www.nature.com/scientificreports OPEN Silver decorated CeO2 nanoparticles for rapid photocatalytic degradation of textile rose bengal dye G. Murugadoss1*, D. Dinesh Kumar1, M. Rajesh Kumar2*, N. Venkatesh3 & P. Sakthivel3 High quality silver (Ag) decorated CeO2 nanoparticles were prepared by a facile one-step chemical method. The samples were characterized by X-ray difraction (XRD), scanning electron microscopy (SEM), High resolution transmission electron microscopy (HR-TEM), fourier transform infrared spectrometer (FT-IR), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), UV–Visible absorption (UV–Vis), photoluminescence (PL) and thermogravimetric analysis. The decoration of Ag on CeO2 surface was confrmed by XRD, EPR and HR-TEM analysis. Harmful textile pollutant Rose Bengal dye was degraded under sunlight using the novel Ag decorated CeO2 catalyst. It was found that great enhancement of the degradation efciency for Ag/CeO2 compared to pure CeO2, it can be ascribed mainly due to decrease in its band gap and charge carrier recombination rate. The Ag/CeO2 sample exhibited an efcient photocatalytic characteristic for degrading RB under visible light irradiation with a high degradation rate of 96% after 3 h. With the help of various characterizations, a possible degradation mechanism has been proposed which shows the efect of generation of oxygen vacancies owing to the decoration of Ag on the CeO2 surface. Metal oxide nanoparticles have been considered in more consideration due its attractive applications including energy conversion, storage, solar fuel, photocatalytic and medical. Particularly, these metal oxides have been successfully used for wastewater management and water splitting. Tey have additionally been used for a wide scope of chemical redox reactions, for example, the mineralization of natural contaminations in wastewater 1,2. Te preparation of semiconductor metal oxide nanoparticles with diferent shapes and sizes has been of interest 3,4 for application in cutting edge oxidation procedures . Various transition metal oxides such as TiO2, NiO, CuO, ZnO and BiVO4 have been have been widely examined as photocatalysts for photocatalytic hydrogen produc- tion and color removal from the textile wastewater5–10. Apart from the transition metal oxides, rare earth oxides have been paid more attention due to its interesting electronic, optical and catalytic properties. As one of the most signifcant earth oxides, ceria (CeO2) has fascinated in more consideration for its promising application in photocatalytic dye degradation, solid oxide fuel cells, electrochemical sensor, ultraviolet flter, supercapacitor, 11,12 solar cells and optical materials . CeO2 is a n-type semiconductor metal oxide, it has a few properties like 13–17 TiO2, for example, chemical inactivity, cheap, photo stability and non-toxicity . For the past one decade, color removal of organic textile dyes using suitable catalyst is an emerging target for wastewater management 18–20. Besides, rose bengal (RB) dyes are widely used in textile, plastic, printing and cosmetic industries. But RB dyes are highly soluble in water, which commonly pollutes water and highly toxic to the living organisms21,22. Terefore, it is highly essential the removal of toxic dye from water. Photocatalyst is one of a most common cost-efective method for decompose textile-dyes from water using efcient nanocatalyst. To improve creation of active species in CeO2, various modifcations were made. Among the modifcations, incorporation or decoration of metal ions like silver (Ag) is an attractive method which enhanced the optical and catalytic properties of metal oxides. Such enhancement of photocatalytic behavior was obtained because of several factors such as tuning size, improved surface to volume ratio, morphology, band gap and various types 23 24 of defects . Dawoud et al. observed that Ag doped ZrO2 nanoparticles are efectively degraded the RB dye in visible light irradiation because of the surface area, band gap and porosity. Similar degradation efect has been 1Centre for Nanoscience and Nanotechnology, Sathyabama Institute of Science and Technology, Chennai, Tamil Nadu 600119, India. 2Institute of Natural Science and Mathematics, Ural Federal University, Yekaterinburg 620002, Russia. 3Department of Nanoscience and Technology, Bharathiar University, Coimbatore, Tamil Nadu 641046, India. *email: [email protected]; [email protected] Scientifc Reports | (2021) 11:1080 | https://doi.org/10.1038/s41598-020-79993-6 1 Vol.:(0123456789) www.nature.com/scientificreports/ observed by Ziashahbi et al.25 using Ag decorated ZnO hybrid nanostructures against methylene blue under visible light. In this study, pure and Ag decorated CeO2 nanoparticles have been synthesized and characterized using experimental techniques. Crystallography, microstructure, optical and magnetic properties of the nanoparticles were systematically analysed. Photocatalytic behaviour of the pure CeO 2 and Ag decorated CeO 2 nanoparticles were evaluated by photodegradation of RB dye under visible-light irradiation. Materials