Oil/water separation has become a worldwide challenge due to large volumes of industrial oily wastewater and frequent oil spill accidents, which constitute an enormous threat to human and biological safety. Herein, a superhydrophilic and underwater superoleophobic composite membrane was fabricated using the vacuum-assisted filtration technique of assembly of chitosan (CS) and titanium dioxide (TiO2) on a cellulose acetate membrane for emulsified oil separation. The hydrophilic chitosan–TiO2 (CST) composite and nanoscale hierarchical structure are beneficial for forming a water layer that can repel the infiltration of oil droplets into the membrane. The modified membrane demonstrated an excellent flux up to 6002.5 L m−2 h−1 for hexadecane-in-water emulsion, which is one order of magnitude higher than traditional filtration membranes. Furthermore, the separation efficiency for all of the emulsified oils is above 97%, indicating superior oil/water separation performance. Most importantly, the modified membrane can maintain underwater superoleophobicity even in corrosive aqueous media, including strongly acidic, strongly alkaline, and highly saline solutions. It is expected that the chitosan–TiO2 composite membrane can be potentially useful in treating oily wastewater from industry and daily life.

In this work, aggregation and deposition of in situ formed magnesium hydroxide (IFM) in the presence of hydrolyzed polyacrylamide (HPAM) were investigated. Relative concentrations of interactants, as well as other experimental conditions, were changed to elucidate the interaction mechanisms from microscopic to macroscopic levels. Light scattering measurements were used to investigate the aggregation kinetics, fractal dimension, and collision efficiency of the aggregates on a microscopic level. Electrophoretic mobility and TEM were utilized to measure the charging properties and morphologies of aggregates, respectively. Adsorption and rheology experiments were performed to determine the deposition mechanism at higher concentrations of interactants on a macroscopic level. The results demonstrate that the initial rapid aggregation of IFM in the presence of HPAM is due to an electrostatic patch mechanism. In addition, the deposition was accelerated by flocculation with different mechanisms. When more IFM is involved, bridging flocculation dominates; when more HPAM is added, depletion flocculation plays a leading role. The results of this work may provide further insight into understanding the aggregation and deposition of in situ formed natural/engineered particles in the presence of oppositely charged polyelectrolytes, as well as provide new possibilities for produced water treatment, biomedical applications, biomineralization, etc.

•Hierarchically modified membranes were fabricated using facile methods.•Hierarchical structure contains layered and rod-like materials.•Layered materials is essential for achieving better anti-fouling performance.•Layered materials properties affect oil/water separation and anti-fouling ability.Membranes with hierarchical architectures consisted of 1D and 2D materials have shown excellent performance in emulsified oil/water separation, but the roles of 2D layered materials in oil/water separation and anti-fouling performance are still to be clarified. Here, we used a facile layer-by-layer assembling approach to fabricate 3D hierarchical membranes using a porous cellulose acetate support membrane coated with graphene oxide (GO) or layered double hydroxides (LDH) grafted with sepiolite (SeP), and then the roles of GO and LDH in oil/water separation and anti-fouling performances of these hierarchically modified membranes were investigated. Results of characterization experiments showed that these membranes were successfully fabricated. Wetting behavior of these membranes indicated that the hierarchical structure can provide high permeate flux and underwater superoleophobic properties. Though the fabrication processes were similar, the surface of SeP + GO and Sep + LDH coated membrane showed different morphologies. After cyclic oil/water separation experiments we found that SeP + GO coated membranes exhibited higher flux and slower decline of permeation than SeP + LDH coated membranes due to its unique properties. Our research demonstrated that the properties of 2D layered materials play important roles in determining water permeability and anti-oil-fouling performance of modified membranes with hierarchical structure.Download high-res image (193KB)Download full-size image

