Removal of Chromate and Nitrate Ions from Aqueous Solutions by Co x Fe 3‐ x O 4 @silica Hybrid Nanoparticles Decorated with Cross‐Linked Tragacanth Gum: Experiment, Modeling and Optimization

SPE of gallic acid and ascorbic acid in fruits using polymerized deep eutectic solvent-modified substrate

Aim: Novel substrates were synthesized by porous and nonporous polymerization of deep eutectic solvents on magnetic silica nanoparticles and introduced for dispersive solid-phase extraction of two analytes. Materials & methods: The prepared substrates were characterized, and an extraction procedure was implemented to select the best substrates and eluent. The central composite design acted to optimize the effects of parameters that influenced the extraction efficiencies. Results: For gallic and ascorbic acids, the limits of detection were obtained at 0.136 and 0.165 μM, respectively, with linear ranges of 0.6-125.2 and 0.5-106.8 μM, respectively. Conclusion: The substrate produced good extractions even after being used three-times and was successfully applied for the analysis of real samples.

Introduction of nitrogen doped graphene nanosheets as efficient adsorbents for nitrate removal from aqueous samples

PURPOSE

Introducing and developing new kinds of adsorbents are always a significant challenge in water treatments. In this work, for the first time, graphene oxide (GO), nitrogen-doped graphene oxide (ND-GO), highly nitrogen-doped graphene oxide (HND-GO), and 3D high nitrogen-doped graphene oxide (3D-HND-GO) were synthesized and comparatively evaluated in the removal of nitrate content of tap and underground waters.

METHODS

The removal of the target analyte was performed through a batch adsorption approach, and the factors influencing its removal efficiency (i.e., initial pH of the sample, primary concentrations of nitrate, amount of adsorbent, and contact time) were evaluated through a central composite design (CCD) and response surface methodology (RSM).

RESULTS

Based on the results, 3D-HND-GO showed the highest removal efficiency in comparison with the other mentioned nanoparticles. The nitrate removal using this adsorbent was modeled successfully so that R 2, adjusted R 2, and predicted R 2 values were 0.9717, 0.9508, and 0.9010, respectively. In addition, the optimal removal condition was achieved using the Nelder-Mead non-linear optimization algorithm as follow: the initial concentrations of nitrate (expressed as nitrogen): 15.0 mg/mL, the amount of the adsorbent: 2.0 mg/mL; pH of the sample: 3.0; and the contact time: 20.0 min. Under this optimal condition, the actual removal result (92.5 ± 4.0%) was in good agreement with the expected value (94.8 ± 5.1%). Additional studies were also performed to comprehensibly evaluate the adsorption activity of the adsorbent (e.g., kinetic, isotherm, and desorption parameters). The adsorption isotherm complied with the Langmuir model illustrating the considerable mono-layer adsorption capacities for the target ions with qm of 8.7 mg/g. The adsorption process was indicated to obey a pseudo 2nd order kinetic model, with the rate-limiting step for the adsorption phase.

CONCLUSIONS

This study revealed which 3D-HND-G leads to improved yield in the nitrate ions elimination, particularly at acidic media, which was related to the enhanced dispersibility and larger surface area. The adsorbent was further successfully used for treating tap and underground water samples. At the present moment, research as grown to modify 3D-HND-G in orders to increase the potentiality for industrial applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00741-7.

Recyclable Functionalized Material for Sensitive Detection and Exceptional Sorption of Hexavalent Chromium and Permanganate Ions with Biosensing Applications

Environmental remediation with a single platform for selective sensing and removal of toxic analytes with recyclability of the material has always been a desirable system for sustainability. However, materials comprising all the abovementioned advantages are rarely known for oxoanions. We herein developed a fluorogenic napthalimide-based functionalized mesoporous silica material (SiO₂@NBDBIA) as a signaling and remediation system for oxoanions (CrO₄^2-, Cr₂O₇^2-, and MnO₄^-) from a pool of several anions. The fluorescence quenching of the SiO₂@NBDBIA material in the presence of CrO₄^2-, Cr₂O₇^2-, and MnO₄^- ions gives the limit of detection (LOD) values of 6.23, 25.2, and 20.32 ppb, respectively, which are well below the maximum contaminant level demarcated by the United States Environmental Protection Agency. The maximum adsorption capacities of the material for the abovementioned oxoanions are found to be 352, 363, and 330 mg/g, respectively, which are well above those mentioned in the literature reports. Contrary to the literature-dominated irreversible ion-exchange mechanism, the reversible hydrogen-bonded binding of the material with the oxoanions leads to the recyclability of the material easily, which is very rare in the literature. The DFT calculations were performed to examine the interactions between the material and oxoanions. For real applications, this material was also used as a fluorescence probe to detect these oxoanions in the actual water samples, and more interestingly, used as a biosensing probe for these oxoanions in the living organism Artemia salina through fluorescence imaging. Thus, the SiO₂@NBDBIA material is a unique example of recyclable material for detecting and remediating oxoanions.

Effective adsorption of methylene blue dye from water solution using renewable natural hydrogel bionanocomposite based on tragacanth gum: Linear-nonlinear calculations

Today, hydrogels opened new windows to the high-tech due to their amazing features. Thus, we applied hydrogel nanocomposite (HNC) made of tragacanth gum (a kind of polysaccharide) and CaCO₃ nanoparticles to remove methylene blue dye (MBD) from the water solution. We used nonlinear and linear isotherms and kinetics as well as thermodynamics to uncover the adsorption mechanism. The results showed that the hydrogel could remove 80% of MBD. Besides, the linear form of the pseudo-second-order kinetic model fits well with the results, showing chemical interactions. We found that this process follows both Sips and Redlich-Peterson models by applying nonlinear and linear isotherm models. The maximum adsorption capacities from nonlinear and linear Sips were 1401 and 2145 mg/g, respectively. Based on the thermodynamic equations, the adsorption of MBD onto HNC was physiochemical and exothermic. According to the phenomenological calculations, diffusion from the bulk (or film diffusion, D_f = 1.2 × 10^-8 cm²/s) is the primary mechanism.

Highly efficient and antibacterial ion exchanger based on graphene oxide for removal of chromate and nitrate from water: synthesis, characterization and application

A novel recyclable antibacterial anion exchanger based on graphene oxide (GO) and quaternary ammonium chloride (TMSQA) as a crosslinker/ion exchanger was prepared and used for the removal of chromate and nitrate from water.