Adsorption Capacity Research Articles

Hollow microporous organic network fiber membrane for efficient extraction of okadaic acid from marine organisms

Membrane-based micro-solid phase extraction (M-μSPE) has garnered great attention in sample pretreatment, suffering an inherent contradiction between permeability and adsorption capacity. In this study, a pure microporous organic network (TEB-DIB-MON) fiber membrane was prepared by combining electrostatic spinning technology, Sonogashira-Hagihara reaction and template sacrifice method. The prepared TEB-DIB-MON membrane exhibited a large specific surface area with a hollow and porous structure, thereby providing excellent solvent permeability and high adsorption capacity for okadaic acid (OA, an algal toxin). Under the optimized conditions, a sensitive analytical method was established by coupling M-μSPE with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The established method has a low detection limit (0.5 pg mL-1), a wide linear range (1.5-1000 pg mL-1, R ≥ 0.9991), and good reproducibility (RSD ≤ 9.4 %, n = 6), which was then successfully applied for OA detection in marine organisms. Trace amounts of OA (59.3-89.0 pg mL-1) was detected in the oyster and prawn samples. This work demonstrated that the excellent application potential of MON membranes in sample pretreatment, while also presents a novel synthesis strategy for MONs membranes.

Removal of Methylene Blue dye from aqueous solution using Fenton-modified submerged aquatic plant Schoenoplectus species (Bulrush)

When dumping coloured effluent into the ecosystem, methylene blue dye contributes significantly to environmental health problems. In this investigation, Schoenoplectus species, commonly known as Bulrush, underwent modification using a Fenton reagent to enhance its effectiveness in adsorbing methylene blue (MB) from effluent. The Fenton-treated Bulrush was analysed using SEM, FTIR, BET, and TGA techniques, while various operational parameters were systematically explored to optimise the adsorbent. The FTIR results revealed an increase in the intensity of chemical compounds (–OH, C=C, and C–O, etc.) The FTIR data showed an increase in the intensity of chemical compounds (-OH, C=C, and C-O, among others) and aromatic structures on the exterior of the adsorbent, which aided in MB removal. The results exhibited conformity with the Langmuir model, with an R2 value of 0.9904 with an optimal adsorption capacity of 41.23 mg/g achieved for the Fenton-treated Bulrush. Kinetic analysis indicated adherence to the pseudo-second-order model (R2 = 1), with chemical bonding adsorption primarily governing the adsorption rate. Optimal adsorption conditions were determined to be 26°C, pH 8, a reaction time of 60 minutes, a dosing amount of 2 g, and a preliminary concentration of 100 mg/L. Enhanced pH and increased dosing of Fenton-treated Bulrush led to improved adsorption capacity. Crystal structural characteristics and surface functional groupings of Fenton-treated Bulrush emerged as crucial factors influencing adsorption, describing the three main processes that control MB absorption by the adsorbent: physical adsorption, electrostatic attraction, and π-π interaction. These processes demonstrated the economical, efficient, and environmentally friendly attributes of Fenton-treated Bulrush, which shows promise for eliminating dye contaminants from aquatic environments.

Electronic structure of biochar modified through self-doping with boron, nitrogen and sulfur atoms for rapid and efficient adsorption of COVID-19 drug residues

Self-doping of biochar with various heteroatoms can significantly modify its electronic structure and surface properties, thereby enhancing its adsorption capacity. Allium mongolicum Regel (AM) was a desert herb known for hyperaccumulating boron and possessing a cavity structure. AMAC-3 derived from the pyrolysis of AM, exhibited a high specific surface area (2754 cm2g−1), a larger pore volume (2.513 cm3g−1), an appropriate degree of graphitization (IG/ID = 0.99), and a certain content of heteroatoms (boron, nitrogen and sulfur). AMAC-3 achieved equilibrium adsorption of 20 mg L−1COVID-19 drugs residues within 5–8 min, with equilibrium adsorption capacity ranging from 158 to 195mg g−1 and the drug removal rate between 79 % and 98 %. Furthermore, AMAC-3 maintained high adsorption efficiency in the presence of coexisting anions and spiked real water samples. The shorter adsorption equilibrium time and higher removal rate of AMAC-3 were attributed to the rapid mass transfer in the 3D pores, as well as the rapid binding of more electrons. Boron was the preferred binding site for heteroatom sites due to its electron deficient nature. This study offered insights into the utilization of self-doped heteroatoms for modulating the electronic structure of adsorbent, thereby reducing adsorption equilibrium time and enhancing removal efficiency.

