Search

To efficiently remove high concentrations of hexavalent chromium (Cr(VI)), calcium–aluminum-layered double hydroxide (CaAl-LDH, denoted as CAL), and polypyrrole-modified CAL (CAL-PPy) were prepared by hydrothermal and in situ polymerization methods, respectively. The chemical structure, morphology, and elemental results indicated that the chain-like polypyrrole was decorated with hexagonal CAL. The specific surface area of CAL-PPy increased from 8.746 m2/g to 24.24 m2/g. The adsorption performances of CAL and CAL-PPy for aqueous Cr(VI) were investigated using batch equilibrium experiments. The decontamination process of aqueous Cr(VI) (100 mg/L) reached the equilibrium state within 50 min, and the kinetic data met the pseudo-second-order kinetic equation. The Langmuir model described the isothermal data properly, and the obtained theoretical adsorption capacity of CAL for Cr(VI) at 318 K was 34.06 mg/g, while that of CAL-PPy was 66.14 mg/g. The removal mechanisms involved electrostatic attraction, surface complexation, anion exchange, and reduction to low-toxicity Cr(III). Therefore, CAL and CAL-PPy have underlying applications in treating real wastewater containing Cr(VI).

To improve the adsorption efficiency of layered double hydroxides (LDHs) for heavy metals, a novel sodium alginate (SA) intercalated MgAl-LDH (SA-LDH) was synthesized in this work. SA-LDH was characterized by XRD, FTIR, XPS and employed as adsorbent for Cd(II), Pb(II), Cu(II) elimination. Adsorbent dosage, initial pH and contact time, which are regarded as several key parameters, were optimized. The results showed that SA-LDH exhibited better adsorption performance compared with the pristine MgAl-LDH. The maximum adsorption capacities of SA-LDH for Cu(II), Pb(II) and Cd(II) reached 0.945, 1.176 and 0.850 mmol/g, respectively. The possible mechanisms were analyzed by XPS, XRD and FTIR. The results showed that Cd(II), Pb(II) and Cu(II) may be removed by SA-LDH via (i) bonding or complexation with Sur-OH or Sur-O- of SA-LDH, (ii) precipitation of metal hydroxides or carbonates, (iii) isomorphic substitution, and (iv) chelation with −COO− in the interlayers. This work provides an effective method for the development of LDH-based adsorbent and the treatment of wastewater containing heavy metals.

Removing heavy metal ions from acidic mine wastewater is a big challenge. In this paper, a novel porous thiophosphoryl polyethyleneimine (TPEI) adsorbent was designed for removing Pb(II) and Cr(VI) from acidic wastewater. The optimum adsorption pH value of TPEI for Pb(II) and Cr(VI) is 3 and 2, respectively. At 298 K, the maximum adsorption capacity for Pb(II) and Cr(VI) is 421.9 mg g−1 and 191.04 mg g−1, respectively. The adsorption equilibrium time of Pb(II) and Cr(VI) is 25 min and 10 min, respectively. The adsorption of Pb(II) and Cr(VI) both conform to the pseudo-second-order model and the Langmuir isotherm model. The adsorption mechanism of Pb(II) depends on the chelation interaction, while Cr(VI) depends on the electrostatic interaction. The regeneration test shows that the adsorbent is stable and reusable. This study provides a new strategy for the purification of acidic heavy metal wastewater.

To evaluate the adsorption mechanism and performance of phosphate onto the composite of low-cost biochar and iron oxide, four biochar–iron oxides, namely biochar–magnetite (BC-M), biochar–ferrihydrite (BC-F), biochar–goethite (BC-G), and biochar–hematite (BC-H), were prepared by fabricating iron oxide to porous biochar. The biochar–iron oxides had huge surface areas of 691–864 m2/g and average pore diameters of 3.4–4.0 nm. Based on the characterization analysis of FTIR, XRD, XPS, and zeta potential, the interactions of electrostatic attraction, ligand exchange, and deposition dominated the phosphate adsorption onto biochar–iron oxides. The maximum adsorption capacity of phosphate followed the order of BC-G > BC-F > BC-H > BC-M. The isotherm data of BC-M and BC-H were well fitted by the Langmuir and Freundlich models, while those of BC-G and BC-F followed the Langmuir model. In addition, BC-M, BC-F, BC-G, and BC-H owned excellent regeneration ability and adsorption performance in practical (simulated) wastewater environment. Then the biochar–iron oxides exerted extensive and satisfactory prospect in wastewater remediation and recycling application in soil.

To evaluate the synergetic adsorption capacity of layered double hydroxide (LDH) and photocatalytic reduction property of TiO2 for aqueous Cr(VI), the Fe3O4-ZnAl-LDH and TiO2 composites (FLT) were prepared via sol-gel method. The removal efficiency of FLT composites for Cr(VI) changed with the mass ratio of Fe3O4-LDH/TiO2, and the optimal ratio was 20% (FLT-2). The adsorption efficiencies of 100 mg FLT-2 were 74% and 64% for 20 and 50 mg/L Cr(VI) solution, and the total removal ratios of Cr(VI) were all over 97% after UV irradiation. The experimental data of adsorption kinetic, adsorption isothermal, and photocatalytic reduction were consistent with the pseudo-second-order, Langmuir, and first-order reaction equations, respectively. From the X–ray photoelectron spectra analysis, FLT composites adsorbed Cr(VI) directly via surface complexation, also reduced aqueous Cr(VI) to Cr(III). The photocurrent and electrochemical impedance spectroscopy of FLT composites indicated the photo-induced electron-hole pairs were separated effectively. The regeneration results show that the FLT composites had good stability and reusability after five consecutive cycles. Therefore, FLT composites are promising materials in the disposal of wastewater containing Cr(VI).

To understand the interaction mechanisms between heavy metals and functional groups modified nanomaterials, the l -cysteine (Cys) intercalated MgAl-layered double hydroxide (MgAl-Cys-LDH) was designed by a facile co-precipitation method and used to remove Cu(II), Pb(II) and Cd(II) in water solutions. The XRD, FTIR, SEM, TEM, EDS and XPS characterization analyses proved the carboxyl, thio and amido groups were successfully introduced into MgAl-LDH. The possible mechanisms were analyzed by the XPS and XRD spectra and involved the precipitation of metal hydroxides or sulfides, surface complexation with abundant surface groups, and the isomorphic substitution of Mg(II). The adsorption kinetics and isotherms data of Cu(II), Pb(II) and Cd(II) on MgAl-Cys-LDH were well described by the pseudo-second-order kinetic equation and the Langmuir model. The influence factors such as initial solution pH of heavy metals, dosage of MgAl-Cys-LDH, adsorption time and various types of water were investigated, and the results suggested that MgAl-Cys-LDH had potential applications in real wastewater treatment containing heavy metals.

