Search Results (30)

Enhanced silicate rock weathering (ESRW) has been proposed as a promising carbon dioxide removal strategy, yet its carbon sequestration pathways, durability, and ecosystem dependence remain incompletely understood. Here, we synthesize evidence from field experiments, observational studies, and modeling to compare ESRW-induced carbon dynamics across forest and cropland ecosystems using a unified SOC–SIC dual-pool framework. Across both systems, ESRW operates through shared geochemical processes, including proton consumption during silicate dissolution and base cation release, which promote atmospheric CO₂ uptake. However, carbon fate diverges markedly among ecosystems. Forest systems, characterized by high biomass production, deep rooting, and strong hydrological connectivity, primarily favor biologically mediated pathways, enhancing net primary productivity and mineral-associated organic carbon (MAOC) formation, while facilitating downstream export of dissolved inorganic carbon (DIC). In contrast, intensively managed croplands more readily accumulate measurable soil inorganic carbon (SIC) and soil DIC over short to medium timescales, particularly under evapotranspiration-dominated or calcium-rich conditions, although SOC responses are often moderate and variable. Importantly, only a subset of ESRW-driven pathways—such as MAOC formation and secondary carbonate precipitation—represent durable carbon storage on decadal to centennial timescales. By explicitly distinguishing carbon storage from carbon transport, this synthesis clarifies the conditions under which ESRW can contribute to climate change mitigation and highlights the need for ecosystem-specific deployment and monitoring strategies. Full article

Magnesium whitlockite (Mg-WH) has emerged as a promising biomaterial for bone regeneration due to its compositional similarity to natural bone minerals. This study aimed to systematically modify a dissolution–precipitation synthesis method to produce Mg-WH granules with tailored morphologies and controlled phase compositions for possible use in bone regeneration applications. Three distinct precursor granules were prepared by mixing varying amounts of ammonium dihydrogen phosphate and magnesium hydrogen phosphate with calcium sulfate. The precursors were then transformed into biphasic and single-phase Mg-WH granules by means of immersion in magnesium- and phosphate-containing solutions under controlled conditions. The X-ray diffraction results demonstrated that biphasic materials containing Mg-WH and either calcium-deficient hydroxyapatite (CDHA) or dicalcium phosphate anhydrous (DCPA) formed after 24 h of synthesis, depending on the synthesis conditions. Prolonging the reaction time to 48 h resulted in complete transformation into single-phase Mg-WH granules. Fourier-transform infrared spectroscopy confirmed the presence of functional groups characteristic of Mg-WH, CDHA, and DCPA in the intermediate products. The spectra also indicated the absence of precursor phases and the progressive elimination of secondary phases as the reaction time increased. Scanning electron microscopy analyses revealed notable morphological transformations from the raw granules to the product granules, with the latter exhibiting interlocked spherical and rod-like particles composed of fine Mg-WH rhombohedral crystals. N₂ adsorption–desorption analyses exposed significant differences in the surface properties of the synthesized granules. By varying precursor, reaction solution compositions, and reaction times, the study elucidated the phase evolution mechanisms and demonstrated their impact on the structural, morphological, and surface properties of Mg-WH granules. Full article

In this study, phosphogypsum waste collected from a factory dump in Kedainiai, Lithuania, was used for the first time as a starting material in the dissolution–precipitation synthesis of high-quality bioceramic calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂; CHA). The CHA powders were synthesized using the dissolution–precipitation method, employing phosphogypsum in four different conditions: untreated, dried at 100 °C, dried at 150 °C, and annealed at 1000 °C. Various phosphorus sources were used in the CHA synthesis process: Na₂HPO₄; a mixture of Na₂HPO₄ and NaH₂PO₄; or a combination of Na₂HPO₄, NaH₂PO₄, and NaHCO₃. These mixtures were allowed to react at 80 °C for 48 h, 96 h, 144 h, and 192 h. X-ray diffraction (XRD) analysis revealed slight variations in the synthesized products depending on the specific starting materials used. Fourier transform infrared spectroscopy (FTIR) was conducted to confirm the structural characteristics of the synthesized CHA samples. The surface microstructure of the synthesized CHA samples differed notably from that of the raw phosphogypsum. All synthesized CHA samples exhibited Type IV nitrogen adsorption–desorption isotherms with H3-type hysteresis loops, indicating the presence of mesoporous structures, typically associated with slit-like pores or aggregates of plate-like particles. To the best of our knowledge, an almost monophasic CHA has been fabricated from phosphogypsum waste for the first time using a newly developed dissolution–precipitation synthesis method. A key challenge in the high-end market is the development of alternative synthesis technologies that are not only more environmentally friendly but also highly efficient. These findings demonstrate that phosphogypsum is a viable and sustainable raw material for CHA synthesis, with promising applications in the medical field, including the production of artificial bone implants. Full article

