| XRD, montmorillonite (02,11) reflection band | Broad, low-intensity reflection centered near 2θ = 19–21° |
|---|---|
| XRD, reference peak | 2θ = 26.5–27.0°, assigned to quartz |
| XRD, (001) basal reflection at 2θ < 10° | Could not be reliably resolved from the background |
| XRD, 2θ = 20.7–21.0° region | Dominated by the broad, unresolved montmorillonite hump; no discrete peak is distinguishable above it |
| XRD, reflection near 2θ = 50.0° | Not clearly resolved above background |
| FTIR, Si–O–Si stretching band | 998.9 cm⁻¹ |
| FTIR, Si–O–Si bending band | 775.3 cm⁻¹ |
| Electrokinetic point of zero charge | Near pH 2.5 |
| Zeta potential at pH 7 | −28.6 ± 1.6 mV |
| Zeta potential across the full pH range | Negative or near-zero |
| SEM | Aggregated, blocky particles with relatively smooth surfaces and well-defined interparticle voids |
| SEM–EDS, Si atomic concentration | 41.83 % |
| SEM–EDS, Al atomic concentration | 17.48 % |
| SEM–EDS, Na atomic concentration | 21.42 % |
| SEM–EDS, Fe atomic concentration | 5.95 % |
| SEM–EDS, Cl atomic concentration | 4.92 % |
| SEM–EDS, Mg atomic concentration | 2.54 % |
| SEM–EDS, K atomic concentration | 1.89 % |
| SEM–EDS, Ti atomic concentration | 1.10 % |
| SEM–EDS, S atomic concentration | 1.55 % |
| SEM–EDS, P atomic concentration | 1.32 % |
| BET surface area (N2 physisorption, 77 K) | 42.3 ± 1.8 m² g⁻¹ |
| Total pore volume | 0.048 ± 0.003 cm³ g⁻¹ |
| Mean pore diameter | 4.52 ± 0.18 nm |
| N2 adsorption-desorption isotherm | Type IV with H3 hysteresis |
| XPS, O 1s atomic concentration | 65.5 % |
| XPS, Si 2p atomic concentration | 20.4 % |
| XPS, Al 2p atomic concentration | 7.6 % |
| XPS, Na 1s atomic concentration | 2.6 % |
| XPS, Zn 2p | Not detected |
| XPS, C 1s atomic concentration | 3.9 % |
Bukar Lawan, Abubakar Shettima Kubri. “Deep eutectic solvent-driven surface activation of montmorillonite enhances heavy metal uptake and electrochemical charge-transfer properties.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15007487/v1
The main paper refers to supporting information, but no separate supporting information file was found among the files available from the ChemRxiv record
| XRD, montmorillonite (02,11) reflection band | Broad, low-intensity reflection centered near 2θ = 19–21° |
|---|---|
| XRD, reference peak | 2θ = 26.5–27.0°, assigned to quartz |
| XRD, (001) basal reflection at 2θ < 10° | Could not be reliably resolved from the background |
| XRD, discrete peak | Near 2θ = 20.7–21.0°, assigned to quartz (100) |
| XRD, sharp reflection | Near 2θ = 50.0°, assigned to quartz (112)/albite |
| FTIR, Si–O–Si stretching band | 998.9 cm⁻¹ |
| FTIR, Si–O–Si bending band | 775.3 cm⁻¹ |
| FTIR, relative transmittance at the Si–O–Si bands | Markedly increased after DES treatment |
| FTIR, O–H stretching region | Band narrowing and redistribution |
| Electrokinetic point of zero charge | pH 3.2 |
| Zeta potential at pH 7 | −23.4 ± 1.5 mV |
| SEM | Noticeably rougher particle surfaces, with greater fragmentation of aggregate boundaries and increased exposure of platelet edges |
| BET surface area (N2 physisorption, 77 K) | 68.1 ± 2.4 m² g⁻¹ |
| BET surface area increase | 61 % |
| Total pore volume | 0.082 ± 0.004 cm³ g⁻¹ |
| Total pore volume increase | 71 % |
| Mean pore diameter | 4.81 ± 0.22 nm |
| N2 adsorption-desorption isotherm | Type IV with H3 hysteresis |
| XPS, Zn 2p survey signal | Approximately 1022 eV |
| XPS, Zn survey transitions | Zn 3s and Zn 3p transitions at lower binding energy |
| XPS, Cl 2p at 198–200 eV and Cl 2s at ~270 eV | Not detected |
| XPS, Zn 2p3/2 | 1021.7 eV, assigned to surface-coordinated Zn2+ (Zn–O–Si and/or Zn–OH) |
