Liquid core waveguide photoreactor and liquid core waveguide illumination method

Abstract

A liquid core waveguide photoreactor and a liquid core waveguide illumination method. The difference between the refractive index of a channel wall and the refractive index of a medium on the outer side of the channel wall is used, and an included angle between light and the channel wall is set, such that light transmission meets a total-reflection condition; and multiple total-reflection transmissions are performed by using a medium in the channel as a light guide medium, such that a light guide method similar to an optical fiber is implemented. The liquid core waveguide illumination method allows light to repeatedly run through an inner channel (2) multiple times in a longitudinal direction, and thus strong and uniform illumination can both be maintained in a flow photoreactor having a length of up to several centimeters, such that the length of the effective illumination received by a photocatalytic organic reaction sample in the channel is improved.

Description

Liquid core waveguide photoreactor and liquid core waveguide illumination method Technical Field

[0001] The invention belongs to the technical field of photocatalytic organic reactions, and in particular relates to a liquid core waveguide photoreactor and a liquid core waveguide illumination method. Background Art

[0002] Photocatalytic organic reactions have become one of the powerful tools for researchers due to their advantages such as low cost, high safety, environmental friendliness, green environmental protection, simple equipment and few side reactions, significantly expanding the application range of organic synthesis. However, since commonly used photoreactors still have problems such as insufficient light intensity, low light utilization and uniformity, photocatalytic organic reactions often take several hours or even days to complete, requiring researchers to invest a lot of time and energy ([1] S. Steiner et al., Science, 2019, 363, 144-144.). The application of ideal illumination methods and photoreactor design are expected to shorten the time of photocatalytic organic reactions, increase screening throughput, reduce sample consumption, accurately control reaction conditions and achieve high reproducibility of results. To achieve the above goals, the development of new photoreactors is a key technology for realizing high-throughput screening and rapid development of conditions for photocatalytic organic reactions, which is of great significance for in-depth research on this type of reaction and the expansion of its application fields.

[0003] Currently, commonly used photoreactors mainly include traditional batch photoreactors, microbatch photoreactors, and flow photoreactors. Traditional batch photoreactors have a simple structure and are widely used, but they consume a large amount of sample and take a long time to react. Microbatch photoreactors increase the throughput of reactions by parallelizing microreactors (e.g., 96-, 384-, and 1536-well plates), but they have problems such as difficulty in scaling up reactions, difficulty in integrating online detection methods, and screening throughput being limited by detection throughput. Flow photoreactors are based on channel structures constructed in pipes or chips. Since the channel size (micrometers to millimeters) is close to the effective illumination distance and the surface area to volume ratio is high, the reaction time can be shortened to several hours or even minutes ([1] LD Elliott et al., Chem. Eur. J., 2014, 20, 15226-15232; [2] P. Sagmeister et al., Angew. Chem., Int. Ed., 2021, 60, 8139-8148; [3] JH Harenberg et al., Angew. Chem., Int. Ed., 2021, 60, 731-735.). Due to these advantages, some research groups have applied flow photoreactors to photocatalytic organic synthesis in recent years. However, since the most commonly used illumination method, the side illumination method, still has problems such as weak illumination intensity, low uniformity and low light utilization, the reaction time in the flow photoreactor is still difficult to meet the requirements of high-throughput screening.

[0004] Currently, common photoreactors (including traditional batch photoreactors, microbatch photoreactors, and flow photoreactors) typically utilize side illumination, which involves simply placing a side light source next to the reaction flask or test tube. Due to its simplicity and low cost, side illumination has been widely used in photoreactor design. However, this approach leaves significant room for improvement in terms of illumination depth, intensity, uniformity, and light utilization efficiency. In practice, light is lost when penetrating the vessel wall. This side illumination approach only utilizes a minimal portion of the light energy, wasting the vast majority, which is inconsistent with the development of green chemistry. Furthermore, according to the Lambert-Beer law, light decays exponentially with increasing depth after entering the photoreactor. Therefore, side illumination only effectively illuminates a very thin layer of liquid on the photoreactor surface. Similarly, axial illumination, which involves arranging the light source so that light shines inward from the channel exit, also suffers from issues such as low effective illumination depth and uniformity. For photocatalytic organic synthesis, uneven illumination can affect reaction outcomes and potentially lead to undesirable byproducts.

[0005] The liquid core waveguide illumination method utilizes the refractive index difference between the channel wall and the medium outside it, using the medium inside the channel as the light guide to perform multiple total reflection transmission, thus achieving a light guiding method similar to that of an optical fiber. In reported work, the liquid core waveguide illumination method has been used for online detection of long-path absorption spectra of trace samples ([1] MP Duggan et al., Analyst, 2003 128, 1336-1340; [2] J.-Z. Pan et al., Anal. Chem., 2010, 82, 3394-3398.). There are no reports in the prior art on the application of the liquid core waveguide illumination method to photoreactors.

[0006] Summary of the Invention

[0007] Existing photoreactors all use a side illumination method, which has problems such as insufficient light intensity, low uniformity, and low light utilization rate, which results in a long time-consuming photocatalytic organic synthesis reaction, many by-products, and poor reproducibility. The present invention introduces the liquid core waveguide illumination method previously used for online spectral analysis into the design of the photoreactor, significantly improving the light intensity and light uniformity, and can maintain strong light within a range of several centimeters in length of the photoreactor. This new reactor can shorten the time-consuming photocatalytic organic synthesis reaction, reduce the occurrence of side reactions, and have a high yield of the target product and good reaction reproducibility. In addition, the liquid core waveguide illumination method significantly improves light utilization, reduces light loss, and meets the development requirements of green chemistry.

