Adsorption Breakthrough Research Articles

Reaction kinetics and isotherms of commercial activated carbon in variable pressure adsorption of high compound VOCs

ABSTRACT This study investigated the feasibility of using/reusing commercial activated carbon (CAC) for the capture of high molecular weight and high-boiling point volatile organic compounds (HBPVOCs). The CAC was first characterized using proximate analysis, heat value analysis, iodine value analysis, element analysis, inductively coupled plasma spectrometry, and specific surface area analysis. We then assessed the adsorption/desorption performance of a CAC-based PSA system for the removal of Butyl Cellosolve (BCS), a HBPVOC commonly used in paints, coatings, cleaners, and industrial processes. This involved deriving the BCS adsorption capacity of CAC as a function of adsorbent quantity (2.5, 5, and 10 g), flow rate (4, 6, and 8 L/min), and pressure (1.3, 2.3, and 3.4 kg/cm2). The BCS adsorption capacity of the CAC varied with pressure as follows: 1.3 kg/cm2 (652.85 mg/g), 2.3 kg/cm2 (817.20 mg/g) and 3.4 kg/cm2 (1324.05 mg/g). The adsorption mode most closely resembled pseudo-first-order kinetics (i.e. single-layer physical adsorption). Desorption was performed using an adjustable tubular high-temperature furnace under a nitrogen atmosphere (0.93 kg/cm2). Following desorption with a set desorption duration of 1 hr, the BET values varied with temperature as follows: 350°C (75.58% of the original value) and 450°C (86.04% of the original). Desorbed CAC (DCAC) was also examined to detect changes in pore structure due to the effects of recycling. We obtained breakthrough curves and adsorption capacity curves of CAC as functions of flow rate and pressure. We also investigated adsorption performance under pressure swing conditions from the perspective of reaction kinetics and density functional theory. Our results demonstrate the efficacy of CAC in the adsorption of BCS as well as the recyclability of this material. Implication Statement This study demonstrates the potential for reusing commercial activated carbon (CAC) to capture high molecular weight and high-boiling point volatile organic compounds (HBPVOCs). Through comprehensive characterization and performance evaluation, we found that CAC effectively adsorbs Butyl Cellosolve (BCS), a common industrial solvent, with adsorption capacity increasing with pressure. The adsorption process follows pseudo-first-order kinetics, indicating single-layer physical adsorption. Additionally, the study highlights the recyclability of CAC, as desorption and subsequent analysis revealed minimal changes in pore structure, maintaining a significant portion of its original BET value. These findings suggest that CAC is not only effective for BCS adsorption but also sustainable for repeated use, offering an efficient and eco-friendly solution for managing industrial HBPVOCs.

CO2 capture enhancement by metal oxides impregnated coal fly ash: a breakthrough adsorption study.

Coal fired power plants are significant contributors to CO2 emissions and produce solid waste in the form of coal fly ash, posing severe environmental challenges. This study explores the application of dry-impregnated coal fly ash for CO2 capture from gas stream. The modification of coal fly ash was achieved using alkaline earth metal oxides, specifically CaO and MgO, to alter its physical and chemical properties. Characterization techniques like X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and BET (Brunauer-Emmett-Teller) analysis were employed for physio-chemical changes in the adsorbent. Breakthrough experiments were conducted using a laboratory-scale fixed packed-bed reactor to assess the influence of temperature and gas flow rate on CO2 adsorption. Among the synthesized sorbents, calcium oxide-impregnated ash showed the highest CO2 uptake capacity, achieving 9.41mg/g at 30°C and a flow rate of 20 L/hr under atmospheric pressure. Isotherm modeling indicated a heterogeneous adsorbent surface, with the data best fitting the Sips isotherm model. Furthermore, the adsorption data conformed well to the Yoon-Nelson and Thomas kinetic models, affirming their relevance in characterizing the adsorption process under varying conditions. This research emphasizes the potential of coal fly ash-an abundant, cost-free material-as an effective CO2 adsorbent, contributing to both CO2 mitigation and landfill waste reduction.

