The activity and mechanism of uranium oxide catalysts for the oxidative destruction of volatile organic compounds

Uranium oxide based catalysts have been investigated for the oxidative destruction of volatile organic compounds (VOCs) to carbon oxides and water. The catalysts have been tested for the destruction of a range of organic compounds at space velocities up to 70 000 h⁻¹. Destruction efficiencies greater than 99% can be achieved over the appropriate uranium based catalyst in the temperature range 300–450°C. Volatile organic compounds investigated include benzene, butylacetate, cyclohexanone, toluene, methanol, acetylene, butane, chlorobutane and chlorobenzene. The catalysts are thermally stable, destroy low concentrations and mixtures of VOCs and lifetime studies indicate that deactivation during oxidation of chlorinated VOCs did not occur. A temporal analysis of products (TAPs) reactor is used to investigate the mechanism of oxidation of VOCs by uranium oxide catalysts. Studies indicated that VOCs were oxidised directly to carbon oxides on the catalyst surface. A combination of TAP pulse experiments with oxygen present and absent in the gas phase has indicated that the lattice oxygen from the catalyst is responsible for the total oxidation activity. This has been confirmed by studies using isotopically labelled oxygen which indicates that the catalyst operates by a redox mechanism.     

The preparation of flat H–Si(111) surfaces in 40% NH4F revisited

The reasons why ideally flat H–Si(111) surface can be prepared by NH₄F etching are investigated from correlation between AFM observations and experimental conditions used for etching. It is shown that pitting may be completely suppressed if a one side polished wafer is immersed in an oxygen free solution. An analytical electrochemical study of the (111) and rough face of the same n-Si wafer is presented to yield insight into observations.     

Ditopic, flexible hydrazone-based building blocks with pendant 2,2′:6′,2′′-terpyridine metal-binding domains

The synthesis and characterization of three new bis(2,2′:6′,2′-terpyridine) (tpy) ligands containing different hydrazone spacers between the metal-binding domains are described. Treatment of 1,4-benzenedicarbaldehyde bis(2,2′:6′,2′′-terpyridin-4′-ylhydrazone) (1) with [(tpy)RuCl₃] in the presence of N-ethylmorpholine results in the formation of [(tpy)Ru(μ-1)Ru(tpy)]⁴⁺. Single crystal X-ray diffraction data for [(tpy)Ru(μ-1)Ru(tpy)][PF₆]₄·8MeCN confirm the ability of the hydrazone-based ligand to bridge two ruthenium(II) centres, providing proof-of-principle for the application of this class of flexible ligand in the design of coordination polymers.     

Dung pads increase pasture production,soil nutrients and microbial biomass carbon in grazed dairy systems

In grazing systems dung is an important source of nutrients which can increase soil fertility and contribute to nutrient cycling through increased pasture production. Changes in soil chemical and biological properties and pasture production were measured below and around dung pads created in the field. Almost 65% of the total dung P remained after 45 days and about two-thirds of the pad fresh weight had disappeared in that time, indicating that physical degradation is the mechanism of incorporation of dung P. All the pads bar one were completely degraded by 112 days. At this time, soil pH and EC increased under dung pads as did Olsen extractable inorganic phosphorus (Pi) and total phosphorus (Pt), with these changes observed at 0–5 and 5–10 cm depths. Bicarbonate extractable soil organic phosphorus (Po) was not affected by dung and the observed differences in soil Po:Pi ratios were largely influenced by the substantial addition of inorganic P from dung. Dung increased the P buffering capacity of the 0–5 cm soil samples collected at the end of the experiment, potentially contributing to the increased extractable soil P measured under the pads. Dung also changed soil properties in 0–10 cm samples with increases in soil pH, EC, Colwell P and Colwell K recorded even long after the dung had completely disappeared. Microbial biomass carbon increased under dung pads in the 0–10 cm soil samples in the first 45 days after pads were applied. Total herbage production and ryegrass biomass increased significantly under and around the pads by 112 days after dung was applied. The botanical composition changed significantly with increased ryegrass contents observed, but only under the dung pads. This experiment demonstrated that increases in pasture around dung pads in the field are not solely due to animal rejection.     

