Sorbent Selection Research Articles

Twofold Interpenetrated Cationic Metal-Organic Framework with Hydrophobic Channels for Effectively Trapping Toxic Oxo-Anions.

Sequestration of toxic oxo-anions (such as 99TcO4- and ClO4-) from wastewater has received constant attention due to the existing serious threat to public health and the sustainability of the environment. In view of the low energy of hydration of TcO4- and ClO4-, cationic metal-organic framework (MOF) materials with the hydrophobic microenvironment are preferred in the selection of sorbents. Herein, a twofold interpenetrated cationic MOF (ZJU-X15) with double-helical chains was constructed by tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPPE) and Cd2+ for the elimination of 99TcO4- and ClO4-. Profiting from hydrophobic channels, ZJU-X15 could remove most of ReO4- (a surrogate for 99TcO4-) and ClO4- in less than 10 and 20 min, respectively. As the result of batch experiments, ZJU-X15 could capture 356 mg of ReO4- and 221 mg of ClO4- per 1 g of sorbent, showcase decent selectivity, and still maintain high removal efficiency for anions after four recycles. Furthermore, the process of anion-exchange was confirmed by ion chromatography, Fourier-transform infrared spectroscopy, scanning electron microscopy combined with an energy-dispersive X-ray spectrometer, and X-ray photoelectron spectroscopy, indicating that target anions successfully entered into the body of ZJU-X15 through anion exchange.

A novel passive polymer-sorbent thermal battery for low-temperature energy applications: A numerical feasibility study

Sorption thermal energy storage (STES) systems offer great potential for meeting the growing energy needs and increasing the use of renewable energy resources. However, the complexity and large-scale of current STES technologies lead to relatively low-efficiency systems, severely limiting their widespread implementation. To address this challenge, this study presents a novel and compact smart-polymer sorbent (SPS) thermal battery with passive material-enabled mechanisms for controlled low-temperature thermal energy storage applications. A numerical model is established to investigate the coupled heat and mass transport processes underlying the working behavior of the SPS battery. It is also used to reveal the interdependence of the two processes and the limiting factors for the battery's thermal performance. The heating performance of several SPS battery designs was studied as an example, focusing on their application for cold environment thermal protection. Moreover, the influence of various design parameters was examined, including sorbent selection, void fraction, relative humidity, gate thickness, and gate-to-sorbent area, along with their implications to the coupled mass-heat transport processes. The results revealed that diffusion-based mass transport is the limiting process affecting the SPS battery thermal performance. The numerical simulation results also indicated that the sorbent selection should consider their low recharge temperature (40 °C–100 °C) and less pronounced temperature-dependent adsorption behavior to maximize the heating performance of the SPS battery. In addition, the SPS battery heating efficiency could be enhanced by increasing the sorbent void fraction to 0.35, relative humidity (RH) to 40 %, and gate-to-sorbent area to 60 % while decreasing the gate thickness to 0.1 μm effectively, which facilitate the diffusion-controlled mass transport process. Lastly, a single layer SPS battery is beneficial for thermal regulation at low temperatures; however, using distributed battery designs had a significant thermal performance enhancement benefit of 90 % compared to the single layer design. Hence, our study reveals the complex coupling effects of the heat and mass transport processes within the proposed SPS battery and provides insights and guidance (e.g., materials selections and SPS design) for engineering emergent small-scale passive STES applications.

Ammonium recovery from municipal wastewater by ion exchange: Development and application of a procedure for sorbent selection

