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Two-dimensional montmorillonite nanolayers (2D Mnt) are excellent adsorbents for methylene blue due to the fully exposed active sites, but the separation of 2D Mnt from water is difficult. The objective of the present study was to assemble 2D Mnt and graphene oxide sheets into a three-dimensional aerogel (3D Mnt-rGO Gel) to achieve easy solid–liquid separation. Structural characterization demonstrated that the Mnt-rGO Gel has a porous 3D structure with Mnt nanolayers distributed uniformly within; the introduction of 2D Mnt could reduce significantly the degree of restacking of graphene sheets. Adsorption tests indicated that 2D Mnt enhances the methylene blue (MB) removal performance of Mnt-rGO Gel with a large adsorption capacity of 207 mg g–1, which may be attributed to the adsorption of MB onto 2D Mnt and the increased adsorption surface of rGO resulting from the reduced restacking of graphene sheets. The MB was removed completely by 300 mg L–1 of Mnt-rGO Gel-3 in 180 min. The adsorption process of MB onto Mnt-rGO Gel followed the pseudo-second order kinetic model and the Langmuir isotherm model. Mnt-rGO Gel also showed good reusability. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results suggested that the adsorption of MB onto Mnt-rGO Gel may be attributed to the π–π interactions between aromatic rings of MB and graphene, hydrogen bonding, and the electrostatic interactions between the nitrogen groups on the MB and oxygen-containing groups on the Mnt-rGO Gel. [ABSTRACT FROM AUTHOR]

The adsorption of chelating collector octyl hydroxamate onto malachite was studied at various pH to reveal the adsorption mechanism. Below pH 6, a substantial amount of octyl hydroxamate was consumed by copper ions in solution, leading to low malachite recovery. In the pH range from 6 to 9, octyl hydroxamate mainly existed in the molecular form. The collector reacted with the chemisorbed Cu(OH)+ and Cu(CO3)22− on the malachite surface. The octyl hydroxamate anion was the predominant species above pH 9. The reaction between the anion and the chemisorbed Cu(OH)+ and Cu(CO3)22− on the malachite surface, was responsible for flotation of malachite. At pH 9, the maximum collector adsorption and flotation recovery were achieved, presumably as a result of the coadsorption of octyl hydroxamate molecules and anions. Although Cu(OH)+ and Cu(CO3)22− were the predominant active species for malachite surface below and above pH 8.3, respectively, and octyl hydroxamate anion and molecule were the predominant species below and above pH 9, respectively, the same copper hydroxamate chelate was formed on the malachite surface above pH 6. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substance (EPS)-mineral associations occur naturally in soil and sediments, and they might play crucial roles in heavy metals immobilization. In this study, EPS-montmorillonite composites with different weight ratios were characterized and investigated for their Cd(II) sorption behavior. The results showed that the EPS chains can intercalate into montmorillonite layers by hydrogen bonding connection and chemical reaction between C O, C–N and COO− groups with interlayer cations of montmorillonite, therefore promoting delamination of montmorillonite, especially under a lower weight ratio. An enhancement adsorption of heavy metals was obtained with the composites at lower weight ratios of 1:50 and 0.5:50, whereas composites with higher weight ratio of 5:50 presented a reduced adsorption ability, demonstrating that adsorption of Cd(II) onto the EPS-montmorillonite composites was weight ratio dependent. AFM, CLSM, FT-IR and XPS analysis illustrated that the enhancement of sorption under low weight ratio can be attributed to the release of surface active sites of EPS because of reduced aggregation, the increase of negative surface charges when EPS and montmorillonite were interacted and additional bridging of cadmium ions between EPS and montmorillonite. These findings extend the knowledge into the mobility and fate of Cd(II) in organic matter rich soils and sediments. Image 1 • Cd(II) sequestration in the composites depends on EPS to montmorillonite mass ratio. • Enhancement of Cd(II) sorption by EPS-montmorillonite composite with low mass ratio. • Promotion of surface charge, reduction of aggregation and Cd(II) bridging contribute to the larger sorption. This study firstly reports an enhanced Cd(II) sorption by EPS-montmorillonite composite at low weight ratio. The results provided basic information for studying the fractionation effect of EPS on minerals in heavy metal retention in the natural soil environment. [ABSTRACT FROM AUTHOR]

Highlights • Good floatability of fluorite and barite were obtained by use of NaOL. • Effect of TSP on the flotation separation of fluorite and barite was attempted. • TSP exhibited selective depressant effect on barite flotation in the presence of NaOL. • Zeta potential experiments confirmed the separation mechanism in this study. Abstract In this paper, trisodium phosphate (TSP) was utilized for the flotation separation of fluorite from barite. Micro-flotation results showed that good floatability of both fluorite and barite was obtained at around pH 8.5 using sodium oleate (NaOL) as a collector. TSP showed a selective depression for barite, and flotation separation of fluorite from barite was achieved using TSP as a depressant and NaOL as a collector. Zeta potential measurements indicated that the addition of TSP prior to NaOL did not prevent the adsorption of NaOL on fluorite surface while it prevented NaOL to adsorb on barite surface. [ABSTRACT FROM AUTHOR]

Highlights • The effect of calcite on the malachite sulfidization flotation was attempted. • Calcite slime decreased the flotation recovery of malachite. • Calcite slime prevented the adsorption of S species at malachite surface. • Calcite slime fully coated on malachite surface in malachite-system. Abstract The effect of calcite on malachite sulfidization flotation was investigated by micro-flotation tests, adsorption, sedimentation and zeta potential test. The micro-flotation results showed that the finer the calcite particles size is, the lower the malachite recovery will be in the sulfidization flotation of malachite at around pH 9.5. The addition of calcite slimes prevented the S species adsorption at malachite surface. Zeta potential distribution measurements confirmed that slimes coating of calcite on malachite surface is detrimental to sulfidization flotation of malachite. [ABSTRACT FROM AUTHOR]

