Continuous microwave flow synthesis (CMFS) of nano-sized tin oxide: Effect of precursor concentration

Tin oxide (SnO₂) nanoparticles exhibit an intense luminescent behavior under UV-light in contrast to the bulk tin oxide and therefore have become focus of many investigations. SnO₂ nano-agglomerates were successfully prepared by continuous microwave flow synthesis (CMFS) method using tin chloride pentahydrate as a tin precursor. The effect of concentration of reacting species on the degree of crystallinity, particle size, lattice parameters, morphology, and photocatalytic behavior was probed. Structural and morphological features of the resulting SnO₂ nano-structures were examined by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunar Emmett Tellar (BET), Transmission electron microscopy (TEM) and ultra-violet (UV/Visible) spectroscopy. From the XRD spectra the crystal structure of the synthesized product was confirmed as phase pure tetragonal cassiterite type with particle size of 4.43 nm. TEM images further confirmed the formation of highly agglomerated nanoparticles, whereas the change in concentration had no appreciable effect on the particle morphology. BET surface area measurements confirmed that the surface area of the SnO₂ nanoparticles decreased with increase in Sn precursor concentration. The optical band gap values of SnO₂ nanoparticles were calculated to be 3.19 eV, which is a red-shift compared with that of the bulk SnO₂ (3.6 eV). The nano-agglomerates were efficient catalyst for the photodegradation of methylene blue (MB) dye. Our results indicate that the synthesized SnO₂ nanoparticles can have potential applications in liquid photovoltaic, photocatalysis and sensors.     

Photocatalytic Activity of Pure and Zinc Doped Tin Oxide Nanoparticles Synthesized by One Step Direct Injection Flame Synthesis

A very simple and rapid Direct Injection Flame Synthesis (DIFS) method is effectively used to synthesize pure tin oxide (SnO₂) and zinc doped tin oxide (Zn:SnO₂) nanoparticles from the metallic tin (Sn) and zinc (Zn) powders for the photocatalytic degradation of methylene blue (MB) dye. The DIFS nanoparticles were characterized using XRD, Raman, UV–Vis, FESEM, PL and EDX studies. The X-ray diffraction analysis indicated that the synthesized SnO₂ and Zn:SnO₂ nanoparticles have pure tetragonal phases and their average crystallite size decreases when Zn was doped with SnO₂. Raman study confirmed the various mode of vibrations and the crystal structure of the synthesized nanoparticles. Purity, atomic percentage and chemical composition were analysed using Energy dispersive X-ray analysis and found to be free from impurities. The band gap energy increases from 3.5 to 3.6 eV upon doping which was revealed from the UV–Visible spectroscopic analysis. Photoluminescence analysis confirms the red shifted emission for Zn:SnO₂ due to the oxygen deficiency. The CIE chromaticity (x,y) for SnO₂ and Zn:SnO₂ was calculated from the emission spectra and the co-ordinates represents blue and violet region respectively. Field Emission Scanning Electron Microscopy analysis showed that the pure SnO₂ nanoparticles have irregular, agglomerated, nanoflowered and nanoclustered formation whereas Zn:SnO₂ nanoparticles has more crystalline, cubical and nanoflake structure. The photocatalytic activity was enhanced due to the presence of Zn in SnO₂ under UV light irradiation. The efficiency of MB degradation by SnO₂ was found to be 82% and enhanced to 88% upon doping. Thus the Zn doped SnO₂ nanoparticles synthesized by DIFS was found to be an effective photocatalyst than the pure SnO₂.

     

Magnetic Properties of Mn‐doped SnO2 Thin Films Prepared by the Sol–Gel Dip Coating Method for Dilute Magnetic Semiconductors

