Adsorption Of Chromium Research Articles

Chromium adsorption using a composite adsorbent of corn waste and bentonite

Chromium, a highly toxic heavy metal, poses significant risks to both human health and environmental quality. Its adsorption in wastewater using low-cost, easily implementable technologies has emerged as a crucial solution for mitigating its harmful impact. This study explores the effectiveness of a composite adsorbent made from bentonite and corn waste for chromium adsorption. Experiments were conducted in a laboratory-scale batch system. The research examined the adsorption kinetics and equilibrium, process optimization, and the mechanisms of chromium adsorption. For optimization, a response surface methodology was applied considering three variables: adsorption time (min), adsorbent dosage (g/L), and initial chromium concentration (mg/L). The findings suggest that the adsorption kinetics fit best with the pseudo-first-order model (R2 = 0.968), and the adsorption equilibrium fits with the Freundlich model (R2 = 0.997). During optimization, the adsorbent dosage emerged as the most critical factor for chromium removal. The optimal operating conditions were determined to be 103 minutes, 29.71 g/L of adsorbent, and an initial chromium concentration of 31.13 mg/L. The results indicate that chromium adsorption is a multifaceted process involving diffusion and subsequent interaction at the surface and edges of the bentonite layers. Chemical analysis, coupled with changes in the FTIR spectrum, suggests an interaction between chromium and the silicon and aluminum components of the bentonite. These findings underscore the potential of the composite adsorbent for effective chromium removal.

Adsorption of Copper and Chromium Mixed Solution on N-Doped Biomass-Activated Carbon

N-doped biomass activated carbon was prepared by direct ultrasonic method and redox method. Scanning electron microscopy, energy-dispersive spectroscopy, Brunnauer-Emmett-Teller, X-ray photoelectron spectroscopy, Zeta potential test, and other characterization methods were used to observe the pore structure, surface functional groups, elemental composition and distribution, and surface charged properties of the two samples. The adsorption experiment of Cu(II)/Cr(VI) mixed solution of two samples was carried out, and the influence of pH value, temperature, and concentration on material properties was explored. The results show that the equilibrium time, adsorption rate, and adsorption capacity of Cu(II)/Cr(VI) mixed solution are shorter, faster, and three times larger compared with the adsorption of single Cu(II) solution. The co-adsorption of Cu(ii) and Cr(vi) was observed. The adsorption capacity of Cr(vi) is not affected by the properties of the materials themselves, but increases with the increase of the initial concentration of Cu(II). The adsorption performance of activated carbon modified by redox method is better than that modified by direct ultrasonic method when adsorbing mixed solution of copper and chromium ions.

Evaluation of the efficiency of shell powder as a natural adsorbent for the adsorption of chromium in aqueous solutions: kinetic and thermodynamic approach and modeling of adsorption isotherms

Water pollution by heavy metals such as chromium is a major environmental issue requiring effective remediation solutions. In this study, shellfish powder was used as a natural material to adsorb chromium (III) from aqueous solutions. The results show that shellfish have a significant adsorption capacity, indicating their effectiveness under a variety of conditions. Adsorption kinetics tests showed that the adsorption mechanism followed a pseudo-second-order kinetic model. In addition, thermodynamic parameters show that the adsorption process is a beneficial, spontaneous and endothermic phenomenon. Isotherm models such as Langmuir, Freundlich and Temkin were applied to analyze adsorption behavior. This research could contribute to the development of more sustainable wastewater treatment methods, incorporating natural materials into remediation strategies.

Amino-functionalized manganese oxide for effective hexavalent chromium adsorption.

This study explores the use of functionalized manganese oxide (K-MnO2-NH2) for the removal of hexavalent chromium (Cr(VI)) ions, a highly toxic heavy metal contaminant, from wastewater. The synthesis of K-MnO2-NH2 was achieved through a two-step process, followed by comprehensive characterization using various analytical techniques, which confirmed the material's formation as a pure phase. The K-MnO2-NH2 exhibited exceptional chromium removal efficiency, achieving up to 90% (4.53mg/g) of Cr(VI) removal at pH 2. This high efficiency is attributed to the incorporation of amine groups via functionalization with 3-aminopropyltriethoxysilane (APTES), which introduces active sites with a strong affinity for Cr(VI) ions. Kinetics studies indicated that a chemical reaction governs the adsorption process, while thermodynamic data suggested it to be exothermic, and thermodynamic data reveal the process to be exothermic. The Freundlich isotherm best described the adsorption behavior. The Cr(VI) adsorption capacity of K-MnO2-NH2 was determined to be 45.17mg/g. K-MnO2-NH2 effectively removed Cr(VI) from industrial wastewater, achieving a removal efficiency of around 41% (25.5mg/g) and visible discoloration showing excellent reusability, maintaining over 80% removal efficiency after five cycles without requiring regeneration. This innovative approach highlights the potential of K-MnO2-NH2 as a sustainable and effective solution for Cr(VI) removal in environmental remediation and water purification.

