Repeated Adsorption Desorption Cycles Research Articles

Hierarchically porous carbon foams coated with carbon nitride: Insights into adsorbents for pre-combustion and post-combustion CO2 separation

Adsorption is fundamental to many industrial processes, including separation of carbon dioxide from other gases in pre- or post-combustion gas mixtures. Adsorbents should have high capacity and selectivity, which are both intimately linked with surface area, pore size distribution, and surface energy. Porous carbons are cheap and scalable adsorbents, but greater understanding of how their textural properties and surface chemistry affects their performance is needed. Here, we investigate the effect of nitrogen doping on CO2 adsorption. Microporous carbon foams with large surface area (>2500 m2 g−1) and pore volume (1.6 cm3 g−1) are synthesized, then coated with varying amounts of carbon nitride (up to 17 at% nitrogen) to achieve high CO2 uptake (25.5 mmol g−1) and selectivity (CO2:N2 = 21), whilst also giving insights into the relationship between structure and function. At low pressure (relevant to post-combustion capture), moderate carbon nitride loading leads to enhanced uptake and selectivity by combining large ultramicropore volume with the introduction of Lewis base sites, leading to high isosteric heat of adsorption. Higher carbon nitride loading further increases selectivity but lowers uptake by blocking micropores. Conversely, at high pressure (relevant to pre-combustion capture) the uncoated carbon foam displays superior uptake, because mesoporosity is the dominant factor in this regime, rather than the presence of ultramicropores. Finally, the samples displayed excellent regeneration under repeated adsorption–desorption cycles, and breakthrough curves were measured. These results underscore the delicate balance required for optimal material design when applying porous carbon adsorbents to CO2 separation processes. Moving forward, improved adsorbents will contribute to the proliferation of carbon capture and storage (CCS) and carbon capture and utilisation (CCU) technologies, ultimately contributing reduced anthropogenic CO2 emissions.

Electrospinning and Partial Etching Behaviors of Core-Shell Nanofibers Directly Electrospun on Mesh Substrates for Application in a Cover-Free Compact Air Filter.

The exposure of workers to propylene glycol monomethyl ether acetate (PGMEA) in manufacturing environments can result in potential health risks. Therefore, systems for PGMEA removal are required for indoor air quality control. In this study, core-shell zeolite socony mobil-5 (ZSM-5)/polyvinylpyrrolidone-polyvinylidene fluoride nanofibers were directly electrospun and partially wet-etched on a mesh substrate to develop a cover-free compact PGMEA air filter. The electrospinning behaviors of the core-shell nanofibers were investigated to optimize the electrospinning time and humidity and to enable the manufacture of thin and light air-filter layers. The partial wet etching of the nanofibers was undertaken using different etching solvents and times to ensure the exposure of the active sites of ZSM-5. The performances of the ZSM-5/PVDF nanofiber air filters were assessed by measuring five consecutive PGMEA adsorption-desorption cycles at different desorption temperatures. The synthesized material remained stable upon repeated adsorption-desorption cycles and could be regenerated at a low desorption temperature (80 °C), demonstrating a consistent adsorption performance upon prolonged adsorption-desorption cycling and low energy consumption during regeneration. The results of this study provide new insights into the design of industrial air filters using functional ceramic/polymer nanofibers and the application of these filters.

Converting lignocellulosic biomass into mesoporous carbons for the assessment of single adsorption equilibrium: the competing role of moisture and temperature on gaseous benzene adsorption

AbstractFor the present study, the activated carbon were obtained from Lotus corniculatus L. as waste biomass using carbonization at 700 °C and alkali potassium hydroxide (KOH) chemical activation technique. Single gaseous benzene (C6H6) adsorption (SGBA) experiments were performed to benchmark the efficiency of the L. corniculatus-derived activated carbons (LCACs), which were LCAC2 (609 m2 g−1, KOH 1:2 w/w), LCAC3 (742 m2 g−1, KOH 1:3 w/w), and LCAC4 (826 m2 g−1, KOH 1:4 w/w), respectively. Also, the physicochemical properties of LCACs were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and proximate-elemental assessment. The isotherm models (Langmuir and Freundlich) of C6H6 demonstrate the complex adaptation results of LCAC4 at different relative humidity (RH) levels, and Freundlich isotherm is highly suitable to C6H6/LCAC4 as multilayer adsorption. Kinetic behavior was also analyzed and showed that of C6H6 is well illustrated by the pseudo second order (PSOM). The C6H6 competitive adsorption of LCAC2, LCAC3, and LCAC4 at 25 °C + 0 RH%, 25 °C + 80 RH%, 45 °C + 0 RH%, and 45 °C + 80 RH% corresponds to reductions of 12.9–11.6%, 7.8–11.5%, and 9.9–18.4%. The LCAC4 is confirmed to be a perfect adsorbent in the elimination of a single gaseous stream at 45 °C + 0 RH%. Regeneration showed that the LCAC4 maintained more than 25% of the initial adsorption capacity after five repeated adsorption–desorption cycles. The promising properties of LCAC4 are recommended to be exploited for the other volatile organic compounds in the gas phase in indoor environments, under the best conditions.

