Langmuir-Freundlich Isotherm Model Research Articles

Adsorption of arsenic and fluoride: Modeling of single and competitive adsorption systems

The elevated co-occurrence of arsenic and fluoride in surface and groundwater poses risks to human health in many parts of the world. Using single and competitive batch equilibrium adsorption studies, this research focuses on As(V) and F adsorption by activated carbon and its modeling. BET, XRD, FESEM, EDS, and FTIR analysis were used to discern the structural characteristics of activated carbon. The influence of dosage, pH, and contact time were also investigated in single and simultaneous adsorption systems. The maximum adsorption capacity of activated carbon for arsenic and fluoride were found to be 3.58 mg/g and 2.32 mg/g, respectively. Kinetics studies indicated that pseudo-second-order kinetic model fit better than pseudo-first-order, Elovich, and intraparticle diffusion kinetic models. The non-linear regression analysis of Langmuir, Freundlich, Toth, Redlich Petersons, and Modified Langmuir Freundlich models was used to determine single-component asorption model parameters. Additionally, the simultaneous adsorption was rigorously modeled and compared using the Extended Langmuir (EL), Extended Langmuir Freundlich (ELF), Modified Competitive Langmuir (MCL), and Jeppu Amrutha Manipal Multicomponent (JAMM) isotherm models, and competitive mechanisms were interpreted for the simultaneous adsorption system. Further, the model performances were evaluated by statistical error analysis using the normalized average percentage error (NAPE), root mean square errors (RMSE), and the correlation coefficient (R2). According to the modeling results, single equilibrium data fitted better with the Modified Langmuir Freundlich isotherm model, with a higher R2 of 0.99 and lower NAPE values of 3.8 % and 1.28 % for As(V) and F, than other models. For the binary adsorption, the Extended Langmuir Freundlich isotherm model demonstrated excellent fit with lowest errors. All the competitive isotherm models fit the As(V) and F simultaneous sorption systems reasonably well. Furthermore, the research unveiled a nuanced hierarchy of isotherm fitting, with ELF > EL > MCL > JAMM in varying arsenic at a constant fluoride concentration, and ELF > JAMM > EL > MCL in varying fluoride at a constant arsenic concentrations. In addition, competitive studies divulged crucial insights into selective adsorption, as As(V) exhibits a pronounced adsorption selectivity over F on activated carbon. In essence, As(V) showed a more pronounced antagonistic behavior over F, whereas F exhibited a much lesser competitive behavior in the adsorption of arsenic.

Management of ibuprofen in wastewater using electrospun nanofibers developed from PET and PS wastes

Electrospinning is a promising technique for the beneficial use and recycling of plastic waste polymers using simple methodologies. In this study, plastic bottles and Styrofoam wastes have been used to develop polyethylene terephthalate (PET) and polystyrene (PS) nanofibers using electrospinning technique separately without any further purification. The effect of the concentration onto the nanofiber's morphology was studied. The fabricated nanofibers were characterized using Field Emission Scanning Electron Microscope (FE-SEM), Fourier Transformed Infrared Spectroscopy (ATR-FTIR), N2 adsorption/desorption analysis, and water contact angle (WCA). Furthermore, the prepared nanofibers were applied for the adsorption of ibuprofen (IBU) from wastewater. Some parameters that can influence the adsorption efficiency of nanofibers such as solution pH, wt.% of prepared nanofibers, drug initial concentration, and contact time were studied and optimized. The results show that the equilibrium adsorption capacity was achieved after only 10 min for 12 wt% PET nanofibers which is equivalent to 364.83 mg/g. For 12 wt% PS nanofibers, an equilibrium adsorption capacity of 328.42 mg/g was achieved in 30 min. The experimental data was fitted to five isotherm and four kinetics models to understand the complicated interaction between the nanofibers and the drug. Langmuir-Freundlich isotherm model showed the best fit for experimental data for both PET and PS nanofibers. The adsorption process was characterized by predominantly physical reaction rather than chemical adsorption for both materials. The reusability study revealed that the synthesized nanofibers maintain their ability to adsorb/desorb IBU for up to five cycles. The results obtained demonstrated that fabricated nanofibers from plastic wastes could perform promising adsorbents for the management of IBU in wastewater. However, further research is needed for the scaling-up the fabrication which is required for real-world applications.

