Desorption Cycles Research Articles

Studies of hybrid ceria polypyrrole CPP-2 composite for effective defluoridation from potable water

Drinking water sources should eliminate fluoride ions, as they pose a serious threat to human health. By using in situ oxidative polymerization and Pechini’s method of CeO2 (CO), a new hybrid composite, CPP-2, was designed. Several physicochemical techniques were used to establish the properties of the adsorbent in its as synthesized state. The F- ions were removed from effluent using the hybrid composite adsorbent. The adsorption isotherm model was best represented by the Langmuir adsorption isotherm model. It yielded a maximum adsorption capacity of 351.8 mg/g at an optimal pH of 4 ± 0.2 at room temperature. The pseudo second order model best describes the adsorption process according to kinetic results. To get a detailed understanding of the fluoride adsorption mechanism, FTIR and XPS spectra are analyzed. Anionic exchange of the hydroxyl groups with F- ions and electrostatic attractions of the protonated hydroxyl on the surface of the adsorbent, as well as the nitrogen atoms of the amino groups from the polypyrrole (PP) moiety with the F- ions, were responsible for the process. The enthalpy change (ΔH° = +6.32 KJ/mol) and Gibbs free energy (ΔG° = -8.95 KJ/mol) were obtained from the thermodynamic data, which demonstrated the spontaneity, feasibility, and endothermic nature of adsorption. It had a great potential for defluoridation from groundwater at a pH level below the thresholds specified by the WHO and could withstand up to five cycles of adsorption and desorption. The overall results exhibited that CPP-2 has an enormous promise for defluoridation.

Enhanced capacitive deionization via modulating local electron of electro-adsorption sites in a Trace-Fe-modified carbon framework

In order to alleviate the crisis of freshwater resources, it is essential to explore a clean, efficient, and low-consumption water treatment technology. As a kind of electro-adsorption water purification technology, capacitive deionization (CDI) has drawn continuously growing attention because of its advantages. The ion adsorption capability of CDI is closely related to the electrodes. Unfortunately, the ion adsorption capacity of common carbon materials is limited and far from reaching the rapidly increasing requirements of fresh water treatment. In this study, Fe-N-HPC electrode materials with trace Fe uniformly dispersed in N-doped hollow carbon polyhedral frameworks were tactfully prepared by a simple in-situ growth and pyrolysis method. The structure and morphology of the heterostructure material were verified by various analysis. Electrochemical tests showed the Fe-N-HPC electrode had an enhanced performance with a higher specific capacitance and fast ions diffusion coefficient. The Fe-N-HPC showed excellent CDI performance, with an enhanced desalinization capacity (34.38 mg/g, 500 mg/L NaCl solution, 1.2 V), and regenerative stability after 100 adsorption–desorption cycles. In addition, it also exhibited higher charge efficiency, energy efficiency and lower specific energy consumption. The removal mechanism of Na+ on the electrode and the participation of trace Fe can modulate the local electron of the electro-adsorption sites were reasonably verified by ex-situ XRD, Raman, and XPS characterizations, which finally facilitated the electro-adsorption property. This work presents a promising scheme for the advance of high efficiency capacitive desalination system.

Seed-assisted two-step ZIF-67 growth on CS/PVA nanofibers for high-efficiency cadmium and tetracycline adsorption

