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Trichloroisocyanuric Acid (TCCA) tablets of encapsulation of essential oils in porous silica and MOFs used for water treatment in swimming pools

Trichloroisocyanuric acid(TCCA) tablets are used for water treatment in swimming pools. This is a safe way of releasing hypochlorous acid with disinfectant, algaecide and bactericide functions. This work investigates the inclusion in such tablets of insect repellents with a simultaneous perfume function. A simple mixture of trichloroisocyanuric acid(TCCA) with the repellents is not possible due to the incompatibility between both components. A strategy of encapsulation in silica and MOFs MIL-53(Al) and MIL-88A(Al) has been developed. The subsequent formulation of trichloroisocyanuric acid(TCCA) with the encapsulated repellents avoided the compatibility problems and produced marketable stable multifunctional (water treatment–insect repellency–perfume) tablets for water treatment. 
The encapsulation of insect repellents with a simultaneous perfume function in silica and the MOFs MIL-53(Al) and MIL-88A(Al) allows, from thepoint of view of Cl2 outgassing, a stable formulation of such additives with trichloroisocyanuric acid (TCCA). The FTIR characterization carried out demonstrates that the additives remain unchanged upon their encapsulation. The impregnation/encapsulation with silica has the only advantage of allowing a homogeneous dispersion with trichloroisocyanuric acid(TCCA) without significantly altering its Cl2 outgassing. However, encapsulation in MOFs would bring to the final tablet the function of controlled release. As in other examples of encapsulation in MOFs, the presence of the additive in intimate contact with the porous structure produces modifications in the corresponding thermogravimetric curves (both MIL-53(Al) and MIL-88A(Al)) and X-ray diffraction patterns (MIL-53(Al)). Repellents are more efficiently encapsulated in MIL-53(Al) than in MIL-88A(Al) due to pore size and chemical compatibility (estimated using Hansen solubility parameters) issues.
In any event, the encapsulation of the additives in either silica or MOF (MIL-53(Al) gives rise to composite materials with a high loading of additive. Furthermore, this encapsulation makes the additives compatible with trichloroisocyanuric acid(TCCA), allowing a homogeneous mixture. Consequently, besides having a low Cl2 outgassing, the modified trichloroisocyanuric acid(TCCA) tablets (with only 0.2 wt% additive loading) may provide additional functions (for example, insect repellent or perfume) to the trichloroisocyanuric acid(TCCA) beyond the disinfectant, algaecide and bactericide functions.