Desorption of rare earth elements biosorbed on Euglena mutabilis suspensions and biofilms

AbstractIncreasing demand for rare earth elements (REEs) has stimulated research on novel recovery methods from sources like industrial effluents. Our recent study demonstrated that algal biofilms are good candidates for the adsorption of REEs and that the extracellular polymeric substances (EPS) within the biofilm were a key accumulator of REEs. In this work, we measured the desorption kinetics, extents, and selectivity of REEs from the algae Euglena mutabilis in suspensions and biofilms using aqueous solutions of HCl at pH between 1.5 and 4, and Na2EDTA at pH 5. We examined the potential for reusing suspended and biofilm biomass for repeated adsorption–desorption cycles. The desorption kinetics were similar for suspensions and biofilms, with equilibrium being reached within 20 min. The extent of desorption was higher in biofilms with 86% and 95% desorption, compared to suspensions which had 72% and 74% desorption using HCl and Na2EDTA, respectively. We postulate that the difference between suspensions and biofilms is attributed to the binding sites in the EPS matrix of the biofilm being more readily protonated than those at the algal cell wall surface. Heavy REEs were found to preferentially desorb at pH 4 over lighter REEs. After 3 repeated adsorption–desorption cycles, the adsorption capacity of biofilms increased by 280% and 80% using HCl and Na2EDTA, respectively, compared to an 80% decrease in biosorption capacity for the suspension. The increase in biofilm biosorption capacity was attributed to the simultaneous desorption of divalent cations alongside REEs from the EPS increasing the number of available binding sites.

Facile fabrication of sulfonated porous yeast carbon microspheres through a hydrothermal method and their application for the removal of cationic dye

Water pollution containing dyes become increasingly serious environmental problem with the acceleration of urbanization and industrialization process. Renewable adsorbents for cationic dye wastewater treatment are becoming an obstacle because of the difficulty of desorbing the dye from the adsorbent surface after adsorption. To overcome this dilemma, herein, we report a hydrothermal method to fabricate sulfonic acid modified yeast carbon microspheres (SA/YCM). Different characterization techniques like scanning electron microscopy, FTIR spectroscopy, and X-ray diffraction have been used to test the SA/YCM. Decorated with sulfonic acid group, the modified yeast carbon microspheres possess excellent ability of adsorbing positively charged materials. The removal rate of Methyl blue (MB) by renewable adsorbent SA/YCM can reach 85.3% when the concentration is 500 mg/L. The SA/YCM regenerated by HCl showed excellent regeneration adsorption capacity (78.1%) after five cycles of adsorption–desorption regeneration experiment. Adsorption isotherm and kinetic behaviors of SA/YCM for methylene blue dyes removal were studied and fitted to different existing models. Owing to the numerous sulfonic acid groups on the surface, the SA/YCM showed prominent reusability after regeneration under acidic conditions, which could withstand repeated adsorption–desorption cycles as well as multiple practical applications.

Green Synthesis of Cerium-Based Metal-Organic Framework (Ce-UiO-66 MOF) for Wastewater Treatment.

