{
  "abstract": "Cobaltoan magnesite, (Mg1−xCox)CO3 (R3c; x = 0–1), has previously been accessible only under extreme solid-state conditions (≥600 °C, ≥15 kbar; Goldsmith & Northrop, 1965) or over geological timescales in supergene ore environments (Barton et al., 2014). We report the first deliberate laboratory synthesis of phase-pure (Mg,Co)CO3 solid-solution nanoparticles at 250 °C under autogenous pressure (~40 bar) via a modified polyol-assisted aqueous coprecipitation route. Thermodynamic feasibility is established through saturation-index analysis (SI(CoCO3) = +10.6, ΔG° = −60.5 kJ mol−1; SI(MgCO3) = +2.6, ΔG° = −14.8 kJ mol−1), confirming that both carbonate end-members are thermodynamically driven to precipitate from solution at ambient conditions and that the hydrothermal step supplies kinetic — not thermodynamic — activation energy. The principal kinetic challenge, the seven-order-ofmagnitude disparity in solubility products (Ksp(CoCO3) = 10−13 vs. 6.8×10−6 for MgCO3), is surmounted by ethylene glycol (EG) coordination of Co2+, confirmed in situ by a spontaneous pink→blue colour transition upon EG addition, which elevates the desolvation activation barrier and synchronises Co2+ and Mg2+ precipitation rates. Convergent evidence from five independent characterisation techniques confirms the R3c solid-solution product: (i) PXRD with Vegard's Law analysis of the composition-sensitive (113) reflection yields x(Co) ≈ 0.73 (Sample 3, pre-hydrothermal) and x(Co) ≈ 0.44 (Sample 4, post-hydrothermal); (ii) FTIR reveals a single ν2(CO32−) band at 870 cm−1, intermediate between MgCO3 (880) and CoCO3 (860 cm−1) endmembers — a necessary and sufficient criterion for isomorphic solid-solution identification by infrared spectroscopy; (iii) SEM-EDX shows a continuous unimodal composition distribution (x(Co) = 0.27–0.73) with no bimodal clustering indicative of phase separation; (iv) UV–Vis spectroscopy identifies characteristic Co2+ ligand-field and charge-transfer transitions with a direct optical band gap of ~3.1–3.4 eV; (v) DLS confirms near-monodisperse product (PDI = 0.053, Dh = 306 nm) following hydrothermal treatment, representing an 83% reduction in polydispersity relative to the amorphous precursor (PDI = 0.314). Prospective applications spanning heterogeneous catalysis, Li-ion battery cathode precursors, CO2 mineralisation, photocatalysis, and pH-responsive drug delivery are evaluated on the basis of the crystal chemistry and mixed-metal composition of the product phase.",
  "abstract_shown": true,
  "affiliations": [
    "Institute of Engineering and Applied Sciences (PIEAS",
    "Department of Physics and Applied Mathematics",
    "PIEAS"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 7,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Abdul Haseeb Tanoli"
    },
    {
      "affs": [
        0
      ],
      "name": "Arfeen"
    },
    {
      "affs": [
        0
      ],
      "name": "Laiba Irshad Khattak"
    },
    {
      "affs": [
        0,
        1,
        2
      ],
      "name": "Tasbiha Rehman Bhatti"
    },
    {
      "affs": [
        0
      ],
      "name": "Muhammad Muneeb Yousafzai"
    },
    {
      "affs": [
        0
      ],
      "name": "Tayyaba Ghani"
    },
    {
      "name": "ABDUL HASEEB TANOLI"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/c91rzz9xh59am.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15010073/v1",
  "fulltext_url": null,
  "id": "c91rzz9xh59am",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010073/v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2502|Calcium Carbonate Crystallization and Inhibition"
    ]
  ],
  "openalex": "W7220940232",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15010073/v1",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-07",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/c91rzz9xh59am.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:22Z",
      "native_id": "10.26434/chemrxiv.15010073",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010073/v1"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:2502|Calcium Carbonate Crystallization and Inhibition",
      "subfield": "materials-polymers"
    }
  ],
  "title": "Kinetically Synchronized Aqueous Co-precipitation and Hydrothermal Crystallisation of (Mg1−xCox)CO3 Rhombohedral Solid-Solution Nanoparticles: Thermodynamic Feasibility, Ethylene Glycol Kinetic Control, and Prospective Functional Applications",
  "title_text": "Kinetically Synchronized Aqueous Co-precipitation and Hydrothermal Crystallisation of (Mg1−xCox)CO3 Rhombohedral Solid-Solution Nanoparticles: Thermodynamic Feasibility, Ethylene Glycol Kinetic Control, and Prospective Functional Applications",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:22Z",
  "url": "https://research.draconitic.com/paper/c91rzz9xh59am",
  "venue": "ChemRxiv",
  "versions": []
}