Inquiring the photocatalytic activity of cuprous oxide nanoparticles synthesized by a green route on methylene blue dye

Int J Ind Chem (2016) 7:157–166 DOI 10.1007/s40090-016-0075-y RESEARCH Inquiring the photocatalytic activity of cuprous oxide nanoparticles synthesized by a green route on methylene blue dye Manoranjan Behera1 • Gitisudha Giri1 Received: 16 June 2015 / Accepted: 23 February 2016 / Published online: 17 March 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract We synthesized cuprous oxide (Cu2O) nanoparticles (NPs) with an average crystallite size of 8.8 nm in presence of Arka (Calotropis gigantea) leaves extract. The photo-bleaching activity of Cu2O NPs on the aqueous methylene blue (MB) dye was studied by illumination of visible light. In the absorption spectra, a decrease in the absorption peak intensity at 665 nm of MB was observed in presence of Cu2O NPs. A red shift in its peak position as a function of irradiation time is suggesting that oxide particles are degrading the organic dye in an aqueous medium. In the vibration spectra, red shift in the C–H stretching band (2954, 2926, and 2855 cm-1) of methylene group and C–N stretching band (1343 and 1226 cm-1) of MB in presence of Cu2O NPs proposes a surface adsorption of MB over NP’s surfaces. Quenching in the emission band intensity and red shifts in the peak maxima of MB in presence of Cu2O NPs is ascribed to the charge transfer interaction between MB and oxide NPs. A linear Stern– Volmer plot reveals that decrease in the emission intensity of MB dye occurs via the dynamic quenching mechanism. Synthesis of Cu2O NPs of various architectures using a green route could be use as an approach towards the costeffective treatment of water pollutants. Keywords Photodegradation  Methylene blue dye  Surface adsorption  Charge transfer interaction  Photoluminescence quenching & Manoranjan Behera 1 Silicon Institute of Technology, Bhubaneswar, Odisha, India Introduction Organic dyes are the major threats to our environments. It is not an easy task to remove them from dye-bearing waste waters owing to their stability towards oxidizing agents [1– 3]. Amongst the various organic dyes, methylene blue (MB)—a cationic dye mostly used in paper, rubber, and textile industry as colorants—is found in waste water [4– 6]. It is reported that acute exposure to MB dye might cause tissue narcosis, heart stroke, jaundice, etc., in humans [7, 8]. Presently a variety of physical, chemical, and biological methods were available for the treatment of dye contaminated water. From an extensive literature study, we concluded that a chemical method such as adsorption process is an economical and efficient route for elimination of toxic dyes from polluted water [9–12]. In this regards, various low-cost adsorbents such as fly ash, metal sulfides (Ag2S), and metal oxides (titania TiO2, cuprous oxide Cu2O) have already been tested to treat polluted water [4, 9–13]. In recent years, semiconductor nanoparticles (NPs) were extensively used by scientists and academicians around the globe for the removal of various organic dyes via adsorption route. Pourahmad [4] reported that Ag2S NPs encapsulated in a mesoporous material can efficiently degrade MB dye in aqueous solution. In another work, Srinivasan and White [13] reported an accelerated photodegradation of MB over three-dimensionally ordered macroporous TiO2 pore sizes lies between 0.5 and 1 lm. However, owing to high band gap of 3.2 eV, TiO2 cannot perform in the visible region. Among the various semiconductor metal oxides as photocatalyst, Cu2O NPs find a special place in photocatalysis under visible light [10–12, 14–16]. Wide applications of this oxide NPs are mainly owing to its nontoxicity, easy availability of cheap and up-scalable 123 158 Int J Ind Chem (2016) 7:157–166 synthetic routes, lying of the band gap (i.e., 2.17 eV) in the visible range, tunability of band gap, and strong tendency to adsorb molecular oxygen which helps in scavenging the photogenerated electrons so that electron–hole pairs recombination can be restrained easily at the interface [10– 12, 14–16]. It is reported that size and shape are of paramount importance in tailoring the various properties and applications of the Cu2O NPs. A variety of Cu2O nanostructures such as wires, boxes, cubes, truncated cubes, octahedra, nanocages, nanomultipods, spheres, and a variety of hollow structures have already been synthesized and tested for their photocatalytic activity on various organic compounds [14, 15]. To develop diverse architectures of Cu2O, the various methods widely used includes hydrothermal method, microemulsion method, surfactantassisted route, and wet chemical method [10–12, 14–16]. Sun et al. [9] have reported an enhanced photocatalytic activity for Cu2O–graphene oxide (GO) nanocomposite synthesized via solvothermal route towards Rhodamine B (RhB) dye. They reported that more than 65 % RhB was degraded within 80 min of visible light irradiation. Cai et al. [10] have reported synthesis of Cu2O-reduced GO (rGO) composite by a one-pot hydrothermal method using glucose as reducing and cross-linking agent. They reported that as rGO promotes the charge carrier separation, it increases the aqueous photocatalytic efficiency. But, nearly 70 % methyl orange (MO) degradation was reported for this nanocomposite after a long irradiation time of 300 min. In another article, Zhang et al. [11] have reported 80 % MO degradation after 30 min irradiation by graphene/defected Cu2O nanocomposite synthesized via a chemical vapor deposition method. They stressed on the importance of O-atoms towards the charge carrier separation. Zou et al. have reported synthesis of Cu2O–rGO nanocomposites of various Cu2O crystal facets. They have reported only 72, 60 and 28 % MB degradation after 120 min for octahedral, dodecahedral and cubic faceted Cu2O–rGO NPs. A few reports are available on photocatalytic activity study of Cu2O NPs synthesized by green chemical route. Cu2O microcrystals with well-formed facets were synthesized by a simple hydrothermal method by Zheng et al. [14] and investigated the surface stabilities and photocatalytic properties of the synthesized Cu2O microcrystals. It is reported that Cu2O {100} and {110} facets gradually disappear and transform into nanosheets during the photodegradation of MO dye. With the increase of irradiation time, Cu2O microcrystals completely transform into nanosheets with {111} facets and the finally formed nanosheets exhibit stable photocatalytic activities. Zhu et al. [17] have synthesized Cu2O micro-/nanocrystals using a simple liquid phase reduction process under microwave irradiation. In particular, for the dandelion 123 morphology, the photocatalytic degradation rates of RhB dye is reported to be highest, i.e., 56.37 %. From above literature studies we concluded that photodegradation efficiency of Cu2O towards a dye depends on various parameters such as nature of the dye, synthesis route, shape and size of NPs, attachment of charge carrier se (...truncated)