Zhaohong Zhang

Sonocatalytic degradation of acid red B and rhodamine B catalyzed by nano-sized ZnO powder under ultrasonic irradiation

Nano-sized ZnO powder was introduced to act as the sonocatalyst after the treatment of high-temperature activation, and the ultrasound of low power was used as an irradiation source to induce nano-sized ZnO powder performing sonocatalytic degradation of acid red B and rhodamine B. At the same time, the effects of operational parameters such as solution pH value, initial concentration of dyestuff and addition amount of nano-sized ZnO powder have been examined in this paper. We found that the degradation ratios of acid red B and rhodamine B in the presence of nano-sized ZnO powder were much higher than that with only ultrasonic irradiation. However, the degradation ratio of acid red B was about two times higher than that of rhodamine B for the initial concentration of 10.0mg/L, addition amount of 1.0 g/L nano-sized ZnO powder, solution acidity of pH 7.0 and 60 min irradiation experimental condition. The difference of the degradation ratios can be illustrated by the difference of chemical forms of acid red B and rhodamine B in aqueous solution and the surface properties of nano-sized ZnO particles. In addition, the researches on the kinetics of sonocatalytic reactions of acid red B and rhodamine B have also been performed and found to the follow pseudo first-order kinetics. All the experiments indicated that the sonocatalytic method in the presence of nano-sized ZnO powder was an advisable choice for the treatments of non- or low-transparent organic wastewaters in future.

Microwave degradation of methyl orange dye in aqueous solution in the presence of nano-TiO2-supported activated carbon (supported-TiO2/AC/MW).

In this study, nano-TiO(2)-supported activated carbon (TiO(2)/AC) was developed for the microwave (MW) degradation of an azo dye, methyl orange (MO), selected as a model contaminant in aqueous solution. The effects of selected process parameters such as supported TiO(2) content, MW irradiation time, initial MO concentration, catalyst dose, and solution pH on the degradation were assessed in detail. The results showed that the supported TiO(2) on AC could be excited resulting in the production of hydroxyl radical (OH) in aqueous solution under MW irradiation, which significantly enhanced the performance of AC/MW process for the degradation of MO. Also, the supported-TiO(2)/AC displayed higher catalytic activity than AC alone under MW irradiation. By comparison, the supported-TiO(2)/AC/MW process exhibited several advantages, including high degradation rate, short irradiation time, no residual intermediates and no secondary pollution. Hence, it shows to be a promising technology for the destruction of organic contaminants in dye treatment applications.

Preparation of Fe-doped mixed crystal TiO2 catalyst and investigation of its sonocatalytic activity during degradation of azo fuchsine under ultrasonic irradiation.

In this work, Fe-doped mixed crystal TiO2 powder as sonocatalyst was prepared by the sol-gel method and heat treatment, and a novel method combined with ultrasonic irradiation was propounded to degrade the organic polluted water. First, the Fe-doped mixed crystal TiO2 powder was characterized by TG-DTA, XRD, and TEM techniques. Ultrasound was used as the irradiation source and the azo fuchsine was chose as the model compound. Then a series of degradation experiments was carried out in the presence of Fe-doped mixed crystal TiO2 powder. Also, the degradation process and some influencing factors, such as irradiation time, doping Fe3+ ion content, added amount of catalyst, and initial concentration of azo fuchsine solution, on the degradation were investigated by UV-vis spectra, ion chromatography, and HPLC. Through the degradation of azo fuchsine, it was found that the combination of ultrasonic irradiation and Fe-doped mixed crystal TiO2 powder can completely degrade the azo fuchsine in aqueous solution. Because of the good degradation efficiency, this method may be an advisable choice for the treatments of non- or low-transparent wastewaters in the future.

NF-TiO2 photocatalysis of amitrole and atrazine with addition of oxidants under simulated solar light: Emerging synergies, degradation intermediates, and reusable attributes

In order to investigate sustainable alternatives to current water treatment methods, the effect of NF-titania film thickness and subsequent photocatalysis in combination with oxidants was examined under simulated solar light. Such a combination presents a theoretical possibility for a synergistic interaction between the photocatalyst and the oxidant (activation of the oxidant by the catalyst under conditions under which it may not conventionally be activated). To investigate, peroxymonosulfate (PMS) and persulfate (PS) were used as oxidants, and two pesticides, amitrole and atrazine, were used as target contaminants. In the absence of a film, activation of PMS under simulated solar conditions is demonstrated by removal of atrazine, whereas PS provided minimal removal, suggesting inefficient activation. Combining photocatalytic films with PMS and PS manifested synergies for both oxidants. The effect was most pronounced for PS since PMS already underwent significant activation without the photocatalyst. Amitrole degradation results indicated a lack of removal of amitrole by activated PS alone, suggesting that this sulfate radical-based treatment technology may be ineffective for the removal of amitrole. The NF-TiO₂ films demonstrated reusability under solar light both with and without oxidants. Finally, the degradation intermediates were analyzed, and a new intermediate appeared upon incorporating oxidants into the system.

