Yujiang Li

Hexavalent chromium removal from aqueous solution by adsorption on aluminum magnesium mixed hydroxide

A series of sols consisting of aluminum magnesium mixed hydroxide (AMH) nanoparticles with various Mg/Al molar ratios were prepared by coprecipitation. The use of AMH as adsorbent to remove Cr(VI) from aqueous solution was investigated. Adsorption experiments were carried out as a function of the Mg/Al molar ratio, pH, contact time, concentration of Cr(VI) and temperature. It was found that AMH with Mg/Al molar ratio 3 has the largest adsorption efficiency due to the smallest average particle diameter and the highest zeta potential; AMH was particularly effective for the Cr(VI) removal in a pH range from acid to slightly alkaline, even though the most effective pH range was between 2.5 and 5.0. The adsorption of Cr(VI) on AMH reached equilibrium within 150 min. The saturated adsorption capacities of AMH for Cr(VI) were 105.3-112.0mg/g at 20-40 degrees C. The interaction between the surface sites of AMH and the Cr(VI) ions may be a combination of both anion exchange and surface complexation. The pseudo-second-order model best described the adsorption kinetics of Cr(VI) onto AMH. The results showed that AMH can be used as a new adsorbent for Cr(VI) removal which has higher adsorption capacity and faster adsorption rate at pH values close to that at which pollutants are usually found in the environment.

Adsorption properties of aluminum magnesium mixed hydroxide for the model anionic dye Reactive Brilliant Red K-2BP.

The use of aluminum magnesium mixed metal hydroxide (MMH) as adsorbent to remove Reactive Brilliant Red K-2BP (RBR K-2BP), as a model anionic dye, from aqueous solution was investigated. MMH was prepared by coprecipitation and was characterized by XRD, TEM and average particle diameter. Adsorption experiments were carried out as a function of pH, contact time, concentration of dye, adsorbent dosage, and temperature. The results showed that MMH was particularly effective to remove RBR K-2BP, and that the effective pH range for the dye removal was between 4.0 and 11.0, but at pHs lower than 4, dissolution of MMH took place. A significant decline of dye adsorption occurred at pHs above the isoelectric point (IEP). The adsorption of RBR K-2BP on MMH reached equilibrium within 4h. The appropriate adsorbent dosage was 1000 mg/L. The interaction between the surface sites of MMH and the dye ions may be a combination of both anion exchange and surface complexation. Three kinetic models have been evaluated to fit the experimental data. It was shown that the pseudo-second-order model best described the adsorption kinetics of RBR K-2BP on MMH. The equilibrium isotherm showed that the adsorption of RBR K-2BP onto MMH was consistent with the Langmuir and Freundlich equations. And the saturated adsorption capacity of MMH for RBR K-2BP was 657.5mg/g. The adsorption process was endothermic in nature. MMH displayed superior treatment efficiency to the industrial dye effluents from a printing and dyeing plant with a removal efficiency of 93.8-96.7% for colored materials and 77.9-83.6% for COD.

Removal of petroleum sulfonate from aqueous solutions using freshly generated magnesium hydroxide

Freshly generated magnesium hydroxide (FGMH), produced by adding water-soluble magnesium salts to highly alkaline solutions, was used to remove anionic surfactant petroleum sulfonate (PS) from aqueous solutions. Adsorption experiments were carried out to investigate the effects of pH, adsorbent dosage, contact time, PS concentration, and temperature. The results showed that FGMH displayed excellent treatment efficiency for PS in the pH range 12.0-13.0. The maximum PS removal efficiency was reached within 60 s. The best dosage of magnesium chloride was 2.0 g/L. The adsorption capacity of FGMH for PS decreased as the temperature increased from 303 K to 333 K. The adsorption process was exothermic. The removal mechanism of PS by FGMH may be a coagulation-adsorption process involving a combination of flocculation, adsorption, charge neutralization, and netting catch affection. The results of this study showed that FGMH can be effectively used to treat surfactant wastewaters.

Thiocyanate removal from aqueous solution by a synthetic hydrotalcite sol.

