Conjugated Microporous Polymer Hybrid Microparticles for Enhanced Applicability in Silica‐Boosted Diclofenac Adsorption

Diclofenac (DCF) is one of the most widespread and consumed analgesics, thereby causing contamination of water bodies on a global scale. A common approach to tackle this pressing issue is the adsorption of DCF exploiting highly hydrophobic polymers. However, controlling the morphology of such polymers is essential. Adsorption capacities of the presented conjugated microporous polymer (CMP) in bulk‐form, for DCF (qsat) are as low as 13.0 mg g−1 despite exhibiting additional nitrogen moieties to specifically target DCF. Herein, an approach to drastically increase the DCF adsorption by increasing the accessible hydrophobic surface area by coating it around mesoporous silica microspheres is shown. These microspheres do not attribute to the adsorption of DCF themselves, but increase the accessibility of the CMP. Simultaneously, the applicability of the hybrid material is enhanced through higher wettability and more facile separation. As a consequence, an effective adsorbent is formed featuring an adsorption of up to 422 mg DCF per 1 × g CMP for the optimized silica/monomer ratio — comparable to expensive state‐of‐art materials. As the approach combines the advantages of the nano‐ and the micro‐dimension and does not depend on the actual adsorbent material, it holds great potential for general adsorption problems requiring highly engineered systems.

Several reports exist of CMPs as adsorber materials that target the aromatic functionalities inherent to many organic compounds through π-π interaction. [27][28][29][30] Contrarily more hydrophilic CMPs perform better at adsorbing the organic compounds due to improved wettability with the aqueous media. [23] It is therefore paramount to preserve the hydrophobic character whilst at the same time enhancing the dispensability within the aqueous media to fully exploit the potential of the CMP.
In terms of applicability, macroscale CMPs are necessary to ensure both removability of the adsorber after batch-adsorption, or in case of column-based water purification, to ensure sufficient diffusion within the inter-particle spaces. Some studies approached this problem by coating CMPs onto macroscale structures such as paper, [31] metal sieves, [32] or sponges. [32,33] While especially the sieves and sponges proved to be very easy to handle for separating organic pollutants, [33] they lack the advantages of the smaller domain, such as larger specific surface areas and enhanced mobility.
Other studies have coated CMPs around silica nanospheres that exhibit the necessary mobility and surface area but are hard to apply, since they are difficult to retain and may pose hazards to human health themselves. [34,35] Herein a first-time approach is presented whereby a CMP is coated around mesoporous SiO 2 microspheres. This preserves the advantageous properties of the nanodomain, especially since the microspheres themselves have a high internal surface area. Furthermore, the necessary particle size for handling is provided, since the particles are easily removed from the solution via sedimentation. At the same time, the polarity of the SiO 2 microspheres leads to an improved dispensability in the aqueous phase whilst preserving the hydrophobic character of the CMP. This CMP is distributed around the abundant, low-cost silica, in a thin layer, increasing the accessibility for DCF, the model compound, and thereby raising the adsorbable amount. In addition, this represents a solution approach to the high production costs-a major drawback of CMPs-since high adsorption capacities are achieved by small material quantities which, moreover, also have advantageous recyclability properties.
PTP is a good example of the exact tailoring of properties of a CMP network through monomer choice: While the extended conjugation results in a strong hydrophobic characteristic the integrated nitrogen atoms, with their free electron pairs allow for more polar interactions with the DCF target molecule. Simulations of DCF adsorption onto graphene show that the adsorbed DCF orients both its aromatic structure and its carboxylic acid functionality toward the graphene. [36] Here, the multivalent features of the PTP mirror the amphiphile character of DCF, to increase attraction.
The plain PTP is composed of both small, fused spheres as well as compact, larger platelet structures (compare Figure 1 optical microscopy (OM), scanning electron microscopy (SEM), and Figure S2, Supporting Information for additional SEM images). The SEM-energy-dispersive X-ray (EDX) measurement of the material shows a homogenous distribution of nitrogen, originating from the pyrimidine subunit, suggesting that both, the spherical and the platelet structures, consist of the CMP material ( Figure S3, Supporting Information).
To enhance the accessible surface area and generate particles large enough for adsorption application the PTP was coated around commercially available spherical silica macrospheres (40-70 μm, SEM and OM image in Figure S4, Supporting Information). Silica, aside from being abundantly available, was chosen due to its polarity and its high stability toward chemical and physical influences. The particle size within the μm range facilitates the separation from the aqueous media after the adsorption process, since it allows filtration or sedimentation. Further, potential application strategies include column adsorption where it is impossible to use nanoparticles.
