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Emission spectra of different LEDs; red (λ max = 633 nm), blue (λ max = 448 nm), green (λ max = 520 nm), warm white (λ max = 600 nm), and Osram Dulux Superstar.
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A home-built microreactor system for light-mediated biphasic gas/liquid reactions was assembled from simple commercial components. This paper describes in full detail the nature and function of the required building elements, the assembly of parts, and the tuning and interdependencies of the most important reactor and reaction parameters. Unlike ma...
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Context 1
... light bulbs and light-emitting diodes (LEDs) of different wavelengths (red, green, blue, white) were used for ir- radiation of the reactions. The light source was placed in the center of the reactor to achieve optimal irradiation [66]. Key characteristics are the emission spectrum and the light intensity. correct matching of lamp emission and chromophore absorp- tion bands (Figure 4 and Figure 5). The absence of UV emis- sion bands regarding the used red and warm white LEDs enhances the selectivity of many organic reactions by suppres- sion of unwanted UV-mediated degradation ...
Citations
... This stability issue is even more important when considering low energy light activation (above 600 nm), which has recently gained high interest in photocatalysis due to the higher photon throughput and improved light penetration in the reaction medium. [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] Red or Near Infrared (NIR) light also offers advantages in terms of irradiation selectivity due to orthogonal absorption of the photocatalyst and the reaction medium (which is sometimes not achievable for UV or blue light activations). 49,50 In addition, the triplet to singlet transition of molecular oxygen is far lower in energy (24 kcal/mol) compared to blue light activation (90 kcal/mol). ...
... Computer screens (and TVs) are basically LCDs or organic LEDs, that have optical filters of broad bandwidth placed in their pixels. LEDs with narrower bandwidth are used as backlights [26,27]. The colouring of the displays results from the light emitted by the LEDs that cross the optical filters, a very different process from what occurs in the production of colour with RGB LEDs whose bandwidth of each colour depends on the materials they are made of [26]. ...
The phenomenon of adding colours is a relevant topic and integrates school programmes in different countries. In most cases, it is presented by teachers through static images, drawn on the board or schematised in school textbooks. This approach stems, in many cases, from the lack of adequate resources that allow a discussion without inducing misunderstandings, which unfortunately does not meet the necessary demands for learning. From the perspective of a necessary methodological change, a path is presented: the use of active methodologies enrolling students in their learning process based on the joint discussion of science and technology. Based on these principles, we present in this work a proposal for an experimental setup that can be used in classes where the discussion of adding colours occurs, allowing students to carry out a real-time comparison between the colour perceived in an RGB light-emitting diode display, and the colour produced in a computer screen. In addition to the phenomenological aspects, the setup will allow students to perceive the differences in shades and, consequently, how technology in the perception of colour.
... A back pressure regulator of moderate pressure (i.e., 100 psi or 6.9 bar) was used to expedite the solubility of O 2 in α-terpinene because of the enhanced mixing and O 2 diffusion rate. 19,21 Liquid and gas flow rates were varied from 0.2 to 2.0 and 2.21−30.87 mL/min, respectively, and the photooxidation of α-terpinene with singlet oxygen led to the ascaridole formation, as indicated by Scheme 1. Potential side reactions during this [4 + 2] cycloaddition result in the formation of several byproducts such as p-cymene, allylic peroxide, hydrogen peroxide, and isoascaridole due to the αterpinene autoxidation, photosensitized pathway, and photochemically induced ascaridole isomerization. ...
Recent advancements in LED technology and photomicroreactor have provided a prudent roadmap for scaling-up the photooxidation processes. In this work, we presented a highly efficient, chromoselective and wavelength selective high-power LED-based photomicroreactor (HLPMR) for the multikilogram ascaridole production through the solvent-free α-terpinene photooxidation. Firstly, we segregated kinetically controlled and mass transfer limited zones by implementing various operating schemes. Numerical investigations indicated that a simultaneous drop in molar diffusion coefficient and reaction rate led to the decrease of α-terpinene conversion in the mass transfer limited zone. Kinetic investigations showed that apparent rate constants were improved by increasing LED input power. Based on the rise in apparent constants and the control over the selectivity, we varied PFA microchannel design configurations and its volume to increase the irradiated area for efficiently scaling-up the ascaridole productivity, space-time yield, and photochemical space-time yield to 3.5 kg/Day, 9303.5 g L-1 h-1 and 34.7 mol kW-1 Day-1, respectively. Predictive modeling using various supervised machine learning classifiers was executed to select the best possible photoreactor for this benchmark photooxidation. Random forest classifier showed better prediction performance using the train test split, cross-validation and folding approaches among the implemented classifiers. Overall, HLPMR ensured a green and sustainable production of ascaridole with the multikilogram per day capacity.