Deciphering the mechanistic role of Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) in bio-sorption and phyto-assimilation of Cadmium via Linum usitatissimum L. Seedlings

Three Cd2+ resistant bacterium's minimal inhibition concentrations were assessed and their percentages of Cd2+ accumulation were determined by measurements using an atomic absorption spectrophotometer (AAS). The results revealed that two isolates Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52), identified by 16S rDNA gene sequencing, showed a higher percentage of Cd2+ accumulation i.e., 83.78% and 81.79%, respectively. Moreover, both novel strains can tolerate Cd2+ levels up to 2000 mg/L isolated from district Chakwal. Amplification of the czcD, nifH, and acdS genes was also performed. Batch bio-sorption studies revealed that at pH 7.0, 1 g/L of biomass, and an initial 150 mg/L Cd2+ concentration were the ideal bio-sorption conditions for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52). The experimental data were fit to Langmuir isotherm measurements and Freundlich isotherm model R2 values of 0.999 for each of these strains. Bio sorption processes showed pseudo-second-order kinetics. The intra-diffusion model showed Xi values for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) of 2.26 and 2.23, respectively. Different surface ligands, was investigated through Fourier-transformation infrared spectroscopy (FTIR). The scanning electron microscope SEM images revealed that after Cd2+ adsorption, the cells of both strains became thick, adherent, and deformed. Additionally, both enhanced Linum usitatissimum plant seed germination under varied concentrations of Cd2+ (0 mg/L, 250 mg/L,350 mg/L, and 500 mg/L). Current findings suggest that the selected strains can be used as a sustainable part of bioremediation techniques.

Polymer-grade propylene production through temperature swing adsorption: Molecular simulation and techno-economic analysis

Producing polymer-grade propylene from the propylene-rich mixtures can be quite challenging since the most commonly employed technology, distillation, requires high-energy input and is expensive. Therefore, identifying less-costly, efficient, and environmentally friendly methods, such as the use of the adsorptive process, is highly desirable. In this regard, six pure silica zeolites (AFV, AST, AVL, IFR, LEV, and SWY) as propane selective adsorbents are investigated for the separation of 10 mol.% propane and 90 mol.% propylene mixture. Molecular simulation Monte Carlo (MC) is used to calculate framework structure parameters such as pore volume, surface area, and framework density of pure silica zeolites. Also, adsorption isotherms, propane selectivity, and working capacity are presented using MC calculations. The Langmuir-Freundlich isotherm model is utilized to calculate isotherm parameters. A system model is implemented in Aspen Adsorption software (version 11) and breakthrough curves are achieved. The Temperature Swing Adsorption (TSA) cycle is simulated and key performance parameters such as propylene purity, recovery, and productivity for all six silica zeolites are calculated. Finally, economic analysis of the TSA process is performed using the Aspen Capital Cost Estimator (version 11) and Aspen Process Economic Analyzer (version 11) and compared with the cost of the conventional distillation process. Results showed that the capital cost and operating cost of temperature swing adsorption are 42.3 % and 91.37 % less than those of distillation, respectively.

Facilely tuning the morphologies of tertiary amine-functionalized SBA-15 for optimizing selective SO2 capture

The amine-based materials pose high potential for the adsorption of sulfur dioxide (SO2). This work is aimed at modulating the morphologies of SBA-15 adsorbents by controlling the precursor self-assembly processes, for the sake of optimizing the utilization efficiency of amine species in the polytertiary amine (PTA)-functionalized SBA-15. It results that worm-like SBA-15 (WLS) material shows a better particle aspect ratio and well-defined pore structure, which helps to optimize the adsorption sites invoked by the preferable dispersion and exposure of PTA, thus amplifying the chemisorption of SO2 on the adsorbent. Consequently, the functionalized WLS-PTA adsorbent exhibits remarkable SO2 adsorption performance (15.43 mmol/g), exceptionally high selectivities of SO2/N2 (27522) and SO2/CO2 (652). Surprisingly, the desulfurization capacity can be further enhanced by the positive effect of the water vapor co-fed. It is unveiled that the whole SO2 adsorption process mainly follows the dual site Langmuir-Freundlich isotherm model and Bangham model. This work sheds light on the design of polymer-solid composite adsorbents for selective capture of SO2.