With widespread utilization of graphene oxides (GO) in industry, it is ineluctably discharged into environment and has been found to be toxic to cells and animals. Effective techniques and functional materials are necessary for the elimination of GO from wastewater. In this work, the GO was removed by the magnetic Fe3O4/MgAl-layered double hydroxide (MLDH) and its oxide (MLDO) from aqueous solution. The effects of dosage, time and solution pH on the removal capacity of the MLDH and MLDO was carried out in detail through batch experiments. The results showed that the MLDH and MLDO can remove GO from aqueous solution quickly and efficiently. The maximum adsorption capacities were 82.4 mg/g of MLDH and 86.7 mg/g of MLDO. The pseudo-second-order equation was well accorded with the adsorption kinetic data. The isothermal data followed the Langmuir and Freundlich models. The interaction mechanisms of GO were ascribed to the surface complexation and electrostatic attraction by using zeta potential determination and XRD spectra. Moreover, the MLDH and MLDO after adsorbing GO can be separated in 10 s by a magnet. The short adsorption time, excellent removal capacity and extremely fast solid-liquid separation indicated that the MLDH and MLDO were potential magnetic adsorbents to remove the GO nanoparticles in aqueous system.

Phosphorylated magnetic chitosan composite (P-MCS) was successfully synthesized and applied to adsorb Pb(II) and Cd(II) from aqueous solutions. The as-prepared P-MCS composite was characterized by EDS, SEM, FTIR, XRD, XPS and zeta potential analysis. Factors affecting adsorption including adsorbent dose, pH value and contact time were optimized to improve the adsorption performance. The adsorption isotherm and kinetic model could well conform to Langmuir model and pseudo-second-order kinetic model. The as-prepared adsorbent exhibited good adsorption capacities for Pb(II) (151.06 mg g−1) and Cd(II) (71.53 mg g−1) from Langmuir isotherm. Besides, spectroscopic analysis after adsorption including FTIR and XPS were also performed to further reveal the adsorption mechanism. The results indicated that surface complexation and ion exchange between functional groups and metal ions played an important role in adsorption process. Thermodynamic studies (∆G 0, ∆S > 0) implied that the adsorption process is an endothermic and spontaneous reaction. Furthermore, the excellent magnetic separation and regeneration performance indicated the feasibility of using P-MCS composite for Pb(II)/Cd(II)-bearing wastewater remediation.

A new nanocomposite based on chitosan (CS) and Mg-Al-layered double hydroxide (Mg-Al-LDH) was prepared using an emulsion-crosslinking method. CS was immobilized within the Mg-Al-LDH matrix to form the CS-LDH after crosslinking by epichlorohydrin. The characterization of XPS, SEM, TEM, FTIR, and BET analysis showed that the CS-LDH had a high specific surface area and contained many different functional groups. The adsorption capacity of the CS-LDH was evaluated by adsorbing Pb2+ and Cd2+ as representative heavy metals. Batch adsorption method was used to investigate the effects of the amount of adsorbent, pH of the initial solution, and contact time. We also examined the adsorption kinetics, isotherms, and mechanisms. The capacity of the CS-LDH for Pb2+ and Cd2+ adsorption was higher than that of CS and the Mg-Al-LDH, and the isothermal data followed the Langmuir isotherm model. The adsorption equilibrium was quickly achieved and the kinetic data obeyed the pseudo-second-order kinetic model. The adsorption process was almost not affected by solution pH above 3. The CS-LDH and heavy metals interacted via the following mechanisms: precipitation, surface complexation, and isomorphic substitution.

To understand the possible mechanisms of hexavalent chromium (Cr(VI)) adsorption on the surface of modified layered double hydroxides (LDHs), we synthesized ethylenediaminetetraacetic acid intercalated MgAl-LDH (LDH-EDTA) and its magnetic product (Mag-LDH-EDTA), and evaluated their adsorption performance for Cr(VI) by batch equilibrium experiments. The characterization analysis proved that the EDTA was intercalated into MgAl-LDH and the adsorbents had an ordered structure and abundant functional groups. The adsorption mechanisms of Cr(VI) by LDH-EDTA and Mag-LDH-EDTA could be attributed as electrostatic attraction, surface complexation, anion exchange, and reduction reaction speculating from the detailed X-ray diffraction patterns (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and zeta potential analysis. The removal ratio remained above 96% and 79% for 50 mg L−1 Cr(VI) using 0.03 g LDH-EDTA and Mag-LDH-EDTA, respectively. The adsorption process was less influenced by the pH value of the aqueous solution. The pseudo-second-order model and the Langmuir equation well fitted to the adsorption kinetic and isotherm data. Thus, the EDTA intercalated LDH materials had potential applications for Cr(VI) removal in real wastewater treatment.

In the present study, a novel magnetic activated sludge (MAS) was successfully synthesized and applied for heavy metal removal. The MAS was characterized by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), zeta potential analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optimum sorption conditions were identified in view of different adsorbents, adsorbent dosages, pH values and contact times. The batch experiment implied that the pseudo-second-order model was better to describe the adsorption kinetics of Cu(II) and Cd(II) onto the MAS. The adsorption levels of Cu(II) and Cd(II) onto the MAS were in accordance with the Langmuir isotherm with maximum adsorption capacities of 72.1 and 71.3 mg g−1, respectively. According to XPS analysis, the metal sorption process was mainly caused by surface complexation, electrostatic attraction and precipitation. After four desorption cycles using Na2EDTA, the removal efficiencies of Cu(II) and Cd(II) decreased to 88.2% and 87.1%, respectively. The experimental result illustrated that the MAS could be an economical adsorbent for actual heavy metal contaminated wastewater treatment.

In this work, the magnetic alginate microsphere of Fe3O4/MgAl-LDH (Fe3O4/LDH-AM) was prepared by immobilizing the Fe3O4/LDH with calcium alginate (CA) and was used to remove Cd2+, Pb2+, and Cu2+ from aqueous solutions. The obtained Fe3O4/LDH-AM was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller surface area determination. The results indicated that the surface groups of the alginate and LDH were retained and so was the crystal structure in the alginate microsphere. The adsorption performance of the Fe3O4/LDH-AM for Cd2+, Pb2+, and Cu2+ in aqueous solutions was evaluated by batch and column adsorption experiments. The effects of adsorption conditions, kinetics, isotherms, mechanisms, and potential applications were investigated. The adsorption kinetic data conformed to the pseudo-second-order kinetic equation, and the isotherm data fit well with the Freundlich and Langmuir isotherm models. The adsorption mechanism of Cd2+, Pb2+, and Cu2+ by the Fe3O4/LDH-AM entailed complexation and precipitation. The experimental breakthrough curves were correlated with the Thomas model. Moreover, the Fe3O4/LDH-AM displayed superior regeneration and reusability. These results suggest that the Fe3O4/LDH-AM is an efficient adsorbent for the removal of heavy metals and can be effectively employed in practical applications.

