Adsorption Kinetic Tests Research Articles

Study of heavy metals adsorption using a silicate-based material: Experiments and theoretical insights

Heavy metal toxicity in water is a serious problem with harmful effects on human health and the ecosystem. This research studied a silicate-based material as an adsorbent for removing four heavy metals from aqueous solutions. The target metal pollutants selected include manganese (Mn2+), copper (Cu2+), cobalt (Co2+), and zinc (Zn2+). First, theoretical tools including potential energy surface analysis, Natural Population Analysis, AIM, Wiberg Bond Index, QTAIM, and topological methods offer profound insights into the nature of interactions present in the Mg2O8Si3M (M = Mn2+, Cu2+, Co2+, Zn2+) clusters. Second, the synthesis and characterization of eco-friendly hydrated amorphous magnesium silicate (MgOSiO2nH2O) was developed. Last, a simple kinetic adsorption test was applied to assess the material selectivity towards heavy metals and support theoretical results. The kinetic adsorption study was analyzed through the pseudo-first and second-order kinetics, Elovich, and the intraparticle diffusion models. The theoretical analysis of the adsorption energies indicates that the adsorption of four metal ions on the Mg2O8Si3 surface is energetically favorable in all cases. The material displayed the following adsorption sequence: Cu2+ (59 mg g-1) > Zn2+(25 mg g-1) ≈ Co2+ (23 mg g-1) > Mn2+ (15 mg g-1). This knowledge can then be used to design and optimize low-cost silicate-based materials for effective heavy metal removal, contributing to efforts to address environmental pollution and protect public health.

Amino-Functionalized Metal-Organic Frameworks Featuring Ultra-Strong Ethane Nano-Traps for Efficient C2H6/C2H4 Separation.

Developing high-performance porous materials to separate ethane from ethylene is an important but challenging task in the chemical industry, given their similar sizes and physicochemical properties. Herein, a new type of ultra-strong C2H6 nano-trap, CuIn(3-ain)4 is presented, which utilizes multiple guest-host interactions to efficiently capture C2H6 molecules and separate mixtures of C2H6 and C2H4. The ultra-strong C2H6 nano-trap exhibits the high C2H6 (2.38mmolg-1) uptake at 6.25kPa and 298K and demonstrates a remarkable selectivity of 3.42 for C2H6/C2H4 (10:90). Additionally, equimolar C2H6/C2H4 exhibited a superior high separation potential ∆Q (2286mmolL-1) at 298K. Kinetic adsorption tests demonstrated that CuIn(3-ain)4 has a high adsorption rate for C2H6, establishing it as a new benchmark material for the capture of C2H6 and the separation of C2H6/C2H4. Notably, this exceptional performance is maintained even at a higher temperature of 333K, a phenomenon not observed before. Theoretical simulations and single-crystal X-ray diffraction provide critical insights into how selective adsorption properties can be tuned by manipulating pore dimensions and geometry. The excellent separation performance of CuIn(3-ain)4 has been confirmed through breakthrough experiments for C2H6/C2H4 gas mixtures.

Sequential adsorption- dehalogenation removal of PFOA and 2,4,6-TCP with F-CTF as the adsorbent and hydrated electron as the reduction species

Perfluorooctanoic acid (PFOA) and 2,4,6-trichlorophenol (2,4,6-TCP) were typical POPs (Persistent Organic Pollutants) in water. In this study, fluorine-doped covalent triazine framework (F-CTF) was synthesized using an ionothermal method, and the adsorption behavior for PFOA and 2,4,6-TCP on F-CTF was investigated using batch experiments and adsorption kinetic tests. Characterization results showed that the large surface area and abundant pore structure of F-CTF provide a large number of adsorption sites for PFOA and 2, 4, 6-TCP. Batch adsorption tests showed that F-CTF adsorbent exhibited high adsorption affinity to PFOA and 2,4,6-TCP, and the adsorption ability could be described well by the Langmuir adsorption model. The maximum adsorption capacity (qmax) of F-CTF for PFOA and 2,4,6-TCP reached 262.5 mg/g and 709.2 mg/g, respectively. The adsorption process obeyed the pseudo-second-order kinetics. The adsorption mechanism including electrostatic attraction, hydrophobic interaction, and ion-dipole interaction was further confirmed by pH and ionic strength experiments. Additionally, the UV/Na2SO3/KI system achieved 100 % degradation rate of PFOA and 2, 4, 6-TCP within 40 minutes and the influence factors were further studied. The eaq− was the main active species for the high reduction of PFOA and 2,4,6-TCP in the UV/Na2SO3/KI system.

