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Biotemplating technique allows the synthesis of catalysts, recreating the sophisticated structure of nature templates. In this work, some biotemplated TiO2 semiconductors were synthesized using Olea europaea leaves as templates. Then, g-C3N4 was coupled to materials to later incorporate Pt on the surface or as dopant in the structure to evaluate the efficiency of the solids in two photocatalytic applications to valorize biomass: hydrogen production through glycerol photoreforming, and photoacetalization of cinnamaldehyde with 1,2-propanediol. In glycerol photoreforming, the presence of Pt (superficial or dopant) enhanced hydrogen production, being Pt@AOLCN (a heterojunction containing biotemplated TiO2, g-C3N4, and Pt) the system that exhibited the highest efficiency (3053.4 µmol·gcat−1·h−1). For photoacetalization, while Pt reduced cinnamaldehyde conversion, it improved selectivity when incorporated on TiO2. Notably, carbon nitride (CN) exhibited the highest yield after 16 h of testing. The study emphasizes the importance of tailoring catalyst selection to specific reactions, as efficiency is closely tied to the structural and chemical properties of the materials. These findings contribute to the development of efficient photocatalysts for sustainable biomass valorization processes. [ABSTRACT FROM AUTHOR]

Pt-TiO2 systems are the most widely used photocatalysts in the production of green hydrogen from glycerol photoreforming. To incorporate metals on the surface of materials, photodeposition is the most used method because it employs mild conditions. However, despite its use, there are some parameters that have not been deeply studied, such as the appropriate metal loading and the method itself, to obtain a better dispersion of Pt. In this work, six Pt-TiO2 catalysts were synthesized by a classical photodeposition method employing UV radiation. The studied Pt wt.% range was 0.15–0.60 wt.%, being incorporated in one step or in subsequent ones. HRTEM analyses showed that both methods allowed a homogeneous distribution of Pt, and in both, the particle size was around 2.3–3.6 nm, increasing with metal loading. The photocatalytic activity of materials was tested in glycerol photoreforming under UV radiation, and the 0.45 wt.% Pt-containing solid that had been synthesized in one step was the one that allowed the highest hydrogen production. This might suggest that around 0.40% is the appropriate metal loading for hydrogen production under these conditions and that incorporating the desired metal percentage in one step is the most efficient method in terms of energy and time savings. [ABSTRACT FROM AUTHOR]

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/gTiO2, 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. [ABSTRACT FROM AUTHOR]

Hydrogen production is mainly based on the use of fossil fuels, but currently, many alternative routes are being developed, among which the photo-reforming of oxygenated organic compounds stands out. Recently, several studies have been carried out in order to develop new techniques to create bio-inspired TiO2 structures. One of these is 'biotemplating', a process that replicates a biological system in an inorganic TiO2-based structure. In this study, olive by-products—olive leaves—are valorized as a biotemplate for the synthesis of new Fe-TiO2- and Cu-TiO2-based photocatalysts with the aim of improving the replication of the leaf structure and enhancing hydrogen photoproduction. In conclusion, the incorporation of iron and copper decreases the band gap and increases the energetic disorder at the band edges. Moreover, it is verified by SEM and TEM that the metals are not found forming particles but are introduced into the formed TiO2 structure. The accuracy of the internal and external structure replication is improved with the incorporation of Fe in the synthesis, while the incorporation of Cu substantially improves the production of hydrogen, which is multiplied 14 times under UV light and 6 times under sunlight, as compared to a pure TiO2 structure. [ABSTRACT FROM AUTHOR]

Platinum was incorporated onto titania-mesoporous carbon composite and tested for glycerol photoreforming. The relative high surface area of the mesoporous carbon favored the good dispersion of anatase titania during sol-gel process, whereas photodeposition led to preferential incorporation of platinum onto titania. Dispersion of titania (ca. 18.4 wt%) on mesoporous carbon and subsequent photodeposition of platinum (ca. 1.3 wt%) led to the Pt/TiO 2 -MCH catalyst that exhibited a hydrogen production, expressed per gram of titania, three times higher than Pt/TiO 2 (863 mmol /gTiO 2 and 274 mmol /gTiO 2 , respectively, after 12 h). Reutilisation studies showed that there is a progressive loss in activity accompanied by an increase in H 2 /CO 2 ratio. This suggests that reaction intermediates adsorbed on titania hinder light absorption and thus promotion of electrons from its conduction to the valence band (and then to platinum) which leads to a decrease in both glycerol oxidation and hydrogen production. Reduction in CO 2 production is greater than that on H 2 , thus accounting for the observed increase in H 2 /CO 2 ratio with reuses. A study starting from different glycerol in water concentrations (in the 0.01–10% v/v range) showed that hydrogen production rate increases with concentration up to 1% v/v, higher values mainly resulting in an increase in H 2 /CO 2 ratio. [Display omitted] • Highly dispersed TiO2 nanocrystals were homogeneously supported on Carbon material. • Pt preferential incorporation on TiO2 phase in TiO2-Carbon composites was attained. • High hydrogen production capability was obtained with Pt/TiO2-Carbon composites. • Deactivation was associated to adsorption of reaction intermediates on TiO2 phase. • Catalyst reuses showed a progressive deactivation with an increase of H2/CO2 ratio. [ABSTRACT FROM AUTHOR]

