Dubinin-Radushkevich Models Research Articles

Banana stem and leaf biochar as an effective adsorbent for cadmium and lead in aqueous solution

Lead (Pb) and cadmium (Cd) are toxic heavy metals commonly found in aqueous environments. Biochar as a green adsorbent generated from biomass feedstock may be used for effective removal of these heavy metals. This study investigated the adsorption kinetics and isotherms of Pb2+ and Cd2+ in aqueous solutions at different pH by biochar prepared from banana stem and leaf (BSL-BC) at 400 °C. Characterizations using scanning electron microscope, X-ray diffraction, and Fourier-transform infrared spectroscopy showed that the synthesized BSL-BC had rough surface, porous structure, and oxygen-containing functional groups. The adsorption of Pb2+ and Cd2+ onto BSL-BC reached equilibrium in 8 h and 200 min, respectively, with faster adsorption attained at higher pH and the optimum pH occurred at 5 (Pb2+) and 8 (Cd2+). All adsorption kinetic data followed the pseudo-second-order rate model. The adsorption isotherm data of Pb2+ and Cd2+ could be well-described by the Langmuir and Freundlich models, respectively, whereas neither the Temkin or Dubinin–Radushkevich models provided satisfactory fitting results. The maximum adsorption capacities for Pb2+ and Cd2+ were 302.20 and 32.03 mg/g, respectively. The calculated mechanism contributions showed that complexation with oxygen-containing functional groups, ion exchange, mineral precipitation, and Pb2+/Cd2+-π coordination accounted for 0.1%, 8.4%, 88.8%, and 2.6% to Pb2+ adsorption, and 0.4%, 6.3%, 83.0%, and 10.4% to Cd2+ adsorption, respectively. Therefore, mineral precipitation was likely the major mechanism responsible for adsorption of both Pb2+ and Cd2+ by BSL-BC. The results suggest that the synthesized BSL-BC has great potential for adsorption of Pb2+ and Cd2+ from aqueous solutions.

Fabrication of iron nanoparticles from tea waste as an efficient adsorbent towards the removal of profenofos pesticide from aquatic environment

ABSTRACT Pesticide contamination has led to serious environmental issues that pose a significant threat to living organisms throughout the world. Therefore, the significant removal of pesticides from aquatic environments has attracted the attention of environmental scientists and academicians in recent decades. Hence, in the present investigation, the iron nanoparticles (INPs) from tea waste were fabricated as an efficient adsorbent towards the removal of profenofos (PF) from aqueous solution. The as-synthesised INPs were systematically characterised by various analytical techniques such as Ultra Violet-visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD) and dynamic light scattering (DLS). Various influencing factors such as contact time, adsorbent dosage, solution pH and initial concentration of pesticide were systematically optimised for the maximum adsorption efficiency of PF by the prepared INPs. Based on the obtained results, the INPs showed greater adsorption efficiency towards the removal of PF. The kinetic data were analysed using various adsorption kinetic models such as pseudo-first-order, pseudo-second-order and intra-particle diffusion. Further, the interaction between prepared INPs and PF was evaluated using various adsorption isotherm models such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) models. The monolayer Langmuir adsorption capacity of 43.67 mg g−1 was obtained with a minimum contact time of 15 min. According to the kinetic and isotherm data, the pseudo-second-order kinetic and Langmuir isotherm models were found to be well fitted for PF adsorption using the prepared INPs. The obtained findings of this study clearly demonstrated that the fabricated INPs are an efficient material towards the removal of pesticide molecules from aquatic environments.

Thermodynamic Characteristics of the Hydrogen Sulfide Sorption Process by Ferromanganese Materials.

