Pb Adsorption Capacity Research Articles

Potential of silica from water treatment sludge modified with chitosan for Pb(II) and color adsorption in sasirangan waste solution

Water treatment sludge (WTS) still contains a lot of silica oxide (SiO2) as much as 43.12-66.90% by weight and can act as an adsorbent to be applied to the treatment of Sasirangan wastewater. Silica extraction from WTS was carried out by microwave-assisted leaching, which - compared to conventional extraction - had several advantages including high extraction yields, fast, uniform, and more selective processing time. In addition, Sasirangan liquid waste is a by-product of the dyeing process of Sasirangan cloth, which still contains heavy metals in amounts exceeding the quality standard. This study aims to extract silica from WTS by microwave-assisted leaching process to synthesize silica modified by chitosan (Si-Kit) as an adsorbent to reduce Pb(II) from Sasirangan wastewater, and to obtain a kinetic model of the adsorption process. The silica from microwave-assisted leaching process (Si-MaL) and Si-Kit adsorbents were characterized using FTIR and SEM. The results showed that the dominant functional groups of Si-Kit included Si-O-Si, Si-O-C stretching vibrations, and stretching vibration of C=N showing that the condensation between aldehyde groups and amino groups occurred to form base after the addition of glutaraldehyde. The SEM images showed that Si-MaL and Si-Kit adsorbent obviously increased in particle size with the presence of visible particles of homogeneous granules and large pores. The removal efficiency percentage of Pb(II) and color occurred at 6% w/v adsorbent weight and 70 min was 87.20% and 61.87% respectively. Meanwhile, the adsorption kinetics of Pb(II) and color followed the zero order kinetics model at weight variation of 6%-w/v based on the value of R2 close to one and the adsorption capacity of Pb(II) ion and color were 12.01 mg g-1 and 467 mg g-1, respectively.

High-efficiency decontamination of Pb(II) and tetracycline in contaminated water using ball-milled magnetic bone derived biochar

Herein, bone-derived biochar loaded with Fe3O4 (MBBCBM) was synthesized by ball-milling process and was employed for the elimination of Pb(II) and tetracycline (TC) from water. Characterizations revealed that ball milling effectively ground the bone-derived biochar to nanometer size and achieved the loading of Fe3O4 with excellent magnetism. The adsorption of Pb(II) and TC onto MBBCBM reached equilibrium within 20/100 min and was appropriately described by Avrami fractional-order model. Moreover, the isotherm data was well fitted by Sips and Langmuir models with outstanding adsorption capacities of Pb(II) (339.39 mg/g) and TC (237.51 mg/g). The thermodynamic studies showed negative ΔG0 values, and positive ΔH0 values for Pb(II) (18.54 kJ/mol) and TC (32.92 kJ/mol), indicating the endothermic and spontaneous properties of the adsorption. Moreover, the adsorption performance of MBBCBM was basically steady during extensive pH range with high tolerance to co-existing ions, and the removal rate and desorption efficiency decreased slightly after three cycles. In addition, the MBBCBM achieved high Pb(II) capture through electrostatic attraction, precipitation, complexation, cation exchange, and coprecipitation, whereas the TC elimination was achieved through π-π stacking interaction, H-bonding, complexation, and pore-filling. All these findings suggested the ball milling-tailored MBBCBM to be an ideal adsorbent for decontamination of TC and Pb(II) contaminated water.

Adsorption of Pb(II), Hg(II) and Cu(II) ions on azacrown ether grafted chitosan films

The adsorption and desorption of Cu(II), Pb(II) and Hg(II) ions from aqueous solutions by porous azacrown ether grafted chitosan films (Ch-DAC) were studied in a batch adsorption system. The porous Ch-DAC films were prepared by hydroamination reaction of azacrown ether activated double bonds with chitosan by changing the proportion of Ch/DAC with 1:0, 1:0.125, 1:0.167, 1:0.25 and 1:0.5 ratios. Characteristics of the films such as pH of aqueous slurry, pH of zero-point charge (pHzpc), surface area and pore volume, energy dispersive X-ray spectroscopy (EDX), Field Emission - Scanning Electron Microscopy (FE-SEM), Fourier transform infrared (FTIR) were investigated. Factors influencing adsorption performance such as pH of the solution, metal ion concentration, adsorbent dosage and the DAC content were studied. Batch studies, investigating film adsorption capacity and adsorption isotherms for Pb(II), Hg(II) and Cu(II) ion adsorption equilibrium correlated well with Langmuir model. The maximum capacity for the adsorption of Pb(II), Hg(II) and Cu(II) ions calculated from the Langmuir isotherm was 256, 200 and 143 mg/g respectively. Compared with the pure non-grafted chitosan films, the azacrown ether films were proved to have better sorption performance for the Pb(II), Hg(II) and Cu(II) ions at pH 5 to 6.

