Sorption Sites Research Articles

Effects of freeze-drying and use of artificial seawater on phosphorus exchange isotherms in brackish water sediments

This study reports results on the estimated magnitude of changes in P sorption isotherms in clayey mud sediments when performed using (1) freeze-dried instead of fresh sediment samples and (2) artificial sea water (ASW) instead of ambient near-bottom water. The sediments used differed in their P sorption. For the isotherms, sediments were equilibrated for 48 h in solutions of varying P concentration whereafter the amount of P sorbed or desorbed was determined. We adjusted the modified Freundlich equation to the isotherm data and assessed differences in the isotherms between the treatments by comparing equilibrium P concentrations and P buffering capacities determined from the isotherm equation. Freeze-drying decreased the P sorption in all investigated sediments, but the magnitude of the changes varied depending on the properties of the sediments. The effect was minor in the sediment abundant in P sorption sites and low in easily exchangeable P, while it was clearer in the sediments originally high in P or low in sorption surfaces. ASW and ambient water produced similar isotherms suggesting that ASW is a suitable equilibrium solution in P exchange experiments with muddy clay sediments. This study enlightens the processes occurring in freeze-drying. The results highlight that when examining the effects of dissimilar treatments or experimental conditions on the P exchange isotherms the magnitude and significance of the observed changes should be evaluated in a proper context considering the precision of the method.Article highlightsThe effects of freeze-drying on P sorption isotherms are minor in sediments abundant in unoccupied sorption surfaces.Artificial sea water is a suitable background matrix for the P exchange isotherms.The precision of the method should be considered when comparing the effects of differing isotherm treatments.

Effects of hemicellulose removal combined with polyethylene glycol impregnation on dimensional stability of wood

ABSTRACT To investigate the combined effects of hemicellulose removal and polyethylene glycol (PEG) impregnation on the dimensional stability of wood, Cunninghamia lanceolata (Lamb.) Hook. was hydrothermally treated and vacuum-impregnated with PEG. About 19.43% hemicellulose was removed, which partially facilitated the penetration and uniform distribution of PEG in wood cells suggested by SEM and FTIR analyses. The mass and volume increase as well as cell wall bulking were positively correlated with PEG concentration. Both solely hemicellulose removal and PEG treatment enhanced wood dimensional stability. The wood after combined treatments exhibited much better dimensional stability mainly due to water path block, cell wall bulking and sorption site reduction calculated by Hailwood-Horrobin theory. Moreover, higher PEG impregnation combined with hemicellulose removal caused lower water absorption, and the corresponding ASE reached 68%. Moisture sorption of wood after combined treatment was lower below about 77.6% RH, but then increased sharply because PEG 2000 became more hygroscopic at higher RH. The results confirmed the efficiency of combined modification on improving dimensional stability of wood and also indicated the importance of appropriate use of PEG in moisture sorption. The study could potentially provide useful knowledge of developing new modification techniques to improve wood dimensional stability for better utilization.

Biochar colloids facilitate transport and transformation of Cr(VI) in soil: Active site competition coupling with reduction reaction

Biochar has been demonstrated as an efficient amendment for immobilizing contaminants. However, a certain number of micro/nano-scale particles are inevitably present in the fresh or aged biochar, which may facilitate the downward transport of contaminants along the soil profile, posing a detrimental impact on the groundwater. Herein, the effects of biochar colloids derived from wood chip and wheat straw at two temperatures (350 °C and 500 °C) on the transport and transformation of Cr(VI) in soil were investigated. All biochar colloids facilitated the transport of Cr(VI) in a loam clay Ultisol, which was attributed to the competition between biochar colloids and Cr(VI) for the available sorption sites on the soil surface. Wheat straw biochar colloids caused more transport of Cr(VI) than wood chip ones due to the more negative charge and higher polarity, which resulted in stronger electrostatic repulsion and competition with Cr(VI). It is soluble Cr(VI) that dominated the transport of Cr in the effluent solution, however, the particulate Cr(VI) could be reduced into Cr(III) before being carried by biochar colloids for co-transport. The 350 °C biochar colloids had higher electron donating capacities than 500 °C ones, resulting in more reduction of Cr(VI) and more co-transport as biochar colloids-associated Cr(III) in the effluent. Moreover, the more negatively charged 350 °C biochar colloids could also attach more soil Fe oxides, further facilitating the cotransport of Cr via the formation of a binary or ternary complex. Modeling showed the experimental-consistently results that biochar colloids caused 0.5–7.0 times faster transport of Cr(VI) than no biochar colloids in the long-term period. Our findings demonstrate that biochar colloids can enhance transport and transformation of Cr(VI) in soils, which arouse migration risk concern about in-situ remediation of Cr(VI)-contaminated soils by biochar.

