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This study investigates the removal of Congo red dye from aqueous solution using functionalized generation 3.0 and 5.0 Polyamidoamine dendrimer – silica gel composite (G-3PS, G-5PS). Fourier Transform-Infra Red spectroscopy, Brunauer Emmett and Teller, Thermogravimetric Analysis, pH at point of zero charge, and Scanning Electron Microscopy measurements have been applied to characterize the synthetic nanohybride composite, these techniques revealed the successful functionalization of both dendrimer molecules and subsequent immobilization onto silica gel. The implications of varying adsorption parameters such as contact time, initial concentration of adsorbate, temperature and pH on both composites were studied. Experimental data obtained from batch adsorption processes were fitted into two equilibrium isotherms (Langmuir and Freundlich) and 3 kinetic models (Pseudo-First-Order, Pseudo-Second-Order, Intra Particle Diffusion). Adsorption mechanism was mainly governed by film diffusion due to electrostatic interactions between the functionalized dendrimer surface and Congo red molecules. Thermodynamic parameters illustrate that the adsorption is endothermic and spontaneous. Findings suggest the Nanocomposites G-3PS G-5PS) are good adsorbents for the removal of Congo red dye from aqueous solutions. [ABSTRACT FROM AUTHOR]

Industrial wastewater discharge, tainted with hazardous substances, including dyes like methylene blue (MB) from the textile sector, further emphasizes the need for water treatment to produce safe drinking water. This study explores the potential of olive mill solid waste, an abundant and cost-effective agricultural waste in Mediterranean regions, to yield high-quality activated carbon (AC) with zinc chloride activation for MB adsorption. The activation process, carried out at a modest temperature of 500 °C without the need for an inert atmosphere, resulted in AC with remarkable characteristics, boasting a substantial surface area of 1184 cm2·g−1 and a total pore volume of 0.824 cm3·g−1. Extensive characterization of the AC was carried out through a large range of surface techniques. The pH of the solution had minimal influence on MB adsorption, the maximum removal was 95%, which was under slightly acidic pH conditions (5.8), and the adsorbent dose was 0.4 g·L−1 for a 50 mg·L−1 MB concentration. Equilibrium data pertaining to MB adsorption were subjected to fitting with different models, namely Langmuir, Freundlich, and Temkin. Notably, the Langmuir model exhibited the best fit, revealing a maximum monolayer adsorption capacity of 500 mg·g−1 at 25 °C, and the adsorption kinetics closely followed a pseudo-second-order model. [ABSTRACT FROM AUTHOR]

The bentonite clay has been activated by acid treatment and utilized as a lower‐cost and eco‐friendly adsorbent required to remove Fast Green FCF dye from the aqueous solution. At first acid activated bentonite clay minerals were analyzed by various analytical techniques like Fourier Transform Infrared Spectroscopy (FTIR), x‐ray diffraction (XRD), and x‐ray fluorescence (XRF) analysis. The batch adsorption research was performed to investigate the Fast Green FCF dye adsorption onto the acid‐treated (Bent) bentonite clay. Sorption studies investigated the impacts of adsorbent dosage, initial pH, and time of contact on Fast Green FCF color elimination. The adsorption capacity decreased as the pH was above 7 and then remained almost the same after a pH value of 9. At acidic conditions (below pH value 7), the capacity of adsorption diminished by a decrease in the pH of the solution. The results indicated that the maximum capacity of adsorption has been obtained at an adsorbent dosage of 0.1 g. As the dosage of the adsorbent was improved, several active sites that were available at the time of the dye adsorption increased. As a result, the dye percentage that was removed from the clay increased. Besides these, adsorption kinetics, adsorption equilibrium isotherm, and thermodynamics studies have been also conducted. While studying the adsorption kinetics pseudo‐2nd‐order kinetics has been seen to be more appropriate as compared to pseudo‐1st‐order model. The experimental findings indicated that the attachment of the dye to the clay surface followed the "Langmuir adsorption" isotherm rather than the Freundlich adsorption isotherm with a monolayer coverage of 18.93 mg/g. From the thermodynamics study, it was revealed that the process of adsorption takes place instantly at high temperatures. [ABSTRACT FROM AUTHOR]

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High rainfall areas suffer from severe leaching loss of sulfate owing to their negatively charged nature. Sorption of sulfur (S) onto soil particles protect it from leaching out of the system. The S-sorption characteristics in humid soils from north-eastern India was studied with the objective to identify factors controlling S-sorption behavior in these acidic soils. Soils were collected from six different locations of north-eastern India. The soils were equilibrated with increasing concentrations of S for the sorption study, and later equilibrated with 0.01 N CaCl2 for desorption study. Results were fitted to three different isotherm models (Freundlich, Langmuir and Tempkin). The data fitted well to all three isotherm models. However, Freundlich adsorption isotherm yielded the best fit. Sorption parameters like S-sorption maxima (k), bonding energy (b), adsorption capacity (K), bonding energy constant (A) were positively correlated with the clay and, crystalline iron (Fe) and aluminum (Al) content in soil. Supply parameter increased with the increasing concentration of sulfate, while equilibrium buffering capacity was found decreasing. Soils from Nongpoh and Mustem with higher clay and crystalline Fe and Al content exhibited higher S-sorption capacity, whereas those of Padu having lowest clay content reported least S-sorption. It is recommended that in a soil having low S-sorption capacity, the minimal amount of S should be applied at a time. [ABSTRACT FROM AUTHOR]

