Adsorbent Loading Research Articles

Pillar[5]arene-based Polymer Network for Efficiently Removing Perfluorooctanoic Acid through Synergistic Binding Interactions.

Perfluorooctanoic acid (PFOA) is currently one of the most important chemicals posing environmental risks, and there is an urgent need to find methods to efficiently remove PFOA from environmental media. Here, two decaamino-pillar[5]arene-based fluorine-rich polymer networks, called FA2P-P and FA6P-P, were constructed using a convenient method. FA6P-P had an excellent ability to take up PFOA, and had a capacity of 1423 (mg PFOA) (g FA6P-P)-1, which is the second highest adsorption capacity reported for any PFOA sorbent. FA6P-P removed >99 % of the PFOA from a solution and decreased the PFOA concentration from 1000 μg L-1 in 5 min at an exceedingly low adsorbent loading of 0.7 mg L-1, giving a final PFOA concentration <4 ng L-1, which is lower than the most recent enforceable maximum concentration set by the United States Environmental Protection Agency. A high rate constant (kobs) of 55.8 g mg-1 h-1 was observed. Pillar[5]arene gives the material hydrophobic properties and also amino sites and hydrophobic chains, which are synergistic PFOA binding sites. The polymer was very stable and readily regenerated. The results indicated that pillar[5]arene-based porous organic polymer sorbents are excellent candidates for capturing PFOA.

Tailored nano clay blends for enhanced dye mixture adsorption in wastewater treatment

Natural clays are eco-friendly, cost-effective, and industrially acceptable adsorbents employed in wastewater treatment. Textile effluents contains mixture of dyes where a single adsorbent often fails to treat completely. Herein, the simplest strategy for the efficient treatment of effluent with multicomponent pollutants using an tailored blend of two clay minerals has been presented. This strategy was studied using a binary blend of halloysite and montmorillonite clays (HAMT) to remove a mixture of industrial dyes, reactive Black-B (BB) and methyl red (MR) from the model effluent. Here, halloysite (HA) and montmorillonite (MT) selectively adorbs reactive black-B and methyl red respectively and could not completely treat model effluent individually whereas HAMT blend proved to be most effective. HAMT blend was prepared by convenient ultra-sonication assisted solution process and characterized using the various analytical techniques such as FT-IR, DR-UV spectra, XRD and SEM to determine structural, morphological features. Adsorption of model effluent studied as a function of pH, time, adsorbent loading and adsorbate concentration. The dye removal efficiency was remarkably enhanced when the HAMT blend was used according to the concentration of dyes present in the model effluent. The maximum dye removal efficiency was attained using HAMT (1:1) blend for effluent with an equimolar concentration of selected dyes. Similarly, HAMT (2:1) found suitable for the treatment of real textile effluent collected from local textile industries based on its assessment. This study aids in the development of a tailored adsorbent blend using conventional adsorbents for complex effluent treatment in a cost-effective way, eliminating the need for specialized materials.

Removal of ammonia from rubber wastewater using rubber-sludge-based biochar to enhance biogas production

Anaerobic digestion of rubber wastewater (ADRW) is an option for methane derivation for biogas production. However, the ammonia content in rubber wastewater, known as ammonia inhibition, has made the practical implementation of ADRW not yet feasible due to anaerobic digestion (AD) instability and low substrate degradation. Numerous studies have mentioned the use of biochar to overcome its inhibitory effect in AD. However, there are no report on the performance of rubber-sludge-based biochar (RSB) for removing ammonia from rubber wastewater to enhance biogas production. Therefore, this study investigates the potential of RSB to remove ammonia from wastewater to enhance biogas production. Initially, the RSB adsorbent was prepared by facile carbonization method and characterized with scanning electron microscopy (SEM), N2 physisorption, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis. The performance of the RSB adsorbent for ammonia removal from wastewater was examined using the one -factor -at -one -time (OFAT) adsorption method. The AD process was then conducted using the treated wastewater. The results show that RSB possessed significant porous structure with high carbon content and a surface area of 20.3218 m2/g. The highest ammonia removal was 7.5mg/l at an initial adsorbent loading dosage of 1.5g of RSB for 30min of mixing. Further, during the AD process, the highest biogas yield of 19.061ml/g was achieved after 28 days at pH 8. Approximately 83% of the methane composition was obtained from the biogas yield, indicating that the RSB contributes to the enhancement of biogas production by removing ammonia from rubber wastewater.

