Effect of Mg2+ on hydrothermal formation of α-CaSO4·0.5H2O whiskers with high aspect ratios

Recent Advances in Whiskers: Properties and Clinical Applications in Dentistry

Whiskers are nanoscale, high-strength fibrous crystals with a wide range of potential applications in dentistry owing to their unique mechanical, thermal, electrical, and biological properties. They possess high strength, a high modulus of elasticity and good biocompatibility. Hence, adding these crystals to dental composites as reinforcement can considerably improve the mechanical properties and durability of restorations. Additionally, whiskers are involved in inducing the value-added differentiation of osteoblasts, odontogenic osteocytes, and pulp stem cells, and promoting the regeneration of alveolar bone, periodontal tissue, and pulp tissue. They can also enhance the mucosal barrier function, inhibit the proliferation of tumor cells, control inflammation, and aid in cancer prevention. This review comprehensively summarizes the classification, properties, growth mechanisms and preparation methods of whiskers and focuses on their application in dentistry. Due to their unique physicochemical properties, excellent biological properties, and nanoscale characteristics, whiskers show great potential for application in bone, periodontal, and pulp tissue regeneration. Additionally, they can be used to prevent and treat oral cancer and improve medical devices, thus making them a promising new material in dentistry.

Role of Additives: Modified Hemihydrate Phosphogypsum Morphology and Enhanced Filtration Performance of Wet-Process Phosphoric Acid

The morphology of hemihydrate phosphogypsum crystals is of vital importance in the hemihydrate-dihydrate (HH-DH) wet-process phosphoric acid production for high filtration strength. The morphology of hemihydrate phosphogypsum is commonly needlelike due to the strong acidic crystallization environment, which is unfavorable to the following filtration process. In this study, the crystal habit of hemihydrate phosphogypsum with a large aspect ratio was skillfully modified by additives to achieve a higher filtration strength. d-Glucitol (DG) reduces the theoretical aspect ratio of hemihydrate phosphogypsum crystals from 2.076 to 1.583 by interacting with the (002) face of CaSO4·0.5H2O preferentially, and poly(vinyl alcohol) (PVA) facilitates the aggregation of small grains to gather into a clusterlike structure. The modified morphologies of hemihydrate phosphogypsum have a lower bulk density and a larger porosity of the formed filter cake, which increases the filtration strength up to 45.9% when DG is added. Our work provides an in-depth explanation of the evolution mechanism of hemihydrate phosphogypsum morphology with the additives and its influence on the filtration performance. The improved filtration strength would reduce the water content of hemihydrate phosphogypsum and relieve the storage pressure of the phosphogypsum slag dump, which is meaningful to the clean production and process emission reduction of the phosphorus chemical industry.

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.

Pyrolysis of Ca/Fe-rich antibiotic fermentation residues into biochars for efficient phosphate removal/recovery from wastewater: Turning hazardous waste to phosphorous fertilizer

Ca/Fe-rich antibiotic fermentation residues (AFRs), a type of hazardous waste, can be regarded as recyclable biomass and metal resources. However, concurrent detoxification and reutilization of biomass and metals resources from AFRs have never been reported before. In this study, Ca/Fe-rich vancomycin fermentation residues were pyrolyzed into biochar to adsorb phosphate for the first time. The residual vancomycin and antibiotic resistance genes were completely decomposed during pyrolysis. The resultant Ca/Fe-rich biochar exhibited excellent performance at adsorbing phosphate without further modifications. The process had rapid kinetics and a maximum adsorption capacity of 102 mg P/g. Ca and Fe were the active sites, whereas different mechanisms were observed under acidic and alkaline conditions. Surprisingly, HCO₃^- enhanced phosphate adsorption with an increase of adsorption capacity from 43.9 to 71.0 mg/g when HCO₃^- concentration increased from 1 to 10 mM. Furthermore, actual wastewater could be effectively treated by the biochar. The phosphate-rich spent biochar significantly promoted seed germination (germination rate: 96.7 % vs. 80.0 % in control group, p < 0.01) and seedling growth (shoot length was increased by 57.9 %, p < 0.01) due to the slow release of bioavailable phosphate, and thus could be potentially used as a phosphorous fertilizer. Consequently, the hazardous waste was turned into phosphorous fertilizer, with the additional benefits of detoxifying AFRs, reutilizing biomass and metal resources from AFRs, controlling phosphate pollution, and recovering phosphate from wastewater.

