Polycarbonate Microchip Containing CuBTC-Monopol Monolith for Solid-Phase Extraction of Dyes

In the present study, preparation of CuBTC-monopol monoliths for use within the microchip solid phase extraction was undertaken through a 20-min UV lamp-assisted polymerization for 2,2-dimethoxy-2-phenyl acetophenone (DMPA), butyl methacrylate (BMA), and ethylene dimethacrylate (EDMA) alongside inclusion of the porogenic solvent system (1-propanol and methanol (1 : 1)). The resultant coating underwent coating using CuBTC nanocrystals in ethanolic solution of ethanolic solution of 1,3,5-benzenetricarboxylic acid (H3BTC, 10 mM) and 10 mM copper(II) acetate Cu(CH3COO)2. This paper reports enhanced extraction, characterization, and synthesis studies for porous CuBTC metal organic frameworks that are marked by different methods including SEM/EDAX analysis, atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy (FT-IR). The evaluation of the microchip's performance was undertaken as sorbent through retrieval of six toxic dyes (anionic and cationic dyes). Various parameters (desorption and extraction step flow rates, volume of desorption solvent, volume of sample, and type of desorption solvent) were examined to optimize dye extraction using fabricated microchips. The result indicated that CuBTC-monopol monoliths were permeable with the ability of removing impurities and attained high toxic dye extraction recovery (83.4–99.9%). The assessment of reproducibility for chip-to-chip was undertaken by computing the relative standard deviations (RSDs) of the six dyes in extraction. The interbatch and intrabatch RSDs ranged between 3.8 and 6.9% and 2.3 and 4.8%. Such features showed that fabricated CuBTC-monopol monolithic disk polycarbonate microchips have the potential of extracting toxic dyes that could be utilized for treating wastewater.

For industrial application of such MOF powders, they must be transformed into structures that can be monoliths or particles [26]. MOF particles usually suffer from irregular shapes and widely distributed sizes that might lead to undesirable peak shapes, high column backpressure, and low column efficiency [27][28][29]. e most energy-efficient and economical structure for application within any given absorption system might be in monolith form as its structure is characterized by high mass transfer and low pressure reduction rates than other structures [30,31]. Experimental studies examining the absorption processes of MOFs are usually conducted with its powder and structured MOF production, especially the industrial adsorption process monolithic structure is rare [32][33][34].
MOF-polymer composites that shape mixed-matrix monoliths for catalysis [35][36][37], separation [38][39][40][41][42], and gas storage [43][44][45] have already been examined. In the previous years, MOF use within the field of analytical chemistry has been increasing constantly [7,[46][47][48]. Nevertheless, such composite components are yet to be examined as SPE supports. e possible benefits of MOF-matrix SPE supports are as follows: (i) simple sorbent preparation allowing enrichment of targeted compounds and concurrently the exclusion of size within desorption phase of larger molecular sized compounds than the chosen MOF pore size, (ii) simple sorbent functionalization, merely through selection of proper organic connecters utilized within the synthesis of MOF, (iii) simple SPE automation process through flowdriven methods, avoiding high backpressure or tiny particles clogging the flow manifold tubing, and (iv) excellent flowthrough characteristics, allowing SPE applications to use MOFs (independently regardless of their shape and crystal size) [44,[49][50][51][52].
e pattern in analysis towards microfluidic devices can be attributed to the ability of integrating several analytical processes into one microfluidic device, reduced reagent consumption, decrease in the time of analysis, and sample volume reduction [53][54][55]. A trend for using microfluidic devices on tasks including chemical modification, immunoassays, separation, and sample pretreatment exists [56][57][58][59][60][61]. is work is aimed at exploring the application of polycarbonate microchips with the CuBTC-monopol monolithic disk as dye extraction supports. HKUST-1 that constitutes one extensively examined MOF, experimentally and theoretically, is obtained from benzene-1,3,5-tricarboxylate (BTC) connecter molecules and Cu 2+ cations, which contain paddle wheel structures [62][63][64][65]. In the present study, HKUST-1 is utilized as a MOF model for demonstrating in situ stratum-by-stratum self-assembly technique for grafting MOFs on poly(BuMA-co-EDMA) (butyl methacrylate-co-ethylene dimethacrylate) monolith surfaces. Notably, studies exploring in situ synthesized MOF development within the porous polymer monolith as the SPE stationary phase are nonexistent. e emerging CuBTCpoly(BuMA-co-EDMA) monolith underwent evaluation and was suggested as the stationary extraction phase of various dyes, which were congo red, fast green, methyl orange, methyl blue, bromophenol blue, and coomassi brilliant blue.

