Method for preparing porous adsorbent particles, porous adsorbent particles and sampling device, and their use

Abstract

The present invention relates to a method for preparing porous sorbent particles. The present invention also relates to porous sorbent particles and to a sampling device containing a plurality of said particles. The present invention also relates to the use of said particles or said sampling device.

Description

[Technical Field]

[0001] The present invention relates to a method for preparing porous adsorbent particles. The present invention also relates to porous adsorbent particles of poly(2,6-diphenyl-p-phenylene oxide), and to a sample collection device containing a plurality of said particles. The present invention also relates to the use of said particles or said sample collection device. [Background technology]

[0002] To ensure air quality, it is necessary to monitor the presence and concentration of airborne compounds, especially volatile organic compounds. Other reasons why it is desirable to monitor the presence of airborne compounds in the air include the detection of explosives or drugs, or sample collection for scientific purposes, such as space missions.

[0003] Particularly when multiple target compounds are expected to be present or need to be monitored, it is common practice to collect the target compounds on a solid sorbent contained within a sampling device, such as a sampling tube, which is then desorbed and analyzed in a suitable laboratory, often involving gas chromatography (GC).

[0004] Desorption of analytes from adsorbents is based on the principle that previously adsorbed materials are released from the adsorbent by increasing the temperature. The desorption temperature should be high enough to extract all the analytes, but not so high that it increases the risk of generating artifacts due to thermal decomposition of the adsorbent.

[0005] Highly suitable materials for use as adsorbents in combination with thermal desorption are based on poly(2,6-diphenyl-p-phenylene oxide), also known as poly(2,6-diphenylphenol, PPPO, or 3PO). In this application, this compound will primarily be referred to as PPPO. PPPO-based products are commercially available. An example of this is the adsorbent product TENAX® from the Dutch company Buchem BV, which is widely used as a column packing material for capturing volatile substances from air (VOCs) or liquids. The use of TENAX® is specified in the standard methods of EPA, NIOSH, ISO 2011 16000-6 (indoor air sampling), ISO 16017-1 (VOC sampling and analysis), and EN 14338:2004, EU Regulation No. 10 / 2011 (food simulants).

[0006] Because the intermolecular bonding forces are weak, contaminants are easily removed from PPPO adsorbents. PPPO-based adsorbents are particularly useful for analyzing high-boiling compounds such as alcohols, polyethylene glycols, diols, phenols, monoamines and diamines, ethanolamines, amides, aldehydes, ketones, and chlorinated aromatic compounds. Using thermal desorption equipment, measurements at parts per billion (ppb) and parts per trillion (ppt) levels are possible.

[0007] Although currently available PPPO-based adsorbents perform well, the inventors have noted that there is still room for improvement. Summary of the Invention [Problem to be solved by the invention]

[0008] In a first aspect, the present invention relates to a method for preparing porous adsorbent particles, the method comprising the steps of: i) providing a solution of poly(2,6-diphenyl-p-phenylene oxide) in an organic solvent medium; ii) holding droplets of the solution in air without any mechanical support by physical contact; and iii) evaporating the organic solvent medium while maintaining the solution in said state at least until the solution is converted into particles in a semi-solid or solid state.

[0009] In a second aspect, the present invention relates to PPPO-based porous adsorbent particles obtainable by the process of the first aspect of the invention.

[0010] In a third aspect, the present invention relates to a sampling tube comprising a plurality of porous sorbent particles according to the second aspect of the invention.

[0011] In a fourth aspect, the present invention relates to the use of porous particles according to the second aspect of the invention as adsorbents in air collection. Accordingly, the present invention also relates to the use of a sampling tube according to the third aspect of the invention in air collection.

