Growth and Optical Properties of Quantized CdS Crystallites in TEOS Silica Xerogels

Quantized CdS crystallite-doped tetraethylorthosilicate (TEOS) silica xerogels are prepared by the sol-gel method. In this method, cadmium acetate [Cd(CH₃COO)₂2H₂O]-doped TEOS alcogel is formed by the hydrolysis and polycondensation of ethanolic TEOS in the presence of hydrochloric acid (HCl) and ammonium hydroxide (NH₄OH) catalysts and Cd(CH₃COO)₂.2H₂O. The CdS crystallites are formed in the alcogel by the reaction of Cd(CH₃COO)₂.2H₂O present in the gel and methanolic sodium sulfide (Na₂S), which is added over the alcogel. The effect of CdS/TEOS, EtOH/TEOS, S/Cd molar ratios, and temperature on the optical properties and CdS crystallite sizes in the xerogels are studied. A blue shift is observed in optical absorption spectra by decreasing the CdS/TEOS molar ratio from 2 × 10^–2 to 1 × 10^–4. It is observed that the crystallite size is increased from 1.6 to 3.4 nm by increasing the EtOH/TEOS molar ratio from 2 to 20, respectively, for a constant CdS/TEOS molar ratio of 5 × 10^–4. Emission spectra of xerogels are measured and found that the emission peak maxima shifted toward lower energies (higher wavelengths) by increasing the CdS/TEOS molar ratio in the xerogels. It is known from the X-ray diffraction (XRD) measurements of CdS-doped xerogels that the CdS crystallite structure in the xerogels is hexagonal wurtzite. The crystallite sizes were calculated from the XRD patterns and tight bonding calculations. There is a significant change in the color and size of CdS crystallite in the xerogels with a variation in temperature from 200 to 400°C.     

Studies on the effect of organic additives on the monolithicity and optical properties of the rhodamine 6G doped silica xerogels

Rhodamine 6G (R6G) laser dye doped silica xerogels were prepared by sol–gel processing using tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] precursor, citric acid (CTA) catalyst and ethanolic R6G in the presence of various organic additives such as formamide (FA), N′methylformamide (N′MF), dimethylformamide (DMF), acetamide (AA), glycerol (GLY), oxalicacid (OXA), ethyleneglycol (EG) and diethyleneglycol (DEG). The organic additive/TEOS molar ratio was varied from 0.001 to 0.1 by keeping the TEOS/EtOH/H₂O/CTA/R6G molar ratio constant at 1:5:7:1.2×10⁻³:9.2×10⁻⁶. It was found from the spectral studies of the additive modified R6G doped silica xerogels that the absorption maxima at 530 nm and emission maxima at 565 nm were increased with the addition of organic additive and with the increase of the additive/TEOS molar ratio. The transparency of the R6G doped silica xerogels was increased with the increase of additive/TEOS molar ratio from 0.001 to 0.1 with OXA, DEG and EG and in the case of DMF, N′MF, FA, AA and GLY, the transparency of the samples increased up to 0.014 of additive/TEOS molar ratio and then decreased for >0.014 of additive/TEOS molar ratio. Monolithic samples were obtained with all the organic additives. The percentage volume shrinkage of the samples was less EG and DEG and more with OXA additives.     

Luminiscent dye Rhodamine 6G doped monolithic and transparent TEOS silica xerogels and spectral properties

