Overview
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:
| Model | Fitting equation | Key capacity/rate values | R2 |
|---|---|---|---|
| Pseudo-first-order | y = -0.07x + 7.75 | Qe,cal = 2312.00 mg/g; k1 = 0.075 min-1 | 0.98 |
| Pseudo-second-order | y = 4e-4 x + 0.0023 | Qe,cal = 2528.36 mg/g; k2 = 6.92e-5 g mg-1 min-1 | 0.99 |
| Intraparticle diffusion, stage 1 | y = 121.00x + 850.35 | C1 = 850.35; kip1 = 121.00 | 0.94 |
| Intraparticle diffusion, stage 2 | y = 38.61x + 2022.19 | C2 = 2022.19; kip2 = 38.61 | 0.70 |
| Experimental result | not applicable | Qe,exp = 2407.00 mg/g | not reported |
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:
| Model | Fitting equation | Main parameter values | R2 |
|---|---|---|---|
| Langmuir | y = 5.24e-4 x + 0.11 | Qmax = 1908.39 mg/g; KL = 4.76e-3 mg/L | 0.98 |
| Freundlich | y = 0.1895x + 6.36 | KF = 578.25; n = 5.277 | 0.79 |
| Temkin | y = 230.24x + 409.93 | A = 230.24; B = 409.93 | 0.77 |
The paper states that the maximum capacity of 1908 mg/g was about 3-20 times higher than previously reported comparator adsorbents. The Langmuir, Freundlich, and Temkin fits used only the high-concentration range of 80 to 500 mg/L Pb(II), because at 5 to 50 mg/L the Pb(II) was adsorbed essentially completely and the residual equilibrium concentration could not be reliably resolved. 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 the absolute value of delta H decreased from 64.30 to 17.91 kJ/mol as the initial Pb(II) concentration rose from 100 to 500 mg/L (both ΔH values negative). 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:
| Metal ion | Adsorption efficiency |
|---|---|
| Pb(II) | 99.75% |
| Cd(II) | 23.77% |
| Ni(II) | 18.76% |
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.
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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.
The matrices slugs (silk-fibroin, protein-inorganic-hybrid-nanoflower, aqueous-sorption-test, wastewater-remediation) are remediation-domain proposals outside the current controlled food-matrix vocabulary; they follow the precedent set by wang2020-lignin-residue-biochar-heavy-metal-remediation and are flagged here for a future taxonomy refresh that adds a remediation-matrix controlled vocabulary.
Audit subagent 2026-06-02 (v2 skill, fresh-context general-purpose agent) returned PROMOTE on all five checks; two optional completeness concerns were applied to the Key numbers Pb(II) isotherms and thermodynamics paragraph (added the 80-500 mg/L isotherm-fitting concentration range that the paper used because 5-50 mg/L was fully adsorbed, and added the source’s absolute delta H magnitudes of 64.30 and 17.91 kJ/mol at 100 and 500 mg/L Pb(II)).
Update history
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