Examinando por Autor "Grieken, Rafael van"

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A review on LED technology in water photodisinfection
(Elsevier, 2023) Martín-Sómer, Miguel; Pablos, Cristina; Adán, Cristina; Grieken, Rafael van; Marugán, Javier
The increase in efficiency achieved by UV LED devices has led to a compelling increase in research reports on UV LED water treatment for consumption in the past few years. This paper presents an in-depth review based on recent studies on the suitability and performance of UV LED-driven processes for water disinfection. The effect of different UV wavelengths and their combinations was analysed for the inactivation of various microorganisms and the inhibition of repair mechanisms. Whereas 265 nm UVC LED present a higher DNA damaging potential, 280 nm radiation is reported to repress photoreactivation and dark repair. No synergistic effects have been proved to exist when coupling UVB + UVC whereas sequential UVA-UVC radiation seemed to enhance inactivation. Benefits of pulsed over continuous radiation in terms of germicidal effects and energy consumption were also analysed, but with inconclusive results. However, pulsed radiation may be promising for improving thermal management. As a challenge, the use of UV LED sources introduces significant inhomogeneities in the light distribution, pushing for the development of adequate simulation methods to ensure that the minimum target dose required for the target microbes is achieved. Concerning energy consumption, selecting the optimal wavelength of the UV LED needs a compromise between the quantum efficiency of the process and the electricity-to-photon conversion. The expected development of the UV LED industry in the next few years points to UVC LED as a promising technology for water disinfection at a large scale that could be competitive in the market in the near future.
Chromium oxide/metallocene binary catalysts for bimodal polyethylene: hydrogen effects.
(Elsevier, 2012-12) Paredes, Beatriz; Grieken, Rafael van; Carrero, Alicia; Moreno, Jovita; Moral, Alberto
Bimodal resins came up to meet application requirements: low molecular weight for good processability and high molecular weight for mechanical properties. For obtaining this bimodality there are several strategies: physical melt mixing of the two components produced separately, a single catalyst in two different serial reactors and a single reactor technology employing a tailor made catalyst and/or switching conditions. This last method has many advantages such as lower investment costs, less process complexity and intimate mixing of high and low molecular weight components (improved product quality). By means of this single reactor technology, bimodal polyethylene was synthesized using a mesostructured catalyst based on Al-SBA-15 where two active centers, chromium and metallocene, were incorporated. Ethylene polymerizations were carried out over binary catalysts (hybrid and mixed Crmetallocene) and the polyethylenes obtained were compared with those obtained with individual catalysts in order to determine the contribution of each active centre. As well, the effect on polymer properties of the partial pressure of hydrogen in the reactor was evaluated. Results indicate that the hybrid catalyst (metallocene supported over Cr-Al- SBA-15) and physical mixture (Cr-Al-SBA-15 mixed with met-Al-SBA-15) lead to bimodal polyethylenes which combine high molecular weight, crystallinity and melting point with good processability (high melt index).
Correlation between photoelectrochemical behaviour and photoelectrocatalytic activity and scaling-up of P25-TiO2 electrodes
(Elsevier, 2014) Pablos, Cristina; Marugán, Javier; Grieken, Rafael van; Adán, Cristina; Riquelme, Ainhoa; Palma, Jesús
The use of TiO2 electrodes may solve the two main drawbacks of photocatalytic processes: i) the necessity of recovering the catalyst and ii) the low quantum yield in the use of the radiation. This work focuses on the correlation between the photoelectrochemical properties of TiO2 electrodes and their activity for the photoelectrocatalytic oxidation of methanol. Particulate TiO2 electrodes prepared by deposition of P25-TiO2 nanoparticles on titanium (TiO2/Ti) or conductive glass support (TiO2/ITO) seem to be effective for charge carrier transference on TiO2 surface favouring the formation of ¿OH radicals and consequently, the oxidation of molecules. In contrast, thermal TiO2 electrodes prepared by annealing of titanium (Ti) present better properties for charge carrier separation as a consequence of the application of a potential bias. Despite reducing charge carrier recombination by applying an electric potential bias, the activity of thermal electrodes remains lower than that of P25-particulate electrodes. TiO2 structure of P25-particulate electrodes does not completely allow developing a potential gradient. However, their adequate TiO2 layer characteristics for charge carrier transfer lead to a reduction in charge carrier recombination making up for the lack of charge carrier separation when applying an electric potential bias. TiO2/Ti showed the highest values of activity. Therefore, the combination of the suitable TiO2 surface properties for charge carrier transfer with an adequate conductive support seems to increase the properties of the electrode for allowing charge carrier separation. The scaling-up calculations for a TiO2/ITO electrode do lead to good estimations of the activity and photocurrent of larger electrodes since this photoanode made from ITO as conductive support does not seem to be significantly affected by the applied potential bias.