Sol–gel process was used for the preparation of Rhodamine 6G (R6G) doped silica xerogels, using tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] as the precursor for the silica network. Silica alcosol was prepared by hydrolysis and polycondensation of ethanol (EtOH) diluted TEOS in the presence of citric acid (CTA) catalyst. The ethanolic R6G was added to the alcosol to trap R6G molecules inside the SiO₂ gel network during the gelation of the TEOS alcosol. The effect of CTA/TEOS molar ratio on the gelation time of the R6G doped TEOS alcosol, transparency and monolithicity of the R6G doped silica xerogel was studied by varying the CTA/TEOS molar ratio from 1.2×10⁻⁴ to 180×10⁻⁴ by keeping the molar ratios of TEOS:EtOH:H₂O:R6G constant at 1:5:7:9.2×10⁻⁶, respectively. It was found that the minimum (<70 h) gelation time was observed at higher and lower CTA/TEOS molar ratios of 72×10⁻⁴ where as maximum (>180 h) gelation time was observed for CTA/TEOS molar ratio of 72×10⁻⁴. While opaque and monolithic R6G doped SiO₂ xerogels were obtained for <4.8×10⁻⁴ CTA/TEOS molar ratios, whereas cracked and transparent xerogels were obtained for >120×10⁻⁴ molar ratios of CTA/TEOS. Transparent, homogeneous and monolithic samples were obtained between 4.8×10⁻⁴ and 120×10⁻⁴ of CTA/TEOS molar ratios. Leaching out property was studied by using water, methanol and ethanol solvents for the R6G doped SiO₂ xerogels of 9.2×10⁻⁶ and 12×10⁻⁴ of R6G/TEOS and CTA/TEOS molar ratios, respectively, and found that R6G molecules were trapped in the pores of the SiO₂ network.Bleaching out phenomena of the R6G doped SiO₂ xerogels was studied by focusing the high intensity light on some part of the samples for a period of 1 h and found that the pores were continuous in SiO₂ network. Visible spectra of R6G in water, ethanol, SiO₂ alcosol and xerogel were taken for 1.6×10⁻⁴ M R6G and observed that there were two absorption peaks at 499 and 525 nm in the spectrum of R6G in water due to dimerization of R6G molecules and only one absorption peak at 530 nm in the spectra of ethanol, SiO₂ alcosol and xerogel because of monomerization of R6G molecules. Visible spectra of the R6G doped silica xerogels for varying R6G/TEOS molar ratios from 9.2×10⁻⁸ to 9.2×10⁻⁵ were taken and found the red shift (5–10 nm) with increasing the R6G/TEOS molar ratio from 9.2×10⁻⁸ to 9.2×10⁻⁵. The effect of temperature on these sample was studied by varying the temperature from 50 to 300 °C and found that the R6G doped silica samples were stable up to 200 °C. IR spectra were taken for pure R6G powder and R6G doped silica xerogels of 9.2×10⁻⁸ and 9.2×10⁻⁵ R6G/TEOS molar ratios and found that most of the peaks present in pure R6G powder spectrum were absent in the spectra of trapped R6G SiO₂ xerogels. This shows that, the SiO₂ network hinders the rotational and vibrational transitions of R6G when it is caged in the SiO₂ network. The peaks related to bending motion in R6G molecules were not disturbed by the SiO₂ network     

Luminiscent dye Rhodamine 6G doped monolithic and transparent TEOS silica xerogels and spectral properties

Sol–gel process was used for the preparation of Rhodamine 6G (R6G) doped silica xerogels, using tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] as the precursor for the silica network. Silica alcosol was prepared by hydrolysis and polycondensation of ethanol (EtOH) diluted TEOS in the presence of citric acid (CTA) catalyst. The ethanolic R6G was added to the alcosol to trap R6G molecules inside the SiO₂ gel network during the gelation of the TEOS alcosol. The effect of CTA/TEOS molar ratio on the gelation time of the R6G doped TEOS alcosol, transparency and monolithicity of the R6G doped silica xerogel was studied by varying the CTA/TEOS molar ratio from 1.2 × 10^-4 to 180 × 10^-4 by keeping the molar ratios of TEOS:EtOH:H₂O:R6G constant at 1:5:7:9.2× 10^-6, respectively. It was found that the minimum (<70 h) gelation time was observed at higher and lower CTA/TEOS molar ratios of 72 × 10^-4 where as maximum (>180 h) gelation time was observed for CTA/TEOS molar ratio of 72 × 10²⁴. While opaque and monolithic R6G doped SiO₂ xerogels were obtained for <4.8 × 10^-4 CTA/TEOS molar ratios, whereas cracked and transparent xerogels were obtained for >120 × 10^-4 molar ratios of CTA/TEOS. Transparent, homogeneous and monolithic samples were obtained between 4.8 × 10^-4 and 120 × 10^-4 of CTA/TEOS molar ratios. Leaching out property was studied by using water, methanol and ethanol solvents for the R6G doped SiO₂ xerogels of 9.2 × 10^-6 and 12 × 10^-4 of R6G/TEOS and CTA/TEOS molar ratios, respectively, and found that R6G molecules were trapped in the pores of the SiO₂ network.

