Synthesis,characterization, and 2,4-dichlorophenoxyacetic acid degradation on In-Na<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> sol–gel prepared photocatalysts

Indium-Na₂Ti₆O₁₃ doped semiconductors were prepared by the sol–gel method using titanium and sodium alkoxides as precursors. The gelled samples were annealed at 700 °C for 4, 6, and 8 h, and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and UV–Vis diffused reflectance spectroscopy (DRS). XRD patterns of the samples show the formation of the Na₂Ti₆O₁₃ phase, whose crystallinity depends on the annealing time. The band gap calculated from the UV–Vis Kubelka–Munk function report similar values (3.2–3.4 eV) for all of the samples annealed at different times. SEM observations of the semiconductors showed microfiber bundle morphologies of about 5 μm. Meanwhile, by EDS analysis, indium oxide highly homogeneously dispersed on the hexatitanate surface was identified. The evaluation of the In-Na₂Ti₆O₁₃ semiconductors in the 2,4-dichlorophenoxyacetic acid (2,4-D) photodecomposition using ultraviolet light (λ = 254 nm) irradiation show that the photoactivity of the solids depends on the annealing time applied to the samples. The role of indium oxide is related to the indium oxide dispersed on the surface of the titanate diminishing the electron-hole recombination rate.     

Influence of pH and microwave calcination on the morphology of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> particles derived by Pechini Sol–Gel method

KGd(WO₄)₂ (KGW) particles were synthesized at 3.5, 5.5 and 7.5 pH values by Pechini polymeric complex sol–gel method using potassium nitrate, gadolinium nitrate, ammonium paratungstate, citric acid and ethylene glycol as starting materials. Deionized water was used as solvent. Polymeric precursor gel was formed with citric acid as complexing agent and ethylene glycol as binder. Synthesized gel was analyzed by FT-IR spectroscopy. Prepared precursor gels were further annealed using resistive and microwave processes at 550 and 700 °C, respectively. The properties of heat treated samples were characterized by powder XRD, FT-IR, Raman and SEM analysis to understand the crystallinity, organic liberation, tungstate ribbon formation and surface morphology, respectively. The phase formation and different phases of intermediate oxides in pre-fired samples were investigated by powder XRD. Organic liberation in the samples in relation to temperature, and the carbon content in the pre-fired powder was analyzed using FT-IR spectrum. Raman spectrum reveals the formation of tungsten ribbons as well as the quality of the samples. The morphological changes at different synthesis conditions were observed with SEM micrographs.     

Synthesis and characterization of zinc titanate fibers by sol-electrospinning method

A facile and economic electrospinning approach has been developed for the synthesis of zinc titanate-rutile composite fibers as a nanofibrous mat at the first time. The composite fibers with different morphologies were obtained by calcination of the PVP/Ti(OC₄H₉)₄–Zn(CH₃COO)₂ fibers. The reaction mechanism was characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infraction spectroscopy (FT-IR) spectra techniques. According to the thermal analysis, the phase of ZnTiO₃ occurred at 450 °C and it decomposed at 885 °C. FE-SEM micrographs indicated that the as-spun fibers were round and had a rather uniform and smooth surface with the diameters in the range of 300–800 nm over its length. Its morphology is greatly affected by the calcination temperatures.     

Role of calcination on geopolymerization of lateritic clay by alkali treatment

In the present study, the role of calcination of a low iron lateritic clay sample was investigated to synthesize the geopolymer. The analyses like X-ray fluorescence (XRF) spectroscopy for chemical composition, X-ray diffractometry (XRD) for mineral composition, and Fourier transform infrared (FT-IR) spectroscopy & scanning electron microscopy (SEM) for structural changes upon calcination at 500, 700 and, 900 °C were used to assess the suitability of selected lateritic clay sample for geopolymer. The drop in electrical conductivity and greater consumption of calcium hydroxide by CS-900 confirmed its potential reactivity than CS-700, CS-500, and CS-Control. The quality of geopolymer derived from un-calcined and calcined lateritic clay samples by alkali activation was evaluated by comparing results of compressive strength, water absorption test, and stability in the aggressive environment of chloride, FT-IR, XRD, and SEM analyses. The experimental results reveal that the quality of geopolymer enhances as the calcination temperature of the lateritic clay sample increases, However, calcination of the lateritic clay sample at 900 °C gives significant results and yield good quality geopolymer with 24.8 MPa of compressive strength, 7.07% of water absorption and 2.22% loss in mass in an aggressive environment.     

