Increase In Sorption Capacity Research Articles

Hydrogen bonds between the oxygen-containing functional groups of biochar and organic contaminants significantly enhance sorption affinity

Sorption affinity is an essential parameter to immobilize contaminants, but the controlling structures of biochar with strong sorption affinity to organic compounds are unidentified, hindering targeted biochar modification. In the face of multiple types and structures of organic contaminants in the aquatic environment, it is urgent to prepare biochar which can remove a large number of contaminants by targeted biochar modification. This study compared the sorption and desorption of five different type organic contaminants on biochar and graphite to understand sorption affinity and to inform the structural regulation of biochar. The sorption capacity of organics on biochar was 3–7 times higher than graphite, and the desorption ratios of organics on biochar were approximately one-fourth of those on graphite. Hydrophobic areas and aromatic rings were confirmed to be low-energy sorption sites, and most pores were inaccessible. The stronger sorption affinity was thus attributed to the hydrogen bonds between biochar surface functional groups and organics. Furthermore, sorption capacity and desorption ratios correlated positively with calculated sorption thermodynamics and binding energies, aligning with theoretical models based on oxygen- and nitrogen-containing groups. Further verification experiments revealed that functionalized graphite with hydroxyl and carboxyl groups showed the most significantly increased sorption capacity and rate, and decreased desorption ratios, enhancing sorption affinity through hydrogen bonds. These findings offer valuable insights into biochar sorption affinity to organics and guide its structural regulation for organic pollution control in the aquatic environment

Deep eutectic solvent engineered GO/ZrO2 nanofiller for mixed matrix membranes: An efficient hydrogen gas separation

AbstractThis study explores fabrication and characterization of mixed matrix membranes (MMMs) for gas separation, employing a cost‐effective solution casting method. Polycarbonate (PC) and polystyrene (PS) blends are combined with graphene oxide (GO) and zirconium dioxide (ZrO2) nanofillers, with and without a deep eutectic solvent (DES) obtained through hydrogen bond exchange. Various MMMs compositions (2–20 wt%) are systematically examined using diverse characterization techniques, including differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, porosity determination, and water contact angle analysis. The MMMs exhibit enhanced gas permeability and selectivity, surpassing conventional membrane materials. Notably, H2 gas permeability reaches outstanding levels, with the composition PC/PS‐DES‐GO/ZrO2 at 20 wt% (PBC20‐IV) demonstrating the highest value of 86.32 Barrer. This superior performance is attributed to the unique properties of ZrO2, increased sorption capacity of GO, and enhanced thermal stability due to DES. Permeability data for CO2, N2, O2, and CH4 also show significant values, aligning with the observed trends in H2 permeability. Robeson's plot for the H2/CO2 gas pair surpasses the 2008 upper bound, placing the MMMs in a novel category for gas separation membranes. The incorporation of DES‐modified nanofiller blend composites presents a promising strategy for the potential production of pure hydrogen.

Sorption of Pt(II) on inactive biomass of Aspergillus Niger O-5 treated with cetyltrimethylammonium bromide

Platinum-group cytostatic have been found in natural waters due to the current inefficiency of wastewaters treatment plants. This study was aimed to the assessment of inactive biomass of Aspergillus niger O-5 treated with cetyltrimethylammonium bromide as sorbent for solid phase extraction of [PtCl4]2-complex from aqueous dissolutions for the subsequent development of new water treatment technologies. Maximum sorption capacity of 54 mg·g−1 was achieved at 25 °C under the following experimental conditions: pH of dissolution = 5, biomass mass = 10 mg, dissolution volume = 10 mL, Pt(II) mass = 0.5 mg and contact time = 30 min. The good fitting of the model of Ho and the increase of sorption capacity up to 102 mg·g−1 with temperature suggested the chemisorption as predominant mechanism. The mean free energy of adsorption was higher than 8 kJ·mol−1 for all temperatures, which also indicated the chemical character of the interaction. The absolute value of the standard molar Gibbs free energy of formation increased from 3.032 to 8.336 kJ· mol−1 with temperature signifying that the sorption was thermodynamically favored, occurred spontaneously and the degree of spontaneity increased with temperature. The positive value (32.3 kJ·mol−1) of the standard molar enthalpy qualified the sorption as an endothermic process, after which the adsorbent/sorbate system became more thermodynamically stable.

