Vanadium doped SnO2 nanoparticles for photocatalytic degradation of

J Mater Sci: Mater Electron DOI 10.1007/s10854-017-7477-2

Vanadium doped S nO2 nanoparticles for photocatalytic degradation of methylene blue Wissem Ben Soltan1,2,3 · Mohamed Saber Lassoued1 · Salah Ammar1 · Thierry Toupance2

Received: 4 May 2017 / Accepted: 3 July 2017 © Springer Science+Business Media, LLC 2017

Abstract Nanometric V-doped particles with vanadium concentration varying from 0 to 10% were prepared using the polyol method. The influence of the doping on the textural, structural and optical properties was studied by various methods of characterization. X-ray diffraction (XRD) patterns disclose that nanocrystallites of cassiterite, i.e. rutile-like tetragonal structure SnO2 and the absence of a new vanadium phase in the XRD pattern in the different concentration of doping were formed after annealing, the ordinary crystallite size decreased from 20.6 to 12.3 when the doping concentration increased from 0 to 10%, respectively. Moreover, the N2 sorption porosimetry and transmission electron microscopic show that all samples synthesized were constituted of an aggregated network of almost spherical nanoparticles, which sizes changed with the altitude in the doping concentration to 10%. In accordance with UV–visible absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.25 eV, for undoped SnO2, to 2.75 eV, for SnO2 doped at 10%. On the other part, the photocatalytic activity of undoped and V-doped S nO2 nanoparticles was studied using methylene blue (MB) as model * Thierry Toupance [email protected]‑bordeaux1.fr Wissem Ben Soltan [email protected] 1

Unité de Recherche Electrochimie, Matériaux et Environnement (UREME), Faculté des Sciences de Gabès, Université de Gabès, Cité Erriadh, 6072 Gabes, Tunisia

2

Institut des Sciences Moléculaires, UMR CNRS 5255, Université de Bordeaux, 351 cours de la Libération, 33405 Talence Cedex, France

3

Département de chimie, Faculté des Sciences de Gabès, Université de Gabès, Cité Erriadh, 6072 Gabes, Tunisia

organic pollutants. The SnO2 nanoparticles doped at 10% of vanadium disclosed that the discoloration of MB reached 97.4% after irradiation of 120 min, with an apparent constant rate of the degradation reaching 0.035 min−1 for MB degradation that was about 2.5 times more than that of pure SnO2 (0.014 min−1).

1 Introduction Over the past two decades, the synthesis of nanostructured metal oxide semiconductors has been the topic of intense research efforts owing to the peculiar structural, textural, optical, and electrical properties of these materials and their numerous potential or demonstrated applications. Among these sought-after materials, tin oxides, as rutile-type SnO2 have received considerable attention as functional materials. They presents a board band gap (Eg = 3.6 eV) and unique characteristics acting as high infrared reflectance, bight electrical conductivity and high transmittance in the ultraviolet (UV) visible (Vis) region [1]. Thus, S nO2 nanoparticles have been investigated using various methods such as co-precipitation methods [2], chemical precipitation [3], sol–gel method [4], hydrothermal [5], and polyol procedures [6–9]. Among these different methods, the polyol method is well-adapted to the fabrication of nanostructured materials because of its relatively low dealing cost and its capacity to control the grain size. The properties of tin oxide obtained can be adjusted by playing with different parameters during the preparation process. In this context, some researchers have stressed the strong need for more detailed studies on the impact of impurities on various SnO2 properties including crystal size, pore size and optical characteristics [10, 11]. Doping constitutes of the more efficient strategy to adjust the properties of SnO2.

