Enhancing Removal of Pollutants by Combining Photocatalysis and Photo-Fenton Using Co, Fe-Doped Titanate Nanowires.

Aiming to improve their photocatalytic performance, titanate nanowires (TNW) were modified by Fe and Co (co)-doping, FeTNW, CoTNW and CoFeTNW samples, using a hydrothermal methodology. XRD characterization agrees with the existence of Fe and Co in the lattice structure.and the existence of Co2+ together with the presence of Fe2+ and Fe3+ in the structure was confirmed by XPS. The optical characterization of the modified powders shows the impact of the d-d transitions of both metals in the absorption properties of TNW, mainly in the creation of additional 3d energetic levels within the prohibited zone. The effect of the doping metal(s) in the recombination rate of photo-generated charge carriers suggests a higher impact of Fe presence when compared to Co. The photocatalytic characterization of the prepared samples was evaluated via the removal of acetaminophen. Furthermore, a mixture containing both acetaminophen and caffeine, a well-known commercial combination, was also tested. CoFeTNW sample was the best photocatalyst for the degradation of acetaminophen in both situations. A mechanism for the photo-activation of the modified semiconductor is discussed and a model proposed. It was concluded that both Co and Fe are essential, within the TNW structure, for the successful removal of acetaminophen and caffeine.

Impact of Fe, Mn co-doping in titanate nanowires photocatalytic performance for emergent organic pollutants removal.

The unexpected incorporation of ionic Mn and Fe in the crystalline structure of titanate nanowires was accomplished when a contaminated a titanium source was used. The presence of Mn (8.1 mg L-1) and Fe (4.3 mg L-1) result in the production of a novel co-doped (Fe,Mn) titanate nanowires (TNW) material with improved optical and photocatalytic properties. After structural characterization, the results indicate that both Mn and Fe were incorporated in the TNW structure by replacement of Na+ in the interlayers, together with Ti4+ substitution in the TiO6 octahedra. The potential of this new material to be used for pollutants photocatalytic degradation was further investigated. The terephthalic acid was used as probe molecule to first evaluate the catalytic ability of the pristine and FeMnTNW modified powders for the photo-assisted hydroxyl radical formation. Afterwards, the degradation process of a model emergent pollutant, caffeine, was studied. The results showed that FeMnTNW was the best photocatalyst, with the complete caffeine removal (20 mg L-1) within 60 min of radiation (13 mg catalyst/L solution). The action of several oxidant species, including h+, OH• and O2•-, during caffeine removal was carefully analyzed using specific radical scavengers. A mechanism for the charge-transfer in irradiated FeMnTNW particles, including the possibility of a photo-Fenton and photodegradation combination process, is proposed and discussed.

The effect of ionic Co presence on the structural, optical and photocatalytic properties of modified cobalt-titanate nanotubes.

With the aim of producing materials with enhanced optical and photocatalytic properties, titanate nanotubes (TNTs) modified by cobalt doping (Co-TNT) and by Na(+)→ Co ion-exchange (TNT/Co) were successfully prepared by a hydrothermal method. The influence of the doping level and of the cobalt position in the TNT crystalline structure was studied. Although no perceptible influence of the cobalt ion position on the morphology of the prepared titanate nanotubes was observed, the optical behaviour of the cobalt modified samples is clearly dependent on the cobalt ions either substituting the Ti(4+) ions in the TiO6 octahedra building blocks of the TNT structure (doped samples) or replacing the Na(+) ions between the TiO6 interlayers (ion-exchange samples). The catalytic ability of these materials on pollutant photodegradation was investigated. First, the evaluation of hydroxyl radical formation using the terephthalic acid as a probe was performed. Afterwards, phenol, naphthol yellow S and brilliant green were used as model pollutants. Anticipating real world situations, photocatalytic experiments were performed using solutions combining these pollutants. The results show that the Co modified TNT materials (Co-TNT and TNT/Co) are good catalysts, the photocatalytic performance being dependent on the Co/Ti ratio and on the structural metal location. The Co(1%)-TNT doped sample was the best photocatalyst for all the degradation processes studied.

Green synthesis of covellite nanocrystals using biologically generated sulfide: potential for bioremediation systems.

This work describes the synthesis of CuS powders in high yield and via an environmentally friendly and straightforward process, under ambient conditions (temperature and pressure), by adding to aqueous copper (II) a nutrient solution containing biologically generated sulfide from sulfate-reducing bacteria (SRB). The powders obtained were composed of CuS (covellite) nanoparticles (NPs) exhibiting a spheroid morphology (<5 nm). The relevance of this method to obtain CuS supported solid substrates has been demonstrated by performing the synthesis in the presence of TiO2 and SiO2 submicron particles. We further extended the work carried out, which substantiates the potential of using biogenic sulfide for the production of covellite nanocrystals and composites, using the effluent of a bioremediation column. Hence, such process results in the synthesis of added value products obtained from metal rich effluents, such as metallurgical and industrial ones, or Acid Mine Drainage (AMD), when associated with bioremediation processes.

Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders.

This paper reports on the ferromagnetic properties of aged Ti(1-x)CoxO(2-delta) anatase nanopowders with different Co contents (0.03 < or = x < or = 0.10). It is shown for the first time that aged Co:TiO2 anatase samples retain rather high values of magnetization (M), remanence (Mr) and coercivity (Hc) which provide strong evidence for a preserved long-range ferromagnetic order. Room temperature M, Mr and Hc values were measured in the ranges of [0.05, 0.79] microB/Co, [0.044, 0.096] microB/Co and [366.7,494.8]Oe, respectively, which are in the same range as in general reported either for newly prepared thin films or nanoparticles.

Photocatalytic decolorization of methylene blue in the presence of TiO2/ZnS nanocomposites.

The synthesis of distinct nanocrystalline TiO2 capped ZnS samples was carried out using a chemical deposition method. The materials characterization showed that the presence of ZnS onto TiO2 surface results in a red shift of the material band edge when compared with the initial semiconductor. The photocatalytic activity of the prepared nanocomposites was tested on the decolorization of methylene blue (MB) aqueous solutions. The dye photodecolorization process was studied considering the influence of experimental parameters such as catalyst concentration, TiO2/ZnS ratio, pH and methylene blue adsorption rate. The material with the best catalytic activity towards the methylene blue photodecolorization was the TiO2 doped with 0.2% of ZnS. The complete photodecolorization of a 20ppm methylene blue solution, at natural pH was achieved in less than 20min, nearly 70min faster than the TiO2 photoassisted process.