Fixed-bed Experiments Research Articles

Removal of Sb(III) by 3D-reduced graphene oxide/sodium alginate double-network composites from an aqueous batch and fixed-bed system

We created 3D-reduced graphene oxide/sodium alginate double network (GAD) beads to address the problem of local water pollution by antimony. GAD is a novel material with the high specific surface area of graphene and biosecurity of sodium alginate. Due to the introduction of graphene, the thermal stability and specific surface area of GAD are enhanced, as shown from the FTIR, TGA, BET, Raman, and XRD characterizations. The influence of different environmental variables-such as the pH, dosage, temperature, contact time, and sodium chloride concentration on the Sb(III) sorption with GAD-was investigated. The adsorption results fit well with both the pseudo-second order (R2 > 0.99) and Freundlich (R2 > 0.99) isotherm models. The temperature rise has a negative influence on the adsorption. The Langmuir adsorption capacity is 7.67 mg/g, which is higher than many adsorbents. The GAD results from the fixed-bed adsorption experiment were a good fit with the Thomas model (R2 > 0.99). In addition, GAD appears to be a renewable and ideal adsorbent for the treatment of antimony pollution in aqueous systems.

Antimony removal from water by pine bark tannin resin: Batch and fixed-bed adsorption

Antimony is present in water by natural causes but is also mobilized in the environment by anthropogenic activities, particularly mining. Considering its toxicological behavior, antimony removal from contaminated groundwater and mine effluents is necessary. In this work, Sb(III) and Sb(V) removal from aqueous solution was studied using a resin prepared from pine bark tannins. Subsequent iron loading of the tannin resin was tested, but this chemical modification was shown not to improve adsorptive properties. Tannin resin (unmodified form) presented a good ability to uptake antimony, with maximum adsorption capacities, evaluated in batch mode, of 30–33 mg g−1 (Sb(III), pH 6) and 16–47 mg g−1 (Sb(V), pH 2), depending on the particle size. The performance of the adsorbent was not affected by high levels of sulfate, which characterize most mining-impacted waters, but depending on Sb-load of the water it could be moderately affected by metal cations coexisting in solution. The applicability of the tannin resin on Sb(III) uptake was confirmed in continuous fixed-bed experiments. Breakthrough curves were obtained for different inlet adsorbate concentrations, bed heights, flow rates and aqueous media (distilled water and a simulated mine effluent). The adsorptive capacity of the tannin resin was practically maintained and adsorbent usage rates as low as 0.11 kg m−3 were determined to treat efficiently (90% removal) 1 mg-Sb(III) L−1 contaminated water. Overall, tannin resin is a bio-derived sorbent that shows affinity for antimony in both redox states, being stable in pH conditions commonly found in Sb-contaminated waters.

Selective removal and recovery of La(III) using a phosphonic-based ion imprinted polymer: Adsorption performance, regeneration, and mechanism

It is significant and difficult to selective removal and recovery rare earth elements in wastewater. A novel La(III) imprinted polymer (La-IIP) was synthesized by taking advantage of the strong interaction between Lanthanum and phosphorus combined the adsorption selectively of ion imprinted technology. The adsorption capacity of La-IIP is 62.8 mg g–1 and the selectivity coefficient kLa/Cu is 54.57. La-IIP can reach adsorption equilibrium within 0.5 h, the adsorption process was well revealed by the Intra-particle diffusion model. The regeneration properties (desorption rate, extent, and recycle times) of La-IIP were investigated. About 88% of the adsorbed La(III) was desorbed in the first 10 min. The high desorption rate was further confirmed in a fixed-bed column experiment. More significantly, the removal efficiency of the La-IIP remained about 100% after five regeneration cycles. Results of FT-IR, XPS, and DFT calculation indicated that the La(III) adsorption by La-IIP involves the reaction between La and O in the phosphonic group. This study not only demonstrated a high adsorption capacity, acid-stable, quick-desorption, and reusable adsorbent for La(III) recovery, but also developed a more comprehensive strategy for the design and testing of adsorbents with practical application prospects.