[0008] The present invention first provides a liquid core waveguide photoreactor for photocatalytic organic reaction flow synthesis, comprising:

[0009] The flow photoreactor of the nested channel structure comprises an outer channel and an inner channel arranged in a nested manner. The inner cavity of the inner channel is used for passing a photocatalytic organic reaction sample, and the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel is used for passing a cooling fluid.

[0010] The temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid entering the cavity between the inner wall of the outer channel and the outer wall of the inner channel.

[0011] An optical fiber-based light coupling and conduction device includes an optical fiber having an incident end and an output end. The incident end is used to couple with a light source when in use, and the output end extends into a cavity between the inner side wall of the outer channel and the outer side wall of the inner channel of the flow light reactor. The angle of the light emitted by the output end satisfies the total reflection of the light on the side wall of the outer channel.

[0012] The light source can be configured together with the liquid core waveguide photoreactor as a whole, or it can be configured separately and assembled together when in use. The light source can be an LED, laser, incandescent lamp, halogen tungsten lamp, fluorescent lamp or other light source with high light intensity. Preferably, the liquid core waveguide photoreactor also includes a light source, which is coupled to the incident end of the optical fiber to provide the light required for the flow synthesis of photocatalytic organic reactions. The laser is the preferred light source. The light source required by the present invention should be able to output relatively strong light to ensure the progress of the photocatalytic organic synthesis reaction. Preferably, the light source output light intensity should be greater than 100mW, and the light intensity should be flexibly adjustable. The spot diameter after focusing the light source should be as small as possible to ensure the coupling ratio of light from the light source to the optical fiber and reduce light loss. Preferably, the spot diameter after focusing should be less than 600μm.

[0013] The optical fiber can be a high-purity quartz optical fiber, a plastic optical fiber, or a multi-component glass optical fiber with optical transmission performance, etc. Preferably, the material used is glass, quartz, or PEEK / PFA / PTFE.

[0014] The realization of multiple total reflection transmission of light should comprehensively consider the numerical aperture angle of the optical fiber, the angle between the optical fiber and the external channel, and the refractive index of the side wall of the external channel as a medium.

[0015] The interface at which total internal reflection occurs in the liquid-core waveguide illumination method is determined by the refractive index relationship between the outer channel sidewall medium and the inner fluid medium. In either case, the light exiting the optical fiber must meet the following conditions for total internal reflection: (A) light travels from a denser medium to a less dense medium, meaning the refractive index of the incident medium exceeds that of the exit medium; and (B) the angle of incidence exceeds the critical angle.

[0016] In order to satisfy condition (A), the refractive index of the outer channel sidewall and the media inside and outside the outer channel needs to be considered.

[0017] Preferably, the angle of the light emitted from the exit end satisfies that when the light is totally reflected on the side wall of the outer channel, the total reflection occurs on the inner side wall surface or the outer side wall surface of the outer channel.

[0018] More preferably, if total internal reflection occurs on the inner sidewall surface of the outer channel, the refractive index of the cooling fluid as a medium is greater than the refractive index of the outer channel sidewall as a medium;

[0019] If total internal reflection occurs on the outer wall of the outer channel, the refractive index of the outer channel wall must be greater than that of the surrounding environment, or a reflective layer with a greater refractive index than that of the outer channel wall must be provided on the outer wall. For example, this reflective layer can be silver-plated.

[0020] The refractive index of the media on both sides of the total internal reflection interface also determines the critical angle for total internal reflection. Based on this, the placement angle of the optical fiber exit end within the photoreactor is designed so that the incident angle of light exceeds the critical angle, satisfying the total internal reflection condition (B). The incident angle of light = the angle between the optical fiber exit end and the total internal reflection interface + the numerical aperture angle of the optical fiber.

[0021] Generally speaking, the angle between the optical fiber output end and the channel wall where total reflection occurs should be in the range of 0-45°; after the light is emitted from the optical fiber output end, it is evenly dispersed according to its numerical aperture angle. In order to make the light meet the requirement that the total reflection incident angle is greater than the critical angle when it reaches the outer channel wall, the influence of the numerical aperture angle on the angle of the output light should be considered when setting the specific angle between the optical fiber output end and the channel wall. In addition, the light beam emitted from the optical fiber will naturally spread out according to the numerical aperture angle. Generally, the numerical aperture angle (NA value) of multimode optical fiber is in the range of 0.1-0.5, and the corresponding angle is 6-30°. In the design of the actual photoreactor, when setting the specific angle between the optical fiber output end and the outer channel, the above factors need to be comprehensively considered so that the light meets the total reflection condition (B) when it reaches the interface.

[0022] The liquid-core waveguide illumination method causes light to undergo multiple total internal reflections along the longitudinal direction of the photoreactor, repeatedly passing through the inner channel, providing uniform, high-intensity light over an area several centimeters long. To ensure light transmission, the inner channel wall material must be resistant to common organic reaction samples and non-absorbent of the target wavelength. The inner and outer surfaces of both channels must be smooth and flat, without structures that alter surface symmetry, to prevent disruption of total internal reflection or loss of light due to scattering or refraction.

