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Inorganics
Volume 14
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10.3390/inorganics14080198
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Article

Green Synthesis of Nd-Doped ZnO Powders via Freeze-Drying and Hydrothermal Processes

by
Irina Stambolova
1,*,
Daniela Stoyanova
1,
Katerina Zaharieva
2,
Delyana Marinova
1,
Ralitsa Mladenova
3,
Mariela Dimitrova
4,
Ognian Dimitrov
4,
Pavel Markov
1,
Milen Dimov
5,
Petya Todorova
2 and
Silvia Dimova
6
1
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, “Acad. G. Bonchev” St., Bl. 11, 1113 Sofia, Bulgaria
2
Institute of Mineralogy and Crystallography, “Acad. I. Kostov”, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Block 107, 1113 Sofia, Bulgaria
3
Institute of Catalysis, Bulgarian Academy of Sciences, “Acad. G. Bonchev” St., Bl. 11, 1113 Sofia, Bulgaria
4
Institute of Electrochemistry and Energy Systems, “Acad. Evgeni Budevski”, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Block 10, 1113 Sofia, Bulgaria
5
Department of Food Technologies, Faculty of Technics and Technologies, Trakia University, 8600 Yambol, Bulgaria
6
Institute of Polymers, Bulgarian Academy of Sciences, “Akad. G. Bonchev” St., Block 103A, 1113 Sofia, Bulgaria
*
Author to whom correspondence should be addressed.
Inorganics 2026, 14(8), 198; https://doi.org/10.3390/inorganics14080198
Submission received: 1 July 2026 / Revised: 20 July 2026 / Accepted: 20 July 2026 / Published: 25 July 2026
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Abstract

Green-synthesized Nd-doped (2%)-ZnO samples were produced using hydrothermal synthesis (HT) and freeze-drying (FT) procedures. A water extract from Vaccinium vitis-idaea leaves was used to modify the Nd-containing zinc acetate solution. The hydrothermal synthesis was carried out in an autoclave at 170 °C for 8 h. The lyophilization process was carried out for 20 h at 0.15 mbar and then for a further 4 h at 0.10 mbar and at a temperature of −100 °C. The final treatment after both these procedures was carried out at 400 °C for 2 h. Both synthesis methods produced mixtures of rugby-like and ridged ZnO particles. The FT particles possess smaller crystallites sizes (24 nm) and higher polarity (I002/I100) in comparison with the hydrothermally obtained particles. It was ascertained by EPR analyses that there was a higher concentration of oxygen-vacancies-related paramagnetic centers after freeze-drying synthesis (more intensive line at g = 2.000). The photocatalytic reaction rates of the freeze-dried samples toward Malachite Green dye discoloration were found to be higher than those of the HT samples. These rates were greatly affected by the smaller crystallites sizes, higher number of singly ionized oxygen vacancies in the crystal lattice and higher surface polarity.
Keywords: freeze-drying; hydrothermal synthesis; neodymium-doped ZnO; lattice defects; morphology; photocatalytic efficiency freeze-drying; hydrothermal synthesis; neodymium-doped ZnO; lattice defects; morphology; photocatalytic efficiency

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MDPI and ACS Style

Stambolova, I.; Stoyanova, D.; Zaharieva, K.; Marinova, D.; Mladenova, R.; Dimitrova, M.; Dimitrov, O.; Markov, P.; Dimov, M.; Todorova, P.; et al. Green Synthesis of Nd-Doped ZnO Powders via Freeze-Drying and Hydrothermal Processes. Inorganics 2026, 14, 198. https://doi.org/10.3390/inorganics14080198

AMA Style

Stambolova I, Stoyanova D, Zaharieva K, Marinova D, Mladenova R, Dimitrova M, Dimitrov O, Markov P, Dimov M, Todorova P, et al. Green Synthesis of Nd-Doped ZnO Powders via Freeze-Drying and Hydrothermal Processes. Inorganics. 2026; 14(8):198. https://doi.org/10.3390/inorganics14080198

Chicago/Turabian Style

Stambolova, Irina, Daniela Stoyanova, Katerina Zaharieva, Delyana Marinova, Ralitsa Mladenova, Mariela Dimitrova, Ognian Dimitrov, Pavel Markov, Milen Dimov, Petya Todorova, and et al. 2026. "Green Synthesis of Nd-Doped ZnO Powders via Freeze-Drying and Hydrothermal Processes" Inorganics 14, no. 8: 198. https://doi.org/10.3390/inorganics14080198

APA Style

Stambolova, I., Stoyanova, D., Zaharieva, K., Marinova, D., Mladenova, R., Dimitrova, M., Dimitrov, O., Markov, P., Dimov, M., Todorova, P., & Dimova, S. (2026). Green Synthesis of Nd-Doped ZnO Powders via Freeze-Drying and Hydrothermal Processes. Inorganics, 14(8), 198. https://doi.org/10.3390/inorganics14080198

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