Chalcopyrite flotability were investigated in four common chloride salts. The results indicated that NaCl, KCl, CaCl2 increased chalcopyrite recovery while MgCl2 decreased its recovery. The monovalent salts played an insignificant role while divalent salts apparently decreased the contact angle of chalcopyrite, regardless of the presence of collectors. Furthermore, the zeta potential was increased in divalent salts and even changed from negative to positive values in MgCl2, highly due to Mg(OH)2 precipitation on chalcopyrite surface. In addition, molecular dynamics simulation indicated that Mg(OH)2 precipitates on chalcopyrite (112) surface stabilized the liquid layer and formed a hydrophilic barrier to inhibit SBX adsorption. [ABSTRACT FROM AUTHOR]

In this work atomic force microscopy (AFM) was applied to study the wettability of mica and graphite modified with surfactant dodecyltrimethylammonium bromide (DTAB) at varying DTAB concentrations (below the cmc) and adsorption time. The coverage states of DTAB on surfaces were analyzed from the AFM images, while the contact angle measurement was made for the wettability of DTAB-modified surfaces. The experimental results have shown that the adsorption aggregates formed as needle-like dots covering on the mica surface with the surfactant concentration of 10−6-10−4 mol/L. The coverage of DTAB aggregates increased with the increasing concentration, leading to a strong hydrophobicity on the surfaces. However, the large aggregates which might be caused by bilayer adsorption of surfactant occurred on mica surface at surfactant concentration of 10−3 mol/L, resulting in the reverse of the wettability as the adsorption time extended. In the case of hydrophobic graphite, DTAB aggregates mainly formed as stripe covering on the surfaces, leading to the reduction of hydrophobicity. This reduction became stronger as more DTAB aggregates covered on graphite surfaces. [ABSTRACT FROM AUTHOR]

The Hg2+ removal performance of fishbone charcoal prepared from discarded fishbone has been investigated in this work. The XRD, FTIR, and BET results demonstrated that the main composition of fishbone charcoal was hydroxyapatite and the specific surface area was 117 m2/g. The adsorption experiments indicated that fishbone charcoal had an extremely high adsorption capacity for Hg2+ (243.77 mg/g). The excellent Hg2+ adsorption capacity might be ascribed to the ion exchange of Hg2+ to the Ca2+ in the structure of fishbone charcoal, complexation of Hg2+ with ≡Ca(OH)2+ on the surface of fishbone charcoal, as well as electrostatic interaction between electronegative fishbone charcoal surface and cation Hg2+. This work transformed kitchen garbage (i.e., fishbone) into an effective mercury adsorbent with considerable capacity, giving a perspective sight for the utilization of solid waste. [ABSTRACT FROM AUTHOR]

This work attempted to explore the feasibility of using iron-contaminated graphite concentrate as an effective adsorbent for Cr(VI) removal from polluted water. Adsorption isotherm and kinetics were conducted to investigate the Cr(VI) removal capacity by the iron-contaminated amorphous graphite concentrates. In addition, SEM-EDS, XPS were carried out to further examine the solid samples. The results showed that amorphous graphite concentrate had a 1.52 mg/g adsorption capacity of Cr(VI), with the adsorption being fitted well with the pseudo-second-order kinetics model. In addition, chemical adsorption of Cr(V) on iron-contaminated graphite concentrate due to the formation of ≡Fe-O4HCr and Fe2-(CrO4)3 complexes was proposed. This study revealed that iron-contaminated amorphous graphite concentrate would be a cheap and good adsorbent for the removal of Cr(VI) from contaminated water. [ABSTRACT FROM AUTHOR]

This work aimed to study the feasibility of using iron-contaminated graphite as an adsorbent for As(V) removal from water. The adsorbent was prepared by grinding graphite concentrate with steel ball. The study was performed through the measurements of adsorption capacity, BET surface area and XPS analysis. The experimental results showed that the iron-contaminated graphite exhibited significantly high adsorption capacity of As(V). The higher the iron contaminated on the graphite surface, the higher the adsorption capacity of As(V) on the material obtained. It was suggested that the ion-contaminated graphite was a good adsorbent for As(V) removal. [ABSTRACT FROM AUTHOR]

New microscale zero-valent iron adsorbent on fly ash and bentonite matrix for removal of crystal violet (CV) and methylene blue (MB) was synthesized through direct reduction of iron oxide using coke and palm kernel shell. The adsorbent was prepared as cylindrical shaped pellets to remove the CV and MB from the aqueous solution. Nitrogen adsorption-desorption isotherm and scanning electron microscopy (SEM) studies showed that the adsorbent is highly porous, and the iron particles are finely dispersed on the supporting material surfaces. FTIR and UV studies indicated that the C=C bonds in CV and C=N(CH) bonds in MB were affected in the adsorption process. MB switched to the reduced MBH species while CV was reduced to two small-size molecular compounds, explaining the higher CV adsorption in comparison to that of MB. The reduction of these compounds was coupled to the oxidation of Fe to FeO as revealed by XRD characterization of the adsorbent after adsorption. CV and MB adsorption isotherms fitted well with the Langmuir adsorption model. Different adsorption and reduction kinetic models were examined for the MB and CV removal processes. A better fit of the experimental data with the pseudo-second-order model was observed. CV and MB adsorption increased with temperature in the 30-50 °C range. At 50 °C, adsorption capacities of CV and MB reached to 89.9 and 42.8 mg/g, respectively. This new adsorbent showed a superior adsorption capacity for CV and MB when compared to other adsorbents. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the adsorption properties of Cd(II) on graphene oxide prepared from amorphous graphite and flaky graphite. The natural graphite was characterized by Scanning electron microscope, X-ray fluorescence spectrometer and X-ray diffraction. The equilibrium data were described well by both Langmuir model and Freundlich model, and the adsorption rate was fitted by Pseudo-second-order precisely. The GOs before and after adsorption were measured by Atomic force microscope, Fourier transform infrared spectrometer and Energy dispersive system. It was found that the larger adsorption capacity of Cd(II) on GO prepared from amorphous graphite was largely attributed to the more oxygenous functional groups appeared on GO-AG. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of inorganic cations (Na+, Ca2+, and Al3+) with different valences and concentrations on the stability of Na-montmorillonite (Na-MMT) suspension. The stability was studied by turbidity and zeta potential measurements and adsorption thermodynamics. The results showed that the Na-MMT particles coagulated at pH 3-4.8, the stability of which was much inhibited by cations with higher concentration and higher valence. This was caused by the adsorption of cations and the reduction of electrostatic repulsion. Adsorption of Ca2+ on Na-MMT surface fits the Freundlich curve model well. Furthermore, the adsorption reduced the zeta potential of Na-MMT and then the energy barrier between the particles which well obeyed the classic DLVO theory. [ABSTRACT FROM AUTHOR]

