Ultrafast Adsorption Research Articles

Facile fabrication of Fe/Zr binary MOFs for arsenic removal in water: High capacity, fast kinetics and good reusability

A water-stable bimetallic Fe/Zr metal-organic framework [UiO-66(Fe/Zr)] for exceptional decontamination of arsenic in water was fabricated through a facile one-step strategy. The batch adsorption experiments revealed the excellent performances with ultrafast adsorption kinetics due to the synergistic effects of two functional centers and large surface area (498.33 m2/g). The absorption capacity of UiO-66(Fe/Zr) for arsenate [As(V)] and arsenite [As(III)] reached as high as 204.1 mg/g and 101.7 mg/g, respectively. Langmuir model was suitable to describe the adsorption behaviors of arsenic on UiO-66(Fe/Zr). The fast kinetics (adsorption equilibrium in 30 min, 10 mg/L As) and pseudo-second-order model implied the strong chemisorption between arsenic ions and UiO-66(Fe/Zr), which was further confirmed by DFT theoretical calculations. The results of FT-IR, XPS analysis and TCLP test demonstrated that arsenic was immobilized on the surface of UiO-66(Fe/Zr) through Fe/Zr-O-As bonds, and the leaching rates of the adsorbed As(III) and As(V) from the spent adsorbent were only 5.6% and 1.4%, respectively. UiO-66(Fe/Zr) can be regenerated for five cycles without obvious removal efficiency decrease. The original arsenic (1.0 mg/L) in lake and tap water was effectively removed in 2.0 hr [99.0% of As(III) and 99.8% of As(V)]. The bimetallic UiO-66(Fe/Zr) has great potentials in water deep purification of arsenic with fast kinetics and high capacity.

Facile and novel preparation of 2D-MoS2/carbon nanodots composite with high adsorption efficiency and capacity for dye removal

Here, hydrophobic bulk molybdenum disulfide (MoS2) was efficiently exfoliated into two dimensional (2D) nanosheets assisted with amphiphilic carbon nanodots (CNDs) in pure water. The optimized concentration of obtained 2D-MoS2 is as high as 0.41 mg/mL, which is higher than that of reported literatures. The average lateral size and layer number of 2D-MoS2 is 142.6 (±2.3) nm and 4, respectively. The characterizations and simulation demonstrated that CNDs can be instantly adsorbed on the surface of 2D-MoS2 and form 2D-MoS2/CNDs composite. Thus, after standing for 1000 h, the concentration of 2D-MoS2 still accounts for 90 % of the initial concentration with the help of CNDs. Further, this technique can also be used to prepare graphene and 2D-WS2 nanosheets. 2D-MoS2/CNDs composite as adsorbent showed excellent adsorption capacity (1136.9 mg/g) and ultrafast adsorption rate (1 min) for methylene blue removal, which benefits from abundant adsorption sites and high dispersion. This work not only develops a facile and universal technique for green preparation of 2D nanomaterials in one pot, but also provides a promising adsorbent for removing organic pollutants from aqueous solution.

Highly magnetically responsive porous nanoparticles based on tris(β-keto-hydrazo)-cyclohexane subunit: Fast removal of dyes from water with convenient recyclability

Porous organic polymers with magnetic responsibility have been developed for removal of hazardous substances from water, and attracted much attention. However, the technique to incorporate the polymers and magnetic particles well to give the composite as a whole remained challenging, as well as ultrafast adsorption and convenient recycling. In this paper, the tris(β-keto-hydrazo)-cyclohexane-based highly magnetically responsive porous magnetic nanoparticles (Fe3O4 @TKH-POPs) have been synthesized via a one-pot azo coupling reaction in water with the Fe3O4 magnetic nanoparticles as templates. And the resulted Fe3O4 @TKH-POPs showed very fast removal of organic dye pollutants such as methylene blue (MB) and acid red-18 (AR-18) from water, requiring less than 1 min to reach adsorption equilibrium. Additionally, the superparamagnetism of Fe3O4 @TKH-POPs made the separation and recovery very convenient, and their stability lead to good reusability, i. e., no any loss of adsorption capacity after 5 recycles. This work represented successful examples to design of magnetically responsive porous organic polymers of novel structure with irreversible tautomerization

Hydroxyl-functionalized hypercrosslinked polymers with ultrafast adsorption rate as an efficient adsorbent for phenol removal