and methods Synthesis of pure CeO2 and Ag decorated CeO2 nanoparticles. All chemicals were used without further purifcation with analytical grade reagent. To synthesis of Ag doped CeO2 nanoparticles, 4.3 g (0.2 M) of Ce (NO3)3·6H2O in 50 mL of deionized water and 50 ml of 0.5 g polyvinylpyrrolidone (PVP; MW:40,000) were mixed under stirring at 80 °C. Ten, 1 M of sodium hydroxide (NaOH) was added drop by drop into the above solution. Afer 1 h, 0.2 M of 1.7 g Ag(NO3) in 50 mL deionized water was added into the above solution. Subse- quently, that the white color solution was transformed into dark brown color solution indicates the decoration of Ag on the surface CeO2 nanoparticles. Afer 2 h stirring, the obtained brown color colloidal was purifed by washing with deionized water and acetone with several times to remove impurities. Te resultant powder sam- ples were dried in an oven at 120 °C for 4 h. Following the same procedure, pure CeO 2 nanoparticles was synthe- sized without adding the silver nitrate. Te growth mechanism of Ag decorated CeO 2 is demonstrated in Fig. 1a. Characterization. Structural information of the pure and doped CeO 2 was studied by powder X-ray difrac- tion (XRD) pattern using Rigaku miniFlex IIC difractometer with Cu Kα radiation (λ = 1.54060 Å). Morphol- ogy of the powder samples and microstructural information were performed using scanning electron micros- copy (SEM, TESCAN, VEGASEM) and HR‒TEM (JEOL 3010) microscopy. Functional groups of molecules presented in the surface of the samples were investigated by FT-IR using an AVATOR 360 spectrometer. Chemi- cal state of the compounds studied using X-ray photoelectron spectroscopy with an Omicron Nanotechnology Te chemical state in the nanocomposites was investigated by X-ray photoelectron spectrometer (XPS) using an ESCA + Omicron XPS system with a Mg-Kα source and photon energy of 1486.7 eV. Free radical informa- tion of the samples was studied by Electron paramagnetic spectroscopy (EPR) using Bruker EMX Plus Electron spectrometer. Optical properties of the samples were investigated using Varian Carry 5000 scan UV–Vis double beam spectrometer. Termal stability and phase transition of the sample was evaluated by thermogravimetric and diferential thermal analysis (TG–DTA) using DST Q600 20 thermometer with heating rate of 10°/min. Photocatalytic study. Photodegradation of rose bengal dye was studied using pure CeO2 and Ag deco- rated CeO2 nanoparticles in aqueous medium under sun light. For the photocatalytic reaction, 20 mg of pho- tocatalyst was dispersed into 50 mL rose bengal dye solution, the concentration of dye was used as 0.2 g/L. Te resultant solution was stirred in dark place for 1 h before the light irradiation. Ten the solution was irradiated for 3 h under sun light. To evaluate degradation performance, the irradiated solution takes out in certain time interval and it was centrifuged at 4000 rpm for 20 min. Finally, the degradation efciency of the reacted solution was determined using UV–Vis absorption spectroscopy. Te degradation study was performed under 1180 watts per square meter light intensity. Te light intensity was measured using the fux meter. Results and discussion Structural properties of CeO2 and Ag-CeO2 nanoparticles. Te XRD patterns of pure and Ag deco- rated CeO2 nanoparticles are shown in Fig. 1b. Te pure nanoparticles show well–defned cubic structure of CeO2 (Fig. 1b) with the characteristic plane of (1 1 1) orientation. Te obtained result is well matched with standard JCPDS data (fle no. 34-0394). In the case of Ag incorporated CeO2 nanoparticles, crystalline Ag peaks are obtained along CeO2 peaks with the primary characteristic of Ag (1 1 1) plane. Te attained Ag peaks are well matched with cubic structure of Ag (JCPDS fle no. 87-0717). Moreover, there is no obvious peak shifs observed in CeO2 pattern by addition of Ag which reveals that Ag is presented on surface rather occupied in the interstitial or vacancy sites of CeO 2. Te estimated average crystallite size of pure CeO 2 nanoparticle is 8.1 ± 1 nm and the size decreased to 6.5 ± 1 nm for the Ag incorporated CeO 2 nanoparticles. Te decrease in crystallite size is clearly evident from the peak broadening as shown in Fig. 1b. Besides the size of Ag crystallites found to be ~ 7.9 nm. Te obtained predominant Ag peaks are revealed that equally distributed on the CeO2 surface. Moreover, it can be noticed that the calculated lattice parameter (~ 5.414 Å) of as-synthesized CeO2 nanoparticle is slightly higher than that of bulk CeO2 (~ 5.411 Å). For Ag incorporated samples, a higher value of CeO2 lattice parameter (~ 5.553 Å) is obtained which may be due to higher surface defects and decreasing crystallite size. Microstructural analysis of pure and Ag incorporated CeO2 nanoparticles. Microstructural characteristics of pure and Ag decorated CeO2 nanoparticles are examined using SEM technique with diferent magnifcations and the results are presented in Fig. 2a–d. It can be clearly seen that the obtained particle sizes are obviously in nanoscale range with agglomeration.