Ion exchange based approach for rapid and selective Pb(II) removal using iron oxide decorated metal organic framework hybrid

Design and application of metal organic frameworks for heavy metals adsorption in water: a review

The growing apprehension surrounding heavy metal pollution in both environmental and industrial contexts has spurred extensive research into adsorption materials aimed at efficient remediation. Among these materials, Metal-Organic Frameworks (MOFs) have risen as versatile and promising contenders due to their adjustable properties, expansive surface areas, and sustainable characteristics, compared to traditional options like activated carbon and zeolites. This exhaustive review delves into the synthesis techniques, structural diversity, and adsorption capabilities of MOFs for the effective removal of heavy metals. The article explores the evolution of MOF design and fabrication methods, highlighting pivotal parameters influencing their adsorption performance, such as pore size, surface area, and the presence of functional groups. In this perspective review, a thorough analysis of various MOFs is presented, emphasizing the crucial role of ligands and metal nodes in adapting MOF properties for heavy metal removal. Moreover, the review delves into recent advancements in MOF-based composites and hybrid materials, shedding light on their heightened adsorption capacities, recyclability, and potential for regeneration. Challenges for optimization, regeneration efficiency and minimizing costs for large-scale applications are discussed.

An Updated Overview of Magnetic Composites for Water Decontamination

Water contamination by harmful organic and inorganic compounds seriously burdens human health and aquatic life. A series of conventional water purification methods can be employed, yet they come with certain disadvantages, including resulting sludge or solid waste, incomplete treatment process, and high costs. To overcome these limitations, attention has been drawn to nanotechnology for fabricating better-performing adsorbents for contaminant removal. In particular, magnetic nanostructures hold promise for water decontamination applications, benefiting from easy removal from aqueous solutions. In this respect, numerous researchers worldwide have reported incorporating magnetic particles into many composite materials. Therefore, this review aims to present the newest advancements in the field of magnetic composites for water decontamination, describing the appealing properties of a series of base materials and including the results of the most recent studies. In more detail, carbon-, polymer-, hydrogel-, aerogel-, silica-, clay-, biochar-, metal-organic framework-, and covalent organic framework-based magnetic composites are overviewed, which have displayed promising adsorption capacity for industrial pollutants.

Remediation of multifarious metal ions and molecular docking assessment for pathogenic microbe disinfection in aqueous solution by waste-derived Ca-MOF

The present study demonstrates an eco-friendly and cost-effective synthesis of calcium terephthalate metal-organic frameworks (Ca-MOF). The Ca-MOF were composed of metal ions (Ca2+) and organic ligands (terephthalic acid; TPA); the former was obtained from egg shells, and the latter was obtained from processing waste plastic bottles. Detailed characterization using standard techniques confirmed the synthesis of Ca-MOF with an average particle size of 461.9 ± 15 nm. The synthesized Ca-MOF was screened for its ability to remove multiple metal ions from an aqueous solution. Based on the maximum sorption capacity, Pb2+, Cd2+, and Cu2+ ions were selected for individual parametric batch studies. The obtained results were interpreted using standard isotherms and kinetic models. The maximum sorption capacity (qm) obtained from the Langmuir model was found to be 644.07 ± 47, 391.4 ± 26, and 260.5 ± 14 mg g-1 for Pb2+, Cd2+, and Cu2+, respectively. Moreover, Ca-MOF also showed an excellent ability to remove all three metal ions simultaneously from a mixed solution. The metal nodes and bonded TPA from Ca-MOF were dissociated by the acid dissolution method, which protonated and isolated TPA for reuse. Further, the crystal structure of Ca-MOF was prepared and docked with protein targets of selected pathogenic water-borne microbes, which showed its disinfection potential. Overall, multiple metal sorption capability, regeneration studies, and broad-spectrum antimicrobial activity confirmed the versatility of synthesized Ca-MOF for industrial wastewater treatment.

Novel Hydrophobic Functionalized UiO-66 Series: Synthesis, Characterization, and Evaluation of Their Structural and Physical-Chemical Properties

A novel set of four functionalized hydrophobic UiO-66-NHR series were synthesized through postsynthetic procedures, utilizing various benzoyl chlorides and UiO-66-NH2 as starting materials. This synthesis method was carried out by employing p- (1) and o-toluoyl (2), as well as 2- (3) and 4-fluorobenzoyl (4) substituents. The analysis of the resulting compounds was performed using conventional spectroscopic methods such as FT-IR and 1H NMR to quantify the conversion rate into amide. Furthermore, SEM and XPS techniques were employed for morphological and surface analysis. Finally, the evaluation of the chemical stability and contact angle using the sessile drop method was performed to evaluate the technological potential of these compounds for application in aqueous and acidic media (such as selective separation of different metals and wastewater recovery).