Fixed-bed natural gas CO2 adsorption performance of ZSM-5 zeolites impregnated with amines

This research studies the fixed-bed natural gas carbon dioxide (CO2) adsorption performance of ZSM-5 zeolites impregnation with different amines: monoethanolamine (MEA), ethylenediamine (ED), ethylenediaminetetraacetic acid (EDTA), and 4-aminophenol. The structural, morphological, and performance characteristics of the modified zeolites were examined through the use of several analytical techniques. These techniques featured Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The thermogravimetric analysis revealed weight losses in two stages linked to the removal of bound water molecules and the breakdown of the hydroxyl structure. Through fixed bed adsorption experiments, it was discovered that ZSM-5 zeolites functionalized with MEA/ED showed the CO2 adsorption capacity. This study investigated how well four different mathematical models—Clark, Yoon-Nelson, Thomas, and Adams-Bohart—could predict CO2 adsorption breakthrough curves from natural gas using non-linear regression methods. The results showed that all models had very high adjusted determination coefficients (Adj. R²) of over 0.99, indicating they matched the experimental data really well for various adsorbents. The analysis highlighted the models' effectiveness in reflecting adsorption kinetics and capacities, particularly noting the superior performance of the Thomas, Adams-Bohart, and Yoon-Nelson models in capturing uniform breakthrough behaviors. These findings underscore the models' utility in enhancing CO2 removal processes in natural gas purification, which is pivotal for optimizing industrial gas processing systems. These results highlight the efficiency of amine-functionalized ZSM 5 zeolites in capturing CO2 from natural gas streams.

Fabrication of core-shell structural Y@VTMS-DVB composites with enhanced hydrophobicity for toluene capture under humid environment

Zeolite Y serves as an effective adsorbent for VOCs capture due to its ordered porous structure, exceptional thermal stability, chemical resistance and fine-tune key properties. However, the hydrophilicity caused by the low SiO2/Al2O3 ratio seriously limits its industrial application, especially in humid environments. In this work, a series of core-shell composites Y@VTMS-DVBn were prepared through surface grafting and copolymerization. A variety of characterizations were utilized to study the structural and morphological changes of the prepared samples. The dynamic breakthrough adsorption experiment showed that the toluene uptake was significantly improved from 1.77 mg/g to 53.09 mg/g under 30 % relative humidity. Moreover, the core-shell composite exhibited excellent regeneration properties, the adsorption capacity remained 90 % under wet conditions after 6 cycles of regeneration. Adsorption kinetic analysis revealed that the adsorption behavior of toluene on the prepared adsorbents was primarily physical adsorption. These results show that the core-shell composite is a promising candidate for VOCs removal in industrial application.

Enhanced cadmium (Cd2+) removal from wastewater using integrated inclined plate settler and composite adsorbent coating

Bottlenecks inherent in batch and column adsorption configurations have impeded the implementation of the adsorption technique in large-scale wastewater treatment systems. This study mainly aimed to develop an innovative wastewater treatment prototype that integrates inclined plate settlers (IPS) and composite adsorbent coating (CAC). The objective is to enable the removal of Cd2+ from aqueous solutions in a continuous setup, thereby enhancing its practicality for large-scale applications. The combined IPS-CAC system was optimized at various angle of inclination (θ), influent flow rate (Q) and adsorbate initial concentration (Co) using the Box–Behnken Design (BBD) of the Response Surface Methodology (RSM). At optimized operating parameters (θ = 45°, Q = 5 ml/min and Ci = 1.87 mg/L) the IPS-CAC Cd2+ predicted (R2 = 0.9926) and experimental removal efficiencies were 75.8% and 69.7 ± 4.67%, respectively. The IPS-CAC breakthrough adsorption capacity was 9.6 mg/g. Comparing IPS-CAC performance with a tank without plates and IPS with plain plates, the Cd2+ removal efficiencies were 2.4 ± 0.1% and 4.6 ± 1.1%, respectively, confirming the synergistic effect of IPS and CAC. Additionally, breakthrough curves were acquired for various flow rates, cadmium influent concentrations, and plate inclination angles. Only a 10% decline in the removal effectiveness (from 69.7 to 59.7%) of the CAC after three adsorption–regeneration cycles was observed, indicating its stability for heavy metal removal. The results underpin the potential of using IPS-CAC for industrial wastewater treatment and enhancing the use of adsorption on a larger scale.

