Cement is a fundamental material for global infrastructure. Global cement production is projected to exceed 4.5 billion tons by 2030. The cement industry contributes about 7.5% of global anthropogenic carbon dioxide (CO₂) emissions. These emissions mainly come from fossil fuel combustion and limestone decomposition during the calcination process. Replacing fossil fuels with concentrated solar energy (CSE) for clinker calcination is a key pathway to achieve carbon neutrality in this sector. The CSE technology can concentrate solar radiation up to 7000 times and generate ultra-high temperatures of above 3000 K. These conditions can meet the thermal requirements for cement clinker production.

The spectral mismatch between cement materials and solar radiation as a critical bottleneck limits the efficiency of solar calcination.. The solar spectrum concentrates its energy in the visible (400–700 nm) and near-infrared (NIR, 700–2500 nm) bands. Most cement raw materials, such as calcium carbonate (CaCO₃), silicon dioxide (SiO₂), and aluminum oxide (Al₂O₃), are wide-bandgap materials. These materials absorb mainly in the ultraviolet region and are nearly transparent to visible and NIR light. This transparency leads to a low solar-to-thermal conversion efficiency. Iron oxide (Fe₂O₃) and iron-bearing ferrite minerals have narrower bandgaps of 2.0–2.2 eV. These minerals offer a stronger light absorption in the solar spectrum. This study was to investigate high-ferrite cement (HFC) clinkers to use the high absorption of the iron phase for better photothermal conversion. The calcination performance in electric furnace and solar furnace was compared and the first-principles calculations were performed. The goal was to reveal the photothermal coupling mechanism that could enable low-temperature and rapid clinker formation.

Three high-ferrite cement raw meals were prepared with analytical-grade reagents. These samples, named HFC-16, HFC-18, and HFC-20, were designed with different mass fractions of tetracalcium aluminoferrite (C₄AF, 16%, 18%, and 20%), respectively. All raw materials were ground and passed through a 200-mesh sieve. The sintering was carried out in a conventional electric elevator furnace and a high-flux solar simulator, respectively. The solar simulator used a xenon lamp array to mimic the solar spectrum (AM1.5). This simulator generated a peak heat flux of > 1800 kW/m² at the focal plane.

For the experiments in the electric furnace, the samples were heated to 800 ℃ and held for 30 min. The samples were then heated at 1000, 1200 ℃, or 1375 ℃ and held for 2 h, respectively. For the experiments in the solar furnace, the samples were rapidly heated to 800 ℃ and held for 1 min. They were then heated to the target temperature and held for 5 min. All the samples were rapidly cooled after firing. The phase composition of each sample was analyzed by X–ray diffraction (XRD). The Rietveld refinement was used for quantitative phase analysis. The optical properties were measured by ultraviolet-visible (UV–Vis) spectrophotometry in the range of 200–2500 nm. The total solar absorptance was calculated by the AM1.5 solar irradiance distribution. The electronic structures were simulated by a software named Vienna Ab initio Simulation Package (VASP). The simulations were based on the Density Functional Theory (DFT) with the GGA-PBE functional and a Hubbard U correction for Fe 3d orbitals.

The UV–Vis spectra of the raw materials show that wide-bandgap oxides (i.e., CaO, SiO₂, Al₂O₃) have a weak absorption in the solar spectrum region. Their absorptance values are all below 20%. Fe₂O₃ is a main absorber among all the raw materials. Its solar absorptance reaches 71.1%. As a result, increasing the Fe₂O₃ content in the raw meal improves the overall light absorption. The solar absorptance of the raw meal increases from 56.6% for HFC-16 to 60.5% for HFC-20. The light absorption of the clinker minerals depends on the calcination temperature. At 1000 ℃, the absorptance decreases slightly. This decrease is due to the decomposition of CaCO₃ into weakly absorbing CaO and the low crystallinity of intermediate phases. At 1200 ℃, the absorptance increases sharply. The iron phase mineral formed at 1200 ℃ shows a solar absorptance of 83.9%. This value is greater than that of the raw Fe₂O₃. For the clinker sample HFC-20, the total light absorptance is 75.6% at 1375 ℃.

