Saif M. Alshrefi
| Hassan A. Majeed | Mariam Kadhim Jawad | Ali Samer Mohammed | Donia Mohsen Diwan | Duaa Maged Ali | Mohammed Hamza K. AL-Mamoori*
© 2026 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
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A Q-switched pulsed Nd: YAG laser ablation technique was used to synthesize the silver/manganese dioxide nanocomposites (AgNPs/MnO₂NPs), and their structural and optical characteristics were investigated. AgNPs and MnO₂NPs were separately synthesized by pulsed laser ablation in liquid (PLAL) and then combined to generate the Ag/MnO₂ nanocomposites. Ultraviolet-Visible (UV-Vis) spectroscopy was used to analyses the optical properties, which showed the surface plasmon resonance (SPR) peaks for AgNPs and the absorption edge for MnO₂NPs. After mixing AgNPs and MnO₂NPs, the absorption edge of AgNPs/MnO₂NPs showed a blue-shift compared to MnO₂NPs and AgNPs, the associated energy band gap of MnO₂NPs and AgNPs/MnO₂NPs were 3.5 eV and 4.0 eV, respectively. Green luminescent emission (PL) from MnO₂ (~550 nm), which correlated to defect-related emissions and AgNPs emissions. The crystallinity, size distribution and morphology of the nanoparticles were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). These findings indicate that the optical performance of the AgNPs/MnO₂ nanocomposites is improved, resulting from the synergism between AgNPs and MnO₂NPs, and suggest that the nanocomposites may be potential optical devices, sensors and photocatalyst novel candidate materials.
silver/manganese dioxide nanocomposites, laser ablation, removal of environmental pollutants
Particularly in optoelectronics, catalysis, and biomedical applications, nanocomposite materials have attracted a lot of interest and are quite valuable due to their unique optical and structural properties [1, 2]. Whereas silver nanoparticles (Ag NPs) have an antimicrobial activity, high electrical conductivity, and strong surface plasmon resonance (SPR) [3], MnO₂ is well-known for its vast surface area, tunable bandgap, and catalytic effectiveness [4, 5]. When coupled with Ag NPs), a material known for its magnetic and catalytic properties, the resulting Ag/MnO nanocomposites are expected to demonstrate synergistic effects. Better structural and optical characteristics can follow from this. Among the several preparation techniques, the laser ablation method distinguishes itself since it generates high-purity nanomaterials with exactly regulated size, shape, and content [6]. This method is quite helpful for producing nanocomposites with unique structural and optical features since the laser parameters can be adjusted to fine-tune the material properties. This work synthesized MnO₂ nanoparticles following Ag NPs originally produced by pulsed laser ablation in liquid (PLAL) [7], MnO₂ nanoparticle manufacturing comes next. Ag/MnO₂ nanocomposites were produced by combining the two components and then investigated structurally and optically using a variety of techniques. We investigated Ag/MnO2 nanocomposites [8] in optical terms using a Ultraviolet-Visible (UV-Vis) spectrophotometer. The outcomes of this work expand our understanding of Ag/MnO nanocomposites and show the need of exact control over material synthesis techniques such as laser ablation for the future development of complex optical devices and sensors.
The samples' morphology was examined by a JSM-6510LV field emission scanning electron microscopy (FESEM) Type - S-1640 HITACHI business Japan under reflection geometry with a Shimadzu 6000 X-ray diffractometer (built in JAPAN), the sample structure was investigated using (Cu Kα) radiation (λ = 1.5406 Å). Mid-IR spectra from (4000 - 400 cm-1) were collected using Fourier Transform Infrared Spectroscopy (FTIR)-Spectrometer, supplied by ALPHA (Made in Germany), for some pure materials and all doped samples. To estimate the spectra for FTIR, Potassium Bromide (KBr) powder was blended with powder samples. The optical characteristics (CECIL CE 7200, ENGLAND) of every produced material were obtained using a UV-Vis diffused reflectance spectroscope.
2.1 Preparation of nanocomposites
Laser ablation method was used in silver/manganese dioxide nanocomposites (AgNPs/MnO₂NPs). Target immersion for pure silver (Ag) and MnO₂ NPs was separately in 10 mL of distilled water. Target Ag and MnO₂ was ablated using Q-Switched a Nd: YAG pulsed laser (wavelength 1064 nm, 3 Hz, 300mj and 300 pulses). This is depicted in Figure 1. The surface of Ag and MnO₂ target was the focus of the laser beam, which produced suspended Ag and MnO2 nanoparticles correspondingly; subsequently, their optical and structural characteristics are determined. Mixed a colloidal solution of AgNPs with MnO₂ NPs in a 1:1 volume ratio as described in flowchart to synthesize Ag/MnO₂ nanocomposites.