Synthesis of magnetic activated carbons derived from Artocarpus heterophyllus peel with different magnetization methods: comparative characterizations and hexavalent chromium adsorption study

Magnetic activated carbon has been proved its separation ability to overcome a main drawback of activated carbon powder. However, effect of magnetization method on characterizations and Chromium (VI) adsorption of this adsorbent from Artocarpus Heterophyllus Peel (jackfruit peel) has not been investigated yet. This study magnetized jackfruit peel activated carbon using thermochemical and co-precipitation methods. Magnetic jackfruit activated carbon (MJAC) were examined and compared to jackfruit activated carbon (JAC) for surface chemistry, texture, morphology and crystalline properties. The isotherm/kinetics of Cr(VI) adsorption on these adsorbents were also analyzed. The results showed that all the adsorbents showed a typical peak of –(COO)n–Fe of iron oxide particles and functional groups but the adsorbent prepared with thermochemical method had the greatest Fe–O–C bond signal. The thermochemical adsorbent also had various particles of Fe3O4, Zero Valent Iron, and α-Fe2O3 while the co-precipitation absorbents gave a greater mesoporous structure and specific surface area than their JAC precursor; especially the adsorbent produced at mild temperature was covered by the highest iron oxide distribution on the surface and better magnetite property. As a result of the high specific surface area, these co-precipitation adsorbents were more effective for Cr(VI) adsorption than others. The PSO model best describes Cr(VI) adsorption on all absorbents with and without magnetite. Cr(VI) adsorption on JAC was dominated by intra-particle diffusion while multistep processes, including external mass transfer, governed the overall MJAC adsorption process. This work has created jackfruit peel-based magnetic activated carbon for wastewater treatment to remove toxic heavy metals and promote the circular economy that uses solid wastes as raw materials.Graphical

Adsorption of pentavalent vanadium and hexavalent chromium from vanadium extraction wastewater using modified diatomite

Vanadium extraction from vanadium (V) slag generates wastewater containing a large number of pentavalent vanadium [V (V)] and hexavalent chromium [Cr (VI)], posing environmental and health risks if discharged untreated. This study investigated the use of Fe2SO4 · 7H2O-modified diatomite as an adsorbent for removing V (V) and Cr (VI) from vanadium extraction wastewater (VEW). Static adsorption experiments were conducted to assess the adsorption capacity and removal efficiency of modified diatomite under varying conditions of adsorbent dosage, pH, and contact time. The results indicated removal rates of 97.4% for V (V) and 65.8% for Cr (VI) at pH 5, using 3 g of adsorbent dosage over 1440 min. In comparison with unmodified diatomite, the modified version exhibited a 667% increase in V (V) removal and a 531% increase in Cr (VI) removal, indicating significant enhancement in adsorption capacity post-modification. Adsorption capacity decreased with increasing dosage of modified diatomite. Moreover, the adsorbent under acidic conditions demonstrated superior adsorption effectiveness over neutral and alkaline conditions. Furthermore, the kinetics model revealed that adsorption followed Pseudo-second-order and Elovich kinetics, indicating chemisorption and complexation with active functional groups as dominant mechanisms. This study elucidated the effectiveness mechanisms of diatomite modification, paving the way for enhanced V (V) and Cr (VI) removal technologies in industrial wastewater treatment.

Adsorption of Copper, Zinc, Chromium and Nickel Using Plantation crop waste as Adsorbents in Contaminated Soil

This study investigates the adsorption behaviour of copper, zinc, chromium and nickel on plantation crops such as Arecanut husk (AH) and Coconut husk (CH) using a batch technique. Key parameters affecting the adsorption phenomenon were contact time, initial metal ion concentration, and temperature. The results showedequilibrium was reached within four hours, with adsorption capacity being temperature-dependent and endothermic. Efficiency of removal was maximumat lower concentrations, while adsorption capacity improved at higher concentration. Freundlich and Langmuir modelsareappropriatefor predicting the adsorption isotherm. At 300C, the maximum adsorption ofCu, Zn, Cr and Ni on AH and CH were 0.95 mg/g,1.27 mg/g, 0.78mg/g, 0.88 mg/g, 1.22mg/g, 1.64mg/g, 1.66mg/g, and 1.69 mg/g respectively. CH exhibited higher removal and adsorption capacities than AH, with zinc showing the strongest adsorption attraction, following the order Cu < Ni < Cr< Zn for plantation croptypes of adsorbents.