Oxide dispersion-strengthened (ODS) alloys demonstrate enhanced mechanical properties at elevated temperatures and show potential as next-generation powder materials for additive manufacturing. These alloys can mitigate defects such as micropores and cracks by regulating solidification and grain growth behaviors during the additive manufacturing process. This study investigates the fabrication technology for ODS Ti-6Al-2Sn-4Zr-2Mo (Ti6242) alloy powder to achieve uniform oxide distribution within the alloy powders. Thermodynamic calculations were employed to determine the optimal Ti6242–Y₂O₃ composition for in situ gas atomization, ensuring complete dissolution of the oxide in the Ti6242 molten metal and subsequent reprecipitation upon cooling. A rod-shaped ingot was produced via vacuum arc melting, resulting in coarse Y₂O₃ precipitating along the grain boundaries. The powder was fabricated through an electrode induction gas atomization method, and the ODS Ti6242 powder exhibited a spherical shape and a smooth surface. Cross-sectional analysis revealed the uniform distribution of Y₂O₃ oxide particles, measuring several tens of nanometers in size, within the alloy powder. This research demonstrates the successful synthesis of oxide-integrated ODS Ti6242 alloy powder through the in situ gas atomization method, potentially advancing the field of additive manufacturing for high-temperature applications. Full article

This study investigates, in the first part, the synthesis and purification of a poorly crystalline hydroxyapatite (HAp) using natural Moroccan phosphate (Boucraa region) as a raw material. Despite its successful preparation, the obtained HAp was contaminated by several metallic cations (mostly Cd, Pb, Sn, Ti, Mn, Mg, Fe, and Al) migrated from the natural rocks during the digestion process, inhibiting HAp application in several sectors. To minimize the existence of these elements, the dissolution–precipitation technique (DP) was investigated as a non-selective purification process. Following the initial DP cycle conducted on the precipitated HAp, the removal efficiency was approximately 60% for Al, Fe, Mg, Mn, and Ti and 90% for Cd and Pb. After three consecutive DP cycles, notable improvement in the removal efficiency was observed, reaching 66% for Fe, 69% for Mg, 73% for Mn, and 74% for Al, while Cd, Pb, and Ti were totally removed. In the second part of this study, the purified HAp was digested using sulfuric acid to produce high-quality phosphoric acid (PA) and gypsum (GP). The elemental analysis of the PA indicates a removal efficiency of approximately 89% for Fe and over 94% for all the examined cations. In addition, the generated GP was dominated by SO₃ and CaO accompanied with minor impurities. Overall, this simple process proves to be practically useful, to reduce a broad spectrum of cationic impurities, and to be flexible to prepare valuable products such hydroxyapatite, phosphoric acid, and gypsum. Full article

In the biomedical field, nanocrystalline hydroxyapatite is still one of the most attractive candidates as a bone substitute material due to its analogies with native bone mineral features regarding chemical composition, bioactivity and osteoconductivity. Ion substitution and low crystallinity are also fundamental characteristics of bone apatite, making it metastable, bioresorbable and reactive. In the present work, biomimetic apatite and apatite/chitosan composites were produced by dissolution–precipitation synthesis, using mussel shells as a calcium biogenic source. With an eye on possible bone reconstruction and drug delivery applications, apatite/chitosan composites were loaded with strontium ranelate, an antiosteoporotic drug. Due to the metastability and temperature sensitivity of the produced composites, sintering could be carried out by conventional methods, and therefore, cold sintering was selected for the densification of the materials. The composites were consolidated up to ~90% relative density by applying a uniaxial pressure up to 1.5 GPa at room temperature for 10 min. Both the synthesised powders and cold-sintered samples were characterised from a physical and chemical point of view to demonstrate the effective production of biomimetic apatite/chitosan composites from mussel shells and exclude possible structural changes after sintering. Preliminary in vitro tests were also performed, which revealed a sustained release of strontium ranelate for about 19 days and no cytotoxicity towards human osteoblastic-like cells (MG63) exposed up to 72 h to the drug-containing composite extract. Full article

