Mika Huuhtanen

Nitrogen-Doped Anatase Nanofibers Decorated with Noble Metal Nanoparticles for Photocatalytic Production of Hydrogen

We report the synthesis of N-doped TiO(2) nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO(2) nanofiber decorated with Pt nanoparticles) was applied to 1 L of water-ethanol mixture, the H(2) evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy conversion percentages of ∼3.6 and ∼12.3%, respectively.

Three-Dimensional Carbon Nanotube Scaffolds as Particulate Filters and Catalyst Support Membranes

Three-dimensional carbon nanotube scaffolds created using micromachined Si/SiO2 templates are used as nanoparticulate filters and support membranes for gas-phase heterogeneous catalysis. The filtering efficiency of better than 99% is shown for the scaffolds in filtering submicrometer particles from air. In the hydrogenation of propene to propane reaction low activation energy of E(a) approximately 27.8 +/- 0.6 kJ x mol(-1), a considerably high turnover rate of approximately 1.1 molecules x Pd site(-1) x s(-1) and durable activity for the reaction are observed with Pd decorated membranes. It is demonstrated that appropriate engineering of macroscopic-ordered nanotube architectures can lead to multifunctional applications.

Production of Activated Carbon from Cocoa (Theobroma cacao) Pod Husk

Activated carbons were obtained from cocoa pod husk using two different initial particle sizes (ranges 0.25 – 0.50mm and 0.50 – 1.00mm), three chemical activation agents (K2CO3, KOH and ZnCl2) and carbonization under nitrogen atmosphere during two hours at three different temperatures (500°C, 650°C and 800°C). The prepared activated carbons were characterized using Brunauer–Emmett–Teller (BET) and Langmuir surface areas, pore volume, average pore size, bulk density, moisture, ash content, and yield. The five best activated carbons were selected for further experiments according to the chemical activation agent used, high BET surface area, high pore volume and low ash content. Additionally, content of impurities, carbon content and FE-SEM micrographs were determined for these five best activated carbons. As adsorption tests were also carried out with these samples. Results of the experiments show that cocoa pod husk is a material that can be used to produce activated carbon by chemical activation and ZnCl2 showed to be the best chemical activation agent based on the highest BET surface area (780 m2/g in the best case) and pore volume (0.58 m3/g in the best case), the lowest ash content (6.14% in the best case), and the highest carbon content (86.1% in the best case), compared with others chemicals. Carbons activated by ZnCl2 are capable to adsorb As(V), getting As(V) removal levels up to 80% in less than 1 hour in the experimental conditions applied (initial pH 6-7, activated carbon concentration 0.1 g/l and 0.5 g/l, initial As concentration 100 ppb).

Photocatalytic Degradation of Organic Pollutants in Wastewater

Even today the efficient treatment of industrial wastewaters is not evident. The effluents may contain large amounts of harmful organic compounds that are not easily removed with conventional methods. This study focuses on the photocatalytic treatment of four organic pollutants originated from different types of industry. The pollutants are diuron (herbicide), p-coumaric acid (agro-industrial wastewater), bisphenol A and phthalic anhydride (plasticizers), which all are widely used and cause significant health and environmental problems. To get deeper understanding, the photocatalytic degradation of the model molecules was studied both in synthetic solutions and in industrial wastewater matrix over TiO2 P25 in two different batch photoreactors under UV-A irradiation. The effects of catalyst loading, pH and initial concentration were studied. To gain understanding on the reactivity of molecules and costs of treatment, the kinetic modelling and energy modelling were compared and the specific applied energy (ESAE) was estimated. ESAE is proposed as a useful value to estimate the energy needed to degrade one mole of pollutant and further to calculate the operating costs to treat the wastewater. Of the model pollutants, diuron was removed the most efficiently and its removal consumed the least amount of energy in terms of the specific applied energy. Bisphenol A was found to be the most difficult to be removed by photocatalysis. The industrial wastewater matrix affected negatively the removal results.

Room temperature chemical deposition of palladium nanoparticles in anodic aluminium oxide templates

Palladium nanoparticles are deposited in the pores of freestanding, mesoporous anodic aluminium oxide (AAO) templates via a chemical route at room temperature. In the precursor, Pd2+ ions are complexed with ammonia and reduced to Pd0 by adding an excess amount of formaldehyde. To enhance the infiltration of pores with the precursor, 2-propanol is added to the solution. After a few hours of plating at room temperature, crystalline Pd0 nanoparticles with an average size of ~4 nm form on the pore walls of the AAO templates. The effect of heat treatment on the structure of the AAO/Pd system is also studied. The specimens are investigated using FESEM, EFTEM/EDX, and electron and x-ray diffraction techniques. Preliminary catalyst activity analyses reveal good selectivity of ~90%, but low conversion of ~1.2% of carbon monoxide to methane in hydrogen flow at 330 °C on AAO/Pd. The oxidized form of the catalyst shows instantaneous oxidation with ~100% selectivity and conversion of carbon monoxide to carbon dioxide in oxygen flow at 140 °C.