Plant Mediated Biosynthesis of Zinc Oxide Nanoparticle Using Aegle marmelos (Bael) Leaf Extract to Study its Antibacterial Activity and Chromium Adsorption

Nanoparticle is a miraculous material of this modern era due to their exceptional applications in various sectors (pharmaceutical, medical, cosmetics, paints, waste treatment process, etc.). In current study, zinc oxide nanoparticles (ZnO NPs) was synthesised using a green approach with Aegle marmelos (Bael) plant leaf extract as reducing agent. Characteristics of synthesised ZnO nanoparticles were examined with Fourier Transform Infrared Spectroscopy and UV-visible spectroscopy. The UV-vis spectroscopy study confirmed the formation of nanoparticles, showed a peak between 220-230 nm. FTIR spectroscopy was used to detect the specific functional groups involved in reducing and stabilizing during the biosynthesis process. Various applications were performed like; antibacterial properties and chromium metal adsorption. Antibacterial activity were analysed using well diffusion method. Nanoparticles of Zinc oxide were highly effective against gram-positive bacteria (Staphylococcus aureus and Bacillus cereus) and gram-negative bacteria (Escherichia coli and Salmonella typhi). So, they can be used as an excellent antibacterial agent for biological purposes. In metal removal, zinc oxide nanoparticle removes about 50% of the chromium from water through adsorption. Current study showed synthesis of ZnO nanoparticle through green approach will have great potential in antibacterial activity and treatment of chromium metal contaminated water.

Adsorption of hexavalent chromium from wastewater using magnetic biochar derived from peanut hulls

In this study, the utilization of peanut hulls as a precursor for the preparation of magnetic biochar through pyrolysis was investigated. To enhance the magnetic and adsorption properties of the biochar, the peanut hulls biomass was modified using ferric chloride hexahydrate and magnesium chloride hexahydrate. Response surface methodology was employed to evaluate the influence of biomass metal concentration, pyrolysis temperature, pyrolysis period and flow of nitrogen on the yield and Cr (VI) adsorption efficiency of the synthesized biochar. A 17-run experimental matrix was generated using Optimal Design to investigate the interactions among four input parameters. The results led to the development of a quadratic model, which demonstrated a high degree of predictability in accordance with the experimental data. Analysis of variance (ANOVA) confirmed that the models for yield and Cr (VI) adsorption efficiency were highly significant (p < 0.05), with coefficients of determination (R2) values of 0.891 and 0.988, respectively. The optimal synthesis conditions for producing biochar with superior physicochemical properties were identified as a pyrolysis temperature of 300 °C, a pyrolysis duration of 2 h, a metal-to-biomass ratio of 0.5, and a constant flow of nitrogen. A desirability of 85% was achieved through numerical optimization, corresponding to a yield of 63% and complete Cr (VI) removal. Further optimization of Cr (VI) adsorption efficiency, considering the effects of pH (3–12), adsorbent loading (1–15 g/L), and initial Cr (VI) concentration (5–20 mg/L), was performed using a 19-run experimental matrix. ANOVA for Cr (VI) adsorption efficiency model revealed high significance (p < 0.05) with an R2 value of 0.916.The magnetic biochar demonstrated a remarkable adsorption efficiency of 98% under the experimental conditions of solution pH 3, adsorbent dosage of 5 g/L, and an initial Cr (VI) concentration of 20 mg/L. The desirability of 100% was obtained by a numerical optimization method representing Cr (VI) removal of 98%. The adsorption behaviour was adequately described by the Freundlich isotherm model, suggesting multilayer adsorption, with a maximum adsorption capacity of 12 mg/g. Biochar also proved to have strong magnetic properties which enhanced solid-liquid separation post adsorption experiments.

