This paper studies the use of fruit peel biomass and waste sludge from municipal wastewater treatment plants in the metropolitan area of Monterrey, Mexico as an alternative way of generating renewable energy. Using a Plackett–Burman experimental design, we investigated the effects of temperature, inoculum source, and the C/N (Carbon/Nitrogen) ratio on dark fermentation (DF). The results indicate that it is possible to produce hydrogen using fruit peels codigested with sewage sludge. By adjusting the C/N ratio in response to the physicochemical characterization of the substrates, it was revealed that the quantities of carbohydrates and nitrogen were sufficient for the occurrence of the fermentation process with biogas production greater than 2221 ± 5.8 mL L⁻¹_Reactor and hydrogen selectivity of 23% (366 ± 1 mL H₂·L⁻¹_Reactor) at the central point. The kinetic parameters (H_max= 86.6 mL·L⁻¹, R_m = 2.6 mL L⁻¹ h⁻¹, and λ = 1.95 h) were calculated using the modified Gompertz model. The quantification of soluble metabolites, such as acetic acid (3600 mg L⁻¹) and ethyl alcohol (3.4 ± 0.25% v/v), confirmed the presence of acetogenesis in the generation of hydrogen.

Soot particles have been associated with respiratory diseases and cancer. To decrease these emissions, perovskite-mixed oxides have been proposed due to their thermal stability and redox surface properties. In this work, SrTiO₃ doped with different amounts of Mn were synthesized by the hydrothermal method and tested for soot combustion. Results show that at low Mn content, structural distortion, and higher O_ads/O_lat ratio were observed which was attributed to the high content of Mn³⁺ in Ti sites. On the other hand, increasing the Mn content led to surface segregation of manganese oxide. All synthesized catalysts showed mesopores in the range of 32–47 nm. In the catalytic combustion of soot, the samples synthesized in this work lowered the combustion temperature by more than 100 °C compared with the uncatalyzed reaction. The sample doped with 1 wt % of Mn showed the best catalytic activity. The activation energy of these samples was also calculated, and the order of decreasing activation energy is as follows: uncatalyzed > Mn0 > Mn8 > Mn4 > Mn1. The best catalytic activity for Mn1 was attributed to its physicochemical properties and the mobility of the oxygen from the bulk to the surface at temperatures higher than 500 °C.

The present investigation is focused on the preparation, characterization, and photocatalytic activity evaluation of TiO₂/zeolite, WO₃/zeolite, WO₃/TiO₂/zeolite, and WO₃/TiO₂ composites. Zeolite fujasite (FAU) was synthesized by the hydrothermal method, while the semiconductor/zeolite composites by a straightforward physical mixture and calcination treatment. The photocatalytic activity of the materials was evaluated through the methyl orange (MO) degradation under near-UV irradiation (365 nm). The photocatalysts were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDX), UV–vis diffuse reflectance spectroscopy and nitrogen physisorption. Results indicated that TiO₂, WO₃, and Zeolite Y kept their crystalline phases after the preparation method. TiO₂ and WO₃ particles were distributed on zeolite surface. Also, no significant changes in the band gap energies of the photocatalysts were found. The surface area of zeolite FAU decreased with the addition of TiO₂ and WO₃. The best MO degradation under near-UV irradiation was obtained with WO₃/TiO₂ heterojunction and TiO₂ P25, no synergistic effect was found between semiconductors and zeolite FAU. Additionally, the kinetic data of the photocatalytic elimination of MO with all photocatalysts under near-UV radiation was investigated with several models: Zero-order, First-Order, Second Order, Modified Freundlich and Parabolic Diffusion, they were consistent with Modified Freundlich model. The effect of initial pH and photocatalyst weight was explored for TiO₂/Zeolite composite and it was found that the best MO degradation was obtained at natural pH of 10.3 and 0.2 g of composite was the optimal amount of photocatalyst. Finally, the positive hole formation in all photocatalysts was detected by UV–vis spectroscopy and it was discovered that the highest density of positive holes was obtained with TiO₂/zeolite composite.