Plasmonic Metal Nanoparticles Research Articles

Real-time LSPR-based study of metal-organic framework (MOF) growth.

MOFs are known for their absorption properties and widely used for accumulation, filtering, sensorics, photothermal, catalytical and other applications. Their combination with plasmonic metal nanoparticles leads to hybrid structures that profit from the stabilizing effect and high porosity of the MOF as well as the optical and electronic properties of the nanoparticles. The growth of MOFs on plasmonic nanoparticles can be monitored in-situ using LSPR spectroscopy, simultaneously applying microfluidic reaction conditions for the fabrication of NP@MOF structures. Here, a systematic study is conducted using LSPR spectroscopy for the monitoring of the Layer-by-Layer deposition of twelve different MOFs, determining the suitability of LSPR spectroscopy for this purpose. In addition to some well-investigated materials like HKUST-1, other MOFs such as MIL-53, MIL-88A and Cu-BDC are deposited successfully. For some MOFs such as Zn-Fum, the LSPR experiment indicates that no deposition had taken place. The results are confirmed with AFM, SEM and XPS measurements. This work shows that LSPR spectroscopy is suitable for the in-situ monitoring of LbL MOF growth and the microfluidic setup is a promising method for the controlled manufacturing of NP@MOF hybrid structures. Further studies may include optimization of the synthesis process or transfer to other materials.

Type-dependent hot carrier behavior in photoelectrochemical reduction and oxidation of Au/GaN junction photoelectrodes

In junctions with semiconductors, plasmonic metal nanoparticles (NPs) can be utilized to efficiently harness solar energy by collecting hot carriers. However, the behavior of hot carriers at the interfaces between semiconductors with opposite doping types is not fully elucidated. Here, Au NPs are attached to n-doped (Au/n-GaN) or p-doped gallium nitrides (Au/p-GaN) to examine the photoelectrochemical performance regarding hot carrier behavior. Direct surface potential measurements revealed that electrons are collected in n-type GaN (n-GaN) when illuminated, while hot holes remain in Au NPs for oxidation reactions via the plasmonic process. Conversely, holes are collected in p-type GaN (p-GaN), thereby promoting the reduction reaction by the electrons left in Au NPs. Specifically, the change in surface potential difference induced by green light illumination in Au/p-GaN is four times greater than that observed in Au/n-GaN. Conversely, the changes in open-circuit potential and photocurrent density under light illumination are approximately six times more significant in Au/n-GaN compared to Au/p-GaN. This difference in efficiency can be attributed to the more favorable oxidation reaction occurring in Au NPs at the interface with GaN materials, as opposed to the reduction reaction, due to the difference in band alignment between the Au/GaN junction systems.

Elastic scattering of gold and silver colloids: Difference between spherical and nonspherical nanoparticles

Light scattering of noble metal nanoparticles was widely used in solar cells, sensing and spectroscopy, so the research on the light scattering itself will be beneficial for their increasing applications. In this paper, gold and silver nanoparticles with different sizes and shapes were synthesized and their elastic scattering was investigated. The results demonstrate that the elastic scattering of metal nanoparticles is influenced by their size and shape, and the scattering behavior has a specific correlation with the surface plasmon resonance. The elastic scattering spectra of gold and silver nanospheres basically cover the extinction spectra, indicating plasmon resonance enhanced scattering of spherical nanoparticles. The elastic scattering spectra of nonspherical gold nanorods and silver nanoprisms only overlap the extinction peaks at short wavelengths. The elastic scattering is considered to be enhanced by the transverse resonance bands at short wavelengths for nonspherical gold or silver nanoparticles, but it cannot be contributed by the longitudinal resonance bands at the corresponding long wavelengths. This result will be helpful in selecting size and shape in the scattering application of plasmonic metal nanoparticles.

Unraveling a Concerted Proton-Coupled Electron Transfer Pathway in Atomically Precise Gold Nanoclusters.

