Nanoscale Res Lett (2010) 5:1408–1417 1411 Fig. 1 IR bands to synthesis of nanoparticles SiO2 obtained for vermicompost. The Figure show the bands more representatives to SiO2 to in rice husk, sugarcane bagasse and coffee husk at temperature of calcination: 500, 600 and 700 C. Representative bands for Aerosil 130 too are shown bioprocesses employed contribute to reduce the size in SiO2 particles. We suggest that this size reduction is induced in earthworm gut with the contribution from sev- eral microorganisms. Figure 3 a–b shows HRTEM images of SiO2 particles obtained through bioprocess. In these images, it is possible appreciate the SiO2 particles in an atomic scale. Nanometric size and crystal structure are observed in these images. Thus, it is shown that these particles present as well a crystalline structure contrary to amorphous synthetic SiO2. In addition, the Fig. 3 shows the diffraction patterns and Miller index corresponding with these structures in a selected area (A). Figures show the nanoparticles obtained from the precursors that contain a higher content of SiO2, such as rice husk (Fig. 3a) and sugarcane bagasse (Fig. 3b). The indexation of nanoparti- cles obtained from rice husk shows SiO2 with crystal arrangement related to a hexagonal quartz with the next lattice parameters: 0.340 nm (1-1 0 0), 0.243 nm (1 1-2 0) and 0.198 nm (2 0-2 0). In the case of nanoparticles obtained from sugarcane bagasse, SiO2 posses a tetragonal arrangement with the next lattice parameters: 0.200 nm (2 0 0), 0.199 nm (0 2 0) and 0.142 nm (2 2 0). In accord with these results, it is possible to suppose an important con- tribution of the vermicompost bioprocess in order to give crystalline phases in SiO2 nanoparticles. In order to conﬁrm the TEM and HRTEM results, par- ticle size was analyzed employing dynamic light scattering (DLS). The results obtained by this technique are sum- marized in Table 1. The mean diameter of particles synthesized employing bioprocess is around 81 nm and do not show polydispersity. In contrast, the mean diameter of particles synthesized without using bioprocess is between 152 and 254 nm with low polydispersity. This is in agreement with TEM and HRTEM images and conﬁrms the contribution of bioprocess in particle size reduction to achieve a nanometric range. It is important to emphasize the presence of agglomerates in the particles obtained without biotransformation, which are not observed in the particles obtained by employing bioprocess. Thus, as well as the bioprocess contribution to particle size reduction also provides speciﬁc arrangement to the particles. It is suggested that this effect is produced by the microorgan- isms which are part of metabolism in the earthworm. The size and morphology of particle in the biosiliﬁcation pro- cess are related with the concentration of inorganic phos- phate and polyamines, both compounds play an important role in order to catalyze the polycondensation of silanol groups [46]. In vermicompost, the concentrations of these compounds vary with the microbial population. Thus, it is supposed that the size and morphology of SiO2 nanopar- ticles could be changed in this kind of bioprocess. Table 2 shows the elemental analysis for SiO2 particles synthesized by bioprocess; a signiﬁcant amount of silicon and oxygen weight percent is observed in all samples obtained with the precursors employed: 41.62% Si and 52.90% O for particles obtained from rice husk; 23.37% Si and 42.37% O in particles synthesized from sugarcane bagasse and 41.68% Si and 55.39% O to particles extracted from coffee husk. Also, in the composition are observed other elements with lower percent than silica and oxygen, such as sodium, magnesium, aluminum, potassium and calcium. These elements are typical in the biomineraliza- tion process and take part in the crystalline phases growing that are produced with this biological mechanism. Figure 4 shows the diffractrograms generated from the particles obtained using the three precursors: rice husk (a–b), sugar cane bagasse (c–d) and coffee husk (e–f). Crystalline nanoparticles are obtained using two different calcination temperatures: 500 C (a, c and e) and 700 C (b, d and f). Figure 4a shows the diffractrogram corresponding to particles obtained from rice husk at 500 C. In this ﬁgure, it is observed an amorphous structure when the bioprocess is not used during the synthesis. In contrast, crystalline phases are found when the bioprocess is employed. In this diffractrogram, it is possible to identify typical peaks cor- responding to diffraction planes from quartz and other polymorphic structures of SiO2, such as trydimite. Also, erionite and albite diffraction planes corresponding to aluminum silicate groups are found. These results support the proposal that biomineralization mechanism is achieved through earthworms contributing in the atomic arrange- ment and modifying the original structure toward speciﬁc 123