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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Tl4CdI6 Nanostructures: Facile Sonochemical Synthesis and Photocatalytic Activity for Removal of Organic Dyes Mojgan Ghanbari and Masoud Salavati-Niasari*
Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 08/30/18. For personal use only.
Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box. 87317-51167, I. R. Iran ABSTRACT: In the present study, Tl4CdI6 nanostructures were synthesized via a facile sonochemical method. The effect of molar ratio of TlI to CdI2, reaction time, power of sonication, and the capping agents was investigated on morphology, size, and purity of the products. The as-prepared nanomaterials were characterized by X-ray diffraction, X-ray energy dispersive spectroscopy, field emission scanning, transmission electron microscopy, and Raman spectroscopy. The optical property of Tl4CdI6 nanoparticles was investigated by ultraviolet−visible spectroscopy (UV−vis), and the band gap was estimated about 2.82 eV. The photocatalytic behaviors of the nanoparticles were investigated by removal and degradation of different organic dyes under the UV irradiation. The results indicated a highest degradation for acid black 1 of 85.7% in 110 min. This sample was selected as an optimum sample for photocatalytic application. and biological strategies (aerobic, anaerobic).8−11 The advanced oxidation processes (AOP) in the presence of ozone (O3), hydrogen peroxide (H2O2), and/or UV light could be used for removing the organic pollutants from wastewater using semiconducting materials which can act as efficient catalysts.12−14 Photocatalysis method is known as a capable nontoxic and environmentally friendly approach for treating the pollution in mild condition by producing eco-friendly byproducts such as CO2 and H2O. In the presence of ultraviolet or visible irradiation by suitable energy, the electron and hole can be generated in the conduction and valence bands of the semiconductor. The generated electron−hole pair can be recombined by releasing the thermal energy and/or transferred to the surface of the photocatalyst and merged with adsorbed species (O2, OH, etc.) to create influential radicals (·O2−, ·OH, etc.). These radicals are known as oxidative or reductive agents for degradation reaction. The crystal property, phase structure, morphologies, and microstructures of photocatalysts can affect the final efficiencies of the catalytic reactions. For example, increasing the crystallinity of semiconductor reduces the number of recombination centers and improves photocatalytic achievement. The formation of an interface or heterojunction between two semiconductors can suppress the recombination and cause to high activity and stability. Nanosized semiconductor catalysts have a large surface area, a good diffusion property, and a high activity; hence, they can be beneficially used as a host for photocatalytic application. Moreover, the transfer distance of photoexcited electrons can be reduced in the small particles comparing to the bulk crystals which can further improve the efficiency. The extended electrons located on the surface of the catalysts can
1. INTRODUCTION Effluent treatment, energy shortage, and pollution decomposition are usually the essential problems for human life.1 Nontraditional water treatment technologies utilize enhanced sensitivity, and selectivity to increase separation efficiencies and reduce environmental and human health problems.2 Therefore, the investigation of a green, reasonable, and safe method for separation and removal of the impurities from the wastewater is essential.3 The major hazardous contaminants in the factories wastewater are mostly aromatic compounds and organic dyes.4 The storage and maintenance of natural sources are important to access healthy, clean, and drinkable water in order to protect the human health and repetitious development of societies. One of the comprehensively used color agent in the manufacturing is xanthine rhodamine B (Rh.B), which has carcinogenic and mutagenic properties. Hence, it is important to eliminate these hazardous compounds from wastewater before releasing to the environment. Various techniques have been developed for removal of the color contaminants such as diverse biological and physicochemical strategies; however, some deficiencies have limited the wide range applications like transferring the dye from the liquid to the solid phase, producing slush, and the biorefractory of dyes.5 Photocatalytic removal has recently achieved a great interest due to the daily lives and versatile features. Azo dyes like methyl orange (MO) are widely used in textile, food, leather, and pharmaceutical industries as a colorant.6 MO permeated into water and triggered health hazards because of the toxicity, mutagenicity, and carcinogenicity of this dye.7 It is renowned that the MO cannot degrade biologically; hence, other methods should be applied in order to eliminate MO from the wastewater. These methods involve physical approaches (reverse osmosis, coagulation, and membrane filtration), chemical methods (oxidation or reduction, ion exchange, complex metric), © XXXX American Chemical Society
Received: May 11, 2018
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DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