Metal nanoclusters (MNCs) represent a promising class of materials for catalytic carbon dioxide and proton reduction as well as dihydrogen oxidation. In such reactions, multiple proton-coupled electron transfer (PCET) processes are typically involved, and the current understanding of PCET mechanisms in MNCs has primarily focused on the sequential transfer mode. However, a concerted transfer pathway, i.e., concerted electron-proton transfer (CEPT), despite its potential for a higher catalytic rate and lower reaction barrier, still lacks comprehensive elucidation. Herein, we introduce an experimental paradigm to test the feasibility of the CEPT process in MNCs, by employing Au18(SR)14 (SR denotes thiolate ligand), Au22(SR)18, and Au25(SR)18- as model clusters. Detailed investigations indicate that the photoinduced PCET reactions in the designed system proceed via an CEPT pathway. Furthermore, the rate constants of gold nanoclusters (AuNCs) have been found to be correlated with both the size of the cluster and the flexibility of the Au-S framework. This newly identified PCET behavior in AuNCs is prominently different from that observed in semiconductor quantum dots and plasmonic metal nanoparticles. Our findings are of crucial importance for unveiling the catalytic mechanisms of quantum-confined metal nanomaterials and for the future rational design of more efficient catalysts.

Development of excitation power-responsive anti-stokes emission wavelength switching and their energy saving induced by localized surface plasmon resonance

We designed an external stimulus-responsive anti-Stokes emission switching using dual-annihilator-based triplet–triplet annihilation upconversion systems. This system, which was constructed by incorporating a palladium porphyrin derivative as a sensitizer and 9,10-diphenylanthracene (DPA) and 9,10-bis(triisopropylsilyl)ethynylanthracene (TIPS) as annihilators into polymer thin films, produced TIPS- and DPA-based anti-Stokes emission under low and high excitation powers, respectively. The mechanism involves the following: under low excitation power, triplet energy transfer from triplet-excited PdOEP to DPA is induced, followed by relay to TIPS. This results in the generation of triplet-excited TIPS, and the subsequent triplet–triplet annihilation between them produces TIPS-based anti-Stokes emission. Conversely, under high excitation power, the high-density triplet-excited DPA, generated through triplet energy transfer from PdOEP, undergoes triplet–triplet annihilation among themselves, resulting in the generation of DPA-based anti-Stokes emission. Additionally, we achieved energy savings by reducing the required excitation power for switching through the utilization of plasmonic metal nanoparticles. The strong local electromagnetic fields associated with the localized surface plasmon resonance of metal nanoparticles enhance the photoexcitation efficiency of PdOEP, subsequently increasing the density of triplet-excited DPA. As a result, anti-Stokes emission switching becomes feasible at lower excitation powers.

Plasmon-enhanced multi-photon excited photoluminescence of Au, Ag, and Pt nanoclusters

In this work, we have studied the multi-photon excited photoluminescence from metal nanoclusters (NCs) of Au, Ag and Pt embedded in Al2O3 matrix by ion implantation. The thermal annealing process allows to obtain a system composed of larger plasmonic metal nanoparticles (NPs) surrounded by photoluminescent ultra-small metal NCs. By exciting at 1064 nm, visible emission, ranging from 450 to 800 nm, was detected. The second and fourth-order nature of the multiphoton process was verified in a power-dependent study measured for each sample below the damage threshold. Experiments show that Au and Ag NCs exhibit a four-fold enhanced multiphoton excited photoluminescence with respect to that observed for Pt NCs, which can be explained as a result of a plasmon-mediated near-field process that is of less intensity for Pt NPs. These findings provide new opportunities to combine plasmonic nanoparticles and photoluminescent nanoclusters inside a robust inorganic matrix to improve their optical properties. Plasmon-enhanced multiphoton excited photoluminescence from metal nanoclusters may find potential application as ultrasmall fluorophores in multiphoton sensing, and in the development of solar cells with highly efficient energy conversion modules.

A hybrid quantum-classical theory for predicting terahertz charge-transfer plasmons in metal nanoparticles on graphene.

Metal nanoparticle (NP) complexes lying on a single-layer graphene surface are studied with a developed original hybrid quantum-classical theory using the Finite Element Method (FEM) that is computationally cheap. Our theory is based on the motivated assumption that the carrier charge density in the doped graphene does not vary significantly during the plasmon oscillations. Charge transfer plasmon (CTP) frequencies, eigenvectors, quality factors, energy loss in the NPs and in graphene, and the absorption power are aspects that are theoretically studied and numerically calculated. It is shown the CTP frequencies reside in the terahertz range and can be represented as a product of two factors: the Fermi level of graphene and the geometry of the NP complex. The energy losses in the NPs are predicted to be inversely dependent on the radius R of the nanoparticle, while the loss in graphene is proportional to R and the interparticle distance. The CTP quality factors are predicted to be in the range ∼10-100. The absorption power under CTP excitation is proportional to the scalar product of the CTP dipole moment and the external electromagnetic field. The developed theory makes it possible to simulate different properties of CTPs 3-4 orders of magnitude faster compared to the original FEM or the finite-difference time domain method, providing possibilities for predicting the plasmonic properties of very large systems for different applications.