Hierarchically N-doped porous carbon synthesized from 3D cellulose alcogel decorated by in-situ growth of ZIF-8 for high performance CO2 capture

The physical properties and chemical compositions of porous carbons are crucial factors in determining their effectiveness in adsorbing CO2. Cellulose-based porous carbon has emerged as an outstanding candidate adsorbent for CO2 capture. The research involved the creation of hierarchically nitrogen-doped porous carbon (HNC) using a 3D cellulose alcogel (CA) as substrate, which was prepared through a thermal introduced phase separation (TIPS) method combined with hydrolysis treatment. The plentiful functional groups of CA offered abundant growth sites for the introduction of ZIF-8 crystals. CA/ZIF-8 composite alcogel (CZA) with greater surface area and superior thermal stability compared to CA was successfully fabricated and used as precursor for the production of HNC. The important effects of microporosity and surface chemistry of HNC samples on CO2 capture were discussed in-depth. HNC-350–850 displayed a hierarchically porous structure with a large number of micropores and abundant N/O/Zn-doped functional groups, exhibiting high CO2 uptakes at 1 bar (3.56 mmol/g at 25 °C), good IAST CO2/N2 (15/85, V/V) selectivity of 16.31 at 25 °C, and outstanding regenerability with ∼100 % CO2 adsorption capacity retained after ten cycles. In the two-component CO2/N2 (15/85, V/V) competitive adsorption process, the maximum breakthrough periods for CO2 (433.1 s) is significantly longer than that of N2 (3.8 s). The CO2 breakthrough adsorption capacity reached 1.79 mmol/g at 25 °C and 1 bar with the separation coefficient of 45.8 for CO2 over N2. These results confirmed that HNC, in addition to having excellent CO2/N2 selectivity, demonstrated good feasibility for practical use. The green and practicable synthetic route described in this study is not only expected to offer novel adsorbents for high performance CO2 capture, but also provide a new theoretical foundation for the development of cellulose-based porous materials.

Monometallic/Bimetallic Co‐ZIFs Synthesis, Characterization, and Application for Adsorption of SO2 and CO2 in Continuous Flow System

ABSTRACTSulfur dioxide is serious ultimatum to human health as well as environment, while carbon dioxide is viewed as one of the primary drivers of the worldwide temperature alteration. Therefore, capturing of these gases is a dynamic research subject attracting much consideration from scientists. Herein, we report synthesis of a series of Co‐ZIF and bimetallic M‐Co‐ZIF adsorbents and application for room temperature adsorption of SO2 and CO2. In this work, the breakthrough curves for the adsorption of sulfur dioxide and carbon dioxide on Co‐ZIF and M‐Co‐ZIF were obtained experimentally and theoretically using a laboratory‐scale fixed bed column at room temperature. In this work, the adsorption capacities and breakthrough points for modified bimetallic M‐Co‐ZIF were found to be relatively higher than parent Co‐ZIF. Notably, a high SO2 uptake capacity of 7.1 mmol/g for Zr‐Co‐ZIF and high CO2 uptake capacity of 69.9 mmol/g for Ni‐Co‐ZIF were achieved. The parent cobalt and bimetallic ZIF materials were characterized by XRD, FTIR, SEM, and nitrogen physisorption. The XRD results confirm the formation of pure phase highly crystalline ZIF materials while BET analysis suggests high surface area of prepared adsorbents. Finally, the results of dynamic adsorption combined with characterization show great potential for preparation of bimetallic ZIF adsorbents for effective SO2 and CO2 adsorption.

SO2 removal performance and breakthrough prediction of activated carbon-based chemical filters for electronics cleanroom air purification

Electronic cleanrooms have strict control requirements for SO2 concentration due its significant influence on product yield, and application of chemical filters is the main measure of SO2 control. In this study, 8 activated carbon (AC)-based chemical filters were collected and tested for their SO2 purification performance and resistance. These filters had very similar initial efficiencies (all >95 %) but large differences in 20 % breakthrough adsorption capacity (49–294 g at 9 ppm and 0.35 m/s). The adsorption capacity is found to be positively correlated with pleat density, which is a main structural parameter of pleated chemical filter. Meanwhile, the filter resistance (9.3–34 Pa at 0.35 m/s) demonstrates a decreasing and then increasing trend with increasing pleat density. This indicated the existence of an optimal range of pleat numbers that can be used to achieve a balance between resistance and adsorption capacity. A comprehensive performance evaluation index (Z′-index) is proposed for assessing the integrated resistant and adsorption capacity performance of chemical filters (19–210 g/W for 8 samples). A lumped parameter model was proposed for predicting the breakthrough curves at low concentration based on the traditional semi-empirical breakthrough models. The prediction deviation of the breakthrough curve at real cleanroom scenario (2 ppb) is less than 15 %. In addition, a rapid filter life prediction method based on filter design parameters is developed from the lumped parameter model. This work helps the understanding of the impact of filter structure parameters on performance and facilitate the development of high-performance chemical filters for SO2 contaminant control in electronic cleanrooms.

