Water pollution and contamination are critical global challenges that require immediate, practical solutions. Industrial wastes contain a variety of highly toxic inorganic and organic pollutants, including dyes and heavy metals, which adversely affect the environment and human health. Among different types of water pollution, synthetic dyes are considered one of the most hazardous classes of wastewater pollutants. Numerous studies have demonstrated that many dyes exhibit carcinogenic, mutagenic, and teratogenic properties. Every year, large quantities of different dyes, such as methylene blue, methyl orange, rhodamine B, and Congo Red, are produced and widely used in various industries, such as pharmaceuticals, textiles, paper, cosmetics, plastics, leather, agriculture, photoelectrochemical cells, and food processing [1].
Methylene blue and Rhodamine B are classified as cationic dyes and are more toxic than anionic dyes, such as methyl orange and Congo red [2, 3]. Various methods have been developed for dye removal from natural ecosystems, including chemical methods (oxidation, neutralization, ion exchange, and recovery), physical methods (adsorption, filtration, sedimentation, and reverse osmosis), and biological methods (using bacteria, fungi, and actinomycetes). However, conventional physical and chemical methods are often limited by high costs and the generation of secondary pollutants, such as toxic sludge. In addition, biological approaches are associated with low efficiency and long processing time for dye degradation, and inability to degrade highly stable synthetic dyes. Photocatalysis, as an efficient alternative, uses metal-based nanoparticles under ultraviolet or visible light to drive the total oxidation and decomposition of organic contaminants. This advanced oxidation process has been proposed as a cost-effective, eco-friendly, and efficient method to completely decompose organic chemicals into CO2 and H2O or transform them into safer molecules [1, 4]. 
In recent years, nanotechnology has played a central role in advancing wastewater treatment strategies. In particular, green nanoparticles have gained considerable attention due to their cost-effective, environmentally friendly, and sustainable nature. Green synthesis utilizes biological resources (plant extracts, bacteria, fungi, and algae) as reducing and stabilizing agents. Among these, plant-mediated synthesis is especially attractive because of its simplicity, scalability, and rich phytochemicals, including flavonoids, alkaloids, phenolics, and terpenoids, which facilitate nanoparticle formation and stabilization [5]. In addition, green-synthesized nanoparticles often show improved physicochemical stability. Natural organic matter present in environmental systems can adsorb onto nanoparticle surfaces, reducing agglomeration, improving dispersion, and increasing catalytic efficacy while potentially lowering toxicity. The green synthesis method is safer, more economical, and environmentally benign compared to physical and chemical synthesis methods, which often involve expensive reagents, high energy consumption, and toxic solvents. Notably, green-produced nanoparticles are generally less toxic and more biocompatible and are suitable for environmental applications [6].
In recent years, green synthesis of plant-based nanoparticles, such as silver (Ag) [7], gold (Au) [8], selenium (Se) [9-11], copper oxide [12, 13], zinc oxide (ZnO) [11], titanium dioxide (TiO2) [14], zero-valent iron [15], and cobalt oxide [16] or rare-earth oxides [17] have been investigated for different applications, and they proved potential antimicrobial, anticancer, and photocatalytic activities. The ability of green nanoparticles to efficiently degrade a wide range of dyes, including methylene blue, rhodamine B, and methyl orange, highlights their potential as powerful tools for advanced wastewater treatment. More importantly, their synthesis from renewable biological resources offers a pathway toward the development of sustainable remediation technologies. 
Photocatalysis using metal oxide semiconductors, particularly ZnO and TiO2 nanoparticles, has attracted considerable attention for wastewater treatment. However, several limitations hinder their practical applications, including limited visible light absorption, rapid electron-hole recombination, and reduced efficiency in turbid wastewater. To overcome these challenges, researchers have developed modified systems containing doped semiconductors, heterojunction structures, and composite materials. These modifications significantly enhance photocatalytic efficiency by improving charge separation and extending light absorption into the visible region. Similarly, reduction-based catalytic systems employ nanoparticles, such as Au, Se, and Ag, which rely on external reducing agents, such as sodium borohydride. 
Future research should focus on agro-industrial residues-fruit peels and agricultural by-products- as reducing agents instead of utilizing fresh plant extracts. This approach not only reduces the cost of nanocatalyst production but also aligns with circular economy principles by converting environmental waste into high-value functional materials. Despite substantial progress, several critical challenges remain. Most studies are limited to laboratory-scale experiments using model dye solutions, which do not adequately represent the complexity of real industrial wastewater containing mixed contaminants, salts, and organic matter. Additionally, nanoparticle recovery, long-term environmental fate, scalability of green synthesis methods, and potential ecotoxicological effects require further investigation. Addressing these challenges will require a shift toward real-world applications, comprehensive lifecycle assessments, and process integration. Interdisciplinary collaboration among materials scientists, environmental engineers, toxicologists, and policymakers will be essential to accelerate the translation of laboratory findings into practical solutions.
In conclusion, green-synthesized nanoparticles represent a promising yet underexploited solution to the persistent problem of dye pollution in wastewater. Their high catalytic capabilities, combined with environmentally friendly synthesis methods, align strongly with the goals of sustainable development. However, realizing their full potential requires a shift from laboratory-scale validation to real-world implementation. By addressing challenges related to scalability, standardization, and safety, green nanotechnology can evolve from a promising concept into a practical, impactful solution to global water pollution. 