SERS aptasensor utilizing aptamer-conformation-mediated regulation of Au dumbbell dimers for the ultrasensitive detection of β-phenethylamine in foods

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for the detection of target analytes in foods, with the realization of “hot spots” between plasmonic metal nanoparticles (NPs) being critical for ultrasensitive detection. Herein, we proposed a new aptamer conformation-mediated SERS “hot spots” strategy. Au NPs were functionalized with strands of complementary DNA containing β-phenethylamine aptamers and the Raman reporter 4-mercaptobenzonitrile (4-MBN). This allowed DNA-driven self-assembly of an Au dumbbell dimer-based SERS aptasensor for the detection of the β-phenethylamine. After selective recognition of β-phenethylamine by the aptamer, the aptamer folded, bringing AuNPs in the dimers close together to create SERS “hot spots”. This produced an intense SERS signal in the “biologically silent” region for 4-MBN (2225 cm−1), the intensity of which increased linearly with the logarithm of the β-phenethylamine concentration. Under the optimized conditions, the linear range of SERS aptasensor was 10−6 to 10−2 mg L−1, with a low limit of detection of 3.8 × 10−7 mg L−1. Further, the developed SERS aptasensor was successfully employed to determine the β-phenethylamine in a range of food samples, with the results being identical to those obtained using a high-performance liquid chromatography method.

Modeling the near-field effect on molecular excited states using the discrete interaction model/quantum mechanical method.

Strong light-matter interactions significantly modify the optical properties of molecules in the vicinity of plasmonic metal nanoparticles. Since the dimension of the plasmonic cavity approaches that of the molecules, it is critical to explicitly describe the nanoparticle junctions. In this work, we use the discrete interaction model/quantum mechanical (DIM/QM) method to model the coupling between the plasmonic near-field and molecular excited states. DIM/QM is a combined electrodynamics/quantum mechanical model that uses an atomistic description of the nanoparticle. We extend the DIM/QM method to include the local field effects in the sum-over-state formalism of time-dependent density functional theory. As a test of the method, we study the interactions between small organic chromophores and metal nanoparticles. In particular, we examine how the inclusion of multiple electronic transitions and intermolecular interactions modify the coupling between molecules and nanoparticles. Using the sum-over-state formalism of DIM/QM, we show that two-state models break down when the plasmon excitation is detuned from the molecular excitations. To gain further insight, we compare the simple coupled-dipole model (CDM) with the DIM/QM model. We find that CDM works well for simple systems but fails when going beyond the single molecule or single nanoparticle cases. We also find that the coupling depends strongly on the site of the nanoparticle in which the chromophore couples to. Our work suggests the importance of explicitly describing the cavity to capture the atomistic level local field environment in which the molecule strongly couples to.

Strongly coupled plasmonic metal nanoparticles with reversible pH-responsiveness and highly reproducible SERS in solution.

We report a facile method to prepare polymer-grafted plasmonic metal nanoparticles (NPs) that exhibit pH-responsive surface-enhanced Raman scattering (SERS). The concept is based on the use of pH-responsive polymers, such as poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH), as multidentate ligands to wrap around the surface of NPs instead of forming polymer brushes. Upon changing the solvent quality, the grafted pH-responsive polymers would drive reversible aggregation of NPs, leading to a decreased interparticle distance. This creates numerous hot spots, resulting in a secondary enhancement of SERS as compared to the SERS from discrete NPs. For negatively charged PAA-grafted NPs, the SERS response at pH 2.5 showed a secondary enhancement of up to 104-fold as compared to the response for discrete NPs at pH 12. Similarly, positively charged PAH-grafted AuNPs showed an opposite response to pH. We demonstrated that enhanced SERS with thiol-containing and charged molecular probes was indeed from the pH-driven solubility change of polymer ligands. Our method is different from the conventional SERS sensors in the solid state. With pH-responsive polymer-grafted NPs, SERS can be performed in solution with high reproducibility and sensitivity but without the need for sample pre-concentration. These findings could pave the way for innovative designs of polymer ligands for metal NPs where polymer ligands do not compromise interparticle plasmon coupling.

Recent advances and mechanism of plasmonic metal-semiconductor photocatalysis.