A key element is the investigation of how an increase of the added silica amount at fixed monomer and linker masses influences the adsorption performance and to which structural TEB DBP
www.advancedsciencenews.com www.small-structures.com features these influences are related. The synthesis of the hybrid materials is described in Section 4 (see Table 1 and Figure S1, Supporting Information). The hybrid material based on PTP is named PTP@SiO 2 -x with "x" being the amount of added silica in grams. PTP@SiO 2 -0.9 is the hybrid material with the lowest amount of added silica, where no separate PTP structures from the substrate were observed with OM, meaning no free PTP was visible.
To investigate the coating homogeneity and to determine the influence of the added silica on the growth of the PTP, OM, SEM ( Figure S5, Supporting Information), and scanning electron microscopy with energy dispersive X-ray measurements (SEM-EDX, Figure S6, Supporting Information) were conducted. The OM images of the PTP@SiO 2 -0.9 hybrid material used as reference material show a consistent coating of the silica substrate, indicating a high affinity of the PTP toward the SiO 2 ( Figure 1). Close-up SEM images ( Figure 1 and S5, Supporting Information) reveal that the coating is made up of the smaller, spherical satellites fused together, whereas the larger, bulky structures observed in the plain PTP are completely absent, which can be considered a new achievement in CMP morphology control. Regarding the application as a DCF adsorbent, these half-spheres can be considered favorable since they exhibit more easily accessible surface area than a plain coating would.
The nitrogen distribution on the silica surface determined via SEM EDX affirms that these satellites are actually the desired PTP ( Figure S6, Supporting Information).
Based on these results, the amount of SiO 2 spheres added to the reaction solution was successively increased up to 9.0 Â g (compare Table 1).
The chemical structure of the PTP and whether the integration of silica has an impact on network formation were observed by 13 C{ 1 H} cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C{ 1 H} CP-MAS NMR) ( Figure S7, Supporting Information peak assignments). The peaks coincide with the literature, suggesting that the PTP network was formed within the plain and all hybrid materials (further discussion in Supporting Information, Figure S7, S8, and S9, Supporting Information). Similar to NMR, the FTIR spectra are consistent with the literature ( Figure S10, S11, and S12, Supporting Information), indicating the formation of the extended conjugation in all materials. Via inductively coupled plasma optical emission spectrometry (ICP-OES), the residual metal catalyst were determined to be 0.69 wt% (Pd) and 0.15 wt% (Cu) in the PTP, while the values of the hybrid materials were significantly lower (Table S1, Supporting Information). Combined with the data from the microscopic measurements, it can be stated that the coating of the silica with PTP was successful and the amphiphilic character necessary for superior adsorption of DCF is generated.
The thermogravimetric analysis (TGA) measurements confirm the PTP formation and show an indirectly proportional relationship between the wt% CMP and the added SiO 2 amount. Therefore, the amount of PTP per silica decreases  (exact calculation see Table S2, Supporting Information) which should lead to a wider spread of the coating. Thereby the surface area accessible for DCF adsorption should increase.
To investigate the specific surface area (SSA) and the porosity of the different materials nitrogen ( Figure S14 and S15, Supporting Information) and carbon dioxide sorption experiments ( Figure S16, Supporting Information) were performed. While PTP shows a type I nitrogen adsorption isotherm with an SSA of 508 m 2 g À1 (BET) indicating an extensive micropore formation, the hybrid material PTP@SiO 2 -0.9 exhibits the type IV character of the SiO 2 substrate. The hysteresis area of the hybrid material is reduced compared to plain SiO 2 suggesting that the CMP material partially enters the mesopores of the SiO 2 . Further, the SSA is lower than that of the SiO 2 for all hybrid materials indicating that the PTP coating is not microporous, presumably due to the attractive interaction of the SiO 2 restricting the mobility required for rearrangement and inter-network crosslinking, known to be the final step in CMP synthesis. Nevertheless, the previous measurements confirmed the formation of a conjugated network, exhibiting all the required functionalities. To determine the influence of these findings the adsorption properties of the PTP and hybrid material samples were investigated by batch sorption experiments at the native pH values of the DCF sodium salt in ultrapure water. These values range from pH 5.5 to 6.5 and did not vary significantly throughout the differing concentrations of the experiments ( Figure S17, Supporting Information). This is near the neutral point and comparable to many waterbodies.
