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In this research, the efficiency of Midyat stone modified with sulphuric acid (H2SO4) in the removal of Methyl Orange (MO) from wastewater is evaluated. Various factors such as contact time, initial MO concentration, and adsorbent dosage were investigated to understand their influence on adsorption efficiency. The optimal conditions for MO removal were as follows: initial concentration 300 mg/L, contact time 70 min, adsorbent dosage 0.5 g. The surface properties of modified Midyat stone (MMS) were investigated using methods such as Fourier transform infrared spectroscopy (FT-IR) and Brunauer, Emmett, and Teller (BET). According to the findings, the isotherm data agreed with the Langmuir isotherm model, indicating both chemical sorption and irreversibility potential. The adsorption capacity of MO at 298, 308 and 318 K was calculated to be 50.02, 54.05 and 58.48 mg/g, respectively. In addition, adsorption kinetics data supported the pseudo-second-order (PSO) kinetic model for MO removal. The research identified MMS as a capable and adaptable substance for capturing MO ions from the aqueous environment due to its significant removal capacity, easy availability, and cost-effectiveness. [ABSTRACT FROM AUTHOR]

This study investigates the removal of heavy metals, particularly copper and nickel, from acidic aqueous solutions using the weakly base polymeric chelating resin Dowex M-4195. The research conducts comprehensive cost–benefit and statistical analyses of various kinetic and isotherm adsorption models. The results show that the PSO and general order models provide high accuracy for the Cu2⁺ adsorption kinetics, while the Avrami fractional order model excels for Ni2⁺. In terms of the isotherm models, the Langmuir and Jovanovic models are highly accurate for both metals, with the Toth model being particularly effective for Ni2⁺ due to its ability to account for surface heterogeneity and multi-layer adsorption. This study also reveals that the kinetic adsorption process is more economically beneficial than the isotherm adsorption process, highlighting the importance of model selection for optimizing heavy metal removal. Incorporating circular economy principles, this research emphasizes the sustainability of using regenerable and reusable adsorbents like Dowex M-4195. The findings provide valuable insights for designing efficient adsorption systems, promoting environmental sustainability, and ensuring public health safety. [ABSTRACT FROM AUTHOR]

In this work, the efficacy of two metal–organic frameworks (MIL-101(Fe) and NH2-MIL-101(Fe)) in eliminating acetamiprid (ATP) insecticide and eosin Y (EY) dye from aqueous solution is tested. An analysis was conducted on the developed nanocomposite's optical, morphological, and structural characteristics. The adsorption isotherm, kinetics, thermodynamics, reusability, and mechanisms for ATP and EY dye removal were assessed. NH2-MIL-101(Fe) adsorbed 76% and 90% of ATP pesticide and EY dye, respectively after 10 to 15 min in optimum conditions. For both adsorbents, with regard to explaining the isotherm data, the Langmuir model offered the most accurate description. Moreover, the adsorption of ATP and EY dye is described by the pseudo-second-order kinetic model. The maximum adsorption capacities of ATP and EY dye on MIL-101(Fe) were 57.6 and 48.9 mg/g compared to 70.5 and 97.8 mg/g using NH2-MIL-101(Fe). The greatest amount of ATP and EY dye clearance was obtained at a neutral medium for both adsorbents. The results of this investigation demonstrate the effectiveness of MIL-101(Fe) and NH2-MIL-101(Fe) as effective substances in the adsorption process for removing pesticides and dyes from aqueous solution. [ABSTRACT FROM AUTHOR]

Methyl violet 6B (MV6B), found in wastewater, poses hazardous effects to aquatic ecosystems and human health; therefore, it must be removed immediately. In response, this study pioneered the development of a dye adsorbent by incorporating phenolated alkali lignin (PAL) into magnetite (Fe3O4), offering a solution for MV6B removal. Lignin was extracted from coconut husk through alkali extraction, chemically modified using phenolation, and integrated onto the magnetite surface. SEM and FTIR spectroscopy were used to characterize the adsorbent, and various parameters were optimized, along with evaluations of the adsorption kinetics and isotherm models, as well as the adsorbent’s reusability. PAL was successfully deposited onto the magnetite based on the characterization. The experimental results revealed that the optimal conditions for the removal of MV6B using PAL/Fe3O4 composite are pH 4, a temperature of 313 K, a dosage of 0.10 g PAL/Fe3O4 per 15 mL of MV6B, and a contact time of 150 minutes. MV6B’s equilibrium removal rate was 95.1%, with an adsorption capacity at equilibrium of 6.42 mg/g. The adsorption of MV6B followed a pseudo-second-order kinetic model and the Freundlich model isotherm. A thermodynamic study showed that the adsorption process was spontaneous and exothermic. PAL/Fe3O4 was highly reusable after three cycles without the need for desorption. Hence, this study has demonstrated that the PAL/ Fe3O4 adsorbent is practical, economical, and efficient for wastewater treatment.

In this study, waste tires (WTs) were carbonized under an N2 atmosphere. Subsequently, KOH/WTs‐char with KOH‐assisted CO2 activation was used to prepare activated carbon (AC) as a highly porous carbon material for the removal of Cr(VI) and Cd(II) from water. Various techniques such as elemental analysis, Fourier‐transform infrared spectroscopy, scanning electron microscopy, and N2 adsorption/desorption were employed to investigate the physical and chemical characteristics of the prepared carbons. The WTs‐char activated with KOH under CO2 exhibited a microstructure with a high BET surface area and pore volume of 1841 m2/g and 0.869 cm3/g, respectively, demonstrating excellent adsorbent performance. The maximum removal efficiencies of 99.91 % for Cd(II) and 99.81 % for Cr(VI) were achieved using AC2 carbon under the following conditions: pH 2 for Cr(VI) and pH 5 for Cd(II), contact time of 120 min, adsorbent dose of 0.4 g/100 mL, and temperature of 298 K. The adsorption kinetics followed the pseudo‐second‐order equation, and the equilibrium data fit well with the Redlich–Peterson isotherm equation. The positive values of ▵G indicated that the uptake process for both ions was nonspontaneous and nonfeasible over the temperature studied. Both ions showed negative values of ΔH and ΔS on carbon, suggesting exothermic adsorption and a decrease in disorder. Regeneration studies showed that NaOH was a better desorbing agent than HCl. Cr(VI) desorption resulted in over 90 % removal recovery by AC2 using 1.0 M NaOH even after the fifth cycle. However, the low activation energy indicated that the adsorption was favorable kinetically. Overall, this study demonstrated the effective preparation of highly porous carbon and its successful performance in removing Cr(VI) and Cd(II) ions. [ABSTRACT FROM AUTHOR]

Methyl violet 6B (MV6B), found in wastewater, poses hazardous effects to aquatic ecosystems and human health; therefore, it must be removed immediately. In response, this study pioneered the development of a dye adsorbent by incorporating phenolated alkali lignin (PAL) into magnetite (Fe3O4), offering a solution for MV6B removal. Lignin was extracted from coconut husk through alkali extraction, chemically modified using phenolation, and integrated onto the magnetite surface. SEM and FTIR spectroscopy were used to characterize the adsorbent, and various parameters were optimized, along with evaluations of the adsorption kinetics and isotherm models, as well as the adsorbent’s reusability. PAL was successfully deposited onto the magnetite based on the characterization. The experimental results revealed that the optimal conditions for the removal of MV6B using PAL/Fe3O4 composite are pH 4, a temperature of 313 K, a dosage of 0.10 g PAL/Fe3O4 per 15 mL of MV6B, and a contact time of 150 minutes. MV6B’s equilibrium removal rate was 95.1%, with an adsorption capacity at equilibrium of 6.42 mg/g. The adsorption of MV6B followed a pseudo-second-order kinetic model and the Freundlich model isotherm. A thermodynamic study showed that the adsorption process was spontaneous and exothermic. PAL/Fe3O4 was highly reusable after three cycles without the need for desorption. Hence, this study has demonstrated that the PAL/ Fe3O4 adsorbent is practical, economical, and efficient for wastewater treatment. [ABSTRACT FROM AUTHOR]