Benefiting from the unique surface plasmon properties, plasmonic metal nanoparticles can convert light energy into chemical energy, which is considered as a potential technique for enhancing plasmon-induced semiconductor photocatalytic reactions. Due to the shortcomings of large bandgap and high carrier recombination rate of semiconductors, their applications are limited in the field of sustainable and clean energy sources. Different forms of plasmonic nanoparticles have been reported to improve the photocatalytic reactions of adjacent semiconductors, such as water splitting, carbon dioxide reduction, and organic pollutant degradation. Although there are various reports on plasmonic metal-semiconductor photocatalysis, the related mechanism and frontier progress still need to be further explored. This review provides a brief explanation of the four main mechanisms of plasmonic metal-semiconductor photocatalysis, namely, (i) enhanced local electromagnetic field, (ii) light scattering, (iii) plasmon-induced hot carrier injection and (iv) plasmon-induced resonance energy transfer; some related typical frontier applications are also discussed. The study on the mechanism of plasmonic semiconductor complexes will be favourable to develop a new high-performance semiconductor photocatalysis technology.

Bimetallic and plasmonic Ag and Cu integrated TiO2 thin films for enhanced solar hydrogen production in direct sunlight

Plasmonic metal nanoparticle integrated mesoporous TiO2 nanocomposites (Ag/TiO2, Cu/TiO2 and Ag–Cu/TiO2), prepared by a simple chemical reduction method, have been demonstrated to show superior activity in thin-film form for solar H2 generation.

Microplasma Nanoengineering of Hybrid Plasmonic Nanostructures for Rapid and Ultrasensitive Surface-Enhanced Raman Scattering-Based Sensing

Surface-enhanced Raman scattering (SERS) is a useful analytical tool that allows ultrasensitive molecular-level detection through an enhanced electromagnetic field generated by plasmonic metal nanoparticles (MNPs), which is helpful for biomedical-based detection, environmental pollution monitoring and chemical industry. Recent study suggests that porous MNP with enhanced SERS active area and hybrid plasmonic nanostructures such as core-shell NPs and metal-semiconductor-based NPs with designed and controlled plasmonic properties can further improve the SERS responses.Here we report a microplasma nanoengineering of plasmonic nanostrutures including Au-Ag core-shell NPs, Ag-GQD nanohydrids, and porous Au nanosturtures for ultrasensitive SERS-based applications. Microplasmas are low-emperature plasmas that feature microscale dimensions and a unique high-energy-density and a nonequilibrium reactive environment, which makes them promising for the fabrication of advanced nanomaterials and devices for diverse applications. Detailed characterization indicates the microplasma-enable controllable-designed growth of plasmonic nanomaterial with heterostructure effect, the providing enhanced charge transportation , adsorption ability or forster resonance energy transfer during Raman scattering. To understand the plasmonic effect, we use 3D confocal microRaman scattering study that shows that a large SERS volume was formed in the as-fabricated SERS-active substrates, leading to significant SERS properties of low limit of detection and high enhanced factor (EF) with the Rhodamine 6G (R6G) as the Raman probe. Furthermore, we also used the biomoleculars , medicines , and dyes as the target molecule. Our work not only provides environmentally friendly fabrication technique with strong potential for the design and growth of the nanostructure but also the fundamental insight of plasmonic nanostrutures for emerging applications including nanocataysis, sustainable energy, and biomedical imaging.

(Invited) Plasmonic Aerogels for Gas-Phase Photocatalytic Reactions

As a special form of material, aerogel has emerged as a promising type of photocatalyst. Owing to the large specific surface area and the developed pore texture, it would be suitable to drive various gas-phase reactions such as CO2 reduction and CH4 conversion. More importantly, the size of the fundamental building blocks in an aerogel, which is typically 5-20 nm, is approaching that of the noble metals with the surface plasmon resonance (SPR) effect. Innovated by Rolison and Niederberger(1, 2), aerogels with plasmonic effect have been extensively studied as photocatalysts for hydrogen evolution and dye degradation in liquid mediumThis talk then aims to introduce some of our recent results on the construction and evaluation of plasmonic noble metal/ceria composite aerogels, which cover the content from the synthesis to new applications. Modified synthesis methods are developed for the rational incorporation of plasmonic metal nanoparticles such as Ag and Au into an aerogel backbone in one step, which offers an alternative route to tune the composition and size of these nanoparticles, or even building single-atom composite aerogels in the conventional sol-gel methodology(3). When these plasmonic aerogel photocatalysts are applied for gas-phase CO2 reduction and non-oxidative CH4 coupling reaction, good performance is observed. The synergistic effect of plasmonic sensitizer and co-catalyst is discussed and is responsible for the performance enhancement. P. A. DeSario, J. J. Pietron, A. Dunkelberger, T. H. Brintlinger, O. Baturina, R. M. Stroud, J. C. Owrutsky and D. R. Rolison, Langmuir, 33, 9444 (2017). F. Rechberger and M. Niederberger, Nanoscale Horizons, 2, 6 (2017). M. Wu, C. Ouyang, Z. Ye, S. Li, Z. Hong and M. Zhi, ACS Applied Energy Materials, 5, 7335 (2022).