[0023] Furthermore, the design of the photoreactor must consider temperature control for photocatalytic organic synthesis reactions. Liquid-core waveguide illumination methods confine intense light within the photoreactor, which can lead to temperature increases that are detrimental to the results of the photocatalytic organic synthesis. A temperature control device uses a cooling fluid flowing through an external channel to promptly remove unwanted heat and thereby control the temperature of the photocatalytic organic synthesis reaction.

[0024] Preferably, the optical fiber is provided at one end of the nested channel structure flow photoreactor, or at both ends of the nested channel structure flow photoreactor. When the optical fiber is provided at both ends of the nested channel structure flow photoreactor, the optical fibers at both ends are preferably arranged symmetrically. The number of optical fibers provided at each end is one, or multiple optical fibers are arranged around the end face.

[0025] The number of optical fibers and the position of the optical fiber output ends in the light reaction can be set according to the requirements of the specific reaction. Preferably, the number of optical fibers can be greater than 1 to increase the illumination intensity in the photoreactor. Preferably, when the number of optical fiber output ends provided on the left and right sides of the photoreactor is equal (the number of optical fibers on each side can be greater than 1), that is, when they are symmetrically distributed, the light uniformity of the liquid core waveguide illumination method can be further improved. If the number of optical fibers fixed on the photoreactor is greater than 1, the number of light sources also increases accordingly, and the light sources and optical fibers correspond one to one.

[0026] The diameters of the inner and outer channels of the nested channel structure and the thickness of the channel walls will affect the effect of the liquid core waveguide illumination method. Preferably, the outer diameter of the inner channel is less than 2 mm, and the outer diameter of the outer channel is no more than 10 times the outer diameter of the inner channel. And the side wall thicknesses of the inner and outer channels are as thin as possible. The side wall thickness of the inner channel is as thin as possible to ensure that the organic reaction samples in the inner channel can all be effectively illuminated. The side wall thickness of the outer channel is as thin as possible to ensure the uniformity and utilization rate of light under the liquid core waveguide illumination method. Preferably, the side wall thickness of the inner channel is less than 1 mm, and the side wall thickness of the outer channel is less than 2 mm.

[0027] The photoreactor should be neither too long nor too short. Considering light uniformity, the reactor should not be too long. When the photoreactor length exceeds a certain limit, the illumination and temperature uniformity across the inner channel cross-section decrease as the photoreactor length increases, potentially leading to undesirable side reactions. At the same time, the photoreactor should be neither too short nor too short to ensure that the organic reaction sample remains under illumination for an effective period of time. Preferably, the flow photoreactor is 1 to 20 cm long.

[0028] The fiber core diameter should be carefully considered to optimize light utilization within the photoreactor. It should be moderately small to maximize the ratio of the inner channel's cross-sectional area to the outer channel's, ensuring high light utilization. Furthermore, to ensure a high proportion of light from the light source is coupled into the fiber and minimize light loss, the fiber core diameter should also be moderately small. Preferably, the fiber core diameter is 50-1500 μm. More preferably, it is 100-600 μm.

[0029] The length of the optical fiber should be selected based on the connection between the optical fiber and the light source and the photoreactor, and should ensure efficient light transmission within the optical fiber. Preferably, the optical fiber is 1 to 5 meters long. The optical fiber can be single-mode or multimode, with multimode fiber being preferred. This type of fiber has a thicker core, a suitable length, and exhibits less loss over short-distance light transmission, resulting in more uniform light at the optical fiber output end. When the optical fiber is multimode, the NA value of the multimode fiber is preferably between 0.1 and 0.5. More preferably, the NA value of the multimode fiber should be between 0.18 and 0.37.

[0030] Preferably, the output end of the optical fiber is a plane or an inclined surface. If it is an inclined surface, the inclined surface can be facing the side wall facing the outer channel, or facing the side wall facing the inner channel, or it can be inclined. Preferably, it is facing the side wall facing the outer channel, which is conducive to improving light utilization efficiency. More preferably, when the output end of the optical fiber is an inclined surface, the angle between the inclined surface and the side wall of the outer channel is not less than 60°. For example, the angle can be selected to be 75°. When the output end of the optical fiber is an inclined surface, the light utilization efficiency in the reactor can be further improved.

[0031] The present invention further provides a liquid core waveguide illumination method for photocatalytic organic reaction flow synthesis, using the liquid core waveguide photoreactor, the liquid core waveguide illumination method comprising the following steps:

[0032] (1) introducing a photocatalytic organic reaction sample into the cavity of the inner channel, and introducing a cooling fluid into the cavity between the inner wall of the outer channel and the outer wall of the inner channel;

[0033] (2) A light source is used to inject light into the incident end of the optical fiber, and the light emitted from the output end of the optical fiber is continuously totally reflected at the side wall of the outer channel, so that the light acts on the photocatalytic organic reaction sample to realize the photocatalytic organic reaction flow synthesis. During the reaction, the temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid entering the cavity between the inner wall of the outer channel and the outer wall of the inner channel.

[0034] When multiple total reflection transmission of light occurs, the cooling fluid in the outer channel acts as both a heat dissipation medium and a light guiding and uniform light medium; the nested channel structure and temperature control device can achieve temperature control of the photocatalytic organic reaction sample while providing strong light.

