Effect of Relative Humidity on Adsorption Breakthrough of CO₂ on Activated Carbon Fibers

Biochar mitigates the postponed bioavailability and toxicity of phthalic acid esters in the soil

Observed nowadays wide pollution of the environment with microplastic and phthalic acid esters (PAEs) (such as dimethyl phthalate, DMP; diethyl phthalate, DEP; dibutyl phthalate, DBP; benzyl butyl phthalate, BBP; di-(2-ethylhexyl) phthalate, DEHP and di-n-octyl phthalate, DNOP) is a result of their increased production and usage. Weak bonding with polymer matrix enables their easier mobilization in the environment and increased bioavailability. The aim of the presented studies was the estimation of the fate of six priority PAEs in the soil-vegetable system and the application of biochar to immobilize PAEs in the soil preventing their bioavailability to lettuce. Both the acute (one full lettuce development period) and prolongated effect (lettuce cultivated after 10 weeks from the first PAEs contamination) were estimated to examine the long-time exposure under crop rotation. The addition of 1 % of corn-derived biochar immobilized PAEs in the soil efficiently (up to 4 times increased concentration) with the following order: DBP < DEP < DMP < DEHP < DNOP < BBP. Bioavailable PAEs were determined in lettuce roots (DMP, BBP, DEHP), and lettuce leaves (DEP, DBP, DNOP) but the presence of biochar lowered their content. PAEs, although not available for lettuce, were available for other organisms, confirming that the bioavailability or lack of nutrients is of great importance in PAEs-polluted soil. In long-time experiments, without biochar amendment, all PAEs were 3-12 times more bioavailable and were mainly accumulated in lettuce roots. The biochar addition significantly reduces (1.5-11 times) PAEs bioavailability over time. However, the PAEs content in roots remained significantly higher in samples with crop rotation compared to samples where only lettuce was grown. The results confirmed that biochar addition to the soil reduces their bioavailability and mobility inside the plant, limiting their transport from roots to leaves and reducing the exposure risk but confirming that lettuce leaves may be a safe food when cultivated in PAEs-polluted soil.

Carbon Dioxide Capture on Oxygen- and Nitrogen-Containing Carbon Quantum Dots

To address global climate change challenges, an effective strategy involves capturing CO2 directly at its source using a sustainable, low-cost adsorbent. Carbon quantum dots (CQDs), derived from lignin, are employed to modify the internal surface of an activated carbon adsorbent, enabling selective adsorption based on electrostatic interactions. By manipulating charge distribution on CQDs through either doping (nitrogen) or functionalization (amine, carboxyl, or hydroxyl groups), the study confirms, through classical molecular dynamics simulations, the potential to adjust binding strength, adsorption capacity, and selectivity for CO2 over N2 and O2. For simulations with a single component gas, maximum selectivities of 3.6 and 6.7 are shown for CO2/N2 and CO2/O2, respectively, at 300 K. Simulations containing a wet flue gas indicate that the presence of water increases the CO2/N2 and CO2/O2 selectivities. The highest CO2/H2O selectivity obtained from a CQD/graphite system is 4.3. A comparison of graphite and lignin-based carbon composite (LBCC) substrates demonstrated that LBCC has enhanced adsorptive capacity. The roughness of the LBCC substrate prevents the diffusion of the CQD on the surface. This computational study takes another step toward identifying optimal CQD atomic architecture, dimensions, doping, and functionalization for a large-scale CQD/AC adsorbent solution for CO2 capture.

Effect of pyrolysis temperature on characteristics and chloramphenicol adsorption performance of NH2-MIL-53(Al)-derived amine-functionalized porous carbons

Several activities such as aquaculture, human and feedstock therapies can directly release antibiotics into water. Due to high stability, low hydrolysis and non-biodegradation, they can accumulate in the aqueous environment and transport to aquatic species. Here, we synthesized amine-functionalized porous carbons (ANC) by a direct-pyrolysis process of NH2-MIL-53(Al) as a sacrificial template at between 600 and 900 °C and utilized them to eliminate chloramphenicol antibiotic from water. The NH2-MIL-53(Al)-derived porous carbons obtained high surface areas (304.7-1600 m2 g-1) and chloramphenicol adsorption capacities (148.3-261.5 mg g-1). Several factors such as hydrogen bonding, Yoshida hydrogen bonding, and π-π interaction, hydrophobic interaction possibly controlled adsorption mechanisms. The ANC800 could be reused four cycles along with high stability in structure. As a result, NH2-MIL-53(Al)-derived porous carbons are recommended as recyclable and efficient adsorbents to the treatment of antibiotics in water.