We prepared ethylenediaminetetraacetic acid (EDTA)-intercalated MgAl-layered double hydroxide (LDH-EDTA), then grafted acrylamide (AM) to the LDH-EDTA by a cross-linking method to yield a LDH-EDTA-AM composite; we then evaluated its adsorptive ability for Congo red (CR) and hexavalent chromium (Cr(VI)) in single and binary adsorption systems. The adsorption process on LDH-EDTA-AM for CR and Cr(VI) achieved equilibrium quickly, and the removal efficiencies were minimally affected by initial pH. The maximum uptake quantities of CR and Cr(VI) on LDH-EDTA-AM were 632.9 and 48.47 mg/g, respectively. In mixed systems, chromate removal was stimulated by the presence of CR, while the adsorption efficiency of CR was almost not influenced by coexisting Cr (VI). The mechanisms involved electrostatic attraction, surface complexation, and anion exchange for the adsorption of both hazardous pollutants. In the Cr(VI) adsorption process, reduction also took place. The removal efficiencies in real contaminated water were all higher than those in the laboratory solutions.

Though molybdenum disulfide (MoS2) has attracted widely attention in SO4•– based advanced oxidation process recently, the effect of ball milling on its catalytic efficiency is less studied. In this work, the purchased MoS2 was ball milled and applied as peroxymonosulfate (PMS) activator for degradation of tetracycline (TC). MoS2 materials with different milling time or ball-to-MoS2 mass ratio all exhibited higher degradation efficiency (77.2%–83.6%) compared with pristine MoS2 (68.1%). It was supposed that ball milling could optimize the surface properties of MoS2, especially increased the surface area and the amount of S-vacancies, thus exposed more Mo(IV) sites, which were the main active sites to react with PMS. Besides, the enhanced adsorption capacity and the accelerated generation of reactive species both benefited the catalytic efficiency of ball-milled MoS2. EPR spectra and quenching experiments showed that ball-milled MoS2 could generate more reactive species (SO4•–, •OH, O2•–, and 1O2), which favored TC degradation. The above results implied that ball-milled MoS2 materials are promising in advanced oxidation processes.

MoS2 nanosheets were vertically aligned on the surface of biochar calcined from Chinese cabbage and applied to efficiently activate peroxymonosulfate (PMS), which promoted the removal of tetracycline (TC) in aqueous solutions. In heterogeneous PMS systems, the composites with different mass ratios of biochar and MoS2 all exhibited excellent catalytic efficiencies for TC removal. Specially, the extraordinary catalytic efficiency of BC300-MoS2-1 was achieved through the synergistic radical (•OH, SO4•−, and O2•−) and non-radical (1O2) processes, which was demonstrated by the quenching experiments and EPR. Besides, the composites showed better catalytic abilities than pristine biochar, which was mainly due to the increased adsorption affinity and accelerated generation of the reactive oxygen species. On the basis of the intermediates and toxicity estimation, the possible TC degradation pathways were proposed and the degradation by-products were less toxic. Above all, biochar/MoS2 materials are prospective catalysts in SO4•− based advanced oxidation processes.

In this work, we report the fabrication of composition-tunable heterostructured bismuth oxyiodides photocatalysts using a facile ionic liquid-assisted precipitation method at room temperature. Through elaborately governing the reaction parameters, two groups of bismuth oxyiodide hybrids (Group 1: BiOI/Bi4O5I2, and Group 2: Bi4O5I2/Bi5O7I) with different components were prepared. The DRS spectra shows that the absorption edges of the hybrids were gradually tuned from 550 to 660 nm, which was in accordance with the color gradient from light yellow (Bi5O7I) to brick red (BiOI). The SEM images show that the products mainly exhibited 3D hierarchical architecture, which was beneficial for the adsorption of contaminants over the catalyst’s surface. The two groups of heterojunction photocatalysts all exhibited remarkably improved photocatalytic activity in decomposing o-phenylphenol (OPP) and 4-tert-butylphenol (PTBP) under visible light irradiation respect to single phase photocatalyst (BiOI, Bi4O5I2, or Bi5O7I). For BiOI/Bi4O5I2 hybrids, the S5 sample exhibited the optimal activity, which was approximately 5.35 and 1.85 times higher than that of pristine BiOI and Bi4O5I2, respectively. For the second group of Bi4O5I2/Bi5O7I, the optimal activity was observed for S9 hybrid, which was approximately 2.43 and 2.12 times higher than that of bare Bi4O5I2 and Bi5O7I under identical conditions. This activity enhancement should be attributed to the balanced band levels of the components, which facilitates the fast interfacial charge transmigration of photo-generated carriers, resulting in highly promoted charge separation efficiency. This deduction was proved by the photocurrent, electrochemical impedance spectroscopy, and photoluminescence measurements. The possible degradation mechanisms for BiOI/Bi4O5I2 and Bi4O5I2/Bi5O7I hybrids were proposed based on the band potentials and trapping experiment results.

EDTA modified β-cyclodextrin/chitosan (CDCS-EDTA) was fabricated successfully by a two-step method and applied to remove Pb(II) and anionic dye acid red 73 (AR). CDCS-EDTA was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and zeta potential analysis. The effects of experimental parameters including adsorbent dose, contact time and pH value on the adsorption efficiency of CDCS-EDTA for the pollutants were investigated. The maximum adsorption capacities were 114.8 mg g−1 for Pb(II) and 754.6 mg g−1 for AR under the optimal conditions. 93.4% of Pb(II) and 92.1% of AR could be adsorbed within 5 min, and the adsorptions reached equilibrium rapidly within 20 min and 10 min for Pb(II) and AR, respectively. A possible adsorption mechanism had been proposed that chelation of EDTA and electrostatic attraction of hydroxyl and amino groups dominated the adsorption of Pb(II), while the adsorption of AR mainly by the formation of inclusion complex with cyclodextrin cavities and electrostatic attraction with functional groups. For these two pollutants, the adsorption kinetic and isotherm data fitted well with the pseudo-second-order model and the Langmuir model, respectively. Thermodynamic studies implied that the adsorption process of Pb(II) and AR were spontaneous. Furthermore, the excellent regeneration performance indicated that CDCS-EDTA has a promising application in water treatment.

