Band Structure, Phonon Spectrum and Thermoelectric Properties of Ag3CuS2.

Sulfides and selenides of copper and silver have been intensively studied, particularly as potentially efficient thermoelectrics. Ag3CuS2 (jalpaite) is a related material. However very little is known about its physical properties. It has been found that the compound undergoes several structural phase transitions, having the tetrahedral structural modification I41/amd at room temperature. In this work, its band structure, phonon spectrum and thermoelectric properties were studied theoretically and experimentally. Seebeck coefficient, electrical conductivity and thermal conductivity were measured in a broad temperature range from room temperature to 600 K. These are the first experimental data on transport properties of jalpaite. Ab initio calculations of the band structure and Seebeck coefficient were carried out taking into account energy dependence of the relaxation time typical for the scattering of charge carriers by phonons. The results of the calculations qualitatively agree with the experiment and yield large values of the Seebeck coefficient characteristic for lightly doped semiconductor. The influence of intrinsic defects (vacancies) on the transport properties was studied. It was shown that the formation of silver vacancies is the most probable and leads to an increase of hole concentration. Using the temperature dependent effective potential method, the phonon spectrum and thermal conductivity at room temperature were calculated. The measurements yield low lattice thermal conductivity value of 0.5 W/(m K) at 300 K, which is associated with the complex crystal structure of the material. The calculated room temperature values of the lattice thermal conductivity were also small (0.14-0.2 W/(m K)).

Nature-Inspired Coral-like Layered [Co0.79Al0.21(OH)2(CO3)0.11]·mH2O for Fast Selective ppb Level Capture of Cr(VI) from Contaminated Water.

Rapid industrialization has led to the release of hexavalent chromium (Cr(VI)), a "Class A" human carcinogen, mutagen, and teratogen in biological systems. Current adsorbents like anionic exchange resins and metal-organic frameworks can remove harmful heavy metal oxyanions from water but are not stable in a broad pH range, suffer from selectivity, and cannot capture them from trace values below the tolerance limits given by the U.S. EPA (100 ppb) and WHO (50 ppb). Herein, we have synthesized nature-inspired coral-like three-dimensional hierarchical structures of [Co0.79Al0.21(OH)2(CO3)0.11]·mH2O (CoAl-LDH) that sets a new benchmark for sequestering oxyanions of Cr(VI). CoAl-LDH shows a broad pH working range (1.93-12.22), high selectivity toward saturated water samples containing monovalent (Cl-, F-, Br-, and NO3-) and divalent (SO42-) anions with fast kinetics (reaches equilibrium within a minute), high capacity (93.4 ± 7.8 mg g-1), and high distribution coefficient of 1.09 × 106 mL g-1. Unlike other materials, it can decrease Cr(VI) concentration up to 0.012 ppb. This high selectivity for Cr(VI) is linked to the weak bonding interaction between Cr2O72- and brucite-like layers, as revealed from thermogravimetric and infrared spectroscopy. With these remarkable features coupled with low cost and an environmentally friendly nature, we have also designed an anion exchange column that can remove >99% Cr(VI) with just 1 wt % of CoAl-LDH and 99 wt % of sand and is a prominent candidate for the elimination of Cr(VI) from industrial effluents.

Charge Transfer in the Heterostructure of CsPbBr3 Nanocrystals with Nitrogen-Doped Carbon Dots.

Heterostructures of inorganic halide perovskites with mixed-dimensional inorganic nanomaterials have shown great potential not only in the field of optoelectronic energy devices and photocatalysis but also for improving our fundamental understanding of the charge transfer across the heterostructure interface. Herein, we present for the first time the heterostructure integration of the CsPbBr3 nanocrystal with an N-doped carbon dot. We explore the photoluminescence (PL) and photoconductivity of the heterostructure of CsPbBr3 nanocrystals and N-doped carbon dots. PL quenching of CsPbBr3 nanocrystals with the addition of N-doped carbon dots was observed. The photoexcited electrons from the conduction band of CsPbBr3 are trapped in the N-acceptor state of N-doped carbon dots, and the charge transfer occurs via quasi type II-like electronic band alignment. The charge transfer in the halide perovskite-based heterostructure should motivate further research into the new heterostructure synthesis with perovskites and the fundamental understanding of the mechanism of charge/energy transfer across the heterostructure interface.

Reversible and Efficient Sequestration of Cesium from Water by the Layered Metal Thiophosphate K0.48 Mn0.76 PS3 ⋠H2 O.

Water body contamination with radioactive species is an important issue due to significant developments in nuclear energy. Cesium (137 Cs) radioisotope is a non-actinide fission product of uranium and plutonium that is long-lived. Hence, selective removal/capture of cesium is essential for managing radioactive waste. Herein, a detailed Cs+ ion-exchange study on a potassium intercalated layered metal thiophosphate, K0.48 Mn0.76 PS3 ⋅H2 O (K-MPS-1), is reported. The sorption of Cs+ by K-MPS-1 follows the Langmuir model with a high capacity of 337.5 mg g-1 and high distribution coefficients in the order of about 104  mL g-1 . K-MPS-1 can sequester Cs+ efficiently, even from very low concentrations (ppb level). K-MPS-1 exhibits high cesium uptake over a broad pH range of 2-12 and the ion-exchange process reaches equilibrium within a short time (≈15 min), following pseudo-second-order kinetics. Moreover, K-MPS-1 demonstrates selectivity towards Cs+ capture in the presence of complex solutions containing excess Na+ , Ca2+ , and Mg2+ ions; this is due to favorable interactions between Cs (soft Lewis acid) and S (soft Lewis base). K-MPS-1 reversibly captures Cs+ and it can be regenerated by treating Cs-MPS-1 with a solution of KCl.