Batch adsorption of diesel oil in water using saba banana peel biochar immobilized in teabags

Diesel oil contamination is a threat to environment and human health. Many technologies have been developed to address this issue; however, they are costly to be deployed in real-world oil remediation. Adsorption remains to be one of the most economical methods to remove oil from water. Here, we used banana peel biochar (BPBC) immobilized in teabags as an adsorbent for the removal of diesel oil in water. We investigated the adsorption behavior of BPBC under different conditions, examining the influence of adsorbent loading, pH, salinity, and contact time on its efficiency for removing diesel oil in water. Our results show that the sorption capacity of BPBC is significantly affected by the amount of adsorbent used. Lower biochar loadings enhance the sorption capacity due to greater surface area accessibility, while higher loadings lead to decreased efficiency due to pore blockage and reduced surface exposure. Interestingly, the pH of the solution was found to have minimal impact on the sorption process. This is attributed to diesel oil’s hydrophobic and non-polar nature, which leads to its interaction with BPBC being predominantly governed by hydrophobic forces instead of pH-sensitive electrostatic interactions. Salinity emerged as a crucial factor in the adsorption process. An increase in salinity enhances the sorption capacity, likely due to the “salting-out” effect, where higher salt concentrations decrease the solubility of diesel oil, promoting its adsorption onto the biochar surface. Furthermore, the study highlights the importance of contact time, with longer exposure resulting in increased sorption capacity. This trend is explained by the adsorption kinetics, initially characterized by rapid adsorption, followed by a slower, progressive occupation of the biochar’s adsorption sites. The kinetic analysis of the process suggests that the pseudo-second-order model is more suitable, indicating a chemisorption mechanism. The Harkins–Jura isotherm model was identified as the best fit for explaining the isotherm behavior, owing to its capacity to account for the heterogeneous nature of the biochar surface and the formation of multiple adsorbate layers. The optimum conditions for maximum diesel oil removal are as follows: BPBC loading of 0.50 g, a solution pH of 5.00, a salinity concentration of 12,656.57 mg/L, and a contact time of 240 min. Under these conditions, BPBC exhibited an adsorption capacity of 19.04 g/g. In summary, our research establishes BPBC, particularly when contained within teabags, as an efficient and practical adsorbent for diesel oil removal in water. Its effectiveness, superior to other biochar, is mainly due to its porosity and hydrophobic properties. These findings not only enhance our understanding of BPBC’s adsorption capabilities but also underscore its potential for environmental remediation.Graphical

Removal of dyes from aqueous media using environmentally friendly aerogels based on chitosan

According to the World Health Organization, between 17% and 20% of water pollution is caused by dye treatments in the textile industry, which makes the development of efficient technologies for its removal essential. Environmentally friendly adsorbent materials, such as aerogels, can be effectively used in adsorption processes involving water remediation because of their high specific surface area and the possibility of an easy separation from the contaminated solutions. In this work, aerogels were obtained by a simple procedure that includes the cross-linking of chitosan with glutaraldehyde, followed by a freeze-drying step to eliminate water by water sublimation. The obtained aerogels presented low density (0.049–0.083 g/cm3), a three-dimensional skeletal structure that provides them with high porosity, acceptable swelling capacity and good dimensional stability. FTIR and X-Ray analysis were used to identify aerogels’ chemical structure and dynamic-mechanical analysis to complement the characterization of these materials. Selected formulations were also tested as adsorbents of Congo Red in aqueous media. The adsorption results demonstrated that the aerogels adsorption capacity strongly depended not only on the crosslinking agent content but also on the amount of chitosan in the initial solution used in their synthesis. Moreover, preliminary thermodynamic studies of the adsorption process indicate that both adsorption rate and aerogel sorption capacity increase with increasing temperature.

