This article explores the effect of the synthetic method of titanium dioxide (TiO₂)/C composites (physical mixture and the water-assisted/unassisted sol-gel method) on their photocatalytic activity for hydrogen production through glycerol photoreforming. The article demonstrates that, apart from a high surface area of carbon and the previous activation of its surface to favor titania incorporation, the appropriate control of titania formation is crucial. In this sense, even though the amount of incorporated titania was limited by the saturation of carbon surface groups (in our case, ca. 10 wt.% TiO₂), the sol-gel process without water addition seemed to be the best method, ensuring the formation of small homogeneously-distributed anatase crystals on mesoporous carbon. In this way, a ca. 110-fold increase in catalyst activity compared to Evonik P25 (expressed as hydrogen micromole per grams of titania) was achieved.

Several biochars were synthesized from olive stones and used as supports for TiO₂, as an active semiconductor, and Pt as a co-catalyst (Pt/TiO₂-PyCF and Pt/TiO₂-AC). A third carbon-supported photocatalyst was prepared from commercial mesoporous carbon (Pt/TiO₂-MCF). Moreover, a Pt/TiO₂ solid based on Evonik P25 was used as a reference. The biochars used as supports transferred, to a large extent, their physical and chemical properties to the final photocatalysts. The synthesized catalysts were tested for hydrogen production from aqueous glycerol photoreforming. The results indicated that a mesoporous nature and small particle size of the photocatalyst lead to better H₂ production. The analysis of the operational reaction conditions revealed that the H₂ evolution rate was not proportional to the mass of the photocatalyst used, since, at high photocatalyst loading, the hydrogen production decreased because of the light scattering and reflection phenomena that caused a reduction in the light penetration depth. When expressed per gram of TiO₂, the activity of Pt/TiO₂-PyCF is almost 4-times higher than that of Pt/TiO₂ (1079 and 273 mmol H₂/g_TiO2, respectively), which points to the positive effect of an adequate dispersion of a TiO₂ phase on a carbonaceous support, forming a highly dispersed and homogeneously distributed titanium dioxide phase. Throughout a 12 h reaction period, the H₂ production rate progressively decreases, while the CO₂ production rate increases continuously. This behavior is compatible with an initial period when glycerol dehydrogenation to glyceraldehyde and/or dihydroxyacetone and hydrogen predominates, followed by a period in which comparatively slower C-C cleavage reactions begin to occur, thus generating both H₂ and CO₂.

In this paper the development of a potentiometric biosensor based on the use of the enzyme lipase immobilized in a Nafion membrane on a graphite-epoxy transducer is reported. This device has been used to quantify triglycerides in food samples from the aqueous extracts obtained by emulsion with Arabic gum. The proposed methodology does not present significant differences with the spectrophotometric determination used as contrast. This work constitutes the first report of a potentiometric biosensor based on the detection of changes of pH using a graphite-epoxy composite transducer and the first potentiometric triglyceride biosensor which is not based in ISFET transducers. The methodology designed is a simple and inexpensive alternative that minimizes the use of organic solvents without affecting the precision and accuracy of the analysis in complex food samples such as butter, chips and pastries.