An avant-garde step towards the use of the long infrared tail of the incident solar radiation with untapped and crucial applications in photocatalysis and energy harvesting schemes is presented: "there is plenty of energy at the bottom". In detail, a pure photonic approach to enhance titanium dioxide (TiO2) photocatalytic activity is proposed, by using rare-earth doped luminescent glassy materials, capable of performing NIR-to-UV-VIS spectral conversion (up-conversion). Therefore we report infrared-driven boosting of green hydrogen production in a photo-electrochemical water-splitting cell using TiO2 electrodes, revisiting the original design of Fujishima and Honda fifty years later. This proof-of-concept comprises infrared-induced hydrogen and oxygen evolution via water-splitting and determines univocally the role of a solely photonic effect to split water. Thus, the conversion of the incident NIR radiation, before its interaction with the photocatalyst, emerges as a significant contribution to the state-of-the-art for an effective harvest of the near-infrared portions of sunlight.

Conventional photovoltaic systems frequently struggle to fully exploit the vast solar spectrum, falling short in efficiently converting the entire potential of each photon into electricity. This quest for maximizing solar spectrum utilization emerges as a cutting-edge research frontier within the realm of photovoltaics. In this context, we introduce a tandem luminescent solar concentrator featuring rare-earth materials (Yb3+-Er3+ doped ZBLAN) and organic dyes (Lumogen yellow and Lumogen pink) embedded within EVA polymer matrices. The incorporation of various luminescent entities plays a pivotal role in augmenting energy capture across different parts of the solar spectrum (UV, visible, and NIR). At the same time, our approach targets the synergistic integration of up-conversion and down-shifting mechanisms to achieve an optimal spectral alignment with the response profile of amorphous silicon solar cells. This involves converting UV-visible photons from incoming sunlight and visible up-converted photons from near-infrared radiation into the orange-red segment of the spectrum. Notably, this marks the initial demonstration, to the best of our knowledge, of a proof-of-concept employing a tandem luminescent solar concentrator wherein up-conversion and down-shifting photonic processes collaboratively operate in a sequential manner.

In a biodiesel production industry a quick monitorization of the reaction extent achieved in the process it is important. The usual way to determine the reaction yield is to analyze the FAME content in the biodiesel reaction product. Analytic methods used, mainly gas chromatography, require previous sample treatment or tedious calibrations. Recently, less complicated analytic methods (nuclear magnetic resonance, infrared spectrophotometry) have been developed but they require costly equipment and analysis. The aim of this paper is to develop a cheap and fast method in order to quantify the FAME content in the reaction mixture from simple dynamic viscosity measurements and then the transesterification reaction yield. Therefore, experimentally obtained correlations from biodiesel proceeding of several oil feedstocks are presented in order to estimate the biodiesel FAME content from its dynamic viscosity, a fast determination parameter.

Photocatalysis is an advanced oxidation process that is an environmentally friendly option and one of the most critical technologies in green chemistry today. This work studied the upscaling of photocatalysis as a suitable process for wastewater treatment to remove emerging pollutants. For this purpose, unsupported and supported TiO2 photocatalysts were tested in the photodegradation of ciprofloxacin as a model molecule of an emerging wastewater component, using visible, UV radiation, and solar light. The suitability of TiO2 as a photocatalyst to decompose ciprofloxacin was confirmed in batch photoreactor under Visible and UV radiation, with degradation rates up to 90% after 30 min of irradiation and low adsorption values. TiO2 as a photocatalyst coated in glass support material at the packed bed photoreactor showed good photoactivity for emergent contaminants degradation (95%) under solar radiation. It has been possible to verify that the photocatalytic reactor system constitutes a viable process for eliminating emerging contaminants through environmentally sustainable treatments. Our results corroborate the possibility of degrading emerging contaminants by solar radiation using a packed bed photoreactor, providing a more effective option from a practical and economical point of view for wastewater effluent treatments.