To investigate the co-influence of the pore size of adsorbents and the structure of adsorbates on adsorption capacity and rate, the adsorption of basic dyes, methylene blue (MB), and crystal violet (CV) onto a granular adsorbent based on fly ash (GAF) and a granular activated carbon (GAC) were conducted. MB and CV were selected as the target adsorbates due to their similar molecular weights (MB: 319.85 g/mol and CV: 407.98 g/mol) but different molecular structures (MB is line-shaped and CV is fork-shaped). Two different kinds of adsorbents, GAF and GAC, were used here: GAF, a mesoporous adsorbent (average pore diameter ≈ 4.28 nm) with small surface area (21.94 m2/g), and GAC, a microporous adsorbent (average pore diameter ≈ 0.45 nm) with high surface area (1,306 m2/g). Although the surface area of GAC was almost 60 times of GAF, the results of adsorption showed the adsorption capacity of GAC for MB was only 1.5 times of GAF (354.59 mg/g of GAC and 262.58 mg/g of GAF), whereas the adsorption capacity of GAC for CV was even less than that of GAC (327.77 mg/g of GAC and 430.73 mg/g of GAF). Moreover, thekpvalues obtained from intra-particle diffusion theory showed that the adsorption rate of both MB and CV in GAF were far bigger than in GAC. Thus, when choosing an adsorbent, surface area is not only the parameter should be considered, the pore size of adsorbents and the structure of adsorbates should also be considered. [ABSTRACT FROM AUTHOR]

Effects of co-existing ions on the adsorption of As(V) in aqueous solutions by porous hematite have been investigated in this work. The porous hematite was prepared by the goethite concentrate which was concentrated from the iron oxide tailings. The co-existing ions include Cl − , NO 3 − , HCO 3 − , SO 4 2− , PO 4 3− anions and Na + , K + , Mg 2+ , Ca 2+ . The arsenic aqueous solutions with these co-existing ions were simulated using chemical reagents and deionized water. The adsorption isotherm and kinetics were all examined. The experimental results showed that HCO 3 − and PO 4 3− anions inhibited the As(V) adsorption, whereas Mg 2+ and Ca 2+ ions have promoting effects on the As(V) adsorption. Furthermore, the ionic strength has no significant effect on the arsenate adsorption to the porous hematite. These results may be attributed to competitive adsorption of As(V) on porous hematite in aqueous solutions. [ABSTRACT FROM AUTHOR]

A porous-nanostructured material made of short-chain eskolaite (α-Cr2O3) nanoparticles has been synthesized from Cr2O3-loaded activated carbon. The size of the nanoparticles in the chain ranges from 2 to 100 nm. The Cr2O3-loaded activated carbon was prepared by adsorption of dichromate () ions from aqueous solutions on ultrafine activated carbon (less than 12 µm in size) in a batch-glass-stirred reactor at 28°C. After a filtration step, the Cr2O3-loaded activated carbon was processed at high temperature under an oxidizing atmosphere to remove the carbon as CO2(g) and obtain a product high in Cr2O3. This thermal process was carried out in a tube furnace using air as the oxidant. At 1100°C, a product with 98% Cr2O3was produced. The synthesized material is highly porous and is composed by agglomerates of short chains of eskolaite nanoparticles. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area (electron) diffraction (SAED) microscopy were used to determine the chemical composition, texture, crystal structure, and size of the product components. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a recently developed electrosorption technology for deionization using porous electrodes. The electrode materials play an important role in the efficiency. This paper highlights the current research status of carbon-based materials as the electrode and the adsorption models in the CDI. It includes the types and performances of carbon-based materials and the main influencing factors of the desalination characteristics. Also, operating parameters such as charging voltage, flow rate, concentration of feed solution, treating time and temperature are summarized. [ABSTRACT FROM AUTHOR]

This review highlights the adsorption process by using iron oxide minerals as the adsorbent for arsenic removal from water. It includes the characteristics of arsenic in water and its toxicities, the adsorption process for arsenic removal from contaminated water, iron oxide minerals as the adsorbent, arsenic adsorption capacity on iron oxide minerals, main factors of the adsorption, and arsenic removal from water by the adsorption process, as well as the mechanisms by which arsenic species adsorb on iron oxide minerals. [ABSTRACT FROM PUBLISHER]

Specific adsorption of hydrolyzed chromium species on kaolinite surface was studied. Electrokinetic behavior of kaolinite particles in aqueous solutions in the presence of CrCl3 showed that the hydrolyzed chromium species can adsorb on kaolinite surfaces and reverse its charge. This adsorption reached the maximum near the precipitation pH (ppt) of chromium hydroxide. The adsorption followed Langmuir isotherm and was irreversible. It might be resulted from hydrogen bonding between the hydrolyzed metal species and kaolinite surfaces. A novel chemical adsorption model was proposed between kaolinite surfaces and the hydrolyzed multivalent metal species. [ABSTRACT FROM PUBLISHER]