Selective recovery of copper from copper tailings and wastewater using chelating resins with bis-picolylamine functional groups

Industrial and mining wastewater, along with copper tailings, are typically highly acidic and contain copper and other heavy metals, which may contaminate and damage the environment. Copper (Cu) is, however, a valuable metal, making its removal and recovery from such wastewater and tailings environmentally and economically advantageous. Chelating ion exchange resins featuring bis-picolylamine functional groups are especially suitable for application requiring selective recovery of Cu(II) from highly acidic media. In this study, and for the first time, the kinetics, binding capacity and selectivity of Lewatit MDS TP 220 chelating resin towards Cu(II) are reported. The resin was characterized by Zeta potential, scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Factors including pH, initial concentration, contact time, temperature, and selectivity were investigated to assess the adsorption performance of the chelating resin. The adsorption kinetics tests revealed fast adsorption within the first 5–30 min and fitted the pseudo-second-order model, signifying chemisorption process. The adsorption isotherm followed the Langmuir model, implying monolayer adsorption process. The maximum adsorption capacity (qm) for Cu(II) determined by the Langmuir model was 103.9 mg/g. The adsorption thermodynamics showed an endothermic and spontaneous adsorption. FTIR and XPS studies suggested coordination or chelation as the possible adsorption mechanism. Lewatit MDS TP 220 exhibited excellent Cu(II) adsorption, desorption with 2 M ammonium hydroxide (NH4OH), and selectivity in multi-metal ions solution. Additionally, the resin demonstrated excellent reusability after five regeneration steps. This chelating resin is a potential adsorbent for effective and recurrent recovery of Cu(II) from copper tailings and wastewater, thereby contributing to environmental remediation.

Effect of dry-wet alternation on the adsorption of dissolved organic matter by soil minerals

Dry-wet alternation has an essential effect on soil minerals' adsorption of dissolved organic matter. In this study, kaolin, illite, and hematite were subjected to 0, 1, 3, and 6 dry-wet alternation incubation tests, respectively, and the changes in the characterization of the three minerals were explored by using a BET specific surface area analyzer and an X-ray diffractometer. The effects of different dry-wet alternation treatments on the adsorption of tannic acid and glucose as the representatives of dissolved organic matter were investigated by isothermal and kinetic adsorption tests as well as by different model-fitting methods. The effects of different dry-wet alternation treatments on the adsorption of tannic acid and glucose by the three minerals were investigated by isothermal and kinetic adsorption tests and different model fitting methods. The results showed that alternating dry-wet treatment could change the three minerals' specific surface area and average pore diameter to different degrees. Still, the spacing of the crystal layers did not change significantly. The dry-wet alternation did not alter the adsorption process and tannic acid and glucose adsorption mode. Still, it affected the equilibrium adsorption amount to different degrees, which was illite>hematite>kaolin, and the intensity of the effect was mainly affected by the decrease of the specific surface area of the minerals, which was not related to the change of the average pore diameter and the spacing of the crystal layers.

Utilization of oyster shell nano-hydroxyapatite modified red-brick waste as an environmentally friendly composite filler for Cd(II) and Cr(VI) adsorption: Preparation, property and mechanism

The ongoing process of urbanization in China has led to a growing concern regarding environmental contamination caused by the significant accumulation of construction demolition trash. This study employs the water thermal method to synthesize hydroxyapatite using natural waste oyster shells as the primary raw material. This study explores the use of synthesized hydroxyapatite (O-HA) on building waste red-brick fragments (RBF) for removing cadmium (Cd(II)) and chromium (Cr(VI)) from water. The RBF fillers, both before and after modification, underwent comprehensive characterization using various techniques, including automated analysis of specific surface area and porosity (BET), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). In the sixth cycle of purification experiments, the average removal rate of Cd(II) by O-HA-modified red-bricks (O-HA/RBF) could still reach 88.18 %, which was about 20.00 % higher than that of the RBF. However, the removal of Cr(VI) by O-HA/RBF was unsatisfactory at 5.33 %. The adsorption mechanisms of Cd(II) and Cr(VI) were explored by isothermal adsorption tests and adsorption kinetic tests. According to the mechanism analysis, physical adsorption and chemical adsorption were the main reasons for Cd(II) adsorption by O-HA/RBF. This involves ion exchange and surface complexation between calcium ions in O-HA and Cd(II), forming a low-solubility precipitate for effective removal. However, for Cr(VI), physisorption predominantly governs O-HA/RBF, elucidating the limited efficacy in Cr(VI) removal. The cost analysis showed that using O-HA/RBF as filler reduced overall expenses in wetland development, offering promising prospects for engineering applications.

