Adsorption-desorption Cycles Research Articles

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.

Enhancing kaolin's structure for efficient removal of lead ions from aqueous solutions

This research demonstrates a novel methodology for structurally modifying kaolin clay to efficiently remove toxic lead ions from water through adsorption. Kaolin was systematically treated with hydrochloric acid, cetylpyridinium chloride surfactant, and calcium chloride to enhance its physico-chemical properties. BET surface area analysis, transmission electron microscopy, scanning electron microscopy, and BJH pore size measurements confirmed successful intercalation of surfactants between kaolin sheets, increasing the surface area from 43.2 to 57.1 m2 g-1 and inducing larger mesopores. Operational factors such as pH, dosage of adsorbent, time spent in contact, starting lead concentration, and temperature were tuned using batch adsorption tests. Maximum lead uptake of 29.58 mg g-1 was attained at pH 5, 20 mg adsorbent dose, 30 mg L-1 initial lead concentration, 80 min contact time, and 30°C temperature. Pseudo-second order kinetics and Sips isotherm models aptly characterized the adsorption, indicating chemisorption on heterogeneous sites. Positive enthalpy and entropy changes signified an endothermic and irreversible process. Regeneration studies demonstrated stable performance over five adsorption-desorption cycles. This comprehensive methodology integrates acid, surfactant, and cationic treatments to synthesize an eco-friendly kaolin adsorbent with enhanced selectivity and adsorption capacity for removing toxic lead from water.

Modulating porosity and hydrophilicity of granular adsorbent by water-soluble polymers to enhance lithium extraction from ultrahigh Mg/Li ratio brine

The development of granular adsorbents with high adsorption capability and high cycle stability is of great significance for the application in efficiently extracting lithium from salt lake brine. Herein, the structure of granular aluminum-based adsorbents was regulated by adding water-soluble polymer PEG. The results showed that the molecular weight of PEG was closely related to the pore structure and surface hydrophilicity of the granular adsorbents. With the decrease of the molecular weight of PEG, the specific surface area, the average surface pore size, and the hydrophilicity of granular adsorbents increase. The optimized adsorbent PSF-PEG600@AD formed a complex pore structure with surface macropores and internal mesopores as well as excellent hydrophilicity. The mechanical strength and wear resistance are enhanced. This unique porous structure and surface hydrophilicity enable PSF-PEG600@AD rapid adsorption equilibrium in the old brine of Qarhan salt lake with a Mg/Li ratio of 323 within 4 h. The adsorption capacity remains as high as 99.02 % after 10 static adsorption-desorption cycles, showing excellent cyclic stability. This study guides a direction in preparing high-performance granular adsorbents with adjustable pore structure and surface properties.

Highly efficient mesoporous aluminium-magnetite-alginate magnetic composite for defluoridation of water

One of the few elements that can have negative health impacts in both conditions, when consumed in excess or insufficiency is fluoride. In current study, aluminium magnetite alginate composite (AMA) was fabricated and applied using batch adsorption of fluoride as well as by using statistical modelling. Heterogeneous surface as revealed from scanning electron micrograph, thermal stability shown by thermal studies, high surface area of 29.77 m2 g−1, pore volume 0.1987 cm3 g−1 with mesoporous structure having average pore radius of 133 Å shown by BET analysis, fare degree of magnetization from VSM analysis were the important features of this material. Screening experiments and batch trials were carried out to obtain optimum working conditions. pH of 3.0, dosage of 50 mg, interaction period of 60 min and concentration of 50 mg L−1 depicted maximum defluoridation efficacy of about 94%. The adsorption capacity was found to be 60.08 mg g−1 in accordance with Langmuir adsorption isotherm, while pseudo second order kinetics was followed. Overall effects of various factors on sorption process were optimized using response surface methodology (RSM). Regeneration potential of AMA has been demonstrated for 10 adsorption-desorption cycles, showing more than 60% efficiency in tenth cycle. The AMA composite shows E-factor value 0.004 depicting it is sustainable in environment. In short, this novel composite showed excellent morphological, magnetic, functional properties that led to enhanced adsorption efficiency in short span of time that can be regenerated and reused in multiple cycles.