[0035] The cooling fluid should have a high specific heat capacity to promptly remove unwanted heat generated by intense light within the photoreactor. It should also be transparent to light and not interfere with the multiple total reflections of light as it flows through the photoreactor. Preferably, the cooling fluid is a homogeneous, transparent liquid or gas. Specifically, the cooling fluid, when liquid, is water, ethanol, or fluorinated oil.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] Different from the side illumination method adopted by traditional batch reactors, micro-batch reactors and flow reactors, the flow photoreactor of the present invention adopts a liquid core waveguide illumination method. The liquid core waveguide illumination method utilizes the refractive index difference between the channel wall and the medium outside it, and sets the angle between the light and the channel wall so that the transmission of light meets the total reflection condition, and uses the medium in the channel as the light guiding medium to perform multiple total reflection transmissions, thereby realizing a light guiding method similar to that of optical fiber. The liquid core waveguide illumination method allows light to pass through the inner channel repeatedly in the longitudinal direction, and can maintain strong and uniform illumination in a flow photoreactor as long as several centimeters, so that the effective illumination length of the photocatalytic organic reaction sample in the inner channel is increased from 2mm of the side illumination method to several centimeters. The liquid core waveguide illumination method is beneficial to shortening the time consumed by the photocatalytic organic reaction, completing the reaction efficiently and quickly, and also reduces the loss of light due to refraction, scattering and absorption, significantly improving the utilization rate of light, and meeting the development needs of green chemistry. Furthermore, the nested channel structure and temperature control device of the photoreactor of the present invention can promptly remove unwanted heat caused by strong light, achieving effective and precise temperature control of the photocatalytic organic reaction and avoiding the increase in side reactions caused by the actual temperature deviating from the optimal reaction temperature. The liquid-core waveguide photoreactor of the present invention for flow synthesis of photocatalytic organic reactions has the advantages of simple structure, easy operation, integration, automation, traceable system, environmental friendliness, repeatability, high versatility, short photocatalytic organic reaction time and high efficiency. It is suitable for mechanism exploration in the research and development stage of photocatalytic organic reactions and high-throughput screening of reaction conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic diagram of light transmission of the liquid core waveguide illumination method, wherein A: a schematic diagram of the liquid core waveguide illumination method in which total reflection occurs on the outer wall surface of the outer channel; B: a schematic diagram of the liquid core waveguide illumination method in which total reflection occurs on the inner wall surface of the outer channel.

[0039] FIG2 is a schematic diagram of the structure of a liquid core waveguide photoreactor with an optical fiber on one side.

[0040] FIG3 is a schematic diagram of the structure of a liquid core waveguide photoreactor with optical fibers symmetrically distributed on both sides.

[0041] FIG4 is a schematic diagram of the structure of a liquid core waveguide photoreactor having a microstructure at the optical fiber output end.

[0042] Figure annotation:

[0043] External channel 1, including external channel liquid inlet 11 and external channel liquid outlet 12;

[0044] The inner channel 2 includes an inner channel liquid inlet 21 and an inner channel liquid outlet 22;

[0045] A three-way structure 3, comprising a three-way connection to an inner channel end 31, a three-way connection to an outer channel end 32, and a three-way connection to a temperature control device end 33;

[0046] The optical coupling and transmission device 4 includes an optical fiber input end 41, an optical fiber output end 42, and a light source 43;

[0047] Temperature control device 5.

[0048] Specific implementation methods

[0049] A liquid core waveguide photoreactor for photocatalytic organic reaction flow synthesis, comprising:

[0050] The flow photoreactor of the nested channel structure comprises an outer channel and an inner channel arranged in a nested manner. The inner cavity of the inner channel is used for passing a photocatalytic organic reaction sample, and the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel is used for passing a cooling fluid.

[0051] The temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid entering the cavity between the inner wall of the outer channel and the outer wall of the inner channel.

[0052] An optical fiber-based light coupling and conduction device includes an optical fiber having an incident end and an output end. The incident end is used to couple with a light source when in use, and the output end extends into a cavity between the inner side wall of the outer channel and the outer side wall of the inner channel of the flow light reactor. The angle of the light emitted by the output end satisfies the total reflection of the light on the side wall of the outer channel.

[0053] The light source can be configured together with the liquid core waveguide photoreactor as a whole, or it can be configured separately and assembled together when in use. The light source can be an LED, laser, incandescent lamp, halogen tungsten lamp, fluorescent lamp or other light source with high light intensity. Preferably, the liquid core waveguide photoreactor also includes a light source, which is coupled to the incident end of the optical fiber to provide the light required for the flow synthesis of photocatalytic organic reactions. The laser is the preferred light source. The light source required by the present invention should be able to output relatively strong light to ensure the progress of the photocatalytic organic synthesis reaction. Preferably, the light source output light intensity should be greater than 100mW, and the light intensity should be flexibly adjustable. The spot diameter after focusing the light source should be as small as possible to ensure the coupling ratio of light from the light source to the optical fiber and reduce light loss. Preferably, the spot diameter after focusing should be less than 600μm.

[0054] The optical fiber can be a high-purity quartz optical fiber, a plastic optical fiber, or a multi-component glass optical fiber with optical transmission performance, etc. Preferably, the material used is glass, quartz, or PEEK / PFA / PTFE.

