Surface-Functionalized Diatoms as Green Nano-Adsorbents for the Removal of Methylene Blue and Methyl Orange as Model Dyes from Aqueous Solution

Water pollution from the chemical industry has become a significant and widespread global environmental problem. This necessitates the development of cost-effective adsorbents with rapid removal efficiency. In this paper, the use of low-cost and globally available diatomaceous earth (DE) is decribed as a sorbent for the removal of model dyes, methylene blue (MB) and methyl orange (MO). The skeleton is chemically modified to achieve highly selective sorption and the results are compared with silica (Si) which has the same functionalities. The adsorption performance of the sorbents obtained is investigated by varying different parameters such as pH value, adsorbent dosage, initial concentration of dye, and contact time. Diatomaceous earth functionalized with carboxyl groups showed a better removal efficiency of MB (up to 100%) than functionalized silica. The removal of MO with functionalized imidazolium species is found to be comparable (up to 70%). The adsorption kinetics are investigated using first and second-order pseudo-models, with the latter showing superior agreement with the experimental data. The results demonstrate the potential of biosorbents to enable energy-efficient water remediation.