INTRODUCTION:

Fluorescent Organic Nanoparticles (FONs) are utilized for metal ion detection through fluorescence-based methods, leading to three key changes: fluorescence enhancement, quenching, or a shift in emission. Enhancement occurs as certain fluorophores become fluorescent upon metal ion binding due to conformational changes. Quenching involves molecules that fluoresce strongly without metal ions but lose their fluorescence when exposed to them (Quang, 2010) (Carter, 2014). Emission changes are driven by shifts in the emission band, often influenced by photoinduced electron transfer (PET), intramolecular charge transfer (ICT), or photoinduced charge transfer (PCT). These shifts include chelation-enhanced fluorescence (CHEF) and fluorescence-chelation-enhanced quenching (CHEQ). Main group metal ions enhance fluorescence by inhibiting PET, while transition metals typically quench fluorescence through energy transfer. Other mechanisms like Förster resonance energy transfer (FRET), fluorescence resonance energy transfer (FRET), resonance energy transfer (RET), and electronic energy transfer (EET) may also be involved in metal ion sensing. Sensing mechanisms depend on metal-ion interactions with sensor binding sites, with some cases involving metal ion adsorption on nanoparticle surfaces, enhancing sensitivity compared to traditional water-soluble sensors (He, 2016).

The urgency of addressing metal ion toxicity in water led to the development of Fluorescent Organic Nanoparticles (FONs) as effective and practical chemo sensors. Ideal FONs-based chemo sensors should be cost-effective, stable under various conditions, non-corrosive, soluble, selective, and sensitive. They have gained attention for swiftly and accurately detecting metal ions, particularly in water contamination scenarios. The review is structured into two sections, covering transition and main group metal ions, along with insights into the sensing mechanisms. Overall, it aims to inspire further progress in this field (Ahmed, 2019).

A polymer-based nanosensor utilizing fluorescence resonance energy transfer (FRET). They synthesized fluorescent polymer nanoparticles through copolymerization of estrone vinyl benzyl chloride and fluorescein-o,o-bis-propene (FBP) in an oil-in-water mini-emulsion, stabilized with dodecyl trimethylammonium bromide (DTAB). Cyclen was grafted onto the nanoparticle surface as a metal ion-binding ligand (Chen, 2015).

The nanosensor exhibited selective "on-off" response to Cu²⁺ in pure aqueous media due to FRET between FBP and the Cu²⁺-cyclen complex, with a remarkable sensitivity to Cu²⁺concentrations as low as 340 nM. Similarly, Su et al. developed a PDNPs-based "turn-off" nanoprobe for Cu²⁺ detection in aqueous media. It displayed high specificity to Cu²⁺ with a detection limit of 0.10 µM, well below the EPA's safety limit for Cu²⁺ in drinking water (Su, 2016).

The study's primary objective was to synthesize and characterize cobalt-iron oxide nanoparticles (CoFeNPs) functionalized with hydrazine and dodecylamine, yielding CoFeNPs1 and CoFeNPs², respectively. Both nanoparticles were evaluated for their efficacy in removing six negatively charged azoic dyes (Amaranth, Acid Orange 7, Naphthol Blue Black, Reactive Orange 16, Acid Orange 52, and Reactive Red-P2B) from water, considering various factors such as reaction time, the type of anchored amine, CoFeNPs size, and dye structure. Characterization encompassed FT-IR spectra, AFM, SEM-EDS, z-potential, and thermal analysis. CoFeNPs¹exhibited 44.5-82.1% dye removal with a qe of 5.4-13.5 mg/g under unoptimized conditions. CoFeNPs2 showed significantly improved removal (68.0-98.9%, qe 6.6-23.5 mg/g) under similar conditions, attributed to factors like larger size, complex structure, hydrophobicity, and more phenyl SO^3- groups in the tested dyes. CoFeNPs₂ exhibited some dye aggregation, whereas CoFeNPs1 primarily displayed adsorption. The data favored pseudo-second-order kinetics, emphasizing film diffusion. Adsorption isotherms and thermodynamics supported CoFeNPs²'s efficiency in spontaneously and exothermically removing Reactive Orange 16. These amine-functionalized CoFeNPs emerge as cost-effective, reusable adsorbents ideal for selectively and efficiently purifying azo dyes from textile wastewater, taking into account size, structure, charge, and sulfur content in the dye (Khurshid, 2020).