Synthesis, characterization of hydroxyapatite from pomegranate fruit peel for Cr (VI) adsorption: Process modelling, kinetic and isotherm studies

The present work focuses on preparation of hydroxyapatite from pomegranate peels by precipitation method. The hydroxyapatite derived from pomegranate fruit peels (HA-PP) was characterized by XRD, FT-IR, SEM-EDS and BET techniques. The HA-PP has mesoporous in structure and had an area of 99.021 m2/g. Further HA-PP was used as adsorbent for the removal of Cr (VI) ion particles from K2Cr2O7. The adsorption trials were executed and found the optimized solution using response surface methodology (RSM). The experiments included parameters like pH 2, initial chromium concentration 200 mg/L, adsorbent loading 0.8 g, and contact time 60 min, respectively. Cr (VI) removal was 89.4 % at the optimum combination of these process parameters. A mathematical and statistical optimizing technique response surface methodology (RSM) was applied to verify the interactive effects of various parameters on the adsorption capacity. The analysis of variance (ANOVA) was used to predict the adequacy of the model (F 82.16) shows developed model is valid with R2 value 0.987, and p-value (>0.1). In this the Langmuir adsorption isotherm and the pseudo-second-order kinetic model are well explained for Cr (VI) adsorption onto HA-PP. This reaction is spontaneous and endothermic, as indicated by the negative change in the standard free energy (ΔG0 = −0.1732) and ΔH0 (+4.71) value at the selected temperature. The ΔS0 (+15.89) further confirms that the randomness increased at the solid-solution interface during adsorption.

Green synthesis of zinc oxide nanoparticles for the removal of phenol from textile wastewater

This study investigated the use of zinc oxide nanoparticles (ZnO NPs) as an adsorbent for removing total phenols from textile wastewater. The ZnO NPs were synthesized by reducing Zn(NO3)2⋅6H2O using an extract from Neem leaves (Azadirachta indica). Characterization of the adsorbent was performed using Fourier Transform Infrared (FTIR) spectroscopy to identify functional group modifications, high-resolution scanning electron microscopy (HRSEM) for structural orientation, energy dispersive spectroscopy (EDS) for elemental analysis, and X-Ray diffraction analysis (XRD) for crystallinity, revealing particle crystallinity around 200 nm. Adsorption experiments were conducted over contact times of 20–60 min, with adsorbent loadings between 0.2 and 1 g/100 mL, and temperatures ranging from 30 to 50 °C. Optimal phenol removal, achieving 55.93% (0.67 mg/L), occurred at 43.40 min, 33.70 °C, and an adsorbent dosage of 0.69 g/L of textile wastewater. The phenol adsorption process using ZnO NPs was exothermic, spontaneous, and required low energy, fitting well with the Langmuir isotherm and following a pseudo-second-order kinetic model.

Ultrasound-assisted enhanced adsorption of textile dyes with metal organic frameworks