Agricultural waste valorisation – Novel Areca catechu L. residue blended with PVA-Chitosan for removal of chromium (VI) from water – Characterization, kinetics, and isotherm studies

Arecanut, an industrial crop prevalent in tropical regions such as India, Sri Lanka, and parts of Southeast Asia, generates significant agricultural waste during processing. This study explores a waste-to-wealth approach by incorporating arecanut organic residue into Polyvinyl alcohol (PVA) - Chitosan blends via an eco-friendly continuous stirring method to develop an adsorbent film for removing chromium (VI) from water. Morphological analyses confirmed enhanced surface area, porosity, and roughness in the blended films. XRD and FTIR analyses indicated a semi-crystalline nature with a decrease in the characteristic peak intensity of PVA and chitosan, confirming the incorporation of arecanut residue. Optimal conditions identified OR-4 film, using 0.4 g of adsorbent, achieving 88.68 % removal of 173 mg/L chromium (VI) at pH 9.0, within 45 minutes at 40°C. SEM images demonstrated significant surface roughness reduction before and after adsorption, confirming chromium adsorption. Kinetic studies revealed a pseudo-second-order model and adsorption isotherms confirmed film surface heterogeneity. This research advances eco-friendly materials for water purification and offers a sustainable solution for managing agricultural residues.

Application of a magnetic graphene nanocomposite modified with 5-aminoisophthalic acid amine group for chromium (VI) adsorption from aqueous solutions: kinetic and thermodynamic studies

ABSTRACT Polymer nanocomposites are composite materials that incorporate nanomaterials, such as magnetic graphene oxide (mGO), into a polymer matrix. To enhance its adsorption capacity, the surface of mGO nanoparticles was polymerised by a 5-aminoisophthalic acid amine group (mGO-AIPA) through a simplified co-precipitation method. The structural and morphological characteristics of the synthesised nanoparticles were evaluated through techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), Thermogravimetric analysis (TGA), and Vibrating sample magnetometer (VSM). Response surface method (RSM) was used to evaluate the effectiveness of mGO-AIPA nanocomposite in removing chromium (VI) ions by examining variables such as solution of pH, contact time, adsorbent dose and initial concentration. Also, the study of kinetic models, adsorption isotherms and thermodynamic modelling of the process were evaluated. The results found that the mGO-AIPA nanocomposite has the maximum removal of chromium (VI) ions from the aqueous solution by 83.11% in optimal conditions including pH 3.5, contact time of 35 min, an adsorbent dosage of 25 mg g−1 and an initial concentration of 55 mg L−1. The pseudo-second-order kinetic and Langmuir isotherm models had a better fit with the experimental data of adsorption and the maximum adsorption capacity of chromium (VI) the base of the Langmuir model was 90.91 mg g−1. Moreover, the thermodynamic analysis indicated that the process was exothermic and nonspontaneous process, implying that it was energetically unfavourable. These findings suggest that the mGO-AIPA nanocomposite has a high performance as an effectual adsorbent to eliminate chromium heavy metal from an aqueous medium.

Hexavalent Chromium Adsorption on Adsorbent Derived From Biomass of Fabaceae Plant in Vietnam: Effect of Preparation Conditions on Equilibrium Adsorption Capacity

ABSTRACTThe present work is devoted to examining the potential of Sesbania sesban biochar produced through slow pyrolysis for 120 min at 300°C in removing hexavalent chromium from the aqueous phase. The physicochemical characteristics of biochar were analyzed utilizing a variety of analytical tools including SEM, BET, and FTIR. Results revealed that the biochar had a smooth surface, an even stacking pattern with a porous texture, a large BET surface area equal to 562 m2/g, and a pHpzc of 6.9. The biochar efficiency in eliminating Cr (VI) was investigated through several variables, including biochar dosage (0.1–0.4 g), pH (2–8), initial chromium ion concentration (10–40 mg/L), and adsorption time (15–120) min. The results identified the best conditions for adsorbing Cr (VI): an initial concentration of 10 mg/L, an absorbent dosage of 0.3 g, a pH solution of 2, and a reaction time of 90 min. The experiment achieved a Cr (VI) removal efficiency of over 90% by applying these conditions. The adsorption isotherm data were analyzed and showed a strong correlation coefficient (R2 = 0.985) for Langmuir monolayer model, in which the maximum adsorption capacity achieved was 5.3 mg/g. According to the kinetic investigation, the adsorption of Cr (VI) was adapted to a pseudo‐second‐order model having a high R2 value of 0.998. These results demonstrate that Sesbania sesban biochar has excellent potential as a cost‐effective and highly efficient adsorbent for removing hexavalent chromium and improving water quality.