RESUMO Este trabalho teve por objetivos avaliar que parâmetros obtidos dos modelos de isotermas de Freundlich e Langmüir melhor refletem a adsorção de Pb, Cu e Zn em solos intemperizados e identificar a relação entre os parâmetros selecionados e os atributos químicos e físicos das doze classes de solos mais representativas do Brasil. Os locais de coleta foram os mais abrangentes possíveis, englobando “pedons“ das regiões Sul, Sudeste e Norte do país. Avaliou-se, através da análise de trilha o desdobramento do coeficiente de correlação entre variáveis dependentes obtidas através das isotermas de adsorção (parâmetros de adsorção) e variáveis independentes (atributos químicos e físicos do solo), em efeitos diretos e indiretos para os elementos Pb, Cu e Zn. Os atributos do solo: argila (ARG); carbono orgânico (Corg.); capacidade de troca catiônica efetiva (CTCE); ferro citrato ditionito-bicarbonato (FeD); teor de alumínio total (Al2O3), foram os que apresentaram maiores coeficientes de correlação simples com os parâmetros de adsorção e foram utilizados no modelo da análise de trilha para explicar adsorção de metais pesados. As principais conclusões deste trabalho foram: a análise de trilha mostrou-se como uma ferramenta importante no estudo do comportamento dos metais pesados no solo; a constante KF (constante da equação de Freundlich) para todos os elementos apresentou o coeficiente de determinação mais elevado e o menor valor do efeito da variável residual e, as variáveis que mais contribuíram com a adsorção de metais pesados foram Corg., CTCE, pH, ARG e Al2O3.

Today, increasing dyes pollution is of great importance for life. Leaving the dyes used in industries such as textiles without being discharged pollutes other water sources. In order to prevent this, different methods are used in the literature. In this study, SrAl2B2O7, a borate metal, was used to remove methyl blue (MB), an anionic dye, by batch adsorption method. Strontium aluminoborate (SrAl2B2O7) was prepared using a solution combustion method at 950 °C for 4 h in air. The prepared adsorbent was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The particle morphology of the adsorbent was investigated using scanning electron microscope (SEM). By using N2 adsorption–desorption, the Brunnauer, Emmet, and Teller (BET) specific surface area was found to be 1.9578 m2 g−1. The surface charge of the dye-adsorbed SrAl2B2O7 was determined based on zeta-potential measurements. Langmuir (R2=0.9897), Freundlich (R2=0.985), Dubinin & Radushkevic (R2=0.976), Scatchard (R2=0.881), Temkin & Pyzhev (R2=0.978) isotherms were calculated in the study. SrAl2B2O7 showed good adsorption performance for methyl blue (MB) with maximum adsorption capacities of 29.069 mg g−1 (Langmuir). Adsorption processes were also studied in detail. Thermodynamic and kinetic models; pseudo-first-order (R2=0.415), pseudo-second-order (R2=0.999), Elovich (R2=0.968) showed that adsorption using SrAl2B2O7 in MB removal is endothermic and pseudo-second order. [ABSTRACT FROM AUTHOR]

AbstractThe adsorption performance of 2-mercaptobenzothiazole from an aqueous solution on activated carbon synthesized through grape marc was explored. In this research, the agricultural waste was chemically treated with phosphoric acid (40% H3PO4, 170 °C, 3 h), then pyrolyzed at 650 °C for 2 h, to obtain the GMAC-650 to be used as an adsorbent. The resulting material was characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, and Brunauer–Emmett–Teller (BET). Maximum uptake (∼99%) is obtained under ideal conditions: an adsorbent dose of 0.8 g L−1 and pH = 8 for an initial concentration of 10 mg L−1 at 45 °C. The adsorption equilibrium data were fitted to the following isotherm models: Langmuir and Freundlich. For optimal equilibrium isotherm selection, a comparison of linear and non-linear methods for the adsorption of MBT. It was based on four error functions: the coefficient of determination R2, the sum of squared errors, the Chi-square (χ2), and the root mean square error. The current work has shown that the non-linear method is a more adequate method for estimating the parameters of the isotherm compared with the linear method. The comparative analysis of the models shows that the Freundlich model is more appropriate for describing equilibrium data. [ABSTRACT FROM AUTHOR]

AbstractIn the study, the removal of dye (methyl blue) from aqueous solutions by batch/agitation adsorption method was investigated using Pinus brutia (PB). For this purpose, first, PB wood was collected and made into wood chips (PB), and then Pinus brutia biochar (PBB) was made. The PBB was modified to gain nano-magnetic properties. The biochar structure was characterized by FT-IR. PBB and nM-PBB were used for the removal of MB dye. The adsorbent amount, temperature, pH, time and dye concentration were investigated in the adsorption process with adsorption isotherms, kinetics and thermodynamics to estimate their MB removal efficiency. Sorption equilibrium for MB dye was reached by nM-PBB within 60 min and adsorption efficiency up to 99.007% was reached. While the adsorption kinetics followed a pseudo-second-order kinetic model, the Langmuir isotherm model, with a maximum adsorption capacity of 107.527 mg/g (nM-PBB), showed homogeneous physiochemical adsorption. The efficiency was found to be a spontaneous endothermic reaction. It can be suggested that nM-PBB can be used to remove MB. [ABSTRACT FROM AUTHOR]

Adsorption has been traditionally modeled using equilibrium models like the Langmuir and the Freundlich isotherm models, and kinetic models such as pseudo-first and pseudo-second order equations. However, most of these equations are not in an Indepedant, and single-equation form. A novel mathematical framework that combines adsorption kinetics and isotherm equations to an independant, single-equation form is presented herin. The adsorption isotherm equations were first solved using the mass balance equations to derive an independant equation, eliminating the intermediate variables. This derivation was done for the commonly used adsorption isotherms such as Langmuir, Freundlich, Langmuir-Freundlich and Linear isotherms. The simplified equations can be used for predicting solid phase adsorption (qe) and aqueous phase concentration (Ce) in terms of equilibrium constants, and was called as Equilibrium Adsorption Solution Equation (EASE). This EASE equation was further integrated into adsorption kinetic equations to give a solution which can also predict kinetic adsorption. This framework was named as Combined Adsorption Kinetic and Equilibrium (CAKE) equation and was further validated with experimental data. The CAKE equation offers the following advantages: By using this combined equation, both the kinetics and equilibrium concentrations of the batch adsorption systems can be predicted. Further, the intermediate variables are eliminated, and the final equation involving only model constants such as maximum adsorption capacity (qmax), affinity constant (ka), initial concentration (Co), and kinetic rate constants (kt) are required to to calculate pollutant concentration at any given time. The model was validated using an experimental dataset of 2,4-Dichlorophenol adsorption studies on activated carbon. The CAKE and EASE models fitted the experimental datasets very well with an R2 of 0.85, and a normalized absolute percentage error (NAPE) of 7.5%., thus validating the developed equations. [ABSTRACT FROM AUTHOR]

