Particle Size Of ZnS Research Articles

Inhibition of the growth rate of ZnS anode crystal plane: boosting photocatalytic hydrogen production performance

The catalyst's particle size plays a crucial role in enhancing photocatalytic performance. However, it is still unclear to analyse the mechanism by which surfactants affect the particle size of photocatalysts from the perspective of crystal growth. Herein, ZnS nanomaterials with different particle sizes were synthesized using a simple solid-state chemical synthesis method, and the intrinsic influence mechanism between surfactant and catalyst particle size was analyzed from the perspective of crystal growth. It was discovered that the particle size of ZnS kept getting smaller due to changes in polyethylene glycol, cetyltrimethylammonium bromide, and sodium dodecyl sulfate. Analyzing the reasons revealed that the catalyst's particle size was related to the type of surfactant: anionic surfactants could reduce the catalyst size. Correspondingly, the catalyst with a smaller particle size has the optimal performance for photocatalytic hydrogen production. Photocatalysts Z-SDS exhibited outstanding photocatalytic performance, yielding 11.47 mmol/g of hydrogen after a five-hour illumination. Furthermore, the intrinsic influence mechanism between anionic and cationic surfactants, photocatalyst particle size, and catalytic performance was investigated. This investigation provides a new idea for synthesizing small-size and high-performance photocatalysts.

Controllable Synthesis of Sub‐10 nm ZnS Nanograins Confined in Micro‐Size Carbon Skeleton for Aqueous Zn–S Batteries

AbstractAqueous zinc–sulfur battery (AZSB) is a promising technology for energy storage, but its practical application is severely limited by the sluggish redox kinetics and large volume expansion of the sulfur cathode. Herein, the controllable synthesis of sub‐10 nm ZnS nanograins confined in micro‐size carbon skeleton (MN‐ZnS/C─H) and its application as the cathode for AZSB is reported. It is revealed that the carbon source, polyvinylpyrrolidone (PVP), can weakly coordinate with Zn2+ and provide a physical confinement for inhibiting the agglomeration of ZnS nanograins during the calcination process. Moreover, the particle size of ZnS (from sub‐10 to 350 nm) and the shape of ZnS/carbon composite (from bulk to sphere) can be well controlled by tuning the chain length of PVP. In the unique hierarchical structure, the ZnS nanograins can provide an optimized ion transmission path, and the micro‐size carbon network not only ensures high electronic conductivity but also maintains structure integrity upon volume variation, endowing the MN‐ZnS/C─H electrode with a high reversible capacity of 370 mA h g−1 at 0.2 A g−1, high rate capability of 209 mA h g−1 at 4 A g−1, and a long lifespan of 210 cycles with 93.2% capacity retention at 2 A g−1.

Solid state low temperature synthesis approach for ZnO-ZnS nanoheterostructure with functionality as a photocatalyst for H2 production and for DSSC

Herein, we demonstrate a facile, template free, scalable, solid-solid, single step synthesis approach to produce ZnO/ZnS nanoheterostructure. Commercially available ZnO and thiourea have been used as precursors. Interestingly, it is observed that ZnO particle is covered with ZnS and the ZnS shell thickness can be varied depending on the sulfidation time. The crystal structures, morphology of samples are verified by XRD, FETEM and EDX. The XRD results show the mixed phases of hexagonal ZnO and ZnS. The broad peak of ZnS clearly reveals the nanocrystalline nature and also increase in intensity of peak with respect to sulfidation time. The optical spectra of the samples exhibits two band absorption edges and blue shift in the absorption edge depending on the ZnS thickness deposited. Particle size of the ZnS (5–3 nm) coated on the ZnO by varying the sulfidation time influences the performance of the DSSC and photocatalytic H2 evolution from water has been investigated, systematically. The DSSC performance of ZnO/ZnS nanoheterostructure shows maximum efficiency of 3.30% with increment in Jsc (9.04 mA/cm2). The performance is much better than pristine ZnO and earlier report of ZnO-ZnS nanostructure. This good performance is due to excellent light absorbing capability of the ZnO/ZnS nano heterostructure by providing ZnO core by providing easy electron transfer at the interface and the ZnS shell facilitate to reduce the recombination of diffuse electrons with either the dye or the electrolyte. The H2 evolution rate reported herewith is 3209 and 1685 μmol h−1g−1 under UV and Natural sunlight, respectively which is significantly higher than pristine ZnS and ZnO. The H2 evolution rate increases with decrease in particle size of ZnS which is quite ovibius because lowering particle size exhibits increase in surface area. The fabrication of ZnO/ZnS nanoheterostructure is the simple and cost effective, which can open new avenues strategy for large scale applications of the novel materials in the energy storage and photovoltaic devices.

