Solid Adsorbent Research Articles

Two-dimensional interfacial enhanced CO2 adsorption performance of porous organic amine solids: Structure-activity relationships and DFT calculations

The utilization of inexpensive and efficient amine-functionalized adsorbents has become a research hotspot in post-combustion capture technology. Meanwhile, the structure of the support and the selection of organic amines are the primary considerations affecting the CO2 adsorption performance. Herein, the novel solid amine adsorbent materials with amine-support interfacial effect were successfully synthesized in this study by loading four organic amines (TETA, TEPA, PEHA, and PEI) onto expanded vermiculite (EVMT) support with the layered structure. The results indicated that EVMT-50TETA exhibited superior CO2 adsorption capacity (132.5 mg/g) along with effective regeneration capability. This was attributed to the unique layered structure of EVMT that facilitates the dispersion of TETA on its surface or between layers as well as the formation of hydrogen bonds between surface functional groups (–OH) and amines to enhance the amine-support interfacial interaction. Furthermore, the minimal volume expansion of TETA during CO2 adsorption enables improved diffusion of CO2 in channels and enhanced accessibility to active sites. DFT calculations show higher binding energies and faster CO2 adsorption-diffusion rates between TETA and EVMT support. In situ DRIFTS experiments revealed that the process of CO2 adsorption followed the zwitterion mechanism, in which the zwitterion can be reversibly deprotonated to form ammonium carbamate and carbamic acid. This study provides comprehensive insights into the supports and amines interfacial effects through systematic investigation, offering both simplified synthesis strategies and profound theoretical support for studying solid amine adsorbents.

Adsorption of high-temperature CO2 by Ca2+/Na+-doped lithium orthosilicate: characterization, kinetics, and recycle.

High-temperature solid adsorbent Li4SiO4 has received broad attention due to its high theoretical adsorption capacity, high regeneration capacity, and wide range of raw materials for preparation. In this paper, a Li4SiO4 adsorbent was prepared by MCM-48 as the silica precursor and modified by doping with metal ions (Ca2+ and Na+) for high-temperature capture of low-concentration CO2. The results showed that the surface of the Ca-doped (or Na-doped) Li4SiO4 adsorbent developed some particles that are primarily composed by Li2CaSiO4 (or Li3NaSiO4). Furthermore, the grains of the adsorbents became finer, effectively increasing the specific surface area and enhancing adsorption performance. Under 15 vol% CO2, the maximum CO2 adsorption was 25.63 wt% and 32.86 wt% when the Ca2+ doping amount was 0.06 and the Na+ doping amount was 0.12, respectively. These values were both higher than the adsorption capacity before the metal ion doping. After 10 adsorption/desorption cycles, the adsorption capacity of Na-doped Li4SiO4 increased by 9.68 wt%, while that of Ca-doped Li4SiO4 decreased by 7.98 wt%. This difference could be attributed to the easy sintering of the Ca-containing adsorbent. Furthermore, a biexponential model was used to fit the CO2 adsorption curve of the adsorbent in order to study the adsorption kinetics. Compared to the conventional Li4SiO4, the Ca/Na-doped adsorbent offers several advantages, such as a high CO2 adsorption capacity and stable cycling ability.

Sustainable bio-based solid phase extraction adsorbent for the determination of various types of organic compounds.

A sustainable, bio-based, mesoporous material, Starbon A800, was explored for use as an adsorbent in solid phase extraction (SPE). A solution containing seven nitrosamines was first used as a standard to optimise conditions for extraction efficiency with Starbon A800. After optimising conditions, 25 compounds of varying polarity (terpenes, phenolics, pesticides, PAHs, amines, and nitrosamines) were extracted with SPE using either Starbon® A800, C18 or Porous Graphitic Carbon (PGC) as the adsorbent, for comparison purposes. At the same time, 3 different elution solvents (heptane, dichloromethane, and ethanol) were used for each type of adsorbent. Hansen solubility parameters can be used to choose an appropriate elution solvent for the selected SPE adsorbent. The best average SPE recoveries found for the 25 various compounds were 83%, 79%, and 65% using Starbon A800, PGC, and C18 adsorbents respectively and these had dichloromethane as the elution solvent. The identification and quantification of components was carried out using UV-visible spectroscopy, two-dimensional gas chromatography (GCxGC) with time of flight/mass spectrometry (TOF/MS) or a nitrogen chemiluminescence detector (NCD). The optimized method was successfully applied to extract volatile organic compounds from red wine and tap water using Starbon A800. Starbon A800 was shown to be a promising, low-cost, green, scalable, alternative adsorbent for the extraction of various types of organic compounds of a wide range of polarities using SPE.

