Qianfeng Zhang

Low temperature synthesis of magnesium oxide and spinel powders by a sol-gel process

Magnesium oxide and magnesium aluminate (MgAl2O4) spinel (MAS) powders have been synthesized by a simple aqueous sol-gel process using citrate polymeric precursors derived from magnesium chloride, aluminium nitrate and citrate. The thermal decomposition of the precursors and subsequent formation of cubic MgO and MAS were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry-differential scanning calorimetry (TG-DSC) and Fourier transform infrared spectra (FTIR). The single phase cubic MgO powder and MAS powder form after heat treatment at 800 and 1200 °C, respectively. The particle size of the MgO and MAS powders is about 100 nm and several micrometers, respectively. Ball milling eliminates the size of MgO and MgAl2O4 spinel powders by decreasing the conglomeration of the powders.

Preparation of flake-like polyaniline/montmorillonite nanocomposites and their application for removal of Cr(VI) ions in aqueous solution

In this study, flake-like polyaniline/montmorillonite (PANI/MMT) nanocomposites with rough surface were successfully prepared by in situ chemical oxidation polymerization during which poly(2-acrylamido-2-methylpropanesulfonic acid), a polymer acid, on the surface of clay platelets was used as dopant of PANI and played a ‘bridge’ role to combine PANI with clay. Flake thickness and surface roughness of PANI/MMT composites decreased with the increase of montmorillonite/aniline feeding ratio. The effects of operating parameters including pH, contact time, Cr(VI) concentration, and adsorbent dose were studied. The pseudo-second-order equation and three adsorption isotherms including Langmuir, Freundlich, and Temkin equations were applied to determine the adsorption rate and capacity. The results show that the flake-like PANI/MMT nanocomposites exhibited a high adsorption capacity (167.5xa0mg/g). The excellent adsorption characteristic of flake-like PANI/MMT nanocomposites will render it a highly efficient and economically viable adsorbent for Cr(VI) removal.

Removal of hexavalent chromium from aqueous solution using exfoliated polyaniline/montmorillonite composite

Exfoliated polyaniline/montmorillonite (PANI/MMT) composites with nanosheet structure were successfully prepared by in situ chemical oxidation polymerization with MMT platelets as the scaffold. Amphoteric polymer, (2-methacryloyloxyethyl)trimethyl ammonium chloride and methacrylate acid copolymer, was used to modify montmorillonite and a large number of carboxylic acids were introduced on the surface of the clay platelets, which can be used as a dopant of PANI and play a bridge role to combine PANI with clay. Adsorption experiments were carried out to study the effects of pH, contact time, Cr(VI) concentration, adsorbent dose and temperature. The adsorption of Cr(VI) on the PANI/MMT was highly pH dependent and the adsorption kinetics followed a pseudo-second-order model. The Langmuir isothermal model described the adsorption isotherm data well and the maximum adsorption capacity increased with the increase in temperature. Thermodynamic investigation indicated that the adsorption process is spontaneous, endothermic and marked with an increase in randomness at the adsorbent - liquid interface. The maximum adsorption capacity of the PANI/MMT composites for Cr(VI) was 308.6 mg/g at 25 °C. The excellent adsorption characteristic of exfoliated PANI/MMT composites will render it a highly efficient and economically viable adsorbent for Cr(VI) removal.

Highly efficient removal of chromium(VI) from aqueous solution using polyaniline/sepiolite nanofibers

Polyaniline/sepiolite (PANI/sepiolite) nanofibers were prepared by in situ chemical oxidation polymerization in the presence of sepiolite. The effect of aniline/sepiolite weight ratio on the nanostructure of PANI/sepiolite composites was investigated by field-emission scanning electron microscopy. The adsorption of Cr(VI) onto the PANI/sepiolite nanofibers was highly dependent on pH values. The pseudo-second-order and Langmuir isothermal models can well describe the adsorption kinetics and adsorption isotherm, respectively. The maximum adsorption capacity of the PANI/sepiolite nanofibers for Cr(VI) was up to 206.6 mg/g at 25 °C and increased with the increase in temperature. Desorption experiments indicated that PANI/sepiolite can be regenerated and reused for two consecutive cycles with no loss of its removal efficiency. PANI/sepiolite nanofibers can be used as a highly efficient and economically viable adsorbent for Cr(VI) removal due to their excellent adsorption characteristics.

Exfoliated polypyrrole/montmorillonite nanocomposite with flake-like structure for Cr(VI) removal from aqueous solution

Exfoliated polypyrrole/montmorillonite (PPy/MMT) nanocomposites with flake-like structure were prepared by in situ chemical oxidation polymerization. Amphoteric polymer, (2-methacryloyloxyethyl) trimethyl ammonium chloride and methacrylate acid copolymer, was used to modify montmorillonite and a large amount of carboxyl acid was introduced on the surface of clay platelets which can play a ‘bridge’ role to combine PPy with clay. The adsorption of Cr(VI) on the PPy/MMT was highly pH-dependent and the adsorption kinetics followed the pseudo-second-order model. The Langmuir isothermal model well described the adsorption isotherm data, whiler the maximum adsorption capacity increased with the increase of temperature. Thermodynamic investigation indicated that the adsorption process is spontaneous, endothermic and marked with an increase in randomness at the adsorbent–liquid interface. The maximum adsorption capacity of the PPy/MMT composites for Cr(VI) was 166.7xa0mg/g. A desorption experiment showed PPy/MMT composites can be regenerated and reused for two consecutive cycles with no loss of their removal efficiency.

Polyvinyl pyrrolidone-assisted synthesis of crystalline manganese vanadate microtubes

Manganese vanadate microtubes have been synthesized by a facile polyvinyl pyrrolidone-assisted hydrothermal route. X-ray diffraction pattern confirms that the microtubes are composed of monoclinic MnV2O6, tetragonal V2O5 and orthorhombic MnO2 phases. The outer diameter and inner diameter of the microtubes are about 300 nm-3 µm and 200 nm-1 µm, respectively. The tube wall thickness of the microtubes is about 50 nm-1 µm. The possible formation process of the manganese vanadate microtubes has been proposed as a polyvinyl pyrrolidone-assisted growth mechanism.

Ca2Ge7O16 nanowires grown from CaO and GeO2

Single crystalline Ca2Ge7O16 nanowires have been synthesized using CaO and GeO2 as the raw materials. Various factors that affect the formation and size of the Ca2Ge7O16 nanowires have been analyzed. The obtained products are characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the calcium germanate nanowires are composed of orthorhombic Ca2Ge7O16 phase with the length and diameter of several dozens of micrometers and about 50 nm, respectively. Hydrothermal temperature plays an important role on the formation and growth of the Ca2Ge7O16 nanowires. The formation process of the Ca2Ge7O16 nanowires is initially interpreted according to the shape evolution of the products obtained from different growth conditions.