Comparative study on synchronous adsorption of arsenate and fluoride in aqueous solution onto MgAlFe-LDHs with different intercalating anions

In this study, a series of MgAlFe-LDHs (Cl⁻, NO₃⁻, intercalation, and calcined products of a CO₃²⁻ interlayer) was synthesized and used for adsorption of arsenate and fluoride in individual contaminants and coexisting pollutant systems. Effects of various factors such as initial pH of solution, dosage of materials, coexisting ions, contact time, and initial pollutant concentrations were evaluated. Experimental results showed that different intercalating anions had a significant effect on adsorption performance of arsenate and fluoride in water. The adsorption of arsenate and fluoride on MgAlFe-CLDH, MgAlFe–Cl-LDH or MgAlFe–NO₃-LDH can be described by different adsorption isotherm equations. During the simultaneous removal process, arsenate and fluoride competed for adsorption sites of the adsorbent materials, and the fluoride ions had advantages in the competitive adsorption on MgAlFe–Cl-LDH and MgAlFe–NO₃-LDH. MgAlFe–NO₃-LDH was used to adsorb arsenate and fluoride in coexisting pollution systems (the concentration of each pollutant was 2 mg L⁻¹, the adsorbent dosage was 1.5 g L⁻¹). The remaining arsenic concentration was reduced to less than 10 μg L⁻¹ and the remaining fluoride ion concentration to below 20 μg L⁻¹ which meets the World Health Organization''s, EPA''s and China''s drinking water standards for arsenic and fluoride limits. A possible mechanism is discussed with support from further XRD, SEM, and XPS analysis of the materials after their adsorption.

During the simultaneous removal process, arsenate and fluoride competed for the adsorption sites of the adsorbent materials.     

Quantification and isotherm modelling of competitive phosphate and silicate adsorption onto micro-sized granular ferric hydroxide

Adsorption onto ferric hydroxide is a known method to reach very low residual phosphate concentrations. Silicate is omnipresent in surface and industrial waters and reduces the adsorption capacity of ferric hydroxides. The present article focusses on the influences of silicate concentration and contact time on the adsorption of phosphate to a micro-sized iron hydroxide adsorbent (μGFH) and fits adsorption data to multi-component adsorption isotherms. In Berlin drinking water (DOC of approx. 4 mg L⁻¹) at pH 7.0, loadings of 24 mg g⁻¹ P (with 3 mg L⁻¹ initial PO₄³⁻–P) and 17 mg L⁻¹ Si (with 9 mg L⁻¹ initial Si) were reached. In deionized water, phosphate shows a high percentage of reversible bonds to μGFH while silicate adsorption is not reversible probably due to polymerization. Depending on the initial silicate concentration, phosphate loadings are reduced by 27, 33 and 47% (for equilibrium concentrations of 1.5 mg L⁻¹) for 9, 14 and 22 mg L⁻¹ Si respectively. Out of eight tested multi-component adsorption models, the Extended Freundlich Model Isotherm (EFMI) describes the simultaneous adsorption of phosphate and silicate best. Thus, providing the means to predict and control phosphate removal. Longer contact times of the adsorbent with silicate prior to addition of phosphate reduce phosphate adsorption significantly. Compared to 7 days of contact with silicate (c₀ = 10 mg L⁻¹) prior to phosphate (c₀ = 3 mg L⁻¹) addition, 28 and 56 days reduce the μGFH capacity for phosphate by 21 and 43%, respectively.

Adsorption of phosphate onto ferric hydroxide in complex waters is influenced by effects of competition, displacement and surface blockage.     

Activated carbons derived from hydrothermal impregnation of sucrose with phosphoric acid: remarkable adsorbents for sulfamethoxazole removal