Herein, novel ZIF-67/CS/PVA (CNF-2) nanofiber composites using a two-step seed-assisted in situ electrospinning method, with cobalt-based zeolitic imidazolate framework (ZIF-67) as the precursor was prepared. SEM, EDX, AFM, FTIR, and XRD analyses revealed the optimal formation of ZIF-67 nanoparticles both inside and on the surface of CS/PVA nanofibers without compromising the structure of these electrospun nanofibers. The unique porous structure and heterointerfaces of the ZIF-67/CS/PVA (CNF-2) nanofiber composites demonstrated remarkable adsorption capacities for cadmium (Cd) and tetracycline hydrochloride (TCH), achieving 1137.94 and 1029.5 mg/g, respectively. The adsorption effectiveness for Cd and TCH was 94.83 % and 85.79 %, respectively, under optimal adsorption conditions: pH 8, adsorbent dosage of 0.01 g, initial Cd and TCH concentration of 80 mg/L, and a contact time of 120 min. The study of coexisting Cd and TCH adsorption on CNF-2 under varying pH conditions (4–8) reveals a significant enhancement in Cd adsorption efficiency, increasing from 41.91 % to 97.49 %. Conversely, TCH exhibits a more modest improvement, with its adsorption efficiency rising from 72.53 % to 85.96 %. Kinetic and equilibrium studies revealed that the adsorption followed pseudo-second-order kinetics and the Langmuir isotherm. The prepared nanofiber adsorbed 60 % of Malachite green dye. The engineered adsorbent demonstrated impressive regeneration potential, maintaining its efficiency over three successive adsorption–desorption cycles.

Enhanced capacity of thiol-functionalized sugarcane bagasse and rice husk biochars for arsenite sorption in aqueous solutions

The utilization of biowastes for producing biochar to remove potentially toxic elements from water represents an important pathway for aquatic ecosystem decontamination. Here we explored the significance of thiol-functionalization on sugarcane bagasse biochar (Th/SCB–BC) and rice husk biochar (Th/RH–BC) to enhance arsenite (As(III)) removal capacity from water and compared their efficiency with both pristine biochars (SCB–BC and RH–BC). The maximum As(III) sorption was found on Th/SCB–BC and Th/RH–BC (2.88 and 2.51 mg g−1, respectively) compared to the SCB–BC and RH–BC (1.51 and 1.40 mg g−1). Relatively, a greater percentage of As(III) removal was obtained with Th/SCB–BC and Th/RH–BC (92% and 83%, respectively) at a pH 7 compared to pristine SCB–BC and RH–BC (65% and 55%) at 6 mg L−1 initial As(III) concentration, 2 h contact time and 1 g L−1 sorbent dose. Langmuir (R2 = 0.99) isotherm and pseudo-second-order kinetic (R2 = 0.99) models provided the best fits to As(III) sorption data. Desorption experiments indicated that the regeneration ability of biochars decreased and it was in the order of Th/SCB–BC (88%) > Th/RH–BC (82%) > SCB–BC (77%) > RH–BC (69%) up to three sorption–desorption cycles. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy results demonstrated that the thiol (-S–H) functional groups were successfully grafted on the surface of two biochars and as such contributed to enhance As(III) removal from water. Spectroscopic data indicated that the surface functional moieties, such as -S–H, − OH, − COOH, and C = O were involved to increase As(III) sorption on thiol-functionalized biochars. This study highlights that thiol-grafting on both biochars, notably on SCB–BC, enhanced their ability to remove As(III) from water, which can be used as an effective technique for the treatment of As from drinking water.Graphical

Efficient separation of carbon dioxide and methane in high-pressure and wet gas mixtures using Zr-MOF-808

The capture and separation of carbon dioxide (CO2) has been the focus of a plethora of research in order to mitigate its emissions and contribute to global development. Given that CO2 is commonly found in natural gas streams, there have been efforts to seek more efficient materials to separate gaseous mixtures such as CO2/CH4. However, there are only a few reports regarding adsorption processes within pressurized systems. In the offshore scenario, natural gas streams still exhibit high moisture content, necessitating a greater understanding of processes in moist systems. In this article, a metal-organic framework synthesis based on zirconium (MOF-808) was carried out through a conventional solvothermal method and autoclave for the adsorption of CO2 and CH4 under different temperatures (45–65 °C) and pressures up to 100 bar. Furthermore, the adsorption of humid CO2 was evaluated using thermal analyses. The MOF-808 synthesized in autoclave showed a high surface area (1502 m2/g), a high capacity for CO2 adsorption at 50 bar and 45 °C and had a low selectivity to capture CH4 molecules. It also exhibited a fine stability after five cycles of CO2 adsorption and desorption at 50 bar and 45 °C − as confirmed by structural post-adsorption analyses while maintaining its adsorption capacity and crystallinity. Furthermore, it can be observed that the adsorption capacity increased in a humid environment, and that the adsorbent remained stable after adsorption cycles in the presence of moisture. Finally, it was possible to confirm the occurrence of physisorption processes through nuclear magnetic resonance (NMR) analyses, thus validating the choice of mild temperatures for regeneration and contributing to the reduction of energy consumption in processing plants.