The work analyzes hydrogen sulfide sorption from model gas mixtures containing H2S from 1.25 × 10–3 to 1.28 × 10–4 mol/L under static conditions at temperatures 253 and 298 K on the raw manganese ore of the Ulu-Telyak deposit (Bashkortostan, Russia), manganese(IV) oxide, and manganese(IV) and iron(III) oxide mixtures. The thermodynamic models for calculating the equilibrium constants and Gibbs energy changes were analyzed. The sorption isotherms were described by the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models. The value of enthalpy of hydrogen sorption on the ore was −68.98 ± 3.45 kJ/mol and those on model mixtures Mn4 + Fe2O3 and MnO4 were ±12.20 kJ/mol and −103.826 ± 5.19 kJ/mol, respectively, and the entropies of the hydrogen sulfide sorption process on three manganese materials at 253 K were calculated. The limiting capacity values of manganese materials at 253 and 298 K were obtained. The morphological analysis of the ore samples, Mn4 + Fe2O3, and MnO4, before and after hydrogen sulfide sorption, was carried out at 253 K. The obtained thermodynamic parameters determine the advantage of using the raw manganese ore over pure oxides, which characterizes its effective practical application in the desulfurization process.

RESEARCH INTO SORPTION CONDITIONS OF 2-(4-SULFOPHENYLAZO)-1-AMINO-8-HYDROXYNAPHTHALENE-3,6-DISULFONIC ACID BY COMMERCIAL ANION EXCHANGER AB-17

To obtain a new modified sorbent, the conditions for maximum sorption of the chelate reagent 2-(4-sulfophenylazo)-1-amino-8-hydroxynaphthalene-3,6-disulfonic acid (SPAAHS) by a strongly basic AB-17 anion exchanger were selected. The conditions for modifying the anion exchanger were studied by spectrophotometric analysis on a Specord 210 Plus spectrophotometer from Analytik Jena. The influence of such factors as the acidity of the solution, the contact time of the sorbent with the sorbate, and the concentration of SPAAHS on the sorption process was analyzed. According to the saturation curves, the static capacity of the anion exchange resin for the sorbed reagent was established. Also, the description of the adsorption isotherm of SPAAHS with the AB-17 anion exchanger was performed using the models of Langmuir, Freundlich, Temkin and Redlich-Peterson. To calculate the value of the ABerage free energy of adsorption, the adsorption isotherm of SPAAHS with the AB-17 anion exchanger was processed using the Dubinin-Radushkevich model. On the basis of the results obtained, conclusions were made about the nature of the bond between the anion exchanger and the sorbed reagent. To prove the proposed mechanism of sorption of SPAAHS by the AB-17 anion exchanger by the density of functional theory (DFT) method, using the Orca 4.2.0 program, an estimated quantum-chemical calculation of the dissociation energies of various acidic functional groups according to which an exchange reaction is possible on the anion exchanger AB-17.

Adsorption of Pb(II) from Water onto ZnO, TiO2, and Al2O3: Process Study, Adsorption Behaviour, and Thermodynamics

This study is aimed at comparing the use of zinc oxide (ZnO), titanium dioxide (TiO2), and aluminium oxide (Al2O3) for removing lead ions from water through adsorption. The point of zero charge was obtained for ZnO, TiO2, and Al2O3 and was found to be 7.3, 7.1, and 9.0, respectively. The effect of pH, adsorbent dose, contact time, initial concentrations, and temperature was investigated in batch experiments. The optimal conditions obtained were 7, 2 g/L, 120 mins, 100 ppm, and 41°C, respectively, where the optimal removal efficiencies were 98.43%, 96.45%, and 85.50% for ZnO, TiO2, and Al2O3, respectively. In addition, analyses of adsorption kinetics, mechanisms, isotherms, and thermodynamics were performed. The adsorption kinetics of Pb(II) were compared to popular models, and it was found that the pseudo-second-order (PSO) model best fitted the Pb(II) uptake for all adsorbents at correlation coefficient ([Formula: see text]). The adsorption isotherms of Pb(II) were also compared to popular models, and it was found that the Pb(II) uptake by TiO2 and ZnO was well-described by the Langmuir model ([Formula: see text]) with maximum adsorption capacities of 55.04 and 58.88 mg/g, respectively. On the other hand, the behaviour of Al2O3 is described more accurately by the Dubinin-Radushkevich (D-R) model ([Formula: see text]), and the maximum adsorption capacity was 53.64 mg/g. The isotherm analysis proved that the limiting step of the adsorption process is the film diffusion mechanism. In addition, studying the heat of adsorption of Pb(II) implied that the adsorption is endothermic due to the positive values of enthalpy ([Formula: see text]) for all adsorbents. The absorbents were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) to study the morphology of surfaces and the chemical characterization of the adsorbents to ensure that adsorption is achieved. ZnO showed better performance for the uptake of lead followed by TiO2 then Al2O3.