Effective adsorptive removal of heavy metal anion Cr(Ⅵ) and dye cation methylene blue by the novel 2D material TiVCTx MXene

With the increasingly serious industrial pollution, the effective removal of heavy metal ions and organic pollutants from wastewater has become a key issue of environmental protection. In this paper, a new MXene material, TiVCTx, was prepared by in situ etching, and its adsorption capacity of heavy metal anion Cr(Ⅵ) and methylene blue (MB) dye cation was studied. The effect of adsorption time, pH values, temperatures, initial concentrations of adsorbent and adsorbate, interfering ions on the Cr(Ⅵ) and MB adsorption of TiVCTx was systematically investigated. It is found that TiVCTx has excellent Cr(Ⅵ) and MB adsorption property, the adsorption capacity can be as high as 600mg/g and 1430mg/g, respectively. The adsorption experiments revealed that the adsorption process of Cr(Ⅵ) conformed to the Langmuir isotherm model and the Pseudo-second-order kinetic model, which indicated that the Cr(Ⅵ) adsorption was a heat-absorbing monolayer chemisorption. In contrast, the adsorption process of MB is in accordance with the Freundlich isotherm model and the Pseudo-second-order kinetic model, suggesting that the MB adsorption was an exothermic multilayer chemisorption. The results of X-ray electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis further confirmed that the reductive adsorption and electrostatic adsorption can account for the outstanding Cr(VI) and MB adsorption capacity of TiVCTx, respectively.

Preparation of magnetic composite titanium-based MOFs for rapid and effective lead ion adsorption in aqueous solution

Lead contamination constitutes a significant risk to ecology and human beings, which necessitates the development of efficient lead removal adsorbents. In this context, magnetic composite MOFs are promising as they combine the tunable properties and high specific surface area of MOFs with the easy recyclability of magnetic materials. In this study, a novel magnetic composite material, DMP-MIL@Fe3O4, was synthesized by loading magnetic Fe3O4 on titanium-based MOFs and postmodifying it with 4,6-diamino-2-mercaptopyrimidine. The adsorption capacity was maximized within 20 min at pH 6.0 and room temperature. At the same time, it has very high adsorption efficiency for lead ions, with a maximum adsorption capacity of 200.1 mg/g. The adsorption mechanism of DMP-MIL@Fe3O4 was elucidated by kinetic, isothermal and thermodynamic analyses. Pseudo-second-order modeling showed that the binding of functional groups to lead ions was the key rate-limiting step. Isotherm modeling confirmed that multiple functional groups work together to promote the adsorption of lead ions, while thermodynamic analysis demonstrated the spontaneous endotherm of the adsorption process. DMP-MIL@Fe3O4 also exceled in selective adsorption of lead ions and recyclability.

Unveiling the Role of Strong Metal-Support Interactions in Gold-Catalyzed CO Oxidation on MnO2 Polymorphs.

The effectiveness of gold (Au)-based catalysts in CO oxidation is significantly influenced by strong metal-support interactions with surface oxygen structures, the mechanisms of which remain elusive. To investigate this property, we selected γ-MnO2, featuring Mn(-O-)2Mn and Mn-O-Mn structural motifs, and β-MnO2, characterized by Mn-O-Mn linkages, as support materials. The CO oxidation process was investigated by fabricating Au nanoparticles supported on these two MnO2 polymorphs. Our findings reveal that Au supported on β-MnO2 substantially enhanced CO oxidation, in stark contrast to the inhibitory effect observed with Au on γ-MnO2. Using operando diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry, we detected an increase in the production of surface-adsorbed oxygen following Au deposition on β-MnO2. Conversely, Au supported on γ-MnO2 resulted in a diminished capacity for surface oxygen adsorption. The presence of Au+ and Mn2+ ions was identified as pivotal for CO oxidation. Moreover, the engagement of the Mn(-O-)2Mn structure in the reaction was impaired after Au loading on γ-MnO2, and the regeneration of the Mn-O-Mn linkage was similarly hindered. We propose a mechanism for the interactions between Au and the oxygen species associated with Mn(-O-)2Mn and Mn-O-Mn structures on MnO2, offering insights into the divergent catalytic behaviors exhibited by different MnO2 polymorphs.