Algerian Eucalyptus Leaves (AEL), a natural biodegradable adsorbent abundantly available, was used for the removal of methylene blue (MB) dye. The AEL properties for the removal of MB were investigated under different conditions by varying the AEL amount, MB concentration, pH of the solution and the reaction temperature. Scanning electron microscopy (SEM) and infrared spectroscopy (FTIR) techniques have been used to characterize AEL biosorbent. Experimental results showed that the adsorption of MB dye at the concentration of 50 mg L−1 reached to 91 % at pH 10 with a stirring speed of 200 rpm and after 180 min of reaction time. The experimental data were analyzed using the linear forms of different kinetic models (pseudo-first order kinetic model, pseudo-second order kinetic model, and intra-particle diffusion models). The results demonstrated that the adsorption kinetics of MB was consistent with the pseudo-second order model with R2 value of 0.9969. The isotherm models Langmuir, Freundlich, Dubinin, Elovich, Brunaut Emmet Teller and Temkin models were also investigated to describe the adsorption equilibrium. The results show that the AEL adsorption is in accordance with Temkin isotherm. The thermodynamic study revealed that the adsorption is spontaneous and exothermic. Therefore, as a cheap green adsorbent with high MB adsorption performance, AEL is expected to become one of the best candidate materials for future industrial wastewater treatment. [ABSTRACT FROM AUTHOR]

This study presents two environmental aspects: valorisation of natural oil shale (NOS), on the one hand, and, on the other hand, to study the effectiveness of adsorption of methylene blue (MB) dye onto material (NOS). In this context, the most characterisations of adsorbent before and after adsorption process were investigated by several methods such as x-ray diffraction (XRD), scanning electronic microscopy (SEM) and Fourier transforms infrared spectrometry (FTIR), according to these results, the NOS is rich in quartz and calcite, the matrix clay contains the kaolin and illite and present a layer structure. The total number of results showed that the adsorption of MB onto NOS is best by pseudo-second-order fitting model with a good correlation (R2 = 0.98), on the other hand the adsorption process was described well by Langmuir isotherm with a maximal capacity of adsorption equal 29 mg/g. The effect of temperature on the adsorption of the dye was also evaluated and the thermodynamic parameters were determined. The negative values of the three thermodynamic parameters ΔH °, ΔG ° and ΔS ° of the NOS/MB system indicate that the adsorption is spontaneous, exothermic and the activated energy indicates that the adsorption mechanism might be a physical sorption process. [ABSTRACT FROM AUTHOR]

Environmental pollution from chemicals utilized in manufacturing, pharmaceuticals, and chemical process industries is of serious concern nowadays due to the contamination that ensues when these chemicals are discharged into water bodies. Activated carbon adsorption provides an efficient and economically viable means for mitigation of toxic chemicals (i.e., heavy metals, dyes, pharmaceutics, and antibiotics). However, the exorbitant cost of commercial activated carbons has resulted in the search for low-cost alternatives for the treatment of contaminated effluents. An exhaustive literature survey in this area is necessary to know the extent of work done in this area and seek out the gaps that future research will provide answers to. In this review, various works on activated carbon utilization, batch adsorption, fixed-bed adsorption (experimental and numerical studies) are summarized. This review elucidates the different kinetic and isotherm models of agrowastes-derived activated carbon materials in context with pollutants (dyes, heavy metals, pharmaceuticals, miscellaneous adsorbates) removal through batch and column methods. In addition, fixed-bed column adsorption/regeneration methods using various activated carbons derived from agrowastes are discussed. Among these methods, heavy metal adsorption from aqueous solutions by the activated carbons is the most efficient. The deployment of mathematical and machine learning approaches (ANN and novel GMDH algorithms) in optimization of batch and continuous adsorption processes are also highlighted. Numerical simulation of fixed-column adsorption systems for more improved industrial-scale column designs is described. Conclusions and future challenges of chemicals removal from polluted wastewater utilizing agrowaste-derived activated carbons are also presented.

This study investigates the removal of heavy metals, particularly copper and nickel, from acidic aqueous solutions using the weakly base polymeric chelating resin Dowex M-4195. The research conducts comprehensive cost–benefit and statistical analyses of various kinetic and isotherm adsorption models. The results show that the PSO and general order models provide high accuracy for the Cu2⁺ adsorption kinetics, while the Avrami fractional order model excels for Ni2⁺. In terms of the isotherm models, the Langmuir and Jovanovic models are highly accurate for both metals, with the Toth model being particularly effective for Ni2⁺ due to its ability to account for surface heterogeneity and multi-layer adsorption. This study also reveals that the kinetic adsorption process is more economically beneficial than the isotherm adsorption process, highlighting the importance of model selection for optimizing heavy metal removal. Incorporating circular economy principles, this research emphasizes the sustainability of using regenerable and reusable adsorbents like Dowex M-4195. The findings provide valuable insights for designing efficient adsorption systems, promoting environmental sustainability, and ensuring public health safety.

Iron concentration in drinking water higher than the recommended value imposes different health problems. There are advanced chemical-based iron extraction techniques, in spite of having certain limitations in developing countries. Due to this, iron removal by using locally available plants is a paramount sustainable option. Therefore, the current study was intended to explore the iron removal efficiency of the powder of Ocimum sanctum Linn. (OSL) leaves from water and investigate its capability by assessing various conditions of operation. The bioadsorption equilibrium isotherm and kinetics of iron extraction onto OSL leaf powder were studied and modelled. The experimental adsorption equilibrium observations served as the basis for a comparison of linear and nonlinear regression techniques for predicting the optimal isotherms and kinetics. The optimum conditions for the extraction of iron were observed to be pH of 5, biomass concentration of 0.2 g, contact time of 2 h, speed of agitation of 150 rpm at 25 °C temperature, while maximum bioadsorption capacity was 123.26 mg/g. The batch bioadsorption of iron obeys the Fritz–Schlunde isotherm and the pseudo-first-order-kinetic model. The isotherm and kinetics parameters obtained using the nonlinear regression method outperformed the linear approach. Moreover, the potential applicability of OSL leaves-based bioadsorbent could be further examined on a large-scale for industrial application. HIGHLIGHTS The potential of Ocimum sanctum Linn. (OSL) leaf powder for iron removal under various experimental conditions was presented.; Maximum adsorption capacity of OSL leaf powder was 123.26 mg/g at pH 5.; Thermodynamic parameters indicate that the bioadsorption process was possible, spontaneous, and exothermic.; The comparison of linear and nonlinear regression approaches for isotherm and kinetics modelling was discussed.;

Heavy metal pollution has become one of the most severe environmental issues. Adsorption is an effective method for removing heavy metals from aquatic environments. The adsorption isotherm and kinetics models can provide information on the adsorption process, maximal adsorption capacity, and mass transfer steps, which are essential to evaluate the performance of an adsorbent and to design an adsorption system. In this review, the adsorption kinetics and isotherms of heavy metals by various adsorbents were summarized and discussed in depth. First, the sources of heavy metal pollution and the adsorption technology to remove heavy metals were reviewed. The adsorption capacity of Cu, Cd, Zn, Ni, Cr, As, Fe, Hg, Co, Sr, and Cs by biosorbents (e.g. algae, agriculture waste biochar/activated carbon, and bacteria) and by abiotic adsorbents (e.g. metal–organic frameworks (MOFs), microtubes, polymers, clays, minerals, and coal) were systematically summarized. Second, the origins, basic assumptions, importance, physical meanings, and applications of the adsorption kinetics and isotherm models were discussed in depth. Third, the methods for selecting adsorption models in different conditions were explained, and the statistical parameters which can be applied to evaluate the performance of the models were illustrated. Finally, two Excel sheets are provided for solving the adsorption models, which are available in . This review article will deepen the understanding of the interaction between heavy metals and adsorbents and facilitate the development of adsorptive technology for heavy metal removal from water and wastewater. [ABSTRACT FROM AUTHOR]