| XPS, Zn 2p3/2 oxidation-state limitation | Binding energy alone cannot unambiguously distinguish metallic Zn0 at 1021.8 eV from Zn2+ oxide/hydroxide species at 1021.9–1022.0 eV |
| XPS, Zn 2p1/2 | 1044.8 eV |
| XPS, Zn 2p spin–orbit splitting | Δ = 23.1 eV |
| XPS, O 1s surface hydroxyl component | Dominant component at 532.6 eV (–OH, encompassing Si–OH, Al–OH, and Zn–OH) |
| XPS, O 1s lattice oxygen component | 531.1 eV (Si–O/Al–O) |
| XPS, O 1s adsorbed molecular water component | 533.6 eV |
| XPS, O 1s atomic concentration | 63.9 % |
| XPS, Si 2p atomic concentration | 19.6 % |
| XPS, Al 2p atomic concentration | 7.1 % |
| XPS, Na 1s atomic concentration | 1.9 % |
| XPS, Zn 2p atomic concentration | 0.74 % |
| XPS, C 1s atomic concentration | 6.7 % |
| XRD, montmorillonite (02,11) reflection band | Broad, low-intensity reflection centered near 2θ = 19–21° |
|---|---|
| XRD, reference peak | 2θ = 26.5–27.0°, assigned to orthoclase |
| XRD, (001) basal reflection at 2θ < 10° | Could not be reliably resolved from the background |
| XRD, discrete peak | Near 2θ = 20.7–21.0°, assigned to quartz (100) |
| XRD, reflection near 2θ = 50.0° | Not clearly resolved above background |
| XRD | No new peaks associated with metal hydroxide precipitation or framework degradation were detected |
| FTIR, Si–O–Si stretching band | 998.9 cm⁻¹ |
| FTIR, Si–O–Si bending band | 775.3 cm⁻¹ |
| FTIR, relative transmittance at the Si–O–Si bands | Decreased again after metal adsorption |
| FTIR | O–H and Si–O–Al vibrational bands remain present |
| Electrokinetic point of zero charge | Near pH 2.1 |
| Zeta potential at pH 7 | −32.1 ± 1.7 mV |
| Zeta potential across the entire working pH range | Negative |
| SEM | A finer, more uniformly distributed particulate layer across the aggregate surfaces; the overall aggregate architecture remains intact |
| Mean pore diameter | 4.63 ± 0.19 nm |
| BET surface area | Reduced after adsorption |
| Total pore volume | Reduced after adsorption |
| N2 adsorption-desorption isotherm | Type IV with H3 hysteresis |
| SEM–EDS | Si, Al, and Na as the dominant elements, with minor Fe, Mg, and K |
| XRD, zinc-specific crystalline phase | No phase identified at any stage |
|---|---|
| XRD, accessory phases across the three diffractograms | Quartz, albite, kaolinite, and chlorite |
| FTIR spectral resolution | 16 cm⁻¹ |
| FTIR positional differences below 16 cm⁻¹ | Not interpreted as significant |
| SEM–EDS composition across all three stages | Dominated by Si, Al, and Na |
| AAS, initial Cr3+ concentration | 0.452 mg L⁻¹ |
|---|---|
| AAS, initial Cd2+ concentration | 0.128 mg L⁻¹ |
| AAS, initial Pb2+ concentration | 0.612 mg L⁻¹ |
| CV, anodic peak current (Ipa) | 28.4 ± 0.3 µA |
|---|---|
| CV, peak-to-peak separation (ΔEp) | 90 mV |
| EIS, charge-transfer resistance (Rct) | 380 ± 4 Ω |
| EIS, double-layer capacitance (Cdl) | 18.0 µF |
| CV, anodic peak current (Ipa) | 14.2 ± 0.3 µA |
|---|---|
| CV, peak-to-peak separation (ΔEp) | 136 mV |
| EIS, charge-transfer resistance (Rct) | 2850 ± 5 Ω |
| EIS, charge-transfer resistance increase relative to bare GCE | 650 % |
| EIS, double-layer capacitance (Cdl) | 8.0 µF |
| EIS, Warburg coefficient | 25.0 Ω s−0.5 |
| CV, anodic peak current (Ipa) | 47.6 ± 0.3 µA |
|---|---|
| CV, anodic peak current increase relative to bare GCE | 67.6 % |
| CV, anodic peak current increase relative to MMT/GCE | 235.2 % |
| CV, peak-to-peak separation (ΔEp) | 58 mV |
| EIS, charge-transfer resistance (Rct) | 620 ± 9 Ω |
| EIS, charge-transfer resistance decrease relative to MMT/GCE | 78.2 % |
| EIS, double-layer capacitance (Cdl) | 22.0 µF |
| EIS, Warburg coefficient | 10.0 Ω s−0.5 |
| EIS, solution resistance (Rs) | 44–47 Ω across all conditions |
|---|