Magnetically nanorized seaweed residue for the adsorption of methylene blue in aqueous solutions.

The cost-effective and green separation of dye pollutants from wastewater is of great importance in environmental remediation. Industrial seaweed residue (SR), as a low-cost cellulose source, was used to produce carboxylated nanorized-SR (NSR) via oxalic acid (OA)-water pretreatments followed by ultrasonic disintegration. Fourier transform infrared spectroscopy, X-ray polycrystalline diffraction, nitrogen isotherms, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, X-ray photoelectron spectrometry, particle charge detection, zeta potential and retro titration experiments were utilized to explore the physiochemical properties of samples. The NSRs with carboxyl content of 4.58-6.73 mmol g-1 were prepared using 10-60% OA-water pretreatment. In the case of 20% OA-water pretreatment, the highest NSR yield (73.9%) and nanocellulose content (80.2%) were obtained. Through self-assembly induced by the electrostatic interaction, magnetic NSR composite adsorbents (MNSRs) were prepared with the combination of NSR and Fe3O4 nanoparticles (NPs). The carboxylated NSR with negative charge demonstrated good affinity for Fe3O4 NPs. The Fe3O4 NPs were perfectly microencapsulated with the NSR when the NSR/Fe3O4 mass ratio was higher than 1/1. The adsorption properties of the MNSR for methylene blue (MB) removal from aqueous solution were investigated. The adsorbent with NSR/Fe3O4 mass ratio of 1/1 (MNSR1/1) exhibited optimum performance in terms of the magnetic properties and adsorption capacity. The MNSR1/1 showed high adsorption ability in a pH ≥7 environment. According to the Langmuir fitting, the maximum adsorption capacity of MNSR1/1 for MB reached 184.25 mg g-1. The adsorption of MB complies with the pseudo-second-order kinetic model. MNSR1/1 still maintained good adsorption properties after the fifth cycle of adsorption-desorption. MNSR1/1 could selectively adsorb cationic dye (i.e., MB and methyl violet) from wastewater, with hydrogen bonding and electrostatic interaction as the main force.

Efficient Capture and Low Energy Release of NH3 by Azophenol Decorated Photoresponsive Covalent Organic Frameworks.

In NH3 capture technologies, the desorption process is usually driven by high temperature and low pressure (such as 150-200 °C under vacuum), which accounts for intensive energy consumption and CO2 emission. Developing light responsive adsorbent is promising in this regard but remains a great challenge. Here, we for the first time designed and synthesized a light responsive azophenol-containing covalent organic framework (COF), COF-HNU38, to address this challenge. We found that at 25 °C and 1.0 bar, the cis -COF exhibited a NH3 uptake capacity of 7.7 mmol g-1 and a NH3/N2 selectivity of 158. In the adsorbed NH3, about 29.0 % could be removed by vis-light irradiated cis-trans isomerization at 25 °C, and the remaining NH3 might be released at 25 °C under vacuum. Almost no decrease in adsorption capacity was observed after eight adsorption-desorption cycles. As such, an efficient NH3 capture and low energy release strategy was established thanks to the multiple hydrogen bond interactions (which are strong in total but weak in individuals) between NH3 and the smart COF, as well as the increased polarity and number of hydrogen bond sites after the trans-cis isomerization.

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.

