Compound characterization data — Fülöp et al., 2026

Isopropanol-derived carbon dots
AFM acquisition	Nanosurf FlexAFM in phase contrast mode (tapping mode) with MikroMasch NSC15 cantilevers; randomly selected locations; 2.5 µm × 2.5 µm scan windows. Gwyddion v2.70 processing comprised mean plane leveling, row alignment, and polynomial background subtraction; grain segmentation used each grain’s maximum Z-height as its representative particle diameter to minimize tip-convolution artifacts. At least 3000 particles per sample; standard error of the mean below 0.01 nm for all samples
TEM and EDS acquisition	Thermo Fisher Titan Themis 200 kV spherical aberration (Cs)-corrected TEM/STEM microscope with 0.08 nm HR-TEM point resolution and four Super-X EDS detectors
Electrophoretic mobility acquisition	Malvern Zetasizer Nano Z apparatus (Malvern Panalytical, United Kingdom); zeta potential ζ was calculated from measured electrophoretic mobility µ using Henry’s equation under the Smoluchowski approximation; 25 °C; 0.5 g·L⁻¹ in 1 mM aqueous NaCl background electrolyte; five parallel runs per sample demonstrated a reproducibility within ±3 mV
Surface-tension acquisition	OCA 25 pendant drop tensiometer (DataPhysics, Germany); air–water interfacial tension at 25 °C using 5.0 g·L⁻¹ aqueous dispersions; adsorption kinetics recorded over 1 h across at least three parallel replicates per sample
ATR-IR acquisition	Jasco FT/IR-4700 spectrometer with a Jasco ATR Pro One single-reflection accessory; 4 cm⁻¹ spectral resolution; 512 scans per sample. Jasco Spectra Manager version 2, Spectra Analysis module, applied an ATR penetration depth correction to yield spectra comparable to conventional transmission-mode FT-IR; subsequent processing, including baseline correction, used Fityk 1.3.1
XPS acquisition	Thermo Scientific ESCALAB Xi+ spectrometer with an information depth of 5 to 10 nm; monochromatic Al Kα X-radiation, 1486.6 eV, spot size 900 µm, with flood-gun charge compensation. Survey spectra: 0.5 eV step size and 10 ms dwell time. High-resolution C 1s, O 1s, Si 2p, and S 2p spectra: 20 eV pass energy, 0.1 eV step size, 50 ms dwell time, and 20 eV windows centered on the relevant core-level emission lines. Thermo Scientific Avantage processing; atomic concentrations after background subtraction using the Althermo1 sensitivity factor library; binding energy calibration to adventitious C 1s C–C/C–H at 284.8 eV; CasaXPS deconvolution with 30 % Gaussian-Lorentzian line shapes. The PDF omits the space in the percentage expression
Ultraviolet-visible absorbance acquisition	The same Specord 40 spectrophotometer; 200 to 800 nm; scan speed 5 nm/s; spectral resolution 1 nm
Fluorescence acquisition	Cary Eclipse fluorimeter (Varian, USA); aqueous samples diluted to optical density 0.1 within 330 to 360 nm. Excitation wavelengths scanned from 200 to 800 nm in 5 nm increments with detector voltages of 650 to 750 V depending on sample brightness; emission spectra collected from 200 to 800 nm at 600 nm/min with 1 nm resolution. Intensities normalized using the integrated water Raman scattering signal recorded between 380 and 420 nm under 350 nm excitation
