Carbonized metal-organic frameworks with trapped cobalt nanoparticles as biocompatible and efficient azo-dye adsorbent

Background Metal-organic frameworks (MOFs) derived carbonaceous materials functionalized with metal/metal-oxide nanoparticles are obtained by its carbonization. The carbonization of MOFs occurs simultaneously with the metal and metal-oxide particle formation. The carbon-based flake-like nanostructures with trapped metal/metal-oxide nanoparticles have been formed. Due to its non-toxicity and environmental friendliness, the capacity for pollution adsorption using model anionic dye has been revealed. Results The structure of the hybrid is formed as the effect of carbonization of metal-organic frameworks with cobalt as a metal counterpart (CoOF). The cobalt nanoparticles are placed between the carbon layers what limits the dissolution of cobalt nanoparticles and protects the environment from its toxicity. It is preliminary validated by means of two reference micro-organisms (Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus) and in in vitro analysis with human cell line (A375). The efficiency of the adsorption properties of the material was tested with Acid Red 18 as a model anionic dye. The mechanism of dye adsorption was analyzed in details. In addition, various thermodynamic parameters, such as standard enthalpy, standard entropy, and standard Gibbs free energy, were tested. In addition, it was proved that the main substrate of CoOF (terephthalic acid) can be used from PET bottles, while the organic solvent used in its synthesis (N,N-dimethylformamide) was distilled and reused. The obtained carbonized CoOF revealed the same morphology and properties as pristine material. Conclusions The kinetic data of dye adsorption fit well with the pseudo-second-order model and Langmuir type. Acid Red 18 adsorption is more favourable at lower temperatures and lower pH. The location of the cobalt nanoparticles between the carbon flakes effectively limits their toxicity compared to the free metal nanoparticles. The CoOF can be obtained from recycled substrates, which revealed the same morphology as pristine material. Therefore, it is believed that this work highlights the practical application of carbonized CoOF as an adsorbate and provides the evidence that such nanocomposite can be applied without environmental risks.