Removal of sulfur trioxide by wet injection with alkaline absorbent: Model and experimental studies

Sulfur trioxide (SO3) emissions from coal flue gas have become an increasingly serious issue, and alkaline absorbent injection technology has been successfully applied in industry as an effective control method. To accurately predict the SO3 removal effect, a new mathematical model based on the shrinking core model and mass conservation was proposed in this study. In this model, a fixed-bed adsorption experiment was used to estimate the absorption capacity of individual particles, and other model parameters were estimated. The theoretical results of the model were compared with the experimental results of an entrained flow reactor, the fitting parameters were determined, and the model was verified. In addition, the effects of key parameters such as the residence time, molar ratio, flue gas composition, and particle size of absorbers on the SO3 removal efficiency were compared and evaluated. Finally, the Sobol method was used to analyze the parameter sensitivity of the model. The results showed that particle size and porosity have an important influence on the removal of SO3, and thus should be considered when determining the type of absorbent.

Enhancement effect on adsorbent utilization rate based on Twin–Bed tandem adsorption

The actual adsorption loading of the adsorbent is usually less than the equilibrium capacity in the abatement of volatile organic compounds (VOCs) with industrial fixed-bed adsorption. In this study, the twin-bed tandem adsorption (TBTA) cycle was proposed. Adequate time was ensured for the upstream bed to adsorb and reach saturation via the take-up and protection of the downstream bed, thus utilizing the full capacity of the adsorbent. A mathematical model and an extended bed depth service time (BDST) model were developed to describe the characteristics of the TBTA. Then, fixed-bed adsorption experiments were performed to validate the accuracy of the aforementioned two models. Results of the parametric analysis showed that the best enhancement effect could be achieved at low packing height, low feed concentration and high superficial velocity conditions. By defining the unit energy consumption (UEC) as the fan power consumption for the recovery of contaminants per unit amount, suggestions for adsorption parameters were provided. Tracking the UEC at each concentration point on the breakthrough curve, the relative concentration of 70% to 80% was found to be the cost-efficient switch point for TBTA. This study demonstrated the operational dynamics of the TBTA and parametric effects on adsorption performance. Our findings can help to improve the adsorbent utilization rate in fixed-bed systems.

H-Clinoptilolite as an Efficient and Low-Cost Adsorbent for Batch and Continuous Gallium Removal from Aqueous Solutions

In this paper, the gallium (III) ions’ adsorption onto protonated clinoptilolite (H-CLP) was investigated both in batch and fixed-bed column experiments. Regarding batch experiments, the influence of some parameters such as adsorbent dosage, size particle, and temperature was studied, determining that a dosage of 10 g/L for an initial pollutant concentration of 40 mg/L leads to a removal percentage over 85% regardless of particle size and temperature. On the other hand, adsorption of gallium onto H-CPL is an endothermic and spontaneous process in the studied temperature range, concluding that the maximum adsorption capacity was 16 mg/g for 60 °C. Concerning to the effect of the presence of other cations in solution, such as Na+, K+, or Ca2+, gallium adsorption capacity only drops by 20%, although the initial concentration of other cations in the solution is 50 times higher than gallium concentration. This means that clinoptilolite has a high affinity for gallium which can be very favorable for further selectivity tests. A crucial factor for this high selectivity could be the protonation of clinoptilolite which allows working without modifying the pH of the aqueous solution with acid. In the fixed-bed experiments, breakthrough curves were obtained, and the effect of operation variables was determined. A breakpoint value of 254 min for 64 g of adsorbent and flow rate of 9.0 mL/min (7.0 BV/h) were obtained, when treating a pollutant volume of 33 BV. Additionally, the breakthrough curves were fitted to different models to study the particle size effect, being the best fit corresponding to the Adams–Bohart model. This fact confirmed the influence of particle size on adsorption kinetics.Graphical

High-efficiency removal of lead/cadmium from wastewater by MgO modified biochar derived from crofton weed