The presence of sulfur in transportation fuels has bad consequences for health and the environment, and there are many techniques used for removing or eliminating sulfur content, especially hydrodesulfurization. Hydrodesulfurization is the classical technique for desulfurization, but it is characterized by working at elevated temperatures and pressures as well as high costs. For this, there are many alternative methods, such as adsorptive, oxidative, extractive, and so on. The adsorptive desulfurization (ADS) is one of the most promising methods for sulfur reduction because of its ability to work under ambient conditions and ADS can significantly enhance the quality of light naphtha by reducing its sulfur content and improving its suitability for downstream processes such as catalyst poisoning and corrosion. The calcite prepared from eggshell was investigated here as an adsorbent for sulfur compounds from light naphtha. The adsorbent was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The investigation of adsorbent activity was done by batch adsorption, and the chosen studied variables are temperature, adsorbent dosage, and contact time with ranges of 20–40 C°, 1–3 g, and 15–45 min, respectively, which were designed according to the Box–Behnken experimental design and the experiment results were analyzed using Minitab software version 17. The results show that the sulfur-removing efficacy ranged between 45 and 60%, while optimum sulfur removal efficiency is 61% at the following operation conditions: 40 °C, 3 g, and 45 min for temperature, adsorbent dosage, and adsorption time respectively.Adsorption isotherms Langmuir and Freundlich were examined, and the results show the Freundlich isotherm is more suitable to describe the adsorption of these sulfur compounds.

Adsorption is vital for the elimination of Cr6+ and Pb2+ ions in the contaminated solution medium. A ternary blend made up of chitosan, nylon 6 and polyurethane foam (CS/Ny 6/PUF) blend in the ratio of 2:1:1 has been investigated. These blends are used as an adsorbent due to the insoluble nature in acidic and basic medium. The adsorption efficacy was analyzed by modifying pH, contact time, and adsorbent dosage. The maximum uptake of metal ions has been exhibited in the pH range 5. An equilibrium adsorption statistic indicated that adsorption isotherm follows the Freundlich model. The adsorption kinetic parameters specified that the adsorption of chromium has shown pseudo-second-order and lead pseudo-first-order reaction. HIGHLIGHTS CS/NY 6/PUF blends adsorption efficacy was analyzed by modifying pH.; Contact time, and adsorbent dosage.; Langmuir and Freundlich adsorption isotherm was utilized.; An adsorption harmony of metal particles was adsorbed by the adsorbent.; The adsorption of chromium and lead ions exhibits pseudo-second-order and pseudo-first-order kinetic reaction.;

Adsorption equilibrium on bioadsorbents was studied, and fitted to Langmuir, Freundlich and Dubinin-Radushkevich isothermal models, using yam peels (YP) and oil palm wastes (OPW) as bioadsorbents in the removal of hexavalent chromium present in aqueous solution, in a batch system, evaluating the effect of temperature, adsorbent dose and particle size on the process. Thermodynamic parameters were estimated by the Van't Hoff graphical method. It was found that the highest adsorption capacity was obtained at 0.03 g of adsorbent, 55 °C and 0.5 mm of particle size. The equilibrium of adsorption on OPW is described by Langmuir and Freundlich isotherms, while that of YP by Dubinin- Radushkevich's model, indicating the adsorption is given by the ion exchange between the active centers and the metallic ion. The thermodynamic study determined that the elimination of YP is endothermic, irreversible, and not spontaneous and that for OPW it is exothermic, spontaneous at low temperatures, and irreversible. [ABSTRACT FROM AUTHOR]

Chitosan was prepared and coupled with Furfural. The resulting chitosan furfural Schiff base was characterized using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Brunauer Emmett Teller (BET) analysis. It was observed that Chitosan furfural Schiff base shows characteristic absorption peaks at 3290.35cm-1„ 1644.47cm-1, 1552.69 cm-1„ which confirms the stretching vibration attributed to OH and NH groups of chitosan, NH=C (Imine linkage) of the Schiff base and aromatic ring of the furfural respectively. The SEM analysis, showed a rough large pore surface, the BET analysis revealed a large surface area of 339.85 m²/g, a pore diameter of 2.94nm, and a pore volume of 0.1194 cm³,/g. The material was used to adsorb aqueous 2, 4-Dinitrophenol (2, 4-DNP). The results obtained were evaluated with Langmuir and Freundlich adsorption isotherm. The material data fitted best with Freundlich isotherm R2 value of 0.9690 when compared to Langmuir isotherm R2 value of 0.8560. This indicates that the material proved uptake onto heterogeneous adsorbent surfaces. The R2 values are regarded as a measure of the best fit of experimental data on the isotherm model. [ABSTRACT FROM AUTHOR]

The objective of this work is to use sediments of an Algerian dam in adsorbing cationic dye, methylene blue (MB) onto aqueous solution, and test their aptitudes in the fixation of organic pollutants. The raw mud sediment (RMS) is characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, Fourier-transform infrared spectroscopy, and BET method (Brunauer-Emmett-Teller). The results show that the sediments consist of clay phases; the RMS featured a high surface area of 102.42 m²·g-1 using the Hang method and 42.39 m²·g-1 by BET. Adsorption results show that the adsorption kinetics is rapid and adjusted to best fit the pseudo-second-order model. The equilibrium adsorption data analyzed by the Langmuir, Freundlich, and Temkin isotherm models revealed that the isotherm of the solution with initial concentration C0 < 100 mg·L-1 obeys to the Freundlich isotherm, and those of concentrations greater than 100 mg·L-1 follows the Langmuir model (R² = 0.9919), equilibrium adsorption 93.72 mg·g-1 for an initial concentration of 1,000 mg·L-1 was achieved at a temperature of 293 K and pH of 6. The values of the activation parameters such as free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also determined. The results indicate that the process of adsorption of MB on the RMS is spontaneous (ΔG° < 0) and exothermic (ΔH° < 0). This study reveals that RMS can be used as an effective low-cost adsorbent of MB from aqueous solutions. [ABSTRACT FROM AUTHOR]