The results by the First-principles calculations explain the mechanism behind this enhancement. In the high-temperature ferrite solid solution (C₄AF), Fe³⁺ ions occupy both tetrahedral and octahedral sites. This mixed coordination induces a crystal field splitting and creates diverse intermediate energy levels. The substitution of Al³⁺ for Fe³⁺ also introduces lattice defects. These defects create dense defect states within the bandgap. The density of states (DOS) analysis indicates that Fe 3d orbitals dominate the conduction band minimum. O 2p orbitals dominate the valence band maximum. The strong O 2p → Fe 3d transitions are responsible for the intense broadband absorption in the visible and NIR regions.

The comparison between the two heat sources shows a clear photothermal coupling effect in the solar furnace. The XRD patterns indicate that the solar-calcined samples processed at a thermocouple-measured temperature of only 800 ℃ already contain distinct silicate mineral phases (i.e., tricalcium silicate, C₃S, and dicalcium silicate, C₂S). In the conventional electric furnace, these phases only form at 1200 ℃. This result indicates that the iron phase absorbs a high-intensity photon energy locally and lowers the formation temperature of clinker minerals by approxiamtely 400 ℃. The electric furnace transfers heat slowly through conduction from the surface to the interior. The solar furnace delivers energy directly to the reactive iron-bearing sites. This direct energy delivery greatly accelerates the solid-state reaction kinetics.

At the final sintering temperature of 1375 ℃, the two methods both produce clinkers with the target mineral phases (i.e., C₃S, C₂S, tricalcium aluminate C₃A, and C₄AF). No free CaO appears in either case. This result confirms that the solar furnace can fully sinter cement clinker. The Rietveld refinement of the XRD patterns shows that the solar-calcined clinker exhibits broader diffraction peaks than the electric furnace clinker. The rapid heating rate and the unique photothermal environment in the solar furnace likely caused this broadening. Smaller crystallite sizes or higher lattice defect concentrations are the probable reasons. These findings indicate that solar calcination saves energy and changes the microstructural evolution of the cement minerals.

Based on the UV–Vis absorption testing and XRD analysis of raw materials, raw meals, and samples calcined at different temperatures, the overall light absorption intensity of the raw meal increased significantly as the Fe₂O₃ content in the raw meal increased. Furthermore, the light absorption intensity of the iron phase in the clinker minerals increased with increasing the calcination temperature. At 1200 ℃, its light absorption rate reached 83%. The light absorption intensity of the clinker also increased with the calcination temperature, reaching 75.6% at 1375 ℃. More importantly, the iron phase could trigger a photothermal coupling effect when calcined in a simulated high-concentration solar furnace, significantly lowering the formation temperature of clinker minerals. The results by the XRD Rietveld refinement and hydration calorimetry indicated that, compared with the electric furnace clinker, the simulated concentrated solar calcined clinker (SF-HFC) exhibited diffraction peak broadening characteristics. This could demonstrate that the photothermal effect of the iron phase significantly reduced the calcination temperature of cement clinker and lowered the production energy consumption, providing a material design strategy for high-efficiency and low-carbon cement manufacturing.

Through billions of years of natural selection, nature has nurtured a wide range of biomaterials with exquisite microstructures, excellent mechanical properties, and unique functional characteristics. Their advantages in resource utilization efficiency and sustainable preparation processes provide important references for the development of artificial materials. However, current biomimetic material research faces a significant contradiction: biomimetic designs pursuing high performance often rely on high-energy consumption preparation processes such as high temperature and high pressure, which achieve performance breakthroughs but contradict sustainable development goals. In contrast, green preparation technologies imitating biomineralization face engineering transformation challenges such as performance, efficiency, and costs, leading to an imbalance of “performance priority” and “process lag” in the field of biomimetic materials. Most existing preparation strategies rely on energy-intensive processes such as high temperature (above 1000 ℃) sintering or ultrahigh pressure (exceeding 800 MPa) molding, which not only increase production costs (energy consumption accounts for over 60% of total costs for high-temperature ceramics) but also limit the incorporation of thermally sensitive functional components and large-scale industrialization.