Since the synthetic dye Congo red and nitrate are notorious contributors to water pollution due to their persistent and potentially toxic nature, it is necessary to develop new efficient methods to remove them from water bodies. Native lignocellulosic materials as biosorbents are mostly inferior, i.e., the adsorption capacities of native materials are lower. Therefore, attempts have been made to improve the adsorption capacities of such materials by physical and/or chemical methods, including the production of biochar. In this study, adsorptive removal was investigated using a novel biosorbent (mPWS) obtained by modifying poplar (waste) sawdust through quaternisation. The characterisation of mPWS included SEM/EDX, FTIR, and MIP analysis. The adsorption of CR and nitrate onto mPWS was studied in a batch system, as a function of contact time (1–240 min), biosorbent concentration (1–8 g·dm−3), and initial adsorbate concentration (25–200 mg·dm−3). In all experiments, a high removal of both adsorbates, from 60 to over 90%, was achieved. Langmuir and Freundlich adsorption isotherm models were used in order to describe equilibrium adsorption data, while pseudo-first-order and pseudo-second-order kinetic models, and the intraparticle diffusion model, were used to describe possible adsorption mechanisms. The Langmuir model fit the adsorption data of CR well, while the nitrate adsorption process was better interpreted with the Freundlich isotherm model. The kinetics data for both CR and nitrate agreed with the pseudo-second-order kinetics model, while analysis using the intraparticle diffusion model indicated two rate-limiting steps during the adsorption process. Based on the results, it can be concluded that the tested novel biosorbent can be effectively used for the removal of CR and nitrate from water (with its adsorption capacities being 70.3 mg·g−1 and 43.6 mg·g−1, respectively). [ABSTRACT FROM AUTHOR]

Commercial industries which employ metallurgical extraction, cement manufacturing and fuel cells expulse heavy volumes of fluoride-containing wastewater into the natural environment posing grave threats to public health. In the current study, a locally available plant known as Jamun (Eugenia Jambolana), was used as an adsorbent for fluoride removal from aqueous solutions. Physico-chemical experiments were conducted to reveal the size and surface distribution of natural fluoride adsorption on the adsorbent surface using SEM, XRD, and FT- IR. Effects of different parameters such as solution pH, adsorbent dosage (m), co-ions contact time (t), fluoride concentration, and flow rates were investigated. Additionally, the adsorption efficiency of competing ions like Cl-, NO 3 - , SO 4 2 - , PO 4 3 - , Ca2+, and Mg2+ and their physiological effects were studied under different solution concentrations ranging from 20 – 200 mg / L at pH 6.90±0.10 for 1 hour. Results showed that the adsorption equilibrium and kinetic data were matched with the isotherm Langmuir model (R2 = 0.98) and Freundlich model (R2 = 0.97). Also, we could conclude that the adsorption process of fluoride using the natural adsorbent resu bivalve shells was an endothermic reaction and resulted in a spontaneous adsorption process. Adsorption kinetic models revealed a swift adsorption rate with minimum and maximum fluoride concentrations as 100 mg / L and 500 mg / L with contact time (t) = 60 minutes at adsorbent dosage (m) = 1 g / L. [ABSTRACT FROM AUTHOR]

The Ni0.5Zn0.5Fe2O4 magnetic nanoparticles (MNPs) were synthesised using Plantago major seed extract through an environment-friendly, economic, and easy procedure. The nanoparticles were characterised by FTIR, XRD, SEM, TEM, EDX, BET surface area analysis, and VSM. The Ni0.5Zn0.5Fe2O4 MNPs were investigated as a nanoadsorbent for removal of reactive blue 21 (RB 21) and the results showed that the nanoparticles were effective for adsorption of RB 21. More than 93% of RB 21 was removed by the nanoadsorbent after a short time of 10 min (60 mg of nanoadsorbent dosage at concentration of 20 ppm for RB 21). The effect of initial concentration of RB 21 and nanoparticle dosage on dye adsorption were investigated. The Langmuir and Freundlich isotherm models used for adsorption equilibrium of RB 21 on Ni0.5Zn0.5Fe2O4 MNPs. The isotherm studies showed that the Langmuir model (KL = 2.76 L/mg, qmax = 18.08 mg/g) provides more compatible than the Freundlich model and thus RB 21 adsorb on the surface of Ni0.5Zn0.5Fe2O4 MNPs by a mono layer adsorption. The adsorption kinetics studies for the adsorption of RB 21 on Ni0.5Zn0.5Fe2O4 MNPs were conducted using the pseudo first-order, the pseudo second-order, and the intraparticle diffusion models and the results indicated that the pseudo second-order model (qe = 15.19 mg/g) provides more compatible than the other models for the adsorption of RB 21 on Ni0.5Zn0.5Fe2O4 MNPs. The maximum adsorption capacity was determined as 16.65 mg/g. [ABSTRACT FROM AUTHOR]

This work aimed to use Algerian Zean oak (AZO) sawdust in its raw state, without undergoing any physico-chemical treatment, to estimate its efficiency for removing methylene blue (MB), a cationic dye widely used in the textile industry. The physico-chemical properties of the biomaterial were characterized by scanning electron microscopy, Fourier-transform infrared, X-ray diffraction, and Brunauer–Emmet–Teller for measuring its specific surface area. The chemical characteristics of the AZO sawdust surface were further examined by the zero-charge point (pHPZC), iodine, MB numbers, and Boehm titration tests. The batch study was performed by varying parameters such as contact time, particle size, pH, temperature, adsorbent dose, and initial dye concentration. By optimizing these parameters, an adsorption capacity of 52.376 mg/g was attained, at pH = 7 and room temperature, using a dose of 1 g/L AZO at C0 = 20 mg/L for an equilibrium time of 45 min. The adsorption capacity of the MB is enhanced by increasing the initial dye concentration and the biosorbent dose. The kinetic data were modeled using the pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The results reveal that the pseudo-second-order model better describes the experimental data. Furthermore, the adsorption isotherms well follow the Sips and Langmuir models. The thermodynamic study revealed that the adsorption process of MB on AZO sawdust is a spontaneous, exothermic, and favorable phenomenon. Therefore, AZO sawdust could be considered an efficient biosorbent and a preferred alternative to activated carbon to remove MB. [ABSTRACT FROM AUTHOR]

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Abstract Calcium hydroxyapatite (Ca-HAp) was synthesized from calcium carbonate (CaCO3) extracted from a paper mill sludge. The extraction of CaCO3 was carried out by chemical precipitation process and synthesized to HAp nanoparticle under appropriate stoichiometric condition through wet chemical precipitation process. The size of the HAp nanoparticle was 42.5 nm under an optimized aging period of 24 h. This work aims in the batch adsorption of arsenic, an anionic metal arsenic in the form of Arsenite: As(III) on the synthesized Ca-HAp in laboratory scale. Batch kinetics studies were conducted for varying operational parameters such as temperature, initial adsorbate concentration, dye solution pH and rotation speed (RPM). In comparison with the two suggested isotherm models, Langmuir isotherm was suited to this adsorption process with a correlation coefficient of 0.92 and isotherm constant as 1.18 (K L ). Chemisorption was found to be the rate-limiting mechanism for the sorption of arsenite onto Ca-HAp and thus followed pseudo-second-order kinetics. A maximum monolayer adsorption of 0.43 mg/g of arsenic was obtained at an equilibrium time of 60 min with 93% to 94.2% removal efficiency.