Effects of Oxygen Adsorption on the Optical Properties of Ag Nanoparticles.

Plasmonic metal nanoparticles are efficient light harvesters with a myriad of sensing- and energy-related applications. For such applications, the optical properties of nanoparticles of metals such as Cu, Ag, and Au can be tuned by controlling the composition, particle size, and shape, but less is known about the effects of oxidation on the plasmon resonances. In this work, we elucidate the effects of O adsorption on the optical properties of Ag particles by evaluating the thermodynamic properties of O-decorated Ag particles with calculations based on the density functional theory and subsequently computing the photoabsorption spectra with a computationally efficient time-dependent density functional theory approach. We identify stable Ag nanoparticle structures with oxidized edges and a quenching of the plasmonic character of the metal particles upon oxidation and trace back this effect to the sp orbitals (or bands) of Ag particles being involved both in the plasmonic excitation and in the hybridization to form bonds with the adsorbed O atoms. Our work has important implications for the understanding and application of plasmonic metal nanoparticles and plasmon-mediated processes under oxidizing environments.

One-pot synthesis of multipod Au-Cu nanocrystals with tunable branching for efficient photothermal treatment against multidrug-resistant bacteria

The plasmonic metal nanoparticle endowed with attractive localized surface plasmon resonance (LSPR) property is promising in the biomedical application. Herein, branched AuCu nanoalloys have been fabricated in one-pot, the morphology of which could be modified by altering the amine capping agent and thus obtaining monopods, tetrapods and pentapods nanostructure. Corresponding to nanoparticles with variable shape in aqueous solution, LPSR peaks were observed in the UV–vis extinction spectra, covering the visible region around 530 nm and the extended near-infrared (NIR) region at 780 nm and more than 1100 nm for AuCu nano-tetrapods and nano-pentapods respectively. The effective photothermal conversion is detected for the as-mentioned three nanostructures, among which AuCu nano-tetrapods and AuCu nano-pentapods achieved superb photothermal efficiency value under the 808-nm and 1064-nm laser irradiations, respectively, in consistence with their strong LPSR absorption wavelength around 780 nm and 1100 nm. Arising from such photothermal properties, the AuCu nano-tetrapods exhibited excellent antibacterial efficiency with minimal inhibitory concentration (MIC) of 29.3 μg mL−1 and facilitated to inhibit a wide range of multidrug-resistant bacteria.

Hybrid Bio-Nanocomposites by Integrating Nanoscale Au in Butterfly Scales Colored by Photonic Nanoarchitectures

Plasmonic metallic nanoparticles, like Au, can be used to tune the optical properties of photonic nanoarchitectures occurring in butterfly wing scales possessing structural color. The effect of the nanoscale Au depends on the location and the amount deposited in the chitin-based photonic nanoarchitecture. The following three types of Au introduction methods were compared regarding the structural and optical properties of the resulting hybrid bio-nanocomposites: (i) growth of Au nanoparticles inside the nanopores of butterfly wing scales by a light-induced in situ chemical reduction of HAuCl4 in aqueous solution containing sodium citrate, as a new procedure we have developed, (ii) drop-drying of the aqueous Au sol formed during procedure (i) in the bulk liquid phase, and (iii) physical vapor deposition of Au thin film onto the butterfly wing. We investigated all three methods at two different Au concentrations on the wings of laboratory-bred blue-colored male Polyommatus icarus butterflies and characterized the optical properties of the resulting hybrid bio-nanocomposites. We found that the drop-drying and the in situ growth produced comparable redshift in the spectral position of the reflectance maximum associated with the chitin-based photonic nanoarchitecture in the wing scales, while the 5 nm or 15 nm thick Au layers vacuum deposited onto the butterfly wing behaved like an optical filter, without inducing spectral shift. The in situ growth in the photonic nanoarchitecture under intense illumination produced uniform Au nanoparticles located in the pores of the biological template, which is more advantageous for further applications. An additional benefit of this method is that the Au nanoparticles do not aggregate on drying, like in the case of drop-drying of preformed Au nanoparticles from the citrate-stabilized sol.