A series of activated carbons with surface areas of 925–1929 m² g⁻¹ were synthesized by in situ hydrothermal impregnation of sucrose with H₃PO₄ and subsequent calcination at 500–900 °C. The prepared various types of activated carbons were utilized for the removal of sulfamethoxazole (SMX) from its solution by adsorption, and the effects of contact time, adsorbent dosage, initial concentration, adsorption temperature and pH on SMX adsorption were studied. The pseudo-second-order and the intra-particle diffusion model were used to analyze the adsorption kinetic data. The adsorption isotherm studies showed that the activated carbon prepared at 900 °C (C-900) showed the highest Langmuir maximum adsorption capacity of 808.7 mg g⁻¹ among them, much higher than that of C-500 (274.0 mg g⁻¹). Adsorption thermodynamic results showed that the adsorption of SMX was a spontaneous exothermic process, with a standard enthalpy change of −6.59 kJ mol⁻¹ and a standard entropy change of 47.7 J mol⁻¹ K⁻¹. It was deduced that hydrophobic, electron donor–acceptor and electrostatic interactions were involved in the adsorption mechanism. Finally, regeneration experiments showed that more than 90% of the adsorption capacity could be recovered after four cycles through ethanol washing. Considering the remarkable and regenerable adsorption ability as well as the economic and environmental merits, these activated carbons are considered as promising candidates for potential practical applications in adsorptive removal of SMX.

Activated carbons obtained by hydrothermal impregnation of sucrose with H₃PO₄ for highly efficient sulfamethoxazole adsorption.     

Characterization of CMC–LDH beads and their application in the removal of Cr(vi) from aqueous solution

In this study, CMC–LDH beads were prepared and characterized using SEM, FTIR and TG analysis. The beads were applied for the removal of Cr(vi) from aqueous solution. The effects of adsorbent dosage, initial pH and initial concentration of Cr(vi) solution on Cr(vi) uptake were investigated in detail. Moreover, adsorption isotherms and adsorption kinetic models were employed to analyze the adsorption process, and a preliminary study of the reusability of the adsorbent was performed. The experimental results showed that the CMC–LDH beads could remove Cr(vi) from aqueous solution efficiently. When the initial concentration of the Cr(vi) solution was 100 mg L⁻¹ and the adsorbent dosage was 12 g L⁻¹, the removal efficiency of Cr(vi) reached 96.2%. After the CMC–LDH beads were reused 10 times, the removal efficiency of Cr(vi) still remained at 89.6%.

CMC–LDH beads were prepared, characterized and applied for the removal of heavy metal ions in this study.     

Sulfated zirconium oxide-decorated magnetite KCC-1 as a durable and recyclable adsorbent for the efficient removal of asphaltene from crude oil

Sulfated zirconium oxide (ZrO₂/SO₄²⁻) as a highly durable acidic reagent was immobilized on magnetite KCC-1 nanoparticles (Fe₃O₄@SiO₂/KCC-1@ZrO₂/SO₄²⁻ NPs), and the resulting hybrid was used as a highly efficient recyclable adsorbent for the adsorption and removal of asphaltene from crude oil. The presence of ZrO₂/SO₄²⁻ groups not only promotes the adsorption capacity, but also helps recycle the adsorbents without any significant efficiency loss arising from its high chemical resistance. The results showed an obvious synergistic effect between the magnetic core (Fe₃O₄ NPs), fibrous silica (KCC-1) and the sulfated zirconium oxide groups with high correlation for asphaltene adsorption. The effective parameters in asphaltene adsorption, including initial asphaltene concentration, catalyst concentration and temperature, were investigated. Maximum adsorption occurred in the presence of 0.7 g L⁻¹ of the adsorbent, at a concentration of 2000 mg L⁻¹ of asphaltene. The asphaltene adsorption by NPs follows a quasi-second order adsorption kinetics. Asphaltene adsorption kinetics were studied by Langmuir, Freundlich, and Temkin isotherms. The prominent advantage of the adsorbent is its ability to be recovered after each adsorption by acid treatment, so that no significant reduction in adsorbent adsorption activity was observed, which can be directly attributed to the presence of ZrO₂/SO₄²⁻ groups in the hybrid.

A new, efficient and recyclable hybrid based on immobilized sulfated zirconium oxide on magnetite fibrous silica (KCC-1) has been developed and utilized for the efficient adsorption and removal of asphaltene from crude oil.     