Manganese‐doped tin oxide (SnO₂:Mn) thin films were deposited on glass substrates by the sol–gel dip coating technique. The effect on structural, morphological, magnetic, electrical, and optical properties in the films with different Mn concentrations (0–5 mol%) were investigated. X‐ray diffraction patterns (XRD) showed the deterioration of crystallinity with increase in Mn‐doping concentration. Scanning electron microscopy (SEM) studies showed an inhibition of grain growth with an increase in Mn concentration. X ray photoelectron spectroscopy (XPS) revealed the presence of Sn⁴⁺ and Mn³⁺ in SnO₂: Mn films. SnO₂: Mn films show ferromagnetic and paramagnetic behavior. These SnO₂:Mn films acquire n‐type conductivity for 0–3 mol% (SnO₂ ‐ Sn_0.97Mn_0.03O_{2) ‐}doping concentration and p type for 5 mol% Mn‐doping concentration(Sn_0.95Mn_0.05O₂) in SnO₂ films. An average transmittance of > 75% (in UV‐Vis region) was observed for all the SnO₂:Mn films. Optical band gap energy of SnO₂: Mn films were found to vary in the range 3.55 to 3.71 eV with the increase in Mn‐doping concentration. Photoluminescence (PL) spectra of the films exhibited an increase in the emission intensity with increase in Mn‐doping concentration which may be due to structural defects or luminescent centers, such as nanocrystals and defects in the SnO₂. Such SnO₂:Mn films with structural, magnetic and optical properties can be used as dilute magnetic semiconductors.     

Feasibility of using a rotating packed bed in preparing coupled ZnO/SnO2 photocatalysts

In this work, coupled ZnO/SnO₂ photocatalysts were prepared in a rotating packed bed (RPB) via co-precipitation. The precursors of coupled ZnO/SnO₂ photocatalysts were formed from solutions of zinc sulfate, tin tetrachloride and sodium hydroxide. The calcinations of these precursors yielded coupled ZnO/SnO₂ photocatalysts. The effect of calcination temperature on the characteristics and photocatalytic activity of coupled ZnO/SnO₂ photocatalysts was studied. The photocatalytic activity of coupled ZnO/SnO₂ photocatalysts was evaluated using the photocatalytic decolorization of methylene blue. The experimental results reveal that coupled ZnO/SnO₂ photocatalysts that were obtained by calcination at 600 °C for 10 h were the most efficient in decolorizing methylene blue.     

High-density ZnSnO3 nanowire arrays fabricated using single-step hydrothermal synthesis

This study examined the fabrication of high-density rhombohedral ZnSnO₃ nanowire arrays on fluorine-doped SnO₂ (FTO) substrates through single-step hydrothermal synthesis and their synergistic piezo-related performance. The band gap (approximately 3.7 eV) and valence band (E_v) position (approximately 2.7 eV below the Fermi energy of Au [approximately −4.9 eV]) of the arrays were obtained using ultraviolet-visible (UV-Vis) spectrometry and UV photoelectron spectroscopy, respectively. An energy band diagram was obtained, revealing the favorable band positions of the samples for photodegradation and water splitting. Reliable and superior piezophotodegradation capability with a degradation rate constant of approximately 17.6 × 10⁻³ min⁻¹ was also observed. Holes and •OH were predominant for the degradation mechanism, as determined by scavenger studies. Moreover, the samples exhibited favorable piezophotoelectrochemical (PPEC) performance, which was validated by the obtained applied bias photon-to-current efficiency. The stress-induced photocurrent density observed in a PPEC reaction was more than twice that observed in a photoelectrochemical reaction. Both piezophotodegradation and PPEC reactions were attributable to the inhibition of electron-hole pair recombination because of the excellent alignment of the nanowires, piezopotential buildup, and band bending of the ZnSnO₃ nanowires. Our results indicate a positive effect of piezoelectricity on the piezo-related applications of the sample.     

Ink‐jet Printing of Hollow SnO2 Nanospheres for Gas Sensing Applications

Hollow tin‐oxide (SnO₂) nanospheres were synthesized by coating, carbon nanospheres (CNs) as hard templates, with a tin(IV) sol obtained by partial hydrolysis of [Sn(OBu^t)₄] under ambient conditions. Formation of crystalline SnO₂ spheres upon calcination was confirmed by powder X‐ray diffraction data, whereas the hollow interiors of SnO₂ particles were verified by scanning and transmission electron microscopy of both intact and broken spheres. The shell of SnO₂ nanospheres sintered at 700°C consisted of a single layer of nanocrystallites (~6 nm) self‐assembled in a ball‐like superlattice. Tin‐oxide hollow spheres showed an average diameter of 150 nm and could be homogeneously dispersed in water/ethylene glycol (50:50 vol%) mixture to form stable inorganic inks viable for their use in commercial ink‐jet printers demonstrated by printing porous ceramic structures on an interdigitated sensor chip. The integration of large surface and nanoscopic voids in the final structures imparted higher sensitivity to the as‐printed sensors toward both oxidizing (nitrogen dioxide) and reducing gases (methane and ethanol), which validates the enormous potential of printable inorganics in functional applications.     