BIOADSORVENTES DE RESÍDUOS DA AGROINDÚSTRIA UTILIZADOS NA REMOÇÃO DE Cd(II)

BIOADSORBENTS FROM AGROINDUSTRIAL WASTE USED IN Cd(II) REMOVAL. The use of agroindustry waste in the synthesis of bioadsorbents provides a solution to reduce the disposal of solid waste in the environment while increasing the added value of recovering locally sourced waste. However, technical and environmental issues must be considered when selecting the appropriate synthesis method to avoid creating a new environmental impact and evaluate the feasibility of applying the method. In this work, yellow mombin, guava and mango seeds were used to synthesize bioadsorbents capable of removing cadmium(II) in solution. The materials were characterized according to their chemical composition, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and evaluated by adsorption kinetics tests. Energy analysis of biomass processing was performed by life cycle analysis (LCA). The bioadsorbents presented typical characteristics of lignocellulosic biomass, with the presence of functional groups favorable to the adsorption of metals and were effective in removing cadmium(II), with efficiency of 95.7, 92.4 and 60.2%, for BSG (guava seed bioadsorbent), BSC (yellow mombin seed bioadsorbent) and BSM (mango seed bioadsorbent), respectively. The error functions provided a more appropriate criterion for analyzing the kinetic data. The methodology proposed in this work is simple to implement and has a low estimated energy demand, therefore being promising for application in small fruit processing industries in the semi-arid region of Bahia.

The implementation of ZnS–SnS BM NPs for phenanthrene degradation: An adsorptive photocatalyst approach and its toxicity studies in adult zebrafish

Phenanthrene is a persistent organic pollutant released by numerous industries. The purpose of the study is to construct a batch reactor for phenanthrene degradation using a bimetallic (BM) ZnS–SnS nanoparticle as a photocatalyst. ZnS–SnS BM NPs were used as a photocatalyst, employed from precursors Zinc acetate dihydrate and tin (II) chloride dihydrate, with crystalline cubic-shaped particle sizes. ZnS–SnS BM NPs were utilized in batch adsorption assays to assess the impact of phenanthrene degradation parameters on various PAHs (Polycyclic aromatic hydrocarbons) concentrations, pH levels, and irradiation sources. Adsorption kinetic and isotherm tests revealed that the pseudo-first order kinetic model, pseudo-second order kinetic model, and Langmuir isotherm model all fit effectively with the effective phenanthrene degradation using ZnS–SnS BM NPs. The degraded product were analyzed for GC-MS, revealing that organic pollutant phenanthrene was converted into harmless by-products like n-hexadecenoic acid, oleic acid, and octadecanoic acid. The toxicity of phenanthrene was observed to decrease with an increase in ZnS–SnS BM NPs concentration. ZnS–SnS BM NP concentration of 150 μg/mL, the zone of inhibition values was recorded highest zone of inhibition (19 ± 1.2 mm) against the strains S. epidermis followed by B. cereus and Clostridium spp. Further adult zebrafish were found to be less toxic to ZnS–SnS BM NPs after 96 h of exposure, with an LD50 of 100 μg/L. The toxicity escalated as concentrations increased. Behavior test showed normal swimming, learning, and memory in open tank and T-maze tests, while 100 μg/L showed pausing/frozen time in zebra fish therefore low doses are considered safe. Hence by employing ZnS–SnS BM NPs can be engaged in waste water treatment for PAH degradation.