In the present study, the adsorptive potential of hypercrosslinked polymers (HCPs) was investigated for the removal of phenol from aqueous solutions. Herein, two HCPs were one-step synthesized by the Friedel-Crafts reaction using 4,4′-biphenyldiol (BPD) or hydroquinone (HQ) as the building unit and 1,4-bis(chloromethyl)benzene (DCX) as the external crosslinker. The results showed that the HCPs, derived from BPD and DCX (called as BPD-D), exhibited more excellent pore structures with the higher surface area of 697 m2 g−1 and the micropore volume of 0.23 cm3 g−1 and allowed for the extremely fast equilibrium adsorption of phenol, attributed to the hierarchical pore structure and the great hydrophilicity; meanwhile, the maximum adsorption capacity of BPD-D towards phenol was calculated to be 156.74 mg g−1. Moreover, the adsorption equilibrium and kinetic processes of BPD-D towards phenol were well described by the Freundlich model (R2 > 0.99) and the pseudo-second-order kinetic model (R2 > 0.9999) at 303 K. Moreover, negative changes in Gibbs free energy and enthalpy reflect that the adsorption of BPD-D for phenol is a spontaneous and exothermic process. In addition, adsorption performances were investigated under different conditions, e.g., the initial concentrations of phenol, the dosage of the BPD-D, the initial pH of phenol aqueous solution and recyclability. Our finding demonstrates that HCPs show potential application prospects in the removal of organic pollutants from wastewater.

Water-Insoluble Cyclodextrin-based nanocubes for highly efficient adsorption toward diverse organic and inorganic pollutants

Cyclodextrin (CD), as a naturally green starch derivative, is a promising candidate for water treatment through adsorption. Unfortunately, the soluble nature of CD in water limits its application greatly. In this work, a water-insoluble CD-based nanocube (CL-CD@PNC) with high adsorption performance toward dissolved pollutants is first developed through a facile two-step route. The prepared CL-CD@PNC has high water stability and well-defined cubic morphology with a porous structure. Additionally, the CL-CD@PNC nanocubes present prominent adsorption performance with the maximum adsorption capacities of 2173.21, 998.54, and 966.06 mg g−1 towards methylene blue (MB), bisphenol A (BPA), and Pb(Ⅱ), respectively, which is much higher than those of many other adsorbents. The adsorption equilibrium can be achieved within 10 and 30 s for MB and Pb(Ⅱ) adsorption, respectively, indicating the ultrafast adsorption rate. These adsorption processes are ascribed to the pseudo-second-order adsorption kinetics and Langmuir isotherm model, signifying the chemical and monolayer adsorption process. Moreover, the removal efficiency of the CL-CD@PNC nanocubes towards three different pollutants remains over 85% even after 10 recycles of regeneration. The superior adsorption performance of our CL-CD@PNC is attributed to the synergetic effect of host–guest interaction, electrostatic adsorption, hydrogen bond interaction, and chelation. More importantly, the applicability of CL-CD@PNC is successfully demonstrated under real industrial wastewater conditions. This work provides a promising strategy to prepare the water-insoluble CD-based adsorbent with a regular cubic structure, which can be potentially applied in the practical applications of industrial wastewater treatment.

PH‐Controlled Switch over Coadsorption and Separation for Mixed Cs+ and Sr2+ by an Acid‐Resistant Potassium Thioantimonate

AbstractSwitchable coadsorption and separation for elimination/partitioning of Cs+ and Sr2+ is achieved by pH‐controlled ion exchange using a potassium thioantimonate K2Sb4S7·2H2O (SbS‐1K) with fantastic pH durability from diluted NaOH (pH 12) to concentrated HCl (3 m). At pH 6, SbS‐1K exhibits ultrafast adsorption kinetics (R ≈ 90% in 2 min for Cs+ and 20 min for Sr2+) and high removal rates (R ≈ 98–99%) at equilibrium for both Cs+ and Sr2+. At pH 2, the Sr2+ adsorption is inhibited by H+ with a great loss in RSr to 11.18%, whereas the RCs remains at 96.99%, contributing to a top‐ranked separation factor SFCs/Sr of 256. The SbS‐1K‐filled ion exchange column can be switched between the eliminating (RCs > 99.91%; RSr > 98.19%) and separating (RCs > 98.99%; RSr ≈ 0±3%) modes for treating continuous flow with a variation from pH 6 to pH 2 or vice versa. The SbS‐1K/PTFE membrane exhibits coadsorption and separation effects for filtration of low concentrated mixed Cs+ and Sr2+ solution (1 ppm for each), even at an ultrafast vacuum filtration speed (30 mL min–1). Combined with easy synthesis and high β/γ irradiation resistance, SbS‐1K represents a new‐concept bifunctional exchanger with discriminating intelligence for equipment innovation.