[0012] The present invention provides PPPO-based adsorbent particles with good accessible surface area and more uniform pore size and distribution than prior art PPPO-based materials, demonstrating improved adsorption properties. Prior art materials, i.e., have highly heterogeneous pore size distributions and irregular structures. The present invention allows for the creation of monodisperse, uniform, and precise pore arrays and particle sizes. In particular, the method of the present invention allows for control of pore size and distribution, enabling the design of adsorbent particles targeted to specific classes of molecules to be adsorbed. In this regard, it should also be noted that particles with very small pores can be prepared, which can be used for the adsorption of very small molecules, such as volatile organic compounds and compounds selected from C1-C5 hydrocarbons, including CH4, CO2, and CO. The porous adsorbent particles are thermally stable at high temperatures above C. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 shows a schematic diagram of the preparation of particles according to the invention using suspended droplets of a PPPO solution. [Figure 2] FIG. 2 shows the surface of a prior art PPPO adsorbent product (A) having an irregularly shaped surface and pores, and the surface of a particle according to the invention (B) having a pore structure of uniform size and distribution. [Figure 3] FIG. 3 illustrates an exemplary sampling tube according to the present invention. [Figure 4] Figure 4 shows SEM images of PPPO particles formed from a 0.5 w / w% solution of PPPO in DCM exposed to a temperature of 375°C. The top image shows the whole particle, the bottom image shows an enlarged cross section, and the left and right images show particles without heat treatment and those heat-treated at 375°C for 4 hours under a nitrogen atmosphere, respectively. [Figure 5] Figure 5 shows SEM images of PPPO particles formed from a 5 wt% solution of PPPO in DCM exposed to a temperature of 375°C. The top image shows the whole particle, the bottom image shows an enlarged cross-section, and the left and right images show particles without heat treatment and those heat-treated at 375°C for 4 hours under a nitrogen atmosphere, respectively. [Figure 6] FIG. 6 shows a porous array on a 20 μm×20 μm surface area of particles produced from an 8 w / w% solution of PPPO in DCM at 60% relative humidity (RH) (T=21° C.). [Figure 7] FIG. 7 shows a porous array on a 20 μm×20 μm surface area of particles produced from a 5 w / w% solution of PPPO in DCM at 10% relative humidity (RH) (T=21° C.). [Figure 8] FIG. 8 shows a porous array on a 20 μm×20 μm surface area of particles produced from a 5 w / w% solution of PPPO in DCM at 80% relative humidity (RH) (T=21° C.). [Figure 9]Figure 9 shows a series of SEM images of (a) the surface structure of particles formed from a binary mixture of PPPO:DCM (5 w / w% PPPO) at 40% RH (T = 21 °C) by droplet air levitation, and (b) the surface structure of a film from a binary mixture of PPPO:DCM (5 w / w% PPPO) deposited on a glass slide at the same RH in (a) (T = 21 °C). [Figure 10] Figure 10 shows a series of SEM images of the surface structure of particles formed by air levitation (T = 21 °C, RH = 60%). The vertically aligned images show particles from a binary mixture of PPPO:DCM with increasing initial polymer concentrations of 0.5, 3, 5, and 8 wt%. The horizontally aligned SEM images show particles formed from a ternary solution of 5 wt% PPPO, DCM, and heptane, starting with 0 wt% heptane and increasing the initial heptane concentration to 4, 6, 10, 14, and 16 wt%. [Figure 11] Figure 11 shows a 3D graph with varying heptane concentration, PPPO concentration, and RH represented on the x, y, and z axes, respectively, with the intersection of the data set at the initial binary solution concentration of 5 wt% PPPO and RH. Optical images of the final particles are displayed along the axes, and SEM micrographs are shown for some particles to illustrate the surface structure trends. [Figure 12] Figure 12 shows a scheme for estimating particle surface area for particles according to the invention: A) particle dimensions; B) image of a particle showing the presence of pores in a layer within the skin; C) image of the particle skin with pores visualized as multiple interconnected spheres. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention is based on the inventors' finding that porous PPPO particles with improved properties can be obtained by holding droplets of PPPO dissolved in an organic solvent medium in an airborne state without any mechanical support through physical contact, allowing most of the solvent medium to evaporate. The inventors have particularly discovered that by holding the PPPO solution in an airborne state without any mechanical support through physical contact during evaporation of the solvent medium, it is possible to design and obtain adsorbent particles with a pore structure of uniform size and distribution. This effect is clearly shown in Figure 2, where Figure 2A shows the surface of a prior art PPPO adsorbent product with irregularly shaped surfaces and pores, and Figure 2B shows the surface of particles according to the present invention with a pore structure of uniform size and distribution.

[0015] During drying of the polymer solution droplets, the resulting particle size, shape, and surface structure can be controlled, with emphasis on the reliable predictive design of particles with uniform and specified morphology. In particular, the present invention makes it possible to design and control pore sizes ranging from very small to larger pores in order to specifically target molecules to be adsorbed. In particular, the present invention makes it possible to prepare highly porous particles from polymer solutions with low polymer concentrations, where the particles surprisingly do not collapse even when exposed to high temperatures of 375°C or higher. The applications of the adsorbent particles according to the present invention are widespread in sensing / adsorption devices.

[0016] The above-described state in which the solution is held in the air without any mechanical support from any physical contact can be suitably achieved by actually suspending the particles. In a practical embodiment, the solution is suspended in the air against gravity. To keep a droplet of solution suspended in the air, an upward force is required to counteract the weight of the solution, so that the solution does not fall (accelerate downward) or rise (accelerate upward).