Equilibrium and kinetic studies of sorption of Fe(III) ions on R-modified sorbent with CSMA

The sorbent was obtained based on a copolymer of styrene with maleic anhydride and 2-nitro-4- sulphoaniline (S) and subsequently modified with the reagent 4,4'-(ethane-1,2-diylbis(azanilidene))bis(pentan- 2-one) (S1). The sorption of the resulting product with respect to Fe(III) ions was studied. During the study, the influence of various factors on adsorption was studied, such as: pH, contact time, ionic strength, initial concentration of the metal ion, etc. The results were characterized using various adsorption isotherm and kinetic models. The results of the research showed that sorption is best described by the Langmuir model and the pseudo-second order kinetic model. The maximum sorption capacity was 348 mg/g for S and 479.2 mg/g for S1. For the adsorption studies, solutions of 5∙10-3 mol/dm3 Fe(III) were used. Static sorption studies were carried out at room temperature. For the desorption studies, acids of various concentrations were used, in particular solutions of 0.5 mol/dm3 HNO3, HCl, H2SO4 and HClO4. Studies have shown that the modification of the adsorbent with a reagent led to an increase in sorption capacity, which means that the efficiency of extraction of Fe(III) ions by the corresponding product also increased. Thus, we can continue research in this area and modify the adsorbent with other reagents. A comparison of maximum adsorption capacities qmax of various adsorbents for the removal of Fe(III) ions showed that the adsorbents used in this study have higher sorption abilities. The resulting products were used for the sorption-photometric de- termination of Fe(III) in apricot and provided positive results. These factors suggest that the synthesized prod- ucts can be considered as being effective materials for the extraction of Fe(III) ions.

Preparation of Nanoporous Carbon from Rice Husk with Improved Textural Characteristics for Hydrogen Sorption

This study proposes a method to control the pore-forming process by performing preliminary mechanical activation of the initial rice husk before carbonization. Preliminary mechanical activation of the initial rice husk leads to the loosening of the intercellular substance and its partial depolymerization, thereby increasing the availability of its internal structure for pore formation during carbonization and chemical activation. Using the method described above, nanoporous carbon was obtained with a Brunauer–Emmett–Teller (BET)-calculated specific surface area of 2713 m2/g, a micropore specific surface area calculated by using the Dubinina–Radushkevich (D-R) method of 3099 m2/g, and a total pore volume calculated by using the Barett–Joyner–Halenda (BJH) method of 1.625 cm3/g. Due to these characteristics, the adsorption capacity in the obtained sample was for hydrogen 3.7 wt.% at a temperature of −190 °C and a pressure of 9 kgf/cm2, which is 29.7% higher than the adsorption capacity of nanoporous carbon obtained based on rice husk without mechanical activation. The composite “carbon–platinum” NC-2/Pt10%, at a temperature of 20 °C and a pressure of 9 kgf/cm2, showed an increase in sorption capacity of 27% compared to pure nanoporous carbon NC-2, which is explained by the emergence of the spillover effect.

Influence of chemical activation on the ability of Transcarpathian clinoptilolite to adsorb direct dyes

Significant quantities of wastewater are generated in dyes synthesis processes and in technologies involving their use, which are toxic to living organisms, making the purification of industrial wastewater from organic colouring substances a pressing issue nowadays. The aim of this study was to investigate the prospects of using natural clinoptilolite from the Sokyrnytske deposit and its activated forms in the purification processes of wastewater from direct dyes. Natural clinoptilolite was activated by treatment with 5% H2SO4 and HCl aqueous solutions and heating at 300°C for two hours. The impact of activation conditions on the structural adsorption properties of clinoptilolite has been determined using a comprehensive thermal analysis method. The adsorption of the direct violet dye by natural and activated clinoptilolite has been investigated using spectrophotometric methods at pH 7 and a light wavelength of 550 nm, corresponding to the maximum value of light absorption coefficient. According to the results of thermal analysis, activated clinoptilolite samples exhibited a more developed specific surface area and a higher presence of hydroxyl groups, which can serve as active adsorption sites on the surface. The results of the violet dye adsorption have corresponded to the monomolecular Langmuir theory, indicating the energetic homogeneity of the adsorption centres. By linearizing the Langmuir adsorption isotherm equation, adsorption characteristics of natural and activated clinoptilolite with a 5% HCl aqueous solution relative to the direct violet dye have been determined. Activated clinoptilolite has shown increased sorption capacity (9.53 mmol/kg) compared to natural clinoptilolite (2.28 mmol/kg). The improvement in adsorption characteristics of activated clinoptilolite has been explained by its partial dealumination, resulting in the appearance of meso- and macropores capable of retaining dye molecules. The use of a 30% H2SO4 aqueous solution in activation processes and heating above 400°C has caused mineral degradation, confirmed by electron images of its surface. Practical value of the study lies in the recommendation to apply activated clinoptilolite in the purification processes of wastewater from organic pollutants