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Tin dioxide was doped successfully with different transition metals such as vanadium [12], cobalt [13], nickel [14], chromium [15], iron [16] and magnesium [17]. Furthermore, environmental and human health issues related to the release of organic pollutants and toxic water pollutants produced by some industries require the development of new technologies. Photocatalysis using metal oxide semiconductors represents a green process showing a great potential for completely cancelling of toxic chemicals in the environment through its broad applicability and efficiency [18]. Thus nanostructured semiconductors can efficiently degrade different organic pollutants under UV light irradiation [19]. However, owing to the lean quantum yield caused by the rapid recombination of photogenerated electrons and holes, enhancing the photocatalytic activity of semiconductors to meet the practical application requirements still remain a huge challenge [20]. Typically, the decomposition of organic dyes such as methylene blue (MB) and methyl orange [21–23], in aqueous suspension is used as a probe reaction to evaluate the catalytic activity of metal oxide nanomatrials. Even though many studies concern the use of nanocomposite or heterojunction catalysts such as ZnO/SnO2 [24], Ag–NiTiO3 [25], ZnLaFe2O4/NiTiO3 [26], NiFe2–xEuxO4 [27], TiO2/SnO2 [19], Fe2O3/SnO2 [28] and V2O5/SnO2 [29], few reports have been devoted to the photocatalytic activity of doped SnO2 nanomaterials [30, 31]. In particular V-doped SnO2 nanopowders appeared to be more active as catalyst than pure S nO2 [32]. As most of the studies reported on vanadium-doped SnO2 deals with the formation of thin films [33], investigations concerning the effect of doping concentration on chemical, physical and structural properties of nanoparticles are of upmost importance for technological application purposes. In the present paper, we describe undoped and V-doped SnO2 nanocrystals prepared by the polyol method and their characterization by XRD, N2 sorption porosity, and N2 sorption porosimetry, TEM and UV absorption spectroscopy. The effect of the vanadium content on the properties of SnO2 nanopowders (crystal structure, grain size, specific surface area, and pore size) was carefully investigated. Finally, the photocatalytic properties of the materials prepared were investigated in the case of the photodegration of MB under UV-light illumination, the greatest activity being found for the 10 at.% V-doped SnO2 nanomaterials.

2 Experimental 2.1 Synthesis of V‑doped SnO2 nanoparticles V-doped SnO2 nanoparticles were synthesized by the polyol method. It was achieved from a combination of vanadium and tin precursors by applying a procedure

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J Mater Sci: Mater Electron

previously developed for pure SnO2 nanomaterials [6]. 4.23 g of stannous chloride dihydrate (SnCl2·2H2O, 98%, Aldrich) were dissolved in 50 mL of diethylene glycol (DEG, 99%, Aldrich) and 5.1 g of sodium acetate trihydrate (CH3COONa·3H2O, 99%, Scharlau) in 50 mL of DEG and of a suitable amount of ammonium metavanadate (NH4VO3, 99.996%, Aldrich) in DEG (25 mL) were prepared at room temperature. After introducing the stannous chloride dihydrate solution in a three-necked flask, an appropriate volume of demineralized water was added to adjust the hydrolysis ratio h1 (for instance, considering into account the water molecules provided by the precursors used, 3.03 mL to reach h = 17) and the resulting solution was heated up to 120 °C. Then the ammonium metavanadate and the sodium acetate solutions were added dropwise using a dropping funnel and the obtained mixture was heated at 160 °C for 7 h. The white precipitate obtained was isolated by centrifugation and then calcined in air at 600 °C for 8 h to yield the target V-doped SnO2 samples. Samples including 2, 6, and 10 at.% of vanadium were synthesized by using 0.041, 0.123, 0.164 and 0.411 g of ammonium metavanadate, respectively. The resulting samples are hereafter denoted 2 at.% V–SnO2, 6 at.% V–SnO2 and 10 at.% V–SnO2 samples. 2.2 Characterization Specific surface areas [Brunauer–Emmett–Teller (BET)] were inferred from N2 sorption analyzes performed with Micromeritics ASAP2010 equipment. Nitrogen adsorption–desorption isotherms were measured at liquid nitrogen temperature (77 K) in the 0–0.99 relative pressure range (P/P0). Pore size distributions were studied by the Barrett, Joyner, Halenda (BJH) model applied to the adsorption branch of the isotherms. Diffuse reflectance UV–visible spectra were recorded using a Schimadzu UV-3101 PC spectrophotometer with an integrating sphere in the 200–2000 nm wavelength range. X-ray diffraction studies were bearded out using a Bruker AXS Advance diffractometer (D2 PHASER A26-X1-A2B0D3A) equipped using a source delivering a monochromatic Cu anode (Kα radiation, λ = 1.54056 Å). The θ–2θ scans were recorded in an angular range between 10° and 80° with a step of 0.02°. TEM images were recorded on a JEOL JEM-2100 microscope and elemental analyses were performed using an EDS (Energy dispersive X-ray spectroscopy) system (Oxford, Wiesbaden, Germany) connected to the JEOL JEM-2100 microscope.