Artificial intelligence application in adsorption of uremic toxins: Towards the eco-friendly design of highly efficient with potential applications as hemodialysis membranes

Six Functionalized Activated Carbon Cloths (FACCs) were designed to obtain fundamental information for training a Bayesian Regularized Artificial Neural Network (BRANN) capable of predicting adsorption capacity of the FACCs to synthesize tailor-made materials with potential application as dialysis membranes. Characterization studies showed that FACCs have a high surface area (1354-2073 m2 g-1) associated with increased microporosity (W0, average: 0.57 cm3 g-1). Materials are carbonaceous, with a carbon content between 69 and 92%. Chemical treatments modify the pHpzc of materials between 4.1 and 7.8 due to incorporating functional groups on the surface (C=O, -COOH, -OH, -NH, -NH2). Uremic toxins tests showed a high elimination rate of p-cresol (73 mg g-1) and creatinine (90 mg g-1) which is not affected by the matrix (aqueous solution and simulated serum). However, in the case of uric acid, adsorption capacity decreased from 143 mg g-1 to 71 mg g-1, respectively. When comparing the kinetic constants of the adsorption studies in simulated serum versus the studies in aqueous solution, it can be seen that this does not undergo significant changes (0.02 min-1), evidencing the versatility of the material to work in different matrices. The previous studies, in combination with characterization of the materials, allowed to establish the adsorption mechanism. Thus, it permitted to train the BRANN to obtain mathematical models capable to predict the kinetic adsorption of the toxins studied. It is concluded that the predominant adsorption mechanism is due to π-π interactions between the adsorbate unsaturations with the material's pseudo-graphitic planes. Results show that FACCs are promising materials for hemodialysis membranes. Finally, taking into consideration the adsorption capacities and rates, as well as the semiquantitative analysis of the environmental impact associated with the preparation of the adsorbents, the best adsorbent (CC, Eco-Scale = 91.5) was selected. The studies presented show that the material is eco-friendly and highly efficient in the elimination of uremic toxins.

Novel carbon-based composites enriched with Fe and Mn as effective and eco-friendly adsorbents of heavy metals in multicomponent solutions

With increasing demand for adsorbents highly effective in pollutant removal, carbon-based porous materials are becoming more and more popular. In this work, a new approach to the synthesis of such solids using an environmentally friendly, two-step preparation method is presented. A series of hybrid porous silica-containing carbon composites was synthesized, namely: metal free (C/SiO2), enriched with manganese (C/Mn/SiO2), as well as iron (C/Fe/SiO2). The effect of additives on the structure and morphology of the composites was evaluated using X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption and scanning electron microscope (SEM). The as-synthesized carbons were used as effective adsorbents for the simultaneous removal of heavy metals, including lead (Pb(II)) and zinc (Zn(II)) ions. In particular, it was determined that C/Mn/SiO2 sample demonstrated the highest adsorption capacity towards Pb(II) and Zn(II) ions. It was equal to 211.60 mg/g for Pb(II) and 74.95 mg/g for Zn(II). Zeta potential and surface charge density of the solids, with and without metals, were investigated to determine electrical double layer structure, whereas stability studies and aggregate size measurements were performed to estimate solid aggregation under selected conditions. It was established that solids with adsorbed metals formed suspensions with lower stability than those without ions. This, in turn, facilitates their separation from aqueous solutions.

Chemical Studies of Multicomponent Kidney Stones Using the Modern Advanced Research Methods

Defining the kidney stone composition is important for determining a treatment plan, understanding etiology and preventing recurrence of nephrolithiasis, which is considered as a common, civilization disease and a serious worldwide medical problem. The aim of this study was to investigate the morphology and chemical composition of multicomponent kidney stones. The identification methods such as infrared spectroscopy (FTIR), X-ray diffraction (XRD), and electron microscopy with the EDX detector were presented. The studies by the X-ray photoelectron spectroscopy (XPS) were also carried out for better understanding of their chemical structure. The chemical mapping by the FTIR microscopy was performed to show the distribution of individual chemical compounds that constitute the building blocks of kidney stones. The use of modern research methods with a particular emphasis on the spectroscopic methods allowed for a thorough examination of the subject of nephrolithiasis.

Synthesis and Sensing Performance of Chitin Fiber/MoS2 Composites

In this study, chitin fibers (CFs) were combined with molybdenum sulfide (MoS₂) to develop high-performance sensors, and chitin carbon materials were innovatively introduced into the application of gas sensing. MoS₂/CFs composites were synthesized via a one-step hydrothermal method. The surface properties of the composites were greatly improved, and the fire resistance effect was remarkable compared with that of the chitin monomer. In the gas-sensitive performance test, the overall performance of the MoS₂/CFs composite was more than three times better than that of the MoS₂ monomer and showed excellent long-term stability, with less than 10% performance degradation in three months. Extending to the field of strain sensing, MoS₂/CFs composites can realize real-time signal conversion in tensile and motion performance tests, which can help inspectors make analytical judgments in response to the analysis results. The extensive application of sensing materials in more fields is expected to be further developed. Based on the recycling of waste chitin textile materials, this paper expands the potential applications of chitin materials in the fields of gas monitoring, biomedicine, behavioral discrimination and intelligent monitoring.