Improper management of organic industrial wastes, such as empty fruit bunch (EFB) from the palm oil industry and pressmud, i.e., a by-product of the sugar refinery industry can lead to environmental problems. This study aims to investigate the potential of pressmud and EFB as adsorbent materials in wastewater pollution removal. The chemical analysis in this study revealed that the EFB sample contained 7.30% of SiO2, 2.11% of Fe2O3, 1.91% of MgO, 28.02% of CaO, 37.59% of K2O, 1.45% of P2O5, 14.51% of Cl, 4.39% of SO3, and 2.38% of other elements. Meanwhile, the pressmud sample contained 14.32% of SiO2, 1.39% of SO3, 81.71% of CaO, 1.03% of Fe2O3, and the remaining 1.56% of other compounds. The possible adsorption capacities of pressmud and EFB were determined using the Langmuir and Freundlich isotherms. The absorption of Cd, Cr, Cu, Fe, Mn, Ni, and Zn in these samples was analyzed using the Langmuir and Freundlich isotherm models. By comparing both models, the research revealed that the Langmuir model provided a more precise description of the adsorption process for the EFB and pressmud samples and was competently compared to the Freundlich model, as indicated by the highest R2 values. The results indicate the potential of EFB and pressmud as promising reactive materials for heavy metal adsorption, and this involves recognizing possibilities for repurposing these economical and sustainable waste materials. [ABSTRACT FROM AUTHOR]

Abstract Analytical isotherm models such as Langmuir isotherm, Freundlich isotherm, and other linear isotherms are commonly used for modeling adsorption datasets for a wide range of adsorption studies. Most of these studies consider pH to be fixed. However, pH is an important parameter that varies widely. Hence, the model parameters developed for one set of experiments cannot be used in another scenario where the pH is different. Surface complexation models that can simulate pH changes are complex, multi-parameter models that are difficult to use. The modified Langmuir–Freundlich (MLF) isotherm developed earlier by us could simulate pH-dependent adsorption on goethite-coated sands. However, it has only been tested for arsenic adsorption on goethite-coated sands. Therefore, chromium adsorption datasets were considered to extend this MLF isotherm for other metal ions. Two different adsorbents, viz. coconut root activated carbon (CoAC) and palm male flower activated carbon (PaAC), were selected for the adsorption modeling of Cr(VI) using the MLF isotherm model. An improved modeling strategy was developed for fitting the MLF isotherm, which required only a single pH versus adsorption dataset, instead of several isotherms at different pH values. The new methodology could simulate the pH-dependent adsorption satisfactorily for various experimental datasets. The maximum adsorption capacity was 88.64 (mg/g) and 100.1 (mg/g) for PaAC and CoAC, respectively. The affinity constant for this model (K a) was found to be 0.007 (L/mg) for PaAC dataset and 0.0106(L/mg) and 0.004 (L/mg) for the CoAC dataset. The average R 2 values of fitting were calculated and found to be 0.98 for PaAC and 0.85 for CoAC. The average root mean square error (RSME) of the fitting of the model was 0.07 (less than 10%). This modeling strategy required less experimental data and did not require advanced characterization studies. Therefore, this study indicates that the MLF isotherm can be extended to other contaminants and for different adsorbents to model the pH-dependent adsorption.

Activated carbon was produced from orange peel using H2SO4 and ZnCl2 as activating agents at a temperature of 400 ℃. The impregnation was done in 1:1 (wt/v). FTIR analysis of the precursor and activated carbon shows different functional groups present in the precursor and activated carbon. The FTIR spectral also shows shifts in bands and changes in wave number between the precursor and activated carbon indicating chemical transformation during activation and carbonization. SEM analysis was used to study the internal structure and pores development of the activated carbon. The methylene blue adsorption capacity of the activated carbon was determined using standard methods. Langmuir and Freundlich adsorption isotherms were employed in determining the adsorption process and Pseudo first-order and Pseudo secondorder kinetics were employed in determining the rate of adsorption by the adsorbents. [ABSTRACT FROM AUTHOR]

The increasing interest of all stakeholders to achieve environmental protection with socioeconomic development puts pressure on industrial processes for less negative impact on the environment. The use of biomass for wastewater treatment has increased due to its low costs and technical feasibility. The present study aimed the use of biomass from a waste of known polluted area for the adsorption of Zn and Cu in a fixed-bed reactor. Samples were collected in Cubatão (Brazil) and cultivated in LB medium. Resulting cultivable bacterial communities were identified as Enterococcus faecalis and Pseudomonas aeruginosa. Adsorption experiments were performed varying the metallic ion concentration and the amount of biomass. Adsorption experiments showed efficiency rates up to 90%. As the concentration of metallic ions increased, the adsorption efficiency decreased, indicating that the active sites were saturated. Activated charcoal demonstrated lower adsorption rates than biomass. Elution process showed that HNO3 had better efficiency than HCl. Zn adsorption fitted better for Lineweaver–Burk model (Qmax = 200 mg/g of biomass), while Cu adsorption fitted better for Langmuir model (Qmax = 164 mg/g of biomass). Results here demonstrated that the adsorption of Zn and Cu simulating an industrial wastewater by the biomass from a contaminated area is technically feasible. [ABSTRACT FROM AUTHOR]