1

h: The hydrolysis ratio (h) defined as the ratio of the amount of water by the total measured of metal cation [n(H2O)/n(Sn4+)].


2.3 Photocatalytic experiments Photocatalytic efficiency was estimated by the decomposition of methylene blue (MB) (Alfa Aesar) dye by using a previously established methodology [34]. MB was reagent grade and used as supplied. All the experiments were conducted at room temperature in air. In each experiment, 0.1 g of photocatalyst was sprinkled in 100 mL of MB solution (10 mg/L) to obtain the concentration of the catalyst at 1.0 g/L. The experiments were carried out in a Pyrex beaker illuminated with a 125 W high pressure mercury lamp (Philips, HPL-N 125 W/542 E27) emitting UV light (365 and 313 nm). The UV lamp was localized above the beaker containing the solution. The elder was stirred for 30 min prior to irradiation to reach the adsorption/desorption equilibrium. Then it was continuously stirred during the experiments. At given irradiation time intervals, 4 mL of the suspension were collected, and then centrifuged (6000 rpm, 10 min) to segregate the photocatalyst particles. The MB concentration was evaluated by UV–visible spectrophotometer (Shimadzu, UV-1650 pc) monitoring the absorption maximum at λmax = 664 nm. A calibration plot based on Beer–Lambert’s law was settled by relating the absorbance to the concentration.

3 Results and discussions 3.1 Structural studies The X-ray diffraction (XRD) spectra of the undoped and V-doped SnO2 nanoparticles are shown in Fig. 1. Based on the Fig. 1a, the diffraction peaks observed can be indexed to tetragonal phase of S nO2 with space group of P 42/mnm and JCPDS card No. 41-1445. All the observed diffraction peaks in the pattern tie in the tetragonal rutile structure of the polycrystalline SnO2. No phase corresponding to vanadium or other vanadium compound can be detected in the pattern, indicating that vanadium gets merged into the tin oxide lattice (Fig. 1a). Increasing the vanadium concentration, the diffraction peaks shift towards the high diffraction angle and become broadens (Fig. 1b). This suggests the incorporation of vanadium into the S nO2 lattice which leads to imperfection in crystals [35, 36]. The shift of the diffraction peaks arises towards the highest angle of diffraction owing to substitution of V x+ (x = 3, 4 or 5) ion for Sn4+, and V x+ possesses 4+ a smaller size than Sn . The lattice constants (a = b, and c) of the prepared samples were determined by Eq. (2) [37, 38] given as follows:

D=

0.9𝜆 𝛽 cos 𝜃

(1)

Fig. 1 XRD patterns of calcined undoped S nO2 and V-doped S nO2

d(hkl) = √

1 h2 +k2 a2

+

( 2) l c2

(2)

where λ, β, and θ are the X-ray wavelength (λ = 1.54056 Å for Cu-Kα), Bragg diffraction angle, and the full width at half-maximum of the diffraction peak (fwhm), respectively. The lattice parameters and crystallite size of the as prepared samples are given in Table 1. It is observed that the crystallite size of the undoped and V-doped SnO2 nanoparticles decreases from 20.6 to 12.3 nm when the concentration of vanadium is raised from 0 to 10 at.%. This can be attributed to the enhancement in the density of nucleation centers in the doped samples, which results in the development of smaller crystallites [39]. Moreover, the lattice parameters (a, b and c) were found to decrease with increasing of doping concentration. This may be assigned to the substitution of Vx+ ions for Sn4+ ions in the crystal lattice as

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Fig. 2 TEM images of calcined samples: b undoped S nO2, c 2 at.% V–SnO2, d 6 at.% V– SnO2, f 10 at.% V–SnO2. EDX elemental mapping of undoped SnO2 (a) and 10 at.% VSnO2 (e)

their ionic radii match (ionic radius of Sn4+ = 0.069 nm and that of Vx+ (V4+= 0.063 nm, V5+= 0.059 nm) [39]. Figure 2 shows the TEM images of undoped and doped SnO2 samples obtained from polyol method at 600 °C for 8 h. The particles were almost homogeneous in composition and uniform in shape and showed almost spherical morphology. Moreover an increase in the vanadium amount

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results in a diminution in the particle size. The crystal sizes of SnO2 nanoparticles measured by TEM shows a significant decrease from 22.8 to 11.6 nm when increasing of the doping concentration from 0 to 10% [40, 41] (see Fig. 2). These values are in good accordance with those generated by XRD. Furthermore, EDX analyses assessed the presence of vanadium ions. Thus, peaks corresponding to Sn,