Magnesium whitlockite (Mg-WH) powders were synthesized with remarkable efficiency via the dissolution–precipitation method by employing an environmentally benign precursor, gypsum. Under optimized conditions, each 5.00 g of initial gypsum yielded an impressive amount of 3.00 g (89% yield) of Mg-WH in a single batch. Remarkably, no XRD peaks attributable to impurity phases were observed, indicating the single-phase nature of the sample. FT-IR analysis confirmed the presence of the PO₄³⁻ and HPO₄²⁻ groups in the obtained Mg-WH phase. The SEM-EDX results confirmed that Mg-WH crystals with homogeneous Ca, Mg, P, and O distributions were obtained. In previously published research papers, the synthesis of Mg-WH has been consistently described as a highly intricate process due to material formation within a narrow pH and temperature range. Our proposed synthesis method is particularly compelling as it eliminates the need for meticulous monitoring, presenting a notable improvement in the quest for a more convenient and efficient Mg-WH synthesis. The proposed procedure not only emphasizes the effectiveness of the process, but also highlights its potential to meet significant demands, providing a reliable solution for large-scale production needs in various promising applications. Full article

GeTe and Ge_0.99-xIn_0.01Sn_xTe_0.94Se_0.06 (x = 0, 0.01, 0.03, and 0.06) samples were prepared by vacuum synthesis combined with spark plasma sintering (SPS). The thermoelectric properties of GeTe were coordinated by multiple doping of Sn, In, and Se. In this work, a maximum zT(zT = S²σT/κ) of 0.9 and a power factor (PF = S²σ) of 3.87 μWmm⁻¹ K⁻² were obtained in a sample of Ge_0.99In_0.01Te_0.94Se_0.06 at 723K. The XRD results at room temperature show that all samples are rhombohedral phase structures. There is a peak (~27°) of the Ge element in GeTe and the sample (x = 0), but it disappears after Sn doping, indicating that Sn doping can promote the dissolution of Ge. The scattering mechanism of the doped samples was calculated by the conductivity ratio method. The results show that phonon scattering Is dominant in all samples, and alloy scattering is enhanced with the increase in the Sn doping amount. In doping can introduce resonance energy levels and increase the Seebeck coefficient, and Se doping can introduce point defects to suppress phonon transmission and reduce lattice thermal conductivity. Therefore, the thermoelectric properties of samples with x = 0 improved. Although Sn doping will promote the dissolution of Ge precipitation, the phase transition of the samples near 580 K deteriorates the thermoelectric properties. The thermoelectric properties of Sn-doped samples improved only at room temperature to ~580 K compared with pure GeTe. The synergistic effect of multi-element doping is a comprehensive reflection of the interaction between elements rather than the sum of all the effects of single-element doping. Full article

The geochemical characterization and evolution of shallow groundwater in the Zihe River source area is a key issue that needs to be addressed. In this study, a combination of traditional geochemical techniques and geochemical modeling was used to explain the geochemical processes and major ion sources in the chemical evolution of shallow groundwater in the Zihe River source area, Northeast China. Fifty-seven water samples were collected in June 2020 for chemical analysis, and the results showed that the main groundwater chemistry types in the three major aquifers are HCO₃·SO₄-Ca_·Mg-type pore water from loose quaternary rocks, HCO₃·SO₄-Ca_·Mg-type karstic fissure water from carbonate rocks, and HCO₃·SO₄-Ca-type weathered fissure water from massive rocks. Water–rock interactions in alkaline environments were the main causes of changes in groundwater chemistry. Rock weathering dominated the geochemical evolution of each aquifer. The analysis of ion concentration ratios and modeling revealed that the aquifer’s chemical components are mainly derived from the dissolution of dolomite and calcite and partly from the infiltration of pollutants containing ${\mathrm{C}\mathrm{l}}^{-}$ and ${\mathrm{N}\mathrm{O}}_3^{-}$, as well as from the dissolution of quartz. Mg²⁺ is derived from the dissolution of dolomite. ${\mathrm{H}\mathrm{C}\mathrm{O}}_3^{-}$ is primarily derived from the co-dissolution of calcite and dolomite, and to a lesser extent, its content is also influenced by the recharge of rainfall. ${\mathrm{S}\mathrm{O}}_4^{2-}$ has two sources: it mainly originates from the dissolution of gypsum and the anhydrite layer, followed by atmospheric precipitation. The synthesis showed that the groundwater quality in the source area of Zihe River is good, all the indices reached the standard of class III groundwater quality, and the overall degree of human pollution is low. The results of this research will provide a scientific basis for the local authorities to delineate karst groundwater protection zones in the Zihe River source area and to formulate resource management strategies for the development, utilization, and protection of karst groundwater. Full article