Efficient removal of Eosin Yellow dye using solvothermal synthesised Ni/Al layered double hydroxide and layered double oxide: insights into adsorption kinetics and thermodynamics

ABSTRACT The accumulation of organic pollutants in the environment is swelling steadily and raising the alarm for their redressal. Layered double hydroxides (LDH) and layered double oxides (LDO) are gaining prominence for their potential to address this challenge. This work includes an eco-friendly facile solvothermal synthesis of Ni/Al LDH and their calcination to Ni/Al LDO. The prepared nanomaterials were characterised by XRD, FE-SEM, HR-TEM, FT-IR, BET and TGA techniques, which confirm the highly porous structure of synthesised nanomaterials with a high specific area of 109.94 m2g−1 and 188.94 m2g−1 for Ni/Al LDH and Ni/Al LDO, respectively. A systematic study was conducted to explore the adsorptive potential of these materials towards the removal of organic dye Eosin Yellow (EY). The adsorptive efficiency was found to be 95% and 99% for Ni/Al LDH and Ni/Al LDO, respectively, under the optimised conditions of pH, adsorbent dose, contact time, dye concentration and temperature on adsorptive removal of EY dye, which was analysed by BBD-RSM (Box-Behnken Design Response surface methodology). The adsorption data fits best with the Freundlich isotherm model and pseudo-second-order kinetics. The thermodynamic study confirms the exothermic adsorptive process. The durability and reusability of the synthesised adsorbents were ascertained by their retention of the adsorptive efficiency even after five adsorption-desorption cycles which were as high as 91% and 85% for Ni/Al LDH and Ni/Al LDO, respectively. The mechanism of adsorption involves electrostatic interaction and hydrogen bonding between the surface of adsorbent and adsorbate as well as intercalation of dye molecules.

Simultaneous effect of oxygen impurity and flow rate of purge gas on adsorption capacity of and heel buildup on activated carbon during cyclic adsorption-desorption of VOC

Irreversible adsorption, or heel buildup, negatively impacts activated carbon performance and shortens its lifetime. This study elucidates the interconnections between flow rate and the oxygen impurity of desorption purge gas with heel buildup on beaded activated carbon (BAC). Nine thermal desorption scenarios were explored, varying nitrogen purge gas oxygen impurity levels (<5 ppmv, 10,000 ppmv, 210,000 ppm (21 %)) and flow rates (0.1, 1, 10 SLPM or 1 %, 10 %, 100 % of adsorption flow rate) during thermal desorption. Results reveal that increasing purge gas flow rate improves adsorption capacity recovery and mitigates adverse effects of purge gas oxygen impurity. Cumulative heel increased with higher purge gas oxygen impurity and lower flow rates. In the least effective regeneration scenario (0.1 SLPM N2, 21 % O2), a 32.8 wt% cumulative heel formed on BAC after five cycles, while the best-case scenario (10 SLPM N2, <5 ppmv O2) resulted in only 0.3 wt%. Comparing the pore size distributions of virgin and used BAC shows that heel initially forms in narrow micropores (<8.5Å) and later engages mesopores. Thermogravimetric analysis (TGA) showed that oxygen impurity creates high boiling point and/or strongly bound heel species. TGA confirmed that higher purge gas flow rates reduce heel amounts but encourage chemisorbed heel formation in oxygen's presence. These findings can guide optimization of regeneration conditions, enhancing activated carbon's long-term performance in cyclic adsorption processes.

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.

Design parameters for fixed bed column of biosorbent developed from Syagrus romanzoffiana for the removal of mono and multicomponent metallic ions

A biosorbent produced from Jerivá coconut (Syagrus romanzoffiana) was utilized for removal of Cd2+, Cu2+, Ni2+, and Zn2+ ions in both single and multi-component systems. Adsorption equilibrium batch tests indicated that the Langmuir model best represented the adsorption of both mono and multi-component metal ions, with the multi-component adsorption classified as antagonistic. Among the desorbing solvents tested, 0.1 M H₂SO₄ was the most effective, achieving recovery efficiencies of 98.2 % for Cu2+, 77.9 % for Zn2+, 69.9 % for Cd2+, and 29.4 % for Ni2+. Continuous system tests were performed with an initial concentration of 25 mg L−1 for each metal in the single-component setup and a total concentration of 100 mg L−1 in the multi-component mixture. To evaluate the biosorbent's efficiency in adsorbate recovery, 4 cycles of adsorption-desorption were conducted in a fixed-bed column, revealing a gradual decrease in desorption efficiency over successive cycles. The biosorbent desorbed all four metal ions within approximately 40 min. Cu2+ was the most desorbed ion (193.1 mg L−1), followed by Cd2+ (98.6 mg L−1), Zn2+ (66.2 mg L−1), and Ni2+ (51.7 mg L−1). The operational parameters of the fixed-bed column demonstrated good adsorption performance after column regeneration.

