Qiaohui Fan

Sorption of copper(II) onto super-adsorbent of bentonite-polyacrylamide composites.

In this work, bentonite embedded in the polyacrylamide (PAAm) gels was used as a novel adsorbent for the removal of Cu(II) from aqueous solution. The sorption and desorption of Cu(II) on bentonite-polyacrylamide (BENT-PAAm) was investigated as the function of pH, ionic strength, adsorbent content, Cu(II) concentrations and temperature. The results indicated that the sorption of Cu(II) on BENT-PAAm was strongly dependent on pH, ionic strength and temperature. The sorption increased from about 9% to 97% at pH ranging from 2.4 to 7. The sorption of Cu(II) on BENT-PAAm increased with increasing temperature and decreasing ionic strength. The sorption of Cu(II) on BENT and on BENT-PAAm was an endothermic and irreversible process. The results of desorption indicated that the adsorbed Cu(II) ions on solid particles were difficult to be desorbed from solid to liquid phase. From the comparison with BENT, BENT-PAAm showed higher sorption capacity with C(smax) increasing from 29 to 33 mg/g at pH 6.2 and from 11 to 20mg/g at pH 5.0 for the sorption of Cu(II) from BENT to BENT-PAAm composites. The average standard enthalpy change (Delta H degrees) and the entropy change (DeltaS degrees ) of Cu(II) sorption on BENT-PAAm are higher than those of Cu(II) sorption on BENT. The BENT-PAAm composites can be used as a super-adsorbent for the removal of Cu(II) from aqueous solution.

NiO/CoN Porous Nanowires as Efficient Bifunctional Catalysts for Zn–Air Batteries

The development of highly efficient bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for improving the efficiency of the Zn-air battery. Herein, we report porous NiO/CoN interface nanowire arrays (PINWs) with both oxygen vacancies and a strongly interconnected nanointerface between NiO and CoN domains for promoting the electrocatalytic performance and stability for OER and ORR. Extended X-ray absorption fine structure spectroscopy, electron spin resonance, and high-resolution transmission electron microscopy investigations demonstrate that the decrease of the coordination number for cobalt, the enhanced oxygen vacancies on the NiO/CoN nanointerface, and strongly coupled nanointerface between NiO and CoN domains are responsible for the good bifunctional electrocatalytic performance of NiO/CoN PINWs. The primary Zn-air batteries, using NiO/CoN PINWs as an air-cathode, display an open-circuit potential of 1.46 V, a high power density of 79.6 mW cm-2, and an energy density of 945 Wh kg-1. The three-series solid batteries fabricated by NiO/CoN PINWs can support a timer to work for more than 12 h. This work demonstrates the importance of interface coupling and oxygen vacancies in the development of high-performance Zn-air batteries.

Formation of Fe3O4@MnO2 ball-in-ball hollow spheres as a high performance catalyst with enhanced catalytic performances

While the synthesis of heterogeneous catalysts is well established, it is extremely challenging to fabricate complex hollow structures with mixed transition metal oxides. Herein, we report a facile in situ growth process of SiO2@Fe3O4@MnO2, followed by an etching method to synthesize a hierarchical hollow structure, namely Fe3O4@MnO2 ball-in-ball hollow spheres (Fe3O4@MnO2 BBHs). The as-prepared Fe3O4@MnO2 BBHs were applied to degrade methylene blue (MB) by catalytic generation of active radicals from peroxymonosulfate (PMS), exhibiting the merits of excellent catalytic performance, easy separation, good stability and recyclability. In this architecture, the degradation process can be divided into three layers. The outer hierarchical MnO2 nanosheets could accumulate and transport the pollutants by electrostatic interactions and catalyze the generation of active radicals for degradation. Both the inner MnO2 nanosheets and the outer Fe3O4 hollows could produce active radicals to accelerate the pollutant degradation. The active catalytic sites also existed in the inner Fe3O4 hollows, which could further degrade the highly concentrated pollutants in the hollows. This work provides new strategies for the controllable synthesis of complex hollow structures and their application in environmental remediation.

Effect of pH, ionic strength and humic acid on the sorption of uranium(VI) to attapulgite.