Sol–gel-derived nanocomposite coatings filled with inorganic fullerene-like WS<Subscript>2</Subscript>

Silica coatings filled with nanoscaled inorganic fullerene-like tungsten disulphide (IF-WS₂) have been prepared through a sol–gel process on stainless steel substrates, and the structure and mechanical properties have been investigated. The precursor was prepared from a mixture of colloidal silica, 3-glycidoxypropyltrimethoxysilane (GLYMO), water and ethanol, adjusted to pH 4 with HNO₃. In this solution WS₂ is dispersed and in some cases immediately before coating ethylenediamine (ED) is added. The stainless steel substrates are dip-coated, dried in air and heat-treated in the temperature range of either 150–360 °C in air or up to 900 °C in vacuum. The solidification process is followed by differential thermal analysis (DTA). The resulting brown coloured coatings have a thickness of 1.5–4 μm. Scanning electron microscopy investigations (SEM) show that the WS₂ nanoparticles are embedded as small aggregates in a hybrid silica matrix. X-ray diffraction (XRD) measurements prove that most of the tungsten disulphide embedded in the matrix can be protected against oxidation even after curing the samples at temperatures up to 900 °C. Hardness and modulus of the hybrid silica films were measured through an instrumented indentation test. Increasing the temperature of the heat treatment yields an increase of hardness from 0.3 to 1 GPa and of modulus from 3 to 17 GPa. The amount of up to 10 wt.% WS₂ in the coatings has no remarkable influence on hardness and modulus of the samples.     

On the Formation of TiO<Subscript>2</Subscript> Nanoparticles Via Submerged Arc Discharge Technique: Synthesis,Characterization and Photocatalytic Properties

We report a simple and inexpensive synthesis route of TiO₂ nanoparticles using electrical arc discharge between titanium electrodes in oxygen bubbled deionized (DI) water followed by heat treatment. The resulting nanoparticles were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD patterns demonstrate formation of TiO₂ phase in oxygen bubbled water after heat treatment and dominance of rutile to anatase phase. The size and morphology of TiO₂ nanoparticles were studied using different arc currents as a crucial parameter in properties of final product. Microscopic studies reveal nanosize spherical particles. DLS results indicate that at 20 A arc current, the size of the particles is about 37 nm and increases to 59 nm by increasing the arc current up to 40 A. Photodegradation of Rhodamine B (Rh. B) as a standard pollution shows that heat treated samples in oxygen bubbled water for 2 h at 500 °C, have more photocatalytic activity due to enhancement in crystallinity.     

Synthesis of MCM-48 from silatrane via sol–gel process

High-quality cubic MCM-48 is successfully synthesized using a new silica source known as silatrane and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent via sol–gel process. The effects of synthesis parameters, viz. crystallization temperature, crystallization time, surfactant concentration, quantity of NaOH, and silica source, on the product structure are investigated. The synthesized samples are characterized using X-ray diffractometer (XRD), N₂ adsorption–desorption isotherms, and electron microscopy. Optimally, this product is synthesized from samples crystallized at 140°C for 16 h with a CTAB/SiO₂ ratio of 0.3 and NaOH/SiO₂ ratio of 0.5. The XRD result exhibits a well-resolved pattern, corresponding to the Ia3d space group of MCM-48. The BET surface area of this product is as high as 1,300 m²/g with a narrow pore-size distribution of 2.86 nm. The scanning electron microscopic (SEM) images also show the truncated octahedral shape and well-ordered pore system of MCM-48 particles.     

Hydration behavior of C2S and C2AS nanomaterials, synthetized by sol–gel method

Hydration behavior of dicalcium silicate (C₂S) (Cement chemistry nomenclature is used where C=CaO, S=SiO₂, A=Al₂O₃, S=SO₃) and gehlenite (C₂AS), synthesized by sol–gel method was investigated by means of isothermal heat flow calorimeter at different temperatures. These phases were obtained by crystallization processing at different temperatures from their xerogels (nano-crystalline) prepared by the sol–gel method at ambient temperature. The crystallization of C₂S begins below 600°C and it is well crystallized at 900°C. X-ray diffraction patterns reveal that β-C₂S is formed and it remains stable since after slow cooling. The crystallization of C₂AS xerogels starts with the formation of C₂S, then it reacts with alumina to form mineral C₂AS at 1100°C. The effect of hydration temperature upon the hydration reaction of C₂S obtained at 600 and 900°C and C₂AS annealed at 600 and 1100°C was investigated by means of isothermal calorimeter. An increase in the temperature of hydration brought about initial acceleration of all samples, as indicated by the increased magnitude of peak of calorimetric curves. The microstructure of the samples cured at hydrothermal condition after 1 and 7 days has been examined by means of scanning electron microscopy (SEM). Fine crystals of calcium silicate hydrate (C–S–H) were developed in C₂S samples, while C₂AS has been hydrated to form gehlenite hydrate supplemented by C–S–H.     

