The synthesis itself is strikingly economical. The researchers combined a minimal set of reagents in a single pot at just 100 degrees Celsius, avoiding the high-temperature furnaces, vacuum systems and template chemicals that often accompany the production of engineered chalcogenide nanomaterials. The team describes the route as green, and the modest thermal budget matters for more than convenience: the temperature at which the reaction bath is held appears to determine which crystalline phases nucleate, and therefore how the final powder behaves under illumination. By tuning that single parameter, the group could steer the material between single-phase and mixed-phase outcomes.

Characterization confirmed that the one-pot product was genuinely a composite of two sulfide phases rather than a contaminated single phase. X-ray diffraction revealed the coexistence of tetragonal In2S3 and monoclinic In6S7, with an average crystallite size of 70.98 nanometers. Scanning electron microscopy showed a microcrystalline morphology, while X-ray photoelectron spectroscopy ruled out the presence of indium-oxygen bonds, excluding In(OH)3 impurities that can complicate the interpretation of photocatalytic results in sulfide systems. That spectroscopic check is important because hydroxide contamination is a common artifact in aqueous synthesis and can mask or mimic catalytic activity.

Perhaps the most consequential structural finding came from gas adsorption measurements. Brunauer-Emmett-Teller analysis showed that the mixed-phase powder is mesoporous, with a mean pore size of 3.39 nanometers and a specific surface area of 45.59 square meters per gram. Porosity at this scale gives dye molecules in solution access to a large internal reaction surface, and the authors link this mesoporous architecture, together with an optimal optical band gap, to the material’s strong performance as a photocatalyst. In photocatalysis, surface area and light absorption must work in tandem; a material that absorbs light well but offers little accessible surface, or vice versa, wastes part of its potential.

To test performance, the team chose two structurally related xanthene dyes, Rhodamine B and Sulforhodamine B, both of which serve as common model pollutants and, in the case of Sulforhodamine B, as a compound of environmental concern. Comparative experiments against single-phase indium sulfide samples synthesized at bath temperatures of 30 and 70 degrees Celsius produced a clear hierarchy. The lowest-temperature sample managed only about 14.3 percent degradation, the 70-degree sample reached 63.1 percent, and the mixed-phase material prepared at 100 degrees achieved 66.5 percent. The trend suggests that both crystallite quality and phase composition improve as the synthesis temperature rises, with the mixed-phase sample capturing the best of both.

Understanding why the mixed-phase material wins required probing the chemistry happening on its surface under light. When a photocatalyst absorbs a photon, it generates electron-hole pairs that can react with oxygen and water to produce reactive oxygen species, the chemical agents that actually tear dye molecules apart. Chandran and colleagues ran scavenging experiments, adding chemicals that selectively neutralize particular radical species, to determine which agents dominate the degradation of each dye. The results revealed that the two dyes, despite their structural similarity, are broken down by different mechanisms depending on the light source used.

Under halogen irradiation, the degradation of Sulforhodamine B was governed primarily by superoxide radical anions, O2 radical anions, which the scavenging data identified as controlling the rate-determining step of the reaction. Under natural sunlight, the degradation of Rhodamine B drew on a broader toolkit: both superoxide radical anions and hydroxyl radicals contributed significantly to the breakdown process. This mechanistic split is more than an academic curiosity. It indicates that the mixed-phase catalyst can operate through different oxidative pathways depending on the illumination available, which is directly relevant to real-world deployment where sunlight, not laboratory lamps, is the practical light source.

The work builds on a line of earlier research from the same group, which had previously examined how pore size influences the photocatalytic breakdown of Sulforhodamine B in mesoporous In2S3 and developed template-free aqueous routes to microporous indium sulfide for water purification. It also fits into a broader international effort to exploit indium sulfide nanostructures, from sulfur-vacancy nanotubes for nitrogen fixation to beta-In2S3 quantum dots and nanoflowers for antibiotic and dye degradation. What distinguishes the new study is its focus on phase coexistence as a design variable rather than a defect to be eliminated, and its demonstration that a single, inexpensive synthesis step can deliver that coexistence reproducibly.

The practical implications are considerable. Textile and dyeing industries discharge large volumes of colored, chemically persistent wastewater, and conventional treatment plants are often poorly equipped to destroy these molecules rather than simply transfer them to a sludge phase. Photocatalysts that can run on sunlight offer a route to genuine mineralization of such pollutants. A material that can be synthesized at 100 degrees Celsius with minimal reagents, no templates and no oxygen contamination lowers the cost barrier substantially compared with routes that demand high-temperature annealing or elaborate precursor chemistry. The Kerala team’s work was supported by the Directorate of Environment and Climate Change, Government of Kerala, reflecting regional interest in applied water-treatment technology.

There remain, of course, the usual caveats that separate a laboratory result from a deployed technology. The reported efficiencies, while clearly superior to the single-phase controls, were measured on model dye solutions under defined illumination, and questions of catalyst recovery, recyclability over many cycles, and performance in real effluents will need attention before mixed-phase indium sulfide powders see industrial use. Indium is also a relatively scarce element, which argues for efficient material use and eventual recovery strategies. Nevertheless, the study makes a persuasive case that in semiconductor photocatalysis, the phase diagram itself is a tool. By holding a reaction bath at the right temperature, the researchers coaxed two sulfide phases into coexisting within one powder, and that coexistence, paired with mesoporosity and a favorable band gap, translated into measurably better pollutant destruction. For a field searching for greener, cheaper catalysts, the message is that sometimes the most productive thing to do with a pure phase is to share the crystal lattice with another one.

Subject of Research: Green synthesis of mixed-phase indium sulfide nanostructures for photocatalytic dye degradation

Article Title: Mixed-phase indium sulfide via one-pot synthesis: superior dye degradation over single-phase

Article References: Chandran, N., Abraham, R., & Jayakrishnan, R. (2026). Mixed-phase indium sulfide via one-pot synthesis: superior dye degradation over single-phase. Applied Nanoscience, 16(5), Article 56. https://doi.org/10.1007/s13204-026-03190-6

Image Credits: AI Generated

DOI: 10.1007/s13204-026-03190-6

Keywords: indium sulfide, mixed-phase nanomaterials, photocatalysis, dye degradation, mesoporous materials, superoxide radical, hydroxyl radicals, green synthesis, water purification, In2S3, In6S7, reactive oxygen species

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