Antimicrobial polymer-based zeolite imidazolate framework composite membranes for uranium extraction from wastewater and seawater

Extraction uranium (VI) (U(VI)) from wastewater and seawater is highly important for environmental protection and life safety, but it remains a great challenge. In this work, the growth of the zeolitic imidazolate framework-8 (ZIF-8) nanoparticles on the tannic acid (TA)-3-aminopropyltriethoxysilane (APTES) modified PVDF (TAP) membrane was designed to obtain an excellent U(VI) adsorbent. The zeolite imidazolate framework composite membrane (TAPP-ZIF-60) was prepared through polyethyleneimine (PEI) bridging strategy and temperature regulation strategy in solvothermal method. The coordination bond between PEI and ZIF-8 and the covalent bond between PEI and TAP are essential in forming stable composite membrane. TAPP-ZIF with different properties was synthesized through a temperature regulation process and the TAPP-ZIF prepared at 60 °C has the uniform morphology and good performance. The adsorption capacity of TAPP-ZIF-60 is 153.68 mg/g (C0 = 95.01 mg/L and pH = 8.0) and water permeability is 5459 L m−2 h−1 bar−1. After ten adsorption–desorption cycles, it is proved that TAPP-ZIF-60 has good repeatability and stability. In addition, the TAPP-ZIF-60 composites membrane has a good inhibitory effect on Staphylococcus aureus and Escherichia coli. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analysis reveal that the coordination between TAPP-ZIF-60 and uranyl ions is the primary factor contributing to the high adsorption capacity.

Scaling up a hollow fibre adsorption unit for on-board CCS applications using a real gasoline engine exhaust

Decarbonising road transport using on-board carbon capture and storage (CCS) is challenged by inherent space and energy limitations. Thus, to be technically and economically viable, robust and compact carbon capture units need to be developed. Hence, in this work, a scaled up hollow fibre adsorption unit was tested downstream of a real 90:10 gasoline-ethanol engine exhaust gas to evaluate its CO2 capture performance after 100 adsorption–desorption cycles. The scaled up hollow fibre adsorption unit consisted of 37 four-channel hollow fibre adsorption units coated with a thin carbon xerogel layer, referred to as the CX-coated hollow fibre module (HFM). It should be noted that this is the first study to report the results of a HFM tested under real conditions over 100 adsorption–desorption cycles and is one of the few studies that reports the desorption step. Furthermore, despite the presence of CO, THC, NOx, and H2O in the exhaust gas, the CX-coated HFM exhibited high CO2 capture stability and mechanical integrity. This was evidenced through the CX-coated HFM obtaining and maintaining an average total capacity of 1.2 mmol/g over 100 adsorption–desorption cycles, and showing no visible signs of deterioration or a loss of mechanical integrity.

Enhanced performance of amine and thiol chemically modified graphene oxide for effective removal of Hg(II), Pb(II), and Cr(VI) from aqueous solution