Effects of common ions, namely hydroxyl ions and carbonate, on the adsorption and flotation of malachite with salicylaldoxime as a collector was investigated, making use of solubility, micro-flotation, zeta potential, contact angle, FTIR, and XPS measurements. The results suggested that hydroxyl and carbonate ions affect malachite recovery through altering solubility of this mineral. Under conditions of lower solubility, more stable copper atoms acted as adsorption sites for retaining salicylaldoxime on the malachite surface, and the collector consumed by copper species in slurry was reduced. This allowed more collectors to get adsorbed onto malachite surface, resulting in improved malachite recovery. Zeta potential, FTIR, and XPS measurements indicated that salicylaldoxime chemically adsorbs onto malachite by forming copper salicylaldoxime chelates, in which two salicylaldoxime molecules react with one copper atom by N atom and the O atom combined with benzene ring. [ABSTRACT FROM AUTHOR]

Abstract Effects of sodium chloride on the sulfidization flotation of cerussite (PbCO 3) were investigated by micro-flotation tests, adsorption tests and zeta potential measurements. The micro-flotation test results indicated that sodium chloride effectively improved the sulfidization flotation performance of cerussite. The electrical double layers of cerussite particles were compressed in sodium chloride solution, thus providing more lead sites on the cerussite surface and promoting the adsorption of sulfide ions. In sodium chloride solution, more lead sulfide species were formed on the cerussite surfaces and improved its sulfidization flotation performance. Graphical abstract Unlabelled Image Highlights • Effect of sodium chloride on cerussite sulfidization flotation was investigated. • Sodium chloride improved the sulfidization flotation performance of cerussite. • Electrical double layer of cerussite was compressed by sodium chloride. • More lead sites on cerussite surface enhanced the sulphur ion adsorption. [ABSTRACT FROM AUTHOR]

Graphical abstract Magnesium ions dissolved from lizardite lattice at acid condition that adsorbed on the talc surface at pH 8.5 and enhanced the adsorption of CMC on talc surface. Highlights • A method to improve CMC depression on talc floatability was proposed. • CMC completely depressed talc flotation when the pulp pH was adjusted from 4.0 to 8.5. • Chalcopyrite was more efficiently separated from talc when using the proposed method. • Mg2+ dissolved from talc lattice at pH 4 then adsorbed onto talc surface at pH 8.5. • Mg2+ promoted CMC adsorption on talc surface and enhanced its depression performance. Abstract A novel method to improve carboxymethyl cellulose (CMC) performance in talc flotation is described in this paper. Micro-flotation results showed that using CMC as the depressant, strong depression on talc floatability was observed when the pulp pH was adjusted from low (4.0) to high (8.5), which improved the separation performance between chalcopyrite and talc. Zeta potential measurements illustrated that talc surface charge was less negative when the pH was regulated from acid to base than the situation that the pulp pH was altered from base to acid. ICP test and XPS results indicated that more magnesium ions were dissolved from the talc lattices at pH 4 and the hydrolyzed species of magnesium cations were adsorbed onto the talc surfaces when the pulp pH was adjusted to 8.5, and thus promoting the CMC adsorption on the talc surfaces, which further decreased its floatability. [ABSTRACT FROM AUTHOR]

The recovery of gold cyanide complex Au(CN) 2 − from gold cyanidation with graphene oxide (GO) and GO hydrogel have been studied to explore the possibility of the application of GO or GO hydrogel in gold cyanidation process for extracting gold. The study was performed on the adsorption of artificial Au(CN) 2 − aqueous solution on GO and GO hydrogel. The adsorption results, as well as the SEM-EDS, AFM and XPS, demonstrated that GO was a better adsorbent for the recovery of Au(CN) 2 − from aqueous solution than conventional activated carbon because of its higher adsorption capacity and adsorption rate. It has been also found that the adsorption of Au(CN) 2 − on GO followed the Langmuir isotherm and fitted well with both the pseudo-first-order and pseudo-second-order kinetics models. The recovery of Au(CN) 2 − with GO might be attributed to the interaction between Au(CN) 2 − and oxygenous function groups on GO surface. GO hydrogel exhibited excellent Au(CN) 2 − adsorption property and easy separation, which enabled it a potential adsorbent in gold cyanidation. [ABSTRACT FROM AUTHOR]

As(V) adsorption inside the pores of porous hematite in water has been studied in this work. This study was performed on nonporous hematite and porous hematite prepared from the thermal decomposition of goethite and siderite through the measurements of adsorption isotherm, SEM–EDX, XRD and BET. The results demonstrated that the As(V) adsorption was difficult to be realized inside pores if they were too small. This observation might be due to that the pore entrances were blocked by the adsorbed ions and thus the inside surfaces became invalid for the adsorption. Only if the pore size is large enough, the effective surface area inside pores would be close to that on non-porous hematite for As(V) adsorption. In addition, it was found that siderite is better than goethite for preparing porous hematite with thermal decomposition as adsorbent for arsenic removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient GP composite hydrogel was prepared to adsorb NaOL. • GP composite hydrogel showed an excellent adsorption capacity towards NaOL. • Chemical adsorption and hydrogen bond dominate the NaOL adsorption process. Sodium oleate (NaOL) is commonly employed as a traditional organic collector during the flotation process of phosphate ore. However, the residual NaOL in mineral processing wastewater not only poses a great threat to the environment, but also reduces the qualities of subsequent flotation products. In this study, an effective adsorbent graphene oxide/polyethyleneimine (GP) composite hydrogel was prepared and applied for the adsorption of NaOL. The successful association between GO and PEI was elucidated through various characterizations. Further to that, the adsorption performance was systematically determined through adsorption isotherm, adsorption kinetics, co-existing ions and reusability experiments. The results clearly demonstrated that the adsorption behavior of NaOL could be well described by both pseudo-second-order (PSO) kinetic and Langmuir isotherm models. GP composite hydrogel was able to achieve superior NaOL adsorption with an excellent adsorption capacity (295.95 mg/g) and a quick kinetic (120 min). The existence of competitive ions, such as CO 3 2−, SO 4 2− and PO 4 3−, had a negative effect on NaOL adsorption. The mechanism investigation suggested that chemical adsorption and hydrogen bonds were central and played imperative roles for the adsorption of NaOL on GP composite hydrogel. Overall, the current work provides a valuable reference for the efficient adsorption of NaOL. [ABSTRACT FROM AUTHOR]