Green Clay Materials Applied in Packed Bed Columns for the Hexavalent Chromium Adsorption from Aqueous Solutions

Green Clay Materials Applied in Packed Bed Columns for the Hexavalent Chromium Adsorption from Aqueous Solutions

Direct synthesis of N-doped porous carbon materials from EDTA dipotassium salt for the rapid adsorption of hexavalent chromium from aqueous solutions

The development of versatile, sustainable, and efficient N-doped porous carbon materials for the removal of trace contaminants has attracted considerable interest. Traditional methods for preparing porous carbon materials often involve the use of potent and hazardous activating agents such as KOH, H3PO4, and ZnCl2, which not only restrict the choice of production equipment but also pose environmental hazards. In this study, we introduce a self-activating method to synthesize N-doped porous carbon materials specifically designed for the removal of hexavalent chromium [Cr(VI)]. This approach involves the direct carbonization of EDTA dipotassium salt at different temperatures under a N2 atmosphere without any activators. The influence of adsorbent dosages, pH, temperature, initial concentration of Cr(VI) ions, and competing ions on the adsorption behavior of Cr(VI) was systematically examined. The findings reveal that the optimal conditions for adsorption are a pH of 2 and an adsorbent dosage of 1.0 g L−1. Furthermore, Cr(VI) rapid adsorption onto N-doped porous carbon follows Freundlich isotherm and pseudo-second-order kinetic models. Notably, adsorbent KNC-700 exhibits an exceptional specific surface area of 2124.6 m2 g−1 and a well-defined pore structure. It shows maximum adsorption capacity for Cr(VI) of 270.3 mg g−1 at 328 K with an equilibrium time of 20 min. Further mechanistic investigations suggest that efficient uptake of Cr(VI) primarily occurs through physico chemical adsorption involving electrostatic interactions and reduction reactions. This study provides novel insights into the preparation of porous carbon materials and their potential applications in addressing Cr(VI) pollution.

New insights into the remediation of chromium-contaminated industrial electroplating wastewater by an innovative nano-modified biochar derived from spent mushroom substrate: Mechanisms, batch study, stability and application

To enhance the adsorption and detoxification capabilities of hexavalent chromium (Cr(VI)) using agricultural spent mushroom substrate (SMS), this study pioneered the preparation of biochar (NBC) from Lentinus edodes spent substrate. Subsequently, nano iron sulfide (FeS) particles were integrated onto NBC with carboxymethyl cellulose (CMC) as a stabilizer, resulting in a novel composite biosorption material, nFeS-BC. The adsorption and reduction potential of both NBC and nFeS-BC against Cr(VI) were evaluated through batch experiments, which identified pH as a critical factor influencing adsorption efficiency. Remarkably, nFeS-BC exhibited a superior maximum adsorption capacity (qmax) of 99.57 mg g−1 and a reduction efficiency of 68.65%, outperforming NBC by 277.73% and 211.76% under optimized conditions, respectively. Characterization techniques including Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared Spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS) elucidated the removal mechanisms, predominantly attributed to ion exchange, electrostatic attraction, functional group interaction, and redox reaction. The carbon-oxygen functional groups and nano particles were crucial in the adsorption and reduction processes. Compared with NBC, the incorporation of FeS particles increased the specific surface area and pore volume of nFeS-BC by 130.86% and 183.77%, respectively. nFeS-BC owned a shelf-life of up to ∼3 months of use and exhibited excellent performance in the processing of actual electroplating wastewater with q of 16.71 mg g−1 under 0.1 g L−1 dosage. These findings underscore the potential of nFeS-BC as an efficient material for Cr(VI) removal, presenting a novel adsorbent for the sustainable detoxification of contaminated water resources and the potential for using agricultural waste materials in environmental remediation.

Development and characterization of fluorescent cellulose succinate hydrogels for efficient chromium adsorption

Development and characterization of fluorescent cellulose succinate hydrogels for efficient chromium adsorption

Remoción de cromo (VI) de agua residual de curtiembre empleando biomasa orgánica vegetal en un reactor biológico secuencial aerobio