Effective response of multiple kinetic models and DFT calculations to the ultrafast adsorption behaviors of cellulose-titanium dioxide composites

A cellulose-polyacrylic acid-TiO2 composite (CAT) with multiple carboxyl groups in the network structure and that could undergo ultrafast adsorption was successfully synthesized, and the adsorption capacity for cadmium(II) (Cd(II)) under optimal conditions was as high as 105 mg/g within 5 min. Additionally, CAT maintained the advantages of fast and efficient adsorption even when the concentrations of potentially interfering ions (NaCl, MgSO4, HA) were high. Importantly, 13 nonlinear kinetic models, including 6 empirical models and 7 diffusional models with their 5 error functions, were used to evaluate the adsorbent performance and mass transfer mechanism. As a result, regardless of whether interfering ions were present, the PNO model and Langmuir kinetics model were perceived as the best fit for the adsorption reaction and empirical model and mass transfer model, respectively. Adsorption at active centers was the rate limiting step for CAT. Moreover, the micromechanisms were also quantitatively explained with multiple DFT calculations, which illustrated ion exchange and electrostatic interactions with the oxygen atom on the introduced carboxyl group.

Zero-valent iron supported-lemon derived biochar for ultra-fast adsorption of methylene blue

Green-based materials represent a new promising class of ecofriendly and economic adsorbents. Herein, nano zero-valent iron supported-lemon derived biochar (NZVI-LBC) was prepared for the first time and examined in the adsorptive removal of methylene blue as a model pollutant. Different characterization tools were used to ensure the successful fabrication of the NZVI-LBC composite including FTIR, XRD, TEM, XPS, VSM, BET, and zeta potential analysis. It was found that the fabricated NZVI–supported biochar composite attained the propitious adsorbent criteria since it provided a supreme efficient adsorption process at short time. The reckoned maximum adsorption capacity of MB onto NZVI-LBC reached 1959.94 mg/g within merely 5 min. The obtained data clarified that the adsorption process of MB onto NZVI-LBC fitted pseudo 2nd order kinetic model and Freundlich isotherm model. Besides, the adsorption process of MB onto NZVI-LBC was found to be endothermic in nature. In addition, NZVI-LBC composite revealed an excellent adsorption behavior even after seven cycles. The concrete results reflect the potentiality of NZVI-LBC composite to be a superb candidate to remove cationic pollutants from their aqueous solutions.Graphical abstract

CO2-responsive functional cotton fibers decorated with Ag nanoparticles for “smart” selective and enhanced dye adsorption

Novel Ag nanoparticles (NPs) decorated CO2-responsive cotton fiber (PCCF@Ag) as eco-friendly adsorbent was prepared via in-situ growth of Ag NPs on the poly(2-(dimethylamino) ethyl methacrylate-co-4-acryloyloxybenzophenone) coated cotton fiber. The as-prepared PCCF@Ag displayed excellent adsorption performance toward both anionic and cationic dyes with or without CO2 stimulation, even under a wide range of pH from 3 to 11. The maximum adsorption capacities of the as-prepared PCCF@Ag toward anionic dye (1538.5 mg g−1 for MO) and cationic dyes (944.0 mg g−1 for MEB and 415.6 mg g−1 for NR) were satisfactory. The adsorption processes were described better by the Langmuir isotherm and pseudo-second-order kinetic models, respectively. Notably, upon CO2 stimulation, the PCCF@Ag exhibited significantly enhanced adsorption capacity toward anionic dyes, following ultrafast adsorption rate, which made the PCCF@Ag could selectively adsorb anionic dyes from mixture because of greatly different adsorption rates between anionic dyes (adsorption equilibrium within 2 min) and cationic dyes (adsorption equilibrium over 12 h). Additionally, the PCCF@Ag could maintain over 91.0% of adsorption capacity even after ten cycles, indicating its outstanding reusability. Meanwhile, the as-obtained PCCF@Ag exhibited excellent antibacterial activity. Overall, the as-obtained PCCF@Ag could be considered as a promising dye scavenger for wastewater remediation.

