Barium sulfate crystallization in non-aqueous solvent

Crystallisation is performed in a non-aqueous solvent, dimethylsulfoxide (DMSO), in order to determine what the role of water is on the crystallisation pathway. In both water and DMSO environments the particles do not appear to grow by ion addition but rather appear to grow through aggregation. The main difference in water is that the aggregation processes are not random and result in particle morphologies that bear relation to the single-crystal faces, suggesting an oriented attachment mechanism. In DMSO, the aggregation processes appear less oriented and while there is some lattice registry, lattice mismatch is also observed and the aggregate shape is spherical overall. This is confirmed in the 1200 cm−1infrared band shift to 1174 cm−1suggesting a strained solid is formed. It is observed that the solubility of barium sulfate in DMSO is higher than in water (presumably caused by a strong Ba2+O-S(CH3)2interaction), which explains the lower nucleation rates in DMSO compared to water at the same concentration. Intriguingly, there is a lower nucleation rate observed (even at a relatively high supersaturation) when Ba2+is solvated with DMSO supporting the hypothesis that de-solvation of the cation is the rate determining step in nucleation and is of higher activation energy in DMSO than in water

Metal organic frameworks with carbon black for the enhanced electrochemical detection of 2,4,6-trinitrotoluene

The sensing of explosives such as 2,4,6-trinitrotoluene (TNT) directly at an explosion site requires a fast, simple and sensitive detection method, to which electrochemical techniques are well suited. Herein, we report an electrochemical sensor material for TNT based on an ammonium hydroxide (NH4OH) sensitized zinc-1,4–benzenedicarboxylate Zn(BDC) metal organic framework (MOF) mixed with carbon black on a glassy carbon electrode. In the solvent modulation mechanism, by merely changing the concentration of NH4OH during synthesis, two Zn(BDC) MOFs with novel morphologies were fabricated via a hydrothermal approach. The as-prepared MOFs were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and high-resolution field emission electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS). The different morphologies of the MOFs, and their impact on the performance of the modified electrodes towards the electrochemical detection of TNT was investigated. Under optimum conditions, 0.7–Zn(BDC) demonstrated the best electrochemical response for TNT detection using square wave voltammetry (SWV) with a linear calibration response in the range of 0.3–1.0 M, a limit of detection (LOD) of 0.042 M, a limit of quantification (LOQ) of 0.14 M and a high rate of repeatability. Atomic-scale simulations based on density functional theory authenticated the efficient sensing properties of Zn(BDC) MOF towards TNT. Furthermore, the promising response of the sensors in real sample matrices (tap water and wastewater) was demonstrated, opening new avenues towards the real-time detection of TNT in real environmental samples

Nonepitaxial Gold-Tipped ZnSe Hybrid Nanorods for Efficient Photocatalytic Hydrogen Production

For the first time, colloidal gold (Au)–ZnSe hybrid nanorods (NRs) with controlled size and location of Au domains are synthesized and used for hydrogen production by photocatalytic water splitting. Au tips are found to grow on the apices of ZnSe NRs nonepitaxially to form an interface with no preference of orientation between Au(111) and ZnSe(001). Density functional theory calculations reveal that the Au tips on ZnSe hybrid NRs gain enhanced adsorption of H compared to pristine Au, which favors the hydrogen evolution reaction. Photocatalytic tests reveal that the Au tips on ZnSe NRs effectively enhance the photocatalytic performance in hydrogen generation, in which the single Au-tipped ZnSe hybrid NRs show the highest photocatalytic hydrogen production rate of 437.8 µmol h−1 g−1 in comparison with a rate of 51.5 µmol h−1 g−1 for pristine ZnSe NRs. An apparent quantum efficiency of 1.3% for hydrogen evolution reaction for single Au-tipped ZnSe hybrid NRs is obtained, showing the potential application of this type of cadmium (Cd)-free metal–semiconductor hybrid nanoparticles (NPs) in solar hydrogen production. This work opens an avenue toward Cd-free hybrid NP-based photocatalysis for clean fuel production.W.C. and X.L. contributed equally to this work. This work was supported by the Australian Research Council (ARC) Discovery Early Career Researcher Award (DECRA) (DE 160100589) and discovery project (DP 170104264). Y.L. acknowledges support from the NSFC (grant no. 11674131). W.C. acknowledges the scholarship from the China Scholarship Council

Synthesis of Atomically Thin CdTe Nanoplatelets by Using Polytelluride Tellurium Precursors