In this study, ZIF-67 based metal–organic framework (MOF) is used for the adsorption of several synthetic dye effluents (Malachite green (MG), Rhodamine-B (Rh-B), Methylene Blue (MB) and Congo Red (CR)) with intensified adsorption in the presence of ultrasound. The adsorption capacity of ZIF-67 is evaluated for multiple single dye systems and binary dye mixtures. The effect of different operational parameters such as contact time, adsorbent dosage, dye concentration, temperature, pH, binary dye systems, real effluents, and the presence of ultrasound is explored in detail. The adsorption for single dye systems shows the removal efficiencies in the order of MG > CR > Rh-B > MB. The adsorption of CR and MG on ZIF-67 followed Langmuir isotherm which estimated the maximum adsorption capacity of 701 and 3623 mg. g−1 respectively. An optimum adsorbent loading of 1 g.L−1 is effective for the efficient removal of MG and CR. Further, thermodynamic studies indicate that the adsorption process is spontaneous and endothermic. The kinetic models for both dyes suggested a prevailing chemisorption mechanism, in line with the pseudo second-order model (PSOM). For binary dye systems of MG and CR, the selectivity towards maximum adsorption capacity is favored with MG compared to CR. Ultrasound-assisted adsorption intensified the removal efficiency up to ∼ 67 % and ∼ 93 % within 5 min for CR and MG respectively. ZIF-67 is stable over multiple consecutive cycles affirming its reliability for reuse. Maximum removal of dyes was also obtained with real textile dye effluents.

Enhanced Cd(II) adsorption and antibacterial performance of hydrothermally synthesized FeS2/Chitosan composite

This study demonstrates the efficacy of FeS2/Chitosan composites as adsorbents for removing cadmium (Cd) from wastewater, showcasing a promising approach for environmental pollution treatment. The hydrothermal synthesis method successfully produced FeS2 and FeS2/Chitosan composites with desirable properties obtained from XRD, FTIR, SEM EDX, XPS, and UV–Vis DRS, including a pyrite crystal structure, 15 nm crystalline size, and a 2.77 eV bandgap energy. The optimized conditions for maximum Cd(II) removal were determined to be a pH of 6, a 12 mg/L Cd(II) solution, a 40 mg adsorbent loading, and a 40 min contact time, achieving complete removal through a pseudo-first-order process. Moreover, the biological studies indicated that the FeS2/Chitosan composite shows significant antibacterial activity against E.coli, further enhancing its utility in wastewater treatment applications. The composite’s dual functionality in heavy metal adsorption and antibacterial efficacy highlights its potential for comprehensive wastewater management solutions. Future research could explore the scalability of this approach and its application to other heavy metals and contaminants, further contributing to sustainable environmental practices.

A novel lignin-steel sludge composite for dyes adsorption from water: Surface functionalities and structural alteration mechanisms

The study focuses on fabricating and utilizing a lignin-steel sludge magnetic carbon composite (SLNa) to efficiently remove two dyes from an aqueous medium. The SLNa composite was fabricated through a simple two-step strategy involving the activation and thermal treatment of lignin and steel sludge. The SLNa possessed lignin and steel sludge starring properties, viz. abundant surface functionalities, graphitic carbon matrix, and magnetic characteristics. The synergistic combination of lignin and steel sludge resulted in composite's high adsorption potential for Methylene Blue (MB; 153.92 mg/g) and Acid Orange 7 (AO7; 64.84 mg/g) in batch mode. Additionally, the rapid adsorption kinetics and effective dye removal for MB (> 99 %) and AO7 (72 %) from simulated effluent revealed the potential of fabricated adsorbent for water remediation. Furthermore, the composite's applicability for continuous adsorption was also evaluated through a series of dynamic flow experiments using fixed-bed column systems. The demonstrated efficacy of SLNa, viz., 48.18 and 15.00 mg/g for MB and AO7, respectively, at high adsorbent loading and lower dye concentrations, highlights its potential for scalable water treatment applications. Thus, the versatility and effectiveness of the novel composite underscore its potential for practical application in both batch and continuous water remediation processes.