Attapulgite was investigated to remove UO(2)(2+) from aqueous solutions because of its strong sorption capacity. Herein, the attapulgite sample was characterized by Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and acid-base titration in detail. Sorption of UO(2)(2+) on attapulgite was strongly dependent on pH values and ionic strength. The presence of humic acid enhanced the sorption of UO(2)(2+) on attapulgite obviously because of the strong complexation of humic acid (HA) with UO(2)(2+) on attapulgite surface. Sorption of UO(2)(2+) on attapulgite was mainly dominated by ion-exchange or outer-sphere complexation at low pH values, and by inner-sphere complexation at high pH values. The results indicated that attapulgite was a suitable material for the preconcentration and solidification of UO(2)(2+) from large volume of solutions because of its negative surface charge and large surface areas.

Magnetic polydopamine decorated with Mg–Al LDH nanoflakes as a novel bio-based adsorbent for simultaneous removal of potentially toxic metals and anionic dyes

Potentially toxic metals and dyes commonly coexist in industrial wastewaters, posing a serious threat to public health and the environment and making the treatment more challenging. Herein, we report a novel magnetic polydopamine (PDA)–LDH (MPL) bifunctional material, which is fabricated by an easy and green approach for the simultaneous removal of potentially toxic metals and anionic dyes. In this assembly, both PDA and LDHs are expected to capture these pollutants. In a mono-component system, the removal behaviors showed heterogeneous removal capacities of 75.01, 624.89 and 584.56 mg g−1 for Cu(II), methyl orange (MO) and Congo red (CR), respectively. Interestingly, the presence of CR and MO enhanced the removal of Cu(II) significantly in the Cu(II)–dye binary system. However, the presence of Cu(II) had no significant effect on dyes. Based on the characterization results including X-ray diffraction (XRD) analysis, Fourier transformed infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and elemental mapping, the removal of Cu(II) was mainly controlled by bonding with surface functional groups (hydroxyl, catechol, imine and amine groups), coupled with isomorphic substitution and surface precipitation. In summary, such a green and facile synthesis method, efficient removal performance and superior reusability suggest that the MPL assemblies have practical application potential for integrative and efficient treatment of coexisting toxic pollutants.

A core–shell structure of polyaniline coated protonic titanate nanobelt composites for both Cr(VI) and humic acid removal

The current methods for chromium and natural organic matter decontamination from wastewater present limitations, such as high cost, poor reproducibility, and detrimental environmental effects as well as by secondary waste. Herein, we synthesized a core–shell structure of polyaniline/hydrogen-titanate nanobelt (PANI/H-TNB) composites through chemical oxidation in the presence of phytic acid, which played an important role in the formation and regeneration of PANI. The adsorption performance of PANI/H-TNB composites as an adsorbent of Cr(VI) and humic acid (HA) from aqueous solutions was tested. A batch technique was adopted to investigate the removal efficiency toward Cr(VI) and HA under various environmental conditions. The PANI/H-TNB composites exhibited excellent adsorption capacity toward Cr(VI) (156.94 mg g−1) and HA (339.46 mg g−1), outperforming that of PANI nanowires and many other materials. Large Kd values (>104 mL g−1) demonstrated the high affinity of the composites for both of Cr(VI) and HA. The analysis of Fourier transformed infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed that the removal of Cr(VI) was a combined effect of reduction Cr(VI) to Cr(III) and chemical sorption, while HA adsorption was mainly via surface complexation between the disassociated HA macromolecules and the positively charged PANI. The PANI/H-TNB composites presented satisfactory regeneration performance and reusability, which greatly reduced the wastewater disposal expenses. For the sake of industrial application, the PANI/H-TNB composites with high adsorption capacities can be applied as a suitable adsorbent for simultaneous removal of Cr(VI) and HA in wastewater cleanup.

Preparation and application of attapulgite/iron oxide magnetic composites for the removal of U(VI) from aqueous solution.

