Selective adsorption of Congo red and Cu(II) from complex wastewater by core-shell structured magnetic carbon@zeolitic imidazolate frameworks-8 nanocomposites

High efficiency adsorption of boron by sodium alginate/polyethyleneimine/polysiloxane composite aerogel

In this work, a new biomass boron adsorbent of N-methyl-D-glucosamine embedded sodium alginate/polyethyleneimine/polysiloxane composite aerogel (SKPN) was reported. Relevant characterization proved that the aerogel exhibited 3D porous structure with plenty of hydroxyl and amino functional groups, which was beneficial to the diffusion of boron and the chelation between boron and SKPN. Various parameters affecting the adsorption performance including pH value, contact time initial concentration, temperature and reusability were investigated. The maximum adsorption capacity was found at pH 8.0, and the adsorption capacity reached equilibrium within 3.75-5.75 h. Adsorption kinetics were more in line with the pseudo-second order kinetic model, suggesting the predominance of chemisorption. The adsorption isotherm was more in line with the Langmuir model, and the maximum adsorption capacities were calculated up to 38.41-49.39 mg/g (3.55-4.57 mmol/g) within the temperature range of 298 to 318 K, which were higher than most of the previous works. In addition, SKPN still showed good resistance to external ion interference and good reusability. The adsorption mechanism proved that the chelation interactions between boron and cis-diol and amino groups were the main driving forces. These results instructed that the adsorbent exhibited a good application prospect for boron adsorption, with the advantages of high adsorption performance, simple preparation process and environmental friendliness.

An innovative and efficient strategy for removing Congo red using magnetic hollow Zn/Co zeolitic imidazolate framework composite

The discharge of wastewater containing Congo red (CR) poses a significant threat to aquatic ecosystems and human health, underscoring the urgent need for effective removal methods. In this study, we have developed a novel strategy for efficient removing CR, utilizing the synthesized magnetic hollow Zn/Co zeolitic imidazolate framework composite (MH-ZIF). Comprehensive characterization of MH-ZIF and comparison with contrasting materials were conducted. The adsorption behavior of MH-ZIF towards CR followed the pseudo-second-order kinetic model and Langmuir isothermal adsorption model, demonstrating monolayer chemisorption. Remarkably, MH-ZIF exhibited an impressive adsorption capacity of 1167.9 mg g-1 for CR at 293 K. The addition of merely 0.15 g L-1 of MH-ZIF achieved nearly complete adsorption of CR within a concentration of 150 mg L-1. With the assistance of an external magnetic field, CR adsorbed on MH-ZIF can be effectively and swiftly removed within just 30 s. Hence, MH-ZIF demonstrates great promise in effectively removing CR from wastewater, attributed to its high adsorption capacity, selectivity, and magnetic properties.

Biobased amphoteric aerogel with core-shell structure for the hierarchically efficient adsorption of anionic and cationic dyes

Efficient and simultaneous removal of anionic and cationic dyes from wastewater using low-cost and environmentally-friendly adsorbent is highly required. Herein, the carboxylated cellulose (carboxyl content: 2.97 mmol/g) derived from pomelo peel was extracted by a one-step H2O2/H2SO4-mediated oxidation method. Subsequently, a novel pomelo-peel cellulose/chitosan/sodium alginate (PCS) amphoteric aerogel with a specific core-shell structure was synthesized by multiple physical cross-linking strategies. The shell layer and core layer of the optimized P3CS0.75 aerogel can selectively adsorb cationic dyes and anionic dyes, in which, the theoretical maximum adsorption capacities were 888.27 mg/g and 1816.87 mg/g towards methylene blue (MB) and Congo red (CR), respectively. Especially, the aerogel's core/shell layer exhibited hierarchical adsorption behavior without overlapping sites even in the binary dye systems. The adsorption performance of obtained amphoteric aerogel remained effective in a wide pH range and under different practical water systems. Moreover, the removal efficiencies for MB and CR were slightly reduced from 90.76 % and 99.66 % to 88.08 % and 91.39 %, respectively, after 5 adsorption-desorption cycles, and the aerogel's structural integrity was also maintained due to its good compressive strength (487.16 KPa). In addition, the adsorption mechanism of PCS aerogel was investigated using adsorption kinetics, isotherm, thermodynamics, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It was proved that the adsorption process was endothermic spontaneous-monolayer adsorption driven by electrostatic attraction and hydrogen bonding. Therefore, the prepared biobased aerogel was expected to be a prospective material for removing mixed dyes from wastewater.