Aqueous and solid phase photocatalytic degradation of perfluorooctane sulfonate by carbon- and Fe-modified bismuth oxychloride

In this study, we prepared and tested a carbon-modified, Fe-loaded bismuth oxychloride (Fe–BiOCl/CS) photocatalyst for photocatalytic degradation of perfluorooctane sulfonate (PFOS). Structural analyses revealed a (110) facet-dominated sheet-type BiOCl crystal structure with uniformly distributed Fe and confirmed carbon modification of the photocatalyst. The presence of d-glucose facilitated the growth control of BiOCl particles and enhanced the adsorption of PFOS via added hydrophobic interaction. Adsorption kinetic and equilibrium tests showed rapid uptake rates of PFOS and high adsorption capacity with a Langmuir Qmax of 1.51 mg/g. When used for directly treating PFOS in solution, Fe–BiOCl/CS was able to mineralize or defluorinate 83% of PFOS (C0 = 100 μgL−1) under UV (254 nm, intensity = 21 mW cm−2) in 4 h; and when tested in a two-step mode, i.e., batch adsorption and subsequent photodegradation, Fe–BiOCl/CS mineralized 65.34% of PFOS that was pre-concentrated in the solid phase under otherwise identical conditions; while the total degradation percentages of PFOS were 83.48% and 80.50%, respectively, for the two experimental modes. The photoactivated electrons and/or hydrated electrons and superoxide radicals primarily initiated the desulfonation of PFOS followed by decarboxylation and defluorination, through a stepwise chain-subsiding mechanism. The elevated photocatalytic activity can be attributed to the effective separation of e−/h+ pairs facilitated by the (110) interlayer electrostatic field, Fe doping, and the presence of oxygen vacancies. This work reveals the potential of carbon-modified and Fe-co-catalyzed BiOCl for concentrating and degrading PFOS and possibly other persistent organic pollutants.

Removal of short- and long-chain PFAS from aquatic systems using electrostatic attraction of polyethylenimine-polyvinyl chloride electrospun nanofiber adsorbent

The presence of per- and polyfluoroalkyl substances (PFAS) in the water environment raises serious concerns due to their persistence and toxicity that links to adverse health consequences. Short-chain PFAS are more challenging to remove from water by adsorption than long-chain PFAS due to the weaker hydrophobic interaction, and conventional adsorbents usually demonstrated poor PFAS adsorption capacities near neutral pH. We have examined a novel polyethylenimine-polyvinyl chloride electrospun nanofiber (PEI-PVC NF) adsorbent to improve the adsorption capacity of both short- [perfluorobutanoic acid (PFBA) and perfluorobutanesulfonic acid (PFBS)] and long-chain [perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)] PFAS by maximizing electrostatic attraction using a PEI functional group with nanopore structure. At pH 7, PEI-PVC NF demonstrated adsorption capacities of 84.26 mg/g for PFBA and 214.37 mg/g for PFBS (short-chain PFAS), and 213.76 mg/g for PFOA and 326.39 mg/g for PFOS (long-chain PFAS). These adsorption capacities were only 20.1–61.3% lower than those obtained under acidic conditions. Excellent adsorption capacities by PEI-PVC NF are likely due to the strong electrostatic attraction with PEI under acidic to neutral pHs as well as pore-mediated adsorption driven by nanopore structure. The isotherm adsorption data were well fitted with the Langmuir model, which supports dominant monolayer adsorption driven by electrostatic attraction. Maximum adsorption capacities (qmax, 98.70 mg/g for PFBA, 222.36 mg/g for PFBS, 234.85 mg/g for PFOA, and 319.82 mg/g for PFOS) were superior to adsorbents that were previously reported at pH 7. Adsorption kinetic tests demonstrated remarkable PFAS adsorption rates (reached equilibrium in 300 min) by PEI-PVC NF likely driven by electrostatic and intraparticle diffusion into nanopores.

Boosting kinetic separation of ethylene and ethane on microporous materials via crystal size control

The adsorptive separation of C2H4 and C2H6, as an alternative to distillation units consuming high energy, is a promising yet challenging research. The great similarity in the molecular size of C2H4 and C2H6 brings challenges to the regulation of adsorbents to realize efficient dynamic separation. Herein, we reported the enhancement of the kinetic separation of C2H4/C2H6 by controlling the crystal size of ZnAtzPO4 (Atz = 3-amino-1,2,4-triazole) to amplify the diffusion difference of C2H4 and C2H6. Through adjusting the synthesis temperature, reactant concentration, and ligands/metal ions molar ratio, ZnAtzPO4 crystals with different sizes were obtained. Both single-component kinetic adsorption tests and binary-component dynamic breakthrough experiments confirmed the enhancement of the dynamic separation of C2H4/C2H6 with the increase in the crystal size of ZnAtzPO4. The separation selectivity of C2H4/C2H6 increased from 1.3 to 98.5 with the increase in the crystal size of ZnAtzPO4. This work demonstrated the role of morphology and size control of adsorbent crystals in the improvement of the C2H4/C2H6 kinetic separation performance.