voltage. A multiwave ultrasonic generator (MPI Ultrasonics; welding, 1000 W, 20 kHz, Switzerland) equipped with a converter/transducer and titanium oscillator were used for the ultrasonic irradiation. The UV−vis spectra were recorded using a JASCO UV−Visible scanning spectrometer (Model V-670). The surface areas (BET) were determined via nitrogen adsorption at −196 °C using an automated gas adsorption analyzer (Tristar 3000, Micromeritics). 2.3. Synthesis of Precursors. 2.3.1. Synthesis of TlI. The TlI precursor was synthesized via a coprecipitation method using LiI· 2H2O and TlNO3 as starting materials. Primarily, stoichiometric amounts of TlNO3 (3.75 mmol) and LiI·2H2O (3.88 mmol) were dissolved in distilled water in separate beakers. These two beakers were mixed up to obtained a clear solution. Finally, the certain amount of capping agent was added to the above solution. 2.3.2. Synthesis of CdI2. The CdI2 was obtained by mixing the Cd(NO3)2·2H2O (1.94 mmol) with a stoichiometric amount of LiI· 2H2O (0.53 g, 3.88 mmol) (by considering the desired molar ratio of TlI to CdI2 in different experiments). 2.3.3. Synthesis of Tl4CdI6. The solution consisting of CdI2 was added into the TlI container and sonicated for 20 min. The resultant yellowish precipitates were filtered, washed using distilled water, and finally dried in an oven at 80 °C. Various experimental setups were applied in order to obtain the optimum condition. Detailed information of various formulation ingredients are illustrated in Table 1. Caution! Beware of the hazards of using thallium and cadmium. To measure the power output, during the experiments, the temperature of the solutions was recorded versus time. dT/dt could be estimated from the plots of T (temperature) versus t (time) data. Then the power can be calculated as26
take part in the photocatalytic reactions; therefore, the nanosized photocatalysts can be beneficially used in aqueous photocatalytic reactions, while the nanocatalysts regularly endure from deactivation, agglomeration, and difficulty to be separated in recycling of catalyst.14−16 Synthesis of a new class of nanomaterials with unique structure and electronic/optoelectronic properties is one of the major challenges in the scientific society. For a long time, researchers have been attending to the single crystalline semiconductor materials by a wide band gap. The wide-bandgap semiconductors which have high mass density could be used in different fields such as homeland security, medical imaging, and the nonexpansion of nuclear materials and so on.17,18 One of the fascinating and encouraging items is a group of A4BX6 crystals, with A = Tl, In, and B = Hg, Pb, Zn, Mg, Cd, Ge, and X = Cl, Br, I. Recently, semiconductor ternary halides such as Tl4PbI6, Tl4CdI6, In4CdI6, and Tl4HgI6 have attracted much attention in the scientific researches.19 Many ternary halides, for example, Tl4CdI6, reveal an attractive conductivity performance and demonstrate the solid-state ionic conductivity with the heavy metal (e.g., thallium).20−23 Up to now, Tl4CdI6 is synthesized by a solid state reaction and also Bridgman−Stock burger technique under high temperature and hard conditions.24,25 In addition to the synthesis of host materials, in the recent past, much attention has been given by the researchers to design and develop nanophotocatalysts with desired figure of merits for potential application in environmental purification and energy conversion. It is renowned that the performance of the photocatalysts is related to the synthesis method. High-intensity ultrasound irradiation could supply a unique tool for fabrication of photocatalysts with novel structural features. It is reported that the selection of an acceptable artificial route is the key to enhance the performance of photocatalytic reaction.14 In this work, Tl4CdI6 nanostructures have been synthesized by a sonochemical method as a novel technique which provides the small size and high homogeneity product. The parameters such as time and power of sonication as influential parameters, the type of capping agent, and the molar ratio of CdI2 to TlI as experimental variables have been selected, and the effects of these parameters were investigated on size, morphology, and purity of the products. Finally, the products have been analyzed in order to obtain the optimum condition for synthesis of desired product.
i dT y power = jjj zzzcpM k dt {
where the cp is the heat capacity of solvent (J kg−1 K−1) and M is mass of solvent (kg). The power output is calculated to be around 16.2 W in distilled water, in 60 W of power input. Scheme 1 depicts nanostructures and microstructures formations of the Tl4CdI6, where affected by ultrasonic irradiation. Ultrasonic irradiation can influence the size and the morphology of the products. In addition, it can be observed that how the capping agents can cap/orient the particles to form desirable structures. 2.4. Photodegradation of Organic Dyes. The photodegradation was performed in a homemade glass reactor system containing 100 mL of 5 ppm (pH = 3) of aqueous solutions of methyl orange (MO), acid black 1 (AB1), and rhodamine B (Rh.B) (pH = 10 was arranged for methylene blue (MB)). The above suspensions were stirred (500 rpm) at room temperature and kept under dark conditions for 30 min. Finally, the system was irradiated under a UV lamp (Osram ULTRA-VITALUX 300 W). This lamp releases a UVA mixture, ranging from 320 to 400 nm and UVB with 290−320 nm wavelengths, and it emits 13.6 and 3.0 W radiation, respectively. It is ozone-free and radiation encapsulated into a quartz tube, which is adrift into the dyes solution located in the center of the reactor.