Green synthesis of metal-organic frameworks (MOFs) in aqueous solutions under ambient conditions with reduced production costs and environmental effects is an efficient technique to transfer lab-scale production to industrial large scale. Hence, this work proposes a green, low-cost, sustainable, rapid, and innovative synthetic strategy to produce cerium-based (Ce-UiO-66) MOFs under ambient conditions in the presence of water as a green solvent. This synthetic strategy exhibits great potential compared to conventional solvothermal synthetic techniques, and it does not need external activation energy and organic solvents, which can achieve the standards of green chemistry. Ce-UiO-66 MOF was synthesized successfully and utilized as a green adsorbent to efficiently eliminate anionic Congo Red (CR) dye from dye-containing wastewater. The experimental adsorption results were well matched to the pseudo-second-order kinetic and Langmuir isotherm models, in which the maximum CR adsorption capacity was measured to be about 285.71 mg/g. To evidence the applicability of Ce-UiO-66 MOFs in CR adsorption, the CR adsorption reaction was performed in the presence of interfering pollutants [e.g., salts (NaCl, KCl, and MgCl2) and cationic organic dyes (Malachite Green (MG) and Methylene Blue (MB)], where the results prove the promising adsorption performances of Ce-UiO-66 MOFs toward CR dye. Interestingly, the synthesized adsorbent exhibited high structural stability during repeated adsorption-desorption cycles, where the surface area of MOFs decreased from 555 to 376 m2/g after three cycles, while its CR adsorption capacity decreased by only 10% compared to that of the fresh adsorbent. All these outstanding properties indicate that the Ce-UiO-66 MOFs will be an effective adsorbent for water and wastewater treatment applications.

Adsorption properties of cellulose beads prepared by emulsion-gelation method and subsequent oxidation

Cellulose beads with diameters in the micro- to millimeter scale are used in various fields. The search for a novel and straightforward method for producing cellulose beads has attracted significant research attention. In this study, we successfully manufactured cellulose beads using a simple cellulose/LiBr solution-in-oil emulsion-gelation method. Subsequently, we evaluated the dye adsorption capacity of the resultant cellulose beads. The effects of the ratio of the cellulose solution to oil, surfactant concentration, stirring speed, cellulose concentration, and type of surfactant on the size of the beads were investigated. The cellulose beads exhibited a highly porous structure, with a high specific surface area and high adsorption performance for the anionic dye Congo red. In addition, carboxyl groups were introduced into the cellulose beads by oxidation, while retaining their highly porous structure. The adsorption capacity of the cationic dye methylene blue on the oxidized cellulose beads significantly increased with increasing oxidation time and carboxyl group content. In contrast, the adsorption of the anionic dye, Congo red, was inhibited. Cellulose beads with a high carboxyl group content maintained a high adsorption capacity even after repeated adsorption-desorption cycles, demonstrating their potential as reusable adsorbent materials.

Synthesis of zeolite A and zeolite X from electrolytic manganese residue, its characterization and performance for the removal of Cd2+ from wastewater

Electrolytic manganese residue (EMR) can cause serious environmental and biological hazards. In order to solve the problem, zeolite A (EMRZA) and zeolite X (EMRZX) were synthesized by EMR. The pure phase zeolites were synthesized by alkaline melting and hydrothermal two-step process, which had high crystallinity and excellent crystal control. And the optimum conditions for synthesis of zeolite were investigated: NaOH-EMR mass ratio = 1.2, L/S = 10, hydrothermal temperature = 90 °C, and hydrothermal time = 6 h. Then, EMRZA and EMRZX showed excellent adsorption of Cd2+. When T = 25 °C, time = 120 min, pH = 6, C0 = 518 mg·L−1, and quantity of absorbent = 1.5 g·L−1, the adsorption capacities of EMRZA and EMRZX reached 314.2 and 289.5 mg·g−1, respectively. In addition, after three repeated adsorption–desorption cycles, EMRZA and EMRZX retained 80% and 74% of the initial zeolites removal rates, respectively. Moreover, adsorption results followed quasi-second-order kinetics and monolayer adsorption, which was regulated by a combination of chemisorption and intra-particle diffusion mechanisms. The adsorption mechanism was ions exchange between Cd2+ and Na+. In summary, it has been confirmed that EMRZA and EMRZX can be reused as highly efficient adsorbents to treat Cd2+-contaminated wastewater.