[0017] While various techniques are available for keeping objects suspended in air, in practical embodiments, the solution can be suspended and maintained in air against gravity by using particle levitation techniques, such as acoustic levitation. Acoustic levitation is a method of suspending a substance in air against gravity using acoustic radiation pressure from high-intensity sound waves. Alternative droplet levitation methods, such as spray-drying techniques, can be used within the context of the present invention, as long as the suspended polymer solution is held in air without any mechanical support from physical contact.

[0018] When particles are prepared according to the present invention during drying, the polymer accumulates on the droplet surface, reaching a critical concentration and forming a gel-like skin at the interface. The droplet core remains liquid for some time. The solvent continues to evaporate through the skin, and eventually, depending on the skin's thickness and shear modulus, a cavity forms in the center of the droplet. The cavity formation creates a pressure difference that causes mechanical instability in the skin as the droplet further reduces its volume, resulting in a hollow particle with a wavy surface structure. This process is illustrated in Figure 1, where, as a non-limiting example, an acoustic levitation device is used to prepare particles according to the present invention. Figure 1 shows solvent evaporation, skin and cavity formation, and surface buckling. After drying over time due to solvent evaporation, this ultimately results in a polymer particle.

[0019] The organic solvent is evaporated while maintaining the solution in this state until the solution is converted into particles in a semi-solid or solid state. Once the particles are in a semi-solid or solid state, the remaining liquid can be evaporated using conventional drying techniques without changing their structure and morphology. This makes the manufacturing process more efficient. Therefore, after step iii), it is preferable to recover the particles and subject them to a drying step iv). This drying step can be suitably carried out by incubating the recovered particles in an oven.

[0020] During drying of the PPPO solution in the organic solvent medium, so-called self-assembly occurs. This is a spontaneous process that leads to the formation of nano- and micro-scale honeycomb structures (pore arrays) through the condensation of water droplets. The main physical processes involved in the formation of these arrays typically include: 1) evaporation of the polymer solution, 2) nucleation of water droplets, 3) condensation of water droplets, 4) droplet growth, 5) rearrangement and stabilization of the droplets on the surface, 6) evaporation of water, and 7) solidification of the polymer, which produces nano- and micro-porous honeycomb patterns called "breath figures." The inventors surprisingly found that these porous arrays on the resulting particles can withstand high temperatures (up to 400°C) without losing the resulting particle structure, even when heated above the glass transition temperature. Current PPPO-based adsorbents are typically used in this temperature range, which means that the adsorbent particles of the present invention can withstand temperatures suitable for their application while maintaining their microstructure. Best results are obtained when the solution of PPPO in the organic solvent medium is provided in step i) at a concentration of at least 1 wt. %, preferably at least 2 wt. %, based on the weight of the solution. In this respect, it should be noted that whenever the notation w / w. % is used, this refers to the % by weight of the particular component based on the weight of the solution in which it is dispersed / dissolved.

[0021] The higher the PPPO concentration in step i), the smaller the size and number of pores in the particles. On the other hand, if the solution concentration is too low, the particle skin formed during drying will be too thin, which may adversely affect particle stability. From this perspective, the PPPO solution in the organic solvent medium is preferably provided at a concentration of 0.5% w / w to 20% w / w, with the optimum concentration being 2-8% w / w, e.g., 3-7% w / w, e.g., 4-6% w / w. Within these ranges, a good balance is achieved between pore size and distribution, thus achieving a good balance between, on the one hand, adsorption capacity and, on the other hand, increased thermal and mechanical stability. In this regard, it is even more preferable that the PPPO solution in the organic solvent medium be provided at a concentration of about 5% w / w.

[0022] The relationship between the initial concentration of PPPO and the pore size and distribution also allows for particle design with respect to pore size and distribution to be tailored to desired specifications by varying the initial concentration of PPPO.

[0023] The solvent medium for the PPPO solution may consist of a single solvent or may be a medium consisting of a mixture of solvents.

[0024] Regarding the organic solvent medium for the PPPO solution, good results were obtained when the solution was based on dichloromethane (DCM). PPPO dissolves well in this solvent and can be evaporated efficiently. Other solvents that can be used based on their polarity and evaporation properties can be selected from the group consisting of, but not limited to, chloroform, toluene, and tetrahydrofuran (THF). The inventors have noted that these solvents can dissolve PPPO for the purpose of obtaining particles according to the present invention.

[0025] We have found that by using non-solvent-induced phase separation (NIPS), the surface structure and morphology of particles can be further tuned using a ternary system of PPPO, a good solvent, and a non-solvent. Small amounts of non-solvent can affect pore size and distribution to the desired extent, and such can be applied to tailor particles to desired specifications in terms of pore size and distribution. Any of the solvents listed above can be used as the good solvent, and heptane, for example, can be used as the non-solvent. A preferred solvent / non-solvent combination for the purposes of this invention is DCM as the solvent and heptane as the non-solvent. Good results can be obtained with heptane concentrations up to 6% w / w, such as 4-6% w / w.