Scheme 1 Synthesis of cobalt–iron oxide NPs (CoFeNPs) functionalized with hydrazine (CoFeNPs1) and dodecylamine (CoFeNPs2) (Qurrat-ul-Ain et al., 2020a).

Scheme 1 Preparation of hydrazine-functionalized cobalt–iron oxide nanoparticles (CoFeNPs1) and dodecylamine-functionalized counterparts (CoFeNPs2) (Qurrat-ul-Ain et al., 2020b).

Antipsychotic medications, such as phenothiazines like tricyclic compounds, work by blocking dopamine D2 receptors in the brain's dopamine pathway, reducing the impact of dopamine release, which is associated with psychotic experiences. High-potency antipsychotics like haloperidol can induce drowsiness and a calming effect within minutes with just a few milligrams, while low-potency antipsychotics like CPZ or TZ require much higher doses to achieve the same effect due to their stronger anticholinergic and antihistaminic actions, which counteract dopamine-related side effects. Phenothiazines primarily affect the plasma membranes of both prokaryotes and eukaryotes. In prokaryotes, they impact components such as efflux pumps, energy sources, ATPase enzymes, and genes regulating bacterial permeability. Phenothiazines have shown promise as an alternative therapy for multidrug and extensively drug-resistant tuberculosis, potentially reducing the impact of these deadly diseases. Moreover, some phenothiazines have demonstrated synergy with various antibiotics, enabling lower antibiotic doses for specific bacterial infections. Additionally, certain phenothiazines possess plasmid-curing abilities, making infectious bacterial cells more susceptible to antibiotics. For instance, trimeprazine synergizes with trimethoprim, while CPZ, in combination with certain antibiotics, also exhibits synergistic effects. The use of phenothiazines, like TZ, can serve not only as an additional antibacterial agent but also as a means to eliminate drug-resistant plasmids from infectious bacterial cells (Amaral, 1991) (Costa, 2010) (Wolfart, 2006) (Spengler, 2003) (Radhakrishnan, 1999) (Evdokimova, 1997) (Molnár, 1984).

Recent innovations in treating industrial wastewater with heavy metal contamination to meet treatment standards. It focuses on physicochemical processes like adsorption on new adsorbents, membrane filtration, electrodialysis, and photocatalysis, assessing their advantages and limitations. New adsorbents and membrane filtration are frequently studied, but photocatalysis shows promise by utilizing affordable UV-near visible region photons for organic pollutant degradation and metal recovery in one process. Lime precipitation is effective for inorganic effluent with metal concentrations above 1000 mg/L. Treatment costs vary based on the method and local conditions, with technical feasibility, simplicity, and cost-effectiveness being key factors in method selection (Barakat, 2011).

Synthesis of water-dispersible angular-shaped amine-functionalized superparamagnetic iron oxide nanoparticles (A-SPIONs). A-SPIONs were prepared by heating iron (III) acetylacetonate in a solvent mixture containing polyethylene glycol (PEG) and branched polyethyleneimine (b-PEI) under vigorous stirring. PEG and b-PEI competed to coat the A-SPIONs, ensuring high water dispersibility. Notably, b-PEI influenced the A-SPIONs' morphology, resulting in polyhedral nanocrystals when halide ions were introduced. The amine groups from b-PEI conferred a positive surface charge (+29.1 mV) and active sites, facilitating functionalization. Characterized as 9.42 x 2.93 nm nanoparticles via TEM, these A-SPIONs exhibited a high saturation magnetization of 75.61 emu g^-1 (measured by SQUID). They remained stably dispersed in aqueous media across varying pH levels, with a hydrodynamic size of approximately 13.97 nm in 0.10 M NaCl solution. Cellular toxicity assessments using the MTT assay demonstrated minimal harm to SKOV-3, U87-MG, and U251 cell lines. Furthermore, these angular-shaped iron oxide nanoparticles displayed impressive relaxivity for magnetic resonance imaging (MRI) due to their high magnetization. To explore their potential in fluorescence imaging, we prepared Cyanine 5.5 dye-functionalized A-SPIONs (Cy 5.5@A-SPIONs) and conducted serial experiments. The results suggest that A-SPIONs hold promise for bimodal imaging applications (Yoo, 2017).

Scheme 1 Schematic for the synthesis of A-SPIONs and Cy 5.5@ASPIONs

Scheme 2 Diagram illustrating the synthesis process of A-SPIONs (aminated superparamagnetic iron oxide nanoparticles) and Cy 5.5@ASPIONs (Cy5.5-conjugated aminated superparamagnetic iron oxide nanoparticles) (Yoo et al., 2017).