Colloidal two-dimensional (2D) semiconductor nanocrystals are of great importance due to their remarkable optical and electronic properties. Herein, shape-controllable synthesis of 2D wurtzite CdTe nanoplatelets (NPLs) by simply tailoring the reactivity of a tellurium (Te) precursor is reported. Ribbon-, shield-, and bullet-like 2D CdTe NPLs were prepared by a stepwise conversion from CdTe magic-size nanoclusters (MSNCs) by using Te32-, Te22-, and Te2- polytellurides as the tellurium precursor, respectively. This work not only develops a synthetic strategy capable of synthesising wurtzite CdTe nanoplatelets with controlled shapes by tailoring the reactivity of tellurium precursors but also gives insights into the growth mechanisms of colloidal 2D semiconductor nanocrystals

Spontaneous shape and phase control of colloidal ZnSe nanocrystals by tailoring Se precursor reactivity

Herein we demonstrated that the shape and phase of colloidal ZnSe nanocrystals can be spontaneously tuned through tailoring the selenium precursor reactivity in a phosphine-free reaction system. Selenium species with diverse reaction activities, i.e. Se22- or Se2-, were produced by the addition of different volumes of reductant superhydride (lithium triethylborohydride). Theoretical calculation of ΔGr indicates that superhydride-reduced Se22- is less active than Se2- for the reaction with a Zn precursor. Nanoparticle growth using Se22- produces wurtzite ZnSe nanorods whereas the reaction of more reactive Se2- with the zinc precursor leads to the formation of spherical zinc blende ZnSe nanodots. This work not only provides a facile synthetic approach for the preparation of high quality ZnSe nanocrystals but also gives insights into the shape and phase control of other colloidal nanocrystals

Colloidal Single-Layer Photocatalysts for Methanol-Storable Solar H-2 Fuel

Molecular surfactants are widely used to control low-dimensional morphologies, including 2D nanomaterials in colloidal chemical synthesis, but it is still highly challenging to accurately control single-layer growth for 2D materials. A scalable stacking-hinderable strategy to not only enable exclusive single-layer growth mode for transition metal dichalcogenides (TMDs) selectively sandwiched by surfactant molecules but also retain sandwiched single-layer TMDs’ photoredox activities is developed. The single-layer growth mechanism is well explained by theoretical calculation. Three types of single-layer TMDs, including MoS2, WS2, and ReS2, are successfully synthesized and demonstrated in solar H2 fuel production from hydrogenstored liquid carrier—methanol. Such H2 fuel production from single-layer MoS2 nanosheets is COx-free and reliably workable under room temperature and normal pressure with the generation rate reaching ≈617 µmole g−1 h−1 and excellent photoredox endurability. This strategy opens up the feasible avenue to develop methanol-storable solar H2 fuel with facile chemical rebonding actualized by 2D single-layer photocatalysts.Y.P. and M.N.U. contributed equally to this work. This work was supported by Australian Research Council (ARC) Discovery Early Career Researcher Award (DECRA) (DE 160100589), ACR Discovery Project (DP190100295), ARC LIEF scheme (LE190100014), the ANU Futures Scheme (Q4601024), and ANU Global Research Partnership Scheme (R468504649). Y.L. acknowledges support from the NSFC (Grant No. 11674131). Y.P. acknowledged the scholarship from the China Scholarship Council. M.N.U. acknowledged the Australian Government Research Training Program scholarship

Ni2+/Co2+ doped Au-Fe7S8 nanoplatelets with exceptionally high oxygen evolution reaction activity

To overcome the limited potency of energy devices such as alkaline water electrolyzers, the construction of active materials with dramatically enhanced oxygen evolution reaction (OER) performance is of great importance. Herein we developed an ion diffusion-induced doping strategy that is capable of producing Ni2+/Co2+ doped two-dimensional (2D) Au-Fe7S8 nanoplatelets (NPLs) with exceptionally high OER activity outperforming the benchmark RuO2 catalyst. The co-existence of Co and Ni in Au-Fe7S8 NPLs led to the lowest OER overpotential of 243 mV at 10 mA cm-2 and fast kinetics with a Tafel slope of 43 mV dec-1. Density functional theory (DFT) calculations demonstrated that Ni2+/Co2+ doping improves the binding of OOH species on the {001} surfaces of Au-Fe7S8 NPLs and lowers the Gibbs free energy of the OER process, which are beneficial to outstanding OER activity of the nanoplatelets