Enhanced synergistic removal of Cu(II) and Cr(VI) with multifunctional biomass hydrogel from strong-acid media

Simultaneous recovery of heavy metal ions (HMIs) such as Cu(II) and Cr(VI) from strong-acid media was a great challenge due to the inhibition of protons. Herein, a novel biomass hydrogel (CMC/PEI-PD) containing various groups (bis-picolylamine, amino, and hydroxyl groups) was newly prepared by a facile two-step process. The static experiments relating pH, kinetics and isothermal co-adsorption confirmed the synergistic effect towards Cu(II) and Cr(VI) consistently. Specifically, the adsorption capacities of Cu(II) and Cr(VI) at pH 2.0 increased by 23.73% and 40.18% in comparison with the single systems. Moreover, coexistence of inorganic anions and cations could further increase the adsorption of Cu(II) and Cr(VI) by 59.90% and 43.39%, respectively. At the same time, the adsorption and desorption ratios for both HMIs remained stable. The superior performance came from the two dominant mechanisms of co-removal. On the one hand, Cu(II) chelated by bis-picolylamine group attracted Cr(VI) in the form of cation bridge, thus promoting Cr(VI) adsorption. On the other hand, the protonated amine group attracted Cr(VI) by electrostatic interaction and weakened the inter-cationic repulsion by electrostatic shielding, thus promoting Cu(II) adsorption. In addition, the dynamic column experiment towards simulated acidic electroplating wastewater involving Cu(II)-Cr(VI)-Ni(II) certified the high efficiency and feasibility of the co-removal. Therefore, CMC/PEI-PD owned great potential in the separation of typical HMIs even directly from strong-acid media.

A correlation of the adsorption capacity of perovskite/biochar composite with the metal ion characteristics

LaFeO₃/biochar composite is prepared by cellulose-modified microwave-assisted method at 450 °C. The structure is identified by Raman spectrum which, consists of characteristics biochar bands and octahedral perovskite chemical shifts. The morphology is examined by scanning electron microscope (SEM); two phases are observed, rough microporous biochar and orthorhombic perovskite particles. The BET surface area of the composite is 57.63 m²/g. The prepared composite is applied as a sorbent for the removal of Pb²⁺, Cd²⁺, and Cu²⁺ ions from aqueous solutions and wastewater. The adsorption ability reaches a maximum at pH > 6 for Cd²⁺, and Cu²⁺ ions, and is pH-independent for Pb²⁺ ions adsorption. The adsorption follows pseudo 2nd order kinetic model, Langmuir isotherm for Pb²⁺ ions, and Temkin isotherms for Cd²⁺, and Cu²⁺ ions. The maximum adsorption capacities, q_m, are 606, 391, and 112 mg/g for Pb²⁺, Cd²⁺, and Cu²⁺ ions, respectively. The electrostatic interaction is responsible for the adsorption of Cd²⁺, and Cu²⁺ ions on LaFeO₃/biochar composite. In case of Pb²⁺ ions form a complex with the surface functional groups of the adsorbate. LaFeO₃/biochar composite shows high selectivity for the studied metal ions and excellent performance in real samples. The proposed sorbent can be easily regenerated and effectively reused.

Selective removal behavior of lead and cadmium from calcium-rich solution by MgO loaded soybean straw biochars and mechanism analysis

Modified biochars has great potential for removing heavy metals from aquatic environments, but the removal of heavy metals by biochars is usually significantly affected by the co-presence of the macro amount of metal ions, such as Ca. Enhancing the ion exchange capacity of biochar by increasing its alkali metal content is a very prospective method to improve its selectivity. In this paper, MgO loaded biochar (MBC) was synthesized by co-pyrolysis of soybean straw and MgCl₂·6H₂O for selective remove Pb and Cd from calcium-rich wastewater. MBC exhibited excellent selective adsorption performance for Pb and Cd in calcium-rich wastewater due to the successful loading of MgO. The adsorption capacities of MBC for Pb and Cd were 582.57 and 167.40 mg/g, and the removal efficiency of Ca below 2.5% with an initial concentration of 800 mg/L. The ion exchange capacities of Pb and Cd enhanced almost 27 and 23 times than BC. By analyzing the results of BET, XRD, SEM-EDS, XPS and FTIR, the adsorption mechanisms of MBC were mainly including ion exchange, precipitation with minerals, and interaction with oxygen-containing functional groups. The easy preparation method and high selective adsorption capacity makes MBC an ideal alternative for efficiently selective removal Pb and Cd from calcium-rich wastewater.