The Generation Process, Impurity Removal and High-Value Utilization of Phosphogypsum Material

As phosphogypsum constitutes a large amount of solid waste material, its purification treatment and comprehensive utilization have close connection with economic development and ecological environmental protection. For the moment, the storage quantity of phosphogypsum is still rising as a result of the increasing phosphate fertilizer production to meet the food demand in China. This paper summarizes the generation process, impurity removal treatment (physical method, chemical method, heat method), high-value utilization (nanometer calcium sulfate whisker, nanometer calcium carbonate) of phosphogypsum material and some existing problems. It puts forward some views on the challenges in this field and the direction of future development. It is hoped that the investigation and summary in this paper could supply some significant information for the impurity removal and high-value utilization of phosphogypsum material as a contribution to sustainability.

Insights into the Role of Na+ on the Transformation of Gypsum into α-Hemihydrate Whiskers in Alcohol-Water Systems

Alcohol-water solution-mediated transformation of gypsum into α-hemihydrate (α-HH) whiskers provides a green alternative for the high-value-added recycling of flue gas desulfurization (FGD) gypsum. However, the role of non-lattice cations during the transformation is still unclear. We report an evolution from "boosting-retarding" to "boosting-retarding-boosting" and finally to "boosting only" effect of non-lattice Na⁺ functioned by the concentration of ethylene glycol (EG) in water solutions. The driving force increased almost linearly upon the introduction of Na⁺ through the formation of ion pairs, and a higher slope was obtained at a higher EG concentration. Adsorption of Na⁺ ions and solidification of eugsterite on gypsum surfaces blocked the nucleation sites of α-HH. The retarding effect first rapidly increased and gradually approached a limit, following a parabolic trend after Na⁺ ions were introduced. Pentasalt, with a structure similar to that of α-HH, precipitated on the gypsum surface at higher c(Na⁺). The interaction of the driving force and the structural evolution of calcium sulfate ionic clusters accounts for the evolution of transformation kinetics. The retardation zone was compressed with the increase in EG volume ratios, and a monotonic boosting effect upon Na⁺ was observed at a 35.0 vol % of EG. Nucleation kinetics dominates the aspect ratio of α-HH whiskers. This study may provide a significant guidance for the utilization of FGD gypsum.

The study on the effect of flotation purification on the performance of α-hemihydrate gypsum prepared from phosphogypsum

Phosphogypsum (PG) is a massive industrial solid waste. In this paper, PG was purified by flotation method, and α-hemihydrate gypsum (α-HH) was prepared by the autoclaving method. The morphology of α-HH was adjusted by adding different doses of Maleic acid and Aluminium sulfate. The results showed that after flotation purification, the impurity content in PG was significantly reduced, the soluble phosphorus content decreased from 0.48 to 0.07%, the PG purity increased from 73.12 to 94.37%, and the PG whiteness risen from 19.4 to 40.5. Then the performance of α-HH prepared from PG before and after purification was compared. Fixing the amount of aluminium sulfate at 0.2 wt%, the reaction temperature at 140 °C, and the reaction time at 120 min, the average length/diameter ratio of α-HH crystals decreased from 7.2 to 0.6 as the amount of Maleic acid increased from 0 to 0.17 wt%. When the amount of Maleic acid was 0.13 wt%, the α-hemihydrate gypsum reached the best mechanical properties. The mechanical strength of high strength gypsum prepared from PG concentrate was significantly better than that of raw PG, indicating that flotation purification can effectively improve the performance of PG. In this study, a new method of PG purification and resource utilization was proposed.

Detrimental effects of SO2 on gaseous mercury(II) adsorption and retention by CaO-based sorbent traps: Competition and heterogeneous reduction