In the low-concentration regions of 0.5 mg L À1 , the plain PTP, PTP@SiO 2 -0.9, and PTP@SiO 2 -1.5 remove 100% of the DCF from the solution ( Figure S18, Supporting Information) and show a very similar adsorption profile.
Additionally, the adsorption behavior of DCF toward the plain SiO 2 as well as the methoxy-modified SiO 2 spheres (SiO 2 -OMe, functionalization through soxhlet compare Supporting Information) was studied by batch adsorption experiments ( Figure S18, Supporting Information). Both substrates exhibit little to no uptake of DCF, affirming that the hydrophobic PTP is responsible for the adsorption at this neutral pH. To investigate the character of this adsorption, the equilibrium capacity and concentration were plotted and fitted with the Langmuir model ( Figure 2a) and the Freundlich model ( Figure S19, Supporting Information). As for PTP and PTP@SiO 2 -9.0 the Langmuir model renders the best fit that shifts toward the Freundlich model for PTP@SiO 2 -1.5 and higher silica contents (fitting parameters in Table S3, Supporting Information). This indicates an increased heterogeneity of the adsorption sites. Although the silica does not contribute to adsorption, it alters the distribution of hydrophobic sites of the material and accounts for its heterogeneity. Despite the apparent shift toward the Freundlich model, the Langmuir model still renders quite accurate approximations (compare Table S3, Supporting Information, Figure 2a), that allows a determination of the saturation capacity (q sat ). Figure 2b shows the q sat throughout the optimization series, plotted against the added silica amount. The plain PTP exhibits an adsorption capacity of 13 mg g À1 that is comparable with activated carbons from biological waste products (compare Table S4, Supporting Information). A drawback for this plain PTP material was poor miscibility with the aqueous media that significantly improved when it was coated onto the silica spheres leading to an increase of q sat, to 16 mg g À1 (PTP@SiO 2 -0.9), 29 mg g À1 (PTP@SiO 2 -1.5) and 35 mg g À1 (PTP@SiO 2 -3.0). Thereafter q sat decreases again with increasing silica amount due to the reduction in CMP mass. Since the silica does not contribute to the adsorption the q sat , the specific capacity reached for the applied mass of CMP can be calculated (q sat-cmp ). Here, the q sat determined by the Langmuir model was divided by the CMP wt% derived from TGA.
The respective isotherms are depicted in Figure S20, Supporting Information. E.g., when calculating the adsorption capacity of PTP@SiO 2 -0.9, only the 12.2 wt% of PTP material is accountable for adsorbing, leading to a value of 128.0 mg DCF per g CMP that is comparable to high-performance adsorbers such as the carbon xerogels from Álvarez et al. [12] .
The following q sat-cmp steadily increases (Figure 2b) approximating a value of about 422 mg g À1 that is comparable to the best adsorber materials reported for DCF such as graphene oxide, [37] oxidized activated carbon [38] and the functionalized UiO-66-NH2 MOF [15] (overview Table S4, Supporting Information). This value seems to be the limit determined by the opposing interplay of increased capacity due to better PTP distribution and accessibility with a simultaneous decline of adsorption capability due to effectively less material.
As shown by the adsorption experiments, the most efficient ratio is reached for the sample PTP@SiO 2 -3.0. To explain these drastically increased adsorption capacities, additional analyses targeting the morphology and structural composition were performed.
SEM images ( Figure 3) show that all samples are covered by the PTP sphere structures, whereby PTP@SiO 2 -0.9 to PTP@SiO 2 -6.0 show a homogenous distribution of these substructures whilst PTP@SiO 2 -9.0 shows an inhomogeneous, spotted distribution.
SEM image analysis determining the PTP coverage degree on the silica surface was conducted via optical analysis ( Figure S21, Supporting Information). When plotting the coverage degree Θ against the amount of added silica ( Figure S22, Supporting Information), an initial drop from 40% coverage for PTP@SiO 2 -0.9 to about 21% for PTP@SiO 2 -1.5, followed by stabilization at 17% (PTP@SiO 2 -3.0) and 18% (PTP@SiO 2 -6.0) are observed. The high coating coverage degree leads to a very similar DCF removal behavior to the pure PTP, although effectively less PTP is applied in the experiment. Further, the constant coverage degree of PTP@SiO 2 -3.0 and PTP@SiO 2 -6.0 leads to similar removal of about 75% at 1 mg L À1 DCF. The inhomogeneity of PTP@SiO 2 -9.0 did not allow meaningful image analysis and further caused a drop in the adsorption.