A Cu-TiO₂-SiO₂nanocomposite photocatalyst was synthesized using a sol-gel method for the degradation of Rhodamine B (RB), a common organic compound found in dye wastewater. The morphological and structural properties of the Cu-TiO₂-SiO₂ nanocomposite were analyzed using low-temperature N₂ adsorption (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis diffuse reflectance spectroscopy (DRS). Fourier-transformed infrared spectroscopy (FT-IR) indicated enhanced chemical bonding of O-Ti and O-Ti-O after the incorporation of Cu and SiO2 species into TiO₂. Notably, the Cu-TiO₂-SiO₂ nanocomposite exhibited significantly higher photocatalytic activity under both UV and visible light compared to commercial titania (Degussa P25) when used for treating dye wastewater containing RB. The photodegradation rate of RB (5 mg/L) exceeded 95.0% under sunlight after 3 hours. SiO₂ incorporation not only suppressed the crystal growth and anatase-to-rutile transformation of TiO₂ but also improved the adsorption of organic compounds. The introduction of Cu extended the photocatalyst's light response into the visible region. Synergistic effects between Cu-SiO₂ and TiO₂ were explored, offering a promising material and approach for degrading dye wastewater (Li, 2012).

A study utilized a spray pyrolysis process with flame-synthesized nanopowder to produce composite nanoparticles comprising iron oxide (γ-Fe₂O₃) and titanium dioxide (TiO₂), selected for their magnetic and photocatalytic properties, respectively. Initially, dry γ-Fe₂O₃ nanopowder was prepared using liquid flame spray. Subsequently, these nanoparticles were mixed with liquid titanium (IV) isopropoxide (TTIP) and isopropyl alcohol, forming a mixed-phase precursor. This precursor was then sprayed into a tube furnace, where TTIP thermally decomposed, resulting in the formation of solid TiO2 that encapsulated the γ-Fe₂O₃powder particles. Characterization of the synthesized nanoparticles involved aerosol measurements, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The composite nanoparticles exhibited broad size distributions (mode diameters: 80–130 nm) and comprised γ-Fe₂O₃ agglomerates partially or fully enclosed by spherical TiO₂ particles, depending on TTIP concentration. The iron oxide powder was crystalline maghemite, while the spray pyrolyzed titanium dioxide was amorphous, with subsequent calcination yielding crystalline anatase TiO₂. These composite nanoparticles possess a unique combination of structural properties, photocatalytic activity, and magnetic response, making them suitable as magnetically separable photocatalysts for diverse applications (Harra, 2013).

Novel magnetic bayberry-like Fe₃O₄/Bi₂S₃ microspheres (Fe₃O₄/Bi₂S₃ MSs) were synthesized through a straightforward hydrothermal method, offering a combination of highly efficient adsorption and photocatalytic regeneration capabilities. Characterization of the resulting Fe₃O₄/Bi₂S₃ MSs was conducted revealing a relatively large surface area of 36.0 m²/g and a narrow pore size distribution around 4.72 nm. The adsorption process achieved equilibrium and followed the Langmuir isotherm model, while kinetics was consistent with the pseudo-second-order kinetic model (Mehta et al., 2024). Fe₃O₄/Bi₂S₃ MSs exhibited a maximum adsorption capacity of 92.24 mg/g for Congo Red (CR), surpassing the 66.28 mg/g capacity of Bi₂S₃MSs. The magnetic properties of Fe₃O₄/Bi₂S₃ MSs, characterized by high saturation magnetization, low coercivity, and remnant magnetization values, facilitated easy separation and rapid re-dispersion in aqueous solutions. Notably, Fe₃O₄/Bi₂S₃ MSs exhibited enhanced visible light absorption and could be regenerated through photocatalysis under simulated solar light irradiation. These microspheres demonstrated exceptional stability and reusability in the continuous removal of CR dye, employing a synergistic approach combining adsorption and photocatalytic regeneration. Overall, Fe₃O₄/Bi₂S₃ MSs present a promising and easily recyclable solution for environmental remediation, offering facile preparation, efficient magnetic separation, high adsorption capacity, and straightforward regeneration mechanisms (Zhu, 2017).