The magnetic graphene oxide and MgAl-layered double hydroxide nanocomposite (MGL) was synthesized via a simple one-pot solvothermal method, and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM) and N2 adsorption-desorption. The results proved that the MGL nanocomposite had typical features of graphene oxide and MgAl-layered double hydroxide. Moreover, the MGL had magnetism which related to the fabrication of Fe3O4 during the solvothermal reaction, and could be easily separated from mixture with easy magnetic separation assistance. Subsequently, the MGL was used to evaluate the adsorption efficiency for lead, copper and cadmium in aqueous solutions by batch equilibrium experiments. The MGL showed excellent adsorption ability for Pb2+, Cu2+, and Cd2+. The pseudo-second-order kinetic equation and Langmuir model well fit the adsorption kinetic data and isotherm data, respectively. Furthermore, the adsorption mechanisms of Pb2+, Cu2+ and Cd2+ by MGL were detailed conducted by XRD and XPS analysis, and could be ascribed to the surface complexation, precipitation and isomorphic replacement.

In present study, magnetic anaerobic granule sludge/chitosan (M-CS-AnGS) composite was synthesized and applied to remove Pb(II) and Cu(II) from aqueous solution. The physicochemical properties of prepared M-CS-AnGS were characterized by using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Zeta potential analysis and X-ray photoelectron spectroscopy (XPS). The factors affecting adsorption performance in view of different sorbents, adsorbent dosage, pH value and contact time were conducted to obtain optimum conditions of Pb(II) and Cu(II) onto M-CS-AnGS. The adsorption kinetics of Pb(II) and Cu(II) were better fitted with pseudo-second-order kinetic mode and Langmuir isotherm. The maximum adsorption capacities for Pb(II) and Cu(II) were 97.97 and 83.65 mg/g, respectively. According to FTIR, Zeta potential and XPS analysis, it was found that the adsorption mechanisms Pb(II) and Cu(II) onto M-CS-AnGS were mainly caused by surface complexation and electrostatic attraction. In addition, M-CS-AnGS could be easily separated under an external magnetic field. The obtained result suggested that M-CS-AnGS composite could be used as a promising adsorbent for metal removal from aqueous solution.

The direct removal of heavy metal ions from acidic wastewater is a hard problem. In this study, a novel superabsorbent, polyvinyl alcohol phosphate ester (PVAP), was designed and prepared to remove Pb(II) from acidic wastewater (pH = 3). The PVAP can absorb water and swell to reach equilibrium within 30 s, which provides the conditions for ultrafast kinetic adsorption. For 100 mg/L Pb(II) solution, the adsorption reaches equilibrium within 5 min, and the removal ratio is more than 99.9% over a wide pH range of 3–6. Adsorption kinetics and isotherm data are consistent with pseudo-second-order and Langmuir model, respectively. The calculated maximum adsorption capacity for Pb(II) is 558.66 mg/g. Thermodynamic results show that the adsorption is spontaneous and exothermic process. The removal ratio for Pb(II) of PVAP still maintains above 99% after ten recycles. The PVAP can also simultaneously remove more than 97% of other heavy metal ions (Cu(II), Cd(II), Zn(II), Co(II), and Ni(II)) from an acidic solution. Moreover, the PVAP can efficiently purify simulated acid mine heavy metal wastewater, and the results meet EPA drinking water standards. The studies of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy prove that the adsorption mechanism involves surface complexation. This new superabsorbent is a promising candidate for acidic heavy metal sewage disposal.

In this study, branched polyethylenimine (PEI) enhanced magnetic carboxymethyl chitosan (MCMC-PEI) was synthesized and applied as adsorbent for the rapid removal of Pb(II) from aqueous solution. The successful synthesis of the adsorbent was proved by scanning electron microscope (SEM), Fourier transform infrared spectrum (FTIR) and X-ray powder diffraction (XRD). Simultaneously, the effect of the parameters such as initial concentration, adsorbent mass and pH of the solution on the removal of Pb(II) was studied by using response surface methodology (RSM). And central composite design (CCD), which is a widely used form of RSM, was employed in the experimental design procedure. The adsorption results revealed that the adsorption process could reach equilibrium rapidly within 10 min. Furthermore, the adsorption kinetic data could be well described by pseudo-second order model. The maximum adsorption capacity was 124.0 mg/g according to the Langmuir-Freundlich model, which fitted the adsorption isotherm of Pb(II) better than Langmuir model and Freundlich model, respectively. Thermodynamic studies (ΔG H S > 0) implied a spontaneous and exothermic process in nature. Meanwhile, the fabricated adsorbent exhibited excellent reusability. Therefore, the excellent adsorption property of MCMC-PEI made it a promising application in water treatment.

Two biochars, from Chinese cabbage (Cc, Brassica rapa pekinensis) and rape (Ra, Brassia campestris L.), were used to prepare biochar/Mg-Al layered double oxides (LDOs) as adsorbents for phosphate removal from aqueous solution. The biochar/LDOs were horizontally alternated lamellar particles and had abundant groups of oxides and biochars. The phosphate removal percentage remained above 92% at a pH range of 2–10, and above 95% during the first 5 min for 50 mg/L phosphate by 0.05 g biochar/LDOs. The adsorption kinetics and isotherms data were well fitted by the pseudo-second-order kinetic equation, as well as by the Freundlich and Langmuir models. Based on FTIR, XPS, and zeta potential analysis, the interaction mechanisms were defined as “memory effect”, electrostatic attraction, surface complexation, and anion exchange. The results indicate that vegetable biochar/LDOs can be considered a novel and efficient sorbent for phosphate removal from water or wastewater.

Magnetic nanoparticles have attracted considerable attention due to their unique properties and versatile applications. Herein, we synthesized nanosized Fe 3 O 4 /bentonite nanocomposites (Fe 3 O 4 /Bents) by the facile one-step solvothermal method (200 °C, 8.0 h) using natural bentonite and ferric chloride as raw materials. The XRD, FTIR, TEM, SEM, BET, and VSM techniques were used to characterize the material and the results indicated that the Fe 3 O 4 /Bents exhibited nanosized and spherical shape with functional groups via the magnetic Fe 3 O 4 orderly assembling on the surface of bentonite. The Fe 3 O 4 /Bents had superparamagnetism feature due to their higher magnetization saturation and lower remanence values. The surface area and total pore volume of the Fe 3 O 4 /Bents were all larger than the nature bentonite and pure Fe 3 O 4 . The feasibility of the as-synthesized Fe 3 O 4 /Bent-2.0 for removal of heavy metals (Pb 2 + , Cd 2 + and Cu 2 + ) from aqueous solution were also evaluated by batch equilibrium experiments. The kinetic and isothermal data well fitted the pseudo-second-order equation and Langmuir model, respectively. The adsorption reached equilibrium within 30 min and the Langmuir maximum adsorption capacities of Fe 3 O 4 /Bent-2.0 were 81.5, 21.7 and 19.6 mg/g for Pb 2 + , Cd 2 + and Cu 2 + , respectively. Furthermore, the magnetic Fe 3 O 4 /Bents can be quickly and easily separated using a magnet before and after the adsorption process.