Removal of an organophosphate insecticide from aqueous media using phyllosilicate clay: multivariable optimization, nonlinear kinetic modelling and thermodynamic study

The excessive and irrational use of organophosphate insecticides in our lives has resulted in a serious environmental problem, necessitating the proposal of novel and cost-effective plans to remove these organophosphate insecticides from agricultural or industrial wastewater. In this approach, we investigated the use of phyllosilicate clay as a low-cost and environmentally friendly adsorbent to eliminate an organophosphate insecticide (Diazinon DZN) from an aqueous medium. To achieve an adequate elimination of this insecticide from contaminated water, three main parameters including clay dose ( D c ) (0.1–1.5 g L−1), medium pH (5–9), and initial DZN concentrations ( C DZN ) (55–40 mg L−1) were optimized using a multivariable optimization based on Box-Behnken Design (BBD). The response surface method (RSM) and composite desirability function technique were used to find the ideal conditions for the three input variables and the adsorption amount ( Q e ) was selected as the output variable. The higher adsorption amount ( Q max ) was achieved with an adsorbent amount of 1.5 g L−1 in an acidic medium (pH = 5) at room temperature and a Diazinon initial dose of 25.85 mg L−1, with a maximum adsorbent loading of 12.20 mg g−1. The nonlinear modeling study showed that the adsorption kinetics of Diazinon follows the pseudo-second-order model. The thermodynamic study shows that the DZN removal process is exothermic, spontaneous, and of a stable configuration.

Adsorption of Cr(VI) from aqueous solutions using inorganic clays modified magnetic chitosan adsorbent: Kinetic and thermodynamic study

Inorganic clays modified magnetic chitosan adsorbent (ICMMCA) was successfully prepared and systematically characterized in chemical structure and morphology. Effect of variables including initial pH and concentration of Cr(VI) in the solution, adsorption time, adsorption temperature and coexisting ions on the performance of ICMMCA in Cr(VI) removal from water were evaluated. Furthermore, the kinetic and thermodynamic studies were conducted to elucidate the adsorption mechanisms and thermodynamic characteristics of the adsorption process. The results demonstrated that the maximum Cr(VI) adsorption capacity of 94.67 mg/g could be achieved when the adsorbent loading was 1 g/L, the initial concentration of Cr(VI) was 100 mg/L, the adsorption time was 60 min and solution pH was at 5. The adsorption data could be well fitted by the Freundlich isotherm model. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic in nature. The adsorption process could be described by the pseudo-second-order kinetic model.

3D printing of poly(ethyleneimine)-functionalized Mg-Al mixed metal oxide monoliths for direct air capture of CO2

Direct air capture (DAC) of CO2 plays an indispensable role in achieving carbon-neutral goals as one of the key negative emission technologies. Since large air flows are required to capture the ultradilute CO2 from the air, lab-synthesized adsorbents in powder form may cause unacceptable gas pressure drops and poor heat and mass transfer efficiencies. A structured adsorbent is essential for the implementation of gas-solid contactors for cost- and energy-efficient DAC systems. In this study, efficient adsorbent poly(ethyleneimine) (PEI)-functionalized Mg-Al-CO3 layered double hydroxide (LDH)-derived mixed metal oxides (MMOs) are three-dimensional (3D) printed into monoliths for the first time with more than 90% adsorbent loadings. The printing process has been optimized by initially printing the LDH powder into monoliths followed by calcination into MMO monoliths. This structure exhibits a 32.7% higher specific surface area and a 46.1% higher pore volume, as compared to the direct printing of the MMO powder into a monolith. After impregnation of PEI, the monolith demonstrates a large adsorption capacity (1.82 mmol/g) and fast kinetics (0.7 mmol/g/h) using a CO2 feed gas at 400 ppm at 25 °C, one of the highest values among the shaped DAC adsorbents. Smearing of the amino-polymers during the post-printing process affects the diffusion of CO2, resulting in slower adsorption kinetics of pre-impregnation monoliths compared to post-impregnation monoliths. The optimal PEI/MeOH ratio for the post-impregnation solution prevents pores clogging that would affect both adsorption capacity and kinetics.