•In-situ generated metallic hydroxides from leaching solution of white mud.•Approximately 95–99% of the emulsified oil was removed by IGMHs.•IGMHs could be used for at least four cycles.•Recovery of oil from oily wastewater could improve economic competitiveness.Leaching solution of white mud (LSWM), a form of industrial waste from alumina plants, was added to alkaline oily wastewater, and metallic hydroxides were in-situ generated (IGMHs). We evaluated the removal efficiency of emulsified oil by IGMHs from simulated alkali/surfactant/polymer flooding produced water. The influence of various factors, such as LSWM dosage, initial pH, temperature, and contact time on oil removal efficiency was investigated. It was found that approximately 95–99% of emulsified oil was successfully removed by the co-precipitation/adsorption process. In addition, highly basic conditions and lower temperatures were preferred for IGMHs to remove emulsified oil. Thermodynamic analysis showed that the co-precipitation/adsorption process was spontaneous, exothermic and physical in nature, involving weak interactions, such as electrostatic attraction, hydrogen bonding, and adhesive force between the emulsified oil droplets and the binding sites on the surface of IGMHs. It was observed that IGMHs lost approximately 18.9% adsorption capacity for emulsified oil after more than four cycles. Therefore, IGMHs could be used effectively for at least four cycles. Moreover, recovery of oil from oily wastewater could improve the economic viability of this treatment process.Download high-res image (68KB)Download full-size image

•Exfoliation of LDHs into single-layer nanosheets with a high LDHNSs content is achieved in water.•This is a green alternative to the traditional method with the use of organic solvents for exfoliation.•LDHNSs provide stable colloidal properties, which are useful in water remediation and pollution control fields.•Adsorption rate was enhanced 15–30 times by exfoliating LDH nanosheets.•The synergism of electrostatic attraction, ion-exchange, and hydrogen bonding promoted the adsorption efficiency.Direct exfoliation of lactate-intercalated [MgAl-NO3]-LDH nanocomposites (LCT-LDH) into single-layer LDH nanosheets in water media, termed LDHNSs, to enlarge the overall surface area and adsorption rate. The LDHNs were then used as adsorbents to remove Cr(VI) from aqueous solution by batch adsorption method. Adsorption experiments considered the effects of various factors such as pH, dosage, contact time, and temperature on Cr(VI) removal efficiency. The morphology, texture, and surface properties of the [MgAl-NO3]-LDH, LCT-LDH, LDHNSs, and Cr-LDHNSs were characterized by HRTEM, AFM, XRD, FT-IR, XPS, elemental analyzer and zeta potential analyzer. It was found that the optimum pH for Cr(VI) maximum removal efficiency onto LDHNSs was pH 6.0. Adsorption data were found to be better fitted by the Langmuir isotherm, and the maximum adsorption capacity of LDHNSs for Cr(VI) was 125.97 mg/g at 308 K. The adsorption of Cr(VI) onto LDHNSs was rapid, and the contact time required to reach complete adsorption equilibrium within 8 min. Thermodynamic analysis showed that the adsorption process was endothermic, spontaneous, and physical in nature, involving weak interactions such as electrostatic attraction, ion-exchange, and hydrogen bonding between the Cr(VI) species and the binding sites on the LDHNSs.Download high-res image (146KB)Download full-size image

•Nanographite oxide (NGO) was prepared and used as adsorbent to treat p-nitrophenol.•NGO possessed good adsorption ability to p-nitrophenol with rapid reaction time.•The adsorption of p-nitrophenol onto NGO was physisorption and exothermic.Nanographite oxide prepared by a chemical oxidation method was characterized by SEM, XRD, FT-IR, zeta potential and BET surface area. The use of nanographite oxide as an adsorbent to remove p-nitrophenol from aqueous solutions was investigated. Adsorption experiments were carried out as a function of the contact time, initial p-nitrophenol concentration, pH, adsorbent dosage, and temperature. It was found that the nanographite oxide possessed a large surface area and was particularly effective for the removal of p-nitrophenol. The removal efficiency of p-nitrophenol decreased with an increase of the solution pH from 4.0 to 7.0 and an increase in the temperature. The adsorption of p-nitrophenol onto nanographite oxide reached equilibrium within 2 h. The maximum adsorption capacity of nanographite oxide for p-nitrophenol was 268.5 mg/g at 283 K and a natural pH. The Freundlich isotherm was the best choice to describe the adsorption behavior. The kinetic data were presented by the pseudo-second-order kinetic model. The parameters suggested that the adsorption process of p-nitrophenol onto nanographite oxide occurred via physisorption process and was exothermic in nature. Hydrogen-bonding, electron donor–acceptor and Lewis acid/base interactions were the main mechanisms affecting the adsorption capacity, while dispersive interactions were also found to influence the adsorption of p-nitrophenol through the influence of its deactivating functional groups on the aromatic ring. The results showed that nanographite oxide can be used as a new adsorbent which has higher adsorption capacity and faster adsorption rate for the removal of p-nitrophenol.

