Silver-Based Ternary Photocatalysts Push Solar Energy and Water Cleanup Forward

Turning sunlight into clean fuel and using the same trick to destroy toxic pollutants has long been one of chemistry’s most seductive promises. A new open-access review published in Advances in Industrial and Engineering Chemistry by Rama Krishna Chava, Basavaiah Chandu, Young-Ae Lee, Nagaprasad Puvvada and Misook Kang argues that a surprisingly elegant family of materials, ternary photocatalysts built entirely from silver-containing components, may be the key to making that promise real. The review, published on 27 March 2025, pulls together the synthesis strategies, charge-transfer physics and performance data behind these composites, and it arrives at a striking conclusion: when metallic silver nanoparticles are deliberately woven between two silver-based semiconductors, the resulting three-component systems can harvest visible and even near-infrared light, separate charge carriers with remarkable efficiency, and resist the photocorrosion that has plagued single-component silver catalysts for years.

The underlying problem the review addresses is as old as semiconductor photocatalysis itself. Since the landmark 1972 demonstration of TiO2 photoelectrochemistry, researchers have known that a photocatalyst must absorb light, generate electron-hole pairs, and shuttle those carriers to its surface before they recombine and waste their energy as heat. In practice, recombination wins far too often. Most conventional photocatalysts absorb only a sliver of the solar spectrum, typically in the ultraviolet, and the carriers that are generated tend to annihilate each other before they can drive useful reactions such as hydrogen evolution, carbon dioxide reduction or the breakdown of organic dyes. The authors frame the entire field around this bottleneck: the overall efficiency of any semiconducting photocatalyst is governed by how much light it harvests and how effectively it separates the charges that light creates.

Silver-based semiconductors have long stood out as candidates for solving the light-harvesting half of the problem. Compounds such as Ag3PO4 with a bandgap of about 2.55 electron volts, AgBr at 2.57 electron volts, AgI at 2.7 electron volts, Ag2O at 1.3 electron volts, Ag2S at 1.05 electron volts and Ag2CO3 at 2.4 electron volts all absorb visible light, and their filled d10 electronic configurations contribute to strong redox power. Metallic silver nanoparticles add another weapon: the localized surface plasmon resonance, or LSPR, a collective oscillation of conduction electrons that produces intense visible-light absorption and can inject energetic hot electrons into adjacent semiconductors. Under illumination, silver nanoparticles accelerate electron transfer and suppress recombination, which is precisely what a photocatalyst needs. Yet single-component silver photocatalysts fail in a frustrating way. Their photoinduced charges recombine rapidly, and during reactions the silver ions are photoreduced to metallic silver, a photocorrosion process that blocks active sites and destroys reusability.

The standard fix has been to build heterojunctions, pairing two semiconductors with aligned band structures so that electrons and holes migrate away from each other across the interface. The review walks through the classical taxonomy. In a type-I heterojunction, both carriers funnel onto the same semiconductor, which does nothing for spatial charge separation. In a type-II heterojunction, electrons move from the higher conduction band to the lower one while holes migrate in the opposite direction, achieving genuine separation but at the cost of redox power, because the reactions end up occurring on bands with weaker oxidizing or reducing ability. Type-III junctions have such staggered, non-overlapping bands that no transfer occurs at all. A more sophisticated option is the p-n heterojunction, in which diffusion of electrons and holes across the interface before illumination creates an internal electric field that then drives carriers in opposite directions under light. The most celebrated design, however, is the Z-scheme, proposed by Allen Bard and colleagues in 1979, in which the conduction-band electrons of one photocatalyst recombine with the valence-band holes of the other, deliberately sacrificing the weakest carriers so that the strongest electrons and holes survive to drive reduction and oxidation reactions with full redox power.

What makes the new review distinctive, according to the authors, is that it is the first comprehensive survey restricted to ternary heterostructures in which every component is silver-based, spanning silver metal, silver oxides and silver sulfides. The central insight is architectural: metallic silver nanoparticles do double duty as plasmonic light absorbers and as electron mediators that stitch two semiconductors into an all-solid-state Z-scheme. In such a system, electrons from the conduction band of one semiconductor recombine with holes from the other through the silver bridge, an Ohmic contact with minimal resistance. This eliminates the weaknesses of older liquid-phase Z-schemes, which relied on dissolved electron acceptor-donor pairs such as IO3-/I- or Fe3+/Fe2+. Those mediators suffer from backward reactions, poor stability across pH ranges and incompatibility with pollutant degradation, since dye molecules can interfere with the mediator’s own redox chemistry. A solid silver conductor sidesteps all of that while shortening the charge-separation distance dramatically.