Adsorption Investigations on the Removal of Azoic Dye by Untreated Wood Sawdust

Batch adsorption of the azoic dye Congo red (CR) was carried out successfully on untreated low-cost wood sawdust. The impact of several variables (contact time, amount of solid adsorbent, initial adsorbate concentration, temperature, and pH) on the sorption process was studied. A maximum removal efficiency was achieved after 50 minutes at pH = 5 and 25 °C. To characterize the adsorbent, FTIR, SEM, EDX, and BET analyses were performed. The equilibrium isotherms were described using four alternative models. The data were found to fit the Freundlich model the best. The kinetic analysis demonstrates that the process is best represented by a pseudo-second-order model. The thermodynamic studies revealed the spontaneity and the exothermic nature of the sorption process. The optimal isotherm model served as the foundation for the design of a one-stage batch adsorber for the sorption of CR onto wood sawdust.

Interior and Exterior Surface Modification of Zr-Based Metal-Organic Frameworks for Trace Benzene Removal.

The emission of volatile organic compounds (VOCs) significantly contributes to air pollution and poses a serious threat to human health. Benzene, one of the most toxic VOCs, is difficult for the human body to metabolize and is classified as a Group 1 carcinogen. The development of efficient adsorbents for removing trace amounts of benzene from ambient air is thus of great importance. In this work, we studied the benzene adsorption properties of four Zr-based metal-organic frameworks (Zr-MOFs) through static volumetric and dynamic breakthrough experiments. Two previously reported Zr-MOFs, BUT-12 and STA-26, were prepared with a tritopic carboxylic acid ligand (H3L1) functionalized with three methyl groups, and STA-26 is a 2-fold interpenetrated network of BUT-12. Two new isoreticular Zr-MOFs, BUT-12-Et and STA-26-Et, were synthesized using a similar ligand, H3L2, where the methyl groups are replaced with ethyl groups. There are mesopores in BUT-12 and BUT-12-Et and micropores in STA-26 and STA-26-Et. The four Zr-MOFs all showed high stability in liquid water and acidic aqueous solutions. The microporous STA-26 and STA-26-Et showed much higher benzene uptakes than mesoporous BUT-12 and BUT-12-Et at room temperature under low pressures. Particularly, the benzene adsorption capacity of STA-26-Et was high up to 2.21 mmol/g at P/P0 = 0.001 (P0 = 12.78 kPa), higher than those of the other three Zr-MOFs and most reported solid adsorbents. Breakthrough experiments confirmed that STA-26-Et could effectively capture trace benzene (10 ppm) from dry air; however, its benzene capture capacity was reduced by 90% under humid conditions (RH = 50%). Coating of the crystals of STA-26-Et with polydimethylsiloxane (PDMS) increased the hydrophobicity of the exterior MOF surfaces, leading to a more than 2-fold improvement in its benzene capture capacity in the breakthrough experiment under humid condition. PDMS coating of STA-26-Et likely slowed down the water adsorption process, and thus, the adsorbent afforded more efficient capture of benzene. This work demonstrates that modifying both the interior and exterior surfaces of MOFs can effectively enhance their performance in capturing trace benzene from ambient air, even under humid conditions. This finding is meaningful for the development of new adsorbents for effective air purification applications.