Preparation,characterization serpentine-loaded hydroxyapatite and its simultaneous removal performance for fluoride,iron and manganese

Aiming at the problem of excessive fluorine, iron, and manganese pollution in groundwater in mining areas, a serpentine-loaded hydroxyapatite (Srp/HAP) composite adsorbent was prepared by wet chemical coprecipitation. The preparation conditions of the Srp/HAP composite adsorbent were explored, Srp/HAP was microscopically characterized, and the adsorption performance and adsorption mechanism of the Srp/HAP composite adsorbent for F⁻, Fe²⁺ and Mn²⁺ were analyzed. The results showed that the optimal preparation conditions for the composite particles were as follows: solid–liquid ratio of Srp to calcium nitrate solution 20%, aging time 20 h, calcination temperature 180 °C, and calcination time 90 min. Compact Srp/HAP composite adsorbent particles were successfully prepared, and both the lamellar crimp structure of the Srp surface and the problem of HAP surface agglomeration were resolved. After loading, the specific surface area and pore volume of the particles significantly increased, and the surface pore structure improved, which is conducive to the simultaneous adsorption and removal of fluorine, iron and manganese. The optimal reaction conditions for Srp/HAP treatment of composite water samples with F⁻, Fe²⁺ and Mn²⁺ mass concentrations of 5 mg L⁻¹, 20 mg L⁻¹ and 5 mg L⁻¹, respectively, are as follows: dosage of Srp/HAP 3 g L⁻¹, pH 7, temperature 35 °C, and reaction time 150 min. Under these conditions, the removal rates of F⁻, Fe²⁺ and Mn²⁺ were 98.6%, 99.9% and 99.8%, respectively. The quasi-second-order kinetic model and Langmuir isothermal adsorption model described the adsorption process of F⁻, Fe²⁺ and Mn²⁺ by the composite particles well. The adsorption process includes both surface physical adsorption and chemical adsorption. Chemical adsorption is mainly characterized by ion exchange and surface complexation. The Srp/HAP composite particles can be used as an excellent adsorbent for the treatment of groundwater containing fluorine, iron and manganese ions in mining areas.

A new adsorbent Srp/HAP for simultaneous removal of fluoride, iron and manganese was prepared, characterized and analyzed.     

Novel easily separable core–shell Fe3O4/PVP/ZIF-8 nanostructure adsorbent: optimization of phosphorus removal from Fosfomycin pharmaceutical wastewater

A new easily separable core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent was synthesized and then examined for removal of Fosfomycin antibiotic from synthetic pharmaceutical wastewater. The removal process of Fosfomycin was expressed through testing the total phosphorus (TP). A response surface model (RSM) for Fosfomycin adsorption (as mg-P L⁻¹) was used by carrying out the experiments using a central composite design. The adsorption model showed that Fosfomycin adsorption is directly proportional to core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent dosage and time, and indirectly to initial Fosfomycin concentration. The removal increased by decreasing the pH to 2. The Fosfomycin removal was done at room temperature under an orbital agitation speed of 250 rpm. The adsorption capacity of core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent reached around 1200 mg-P g⁻¹, which is significantly higher than other MOF adsorbents reported in the literature. The maximum Langmuir adsorption capacity of the adsorbent for Fosfomycin was 126.58 mg g⁻¹ and Fosfomycin adsorption behavior followed the Freundlich isotherm (R² = 0.9505) in the present study. The kinetics was best fitted by the pseudo-second-order model (R² = 0.9764). The RSM model was used for the adsorption process in different target modes.

The synthesis of an easily separable novel core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent and its usage for Fosfomycin pharmaceutical wastewater treatment.     

Fast adsorption of methylene blue,basic fuchsin,and malachite green by a novel sulfonic-grafted triptycene-based porous organic polymer

In this study, a novel triptycene-based porous polymer grafted with sulfonic acid (TPP-SO₃H) was successfully synthesized by the post-synthetic modification of the non-functionalized polymer TPP. The polymer TPP-SO₃H was well-characterized and was found to be a fast and effective absorbent for the cationic dyes methylene blue (MEB), basic fuchsin (BF), and malachite green (MG), with over 95% removal being observed within 10 min from initial concentrations of 100 mg L⁻¹, 100 mg L⁻¹, and 300 mg L⁻¹, respectively. The adsorption process for MEB, BF, and MG was pH-dependent. The adsorption behaviours for MEB, BF, and MG follow pseudo-second-order kinetics and fit the Langmuir model. Moreover, the maximum adsorption capacities of MEB, BF, and MG at room temperature were 981.8 mg g⁻¹, 586.2 mg g⁻¹, and 1942.5 mg g⁻¹, respectively. It is worth noting that the values of the MEB, BF, and MG adsorption capacities on TPP-SO₃H were 5.5, 3, and 1.8 times that of the non-functionalized polymer TPP based on the same adsorbent weight. It is suggested that (i) there are strong electrostatic attractions between the sulfonic groups of the TPP-SO₃H and cationic dyes and (ii) the higher surface area and good porosity may contribute to the high dye adsorption capacity. Furthermore, TPP-SO₃H exhibited good cyclic stability, which can be regenerated at least five times without a significant loss of adsorption capacity. Therefore, the facile strategy synthesis, as well as the excellent adsorption capacity and reusability, make polymer TPP-SO₃H an attractive adsorbent for wastewater treatment.