Removal of Pb(II) ion by activated carbon synthesised from Musa Acuminate stem waste: surface properties, kinetics, adsorption mechanism, and reusability

ABSTRACT We present the synthesis of Activated Carbon (AC) by pyrolysis of Banana (Musa Acuminate) Stem Waste (BSW), and the ability of obtained AC for adsorptive removal of Pb(II) ions from water. Importantly, pyrolysis was performed at 750°C for 2.0 h in the presence of high surface area producing chemical activators such as NaOH, LiOH, H3PO4, ZnCl2, and KOH. BET-surface areas of AC produced with activators NaOH, LiOH, H3PO4, ZnCl2, and KOH were determined to be 908, 1531, 1670, 2245, and 2485 m2 g−1, respectively. Pore volume ascending order was determined as 0.59 (NaOH) < 0.68 (LiOH) < 0.86 (H3PO4) < 0.97 (ZnCl2) <1.18 (KOH) cm3 g−1. SEM and TEM images revealed the porous nature of the ACs. ACs produced with H3PO4, ZnCl2, and KOH exhibit type I adsorption isotherms, indicating their microporous nature. ACs prepared with NaOH and LiOH exhibit type II adsorption isotherms, indicating their macroporous nature. X-ray diffraction, X-Ray photoelectron, and Raman spectroscopy analysis revealed the graphitic structure of ACs. Pb(II) ion adsorption onto ACs surface obeyed the Langmuir model. It was found that the Pb(II) adsorption capacities of the ACs produced with NaOH, LiOH, H3PO4, ZnCl2, and KOH as the chemical activators were 220, 283, 326, 329, and 435 mg g−1, respectively, at the optimised conditions (pH = 6.6, contact time = 100 min, [ACs] = 0.125 g L−1, at 30°C). The interaction between surface functional groups of ACs and Pb(II) ions was confirmed by X-Ray photoelectron and FT-Infrared spectroscopy. The negative values of ΔGo and ΔHo reveal that the Pb(II) ion adsorption onto the ACs surface is spontaneous and exothermic. The Pb(II) ion adsorption capacity increased with an increase in BET-SA and pore volume of ACs, with AC obtained from BSW with KOH exhibiting the highest adsorption capacity of 435 mg g−1. Thus, the study highlights BSW, agricultural biomass waste is a low-cost and abundantly available carbon precursor to synthesise potential AC adsorbent for water treatment.

Removal of heavy metal ions with magnetic carbon prepared from corncob biomass

Four novel magnetic-activated carbons (MACs) were prepared, characterized, and used as adsorbents to remove heavy metal ions from wastewater samples. The MACs prepared, are advanced adsorbents for the removal of Hg(II), Cr(III), Cd(II), and Pb(II). The nature of the acid, amount, composition of the MACs, and the remotion time were evaluated in aqueous solutions. The ions removal percentages obtained, under the best conditions, were 93% for Hg(II) and higher than 99% for Pb(II), Cr(III), and Cd(II) (100 mg L-1, initial concentration in solution), with 100 mg of the MAC-3 in HNO3 3 mM. The capacity of the best adsorbent, MAC-3, for removing heavy metals ions Hg(II), Cr(III), Cd(II), and Pb(II) was studied using Langmuir and Freundlich adsorption isotherms under the best condition. The maximum adsorption capacities of Hg(II), Cr(III), Cd(II), and Pb(II) were found to be 10.72, 11.51, 11.49 and 11.49 mg g−1, the values of constants of Freundlich models were 17.98, 26.83, 9.18, and 7.18 mg g−1 respectively. For Hg(II) and Pb(II) the correlation factor (R2) was better for Freundlich model, while Cr(III) and Cd(II) showed better R2 with Langmuir model. Finally, the treatment for the elimination of heavy metal ions was carried out, with wastewater samples of industrial and domestic origin, and used for crop irrigation. The samples were collected in Irrigation District 003, Hidalgo, Mexico. The MAC-3 removes heavy metal ions from the wastewater matrix above 99%.