Composites containing resins and carbon nano-onions as efficient porous carbon materials for supercapacitors

Herein, we report the functionalization of carbon nano-onions (CNOs) with the hydroxyaryl group and subsequent modifications with resins: resorcinol-formaldehyde using porogenic Pluronic F-127, resorcinol-formaldehyde-melamine, benzoxazine made of bisphenol A and triethylenetetramine, and calix[4]resorcinarene-derived using F-127. Following the direct carbonization, extensive physicochemical analysis was carried out, including Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and adsorption-desorption of N₂. The addition of CNO to the materials significantly increases the total pore volume (up to 0.932 cm³ g^-1 for carbonized resorcinol-formaldehyde resin and CNO (RF-CNO-C) and 1.242 cm³ g^-1 for carbonized resorcinol-formaldehyde-melamine resin and CNO (RFM-CNO-C)), with mesopores dominating. However, the synthesized materials have poorly ordered domains with some structural disturbance; the RFM-CNO-C composite shows a more ordered structure with amorphous and semi-crystalline regions. Subsequently, cyclic voltammetry and galvanostatic charge-discharge method studied the electrochemical properties of all materials. The influence of resins' compositions, CNO content, and amount of N atoms in carbonaceous skeleton on the electrochemical performance was studied. In all cases, adding CNO to the material improves its electrochemical properties. The carbon material derived from CNO, resorcinol and melamine (RFM-CNO-C) showed the highest specific capacitance of 160 F g^-1 at a current density of 2 A g^-1, which is stable after 3000 cycles. The RFM-CNO-C electrode retains approximately 97% of its initial capacitive efficiency. The electrochemical performance of the RFM-CNO-C electrode results from the hierarchical porosity's stability and the presence of nitrogen atoms in the skeleton. This material is an optimal solution for supercapacitor devices.

A New Strengthening Process for Carbon-Fiber-Reinforced Thermoplastic Polyphenylene Sulfide (CFRTP-PPS) Interlayered Composite by Electron Beam Irradiation to PPS Prior to Lamination Assembly and Hot Press

Impact by hailstone, volcanic rock, bird strike, or also dropping tools can cause damage to aircraft materials. For maximum safety, the goal is to increase Charpy impact strength (a_uc) of a carbon-fiber-reinforced thermoplastic polyphenylene sulfide polymer (CFRTP-PPS) composite for potential application to commercial aircraft parts. The layup was three cross-weave CF plies alternating between four PPS plies, [PPS-CF-PPS-CF-PPS-CF-PPS], designated [PPS]₄[CF]₃. To strengthen, a new process for CFRP-PPS was employed applying homogeneous low voltage electron beam irradiation (HLEBI) to both sides of PPS plies prior to lamination assembly with untreated CF, followed by hot press under 4.0 MPa at 573 K for 8 min. Experimental results showed a 5 kGy HLEBI dose was at or near optimum, increasing a_uc at each accumulative probability, P_f. Optical microscopy of 5 kGy sample showed a reduction in main crack width with significantly reduced CF separation and pull-out; while, scanning electron microscopy (SEM) and electron dispersive X-ray (EDS) mapping showed PPS adhering to CF. Electron spin resonance (ESR) of a 5 kGy sample indicated lengthening of PPS chains as evidenced by a reduction in dangling bond peak. It Is assumed that 5 kGy HLEBI creates strong bonds at the interface while strengthening the PPS bulk. A model is proposed to illustrate the possible strengthening mechanism.

Long-term physical and chemical aging of biochar affected the amount and bioavailability of PAHs and their derivatives

Biochar applied into the soil is recommended as an effective tool for increasing its properties and crop productivity. However, biochar can contain some potentially toxic compounds such as polycyclic aromatic hydrocarbons (PAHs). Moreover, during biochar production or environmental application (e.g. as soil fertilizer), more toxic PAHs derivatives containing nitrogen, oxygen or sulfur can be formed. There is a lack of information on how the environmental factors affect the bioavailability of such compounds during the long-term application of BC into the soil. In the presented studies the effects of physical (freeze-thaw cycles) and chemical aging (temperatures 60 °C and 90 °C) on the total and bioavailable content of PAHs and their derivatives were estimated. The results indicate that long-term (6 months) aging affected the physicochemical characteristic of biochars promoting the formation of new C and O-containing species on the BC surface increasing their polarity and hydrophilicity. Physical and chemical aging promoted the formation of compounds with higher molecular weight and a significant (up to 550 %) increase in the bioavailability of PAHs and their derivatives. The results of this study highlight the importance of the bioavailable fraction of PAHs and their derivatives for evaluation of the toxicity of aged biochar.