Adsorption Kinetics of Banana Stem Activated Carbon in Reducing Phosphate Levels

Introduction: High levels of phosphate in water are caused by wastewater pollution such as laundry waste water causing eutrophication. Adsorption is a method that can be used to reduce phosphate level. Banana stem that contains high levels of cellulose can be used as the main ingredient for making activated carbon. The aims of this study were to analyze the adsorption capacity and adsorption kinetics of banana stem activateld carbon in relducing phosphatel lelvells. Methods: The design of this research was true experiment with a pretest-posttest controlled group. Adsorption process was carried out with batch method that used three variations of adsorbate concentration and four variations of mixing time. Adsorption took place at pH 3 and 30 rpm of mixing time. Adsorption capacity was analyzed using the Langmuir isotherm and Freundlich isotherm models. Adsorption kinetic was analyzed using pseudo-first-order and pseudo-second-order kinetic models. Results and Discussion: The X-Ray Diffraction (XRD) difactogram and Scanning Electron Microscopy (SEM) results prove that the activateld carbon was successfully made. The iodine number of banana stelm activateld carbon was 698.12 mg/g. The results showed that activated carbon from banana stem successfully reduced phosphate levels in water with adsorption capacity 0.10708 mg/g and following the Langmuir isotherm model. The kinetics adsorption of banana stem activated carbon was validated by the pseludo-selcond-ordelr kinetics model with a kinetics constant of 0.17137 g/mg.min. Conclusion: The Langmuir models indicated that adsorption of phosphate occurred in monolayer. Modifications of activated carbon were needed based on characterization results.

Integrating DFT and machine learning for the design and optimization of sodium alginate-based hydrogel adsorbents: Efficient removal of pollutants from wastewater

This study presents a novel approach to design and optimize a sodium alginate-based hydrogel (SAH) for efficient adsorption of the model water pollutant methylene blue (MB) dye. Utilizing density functional theory (DFT) calculations, sodium alginate-g-poly (acrylamide-co-itaconic acid) was identified with the lowest adsorption energy (Eads) for MB dye among 14 different clusters. SAHs were prepared using selected monomers and sodium alginate combinations through graft co-polymerization, and swelling studies were conducted to optimize grafting conditions. Advanced characterization techniques, including FTIR, XRD, XPS, SEM, EDS, and TGA, were employed, and the process was optimized using statistical and machine learning tools. Screening tests demonstrated that Eads serves as an effective predicting indicator for adsorption capacity (qe) and MB removal efficiency (RRMB,%), with reasonable agreement between Eads and both responses under given conditions. Process modeling and optimization revealed that 5 mg of selected SAH achieves a maximum qe of 3244 mg g−1 at 84.4% RRMB under pH 8.05, 98.8 min, and MB concentration of 383.3 mg L−1, as identified by the desirability function approach. Moreover, SAH effectively eliminated various contaminants from aqueous solutions, including sulfasalazine (SFZ) and dibenzothiophene (DBT). MB adsorption onto selected SAH was exothermic, spontaneous, and followed the pseudo-first-order and Langmuir-Freundlich isotherm models. The remarkable ability of SAH to adsorb MB is attributed to its well-designed structure predicted through DFT and optimal operational conditions achieved by AI-based parametric optimization. By integrating DFT-based computations and machine-learning tools, this study contributes to the efficient design of adsorbent materials and optimization of adsorption processes, also showcasing the potential of SAH as an efficient adsorbent for the abatement of aqueous pollution.

