Mechanistic insights into ball milling enhanced montmorillonite modification with tetramethylammonium for adsorption of gaseous toluene

Aminated clay-polymer composite as soil amendment for stabilizing the short- and long-chain per- and poly-fluoroalkyl substances in contaminated soil

Soils contaminated with per- and poly- fluoroalkyl substances (PFAS) require immediate remediation to protect the surrounding environment and human health. A novel animated clay-polymer composite was developed by applying polyethyleneimine (PEI) solution onto a montmorillonite clay-chitosan polymer composite. The resulting product, PEI-modified montmorillonite chitosan beads (MMTCBs) were characterized as an adsorptive soil amendment for immobilizing PFAS contaminants. The MMTCBs exhibited good efficiency to adsorb the PFAS, showing adsorption capacities of 12.2, 16.7, 18.5, and 20.8 mg g-1 for PFBA, PFBS, PFOA, and PFOS, respectively, which were higher than those obtained by granular activated carbon (GAC) (i.e., an adsorbent used as a reference). Column leaching tests demonstrated that amending soil with 10% MMTCBs resulted in a substantial decrease in the leaching of PFOA, PFOS, PFBA, and PFBS by 90%, 100%, 64%, and 68%, respectively. These reductions were comparable to the values obtained for GAC-modified soil, particularly for long-chain PFAS. Incorporating MMTCBs into the soil not only preserved the structural integrity of the soil matrix but also enhanced its shear strength (kPa). Conversely, adding GAC to the soil resulted in a reduction of the soil's mechanical properties.

Pristine and modified biochar applications as multifunctional component towards sustainable future: Recent advances and new insights

Employing biomass for environmental conservation is regarded as a successful and environmentally friendly technique since they are cost-effective, renewable, and abundant. Biochar (BC), a thermochemically converted biomass, has a considerably lower production cost than the other conventional activated carbons. This material's distinctive properties, including a high carbon content, good electrical conductivity (EC), high stability, and a large surface area, can be utilized in various research fields. BC is feasible as a renewable source for potential applications that may achieve a comprehensive economic niche. Despite being an inexpensive and environmentally sustainable product, research has indicated that pristine BC possesses restricted properties that prevent it from fulfilling the intended remediation objectives. Consequently, modifications must be made to BC to strengthen its physicochemical properties and, thereby, its efficacy in decontaminating the environment. Modified BC, an enhanced iteration of BC, has garnered considerable interest within academia. Many modification techniques have been suggested to augment BC's functionality, including its adsorption and immobilization reliability. Modified BC is overviewed in its production, functionality, applications, and regeneration. This work provides a holistic review of the recent advances in synthesizing modified BC through physical, chemical, or biological methods to achieve enhanced performance in a specific application, which has generated considerable research interest. Surface chemistry modifications require the initiation of surface functional groups, which can be accomplished through various techniques. Therefore, the fundamental objective of these modification techniques is to improve the efficacy of BC contaminant removal, typically through adjustments in its physical or chemical characteristics, including surface area or functionality. In addition, this article summarized and discussed the applications and related mechanisms of modified BC in environmental decontamination, focusing on applying it as an ideal adsorbent, soil amendment, catalyst, electrochemical device, and anaerobic digestion (AD) promoter. Current research trends, future directions, and academic demands were available in this study.

Defective UiO-66 metal-organic gels for optimizing gaseous toluene capture

Developing high-performance sorbents for volatile organic compounds (VOCs) is urgently required for environmental cleaning and personnel protection. Zirconium-based metal-organic frameworks (Zr-MOFs) have been deemed attractive candidates for gaseous toluene capture due to their superior stability and high adsorption capacity. However, the practical application of powdered Zr-MOFs is hindered by inherent limitations. Here, we report a series of defective UiO-66 metal-organic gels (G66-X) with variable missing linker deficiency by altering the modulator concentration. The defect concentration of the adsorbents has a significant impact on the porosity and gaseous toluene adsorption capacity. Dynamic breakthrough results reveal that G66-9 demonstrates optimal breakthrough time of 336 min/g and uptake amount of 334 mg/g, outperforming those of many other typical toluene adsorbents. The breakthrough times and the uptake capacities dramatically decrease with the increase of adsorption temperature. An outstanding regeneration performance of adsorbents can almost maintain even after five adsorption-desorption cycles.