[0026] Maintaining the solution in an airborne state can be carried out in an atmosphere of any relative humidity (RH), with the understanding that RH affects the size and distribution of pores, as explained below. In this regard, any RH between 0 and 100%, e.g., 10 and 80%, is contemplated. Increasing the RH of the atmosphere in which the droplets were dried increases the extraction time but also the final particle size. In this sense, RH can be applied to tailor the structure and morphology of the adsorbent particles. Higher RH means that more water condenses on the droplet surface during drying, which, combined with complex internal and external flows, results in some water being trapped inside the gel-like skin as it develops. The resulting water pockets behave much like solvent-rich pockets in that they provide support and prevent the skin from wrinkling. As a result, the particles become increasingly porous as RH increases. On the other hand, porous arrays are formed at low RHs (below 10%), with pores of increasing size, packing irregularity, and polydispersity increasing with increasing RH, so a wide range of RH is suitable for the purposes of this invention. For very small pores, a RH of less than 10%, for example 0.1% to 10%, can be utilized to allow for pore design for C1-C2 hydrocarbon adsorption.

[0027] In a highly preferred embodiment, the solution is suspended and maintained in airborne form in an atmosphere with a relative humidity of 50-70%, preferably about 60%. At these relative humidity levels, a very good balance is achieved between pore size and distribution, and therefore between adsorption capacity on the one hand and increased thermal and mechanical stability on the other hand.

[0028] Therefore, the adsorbent particles can be tailored to the user's needs by varying the initial concentration of the PPPO solution and the relative humidity of the environment in which evaporation occurs. A non-solvent may also be used to provide a ternary solution to tailor the morphology and surface of the PPPO adsorbent particles.

[0029] According to the present invention, no additional heating is required between steps ii) and iii) and the particle formation process can be conveniently carried out at room temperature. In this regard, suspending and maintaining the solution in an airborne state is suitably carried out at a temperature of 15-25°C, preferably at room temperature (20-25°C), although heating may be applied.

[0030] As described above, the method according to the present invention results in porous adsorbent PPPO particles that are distinguishable from prior art PPPO adsorbents in the sense that they have a higher uniformity in terms of pore size and distribution than prior art PPPO-based materials, which exhibit improved adsorption properties. In this respect, the present invention therefore also relates to porous adsorbent PPPO particles that can be obtained by the method described in the preceding claims. In accordance with the above, the particles of the present invention can have a surface structure consisting of a porous array.

[0031] In one embodiment, the particles are spheroidal particles with a porous PPPO skin having a thickness of 30 to 50 μm. Such particles can be obtained by the above-mentioned preferred method and conditions and have good mechanical strength.

[0032] The pores preferably have an apparent pore diameter R of 0.5 μm to 1 μm. ap and / or an average pore spacing R of 0.4 μm to 1 μm s which achieves a good balance between pore size and distribution, and therefore between adsorption capacity on the one hand, and increased thermal and mechanical stability on the other hand.

[0033] To make the particles particularly suitable for the adsorption of very small molecules such as C1-C5 hydrocarbons, an apparent pore size smaller than 0.5 μm may be desired, which can be engineered by increasing the PPPO concentration and / or decreasing the RH and / or adding a non-solvent such as heptane.

[0034] Due to their improved thermal stability, the particles of the present invention can be used as adsorbents in air recovery, particularly in high-temperature environments. In this regard, the present invention also relates to the use of the particles of the present invention as adsorbents in air recovery. In a particularly preferred embodiment, the adsorbent particles of the present invention can be used to adsorb volatile organic compounds and / or C6-C26 hydrocarbons. Meanwhile, the present invention also provides particles that can capture very small molecules if the particles are designed with very small pore sizes. Therefore, instead of particles that adsorb a wide range of these molecules, by designing the pore size and structure to a specific form, particles can be prepared for the capture of specific molecules or a narrow distribution within the C1-C26 range.

[0035] In practical applications of the present invention, the sorbent particles of the present invention are used in a sampling tube. Accordingly, the present invention also relates to a sampling device, which comprises a plurality of porous sorbent particles according to the present invention. In practice, a sampling tube is preferably used as the sampling device. An exemplary embodiment of such a tube is shown in FIG. 3. The sampling tube of FIG. 3 consists of a glass tube 1 containing a quantity of sorbent particles 2. Glass wool 3 and a foam separator 6 can be used to provide a uniform pressure drop. The tip 5 of the tube may be precisely sealed so that it can be safely and easily broken to the desired opening size. A sealing cap 4 prevents contamination.