Bleaching out phenomena of the R6G doped SiO₂ xerogels was studied by focusing the high intensity light on some part of the samples for a period of 1 h and found that the pores were continuous in SiO₂ network. Visible spectra of R6G in water, ethanol, SiO₂ alcosol and xerogel were taken for 1.6 × 10^-4 M R6G andobserved that there were two absorption peaks at 499 and 525 nm in the spectrum of R6G in water due to dimerization of R6G molecules and only one absorption peak at 530 nm in the spectra of ethanol, SiO₂ alcosol and xerogel because of monomerization of R6G molecules. Visible spectra of the R6G doped silica xerogels for varying R6G/TEOS molar ratios from 9.2 × 10^-8 to 9.2 × 10^-5 were taken and found the red shift (5–10 nm) with increasing the R6G/TEOS molar ratio from 9.2 × 10²⁸ to 9.2 × 10^-5. The effect of temperature on these sample was studied by varying the temperature from 50 to 300 8C and found that the R6G doped silica samples were stable up to 200 8C. IR spectra were taken for pure R6G powder and R6G doped silica xerogels of 9.2 × 10^-8 and 9.2 × 10^-5 R6G/TEOS molar ratios and found that most of the peaks present in pure R6G powder spectrum were absent in the spectra of trapped R6G SiO₂ xerogels. This shows that, the SiO₂ network hinders the rotational and vibrational transitions of R6G when it is caged in the SiO₂ network. The peaks related to bending motion in R6G molecules were not disturbed by the SiO₂ network     

Study the Influence of Drying Control Chemical Additives on the Physical and Optical Properties of Nanocrystalline Cadmium Sulfide–Doped Tetraethylorthosilicate Silica Xerogels

The experimental results of the influence of drying control chemical additives (DCCAs)—such as formamide (FA), N-methyl formamide (NMF), N-N-dimethyl formamide (DMF), acetamide (AA), glycerol (GLY), and oxalic acid (OXA)—on the physical and optical properties of nanocrystalline cadmium sulfide (CdS)–doped silica xerogels were reported in this paper. Tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] was used as a precursor for the three-dimensional silica network in which the CdS nanocrystallites were trapped. Silica alcosol was prepared by taking the mixture of ethanolic (EtOH) TEOS, water (H₂O), hydrochloric acid (HCI), and ammonium hydroxide (NH₄OH). Ethanolic cadmium acetate [Cd(CH₃COO)₂ 2H₂O] and thiourea [CS(NH₂)₂] were added to the alcosol for the formation of CdS crystallites. To study the effect of DCCAs on the physical and optical properties of nanocrystalline CdS-doped silica xerogels, the molar ratio of TEOS:EtOH:H₂O:HCl:NH₄OH:Cd(CH₃COO₂)₂ 2H₂O:CS(NH₂)₂ was kept constant at 1:5:7:0.01:0.0027:0.001:0.002, respectively, and the molar ratio of DCCA/TEOS was varied from 0.001 to 1. The addition of DCCAs (e.g., formamide) resulted in decreased gelation time (tg) from 240 to <20 hrs. Transparent CdS-doped alcogels and xerogels were obtained for the DCCA/TEOS molar ratios of <0.5, whereas turbid alcogels and translucent nanocrystalline CdS-doped silica xerogels were obtained for higher DCCA/TEOS molar ratios (>0.5). It has been found that the percentage of volume shrinkage of the samples, when heated at 300°C for 3 hr, was more (>15%) for OXA, GLY, and DMF and the shrinkage was less (<15%) for AA, NMF, and FA. The density of the CdS-doped silica xerogels with DCCAs was less than that without DCCAs. Red shift was observed in the optical absorption spectra of the samples with addition of the DCCAs. An increase in CdS crystallite size in the silica matrix with the incorporation of DCCAs was observed in the X-ray diffraction patterns in the order: OXA < GLY < DMF < AA < NMF < FA. From XRD studies, the structure of the CdS crystallites in the silica matrix was found to be hexagonal wurtzite.     