Novel polyarylether nitrile/layered bimetallic oxide/2-Methylimidazole composite membrane for efficient synergistic adsorption and degradation of organic pollutants under visible light

The difficulty of recycling and the finite photocatalytic performance of primitive nano-photocatalysts restrict their application in wastewater purification. In this study, a multifunctional membrane with efficient synergistic adsorption and degradation performance was constructed. The nano-photocatalyst layered bimetallic oxide (LDO) was combined with the matrix membrane polyarylether nitrile (PEN) by delayed phase transition technology. The introduced 2-Methylimidazole (2-MeIm) provided a virtual electron transfer pathway between PEN and LDO and enhanced the photocatalytic performance. The results suggested that PEN/LDO/2-MeIm has outstanding removal performance to organic dyes methylene blue (MB). After three consecutive cycles, the reacted membrane can be readily recovered from the system. The MB removal rate remained high at 89.38%, suggesting that the functional membrane is eligible for recycling and reuse. Finally, based on liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) calculations, the mechanism and pathway of MB photodegradation by the PEN/LDO/2-MeIm system were proposed. Therefore, constructing PEN/LDO/2-MeIm membranes in this study may offer a novel perspective on creating eco-friendly and functional PEN-based membranes for practical use in wastewater purification.

Advancements in nanoparticle-modified zeolites for sustainable water treatment: An interdisciplinary review

The contamination of water sources with heavy metals, dyes, and other pollutants poses significant challenges to environmental sustainability and public health. Traditional water treatment methods often exhibit limitations in effectively addressing these complex contaminants. In response, recent developments in nanotechnology have catalyzed the exploration of novel materials for water remediation, with nanoparticle-doped zeolites emerging as a promising solution. This comprehensive review synthesizes current literature on the integration of nanoparticles into zeolite frameworks for enhanced contaminant removal in water treatment applications. We delve into synthesis methodologies, elucidate mechanistic insights, and evaluate the efficacy of nanoparticle-doped zeolites in targeting specific pollutants, while also assessing considerations of material stability and environmental impact. The review underscores the superior adsorptive and catalytic properties of nanoparticle-doped zeolites, owing to their high surface area, tailored porosity, and enhanced ion-exchange capabilities. Furthermore, we highlight recent advancements in heavy metal and organic pollutant uptake facilitated by these materials. Additionally, we explore the catalytic degradation of contaminants through advanced oxidation processes, demonstrating the multifunctionality of nanoparticle-doped zeolites in water treatment. By providing a comprehensive analysis of existing research, this review aims to guide future developments in the field, promoting the sustainable utilization of nanoparticle-doped zeolites as efficient and versatile materials for water remediation endeavors.

Selective adsorption of Cu(II) on amino-modified alginate-based aerogel: As a catalyst for the degradation of organic contaminant

In this study, amino-modified graphene oxide(NGO) was prepared by introducing amino functional groups. Based on the cross-linking between Ca(II) and sodium alginate (SA), associated with dense slit-like pore resulted from the nano-sheet accumulation of NGO and montmorillonite (MMT), composite aerogels (NGM) with stable pore structure were constructed, thus it realized the selective recovery of hydrated copper ions in complex wastewater systems. Raman analysis and density functional theory calculation confirmed the construction of amino-modified defect GO and significantly improved its chemical reactivity, which laid the foundation for the construction of slit pore structure of NGM (SEM can confirm). At the same time, it proposed that the good selective adsorption of Cu(II) on NGM was related to the synergism of strong electrostatic force, ion exchange and complexation based on the characterizations of FT-IR and XPS. In order to realize the value-added utilization of NGM aerogel (NGMC) after adsorbing Cu(II), NGMC was used as a catalyst to degrade organic pollutants in wastewater. Systematic experiments shown that NGMC can degrade organic pollutants with a degradation efficiency >80 %. In summary, NGM had a broad application prospect for selective recovery of Cu(II) from complex wastewater systems without second pollution.

