Electrical and Thermal Transport in CaCO3 Graphene Nanocomposites Derived from Oyster Shell Waste

Abstract

Waste oyster shells provide a calcium carbonate, as Mg-calcite, feedstock for functional mineral composites. Here, shell-derived biogenic calcium carbonate (BCC) and few-layer graphene (FLG; nominally 1, 5, 7, and 10 wt % relative to BCC) were processed by aqueous planetary ball milling with Pluronic P123. Microscopy, diffraction, spectroscopy, thermogravimetry, and transport measurements were combined to examine the resulting powders and pressed pellets. Mg-calcite nanocrystallites and graphene sheets coexisted within micrometer-scale aggregates, with mineral particles preferentially observed near sheet edges. At 25 °C, the thermal conductivity of the 10 wt % formulation was 0.516 W·m–1·K–1, compared with 0.194 W·m–1·K–1 for the dry-milled shell. This approximately 166% reference-to-composite difference combines changes in composition and processing and cannot be assigned to FLG addition alone. Stable electrical measurements were obtained from 5 wt % FLG; the reported resistivity of the 10 wt % formulation was approximately 0.50 Ω·cm. The shell organic matrix may contribute to interfacial interactions, although its effect cannot be distinguished from those of Pluronic and processing in the present experiments. The observed transport differences among the prepared formulations provide a basis for future studies using matched processing controls to clarify the contribution of each constituent.