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. 2025 Jul 28;15(15):1159.
doi: 10.3390/nano15151159.

Catalytically Active Oxidized PtOx Species on SnO2 Supports Synthesized via Anion Exchange Reaction for 4-Nitrophenol Reduction

Izabela Ðurasović  1 , Robert Peter  2 , Goran Dražić  3 , Fabio Faraguna  4 , Rafael Anelić  4 , Marijan Marciuš  5 , Tanja Jurkin  6 , Vlasta Mohaček Grošev  1 , Maria Gracheva  7 , Zoltán Klencsár  7 , Mile Ivanda  1 , Goran Štefanić  1 , Marijan Gotić  1
Affiliations

Catalytically Active Oxidized PtOx Species on SnO2 Supports Synthesized via Anion Exchange Reaction for 4-Nitrophenol Reduction

Izabela Ðurasović et al. Nanomaterials (Basel). .

Abstract

An anion exchange-assisted technique was used for the synthesis of platinum-decorated SnO2 supports, providing nanocatalysts with enhanced activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). In this study, a series of SnO2 supports, namely SnA (synthesized almost at room temperature), SnB (hydrothermally treated at 180 °C), and SnC (annealed at 600 °C), are systematically investigated, all loaded with 1 mol% Pt from H2PtCl6 under identical mild conditions. The chloride ions from the SnCl4 precursors were efficiently removed via a strong-base anion exchange reaction, resulting in highly dispersed, crystalline ~5 nm cassiterite SnO2 particles. All Pt/SnO2 composites displayed mesoporous structures with type IVa isotherms and H2-type hysteresis, with SP1a (Pt on SnA) exhibiting the largest surface area (122.6 m2/g) and the smallest pores (~3.5 nm). STEM-HAADF imaging revealed well-dispersed PtOx domains (~0.85 nm), while XPS confirmed the dominant Pt4+ and Pt2+ species, with ~25% Pt0 likely resulting from photoreduction and/or interactions with Sn-OH surface groups. Raman spectroscopy revealed three new bands (260-360 cm-1) that were clearly visible in the sample with 10 mol% Pt and were due to the vibrational modes of the PtOx species and Pt-Cl bonds introduced due the addition and hydrolysis of H2PtCl6 precursor. TGA/DSC analysis revealed the highest mass loss for SP1a (~7.3%), confirming the strong hydration of the PtOx domains. Despite the predominance of oxidized PtOx species, SP1a exhibited the highest catalytic activity (kapp = 1.27 × 10-2 s-1) and retained 84.5% activity for the reduction of 4-NP to 4-AP after 10 cycles. This chloride-free low-temperature synthesis route offers a promising and generalizable strategy for the preparation of noble metal-based nanocatalysts on oxide supports with high catalytic activity and reusability.

Keywords: 119Sn Mössbauer; 4-nitrophenol; Dowex 550; SnO2; XPS; anion exchange; catalyst; platinum.

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Conflict of interest statement

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Anion exchange synthesis of SnA, SnB, and SnC supports.
Figure 2
Figure 2
Platinum (H2PtCl6) was added to the three distinct SnO2 supports (SnA, SnB, and SnC) in the same way and in an identical amount—1 mol% Pt relative to the amount of SnO2 support.
Figure 3
Figure 3
Rietveld refinements of samples SP1a, SP1b, and SP1c.
Figure 4
Figure 4
STEM DF image at high magnification, with arrows pointing towards PtOx nanoparticles (a); STEM BF image at high magnification (b); a high-resolution image with a SAED image in the inset; the powder patterns are indexed to SnO2 (cassiterite) (c); a high-resolution BF/STEM image of several SnO2-NPs with clearly visible lattice fringes (d).
Figure 5
Figure 5
STEM image of the SP1a sample (a) and corresponding EDXS elemental mapping images of Sn L edge (b), Pt M edge (c), O K edge (d), and superposition of Sn L, Pt M, and O K edges (e). The EDXS spectrum in (f) confirms the presence of platinum and contains a small amount of chloride, as shown in the table. The asterisk * represents manually added Pt as a trace element.
Figure 6
Figure 6
STEM DF image at high magnification of the sample with 10 mol % Pt (the SP10a sample) (a), and size distributions of the platinum particles calculated using the normal and lognormal functions (b) from the image in (a).
Figure 7
Figure 7
TGA-DTG-DSC thermograms (black–blue–red curves) of SnA (top), SnB (middle), and SnC (bottom) supports recorded in nitrogen atmosphere up to 1000 °C.
Figure 8
Figure 8
Isotherms of adsorption of nitrogen (N2) (red line, squares) and desorption (blue line, triangles) for the SnA–C and SP1a–c supports, together with the determined BET surface areas. The corresponding pore volume distribution provides information about the porosity of the material.
Figure 8
Figure 8
Isotherms of adsorption of nitrogen (N2) (red line, squares) and desorption (blue line, triangles) for the SnA–C and SP1a–c supports, together with the determined BET surface areas. The corresponding pore volume distribution provides information about the porosity of the material.
Figure 9
Figure 9
XPS spectra of samples SP1a–c, measured around Sn 3d (left panel), Pt 4f (middle panel), and O1s (right panel) core levels.
Figure 10
Figure 10
Visual representation of the supports and samples that were analyzed using Raman spectroscopy and shown in Figure 11.
Figure 11
Figure 11
Raman spectra (532 nm excitation) for supports and samples: (a) SnA and SP1a, (b) SnB and SP1b, and (c) SnC and SP1c.
Figure 12
Figure 12
Room-temperature 119Sn Mössbauer spectra (dots) of the SP1a–c samples along with the envelope (solid line) of the Lorentzian quadrupole doublet fitted. The fit residual is shown below the spectra.
Figure 13
Figure 13
Time-dependent catalytic reduction process of 4-nitrophenol (4-NP) to 4 aminophenol (4-AP) using platinum-decorated SnO2 samples (SP1a, SP1b, and SP1c). The insets show the ln(At/A0) plot versus the reaction time and the calculated values of the rate constants (kapp in s−1) derived from the slopes of the linear segments.
Figure 14
Figure 14
Reusability test of the SP1a sample for 10 cycles.
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