Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwinia

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Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwinia herbicola and Their Photocatalytic Activity for Degradation of Dyes Nishant Srivastava and Mausumi Mukhopadhyay* Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat 395007, Gujarat, India ABSTRACT: Tetragonal SnO2 nanoparticles (15−40 nm) were synthesized according to a green biological synthesis technique using Gram-negative bacteria Erwinia herbicola followed by an annealing treatment over 425 K. The SnO2 nanoparticles were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy with energy dispersive X-ray (SEM-EDX). The zeta potential of biosynthesized SnO2 nanoparticles was 7.53 mV. A biosynthesis mechanism for SnO2 nanoparticles was also proposed. In the biosynthesis, the bacterial protein and biomolecules served as the template for reduction and stabilization of SnO2 nanoparticles. These biomolecules also helped in controlling SnO2 nanoparticle size and aggregation. The SnO2 nanoparticles exhibited excellent photocatalytic activity for photodegradation of organic dyes such as methylene blue, methyl orange, and erichrome black T. Approximately 93.3, 97.8, and 94.0% degradations of methylene blue, erichrome black T, and methyl orange were observed with biosynthesized SnO2 nanoparticles in the photocatalytic degradation process, respectively.

1. INTRODUCTION In recent years, stannic oxide (SnO2) nanomaterial has attracted research interest due to its unique optical and electrical properties.1 SnO2 is stable, with peculiar optical transparency, low resistivity, and high theoretical specific capacity.2 These unique properties of SnO2 provide its several cutting-edge applications in gas sensing, lithium ion batteries, heat mirrors, glass coatings, and photocatalysis.2−4 At the nanoscale, SnO2 exhibits extraordinary properties due to the fact that the size and shape of a nanomaterial exert a significant influence on its properties because of high surface to volume ratio.5 It is an n-type semiconductor with a wide band gap of 3.6 eV.6 The high band gap energy and high stability of SnO2 nanoparticles make it a unique photocatlyst. SnO2 nanoparticles retain their original photocatalytic properties and morphology after repeated use at acidic or basic pH.7 Over the past decades, researchers have developed several chemicals and physical methods for fabrication of SnO2 nanoparticles. Chemical and physical methods such as hydrothermal, electrochemical, laser ablation, microwave irradiation, and photochemical synthesis are used widely for fabrication of SnO2 nanomaterial because of its high growth rate.5,8−12 However, these chemical and physical processes of fabrication involve extensive use of hazardous, toxic chemicals, high energy, and elevated temperature and a high cost of operation. Due to environmental concerns, researchers want to replace this fabrication methodology with clean, nontoxic, and environmentally friendly, green chemistry approaches.13,14 The utilization of living creatures such as plants and microorganisms drew attention due to its ease of handling, nontoxicity, and green chemistry approach toward nanoparticles synthesis and the development of environmentally benign and sustainable methodologies in material synthesis.15,16 The synthesis of metallic oxide nanoparticles by utilizing biological entities is a novel step for the development of nanomaterials applying nanobiotechnological pathways.17,18 © XXXX American Chemical Society

Bacteria are economical potential nanofactories with innate ability to reduce metal ions into their respective metallic nanoparticles.19 Recently, researchers have studied the process of bacterial detoxification by transformation of toxic metal ions into nontoxic metal nanoparticles.20,21 The chemical detoxification mechanism and energy-dependent ion efflux from the bacterial cell by membrane protein are responsible for an interesting reduction performance.19,22,23 Therefore, these exciting properties of bacteria make them a priority for the biosynthesis of nanomaterial. In bacteria, proteins and other biomolecules have the capability of controlling inorganic crystal growth during biomineralization processes.16 In recent years some bacterial species such as Pseudomonas aeruginosa, Rhizopus oryzae, and Zooglea ramigera and many more have been explored for fabrication of metallic nanoparticles.19,24,25 Authors have tried several bacterial species but found only Erwinia herbicola to possess the ability to synthesize SnO2 nanoparticles. Dyes exert significant environmental hazard to living organisms, the hydrosphere, and humans due to their toxicity and tendency toward eutrophication.26−28 The extensive use of these dyes in the textile, cosmetics, paper, drug, and foodprocessing industries around the world causes serious water and soil pollution problems.28 Due to the complex structure and high stability, dyes are difficult to remove or degrade completely from effluents. Several studies for the removal of dyes from effluents have been conducted employing physical, chemical, and biological remediation processes,29,30 but these methods have certain demerits. A photocatalytic approach with the aid of nanocatalyst offers the potential for complete removal of pollutants from the environment.31 In the photocatalytic Received: May 20, 2014 Revised: August 20, 2014 Accepted: August 22, 2014

