# Wastewater Treatment by Polymeric Microspheres: A Review
## 2 Synthetic Polymer
TGA curves revealed that the main decomposition occurred at 250-400 \({}^{\circ}\)C. Different properties of the magnetic microsphere proved that the microsphere was a reusable adsorbent for the efficient removal of anionic and aromatic dyes by binding the anionic organic compounds to porous magnetic microsphere during wastewater treatment. Its magnetic and adsorption properties were also maintained, even in harsh conditions. Another magnetic microsphere as adsorbent for cationic dyes is made from polyacrylamide (PAM) [29]. The porous magnetic PAM microsphere was prepared using the phase separation method induced by polymerization. The adsorption capacity of methylene blue increased from 263 mg/L to 1977 mg/L as initial concentration increased from 5 mg/L to 300 mg/L. The adsorption capacity increased with increasing initial pH and reached a maximum of 1990 mg/g at pH 8, indicating the electrostatic interaction between the microsphere and dye. The microsphere also showed high adsorption capacities for other dyes (1937 mg/g for neutral red (NR) and 1850 mg/g for gentian violet) and the mixed-dye solution. Complete adsorption was possible even for a very low initial concentration by using a different pore structure PAM microsphere with different PEG concentrations. The TGA curve showed that 70 wt% weight loss occurred at 200-500 \({}^{\circ}\)C. The adsorption followed the Langmuir isotherm model. The dye-absorbed microsphere could be easily desorbed and used for six cycles without resulting in a loss of adsorption capacity. Mesoporous microsphere made up of melamine formaldehyde resin (MMFRS) without any inorganic materials is also made. MMFRS was fabricated for the removal of organic compound perfluorooctanoic acid from wastewater [30]. It was fabricated through suspension polymerization. Its mesoporous property with an average pore size of around 10 nm (analyzed from the TEM image) and its large anion-exchange capacity of 0.3 mmol/g make it a promising adsorbent of perfluoroalkyl and polyfluoroalkyl substances, particularly perfluorooctanoic acid from wastewater. TGA curves confirmed that the greatest mass loss occurred at temperatures between 400 and 800 \({}^{\circ}\)C. The sorption process followed the PSO kinetic model, and the sorption isotherms followed the Freundlich and Langmuir model. The absorption amount of MMFRS exceeded the current commercial powdered activated carbon, as it reached equilibrium within 24 h and could be used in broad pH range. MMFRS is also easily and economically regenerated by using a 7.5 mM dilute of NH\({}_{3}\cdot\)H\({}_{2}\)O, and it reached over 85% of regeneration percentage after 20 manifold cycles. The degradation of pollutants is another way to get rid of pollutants, and TiO\({}_{2}\) is an excellent semiconductor used for photocatalysis. It was incorporated into a poly[ANE + N-PMI] microsphere to decompose carcinogenic compounds into harmless product [31]. The biomass polymer microsphere was prepared via precipitation polymerization. Amino-modified TiO\({}_{2}\) nanoparticles were covalently linked to the surface of the biomass-driven phenylpropenes trans-anethole (ANE) and N-phenylmaleimide (N-PMI) polymer. The microspheres were used as photocatalysts for the degradation of RhB dyes and tetracycline (TC) antibiotics. The microsphere and the TiO\({}_{2}\) nanoparticles were covalently bonded, and the microspheres participated in the electron transmission at the surface of the nanoparticles to minimize the recombination between electrons and holes. The intensity of the photoluminiscent (PL) spectroscopy peak at 480 nm (which was lower than that of single TiO\({}_{2}\)) indicates the low recombination rate. The large surface area of microsphere provided more active sites for degradation. Superoxide free radicals (-O\({}_{2}^{-}\)) and hydroxyl radicals (OH) were the primary and secondary reactive species during photo-degradation. The degradation rate of microsphere reached 95% for 50 mg/L RhB and 97% for 100 mg/L TC.