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.

Electrospinning and Partial Etching Behaviors of Core-Shell Nanofibers Directly Electrospun on Mesh Substrates for Application in a Cover-Free Compact Air Filter.

The exposure of workers to propylene glycol monomethyl ether acetate (PGMEA) in manufacturing environments can result in potential health risks. Therefore, systems for PGMEA removal are required for indoor air quality control. In this study, core-shell zeolite socony mobil-5 (ZSM-5)/polyvinylpyrrolidone-polyvinylidene fluoride nanofibers were directly electrospun and partially wet-etched on a mesh substrate to develop a cover-free compact PGMEA air filter. The electrospinning behaviors of the core-shell nanofibers were investigated to optimize the electrospinning time and humidity and to enable the manufacture of thin and light air-filter layers. The partial wet etching of the nanofibers was undertaken using different etching solvents and times to ensure the exposure of the active sites of ZSM-5. The performances of the ZSM-5/PVDF nanofiber air filters were assessed by measuring five consecutive PGMEA adsorption-desorption cycles at different desorption temperatures. The synthesized material remained stable upon repeated adsorption-desorption cycles and could be regenerated at a low desorption temperature (80 °C), demonstrating a consistent adsorption performance upon prolonged adsorption-desorption cycling and low energy consumption during regeneration. The results of this study provide new insights into the design of industrial air filters using functional ceramic/polymer nanofibers and the application of these filters.

Activated carbon from hydrothermal carbonization of ice cream factory wastewater with H3PO4 activation. Synthesis, characterisation and adsorption properties

This work aims to treat ice cream wastewater (ICWW) by hydrothermal carbonization (HTC) and to produce activated carbon (AC). The HTC reduces COD, BOD5 and KTN by up to 80%, 55% and 93%, respectively. The obtained hydrochar was activated with H3PO4 at various impregnation ratios (1−4) and different temperatures (400−600 °C). The material with the best properties, named AC-2-500, was obtained at 500 °C with an acid impregnation rate of 2 and represents a spherical shape (specific surface area of 1432.44 m2 g−1, pore volume of 0.80 cm3g-1, and average pore diameter around 2.24 nm). The porous structure of AC-2-500 enabled to achieve high adsorption capacities of the order of 588.23 mg g−1 and 250 mg g−1 for rhodamine B (RhB) and acid red 97 (AR97), respectively. The adsorption equilibrium was reached in 30 min for RhB and 60 min for AR97. The linear forms of the Langmuir and Freundlich isotherms appear to produce reasonable models for the adsorption of dyes onto AC-2-500, with best results when applying Langmuir model. Both dyes adsorb spontaneously and endothermically, with an increase in the randomness at the solid/solution interface. Furthermore, the regeneration study revealed that during several adsorption-desorption cycles, AC-2-500 demonstrated a strong adsorption capability.

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.