... Papailias et al. [33] obtained a 24% degradation of nitric oxide (NO) under UV irradiation against 14% when visible light was applied, using a melamine-based g-C3N4 even with the catalyst presenting a relatively lower band gap energy (2.76 eV). A possibl explanation for this fact would be that the main peak regarding light absorption by th material could be situated near the transitional wavelengths between UVA and visibl regions (<490 nm), while the used white LED strips mainly emit at 580-590 nm [34]. Different from what was expected for known visible-light-driven materials, the photoactivity of all g-C 3 N 4 was lower under visible radiation than UV, with the best result of 20.7% against a 51.3% removal of propylparaben using UCN under visible and UV radiation, respectively. ...
... Papailias et al. [33] obtained a 24% degradation of nitric oxide (NO) under UV irradiation against 14% when visible light was applied, using a melamine-based g-C 3 N 4 , even with the catalyst presenting a relatively lower band gap energy (2.76 eV). A possible explanation for this fact would be that the main peak regarding light absorption by the material could be situated near the transitional wavelengths between UVA and visible regions (<490 nm), while the used white LED strips mainly emit at 580-590 nm [34]. ...
... In photocatalytic reactions under UVA radiation (λ = 365 nm), 3 lamps (Philips TL 6 W BLB, 16 mm, Amsterdam, the Netherlands) were used, while for visible radiation tests, a light emission diode (LED) strip, 26 W, was employed (λ = 580-590 nm) [34]. For solar photocatalysis, the information regarding solar radiation intensity was obtained from a near forecast station at Coimbra, Portugal (40.186622 • , −8.4182372 • ). ...
Graphitic carbon nitride (g-C3N4) is a promising catalyst for contaminants of emerging concern removal applications, especially as a visible-light-driven material. In this study, g-C3N4 catalysts were effectively synthesized through a simple thermal polymerization method, using melamine, urea, and thiourea as precursors to elucidate the influence of these compounds on the final product’s photocatalytic performance. The degradation of a mixture of three parabens was investigated under different types of radiation: two artificial, ultraviolet-A (UVA) and visible LED, and natural sunlight. The urea-based catalyst (UCN) presented better results under all radiation sources, followed by thiourea, and finally, melamine. Among the artificial light sources, the degradation of parabens under UVA was considerably higher than visible—up to 51% and 21%, respectively—using UCN; however, the broader spectrum of natural sunlight was able to achieve the highest removals, up to 92%, using UCN. Comparing artificial radiation sources, UVA lamps presented 45% lower energy consumption and associated costs. Photocatalytic ozonation was tested using UCN and MCN, with UCN once more possessing superior performance and a synergetic effect between photocatalysis and ozonation, with complete removal under 12 min. The use of g-C3N4 was then successfully tested in initial screening and found to be an efficient alternative in more low-cost and feasible solar photocatalysis water treatment.
... MB produces singlet oxygen ( 1 O 2 ) with a good quantum yield (Φ Δ 0.60 in CH 3 CN, Rossi et al., 2008) and has been applied in 1 O 2 photooxidation reactions on several occasions (Nilsson et al., 1972;Matheson et al., 1975;Jahnke and Frenkel, 1978;Cocquet et al., 2000;Oelgemöller et al., 2006;Lancefield et al., 2012;Schachtner et al., 2016). The main drawback of MB is its tendency to agglomerate and its intermolecular reactivity leads to the formation of leuco-forms which account for a low stability in solution (Nassar et al., 2019). ...