Two dimensional molybdenum disulfide (2D-MoS 2) has been recently developed to be used as superb adsorbents for removing heavy metals from water due to its huge sulfur-rich surface area. In this work, single adsorption and co-adsorption performances of H 2 O, Hg2+ and O 2 on MoS 2 surface with and without S-vacancy defects have been theoretically studied to explore the Hg2+ adsorption and surface oxidation through density function theory (DFT) calculations. Moreover, the Hg2+ adsorption and surface oxidation have experimentally studied through atomic force microscopy (AFM) to verify the theoretical calculation results. It has been found that S-vacancy defects make MoS 2 surface more reactive, leading to the much stronger adsorption energy of H 2 O, Hg2+ and O 2 on defective MoS 2 surface. O 2 can only be physically adsorbed on the perfect MoS 2 surface, while it bonds to the unsaturated Mo atoms at the vacancy site on defective MoS 2 surface. Besides, co-adsorption results illustrate that Hg2+ have priority to react with MoS 2 surface than O 2 due to the much stronger binding affinity, and surface oxidation occurs only when there are enough reaction sites for the Hg2+ adsorption and surface oxidation simultaneously. These theoretical co-adsorption results are consistent with the experimental Hg2+ adsorption and surface oxidation results obtained by AFM. These findings in this study are of great significance for the development and utilization of MoS 2 -based nanomaterials as a heavy metal adsorbent. Unlabelled Image • The S-missing vacancy influences both the Hg2+ adsorption and surface oxidation. • MoS 2 has preference for Hg2+ adsorption when there are limited reaction sites. • Oxidation and Hg2+ adsorption both occur when there are redundant reaction sites. [ABSTRACT FROM AUTHOR]

Highlights • Al/MoS 2 has the best adsorption energy, the shortest distance and the good charge transfer. • We found that the top of S atom has enormous energy for adsorbed SO 2 gas molecules in the MoS 2. • The energy band of MoS 2 is changed greatly by B, N, P and Al doping. Abstract In this paper, we investigated SO 2 adsorption on B, N, P and Al doped MoS 2 , which band structure, density of states, charge transfer, etc by the density function theory (DFT) calculation. Results show that the SO 2 prefer to be absorbed at the top of Mo atom of MoS 2. It is found that SO 2 is strongly adsorbed on Al-MoS 2 with considerable adsorption energy of −1 to −2.33 eV, however, the best adsorption position is the top of Mo atom of Al-MoS 2 , which the biggest E a is −2.33 eV, the best charge is −0.343e and the shortest d is 1.763 Å. So these findings confirm that Al-MoS 2 can be used to detect the presence of SO 2 in the environment. [ABSTRACT FROM AUTHOR]

The interaction between chitosan and kaolinite has an important influence on the performance of their composites, the adsorption mechanism of chitosan onto kaolinite surface was investigated by density functional theory (DFT) calculation. The results show that the adsorption energies of chitosan have significant difference on different kaolinite surfaces, but has few difference at different sites on the same kaolinite surface. Chitosan structural unit can interact stablely with kaolinite (001) surface through two strong hydrogen bonds and two moderately strong hydrgeon bonds, and the hydrgeon bond formed between the N atom of chitosan and H atom of hydroxyl group is the strongest. However, the interaction between chitosan and kaolinite(00 1 ¯ ) surface is through two weak hydrogen bonds between the H(N-H, O-H) atoms on chitosan and O atoms on kaolinite(00 1 ¯ ) surface. The structural difference between kaolinite (001) and (00 1 ¯ ) surface is the main reason for the obvious difference in their interaction with chitosan. [ABSTRACT FROM AUTHOR]

Arsenite (As(III)) is toxic in drinking water, which becomes an environmental concern worldwide. This work was to synthesize porous hematite through the calcination of natural goethite concentrate for As(III) adsorption, including adsorption kinetics, isotherms and the influence of pH and temperature. The calcination was performed at 300 °C for 180 min, producing porous hematite with large amount of micropores. The maximum adsorption capacity of As(III) on porous hematite was achieved at pH 6.0 and 25 °C, about 14.46 mg g −1 , compared with 2.965 mg g −1 on the original goethite concentrate. The improvement might be attributed to the formation of micropores and thus the increase in the surface area. Also, it was found that the adsorption was strongly pH dependent and reduced with increasing temperature. It is indicated that the low-cost porous hematite has great potential in As(III) removal from contaminated water. [ABSTRACT FROM AUTHOR]