Synthesis of nanosized IM-5 zeolite and its CH4/N2 adsorption and separation

Reduction of zeolite crystal size from the micron scale to the nanoscale leads to a significant increase in specific surface area, favoring mass-transfer pathways. Here, we have prepared nanoscale (ca. 30–80 nm) IM-5@100 zeolite (IMF type) by a facile strategy of regulating the amount of Al source in the starting gel, and have investigated its CH4/N2 adsorption and separation properties. We found that on decreasing the amount of Al source, the crystal size of the product changed significantly, decreasing from strips of length about 1 μm to irregular nanocrystals. Compared with micron-sized IM-5@50, the mesopore volume of IM-5@100 was increased fourfold from 0.12 cm3/g to 0.49 cm3/g, its external surface area was increased from 38 m2/g to 118 m2/g, and its DFT pore size distribution based on N2 adsorption/desorption showed a mesopore distribution in the range 5–10 nm. Adsorption kinetics tests showed that nano-IM-5@100 can achieve adsorption equilibrium more swiftly and exhibits better mass-transfer performance. Moreover, IM-5@100 showed good adsorption capacity for CH4 (17.8 cm3/g) and high IAST selectivity (4.7) for CH4/N2 (50:50, v/v). Breakthrough experiments have indicated that IM-5@100 permits efficient practical separation of CH4/N2.

Comparison of Kinetics of Adsorption of Permanganate on Co-Al-Layered Double Hydroxide and MoS2 Nanocompounds.

Permanganate ions were adsorbed on carbonate intercalated Co-Al-layered double hydroxide (Co-Al-LDH) and MoS2 and after a while the adsorbed ions were reduced to MnO2. Reduction of adsorbed ion was catalyzed on the surface of carbonate intercalated Co-Al-LDH but ions reacted with MoS2 surface. Adsorption kinetic tests were carried out at different temperatures, ionic strengths, pH, initial adsorbate concentrations and shaking rates. The adsorption kinetics was studied by the kinetics of adsorption study in the regions with constant adsorption acceleration (KASRA) model and KASRA, ideal-second-order (ISO), intraparticle diffusion, Elovich and (non-ideal process of adsorption kinetics (NIPPON) equations.In this work, a new equation called NIPPON equation was introduced. In this equation, it was assumed that during a non-ideal process, adsorbate species molecules were adsorbed simultaneously on the same type adsorption sites with different activities. Indeed, the average values of adsorption kinetic parameters were calculated by the NIPPON equation. Also, the character of boundaries of regions obtained from the KASRA model can be determined by this equation.

Adsorption Characteristics of Cd2+ Ions in Aqueous Solution on Modified Straw Biochar

Rice straw and corn straw were selected as raw materials to prepare biocharby anoxic carbonization and the biochar was loaded on the surface with FeCl3, MnCl2 and Fe(NO3)3 & KMnO4, respectively, and then two types of straw biochar and six types of modified biochar were prepared. FT-IR, SEM, and XRD were used to characterize and analyze the physical and chemical properties of the biochar. The adsorption kinetics and adsorption isothermal tests of Cd2+ ions in aqueous solution were carried out. The results showed that modified biochars attached more active sites and surface group, especially iron-manganese-modified biochar (FMBC1, FMBC2). The kinetic adsorption tests showed that the adsorption process of eight kinds of biochar all conformed to the quasi-second-order kinetic equation, and chemisorption maybe dominated the adsorption process. The adsorption isothermal test showed that the adsorption process of Cd2+ ions by FeCl3-modified biochar (FBC1, FBC2) and Fe(NO3)3 & KMnO4-modified biochar (FMBC1, FMBC2) conforms to the Freundlich model, and the adsorption process of Cd2+ ions by MnCl2-modified biochar (MBC1, MBC2) conforms to Langmuir model. Compared with other kinds of biochar, the KF value of Fe(NO3)3 & KMnO4-modified biochar of rice straw biochar (FMBC1) was the largest, reached 18.602 L·mg−1, and its 1/n value was the smallest, it reached 0.474, indicating that the adsorption effect on Cd2+ of FMBC1 was the best.

