (anorthite) and natural plagioclases of different Ca contents is investigated, covering ranges of [M3+] (52 nM–10 μM), solid-liquid ratios (1–3 g/L), pH (3–9), and ionic strengths (0.01–0.1 M NaCl) under both ambient and CO2-free conditions. As a first step to understand the uptake behavior of the heavy metals, the hitherto unknown surface charge and (de-)protonation reaction of Ca-feldspars is characterized. The zeta potential shows an unusual increase and charge reversal between pH 4 and 7 , which becomes more pronounced with increasing amounts of Ca in the crystal lattice and is likely connected to adsorption and/or surface precipitation of dissolved Al3+. Streaming potential measurements yield (de)protonation constants for anorthite surface sites of log K- = −6.94 ± 0.38 and log K+ = +6.84 ± 0.38. Batch sorption data shows strong immobilization of M3+ by plagioclases at mildly acidic and basic pH. Time-resolved laser fluorescence spectroscopy using Cm indicates the formation of an inner-sphere complex and its two hydrolyzed forms. The complex reactivity of dissolved Al3+ at the plagioclase-water interface severely complicated the development of a surface complexation model, emphasizing the need for additional research in this area. Our study highlights the importance of molecular-level studies to understand surface reactions and uncover unknown processes, which may have significant impact on the transport of (radiotoxic) contaminants in the geosphere.

Static and dynamic adsorption of arsenate from water by Fe3+ complexed with 3-aminopropyltriethoxysilane-modified carboxymethyl chitosan.

Fe3+ complexed with 3-aminopropyltriethoxysilane (APTES)-modified carboxymethyl chitosan (CMC) named Fe-ACMC was synthesized by a one-step method at room temperature and pressure. The surface morphology and chemical structure of Fe-ACMC were characterized by SEM-EDS, XRD, BET, FT-IR, XPS, and ζ-potential. In batch adsorption, the optimum pH for arsenate [As(V)] adsorption onto Fe-ACMC was 3-9 with removal efficiency > 99%. The adsorption of As(V) could reach equilibrium within 25min and the maximum adsorption capacity was 84.18mgg-1. The pseudo-second-order model fitted well the kinetic data (R2 = 0.995), while the Freundlich model well described the adsorption isotherm of As(V) on Fe-ACMC (R2 = 0.979). The co-existing anions (NO3-, CO32-, and SO42-) exhibited a slight impact on the As(V) adsorption efficiency, whereas PO43- inhibited As(V) adsorption on Fe-ACMC. The real applicability of Fe-ACMC was achieved to remove ca. 10.0mg L-1 of As(V) from natural waters to below 0.05mg L-1. The regeneration and reuse of Fe-ACMC for As(V) adsorption were achieved by adding 0.2mol L-1 HCl. The main adsorption mechanism of As(V) on Fe-ACMC was attributed to electrostatic attraction and inner-sphere complexation between -NH2···Fe3+ and As(V). In fixed-bed column adsorption, the Thomas model was the most suitable model to elucidate the dynamic adsorption behavior of As(V). The loading capacity of the Fe-ACMC packed column for As(V) was 47.04mgg-1 at pH 7 with an initial concentration of 60mg L-1, flow rate of 3mLmin-1, and bed height of 0.6cm.

A new strategy for enhanced phosphate removal from waters using ferric oxide impregnated biochar

To overcome application limitation of the available biochar-based metallic oxide composites for the removal of anionic pollutants like phosphate, a new strategy was proposed that metallic oxide was anchored in the positively charged biochar, acquired by introducing high-density quaternary ammonium groups. The resultant nanocomposite adsorbent Fe@N-BC exhibited high adsorption speed, capacity and preference to phosphate. In the existence of competing anion Cl- at higher levels, Fe@N-BC possessed 3–5 times greater working adsorption capacity of phosphate than a commercial phosphate adsorbent D201 and the mixture of ferric oxide and N-BC with the same proportion as the composite. Fixed-bed adsorption runs of Fe@N-BC could treat ∼ 194 bed volumes (BV) of a synthetic phosphate-polluted wastewater before breakthrough achieving (<0.1 mg P/L in effluent), about 7.46 times greater than that of D-201. The saturated Fe@N-BC could be thoroughly regenerated with 10 % NaOH solution for repeated use with negligible loss of adsorption capacity and ferric. The specific inner-sphere complexation between phosphate and the immobilized ferric oxide was proven to the dominant pathway for preferable adsorption of phosphate onto Fe@N-BC. The obviously enhanced removal of phosphate by Fe@N-BC was ascribed to the introduced quaternary ammonium groups in N-BC, which triggered the dispersion of the impregnated ferric oxide nanoparticles (with sizes of 8.8 ± 1.0 nm) and Donnan member effect. Besides, Fe@N-BC was preliminarily proven to have no biotoxicity. This study can shed new light on how to expand the application of the traditional biochar-based composites to the decontamination of anionic pollutants.