Instrumentation.
e FT-IR spectrum included Per-kinElmer RXFTIR ×2 containing DRIFT attachment and diamond ATR (PerkinElmer-Buckinghamshire, UK). XRD was get using the D8-ADVANCE Bruker diffractometer (Coventry, UK). High-resolution atomic force microscopy (AFM) was utilized for testing morphological properties and to generate topological maps (Veeco-di Innova Model-2009-AFM-USA). e energy-dispersive analysis of X-ray spectroscopy (EDAX) and scanning electron microscope (SEM) equipment include Cambridge S360 from Cambridge Instruments (Cambridge, UK). UV-Vis spectrophotometers were purchased from ermo-Scientific GENESIS 10S (Toronto, Canada

Fabrication of the MOF-Polymer Monolith.
Preparation of organic polymer-based monoliths in the plastic syringe in room temperature under UV irradiation was undertaken using photoinitiated free radical polymerization. e preparation of organic polymer-based monolith was undertaken based on descriptions presented in our study [66]. e polymerization mix featured the porogenic solvent system that constituted 1-propanol and methanol binary mixture (50 : 50), 2,2-dimethoxy-2-phenyl acetophenone (DMPA, the free radical photoinitiator), ethylene dimethacrylate (EDMA, crosslinker), and butyl methacrylate (BuMA, monovinyl monomer). Sonication was conducted on the mixture, which was then placed into the plastic syringe and heated using the UV lamp. e duration of exposure was 20 minutes, whereas the distance separating the plastic syringe and the UV lamp (365 nm at room temperature) was 5 cm. After monolithic materials have formed within the plastic syringe, methanol was used to wash the monolithic rod for 12 hours to eliminate the unreacted materials.
For preparation of CuBTC nanocrystals placed within the organic-based monolith mesoporosity, the monolithic materials that were prepared were immersed in a solution of ethanol containing Cu(CH 3 COO) 2 (10 mM) for 120 minutes. After washing in ethanol, the monolithic material improved using Cu 2+ was soaked within a BTC ethanolic solution (10 mM) for 120 minutes. Finally, the materials were subjected to washing and immersed in ethanol at 90°C for 12 hours, and then methanol added for preservation until used.

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International Journal of Analytical Chemistry

Fabrication of the Polycarbonate Microchip.
e polycarbonate microchip's design contained two plates; base and top plate dimensions were 13.5 mm in width and length, and thickness of 2.8 mm. e top plate contained microchannels (depth 1 mm, width 1 mm, and length 4 mm) and two access holes (1.5 mm). e base plate had extraction chamber (2 mm depth and 6.5 mm width), which underwent milling using CNC (computer numerical control) milling machine. e monolithic organic disks were cut and placed in the extraction chamber [53,67]. Epoxy resin was used for fixing the two plates, whereas ETFE tubing was placed into access holes drilled into microfluidic devices with epoxy resin. After the two plates were bonded, microchips were used for extracting dyes.

Characterisation of Fabrication Materials.
e characterization of monolith's morphology was through SEM. Images were acquired using an increasing voltage of 20 kV alongside 100 pA probe current within high vacuum mode with SEM from Cambridge S360. Coating was undertaken on the samples using thin gold platinum layer (thickness about 2 nm) using a Nanotechnology Ltd. (Sandy, UK) SEMPREP 2 sputter coater. XRD with CuKα radiation in the 2 theta (2θ) range from 10°to 50°. Compositional analysis was examined with EDAX spectroscopy. Topological map (Veeco-di Innova Model-2009-AFM-USA) and morphological properties were tested using high-resolution AFM. Noncontacting mode tapping constituted the mode that was applied. Surface topology was accurately mapped by forwarding the AFM-raw data to the Origin-Lab version 6-USA program for accurate visualization of 3D surfaces for the sample being investigated. e FT-IR spectrum was gathered within the attenuated total reflectance (ATR) mode in ranges of 500-4000 cm − 1 .