Synthesizing multifunctional Fe₃O₄@C@Ag hybrid nanoparticles, achieved through the direct adsorption and spontaneous reduction of silver ions onto the surface shell of carbon-coated magnetic nanoparticles. Characterization of the nanoparticles has been done. The Ag nanocrystals deposited on the surface shell of carbon-coated magnetic nanoparticles exhibited nearly spherical shapes with an average diameter of 10 nm. The carbonaceous polysaccharide shell, formed through a glucose hydrothermal reaction, acted as a bridge between the magnetic Fe₃O₄ core and noble metallic Ag nanocrystals. These hybrid nanoparticles were found to be efficient catalysts for the photodegradation of organic dyes, particularly neutral red, when exposed to visible light. The results demonstrated a rapid photocatalytic activity, with a dye degradation rate of 93.7% within 30 minutes, highlighting the high-efficiency of the as-prepared samples for photocatalytic applications (Liang, 2013).

Scheme 1. Schematic illustration of the synthetic process of Ag-loaded Fe3O4@C nanoparticles (Liang et al., 2013)

Scheme 3 Diagram depicting the synthetic procedure for Ag-loaded Fe3O4@C nanoparticles (Bhat et al., 2013).

Synthesis of a highly efficient photocatalyst for degrading methyl orange and rhodamine B. A novel method is introduced to fabricate Fe₃O₄@SiO₂@TiO₂@Ho magnetic core-shell nanoparticles, featuring a spherical morphology. Characterization techniques has been done, were employed to analyze the crystal structures, morphology, and chemical properties of the synthesized nanoparticles. The photocatalytic activity of Fe₃O₄@SiO₂@TiO₂@Ho was evaluated through the degradation of methyl orange (MO) and rhodamine B (RhB) in aqueous solutions under UV/V is irradiation. The results revealed impressive degradation rates, with approximately 92.1% of RhB and 78.4% of MO degraded after 120 and 150 minutes, respectively. These findings indicate that Fe₃O₄@SiO₂@TiO₂@Ho nanoparticles exhibit superior photocatalytic performance compared to Fe₃O₄@SiO₂@TiO₂ for MO and RhB degradation. Furthermore, the catalyst demonstrates excellent recovery and stability, even after multiple separation cycles, rendering it a promising candidate for environmental remediation applications (Mortazavi-Derazkola, 2017).

Preliminary results from an investigation into the direct coating of nanocrystalline titanium dioxide particles onto a magnetic core. A modified hydrolyzed alkoxide process was employed, wherein the hydrolysis and condensation of titanium alkoxide (titanium isopropoxide) occurred under acidic conditions with a high water-to-alkoxide ratio. This approach enabled the synthesis of crystalline titanium dioxide at relatively low temperatures (90°C), eliminating the need for a high-temperature heat treatment step typically required in conventional sol–gel methods to transform amorphous titanium dioxide into a photoactive crystalline phase. The resulting particles demonstrated photoactivity and could be easily separated from a slurry-type photoreactor using an external magnetic field. While additional mild heat treatment was necessary to enhance crystallinity while maintaining good separation properties, this novel particle preparation method shows promise in eliminating the high-temperature (450°C) heat treatment step typically associated with conventional sol–gel techniques for particle coating. Ongoing research aims to optimize the coating process by identifying conditions that achieve complete surface coverage of the core particles while further improving the crystalline nature of the deposited nanosized titanium dioxide (Watson, 2002).

Another research focuses on addressing the treatment of chemical dyes in textile wastewater, aiming for their potential reuse in irrigation, a critical environmental concern. The study presents novel magnetically separable n-p junction TiO₂/Fe₃O₄/BiOI nanocomposites, designed as visible-light photocatalysts, through a straightforward synthesis method for decontaminating various dyes. A comprehensive set of characterization techniques were employed to analyze the nanocomposites' optical properties, phase structures, and morphologies. The findings revealed that the TiO₂/Fe₃O₄/BiOI (20%) photocatalyst exhibited the highest photo-degradation activity, particularly for Rhodamine B (RhB), surpassing TiO₂ and TiO₂/Fe₃O₄ photocatalysts by 6.85-fold and 4.39-fold, respectively. This enhanced activity was attributed to the larger specific surface area and the formation of n-p hetero-junctions between TiO₂and BiOI semiconductors. The TiO₂/Fe₃O₄/BiOI (20%) nanocomposite also demonstrated excellent efficacy in degrading other dyes like Methyl Orange, Fuchsine, and Malachite Green. The study elucidated the critical role of •O₂, in the photocatalytic removal of RhB and highlighted the nanocomposite's high photocatalytic stability. Overall, this research introduces a novel approach to developing ternary visible-light photocatalysts based on TiO₂ with enhanced performance for water purification, offering potential applications beyond dye degradation, including the treatment of hazardous agricultural wastewater pollutants such as pesticides (Gholamian, 2021).

