The achievement matters because photocatalysis, the use of light-activated semiconductors to drive chemical reactions that shred organic contaminants, has long been hampered by an uncomfortable trade-off. Titanium dioxide, the workhorse of the field, is cheap and stable but absorbs only ultraviolet light, a sliver of the solar spectrum. Tantalum pentoxide suffers from the same limitation: it is a wide-bandgap oxide with excellent charge-transport properties and chemical robustness, yet it largely ignores the visible photons that make up most of the sunlight reaching the Earth’s surface. Closing that gap is one of the central challenges of environmental photocatalysis, and the new study offers a layered answer.

The researchers built their catalyst films in two stages. First, they used a hydrothermal process to produce the components and then employed doctor blading, a technique borrowed from industrial coating, to cast the films onto substrates. Platinum and ruthenium were introduced afterward by wet impregnation, allowing the noble metals to anchor onto the composite. By systematically varying the proportion of indium sulfide from 25 to 75 weight percent, the team could tune the composition and identify the recipe that delivered the best combination of light harvesting and charge handling.

Characterization told a compelling story. X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were all brought to bear on the films. The optimized composite, containing 75 weight percent indium sulfide, exhibited a narrowed bandgap of roughly 2.14 electron volts, comfortably within the visible-light regime, along with increased absorption across the visible spectrum. Electron microscopy revealed uniformly distributed plate-like indium sulfide particles resting on the tantalum oxide framework, and the composite also possessed a larger surface area than its counterparts, providing more active sites for reactions.

The most intriguing findings came from the spectroscopy. X-ray photoelectron spectra showed binding energy shifts that pointed to strong electronic interactions between the platinum and ruthenium species and the tantalum pentoxide support. The analysis also revealed the formation of partially oxidized metal species and oxygen vacancies in the oxide lattice. These defects are far from flaws in this context; they act as effective charge-trapping sites, catching the electrons and holes that light excites inside the semiconductor before they can recombine and waste the absorbed energy as heat. In photocatalysis, keeping those charge carriers alive long enough to do chemistry is half the battle.

When the films were immersed in Rhodamine B solution and illuminated with visible light, the performance followed directly from that design. The optimized indium sulfide/platinum,ruthenium-modified tantalum pentoxide composite achieved up to 92.0 percent dye removal after 120 minutes, and the researchers report high recyclability, an essential quality for any catalyst hoped to leave the laboratory. Scavenger experiments, in which specific chemicals are added to neutralize particular reactive species, revealed that superoxide radicals were the dominant actors in the degradation. That result is significant because it indicates that electrons leaving the catalyst are efficiently transferred to dissolved oxygen molecules, converting them into the aggressive radical species that attack and dismantle the dye.

According to the authors, the enhanced performance arises from the interplay of three mechanisms working in concert. The heterojunction formed between indium sulfide and the modified tantalum oxide creates an internal electrical field that drives photogenerated charges in opposite directions, suppressing recombination. The platinum and ruthenium dopants further improve charge separation by acting as electron sinks with favorable electronic structures. And the defect-mediated electronic interactions, including the oxygen vacancies and partially oxidized metal species identified by photoelectron spectroscopy, provide the trapping sites that shepherd charges toward the surface reactions that generate superoxide. It is, in effect, a division of labor in which every component handles a different bottleneck of the photocatalytic process.

The broader context makes the work timely. Rhodamine B and related dyes are persistent, colored, and often toxic constituents of textile wastewater, and conventional treatment plants struggle to remove them completely. Advanced oxidation processes, including photocatalysis, have emerged as promising complements because they can mineralize organic pollutants rather than merely transferring them to another phase. Reviews of the field have emphasized that heterojunction photocatalysts, in which two semiconductors with staggered band structures are combined, are among the most active research directions, and this study adds a refined example that also leverages noble-metal modification and defect engineering simultaneously.

The choice of tantalum pentoxide as the oxide partner is deliberate. The material has a distinguished record in catalysis, supporting platinum nanoparticles in electrocatalysts and serving as a precursor for visible-light absorbers such as barium tantalum oxynitride. Its conduction band position is favorable for reducing oxygen, and its stability resists photocorrosion. Pairing it with indium sulfide, a narrow-gap visible absorber, covers the weakness of each partner: the sulfide brings the light absorption, while the oxide and its metal dopants bring the charge management and stability. The resulting films, cast by a scalable coating method rather than a batch slurry, also point toward practical reactor designs in which the catalyst can be recovered and reused without filtration.

For a field that often advances one parameter at a time, the study demonstrates the payoff of co-designing composition, defect chemistry, and interface structure in a single system. The researchers suggest that the rational integration of indium sulfide with platinum,ruthenium-modified tantalum pentoxide represents a successful general approach for altering electronic structure and improving charge carrier dynamics in oxide-based photocatalysts. If the strategy transfers to other oxide-sulfide pairings and other pollutants, dye-laden industrial wastewater may one day meet its match in a thin film powered by nothing more than sunlight and cleverly arranged atoms. The work was supported by Thailand Science Research and Innovation, with synchrotron-based characterization provided through the SUT-NANOTEC-SLRI Joint Research Facility.

Subject of Research: Visible-light photocatalytic degradation of Rhodamine B using Pt,Ru-codoped In2S3/Ta2O5 heterostructured films

Article Title: Novel Pt,Ru-Codoped In₂S₃/Ta₂O₅ heterostructured films for the effective enhancement of visible-light photocatalytic degradation of Rhodamine B

Article References: Boonprakob, N., Huatong, N., Chanlek, N., Udonpan, K., Sae-Kung, C., & Zhao, C. (2026). Novel Pt,Ru-Codoped In₂S₃/Ta₂O₅ heterostructured films for the effective enhancement of visible-light photocatalytic degradation of Rhodamine B. Journal of Nanoparticle Research, 28(10), Article 246. https://doi.org/10.1007/s11051-026-06754-3

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06754-3

Keywords: photocatalysis, In2S3, Ta2O5, heterostructure, platinum, ruthenium, Rhodamine B, dye degradation, oxygen vacancies, superoxide radicals, visible light, wastewater treatment