•Different alkyl chain length surfactants were used to modify Na-montmorillonite.•The organoclays were used as adsorbents for the removal of chlorophenols.•The adsorption process is complex and involves multiple mechanisms.•Adsorption involves partitioning, electrostatic and van der Waals forces.Organoclays were prepared by replacing exchangeable Na+ ions in Na-montmorillonite (Na-Mt) with dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB). Organic modification is important in order to obtain good affinity between organoclays and organic pollutants. Hydrophobic DTAB-montmorillonite (DTAB-Mt) and CTAB-montmorillonite (CTAB-Mt) were studied as adsorbents for 4-chlorophenol and 2,4-dichlorophenol. The morphology, structure, and surface properties of Na-Mt and organoclays were characterized by scanning electron microscopy, X-ray diffraction, Fourier infrared spectroscopy, specific surface area, and zeta potential measurements. Adsorption was determined as a function of adsorbent dosage, pH, contact time, and temperature. It was found that pH and temperature had very important effects on the adsorption of chlorophenols. The Langmuir isotherm was the best choice to describe the adsorption behavior. The maximum adsorption capacities of CTAB-Mt for 4-chlorophenol and 2,4-dichlorophenol were 395.0 and 585.8 mg/g, respectively, whereas the maximum adsorption capacities of DTAB-Mt for 4-chlorophenol and 2,4-dichlorophenol were 331.1 and 458.2 mg/g, respectively. The kinetic data fitted the pseudo-second-order kinetic model. Thermodynamic parameters suggested that the adsorption process of chlorophenols onto organoclays was physisorption and exothermic. The adsorption mechanism is a complex process that involves a combination of partitioning, electrostatic attraction, and van der Waals forces.

•LDHs-SDS has a hydrophobic surface and great affinity toward organic dyes.•LDHs-SDS effectively remove anionic, cationic and nonionic dyes from wastewater.•The treatment of LDHs-SDS to an actual dye wastewater proved to be favorable.Organic dyes are an important class of pollutants in wastewater, and it is necessary to find a broad-spectrum adsorbent that can effectively remove different kinds of organic dyes. Through the organic modification of layered double hydroxides (LDHs), the surface properties of the LDHs change from hydrophilic to hydrophobic, resulting in a greater affinity for organic pollutants. Dodecylsulfate-intercalated layered double hydroxide (LDHs-SDS) was prepared with a Mg/Al molar ratio of 2:1 using a co-precipitation method, and was characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The synthesized LDHs-SDS was used as an adsorbent to remove anionic (direct blue G-RB (DB), reactive yellow 4GL (RY), acid red GR (AR)), cationic (basic blue (BB)) and nonionic dyes (disperse red 3B (DR)) from aqueous solution. The sorption was found to be independent of pH from 5 to 10. The maximum removal capacities for DB, RY, AR, DR and BB were 707.76, 392.88, 137.33, 249.24 and 165.11 mg/g, respectively, at 298 K. The adsorption isotherm for AR fitted the Freundlich model well, and data for the other dyes fitted the Langmuir model. The sorption kinetics of all five dyes were well described by the pseudo-second-order model. After treating actual dye wastewater with LDHs-SDS, the results indicate that this could be a potentially effective adsorbent for dye effluent treatment.