• Graphene oxide was modified by polyaluminium chloride; • HAO@GO exhibited an excellent adsorption capacity towards fluoride; • Chemical adsorption and ligand exchange are responsible for the adsorption of fluoride onto HAO@GO. Adsorption methods have garnered significant attention for fluoride removal from water bodies owing to their superior selectivity, simple operations, and wider applicability. However, the development of adsorbents with higher adsorption performances requires significant attention. Here, graphene oxide is endowed with excellent affinity towards fluoride by doping polyhydroxy complexes onto its surface structure and regulating the potential charge. Multiple detection measurements involving scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were employed to demonstrate the textural properties of graphene oxide (GO) modified by polyaluminium chloride (HAO@GO). Conversely, the effects of parameters including the preparation conditions, co-existing competitive ions, recyclability, contact time, and initial concentration on the adsorption behaviors were systematically determined. The adsorption experimental data were fitted well by the Langmuir isotherm model and pseudo-first-order model. The calculated maximum adsorption capacity was 129.23 mg/g at room temperature (25 °C) and a pH of 7.00, which is greater than that of most reported adsorbents. The existence of competitive anions, such as NO 3 - , SO 4 2 - , and PO 4 3 - , unavoidably interferes with fluoride adsorption. TEM, zero point of charge test, adsorption isotherm, and X-ray photoelectron spectroscopy (XPS) tests indicated that chemical adsorption and ligand exchange are responsible for the adsorption of fluoride onto HAO@GO. [ABSTRACT FROM AUTHOR]

The necessity for application of molybdenum disulfide (MoS 2) in photocatalytic reduction field required speedy improvement with high reduction and adsorption performance. Here, manganese (Mn) and oxygen (O) dual-doping strategy were taken for demonstrating that enhancing photocatalytic reduction could achieve simultaneous modulation of the reduction and adsorption parameters by optimizing the electronic configuration and hydrophilicity ability in MoS 2. Benefiting from the Mn and O dual-doping collective effect, the developed Mn,O-MoS 2 exhibited outstanding photocatalytic reduction and recovery performances of gold(I) from thiosulfate leaching solutions with reduction capacity of 1386.98 mg/g and the corresponding recovery of 92.50%. Besides, Mn and O atoms dual doping in MoS 2 accelerated the recovery rate, which was 3 folds higher compared with that of MoS 2. Experimental and first-principle approaches suggested that the reduction and adsorption ability of MoS 2 were strengthened through tuning the electronic structure and surface property with Mn and O dopants: (1) Mn atoms notably enhanced the conductivity and optimized the electronic structure for facilitating the reduction performance; (2) The incorporated O atoms greatly promoted the adsorption of [Au(S 2 O 3) 2 ]3- by improving the affinity of water molecules and Mn,O-MoS 2. The work provides a promising strategy to manipulate two-dimensional materials for various applications about catalysts and adsorbent. [Display omitted] • Mn,O-MoS 2 is firstly synthesized by a one-pot hydrothermal approach. • Photocatalytic reduction performances of MoS 2 are strengthened through improving the adsorption and reduction ability. • Excellent reduction property is attributed to the optimized electronic structure. • Adsorption capacity is enhanced by adjusting the affinity of H 2 O and MoS 2. [ABSTRACT FROM AUTHOR]

The adsorption of methylene blue (MB) on graphene oxide (GO) prepared from an economical and resourceful amorphous graphite (AG) was studied. The effects of pH, foreign ions and concentrations of KClO 4 on MB removal were also evaluated. XRD, FT-IR, XPS, AFM and an Analyzer were employed to characterize the prepared GO. The results indicated that the C/O mass ratio of GO reached 1.84 and that thin layers (thickness of which less than 2 nm) accounted for 83.76%. The results of batch experiments showed that the adsorption of MB in the presence of cations decreased in the sequence Li + ≈ Na + > K + , while it was reduced in the order ClO 4 − > NO 3 − > Cl − in the presence of anions. MB removal in ClO 4 − was independent of solution pH, which may be ascribed to the synergistic effect between GO and ClO 4 − . The adsorption process was well described by a pseudo-second-order kinetics model, and the adsorption isotherm agreed well with the Langmuir model. [ABSTRACT FROM AUTHOR]

Comparative study has been performed on the adsorption of Pb(II) on graphene oxides (GOs) prepared from flaky, lump and amorphous graphites with the Hummers method in this work. The GOs were characterized by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, Chemical analysis, Raman spectroscopy and Atomic force microscope. The results indicated that GO prepared from amorphous graphite had lower C/O ratio and more thin layers (less than 2 nm in thickness) than those prepared from the other two natural graphites. The adsorption process was well described by the pseudo-second-order kinetics model, and the equilibrium data agreed precisely with the Langmuir model. The hydroxyl and carboxyl located at the edges of GO sheets mainly participated in the complexation of Pb(II), and different GO sheets were bridged by Pb(II) through simultaneously bonding the marginal oxygenous groups. [ABSTRACT FROM AUTHOR]

Abstract: The stability of colloidal kaolinite dispersions in the presence of NaCl and AlCl3 was studied by measuring turbidity, electrophoretic mobility and adsorption. The kaolinite particles coagulated at pH 2.5–3.5 and were dispersed at pH >4.5. These results well obeyed the classic DLVO theory if the mean zeta potential of the kaolinite particles in aqueous solutions was taken into account in the computation of potential energy of electrical double layer repulsion, which suggests that the kaolinite particles might coagulate in the same way as normal colloidal particles. The kaolinite particles in aqueous aluminum salt solution only coagulated at a medium AlCl3 concentration, and formed a stable dispersion at a high salt concentration. This is caused by Stern-layer adsorption of hydrolyzed aluminum species, probably adsorbed on the kaolinite surfaces through hydrogen bonds between the hydroxyl groups of the aluminum species and the oxygen atoms on the kaolinite surfaces. [ABSTRACT FROM AUTHOR]