Prospects for Simultaneously Capturing Carbon Dioxide and Harvesting Water from Air

Mitigation of anthropogenic climate change is expected to require large-scale deployment of carbon dioxide removal strategies. Prominent among these strategies is direct air capture with sequestration (DACS), which encompasses the removal and long-term storage of atmospheric CO₂  by purely engineered means. Because it does not require arable land or copious amounts of freshwater, DACS is already attractive in the context of sustainable development, but opportunities to improve its sustainability still exist. Leveraging differences in the chemistry of CO₂  and water adsorption within porous solids, here, the prospect of simultaneously removing water alongside CO₂  in direct air capture operations is investigated. In many cases, the co-adsorbed water can be desorbed separately from chemisorbed CO₂  molecules, enabling efficient harvesting of water from air. Depending upon the material employed and process conditions, the desorbed water can be of sufficiently high purity for industrial, agricultural, or potable use and can thus improve regional water security. Additionally, the recovered water can offset a portion of the costs associated with DACS. In this Perspective, molecular- and process-level insights are combined to identify routes toward realizing this nascent yet enticing concept.

Raspberry stalks-derived biochar, magnetic biochar and urea modified magnetic biochar - Synthesis, characterization and application for As(V) and Cr(VI) removal from river water

Raspberry stalks-derived biochar (BC), magnetic biochar-iron oxide composite (BC-Fe) and its derivative modified with urea (BC-Fe-U) were synthesized, characterized and tested as(V) and Cr(VI) ion sorbents. The surface area of BC, BC-Fe and BC-Fe-U was 259, 163 and 117 m² g^-1, respectively. The structure of BC was dominated by micropores, while in BC-Fe and BC-Fe-U mesopores predominated. Based on the XRD results, it was found that the magnetic properties of the biochar-iron oxide composites are due to the presence of ferrimagnetic magnetite (Fe₃O₄) and maghemite (Fe₂O₃). The optimal pH of As(V) and Cr(VI) adsorption onto the studied sorbents is in the range of 2.3-5.7. Pristine biochar (BC) does not adsorb As(V) ions; however, it enables rapid adsorption of Cr(VI) with the static adsorption capacity of 19.2 mg g^-1. The maximum static adsorption capacities of As(V) and Cr(VI) ions onto BC-Fe and BC-Fe-U are within the range of 13.5-16.3 mg g^-1. For most adsorption systems tested, adsorption equilibrium is reached within 4 h, though even a few minutes is enough to reach half of the adsorption static value. Phosphates over 0.005 mol L^-1 hinder adsorption of As(V) and Cr(VI) ions. Application of at least 5 mol L^-1 nitric acid allows about 95% of Cr(VI) and As(V) to be desorbed from adsorbate-loaded BC-Fe material. For other materials, the desorption efficiencies are significantly lower. BC-Fe and BC-Fe-U materials were successfully used for simultaneous Cr(VI) and As(V) removal from river water.

CO2 /N2 Separation on Highly Selective Carbon Nanofibers Investigated by Dynamic Gas Adsorption

The development of highly selective adsorbents for CO2 is a key part to advance separation by adsorption as a viable technique for CO2 capture. In this work, polyacrylonitrile (PAN) based carbon nanofibers (CNFs) were investigated for their CO2 separation capabilities using dynamic gas adsorption. The CNFs were prepared by electrospinning and subsequent carbonization at various temperatures ranging from 600 to 1000 °C. A thorough investigation of the CO2 /N2 selectivity resulted in measured values of 53-106 at 1 bar and 25 °C on CNFs carbonized at 600, 700, or 800 °C. Moreover, the selectivity increased with lower measurement temperatures and lower CO2 partial pressures, reaching values up to 194. Further analysis revealed high long-term stability with no degradation over 300 cycles and fast adsorption kinetics for CNFs carbonized at 600 or 700 °C. These excellent properties make PAN-based CNFs carbonized at 600 or 700 °C promising candidates for the capture of CO2 .

