An Evonik P25 TiO₂ material is modified using a porphyrin containing Si-(OR)₃ extremities to extend its absorption spectrum in the visible range. Two different loadings of porphyrin are grafted at the surface of P25. The results show that the crystallinity and the texture of the P25 are not modified with the porphyrin grafting and the presence of the latter is confirmed by Fourier-transform infrared spectroscopy (FTIR) measurements. All three samples are composed of anatase/rutile titania nanoparticles around 20 nm in size with a spherical shape. The absorption spectra of the porphyrin modified samples show visible absorption alongside the characteristic Soret and Q bands of porphyrin, despite slightly shifted peak values. The ²⁹Si solid state nuclear magnetic resonance (NMR) spectra show that the porphyrin is linked with Ti–O–C and Ti–O–Si bonds with the Evonik P25, allowing for a direct electron transfer between the two materials. Finally, the photoactivity of the materials is assessed on the degradation of a model pollutant—p-nitrophenol (PNP)—in water. The degradation is substantially enhanced when the porphyrin is grafted at its surface, whereas a very low activity is evidenced for P25. Indeed, with the best sample, the activity increases from 9% to 38% under visible light illumination. This improvement is due to the activation of the porphyrin under visible light that produces electrons, which are then transferred to the TiO₂ to generate radicals able to degrade organic pollutants. The observed degradation is confirmed to be a mineralization of the PNP. Recycling experiments show a constant PNP degradation after 5 cycles of photocatalysis of 24 h each.

The present work investigates the enhancement effect of seven different catalysts made of Cu/SiO₂, Pd/SiO₂, Pt/SiO₂, Ni/SiO₂, Co/SiO₂, Ag/SiO₂ and Fe/SiO₂ nanoparticles (NPs) on methane production during thermophilic anaerobic digestion. The tested NPs were synthesized by the sol-gel process and encapsulated in porous silica (SiO₂) to prevent their coagulation and agglomeration. Transmission electron microscopy (TEM) pictures confirmed the specific morphologies of all seven catalysts.

Then, these 7 NPs were tested first in batch experiments with acetate as a carbon substrate for bio-methane production. Ni/SiO₂ and Co/SiO₂ showed the best enhancement of methane production from acetate. From this part, both NPs were tested for bio-methane production on two different substrates: starch and glucose. With the starch substrate, the improvements of methane production were equal to 47% and 22%, respectively, for Ni- and Co/SiO₂ compared to control sample. In the last part of this work, the influences of NP concentration and thermal pre-treatment applied to the NPs on bio-methane production from glucose were investigated. The results showed that all forms of nickel and cobalt NPs enhance the methane production, and their effect increased with the increase of their concentrations. The best sample was the calcined nickel NPs at a concentration of 10^–4 mol L^–1, leading to a methane production rate of 72.5% compared to the control.