Genetic algorithm-assisted artificial neural network modelling for remediation and recovery of Pb (II) and Cr(VI) by manganese and cobalt spinel ferrite super nanoadsorbent

MnFe₂O₄ and CoFe₂O₄ nanoparticles were hydrothermally synthesized to examine their capability in adsorption of Pb (II) and Cr (VI). The adsorbents exhibited a high rate of adsorption, reaching 90% of their adsorption capacity in less than 30 min. Furthermore, the adsorption capability of the Magnetic Nanoparticles (MNPs) was noticeably greater at initial pollutant concentrations smaller than 40 mg/L. Maximum adsorption capacity on MnFe₂O₄ and CoFe₂O₄ nanoparticles were 40 and 25.38 mg/g for Cr (VI) and 523.32 and 476.19 mg/g for Pb (II), respectively. A data-driven model of Artificial Neural Network was used for prediction of adsorption capacity at both equilibrium and non-equilibrium condition. The model parameters including the numbers of neuron (n = 7) and data portioning for training (49.5%), validation (40.5%), and testing (10%) were obtained using Genetic Algorithm. The results indicated that the model could predict the data with high accuracy (R² = 0.998). The input parameters were initial concentration, time, pH, temperature, adsorbent dosage, and other parameters that is dependent to the physico-chemical properties of ions and adsorbents' surface (ε, α₁, α₂). The mechanism involved in Cr(VI) and Pb(II) adsorption are electrostatic physisorption and a combination of ion exchange chemisorption and electrostatic physisorption, respectively. Desorption capability and adsorbent reuse capability were also examined.

Amphiphilic Grafted Polymers Based on Citric Acid and Aniline Used to Enhance the Antifouling and Permeability Properties of PES Membranes

Water treatment technology based on ultrafiltration (UF) faces the problem of severe membrane fouling due to its inherent hydrophobicity. The use of amphiphilic polymers that possess both hydrophobic and hydrophilic chain segments can be advantageous for the hydrophilic modification of UF membranes due to their excellent combination in the membrane matrix. In the present study, we examined a novel amphiphilic CA-g-AN material, constructed by grafting citric acid (CA) to aniline (AN), as a modified material to improve the hydrophilicity of a PES membrane. This material was more compatible with the polymer membrane matrix than a pure hydrophilic modified material. The polyethersulfone (PES) membranes modified by amphiphilic CA-g-AN demonstrated a higher water flux (290.13 L·m^-2·h^-1), which was more than eight times higher than that of the pure PES membrane. Furthermore, the flux recovery ratio (FRR) of the modified membrane could reach 83.24% and the value of the water contact angle (WCA) was 76.43°, demonstrating the enhanced hydrophilicity and antifouling ability of the modified membranes. With this study, we aimed to develop a new amphiphilic polymer to improve the antifouling property and permeability of polymer-based UF membranes to remove organic pollutants from water.

Overview on recent advances of magnetic metal-organic framework (MMOF) composites in removal of heavy metals from aqueous system

Developing a novel, simple, and cost-effective analytical technique with high enrichment capacity and selectivity is crucial for environmental monitoring and remediation. Metal-organic frameworks (MOFs) are porous coordination polymers that are self-assembly synthesized from organic linkers and inorganic metal ions/metal clusters. Magnetic metal-organic framework (MMOF) composites are promising candidate among the new-generation sorbent materials available for magnetic solid-phase extraction (MSPE) of environmental contaminants due to their superparamagnetism properties, high crystallinity, permanent porosity, ultrahigh specific surface area, adaptable pore shape/sizes, tunable functionality, designable framework topology, rapid and ultrahigh adsorption capacity, and reusability. In this review, we focus on recent scientific progress in the removal of heavy metal ions present in contaminated aquatic system by using MMOF composites. Different types of MMOFs, their synthetic approaches, and various properties that are harnessed for removal of heavy metal ions from contaminated water are discussed briefly. Adsorption mechanisms involved, adsorption capacity, and regeneration of the MMOF sorbents as well as recovery of heavy metal ions adsorbed that are reported in the last ten years have been discussed in this review. Moreover, particular prospects, challenges, and opportunities in future development of MMOFs towards their greener synthetic approaches for their practical industrial applications have critically been considered in this review.