Charcoal prepared from Kail Sawdust (waste obtained from carpenter shop) has been used as adsorbent for the simultaneous removal of red RB (RRB) and yellow M4G (YMG) dyes from water. The interactive effect of both dyes is found as antagonistic. The experiments are performed on optimized operating parameters, which are based on individual dye adsorption. Experimental results are tested for Langmuir, Freundlich, and Temkin adsorption isotherm models but the equilibrium data fitt well with Langmuir isotherm model. Adsorption kinetics fit well pseudo second order kinetic model. FTIR, SEM, and BET analysis are used to characterize the adsorbent. Adsorption process is spontaneous, feasible, and exothermic as proved by thermodynamic parameters. From the outcomes, it is presumed that removal of dyes by KSC (bioadsorbent) can be proved as successful and green innovation for the treatment of textile industrial wastewater. [ABSTRACT FROM AUTHOR]

Because radioactive 177Lu has a wide range of possible applications in radiopharmaceuticals, its removal from medical wastewater is particularly important. Montmorillonite clay was employed as an adsorbent in this study. Radioactive solutions were prepared with dilutions of the solution containing 177Lu at various concentrations, in which it was present as Lu3+. ULEGe detector in gamma spectrometer was used to measure 177Lu gamma rays emitted from the radioactive aqueous solutions. The results obtained showed that it is possible to remove 177Lu with a high yield of approximately 90% and it is effective in a period of 90 min under acidic conditions. From the findings, it can be argued that Montmorillonite clay, as an abundant and sustainable adsorbent, may also be suitable for the disposal of different radioactive medical wastes such as 131I and 99mTc, and also the technique based on gamma ray spectroscopy can be used for fast and practical measurements of radioactive material amounts. • 177Lu could be removed from aqueous systems in a relatively short time, with an efficiency of about 90%, by Montmorillonite. • The adsorption mechanism is predominantly ion exchange and ion coupling, and the interactions between Lu3+ ions. • The adsorption of Lu3+ is in agreement with the pseudo-second-order kinetic model and the Freundlich isotherm equation. [ABSTRACT FROM AUTHOR]

Calcium hydroxyapatite (Ca-HAp) was synthesized from calcium carbonate (CaCO3) extracted from a paper mill sludge. The extraction of CaCO3 was carried out by chemical precipitation process and synthesized to HAp nanoparticle under appropriate stoichiometric condition through wet chemical precipitation process. The size of the HAp nanoparticle was 42.5 nm under an optimized aging period of 24 h. This work aims in the batch adsorption of arsenic, an anionic metal arsenic in the form of Arsenite: As(III) on the synthesized Ca-HAp in laboratory scale. Batch kinetics studies were conducted for varying operational parameters such as temperature, initial adsorbate concentration, dye solution pH and rotation speed (RPM). In comparison with the two suggested isotherm models, Langmuir isotherm was suited to this adsorption process with a correlation coefficient of 0.92 and isotherm constant as 1.18 (KL). Chemisorption was found to be the rate-limiting mechanism for the sorption of arsenite onto Ca-HAp and thus followed pseudo-second-order kinetics. A maximum monolayer adsorption of 0.43 mg/g of arsenic was obtained at an equilibrium time of 60 min with 93% to 94.2% removal efficiency. [ABSTRACT FROM AUTHOR]

In the present study, the natural biosorption capacity of Acacia nilotica sawdust (wood biomass) was studied for the removal of copper (Cu) and zinc (Zn) heavy metal ions. The process was optimized for several important factors such as pH, contact time, biomass amount, and metal ion concentration. The maximum biosorption of Zn onto Acacia nilotica sawdust was 66.092% at pH 7.0, contact time 20 min, biomass concentration 0.4 g, and initial Zn concentration 8.4 mg/L. The maximum Cu biosorption to Acacia nilotica sawdust was 66.097% at pH 4, contact time 45 min, biomass 0.8 g, initial metal ion concentration 27 mg/L. The experimental data were analyzed by two different adsorption isotherms i.e. Langmuir and Freundlich models. Based on the regression coefficient the Freundlich isotherm model showed the best fit for Zn whereas Cu metal ion adsorption gave a favorable fit for Langmuir isotherm. Both metal ions followed pseudo-second-order kinetics in the adsorption process using sawdust of Acacia nilotica. [ABSTRACT FROM AUTHOR]

Release of dye-containing wastewater into ecosystems has posed serious risks to the environment and aquatic life because of toxicity and adverse effects on the water bodies. Malachite green is a basic dye that has very wide industrial applications, especially in the aquaculture industry. This study was carried out in order to remove the malachite green from aqueous solutions by thiolated graphene oxide in batch system. In the present work, the effects of experimental parameters such as adsorbent dosage, solution pH, initial dye concentration, thermodynamics and adsorption mechanism were comprehensively studied in batch system. In order to characterize the physical and chemical properties of the synthetized nanostructure and also to confirm the functionalization steps, different analyses including SEM and FT-IR were used. Batch studies showed that the experimental data fitted logically to applied isotherms, namely Langmuir (R2=0.991) and Freundlich (R2=0.983) models. Kinetic calculations confirmed that malachite green adsorption was described more accurately by pseudo-second order model compared to the pseudo-first order model. The study showed that thiolated graphene oxide is an effective adsorbent for malachite green removal from aqueous solution. Under controlled reaction conditions, Gibbs free energy (ΔG) varied from -1.46 to -3.25 kJ/mol, besides, the resulting ΔH° and ΔS° values were obtained 0.059 kJ/mol and 15.67 kJ/mol.K, respectively. So, it can be considered that the adsorption of malachite green onto the thiolated graphene oxide nanostructure is a physico-chemical and spontaneous process.

The study aims to determine Cu(II) adsorption from wastewater in the laboratory condition using modified sewage sludge ash as adsorbent which was obtained from a thermal drying and incineration facility. This procedure was completed with an inexpensive pollutant material which has high metal-binding capacity and is available in abundant amounts. During experiments, the effects of particle size, pH, stirring speed, initial ion concentration, adsorbent dosage and temperature were investigated. Adsorption equilibrium was obtained in 10 min. Maximum Cu(II) removal was calculated as 83.63% with 20 mg L−1 initial Cu(II) ion concentration and 5 g L−1 adsorbent dosage. Kolmogorov–Smirnov normality test was performed to test the conformity of the data obtained as a result of the study to variance analysis, and it was determined that the data were distributed normally (p > 0.05). Levene test was performed for homogeneity test, and it was determined that the data were distributed homogeneously (p > 0.05). Langmuir was determined as the most suitable isotherm model for Cu(II) adsorption. Adsorption kinetics abided by the pseudo-second-order model. Based on kinetic studies, the adsorption process was endothermic with maximum adsorption capacity calculated as 7.53 mg g−1. The results of thermodynamic research showed the adsorption reaction was spontaneous (ΔG° < 0), endothermic (ΔH° > 0) and reversible (ΔS° > 0 and close to zero). [ABSTRACT FROM AUTHOR]

In this study, isotherm models were used to describe the interactions between adsorbent (zeolite 4A) and adsorbate (Cu2+, Ni2+, and Zn2+) at different concentrations in both simple and multicomponent systems. To assess the effect of the mass transfer parameters on the adsorption kinetics, the pore diffusivity model was also applied. The adsorption selectivity of the adsorbent material was evaluated as a function of the initial concentration in binary and ternary systems, as well as the competitive adsorption between the metallic ions in synthetic zeolite 4A. The synthesized zeolite was characterized by different techniques such as powder X-ray diffraction, infrared vibrational spectroscopy, and scanning electron microscopy. Langmuir, Freundlich and Sips isotherm models fitted the experimental data of Cu2+ and Ni2+, whereas Langmuir and Freundlich models fitted the experimental data of Zn2+. The adsorption kinetics was fast for Cu2+ and Zn2+, and slow for Ni2+, which is consistent with the pore diffusivity results, in which higher diffusion values for Cu2+ and Zn2+ were obtained, and indicates a higher selectivity of the synthesized zeolite 4A for Cu2+ and Zn2+. [ABSTRACT FROM AUTHOR]

Nowadays, it is admitted to using of suitable carrier results in improving drug delivery such as nanotubes. So, multi‐walled carbon nanotube (MWCNTs) has been proposed as a carrier (adsorbent) to improve the neurological Oxazepam (OZ) drug delivery. Freundlich, Temkin, and Langmuir isotherm models have been used in order to do assay adsorption of the OZ on the MWCNT. The maximum value of the isotherm constant (b = 0.14 L/mg) at 303 K temperature indicates stronger (better) adsorption of the OZ on the MWCNT surface in low concentrations (20 mg/L) and acidic pH; in fact, increasing of pH led to decreasing adsorption (60 → 35.91 mg/g) and dehydrogenation of the OZ drug. Reaching to the equilibrium state after 90 min and negative value of the ∆H (−41.57 kJ/mol) shows that the OZ adsorption has fast kinetic and exothermic processes. These issues imply depending of the OZ adsorption on the OZ concentration and the weight of adsorbent in the adsorption process. [ABSTRACT FROM AUTHOR]

