The abilities of adsorption and separation of electron hole pairs are two important factors in photodegradation, and a balance between them is required to obtain an excellent photodegradation performance. As a new photocatalyst, silver silicate has a poor conductivity that hinders its photodegradation ability. Herein, silver silicate (AgSiOx)@carbon nanotube (CNT) and AgSiOx@reduced graphene oxide (RGO) nanocomposites are prepared for the first time to improve the photodegradation performance of AgSiOx. The influences of CNT and RGO contents on improving the photodegradation efficiency of AgSiOx are different due to the differences in the concentration of oxygen-containing groups and the electrical conductivity. The photodegradation efficiency of AgSiOx@CNT nanocomposites first increases and then decreases with increasing the concentration of CNTs, while the removal efficiency of pollutants by AgSiOx@RGO nanocomposites increases with the GO concentration owing to the residual oxygen-containing functional groups on RGO. The AgSiOx@CNT nanocomposite with a trace amount of CNTs (0.1 wt %) shows fairly effective photodegradation activity, and its photodegradation process is completed in 10 min with a higher removal efficiency and rate constant than reported.Keywords: Carbon nanotube; Photodegradation; Reduced graphene oxide; Silver silicate; Visible light;

Increasing demands for lithium-ion batteries (LIBs) with high energy density and high power density require highly reversible electrochemical reactions to enhance the cyclability and capacities of electrodes. As the reversible formation/decomposition of the solid electrolyte interface (SEI) film during the lithiation/delithiation process of Fe3S4 could bring about a higher capacity than its theoretical value, in the present work, synthesized Fe3S4 nanoparticles are sandwich-wrapped with reduced graphene oxide (RGO) to fabricate highly reversible and long cycling life anode materials for high-performance LIBs. The micron-sized long slit between sandwiched RGO sheets effectively prevents the aggregation of intermediate phases during the discharge/charge process and thus increases cycling capacity because of the reversible formation/decomposition of the SEI film driven by Fe nanoparticles. Furthermore, the RGO sheets interconnect with each other by a face-to-face mode to construct a more efficiently conductive network, and the maximum interfacial oxygen bridge bonds benefit the fast electron hopping from RGO to Fe3S4, improving the depth of the electrochemical reactions and facilitating the highly reversible lithiation/delithiation of Fe3S4. Thus, the resultant Fe3S4/RGO hybrid shows a highly reversible charge capacity of 1324 mA h g–1 over 275 cycles at a current density of 100 mA g–1, even retains 480 mA h g–1 over 500 cycles at 1000 mA g–1, which are much higher than reported values.Keywords: anode; Fe3S4; lithium ion batteries; reduced graphene oxide; solid electrolyte interface film;

Construction of a heterostructure to prolong the life of electron-hole pairs is a very important approach to endow it with excellent photodegradation performances. Particularly, one-pot synthesis of heterostructures with the same component but different crystal structures to form a proper band gap is still challenging. Herein, bismuth silicate (BSO) heterostructures are synthesized using a one-pot hydrothermal approach without adding any other inorganic components. The crystal phase, morphology, surface state, and photochemical properties of the BSO materials are precisely tuned to fabricate two kinds of bismuth silicate heterostructures: rod-like Bi2SiO5/Bi12SiO20 and flower-like Bi2SiO5/Bi4Si3O12 heterostructures. Thanks to the two heterostructures and clean surface, the optimized BSO material exhibits a highly active photocatalytic performance with a remarkable cycling stability. It photodegrades Rhodamine B under visible light irradiation as fast as 15 min with the reaction rate constants k and ks to be 0.399 min−1 and 0.698 min−1 L m−2, respectively, which is up to 189 times faster than reported.Download high-res image (113KB)Download full-size image

Developing graphene-based membranes is important for a wide range of applications such as in desalination, wastewater treatment, separation and purification. Herein, a novel graphene-based nanofiltration (NF) membrane was fabricated by depositing the magnesium silicate modified reduced graphene oxide (MgSi@RGO) nanosheets on a polyacrylonitrile (PAN) ultrafiltration membrane via a vacuum filtration method. The MgSi@RGO/PAN composite membrane exhibits special selectivities for separation of organic molecules. Molecule permeation through the MgSi@RGO selective skin layer was observed with the broadened nanochannels propped up by MgSi nanosheets. The rejections of different PEG molecules (PEG200, PEG400, PEG600 and PEG1000) were tested, and the experimental results and theoretical calculations showed high consistency, which means the theoretical model can be effectively used for calculating the real diameter of “pore” in NF membrane. Additionally, three dye molecules were selected to investigate the NF membrane performance, and the MgSi@RGO/PAN composite membrane showed different separation characteristics of charged molecules.