In this study, a novel triptycene-based porous polymer grafted with sulfonic acid (TPP-SO₃H) was successfully synthesized by the post-synthetic modification of the non-functionalized polymer TPP.     

Enhancing the removal efficiency of methylene blue in water by fly ash via a modified adsorbent with alkaline thermal hydrolysis treatment

An effective adsorbent of methylene blue was synthesized from coal fly ash (FA; waste material from a coal power plant) by a denaturing process with an alkaline solution at 90 °C. The denatured fly ash (D-FA) has a surface area and pore volume of 66.39 m² g⁻¹ and 15.33 cm³ g⁻¹, respectively, whereas the values of the original FA are negligible, i.e., 3.55 m² g⁻¹ and 0.02 cm³ g⁻¹. The removal of methylene blue (MB) in aqueous solution by D-FA was increased in the range of initial MB concentration (10–20 mg L⁻¹); contact time (0–120 min); pH (2–8); D-FA dosage (1–4 g L⁻¹). However, a larger value of those operational parameters would not improve the removal activity. Furthermore, the methylene blue adsorption on the denatured FA was fitted with the Langmuir model with R² = 0.9991; the maximum adsorption capacity was determined as 28.65 mg g⁻¹ from the model. Overall, the highest removal efficiency of MB using D-FA with the dosage of 4 g L⁻¹ was 97.1% in 30 mg L⁻¹ solution of methylene blue at pH = 7. The alkaline hydrothermal denaturation of waste FA is a promising approach to produce an adsorbent with beneficial environmental engineering applications.

High efficiency of methylene blue adsorbent from waste coal fly ash by treatment with alkaline thermal hydrolysis.     

Adsorption of ng L−1-level arsenic by ZIF-8 nanoparticles: application to the monitoring of environmental water

The provisional contamination level of arsenic in drinking water is 10 μg L⁻¹. For decreasing this value to a safer level, a more precise method for analyzing dissolved arsenic is required. With this aim, we synthesized zeolitic imidazolate framework-8 (ZIF-8) in the aqueous phase and characterized its potential application for monitoring the trace arsenic in fresh water. In this regard, we report following three notable outcomes. First, we demonstrate the excellent performance of ZIF-8 nanoparticles (nZIF-8) for the adsorption of ng L⁻¹ levels of AsO₄³⁻. nZIF-8 is able to adsorb over 99% of arsenic from as low as 10 ng L⁻¹ AsO₄³⁻ solutions. This performance was maintained even in the presence of commonly coexisting anions, for example, >90% adsorption from a 0.1 μg L⁻¹ arsenic solution was observed in the presence of 10 mg L⁻¹ of Cl⁻, NO₃⁻, CO₃²⁻, or SO₄²⁻, or 1 mg L⁻¹ of PO₄³⁻. Second, we clarified that the mechanism of arsenic adsorption by ZIF-8 is simply a ligand exchange process, in which the As(v) oxide anion replaces the imidazolate unit in the framework. Third, we propose a handy scheme for the analysis of ng L⁻¹ levels of arsenic in drinking water, in which nZIF-8 is used for the concentration of trace level AsO₄³⁻. By doing this, as low as 100 ng L⁻¹ arsenate in drinking water can be quantified by colorimetric analysis, the detection limit of which is 5 μg L⁻¹ in pure water. The application of this scheme is expected to highly enhance AsO₄³⁻ detection first by concentrating it to an easily detectable range, and second by excluding the majority of interfering ions present in the system. Therefore, a reduction in the minimum quantifying limit of arsenic in fresh water to as low as 1 ng L⁻¹ can be expected if the method is coupled with ICP-MS.

ZIF-8 nanoparticles highly selectively uptakes ultra-trace concentration arsenate. The material can be used for high precision monitoring of the ion when coupled with handy analytical tools.     