Solar energy harvesting is largely limited by the spectral sensitivity of the employed photovoltaic solar cell, since typically the full potential of each photon of the whole solar spectrum is not efficiently used in the generation of electricity. Therefore, increasing the overall solar spectrum utilization is of crucial interest and stands up as a frontier-of-research approach in the photovoltaic sector. Here we present an innovative ultra-broadband absorption and multiple spectral conversion approach, by means of rare-earth doped materials together with organic dyes embedded in a luminescent solar concentrator. The combination of different luminescent materials is a key factor for improving energy harvesting over the whole solar spectrum. At the same time, a simultaneously combined effect of up-conversion and down-shifting of light is aimed to optimal spectral matching with amorphous silicon solar cells response. Thus, UV–visible photons coming from the incoming sunlight, together with UV–visible up-converted photons coming from near-infrared radiation, can be all shifted to the yellow-orange-red part of the spectrum. To the best of our knowledge, this represents the first reported proof-of-concept using LSCs with up-conversion and down-shifting photonic processes working together and sequentially.

The transesterification reaction is the most utilized process to obtain biodiesel. Fried oil transesterification reactions with methanol have been studied using several zeolites Y and interchanged with CsCl and KOH. The reaction has been carried out both in a slurry reactor and a fixed bed catalytic reactor. The catalytic effects of zeolites have been tested within a temperature range of 60-476°C, 2.5-5% catalyst/waste oil weight ratio, and 6:1 - 100:1 methanol/oil molar ratio. Cosolvents (THF, n-hexane) in the reaction feedstock effect have also been studied as well as catalyst regeneration effects. Viscosity of both the oil and the transesterification reaction products was determined as an initial guide to investigate the degree of conversion to biodiesel as well as FAME content by GC. When interchanged zeolites are used conversions are improved, getting the best yields (98% FAME) for the Y756 zeolite interchanged with KOH. Viscosities of the reaction product obtained reached values next to diesel standard ones.

3D printing technology has become a powerful tool to produce 3D structures in any type of materials. In this work, 3D printing technology is used to produce 3D porous structures in CaSO 4 which can be later activated with an appropriate photocatalyst. TiO 2 was selected as an ideal photocatalyst producing activated 3D structures which can be used to study their effectiveness in the degradation of pollutants in wastewater. Methylene blue was used as a model molecule in these studies. The photocatalytic studies showed that TiO 2 -activated 3D structures using nanoparticles of SiO 2 in the process produce more than 50% of conversion of methylene blue in just 1 h of irradiation and almost 90% in 5 h.

Multiphase reactors combined with bifunctional catalysts have great potential for producing biodiesel from waste oil. In this chapter, an example is described for continuous biodiesel fuel production from sunflower oil, non-edible oil and waste oil with a fixed-bed multiphase reactor packed with a bifunctional heterogeneous catalyst. The performance of the catalyst is demonstrated for biodiesel production reaction using the multiphase reactor for several oils as feedstock at low reaction temperatures (ca. 55 degrees C). The catalytic material, 3D-microstructured bifunctional catalyst showed good conversions for low-quality feedstocks that have high free fatty acid and water content. Multiphase reactors combined with microstructured bifunctional catalyst are a promising new technology for biodiesel production.

This work deals with the sustainable biodiesel production from low-cost renewable feedstock (waste and non-edible oils) using a heterogeneous catalyst constituted by potassium loaded on an amorphous aluminum silicate naturally occurring as volcanic material (pumice). The main challenge to biodiesel production from low-quality oils (used oils and greases) is the high percentage of free fatty acids (FFAs) and water in the feedstock that causes undesirable side reactions. The catalytic materials studied were tested in the transesterification reaction when using low-quality oils containing a high proportion of free fatty acids (FFAs) and water. Results indicated that the amount of acid and basic sites on the catalytic surface increases upon increasing potassium loading in the catalyst, displaying better performance for biodiesel production. Indeed, the modification of the aluminum silicate substrate upon potassium incorporation results in a catalytic material containing both acidic and basic sites, which are responsible for both triglycerides transesterification and FFA esterification reactions. The studied catalyst not only showed good performance in the biodiesel production reaction but also good tolerance to FFA and water contained in the feedstock for biodiesel production. The catalytic material was microstructured by 3D printing in order to design a catalytic stirring system with high mechanical strength, efficient and reusable. The use of 3D printing in biofuel production is a novelty that brings good solutions for catalyst production.