The amino-functionalized magnetite/kaolin clay (MKC) was synthesized via a simple solvothermal method and used to remove Pb2+, Cu2+, and Cd2+ from aqueous solutions. In comparison, the kaolin clay (KC) and MKC were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning and transmission electron microscopy with energy dispersive spectrometry. The results indicated amino-functionalized MKC was formed with Fe3O4 particles adhering to the surface by interactions with negatively charged KC. The optimal experimental conditions were evaluated, and the adsorption performance of MKC for Pb2+, Cu2+, and Cd2+ was far better than that of KC. This was mainly caused by adding an amino group, in which the amino group displayed complexing ability toward metal ions. In kinetic data representation, the pseudo-first-order, pseudo-second-order, and Elovich models were employed, and the second one gave the better fitting. Langmuir, Freundlich, and Dubinin–Radushkevich models were chosen for ...

We present magnetic diatomite and illite clay nanocomposites by loading Fe3O4 nanoparticles onto the raw diatomite or illite clay surfaces via a simple one-pot solvothermal method. The magnetic clays have ordered structure, rich functional groups and strong magnetism as verified by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning and transmission electron microscope (SEM, TEM), and vibrating sample magnetometer (VSM). Subsequently, the magnetic diatomite (MDC) and illite clay (MIC) were used as adsorbents for fast and efficient removal of phosphate from aqueous solution by batch equilibrium experiments. The adsorption kinetic, isothermal and mechanistic properties were studied. The results demonstrated that the phosphate adsorption onto MDC and MIC was pH-dependent, completed within 30 min and possessed higher capacities than the raw clays. The adsorption kinetic and isotherm data followed the pseudo-second-order equation and the Langmuir model, respectively. The adsorption mechanisms of phosphate were ascribed to the electrostatic attraction and ligand exchange. Furthermore, the MDC and MIC endowed a superior selectivity, regeneration, reusability and can be quickly and easily separated using a magnet before and after the adsorption process.

Magnetic modified vermiculite was prepared by a simple one-pot solvothermal method to remove lead from aqueous solution. The physiochemical properties of vermiculite and magnetic vermiculite were analyzed by X-ray diffraction (XRD), surface-enhanced Raman scattering (SERS), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), specific surface area determination, and magnetic property and zeta potential measurement. The results proved that the vermiculite was successfully functionalized by nanoparticles of Fe3O4. The magnetic vermiculite had superparamagnetic property and higher specific surface areas (52.6 cm3 g−1). Batch adsorption experiments of Pb(II) by vermiculite and magnetic vermiculite were carried out. The results indicated that the adsorption isotherm and kinetic data followed the Langmuir model and the pseudo-second-order equation, respectively. The adsorption process of vermiculite and magnetic vermiculite was fast and the maximum adsorption capacities were 37.0 mg g−1 and 70.4 mg g−1, respectively. In addition, the magnetic vermiculite can be fleetly and easily separated using a magnet after adsorption. It has good potential for cost-effective treatment of lead-contaminated wastewater.

Understanding the adsorption mechanisms of metal cations on the surfaces of solids is important for determining the fate of these metals in water and wastewater treatment. The adsorption kinetic, isothermal, thermodynamic and mechanistic properties of cadmium (Cd(II)) in an aqueous solution containing Mg-Al-CO3- and magnetic Fe3O4/Mg-Al-CO3-layered double hydroxide (LDH) were studied. The results demonstrated that the adsorption kinetic and isotherm data followed the pseudo-second-order model and the Langmuir equation, respectively. The adsorption process of Cd(II) was feasible, spontaneous and endothermic in nature. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to explain the adsorption mechanisms. The characteristic XRD peaks and FTIR bands of CdCO3 emerged in the LDH spectra after Cd(II) adsorption, which indicated that the adsorption of Cd(II) by LDHs occurred mainly via CdCO3 precipitation, surface adsorption and surface complexation. Furthermore, the magnetic Fe3O4/Mg-Al-CO3-LDH can be quickly and easily separated using a magnet before and after the adsorption process.

EDTA functionalized magnetic graphene oxide (EDTA-mGO), a good adsorbent for Pb(II), Hg(II) and Cu(II), was synthesized in the present work. It was characterized by SEM, FTIR, BET, XRD, XPS, TGA and zeta potential analysis. Contact time, adsorbent dose, pH and initial concentration were optimized to improve the removal efficiency. Most importantly, EDTA-mGO displayed better adsorption performance than EDTA-GO, EDTA-Fe3O4 and mGO. The adsorption of Pb(II), Hg(II) and Cu(II) mainly depend on the metal chelation of EDTA and the electrostatic attractions of abundant functional groups on GO surface. Besides, good magnetic performance of EDTA-mGO makes it easy to achieve the solid–liquid separation. The magnetic separation process only took 25 s. The adsorption kinetic data described well with the pseudo-second-order model and the equilibrium data fitted well to Freundlich and Temkin isotherms. The maximum adsorption capacity was 508.4 mg g−1 for Pb(II), 268.4 mg g−1 for Hg(II) and 301.2 mg g−1 for Cu(II) from Langmuir isotherm. Thermodynamic studies (ΔG 0, ΔS > 0) implied an endothermic and spontaneous adsorption process in nature. Furthermore, the excellent reproducibility indicated that EDTA-mGO has a promising application in water treatment.

To reuse the spent magnetic MgAl-layered double hydroxide after humic acid adsorption, this work provided a simple calcination method to prepare the magnetic layered double oxide/carbon (Mag-LDO/C) nanocomposite. The characterization results indicated the Mag-LDO/C was a carbonaceous composite with a large number of functional groups and superparamagnetic property. Then the adsorption performance of Mag-LDO/C for heavy metals was studied by batch experiments. The Mag-LDO/C exhibited excellent removal efficiencies for Cd(II), Pb(II), and Cu(II) with maximum adsorption capacities of 386.1, 359.7, and 192.7 mg/g, respectively. The batch sorption data were studied by the pseudo-second-order kinetic equation and the Langmuir isothermal model, and they matched well. According to the zeta potentials, X-ray diffraction patterns, and X-ray photoelectron spectra of Mag-LDO/C after heavy metals adsorption, the interaction mechanisms were ascribed to the precipitation, surface complexation, and electrostatic attraction. After reaction, the solid-liquid separation of Mag-LDO/C could quickly achieve using a magnet. Additionally, the Mag-LDH/C exhibited excellent adsorption capacities in various simulated wastewater and well sorption recyclability, proving the valuable applications of Mag-LDO/C synthesized from spent adsorbent for metal ions removal in actual water environment.