Two-dimensional montmorillonite nanosheets (2DMMT), acrylic acid and acrylamide were used as raw materials to synthesize the three-dimensional reticular-structured hydrogel via hydrogen-bond, polymerization, amidation and electrostatic interactions. Morphology characteristics shown the porous structure of montmorillonite hydrogel, offering an open-access for Pb(II) to react with internal adsorption sites. Adsorption tests indicated that 2DMMT hydrogel could achieve the effective removal (99%) for high concentrated Pb(II) solution (125 mg/L) via small hydrogel dosage (1 g/L) within short contact time (60 min). High removal of Pb(II) (70%, adsorption capacity: 90 mg/g) could be still achieved even after five adsorption-regeneration cycles, achieving the long-term servicing for wastewater treatment with cost-optimal operation. Adsorption kinetics and isotherm tests indicating the homogeneous monolayer physical and chemical adsorption between Pb(II) and hydrogel, and the adsorption capacity of Pb(II) was controlled by the amount of adsorption sites on hydrogel. Characteristics of XPS and EDS revealed the adsorption mechanism of ion exchange, chelation reaction and chemical precipitation. Two-dimension montmorillonite with high surface area and fully-exposed active sites formed the reticular-structured hydrogel, showing high removal ability for Pb(II). [Display omitted] • Hydrogen-bond, polymerization, amidation and electrostatic interaction generated the 3D reticular-structured hydrogel. • 3D reticular structure offered an open-access for Pb(II) to react with internal adsorption sites in hydrogel. • Efficient removal for Pb(II) at high concentration is achieved via small dose of hydrogel within a short time. [ABSTRACT FROM AUTHOR]

Hg0 has gradually become a serious environmental problem that need to be solved, due to its strong volatility and insolubility in water. In this study, the adsorption behavior of X(O, Se, Te)-doped monolayer MoS 2 for was studied via DFT calculation to evaluate its potential for Hg0 removal. Oxygen group atoms X(O, Se, Te) doped MoS 2 systems all have extremely high bonding energies, in which the strong interaction between the dopant atoms and the S vacancy of monolayer MoS 2 , resulting that dopant systems were greatly stable. Compared with pristine monolayer MoS 2 , X(O, Se, Te)-doped MoS 2 has stronger adsorption performance and electrical conductivity in adsorbing Hg0, which is mainly attributed to the facilitation of electrons transfer between Hg0 and MoS 2. The oxygen doping system exhibits best adsorption performance to Hg0, primarily due to the relatively stronger interaction between the dopant oxygen and Hg0. The results reveal that the O-doped monolayer MoS 2 can effectively improve the adsorption efficiency of Hg0 increasing the application potential for mercury emissions control in coal-fired power plants. • X(O, Se, Te)-doped MoS 2 exhibited excellent stability. • Superb Hg0 adsorption performance owing to the facilitation of electrons transfer. • The O-doped MoS 2 possessed the top Hg0 adsorption performance. • The most stable adsorption site of O-doped MoS 2 was Tx site. • The strongest interaction between dopant O and Hg0 led to the enhanced adsorption. [ABSTRACT FROM AUTHOR]

Thermal modification was simply performed on molybdenite to enhance the adsorption of Pb(II) in aqueous solutions, and the root of this phenomenon was well studied in this work. Various thermal modification temperatures at 300 °C, 400 °C and 500 °C were applied to modify the surface property of molybdenite, producing different degrees of edge defect and surface wettability in molybdenite samples. Contact angle tests, atomic force microscopy (AFM) observations and adsorption tests illustrated that molybdenite thermally modified at 400 °C contained most edge defects and achieved a 147.846 mg/g Pb(II) adsorption, which was almost 10 times of that obtained by natural molybdenite. The adsorption experiment also indicated that the increase of surface hydrophilia of molybdenite would slightly benefit the Pb(II) adsorption. The X-ray photoelectron spectroscope (XPS) exhibited that a strong chemical adsorption existed between Pb(II) and S elements. AFM study further demonstrated that the interaction between Pb(II) and S atoms exposed at the triangular edges of molybdenite were the intrinsic reason for the great enhancement of Pb(II) adsorption. This work provides a new insight to absorb Pb(II) in aqueous solutions using natural molybdenite. Image 1098194 • M-400 achieved 147.8 mg/g Pb (II) adsorption in aqueous solutions. • Thermal modification enabled molybdenite with a 10 times enhancement on Pb (II) adsorption compared with natural molybdenite. • Sulfur vacancies on edges had strong affinity to Pb ions. [ABSTRACT FROM AUTHOR]

Novel molybdenum disulfide-montmorillonite (MoS 2 @2DMMT) hydrogels for Cu(II) removal and inhibition on bacterial growth were successfully prepared. MoS 2 was first in-situ growth onto 2DMMT platelet through hydrothermal method and then cross-linked with organic reagents to form hydrogels. The flower-like structure of synthesized MoS 2 could be clearly observed in MoS 2 @2DMMT by SEM. The synthesized hydrogels possessed a three-dimensional macroporous structure, offering a free access for contaminants to get inside and combine with the active sites. Adsorption tests revealed that efficient Cu(II) removal (65.75 mg/g) could be achieved within a short time (30 min) at pH 5. The pseudo-second-order kinetics model and Langmuir isotherm model indicated the existence of chemisorption and monolayer absorption for Cu(II) onto MoS 2 @2DMMT hydrogels. Characterizations of EDS and XPS indicated that Cu(II) reacted with groups of carboxyl, hydroxyl and amidogen. Bacteriostatic tests revealed that almost a complete bacteriostatic was achieved with just small dosage (0.8 mg/mL) of MoS 2 @2DMMT hydrogels after the Cu(II) removal under the normal illumination. The mechanism was ascribed to the destructive effect of Cu(II) to the cytomembrane and the damage of reactive oxygen species (ROS) to the DNA. Such hydrogel not only provided insights for treating co-existing contaminates, but also guides for designing novel polymer materials from two-dimensional (2D) nano-materials. Image 1 • Novel molybdenum disulfide-montmorillonite hydrogel with three-dimensional macroporous construction is prepared. • Hydrogel can achieve an effective treatment for heavy metal removal and inhibition on bacterial growth. • Such hydrogel guides for designing novel materials from 2D nanomaterials. [ABSTRACT FROM AUTHOR]

