Wastewater treatment plants already draw on physical, chemical and biological technologies, but each approach has important limitations. Adsorption and membrane filtration can remove color effectively, yet they generally transfer contaminants into another phase rather than destroying them, creating concentrated waste and regeneration challenges. Coagulation can produce secondary sludge, while biological treatment may be slow or unreliable when confronted with complex, non-biodegradable compounds. Chemical oxidation methods can be powerful, but some require expensive reagents, elevated temperatures or pressures, acidic conditions, or additional treatment for unwanted by-products. Advanced oxidation processes improve on several of these weaknesses by generating short-lived oxidants, especially hydroxyl radicals, with an oxidation potential of about 2.80 volts relative to the normal hydrogen electrode. The review positions photocatalysis as a potentially more sustainable route because the energy-driving input can be sunlight or another light source, while the catalyst itself may be recovered and reused.

Photocatalysis begins when a semiconductor absorbs a photon with energy equal to or greater than its band gap. The absorbed energy promotes an electron from the valence band to the conduction band, leaving behind a positively charged hole. These electron-hole pairs must reach the material’s surface before they recombine, a loss process that wastes the absorbed light. At the surface, conduction-band electrons can reduce dissolved oxygen to superoxide radicals, while valence-band holes can oxidize water or hydroxide ions to form hydroxyl radicals. The resulting reactive oxygen species can break chromophore groups, open aromatic rings and progressively simplify large organic molecules. The review emphasizes that the efficiency of this sequence depends on pH, catalyst loading, starting dye concentration, light intensity, temperature and substances that scavenge reactive species. Decolorization alone is not enough to prove complete treatment; identifying intermediate products and demonstrating mineralization are essential for judging environmental performance.

Perovskites are attractive because their crystal structures can be engineered across a wide chemical range. Their general formula, ABX₃, describes a framework in which a larger ion occupies the A site, a smaller metal cation occupies the B site and an anion occupies the X site. In oxide perovskites, oxygen forms networks of corner-connected BO₆ octahedra. Substituting elements at the A, B or anion sites can alter the lattice, electronic states, band gap, surface chemistry and charge-carrier behavior. The reviewed systems span band gaps from about 1.06 to 5.31 electron volts, illustrating the breadth of possible light responses. Examples include SrTiO₃, valued for chemical stability; LaFeO₃, whose narrower band gap supports visible-light activity; BiFeO₃, whose ferroelectric and multiferroic characteristics can promote charge separation; and BaTiO₃, which can add piezoelectric effects when mechanical motion is present. These properties make perovskites more than passive light absorbers: they can be designed as platforms for directing electrons and holes toward different chemical tasks.

One of the strongest trends identified in the review is the movement from single perovskites toward doped materials and heterojunctions. Doping introduces a small amount of a foreign metal, rare-earth element or non-metal into the lattice. The added atoms can create intermediate energy levels, narrow the effective band gap and provide temporary charge-trapping sites. For example, the review describes Gd-doped potassium tantalate in which a concentration of 0.075 mole percent produced the most favorable combination of visible-light absorption and charge separation. Optical measurements showed a reduction in the estimated band gap from 4.78 electron volts for the undoped material to 4.68 electron volts at the optimum composition. Photoluminescence intensity also declined, a sign that fewer excited electrons and holes were recombining. Too much dopant, however, can reverse the benefit by creating recombination centers. This concentration dependence is a recurring lesson: more modification does not automatically mean more activity.

Heterojunctions take a different approach by coupling two or more semiconductors with complementary band structures. When the materials touch, their interfaces can create internal electric fields that guide photogenerated charges and reduce recombination. Type-II junctions separate electrons and holes spatially, although the transfer can weaken their oxidation and reduction power. Z-scheme and S-scheme architectures are designed to preserve the most energetic electrons and holes while allowing less useful carriers to recombine at the interface. The review highlights combinations such as BiFeO₃/TiO₂, in which the perovskite broadens visible-light absorption and titanium dioxide contributes stability and oxidative strength. Other systems combine perovskites with graphitic carbon nitride, reduced graphene oxide, carbon spheres, biochar or MXene materials. Carbon supports can adsorb pollutants, conduct electrons and make a powdered catalyst easier to immobilize or recover. In one cited example, a BiFeO₃-GdFeO₃ system achieved 98 percent methylene-blue degradation under sunlight, while a separate bismuth-vanadate composite completely removed Congo red in 10 minutes under its reported test conditions.