Modeling of moving bed CO2 capture process using amine solid adsorbent and its validation using pilot plant test data

A modeling study is presented for a pilot plant of a moving bed adsorption process for carbon dioxide (CO2) capture using an amine solid sorbent. The pilot plant consists of four towers—adsorption, desorption, and two drying towers. The plant has a capacity of approximately 5 ton-CO2/day, which is the largest scale in the world as a moving bed for CO2 capture using an amine-loaded solid sorbent. Using this plant, 11 operating conditions were implemented and tested. The isotherm in the model were established from lab-scale measurements. For the 11 conditions, the model successfully captured the influences of operating conditions, such as the circulation flow rate of solid sorbent, amount of solid sorbent, temperature and humidity of the feed gas, and amount of steam introduced in the desorption step. Furthermore, the temperature of the solid sorbent and composition of the outlet gases was found to be in agreement with the model.

Highly selective extraction of Pd from nuclear glass waste through the combination of ultrasound-assisted acid leaching and solid phase adsorption

The extraction of long-lived radionuclides from nuclear glass waste (NGW) is a prerequisite for nuclear transmutation and resource recovery. However, this remains a great challenge due to the recognized extreme chemical stability of NGW. Here, we demonstrate an ultrasound-assisted wet chemical dissolution method for the efficient elution of radionuclides from NGW. Most elements, including glass major constituents and radionuclides, were significantly leached out from NGW in 1 mL H2O2/2 M HCl solution within 1 h at 35 °C and 270 W ultrasound, which is much milder than conventional glass dissolution methods such as corrosive HF digestion and molten alkali fusion. In particular, the leaching of insoluble palladium is controlled by its redox reactions and coordinating chemistry, where Pd0 in the NGW is oxidized to Pd2+ by H2O2, which in turn coordinates with Cl- to form soluble PdCl42-. Moreover, insoluble Zr species can be efficiently eluted in ultrasound-assisted low concentration H2SO4 solution by strong coordination with SO42-. As a bonus, the NGW is converted into high-value-added microporous silica after elution, and PdCl42- can be selectively extracted from the complex eluent by an imidazole-modified mesoporous silica, which was further calcined to obtain the PdO-loaded silica nanomaterials for the efficient catalysts of the reductive conversion of 4-nitrophenol to 4-aminophenol. Therefore, our results provide new avenues for the highly selective extraction of key radionuclides from NGW and offer the possibility of their nuclear transmutation and reuse in the future.

Substitution and Orientation Effects on the Crystallinity and PFAS Adsorption of Olefin-Linked 2D COFs.

Solid phase adsorbents with high removal affinity for per- and polyfluoroalkyl substances (PFAS) in aqueous environments are sought. We report the synthesis and investigation of COF-I, a new covalent organic framework (COF) with a good affinity for PFAS adsorption. COF-I was synthesized by the condensation reaction between 2,4,6-trimethyl-1,3,5-triazine and 2,3-dimethoxyterephthaldehyde and fully characterized. In addition to the high crystallinity and surface area, COF-I showed high hydrolytic and thermal stability. Further, we converted its hydrophobic surface to a hydrophilic surface by converting the ortho-methoxy groups to hydroxyl derivatives and produced a new hydrophilic olefin-linked two-dimensional (2D) COF. We experimentally measured the crystallinity of both COFs by X-ray diffraction and used atomistic simulations coupled with cross-polarization/magic angle spinning solid-state nuclear magnetic resonance (CP/MAS ssNMR) to determine the relative amounts of AA-stacking and AB-stacking present. COF-I, with its hydrophobic surface and methoxy groups in the ortho positions, showed the best PFAS adsorption. COF-I reduced the concentration of perfluorooctanoic acid from 20 to 0.069 μg L-1 and to 0.052 μg L-1 for perfluorooctanesulfonic acid. These amounts are lower than the U.S. Environmental Protection Agency advisory level (0.070 μg L-1). High efficiency, fast kinetic adsorption, and reusability of COF-I are advantages of COF-I for PFAS removal from water.

