Gaoke Zhang

Fe2O3-Pillared Rectorite as an Efficient and Stable Fenton-Like Heterogeneous Catalyst for Photodegradation of Organic Contaminants

An efficient Fe(2)O(3)-pillared rectorite (Fe-R) clay was successfully developed as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants. X-ray diffraction analysis and high-resolution transmission electron microscope analysis clearly showed the existence of the Fe(2)O(3) nanoparticles in the Fe-R catalyst. The catalytic activity of the Fe-R catalyst was evaluated by the discoloration and chemical oxygen demand (COD) removal of an azo-dye rhodamine B (RhB, 100 mg/L) and a typical persistent organic pollutant 4-nitrophenol (4-NP, 50 mg/L) in the presence of hydrogen peroxide (H(2)O(2)) under visible light irradiation (lambda > 420 nm). It was found that the discoloration rate of the two contaminants was over 99.3%, and the COD removal rate of the two contaminants was over 87.0%. The Fe-R catalyst showed strong adsorbability for the RhB in the aqueous solution. Moreover, the Fe-R catalyst still showed good stability for the degradation of RhB after five recycles. Zeta potential and Fourier transform infrared spectroscopy were used to examine the photoreaction processes. Finally, a possible photocatalytic mechanism was proposed.

Effects of alcohol content and calcination temperature on the textural properties of bimodally mesoporous titania

Bimodally mesoporous titania was prepared by hydrolysis of titanium tetraisopropoxide in pure water or the EtOH–H2O mixed solution under ultrasonic irradiation. Effects of alcohol content and calcination temperature on the phase composition and porosity of bimodally mesoporous titania was investigated by thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface areas. The results showed that for all TiO2 powders calcined from 400 to 600 ◦ C, the pore size distribution is bimodal with fine intra-particle pore diameter at maximum pore diameters of ca. 2–4 nm and larger inter-particle pore diameter at maximum pore diameters of ca. 18–50 nm. The EtOH/H2O molar ratios obviously influenced the crystallization, crystallite size, BET surface areas, porosity and morphology of the prepared TiO2 powders.

Facile synthesis and photocatalytic properties of AgAgClTiO2/rectorite composite

In this study, we prepared a new visible light induced plasmonic photocatalyst AgAgClTiO(2)/rectorite using a facile deposition-photoreduction method. The catalysts were characterized using X-ray diffraction (XRD), UV-visible diffused reflectance spectra (UV-vis DRS), Raman spectra, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The as-prepared AgAgClTiO(2)/rectorite powders exhibited an efficient photocatalytic activity for the degradation of acid orange (ARG) and 4-nitrophenol (4-NP) under visible light irradiation (λ>400 nm). Moreover, the mechanism suggested that the high photocatalytic activity is due to the charge separation and the surface plasmon resonance of metallic Ag particles in the region of visible light. The active species measurements suggested that HO() is not the dominant photooxidant. Direct hole transfers and O(2)(-) were involved as the active species in the photocatalytic reaction.

Photo-Fenton degradation of rhodamine B using Fe2O3-Kaolin as heterogeneous catalyst: characterization, process optimization and mechanism.

An efficient Fe2O3-Kaolin was synthesized as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants. X-ray photoelectron spectroscopy analysis and high-resolution transmission electron microscope analysis confirmed the existence of Fe2O3 nanoparticles in the Fe2O3-Kaolin composite. The specific surface area of the Fe2O3-Kaolin catalyst increased from 19.47 to 39.32m(2)/g compared to kaolin. The catalytic activity of the Fe2O3-Kaolin catalyst was evaluated by the photo-Fenton degradation of rhodamine B (RhB) under visible light irradiation and the results showed that the catalyst was highly effective for the degradation of RhB in a wide pH range of 2.21-10.13. At optimal conditions, 98% discoloration and 66% mineralization of RhB were achieved in 120min. The catalyst was efficient for the degradation of methylene blue as well. Leaching test indicated that the leached iron from the catalyst was negligible and the catalyst still showed high photocatalytic activity after five reaction cycles, which all showed that the Fe2O3-Kaolin catalyst is a promising heterogeneous photocatalyst for the degradation of various dyes in wastewater. Finally, a possible photocatalytic mechanism was proposed based on photoluminescence measurements and a series of operating conditions.

Enhanced visible-light-driven photocatalytic inactivation of Escherichia coli by Bi2O2CO3/Bi3NbO7 composites

The Bi2O2CO3/Bi3NbO7 (BiCO/BiNbO) composite was successfully fabricated by a simple hydrothermal method and found to be an effective visible-light-driven photocatalyst for inactivation of Escherichia coli (E. coli). The BiCO/BiNbO composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectrum (UV-vis DRS), and Fourier transform infrared (FT-IR) spectroscopy. The BiCO/BiNbO composite exhibited largely enhanced photocatalytic inactivation of E. coli as compared to the pure Bi3NbO7 under visible light irradiation. The enhanced photocatalytic performance can be attributed to the improved separation efficiency of the photogenerated holes and electrons. In addition, the possible bactericidal mechanism of the BiCO/BiNbO composite under visible light irradiation was discussed.