Removal of wood dyes from aqueous solutions by sorption on untreated pine (Pinus radiata) sawdust

In this work, the possibility of using un-treated pine (Pinus radiata) sawdust as biosorbent for the removal of three wood dyes (blue, red and black) from aqueous solutions was investigated. The BET surface area of the material was 1.55 ± 0.81 m2 g−1 using N2 at − 196 °C and 17.83 ± 0.032 m2 g−1 using CO2 at 0 °C. The point of zero charge was 4.8. In addition, the material was characterized before and after adsorption by surface analytical techniques. Assays were performed to analize the stability of wood dyes with time and pH and also to estimate the pKa values. Batch adsorption experiments were performed and the influence of experimental parameters such as contact time (up to equilibrium), stirring rate (100 and 210 rpm), adsorbent dose (2–10 g L−1), pH (2–9) and initial dye concentration (5 and 300 mg L−1) were studied. The optimum conditions were pH 2 and adsorbent dose of 6 g L−1 and the highest adsorption percentages achieved at 5 mg L−1 were: 100.0% for the blue, 99.7% for the black and 92.4% for the red. For 300 mg L−1 adsorption efficiency decreased to 85.6, 57.0 and 63.8% for the blue, black and red ones, respectively. Kinetic data were best fitted to the pseudo-second order model, suggesting a chemisorption process. Freundlich and Dubidin-Radushkevich were the best isotherm models. Regeneration study showed that un-treated pine sawdust could be reused efficiently for red dye removal at least in up to four repeated adsorption–desorption cycles using NaOH as desorption agent.

Synthesis of PHEMA-Based Polymeric Particles for Gallic Acid Purification

Gallik asit mantarlarda ve bitkilerde, özellikle mazı, meşe kabuğu, sumak, üzüm ve çay yapraklarında yaygın olarak bulunur. Sahip olduğu antioksidan, antikanser, anti-HIV, antiinflamatuar, antimikrobiyal ve antifungal özellikleri nedeniyle sağlık alanında; bunun yanı sıra kozmetik, gıda, baskı ve boyama endüstrileri gibi çeşitli alanlarda yaygın olarak kullanılmaktadır. Bu yüzden, gallik asitin saflaştırılması büyük önem taşımaktadır. Bu çalışmada, gallik asidin saflaştırılması için VIM ile fonksiyonel hale getirilmiş partiküller sentezlenmiştir. Sentezlenen partiküller, taramalı elektron mikroskobu (SEM), şişme çalışmaları ve yüzey alanı ölçümleri (Brauner-Emmet-Teller; BET) ile karakterize edilmiştir. Partiküllerin polimerizasyon verimi %94, şişme oranı ise %92.5 olarak hesaplanmıştır. SEM analizi sonuçlarına göre yaklaşık 1 μm altında boyutlara sahip olduğu açıkça görülen partiküllerin yüzey alanı BET analizi ile 45 m2/g polimer olarak belirlenmiştir. Optimum koşullar altında maksimum gallik asit adsorpsiyonu 54.5 mg/g partikül olarak elde edilmiştir. Partiküllerin yeniden kullanılabilirliği tekrarlı adsorpsiyon-desorpsiyon döngüsü ile test edilmiş ve 10 döngü sonunda partiküllerin gallik asit adsorpsiyon kapasitesini yaklaşık %94.5 oranında koruduğu sonucuna varılmıştır.

Carbon dioxide adsorption/desorption performance of single- and blended-amines-impregnated MCM-41 mesoporous silica in post-combustion carbon capture

Abstract High-surface-area, hexagonal-structured mesoporous silica, MCM-41, was synthesized and wet impregnated with three different amines of 2-(ethylamino) ethanol (EAE), ethylenediamine (EDA), and tetraethylenepentamine (TEPA) for use as solid adsorbents in post-combustion CO2 capture application. The CO2 adsorption test was performed at 25°C and atmospheric pressure using 15/85 vol% of CO2/N2 at a 20-mL/minute flow rate. Desorption was carried out at 100°C under 20 mL/minute of N2 flow. The results show that the capacity and rate of CO2 adsorption obtained from all the amine-modified adsorbents were significantly increased with increasing amine loading due to carbamate formation. Desorption efficiency and heat duty for regeneration were also affected by the amount of amine loading. The more stable the carbamate produced, the higher the energy was required. They exhibited the highest adsorption–desorption performance at 60 wt% amines used for impregnation. Blended EAE/TEPA at different weight ratios at a total concentration at 60 wt% amines was impregnated on MCM-41 adsorbent. Sorbent impregnated with 50%/10% of EAE/TEPA showed the best performance of 4.25 mmolCO2/g at a high adsorption rate, a low heat duty of 12 kJ/mmolCO2 and with 9.4% reduction of regeneration efficiency after five repeated adsorption–desorption cycles.