Sodium humate based double network hydrogel for Cu and Pb removal

Sodium humate (SH) is one of the derivatives humic substances, which can be utilized for heavy metal removal from water due to its containing plenty of functional groups. In this study, a double network hydrogel SH/polyacrylamide (SH/PAM) was synthesized by a simple free-radical polymerization and used for Cu2+ and Pb2+ removal from water. The adsorption process can be well described by Langmuir-Freundlich model, indicating that both physical and chemical adsorption were involved. X-ray photoelectron spectroscopy (XPS) characterization demonstrated that complexation was the main mechanism for the adsorption. Two-dimensional correlation analysis of FTIR (2D-FTIR-COS) results showed that the variation order of functional groups during Cu2+ and Pb2+ adsorption in the following order: COOH ≈ –CO > –OH > C–O and –COOH ≈ C–O > –CO > –OH, respectively. According to the density functional theory (DFT) calculation results, the O atom of SH in the COO− was the main adsorption site. Meanwhile, the adsorption energy of Pb2+ was more negative than that of Cu2+ and the orbital hybridization between O atom of SH and Pb2+ was denser than that of Cu2+, which suggested that SH/PAM had a stronger combining capacity for Pb2+ than Cu2+. Therefore, the adsorption capacity for Pb2+ was larger than Cu2+. Moreover, the removal efficiencies are 30.2% for Al, 98.79% for Cu, 99.0% for Fe, 17.2% for Mn, 93.4% for Pb, and 62.4% for Zn in actual acid mine drainage using 6 g L−1 adsorbent. Collectively, this study not only provided a new adsorbent for heavy metal removal but also explicated the mechanism of heavy metal removal by SH from molecule and electron perspective, which is helpful for the application of SH in the environmental field.

Simultaneous Removal of Metal Ions from Wastewater by a Greener Approach

The examination of the performance of raw and immobilized S. (Saccharomyces) cerevisiae in the simultaneous abatement of metal ions from wastewater effluent is the focal point of this article. The optimal storage time for raw and immobilized S. cerevisiae, during which they can be utilized, was estimated. The outcomes revealed that as the initial metal ion concentrations increased, the adsorption capacity improved, while the removal efficiency of S. cerevisiae yeast cells decreased, with the highest uptake obtained at the optimal conditions: pH = 5.0, 2.0 g S. cerevisiae/L, 25 °C, and a contact time of 25 min. The maximum adsorption capacities (qmax) for Pb(II), Cd(II), and Ni(II) ions are shown by Langmuir at 65, 90, and 51 mg/g, respectively. It was discovered that the metal ions’ biosorption reactions were spontaneous and were fitted by the pseudo-second-order model. The mechanisms of the metal ions’ abatement were explained by using XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), (BET) Brunauer–Emmett–Teller, and TEM (transmission electron microscopy) outputs. EDTA and citric acid can eliminate more than 70 ± 4 and 90 ± 5% of the adsorbed ions, respectively. The experiment of storage demonstrated that the immobilized S. cerevisiae was more stable for 8 months than the raw yeast.

Removal of Lead Ions (Pb&lt;sup&gt;2+&lt;/sup&gt;) Using Acid-Activated Clay from East Kalimantan

This study aims to determine the optimal conditions of acid-activated clay adsorbent in adsorption of Pb2+ metal ions. Clay was taken around East Kalimantan, Karang Joang. This adsorbent was prepared by mixing clay into a solution of KMnO4, H2SO4 and HCl successively, and stirred for 4 hours at a temperature of 80°C. The morphology and active groups of the adsorbent were analyzed using BET and FTIR. The variables of this study were the mass of the adsorbent 0.1, 0.3 and 0.5 grams and the contact time of 5, 30 and 55 minutes. Adsorption capacity of this adsorbent was analyzed using Atomic Absorption Spectrophotometry (AAS). The results of this study indicate that the optimum mass of adsorbent is 0.1 g, and contact time is 30 minutes. Adsorption capacity of Pb2+ metal ions by acid-activated clay adsorbent at the optimum condition of 0.1 gram was 23,585 mg/g and adsorption energy was 2,338 kJ/mol. Meanwhile, at the optimum condition for 30 minutes, the adsorption capacity was 0.771 mg/L, and the adsorption energy was 2.895 kJ/mol. So that the adsorption process in this study can be known, namely physical adsorption because the adsorption energy value is less than 40 kJ/mol.