A series of malonic acid treated camelthorn (MATC) sorbents were produced via the reaction of camelthorn biomass with malonic acid, and factors affecting the extent of modification were investigated, including malonic acid concentration, dehydration time and temperature. The optimum sorbent, by carboxylic acid content, was subsequently characterised for surface charge behaviour (pHPZC), surface chemical functionalities (FTIR), morphological structure (SEM), and available surface area. The sorbent was subsequently utilised for adsorption of Cd(II) ions from aqueous media, and parameters influencing adsorption at 30 °C, such as sorbent dose, initial solution pH, exposure time, metal concentration, were investigated. Isothermal analyses were performed using eight models, including two and three parameter equations, with appropriateness of fit assessed via non-linear regression analysis. The adsorption data indicated that the Langmuir model gives the most appropriate fit to experimental curves, with the models ordered as Langmuir > Hill > Toth > Sips > Jossens > Khan > Redlich-Peterson > Freundlich. The highest uptake (qmax) of 582.6 mg g−1 was determined at pH 6. The Freundlich constants, KF and n, at 30 °C were found to be 24.94 mg g−1 and 2.33, respectively. The value of n (2.33), being in the range 0–10, indicates that adsorption of Cd(II) ions onto malonic acid treated camelthorn biomass is favourable. Evaluation of a series of kinetic models, allowed elucidation of the adsorption mechanism, as a pseudo-second order model gave the most appropriate fit, indicating that chemisorption processes are involved. Cd(II) ions adsorption onto MATC is enhanced by a higher level of active surface sites but was show to be independent of surface area. The work presented here indicates that this sorbent offers effective adsorption potential for Cd(II) ions from water, with potential in wastewater processing. [ABSTRACT FROM AUTHOR]

Microcrystalline cellulose (MCC) has been utilized as an adsorbent material for the removal of Pb(II) ions from aqueous solution after treatment with 1,2,3,4-butanetetracarboxylic acid (BTCA) at elevated temperature to obtain MMCC. The resulting adsorbent was characterized for point of zero point charge (pHZPC), estimation of carboxyl content, Fourier transform infrared spectroscopy (FT-IR), scan electron microscopy (SEM), and textural properties, including surface area, and subsequently utilized for the removal of Pb(II) ions from aqueous solution. The adsorption process was probed by investigating the effect of adsorbent dose, pH of solution, temperature, agitation time, and Pb(II) ion concentration. The results showed successful functionalization of MCC using BTCA, significantly improved the binding properties of the adsorbent towards Pb(II) ions. Isothermal adsorption data was analyzed using Langmuir, Freundlich and Temkin models, evaluated via nonlinear regression analysis. The maximum adsorption capacity was found to be 1155 mg/g (at pH 5 and 30 °C) from Langmuir theory, and appears independent of surface area. The Freundlich model was found to provide the best fit and the constant n was determined to be 2.69, indicating that adsorption of Pb(II) ions onto MMCC is favorable. Kinetic modelling showed good agreement for the pseudo-second order kinetic model, supporting the theory that chemisorption is involved in the adsorption process, which is promoted by a high density of active sites. Thermodynamic analysis showed that the adsorption of Pb(II) ions onto MMCC was endothermic and nonspontaneous; hence, MMCC offers an effective method of Pb(II) ion removal from aqueous solutions, with potential for water remediation processes. [ABSTRACT FROM AUTHOR]

This work was an attempt to prepare a new eco-friendly adsorbent for the recovery of uranium from the Egyptian radioactive deposits. So, cellulose/p-toluidine was prepared as a potential sorbent for uranium (VI) in highly alkaline solutions, from a condensation reaction of p-toluene with dialdehyde cellulose which resulting from periodate selective oxidative of cellulose. We have studied the kinetics, isotherm models, and thermodynamic of uranium adsorption from aqueous solutions by dissolved the deposits uranium in sodium carbonate aqueous solution. The effect of adsorption time, and temperature, pH, as well as uranium concentration on adsorption capacity were investigated. The adsorption capacity of uranium by cellulose p-toluidine has been found to attain 80 mg/g. Scanning electron microscopy, X-ray diffractometer, and Fourier transform infrared spectroscopy were used to study the morphological characterization, and chemical structure of the prepared adsorbent. In addition, the computational calculation of dialdehyde cellulose, p-toluidine, and cellulose/p-toluidine by DFT/B3LYP/6-31G (d) basis sets was studied. The adsorption of uranium using cellulose p-toluidine followed fitted with pseudo-second-order reaction as well as Langmuir isotherm. Also, the prepared adsorbent displayed excellent antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, E. coli and Candida albicans. [ABSTRACT FROM AUTHOR]

The 21st century has witnessed a tremendous increase in textile wastewater effluent and consequently the pollution of water bodies that affects aquatic flora and fauna. This necessitates for a sustainable clean-up material to remove this contaminant. To realize this purpose, investigation of batch adsorption was conducted using Congo red (CR) as the adsorbate and Jatropha curcas seed (chaff) as the adsorbent material. Adsorption kinetics and isotherms analysis were conducted and results obtained confirmed the adsorption process as highly dependent on effects such as contact time, adsorbent dosage, initial dye concentration and the particle sizes of the adsorbate. The sorption equilibrium for CR dye unto Jatropha curcas seed (chaff) was achieved within 180 min and the adsorption efficiency was recorded at 82.05%. Furthermore, the result shows that the amount of CR adsorbed per unit mass of adsorbent increases from 11.47 to 82.05 mg/L as the initial concentration increase from 20-100 mg/L. Thus, the driving force for the CR adsorption gradient was due to the high adsorption capacity of Jatropha curcas. The process of the experimental sorption kinetics followed a pseudo-second-order kinetic model while the Freundlich and Langmuir isotherm model was both applicable for obtaining the equilibrium behavior of the adsorption. The chaff from Jatropha curcas seed possess carbonyl, acid amino and phenolic hydroxyl functional groups that act as chemical bonding agents for chemisorptions process at the surfaces of the adsorbent. This confirms the performance of Jatropha curcas (chaff) as an environmentally friendly and low-cost agromaterial for dye removal in aqueous solutions. [ABSTRACT FROM AUTHOR]

This study aims mainly to use the soybean leaves (SL), agricultural wastes, as a new low-cost adsorbent for Reactive Red 195 (RR195) dye removal from aqueous solutions. The dried SL was chemically modified by acetic acid (AA) to improve its adsorption capacity. The adsorbent (AA-SL) was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The effects of operational parameters such as contact time, pH, adsorbent dose, initial dye concentration, and temperature were investigated in batch experiments. Adsorption kinetics, isotherm, and thermodynamic of AA-SL have been studied. The AA-SL structure was found to be irregular and porous. FTIR revealed that the surface of AA-SL was abundant in various functional groups. The solution pH strongly affects RR195 removal efficiency. The highest removal efficiency equal to 97.8% was achieved using a solution pH equal to 1 at 50°C. The removal efficiency was increased by increasing the solution temperature. The adsorption of RR195 was decreased from 15.32 to 2.29 mg g-1 with increasing the adsorbent dose from 0.25 to 3 g L-1, respectively. Increasing initial dye concentration from 5 to 40 mg L-1 resulted in increasing the adsorption capacity from 2.2 to 9.2 mg g-1, respectively and decreasing the removal rate from 88% to 45.8%, respectively. The adsorption of RR195 onto AA-SL obeyed Langmuir (R² = 0.998) and D–R (R² = 0.967) models with a theoretical maximum adsorption capacity of about 12 mg g-1 at 50°C. The experimental data fitted very well with the pseudo-second-order kinetic (R² = 0.991). Thermodynamic studies indicated that the reaction is irreversible and endothermic adsorption. AA-SL, as a low-cost material has the potential to be used as a new alternative adsorbent for the removal of RR195 dye from aqueous solutions. [ABSTRACT FROM AUTHOR]

