Green synthesis, characterization and sorption efficiency of MnO₂ nanoparticles and MnO₂@waste eggshell nanocomposite

Figures & data

Figure 1. (a) Effect of precursor concentration on the biogenic synthesis of Mn dioxide NPs. (b) Effect of plant concentration on the biogenic synthesis of Mn dioxide NPs. (c) Effect of pH on the biogenic synthesis of Mn dioxide NPs. (d–f) Effect of nucleation time on the biogenic synthesis of Mn dioxide NPs. (g) Effect of temperature on the biogenic synthesis of Mn dioxide NPs.

Scheme 1. Possible mechanism of MnO₂ nanoparticle formation.

Scheme 2. Possible mechanism of MnO₂@waste eggshell nanocomposite formation.

Scheme 3. Possible mechanism of dye removal procedure by MnO₂ nanoparticles and MnO₂@waste eggshell nanocomposite.

Figure 2. (a) UV-visible spectrum of aqueous leaf extract of Ocimum basilicum. (b) UV-Visible Spectrum of Mn dioxide NPs. (c) UV-visible spectrum of fabricated Mn oxide/eggshell as NC.

Figure 3. (a) FTIR Spectrum of Ocimum basilicum leaves extract. (b) FTIR Spectrum of biogenic synthesized Mn dioxide NPs. (c) FTIR Spectrum of eggshell. (d) FTIR Spectrum of nanocomposite.

Figure 4. (a) XRD Spectrum of Mn dioxide NPs. (b) XRD Spectrum of nanocomposite.

Figure 5. (a–c) SEM images of biosynthesized Mn dioxide NPs. (d–f) SEM images of fabricated Mn dioxide/eggshell NC.

Figure 6. (a) EDX spectrum of biosynthesized Mn dioxide NPs. (b) EDX spectrum of biosynthesized Mn dioxide NPs/eggshell NC.

Figure 7. (a) Comparative graph showing the effect of dye concentration for the removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshell NC. (b) Comparative graph showing the effect of adsorbent dosage for removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshell NC. (c) Comparative graph showing the effect of pH for the removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshell NC. (d) Comparative graph showing the effect of temperature for the removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshell NC. (e) Comparative graph showing the effect of time for removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshell NC. (f) Comparative graph showing effect of ionic strength for removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshell NC. (g) Regeneration studies for removal of crystal violet dye by Mn dioxide NPs. (h) Regeneration studies for removal of crystal violet dye by Mn dioxide/eggshell NC.

Table 1. Thermodynamic parameters calculated for CV dye removal by Mn dioxide NPs and Mn dioxide/eggshell NC.

Parameters	ΔH	ΔG	ΔS
Mn dioxide NPs	22.05	−9.21	91.28
Mn dioxide/eggshell NCs	9.77	−9.79	56.77

Figure 8. (a) Plot of Langmuir isotherm for Mn dioxide NPs. (b) Plot of Langmuir isotherm for Mn dioxide/eggshell NC. (c) Plot of Freundlich isotherm for Mn dioxide NPs. (d) Plot of Freundlich isotherm for Mn dioxide/eggshell NC.

Table 2. Langmuir isothermal parameters for the removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshell NC.

Parameters	Slope	Intercept	R^2	qm (mg/g)	B	RL
Mn dioxide NPs	0.059	0.019	0.96	52.63	0.31	0.17
Mn dioxide/eggshell NCs	0.037	0.0067	0.99	149.25	0.17	0.27

Table 3. Freundlich isothermal parameters for the removal of crystal violet dye by Mn dioxide NPs and Mn dioxide/eggshells NC.

Parameters	Slope	Intercept	R^2	KF	N
Mn dioxide NPs	0.55	1.07	0.89	11.86	1.79
Mn dioxide/eggshell NCs	0.78	1.33	0.98	21.55	1.27

Table 4. Comparison of Mn dioxide NPs and Mn dioxide /eggshells NC with other reported adsorbents used for removal studies of CV dye.

Adsorbent	Contact time (min)	Amount of adsorbent	Adsorption capacity (mg/g)	Percentage removal	References
Iron oxide nanoparticles	120	8 g/L		94.7%	[69]
Activated carbon	80	2 g/L	23.6		[70]
Activated carbon coated with Fe3O4 nanoparticles	60	1.25 g/L	35.5		[70]
Magnetic nanoparticles	180	500 mg/L	88.65		[71]
Magnetite nanoparticles	200	50 mg/50 mL	56		[72]
Magnetite nanoparticles loaded on Azolla leaves	25	300 mg/20 mL	30.21		[73]
Magnetite nanoparticles loaded on Fig leaves	25	500 mg/20 mL	53.47		[73]
Starch-g-poly (acrylic acid)/ZnSe	30	50 mg/50 mL	74.6		[74]
Hydrogel composite membrane based on polyvinyl alcohol (PVA), agar and maltodextrin	180	0.1 g/L	19.17		[75]
Chitin nanowhiskers		500 mg/L	59.52		[76]
NaOH-activated Aerva javanica leaf (NAJL) powder	30	20 mg	315.2		[77]
Mn dioxide NPs	120	20 mg/25 mL	52.63		This study
Mn dioxide/eggshell NCs	100	20 mg/25 mL	149.25		This study

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Data availability statement

All data generated or analyzed during this study are included in this submitted manuscript and its supplementary information file.