Efficient removal of low concentrations of copper and lead ions in water using chitosan-condensed tannin composite microspheres

Condensed tannin was solidified onto chitosan microspheres to prepare chitosan-tannin (CT) composite microspheres with a simple preparation method to study its performance in adsorbing copper (Cu2+) and lead ions (Pb2+) in aqueous media. The study investigated the influence of the mass ratio of tannin and chitosan, pH value, adsorption time, and initial concentrations of Cu2+ and Pb2+ on the adsorption capacity of Cu2+ and Pb2+ ions. Additionally, the study examined the adsorption isotherms and kinetics of Cu2+ and Pb2+ on CT composite microspheres. The adsorption process aligns more closely with the fitting results of the Langmuir model. The maximum capacity for saturated monolayer adsorption of CT composite microspheres for Cu2+ and Pb2+ was 37.6 and 52.9 mg/g, respectively. The adsorption process of CT composite microspheres for Cu2+ and Pb2+ was primarily driven by single-layer chemical adsorption. In addition, metal ions adsorbed onto CT composite microspheres can be released by treating them with a dilute solution of strong acid. Furthermore, the CT composite microspheres exhibited impressive removal efficiencies of 82 % and 95 % for Cu2+ and Pb2+ respectively, even at low concentrations of 2 mg/L. The CT composite microspheres have the ability to easily separate the adsorbed Cu2+ and Pb2+ ions.

Selective CO2 hydrogenation to methanol over a novel ternary In-Co-Zr catalyst

To address the challenges of global warming and energy shortages, the technology to convert CO2 into methanol is of great significance Indium-cobalt catalysts have attracted widespread attention due to their significant activity and excellent stability. Herein, In-Co and In-Co-Zr catalyst rich in In2O3 were prepared through a citric acid-assisted co-precipitation method. The results show that the In-Co-Zr catalyst can significantly enhance the activity for hydrogenating CO2 to methanol, achieving a CO2 conversion rate of 17.4 % and a methanol selectivity of 77.7 % under the conditions (5.0 MPa, 310 °C, GHSV = 10.28 l·gcat-1·h-1, H2/CO2 ratio of 4). At a GHSV of 48 l·gcat-1·h-1, the space–time yield of methanol was 0.79 gMeOH·gcat-1·h-1, and the catalyst exhibited stable catalytic activity over a continuous reaction period of 120 h. It was revealed that the incorporation of ZrO2 could significantly improve methanol selectivity of In-Co catalyst. Moreover, an increased oxygen vacancy and strong interaction of the In-Co-Zr catalysts are conducive to improving the CO2 adsorption strength and capacity. It is expected that this novel ternary In-Co-Zr catalyst could inspire new opportunities for designing and developing multi-component hybrid catalysts for highly active, stable and selective CO2 hydrogenation to methanol

Efficient recovery of Pd(II) from nuclear wastewater using a functionalized covalent organic frameworks with uniform spherical structure: Size control, performance and mechanism insight

The efficient recovery of palladium from the spent nuclear fuel was of great significance to the sustainable development of nuclear energy. Herein, the uniform spherical COFs were constructed by a facile approach at room temperature, which were further surface functionalized by a thiol-ene “click” reaction to recover Pd(II). Microscopic and spectroscopic studies manifested that the formation mechanism and size of spherical COFs were greatly affected by the amount of catalyst and solvent type. The TAPB-BPTA-DTT and TAPB-BPTA-S-β-CD exhibited high Pd(II) recovery efficiency due to the introduction of sulfhydryl groups, and the maximum adsorption capacities were 489.3 and 234.3 mg/g, respectively. Meanwhile, the water environmental condition played an important role in the separation process, and the classical adsorption models demonstrated that monolayer chemisorption was the dominant removal mechanism. Mechanism analysis showed that the excellent adsorption performance was mainly attributed to the electrostatic interaction, physical absorption and chelation of N, O, and S groups with Pd(II). Thus, it is expected that this work could provide more insight into COFs materials, thereby promoting palladium removal advancements in the spent nuclear fuel.