Ion exchange represents one of the most promising processes for ammonium recovery from municipal wastewater (MWW). However, most previous studies on ammonium ion exchange did not optimize the process or evaluate its robustness under real operational conditions. This experimental study aimed at (i) developing a procedure for the selection of a sorbent for selective ammonium removal/recovery from MWW, (ii) validating the procedure by applying it to several sorbents, (iii) performing a preliminary optimization and robustness assessment of ammonium removal/recovery with the selected sorbent. The application of the procedure to natural and synthetic zeolites and a cation exchange resin confirmed that batch isotherm tests need to be integrated by continuous-flow tests. The selected sorbent, a natural mixture of Chabazite and Phillipsite, resulted in high performances in terms of cation exchange capacity (33 mgN gdry resin−1), ammonium operating capacity (5.2 mgN gdry resin−1), ammonium recovery yield (78–91%) and selectivity towards ammonium. The process performances resulted stable during 7 adsorption/desorption cycles conducted with MWW treatment plant effluents in a 60-cm column. The switch to a highly saline effluent produced in a hotspot of seawater intrusion did not determine significant changes in performances. Contact time was reduced to 6 min without any decrease in performances. Potassium – well tolerated by crops – was selected as the regenerating agent, in the perspective to produce a desorbed product to be re-used as fertilizer. The study shows that Chabazite/Phillipsite has a high capacity to recover ammonium from MWW in a circular economy approach.

Hydrogen Production with In Situ CO2 Capture at High and Medium Temperatures Using Solid Sorbents

Hydrogen is a versatile vector for heat and power, mobility, and stationary applications. Steam methane reforming and coal gasification have been, until now, the main technologies for H2 production, and in the shorter term may remain due to the current costs of green H2. To minimize the carbon footprint of these technologies, the capture of CO2 emitted is a priority. The in situ capture of CO2 during the reforming and gasification processes, or even during the syngas upgrade by water–gas shift (WGS) reaction, is especially profitable since it contributes to an additional production of H2. This includes biomass gasification processes, where CO2 capture can also contribute to negative emissions. In the sorption-enhanced processes, the WGS reaction and the CO2 capture occur simultaneously, the selection of suitable CO2 sorbents, i.e., with high activity and stability, being a crucial aspect for their success. This review identifies and describes the solid sorbents with more potential for in situ CO2 capture at high and medium temperatures, i.e., Ca- or alkali-based sorbents, and Mg-based sorbents, respectively. The effects of temperature, steam and pressure on sorbents’ performance and H2 production during the sorption-enhanced processes are discussed, as well as the influence of catalyst–sorbent arrangement, i.e., hybrid/mixed or sequential configuration.

Improvement of Emergency Oil Spill Management Technology

As a result of the study, the main causes of emergencies at oil fields were analyzed. Most often, emergency spills occur due to violations of the tightness of field pipelines. Basically, accidents occur from pipe wear due to internal corrosion under the influence of oil and oil products. In the paper, existing methods of oil spills elimination are considered. In order to reduce the negative impact of oil spills on the environment, it is necessary to pay special attention to the study of methods for containment of spilled oil and eliminating the consequences of emergencies and to developing a set of necessary measures. Today, there is a large selection of sorbents offered by various companies. For rapid oil gathering in case of emergency spills, it is proposed to use a biological sorbent “Peat-sorb” based on peat sphagnum moss which has the ability to self-biodegrade the absorbed hydrocarbons.

Performance comparison between solid phase extraction and magnetic carbon nanotubes facilitated dispersive-micro solid phase extractions (Mag-CNTs/d-\xb5SPE) of a cyanide metabolite in biological samples using GC\u2013MS

Dispersive-micro solid phase extraction (d-µSPE) has gained increasing attention due to its convenience, effectiveness, and flexibility for sorbent selection. Among a various selection of materials, magnetic carbon nanotubes (Mag-CNTs) is a promising d-µSPE sorbent with excellent separation efficiency in addition to its high surface area and adsorption capability. In this work, two different surface-modified Mag-CNTs, Mag-CNTs-COOH and Mag-CNTs-SO3H, were developed to facilitate d-µSPE (Mag-CNTs/d-µSPE). The cyanide metabolite, 2-aminothiazoline-4-carboxylic acid (ATCA), was selected to evaluate their extraction performance using gas chromatography–mass spectrometry (GC–MS) analysis. The Mag-CNTs-COOH enabled a one-step derivatization/desorption approach in the workflow; therefore, a better overall performance was achieved. Compared to the Mag-CNTs-SO3H/d-µSPE and SPE workflow, the one-step desorption/derivatization approach improved the overall extraction efficiency and reduced solvent consumption and waste production. Both Mag-CNTs/d-µSPE workflows were validated according to ANSI/ASB 036 guidelines and showed excellent analytical performances. The limit of detection (LOD) and limit of quantitation (LOQ) of ATCA in synthetic urine were 5 and 10 ng/mL, respectively, and that in bovine blood were achieved at 10 and 60 ng/mL. The SPE method’s LOD and LOQ were also determined at 1 and 25 ng/mL in bovine blood samples. The Mag-CNTs/d-µSPE methods demonstrated great potential to extract polar and ionic metabolites from biological matrices. The extraction processes of ATCA described in this work can provide an easier-to-adopt procedure for potential routine forensic testing of the stable biomarker in cyanide poisoning cases, particularly for those cases where the cyanide detection window has passed.

