Elsevier

Chemical Physics Letters

Volume 715, January 2019, Pages 252-262
Chemical Physics Letters

Research paper
Sonochemical synthesis and high-efficient solar-light-driven photocatalytic activity of novel cobalt and manganese codoped tungsten oxide nanoparticles

https://doi.org/10.1016/j.cplett.2018.11.039Get rights and content

Highlights

  • Solar light active Co-Mn/W3O8 photocatalyst was synthesized by a facile sonochemical technique.

  • Solar light photocatalytic changed in order: W3O8 < Mn-W3O8 < Co-W3O8 < Co-Mn/W3O8.

  • The kinetics of the degradation of amaranth was investigated.

  • Mechanism of enhanced activity under solar light irradiation was also proposed.

Abstract

This work presents a new approach to preparation of Co/Mn-W3O8 nanoparticles via facile sonochemical route. Cobalt and manganese codoped tungsten oxide (W3O8) nanoparticles was studied as a photocatalyst for the removal of amaranth under solar light irradiation (λmax 520 nm). The results indicated that the Co/Mn-W3O8 composite photocatalyst showed higher photocatalytic activity the single element doped and pure W3O8. Moreover, the stability of Co/Mn-W3O8 was tested using recycling experiments. It is suggested that the band gap energy difference between the Co/Mn-W3O8 and W3O8 accelerates the separation of photogenerated electron-hole pairs, dominating the enhanced photocatalytic activity.

Introduction

Nanomaterials involved transition metals and metal oxides become one in each of the foremost widespread topics in materials science as a result of their distinctive properties and potential applications. The properties of these materials area unit extraordinarily obsessed with their morphology and size. So, the scientific researchers centered their researches throughout the preparation of nanomaterials on dominant the morphology and size of the as prepared materials [1], [2], [3]. Till now, many investigations are assigned to provide of assorted nanostructures with an unbearable approach as a straight forward and fast route. Semiconductor photocatalysis could also be a promising technique for the treatment of dye waste material owing to its clean, harmful and solar-driven technique [4], [5].

Especially, visible-light-driven photocatalyst have attracted nice interest owing to their high utilization of daylight, low energy consumption and easy production [6], [7], [8]. One of the foremost sometimes used photocatalyst, owing to its characteristics (inexpensive, insoluble beneath most conditions, photochemically stable and nontoxic) is TiO2 used, has been established effective in degrading dyes and diverse organic compounds, it absorbs sun light very poorly [9], [10]. Modification of metals may increase the activity of TiO2 at intervals vary of sunshine (λ > 400 nm) and thus permits the employment of renewable energy-solar radiation at intervals the atmosphere [11], [12].

Among the various candidates W compound (WO3) may well be a promising photocatalyst beneath actinic ray illumination, because of its very little band gap (which varies 4.8 eV) [13], [14], [15], [16], [17], [18], [19]. More a lot of W compound has attracted hefty attention for applications in energy conversion through photocatalysis [20], [21], [22], [23], [24] or photoelectrolysis of water [25], [26], [27], [28], [29], [30]. This compound could be a semiconductor, and is capable of harvest the blue a locality of the star spectrum.

Ultrasound method has been used for the synthesis of nanocrystalline materials because of its distinctive effects in recent years [31], [32], [33], [34]. The utilization of ultrasound within the preparation of nanostructures resembling high-surface space transition metals, alloys, carbides, oxides, and colloids plays a very important role in fine dispersion, size of nanoparticles, agglomeration and uniform loading of nanoparticles on support [35], [36], [37], [38], [39], [40]. The cavity generated because of inaudible irradiations gets collapse which generates localized hotspots with terribly hot temperature of concerning 10,000 K, pressures of concerning 1000 atm, below these intense surroundings, many chemical reactions and physical changes crop up and nanostructured materials resembling metals, alloys, oxides and biomaterials may be with success ready with needed particle size distribution. As compared to traditional ways, ultrasound-assisted preparation is economical and facile for fast preparation of nanostructured materials. The collapse of cavitations bubbles generates localized hot temperature (about 104 K), pressure (about 105 kPa) and cooling rates (in way over 109 K s−1) below inaudible condition, which may promote self-assembly and crystallization of nanostructured materials [41], [42], [43], [44], [45]. May be, Meskin et al. synthesized nanocrystalline ZrO2, TiO2, NiFe2O4 and Ni0.5Zn0.5Fe2O4 powders by ultrasonic-hydrothermal treatment [46]. Shirsath et al. synthesized TiO2 nanoparticles doped with iron and metallic element mistreatment sonochemical approach [41]. Anandan et al. sonochemically ready Au-TiO2 nanoparticles [31]. Still, to the most effective of our data, very little work has been created to the ultrasound-assisted preparation of AgX/TiO2 nanocomposites with visible-light responsive photocatalytic activity.