In the present work, the low-temperature synthesis of substituted calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAP) with copper and zinc ions on titanium substrates was performed. Initially, CaCO₃ coatings were synthesised on titanium substrate using the sol-gel method at 550 °C in a CO₂ atmosphere. Crystalline calcium hydroxyapatite was then synthesised from these CaCO₃ coatings through the dissolution-precipitation method at low temperature (80 °C). X-ray diffraction (XRD) analysis, FTIR and Raman spectroscopies, and scanning electron microscopy (SEM) were employed to evaluate the phase composition, surface functional groups, crystallinity, and morphology of the coatings. The results showed the formation of hexagonal HAP particles with a size of 20 nm at low temperature, exhibiting high homogeneity in particle size distribution. In the calcium hydroxyapatite, some of the Ca²⁺ ions were replaced by Cu²⁺ ions. Heating the mixture of Ca(NO₃)₂ and Cu(NO₃)₂ solutions at 550 °C in a CO₂ atmosphere led to the formation of copper hydroxide carbonate (malachite, Cu₂(OH)₂CO₃) along with CaCO₃. The reaction between the sol-gel precursor obtained and Na₂HPO₄ resulted in the formation of copper-substituted hydroxyapatite (Cu-HAP). Different synthesis methods were tested with Zn²⁺ ions, and on the surface of the coating, Zn(OH)(NO₃)(H₂O), Zn₃(OH)₄(NO₃)₂, and unreacted CaCO₃ were formed. Antibacterial properties of the coatings were tested using the inhibition zone method. No inhibition zones were observed for HAP. However, in the Cu and Zn containing coatings, inhibition zones were observed in the presence of a colony of B. subtilis bacteria. However, no inhibition zones were detected in the presence of E. coli bacteria. Full article

The effect of pH on the structural, textural, morphological, and electronic properties of ZnGa₂O₄ nanoparticles obtained by coprecipitation using mild reaction conditions (25 °C; 30 min) was studied. The pH ranges in which coprecipitation reactions occurred and the chemical species associated with the reaction mechanism were identified. It was determined that the samples synthesized at pH values between 6 and 10 consisted of Zn-Ga oxide blends, with spinel ZnGa₂O₄ being the majority phase. Conversely, the material prepared at pH 12 was constituted by Zn-Ga layered double hydroxide phase along with wurtzite ZnO traces. The synthesis pH determined the reaction product yield, which decreased from 51 to 21% when the reaction medium turned from softly acidic (pH 6) to strongly alkaline conditions (pH 12). The bandgap energies of the synthesized materials were estimated to be in the range of 4.71–4.90 eV. A coprecipitation-dissolution-crystallization mechanism was proposed from the precipitation curve, with specific mononuclear and polynuclear species being involved in the formation of the different precipitates. Phenol was employed as a probe molecule to evaluate the photocatalytic performance of the synthesized samples. Among the samples, the one prepared at pH 6 showed the largest photodegradation efficiency (~98%), which was superior to commercial TiO₂-Degussa P25 (~88%) under the same process conditions, which can be attributed to both its high specific surface area (140 m² g⁻¹) and the formation of a Zn_2xGa_2−2xO_3+x/ZnGa₂O₄ heterojunction. Full article

Obvious volume change and the dissolution of polysulfide as well as sluggish kinetics are serious issues for the development of high performance metal sulfide anodes for sodium-ion batteries (SIBs), which usually result in fast capacity fading during continuous sodiation and desodiation processes. In this work, by utilizing a Prussian blue analogue as functional precursors, small Fe-doped CoS₂ nanoparticles spatially confined in N-doped carbon spheres with rich porosity were synthesized through facile successive precipitation, carbonization, and sulfurization processes, leading to the formation of bayberry-like Fe-doped CoS₂/N-doped carbon spheres (Fe-CoS₂/NC). By introducing a suitable amount of FeCl₃ in the starting materials, the optimal Fe-CoS₂/NC hybrid spheres with the designed composition and pore structure exhibited superior cycling stability (621 mA h g⁻¹ after 400 cycles at 1 A g⁻¹) and improved the rate capability (493 mA h g⁻¹ at 5 A g⁻¹). This work provides a new avenue for the rational design and synthesis of high performance metal sulfide-based anode materials toward SIBs. Full article