The chemistry of dye destruction can be illustrated by perovskite systems based on LaMnO₃ or Gd-modified potassium tantalate. Under illumination, electrons move into the conduction band and holes remain in the valence band. Electrons transferred to oxygen can generate superoxide, which participates in reactions that form hydrogen peroxide and ultimately hydroxyl radicals. At the same time, holes can oxidize water or hydroxide at the surface. Hydroxyl radicals and holes then attack dye molecules, including methylene violet, methylene blue or rhodamine B, breaking their chromophoric structures and producing smaller compounds. In a CuO/SmFeO₃ junction, band alignment directs electrons and holes toward different components, where oxygen reduction and direct dye oxidation proceed through complementary pathways. Such mechanistic details matter because the dominant reactive species can differ between materials. Scavenger experiments, band-edge measurements and product analysis are therefore needed to distinguish genuine photocatalytic mineralization from simple adsorption or fading caused by light.

How a perovskite is made can be just as important as what it is made from. The review surveys sol-gel, Pechini, co-precipitation, hydrothermal, solvothermal and microwave-assisted synthesis. Sol-gel processing can provide compositional uniformity, high surface area and control over particle morphology, although it may require long processing times and organic solvents. The Pechini route uses a polymeric metal-citrate network to improve stoichiometric control and phase purity. Co-precipitation offers high yield and economic feasibility, while hydrothermal and solvothermal processing can produce highly crystalline particles with controlled growth inside sealed vessels. Microwave heating reduces reaction times through rapid volumetric heating. Researchers also use X-ray diffraction to verify crystal phases and estimate crystallite size, infrared spectroscopy to examine bonds and oxygen vacancies, electron microscopy to inspect morphology and interfaces, diffuse-reflectance spectroscopy to estimate band gaps, photoluminescence to track recombination, X-ray photoelectron spectroscopy to determine chemical states and band alignment, and Brunauer-Emmett-Teller analysis to measure surface area and porosity. Together, these tools connect microscopic structure with treatment performance.

Despite impressive laboratory results, the review does not present perovskites as a ready-made industrial solution. Many reported systems work best under acidic conditions, often between pH 2 and 6, whereas real industrial effluents contain competing ions, suspended solids, fluctuating acidity and mixtures of pollutants. Most catalysts retain useful activity for three to five reuse cycles, but gradual losses remain common. Powder recovery, particle aggregation and the possibility of releasing catalyst components must be addressed before deployment. Halide perovskites can be particularly vulnerable to moisture, and lead-containing compositions raise clear concerns about toxicity and secondary contamination. The review therefore points toward stable oxide, bismuth-based and other lead-free double perovskites, along with protective coatings, magnetic recovery, immobilized reactors and standardized testing. Future studies will need to report energy consumption, catalyst lifetime, intermediate toxicity, complete product profiles and performance in authentic wastewater rather than only model dye solutions. Machine learning and computational modeling may help identify compositions and degradation pathways, but pilot-scale validation will determine whether these light-driven materials can move from promising chemistry to safe, durable and economically credible water treatment.

The chemical architecture of a dye helps determine how it responds to treatment. Azo compounds contain nitrogen–nitrogen double bonds, while anthraquinone, triphenylmethane, indigoid, xanthene and phthalocyanine dyes rely on different chromophore frameworks. These structures influence color, solubility, light stability and resistance to biological attack. Application categories, including acid, basic, direct, reactive, sulfur and vat dyes, also reflect how molecules interact with fibers and process chemicals. Consequently, a catalyst that rapidly removes one model dye may perform differently against another, and mixtures can introduce competition for reactive sites or light absorption.

Meaningful assessment therefore requires more than measuring the disappearance of visible color. Treatment studies should distinguish adsorption from chemical transformation and should examine whether aromatic intermediates remain after the chromophore is destroyed. Catalyst composition, crystal structure, particle morphology and surface characteristics are commonly linked to performance through diffraction, spectroscopic and microscopic analyses. Operational variables also matter: acidity, catalyst dose, pollutant concentration, irradiation conditions and temperature can alter reaction rates and reactive-species formation. For wastewater applications, these measurements should be paired with tests of reuse, stability and by-product toxicity. Such comparisons would help determine whether a perovskite system offers a genuine advantage over established oxidation, adsorption or biological processes under realistic treatment conditions.

Subject of Research: Perovskite photocatalysts for dye degradation in wastewater

Article Title: Emerging trends in perovskite based advanced photocatalysts for sustainable dye degradation from wastewater

Article References: Bhardwaj, P., Bughani, A., Maheshwari, J., Mohan, M., Zaidi, M. G. H., & Mehtab, S. (2026). Emerging trends in perovskite based advanced photocatalysts for sustainable dye degradation from wastewater. Discover Industrial Chemistry and Materials, 1(1), Article 16. https://doi.org/10.1007/s44508-026-00017-8

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00017-8

Keywords: Perovskites, Photocatalysis, Wastewater treatment, Dye pollution, Advanced oxidation, Heterojunctions, Solar remediation, Water purification, Emerging, trends, perovskite, based