The effect of Zr(IV) addition on the phosphate removal properties of MgAl-LDH

Recovery of phosphate from wastewater represents a sustainable alternative to phosphate rock, a limited resource. Magnesium aluminum layered double hydroxides (MgAl-LDH), are promising sorbents due to their high phosphate removal capacity by anion-exchange (26–124 mgP/g). Furthermore, an increased sorption capacity has been reported by the addition of zirconium (Zr(IV)) into the LDH lattice. However, ambiguity exists especially in relation to the incorporation of Zr and the stability of the MgAl-LDH. To understand how Zr(IV)-addition affects the phosphate sorption properties (both capacity and mechanism) on the atomic level, solid state multi-nuclear NMR spectroscopy was combined with complimentary characterization techniques to study a series of MgAl-LDH with Zr to Al ratios of 1:9 and 1:1, which had the Mg to (Al + Zr) ratio fixed at 2:1. The LDH were synthesized by coprecipitation and subsequently aged or hydrothermally treated to improve the crystallinity (particle size). No evidence of Zr(IV) incorporation in the LDH was observed, instead Zr was present as Zr(IV)-hydroxide (X-ray amorphous) and crystalline Zr(IV) oxide after aging and hydrothermal treatment, respectively. The segregation of Zr(IV) and resulting lower Al content in the MgAl-LDH decreased the phosphate sorption capacity from 45 to 54 to 16–20 mgP/g. Zr (hydr)oxide impurities removed <3 mgP/g. Moreover, 31P MAS NMR spectroscopy quantified that the MgAl-LDH contributed to <62% of the total P removal capacity.

Extended Rate Constants Distribution (RCD) Model for Sorption in Heterogeneous Systems: 4. Kinetics of Metal Ions Sorption in the Presence of Complexing Agents-Application to Cu(II) Sorption on Polyethyleneimine Cryogel from Acetate and Tartrate Solutions.

Here, we report a new version of the extended Rate Constants Distribution (RCD) model for metal ion sorption, which includes complex-formation equilibria. With the RCD-complex model, one can predict sorbent performance in the presence of complexing agents using data on metal ion sorption from ligand-free solutions and a set of coefficients for sorption rate constants of different ionic species. The RCD-complex model was applied to breakthrough curves of Cu(II) sorption from acetate and tartrate solutions on polyethyleneimine (PEI) monolith cryogel at different flow rates and ionic speciation. We have shown that, despite the lower stability of Cu(II)-acetate complex, at high flow rates, acetate has a more pronounced negative effect on sorption kinetics than tartrate. The RCD model was successfully used to predict the shape of the breakthrough curves at an arbitrary acetate concentration but failed to predict Cu(II) sorption from tartrate solutions in a broad range of ligand concentrations. Since a twofold increase in sorption capacity was observed at low tartrate concentrations, the latter fact was related to an alteration in the sorption mechanism of Cu(II)-ions, which depended on Cu(II) ionic speciation. The obtained results emphasize the importance of information about sorption kinetics of different ionic forms for the optimization of sorption filter performance in the presence of complexing agents.

New organo-mineral materials based on silica gels modified in situ with nitrogen-containing polymers: synthesis and adsorption properties for Pb(ІІ), Сu(ІІ), Cd(II), and Fe(III) ions

Three new organo-mineral composite materials were obtained by in situ immobilization of polymers containing azo-, nitro-, and oxyquinoline groups in various combinations on the surface of silica gel. The fact of modification of the silica gel surface by nitrogen-containing polymers was confirmed by IR spectroscopy and thermogravimetric analysis combined with mass spectrometry. The SEM-photo analysis of the surface of the synthesized composites allows us to state that all in situ immobilized polymers are on the surface of silica gel in the form of individual convex formations that practically do not affect the structure of the original silica gel. Regarding Fe(III) cations, all composites showed an increase in sorption capacity by 4.5–6.4 times compared to the original silica gel and did not reveal additional sorption activity compared to the original silica gel for Cd(II) and Pb(II) ions. Regarding Cu(II) ions, an increase in the sorption capacity by more than five times compared to the original silica gel was observed for the composite with in situ immobilized poly-5-(4-nitro)phenylazo-8-methacryloxyquinoline only.

Silicas with Polyoxyethylene Branches for Modification of Membranes Based on Microporous Block Copolymers.

