Adsorption-desorption Cycles Research Articles

Efficient Removal of Cadmium (Cd2+) from Aqueous Solutions by Chitosan@fig Branch Biochar: Adsorption Performance and Enhanced Complexation.

In this study, fig branch biochar (FBB) was modified by chitosan to improve the Cd2+ adsorption performance from an aqueous solution. The surface area, pores, and functional groups of chitosan-modified fig branch biochar (CMFBB) were characterized by DTG-TGA, BET, SEM-EDS, FTIR, and XRD. In addition, the impact of various conditions on the Cd adsorption performance of the biochar was analyzed, including dosage, initial pH, concentration, temperature, reaction time, and coexisting cations. The adsorption kinetics, isotherms, and practical applications were also investigated. Under the optimized conditions including pH 6, adsorbent dose 2 g L-1, reaction time 90 min, Cd2+ concentration 100 mg L-1, and 25 °C, the Cd2+ adsorption capacity was 62.25 mg g-1, representing a 78.26% increase compared to FBB. The adsorption data for Cd2+ by CMFBB were found to be well-described by the pseudo-second-order kinetic and Langmuir isothermal models, indicating that a monolayer chemical adsorption process occurred. The Cd2+ adsorption was a spontaneous endothermic process, and the coexisting cations exerted negligible influence on the adsorption process. After five adsorption-desorption cycles, CMFBB maintained an adsorption efficiency of 92.3%, demonstrating excellent regeneration capability. The quantification of adsorption mechanisms suggested that physical adsorption, cation exchange, precipitation, complexation, and π-π interactions accounted for 3.70, 2.50, 33.04, 58.76, and 2.0% of the total adsorbed Cd2+ in CMFBB, respectively. Compared with FBB, the level of CMFBB increased 26.52% in complexation. This work implies that CMFBB has great potential as an effective absorbent for treating Cd2+ polluted water.

Synthesis of novel magnesium ferrite Schiff base chitosan nanocomposite for efficient removal of pb(II) ions from aqueous media

In this study, a novel MgFe2O4-Schiff base-chitosan nanocomposite was synthesized using a straightforward crosslinking method. The synthesis involved integrating MgFe2O4 nanoparticles with modified chitosan through a Schiff base formed by the reaction between terephthalaldehyde and aminopyrazine. A comprehensive characterization was performed, including X-ray diffraction analysis, which verified the crystalline structure and the successful incorporation of MgFe2O nanoparticles into the chitosan-Schiff base matrix. Scanning electron microscopy revealed a distinct surface morphology, characterized by a rough, non-uniform alignment resulting from the strong interactions between the nanoparticles and the Schiff base-chitosan matrix. Additionally, energy-dispersive X-ray analysis verified the elemental composition of the nanocomposite, revealing distinct peaks corresponding to carbon, nitrogen, oxygen, magnesium, and iron. The nanocomposite exhibited outstanding performance as a nanoadsorbent for the efficient removal of Pb(II) ions from aqueous media through electrostatic attraction and complexation mechanisms, achieving a maximum adsorption capacity of 290.7 mg g-1. The adsorption process was determined to be spontaneous, endothermic, and chemically driven, aligning well with the Langmuir isotherm model and pseudo-second-order kinetics. The optimal conditions for maximum Pb(II) ions removal were determined to be a pH of 5.5, a contact time of 100 min, and a temperature of 328 K. Furthermore, the nanocomposite demonstrated excellent recyclability, retaining over 94.8% of its initial removal efficiency after five consecutive adsorption-desorption cycles. This study highlights the nanocomposite’s potential as an eco-friendly, cost-effective, and highly efficient material for practical applications in water treatment, addressing the urgent need for sustainable solutions to heavy metal contamination.

Synthesis and characterization of polyaniline, sucrose octaacetate and chitosan blend for removal of remazol black by adsorption: Equilibrium, kinetics, and regeneration.