Ethyl acetoacetate ligand distribution in the course of titanium n-butoxide chelation

Sols obtained by chelation of titanium n-butoxide with ethyl acetoacetate, Eaa, in various ratios have been subjected to FTIR, ¹H and ¹³C NMR, HSQC and UV–Vis spectroscopy in order to provide insight in the compounds obtained, their structure and quantitative relationships. Three compounds, the bis-chelated monomer, Ti(OⁿBu)₂(Eaa)₂, bis-chelated dimer, (Ti(OⁿBu)₃Eaa)₂ and monochelated dimer, Ti₂(OⁿBu)₇Eaa have been established. As the molar ratio Eaa/Ti(OⁿBu)₄ increases, the coordination changes from the monochelated and bis-chelated dimer to the bis-chelated monomer. Additionally, the transesterification reaction, influencing the chemical composition of the compounds was noted. The hydrolysis of the prepared sols was partial, leaving some residual butoxy and ethyl acetoacetate groups attached to titanium. Thermal treatment of the prepared amorphous gels at 350 °C yielded with the formation of nanocrystalline anatase. It was noted that high Eaa/Tnb ratio slightly retards the anatase formation.     

Insights into the synthesis optimization of Fe@SiO2 Core-Shell nanostructure as a highly efficient nano-heater for magnetic hyperthermia treatment

Maintaining the intact iron core, protecting the extra iron ion release, and generating biologically sufficient heat, are the critical aspects for magnetic hyperthermia treatment (MHT). Thus, the composition of silica-coated nanoscale zero-valent iron (nZVI) was optimized by applying response surface methodology (RSM) and changing the molar ratio of tetraethyl orthosilicate (TEOS) and iron(II) sulfate (FeSO₄·7H₂O) as the silica and iron precursors, respectively. The TEOS/FeSO₄·7H₂O molar ratio of 1.67 results in the maximized saturation magnetization (99.3 emu/g) and the crystalline phase of pure iron. In comparison with the previously reported studies, the synthesized core–shell nanostructures demonstrate superior heat production features. As silica coating protects the inner core from oxidation and results in more effective heat-generating seeds, nanostructures with a higher amount of silica precursors, i.e., 10.3 mm, demonstrate an efficient specific absorption rate (SAR). Moreover, the medium and higher TEOS amounts represent acceptable cytocompatibility up to 125 μg/mL and 250 μg/mL, respectively. In vitro hyperthermia evaluation depicts the cancer cell viability reduction indicating the hyperthermia-induced apoptosis. Based on the data mentioned above, we could introduce a potential successful nanoparticle for magnetic hyperthermia treatment.     

Synthesis of sustainable silica xerogels/aerogels using inexpensive steel slag and bean pod ash: A comparison study

Low cost silica xerogels/aerogels were synthesized from steel slag and bean pod ash by sol–gel method. Comparison study showed differences between structural, morphological, textural, thermal and physical properties of the silica xerogels and aerogels. Formation of amorphous structure and silica network was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses, respectively. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses revealed that silica xerogels had smaller interlinked network in contrast to silica aerogels. Typical type IV isotherm was observed for all samples in N₂ adsorption-desorption isotherms. The highest surface area was determined as 371 m² g⁻¹ for silica aerogel synthesized from steel slag. Particle size of silica aerogels was lower than that of the silica xerogels. The more porous structure made silica aerogels desirable materials with lower bulk density and thermal conductivity when compared to silica xerogels. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) exhibited high thermal stability of the silica xerogels/aerogels. Although silica xerogels had highly hydrophilic structure, contact angle of silica aerogels synthesized from steel slag and bean pod ash was 60° and 74°, respectively. The comparison study will give a new point of view about differences between silica xerogels and aerogels synthesized from by-products or inorganic/organic waste instead of silicon alkoxides.     

Synthesis and characterization of ordered mesoporous silica by using polystyrene microemulsion as templates

A simple room temperature synthesis of pure mesoporous silica by using a homemade and functional template: polystyrene microemulsion is reported. The process consists of HCl-catalysed sol-gel reactions of tetraethyl orthosilicate (TEOS) in polystyrene microemulsion, followed by removal of the template via solvent extraction or calcining. X-ray diffraction, Transmission Electron Microscope and N₂ adsorption-desorption isotherms are then used to characterize the mesostructure. The results indicate that the synthesized mesoporous silica has a large BET surface area with more than 900 m²/g, large pore volume with more than 0.8 cm³/g and ordered mesopore-structure. This provides a possible way to control the meso-structure and pore size of mesoporous materials via potential functional templates.     