Chitosan grafted tetracarboxylic functionalized magnetic nanoparticles for removal of Pb(II) from an aqueous environment

In this study, the chitosan-grafted tetracarboxylic functionalized magnetic nanoparticle (Fe₃O₄@TCA@CS) was synthesized via in situ co-precipitation process and amidation reaction to improve efficiency of adsorption process and obtain cost-effective adsorbents for removal of toxic Pb(II) metal from aqueous environment. The Fe₃O₄@TCA@CS nanocomposite was analyzed by FTIR, TEM-EDX, TGA, XRD, BET, and Zeta potential. The performance of Fe₃O₄@TCA@CS for Pb(II) ions adsorption was achieved as a function of pH, dose, contact time, initial Pb(II) concentration, and temperature. The influence of coexisting ions such as Na⁺, Ca²⁺, Mg²⁺, and Cd²⁺on removal efficiency of Pb(II) was also investigated. The results revealed that the coexisting ions had little influence on Pb(II) removal efficiency. The pseudo-first-order and Freundlich models were better to describe the adsorption of Pb(II) onto Fe₃O₄@TCA@CS and the maximum adsorption capacity of Pb(II) was 204.92 mg/g at pH:5.5; adsorbent dose: 0.015 g; and temperature: 298 K. Thermodynamic studies revealed that the Pb(II) adsorption onto Fe₃O₄@TCA@CS was an exothermic process. In conclusion, the study provides a new, simple, low-cost, and effective chitosan-based magnetic nanocomposite as a promising adsorbent with excellent adsorption capacity, magnetic separation, and reusability for Pb(II) removal from an aqueous environment.

Regulating the exposed crystal facets of α-Fe2O3 to promote Fe2O3-modified biochar performance in heavy metals adsorption

α-Fe₂O₃ modified biochar (Fe₂O₃/BC) was prepared to remove Cu(II), Pb(II) and As(V). By adjusting the calcination temperature, the morphology and exposed crystal facets of α-Fe₂O₃ on the biochar were changed which further affected the adsorption performance. The kinetics and isotherms were investigated systematically to reveal adsorption effect of the adsorbent on Cu(II), Pb(II) and As(V). The results indicated that chemisorption process was the dominant adsorption mechanism. Fe₂O₃/BC-350 exhibited superior adsorption capacity for Cu(II) (258.22 mg/g) and Pb(II) (390.60 mg/g), and Fe₂O₃/BC-250 showed relatively good adsorption capacity for As(V) (5.78 mg/g). By adsorption mechanism analysis, electrostatic adsorption, ion exchange, precipitation and complexation were coexisted in the process of removing metal ions by Fe₂O₃/BC. The repeatability test and the effect of ion strength exhibited the strong stability of Fe₂O₃/BC. Meanwhile, density functional theory (DFT) calculations manifested that the (202) facet of α-Fe₂O₃ on Fe₂O₃/BC-350 possessed the lowest adsorption energies of Cu(II) and Pb(II). While for As(V), it was the (104) facet of α-Fe₂O₃ on Fe₂O₃/BC-250 that exhibited the lowest adsorption energy. DFT results revealed that different Fe₂O₃/BC had different adsorption affinities to various heavy metals. In general, this work not only prepared a promising adsorbent via a simple procedure, but also served as a reference for researchers in designing absorbents with specific active facet for efficient heavy metals remediation.

Layered Double Hydroxides Derived from MIL-88A(Fe) as an Efficient Adsorbent for Enhanced Removal of Lead (II) from Water

The efficient removal of lead (II) from aqueous solution remains a big problem and the development of novel nanomaterials as adsorbents by various technologies to solve this problem is promising. This study contributed a novel nanostructure of MIL-88A-layered double hydroxides (LDHs) as the adsorbent for Pb²⁺, which was synthesized by a two-step solvothermal method with MIL-88A(Fe) as the precursor. The as-prepared material featured a chestnut-like core-shell structure, and exhibited excellent removal performance towards Pb²⁺ from water in comparison to MIL-88A(Fe) and LDHs (directly synthesized). The adsorption of Pb²⁺ by the MIL-88A-LDHs conformed to the pseudo-second-order kinetic model and the Langmuir and Freundlich isotherm models. The maximal adsorption capacity was 526.32, 625.00, and 909.09 mg g^-1 at 278, 298, and 318 K, respectively. The thermodynamic parameters suggested that the adsorption was an endothermic, entropy-increasing, and spontaneous reaction. X-ray photoelectron spectroscopy (XPS) analysis indicated that the surface complexation was mostly responsible for Pb²⁺ elimination. The MIL-88A-LDHs can be readily regenerated and showed good cyclic performance towards Pb²⁺. Thus, the as-prepared MIL-88A-LDHs may hold promise for the elimination of aqueous heavy metals.