Exploration of the adsorption and desorption performance of volatile organic compounds by activated carbon with different shapes based on fixed-bed experiments

Activated carbon (AC) has been widely used in volatile organic compounds (VOCs) treatment of industrial exhaust gases. Rather than modifying specific pore size distributions and surface properties, altering the shape of AC offers a more feasible approach to enhance its adsorption performance. This study investigates the adsorption-desorption performance of two different shaped ACs with highly similar properties for the removal of VOCs. The clover-shaped AC (CSAC) has a 27.46% lower internal void fraction and a 39.10% higher external void fraction compared to cylindrical AC (CAC), resulting in denser packing and longer contact time with VOCs. Adsorption experiments showed the CSAC has 40% longer adsorption breakthrough (BT) times for ethanol, ethyl acetate, and n-hexane on average, and 20% higher saturation adsorption capacity per unit volume. CSAC also has higher partition coefficients, with the highest values for ethanol, ethyl acetate, and n-hexane being 0.0187, 0.0382, and 0.0527 mol kg−1·Pa−1, respectively. The desorption process for selected VOCs is non-spontaneous and endothermic. Optimal desorption conditions were identified as an inlet space velocity of 3535 h−1, a desorption temperature of 150 °C, and a pulsed inlet method. To investigate the possibility of the application of CSAC in real-world scenarios, xylene was chosen as a representative industrial VOC. Results showed CSAC has 20% higher BT time and saturation adsorption capacity for xylene compared to CAC under different bed heights. The desorption efficiency for xylene on both ACs is below 40%. With increasing xylene inlet concentration, the mass transfer zone (MTZ) height initially increases but stabilizes beyond 1704 mg m−3. At identical bed heights, the MTZ height of CSAC is 29% shorter than CAC, indicating a higher bed utilization efficiency.

Preparation of porous imidazole-based poly(ionic liquid) adsorbents and their toluene adsorption performance.

Efficient, economical, and durable adsorbents are required to remove volatile organic compounds (VOCs) from air. Cross-linked polyvinylic ionic liquids (PVIC) with porous structures were synthesized by quaternizing 1-vinylimidazole (1VI) with 1-bromobutane to obtain 3-butyl-1-vinylimidazolium bromide (VIC), which was then co-polymerized with divinylbenzene (DVB) radicals. 1H NMR, 13C NMR, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and N2 adsorption-desorption isotherms were applied in characterizing the composites. Through modification of the polymer structure by adjustment of DVB concentration（the ratio of DVB concentration to VIC concentration was x: 1 (x=0.4, 0.6, 0.8, 1.0) and the product was named PVIC-s (s=2, 3, 4, 5)）, the optimal PVIC-4 pore structure was obtained, with a specific surface area and total pore volume of 192.5 m2 g-1 and 0.192 cm3 g-1, respectively. A toluene adsorption test verified the adsorption capacity. The adsorption behavior for VOCs, based on toluene, was investigated using adsorption breakthrough curves, adsorption kinetics, and isotherms. The adsorption process is well describing by the Bangham kinetic and Langmuir isotherm models. The dynamic adsorption of toluene followed the order PVIC-4 > PVIC-5 > PVIC-3 > PVIC-2. The optimum toluene adsorption by PVIC-4 was 264.4 mg g-1 as a result of its excellent pore structure. PVIC-4 also performed well in terms of recovery and has potential for the removal of VOCs from air.

Cu-based metal-organic framework with dual open metal sites for efficient separation of CO2 from flue gas

Excessive carbon dioxide (CO2) emissions from flue gases intensify the greenhouse effect. Exploring porous adsorbents with high CO2/N2 selectivity is of great significance to reducing the CO2 content in flue gases. Herein, we report a novel PtS-type metal-organic framework (MOFs), termed ZSTU-21, with narrow pore size and excellent CO2/N2 separation performance with dual open copper sites. At 298 K, ZSTU-21 exhibits a CO2 uptake capacity of 62 cm3 g−1 and a high selectivity of 105 for CO2/N2 (CO2/N2 = 15/85, v/v). Multicomponent adsorption breakthrough experiments further verified the superior performance of ZSTU-21 MOF in CO2/N2 separation. Moreover, the synthesis of ZSTU-21 MOF can be carried out under mild experimental conditions at room temperature, making the process simple and cost-effective, thus laying a solid foundation for its widespread application in CO2/N2 separation.