Integrated study of antiretroviral drug adsorption onto calcined layered double hydroxide clay: experimental and computational analysis

This study focused on the efficacy of a calcined layered double hydroxide (CLDH) clay in adsorbing two antiretroviral drugs (ARVDs), namely efavirenz (EFV) and nevirapine (NVP), from wastewater. The clay was synthesized using the co-precipitation method, followed by subsequent calcination in a muffle furnace at 500 °C for 4 h. The neat and calcined clay samples were subjected to various characterization techniques to elucidate their physical and chemical properties. Response surface modelling (RSM) was used to evaluate the interactions between the solution’s initial pH, adsorbent loading, reaction temperature, and initial pollutant concentration. Additionally, the adsorption kinetics, thermodynamics, and reusability of the adsorbent were evaluated. The results demonstrated that NVP exhibited a faster adsorption rate than EFV, with both reaching equilibrium within 20–24 h. The pseudo-second order (PSO) model provided a good fit for the kinetics data. Thermodynamics analysis revealed that the adsorption process was spontaneous and exothermic, predominantly governed by physisorption interactions. The adsorption isotherms followed the Freundlich model, and the maximum adsorption capacities for EFV and NVP were established to be 2.73 mg/g and 2.93 mg/g, respectively. Evaluation of the adsorption mechanism through computational analysis demonstrated that both NVP and EFV formed stable complexes with CLDH, with NVP exhibiting a higher affinity. The associated adsorption energies were established to be −731.78 kcal/mol for NVP and −512.6 kcal/mol for EFV. Visualized non-covalent interaction (NCI) graphs indicated that hydrogen bonding played a significant role in ARVDs-CLDH interactions, further emphasizing physisorption as the dominant adsorption mechanism.

Ethanol-enhanced wash-coating of zeolite 13X on microchannel walls for CO2 capture

Minimizing the energy demand for capturing carbon dioxide (CO2) from air and post-combustion sources is critical to mitigate the effects of climate change. Adsorbent-coated microchannels have been shown to significantly enhance the performance of CO2 capture systems. A novel single-dip wash-coating approach is developed in this work using silica nanoparticles and various base solvents to create a uniform and porous zeolite 13X adsorbent layer on cordierite microchannels. Extensive exploration of base solvents is undertaken to enhance adsorption performance and structural integrity, culminating in identifying a 70 % ethanol mixture as the most effective solvent. The coatings are characterized through a materials characterization suite and image analysis in conjunction with CO2 adsorption performance to determine the optimum adsorbent loading conditions. Equilibrium adsorption performance tests are performed for the coated samples in CO2 capture systems. The specific surface area (SSA) of the powdered 13X, initially measured at 662 m2/g, decreased to 553 m2/g in the coated form (utilizing a 20 % solid fraction with 70 % ethanol as the solvent), which is consistent with the observed adsorption performance results. The results underscore the scalability potential of these coated microchannels, presenting a promising alternative for CO2 separation systems to the conventional packed adsorbent beds.

Ni2+ removal by ion exchange resins and activated carbon: a benchtop NMR study

Heavy metal pollution in water is a critical environmental concern, demanding effective remediation techniques. Traditional methods, including ion exchange and adsorption, often rely on inductively coupled plasma (ICP) atomic emission spectroscopy/mass spectrometry (AES/MS) for the indirect and time-consuming measurement of residual metal concentrations. In contrast, this study employs innovative direct monitoring of nickel removal by benchtop NMR relaxometry using the paramagnetic properties of Ni2+. To prove the feasibility of the NMR follow-up of Ni2+ uptake, batch experiments were performed with Amberlite IR120, Amberlite IRC748, Dowex Marathon MSC, and activated carbon (AC), which were previously characterized by various techniques. The effect of contact time, pH, and Ni2+ concentration on removal efficiency were studied. Pseudo-first and pseudo-second order kinetic models were used. The Langmuir model effectively described the equilibrium isotherms. The longitudinal and transverse relaxation curves of the loaded resins were biexponential. For sulfonic resins, a strong correlation was observed between the relaxation rates of the fast-relaxing fraction and the Ni2+ content determined by ICP-AES/MS. For IRC748, the effect of Ni2+ loading on the relaxation rates was weaker because of Ni2+ complexation. The relaxation curves of loaded AC revealed multiple fractions. Centrifugation was employed to eliminate the contribution of intergranular water. The remaining intragranular water contribution was biexponential. For high Ni2+ loadings, the relaxation rates of the slow relaxing fraction increased with the AC Ni2+ content. These results mark the initial stage in developing a column experiment to monitor, in real-time, adsorbent loading by NMR relaxometry.