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dx.doi.org/10.1021/ie5020052 | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

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solution of 1 mM SnCl2·2H2O without any bacterial cells, were incubated in the same condition. 2.4. Characterization of SnO2 Nanoparticles. The size and morphology of biogenic SnO2 nanoparticles were characterized by TEM (Philips Holland Tecnai-20) at an accelerating voltage of 200 kV providing 0.27 nm point resolution. The sample for TEM analysis was prepared by dispersing nanoparticles in acetone and placing a droplet of nanoparticles on a copper grid with a mesh size of 300 and a diameter of 3 nm. Excess solvent was allowed to evaporate at room temperature. The size, size distribution, and zeta potential of biogenic SnO2 nanoparticles were measured by using a DLS particle size analyzer (Nano ZS 90, Malvern, UK). The elemental analysis of nanoparticles was carried out by using an EDX analyzer associated with a SEM (JSM-7600F, JEOL, Japan) at an accelerating voltage of 20 kV. XRD analysis was carried out (Xpert pro, PANalytical, Holland) at a voltage of 45 kV with Cu Kα radiation (K = 1.5406 Å) to examine the crystalline phase of synthesized nanoparticles. The Fourier transform infrared spectroscopy (FT-IR) spectrum was recorded on a FT-IR spectrometer (Vertex 80, Bruker, Germany) to identify the functional group present on the biosynthesized SnO2 nanoparticles and responsible for the stability of nanoparticle. All measurements were carried out in the range of 5000−450 cm−1 at a resolution of 2.0 cm−1. 2.5. Photocatalytic Activity of SnO2 Nanoparticles for Degradation of Dyes. The potential photocatalytic activity of the biosynthesized SnO2 nanoparticles was investigated for photocatalytic degradation of the dyes methylene blue (MB), methyl orange (MO), and erichrome black T (EBT) prepared in an aqueous medium. The photocatalytic degradation reaction was carried out in the UV batch reactor with a lowpressure 125 W UV lamp (254 nm) and continuous stirring. In a typical experiment, the reactor was loaded with 0.2 g of SnO2 nanoparticles with 100 mL of a 20 mg L−1 aqueous dye solution. The absorption intensity of the reaction mixture of dye was monitored at different time intervals using a UV− visible spectrophotometer (HACH, DR 5000, USA). A similar procedure was followed for all dyes. The rate of decolorization of dyes to their colorless reduced form (Leuco form) in the presence of SnO2 nanoparticles was observed by UV−visible spectrophotometer during a certain time interval at wavelengths of 350 nm for MO, 664 nm for MB, and 530 nm for EBT.

process the nanoparticle is activated because of UV radiation, which forms a redox environment in aqueous solution and acts as a sensitizer for a light-induced redox mechanism.32 The available literature shows that a wide range of effluents containing dyes are treated by photocatalytic processes such as UV/SnO2 and UV/SnO2/ZnO nanoparticles.7,8,11 In this work, a facile, green, biogenic method for the synthesis of SnO2 nanoparticles using Gram-negative bacteria E. herbicola is developed and demonstrated. The stable nanoparticles of well-defined size are fabricated without the use of any stabilizing agent. The biosynthesized nanoparticles of SnO2 are characterized with dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy with energy dispersive X-ray (SEM-EDX). The bacteria-mediated synthesis mechanism is also investigated. In addition, the photocatalytic activity of biogenic SnO2 nanoparticles for removal of the dyes methyl orange, methylene blue, and erichrome black T is also studied.