Recent developments in MOF and MOF based composite as potential adsorbents for removal of aqueous environmental contaminants

With the growth of globalization which has been the primary cause of water pollution, it is utmost necessary for us living being to have access to clean water for the purpose of drinking, washing and various other useful applications. With the purpose of future security and to restore our ecological balance, it is essential to give much significance towards the removal of unwanted toxic contaminants from our water resources. In this regard adsorptive removal of toxic pollutants from wastewater with porous adsorbent is regarded as one of the most promising way for water decontamination process. Metal organic frameworks (MOFs) comprising of uniformly arranged pores, abundant active sites and containing an easily tunable structure has aroused as a promising material for adsorbent to remove the unwanted contaminants from water sources. The adsorption of pollutants by the different MOFs surface are driven by various interactions including π-π, acid-base, electrostatic and H-bonding etc. On the other hand, the removal of various contaminants by MOFs is influenced by various factors including pH, temperature and initial concentration. In this review we will specifically discuss the adsorptive removal of different organic and inorganic pollutants present in our water systems with the use of MOFs as adsorbent along with the various factors and interaction mechanism manipulating the adsorption behaviour.

Removal of hazardous ions from aqueous solutions: Current methods, with a focus on green ion flotation

Hazardous ions, like those of heavy metals, cause significant health and environmental problems when they are discharged into water resources naturally or through various industrial processes. Removing these ions from water is of significant importance in the provision of high-quality water for drinking and agricultural usage. This work discusses current techniques that are frequently used for the removal of heavy-metal ions from aqueous solutions by absorption, particularly the use of biodegradable surfactants in ion flotation. Certain new surfactants promise high efficiency in their use in the ion-flotation process and in their application in industrial-water treatment to remove heavy metals. As an example, this work demonstrates the high efficiency of surfactants based on an amino-acid (L-cysteine) in removing a range of heavy-metal ions in a simple, single-stage ion-flotation process. High foaming ability, the ability to operate in various temperatures and pHs, decomposing into natural products and high binding affinity for heavy-metal ions make the cysteine-based surfactants a highly suitable compound to replace current commercial surfactants in ion- and froth-flotation processes. Removal of particular ions can also be achieved in ion flotation; a suitable choice of parameters, such as pH and surfactant concentration, favours the surfactant binding to those ions. Further intensive work is required to develop an optimal process to recover valuable elements from waste solutions.

Removal of lead (Pb+2) from contaminated water using a novel MoO3-biochar composite: Performance and mechanism

Removal of toxic chemicals from the environment using novel adsorbents is of great concern. In this study, a novel composite of molybdenum trioxide (MoO₃)-engineered biochar (MoO₃-BC) was derived from corn straw and synthesized for the removal of Pb(II) from water. The pyrolysis temperature of 600 °C was suitable for the thermal self-assembly of MoO₃-BC. Although MoO₃-BC had lower S_BET (59.3 m²/g) than the pristine BC (157.8 m²/g), it had a stronger adsorption affinity to Pb(II). The Pb(II) removal capacity of MoO₃-BC was 229.87 mg/g at pH 4.0, and the adsorptive removal of Pb(II) was fit using a pseudo-second-order model and the Langmuir model. High temperature favored the removal of Pb(II) by MoO₃-BC; However, the removal of Pb(II) was inhibited with increasing the ion strength. The MoO₃-BC revealed an acceptable stability and reusability, since the removal efficiency of Pb(II) remained above 80.7%, even after 8 cycles. The MoO₃-BC effectively reduced ≥99.9% of Pb(II) in the polluted irrigation water. The Pb(II) removal mechanisms involved surface electrostatic attraction, ion exchange and surface complexation. These findings conclude that the MoO₃-BC is a novel composite that can be used for the removal of Pb from contaminated water. More studies are needed to investigate the potentiality of MoO₃-biochar composite for the removal of other metals from water in a mono and competitive sorption system.

Biosorption potential of brown algae, Sargassum polycystum, for the removal of toxic metals, cadmium and zinc

In this research work, the biosorption potential of brown algae, Sargassum polycystum, was investigated for the removal of toxic metals, cadmium (Cd) and zinc (Zn), under controlled environmental conditions. The biosorbent prepared from the S. polycystum was characterized by Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The optimal conditions identified using Box-Behnken design (BBD) for Cd removal were pH: 4.65, biosorbent mass: 1.8 g/L and shaking speed: 76 rpm. For zinc, the optimum values were pH: 5.7, biosorbent mass: 1.2 g/L and shaking speed: 125 rpm, respectively. The equilibrium uptake of the metals, Cd and Zn, was evaluated by isotherm models. The Langmuir isotherm proved to be an excellent fit confirming single layer of sorption. The maximum Cd and Zn uptakes achieved were 105.26 mg/g and 116.2 mg/g respectively. The kinetics of Cd and Zn biosorption onto brown algae Sargassum polycystum, follows pseudo-second order. The thermodynamic parameters were determined, and the sorption process was found to be feasible. Desorption studies of Cd and Zn were performed, and the bio sorbent reproduced appreciable efficiency for five successive cycles of sorption-desorption process using HCl.