Lignocellulose Nanofiber Media for the Enhanced Removal of Copper From Aqueous Solutions

Nowadays, the entry of heavy metals entry into aqueous environments has jeopardized the health of human societies. The experiment was conducted in discontinuous conditions, and the study focused on examining the effect of five parameters including initial concentration, temperature, contact time, pH, and adsorbent dose on the adsorption of Cu heavy metals. In addition, the two-parameter models of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich were studied and compared to evaluate isothermal absorption. The highest correlation coefficients were obtained for Freundlich (0.969) and Dubinin-Radushkevich (0.9603) models. Finally, thermodynamic parameters such as enthalpy and entropy changes and Gibbs-free energy were calculated as well. The pH parameters, adsorption dose, contact time, temperature, and initial Cu concentrations in the discontinuous system had a statistically significant effect on the adsorption process. The results showed that the maximum efficiency of Cu adsorption by Lignocellulose nanofiber (LCNF) occurred at the pH of 6, contact time of 60 minutes, the ambient temperature of 25°C, and adsorption dose of 0.2 g. In the case of adsorption kinetics, the pseudo-second order model and intra-particle diffusion had more fitness with the experimental data indicating a chemical equilibrium between the adsorbate and the absorbent. Thermodynamic studies demonstrated that the process (negative ΔG) is spontaneous (negative ΔG), endothermic (negative ΔH), and non-random (positive ΔS). Thus, LCNF can be used as an effective adsorbent in the removal of metals by having an extremely high surface area.

Congo Red removal using Fesdis soil: kinetic, equilibrium and thermodynamic studies

ABSTRACT The removal of Congo Red dye from an aqueous solution using the soil from Fesdis (FS) area (Batna, Algeria) was studied. The soil was characterised using ATR, BET, SEM and XRF techniques. The characterisation results showed the existence of clay, carbonate and quartz in this soil. The adsorption results demonstrated that the CR dye adsorption onto the Fesdis soil is dependent on the different investigated parameters as the biosorbent concentrations, the pH, the initial dyes concentrations, temperature and the ionic strength effect. The results show that the dye removal was increased with the raise of the reaction temperature, adsorbent dose, and dye initial concentration. The efficiency dye removal increased to 96% and achieved the value 99% when CaCl2 was added. The optimum conditions determined at room temperature were [dye] = 50 mg/L, [adsorbent] = 12 g/L, neutral pH with a maximum adsorption capacity (qmax) was around 6.693 mg.g−1. Equilibrium isotherms were analysed by the Langmuir model, Freundlich model, and the Dubinin–Radushkevich models. The pseudo-first-order, the pseudo-second-order and intraparticle diffusion models were used for kinetic analysis. The thermodynamic study reveals that CR dye adsorption onto the Fesdis soil is a spontaneous, physical and endothermic process.

Isotherm study of banana stem waste adsorbents to reduce the concentration of textile dying waste

The purpose of this study was to make carbon from banana stem waste and determine the isotherm adsorption characteristics of carbon from banana stem waste to methyl orange compounds. The process for making carbon from banana stem waste was done through the stages of preparation and carbonization at a temperature of 250°C for 1.5 h. Before being used as carbon, banana stem waste was cleaned, washed, dried, and mashed using a mill. The carbon then went through a washing process to remove impurities and tested for its absorbance ability into a solution containing a methyl orange compound under constant conditions of pH, temperature, and pressure. The experimental results showed that the appropriate sequence of adsorption models is the Langmuir, Temkin, Freundlich, and Dubinin-Radushkevich models. Adsorption occurs on the surface of a single layer (monolayer) and the interaction between the adsorbent and the adsorbate occurs physically. The value of maximum adsorption capacity (Qmax) is 37.5940 mg/g. The presence of banana stem carbon is expected to reduce the negative impacts, one of which is the disposal of industrial wastewater from textile factories.

Analysis of NMR Adsorption Isotherms of Zeolite ZSM-5: Adsorption Profiles Derived from the Pressure and Temperature Dependences of 129Xe NMR Chemical Shift and Signal Intensity.