2. EXPERIMENTAL SECTION 2.1. Materials. All chemical reagents used in the current study were supplied in analytical grade. Thallium(I) nitrate (TlNO3), lithium iodide (LiI·2H2O), cadmium nitrate (Cd(NO3)2·4H2O), cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), sodium salicylate (NaHSal), ethylenediaminetetraacetic acid (EDTA), and polyvinylpyrrolidone (PVP-40000) were purchased from Merck and used without further purification. 2.2. Physical Measurements. X-ray diffraction (XRD) patterns were recorded using an X-ray diffractometer (Philips) with X’ Pert Pro filtered by Cu Ka radiation (λ = 1.54 Å). GC-2550TG (Teif Gostar Faraz Company, Iran) was used for all chemical analyses. Microscopic morphology of the products was obtained by a LEO 1455VP scanning electron microscope. Prior to taking images, the samples were coated with a very thin layer of Au to make the sample surface a conductor and prevent charge accumulation, and to obtain a better contrast. The elemental analysis of the sample was recorded using an X-ray energy dispersive spectroscopy (EDS) analyzer with 20 kV accelerating voltage. Transmission electron microscopy (TEM) was performed using a HETEM Philips EM208S operating at 200 kV accelerating
3. RESULTS AND DISCUSSION The XRD pattern of the sample 1 (prepared in the absence of sonochemical process) is shown in Figure 1a. In this pattern, minor impurity phases can be observed out of the major phase of Tl4CdI6 or related compounds. In Figure 1b,c, the bulk morphology without any homogeneity can be observed. Unwanted and large morphology of the sample 1 as compared to sample 3 can be due to the effect of ultrasonic irradiation. Ultrasonic irradiation can break the large particles into the fine and homogeneous particles. 3.1. Structural Determination. In this work, four molar ratios of TlI to CdI2 were studied in order to prepare the highpurity Tl4CdI6. The XRD patterns of the samples 2−5 are illustrated in Figure 2a−d, respectively. The XRD pattern of B
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Table 1. Preparation Conditions for Tl4CdI6
c = 9.603. This ratio was selected as an optimum for further investigations. Upon increasing the concentration of CdI2 (1:2), besides the Tl4CdI6 with literature values of JCPDS No. 79-1303 (tetragonal structure), a series of unknown phases (impurity) were composed (Figure 2c). In the sample with molar ratio of 4:1, a pure phase of the Tl4CdI6 structures can be observed by literature values of JCPDS No. 79-1303 (Figure 2d). The XRD patterns of the Tl4CdI6 nanostructures synthesized in the presence of various capping agents such as CTAB, SDS, EDTA, NaHSal, and PVP are shown in Figure 3a−e, respectively. In the presence of cationic capping agent (CTAB), the major phase of Tl4CdI6 nanostructures (JCPDS No. 79-1303, tetragonal structure) contains the diffraction lines of unreacted TlI (JCPDS No. 06-0279 - orthorhombic structure) and Tl2I3 (JCPDS No. 34-1180 - hexagonal structure) (Figure 3a). Upon increasing the SDS (anionic capping agent), a single phase of Tl4CdI6 nanostructures with tetragonal structure (JCPDS No. 79-1303) can be observed as a major phase (Figure 3b). In the presence of EDTA as a chelating capping agent, in addition to the major phase, i.e., Tl4CdI6 (JCPDS No. 79-1303), a minor phase of TlI (JCPDS No. 37-0989) is composed (Figure 3c). The same trend can be observed in the XRD pattern of the sample synthesized in the presence of NaHSal as a complexing capping agent, i.e., Tl4CdI6 and TlI (Figure 3d). Using a polymeric surfactant (PVP) for Tl4CdI6 preparation, the product was composed of TlI with literature values of JCPDS No. 37-0989 and Tl4CdI6 (JCPDS No. 79-1303) (Figure 3e). Hence, from all the above results, it can be concluded that a pure and crystalline phase of Tl4CdI6 can be formed in the presence of an anionic capping agent, i.e., SDS. The crystallite sizes of the products are in the range of 25−33 nm. Furthermore, the effect of the time and power of ultrasonic irradiation on purity of the products was investigated. The XRD patterns of the samples 10−13 are presented in Figure 4a−d,
Scheme 1. Schematic Diagram of the Formation of the Nanostructures and the Effect of Ultrasonic Irradiation on the Particle Size and Morphology
the sample 2 (Figure 2a) (TlI:CdI2 = 1:1) contains a major phase of Tl4CdI6 and a minor phase of TlIO3, well-matched to JCPDS Nos. 79-1303 (tetragonal) and 08-0054 (rhombohedral), respectively. A product with high purity and good crystallinity was achieved in molar ratio = 2 (Figure 2b). In this pattern, the diffraction peaks are in accordance with the JCPDS No. of pure Tl4CdI6 (79-1303), having a tetragonal structure with lattice constants of the unit cell: a = b = 9.222, C
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
Figure 1. XRD pattern and SEM images of sample 1.