J Mater Sci: Mater Electron Table 1 X-ray diffraction analyses of undoped and V-doped SnO2 nanoparticles

Samples

Positions (2θ°)

(hkl)

a = b (Å)

C (Å)

Average crystallite size (nm) (XRD)

Average crystallite size (nm) (TEM)

Undoped SnO2

26.52 33.81 51.74 26.58 33.85 51.75 26.6 33.91 51.90 26.64 33.95 51.92

110 101 211 110 101 211 110 101 211 110 101 211

4.751 – – 4.744 – – 4.738 – – 4.727 – –

3.190 – – 3.188 – – 3.184 – – 3.178 – –

20.6 – – 15.2 – – 14 0.7 – – 12.3 – –

22.7 – – 14.6 – – 13.0 – – 11.6 – –

2 at.% V–SnO2

6 at.% V–SnO2

10 at.% V–SnO2

V and O were observed in the EDX pattern of the 10 at.% V–SnO2 sample (Fig. 2e) compared with undoped SnO2 sample (Fig. 2a). Moreover, the vanadium feature was also detected in each V-doped SnO2 sample and their relative intensity increased as a function of the vanadium content as previously reported in the literature which reveals the formation of V–SnO2 composite [17, 42]. 3.2 Textural properties Textural porperties of undoped and V-doped S nO2 nanoparticles were then analyzed by the N 2 adsorption isotherm technique. Figure 3 shows N2 adsorption–desorption isotherms for pure SnO2, 2 at.% V–SnO2, 6 at.% V–SnO2 and 10 at.% V–SnO2 samples. On the basis of IUPAC classification, each material showed a type II isotherm which is characteristic of materials including large mesopores and/or macropores [43]. Furthermore, as shown the inset of Fig. 3, the porosity detected, with an average pore size diameter comprised between 12 and 24 nm, can be attributed to the intercrystallite space. Indeed, the grains consist of a network of aggregated nanoparticles, the voids between the nanoparticles accounting for the porosity detected by N 2 sorption measurements. Table 2 summarizes the textural Table 2 Nitrogen sorption porosimetry dataa, apparent (kapp) constant rate for the degradation of MB and band gap energiesb of undoped and V-doped SnO2 nanopowders

Fig. 3 Nitrogen adsorption–desorption isotherms of undoped S nO2 and V-doped S nO2 samples; Pore size distribution of undoped SnO2 and V-doped S nO2 samples (inset)

data of undoped and V-doped SnO2 nanoparticles, i.e. BET surface area, mean pore diameter, and total pore volume. The undoped SnO2 exhibited a rather weak BET surface area, i.e. 9.8 m2 g−1, with a mean pore diameter of 23.5 nm. Introduction of vanadium into S nO2 induced an increase

Sample

SBET (m2 g−1)

Mean pore size (nm)

Pore volumes ( cm3 g−1)

Eg (eV)

kapp (min−1)

Undoped SnO2 2 at.% V–SnO2 6 at.% V–SnO2 10 at.% V–SnO2

9.8 ± 0.5 16.2 ± 1 18.8 ± 1 21.6 ± 1

23.5 ± 1 13.4 ± 0.5 10.8 ± 0.5 12.1 ± 0.5

0.057 ± 0.005 0.054 ± 0.005 0.050 ± 0.005 0.065 ± 0.005

3.25 3.03 2.87 2.75

0.014 0.017 0.024 0.035

a

Surface areas were determined by BET, mean pore diameters by BJH theory (applied to the adsorption branch), and pore volumes by single-point analysis