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Mechanisms and influencing factors of yttrium sorption on paddy soil: Experiments and modeling

High-technology rare earth elements (REEs) as emerging contaminants have potentially hazardous risks for human health and the environment. Investigating the sorption of REEs on soils is crucial for understanding their migration and transformation. This study evaluated the sorption mechanisms and influencing factors of the rare earth element yttrium (Y) on paddy soil via integrated batch sorption experiments and theoretical modeling analysis. Site energy distribution theory (SEDT) combined with kinetics, thermodynamics, and isotherm sorption models were applied to illustrate the sorption mechanism. In addition, the effects of phosphorus (P), solution pH, particle size of soil microaggregates, and initial Y content on the sorption processes were evaluated by self-organizing map (SOM) and Boruta algorithm. The sorption kinetic behavior of Y on paddy soil was more consistent with the pseudo-second-order model. Thermodynamic results showed that the Y sorption was a spontaneous endothermic reaction. The generalized Langmuir model well described the isotherm data of Y sorption on heterogeneous paddy soil and soil microaggregates surface. The maximum sorption capacity of Y decreased with increasing soil particle size, which may be related to the number of sorption sites for Y on paddy soil and soil microaggregates, as confirmed by SEDT. The heterogeneity of sorption site energy for Y was the highest in the original paddy soil compared with the separated soil microaggregates. The SOM technique and Boruta algorithm highlighted that the initial concentration of Y and coexisting phosphorus played essential roles in the sorption process of Y, indicating that the addition of phosphate fertilizer may be an effective way to reduce the Y bioavailability in paddy soil in practice. These results can provide a scientific basis for the sustainable management of soil REEs and a theoretical foundation for the remediation of REEs-contaminated soils.

Water Sorption and Mechanical Properties of Cellulosic Derivative Fibers.

In this study, water vapor sorption, desorption properties and tensile mechanical properties of four cellulosic fibers, cotton (C), flax (F), viscose (V) and cellulose acetate (CA), were determined. The sorption and desorption isotherms were modeled using the Park model, which allowed an accurate fitting on the whole range of water activity. This model corresponds to a multi-sorption mode dividing in three sorption modes: Langmuir sorption, Henry’s law and water clustering. Park’s parameters were compared for the sorption and desorption isotherms for each fiber. Regardless of the fiber, differences between sorption and desorption were obtained only for the Henry sorption. The obtained sorption properties were correlated to the accessibility and the amount of sorption sites and also to the crystallinity level of the fibers. It was found that V exhibited the highest water sorption capacity due to a higher hydroxyl groups accessibility and a low amorphous fraction, followed by F, C and CA. Results from tensile tests demonstrated that F and C fibers were more rigid, more resistant and less ductile than CA and V fibers due to a difference of microstructure of the fibers. Finally, the presence of water-sorbed molecules led to a decrease in tensile modulus due to plasticization phenomenon.