Alkaline modified oil shale fly ash: optimal synthesis conditions and preliminary tests on CO2 adsorption.

Environmentally friendly product, calcium-silica-aluminum hydrate, was synthesized from oil shale fly ash, which is rendered so far partly as an industrial waste. Reaction conditions were: temperature 130 and 160°C, NaOH concentrations 1, 3, 5 and 8M and synthesis time 24h. Optimal conditions were found to be 5M at 130°C at given parameter range. Original and activated ash samples were characterized by XRD, XRF, SEM, EFTEM, (29)Si MAS-NMR, BET and TGA. Semi-quantitative XRD and MAS-NMR showed that mainly tobermorites and katoite are formed during alkaline hydrothermal treatment. Physical adsorption of CO(2) on the surface of the original and activated ash samples was measured with thermo-gravimetric analysis. TGA showed that the physical adsorption of CO(2) on the oil shale fly ash sample increases from 0.06 to 3-4 mass% after alkaline hydrothermal activation with NaOH. The activated product has a potential to be used in industrial processes for physical adsorption of CO(2) emissions.

Biobutanol Production from Biomass

There is a demand for the increased production and usage of biofuels from both environmental and a political point of view. Biobutanol has great potential to become a novel replacement fuel for gasoline and diesel or an additive compound of these fuels in the future. This chapter reveals the superior fuel properties of butanol over ethanol, including better energy content, usability, safety, and easier distribution of the fuel. Traditional biochemical (acetone-butanol-ethanol fermentation) and chemical production processes of butanol are reviewed. In addition, the novel production routes of biobutanol are highlighted. Challenges in the implementation of feasible biochemical production processes of butanol in industrial scale include cost of raw materials, low product yield from fermentation, and expensive processing techniques. Process development techniques and different methods in order to increase the yield of fermentative butanol production by means of for instance new processing technologies and metabolic engineering are discussed.

Photocatalytic activity of nitrogen-doped TiO2-based nanowires: a photo-assisted Kelvin probe force microscopy study

In this study, a set of nitrogen-doped TiO2-based nanomaterials demonstrating photocatalytic activity was developed by combining the efforts of lattice doping and metal nanoparticle decoration and tested for photo-degradation of methylene blue dye by applying solar simulator irradiation. The surface potential shifts of these TiO2-based photocatalytic nanomaterials measured by Kelvin probe force microscope have been used to study the degree of electron generation of the photocatalysts after irradiation and were well correlated with the photocatalytic activity. The nitrogen-doped TiO2 nanowires decorated with Pt nanoparticles can induce obvious electron accumulation and result in a large shift of surface potential. The analysis shows a clear correlation between the surface potential shift and the photodegradation activity. Furthermore, a thorough comparative photocatalytic activity study combined with X-ray photoelectron spectroscopy analysis of the materials—doped with nitrogen under various conditions—reveals that the photocatalytic efficiency of the catalysts is maintained even if the lattice doping is leached e.g., by thermal treatments after doping.Graphical AbstractBy monitoring the surface potential shifts of various TiO2-based photocatalysts by photo-assisted Kelvin probe force microscopy, we obtain a useful tool for developing novel materials with high photocatalytic activity.

Deactivation of Diesel Oxidation Catalysts by Sulphur in Laboratory and Engine-Bench Scale Aging

The activity of sulphur–water- and water-treated PtPd/Al2O3- and Pt/Al2O3-based monolith catalysts was investigated. The catalysts were characterized by X-ray photoelectron fluorescence, X-ray photoelectron spectroscopy, transmission electron microscopy and BET–BJH. The sulphur poisoning had a diminishing effect on the catalyst activity. The correlation between the laboratory-poisoned and engine-bench-aged catalyst activity was detected and found to have a relatively good correspondence.

Photocatalytic Degradation of Butanol in Aqueous Solutions by TiO2 Nanofibers

Removal of butanol from aqueous solutions was studied using both custom made and commercial TiO2 photocatalysts. The custom made photocatalytic materials were nanofibers of titanium dioxide doped with nitrogen and subsequently decorated with nanoparticles of platinum or palladium. Pd-decorated photocatalysts were found to be highly efficient in the degradation of butanol under UV-A irradiation compared to Pt-decorated nanofibers or to commercial Degussa P25.