Relative fluorescence quantum-yield acquisition	Optical standards: L-tryptophan in water, excitation 280 nm and quantum yield 0.12; quinine sulfate in 0.5 M sulfuric acid, excitation 350 nm and quantum yield 0.55; Coumarin 153 in ethanol, excitation 460 nm and quantum yield 0.54. At the fluorescence emission maximum, Equation 1 is printed as φ(S) = [I(S)A(R)/(I(R)A(S))][n(S)/n(A)]²φ(R), where φ is fluorescence quantum yield, A is absorbance at λ(ex), I is integrated fluorescence intensity of the emitted light, and n is solvent refractive index; subscripts S and R denote the sample and reference standard, respectively
AFM morphology and size	Average sizes ranged from 1 to 5 nm number-average values, with narrow size distributions indicated by low dispersity (Đ) indices. Particle size increased systematically with reaction temperature; ACD_T190_V500 had the largest particles
AFM size-distribution metrics	For ACD carbon dot systems synthesized with pure IPA precursor, number-average size Dₙ, volume-average size D₄,₃, dispersity Ð, span S, and aspect ratio R: ACD_T150_V500, 4.36 nm, 7.96 nm, 1.83, 1.72, 0.17; ACD_T190_V500, 4.37 nm, 8.69 nm, 1.99, 1.59, 0.21; ACD_T170_V300, 3.57 nm, 5.32 nm, 1.49, 1.06, 0.21; ACD_T170_V500, 1.55 nm, 2.35 nm, 1.52, 1.13, 0.21; ACD_T170_V700, 3.83 nm, 5.06 nm, 1.32, 0.64, 0.24. The table title and header print dispersity as Ð, while the footnote prints Đ and defines it as D₄,₃/Dₙ; S = (d₉₀ − d₁₀)/d₅₀, where d₁₀, d₅₀, and d₉₀ are the diameters below which 10 %, 50 %, and 90 % of the cumulative number distribution of particles reside, respectively; the PDF omits the spaces in these three percentage expressions
UV–Vis absorbance	For ACD_T170_V500, tail of an intense absorption band below 200 nm, distinct shoulder around 250 nm, weaker band at 300–350 nm, and broad absorption tail extending to approximately 450 nm. The feature below 200 nm arises from high-energy π → π* transitions of isolated C=C bonds alongside σ → σ* or σ → π* transitions of non-conjugated groups; the 250 nm feature is attributed to π → π* transitions within the delocalized sp2 core framework; the 300–350 nm feature arises from n → π* transitions associated with surface functional groups and edge states
Fluorescence	Broad fluorescence across the 300–500 nm emission window. 3D excitation–emission spectra revealed three distinct UV fluorophore features at λ(ex)/λ(em) approximately 230/360 nm, 275/400 nm, and 325/400 nm. These results indicate that the 250 nm UV–Vis shoulder is a convolution of absorption bands centered at 230 and 275 nm. The 230 and 275 nm centers had Stokes shifts of 1.95 and 1.41 eV, respectively, indicating core-related electronic transitions. The high-energy excitation band at 230 nm was attributed to direct π → π* transitions within the conjugated aromatic core; the 275 nm band was assigned to π → π* transitions involving surface edge states conjugated with oxygen-containing functional groups, specifically delocalized π-domains directly bound to surface oxygen heteroatoms. The final feature is subsequently described at 320 nm excitation, rather than 325 nm, with a Stokes shift of approximately 0.71 eV and a similar emission profile; it can likewise be attributed to edge-state transitions involving the same boundary-delocalized bonds within the core’s π-domains and their conjugated surface oxygen-containing functional groups