[0055] The angle of the light emitted from the optical fiber output end satisfies that when the light is totally reflected on the side wall of the outer channel, the total reflection occurs on the inner side wall surface or the outer side wall surface of the outer channel.

[0056] The light emitted from the optical fiber must meet the conditions for total internal reflection to occur: (A) the light is transmitted from the optically denser medium to the optically less dense medium, that is, the refractive index of the incident medium is greater than the refractive index of the exiting medium; (B) the incident angle is greater than the critical angle.

[0057] To satisfy condition (A), if total internal reflection occurs on the inner wall of the outer channel, the refractive index of the cooling fluid as the medium must be greater than the refractive index of the outer channel sidewall as the medium. If total internal reflection occurs on the outer wall of the outer channel, the refractive index of the outer channel sidewall as the medium must be greater than the refractive index of the environment outside the outer channel, or the outer wall of the outer channel must be provided with a reflective layer with a refractive index greater than that of the outer channel sidewall, and the refractive index of the reflective layer as the medium must be greater than the refractive index of the environment outside the outer channel. For example, this reflective layer can be a silver-plated layer.

[0058] The refractive index of the media on both sides of the total internal reflection interface also determines the critical angle for total internal reflection. Based on this, the placement angle of the optical fiber exit end within the photoreactor is designed so that the incident angle of light exceeds the critical angle, satisfying the total internal reflection condition (B). The incident angle of light = the angle between the optical fiber exit end and the total internal reflection interface + the numerical aperture angle of the optical fiber.

[0059] Generally speaking, the angle between the optical fiber output end and the channel wall where total reflection occurs should be in the range of 0-45°; after the light is emitted from the optical fiber output end, it is evenly dispersed according to its numerical aperture angle. In order to make the light meet the requirement that the total reflection incident angle is greater than the critical angle when it reaches the outer channel wall, the influence of the numerical aperture angle on the angle of the output light should be considered when setting the specific angle between the optical fiber output end and the channel wall. In addition, the light beam emitted from the optical fiber will naturally spread out according to the numerical aperture angle. Generally, the numerical aperture angle (NA value) of multimode optical fiber is in the range of 0.1-0.5, and the corresponding angle is 6-30°. In the design of the actual photoreactor, when setting the specific angle between the optical fiber output end and the outer channel, the above factors need to be comprehensively considered so that the light meets the total reflection condition (B) when it reaches the interface.

[0060] The liquid-core waveguide illumination method causes light to undergo multiple total internal reflections along the longitudinal direction of the photoreactor, repeatedly passing through the inner channel, providing uniform, high-intensity light over an area several centimeters long. To ensure light transmission, the inner channel wall material must be resistant to common organic reaction samples and non-absorbent of the target wavelength. The inner and outer surfaces of both channels must be smooth and flat, without structures that alter surface symmetry, to prevent disruption of total internal reflection or loss of light due to scattering or refraction.

[0061] One end of the flow light reactor of the nested channel structure is provided with the optical fiber, or both ends of the flow light reactor of the nested channel structure are provided with the optical fiber. The number of optical fibers provided at each end is one, or a plurality of optical fibers arranged around the end face. The number of optical fibers and the position of the optical fiber exit end in the light reaction can be set according to the requirements of the specific reaction. Preferably, the number of optical fibers can be greater than 1 to improve the illumination intensity in the light reactor. Preferably, when the number of optical fiber exit ends arranged on the left and right sides of the light reactor is equal (the number of optical fibers on each side can be greater than 1), that is, when they are symmetrically distributed, the light uniformity of the liquid core waveguide illumination method can be further improved. If the number of optical fibers fixed on the light reactor is greater than 1, the number of light sources also increases accordingly, and the light sources correspond to the optical fibers one to one.

[0062] The diameters of the inner and outer channels of the nested channel structure and the thickness of the channel walls will affect the effect of the liquid core waveguide illumination method. Preferably, the outer diameter of the inner channel is less than 2 mm, and the outer diameter of the outer channel is no more than 10 times the outer diameter of the inner channel. And the side wall thicknesses of the inner and outer channels are as thin as possible. The side wall thickness of the inner channel is as thin as possible to ensure that the organic reaction samples in the inner channel can all be effectively illuminated. The side wall thickness of the outer channel is as thin as possible to ensure the uniformity and utilization rate of light under the liquid core waveguide illumination method. Preferably, the side wall thickness of the inner channel is less than 1 mm, and the side wall thickness of the outer channel is less than 2 mm.

[0063] The length of the photoreactor should not be too long or too short. Preferably, the length of the flow photoreactor is 1 to 20 cm. The core diameter of the optical fiber needs to take into account the light utilization in the photoreactor. Preferably, the core diameter of the optical fiber is 50-1500 μm. More preferably, the core diameter of the optical fiber is 100-600 μm. The length of the optical fiber should be selected taking into account the connection between the optical fiber and the light source and the photoreactor, and ensuring the effective transmission of light in the optical fiber. Preferably, the length of the optical fiber is 1 to 5 m. The optical fiber is a single-mode optical fiber or a multi-mode optical fiber. The preferred type of optical fiber is a multi-mode optical fiber. This type of optical fiber has a thicker core and a suitable length, and has less loss in short-distance light transmission, and the light at the optical fiber output end is more uniform. When the optical fiber is a multi-mode optical fiber, the NA value of the multi-mode optical fiber is 0.1 to 0.5. More preferably, the NA value of the multi-mode optical fiber should be in the range of 0.18 to 0.37.