Particles of natural volcanic ashes as photocatalyst configured in a packed-bed photocatalytic reactor were studied for the photodegradation of wastewater pollutants under solar light. The photocatalytic system was equipped with a cylindrical parabolic sunlight concentrator, and the photocatalytic treatment has been developed with a continuous flow of wastewater under sunlight irradiation. The influence of incident radiation, amount of photocatalyst, and several configurations in the photoreactor hydrodynamics were studied. Moreover, results obtained were compared with those obtained from the photolysis and adsorption studies. Good photocatalytic activities have been observed, and this allows concluding that heterogeneous photocatalytic system in a packed bed is an effective method for wastewater pollutants removal. In a sunny day, more than 90% of the contaminant can be removed after 5 h by the continuous-flow photocatalytic treatment of the wastewater in the packed-bed reactor under sunlight. The possibility of combining the renewable energy (solar energy) and the photocatalytic technology, by means of a sustainable photocatalytic material, offers a powerful alternative in the wastewater treatment sector.

•High rate of photocatalysis under solar light.•Photocatalysis combining economical and sustainable components including TiO2, black volcanic ashes and solar light.•TiO2 nanoparticles loaded on a natural material (black volcanic ashes).•Catalyst can absorb both UV and visible light.•Photocatalyst in particles for eliminating the complex liquid/powder separation process for wastewater treatment.

Solar energy, along with other renewable resources, could potentially solve environmental problems, as demonstrated by recent developments in the use of solar energy, such as solar photocatalysis. Solar photocatalytic technology has been demonstrated to be effective for treating groundwater, drinking water, wastewater and air and soil pollution. In this study, a solar photocatalytic application for wastewater decontamination is presented. Luminescent material has been evaluated as up-conversion material for enhancing the photocatalytic activity. Wastewater decontamination by heterogeneous photocatalysis has been developed in a slurry photo-reactor, using TiO2 as a photocatalyst. The photoactivity of TiO2 under several sun irradiation conditions was investigated. The up-conversion luminescence agent ZBLAN, a rare-earth (Yb-Er-Tm) co-doped fluoride glass (ZrF4– BaF2–LaF3–AlF3–NaF), was incorporated to enhance the solar-driven activity of TiO2 because this material could transform the unused near-infrared sunlight tail into UV–vis radiation available for photoreaction activation. The use of ZBLAN has demonstrated an improvement over ordinary titanium dioxide photocatalytic activity under sunlight irradiation for the photocatalytic degradation of pollutants in wastewater. Our results demonstrating the contribution of up-conversion luminescence to the improved photoactivity of titanium dioxide suggest that it can be used to develop new technologies for treating wastewater using solar light.

Up-conversion luminescent materials have emerged recently for the improvement of the photocatalytic activity of semiconductor electrodes, such as TiO2 and Fe2O3, used for the sustainable production of hydrogen via water-splitting. Here we present novel up-conversion luminescent organic resins doped with heavy rare-earth ions, which are used as constructive elements in the 3D technique, that open a fully unexplored path for the development of cost-effective, room-temperature and endlessly shaped 3D photonic structures, avoiding the technical difficulties of glass melting or crystal growth when used as rare-earth hosts. Moreover, these synthesized resins also present outstanding UV-Vis up-conversion luminescence of Er3+ and Tm3+ ions sensitized by Yb3+ ions under near-infrared excitation at 980 nm, and have been extensively analyzed as a function of the doping concentration. Furthermore, the increase in the Yb3+ to Er3+ and Tm3+ ratio results in a notable enhancement of the UV-blue high energetic emission bands, allowing the tailoring of the overall up-conversion luminescence to match the different band-gaps of selected photocatalysts.