Regarding the morphology, the similar coverage degree Θ of PTP@SiO 2 -3.0 and PTP@SiO 2 -6.0 indicates that with increasing silica amount the volume of the PTP satellites and not the surface coverage decreases. By embedding the PTP@SiO 2 in resin and cutting ultra-thin sections, an investigation of the surface profile via scanning transmission electron microscopy (STEM) was conducted ( Figure S23 and S24, Supporting Information). Thereby, it was found that the majority of the PTP@SiO 2 -0.9, PTP@SiO 2 -1.5, and PTP@SiO 2 -3.0 satellites exhibit an obtuse contact angle with the silica surface. PTP@SiO 2 -6.0, in contrast, shows more acute contact angles and flatter satellite structures. This effect is presumably due to an equilibrium of two counteracting driving forces. The first driving force is the minimization of surface energy through the homogenous distribution of the PTP on the silica surface. The second force is the tendency to form spherical PTP satellites to minimize the interaction with the solvent via the surfaceto-volume ratio. At PTP@SiO 2 -3.0, the surface energy minimization seemingly outweighs the necessity to form spherical particles, which affects the adsorption of DCF.
The increase of both q sat and q sat-cmp from PTP@SiO 2 -0.9 to PTP@SiO 2 -3.0 is related to the decreasing coverage degree. Contact angle measurements show similar results for PTP (120.5°) and PTP@SiO 2 -0.9 (122.0°), whilst the hybrid materials with 1.5 Â g SiO 2 or higher were not measurable, since the lower coverage degree leads to a total absorption of the water droplet. The obviously decreasing hydrophobicity improves the miscibility with the aqueous media leading to better DCF adsorption. This trend stops after the transition from wider spread to flatter satellites. It is significant that the coverage degree of PTP@SiO 2 -1.5 and PTP@SiO 2 -3.0 only differ by 4% while the q sat-cmp jumps from 285 to 422 mg g À1 . This suggests that the transition is accompanied by changes within the network structure that also influence the adsorption.
Due to the small wt% of PTP on the silica, the CP-MAS NMR and Fourier transform infrared (FTIR) measurements were insufficient for the quantification of specific functional groups. Therefore, further investigations were undertaken with UV/vis 10 µm 50 µm 0.9 g 3.0 g 6.0 g 9.0 g 1.5 g www.advancedsciencenews.com www.small-structures.com measurements since the absorption is related to the conjugation length, which in turn provides information about the network linkage ( Figure S25, Supporting Information). When comparing the direct optical bandgaps (Kubelka-Munk calculation, fits see Figure S26, Supporting Information) related to the silica content ( Figure S27, Supporting Information) the bandgap steadily increases from PTP@SiO 2 -1.5 on. It is likely that preferential adsorption of the more polar pyrimidine to the silica causes a disruption of the stoichiometric ratio between TEB and DBP. This results in an increased number of unreacted alkyne functionalities leading to a decrease in the conjugation length. This reduces the hydrophobic character of the network diminishing the strength of the hydrophobic interactions between the DCF and the PTP.
When considering the aspect of the network structure's influence on the adsorption the bromine content is bound to affect the interactions with the DCF molecule. To address this aspect, for the first time STEM-EDX measurements of a CMP were conducted ( Figure 4).
While the mapping of nitrogen reveals, where the pyrimidine is preferentially integrated into the network, the bromine distribution provides insight into whether the pyrimidine is single bonded or acts as a bridging element. Through integration along the particle-silica interface, the atom% N and atom% Br and their ratio in relation to the location within the polymer particle can be determined ( Figure S28, Supporting Information) Thereby no preferential integration of pyrimidine nor a trend within the ratio could be observed throughout the profile of the respective satellites.
Further, the degree of conversion (DOC) of pyrimidine can be derived from the ratio atom% Br /atom% N (see Supporting Information). At a DOC of 0.5, the pyrimidine subunits are singly bonded to the TEB, meaning that network formation can only occur at a DOC > 0.5, with higher values indicating a more complete integration of the pyrimidine. When integrating the entire polymeric satellites on the silica surface the average DOC for the respective material in the optimization series can be calculated ( Figure S29, Supporting Information).