This study examined the ability of the green microalgae Chlorella vulgaris to remove arsenic from aqueous solutions. A series of studies was conducted to determine the optimal conditions for biological arsenic elimination, including biomass amount, incubation time, initial arsenic level, and pH values. At 76 min, pH 6, 50 mgL−1 metal concentration, and 1 gL−1 bio-adsorbent dosage, the maximum removal of arsenic from an aqueous solution was 93%. The uptake of As (III) ions by C. vulgaris reached an equilibrium at 76 min of bio-adsorption. The maximum adsorptive rate of arsenic (III) by C. vulgaris was 55 mg/gm. The Langmuir, Freundlich, and Dubinin–Radushkevich equations were used to fit the experimental data. The best theoretical isotherm of Langmuir, Freundlich, or/and Dubinin–Radushkevich for arsenic bio-adsorption by Chlorella vulgaris was determined. To choose the best theoretical isotherm, the coefficient of correlation was used. The data on absorption appeared to be linearly consistent with the Langmuir (qmax = 45 mgg−1; R2 = 0.9894), Freundlich (kf = 1.44; R2 = 0.7227), and Dubinin–Radushkevich (qD–R = 8.7 mg/g; R2 = 0.951) isotherms. The Langmuir and Dubinin–Radushkevich isotherms were both good two-parameter isotherms. In general, Langmuir was demonstrated to be the most accurate model for As (III) bio-adsorption on the bio-adsorbent. Maximum bio-adsorption values and a good correlation coefficient were observed for the first-order kinetic model, indicating that it was the best fitting model and significant in describing the arsenic (III) adsorption process. SEM micrographs of treated and untreated algal cells revealed that ions adsorbed on the algal cell's surface. A Fourier-transform infrared spectrophotometer (FTIR) was used to analyze the functional groups in algal cells, such as the carboxyl group, hydroxyl, amines, and amides, which aided in the bio-adsorption process. Thus, C. vulgaris has great potential and can be found in eco-friendly biomaterials capable of adsorbing arsenic contaminants from water sources. [ABSTRACT FROM AUTHOR]

The sorption kinetics of two of the most frequently used antibiotics onto recycled (weathered) polyvinyl chloride (PVC) was investigated, using Freundlich and Langmuir isotherm models. Various experimental conditions were set, including pH, contact time, rotational speed, temperature, and initial concentration. The batch experimental results indicated that Freundlich model was better fitted than Langmuir (R2: 98.7 and 84.7, for CIP and CLA respectively). Maximum adsorption capacity is 45.9 mg/g and 22.0 mg/g for CIP and CLA, respectively. Enthalpy (ΔH), and entropy (ΔS) values were negative for CIP, indicating that the reaction was exothermic and spontaneous, respectively. It was vice versa for CLA. Field emission scanning electron microscope (FESEM) and Fourier transform infrared spectrometer (FT-IR) analysis confirmed the physical adsorption mechanism. The results demonstrated that the recycled PVC microplastic has a good capacity for adsorption for both antibiotics. [ABSTRACT FROM AUTHOR]

In the present study, the adsorption of zinc (Zn), lead (Pb), copper (Cu), and cadmium (Cd) was studied in two already polluted urban soil samples with different pH values, an acidic and an alkaline one. The Langmuir and Freundlich adsorption isotherm equations were used to thoroughly study the adsorption of the metallic elements on the solid surface of the soils. Langmuir equation described the adsorption of each metal satisfactorily, with a slight predominance over Freundlich, in both soils, as the R2 value approached almost unity. Even though Zn and Cu were adsorbed on the soil phase, their adsorption was minimal compared to the adsorption of more harmful metals such as Pb and Cd. Using the values of the coefficients obtained from the equations of the mathematical models, we concluded that in alkaline soils, the retention of metals was much greater than in acidic soils. The simultaneous presence of metals during the addition of the single-element solutions of the metals to the already metal-contaminated soils caused competitive adsorption increasing the retention of the more toxic metals on the solid surface of the alkaline soil. Factors affecting soil sorption (such as soil pH and CaCO3 content) were studied to provide theoretical support for understanding the laws and causes of metal sorption in the soils of the survey. [ABSTRACT FROM AUTHOR]

Adsorption is kinetically time-dependence controlled retention/ release mobility as a natural phenomenon in base and applicable in industry or in science. It is well-studied and modulated by known Langmuir, Temkin, Freundlich, and other models to describe how it occurred and explains kinetic- thermodynamic material behaviour. Linear and/ or non- linear expressions may take place according to the theoretical base of these models to conclude the layer formation, uniformity besides reaction reversibility, and favourability from kinetic- thermodynamic principles. Coefficient of determination (R²) is a mean variation of data or a degree of proper or fitting as mostly used in kinetic and isotherm literatures. In adsorption investigations, experimental physical- chemical conditions and error sources are the main influenced factors, for example, at surface coverage (or inhibition efficiency) in corrosion treatments or adsorption capacity in pollution subject. Linearity variation will govern R² to predict adsorbate behaviour on adsorbent surface that is highly influenced by concentration, temperature, pH, type of measuring method, physical and chemical structures of the adsorbent and adsorbate, and error sources in each experiment. [ABSTRACT FROM AUTHOR]

The dyes of the textile dyeing industry wastewater are harmful to humans and the environment. They should be treated before discharging into the environment. The adsorption using the spherical activated carbon can be effective to reduce the dyes. The spherical activated carbon of 3-7 µm in diameter was successfully prepared from the waste bagasse liquid using the hydrothermal method. The activation of this carbon was carried out using the KOH solution. The optimum pH and contact time were achieved in 2 and 200 min, respectively. Adsorption kinetic for RhB on activated spherical carbon follows the second-order kinetics and its adsorption mechanism follows the Langmuir isotherm. The maximum adsorption capacity of spherical activated carbon to Rhodamine B was achieved in 64.52 mg/g. [ABSTRACT FROM AUTHOR]