A novel method of preparing ultrafine ZnS particles from waste zinc–manganese batteries by evaporation–separation, sulfurization and inert gas condensation

This paper explores a novel method to produce ultrafine ZnS particles, a high value-added product, from waste zinc–manganese battery through evaporation–separation, sulfurization and inert gas condensation process. The heating temperature, condensation temperature, nitrogen gas pressure and condensation distance were identified as the main factors influencing the morphology of ZnS nanoparticles produced. Ultrafine ZnS particles can be prepared when the heating temperature is 873 K, the condensation temperature is 723 K and the nitrogen gas pressure is 1000–1500 Pa at the condensation distance of 30 cm. Size of ZnS particles was between 10 and 100 nm with average size of about 40 nm. Based on the scientific graphing and statistical analysis, the size of ZnS particles follows the log-normal distribution. This study not only provides the theoretical fundamentals for preparing ultrafine ZnS particles, but also provides a simple and efficient method to recycle the high value-added ZnS products from waste zinc–manganese batteries.

Structural, optical and photocatalytic properties of ZnS/zeolite Y nanoparticles synthesized by γ-ray irradiation

The present study deals with würtzite ZnS nanoparticles embedded in zeolite Y, synthesized by γ-radiolysis of exchanged zeolite ZnY in the presence of 2-mercaptoethanol (RSH). The nanocomposites were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), UV–Visible absorption, and photoluminescence (PL). Compared to the bulk state, ZnS nanocrystals have blue – shifted UV visible absorption with an excitonic peak situated at around 320 nm. They display a wide photoluminescence band with seven peaks in the range of 320–550 nm. The increase of the irradiation dose and RSH concentration results in a growth the ZnS nanocrystals and improves their optical performances. The optical as well as the structural characterizations confirmed the nanometric size of ZnS particles (Φ = 5–18 nm). When tested in photodegradation of Congo red under sun light, ZnS-zeolite Y catalyst exhibit high efficiency. For the experimental conditions: [ZnS-Y] = 0.5 g L−1; [CR] = 10 mgl−1+; pH = 6.6, the pseudo-first order constant is 0.076 min−1.

Simple Fabrication of PVA-ZnS Composite Films with Superior Photocatalytic Performance: Enhanced Luminescence Property, Morphology, and Thermal Stability.

Poly(vinyl alcohol) (PVA)–ZnS composite films were prepared by varying the composition of PVA ranging from 1–5 wt % through a simple solvent casting method. The photocatalytic enactment of the composites was evaluated along with the investigations of their photoluminescence (PL), optical transparency, morphology, and thermal properties. The firm interaction between the ZnS and PVA was confirmed by Fourier transform infrared, UV–vis, and PL spectroscopies. PVA–ZnS composites showed enhanced luminescence property than PVA. The composites exhibited very good optical transparency regardless of the amount of PVA addition. The thermogravimetric analysis data indeed exhibited better thermal stability of the composites. The glass transition temperature (Tg), melting temperature (Tm), enthalpy of melting (ΔHm), and crystallinity were evaluated for such composites. The composites demonstrated morphological variations depending on the amount of PVA addition, although the particle size of ZnS remained similar in the nanometer range (50–120 nm) for all composite samples. The prepared composite films exhibited superior photocatalytic performance in the degradation of methylene blue compared with the bare ZnS and PVA. This study may give a new insight into the fabrication of PVA–ZnS photocatalysts for the treatment of organic pollutants.