[0064] The cooling fluid should have a high specific heat capacity to promptly remove unwanted heat generated by intense light within the photoreactor. It should also be transparent to light and not interfere with the multiple total reflections of light as it flows through the photoreactor. Preferably, the cooling fluid is a homogeneous, transparent liquid or gas. Specifically, the cooling fluid, when liquid, is water, ethanol, or fluorinated oil.

[0065] Example 1

[0066] Figure 1 is a schematic diagram of light transmission in the liquid core waveguide illumination method. The liquid core waveguide illumination method is based on the principle of total reflection. Light undergoes multiple total reflections and propagates in the photoreactor channel, ultimately achieving uniform light distribution. When light reaches the side wall of the outer channel, it is necessary to simultaneously meet the two conditions of light entering from a denser medium into a less dense medium and the angle of incidence being greater than the critical angle. Whether total reflection is emitted on the outer surface or the inner surface of the outer channel side wall depends on the difference in refractive index between the fluid in the outer channel cavity and the outer channel side wall. If the refractive index of the outer channel side wall is greater than the refractive index of the fluid in the outer channel cavity, and the refractive index of the outer channel side wall is greater than the refractive index of the medium outside the outer channel, then total reflection occurs on the outer surface of the outer channel side wall; conversely, if the refractive index of the outer channel side wall is less than the refractive index of the fluid in the outer channel cavity, then total reflection occurs on the inner surface of the outer channel side wall.

[0067] FIG1A is a schematic diagram of a liquid core waveguide illumination method in a photoreactor with a nested channel structure, when multiple total reflections occur on the outer surface of the outer channel sidewall;

[0068] FIG1B is a schematic diagram of a liquid core waveguide illumination method in a photoreactor with a nested channel structure, when multiple total reflections occur on the inner surface of the outer channel sidewall;

[0069] Example 2

[0070] Figure 2 is a schematic diagram of the structure of a liquid core waveguide photoreactor with an optical fiber on one side. The photoreactor consists of a flow photoreactor with a nested channel structure, an optical coupling and conduction device, and a temperature control device.

[0071] The flow photoreactor with a nested channel structure is used to pass the flowing organic reaction sample, provide strong and uniform illumination and control the reaction temperature. The nested channel structure includes an outer channel 1, an inner channel 2, and a three-way structure 3. The outer channel 1 and the inner channel 2 are arranged in a sleeve. The outer channel 1 flows through a cooling fluid, and the inner channel 2 flows through a photocatalytic organic reaction sample. Between the outer channel 1 and the inner channel 2, the three-way connection inner channel end 31 and the three-way connection outer channel end 32 of the two three-way structures 3 are sealed with the inner channel side wall and the outer channel side wall respectively by a stopcock or other methods, allowing the inner channel to pass through the outer channel to form a nested structure, ensuring that the fluids between the two channels do not contact each other. In addition, the three-way structure 3 allows the optical fiber output end 42 to be placed between the inner and outer channels. The three-way connection temperature control device end 33 is connected to the temperature control device to pass the cooling fluid.

[0072] The optical coupling and transmission device 4 includes an optical fiber input end 41, an optical fiber output end 42, and a light source 43. The optical fiber input end 41 couples the intense light from the light source 43, which is then transmitted through the optical fiber to the optical fiber output end 42, which is positioned between the outer channel 1 and the inner channel 2 of the photoreactor. This light is then introduced into the photoreactor, achieving the liquid-core waveguide illumination method.

[0073] The temperature control device 5 includes a cooling fluid and a driving device for the fluid. The temperature control device 5 controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid flowing into the cavity between the inner wall of the outer channel 1 and the outer wall of the inner channel 2.

[0074] The specific steps of using the photoreactor of the present invention are as follows:

[0075] Step 1: Select a light source 43 with an appropriate wavelength based on the specific requirements of the organic synthesis reaction, determine the required light intensity, and then determine the number of optical fibers required. The number of optical fibers can be greater than one. Set the temperature range of the cooling fluid based on the specific requirements of the organic synthesis reaction.

[0076] Step 2: Use optical fiber to couple light from the light source to the photoreactor. First, couple the focused light from the light source 43 to the optical fiber input end 41, ensuring that most of the light enters the optical fiber. Use a dimming fiber with the same specifications as the actual optical coupling device and a laser power meter to detect the coupling ratio. Detect the light spot at the light source and the light intensity at the optical fiber output end 42 respectively. During this process, the relative position between the light source and the optical fiber input end 41 can be fine-tuned to ensure that the proportion of light coupled into the optical fiber to the total light intensity of the light source is greater than 70%. If the optical coupling part has more than one set of light sources and optical fibers, each set needs to be adjusted one by one to ensure that the coupling ratio is greater than 70%. Finally, after obtaining the ideal coupling ratio, remove the dimming fiber and replace it with the optical fiber connected to the photoreactor.

[0077] Step 3: Determine the location of total internal reflection for the liquid-core waveguide illumination method based on the refractive indices of the sample solvent and cooling fluid for the desired photocatalytic organic reaction. Fine-tune and determine the placement angle of the optical fiber output end 42 to ensure that no significant light beam is emitted from the sidewalls of the photoreactor's outer channel and that uniform light distribution is observed within the photoreactor.