Reliable gaseous Hg(II) measurement is crucial to mercury emissions control from coal-fired flue gas, but Hg(II) sampling under SO₂ condition could probably increase the uncertainty of sorbent traps. CaO-AcS synthesized from calcium acetate and porous support were previously demonstrated to be effective for Hg(II) trapping under SO₂-free condition. This work further evaluated SO₂ influence on its Hg(II) retention ability via integrating experimental and DFT computational studies. Increased breakthrough rate of HgCl₂ was found in a two-section CaO-AcS trap under SO₂ conditions. Significant basicity and porosity loss of CaO-AcS were attributed to the formation of agglomerate CaSO₃. Hg⁰ release from CaO-AcS samples suggested potential reactions between Hg(II) and SO₂. The detected HgO and Hg₂SO₄ species by Hg-TPD in CaO-AcS further confirmed this speculation. Moreover, both competition and reduction effects of SO₂ on surface-bound Hg(II) species were substantiated by DFT calculations. SO₂ showed a stronger interaction with CaO than HgCl₂ because SO₂ has a lower LUMO level and can accept electrons easier. Reaction pathways indicated Hg(II) was partially reduced to Hg₂SO₄ under SO₂-deficient condition, or directly reduced to Hg⁰ under SO₂-rich condition. This work fully proposed the SO₂ influence mechanisms and improvement countermeasures for practical gaseous Hg(II) sampling.

Aspect ratio-controlled preparation of α-CaSO4·0.5H2O from phosphogypsum in potassium tartrate aqueous solution

In this study, a simple and efficient strategy is developed to synthesize rod-shaped α-CaSO4·0.5H2O crystals with tunable aspect ratio from industrial phosphogypsum only in potassium tartrate aqueous solution at a low temperature. Industrial phosphogypsum can be effectively converted into rod-shaped α-CaSO4·0.5H2O crystals with the assistance of potassium tartrate, and the aspect ratio of α-CaSO4·0.5H2O crystals gradually decreases from 52 : 1 to 1 : 1 with increasing the concentration of potassium tartrate. The formation process of the rod-shaped α-CaSO4·0.5H2O crystals in this system involves the dissolution of CaSO4·2H2O and nucleation of α-CaSO4·0.5H2O crystals. The tartrate ions from potassium tartrate in this system preferentially bind to (001) and (002) facets of α-CaSO4·0.5H2O crystals, inhibiting the growth of α-CaSO4·0.5H2O crystals along the c-axis and controlling its morphology and aspect ratio.

Microemulsion Synthesis of Nanosized Calcium Sulfate Hemihydrate and Its Morphology Control by Different Surfactants

Calcium sulfate hemihydrate with different structures and morphologies has a broad scope of applications. Herein, we reported a strategy for nanosized calcium sulfate through room-temperature microemulsion by using calcium carbonate and sulfuric acid. After characterizations, it was indicated that the morphology of calcium sulfate products fabricated could be changed and controlled using different surfactants TritonX-114, SDBS, and CTAB by the microemulsion method. The method demonstrated in this work would be a benefit for the synthesis of nanomaterials with special structures in the future.

Investigation of the Effects of Sodium Dicarboxylates on the Crystal Habit of Calcium Sulfate α-Hemihydrate

The effects of disodium malonate, disodium succinate, disodium glutarate, and disodium adipate on the crystal habit of calcium sulfate α-hemihydrate (CaSO₄·0.5H₂O, α-CSH) were studied using experimental studies and molecular dynamics simulations. The calculation and experimental results provided insight into the mechanism of the interaction between the additives mentioned above and the different faces of α-CSH that dominate the morphology of α-CSH. The calculation results indicated that the formation of high-aspect-ratio α-CSH, namely, calcium sulfate α-hemihydrate whiskers (α-CSH whiskers), in aqueous solution was due to the interaction between liquid water and side faces of the α-CSH crystal, which inhibits the growth of α-CSH along the radial direction. However, when a trace amount of crystal habit modifier, such as disodium succinate or disodium glutarate, was added to the aqueous solution, the growth rates along the directions normal to the {0 0 1} and {1 1 4} faces were considerably inhibited. Thus, α-CSH crystals with a low aspect ratio were synthesized using a hydrothermal method. In addition, the calculation methodology used in this work could provide a powerful tool for selecting suitable crystal habit modifiers for preparing α-CSH and other inorganic crystals.

Calcium Sulfate Hemihydrate Nanowires: One Robust Material in Separation of Water from Water-in-Oil Emulsion

