A novel inorganic precipitation–peptization method for VO 2 sol and VO 2 nanoparticles preparation: Synthesis, characterization and mechanism

Influence of VO2 based structures and smart coatings on weather resistance for boosting the thermochromic properties of smart window applications

Vanadium dioxide (VO₂)-based energy-saving smart films or coatings aroused great interest in scientific research and industry due to the reversible crystalline structural transition of VO₂ from the monoclinic to tetragonal phase around room temperature, which can induce significant changes in transmittance and reflectance in the infrared (IR) range. However, there are still some obstacles for commercial application of VO₂-based films or coatings in our daily life, such as the high phase transition temperature (68 °C), low luminous transmittance, solar modulation ability, and poor environmental stability. Particularly, due to its active nature chemically, VO₂ is prone to gradual oxidation, causing deterioration of optical properties during very long life span of windows. In this review, the recent progress in enhancing the thermochromic properties of VO₂-hybrid materials especially based on environmental stability has been summarized for the first time in terms of structural modifications such as core–shell structures for nanoparticles and nanorods and thin-films with single layer, layer-by-layer, and sandwich-like structures due to their excellent results for improving environmental stability. Moreover, future development trends have also been presented to promote the goal of commercial production of VO₂ smart coatings.

VO₂ based energy saving smart coatings are of great interest in research and industry due to the reversible crystalline structural transition of VO₂ which can induce significant transmittance and reflectance changes in the infrared range.

Low-Temperature Synthesis of Vanadium Dioxide Thin Films by Sol-Gel Dip Coating Method

The vanadium dioxide (VO2) thin films were synthesized by sol-gel dipping on a glass slide substrate at low temperature of 500°C in a vacuum tube furnace at a pressure of 2 × 10−3 mbar by 2-step calcination without an intermediate gas purging. Synthesis conditions, including temperature, vacuum pressure, and calcination steps in the vacuum tube furnace, were investigated to find the optimum condition that promoted the formation of VO2 phase. It was found that the 2nd calcination step was very important in realizing the monoclinic vanadium dioxide (VO2 (M)). The results of the valence electron analysis revealed the outstanding phase of VO2 and a small amount of V2O5 and V2O3 phases. The small crystallites of the VO2 were homogeneously distributed on the surface, and the grain was of an irregular shape of ∼220−380 nm in size. The film’s thickness was in a range of 69−74 nm. The film exhibited a metal-to-insulator transformation temperature of ∼68oC and good thermochromic property. Visible optical transmittance remained at ∼40−50% when the sample’s temperature changed from 25 to 80°C for a near infrared (NIR) region.

Preparation of Ni-Doped Li2TiO3 Using an Inorganic Precipitation–Peptization Method

The precursor for a lithium-ion sieve is prepared using an inorganic precipitation-peptization method with titanium sulfate as the titanium source and lithium acetate as the lithium source. The effects of Ni2+ (Nickel ions) doping on the stability of the sol, crystal morphology and interplanar spacing of Li2TiO3 are investigated. The results indicate that, after Ni2+ doping with varying fractions, the stability of the precursor sol first increases then decreases, and the maximum stabilization time of the precursor sol doped with 1% Ni2+ is 87 h. When doped with 1% Ni2+, the sol performance is most stable, the porous Li2TiO3 is obtained, and the specific surface area of Li2TiO3 increases by up to 1.349 m2/g from 0.911 m2/g. Accompanying the increase in calcination temperature, the inhibition of Ni2+ doping on the growth and crystallization of grains decreases. When the temperature is lower than 750 °C, Ni atoms replace the Ti atoms that are substituted for Li atoms in the original pure Li layer, forming lattice defects, resulting in the disappearance of (002) and (−131) diffraction peaks for Li2TiO3, the reduced ordering of crystal structure, a decrease in the interplanar spacing of the (002) plane, lattice expansion and an increase in the particle size to 100–200 nm. When the temperature exceeds 750 °C, with the increase of calcination temperature, the influence of Ni doping on the growth and crystallinity of grains decreases, and the (002) crystal surface starts to grow again.

A novel study on preparation of H2TiO3–lithium adsorbent with titanyl sulfate as titanium source by inorganic precipitation–peptization method

A peroxy lithium titanate sol was prepared with low-cost and easily available titanyl sulfate as the titanium source, lithium acetate as the lithium source, and aquae hydrogenii dioxidi as the complexing agent using an inorganic precipitation–peptization method. The sol system was aged, centrifugal-washed, dried and calcined to obtain a pure precursor, Li₂TiO₃, followed by pickling with hydrochloric acid to obtain the H₂TiO₃–lithium adsorbent. The effects of aging time and calcination temperature on the target product were investigated. The results indicate that the sol-system is stable, which is beneficial for loading on a suitable carrier, such as ceramic foams. Centrifugal-washing, instead of vacuum filtration-washing, is conducive to product formation. The most suitable aging time of precursor sol is 24 h and the appropriate calcination temperature is 750 °C. The lithium drawn-out ratio of samples synthesized in this condition reaches 89.50% after pickling with 0.2 M hydrochloric acid for 8 h at 70 °C. Moreover, the Li⁺ uptake of the adsorbent (adsorption capacity) reaches 29.96 mg g⁻¹ and 33.35 mg g⁻¹ when the adsorption time is 1 h and 8 h, respectively.

A peroxy Li₂TiO₃ sol was prepared with low-cost TiOSO₄ as titanium source, CH₃COOLi as lithium source, and H₂O₂ as complexing agent by inorganic precipitation–peptization method.