Numerical simulation on adsorption of CO2 using K2CO3 particles in the bubbling fluidized bed

AbstractWith the increase of greenhouse gas emissions, global warming has become an urgent problem, and the use of solid adsorbents to capture CO2 gas in flue gas has attracted more and more attention. In this study, the process of CO2 capture by K2CO3 particles in the bubbling fluidized bed (BFB) is numerically simulated with Eulerian–Eulerian(E–E) two fluid model incorporating with the kinetic theory of granular flows (KTGF). The results are verified through a detailed comparison with experimental data from Ayobi et al. Furthermore, Regarding the fundamental factors influencing CO2 adsorption rate is revealed, diminishing the inlet gas superficial velocity and augmenting the particle size of the solid adsorbent both contribute to improve adsorption performance. Specifically, the adsorption rate increases from 76.7% to 81.7% at the gas superficial velocity reducing from 1.10 to 0.71 m/s, while the adsorption rate from 77.6% to 79.7% with the particle size ranging from 400 to 600 μm. Additionally, the study delves into an exploration of fluid dynamic characteristics pertaining to gas particles within the bubbling fluidized bed while systematically considering varied inlet gas superficial velocities and particle sizes.

Electrochemical CO2 reduction integrated with membrane/adsorption‐based CO2 capture in gas‐diffusion electrodes and electrolytes

AbstractElectrochemical CO2 reduction reaction (CO2RR) has attracted much attention in the last decade, owing to its unique advantages such as operation at ambient conditions, coupling with renewable electricity, and producing a wide range of products and commodities. The majority of CO2RR studies are focused on pure CO2 as feed, while in real CO2 waste streams, such as flue gas or biogas, CO2 concentration does not exceed 40%. Therefore, the economic feasibility of CO2RR and its carbon footprint are greatly limited by the CO2 purification steps before electrolysis ($70–100 per ton of CO2 for CO2/N2 separation). In recent years, studies have exhibited the importance of this matter by integrating CO2 capture and electroreduction in a single unit. Mostly, CO2 capture solutions as electrolytes have been under attention, and promising results have been achieved to significantly improve the overall economy of CO2RR. The focus on CO2 capture‐electroreduction integration can go beyond the solution/electrolyte‐based CO2 capture (e.g., amine solutions and ionic liquids) and other processes such as solid adsorption and membrane‐based processes, as more efficient options, can be potentially integrated with CO2 electroreduction in the gas‐diffusion electrode design. This article aims to review the recent efforts in integrating capture and electroreduction of CO2 and provides new perspectives in material selection and electrode design for membrane‐ and adsorption‐based CO2 capture‐reduction integration, in addition to the analysis of the economic feasibility of this integration.

A New Porphyrin-based Covalent Organic Framework with High Iodine Capture Capacity and I-doping Enhanced Conductivity.

Covalent organic frameworks (COFs) are porous organic materials with well-defined and uniform structure. The material is an excellent candidate as a solid adsorbent for iodine adsorption. In the present study, we report the synthesis of COF with porphyrin moiety, TF-TA-COF, by solvothermal reaction, which was characterized by XRD, solid-state 13 C NMR, IR, TGA, and nitrogen adsorption-desorption analysis. TF-TA-COF showed a high specific surface area of 443 m2 g-1 , and exhibited good adsorption performance for iodine vapor, with an adsorption capacity of 2.74 g g-1 . XPS and Raman spectrum indicated that a hybrid of physisorption and chemisorption took place between host COF and iodine molecules. The electric properties of iodine-loaded TF-TA-COF were also studied. After doped with iodine, the conductivity of the material increased by more than 5 orders of magnitude. The photoconductivity of I2 -doped COF was also studied and TF-TA-COF showed doping-enhanced photocurrent generation.

Effective Strategy toward Obtaining Reliable Breakthrough Curves of Solid Adsorbents.

