Synthesis and characterization of cationic hydrogels and its use in anionic dye removal

The increase in environmental pollution caused by toxic dyes due to its dangerous nature is a major concern. Even small amounts of non-biodegradable and highly toxic dyes can cause serious harm to humanity and nature. Adsorption method is one of the methods used to remove the paint from the wastes from paint production, dye mills and the wastes formed as a result of the dyes used in the textile industry. Within the scope of adsorbent development studies, hydrogels were prepared using MOEAMCl and MAAm monomers, N, N methylene bisacrylamide crosslinker and potassium persulfate radicalic initiator. The prepared hydrogels were characterized by FTIR, SEM, EDAX and TGA analysis. The swelling studies of the prepared hydrogels in different medium (pH = 2,4,8 and 9 buffer solutions and urea and NaCl solutions) and temperatures (25 oC, 35 oC, 45 oC and 55 oC) were carried out. In addition, the use of synthesized hydrogels as an adsorbent for anionic dye removal was investigated. For this purpose, anionic dye Methyl Orange (MO) was used as a contaminant in adsorption studies. It was found that the hydrogels prepared in the MOEAMCl-MAAm (75:25 and 50:50) (HD–2 and HD–3) monomer feed ratios are effective in MO removal. Effects of medium pH, amount of adsorbent, time, dye initial concentration, temperature and matrix in MO adsorption to HD–2 and HD-3 hydrogels were investigated. The optimum pH, adsorption time and the amount of adsorbent was found 9, 6 hours and 0.1 g, respectively. Under optimum adsorption conditions, dye removal at 1000 ppm MO concentration for HD–2 and HD–3 hydrogels was determined as 89.4% and 90.9% and adsorption capacities as 950 and 994 mg/g. It was observed that MO adsorption to both hydrogels decreased with the amount of adsorbent and temperature increase, but it was not affected by the medium matrix. In addition, studies were conducted on adsorption isotherms and adsorption kinetics, and the appropriate isotherm model was determined as Freundlich isotherm. According to kinetic studies, it was understood that HD-3 hydrogel fits more to all kinetic models examined than HD-2. According to thermodynamic parameters, MO dye removal was found to be exothermic. As a result of the studies, it was concluded that the adsorbent obtained can be used for dye removal.