From Hazardous Waste to Green Applications: Selective Surface Functionalization of Waste Cigarette Filters for High-Performance Robust Triboelectric Nanogenerators and CO2 Adsorbents

This article reports a novel and rational approach to convert waste cigarette filters (CFs), one of the largest sources of ocean pollution, into high-performance triboelectric nanogenerators (TENGs) and efficient CO₂-capturing adsorbents. CFs are plasticized cellulose acetate, which take several years to degrade. To revalorize these fibers, selective amine surface functionalization is performed (10PAL-20T-CFs). For the proof of concept, when the modified fibers are employed in a TENG, it could generate an output voltage (96.63 V) and current (9.37 μA) that are, respectively, 43 and 8 times higher than those obtained employing the pristine CFs for the nanogenerator. The proposed TENG displays an instantaneous peak power of 3.75 mW, which is higher than that of many recently reported TENGs made from cellulose materials. Moreover, the TENG displayed outstanding durability to humidity and high-performance stability when it is subjected to cyclic loading (i.e., 12,000 cycles of loading-unloading). A 9 cm² TENG could effectively light up 100 or more colored light-emitting diodes when it is manually pressed. Finally, the modified filter fibers show an excellent CO₂ adsorption capacity of 1.93 mmol/g, which is 9.2 times higher than that obtained using the pristine fibers. These results demonstrate that hazardous wastes such as CFs can be upcycled into valuable resources.

Carbon nano-onion induced organization of polyacrylonitrile-derived block star polymers to obtain mesoporous carbon materials

Herein, we report the synthesis of mesoporous carbon materials from diblock star copolymers derived from polyacrylonitrile. The size of the pores was controlled by manipulating the length of the polymer blocks. Furthermore, the organization of polymers on the carbon nano-onion's surface resulted in materials of higher surface area and superficial electrochemical performance.

Mechanical Properties Evolution and Damage Mechanism of Kevlar Fiber under Ozone Exposure in Near-Space Simulation

The stratospheric airship, a long-term floating vehicle in near-space, has become a new hotspot in aerospace exploration. The airship’s envelope material is vulnerable to ozone exposure in near-space and degrades. This paper used typical Kevlar fiber as the research material for an ozone exposure experiment in a near-space simulated environment. The results showed that the elongation of the Kevlar fiber decreased and the elastic modulus increased after ozone exposure. The tensile strength of fiber decreased gradually with an increase in ozone concentration and exposure time. When ozone concentration increased from 0 pphm to 1000 pphm, the tensile strength of fiber decreased from 2397 MPa to 2059 MPa. With increasing ozone exposure time from 0 h to 1000 h under ozone concentration 1000 pphm, the tensile strength of fiber decreased from 2332 MPa to 1954 MPa. The hydrogen bonds and partial amide groups in the fiber structure were damaged, and the surface chemical functional groups of the Kevlar fiber were reassembled under ozone exposure. Low molecular weight oxidation products, including -COO- structures, formed on the surface of the Kevlar fiber. This work explores the ground simulation method in a near-space environment and enriches the service data of airship envelope materials.

Polymeric Network Hierarchically Organized on Carbon Nano-onions: Block Polymerization as a Tool for the Controlled Formation of Specific Pore Diameters

The organization of specific pores in carbonaceous three-dimensional networks is crucial for efficient electrocatalytic processes and electrochemical performance. Therefore, the synthesis of porous materials with ordered and well-defined pores is required in this field. The incorporation of carbon nanostructures into polymers can create material structures that are more ordered in comparison to those of the pristine polymers. In this study we applied polymer-templated methods of carbon material preparation, in which outer blocks of the star copolymers form the carbon skeleton, while the core part is pore-forming. Well-defined 6-star-(poly(methyl acrylate)-b-poly(4-acetoxystyrene)) dendrimers were synthesized by reversible addition-fragmentation chain-transfer polymerization. They were then transformed into poly(4-vinylphenol) derivatives (namely 6-star-(poly(methyl acrylate)-b-poly(4-vinylphenol)), subjected to polycondensation with formaldehyde, and pyrolyzed at 800 °C. Cross-linking of phenolic groups provides a polymer network that does not depolymerize by pyrolysis, unlike poly(methyl acrylate) chains. The selected star polymers were attached to carbon nano-onions (CNOs) to improve the organization of the polymer chains. Herein, the physicochemical properties of CNO-polymer hybrids, including the textural and the electrochemical properties, were compared with those of the pristine pyrolyzed polymers obtained under analogous experimental conditions. For these purposes, we used several experimental and theoretical methods, such as infrared, Raman, and X-ray photoelectron spectroscopy, nitrogen adsorption/desorption measurements, scanning and transmission electron microscopy, and electrochemical studies, including cyclic voltammetry. All of the porous materials were evaluated for use as supercapacitors.