Insights into the heavy metal adsorption and immobilization mechanisms of CaFe-layered double hydroxide corn straw biochar: Synthesis and application in a combined heavy metal-contaminated environment

Biochar is an emerging eco-friendly and high-efficiency heavy metal (HM) adsorbent that exhibits satisfactory HM remediation effects in both water and soil environments. However, few studies have investigated the mechanisms and application of biochar in the remediation of combined HM-contaminated environments. Therefore, in the present study, a novel corn straw biochar-loaded calcium-iron layered double hydroxide composite (CaFe-LDH@CSB) was synthesized via the coprecipitation method and applied as a remediation adsorbent to remove HMs in both water and soil environments. The results indicated that the HM adsorption mechanism of CaFe-LDH@CSB in the aquatic phase involved a chemical endothermic adsorption process of functional group-complexed monolayers, dominated by precipitation, ion exchange, complexation and π bond interactions. The maximum adsorption capacity for Cd(II), Pb(II), Zn(II) and Cu(II) in the aqueous phase reached 24.58, 240.96, 57.57 and 39.35 mg g−1, respectively. In addition, application of CaFe-LDH@CSB in the combined HM-contaminated soil treatment helped to increase the soil pH, which increased by 5.1–17.9% in low-contamination (LC) soil and by 7.0–13.9% in high-contamination (HC) soil. Moreover, application of CaFe-LDH@CSB effectively decreased the acid-soluble fraction of HMs and increased the HM residual fraction. The immobilization mechanism of CaFe-LDH@CSB in the soil was concluded to involve pore filling, functional group action and electrostatic interactions. Overall, this study provided a novel LDH biochar composite that can be effectively applied in the remediation of combined HM-contaminated water and soil environments.

Pb(II) adsorption by biochar from co-pyrolysis of corn stalks and alkali-fused fly ash

AbstractNumerous studies have reported the potential of silica as a biochar (BC) modifier. However, despite its high silica content, fly ash is rarely used for BC modification. Herein, modified BCs were produced by co-pyrolysis of corn stalks with alkali-fused fly ash (AFFA) at 200 and 600 °C (denoted as AFFA/BC). The Pb(II) adsorption mechanism and adsorption performance were investigated. The AFFA/BC had larger specific surface areas than the pure BC samples (2.54–137 vs. 0.50 m2 g−1) owing to their stable carbon structure. The Pb(II) adsorption capacity of AFFA/BC in water was approximately 6% higher than that of BC owing to the increased cation (Na+) exchange and new bonding sites, such as C–O and Si–O. AFFA/BC exhibited good Pb(II) adsorption performance in high-concentration simulated wastewater (pH 4–6), with a maximum adsorption capacity of 110.29 mg g−1. The Pb(II) adsorption mechanism was in accordance with the pseudo-second-order kinetic and Langmuir isotherm models. At 25 °C and pH 5, the theoretical Pb(II) adsorption capacities of AFFA200/BC and AFFA600/BC were 201.66 and 186.81 mg g−1, respectively, compared to 145.98 mg g−1 of BC. Physical adsorption, precipitation, cation exchange, and complexation were identified as the main Pb(II) adsorption mechanisms through X-ray photoelectron spectrometry. Graphical Abstract

Comparative study on high-efficiency Pb(II) removal from aqueous solutions using coal and rice husk based humic acids

Different sources of humic acids (HAs) have been reported as promising adsorbents for the removal of heavy metals from wastewater. However, comparative studies on the characteristics and adsorption mechanisms of HAs from different sources are not comprehensive. In this study, commercial mineral- and biological-HAs (CHA and BHA) were prepared from coal and rice husk. Their adsorption effects and mechanisms on Pb(II) were studied and compared through batch adsorption tests, elemental analyses, Zeta potential, BET analysis, SEM, EDS, XRD patterns, and XPS spectrum. Adsorption isotherm data of CHA and BHA were more fitted to the Langmuir model and showed their high Pb(II) adsorption capacities were 229.9 and 221.6 mg/g, respectively. The best fit of the pseudo-second-order kinetic model demonstrated the efficient Pb(II) adsorption by CHA and BHA, the adsorption equilibrium was reached at 20 and 40 min, respectively. Furthermore, desorption rates of both CHA and BHA could reach 70 % at pH = 2.0, which promoted the regeneration and recycling of adsorbents. The common adsorption mechanisms of CHA and BHA are electrostatic interaction, surface complexation, and ion exchange, besides, π-π interaction is of great significance to BHA. Overall, CHA and BHA have promising applications for the removal of Pb(II) because of their resource utilization, high cost-efficiency, and environmental friendliness.