Rare-earth doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride glasses have been successfully synthesized showing outstanding UV-VIS up-conversion luminescence of Er3+ and Tm3+, sensitized by Yb3+ ions, under near-infrared excitation at 980 nm. The ratio between blue, green and red up-conversion emission bands can be adjusted by varying the pump power density of the incident infrared radiation, resulting in a controlled tuneability of the overall emitting colour from greenish to yellowish. Additionally, the observed high energy UV intense up-conversion emissions are suitable to enhance photocatalytic activity of main water-splitting semiconductor electrodes (such as TiO2) used in sustainable production of hydrogen. Photocatalysis and photolysis degradation of methylene blue in water under sun-like irradiation using benchmark photocatalyst (TiO2 Degussa P25) have been boosted by 20% and by a factor of 2.5 respectively, due to the enhancement of UV radiation that reaches the TiO2 particles by the addition of ZBLAN powder into a slurry-type photo-reactor. Hence, up-conversion ZBLAN phosphors contribute to demonstrate the possibility of transforming the incoming infrared radiation into the UV region needed to bridge the gap of photocatalytic semiconductors. (C) 2014 Elsevier B.V. All rights reserved.

We have explored the emerging and ground-breaking photonics approach to enhance the photocatalytic activity of one of the main semiconductor electrodes used in water-splitting reactions, titanium dioxide (TiO2): the blue shifting of the incident radiation by means of a highly efficient up-conversion by a rare-earth (RE) doped luminescent material to assist in the harvesting of long wavelengths in unused portions of infrared light. We present an up to 20% improvement of the photocatalytic action of the commercial benchmark TiO2 efficient photocatalyst in the decomposition of methylene blue in water under Xe-lamp irradiation, and also an outstanding enhancement by a factor of about 2.5 of the photolytic degradation rate of this pollutant. Our results prove that the ultraviolet (UV) radiation that reaches the TiO2 particles is increased by the addition of the RE-doped powder material into a slurry-type photo-reactor, boosting both the photocatalytic and photolytic degradation rates. Thus, we show the feasibility of handling and transforming the incoming infrared radiation, bridging the UV gap of the photocatalytic semiconductor. Let us turn the infrared into the blue; there is plenty of energy at the bottom.

Heterogeneous photocatalysis based on TiO2 materials is an interesting method for the treatment of polluted water because it allows degradation of a wide variety of organic contaminant compounds. The performance of TiO2 based photocatalysts was studied by aqueous solutions of methylene blue (MB) as a model contaminant compound by using 50mgL−1 as initial water contaminant concentration in order to compare the photocatalytic behaviour of TiO2 Degussa P25 and some synthesized photocatalysts by hydrothermal treatment (nanostructured TiO2 and metal-doped nanostructured TiO2 photocatalysts: nanostructured Co–TiO2, nanostructured Fe–TiO2 and nanostructured Mn–TiO2) under UV and visible light irradiation. Photocatalytic materials characterization was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption, mercury porosimetry, XPS and diffuse reflectance UV–vis spectra. An improvement of the photocatalytic activity has been observed when nanostructured and doped photocatalysts were used under visible light irradiation, concluding that the hydrothermal treatment produces a nanostructuration of commercial titania by the formation of nanoparticles, which results in a large decrease of average crystallite size of undoped and doped titania, and in an important increase of BET specific area and total pore area.