Effect of pH,Aging, and Drying on the Size of CdS Nanocrystallites,Monolithicity, and Transparency of Nanocrystalline CdS-Doped Silica Xerogels

CdS semiconductor nanocrystals are prepared in SiO₂ matrix xerogels by a sol–gel method using ethanolic tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄], catalyst (HCl or NH₄OH), cadmium acetate [Cd (CH₃COO)₂ 2 H₂O], and thiourea [SC (NH₂)₂] and drying the alcogels at room temperature and heating up to 250°C. The effect of alcosol pH on the CdS crystallite size in silica matrix, color, monolithicity, and transparency of the xerogels is studied by varying the pH from 1 to 10, and maintaining the CdS/SiO₂ molar ratio constant at 0.0025. It was found that the color of samples varied from light yellow to orange and transparency decreased from 85 to 15% with the variation of alcosol pH from 1 to 10, respectively. The cracked sample were found for pH < 3, opaque, powdery samples for the pH > 8, and transparent monolithic yellow-colored samples in the pH range 3–7. The quantum size effect was observed in the optical absorption spectra of the samples. The threshold peak decreased from 520 to 250 nm, energy increased from 2.4 to 4.9 eV, and the CdS crystallite size decreased from 6 to 1 nm with the variation of pH of the alcosol from 10 to 1, respectively. In the case of the effect of aging, a minimum of 5 days aging is required for monolithic samples and the CdS crystallite to increase in size with and remain constant, even when the aging period is increased for 10 days. Monolithic samples were obtained with drying and heating rates of <0.4 wt.% loss/h and 30–50°C/h range and cracked samples with >0.4 wt.% loss/h and >50°C/h drying and heating rates, respectively. The density of the CdS crystallites doped-silica xerogels decreased from 1.57 to 1.30 gm/cm³ with an increase in pH from 1 to 10, respectively. From XRD spectra, the CdS crystallite structure was found to be a hexagonal wurtzite structure. The intensity of the peaks increased and the breadth decreased with the variation of pH of the alcosol from 1 to 10 because of an increase in CdS crystallite size.     

Synthesis of electrically active biopolymer–SiO2 nanocomposite aerogel

Silica nanoparticles encapsulated acacia gum–silica (AgSiO₂) composites were synthesized through sol–gel method using tetraethyl orthosilicate (TEOS) as silica precursor in basic condition. The nanocomposite gels were dried at different temperatures to form aerogels. The incorporation of nanostructured silica will influence the electronic behavior of composite. The composition of silica with acacia gum was tailored to optimize the material having good electronic properties. The resulting material was characterized by FTIR, XRD and AFM. The control curing of the composite resulted to mesoporous material with nanosize silica. At optimum composition, electrical conductivity and ion transference number of hybrid material are found to be 18.3 × 10^− 2 Scm^− 1 and 4.26 × 10² cm² V^− 1 s^− 1 respectively. The electrical conductivity of biopolymeric hybrid is comparable to that of commercially used synthetic conducting polymers. The ion transfer number of AgSiO₂ nanocomposites attributes the superionic character for electrical conduction.     

PMMA–SiO2 hybrid films as gate dielectric for ZnO based thin-film transistors

In this paper we report a low temperature sol–gel deposition process of PMMA–SiO₂ hybrid films, with variable dielectric properties depending on the composition of the precursor solution, for applications to gate dielectric layers in field-effect thin film transistors (FE-TFT). The hybrid layers were processed by a modified sol–gel route using as precursors Tetraethyl orthosilicate (TEOS) and Methyl methacrylate (MMA), and 3-(Trimethoxysilyl)propyl methacrylate (TMSPM) as the coupling agent. Three types of hybrid films were processed with molar ratios of the precursors in the initial solution 1.0: 0.25, 0.50, 0.75: 1.0 for TEOS: TMSPM: MMA, respectively. The hybrid films were deposited by spin coating of the hybrid precursor solutions onto p-type Si (100) substrates and heat-treated at 90 °C for 24 h. The chemical bonding in the hybrid films was analyzed by Fourier Transform Infrared Spectroscopy to confirm their hybrid nature. The refractive index of the hybrid films as a function of the TMSPM coupling agent concentration, were determined from a simultaneous analysis of optical reflectance and spectroscopic ellipsometry experimental data. The PMMA–SiO₂ hybrid films were studied as dielectric films using metal-insulator-metal structures. Capacitance–Voltage (C–V) and current–voltage (I–V) electrical methods were used to extract the dielectric properties of the different hybrid layers. The three types of hybrid films were tested as gate dielectric layers in thin film transistors with structure ZnO/PMMA–SiO₂/p-Si with a common bottom gate and patterned Al source/drain contacts, with different channel lengths. We analyzed the output electrical responses of the ZnO-based TFTs to determine their performance parameters as a function of channel length and hybrid gate dielectric layer.     

