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Copper oxide (CuO) is an abundant and low-cost material, which is active as a photocatalyst under visible light due to its narrow band gap (1.3 eV). In the present work, CuO thin films at different Ni doping amounts (5, 10, and 30 % mol) were prepared using two different techniques: dip-coating and electrodeposition of Cu precursors over glass and PET substrates. X-Ray analysis results indicate the presence of Cu2O, CuO and Cuo phases in PET substrate films, while only CuO phase in Glass-substrate films. Glass substrate films presented a higher formic acid production performance reaching 50,000 μmol/g·h using 5% Ni doping on CuO. This higher activity was associated with a lower ratio between the adsorbed oxygen and the oxygen located in the crystal lattice, attributing this to the oxygen species adsorbed over the surface that could hinder the active sites of the material. Finally, PET substrate samples present a higher ratio between adsorbed oxygen and lattice oxygen, however, the Cu2O phase presents less affinity to adsorb CO2 molecules than CuO monoclinic phase reducing the photoactivity of the CO2 photoreduction. Majority charge carrier mobility of 4 cm2/Vs and 35 cm2/Vs for Cu2O and CuO respectively, with the charge carrier concentration of ∼1 × 1019 order was achieved switching the conducting type.

To date, synthesis of visible light-active materials for photocatalytic water splitting is a promising challenge for future applications, e.g., photocatalytic reactors for hydrogen production with solar energy. Type p-n heterojunctions are an alternative to improve electronic properties of pure phase semiconductors and achieve a higher hydrogen production with photocatalytic water splitting. In this work, heterojunctions of NiFe2O4/Cu2O at mass percentages of 75/25, 50/50 and 25/75, are generated by impregnation method and thermal annealing starting from pristine materials NiFe2O4 and Cu2O synthesized by Pechini's method and Benedict's reaction respectively. A photocatalytic evaluation for hydrogen production was performed by means of gas chromatography for pristine and heterojunctions in order to correlate their textural, structural, chemical and electronic properties with their photocatalytic activity, finding a direct correlation between charge carrier concentration and hydrogen production. Finally, the material that exhibited higher hydrogen production was the 50/50 ratio with a production 120 times greater at 24 h in comparison with pristine photocatalysts.

Ternary of titania-based composites were prepared in two steps. First, pure and nitrogen-doped titanium dioxide powders were obtained using Pechini´s method. Then, these powders were impregnated with 3% wt. of cerium and copper oxide particles. The X-ray diffraction characterization shows the presence of rutile and anatase phases. The morphological characterizations exhibited some CuO agglomeration that resulted in a limited dispersion. Nitrogen-doped composite materials present better surface area due to the synergy effect of the urea precursor employed in their synthesis. UV–Vis analysis shows a redshift displacement for double and triple composites related to enhancing light absorption. XPS characterization made it possible to identify a mixed-valence state of Ti associated with the presence of oxygen vacancies, which presumable are responsible for the increase of adsorption of interest molecules. N-TiO2/CuO presents the highest formic acid production (33 µmol g−1 min-1) attributed to a better capacity to adsorb CO2 molecules and the formation of a Z-scheme where charges are spatially separated. The addition of CeO2 co-catalyst decreases formic acid performance due to its inherent ability to adsorb CO3−2 and OH ions that could hinder available active sites. On the other hand, in the case of hydrogen production, N-TiO2/CeO2/CuO material exhibited the highest production due to its highest Ti3+/Ti4+ valence state ratio, which presumably increases available active sites for molecular water adsorption and consequently for transformation into H2.

This study is aimed at the analysis of the pyrolysis kinetics of Nanche stone BSC (Byrsonima crassifolia) as an agro-industrial waste using non-isothermal thermogravimetric experiments by determination of triplet kinetics; apparent activation energy, pre-exponential factor, and reaction model, as well as thermodynamic parameters to gather the required fundamental information for the design, construction, and operation of a pilot-scale reactor for the pyrolysis this lignocellulosic residue. Results indicate a biomass of low moisture and ash content and a high volatile matter content (≥70%), making BCS a potential candidate for obtaining various bioenergy products. Average apparent activation energies obtained from different methods (KAS, FWO and SK) were consistent in value (~123.8 kJ/mol). The pre-exponential factor from the Kissinger method ranged from 105 to 1014 min−1 for the highest pyrolytic activity stage, indicating a high-temperature reactive system. The thermodynamic parameters revealed a small difference between EA and ∆H (5.2 kJ/mol), which favors the pyrolysis reaction and indicates the feasibility of the energetic process. According to the analysis of the reaction models (master plot method), the pyrolytic degradation was dominated by a decreasing reaction order as a function of the degree of conversion. Moreover, BCS has a relatively high calorific value (14.9 MJ/kg) and a relatively low average apparent activation energy (122.7 kJ/mol) from the Starink method, which makes this biomass very suitable to be exploited for value-added energy production.

In the present work, zinc titanates (ZTO) as photocatalysts were synthesized, characterized, and evaluated aiming to study their photocatalytic properties for hydrogen production under visible-light irradiation and employing MeOH (methanol) and TEOA (Triethanolamine) as sacrificial agents. ZTO were synthesized by modified Pechini method. Characterization of materials consisted in TGA, XRD, TEM, EELS, BET, and UV–Vis. Surface interaction studies consisted of FT-IR spectroscopy and determination of MeOH and TEOA adsorption–desorption capacities on the ZTO by TGA. Zinc titanates were evaluated as photocatalyst for H2 production using an artificial visible light and monitored by GC. TGA results led to establish calcination temperatures of 550 °C (Zn2Ti3O8) and 700 °C (ZnTiO3) to reach their crystalline phases. XRD analysis of sample cds-ZTO found cubic Zn2Ti3O8 and traces of the ZnO crystalline phase, while p-ZTO exhibited a mixture of cubic and hexagonal ZnTiO3 crystalline phases. Surface area for cds-ZTO was 88 m2/g, while ZnTiO3 had 13 m2/g. Photocatalytic H2 production for cds-ZTO and p-ZTO using TEOA as sacrificial agent showed the highest photocatalytic activities generating 548 and 441 µmolH2/h.gcat. TEOA adsorption–desorption capacity was found superior on cds-ZTO and p-ZTO than that for MeOH on both samples.