Emerging micropollutant oxidation during disinfection processes using UV-C, UC-C/H2O2, UV-A/TiO2 and UV-A/TiO2/H2O2
(Elsevier, 2013) Marugán, Javier; Pablos, Cristina; Grieken, Rafael van; Serrano, Elena
Regeneration of wastewater treatment plant effluents constitutes a solution to increase the availability of water resources in arid regions. Water reuse legislation imposes an exhaustive control of the microbiological quality of water in the operation of disinfection tertiary treatments. Additionally, recent reports have paid increasing attention on emerging micropollutants with potential biological effects even at trace level concentration. This work focuses on the evaluation of several photochemical technologies as disinfection processes with the aim of simultaneously achieving bacterial inactivation and oxidation of pharmaceuticals as examples of emerging micropollutants typically present in water and widely studied in the literature. UV-C-based processes show a high efficiency to inactivate bacteria. However, the bacterial damages are reversible and only when using H2O2, bacteria reproduction is affected. Moreover, a complete elimination of pharmaceutical compounds was not achieved at the end of the inactivation process. In contrast, UV-A/TiO2 required a longer irradiation time to inactivate bacteria but pharmaceuticals were completely removed along the process. In addition, its oxidation mechanism, based on hydroxyl radicals (¿OH), leads to irreversible bacterial damages, not requiring of chemicals to avoid bacteria regrowth. For UV-A/TiO2/H2O2 process, the addition of H2O2 improved E. coli inactivation since the cell wall weakening, due to ¿OH attacks, allowed H2O2 to diffuse into the bacteria. However, a total elimination of the pharmaceuticals was not achieved during the inactivation process.
Hybrid zeolitic-mesostructured materials as supports of metallocene polymerization catalysts
(ELSEVIER, 2012) Carrero, A.; Grieken, Rafael van; Paredes, B.
The potential application of hybrid ZSM-5/Al-MCM-41 zeolitic-mesostructured materials as supports of metallocene polymerization catalysts has been investigated and compared with the behaviour of standard mesoporous Al-MCM-41 and microporous ZSM-5 samples. Hybrid zeolitic-mesostructured solids were prepared from zeolite seeds obtained with different Si/Al molar ratios (15, 30 and 60), which were assembled around cetyltrimethylammonium bromide (CTAB) micelles to obtain hybrid materials having a combination of both zeolitic and mesostructured features. (nBuCp)2ZrCl2/MAO catalytic system was impregnated onto the above mentioned solid supports and tested in ethylene polymerization at 70 Cº and 5 bar of ethylene pressure. Supports and heterogeneous catalysts were characterized by X-ray powder diffraction, nitrogen adsorption-desorption isotherms at 77 K, transmission electron microscopy, 27Al-MAS-NMR, ICP-atomic emission spectroscopy and UV-vis spectroscopy. Catalysts supported over hybrid ZSM-5/Al-MCM-41 (Si/Al = 30-60) exhibited the best catalytic activity followed by those supported on Al-MCM-41 (Si/Al = 30-60). However, catalyst supported on ZSM-5 gave lower polymerization activity because of its microporous structure with narrower pores and lower textural properties than hybrid and mesoporous materials. Although higher acid site population shown by hybrid materials could contribute to the stabilization of the metallocene system on the support, in this case their better catalytic performance is mainly ascribed to the larger textural properties.
Kinetic modelling of Escherichia coli inactivation in a photocatalytic wall reactor
(Elsevier, 2014) Marugán, Javier; Grieken, Rafael van; Pablos, Cristina; Satuf, M. Lucila; Cassano, Alberto E.; Alfano, Orlando M.