Dye Extraction.
e performance for microfluidic CuBTC-monopol monolith devices containing was investigated. e standardized dyes (congo red, methyl orange, fast green, bromophenol blue, commassi brilliant blue, and methyl blue) underwent dissolution in a buffer solution of ammonium acetate (10 mM, pH 9.3) and were utilized in extraction experiments. 100 μL of ACN was used for activating the polymer-based monoliths within the microchip, which was then subjected to equilibration with using 100 μL of 10 mM buffer solution of ammonium acetate (pH 9.3). e solution of the dye sample (100, 200, 300, or 400 μL) was used on the monolithic microchips with flow rates of 5, 10, 15, or 20 μL·min − 1 . Finally, extract portions (50, 100, 150, or 200 μL) were eluted with eluents (acetone, acetonitrile, isopropanol, ethanol, or methanol) utilizing flow rates of 5, 10, 15, or 20 μL·min − 1 and collected into Eppendorf tubes and analyzed with the UV-Vis spectrophotomer. e reason for utilizing UV-Vis spectrophotomer was to examine the peak area of the preconcentrated dyes and comparing them against the peak levels of nonprocessed dye standardized solutions to compute the recovery of extraction. Calculation of the preconcentrated dyes' extraction efficiency was undertaken with the previous technique [1].

Fabrication of Metal-Organic Monolith.
is study sought to hierarchically fabricate porous metal-organic monoliths consisting of organic struts and metal clusters/ ions, which integrate the advantages of lights aerogels and crystalline MOFs [68][69][70][71]. Figure 1 shows the major steps for fabricating CuBTC-monopol monolithic rods. e fabrication for the monoliths was premised on organic-based monolith fabrication followed by combination of Cu-BTC nanocrystals and organic monolithic components. e polymerized mix contained divinyl monomers (EDMA) and monovinyl (BuMA) within the existence of free radical initiators (DMPA) and porogenic solvents [72]. After putting the polymerized mixture into the plastic syringe, it was heated using the UV lamp, which led to the formation of polymers and later precipitation [72]. In the event the polymer-based monolith has bright white materials (satisfactory appearance), Figure 2(a), the washing of monolithic rods is undertaken. Washing of the soluble oligomer remnants within the pores, the unreacted monomeric material, and porogenic system solvents was undertaken using methanol for 12 hours to avert further polymerization reactions, since the crosslinker and the monomer have affinities of continuing the polymerization reactions [73]. e organic monolith formed underwent coating using CuBTC nanocrystals with ethanolic solution of H 3 BTC (10 mM) and ethanolic solution Cu(CH 3 COO) 2 (10 mM). e resultant monolith (CuBTC-monopol) yields a homogeneous blue colored material showing homogenously distributed copper in the whole monolith, Figure 2(a). For generation of pure crystalline materials, the as-prepared monoliths in room temperature were soaked or washed in ethanol at 90°C for 12 hours. is sought to cause further reaction, increase porosity, and eliminate unreacted impurities to enhance the crystalline stage. Figure 2(b) illustrates the cross section (bottom, middle, and top) of the MOF monolithic rods formed. e monolith's central and external parts have similar colors. e result proves the surface functionalization of organic based monoliths with equal CuBTC, and no recurrent treatment is needed to increase the CuBTC within the organic monoliths.