Construction of 3D-Printed Sodium Alginate/Chitosan/Halloysite Nanotube Composites as Adsorbents of Methylene Blue.

In this study, sodium alginate/chitosan/halloysite nanotube composites were prepared by three-dimensional printing and characterized in terms of morphology, viscosity, thermal properties, and methylene blue (MB) adsorption performance. The high specific surface area and extensively microporous structure of these composites allowed for effective MB removal from wastewater; specifically, a removal efficiency of 80% was obtained after a 60 min treatment at an adsorbent loading of 1 g L-1 and an MB concentration of 80 mg L-1, while the maximum MB adsorption capacity equaled 376.3 mg g-1. Adsorption kinetics and isotherms were well described by quasi-second-order and Langmuir models, respectively. The composites largely retained their adsorption performance after five adsorption-desorption cycles and were concluded to hold great promise for MB removal from wastewater.

Porous Fe-Porphyrin as an Efficient Adsorbent for the Removal of Ciprofloxacin from Water.

Antibiotics are widely used in medicine, but they are not fully metabolized in the body and can end up in wastewater. Conventional wastewater treatment methods fail to completely remove antibiotic residues, which can then enter rivers and streams. Adsorption is a promising technique for removing antibiotics from wastewater, even at low concentrations. The successful one-pot synthesis of an adsorbent, iron-containing porphyrin-based porous organic polymer (Fe-POP), was achieved through the reaction of pyrrole groups and terephthalaldehyde in the presence of FeCl3. Characterized by a substantial BET surface area of 597 m2 g-1, Fe-POP was systematically investigated for its adsorption potential in the removal of the antibiotic Ciprofloxacin (CIP) from aqueous solutions. By systematic variation of key parameters, including pH, adsorbent loading, and CIP concentration, the adsorption conditions were optimized. Under the optimal conditions at pH = 3, CIP concentration of 5 ppm, and 25 mg of Fe-POP, the maximum adsorption capacity reached an impressive 263 mg g-1. The robust adsorption behavior was elucidated through the fitting of experimental data to the Langmuir adsorption isotherm (R2 = 0.962) and the pseudo-second-order kinetic model (R2 = 0.999) with lower error values. These models suggested that the adsorption process predominantly involved chemical interactions between CIP molecules and the Fe-POP surface. Fe-POP exhibited a robust structure with a high adsorption capacity, showcasing its efficacy in removing CIP contaminants from water. Therefore, Fe-POP can be considered a valuable adsorbent for water treatment applications, specifically for antibiotic removal.

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

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

Enhancement of sorption of the azoic dye (Azucryl Red) by natural and calcined hyper-aluminous kaolins