Sonocatalytic degradation of azo fuchsine in the presence of the Co-doped and Cr-doped mixed crystal TiO2 powders and comparison of their sonocatalytic activities

In order to degrade some pollutants effectively under ultrasonic irradiation, the Co-doped and Cr-doped mixed crystal TiO(2) powders, with high sonocatalytic activity, were prepared as sonocatalyst. The Co-doped and Cr-doped mixed crystal TiO(2) powders as sonocatalyst were prepared through sol-gel and heat-treated methods from tetrabutylorthotitanate, and then were characterized by XRD and TG-DTA technologies. In order to compare and evaluate the sonocatalytic activity of the Co-doped and Cr-doped mixed crystal TiO(2) powders, the low power ultrasound was as an irradiation source and the azo fuchsine was chosen as a model compound to be degraded. The degradation process was investigated by UV-vis, TOC, ion chromatogram and HPLC techniques. The results indicated that the sonocatalytic activity of Cr-doped mixed crystal TiO(2) powder was higher than that of Co-doped and undoped mixed crystal TiO(2) powder during the sonocatalytic degradation of the azo fuchsine in aqueous solution. These results may be of great significance for driving sonocatalytic method to treat non- or low-transparent industrial wastewaters.

Microwave-induced carbon nanotubes catalytic degradation of organic pollutants in aqueous solution

In this study, a new catalytic degradation technology using microwave induced carbon nanotubes (MW/CNTs) was proposed and applied in the treatment of organic pollutants in aqueous solution. The catalytic activity of three CNTs of 10-20nm, 20-40nm, and 40-60nm diameters were compared. The results showed that organic pollutants such as methyl orange (MO), methyl parathion (MP), sodium dodecyl benzene sulfonate (SDBS), bisphenol A (BPA), and methylene blue (MB) in aqueous solution could be degraded effectively and rapidly in MW/CNTs system. CNTs with diameter of 10-20nm exhibited the highest catalytic activity of the three CNTs under MW irradiation. Further, complete degradation was obtained using 10-20nm CNTs within 7.0min irradiation when 25mL MO solution (25mg/L), 1.2g/L catalyst dose, 450W, 2450MHz, and pH=6.0 were applied. The rate constants (k) for the degradation of SDBS, MB, MP, MO and BPA using 10-20nm CNTs/MW system were 0.726, 0.679, 0.463, 0.334 and 0.168min(-1), respectively. Therefore, this technology may have potential application for the treatment of targeted organic pollutants in wastewaters.

Syntheses and structural determinations of the nine-coordinate rare earth metal: Na4[DyIII(dtpa)(H2O)]2·16H2O, Na[DyIII(edta)(H2O)3]·3.25H2O and Na3[DyIII(nta)2(H2O)]·5.5H2O

Three complexes, Na4[DyIII(dtpa)(H2O)]2 · 16H2O, Na[DyIII(edta)(H2O)3] · 3.25H2O and Na3[DyIII (nta)2(H2O)] · 5.5H2O, have been synthesized in aqueous solution and characterized by FT–IR, elemental analyses, TG–DTA and single-crystal X-ray diffraction. Na4[DyIII(dtpa)(H2O)]2 · 16H2O crystallizes in the monoclinic system with P21/n space group, a = 18.158(10) Å, b = 14.968(9) Å, c = 20.769(12) Å, β = 108.552(9)°, V = 5351(5) Å3, Z = 4, M = 1517.87 g mol−1, D c = 1.879 g cm−3, μ = 2.914 mm−1, F(000) = 3032, and its structure is refined to R 1(F) = 0.0500 for 9384 observed reflections [I > 2σ(I)]. Na[DyIII(edta)(H2O)3] · 3.25H2O crystallizes in the orthorhombic system with Fdd2 space group, a = 19.338(7) Å, b = 35.378(13) Å, c = 12.137(5) Å, β = 90°, V = 8303(5) Å3, Z = 16, M = 586.31 g mol−1, D c = 1.876 g cm−3, μ = 3.690 mm−1, F(000) = 4632, and its structure is refined to R 1(F) = 0.0307 for 4027 observed reflections [I > 2σ(I)]. Na3[DyIII(nta)2(H2O)] · 5.5H2O crystallizes in the orthorhombic system with Pccn space group, a = 15.964(12) Å, b = 19.665(15) Å, c = 14.552(11) Å, β = 90°, V = 4568(6) Å3, Z = 8, M = 724.81 g mol−1, D c = 2.102 g cm−3, μ = 3.422 mm−1, F(000) = 2848, and its structure is refined to R 1(F) = 0.0449 for 4033 observed reflections [I > 2 σ(I)]. The coordination polyhedra are tricapped trigonal prism for Na4[DyIII(dtpa)(H2O)]2 · 16H2O and Na3[DyIII(nta)2(H2O)] · 5.5H2O, but monocapped square antiprism for Na[DyIII(edta)(H2O)3] · 3.25H2O. The crystal structures of these three complexes are completely different from one another. The three-dimensional geometries of three polymers are 3-D layer-shaped structure for Na4[DyIII(dtpa)(H2O)]2 · 16H2O, 1-D zigzag type structure for Na[DyIII(edta)(H2O)3] · 3.25H2O and a 2-D parallelogram for Na3[DyIII(nta)2(H2O)] · 5.5H2O. According to thermal analyses, the collapsing temperatures are 356°C for Na4[DyIII(dtpa)(H2O)]2 · 16H2O, 371°C for Na[DyIII(edta)(H2O)3] · 3.25H2O and 387°C for Na3[DyIII(nta)2(H2O)] · 5.5H2O, which indicates that their crystal structures are very stable.