Biosorption of pb(II) from aqueous solution by citrus reticulate: adsorption studies, and modeling

Removing toxic Pb(II) ions from aqueous solution by the peels of citrus reticulate (mandarin orange), a fruit industry waste, presents suitable scale-up possibilities. The Scanning Electron Microscope (SEM) and Brunauer-Emmett-Teller (BET) studies reflected that the mandarin orange peel powder had a porous surface area (32.46 m2g−1), average pore size and pore volume was 38.6 Å and 0.402 cm3g−1, respectively, favorable for binding Pb(II) ions. Fourier-transform infrared spectroscopy (FTIR) showed C-Br stretching, primary alcohol (C-O), phenolic O-H, and carbodimide N = C = N bands primarily helped to bind Pb(II) ions. The study evaluated and optimized the parametric influences of pH, adsorbate and biosorbent concentration, contact time and temperature on the removal efficiency of Pb(II) ions. A maximum of 97.08% Pb(II) was removed from 20 mg L−1 solution when 2.5 g L−1 adsorbent was present. The reaction obeyed the pseudo-second-order kinetic model. The intra-particle diffusion was involved in lead sorption. The Langmuir isotherm model resulted in an adsorption capacity of 23.04 mg g−1. 35.28% Pb(II) was removed in the 3rd adsorption-desorption cycle with 0.4 M HCl. The adsorption process was natural, impulsive and endothermic. The statistical investigation used Multiple Polynomial Regression (MPR) and Genetic Algorithm (GA). The analysis effectively forecasted the percentage removal at the optimized condition.

Effect of Temperature on CO2 Adsorption onto Amine-Functionalized KIT-6 Adsorbents.

The mesoporous silica KIT-6 was synthesized and functionalized with 3-aminopropyltriethoxysilane (APTES) by grafting at 110 °C. The composites were prepared with three different concentrations of APTES: 20, 30 and 40 wt.%. The as-prepared samples were characterized by thermal gravimetric analysis in air and nitrogen atmosphere (TG/DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction and nitrogen adsorption-desorption. In this study, CO2 adsorption-desorption was investigated using temperature programmed desorption mass spectrometry (TPD-MS) at different temperatures. The adsorption capacity of the prepared composites is 2.23 mmol CO2/g at 40 °C and decreases to 0.95 mmol/g at 70 °C. Regarding the efficiency of the amino groups, the best result was obtained for APTES-grafted KIT-6 at 40 °C, with 0.512 mmol CO2/mmol NH2. The results showed good cyclical stability in adsorption capacities even after nine adsorption-desorption cycles.

Investigation of synergistic effects using alkanolamines on post-synthetic modification of metal-organic framework and CO2 adsorption capacity

The net global carbon balance is a key modern and even existential environmental issue to humans. Therefore, developing highly efficient gas separation technologies, e.g. based on the application of solid adsorbents, is critically important. Among the advanced solid adsorbents metal-organic frameworks (MOFs), especially MIL-101(Cr), which offers superior physicochemical properties, have proven to be highly promising porous materials for such purposes. In this approach, MIL-101(Cr) nanoadsorbent was functionalized using four alkanolamines (MIL-101(Cr)-alkanolamine) to enhance its CO2 adsorption capacity by increasing the polarity of its pores. Additionally, the synergistic effects of steric hindrance (-CH3 and –CH2CH2OH) and the basicity strength (pKa) of alkanolamines on post-synthetic modification (PSM) of MIL-101(Cr) were investigated. Alkanolamines were selected as the organic ligands because their nitrogen atoms (amino group) coordinate with the chromium ion in MIL-101(Cr), while the hydroxyl groups increase pore polarity and improve the CO2 adsorption capacity through creating weak hydrogen bonding (H-bonding) interactions, resulting in reduced energy consumption during regeneration. In this study, PXRD, IR, and FE-SEM results demonstrated that the crystal structure and morphology of nanoadsorbents remained intact after modification. CHN and ICP analyses were additionally employed to calculate the Nalkanolamine/Cr ratios. CO2 adsorption capacities of all MIL-101(Cr)-alkanolamine nanoadsorbents (∼30–∼45 %) and their selectivity profile (CO2:CH4 and CO2:N2) exhibited significant improvement as opposed to MIL-101(Cr). Investigations revealed that the adsorption capacities of all nanoadsorbents negligibly changed after five adsorption-desorption cycles.

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.