Methylene blue was efficiently immobilized on silica micro- and nanoparticles by electrostatic interactions and the performances of the heterogenized photocatalysts were compared against the homogeneous conditions using the photooxidation of citronellol as a model reaction under red light, in a batch and a continuous flow photochemical reactor. In batch, the heterogeneous photocatalyst outperforms the homogeneous one, presumably due to kinetic and stability effects. The two catalytic systems are also compared in a flow reactor displaying improved mass transfer properties. We demonstrate that this results in a dramatic enhancement in photocatalyst stability, reactivity and productivity. This study highlights the importance of photocatalyst stability under homogeneous versus heterogenized conditions and in batch versus flow photochemistry.
... Moreover, microreactors are suitable for chemical reactions at the interfaces and generation of small droplets, which contribute to a decrease in the usage of reagents (Benson and Ponton, 1993;Bier et al., 1993;Ehrfeld et al., 1999). ree ow patterns for the microreactors such as parallel laminar ow (Sobieszuk et al., 2012;Pieber and Kappe, 2016;Sobieszuk and Napieralska, 2016), slug ow (Günther et al., 2004;Fischer et al., 2010;Al-Rawashdeh et al., 2012;Sobieszuk et al., 2012;Hangai et al., 2015;Schachtner et al., 2016), and dispersion (Hessel et al., 2005b;Noël and Hessel, 2013;Brzozowski et al., 2015) have been reported. ...
... However, the reaction times of the gas-liquid reactions using the reported systems have been several tens of min at the longest. ere have been systems that need a longer microchannel of several tens of meters and a pump with higher discharge pressure such as an HPLC (high performance liquid chromatography) pump (Schachtner et al., 2016). Furthermore, the number of numbering-up is known to be limited (Togashi et al., 2009). ...
A recirculation microreactor system for gas–liquid reactions has been developed, in which gas is continuously introduced into liquid, in order to effectively perform reactions with longer reaction times under slug flow at the desired volume ratio between gas and liquid. The slug flow was produced in a T-shaped mixer with an inner diameter (ID) of 0.5 mm and the obtained solution collected into a 20-mL (2.0×10⁻⁵ m³) vessel through a tube with an ID of 1 mm was introduced into the mixer again. This system was evaluated by the absorption of carbon dioxide into water. At first, this absorption with the conventional batch method was performed. It was clarified that pH decreased with time by introducing carbon dioxide. Then, the recirculation microreactor system was applied to this absorption. The solubility of carbon dioxide into water reached above the solubility equilibrium of 1.67×10⁻⁵ mol/L (1.67×10⁻⁵ kmol/m³) with both this system and the conventional batch method. However, the solubility with this system increased faster than that with the conventional batch method. The absorption rate with this system was improved by over three times compared to that with the conventional batch method. This tendency with this system and the conventional batch method was in good agreement with the reported tendencies. Furthermore, a mass transfer capacity coefficient, KLa had a peak at the flow rate of the aqueous solution of around 2.5 mL/min (2.5×10⁻⁶ m³/min), which was closer to that of carbon dioxide of 1.8 mL/min (1.8×10⁻⁶ m³/min). It would be better to perform this absorption under slug flow at a smaller volume ratio regardless of the total volume ratio between carbon dioxide and water. It was concluded that our recirculation microreactor system could effectively perform gas–liquid reactions with appropriate reaction times under slug flow at the desired volume ratio between gas and liquid.
... Edwards and co-workers gave an outline in Nature Communications of the minimum information that should be provided within a photochemical manuscript to help facilitate reproducibility. [64] Furthermore, Noël and co-workers [26] as well as Wangelin and co-workers [65] have previously outlined the important aspects to consider for performing photooxygenation reactions in flow systems. In terms of electrochemistry, we refer readers to an article in Angewandte Chemie by Waldvogel and co-workers for improving reproducibility within these setups. ...