129Xe NMR spectroscopy of nanomaterials, such as zeolites, can provide valuable information on the nanostructure and physicochemical properties of adsorption. In the present study the pressure and temperature dependences of the 129Xe NMR chemical shift and the signal intensity were investigated in detail with a zeolite ZSM-5. The pressure dependence of the signal intensity at constant temperature was analyzed based on the Langmuir and Dubinin-Radushkevich (D-R) models, from which the thermodynamic parameters and energetic profiles of adsorption were obtained together with information concerning the nanospace size. From this isotherm analysis the coverage, θ, was calculated and used for isotherm analysis of the chemical shift. The θ dependence of the chemical shift was successfully fitted by an exponential function, and the results were discussed in relation to the chemical shift at zero coverage, that at full coverage and the curvature of the exponential function. The chemical shift data reported with the zeolites NaA and KA, where separated signals were observed for the different number of encapsulated Xe atoms in the α cage, were analyzed and discussed collectively.

Removal of basic fuchsine dye using (TiO2/MWCNTs) nanomaterial

In this study, antase-type titanium dioxide (TiO2) was produced and mixed with multi-walled carbon nanotubes using an ultrasonic. To aid the mixing process, ethanol was employed as a dispersing solvent. The nano titanium dioxide was loaded onto multi-walled carbon nanotubes for prepared (TiO2/MWCNTs). Thestructuralcharacteristicsofananocomposite(TiO2/MWCNTs)wereinvestigated(FTIR, XRD, AFM, SEM, EDX). The (TiO2 Anatase) was discovered to have a 15.65 nm average particle size. The (TiO2/MWCNTs) nanocomposite had a composition of (0.75TiO2/0.016MWCNTs) (w/w), which resulted in an increase in the developed interfacial area ratio from (159.07%) for (TiO2) to (210.3%) for (TiO2/MWCNTs). Batch adsorption tests were used to assess the efficacy of utilizing (TiO2/MWCNTs) to remove basic fuchsin dye from aqueous solution. With increasing contact time, the amount of dye removed by the adsorbent increased, and optimal adsorption was reached in 40 min. The adsorption process was affected by the pH of the aqueous solution, with the best dye removal happening at pH = 6. The adsorbent's ability to absorb dye decreased as the original dye concentration and adsorbent dose increased. Adsorption equilibrium data was fitted with Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin equations to describe the isotherms. The Freundlich and Temkin models performed better than the Langmuir and Dubinin-Radushkevich models in describing the experimental results. The pseudo-first and second order models were used to fit the kinetic data. The Pseudo-second-order model suited the data better than the Pseudo-first-order model. The maximum rate of removal is approximately 98 percent. Thermodynamic studies revealed that the adsorption was exothermic. Out of five distinct temperatures, the free energy of adsorption (Δ G°) was found to be −35.35 kJ.mol-1 at 25 °C. The fact that (Δ G°) was negative indicated the technique's viability and the spontaneous nature of adsorption.

Valorization of olive endocarp from olive oil and table olive processing as a low-cost bioadsorbent for the removal of furfural from aqueous solutions

Furfural presence in fermentation culture media provokes an inhibition effect in yeast growth. In fact, is a key toxin in lignocellulosic hydrolyzates. This research work attempts to analyze the use of olive endocarp (OE) as adsorbent to remove furfural from aqueous solutions. The adsorption experimental sets studied the effect of particle size, agitation speed, adsorbent load, temperature, and initial furfural concentration. As results, higher adsorption percentages were observed when fragmented OE was smaller than 1.2 mm, agitation speed in the range 80–250 rpm, and the adsorbent load was 90 g OE/300 cm3 of furfural solution (1 g dm−3). The equilibrium adsorption capacities, qe, values were varied from 0.270 to 4.750 mg g−1 for initial furfural concentrations of 0.78 g dm−3 to 5.89 g dm−3. The adsorption data fit to pseudo-second order kinetic model showed good fit values (R2 ≥ 0.997, SE ≤ 5%). Dubinin-Radushkevich (DR) model was considered as the best fit (R2 = 0.999, SE = 2.95%) for the different studied isotherms. An adsorption free energy value of 896 J mol−1 indicated a physical adsorption mechanism. Remarkable increases in furfural adsorption percentages have been achieved submitting natural olive endocarps to acid treatments.