In present study, aerobic granular sludge (AGS) was applied as a high-efficient biosorbent for dye wastewater treatment. The feasibility of acid TiO

Adsorption of four acid dyes onto cetyltrimethyl ammonium bromide (CTMAB) modified organobentonite from aqueous solution was studied, and effects of the parameters like adsorbent dosage, solution pH, contact time and dye concentration were investigated. The adsorption onto CTMAB-Bent attained equilibrium quickly within 10 min for Acid Blue 93 (AB93), Acid Turquoise Blue A (ATBA), Acid Golden Yellow G (AGYG) and 50 min for Acid Blue 25 (AB25). The adsorption capacity decreased slightly along with the increasing solution pH of 7.0. Four adsorption kinetics equations (pseudo-first-order, pseudo-second-order, intraparticle diffusion and Elovich) were employed to evaluate experimental kinetics data. The rates of the acid dyes adsorption conformed to the pseudo-second-order equation well. The adsorption equilibrium data were analyzed with six models. Both linear and nonlinear regression methods were implemented to calculate isotherm parameters, and the nonlinear regression was more favorable. Regarding to the results of nonlinear analysis, the most applicable adsorption isotherm models were found to be Freundlich, Langmuir, Radke–Prausnitz, Fritz–Schlunder, and Sips equations. The removal ratios of the acid dyes by CTMAB-Bent were all above 88% at the experimental conditions, suggesting that CTMAB-Bent was an excellent adsorbent for acid dyes removal from aqueous solution.

Anaerobic granular sludge-derived activated carbon (AGSC) was prepared as a novel adsorbent for the removal of malachite green (MG) from aqueous solution. The composition and structure of AGSC were characterized by Fourier transform infrared spectroscopy, N2 adsorption–desorption isotherms, Scanning electron microscope, Zeta potential, and X-ray photoelectron spectroscopy. Adsorption capacity of MG onto AGSC was investigated in a batch system by considering the effects of various parameters including pH value, adsorbent dose, contact time, and temperature. AGSC exhibited a high surface area (741.1 m2/g) and adsorption capacity (304.9 mg/g). The pseudo-second-order kinetic model and the Langmuir model could well explain the adsorption processes of AGSC. Thermodynamic parameters of the adsorption processes, such as ΔG (−2.23 kJ/mol), ΔH (5.50 kJ/mol K) and ΔS (25.8 J/mol K), were also calculated. The negative ΔG and the positive ΔH indicated that the adsorption was spontaneous and endothermic. The r...

In this study, three different magnetic core-shell Fe3O4@LDHs composites, Fe3O4@Zn-Al-, Fe3O4@Mg-Al-, and Fe3O4@Ni-Al-LDH were prepared via a rapid coprecipitation method for phosphate adsorptive removal. The composites were characterized by XRD, FTIR, TEM, VSM and BET analyses. Characterization results proved the successful synthesis of core-shell Fe3O4@LDHs composites with good superparamagnetisms. Batch experiments were conducted to study the adsorption efficiency of phosphate. Optimal conditions for the phosphate adsorption were obtained: 0.05 g of adsorbent, solution pH of 3, and contact time of 60 min. Proposed mechanisms for the removal of phosphate species onto Fe3O4@LDHs composites at different initial solution pH were showed. The kinetic data were described better by the pseudo-second-order kinetic equation and KASRA model. The adsorption isotherm curves showed a three-region behavior in the ARIAN model. It had a good fit with Langmuir model and the maximum adsorption capacity followed the order of Fe3O4@Zn-Al-LDH>Fe3O4@Mg-Al-LDH>Fe3O4@Ni-Al-LDH. Thermodynamic analyses indicated that the phosphate adsorption process was endothermic and spontaneous in nature. The three Fe3O4@LDHs composites could be easily separated from aqueous solution by the external magnetic field in 10s. These novel magnetic core-shell Fe3O4@LDHs adsorbents may offer a simple single step adsorption treatment option to remove phosphate from water without the requirement of pre-/post-treatment for current industrial practice.

Xanthate functionalized magnetic graphene oxide (Fe3O4-xGO) was successfully synthesized through linking xanthate groups to a kind of graphenes magnetic material (Fe3O4-GS). Fe3O4-xGO was found to be an ideal adsorbent for Hg(II) and methylene blue removal with a higher adsorption capacity. The synthesized adsorbent was characterized by SEM, TEM, FTIR, XRD, and BET respectively. Fe3O4-xGO can be simply recovered from water with magnetic separation at low magnetic field within only 1min. The adsorption capacity was found to be 118.55mg g(-1) for Hg(2+) (contact time for 180min, pH at 7 and temperature at 25°C) and 526.32mg g(-1) for methylene blue (contact time for 120min, pH at 5.5 and temperature at 25°C), respectively. Kinetic data showed good correlation with pseudo-second-order equation and the Langmuir model was found to fit for the isotherm data, which showed the contaminant sorption was accomplished mainly via chelation or ion exchange. The results of thermodynamic studies (ΔG0, ΔH0, ΔS0) illustrate that the adsorption process was endothermic and spontaneous in nature. The experimental results suggest that Fe3O4-xGO has the potential applications in the environmental management.

In this paper, carboxymethyl functionalized chitosan was used for the synthesis of a magnetic polysaccharide–graphene oxide composite (SCGO). Compared with the magnetic chitosan–graphene oxide composite reported before, adsorption capacity in this research had improved significantly. The calculated maximum adsorption capacity values for methylene blue (MB) and malachite green (MG) were 358.4 mg g−1 and 289.1 mg g−1, respectively. The morphology, chemical properties and physical structure of SCGO were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). The influence factors which included pH, adsorbent dose, ionic strength and contact time on the adsorption properties of MB and MG onto SCGO were investigated. The adsorption kinetics of MB and MG on SCGO were well-described by pseudo-second order kinetic models. The experimental data of the isotherm followed the Temkin isotherm model and the Langmuir model, respectively. Thermodynamic analysis was also performed to calculate the changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS). The results obtained from this research suggested that SCGO was a potential adsorbent for effective removal of methylene blue and malachite green.

