Shubin Yang

Highly Efficient Enrichment of Radionuclides on Graphene Oxide-Supported Polyaniline

Graphene oxide-supported polyaniline (PANI@GO) composites were synthesized by chemical oxidation and were characterized by SEM, Raman and FT-IR spectroscopy, TGA, potentiometric titrations, and XPS. The characterization indicated that PANI can be grafted onto the surface of GO nanosheets successfully. The sorption of U(VI), Eu(III), Sr(II), and Cs(I) from aqueous solutions as a function of pH and initial concentration on the PANI@GO composites was investigated. The maximum sorption capacities of U(VI), Eu(III), Sr(II), and Cs(I) on the PANI@GO composites at pH 3.0 and T = 298 K calculated from the Langmuir model were 1.03, 1.65, 1.68, and 1.39 mmol·g(-1), respectively. According to the XPS analysis of the PANI@GO composites before and after Eu(III) desorption, nitrogen- and oxygen-containing functional groups on the surface of PANI@GO composites were responsible for radionuclide sorption, and that radionuclides can hardly be extracted from the nitrogen-containing functional groups. Therefore, the chemical affinity of radionuclides for nitrogen-containing functional groups is stronger than that for oxygen-containing functional groups. This paper focused on the application of PANI@GO composites as suitable materials for the preconcentration and removal of lanthanides and actinides from aqueous solutions in environmental pollution management in a wide range of acidic to alkaline conditions.

Mutual Effects of Pb(II) and Humic Acid Adsorption on Multiwalled Carbon Nanotubes/Polyacrylamide Composites from Aqueous Solutions

This paper examines the adsorption of Pb(II) and a natural organic macromolecular compound (humic acid, HA) on polyacrylamide (PAAM) -grafted multiwalled carbon nanotubes (denoted as MWCNTs/PAAM), prepared by an N(2)-plasma-induced grafting technique. The mutual effects of HA/Pb(II) on Pb(II) and HA adsorption on MWCNTs/PAAM, as well as the effects of pH, ionic strength, HA/Pb(II) concentrations, and the addition sequences of HA/Pb(II) were investigated. The results indicated that Pb(II) and HA adsorption were strongly dependent on pH and ionic strength. The presence of HA led to a strong increase in Pb(II) adsorption at low pH and a decrease at high pH, whereas the presence of Pb(II) led to an increase in HA adsorption. The adsorbed HA contributed to modification of adsorbent surface properties and partial complexation of Pb(II) with the adsorbed HA. Different effects of HA/Pb(II) concentrations and addition sequences on Pb(II) and HA adsorption were observed, indicating different adsorption mechanisms. After adsorption of HA on MWCNTs/PAAM, the adsorption capacity for Pb(II) was enhanced at pH 5.0; the adsorption capacity for HA was also enhanced after Pb(II) adsorption on MWCNTs/PAAM. These results are important for estimating and optimizing the removal of metal ions and organic substances by use of MWCNT/PAAM composites.

Biomass-Derived Sponge-like Carbonaceous Hydrogels and Aerogels for Supercapacitors

As a newly developed material, carbon gels have been receiving considerable attention due to their multifunctional properties. Herein, we present a facile, green, and template-free route toward sponge-like carbonaceous hydrogels and aerogels by using crude biomass, watermelon as the carbon source. The obtained three-dimensional (3D) flexible carbonaceous gels are made of both carbonaceous nanofibers and nanospheres. The porous carbonaceous gels (CGs) are highly chemically active and show excellent mechanical flexibility which enable them to be a good scaffold for the synthesis of 3D composite materials. We synthesized the carbonaceous gel-based composite materials by incorporating Fe3O4 nanoparticles into the networks of the carbonaceous gels. The Fe3O4/CGs composites further transform into magnetite carbon aerogels (MCAs) by calcination. The MCAs keep the porous structure of the original CGs, which allows the sustained and stable transport of both electrolyte ions and electrons to the electrode surface, leading to excellent electrochemical performance. The MCAs exhibit an excellent capacitance of 333.1 F·g(-1) at a current density of 1 A·g(-1) within a potential window of -1.0 to 0 V in 6 M KOH solution. Meanwhile, the MCAs also show outstanding cycling stability with 96% of the capacitance retention after 1000 cycles of charge/discharge. These findings open up the use of low-cost elastic carbon gels for the synthesis of other 3D composite materials and show the possibility for the application in energy storage.