2. EXPERIMENTAL PROCEDURE 2.1. Materials. Stannous chloride (SnCl2·2H2O, 98% pure) was purchased from Finar, India. The microbiological nutrient media was procured from Hi-Media, India. Milli-Q (Millipore, Elix, India) deionized water was used in all experiments. The lyophilized strain of bacteria E. herbicola (MTCC 3609) was obtained from the Microbial Type Culture Collection (MTCC), Institute of Microbial Technology (IMTECH), Chandigarh, India. All chemicals used were of analytical grade. 2.2. Growth and Preparation of E. herbicola Biomass. The lyophilized culture was revived and maintain on Luria agar slant as described by MTCC guidelines. The E. herbicola strain was grown aerobically in Luria broth (LB) medium (Himedia Lab, India). The flask containing growth medium was inoculated with E. herbicola loop full cells and incubated at 30 °C, 100 rpm, for 24 h in an orbital shaking incubator (REMI, India). After incubation for about 24 h in Luria broth medium, the biomass was harvested by centrifugation (C30BL, REMI, India) at a speed of 5000 rpm at room temperature for 15 min. The resulting pellets were washed thoroughly with sodium saline solution followed by several washings with sterile distilled water under aseptic conditions for removal of medium component and other impurities, if any, from the bacterial cells. Fresh and clean E. herbicola cells were weighed and suspended in 10 mL of sterile distilled water. All of the glassware, distilled water, and growth medium used in the experiment were autoclaved using an autoclave (Obromax, India) and sterilized to avoid any contamination. 2.3. Synthesis of SnO2 Nanoparticles by Bacteria. Fresh and clean bacterial cells (0.4 g) were added into 100 mL of an aqueous solution of 1 mM SnCl2·2H2O. The sample was incubated at 30 °C, 120 rpm, for 48 h in an orbital shaking incubator. After complete reaction, the sample was centrifuged at 12000 rpm for 10 min for isolation of nanoparticles from sample solution. The synthesized nanoparticles were washed several times by sterilized distilled water and acetone to remove any impurities present. The purified nanoparticles were then dried in a vacuum oven at 60 °C, followed by annealing at 150 °C for 2 h. In the control experiment, two controls, one positive control containing 100 mL of an aqueous solution of 1 mM SnCl2·2H2O inoculated with heat-killed bacterial cells and one negative control containing only 100 mL of an aqueous

3. RESULTS AND DISCUSSION 3.1. X-ray Diffraction Pattern Analysis (XRD). The XRD patterns without and with heat-treated biosynthesized SnO2 nanoparticles are shown in Figure 1. The non-heat-treated biosynthesized nanoparticles showed an amorphous structure (Figure 1a). However, the heat-treated biosynthesized nanoparticles were crystalline in nature, and the diffraction peaks indicated the tetragonal structure of SnO2 (Figure 1b). The diffraction peaks at 2θ = 26.7°, 33.8°, and 52° were for the (110), (101), and (211) reflections of the pure tetragonal phase of SnO2 crystals with lattice parameters a = 4.738 Å and c = 3.188 Å (JCPDS 21-1250). The average crystalline size of SnO2 nanoparticles was calculated from the XRD 110 peak by applying Scherrer’s equation: D = kλ/β cos θ, where λ is the Xray wavelength of Kα (1.54 Å), θ is the Bragg angle, β is the full width at half-maximum in radians, and k (0.9) is an unknown shape factor.24,33 The average calculated crystalline size of biosynthesized SnO2 nanoparticles was 28.89 nm. B



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nearly spherical in shape with sizes in the range of 3−18 nm. The TEM images shown in Figure 2c,d are of the biosynthesized SnO2 nanoparticles after annealing at 150 °C for 2 h. Annealed SnO2 nanoparticles were mostly spherical in shape with sizes in the range of 10−42 nm. The TEM images revealed that particle size ranges were in agreement with the crystalline size calculated from the XRD patterns. Figure 2e shows the SEM image of biosynthesized SnO2 nanoparticles. The SEM image also indicated that particles were spherical in shape, in agreement with TEM micrographs. The selected area electron diffraction (SAED) ring patterns (Figure 2f) corresponded to the (110), (101), (211), and (112) planes of the trigonal phase of SnO2 nanoparticles. The heattreated biosynthesized SnO2 nanoparticles were larger in size compared to the as-synthesized SnO2 nanoparticles. The large size can be attributed to the annealing process. Previous findings suggested that the particle size increases with an increase in annealing temperature. A significant particle growth of SnO2 nanoparticles might occur during the annealing process at elevated temperature.34 3.3. Dynamic Light Scattering Analysis. The preliminary analysis for size and zeta potential of the as-synthesized SnO2

Figure 1. XRD patterns of the (a) biosynthesized (without heat treatment) and (b) heat-treated SnO2 nanoparticles.