Surface modified of chitosan by TiO2@MWCNT nanohybrid for the efficient removal of organic dyes and antibiotics

Considering the increase in the discharge of industrial effluents containing dyes and antibiotic resistance as a consequence of increasing the prescription and easy distribution of antibiotic drugs at the global level, designing efficient, biodegradable and non-toxic absorbents is necessary to reduce environmental harm effects. Herein, we present a series of novel eco-friendly ternary hybrid nanocomposite hydrogels CS/TiO2@MWCNT (CTM) composed of chitosan (CS), TiO2, and multiwalled carbon nanotube (MWCNT) for removal of methylene blue (MB) and methyl orange (MO) and common antibiotic ciprofloxacin (CIP) in aqueous medium. The combination of MWCNT and TiO2 improves the physicochemical properties of CS hydrogel and increases the adsorption capacity toward pollutants in the presence of different loadings. CTM hydrogel showed a specific surface area of 236.45 m2 g-1 with a pore diameter of 7.89 nm. Adsorption mechanisms were investigated in detail using kinetic, isotherm, and thermodynamic studies of adsorption as well as various spectroscopic techniques. Adsorption of these pollutants by CTM nanocomposite hydrogel occurred using various interactions at different pHs, which showed the obvious dependence of CTM adsorption capacity on pH. Electrostatic attractions, complex formation, π-π stacking and hydrogen bonds played a key role in the adsorption process. The adsorption of MB, MO, and CIP was fitted with the Langmuir isotherm with maximum adsorption capacities of 531.91, 1763.6, and 1510.5 mg g-1, respectively. CTM had a minor decrease in adsorption strength and showed good structural stability even after 8 adsorptions-desorption cycles. The total cost of producing a 1 kg adsorbent was calculated to be $ 450, which helped us determine the economic feasibility of the adsorbent in large-scale applications.

One stone, two birds: An eco-friendly aerogel based on waste pomelo peel cellulose for the efficient adsorption of dyes and heavy metal ions

To achieve the objective of "waste control by waste", in this study, a green aerogel adsorbent comprised of pomelo-peel cellulose and sodium alginate (PCC/SA) was prepared through dual-network crosslinking. The resulting 3D hierarchical porous structured PCC/SA aerogel exhibited good structural stability, and kept the morphological integrity during 10 days in a wide pH range (2-10), suggesting its potential for recycling in diverse complex environments. Besides, the superior adsorption capacities for methylene blue (MB) and Cu(II) were observed, with the qm values and adsorption equilibrium times were recorded to be 1299.59 mg/g (300 min) and 287.55 mg/g (120 min), correspondingly. Furthermore, the favorable reusability of the PCC/SA aerogel was also demonstrated, with the removal efficiency for MB remaining almost unchanged (about 94 %) after 10 adsorption-desorption cycles, while there was a slight reduction for Cu(II) from 85.28 % to 72.47 %. XPS and FTIR analysis revealed that electrostatic attraction, hydrogen bonding, cation exchange and coordination were the major adsorption mechanisms. Importantly, the PCC/SA aerogel can be naturally degraded in soil within 10 weeks. Therefore, the as-prepared aerogel bead derived from pomelo peel shows great promise as an adsorbent for wastewater treatment containing dye and heavy metal ions.

Magnetically separable Co0.6Fe2.4O4/MIL-101-NH2 adsorbent for Congo red efficient removal

The development of effective and practical adsorbents for eliminating pollutants still remains a significant challenge. Herein, we synthesized a novel magnetically separable composite, Co0.6Fe2.4O4/MIL-101-NH2, through the in-situ growth of MIL-101-NH2 on magnetic nanoparticles, designed specifically for the removal of Congo red (CR) from aqueous solutions. MIL-101-NH2 possessed high BET surface area (240.485 m2•g-1) and facile magnetic separation function and can be swiftly separated (within 30 s) through an external magnetic field post-adsorption. The investigation systematically explored the influence of crucial parameters, including adsorbent dosage, pH, adsorption duration, temperature, and the presence of interfering ions, on CR adsorption performance. Findings indicate that CR adsorption adheres to the pseudo-second-order (PSO) kinetic model and the Langmuir isotherm model. Thermodynamic analysis reveals the spontaneity, endothermic nature, and orderly progression of the adsorption process. Remarkably, the adsorbent with 0.1 g•L-1 boasts an impressive maximum adsorption capacity of 1756.19 mg•g-1 for CR at 298.15 K, establishing its competitive advantage. The reuse of the adsorbent over 5 cycles remains 78% of the initial adsorption. The CR adsorption mechanisms were elucidated, emphasizing the roles of π-π interactions, electrostatic forces, hydrogen bonding, and metal coordination. Comparison with other dyes, such as methylene blue (MB) and methyl orange (MO), and exploration of adsorption performance in binary dye systems, demonstrates the superior capacity and selectivity of this adsorbent for CR. In conclusion, our magnetically separable metal-organic framework (MOF)based composite presents a versatile and effective solution for CR removal, with promising applications in water treatment and environmental remediation.