[0036] In a preferred embodiment, the sampling tube is a thermal desorption (TD) tube. PPPO is a well-known adsorbent used in thermal desorption techniques. Furthermore, the high thermal stability of the particle material allows desorption at very high temperatures. In this way, complete desorption of the adsorbed analytes is ensured without the risk of artifacts due to thermal decomposition of the adsorbent particles. [Example]

[0037] The following examples are included to illustrate the invention and not to limit the scope of the claims.

[0038] Example 1: General preparation of particles

[0039] This section describes the process steps and features applicable to all routes to PPPO particle production. Subsequent sections include modifications to specific parameters to achieve certain structures.

[0040] Chemicals Poly(2,6-diphenyl-p-phenylene oxide) (PPPO) (reported M in the range 11-250 kg / mol) n ), dichloromethane (DCM, VWR Chemicals, 99.9%, ρ = 1.33 g / cm 3 ) and heptane (VWR Chemicals, 99.8%, ρ = 0.67 g / cm 3 ) were used as the solvent and non-solvent, respectively.

[0041] 1.2. Acoustic levitation and imaging For the current experimental demonstration, a single-axis acoustic levitation device based on opposing arrays of ultrasonic transducers (TinyLev) was used for the droplet drying experiments, all of which were performed under controlled RH (Coy Labs RH chamber, coupled with an Electrotech Systems microcontroller). A horizontal tube microscope equipped with a 5x objective and a Basler acA2040-90uc camera was used for image acquisition, and the levitated droplets were backlit to enhance image contrast. The camera's narrow field of view was adjusted to align with the central pressure node of the standing wave, meaning that the polymer solution droplet could be precisely positioned using a syringe at the point where it would be supported by the acoustic force. Images were acquired during drying at a rate of 1 fps for 5 min for polymer solution droplets and until complete evaporation for pure solvent droplets. Images were analyzed using open-source image analysis software (ImageJ). The dried polymer particles were coated with gold and photographed with a Zeiss Auriga Crossbeam scanning electron microscope (SEM).

[0042] 1.3 Preparation of particles according to the invention For the experiments presented in this Example section, the following general steps were performed.

[0043] Step 1. At room temperature (21 °C), use a 1 mL HENKE-JECT syringe and a 23-gauge needle to inject approximately 1.5 × 10 mL of the DCM solution. -3 Place 1 mL of PPPO and allow it to float.

[0044] Step 2. The solution is allowed to float in the field for 5 minutes to ensure that the DCM is sufficiently removed and that the particles are concentrated to at least a "gel-like" or semi-solid state, and that the structure does not develop further.

[0045] Step 3. Further solvent removal beyond this point is very slow and the particles are collected in a glass vial (but not sealed, as the solvent is still present) and left to dry for at least 24 hours.

[0046] Step 4. The "dry" particles at this point still contain some entrapped DCM, so they are placed in a 40°C oven for approximately 12 hours to facilitate further solvent removal (DCM boiling point is 39.6°C).

[0047] Example 2. Particles prepared with low concentrations of PPPO (heat-treated) In this example, particles were prepared from a 0.5 w / w% solution of PPPO in DCM. At room temperature (21°C), the relative humidity of the atmosphere was set at 60%. Approximately 1.5 x 10 particles were prepared in a 0.5 w / w% DCM solution. -3 1 mL of PPPO was suspended in the solution. Figure 4 shows SEM images of these particles. The particles prepared in this manner have a "coral"-like morphology, as shown in the left panel of Figure 4. The entire particle is shown in the upper image, and an enlarged cross-section is shown in the lower image.

[0048] When the particles were heat treated at 375 °C for 4 h under a nitrogen atmosphere, the particle structure changed significantly, as can be seen from the comparison of the left panel (without heat treatment) with the right panel (with heat treatment), and it appeared that the particle structure could not withstand this heat treatment.

[0049] Before heat treatment, the 0.5 w / w% particle in Figure 4 had a highly complex structure that appeared to consist of a series of surface undulations: the concave portions of the surface were thin folds of crumpled paper-like polymer, while the convex portions consisted of "coral"-like structures. These structural details were lost after heating, leaving small pores in the "coral" regions, as the openings were quite clearly plasticized prior to crystallization. Conversely, in the concave regions, the openings became larger as the very thin polymer matrix broke down and fused as it plasticized, leaving a "chewing gum" structure. The particle itself appeared to shrink and collapse.

