Daimei Chen

N-doped P25 TiO2–amorphous Al2O3 composites: One-step solution combustion preparation and enhanced visible-light photocatalytic activity

Nitrogen-doped Degussa P25 TiO2-amorphous Al2O3 composites were prepared via facile solution combustion. The composites were characterised using X-ray diffraction, high-resolution transmission microscopy, scanning electron microscopy, nitrogen adsorption-desorption measurements, X-ray photoelectron spectroscopy, UV-vis light-diffusion reflectance spectrometry (DRS), zeta-potential measurements, and photoluminescence spectroscopy. The DRS results showed that TiO2 and amorphous Al2O3 exhibited absorption in the UV region. However, the Al2O3/TiO2 composite exhibited visible-light absorption, which was attributed to N-doping during high-temperature combustion and to alterations in the electronic structure of Ti species induced by the addition of Al. The optimal molar ratio of TiO2 to Al2O3 was 1.5:1, and this composite exhibited a large specific surface area of 152 m2/g, surface positive charges, and enhanced photocatalytic activity. These characteristics enhanced the degradation rate of anionic methylene orange, which was 43.6 times greater than that of pure P25 TiO2. The high visible-light photocatalytic activity was attributed to synthetic effects between amorphous Al2O3 and TiO2, low recombination efficiency of photo-excited electrons and holes, N-doping, and a large specific surface area. Experiments that involved radical scavengers indicated that OH and O2- were the main reactive species. A potential photocatalytic mechanism was also proposed.

Synthesis and photocatalytic performances of the TiO2 pillared montmorillonite

TiO(2) pillared clay materials were prepared by montmorillonite (Mt) and acidic solutions of hydrolyzed Ti alkoxides in the presence of high-molecular-weight polyoxypropylene (POP)-backboned di-quaternary salts (POP). The as-prepared materials were characterized by means of XRD, FTIR, TG-DTA, XRF, specific surface area and porosity determinations, TEM and SEM, respectively. The experiments showed that the resulting material was a porous delaminated structure containing pillared fragments and nano-scaled TiO(2) particles well dispersed among each other. Introducing polymer surfactant POP as an expanding agent of Mt cannot only promote the formation of the delaminated structure, but significantly improve the porosity and surface area of the composites. The resulting TiO(2) pillared Mt exhibited a good thermal stability as indicated by its surface area after calcination at 800 °C. No phase transformation from anatase to rutile was observed even under calcination at 900 °C. The grain size of anatase in as-prepared sample decreased with the increase of the POP concentration, but increased with the increment of calcination temperature. The photocatalytic performances of these new porous materials were evaluated by using methylene blue degradation. The composite solid exhibited superior photocatalyic property and the maximum removal efficiency was up to 98% within 90 min.

Synthesis and characterization of TiO2 pillared montmorillonites: application for methylene blue degradation.

TiO2 pillared clay composites were prepared by modifying of montmorillonite (Mt) with cetyl-trimethyammoniumbromide (CTAB) and then using an acidic solution of hydrolyzed Ti alkoxide to intercalate into the interlayer space of the organic modified Mt. The as-prepared materials were characterized by XRD, FTIR, TEM, SEM TG-DTA, specific surface area and porosity measurements. The composites had a porous delaminated structure with pillared fragments and well dispersed TiO2 nanoparticles. Introduction of CTAB into the synthetic system accelerated the hydrolysis and condensation of the Ti source, which promoted TiO2 formation. In addition, the CTAB also significantly increased the porosity and surface area of the composites. A number of anatase particles, with crystal sizes of 5-10 nm, were homogenously distributed on the surface of the Mt as the result of the templating role of CTAB. The resultant TiO2 pillared Mt exhibited good thermal stability as indicated by its surface area after calcination at 800°C. No phase transformations from anatase to rutile were observed even under calcination at 900°C. The grain size of the anatase in prepared sample increased from 2.67 nm to 13.42 nm as the calcination temperature increased from 300°C to 900°C. The photocatalytic performance of these new porous materials was evaluated by using methylene blue degradation. The composite exhibited better photocatalytic property than P 25. The maximum removal efficiency of this composite was up to 99% within 60 min.

Preparation of black-pearl reduced graphene oxide–sodium alginate hydrogel microspheres for adsorbing organic pollutants

The black-pearl reduced graphene oxide-sodium alginate (rGO-SA) hydrogel microspheres are prepared by the external emulsification and thermal reduction method, which are characterized by scanning electron microscope (SEM) and X-ray Diffraction (XRD). Sodium alginate (SA) serves as a template to form a 3D porous network structure, which can prevent the agglomeration and restacking of rGO sheets efficiently. The size of hydrogel microsphere can be controlled by adjusting the size of the liquid drop. The effects of rGO content (wt%), contact time, initial concentration of phenol, adsorption temperature and adsorption dose on the adsorption capacity of rGO-SA microspheres are investigated. The kinetics and isotherm data are well described by the pseudo-second-order kinetic model and the Langmuir equation, respectively. Thermodynamic results demonstrate the spontaneous and endothermic nature of adsorption. This rGO-SA microsphere exhibits the favorable adsorption performance for phenol, BPA and tetracycline. The rGO-SA microsphere might be a potential candidate for efficient adsorbents in water treatment.