High Selectivity and Reusability of Biomass-Based Adsorbent for Chloramphenicol Removal.

Recently, biomass-based materials have attracted increasing attention because of their advantages of low cost, environment-friendly and nonpollution. Herein, the feasibility of using corn stalk biomass fiber (CF) and Fe3O4 embedded chitosan (CS) as a novel biomass-based adsorbent (CFS) to remove chloramphenicol (CAPC) from aqueous solution. Structure of CFS was characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and zeta potential techniques. The effects of solution pH, adsorption time and ion strength on the adsorption capacity were examined. Adsorption isotherms obtained from batch experiments were better fitted by Langmuir model compared with Freundlich model, Dubinin–Radushkevich model and Temkin model. Adsorption kinetic data matched well to the pseudo-second order kinetic model. CAPC adsorption was endothermic, spontaneous, and entropy-increasing nature on CFS. In addition, the CFS could be separated by an external magnetic field, recycled, and reused without any significant loss in the adsorption capacity of CAPC. Based on these excellent performances, there is potential that CFS can be considered as a proficient and economically suitable material for the CAPC removal from the water environment.

Treatment of real industrial wastewater with high sulfate concentrations using modified Jordanian kaolin sorbent: batch and modelling studies

In the present study, BaCl2 modified Jordanian kaolin sorbent (obtained from Mahis, Jordan) was used to remove sulfate-contaminated industrial wastewater. The kaolin sample was pretreated to enhance its adsorption capacity and then characterized using X-Ray fluorescence (XRF) and Fourier Transform Infrared Spectroscopy (FTIR). Equilibrium isotherms for the adsorption parameters were carried out experimentally, and the adsorption data correlated very well with Freundlich and Temkin and Dubinin-Radushkevich models. Furthermore, the adsorption kinetics followed the pseudo-first-order and intraparticle diffusion models perfectly. The estimated value of the maximum adsorption capacity qm = 85.08 mg/g indicates that kaolin has a very high capacity to adsorb sulfate ions at studied parameters. The estimated value of the mean free energy (4.87 kJ/mol) is very low, confirming physical type adsorption. The study results established that modified Jordanian kaolin could serve as a safe and effective natural adsorbent for sulfate-contaminated industrial wastewater.

Aptamer-functionalized and silver-coated polydopamine-copper hybrid nanoflower adsorbent embedded with magnetic nanoparticles for efficient mercury removal

Mercury (Hg) emissions are increasing annually owing to rapid global industrialization. Hg poisoning can severely affect the human body owing to its persistence and bioaccumulation. In this study, hybrid nanoflowers (NFs) were synthesized by promoting the formation of primary copper-phosphate crystals coordinated with polydopamine (PDA) and Fe3O4 magnetic nanoparticles (MNPs), followed by coating with silver nanoparticles on the surface of the NFs (Ag-MNP-PDA-Cu NFs). The results suggest that the hierarchical structure of the NFs enabled a large surface area with nanosized pores, which were exploited for Hg adsorption. The adsorbed Hg ions could be further eliminated from the solution based on the magnetic characteristics of the NFs. Additionally, hybrid NFs functionalized with Hg2+-binding aptamers (Apt-Ag-MNP-PDA-Cu NFs) were prepared based on the silver–sulfur interactions between the Ag-MNP-PDA-Cu NFs and thiol-modified aptamers. The performance of both adsorbents demonstrated that the immobilization of Hg2+-binding aptamers significantly improved the elimination of Hg from solution. The Hg2+ adsorption isotherm of the Apt-Ag-MNP-PDA-Cu NFs followed the Dubinin–Radushkevich model, with a maximum adsorption capacity of 1073.19 mg/g. The Apt-Ag-MNP-PDA-Cu NFs adsorbed greater amounts of Hg2+ than the non-functionalized NFs at the same concentrations, which confirmed that the functionalization of Hg2+-binding aptamers on the NFs improved the Hg2+ removal performance. The results suggest that Apt-Ag-MNP-PDA-Cu NFs could serve as an efficient Hg-removing adsorbent, possibly by providing binding sites for the formation of T-Hg2+-T complexes.