Enhanced removal efficiency of toluene over activated carbon under visible light

Toluene removal rates using activated carbon (AC) at various relative humidity (RH) levels (0%, 30%, 60%) were compared under dark and visible-light conditions. Light exposure significantly increased toluene-removal efficiency independent of RH. When AC was pre-treated with an optimal concentration of HNO₃, its toluene-removal efficiency was enhanced further with light, an effect that can be attributed to increased surface-area and porosity. Fourier-transform infrared analysis confirmed that exposure of HNO₃-modified AC to light induced partial oxidation of toluene. Within visible-light range (380-650 nm), shorter wavelengths were more effective for toluene-removal compared with longer wavelengths. This suggests that hydroxyl groups formed on AC-surface under light strongly interact with aromatic rings of toluene, allowing for greater uptake of toluene. Moreover, AC can sustain its photo-activity when mixed with cement and cured, suggesting its potential applications in air-purifying building materials. An efficient and practical method for regeneration of spent AC is also demonstrated.

CO2 Capture by Low-Cost Date Pits-Based Activated Carbon and Silica Gel

The rising levels of CO2 in the atmosphere are causing escalating average global temperatures. The capture of CO2 by adsorption has been carried out using silica gel type III and prepared activated carbon. The date pits-based activated carbon was synthesized using a tubular furnace by physical activation. The temperature of the sample was increased at 10 °C/min and the biomass was carbonized under N2 flow maintained continuously for 2 h at 600 °C. The activation was performed with the CO2 flow maintained constantly for 2 h at 600 °C. The temperature, feed flow and adsorbate volume were the parameters considered for CO2 adsorption. The success of CO2 capture was analyzed by CO2 uptake, efficiency based on column capacity, utilization factors and the mass transfer zone. The massively steep profiles of the breakthrough response of the AC demonstrate the satisfactory exploitation of CO2 uptake under the conditions of the breakthrough. The SG contributed to a maximal CO2 uptake of 8.61 mg/g at 298 K and Co = 5% with F = 5 lpm. The enhanced CO2 uptake of 73.1 mg/g was achieved with a column efficiency of 0.94 for the activated carbon produced from date pits at 298 K. The AC demonstrated an improved performance with a decreased mass transfer zone of 1.20 cm with an enhanced utilization factor f = 0.97 at 298 K. This finding suggests that a date pits-based activated carbon is suitable for CO2 separation by adsorption from the feed mixture.

Understanding the Effect of Water on CO2 Adsorption

Carbon capture from large sources and ambient air is one of the most promising strategies to curb the deleterious effect of greenhouse gases. Among different technologies, CO₂ adsorption has drawn widespread attention mostly because of its low energy requirements. Considering that water vapor is a ubiquitous component in air and almost all CO₂-rich industrial gas streams, understanding its impact on CO₂ adsorption is of critical importance. Owing to the large diversity of adsorbents, water plays many different roles from a severe inhibitor of CO₂ adsorption to an excellent promoter. Water may also increase the rate of CO₂ capture or have the opposite effect. In the presence of amine-containing adsorbents, water is even necessary for their long-term stability. The current contribution is a comprehensive review of the effects of water whether in the gas feed or as adsorbent moisture on CO₂ adsorption. For convenience, we discuss the effect of water vapor on CO₂ adsorption over four broadly defined groups of materials separately, namely (i) physical adsorbents, including carbons, zeolites and MOFs, (ii) amine-functionalized adsorbents, and (iii) reactive adsorbents, including metal carbonates and oxides. For each category, the effects of humidity level on CO₂ uptake, selectivity, and adsorption kinetics under different operational conditions are discussed. Whenever possible, findings from different sources are compared, paying particular attention to both similarities and inconsistencies. For completeness, the effect of water on membrane CO₂ separation is also discussed, albeit briefly.

Cycling system for decomposition of gaseous benzene by hydrogen peroxide with naturally Fe-containing activated carbon

For the removal of volatile organic compounds (VOCs) from environmental systems, gaseous benzene, a model VOC, was adsorbed on naturally Fe-containing activated carbon and subsequently, decomposed in the presence of de-ionized water, and low (0.03%, pH 6.5) and high (30%, pH 2.5) concentration H2O2 solutions. The intermediates produced during benzene decomposition were analyzed and compared using gas chromatography-mass spectrometry. After the decomposition process, the activated carbon sample was air dried. Three cycles were carried out with de-ionized water and low and high concentration H2O2 solutions as oxidants. The adsorption capacity of the activated carbon sample treated with DI water gradually decreased as the number of cycles increased. On the other hand, the benzene adsorption capacity of the activated carbon samples treated with the H2O2 solutions was improved due to the relatively higher specific surface areas of these samples. After treatment with the low-concentration H2O2 solution, intermediates such as glyoxylic acid, oxalic acid, phenol, malonic acid, and pyrocatechol were observed. After treatment with high-concentration H2O2 solution, intermediates such as glyoxylic acid, formic acid, and acetic acid were formed. With increasing H2O2 concentration, the number and the molecular weight of the intermediate formed by the oxidative degradation of benzene, simultaneously decreased. The Fenton reaction induced by naturally Fe-containing activated carbon and H2O2 could lead to more efficient decomposition of benzene.