Solvent regulation and template-free synthesis of β-cyclodextrin-based microporous organic network nanosheets for ultrafast and efficient removal of aromatic pollutants

Layer-stacking structures via the template-free synthesis are rare in two-dimensional microporous organic networks (2D MONs). Herein, we report a facile solvent regulation and template-free strategy by tuning the aggregation degree of 2D β-cyclodextrin (CD)-based MONs nanosheets. The 2D MON nanosheets provided larger uptake capacity and faster kinetics than the aggregated CD-MONs, revealing the significance of morphology control for the removal of pollutants. The prepared 2D CD-MON-DMF gave ultrafast adsorption kinetics and exhibited much larger saturation sorption capacity (327.9 mg g−1) than previous adsorbents for bisphenol AF. The developed strategy not only provides a novel way to construct 2D MON nanosheets for highly efficient removal of organic pollutants from water but also promotes the utilization of MONs in material and environmental sciences.

Graphene oxide-supported highly porous TiO2 nanoleaflets for the ultrafast adsorption and photochemical decomposition of 2,4,6-trinitrotolune in water

Synthesis of a novel, reduced graphene oxide TiO2 nanoleaflets composite as a photocatalyst for the removal of trinitrotoluene explosive from water is reported.

Enhanced capacitive removal of hardness ions by hierarchical porous carbon cathode with high mesoporosity and negative surface charges

Capacitive deionization (CDI), as a promising desalination technology, has been widely applied for water purification, heavy metal removal and water softening. In this study, the hierarchical porous carbon (HPC) with extremely large specific surface area (∼1636 m2 g−1), high mesoporosity and negative surface charges, was successfully prepared by one-step carbonization of magnesium citrate and acid etching. HPC carbonized at 800 ℃ exhibited an excellent specific capacitance (207.2 F g−1). The negative surface charge characteristic of HPC was demonstrated by potential of zero charge test. With HPC-800 as a CDI cathode, the super high adsorption capacity of hardness ions (Mg2+: 472 μmol g−1, Ca2+: 425 μmol g−1) with ultrafast adsorption rate was realized, attributed to its abundant mesoporous structure and negative surface charges. The priority order of ion adsorption on HPC in the multi-component salt solution was Mg2+ > Ca2+ > K+ ≈ Na+. The desalination and softening of the actual brackish water have been simultaneously achieved by three-cell CDI stack after four times of adsorption, with 63% decrease of total dissolved solids and 76% reduction of hardness. The current HPC material with outstanding adsorption performance for hardness ions shows great potential in brackish water purification.

Engineering linkage as functional moiety into irreversible thiourea-linked covalent organic framework for ultrafast adsorption of Hg(II)

Development of novel functionalized covalent organic frameworks (COFs) as adsorbent for removal of mercury from environment is of great significance, but the conventional strategies for functionalizing COFs always sacrifice porous properties and suppress the exposure of functional sites, which goes against the rapid adsorption of Hg(II). Here, we show the rational design and preparation of the first thiourea-linked COFs via engineering the COFs linkage as functional moiety for ultrafast and selective adsorption of Hg(II). Two thiourea-linked COFs JNU-3 and JNU-4 were prepared via tautomerism reaction of 1,3,5-triformylphloroglucinol with 1,4-phenylenebis(thiourea) and 1,4-biphenylenebis(thiourea), respectively. The thiourea serves as not only linkage to connect the building block into irreversible crystalline structure, but also functional moiety to give no occupation of the COF pore and full exposure to Hg(II) with strong affinity, offering the JNU-3 and JNU-4 large adsorption capacity (960 and 561 mg g−1, respectively) and ultrafast kinetics (equilibrium time of 10 s) for Hg(II). The proposed strategy for the design of functional COFs with inherent linkage as functional moiety largely promotes the performance of COFs for diverse applications.

Ultra-fast adsorption of radioactive-U(VI) and Cs(I) with high adsorption capacity towards CAA@MgAlFe spongy-like aerogel: Mechanism and application feasibility study

Secure disposal of radioactive wastewater had aroused global concerns for human health and ecological environment. Uranium (U) and Cesium (Cs) were both typical radioactive elements detected in contaminated water bodies. In response to the environmental problem, a spongy-like aerogel adsorbent was firstly prepared for the removal of radioactive U(VI) and Cs(I) and potential application in sea water. MgAlFe layered double hydroxides (LDHs) were prepared by hydrothermal method, and were then gelated by freeze-drying technique to synthesize the calcium alginate aerogels doped with MgAlFe LDHs (CAA@MgAlFe). The prepared CAA@MgAlFe was a kind of porous sponge-like aerogel, on which the LDHs dispersed uniformly. Batch adsorption experiments presented that the adsorption of U(VI) and Cs(I) could reach the equilibrium rapidly in only 4 min and 3 min, respectively. This suggested the reduction of radioactive exposure during the treatment was at a high extent. The adsorption capacities of U(VI) and Cs(I) were as high as 533 and 58 mg/g, respectively. Furthermore, the adsorption isotherms showed that U(VI) and Cs(I) matched well with the Langmuir and Freundlich models, respectively. CAA@MgAlFe could be easily separated and compressed, and its application on sea water was proved to be feasible. The adsorption mechanism of CAA@MgAlFe towards U(VI) included complexation, ion exchange and reduction, while that of Cs(I) was electrostatic attraction.