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.

Overlooked mechanism of Pb immobilization on montmorillonite mediated by dissolved organic matter in manure compost

In this study, three kinds of dissolved organic matter (DOM) derived from fresh chicken manure (FDOM), immature compost (IDOM) and mature compost (MDOM) were employed to compare their effects on Pb adsorption onto montmorillonite (MMT). The potential mechanism was revealed by characterization of mineral structure and calculation of interface force. The results demonstrated that the adsorption capacity (qmax) of Pb onto MMT was decreased by 14.3% and 29.8% in the presence of FDOM and IDOM, respectively, while increased by 44.4% in the presence of MDOM, resulting from the release or co-adsorption of DOM-Pb complexes. Parallel factor (PARAFAC) further indicated that Pb mainly bound to protein-like substances in FDOM and IDOM, and fulvic-like in MDOM. The X-ray diffraction (XRD) analysis proved that MDOM-Pb complex had a stronger ability to enter into the interlayer of MMT. The van der Waals force dominated the adsorption of FDOM-Pb and IDOM-Pb, while ligand exchange was involved in the case of MDOM-Pb. This study provided a comprehensive insight into the geochemical behavior of livestock manure and its compost as well as their interactions with heavy metal and soil mineral.

Preparation and Application of a Magnetic Oxidized Micro/Mesoporous Carbon with Efficient Adsorption for Cu(II) and Pb(II).

Water pollution is a worldwide problem that requires urgent attention and prevention and exceeding use of heavy-metal ions is one of the most harmful factors, which poses a serious threat to human health and the ecological environment. In this work, a magnetic oxidized micro/mesoporous carbon (MOMMC) was prepared for the easy separation of Cu(II) and Pb(II) from water. The dual-template method was used to prepare micro/mesoporous carbon using sucrose as the carbon source, silica nanoparticles formed by tetraethyl orthosilicate as the microporous templates, and triblock copolymer F127 as the mesoporous template. MOMMC was obtained by oxidation using potassium persulfate and then magnetized through in situ synthesis of Fe3O4 nanoparticles. FTIR, TG-DSC, XRD, TEM, SEM, nitrogen adsorption-desorption isotherms, zeta potential, and VSM were used to confirm the synthetic process, structure, and basic properties of MOMMC. The high-saturation magnetization (59.6 emu·g-1) of MOMMC indicated its easy and fast separation from water by an external magnetic field. Kinetics studies showed that the adsorption of Cu(II) and Pb(II) on MOMMC fit the pseudo-second-order model well. Isotherm studies showed that the adsorption behavior of Cu(II) was better described by the Langmuir model, and the adsorption behavior of Pb(II) was better described by both Langmuir and Redlich-Peterson models. MOMMC obtained efficient adsorption for Cu(II) and Pb(II) with the large adsorption capacity of 877.19 and 943.40 mg·g-1 according to the Langmuir adsorption isotherm equation, and a better selectivity for Pb(II) was observed in competitive adsorption. MOMMC still possessed a large adsorption capacity for Cu(II) and Pb(II) after three adsorption-desorption cycles. These findings show that MOMMC represents an excellent adsorption material for the efficient removal of heavy-metal ions.

Highly efficient preferential adsorption of Pb(II) and Cd(II) from aqueous solution using sodium lignosulfonate modified illite.