Metal-organic frameworks (MOFs) have demonstrated their versatility in a wide range of applications, including chemical separation, gas capture, and storage. In industrial adsorption processes, MOFs are integral to the creation of selective gas adsorption fixed beds. In this context, the assessment of their separation performance under relevant conditions often relies on breakthrough experiments. One aspect frequently overlooked in these experiments is the shaping of MOF powders, which can significantly impact the accuracy of breakthrough results. In this study, we present an approach for immobilizing MOF particles on the surface of glass beads (GBs) utilizing trimethylolpropane triglycidyl ether (TMPTGE) as a binder, leading to the creation of MOF@GB materials. We successfully synthesized five targeted MOF composites, namely, SIFSIX-3-Ni@GB, CALF-20@GB, UiO-66@GB, HKUST-1@GB, and MOF-808@GB, each possessing distinct pore sizes and structural topologies. Characterization studies employing powder X-ray diffraction and adsorption isotherm analyses demonstrated that MOFs@GB retained their crystallinity and 73-90% of the Brunauer-Emmett-Teller area of their parent MOFs. Dynamic breakthrough experiments revealed that, in comparison to their parent MOFs, MOF@GB configurations enhanced the accuracy of breakthrough measurements by mitigating pressure buildup and minimizing reductions in the gas flow rate. This work underscores the significance of meticulous experimental design, specifically in shaping MOF powders, to optimize the efficacy of breakthrough experiments. Our proposed strategy aims to provide a versatile platform for MOF powder processing, thereby facilitating more reliable breakthrough experiments.

3D printed electrically conductive amine based sorbent for CO2 capture

CO2 capture technologies are key to the ongoing energy transition towards a low-carbon future. Solid adsorption is a promising technology for carbon capture with potential energy savings for regeneration of the material compared to liquid absorption. An interesting route for regeneration is electrical swing adsorption (ESA). An electrically conductive sorbent for direct air capture (DAC) was developed by 3D printing. As sorbent material an amine based ion-exchange resin was selected based on its high CO2 capacity for DAC with silver coated glass flakes as electrically conductive additive. Different amount of flakes were added to study the percolation threshold of the sorbent. The heating of the sorbents was done by Joule heating and monitored by an infrared camera. Furthermore, the influence of humidity and temperature on the electrical resistivity and volume of the sorbent structures were evaluated.Solid amine based sorbents with 15 to 35 vol% of silver coated glass flakes were successfully printed. At 20 vol% of flakes, a higher electrical conductivity could be obtained at room temperature and lower humidity. If the humidity increases up to 75 %, the volume of the structures expands with 7 % which causes an increase in electrical resistivity and loss of percolation. At 25 vol% of flakes, percolation is obtained and the resistivity is low enough (<10 Ohm.m) for Joule heating. This resistivity resulted in a heating time of 60 s for heating up to 70 °C, the regeneration temperature of the sorbent. These experiments demonstrate that printed solid amine based sorbent were successfully developed for CO2 capture and regeneration by ESA.

Lignin-derived nitrogen doped hierarchical porous carbon spheres for highly efficient dichloromethane adsorption

Biomass-prepared porous carbon materials are promising solid adsorbents for the removal of volatile organic compounds (VOCs). However, their application is hindered due to the insufficient number of pores and poor surface activity. In this study, a lignin-derived nitrogen-doped hierarchical porous carbon sphere (NHPCS-0.5) with abundant surface active sites was synthesised through spray drying and carbonisation–activation methods. The optimised NHPCS-0.5 displayed a high BET specific surface area (2961 m2·g−1) and total pore volume (1.57 cm3·g−1), developed hierarchical porous distribution with micro-/meso-/macropores and satisfactory surface nitrogen content. Moreover, it exhibited an excellent dichloromethane adsorption capacity of 156 mg·g−1 and maintained 86% of initial capacity after five regeneration cycles, indicating an outstanding regenerative ability. The nitrogen introduction improved the micropore volume and adsorption capacity. Adsorption mechanism reveals that micropore filling and enhanced van der Waals interaction of carbon surface with dichloromethane molecule by N-containing functional groups played a vital role in adsorption, and mesopores contributed to the high adsorption rates. The above results indicate the potential of NHPCS-0.5 as an adsorbent for VOC removal and provide new ideas for the utilisation of lignin and design of carbon sphere materials.