[0078] Step 4: Determine the required number of light sources and the required total light intensity according to the specific requirements of the photocatalytic organic reaction, set the output power of the light source accordingly, and then turn on the power of the light source.

[0079] In step 5, the photocatalytic organic reaction sample is introduced into the photoreactor via the inner channel inlet 21 via the sample injection device. The reaction proceeds at the configured wavelength, intensity, flow rate, and temperature. After the reaction, the sample flows out of the inner channel outlet 22 and is collected for subsequent testing.

[0080] Step 6: When the reaction is complete, disconnect all power supplies and end use.

[0081] Example 3

[0082] Figure 3 is a schematic diagram of the device structure of a liquid-core waveguide photoreactor with optical fibers symmetrically arranged on both sides. Unlike Example 2, in Example 3, the optical fibers are placed symmetrically on both sides of the photoreactor. This symmetrical structure not only significantly increases the light intensity within the photoreactor, but also significantly improves the uniformity of light distribution within the photoreactor, shortening the organic synthesis reaction rate and reducing undesirable side reactions. The remaining structure and method of use are the same as in Example 2.

[0083] Setting up the side lighting method in the laboratory. Photocatalytic organic reactions require as uniform illumination as possible, so a commonly used light source is a coiled LED light strip. A light-transmitting reaction vessel, such as a test tube or flask, is placed in the middle of the coiled LED light strip, and light evenly illuminates the reaction vessel inside from the side. Considering that most photocatalytic organic reactions require temperature control, the light source should be set to avoid excessive heat from the light causing the reaction temperature to rise too high, ensuring that the photocatalytic reaction is carried out at the required room temperature or low temperature. Therefore, the coiled LED light strip should not be too close to the reaction vessel. Generally, the diameter of the coiled light strip cylinder is 10-20 cm.

[0084] Experimental data: In this case, the liquid core waveguide illumination method has significant advantages over the side illumination method in terms of illumination intensity, effective illumination depth, and light utilization rate. In terms of illumination intensity, the side illumination method has an illumination intensity of 3.4mW / cm on the reactor surface. 2 , while the illumination intensity of the liquid core waveguide illumination method can reach 3.5×10 4 mW / cm 2 , an increase of about 10,000 times. In terms of effective illumination depth, due to the exponential attenuation of light when penetrating the reactor, the side illumination method can only provide effective illumination for samples about 2mm deep from the reactor surface. The liquid core waveguide illumination method can provide effective illumination for samples up to 5cm through repeated total reflection. In comparison, the effective illumination depth is increased by about 25 times. In addition, the light utilization rate of the liquid core waveguide illumination method is about 10 times higher than that of the side illumination method, significantly reducing the waste of light energy and being more in line with the concept of green chemistry.

[0085] Reaction type and results: To verify the practical effect of the liquid core waveguide illumination method in the application of photocatalytic organic reactions, we took a typical and widely used organic photocatalytic synthesis - the visible light catalyzed [2+2] cycloaddition reaction as an example (the reaction formula is shown in Formula I). ​​This type of reaction is of great significance in organic synthesis because the cyclobutane obtained by this type of reaction is widely present in a variety of natural products with biological activity. Under the same compound composition, compound ratio, concentration and temperature conditions, the [2+2] cycloaddition reaction requires 4 hours to complete in the side illumination method and batch reactor, but only requires a residence time of 3.3 seconds in the liquid core waveguide illumination method and the corresponding photoreactor, significantly improving the reaction efficiency and shortening the time by about 4300 times. From the reaction results, the yield result of 91% obtained by the liquid core waveguide illumination method is comparable to the yield result of 89% obtained by the side illumination method.

[0086] Therefore, the liquid core waveguide illumination method of the present invention can significantly improve the illumination intensity and effective illumination depth, thereby improving light utilization efficiency and significantly shortening the time consumption of photocatalytic organic reactions such as [2+2] cycloaddition.

[0087] Example 4

[0088] Figure 4 is a schematic diagram of the structure of a liquid-core waveguide photoreactor with microstructures at the optical fiber exit end. Unlike Example 3, in Example 4, the microstructures machined at the optical fiber exit end better control the light's exit angle, reducing excessive dispersion caused by the numerical aperture angle after exiting the optical fiber. This prevents light loss caused by refraction or scattering when reaching the channel walls due to failure to meet total internal reflection conditions, further improving light utilization. The remaining structure and method of use are the same as in Example 3.

[0089] Microstructure Description: The primary purpose of the microstructure at the fiber's exit end is to modify the morphology of the fiber's exit endface, increasing the proportion of total internal reflection (TRI) of the emitted light and reducing light loss. For example, a beveled surface can be machined onto the fiber's exit endface through sandpaper polishing or other methods. The specific angle between this beveled surface and the outer channel wall should be considered based on the fiber's diameter, numerical aperture angle, and placement, but should be within a range of 60° to 90°. After the beveled surface is polished onto the fiber's core endface, it should be polished with sandpaper or abrasive with a grit higher than 5000 until the surface is flat and smooth. When positioning the microstructured fiber in the liquid-core waveguide photoreactor, the polished beveled surface should face the outer channel wall. This is because light exiting the microstructured beveled surface will first reach the outer channel wall and be evenly distributed within the channel through total internal reflection. Alternatively, the beveled surface can face the inner channel wall, which also slightly improves light utilization compared to photoreactors without microstructures at the fiber's exit endface. However, light is emitted from the processed microstructure slope, passes through the inner channel first, then reaches the side wall of the outer channel and realizes total reflection, which may cause the uniformity of light distribution in the inner channel to decrease.