Analytical Extraction Methods and Sorbents' Development for Simultaneous Determination of Organophosphorus Pesticides' Residues in Food and Water Samples: A Review.

Extensive use of organophosphorus pesticides in agriculture leads to adverse effects to the environment and human health. Sample preparation is compulsory to enrich target analytes prior to detection as they often exist at trace levels and this step is critical as it determines the concentration of pollutants present in samples. The selection of a suitable extraction method is of great importance. The analytical performance of the extraction methods is influenced by the selection of sorbents as sorbents play a vital role in the sensitivity and selectivity of an analytical method. To date, numerous sorbent materials have been developed to cater to the needs of selective and sensitive pesticides’ detection. Comprehensive details pertaining to extraction methods, developed sorbents, and analytical performance are provided. This review intended to provide a general overview on different extraction techniques and sorbents that have been developed in the last 10 years for organophosphorus pesticides’ determinations in food and water samples.

Comparison study of nanofibers, composite nano/microfiber materials, molecularly imprinted polymers, and core-shell sorbents used for on-line extraction-liquid chromatography of ochratoxins in Tokaj wines

On-line solid phase extraction coupled with liquid chromatography enables high sample throughput, preconcentration of analytes, efficient clean-up, and separation in a single step. Our comparison study focused on the selection of an optimal SPE sorbent for on-line extraction of ochratoxins A and B allowing fast and sensitive control of mycotoxin contamination. Four types of fibrous sorbents including polyethylene microfibers, polypropylene microfibers, polycaprolactone microfibers/nanofibers composite, and polycaprolactone microfibers/polyvinylidene difluoride nanofibers composite together with selective molecularly imprinted polymers, and conventional C18 core–shell particle sorbent were tested, and efficiency of extraction was compared in on-line mode. Clean-up efficiency and ability to remove matrix interferences with the subsequent chromatographic separation were optimized for all extraction materials followed by validation of the methods. Both nanofibers and molecularly imprinted polymer sorbents were packed in a stainless-steel cartridge and directly connected to the HPLC system. Only polyethylene microfibers among all the tested fibers achieved the selectivity desired for resolution of ochratoxins from the wine matrix with the validation parameters comparable to commercial C18 sorbent. The best results featuring a limit of detection 0.03–0.06 µg L-1, recoveries 92–97% with RSD < 2%, and only 6 min overall analysis time were obtained after extraction using C18 particles. Features including stability of fibers in organic solvents, under high pressure, and their multiple reusability were also proven. Comparison of several types of extraction sorbents for ochratoxins was demonstrated with their on-line extraction followed by liquid chromatography with fluorescence determination using Tokaj wine as a complex matrix.