• Incorporation of oxygen dramatically improves the adsorption of Hg2+ on MoS 2. • Oxygen atom greatly facilitates the hydrated Hg2+ ions to approach to MoS 2 surfaces. • Oxygen greatly enhance complexation between sulfur atoms and Hg2+ on MoS 2 surfaces. • Increase of adsorption capacity with increasing oxygen atoms will reach a plateau. Molybdenum disulfide (MoS 2) was incorporated controllably by oxygen in order to modify the hydrophobic surfaces and thus to improve the adsorption of Hg2+ on MoS 2 in aqueous solutions in this work. The experimental results indicated that the incorporation of oxygen could dramatically improve the adsorption of Hg2+ on MoS 2. With 11% oxygen atom incorporation, the adsorption rate and capacity increased over 17 times and 21 folds, respectively, compared with that without oxygen incorporation. This vast improvement was found to be contributed to that the incorporation of oxygen would greatly enhance the complexation between S atoms and Hg2+ on MoS 2 surfaces, resulting in the great increase of the Hg2+ adsorption. The increase of the adsorption capacity with increasing incorporated oxygen reached a plateau, which might be due to the saturation of covalent bond. In addition, the incorporation of oxygen atom greatly enhanced the hydrophilicity of MoS 2 surfaces, facilitating the hydrated Hg2+ ions to approach to MoS 2 surfaces. This finding might provide a highly potential adsorbent for efficiently removing Hg2+ from water. [ABSTRACT FROM AUTHOR]

• Gel of Fe-chitosan/montmorillonite nanosheets efficiently degraded methylene blue. • Synergistic effect of adsorption and photo-Fenton reaction led to dye degradation. • Gel had effective reusability due to continuous reactivation of adsorption sites. • Gel was stable and worked efficiently under a wide range of pH conditions. • Methylene blue was decomposed by demethylation and oxidation reactions. Self-assembled gel of Fe-chitosan/montmorillonite nanosheets (Fe-CS/MMTNS) was prepared for elimination of methylene blue (MB) under visible light in the presence of H 2 O 2. The Fe-CS/MMTNS gel was characterized by FTIR, SEM-EDS, XPS and TG. The Fe-CS/MMTNS gel performed well in the removal of MB through the synergistic effect of adsorption and photo-Fenton reaction. Moreover, this gel worked efficiently under a wide range of pH conditions. This composite gel also showed effective reusability because the adsorption sites of the Fe-CS/MMTNS are continually reactivated through photo-Fenton degradation. Additionally, the Fe-CS/MMTNS gel was found to be stable and the iron ions were hardly leached out because of the complexation between iron and chitosan (CS). The MB degradation occurred by two pathways: a part of MB was directly attacked by reactive radicals and gradually converted into inorganic substances while another part of MB was firstly adsorbed by Fe-CS/MMTNS gel and then degraded by reactive radicals. [ABSTRACT FROM AUTHOR]

In this work, multifunctional MoS 2 prepared by hydrothermal method was studied as an adsorbent for the simultaneous removal of Hg2+, Pb2+ and Cd2+ in aqueous solutions. This study was performed through the adsorption experiments in single- and multi-metal systems. It was shown that MoS 2 exhibited a highest adsorption capacity for Hg2+, and lowest for Cd2+, which was mainly attributed to the different affinities between the S sites and the heavy metals. Based on the results of XPS and Zeta potential, the adsorption mechanisms were investigated in depth, which involved oxidation-reduction between Hg2+ and MoS 2 , electrostatic attraction between positively charged heavy metals and negatively charged MoS 2 , complexation of Hg–S, Pb–S, Cd–S, Hg–O and Pb–MoO 4 and ion-exchange reaction occurred on –SH and –OH. In the coexistence of Hg2+, Pb2+ and Cd2+, the excess MoO 3 generated during the oxidation-reduction between MoS 2 and Hg2+ resulted in a higher adsorption capacity for Pb2+ compared with the condition in single-metal system. However, the adsorption sites of S on MoS 2 would be occupied competitively by the three heavy metals so that it caused lower adsorption capacities for Hg2+ and Cd2+. These findings would make a great significance in the field of water treatment by MoS 2. Image 1 • The co-adsorption on MoS 2 for Hg2+, Pb2+ and Cd2+ has been studied first. • An original adsorption mechanism is come up with in multi-metal system. • The analysis of characteristic and mechanism is productive. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2)-based nanomaterials stand out from two-dimensional (2D) materials as a promising adsorbent for the removal of heavy metals from aqueous solution due to their extremely marvelous adsorption performances. The superb uptake capacity is primarily ascribed to the intrinsically rich S atoms exposed on the surface of MoS 2 , which distinguishes MoS 2 -based nanomaterials from other 2D materials. This work presents the latest advances of MoS 2 nanomaterials as adsorbent for the removal of heavy metal ions in water. Various preparation methods, as well as the structure, property and modification of MoS 2 , is summarized. The adsorption capacity and mechanisms, affecting factors and regeneration are highlighted. The practical application of MoS 2 as potential adsorbent for the removal of heavy metals from water is emphasized, and research needed for future application is simultaneously identified. • We summarize the preparation and modified methods of MoS 2 -based nanomaterials. • We describe the adsorption capacities of MoS 2 to remove heavy metals. • We summarize the mechanisms and affecting factors of MoS 2 as an adsorbent. • We propose the research of MoS 2 -based adsorbents needed for future application. [ABSTRACT FROM AUTHOR]