3.2. Electron Microscopic Analysis. The electron microscopic observations for detailed morphological and size analysis of biosynthesized SnO2 nanoparticles are shown in Figure 2. The as-biosynthesized SnO2 nanoparticles (Figure 2a,b) were

Figure 2. TEM micrographs of biosynthesized SnO2 nanoparticles at 50 nm scale (a), 100 nm scale (b), after annealing at 150 °C at 100 nm scale (c), and 200 nm scale (d) and SEM micrographs showing cluster of spherical nanoparticles at 100 nm scale (e) and SAED pattern (f). C



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the particle size measured from TEM micrographs because the DLS method measures the hydrodynamic diameter.14 3.4. Energy Dispersive X-ray Analysis. The EDX spectrum shown in Figure 4 of biosynthesized SnO2 nanoparticles represented intense peaks of Sn at 3.4 eV and of oxygen at 0.5 eV. The EDX spectrum ranges from 3 to 4 eV represented the presence of Sn. The presence of intense peaks of Sn and O in EDX spectra clearly indicated the composition of Sn and O only. The quantitative analysis of EDX also revealed the fact that the average Sn:O composition of 1:2, which was in conformity with the SnO2 stoichiometry. Some weak signals of copper (Cu), middle-range signals of phosphorus (P) and sodium (Na), and an intense signal of carbon (C) were also recognized. P, Na, and C signals appeared due to biomolecules such as proteins, enzymes, and amino acids on the surface of the biosynthesized nanoparticle. The Cu and C signals were perhaps associated with the SEM grid used. 3.5. Fourier Transform Infrared Spectroscopy. Figure 5 shows the FT-IR spectrum recorded from the biosynthesized SnO2 nanoparticles. The functional groups present on the nanoparticles were responsible for their reduction from metal ions to nanoparticles and stability. The presence of the absorption band at 3287 cm−1 was associated with the primary amine’s stretching. The peak at 2924 cm−1 might be from the C−H stretching. The bands present at 1653 and 1540 cm−1 were assigned to the stretching of primary amides I and II of amino acids present in the proteins. The carboxyl bands appeared at 1395 cm−1. The bands at 1278 and 1232 cm−1 were associated with C−N bonds, whereas the band at 1066 cm−1 was due to C−O stretching. The FT-IR finding clearly indicated the carboxyl, amide, and amine groups of the proteins present on the nanoparticles’ surface. These protein molecules were responsible for the reduction and subsequent stabilization of SnO2 nanoparticles. The study supported the in situ protein template directed formation mechanism of SnO2 nanoparticles. 3.6. Mechanism of SnO2 Biosynthesis. The formation of nanoparticles by bacteria is an integral part of their detoxification mechanism. Bacteria protect themselves from toxic metallic ions by reduction and accumulation on their cell surface in the form of metallic nanoparticles. The exact mechanism of detoxification of metal ion by bacteria is not yet completely understood. Mostly, transformations of metal ions into metallic nanoparticles are the result of the direct enzymatic activity of bacterial enzymes.36 The enzymes or proteins such as

was carried out by DLS spectroscopy. Figure 3a revealed the size distribution plot obtained with DLS; 99.4% of the as-

Figure 3. DLS size distribution plot (a) and zeta-potential plot (b).

synthesized SnO2 particles were below 100 nm, with an average particle diameter of 64.09 nm. The polydispersity index (PDI), 0.5, of the biosynthesized nanoparticles was clearly indicative of the minimum homogeneity in the colloidal solution. The corresponding zeta potential of 7.53 mV is as shown in Figure 3b. The magnitude of the zeta potential was used to anticipate the stability of nanoparticles in colloidal solution.35 The zeta potential of the biosynthesized SnO2 nanoparticles indicated the relatively neutral nature of the nanoparticles. The electrostatic measurement indicated that the as-synthesized nanoparticles were stable in colloidal solution to a certain extent. The neutral behavior of the biosynthesized SnO2 was due to the presence of amino acids and proteins on its surface, which neutralize the surface charge of SnO2. The particles were bigger in size in DLS observations compared to TEM measured particle size. The DLS measured size was bigger compared to

Figure 4. EDX spectrum of biosynthesized SnO2 nanoparticles. D



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Figure 5. FT-IR spectrum of biosynthesized SnO2 nanoparticles.