CuO improved (Sn,Sb)O2 ceramic anodes for electrochemical advanced oxidation processes

Antimony-doped tin oxide electrodes with CuO as sintering aid are presented as an economical alternative to metal-based electrodes, intended for the electrooxidation process of emerging and recalcitrant organic contaminants in wastewaters. The CuO proportion has been optimized to obtain densified electrodes with a mild thermal cycle (T_max = 1200°C). One of the manufactured electrodes (97.8 mol.% of SnO₂, 1.0 mol.% of Sb₂O₃, and 1.2 mol.% of CuO) was selected for electrochemical characterization from a physical and morphological analysis. The electrochemical behavior of the selected electrode showed that the addition of CuO as sintering aid widens the electrochemical window and increases the electrode “inactivity”, with respect to an (Sn, Sb)O₂ electrode synthesized in the same conditions. In return, the (Sn,Sb,Cu)O₂ electrode presents a significantly lower electrochemical rugosity factor. Moreover, the addition of CuO does not change the oxygen evolution reaction mechanism, but it modifies the kinetic parameters, leading to a larger accumulation of hydroxyl radicals. Consequently, the addition of CuO as sintering aid significantly improves the electrochemical properties of the electrode as an electrochemical advanced oxidation process anode with respect to the (Sn,Sb)O₂ electrode, at the expense of worsening its electrochemical roughness factor. The results of the electrochemical characterization were confirmed by Norfloxacin degradation tests.     

Al3+ doping induced changes of structural,morphology, photoluminescence,optical and electrical properties of SnO2 thin films as alternative TCO for optoelectronic applications

Highly transparent and conductive pure (SnO₂) and aluminum doped tin oxide (Al:SnO₂) thin films were deposited on glass substrates by the sol-gel spin-coating method. The structural, morphological, optical and electrical properties of the prepared thin films at different doping rates have been studied. X-ray diffraction results revealed that all the films were polycrystalline in nature with a tetragonal rutile structure. SEM images of the analyzed films showed a homogeneous surface morphology, composed of nanocrystalline grains. The EDS results confirmed the presence of Sn and O elements in pure SnO₂ and Sn, O, Al in doped SnO₂ thin films. The optical results revealed a high transmittance greater than 85% in the visible and near infrared and a band gap varying between 3.82 and 3.89 eV. PL spectra at room temperature showed that the most dominant defects correspond to oxygen vacancies. A low resistivity of order varying between 10^?3 and 10^?4 Ω cm and a high figure of merits ranging between 10^?3 and 10^?2 Ω^?1 in the visible range were obtained. The best performances were obtained for samples containing 2 at. % Al, which could be used as an alternative TCO layer for future optoelectronic devices.     

Synthesis and characterization of Sb–SnO2/kaolinites nanoparticles

In this paper, we reported the synthesis of composite conductive powders of antimony-doped tin oxide (Sb–SnO₂) coated onto kaolinite. Structure and morphology of the samples were systematically characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS). The results showed that Sb–SnO₂ nanoparticles (< 10 nm) were successfully coated as thin layers on the surface of kaolinite. The antimony-doped tin oxide/kaolinite (ATK) composites retained the flake morphology like the original kaolinite and had a resistivity of 273.2 Ω·cm. Sb–SnO₂ layers were proved to attach to the kaolinite surface via the Sn–O–Si or Sn–O–Al bonds. The growth mode of Sb–SnO₂ layers onto the kaolinite was investigated.     