Adsorption of polycyclic aromatic hydrocarbons on graphene oxides and reduced graphene oxides

Graphene has attracted increasing attention in multidisciplinary studies because of its unique physical and chemical properties. Herein, the adsorption of polycyclic aromatic hydrocarbons (PAHs), such as naphthalene (NAP), anthracene (ANT), and pyrene (PYR), on reduced graphene oxides (rGOs) and graphene oxides (GOs) as a function of pH, humic acid (HA), and temperature were elucidated by means of a batch technique. For comparison, nonpolar and nonporous graphite were also employed in this study. The increasing of pH from 2 to 11 did not influence the adsorption of PAHs on rGOs, whereas the suppressed adsorption of NAP on rGOs was observed both in the presence of HA and under high-temperature conditions. Adsorption isotherms of PAHs on rGOs were in accordance with the Polanyi-Dubinin-Ashtahhov (PDA) model, providing evidence that pore filling and flat surface adsorption were involved. The saturated adsorbed capacities (in mmol g(-1)) of rGOs for PAHs calculated from the PDA model significantly decreased in the order of NAP>PYR>ANT, which was comparable to the results of theoretical calculations. The pore-filling mechanism dominates the adsorption of NAP on rGOs, but the adsorption mechanisms of ANT and PYR on rGOs are flat surface adsorption.

Enhanced adsorption of Eu(III) on mesoporous Al2O3/expanded graphite composites investigated by macroscopic and microscopic techniques

Mesoporous Al(2)O(3) was intercalated into an expanded graphite (EG) interlayer to prepare mesoporous Al(2)O(3)/EG composites. The basal spacing of mesoporous Al(2)O(3)/EG composites was enlarged as compared to raw graphite from the X-ray diffraction analysis. The massive surface functional groups and wedge-shaped pores were observed in terms of potentiometric acid-base titration analysis and scanning electron microscope, respectively. The pH-dependent adsorption of Eu(III) on mesoporous Al(2)O(3)/EG composites was evidently independent of ionic strength. The maximum adsorption capacity of Eu(III) on mesoporous Al(2)O(3)/EG composites at pH 6.0 and T = 293 K was calculated to be 5.14 mg g(-1). Desorption kinetics and cyclic operation results showed that mesoporous Al(2)O(3)/EG composites presented high hydrothermal stability in aqueous solution. The thermodynamic parameters suggested that Eu(III) adsorption on mesoporous Al(2)O(3)/EG composites is an endothermic and a spontaneous process. The decrease of Eu-O bond distance with the increasing pH demonstrated that the adsorption mechanism between Eu(III) and mesoporous Al(2)O(3)/EG composites would shift from outer-sphere surface complexation to inner-sphere surface complexation in terms of extended X-ray absorption fine structure spectroscopy analysis.

Characteristics of cesium ion sorption from aqueous solution on bentonite- and carbon nanotube-based composites

The technology development of Cs(+) capture from aqueous solution is crucial for the disposal of nuclear waste and still remains a significant challenge. Previous researches have been proven that ion exchanges with the cations and hydroxyl exchange are the main sorption mechanisms for Cs(+). Therefore, how important are the cation exchange and the hydroxyl exchange mechanisms to Cs(+) sorption? And whether can we improve the sorption capacity of the material by increasing the amount of hydroxyl groups? With these in mind, we herein designed the chitosan-grafted carbon nanotubes (CS-g-CNTs) and the chitosan-grafted bentonite (CS-g-bentonite) by plasma-induced grafting method. The interactions of Cs(+) with CNTs, bentonite, CS-g-CNTs and CS-g-bentonite composites were investigated. The sorption of Cs(+) is mainly dominated by strong cation exchange in monovalent Group I and divalent Group II. And the cation-exchange mechanism is much more effective than the hydroxyl group exchange. The effect of hydroxyl groups is dependent on the property of the matrix. We cannot improve the Cs adsorption capacity of material for Cs(+) only by increasing the amount of hydroxyl groups in any case. The spatial structure and the cation-exchange capacity of the material are important factors for choosing the sorbent for Cs(+) removal from radioactive waste water.

