Photocatalytic reforming of glucose over La doped alkali tantalate photocatalysts for H2 production

Box-Behnken Design for Hydrogen Evolution from Sugar Industry Wastewater Using Solar-Driven Hybrid Catalysts

Hydrogen is a clean and green fuel and can be produced from renewable sources via photocatalysis. Solar-driven hybrid catalysts were synthesized and characterized (scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, and UV-vis diffuse reflectance spectroscopy (DSR)), and the results implied that graphene-supported LaRuO₃ is a more promising photocatalyst to produce hydrogen and was used to produce hydrogen from sugar industry wastewater. To investigate the main and interaction effects of reaction parameters (pH, catalyst amount, and [H₂O₂]₀) on the evolved hydrogen amount, the Box-Behnken experimental design model was used. The highest hydrogen evolution obtained was 6773 μmol/g_cat from sugar industry wastewater at pH 3, 0.15 g/L GLRO, and 15 mM H₂O₂. Based on the Pareto chart for the evolved hydrogen amount using GLRO, among the main effects, the only effective parameter was the catalyst amount for the photocatalytic hydrogen evolution from sugar industry wastewater. In addition, the squares of pH and two-way interaction of pH and [H₂O₂]₀ were also statistically efficient over the evolved hydrogen amount.

Hydrogen Generation over RuO2 Nanoparticle-Decorated LaNaTaO3 Perovskite Photocatalysts under UV Exposure

The efficacy of LaNaTaO₃ perovskites decoration RuO₂ at diverse contents for the photocatalytic H₂ generation has been explored in this study. The photocatalytic performance of RuO₂ co-catalyst onto mesoporous LaNaTaO₃ was evaluated for H₂ under UV illumination. 3%RuO₂/LaNaTaO₃ perovskite photocatalyst revealed the highest photocatalytic H₂ generation performance, indicating that RuO₂ nanoparticles could promote the photocatalytic efficiency of LaNaTaO₃ perovskite significantly. The H₂ evolution rate of 3%RuO₂/LaNaTaO₃ perovskite is 11.6 and 1.3 times greater than that of bare LaNaTaO₃ perovskite employing either 10% CH₃OH or pure H₂O, respectively. Interestingly, the photonic efficiency of 3%RuO₂/LaNaTaO₃ perovskite was enhanced 10 times than LaNaTaO₃ perovskite in the presence of aqueous CH₃OH solutions as a hole sacrificial agent. The high separation of charge carriers is interpreted by the efficient hole capture using CH₃OH, hence leading to greater H₂ generation over RuO₂/LaNaTaO₃ perovskites. This is attributed to an adjustment position between recombination electron-hole pairs and also the reduction of potential conduction alignment as a result of RuO₂ incorporation. The suggested mechanisms of RuO₂/LaNaTaO₃ perovskites for H₂ generation employing either CH₃OH or pure H₂O were discussed. The photocatalytic performances of the perovskite photocatalyst were elucidated according to the PL intensity and the photocurrent response investigations.

Hydrothermal preparation of novel rGO-KTaO3 nanocubes with enhanced visible light photocatalytic activity

In this study, nanocubes KTaO₃-reduced graphene oxide (rGO-KTaO₃) photocatalysts were synthesized by a facile hydrothermal method. Different technical methods were carried out to characterize the as-prepared compounds. UV-Vis spectra show that the absorption sideband of the complexes red-shift to visible light region, which enhances the light utilization. Meanwhile, X-ray photoelectron spectroscopy (XPS) reveals that the graphene oxide (GO) in the composite has been partially reduced, leading to more effective electron transport and thus improving the photocatalytic efficiency. Furthermore, photocatalytic degradation efficiency of Methylene blue (MB) and Rhodamine B (RhB) in the presence of rGO-KTaO₃ reaches 96% and 98%, which is 10 times of that of KTaO₃. The synthesized rGO-KTaO₃ has good photocatalytic properties. Moreover, the stability of this photocatalyst is particularly excellent. The detailed mechanism of photocatalysis has been carefully discussed in the article.