Figure 2. XRD patterns of samples (a) 2, (b) 3, (c) 4, and (d) 5.
Figure 3. XRD patterns of samples (a) 6, (b) 7, (c) 8, (d) 9, and (e) 10. D
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 4. XRD patterns of the samples (a) 11, (b) 12, (c) 13, and (d) 14.
respectively. The results indicate that the time and power of sonication are two main factors that play an important role in the purity of the products. In Figure 4a,b, in addition to the Tl4CdI6 with tetragonal structure (JCPDS No. 30-1321) as the main phase, the diffraction lines of TlI (JCPDS No. 06-0279 with orthorhombic structure) and TlI (JCPDS No. 37-0989 with cubic structure) phases can be also observed. The best time for preparation of pure Tl4CdI6 (main product) is around 20 min. The importance of using the sonochemical method in the synthesis route was obviously emerged. In constant time and power of sonication (20 min and 40 W), the diffractogram of the sample contains a major phase of Tl4CdI6 (unknown structure, JCPDS No. 30-1321) and a minor phase of TlI (unknown structure, JCPDS No. 46-0976). Upon increasing the sonication power, the product was composed of two phases, a tetragonal structure of Tl4CdI6 (JCPDS No. 79-1303) and a cubic structure of TlI (JCPDS No. 78-0619). On the other hand, as illustrated in these figures, increasing the sonication time can increase the crystallinity of the products. 3.2. Morphological Observations. The morphology and particle sizes of the products in different conditions were investigated by SEM and TEM images. Figure 5 illustrates the SEM images of the products obtained via changing the mole ratio of precursor. Figure 5a,b reveals that the microstructures were formed in 1:1 mol ratio of precursor (sample 2). Figure 5c,d shows that the SEM images of sample 3 (prepared in 2:1 mol ratio of precursors) are composed of nanoparticles by very similar and uniform size and morphology. The size distribution is less than 15 nm, and homogeneity in this sample is high. In other molar ratios, the morphologies are inhomogeneous, in accordance to XRD patterns of these products (Figure 5a,b
Figure 5. SEM images of the samples (a, b) 2, (c, d) 3, (e, f) 4, and (g, h) 5.
and 5e−h). Hence, it can be concluded that the ideal ratio of TlI:CdI2 is 2:1. This ratio is applied for studying the effect of the various capping agents on the morphology of the products. Figure 6 shows the SEM images of the products in the presence of various capping agents. In the presence of CTAB (Figure 6a), the product contains fine nanoparticles; however, the particles agglomerate in some areas. The average particle size in this sample is measured to be around 24 nm. By using SDS, the product was formed from homogeneous nanoparticles with the average particle size of 11 nm (Figure 6b). In the presence of EDTA, a homogeneous morphology can be observed (Figure 6c), while the SEM images of the sample synthesized with NaHSal displays nanoparticles with small amounts of agglomerated product. The average particle size of this sample (synthesized in NaHSal) is about 24 nm (Figure 6d). Finally, the morphology of the sample in the presence of polymeric surfactant (PVP) is composed of agglomerated areas with the average particle size of 35 nm (Figure 6e). The effects of time and power of ultrasound irradiation were optimized as two constructive persuasive parameters on morphology and size of products. SEM images of the samples 11−14 are shown in Figure 7a−d, respectively. In order to study the effect of sonication time and power on the morphologies, three sonication times (10, 20, and 30 min) and three sonication powers (40, 60, and 80 W) were selected. As illustrated in Figure 7, increasing the sonication time from 10 to 30 min can reduce the size of aggregation. In Figure 7a E
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
(10 min sonication time), a small amount of agglomeration can be observed with the average particle size of 22 nm. By increasing the time of sonication, the morphology of the products was changed to uniform nanoparticles (Figure 7b). As the time of sonication was extended to 20 min with 40 W power of ultrasound, the product was composed of agglomerated particles (Figure 7c). Upon increasing the power of sonication, the morphology of product became almost homogeneous (Figure 7d). Frequently, increasing the sonication time may not be positively affected in all the time range. The optimum of sonication time has been considered to be around 20 min. It is renowned that increasing the sonication power caused the fast growth of primary nuclei, hence increased the agglomeration of the particles. Increasing the power of sonication can positively affect the preparation of fine particles since bulk structures are formed. Therefore, from the results, the optimum sonication power has been considered to be 60 W. The histograms of the particle diameters of the sample 2 were measured from their respective SEM image using Digimizer software (Figure 8). The particle size distribution of the sample 2
Figure 8. Particle size distribution of the sample 3. Figure 6. SEM images of the samples (a) 6, (b) 7, (c) 8, (d) 9, and (e) 10.