Different CuO nanoparticles were synthesized and tested in CuO:TiO 2 physical mixtures for hydrogen production through glycerol photoreforming. CuO alone was inactive whereas its presence in CuO:TiO 2 mixtures significantly improved the photoactivity of TiO 2 , with smaller CuO nanoparticles leading to higher hydrogen productions. Results obtained through combination of EPR and CV studies suggested the existence of a Cu(II)-Cu0 catalytic cycle. Thus, electrons promoted to the conduction band of titania could be used for CuO reduction to Cu which in turn would enable hydrogen production regenerating Cu2+ for a new catalytic cycle. All in all, a hydrogen production of 88 mmol·g−1 was obtained after 5 h on a CuO:TiO 2 (10% w/w) physical mixture which is comparable to that achieved in a previous study under identical reaction conditions on 1.5%Pt/TiO 2. [Display omitted] • H 2 production via glycerol photoreforming enhanced on CuO:TiO 2 physical mixtures. • H 2 production values in the same order as those found for supported noble metals. • EPR studies evidenced the formation of Cu(I) or Cu0 species on UV irradiation. • CV studies suggested the existence of a CuO to Cu(0) photocatalytic cycle. • Electrons for H 2 generation are first transferred from titania to copper species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Olive leaf structure successfully replicated in TiO 2 -CuO composites. • There is an optimum surface Cu/(Ti + Cu) mol % close to 17 for glycerol photoreforming. • H 2 production of bare TiO 2 was multiplied by 84 through TiO 2 -CuO heterojunction. Olive leaves were used as biotemplates to synthesize diverse TiO 2 -CuO solids. A successful replication of trichomes and internal channels was evidenced by SEM, whereas a good dispersion of Cu and Ti atoms was observed by EDX. The systems consisted in pure anatase titania, with monoclinic CuO detected by XRD and Raman for large copper contents (over 15 wt%). XPS evidenced the existence of a TiO 2 -CuO strong interaction. Incorporation of copper resulted in an enhancement of photocatalytic activity, hydrogen production being 84 times higher with the best TiO 2 -CuO system than with bare titania. It seems that there is a maximum surface copper content (close to a Cu/(Ti + Cu) mol % value of 17) above which CuO particles could promote electron-hole recombination and/or have a shielding effect thus preventing light absorption by titania. The smaller the CuO crystallite sizes the better their reducibility and the catalytic performance of the systems under solar light irradiation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Olive leaves (by-product from olive oil production in olive mills) were used as biotemplates to synthesize a titania-based artificial olive leaf (AOL). Scanning electron microscopy (SEM) images of AOL showed the successful replication of trichomes and internal structure channels present in olive leaves. The BET surface area of AOL was 52 m2·g−1. X-ray diffraction (XRD) and Raman spectra revealed that the resulting solid was in the predominantly-anatase crystalline form (7.5 nm average particle size). Moreover, the synthesis led to a red-shift in light absorption as compared to reference anatase (gap energies of 2.98 and 3.2 eV, respectively). The presence of surface defects (as evidenced by X-ray photoelectron spectroscopy, XPS, and electron paramagnetic resonance spectroscopy, EPR) and doping elements (e.g., 1% nitrogen, observed by elemental analysis and XPS) could account for that. AOL was preliminarily tested as a catalyst for hydrogen production through glycerol photoreforming and exhibited an activity 64% higher than reference material Evonik P25 under solar irradiation and 144% greater under ultraviolet radiation (UV). [ABSTRACT FROM AUTHOR]