Spectroscopic and Microscopic Characterization of Microbial Biofouling on Aircraft Fuel Tanks.

Avoiding microbial contamination and biofilm formation on the surfaces of aircraft fuel tanks is a major challenge in the aviation industry. The inevitable presence of water in fuel systems and nutrients provided by the fuel makes an ideal environment for bacteria, fungi, and yeast to grow. Understanding how microbes grow on different fuel tank materials is the first step to control biofilm formation in aviation fuel systems. In this study, biofilms of Pseudomonas putida, a model Gram-negative bacterium previously found in aircraft fuel tanks, were characterized on aluminum 7075-T6 surfaces, which is an alloy used by the aviation industry due to favorable properties including high strength and fatigue resistance. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) showed that extracellular polymeric substances (EPS) produced by P. putida were important components of biofilms with a likely role in biofilm stability and adhesion to the surfaces. EDX analysis showed that the proportion of phosphorus with respect to nitrogen is higher in the EPS than in the bacterial cells. Additionally, different morphologies in biofilm formation were observed in the fuel phase compared to the water phase. Micro-Fourier transform infrared spectroscopy (micro-FTIR) analysis suggested that phosphoryl and carboxyl functional groups are fundamental for the irreversible attachment between the EPS of bacteria and the aluminum surface, by the formation of hydrogen bonds and inner-sphere complexes between the macromolecules and the aluminum surface. Based on the hypothesis that nucleic acids (particularly DNA) are an important component of EPS in P. putida biofilms, the impact of degrading extracellular DNA was tested. Treatment with the enzyme DNase I affected both water and fuel phase biofilms─with the cell structure disrupted in the aqueous phase, but cells remained attached to the aluminum coupons.

Spectra metrology for interaction of heavy metals with extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 reveals static quenching and complexation dynamics of EPS with heavy metals

The adsorption behavior and interaction mechanisms of extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 towards chromium (Cr), lead (Pb), and cadmium (Cd) were investigated. EPS-covered (EPS-C) cells exhibited significantly higher (p < 0.0001; two-way ANOVA) removal of Cr (85.58 ± 0.39%), Pb (81.98 ± 1.02%), and Cd (73.88 ± 1%) than EPS-removed (EPS-R) cells. Interactions between EPS-heavy metals were spontaneous (ΔG<0). EPS-Cr(VI) and EPS-Pb(II) binding were exothermic (ΔH<0), while EPS-Cd(II) binding was endothermic (ΔH>0) process. EPS bonded to Pb(II) via inner-sphere complexation by displacement of surrounding water molecules, while EPS-Cr(VI) and EPS-Cd(II) binding occurred through outer-sphere complexation via electrostatic interactions. Increased zeta potential of Cr (29.75%), Pb (41.46%), and Cd (46.83%) treated EPS and unchanged crystallinity (CIXRD=0.13), inferred EPS-metal binding via both electrostatic interactions and complexation mechanism. EPS-metal interaction was predominantly promoted through hydroxyl, amide, carboxyl, and phosphate groups. Metal adsorption deviated EPS protein secondary structures. Strong static quenching mechanism between tryptophan protein-like substances in EPS and heavy metals was evidenced. EPS sequestered heavy metals via complexation with C-O, C-OH, CO/O-C-O, and NH/NH2 groups and ion exchange with –COOH group. This study unveils the fate of Cr, Pb, and Cd on EPS surface and provides insight into the interactions among EPS and metal ions for metal sequestration.

Removal of phosphorus by modified bentonite:polyvinylidene fluoride membrane-study of adsorption performance and mechanism.

Enhanced phosphorus management, geared towards sustainability, is imperative due to its indispensability for all life forms and its close association with water bodies' eutrophication, primarily stemming from anthropogenic activities. In response to this concern, innovative technologies rooted in the circular economy are emerging, to remove and recover this vital nutrient to global food production. This research undertakes an evaluation of the dead-end filtration performance of a mixed matrix membrane composed of modified bentonite (MB) and polyvinylidene fluoride (PVDF) for efficient phosphorus removal from water media. The MB:PVDF membrane exhibited higher permeability and surface roughness compared to the pristine membrane, showcasing an adsorption capacity (Q) of 23.2 mgP·m-2. Increasing the adsorbent concentration resulted in a higher removal capacity (from 16.9 to 23.2 mgP·m-2) and increased solution flux (from 0.5 to 16.5 L·m-2·h-1) through the membrane. The initial phosphorus concentration demonstrates a positive correlation with the adsorption capacity of the material, while the system pressure positively influences the observed flux. Conversely, the presence of humic acid exerts an adverse impact on both factors. Additionally, the primary mechanism involved in the adsorption process is identified as the formation of inner-sphere complexes.