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 FeCl(3) 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.

Investigation into the adsorption of partially hydrolyzed polyacrylamide onto in situ formed magnesium hydroxide particles

In situ formed magnesium hydroxide (Mg(OH)2) particles were investigated through the direct wet precipitation method in the presence of two partially hydrolyzed polyacrylamides (HPAM) of different molecular weights. The influence of the reaction parameters, such as MgCl2 concentration, pH, and reaction temperature, on the interactions between in situ formed Mg(OH)2 particles and HPAM molecules was investigated. The Mg(OH)2 particles obtained in the absence and presence of polymers were characterized in terms of their morphology, particle size, and crystal habit by high-resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, dynamic light scattering, and zeta potential measurements. It was found that different pH values of the reaction solution led to different predominant species distribution for MgCl2. The adsorbed polymer led to the formation of four distinct adsorption regions as the concentration of polymer increased. The adsorption of partially hydrolyzed polyacrylamide on the oppositely charged Mg(OH)2 particles was explained by electrostatic attraction, hydrogen bonding, and bridging.

Rapid and effective removal of sodium lignosulfonate from aqueous solutions by in-situ formed magnesium hydroxide

We investigated the efficiency of in-situ formed magnesium hydroxide (Mg(OH)2) for the removal of sodium lignosulfonate (SLSN) from aqueous solution. Adsorption experiments considered the effects of various conditions such as pH, MgCl2 concentration, contact time, and temperature on SLSN removal efficiency. It was found that approximately 93%-99% SLSN was removed by in-situ formed Mg(OH)2. The adsorption was rapid, and the contact time required to reach complete adsorption equilibrium was less than 2min. Moreover, that the Mg(OH)2 lost about 0.5–3.0% adsorption capacity for SLSN when NO3−, HCO3−, H2PO4− and SO42− anions were simultaneously present with SLSN. The experimental data suggested that there was little competitive adsorption of SLSN with other coexisting anions on Mg(OH)2. The co-precipitation/adsorption process was exothermic and physical, involving weak interactions such as electrostatic attraction, hydrogen bonding, adhesive forces, and van der Waals forces between SLSN molecules and the binding sites on Mg(OH)2.

Fabrication of a magnetite/diazonium functionalized-reduced graphene oxide hybrid as an easily regenerated adsorbent for efficient removal of chlorophenols from aqueous solution

A magnetic hybrid nanomaterial, which contains magnetite (Fe3O4) particles and diazonium functionalized-reduced graphene oxide (DF-RGO), was fabricated via a three-pot reaction. First, the reduced graphene oxide (RGO) was synthesized via a redox reaction. Second, diazonium functionalized-RGO was prepared via a feasible chemical reaction. Third, Fe3O4 particles were loaded onto the surface of DF-RGO by covalent bonding, fabricating the M-DF-RGO hybrid. The fabricated hybrid was characterized by SEM, TEM, AFM, XRD, XPS, FT-IR, TGA, Raman spectroscopy, and magnetometry. The resulting M-DF-RGO hybrid possessed unique magnetic properties and was applied to remove 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) from aqueous solution. The adsorption of 4-CP and 2,4-DCP on the M-DF-RGO hybrid was performed under various conditions, with respect to initial chlorophenol concentration, pH, and contact time. The results suggest that the adsorption of 4-CP and 2,4-DCP onto the M-DF-RGO hybrid is strongly dependent on pH and weakly dependent on contact time. In addition, the adsorption isotherm of 4-CP and 2,4-DCP on the M-DF-RGO hybrid fits the Freundlich model well and the adsorption capacities of 4-CP and 2,4-DCP on M-DF-RGO reached 55.09 and 127.33 mg g−1, respectively, at pH 6 and 25 °C. In this situation, intermolecular interactions including π–π interactions and hydrogen bonding are operative. The calculated results of density functional theory further demonstrate that 2,4-DCP molecules could be more easily absorbed than 4-CP molecules by the M-DF-RGO hybrid. Moreover, the M-DF-RGO hybrid could be easily separated by a magnetic separation process, and showed good recyclability of more than five cycles.

