The various methods of melamine thermolysis

The relevance of this work lies in its contribution to water purification through two approaches. On the one hand, using sorbents made from foamed nanographite-structured materials, and on the other,employing eco-safe nanocomposites of carbon nitride with titanium dioxide, which is widely applied as a photocatalyst for water treatment via an advanced method: the generation of reactive oxygen species (ROS).

In the first stage of this work, the hypothesis posited that the earlier TiO₂ engages with and simultaneously synthesizes C₃N₄ during its formation , the more effective the resultant photocatalyst will be.

The first stage of this work included several steps:

1. SiO₂∙xEtOH and HₓTiᵧO₂∙H₂SO₄ sols were prepared and converted into gels: SiO₂∙8.6H₂O and TiO₂∙25.9H₂O (TGA).
2. Annealing in an inert atmosphere (3 h at 500°C; 3°C/min) was performed for melamine and its mixtures with desulfated titanyl sols: SiO₂‧8.6H₂O; TiO₂‧25.9H₂O and nano-TiO₂ P25. TGA modeling demonstrated that mass loss in the presence of TiO₂ was lower than with SiO₂.
3. AFM data revealed that the smallest particle size was observed in the thermolysis products of melamine mixtures either with the sol derived from (NH₄)₂TiO(SO₄)₂ (STA) or with the TiO₂‧25.9H₂O gel.
4. From the mixture of melamine with the STA-derived sol, semi-amorphous nanocrystalline g-C₃N₄ and rutile were formed (XRD). The mixture with the TiO₂‧25.9H₂O gel yielded the same phases, plus anatase.
5. The most effective photocatalyst for methyl orange degradation was C₃N₄ with TiO₂ from the STA-derived sol.

If, under the same temperature program, foamed melamine is subjected to thermolysis, a foamed product reproducibly crystallizes, which, according to XRD, is single-phase nanographite. The nanostructured layered morphology is confirmed by SEM. At the same time, according to CHNS analysis, this product contains carbon and 44% nitrogen. As a sorbent, this material absorbs 11 g/g of gasoline.