b

Deduced from UV–visble absorption spectroscopy

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quantitative insight in this behavior, the band gap energy (Eg) of the synthesized samples was estimated from their absorption spectra according to Eq. (3) [48]: (3) where α, hν, Eg, A and n are the absorption coefficient (or optical density), photon energy, band gap energy, a constant and a parameter belonging to the nature of the semiconductor, respectively. Since cassiterite SnO2 is a direct semiconductor [49], the optical band gap energies of the undoped and V-doped S nO2 nanopowders for direct transition (n = 1/2) can thus be estimated from a plot of (αhν)² vs hν the intercepts of the tangent with the abscissa axis yielding the band gap energies (Eg) of the undoped and V-doped SnO2 nanopowders. The band gap of as-synthesized pure SnO2 nanopowders as calculated from the extrapolation of the absorption edge onto the energy axis was 3.25 eV which was consistent with the results of inset Fig. 4. It can be observed that the band gap energy decreased gradually with increasing the vanadium amount. The band gap energies decreased from 3.25 eV for pure S nO2 to 3.03, 2.87and 2.75 eV for 2 at.% V–SnO2, 6 at.% V–SnO2 and 10 at.% V–SnO2, respectively (Table 2), corresponding to the violet–blue region of the electromagnetic spectrum. As a result a significant decrease of the Eg value was observed when the vanadium content was increased. On the basis of similar trend observed for transition metal doped S nO2 nanomaterials [50, 51], the reduction in the band gap energy was rationalized by postulating an sp-d exchange interaction between d electrons of the vanadium ions (V) substituted on the tin sites and the s and p band electrons of the host SnO2 matrix [32]. The band gap of prepared nanoparticles are narrowed from 3.25 to 2.75 eV, after vanadium doping, which indicates the electronic connection between the two components. The absorption edge is red shifted from pure SnO2 to 10 at.% V–SnO2 samples which correspond to decrease in their band gap energy, the lower band gap energy of a semiconductor results in an increase in photon harvesting and photo responsive. Then, it is expected that sample 10 at.% V–SnO2 should show a higher photocatalytic activity than other samples.

(𝛼h𝜈) = A(h𝜈 − Eg)n

Fig. 4 Diffuse reflectance UV–visible spectra of undoped S nO2 and V-doped SnO2 samples; Plot of (αhν) 2 versus photon energy (hν) of SnO2 and V-doped S nO2 samples (inset)

in the BET surface area with a slight decrease of the mean pore size. Indeed, BET surface area for pure SnO2, 2 at.% V–SnO2, 6 at.% V–SnO2 and 10 at.% V–SnO2 samples were found to be 16.2, 18.8 and 21.6 m2 g−1 and mean pore diameter were estimated to be 13.4, 10.8 and 12.1 nm, respectively [35, 39]. However, the lower average pore size and the larger specific areas observed as the vanadium amount was raised are in agreement with the diminishing in average crystallite and particle sizes determined by TEM and XRD analyses. Consequently, calcined undoped and V-doped SnO2 nanomaterials showed required mesoporosity and surface areas to be employed in applications such as gas sensing [17, 44–46] and photocatalysis [32, 47], which necessitates specific textural properties. 3.3 Optical properties Absorption spectroscopy is a very versatile technique to highlight the optical properties of nanomaterials. The absorption spectra of undoped and V-doped SnO2 samples after calcination in the UV–visible range are depicted in Fig. 4. A sharp absorption edge around 360 nm was detected for undoped S nO2 due to the relatively large exciton binding energy which is charcateristic of cassiterite SnO2 [34]. Insertion of vanadium ions in tin oxide nanoparticles increased the absorption over the whole visible region. This trend is generally attributed to charge transfer processes from the valence band of S nO2 to the t2g energy level of vanadium ions that are situated just below the conduction band of SnO2 [32]. Furthermore, a significant bathochromic shift of the absorption edge of the S nO2 nanoparticles was observed when the vanadium amount in the S nO2 nanoparticles was increased. To get a more

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3.4 Photocatalytic activity Decolorization of MB solution in the presence of the assynthesized catalysts was achieved by monitoring the change in the intensity of the maximum absorption peak at 664 nm of MB. As shown in Fig. 5, the intensity of the characteristic absorption peak diminished progressively with increasing the exposure time indicating the photocatalytic degradation of the dye in the attendance of V–SnO2 nanocomposites. Under UV light irradiation, the maximum absorption peak of MB around 664 nm was diminished