Bio-adsorption of heavy metals from aqueous solution using the ZnO-modified date pits

The bio-adsorption of heavy metals (including Cu2+, Ni2+, and Zn2+) in aqueous solution and also in an industry wastewater using the ZnO-modified date pits (MDP) as the bio-adsorbent are investigated. The fresh and used bio-adsorbents were characterized by FT-IR, SEM, BET, and XRD. The bio-adsorption parameters (including the pH of solution, the particle size of MDP, the shaking speed, the initial concentration of heavy metals, the dosing of MDP, the adsorption time, and the adsorption temperature) were screened and the data were used to optimize the bio-adsorption process and to study the bio-adsorption isotherms, kinetics, and thermodynamics. Two adsorption models (Langmuir isotherm model and Freundlich isotherm model) and three kinetic models (pseudo-first-order model, pseudo-second-order model, and intra-particle diffusion model) were applied to model the experimental data. Results show that the maximum adsorption amount of Cu2+, Ni2+, and Zn2+ on a complete monolayer of MDP are 82.4, 71.9, and 66.3 mg g−1, which are over 4 times of those of date pits-based bio-adsorbents reported in literature. The bio-adsorption of heavy metals on MDP is spontaneous and exothermic, and is regulated by chemical adsorption on the homogeneous and heterogeneous adsorption sites of MDP surface. This work demonstrates an effective modification protocol for improved bio-adsorption performance of the date pits-based bio-adsorbent, which is cheap and originally from a waste.

A sustainable approach for the removal of chlorpyrifos pesticide from aqueous phase using novel nano magnetized biochar

In last two decades, organophosphate pesticides have become a prominent class of toxic water pollutants. Besides, these are not only poisonous for living beings, but their decomposition is also a time-taking process. For the first time, our study reports the application of nano-magnetized and carbonaceous adsorbents, obtained from orange peels (bio-waste), for the removal of chlorpyrifos from water resources. The -nano magnetized orange peels (NMOPs) were synthesized by the co-precipitation method with the use of iron salts. The competency of orange peels for chlorpyrifos adsorption was further enhanced by converting untreated orange peels (UOPs) into carbonaceous orange peels (COPs). The adsorbents were analyzed with FT-IR, SEM, EDX, XRD and VSM. The peak at 540 cm−1 in FTIR spectra corresponded to the Fe-O bond and confirmed the successful doping of iron salts on orange peels. Biosorption studies carried out by varying different parameters showed that these adsorbents are efficient for the uptake of chlorpyrifos. The effects of adsorbent dose, contact time, chlorpyrifos initial concentration, and pH were investigated to assess the adsorbents’ efficiency via biosorption studies. It was noted that the adsorbents showed maximum adsorption with adsorbent dose = 0.4 g, contact time = 50 mins, chlorpyrifos concentration = 150 ppm, pH = 4 and temperature = 30 °C. The adsorption maximum values (qmax) were found to be 68, 108 & 100 mg g−1 for the UOPs, COPs and NMOPs, respectively. Kinetic studies indicate that the removal of chlorpyrifos followed the pseudo-second-order model of adsorption. The adsorption results were effectively described by the Langmuir isotherm and Freundlich isotherm models.

Hydrothermal synthesis of Fe3O4 nanoparticles at different pHs and its effect on discoloration of methylene blue: Evaluation of alternatives by TOPSIS method