Good sorption properties and simple synthesis route make schwertmannite an increasingly popular adsorbent. In this work, the adsorption properties of synthetic schwertmannite towards Cr(VI) were investigated. This study aimed to compare the properties and sorption performance of adsorbents obtained by two methods: Fe3+ hydrolysis (SCHA) and Fe2+ oxidation (SCHB). To characterise the sorbents before and after Cr(VI) adsorption, specific surface area, particle size distribution, density, and zeta potential were determined. Additionally, optical micrographs, SEM, and FTIR analyses were performed. Adsorption experiments were performed in varying process conditions: pH, adsorbent dosage, contact time, and initial concentration. Adsorption isotherms were fitted by Freundlich, Langmuir, and Temkin models. Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and liquid film diffusion models were used to fit the kinetics data. Linear regression was used to estimate the parameters of isotherm and kinetic models. The maximum adsorption capacity resulting from the fitted Langmuir isotherm is 42.97 and 17.54 mg·g−1 for SCHA and SCHB. Results show that the adsorption kinetics follows the pseudo-second-order kinetic model. Both iron-based adsorbents are suitable for removing Cr(VI) ions from aqueous solutions. Characterisation of the adsorbents after adsorption suggests that Cr(VI) adsorption can be mainly attributed to ion exchange with SO42− groups.

The contamination of surface and groundwater with phosphate originating from industrial and household wastewater remains a serious environmental issue in low-income countries. Herein, phosphate removal from aqueous solutions was studied using low-cost volcanic rocks such as pumice (VPum) and scoria (VSco), obtained from the Ethiopian Great Rift Valley. Batch adsorption experiments were conducted using phosphate solutions with concentrations of 0.5 to 25 mg·L−1 to examine the adsorption kinetic as well as equilibrium conditions. The experimental adsorption data were tested by employing various equilibrium adsorption models, and the Freundlich and Dubinin-Radushkevich (D-R) isotherms best depicted the observations. The maximum phosphate adsorption capacities of VPum and VSco were calculated and found to be 294 mg·kg−1 and 169 mg·kg−1, respectively. A pseudo-second-order kinetic model best described the experimental data with a coefficient of correlation of R2 > 0.99 for both VPum and VSco; however, VPum showed a slightly better selectivity for phosphate removal than VSco. The presence of competitive anions markedly reduced the removal efficiency of phosphate from the aqueous solution. The adsorptive removal of phosphate was affected by competitive anions in the order: HCO3− >F− > SO4−2 > NO3− > Cl− for VPum and HCO3− > F− > Cl− > SO4−2 > NO3− for VSco. The results indicate that the readily available volcanic rocks have a good adsorptive capacity for phosphate and shall be considered in future studies as test materials for phosphate removal from water in technical-scale experiments.

Abstract Anionic surfactants are widely used as an effective chemical for enhanced oil recovery because of their unique characteristics of reducing interfacial tension (IFT) between the trapped crude oil and water, and alteration of wettability of reservoir rock from oil-wet to water-wet. However, the loss of surfactant by adsorption onto the solid rock surface is a major concern that reduces the efficiency of the surfactant flooding process and must be considered while designing the process. Present study highlights the equilibrium adsorption and kinetics of an anionic surfactant synthesized from soap-nut fruit on sandstone, carbonate and bentonite clay as representative of reservoir rocks. The mineralogy and morphology of the rocks were investigated by FE-SEM, XRD and BET surface area analysis. UV–Visible spectroscopy was used to measure the amount of surfactant adsorbed on solid rock/clay surface in batch experiments. The experimental equilibrium adsorption data were analyzed by using Langmuir, Freundlich, Temkin and Redlich-Peterson isotherm models and adsorption parameters were calculated. Adsorption kinetics of the surfactant system were studied and pseudo second order kinetic model was best fitted for the surfactant/rock/clay systems. Presence of salt was found to increase surfactant adsorption on rock/clay marginally. However, presence of alkali and nanoparticles was found to reduce the loss of surfactant by adsorption and shows synergistic effects on IFT reduction, which is beneficial for application of the surfactant in oil recovery. The findings of the study are quite helpful in proper designing of the surfactant flooding for enhanced oil recovery. Graphical abstract Image 1 Highlights • Mineralogical and morphological characterization of sandstone, carbonate, bentonite. • Effect of mineralogy, salt, pH, alkali, nanoparticles on adsorption of surfactant. • Modelling of Experimental data with various Isotherm Models. • Adsorption kinetic study along with mathematical fitting with kinetic equations. • Surfactant adsorption ability follow the trend bentonite > carbonate > sandstone. [ABSTRACT FROM AUTHOR]

In the current study, the removal of Cd(II) ions from aqueous solution using chitosan-iso-vanillin biosorbent has been investigated. The impacts of pH, exposure time, adsorbent dosage and initial amount of studied ion on the removal process have been carried out using batch experiments. The quantity of residual ions has been estimated via atomic absorption spectrometry. The synthesized biosorbent is characterized using infrared spectroscopy, DTA, and SEM techniques. The maximum sorption of Cd(II) ions is achieved at pH 5. Langmuir isotherm works as the best explanation model for the experimental data with the highest adsorption capacity equal to 38.31mgg-1. Kinetic studies reveal that chemisorption is the rate-determining step, and the results point out fast rates of metal ion uptake with 77% highest percentage achieved after 60 min. Thermodynamics suggest spontaneous and endothermic process with raise in randomness at the solid/solution interface throughout the bio-adsorption of Cd(II) ions onto modified chitosan. [ABSTRACT FROM AUTHOR]

Ziziphus spina-christi L. (ZscL) is a plant residue that has been used as adsorbent for the removal of Hg(II) ions from an aqueous solution. The ability of ZscL to adsorb Hg(II) ions was investigated by using the batch adsorption procedure. It was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to support the adsorption of Hg(II) ions. The effects of various parameters on the adsorption process, such as contact time, adsorbent concentration, solution pH and initial concentrations of metal ions were studied to optimize the conditions for maximum adsorption. Experimental equilibrium data were fitted to the Freundlich, Langmuir, Dubinin-Radushkevich, Halsey and Temkin (two parameter models), Redlich-Peterson, Sips, Khan, Hill, Radke-Prausnitz, Langmuir-Freundlich and Toth (three parameter models), Fritz-Schlunder and Baudu (four parameter models) and Fritz-Schlunder (five parameter model) at 30°C by using nonlinear regression analysis. The examination of error analysis methods showed that the Halsey model provides the best fit for experimental data compared with the other isotherms. Various kinetic models have been applied to the experimental data to predict the adsorption kinetics. It was found that pseudo-second-order rate was better obeyed than pseudo-first-order reaction, supporting that the chemisorption process was involved. The obtained results show that ZscL can be used as an effective and natural low-cost adsorbent for the removal of Hg(II) ions from aqueous solutions.

Retama raetam (RR), a desert plant, was chemically modified by the reaction with succinic acid at high temperature to form succinic acid treated R. raetam (STRR). Three levels containing different carboxyl contents of STRR were prepared. Native RR and STRR were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and estimation of carboxyl content to support the adsorption of Pb(II) ions. The STRR adsorbent was utilized as adsorbent material for the removal of Pb(II) ions from aqueous solutions. The effect of various parameters like pH, adsorbent concentration, contact time, temperature and initial concentration was investigated using batch process to optimize conditions for maximum adsorption. The adsorbent data were analyzed using two-, three-, four- and five-parameter models at 30°C by non-linear regression analysis. The examination of error analysis methods showed that the Langmuir-Freundlich model provides the best fit for experimental data compared with other isotherms. The maximum biosorption capacity of Pb(II) ions was up to 270.27 mg/g at 30°C. The thermodynamics constants of the adsorption process, viz., ΔHo, ΔGo and ΔSo, were evaluated. The results showed that the adsorption of Pb(II) ions onto STRR was endothermic and spontaneous. The adsorption data followed second-order kinetics, supporting that chemisorption process was involved.