The use of a chloride-containing synthetic hydrotalcite sol (LDHC) as adsorbent to remove thiocyanate from aqueous solution was investigated. LDHC was prepared by coprecipitation and was characterized by HRTEM, particle size, XRD, and FTIR. The experiments showed that LDHC was particularly effective in removing thiocyanate due to its small particle size and high zeta potential. The adsorption of thiocyanate on LDHC was favored when the initial solution pH was in the range 3–10, though the most effective pH range was between 4.0 and 8.0. The adsorption reached equilibrium within 150 min. The interaction between the surface sites of LDHC and thiocyanate ions may be a combination of both anion exchange and surface complexation. The pseudo-second-order model best described the adsorption kinetics of thiocyanate onto LDHC. The equilibrium isotherm showed that the adsorption of thiocyanate on LDHC was consistent with the Langmuir equation and the saturated adsorption capacity of LDHC for thiocyanate was 98.3 mg/g at 20 °C. The regenerated LDHC in FeCl3 solution can be used repeatedly in adsorption–regeneration cycles. The results showed that LDHC can be used as a new adsorbent for thiocyanate removal from aqueous solution because of its high adsorption capacity and rapid adsorption rate.Graphical abstractThe adsorption of thiocyanate on LDHC was consistent with the Langmuir equation and the saturated adsorption capacity of LDHC for thiocyanate was 98.3 mg/g at 20 °C. Adsorption isotherms of thiocyanate onto LDHC (LDHC dosage 2.0 g/L, T = 20 °C, initial pH 5.5).Research highlights► Previous research on adsorption of thiocyanate anions in aqueous solution by LDHC is limited. ► LDHC can be used as a new adsorbent for thiocyanate removal from aqueous solution because of its high adsorption capacity and fast adsorption rate. ► The adsorbed thiocyanates on LDHC can be desorbed in FeCl3 solution and the regenerated LDHC can be used repeatedly in adsorption-regeneration cycles.

Alkaline/surfactant/polymer (ASP) flooding technology has been successfully used in Chinese oil fields, such as Daqing and Shengli. However, water produced from ASP flooding contains large quantities of residual chemicals (alkali, surfactant and polymer) making it a complex and stable emulsion system which is difficult to treat. The emulsion stability of water produced from ASP flooding was investigated by conducting settling experiments and measuring the oil–water interfacial properties. The experimental results showed that the addition of polymer (HPAM, hydrolyzed polyacrylamide) degrades the emulsion stability when its concentration is below 300 mg/L for the 1.2 × 107 MW polymer, and 800 mg/L for the 3.0 × 106 MW polymer. But it enhances the emulsion stability when polymer concentrations are above those levels. At low polymer concentrations, flocculation induced by the polymer on oil droplets in the produced water is the dominant factor, while at high polymer concentrations the produced water viscosity plays an important role in the emulsion stability. The adsorption of surfactant on the oil–water interface increases the zeta potentials and decreases interfacial tension, and thus remarkably enhances the emulsion stability. Furthermore, the emulsion stability is enhanced gradually with the increase of NaOH concentration up to 300 mg/L due to the increase of zeta potentials and decrease of interfacial tension, and then weakened with the further increase of NaOH concentration, which is attributed to the decreased strength of the interfacial film. A pilot experiment for the treatment of simulated water was done, and the result showed that the simulated produced water from ASP can be successfully treated by using a leaching solution of alkaline white mud.

Calcined hydrotalcite is a potential ion exchanger/adsorbent which can be used to remove toxic anions from contaminated water. The adsorptive removal of thiocyanate from aqueous solutions by calcined hydrotalcite was investigated in a batch mode. The influence of initial thiocyanate concentration, adsorbent concentration and temperature on the kinetics of thiocyanate removal was tested in kinetic runs. Three kinetic models were used to fit the experimental data, and it was found that the pseudo-second-order kinetics model is most appropriate to describe the adsorption kinetics. A Langmuir isotherm was used to fit the equilibrium experiments, and the saturated adsorption capacity was approximately 96.7 mg/g, under the experimental conditions. The calculated activation energy for the process was 48.9 kJ/mol.

•Effective broad-spectrum adsorbent for the removal of dyes.•The surface property inversion from hydrophilic to hydrophobic.•The intercalation of the surfactant chains created organic partition medium.•Electrostatic, partition interactions affect the adsorption of dyes.The utilization of organo-modified layered double hydroxides with anionic surfactants (organo-LDHs) as adsorbents were successfully carried out to remove various synthetic dyes from aqueous solution. Intercalation of anionic surfactants changed the surface properties of MgAl-LDH from hydrophilic to hydrophobic, and a charge inversion occurred with increasing the length of surfactant chains. Such changes in the surface properties of the organo-LDHs were important. Experimental data shown that the SNS-modified MgAl-LDH could be used as a broad-spectrum adsorbent to effectively remove anionic, non-ionic, and cationic dyes from aqueous solution.HRTEM images of (a) MgAl-LDH, (b) SHS-LDH, (c) SNS-LDH, and (d) SDS-LDH.Download high-res image (470KB)Download full-size image