Photoluminescence of ZnS:Cu quantum dots embedded in silica thin films

Copper-doped zinc sulfide quantum dots embedded in silica films (ZnS:Cu/SiO2) have been synthesized by sol-gel dip-coating with subsequent thermal annealing. The considered Cu/Zn molar ratios ranged from 0.2% to 2%. Atomic force microscopy analysis shows mostly a granular nanostructure of the deposited films with a roughness less than 30 nm depending on Cu content; i.e. the lowest value of 14 nm is obtained for 0.5% Cu doping. The mean particle size of ZnS:Cu quantum dots (QDs) has been found to be around 2.5 nm as measured by UV–Vis spectroscopy, in agreement with the value of 3 nm estimated by Scherrer equation using X-ray diffraction patterns. Photoluminescence (PL) spectra reveal new features regarding the intensity and width of the peaks. Two well-resolved emission bands are essentially observed in the blue and green regions centered respectively at 438 nm and from 510 to 514 nm. The blue band shows a variation of width with Cu content and a quenching of PL at 2% Cu doping. At 0.5% Cu, a PL line-width of approximately 3 nm is measured for this blue band. Contrarily to the blue emission, the green band is not quenched at 2% Cu content. Finally, the origin of the PL bands has been discussed.

Gelatin-assisted synthesis of ZnS hollow nanospheres: the microstructure tuning, formation mechanism and application for Pt-free photocatalytic hydrogen production

Nano-sized hollow spheres with tunable microstructures are urgently needed for their applications in advanced fields. The ZnS hollow spheres reported previously have usually required a complex multi-step process, and/or large size and/or less tunability in the microstructure. Here, a simple gelatin-assisted hydrothermal reaction of Zn(OAc)2 and thiourea was developed for the synthesis of ZnS hollow nanospheres. The size of the hollow spheres could be controlled below 100 nm with good homogeneity. The presence of gelatin is essential to decrease the size of ZnS particles and to form hollow structures. Only solid spheres with a large size were prepared in the absence of gelatin. The structure of hollow nanospheres could be regulated by altering the reaction parameters. Typically, the size of voids increases with prolonged reaction time. Also, the grain size of the hollow spheres increased with increasing reaction temperature (from about 3 nm to 10 nm) accompanied by a decrease in shell thickness. The results indicated that the hollow structure was formed through an “Ostwald ripening” process. The ZnS hollow nanospheres were used as catalyst for photocatalytic hydrogen production without additional co-catalyst. The maximum H2 production rate reached was 340 μmol h−1 (about 6.8 mmol h g).

A new solid-phase nanoparticle FRET assays based on GO/CS/ZnS nanocomposite film and developed in sensing for bromonium ion

Composite thin films consisting of nano-sized ZnS particles dispersed in chitosan/GO films have been prepared by in-situ method. The films obtained were characterized by FTIR and UV–Vis spectroscopy. The ZnS nanoparticles with 90 nm in diameter were dispersed uniformly in the film matrix. Optical absorption peak due to the size of ZnS particles was observed around 350 nm. The fluorescence emission at 430 nm of the GO/CS/ZnS nanocomposite films is very sensitive to the presence of bromonium ion from aqueous solutions. New solid-phase nanoparticles FRET assays are firstly immobilized on the substrate and then interacted with functionalized acceptor molecules in the solution to trigger the FRET effect to detect Br–.

Effect of Hydrothermal Reaction Temperatures on Structural and Optical Properties of ZnS Nanoparticles

A ZnS nanoparticle was prepared using hydrothermal interaction of zinc acetate with Thiourea in different reaction temperatures (170oC, 180oC, 185oC, 190oC). The structural characterization of synthesized nanoparticle was determined by X-ray diffraction (XRD) which showed a hexagonal structural of ZnS. Scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) analysis were confirmed that the morphology and elemental analysis was formed ZnS nanoparticle. Absorption study has been carried out using UV-VIS spectrophotometer to determine the band gap of ZnS nanoparticle. The optical energy band gap was changed at values equal to (4.16, 4.46, 4.1 and 4.35eV) with different hydrothermal temperatures at (170oC, 180oC, 185oC and 190oC) respectively. However, these values of energy gaps for ZnS nanoparticles are blue shift and larger than that bulk value due to quantum confinement. Fourier Transform Infrared Spectra (FTIR) is recorded in an FTIR spectrometer to verify the presence of ZnS powder. The particle size of ZnS calculated was ranged between 3.5 to 3.9 nm according to Sherrer's equation and the results were compatible when using Effective Mass Approximation (EMA).