In this study, hydrothermal synthesis was employed to produce Fe3O4 nanoparticles for the methylene blue removal from an aqueous medium. The production of magnetite nanoparticles involved the utilization of Fe2+ and Fe3+ salts, and their respective solutions were created at pH levels of 10, 11, and 12, subsequently subjected to autoclave treatment. The evaluation of pH-induced variations in nanoparticle characteristics was conducted through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), vibrating-sample magnetometer (VSM), and Dynamic light scattering (DLS) analyses. pH levels within the synthetic medium yielded diminutive Fe3O4 nanoparticles characterized by augmented saturation magnetization, heightened zeta potential, and a narrower size distribution. Following nanoparticle synthesis under varied pH conditions, their efficacy in methylene blue (MB) adsorption was investigated. Notably, nanoparticles synthesized at pH 11 demonstrated the highest adsorption capacity, registering maximum MB adsorption capacities of 188.68 mg/g, while pH 10 and 12 counterparts exhibited capacities of 169.49 mg/g and 175.44 mg/g, respectively. The adsorption processes conformed to the Langmuir–Freundlich isotherm model, with the pseudo-second-order model offering superior fitting to elucidate MB adsorption kinetics, thereby indicating the involvement of chemical adsorption mechanisms. It was discerned that MB adsorption encompassed both physical and chemical mechanisms, encompassing electrostatic attraction between the negatively charged surface of the nanoparticles and the cationic dye, as well as electron exchange interactions between MB and the functional groups present on the adsorbent surface. Thermodynamically speaking, this adsorption process exhibited an exothermic nature, with a preference for ambient temperatures. Magnetic separation post-adsorption was conveniently executed, and all nanoparticles demonstrated potential for reuse for a minimum of five cycles. Moreover, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method was employed to assess and select the most favorable alternative from the available options. Based on the evaluation of 27 distinct criteria, it was determined that Fe3O4 synthesized in an environment with pH 11 emerged as the optimal choice, aligning with the initial findings from the adsorption assessments.

Preparation of graphene oxide/carboxymethyl chitosan/polyvinyl alcohol composite nanofiber membranes by electrospinning for heavy metal adsorption

AbstractIn this paper, a graphene‐oxide/carboxymethyl‐chitosan/polyvinyl‐alcohol (GO/CMC/PVA) composite nanofiber membrane was prepared by electrospinning and cross‐linking with glutaraldehyde (GA) to improve the water resistance. The composite nanofiber membrane can be used in the field of heavy metal adsorption. The membrane was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. The effects of GO concentration, adsorption time, and initial concentration of heavy‐metal ion (Ni2+, Cu2+, Ag+, and Pb2+) solution on the adsorption performance of the fiber membranes were investigated. The results showed that the addition of GO can reduce the diameter of nanofibers. GO, CMC, and PVA exhibited good compatibility, and the intermolecular hydrogen bonding improved. The addition of GO also improved the crystalline properties of the composite fiber membrane. In the optimal cross‐linking condition, GA was saturated by steam cross‐linking for 6 h. The introduction of GO improved the adsorption capacity of the membrane for heavy metals in water. The utmost adsorption capacities for Ni2+, Cu2+, Ag+, and Pb2+ were 262.1, 237.9, 319.3, and 413.6 mg/g when using the cross‐linked composite fiber membranes, respectively. The results of adsorption kinetics and thermodynamics showed that the adsorption process accorded with the pseudo‐second‐order kinetic model and Langmuir–Freundlich isotherm model.

Development of a portable, low-cost QCM sensor-based device for detecting α-pinene in Indian cardamom

One of the key quality indicators for Indian cardamom is α-pinene. To detect α-pinene, linoleic acid, a constituent fatty acid present in rice bran oil, was found responsible for the physisorption of α-pinene through Van der Waals (vdW) interaction. For the analysis and study of the sensing behaviour of α-pinene, a portable gas measuring device incorporating the rice bran oil coated quartz crystal microbalance sensor (RB-QCM) is developed for real-time detection. The sensor offers a good sensitivity (0.367 Hz/ppm) and a rapid response/recovery time (6 s/11 s). The physical adsorption affinity of α-pinene is calculated using the Langmuir, Freundlich, and Langmuir-Freundlich isotherm models. For estimating α-pinene in cardamom samples, the sensor demonstrated a coefficient of 0.98, with the peak area (%) determined by gas chromatography-mass spectrometry (GC–MS). SEM, FTIR, and AFM are used to analyse the structure and morphology of the sensor coating. According to this study, the rice bran oil-coated QCM sensor is a promising method for detecting α-pinene.