A kinetic model of the photocatalytic inactivation of Escherichia coli in an annular wall reactor is presented. The model is based on a reaction scheme that involves a series of events in which bacteria are progressively damaged and eventually led to cell lysis. The model explicitly takes into account radiation absorption effects. Photocatalytic inactivation experiments were carried out in a photoreactor operated in a closed recirculating circuit with a reservoir tank and irradiated with a 6W black light lamp situated in the axis of the reactor. Immobilization of TiO2 Aeroxide P25 has been carried out by the dip-coating procedure onto the inner-tube wall of the annular reactor. Experimental results for different TiO2 layer thicknesses were used to estimate the kinetic parameters of the model. Good agreement between model predictions and inactivation experiments was achieved in the whole range of TiO2 thicknesses studied.
Mitoxantrone-Derivative Drug Structure-Directing Agent for the Synthesis of Magnetic Mesoporous Silica Nanoparticles for Breast Cancer Treatment
(American Chemical Society, 2024-05-20) Romaní-Cubells, Eva; Martinez-Erro, Samuel; Morales, Victoria; Grieken, Rafael van; García Muñoz, Rafael A.; Sanz, Raúl
Cancer causes hundreds of thousands of deaths worldwide each year. Chemotherapy, the treatment of choice for invasive cancers, presents severe side effects related to off-target exposure that limit its dosage and, thus, its efficacy. Nanomedicine has emerged as a potential tool to overcome these problems. Among the nanocarriers, mesoporous silica nanoparticles (MSNs) have attracted much attention due to their high surface area (up to 1000 m2 g–1), the versatility in size and pore diameter, and their ease of functionalization. However, drug leakage from the MSNs usually occurs before the nanocarriers reach their target, reducing drug efficacy and causing adverse effects. Our group has developed a promising method to increase drug loading capacity while preventing premature drug release. This strategy consists of the use of a drug structure-directing agent (DSDA) that plays a dual role, acting as a pharmacological prodrug and as a template for the synthesis of MSNs. Here, we successfully synthesized a DSDA from the anticancer drug mitoxantrone (MTO), which is used in clinical practice for the treatment of metastatic breast cancer, and used it to synthesize magnetic MSNs whose porosity was fully filled with the MTO prodrug (magnetic MTO-C12@MSNs). The release behavior was pH-dependent, showing negligible drug release at physiological pH and a significant increase at the pH of the tumoral microenvironment. Finally, the efficacy of magnetic MTO-C12@MSNs in reducing breast cancer cell viability was confirmed, demonstrating the potential of this material as an efficient drug delivery system to target breast cancer tumors while avoiding side effects.
Photocatalytic Degradation of Methylisothiazolinone in Water by TiO2 and TiO2/Persulfate systems with Simulated Solar Radiation
(Elsevier, 2022) Gómez-Rodríguez, Pilar; Calza, Paola; Fabbri, Debora; Medana, Claudio; Grieken, Rafael van; López-Muñoz, María-José
The photocatalytic decomposition of methylisothiazolinone (MIT) in water was successfully attained with TiO2 and TiO2/persulfate systems under simulated solar irradiation. The TiO2 catalysts were synthesized by sol-gel process, controlling the hydrolysis rate of titanium n-butoxide by two procedures: external addition of water and in situ production of water via esterification between ethanol and a carboxylic acid. Crystalline structure, morphology and textural properties of materials were characterized by XRD, SEM and N2 adsorption-desorption isotherms. The photocatalytic activity of the obtained catalysts for MIT degradation was proved to be significantly dependent on both the procedure of water provision for the alkoxide hydrolysis and the calcination temperature. Adding persulfate (PS) to the system resulted in a great enhancement of the MIT degradation rate, which was kept in different water matrices due to a synergistic effect between the titania catalysts and PS activation. MIT transformation products (TPs) were identified by HPLC-HRMS and a mechanism for MIT degradation was proposed. Total Organic Carbon and toxicity measurements established the complete MIT mineralization and non-toxicity of the water solution after the photocatalytic treatment.