Single-Crystal Regular Hexagonal Microplates of Two-Dimensional α-Calcium Sulfate Hemihydrate Preparation from Phosphogypsum in Na2SO4 Aqueous Solution

Synergistic preparation and application in PCU of α-calcium sulfate hemihydrate whiskers from phosphogypsum and electrolytic manganese residue

The α-calcium sulfate hemihydrate whiskers (α-CSHWs) were first prepared using phosphogypsum (PG) and electrolytic manganese residue (EMR) as raw materials for coating urea, demonstrating excellent controlled-release properties. The effects of different reaction conditions on α-CSHWs, achieved by optimizing the reaction time, the concentrations of NH4+, Mn2+, and other factors, were discussed. Results showed that when the EMR content was 25 wt%, the reaction temperature was 100 °C, and the reaction time was 3 h, α-CSHWs with a length-to-diameter ratio of 39 were obtained. Through experiments and density functional theory (DFT), the mechanism of α-CSHWs preparation was elucidated. The results show that the addition of EMR reduces the content of impurity ions PO43- and F- in PG while introducing NH4+ and Mn2+. Interestingly, both NH4+ and Mn2+ can reduce the nucleation time of α-CSHWs, while PO43-, Mn2+, and F- are more likely to adsorb on the (0 0 6) crystal plane of α-CSHWs, NH4+ readily adsorbs on the (4 0 0) crystal plane. The controlled-release performance of modified α-CSHWs incorporated into polyurethane-coated urea (PCU) was investigated, and it was found that the addition of Mα significantly prolonged the nutrient release period, with the period extending up to 116 days for coatings of 5wt% and above. This work not only enhances the efficiency of PG and EMR utilization but also serves as a reference for the straightforward synthesis and application of α-CSHWs.

Mussel-inspired dynamic facet-selective capping approach to highly uniform α-calcium sulfate hemihydrate crystals

We report herein a dynamic facet-selective capping (dFSC) strategy for α-calcium sulfate hemihydrate crystal growth from dihydrate gypsum in the presence of a catechol-derived PEI capping agent (DPA-PEI) with inspiration by the biomineralization process of mussel. The crystal shape is controllable and varies from long and pyramid-tipped prisms to thin hexagonal plate. The highly uniform truncated crystals have extremely high compression and bending strengths after hydration molding.

Effects of Co Doping on the Growth and Photocatalytic Properties of ZnO Particles

The present work reports on the synthesis of ZnO photocatalysts with different Co-doping levels via a facile one-step solution route. The structural and optical properties were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and UV-Vis diffuse reflectance spectra. The morphology of Co-doped ZnO depends on the reaction temperature and the amount of Co and counter-ions in the solution. Changes with the c-axis lattice constant and room temperature redshift show the replacement of Zn with Co ions without changing the wurtzite structure. Photocatalytic activities of Co-doped ZnO on the evolution of H₂ and the degradation of methylene blue (MB) reduce with the doping of Co ions. As the close ionic radii of Co and Zn, the reducing photocatalytic activity is not due to the physical defects but the formation of deep bandgap energy levels. Photocurrent response experiments further prove the formation of the recombination centers. Mechanistic insights into Co-ZnO formation and performance regulation are essential for their structural adaptation for application in catalysis, energy storage, etc.

α-calcium sulfate hemihydrate with a 3D hierarchical straw-sheaf morphology for use as a remove Pb2+ adsorbent

Novel three-dimensional hierarchical α-calcium sulfate hemihydrate with a straw-sheaf morphology (3D α-HH straw-sheaves) are synthesized successfully in glycerin aqueous solution by a simple one-pot method, using as an efficient adsorbent for Pb²⁺ removal from water. The 3D straw-sheaf morphology, that closely depends on the glycerin/water volume ratio (V_Gly/V_H2O), can be accurately fabricated only when V_Gly/V_H2O is not lower than 3/1. 3D α-HH straw-sheaves are generated via multistep-splitting growth coupled with self-assembly. The obtained 3D α-HH straw-sheaves are further used as an adsorbent to remove Pb²⁺ from water, exhibiting excellent Pb²⁺ removal performance with an equilibrium adsorption capacity of 79.19 mg_Pbg_α-HH^-1 and removal efficiency of 98.98%, that both higher than those of plate- and columnar-like α-HH. Moreover, the experimental adsorption data for the 3D α-HH straw-sheaves is well fitted with pseudo-second-order kinetic model, and the adsorption isotherm is in good agreement with Langmuir model. The Pb²⁺ adsorption mechanism is thought to be a chemical adsorption process enforced by chemical bonding and ion exchange. This work demonstrates that 3D α-HH straw-sheaves are highly promising in removing Pb²⁺ from wastewater, thereby broadening the research field for the practical application of gypsum-based materials.

Self-Symmetrical 3D Hierarchical α-Calcium Sulfate Hemihydrate Twin-Flowers Composed of Microplates as a Renewable Material for Water Separation from Water-in-Oil Emulsion

Novel three-dimensional hierarchical α-calcium sulfate hemihydrate twin-flowers with a self-symmetrical structure (3D α-HH HTFs) are synthesized successfully assisted by trisodium citrate (TSC). The morphology of α-HH is closely dependent on TSC, and with increasing TSC concentration from 0 to 15 mM, the morphology gradually evolves from a long column to rod, hexagonal plate, twin-flower-like, and eventually microgranule. 3D α-HH HTFs are formed via heterogeneous nucleation coupled with Ostwald ripening. The 3D α-HH HTFs are further used as an immobilized water material to separate water from a surfactant-stabilized water-in-oil emulsion, and exhibit excellent separation performance with a separation efficiency of 99.31 wt % and immobilization efficiency of 93.03 wt %. Impressively, the separated solid after water separation can be regenerated into 3D α-HH HTFs, which retain the high separation performance of the original 3D α-HH HTFs. This work demonstrates that 3D α-HH HTFs are highly promising in purifying oil with undesired water contamination.