Azo Dye Adsorption onto Cobalt Oxide: Isotherm, Kinetics, and Error Analysis Studies

The current study focused on utilizing cobalt oxide to eliminate hazardous Eriochrome Black T (EBT) dye. The impact of pH (2, 4, 7, 8, and 10) and temperature (45, 50, and 55 °C) was examined for EBT removal. The results show that the maximum sorption occurred at pH = 2 and that the removal percentage increased with increasing temperature. Five non-linear regression methods were used to predict the best isotherm and kinetic models. A coefficient of non-determination, K2, was very helpful for selecting the RMSD function as a preferable error function among the five methods. Isothermal models to illustrate equilibrium sorption information, the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models were used. The results showed that the Langmuir model (R2 = 0.99) was the most favorable, indicating monolayer sorption of EBT occurred. The kinetics models were analyzed using pseudo-first-order and pseudo-second-order whereas the sorption information was well described by the pseudo-second-order model (R2 = 0.99). The results of the thermodynamic study appeared that the adsorption of EBT was endothermic, feasible, spontaneous, and physical adsorption.

Methylene Blue and Iron (II) Adsorption onto Raphia Hookeri Seed: A Comparative Equilibrium Isotherm Study

In this study, activated carbon prepared from Raphia hookeri seed was employed as an adsorbent to take up methylene blue (an organic ion-in-solution) and iron (II), a metal ion-in-solution. The biosorbent was prepared using chemical activation using sodium hydroxide (NaOH) as an impregnating agent. Calibration was performed with a focus on the change in the adsorbate concentration. The equilibrium isotherms study was conducted by considering a range of sorbate concentrations, to determine the optimal conditions for the adsorption systems. The same sorbate volume (10 ml), and the same dosage (0.3g) of biosorbent were used for both adsorption processes. Linear analysis was used to compare the best-fitting isotherms. Langmuir, Freundlich, and Dubinin-Radushkevich models were tested. The highest coefficient of determination values (R2) for both iron (II) and Methylene blue was obtained from the Langmuir isotherm as 0.9266 and 0.9572, respectively, compared to values from the other isotherms tested – indicative of Langmuir isotherm’s superior fit. Estimated values of ‘separation factor’, KR, for Methylene blue (0.29457), however, was lower than that of iron (II) (0.42141) - an indication that the sorbent treats methylene blue better than iron (II), though both processes are feasible.

Adsorption of azo dye Congo red on the Sn-doped TiO2 surface

In this paper, the effect of SnO2 impurity on the surface charge and adsorption properties of TiO2 samples is investigated. The experimental value of the zero charge point for TiO2 with 3%, 6% and 12% of SnO2 equals 3.53, 3.97 and 3.2, respectively. The adsorption activity of the samples was studied on model solutions of the anionic dye – Congo red. The maximum adsorption capacity (qexp) equals 24.6 mg/g for 3Sn/TiO2, 25.0 mg/g for 6Sn/TiO2 and 39.1 mg/g for 12Sn/TiO2. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to describe the adsorption mechanism of Congo red dye on the surface of Sn/TiO2 samples. Based on the results of the studies of Congo red adsorption by the surface of titanium dioxide doped with Sn, all samples agree best with the Langmuir model. The correlation coefficients for the Langmuir isotherms are in the range of 0.9927 - 0.9996, while the values ​​of R2 for the Freundlich and Dubinin-Radushkevich isotherms are in the range of 0.721 - 0.8329 and 0.8283 - 0.9433, respectively. Experimental data obtained from adsorption isotherms show that the TiO2 sample containing 12% SnO2 is the most active. The best result of Congo red removal occurred at a concentration of Co = 5 mg/l (% of removed dye ≈ 83% for 12Sn/TiO2; 81% for 6Sn/TiO2 and 71% for 3Sn/TiO2). Therefore, the studied samples of TiO2 doped with SnO2 can be used as effective adsorbents of Congo red from aqueous solutions.