Near-field enhancement by waveguide-plasmon polaritons in a nonlocal metasurface

Localized surface plasmons in metal nanoparticles are widely used in nano-optics to confine and enhance optical fields. It has been previously shown that, if the nanoparticles are distributed periodically, an additional enhancement can be achieved by coupling the localized surface plasmons to the diffraction orders of the lattice, forming surface lattice resonances. In this work, we study an even further improvement of the near-field enhancement by placing a metal-dielectric slab waveguide beneath the lattice of the particles to excite coupled waveguide-plasmon polaritons. These excitations can extend over many periods of the lattice, making the metasurface highly nonlocal. We numerically demonstrate that the approach can provide a significant extra increase in the near-field intensity—by a factor of 80 over that produced by a single-particle plasmon resonance and by 7 over the lattice-resonance enhancement. The described enhancement mechanism can be used to design extraordinarily efficient nonlocal optical metasurfaces for many applications, including surface-enhanced Raman spectroscopy, fluorescence spectroscopy, nonlinear optics, and solar energy harvesting.

Enhancing photovoltaic performance of carbon-based perovskite solar cells by introducing plasmonic Au NPs

The plasmonic property of metal nanoparticles could improve the photovoltaic performance of perovskite solar cells (PSCs). In this work, the plasmonic Au nanoparticles (Au NPs) was introduced into the SnO2 electron transport layer (ETL), improving the photovoltaic performance of perovskite solar cells (PSCs) based on carbon electrode by approximately 26.28 %. The device structure is the FTO glass/SnO2/perovskite (CH3NH3PbI3)/carbon electrode. By optimizing the volume of Au NPs, the photocurrent of PSCs increased from 18.49 mA cm−2 to 23.25 mA cm−2 by 25.74 %, and the power conversion efficiency (PCE) from 10.96 % to 13.84 % by 26.28 %. The improved performance of the device is due to the local surface plasmon resonance (LSPR) of Au NPs, which enhances the optical absorption in the perovskite layer and improves the conductivity of the electron transport layer (ETL). Fluorescence spectroscopy showed that PSCs containing Au NPs reduced the recombination of electron and hole between the interface of ETL and perovskite and could transmit charge faster than PSCs without Au NPs. These results indicate that the plasmonic metal nanoparticles can greatly improve the efficiency of PSCs.

Investigation of sunlight driven SPR assisted photocatalytic activity of Ag doped SnO2 nanoparticles

Photocatalysis triggered by visible light has emerged as a viable method for addressing environmental pollution and the energy crisis in our society. Numerous metal oxide semiconductors are transformed into visible light active photocatalysts by adopting some straightforward methods. One such efficient way of creating a visible light active photocatalyst is doping a pure semiconductor with plasmonic metal nanoparticles. Our work thoroughly investigates the photocatalytic properties of pure SnO2 nanoparticles (NP) and SnO2 doped with 1%, 3%, and 5% ‘Ag’ under sunlight. These samples are prepared using a straightforward sol–gel approach, followed by a hydrothermal procedure. To examine the different properties and morphology of the synthesized samples, several analytical tools, including UV–visible spectrometer, XRD, XPS, TEM, PL spectrometer and FTIR are used. Analysis of UV-visible absorbance spectra shows a noticeable narrowing of the band gap with increased ‘Ag’ doping. XRD analysis confirms the tetragonal structure of all samples. Methyl orange (MO) dye is used as an imitation of an organic pollutant to examine the photocatalytic activity under sunlight. When compared to pure SnO2 NP, every ‘Ag’ doped SnO2 NP sample exhibits a considerable improvement in the photodegradation of methyl orange. Analysis of PL spectra of SnO2 NPs doped with ‘Ag’ suggests that the major causes of this enhancement in photocatalysis are surface defects and the surface plasmon resonance (SPR) effect caused by ‘Ag’ doping. The scavenging test claims that the holes are the primary and the superoxide radicals are the secondary reactive species which are responsible for MO degradation under sunlight.