Li et al. 2020 - Silk-fibroin nanoflowers for Pb(II) remediation

Li and colleagues synthesized silk-fibroin/copper-phosphate hybrid nanoflowers (SF@Cu-NFs) and tested them as aqueous sorbents for Pb(II). This is primary remediation-method evidence, not food or product occurrence evidence: the measured endpoints are adsorption capacity, kinetics, selectivity, and surface-interaction mechanisms for a laboratory adsorbent.

Key numbers

Adsorbent preparation and operating conditions

The optimized nanoflowers used 100 mg/L silk fibroin during synthesis and a 12 hour incubation time. The Pb(II) adsorption optimum was pH 5.0. The authors report that pH had to remain below the Pb(OH)2 precipitation region and that the SF@Cu-NFs surface was most stable at pH 5.0, with an absolute zeta potential of 12.83 mV.

Pb(II) kinetic tests dispersed 30 mg SF@Cu-NFs into 300 mL of 300 mg/L Pb(II) solution and measured residual Pb by atomic absorption spectroscopy. Isotherm tests used 1 mg SF@Cu-NFs in 10 mL Pb(II) solutions at 5, 20, 50, 80, 100, 400, and 500 mg/L.

Pb(II) kinetics

Table 2 reports that the pseudo-second-order model fit the kinetic data better than the pseudo-first-order model. Source-reported values:

The authors interpret the two intraparticle-diffusion line segments as a boundary-layer adsorption stage followed by intraparticle diffusion. The relative error between the pseudo-second-order calculated capacity and experimental capacity was 4.8%.

Pb(II) isotherms and thermodynamics

Table 3 reports that the Langmuir model fit the equilibrium data better than Freundlich or Temkin models:

The paper states that the maximum capacity of 1908 mg/g was about 3-20 times higher than previously reported comparator adsorbents. Thermodynamic calculations indicated spontaneous and exothermic Pb(II) adsorption: the absolute value of delta G decreased from 9.07 to 3.63 kJ/mol as temperature rose from 298 to 328 K, and delta H was negative for both 100 and 500 mg/L Pb(II). The authors classify the adsorption as physical because the absolute delta G values were below 40 kJ/mol and no new FTIR functional group appeared after Pb(II) uptake.

Selectivity

In 20 mL of 100 mg/L metal-ion solution with 3 mg SF@Cu-NFs adsorbent, the source reports adsorption efficiencies of:

The source-calculated Pb(II) selectivity factors were 4.2 relative to Cd(II) and 5.3 relative to Ni(II).

Methods (brief)

The authors prepared phosphate buffer at pH 7.4, added silk fibroin solution and CuSO4, gently shook the mixture for 5 minutes, incubated it at 25 C, washed the blue hybrid nanoflowers, and vacuum freeze-dried them. Morphology and composition were characterized by SEM/EDS, XRD, FTIR, thermogravimetric analysis, and zeta-potential measurements. Pb(II), Cd(II), and Ni(II) stock solutions were prepared from nitrate salts; residual Pb(II) concentrations were measured by atomic absorption spectroscopy.

Implications

Certification: Do not use this source in any food, infant-food, supplement, cosmetic, or ingredient occurrence pool. It is a laboratory adsorbent study in aqueous metal-ion solutions, not a measured concentration dataset for consumer products.

App: Context for remediation and water-treatment notes. The paper supports the claim that silk-fibroin/copper-phosphate nanoflowers can show high and selective Pb(II) uptake under controlled laboratory conditions, but it does not establish field performance or product-risk reduction.

Courses: Useful for teaching adsorbent selectivity, pH/precipitation control, and the difference between an adsorption capacity endpoint and an occurrence concentration endpoint.

Wiki pages this source may touch

• remediation-evidence
• lead
• cadmium
• nickel
• index

Verification notes

This page was built from the full PDF, including the self-assembly synthesis method, pH optimization section, adsorption kinetics, Table 2 kinetic parameters, Table 3 isotherm parameters, selectivity experiment, FTIR/zeta/XRD mechanism discussion, conclusion, and supplementary-materials note. The source is specific to Pb(II) adsorption, with Cd(II) and Ni(II) used for selectivity comparison. Products and ingredients are intentionally empty because no food, ingredient, drinking-water sample, or consumer-product matrix was sampled.

Page history

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