However, the photocatalytic activity of pure WO3 is implausibly low as a results of its conduction band level is extra positive than the reduction potential of O2/O2, that indicates it cannot decrease O2 via single-electron methodology [47]. Many makes and effort are created to spice up the photocatalytic activity of WO3, like size-controlling, metal deposition, coupling with different semiconductors. Many experimental and theoretical makes a effort are created to chop back the band gap in metal oxides by pattern non-metal and metal dopants. However, the photocatalytic properties are still far from satisfactory owing to low solar utilization and fast recombination of electron hole pairs [48].

Mono-doping of non-metal (or p-type doping) in metal oxides forms localized s/p states merely on prime of the framing band most (VBM) resulting in a decrease of the band gap by however one unit that won't enough for the economical use of actinic ray. In addition, it had been through an experiment determined that the impurity levels act as charge recombination centers, thus reducing the photogenerated current. Inside the case of transition metal mono-doping (n-type: V, Cr, Mn, etc.), localized d states are generated for the most part below the conduction band minimum (CBM) and thus the relative overlapping effectively reduces the band gap. However, the photocatalytic activity of co-doped semiconductors is on prime of that of single element doped semiconductor nanoparticles.

Azo dyes unit of measurement aromatic organic compounds containing conjugated one or multiple chemical group bond (single bondNdouble bondNsingle bond) [49]. Many methods are utilized for the removal of organic contaminants in conjunction with varied physical (Coagulation, action, deposit, sorption on C, nano-filtration, reverse diffusion, etc.) chemical (ozonation, chemical precipitation, ion-exchange, chlorination) and biological (aerobic or anaerobic processes) methods severally [50], [51], [52]. Among them the new chemical reaction methods or advanced oxidation process (AOP), heterogeneous photocatalysis looks as associate rising harmful technology leading to the general mineralization of the numerous organic pollutants [53], [54], [55], [56], [57], [58], [59]. Amaranth might be a redness, soluble mono dye (C20H11N2Na3O10S3, relative molecular mass 604.47 g mol−1) used as a coloring agent for foodstuff, jams, jellies, catsup and cake decoration, beverages and cosmetics. It’s fascinating to mention that a prolong uptake of amaranth dye cause tumors, allergy, biological process problems and birth defects inside the individual [60], [61], [62]. However, to the most effective of our information, there have been no reports on the preparation of Co-Mn codoped W3O8 photocatalyst by sonication method and its photocatalytic activity. During this work we tend to demonstrate, for the primary time, that it's doable to synthesize W3O8 nanoparticles that satisfy of these conditions and characterized by XRD, UV–vis-DRS, FT-IR, SEM-EDX, HRTEM, XPS and PL spectroscopy. This synthesis being facile, faster, cleaner, and a lot of economical than the standard strategies. The photocatalytic activity for amaranth dye was studied victimization these synthesized NPs. Study shows that Co/Mn-W3O8 NPs could be a potential candidate as catalyst for photodegradation of amaranth dye in water with the usage of terribly touch of NPs.

Section snippets

Materials

Sodium tungstate dihydrate (H42 N10 O42 W12·2H2O), ethanol (C2H6O), cobalt nitrate hexa hydrate (Co(NO3)2·6H2O) and manganese sulphate (MnSO4·H2O) (analytical grade purity) were purchased from Sigma-Aldrich company, Amaranth (C20H11N2Na3O10S3) was purchased from Merck Chemicals Ltd. All chemicals were of analytical grade and used as received without further purification. Distilled water was used throughout the experiment.

Sonochemical synthesis of Mn-Co/W3O8

Manganese and cobalt codoped tungsten oxide nanoparticles were synthesized

UV–vis-DRS

Diffuse reflectance spectrographic analysis permits getting information about concerning light absorption vary and band gap of the semiconductor. Fig. 1a depicts diffuse reflectivity spectra of the synthesized materials. The band gap energy of a semiconductor is also calculated from equation two [63], [64].α=A(hν-Eg)n/2/hνwhere α, h, ν, Eg and A unit the absorption, the Planck’s constant, the sunshine frequency, band gap energy and a quotient constant, severally. The exponent n is determined by

Conclusion

This study illustrates the successful and facile synthesis is of Co and Mn codoped W3O8 nanoparticles via sonication method. XRD analysis shows that the crystalline size of the samples is in nanometer range. The SEM analysis reveals the formation of Co-Mn/W3O8 nanoparticles has plate with needle like morphology and homogeneous shape. EDX spectrum analysis confirms the present of cobalt manganese, tungsten and oxygen elements. Co-Mn/W3O8 nanoparticles present unique photocatalytic properties

Acknowledgment

Dr. A. Suganthi was highly thankful for the Management of Thiagarajar College for providing necessary laboratory facilities to carry out this work.

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