Containment of phenol-impacted groundwater by vertical cutoff wall with backfill consisting of sand and bentonite modified with hydrophobic and hydrophilic polymers

A novel soil-bentonite backfill is proposed for use in vertical cutoff walls to contain phenol in groundwater at contaminated sites. The backfill consists of sand and bentonite modified with tetramethylammonium and carboxymethylcellulose, labeled as STCMB backfill. Flexible-wall permeability and double-reservoir diffusion tests were conducted to investigate the impact of phenol solution on hydraulic conductivity (k), effective diffusion coefficient (D*) and partition coefficient (Kp) of the backfill, respectively. The permeability results showed k of the STCMB backfill decreased by 0.91 times when the permeating liquid was changed from tap water to phenol solution. The diffusion testing results showed that D* values for the STCMB and conventional backfill (labeled as SCB backfill) were 4.0 × 10-10 m2/s and 3.0 × 10-10 m2/s, respectively, whereas Kp values for the STCMB and SCB backfills were 2.0 mL/g and 0.75 mL/g, respectively. The octanol-water partition coefficient model is suitable for estimating Kp for nonpolar organics. Furthermore, a series of solute transport simulations using Pollute V7 program was performed to evaluate the performance of vertical cutoff walls comprising STCMB and SCB backfills in containing phenol in lateral flowing groundwater. Overall, the STCMB backfill has demonstrated superior effectiveness in containing phenol in groundwater.

Novel Floating Adsorbent for Water Treatment: Organically Modified Layered Alkali Silicate by Facile Mechanochemical Reaction

Adsorption serves as an effective way to collect (remove) contaminants from aqueous solution. In the present study, a novel floating adsorbent was designed through surface modification of a layered alkali silicate (octosilicate) using a silane coupling reagent (chlorodimethyl[3-(2,3,4,5,6-pentafluorophenyl)propyl]silane) to collect metal ions from water. By conducting the grafting by solvent-free mechanochemical reaction at room temperature, the external surface of octosilicate was modified to be hydrophobic while preserving the ion exchange capability in the interlayer space. Characterizations of XRD, IR, SEM, TGA, 29Si MAS NMR, and 19F MAS NMR confirmed the successful grafting at the external surface of octosilicate particles. The modified silicate demonstrated buoyancy at the air-water interface, facilitating the concentration of methylene blue, Ni2+, and Pb2+ from aqueous solutions. The adsorbed amounts of metal ions on the floating adsorbent were greater than those reported for the common nonfloating adsorbents (zeolites, clays, and clay minerals).

Removal of hydrogen sulfide in the gas phase by carbide slag modified bentonite

Bentonite-based adsorbents for the removal of hydrogen sulfide (H₂S) were prepared by a wet-mixing method using carbide slag as the active component. The effects of carbide slag content, calcination temperature, calcination time, and reaction temperature on the H₂S adsorption capacity were investigated. The results showed that compared with the blank bentonite adsorbent, the carbide slag-modified bentonite-based adsorbent enhanced the chemisorption of H₂S. The adsorption capacity of the carbide slag modified bentonite adsorbent (2.50 mg g^-1) was more than 40 times higher than that of the blank bentonite-based adsorbent (0.06 mg g^-1) under optimal conditions. The optimal conditions for H₂S removal were 3 : 5 ratio of carbide slag-to-bentonite, calcination temperature of 450 °C for 2 h, and reaction temperature of 95 °C. H₂S was mainly removed in the mesopores and macropores of the adsorbent and was finally transformed to CaS and sulfate on the adsorbent surface. The adsorption process of H₂S followed the Freundlich adsorption isotherm equation and Bangham adsorption kinetic model.