This study describes a novel adsorbent with a multidentate ligand that was facilely fabricated by covalently bonding 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole on graphene oxide (AHMT-PRGO). The AHMT-PRGO nano-adsorbent was used for the effective removal of Hg(II), Pb(II), and Cr(VI) from wastewater. The AHMT-PRGO nano-adsorbent was synthesized by a nucleophilic substitution reaction between GO acyl chloride and AHMT chelating ligand in the presence of tetrabutyl-ammonium bromide as a catalyst. The successful modifications were confirmed via several spectroscopic and electron microscopy instrumentations including UV–Vis, FTIR, Raman, XRD, XPS, SEM, and TEM. The maximum adsorption capacities of Hg(II), Cr(VI), and Pb(II) on the AHMT-PRGO nano-adsorbent were 370.0, 136.2, and 109.6 mg/g, respectively, exceeding those of most previously reported adsorbents. Additionally, the equilibrium contact times for Hg(II), Pb(II), and Cr(VI) were 60, 30, and 400 min, respectively. In a mixture of nine heavy metal ions containing 250 ppm of each ion, the AHMT-PRGO nano-adsorbent exhibited high selectivity for Hg(II) ions. Furthermore, the AHMT-PRGO nano-adsorbent showed high stability over five adsorption–desorption cycles. Additionally, the AHMT-PRGO nano-adsorbent was successfully applied to remove heavy metal ions from real water samples. The novelty of AHMT-PRGO lies in the combination of a multidentate ligand for strong and selective binding with the high surface area and stability offered by covalently bonded graphene oxide. This combination offers potential advantages over traditional adsorbents in terms of adsorption capacity, selectivity, and reusability.

Reversible Adsorption of Ammonia in the Crystalline Solid of a CO2H-Functionalized Cyclic Oligophenylene.

Ammonia (NH3) is a viable candidate for the storage and distribution of hydrogen (H2) due to its exceptional volumetric and gravimetric hydrogen energy density. Therefore, it is desirable to develop NH3 storage materials that exhibit robust stability across numerous adsorption-desorption cycles. While porous materials with polymeric frameworks are often used for NH3 capture, achieving reversible NH3 uptake remains a formidable challenge, primarily due to the high reactivity of NH3. Here, we advocate the use of CO2H-functionalized cyclic oligophenylene 1a with high chemical stability as a novel single-molecule-based adsorbent for NH3. Simple reprecipitation of 1a selectively yielded microporous crystalline solid 1a (N). Crystalline 1a (N) adsorbs up to 8.27 mmol/g of NH3 at 100 kPa and 293 K. Adsorbed NH3 in the pore of 1a (N) has a packing density of 0.533 g/cm3 at 293 K, which is close to the density of liquid NH3 (0.681 g/cm3 at 240 K). Crystalline 1a (N) also exhibits reversible NH3 adsorption over at least nine cycles, sustaining its storage capacity (1st cycle: 8.27 mmol/g; 9th cycle: 8.25 mmol/g at 100 kPa and 293 K) and crystallinity. During each desorption cycle, NH3 was removed from 1a (N) under reduced pressure (∼65 Pa), leaving <3% of the total uptake, and 1a (N) was fully purged under dynamic vacuum conditions (∼5 × 10-4 Pa at 293 K for 1 h) before the subsequent adsorption cycles. Thus, microporous crystalline 1a (N) can reliably adsorb and desorb NH3 repeatedly, which avoids the need for heat-based activation between cycles.

Fluorinated/sulfonated dual-functional three-component covalent organic polymer for adsorption of fluoroquinolones: Preparation, adsorption performance and mechanism

Due to the low performance of traditional water treatment methods, the effective removal of fluoroquinolone (FQs) is of great significance for environmental protection. Based on the structural characteristics of FQs, a fluorinated/sulfonated dual-functional three-component covalent organic polymer [COP, named TpBD-CF3(0.25)SO3H0.75)] was deliberately designed via Schiff reaction, which attempted to realize high removal performance of FQs from different environmental water samples. The results of adsorption performance showed that TpBD-CF3(0.25)SO3H(0.75) could realize high removal performance of FQs via synergistic effect of electrostatic, hydrogen bonding, F-F affinity, π-π and hydrophobic interactions. The adsorbent exhibited fast adsorption rate (can reach adsorption equilibrium in 10 min) and high removal efficiency (> 90 %) for the four concerned FQs, and their adsorption capacity ranged from 65 to 81 mg/g. The results of adsorption kinetics, thermodynamics and isotherm consistently showed that the adsorption of FQs was chemical adsorption. The removal efficiencies of FQs in different water samples were all above 90 % after treated by the adsorbent. The adsorbent has good reusability, and the removal efficiency decreased only by 1 %−4 % after four adsorption–desorption cycles. In addition, the adsorbent has the potential to be used for enrichment of trace FQs in aqueous samples.