Titanium Dioxide-Based Nanocomposites for Enhanced Gas-Phase Photodehydrogenation

Light-driven processes can be regarded as a promising technology for chemical production within the bio-refinery concept, due to the very mild operative conditions and high selectivity of some reactions. In this work, we report copper oxide (CuO)-titanium dioxide (TiO₂) nanocomposites to be efficient and selective photocatalysts for ethanol photodehydrogenation under gas phase conditions, affording 12-fold activity improvement compared to bare TiO₂. In particular, the insertion method of the CuO co-catalyst in different TiO₂ materials and its effects on the photocatalytic activity were studied. The most active CuO co-catalyst was observed to be highly dispersed on titania surface, and highly reducible. Moreover, such high dispersion was observed to passivate some surface sites where ethanol is strongly adsorbed, thus improving the activity. This kind of material can be obtained by the proper selection of loading technique for both co-catalysts, allowing a higher coverage of photocatalyst surface (complex-precipitation in the present work), and the choice of titania material itself. Loading copper on a high surface area titania was observed to afford a limited ethanol conversion, due to its intrinsically higher reactivity affording to a strong interaction with the co-catalyst.

Photocatalytic reforming of biomass for hydrogen production over ZnS nanoparticles modified carbon nitride nanosheets

Hydrogen generation from biomass reforming via solar energy utilisation has become a fascinating strategy toward future energy sustainability. In this study, ZnS nanoparticles with an average size around 10-15 nm were synthesised by a facile hydrothermal method, and then hybridised with g-C₃N₄ (MCN, DCN, and UCN) derived from melamine, dicyandiamide and urea, producing the heterojunctions denoted as ZMCN, ZDCN and ZUCN, respectively. Advanced characterisations were employed to investigate the physiochemical properties of the materials. ZMCN and ZDCN showed a slight red shift and better light absorbance ability. Their catalytic performances were evaluated by photocatalytic biomass reforming for hydrogen generation. The hydrogen generation rate on ZMCN, the best photocatalyst among MCN, DCN, UCN, ZDCN and ZUCN, was around 2.5 times higher than the pristine MCN. However, the photocatalytic efficiency of ZUCN experienced decrease of 36.6% compared to pure UCN. The mechanism of the photocatalytic reforming process was discussed. The photoluminescence spectra of ZMCN suggested that the introduction of ZnS for ZMCN would reduce the recombination of photoinduced carriers. It was also found that both microstructure and band structure would influence the photocatalytic reforming efficiency.

Photocatalyzed Transformation of Free Carbohydrates

In the growing context of sustainable chemistry, one of the challenges of organic chemists is to develop efficient and environmentally friendly methods for the synthesis of high-added-value products. Heterogeneous photocatalytic transformations have brought revolution in this regard, as they take advantage of an unlimited source of energy (solar light) or artificial UV light to onset organic chemical modifications. The abundance of free carbohydrates as chemical platform feedstock offers a great opportunity to obtain a variety of industrial interest compounds from biomass. Due to their chirality and polyfunctionality, the conversion of sugars generally requires multi-step protocols with protection/deprotection steps and hazardous chemical needs. In this context, several selective and eco-friendly methodologies are currently under development. This review presents a state of art of the recent accomplishments concerning the use of photocatalysts for the transformation and valorization of free carbohydrates. It discusses the approaches leading to the selective oxidation of free sugars, their degradation into organic chemicals, or their use for hydrogen production.

Solar Fuels by Heterogeneous Photocatalysis: From Understanding Chemical Bases to Process Development

The development of sustainable yet efficient technologies to store solar light into high energy molecules, such as hydrocarbons and hydrogen, is a pivotal challenge in 21st century society. In the field of photocatalysis, a wide variety of chemical routes can be pursued to obtain solar fuels but the two most promising are carbon dioxide photoreduction and photoreforming of biomass-derived substrates. Despite their great potentialities, these technologies still need to be improved to represent a reliable alternative to traditional fuels, in terms of both catalyst design and photoreactor engineering. This review highlights the chemical fundamentals of different photocatalytic reactions for solar fuels production and provides a mechanistic insight on proposed reaction pathways. Also, possible cutting-edge strategies to obtain solar fuels are reported, focusing on how the chemical bases of the investigated reaction affect experimental choices.