Once more PTP@SiO 2 -3.0 poses an extremum in an observed trend: here being the sample with the poorest pyrimidine conversion which is a consequence of the transition from widespread satellites to flatter satellites. Further, it suggests that the presence of bromine is favorable for DCF adsorption, most likely by adding polarity to the network structure and therefore addressing the amphiphilic character even better.
From PTP@SiO 2 -3.0 onward the DOC increases, indicating a reduction of bromine end-capping. Together with the decrease in the conjugation length this leads to a reduction of the hydrophobic and hydrophilic domains within the network. This explains why q sat-cmp slightly decreases at the higher silica amounts. PTP@SiO 2 -3.0, therefore, represents the best PTP@SiO 2 hybrid material for DCF adsorption with a q sat-cmp of 422 mg g À1 and about 72% removal at a lower concentration.
To further test the feasibility in application this PTP@SiO 2 -3.0 material was chosen for cycling studies of 3 separate adsorption cycles with intermediate short (3 h) desorption periods with small amounts of ethanol. Thereby a low concentration of 1 mg L À1 and a high concentration of 300 mg L À1 DCF were tested. Figure S30 shows that despite a decrease in the desorbable percentage, the adsorption slightly increases with each cycling step. Further, stability and no leaching of toxic metal ions are essential for a long-term application. The latter was investigated via ICP-OES measurements of the adsorption solutions after the first cycle. Thereby no, or negligibly little (<0.13 ppm) amounts of Pd and Cu were observed (Table S5, Supporting Information) proving that no environmental contamination occurs during the adsorption process. The stability was proven via SEM images ( Figure S31, Supporting Information) that show that the particles maintain their structural integrity throughout the cycling study. These results hold the promise of long-term application, which has a positive impact on the cost-benefit balance.

Conclusion
Due to increasing water pollution with organic substances like DCF new materials for separation are inevitable. Synthetic materials show high capacities but often suffer from high costs. In this study, the CMP PTP-specifically designed to adsorb amphiphilic molecules-is homogeneously coated around varying amounts of low-cost SiO 2 microspheres to expand the accessible surface area to DCF adsorption and improve applicability.
At low DCF concentrations of 1 mg L À1 , the hybrid materials with low silica amounts of 0.9 and 1.5 Â g completely remove the DCF due to their higher PTP coverage degree and thereby predominant hydrophobic character. The materials with higher silica amounts of 3.0-9.0 Â g, in contrast, exhibit significantly higher CMP-specific adsorption capacities q sat-cmp . Of the total series the PTP@SiO 2 -3.0 was found to be the best-performing adsorber showing a q sat-cmp of 422 mg g À1 and 72% removal at a low concentration of 1 mg L À1 DCF. This optimum was observed to be the result of different influences throughout the course of the series: The decreasing coverage degree from PTP@SiO 2 -0.9 to PTP@SiO 2 -3.0 leads to an increased distribution in the solution that enhances the q sat-cmp . At PTP@SiO 2 -3.0, a transition from wider spread PTP satellites on the silica surface to flatter satellites occurs. This impacts the PTP structure by reducing the conjugation length (UV/vis). Further, for the first time, STEM-EDX measurements of ultra-thin sections of the CMP satellites were used to determine the conversion of the pyrimidine subunit, which increased with higher silica content. Both the reducing conjugation length and decreasing bromine  content are held responsible for a decrease of q sat-cmp at 6.0 and 9.0 Â g silica. Nevertheless, the achieved capacities are comparable with the worldwide leading DCF adsorber materials such as the UiO-66-NH2 MOF and exfoliated graphene. They demonstrate that through simple and cost-efficient hybrid material formation the adsorption capacities of hydrophobic systems can be elevated not only to mediocre levels but up to the ranks of state-of-the-art adsorber materials. Simultaneously the applicability is significantly improved due to increased adsorber masses and facilitated the separation of the adsorbate. Further, cycling studies proved the reusability, ensuring long-term applicability.
Since the opposing interplay of hydrophobic and hydrophilic character is a key aspect of the adsorption of amphiphilic organic molecules, many adsorber systems face similar problems of distribution, wettability, and accessibility in aqueous media. The presented technique opens up new perspectives that when adapted to the wide variety of different adsorber systems such as CMPs, hold great potential for the solution of various contamination problems.
All adsorption experiments were carried out in ultrapure water, purified by a Milli-Q Advantage A10 system (Millipore, Darmstadt, Germany) (total organic carbon = 5 ppb, resistivity of 18.2 MΩ cm).