The adsorption performance and mechanisms of Pb2+ and Cd2+ in wastewater using MgO modified biochar derived from crofton weed (MBCW600) are investigated. The Pb2+ and Cd2+ adsorption capacities of MBCW600 by the Hill model reach 384.08 mg/g and 207.02 mg/g, respectively, which is larger than that of original biochar. Pb2+ could be more easily captured by MBCW600 compared to Cd2+ in the multimetal system. Mg2+ contributes to Pb2+ and Cd2+ adsorption among coexisting cations. The exhausted MBCW600 could be well regenerated by simple method after use. The adsorption mechanism study indicates that Pb2+ and Cd2+ removal are primary contributed to mineral precipitation and ion exchange. The effective treatment volumes of Pb2+ and Cd2+ wastewater achieve 3050 mL and 2150 mL in the fixed-bed column experiment, respectively. Therefore, MBCW600 presents remarkable adsorption capability, excellent recoverability and large throughput, which shows the potential application in future treatment of wastewater containing heavy metal.

Instantaneous adsorption and synergic effect in simultaneous removal of complex dyes through nanocellulose/graphene oxide nanocomposites: Batch, fixed-bed experiments and mechanism

This study aimed at an instantaneous adsorption of a mixture of complex dyes by nanocomposites of non-toxic cellulose nanocrystals (CNC) and graphene oxide (GO). Despite advances in adsorption, the removal of complex dye with four or more aromatic rings is the least reported in the literature. Herein, we prepared and characterized three novel CNC:GO composites and applied them for removing complex dyes basic blue 7 (BB7), reactive orange 122 (RO) and rhodamine B (RhB) in a binary systems with the non-complex dyes methyl orange (MO) and basic brown 4 (BB4). The adsorption capacity of nanocomposite increased with the amount of aromatic ring in dyes’ structure. The CNC:GO 70:30 composite was the most efficient for removing BB7, showing incredible instantaneous adsorption capacity of 1943 mg g−1 (0.1 g.L-1 CNC:GO and 100 mg.L-1 BB7). Under real conditions, the BB7 removal rate from river water sample was 77%. Also, a complex dye (RO) and MO were not adsorbed in single systems, however in the presence of BB7 the qmax was 681 and 516 mg g−1 (0.1 g.L-1 CNC:GO and 100 mg.L-1 of dye), respectively, indicating a synergic effect. In the presence of a complex (RhB) and BB4 cationic dyes, BB7 was preferentially adsorbed. BB7 adsorption was also studied in a dynamic fixed-bed process, whose 80% breakthrough time occurred after 13.5 h (qmax of 213 mg g−1). XPS and FTIR analyses confirmed that electrostatic and ion exchange are the main adsorption mechanism. CNC:GO composite has potential for removing mixtures of complex and ordinary dyes.

Cellulose gasification with Ca–Fe oxygen carrier in chemical-looping process

Biomass-derived chemical looping gasification (BCLG) is a novel technology for lignocellulose energy applications. Ca–Fe oxygen carriers have been proven to be a potential material for efficient lignocellulose conversion and hydrogen-enriched syngas production in process studies. In this study, Thermogravimetry-mass spectrometry (TG-MS), pyrolysis chromatography-mass spectrometry (Py-GC-MS) and fixed-bed experiments were conducted, and the cellulose BCLG product was analyzed to explore the mechanism of reaction between Ca–Fe OCs and biomass char or volatiles. The mechanism of the synergistic effect of Ca–Fe was analyzed to explain the characteristics of the OCs. The results suggest the Ca-based materials act as catalysts to promote the decomposition of cellulose monomers at primary reaction and char at secondary reaction, and also promote the reforming and oxidation of volatiles by chemisorption. Ca participates in the construction of inert substances, such as Ca2Fe2O5, to avoid the deep oxidation of CO and H2. Fe-based material supplies oxygen and promotes the reforming of volatile. Compared with Fe2O3 and CaO/Fe2O3, CaFe2O4 shows a better performance on carbon conversion and H2 production below 850 °C.