Adsorptive,kinetics and regeneration studies of fluoride removal from water using zirconium-based metal organic frameworks

Fluoride contamination has been recognised as one of the major problems worldwide, imposing a serious threat to human health and affecting the safety of drinking water. Adsorption is one of the widely considered appropriate technologies for water defluorination. The present study describes the preparation of a zirconium-based metal organic framework (MOF-801) adsorbent using a solvothermal method and its adsorption efficiency for removal of fluoride ions from water. The morphology of MOF-801 was characterized by PXRD, FESEM and XPS, and the pore structure and surface area were calculated according to BET. It was found that the synthesized MOF-801 showed the distinguishable octahedral shape particle with a lattice spacing of 0.304 nm, indicative of (011) planes of ZrO₂. Adsorption studies were carried out to study the defluorination effectiveness by varying contact time (30–150 min), adsorbent dose (0.3–1.5 g L⁻¹), adsorbate concentration (5–25 mg L⁻¹), as well as kinetics and isotherms. The maximum removal efficiency for fluoride using MOF-801 at equilibrium was found to be 92.3%. Moreover, the adsorption kinetic studies indicate that the overall fluoride adsorption process was best described by pseudo-second-order kinetics. The adsorption data were well-fitted with the Langmuir isotherm model (R² = 0.9925) with maximum adsorption capacity of 19.42 mg g⁻¹. The synthesized MOF-801 had good reusability and was used in up to four cycles for fluoride removal attaining around 79% removal efficiency after the fourth cycle. All the results suggested that the synthesized MOF-801 has potential to be an excellent adsorbent for wastewater defluorination treatment.

A facile solvothermal method is used to prepare octahedral MOF-801 with a lattice spacing of 0.304 nm representative of ZrO₂ (011) planes for water defluorination.     

Synthesis and adsorption performance of La@ZIF-8 composite metal–organic frameworks

In this study, ZIF-8 with a rhombic dodecahedron structure was prepared by a hydrothermal method. Then La(OH)₃, was successfully loaded onto the ZIF-8 by an immersion deposition method, to form a lanthanide-based metal–organic framework (La@ZIF-8) composites. The structure and properties of La@ZIF-8 were verified by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and zeta potential measurements. The optimum process conditions are discussed within the materials and methods. The effects of initial phosphorus concentration, dosage, pH and contact reaction time on the phosphorus removal performance of the nanomaterial were investigated. The results indicated that La@ZIF-8 exhibited an excellent adsorption capacity (147.63 mg g⁻¹) and its phosphorus removal efficiency could reach as high as 99.7%. Experimental data were interpreted using different adsorption kinetic and isotherm models. The kinetic behavior conformed to the pseudo-second-order kinetic model, which indicated the chemisorption of phosphorus by La@ZIF-8. The adsorption behavior of phosphorus by La@ZIF-8 fitted well to the Langmuir isotherm model, suggesting a monolayer chemical adsorption process. The majority of the adsorbed phosphate could be desorbed by NaOH (2 mol L⁻¹), and the removal efficiency of the recycled La@ZIF-8 reached 90%, even after the fifth cycle. The obtained results demonstrate the great application potential of the prepared La@ZIF-8 as a fascinating adsorbent for the removal of phosphate.

In this study, La(OH)₃ was successfully loaded on ZIF-8 by immersion deposition method, to form lanthanide-based metal–organic frameworks (La@ZIF-8) composites.     

Recovery of NH4+–N and PO43−–P from urine using sludge-derived biochar as a fertilizer: performance and mechanism

Sludge-derived biochar (BS) was prepared by pyrolyzing municipal sludge at different temperatures and was used to recover NH₄⁺–N and PO₄³⁻–P from urine. The effects of dosage, adsorption time, and urine concentration on the adsorption of NH₄⁺–N and PO₄³⁻–P were investigated, and the adsorbed BS was used as a fertilizer to study its effect on the growth of pakchoi cabbage. The Elovich model was more consistent with the adsorption processes of NH₄⁺–N and PO₄³⁻–P. Both the NH₄⁺–N and PO₄³⁻–P adsorption isotherm model agreed with the Redlich–Peterson model. The Langmuir model showed that the largest adsorption capacity of BS600 for NH₄⁺–N and PO₄³⁻–P could reach 114.64 mg g⁻¹ and 31.05 mg g⁻¹, respectively. The NH₄⁺–N adsorption mechanism of BS may have complexation with O-containing functional groups and precipitation reactions, while the removal mechanism of PO₄³⁻–P was co-precipitation. The pot experiment demonstrated that adsorbed BS600 can better promote the growth of pakchoi cabbage with the same amount of addition. With the addition of 5% adsorbed BS600, the weight of cabbage was 64.49 g heavier than without the addition of BS600. This research provided theoretical support for the recovery of NH₄⁺–N and PO₄³⁻–P from urine as a fertilizer.