Synthesis of the PTP CMP Material: A 100 mL 3-neck flask, equipped with a reflux condenser, was loaded with TEB (40 mg; 0.266 mmol) and the comonomer DBP (95 mg; 0.399 mmol). After the addition of the monomers, the flask was evacuated and flushed with nitrogen three times. Subsequently, both monomer and comonomer were dissolved in a mixture of degassed (3 Â freeze pump) toluene (20 mL) and TEA (15 mL) at 70°C. In a separate flask, the catalyst was prepared by adding and degassing Pd(PPh 3 ) 4 (21 mg; 0.019 mmol) and CuI (5 mg; 0.0026 mmol). Both catalyst and cocatalyst were dispersed in toluene (2 Â 5 mL) and added to the hot monomer solution via a syringe. The reaction was stirred at around 500 rpm with a magnetic stir bar under nitrogen for 3 days at 70°C. The precipitated product was collected by filtration and washed with toluene (50 mL) before being transferred to a soxhlet extractor with methanol for another 5 days. The product was then dried in vacuo at 100°C overnight.
Synthesis of the Hybrid Materials: Since stirring with the magnetic bar led to the destruction of the SiO 2 particles, an apparatus with a KPG stirrer was used for the synthesis of the hybrid materials. Thereby, the reaction parameters were kept as similar as possible to the synthesis of the plain CMPs. Instead of using a magnetic stir bar the IKA overhead stirrer (RW16basic, IKA-Werke GmbH & CO. KG, Staufen, Germany) was set on a 250 mL 3-neck flask equipped with a sealing Teflon hole plug and associated cap ( Figure S1, Supporting Information). The 3-neck flask, equipped with a reflux condenser on the side, was loaded with TEB (40 mg; 0.266 mmol), the SiO 2 particles (varying amount, compare Table 1), and the comonomer DBP (95 mg; 0.399 mmol) to yield the respective PTP@SiO 2 . After the addition of the monomers, the flask was evacuated and flushed with nitrogen three times. The hole for the mixing lever was sealed with an o-ring during the evacuation and nitrogen-purging process and only reopened (slightly unscrewing the cap to allow rotation of the stirrer) when under nitrogen pressure. Subsequently, the SiO 2 , the monomer, and comonomer were dissolved in a mixture of degassed (3 Â freeze pump) toluene (varying amount, compare Table 1) and TEA (varying amount, compare Table 1) and stirred for 30 min. Due to solubility issues the solvent amount was slightly increased corresponding to the applied mass of SiO 2 (Table 1). Afterward, the temperature was increased to 70°C. In a separate flask, the catalyst was prepared by adding Pd(PPh 3 ) 4 (21 mg; 0.019 mmol) and CuI (5 mg; 0.0026 mmol). Both the catalyst and cocatalyst were dispersed in toluene (2 Â 5 mL) and added to the hot monomer solution via a syringe. The reaction was stirred at around 60 rpm under nitrogen for 3 days at 70°C. The precipitated product was collected by filtration and washed with toluene (50 mL) before being transferred to a soxhlet extractor with methanol for another 5 days. The product was then dried in vacuo at 100°C for 24 h.
Characterization Methods: Optical Microscopy: For OM measurements, the ECLIPSE LV100ND from Nikon (Nikon Metrology Europe NV, Leuven, Belgium) with an attached camera (Digital sight DS-Fi2, Nikon Metrology Europe NV, Leuven, Belgium) was used. The samples were placed on a microscope slide that was set on the dark region of the sample table. All images were captured using the dark field modus at magnifications of Â5, Â20, and Â50, using TU Plan Fluor oculars (Nikon).
Characterization Methods: Scanning Electron Microscopy: SEM measurements were carried out using an SEM Ultra Plus from Carl Zeiss Microscopy GmbH (Oberkochen, Germany). The samples were fixed on an aluminum pin with double-sided adhesive carbon tape and afterward purged with N 2 to obtain a thin layer of particles. Using a Sputter Coater SCD050 (Leica Microsystems, Wetzlar, Germany) the samples were sputtered with 3 nm of platinum before the measurement, which was carried out with an acceleration voltage of 3 keV at different magnifications.