Wastewater Treatment by Polymeric Microspheres: A Review.

This review addresses polymer microspheres used as adsorbent for wastewater treatment. The removal of various pollutants (including dyes, heavy metal ions, and organic pollutants) is a prominent issue, as they can cause severe health problems. Porous microspheres can provide large specific area and active sites for adsorption or photo degradation. Enhancement in performance is achieved by various modifications, such as the introduction of nanoparticles, magnetic particles, and ZIF-8. Some microspheres were synthesized from synthetic polymers such as vinylic polymer and polydopamine (PDA) through a facile fabrication process. Natural polymers (such as cellulose, alginate, and chitosan) that are biodegradable and eco-friendly are also used. The adsorbents used in industrial application require high adsorption capacity, thermal stability, and recyclability. Batch adsorption experiments were conducted to investigate the optimal conditions, influence of related factors, and adsorption capacities. Insights regarding the adsorption mechanisms were given from the kinetic model, isotherm model, and various characterization methods. The recyclability is investigated through regeneration ratio, or their maintenance of their capability through repeated adsorption-desorption cycles. The high potential of polymer microsphere for the removal of pollutants from wastewater is shown through the high adsorption capacities, environmentally friendliness, and high stability.

Eddy current measurement of chemiresistive sensing transients in monolayer graphene

Eddy current measurement of sheet conductance in monolayer graphene avoids experimental uncertainties associated with the vulnerability of atomic scale films to mechanical damage, in particular due to electrode deposition or during contact-based conductance measurements. The development of constitutive models which account for hysteretic variations in sheet conductance, associated with repeated adsorption-desorption cycles, offers a systematic approach to address a second major complication in comparing nominally similar experiments on chemiresistive gas sensing performance. Transient, multi-cycle oxygen sensing experiments conducted on large-area graphene measured a sheet conductance in the mid range of an order of magnitude variation reported in previous work. A constitutive model developed from the test data separates the deterministic, material history dependent response measured at fixed material points from the stochastic variations in conductance associated with imperfections in the monolayer film.

Preparation of a novel ion-imprinted membrane using sodium periodate-oxidized polydopamine as the interface adhesion layer for the direction separation of Li+ from spent lithium-ion battery leaching solution

In this paper, a novel ion-imprinted membrane (SP-IIM) was prepared by combining graft polymerization with chemical modification and from polydopamine (PDA) oxidized by sodium periodate (SP-PDA) as the interface adhesion layer. The PDA was oxidized by sodium periodate at pH 5.0, causing it to undergo extensive cross-linking within the adhesion layer to provide better chemical stability for improving the reusability of the membrane. The flaky microstructure of the SP-PDA provided more surface area for the loading of 12-Crown-4 (12C4). The optimal adsorption capacity of the SP-IIM for Li+ was 42.58 mg·g−1 after incubating the membrane in a 200 mg·L–1 solution of Li+ for 180 min. The kinetics and isotherm data of the adsorption of Li+ onto the SP-IIM were fitted to pseudo-second-order kinetics and Langmuir model, respectively. Through selective adsorption experiments, the optimal selective separation factors of Li+/Mn2+, Li+/Co2+, Li+/Ni2+ were 6.71, 5.84 and 3.03, respectively. Density functional theory (DFT) calculations were performed on the coordination of metal cations (Li+, Mn2+, Co2+, and Ni2+) by 12C4, the results of which showed that the weak binding of Li+ to 12C4, as well as the favorable dehydration of Li+, made it easier for Li+ to be coordinated by 12C4 in a multicomponent solution containing Li+, Mn2+, Co2+, and Ni2+. The oxidation of the PDA by sodium periodate caused significant intermolecular cross-linking within the SP-PDA layer to reduce the possibility of the ion-imprinted layer detaching from the membrane, thereby increasing the reusability of the SP-IIM. After five repeated adsorption–desorption cycles, the adsorption capacity of the SP-IIM only decreased by 4.6%, which indicated that the SP-IIM was highly reusable. This work improved the adsorption capacity and reusability of ion-imprinted membranes by changing the microstructure of the interface adhesion layer, which was of great significance to the further development of ion-imprinted membranes.