Gas barrier properties of polylactide/cellulose nanocrystals nanocomposites

The development of polylactide (PLA)/cellulose nanocrystals (CNC) nanocomposites in the aim to increase gas barrier properties has been widely studied, but gave rise to conflicting results. To better understand the underlying gas transport mechanisms, PLA/CNC nanocomposites were produced at concentrations between 5 and 50 wt%. The role of the PLA/CNC interface for the permeability was investigated using three different CNC surface grafts, namely lauric acid (slightly interacting with PLA), stearic acid (non-interacting with PLA), and poly glycidyl methacrylate bearing a reactive epoxy end-group (crosslinking with PLA). While PLA/CNC composites contained a large number of aggregates, homogenously dispersed nanocomposites were obtained with surface modified CNCs even at high concentration of CNC (up to 30 wt%). All nanocomposites had better O2 and CO2 barrier properties than PLA. Surprisingly, the nanocomposites prepared with surface grafted CNC did not perform better than the ones prepared with neat CNC. The diffusion coefficient was successfully modeled with Nielsen's law, showing the importance of the shape factor and resulting tortuosity for the barrier performance notwithstanding PLA/CNC surface compatibility. The analysis of the dual-mode O2 sorption isotherm showed the creation of a similar quantity of supplementary sorption sites in nanocomposites prepared with neat or lauric acid grafted CNC. PGMA grafts induced a higher number of sorption sites. The most important advantage of CNC surface grafts was the shielding of CNC against water vapor uptake. As a result, the O2 barrier properties could be maintained constant up to 90% relative humidity.

Biochar modification with hematite and goethite as efficient persulfate activation catalysts for sulfamethoxazole degradation: one-step biochar synthesis method and solution matrix effect on sulfamethoxazole removal kinetics.

Using biochar to adsorb and degrade organic contaminants has attracted increasing attention due to its relatively low cost and high efficiency. In this work, two magnetic biochars were synthesized by pyrolyzing a mixture of naturally occurring hematite or goethite mineral and pine needle biomass. The biochar composite was characterized with X-ray diffraction, scanning electron microscopy, and surface area analyzer. The result demonstrated iron minerals have been deposited on carbon surfaces and been reduced to magnetite or wustite minerals. In comparison to the unmodified biochar, the iron mineral-modified biochar had better sorption ability, likely because the iron mineral particles on the carbon surface served as additional sorption sites for sulfamethoxazole (SMX) removal. After modification, the biochar also showed higher persulfate activation capacity with radical generation: at 4h, neutral pH, 67.5 and 77.9% of persulfate is activated with hematite and goethite modified biochar, where only 11.7% persulfate is activated by unmodified biochar. With persulfate, goethite-modified biochar showed better SMX removal capacity than hematite-modified biochar with about 79% of SMX removed in 4h. Solution chemistry such as pH and co-exist humic acid can affect SMX removal by affecting iron minerals. Because the magnetized biochar can be easily isolated and removed with external magnets, it can be used in various contaminant removal applications.

Experimental study on improving coalbed methane extraction by chemical treatment using acetic acid or ammonium persulfate

AbstractAd‐/desorption and diffusion processes are the key factors controlling methane production from coal. The experiments used samples from methane‐producing coal seams with different contents of carbonate mineral and different ranks. Acid treatment using 1.0 mol/L acetic acid (CH3COOH) and oxidant treatment using 1.0 mol/L ammonium persulfate ((NH4)2S2O8) were conducted on these coal samples to observe the changes in surface functional groups that act as primary sorption sites and pore structure that determines diffusivity by Fourier transform infrared spectrometer, in situ scanning electron microscopy (SEM) imaging and energy dispersive spectroscopy. The results showed that the acidizing‐related mass loss of coal samples is in the range of 3.78%–7.57% due to the complete dissolution of pore‐ and fracture‐filling carbonate minerals. For the coal samples after oxidizing treatment, dissolution evidence can be observed in both carbonate minerals and organic matter, with a mass loss ranging from 2.01% to 3.0%. Acidizing or oxidizing induced dissolution can destroy aliphatic functional groups and the cross‐linked structure of coal, resulting in a decrease in methane adsorption capacity that is beneficial to methane desorption. More opened pores and interconnected fractures can be observed in SEM images due to the dissolution of carbonate minerals, suggesting an alteration of methane diffusion pathways in the coal matrix. Although only some of the carbonate minerals were dissolved following oxidant treatment, coal organic matter is partially oxidized and generates some dissolution pores, which provides more methane diffusion pathways in the coal matrix. Therefore, all the treated coal samples showed a reduction in methane adsorption capacity and an enhancement of desorption capacity and diffusivity. This result suggests that chemical treatment in coal seams using acetic acid or oxidant has the potential to improve coalbed methane extraction.