Confirmation of hydroxyl radicals (•OH) generated in the presence of TiO2 supported on AC under microwave irradiation.

In order to study the degradation mechanism of technology of microwave (MW) combined with TiO2 supported on activated carbon (TiO2/AC), the reactive oxygen species (ROS) was explored through oxidation of 1,5-diphenyl carbazide (DPCI) to 1,5-diphenyl carbazone (DPCO). Furthermore, 2,6-di-tert-butyl-4-methylphenol (BHT), Mannitol (MT) and Vitamin C (VC) were used as radical scavengers to confirm the generation of the hydroxyl radicals ((•)OH). In addition, the influence of some parameters such as TiO2 mass ratio content, irradiation time, material dose, DPCI concentration and MW power on the determination of (•)OH were examined. The results showed that the (•)OH could be generated under MW combined with loaded TiO2/AC. Also, anatase TiO2/AC can generate more (•)OH radicals than rutile TiO2/AC under MW irradiation. This work would provide new mechanistic insights on the enhanced degradation effect of organic pollutants in water using the supported TiO2/AC coupled with MW technology.

Syntheses of rare earth metal complexes with aminopolycarboxylic acids and study on structural changes: Nine-coordinated mononuclear K2[DyIII(dtpa)(H2O)]·6H2O and binuclear K4[HoIII 2(dtpa)2]·4H2O

The crystal and molecular structures of mononuclear K2[DyIII(dtpa)(H2O)]·6H2O (H5dtpa = diethylenetriaminepentaacetic acid) and binuclear K4[HoIII 2(dtpa)2]·4H2O complexes have been determined by single-crystal X-ray structure analyses. The crystal of K2[DyIII(dtpa) (H2O)]·6H2O complex belongs to the triclinic crystal system, space group. The [DyIII (dtpa)(H2O)]2− complex anion has a nine-coordinate pseudo-monocapped square antiprismatic structure, in which the nine coordinated atoms (three N and six O) are from one dtpa ligand and one water molecule. The crystal of K4[HoIII 2(dtpa)2]·4H2O complex belongs to triclinic crystal system, space group. The [HoIII 2(dtpa)2]4− complex anion is composed of two identical parts and every HoIIIO6N3 has a nine-coordinate, distorted monocapped square antiprismatic structure, in which the dtpa ligand coordinates to one central HoIII ion with three N atoms and five O atoms and to the other HoIII ion with one O atom in the same coordinated carboxylic group. Although the DyIII and HoIII ions have close ionic radii (1.052 and 1.041 Å) and electronic configuration (f 9 and f10) they form mononuclear and binuclear nine-coordinate complexes, respectively. Perhaps there is a critical ionic radius for mononuclear and binuclear structures, namely the dtpa complexes of rare earth metals with larger ionic radii than 1.052 Å of DyIII ion adopt a mononuclear nine-coordinate structure, while those with smaller ionic radii than 1.041 Å of HoIII ion adopt a binuclear nine-coordinate structure.

Degradation of surfactant wastewater under microwave irradiation in the presence of activated carbon assisted with nano-sized TiO2 or nano-sized ZnO

An improved method treating surfactant wastewater by the addition of semiconductor material such as nano-sized TiO2 or ZnO to activated carbon (AC) with microwave (MW) irradiation was proposed so as to assist efficient degradation of organic pollutants. A series of degradation experiments of sodium dodecyl benzene sulfonate (SDBS) were carried out under MW irradiation in the presence of AC/TiO2 or AC/ZnO. The influences of catalyst dose, irradiation time, initial SDBS concentration and solution acidity on the degradation were assessed in detail. The results showed that the addition of TiO2 or ZnO obviously promoted the degradation and AC/TiO2 system displayed higher catalytic activity under MW irradiation. Thus the method of MW irradiation with AC/TiO2 or AC/ZnO revealed many advantages of rapid degradation rate, short irradiation time, low cost, no residual intermediates and no secondary pollution in applications.