In-situ formed Cyclodextrin-functionalized graphene oxide / poly (N-isopropylacrylamide) nanocomposite hydrogel as an recovery adsorbent for phenol and microfluidic valve

Phenolic compounds are important industrial raw materials for various industrial applications, but phenol-containing wastewater creates significant environmental and biological hazards. To address these issues, a three-dimensional network graphene oxide-cyanoethyltriethoxysilane-β-cyclodextrin/poly (N-isopropylacrylamide) (GO-CTES-β-CD/PNIPAM) nanocomposite hydrogel as a phenol recovery adsorbent is prepared herein by in-situ polymerization. Double graft modification on the graphene oxide (GO) via the silane coupling agent 2-cyanoethyltriethoxysilane (CTES) and single (6-tetraethylenepentamine-6-deoxy)-β-cyclodextrin (NH-β-CD) compensated the loss of the active sites on both GO and N-isopropylacrylamide (NIPAM), and the hydrogel shows excellent mechanical properties as the chemical crosslinking and physical entanglement of the two components. Consequently, the composite hydrogel achieved an adsorption capacity of 131.64 mg·g−1 for the common environmental toxin 4-NP. After five repeated adsorption–desorption cycles, the hydrogel retained 74% of the initial 4-NP removal ratio. The adsorption results followed pseudo-first-order kinetics, corresponding to heterogeneous multilayer adsorption, which was regulated by a combination of surface adsorption and intra-particle diffusion mechanisms. In general, the nanocomposite hydrogel shows promising application in the field of recycling phenols from wastewater. Also, high photothermal conversion and temperature-sensitive properties are also demonstrated, which makes the hydrogel possessing great potential to be applied in smart microvalves.

Multifunctional amphoteric resin to remove both anionic and cationic dyes from aqueous solution

AbstractThis study reports the synthesis and characterization of a new amphoteric resin, which can be used for the removal of both cationic, methylene blue (MB) and anionic dyes, reactive red‐120 (RR‐120). The amphoteric resin was characterized by ATR‐FTIR, SEM–EDX, TGA/DTA, DLS, BET analysis and also its surface pHpzc was determined. The prepared resin has micro porous structure and its particle size was at the nano level. The prepared amphoteric resin showed high removal affinity for MB in both acidic and basic medium, while for RR‐120 high removal affinity in acidic medium. Moreover, it was observed that the amphoteric resin has exhibited almost 100% dye removal up to 600 ppm for MB and up to 300 ppm for RR‐120, respectively. The adsorption behavior of both dyes on the amphoteric resin is in agreement with the Langmuir isotherm and the pseudo‐second order kinetic model and also electrostatic interaction is dominant in adsorption. Its capacity was slightly low for the MB than that of the commercial activated carbon, but higher for the RR‐120. Furthermore, it was observed that the amphoteric resin almost did not lose its high removal efficiency in the concentrated matrix environment for both dyes. After five repeated adsorption–desorption cycles, the high removal efficiency of the resin for the MB (almost 100%) unchanged, but for the RR‐120 decreased to 83%.

Preparation of magnetic kaolin embedded chitosan beads for efficient removal of hexavalent chromium from aqueous solution

The removal of toxic hexavalent chromium (Cr(VI)) ions is highly demanded. Herein, the magnetic kaolin embedded chitosan (MKCS) beads with different mass ratios of MK/CS were prepared by a simple pH-precipitation method and applied for the removal of Cr(Ⅵ) ions from aqueous solution. Factors influencing the removal of Cr(Ⅵ) ions such as solution pH, adsorbent dosage and contact time were investigated systematically by batch experiments. The results showed that MK0.2CS beads (the mass ratio of MK to CS equals 0.2) can remove more than 92% and 72% of Cr(Ⅵ) respectively with the initial concentrations of 40 and 60 mg/L. And the MK0.2CS beads showed an adsorption capacity of 144.0 mg/g with the initial Cr(VI) concentration of 300 mg/L at 25 °C. The adsorption data is fitted well with the pseudo-first-order kinetic model, indicating that the adsorption is a physical process. The adsorption isotherm study and thermodynamic study revealed a multilayer and exothermic adsorption, respectively. After Cr(Ⅵ) uptake, the adsorbent was well-regenerated by 1 M NaOH, and the results showed that the MKCS beads can be reused successfully in repeated adsorption-desorption cycles. The MKCS beads were thoroughly characterized before and after Cr(VI) adsorption. XPS analysis revealed that the adsorption of Cr(Ⅵ) on MKCS beads could be attributed to electrostatic interaction. The results suggested that the MKCS beads can be considered as an effective and promising adsorbent for wastewater treatment.