dependent reductase or NAD-linked dehydrogenases. NADH/ NADPH is a coenzyme, which acts as an electron carrier to assist oxidoreductase enzymes by accepting or donating electrons required by the substrate.38 NADH/NAD+ undergoes reversible oxidation and reduction by accepting or losing electrons and protons in several electron transfer reactions. Most of the electrons in biological oxidation reduction reaction arise due to the dehydrogenation reaction carried out in the presence of dehydrogenases enzyme. Dehydrogenases collect the electrons from the catabolic pathway and transfer them to universal electron acceptors NAD+/NADP+. The enzyme NAD-linked dehydrogenases are responsible for the removal of two hydrogen atoms from its substrate and transfer one as a hydride ion (:H−) to NAD+ and the other one as H+ ion in the medium. Metal ions are capable of mediating oxidation reduction reaction by reversible changes in its oxidation state.39 The Sn2+ ion may be reduced by the gain of two electrons, and a molecule of NAD+ is oxidized to form NADH. This may be carried out by NAD+/NADH, which finally results in the formation of extracellular Sn nanostructures. The assynthesized Sn nanoparticles are oxidized by bacteria by the oxygen present in the solution, which leads to the formation of SnO2 nanoparticles. The biosynthesized SnO2 nanoparticles are capped or covered by the amino acids, proteins, or other biomolecules involved in the reaction, providing natural support and stability. Analysis of the FT-IR spectrum reveals the presence of protein-like molecules on the surface of nanoparticles. The FT-IR study supports the hypothesis of the role of protein and biomolecules in the reduction and stabilization of nanoparticles. 3.7. Photocatalytic Activity of Biosynthesized SnO2 Nanoparticles. The change in the absorption spectra of MB with time during the photocatalytic degradation in the aqueous medium is shown in Figure 7a. The absorption peak at 664 nm corresponding to the MB depreciated gradually with higher

an oxidoreductase associated with the membrane may be attributed to the reduction of metal ions into metallic nanoparticles. The metal ions are trapped on the surface of the enzymes secreted by the bacteria via electrostatic interaction followed by metal ion reduction by the associated enzymes, which leads to the formation of metallic nanoparticles.37 On the basis of the experimental observation and available literature, the possible mechanism for the formation of SnO2 nanoparticles is elucidated in Figure 6. The Sn2+ ions are trapped by the extracellular enzymes secreted from the bacterial cell (Scheme 1 of Figure 6) or by membrane-associated proteins on the cell surface (Scheme 2 of Figure 6). The reduction seems to be initiated by enzymes such as NADH-

Figure 6. Mechanism of biosynthesis of SnO2 nanoparticles: 1, synthesis due to extracellular secretion of enzymes; 2, synthesis on the cell surface due to membrane-associated proteins. E



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Figure 7. Photocatalytic activity of biosynthesized SnO2 nanoparticles irradiated by a 125 W UV lamp for degradation of MB, EBT, and MO dye; absorption spectra for photocatalytic degradation of MB (a), EBT (b), and MO (c) at different time intervals; percent rate of degradation at different time intervals (d) for MB, EBT, and MO.

Table 1. Comparative Analysis of the Experimental Output of the Present Study and Studies Conducted by Other Researchers for the Photocatalytic Degradation of Dyes Using Nanoparticles nanoparticle SnO2

Sn−SnO2 ZnO-doped SnO2 TiO2 Ni−S P zeolite

dye

volume (mL)

% degradation

time (h)

methylene blue methyl orange erichrome black T methylene blue methylene blue erichrome black T methyl orange erichrome black T

100

93.3 94 97.8 98 (approx) 100 100 20 98

2 2 2 3 4 3.5 3.5 3

50 250 100 50

catalyst concn (g) 0.2

photon flux

ref

4.09 × 10−5

present study

0.1 0.1 0.1

7 43 40

0.004

41

radicals, and times of reaction.40 The chemical structure of the targeted dye was also responsible for the rate of degradation. Recently, researchers reported the significant effect of pH on EBT rapid degradation. The increase in pH provides higher degradation efficiency of EBT dye.41,42 The higher pH value provided a large concentration of hydroxyl ions, which was responsible for the higher photocatalytic activity and rapid degradation rate of the EBT dye.42 Subsequently, a control experiment was carried out to confirm the photocatalytic activity of SnO2 nanoparticles. When solutions of dyes were irradiated with UV light in the absence of SnO2 nanoparticles, all three dyes showed no degradation. Similarly, dyes showed almost negligible degradation when placed in the dark without UV light in the presence of SnO2 nanoparticles. The gradual disappearance of the absorption peak with time was attributed to the occurrence of cleavage in the aromatic ring of the dye molecules.