Fabrication of chitosan/magnetite-graphene oxide composites as a novel bioadsorbent for adsorption and detoxification of Cr(VI) from aqueous solution

By utilizing the synergistic effect of chitosan (CS), magnetite (Fe3O4) particles, and graphene oxide (GO), a series of efficient and eco-friendly chitosan/magnetite-graphene oxide (CS/MGO) composites were fabricated through a facile chemical route. First, Fe3O4 particles were chemically deposited on the surface of GO to fabricate MGO hybrid. Then, chitosan was attached on MGO sheets, assembling to CS/MGO composites. According to the results of characterization, the covalent Fe-O-C bonds, electrostatic attraction, and hydrogen bonding between GO, Fe3O4, and chitosan ensure excellent structural stability and physico-chemical properties. The adsorption of Cr(VI) onto CS/MGO composites was also carried out under various conditions (content of CS, pH, initial concentration, contact time, and temperature). The CS/MGO composites possess high removal capacity for Cr(VI) from aqueous solution. Moreover, results also suggested that the CS/MGO composites had a strong reducing action for Cr(VI). When adsorption occurred, Cr(VI) and Cr(III) were simultaneously removed by CS/MGO composites. In addition, CS/MGO composites could retain good Cr(VI) removal efficiency after reuse over five cycles. CS/MGO composites are expected to have potential applications as easily regenerative bioadsorbents for Cr(VI) polluted water cleanup.

Experimental and theoretical calculation investigation of 2,4-dichlorophenoxyacetic acid adsorption onto core–shell carbon microspheres@layered double hydroxide composites

Layered double hydroxides (LDHs) usually aggregate irregularly and hardly redisperse in water. Moreover, the affinity of LDHs is poor for organic compounds. In this study, three different core–shell composites, i.e. CMS@MgAl–LDH, CMS@NiAl–LDH, and CMS@ZnAl–LDH, were synthesized by direct fabrication of LDH nanoplatelets onto carbon microspheres (CMS) for the removal of the adsorbed 2,4-dichlorophenoxyacetic acid (2,4-D). The CMS@LDH composites show good water-dispersity due to the 3D hierarchical sphere structure and high affinity for 2,4-D due to the organic carbon cores that possess abundant hydrophobic compounds. It was found that the adsorption process was rapid, and the time required to reach the sorption equilibrium was within 100 min. The theoretical DFT calculation analysis suggested that the adsorption of 2,4-D on the CMS@LDH composites was dominated by π–π interactions, ion-exchange, and hydrogen bonding. The core–shell CMS@LDH composites can serve as a promising adsorbent that offers a rapid and effective adsorption capacity for the removal of 2,4-D in an aqueous solution.

Rapid removal and recovery of emulsified oil from ASP produced water using in situ formed magnesium hydroxide

Due to the strong emulsion stability of alkaline/surfactant/polymer (ASP) produced water, its treatment and reuse constitute an urgent issue in the petroleum industry. This study presents an effective and economical method to decontaminate emulsified oil via in situ formed magnesium hydroxide (IFM). IFM was directly synthesized in ASP produced water by a wet precipitation method, which is simple for industrial production, and the emulsified oil was simultaneously removed during the precipitation process of IFM. The roles of contact time, pH, interface-active components, temperature, and initial oil concentration in oil removal were systematically investigated. Under optimal experimental conditions, the residue oil concentration could be reduced below 5.0 mg L−1 within 8 min. Even if the emulsion stability was enhanced by an increase in concentration of interface-active components, efficient oil removal could still be achieved. The adsorption capacity of IFM for oil was 10 959 mg g−1 at 293 K. MgOH+ played a significant role during treatment. The oil removal mechanism was mainly dominated by electrostatic attraction and the network structure of IFM. Crude oil could be recovered and the regenerated IFM maintained an oil removal efficiency of 91% in the fifth cycle. The results showed that the co-precipitation/adsorption process by IFM can be used as a promising technology for emulsified oil removal and recovery.