α-Fe2O3 nanoparticles have been widely used in water purification because of their effective adsorption performance. However, aggregation and difficulty in separation limit their practical application. Herein, we presented a polyacrylonitrile (PAN) nanofiber mat decorated with α-Fe2O3 as an adsorbent for effective removal of Pb2+ from contaminated water, which can solve the above problems easily. The α-Fe2O3/PAN nanofiber mats were prepared via electrospinning followed by a facile hydrothermal method and characterized by SEM, HRTEM, FTIR and XRD. We demonstrated that the formation mechanism of α-Fe2O3 anchored on the PAN nanofiber surface consists of the adsorption of iron ions on the surface of PAN, and then the nucleation and growth of α-Fe2O3. The pH value of FeCl3 solution has a great impact on the formation process of the α-Fe2O3/PAN nanofiber mat, which leads to the variation of morphology and quantity of the coating coverage. When the pH value was 2.4, polyhedral particles were coated on PAN nanofibers uniformly and the optimized α-Fe2O3/PAN nanofiber mat was obtained. Control experiments were carried out to quantify the adsorption capacities of different samples and adsorption kinetics. The isotherm data from our experiments fitted well to the Langmuir model and the adsorption process can be described using the pseudo-second-order model. Finally, the adsorption mechanism for Pb2+ was investigated and the results revealed that ion exchange between the proton of surface hydroxyl groups and Pb2+ accounted for the adsorption.

The combination of active materials with electrically conductive carbon materials and their contact efficiency are crucial for improving the electrochemical performances of active materials. Here, nickel silicate (NiSiOx) nanoplates are planted in situ on the surface of reduced graphene oxide (RGO) nanosheets to form a two dimensional face-to-face nanocomposite of NiSiOx/RGO for lithium storage. The face-to-face structure enhances the contact efficiency of NiSiOx with RGO, and thus leads to a higher reversible capacity and better rate performance of the NiSiOx/RGO nanocomposite than both carbon nanotube (CNT)@NiSiOx nanocables and NiSiOx. The layered NiSiOx/RGO nanocomposite exhibits a high reversible specific capacity of 797 mA h g−1, which is 62% and 806% higher than those of CNT@NiSiOx nanocables and NiSiOx alone, respectively.

Layered nickel silicate provides massive interlayer space similar to graphite for the insertion and extraction of lithium ions and sodium ions; however, the poor electrical conductivity limits its electrochemical applications in energy storage devices. Herein, carbon nanotube@layered nickel silicate (CNT@NiSiOx) coaxial nanocables with flexible nickel silicate nanosheets grown on conductive carbon nanotubes (CNTs) are synthesized by a mild hydrothermal method. CNTs serve as conductive cables to improve the electron transfer performance of nickel silicate nanosheets, resulting in reduced contact and charge-transfer resistances. In addition to a high specific surface area, short ion diffusion distance and good electrical conductivity, one-dimensional coaxial nanocables have a stable structure to sustain volume change and avoid structure destruction during the charge–discharge process. As an anode material for lithium storage, the first cycle charge capacity of the CNT@NiSiOx nanocables reaches 770 mA h g−1 with the first cycle coulombic efficiency as high as 71.5%. Even after 50 cycles, the charge capacity still reaches 489 mA h g−1 at a current density of 50 mA g−1, which is nearly 87% and 360% higher than those of the NiSiOx/CNT mixture and nickel silicate nanotube, respectively. As anode materials for sodium storage, the coaxial nanocables exhibit a high initial charge capacity of 576 mA h g−1, which even retains 213 mA h g−1 at 20 mA g−1 after 16 cycles.