In this study, sodium lignosulfonate modified illite (LS-ILT), an environmentally friendly adsorbent, was prepared by hydrothermal modification. An extensive study of Pb(II) and Cd(II) adsorption behavior and the mechanisms were conducted by evaluating the effects of initial pH value, sorbents dosage, and initial concentration of Pb(II) and Cd(II). Results showed that the adsorption characteristics of Pb(II) and Cd(II) by LS-ILT were well described by quasi-second-order kinetics and the Freundlich model, and the maximum adsorption capacity of Pb(II) and Cd(II) was 42.3mg/g and 17.0mg/g, respectively. The optimal application conditions for adsorption equilibrium were the dosage of 4g/L and reaction pH = 5.5-5.8. The adsorption stability of Pb(II) by LS-ILT was better than that of Cd(II), and most of the existence of coexisting cations had no obvious inhibitory effect on the removal of Pb(II) and Cd(II). Furthermore, the dynamic adsorption results showed that LS-ILT can meet the ultra-low emission standard, and the adsorption capacity could maintain over 50% after four cycles, further providing certain guiding significance for the treatment of wastewater with ultra-low concentrations of heavy metals Pb(II) and Cd(II).

Graphene oxide-based novel MOF nanohybrid for synergic removal of Pb (II) ions from aqueous solutions: Simulation and adsorption studies

Heavy metals represent a considerable threat, and the current study deals with synthesizing a novel MOF nanocomposite by intercalating graphene oxide (GO) and linker UiO-66-NDC. It was shown that UiO-66-NDC/GO had enhanced the removal efficiency of Pb (II) ions at pH 6. The adsorption kinetics data followed the PSO (Type 2) representing chemisorption. Adsorption data were also fitted with three different isotherms, namely Temkin, Freundlich, & Langmuir, and the Temkin model exhibited the best correlation (R2 0.99), representing the chemisorption nature of the adsorption process. The maximum adsorption capacity (qmax) of Pb (II) ions using Langmuir was found to be 254.45 mg/g (298 K). The Pb (II) adsorption process was confirmed to be exothermic and spontaneous as the thermodynamic parameters H° and G° were determined to have negative values. MOF nanocomposite also represents significant reusability for up to four regeneration cycles using 0.01 M HCl; for the next four, it works quite efficiently after regeneration. Meanwhile, the simulation findings confirm the superior dynamic stability (∼08 times) of the MOF nanocomposite as compared to the GO system. The removal of Pb (II) from simulated wastewater samples using a super nano-adsorbent using a MOF nanocomposite is described here for the first time.

Unrolling the tubes of halloysite to form dickite and its application in heavy metal ions removal

Aluminol groups are effective for removing toxic metal ions. However, their use is significantly limited because they are usually on the inner surface of halloysite tubes. Herein, we realign and expose the abundant aluminol groups using a hydrothermal process. We found that dickite was gradually formed with increased sodium metasilicate proportion. Also, a uniform mushroom-like structure was formed, extending from the orifice to the middle of the hollow tubes and eventually forming a sphere. Further, part of the halloysite tube gradually broke, expanding into lamellar, eventually forming a small spheroid. The Al-O-Si groups were fractured by sodium metasilicate and aluminol groups on the inner surface of halloysite tubes, forming many aluminol groups. Moreover, the average pore size of the halloysite increased, indicating that numerous halloysite mesopores converted to dickite macropores. Thus, we inferred that the tubes gradually unfolded when the metasilicate first binds with the aluminol groups on the inner of the halloysite tubes. The modification enhanced the material's adsorption capacity for Pb2+, Cd2+, and Cr3+ nearly 20, 12, and 10 times, respectively, stronger than the original halloysite mineral. Consequently, exposing and realigning aluminol groups of halloysite significantly improved toxic metal ions' removal.

High performance nanohybrid ZnO-α-FeOOH nanocomposite prepared for toxic metal ions removal from wastewater: Combined sorption and desorption studies

ZnO-α-FeOOH Nanohybrid (NH) was synthesized from zinc nitrate hexahydrate and hydrothermally synthesized α-FeOOH nanoparticles. X-ray diffraction (XRD) confirmed the composition, while Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) methods were used to determine the functional groups, morphology, crystallinity and particle sizes of the synthesized mineral respectively. The results showed crystalline material in spherical shape with some rod-like structures embedded in the structures. The average sizes was determined from DLS as 41.11 nm. The NH was used in batch mode at different experimental conditions, and optimum adsorption capacity of Cd(II) and Pb(II) onto the NH were 279.2 mg/g and 538.9. mg/g at pH 6 in 180 min at 318 K. The Langmuir isotherm and pseudo-second-order models fitted well for the adsorption process. The negative values of ΔG◦ indicated spontaneity of the adsorption process, while the positive values of ΔH (+12.48 and +15.85 kJ/mol) and ΔS (+0.418 and +0.536 kJ/mol/K) for Cd(II) and Pb(II) respectively, revealed endothermic and randomness of the adsorption process. The activation energy, Ea, were found to be +7.982 and +4.771 kJ/mol for adsorption of Cd(II) and Pb(II) respectively, which showed that adsorption onto ZnO-α-FeOOH NH were physical process (Ea < +40 kJ/mol). The adsorption–desorption studies revealed that the adsorption efficiency of ZnO-α-FeOOH NH in the third cycles were 90.18 % and 93.87 % Cd(II) and Pb(II) respectively. These suggest that the adsorbent could be reused in up to three cycles without remarkable losses in its adsorption capacity.