Characterization Methods: Scanning Electron Microscopy Image Analysis: To increase the contrast, SEM images for the algorithm-based analysis were taken using the Phenom XL Workstation from Thermo Scientific (Waltham, MA, USA) equipped with a backscattering detector. For particle analysis, SEM images were analyzed using the program ImageJ in the configuration Fiji (version 1.53p). This involved transferring the scale bar of the image into the program and then selecting a region of interest of 30 Â 30 μm on the SEM image. With the Auto Local Threshold function, binary images were generated using the Otsu algorithm [39] and a pixel radius of 100. The Median Filter function with a pixel radius of 0 was used to minimize image noise in the binary images.
Using the Analyze-Particles function, all white areas of the binary image with a minimum area of 5 pixels were captured as particles with the associated area and saved in CSV file format. From this data, a colored overlay of the captured particles on the original SEM image could be generated.
Characterization Methods: Scanning Electron Microscopy with Energy-Dispersive X-ray Analysis: SEM-EDX measurements of the samples were carried out using a Phenom XL Workstation from Thermo Scientific match condition were adjusted with Adamantane and decoupling power was optimized with 13C2 enriched Glycine. The pure polymer was acquired with 6 k scans. The polymer-coated SiO 2 was acquired with 100 k scans. Original data are available by request. Characterization Methods: Fourier-Transform Infrared Spectroscopy: Attenuated total reflection infrared spectroscopy (ATR-FTIR) measurements were carried out using a Tensor 27 device equipped with a Platinum ATR module both from Bruker Corporation (Billerica, MA, USA). The samples were measured in dry state with a resolution of 2 cm À1 and with 100 scans. The acquired spectra were subjected to atmospheric compensation to remove the rotation bands of water.
Characterization Methods: Inductively Coupled Plasma Optical Emission Spectrometry: For digestion, a Discover SP (CEM GmbH, Kamp-Lintfort, Germany) was used. Therefore, 5.0 mg of the particles were weighed in a 10 mL microwave vial (CEM GmbH), and 1 mL of fresh aqua regia was added. The vessels were closed and heated in the microwave reactor in three subsequent steps: 1) Setpoints: 50°C with max. 30 W and max. 17 bar for 30 s; 2) Setpoints: 90°C with max. 50 W and max. 17 bar for 30 s; 3) Setpoints: 100°C with max. 50 W and max. 17 bar for 5 min.
Afterward, the solution was transferred to a centrifuge vial whereby the microwave vial was carefully rinsed several times. The solution was centrifuged three times at 6726 g, whereby the solid was washed in between to wash out all metal ions. All fractions were gathered and filled up to 25 mL. Of these solutions, ICP-OES (iCAP 7400 from Thermo Fischer Scientific, Waltham, Massachusetts, USA) was used to determine the concentrations of Pd and Cu of the digested samples.
For the ICP-OES analysis, four matrix-matched, external standard solutions were used for calibration, containing Pd and Cu each in the same concentration of 0.1, 0.5, 1, and 5 mg L À1 . Each sample was measured fivefold. The respective detection limits for the measurements were 0.072 mg L À1 Pd and 0.008 mg L À1 Cu.
Characterization Methods: Thermogravimetric Analysis: TGA was performed using the 1 Star System device from Mettler Toledo (Gießen, Germany). Therefore, 5 to 8 mg of the sample was loaded into a platinum crucible. The temperature range was from 25 to 1000°C with a heating rate of 10°C min À1 , under an air atmosphere at a flow rate of 40 mL min À1 .
Characterization Methods: Ultra-Thin Section Transmission Electron Microscopy Measurements: Samples were embedded in epoxy resin to make sure a good handling of preparation. For investigation by TEM, ultrathin sections of the samples were sliced with a diamond knife (35°knife angle; DIATOME, Switzerland) using ultramicrotome EM UC/FC 6 (Company Leica/Austria). The thickness of sections was in the range of 60-70 nm. Sections were generated with a speed of sectioning of 0.6 mm s À1 at room temperature. Afterward, ultrathin sections were flooded with water and transferred on carbon hole filmed TEM copper grids.
TEM measurements were performed using TEM LIBRA 120 MC of the company Carl Zeiss SMT (Oberkochen, Germany) with an acceleration voltage of 120 kV.
Characterization Methods: Scanning Transmission Electron Microscopy Energy-Dispersive X-ray Analysis: STEM-EDX measurements of the ultra-thin sections were performed using a JEOL JEM F200 (JEOL Germany, Freising, Germany) with an operating voltage of 200 kV and a cold FEG energy spread of 0.46 eV. The energy dispersive spectroscopy was detected by two 100 mm 2 window-less silicon drift detectors (solid angle 0.98 sr). For data analysis, GATAN Digitalmicrograph suite was used.