Heterogeneous UV-photocatalytic process has been studied as tertiary treatment of real municipal wastewater. Wastewater photocatalytic treatment was carried out using several materials previously developed as photocatalysts: volcanic ashes and nanostructured titania supported over volcanic ashes. Both material activities in particles were compared with Degussa TiO2 (powder). Photocatalyst amount influence was studied by varying it between 2 and 10 g L−1. Wastewater decontamination process was evaluated measuring the chemical oxygen demand evolution with phototreatment time in order to choose the best photocatalytic material and its optimal operation concentration. Moreover, the photocatalytic results obtained were compared with those obtained from photolysis and adsorption studies in wastewater using the same operation conditions. In addition, analyses of main wastewater parameters were made in order to evaluate the complete water decontamination process. Possibility of using photocatalysts in particles shows the main advantage of continuous photocatalyst separation from the water effluent once the decontamination process has finished. Good photocatalytic activities were observed, and it allows to conclude that heterogeneous photocatalysis is an effective method for municipal wastewater treatment, achieving water disinfection and phosphates removal.

Pumice, a natural porous silica material, exchanged with potassium is an efficient heterogeneous particulate catalytic material for triglycerides and free fatty acids transesterification reaction from sunflower oil and waste frying oil at low temperature. In this work, a packed-bed catalytic configuration reactor using this catalytic material was developed for biodiesel fuel production from sunflower oil and frying oil feedstock. Reactor operation variables as methanol/oil molar ratio, catalyst amount, reaction time, and reaction temperature were studied. Results were compared with those obtained from the same transesterification reaction proceeding in a slurry batch reactor. The packed-bed catalytic reactor configuration can be useful in order to minimize catalyst mechanical damage occurring in the slurry reactor due to continuous stirring. The possibility of using a packed-bed reactor shows some advantages because the catalyst stays confined in the reactor bed and the reaction products can be easily separated, besides the mechanical stability of the catalyst particles is achieved.

Noticeable UV–vis up-conversion luminescence of Er3+ and Tm3+ ions sensitised by Yb3+ ions in ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) fluoride glasses have been obtained under near-infrared excitation at 980nm. Red, green and blue simultaneous emissions were observed yielding to a white-balanced overall colour. Moreover significant UV up-conversion emissions observed can contribute to enhance spectral response of semiconductor electrode, such as TiO2 and Fe2O3, for sustainable production of hydrogen via water photolysis by harvesting of long wavelength solar irradiation, emerging as an interesting solely luminescent approach for improving water-splitting. Total infrared to UV–vis up-conversion efficiency has been calculated to be at around 46%. Laboratory tests prove the improvement in the photocatalytic action of a commercial benchmark photocatalyst (TiO2 Degussa P25) in the decomposition of methylene blue in water under sun-like irradiation, by a factor of 16% driven by up-conversion effects due to the inclusion of RE-doped ZBLAN powders into a slurry-type photo-reactor.

Waste oils are a promising alternative feedstock for biodiesel production due to the decrease of the industrial production costs. However, feedstock with high free fatty acids (FFA) content presents several drawbacks when alkaline-catalyzed transesterification reaction is employed in biodiesel production process. Nowadays, to develop suitable processes capable of treating oils with high free fatty acids content, a two-step process for biodiesel production is being investigated. The major problem that it presents is that two catalysts are needed to carry out the whole process: an acidic catalyst for free fatty acids esterification (first step) and a basic catalyst for pretreated product transesterification (second step). The use of a bifunctional catalyst, which allows both reactions to take place simultaneously, could minimize the production costs and time. In the present study, the behavior of pumice, a natural volcanic material used as a heterogeneous catalyst, was tested using oils with several FFA and water contents as feedstock in the transesterification reaction to produce biodiesel. Pumice as a bifunctional solid catalyst, which can catalyze simultaneously the esterification of FFA and the transesterification of fatty acid glycerides into biodiesel, was shown to be an efficient catalyst for the conversion of low-grade, nonedible oil feedstock into biodiesel product. Using this solid catalyst for the transesterification reaction, high FAME yields were achieved when feedstock oils presented a FFA content until approximately 2% wt/wt and a water content until 2% wt/wt.