We have synthesized cubic and linear polysiloxanes containing polyoxyethylene branches (ASiP-Cu) using tetraethoxysilane, polyoxyethylene glycol, and copper chloride as precursors; the products are stable to self-condensation. The effect of copper chloride content on the chemical structure of ASiP-Cu has been established. A special study was aimed at defining the modifying effect of ASiP-Cu on the sorption characteristics of membranes based on microporous, optically transparent block copolymers (OBCs). These OBCs were produced using 2,4-toluene diisocyanate and block copolymers of ethylene and propylene oxides. The study demonstrated significantly increased sorption capacity of the modified polymers. On the basis of the modified microporous block copolymers and 1-(2-pyridylazo)-2-naphthol (PAN) analytical reagent, an analytical test system has been developed. Additionally, the modified OBCs have the benefit of high diffusion permeability for molecules of organic dyes and metal ions. It has been shown that the volume of voids and structural features of their internal cavities contribute to the complex formation reaction involving PAN and copper chloride.

Aminophosphonate CuO nanocomposites for uranium(VI) removal: Sorption performance and mechanistic study

Two aminophosphonate matrices (mono-aminophopshonate, MAP, and bi-aminophosphonate, BAP) are synthesized, varying the molar proportions of three precursors (thiocarbazide, p-phthalaldehyde, and triphenylphosphite). Nano-composites (CuO-MAP and CuO-BAP) are successfully elaborated by impregnation of the matrices with copper sulfate solution before processing to in situ precipitation of copper in alkaline solution (simultaneous partial Cu reduction). The sorbents are characterized using: TEM, XRD, elemental analysis, SEM-EDX, BET, titration (pHPZC), XPS and FTIR analyses. Uranium sorption properties are compared for the different sorbents through the study of pH effect (optimum close to 4.5), the uptake kinetics (equilibrium reached in 60 min) and sorption isotherms. Uptake kinetics are finely fitted by the pseudo-second order rate equation (and the resistance to intraparticle diffusion). The sorption isotherms are modeled by the Langmuir equation with maximum sorption capacity (mmol U g−1) decreasing according to CuO-BAP(1.15) ≫ CuO-MAP(0.80) > BAP(0.74) ≫ MAP(0.50). The enhanced textural properties and the increase in the density of sorption sites (probably completed by a better steric arrangement for improved reactivity) may explain this ranking. The sorption is endothermic: sorption capacity and affinity coefficient increase with temperature. Uranium is readily desorbed from loaded-sorbents (efficiency > 98 %) using either HCl (0.2 M) solution or acidified urea (0.25 M) solution (pH 2.5) for aminophosphonate matrices and nano-composites, respectively. The type of sorbent does not affect the stability at recycling: at the sixth cycle, the loss in sorption and desorption performances varies by 6.2–7 % and 4.2–4.9 %, respectively. CuO-BAP sorbent shows high potential for uranium recovery from complex acid ore leachate. The broad spectrum of bound metals does not allow producing a pure yellow cake after ammonia precipitation of eluate (containing up to 15–22 % impurities).

Enterosorbents Based on Rhubarb Biomass with a Hybrid Polymer-Inorganic Coating for the Immobilization of Azaheterocyclic Mycotoxins

The aim of the study was the improvement of the phytosorbent range to solve the actual problems of preventing mycotoxicosis caused by numerous types of azaheterocyclic mycotoxins. Technological approaches to structural released pectin and to the formation of a surface layer that was capable of adhesive interaction with montmorillonite particles was identified. The increase in the material porosity and the formation of a hybrid polymer-inorganic coating on a cellulose matrix surface were revealed by scanning electron microscopy and gas adsorption. The modification of rhubarb biomass increased sorption capacity in comparison with the raw material seven-fold. The properties of rhubarb pectin and a hybrid composite based on it were investigated using FTIR spectroscopy, viscometry, laser diffraction and X-ray diffraction analysis. The results were compared with the characteristics of commercial citrus pectin. Models of the molecular structure of the polymer chain and the spatial interaction between macromolecules in the structure of the sorbing grain were proposed based on the pectin chemical state. The influence of the pectin structural organization on the kinetic parameters of the pH-regulated sorption of the test alkaloid under conditions simulating the functioning of the human digestive organs and those of farm animals was traced. The results of the studies allow prognoses on the sorption binding of alkaloids and determinations of the dosage of pectin-containing phytopreparations for mycotoxicos prevention.