It is advantageous that the resin used for the production of the ultrathin section contains neither nitrogen nor bromine in significant amounts (compare background Figure 4). This allows for a mapping of the N and Br distribution in the PTP particles.
Characterization Methods: Contact Angle Measurements: Contact angle measurements were conducted by pressing the samples into a thin film and then using an OCA 40 Micro (Dataphysics, Filderstadt, Germany) device for dynamic measurements. 5 μL of water was dispensed onto the film and an additional 5 μL was slowly added using the "needle in" method. A CCD camera filmed the proceeding angle, which was subsequently calculated using the "tangent leaning" method (SCA software, Dataphysics, Filderstadt, Germany).
Diclofenac Adsorption: pH Measurements: The measurement of pH was carried out with the device SevenEx-cellence from Mettler Toledo (Gießen, Germany) at r.t., with the electrode kept within a saturated KOH solution when not used.
Diclofenac Adsorption: Batch Adsorption Procedure: For batch adsorption experiments solutions of 0.5; 1; 2; 5; 10; 20 30; 40; 50; 75; 100; 150; 200 and 300 mg L À1 DFC were prepared using ultrapure water. The pH of these solutions was monitored. In a 50 mL Falcon tube, 10 mg of the respective CMP or CMP/SiO 2 hybrid material was added and then filled with 20 mL of the respective DCF solution. The solution shook on an IKA shaker (Orbital Rotary Shaker KS 501 D) at around 150 rpm for 24 h. Subsequently, the solution was centrifuged twice at (6726 g) for 15 min to separate all solid components and the supernatant was measured using UV/vis measurements.
Diclofenac Adsorption: UV/Vis Measurements and Subsequent Calculation: The adsorption was determined by measuring the DCF concentration in the supernatant using the adsorption at 275 nm (Cary 5000 UV-Vis-NIR, Agilent Technologies Inc. Santa Clara, CA, USA). Therefore, two calibration curves using 5; 10, 50, 75, 100, and 150 mg L À1 and due to necessary dilution an extra calibration for 150, 200, 300, 400, and 500 mg L À1 were made. Blank samples were run for each isotherm and used as the baseline. The adsorption was calculated using the following equation with c 0 as the concentration of DCF in the initial solution and c eq as the concentration after reaching equilibrium (Equation (1)) Adsorption in % ¼ c 0 À c eq c 0 (1) Diclofenac Adsorption: Cycling Adsorption Studies: For cycling adsorption studies 20 mg of PTP@SiO 2 -3.0 were added to four 50 mL Falcontubes each of which two were filled with 40 mL of DCF solution of 1 mg L À1 and 300 mg L À1 , respectively. These were shaken for 24 h after which the tube was centrifuged (6300 g, 15 min) and the adsorption was measured via UV/vis. The adsorber was separated from the solution through additional two centrifugation steps (6300 g, 10 min), where the solid was briefly washed with 5 mL of MilliQ in between to remove residual dissolved DCF. After thorough drying, the desorption was carried out by shaking the adsorber in 10 mL of absolute ethanol for 3 h. After centrifugation (6300 g, 15 min), the ethanol was separated from the adsorber and the desorbed amount was measured via UV/vis (separate calibration for ethanol). The adsorber was dried after which the procedure was repeated to obtain the next cycle.
Diclofenac Adsorption: Theory of Isotherm Fitting Models: To determine the sorption efficiency of the CMP and the hybrid materials, the sorption capacity (q eq ) was calculated using Equation (2) q eq ¼ ðc 0 À c eq ÞÃV s m A Thereby V s is the volume of the adsorption solution, which is constant at 20 mL and m A is the mass of the adsorber material being 10 mg. For the calculation of the sorption capacity only related to the CMP material (q eq-CMP ), the equation was extended with the CMP wt% determined via TGA as the following (Equation (3)) Both sorption capacities were plotted against c eq to give the adsorption isotherms, which were subsequently fitted using the following nonlinear models Langmuir model [40] q eq ¼ q sat ÃK L Ãc eq 1 þ K L Ãc eq (4) Freundlich model [41] q eq ¼ K F Ãc 1=n eq (5) www.advancedsciencenews.com www.small-structures.com Small Struct. 2023, 4, 2200385