Development of amine-pillar[5]arene modified porous silica for CO2 adsorption, and CO2/CH4, CO2/N2 separation

Solid amine adsorbents with macrocycle are emerging as promising candidate for efficient CO2 adsorption due to their abundance of active sites, inherent cavities, and ease of encapsulation. Herein, a novel amine­pillar[5]arene functionalized porous silica adsorbent (EDA-P5S) was synthesized to investigate CO2 adsorption, the adsorption process of CO2 was executed using a fixed-bed (FD-2000) reactor. The dynamic adsorption capacities of EDA-P5S were 7.62 (0.46) and 7.72 (0.41) mmol/g for CO2/CH4 and CO2/N2, respectively, both the gas mixtures showed high separation selectivity. Subsequent research indicated that its porous structure facilitated the dispersion of amines and increased the exposure of active sites, thereby enhancing CO2 adsorption. Furthermore, the in-situ FTIR, 13C NMR spectra, and computational results collectively confirmed that the CO2 adsorption mechanism on EDA-P5S was consistent with the zwitterion mechanism. This work may provide a useful strategy for CO2 solid amine porous adsorbents to obtain high-purity CO2 by selectively removing CO2 from CH4 or N2.

Using solid phase adsorption toxin tracking and extended local similarity analysis to monitor lipophilic shellfish toxins in a mussel culture ranch in the Yangtze River Estuary

Harmful algal blooms (HABs) and their associated phycotoxins are increasing globally, posing great threats to local coastal ecosystems and human health. Nutrients have been carried by the freshwater Yangtze River and have entered the estuary, which was reported to be a biodiversity-rich but HAB-frequent region. Here, in situ solid phase adsorption toxin tracking (SPATT) was used to monitor lipophilic shellfish toxins (LSTs) in seawaters, and extended local similarity analysis (eLSA) was conducted to trace the temporal and special regions of those LSTs in a one-year trail in a mussel culture ranch in the Yangtze River Estuary. Nine analogs of LSTs, including okadaic acid (OA), dinophysistoxin-1 (DTX1), yessotoxin (YTX), homoyessotoxin (homoYTX), 45-OH-homoYTX, pectenotoxin-2 (PTX2), 7-epi-PTX2 seco acid (7-epi-PTX2sa), gymnodimine (GYM) and azaspiracids-3 (AZA3), were detected in seawater (SPATT) or rope farmed mussels. The concentrations of OA + DTX1 and homoYTX in mussels were positively correlated with those in SPATT samplers (Pearson test, p < 0.05), indicating that SPATT (with resin HP20) would be a good monitoring tool and potential indicator for OA + DTX1 and homoYTX in mussel Mytilus coruscus. The eLSA results indicated that late summer and early autumn were the most phycotoxin-contaminated seasons in the Yangtze River Estuary. OA + DTX1, homoYTX, PTX2 and GYM were most likely driven by the local growing HAB species in spring and summer, while Yangtze River diluted water may impact the accumulation of HAB species, causing potential phycotoxin contamination in the Yangtze River Estuary in autumn and winter. Together, the results showed that the mussel harvesting season, late summer and early autumn, would be the season with the greatest phycotoxin risk and would be the most contaminated by local growing toxic algae. Routine monitoring sites should be set up close to the local seawaters.

Modeling of multi-temperature Type I and II benzene/ammonia adsorption isotherms: Dual LF model and linearized DR model

Adsorption isotherm is basic data for evaluating the porous adsorbent adsorption capacity and explaining gas–solid adsorption behavior. Adsorption equilibrium modeling is a simple method to describe isotherm data in application. In this paper, taking C6H6 and NH3 as an example, multi-temperature Type I or Type II adsorption isotherms on AC, ASZMT, and 13X were investigated and fitted. Results show that C6H6 and NH3 adsorption behaviors on 13X both existed in chemisorption. At certain adsorbed capacity, the isosteric heats are higher than 50 kJ·mol−1. Type I and Type II C6H6 or NH3 adsorption isotherms could be successfully described using the extended Dual LF model·NH3 temperature-independent characteristic curves on AC and ASZMT were obtained using the Linearized DR model and successfully used to predict NH3 adsorption data at any pressure within the whole room temperature. Further, the Dual LF model was extended to describe other adsorption isotherms including IUPAC Type III, IV, and V. The R2 between the model and data were higher than 0.98, proving that it has universal applicability than other classical models such as Langmuir, Freundlich, Toth, and so on. It has the potential to be used as a general equilibrium model for adsorption process simulation in the future.