Synthesis and characterization of chitosan-polyacrylamide cryogels for the purification of human IgG by IMAC

The performance of polyacrylamide-chitosan monolithic cryogels functionalized with iminodiacetic acid (IDA) was evaluated for the chromatographic separation of Immunoglobulin G (hIgG) from human serum using immobilized metal ion affinity chromatography (IMAC). Monoliths were prepared using the cryopolimerization technique, varying the type of chitosan (CS) used, and final concentrations of allyl glycidyl ether (AGE) and glutaraldehyde (GA), keeping the amount of acrylamide (AAm) and bisacrylamide (MBAm) constant. Cryogels were characterized by their surface area, SEM, FTIR, porosity, ligand density, mechanical resistance, and flow rate. Purification of hIgG was investigated using the PAAm-CS-GA-AGE-IDA cryogel chelated with Cu(II) and Ni(II) ions. The analysis demonstrated isolation of hIgG from human serum in a sodium phosphate buffer at pH 7.0 containing 2 mmol/L imidazole on PAAm-CS-GA-AGE-IDA-Ni(II) cryogel, with purity of 96% and purification factor of 12.4 (based on total protein concentration and radial immunodiffusion). The hIgG adsorption equilibrium data on the IDA-Ni(II) cryogel followed the Langmuir–Freundlich isotherm model, showing maximum hIgG binding capacity of 31.19 mg hIgG/g dry cryogel and a dissociation constant in the order of 10−7 to 10−8 mol/L. These results demonstrate the potential of PAAm/CS-based cryogels with chelated Ni(II) ions for the purification of hIgG from human serum using IMAC.

Analytical modeling of adsorption isotherms for pristine and functionalized carbon nanotubes as gas sensors

Abstract The modeling of experimental data for adsorption is a very important means of predicting the mechanism of various adsorption systems. The experimental data for variation of conductivity of pristine and SnO2 functionalized single walled carbon nanotubes with concentration of nitrogen dioxide and ammonia gases (2 ppm–20 ppm) has been correlated with theoretical isotherm models. Studies are done with a one parameter model: Henry’s isotherm and two parameter models: Langmuir isotherm, Freundlich isotherm and Temkin models. Regression analysis is used to see the compatibility of theoretical models with the experimental data. The Freundlich isotherm shows the maximum compatibility with the experimental results with maximum value of regression coefficient and minimum value of average relative error suggesting the heterogenous nature of the surface. The calculated values of different constants for the four models indicate the increased adsorption capacity in case of functionalized single walled carbon nanotubes. This may be attributed to increase in heterogeneity and enhanced surface area.

Effectiveness and mechanisms of the adsorption of phenol from wastewater onto N-doped graphene oxide aerogel

Phenol, as a representative toxic substance in coking wastewater, will cause harm to the ecology and human beings. Therefore, advanced treatment of phenol is urgently needed. However, most adsorbents have the problems of low adsorption capacity and difficult recovery in water dephenolization. It is imminent to develop a recyclable and effective adsorbent. Herein three-dimensional (3D) N-doped graphene oxide aerogel (NGOA) was synthesized by using ammonium citrate as reductant and nitrogen source. NGOA exhibits large specific surface area, developed pores, excellent hydrophilicity and mechanical properties. The static and dynamic adsorption properties of NGOA were investigated. NGOA has good adsorption performance and reusability. The static saturated adsorption capacity of NGOA for phenol reached 108.19 mg g−1, which was obviously higher than most adsorbents. Furthermore, the dynamic adsorption capacity of NGOA was 43.69 mg g−1, which illustrates that NGOA has immense potential in the uptake of phenol for industrial application. Importantly, monolithic NGOA could be easily separated and recovered after adsorption saturation. The adsorption behavior conforms to the endothermic physical adsorption process, which is matched with the Pseudo-first-order kinetic model and Langmuir-Freundlich isotherm model. This work has good scientific research value and practical application prospect.

