Qingze Chen

Templated synthesis of nitrogen-doped graphene-like carbon materials using spent montmorillonite

Montmorillonite (Mt) as an environmentally-friendly, low-cost, and highly-efficient adsorbent for cationic dyes has a promising application in dye wastewater treatment. However, proper disposal of the spent Mt is still a challenge holding back the wide application of Mt. This article reports a simple method which can synthesize N-doped graphene-like carbon materials using the spent Mt after the adsorption of crystal violet (CV). The spent Mt was pyrolyzed under the protection of N2 to carbonize the adsorbed CV within the interlayer space of Mt, and the interlayer spacing of Mt decreased from 11.0 A to approximately 3.6 A, close to the thickness of a single graphene layer (3.4 A). After demineralization (i.e., washing with a mixture of HF and HCl), the carbon material was released from the interlayer space of Mt. Raman spectra showed the presence of both the D-band and G-band on the obtained carbon materials, and transmission electron microscopy observed the thin layers of carbon material. X-ray photoelectron spectroscopy results indicated the simultaneous presence of pyridinic, pyrrolic, and quaternary N on the carbon materials. In addition, the percentage of pyridinic N increases with increasing pyrolysis temperature; whereas that of quaternary N decreases and of pyrrolic N remains relatively constant. The above results suggested the successful synthesis of N-doped graphene-like carbon material. Finally, the obtained materials show interesting electrocatalytic activity for the oxygen reduction reaction and show potential to be used as efficient metal-free electrocatalysts in fuel cells.

From spent Mg/Al layered double hydroxide to porous carbon materials.

Adsorption has been considered as an efficient method for the treatment of dye effluents, but proper disposal of the spent adsorbents is still a challenge. This work attempts to provide a facile method to reutilize the spent Mg/Al layered double hydroxide (Mg/Al-LDH) after the adsorption of orange II (OII). Herein, the spent hybrid was carbonized under the protection of nitrogen, and then washed with acid to obtain porous carbon materials. Thermogravimetric analysis results suggested that the carbonization could be well achieved above 600°C, as mass loss of the spent hybrid gradually stabilized. Therefore, the carbonization process was carried out at 600, 800, and 1000°C, respectively. Scanning electron microscope showed that the obtained carbon materials possessed a crooked flaky morphology. Nitrogen adsorption-desorption results showed that the carbon materials had large BET surface area and pore volume, e.g., 1426 m(2)/g and 1.67 cm(3)/g for the sample carbonized at 800°C. Moreover, the pore structure and surface chemistry compositions were tunable, as they were sensitive to the temperature. Toluene adsorption results demonstrated that the carbon materials had high efficiency in toluene removal. This work provided a facile approach for synthesizing porous carbon materials using spent Mg/Al-LDH.

Self-templating synthesis of silicon nanorods from natural sepiolite for high-performance lithium-ion battery anodes

Nanostructured silicon is an attractive anode material for next-generation lithium-ion batteries, but its commercialization remains a challenge owing to the energy-intensive, costly, and complex preparation of nanostructured silicon. Herein, one-dimensional (1D) silicon nanorods (SNRs) have been synthesized from natural sepiolite by a simple self-templating synthesis method. The intrinsic crystal structure and chemical composition of sepiolite allow for the maintenance of 1D structures during magnesiothermic reduction without any additional templates and heat scavengers. The as-prepared SNRs showed a large specific surface area (∼122 m2 g−1) and hierarchical porous structure (i.e., macro- and meso-pores). As anodes for lithium-ion batteries, SNRs exhibited a high reversible capacity of 1350 mA h g−1 at 1.0 A g−1 after 100 cycles, and 816 mA h g−1 at 5.0 A g−1 after 500 cycles (with a capacity retention of 98%). With a low-cost precursor and facile approach, this strategy for synthesizing 1D nanostructured Si would be promising in practical production of high-performance anode materials for lithium-ion batteries.

Superior adsorption of phosphate by ferrihydrite-coated and lanthanum-decorated magnetite

Present study reports the successful development of a novel lanthanum (La)-based magnetic adsorbent and its use for phosphate removal from water. For its synthesis, natural magnetite (Mag), Fe3O4, was subjected to partial dissolution in HCl solution and the obtained suspension was mixed with an alkaline solution for in-situ synthesis of ferrihydrite (Fh)-coated Mag (Mag@Fh). Mag@Fh was then decorated with La (hydr)oxides followed by calcination to produce Fh-coated and La-decorated Mag (Mag@Fh-La). Obtained Mag@Fh-La represented high phosphate adsorption capacity (44.8 mg P/g at 15.7% La in its structure) and La usage efficiency. Moreover, Mag@Fh-La retained its high adsorption capacity (>35.0 mg P/g) over a wide range of equilibrium solution pH (3.2-10.7). The combination of FTIR, XPS analysis and adsorption experiments revealed that ligand exchange and electrostatic attraction were the main mechanisms that jointly facilitated the adsorption of phosphate. Adsorption-desorption cycle studies confirmed the well-retained adsorption efficiency of regenerated Mag@Fh-La for repeated applications. Final experiments with real domestic wastewater (initial phosphate concentration of 1.7 mg/L) revealed that 0.2 g/L Mag@Fh-La efficiently reduced the phosphate concentration to below 0.02 mg/L. Overall, this work clearly highlights that the synthesized novel adsorbent has promising applications in phosphate removal from real wastewater.