was measured in the range of 1−20 nm. This histogram reveals that most of the particles are in the range of 10−20 nm. Figure 9a−c illustrates the TEM images of the optimized product (sample 3). The average particle size of these
Figure 7. SEM images of the samples (a) 11, (b) 12, (c) 13, and (d) 14.
Figure 9. TEM images of the sample 3. F
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry nanoparticles was estimated to be around 9 nm which is in good agreement by the SEM. 3.3. EDS Spectrum. Figure 10 demonstrates the EDS spectrum of Tl4CdI6 nanostructures (sample 3). In this
Figure 10. EDS spectrum of the sample 3.
spectrum, the peaks of Tl, Cd, and I elements can be observed. The reason for the presence of O in the spectrum is the surface oxidation of product in the atmosphere.27 3.4. Optical Properties and Band Gap Calculation. Figure 11a shows the optical absorption spectrum of Tl4CdI6 nanoparticles. The DRS spectrum was used for additional access to the information about quality and electronic structure. An intense absorption peak can be observed in 346 nm, and other absorption peaks with low intensity are in the range of 300−400 nm. The fundamental absorption in the band gap of Tl4CdI6 nanoparticles grows at around 246 nm. The other absorption bands are most probably due to the presence of impurities or vacancies.28,29 Optical band gap (Eg) can be calculated based on the optical absorption spectrum using the equation:30 (Ahυ)n = B(hυ − Eg), where hυ is the photon energy, A is absorbent, B is a material constant, and n is 2 or 1/2 for direct and indirect transitions, respectively. The optical band gap for the absorption peak is obtained by extrapolating the linear part of the (Ahυ)n curve versus hυ to zero. No linear relation was found for n = 1/2, recommending that the composed Tl4CdI6 nanostructures are semiconductors with direct transition at this energy.24 The band gap of as-prepared Tl4CdI6 nanostructures was estimated to be about 2.82 eV (Figure 11b). The calculated band gap was in accordance with the effective compound by good performance in the photocatalytic reaction.24
Figure 12. Raman spectra of the samples (a) 3 and (b) 5.
