Lithium Intercalation into the Excitonic Insulator Candidate Ta2NiSe5

A new reduced phase derived from the excitonic insulator candidate Ta₂NiSe₅ has been synthesized via the intercalation of lithium. LiTa₂NiSe₅ crystallizes in the orthorhombic space group Pmnb (no. 62) with lattice parameters a = 3.50247(3) Å, b = 13.4053(4) Å, c = 15.7396(2) Å, and Z = 4, with an increase of the unit cell volume by 5.44(1)% compared with Ta₂NiSe₅. Significant rearrangement of the Ta-Ni-Se layers is observed, in particular a very significant relative displacement of the layers compared to the parent phase, similar to that which occurs under hydrostatic pressure. Neutron powder diffraction experiments and computational analysis confirm that Li occupies a distorted triangular prismatic site formed by Se atoms of adjacent Ta₂NiSe₅ layers with an average Li-Se bond length of 2.724(2) Å. Li-NMR experiments show a single Li environment at ambient temperature. Intercalation suppresses the distortion to monoclinic symmetry that occurs in Ta₂NiSe₅ at 328 K and that is believed to be driven by the formation of an excitonic insulating state. Magnetometry data show that the reduced phase has a smaller net diamagnetic susceptibility than Ta₂NiSe₅ due to the enhancement of the temperature-independent Pauli paramagnetism caused by the increased density of states at the Fermi level evident also from the calculations, consistent with the injection of electrons during intercalation and formation of a metallic phase.

River toxicity assessment using molecular biosensors: Heavy metal contamination in the Turag-Balu-Buriganga river systems, Dhaka, Bangladesh

Pollution in rapidly urbanising cities and in delta systems is a serious problem that blights the lives and livelihoods of millions of people, damaging and restricting potable water supply and supplies to industry (Whitehead et al, 2015, 2018). Employing new technology based on luminescent molecular biosensors, the toxicity in the rivers around Dhaka in Bangladesh, namely the Turag, Tongi, Balu and Buriganga, has been assessed. Samples taken at 36 sites during medium and low flow conditions and during the Bishwa Ijtema Festival revealed high levels of cell toxicity, as well as high concentrations of metals, particularly aluminium, cadmium, chromium, iron, zinc, lithium, selenium and nickel. Chemical analysis also revealed low dissolved oxygen levels and anoxic conditions in the rivers at certain sites. The bacterial molecular biosensors were demonstrated to be fast, with results in 30 min, robust and a highly sensitive method for the assessment of water toxicity in the field. Furthermore, the biosensor toxicity analysis correlated with the metals data, and a multivariate regression relationship was developed relating toxicity to key metals, such a selenium, zinc and chromium. The resulting model has been validated against split samples and the Bishwa Ijtema Festival data. The combination of modelling and the molecular biosensor technology provides a new approach to detecting and managing pollution in urban river systems.

Modelling heavy metals in the Buriganga River System, Dhaka, Bangladesh: Impacts of tannery pollution control

Heavy metal pollution from tanneries is a global problem in many rapidly developing economies. Effluent discharges into rivers cause serious problems for water quality, damaging ecology and threatening the livelihoods of people, especially in developing urban centres which often have a high concentration of factories. The industry intensive capital area of Bangladesh is impacted with high levels of metals pollution in rivers in the Greater Dhaka Watershed. Sampling and modelling studies have been undertaken to assess pollution in the Buriganga River System in Dhaka. The process based, dynamic model INCA (Integrated Catchments) model has been used to simulate metals along the Buriganga River System in Central Dhaka. Observed and simulated metals concentrations are high, and the model shows that the proposed transfer of the tannery industry upstream helps to reduce the pollution significantly downstream. However, moving the industry upstream may be counterproductive as it is discharged into the upper reaches of the river. This will create pollution upstream unless the newly constructed effluent treatment system can operate at a high level.