Construction and characterization of sodium alginate/polyvinyl alcohol double-network hydrogel beads with surfactant-tailored adsorption capabilities for efficient tetracycline hydrochloride removal

The extensive use of tetracycline (TC) for disease control and the residuals in wastewater has resulted in the spread and accumulation of antibiotic resistance genes, posing a severe threat to the human health and environmental safety. To solve this problem, a series of double-network hydrogel beads based on sodium alginate and polyvinyl alcohol were constructed with the introduction of various surfactants to modulate the morphology. The results showed that the introduction of surfactants can modulate the surface morphology and internal structure, which can also regulate the adsorption ability of the hydrogel beads. The SDS-B beads with SDS as surfactant exhibited highest adsorption efficiency for removal of TC with a maximum adsorption capacity up to 121.6 mg/g, which possessed a resistance to various cations and humic acid. The adsorption mechanism revealed that the superior adsorption performance of the hydrogel beads was primarily attributed to hydrogen bonding, electrostatic attraction, and π-π EDA interactions. Adsorption kinetics demonstrated that the pseudo-second-order model fitted the adsorption process well and adsorption isotherm showed the adsorption of TC occurred through both chemical and physical interactions. Moreover, the adsorption efficiency remained approximately 87.5 % after three adsorption-desorption cycles, which may have potential application and practical value in TC adsorption.

Re3P4@C/TiO2 Ohmic junction Boosts charge carrier separation for photocatalytic hydrogen evolution

Construction of heterostructures featuring a well-designed transport pathway is pivotal in regulating the behavior of charge carriers, thereby achieving boosted separation efficiency. One of the primary factors leading to poor charge transfer and separation efficiency in heterostructures lies in the presence of interface barriers that hinder their transfer. Establishing an Ohmic contact with a low energy barrier can significantly reduce charge transfer resistance during photocatalysis. In this contribution, we have successfully developed an Re3P4@C/TiO2 Ohmic junction for highly improved photocatalytic H2 evolution rate, which exhibited a 68-fold increase compared to pristine TiO2. Experimental results combined with density functional theory calculations confirm the successful construction of Ohmic junction, which effectively facilitates the separation and transfer of photogenerated charge carriers while prolongs their lifetimes. This heterojunction also enhances the adsorption capacity for reactants and thus promotes the surface photocatalytic reactions. This work provides valuable insights into novel Ohmic junction construction to improve the photocatalytic activity.

Fabrication of core–shell nanostructure via novel ligand-defect reassembly strategy for efficient photocatalytic hydrogen evolution and NO removal

The core–shell structure often exhibits unique properties, resulting in superior physical and chemical performance distinct from individual component in the field of photocatalysis. However, traditional prepared methods such as template synthesis and layer-by-layer self-assembly are relatively complex. Therefore, it is necessary to explore an efficient and expedient approach. Here, we have proposed a convenient method to gradually destroy the terephthalic acid (BDC) of MIL-125 from the outer to inner layers through hydrothermal stirring, followed by reassembling with photosensitive 2-amino-terephthalic acid (BDC-NH2) into the exposed Ti-oxo clusters left by the BDC to create photocatalysts featuring a core–shell configuration. The special core–shell sample with the analogous mixture of MIL-125 and MIL-125-NH2 function as a high-performance dual-functional photocatalyst for hydrogen generation and NO elimination. The optimal core–shell material (M-125-45-N) exhibits an outstanding photocatalytic hydrogen production rate of 3.74 mmol·g−1·h−1 and an excellent photocatalytic NO removal rate of 70.15 %. The apparent quantum yield (AQY) value and solar-to-hydrogen energy conversion efficiency (STH) at specific wavelengths are also investigated. The Density functional theory (DFT) calculation, In-situ Fourier transform infrared (In-situ FT-IR) and Electron spin resonance (ESR) have suggested that the enhanced photocatalytic activity of optimal core–shell material arised from its stronger adsorption capacity towards reactants, promoting the production of reactive oxygen species (ROS) conducive to photocatalytic reactions. This study represents the first investigation of a dual functional core–shell MOFs formed via ligand-defect reassembly, showcasing the excellent efficacy in photocatalytic hydrogen evolution and NO removal, which contributes to the feasible development of novel dual-functional photocatalysts with core–shell structures.