In this work, photocatalysts consisting of TiO 2 supported on zeolite (USY62) were synthesized by sol-gel method and, subsequently, a noble metal (Pt, Au, or Ag) was incorporated by impregnation or photodeposition. Zeolite-TiO 2 composites were characterized by SEM, TEM, XRD, N 2 adsorption-desorption, Raman and UV–vis spectroscopy, and well-dispersed anatase TiO 2 particles (ca. 10 nm) that exhibited a blue-shift in the UV–vis absorption due to the size quantization effect were produced. The photocatalytic activity of all zeolite-TiO 2 composites was examined by the photoreforming of aqueous glycerol solution (10% w/w) under UV and solar-simulated radiation. The activity of the zeolitic photocatalysts decreased in the order Pt > Au > Ag, being catalysts prepared by photodeposition more active than those prepared by impregnation. Moreover, Zeolite-supported TiO 2 , led to a TiO 2 with smaller deactivation in H 2 production than unsupported TiO 2 , which can be ascribed to the small TiO 2 particle size or an interaction zeolite-TiO 2. All in all, a photocatalyst (USY-Ti-PPt) with TiO 2 up to four times more active than unsupported TiO 2 under UV radiation was prepared. [Display omitted] • Zeolite-supported TiO 2 of ca. 10 nm was prepared by sol-gel method • Zeolite structure was maintained after the incorporation of TiO 2 and noble metal • H 2 production via glycerol photoreforming was studied on zeolite-TiO 2 composites • Supported TiO 2 was up to 4-times more active than unsupported TiO 2 in H 2 production • Zeolite-supported TiO 2 had a smaller deactivation than TiO 2 in H 2 production [ABSTRACT FROM AUTHOR]

In the present piece of research, hydrogen production via the photo-reforming of glycerol (a byproduct from biodiesel generation) is studied. Catalysts consisted of titania modified by Ni (0.5% by weight) obtained through deposition–precipitation or impregnation synthetic methods (labelled as Ni-0.5-DP and Ni-0.5-IMP, respectively). Reactions were performed both under UV and solar irradiation. Activity significantly improved in the presence of Ni, especially under solar irradiation. Moreover, pre-reduced solids exhibited higher catalytic activities than untreated solids, despite the "in-situ" reduction of nickel species and the elimination of surface chlorides under reaction conditions (as evidenced by XPS). It is possible that the catalyst pretreatment at 400 °C under hydrogen resulted in some strong metal–support interactions. In summary, the highest hydrogen production value (ca. 2600 micromole H2·g−1) was achieved with pre-reduced Ni-0.5-DP solid using UV light for an irradiation time of 6 h. This value represents a 15.7-fold increase as compared to Evonik P25. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen production using two sacrificial agents (triethanolamine and glycerol) was conducted on several binary (Pt/TiO 2 and Pt/g-C 3 N 4) and ternary systems (Pt on a heterojunction between TiO 2 and g-C 3 N 4 (Pt/(g-C 3 N 4 -TiO 2) and on a physical mixture of semiconductors (Pt/(TiO 2 +g-C 3 N 4)). Reactions were carried out under visible light (450 nm) and UV (365 nm) radiation, from 10% (v/v) and 0.5% (v/v) sacrificial agent aqueous solutions, hydrogen production values being ca- 2–3 times greater in the former case. For visible light, the heterojunction was the most active system using triethanolamine whereas Pt/TiO 2 system and glycerol was the best option under UV radiation. All in all, the highest hydrogen production value from a 10% (v/v) glycerol in water solution was on Pt/TiO 2 (named Ptuv/Ti), under UV light, yielding around 165 mmol H 2 ·g cat −1·after 6 h (that is, ca. 27.5 mmol·g cat −1·h−1). Hydrogen photoproduction studies from glyceraldehyde, dihydroxyacetone, and glycerol either alone or in binary mixtures (i.e., competitive reactions) cast further light on the glycerol reaction mechanism. Results evidenced that the adsorption strength on the catalysts follows the sequence glyceraldehyde > dihydroxyacetone > glycerol, adsorption of the former being particularly high on the heterojunction. Reactions were ca. twice as fast on Pt/TiO 2 as on the Pt/(g-C 3 N 4 -TiO 2) heterojunction and even though initial stages of the mechanism seems to differ a bit for the semiconductors, there is a hydrogen production value from which mechanism is apparently the same on both solids. [Display omitted] • Pt-TiO 2 and a Pt-g-C 3 N 4 -TiO 2 heterojunction used in glycerol (GLY) photoreforming. • Besides, glyceraldehyde (GLAD) and dihydroxyacetone (DHA) photoreforming was studied. • Adsorption coefficients obtained from GLY/GLAD and DHA/GLAD competitive reactions. • GLAD was more adsorbed on the surface of systems, especially on the heterojunction. • Greater contribution of GLAD route in GLY photoreforming with the heterojunction. [ABSTRACT FROM AUTHOR]