High-yield production of monolayer boron nitride nanosheets by cationic-surfactant-assisted solvothermal exfoliation for the ultrafast and selective separation of U(VI) from lanthanides

The efficient separation and recovery of uranium(VI) (U(VI)) from lanthanides is pivotal to reduce the radioactive threat of hydrometallurgical residue solution of lanthanide minerals and benefits the sustainability of U resources. Here, we develop a cationic-surfactant-assisted solvothermal exfoliation method to prepare monolayer boron nitride nanosheets (BNNSs) for the ultrafast and selective separation of U(VI) from lanthanides. With the assistance of the strong “cation–π” interaction between cationic surfactants and BN, the monolayer BNNSs were prepared. Functionalization with diamide phenanthroline (DAPhen) groups endows the pristine BNNSs, which can hardly adsorb U(VI), with outstanding U(VI) adsorption performance. Batch adsorption experiments demonstrate that the obtained DAPhen modified BNNSs (BNNSs-DAPhen) exhibited high maximum adsorption capacity and ultrafast adsorption kinetics. The adsorption process reached equilibrium less than 1 min and the maximum adsorption capacity was estimated to be 313 mg g−1 by fitting with Langmuir model. Even under high concentrations of salts and acids, BNNSs-DAPhen still maintained excellent adsorption performance owing to the strong complexing ability of DAPhen groups with U(VI). The selectivity coefficients of U(VI) toward various lanthanides including lanthanum(III), cerium(III), europium(III), gadolinium(III), ytterbium(III), and lutetium(III) were beyond 120 at a high nitric acid concentration of 5 mol L−1. This work proposed a universal strategy for the production of monolayer BNNSs and the subsequent functionalization, which might be promising in the treatment of residual solution for lanthanides hydrometallurgy and decontamination of U(VI).

Ultrafast selective adsorption of pretreatment inhibitors from lignocellulosic hydrolysate with metal-organic frameworks: Performance and adsorption mechanisms

• Four MOFs were evaluated for adsorption of furfural and four phenolic inhibitors. • MIL-140C exhibited excellent adsorption capacity and ultrafast adsorption kinetics. • MIL-140C demonstrated good reusability and high stability. • Possible adsorption mechanisms were proposed. In this work, four metal-organic frameworks materials (MOFs, MIL-140A, MIL-140C, MIL-101(Fe) and NH 2 -MIL-101(Fe) were prepared, characterized and compared for the adsorptive removal of furfural and four phenolic inhibitors. MIL-140C demonstrated the best adsorption capability among the tested MOFs. Effects of pH, ionic strength, contact time, adsorbent dosage, temperature and sugars on adsorption of inhibitors on MIL-140C were systematically investigated. Inhibitors adsorption was ultrafast within minutes and kinetic data fitted pseudo-second-order model well. The Langmuir isotherm described the adsorption process satisfactorily with maximum adsorption capacities of 222.72, 240.38, 231.48, 207.04 and 60.79 mg/g for vanillin, syringaldehyde, ferulic acid, p-coumaric acid and furfural, respectively. Thermodynamic parameters disclosed that nature of the adsorption was exothermic and spontaneous under the experimental conditions. MIL-140C demonstrated exceptional adsorption selectivity towards inhibitors even with excessive amount of xylose and glucose, as well as excellent regeneration performance after five adsorption/desorption cycles. MIL-140C also exhibited satisfactory detoxification performance after treatment of real corn stover dilute acid hydrolysate. Furthermore, analysis of underlying adsorption mechanism showed that π-π interaction, hydrophobic interaction and hydrogen bonding/metal-coordination (depending on solution pH) were involved in the adsorption of tested phenolic inhibitors, while the π-π and hydrophobic interactions contributed to the furfural adsorption. The overall results revealed that MIL-140C could hold great promise in removing phenolic and furan inhibitors from lignocellulosic hydrolysate.

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.