Recyclable nitrogen-doped biochar via low-temperature pyrolysis for enhanced lead(II) removal

Facile and low-cost preparation are essential in the conversation of agricultural waste into biochar. In this work, nitrogen-doped biochar (NBC-350-0.1) was prepared by thermal decomposition of urea (urea/biochar = 0.1:1 mass ratio) at a low temperature of 350 °C. NBC-350-0.1 showed good performance for Pb(II) removal with the maximum adsorption capacity of 130.87 mg g^-1 at 25 °C, which was five times that of pristine biochar (BC). Adsorption kinetics, isotherms and thermodynamics studies indicated that the adsorption of Pb(II) by NBC-350-0.1 or BC was the homogeneous monolayer adsorption with chemical action as the rate-limiting step, and was accompanied by spontaneous endothermic. Further analysis showed that the removal of Pb(II) on NBC-350-0.1 and BC depended on the complexation with unsaturated carbon bonds and ion exchange with Ca(II). Moreover, graphitic- and pyridinic-N in NBC-350-0.1 exerted a key part in the adsorption of Pb(II). NBC-350-0.1 regenerated by NaOH exhibited excellent recycling performance keeping the original removal efficiency at 84% after five cycles. In addition, this N doping method is suitable for improving the performance of coffee grounds, sawdust, and bagasse biochar. These results would provide an idea for obtaining recyclable N-doped biochar to treat the Pb(II) polluted wastewater.

Pb(II) adsorption mechanism and capability from aqueous solution using red mud modified by chitosan

Red mud modified by chitosan (RM/CS) was utilized as an adsorbent to effectively remove Pb(II) from aqueous solution. The surface area of RM/CS was found to significantly increase by more than 50% compared to that of original red mud. Different factors that affected the Pb(II) removal on this material, such as initial Pb(II) concentration, pH, and contact time, were investigated. The pseudo-first-order, pseudo-second-order, and intra-diffusion models were used to fit the experimental data to investigate the Pb(II)'s removal kinetics. The Pb(II) removal followed the intra-diffusion model. Additionally, the non-zero C value obtained from this model indicates that the removal was controlled by many different mechanisms. We also found that the interaction of Pb(II) and carbonate group on the material's surface played a primary role once the adsorption equilibrium was reached. Finally, the maximum adsorptive capacity was found to be about 209 mg/g. This obtained value is higher than those obtained for some other materials. Therefore, the present RM/CS should be a potential material for removing Pb(II) from aqueous solution.

Cleaner technologies to combat heavy metal toxicity

Heavy metals frequently occur as silent poisons present in our daily diet, the environment we live and the products we use, leaving us victims to various associated drastic health and ecological bad effects even in meagre quantities. The prevalence of heavy metals can be traced from children's toys, electronic goods, industrial effluents, pesticide preparation, and even in drinking water in some instances; necessitating methods to remediate them. The current review discusses the various physicochemical and biological methods employed to tackle the problem of heavy metal pollution. Apart from the conventional methods following the principles of adsorption, precipitation, coagulation, and various separation techniques, the advancements made in the directions of biological heavy metal detoxification using microbes, plants, algae have been critically analyzed to identify the specific utility of different agents for specific heavy metal removal. The review paper is a nutshell of different heavy metal remediation strategies, their merits, demerits, and modifications done to alleviate process of heavy metal pollution.

Adsorption Behavior of Lead Ions from Wastewater on Pristine and Aminopropyl-Modified Blast Furnace Slag