Ecological aspects of sorbents use to improve the efficiency of bioremediation on oil-contaminated lands

Nowadays, polluted soils are one of the primary environmental problems. Due to a large number of oil-contaminated lands, new methods are being developed more and more actively, as well as a combination of various existing methods for disposing of oil spills. In this paper, bioremediation with the use of adsorption is considered to reduce toxicity and accelerate the processes of microbial destruction of hydrocarbons. There is a large selection of sorbents based on carbon, mineral, and natural materials. The effectiveness of a particular sorbent will vary depending on the application region, weather and climate conditions, soil type, and the type and properties of the oil. In this work, peat was tested as an organic sorbent (S1), vermiculite as a mineral sorbent (S2), and sorbent based on carbon (S3). The sorbents were added to the soils contaminated by oil, evaluating the pH, humidity, and phytotoxicity of the soils. The results showed that the soils treated with sorbents maintained the neutral pH, increased the humidity, and decreased the phytotoxicity of the soil. The sorbent efficiency was S3&gt; S2&gt; S1.

Study of RHO zeolite with different cations for CO 2 /CO separation in pressure swing adsorption

A series of cation-exchanged RHO zeolites, including H-RHO, Li-RHO, Na-RHO, K-RHO, Cs-RHO, Cd-RHO and Pb-RHO, were prepared, and the samples were characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, inductive coupled plasma emission spectrometer and N2-BET. The CO2 and CO adsorption behaviours of the samples were measured at 298 K and 0–10 bar. The Langmuir equation was used to fit adsorption isotherms to compare the separation effect of these RHO zeolites. The results show that extra-framework cations can effectively adjust the pore size of RHO. Not only it depends on the size of the cation radius, but other factors also play an important role, such as the position of the cation. Besides, compared with CHA structure, RHO structure has better CO2/CO separation performance. In all researched cationic forms of RHO, Li-RHO, Cd-RHO and Pb-RHO have excellent CO2/CO separation effects. Among them, the pore size of Cd-RHO is significantly reduced, thereby restricting the entry of CO more effectively, ultimately leading to greater shape selectivity. Cd-RHO not only has the highest CO2 saturated adsorption capacity and CO2 working capacity but also has relatively excellent CO2/CO selectivity, resulting in the sorbent selection parameter (S) is also the largest.

A review of micro-solid-phase extraction techniques and devices applied in sample pretreatment coupled with chromatographic analysis

AbstractSample pretreatment is one of the most crucial and error-prone steps of an analytical procedure; it consents to improve selectivity and sensitivity by sample clean-up and pre-concentration. Nowadays, the arousing interest in greener and sustainable analytical chemistry has increased the development of microextraction techniques as alternative sample preparation procedures. In this review, we aimed to show two different categorizations of the most used micro-solid-phase extraction (μSPE) techniques. In essence, the first one concerns the solid-phase extraction (SPE) sorbent selection and structure: normal-phase, reversed-phase, ion-exchange, mixed-mode, molecular imprinted polymer, and special techniques (e.g., doped cartridges for specific analytes). The second is a grouping of the commercially available μSPE products in categories and sub-categories. We present every device and technology into the classifications paying attention to their historical development and the actual state of the art. So, this study aims to provide the state-of-the-art of μSPE techniques, highlighting their advantages, disadvantages, and possible future developments in sample pretreatment.

Investigation on the condensation behavior of the trace element zinc in (Ar/H2O/HCl/H2S) gas mixtures and its practical implications in gasification-based processes for energy and power generation

Fuels used in combustion and gasification, such as coal, biomass and wastes, yield large amounts of trace elements, which can cause both technological and environmental concerns. This work provides an in-depth insight into the condensation behavior of the trace element zinc under gasification-like conditions in atmospheres containing the HCl and H2S trace gases. A lab-scale quartz reactor with a multi-stage cooling zone was used to determine the condensation content and species distribution of the zinc deposition in different gasification atmospheres. The Scheil-Gulliver cooling model was used to simulate the zinc condensation process, since it provides a good reference to analyze the degree of supercooling during the condensation process. Competition of the gaseous species HCl and H2S with respect to the ZnO condensation behavior has been observed. HCl leads to significant supercooling of the ZnO condensation. It is shown that this can be compensated by ZnS acting as nucleation sites for ZnO if significant amounts of H2S are present. It is further shown that there is a significant bypass effect, i.e. even after nucleation has started there is a significant amount of Zn remaining in the gas phase which significantly extends the condensation regime to lower temperatures. To visualize both effects, a H2S-temperature-transition diagram is proposed. The potential applications including the prevention of problematic depositions (slagging and fouling) and sorbent selection as well as design for removal of trace element zinc from the syngas in IGCC power plants are proposed and discussed in the light of developing clean power technologies.