Al2O3-Encapsulated TiO2 flower-like spherical mesoporous material for efficient removal of PCl3 traces

Solar energy is considered the most promising sustainable green energy source. Currently, more than 95% of solar energy development and utilization is based on silicon, especially polysilicon. In the production of polysilicon, the PCl3 impurity content must be removed to the ppb level to ensure product performance. Al2O3 has been confirmed to be effective at removing PCl3 at ppm levels, however, it suffers from weak adsorption capacity, slow adsorption rate and low adsorption efficiency in the case of PCl3 in ppb levels. In this work, by encapsulating Al2O3 on TiO2, a flower-like spherical adsorbent ([Al2O3]3[TiO2]1) was prepared. The experimental results show that after introducing TiO2, the adsorption performance of [Al2O3]3[TiO2]1 for PCl3 in ppb levels is significantly improved, 34.1% higher than that before introducing TiO2. Five adsorption–desorption cycles indicate that [Al2O3]3[TiO2]1 has excellent regeneration property. Characterization analysis and density functional theory(DFT) simulations suggest that PCl3 interacts with the adsorbent primarily through charge transfer.

Miniaturized 3D-printed hand-operable dispersive sample pretreatment device with replaceable chitosan/polydopamine thin film metal sorbent for enhanced metal analysis

To address the increasing demand for sensitive and selective sample preparation methods for metal analysis; preconcentration of intended analyte from complex sample matrices before analysis is required to improve the performance of analysis instruments. In this study, we have engineered a sustainable and portable syringe-based hand-operable three-dimensionally (3D) printed sample pretreatment apparatus equipped with a replaceable bio-based thin- film metal sorbent. This device effectively addresses the challenges of sample matrix interference in metal analysis. A metal sorbent film composed of chitosan (CS) and polydopamine (PDA) leveraged the diverse functional groups in the CS/PDA matrix to significantly enhance the extraction efficiency for various metals. Our approach demonstrated excellent analytical performance, with coefficients of determination (R2) of 0.9982 for copper (Cu) and 0.996 for chromium (Cr). The method achieved low limits of detection (LOD) of 0.3 μg L−1 for Cr and 0.7 μg L−1 for Cu. Precision and practicality assessments using actual urine samples yielded satisfactory relative standard deviations (RSD%) ranging from of 1.6 %–8.5 % for both metals, indicating minimal interference from the sample matrix. Moreover, our approach exhibited robust performance even after seven consecutive extraction and desorption cycles, highlighting its sustainability and practical applicability for laboratory and on-site sample pretreatment.

Unlocking Cd(II) biosorption potential of Candida tropicalis XTA 1874 for sustainable wastewater treatment