Hierarchically structured α-Fe2O3/Bi2WO6 composite for photocatalytic degradation of organic contaminants under visible light irradiation

The α-Fe2O3/Bi2WO6 composite with a sphere-like hierarchical structure assembled by nanosheets was synthesized by a one-step hydrothermal route without any templates or surfactants. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectrum (UV–vis DRS), Fourier transform infrared (FT–IR) spectrum, X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmet–Teller (BET) analysis. The BET specific surface area of the hierarchically structured α-Fe2O3/Bi2WO6 composite is 61.7 m2 g−1, which is much higher than that (3.5 m2 g−1) of the pure Bi2WO6. The hierarchically structured α-Fe2O3/Bi2WO6 composite exhibited a strong adsorption capability and a higher visible light photocatalytic activity than the pure Bi2WO6 for the photocatalytic degradation of acid red G dye or Rhodamine B (RhB) dye in aqueous solution under visible-light irradiation (>420 nm). The composite still showed the high photocatalytic activity after four reaction cycles. On the basis of the experimental results and calculated energy band positions, the enhanced photocatalytic activity of the composite can be attributed to the hierarchical structure and the coupling effect of α-Fe2O3 and Bi2WO6 in the composite.

Preparation of nanosized Bi3NbO7 and its visible-light photocatalytic property.

A nanosized Bi(3)NbO(7) was synthesized by the sol-gel method. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), UV-vis diffuse reflectance spectrum, X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmet-Teller (BET). The UV-vis diffuse reflectance spectrum of the sample obtained by the sol-gel method showed a markedly blue-shift as compared to that of the sample obtained by the solid-state reaction. The band gap of the Bi(3)NbO(7) nanoparticles was estimated to be about 2.43-2.59eV. XPS analysis confirmed that the mixed valence bismuth existed in the crystal structure of the photocatalyst and niobium in the compound Bi(3)NbO(7) was in the Nb(5+) valence state. The as-prepared nanopowders exhibited a high photocatalytic activity in the decomposition of acid red G in water and acetone in air under visible-light irradiation, which may be assigned to larger specific surface area and the oxygen vacancies and mixed valence bismuth in the structure of Bi(3)NbO(7).

Preparation and characterization of bifunctional Ti–Fe kaolinite composite for Cr(VI) removal

A novel bifunctional Ti-Fe kaolinite composite with excellent adsorption and photocatalytic properties was synthesized by a simple precipitation method. X-ray diffraction analysis and high-resolution transmission electron microscope analysis confirmed the existence of rutile phase TiO2 and amorphous iron in the composite. The specific surface area of the Ti-Fe kaolinite composite is 5.5 times higher than that of the original kaolinite. The composite was used as an adsorbent as well as photocatalyst for Cr(VI) removal. The results indicate that the low pH is favorable to the Cr(VI) removal by the composite and the removal rate of Cr(VI) reached 87% at pH 3.0. Visible light irradiation obviously increased the removal of Cr(VI) by the composite and greatly shortened reaction equilibrium time, which may be attributed to the photocatalytic reduction of Cr(VI) to Cr(III) by TiO2 associated with simultaneous redox cycle of Fe(III)/Fe(II). Various common co-existing ions did not show obvious effects on the removal of Cr(VI) by the composite. The composite exhibited very high stability for the Cr(VI) removal. The adsorption models and thermodynamics of Cr(VI) onto the composite were studied.

Enhanced ultrasound-assisted degradation of methyl orange and metronidazole by rectorite-supported nanoscale zero-valent iron

In this study, the rectorite-supported nanoscale zero-valent iron (nZVI/R) was synthesized through a reduction method. X-ray diffraction analysis showed the existence of the nZVI in the nZVI/R composite and X-ray photoelectron spectroscopy analysis indicated that the nZVI particles were partly oxidized into iron oxide. Scanning electron microscopy analysis revealed that the nZVI particles were highly dispersed on the surface of the rectorite. The specific surface area of the nZVI/R composite is 21.43 m(2)/g, which was higher than that of rectorite (4.30 m(2)/g) and nZVI (17.97 m(2)/g). In the presence of ultrasound (US), the degradation of methyl orange and metronidazole by the nZVI/R composite was over 93% and 97% within 20 min, respectively, which is much higher than that by the rectorite and the nZVI. The degradation ratio of methyl orange and metronidazole by the nZVI/R composite under US was 1.7 and 1.8 times as high as that by the nZVI/R composite without US, respectively. The mechanism of the enhanced degradation of methyl orange and metronidazole under US irradiation was studied. These results indicate that the US/nZVI/R process has great potential application value for treatment of dye wastewater and medicine wastewater.

Ultrasonic-assistant fabrication of cocoon-like Ag/AgFeO2 nanocatalyst with excellent plasmon enhanced visible-light photocatalytic activity

The AgFeO2 delafossite was reported as a potential photocatalyst as well as its intense recombination rate of photogeneration charge carriers. In this work, we utilized plasmon modification method to enhance the photocatalytic activity of AgFeO2. Silkworm cocoon like Ag/AgFeO2 nanocatalyst was synthesized by an ultrasonic enhanced reduction method. XRD, HRTEM and XPS results demonstrated the well dispersed Ag0 on the surface of AgFeO2. Under visible light irradiation, 20mg/L of ARG solution was completely degraded by 0.25g/L of Ag/AgFeO2 photocatalyst with pseudo-first-order rate of 0.040min-1. The inducement of the prominently enhanced photocatalytic activity of Ag/AgFeO2 was deeply analyzed. Significant decreased intensity of photoluminescence (PL) spectra suggested the superior separation of photo-induced electrons and holes of Ag/AgFeO2 as compared to that of AgFeO2. The free h+ was confirmed as the dominant active species for the pollutant degradation. Ultimately, the photodegradation mechanism was proposed and discussed.