Xi-Lin Wu

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.

Sorption of Heavy Metal Ions from Aqueous Solutions: A Review

Sorption techniques are widely used to remove heavy metal ions from large volumes of aqueous solutions. Herein, the natural and some artificial materials, such as clay minerals, biosorbents, carbon-nanomaterials, metal oxides, are reviewed as adsorbents in the removal of different heavy metal ions, such as Ni(II), Cu(II), Pb(II), Cd(II), Cs(I), Eu(III), Th(IV), Cr(VI) from large volumes of aqueous solutions. The sorption kinetics and thermodynamics, the influ- ence of environmental factors on the sorption, the possible sorption mechanism of heavy metal ions and the modification of adsorbents on the removal of heavy metal ions are discussed in detail. The sorption properties of the different adsorb- ents are also described. The different methods such as batch sorption techniques and spectroscopy techniques (such as XPS, FTIR, EXAFS, ATR-IR) in the determination of heavy metal ion sorption properties and sorption mechanisms are presented. Different models for the simulation of sorption isotherms and kinetic sorption data are given as a comparison to understand the sorption mechanism. Many amphibolous matters for further research and the necessity in the study of the selective adsorbents in multi-component sorption systems are also summarized. The transfer of substances from a mobile phase (liquid or gaseous) to a solid phase is a universal phenomenon among the mobility of substances in aqueous porous media and aquatic environments. Sorption properties of metal ions are crucial for the evaluation of metal ion behavior in the natural environment. First, various treatment techniques and proc- esses have been used to remove the pollutants from contami- nated water. Among all the approaches proposed, sorption is one of the most popular methods and is currently considered as an effective, efficient and economic method for wastewa- ter purification. Second, the relationship between catalysis and sorption is considered as the most important domain of surface science. The prerequisite of heterogeneous catalysis to occur is sorption (usually chemical one) of molecules of the reacting substances on the inner or outer surface of the adsorbent or of the catalyst; then molecular dissociation of at least one or two reacting components, usually preceded by surface diffusion. Besides, catalysts combined with adsorb- ents owning high sorption capacity are important to achieve high catalytic activity. For example, TiO2 supported adsorb- ent provides higher specific surface area and facilitates more effective sorption sites than bare TiO2 (1, 2). As a result, the degradation rates of organic pollutants are usually higher than that of bare TiO2. Bhattacharyya et al. (3) loaded TiO2 on three different kinds of porous adsorbents, mesoporous (MCM-41), microporous (� -zeolite) and pillared structure (montmorillonite) using sol-gel method, and the photocata- lytic efficiency of the supported catalysts was evaluated

Terbium-based infinite coordination polymer hollow microspheres: preparation and white-light emission

Novel rare earth based 4,4′,4′′-benzene-1,3,5-triyl-tri-benzonate (RE-BTB) infinite coordination polymer (ICP) hollow microspheres have been successfully prepared via a facile surfactant-free mixed-solvothermal route, among which Tb-BTB was studied in detail. These as-prepared hollow microspheres using terbium as the central ion have diameters of 260–500 nm. Influential factors such as reaction temperature, reaction time, dosage of reagents, and solvent composition on the morphology and size of the Tb-BTB ICP hollow spheres have been systematically investigated. An inside-out formation mechanism was proposed for the hollow microspheres. The photoluminescence properties of the Tb-BTB hollow spheres have been systematically studied. It turns out that it is easy to tune the luminescent characteristics of the Tb-BTB ICP hollow spheres within a wide spectral range by simply varying the excitation lines or the doping concentration of Eu3+. Interestingly, white-light emission was realized in the Eu3+ doped Tb-BTB hollow spheres.

Coexistence of adsorption and coagulation processes of both arsenate and NOM from contaminated groundwater by nanocrystallined Mg/Al layered double hydroxides.