Physical Characteristics of CuBTC-Monopol Monolith.
After the drying phase, the monolith morphology was examined using SEM analysis. e analysis estimates the skeleton and through pore size, which would in turn determine the monolithic material's mechanical strength and hydrodynamic properties, whereas the approaches presented below are ideal for determining the through pore size distribution and exact size. e polymeric monoliths' morphologies after and prior to CuBTC-monopol monolith formation were examined through SEM analysis utilizing various magnifications, as can be seen in Figure 3. From the figure, it was found that all sample surfaces were porous, crack-free, smooth, and uniform structures.  networks. Besides, it was reported that the pore size reduced after CuBTC coating because the monolithic material was coated with metallic clusters/ions. Figure 4 presents the XRD pattern of CuBTC-monopol monolith. is pattern is similar to the XRD pattern in the previous study [74] confirmed the formation of metal-organic frameworks.
EDAX analysis was used to further examine fabricated materials to determine the formed materials' composition. As Figure 5 illustrates that the EDXA spectra for bare organic monoliths revealed that the string peak for oxygen is 0.525 keV, whereas that for carbon is 0.227 keV. e CuBTC-monopol monolith's EDAX showed that, besides the oxygen and carbon element peaks, a peak of 8.040 keV which was linked to Cu was observed. e compositions of carbon (74.22%) and oxygen (25.78%) within the sample of organic-based monoliths are presented in Table 1. Notably, the composition of copper (1.88%) in CuBTC-monopol monoliths was found, thus confirming the modification to the organic monolith surface with a CuBTC layer.
Notably, AFM was used for analyzing fabricated materials' surface properties, because the method could yield quantitative and qualitative information concerning the fabricated materials' topography. Figure 6 illustrates the 3D fabricated materials' AFM images derived with the AFM method. As it could be observed clearly in Figure 6(a), the organic-based monolith's flat surface was uniform and smooth, with an optimum surface height of about 4.1 μm. In Figure 6(b), the 3D CuBTC-monopol monolith AFM image revealed that the surface's maximum height rose to 6.4 μm, thus proving that organic monoliths had been coated with a layer of CuBTC. e prepared materials' composition was characterized using the FT-IR spectrometer. Figure 7 presents the FT-IR spectrums; the two spectra are identical with the following string peaks, cm − 1 : 1273-1000 C − O − C [75] vibration within ester groups, 2875-2987 CH stretching within CH 2 and CH 3 groups, 1732 C � O stretching, and the peak for carbonyl is 1675 cm − 1 . Notably, the sole variation on the copolymer spectra pertains to the sharp centered band at 1637 cm − 1 , connected to carbonyl from ester groups originating from EDMA/BuMA alongside other O − H peak at 3438 cm − 1 [76].

Dye Extraction.
is study sought to fabricate polycarbonate microchips containing effective dye extraction sorbents (cationic and anionic dyes). e microchip's photograph and schematic diagram, which was utilized for extracting dyes, is presented in Figure 8. e polycarbonate microchip's design featured two plates, with the top plate having microchannels (depth 1 mm, width 1 mm, and length 4 mm) alongside access holes (1.5 mm) for ETFE tubing attachment, whereas the base plates contained an extraction chamber (2 mm depth and 6.5 mm width).
e CuBTCmonopol monolith disk's diameter (2 mm) was modified using scalpel blades. Epoxy resin was used for fixing the tubing of ETFE within the access holes. e microtight adapter was employed for connecting the ETFE tubing to plastic syringes that were attached to a syringe pump.
is study sought to locate the ideal dye extraction performance. Various dyes were examined in the study including congo red, methyl orange, fast green, bromophenol, coomassi brilliant blue, and methyl blue. As the first experiment, 100 μL of ACN was used for activating the polymer-based monoliths within the microchip, which was then subjected to equilibration using 100 μL of 10 mM buffer solution of ammonium acetate (pH 9.3). e solution of the dye sample (300 μL) was injected into the polycarbonate microchip using a syringe pump at a flow rate of 10 μL·min − 1 , and when the solution of the sample was loaded via extraction monolith, the sorbent was washed using ACN and rinsed to eliminate impurities and keep the analytes. Finally, the preconcentrated dyes were eluted with desorption solvent (150 μL) with a flow rate of 5 μL·min − 1 .

