The potential of laboratory-prepared-activated coconut coir (ACC) for removal of Na⁺ and Mg²⁺ ions from saline water in desalination applications was studied. ACC was prepared by pyrolysis of raw coconut coir dust, treated with 50 wt% phosphoric acid. The ACC was characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, and scanning electron microscopy techniques while its BET surface area, methylene blue, and iodine values were measured to understand the surface characteristics. The laboratory-prepared-activated coir demonstrated a nanoporous structure with a BET surface area of 1,235 m² g⁻¹. The results further indicated the presence of oxygen containing functional groups in weak graphitic structure, while micro- to nanoporous nature was observed in ACC. Na⁺ and Mg²⁺ ion removal efficiencies from standard 0.200 mol dm⁻³ NaCl and MgCl₂ solutions were found to be approximately 50%. The results fit into Langmuir and Freundlich isotherms implying homogeneous monolayer coverage for both Na⁺ and Mg²⁺ adsorption. Optimized ACC dosage for removal of 40% of both cations from seawater was found to be 80.0 g L⁻¹. ACC has the potential to remove up to 80% of Na⁺ and 72% of Mg²⁺ from seawater by repeated filtration. The acidic point zero charge of 5.5 ± 0.1 and the presence of nanopores explain the high cation adsorption characteristics compared to commercially available activated carbon. The used ACC was successfully regenerated by back washing with distilled water followed by pyrolysis.

Environmental DNA (eDNA), i.e., DNA found in the environment, can interact with various geochemical surfaces, yet little is known about these interactions. Mineral surfaces may alter the structure, stability, and reactivity of eDNA, impacting the cycling of genetic information and the reliability of eDNA-based detection tools. Understanding how eDNA interacts with surfaces is crucial for predicting its fate in the environment. In this study, we examined the surface interaction and stability of herring testes DNA, a model system for eDNA, on two common iron oxide phases present in the environment: α-FeOOH (goethite) and α-Fe₂O₃ (hematite). Utilizing spectroscopic probes, including attenuated total reflection Fourier-transform infrared (ATR-FTIR) and UV-vis spectroscopy, we quantified the DNA adsorption capacity at pH 5 and determined its secondary structure. DNA adsorbed irreversibly at pH 5 and 25 °C, primarily through its phosphate groups, and retained the solution-phase B-form structure. However, the infrared data also indicated some distortion of the B-form likely due to additional interactions between nitrogenous bases when adsorbed on the α-Fe₂O₃ particle surfaces. The distortion in the double helical structure of adsorbed DNA on α-Fe₂O₃ led to a lower melting temperature (T_m) of 60 °C compared to 70 °C for DNA in solution. In contrast, DNA adsorbed on α-FeOOH melted at higher temperatures relative to solution-phase DNA and in two distinct phases. Upon testing adsorbed DNA stability at higher pH values, there were distinct differences between the two iron oxide phases. For α-FeOOH, nearly 50% of the DNA desorbed from the surface when the solution pH changed from 5 to 8, while less than 5% desorbed from α-Fe₂O₃ under the same conditions. Overall, these findings underscore the importance of mineral-specific eDNA-surface interactions and their role in adsorbed eDNA stability, in terms of DNA melting and the impact of solution-phase pH changes.