A photothermal MoS2 decorated biomass carbon-based aerogel with a directionally aligned porous structure for mitigating heavy metal stress under seawater acidification

Marine animals and human are threatened by seawater acidification and metal contamination. Especially, the toxicity of copper (Cu) is expected to be boosted with seawater acidification. However, studies on the removal of Cu under seawater acidification are limited for practical applications, owing to obstacles such as instability, secondary contamination, and low adsorption efficiency. In this work, coconut shells were utilized for the synthesis of biomass carbon, which was then decorated with MoS2. A novel porous MoS2/carbon-based aerogel (MCA) with the synergistic effect of photothermal conversion and adsorption was constructed via directional freeze-drying technology. The adsorption properties of MCA were a precise match with Freundlich isotherm and pseudo-second-order kinetic models with a high correlation coefficient (R2) of more than 0.995. Under solar illumination, the surface temperature of MCA reached up to 36.3 °C and the adsorption capacity of MCA increased to 833.8 mg g-1, indicating that the remarkable thermal properties of MCA contributed to achieving high adsorption capacity. The adsorption mechanisms of MCA involved in the removal of Cu(ii) ions were dominated by chemisorption rather than surface physical adsorption. Owing to its outstanding photothermal conversion performance and directionally aligned porous structure, MCA was able to remove Cu(ii) species from seawater, and the adsorption ability of MCA reached 247.1 mg g-1 after ten adsorption cycles. MCA exhibited excellent stability to resist the complex natural environment and was easy to reuse. Overall, MCA with a series of merits, including high adsorption efficiency, excellent photothermal conversion property, and outstanding cycling stability, was confirmed to contribute to addressing heavy metal stress under seawater acidification.

High-efficient removal of anionic dye from aqueous solution using metal-organic frameworks@chitosan aerogel rich in benzene structure

With the exponentially increase of dye pollutants, the purification of dye wastewater has been an urgent ecological problem. As a novel type of porous adsorbent, metal-organic frameworks still face challenges in recyclability, agglomeration, and environmentally unfriendly synthesis. Herein, MOF-525 was in-situ growth onto the surface of the chitosan (CS) beads to fabricate MOF-525@CS aerogel. CS was utilized as substrate to uniformly disperse MOF-525, thereby significantly mitigating agglomeration and improving recyclability of MOF-525. The characterization results shown that MOF-525@CS aerogel had a high specific surface area of 103.0 m2·g-1, and MOF-525 was uniformly distributed in the 3D porous structure of CS, and the presence of benzoic acid was detected. The MOF-525@CS aerogel had a remarkable adsorption capacity of 1947 mg·g-1 for Congo red, which is greater than the sum of its parts. MOF-525@CS aerogel also inherited the rapid adsorption ability of MOF-525, removing 80 % of Congo red within 600 min. Such excellent adsorption performance can be attributed to the benzoic acid trapped by CS via CN band to enhance the π-π stacking interactions. Additionally, the utilization of benzoic acid makes the synthesis process of MOF-525@CS aerogel more environmentally friendly. The high-efficient MOF-525@CS aerogel is a competitive candidate for dye pollution adsorption.

Recent advances in the synthesis and application of magnetic biochar for wastewater treatment

Magnetic biochar (MBC) is a novel bio-carbon material with both desired properties as adsorbent and magnetic characteristics. This review provides an up-to-date summary and discussion on the latest development of MBC, which covers the progress on its synthesis, application, and techno-economic analysis. The review indicates that the direct hydrothermal synthesis has been catching more research attention to produce MBC due to its mild reaction conditions. Instead of the Fe-loaded MBC, there is a trend of using Mn for the magnetization. For the MBC application, how to improve its adsorption performance for water decontamination, ideally to match that of the biochar (BC) or activated carbon, is important. In addition, more studies on the environmental impacts of MBC and life-cycle assessment decoding the process optimization options are necessary. This review will provide valuable references for the development of MBC and MBC-based materials for wastewater treatment.