Enhanced water decontamination from methylated arsenic by utilizing ultra-small hydrated zirconium oxides encapsulated inside gel-type anion exchanger

Methylated arsenic species, including monomethyl arsenate (MMA) and dimethyl arsenate (DMA), are frequently detected in natural waters due to the biochemical methylation of arsenic and various human activities. The presence of MMA/DMA may cause excess total arsenic (>10 μg/L) in drinking water, yet the efficient removal of methylated arsenic still remains challenging. Herein, we reported the utilization of a recently developed nanocomposite HZO@N201 for selective removal of MMA and DMA from water. HZO@N201 contains the gel-type anion exchanger N201, i.e., quaternary ammoniated poly(styrene-co-divinylbenzene) beads, as the host, and the embedded sub-5 nm hydrated zirconium oxide (HZO) for specific adsorption. In comparison with the commercially available nanocomposite HZO@D201, which was prepared through in-situ growth of HZO inside the macroporous anion exchanger D201, the adsorption capacities of HZO@N201 toward MMA and DMA ascended by ∼ 1.9 and ∼ 2.2 times, respectively, mainly benefitting from the sub-5 nm nature of HZO@N201. The competing anions including sulfate, chloride and bicarbonate exerted negligible impact on the removal efficiency toward MMA/DMA, due to inner-sphere complex formation between HZO NPs and MMA/DMA, as verified by SEM-EDS and XPS Zr 3d analysis. The exhausted HZO@N201 was fully regenerated by alkaline treatment for cyclic utilization without obvious efficiency loss. In fixed-bed experiments, HZO@N201 column was able to successively produce ∼ 4000 and ∼ 160 bed volume (BV) clean water from the feeding solutions containing MMA and DMA, while the values for HZO@D201 column were merely ∼ 1600 BV and ∼ 70 BV, respectively.

Evaluation of fluoride adsorption in solution by synthetic Al2 O3 /CeO2 : A fixed-bed column study.

A highly efficient fluoride adsorbent Al2 O3 /CeO2 was synthesized in this work and used it to fluoride removal in the fixed-bed adsorption through changing the different experimental conditions (influent F- concentration, flow velocity, and bed heights). The adsorption capacity was 9.72 mg/g. In addition, the Adams-Bohart and Thomas models were used to fit and evaluate the column breakthrough curve of fluoride removal process by Al2 O3 /CeO2 , and the correlation coefficients (R2 ) of the Thomas model were close to 1 under all experimental conditions. The structure of Al2 O3 /CeO2 and the adsorption mechanism were confirmed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N2 adsorption and desorption isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Moreover, the adsorption of fluoride (F- ) was mainly through metal binding (MF) and hydroxyl binding (AlOH⋯F) on the surface of the Al2 O3 /CeO2 . Furthermore, the regeneration and coexisting anions studies of Al2 O3 /CeO2 were carried out, and the efficiency of adsorption was still above 70% after five cycles. PRACTITIONER POINTS: Removal of fluoride was studied by fixed-bed experiment, and the adsorption capacity of composite Al2 O3 /CeO2 was 9.72 mg/g. The metal complex played important role in fluoride removal and reusability makes a long-term application for fluoride adsorption. Fluoride wastewater is pumped to the fixed-bed column, and fluoride ions are absorbed by Al2 O3 /CeO2 through fluoride metal complex and aluminum hydrofluoride.

Mechanism study on the high-performance BaFe2O4 during chemical looping gasification