Fluorescence quantum yields	All prepared samples showed similar spectral profiles with no observable peak-position shifts. The text states that quantum yields varied between 0.3 % and 2.0 % across the three peak regions and that the third peak had the highest quantum yield among the excitation features; Table 2 includes values below 0.3 %. For samples prepared with pure isopropanol in concentrated sulfuric acid, φ at λ(ex) = 230, 275, and 320 nm, respectively: ACD_T150_V500, 0.52 ± 0.11 %, 0.81 ± 0.19 %, 2.01 ± 0.28 %; ACD_T190_V500, 0.33 ± 0.15 %, 0.48 ± 0.24 %, 1.17 ± 0.54 %; ACD_T170_V300, 0.14 ± 0.07 %, 0.17 ± 0.08 %, 0.30 ± 0.16 %; ACD_T170_V500, 0.26 ± 0.11 %, 0.36 ± 0.12 %, 0.71 ± 0.19 %; ACD_T170_V700, 0.24 ± 0.13 %, 0.35 ± 0.14 %, 0.67 ± 0.21 %. Table 2’s title repeats “values” in “Quantum yield values (φ) values”; the table omits spaces around ± and before percentage signs
AFM metrics for isopropanol–water systems	Five selected systems were characterized to compare water-added samples with samples synthesized in pure isopropanol. For carbon dot systems synthesized using isopropanol-water mixtures in concentrated sulfuric acid, number-average size Dₙ, volume-average size D₄,₃, dispersity Ð, span S, and aspect ratio R: ACD_T150_V500_PW25, 3.23 nm, 4.37 nm, 1.35, 0.86, 0.21; ACD_T190_V500_PW25, 3.09 nm, 4.12 nm, 1.33, 0.82, 0.17; ACD_T170_V500_PW50, 2.12 nm, 2.69 nm, 1.27, 0.44, 0.14; ACD_T150_V500_PW75, 1.30 nm, 2.86 nm, 2.20, 1.64, 0.08; ACD_T190_V500_PW75, 4.20 nm, 4.68 nm, 1.12, 0.53, 0.21. Water incorporation did not substantially alter particle dimensions or size distributions; number-average diameters were 1.3–4.2 nm with comparable dispersity indices. The table title and header print Ð, while the footnote prints Đ and defines it as D₄,₃/Dₙ; S = (d₉₀ − d₁₀)/d₅₀, with d₁₀, d₅₀, and d₉₀ denoting the diameters below which 10 %, 50 %, and 90 % of the cumulative number distribution of particles reside; the PDF omits spaces in those percentage expressions
AFM of surface-modified particles	For surface-modification studies, ACD_T170_V500 was designated ACD1 and ACD_T150_V500_PW75 was designated ACD2; following purification, the modified nanoparticles retained sizes and size distributions comparable to the unmodified base particles, with systematic trends across the samples. C4–C6 functionalization led to slight increases in particle size, whereas C8 modification resulted in reduced measured diameters for both series relative to the unmodified samples
TEM morphology and crystallinity	TEM was employed to evaluate particle morphology but was unsuitable for accurate size quantification because of poor intrinsic contrast and beam-induced damage to organic components. The ACD samples exhibited pronounced sensitivity to the high-energy electron beam, rendering high-resolution imaging of isolated individual particles impossible. Larger nanoparticle aggregates were described as large, semi-crystalline ACD nanoparticle aggregates
TEM lattice periodicities	Aggregated domains showed multiple distinct periodicities. The smallest lattice spacing, 0.261 nm, was consistent with either an expanded, doped graphitic d(100) value, corresponding to the in-plane atomic spacing within the hexagonal carbon basal plane, or a contracted graphitic d(002) interlayer spacing; the pristine graphitic d(100) in-plane reflection was stated to occur typically at approximately 0.213 nm. Larger periodicities of 0.6 and 1.54 nm were also observed