Solvent-free infiltration method for mesoporous SnO2 using mesoporous silica templates

Mesoporous tin oxide (SnO₂) materials, exhibiting high surface areas, crystalline frameworks and various mesostructures, were successfully obtained by a facile solvent-free infiltration method from mesoporous silica templates. Various kinds of mesoporous silica materials, such as KIT-6 (bicontinuous 3-D cubic, Ia3d), SBA-15 (2-D hexagonal, p6mm), SBA-16 (3-D cubic with cage-like pores, Im3m) and spherical mesoporous silica (disordered), were utilized as the hard templates. Tin precursor (SnCl₂ · 2H₂O, m.p. 310–311 K) was infiltrated spontaneously within the mesopores of silica templates by melting the precursor at 353 K without using any solvent. The heat-treatment of SnCl₂-infiltrated composite materials at 973 K under static air conditions and subsequent removal of silica templates by using HF result in the successful preparation of mesoporous SnO₂ materials. The mesostructures as well as the morphologies of mesoporous SnO₂ materials thus obtained were very similar with those of the mesoporous silica templates. The mesoporous SnO₂ materials exhibit high surface areas of 84–121 m²/g as well as high pore volumes in the range of 0.22–0.35 cm³/g. The present solvent-free infiltration method is believed to be a simple and facile way for the preparation of mesoporous materials via nano-replication from mesoporous silica templates.     

High‐performance varistors prepared by hot‐dipping tin oxide thin films in Sb2O3 powder: Influence of temperature

A series of SnO_x–Sb₂O₃ thin film varistors were fabricated through hot‐dipping tin oxide films deposited by radio‐frequency magnetron sputtering in Sb₂O₃ powder at varied temperatures in air. With the increase in hot‐dipping temperature (HDT) from 200°C to 600°C, the nonlinear coefficient (α) of the samples increased first and then decreased, reaching the maximum at 500°C, which was mainly determined by the completeness of high‐resistant Sb₂O₃ layer at tin oxide grain boundary and the chemical composition of tin oxide films. Correspondingly, the leakage current (I_L) decreased first and increased later. The breakdown electric field (E_100 mA) decreased constantly with increasing HDT. The SnO_x–Sb₂O₃ film varistors prepared at 500°C exhibited the optimum nonlinear properties with the maximum α of 10.88, the minimum I_L of 36.3 mA/cm², and an E_100mA of 0.0188 V/nm. The obtained nanoscaled film varistors would be promising in electrical/electronic devices working in low voltage.     

Highly conducting and transparent antimony doped tin oxide thin films: the role of sputtering power density

Sb doped SnO₂ thin films were deposited on quartz substrates by magnetron sputtering at 600 °C and the effects of sputtering power density on the preferential orientation, structural, surface morphological, optical and electrical properties had been studied. The XRD analyses confirm the formation of cassiterite tetragonal structure and the presence of preferential orientation in (2 1 1) direction for tin oxygen thin films. The dislocation density analyses reveal that the generated defects can be suppressed by the appropriate sputtering power density in the SnO₂ lattice. The studies of surface morphologies show that grain sizes and surface roughness are remarkably affected by the sputtering power density. The resistivity of Sb doped SnO₂ thin films gradually decreases as increasing the sputtering power density, reaches a minimum value of 8.23×10⁻⁴ Ω cm at 7.65/cm² and starts increasing thereafter. The possible mechanisms for the change in resistivity are proposed. The average transmittances are more than 83% in the visible region (380–780 nm) for all the thin films, the optical band gaps are above 4.1 eV. And the mechanisms of the variation of optical properties at different sputtering power densities are addressed.     

Morphological and phase control of tin oxide single-crystals synthesized by dissolution and recrystallization of bulk SnO powders

Various types of tin oxide particle, including square SnO platelets, truncated octahedral SnO crystals, and monodispepersed SnO₂ nanoparticles, were synthesized by the dissolution and recrystallization of bulk SnO powder via the thermal decomposition of tin oleate in a coordinating solvent of tri-n-octylamine at 340 °C. The results reveal that the atmosphere and reaction time are important factors that affect the shape of tin(II) oxide and the oxidation state of tin(II or IV) oxide. As tin oleate decomposed in a N₂ atmosphere, truncated octahedral SnO crystals formed. When the thermal decomposition was conducted in air, square SnO platelets formed after a 30-min reaction time. When the reaction time was extended to 180 min, the square SnO platelets decomposed and transformed into nanocrystalline SnO₂ particles.     

