Changyan Cao

Low-cost synthesis of flowerlike α-Fe2O3 nanostructures for heavy metal ion removal: adsorption property and mechanism.

Flowerlike α-Fe(2)O(3) nanostructures were synthesized via a template-free microwave-assisted solvothermal method. All chemicals used were low-cost compounds and environmentally benign. These flowerlike α-Fe(2)O(3) nanostructures had high surface area and abundant hydroxyl on their surface. When tested as an adsorbent for arsenic and chromium removal, the flowerlike α-Fe(2)O(3) nanostructures showed excellent adsorption properties. The adsorption mechanism for As(V) and Cr(VI) onto flowerlike α-Fe(2)O(3) nanostructures was elucidated by X-ray photoelectron spectroscopy and synchrotron-based X-ray absorption near edge structure analysis. The results suggested that ion exchange between surface hydroxyl groups and As(V) or Cr(VI) species was accounted for by the adsorption. With maximum capacities of 51 and 30 mg g(-1) for As(V) and Cr(VI), respectively, these low-cost flowerlike α-Fe(2)O(3) nanostructures are an attractive adsorbent for the removal of As(V) and Cr(VI) from water.

Microwave-assisted gas/liquid interfacial synthesis of flowerlike NiO hollow nanosphere precursors and their application as supercapacitor electrodes

A rapid method based on an efficient gas/liquid interfacial microwave-assisted process has been developed to synthesize flowerlike NiO hollow nanosphere precursors, which were then transformed to NiO by simple calcinations. The wall of the sphere is composed of twisted NiO nanosheets that intercalated with each other. Such hollow structure is different from widely reported flowerlike nanostructures with solid cores. An Ostwald ripening mechanism was proposed for the formation of the hollow nanostructures. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, energy-dispersive X-ray analysis, and N2adsorption-desorption methods. These flowerlike NiO hollow nanospheres have high surface area of 176 m2 g−1. Electrochemical properties show a high specific capacitance of 585 F g−1 at a discharge current of 5 A g−1 and excellent cycling stability, suggesting its promising potentials in supercapacitors.

A Bi/BiOCl heterojunction photocatalyst with enhanced electron–hole separation and excellent visible light photodegrading activity

Under visible light irradiation, excited electrons in heterojunction structure of Bi/BiOCl were transferred into oxygen vacancies states, and then to the Bi metal nanoparticles, resulting in effective separation of electron–hole pairs. The heterojunction photocatalyst exhibited an extraordinary high activity in photodegradation of RhB dye and persistent organic pollutants, i.e. RhB was completely degraded in 2 minutes.

Superb Adsorption Capacity and Mechanism of Flowerlike Magnesium Oxide Nanostructures for Lead and Cadmium Ions

A facile method based on microwave-assisted solvothermal process has been developed to synthesize flowerlike MgO precursors, which were then transformed to MgO by simple calcinations. All the chemicals used (magnesium nitrate, urea, and ethanol) were low cost and environmentally benign. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, and N(2) adsorption-desorption methods. These flowerlike MgO nanostructures had high surface area and showed superb adsorption properties for Pb(II) and Cd(II), with maximum capacities of 1980 mg/g and 1500 mg/g, respectively. All these values are significantly higher than those reported on other nanomaterials. A new adsorption mechanism involving solid-liquid interfacial cation exchange between magnesium and lead or cadmium cations was proposed and confirmed.

One-step synthesis of magnetic composites of cellulose@iron oxide nanoparticles for arsenic removal

Composite materials, containing magnetic nanoparticles and cellulose, were synthesized by one-step co-precipitation using NaOH–thiourea–urea aqueous solution for cellulose dissolution. The NaOH in cellulose solution acted as the precipitant of iron oxide nanoparticles, and low-cost cellulose was used as the template to promote the growing of nanoparticles in the cellulose matrix. The method provided a facile, “green” pathway for the fabrication of magnetic nanomaterials. The synthesized cellulose@iron oxide nanoparticles were characterized by FTIR, XRD, SEM, TEM, XPS, TG and VSM. The FTIR, XRD and XPS results demonstrated the formation of Fe2O3 nanoparticles in the composite materials after the co-precipitation. SEM and TEM characterization showed that the Fe2O3 nanoparticles were dispersed in the cellulose matrix due to the synergistic effect. Magnetometric measurements revealed that the resultant composites of cellulose@Fe2O3 nanoparticles exhibited a sensitive magnetic-induced behavior and could be easily separated from aqueous solution through the external magnetic field. The composite materials were applied to remove arsenic from aqueous solution. The results showed that the magnetic nanoparticle composites displayed excellent adsorption efficiency of arsenic compared with other magnetic materials reported, and the Langmuir adsorption capacities of the composites for the removal of arsenite and arsenate were 23.16 and 32.11 mg g−1, respectively.