Titanium (ca. 11 wt%) was dispersed on a carbonaceous mesoporous support and modified with copper (ca. 5 wt%) photodeposited using either glycerol or methanol as the sacrificial agent ((Cu-TiO 2 /MCH_(Gly) and Cu-TiO 2 /MCH_(Met) solids, respectively). In the former case, copper particles were more preferentially deposited on titania and copper nanoaggregates were more abundant than in the latter. The synthesized catalysts were tested in the glycerol photoreforming reaction and it was found that there was an increase in activity on copper photodeposition as compared to titania-mesoporous carbon composite, being higher in Cu-TiO 2 /MCH_(Gly) than in Cu-TiO 2 /MCH_(Met) (5 and 4 times, respectively). Nevertheless, copper present in Cu-TiO 2 /MCH_(Gly) redisperses as reaction proceeds, the catalyst exhibiting a more similar activity to Cu-TiO 2 /MCH_(Met) after one use. An additional reason for catalyst deactivation is strong adsorption of reaction intermediates. In this sense, competitive reactions with glycolic and glyceric acid (two of the intermediates identified by HPLC-DAD/RID) and glycerol gave some hints on reaction mechanism which could also be helpful for future identification of the species responsible for the catalysts deactivation. [Display omitted] • Cu was photodeposited on TiO 2 /carbon with methanol or glycerol as sacrificial agent. • H 2 production had a 4–5 fold increase when Cu was incorporated. • The use of glycerol led to a higher aggregation of Cu compared to methanol. • Cu was more selectivity deposited on TiO 2 using glycerol, compared to methanol. • The presence of oxidation intermediates slows down the production of H 2. [ABSTRACT FROM AUTHOR]

Platinum (0.5 wt. %) was photodeposited on g-C 3 N 4 -TiO 2 systems using UV or Vis light. Different absorption by semiconductors seemed to somehow influence resulting platinum particle size and distribution. Thus, lower platinum particle sizes were obtained on g-C 3 N 4 utilizing visible light and on TiO 2 using UV radiation. Furthermore, there was a preferential platinum photodeposition on g-C 3 N 4 or TiO 2 , more evident in physical mixtures of both semiconductors, depending on radiation source being visible or UV light, respectively. The solids were tested for hydrogen photoproduction using triethanolamine as the sacrificial agent. g-C 3 N 4 synthesis on P25 TiO 2 allowed the effective formation of a heterojunction (as determined by UV–vis and EPR). Subsequent platinum photodeposition resulted in solids yielding ca. 5100 μmol·g−1·h−1 H 2 under visible light. This represents a ca. 7-fold increase in activity as compared to the physical mixture of platinum-containing semiconductors and a 2-fold increase as compared to simultaneous incorporation of platinum to the reaction medium. [Display omitted] • Platinum was photodeposited on g-C 3 N 4 -TiO 2 systems using UV or visible light. • Preferential Pt deposition on g-C 3 N 4 or TiO 2 with Vis or UV light respectively. • Platinum nanoparticle size and distribution was dependent on the used light source. • Heterojunctions yielded 5.1 mmol·H 2 ·g−1 h−1 using TEOA and visible light. • Prior photodeposition of Pt doubled H 2 production compared to in-situ deposition. [ABSTRACT FROM AUTHOR]

The photoelectrocatalytic (PEC) glycerol oxidation has emerged as a promising technology for the simultaneous valorization of this biomass waste and hydrogen production. Herein, we report the enhancement of the photocatalytic (PC) activity and stability of a monoclinic WO 3 catalyst, by means of an external bias, for the selective generation of value-added C 3 products under near-neutral conditions. Glyceraldehyde and dihydroxyacetone production were increased up to 4.5 and 11.5 times, respectively, while maintaining a liquid selectivity of these C3s above 87% and a stable faradaic efficiency above 50% of the additional holes generated, in a wide potential range (0.5–2.0 V vs. RHE). Indeed, the photo- and electro-catalytic contributing effects are unravelled for the first time herein. The photoelectrocatalytic mechanisms on WO 3 and WO 3 /TiO 2 are discussed, as well as the key role of the sub-stoichiometric WO 3−x content and the oxygen vacancies, which confer advantageous properties for the selective PEC valorization of glycerol. [Display omitted] • WO 3−x photoanodes selectively valorize glycerol at ambient and neutral conditions. • Glyceraldehyde/DHA production is boosted by PEC with selectivity up to 87%. • The PEC mechanism at the electrolyte/reactant/electrode interface is unraveled. • Above 50% of potential-driven holes are employed for targeted C 3 s at 0.3–1.5 V. • WO 3−x has promising properties for sustainable solar-to-chemical energy conversion. [ABSTRACT FROM AUTHOR]