Overview
Lin and colleagues used Coffee Powder Trimmings (CPT), including spent coffee grounds and dried coffee-processing residues, as a bio-adsorbent for copper and iron ions before converting the metal-loaded material into biochar composites for methylene blue removal. This is primary remediation/materials evidence, not coffee-ingredient occurrence evidence: the source reports engineered adsorption and biochar performance rather than metals measured in coffee as consumed.
Key numbers
Metal adsorption and biochar synthesis
The methods describe rinsed and dried CPT mixed with either FeCl3.6H2O at 0.05 g/L in 100 mL DI water or CuCl2.2H2O at 0.03 g/L in 100 mL DI water. Six grams of dried CPT were stirred with the metal solution at room temperature for 3 h, then dried and pyrolyzed at 750 degrees C for 3 h at a 5 degrees C/min ramp to generate Fe/CB or Cu/CB.
The abstract reports that CPT removed more than 95% of Cu2+ and Fe3+ through chelation. Section 3.2 and the Figure 4 captions then label the iron removal experiment as Fe2+ rather than Fe3+; see the verification notes for this source-internal inconsistency.
Kinetic fitting for the metal-removal step favored the pseudo-second-order model. The paper reports R2 = 0.998 for Cu2+ and R2 = 0.999 for iron in the PSO plots, while the PFO fit was weaker for Cu2+ (R2 = 0.883) and stronger for iron (R2 = 0.997). The authors state that both metals reached rapid removal within the first 20 min and approached equilibrium afterward.
Textural properties of CPT-derived biochars
Table 1 reports surface area, pore volume, and Raman ID/IG values:
| Material | BET surface area (m2/g) | Pore volume (cc/g) | ID/IG |
|---|---|---|---|
| CPT | 15.230 | 0.015 | not reported |
| CB | 450.493 | 0.025 | 1.18 |
| Cu/CB | 559.213 | 0.029 | 1.15 |
| Fe/CB | 492.097 | 0.020 | 1.19 |
EDS results in the text report CPT as 51.58 wt% carbon and 47.56 wt% oxygen, with minor sulfur at 0.39 wt% and calcium at 0.47 wt%. After pyrolysis, CB carbon increased to 87.30 wt%. Cu/CB contained Cu at 0.02 wt%, and Fe/CB contained Fe at 0.10 wt%; after methylene blue adsorption, the used materials showed 0.12 wt% Cu and 2.34 wt% Fe.
Dye-removal performance after metal loading
Although dye removal is not HMTc occurrence evidence, it is part of the source’s primary dual-use remediation claim. Table 2 reports methylene blue kinetic parameters at 30 degrees C, initial dye concentration 10 mg/L, adsorbent dosage 6 g, and solution volume 0.1 L:
| Material | Experimental qe (mg/g) | PFO qe (mg/g) | PFO k1 (min^-1) | PFO R2 | PSO qe (mg/g) | PSO k2 (g/mg min) | PSO R2 |
|---|---|---|---|---|---|---|---|
| CB | 41.086 | 47.050 | -0.032 | 0.973 | 44.316 | 0.002 | 0.948 |
| Cu/CB | 52.520 | 64.846 | -0.046 | 0.978 | 55.431 | 0.002 | 0.985 |
| Fe/CB | 55.242 | 46.610 | -0.035 | 0.976 | 57.607 | 0.003 | 0.990 |
Table 3 compares room-temperature methylene blue adsorption capacity and activation energy, reporting qe = 41.086 mg/g and Ea = 53.7 kJ/mol for CB, qe = 52.520 mg/g and Ea = 35.6 kJ/mol for Cu/CB, and qe = 55.242 mg/g and Ea = 48.4 kJ/mol for Fe/CB.
Fe/CB was the best-performing dye-removal material. Figure 6a reports a dose sweep of methylene blue removal at 30 mg = 34.5%, 50 mg = 39.5%, 80 mg = 65.0%, 100 mg = 85.0%, and 150 mg = 97.8%. Figure 6b reports a pH sweep at pH 3 = 90.2%, pH 5 = 86.9%, pH 6 = 91.0%, pH 7 = 80.6%, pH 7.5 = 86.2%, pH 8 = 87.8%, pH 9 = 79.3%, and pH 11 = 87.1%; the running text on page 12 also claims a maximum of 95.2% at pH 4, which is not directly shown in Figure 6b (see verification notes). Figure 6c reports 100% removal across lake, rain, tap, and seawater matrices, and Figure 6d reports recyclability of 100% for cycles 1-3, 97.98% in cycle 4, and 86.88% in cycle 5.
Methods (brief)
Coffee Powder Trimmings were supplied by CH Biotech in Nantou, Taiwan, rinsed with deionized water, dried, and used first as a metal adsorbent and then as a pyrolysis precursor. Metal ions were quantified by ICP-MS. Methylene blue was quantified by UV-Vis absorbance at 664 +/- 1 nm. Materials were characterized with SEM/EDS, TEM, XRD, BET gas adsorption, FTIR, XPS, Raman spectroscopy, and TGA/DTG.
The metal-removal step used metal chloride solutions under laboratory conditions, not environmental or food samples. The biochar step used the metal-loaded CPT after pyrolysis and evaluated dye removal across contact time, temperature, pH, dose, water body, and reuse cycles.
Implications
Certification: Do not use this source in coffee, coffee ingredient, coffee beverage, or product occurrence pools. It does not measure Cu or Fe in coffee for consumption; it uses coffee-processing waste as a remediation material.
App: Context for remediation and circular-material notes involving spent coffee grounds, coffee waste biochar, copper/iron adsorption, and dye removal.
Courses: Useful for teaching why a familiar food-derived material can be a remediation matrix without becoming food-contaminant occurrence evidence.
Related evidence
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