Highly Efficient Iodine Capture and CO2 Adsorption using a Triazine‐Based Conjugated Microporous Polymers

AbstractTriazine‐based conjugated microporous polymers (CMPs) are a class of promising materials for adsorptive separation of CO2, which could be an effective alternative to chemisorption based approaches. Three novel CMPs were synthesized based on mixed building‐block approach under ionothermal conditions (ZnCl2, 400 °C). CMP@1‐3 possess moderate BET surface area of 325–707 m2 g−1. These polymers have a permanent porous structure, plenty of nitrogen atoms in the skeletons as effective sorption sites, and display a high adsorption performance for CO2 and iodine. Among them, CMP@3 displays outstanding CO2 adsorption capacity with uptake up to 120.8 cm3 g−1 at 1 bar and 273 K. In addition, CMP@3 exhibits a superior iodine uptake up to 308 wt.%. After adsorption and release, the structure of CMPs materials does not change and has high stability, which can be used as a convenient, economic and environmentally friendly material to develop its application in the field of I2 adsorption.

Tetracycline Adsorption on Magnetic Sludge Biochar: Effects of pH, Humic Acid (HA), and Fulvic Acid (FA).

Natural organic matters (NOMs) are ubiquitous in the environment, but few systematic studies have examined the influence of NOMs on the sorption ability of magnetic sludge biochar. In this study, magnetic sludge biochar was synthesized, characterized, and used as a sorbent to remove tetracycline (TC) from aqueous solutions. The effects of pH, humic acid (HA), and fulvic acid (FA) on TC adsorption by magnetic sludge biochar were studied using batch experiments. Adding HA and FA can alter the adsorption behavior of TC, except for its pH dependency. The results of this study show that relatively low concentrations of dissolved HA (≤8 ppm) and FA (≤5 ppm) promote the adsorption capacity of TC, but higher concentrations compete against TC for sorption sites on the surface of magnetic sludge biochar. The results of this study promote a better understanding of the application of magnetic sludge biochar in real antibiotic wastewater.

Emerging Contaminant Imidacloprid in Mediterranean Soils: The Risk of Accumulation Is Greater than the Risk of Leaching.

Imidacloprid (IMI) is an extensively used neonicotinoid insecticide whose occurrence in the environment is a worldwide problem. Its sorption/transport properties are recognized as one of the key knowledge gaps hindering policymaking regarding its international routine monitoring in soils. Therefore, we studied IMI transport behaviour in Croatian Mediterranean soils using column experiments. Breakthrough curves were analysed using the two-site adsorption model and compared against dimethoate (DIM). Transport parameters were correlated to soil physicochemical properties. The results indicate that IMI shows a high degree of preference for soil organic matter over any other soil constituent. For IMI, the clay did not exhibit any sorption activity, while hematite did act as an active sorbent. Contrarily, hematite increased the leachability of DIM by blocking the active sorption sites on clay platelets. Both hematite and clay sorption acted as type-2 (i.e., rate-limiting) sites. In all soils, IMI exhibited lower short-term leachability than DIM. Combined with a body of data concerning other aspects of IMI environmental behaviour, the results indicate that the risk of accumulation of IMI in the soil is greater than the risk of contamination by leaching. Thus, continuous monitoring of IMI in soils should be incorporated into future soil health protection programs.

Effect of Ca(II) on U(VI) and Np(VI) retention on Ca-bentonite and clay minerals at hyperalkaline conditions - New insights from batch sorption experiments and luminescence spectroscopy