Fabrication of silica/calcium alginate nanocomposite based on rice husk ash for efficient adsorption of phenol from water.

The current work discusses the synthesis of three different solid adsorbents: silica nanoparticles derived from rice husk (RS), calcium alginate beads (AG), and silica/alginate nanocomposite (RSG). The fabricated solid adsorbents were characterized by using different physicochemical techniques such as TGA, XRD, nitrogen adsorption/desorption analysis, ATR-FTIR, pHPZC, SEM, and TEM. The adsorption efficiencies of the prepared solid adsorbents were considered for the removal of phenol as a selected hazardous pollutant. Because of its improved adsorption capacity and environmentally friendly character, a composite made of biosilica nanoparticles and naturally occurring alginate biopolymer by click chemistry is significant in environmental treatment. Adding silica nanoparticles to the alginate biopolymer hydrogel has many advantages, including increased surface area, easier recovery of the solid adsorbent, and additional surface chemical functional groups. The silica/alginate nanocomposite showed surface heterogeneity with many chemical functional groups present, whereas silica nanoparticles had the highest surface area (893.1 m2 g-1). It has been found that the average TEM particle size of RS, AG, and RSG was between 18 and 82 nm. RSG displayed the maximum adsorption capacity of phenol (100.55 mg g-1) at pH 7 and 120 min as equilibrium adsorption time. Adsorption of phenol onto the solid adsorbents fit well with a nonlinear Langmuir isotherm with favorable adsorption. Kinetic and thermodynamic studies prove that the adsorption process follows a pseudo-second-order kinetic model, endothermic process, physical, and spontaneous adsorption. Sodium hydroxide is effective in desorbing 94% of the loaded phenols, according to desorption investigations. Solid reusability tests showed that, after seven cycles of phenol adsorption/desorption, RSG lost only 8.8% of its adsorption activity.

Optimizing the micro/mesoporous structure of hierarchical graphene aerogel for CO2 capture by controlling the oxygen functional groups of graphene oxide

BackgroundGraphene aerogels as solid porous adsorbents are great candidates for CO2 adsorption based on their tunable hierarchical pore structure and oxygenated groups on graphene oxide can control the self-assembly and pore structure of graphene aerogels. MethodsModified Hummer's method was used to synthesize graphene oxides by using various levels of H2SO4, KMnO4, and H2O2 and 3D graphene aerogels were synthesized via the hydrothermal and freeze-drying method. FTIR, RAMAN, XRD, FE-SEM, and BET analysis were used for characterizations. Significance findingsThe effect of graphite oxidation conditions on the hierarchical porous structure of graphene aerogel for CO2 adsorption was investigated. The graphene aerogel with the high meso and micro surface areas and the highest Sm/ST value (micro surface area/total micro and meso surface area) of 33% and also, the adequate macropores was achieved using high dosage of H2SO4 in the graphene oxidation process led to the highest CO2 adsorption capacity of 1.72 mmol/g. increasing the H2O2 dosages increased the macropores in the aerogel structure and improved the value of Sm/ST leading to an increase in the CO2 adsorption capacity. The high content of KMnO4 led to low Sm/ST value and fewer macropores and decreased the CO2 adsorption capacity (1.04 mmol/g).

Guidelines for the Design of Solid CO2 Adsorbents for Mobile Carbon Capture in Heavy-Duty Vehicles: A Review

Guidelines for the Design of Solid CO2 Adsorbents for Mobile Carbon Capture in Heavy-Duty Vehicles: A Review