[Introduction]: In the removal of chromium (VI) from tannery wastewater, physicochemical methods are the most used. However, these require high operating costs, and worse still, generate secondary pollutants that again require complementary treatments for their elimination. Given this, the applicability of plant organic biomass (VOB) emerges as an environmental alternative based on the adsorption of chromium (VI), the simplicity of obtaining it, the reduction as waste and, above all, it does not generate secondary pollutants. [Objective]: Use VOB waste in an aerobic sequential biological reactor (SBR) for the removal of chromium (VI) in the treatment of tannery wastewater. [Methodology]: 3 aerobic SBR systems were implemented; 2 controls (SBR1 and SBR2) and 1 study subject (SBR+VOB). Each system was fed with tannery wastewater (18 L) and connected to an aeration system (12.7 L/min). The bacterial inoculum, a fundamental part of an SBR system, was obtained from the selective culture of chromium (VI) reducing bacteria (RBCrVI) taken from the wastewater under study, and integrated into SBR2 and SBR+VOB at 0.6 g/L. The VOB was obtained from Stenotaphrum secundatum residues, fragmented, sieved, sterilized and integrated into the SBR+VOB at 1.5 g/L. [Results]: The SBR+VOB system achieved the highest percentage of chromium (VI) removal (93 %), followed by SBR2 (80.1 %), and finally SBR1 (2.8 %). With respect to COD and TSS, the statistical test (Tukey) showed that there was no significant difference between the system under study and the controls, recording COD removal percentages ranging from 87.8 % to 88.4 %, and TSS ranging from 63.8 % to 69.2 %. [Conclusions]: The viability of using VOB waste to remove chromium (VI) in the treatment of tannery wastewater has been evidenced. The results of this research create a promising panorama to mitigate the effects derived from inadequate management of tannery wastewater and organic solid waste.

Metal-organic-framework and walnut shell biochar composites for lead and hexavalent chromium removal from aqueous environments

Extensive research in recent years has explored the realm of porous carbon composites for various applications, including electrochemistry, structural materials, environmental remediation, and more. In particular, the fabrication of porous carbon composites using a metal-organic framework (MOF) and biochar (BC) for aqueous remediation is a fairly new avenue of research. In this study, a MOF-BC composite was synthesized with unmodified and chemically modified BCs using solvothermal synthesis. The composites were used as adsorbents to remediate heavy metals, such as lead (II) and chromium (VI), from aqueous environments. It was verified that the MOF was homogeneously deposited onto the BC's surface using various material characterization techniques. Lead and chromium adsorption studies revealed a high adsorption capacity with greater than 99% removal for lead and ∼65% for chromium, respectively. Impressively, for lead, the highest observed experimental adsorption capacity of the MOF-chemically modified BC composite was 535 mg/g, compared to 240 mg/g for pristine BC. Meanwhile, the adsorption capacity of the same MOF-BC composite for chromium ions was low at 18 mg/g, compared to 80 mg/g for the chemically modified BC. The MOF-BC had a rapid adsorption rate, achieving equilibrium at only 150 min of reaction time for lead ions. MOF-BCs have higher adsorption for cationic lead through physisorption and ion-exchange mechanisms, whereas, for anionic chromium, removal is dominated only by physisorption mechanisms. The outcomes and methodological developments attained in this study offer a novel and compelling approach for synthesizing MOF-BC composites for aqueous remediation applications.

Stabilization effect of trivalent chromium on a Cu-based metal-organic framework: Strengthen the original O–Cu–O metal-ligand bond

Cu-BTC materials are widely used because of the high specific surface areas and special pore structures, but the water instability has also been proven. With the adsorption of trivalent chromium, the long-time stability of Cu-based metal-organic frameworks Cu-BTC was got improved in water treatments. A strategy to improve the framework stability in water by the adsorption of trivalent chromium ions into Cu-BTC has been developed. The results showed that the treated Cu-BTC-Cr material has much better water stability and alkaline resistance than the original Cu-BTC.

Addressing mathematical discrepancies in the adsorption model of Hashem et al. (2024): A technical commentary

This letter provides a critical technical analysis of the application of the Freundlich isotherm in the study by Hashem et al. (2024), entitled "Chromium adsorption capacity from tannery wastewater on thermally activated adsorbent derived from kitchen waste biomass." While the study presents an innovative approach by utilizing pumpkin peel as an adsorbent for chromium removal, a critical issue was identified in the formulation and application of the Freundlich isotherm. The authors presented an incorrect mathematical modification of the isotherm, which significantly impacts the validity of the adsorption parameters derived, such as KF and 1/n, and ultimately affects the conclusions drawn about the system's adsorption capacity. Additionally, the assertion that the adsorption process can continue indefinitely is fundamentally flawed based on the principles of adsorption thermodynamics. This letter aims to rectify these discrepancies by revisiting the correct formulation of the Freundlich isotherm and highlighting the importance of accurate mathematical modeling in ensuring scientifically sound and replicable results. Despite these issues, the study remains a valuable contribution to the field, and the suggested revisions would further strengthen its impact.