The potential possibility of blast furnace slag as a low-cost adsorbent to remove lead ions from wastewater was investigated in detail in the present work. Both single factor experiment and orthogonal experiment were performed to reveal the effect of pH, adsorption temperature, contact time and initial concentration of lead ions on the adsorption performance of pristine slag. In order to make clear the correlation between the lead ion adsorption performance and the structure of slag, solid state nuclear magnetic resonance (NMR) was conducted to reveal the network structure and X-ray fluorescence (XRF) was used to calculate the nonbridging oxygen in the network-forming tetrahedra. For the purpose of improving the adsorption performance, γ-aminopropyltriethoxysilane (APTES) was adopted to modify the slag via post-grafting method. The results show that the slag is predominately composed of SiO2, Al2O3, CaO and MgO, exhibiting an amorphous network structure based on SiO4 and AlO4 tetrahedra. The conditions for adsorption can be optimized as follows: a pH of 7, an adsorption temperature of 60 °C, a contact time of 120 min and an initial lead ion concentration of 40 mg·L−1. Under the optimal conditions, a removal rate of 99.98% and an adsorption capacity of 49.99 mg·g−1 are obtained for the pristine slag. The adsorption complies with the Langmuir model thermodynamically and conforms to the pseudo-second order model kinetically. It is noted that aminopropyl-modification has considerably enhanced the removal rate of lead ions from 20.71 to 64.32% and the adsorption capacity from 29.01 to 96.48 mg·g−1 since amino groups (-NH2) are more inclined to form a complex with lead ions than hydroxyl groups due to the higher nucleophilicity of amino groups than that of hydroxyl groups. However, it is necessary to develop more low-cost modification agents in the future work.

Optimization and mechanisms of methylene blue removal by foxtail millet shell from aqueous water and reuse in biosorption of Pb(II), Cd(II), Cu(II), and Zn(II) for secondary times

Foxtail millet shell as a raw efficient adsorbent was chosen first to eliminate methylene blue (MB) based on the uneven surface with many micropores, lots of negative charges, various functional groups, and some primary elements. And then the adsorbent-loaded MB was used to remove Pb(II), Cd(II), Cu(II), and Zn(II) from aqueous water for secondary adsorption. The effects of various factors were explored and optimized for removal rates of MB on the surface of the adsorbent using response surface methodology (RSM). After these factors were optimized, the confirmed removal rates of MB by the adsorbents were reached at 92.04, 93.05, and 93.36%, respectively from aqueous water while the solution pH was at 3, 7, and 11, respectively. The behavior of adsorption for MB dye was well-described by Langmuir isotherm (R² = 0.9951), demonstrating favorable monolayer adsorption of MB on the adsorbent with the maximum capacity of 165.07 mg·L^-1 in aqueous water. The data of MB dye removal was better assessed by pseudo-second-order model (R² ≥ 0.9033), indicating an exchange of electrons has occurred between the adsorbent and MB particles, especially K and Ca ions of the adsorbent. In addition, the adsorbent-loaded MB has still presented better adsorption abilities for Pb(II), Cd(II), Cu(II), and Zn(II), respectively after MB removal in aqueous water. The adsorption mechanisms of adsorption were explored with the characterizations of the adsorbent before and after adsorption for the target pollutants by the methods of TEM, SEM, nitrogen physisorption isotherms, XPS, EDS, IR, and zeta potential classes. In summary, the results presented that the foxtail millet shell could be applied to remove MB dye effectively from aqueous water with the combined effects of electrostatic attraction, ion exchange, functional groups binding, and pore diffusion, but also, the adsorbent loaded with MB can be still applied to eliminate Pb(II), Cd(II), Cu(II), and Zn(II) by effects of electrostatic attraction and functional groups complexation in aqueous water.Novelty Statement In the present work, (a) the raw foxtail millet shell as a new potential adsorbent was used to remove MB dye from aqueous water for the first times, and operational variables of adsorption MB were investigated and optimized using response surface methodology, (b) the foxtail millet shell loaded MB as a disused adsorbent without any chemical reagent added was carried out to remove Pb(II), Cd(II), Cu(II), and Zn(II) ions, respectively in aqueous water for a secondary cycle, (c) adsorption mechanisms of MB removal on the adsorbent and the target heavy metals on the disused adsorbent were explored by the various analytical methods. This work provides evidence for the adsorption of MB on the natural adsorbent and improves the utilization efficiency of the used adsorbent on Pb(II), Cd(II), Cu(II), and Zn(II) removal in aqueous water.

Chitosan/Phosphate Rock-Derived Natural Polymeric Composite to Sequester Divalent Copper Ions from Water

Herein, a chitosan (CH) and fluroapatite (TNP) based CH-TNP composite was synthesized by utilizing seafood waste and phosphate rock and was tested for divalent copper (Cu(II)) adsorptive removal from water. The XRD and FT-IR data affirmed the formation of a CH-TNP composite, while BET analysis showed that the surface area of the CH-TNP composite (35.5 m²/g) was twice that of CH (16.7 m²/g). Mechanistically, electrostatic, van der Waals, and co-ordinate interactions were primarily responsible for the binding of Cu(II) with the CH-TNP composite. The maximum Cu(II) uptake of both CH and CH-TNP composite was recorded in the pH range 3-4. Monolayer Cu(II) coverage over both CH and CH-TNP surfaces was confirmed by the fitting of adsorption data to a Langmuir isotherm model. The chemical nature of the adsorption process was confirmed by the fitting of a pseudo-second-order kinetic model to adsorption data. About 82% of Cu(II) from saturated CH-TNP was recovered by 0.5 M NaOH. A significant drop in Cu(II) uptake was observed after four consecutive regeneration cycles. The co-existing ions (in binary and ternary systems) significantly reduced the Cu(II) removal efficacy of CH-TNP.