Surface-modified particle metrics	Columns are Dₙ (nm), D₄,₃ (nm), Ð, S, R, electrophoretic mobility u (10⁻⁸ m²·V⁻¹·s⁻¹), ζ (mV), and average surface tension γ(t=1h) (mN·m⁻¹) measured with 5 g·L⁻¹ nanoparticle sols: ACD1, 1.55, 2.35, 1.52, 1.12, 0.21, −2.44 ± 0.10, −31.1 ± 1.3, 42.0 ± 0.2; ACD1_C4, 2.19, 3.35, 1.53, 1.37, 0.08, −1.53 ± 0.15, −19.5 ± 1.9, 46.4 ± 0.6; ACD1_C5, 3.53, 4.67, 1.32, 0.89, 0.22, −1.98 ± 0.21, −25.2 ± 2.6, 35.6 ± 0.3; ACD1_C6, 3.02, 5.03, 1.66, 1.71, 0.18, −1.91 ± 0.25, −24.4 ± 3.2, 33.7 ± 0.2; ACD1_C8, 1.39, 2.27, 1.63, 0.85, 0.13, −2.50 ± 0.18, −31.9 ± 5.9, 33.1 ± 0.3; ACD2, 1.30, 2.86, 2.20, 1.64, 0.08, −2.60 ± 0.07, −33.2 ± 2.4, 50.2 ± 1.0; ACD2_C4, 2.06, 5.59, 2.72, 1.90, 0.11, −1.47 ± 0.10, −18.8 ± 1.3, 40.9 ± 0.4; ACD2_C5, 1.40, 2.02, 1.45, 0.69, 0.06, −1.44 ± 0.11, −18.3 ± 1.4, 33.6 ± 0.2; ACD2_C6, 1.51, 2.52, 1.67, 0.65, 0.06, −0.99 ± 0.07, −12.6 ± 0.9, 30.3 ± 0.2; ACD2_C8, 0.62, 0.97, 1.57, 0.60, 0.03, −1.38 ± 0.18, −17.7 ± 3.6, 32.6 ± 0.1. Table 6 omits the comma between “aspect ratio (R)” and “electrophoretic mobility (u),” calls ζ “electrophoretic-potential,” uses “average surface tension after t = 1 h time,” and prints the mobility unit compactly without spaces, centered dots, or superscripts. It prints ACD1 span as 1.12, while Table 1 prints 1.13 for ACD_T170_V500. The table title/header print Ð and the footnote prints Đ, defined as D₄,₃/Dₙ; S = (d₉₀ − d₁₀)/d₅₀, with d₁₀, d₅₀, and d₉₀ denoting diameters below which 10 %, 50 %, and 90 % of the cumulative number distribution of particles reside. The PDF omits spaces around ± and in the three percentage expressions, and inconsistently inserts spaces after some minus signs
Electrophoretic mobility and zeta-potential trends	Electrophoretic mobility measurements revealed distinct differences in surface charge between the unmodified and functionalized samples. Surface modification decreased the overall magnitude of zeta potential in both series, shifting values toward more positive potential. ACD1 modifications gave modest positive shifts of 5 to 10 mV, except ACD1-C8, which the source says “exhibited virtually same mobilities” as unmodified particles; ACD2 showed more pronounced shifts of approximately 10 to 15 mV
Surface-tension trends	Modified ACD1 samples showed higher overall surface activity than the ACD2 series. Samples treated with 1-butanol showed “negligible deviations from the unmodified control (ACD2_C4)” or a slight surface-tension increase for ACD1_C4; the source’s parenthetical is retained without resolving its mapping. Surface tension decreased systematically with increasing alkyl chain length, reaching 34–36 mN·m⁻¹ for C5 modification, with only slight further reductions for longer chains. Physical-mixture blank controls of carbon dots and alkanols showed no significant surface-tension change from unmodified particles. Covalent grafting cannot be confirmed with absolute certainty
XPS elemental composition	XPS elemental analysis revealed pronounced structural differences between the ACD1 and ACD2 series. Except for the octanol-modified sample ACD1_C8, ACD1 had high carbon contents of 73.5–80.1 % with relatively low oxygen and sulphur heteroatom fractions; ACD2 contained 56.0–62.1 % carbon and was significantly more heteroatom-rich. Sulphur atomic percentages were comparable between series; ACD2’s elevated heteroatom fraction stemmed primarily from oxygen content 1.5 to 2.0 times higher than that of ACD1. ACD1 carbon content varied slightly and non-systematically without correlation to alkanol chain length; no significant unmodified-versus-modified differences were observed except for ACD1_C8, which had markedly lower carbon and higher heteroatom levels resembling ACD2. The PDF omits spaces before percentage signs