The Mg–Al-CO 3 -LDH with Mg 2+ /Al 3+ molar ratio of 2 was prepared via coprecipitation method at constant pH of 9–10 and used to remove three red dyes by batch adsorption method. The results showed the Mg–Al-LDH were well crystallized and can adsorb the red dyes effectively. The optimal adsorbent dosage and contact time were 1.0 g and 60 min, respectively. Adsorbed amount hardly changed when pH

Calcined ZnAl- and Fe3O4/ZnAl–layered double hydroxides (ZnAl–CLDH and Fe3O4/ZnAl–CLDH) were used as adsorbents to evaluate the uptake properties for Cr(VI) removal from aqueous solution by batch equilibrium experiments. The XRD, FTIR and TEM results showed that the calcined ZnAl–LDH and Fe3O4/ZnAl–LDH recovered layered structures according to the memory effect of hydrotalcite. Optimized conditions of Cr(VI) adsorption were obtained: 2.0 g L−1 adsorbent, initial solution pH of 3.0 and contact time of 60 min. The kinetic data was described better by a pseudo-second-order kinetic equation. The adsorption isotherms had a good fit with Langmuir and Freundlich models. Thermodynamic analyses indicated that the adsorption process was endothermic and spontaneous in nature. The adsorption mechanisms involved the reconstruction of LDHs, surface complexation, anion exchange and physical adsorption. The higher adsorption capacities of the calcined products suggested that the ZnAl–CLDH and Fe3O4/ZnAl–CLDH were potential adsorbents for Cr(VI) removal from water and wastewater. Moreover, the magnetic Fe3O4/ZnAl–CLDH can be easily separated using a magnet after the adsorption process.

Magnetic hydroxypropyl chitosan/graphene oxide (MHCGO) composites have been synthesized and employed as adsorbent for removal of lead ions from aqueous solution. X-ray powder diffraction, Fourier transform infrared spectrum, and scanning electron microscope showed that the MHCGO composites were fabricated successfully. The effects of adsorbent dosage, pH, and contact time on the adsorption of lead ions have been discussed, and the optimal adsorption conditions have been acquired. The results indicated that the adsorption of lead ions on MHCGO was dependent on pH with the optimum pH nearly 5.5. The adsorption process was fairly quick and the time to reach adsorption equilibrium is 100 min. The adsorption kinetics could be described by the pseudo-second-order model very well. Adsorption data fitted well with Freundlich model. The effect of temperature on lead ions adsorption was studied and was shown to be spontaneous.

Hydroxy-aluminum pillared bentonite (Al-Bent) was prepared and characterized in this work, and its dye adsorption capacity was comparatively studied in batch experiments. Results of characterization revealed that because of the intercalation of hydroxy-aluminum polyoxycations, a significant increase of interlayer basal spacing, BET surface area and total pore volume was beneficial to dyes' adsorption. The sodium bentonite had a higher adsorption affinity for Basic Fuchsin (BF) and Basic Green (BG) than Acid Turquoise Blue A (ATBA). After pillaring, the adsorption capacity of the three dyes increased and the rise of pH changed insignificantly with solution from 2 to 8. The pseudo-second-order kinetic model provided the best correlation of the experimental data (R2 > 0.99). Henry and Freundlich models both described the adsorption isotherm data well. The adsorption capacity of Al-Bent for the three dyes, especially the basic dyes BF and BG, was high over a wide range of aqueous concentrations and followed the order of BG > BF > ATBA.

In this study, a novel, amino-functionalized magnetic composite of CoFe2O4-chitosan-graphene (MCGS) had been successfully synthesized. The crystal phase, surface morphology and structure of the MCGS were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential measurement, and Brunauer–Emmett–Teller (BET) surface area. The adsorptive characteristics of the MCGS which was intended for removal of Hg(II) from aqueous solutions were deeply studied. The results showed that the adsorption efficiency increased with the increasing of pH and reached the highest point at pH 7.0. The Hg(II) adsorption kinetics on MCGS was consistent with the pseudo second-order process. Langmuir and Freundlich isotherm models were employed to analyze the experimental data, and the Langmuir model was fitted better with a maximum adsorption capacity of 361.0 mg/g at pH 7.0 and 323 K. Thermodynamic studies illustrated that the adsorption process was endothermic and spontaneous.

Magnetic material as adsorbent can provide effective remove and quickly separate of pollutant in wastewater treatment. A magnetic Fe 3 O 4 /MgAl-layered double hydroxide (LDH) composite was prepared by low saturation coprecipitation in the dispersed Fe 3 O 4 suspension. The characterization of XRD, TEM and FTIR revealed that the Fe 3 O 4 /MgAl-LDH composite was combined with Fe 3 O 4 and MgAl-LDH. This provided the composite of magnetic property which improved the separation of solid from aqueous solution. The adsorption of reactive red (RR), congo red (CR) and acid red 1 (AR1) by magnetic Fe 3 O 4 /MgAl-LDH composite depended upon the adsorbent dosage, contact time, initial concentration and temperature. The adsorption of the three red dyes reached equilibrium at 30 min and followed the pseudo-second-order kinetic equation. The equilibrium adsorption isotherm data well fitted the Langmuir model for RR, Freundlich model for CR and AR1. Thermodynamic results demonstrated that the adsorption processes were spontaneous, endothermic for RR and CR or exothermic for AR1. The adsorption capacities changed insignificantly between solution pH 2–10 and the maximum were 97, 253 and 92 mg/g for RR, CR and AR1, respectively. Moreover, the solid composite can be quickly separated from the aqueous solution by an external magnet before and after adsorption process. This indicated that the magnetic Fe 3 O 4 /MgAl-LDH composite was an effective adsorbent for red dyes removal with quick separation.

In the present study, a kind of graphenes magnetic material (Fe3O4-GS) was prepared by compositing graphene sheet with ferroferric oxide, and shown to be effective for removing Cr(VI), Pb(II), Hg(II), Cd(II) and Ni(II) ions from aqueous solution. The synthesized sorbent was characterized by SEM, TEM, FTIR, XRD, XPS and BET, respectively. The pHZPC value of the sorbent was estimated to be 3.5 by alkaline-titration methods. Fe3O4-GS can be simply recovered from water with magnetic separation at low magnetic field within one minute. The sorption capacities of the metals were 17.29, 27.95, 23.03, 27.83 and 22.07 mg g(-1) for Cr(VI), Pb(II), Hg(II), Cd(II) and Ni(II), respectively. Kinetic data showed good correlation with pseudo-second-order equation and the Freundlich model was found to fit for the isotherm data of all the heavy metal ions. It was found that the metals sorption was accomplished mainly via chelation or ion exchange. The results of thermodynamic studies illustrate that the adsorption process was endothermic and spontaneous in nature.