Investigation of Efficient Adsorption of Toxic Heavy Metals (Chromium, Lead, Cadmium) from Aquatic Environment Using Orange Peel Cellulose as Adsorbent

Heavy metals in the environment cause adverse effects on living organisms. Agro-wastes have the potential to remove heavy metals from aqueous solutions. In this study, the orange peel cellulose (OPC) beads were utilized as adsorbents to remove metals from wastewater. The surface of the adsorbent was studied by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDS). The concentrations of the metals before and after adsorption were measured using inductively coupled plasma mass spectrometry. The removal of the metal ions (i.e., Cr6+, Cd2+, and Pb2+) using the OPC was investigated by varying the pH, contact time, and adsorbent dosages parameters. The maximum removal efficiency obtained for the metal ions occurred at pHs 4–8. The use of the Langmuir isotherm and Freundlich isotherm models demonstrated the statistical significance of the heavy metal adsorption processes (R2 > 0.96). At a neutral pH, the OPC adsorption order was Pb2+ > Cd2+ > Cr6+ with % removal values of 98.33, 93.91, and 33.50, respectively. The adsorption equilibrium for Cr6+ was reached after 36 h. For Cd2+ and Pb2+, equilibrium was reached after 8 and 12 h, respectively. The FT-IR and SEM-EDS confirmed the presence of many functional groups and elements on the adsorbent. The adsorption of heavy metals using the OPC is a low-cost, eco-friendly, and innovative method for the removal of metals in aquatic environments. The findings of this study will be highly significant for the public in the affected areas worldwide that have credible health concerns due to water contamination with heavy metals.

Pb(II) Removal from Aqueous Solutions by Adsorption on Stabilized Zero-Valent Iron Nanoparticles—A Green Approach

Nano zero-valent iron particles (nZVFe) are known as one of the most effective materials for the treatment of contaminated water. However, a strong tendency to agglomerate has been reported as one of their major drawbacks. The present study describes a green approach to synthesizing stabilized nZVFe, using biomass as a porous support material. Therefore, in the first step, biomass-derived activated carbon was prepared by thermochemical procedure from rice straw (RSAC), and then the RSAC-supported nZVFe composite (nZVFe–RSAC) was employed to extract Pb(II) from aqueous solution and was successfully synthesized by the sodium borohydride reduction method. It was confirmed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) characteristics that the nZVFe particles are uniformly dispersed. Results of the batch experiments showed that 6 (g L−1) of this nanocomposite could effectively remove about 97% of Pb(II) ions at pH = 6 from aqueous solution. The maximum adsorption capacities of the RS, RSAC, and nZVFe–RSAC were 23.3, 67.8, and 140.8 (mg g−1), respectively. Based on the results of the adsorption isotherm studies, the adsorption of Pb(II) on nZVFe–RSAC is consistent with the Langmuir–Freundlich isotherm model R2=0.996). The thermodynamic outcomes exhibited the endothermic, possible, and spontaneous nature of adsorption. Adsorption enthalpy and entropy values were determined as 32.2 kJ mol−1 and 216.9 J mol−1 K−1, respectively. Adsorption kinetics data showed that Pb(II) adsorption onto nZVFe–RSAC was fitted well according to a pseudo-second-order model. Most importantly, the investigation of the adsorption mechanism showed that nZVFe particles are involved in the removal of Pb(II) ions through two main processes, namely Pb adsorption on the surface of nZVFe particles and direct role in the redox reaction. Subsequently, all intermediates produced through the redox reaction between nZVFe and Pb(II) were adsorbed on the nZVFe–RSAC surface. According to the results of the NZVFe–RSAC recyclability experiments, even after five cycles of recovery, this nanocomposite can retain more than 60% of its initial removal efficiency. So, the nZVFe–RSAC nanocomposite could be a promising material for permeable reactive barriers given its potential for removing Pb(II) ions. Due to low-cost and wide availability of iron salts as well as rice biowaste, combined with the high adsorption capacity, make nZVFe–RSAC an appropriate choice for use in the field of Pb(II) removal from contaminated water.

Magnetic Nanocomposites of Coated Ferrites/MOF as Pesticide Adsorbents.