High-resolution XPS C 1s	Four components: graphitic/sp2 carbon and C–C/C–H bonds at 284.8 eV; single-bonded oxygen species C–O at approximately 286.3 eV; carbonyl C=O at approximately 287.8 eV; carboxyl/carboxylate O–C=O at approximately 288.8 eV. The π–π* shake-up satellite at approximately 291 eV, indicative of aromatic and graphitic character, could not be clearly distinguished. C–C/C–H remained dominant; most oxygen appears as C–O, C–O–C, or C–O–S functionalities, which cannot be strictly separated due to their binding energy overlap in the C 1s region. Samples had only minor C=O and minimal carboxylate below 0.5 at. %. The PDF prints the atomic-percent expression without a space before the percent sign. Functionalization caused no measurable O–C=O change relative to unmodified particles
XPS atomic composition and chemical-state distribution	Columns, all atomic percent, are C, O, S, C–C/C–H at 284.8 eV, C–O/C–O–C/C–O–S at 286.3 eV, C=O at 287.8 eV, O–C=O at 288.7 eV, –SO₂–O at 168.3 eV, and –SO₃–O at 169.1 eV: ACD1, 73.45, 19.80, 6.75, 65.35, 6.49, 1.3, 0.31, 5.84, 0.91; ACD1_C4, 76.09, 16.61, 7.30, 68.56, 6.41, 1.13, 0, 4.05, 3.25; ACD1_C5, 80.12, 13.45, 6.43, 70.24, 8.22, 1.22, 0.43, 4.95, 1.48; ACD1_C6, 77.32, 16.37, 6.31, 70.45, 6.58, 0.29, 0, 4.77, 1.54; ACD1_C8, 58.35, 32.97, 8.68, 51.01, 7.18, 0.17, 0, 0.64, 8.04; ACD2, 59.48, 31.50, 9.02, 53.11, 5.26, 1.09, 0.02, 6.97, 2.04; ACD2_C4, 56.48, 33.11, 10.41, 43.90, 11.16, 1.04, 0.38, 5.07, 5.34; ACD2_C5, 62.00, 29.42, 8.58, 52.59, 7.48, 1.48, 0.44, 4.42, 4.16; ACD2_C6, 55.97, 34.91, 9.12, 46.06, 8.90, 1.02, 0, 1.02, 8.1; ACD2_C8, 62.07, 29.70, 8.23, 54.31, 6.51, 1.26, 0, 1.47, 6.76. Table 7 gives O–C=O at 288.7 eV, while the page-18 prose gives approximately 288.8 eV. The table inconsistently prints “at%” for elemental columns and “at %” for chemical-state columns
High-resolution XPS S 2p	Deconvolution of the high-resolution S 2p spectra revealed two primary species: sulfite-like groups (–SO₂–O, including sulfonate esters) at approximately 168.3 eV and sulfate-like groups (–SO₃–O, including sulfate esters) at approximately 169.1 eV. Both the ACD1 and ACD2 series originally contained a higher proportion of sulfite-like groups; surface modification clearly increased sulfate-like functionalities in both series, indicating significant oxidation during treatment. This oxidation was particularly prominent in ACD1_C8, where sulfate-like species exceeded sulfite-like groups by more than an order of magnitude, confirming that its substantial oxygen increase reflects sulfur-bound oxygen within sulfate groups rather than deep carbon oxidation, consistent with minimal C=O
