Among the agro-industrial residues, the rice husk has stood out for presenting contents higher than 90% of silica, the main oxide of bioglass. Thus, the objective of this research was to compare the use of two different sources of silica, tetraethylorthosilicate (TEOS) and rice husk ash (RHA), in the sol-gel synthesis of the bioglass of the SiO 2 -CaO-Na 2 O system. For the silica extraction, the rice husk was treated with oxalic acid and calcined at 600 °C. This temperature was determined using thermogravimetry and the calcined powder was analyzed by X-ray diffraction and X-ray fluorescence spectroscopy, proving the achievement of highpurity amorphous silica. In the production of the bioglass, the solution made with the rice husk showed great synthesis efficiency, and the powder calcined was evaluated by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and scanning electron microscopy. FTIR spectra presented characteristic bands of siloxane (Si-O-Si) bonds, which indicated a vitreous network and provided the formation of silanol groups, fundamentals for the growth of the hydroxyapatite layer. The microstructures of the samples were similar, but the sample made from RHA (BRHA) presented porous agglomerates, while the BTEOS had smaller and well-defined particles. The silica obtained from rice husk showed potential to be used in the sol-gel synthesis of bioglass.

The coordination of the anticancer drug mithramycin to Tb(III), Fe(II1) and Cu(II) was studied in aqueous solution using absorption measurements. The stability constants were calculated from equilibrium competition experiments by means of the SQUAD program. For both first ions. the compebtor was oxalic acid and for the latter the competitor was the Cu(II) ions. Cu(I1) at pH 7.5, Fe(II1) at pH 3.5 and Tb(II1) at pH 5.5 formed respectively 1:2, 1:3 and 1:4 metal-to-ligand species.

The rice husk, agro-industrial residue, stands out for having silica, the main oxide former of the bioactive glass. To avoid contamination in this biomaterial, substances with bactericidal properties, like silver can be incorporated. Thus, the objective of this work is the synthesis of silver nanoparticles to functionalize a bioactive glass synthesized from rice husk ash (BRHA). The bioglass was prepared by the sol-gel method from the rice husk ash as a silica source. Silver nanoparticles were synthesized from thyme extract with AgNO 3 and their formation was verified by UV-vis spectroscopy. The glass powder was added to this solution and its structure was evaluated by SEM-EDS, ATR-FTIR, and microbiology. The bioglass powder appeared in the form of porous agglomerates and the addition of silver altered its superficial roughness by deposition. The chemical bonds of the glass network related to bioactivity were maintained after the incorporation of the nanoparticles. Microbiological analysis by the agar diffusion test confirmed the inhibitory action of the nanoparticles for P. aeruginosa and S. aureus. Therefore, the developed material presented great potential for biomedical applications.

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