Solar Hydrogen Generation from Lignocellulose

Photocatalytic reforming of lignocellulosic biomass is an emerging approach to produce renewable H2 . This process combines photo-oxidation of aqueous biomass with photocatalytic hydrogen evolution at ambient temperature and pressure. Biomass conversion is less energy demanding than water splitting and generates high-purity H2 without O2 production. Direct photoreforming of raw, unprocessed biomass has the potential to provide affordable and clean energy from locally sourced materials and waste.

Inorganic perovskite photocatalysts for solar energy utilization

This review specifically summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation.

Amorphous and Crystalline Sodium Tantalate Composites for Photocatalytic Water Splitting

A facile hydrothermal synthesis protocol for the fabrication of sodium tantalates for photocatalytic water splitting is presented. Mixtures of tantalum and sodium ethoxide precursors were dispersed in ethanol, and ammonium hydroxide solution was used as mineralizer. By adjusting the amount of mineralizer, a variety of sodium tantalates with various morphologies, textural parameters, band gaps, crystal phases, and degrees of crystallinity were fabricated. The reaction was carefully monitored with a pressure sensor inside the autoclave reactor, and the obtained samples were characterized using X-ray diffraction, transmission electron microscopy, N2-physisorption, and ultraviolet-visible light spectroscopy. Among the series, the amorphous sample and the composite sample that consists of amorphous and crystalline phases showed superior activity toward photocatalytic hydrogen production than highly crystalline samples. Particularly, an amorphous sodium tantalate with a small fraction of crystalline nanoparticles with perovskite structure was found to be the most active sample, reaching a hydrogen rate of 3.6 mmol h(-1) from water/methanol without the use of any cocatalyst. Despite its amorphous nature, this photocatalyst gave an apparent photocatalyst activity of 1200 μmol g(-1) L(-1) h(-1) W(1-), which is 4.5-fold higher than highly crystalline NaTaO3. In addition, the most active sample gave promising activity for overall water splitting with a hydrogen production rate of 94 μmol h(-1), which is superior to highly crystalline NaTaO3 prepared by conventional solid-solid state route.

Perovskite-type KTaO3–reduced graphene oxide hybrid with improved visible light photocatalytic activity

Novel rGO–KTaO₃ composites with various graphene content were successfully synthesized using a facile solvothermal method which allowed both the reduction of graphene oxide and loading of KTaO₃ nanocubes on the graphene sheets.

Formation of combustible hydrocarbons and H2 during photocatalytic decomposition of various organic compounds under aerated and deaerated conditions

A possibility of photocatalytic production of useful aliphatic hydrocarbons and H₂ from various organic compounds, including acetic acid, methanol, ethanol and glucose, over Fe-modified TiO₂ is discussed. In particular, the influence of the reaction atmosphere (N₂, air) was investigated. Different gases were identified in the headspace volume of the reactor depending on the substrate. In general, the evolution of the gases was more effective in air compared to a N₂ atmosphere. In the presence of air, the gaseous phase contained CO₂, CH₄ and H₂, regardless of the substrate used. Moreover, formation of C₂H₆ and C₃H₈ in the case of acetic acid and C₂H₆ in the case of ethanol was observed. In case of acetic acid and methanol an increase in H₂ evolution under aerated conditions was observed. It was concluded that the photocatalytic decomposition of organic compounds with simultaneous generation of combustible hydrocarbons and hydrogen could be a promising method of “green energy” production.

Simultaneous glucose sensing and biohydrogen evolution from direct photoelectrocatalytic glucose oxidation on robust Cu2O–TiO2 electrodes

An efficient solar-driven biofuel hydrogen production from direct photoelectrocatalytic oxidation of glucose on a robust Cu₂O–TiO₂ photoelectrode was demonstrated.

Hydrogen Production by Photoreforming of Renewable Substrates

This paper focuses on the application of photocatalysis to hydrogen production from organic substrates. This process, usually called photoreforming, makes use of semiconductors to promote redox reactions, namely, the oxidation of organic molecules and the reduction of H+ to H2. This may be an interesting and fully sustainable way to produce this interesting fuel, provided that materials efficiency becomes sufficient and solar light can be effectively harvested. After a first introduction to the key features of the photoreforming process, the attention will be directed to the needs for materials development correlated to the existing knowledge on reaction mechanisms. Examples are then given on the photoreforming of alcohols, the most studied topic, especially in the case of methanol and carbohydrates. Finally, some examples of more complex but more interesting substrates, such as waste solutions, are proposed.