Adsorption performance of bentonite and clay for Zn(II) in landfill leachate

BackgroundThe increasing prevalence of the Galvanized and dry battery industries has led to a rise in zinc proportions in landfills, posing environmental risks. This study explores the potential of bentonite, renowned for its metal adsorption capability, as a landfill barrier material.MethodsAdsorption characteristics of Zn(II) in natural bentonite and Shanghai clay were investigated. Various factors affecting Zn(II) adsorption, including pH, Na ion strength, contact time, initial Zn(II) concentration, and adsorption temperature, were analyzed through batch-type adsorption tests.ResultsThe change in pH and Na strength demonstrates no significant impact on the adsorption of Zn(II) onto bentonite, highlighting the strong selectivity of bentonite for Zn(II). Conversely, the equilibrium adsorption capacity of Zn(II) onto clay increases with rising pH or decreasing ion strength. The Zn(II) adsorption onto bentonite is well-described by the pseudo-second-order, intra-particle diffusion, and Elovih models, each achieving an R2 value exceeding 0.9. While both physical and chemical adsorption coexist in Zn(II) adsorption onto bentonite or clay, the primary determinant of the adsorption rate is chemical adsorption. The adsorption onto bentonite is spontaneous, whereas onto clay it is not. The mechanism involves van der Waals forces, ion exchange, and chemical actions such as inner-sphere complexation for Zn(II) adsorption onto both bentonite and clay.

Molecular geochemistry of radium: A key to understanding cation adsorption reaction on clay minerals

Adsorption reactions of various cations on clay minerals have different effects on their environmental behaviors depending on the molecular-scale adsorption structure. Some cations form outer-sphere complexes via hydration, while others create inner-sphere complexes through dehydration. This preference dictates their environmental impact. However, the factors controlling these complex formations remain unclear. Furthermore, research on the adsorption preferences of radium (Ra) is lacking. Thus, this study conducted the first EXAFS study of Ra2+ adsorbed on clay minerals and showed that Ra2+ forms inner-sphere complexes on vermiculite, which can be surprising because Ra2+ is a divalent cation and prefers to be hydrated. In order to investigate the factors controlling the complex formations, this study conducted systematic EXAFS measurements and DFT calculations for alkali and alkaline earth metal cations. The results showed the importance of the size-matching effect between the adsorbed cation and the cavity of the tetrahedral sheets and that the complex formation can be estimated by the combination of the ionic radius and hydration enthalpy of the adsorbed cation. Furthermore, this study also analyzed environmental core samples. Their results showed the fixation of Ra2+ by clay minerals and the controlling factors can effectively predict cation environmental behavior.

Construction of 3D network aluminum sludge-based hydrogel beads: combination of macroization, amino functionalization, and resource utilization.

An aluminum sludge-based composite material was constructed against the problems of phosphorus pollution and the waste of aluminum sludge resources. Utilizing metal Ce doping and hydrogel microbeads with pore preparation, the adsorption performance of the original sludge was improved. Meanwhile, the macroscopic body was constructed, and on this basis, polyethyleneimine (PEI) was introduced to complete the amino functionalization further to enhance the adsorption of phosphorus by the adsorbent, and NH-CeAIS-10 microbeads were successfully prepared. In adsorption, microbeads with larger specific surface area and richer functional groups are better choice compared to original sludge. The results of SEM, BET, FT-IR, and XPS analyses indicate that the adsorption of phosphorus by the microbeads is mainly achieved through electrostatic interactions, ligand exchange, and the formation of inner-sphere complexes. According to the Langmuir model, the maximum phosphorus adsorption capacity of NH-CeAIS-10 was 29.56mgg-1, which was four times higher compared to native aluminum sludge. This also confirms the significant enhancement of phosphorus adsorption through the modification of aluminum sludge. Besides, in dynamic adsorption column experiments, the material exhibited up to 99% removal in simulated wastewater for up to 30days, demonstrating the great adsorption potential of NH-CeAIS-10 in engineering applications.