Selection of the Desorption Solvent.
e effect from various desorption solvents including acetone, acetonitrile, isopropanol, ethanol, and methanol on the CuBTCmonopol monolithic disk analyte desorption was examined to obtain the suitable conditions of desorption for polycarbonate microchip dyes. e solution of the dye sample was pumped into the polycarbonate microchip and ACN used for washing the sorbents, and finally the preconcentrated dyes were eluted with desorption solvent and gathered into Eppendorf tube. e UV-Vis spectrophotometry was used for measuring the preconcentrated dye peak areas. e preconcentrated dyes' UV-Vis spectra using various desorption solvents are presented in Figure 9. From Figure 10, it can be seen that all examined solvents were used for desorption of various dyes; nevertheless, it was reported that application of acetone as desorption solvents could accelerate extraction of various sorbent dyes.
us, in all examined dyes, the desorption solvent was acetone.

Study of the Extraction Parameters.
Desorption steps and extraction flow rates, desorption solvent volume, and sample volume are important parameters for designing SPE procedures conducted using flow-based methods operating in nonequilibrium conditions. All such parameters were examined to increase the dye extraction using fabricated polycarbonate microchips. International Journal of Analytical Chemistry e dye sample solution's volume 100, 200, 300, and 400 μL was another optimized parameter. e sample volume effect on dye preconcentration is shown in Figure 11       e effects of desorption acetone volume on extracted dye elution from CuBTC-monopol monolithic disk is illustrated in Figure 11(b). e volume of the desorption solvent from 50 μL to 200 μL to decrease the consumption of solvent within desorption phase, while ensuring proper desorption of retained sorbent analytes. e method's performance increased when the volume of the desorption solvent increased. In view of this, the volume of desorption solvent (200 μL) was chosen for more experiments. e flow rate of the extracted sample was investigated within the range of 5 μL·min − 1 -20 μL·min − 1 . In higher rates of flow, analyte extraction decreases slightly as illustrated in Figure 10(c). e increase in the flow rate of the sample reduces the time of contact between CuBTC-monopol monolith and dyes, reducing the mass transfer and thus the extracted dye quantity. In the compromise involving high extraction throughputs and high extraction efficiencies, the extraction phase flow rate of 10 μL·min − 1 was used for additional experiments. e effects of desorption solvent's flow rates on retained analytes desorption from CuBTC-monopol monoliths are shown in Figure 11 Figure 9: UV-Vis spectra of the preconcentrated dyes using different desorption solvents (acetone, acetonitrile, isopropanol, ethanol, or methanol). 8 International Journal of Analytical Chemistry enabled maximum effectiveness on desorption phase, was 5 μL·min − 1 , being used for experiments.

Real Sample Analysis.
To investigate the applicable nature of polycarbonate microchips containing CuBTCmonopol monolithic disks for dye SPE, various polluted samples of groundwater were subjected to analysis. Samples of groundwater were gathered from reservoirs of water. Dyes were used for spiking the samples, and a recovery study was conducted by having the samples spiked. Calculation of analyte recoveries was undertaken as the dye concentration ratio measured within the spiked sample and within pure spiked water with similar level of concentration. e chromatograph for samples of polluted groundwater spiked with dye after and before preconcentration using fabricated microchips is shown in Figure 12, and Table 2 shows the results obtained. Following spiking, the recoveries obtained ranged between 78.2% and 92.5% when using unmodified organic monolith, while the recoveries obtained ranged between 83.4% and 99.9% for all analyzed samples. Such results confirm polycarbonate microchip containing CuBTC-monopol monolith suitability for analysis of toxic dyes samples.

Limit of Detection and Quantification.
During calibration, five samples were used with different standard solutions for the analyzed dyes. For each sample, three tests were done and calibration curve calculated using the leastsquares method. e curve generated was concentration against peak area with correlation coefficient. e curves generated were linear where the limit of detection (LOD) and limit of quantitation (LOQ) values were determined. e calculations were based on standard deviation of the detector response (σ) and the slope (S) of the curve, and the validation of analytical procedures is as demonstrated in the following expressions: (1) e value of response σ is the standard deviation of the y intercept of the regression line determined from the plotted calibration curves. e analysis will only take a proportion of efficiency during an extraction. S Denotes the slope of the regression corrected for the SPE recovery value.
During the experiment, six dyes were analyzed including bromophenol blue, coomassi brilliant blue, methyl blue, congo red, methyl orange, and fast green. e HPLC values for these dyes were recorded and corrected for SPE recovery values which were then used to determine the LOD and LOQ calculation for the calibration curves. e values of LODs and LOQs were recorded as shown in Table 3.