Heat stable salts (HSS) form in amine systems as a result of the reaction products of the amine and acidic compounds stronger than H2S and CO2 in the inlet stream to the gas treating unit (GTU). These stable salts are not readily disassociated and removed in the regeneration column. Increased foaming and reduced acid gas carrying of amine solution capacity are results of HSS present in an amine system. In this study, in-depth analyses of degradation compound, HSS anions, metal cation content, BTEX content, mercaptane content, acid gas loading, and foaming tendency of contaminated and treated Methyldiethanol amine (MDEA) solutions were performed to specify the design specific parameters of ion exchange resin system for handling more than 487.61 m3 of contaminated MDEA solution containing a total of 9000 ppm wt of HSS. The ion exchange resin plant design and construction were considered as an alternative method to the MDEA treatment to reduce degradation of the MDEA. Ion exchange resin was based on a strong anionic resin (LEWATIT MP 800). Ultimately, the analytical results exhibited a significant reduction of HSS in the MDEA solution. The equilibrium adsorption studies for anions reduction were fitted into the Langmuir, Freundlich model isotherms. The Langmuir and Freundlich equilibrium isotherms explained the best performance of ion exchange resin with the predicted qmax value of 370.37 mg/g by the Langmuir model. The breakthrough time for removal of anions in ion exchange resin bed with a flow rate of 5.5 × 10−4 m3/s was achieved within 6948s.

Through this investigation, we establish the mechanism and physical characterization of zinc (II) sequestration by Morganella morganii ACZ05 strain, which was isolated and characterized from soil polluted by effluents from electroplating industries. As far as we know, there is very little literature concerning zinc biosorption using an environmental strain of M. morganii. The SEM analysis shows the dark porous gaps in the aggregated cell-matrix of test bacterial biomass which is inferred as water channels usually seen in biofilms, as compared to metal-unexposed control. M. morganii is not known to produce biofilms unless in the rare nosocomial conditions. Here, SEM analysis shows the production of biofilms after exposure to zinc (II) at 500 ppm, which has not been previously reported. EDX analysis of bacterial biomass also specified the sorption of zinc (II) by the bacterial cells and the presence of new peaks for zinc in contrast to control. Both XRD and FTIR analysis observations strongly implicate the potential of physical adsorption as a mechanism for heavy metal resistance. Analysis of the cell surface by Atomic force microscopy and examination of the topography revealed cell aggregation occurs during biofilm production after zinc biosorption. Unlike other reports, regular models such as Langmuir isotherm and Freundlich isotherm were found insufficient to explain the physisorption of zinc (II) metal ions on complex multicomponent adsorbents such as the exopolymeric surface of the bacterial cells. However, adsorption kinetics of zinc (II) to the bacterial biomass was most effectively elucidated by a pseudo-second-order kinetic model, suggesting a certain kind of chemisorption that requires further study. HIGHLIGHTS XRD and FTIR – potential of physical adsorption as a mechanism for heavy metal resistance.; SEM-EDX and AFM – morphological changes were observed after metal addition.; The isotherm studies – fit of pseudo-second order for biosorption experimental data suggests the involvement of cellular mechanisms for the activity of binding sites of metal ions and other chemical sorption processes.; Biosorption, chemisorption,;

Residual lignocellulosic materials can be used as adsorbents for heavy metals present in water, promoting the adsorption of metal ions on the surface and active sites of biomaterials, resulting in a low-cost and efficient removal. In this case, the residues from the agroindustrial use of the fique (Furcraea macrophilla) and the agricultural process of the corn maize (Zea mays) were studied as adsorbing phases of chromium and lead metals, in order to assess their capacity as biosorbents of these metals present in water samples, determined by equilibrium time, type of isotherm and maximum adsorption capacity; finding that in a time of 12 hours, the fique fiber has an adsorption capacity of Cr and Pb of 7,81 ± 1,40 mg/g and 169,51 ± 1,37 mg/g respectively, observing, a form of Freundlich type adsorption isotherm; while the corn layer fiber has an adsorption capacity of 13,35 ± 3,28 mg/g for chromium and 15,01 ± 3,47 mg/g for lead, showing a behavior in its Langmuir-type adsorption isotherm, concluding that both fibers have potential for the removal of the metals studied, especially the fiber of fique. [ABSTRACT FROM AUTHOR]

Analytical isotherm models such as Langmuir isotherm, Freundlich isotherm, and other linear isotherms are commonly used for modeling adsorption datasets for a wide range of adsorption studies. Most of these studies consider pH to be fixed. However, pH is an important parameter that varies widely. Hence, the model parameters developed for one set of experiments cannot be used in another scenario where the pH is different. Surface complexation models that can simulate pH changes are complex, multi-parameter models that are difficult to use. The modified Langmuir–Freundlich (MLF) isotherm developed earlier by us could simulate pH-dependent adsorption on goethite-coated sands. However, it has only been tested for arsenic adsorption on goethite-coated sands. Therefore, chromium adsorption datasets were considered to extend this MLF isotherm for other metal ions. Two different adsorbents, viz. coconut root activated carbon (CoAC) and palm male flower activated carbon (PaAC), were selected for the adsorption modeling of Cr(VI) using the MLF isotherm model. An improved modeling strategy was developed for fitting the MLF isotherm, which required only a single pH versus adsorption dataset, instead of several isotherms at different pH values. The new methodology could simulate the pH-dependent adsorption satisfactorily for various experimental datasets. The maximum adsorption capacity was 88.64 (mg/g) and 100.1 (mg/g) for PaAC and CoAC, respectively. The affinity constant for this model (Ka) was found to be 0.007 (L/mg) for PaAC dataset and 0.0106(L/mg) and 0.004 (L/mg) for the CoAC dataset. The average R2 values of fitting were calculated and found to be 0.98 for PaAC and 0.85 for CoAC. The average root mean square error (RSME) of the fitting of the model was 0.07 (less than 10%). This modeling strategy required less experimental data and did not require advanced characterization studies. Therefore, this study indicates that the MLF isotherm can be extended to other contaminants and for different adsorbents to model the pH-dependent adsorption. [ABSTRACT FROM AUTHOR]