3.5. Raman Spectrum. Figure 12a shows the Raman spectrum at room temperature of Tl4CdI6 nanoparticles (sample 3) to complete vibrational position modes of Tl4Cdl6. The characteristic absorptions of as-prepared Tl4CdI6 were recorded in the range of 44−114 cm−1. In this spectrum, six absorption bands can be observed which are located at 54.4 , 63.3, 69.3, 78.2, 84.1, and 107.7 cm−1. These vibrational modes can be assigned by considering the Tl4Cdl6 consisting of the vibrational modes of TlI and CdI2. The intense band at 69.3 cm−1 was assigned to the symmetric stretching of the Tl-I, and the band at 54.4 cm−1 was assigned to the Tl-I.31 The band located at 107.7 cm−1 was attributed to the symmetric stretching modes of CdI2.32 The bands located
Figure 11. (a) DRS spectrum and (b) optical density (αhν)2 vs energy (E) plot of the sample 3. G
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry at 63.3, 78.2, and 84.1 cm−1 were assigned to Cd-I deformation type bands.33 Raman shift values of as-prepared Tl4CdI6 nanostructures have been compared to the Raman shift values of Tl4CdI6, reported in literatures. The results show a red shift in the Raman spectrum because of the phonon imprisonment effect and the strain which was created by reducing the size of nanomaterials.34,35 The Raman spectrum at room temperature of the sample 5 is shown in Figure 12b. The characteristic absorption of the as-prepared Tl4CdI6 was recorded in the range of 30−130 cm−1. In this spectrum, six absorption bands can be observed at 48.4 , 66.3, 90.0, 95.9, 116.6, and 122.5 cm−1. The bands at 48.4 and 116.6 cm−1 can be assigned to the symmetric stretching modes of CdI2.32 The band located at 66.3 cm−1 is ascribed to the TlI, and the bands located at 80−110 cm−1 which consist of two bands at 90.0 and 95.9 cm−1 are assigned to Cd-I bands.33 3.6. BET Analysis. Figure 13a shows the N2 adsorption/ desorption profile of sample 7. According to the IUPAC classification, this isotherm can be relegated in type III of N2 adsorption/desorption isotherms. The hysteresis of nanoparticles (sample 7) was classified in H3-type hysteresis, which is attributed to the mesopore or macropore materials that enclosed via a matrix of small pore materials. In this nanoparticle hysteresis loop, the sample has a broad pore size distribution, ranging from mesopore to macropore because of the high comparative pressure (p/p0) (Figure 13b). The total volume and mean diameter of the nanoparticles were calculated to be 0.1098 cm3·g−1 and 9.68 nm, respectively. The BET analysis showed 5.84 m2·g−1 specific surface areas. The BJH analysis is multimodal, and the average size of nanostructures is between 1 and 24.49 nm. Figure 13c demonstrates the N2 adsorption/desorption profile of sample 9. According to the IUPAC classification, this isotherm was relegated in the type III of N2 adsorption/desorption isotherms. The size distribution diagram of sample 9 is displayed in Figure 13d. The total volume and mean diameter of nanoparticles are calculated to be 0.1239 cm3·g−1 and 36.34 nm, respectively. In addition, the BET analysis shows 5.39 m2·g−1 specific surface areas. The BJH analysis is multimodal, and the average size of nanostructures is between 1 and 190.55 nm. Figure 13e indicates the N2 adsorption/desorption profile of the sample 10. By considering the IUPAC classification, according to the IUPAC classification, this isotherm is relegated in the type III of N2 adsorption/desorption isotherms. The size distribution diagram of sample 10 is illustrated in Figure 13f. The total volume and mean diameter of nanoparticles were calculated to be 0.3228 cm3·g−1 and 17.00 nm, respectively. In addition, the BET analysis showed 1.40 m2·g−1 specific surface areas. The BJH analysis is multimodal, and the average size of nanostructures is between 1 and 190.55 nm. As-archived data from BET analysis are in good agreement with the results of SEM and TEM images such as estimated size of products. 3.7. Photocatalytic Activity. The photocatalytic behavior of the Tl4CdI6 nanoparticles was investigated by elimination and degradation of different dyes including methyl orange, acid black 1, rhodamine B, and methylene blue as some of the organic pollutions under UV irradiation (Figure 14). The highest amount of degradation percentage was perceived for acid black 1, and the lowest amount of degradation percentage was observed for methylene blue. When the nanopowder of semiconductor photocatalyst was irradiated by UV-irradiation with the suitable energy that is equal or greater than the energy of band gap, a pair of electron and hole can be formed in the conduction and valence band of nanopowders. These pairs of
electrons and holes can be recombined or interact autonomously with other molecules in aqueous solution. The holes could be reacted with water on the surface of Tl4CdI6 or hydroxide ions and prepare hydroxyl radicals (•OH). The electrons could be accepted by the oxygen and form superoxide radical anion (O2−). The hydroxyl radical is known as one of the strong oxidizing agents and it was attached to the dye molecule and furnished the oxidized product. These reactions could be summarized in the following reactions.36−46 Tl4Cdl 6 + hν → h+ + e− h+ + e− → heat