In this study, nanocrystallined Mg/Al layered double hydroxides (LDH-CO3) and chloridion intercalated nanocrystallined Mg/Al LDHs (LDH-Cl) were synthesized and used for simultaneous removal of arsenic and natural organic matter (NOM) from contaminated groundwater. Humic acid (HA) was selected as a model compound of NOM. The maximum adsorption capacities of arsenate (As(V)) on LDH-CO3 and LDH-Cl are 44.66 and 88.30 mg/g, respectively, and those of HA on LDH-CO3 and LDH-Cl are 53.16 and 269.24 mg/g, respectively. It was found that more than 98% of arsenic and 94% of NOM were eliminated by LDH-Cl from both arsenic and NOM-rich groundwater, which is used as drinking water in Togtoh County, Inner Mongolia, China. The arsenic concentration declined from 231 to 4 μg/L, which meets the drinking water standard. The adsorption mechanisms were determined by using X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and extended X-ray absorption fine structure spectroscopy techniques (EXAFS). The results showed that the removal of HA was mainly via surface complexation as well as coagulation at the surface of LDHs, while the adsorption of As(V) was mainly via ion-exchange process. The presence of HA exhibited little inhibiting effect on As(V) adsorption by occupying partial binding sites on LDH surfaces. Nevertheless, it could not affect the ion-exchange process of As(V) with the interlayer anions of LDHs. The removal of As(V) and HA can be carried out independently due to the different adsorption mechanisms. By integrating the experimental results, it is clear that LDH-Cl can be potentially used as a cost-effective material for the purification of both arsenic and NOM contaminated groundwater.

Carbonaceous hydrogels and aerogels for supercapacitors

Carbonaceous hydrogels and aerogels are a large class of gels which have received much attention due to their multifunctional properties. The three-dimensional networks and porous structure of the carbonaceous gels can provide efficient diffusion of electrolyte ions and electrons, leading to promising applications in supercapacitors. This feature article gives an overview of the recent advances in the use of novel carbonaceous gels for supercapacitors. In particular, the synthetic methods for polymer derived carbonaceous gels, carbon nanotube based carbonaceous gels, graphene based carbonaceous gels and biomass derived carbonaceous gels are introduced, and their applications for supercapacitors are systematically discussed. Perspectives for the development of neotype carbonaceous gel based electrode materials for supercapacitors are given.

Core–Shell Carbon-Coated CuO Nanocomposites: A Highly Stable Electrode Material for Supercapacitors and Lithium-Ion Batteries

Herein we present a simple method for fabricating core-shell mesostructured CuO@C nanocomposites by utilizing humic acid (HA) as a biomass carbon source. The electrochemical performances of CuO@C nanocomposites were evaluated as an electrode material for supercapacitors and lithium-ion batteries. CuO@C exhibits an excellent capacitance of 207.2 F g(-1) at a current density of 1 A g(-1) within a potential window of 0-0.46 V in 6 M KOH solution. Significantly, CuO electrode materials achieve remarkable capacitance retentions of approximately 205.8 F g(-1) after 1000 cycles of charge/discharge testing. The CuO@C was further applied as an anode material for lithium-ion batteries, and a high initial capacity of 1143.7 mA h g(-1) was achieved at a current density of 0.1 C. This work provides a facile and general approach to synthesize carbon-based materials for application in large-scale energy-storage systems.

Highly efficient removal of humic acid from aqueous solutions by Mg/Al layered double hydroxides–Fe3O4 nanocomposites

The Mg/Al-layered double hydroxides and iron oxide (LDHs–Fe3O4) nanocomposites were synthesized via a facile two-step wet chemistry route. The fabricated samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption analysis, and thermogravimetric analysis (TGA). The resulting Fe3O4 nanoparticles possess unique magnetic properties for LDHs–Fe3O4 separation and the LDHs–Fe3O4 nanocomposites were applied to remove natural organic macromolecular compound (humic acid, HA) from contaminated groundwater. The results indicate that HA adsorption on LDHs–Fe3O4 is strongly dependent on pH and weakly dependent on ionic strength. The adsorption of HA onto LDHs–Fe3O4 occurs by ion exchange with both the intercalated and surface anions of the LDHs. The magnetite nanoparticles could provide extra adsorption sites for HA removal. In addition, the adsorption isotherm of HA on LDHs–Fe3O4 can be well fitted by the Freundlich model and the maximum adsorption capacity of HA onto LDHs–Fe3O4 reaches 353.82 mg g−1, displaying higher efficiency for HA removal than previously reported adsorbents. This is attributed to the synergistic effect of LDHs and Fe3O4 for HA adsorption. Experimental results demonstrate that HA can be completely and quickly removed by the LDHs–Fe3O4 nanocomposites. Our prepared LDHs–Fe3O4 nanocomposites are expected to become potential and suitable materials for the HA removal from large volumes of water in industrial applications.