Amino acid assisted-construction of 2D-hierarchical MFI zeolites for adsorption of rhodamine B

Hierarchical and two-dimensional (2D) zeolites have drawn much attention in catalysis and separation process due to their fast mass transfer. However, the facile manipulation in controllable mesopore volumes and morphologies for hierarchical nanozeolites is full of challenges. Herein, a facile strategy is presented for the synthesis of single-crystalline 2D hierarchical MFI zeolite nanosheets (HNSs) with tunable mesopore volumes through the amino acid-assisted crystallization of nucleated amorphous silicon precursors (NASPs). The tailored synthesis of HNSs with controllable aspect ratios ((Lc + La)/Lb), b-axis thicknesses (a few tens of nanometers) and mesopore volumes is achieved by adjusting the preparation of the NASPs and the amount of amino acid in the synthesis mixture. The HNSs exhibit large BET surface area (>400 m2/g), high micropore volume (0.16–0.18 cm3 g−1) as well as rich mesopore volume (>0.10 cm3 g−1), indicating the high crystallinity of the hierarchical zeolite nanosheets. Specially, the higher adsorption capability and faster adsorption rate for the dye (Rhodamine B) adsorption demonstrate the excellent performance of the hierarchical zeolite nanosheets, which exhibit the maximum adsorption capacity of 115.7 mg g−1. The controllable manipulation of mesoporous volumes and morphologies in MFI zeolites represents a significant contribution to the field of zeolite microstructure engineering.

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 dimethylaminoethyl methacrylate (DMAEMA) 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.

Biodegradable genipin cross-linked chitosan/pea protein isolate sponges for effective adsorption of methyl blue: Batch experiments and quantum chemical analysis

This study successfully prepared double crosslinked chitosan (CS) and pea protein isolate (PPI) composite sponges using genipin as a crosslinking agent and investigated their effectiveness as an adsorbent for methyl blue (MEB) in aqueous solutions. The composite sponges were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller measurement, swelling tests, gel fraction measurement, zeta potential, and X-ray diffraction. Additionally, the effects of genipin content, pea protein isolate content, sponge dosage, initial pH of the solution, adsorption time, dye concentration, and adsorption temperature on dye removal ability were studied. The results showed that at pH 3.0 and a dye concentration of 100 mg/L, the adsorption capacity of the sponge for methyl blue was found to be 351.6 mg/g. At 298 K and after 720 min, with a dye concentration of 700 mg/L, the maximum adsorption capacity of the sponge for methyl blue reached 959.3 mg/g. The adsorption process follows a pseudo-second-order kinetic model and a Langmuir isotherm. Theoretical analysis using density functional theory suggests that the adsorption of methyl blue by the composite sponge is attributed to the anionic sulfonic acid group of the dye. The composite sponge degraded 76.1 % after being buried in soil for 21 days. This study reveals the enormous potential of biodegradable chitosan-protein-based sponges in effectively removing methyl blue dye pollutants from wastewater.

Removal, mechanistic and kinetic studies of Cr(VI), Cd(II), and Pb(II) cations using Fe3O4 functionalized Schiff base chelating ligands.