exposure time and reached its minimum at 120 min. In Figure 7b, absorption peak at 530 nm, corresponding to EBT, showed rapid degradation for the initial 15 min, which was diminished gradually and disappeared after 120 min. Figure 7c shows the absorption peak at 350 nm corresponding to MO. Figure 7d demonstrates the degradation capability of biosynthesized SnO2 nanoparticles for MB, EBT, and MO, which reached to 93.3, 97.8, and 94.0%, respectively. The gradual blue shift of the absorption peaks (λ max) occurred with time. The blue shifting finally led to the disappearance of absorption peak of dyes. The SnO2 nanoparticles were easily recovered from the reaction mixture after the end of the photocatalytic degradation reaction by a simple centrifugation process and reused. The EBT absorbance disappeared rapidly in comparison to MO and MB dyes as observed in Figure 7. In the present experiment, although the morphologies of SnO2 nanoparticles were the same, the different dyes showed different reaction mechanisms, F



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Figure 8. Schematic representation of the photocatalytic degradation process of dyes using SnO2 nanoparticles.

where At and A0 are the concentrations of methylene blue, methyl orange, and erichrome black T at time t and 0, respectively, kapp is the pseudo-first-order rate constant, and t is the time in minutes. The rate constant (kapp) was calculated from the slope of the plot of ln At/A0 versus time as 0.00566, 0.00751, and 0.01152 s−1 for MB, MO, and EBT, respectively. The R2 values were 0.978, 0.97, and 0.987 for MB, MO, and EBT, respectively.

A comparison between the present study and studies conducted by other researchers regarding dye degradation is shown in Table 1. The comparison also showed the complete time degradation of dye using biogenic SnO2 nanoparticles. A schematic representation of the photocatalytic degradation process is presented in Figure 8. The photocatalytic degradation of dyes in the presence of SnO2 nanoparticles was initiated by the photoexcitation process. The surface of SnO2 was illuminated with light energy due to which the conduction band electrons and valence band holes generated.11,44 The holes were finally trapped on the surface of the hydroxyl group at the catalyst to give OH− radicals, highly oxidizing species.31 Superoxide radical anions O2− were generated due to the reaction of dissolved oxygen molecules with conduction band electrons. Superoxide radical anions O2− on protonation generate hydroxyl radicals, HO2.44 In a final step, dye was degraded due to the activity of superoxide anions. The valence band holes and the conduction band electrons caused the oxidation and reduction of dye.31 The biosynthesized SnO2 nanoparticles showed excellent photocatalytic activity due to their high specific surface area, which provides maximum exposure for reactant to the active site. The rates of degradation of methylene blue, methyl orange, and erichrome black T in the presence of biosynthesized SnO2 nanoparticles were according to the pseudo-first-order reaction kinetics

4. CONCLUSIONS An environmentally friendly, biological green route is developed for the preparation of SnO2 nanoparticles. The method has several advantages over other available methods. The presented method is economical, nontoxic, and free of the use of any organic solvents, surfactants, and specialized instruments. The bacterium used in the present study is nonpathogenic, easy to handle, and human friendly. Biomolecules such as proteins and amino acids are assumed to play a significant role for the formation of SnO2 nanoparticles with the help of bacteria E. herbicola. Tetragonal crystalline SnO2 nanoparticles in size ranges between 10 and 42 nm (TEM) are biologically synthesized. These biosynthesized nanoparticles are directly utilized for the photodegradation of MB, EBT, and MO to study the photocatalytic activity. The photocatalytic degradation process exhibits higher efficiency due to the excitation of surface electrons in the presence of UV irradiation. The high efficiency of SnO2 nanoparticles as photocatalysts may provide a promising application for the degradation of dyes from industrial effluents.

ln(A t /A 0) = −kappt G



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AUTHOR INFORMATION

Corresponding Author

*(M.M.) E-mail: [email protected], mausumi_ [email protected]. Tel.: +91 261 2201645. Fax: +91 261 2227334. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We express sincere gratitude to the Sophisticated Analytical Instrument Facility (SAIF), Indian Institute of Technology Bombay (IIT B), All India Institute of Medical Sciences (AIIMS), and Department of Metallurgical Engineering and Material Science, IIT B, for providing characterization facilities.

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