Figure 1. Flowchart for the synthesis of Ag/MnO₂ nanocomposite
3.1 Optical properties
Consistent with what is reported in the reference [9-11], the peak at 403.4 nm denotes the resonance frequency of the electron oscillations of AgNPs as shown in Figure 2. The energy gap was calculated from the blank equation Eg (eV) = 1240/λ(nm) andis equal to 3.07 eV.
Figure 2. Absorption spectra of AgNPs (Surface Plasmon Resonance)
The MnO2NPs' absorption spectra consistent with what is reported in the reference [12, 13], revealing a typical absorption edge in the UV range at 326.5 nm as shown in Figure 3. The significant UV absorption and relative transparency in the visible range arising from the quantum confinement phenomenon occurring from the employment of pulsed laser and this promises to be used in UV filtering, photocatalyzed, optical sensing.
Figure 3. Absorption spectra of MnO₂ nanoparticles
The absorption spectrum of the Ag/MnO2 nanocomposite shows the presence of an absorption edge at 300 nm as shown in Figure 4. A blue shift is observed for the absorption edge of the MnO2NPs particles in the Ag/MnO2 nanocomposite because of Quantum confinement effects or interactions between MnO2NPs and AgNPs in nanocomposite. Combining MnO₂ nanoparticles with AgNPs causes changes in the electrical structure of MnO₂ such that the absorption edge of MnO₂ moves to somewhat shorter wavelengths (blue shift) and this behavior is similar to what was stated in the reference [14].
Figure 4. Absorption spectra of Ag/MnO2 nanocomposite
The energy gap of the MnO2NPs and Ag / MnO2 nanocomposite was calculated using the Tuck-Plot equation as shown in Figures 5 (a) and (b) and was equal to 3.5 eV and 4 eV for MnO2NPs and Ag/MnO nanocomposite respectively. Tauck Plot equation deal with connection between the photon energy (hʋ) and the absorption coefficient (α) as in $\left.\alpha h v=A\left(h v-E_g\right)^n\right)$ where (h) is the plank constant; (ϋ) is photon frequency; (hʋ) is photon energy in eV; (Eg) is optical band gap in eV; (A) is a constant; (n) is an exponent whose value is (2) for indirect band transitions and (1/2) for direct band transition and (α) is the absorption coefficient as mentioned in the reference [15]. The intercept provides the transition band gap when the straight section of the graph of (αhv)2 against (hυ) is extrapolated to (α = 0).
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(b)
Figure 5. Energy gap of (a) MnO₂ nanoparticles and (b) Ag/MnO₂ nanocomposite
The quantum confinement affects that increase the band gap with smaller particle size, charge transfer and hybridization of electronic states between AgNPs and MnO₂ NPs, surface effects and strain at the interface between the two materials and modification of the MnO₂ band gap due of the interaction with AgNPs and this behavior is similar to what was stated in the references [14, 16, 17] and it’s clear that the energy gap of the Ag / MnO2 nanocomposite larger than the band gap of individual AgNPs or MnO₂ NPs and this is evidence of the smallness of the nanoparticles in the nanocomposite compared to the AgNPs and MnO₂ NPs alone.
3.2 Photoluminescence testing of Ag/MnO₂ nanocomposite
The PL emission of Ag/MnO₂ nanocomposite exhibit green luminescence at 554.6 nm as shown in Figure 6, which they ascribe to defect-related emission modes in the MnO₂ matrix and it is close to what was mentioned in the reference [18]. AgNPs added into MnO₂NPs can either strengthen or change the emission peaks. Because of interactions like SPR and charge transfer processes [19, 20], silver nanoparticles can particularly produce a blue shift or red shift in the PL spectrum.
Ag/MnO2 nanocomposite Raman spectra are shown in Figure 7. A large peak cantered on 3442.9 cm⁻¹ dominates. O-H stretching vibrations from adsorbed water or hydroxyl groups on the surface of the nanocomposite most certainly cause this. Combining AgNPs and MnO₂NPs in a nanocomposite allows the Raman spectra from the two materials to interact or overlap. The interactions among the elements of the nanocomposite can produce either broadening, shifting, or suppression of particular Raman signals. Overlapping with other peaks, such as water or amplified scattering signals from other molecules, may hide or reduce the Raman peaks from AgNPs and MnO₂NPs. The large peak seen in your spectrum around 3442.9 cm⁻¹ most likely results from O-H stretching from water or hydroxyl groups, easily masking smaller signals from AgNPs or MnO2 [21, 22].