Sludge-derived biochar (BS) was prepared by pyrolyzing municipal sludge at different temperatures and was used to recover NH₄⁺–N and PO₄³⁻–P from urine.     

Facile synthesis of TiO2/Ag3PO4 composites with co-exposed high-energy facets for efficient photodegradation of rhodamine B solution under visible light irradiation

In this study, TiO₂/Ag₃PO₄ composites based on anatase TiO₂ nanocrystals with co-exposed {101}, {010}/{100}, {001} and [111]-facets and Ag₃PO₄ microcrystals with irregular and cubic-like polyhedron morphologies were successfully synthesized by combining hydrothermal and ion-exchange methods. The anatase TiO₂ nanocrystals with different high-energy facets were controllably prepared via hydrothermal treatment of the exfoliated [Ti₄O₉]²⁻/[Ti₂O₅]²⁻ nanosheet solutions at desired pH values. The Ag₃PO₄ microcrystal with different morphologies was prepared via the ion-exchange method in the presence of AgNO₃ and NH₄H₂PO₄ at room temperature, which was used as a substrate to load the as-prepared anatase TiO₂ nanocrystals on its surface and to form TiO₂/Ag₃PO₄ heterostructures. The apparent rate constant of the pH 3.5-TiO₂/Ag₃PO₄ composite was the highest at 12.0 × 10⁻³ min⁻¹, which was approximately 1.1, 1.2, 1.4, 1.6, 13.3, and 24.0 fold higher than that of pH 0.5-TiO₂/Ag₃PO₄ (10.5 × 10⁻³ min⁻¹), pH 7.5-TiO₂/Ag₃PO₄ (10.2 × 10⁻³ min⁻¹), pH 11.5-TiO₂ (8.8 × 10⁻³ min⁻¹), Ag₃PO₄ (7.7 × 10⁻³ min⁻¹), blank sample (0.9 × 10⁻³ min⁻¹), and the commercial TiO₂ (0.5 × 10⁻³ min⁻¹), respectively. The pH 3.5-TiO₂/Ag₃PO₄ composite exhibited the highest visible-light photocatalytic activity which can be attributed to the synergistic effects of its heterostructure, relatively small crystal size, large specific surface area, good crystallinity, and co-exposed high-energy {001} and [111]-facets. The as-prepared TiO₂/Ag₃PO₄ composites still exhibited good photocatalytic activity after three successive experimental runs, indicating that they had remarkable stability. This study provides a new way for the preparation of TiO₂/Ag₃PO₄ composite semiconductor photocatalysts with high energy crystal surfaces and high photocatalytic activity.

TiO₂/Ag₃PO₄ composites with co-exposed {101}, {010}/{100}, {001} and [111]-facets were successfully synthesized by combining hydrothermal and ion-exchange methods.     

Preparation of activated carbon from Dipterocarpus alatus fruit and its application for methylene blue adsorption

Activated carbons were prepared from three parts of Dipterocarpus alatus fruit (wing, endocarp and pericarp), an abundant and renewable waste in Southeast Asia, by chemical activation using ZnCl₂, FeCl₃, H₃PO₄ and KOH and physical activation using CO₂ and steam. This study indicated that activated carbon prepared from Dipterocarpus alatus fruit could be employed as a promising adsorbent for the removal of methylene blue from aqueous solution. ZnCl₂ activation led to an activated carbon with a surface area of 843 m² g⁻¹ and was able to remove methylene blue from aqueous solution. Adsorption studies were performed and analysed using Langmuir and Freundlich isotherm equations. Adsorption data demonstrated an excellent fit with the Langmuir isotherm model, with the maximum adsorption capacity of 269.3 mg g⁻¹ at equilibrium. Pseudo-first order and pseudo-second order kinetic models were used in this study to describe the adsorption mechanism. The results show that methylene blue adsorption is pseudo-second order, indicating that liquid film diffusion, intra-particle diffusion and surface adsorption coexisted during methylene blue adsorption on the activated carbon. The activated carbon prepared from Dipterocarpus alatus fruit is a low cost and effective adsorbent with a fast rate for the removal of methylene blue from aqueous solutions when compared with a number of activated carbons studied in the literature.