Magnetic metal-organic frameworks (MMOFs) are gaining increased attention as emerging adsorbents/water remediation agents. Herein, a facile development of novel MMOFs comprised of coated ferrite nanoparticles (MNPs) and UiO-66 metal-organic framework is reported. In specific, coated Co- and Zn-doped ferrite magnetic nanoparticles were synthesized as building block while the metal-organic framework was grown in the presence of MNPs via a semi-self-assembly approach. The utilization of coated MNPs facilitated the conjugation and stands as a novel strategy for fabricating MMOFs with increased stability and an explicit structure. MMOFs were isolated with 13-25 nm crystallites sizes, 244-332 m2/g specific surface area (SSA) and 22-42 emu/g saturation magnetization values. Establishing the UiO-66 framework via the reported semi-self-assembly resulted in roughly 70% reduction in both magnetic properties and SSA, compared with the initial MNPs building blocks and UiO-66 framework, respectively. Nonetheless, the remaining 30% of the magnetization and SSA was adequate for successful and sufficient adsorption of two different pesticides, 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T), while the recovery with a commercial magnet and reuse were also found to be effective. Adsorption and kinetic studies for all three MMOFs and both pesticides were performed, and data were fitted to Langmuir-Freundlich isotherm models.

Magnesium modified activated carbons derived from coconut shells for the removal of fluoride from water

Fluoride presence in water has been recognized as one of the major water related global problems, rendering the development of effective technologies for its removal as a very significant issue, for improving human health and well-being in the affected areas. Among the commonly applied technologies for fluoride removal, adsorption has gained great attention because it offers efficiency, low-cost treatment and simple operation. The present study aimed at developing novel adsorbents, namely activated carbon modified by magnesium or/and lanthanum and silica for fluoride removal. The structure and the morphology of resulted modified activated carbons (AC-Mg and AC-Si-Mg-La) were studied in detail by the application of BET, XRD, FTIR and SEM techniques. The proposed adsorbent materials were tested for the treatment of fluoride containing waters. The effects of the adsorbent's dosage, initial concentration of pollutant, pH value of the water and regeneration efficiency were examined. According to the obtained results, the maximum adsorption was observed at pH 8, after 4 h of reaction and 0.2 g/L of adsorbent dose. Langmuir-Freundlich isotherm model and pseudo-second order kinetic model fitted the experimental data sufficiently. At pH 8 a maximum adsorption capacity of 36.56 mg/g for AC-Mg and 54.48 mg/g for AC-Si-Mg-La, was found. Repeated adsorption and regeneration studies showed only a 10% decrease of adsorption capacity after 4 regeneration cycles of operation.

Outperformance of nano-MgO2-coated sediment in Mn(Ⅱ) capture through adsorption and oxidation relative to VMT/MMT-based nanocomposites

Turning sediment into treasure would provide a sustainable treatment strategy for dredged sediment generated in the restoration process of black and odourous water. The sediment was first recycled as a template to prepare MgO2 nanocomposites (MgO2@Sed) via co-precipitation coupled with high-temperature calcination to capture Mn(Ⅱ). MgO2@VMT and MgO2@MMT were synthesized by using vermiculite (VMT) and montmorillonite (MMT) as supports for comparison with MgO2@Sed, respectively. Multiple characterization analyses pinpointed that nanosized MgO2 was successfully loaded on the sediment. Adsorption kinetics models revealed that MgO2@Sed had the fastest adsorption rate for Mn(Ⅱ) and reached zone IV of “instant approaching equilibrium”. For the main rate-limiting step of MgO2@Sed, boundary layer effects overweighed the inner-sphere diffusion. The Langmuir-Freundlich isotherm model fits the removal of Mn(Ⅱ) on MgO2@Sed well, which indicates the adsorption mechanism of Mg ion exchange and hydroxyl complexation or precipitation. The maximum Mn(Ⅱ) removal capacity of MgO2@Sed for Mn(Ⅱ) was 134.09 mg/g, which is better than most adsorption materials. Oxidation contributed more than adsorption to the removal of Mn(Ⅱ) on MgO2@Sed, while the Mn(Ⅱ) capture process on MgO2@VMT and MgO2@MMT is likely adsorption followed by oxidation. The XPS analysis shows that MgO2@Sed had the strongest manganese oxidation potential. In the pH range of 4–10, the Mn(Ⅱ) removal was almost unaffected by coexisting ions and humic acids. This study introduces the new idea of “waste control by waste” to simultaneously recycle sediment and capture Mn(Ⅱ).