The Schiff base chelating ligands; (E)-2-(3,3-dimethoxy-2-oxa-7,10-diaza-3-silaundec-10-en-11-yl)phenol (L1), (E)-N-(2-((pyridine-2ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L2) and (E)-N-(2-((thiophen-2-ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L3) were immobilized on Fe3O4 magnetic nanoparticles (MNPs) and utilized in the extraction of Cr(VI), Cd(II) and Pb(II) metal cations from aqueous solutions. The compounds synthesized, denoted as L1@ Fe3O4, L2@Fe3O4, and L3@Fe3O4, were characterized using FT-IR spectroscopy, TEM-SEM, VSM, and BET/BHJ techniques for analysis of functional groups, surface morphology, magnetic properties, and degree of porosity of the adsorbents, respectively. BET/BHJ technique confirmed the mesoporous nature of the compounds as their pore diameters ranged between 15 and 17nm. The initial optimization conditions of pH, adsorbent dosage, initial metal concentration, and contact time on adsorption were studied using L1@ Fe3O4. The optimum efficiencies recorded were 68% and 46% for Cr(VI) and Cd(II), respectively, obtained at pH 3, and a metal concentration of 20ppm while an efficiency of 99% was recorded for Pb(II) cations at pH 7 and a metal concentration of 100ppm. Compounds L2@Fe3O4 and L3@ Fe3O4 were also used in the extraction of metal cations from aqueous solution and gave efficiencies of 22%, 56%, and 78% for L2@ Fe3O4 and 19%, 90%, and 59% using L3@ Fe3O4 for Cr(VI), Cd(II), and Pb(II), respectively. The maximum adsorption capacities of L1@ Fe3O4 for Cr(VI), Cd(II), and Pb(II) cations were obtained from the Langmuir isotherm as 32.84, 41.77, and 450.45mg/g, respectively. The experimental data was analyzed using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models. Both linear and non-linear forms of kinetic isotherms; Langmuir, Freundlich, Redlich-Peterson, and Temkin were utilized to investigate the nature of adsorption on L1@Fe3O4. The mechanistic studies deduced that the Langmuir isotherm and pseudo-second-order kinetic model better described the adsorption process both yielding high correlation coefficient values (R2 > 0.98).

Structured PAN@MgAl-NO3 for highly efficient removal of CrO42−, SeO32−, MnO4−, and AsO2−

The removal of metal-based oxyanions is of great urgency due to their high toxicity, ubiquity, and non-biodegradability. Herein, a flexible PAN@MgAl-NO3 (PAN: polyacrylonitrile) was successfully fabricated using electrospinning followed by in-situ growth and nitric acid etching strategy. The as-prepared PAN@MgAl-NO3 exhibited excellent adsorption capacities for single CrO42− (350.39 mg/g), SeO32− (256.97 mg/g), MnO4− (369.69 mg/g) and AsO2− (325.34 mg/g), respectively. Furthermore, the adsorption data of PAN@MgAl-NO3 towards oxyanions can be well-fitted with the pseudo-second-order and Langmuir models. When PAN@MgAl-NO3 was applied for continuous CrO42− (10 mg/L) contaminated water, excellent removal efficiency of >99 % can be maintained for more than 24 h at a high flow rate of 17 mL/min. Moreover, such PAN@MgAl-NO3 can be reused for 10 times with the desorption efficiency > 99 %. Detailed experimental results and density functional theory (DFT) calculation demonstrated that for CrO42−, a “co-intercalation” of CrO42− with CO32– into the MgAl-LDHs interlayer was achieved; while in the case of SeO32−, MnO4−, and AsO2−, the surface adsorption on the LDHs laminates dominated the adsorption process.