H 2O + h+ → H+ + ·OH h+ + OH− → ·OH e− + O2 → ·O2− ·
O2− + HO2· + H+ → H 2O2 + O2
·
O2− + organic species → degradation products + OO·
The percentage of degradation was deliberate as eq 1 D.P.(t ) = (A 0 − A t )/A 0 × 100
(1)
where A0 and At are the absorbencies of the liquid sample at 0 and t min, respectively.47 It was observed that about 71.8%, 85.7%, 69.0%, and 49.1% methyl orange, acid black 1, rhodamine B, and methylene blue were degraded after 110 min for Tl4CdI6 nanostructures, respectively (Scheme 2). 3.7.1. Photocatalytic Activity of TlI. The photocatalytic activity of TlI nanoparticles was investigated by degradation of different dyes including methyl orange, acid black 1, rhodamine B, and methylene blue as some of organic pollutions under UV light irradiation (Figure 15). The highest degradation percentage was perceived for acid black 1, and the lowest amount of degradation percentage was observed for methylene blue. The reason for the increasing photocatalytic activity of Tl4CdI6 is the highest defects in the structure and change of crystalline structure in comparison with TlI. 3.7.2. XRD Results after Degradation. Figure 16a−d shows the XRD patterns of Tl4CdI6 nanostructures after dye degradation reactions for MO, AB1, Rh.B, and MB, respectively. In Figure 16a, all diffraction lines are in accordance with JCPDS No. 79-1303 of tetragonal Tl4CdI6 structure (lattice constants of unit cell: a = b = 9.222, c = 9.603). Figure 16b shows the XRD pattern of Tl4CdI6 after degradation of AB1. This pattern is also well-matched with Tl4CdI6 JCPDS No. 79-1303. Using Rh.B as an organic dye, the Tl4CdI6 phase remains intact after degradation (Figure 16c). The same XRD pattern was also obtained after MB degradation (Figure 16d). It can be observed that, after organic dyes degradation, the host structure remains intact. This proved that the stability of Tl4CdI6 is high in aqueous solvent. 3.7.3. FT-IR Spectrum. FT-IR spectra of the methyl orange (MO), methylene blue (MB), acid black 1 (AB1), and rhodamine B (Rh.B) before and after degradation are shown in Figure 17. In the FT-IR spectrum of MO, the characteristic bands of the azo group (−NN−, at 1440 and 1519 cm−1) and the benzene ring (at 1400−1600 cm−1) can be observed. In addition, three peaks in the range of 2800−3000 cm−1 correspond to the antisymmetric and symmetric stretching vibrations of −CH3. Two vibration frequencies at 1197 and 1038 cm−1 are attributed to the asymmetric stretching vibration of −SO3Na.48 So, it was concluded that the azo bond and H
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 13. N2 adsorption/desorption isotherms of (a) sample 7, (c) sample 9, and (e) sample 10 and their respective pore size distributions of (b) sample 7, (d) sample 9, and (f) sample 10.
corresponded to axial-deformation vibrations of the C−H bond in polynuclear aromatic rings. The bands in the regions 1020−1250 cm−1 and 1266−1342 cm−1 were assigned to the axial deformation vibrations of the C−N bond of aliphatic amines and to the axial deformation of the C−N bond of aromatic amines, respectively.49 The benzene ring and the
the benzene ring were fragmented and with the decolorization of MO were occurred the decoloration that desulfuration. The breaking of chromophore bands in methyl orange formed anilines and benzenesulfonic acids (Figure 17a,b). Figure 17c,d shows the FT-IR spectra of methylene blue. The MB spectrum shows several bands between the regions 675−900 cm−1 that I
DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 15. Degradation of organic dyes solution for TlI. Figure 14. Degradation profiles of the organic dye solutions.
C−N bond disappeared in the MB spectrum. In Figure 17e,f are illustrated the FT-IR spectra of AB1. The characteristic peaks of the azo bond (−NN−, at 1495 and 1564 cm−1) and the benzene ring (at 1400−1600 cm−1) disappeared in the spectrum of acid black 1. The characteristic peaks of the −SO3Na group which were located at 1197 and 1038 cm−1 were deceased.48 So, it was concluded that the azo bond and the benzene ring were fragmented and with the decolorization of acid black 1 were occurred the decoloration that desulfuration. Absorption bands found in the high-frequency (4000−2700 cm−1) region of the spectrum were usually associated with O−H and C−H stretching modes. Figure 17g,h shows a broad band at 3430 cm−1 for Rh.B which is assigned to the stretching vibration of the hydroxyl group. Two vibrational frequencies at 1693 and 2978 cm−1 can be assigned to −CN stretching and −C−H asymmetric stretching, respectively.50−52 Sharp absorption bands at 1589 cm−1 and at 1474 cm−1 were assigned to the stretching vibration of the asymmetric and symmetric COO− group, respectively. The aromatic skeletal C−C stretch and C−O−C stretch were distinguished at 1341 and 1247 cm−1, respectively. The aromatic C−H in-plane and out-of-plane bending and wagging vibrations were observed at 1127 and 861 cm−1 and 680 cm−1, respectively.50−52 As demonstrated in Rh.B spectra, the aromatic skeletal C−C stretch has disappeared. Therefore, due to the results of the infrared spectra, the dyes have been degraded.