Pulsed‐laser deposition of metal acetyl acetonates for sensor devices

Thin layers of tin acetyl acetonate (SnAcAc) were deposited by the laser ablation deposition (LAD) method onto potassium bromide tablets. FTIR and X‐ray photoelectronspectroscopy (XPS) spectra of these layers were investigated to describe changes in chemical composition during the deposition and following a thermal activation process. The main interest was focused on the formation of systems containing conjugated double bonds, tin dioxide (SnO₂), tin suboxides (SnO_x; x < 2), and salts (especially carboxylates). These phases play an important role in the use of LAD‐deposited acetyl acetonates as active layers of chemical sensors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1614–1622, 1999     

One-pot synthesis of core–shell-structured tin oxide–carbon composite powders by spray pyrolysis for use as anode materials in Li-ion batteries

Core–shell-structured tin oxide–carbon composite powders with mixed SnO₂ and SnO tetragonal crystals are prepared by one-pot spray pyrolysis from a spray solution with tin oxalate and polyvinylpyrrolidone (PVP). The aggregate, made up of SnO_x nanocrystals (several tens of nanometers), is uniformly coated with an amorphous carbon layer. The initial discharge capacities of the bare SnO₂ and SnO_x–carbon composite powders at a current density of 1 A g⁻¹ are 1473 and 1667 mA h g⁻¹, respectively; their discharge capacities after 500 cycles are 78 and 1033 mA h g⁻¹, respectively. The SnO_x–carbon composite powders maintain their spherical morphology even after 500 cycles. On the other hand, the bare SnO₂ powder breaks into several pieces after cycling. The structural stability of the SnO_x–carbon composite powders results in a low charge transfer resistance and high lithium ion diffusion rate even after 500 cycles at a high current density of 2 A g⁻¹. Therefore, the SnO_x–carbon composite powders have superior electrochemical properties compared with those of the bare SnO₂ powders with a fine size.     

Evaluation of physicochemical and biological properties of SnO2 and Fe doped SnO2 nanoparticles

In recent decades, nanoparticle synthesis has been used for various physical and chemical methods. However, different toxic chemicals are used during this synthesis process to address these concerns, which has multiple effects on environmental toxicity and high cost. To avoid these problems, we need a cost-effective and environmentally friendly approach. In this study, green synthesis was used to make tin oxide (SnO₂) and ferrous doped tin oxide (SFO) nanoparticles (NPs) from Morinda citrifolia leaf extracts. The X-ray diffraction patterns of SnO₂ and SFO NPs reveal a tetragonal crystalline structure. From the FESEM image of synthesized SnO₂ and SFO NPs, their spherical structure and chemical composition were identified by EDX spectrum. Through the DLS spectrum, the hydrodynamic size was observed at 66 and 61 nm for SnO₂ and SFO NPs, respectively. In the FTIR spectrum, the O–Sn–O stretching vibration peak arises at (606 & 509 cm^?1 for SnO₂ NPs) and (613 & 538 cm^?1 for SFO NPs). Photoluminescence is used in materials to detect surface defects and impurity levels. The antibacterial activity of the SnO₂, SFO NPs, and conventional antibiotics like amoxicillin NPs is effectively inhibited against S. aureus and E. coli bacterial strains. SFO NPs exhibit a higher antibacterial activity as compared to SnO₂ and amoxicillin. The anticancer efficacy of increased SFO NPs compared to SnO₂ NPs was tested against (MDA-MB-237) human breast cancer cells. These results suggest that Fe ions modified SnO2 NPs could be used in healthcare industrial applications to improve human health.     