Double-network cross-linked aerogel with rigid and super-elastic conversion: simple formation, unique properties, and strong sorption of organic contaminants.

Novel adsorbents with high adsorption capacity, broad-spectrum adsorption performance, and good reusability are needed for the treatment of diverse and complex contaminants in water. In this work, we used in situ hydrothermal reaction to fabricate graphene oxide (GO) and poly(vinyl alcohol) (PVA) based aerogels (GPXA, X represented the volume of PVA) through the cross-linking network that meets the above requirement. After adding Ca2+, GP16A (with 16 mL PVA) had surprisingly rigid and super-elastic conversion that is dependent on water stimulus. The strong adsorption of methylene blue (MB) on GP16A illustrated that it had excellent dye removal ability. The adsorption capacity of GP16A to MB was 698.38 mg g-1 and it remained 85.62% after repeated adsorption-desorption cycles. The adsorption was controlled by multiple mechanisms including electrostatic interaction, π-π interaction, and hydrogen bond. In addition, hydrophobically modified GP16A (GP16A-MTMS) effectively absorbed common oils and organic solvents. Repeated absorption of GP16A-MTMS was re-activated by squeezing operation. This study provides an alternative technique for preparing aerogel materials with high recyclability, dimensional stability, and solvent resistance, and for dealing organic contaminants in water.

Aspirin Adsorption onto Activated Carbon Derived from Spent Tea Leaves: Statistical Optimization and Regeneration Study

Contamination of water sources by contaminants of emerging concerns, including pharmaceutical compounds, threatens the well-being of human who relies on the water sources. Development of cost-effective adsorbents for maximum removal of these contaminants is important to ensure clean and safe water access. This study demonstrates the reusability of activated carbon synthesized from spent tea leaves (STL-AC) for aspirin adsorption at optimized conditions. The maximum aspirin removal was 98.97% after optimization of process conditions using Response Surface Methodology. The adsorbent can be reused up to five cycles via solvent elution, with aspirin removal percentage above 85%. The repeated adsorption–desorption cycles affected the adsorbent textural properties, however the adsorbent surface chemistry was not affected by the regeneration. The aspirin adsorption proceeds via pore filling together with hydrogen bonding and π–π interaction between the aspirin molecules, however electrostatic repulsion between the deprotonated aspirin molecules and negatively charged STL-AC resulted in reduced removal percentage at high solution pH. This study signifies the superior property of STL-AC in adsorptive removal of aspirin, therefore the potential of such adsorbent in treatment of municipal wastewater, as well as hospital and pharmaceutical manufacturing effluents will be investigated.

N, S doped carbon quantum dots inside mesoporous silica for effective adsorption of methylene blue dye

This study aimed to develop non-metal elements for doping carbon quantum dots (CQDs) with nitrogen and sulfur (N, S-CQDs), which loaded inside hexagonal mesoporous silica (HMS) in order to effectively remove methylene blue dye (MB) from an aqueous solution. The histidine and cysteine amino acids were used as the source for synthesis N, S-CQDs through the hydrothermal method. Morphology and structure of the N, S-CQDs, and adsorbent (N, S-CQDs/HMS) were characterized by using different microscopic and spectroscopic techniques. The adsorption parameters such as adsorbent dosage (0.25–1 g/L), pH (2–10), contact time (15–75 min), and initial MB dye concentration (20–300 mg/L) were investigated. The maximum adsorption capacity and removal efficiency of MB were determined at 370.4 mg/g and 97%, respectively, under optimum conditions at 303 K. The adsorption isotherm studies were fitted with the Freundlich isotherm equation, and the dye removal kinetics of the adsorbent followed the pseudo-second-order model. Thermodynamic studies showed that the adsorption process had exothermic and spontaneous behavior. The removal of MB next to the Rhodamine B and Reactive Black 5 dyes indicated that the N, S-CQDs/HMS had excellent selective behavior for MB absorption. This prepared adsorbent could be well recycled with suitable activity after four repeated adsorption–desorption cycles. Results revealed that the porous characters, surface area, charge properties, reduction in the bandgap, and quantum yield of the N, S-CQDs/HMS were essential factors that affected dye adsorption.