Research on Indonesia’s natural nano materials is still limited. For environmental remediation application as an adsorbent, their adsorption characteristics and quality are particularly important to be assessed. From Indonesian volcanic tuff material, ‘nanoclay’ fraction of < 200 nm particle size was separated. The separated ‘nanoclay’ exhibits pH-dependent charge characteristics. Therefore, it could be used as an anionic adsorbent since its separation process was adjusted to proceed at pH < 4, resulted in a net positive charged ‘nanoclay’. This study aims to compare phosphate adsorption characteristics of the separated ‘nanoclay’ based on Langmuir, Freundlich, Brunauer-Emmett-Teller (BET), and Dubinin-Radushkevich (D‒ R) iso-thermal models. The results showed that the application of Langmuir and D‒R models produced adsorption capacity (qe parameter) of 461 (two-sites) and 440 mg P.g-1 (heterogeneous-sites), respectively, while BET and Freundlich models produced adsorption at the first adsorptive layer (qmono parameter) of 111,11 mg P.g-1 (multi-layers) and adsorption constant (1/n parameter) of 0,28, respectively. The latter indicated that the assessed ‘nanoclay’ was a high-quality adsorbent (1/n value 0,10-0,50). Therefore, it could be utilized as adsorbent for the removal of anionic contaminants in eutrophic water systems. In this study, Langmuir Model revealed the best application performance compared to the other three adsorption models applied. [ABSTRACT FROM AUTHOR]

Methylene blue is a cationic dye often used for various industries. Methylene blue waste harms aquatic biota. Most ways have been done to reduce the methylene blue pollution that includes photocatalytic, electrochemical, and adsorption. This study aimed to reduce the impact of methylene blue pollution on the aquatic environment and to test the adsorption isothermal for methylene blue adsorption using coconut fiber. The abundant coconut fiber waste around the Kupang city was taken and prepared to be used as an adsorbent. The characterization results showed that the active groups in cellulose were clearly described on the FTIR spectra which showed the presence of O-H vibrations at 3296.35 cm-1, C-O vibrations were seen at 1267.23 and 1060.85 cm-1, at wavelengths 1608.63 cm-1 and 817.72 cm-1 there is a vibration from the C=C bond, while the C-H vibration appears at a wavelength of 2939.52 cm-1. The results of this research analysis showed that the adsorption of methylene blue according to the Langmuir isotherm indicated by the value of the equation of the straight line R2 being one and the direction of the curve depicting occurring the effective adsorption. The maximum adsorption capacity was 4.467 mg g-1 with the percentage of methylene blue adsorbed at 99.3%. Adsorption occurs chemically with an energy of 27.29 kJmol-1 so it can be determined that the adsorption occurs with a monolayer mechanism.

Andisol is a soil that has andic properties and develops from volcanic parent materials, especially ash. Andic soil properties are formed due to weathering of tephra or other parent materials that contain volcanic glass in large quantities. The main components of soil-forming Andisol are amorphous (short-range-order) minerals, such as allophane, imogolite, ferrihydrite, and Al/Fe-humus complexes. The existence of short-range-order minerals causes Andisol to have high P-tapping ability, but efforts to lower the amount of P plunged with organic and inorganic an-ons have not been widely studied. This study aimed to compare the ability of humic acid, fulvic acid, and sulfate in suppressing P adsorption by amorphous minerals from the Andisol of Mount Dieng, Merbabu, and Sumbing. The highest calculation of % ferrihydrite was found at the location of Mount Merbabu with a value of 3.05%, while the % allophane + imogolite was determined by the content of Sio in the ground. The calculation results showed that the highest was found at the location of Mount Sumbing with a value of 7.17%. Based on TEM analysis, Mount Sumbing has allophane diameter of 2.24 -- 5.93 nm and the imogolite length of 24 -- 187 nm. [ABSTRACT FROM AUTHOR]

Calix[4]arene refers to a group of large cyclic compounds involving a sequence of phenols, which are obtained through the hydroxylation reaction process of phenol and aldehyde derivatives. Calixarenes have a rigid and three-dimensional structure. Nanoparticles can be used in drug delivery due to their ability to enter cells. The application of a carrier for drug delivery is very effective on improving their performance. In order to employ calixarene nanoparticles as the carriers of mercaptopurine drug, their ability and type of adsorption were examined on laboratory scale. In this study, by examining the temperature changes on the course of adsorption and by matching the data against Langmuir adsorption isotherm, Freundlich, and Dubinin–Radushkevich, the numbers of all thermodynamic constants of this process were calculated. The obtained adsorption capacities indicated that the elevation of the initial concentration leads to the enhanced adsorption capacity. Moreover, by considering the obtained thermodynamic constants, it was found that the adsorption process is exothermic, while the values of Gibbs free energy ∆G0 and the adsorption energy Ea showed that the adsorption process was spontaneous and chemical. [ABSTRACT FROM AUTHOR]

Heavy metals are generally found in industrial wastewaters, affecting human health and living organisms. This study was therefore aimed to use bioadsorbents rice husk and activated carbon-silica to efficiently remove the heavy metals including lead (Pb) and cadmium (Cd) from an aqueous wastewater. The effects of bioadsorbent content, initial concentration, contact time, and pH value on the metal removal were investigated. An increased metal initial concentration lowered the removal efficiency of the bioadsorbents, and pH 6 provided the best condition for the removal of Pb and Cd. The use of rice husk and activated carbon-silica at pH 6 resulted in a maximum metal removal of 81% and 98% for Pb, while 88% and 100% for Cd respectively. The adsorption parameters were then determined by the Langmuir and Freundlich adsorption isotherms, and the experimental data were better fitted in the Freundlich adsorption isotherm model in comparison with the Langmuir adsorption isotherm model.

