Assembly of 3-D network structures containing oxydiacetate and CeIII or CeIV

Reaction of CeCl₃·7H₂O with Na₂(oda) (oda = O(CH₂CO₂)₂²— oxydiacetate) in a 2:3 ratio gives the neutral cerium(III) complex [Ce₂(oda)₃(H₂O)₃]·9H₂O (1). Treatment of a 1:3 mixture of CeCl₃·7H₂O and H₂oda in water with 4 molar equivalents of NaOH also gives 1 but, with a larger excess of NaOH, the tri-sodium salt Na₃[Ce(oda)₃]·9H₂O (2) is isolated. Formation of a tri-ammonium analogue of 2 can be achieved by neutralisation of an aqueous solution of CeCl₃·7H₂O and H₂(oda) in a 1:3 ratio by NH₄OH, giving (NH₄)₃[Ce(oda)₃]·7H₂O (3). Use of the cerium(IV) reagent (NH₄)₂[Ce(NO₃)₆] with Na₂(oda) results in reduction to cerium(III) under ambient conditions and isolation of 1. However, in the absence of light this reaction yields crystals of the novel cerium(IV) heterobimetallic [Ce(oda)₃Na₄(NO₃)₂] (4). Each of these complexes exhibit a 3-D network structure having a common nine-coordinate [Ce(oda)₃]ⁿ— (n = 2 or 3) subunit, irrespective of the oxidation state of cerium. In 1, six [Ce(oda)₃]³— anions are connected, through bridging bidentate carboxylates, to a second Ce³⁺ site further coordinated by three water molecules. In contrast, the ammonium salt 2, displays isolated [Ce(oda)₃]³— anions, devoid of further carboxylate bonding, but enmeshed within a network of hydrogen-bonded NH₄⁺ cations and water molecules. The remarkable structure of 4 consists of infinite 2-D sheets of [Na₂(NO₃)]+ pillared by [Ce(oda)₃]^2— units, the connectivity arising by multidentate nitrate and carboxylate bridging.

A study of acid/base treatments of polypyrrole films using 13C n.m.r. spectroscopy

Electrodeposited polypyrrole films prepared with paratoluenesulfonate (pTS), dodecylsulfate (DDS) and perchlorate anions were treated with acidic and basic solutions, and their structure was investigated by 13C solid state n.m.r. spectroscopy. This technique has confirmed that pTS is completely removed from the film in both acidic and basic solutions whilst DDS is only partially removed and tends to decompose upon treatment with H2SO4. The appearance of shoulders at 143 ppm upon treatment with 0.5 M base indicates formation of a quinoid pyrrole structure. Substitution on the β-carbon by OH cannot be confirmed from the present spectra. Stronger base causes a more dramatic change in the polypyrrole backbone with an obvious increase in the electron density on the β-carbons, consistent with the reduction of the carbon backbone. There is no indication of quinoid units in this case. Acid treatments result in considerable broadening of the main 127 ppm polypyrrole peak.

Boron nitride nanotube films grown from boron ink painting

The growth of nanotube films can have important applications in building nanoscale functional devices or solving interfacial and heat problems. We report that high-density boron nitride nanotube (BNNT) films with any desired pattern can be grown on complicated surfaces using a boron (B) ink process. The special B ink, a mixture of nanosized B particles, metal nitrate and ethanol, is first painted, sprayed or inkjet printed at the desired location with required pattern, and then the ink layer is annealed in a nitrogen-containing atmosphere to form BNNT film. This is the first method capable of growing BNNTs on complex non-flat surfaces, which greatly broadens the potential application of BNNTs. For example, it is demonstrated here that a BNNT coated steel mesh can separate water and oil on a microlitre scale; a needle given an internal BNNT coating could greatly enhance microfluidic transport; and a coated screw could be used to minimize wear at the interface.

Synthesis of boron nitride nanotubes by boron ink annealing

Ball-milling and annealing is one effective method for the mass production of boron nitride nanotubes (BNNTs). We report that the method has been modified to a boron (B) ink annealing method. In this new process, the nanosize ball-milled B particles are mixed with metal nitrate in ethanol to form an ink-like solution, and then the ink is annealed in nitrogen-containing gas to form nanotubes. The new method greatly enhances the yield of BNNTs, giving a higher density of nanotubes. These improvements are caused by the addition of metal nitrate and ethanol, both of which can strongly boost the nitriding reaction, as revealed by thermogravimetric analysis. The size and structure of BNNTs can be controlled by varying the annealing conditions. This high-yield production of BNNTs in large quantities enables the large-scale application of BNNTs.

Performance of an oxidation ditch retrofitted with a membrane bioreactor during the start-up

The objective of this study is to elucidate the full-scale characteristics of an oxidation ditch (OD) retrofitted with a membrane bioreactor (MBR). Domestic wastewater entering an oxidation ditch at a flow rate of 86 m3/d was directed to a MBR retrofitted into the original secondary sedimentation tank. The MBR contained flat sheet membranes. The data collected for 2 months during the start-up of the system showed that pH was maintained at 7.2 and 6.7 in OD and MBR, respectively. Dissolved oxygen (DO) in MBR remained stable at 7.8 mg/L, while fluctuated in OD. The mixed liquor suspended solids (MLSS) in the OD remained steady at a concentration about 1000 mg/L, but it was gradually building up from 500 mg/L to 2400 mg/L in the MBR during this period. Measurements of carbohydrate and protein were made by extracting the extra cellular polymeric substances (EPS) with sodium hydroxide (NaOH) from the mixed liquor obtained from both OD and MBR. Carbohydrate was predominant in the EPS and the ratios between carbohydrate and protein converged to fixed values from the fourth week; in this case the ratio was 4.5 for OD and 5 for MBR. The variation in EPS contents showed similar trends in both OD and MBR. The integrated treatment facility removed ammonia, COD and BOD at 100, 91.6 and 97.0%, respectively. However, efficiency of nitrate and phosphate removal has not been realized yet.

Mitigation strategies of hydrogen sulphide emission in sewer networks - A review

Hydrogen sulphide (H2S) gas emission in sewer networks is associated with several problems including the release of dangerous odour to the atmosphere and sewer pipe corrosion. The release of odour can endanger public health and corrode sewer pipe walls. Sewer corrosion has the potential to cost water utilities millions of dollars to maintain and rehabilitate the affected sewer pipes. Some chemical mitigation strategies to control hydrogen sulphide emission have been introduced. These include but are not limited to the injection of oxygen, magnesium and sodium hydroxide, calcium nitrate and iron salts. The optimisation of the dosing rate and location of each chemical mitigation strategy is required to achieve maximum hydrogen sulphide gas removal efficiency along with cost effectiveness. In this review paper, the five most popular chemical mitigation strategies that were previously mentioned have been investigated and discussed. The article is broken down into three main discussions. Firstly the sewer transformation processes and factors affecting the hydrogen sulphide generation and emission are highlighted. Secondly, comparisons and differences between each selected chemical mitigation strategy as well as its application covered. Finally, the review of the chemical efficiency and cost is conducted by comparing two case studies in controlling the formation of dissolved sulphide. It was found that the injection of oxygen is the cheapest mitigation strategy of hydrogen sulphide gas generation in sewers, but least effective.