Comparison of Salvianolic Acid A Adsorption by Phenylboronic-Acid-Functionalized Montmorillonites with Different Intercalators

Due to its success in treating cardio-cerebrovascular illnesses, salvianolic acid A (SAA) from Salvia miltiorrhiza is of major importance for effective acquisition. For the adsorption of salvianolic acid, cationic polyelectrolytes, and amino-terminated silane intercalated with phenylboronic-acid-functionalized montmorillonites, known as phenylboronic-acid-functionalized montmorillonites with PEI (PMP) and phenylboronic-acid-functionalized montmorillonites with KH550 (PMK), respectively, were produced. In this paper, detailed comparisons of the SAA adsorption performance and morphology of two adsorbents were performed. PMP showed a higher adsorption efficiency (>88%) over a wide pH range. PMK showed less pH-dependent SAA adsorption with a faster adsorption kinetic fitting in a pseudo-second-order model. For both PMP and PMK, the SAA adsorption processes were endothermic. Additionally, it was clearer how temperature affected PMP adsorption. PMK has a higher adsorption selectivity. This study demonstrates how the type of intercalator can be seen to have an impact on adsorption behavior through various structural variations and offers an alternative suggestion for establishing a dependable method for the synthesis of functional montmorillonite from the intercalator's perspective.

Enhanced Chromium (VI) Adsorption onto Waste Pomegranate-Peel-Derived Biochar for Wastewater Treatment: Performance and Mechanism

Surface chemical modification allows for the rational construction of biochar with desirable structures and functionalities for environment purification. Fruit-peel-derived adsorbing material has been well studied in the adsorption of heavy-metal removal due to its abundance and non-toxicity, but its precise mechanism in removing chromium-containing pollutants remains unclear. Herein, we explored the potential application of engineered biochar prepared from fruit waste via chemical modification to remove chromium (Cr) from an aqueous solution. By synthesizing two types of agricultural residue-derived adsorbents, including pomegranate peel adsorbent (PG) and its modified product, pomegranate-peel-derived biochar (PG-B), via chemical and thermal decomposition methods, we elucidated the adsorption property of Cr(VI) on the studied materials and identified the cation retention mechanism of the adsorption process. Batch experiments and varied characterizations demonstrated that superior activity was exhibited in PG-B, which can contribute to the porous surfaces caused by pyrolysis and effective active sites resulting from alkalization. The highest Cr(VI) adsorption capacity is obtained at pH 4, a dosage of 6.25 g L^-1, and a contact time of 30 min. The maximum adsorption efficiency of 90.50% in a short period (30 min) was obtained on PG-B, while PG reached a removal performance of 78.01% at 60 min. The results from kinetic and isotherm models suggested that monolayer chemisorption dominated the adsorption process. The Langmuir maximum adsorption capacity is 16.23 mg g^-1. This study shortened the adsorption equilibrium time of pomegranate-based biosorbents and presents positive significance in designing and optimizing waste fruit-peel-derived adsorption materials for water purification.

Enhanced gaseous acetone adsorption on montmorillonite by ball milling generated Si-OH and interlayer under synergistic modification with H2O2 and tetramethylammonium bromide

Montmorillonite (Mt) is a potential adsorbent for volatile organic vapor removal from contaminated soils because of its rich reserves and porous nature, but its inertia surface property has limited its application for polar compounds. In this study, modifications of Mt were carried out by high energy ball milling with H₂O₂ and tetramethylammonium bromide (TMAB) to obtain adsorbents with both high porosity and abundant Si-OH groups (BHTMt). The microporous structure produced by TMAB insertion as well as the silanol (Si-OH) groups formed by H₂O₂ oxidation improved the adsorption of acetone by the modified material. The adsorption capacity of BHTMt for acetone was increased by 80% compared to the original Mt. The effect of H₂O₂ dosage on the adsorption performance for gaseous acetone was investigated by dynamic adsorption experiments. The adsorption kinetic results demonstrated that the adsorption of acetone by the modified material was subject to both physical and chemical adsorption. Density functional theory calculations indicated that there was no obvious interaction between TMAB and acetone, and the materials adsorbed acetone mainly through hydrogen bonding interaction of Si-OH as well as pore filling effects.

