How to Quantify the Adsorption of Cyanuric Acid on Activated Carbon Used from Swimming Pool Disinfection?

The physical and chemical characteristics of an adsorbent are key factors determining its efficiency in relation to a particular adsorbate molecule. The adsorption of cyanuric acid (cya) on activated carbon (AC) has not been extensively explored in terms of its basic phenomenon and specific surface interactions. Cya is an important molecule in the swimming pool industry, as it protects free chlorine from UV light degradation. A proper characterization of AC will be beneficial for swimming pool product suppliers to determine the criteria while purchasing it to remove excess cya accumulated in pools. A detailed investigation of the physicochemical properties of activated carbon was conducted to assess its potential to adsorb cya from water. The effect of the adsorption capacity under various pH conditions was studied and it was found that acidic pH favors the adsorption process. With the help of temperature-programmed desorption coupled with mass spectrometry (TPD-MS) and X-ray photoelectron spectroscopy (XPS), the surface chemistry was well analyzed for a proper understanding of the adsorbent-adsorbate interaction. While conventional pool test equipment gives inconsistent readings of the cya concentration, a UV-vis spectroscopy-based methodology has been developed to accurately measure traces of cya in water. This method can be helpful to validate the accuracy of pool-testers for research and development purposes. The batch adsorption experiments revealed that cya adsorption on activated carbon follows pseudo-second-order kinetics, which confirms that the adsorption mechanism is chemisorption, which in fact, depends highly on the surface chemistry of the AC and the reaction pH.