A review of CO2 sorbents for promoting hydrogen production in the sorption-enhanced steam reforming process

Sorption-enhanced-steam-reforming (SESR) is a thermochemical conversion technology that produces a high-purity hydrogen stream by utilizing in-situ removal of CO2 with a sorbent. In this paper, the advantages and disadvantages of CaO based sorbents, alkali-metal based sorbents (Na2ZrO3, Li2ZrO3 and Li4SiO4), hydrotalcite based sorbents, bifunctional materials and sorbents prepared from wastes are briefly discussed, and the techniques to improve the sorption properties of these CO2 sorbents are summarized. In the process of hydrogen production by sorption-enhanced-steam-reforming, the selection of suitable high-temperature CO2 sorbent is the key to produce high purity hydrogen. Furthermore, the hydrogen-production performance of the above-mentioned sorbents in the SESR process is investigated and summarized. Finally, a future perspective and some suggestions regarding these five types of sorbents are put forward.

Investigations of CO2 Capture from Gas Mixtures Using Porous Liquids.

Porous liquids, a new porous material with fluidity, can be applied in numerous fields, such as gas storage and/or separation. In this work, the separation of binary gas mixtures CO2/N2 and CO2/CH4 with porous liquids was examined by molecular dynamics (MD) simulations. The pure gas adsorption capacity was analyzed with different concentrations of porous liquids. The dependence of the separation effect of a gas mixture on the total pressure and temperature was investigated. Meanwhile, for both CO2/N2 and CO2/CH4 systems, the adsorption and separation effects of porous liquids with a cage:solvent ratio of 1:12 are better than those of 1:91 and 1:170. The results of the spatial distribution function and/or trajectories indicated that porous liquids prefer CO2, leading to the location of CO2 in the channels formed in porous liquids. However, N2 and CH4 are hardly adsorbed into the bulk. The diffusion of gas molecules follows the order of CO2 > N2 (for CO2/N2) and CH4 > CO2 (for CO2/CH4) in the bulk and N2 > CO2 (for CO2/N2) and CH4 > CO2 (for CO2/CH4) at the interface of porous liquids. Upon increasing the concentrations of porous liquids, the working capacities of CO2 show small decreases in CO2/N2 and CO2/CH4 systems, but the sorbent selection parameters are higher in pressure- and temperature-swing adsorption processes. The porous liquid with a cage:solvent ratio of 1:12 is more suitable for the separation of CO2/N2 and CO2/CH4 systems than ratios of 1:91 and 1:170.

Calcium Looping: On the Positive Influence of SO2 and the Negative Influence of H2O on CO2 Capture by Metamorphosed Limestone-Derived Sorbents.

The CO2 capture performance of sorbents derived from three distinct limestones, including a metamorphosed limestone, is studied under conditions relevant for calcium looping CO2 capture from power plant flue gas. The combined and individual influence of flue gas H2O and SO2 content, the influence of textural changes caused by sequential calcination/carbonation cycles, and the impact of CaSO4 accumulation on the sorbents’ capture performance were examined using bubbling fluidized bed reactor systems. The metamorphosed limestone-derived sorbents exhibit atypical capture behavior: flue gas H2O negatively influences CO2 capture performance, while limited sulfation can positively influence CO2 capture, with space time significantly impacting CO2 and SO2 co-capture performance. The morphological characteristics influencing sorbents’ capture behavior were examined using imaging and material characterization tools, and a detailed discussion is presented. This insight into the morphology responsible for metamorphosed limestone-derived sorbent’s anomalous capture behavior can guide future sorbent selection and design efforts.

