Synthetic dyes represent a significant class of contaminants released in the environment. Crystal violet is a triarylmethane dye used in several fields such as printing inks, the textile or paper industries, as well as in cell histology. Coating magnetic nanoparticles with functionalized polymers has been proved to improve their efficiency, offering unique properties for applications in wastewater treatment. The current paper focuses on preparing and characterising magnetic core-shell nanoparticles coated with poly(benzofuran-co-arylacetic acid) functionalized with folic acid as an organic shell. The new polymer-based magnetic nanostructures were applied for crystal violet extraction from aqueous solutions. The nanostructures were structurally and morphologically investigated by Fourier-transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). While thermal and magnetic properties of the magnetic nanostructures were determined by thermogravimetric analysis (TGA) and magnetization measurements (VSM). At the same time, crystal violet concentrations were determined by UV-VIS spectroscopy. The influence of initial dye concentration and contact time on the removal efficiency has been studied to achieve the optimum adsorption conditions. The dye adsorbent neoteric magnetic nanostructure was easily desorbed and reused, the adsorption capacity decreasing from 100% to 97.63% in the first five cycles, reaching a minimum of 88.74% after the 10th recycling step.

The compliance of crab shells traditionally used as a complex natural product for agricultural soil amendment with modern biofertilizers’ quality and safety requirements was investigated. Shells waste from the Blue crab, Callinectes sapidus and the Green crab, Carcinus aestuarii were tested for macronutrients, heavy metals, bacteria content, and antimicrobial properties. Such information is crucial for further utilization of the biogenic powders for any composite formulation in added-value by-products. The calcium carbonate-rich hard tissue yield was 52.13% ± 0.015 (mean ± S.D.) and 64.71% ± 0.144 from the blue and green crabs, respectively. The contents of Pb, Ni, Zn, Cr (VI), and Cu were several orders of magnitude below the prescribed limit by EU biofertilizer legislation, with Fe, Mn (not prescribed), and As being the most abundant. The content of As and Cd from the material considered here was within limits. The shells contain no colony-forming units of Salmonella spp. and compliant levels of Escherichia coli; moreover, the shell micro-powder showed dose-dependent growth inhibition of Pseudomonas aeruginosa and Staphylococcus aureus. In summary, the waste crab shells present a complex natural product as plant biofertilizer following the circular economy concepts.

Raw algae waste naturally thrown on shores could pose serious threats for landfilling and its reuse for composting or further processing as added-value by-products require knowledge-based decisions and management for the sustainable development of local ecosystems. Raw marine waste containing salt (halite) and heavy metals that eventually accumulate in algae hamper their safe applicability in soil fertilization or in other exploitations. Here, the suitability of algal biomass for use as an environmentally safe fertilizer was investigated, thereby supporting sustainable coastal management. The simple extraction of the dry algal biomass of three abundant Mediterranean species, Enteromorpha intestinalis, Corallina elongata, and Gelidium pulchellum, in water containing sodium carbonate resulted in a greenish extract containing a reduced heavy metals content, and nutrients such as K⁺, PO₄³⁻, SO₄²⁻, NO₃⁻, Ca²⁺, and Mg²⁺. UV-Vis and Raman techniques, including surface-enhanced Raman scattering (SERS), were employed for the fast evidencing of polyphenols, carotenoids, and chlorophylls in the extracts content, while E. intestinalis extract additionally exhibited polysaccharide signals. Heavy metals analysis showed that the major metals in the extracts were Fe, Ni, Zn, and Cu; however, their levels were an order of magnitude lower than in the dry biomass. The extracts also showed a mild antibacterial effect. The combination option of aqueous extracts with powdered crustacean shells to obtain a novel, eco-friendly, solid biofertilizer complex was further shown, which could be pelleted for convenient use. The immersion of solid biofertilizer pellets in water is accompanied by re-solubilization of the compounds originating from algae extracts, presenting the opportunity for dry storage and easier handling and land applicability. In summary, aqueous extracts of marine algae waste present an environmentally safe and attractive way to recycle excessive algal biomass and to formulate a new, eco-friendly biofertilizer complex.

Implementing new methods to prepare magnetite nanoparticles with a covered or uncovered surface has been, and still is, a significant challenge. In this work, we describe a very clear and effortless way for the preparation of magnetite nanoparticles using two types of bases, namely: 1-(3-aminopropyl)imidazole and sodium hydroxide. Fourier transform infrared spectroscopy (FTIR) served as a tool for the structural investigation of the as-prepared magnetite nanoparticles. The morphology of the samples was investigated using Transmission Electron Microscopy (TEM). Comprehensive high-resolution X-ray photoelectron spectroscopy investigations (XPS) were applied as an effective tool for analyzing the composition of the various types of magnetic nanoparticles. Further polymer linkage was accomplished with poly(benzofuran-co-arylacetic acid) on the amino-functionalized surface of aminopropylimidazole-containing magnetic nanoparticles. The findings are promising for biomedicine, catalysis, and nanotechnology applications.