Experimental investigations of CO2 adsorption behavior in shales: Implication for CO2 geological storage

Injecting CO2 into shale reservoirs has dual benefits for enhancing gas recovery and CO2 geological sequestration, which is of great significance to ensuring energy security and achieving the “Carbon Neutrality” for China. The CO2 adsorption behavior in shales largely determined the geological sequestration potential but remained uncharted. In this study, the combination of isothermal adsorption measurement and basic petro-physical characterization methods were performed to investigate CO2 adsorption mechanism in shales. Results show that the CO2 sorption capacity increase gradually with injection pressure before reaching an asymptotic maximum magnitude, which can be described equally well by the Langmuir model. TOC content is the most significant control factor on CO2 sorption capacity, and the other secondary factors include vitrinite reflectance, clay content, and brittle mineral content. The pore structure parameter of BET-specific surface area is a more direct factor affecting CO2 adsorption of shale than BJH pore volume. Langmuir CO2 adsorption capacity positive correlated with the surface fractal dimension (D1), but a significant correlation is not found with pore structure fractal dimension (D2). By introducing the Carbon Sequestration Leaders Forum and Department of Energy methods, the research results presented in this study can be extended to the future application for CO2 geological storage potential evaluation in shales.

Sorption capacity of organic matter to heavy metals and its use for polluted soils recover soils recover

The article considers the results of leached chernozems and yellow soil research in Central Russia and in the South of Central China. The research has demonstrated that organic matter has an increased sorption capacity for heavy metals (HM), including lead (Pb) and cadmium (Cd), which are hazardous environmental pollutants. Studies conducted on chernozems demonstrate features of HM migration along a soil profile. Thus, the total content of elements accumulates in the upper humus horizon, further down the profile it gradually decreases, following a decrease in an amount of organic matter. In a soil-forming rock an accumulation of metals is again noted due to the alkaline reaction of soil solution and silt fraction, which is enriched in soil-forming rocks. A significant increase in elements content in soils of arable land (farmland soils) was revealed in comparison with a fallow territory and a forest belt. This phenomenon explains by an additional supply of HMs as an admixture of mineral fertilizers applied on plowed chernozems. In addition, HMs are also appear as a result of agricultural machinery operations during flammable fuel combustion. The ability of organic matter to increased sorption of HMs can be used to restore heavily polluted areas. Farmland soils of Sichuan province were studied as a model experiment. Keywords: CHERNOZEMS, YELLOW SOIL, HEAVY METALS, LEAD, CADMIUM, TOTAL CONTENT, EXCHANGE COMPOUNDS, VORONEZH OBLAST, SICHUAN PROVINCE

Сорбционная способность органического вещества к тяжелым металлам и ее применение при восстановлении загрязненных почв

The article considers the results of leached chernozems and yellow soil research in Central Russia and in the South of Central China. The research has demonstrated that organic matter has an increased sorption capacity for heavy metals (HM), including lead (Pb) and cadmium (Cd), which are hazardous environmental pollutants. Studies conducted on chernozems demonstrate features of HM migration along a soil profile. Thus, the total content of elements accumulates in the upper humus horizon, further down the profile it gradually decreases, following a decrease in an amount of organic matter. In a soil-forming rock an accumulation of metals is again noted due to the alkaline reaction of soil solution and silt fraction, which is enriched in soil-forming rocks. A significant increase in elements content in soils of arable land (farmland soils) was revealed in comparison with a fallow territory and a forest belt. This phenomenon explains by an additional supply of HMs as an admixture of mineral fertilizers applied on plowed chernozems. In addition, HMs are also appear as a result of agricultural machinery operations during flammable fuel combustion. The ability of organic matter to increased sorption of HMs can be used to restore heavily polluted areas. Farmland soils of Sichuan province were studied as a model experiment. Keywords: CHERNOZEMS, YELLOW SOIL, HEAVY METALS, LEAD, CADMIUM, TOTAL CONTENT, EXCHANGE COMPOUNDS, VORONEZH OBLAST, SICHUAN PROVINCE

Total organic carbon content as an index to estimate the sorption capacity of micro- and nano-plastics for hydrophobic organic contaminants