Flow chemistry studies can sometimes be difficult to reproduce. In this article we provide guidance to scientists for experimental details that should be considered as part of any organic chemistry‐based continuous flow study. A focus is placed on information that should be provided within reported studies to enable experiments to be more easily and reliably reproduced. Topics covered include flow reactor components and assembly, important parameter effects and useful performance criteria. The article covers aspects of homogeneous systems, multiphase transformations, and catalytic reactions (homogeneous and heterogeneous). A more detailed discussion of photochemistry, biocatalysis and electrochemical flow systems is outside the scope of this review. Making continuous flow studies easier, experimental details that should be provided as part of any organic chemistry‐based continuous flow study are presented and critically discussed. These range from flow reactor components and assembly, to important parameter effects and useful performance criteria. This review covers aspects of homogeneous systems, multiphase transformations and catalytic reactions
... 456−459 Considering the technological challenges associated with the safe handling of gaseous oxygen, many studies have been reported on the development of efficient biphasic 459 or even triphasic flow regimes. 460 465 Up to 2016, several reports about singlet oxygen oxidations in continuous flow were described. 466−469 In particular, various studies reported on the oxidation of sulfides in batch 470 and in flow, 471 reflecting the importance of sulfoxides especially in medicinal chemistry. ...
... The reactor design, a FEP or PFA coil (0.8 mm ID, 6.3 mL volume) irradiated with 190 W white LEDs, was based on a previous report. 460 Once more, the photosensitizers of choice were either MB or TPP, and when evaluated with a set of alkenes both gave high STY values (950−4600 g·L −1 ·h −1 ). Because of the poor solubility of commercially available organic dyes, especially in apolar substrates, a propyl-TPP (PrTPP) photocatalyst was devel-oped and successfully employed, with STY between 300 and 850 g·L −1 ·h −1 . ...
Photoinduced chemical transformations have received in recent years a tremendous amount of attention, providing a plethora of opportunities to synthetic organic chemists. However, performing a photochemical transformation can be quite a challenge because of various issues related to the delivery of photons. These challenges have barred the widespread adoption of photochemical steps in the chemical industry. However, in the past decade, several technological innovations have led to more reproducible, selective, and scalable photoinduced reactions. Herein, we provide a comprehensive overview of these exciting technological advances, including flow chemistry, high-throughput experimentation, reactor design and scale-up, and the combination of photo- and electro-chemistry.
... These results are the justification for the presence of -SO 3 H groups on the surface of heterostructures, which lead to visible-light response and, consequently, more efficient photocatalytic activity. Figure 7 shows the emission spectrum of blue, green and red LEDs [45][46][47]. As it is illustrated, the spectra of all three photocatalysts show a comparatively large overlap with the emission band of blue LED which indicates the excellent response to the blue light. ...
In the present work, a novel class of SO3H-functionalized heterostructure photocatalysts was synthesized for the first time by simple covalent grafting strategy. In these photocatalysts, two nano-semiconductors, TiO2-P25 and a second metal oxide, were anchored via epichlorohydrin as the covalent linker. Then, SO3H groups were immobilized on the surface of the obtained heterostructures by convenient sulfonation process. The properties of nano-photocatalysts were investigated through FTIR, XRD, FESEM, N2 sorption and UV–Visible/DRS techniques. The surface Brønsted acid can extend the absorption edge of the photocatalysts to the visible region, providing excellent to good response to the blue, green and red LED lights. The photocatalysts exhibited considerable activity and high selectivity for oxidation of benzyl alcohol to benzaldehyde. The most important advantages of this strategy are easy procedure, sustainable photocatalytic reaction and the reusability of the obtained catalysts.
... The small diameter of the inner tube results in a high surface-to-volume ratio and effective light penetration. [26,27] The application of such flow reactor to the selective photo-oxygenation of cardanol oils under visible light irradiation proved highly successful and is reported below. ...
The upcycling of waste biomass into valuable materials by resource‐efficient chemical transformations is a prime objective for sustainable chemistry. This approach is demonstrated in a straightforward light‐driven synthesis of polyols and polyurethane foams from the multi‐ton waste products of cashew nut processing. The photo‐oxygenation of cardanol from nutshell oil results in the formation of synthetically versatile hydroperoxides. The choice of the workup method (i. e., reduction, hydrogenation, epoxidation) enables access to a diverse range of alcohols with tunable alkene and OH functions. Condensation with isocyanates to give rigid polyurethane foams provides a resource‐efficient waste‐to‐value chain that benefits from the availability of cardanol and installation of OH groups from aerial O2.