Recently, magnetic sorbents have received considerable attention because of their excellent segregative features and sorption capacities. Herein, attapulgite/iron oxide magnetic (ATP/IOM) composites were prepared and characterized. The sorption results indicated that ATP/IOM composites were superior to ATP and iron oxides individually for the removal of U(VI) from aqueous solution. Based on X-ray photoelectron spectroscopy (XPS) analysis and surface complexation model, the main sorption species of U(VI) on ATP were==X(2)UO(2)(0) below pH 4.0 and==S(s)OUO(2)(+), ==S(w)OUO(2)CO(3)(-), and==S(w)OUO(2)(CO(3))(2)(3-) above pH 5.0. However the prevalent species on ATP/IOM composites were==S(s)OUO(2)(+) and==S(w)OUO(2)(CO(3))(2)(3-) over the observed pH range. ATP/IOM composites are a promising candidate for pre-concentration and immobilization of radionuclides from large volumes of aqueous solutions, as required for remediation purposes.

Size distribution studies of 137Cs in river water in the Abukuma Riverine system following the Fukushima Dai-ichi Nuclear Power Plant accident

The occurrence of (137)Cs in size fractionated samples in river water from the Abukuma River system, (the Kuchibuto and Abukuma Rivers, five sampling events for three sites) was studied from June 2011--approximately some three months after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident until December 2012. The total concentration of (137)Cs (mBq/L) in river water was generally high at the upper stream site in the Yamakiya District within the evacuation/off-limits zone. The (137)Cs concentration was about 1Bq/L for the first sampling campaign (June 2011) at all sites, but then decreased substantially to about one-tenth of that by the time of a second sampling campaign (November or December 2011). The (137)Cs in the <0.45 μm fraction was present exclusively as a dissolved species rather than as a species adsorbed on suspended solids or complexed with organic materials. The contribution of the dissolved fraction ranged from 1.2 to 48.9% (averaged 20%) of the total concentration of (137)Cs throughout the observation period. The maximum contribution of (137)Cs was found in the silt size fraction (3-63 μm), which can be explained by the relatively large Kd values and the suspended solids (SS) concentration of this size fraction. Although the concentration (Bq/g) of (137)Cs in each size fraction did not show any significant trends and/or variations for any of the sampling campaign, Kd values for each site increased with time. Furthermore, it was found that the Kd values decreased with distance from the headstream in the off-limits zone. Thus, the data acquired in this study give an overview of the radiological situation for Fukushima including temporal and spatial variation of radiocaesium in a natural riverine system, within a few years after the accident.

The adsorption behavior of U(VI) on granite

The effects of pH, counter ions and temperature on the adsorption of U(VI) on Beishan granite (BsG) were investigated in the presence and absence of fulvic acid (FA) and humic acid (HA). The adsorption edge of U(VI) on BsG suggested that U(VI) adsorption was mainly controlled by ion exchange and outer-sphere complexation at low pH, whereas inner-sphere complex was the dominant adsorption species in the pH range of 4.0-9.0. Above pH 9.0, Na2U2O7 might play an important role in the rise of U(VI) adsorption again. Counter ions such as Cl(-), SO4(2-) and PO4(3-) can provoke U(VI) adsorption on BsG to some extent, which was directly correlated to the complexing ability of U(VI)-ligand. More noticeably, the large enhancement of U(VI) adsorption in the presence of phosphate can be attributed to the ternary complex formation (BsG-PO4-UO2), precipitation ((UO2)3(PO4)2(s)) and secondary phase (Na-autunite). Both FA and HA can slightly increase U(VI) adsorption at low pH, whereas they strongly inhibited U(VI) adsorption at high pH range. Artificial synthesized granite (AsG) prepared in the laboratory is impossible to use as an analogue of natural granite because of the large difference in the adsorption and surface properties.

Investigation of Cs(I) uptake on Beishan soil combined batch and EDS techniques

The uptake of Cs(I) on Beishan soil (BS) was strongly dependent on ionic strength and hardly dependent on pH over the observed pH range (6-13). The foreign cations competed with Cs(I) in the following order: K(+)>Mg(2+)>Ca(2+)≈Na(+)>Li(+). The uptake of Cs(I) was a pseudo-second-order process and the activation energy, E(a), was about 2.16kJ/mol. EDS analysis suggested that the most of Cs(I) was converged on the basal plane, and a small fraction bound on the frayed sorption site. All the results suggested that ion exchange was the main approach for Cs(I) uptake on BS.