Effect of surfactant microstructures on photocatalytic degradation of phenol and chlorophenols

The effect of hexadecyltrimethylammonium bromide (HTAB) on the photocatalytic degradation of phenol (Phe), 2,5-dichlorophenol (2,5-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) in the presence of aqueous TiO₂ suspensions at pH ca. 5 was investigated using a laboratory photoreactor equipped with a medium-pressure mercury lamp. Inhibition of substrate decomposition was observed for phenol, both below and above the surfactant critical micellar concentration, whereas a more complex behaviour was exhibited by chlorophenols. It was found that adsorption of these compounds onto the surfactant-modified semiconductor particles facilitates their faster decomposition, but the competitive partition of substrates between adsorbed surfactant structures and micellar aggregates tends to limit the beneficial kinetic effects at higher amphiphile concentrations. The crucial influence of surfactant adsorption was clearly evidenced in some runs performed at pH 3. Relevant inhibition of chloride release from chlorophenols, observed in the presence of HTAB, indicates a higher persistence of reaction intermediates in the reaction media, suggesting the need for a careful investigation of surfactant effects on all the degradation steps of the process.     

Surface acidity study of Mn+-montmorillonite clay catalysts by FT-IR spectroscopy: Correlation with esterification activity

A simple method for evaluating the surface acidity of different cation-exchanged montmorillonite (mont) clay catalysts, Mⁿ⁺-mont (Mⁿ⁺=Al³⁺, Fe³⁺, Cr³⁺, Zn²⁺, Ni²⁺, Cu²⁺, and H⁺), involving treatment with pyridine is described. After treating with pyridine, the samples were heated at 120 °C and the FT-IR spectra were directly recorded in the region 1650 and 1350 cm⁻¹. The data obtained show the presence of both Lewis and Brønsted acid sites. The activities of the catalysts to bring about Brønsted acid catalysed esterification of succinic acid with iso-butanol to yield di-(iso-butyl) succinate have been studied. The Brønsted acidity data obtained for Mⁿ⁺-mont correlated well with activity in the esterification reaction. The activities of the catalysts were found to decrease in the order of exchange ions Al³⁺ > Fe³⁺ > Cr³⁺ > Zn²⁺ > Ni²⁺ > Cu²⁺ > Na⁺-mont. They also correlated well with the charge to radius ratio of the cations. The catalysts exchanged with trivalent cations showed stronger absorption bands attributed to Brønsted acidity (1540 cm⁻¹) whereas those exchanged with divalent cations showed an increased Lewis acidity (1450 cm⁻¹) and reduced Brønsted acidity along with charge to radius ratio. Zn²⁺-, Cu²⁺- and Ni²⁺-exchanged clays showed an additional peak around 1605 cm⁻¹ which is attributed to the pyridine adsorption on surface sites through its π electrons. The method suggested here to evaluate the acidity is suitable for active sites which are thermally unstable such as water molecules in the hydration shell of a cation in exchanged clay.     

The potential for rapid coke making using microwave energy

This paper describes initial work into the production of coke from high volatile bituminous coal using microwave energy. A series of batch experiments were carried out using an 8 kW multimode microwave to heat 300 g of a UK high volatile bituminous coal, sized at −3 mm, at different treatment times of 10, 25 and 70 min. Devolatilisation started after 1 min of heating and was complete within 5 min. Subsequent heating yielded no further volatiles and the power was maintained to prolong the coking process. Characterization of each product was carried out using thermogravimetric analysis, microscopy and dielectric property measurement in order to investigate the impact of residence time and provide a comparison with coke material produced using conventional methods. The measured characteristics of each sample became increasingly similar to those of two conventional cokes as treatment time was increased.     

An overview of aqueous-phase catalytic processes for production of hydrogen and alkanes in a biorefinery

In this overview we discuss how aqueous-phase catalytic processes can be used to convert biomass into hydrogen and alkanes ranging from C₁ to C₁₅. Hydrogen can be produced by aqueous-phase reforming (APR) of biomass-derived oxygenated hydrocarbons at low temperatures (423–538 K) in a single reactor over supported metal catalysts. Alkanes, ranging from C₁ to C₆ can be produced by aqueous-phase dehydration/hydrogenation (APD/H). This APD/H process involves a bi-functional pathway in which sorbitol (hydrogenated glucose) is repeatedly dehydrated by a solid acid (SiO₂–Al₂O₃) or a mineral acid (HCl) catalyst and then hydrogenated on a metal catalyst (Pt or Pd). Liquid alkanes ranging from C₇ to C₁₅ can be produced from carbohydrates by combining the dehydration/hydrogenation process with an upstream aldol condensation step to form C–C bonds. In this case, the dehydration/hydrogenation step takes place over a bi-functional catalyst (4 wt.% Pt/SiO₂–Al₂O₃) containing acid and metal sites in a specially designed four-phase reactor employing an aqueous inlet stream containing the large water-soluble organic reactant, a hexadecane alkane sweep stream, and a H₂ inlet gas stream. The aqueous organic reactant become more hydrophobic during dehydration/hydrogenation, and the hexadecane sweep stream removes these species from the catalyst as valuable products before they go on further to form coke.     