ZnS nanoparticles embedded in reduced graphene oxide as high performance anode material of sodium-ion batteries

ZnS nanoparticles embedded in reduced graphene oxide (RGO) were prepared via a facile microwave-assisted method and applied as anode materials of sodium-ion batteries (SIBs). The as-prepared composites exhibit excellent sodium storage properties. A maximum specific capacity of 481mAhg−1 at the specific current of 100mAg−1 can be achieved after 50 cycles by optimizing the RGO content in the composites. The improved sodium-ion storage ability can be ascribed to the enhanced specific surface area and increased electric conductivity due to the introduction of RGO and the decreased size of ZnS particles which can shorten the pathway of sodium-ion diffusion and facilitate the reversible Na+ diffusion kinetics.

Structural and optical properties of copper doped zinc sulfide nanostructures using capping agents

Copper doped ZnS nanoparticles with different capping agents have been synthesized through chemical co-precipitation method. Polyvinylpyrrolidone (PVP), 1-thioglycerol and Trioctylphosphine oxide (TOPO) were used as capping agents. X-ray diffraction (XRD) studies revealed the average particle size of ZnS:Cu2+ with different capping agents to vary from 3 nm to 4 nm. Energy dispersive X-ray spectroscopy (EDAX) measurements confirmed the presence of Cu in the ZnS lattice. UV-Vis spectroscopy revealed blue shift for all the samples with respect to the bulk value. The band gap energy values were in the range of 4.29 eV to 4.86 eV. The blue shift was attributed to the quantum confinement effect. Room temperature photoluminescence (PL) spectrum of the ZnS:Cu2+ capped nanoparticles exhibited emission in the visible region with multiple peaks at an excitation wavelength of 250 nm

Microstructures and luminescence behaviors of Mn2+ doped ZnS nanoparticle clusters with different core/shell assembled orders

Mn2+ doped ZnS nanoparticle (NP) clusters composed of densely packed ZnS:Mn2+ NPs, ZnS/ZnS:Mn2+ core/shell NPs, or ZnS:Mn2+/ZnS core/shell NPs were prepared by a chemical co-precipitation method. Estimation of the lattice parameters and the band gap of the ZnS NP clusters through X-ray diffraction and optical diffuse reflectance spectra showed no noticeable divergence due to Mn2+ dopants. Transmission electron microscopy revealed that ZnS:Mn2+/ZnS NP clusters contained much larger NP crystallites associated with the high growth rate of undoped ZnS shell layers. In contrast, Mn2+ dopants limited the deposition of ZnS:Mn2+ shell layers, leading to smaller particle sizes of ZnS:Mn2+ and ZnS/ZnS:Mn2+ NPs in the clusters. Among all the samples, ZnS/ZnS:Mn2+ NP clusters exhibited the most intense orange emission of Mn2+, which was further confirmed by the estimated energy transfer (from ZnS to Mn2+) efficiency values, i.e., ZnS/ZnS:Mn2+ (42.1%)>ZnS:Mn2+/ZnS (15.9%)>ZnS:Mn2+ (1%). An energy migration mechanism was proposed for interpreting the high energy transfer efficiency of the ZnS/ZnS:Mn2+ structure.

Thermoluminescence properties of graphene–nano ZnS composite

This work describes the thermoluminescence (TL) of graphene oxide (GO), reduced graphene oxide (RGO) and graphene–nano ZnS composite. Graphene oxide was synthesized using Hummer's method and then reduced to graphene by hydrazine hydrate. G–ZnS was synthesized via in-situ reduction of graphene oxide (GO) and zinc nitrate [Zn(NO3)2] by sodium sulfide (Na2S). The structures of samples were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). XRD pattern confirmed the formation of graphene oxide, reduced graphene oxide and G–ZnS lattice. The p-XRD spectrum of G–ZnS shows peaks of ZnS superimposed on those of graphene and the particle size of ZnS in the complex is less than 10nm. Ultra thin graphene and graphene oxide sheets with size ranging between tens to several hundreds of square nanometers are observed in TEM images. The TEM micrographs of G–ZnS show that ZnS particles are embedded in graphene sheets and the average particle size of ZnS particles in the composite is less than 10nm. Samples of RGO, GO and G–ZnS were exposed to different doses of γ-rays in the range of 1Gy to 50kGy. The reduced graphene oxide (RGO) did not show any thermoluminescence emission. The thermoluminescence glow curve of GO has a single broad peak whose peak position varied between 500 and 550K with an absorbed dose increasing from 1Gy to 5000Gy. GO shows most intense TL peak, positioned at 523.6K for a dose of 10kGy. The glow curves of G–ZnS over the entire range of irradiation have single peak positioned between 492 and 527K with variation in dose from 1Gy to 50kGy. G–ZnS shows the most intense TL glow curve for a dose of 50kGy. The TL response curve of G–ZnS is found to be linear over a larger dose range from 1Gy to 50kGy whereas the response curve of GO shows linearity only at low doses up to 100Gy.