"Adsorptive removal of Congo Red dye from its aqueous solution by Ag-Cu-CeO2 nanocomposites: Adsorption kinetics, isotherms, and thermodynamics"

Eliminating synthetic dyes and organic contaminants from water is crucial for safeguarding human health and preserving the environment. In this study, we explored the effectiveness of Ag-Cu-CeO2 nanocomposites as adsorbents to remove Congo Red dye from water. Three compositions of Ag-Cu-CeO2 nanocomposites (10:20:70, 15:15:70, and 20:10:70) have been synthesized by the aqueous coprecipitation method. A comprehensive analysis was performed by different techniques including X-ray diffraction, Fourier transform infrared spectroscopy, BET surface area determination, Thermogravimetric analysis, Scanning electron microscopy, and TEM. The synthesized nanocomposites have a dimension of 5 ± 1 nm and a high surface area (51.832-78.361 m2g-1). Among these, the nanocomposite with composition 15:15:70 showed the highest adsorption capacity of 4.71 mg/g adsorption (96.83 % removal) from the 0.8 × 10-4 M (55.6 mg/l) Congo Red solution at pH values of 2 at 20 °C with contact time of 3h. The adsorption data is best fitted in the Freundlich adsorption isotherm and pseudo-second-order kinetic model. The negative values of enthalpy variation (-27.57, -26.43, and -16.73 kJ/mol) demonstrated that the adsorption was spontaneous and exothermic. The cycling run showed a mere 12 % deactivation after five cycles of use thus indicating that Ag-Cu-CeO2 nanocomposites hold great potential as effective and eco-friendly adsorbents to remove Congo Red from water.

Hydrothermal Synthesis of a Technical Lignin-Based Nanotube for the Efficient and Selective Removal of Cr(VI) from Aqueous Solution

Aminated lignin (AL) was obtained by modifying technical lignin (TL) with the Mannich reaction, and aminated lignin-based titanate nanotubes (AL-TiNTs) were successfully prepared based on the AL by a facile hydrothermal synthesis method. The characterization of AL-TiNTs showed that a Ti-O bond was introduced into the AL, and the layered and nanotubular structure was formed in the fabrication of the nanotubes. Results showed that the specific surface area increased significantly from 5.9 m2/g (TL) to 188.51 m2/g (AL-TiNTs), indicating the successful modification of TL. The AL-TiNTs quickly adsorbed 86.22% of Cr(VI) in 10 min, with 99.80% removal efficiency after equilibration. Under visible light, AL-TiNTs adsorbed and reduced Cr(VI) in one step, the Cr(III) production rate was 29.76%, and the amount of total chromium (Cr) removal by AL-TiNTs was 90.0 mg/g. AL-TiNTs showed excellent adsorption capacities of Zn2+ (63.78 mg/g), Cd2+ (59.20 mg/g), and Cu2+ (66.35 mg/g). After four cycles, the adsorption capacity of AL-TiNTs still exceeded 40 mg/g. AL-TiNTs showed a high Cr(VI) removal efficiency of 95.86% in simulated wastewater, suggesting a promising practical application in heavy metal removal from wastewater.

The Defects, Physicochemical Properties, and Surface Charge of MIL-88A (Al) Crystal Were Regulated for Highly Efficient Removal of Anionic Dyes: Preparation, Characterization, and Adsorption Mechanism

In this paper, the physicochemical properties, surface charge, and crystal defects of MIL-88A (Al) were controlled by adjusting the ratio of metal ligands and temperature in the synthetic system without the addition of surfactants. The adsorption properties of different crystals for Congo red (CR) were studied. Among them, MIL-88A (Al)-130 and MIL-88A (Al)-d have the best adsorption properties. The maximum adsorption capacities are 600.8 and 1167 mg · g^-1, respectively. Compared with MIL-88A (Al)-130, the adsorption performance of MIL-88A (Al)-d was increased by 94.2%, and the adsorption rate was increased by about 4 times. It can be seen that increasing the proportion of metal ligands within a certain range will improve the adsorption capacity. The structure and morphology of the adsorbent were characterized by XRD, FTIR, SEM, EDS, TGA, BET, and zeta potential. The effects of time, temperature, pH, initial solution concentration, and dosage on CR adsorption properties were systematically discussed. The pseudo-second-order kinetic model and Langmuir isothermal model can well describe the adsorption process, which indicates that the adsorption process is a single-layer chemisorption occurring on a uniform surface. According to thermodynamics, this adsorption is an endothermic process. The mechanism of CR removal is proposed as the electrostatic attraction, hydrogen bond, metal coordination effect, π-π conjugation, crystal defect, and pore-filling effect. In addition, MIL-88A (Al)-d has good repeatability, indicating that it is a good material for treating anionic dye wastewater.