Adsorption mechanism of shell powders on heavy metal ions Pb2+/Cd2+ and the purification efficiency for contaminated soils

The adsorption capacity of oyster shell powders (SPs) and the adsorption mechanism of heavy metal ions (HMs; i.e., cadmium ions Cd2+ and lead ions Pb2+) on SPs are discussed by means of adsorption kinetics tests, adsorption-desorption tests, scanning electron microscopy and Fourier transform infrared spectroscopy. The influences of seepage velocity, heavy metal types, and SP addition amount/concentration on the adsorption effect of SPs in the treatment of HMs in laterite as well as quartz sand were analyzed. Studies have shown that i) the adsorption of HMs on SPs can be divided into three stages, i.e., the surface adsorption stage, the internal pore diffusion stage, and the equilibrium stage; ii) with the increase in seepage velocity, the effluent concentration of HMs will slightly increase, and the residual amounts at each section of the column generally decrease rapidly with the increase in migration distance; iii) the increase in the concentration of SP solution provides more adsorption points for the adsorption of HMs, and finally, the amount of HMs desorbed from quartz sand is reduced, which also reduces the concentration of HMs in the effluent. Overall, SPs possess high purification efficiency for the HMs of contaminated soils.

Hydrochar alleviated the inhibitory effects of polyvinyl chloride microplastics and nanoplastics on anaerobic granular sludge for wastewater treatment

The exposure to microplastics (MPs) and nanoplastics (NPs) has been confirmed to exhibit significant inhibitory effects on anaerobic granular sludge (AGS) for wastewater treatment, with effective mitigation strategies being accordingly imperative. Herein, this study innovatively proposed a strategy for mitigating inhibitory effects of MPs/NPs on AGS system based on coconut shell-derived hydrochar through efficiently capturing the existing polyvinyl chloride microplastics and nanoplastics (PVC-MPs and PVC-NPs) from AGS. The hydrochar increased methane production of AGS from 69.4% to 76.2% and from 65.6% to 91.4% of control when the AGSs were exposed to PVC-MPs and PVC-NPs, respectively. More extracellular polymeric substance (EPS) was secreted with the existence of hydrochar, which enhanced the protective capabilities AGS held to against the negative effects from the external toxicity of PVC-MPs and PVC-NPs, thus maintaining better AGS integrity regarding granule size and cell viability (especially for the PVC-NPs affected AGS). The hydrochar showed stronger adsorption capability to PVC-MPs and PVC-NPs than AGS, confirmed by their characteristics and adsorption kinetic tests. As a result, less plastic particles would attach AGS, inducing less oxidative stress to the microbes. Specially, it would also be less likely for PVC-NPs to penetrate through AGS surface and enter the internal core, retaining better richness of bacteria such as Bacteroidales and Syntrophobacterales in AGS. This work demonstrated hydrochar effectively alleviated the suppression on AGS caused by PVC-MPs and PVC-NPs, providing a novel strategy for improving the wastewater treatment performance under the stress of MPs and NPs.

Amino-Functionalized Microporous MOFs for Capturing Greenhouse Gases CF4 and NF3 with Record Selectivity

The capture and separation of fluorinated gases (F-gases) from N2 has the potential to not only reduce greenhouse gas emissions but also provide economic benefits for the semiconductor industry. In this work, two Ni-based metal-organic frameworks (MOFs), Ni-MOF (Ni(ina)2, ina = isonicotinic acid) and amine-functionalized NH2-Ni-MOF (Ni(3-ain)2, 3-ain = 3-aminoisonicotinic acid), were constructed for capturing F-gases (CF4 and NF3). At ambient conditions, both materials exhibit very high CF4 sorption capacities (2.92 mmol g-1 for Ni-MOF and 2.69 mmol g-1 for NH2-Ni-MOF). In addition, NH2-Ni-MOF exhibited a record selectivity of 46.3 for the CF4/N2 mixture at 298 K and 100 kPa, surpassing all benchmark adsorbents, including Ni-MOF (34.7). The kinetic adsorption tests demonstrated that Ni-MOF and NH2-Ni-MOF performed well for CF4/N2 and NF3/N2 mixtures. According to grand canonical Monte Carlo (GCMC) simulations, CF4 or NF3 interacts with NH2-Ni-MOF by multiple van der Waals interactions, resulting in stronger interaction than N2. More importantly, dynamic breakthrough experiments verified the practical separation potential of the two materials for CF4/N2 and NF3/N2 mixtures.