Effects of high relative humidity and dry purging on VOCs obtained during breath sampling on common sorbent tubes

Offline breath analysis by thermal desorption gas chromatography mass spectrometry (TD-GC-MS) requires the use of sorbent traps to concentrate and store volatile compounds. The selection of which sorbent to use and best practices for managing high relative humidity are important considerations to allow for reproducible, untargeted, biomarker discovery in water saturated breath samples. This work aims to assess three commonly used sorbent materials for their use in breath volatile sampling and determine how the high relative humidity inherent in such samples effects the capture of volatile compounds of interest. TenaxGR, TenaxTA/Carbograph1TD and TenaxTA/Carbograph5TD tubes were selected as they are the most commonly used sorbents in the breath sampling literature. The recovery of 29 compounds in a standard mix loaded using high humidity gas was tested for each sorbent and compared to loading in dry gas. Water retention and dry purge rates were determined for each sorbent for 500 ml and 1000 ml breath collections. Finally, breath samples were collected simultaneously on to each sorbent type using the ReCIVA and analysed by TD-GC-MS. All three sorbents exhibited acceptable reproducibility when loaded with the standard mix in dry gas (RSD < 10%). Loading the standard mix in humid gas led to reduced recovery of compounds based on their chemical properties. Dry purging performance for each sorbent material was assessed and was shown to be 1.14, 1.13 and 0.89 mg H2O min−1 for TenaxGR, TenaxTA/Carbograph1TD and TenaxTA/Carbograph5TD respectively when flushed with 50 ml min−1 of N2. A comparison of breath profiles on different sorbents showed differences in background artefacts (sulfur dioxide, cyclopenten-1-one and 3-nonene) and endogenous breath compounds (2-methyl-furan and furfural). This work demonstrates that high relative humidity during sampling reduces the ability of sorbent tubes to capture volatile compounds and could impact method detection limits during breath sampling. Sufficient water to impair accurate analysis was retained on all tubes. Minimal differences were observed between sorbent materials when used to sample breath, however, suggestions are provided for sorbent selection for future studies.

Determination of 10 Haloacetamides in drinking water by gas chromatography with automated solid phase extraction

Drinking water disinfection may result in the formation of different classes of toxic disinfection by-products (DBPs). Haloacetamides (HAcAms) are an emerging class of nitrogenous DBPs (N-DBPs), which are generally more prevalent at lower concentrations in disinfected water than carbonaceous DBPs. Herein a fast, convenient, and effective method of analyzing 10 HAcAms in drinking water samples was demonstrated. This method was developed using gas chromatography /electron capture detection (GC/ECD) supplemented with automated solid phase extraction (auto-SPE). The variables for automated SPE procedures were further optimized, including the selection of SPE sorbents, types and volumes of extraction solvents, SPE washing solvents and wash times. Under optimized conditions, the instrumental linearity range was 0.5–150 μg L-1 with correlation coefficients>0.9975. The limits of detection and quantification of this method were 0.002–0.003 μg L-1 and 0.005–0.010 μg L-1, respectively. The recovery values ranged from 72.4% to 108.5%, and the relative standard deviations ranged from 3.3% to 9.1%. Therefore, the auto-SPE-GC-ECD method showed acceptable linearity and repeatability and was subsequently validated and applied to analyze 10 HAcAms in drinking water.

A simple thermodynamic tool for assessing energy requirements for carbon capture using solid or liquid sorbents

Carbon capture and sequestration is known to be energy intensive and will result in 20–30 % reduction in net output of a power plant. However, a simple thermodynamic tool is currently unavailable for assessing the work of CO2 separation using a given solid or liquid sorbent.This paper provides rigorous yet simple framework of equivalent work to assess the energy requirement for CO2 capture using liquid amines or solid adsorbents. First, the theoretical minimum work is determined by assuming that each step in the sorption - desorption cycle is thermodynamically reversible. Then, irreversible heat transfer losses are added to calculate total work for the actual process.The model provides useful insights into the sorbent and process selection. The minimum work for reversible separation can be calculated merely from CO2 sorption equilibria at ambient temperature without requiring laborious data or complex models. A sorbent with low ab/adsorption heat does require less thermal energy, but this thermal energy is required at a higher temperature. Thus, contrary to conventional thinking, the equivalent work is not reduced. The irreversible heat transfer losses for the amines are mostly dictated by the amine’s circulation rate which will be minimized by using amines with the highest CO2 capacity. On an energy requirement basis, the solid adsorbent based processes cannot compete with amines because practical methods of heat recuperation from the hot regenerated adsorbent are unavailable. Without heat recuperation, the solid adsorbent processes will be attractive only if their capital advantage outweighs their higher energy use.