In deep geological repositories for radioactive waste, interactions of radionuclides with mineral surfaces occur under complex geochemical conditions involving complex solution compositions and high pH resulting from degradation of cementitious geo-engineered barriers. Ca2+ cations have been hypothesized to play an important role as mediators for the retention of U(VI) on Ca-bentonite at (hyper)alkaline conditions, despite the anionic character of both the mineral surface and the aqueous uranyl species. To gain deeper insight into this sorption process, the effect of Ca2+ on U(VI) and Np(VI) retention on alumosilicate minerals has been comprehensively evaluated, using batch sorption experiments and time-resolved laser-induced luminescence spectroscopy (TRLFS). Sorption experiments with Ca2+ or Sr2+ and zeta potential measurements showed that the alkaline earth metals sorb strongly onto Ca-bentonite at pH 8–13, leading to a partial compensation of the negative surface charge, thereby generating potential sorption sites for anionic actinyl species. U(VI) and Np(VI) sorption experiments in the absence and presence of Ca2+ or Sr2+ confirmed that these cations strongly enhance radionuclide retention on kaolinite and muscovite at pH ≥ 10. Concerning the underlying retention mechanisms, site-selective TRLFS provided spectroscopic proof for two dominating U(VI) species at the alumosilicate surfaces: (i) A ternary U(VI) complex, where U(VI) is bound to the surface via bridging Ca cations with the configuration surface ≡ Ca – OH – U(VI) and, (ii) U(VI) sorption into the interlayer space of calcium (aluminum) silicate hydrates (C-(A-)S-H), which form as secondary phases in the presence of Ca due to partial dissolution of alumosilicates under hyperalkaline conditions. Consequently, the present study confirms that alkaline earth elements, which are ubiquitous in geologic systems, enable strong retention of hexavalent actinides on clay minerals under hyperalkaline repository conditions.

Effects of activation parameters on Zeolitic imidazolate framework JUC-160-derived, nitrogen-doped hierarchical nanoporous carbon and its volatile iodine capture properties

Despite its importance in the nuclear industry, the uncontrollable use and/or accidental release of iodine in the environment pose serious threats to human health and endanger wildlife. Therefore, effective removal of radioiodine from various environmental media is necessary to circumvent its adverse effect. Herein, we report on an excellent and highly efficient capture of iodine by ZIF (JUC-160)-derived ultra-porous carbon. The ultra-porous carbon, obtained through KOH activation at high temperature, displayed unprecedented iodine capture properties with uptake capacities of 1567 mg g−1 and 821 wt.% in the aqueous and vapor phases, respectively. Various conditions including activation temperature and residency time effects on material properties and uptake performances were evaluated. The results showed that iodine uptake increased with increasing activation temperature; while activation time beyond 60 min was not favorable because the carbon materials were completely gasified. Kinetics and Isotherm fitting with the experimental data was done to assess sorption behavior of the derived carbon materials and their interactions with iodine. The results showed that chemisorption was the dominant medium through which iodine was captured as confirmed by both pseudo-second order and Langmuir models. Furthermore, the main mechanism involved in the process was mainly attributed to electron donor-acceptor interactions wherein the oxygen-containing functional groups and nitrogen active sorption sites of the carbon materials acted as electron donors. This work provides insight into optimizing KOH activation temperature and residency time for best performance of iodine adsorbents.

Unraveling natural aging-induced properties change of sludge-derived hydrochar and enhanced cadmium sorption site heterogeneity

AbstractHydrochar has potential applications in soil improvement and heavy metal remediation. Hydrochar would undergo the process of aging when introduced into the soil, altering its properties. However, recent studies have focused mainly on the artificial aging of hydrochar, which could not reveal the cumulative effect of multiple environmental factors. Therefore, the periodical monitoring of the property and sorption behavior of hydrochar after amending soils is necessary to better understand the multifaceted mechanisms associated with the natural aging of hydrochar. This study selected the sludge-derived hydrochar (SLHC) as a typical hydrochar and applied a 16-month rice–wheat–rice rotation to mimic the natural aging of hydrochar, focusing on changing properties and cadmium (Cd) sorption and literature contrast between aging strategies and biochar types. The porosity, O abundance, and ash content of 16-month aged SLHC increased by 37%, 47%, and 8.5%, respectively, facilitating Cd sorption due to surface complexation, pore sorption, and precipitation. The sorption percentage of Cd to SLHC was in the range of 11–14% for SLHC-A0 and increased to 17–31% for SLHC-A4 and 20–32% for SLHC-A16 after natural aging. The natural aging of SLHC induced by ash content played an essential role in Cd sorption site heterogeneity. Linear regression analysis showed that aging strategies on sorption behavior significantly differed between biochars. Thus, studies involving natural aging with multiple environmental factors are preferred over those involving chemical or biological aging. Future studies should continue to explore the mechanisms of natural aging-induced heavy metal sorption between hydrochar and pyrochar. These results improve insights to appraise the potential of SLHC as soil amendments to alleviate the adverse effects of heavy metal contamination and provide an essential basis for researchers and staff in soil management and environmental prevention. Graphical Abstract