与掺杂浓度相关的ZnS∶Mn纳米粒子的发光性质

Mn-doped ZnS nanoparticles were prepared by the Sol-Gel process in this paper,and the influence of doping ion concentration on crystal structures and luminescent properties of ZnS:Mn nanoparticles was discussed.The structures of the samples were characterized by an X-ray diffractometer(XRD).The results show that the as-prepared ZnS:Mn nanoparticles belong to the cubic sphalerite structure.The parvafacies do not occur when Mn2+-doping concentration reaches 6% and the average particle sizes of nanoparticles decrease with the increase of doping concentration.Photoluminescence(PL) spectroscopy and fluorescence spectrum results show that the emission wavelengths of ZnS:Mn nanoparticles around 590 nm can be adjusted by changing the concentration of the ions.In addition,the influence of temperature on morphology and luminescent properties of nanoparticles was studied.The result observed from a high resolution transmission electron microscopy(HRTEM) shows that the average particle sizes of ZnS∶Mn samples increase to about 20 nm after ageing for 1 h at the temperature of 50 ℃.The heating ageing is beneficial to Mn2+ fluorescence produced at 590 nm for ZnS∶Mn nanoparticles.

An Analysis of Structural and Optical Properties Undoped ZnS and Doped (with Mn, Ni) ZnS Nano Particles

The behavior of nano-particles finds a wide application in opto-electronic and semi-conductor devices. ZnS nano-crystals were grown into poly-vinyl alcohol matrix by chemical route at different weight percentage. Optical properties of both un-doped and doped with ZnS nano-crystalline compounds were studied. The nano structure was characterized with the help of X-ray diffraction (XRD) and Hi-resolution Transmission Electron Microscopy (HRTEM). Surface morphology was studied with the help of Scanning Electron Microscopy (SEM). The average particle sizes of ZnS, ZnS-Ni and ZnS-Mn were found to be 6.51, 7.3 and 12 nm respectively in TEM and that obtained from Debye-Scherrer formula is about 2.3 and 2.5 nm for undoped and doped ZnS respectively. Peak of Photo-luminescence (PL) emission spectra was obtained at 375 nm at room temperature and another peak at 433 nm for Ni. Again the peak of Photo-luminescence (PL) emission spectra was obtained at 334 nm at room temperature for Mn, Mn dependant emission was found at 580 nm. These data showed successful doping. PL studies also confirmed presence of dopant in the nano crystallites. Optical absorption studies were carried out with UV-VIS Spectrophotometer and showed a strong absorbance at wavelength 400 nm with a tendency towards blue shift. Selected area electron diffraction (SAED) shows a set of four well defined rings corresponding to diffraction from different planes of the nano crystallites. HRTEM image showed a well crystalline ZnS doped with Ni and Mn. Both Raman spectra and XRD studies confirmed the well crystalline states of ZnS.

A new fluorescent film sensor for Pb(II) ions developed by simulating bio-mineralization process synthesizing of ZnS/CS nanocomposite

Abstract Chitosan/zinc sulfide (CS/ZnS) nano-composite films have been prepared by simulating bio-mineralization process. Factors affecting the hydrothermal stability and fluorescence properties of the films have been studied. Furthermore, the sensing properties of nano-composite films to lead ions have been systematically investigated. SEM and TEM observations showed that the size of ZnS particles is 70 nm, and the particles are evenly distributed within the CS films. The fluorescence emission of the nano-composite films indicates that the sizes of real fluorescing ZnS particles are less than 20 nm. This suggests that ZnS particles observed via SEM and TEM may be aggregates of smaller ZnS particles, and the smaller particles may be separated by the organics. The fluorescence emission (363 nm) of the nano-composite films is very sensitive to the presence of Pb ions. C (Pb 2+ ) increased from 0 to 664.2 mg L −1 increases the emission dramatically. The emission is hardly affected by common ions in water, except for the iron ions. The films may be developed as excellent sensing films for Pb ions in water.