Green Ambient-Dried Aerogels with a Facile pH-Tunable Surface Charge for Adsorption of Cationic and Anionic Contaminants with High Selectivity.

The fabrication of reusable, sustainable adsorbents from low-cost, renewable resources via energy efficient methods is challenging. This paper presents wet-stable, carboxymethylated cellulose nanofibril (CNF) and amyloid nanofibril (ANF) based aerogel-like adsorbents prepared through efficient and green processes for the removal of metal ions and dyes from water. The aerogels exhibit tunable densities (18-28 kg m-3), wet resilience, and an interconnected porous structure (99% porosity), with a pH controllable surface charge for adsorption of both cationic (methylene blue and Pb(II)) and anionic (brilliant blue, congo red, and Cr(VI)) model contaminants. The Langmuir saturation adsorption capacity of the aerogel was calculated to be 68, 79, and 42 mg g-1 for brilliant blue, Pb(II), and Cr(VI), respectively. Adsorption kinetic studies for the adsorption of brilliant blue as a model contaminant demonstrated that a pseudo-second-order model best fitted the experimental data and that an intraparticle diffusion model suggests that there are three adsorption stages in the adsorption of brilliant blue on the aerogel. Following three cycles of adsorption and regeneration, the aerogels maintained nearly 97 and 96% of their adsorption capacity for methylene blue and Pb(II) as cationic contaminants and 89 and 80% for brilliant blue and Cr(VI) as anionic contaminants. Moreover, the aerogels showed remarkable selectivity for Pb(II) in the presence of calcium and magnesium as background ions, with a selectivity coefficient more than 2 orders of magnitude higher than calcium and magnesium. Overall, the energy-efficient and sustainable fabrication procedure, along with good structural stability, reusability, and selectivity, makes these aerogels very promising for water purification applications.

Design of bionic amphoteric adsorbent based on reed root loaded with amino-functionalized magnetic nanoparticles for heavy metal ions removal

Renewable and cheap reed roots are rich in polysaccharide and lignin and naturally possesses wastewater purification ability. However, if applied as industrial adsorbent, the active sites of reed roots need further enhancement to fit realistic amphoteric ion adsorption requirement and its recovery also request for optimization to avert secondary pollution caused by adsorbent residues. Under this background, a novel adsorbent based on reed root loaded with magnetic amino-functionalized nanoparticles (RrH@Fe3O4 @SiO2-NH2) with a bionic dendritic structure and a pleated surface was designed. The reed roots were firstly pretreated with hydrogen peroxide solution with strong oxidizing properties under UV light irradiation to expose more oxygen-containing functional groups, which then condensed with the amino groups on the surface of Fe3O4 @SiO2-NH2 nanoparticles, leading to the formation of the final adsorbent. The carboxyl, hydroxyl and methoxy and amino groups on the surface of the adsorbent synergistically contribute to the adsorption of both anions and cations. The maximum adsorption capacity for Pb (II) and Cr (VI) ions per unit mass of reed root in RrH@Fe3O4 @SiO2-NH2 reached 99.1 and 106.5 mg g− 1, much higher than those obtained with raw reed roots (24.8 and 30.6 mg g−1). The superior adsorption performance was ascribed to its physicochemical properties as characterized by a series of characterization methods. The adsorption process followed pseudo-second-order kinetic and Freundlich isotherm model, indicating a chemical multi-layer endothermic adsorption process. The addition of magnetic Fe3O4 endows the easy recovery of the adsorbent by applying a magnetic field, and after five cycles, the adsorption capacity can still reach 82% of that of the first time. In summary, the desirable adsorption performance, easy recovery, and low cost make the bionic RrH@Fe3O4 @SiO2-NH2 a promising amphoteric adsorbent for eliminating heavy metal ions from wastewater.