Norbornene-functionalized acid (548 mg, 2.48 mmol) was dissolved in 12 ml of dry DCM, followed by the addition of DCC (767 mg, 3.72 mmol) to form a white precipitate. After 20 minutes, 8-hydroxyquinoline (300 mg, 2.06 mmol) was added and stirred for 24 hours. Filtration removed dicyclohexylurea (DCU), and the filtrate was washed with saturated bicarbonate solution. The organic layer (DCM) was dried, yielding a yellowish-white solid after DCM evaporation. Purification via silica with hexane-ethyl acetate yielded product N8HQ as a white solid with a 69% yield. Subsequent NMR and CHN analysis confirmed its formation. In polymerization, 20 mg of N8HQ was dissolved in dry DCM with Grubbs catalyst (G2). After 24 hours, ethyl-vinyl ether was added, leading to polymer precipitation, confirmed by 1H NMR.

CONCLUSION:

To conclude, Fluorescent Organic Nanoparticles (FONs) are a great breakthrough into the world of environmental monitoring and remediation, especially in detecting and eliminating metal ions and water pollution. In the search of numerous fluorescence-based actions, including fluorescence enhancement, quenching, and emission shifts, FONs have proven to be capable of being an effective and versatile sensor. Besides being more sensitive than traditional techniques, their use technology can readily monitor heavy metals in real time, a feature that is important given the increasing interest in the topic of water quality and safety.

The innovative approaches that are being adopted to overcome the challenges in wastewater treatment of industries are represented by the synthesis and functionalization of nanoparticles, including cobalt-iron oxide and superparamagnetic particles, their distinctive adsorption and photocatalytic characteristics, etc. The papers under consideration underline the significance of the nanoparticle size, surface charge, and a chemical interaction to reach the best sensor performance and the efficiency of the pollutant removal.

In the future, it is possible that the future development and characterization of nanomaterials based on FONs would lead to more cost-effective, selective, and sustainable solutions. The future studies ought to aim at improving their stability and reusability and investigate new materials and ways of functionalization. Finally, the development achieved in this field not only is promising in terms of development of sensor devices, but it is also beneficial to all that is being done to preserve our water resources and reduce the effects of pollution in our environment. The knowledge can be used as a basis of constant innovation and advancement in the use of nanotechnology in the protection of the environment and human health.

CONFLICT OF INTEREST:

Author shows no conflict of interest.

Abbreviations:

FONs-	Fluorescent Organic Nanoparticles
PET-	Photoinduced electron transfer
ICT-	Intramolecular charge transfer
PCT-	Photoinduced charge transfer
CHEF-	Chelation-enhanced fluorescence
CHEQ-	Fluorescence-chelation-enhanced quenching
FRET-	Förster resonance energy transfer
FRET-	Fluorescence resonance energy transfer
RET-	Resonance energy transfer
EET-	Electronic energy transfer
DTAB	Dodecyl trimethylammonium bromide
FBP-	Fluorescein-o,o-bis-propene
CoFeNPs1-	Cobalt-iron oxide nanoparticles
CoFeNPs2-	Dodecylamine
A-SPIONs-	Amine-functionalized superparamagnetic iron oxide nanoparticles
PEG-	Polyethylene glycol
b-PEI-	Branched polyethyleneimine
RB-	Rhodamine B
XRD-	X-ray diffraction
SEM-	Scanning electron microscopy
DRS-	UV-vis diffuse reflectance spectroscopy
FT-IR-	Fourier-transformed infrared spectroscopy
γ-Fe₂O_3-	Iron oxide
TiO_2-	Titanium dioxide
TTIP-	Titanium (IV) isopropoxide
MO-	Methyl orange
RhB-	Rhodamine B
DCU-	Dicyclohexylurea
G2-	Grubbs catalyst

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Received on 06.01.2026 Revised on 26.01.2026

Accepted on 10.02.2026 Published on 14.02.2026

Available online from February 18, 2026

Research J. Science and Tech. 2026; 18(1):105-113.

DOI: 10.52711/2349-2988.2026.00016

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Creative Commons License.