Determination of Cu(II) in water and food samples by Na+-cloisite nanoclay as a new adsorbent: Equilibrium, kinetic and thermodynamic studies

Highly sensitive colorimetric sensing of copper(ii) ions based on "CLICK-17" DNAzyme-catalyzed azide modified gold nanoparticles and alkyne capped dsDNA cycloaddition

A click chemistry assay based on a newly discovered DNAzyme, CLICK-17, with azide modified gold nanoparticles (azide-AuNPs) and alkyne capped dsDNA (alkyne-linker DNA) was employed for novel and selective detection of Cu²⁺ visually. The strategy involved using CLICK-17 to mediate a catalytic reaction for triazole formation between azide-AuNPs and alkyne-linker DNA under the help of Cu²⁺ (without sodium ascorbate) or Cu⁺, which eventually led to the aggregation of AuNPs. The obvious color change from ruby red to bluish purple was then observed by the naked eye and the absorbance peak shifted from 525 to 570 nm. Interestingly, CLICK-17 and Cu⁺-catalyzed click reaction had the best performance compared to either Cu⁺ alone or CLICK-17 and Cu²⁺-mediated reaction in terms of the reaction time and sensitivity. This system has been demonstrated to allow quantitative measurement of Cu²⁺ with a detection limit as low as 26.8 nM and also has high specificity that can distinguish Cu²⁺ from other metal ions. Further, the method was tested with a real mineral water sample for Cu²⁺ concentration determination. Satisfactory recoveries of 90.8% and 99.8% were achieved.

We report selective and visual detection of Cu²⁺ based on aggregation of azide modified gold nanoparticles induced by CLICK-17 DNAzyme and Cu²⁺ or Cu⁺ catalyzed click reaction between azide-AuNPs and alkyne-dsDNA.

Immobilization of Lead and Nickel Ions from Polluted Yam Peels Biomass Using Cement-Based Solidification/Stabilization Technique

Nowadays, biomass has been employed to prepare biosorbents for heavy metals uptake; however, further disposal of polluted material has limited its application. In this work, nickel and lead removal was performed using yam peels and the resulting polluted biomass was mixed with concrete to produce bricks. The biomass was characterized by FT-IR analysis for testing functional groups diversification before and after adsorption process. The effect of adsorbent dosage, temperature, and initial solution concentration was evaluated to select suitable values of these parameters. Adsorption results were adjusted to kinetic and isotherm models to determine adsorption mechanism. Desorption experiments were also performed to determine the appropriate desorbing agent as well as its concentration. Immobilization technique of cement-based solidification/stabilization was applied and the polluted biomass was incorporated to concrete bricks at 5 and 10%. Mechanical resistance and leaching tests were carried out to analyze the suitability of heavy metals immobilization. The suitable values for dosage, temperature, and initial solution concentration were 0.5 g/L, 40°C and 100 ppm, respectively. The kinetic model that best fitted experimental results was pseudo-second order indicating a dominant physicochemical interaction between the two phases. The highest desorption yields were found in 52.47 and 74.84% for nickel and lead ions. The concrete bricks exhibited compression resistance above 5 MPa and all the leachate reported concentrations below the environmental limit. These results suggested that nickel and lead immobilization using concrete bricks is a good alternative to meet disposal problems of contaminated biomass.

Evaluation of a mixed anionic-nonionic surfactant modified eggshell membrane as an advantageous adsorbent for the solid-phase extraction of Sudan I-IV as model analytes

The coadsorption of mixed anionic-nonionic surfactants, sodium dodecylbenzenesulfonate with Triton X-100, on the surface of eggshell membrane was investigated based on adsorption isotherms to improve the solid-phase extraction performance of eggshell membrane toward organic contaminants. Results showed that even though excess Triton X-100 might inhibit the adsorption of sodium dodecylbenzenesulfonate, a low dosage of Triton X-100 can significantly improve sodium dodecylbenzenesulfonate modification and enhance the extraction efficiency of eggshell membrane from 73.7 to 100.4% because of the formation of mixed hemimicelles. The highest recovery was achieved at 2:8 (Triton X-100/sodium dodecylbenzenesulfonate mass ratios), and multiple mechanisms involving π-π interactions, hydrophobic effect, and π-π electron donor-acceptor interactions contributed to the strong extraction affinity. When mixed, the Triton X-100 and sodium dodecylbenzenesulfonate modified eggshell membrane packed cartridge coupled with high-performance liquid chromatography was applied for the simultaneous determination of trace Sudan I-IV, and low detection limits (0.16-0.26 ng/L) were achieved with satisfactory linearity (R²  > 0.999) in 10-10 000 μg/L. For real samples, Sudan II and III in one chilli sauce sample were found at 4.3 and 1.7 μg/kg. Sudan I-IV recoveries at three spiked levels were 87.4-102.9% with precisions <6.8%. Comparison with commonly used solid-phase extraction adsorbents and methods further reflected the superiorities of the proposed adsorbent in sensitivity, retention ability, and applicability.