4. CONCLUSIONS In the current study, for the first time, the sonochemical method was used in order to synthesize Tl4CdI6 nanostructures in the presence of different salts as precursors. Various parameters
Figure 16. XRD patterns after dyes degradations of (a) MO, (b) AB1, (c) Rh.B, and (d) MB.
Scheme 2. Reaction Mechanism of Photocatalytic Degradations of Various Dyes over Tl4CdI6 Nanostructures under UV Light Irradiation
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DOI: 10.1021/acs.inorgchem.8b01293 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 17. FT-IR spectra of (a, b) methyl orange, (c, d) methylene blue, (e, f) acid black 1, and (g, h) rhodamine B, before and after degradation, respectively. orange with TiO2 nanoparticles using a triboelectric nanogenerator. Nanotechnology 2013, 24, 295401−295406. (2) Wang, Z. L.; Song, J. H. Piezoelectric nanogenerators based on zinc oxide nanowire arrays. Science 2006, 312, 242−246. (3) Wang, Z. L. Self-powered nanosensors and nanosystems. Adv. Mater. 2012, 24, 280−285. (4) Yang, Y.; Zhang, H. L.; Lee, S.; Kim, D.; Hwang, W.; Wang, Z. L. Hybrid energy cell for degradation of methyl orange by self-powered electrocatalytic oxidation. Nano Lett. 2013, 13, 803−808. (5) Yazdani, E. B.; Mehrizad, A. Sonochemical preparation and photocatalytic application of Ag-ZnSMWCNTs composite for the degradation of rhodamine B under visible light: experimental design and kinetics modeling. J. Mol. Liq. 2018, 255, 102−112. (6) Katsuda, T.; Ooshima, H.; Azuma, M.; Kato, J. New detection method for hydrogen gas for screening hydrogen-producing microorganisms using water-soluble wilkinson’s catalyst derivative. J. Biosci. Bioeng. 2006, 102, 220−226. (7) Choudhary, B.; Goyal, A.; Khokra, S. L. New visible spectrophotometric method for estimation of itopride hydrochloride from tablets formulations using methyl orange reagent. Int. J. Pharm. Pharm. Sci. 2009, 1, 159−162. (8) Parshetti, K.; Telke, A. A.; Kalyani, D. C.; Govindwar, S. P. Decolorization and detoxification of sulfonate azo dye methyl orange by kocuriarosea MTCC 1532. J. Hazard. Mater. 2010, 176, 503−509. (9) Mathur, N.; Bhatnagar, P.; Sharma, P. Review of the mutagenicity of textile dye products. Univers. J. Environ. Res. Technol. 2012, 2, 1−18. (10) Li, Z.; Zhang, P.; Shao, T.; Wang, J.; Jin, L.; Li, X. Different nanostructured In2O3 for photocatalytic decomposition of perfluorooctanoic acid (PFOA). J. Hazard. Mater. 2013, 260, 40−46. (11) Brown, J. P.; Dietrich, P. S. Mutagenicity of selected sulfonatedazo dyes in the salmonella/microsome assay: use of aerobic and anaerobic activation procedures. Mutat. Res., Genet. Toxicol. Test. 1983, 116, 305−315. (12) Salavati-Niasari, M.; Mir, N.; Davar, F. ZnO nanotriangles: synthesis, characterization and optical properties. J. Alloys Compd. 2009, 476, 908−912.
were optimized to achieve pure phase and small products. It was illustrated that the power and time of sonication are two effective parameters for optimizing the morphology. The molar ratio of TlI to CdI2 and the type of capping agent can also affect the purity and particle diameters. The role of sonication upon purity and particle size of the products was confirmed by the SEM images and XRD patterns. The results clearly revealed that the smallest particles were formed in 20 min and 60 W. The band gap was measured to be around 2.82 eV. The evaluated band gap confirmed that the Tl4CdI6 nanoparticles could be an efficient photocatalyst. The photocatalytic activity of the product was investigated by employing methyl orange, acid black 1, rhodamine B, and methylene blue as organic dyes. The results confirmed that the products could decompose all four dyes in high value, successfully.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +98 31 55912383. Fax: +98 31 55913201. E-mail:
[email protected]. ORCID
Masoud Salavati-Niasari: 0000-0002-7356-7249 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Authors are grateful to the council of Iran National Science Foundation (INSF) and University of Kashan for supporting this work by Grant No. (159271/89920).
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