Reproducibility of the Fabricated Device.
e CuBTCmonopol monolith fabrication's reproducibility constitutes an important aspect in the procedure's practicality and effectiveness, since CuBTC-monopol monolith fabrication constitutes a multiphase process. Additionally, surface modification reproducibility for CuBTC layer monoliths constitutes a crucial requirement for recognition of the preparation method used, particularly within industrial laboratories. Besides, reusability is one important aspect of using polycarbonate microchips, because fabrication costs are high. e fabrication technique's reproducibility of three monoliths fabricated from three polymerization mixes have a similar composition. e monolith fabrication's reproducibility was evaluated by verifying the morphologies that SEM found for three separate batches of fabricated CuBTC-monopol monoliths. It was reported that visible differences did not exist within the prepared monolith's morphology. Nevertheless, CuBTCmonopol monolith within polycarbonate microchips involve cutting monolithic organic rods using scalpel blades and putting the monolithic CuBTC-monopol disks in polycarbonate microchip's base plate extraction chamber prior to bonding base and top plates using epoxy resin that can cause differences in prepared monolith's size, which in return might cause variability for dye extraction. It is proposed that such variability could be reduced through automated preparatory procedure. e performance's reproducibility of fabricated devices was examined by computing the extraction efficiency's relative standard deviation (RSD) for six samples of dyes. Extraction efficiency's intrabatch RSDs of preconcentrated dyes using the same microchip (4 runs) as well as using various microchips (n � 3) are shown in Table 3. e obtained results from the investigation indicated that the dye preconcentration procedure was reproducible because acceptable run-to-run reproducibility was attained using RSD values ranging from 2.3 to 4.8%, while interbatch RSDs ranged between 3.8 and 6.9% for chip-to-chip reproducibility.
e capacity of size exclusion for developed SPE support offers more advantages for analyzing chemicals; for instance,  enhanced selectivity for analysis of chemicals through chromatographic methods, sample matrix simplification before injection to analytical instrumentation, and increased selectivity of tiny molecule analysis. e major pitfalls regarding the CuBTC-monopol monolith use as SPE sorbents pertain to the limited stability for CuBTC-monopol monolith within acidic media and limited commercial availability of CuBTC-monopol monoliths. Nevertheless,  several CuBTC-monopol monoliths could easily be synthesized from commercially available and cheap precursors and have stability towards experimental conditions utilized in different SPE applications. e advantages of the former, alongside their facile automation, as well as versatile and simple preparation provide CuBTC-monopol monolith with a variety of possibilities for analytically preparing samples.

Conclusion
e preparation of samples is regarded as barrier in the chemical analysis system. is study sought to design a CuBTC-monopol monolith dye-extraction microchip. e monolithic CuBTC-monopol material constitutes high-porosity materials with huge potential for application as toxic dye preconcentration sorbent. e analysis of monolithic CuBTC-monopol material was undertaken using various methods, including SEM/EDAX analysis, AFM analysis, and FT-IR spectroscopy. In the current work, successful designing of novel microfluidic devices that contain crack-free organic monoliths was modified using CuBTC-monopol groups to decrease reagents and analyte volume. e fabricated polycarbonate microchips were evaluated for dye extraction. Different parameters, including desorption steps, extraction flow rates, volume of desorption solvent, sample volume, and type of desorption solvent, were examined to optimize dye extraction using fabricated polycarbonate microchips.
e results indicate that modified monoliths yielded reproducible extraction efficiency for various dyes and had stability over time and low flow resistances. Work is underway to create fully integrated preconcentration devices of various toxic dyes derived from actual samples as well as photodegradation of such dyes.

Data Availability
e data used to support the findings of this study are included within the article.  12 International Journal of Analytical Chemistry