Study on the adsorption performance and regeneration of lignin-derived graphitic carbon for H2S

In pursuit of effective adsorption materials for malodorous gases such as H2S and to broaden the utilization avenues of lignin waste, this study employed the direct pyrolysis method to synthesize three types of alkali lignin graphitized carbons, namely C-800, KC-700, and KEC-700. Among them, KEC-700 exhibits a high specific surface area of 1672.9 m2/g, significantly superior H2S adsorption performance compared to other materials, an adsorption breakthrough time of up to 220 min, and a sulfur capacity of 67.1 mg/g. Structural analysis showed that the more oxygen-containing functional groups of lignin charcoal and the larger specific surface area facilitated the adsorption of H2S. After reaching adsorption saturation, the degree of graphitization of lignin carbon diminishes. The H2S adsorption products primarily manifest as elemental sulfur and sulfate within the pores of lignin carbon measuring less than 2 nm. Through thermal regeneration, the charcoal effectively eliminates the elemental sulfur adsorption product. Nevertheless, sulfate removal proved unsatisfactory, as the adsorption efficiency of KEC-700 following two thermal regenerations was approximately 41% of that observed for fresh samples.

Enhancement of Gaseous o-Xylene Elimination by Chlorosulfonic Acid-Modified H-Zeolite Socony Mobil-5.

It is important to develop effective strategies for enhancing the removal capacity of aromatic volatile organic compounds (VOCs) by modifying conventional porous adsorbents. In this study, a novel HZSM-5 zeolite-supported sulfonic acid (ZSM-OSO3H) was prepared through ClSO3H modification in dichloromethane and employed for the elimination of gaseous o-xylene. The ClSO3H modification enables the bonding of -OSO3H groups onto the HZSM-5 support, achieving a loading of 8.25 mmol·g-1 and leading to a degradation in both crystallinity and textural structure. Within an active temperature range of 110-145 °C, ZSM-OSO3H can efficiently remove o-xylene through a novel reactive adsorption mechanism, exhibiting a removal rate exceeding 98% and reaching a maximum breakthrough adsorption capacity of 264.7 mg. The adsorbed o-xylene derivative is identified as 3,4-dimethylbenzenesulfonic acid. ZSM-OSO3H demonstrates superior adsorption performance for o-xylene along with excellent recyclability. These findings suggest that ClSO3H sulfonation offers a promising approach for modifying various types of zeolites to enhance both the elimination and resource conversion of aromatic VOCs.

Precise Pore Engineering of Zirconium Metal‐Organic Cages for One‐Step Ethylene Purification from Ternary Mixtures

AbstractOne‐step purification of ethylene from ternary mixtures (C2H2, C2H4, and C2H6) can greatly reduce the energy consumption of the separation process, but it is extremely challenging. Herein, we use crystal engineering and reticular chemistry to introduce unsaturated bonds (ethynyl and alkyne) into ligands, and successfully design and synthesized two novel Zr‐MOCs (ZrT‐1‐ethenyl and ZrT‐1‐alkyne). The introduction of carbon‐carbon unsaturated bonds provides abundant adsorption sites within the framework while modulating the pore window size. Comprehensive characterization techniques including single crystal and powder X‐ray diffraction, as well as electrospray ionization time‐of‐flight mass spectrometry (ESI‐TOF‐MS) confirm that ZrT‐1‐ethenyl and ZrT‐1‐alkyne possess an isostructural framework with ZrT‐1 and ZrT‐1‐Me, respectively. Adsorption isotherms and breakthrough experiments combined with theoretical calculations demonstrate that ZrT‐1‐ethenyl can effectively remove trace C2H2 and C2H6 in C2H4 and achieve separation of C2H2 from C2H4 and CO2. ZrT‐1‐ethenyl can also directly purify C2H4 in liquid solutions. This work provides a benchmark for MOCs that one‐step purification of ethylene from ternary mixtures.

Precise Pore Engineering of Zirconium Metal-Organic Cages for One-Step Ethylene Purification from Ternary Mixtures.

