Synthesis of vanadium oxide nanostructures with excellent thermochromic properties via sol-gel chemistry in supercritical carbon dioxide

Vanadium oxide VO2(M) synthesis was investigated using a simple supercritical CO2(scCO2) sol-gel process with vanadium(V) oxytriisopropoxide(VTIP) as the vanadium precursor and acetic acid as catalyst. scCO2 with different temperatures of 40, 60, 80 and 100 degrees C under 41.4 MPa was examined on the prepared sol-gels' chemical constituents by FTIR and morphology by SEM, respectively. 80 degrees C and 41.4 MPa produced aerogel with smaller size of nanofiber. The calcination conditions were studied in regarding to different atmospheres, time durations and aerogel forms, by the XPS and XRD spectrum of the obtained vanadium oxides. Calcination in N2 at 500 degrees C with vanadium oxides aerogel casted on glass substrate for 15 min showed best calcination results, with V(IV) of 49.5%, V(V) of 47.1%, and V(III) of 3.4% in the obtained vanadium oxides. The smart glass was manufactured in scCO2 at 80 degrees C and 41.4 MPa, by direct synthesis of vanadium oxides aerogel on glass substrate, followed by calcination at 500 degrees C in N2 for 15 min. Phase transition of the obtained vanadium oxides was observed at 65 degrees C by DCS analysis. UV-vis-NIR spectrum at temperatures of 23 and 80 degrees C were measured. The prepared glass showed excellent regulation efficiency on IR transmittance (Delta TIR = 3.72%), and stable luminescence trans-mittance (Delta Tlum = 0.03%). This direct scCO2 sol-gel method shows promising application in manufacturing VO2 coated smart glass with excellent thermochromic switching properties.