Activated carbons were prepared from Dipterocarpus alatus fruit by chemical and physical activation and used for the removal of methylene blue from aqueous solution.     

MoS42− intercalated NiFeTi LDH as an efficient and selective adsorbent for elimination of heavy metals

The enormous increase of heavy metal pollution has led to a rise in demand for synthesizing efficient and stable adsorbents for its treatment. Therefore, we have designed a novel adsorbent by introducing (MoS₄)²⁻ moieties within the layers of NiFeTi LDH-NO₃, via an ion exchange mechanism, as a stable and efficient adsorbent to deal with the increasing water pollution due to heavy metals. Characterization techniques such as XRD, FTIR, TGA, SEM, TEM, and Raman spectroscopy were used to confirm the formation of (MoS₄)²⁻ intercalated NiFeTi LDH and structural changes after the adsorption process. The efficiency of the material was tested with six heavy metal ions, among which it was found to be effective for toxic Pb²⁺ and Ag⁺ ions. When selectivity was studied with all six of the metal ions copresent in one solution, the material showed greater selectivity for Pb²⁺ and Ag⁺ ions with the selectivity order of Ni²⁺ < Cu²⁺ < Zn²⁺ < Fe³⁺ < Pb²⁺ < Ag⁺, with great adsorption capacities of 653 mg g⁻¹ for Pb²⁺ and 856 mg g⁻¹ for Ag⁺ metal ions. Further, the kinetics adsorption study for both the metal ions had a great correlation with the pseudo-second-order model and supported the chemisorption process via the formation of M–S bonding. The adsorption process obeyed the Langmuir model. Therefore, the MoS₄-LDH material could be a promising adsorbent for the removal of heavy metals.

Elimination of the heavy metals by using the MoS₄-LDH adsorbent.     

Synthesis of nano-zirconium-iron oxide supported by activated carbon composite for the removal of Sb(v) in aqueous solution

In this study, nano zirconium iron oxide based on activated carbon (ZIC) was successfully prepared by using the coprecipitation method. Compared with unmodified activated carbon, ZIC increases the number of active sites by adding metal oxides and hydroxyl groups and greatly improves the adsorption capacity of Sb(v). The synthesized nanocomposites were characterized and analysed by XRD, SEM, FT-IR, VSM and other techniques. The results showed that the zirconium iron oxide particles were successfully loaded and uniformly distributed on the surface of the activated carbon, and the agglomeration phenomenon was reduced. The saturation magnetization of ZIC was 1.89 emu g⁻¹, which easily achieved solid–liquid separation under the action of an external magnetic field. In batch experiments, when the initial concentration was 1 mg L⁻¹, the dosage of ZIC was 600 mg L⁻¹, the pH value was 5.0, the contact time was 180 min, and the removal rate of Sb(v) reached 97.82%. The maximum adsorption capacity of ZIC for Sb(v) was 11.80 mg g⁻¹. Under the interference of various inorganic ions and dissolved organics, the excellent adsorption capacity was still due to ZIC. The adsorption form was multimolecular-layer adsorption, the adsorption process was an endothermic reaction, and chemical adsorption was dominant as the adsorption mechanism. ZIC has good removal efficiency and is reusable, which indicates that ZIC has prospects for practical wastewater treatment.

The adsorbent was highly effective in the removal of Sb(v). The adsorbent easily achieved solid–liquid separation under the action of an external magnetic field.     

Hectorite-CTAB–alginate composite beads for water treatment: kinetic,isothermal and thermodynamic studies

Encapsulation of hectorite-modified CTAB with Ca-alginate formed reusable adsorbent beads for wastewater treatment. The thermogravimetric analysis (TGA) investigation indicated excellent thermal stability results for BHec-40 compared to Hec-40. Although the mesoporous surface area of BHec-40 decreased to 79.74 m² g⁻¹ compared to 224.21 m² g⁻¹ for Hec-40, the hectorite-CTAB–alginate beads showed high adsorption capacity and stability for methyl orange (MO) adsorption with more than 60% removal after five adsorption–desorption cycles. The influence of pH (3–11), temperature (30, 40, and 50 °C), initial concentration (50–400 mg L⁻¹), and contact time were studied to obtain the kinetics and thermodynamics of adsorption. The outcomes revealed a maximum monolayer adsorption capacity of 117.71 mg g⁻¹ for BHec-40. The kinetics of adsorption demonstrated the suitability of using the pseudo-first-order kinetic model, while the equilibrium adsorption data follows the Langmuir isotherm. Thermodynamic analysis indicates physisorption of MO onto BHec-40. BHec-40 improves the reusability as an adsorbent for the removal of anionic dyes from aqueous media.

