Statement of Retraction: NiO nanoparticles for enhanced removal of methyl orange: equilibrium, kinetics, thermodynamic and desorption studies

In this work, a green hydrothermal method was utilised to synthesise NiO nanoparticles (NiO-NPs) as an effective and low cost adsorbent for dye adsorption from aqueous medium. The product was characterised using powder XRD, FTIR and SEM techniques and the adsorption behaviour of NiO-NPs was assessed using methyl orange (MO) dye. The maximum removal (97.56 mg/g) of MO onto NiO-NPs was observed at pH 4, adsorbent amount 0.03 g and temperature 40°C. Thence, on evaluating and optimising the factors affecting the adsorption, the results exhibited that 95% dye removal was reached in first 30 min, additionally the adsorption equilibrium, kinetics and thermodynamics models were investigated. The results showed that the adsorption followed Langmuir model and pseudo second order model. The thermodynamic assessment of adsorption of MO onto NiO-NPs indicated the feasibility, endothermic and spontaneous nature with enthalpy and entropy of the system being positive (∆H° = 8.661 KJ/mol, ∆S° = 7.310 J/mol K). Also, the order of magnitude of ∆G° and ∆H° revealed the reversibility of reaction that reflects the adsorbent could be regenerated and potential contender for dyes removal form textile wastes.

Efficient phosphate adsorption by a composite composed of Mg6Al2(CO3)(OH)16·4H2O LDH and Chitosan: kinetic, thermodynamic, desorption, and characterization studies

Efficient adsorptive removal of Zinc by green marine macro alga Caulerpa scalpelliformis –Characterization, Optimization, Modeling, Isotherm, Kinetic, Thermodynamic, Desorption and Regeneration Studies

Adsorption removal of zinc (II) from aqueous phase by raw and base modified Eucalyptus sheathiana bark: Kinetics, mechanism and equilibrium study

Chitosan enhancement is essential for establishing an improved adsorbent and binding toxic heavy metal ion. In this investigation, chitosan powder was converted to chitosan beads (CH) for effortless handling and easy penetration into binding sites. The beads were cross-linked with glutaraldehyde, which made them insoluble in acidic media. The cross-linked beads (CCH) were then further grafted with an amino-functionalized solution (5-amino-1,10-phenanthroline) to provide more binding sites. The three sets of chitosan derivatives produced were characterized by Fourier Transform Infrared (FTIR), Scanning Electron Microscope (SEM), Thermogravimetric (TGA), X-ray diffraction (XRD), and BET analysis. The grafted cross-linked chitosan beads (GCCH) were applied in adsorption studies to remove Pb2+ and Cu2+ ions from the synthetic solutions. The equilibrium experiment data were explained using the Langmuir and Freundlich models, while the kinetics data were studied using pseudo-first- and pseudo-second-order kinetic models. A thermodynamic study was carried out, and the parameters from the study, such as Gibb’s free energy change (∆G O), enthalpy change (∆H O), and entropy change (∆H O), were obtained. The Langmuir model reasonably described the equilibrium data well, with a correlation coefficient (R 2) of 0.99 for both metal ions and a maximum binding capacity of 376 mg/g and 348 mg/g for Pb2+ and Cu2+ ions, respectively. The pseudo-second-order kinetic model gave the line of best fit with an R 2 value of 0.97. The results from the thermodynamic study showed that binding Pb2+ and Cu2+ ions onto the adsorbent is endothermic and spontaneous. The spent adsorbent was regenerated with five successive cycles. The study thoroughly covers equilibrium, kinetics, thermodynamics, and desorption, providing insights into adsorption mechanisms. The modified chitosan beads offer increased selectivity, stability, and reusability, making the adsorbent a potential material for heavy metal removal. This method improves adsorption performance while advancing sustainable water treatment.

This study aims to remove arsenic from an aqueous medium by adsorption on a nanocomposite material obtained by the sol–gel method starting from matrices of silica, iron oxide and NaF (SiO2/Fe(acac)3/NaF). Initially, the study focused on the synthesis and characterization of the material by physico–chemical methods such as: X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, atomic force microscopy, and magnetization. Textural properties were obtained using nitrogen adsorption/desorption measurements. The zero load point, pHpZc, was also determined by the method of bringing the studied system into equilibrium. In addition, this study also provides a comprehensive discussion of the mechanism of arsenic adsorption by conducting kinetic, thermodynamic and equilibrium studies. Studies have been performed to determine the effects of adsorbent dose, pH and initial concentration of arsenic solution, material/arsenic contact time and temperature on adsorption capacity and material efficiency. Three theoretical adsorption isotherms were used, namely Langmuir, Freundlich and Sips, to describe the experimental results. The Sips isotherm was found to best describe the experimental data obtained, the maximum adsorption capacity being ~575 µg As(III)/g. The adsorption process was best described by pseudo-second order kinetics. Studies have been performed at different pH values to establish not only the optimal pH at which the adsorption capacity is maximum, but also which is the predominantly adsorbed species. The effect of pH and desorption studies have shown that ion exchange and the physiosorption mechanism are implicated in the adsorption process. From a thermodynamic point of view, parameters such as ΔG°, ΔH° and ΔS° were evaluated to establish the mechanism of the adsorption process. Desorption studies have been performed to determine the efficiency of the material and it has been shown that the material can be used successfully to treat a real-world example of deep water with a high arsenic content.

In this study, the potential of using dried coffee husk adsorbent is systematically evaluated by conducting batch studies involving various process parameters, such as initial pH, dye concentration, adsorbent dosage, particle size, electrolytes, and temperature for the removal of Congo red (CR) dye from aqueous solutions. The prepared adsorbent was characterised with Attenuated Total Reflection, Field Emission Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy, thermogravimetric, particle size, zero-point charge, Brunauer–Emmett–Teller surface area, and pore volume analysis. The maximum adsorption efficiency is obtained at an initial pH, 6, dye concentration, 50 mg L−1, adsorbent dosage, 10.5 g L−1, and adsorbent particle size, 89 µm. The kinetic rate constants and isotherm parameters were determined using various kinetic and isotherm models, respectively. The pseudo-second-order kinetic model gave a good fit to the experimental data at various dye concentrations. The adsorption mechanisms were described by intra-particle diffusion and Boyd plots. The overall rate of adsorption is controlled by external film diffusion of dye molecules. The experimental equilibrium data fit the Langmuir isotherm model with a maximum monolayer adsorption capacity (qmax) of 38.65 mg g−1 at 303 K. Thermodynamic studies were performed to evaluate the change in Gibbs free energy (ΔG), change in enthalpy (ΔH), and change in entropy (ΔS) of the adsorption process. Based on the thermodynamic analysis, the adsorption was found to be endothermic in nature, and the process was chemisorption, spontaneous and favoured at high temperatures. Desorption studies were conducted with various desorbing reagents in various runs and the maximum desorption efficiency (60.36% in third run) was determined using the solvent methanol. Reusability studies demonstrated that the prepared adsorbent was effective up to three runs of operation. These results show that waste coffee husks are cost-effective, eco-friendly bio-sustainable materials, and can be used for the removal of colour from synthetic dye wastewater.

Biosorption of Cr(VI) ions from aqueous solutions: Kinetics, equilibrium, thermodynamics and desorption studies

This review embarks on a comprehensive journey, exploring the application of lignocellulosic biomass materials as highly effective adsorbents for the removal of textile dyes (cationic and anionic dyes) from wastewater. A literature review and analysis were conducted to identify existing gaps in previous research on the use of lignocellulosic biomass for dye removal. This study investigates the factors and challenges associated with dye removal methods and signifies their uses. The study delves into the pivotal role of several parameters influencing adsorption, such as contact time, pH, concentration, and temperature. It then critically examines the adsorption isotherms, unveiling the equilibrium relationship between adsorbent and dye and shedding light on the mechanisms of their interaction. The adsorption process kinetics are thoroughly investigated, and a detailed examination of the adsorbed rate of dye molecules onto lignocellulosic biomass materials is carried out. This includes a lively discussion of the pseudo-first, pseudo-second, and intra-particle diffusion models. The thermodynamic aspects of the adsorption process are also addressed, elucidating the feasibility and spontaneity of the removal process under various temperature conditions. The paper then dives into desorption studies, providing insights into the regeneration potential of lignocellulosic biomass materials for sustainable reusability. The environmental impact and cost-effectiveness of employing lignocellulosic biomass materials in textiles including Congo Red, Reactive Black 5, Direct Yellow 12, Crystal Violet, Malachite Green, Acid Yellow 99, and others dyes from wastewater treatment are discussed, emphasizing the significance of eco-friendly solutions. In summary, this review brings together a wealth of diverse studies and findings to present a comprehensive overview of lignocellulosic biomass materials as adsorbents for textile cationic and anionic dye removal, encompassing various aspects from influential parameters to kinetics, adsorption isotherms, desorption, and thermodynamics studies. Its scope and other considerations are also discussed along with its benefits. The collective knowledge synthesized in this paper is intended to contribute to the advancement of sustainable and efficient water treatment technologies in the textile industry.

The remediation of arsenic contamination in potable water is an important and urgent concern, necessitating immediate attention. With this objective in mind, the present study investigated arsenic removal from water using batch adsorption and fixed-bed column techniques. The material employed in this study was a waste product derived from the treatment of groundwater water for potable purposes, having a substantial iron composition. The material’s properties were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier-transformed infrared spectroscopy (FT-IR). The point of zero charge (pHPZC) was measured, and the pore size and specific surface area were determined using the BET method. Under static conditions, kinetic, thermodynamic, and equilibrium studies were carried out to explore the influencing factors on the adsorption process, namely the pH, contact time, temperature, and initial arsenic concentration in the solution. It was found that the adsorption process is spontaneous, endothermic, and of a physical nature. In the batch adsorption studies, the maximum removal percentage was 80.4% after 90 min, and in a dynamic regime in the fixed-bed column, the efficiency was 99.99% at a sludge:sand = 1:1 ratio for 380 min for a volume of water with arsenic of ~3000 mL. The kinetics of the adsorption process conformed to a pseudo-second-order model. In terms of the equilibrium studies, the Sips model yielded the most accurate representation of the data, revealing a maximum equilibrium capacity of 70.1 mg As(V)/g sludge. For the dynamic regime, the experimental data were fitted using the Bohart–Adams, Thomas, and Clark models, in order to establish the mechanism of the process. Additionally, desorption studies were conducted, serving as an essential step in validating the practical applicability of the adsorption process, specifically in relation to the reutilization of the adsorbent material.

Mustard cake, obtained from local oil mills, has been characterized and used as an inexpensive and effective adsorbent for the removal of rhodamine-B dye from wastewater. The influence of various factors on the adsorption capacity has been studied by batch experiments. The optimum contact time to reach equilibrium was found to be 6 h. Maximum decolorization took place at pH 2.30. The optimum adsorbent dose was 5 g·L−1 of particle size < 106 μm. The ongoing adsorption validates both the Langmuir and the Freundlich adsorption isotherms at temperatures of (40, 50, and 60) °C. Thermodynamic parameters indicate the feasibility of the process. The desorption profile revealed that a significant portion (80 %) of rhodamine-B could be desorbed by using 50 % ethanol as eluting agent. Desorption studies indicated the possibility of recycling and regeneration of both the adsorbent and the dye.

Adsorption/desorption of cationic dye on surfactant modified mesoporous carbon coated monolith: Equilibrium, kinetic and thermodynamic studies

Zeolite supported zinc oxide nanoparticles composite: Synthesis, characterization, and photocatalytic activity for methylene blue dye degradation

The study of new useful, efficient and selective structures for the palladium ions’ recovery has led to the development of a new series of macromolecules. Thus, this study presents a comparative behavior of two crown benzene ethers that modify the magnesium silicate surface used as adsorbent for palladium. These crown ethers are dibenzo18-crown-6 (DB18C6) and dibenzo 30-crown-10 (DB30C10). The obtained materials were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FT-IR). The specific surface area (BET) and point of zero charge (PZC) of the two materials were determined. The palladium ions’ recovery from synthetic aqueous solutions studies aimed to establish the adsorption mechanism. For this desideratum, the kinetic, equilibrium and thermodynamic studies show that MgSiO3-DB30C10 have a higher adsorption capacity (35.68 mg g−1) compared to MgSiO3-DB18C6 (21.65 mg g−1). Thermodynamic studies highlight that the adsorption of Pd(II) on the two studied materials are spontaneous and endothermic processes. The positive values of the entropy (ΔS0) suggest that the studied adsorption processes show a higher disorder at the liquid/solid interface. Desorption studies were also performed, and it was found that the degree of desorption was 98.3%.

Removal of Pb(II) ions from aqueous solution by a waste mud from copper mine industry: Equilibrium, kinetic and thermodynamic study