An all-biopolymer self-assembling hydrogel film consisting of chitosan and carboxymethyl guar gum: A novel bio-based composite adsorbent for Cu2+ adsorption from aqueous solution

A novel bio-based composite adsorbent, all biopolymer self-assembled hydrogel film has been prepared by eco-friendly amalgamating chitosan (CS) and carboxymethyl guar gum (CMGG) biopolymers in water without needing small molecules for cross-linking. Various analysis demonstrated the electrostatic interactions and hydrogen bondings within the network structure are responsible for gelling, crosslinking, and forming a 3D structure. Various experimental parameters were optimized to evaluate the CS/CMGG's potential for removing Cu²⁺ ions from aqueous solution, including pH, dosage, Cu(II) initial concentration, contact time, and temperature. The pseudo-second-order kinetic and Langmuir isotherm models are highly correlated with the kinetic and equilibrium isotherm data, respectively. Using the Langmuir isotherm model for an initial metal concentration of 50 mg/L at pH 6.0 and 25 °C, the maximum adsorption of Cu(II) was calculated to be 155.51 mg/g. A combination of adsorption-complexation and ion exchange must be involved in Cu(II) adsorption on the CS/CMGG. Five cycles of the loaded CS/CMGG hydrogel regeneration and reuse were successfully achieved without an appreciable difference in Cu(II) removal percentage. Thermodynamic analysis indicated that copper adsorption occurred spontaneously (ΔG°: -2.85 J/mol, 298 K) and exothermically (ΔH°: -27.58 J/mol). A reusable bio-adsorbent for removing heavy metal ions was developed that is eco-friendly, sustainable, and efficient.

Application of zeolite based nanocomposites for wastewater remediation: Evaluating newer and environmentally benign approaches

The presence of heavy metal ions and emerging pollutants in water poses a great risk to various biological ecosystems as a result of their high toxicity. Consequently, devising efficient and environmentally friendly methods to decontaminate these waters is of high interest to many researchers around the world. Among the varied water treatment and desalination means, adsorption and photocatalysis have been widely employed. However, the discussion and analysis of the use of zeolite-based composites as adsorbents are somehow minimal. The porous aluminosilicates (zeolites) are excellent candidates in wastewater treatment owing to various mechanisms of pollutants removal that they possess. The purpose of this review is thus to provide a synopsis of the current developments in the fabrication and application of nanocomposites based on zeolite as adsorbents and photocatalysts for the extraction of heavy metals, dyes and emerging pollutants from wastewaters. The review goes on to look into the effect of weight ratio on photocatalyst, photodegradation pathways, and various factors that influence photocatalysis and adsorption.

Preparation of benzenesulfonyl hydrazone modified guar gum and its adsorption properties for dyes and phytotoxicity assays

Herein, a novel environmentally friendly benzenesulfonyl hydrazone modified guar gum (DGH) that carries excellent adsorption performance towards dyes was facilely prepared through oxidation and condensation. The structure, morphology, and physics-chemical of DGH were fully characterized by multiple analysis techniques. The as-prepared adsorbent yielded highly efficient separating performance towards multiple anionic and cation dyes, including CR, MG, and ST with the maximum adsorption capacity of 1065.3839 ± 10.5695, 1256.4467 ± 2.9425, and 1043.8140 ± 0.9789 mg/g at 298.15 K, respectively. The adsorption process well fitted the Langmuir isotherm models and the pseudo-second-order kinetic models. The adsorption thermodynamics revealed that the adsorption of dyes onto DGH was spontaneous and endothermic. The adsorption mechanism indicated that the hydrogen bonding and electrostatic interaction participated in the fast and efficient removal of dyes. Furthermore, the removal efficiency of DGH still remained above 90 % after six adsorption-desorption cycles, and the presence of Na⁺, Ca²⁺, and Mg²⁺ have weakly impacted the removal efficiency of DGH. The phytotoxicity assay was conducted via the germination of mung bean seeds, which confirmed the adsorbent can effectivity decreased the toxicity of dyes. Overall, the modified gum-based multifunctional material has good promising applications for wastewater treatment.