The nitrogen-doped graphene-like carbon nanosheets: Confined construction and oxygen-limited oxidation for higher removal efficiency toward organic contaminants

Due to the excellent properties, including large specific surface area, stable structure, and strong adsorbability, mesoporous carbon material has captured a lot of attention and applied to various fields. Here, we proposed a facile approach to synthesize nitrogen-doped graphene-like carbon (NGLC) nanosheets and investigated the performance in wastewater decontamination. In this work, NGLC nanosheets were obtained via the combination of confined synthesis and low-temperature calcination in oxygen-limited condition. Such NGLC nanosheets were composed of several carbon layers with porous structure, which provided a large specific surface area (421.85 m2 g−1). Meanwhile, the NGLC was endowed with abundant active sites, including oxygen-contained groups and nitrogen species, via low-temperature calcination in oxygen-limited conditions. These properties allow the NGLC to be an excellent adsorbent for organic pollution treatment. The maximum adsorption capacities toward cationic dyes, the rhodamine B (RhB) and methylene blue (MB), reached as high as 1272.74 mg g−1 and 679.55 mg g−1, respectively, indicating the promising potential for the cationic contaminants treatment. The excellent reusability and wide pH suitability (2–10) were observed by batch adsorption experiments. The kinetic adsorption test showed that 98.97% of RhB could be adsorbed by NGLC-450 after 150 min contact time at 25 °C, while the RhB removal efficiencies from bulk polydopamine derived carbon material (denoted as PDA carbon) and NGLC-450-Ar (generated at argon atmosphere) were only 17.56% and 62.03%, respectively. The significant difference in adsorption performance implied the importance of confined synthesis with template-assistance and oxygen-limited oxidation. The adsorption process involved the pore filling & adsorption, electrostatic interaction, and π-π interaction, as well as the hydrogen bonding, which was demonstrated by experiment and Fourier transform infrared (FT-IR) & X-ray photoelectron spectroscopy (XPS) analysis.

Adsorption Characteristics and Mechanisms of Fe-Mn Oxide Modified Biochar for Pb(II) in Wastewater.

This study prepared iron-manganese oxide-modified biochar (FM-BC) by impregnating rice straw biochar (BC) with a mixed solution of ferric nitrate and potassium permanganate. The effects of pH, FM-BC dosage, interference of coexisting ions, adsorption time, incipient Pb(II) concentration, and temperature on the adsorption of Pb(II) by FM-BC were investigated. Moreover, the Pb(II) adsorption mechanism of FM-BC was analyzed using a series of characterization techniques. The results showed that the Fe-Mn oxide composite modification significantly promoted the physical and chemical functions of the biochar surface and the adsorption capacity of Pb(II). The specific surface area of FM-BC was 18.20 times larger than that of BC, and the maximum Pb(II) adsorption capacity reached 165.88 mg/g. Adsorption kinetic tests showed that the adsorption of Pb(II) by FM-BC was based on the pseudo-second-order kinetic model, which indicated that the adsorption process was mainly governed by chemical adsorption. The isothermal adsorption of Pb(II) by FM-BC conformed to the Langmuir model, indicating that the adsorption process was spontaneous and endothermic. Characterization analyses (Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy) showed that the adsorption mechanism of Pb(II) by FM-BC was mainly via electrostatic adsorption, chemical precipitation, complexation, ion exchange, and the transformation of Mn2O3 into MnO2. Therefore, FM-BC is a promising adsorbent for Pb(II) removal from wastewater.

Role of ionic concentration in the kinetic attachment of kaolinite and sand

Clay particle deposition in porous media is critical in many geotechnical applications that rely on filtration. The deposition of particles in the filter medium can result in clogging, which causes a reduction in the hydraulic conductivity of the filter medium. Particle attachment and detachment are a function of the interaction energy between clay particles and the filter bed material, which is frequently sand. These mechanisms are governed by the size of the clay particles as well as the solution chemistry. Batch kinetic adsorption tests were carried out to investigate the impact of ionic strength on the attachment of kaolinite to silica sand grains. Significant attachment of kaolinite was observed as ionic strength of the pore fluid increased and as the size of silica particles decreased. The short-term deposition of clay particles was not sensitive to ionic strength; however, in contrast, long-term deposition was a strong function of ionic strength.