PREPARATION OF CARBOXYLIC FLUOROCARBON POLYMER FIBERS USED AS PHOTOCATALYST CARRIER

The carboxylic fluorocarbon polymer poly(hexafluorobutyl acrylate-co-methacrylic acid)(P(HFBA- co-MAA)) and poly ( dodecafluoroheptyl methacrylate-co-methacrylic acid ) ( P ( DFHMA-co-MAA )) were prepared by solution polymerization.The electrospinning experiments showed that when the amount of MMA in copolymers decreased the spinnability of P( DFHMA-co-MAA) and P( HFBA-co-MAA) copolymers became worse,at the same time the concentration of two coplymers solution decreased,and the polarity and boiling point of solvent gradually reduced;the diameter of fibers enlarged with increasing the amount of butanone in the spinning solvent;the spinnability of P( DFHMA-co-MAA) was better than that of P( HFBA-co-MAA).Using P(DFHMA-co-MAA) fibers as carrier,photocatalyst ZnS were prepared on the surface of fibers by a two-step method.The XPS results showed that Zn2 + were introduced onto the surface of fibers by coordinating with the carboxyl of fluoropolymer first,then coordinated Zn2 + reacted with S2 - provided by thioacetamide to form ZnS.The amount and particle size of ZnS increased with increasing the proportion of MAA in the copolymer.Nano dimension ZnS particles could be obtained when the proportion of MAA in the copolymer was 10 wt% .The photodegradation and FTIR analysis showed that the as prepared ZnS /P(DFHMA-co-MAA) fiber composites had good stability under UV irradiation.

PREPARATION OF CARBOXYLIC FLUOROCARBON POLYMER FIBERS USED AS PHOTOCATALYST CARRIER

The carboxylic fluorocarbon polymer poly(hexafluorobutyl acrylate-co-methacrylic acid)(P(HFBA- co-MAA)) and poly ( dodecafluoroheptyl methacrylate-co-methacrylic acid ) ( P ( DFHMA-co-MAA )) were prepared by solution polymerization.The electrospinning experiments showed that when the amount of MMA in copolymers decreased the spinnability of P( DFHMA-co-MAA) and P( HFBA-co-MAA) copolymers became worse,at the same time the concentration of two coplymers solution decreased,and the polarity and boiling point of solvent gradually reduced;the diameter of fibers enlarged with increasing the amount of butanone in the spinning solvent;the spinnability of P( DFHMA-co-MAA) was better than that of P( HFBA-co-MAA).Using P(DFHMA-co-MAA) fibers as carrier,photocatalyst ZnS were prepared on the surface of fibers by a two-step method.The XPS results showed that Zn2 + were introduced onto the surface of fibers by coordinating with the carboxyl of fluoropolymer first,then coordinated Zn2 + reacted with S2 - provided by thioacetamide to form ZnS.The amount and particle size of ZnS increased with increasing the proportion of MAA in the copolymer.Nano dimension ZnS particles could be obtained when the proportion of MAA in the copolymer was 10 wt% .The photodegradation and FTIR analysis showed that the as prepared ZnS /P(DFHMA-co-MAA) fiber composites had good stability under UV irradiation.

Hydrothermal synthesis and characterization of ZnS microspheres and hollow nanospheres

ZnS hollow nanospheres have been hydrothermally synthesized at 200 °C for 4 h. In same condition ZnS microspheres were obtained when using acrylamide as the surfactant. XRD pattern indicates as-prepared sample is cubic ZnS with cell constant a = 5.391 Å and the average size of ZnS particles was 6.5 nm estimating from the Debye–Scherrer formula. TEM observed the hollow nanospheres have the diameters ranging from 200 to 300 nm with a shell thickness of about 40 nm. UV–vis and PL spectra recorded the optical properties of the sample, a blue-shift (∼19 nm) was observed. It appears that the hollow spheres might be formed by soft-template of gas bubbles of SO 2 produced during the reaction.