As an attractive oxygen carrier, BaFe2O4 shows an outstanding chemical looping gasification (CLG) performance with a high CO yield, but the reaction mechanisms of BaFe2O4 during CLG process are still not clear. The present work aims to reveal the reaction mechanisms of BaFe2O4 with solid carbon (C) and carbon monoxide (CO) by means of experiments and computational methods based on the density functional theory (DFT). The performance of Fe2O3 was also investigated for comparison. Results of fixed-bed experiments show that BaFe2O4 has a better reactivity in solid–solid reaction with high CO yield, while Fe2O3 shows a better performance in solid–gas reaction with high CO2 yield. Components of Fe and FeO were detected in the products of BaFe2O4-C reaction, but not found in the products of Fe2O3-C reaction, indicating that BaFe2O4 is more active in the solid–solid reaction. Pure Fe and FeO phases in the products of Fe2O3-CO reaction suggest that Fe2O3 is more active in the solid–gas reaction. Combining the experimental and calculation results, it can be found that both the solid–solid reaction and the solid–gas reaction can be divided into the steps of C/CO adsorption, formation of CO*/CO2* complex, CO*/CO2* desorption and lattice oxygen migration. The rate-limiting-steps in solid–solid and solid–gas reactions are the formation of CO* and CO2* complex, respectively. The adsorption energy of C/CO on BaFe2O4 surface is lower than that on Fe2O3 surface, and there is a large amount of adsorbed CO on BaFe2O4 surface, indicating that BaFe2O4 surface is more active than Fe2O3 surface. The BaFe2O4-C reaction is more favorable with a lower energy barrier (0.545 eV) than that Fe2O3-C reaction (0.960 eV). In the solid–gas reaction, Fe2O3-CO reaction has a lower reaction energy barrier of 0.791 eV than BaFe2O4-CO reaction (0.997 eV). The large amount of Fe2+ ion in Fe2O3 bulk indicates the strong oxygen migration ability. Therefore, BaFe2O4 displays good potential in CLG process due to its relative stronger surface activity and weaker migration ability of lattice oxygen.

Adsorption properties of sugarcane bagasse and corn cob for the sulfamethoxazole removal in a fixed-bed column

Natural adsorbents are a good alternative to remove antibiotic residues from wastewater. In this study, the adsorption capacity of sulfamethoxazole (SMX) onto sugarcane bagasse (SB) and corn cob (CC) in a continuous fixed-bed was compared. Brunauer Emmett Teller, Fourier transform infrared (FTIR), Boehm titration, and point of zero charge (pHpzc) were used to characterize both adsorbents. The adsorption capacity (qe) and the removal percentage of SMX (% R) were investigated at different different flow rates (2, 5, and 7 mL min− 1) and adsorbent masses (4 and 6.4 g), and a constant initial concentration of 5 mg L− 1. The results of the characterization showed that SB has a morphology with more dispersed particles and a specific surface higher than CC (2.6 > 1.2 m2 g− 1). Boehm titration indicates that both the surface of SB and CC have a greater amount of acid groups, which is in agreement with FTIR and pHpzc results. The continuous fixed-bed experiments showed that % R and qe of SMX are higher with SB in all the tests. The highest qe and maximum % R was 0.24 mg g− 1 and 74% with SB, and 0.15 mg g− 1 and 65% using CC. In most cases, the qe of both adsorbents decreased with the increase of flow rate and bed height. An analysis suggests that hydrogen bonds could be the main factor favoring the SMX adsorption with SB. Finally, the intraparticle diffusion was the rate-controlling step, predominating the pore-volume diffusion resistance.

Emulsion hydrogel microbeads encapsulating extractants prepared by O/W/O double Pickering emulsions for the recovery of Cu(II) from water

In a double emulsion, the cross contamination between internal and external phase is an unavoidable problem, which limits its widely application. This work focused on the preparation of the cross contamination-free O/W/O Pickering emulsions for the fabrication of Pickering emulsion hydrogel (PEHG) microbeads encapsulating copper extractants. KH-570 was used to hydrophobically modify silica for the stabilization of O/W Pickering emulsions. Batch and fixed-bed experiments were conducted for the recovery of Cu(Ⅱ) from water using PEHG microbeads. The results showed that the formed particle-polymer networks in oil-water interface strengthen the stability of O/W Pickering emulsions. The cross contamination ratio of O/W/O Pickering emulsions was reduced to less than 3% under preset conditions. The size of PEHG microbeads was controlled by adjusting the dosage of hydrophobic silica and the optimal diameter used in extraction was 1.8–2.2 mm. The extraction capacity of copper extractants in PEHG microbeads was 86.43 mg/g, with the operation time of 80 min (D = 1.8 mm). The fixed-bed extraction experiment was completed in 250 min and the stripping rate was 97.1%. Compared to previous work, the extractants in PEHG microbeads possessed a better utilization.