Variations in Allelochemical Composition of Leachates of Different Organs and Maturity Stages of <Emphasis Type="Italic">Pinus halepensis</Emphasis>

We investigated changes in the occurrence of allelochemicals from leachates of different Pinus halepensis organs taking into account the stages of pine stand age (i.e., young  < 15-years-old, middle age ± 30-years, and old  > 60-years-old). GC-MS analysis of aqueous extracts revealed approx. 59 components from needles and roots. The major constituents were divided into different phytochemical groups—phenolics (50%), fatty acids (44%), and terpenoids. Further analyses were carried out to characterize the distribution of allelochemicals in different organs and P. halepensis successional stages. Roots and needles had two distinct chemical profiles, while needle leachates were composed mainly of oxygenated terpenoids (e.g., α-eudesmol, α-cadinol, and α-terpineol). Roots mainly contained fatty acids. Needles from young pine stands had the highest content of monoterpenes, suggesting their role as potential allelochemicals that could help young pine stands to establish. Pooling the different functional chemical groups showed that needles and, to a lesser extent, old roots, had higher chemical diversity than the roots of young and medium-aged pines. The highest diversity in phenolic constituents and fatty acids was in young needles (D_chem = 2.38). Finally, caffeic acid, a compound that has allelopathic properties was found in aqueous extracts at high concentrations in both young needles and old roots. The role of this compound in mediation of biological interactions in P. halepensis ecosystem functioning is discussed.     

Chitosan chiral ligand exchange membranes for sorption resolution of amino acids

The concept of chiral ligand exchange is employed in the present study to achieve the chiral resolution of tryptophan (Trp) enantiomers by using chitosan (CS) membrane in a sorption resolution mode and copper(II) ion as the complexing ion. CS porous membranes are prepared by freeze-drying method (CS-LT) and sol-gel process at high temperature (CS-HT), respectively, to investigate their sorption resolution characteristics. The proposed CS chiral ligand exchange membranes exhibit good chiral resolution capability. Meanwhile the sorption selectivity of the CS membranes is found to be reversed from L-selectivity at low copper(II) ion concentration to D-selectivity at high copper(II) ion concentration, which is attributable to the stability difference between the copper(II)-L-Trp and copper(II)-D-Trp complexes. Moreover, the CS-HT membrane shows better performance with respect to both sorption selectivity and sorption capability than the CS-LT membrane, which mainly results from its more amorphous structures compared with the more crystalline structures of the CS-LT membrane. The superiority of sorption capability of the CS-HT membrane is also attributable to its larger specific surface area than that of the CS-LT membrane. The results obtained in this study are conducive to the design and fabrication of chiral ligand exchange membranes for enantiomer separation in sorption mode.     

Supramolecular and nanochemistry

The following contributions describe various research activities of the Department of Chemistry, University of Basel in the area of nanochemistry and supramolecular chemistry.     

Biphasic and Flow Systems Involving Water or Supercritical Fluids

Two processes are described for improving reaction rates for relatively hydrophobic substrates in aqueous biphasic systems. In the first, 1-octyl-3-methylimidazolium bromide ([Octmim]Br) increases the rate of hydroformylation of 1-octene from 8% conversion in 24 h to full conversion of 1.5 h. Phase separation is fast and catalyst retention is good. 1-Hexyl-3-methylimidazolium bromide gives little rate enhancement, whilst 1-decyl-3-methylimidazolium bromide gives stable emulsions., The mechanism of action of these additives is discussed. In the second approach, functionalising PPh₃ with amidine groups allows the rhodium catalysed hydroformylation of 1-octene in toluene with a very high reaction rate. The catalyst can be switched between toluene and water by bubbling CO₂ and back into toluene by bubbling N₂ at 60 °C. This switching has been used to separate the catalyst from hydrophobic (from 1-octene) or hydrophilic (from allyl alcohol) aldehydes obtained from hydroformylation reactions. CO₂ expanded liquids have been shown to be effective media for transporting substrates and catalysts over supported ionic liquid phase (SILP) catalysts. The advantages offered over all gas phase and liquid phase catalysts are discussed.     

Efficient Telomerization of Butadiene with Starch in Water: The Role of the Surfactant

The synthesis of hydrophobic starch was performed via palladium-catalyzed telomerization of butadiene with native starch. This reaction is efficiently performed in water in the presence of neutral or cationic surfactant with high HLB. After optimization of the reaction conditions, TOF up to 446 was achieved.