Synthesis of electrospun BaSrTiO<Subscript>3</Subscript>/PVP nanofibers

Ba_1−x Sr _x TiO₃(x = 0–0.5, BST) nanofibers with diameters of 150–210 nm were prepared by using electrospun BST/polyvinylpyrrolidone (PVP) composite fibers by calcination for 2 h at temperatures in the range of 650–800 °C in air. The morphology and crystal structure of calcined BST/PVP nanofibers were characterized as functions of calcination temperature and Sr content with an aid of XRD, FT-IR, and TEM. Although several unknown XRD peaks were detected when the fibers were calcined at temperatures less than 750 °C, they disappeared with increasing the temperature (above 750 °C) due to its thermal decomposition and complete reaction in the formation of BST. In addition, the FT-IR studies of BST/PVP fibers revealed that the intensities of the O–H stretching vibration bands (at 3430 and 1425 cm⁻¹) became weaker with increasing the calcination temperature and a broad band at 540 cm⁻¹, Ti–O vibration, appeared sharper and narrower after calcination above 750 °C due to the formation of metal oxide bonds. However, no effect of Sr content on the crystal structure of the composites was detected.     

Microstructure,dielectric properties and optical band gap control on the photoluminescence behavior of Ba[Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>]O<Subscript>3</Subscript> thin films

Ba[Zr_0.25Ti_0.75]O₃ (BZT) thin films were synthesized by the complex polymerization method and heat treated at 400 °C for different times and at 700 °C for 2 h. These thin films were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM), Ultraviolet–visible (UV–vis) absorption spectroscopy, electrical and photoluminescence (PL) measurements. FEG-SEM and AFM micrographs showed that the microstructure and thickness of BZT thin films can be influenced by the processing times. Dielectric constant and dielectric loss of BZT thin films heat treated at 700 °C were approximately 148 and 0.08 at 1 MHz, respectively. UV–vis absorption spectra suggested the presence of intermediary energy levels (shallow and deep holes) within the band gap of BZT thin films. PL behavior was explained through the optical band gap values associated to the visible light emission components.     

Cellulose nanofibers from white and naturally colored cotton fibers

Suspensions of white and colored nanofibers were obtained by the acid hydrolysis of white and naturally colored cotton fibers. Possible differences among them in morphology and other characteristics were investigated. The original fibers were subjected to chemical analysis (cellulose, lignin and hemicellulose content), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). The nanofibers were analyzed with respect to yield, elemental composition (to assess the presence of sulfur), zeta potential, morphology (by scanning transmission electron microscopy (STEM)) and atomic force microscopy (AFM), crystallinity (XRD) and thermal stability by thermogravimetric analysis in air under dynamic and isothermal temperature conditions. Morphological study of several cotton nanofibers showed a length of 85–225 nm and diameter of 6–18 nm. The micrographs also indicated that there were no significant morphological differences among the nanostructures from different cotton fibers. The main differences found were the slightly higher yield, sulfonation effectiveness and thermal stability under dynamic temperature conditions of the white nanofiber. On the other hand, in isothermal conditions at 180 °C, the colored nanofibers showed a better thermal stability than the white.     

The effects of oxygen concentration on ultraviolet luminescence of ZnO films by sol–gel technology and annealing

ZnO thin films were successfully deposited on SiO₂/Si substrate using the sol–gel technique and annealed in various annealing atmospheres at 900 °C by rapid thermal annealing (RTA). X-ray diffraction revealed the (002) texture of ZnO thin films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the grains of the ZnO thin film were enlarged and its surface was smoothed upon annealing in oxygen. PL measurement revealed two ultraviolet (UV) luminescence bands at 375 and 380 nm. The intensity of the emission peak at 380 nm became stronger as the concentration of oxygen in the annealing atmosphere increased. The X-ray photoelectron spectrum (XPS) demonstrated that a more stoichiometric ZnO thin film was obtained upon annealing in oxygen and more excitons were generated from the radiative recombination carriers consistently. Additionally, the UV intensity increased with the thickness of ZnO thin film.     

