A user-friendly Ulva lactuca/chitosan composite bead for mercury removal

Development of reusable chitosan-supported nickel sulfide microspheres for environmentally friendlier and efficient bio-sorptive decontamination of mercury toxicant

Mercury emissions from the industrial sector have become an undeniable concern for researchers due to their toxic health effects. Efforts have been made to develop green, efficient, and reliable methods for removal of mercury from wastewater. Sorption process promises fruitful results for the decontamination of cations from wastewater. Among the number of used sorbents, metal sulfides have been emerged as an appropriate material for removing toxic metals that possess good affinity due to sulfur-based active sites for Hg through "Lewis's acid-based soft-soft interactions." Herein, nickel-sulfide nanoparticles were synthesized, followed by their incorporation in chitosan microspheres. FTIR analysis confirmed the synthesis of nickel sulfide-chitosan microspheres (NiS-CMs) displaying sharp bands for multiple functional groups. XRD analysis showed that the NiS-CMs possessed a crystallite size of 42.1 nm. SEM analysis indicated the size of NiS-CMs to be 950.71 μm based on SEM micrographs. The sorption of mercury was performed using the NiS-CMs, and the results were satisfactory, with a sorption capacity of 61 mg/g at the optimized conditions of pH 5.0, 80 ppm concentration, in 60 min at 25 °C. Isothermal models and kinetics studies revealed that the process followed pseudo-second-order kinetics and the Langmuir isothermal model best fitted to experimental data. It was concluded that the NiS-CMs have emerged as the best choice for removing toxic mercury ions with a positive impact on the environment.

Competitive fiber optic sensors for the highly selective detection of mercury in water

Two competitive fiber optic sensors for the rapid, sensitive, and highly selective detection of mercury in water are designed, fabricated, and evaluated. A wavelength-modulated sensor based on an etched single-mode-multimode-single-mode (E-SMS) optical fiber structure and an intensity-modulated sensor based on fiber optics with a slanted end were fabricated by readily reproducible methods. The sensors were activated with a nanostructured chitosan/maghemite (CS/Fe₂O₃) composite thin film for the selective detection of mercury ions (Hg²⁺) in water. The functionalized sensors were implemented to experimentally validate the potential of CS/Fe₂O₃ thin film for optical sensing of Hg²⁺ in drinking water. The sensor based on the E-SMS structure exhibited a wavelength-modulated response with a sensitivity of up to 290 pm/(µg/mL), and the sensor based on the slanted end structure showed an intensity-modulated response with a sensitivity of -0.07dBm/(µg/mL). Validation of the experimental assay method proves the ability to selectively detect chemical interactions as low as 1 ng/mL (one part per billion) of Hg²⁺ in water for both sensors. The high specificity of the two sensors was demonstrated by evaluating their responses to a number of potentially interfering metal ions in water. These sensors are cost-effective, simple to construct, and easy to implement, which makes them very promising for the on-site detection and monitoring of mercury in bodies of water.

Ulva lactuca: A bioindicator for anthropogenic contamination and its environmental remediation capacity

Coastal regions are subjected to degradation due to anthropogenic pollution. Effluents loaded with variable concentrations of heavy metal, persistent organic pollutant, as well as nutrients are discharged in coastal areas leading to environmental degradation. In the past years, many scientists have studied, not only the effect of different contaminants on coastal ecosystems but also, they have searched for organisms tolerant to pollutants that can be used as bioindicators or for biomonitoring purposes. Furthermore, many researchers have demonstrated the capacity of different marine organisms to remove heavy metals and persistent organic pollutants, as well as to reduce nutrient concentration, which may lead to eutrophication. In this sense, Ulva lactuca, a green macroalgae commonly found in coastal areas, has been extensively studied for its capacity to accumulate pollutants; as a bioindicator; as well as for its remediation capacity. This paper aims to review the information published regarding the use of Ulva lactuca in environmental applications. The review was focused on those studies that analyse the role of this macroalga as a biomonitor or in bioremediation experiments.