Nanoscale Res Lett (2010) 5:1408–1417 1413 Fig. 3 HRTEM images and indexation of SiO2 nanoparticles obtained by bioprocess: a nanoparticles obtained from rice husk b nanoparticles obtained from sugarcane bagasse crystalline structures. Figure 4b shows the diffractrogram corresponding to particles obtained from rice husk at 700 C. In spite of the high temperature, even amorphous structure is observed when bioprocess is not used and only one diffraction plane corresponding at low quartz is shown. This crystal is formed probably by temperature effect. In the same Fig. (4b), it is shown the diffractrogram corre- sponding to the samples treated with bioprocess at 700 C. In this ﬁgure, the crystalline structure is related to low quartz, trydimite and albite. Figure 4c and d show the diffractrograms corresponding to particles obtained from sugarcane bagasse. Crystalline phases are present in both procedures (with and without bioprocess). However, some diffraction planes are not the same in both processes. This allows to assume that the calcination temperature and earthworm metabolism play an important role to generate different crystalline phases that involve not only silicon and oxygen atoms, but other ele- ments take part, as well. In Fig. 4c and d, by comparing the diffractrograms (samples obtained without bioprocess at 500 and 700 C), it is possible to observe that the same crystalline phases are found: quartz (different crystallo- graphic planes) and trydimite. However, the diffractro- grams corresponding to samples obtained via bioprocess show different crystalline phases, such as: zinc phosphate, aluminum phosphate at 500 C and albite in 700 C. It is important to mention that silica shows several polyphorms depending on temperature and pressure. Thus, although bioprocess conditions employed to obtain SiO2 particles are favorable to inducing a hexagonal quartz (corroborated by X-ray diffraction), it is possible to ﬁnd others metastable polyphorms such as tetragonal arrange- ment (268–1,470 C). This structure belongs to b crysto- balite [3]. Therefore, some SiO2 nanoparticles obtained from sugarcane bagasse can be found with transitions of hexagonal to tetragonal phase. Thus, tetragonal arrange- ment does not appear in X-ray diffraction; however, in some nanoparticles characterized by HRTEM (Fig. 3b) it is identiﬁed. Diffractrograms corresponding to particles obtained from coffee husk are shown in Fig. 4e and f. Signiﬁcant changes in both processes (using bioprocess and without employing bioprocess), which are produced by temperature and metabolism in earthworms, are observed. At 500 C, by employing bioprocess, the diffraction peaks detected are related to quartz, trydimite, sanidine and magnesium nickel hydride, meanwhile without bioprocesses diffraction peaks appear, corresponding to trydimite, gypsum and calcium aluminim oxide hydrate. At 700 C, by employing bio- process, quartz, aluminim phosphate and caminite are found, meanwhile without bioprocess appears: calcium aluminim oxide hydrate, trikalsilite and quartz. 123