Magnetite/carbon nanocomposites were tested as adsorbents for removal of metal ions from aqueous solutions. The effect of adsorption parameters such as solutions pH (ranging between 2 and 9), the nature and the quantity of the sorbent (10, 20, 40, and 60 mg), initial concentration of metal ions (10, 30, 50, 100, and 150 mg/L), and temperature (25, 45, and 65°C) was evaluated. The removal efficiency of metal ions depends on solution pH and increases with increasing carbon content, the dose of magnetite/carbon nanocomposites, and the temperature and decrease with initial concentration of the metal ions. The adsorption kinetics was described by pseudo-second-order model, and the equilibrium experimental data were well fitted to the Sips isotherm, yielding a maximum adsorption capacity of 41.11, 76.67, and 48.45 mg/g for copper, cadmium, and zinc, respectively. The thermodynamic parameter Gibbs free energy was determined to be negative, which indicated that the adsorption process is spontaneous. The optimum conditions (1 g/L adsorbent, 25°C, and pH 6) were selected for removal of metal ions from real wastewaters, with good results indicating that investigated nanocomposites could be used for the application in real systems. [ABSTRACT FROM AUTHOR]

The present study was conducted to evaluate the feasibility of adsorption of aluminium oxide nanoparticles for arsenite, which is toxic and prevalent arsenic species under anoxic condition in groundwater. Therefore, aluminium oxide nanoparticles were synthesised and characterised by Dynamic Light Scattering, Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray spectrometry, Fourier Transform Infrared Spectroscopy, X-ray Diffraction and Transmission Electron Microscopy. Batch adsorption studies were performed as a function of contact time, initial arsenite concentration, adsorbent dose, temperature, pH and influence of other competing anions. The arsenite adsorption was well explained by Freundlich isotherm model. Langmuir adsorption capacity was found to be 500 μg/g at 298 K. The kinetic data followed pseudo-second-order model with film diffusion step controlling the mechanism. The values of thermodynamic parameter, ΔH° was − 26.09 kJ/mol, while the values of ΔG° were − 3.75, − 2.99, − 2.20 and − 1.49 kJ/mol at 298, 308, 318 and 328 K respectively, suggesting exothermic and spontaneous nature of the process. The change in entropy (ΔS° = − 0.075 kJ/mol) indicated the decrease in entropy of the system, as adsorbate concentration increased on aluminium oxide nanoparticles surface and reduced the mobility of arsenite. The activation energy (Ea) content of the process was found as 5.64 kJ/mol, which confirmed the nature of adsorption as the physical adsorption. The results indicated the potential utility of Al 2 O 3 nanoparticles for arsenite removal from any natural water resources. [ABSTRACT FROM AUTHOR]

This study was carried out to investigate adsorption kinetic and adsorption thermodynamics of Au(III) ions onto γ-aminopropyltriethoxysilane grafted coconut pith. The results from equilibrium adsorption were fitted in various adsorption isotherm models such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich and the best fit for the experimental data was Langmuir isotherm. The maximum adsorption capacity for virgin coconut pith (VCP) and the grafted coconut pith (GCP) were 256.41 and 285.59 mg/g, respectively. The kinetic data was verified using pseudo-first-order, pseudo-second-order, elovich equation and intraparticle diffusion model. The correlation results suggested that the pseudo-second-order model fits the experimental data well. A thermodynamic study revealed the endothermic nature of reaction due to positive enthalpy (ΔH°) values and negative values of Gibbs free energy (ΔG°) describes the spontaneity of adsorption process. The regenerability of VCP and GCP adsorbents were investigated with NaOH (1.0 M). [ABSTRACT FROM AUTHOR]

The main objective of this research is to study the adsorption behaviour of malachite green and methylene blue dyes onto the surfactant modified natural clays. The results of SEM, XRD, IR, and thermal analysis confirms the intercalation of organic moiety in to the clay. The adsorption results show that pseudo-first order kinetics best fitted for both the dyes adsorbed on organo-clay. The data also reveals that both dyes are in a good agreement with Langmuir isotherm in both types of modified clays. The value of separation factor, RL, from Langmuir equation and Freundlich constant, n, give an indication of favourable adsorption. The maximum adsorption capacity qm based on Langmuir model was found to be 294-303 mg/g at 25 °C, is in good agreement with the experimental values. [ABSTRACT FROM AUTHOR]

Competitive adsorption of cadmium (Cd2+) and lead (Pb2+) was investigated using activated carbon (AC) produced from municipal organic solid waste. The effect of pH, contact time, metal concentration and adsorbent dosage on the performance of the adsorption process was investigated using synthetic binary metal solutions. The results showed that optimum removal efficiency of both metals from binary metal solutions could be achieved at a pH value of 5 and a contact time of 120 min. Moreover, the results showed that, for both metal ions, the increase in the initial metal concentration led to an increase in adsorption capacities and decrease in removal efficiencies. At a Cd2+ concentration of 100 mg/L, the removal efficiency of Cd2+ was found to decrease from 21.42% to 6.79% (68.3% decrease), when Pb2+ concentration was increased from 25 to 300 mg/L, respectively. On the other hand, the increase in the AC dosage was found to result in decreasing the adsorption capacity from 19.65 to 10 mg/g and from 61 to 12 mg/g when AC dosages were increased from 25 to 400 mg, for Cd2+ and Pb2+, respectively. The experimental results of both metals were found to fit non-linear Freundlich adsorption isotherm and pseudo-second-order kinetic models. [ABSTRACT FROM AUTHOR]

Heavy metal contamination of natural rivers and wastewaters is a problem for both the environment and human society. The accumulation and adsorption of heavy metals could happen with several organic and inorganic matters, but the most used adsorbents are (biological and chemical) organic compounds. This review article presents the basics of heavy metal adsorption on several organic surfaces. There are many organic matters, which seem to be useful as agents for heavy metal adsorption. All of the cited authors and articles present the adsorption kinetics by the most used isotherm models (such as Langmuir and Freundlich isotherms). By comparing several research results presented by a pre-selected assortment of papers, we would like to give an overview of the microbiological, organic chemical, and other surface adsorption possibilities. We draw conclusions for two new adsorption fields (adsorption with biosorbent and artificial materials). We present an optional possibility to study adsorption kinetics, efficiency and regeneration methods to successfully conclude the heavy metal treatment process, and we make some recommendations about the efficient water usage calculations using the water allowance coefficient (WAC) indicator.

The recovery of ammonium (NH 4 +) from aqueous solutions by zeolite is attractive. In this study, the physical-chemistry of NH 4 + adsorption process from aqueous solution by two zeolitic mixtures, either treated or not treated with NaCl, was assessed. Results suggested that the zeolitic mixture richer in mordenite and with high specific surface area adsorbed more NH 4 + than the one richer in clinoptilolite and heulandite showing a lower specific surface area. NaCl treatment increased the amount of NH 4 + adsorbed by the zeolitic mixtures. The higher amount of NH 4 + adsorbed by the zeolitic mixtures treated with NaCl was explained by the low/high density water model accounting for cation exchange among the two kosmotropic systems: Na-enriched zeolitic mixtures and NH 4 +-enriched aqueous solution. The adsorption kinetics were best approximated by the bimodal pseudo-first-order model. The two sorption kinetic constants, k 1 and k 2 were related to the adsorption (mediated by k 1) and the ion exchange (mediated by k 2) processes. The fitting of NH 4 + data to Langmuir-Sips model suggested that the NaCl treatment increased the number of active sites only of the zeolitic mixture with the large amount of mordenite. Thus, it is conceivable that modulation of NaCl treatment of zeolitic mixtures can be applied to obtain new materials for water remediation from NH 4 + contamination. [Display omitted] • Two zeolitic mixtures with different mineralogy were used for NH 4 + recovery. • Zeolitic mixtures showed good performance for NH 4 + removal from solution. • The mineralogical composition of zeolitic mixtures affected NH 4 + adsorption. • The bimodal-pseudo-first order model well described NH 4 + adsorption kinetics. • The Langmuir-Sips model provides the best fit for the NH 4 + adsorption isotherm. [ABSTRACT FROM AUTHOR]