Enhanced adsorption of ionizable aromatic compounds on humic acid-coated carbonaceous adsorbents

Adsorption of ionizable aromatic compounds (IACs) such as 1-naphthylamine and 1-naphthol on Humic acid (HA)-coated graphene oxide nanosheets (GONs), multiwalled carbon nanotubes (MWCNTs), activated carbon (AC), and flake graphite (FG) were investigated by the batch techniques. The adsorption of 1-naphthylamine on four HA-coated carbonaceous adsorbents was weakly depended on pH, whereas the adsorption of 1-naphthol on these HA-coated carbonaceous adsorbents evidently increased with increasing pH from 2.0 to 8.0. The maximum adsorption capacity of HA-coated carbonaceous adsorbents for IACs was in the order of GONs≫MWCNTs>AC>FG, indicating that the GONs can be regarded as a suitable material for the preconcentration and removal of IACs from aqueous solution in environmental pollution management. The main adsorption mechanism between carbonaceous adsorbents and IACs is the hydrophobic effect. This observation is of great implication for the removal of IACs by HA-coated carbonaceous adsorbents in environmental applications.

The highly effective removal of Cs⁺ by low turbidity chitosan-grafted magnetic bentonite.

Chitosan-grafted magnetic bentonite (CS-g-MB) was successfully synthesized via a plasma-induced method. The CS-g-MB composite shows good magnetic properties, low turbidity, and high stability in aqueous solution and exhibits significant adsorption capacity for Cs(+) ions. The adsorption of Cs(+) by CS-g-MB is dependent on both pH and ionic strength. In the presence of Mg(2+), K(+), Li(+), and Na(+) ions, the Cs(+) exchange is constrained in the order of Li(+)≈Mg(2+)<Na(+)<K(+), primarily as a result of the hydrated radii and hydration energies of these cations in aqueous solution. The stability of the CS-g-MB composite in simulated groundwater and in actual seawater was also investigated and this material was found to be a good candidate for the remediation of both types of water. These results demonstrate that enhanced coagulation achieved by plasma modification represents a viable yet advanced technology for wastewater management, and is capable of synthesizing new adsorbents that can be readily separated from solution and that avoid increasing the turbidity and color of the water being treated.

Sequestration of uranium on fabricated aluminum co-precipitated with goethite (Al-FeOOH)

Abstract Aluminum co-precipitated with goethites (Al-FeOOHs) are ubiquitous within (sub)-surface environments, which are considered one of the most important sinks for radionuclide pollution management. Accordingly, various mole ratios Al-FeOOH were synthesized and characterized by XRD, FT-IR, TEM, specific surface area and potentiometric acid-base titration. According to XRD and TEM images, the morphology of Al-FeOOH was transformed from acicular-like goethite to cotton-like gibbsite with increasing Al content. The adsorption and sequential desorption of U(VI) on Al-FeOOHs were conducted by batch techniques under N2 conditions. The batch adsorption results showed that the adsorption of U(VI) on Al-FeOOHs slightly increased at pH < 4.0, then the significant increase of U(VI) adsorption was observed at pH from 4.0 to 7.0, whereas the suppressed adsorption at pH > 8.0 was due to the electrostatic repulsion between negative charge surface and negative carbonato-complexes. The adsorption of U(VI) on Al-FeOOHs was independent of ionic strength at pH > 5.0, indicating that the inner-sphere surface complexation predominated their adsorption behaviors, whereas U(VI) adsorption on Al-FeOOH could be the outer-sphere surface/cation exchange reaction. The sequential extraction texts showed that the desorption of U(VI) from Al-FeOOHs decreased with increasing Al content. These findings highlighted the effect of Al content on the sequestration and immobilization of U(VI) onto Al-FeOOHs from (sub)-surface environments in pollution management.

Localized in situ polymerization on carbon nanotube surfaces for stabilized carbon nanotube dispersions and application for cobalt(II) removal

We demonstrate a two-step in situ polymerization method to develop localized polymer coatings on the surface of carbon nanotubes (CNTs). CNTs show good chemical stability, relatively large specific area, porous and layered nanosized structures. However, difficulties in dispersion quality hinder the practical application of CNT-based composites. Poly(N,N-dimethylacrylamide) (PNDA) is a well-known soluble polymer and it has been proved to improve the sorption efficiency for some metal ions. With these in mind, the plasma-induced grafting polymer technique is used to improve the adsorption capacity and the dispersion property of CNTs. The synthesized multiwalled CNT/poly(N,N-dimethylacrylamide) (MWCNT/PNDA) composites are characterized. After attaching the polymer, the MWCNT/PNDA composites show highly stable dispersion in aqueous solutions and good properties in the preconcentration and separation of Co(II) ions from aqueous solutions. Co(II) ion sorption by MWCNT/PNDA composites obeyed the Langmuir model, attributed mainly to a outer-sphere surface sorption probably via coordination of Co d-electrons to amide and –O–Co and CC (π-electrons) bonds.