[0050] Example 3. Particles prepared with PPPO at a 5% w / w concentration (heat treated) In this example, particles were prepared from a 5% w / w solution of PPPO in DCM, with further conditions as described for Example 2.

[0051] Figure 5 shows SEM images of these particles. The entire particle is shown in the top image, and an enlarged cross-section is shown in the bottom image. As seen in the bottom left panel of Figure 5, particles with a surface containing a porous array are obtained. When the particles were heat-treated at 375 °C for 4 hours under a nitrogen atmosphere, the particle structure did not change significantly, as can be seen by comparing the left panel (without heat treatment) with the right panel (with heat treatment), suggesting that the particle structure was able to withstand this heat treatment. On the other hand, the 5 wt% polymer had a nearly unchanged structure (Figure 5). The pore size was approximately the same before and after heating, and may have become somewhat smaller after heating due to some plasticization. Clearly, the polymer skin was thicker due to the higher concentration of PPPO, and was apparently robust enough to maintain its structure long enough for crystallization to occur. Therefore, the morphology of the particles heat-treated at 375 °C for 4 hours under a nitrogen atmosphere did not change significantly during this heat treatment, indicating that these particles can withstand high temperatures for extended periods of time.

[0052] Example 4 In this example, particles were prepared from an 8 w / w% solution of PPPO in DCM. The relative humidity of the atmosphere was set to 60% at room temperature (21°C). Approximately 1.5 x 10 particles were prepared in the 8 w / w% DCM solution. -3 mL of PPPO was suspended.

[0053] This results in particles with a porous array structure as seen in Figure 6, which shows the porous array over a 20 μm × 20 μm surface area of the particle. As can be seen in Figure 6, the pores are uniform in size but are not closely packed.

[0054] Example 5 In this example, particles were prepared from an 8 wt% solution of PPPO in DCM. The relative humidity of the atmosphere was set to 10% at room temperature (21°C). Approximately 1.5 x 10 particles were prepared in a 5 wt% DCM solution. -3 mL of PPPO was suspended.

[0055] This results in particles with a porous structure as seen in Figure 7, which shows the porous array over the 20 μm x 20 μm surface area of the particle. As can be seen in Figure 7, the pores are relatively small compared to the pores of the particles of Example 4 (Figure 6).

[0056] Example 6 In this example, particles were prepared from a 5 w / w% solution of PPPO in DCM. The relative humidity of the atmosphere was set to 80% at room temperature (21°C). Approximately 1.5 x 10 particles were prepared in a 5 w / w% DCM solution. -3 mL of PPPO was suspended.

[0057] This results in particles with a porous array structure as seen in Figure 8, which shows the porous array over a 20 μm x 20 μm surface area of the particle. As can be seen in Figure 8, the pores are relatively large compared to the pores of the particles of Examples 4 and 5 (Figures 5 and 6).

[0058] The results of Examples 4, 5 and 6 show that the relative humidity and initial PPPO concentration affect the final morphology of the particles and therefore can be used to tailor the particles to desired specifications.

[0059] It was also observed that increasing the initial PPPO concentration of the droplets increased the extraction time and final particle size. As the PPPO concentration increased, a higher concentration of polymer accumulated on the droplet surface, creating a thicker skin that was more resistant to deformation. The total extraction time of the solvent also increased with PPPO concentration because this thicker skin limited diffusion.

[0060] Example 7 Comparison of Adsorbent Materials Formed as Particles and Films The particles prepared according to the present invention were compared with an adsorbent material made from a film. For this purpose, the particles according to the present invention were prepared from a 5 wt.% solution of PPPO in DCM. The relative humidity of the atmosphere was set to 80% at room temperature (21°C). Approximately 1.5 x 10 PPPO particles in a 5 wt.% DCM solution were used. -3mL of PPPO was suspended and prepared as described in Example 1.

[0061] To prepare adsorbents from films of 5 wt% PPPO, the DCM solution was dropped onto a glass microscope cover slip and dried at 40% RH. The dried films were coated with gold and photographed with a Zeiss Auriga Crossbeam scanning electron microscope (SEM).

[0062] Figure 9 shows an SEM image of the porous array on the surface of a particle (A). As can be seen in Figure 9, a porous array is formed, which is uniform in size and relatively uniformly and closely packed. In contrast, when the polymer solution is dried into a film, under these conditions, the pores are not uniform in size and filling, as can be seen in Figure 9B. Note that the pores formed at higher RH (60, 80, and 100%) are very similar in size, shape, and filling for both the particle and the corresponding deposited film (not shown), but the film of the adsorbent material is less suitable for its primary intended use in a sampling tube.