Exploring the migration and transformation of lattice oxygen during chemical looping with NiFe2O4 oxygen carrier

Chemical looping (CL) technology using an oxygen carrier (OC) offers a versatile platform to convert various fuels (e.g., CH4, coal, and biomass) to value-added products (e.g., heat, syngas, and H2) in a clean and efficient approach. Currently, the migration and transformation mechanisms of lattice oxygen in spinel OCs were not extensively investigated, which are considered the cornerstone of OC. In this work, the release-uptake paths of lattice oxygen and the chemical reaction laws at interface were studied in detail using a composite metal oxide (NiFe2O4) as an OC through (in-situ) XPS technology coupled with fixed bed experiments. Mechanistic studies indicate that the chemical reaction interface is fixed on the surface of OC particles, and the concentration gradient between the surface and the bulk drives the transmission of lattice oxygen to achieve the reduction or oxidation of OC. Additionally, an important hydroxyl ions formation process of OC is confirmed by an in-situ XPS.

Fish scale-based biochar with defined pore size and ultrahigh specific surface area for highly efficient adsorption of ciprofloxacin

A fish scale-based porous activated biochar with defined pore size (DPBC) was fabricated by a one-step calcination and activation method. The DPBC possessed an ultrahigh specific surface area of 3370 m2 g−1 and its pore diameter centered at 1.49 nm which fits into the ciprofloxacin (CIP) molecular dimension, making it an ideal adsorbent for CIP adsorption due to the molecular pore-filling effect. The maximum Langmuir monolayer adsorption capacity of DPBC for CIP was higher than 1000 mg g−1 and the equilibrium time was less than 4 h, superior to most adsorbents reported in literature. Thermodynamic analysis indicated the adsorption process was spontaneous and endothermic. Notably, fixed-bed experiments showed an encouraging adsorption performance towards CIP, with a high saturated dynamic adsorption capacity of 880.3 mg g−1. Both Thomas and Yoon-Nelson models predict the fixed-bed column adsorption performance well. Hydrophobic effect, π-π interaction, π-π EDA, cation exchange, hydrogen bonding formation, pore filling effect, electrostatic and cation-π interaction involved in the CIP adsorption on the DPBC.

Synergistic decomposition of H2S into H2 by Ni3S2 over ZrO2 support via a sulfur looping scheme with CO2 enabled carrier regeneration

Commercially viable H2 production from H2S demands a well-designed and efficient technology concept with superior H2 yield. We propose a novel sulfur looping scheme that involves carrier sulfidation and CO2 enabled carrier regeneration to simultaneously utilize H2S and CO2, the two common industrial waste gases, for valuable H2 production. Using Ni3S2 as the active component, a high-performance sulfur carrier design is developed, where the selection of support is key. ZrO2 and MgAl2O4 supports were tested and both substantially improve the recyclability over cycles by imparting structural stability to Ni3S2. ZrO2 dramatically enhances the carrier performance, exhibiting a maximum increase of ~ 100% in sulfur uptake during the redox cycles compared to MgAl2O4. Furthermore, in fixed bed experiments at a high GHSV of 5000 hr-1, ZrO2 supported carrier maintained its superior performance over MgAl2O4 with a ~ 9.5% higher total H2S consumption. Density functional theory calculations were performed to unveil the role of supports. ZrO2 is identified as a support with bifunctional characteristics that not only improves textural properties of the carrier, but also catalytically decomposes H2S and induces a synergistic dynamic with Ni3S2. On the other hand, MgAl2O4 acts only as a conventional inert support for morphology modifications with negligible interaction with H2S. This work demonstrates a novel strategy for H2S and CO2 utilization and provides new insights into effective support selection aiding the design of a robust and efficient sulfur carrier.