ATR-FTIR	Spectra exhibit straightforward profiles confirming the presence of various functional groups. In the high-wavenumber region, a broad absorption band spans 3200 to 3500 cm⁻¹. Cross-referencing these findings with XPS analysis allows this broad feature to be assigned primarily to O–H stretching vibrations of surface hydroxyl groups and protonated sulfate and sulfonate functionalities. The regions between 2850 and 2960 cm⁻¹ and 1380 and 1500 cm⁻¹ correspond to characteristic C–H stretching and C–H bending vibrations of aliphatic methylene and methyl groups, respectively. Aromatic C–H stretching associated with the graphitic core, typically at 3000–3100 cm⁻¹, cannot be cleanly resolved here due to extensive overlapping with the intense O–H stretching envelope. In the lower-wavenumber region, a prominent 1790–1550 cm⁻¹ envelope centered near 1650 cm⁻¹ comprises C=C stretching from aromatic and conjugated domains at 1600–1650 cm⁻¹ and a higher-frequency shoulder at 1650–1790 cm⁻¹ that reflects C=O stretching vibrations of carbonyl functionalities, primarily ketones and minor carboxyl groups. XPS indicates relatively low carbonyl content in all samples, particularly ACD1_C6 and ACD1_C8. Because the composite peak’s overall profile and intensity remain largely unchanged across the series, C=C stretching vibrations clearly represent its dominant contribution. Intense overlapping bands at 1120–1300 and 1000–1090 cm⁻¹ arise from asymmetric and symmetric S=O stretching of sulfate and sulfonate groups and their ester derivatives, substantiated by characteristic S–O bending near 600 cm⁻¹. C–O stretching vibrations from alcohol and potential ether functionalities also fall within 1000–1300 cm⁻¹, but severe overlap with the stronger S=O modes obscures their individual resolution; the secondary-alcohol C–O region can be identified with reasonable certainty as a faint shoulder centered near 1100 cm⁻¹. Comparing the baseline spectra of the ACD1 and ACD2 series reveals several clear structural differences: in the ACD2 series, the aliphatic-C–H/broad-O–H intensity ratio is lower, the peak near 1650 cm⁻¹ is visibly diminished, and ACD2 exhibits a more pronounced secondary-alcohol C–O shoulder near 1100 cm⁻¹. For the ACD1 series, modification produces no systematic variations in the high-wavenumber region (4000 to 2500 cm⁻¹). The ACD2 series shows a clear, systematic increase in integrated aliphatic C–H stretching intensity that scales directly with alkanol alkyl chain length and peaks for ACD2_C8. Across both series, functionalized samples display an enhancement in the S=O stretching bands attributed to sulfate esters, appearing near 1240 and 1080 cm⁻¹. The most pronounced spectral shift occurs in the ACD1_C8 sample, where these sulfate ester bands increase dramatically
Optical effect of surface modification	Comparison of the absorption profiles and 3D fluorescence spectra showed no shifts in peak positions or alterations in spectral shape following functionalization (Figure 3 vs. Figure 7). However, the modified samples displayed a substantial enhancement in fluorescence quantum yields relative to the pristine nanoparticles (Table 8)
Excitation-dependent quantum yields of surface modified ACD samples	Columns are φ₁ / % at 230 nm, φ₂ / % at 270 nm, and φ₃ / % at 320 nm: ACD1, 0.3 ± 0.1, 0.4 ± 0.1, 0.7 ± 0.2; ACD1_C4, 0.6 ± 0.3, 0.9 ± 0.3, 1.7 ± 0.2; ACD1_C5, 0.8 ± 0.2, 1.2 ± 0.3, 2.4 ± 0.3; ACD1_C6, 0.7 ± 0.3, 0.9 ± 0.3, 1.8 ± 0.2; ACD1_C8, 0.7 ± 0.2, 0.5 ± 0.2, 1.7 ± 0.3; ACD2, 0.9 ± 0.3, 1.3 ± 0.3, 3.9 ± 0.3; ACD2_C4, 0.8 ± 0.3, 1.7 ± 0.4, 5.1 ± 0.7; ACD2_C5, 0.7 ± 0.2, 1.5 ± 0.2, 4.3 ± 0.4; ACD2_C6, 1.1 ± 0.4, 2.6 ± 0.5, 7.7 ± 1.1; ACD2_C8, 0.9 ± 0.3, 2.0 ± 0.4, 5.6 ± 0.7. The PDF omits spaces around ±