Building a research network to better understand climate governance in the Great Lakes

Climate-driven disturbances threaten the sustainability of coastal communities in the Great Lakes Basin. Because such disturbances are unpredictable, their magnitude, number and intensity are changing, and they occur at varying temporal and spatial scales. Consequently, communities struggle to respond in effective ways. The expected intensification of climate-driven disturbances will require that community capacity and governance structures match the spatial and temporal scales of these disturbances, as the most sustainable social and economic systems will be those that can respond at similar frequencies to key natural system drivers. The Climate Governance Variability in the Great Lakes Research Coordination Network (CGVG-RCN) was recently established to address questions about the relationship between climate-driven disturbances and community response. The objective of this short communication is to introduce the ideas behind the CGVG-RCN, outline its goals, and facilitate engagements and collaboration with social and natural scientists interested in social-ecological systems in the Great Lakes Basin.     

Improved electrochemical redox performance of 2,5-dimercapto-1,3,4-thiadiazole by poly(3-methoxythiophene)

High electrocatalytic activity of an electropolymerized film of poly(3-methoxythiophene) (PMOT) is reported toward the redox reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) as a promising cathode material for the lithium ion battery. Cyclic voltammetry showed improved electrochemical performance of DMcT on PMOT-coated Pt electrode, indicating accelerated redox kinetics. Moreover, charge-discharge tests exhibited higher discharge capacity and slower capacity fading of the PMOT-doped DMcT composite cathode compared with pure DMcT.     

PM-10 emissions and power of a Diesel engine fueled with crude and refined Biodiesel from salmon oil

Power response and level of particulate emissions were assessed for blends of Diesel-crude Biodiesel and Diesel-refined Biodiesel. Crude Biodiesel and refined Biodiesel or methyl ester, were made from salmon oil with high content of free fatty acids, throughout a process of acid esterification followed by alkaline transesterification. Blends of Diesel-crude Biodiesel and Diesel-refined Biodiesel were tested in a diesel engine to measure simultaneously the dynamometric response and the particulate material (PM-10) emission performance. The results indicate a maximum power loss of about 3.5% and also near 50% of PM-10 reduction with respect to diesel when a 100% of refined Biodiesel is used. For blends with less content of either crude Biodiesel or refined Biodiesel, the observed power losses are lower but at the same time lower reduction in PM-10 emissions are attained.     

Synthesis and characterization of porous media produced by a sol-gel method

Mesoporous silica materials were synthesized by sol-gel method using tetraethoxysilane (TEOS) as precursors and surfactants i.e., cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyoxyethylene cetyl ether (Brij 56) as templates. Surfactant templates were completely removed by calcination to form mesoporous structure. The effects of type and amount of surfactants on the characteristics of samples were studied. The textural characteristics such as surface area, pore volume, pore size, and pore size distribution were determined by nitrogen sorption isotherms. Fourier transform infrared (FTIR) spectroscopy was employed to qualitatively identify the chemical functionality and to confirm the removal of surfactant template. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to directly observe surface morphology and mesoporous structure, respectively. The adsorption capacity of the synthesized adsorbent for toluene vapor was examined. We found that the pore volume and pore size of mesoporous materials affected the adsorption capacity. The sample prepared with high content of CTAB under basic condition (pH ∼7) yielded large pore volumes and pore sizes and subsequently possessed the high adsorption capacity for toluene vapor.     

In situ generation of hydrogen peroxide from reaction of O2 with hydroxylamine from hydroxylammonium salt in neutral aqueous or non-aqueous medium using reusable Pd/Al2O3 catalyst

In situ generation of H₂O₂ with high yield can be accomplished by reacting O₂ with NH₂OH from hydroxylammonium salt [NH₂OH · HCl or (NH₂OH)₂ · H₂SO₄] in a neutral aqueous medium using a reusable heterogeneous Pd (1.0 wt%)/Al₂O₃ catalyst, even at low temperature (10 °C), with the formation of harmless by-products (viz. N₂ and water). The presence of KCl or KBr in the medium has beneficial effect. The H₂O₂ generation is strongly influenced by the pH of medium, reaction period and temperature; best results are obtained at the optimum pH and reaction medium.     

烟气冷凝热能回收利用装置烟气流动方式优化研究

烟气冷凝热能回收利用装置中烟气的分布与流动对换热起着重要作用,为优化烟气冷凝热能回收利用装置,保证烟气能够在装置中分布均匀、充分换热,分别设计两种烟气流动方式,采用CFD软件Fluent模拟了烟气冷凝热能回收利用装置中的流场及温度场,并将其分别应用于实际工程进行现场实测.结果表明,采用渐变断面设计的烟气流动方式,烟气在换热面上分布更均匀,更有利于强化换热,阻力更小,节能率比采用等高断面最大可提高3.25%,可有效降低和消除噪音.