Highly efficient and selective Hg(II) removal from water by thiol-functionalized MOF-808: Kinetic and mechanism study

Mercury pollution poses a serious threat to the ecological environment and public health due to its high toxicity and persistence, but there is still a lack of rapid and effective Hg(II) removal technology, especially emergency response of Hg(II) leakage. Herein, an effective metal-organic framework adsorbent, MOF-808-SH, was fabricated by grafting thioglycollic acid on MOF-808 for Hg(II) removal. The MOF-808-SH demonstrated high adsorption capacity of 977.5 mg/g, impressively ultrafast adsorption kinetics (C0 = 10 mg/L, removal > 99 % in 10 s) with a rate constant k of 36.89 g mg−1 min−1, which is dozens of times faster than that of ever reported Hg(II) adsorbents. Batch experiments show that MOF-808-SH exhibits high selectivity toward Hg(II) with a distribution coefficient Kd as high as 5.0×106 mL/g. Moreover, MOF-808-SH exhibits excellent recyclability with a negligible loss of capacity after 6 adsorption-regeneration cycles. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectrometry (XPS) unveil that the –SH groups in MOF-808-SH are the key adsorption sites, and specific inner-sphere coordination with Hg(II) is responsible for the high selectivity. In addition, large surface area, well-developed porous structures and high –SH loading of MOF-808-SH reasonably explains ultrafast kinetics and high adsorption capacity for Hg(II). This study indicates the potential of MOF-808-SH to remove Hg(II) from wastewater.

High-performance quaternary ammonium-functionalized chitosan/graphene oxide composite aerogel for remelt syrup decolorization in sugar refining

The decolorization of remelt syrup is the most critical step in the sugar refining process as it directly affects the quality of refined sugar. Adsorption is a useful method that can be applied to decolorize the syrup. A quaternary ammonium-functionalized chitosan/graphene oxide composite aerogel (GO-QACSA) was developed as an effective adsorbent for the removal of high-molecular-weight reducing sugar alkaline degradation products (HRSADPs), the main class of colorants in remelt syrup. The advantages of GO-QACSA to remove HRSADPs can be attributed to its well-connected 3-D network-like porous structure, nontoxicity, high hydrophilicity, and the richness of quaternary ammonium groups. The equilibrium adsorption capacity of GO-QACSA for HRSADPs reached 364.09 mg/g and the removal rate was > 90%. GO-QACSA exhibited an ultra-fast adsorption rate. Recycling experiments indicated that GO-QACSA exhibited good renewability and reusability. The interaction mechanism for the adsorption of HRSADP on GO-QACSA was studied, and the results revealed that two layers of HRSADPs adhered to the surface of GO-QACSA via electrovalent bonds formed between the quaternary ammonium and carboxylate groups. On average, 2–3 carboxylate ions in one HRSADP molecule bonded with the quaternary ammonium cations of GO-QACSA. Four phenomenological mathematical models, namely, External mass transfer resistance (EMTR), Internal mass transfer resistance (IMTR), combined EMTR–IMTR, and Adsorption on active sites (AAS), were presented based on the best-fit equilibrium isotherms. These models could be used to provide new insights into the adsorption mass transfer behaviors of the system.

Facile Microwave Hydrothermal Synthesis of ZnFe2O4/rGO Nanocomposites and Their Ultra-Fast Adsorption of Methylene Blue Dye.

The industry development in the last 200 years has led to to environmental pollution. Dyes emitted by pharmaceutical and other industries are major organic pollutants. Organic dyes are a pollutant that must be removed from the environment. In this work, we adopt a facile microwave hydrothermal method to synthesize ZnFe2O4/rGO (ZFG) adsorbents and investigate the effect of synthesis temperature. The crystal structure, morphology, chemical state, and magnetic property of the nanocomposite are investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and a vibrating sample magnetometer. Furthermore, the synthesized ZFGs are used to remove methylene blue (MB) dye, and the adsorption kinetics, isotherm, mechanism, and reusability of this nanomaterial are studied. The optimal ZFG nanocomposite had a dye removal percentage of almost 100%. The fitting model of adsorption kinetics followed the pseudo-second-order model. The isotherm model followed the Langmuir isotherm and the theoretical maximum adsorption capacity of optimal ZFG calculated by this model was 212.77 mg/g. The π–π stacking and electrostatic interaction resulted in a high adsorption efficiency of ZFG for MB adsorption. In addition, this nanocomposite could be separated by a magnet and maintain its dye removal percentage at almost 100% removal after eight cycles, which indicates its high suitability for utilization in water treatment.