Sustainable removal of cadmium from contaminated water using green alga - Optimization, characterization and modeling studies

This research study reported the feasibility of cadmium removal using green algae, Caulerpa scalpelliformis, under controlled environmental conditions. The algal biosorbent could effectively remove cadmium under broad range of test conditions, namely, initial pH (3-6), adsorbent mass (0.5-2.5 gL^-1) and shaking speed (60-100 rpm). The best operating conditions were identified using Central Composite Design under Response Surface methodology and found to be pH - 4.9, adsorbent mass - 2.1 gL^-1 and shaking speed - 90 rpm. Equilibrium studies were conducted and monolayer sorption was identified as the mechanism, confirmed by Langmuir isotherm (R² = 0.9920). The maximum Cd uptake achieved at optimal conditions was 111.11 mg g^-1. The kinetic constants of the best fit model (pseudo second order) were determined. The thermodynamic feasibility was verified (ΔG ^ͦ < 0) and the biosorption process was found to be endothermic (ΔH ^ͦ > 0). The mass transfer studies shows that the mass transfer coefficient was inversely related to the temperature. Presence of favorable surface functional groups and enhanced surface area confirmed the suitability of the synthesized biosorbent for effective removal of cadmium.

Removal of copper ions by functionalized biochar based on a multicomponent Ugi reaction

Copper is widely present in the natural environment and inevitably poses a risk to both human health and the natural environment. Biochar is an inexpensive, clean and sustainable sorbent material that can be used as a resource for copper removal, and there is interest in new ways to chemically treat biochar to tune its unique properties and modify its atomic structure. In this study, biochar was oxidized, and then polyethyleneimine (PEI) modified chitosan and carboxylated biochar were economically compounded through a multicomponent Ugi reaction to effectively remove Cu(ii). PEI enhances the adsorption of Cu(ii) within an optimum solution pH range of 3.5–5.5. The adsorption process follows a pseudo-second-order kinetic model. When the dosage of BC-NH2 was 4 g L⁻¹ and the temperature was 303 K, the maximum adsorption capacity calculated by the Langmuir model was 26.67 mg g⁻¹. The adsorption process of Cu(ii) on BC-NH2 was heat-trapping and spontaneous. BC-NH2 showed good selectivity for K⁺ and Mg²⁺, and BC-NH2 desorbed by NaOH showed better adsorption performance than H₂SO₄ in the adsorption–desorption cycle. Characterization by SEM, EDS, BET, FTIR, TGA and XPS showed successful coupling and that the amide group of BC-NH2 had chelated with Cu(ii). This atomically economical multicomponent Ugi reaction provides a new option for preparing composite materials that effectively remove heavy metals.

Polyethyleneimine-modified chitosan and carboxylated biochar were economically compounded by a multicomponent Ugi reaction to produce products rich in amide functional groups.

Carbon Dioxide Enrichment PEBAX/MOF Composite Membrane for CO2 Separation

Zeolitic imidazole framework (ZIF-8) was incorporated into poly(ether-block-amide) (Pebax-1657) in differing ratios to prepare mixed matrix membranes (MMMs) for gas separation. As ZIF-8 loading is increased, gas separation selectivity also gradually increases. For economic considerations, the proportion of the increase in selectivity to the amount of MOF loaded per unit was calculated. The results show that mixing 5% MOF gives the best unit performance. With this, a variety of MOFs (UiO-66, UiO-66-NH₂, A520, MIL-68(Al) and MIL-100(Fe)) were mixed with PEBAX at 5 loading to prepare MMMs. In this work, metal-organic frameworks (MOFs) were processed using the dry-free method, where in the synthesized MOF was not dried prior to incorporation. The gas separation performance test carried out shows the highest separation performance was exhibited by P-UiO-66, wherein the CO₂/N₂ gas selectivity was 85.94, and the permeability was 189.77 (Barrer), which was higher than Robeson’s Upper bound in 2008, and obtained a high permeability and selectivity among mixed matrix membranes. In the preparation of high quality MMMs for gas separation, details regarding the interface phenomenon were assessed.