Cd(II) is a potentially toxic heavy metal having carcinogenic activity. It is becoming widespread in the soil and groundwater by various natural and anthropological activities. This is inviting its immediate removal. The present study is aimed at developing a Cd(II) resistant strain isolated from contaminated water body and testing its potency in biological remediation of Cd(II) from aqueous environment. The developed resistant strain was characterized by SEM, FESEM, TEM, EDAX, FT-IR, Raman Spectral, XRD and XPS analysis. The results depict considerable morphological changes had taken place on the cell surface and interaction of Cd(II) with the surface exposed functional groups along with intracellular accumulation. Molecular contribution of critical cell wall component has been evaluated. The developed resistant strain had undergone Cd(II) biosorption study by employing adsorption isotherms and kinetic modeling. Langmuir model best fitted the Cd(II) biosorption data compared to the Freundlich one. Cd(II) biosorption by the strain followed a pseudo second order kinetics. The physical parameters affecting biosorption were also optimized by employing response surface methodology using central composite design. The results depict remarkable removal capacity 75.682 ± 0.002% of Cd(II) by the developed resistant strain from contaminated aqueous medium using 500 ppm of Cd(II). Quantitatively, biosorption for Cd(II) by the newly developed resistant strain has been increased significantly (p < 0.0001) from 4.36 ppm (non-resistant strain) to 378.41 ppm (resistant strain). It has also shown quite effective desorption capacity 87.527 ± 0.023% at the first desorption cycle and can be reused effectively as a successful Cd(II) desorbent up to five cycles. The results suggest that the strain has considerable withstanding capacity of Cd(II) stress and can be employed effectively in the Cd(II) bioremediation from wastewater.

Boric acid-modified activated carbon for glycerol removal from high-salt wastewater

Epoxy resin production wastewater contains glycerol and NaCl, which cause high energy consumption and environmental pollution during wastewater treatment. Therefore, the adsorption of glycerol on boric acid in low-temperature modified activated carbon was investigated for the first time. Under the optimum conditions of a modification temperature of 80℃, a mass ratio of boric acid to activated carbon of 1:1, and a modification time of 6 h, the modification of activated carbon was realized. It was found that the removal of glycerol by activated carbon before and after modification was found to be 0.10 % and 99.67 % (10 °C), indicating that boric acid endows activated carbon with a stronger ability to adsorb glycerol; The higher the pH of the wastewater, the higher the removal rate of glycerol, while the salt content of the wastewater has little effect. This study used batch adsorption to show that modified activated carbon could adsorb up to 1100 mg g−1 of glycerol, which was in line with the proposed pseudo-second-order kinetic model. After 8 cycles of adsorption and desorption, the modified activated carbon lost only 12.46 % of the adsorption capacity. Combined with the results, the existence of boron hydroxyl groups on activated carbon is the key to glycerol adsorption.

Adsorption characteristics and applications of andesite in removing some pollutants from wastewater

Andesite was employed to effectively extract mercury(II) in an aqueous solution. After evaluating its characteristics, andesite was characterized by applying modern techniques such as BET and TGA methods. The study employed SEM and TEM measurements to analyze the variation in the surface shape and crystallinity of the metal due to adsorption. Using the EDX process, the chemical composition, weight, and atomic percentage of each element of andesite were determined. FTIR techniques were also used to confirm the TEM–EDX findings. Zeta potential was estimated. Cycles of regeneration and desorption have been examined. 99.03% was the highest uptake percentage. Adsorbent quantity (0.0025–0.05) g/L, contact time (5–60) min, pH (2–10), temperature (25–60) °C, and dose (0.0027, 0.0044, 0.0125, 0.0155, and 0.0399) mg/L all affect the amount of removal that increases with the increase in contact time, pH, dose, and temperature but drops as the metal ion concentration rises. The ideal values for contact time, pH, metal ion concentration, dose, and temperature were found to be, respectively, 30 min, 0.0155 mg/l, 0.02 g/l, and 40 °C. The calculation of thermodynamic parameters, including ΔH, ΔG, and ΔS, was imperative in establishing that the mechanism of heavy metal adsorption on andesite was endothermic, exhibiting a physical nature that escalated with temperature rise. The Freundlich adsorption equation's linear form is matched by the adsorption of mercury(II) on andesite; constant n was 1.85, 1.06, 1.1, and 1.1, whereas the Langmuir constant qm was found to be 1.85, 2.41, 3.54, and 2.28 mg/g at 25–60 °C. Furthermore, adsorption follows a pseudo-second-order rate constant of (3.08, 3.24, 3.24, and 13) g/mg/min under identical temperature conditions, as opposed to a first-order rate constant of 4, 3, 2.6, and 2. Hg2+, NH4+, Cl−, Br−, NO3−, SO42−, Na+, K+, H2S, and CH3SH were all extracted from wastewater by this application.