BaTi<Subscript>1–x</Subscript>Zr<Subscript>x</Subscript>O<Subscript>3</Subscript> nanopowders prepared by the modified Pechini method

The results reported here based on a study of BaTi_1–xZr_xO₃ (x=0, 0.2 and 1) nanometric powders prepared by the modified Pechini method. The powder samples annealed from 600 to 1000°C/2 h were characterized by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The decomposition reactions of resins were studied using thermal analysis measurements. The barium titanate zirconate system presented just one orthorhombic phase. Furthermore, this study produced BaTiO₃ powders with a tetragonal structure using shorter heat treatments and less expensive precursor materials than those required by the traditional methods.     

DSC investigation of nanocrystalline TiO<Subscript>2</Subscript> powder

The aim of the article is to investigate the influence of particle size on titanium dioxide phase transformations. Nanocrystalline titanium dioxide powder was obtained through a hydrothermal procedure in an aqueous media at high pressure (in the range 25–100 atm) and low temperature (≤200 °C). The as-prepared samples were characterized with respect to their composition by ICP (inductive coupled plasma), structure and morphology by XRD (X-ray diffraction), and TEM (transmission electron microscopy), thermal behavior by TG (thermogravimetry) coupled with DSC (differential scanning calorimetry). Thermal behavior of nanostructured TiO₂ was compared with three commercial TiO₂ samples. The sequence of brookite–anatase–rutile phase transformation in TiO₂ samples was investigated. The heat capacity of anatase and rutile in a large temperature range are reported.     

Thermal study on electrospun polyvinylpyrrolidone/ammonium metatungstate nanofibers: optimising the annealing conditions for obtaining WO<Subscript>3</Subscript> nanofibers

This article demonstrates how important it is to find the optimal heating conditions when electrospun organic/inorganic composite fibers are annealed to get ceramic nanofibers in appropriate quality (crystal structure, composition, and morphology) and to avoid their disintegration. Polyvinylpyrrolidone [PVP, (C₆H₉NO) _n ] and ammonium metatungstate [AMT, (NH₄)₆[H₂W₁₂O₄₀]·nH₂O] nanofibers were prepared by electrospinning aqueous solutions of PVP and AMT. The as-spun fibers and their annealing were characterized by TG/DTA-MS, XRD, SEM, Raman, and FTIR measurements. The 400–600 nm thick and tens of micrometer long PVP/AMT fibers decomposed thermally in air in four steps, and pure monoclinic WO₃ nanofibers formed between 500 and 600 °C. When a too high heating rate and heating temperature (10 °C min⁻¹, 600 °C) were used, the WO₃ nanofibers completely disintegrated. At lower heating rate but too high temperature (1 °C min⁻¹, 600 °C), the fibers broke into rods. If the heating rate was adequate, but the annealing temperature was too low (1 °C min⁻¹, 500 °C), the nanofiber morphology was excellent, but the sample was less crystalline. When the optimal heating rate and temperature (1 °C min⁻¹, 550 °C) were applied, WO₃ nanofibers with excellent morphology (250 nm thick and tens of micrometer long nanofibers, which consisted of 20–80 nm particles) and crystallinity (monoclinic WO₃) were obtained. The FTIR and Raman measurements confirmed that with these heating parameters the organic matter was effectively removed from the nanofibers and monoclinic WO₃ was present in a highly crystalline and ordered form.     

Thermal and electrochemical study of solid-state reaction of mercury with Pt–20% Rh alloy

Thermogravimetry (TG), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), mapping surface and X-ray diffraction (XRD) have been used to study the reaction of mercury with platinum–rhodium (Pt–Rh) alloy. The results suggest that, when heated, the electrodeposited Hg film reacts with Pt–Rh to form intermetallic compounds each having a different stability, indicated by separate third mass-loss steps. In the first step, between room temperature and 170 °C, only the bulk Hg is removed. From this temperature to about 224 °C, the mass loss can be attributed to decomposition of the intermetallic PtHg₄. The third step, from 224 to 305 °C, can be ascribed to thermal decomposition of solid solution composed of intermetallic species RhHg₂ and PtHg₂. Intermetallic compound such as PtHg₄, PtHg₂, and RhHg₂ was characterized by XRD. These intermetallic compounds were the main products formed on the surface of the samples after partial removal of the bulk mercury via thermal desorption.     