Magnetic cobalt ferrite (CoFe 2 O 4 )-reduced graphene oxide (rGO) nanocomposites (CoFe 2 O 4 -rGO) were developed as an adsorbent to remove Pb(II) and Hg(II) from aqueous solution. The CoFe 2 O 4 -rGO was prepared by a facile approach and characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area and Zeta potential measurement. In this work, contact time, adsorbent dose, and solution pH temperature were optimized. The sorption kinetics and isotherm model fitting studies, demonstrated that data fit well to pseudo-second order kinetics and Langmuir isotherm models. The highest adsorption equilibrium for Pb(II) were 299.4 mg/g at pH of 5.3 and 25 °C; while for Hg(II) were 157.9 mg/g at pH of 4.6 and 25 °C. Due to magnetic property, CoFe 2 O 4 -rGO could be simply recovered from water by magnetic separations at low magnetic field within 2 min.

Phosphate removal is important for the natural water or wastewater treatment, and adsorption is an efficient treatment process. In this study, Mg–Al and Zn–Al layered double hydroxides (LDHs) were synthesized by co-precipitation method at a constant pH of 9–10. The prepared LDHs were characterized by X-ray diffraction (XRD) and BET surface area determination. The XRD patterns showed the characteristic basal reflections of hydrotalcite-like LDH materials. BET surface area of Zn–Al LDH was larger than that of Mg–Al LDH. Adsorption experiments were carried out as a function of LDHs dosage, contact time and initial pH of phosphate solution. The adsorption of phosphate reached equilibrium quickly at about 40 min. The experimental data showed a good compliance with the pseudo-second-order kinetic model. The Freundlich and Langmuir models both described the adsorption isotherm data well ( R 2 > 0.98). Zeta potential and fourier transform infrared spectroscopy (FTIR) analyses were used to elucidate adsorption mechanisms. The results indicated that phosphate species were adsorbed via electrostatic attraction, ligand exchange and ion exchange. The removal ratio of phosphate onto Zn–Al LDH was higher than Mg–Al LDH and reached 95% respectively, suggesting that Mg–Al and Zn–Al LDHs were excellent adsorbents for phosphorus removal from aqueous solution.

Chromium(VI) removal is important for wastewater treatment, and adsorption is an efficient treatment process. In this paper, natural bentonite was exchanged to sodium bentonite (Na-Bent) by adding NaCl. Hydroxy-alumina pillared bentonite (OH-Al-Bent), octadecyltrimethylammonium chloride modified bentonite (OTMAC-Bent) and organic-inorganic pillared bentonite (OTMAC-OH-Al-Bent) were prepared via exchange reaction and then characterized through FTIR and BET measuring. Batch experiments were conducted on adsorption of Cr(VI) by the prepared modified bentonites. The results showed that the adsorption of Cr(VI) by Na-Bent and natural bentonite was neglected due to their weak adsorption performance. The adsorption capacity of Cr(VI) on OH-Al-Bent was much lower than on OTMAC-Bent and OTMAC-OH-Al-Bent. The adsorption isotherms of Cr(VI) by OTMAC-OH-Al-Bent and OTMAC-Bent both fit well with Freundlich and Langmuir adsorption model and the adsorption kinetics data of Cr(VI) fit well with the pseudo-second-order model. The adsorption efficiency was over 90%, suggesting that OTMAC-OH-Al-Bent and OTMAC-Bent were excellent adsorbents for effective Cr(VI) removal from aqueous solution. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 39–46, 2015

It is beneficial to establish a rapid prediction approach of sorption by considering various operating variables that can greatly reduce workload and minimize operational costs. In the present study, Pb(II) sorption onto synthetic biochar (BC), magnetic biochar (M-BC) and EDTA functionalized magnetic biochar (EDTA-M-BC) were comparative investigated in view of adsorption factors, adsorption kinetics and adsorption isotherm. Support vector machine (SVM) model was proposed to predict the adsorption performance by considering various operating variables. It was found that the BET surface areas of BC, M-BC and EDTA-M-BC was 499.2, 255.7 and 57.5 m2/g, respectively, and the majority of pores in the BC samples were mesoporous. The Pb(II) sorption processes by three kinds of BCs were well fitted to pseudo-second-order kinetic model and Langmuir model. According to zeta potential and X-ray photoelectron spectroscopy (XPS) analysis, the adsorption mechanism for Pb(II) adsorbed onto BCs were mainly attributed to electrostatic interaction and chemical complexation. The 10-fold cross-validation was performed to estimate SVM validity. The predication results showed approximately 99.4% accuracy for test datasets and 100% accuracy for experiment data. Thus, SVM could be a reliable accurate estimation method to predict adsorption performance.

In this paper, amino functionalized graphenes (NH2-G) were synthesized for the efficient removal of an acid dye, Metanil Yellow (MY). The morphology, physical structure and chemical properties of the NH2-G were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD) and N2 adsorption–desorption isotherms, respectively. Batch experiments were conducted on the adsorption of MY by the prepared modified graphenes to investigate the effect of several parameters such as pH, dye concentration, adsorption time and temperature. Optimal conditions for the adsorption system were as follows: pH of 7, 0.4 g L−1 adsorbent and contact time of 120 min with the maximum adsorption capacity of 71.62 mg g−1. The adsorption mechanism was investigated by (on the basis of) adsorption isotherms, adsorption kinetic and adsorption thermodynamics. MY adsorption by NH2-G was better fitted by both Langmuir isotherm among five different equilibrium models and pseudo-second-order kinetic model. Furthermore, the thermodynamic experiments results with the values of activation parameters such as free energy (ΔG, −4.729 to −5.592 kJ mol−1), enthalpy (ΔH, 8.120 kJ mol−1) and entropy (ΔS, 43.08 J mol−1 K−1) illustrated that the adsorption process of MY onto NH2-G was endothermic and spontaneous in nature. The results obtained in this study suggest that NH2-G is an excellent adsorbent for effective removal of Metanil Yellow from water.

In this paper, graphene oxides and amino functionalized graphenes (NH2-G) were prepared and employed as adsorbent for the removal of a basic dye, malachite green (MG). The effect of several parameters (pH, dye concentration, adsorption time, and temperature) of the adsorption process was investigated for NH2-G. Four different adsorption isotherms were used to analyze the equilibrium of the adsorption system. The adsorption mechanism was investigated by adsorption thermodynamics and adsorption kinetics. The results indicated that NH2-G showed a high efficiency for the removal of the basic dye MG with the maximum adsorption capacity of 91.48 mg g−1. According to the obtained thermodynamic data, the adsorption of MG onto NH2-G was an endothermic process with a large adsorption enthalpy. The kinetic study showed that the whole adsorption process fit the pseudo-second-order kinetics model well.