Opening the internal structure for transport of ions: improvement of the structural and chemical properties of single-walled carbon nanohorns for supercapacitor electrodes

We investigated the electrochemical performance of single-walled carbon nanohorns (SWCNHs) for use as supercapacitor electrodes. For the first time, we used acid-treatment for oxidation of SWCNHs and hole creation in their structure. A detailed study was performed on the correlation between the oxidation of SWCNHs via acid treatment and variable acid treatment times, the structural properties of the oxidized carbon nanostructures, and the specific capacitance of the SWCNH electrodes. We showed that simple functionalization of carbon nanostructures under controlled conditions leads to an almost 3-fold increase in their specific capacitance (from 65 to 180 F g-1 in 0.1 M H2SO4). This phenomenon indicates higher accessibility of the surface area of the electrodes by electrolyte ions as a result of gradual opening of the SWCNH internal channels.

K2CO3-Impregnated Al/Si Aerogel Prepared by Ambient Pressure Drying for CO2 Capture: Synthesis, Characterization and Adsorption Characteristics

A new potassium-based adsorbent for CO₂ capture with Al aerogel used as support is proposed in this work. The adsorbents with different surface modifiers (tetraethyl orthosilicate (TEOS) and trimethyl chlorosilane (TMCS)) and different K₂CO₃ loadings (10%, 20%, 30% and 40%) were prepared by sol-gel and iso-volume impregnation processes with ambient pressure drying. The CO₂ adsorption performance of the adsorbents were tested by a fixed-bed reactor, and their adsorption mechanisms were studied by scanning electron microscopy (SEM), Brunauer Emmett Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray fluorescence spectrometry (XRF). Furthermore, the adsorption kinetics and the cycling performance were investigated. The results show that using TEOS to modify the wet gel can introduce SiO₂ to increase the strength of the skeleton. On the basis of TEOS modification, TMCS can further modify –OH, thus effectively avoiding the destruction of aerogel structure during ambient drying and K₂CO₃ impregnation. In this work, the specific surface area and specific pore volume of Al aerogel modified by TEOS + TMCS are up to 635.32 cm²/g and 2.43 cm³/g, respectively. The aerogels without modification (Al-B), TEOS modification (Al/Si) and TEOS + TMCS modification (Al/Si-TMCS) showed the best CO₂ adsorption performance at 20%, 30% and 30% K₂CO₃ loading, respectively. In particular, the CO₂ adsorption capacity and K₂CO₃ utilization rate of Al/Si-TMCS-30K are as high as 2.36 mmol/g and 93.2% at 70 degrees Celsius (°C). Avrami’s fractional order kinetic model can well fit the CO₂ adsorption process of potassium-based adsorbents. Al-B-20K has a higher apparent activation energy and a lower adsorption rate during the adsorption process. After 15 adsorption-regeneration cycles, Al/Si-TMCS-30K maintain a stable CO₂ adsorption capacity and framework structure, while the microstructure of Al/Si-30K is destroyed, resulting in a decrease in its adsorption capacity by nearly 30%. This work provides key data for the application of Al aerogel in the field of potassium-based adsorbent for CO₂ capture.

TEPA impregnation of electrospun carbon nanofibers for enhanced low-level CO2 adsorption

The CO₂ adsorption selectivity of plain activated carbon nanofibers (ANF) is generally low. For enhancement, nitrogen functionalities favorable for CO₂ adsorption are usually tethered to the ANF. In the current study, we adopted chemical impregnation using 0.5 wt% tetraethylenepentamine (TEPA) solution as an impregnant. To enhance the impregnation of TEPA further, preliminary oxidation of the nanofibers with 70% HNO₃ was conducted. The effects of HNO₃ and TEPA treatments on the modified ANFs were investigated for physical (using N₂ monosorb, thermogravimetric analyzer, scanning electron microscopy) and chemical (X-ray photoelectron spectrometer) changes. From the results, we found that although TEPA impregnation reduced the specific surface area and pore volume of the ANFs (from 673.7 and 15.61 to 278.8 m²/g and 0.284 cm³/g, respectively), whereas the HNO₃ pre-oxidation increased the number of carboxylic groups on the ANF. Upon TEPA loading, pyridinic nitrogen was tethered and further enhanced by pre-oxidation. The surface treatment cumulatively increased the amine content from 5.81% to 13.31%. Consequently, the final adsorption capacity for low (0.3%) and pure CO₂ levels were enhanced from 0.20 and 1.89 to 0.33 and 2.96 mmol/g, respectively. Hence, the two-step pre-oxidation and TEPA treatments were efficient for improved CO₂ affinity.

