Abstarct: Abeatract Part I: Solid Phase Microextraction (SPME) techniques are among the most effective methods for pre-concentration of various analytes from complex matrices. These methods allow for the measurement of analytes with lower costs and faster speeds. In the first section of this study, a Multi-Template Molecularly Imprinted Polymer (MT-MIP) was employed as a selective solid phase for two non-steroidal anti-inflammatory drugs (NSAIDs), namely nalidixic acid and naproxen. The MT-MIP exhibited simultaneous adsorption capability for both analytes. To enhance the dispersion and surface area of the SPME fiber, the MT-MIP structure was encapsulated within the pores of a mextal-Organic frxamework (MOF) and a composite was synthesized. This composite was grown on an inexpensive graphite rod (PG). The designed fiber was affixed to a syringe as a holder baxse. To optimize the surface of the graphite rod for the MT-MIP@MOF composite, its surface laxyers were chemically transformed into graphene oxide. The presence of carboxyl and hydroxyl groups facilitated the bonding of the MOF to the rod structure. In order to evaluate the efficiency of the new SPME fiber, the simultaneous pre-concentration of analytes and their concentration measurement were investigated using High-Performance Liquid Chromatography (HPLC) with high-resolution detection. To enhance effectiveness and achieve better performance, the pre-concentration process was modeled and optimized using Response Surface Methodology (RSM). The detection limit of this method was calculated to be 0.05-0.06 μg/L, and its linear range was 0.5-410 μg.L-1. Keyword: SPME, MT-MIPs, MOFs, NSAIDs, HPLC. Part II: Despite all the progress, photo-catalysts still have some shortcomings, so it is essential to improve them. Herein, we have prepared a magnetic core–shell composite using CoFe2O4 magnetic nanoparticles and poly(chloropropyl-methyl)silsesquioxanes (PCMSQ). Then, its surface was functionalized by -NH2 groups to provide favorable conditions for immobilization of Ag nanoparticles. It can lead to adjusting the bandgap energy of the composite and transmitting it to the visible region of light via a plasmonic sensitization process. Consequently, photo-degradation of pollutants can be easily performed by a LED lamp or sunlight. Hence, the degradation of two organic dyes was simultaneously performed to investigate its photo-catalytic properties in simulating actual conditions. However, due to the overlapping of their spectra, it was difficult to monitor the process and determine the concentration of the species using UV–Vis spectrophotometry. Therefore, a new and fast method, namely EXRSM, was employed to solve this problem. The CCD-RSM was also used to optimize, model, and better understand the effect of main factor interactions in the degradation process. For each dye, the adequacy of the model was proven by statistical analyses such as ANOVA and residual plots. The obtained R2, R2adj, and R2pred show a high correlation between experimental and predicted results. The kinetic investigation revealed that the degradation process follows a pseudo-zero-order model, and the Kapp values for MV and MB were calculated to be 0.0156 and 0.0181 (mol•L−1•min−1), respectively. Finally, we analyzed the recycling ability of Ag@PCMSQ@CoFe2O4, in which the photo-catalytic efficiency of the recovered catalyst was only reduced by less than 10%, after five cycles, for each dye. Keyword: Photodegradation, Bandgap modification, Wastewater treatment, Inorganic polymers, Plasmonic nanoparticles Part III: Designing novel photocatalysts is crucial in improving pollutant removal and promoting a cleaner and healthier environment. The main objective of this study was to create a novel magnetic core-shell structure that could be used for photocatalytic applications. To achieve this goal, we used CoFe2O4 magnetic nanoparticles as the core and a covalent organic frxamework (COF) as the shell, which was designed to have magnetic properties and a suitable surface for further functionalization. To improve its photocatalytic properties, we added silver nanoparticles (Ag NPs) by a facile light-assisted reduction process to create a ternary composite. The presence of Ag NPs is expected to result in a broader absorption range of light and more effective degradation of pollutants through plasmonic sensitization and the transfer of bandgap energy into the visible light spectra. We characterized the prepared composite using various chemical and physical techniques, and then examined its ability to remove two stable organic pollutants, methylene blue (MB) dye and 4-nitrophenol (4-NP), simultaneously. The strong spectral overlap between these pollutants posed a challenge for conventional spectroscopic methods to accurately measure their concentration. To overcome this, a rapid and new method, namely extended ratio subtraction method (EXRSM), was utilized to separate and remove the spectral overlap. We further optimized the reaction conditions using response surface methodology (RSM) modeling techniques. Our findings indicated that the designed composite was capable of degrading organic pollutants under the visible light radiation of an LED lamp.