Optimization of CO2 Sorption onto Spent Shale with Diethylenetriamine (DETA) and Ethylenediamine (EDA)

A novel technique was employed to optimize the CO₂ sorption performance of spent shale at elevated pressure-temperature (PT) conditions. Four samples of spent shale prepared from the pyrolysis of oil shale under an anoxic condition were further modified with diethylenetriamine (DETA) and ethylenediamine (EDA) through the impregnation technique to investigate the variations in their physicochemical characteristics and sorption performance. The textural and structural properties of the DETA- and EDA- modified samples revealed a decrease in the surface area from tens of m²/g to a unit of m²/g due to the amine group dispersing into the available pores, but the pore sizes drastically increased to macropores and led to the creation of micropores. The N-H and C-N bonds of amine noticed on the modified samples exhibit remarkable affinity for CO₂ sequestration and are confirmed to be thermally stable at higher temperatures by thermogravimetric (TG) analysis. Furthermore, the maximum sorption capacity of the spent shale increased by about 100% with the DETA modification, and the equilibrium isotherm analyses confirmed the sorption performance to support heterogenous sorption in conjunction with both monolayer and multilayer coverage since they agreed with the Sips, Toth, Langmuir, and Freundlich models. The sorption kinetics confirm that the sorption process is not limited to diffusion, and both physisorption and chemisorption have also occurred. Furthermore, the heat of enthalpy reveals an endothermic reaction observed between the CO₂ and amine-modified samples as a result of the chemical bond, which will require more energy to break down. This investigation reveals that optimization of spent shale with amine functional groups can enhance its sorption behavior and the amine-modified spent shale can be a promising sorbent for CO₂ sequestration from impure steams of the natural gas.

Reactive Adsorption Performance and Behavior of Gaseous Cumene on MCM-41 Supported Sulfuric Acid

Efficient removal of cumene from gaseous streams and recovery of its derivatives was accomplished using a MCM-41-supported sulfuric acid (SSA/MCM-41) adsorbent. The results indicated that the removal performance of the SSA/MCM-41 for cumene was significantly influenced by the process conditions such as bed temperature, inlet concentration, bed height, and flow rate. The dose–response model could perfectly describe the collected breakthrough adsorption data. The SSA/MCM-41 adsorbent exhibited a reactive temperature region of 120–170 °C, in which the cumene removal ratios (X_c) were greater than 97%. Rising the bed height or reducing the flow rate enhanced the theoretical adsorption performance metrics, such as theoretical breakthrough time (t_B,th) and theoretical breakthrough adsorption capacity (Q_B,th), whereas increasing the inlet concentration resulted in t_B,th shortening and Q_B,th rising. As demonstrated in this paper, the highest t_B,th and Q_B,th were 69.60 min and 324.50 mg g⁻¹, respectively. Meanwhile, the spent SSA/MCM-41 could be desorbed and regenerated for cyclic reuse. Moreover, two recoverable adsorbed products, 4-isopropylbenzenesulfonic acid and 4, 4′-sulfonyl bis(isopropyl-benzene), were successfully separated and identified using FTIR and ¹H/¹³C NMR characterization. Accordingly, the relevance of a reactive adsorption mechanism was confirmed. This study suggests that the SSA/MCM-41 has remarkable potential for application as an adsorbent for the resource treatment of cumene pollutants.