Optimization of Opto-Electrical and Photocatalytic Properties of SnO<Subscript>2</Subscript> Thin Films Using Zn<Superscript>2+</Superscript> and W<Superscript>6+</Superscript> Dopant Ions

Abstract  

A series of Zn²⁺ and W⁶⁺ doped tin oxide (SnO₂) thin films with various dopant concentrations were prepared by spray pyrolysis deposition, and were characterized by X-ray diffraction, atomic force microscopy, contact angle, absorbance, current density–voltage (J–V) and photocurrent measurements. The results showed that W⁶⁺ doping can prevent the growth of nanosized SnO₂ crystallites. When Zn²⁺ ions were used, the crystallite sizes were proved to be similar with the undoped sample due to the similar ionic radius between Zn²⁺ and Sn⁴⁺. Regardless of the dopant ions’ type or concentration, the surface energy has a predominant dispersive component. By using Zn²⁺ dopant ions it is possible to decrease the band gap value (3.35 eV) and to increase the electrical conductivity. Photocatalytic experiments with methylene blue demonstrated that with zinc doped SnO₂ films photodegradation efficiencies close to 30% can be reached.     

Annealing atmospheres induced structural and morphological transformation of zinc tin hydroxide nanostructures

The variation in crystallinity, morphology and phase of zinc tin hydroxide nanostructures are investigated after annealing at different (oxidizing, non-oxidizing and reducing) atmospheres. The zinc tin hydroxide nanostructures are prepared using hydrolysis assisted co-precipitation method. Annealing in oxidizing (oxygen and air) and non-oxidizing (nitrogen and argon) atmospheres do not have a significant effect on morphological and structural properties. However, the annealing in the reducing (ammonia) atmosphere converts the cubic nanostructures into nanorods and spherical particles. The zinc tin hydroxide forms three new phases (ZnON, SnO₂ and Sn) after annealing in reducing atmosphere. The formation of ZnON and SnO₂ phases are evident in Raman and XPS analysis. The reducing atmosphere (ammonia) changes the reaction kinetics leading to diffusion control crystal growth that could be responsible for such structural and morphological transformation. The bandgap is significantly changed after morphological and structural transformation with notable variation in photocurrent density, charge transfer resistance, and charge carrier concentration.     

Microstructural and optical properties of SnO2–ZnSnO3 ceramics

This work deals with some physical investigation on SnO₂–ZnSnO₃ ceramics grown on glass substrates at different temperatures (450 °C and 500 °C). Structural and optical properties were investigated using X-Ray diffraction (XRD), Raman, infrared (IR) absorption (FTIR), UV–visible spectroscopy and Photoluminescence (PL) techniques. XRD results revealed the existence of a mixture of SnO₂/ZnSnO₃ phases at different annealing temperatures. Structural analysis showed that both phases are polycrystalline. On the other hand, the optical constants (refractive index, extinction coefficient and the dielectric constants) have been obtained by the transmittance and the reflectance data. The optical band gap energy changed from 3.85 eV to 3.68 eV as substrate temperature increased from 450 °C to 500 °C. Raman, FTIR modes and PL reinforced this finding regarding the existence of biphasic (SnO₂ and ZnSnO₃) which is detected also by X-Ray diffraction analysis. Finally, the Lattice Compatibility Theory was evoked for explaining the unexpected incorporation of zinc ions in a rhombohedral structure within SnO₃ trigonal lattice, rather than the occupation of SnO₂ available free loci. All the results have been discussed in terms of annealing temperature.     

Structural, Electrical and Optical Properties of p-Type Transparent Conducting SnO2:Zn Film

Highly transparent, p-type conducting SnO₂:Zn films were deposited on quartz substrates by radio frequency (RF) magnetron sputtering using a 12 wt% ZnO doped with 88 wt% SnO₂ ceramic target followed by annealing at various temperatures. The effect of annealing temperature on the structural, electrical and optical performances of SnO₂:Zn films has been studied. XRD results show that all the SnO₂:Zn films possess tetragonal rutile structure with the preferred orientation of (101). Hall effect results indicate that at 873 K for 3 h was the optimum annealing parameters for p-type SnO₂:Zn films with relatively high hole concentration and low resistivity of 3.334 × 10¹⁹ cm⁻³ and 3.588 Ω cm, respectively. The average transmission of the p-type SnO₂:Zn films were above 80% in the visible light range. In addition, p-type conductivity was also confirmed by the non-linear characteristics of a p-type SnO₂:Zn/n-type SnO₂:Sb structure.