Valorization of Coal Fly Ash as a Stabilizer for the Development of Ni/CaO-Based Bifunctional Material

Sorption-enhanced glycerol steam reforming (SEGSR) is considered as one of the promising processes for H₂ production by combining glycerol steam reforming with simultaneous CO₂ capture in a single-unit operation. The key challenge for a successful SEGSR process is the selection of suitable high-temperature CO₂ sorbents with high resistance to sintering. In the present work, an attempt was made to modify a CaO-based sorbent by adding different types of coal fly ash (FA1–FA12) to develop highly effective and economical CaO-based sorbents suitable for CO₂ removal at high temperatures. Among the synthesized sorbents, the 90%CaO–FA5 sorbent offered the most stable CO₂ capture activity over 20 cycles, with a CO₂ capture capacity of 0.58 gCO₂/gₛₒᵣbₑₙₜ at the 1st cycle and 0.45 gCO₂/gₛₒᵣbₑₙₜ at the 20th cycle. This can be attributed to the relatively high amounts of SiO₂ and mullite (inert materials) in FA5 compared with those of the other FA-containing samples. The presence of these inert materials helps enhancing the sorbent stability by hindering their aggregation and sintering. This sorbent was then selected to synthesize a bifunctional catalyst–sorbent material for H₂ production via SEGSR. The 15%Ni–CaO–FA5 bifunctional material exhibited a stable H₂ purity of ∼97% and a H₂ yield of ∼90% for 30 min (prebreakthrough) of the SEGSR reaction. These results highlight the high potential of FA5 as a low-cost stabilizer for improving the stability of CaO-based sorbents.

Adsorbent media for the sustainable removal of organic air pollutants from museum display cases

The application of adsorbents in museum display cases appears auspicious, as the selection of low-emitting building and decoration materials does not necessarily ensure low pollution levels. Furthermore, historical furnishings may form an integral part of a museum and consequently cannot be substituted. Therefore, comprehensive experiments regarding the filtration efficiency of 37 different adsorbent media, both under active and passive conditions, have been conducted in order to simulate conditions in display cases with/without forced air exchange. The adsorbent media comprised pure and impregnated activated charcoal, charcoal foams and cloths, zeolites, molecular sieves and materials specially designed for museum purposes, such as archival cardboard, textiles and silica gels. Formaldehyde, formic acid, acetic acid, toluene and alpha-pinene were chosen as ubiquitous airborne pollutants in the museum environment. Tests were performed in environmental test chambers. The air exchange rate during active-mode tests was 0.5 h−1. The concentrations of single substances in the chamber air ranged between 0.3 mg m−3 and 6 mg m−3. For the passive-mode experiments, the chamber air was doped with 432 µg m−3 to 1371 µg m−3 of the target compounds. Under active conditions, most of the pure and impregnated charcoals were able to reduce pollutant levels quickly. The lowest adsorption efficiency was found for charcoal foam and cloths, zeolites, molecular sieves and special products designed for museum purposes. However, these materials also removed pollutants very efficiently within a short time under passive conditions with no forced air circulation. As pure activated charcoals performed best in both experiments, there is no need to use impregnated or cost-intensive sorbents in museum display cases. However, regular monitoring during application is recommended, as it was found that some adsorbent media might act as emission sources themselves by releasing volatile organics both before and after exposure to pollutants. It was also shown that emissions might be generated due to fragmentation reactions or pollutant-adsorber interactions; the selection and application of sorbents should therefore be performed with caution.