Figure 6. Photoluminescence (PL) emission spectra of Ag/MnO₂ nanocomposite
Figure 7. Raman spectrum of Ag/MnO₂ nanocomposite
3.3 X-Ray diffraction measurements
Layered/birnessite-type MnO₂ (low-angle (00l) basal reflections) are consistent with peaks at 2θ = 17.1° and 2θ = 14.1°; Joint Committee on Powder Diffraction Standards (JCPDS) birnessite patterns reveal first reflections in ~12–18°, as illustrated in Figure 8. These are not Ag metallic peaks (Ag major lines lie outside your 8–28° scan and occur at ≈ 38.1°, 44.3°, and 64.4° for Cu Kα). For MnO₂NPs, the crystallite size was determined using the Scherrer equation for peaks 14.10 and 17.10, which correspond to 1.4 nm and 1.6 nm, respectively. While Ag peaks are outside the scan range, the pattern mostly shows the presence of weakly crystalline MnO₂ layers. The peaks of the very small or poorly crystalline Ag nanoparticles created by the pulsed-laser approach broadened and weakened below detection.
Figure 8. X-ray diffraction (XRD) measurements of Ag/MnO2 nanocomposite
3.4 Scanning Electron Microscopy of the prepared Ag/MnO2 nanocomposite
The surface morphology of the Ag/MnO₂ nanocomposite produced by pulsed laser ablation is displayed in this SEM image. The MnO₂ matrix appears as a rough and porous background, and the bright spherical particles are Ag nanoparticles evenly distributed on it. As seen in Figures 9 (a-c), the image demonstrates the successful decoration of MnO₂ by Ag by the laser ablation process, confirming well-distributed nanosized Ag particles and high surface coverage.
The SEM image demonstrate a dual-morphology, with an ultrafine porous nanostructure (≈ 50 nm features) serving as the substrate and ornamented with larger, distributed nanoparticles and micro-aggregates, as seen in Figure 9 (d). This could be utilized to increase charge/discharge rates in energy storage devices (such as supercapacitors and batteries), as well as catalysis and antibacterial applications.
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(b)
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Figure 9. Scanning electron microscopy (SEM) images of Ag/MnO2 nanocomposite (a) 1 micro, (b) 5 micros, (c) 10 micros, (d) 500 nm
3.5 Using Ag/MnO2 nanocomposite to remove methylene blue dye under the influence of a light source for different times
Ag/MnO2 composite degradation of methylene blue (MB) dye is a high-efficiency technique based on advanced oxidation processes (AOPs) and synergistic photocatalysis, which is essential for contemporary wastewater treatment as shown in Figure 10, where MnO2 functions as a potent oxidant and a catalyst for AOPs. It concentrates the dye close to the active sites due to its large surface area for MB molecule adsorption. Crucially, when oxidants (such H2O2) are activated, MnO2 promotes the production of highly reactive oxygen species (ROS) like hydroxyl radicals (⋅OH), which causes the dye to degrade quickly chemically. Ag's primary function is to increase photocatalytic efficiency when exposed to light. Ag nanoparticles draw photogenerated electrons from MnO2 by acting as electron traps. This prolongs the lifetime of the charge carriers and increases the generation of ROS by suppressing the recombination of the electron-hole (e−/h+) pairs. Additionally, Ag demonstrates Localized Surface Plasmon Resonance (LSPR), which enables the catalyst to efficiently use solar energy and absorb more visible light. This behavior is comparable to that described in the references [23-25].
Figure 10. Photodegradation of methylene blue (MB) by the prepared Ag/MnO2 nanocomposite for different times
This work effectively synthesized AgNPs/MnO₂NPs nanocomposites by Q-switched pulsed Nd: YAG laser ablation. The blue shift in the absorption spectrum shown by UV-Vis. spectroscopy indicated interaction between AgNPs and MnO₂NPs resulting in quantum confinement and modifications in the electronic structure. We calculated the nanocomposite's energy gap to be 4.0 eV. Green luminescence associated with MnO₂ shown by photoluminescence (PL) studies showed possible influence from AgNPs on flaws in MnO₂. XRD and SEM verified the crystalline character, size distribution (15-80 nm), and shape of the nanoparticles. The work emphasizes how synergistic interaction between AgNPs and MnO₂NPs results in enhanced optical characteristics of Ag/MnO₂ nanocomposites. With the laser ablation approach offering a consistent means for manufacturing high-quality nanocomposites with customizable properties, these nanocomposites are promising for uses like photocatalysis, sensors, and optical devices. A discernible change in charge carrier dynamics upon Ag inclusion is indicated by the shift in the absorption edge and the associated change in PL emission intensity. Furthermore, the agreement between optical and structural analyses verifies that the observed changes in properties are directly related to the development of nanocomposites rather than experimental variability.
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