Efficient multifunctional PPy-NTs/PEI@alginate@NiFe2O4 magnetic beads for heavy metals removal: Experimental design and optimization interpretations

A highly effective magnetic nanocomposite alginate beads (PPy-NTs/PEI@Alg@NiFe2O4) were synthesized using alginate as the encapsulation reagent and polypyrrole/polyethylene imine with nano NiFe2O4 as a functional filler to remove toxic Zn2+ and Pb2+ from polluted water. A response surface methodology (RSM) was used to statistically assess the influences of pH and the adsorbent dose on the adsorption performance. PPy-NTs/PEI@Alg@NiFe2O4 magnetic microbeads exhibited the optimal adsorption capacity qe (18.6 mg/g) at pH 6 and a 2 mg/L dose for Zn2+ removal. In comparison, the optimal qe (32.6 mg/g) was reached at pH 4.5 with a 1.5 mg/L dose for Pb2+ remediation. From batch experiments, maximal absorption capacities of 53.3 mg/g and 22 mg/g were achieved for Pb2+ and Zn2+, respectively, at 313 K. The pseudo-second-order kinetic model fitted the results well, suggesting that the chemisorption process regulates adsorption. Isotherm models indicate the presence of homogeneous adsorption sites from the well-fitting to Langmuir isotherm. An investigation of the effects of temperature and thermodynamic considerations revealed the endothermic nature of Zn2+ and Pb2+ absorption. The Fourier transform infrared spectra showed that –NH, –NH2, and –COO− are the main groups in PPy-NTs/PEI@Alg@NiFe2O4 composite beads that were responsible for Zn2+ and Pb2+ removal from polluted water.

Fluoride removal using membrane capacitive deionization: The role of pH-dependent dissolved inorganic carbon

Defluorination technology is crucial for ensuring safe and accessible water. The application of capacitive deionization (CDI) technology faces challenges due to competitive adsorption of fluoride ions within complex natural fluoride-rich brackish water matrices, which often contain high levels of dissolved inorganic carbon (DIC) species (mainly HCO3– and CO32–). These DIC species are pH-dependent, playing a significant role in the selective removal of fluoride by the CDI process. Thus, there is a knowledge gap in understanding the effects of membranes in membrane capacitive deionization (MCDI) on fluoride removal. In this study, we examined the key operating parameters in CDI and MCDI, including applied constant voltages and different types of anion-exchange membranes (AEMs), on the desalination performance in F- and dissolved inorganic carbon water matrices. The application of AEMs significantly improved the salt adsorption capacity (SAC) for both F- and DIC species, and reduced energy consumption. However, it simultaneously resulted in a notable decrease in F- selectivity as membranes control mass transfer. Higher applied voltages enhance the SAC performance for F- and DIC species, but also induce more severe Faradaic reactions, leading to increased energy consumption and lower energy efficiency. Additionally, ion species and pH changes during CDI and MCDI processes are interrelated, indicating that stability tests of CDI electrodes in batch mode are not reliable when using the same testing solution repeatedly. The diverse valence states of ions in the solution impact pH variations under different voltages in the CDI/MCDI process. These findings provide valuable insights into the development of water purification and desalination technology, particularly for the application and further advancement of selective fluoride removal by the CDI process.

Hydrophobic hyper-cross-linked polymer shells encapsulating dispersed nanoscale CuS boosting mercury immobilization

Metal sulfides (MSs) hold significant promise for environmental remediation but are hindered by their low accommodation capacity and poor water resistance. Herein, this work reports a hybrid strategy to address these limitations by assembling highly dispersed CuS nanoparticles within the hyper-cross-linked polymer (HCP). Benefiting from the super-hydrophobicity and well-developed porosity of HCP, alongside the high dispersion and multiple active sites of CuS nanoparticles, the resultant CuS@HCP exhibits exceptional water resistance, enhanced surface area, high mass transfer ability, and substantial Hg0 adsorption capacity. The Hg0 adsorption capacity (Q90) of CuS@HCP3 reaches 1.25 and 1.391 mg/g under N2 and simulated flue gas, respectively. Notably, the normalized Q90 of coated CuS surpasses that of pristine CuS by 25-fold under N2 + 15 % H2O and its durability outstrips most previously reported mineral sulfides even in complex simulated flue gas. Universal research confirms MSs@HCP (M = Zn, Sn, and Fe) equally demonstrate over 15-fold increment in Hg0 retention under high humidity conditions compared to the pristine MSs. Such HCP hybrid strategy universally and effectively optimizes the accommodation capacity and water resistance of MSs, endowing MSs@HCP broad application prospects.