[0063] Example 8 Use of a Non-Solvent in a PPPO Solution In this example, we performed experiments in PPPO solutions using heptane as a nonsolvent. The surface structures of particles formed from binary PPPO:DCM and ternary PPPO:DCM:heptane solutions are shown in SEM images in Figure 10. The composition is indicated in the upper right corner of each image, vertically (increasing PPPO) and horizontally (increasing heptane). First, the structures from the binary solutions (top to bottom, especially at higher concentrations) contain porous cavities that appear to be non-interconnected. Since no nonsolvent was present during drying, we believe the porous array must be the source of this porosity. As mentioned above, the pores on the lowest concentration (0.5 w / w% PPPO) particles appear less isotropic in shape and less uniform in size, resulting in a "coral-like" structure. The pores formed from higher concentrations of PPPO (3, 5, and 8 w / w% PPPO solutions) appear to be wider and more randomly spaced.

[0064] For particles from the ternary mixture of PPPO:DCM:heptane, the structure at low initial heptane concentrations (4 and 6% w / w) does not appear to be formed by separation—small, uniform cells are characteristic of breath figure formation. Therefore, by examining only the surface structure, it appears that these small amounts of nonsolvent are not sufficient to cross the phase boundary during drying. With this ternary system, initial skin formation occurs early, and because the skin does not reach a concentration within the two-phase region, breath figures are the dominant structure, but changes in the internal composition appear to depend on the ability of each solvent to diffuse through the gel-like PPPO skin. In this case, heptane appears to be largely restricted by the PPPO skin, and as a result, the internal liquid composition of the droplets undergoes NIPS during drying. Higher heptane compositions (above 6% w / w) form a typical separated structure with large pores and less uniformity, while at the highest compositions, a nodular surface forms.

[0065] Particle size in heptane-containing solutions also increases with initial heptane concentration, although for a different reason. Because DCM evaporates several times faster than heptane, the concentration drop within the polymer solution can at some point enter a two-phase region—especially near the interface, where polymer accumulation is high—and begin to separate. This phase separation creates pockets of solvent-rich phase that evaporate to form air pockets, effectively reinforcing the polymer skin and preventing particle crumpling, resulting in larger final particles. In addition, these pockets of solvent-rich phase near the surface contain less polymer and therefore evaporate more quickly, resulting in larger final particles. Extraction times also decrease with the addition of heptane.

[0066] Example 9 The above examples demonstrate the formation of suspended PPPO particles.

[0067] Various particle morphologies, sizes, skin thicknesses, surface structures, and surface porosities can be controllably created by varying polymer concentration, heptane concentration, and by utilizing RH to induce pore formation. The following disclosure and Figure 11 provide a summary of findings in this regard.

[0068] Increasing the initial PPPO concentration of the droplets increased the extraction time and final particle size. As the PPPO concentration increased, a higher concentration of polymer accumulated on the droplet surface, creating a thicker skin that was more resistant to deformation.

[0069] FIG. 11 shows SEM images of particles from the binary PPPO solution, showing that pores are formed on the surface of all particles to some extent, even on particles prepared with a starting solution of 0.5% w / w PPPO.

[0070] Figure 11 also shows that segregated structures are visible on the polymer surface above 6 w / w% heptane concentration - below this, porous arrays are visible on the surface.

[0071] As further shown in Figure 11, pores form on the airborne droplets even at RH as low as 10%, with pores of increasing size, packing irregularity, and polydispersity as RH increases.

[0072] Example 10: Estimation of particle area In the following examples, estimates of the surface area of particles according to the invention are made as evidence of the high adsorption capacity of particles according to the invention.

[0073] For this purpose, the particle of FIG. 5 (Example 3) is taken as a model.

[0074] Particle size is determined by modeling the final particles as roughly oblate spheroids, as shown in Figure 12A; assuming no pores, the average particle formed with 5 w / w% PPPO has a surface area of ∼3,200,000 μm 2 The measured skin thickness is 40 μm.

[0075] Based on the SEM images shown in Figure 5, the average pore diameter is estimated to be R = 0.75 μm, and the average pore spacing is R S =0.6μm.

[0076] Assuming each pore is cylindrical, the length corresponds to the skin thickness of the particle (40 μm). The average pore perimeter is 2 × π × 0.75 = 4.71 μm. The average pore area is 4.71 × 40 = 188.50 μm. 2 The measured pore coverage is 47%, and therefore the "void" is 53%. Therefore, the approximate particle surface area is: (3200000×0.53)+(3200000×0.47×188.5)=285000000μm 2 This means that the surface area increases by approximately 90 times.