Preparation of lignite-loaded nano-FeS and its performance for treating acid Cr(VI)-containing wastewater

In this study, lignite-loaded nano-FeS (nFeS@Lignite) was successfully prepared by ultrasonic precipitation, and its potential for treating acid Cr(VI)-containing wastewater was explored. The results showed that the 40--80-nm rod-shaped nFeS was successfully loaded onto lignite particles, and the maximum adsorption capacity of Cr(VI) by nFeS@Lignite reached 33.08 mg∙g^-1 (reaction time = 120 min, pH = 4, temperature = 298.15 K). The adsorption process of Cr(VI) by nFeS@Lignite fitted the pseudo-second-order model and the Langmuir isotherm model, and thermodynamic results showed that the adsorption process was an endothermic process with an adsorption enthalpy of 28.0958 kJ·mol^-1. The inhibition intensity of coexisting anions on Cr(VI) removal was in the order of PO₄^3-  > NO₃^-  > SO₄^2-  > Cl^-, and the increase of ionic strength resulted in more pronounced inhibition. Electrostatic adsorption, reduction, and precipitation were synergistically engaged in the adsorption of Cr(VI) by nFeS@Lignite, among which reduction played a major role. The characterization results showed that Fe²⁺, S^2-, and Cr(VI) were converted to FeOOH, S₈, SO₄^2-, Fe₂O₃, Cr₂O₃, and Fe(III)-Cr(III) complexes. This research demonstrates that nFeS@Lignite is a good adsorbent with promising potential for application in the remediation of heavy metal-contaminated wastewater.

Green and Superior Adsorbents Derived from Natural Plant Gums for Removal of Contaminants: A Review

The ubiquitous presence of contaminants in water poses a major threat to the safety of ecosystems and human health, and so more materials or technologies are urgently needed to eliminate pollutants. Polymer materials have shown significant advantages over most other adsorption materials in the decontamination of wastewater by virtue of their relatively high adsorption capacity and fast adsorption rate. In recent years, "green development" has become the focus of global attention, and the environmental friendliness of materials themselves has been concerned. Therefore, natural polymers-derived materials are favored in the purification of wastewater due to their unique advantages of being renewable, low cost and environmentally friendly. Among them, natural plant gums show great potential in the synthesis of environmentally friendly polymer adsorption materials due to their rich sources, diverse structures and properties, as well as their renewable, non-toxic and biocompatible advantages. Natural plant gums can be easily modified by facile derivatization or a graft polymerization reaction to enhance the inherent properties or introduce new functions, thus obtaining new adsorption materials for the efficient purification of wastewater. This paper summarized the research progress on the fabrication of various gums-based adsorbents and their application in the decontamination of different types of pollutants. The general synthesis mechanism of gums-based adsorbents, and the adsorption mechanism of the adsorbent for different types of pollutants were also discussed. This paper was aimed at providing a reference for the design and development of more cost-effective and environmentally friendly water purification materials.

Enhanced heavy metal adsorption on microplastics by incorporating flame retardant hexabromocyclododecanes: Mechanisms and potential migration risks

Microplastics (MPs) are known to act as carriers of heavy metals; however, little is known about the intrinsic chemical additives of MPs, such as hexabromocyclododecane (HBCD), in terms of the adsorption behaviors and migration risks of heavy metals on MPs. Here, we reported the potential mechanisms and risks of HBCD inherent in polystyrene (PS) MPs with Cu(II), Ni(II), and Zn(II) adsorption/desorption. A comparison of the adsorption capacity of the metals onto HBCD/PS composites (HBCD/PS) MPs (10.31-20.76 μmol/g), pure MPs (0-3.60 μmol/g), and natural minerals (0.11-13.88 μmol/g) showed that the addition of HBCD significantly promoted the metals adsorption onto the HBCD/PS MPs, and even exceeded that of natural particles. Isotherms and thermodynamic data suggested that the adsorption process of the metals onto the HBCD/PS MPs was spontaneous and endothermic, and that the adsorption was a mainly multi-ion process with an inclined direction. Furthermore, the results of SEM-EDS, FTIR, and XPS analyses, as well as density functional theory well explained that the metals were mainly adsorbed on the -O and -Br groups of the HBCD/PS MPs via electrostatic interactions and surface complexation. More importantly, by comparing the desorption activity with natural river water and seawater, HBCD inherent in MPs can enhance the long-range transfer of metals carried by the HBCD/PS MPs from contamination sources to potential sink like oceans. Thus, the HBCD/PS MPs with high loading of Cu(II), Ni(II), and Zn(II) could be potential secondary sources of these metals in seawater. Overall, these findings revealed the potential risks of flame retardant in MPs associated with metal migration, and advocated that flame retardant-related waste MPs should be included in coastal sustainable development.