In this work, a polymeric blend of polyaniline (PAni) and chitosan (Chi), modified with Sucrose Octaacetate (SOA), was synthesized and characterized using different techniques. The blend was used as an adsorbent to remove Remazol Black (RB) dye from aqueous solutions. The blend was synthesized using the chemical oxidation method with ammonium persulfate as the oxidizing agent. Characterization was carried out using SEM, FT-IR, UV-Vis, BET, TGA, Conductivity, and PZc techniques. The blend structure appeared as clusters, providing a favorable surface area for adsorption. The results showed that SOA improved the conductivity of the blend without altering the structure and oxidative state of PAni. The study investigated the adsorption of RB, considering the influence of adsorbent dosage, initial dye concentration, pH, and temperature. Kinetic and equilibrium studies, thermodynamic analysis, synthetic effluent testing, and adsorbent reuse tests were conducted. The optimal adsorption conditions, within the studied range, were adsorbent dosage of 0.25gL-1, dye concentration of 60mgL-1, pH range of 2 to 7, and temperature of 30°C. Equilibrium results indicated that the Langmuir model was the most representative, with a maximum adsorption capacity of qmax=285.23mgg-1 and RL=0.01, indicating favorable adsorption. The kinetic study revealed an equilibrium constant of Keq=0.421Lmg-1 and a process order 0.63. The adsorption process followed a pseudo-first-order kinetics, demonstrating rapid adsorption on the adsorbent surface. The adsorption was physical, endothermic, and spontaneous, showing increased randomness with temperature. RB removal from synthetic effluent was effective within the pH range of 2-7, with the dye removal efficiency from the aqueous phase remaining above 74% for up to 4cycles of adsorption-desorption. The results support the hypothesis that the PAni-SOA@Chi blend is a promising alternative for removing this dye from the waste.

Remediation of wastewater containing methylene blue and acid fuchsin dyes using 2-aminothiazole chemically modified chitosan.

Herein, we report a novel amine and thiol functionalized resin based on chemical modification of chitosan with 2-aminothiazole (AT/EGCS) for effective removal of methylene blue (MB) and acid fuchsin (AF) from aqueous solutions. FTIR, XPS, SEM, and EDX confirm the successful modification of chitosan with 2-aminothiazole via nucleophilic substitution reaction with the epichlorohydrin crosslinked chitosan. The AT/EGCS exhibited superior adsorption performance towards MB and AF with maximum uptake capacities of 882.0mg/g for MB and 1205.0mg/g for AF at optimum conditions of pH (8.0 for MB and 5.0 for AF), 0.5g/L (dosage), 25.0°C, and 120.0min. Additionally, AT/EGCS exhibited 100% removal for AF and MB with concentrations lower than 300ppm. The increased adsorption capacity of AT/EGCS can be explained by the presence of multiple functional groups (-NH-, CS, and OH) in its structure. Furthermore, the data fitted well with the Langmuir isotherm model. Moreover, the results revealed that 100.0% of adsorbed MB and AF can be regenerated by using 0.01M HCl and 0.2M NaOH, respectively, and about 90.0% removal efficiency even after four adsorption-desorption cycles. As a result, the developed resins can be employed as reliable adsorbents to remediate industrial effluents containing dyes.

Novel Ce(III) based Ce-oxide/Fe3O4 composite for high-efficiency removal of Sb(V) and Sb(III) from wastewater at wide pH range.

The pollution of antimony (Sb) in water environment has threatened human health and ecological safety. Fe-Ce adsorbents have been considered as superior materials for Sb removal. However, poor stability and high sensitivity to pH variations limited their application. Herein, a novel Ce(III) based Ce-oxide/Fe3O4 composite (Fe3O4-[Ce(III)]x=1.0) was greenly prepared for adsorption of Sb(V) and Sb(III) from wastewater. Compared with Ce(IV), Ce(III) based Ce-oxide/Fe3O4 composite had better adsorption properties for both Sb(V) and Sb(III). Fe3O4-[Ce(III)]x=1.0 effectively removed Sb(V) and Sb(III) at wide pH range (2.0-9.0), and the maximum adsorption capacities were 106.69 and 91.16mg/g, respectively. Fe3O4-[Ce(III)]x=1.0 not only had strong magnetism, but also removed 91.25% of Sb(V) and 81.47% of Sb(III) after seven adsorption-desorption cycles. Coexisting ions had little impact on removal of Sb(V) and Sb(III) via Fe3O4-[Ce(III)]x=1.0. Various characterization analyses suggested that Ce(III) was crucial to the adsorption processes. The main mechanisms for Sb adsorption included the formations of Fe-O-Sb and Ce-O-Sb complexes, ligand exchange, electrostatic attraction, and hydrogen bonding. Remarkably, the main contributors to Sb(V) and Sb(III) removal were respectively the outer-sphere complex (Fe-O-Sb(V)) and inner-sphere complexes (Ce-O-Sb(III/V) and Fe-O-Sb(III)), showing discrepancies of adsorption mechanisms between Sb(V) and Sb(III). Finally, two actual Sb-containing waters treated with Fe3O4-[Ce(III)]x=1.0 both met the Sb discharge standard, highlighting its potential application value.

Facile synthesis of hierarchically flower-like hollow covalent organic frameworks for enrichment and metabolic analysis of benzophenone derivatives in mouse serum.

Benzophenone derivatives (BPs), as synthetic chemicals widely used in personal care products, have drawn increasing attention due to their potential health risks. However, monitoring BPs in biological samples remains challenging due to their complex matrices and the deficiency in sensitivity and selectivity in current methods. Herein, a method combining hierarchically flower-like hollow covalent organic frameworks (HFH-COFs) with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established for the enrichment and detection of BPs in serum samples. The HFH-COFs were synthesized at room temperature and employed as an adsorbent due to their advantageous properties. The as-prepared HFH-COFs exhibited high specific surface area (2286.53 m²/g), excellent chemical stability, and good thermal stability, making them ideal for efficient enrichment applications. Under optimized experimental conditions, five BPs were effectively enriched and quantified by HPLC-MS/MS in the range of 50.0-5000.0 ng/L with good linearity (r > 0.9992). The limit of detections was 0.5-10.0 ng/L. Furthermore, HFH-COFs showed high enrichment factors even over multiple adsorption-desorption cycles. This study proposed a reliable and efficient method for monitoring endocrine-disrupting compounds in complex biological samples and highlighted the potential of HFH-COFs as a superior adsorbent material for BP.

Experimental and theoretical investigation of allylated chitosan and acrylic acid-based smart polymer hydrogel for the removal of brilliant green from aqueous media.

Smart polymer hydrogels with superior dye adsorption (brilliant green) characteristics were synthesized via free-radical polymerization by grafting acrylic acid segments onto allylated chitosan and inducing crosslinking with a trimethylolpropane triacrylate crosslinker. The synthesized adsorbents were characterized for their chemical structure (FT-IR and 1H NMR), thermal stability (TG/DTG), and morphological features (SEM). The adsorption capacity for brilliant green (934mg/g) and water uptake (712g/g) were determined using spectrophotometric and gravimetric methods, respectively. The interaction between the synthesized adsorbent and brilliant green, including potential dye orientation on the adsorbent and hydrogen bond formation was analyzed using Density Functional Theory. The maximum adsorption of brilliant green (934mg/g) and water uptake was achieved by optimizing the monomer feed compositions. Adsorption studies revealed that dye uptake followed Fickian diffusion and the Langmuir isotherm model, with pseudo-second-order kinetics. Thermodynamic analysis demonstrated that the adsorption process was spontaneous and exothermic, as evidenced by changes in free energy, enthalpy, and entropy under varying temperatures. Theoretical investigations confirmed the excellent affinity of the synthesized adsorbent toward brilliant green. Furthermore, reusability studies showed that the adsorbent retained its dye-holding capability over 20 adsorption-desorption cycles, highlighting its potential for sustainable and efficient dye removal applications.

Efficient Capture of ReO4 - from Water by Imidazolium-Based Cationic Polymeric Nanotraps.

Rhenium represents an irreplaceable metal resource, which finds extensive applications in diverse fields, particularly in the aerospace and petrochemical industry. However, its remarkably low natural abundance and the lack of independent ore deposits pose significant challenges to its extraction and recovery processes. In this study, we present the highly efficient adsorption of perrhenate by a cationic polymeric nanotrap material, namely CPN-3VIm. The maximum adsorption capacity of CPN-3VIm-Cl for ReO4 - attains an impressive value of 1220 mg ⋅ g-1. Notably, even in the low-concentration ReO4 - solution of 8.5 ppm, the removal rate could still exceed 99 %. The recycling performance of CPN-3VIm-Cl also shows exceptional results, with both ReO4 - removal and recovery rates surpassing 90 % throughout five adsorption-desorption cycles. Furthermore, CPN-3VIm-Cl exhibits nearly 100 % extraction efficiency for ReO4 - within a broad pH range of 4-10 and demonstrates remarkable structural stability under extreme conditions, such as 3 M sulfuric acid or 3 M nitric acid. Additionally, a comprehensive investigation into the interaction mechanism between CPN-3VIm-Cl and perrhenate was carried out using SEM-EDS mapping, Raman, FT-IR, and XPS analysis.

A Novel Capacitor Deionization Performance Study Based on Carbon Nanorods/MnO2 Composite Material

The Earth abounds in water resources; however, only 0.4% of the freshwater resources are suitable for drinking. The scarcity of freshwater resources has a severe impact on the sustainable development of human society. Desalination is regarded as one of the most effective solutions. In this study, a research approach integrating materials and devices was utilized to synthesize manganese oxide-coated carbon nanospheres (CS@MnO2). Experimental results demonstrated that the system, by combining the distinctive performance merits of the CS@MnO2 material and the balanced desalination features, exhibited outstanding desalination performance. In the EDS elemental mapping analysis, the relatively feeble signal of carbon was ascribed to the encapsulation of MnO2 on the outer surface of CS. Through computational TGA analysis, the mass fraction of carbon in CS@MnO2-2 was determined to be approximately 51.2%. The excellent hydrophilicity of the material facilitated the permeation of the salt solution throughout the electrode, thereby enhancing the capacitance. CS@MnO2-2 manifested a high salt adsorption capacity of 27.42 mg g⁻¹ and the fastest electrosorption rate of 7.81 mg g⁻¹ min⁻¹. During 50 adsorption desorption cycles, the adsorption capacity showed good results. The adsorption kinetics and adsorption isotherm fitting indicated that the desalination process involved electrostatic and multilayer adsorption. This study holds great significance for reducing the cost of desalinated water and guaranteeing a sustainable supply of freshwater resources.

High-Purity Ethylene Production from Ethane/Ethylene Mixtures at Ambient Conditions by Ethane-Selective Fluorine-Doped Activated Carbon Adsorbents.

Energy-efficient separation of light alkanes from alkenes is considered as one of the most important separations of the chemical industry today due to the high energy penalty associated with the applied conventional cryogenic technologies. This study introduces fluorine-doped activated carbon adsorbents, where elemental fluorine incorporation into the carbon matrix plays a unique role in achieving high ethane selectivity. This enhanced selectivity arises from specific interactions between surface-doped fluorine atoms and ethane molecules, coupled with porosity modulation. Consequently, an equilibrium ethane/ethylene selectivity of as high as 3.9 at 298 K and 1 bar was achieved. Furthermore, polymer-grade ethylene (purity >99.99%) with a productivity of 1.6 mmol/g was obtained in a breakthrough run at ambient conditions from a binary ethane/ethylene (1/9 v/v) mixture. The ethane selectivity of the fluorine-doped carbons was further elucidated through Monte Carlo simulations and density contours of the adsorbed components. In addition to the high ethane selectivity, the adsorbents exhibited a hydrophobic surface, high stability under moisture, and excellent regenerability over multiple adsorption-desorption cycles under both equilibrium and dynamic conditions, demonstrating a sustainable performance.

Cellulose/covalent organic framework aerogel for efficient removal of Cr(VI): Performance and mechanism study.

Cellulose composites have exceptional qualities, particularly in removing heavy metal ions. Nevertheless, these materials' poor mechanical qualities and the restricted exposure of surface-active sites reduce the effectiveness of their removal. The removal efficiency of adsorbent materials largely depends on their macroscopic structural characteristics. This study successfully developed a novel cellulose composite aerogel adsorbent (TBPM). TBPM aerogel possesses not only numerous active sites but also excellent mechanical strength. It is particularly suitable for the efficient removal of hexavalent chromium (Cr(VI))-containing wastewater. The aerogel exhibited a low density of 0.0238 g/cm3 and high porosity of 98.51 %. Incorporating the covalent organic framework (BT-Dg) increased the active sites in the composite aerogel, enhancing its adsorption performance. Compared with other common heavy metal ion adsorbents, the TBPM aerogel demonstrated superior removal performance, with a maximum adsorption capacity of 411.12 mg/g and a removal efficiency of 95.01 % in Cr(VI) solution at 15 °C, pH = 3. The adsorption of Cr(VI) followed pseudo-second-order kinetics and the Langmuir isotherm model. Even after seven adsorption-desorption cycles, TBPM aerogel maintained over 80 % removal efficiency. In addition, the TBPM aerogel successfully filtered 3439 mL of Cr(VI)-containing wastewater. This composite aerogel expands the application of cellulose composites in purifying wastewater.

Separation of Ethanol–Water Azeotrope Using Waste Carrageenan Filter‐Cake Adsorbent

ABSTRACTThe final step in the downstream processing of bioethanol is typically the removal of water from the ethanol–water azeotrope (95.6 wt.% ethanol) to obtain fuel‐grade ethanol (> 99 wt.%). This can be done by various techniques including distillation (azeotropic or extractive), membrane‐based separation, and adsorption using molecular sieves or bio‐based adsorbents. In this work, a waste by‐product of carrageenan production is studied for its efficacy as water adsorbent. This waste carrageenan filter‐cake (CFC) material is primarily composed of organics (22 wt.% cellulose and carrageenan) and ash (78 wt.% perlite) as inferred from the proximate analysis. The functional groups present in the material were identified by FTIR analyses, and the surface morphology was checked by FESEM. Liquid phase water adsorption isotherms at 30°C, 40°C, and 50°C were established and were found to be adequately described by both Langmuir (R2 = 0.93 to 0.97) and Brouers‐Sotolongo (R2 = 0.96 to 0.97) models. An enthalpy change of adsorption of about −17 kJ/mol was computed through the van't Hoff equation. An azeotropic mixture (95.6 wt.% ethanol) was successfully purified to above 99.2 wt.% ethanol in a CFC‐packed column. The CFC adsorbent was used in three adsorption–desorption cycles without much loss in capacity. Moreover, the Thomas model adequately described the breakthrough curves.

Fully biobased and robust antibacterial cellulose aerogel for uranium extraction.