References

1. Barani A, Alizadeh SR, Ebrahimzadeh MA. A comprehensive review on catalytic activities of green-synthesized selenium nanoparticles on dye removal for wastewater treatment. Water. 2023; 15(18):3295. [DOI:10.3390/w15183295]
2. Aaddouz M, Azzaoui K, Akartasse N, Mejdoubi E, Hammouti B, Taleb M, et al. Removal of methylene blue from aqueous solution by adsorption onto hydroxyapatite nanoparticles. J Mol Struct. 2023; 1288:135807. [DOI:10.1016/j.molstruc.2023.135807]
3. Hamad N, Galhoum AA, Saad A, Wageh S. Efficient adsorption of cationic and anionic dyes using hydrochar nanoparticles prepared from orange peel. J Mol Liq. 2024; 409:125349. [DOI:10.1016/j.molliq.2024.125349]
4. Bal G, Thakur A. Distinct approaches of removal of dyes from wastewater: A review. Mat Today. 2022; 50:1575-9. [DOI:10.1016/j.matpr.2021.09.119]
5. Kirubakaran D, Wahid JB, Karmegam N, Jeevika R, Sellapillai L, Rajkumar M, et al. A comprehensive review on the green synthesis of nanoparticles: advancements in biomedical and environmental applications. Biomed Mat Dev. 2026; 4(1):388-413. [DOI:10.1007/s44174-025-00295-4]
6. Saxena R, Kotnala S, Bhatt SC, Uniyal M, Rawat BS, Negi P, Riyal MK. A review on green synthesis of nanoparticles toward sustainable environment. Sustain Chem Climate Action. 2025; 6:100071. [DOI:10.1016/j.scca.2025.100071]
7. Hashemi Z, Mizwari ZM, Mohammadi-Aghdam S, Mortazavi-Derazkola S, Ebrahimzadeh MA. Sustainable green synthesis of silver nanoparticles using Sambucus ebulus phenolic extract (AgNPs@ SEE): Optimization and assessment of photocatalytic degradation of methyl orange and their in vitro antibacterial and anticancer activity. Arab J Chem. 2022; 15(1):103525. [DOI:10.1016/j.arabjc.2021.103525]
8. Alizadeh SR, Seyghalan HN, Hashemi Z, Ebrahimzadeh MA. Scrophularia striata extract mediated synthesis of gold nanoparticles; their antibacterial, antileishmanial, antioxidant, and photocatalytic activities. Inorg Chem Commun. 2023; 156:111138. [DOI:10.1016/j.inoche.2023.111138]
9. Demir C, Aygun A, Gunduz MK, Altınok BY, Karahan T, Meydan I, et al. Production of plant-based ZnO NPs by green synthesis; anticancer activities and photodegradation of methylene red dye under sunlight. Biomass Conversion and Biorefinery. 2025; 15(21):28253-68. [DOI:10.1007/s13399-024-06172-2]
10. Alizadeh SR, Abbastabar M, Nosratabadi M, Ebrahimzadeh MA. High antimicrobial, cytotoxicity, and catalytic activities of biosynthesized selenium nanoparticles using Crocus caspius extract. Arab J Chem. 2023; 16(6):104705. [DOI:10.1016/j.arabjc.2023.104705]
11. Joneidi S, Alizadeh SR, Biparva P, Goli HR, Ebrahimzadeh MA. Taxodium distichum leaf extract mediated green synthesis of SeNPs and ZnONPs: Optimization and evaluation of photocatalytic, in vitro cytotoxicity, and antibacterial activities. J Clust Sci. 2026; 37(2):58. [DOI:10.1007/s10876-026-03011-4]
12. Sarma PP, Borah P, Das MR, Baruah PK. Agro-waste ash extracts facilitated green synthesis of CuO nanoparticles with efficient catalytic and photocatalytic activities for environmental remediation. J Water Proc Engin. 2025; 70:107004. [DOI:10.1016/j.jwpe.2025.107004]
13. Alizadeh SR, Ebrahimzadeh MA. Characterization and anticancer activities of green synthesized CuO nanoparticles, A review. Anti Cancer Agents Med Chem. 2021; 21(12):1529-43. [DOI:10.2174/1871520620666201029111532] [PMID]
14. Muraro PC, Wouters RD, Chuy GP, Vizzotto BS, Viana AR, Pavoski G, et al. Titanium dioxide nanoparticles: Green synthesis, characterization, and antimicrobial/photocatalytic activity. Biomass Conversion Biorefinery. 2024; 14(20):25279-92. [DOI:10.1007/s13399-023-04542-w]
15. Hashemi Z, Ebrahimzadeh MA, Biparva P, Mortazavi-Derazkola S, Goli HR, Sadeghian F, et al. Biogenic silver and zero-valent iron nanoparticles by Feijoa: Biosynthesis, characterization, cytotoxic, antibacterial and antioxidant activities. Anticancer Agents Med Chem. 2020; 20(14):1673-87. [DOI:10.2174/1871520620666200619165910] [PMID]
16. Barani A, Naderi R, Ebrahimzadeh MA. Optimization and evaluation for biomedical activities of green-synthesized cobalt oxide nanoparticles using Astrodaucus persicus and their novel sunscreen applications. Sci Rep. 2026; 16(1):18537. [DOI:10.1038/s41598-026-47981-x] [PMID] [PMCID]
17. Shirzadi-Ahodashti M, Mortazavi-Derazkola S, Ebrahimzadeh MA. Nanostructures of rare earth oxides (Ho2O3 and Nd2O3): Synthesis methods, properties, and comparative analysis. J Mater Res Technol. 2023; 27:1843-56. [DOI:10.1016/j.jmrt.2023.10.079]