Encapsulation of hectorite-modified CTAB with Ca-alginate formed reusable adsorbent beads for wastewater treatment.     

Response surface methodology for optimization of methylene blue adsorption onto carboxymethyl cellulose-based hydrogel beads: adsorption kinetics,isotherm, thermodynamics and reusability studies

Environment-friendly composite hydrogel beads based on carboxymethyl cellulose (CMC), alginate (Alg) and graphene oxide (GO) were synthesized by an ionotropic gelation technique and studied as an efficient adsorbent for methylene blue (MB). The chemical structure and surface morphology of the prepared hydrogel beads were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA) and point of zero charge (pH_pzc). A hybrid response surface methodology integrated Box–Behnken design (RSM-BBD) was successfully developed to model, simulate, and optimize the biosorption process. The synergistic effects between three critical independent variables including adsorbent dose (0.3–0.7 g), pH of the MB solution (6.5–9.5) and initial MB concentration (15–45 mg L⁻¹) on the MB adsorption capacity (mg g⁻¹) and removal efficiency (%) were statistically studied and optimized. The performance of the RSM-BBD method was found to be very impressive and efficient. Results proved that the adsorption process follows a polynomial quadratic model since high regression parameters were obtained (R²-value = 99.8% and adjusted R²-value = 99.3%). Analysis of variance (ANOVA) further confirms the validity of the suggested model. The optimal conditions for 96.22 ± 2.96% MB removal were predicted to be 0.6 g of CMC-Alg/GO hydrogel beads, MB concentration of 15 mg L⁻¹ and pH of 9.5 within 120 min. The adsorption equilibrium is better described by the Freundlich isotherm, indicating that physisorption is the rate controlling mechanism. The MB adsorption process was thermodynamically spontaneous and endothermic. A reusability study revealed that the prepared adsorbent is readily reusable. The adsorbent still maintains its ability to adsorb MB for up to four cycles. Results reported in this study demonstrated that CMC-Alg/GO hydrogel beads are an effective, promising and recyclable adsorbent for the removal of MB from aqueous solutions.

Environment-friendly composite hydrogel beads based on carboxymethyl cellulose (CMC), alginate (Alg) and graphene oxide (GO) were synthesized by an ionotropic gelation technique and studied as an efficient adsorbent for methylene blue (MB).     

Selective aptamer conjugation to silver-coated magnetite nanoparticles for magnetic solid-phase extraction of trace amounts of Pb2+ ions

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection. First, silver-coated magnetite core–shell nanoparticles (Fe₃O₄@Ag MNPs) were synthesized by the chemical reduction of silver ions on the surface of magnetite nanoparticles. After that, the selective DNA aptamer against Pb²⁺ was conjugated on the surface of the synthesized nanoparticles to form aptamer-modified magnetic nanoparticles (Fe₃O₄@Ag-APT). The characterization of the prepared adsorbent was performed through SEM imaging, XRD, FT-IR, EDX, and DRS instruments. The influence of the various experimental parameters on the adsorption and desorption steps in MSPE was investigated via Taguchi experimental design to optimize different parameters. Under the optimized conditions, the Pb²⁺ calibration graph was linear in the range of 33–1000 μg L⁻¹. The relative standard deviation (RSD%) of the method for six replicates containing 100 μg L⁻¹ of Pb²⁺ ions was 0.34%. Furthermore, the limit of detection (LOD) and the limit of quantification (LOQ) were 10 μg L⁻¹ and 33.3 μg L⁻¹, respectively. Finally, the applicability of the proposed method was successfully confirmed by preconcentration and determination of trace amounts of Pb²⁺ ions in tap and seawater samples. We showed a proof of concept for Fe₃O₄@Ag-APT as an efficient bio-adsorbent, offering a promising strategy for the specific binding/removal of toxic heavy metal ions.

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection.