Electronic Supporting Material

Chelation-enhanced fluorescence of phosphorus doped carbon nanodots for multi-ion detection

Khalid M. Omer,1,2* and Aso Q. Hassan2

1 Department of Chemistry, College of Science, University of Sulaimani, Kurdistan region, 42002, Iraq

2 Komar Research Center, Komar University of Science and Technology, Sarchinar-Qularaise district, Sulaymania City, Kurdistan Region-Iraq

Corresponding author, Email: khalid.omer@univsul.edu.iq

Tel#: 964-770-505-6061

Quantum Yield measurement

The Quantum Yield was measured based on The Quantum yield of CNDs were calculated using common

comparison method.1,2,3 The integrated photoluminescence intensity excited at the best excitation

wavelength and absorbance at the best excited wavelength of CNDs is compared with a reference

fluorescent materials, such as fluorescein, QY 0.794 and Rhofamine 6G 0.95. Gradient method was

used inorder to get more reliable measurement.

x = st ( Gradx/Gradst)(x2/st2)

Where St and X represents standard and Sample respectively, Φ is the fluorescence quantum yield, Grad

the gradient from the plot of integrated fluorescence intensity vs absorbance of different

concentrations, and η the refractive index of the solvent. Figure S1 shows the Gradient curves of

different absorbances versus the integrated PL intensity of each species against the reference

fluorophore.

Figure S1. The Gradient graphs for the references fluorophores with CNDs and metal ions combined with CNDs. (A) __ Rhodamine 6G (QY 95%, excited at 530 nm ), __ free CNDs (excited at 420 nm). (B)

__ Fluorescein (QY 91%, excited at 490 nm), __ CNDs-Al3+. (C) __ Fluoresceine (QY 91%, excited at

490 nm), __ CND:Zn2+ (excited at best ex 425 nm). (D) __ Fluorescein (QY 91%, excited at best ex

490 nm, __ CNDs:Cd2+ (excited at 425 nm). The slit width for the spectrofluorometer were constant during all the measurements.

FigureS2 AFM image of P-CNDs on mica and TEM image.

Figure S3. pH effect on the emission intensity and wavelength position of free P-CNDs. The solution is excited at best ex 425 nm.

Figure S4. (A) Photographs of the P-CNDs with and without metal ions (enhancers), under visible light

and under UV lamp illumination (365-395 nm). (B-D) UV-Vis absorption, excitation, and PL spectra for (B)

Al3+ (C) Zn2+, and (D) Cd2+. The pH of all the solutions are 3-4.

Figure S5. (A) Photograph of the P-CNDs with and without metal ions (B) PL spectra of free P-CNDs and

P-CNDs with different metals. (C) Comparison graph of F/Fo of enhancers and quenchers versus free P-

CNDs, (Fo = fluorescence intensity of free P-CNDs, F = fluorescence intensity of P-CNDs combined with

metal ions). Concentration of metal ions 1.0 mM. Excitation wavelength for P-CNDs, P-CND:Zn 2+, P-

CND:Cd2+ is 425 nm, for P-CND:Al3+ is 405 nm.

Figure S6. Excitation-Independence fluorescence spectra. The excitation wavelengths are indicated

inside the graphs in nm. (A) Free P-CNDs. (B) P-CND:Al3+, (C) P-CND:Zn2+, (D) P-CND:Cd2+. All solutions

were in pH 3-4.

Figure S7. Comparison of pH effect on the absorption and emission spectra of P-CNDs with and without

Al3+ and Zn2+. (A) and (B) Fluorescence spectra at different pHs. (C) to (F) Absorption spectra at different

pHs. The composition and pHs are indicated in the graphs.

Figure S8. Schematic illustration of the interaction of the Zn2+ and Al3+ ions with P-CNDs.

Figure S9. (A) Absorption spectra at different heating times for P-CNDs, inset: enlarged peak from 300 to

500 nm, heating times are shown in the inset. (B) Absorbance ratio indicating the two zones. (C)

Excitation-independent PL prepared at 3 hours heating time. (D) Excitation-dependent PL of CNDs-8

prepared by 8 hours heating time.

Figure S10. Solvothermal heating times effect on the chelation between the Al3+ or Zn2+ ions with different P-CNDs. __ free P-CNDs, __ P-CNDs:Al3+, __ P-CNDs:Zn2+. (A) 30 min, (B) P-CNDs-1, (C) P-CNDs-2, (D) P-CNDs-3, (E) P-CNDs-5, (F) P-CNDs-8. The number refer to the hours of heating as shown in the graphs, pH of the solutions are 3.5.

Figure S11. Effect of heating times on the PL spectra of the P-CNDs.

Figure S12. Effect of heating time on absorbance spectra of CNDs comparing to the spectra when combined with Al3+ and Zn2+ ions.

Preparation of real samples

Zinc Table solution

Ten tablets were weighed out accurately and grounded with a motor to make very fine Zinc Tablet

powder (the tablets were bought from the pharmacy). 1 gm of the Zinc Tablet powder was weighed out

and small amounts of dilute HNO3 solution were added with mixing, heating 80-90 oC for almost 30

minutes. Then the solution was filtrated to remove the undissolved materials, and the filtrate was

diluted to 100 mL with DI water.

Antacid solution

Ten tablets were weighed out accurately and grounded with a motor to make very fine Antacid Tablet

powder (the tablets were bought from the pharmacy). 1 gm of the Antacid Tablet powder was weighed

out and small amounts of dilute HNO3 solution were added with mixing, heating 80-90 oC for almost 30

minutes. Then the solution was filtrated to remove the undissolved materials, and the filtrate was

diluted to 100 mL with DI water.

Figure S13. Calibration graphs and standard addition graphs of (A) and (B) Al3+ and (C) and (D) Zn2+ respectively.

Table S1. Surface composition as determined by quantifying XPS survey scans.*

Sample O C P Si

Sample H point 1 25.4 59.9 <0.3 13.1

Sample H point 2 21.4 66.7 <0.3 10.1

Sample C point 1 41.1 40.3 1.3 13.6

Sample C point 2 40.7 42.9 2.8 9.2

* Si is mainly from the glass substrate and not from the carbon nanodots. Sample H and C means same CNDs but in different days, for reproducibility purposes. Points 1 and 2 are different location of the sample on the glass substrate.

References

1 Williams, A. T. R.; Winfield, S. A.; Miller, J. N. Relative fluorescence quantum yields using a computer-controlled luminescence spectrometer. Analyst 1983, 108, 1067-1071.

2 Dhami, S.; De Mello, A.; Rumbles, G.; Bishop, S.; Phillips, D.; Beeby, A. Phthalocyanine fluorescence at high concentration: dimers or reabsorption effect? Photochemistry and photobiology 1995, 61, 341-346.

3 Scaiano, J. C.: CRC handbook of organic photochemistry; CRC press, 1989.4 Umberger, J. Q.; LaMer, V. K. The kinetics of diffusion controlled molecular and ionic reactions in solution as determined by measurements of the quenching of fluorescence1, 2. Journal of the American Chemical Society 1945, 67, 1099-1109.