Biosorption of Cd(II) by Nordic microalgae: Tolerance, kinetics and equilibrium studies

The amount of heavy metals released into the environment has significantly increased. Industrial wastewaters, e.g. from mining or battery manufacturing, are often polluted with heavy metals such as Cd, Cr or Pb. These metals threat the environment and can cause health problems even at low concentrations. Therefore, their proper removal from industrial wastewater before its disposal is of paramount importance (Javanbakht et al. [1]). Here the ability of fourteen wild Nordic microalgal strains to remove cadmium (Cd(II)) from aqueous solutions has been studied. Three of the chosen strains, namely Chlorella vulgaris (13-1), Coelastrella sp. (3-4) and Scenedesmus obliquus (13-8), demonstrated high tolerance towards Cd(II) concentrations up to 2.5 mg L−1 and their sorption kinetics and equilibrium were studied. Metal sorption by Chlorella vulgaris (13-1) and Coelastrella sp. (3-4) was described best by pseudo-second order kinetics, whereas the removal kinetics of Scenedesmus obliquus (13-8) was best fitted by the intraparticle diffusion model. Starting from an initial concentration of 2.5 mg L−1Chlorella vulgaris (13-1) and Coelastrella sp. (3-4) removed 72% and 82%, respectively, of the Cd(II) within only 24 h. Modeling their Cd(II) sorption equilibria revealed that the SIPS- and Dubinin-Radushkevich models were best suited for living microalgae, and the maximum adsorption capacity (qmax) was calculated. While Chlorella vulgaris (13-1) and Coelastrella sp. (3-4) were able to remove about 49 mg g−1 and 65 mg g−1 Cd(II), respectively, Scenedesmus obliquus (13-8) only removed around 25 mg g−1. Fourier-Transform Infrared Spectroscopy (FTIR) analyses of the biomass revealed the carboxylic moieties of the cell wall to be the key player in Cd(II) removal. This study demonstrates the high potential of Nordic microalgae to remove heavy metals at conditions relevant for an industrial tertiary wastewater treatment unit and will support the development of new, biobased, innovative technologies for the bioremediation of heavy metal polluted streams.

Competitive kinetics of adsorption onto activated carbon for emerging contaminants with contrasting physicochemical properties.

Activated carbon (AC) can be used for the removal of emerging contaminants (e.g., drugs) in water and wastewater treatment plants. In the present study, we investigated the performance of two ACs (from coconut shell and Pinnus sp.) in the adsorption of caffeine, carbamazepine, and ricobendazole considering the compounds separately and in combination in batch-scale experiments. The concentrations of the drugs were determined by a validated method using solid-phase extraction with on-line ultra-high performance liquid chromatography-tandem mass spectrometry. The most mesoporous AC provided higher drug removal. The kinetic data were described by the pseudo-second-order, Elovich, and Weber-Morris models, while the adsorption isotherms showed a better fit to the Freundlich model, indicative of multilayer adsorption. The Dubinin-Radushkevich model was used as a first approach to estimate the mean adsorption energy (E) and the results indicate that chemisorption governed the adsorption process, with E higher than 8 kJ mol-1. In the multicomponent assays, the adsorption of caffeine showed the greatest hindrance caused by the presence of other drugs. Multicomponent assays are fundamental to evaluate the potential adsorption capacity in real water treatment plants. Our study suggests that drugs with different structures and physicochemical properties may interact differently with ACs, especially in multicomponent solutions, with important implications for the design (e.g., volumes and areas of treatment plants) and operation (e.g., water residence time) of the treatment plants.

Sanky (Corryocactus brevistylus) Peel as Low-Cost Adsorbent for Removal of Phosphate from Aqueous Solutions

This study aimed to evaluate the adsorption capacity of an adsorbent obtained using sanky peel for the removal of phosphate from aqueous solutions. The study was conducted in two stages: (1) adsorbent preparation considering yield, phosphate removal, adsorption capacity, and textural characteristics; (2) an assessment of the effectiveness of using sanky peel as an adsorbent for removing phosphates from aqueous solutions. Batch adsorption was studied in aqueous solutions containing phosphate and calcium ions with the selected adsorbent. Adsorption kinetics and equilibrium isotherms were studied using mathematical models. The adsorption kinetics followed the pseudo-second-order, Elovich, and Weber–Morris models, thus demonstrating that adsorption rates were not controlled by multiple processes. Adsorption equilibrium data fitted best with the Dubinin–Radushkevich model. Finally, a Fourier transform infrared spectroscopy analysis revealed the presence of brushite spectra bands after adsorption. The results of this study can help better understand the use of sanky peel as an adsorbent and good alternative for aqueous phosphate adsorption.