Concentration of heavy metal ions from aqueous media under dynamic conditions using a composite sorbent based on chitosan and silica

Objectives. The study set out to investigate the sorption, toxicological, and regeneration properties of a composite sorbent based on chitosan hydrogel and unsuspended silicon dioxide (chitosan–colloidal silica), which manifest themselves under dynamic conditions of purification of aqueous solutions, as a means of removing heavy metal ions.Methods. The total dynamic exchange capacity of a chitosan–colloidal silica composite sorbent was evaluated under dynamic sorption conditions by passing solutions containing Zn(II), Cd(II), Cu(II), and Cr(III) ions having a concentration of 240–251 mg/L through a fixed sorption bed. The method for determining acute toxicity using daphnia (Daphnia magna Straus) is based on the direct calculation of the mortality of daphnia exposed to toxic substances contained in the test aqueous extract in comparison with a reference culture in samples that do not contain toxic substances. The regeneration ability of the sorbent was assessed by counting the number of sorption–desorption cycles using 0.1 M NaOH and 0.1 M NaHCO3 eluents, as well as aqueous solutions of H2O2 (1 and 3%).Results. The effectiveness of the chitosan–colloidal silica composite sorbent in the process of dynamic purification of aqueous media to remove Cu(II), Zn(II), Cd(II), and Cr(III) ions was established. After determining the times of ion breakthrough and saturation of the developed sorbent, its dynamic exchange capacity was calculated by processing the kinetic curves of sorption of heavy metal ions under dynamic conditions. The results of regeneration of the sorbent were presented in the context of the possibility of its reuse. It is shown that the sorbent can withstand up to five sorption–desorption cycles while maintaining a level copper cation extraction above 90%.Conclusions. Analysis of the kinetic curves demonstrated that the driving force behind the removal of heavy metals from aqueous media by means of the obtained sorbent is the external diffusion mass transfer of ions from the mobile phase of the solution. Biotesting of samples showed that the developed chitosan-based sorbent does not have acute toxicity.

Utilizing silica fume and synthetically produced mesoporous silicas for simulated flue gas CO2 adsorption

ABSTRACT Carbon capture and storage (CCS) is crucial in mitigating greenhouse gas emissions. Solid adsorbents, notable for their reusability and corrosion resistance, are gaining attention in CO2 gas separation. This study uses Silica fume as an adsorbent and silica source for SiO2 and MCM-41 silica-based adsorbents. Silica was extracted via an alkaline dissolution method, and adsorbents were synthesized using a CO2-induced precipitation method, chosen for its shorter synthesis time and CO2 utilization. The effects of pore volume, average pore diameter, and specific surface area on amine loading and CO2 adsorption capacity were investigated using CTAB surfactant in SiO2 synthesis, resulting in MCM-41. The synthesized adsorbents were modified with TEPA and DEA amines due to their high affinity for CO2. After determining optimal amine loading, the impact of combining TEPA with DEA was examined. The highest CO2 adsorption capacity under simulated flue gas conditions (15% volume CO2 and 85% volume N2) was 198 milligrams per gram of adsorbent for the SiO2 adsorbent functionalized with 50% by weight amine (28% TEPA and 22% DEA). Variations in CO2 adsorption over time, the influence of adsorbent quantity on adsorption capacity, the affinity of the adsorbent for N2 adsorption, and the adsorption–desorption cycle were investigated. The 28%TEPA-22%DEA-SiO2 adsorbent emerged as the optimal choice due to its large total volume and average pore diameter, absence of a template in its structure, excellent performance in CO2 adsorption, lack of affinity for N2, and robust adsorption–desorption stability.