Here we report a facile and cost-effective wet-chemical approach to the synthesis of calcium sulfate hemihydrate nanowires (HH NWs, CaSO₄·0.5H₂O), and their robust performance in immobilizing water molecules to the crystal lattice of CaSO₄ and then separating them from a surfactant-stabilized water-in-oil emulsion (mean droplet size of around 1.2 μm). Every gram of HH NWs are capable of treating 20 mL emulsion (water content: 10.00 mg mL^-1) with a separation efficiency of 99.23% at room temperature, and this efficiency can be further improved by tuning the surface charge density of HH. Along with the water immobilization, HH NWs are converted to large cubic-like calcium sulfate dihydrate microparticles (DH, CaSO₄·2H₂O, mean size: 50 μm), and the accompanied size increment enables efficient collection of the solid phase from oil. DH microparticles can be regenerated into HH NWs, which retain the high performance of the original NWs. Such a unique renewable feature improves the economics of our method and simultaneously prevents the secondary pollution. Further economic evaluation finds that purification of every cubic meters of emulsion (water content: 10.00 mg mL^-1) will cost about $34.18 for HH NWs, much lower than the $490.78 for the previously reported HH NPs, and $11 052.05-$23 420.32 Fe₃O₄ NP-based adsorbents, respectively. With the high efficiency, easy collection, low cost, and renewable feature, HH NWs show highly promising applications in the field of oil purification and recycle.

A facile method of transforming FGD gypsum to α-CaSO4·0.5H2O whiskers with cetyltrimethylammonium bromide (CTAB) and KCl in glycerol-water solution

A facile method to transform flue gas desulfurization gypsum (FGD gypsum) to α- calcium sulfate hemihydrate (α-HH) whiskers with high aspect ratios mediated by cetyltrimethylammonium bromide (CTAB) and KCl in glycerol-water solutions was studied. Addition of KCl facilitated the dissolution of calcium sulfate dihydrate (DH) and created a much higher supersaturation, which could come into being a larger driving force for the phase transformation from DH to α-HH. CTAB as the crystal modifier can significantly promoted 1-D growth of α-HH whiskers along the c axis and the presence of 0.25% CTAB (by weight of FGD gypsum) resulted in the increase of the average aspect ratio of α-HH whiskers from 28.9 to 188.4, which might be attributed to the preferential adsorption of C₁₆H₃₃(CH₃)₃N⁺ on the negative side facets of α-HH crystal.

Synthesis of α-CaSO4·0.5H2O from flue gas desulfurization gypsum regulated by C4H4O4Na2·6H2O and NaCl in glycerol-water solution

A brand new method to prepare α-CaSO₄·0.5H₂O with low aspect ratios from flue gas desulfurization gypsum in glycerol-water solution was presented, in which NaCl was used as the phase transition accelerator and C₄H₄O₄Na₂·6H₂O as the crystal modifier.

Controlling the morphology of calcium sulfate hemihydrate using aluminum chloride as a habit modifier

The morphology of HH is successfully controlled over a large range of size by simply adjusting the concentration of AlCl₃.

Retraction: Effect of ethylene glycol on hydrothermal formation of calcium sulfate hemihydrate whiskers with high aspect ratios

Retraction of ‘Effect of ethylene glycol on hydrothermal formation of calcium sulfate hemihydrate whiskers with high aspect ratios’ by Wenpeng Zhao et al., RSC Adv., 2015, 5, 50544–50548.

Controlled synthesis of monodisperse α-calcium sulfate hemihydrate nanoellipsoids with a porous structure

We report a facile and green chemical solution approach to synthesize monodisperse α-calcium sulfate hemihydrate (α-HH) nanoellipsoids with a length of 600 nm and a width of 300 nm by simply mixing Ca(2+) and SO4(2-) glycerol-water precursor solutions in the presence of Na2EDTA. The α-HH nanoellipsoid is formed through a Na2EDTA-mediated self-assembly of small primary building blocks (α-HH domains: ∼14 nm). The study on the morphological evolution of α-HH reveals that the controlled synergy of supersaturation (precursor concentration) and Na2EDTA is crucial for the development of α-HH into nanoellipsoids. Further thermal annealing of the nanoellipsoid could make the α-HH domains transit into calcium sulfate anhydrites and grow up, generating the gaps between them and resulting in a porous structure. This work paves a new way for preparing high-quality α-HH nanoellipsoids with a monodisperse nanosize and a porous structure, promising their future application in many fields such as biomedicine.

A facile method to control the structure and morphology of α-calcium sulfate hemihydrate

Synergy effect of CaCl₂ and Na₂EDTA on the structure and morphology control of α-HH by regulating G/W.

Retracted Article: Effect of ethylene glycol on hydrothermal formation of calcium sulfate hemihydrate whiskers with high aspect ratios

A facile ethylene glycol-assisted hydrothermal method was developed to synthesis HH whiskers with high aspect ratios.