Adsorption of CO2 on KOH activated carbon adsorbents: Effect of different mass ratios

Nitrogen and oxygen enriched carbons were prepared by the cost-effective synthesis route of carbonization of polyacrylonitrile (PAN) and subsequent KOH activation for CO₂ capture. The effect of four impregnation mass ratios (KOH: PAN = 1-4) and activation temperatures (600-900 °C) on the synthesized carbon adsorbent properties was explored by different analyses. The X-ray photoelectron spectroscopy (XPS) revealed the existence of basic nitrogen and oxygen functionalities on the adsorbent's surface which increases the adsorption rate for CO₂ by providing its basic sites. By increasing mass ratio (KOH:PAN) from 1:1 to 3:1, the surface area increased from 1152.4 to 1884.2 m² g^-1 and the dynamic CO₂ adsorption capacity also increased from 2.1 to 2.5 mmol g^-1 respectively, at 30 °C (approximately ten times the adsorption capacity of untreated PAN, 0.22 mmol g^-1). Physisorption and exothermic nature of the process were confirmed by the decrease in the adsorption capacity of the adsorbents with the increase in adsorption temperature. Moreover, good cyclic stability and regenerability over 5 adsorption-desorption cycles were obtained for the adsorbents. The fractional order kinetic and Temkin isotherm models fitted best with the adsorption data. A heterogeneous interaction between CO₂ and the surface of adsorbents was suggested by the isosteric heat of adsorption values. Combined with the simple method for the preparation of activated carbon adsorbents, efficient CO₂ adsorption and excellent regeneration make it appropriate adsorbents for post-combustion CO₂ capture.

Selected pharmaceuticals removal using algae derived porous carbon: experimental, modeling and DFT theoretical insights

Porous carbon from Laminaria digitata algae activated using NaOH (PCLD@NaOH) was prepared by a chemical activation approach and has been tested for the adsorption of ketoprofen and aspirin molecules. The prepared PCLD@NaOH was characterized using XPS, FTIR, Raman, N2-physisorption, SEM, acidic/basic character (Boehm), and pHPZC. The batch adsorption of ketoprofen and aspirin was investigated under different parameters. The adsorption kinetics on PCLD@NaOH were well described by the Avrami-fractional kinetic model and the equilibrium data by Liu isotherm model. The adsorption capacity of aspirin (970.88 mg g-1 at 25 °C) was higher than ketoprofen (443.45 mg g-1 at 25 °C). The thermodynamic values indicate that the adsorption of ketoprofen and aspirin is exothermic and spontaneous. These results were in good agreement with DFT calculation that shows that the aspirin molecule presents high reactivity, electrophilicity, and softness compared to the ketoprofen molecule. Finally, the response surface methodology was used to optimize the removal efficiency of ketoprofen and aspirin.

Study on Adsorption Mechanism and Failure Characteristics of CO₂ Adsorption by Potassium-Based Adsorbents with Different Supports

In order to obtain the adsorption mechanism and failure characteristics of CO₂ adsorption by potassium-based adsorbents with different supports, five types of supports (circulating fluidized bed boiler fly ash, pulverized coal boiler fly ash, activated carbon, molecular sieve, and alumina) and three kinds of adsorbents under the modified conditions of K₂CO₃ theoretical loading (10%, 30%, and 50%) were studied. The effect of the reaction temperature (50 °C, 60 °C, 70 °C, 80 °C, and 90 °C) and CO₂ concentration (5%, 7.5%, 10%, 12.5%, and 15%) on the adsorption of CO₂ by the adsorbent after loading and the effect of flue gas composition on the failure characteristics of adsorbents were obtained. At the same time, the microscopic characteristics of the adsorbents before and after loading and the reaction were studied by using a specific surface area and porosity analyzer as well as a scanning electron microscope and X-ray diffractometer. Combining its reaction and adsorption kinetics process, the mechanism of influence was explored. The results show that the optimal theoretical loading of the five adsorbents is 30% and the reaction temperature of 70 °C and the concentration of 12.5% CO₂ are the best reaction conditions. The actual loading and CO₂ adsorption performance of the K₂CO₃/AC adsorbent are the best while the K₂CO₃/Al₂O₃ adsorbent is the worst. During the carbonation reaction of the adsorbent, the cumulative pore volume plays a more important role in the adsorption process than the specific surface area. As the reaction temperature increases, the internal diffusion resistance increases remarkably. K₂CO₃/AC has the lowest activation energy and the carbonation reaction is the easiest to carry out. SO₂ and HCl react with K₂CO₃ to produce new substances, which leads to the gradual failure of the adsorbents and K₂CO₃/AC has the best cycle failure performance.