Synthesis, characterization and thermal performance of Fe/N co-doped MgTiO3 as a novel high near-infrared reflective pigment

- A novel near-infrared reflecting inorganic pigments Fe/N co-doped MgTiO3 have been prepared by the Sol-Gel method.
- Fe/N co-doped MgTiO3 displays wide range of colors from white to red-brown.
- The pigments possess high NIR solar reflectance (>53.51%).
- Indoor air temperature difference of boxes in the simulation test reaches 2.0-3.0 °C.
- The interior surface temperature difference of the two pigmented coatings is above 2.4 °C.

To obtain cool materials as inorganic and nontoxic pigments with high near-infrared reflectance, nano-powder of Fe/N co-doped MgTiO3 (FNM), were synthesized by the sol-gel method. The substitution of Fe/N changed the color from white to dark-red due to the point defect equilibrium theory, while the band gap decreased from 2.11 ev to 1.89 ev. Ammonolysis reaction can promote the particle dispersion and increase the particle size. Furthermore, the FNM pigments exhibit high NIR reflectance (>65%) and the NIR solar reflectance (>53.51%) in the range of 700-2500 nm. After the prepared pigments (N-doped Mg1−xFexTiO3+δ, x=0.3) and conventional brown pigments used as building roof materials, the temperature difference of coatings could reach 2.4 °C (the inner surface temperature of substrate plates) and 2.0 °C (the interior temperature of the two boxes), respectively. Moreover, the surface temperature distribution of the coatings was recorded by infrared images and the difference (ΔT) varied at 0-12 °C. According to the maximum value of coatings (x=0.3), energy savings would reduce annual emissions of 1379.35 t carbon dioxide, 41.65 t nitrogen oxides and 34.30 t sulfur oxides. Owing to the wide range of color and good chemical stability, which meets reflectance of solar radiation energy and cooling energy needs, these FNM materials are considered as novel color pigments.

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