Developing efficient adsorbent is imperative for the utilization of uranium resources in seawater. Marine microorganisms and bacteria play an important role in the process of adsorption of uranium. In this work, a completely bio-based antimicrobial aerogel (quaternary cellulose/chitosan aerogel-QCNF/CS) was prepared by cross-linking quaternary cellulose nanofibers (QCNF) and chitosan (CS) via citric acid (CA). The QCNF/CS aerogel has a high adsorption capacity of 565.97mgg1, high selectivity (Kd=1.6×104mLg-1). Moreover, the incorporation of CS improved the mechanical properties and enhanced the shape recovery property. The adsorption system reached equilibrium within 300min and had good recovery of 93% for UO22+. After seven cycles of adsorption-desorption, QCNF/CS aerogel still maintained its original structure and retained 80.7% of its initial adsorption capacity. The introduction of quaternary ammonium salt groups gives the QCNF/CS aerogel strong antimicrobial activity, and the inhibition rate can be up to 96%. The aerogel also showed good adsorption performance in spiked natural seawater. DFT results and XPS analysis further indicated that -COOH of CA and -OH of CNF functional groups could enhance the adsorption capacity of QCNF/CS aerogel. Therefore, QCNF/CS aerogel was a potential adsorbent for the extraction of uranium from seawater.

Biosorption of cobalt (II) from an aqueous solution over acid modified date seed biochar: an experimental and mass transfer studies.

Water pollution because of the presence of heavy metals remains a serious worry. The present work demonstrates the exclusion of cobalt ion (or Co(II)) from water using novel and cost-effective biosorbents. Initially, the biosorbent was chemically modified using orthophosphoric acid and then subjected to calcination to result acid modified date seed biochar (AMDB). Three biosorbents (AMDB400, AMDB500, and AMDB600) were synthesized concerning different activation temperatures (400, 500, and 600°C). The maximum biosorption of Co(II) was achieved on AMDB600(149.5 mg/g), followed by AMDB500 (138.33mg/g), and ADMB400 (129.17mg/g). For all three biosorbents, the Co(II) removal remained effective within 50-100min; later it reached saturation. The kinetic analysis suggested strong Co(II) adsorption on AMDB surfaces. The Co(II)-AMDB biosorption data fits well with Temkin isotherm, indicating the heterogeneity on the biosorbent surface and no interaction between adsorbed Co(II)-Co(II) species. The thermodynamic analysis suggested the exothermic and spontaneous adsorption. The intraparticle diffusion of Co(II) within the biosorbent was surface diffusion controlled, as characterized by pore volume and surface diffusion model. The biosorbent reusability was 88.7% after five adsorption-desorption cycles. Thus, presently synthesized biosorbent could be novel and cost-effective for Co(II) and other heavy metal elimination from water bodies.

Polypyrrole/CoFe2O4 Nanocomposite for the Removal of Basic Blue 3 Dye From Wastewater: Kinetic, Adsorption Isotherm, and Thermodynamic Study

ABSTRACTWater contamination constitutes a substantial global issue that affects the environment. Adsorption materials have demonstrated huge potential in wastewater treatment. For the efficient removal of a cationic dye, basic blue 3 (BB3), a polypyrrole‐coated cobalt ferrite (PPy@CoFe2O4) magnetic nanosorbent is prepared via in situ polymerization of pyrrole on CoFe2O4 nanoparticles. Scanning electron microscopy (SEM) analysis demonstrated spherical nanoparticles with sizes around 50 nm, which was further supported by XRD data. Zeta‐potential study showed that the surface charge of PPy@CoFe2O4 is negative in alkaline media and positive in acidic media. The adsorption system adhered to a pseudo‐second‐order kinetic model, with the equilibrium time being determined at 50 min. The Langmuir model accurately simulated the adsorption isotherms. Under optimal conditions (pH—8.0, volume—30 mL, adsorbent dose—0.67 g/L, and at 303 K temperature), the maximum monolayer adsorption capacity of PPy/CoFe2O4 is 130.1 mg g−1. Even after five desorption–adsorption cycles, the removal efficiency remained above 92%. Negative ΔG° and ΔH° indicate spontaneous BB3 adsorption onto PPy/CoFe2O4, decreasing with temperature. These findings demonstrate that the PPy/CoFe2O4 composite is a highly effective adsorbent with broad potential applications for treating wastewater containing cationic dye.

Bifunctional adsorbents based on hyper-cross-linked polymers containing carbonyl and amine species for the efficient removal of diclofenac from water in a broad pH range.