Camelorum tree (CT), a desert plant, has been utilized as an adsorbent material for the removal of Hg(II) ions from aqueous solution after treatment with malic acid at elevated temperature. Treated Camelorum tree (TCT) were found to exhibit excellent adsorption capacity over a wide range of Hg(II) concentration. Native CT and TCT were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy to support the adsorption of Hg(II) ions. Effect of various parameters such as pH, adsorbent concentration, contact time, initial concentration, and temperature was investigated using batch process to optimize conditions for maximum adsorption. The adsorption data were analyzed using two, three, four, and five parameter models at 30°C using nonlinear regression analysis. The maximum adsorption capacity (qmax) of Hg(II) onto TCT was 357.14 mg/g at an initial pH of 5 and a temperature of 30°C. Thermodynamic parameters such as standard enthalpy change (ΔH°), free energy change (ΔG°), and entropy change (ΔS°) were also evaluated and the results indicated that adsorption of Hg(II) is spontaneous and exothermic. Various kinetics models including the pseudo-first-order, pseudo-second-order, intraparticle diffusion, Bangham, and Elovich models have been applied to the experimental data to predict the adsorption kinetics. Kinetic study was carried out by varying initial concentration of Hg(II) at constant temperature and it was found that pseudo-second-order rate equation was better obeyed than pseudo-first-order equation supporting that chemisorption process was involved. The examination ofR2values and error analysis methods showed that the Langmuir–Freundlich, Dubinin–Radushkevich, Fritz–Schlunder (IV), and Fritz–Schlunder (V) models provide the best fit to experimental data than other isotherms and follow the following order: Langmuir–Freundlich (three parameter isotherm) > Dubinin–Radushkevich (two parameter isotherm) > Fritz–Schlunder (four parameter isotherm) > Fritz–Schlunder (five parameter isotherm). The obtained results show that TCT can be used as an effective and a low-cost adsorbent for the removal of Hg(II) from aqueous solutions. [ABSTRACT FROM PUBLISHER]

In this work, date palm trunk (DPT) fibre was investigated for the eviction of copper ions (Cu2+) from aqueous solution. The surface chemistry of the DPT adsorbent was characterized through Fourier transform infrared spectroscopy and X-ray powder diffraction. The specific surface area and the average crystalline size of the DPT fibre adsorbent were measured as 2.104 m2 g−1and 320 nm, respectively. Equilibrium adsorption was achieved at 150 min and results reflected significantly higher adsorption of Cu2+onto DPT fibre at pH 5 (6 mg g−1, 12%) than at pH 2–4 (1–4 mg g−1, 1–7%). The adsorption data revealed maximum removal (25.4 mg g−1) at the adsorbent dose of 5 g L−1. Significantly, removal (34 mg g−1) was observed with particles 75 μm and Cu2+removal was significantly higher (6–23 mg g−1) with increasing Cu2+concentration from 20 to 100 mg L−1. Adsorption kinetics data were modelled using pseudo-first-order and pseudo-second-order kinetics. The behaviour and the nature of Cu2+adsorption were analysed by employing the Langmuir, Freundlich, Harkins–Jura (H–J) and Dubinin–Radushkevich (D–R) isotherm models. The results reflect that the adsorption isotherm model fitted the experimental data in the following order: Langmuir (R2, 0.9933) > H–J (R2, 0.9869) > Freundlich (R2, 0.9768) > D–R (R2, 0.8827) with monolayer Cu2+adsorption. The experimental data were best explained by a Langmuir isotherm model and pseudo-second-order kinetics withR2= 0.9933 and 0.9905, respectively, andqmaxof 25.25 mg g−1with chemisorption (E = 14.59 kJ mol−1). The homogeneity of the adsorbent surface functional groups makes DPT suited for sequestering toxic Cu2+from wastewater. Suitable physical, chemical and physicochemical surface modifications can further improve the adsorption capabilities of DPT adsorbents. [ABSTRACT FROM AUTHOR]

Graphene-construct nanocomposite materials have gathered considerable scientific importance for their unique ability to detect and remove various bioactive molecules/pollutants. Herein, we report on rGO-CuO nanocomposite as an adsorbent material for removing thiouracil biomolecules, viz-6A2TU and 6A5N2TU, respectively. The synthesized rGO-CuO nanocomposite is characterized using UV-vis, FTIR, XRD, SEM-EDX, Raman, and TEM analysis. The surface morphology of rGO-CuO shows well exfoliation with rGO wrapped on the surface of Cu and CuO nanoparticles. While the FTIR, X-ray diffraction, and UV-vis spectroscopic analysis show successful adsorption of 6A2TU and 6A5N2TU on the outer surface of rGO-CuO. rGO-CuO selectively adsorb the uracil derivatives with good efficiency compared to individual components. The binding kinetics of 6A2TU & 6A5N2TU on rGO-CuO are studied using UV-vis spectroscopy. The order of the reaction; pseudo 2nd order kinetics suites well with correlation coefficient (R2– 0.9999), representing proper surface-oriented chemisorption via coordination mechanism. The rGO-CuO shows excellent adsorption behavior with a maximum removal efficiency of 78.36% and 84.56% for 6A2TU and 6A5N2TU, respectively, and following the Temkin adsorption isotherm model. These characteristic features of the material provide the huge removal capacity of the thiouracil derivatives and reusability up to 92%. This nanocomposite material can remove antibiotics/bioactive molecules (organic pollutants) in the aquatic environment. [Display omitted] [ABSTRACT FROM AUTHOR]

The focus of this study is the characterization of unconventional sand-based substrates used in our previous project EmiSûre, (Interreg Greater Region (German federal states Rhineland-Palatinate and Saarland, the Grand Duchy of Luxembourg, regions Wallonia and Lorraine from Belgium and France, respectively), 2017–2021). The project aimed to develop and test alternative, nature-based technologies for the elimination of micropollutants (MPs) from municipal wastewater. For the characterization, two approaches were chosen. In the first approach, adsorption kinetics with a single compound allowed a perception of the adsorption capacity of the studied substrates compared to conventional substrates (granular activated carbons). This knowledge was completed by the second approach: an implementation of the studied substrates in packed-bed columns, which treated a mixture of 27 MPs in tap water for 10 months. Additionally, all three substrates (bentonite sand, sand with 15% activated biochar and sand with 15% zeolite) were characterized for physical and chemical properties, and the microbial potential of the activated and non-activated biochar was examined. From the studies, it is clear that the sand with an admixture of activated biochar is the most efficient sorbent in terms of single compound adsorption in batch (dye) and adsorption of 27 MPs on packed-bed columns. In contrast to the two other substrates, it shows long-term stable removal efficiencies. In the packed-bed columns, 18 out of 27 compounds were removed on average with high efficiency (80–99%), which is impressive, if we consider the variety of the compounds examined (pharmaceuticals, herbicides, pesticides, etc.) and their removal in conventional treatments. Additionally, adsorption models were created for the experimental data of all compounds adsorbed on the substrate with an admixture of activated biochar resulting in the best fit with the combined Langmuir-Freundlich model. These satisfying results suggest the application of the sand-based substrate with an admixture of activated biochar for further research and possibly upscale installations with the aim to offer and prove a reasonable and efficient alternative for MPs elimination from municipal wastewater. [Display omitted] • Characterization of unconventional sand-based substrates is achieved. • Various types of experiments are performed to optimally observe the adsorption. • Activated biochar is the best substrate for removal of micropollutants from water. • Isotherm models for description of the adsorption are applied. • Based on the results, parameters for industrial scale-up are gained. [ABSTRACT FROM AUTHOR]