To address this challenge, extensive studies have been conducted on the regulatory mechanisms of natural biomineralization, revealing five core principles: molecular recognition, confined growth, organic templating, amorphous precursor transformation, and multi-scale synergistic assembly. Nacre, a representative biological mineral, consists of 95% aragonite calcium carbonate and 5% organic matrix, forming a unique “brick-and-mortar” layered structure. Its formation involves the secretion of β-chitin as a porous scaffold by mantle cells, followed by the assembly of silk fibroin and acidic proteins into a gel network, which precisely regulates crystal growth and interlayer spacing. Inspired by these mechanisms, researchers have developed various biomimetic preparation strategies, including freeze casting, layer-by-layer self-assembly, electrophoretic deposition, and 3D printing. For instance, freeze casting has been used to prepare alumina-cyanate composites with a 3D interlocking skeleton, achieving a flexural strength of 300 MPa and a fracture strain of 5% after sintering at 1600 ℃ for 4 h. Room-temperature high-pressure cold sintering technology has enabled the densification of vaterite powder into ceramics with a compressive strength of 280 MPa under 280–800 MPa. Low-temperature low-pressure strategies, such as evaporation-induced self-assembly combined with hot pressing, have produced phosphate-based composites with a flexural strength of 267 MPa, exceeding that of natural nacre (172 MPa). Ambient-temperature and pressure approaches, represented by cement-based biomimetic materials, have utilized ice templating to create porous structures with 200% higher compressive strength than foamed cement, but suffer from low flexural strength (only 5 MPa) and long curing cycles (28 d).

A breakthrough strategy based on carbon mineralization has emerged as a promising solution for green biomimetic material preparation. Carbon mineralized materials, also known as Engineered LimeStone (ELS), are novel inorganic non-metallic composites formed by the mineralization reaction between CO₂-sequestering cementitious materials (e.g., steel slag, magnesium slag, or calcium silicates) and gaseous CO₂ under ambient conditions, converting CO₂ into solid calcium carbonate (CaCO₃) as the main matrix. This technology mimics natural biomineralization processes such as shell formation and limestone weathering, achieving permanent CO₂ sequestration while producing high-value materials. Three key advantages make ELS ideal for biomimetic systems: mild reaction conditions (ambient temperature and pressure, driven by thermodynamic feasibility and surface-activated CO₂ dissolution), highly controllable composition and structure (tunable CaCO₃ crystal phases, morphologies, and growth rates via organic modifiers or bacterial treatments), and excellent mechanical properties and durability (compressive strength exceeding 200 MPa after 24 h of curing, superior corrosion resistance).

Recent studies have demonstrated the versatility of carbon mineralization-based biomimetic design: 1) Inspired by nacre's “brick-and-mortar” structure, ice templating combined with rapid carbon mineralization has produced lightweight high-strength materials with a flexural strength of 45 MPa (8 times higher than cement-hydrogel composites) and a fracture toughness of 2.03 MJ/m³ (20 times higher than unmodified ELS). 2) Mimicking the “privileged space” in marine biomineralization, sodium alginate hydrogels have been used to create microcompartments for oriented CaCO₃ growth, resulting in materials with a compressive strength of 300 MPa and a CO₂ sequestration capacity of 200 kg per ton. 3) Inspired by natural marble's radiative cooling effect, engineered marble radiative cooling materials (EMM) have been developed via γ-dicalcium silicate (γ-C₂S) carbonation, achieving a solar reflectance of over 95% and an atmospheric window emissivity of over 97%, reducing surface temperature by 8.8 ℃ below ambient and sequestering 357.7 kg CO₂ per ton.

Despite significant progress in biomimetic material design, the trade-off between performance and energy consumption remains a major barrier to industrialization. Traditional strategies rely on harsh conditions (high temperature, high pressure) or suffer from insufficient mechanical properties and long curing cycles. ELS address these limitations by integrating mild preparation conditions, rapid curing, high strength-toughness synergy, large-scale scalability, and CO₂ sequestration. By combining structural and process bionics, this strategy breaks through traditional performance limits and provides a sustainable solution for biomimetic material commercialization. Future research should focus on optimizing the carbon mineralization reaction efficiency, expanding the range of CO₂-sequestering raw materials, and developing multifunctional composites for extreme environments (deep sea, polar regions) and advanced applications (sustainable infrastructure, carbon-neutral buildings, energy-efficient construction). This integration of bionics and green manufacturing not only advances material science but also contributes to global climate goals and the transition to a low-carbon economy.