The worldwide existing micro- and nano-plastics (MNPs) showed high sorption capacity for hydrophobic organic contaminants (HOCs), and thus leading to change of the environmental behaviors and fates of HOCs. However, there is a lack of general index for evaluating the sorption capacity of MNPs for HOCs. Herein, we investigated the sorption of chlorobenzene, naphthalene and phenanthrene to 10 MNPs of different polymer types with and without UV-aging, respectively. It was found that the sorption was well fitted by Freundlich isotherm model with coefficients R2 in the range of 0.892–1.00, and aging of most MNPs resulted in decreased sorption capacity for naphthalene and phenanthrene but slightly increased sorption capacity for chlorobenzene. More importantly, for the 8 MNPs commonly present in the environment and with measured total organic carbon (TOC) covering the range of 23.0–91.9%, the logarithm sorption constant (logKd) values of the studied HOCs positively correlated with TOC contents of MNPs, with a good determination coefficient (R2) of 0.923 for naphthalene, 0.694 for chlorobenzene, and 0.565 for phenanthrene. Our study demonstrated that the TOC content of MNPs is a good index for estimating the contribution of total MNPs to the sorption of nonpolar HOCs in the environmental media.

Can aged microplastics be transport vectors for organic micropollutants? – Sorption and phytotoxicity tests

Microplastics have been investigated over the last decade as potential transport vectors for other pollutants. However, the specific role of plastic aging, in which plastics change their characteristics over time when exposed to environmental agents, has been overlooked. Therefore, sorption experiments were herein conducted using virgin and aged (by ozone treatment or rooftop weathering) microplastic particles of LDPE – low-density polyethylene, PET – poly(ethylene terephthalate), or uPVC – unplasticized poly(vinyl chloride). The organic micropollutants (OMPs) selected as sorbates comprise a diversified group of priority substances and contaminants of emerging concern, including pharmaceutical substances (florfenicol, trimethoprim, diclofenac, tramadol, citalopram, venlafaxine) and pesticides (alachlor, clofibric acid, diuron, pentachlorophenol), analyzed at trace concentrations (each ≤100 μg L−1). Sorption kinetics and equilibrium isotherms were obtained, as well as the confirmation that the aging degree of microplastics plays a major role in their sorption capacities. The results show an increased sorption of several OMPs on aged microplastics when compared to pristine samples, i.e. the sorption capacity increasing from one or two sorbed substances (maximum 3 μg g−1 per sorbate) up to nine after aging (maximum 10 μg g−1 per sorbate). The extent of sorption depends on the OMP, polymer and the effectiveness of the aging treatment. The modifications (e.g. in the chemical structure) between virgin and aged microplastics were linked to the increased sorption capacity of certain OMPs, allowing to better understand the different affinities observed. Additionally, phytotoxicity tests were performed to evaluate the mobility of the OMPs sorbed on the microplastics and the potential effects (on germination and early growth) of the combo on two species of plants (Lepidium sativum and Sinapis alba). These tests suggest low or no phytotoxicity effect under the conditions tested but indicate a need for further research on the behavior of microplastics on soil-plant systems.

The Impact of Support Material of Cobalt‐Based Catalysts Prepared by Double Flame Spray Pyrolysis on CO2 Methanation Dynamics

AbstractMethanation is capable of chemical storage of fluctuating renewable energy, which requires fundamental understanding of the dynamics of the kinetic processes taking place on the catalyst surface. In order to elucidate the impact of the catalyst support on the dynamics, Co‐based model catalysts were synthesized via double flame spray pyrolysis (DFSP) differing only in the support materials. In particular, Co nanoparticles of identical particle size distributions are supported on SiO2, TiO2 and SiO2‐TiO2 mixtures by independent formation of the support and the active metal by means of DFSP. The transient catalyst behavior was studied by step changes of the feed gas composition and the analysis of the reactor response with high temporal resolution, according to the periodic transient kinetics method. It was revealed that H2O adsorption strongly depends on the support with increasing sorption capacity from SiO2, via SiO2‐TiO2 to TiO2. The storage of H2O on the support induces a sorption‐enhancement effect and thereby promotes the transient CH4 formation rate for Co/TiO2 catalysts. Transient experiments before and after a steady‐state operation period under CO2 methanation reveal an unchanging reaction mechanism, while changes in selectivity towards CH4 and CO are observed together with a certain degree of deactivation. Hence, the support material was identified to play a major role in activity, selectivity and deactivation behavior for supported Co catalysts in CO2 methanation.