Development of new adsorbents for the efficient removal of organic pollutants from water is one of the most emerging environmental issues. Current studies in this field focus on improving the adsorption capacity of various materials and/or broadening the pH range in which the adsorbents can efficiently remove target pollutants. In this study, we designed bifunctional hyper-cross-linked polymers (HCPs) containing both carbonyl and amine species to investigate the effect of amine functional groups on the efficiency of adsorptive removal of non-steroidal anti-inflammatory drugs (NSAIDs) from water. We revealed that post-synthesis functionalization of carbonyl-rich HCPs with amine species does not have a significant impact on the adsorption capacity of these polymers under strongly acidic conditions (pH < 4; qe ∼ 544 mg/g), but significantly extends the pH range in which bifunctional polymers can adsorb diclofenac. For example, at native pH (pH ∼ 6), bifunctional HCP-based adsorbents exhibited an adsorption capacity approximately 8 times higher than that of pristine materials (qe = 191 vs. 24 mg/g, respectively). Furthermore, it was revealed that the adsorbents designed in this study can efficiently remove diclofenac from complex water matrices and exhibit high stability in several adsorption-desorption cycles. Moreover, we demonstrated that selecting a cross-linker with a longer chain results in a polymer with a lower surface area and smaller average pore size, while enabling higher efficiency in amine incorporation via post-synthesis functionalization. This latter feature was crucial for ensuring the high adsorption capacity of HCP-based adsorbents in the removal of NSAID at neutral pH.

Synthesis and characterization of advanced Ad-UiO-66@NGO composite for efficient CO2 capture and CO2/N2 adsorption selectivity.

Highly effective adsorbents, with their impressive adsorption capacity and outstanding selectivity, play a pivotal role in technologies such as carbon capture and utilization in industrial flue gas applications, leading to significant reductions in greenhouse gas emissions. This study aims to synthesize advanced composites via solvothermal methods, incorporating a defective Zirconium-based MOF and amine-functionalized graphene oxide. The main objective is to enhance the CO2 adsorption capacity of the composite and improve its CO2/N2 separation selectivity. The samples were characterized using XRD, FT-IR, TGA, FE-SEM, and nitrogen adsorption and desorption analysis. The composites' gas uptake capacity toward pure CO2 and N2 adsorption were tested at various temperatures and pressure ranges of 1-9 bar. The resulting amino-defective UiO-66/NGO composite containing 15 wt.% of amine-modified GO, displayed the highest CO2 uptake capacity of 15.13 mmol/g at 298 K and 9 bar, representing a remarkable 48% increase compared to the pristine MOF. Furthermore, isotherm and kinetic modeling showed a high level of agreement between the experimental data and the Freundlich and Elovich models, as indicated by their R2 values of 0.998 and 0.973, respectively. Moreover, the thermodynamic evaluation confirmed the exothermic and the spontaneity of the reaction. Furthermore, the adsorbent's CO2/N2 selectivity was evaluated using the ideal adsorbed solution theory, revealing a remarkable selectivity value of 148. The regenerability evaluation through cyclic adsorption experiments showed that the optimized composite maintained CO2 adsorption reversibility at over 81.50% after 55 adsorption-desorption cycles.

Assessment of Long-Term Degradation of Adsorbents for Direct Air Capture by Ozonolysis.

Porous adsorbents are a promising class of materials for the direct air capture of CO2 (DAC). Practical implementation of adsorption-based DAC requires adsorbents that can be used for thousands of adsorption-desorption cycles without significant degradation. We examined the potential degradation of adsorbents by a mechanism that appears to have not been considered previously, namely, ozonolysis by trace levels of ozone from ambient air. We focused on amine-appended metal-organic frameworks, specifically amine-functionalized Mg2(dobpdc), as a representative DAC adsorbent. Estimates based on the number of amine sites in these adsorbents and the ozone concentration in air suggest that degradation by ozone may be relevant over thousands of adsorption-desorption cycles if reactions with adsorbed ozone are fast. We used density functional theory calculations to estimate reaction rates for amine groups and carbon-carbon double bonds in amine-functionalized Mg2(dobpdc).