One-step purification of ethylene from ternary mixtures (C2H2, C2H4, and C2H6) can greatly reduce the energy consumption of the separation process, but it is extremely challenging. Herein, we use crystal engineering and reticular chemistry to introduce unsaturated bonds (ethynyl and alkyne) into ligands, and successfully design and synthesized two novel Zr-MOCs (ZrT-1-ethenyl and ZrT-1-alkyne). The introduction of carbon-carbon unsaturated bonds provides abundant adsorption sites within the framework while modulating the pore window size. Comprehensive characterization techniques including single crystal and powder X-ray diffraction, as well as electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) confirm that ZrT-1-ethenyl and ZrT-1-alkyne possess an isostructural framework with ZrT-1 and ZrT-1-Me, respectively. Adsorption isotherms and breakthrough experiments combined with theoretical calculations demonstrate that ZrT-1-ethenyl can effectively remove trace C2H2 and C2H6 in C2H4 and achieve separation of C2H2 from C2H4 and CO2. ZrT-1-ethenyl can also directly purify C2H4 in liquid solutions. This work provides a benchmark for MOCs that one-step purification of ethylene from ternary mixtures.

Fixed-bed adsorption of methylene blue using granular NaX zeolite/attapulgite composite: efficiency, mechanism and reusability of saturated G-NaX/A

A novel granular NaX zeolite/attapulgite (G-NaX/A) composite was developed to address the challenges of high pressure drop in fixed beds with powder synthetic zeolite and low adsorption capacity of natural zeolite. The synthesized G-NaX/A retains the micropores of NaX and the mesoporous of attapulgite. The BET specific surface area reached 481.17 m2/g, and the total pore volume was 0.3549 cm3/g. The G-NaX/A maximum methylene blue (MB) adsorption capacity was 1.56 times that of commercial granular activated carbon (7.41 mg/g). The breakthrough time and adsorption capacity improved with lower influent flow rate and MB concentration and higher pH. Under optimal conditions (flow rate: 150 mL/min, MB concentration: 25 mg/L, pH = 8), it achieved a maximum adsorption capacity of 11.51 mg/g and a breakthrough time of 2.54 h. The adsorption behavior of G-NaX/A was well-fitted by the Yoon–Nelson and Thomas models at different operating conditions. The mechanism studies revealed that MB (cation: C16H18SN3+) removal by G-NaX/A occurred through electrostatic attraction, ion exchange with Na+/Mg2+, surface coordination with ≡Al/SiOH, and surface physical adsorption. The regeneration studies confirmed the reusability potential of G-NaX/A by calcining at 500 °C for 2 h, and significantly improved adsorption capacity reaching about 14.39 mg/g, 16.31 mg/g and 14.07 mg/g across the three adsorption-regeneration cycles respectively. The findings support G-NaX/A technical feasibility, high adsorption capacity and potential for further scaling in fixed bed adsorption studies.

Preparation and characterization of UiO-66-(OH)2/MWCNTs composites for CO2/N2 adsorption separation

The increasing CO2 concentration in the atmosphere can lead to climate change, and CO2 capture technology is one of the most direct and effective means of reducing carbon emissions. In this study, a new composite was prepared in situ by loading multi-walled carbon nanotubes (MWCNTs) onto metal–organic frameworks (MOFs) to efficiently capture CO2 in flue gas. The morphological states and pore structures of the composites were analyzed using characterization methods. The CO2 adsorption properties of the composites were tested at 273 K and 298 K with different MWCNTs loadings. The optimal CO2 adsorption quantities of the composite material were measured to be 4.4 and 5.75 mmol/g, respectively, which increased the adsorption capacity by 66.7 % and 55 %, respectively, compared with the parent material at a pressure of 1 bar. The CO2/N2 separation performance of the composites was examined using ideal adsorption solution theory calculations and dynamic adsorption breakthrough experiments. The stability of the composites was investigated by thermogravimetric analysis, acidification experiments, and cyclical adsorption–desorption experimentation. The UiO-66-(OH)2/MWCNTs composites exhibited superior CO2 adsorption–separation performance, thermal stability, acid resistance, and cycling stability. Therefore, the composite has potential applications in CO2 capture separation technology.