Phosphate Removal from Polluted Water via Lanthanum-Modified Sludge Biochar

Biochar has attracted attention for its capability to remove phosphorus (P) from wastewater. However, the poor dispersion and limited adsorption capacity of unmodified biochar prevent its wide usage in water remediation. Herein, sludge biochar was modified using lanthanum nitrate to improve the removal of P from aqueous solutions. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to elucidate the modification and adsorption mechanisms of biochar. Furthermore, the adsorption performance of the modified biochar was determined through adsorption kinetics and isotherm model fitting. The results showed that the modification process successfully introduced lanthanum-containing functional groups into biochar and considerably improved the complexation performance and ion-exchange capacity. The maximum experimental adsorption capacity for phosphate was 140.237 mg/g at pH 3.0. The adsorption processes of the modified biochar accorded with the Freundlich adsorption isotherm model, which indicates the successful adsorption of phosphate onto the modified biochar via multilayer adsorption. The adsorption mechanism was dominated by chemisorption, which mainly involved inner-sphere complexation, precipitation, and electrostatic attraction. Meanwhile, the adsorption and desorption experiments demonstrated the satisfying recycling performance of the modified biochar and the 72.3% adsorption capacity retention after the sixth desorption cycle. The dynamic adsorption study revealed that the modified biochar had long sustainable treatment durations of 7.58 and 9.08 h at adsorbent dosages of 1 and 2 g, respectively, which proves the feasibility of using biochar as a cost-effective and efficient adsorbent for phosphate-polluted water.

Lanthanum-doped chitosan-based polyacrylamide double network hydrogels for adsorption of phosphorus from wastewater.

Excessive phosphorus in aqueous solutions can cause eutrophication, which can harm aquatic organisms and pose a risk to the safety of drinking water for humans. The Chitosan/Polyacrylamide/Lanthanum (CS/PAM/La) hydrogel was designed to get rid of phosphate from aqueous solutions. La (III) was used to enhance the capacity of adsorption of CS. Polyacrylamide was used to enhance the mechanical properties of CS. The results showed that the adsorption capacity of CS/PAM/La hydrogel for phosphate was increased compared with that of CS. When pH of 5.0, the adsorption capacity was 80.07mg-P/g. In addition, after five adsorption and desorption cycles, the adsorption efficiency remained above 90%. The mechanism of phosphate adsorption on CS/PAM/La material was analyzed using a mass transfer factor model (MTF) and the possible structure of CS/PAM/La hydrogel was calculated by density functional theory calculation (DFT). The application of CS/PAM/La composite hydrogel for removal of phosphate from actual wastewater was investigated, and the results met the requirement of national standard.

Adsorption of fluoride ion on Al/La modified acidified attapulgite composite materials

This study developed a novel fluoride ion adsorbent material (Al/La-A) for efficient removal of fluoride ions in water. The crystal structure, elemental composition, surface morphology, specific surface area, thermal stability and surface electronegativity before and after modification were explored using FTIR, XRD, XPS, SEM-EDS, BET, TG-DSC, and zeta potential measurements. Results showed that the fluoride ion adsorption capacity of Al/La-A reached 130.42 mg/g, with the surface area increasing from 65.66 m2/g to 111.68 m2/g, respectively, compared to unmodified attapulgite. Al/La-A maintained excellent fluoride ion removal performance over a wide pH range, with the best adsorption at pH 2. Coexisting ion experiments indicated weak competitive adsorption effects of Cl-, SO42-, and HCO3–, with fluoride ion adsorption remaining above 100 mg/g in the presence of different concentrations of coexisting anions. After 5 adsorption–desorption cycles, Al/La-A exhibited strong adsorption capacity and reusability. The fitting of Langmuir adsorption model and pseudo-second-order kinetic model to the adsorption of fluoride ions on Al/La-A indicated that the adsorption of fluoride ions on Al/La-A was primarily monolayer chemical adsorption. The adsorption mechanism of fluoride ions involved electrostatic interactions, ion exchange, and coordination complexation. This study provides a new research approach for the optimal utilization of attapulgite-based adsorbent materials and the efficient removal of fluoride-containing wastewater.