Fig. 5 Time-dependent UV–visible absorption spectra for MB dye in the presence of V-doped SnO2 nanoparticles (dye concentration = 10 mg/L, catalyst dose = 0.1 g/L, pH 7.5)

with increasing irradiation time with discoloration of the solution after 120 min of irradiation as shown Fig. 5 (inset). The photocatalytic activities of the as-synthesized samples after calcination are depicted in Fig. 6. C0 and Ct in Fig. 7a represent the initial concentration after the adsorption–desorption equilibrium for 30 min and the real-time concentration of MB, respectively. Blank experiments in the absence of irradiation with the nanoparticles or under UV-illumination without the nanoparticles were first bearded out to rationalize the photocatalytic activity of the S nO2 nanoparticles. Thus, both blank experiment results indicated that MB could not be decomposed without the photocatalyst and/or UV irradiation. The addition of catalysts resulted in obvious degradation of MB. All the V-doped SnO2 samples actually exhibited an enhanced photocatalytic activity compared to that of pure SnO2. In addition, the vanadium content clearly governed the photocatalytic performance of V-doped S nO2 nanocomposites. The percentage of degradation of MB dye was calculated from the following equation: ( ) Percentage of degradation = 1 − Ct ∕C0 × 100% where C0 is the initial concentration of MB dye solutions (mg/L), Ct is the concentration of the dye after irradiation for a given time interval (mg/L). The photodegradation efficiency of MB was about 43, 49, 62, and 76% for undoped SnO2, 2 at.% V–SnO2, 6 at.% V–SnO2 and 10 at.% V–SnO2, respectively, when the reaction was performed under UV light for 40 min (Fig. 7b). Therefore, 10 at.% vanadium content was found to be the optimum concentration. For a better and more quantitative understanding of the photocatalytic efficiency of the undoped and vanadiumdoped samples, the kinetic analysis of MB degradation was

Fig.  6 a Absorbance changes of MB solution after different irradiation times in the presence of undoped SnO2 and V-doped SnO2 nanoparticles; b bar diagram for the % degradation of MB dye in the presence of undoped SnO2 and V-doped S nO2 nanoparticles

Fig. 7 ln (C/C0) as a function of the irradiation time for different doping concentration of SnO2 nanoparticles

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achieved. As shown in Fig. 7, photodegradation of MB by V-doped SnO2 nanocomposites followed a first-order rate law, ln(Ct/C0) = −kappt, where kapp is the apparent rate constant of the degradation (Table 2). It can been clearly seen that the reaction rates of V-doped SnO2 nanocomposite samples were higher than that of as-synthesized undoped SnO2. Especially, 10 at.% V–SnO2 sample showed the highest catalytic activity with an apparent rate constant of 0.035 min−1 for MB degradation that was about 2.5 times larger than that of pure SnO2 (0.014 min−1). At this stage, it is important to mention that the photocatalytic activity is related to many factors, such as their optical absorption characteristics and textural properties as BET specific areas and average pore sizes of the materials [34]. As a consequence, the enhanced photocatalytic properties observed when the vanadium amount was risen could be rationalized on the basis of the increase in BET specific area, i.e. from 9.8 to 21.6 m2 g−1 and the decrease of the optical band gap, i.e. from 3.25 to 2.75 eV, when the vanadium content was increased up to 10 at.% favoring a better light harvesting. This evolution in the photocatalytic activity might also arise from the coupling of materials with different band gap favoring the electron–hole charge separation as in the case of metal oxide various heterojunctions [52–54].

4 Conclusion In summary, undoped and V-doped SnO2 nanopowders were successfully synthesized by a straightforward polyol method and characterized by XRD, TEM, N 2 sorption measurements and diffuse reflectance UV–visible spectroscopy. Vanadium-doped S nO2 nanopowders showed a tetragonal structure similar to that of undoped cassiterite SnO2 with no trace of any other crystalline oxide phase. The average crystallite size of the nanoparticles decreased from 21 to 12 nm when the vanadium content was increased up to 10 at.% suggesting that V-doping subdued the growth of the nanocrystals. Moreover, the augmentation of the vanadium content yielded an increase in the BET specific area and a concomitant decrease in the average pore size which was related to the reduction of the mean crystallite size upon vanadium doping. Furthermore, the band gap of V-doped SnO2 slightly diminished from 3.25 to 2.75 eV as the vanadium concentration increased from 0 to 10 at.%. The effect of the doping concentration on textural, structural and optical properties of SnO2 could be correlated with the variation in crystallite size. On the other hand, the photocatalytic activities of the doped and undoped S nO2 nanoparticles were determined by studying the photodecomposition of MB as a model organic pollutant. The highest photocatalytic activity was obtained with the 10 at.% V-doped S nO2 sample due to larger BET specific area, lower crystallite

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size and enhanced light harvesting ability. Moreover, the absorption in the visible range observed for this optimum dopant concentration opens new prospects for the decomposition of organics under solar light illumination.

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