Yang et al. 2023 - Amidoxime carbon felt for Cr(VI) wastewater removal
Yang and colleagues prepared amidoxime-functionalized carbon felt (Ami-CF) and coupled it with a flow-through asymmetric alternating-current electrochemical system for rapid removal and reduction of Cr(VI) from prepared wastewater solutions. This is primary remediation-method evidence, not food, ingredient, drinking-water field occurrence, or consumer-product evidence.
Key numbers
Batch adsorption
The authors compared original carbon felt (O-CF), polyacrylonitrile-coated carbon felt (PAN-CF), and amidoxime-functionalized carbon felt (Ami-CF) for Cr(VI) adsorption.
| Endpoint | Source-reported result |
|---|---|
| Kinetic test condition | 50 mg/L Cr(VI), pH 6 +/- 0.05, sampled through 72 h, triplicate data points |
| Ami-CF kinetic capacity | Rapid increase through 12 h; equilibrium at about 36 h; highest adsorption capacity 33.86 mg/g |
| O-CF and PAN-CF kinetic capacity | About 1.1 mg/g equilibrium adsorption capacity |
| Kinetic-model fit | R2 0.976 for quasi-first-order; R2 0.993 for quasi-second-order, interpreted as chemisorption-controlled |
| Saturated adsorption capacity | Ami-CF 101.73 mg/g for Cr(VI); O-CF and PAN-CF 1.99-2.71 mg/g |
| Isotherm fit | Langmuir R2 0.992 vs Freundlich R2 0.968; Langmuir judged better |
| Favorability | RL 0.08-0.9, interpreted as favorable adsorption |
The paper states that Ami-CF’s saturated Cr(VI) adsorption capacity was 2.1-5.5 times that of selected literature adsorbents and more than 100 times higher than original carbon felt in the authors’ comparison.
Asymmetric AC operating conditions
The optimized flow-through electrochemical condition was positive bias 1 V, negative bias -2.5 V, duty ratio 20%, frequency 400 Hz, pH 2 +/- 0.05, peristaltic-pump flow 0.5 mL/min, calculated flux 300 L/h/m2, and 30 s contact time.
| Parameter study | Source-reported finding |
|---|---|
| Negative bias | With positive bias fixed at 1 V, increasing negative bias from -1.5 V to -2.5 V increased Cr(VI) removal from 95.97% to 99.98%; mean residual Cr(VI) at -2.5 V was 8.33 ug/L |
| Positive bias | With negative bias fixed at -2.5 V, removal first increased and then decreased from 0.5 V to 2.5 V; 1 V was selected |
| Duty ratio | Removal increased from 10% to 20% duty ratio and then declined from 20% to 50%; 20% was selected |
| Flow rate | At 0.5 mL/min and 0.7 mL/min, Cr(VI) removal was about 99.98% and 95.76%, respectively; 0.5 mL/min was selected |
| pH and concentration | At pH 1, 0.5-250 mg/L Cr(VI) could be completely removed; at pH 2, removal stayed above 85.04% for 0.5-250 mg/L and 0.5-100 mg/L could be lowered below 0.05 mg/L Cr(VI); at pH 3, 0.5-50 mg/L removal exceeded 93.74% |
| Coexisting ions | 100 mg/L Cr(VI) alone had 99.97% removal; 50 mg/L Cu(II), Zn(II), or Ca(II) improved removal, while higher coexisting-ion levels reduced removal |
The authors compare asymmetric AC with direct-current treatment under the same pH, flow, and negative-bias settings. Both DC and AC achieved 100% removal for 0.5-50 mg/L Cr(VI). At 100 mg/L and 250 mg/L Cr(VI), DC removal declined to 77.22% and 64.65%, respectively, while AC removal remained 99.97% at 100 mg/L and 85.37% at 250 mg/L.
Durability and mechanism
For durability testing, 50 mg/L Cr(VI) solution was continuously injected into the electrochemical filtration device at 0.5 mL/min, with 50 mL treated as one dose. Across 10 cycles, removal stayed above 99.9% and treated Cr(VI) remained below 0.05 mg/L, the WHO drinking-water criterion cited by the paper.
XPS characterization found Cr(III) and Cr(VI) peaks after adsorption and after DC/AC treatment. The authors propose a three-step AC mechanism: Cr(VI) oxyanions migrate toward the positively biased electrode and bind amidoxime groups, voltage switching drives cathodic electron transfer that reduces Cr(VI) to Cr(III), and Cr(III) is released so active sites can be reused.
Methods (brief)
Commercial carbon felt discs were coated with polyacrylonitrile/carbon-black slurry and then reacted with hydroxylamine hydrochloride and sodium carbonate at 70 C to form amidoxime-functionalized carbon felt. The electrode was characterized by SEM, FTIR, and XPS.
Batch adsorption used 20-25 mg electrode material in 50 mL Cr(VI) solutions. Kinetic tests used 50 mg/L Cr(VI) at pH 6 +/- 0.05, and isotherm tests used 0-1000 mg/L Cr(VI). The flow-through device used a sandwich-style electrochemical cell with carbon-felt electrodes, asymmetric square-wave AC power, and 50 mL Cr(VI) solution pumped through the device. Cr(VI) was measured by dibenzoyl dihydrazine spectrophotometry under GB 7467-87; total chromium was measured by ICP-OES.
Implications
Certification: Do not use this source in food, ingredient, drinking-water occurrence, infant-food, supplement, cosmetic, or product benchmark pools. It is a prepared-wastewater remediation experiment, not a field sample survey. It is valid Cr(VI) remediation evidence because the target analyte is explicitly hexavalent chromium.
App: Context for Cr(VI) water-treatment and electrochemical remediation notes. The study supports a combined adsorption-reduction mechanism in which Ami-CF captures Cr(VI) and asymmetric AC promotes reduction to Cr(III), with high short-contact-time performance under acidic conditions.
Courses: Useful for teaching Cr(VI) versus total Cr, AC versus DC electrochemical remediation, and why reduction/speciation outcomes are distinct from total chromium removal.
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Verification notes
This page was built from the full PDF, including the electrode synthesis and characterization methods, batch adsorption protocol, flow-through AC device methods, Figure 3 adsorption kinetics/isotherms, Figure 4 bias/duty/flow parameter results, Figure 5 pH/coexisting-ion tests, Figure 6 DC/AC comparison and durability test, Figure 7 mechanism discussion, conclusion, supplementary-materials note, and data-availability statement. Products and ingredients are intentionally empty because the paper measures prepared Cr(VI) wastewater solutions. The title uses “Alternative Current” as printed by the source.
Page history
The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.
| Commit | Date | Description |
|---|---|---|
| c1aef38 | 2026-06-02 | audit-queue: hamid2021-bacterial-plant-biostimulants-review → audited-promote |