Thermal,structural and magnetic studies on chromite spinel synthesized using citrate precursor method and annealed at 450 and 650 °C

Chromite Spinel materials were synthesized in this study by the citrate precursor method using four divalent cations (Ni²⁺, Co²⁺, Zn²⁺, and Cu²⁺). Citrate precursors consisting of mixed chromium citrates were first subjected to a thermogravimetric (TG) analysis for determining optimum temperatures for annealing. TG of coprecipitated chromium(III) citrate–zinc citrate gel has been carried out separately in N₂ and O₂ atmospheres. In both the cases, dehydration is followed by a four-step decomposition. The TG data were subjected to kinetic/mechanistic analysis, and the values of activation energy and Arrhenius factor were approximated. TG curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N₂ atmosphere. A large coercivity of 2701.01 Oe was observed for NiCr₂O₄ at 650 °C. On the basis of the results, 450 °C has been chosen for annealing treatment of the four gels. The samples were accordingly annealed at two different temperatures (450 and 650 °C) in a muffle furnace for 1 h in each case. The annealed powders were characterized using X-ray diffraction (XRD), SEM, and vibrating sample magnetometer (VSM). The XRD patterns show that annealing of CuCr₂O₄, NiCr₂O₄, and CoCr₂O₄ at 450 °C yields very small crystallites with poor Bragg reflections, although ZnCr₂O₄ samples show better peaks in XRD data. Annealing at 650 °C resulted in particle size range of 8–89 nm in the four cases. In the case of ZnCr₂O₄, the particle size was 8 nm.     

Structural,optical and photocatalytic activity of cerium doped zinc aluminate

Zinc aluminate and cerium-doped zinc aluminate nanoparticles are synthesised by co-precipitation method. Ammonium hydroxide is used as a precipitating agent. The synthesised compounds are characterised by powder X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FT-IR), Ultraviolet diffuse reflectance spectroscopy (UV-DRS), Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM) and Surface area measurements. The photocatalytic activity of zinc aluminate and cerium doped zinc aluminate nanoparticles are studied under the UV light and visible light taking methylene blue as a model pollutant. The amount of catalyst, concentration of dye solution and time are optimised under UV-light. Degradation of methylene blue under the UV-light is found to be 99% in 20 min with 10 mg of cerium doped catalyst. Compared to visible light degradation, the degradation of dye under UV-light is higher. Cerium doping in zinc aluminate (ZnAl₂O₄:Ce³⁺) increased the photocatalytic activity of zinc aluminate.     

Preparation of Cd-doped SnO<Subscript>2</Subscript> nanoparticles by sol–gel route and their optical properties

Nanocrystalline cadmium doped tin oxide (SnO₂) powders of about 2.5–4.5 nm in size have been synthesized by using different solvents via sol–gel method. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX), Transmission electron spectroscopy (TEM), UV-Vis absorption and Photoluminescence (PL) spectroscopy. The PL emission spectra revealed that the band centered at 452 nm might be related with oxygen vacancies. A spherical, small rod and slice like morphologies of the prepared Cd-SnO₂ nanoparticles were observed in the SEM and TEM studies. The presence of Cd modifies the structural, morphological and optical properties of the tin oxide nanoparticles.     

Structural and optical characterization of Zn doped TiO<Subscript>2</Subscript> nanoparticles prepared by sol–gel method

Undoped and zinc-doped TiO₂ nanoparticles (Ti_1−xZn_xO₂ where x = 0.00–0.10) were synthesized by a sol–gel method. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–VIS spectrometer. XRD pattern confirmed the tetragonal structure of synthesized samples. Average grain size was determined from X-ray line broadening using the Debye–Scherrer relation. The crystallite size was varied from 10 to 40 nm as the calcination temperature was increased from 350 to 800 °C. The incorporation of 3–5 mol% Zn²⁺ in place of the Ti⁴⁺ provoked a slight decrease in the size of nanocrystals as compared to undoped TiO₂. The SEM and TEM micrographs revealed the agglomerated spherical-like morphology with a diameter of about 10–30 nm and length of several nanometers, which is in agreement with XRD results. Optical absorption measurements indicated a blue shift in the absorption band edge upon 3–5 mol% zinc doping. Direct allowed band gap of undoped and Zn-doped TiO₂ nanoparticles measured by UV–VIS spectrometer were 2.95 and 3.00 eV at 550 °C, respectively.