[0077] Alternatively, the pores may be spherical, with an average apparent pore diameter of R = 0.75 μm and R S = 0.6 μm. In this case, the average internal pore area is 32.52 μm. 2 This becomes:

[0078] The measured pore coverage is 47%, and therefore the "void" is 53%. Therefore, the approximate particle surface area is (3,200,000 x 0.53) + (3,200,000 x 0.47 x 32.52) = 50,600,000 μm 2 This means that the surface area increases by approximately 15.8 times.

[0079] With further reference to this, it is clear from Figure 12B that the pores are present in layers within the skin. Now, assuming a particle with a skin thickness of 40 μm and pore sizes of approximately 2 μm, and assuming the pores within the skin are spheres interconnected in multiple layers of spheres, as shown schematically in Figure 12C, this would look like the following diagram:

[0080] [Table 1]

[0081] By modeling the pores as either cylinders or spheres, a surface area increase factor of 90.0 to 577.3 can be obtained when the particles are prepared according to Example 3, and further adjustments according to the disclosure of this application can result in even higher surface area increases.

Claims

1. 1. A method for preparing porous adsorbent particles, comprising: i) providing a solution of poly(2,6-diphenyl-p-phenylene oxide) in an organic solvent medium; ii) causing a droplet of said solution to be held in air without mechanical support by any physical contact; iii) evaporating the organic solvent medium while maintaining the solution in a semi-solid or solid state at least until the solution is converted into particles in the solid state; A method comprising:

2. The method of claim 1 , wherein the solution is brought into the state by suspending the solution in air against gravity.

3. 3. The method of claim 2, wherein particle levitation technology is used to suspend and maintain the solution in air against gravity.

4. 10. The method of any preceding claim, wherein the particle levitation technique is acoustic levitation technique.

5. 10. A method according to any preceding claim, wherein the solution of poly(2,6-diphenyl-p-phenylene oxide) in the organic solvent medium is provided at a concentration of 0.5 to 20% w / w.

6. 6. The method of claim 5, wherein the solution of poly(2,6-diphenyl-p-phenylene oxide) in the organic solvent medium is provided at a concentration of at least 1% w / w.

7. 7. The method of claim 6, wherein the solution of poly(2,6-diphenyl-p-phenylene oxide) in the organic solvent medium is provided at a concentration of 1% w / w to 8% w / w.

8. 8. The method of claim 7, wherein the solution of poly(2,6-diphenyl-p-phenylene oxide) in the organic solvent medium is provided at a concentration of about 5% w / w.

9. 10. The method of any preceding claim, wherein the solvent medium is a dichloromethane-based solvent medium.

10. 10. The method of claim 9, wherein the solvent medium also contains heptane at a concentration of up to 6% w / w.

11. 10. The method of claim 9, wherein maintaining the solution in said state is carried out in an atmosphere of 10 to 80% relative humidity.

12. 12. The method of claim 11, wherein suspending and maintaining said solution in said state is carried out in an atmosphere of relative humidity of 50-70%, preferably about 60%.

13. The method of any one of claims 1 to 10, wherein suspending and maintaining said solution in said state is carried out in an atmosphere with a relative humidity of less than 10%.

14. 10. A method according to any preceding claim, wherein suspending and maintaining said solution in said state is carried out at a temperature of 15-25°C, preferably at room temperature (20-25°C).

15. 10. The method according to any of the preceding claims, wherein after step iii) the particles are collected and iv) subjected to drying.

16. 16. The method of claim 15, wherein step iv) is carried out by incubating the collected particles in an oven.

17. Porous adsorbent particles obtainable by the method according to the previous claims.

18. 20. The porous adsorbent particle of claim 17, having a particle surface with a porous array.

19. 19. Porous adsorbent particles according to claim 17 or 18, which are spheroidal particles having a porous poly(2,6-diphenyl-p-phenylene oxide) skin having a thickness of 30 to 50 μm.

20. The pores have an apparent pore diameter R of 0.5 μm to 1 μm. ａｐ 19. The porous adsorbent particles of claim 17 or 18, having

21. The pores have an average pore spacing R between 0.4 μm and 1 μm ｓ 21. The porous adsorbent particles of any one of claims 17 to 20, having

22. A sample collection device comprising a plurality of porous sorbent particles according to any one of claims 17 to 21.

23. 23. The sample collection device of claim 22, which is a thermal desorption (TD) tube.

24. Use of porous particles according to any one of claims 17 to 21 as adsorbent in air recovery.

25. 25. Use according to claim 24 for the adsorption of volatile organic compounds and / or C1 to C26 hydrocarbons.

26. Volatile organic compounds, C1-C5 hydrocarbons, e.g., CH ４ , CO ２ 26. The use according to claim 24 or 25 for the adsorption of one or more species selected from the group consisting of CO,

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