abstract
A wide range of emerging pollutants, such as pharmaceuticals and pesticides, has been detected in water sources, due to the ineffectiveness of conventional wastewater treatment technologies to remove efficiently these compounds. This is a matter of great concern due to potential harmful effects on the environment and human health. In this context, the search for eco-friendly and low-cost efficient sorbents have prompted recent developments for biopolymer-based materials and their use in water decontamination. In particular, polysaccharide-based nanocomposites are very attractive as nanosorbents owing to functional groups that provide affinity towards a wide diversity of pollutants. In order to act as efficient nanosorbents, the biopolymers should be easily separated from treated solutions. From a materials chemistry perspective, this may be achieved by grafting the biopolymers to inorganic water-insoluble supports, in the form of organic-inorganic hybrid materials. Due to economic and environmental factors, the concept of recoverable and reusable sorbents has gained importance, and subsequently, the use of magnetic sorbents, namely magnetic nanoparticles, has raised increasing interest. Magnetic nanomaterials are very convenient for removing pollutants because they combine large specific surface area that favors adsorption and magnetic features that allow easy and fast separation from water. The surface modification with biopolymers enhances the adsorptive capabilities of magnetic nanoparticles without compromising the low-cost. However, in order to attain high adsorptive performance, a rational design of the surface of the nanoparticles is essential. Furthermore, the nanosorbents should exhibit high adsorption capacity and reusability. To tackle this challenge, this thesis explores magnetic biopolymer-hybrid based nanomaterials. Core-shell composite nanoparticles comprising a core of magnetite (~50 nm), uniformly coated by a shell of biopolymer-siliceous material were prepared using a one-step sol-gel based procedure. The applicability of the approach was demonstrated by invoking distinct chemical nature and ionic character of biopolymers, namely cationic (chitosan and quaternary derivatives) and anionic (ƙ-, ι-, λ-carrageenan and alginic acid) polysaccharides, and a natural protein (gelatin). The adsorptive performance of the particles towards a number of emerging pollutants, namely pharmaceuticals (diclofenac, naproxen, ketoprofen, sulfamethoxazole, ciprofloxacin and tetracycline) and pesticides (glyphosate) frequently detected in waters was investigated under several operational conditions. Overall, these magnetic nanosorbents showed high adsorption capacity and reusability, as originally intended. Although further research on complex real waters is still required, the results indicate that these biopolymer-based magnetic nanosorbents are among the most effective magnetic systems reported so far, to remove tested pollutants from water.
authors
Sofia F. Soares
our authors
Sofia Soares
Junior Researchersupervisors
Dr. Ana Luísa Daniel da Silva and Professor Tito Trindade