Preparation of Magnetic Metal-Organic Frameworks@Molecularly Imprinted Nanoparticles for Specific Extraction and Enrichment of Bisphenol A in Food

Metal-organic frameworks (MOFs) with systematically tailored structures have been suggested as promising precursors to the preparation of diverse functional materials. Herein, a facile and versatile layer-by-layer strategy without any special surface modifications has been proposed for the preparation of magnetic metal-organic frameworks (MMOFs) supported molecularly imprinted polymer nanoparticles (MMOFs@MIP), which are based on a magnetically susceptible core conjugated with an imidazole-derived self-assembled layer and a silane-based imprinted shell. The obtained MMOFs@MIPs, which integrated the advantages of Fe₃O₄, MOFs, and MIPs, were characterized and exhibited good magnetic properties, a rapid mass transfer rate, and an excellent adsorption selectivity as well as capacity for the targeted molecular - bisphenol A (BPA). Moreover, the MMOFs@MIPs were employed as adsorbents in magnetic solid phase extraction (MSPE) to selectively bind and rapidly separate BPA from real samples with satisfactory recoveries ranging from 88.3% to 92.3%. More importantly, the desirable reusability of MMOFs@MIP was also evaluated, and the recoveries still maintained above 88.0% even after five re-use cycles. Furthermore, combined with high-performance liquid chromatography (HPLC) analysis, a novel MSPE-HPLC method was developed, enabling the highly selective and sensitive detection of BPA in a wide linear range of 0.5–5000 μg L⁻¹ with a low limit of detection (LOD) of 0.1 μg L⁻¹. This work contributes a promising method for constructing various functional nanoparticles @MOFs@MIP hybrid materials for applications in many different fields.

Construction of a Carbon/Lignosulfonate Adsorbent to Remove Pb2+ and Cu2

Removing heavy metal ions from water is an important issue to improve water quality. However, using cost-effective and more environmentally friendly adsorbents to achieve efficient adsorption capacity remains a challenge. Carbon spheres were prepared by the hydrothermal method and then combined with sodium lignosulfonate to form a lignosulfonate carbon (C/SL) adsorbent. C/SL achieved the adsorption of Pb²⁺ and Cu²⁺ after 60 min (the adsorption capacity was 281 mg g^-1 for Pb²⁺ and 276mg g^-1 for Cu²⁺) and had good selectivity and reusability (5 cycles). The simulated experimental data show that the pseudo-second-order kinetics and Langmuir isotherm are closer to the actual adsorption. Thermodynamic studies show that the adsorption of Pb²⁺ and Cu²⁺ is enhanced by the spontaneous process at higher temperature. This study also shows that functional groups such as hydroxyl and amino groups play an important role in the adsorption process.

Facile synthesis of Fe-modified lignin-based biochar for ultra-fast adsorption of methylene blue: Selective adsorption and mechanism studies

A novel Fe-modified lignin-based biochar (Fe-LB) was fabricated via a facile one-step carbonization method for methylene blue (MB) removal from wastewater. Fe-LB exhibited a high specific surface area (885.97 m²/g) and micropore volume (0.3203 m³/g), and demonstrated high affinity for MB with the maximum adsorption capacity of 2.7-fold by Fe-LB than LB. It was found that quick adsorption could be achieved in 15 min with the MB removal efficiency of 100% and adsorption capacity reached 200 mg/g. Selective adsorption studies indicated that Fe-LB preferentially adsorbed MB in high salt and multiple dye systems (binary, ternary, and quaternary) over a wide pH range from 2 to 12. The removal efficiency of CR was greatly improved due to the synergistic effect between MB and CR in the binary system. This work demonstrated that Fe-LB can effectively remove dye contaminants and possessed great potential in the treatment of MB polluted dye wastewater.

Green synthesis of a novel functionalized chitosan adsorbent for Cu(II) adsorption from aqueous solution

Pollution generated by heavy metals has become a global environmental issue with much public concern. Herein, a functionalized chitosan-based adsorbent (CS-PAR) was synthesized via a simple one-step method for the adsorption of copper ions in solutions. A series of characterization methods have shown that CS-PAR was successfully synthesized. The experimental results showed that the maximum adsorption capacity of CS-PAR for Cu(II) ions was 170.23 mg/g. The adsorption process of Cu(II) on CS-PAR conformed to Langmuir and pseudo second-order models and belonged to a single-layer chemical adsorption process on the surface of a homogeneous medium. The adsorption mechanism of the adsorbent to Cu(II) ions was the complexation between the N-containing functional groups existing on the surface of the adsorbent and Cu(II). These results also showed that the adsorbent was an efficient material for removing heavy metal copper in wastewater and had very important practical significance.

Adsorption behavior of Congo red on a carbon material based on humic acid

Humic acid is used as an inexpensive starting material to prepare a strong adsorbent for the removal of Congo red from water.