The Mechanism of Cu2+ Sorption by Rice Straw Biochar and Its Sorption-Desorption Capacity to Cu2+ in Soil.

Copper (Cu) pollution in soils has received considerable research attention globally, and biochar has been widely used as an adsorbent for soil pollution of Cu. However, most of the studies focused on the adsorption capacity of biochar, the bioavailability of Cu absorbed by biochar remains unclear. In this work, rice straw biomass was pyrolyzed under oxygen-limited conditions at 400°C (BC400) and 600°C (BC600), their apparent structure, group characteristics, and basic physical and chemical properties were determined. The isothermal and kinetics adsorption of Cu by BC400 and BC600 were analyzed. A pot experiment was used to evaluate the passivation of Cu in the soil by biochar and the bioavailability of Cu adsorbed by biochar in the soil. The smooth surfaces of BC400 evolved into more rough surfaces for BC600, and both types of surfaces may give active sorption sites for Cu, according to SEM pictures. FTIR analysis suggested that BC600 is endowed with more condensed aromatic carbon structures and more available polar functional groups. The adsorption processes of Cu2+ by biochar were better fitted Langmuir equation and pseudo-second-order kinetic model. The adsorption isotherms showed monolayer adsorption of Cu2+ on biochar. The maximum adsorption capacities of BC600 and BC400 on Cu2+ were 43.75 and 30.70mg g-1, respectively. Moreover, the pot experiment showed that BC400 and BC600 not only have a strong "passivation" effect on Cu in soil but also prevent the release of adsorbed Cu. Overall, more aromatic carbon structure, more polar functional groups, and higher pH are associated with BC600's increased Cu immobilization ability in soil.

Use of mining waste as a novel low-cost material for fluoride removal from groundwater in CKDu endemic areas of Sri Lanka

A cost-effective fluoride removal process from groundwater using locally sourced waste materials was postulated for use in remote areas such as northern Sri Lanka. The process is relatively simple to operate, reduces fluoride levels to meet WHO guidelines and uses locally available waste from lime extraction. The “Natural Red Earth” (NRE) waste was a mixture of clays (12.43 wt%) and iron oxides (8.13 wt%) deposited on quartz (64.04 wt%). The smallest mesh size (<63 μm) of NRE was preferred to remove fluoride due to enrichment with aluminium and iron materials. Fluoride exchange kinetics were relatively fast (ca. 5 min) for NRE which was ascribed to sorption sites present in an active coating. Equilibrium studies revealed a low fluoride loading (0.009 meq/g). Thermal modification of the NRE at 350 °C increased the maximum fluoride uptake to 0.014 meq/g. Exposure of NRE to 1 M hydrochloric acid solution was preferred as the fluoride sorption capacity was promoted to 0.02 meq/g. Protonated surface sites on NRE were considered responsible for the enhanced fluoride sorption capacity. Acid activated NRE successfully batch treated simulated groundwater contaminated with fluoride ions to meet WHO guidelines. Practically, NRE may be used in addition to a sand filter and charcoal bed if required to remove organic matter. The economics for constructing and using a new NRE based treatment system is suitable for rural farming communities in Sri Lanka.