[0090] Experimental results: Four optical fibers with a core diameter of 400 μm and a microstructured bevel were placed in a photoreactor, parallel to the channel. The fibers had an optical fiber NA of 0.37. The results showed that when the microstructured bevel formed a 75° angle with the sidewall of the outer channel, the light utilization efficiency in the reactor was improved by approximately 1.5 times compared to the liquid-core waveguide illumination method without microstructures in Example 3, and by approximately 15 times compared to the side illumination method. Light was evenly distributed throughout the inner channel (5 cm long).

[0091] When the angle between the microstructure slope and the side wall of the inner channel is 75°, the light utilization efficiency in the reactor is further improved by about 1.2 times compared with the liquid core waveguide illumination method of the optical fiber without microstructure in Example 3, that is, it is improved by about 12 times compared with the side illumination method, but the light distribution in the inner channel (5 cm long) decreases uniformly, and the light distribution is weak light area (0-1.5 cm) - strong light area (1.5-3.5 cm) - weak light area (3.5-5.0 cm).

Claims

1. A liquid core waveguide photoreactor for photocatalytic organic reaction flow synthesis, characterized in that: include: The flow photoreactor of the nested channel structure comprises an outer channel and an inner channel arranged in a nested manner, wherein the inner cavity of the inner channel is used for passing a photocatalytic organic reaction sample, and the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel is used for passing a cooling fluid. The temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid passing into the cavity between the inner wall of the outer channel and the outer wall of the inner channel, An optical fiber-based light coupling and conduction device includes an optical fiber having an incident end and an output end. The incident end is used to couple with a light source when in use, and the output end extends into a cavity between an inner wall of an outer channel of the flow light reactor and an outer wall of the inner channel. The angle of the light emitted by the output end satisfies total reflection of the light at the side wall of the outer channel.

2. The liquid core waveguide photoreactor according to claim 1, characterized in that: It also includes a light source, which is coupled to the incident end of the optical fiber and is used to provide light required for photocatalytic organic reaction flow synthesis.

3. The liquid core waveguide photoreactor according to claim 1, characterized in that: The angle of the light emitted from the exit end satisfies that when the light is totally reflected on the side wall of the outer channel, the total reflection occurs on the inner side wall surface or the outer side wall surface of the outer channel.

4. The liquid core waveguide photoreactor according to claim 3, characterized in that: If total reflection occurs on the inner wall surface of the outer channel, the refractive index of the cooling fluid as a medium is greater than the refractive index of the outer channel side wall as a medium; If total reflection occurs on the outer wall surface of the outer channel, it is necessary to satisfy that the refractive index of the outer channel side wall as a medium is greater than the refractive index of the environment outside the outer channel as a medium, or the outer wall surface of the outer channel is provided with a reflective layer with a refractive index greater than that of the outer channel side wall, and the refractive index of the reflective layer as a medium is greater than the refractive index of the environment outside the outer channel as a medium.

5. The liquid core waveguide photoreactor according to claim 1, characterized in that: The optical fiber is disposed at one end of the flow photoreactor with the nested channel structure, or at both ends of the flow photoreactor with the nested channel structure; The number of optical fibers arranged at each end is one, or multiple optical fibers arranged around the end face.

6. The liquid core waveguide photoreactor according to claim 1, characterized in that: The outer diameter of the inner channel is less than 2 mm, and the outer diameter of the outer channel is no more than 10 times the outer diameter of the inner channel; The side wall thickness of the inner channel is less than 1 mm, and the side wall thickness of the outer channel is less than 2 mm.

7. The liquid core waveguide photoreactor according to claim 1, characterized in that: The length of the flow photoreactor is 1 to 20 cm; The length of the optical fiber is 1 to 5 m; the diameter of the optical fiber core is 50 to 1500 μm; the optical fiber is a single-mode optical fiber or a multi-mode optical fiber. When the optical fiber is a multi-mode optical fiber, the NA value of the multi-mode optical fiber is 0.1 to 0.

5.

8. The liquid core waveguide photoreactor according to claim 1, characterized in that: The output end of the optical fiber is a plane or an inclined surface.

9. A liquid core waveguide illumination method for photocatalytic organic reaction flow synthesis, characterized in that: Using the liquid core waveguide photoreactor according to any one of claims 1 to 8, the liquid core waveguide illumination method comprises the following steps: (1) introducing a photocatalytic organic reaction sample into the cavity of the inner channel, and introducing a cooling fluid into the cavity between the inner wall of the outer channel and the outer wall of the inner channel; (2) A light source is used to inject light into the incident end of the optical fiber, and the light emitted from the output end of the optical fiber is continuously and totally reflected at the side wall of the outer channel so that the light acts on the photocatalytic organic reaction sample to realize the photocatalytic organic reaction flow synthesis. During the reaction, the temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid passing into the cavity between the inner wall of the outer channel and the outer wall of the inner channel.

10. The liquid core waveguide illumination method according to claim 9, characterized in that: The cooling fluid is a homogeneous, light-transmitting liquid or gas; When the cooling fluid is liquid, it is specifically water, ethanol or fluorine oil.

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