Adsorption of heavy metal ions from aqueous solution by carboxylated cellulose nanocrystals

A novel nanoadsorbent for the removal of heavy metal ions is reported. Cotton was first hydrolyzed to obtain cellulose nanocrystals (CNCs). CNCs were then chemically modified with succinic anhydride to obtain SCNCs. The sodic nanoadsorbent (NaSCNCs) was further prepared by treatment of SCNCs with saturated NaHCO3 aqueous solution. Batch experiments were carried out with SCNCs and NaSCNCs for the removal of Pb2+ and Cd2+. The effects of contact time, pH, initial adsorption concentration, coexisting ions and the regeneration performance were investigated. Kinetic studies showed that the adsorption equilibrium time of Pb2+ and Cd2+ was reached within 150 min on SCNCs and 5 min on NaSCNCs. The adsorption capacities of Pb2+ and Cd2+ on SCNCs and NaSCNCs increased with increasing pH. The adsorption isotherm was well fitted by the Langmuir model. The maximum adsorption capacities of SCNCs and NaSCNCs for Pb2+ and Cd2+ were 367.6 mg/g, 259.7 mg/g and 465.1 mg/g, 344.8 mg/g, respectively. SCNCs and NaSCNCs showed high selectivity and interference resistance from coexisting ions for the adsorption of Pb2+. NaSCNCs could be efficiently regenerated with a mild saturated NaCl solution with no loss of capacity after two recycles. The adsorption mechanisms of SCNCs and NaSCNCs were discussed.

Sandwichlike Magnesium Silicate/Reduced Graphene Oxide Nanocomposite for Enhanced Pb2+ and Methylene Blue Adsorption

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 m(2)/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.

Metal silicate nanotubes with nanostructured walls as superb adsorbents for uranyl ions and lead ions in water

Silica nanotubes with mesoporous walls of 30 nm thickness were used as morphology templates, as well as the silicon source, to produce various metal silicate nanotubes with nanostructured walls, including magnesium silicate, copper silicate, nickel silicate, cobalt silicate and manganese silicate. These silicate materials retained the tubular structure of the templates, which resulted in large surface areas as high as 649 m2 g−1, large total volumes as high as 1.433 cm3 g−1 and facile mass transportation on their surfaces. These features enabled them to be superb adsorbents for adsorption in water; in particular, magnesium silicates showed maximum adsorption capabilities of 929 mg g−1 for uranyl ions and 424 mg g−1 for lead ions, respectively. In practical usage, magnesium silicates could effectively adsorb uranium directly from the salt lake water, with a practical adsorption capacity of 0.23 mg g−1, and was able to enrich the uranium concentration by 8 times.

Low-cost synthesis of graphitic carbon nanofibers as excellent room temperature sensors for explosive gases

With greatly enhanced surface-to-volume ratios, one-dimensional (1D) carbon nanostructures are believed to be able to deliver superior performance as room temperature sensors for explosive gases. 1D carbon nanofibers composed of graphitic nanorolls were prepared using a simple electrospinning-assisted solid-phase graphitization method. This method is facile and low cost and can allow high-yield production of carbon nanofibers. The unique structure of the as-prepared graphitic carbon nanofibers is different from that of conventional 1D carbon nanostructures. It offers the optimal balance between conductivity and adsorption capacity for gas sensing and thus results in remarkable gas-sensing properties in detecting explosive gases including H2, CO, CH4 and ethanol at room temperature.

Synthesis and characterization of multi-amino-functionalized cellulose for arsenic adsorption

A multi-amino adsorbent for arsenic adsorption was reported in this paper. Glycidyl methacrylate (GMA) was first grafted onto the surface of cotton cellulose using ceric ammonium nitrate (CAN) as the initiator, and then the introduced epoxy groups reacted with tetraethylenepentamine (TEPA) to obtain a multi-amino adsorbent. The adsorbent was characterized by FTIR, elemental analysis, (13)C NMR and SEM. Then, the adsorption of arsenic for this adsorbent was investigated. The results showed that the GMA and TEPA were successfully grafted onto the surface of cellulose, and the modification improved the arsenic adsorption performances. Kinetic study suggested that the chemisorptions were the rate-limiting step. Among the three adsorption isotherm models used, Langmuir model fitted the experimental data best. The adsorption capacities of arsenic were less affected by coexisting ions. The adsorbent could be effectively regenerated for four cycles with 0.1 mol/L NaOH solution.