Sorption kinetics of 1,3,5-trinitrobenzene to biochars produced at various temperatures

Sorption kinetics of organic compounds on biochars is important for understanding the retardation of mobility and bioavailability of organic compounds. Herein, sorption kinetics of 1,3,5-trinitrobenzene on biochars prepared from 200 to 700 °C was investigated to explore the sorption process. Loose partition matrix and condensed partition matrix were formed at relatively low and moderate temperatures, respectively. However, biochars produced at relatively high temperatures formed rich pore structures. Therefore, sorption equilibrium time of 1,3,5-trinitrobenzene increased with increasing preparation temperature from 200 to 350 °C due to the slower diffusion rate in the more condensed matrix, and then decreased when preparation temperature was higher than 400 °C because of the faster adsorption rate in the greater number of pores. Linear positive relationship between matrix diffusion rates of 1,3,5-trinitrobenzene on biochars prepared at 200, 250, 300, 350 °C and H/C ratios of biochars was observed, suggesting that the inhibition of partition process was caused by the condensed matrix in biochars. Linear positive relationships between adsorption rates (i.e., fast outer diffusion rate and slow pore diffusion rate) of 1,3,5-trinitrobenzene on biochars prepared at 400, 450, 550, 700 °C and graphite defects of biochars were observed, because the increase of graphite defects of biochars could promote the adsorption by increasing the quantity of fast diffusion channels and sorption sites. This study reveals the underlying mechanisms of sorption kinetics for organic compounds with relatively large size on biochars, which has potential guidance for the application of biochars and prediction of the environmental risks of organic compounds.Graphical

Competitive and cooperative sorption between triclosan and methyl triclosan on microplastics and soil

The sorption behavior of single contaminant on microplastics (MPs) has been extensively studied; however, little is known about that in the more actual scenario containing multiple contaminants. In this study, the interaction between triclosan (TCS) and its primary metabolite, methyl triclosan (MTCS) on polyethylene (PE), polystyrene (PS), and soil was investigated. Results indicate that the more hydrophobic MTCS had much higher sorption capacity and affinity than TCS. Competitive sorption between them occurred in most cases and appeared to be concentration-dependent (in the range of 0.1–5 mg TCS/L and 0.01–≤0.05 mg MTCS/L of primary solutes, respectively): more pronounced at low concentrations of primary solute, while progressively weaker with the increase of concentrations. Among the sorbents, MTCS exhibited strong antagonistic effect on TCS sorption for MPs, especially PS, while significant suppression of MTCS sorption by TCS took place for soil and PS rather than PE. Additionally, it is interesting to observe that the presence of TCS substantially facilitated the sorption of MTCS exclusively at high concentrations on both PS and soil, presumably attributed to the solute-multilayer formation. Furthermore, the magnitude of the two effects varied with solution pH: TCS sorption at alkaline pH was the most suppressed by MTCS because the less hydrophobic dissociated TCS tended to be displaced, and the highest cooperative sorption of MTCS with TCS occurred at acidic pH because neutral TCS preferentially adsorbed on sorbent surface could provide additional sorption sites for MTCS. Both competitive and cooperative effects between multiple contaminants may affect their fate and transport, thereby these findings are helpful for assessing the environmental risk of MPs and TCS in soil.

Using silver exchange to achieve high uptake and selectivity for propylene/propane separation in zeolite Y

Adsorptive separation of propylene and propane, an important step of polypropylene production, is more energy-efficient than distillation. However, the challenge lies in the design of an adsorbent which exhibits both high selectivity and uptake. Herein, we hypothesise that enhancing the propylene affinity of the adsorption sites while keeping a suitable pore size can address this challenge. To do so, we performed silver exchange of a commercial zeolite Y, thereby making the adsorbent design easily scalable. We characterised the adsorbent using analytical, spectroscopic and imaging tools, tested its equilibrium and dynamic sorption properties using volumetric and gravimetric techniques and compared its performance to those of state-of-the-art adsorbents as well as other silver-functionalised adsorbents. The silver-exchanged zeolite Y (Ag-Y) exhibited one of the best selectivity vs uptake performances reported so far. Ag-Y also displayed fast adsorption kinetics and reversible propylene sorption, making it a promising new benchmark for propylene/propane separation. Synchrotron-based pair distribution function analyses identified the silver cations’ location which confirmed that the silver sites are easily accessible to the adsorbates. This aspect can, in part, explain the propylene/propane separation performance observed. The overall design strategy proposed here to enhance sorption site affinity and maintain pore size could be extended to other adsorbents and support the deployment of adsorption technology for propylene/propane separation.