Purpose. To remove of basic textile dye Azucryl Red (AR) from aqueous solutions using hyper-aluminous kaolins from Charente deposits (France) in natural and calcined states. Methodology. Batch interactive parameter pH, pHpzc contact time, dye concentration, adsorbent loading and temperature are taken to obtain optimums for the AR adsorption process in natural and calcined kaolin named respectively Kca, Kcm, Ckca, and Ckcm. Findings. The adsorption equilibrium was established in 7 min while the second-order kinetic model better described the adsorption kinetics for all kaolins with the chemisorption process. The adsorption isotherm of the results obtained corresponds better to the Langmuir model. The maximum quantity retained was 67.97 and 73.38 mg/g respectively for Kcm and Kca samples. Moreover, in the calcined state, the maximum quantity retained was 76.66 and 75.64 mg/g respectively for the calcined kaolin CKcm and CKca samples for a temperature of 298 K and pH = 6. The thermodynamic nature of the adsorption process was determined by calculating H, S and G° values. The positive value of H° confirms the fact that adsorption is endothermic spontaneous which is enhanced at higher temperatures. Originality. The heat treatments of the different kaolins at 400 °C enhance the adsorption process. Therefore, the results indicate that Ckcm performed with the highest adsorption capacity in the removal of the dye, followed by Ckca. Practical value. Adsorption processes of toxic Azucryl Red dye in the aqueous medium using natural and calcined hyper-aluminous kaolins at 400 °C were investigated. Optimization and modeling of the adsorption parameters with the theories by Langmuir, Freundlich and Elovich allowed us to find the optimal experimental conditions for sorption. Our results therefore indicate that the adsorption process of Azucryl red dye from aqueous solutions was enhanced when calcined kaolin at 400 °C containing organic matters was used.

Adsorption of Cr(VI) ions onto fluorine-free niobium carbide (MXene) and machine learning prediction with high precision

Due to the unique surface microstructure, abundant active sites, and rich functional groups, two-dimensional MXene is increasingly gaining attention in the field of environmental purification. Herein, novel fluorine-free niobium carbide (Nb2CTx) was successfully synthesized using hydrothermal technique and applied towards the Cr(VI) ions elimination from wastewater. The structure and surface properties of the Nb2CTx were analyzed by various characterization techniques. Based on the findings of batch adsorption, the maximum Cr(VI) ions was removed at solution pH 5 with adsorbent loading of 1 g/L and Cr(VI) initial concentration of 10 mg/L just after 20 min of stirring. Besides, the characteristic information of Nb2CTx and their adsorption data was used to build a machine learning CatBoost model with high precision (R2 = 1, RMSE = 0.145, MAE = 0.08). Cr(VI) removal by MXenes displayed rapid kinetics governed by pseudo-second-order reactions, with adsorption isotherm aligning well with Langmuir isotherms (R2 = 0.998), achieving an adsorption capacity of 93.6 mg/g. The removal mechanism investigation proposed that the electrostatic interactions, chemical reduction and hydrogen bonding were the key driving forces. The hydrothermal route proposed in this study enabled the fabrication of environmental friendly Nb2CTx, which can pave the way for their widespread applications in environmental purification.

Adsorption of Heavy Metals on Alkali-Activated Zeolite Foams.

Elevated concentrations of heavy metals in natural waters can cause significant ecological problems. It is therefore essential to ensure their removal from any water discharged into the environment immediately, especially in case of an accident, where there is a risk of releasing large quantities or high concentrations. The aim of this paper is to test a newly developed adsorbent for the removal of heavy metals from aqueous solutions-in particular, it is very fast adsorption, and thus efficiency, during clean-ups. The alkali-activated foamed zeolite adsorbent was laboratory-prepared and -tested in both batch and flow-through arrangements on single and multi-component solutions and compared with natural zeolite. The experimental setup for batch adsorption consisted of a set of samples and solutions containing iron, cobalt, manganese, zinc and nickel. The samples were put on a horizontal shaker with a 500 mg adsorbent loading in a 50 mL solution. The column adsorption experimental setup consisted of a glass column with an inside diameter of 15 mm and a bed length of 165 mm. A measured amount of each adsorbent was added to the column to achieve a filter fixed-bed height of 160 mm. The high efficiency of the tested adsorbent on various heavy metals was confirmed. The adsorbent has a high potential for use in decontamination processes, water protection and landscape revitalization. Due to its rapid precipitation and subsequent fixation of metal cations in the form of insoluble oxide or hydroxide, it can be used as an emergency adsorbent, the great advantage of which is its low production cost and natural origin.