The low solubility and slow dissolution of hydrophobic drugs is a major challenge for the pharmaceutical industry. In this paper, we present the synthesis of surface-functionalized poly(lactic-co-glycolic acid) (PLGA) nanoparticles for incorporation into corticosteroid dexamethasone to improve its in vitro dissolution profile. The PLGA crystals were mixed with a strong acid mixture, and their microwave-assisted reaction led to a high degree of oxidation. The resulting nanostructured, functionalized PLGA (nfPLGA), was quite water-dispersible compared to the original PLGA, which was non-dispersible. SEM-EDS analysis showed 53% surface oxygen concentration in the nfPLGA compared to the original PLGA, which had only 25%. The nfPLGA was incorporated into dexamethasone (DXM) crystals via antisolvent precipitation. Based on SEM, RAMAN, XRD, TGA and DSC measurements, the nfPLGA-incorporated composites retained their original crystal structures and polymorphs. The solubility of DXM after nfPLGA incorporation (DXM–nfPLGA) increased from 6.21 mg/L to as high as 87.1 mg/L and formed a relatively stable suspension with a zeta potential of −44.3 mV. Octanol–water partitioning also showed a similar trend as the logP reduced from 1.96 for pure DXM to 0.24 for DXM–nfPLGA. In vitro dissolution testing showed 14.0 times higher aqueous dissolution of DXM–nfPLGA compared to pure DXM. The time for 50% (T₅₀) and 80% (T₈₀) of gastro medium dissolution decreased significantly for the nfPLGA composites; T₅₀ reduced from 57.0 to 18.0 min and T₈₀ reduced from unachievable to 35.0 min. Overall, the PLGA, which is an FDA-approved, bioabsorbable polymer, can be used to enhance the dissolution of hydrophobic pharmaceuticals and this can lead to higher efficacy and lower required dosage. Full article

The aqueous and thermal stabilities of aragonite (CaCO${}_3$) powders against phase conversion are important for industrial applications that rely on calcium carbonate. We describe the synthesis and characterization of solution-precipitated aragonite powders before and after exposure to different aqueous polyphosphate (SHMP) or orthophosphate (PO${}_4$) treatments with concentrations ranging between 1–10 mM (∼1 g/L). Based on infrared spectra, differential scanning calorimetry, and thermogravimetric analyses, results show that orthophosphate treatments lead to secondary phase formation and complex thermal annealing behaviors. In contrast, polyphosphate treatments help to prevent against aragonite dissolution during water exposure, and also provide a slight increase in the thermal stability of aragonite with regard to conversion to calcite. Full article

Transition metal trialuminides of the Al₃X type of groups 4 and 5 of the periodic system have reduced density, high melting points, and corrosion resistance. Aluminides with a cubic lattice of the Al₃Sc type can be used as a nucleating phase for aluminum alloys. However, low plasticity and a tetragonal lattice limit their application. In this work, we stabilized the metastable cubic lattice of Al₃X-type aluminides by replacing aluminum with copper. The conditions for the formation of L1₂ metastable aluminides in the Al–Cu–TM (TM: Ti, Zr, Hf) alloys were studied using a wide range of copper concentrations. A high concentration of copper (hypereutectic alloys) is the one of the necessary conditions for the formation of (Al_1−xCu_x)₃Ti, (Al_1−xCu_x)₃Zr, (Al_1−xCu_x)₃Hf aluminides. With an increase in the copper concentration, the number of metastable aluminides sharply increased. The process of their formation strongly depended on the sequence of dissolution of the corresponding components in the melts. The low volume fraction of precipitated titanium aluminides was the result of insufficient supersaturation of α-Al with titanium (at the peritectic temperature) compared to that for alloys with zirconium and hafnium. Under identical synthesis conditions in the crystal lattice of metastable aluminides formed in experimental Al–Cu–Ti, Al–Cu–Zr, Al–Cu–Hf alloys, copper was found to substitute up to 8, 10, and 13 at.% of aluminum, respectively. The crystallographic and dimensional similarities of the lattices in metastable transition metal aluminides and in α-Al suggest their usefulness as modifying additions in aluminum-based alloys. Full article