High-Performance La-, Mo-, and W-Doped NiFe-Layered Double Hydroxide for Methyl Orange Dye and Cr(VI) Adsorption

NiFe-layered double hydroxide (NiFe-LDH) and La-, Mo- or W-doped NiFe-LDH microparticles (NiFeX-LDH, X = La, Mo, W) were synthesized via the co-precipitation method. Their adsorption characteristics were evaluated by the removal of methyl orange (MO) and hexavalent chromium (Cr6+). The effects of the metal ion doping type, doping concentration (0–3at%), pH and temperature on the MO adsorption properties were systematically studied. The results show that W-doped NiFe-LDH exhibits superior MO removal capacity compared to undoped or La- or Mo-doped NiFe-LDH at the same 1at% doping level, which is attributed to the increased layer charge density and strong affinity for the π-electron systems of MO molecules. The NiFeW-LDH-1at% sample demonstrated the best MO adsorption performance within the W-doping range of 0–3at%, achieving a superior adsorption capability of 666.67 mg/g with a significantly shorter equilibrium time (10–120 min) compared to the similar LDH. NiFeW-LDH-1at% showed promising reusability, with its adsorption efficiency remaining 78.3% of its initial level after five adsorption–desorption cycles. The MO uptake onto NiFeX-LDH was attributed to the combined effect of anion exchange and the attraction of layer charge. In addition, the adsorption of NiFeW-LDH-1at% matched well with the Langmuir isotherm model and pseudo-second-order kinetic model, indicating a monolayer and chemical adsorption. Furthermore, NiFeW-LDH-1at% effectively adsorbed of Cr2O72− in the aqueous solution, revealing that W doping significantly enhances Cr(VI) removal performance. The maximum theoretical adsorption capacity onto NiFeW-LDH-1at% reached 63.25 mg/g, which was notably higher than that of the pristine NiFe-LDH adsorbent (53.56 mg/g). Overall, the W-doped NiFe-LDH material, as a low-cost and highly efficient adsorbent, shows great potential for wastewater treatment application.

A novel fabrication of graphitic carbon nitride/chitosan composite modified with thiosemicarbazide for the effective static and dynamic adsorption of Pb2+ from aqueous media.

In this work, graphitic carbon nitride (g-C3N4) prepared by thermal treatment, graphitic carbon nitride/chitosan (GCS), and graphitic carbon nitride/chitosan embedded thiosemicarbazide (TGCS) were developed as an effective solid adsorbent. The fabricated adsorbents were characterized by nitrogen adsorption, ATR-FTIR, TGA, XRD, ζ potential, SEM, and TEM, where TGCS composite had a higher surface area (536.79 m2/g), total pore volume (0.4152 cm3 /g), average pore size (3.09 nm), and pHPZC (6.4). TGCS revealed a Langmuir adsorption capacity of 329.61 mg/g for Pb2+ at an adsorbent dosage of 1.5 g/L, pH 5, 45 min of shaking, and 23 °C. The experimental results were applied well by pseudo-second-order kinetic and Langmuir isotherm. Through the first five adsorption-desorption cycles, only 12.2, 6.2, and 5.1 % decline in efficiency were noted for g-C3N4, GCS, and TGCS, respectively. Column adsorption capacity (qo, mg/g) was determined to be 132.24 mg/g at bed height 3 cm, flow rate of 80 mL/min, and 80 mg/L as initial Pb2+ concentration. Based on the lower reduced chi-square values (ꭓ2 × 10-4, 3.8810-12.9000) and the higher correlation coefficients (R2, 0.9917-0.9979), the Yoon-Nelson and Thomas models suggested an acceptable match for the breakthrough curve. Our findings suggested that TGCS had great adsorption capacity, strong selectivity, and quick kinetics, indicating its potential for water treatment applications.