Enhanced ammonia adsorption-desorption properties of synthesized zeolite-carbon composite with the effect of Si/Al ratio

Effective ammonia (NH3) adsorbent is crucial for removing undecomposed NH3 residue after splitting into N2 and H2 fuel. In this study, a zeolite-activated carbon (AC) hybrid was successfully synthesized with a trace AC amount and different Si/Al ratios via hydrothermal method. The NH3 adsorption–desorption properties and mechanisms were investigated through two major activity tests, employing high pressure adsorption isotherm analyzer and breakthrough set up. Incorporating AC at 1 wt%, effectively shortened the regeneration period of the pure zeolite by ∼50 % due to the AC’s pore-widening effect on zeolite network, reducing the trapping of adsorbed NH3 in the zeolite pores. Interestingly, an optimum Si/Al ratio of 1.6 led to the highest specific surface area of 977.57 m2/g by the formation of zeolite mixture with coexisting NaX (faujasite zeolite with high Al atoms per cell) and NaY (higher crystalline faujasite zeolite with low Al atoms per cell). These improved structural characteristics consequently exhibited the highest NH3 (99.9995 %) storage capacity of 15.6 mmol/g at a partial pressure of 300 kPa in isotherm analysis at 25 °C. Besides, the initial breakthrough adsorption capacity for dilute NH3 (5%/N2 balance) under atmospheric conditions reached 8.9 mmol/g, accurately equivalent to isotherm analysis result at 5 kPa. This reproducibility of consistent adsorption uptake within low pressure region in both tests was credited to the compositional presence of both acidic and alkaline surface functionalities in the optimum zeolite-AC hybrid as stable NH3 adsorption sites. These active sites also provided a uniform dynamic adsorption capacity of ∼4 mmol/g throughout 15 cycles. Conclusively, this work highlighted the importance of zeolite composition and AC-incorporated proportion for the H2 purification aspect.

Thiol-Functionalized Adsorbents through Atomic Layer Deposition and Vapor-Phase Silanization for Heavy Metal Ion Removal.

The removal of toxic heavy metal ions from water resources is crucial for environmental protection and public health. In this study, we address this challenge by developing a surface functionalization technique for the selective adsorption of these contaminants. Our approach involves atomic layer deposition (ALD) followed by vapor-phase silanization of porous substrates. We utilized porous silica gel powder (∼100 μm particles, 89 m2/g surface area, ∼30 nm pores) as an initial substrate. This powder was first coated with ∼0.5 nm ALD Al2O3, followed by vapor-phase grafting of a thiol-functional silane. The modified powder, particularly in acidic conditions (pH = 4), showed high selectivity in adsorbing Cd(II), As(V), Pb(II), Hg(II), and Cu(II) heavy metal ions in mixed ion solutions over common benign ions (e.g., Na, K, Ca, and Mg). Langmuir adsorption isotherms and breakthrough adsorption studies were conducted to assess heavy metal binding affinity and revealed the order of Cd(II) < Pb(II) < Cu(II) < As(V) < Hg(II), with a significantly higher affinity for As(V) and Hg(II) ions. Time-dependent uptake studies demonstrated rapid removal of heavy metal ions from aqueous environments, with Hg(II) exhibiting the fastest adsorption kinetics on thiol-modified surfaces. These findings highlight the potential of ALD and vapor-phase silanization to create effective adsorbents for the targeted removal of hazardous contaminants from water.

Regulating cerium location in Y zeolite and its influence on adsorptive desulfurization for thiophene in benzene

CeY zeolite sorbent was reported to have a high adsorptive desulfurization selectivity for thiophene. However, only the cerium in the supercage, which is larger than the thiophene molecule, is effective for thiophene adsorption. In this case, regulating the cerium location to anchor it more in the surpercage of Y zeolite is an important issue. Herein, the glycine was used as a complexing agent with cerium to control its size, ensuring that the cerium precursor is in the supercage. G0.1CeY were prepared by ion exchange technique with glycine and cerium coordination from NaY. The adsorption capacity of sorbents was measured, and their physical and chemical properties were characterized by XRD, SEM, N2 adsorption/desorption, NH3-TPD, and in situ FT − IR. The glycine complexation could effectively control the location of Ce, so that the G0.1CeY has the highest content of Ce located in the supercage. Moreover, in order to further explore the influence of zeolite type, HY was used as the raw material to prepared G0.1CeHY in the same way. G0.1CeHY has a higher desulfurization performance than that of G0.1CeY, whereas the Ce content in its supercage is lower. The NH3-TPD and Py-FT − IR results that the medium-strong Brønsted acid of the G0.1CeHY sorbent is also effectively for the improvement of desulfurization efficiency. The G0.1CeHY exhibits the hightest desulfurization effectiveness (51 %) and the highest breakthrough adsorption capacity of 5.42 mg/g.