Protein adsorption on solid surfaces is characterized by multivalence, binding-unit overlap, sequential adsorption, surface allosterics, lateral interactions and pronounced adsorption-desorption hysteresis, giving rise to the sequential, hystallosteric, adsorption model ("SHA model"). Adsorption isotherms of fibrinogen on a titanium miniplates and of the growth factors rhBMP-2 and rhVEGF165 on PDLLA nanofiber fleeces are presented. Controversial Langmuir type isotherms of fibrinogen and rhVEGF165 can be understood on the basis of singular long-lived metastable states central to the SHA-model.

This study examined the ability of the green microalgae Chlorella vulgaris to remove arsenic from aqueous solutions. A series of studies was conducted to determine the optimal conditions for biological arsenic elimination, including biomass amount, incubation time, initial arsenic level, and pH values. At 76 min, pH 6, 50 mgL−1 metal concentration, and 1 gL−1 bio-adsorbent dosage, the maximum removal of arsenic from an aqueous solution was 93%. The uptake of As (III) ions by C. vulgaris reached an equilibrium at 76 min of bio-adsorption. The maximum adsorptive rate of arsenic (III) by C. vulgaris was 55 mg/gm. The Langmuir, Freundlich, and Dubinin–Radushkevich equations were used to fit the experimental data. The best theoretical isotherm of Langmuir, Freundlich, or/and Dubinin–Radushkevich for arsenic bio-adsorption by Chlorella vulgaris was determined. To choose the best theoretical isotherm, the coefficient of correlation was used. The data on absorption appeared to be linearly consistent with the Langmuir (qmax = 45 mgg−1; R2 = 0.9894), Freundlich (kf = 1.44; R2 = 0.7227), and Dubinin–Radushkevich (qD–R = 8.7 mg/g; R2 = 0.951) isotherms. The Langmuir and Dubinin–Radushkevich isotherms were both good two-parameter isotherms. In general, Langmuir was demonstrated to be the most accurate model for As (III) bio-adsorption on the bio-adsorbent. Maximum bio-adsorption values and a good correlation coefficient were observed for the first-order kinetic model, indicating that it was the best fitting model and significant in describing the arsenic (III) adsorption process. SEM micrographs of treated and untreated algal cells revealed that ions adsorbed on the algal cell’s surface. A Fourier-transform infrared spectrophotometer (FTIR) was used to analyze the functional groups in algal cells, such as the carboxyl group, hydroxyl, amines, and amides, which aided in the bio-adsorption process. Thus, C. vulgaris has great potential and can be found in eco-friendly biomaterials capable of adsorbing arsenic contaminants from water sources.

Astaxanthin is a natural antioxidant, and the highest content of this compound is found in Haematococcus pluvialis microalgae. Microwave-assisted extraction (MAE) is one of the environmentally friendly extraction methods and has many advantages. This study aims to investigate the extraction of astaxanthin through the MAE method using various solvents. Several equilibrium models were proposed to describe this solid-liquid equilibrium. The solid-liquid extraction equilibrium parameters were determined by minimizing the sum of squares of errors (SSE), in which equilibrium constants were needed for scaling up purposes. Previously, the microalgae were pretreated with HCl to soften their cell walls in order to improve the extraction recovery. In this study, dichloromethane, acetone, methanol, and ethanol were used as the solvents for extraction. The astaxanthin concentration was determined by high-performance liquid chromatography (HPLC) and spectrophotometry. Astaxanthin was found to attain equilibrium at 57.42% recovery in a single-step extraction. Thus, several steps were required in sequence to obtain an optimum recovery. The experimental data were fitted to three equilibrium models, namely, Henry, Freundlich, and Langmuir models. The experimental data were well fitted to all the models for the extraction in dichloromethane, methanol, ethanol and acetone, as evident from the almost same SSE value for each model.

This study aims to investigate the adsorption capacity of ammonium NH4+, nitrite NO2- and nitrate NO3- onto rice husk biochar (RHB) obtained from 550 °C pyrolysis temperature in the context of using low-cost absorbent for recirculating aquaculture system (RAS). Raw RHB at its original size 5–8 mm has been choosen for testing its adsorption capacity as well as several key material properties (pHPZC, surface area, and elemental analysis). From surface functional group analysis, there existed the O–H group (at frequency 3443 cm-1), –CH3 (2360 cm-1), and either –C=O or C=C group (in the range of frequency 1600–1650 cm-1) as well as –COOH (1456 cm‒1) that helped enhance chemical adsorption. The experimental adsorption data has been roughly consistent with Langmuir and Freundlich models that used to calculate the maximum saturated monolayer adsorption capacity Q0max of ammonium, nitrite, and nitrate were 0.1003, 0.2477, and 0.1290 mg/g respectively. Therefore, RHB could be a potential candidate for biofilter application in both targets cost-efficient and sustainable that worth applied at scale.

The discharge of wastewater containing heavy metals into waterbodies is a major environmental issue that can influence the quality of the water supply; therefore, it is important to remove the pollutants dangerous to living organisms. The adsorption of copper (II) ions on modified wheat bran was investigated with respect to initial solution pH (2.0-7.0), contact time (5–120 min), adsorbent mass (0.5 g and 1.0 g), and initial metal ion concentration (2.0–20 mg/L). The optimum adsorption conditions were found to be at pH 5.0 and a contact time of 60 min with an adsorbent mass of 1.0 g where the maximum efficiency was recorded as 84.5 %. The adsorption uptake (in mg/g) of copper (II) ions slowly reached equilibrium in around 30 min and this amount was 0.30 mg/g using an adsorbent mass of 0.5 g. The adsorption uptake of copper (II) ions decreased with increasing mass of adsorbent and the adsorption efficiency (in %) increased with increasing mass of adsorbent. The experimental results were described using the Langmuir and Freundlich models, with the Langmuir model fitting better than the Freundlich model. The maximum modelled adsorption capacity was 4.24 mg/g and the modelled specific surface area of modified wheat bran was 6.36 m2. It was observed that the adsorption of copper (II) ions on modified wheat bran is efficient and suitable, therefore modified wheat bran is a relatively good adsorbent for the removal of copper (II) ions from polluted water compared to other agricultural adsorbents.