The experimental case studies the review compiles are impressive in their specificity. A Ag3PO4/AgBr/Ag composite, made by ion exchange followed by photoreduction, degraded methyl orange and methylene blue dyes in just eight minutes, with the anchored silver nanoparticles boosting visible-light harvesting through plasmon resonance. A Ag3VO4/AgBr/Ag plasmonic photocatalyst, prepared by in situ anion exchange between Ag3VO4 and potassium bromide followed by photoreduction, achieved 96.5 percent degradation of Rhodamine B in roughly fifteen minutes, with plasmon-induced electrons flowing to the conduction band of AgBr and onward to Ag3VO4, where they generated oxygen radicals that attacked the dye molecules. In the Ag/Ag2S/Ag3PO4 system, the conduction band of Ag2S sits above that of Ag3PO4, so electrons flow downhill to Ag3PO4 while holes migrate the other way, producing an efficient type-II-like separation augmented by the silver component.

One-dimensional architectures add further refinement. Li and colleagues used Ag2CO3 nanorods as templates, converting them first into Ag2CO3/Ag heterostructures by photoreduction and then into Ag2CO3/Ag/AgBr core-shell nanorods through an ion-exchange reaction with cetyltrimethylammonium bromide. The amount of AgBr in the final catalyst could be tuned simply by adjusting the CTAB precursor, and the optimized core-shell rods showed excellent visible-light degradation of Rhodamine B and methyl orange through a Z-scheme pathway mediated by the silver core. A related anion-exchange route produced Ag2MoO4/Ag/AgBr cubes in which the silver nanoparticles served simultaneously as plasmonic antenna, electron sink and Z-scheme mediator, suppressing photocorrosion and delivering 28.5 percent Rhodamine B degradation within forty minutes. Perhaps most striking is the Ag2S/Ag/Ag3VO4 nanocomposite reported by the review’s own authors, assembled through hydrothermal synthesis and chemical reduction, which evolved hydrogen at a stable rate of 6.64 millimoles per gram per hour under an all-solid-state Z-scheme mechanism.

The performance ceiling keeps rising. A plasmonic p-n heterojunction, Ag/Ag2S/Ag2MoO4, synthesized hydrothermally, extends light absorption into the near-infrared and degraded Rhodamine B, methylene blue, tetracycline and hexavalent chromium at efficiencies of 99, 100, 83 and 77 percent respectively under visible light, retaining more than 50 percent activity even under NIR irradiation. In that system, Ag2S acts as a visible-to-near-infrared active semiconductor, the p-n junction between Ag2S and Ag2MoO4 separates carriers through an internal field, and the silver nanoparticles act as an electron sink that prevents recombination. Meanwhile, a Ag2Mo2O7@AgBr-Ag rod-like heterostructure degraded 45 percent of methylene blue in five minutes and 97.8 percent in thirty minutes, with plasmonic hot electrons cascading from silver through AgBr to Ag2Mo2O7 for superoxide radical generation.

The review’s forward-looking section identifies the remaining weaknesses candidly: relatively low surface area and persistent photochemical corrosion still separate laboratory results from industrial deployment. The authors see carbon integration as the most promising remedy. Loading a Ag2O/Ag3VO4/AgVO3 ternary composite onto functionalized graphene oxide, at an optimal GO content of about 1.2 weight percent, improved charge mobility, added abundant adsorption sites through pi-pi interactions with dye molecules, protected the silver components from photocorrosion and even shaped the catalyst morphology. Reduced graphene oxide served a similar transmission role in Ag2MoO4/Ag/AgBr composites, and a Z-scheme Ag/g-C3N4-Ag-Ag3PO4 photocatalyst used silver’s plasmon effect to mediate charge separation for simultaneous hydrogen evolution and antibiotic degradation. A quaternary g-CN/Ag/Ag3PO4-AgPd system extended the concept to formaldehyde dehydrogenation. Taken together, the evidence assembled in this review suggests that cheap, low-toxicity, easily synthesized silver ternary composites, especially when armored with carbon supports, are edging closer to the durable, broad-spectrum, high-efficiency photocatalysts that real-world water treatment and solar fuel production demand.

Subject of Research: Design of silver-based ternary photocatalysts for solar energy conversion and environmental remediation

Article Title: Advances in designing Ag-based ternary photocatalysts for energy and environmental remediation applications

Article References: Chava, R. K., Chandu, B., Lee, Y.-A., Puvvada, N., & Kang, M. (2025). Advances in designing Ag-based ternary photocatalysts for energy and environmental remediation applications. Advances in Industrial and Engineering Chemistry, 1(1), Article 4. https://doi.org/10.1007/s44405-025-00003-2

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00003-2

Keywords: photocatalysis, silver nanoparticles, ternary nanocomposites, Z-scheme, surface plasmon resonance, charge separation, hydrogen evolution, pollutant degradation, environmental remediation, solar fuels, graphene oxide, heterojunction