Biochar/Mg-Al spinel carboxymethyl cellulose-La hydrogels with cationic polymeric layers for selective phosphate capture

Recently, biochar-related phosphate sorbents have been extensively investigated and achieved significant progress; however, there is still much room for enhancement on capturing performance and recovery of powdery ones after sorption. Herein, a new kind of adsorbent, in which biochar/Mg-Al spinel encapsulated in carboxymethyl cellulose-La hydrogels with cationic polymeric layers, was fabricated, aiming for integrating multi-advantages of each component for enhanced phosphate capture. Batch static experiments were correlated to the phosphate adsorption performance of the adsorbent. The maximum phosphate adsorption capacity of the adsorbent was 89.65 mg P/g at pH = 3. The Langmuir isotherm model and the pseudo-second-order kinetic model fitted well with the adsorption behavior of the adsorbent. More importantly, this composite adsorbent that integrated with biochar, Mg-Al spinel, cationic polymeric components exhibited favorable selectivity over coexisting anions (Cl-, SO42-, HCO3– and NO3–) and performed good reusability after five consecutive cycles. By virtue of the bead-like feature, fixed-bed column experiments demonstrated that the Thomas model fitted the breakthrough curves well under varied experimental conditions. The adsorption mechanism of phosphate on the designed composite adsorbent with multi-components could be described as the electrostatic attraction, ligand exchange and inner-sphere complexation, which might account for the efficient phosphate capturing performance.

A novel 3D superelastic polyethyleneimine functionalized chitosan aerogels for selective removal of Cr(VI) from aqueous solution: performance and mechanisms

Here we unveiled a novel polyethyleneimine (PEI) functionalized chitosan (CS) aerogel (PCA) with three-dimensional (3D) porous network structure and superior reversible compression property and investigated its adsorption behavior toward Cr(VI). The kinetic study displayed that the adsorption of Cr(VI) ions followed the pseudo-second-order model, indicating the adsorption was such as to depend on the chemical reaction between Cr(VI) ions and PCA. Notably, the maximum adsorption capacity fitted according to the Langmuir model was 445.29 mg/g, exceeding those of most previous chitosan-based adsorbents. The major reaction mechanism involving the capture and reduction of Cr(VI) has been systematically investigated based on FTIR, XPS and DFT analyses. Particularly, the fixed-bed column experiments illustrated that the effective treatment volume of PCA was 36367 mL and 7453 mL in simulated chromium wastewater and real chromium wastewater with initial concentrations of 2 mg L−1 and 52.88 mg L−1, respectively, suggesting the promising potential of PCA for large-scale practical applications. More interestingly, the current aerogel adsorbents could significantly reduce the accumulation of heavy metal ions in wheats, which meant that heavy metal wastewater had great prospects for agricultural irrigation after being treated by the aerogel of this work. In summary, this strategy could provide valuable and promising contribution towards the development of scalable and sustainable chitosan-based aerogels for Cr(VI) removal from practical wastewater.

Breaking the trade-off between selectivity and adsorption capacity for gas separation

SummaryThe trade-off between selectivity and adsorption capacity with porous materials is a major roadblock to reducing the energy footprint of gas separation technologies. To address this matter, we report herein a systematic crystal engineering study of C2H2 removal from CO2 in a family of hybrid ultramicroporous materials (HUMs). The HUMs are composed of the same organic linker ligand, 4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, pypz, three inorganic pillar ligands, and two metal cations, thereby affording six isostructural pcu topology HUMs. All six HUMs exhibited strong binding sites for C2H2 and weaker affinity for CO2. The tuning of pore size and chemistry enabled by crystal engineering resulted in benchmark C2H2/CO2 separation performance. Fixed-bed dynamic column breakthrough experiments for an equimolar (v/v = 1:1) C2H2/CO2 binary gas mixture revealed that one sorbent, SIFSIX-21-Ni, was the first C2H2 selective sorbent that combines exceptional separation selectivity (27.7) with high adsorption capacity (4 mmol·g−1).