Core–shell structured MgO@mesoporous silica spheres are synthesized by a two-step programmed method. MgO@mesoporous silica exhibits a high BET specific surface area of 567 m2 g−1 and a pore volume of 1.08 cm3 g−1. The stable mesoporous silica coating not only serves as a strong shell to improve the mechanical stability of MgO, but also enriches the adsorbates in the mesopores to reach a higher adsorption rate. The core–shell MgO@mesoporous silica spheres exhibit excellent removal capabilities of 3297 mg g−1 for Pb2+ and 420 mg g−1 for methylene blue, which are much higher than those of MgO itself.

A sandwichlike magnesium silicate/reduced graphene oxide nanocomposite (MgSi/RGO) with high adsorption efficiency of organic dye and lead ion was synthesized by a hydrothermal approach. MgSi nanopetals were formed in situ on both sides of RGO sheets. The nanocomposite with good dispersion of nanopetals exhibits a high specific surface area of 450 m2/g and a good mass transportation property. Compared to MgSi and RGO, the mechanical stability and adsorption capacity of the nanocomposite is significantly improved due to the synergistic effect. The maximum adsorption capacities for methylene blue and lead ion are 433 and 416 mg/g, respectively.Keywords: adsorption; lead ion; magnesium silicate; nanocomposite; reduced graphene oxide

Layered nickel silicate provides massive interlayer space similar to graphite for the insertion and extraction of lithium ions and sodium ions; however, the poor electrical conductivity limits its electrochemical applications in energy storage devices. Herein, carbon nanotube@layered nickel silicate (CNT@NiSiOx) coaxial nanocables with flexible nickel silicate nanosheets grown on conductive carbon nanotubes (CNTs) are synthesized by a mild hydrothermal method. CNTs serve as conductive cables to improve the electron transfer performance of nickel silicate nanosheets, resulting in reduced contact and charge-transfer resistances. In addition to a high specific surface area, short ion diffusion distance and good electrical conductivity, one-dimensional coaxial nanocables have a stable structure to sustain volume change and avoid structure destruction during the charge–discharge process. As an anode material for lithium storage, the first cycle charge capacity of the CNT@NiSiOx nanocables reaches 770 mA h g−1 with the first cycle coulombic efficiency as high as 71.5%. Even after 50 cycles, the charge capacity still reaches 489 mA h g−1 at a current density of 50 mA g−1, which is nearly 87% and 360% higher than those of the NiSiOx/CNT mixture and nickel silicate nanotube, respectively. As anode materials for sodium storage, the coaxial nanocables exhibit a high initial charge capacity of 576 mA h g−1, which even retains 213 mA h g−1 at 20 mA g−1 after 16 cycles.

α-Fe2O3 nanoparticles have been widely used in water purification because of their effective adsorption performance. However, aggregation and difficulty in separation limit their practical application. Herein, we presented a polyacrylonitrile (PAN) nanofiber mat decorated with α-Fe2O3 as an adsorbent for effective removal of Pb2+ from contaminated water, which can solve the above problems easily. The α-Fe2O3/PAN nanofiber mats were prepared via electrospinning followed by a facile hydrothermal method and characterized by SEM, HRTEM, FTIR and XRD. We demonstrated that the formation mechanism of α-Fe2O3 anchored on the PAN nanofiber surface consists of the adsorption of iron ions on the surface of PAN, and then the nucleation and growth of α-Fe2O3. The pH value of FeCl3 solution has a great impact on the formation process of the α-Fe2O3/PAN nanofiber mat, which leads to the variation of morphology and quantity of the coating coverage. When the pH value was 2.4, polyhedral particles were coated on PAN nanofibers uniformly and the optimized α-Fe2O3/PAN nanofiber mat was obtained. Control experiments were carried out to quantify the adsorption capacities of different samples and adsorption kinetics. The isotherm data from our experiments fitted well to the Langmuir model and the adsorption process can be described using the pseudo-second-order model. Finally, the adsorption mechanism for Pb2+ was investigated and the results revealed that ion exchange between the proton of surface hydroxyl groups and Pb2+ accounted for the adsorption.