Solar photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) using TiO2/SiO2 aerogel composite photocatalysts

Silica aerogels and TiO₂/silica aerogel composite photocatalysts were synthesized by sol–gel technique at ambient pressure using orthosilioate and tetra-n-butyl titanate as precursors, respectively. The prepared composite photocatalysts were characterized by XRD, TEM, BET surface area, FT-IR and UV–vis absorption spectra. The results showed that the TiO₂/silica aerogel composite photocatalysts possess high surface area. The addition of silica aerogels inhibited the grain growth and phase transformation of anatase to rutile during calcination. The TiO₂/silica aerogel composite sample calcined at 500 °C with an optimal silica aerogel content of 7 wt.% afforded the highest photocatalytic activity. The photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) was investigated by using this novel TiO₂/silica aerogel composite photocatalyst under solar light irradiation. The effects of irradiation time, pH, catalyst concentration, temperature and initial DNBP concentration were examined as operational parameters. The optimal operational parameters were found as follows: pH as solution pH 4.82, 8 g L⁻¹ catalyst concentration, 20 °C, and 240 min irradiation time. The kinetics of DNBP degradation by TiO₂/silica aerogel composite fit well a pseudo-first-order kinetic model. The repeatability of photocatalytic activity was also tested. This study showed the feasible and potential use of TiO₂/silica aerogel composite photocatalysts in degradation of toxic organic contaminants.     

A highly-sensitive l-lactate biosensor based on sol-gel film combined with multi-walled carbon nanotubes (MWCNTs) modified electrode

A new type of amperometric l-lactate biosensor based on silica sol-gel and multi-walled carbon nanotubes (MWCNTs) organic–inorganic hybrid composite material was developed. The sol-gel film was used to immobilize l-lactate oxidase on the surface of glassy carbon electrode (GCE). MWCNTs were used to increase the current response and improve the performance of biosensor. The sol-gel film fabrication process parameters such as H₂O : TEOS and pH were optimized, Effects of some experimental variables such as applied potential, temperature, and pH on the current response of the biosensor were investigated. Analytical characteristics and dynamic parameters of the biosensors with and without MWCNTs in the hybrid film were compared, and the results showed that analytical performance of the biosensor could be improved greatly after introduction of the MWCNTs. Sensitivity, linear range, limit of detection (S / N = 3) were 2.097 μA mM^− 1, 0.3 to 1.5 mM, 0.8 × 10^− 3 mM for the biosensor without MWCNTs and 6.031 μA mM^− 1, 0.2 to 2.0 mM, 0.3 × 10^− 3 mM for the biosensor with MWCNTs, respectively. This method has been used to determine the l-lactate concentration in real human blood samples.     

A facile method for production of high-purity silica xerogels from bagasse ash

In this paper, we systematically report the synthesis of mesoporous silica xerogels in high purity from bagasse ash. The bagasse ash was chosen as the raw material due to its availability and low-price, and environmental considerations also were important. Silica was extracted as sodium silicate from bagasse ash using NaOH solution. The sodium silicate was then reacted with HCl to produce silica gel. To produce high-purity silica xerogels, three different purification methods were investigated, i.e., acid treatment, ion exchange treatment, and washing with de-mineralized water. We were able to produce high-purity silica (>99 wt.%) by washing the produced gels with either de-mineralized water or with ion exchange resin. The specific surface area of the prepared silica xerogels ranged from 69 to 152 m² g^?1 and the pore volume ranged from 0.059 to 0.137 cm³ g^?1. The pore radii were 3.2–3.4 nm, which indicated that the silica xerogels was mesoporous. From the adsorption characterization, it was obvious that adsorptive capacity was better for high-purity silica xerogels compared with low-purity. The maximum adsorption capacity by high-purity silica xerogel was 0.18 g-H₂O/g-SiO₂. Finally, we demonstrate the potential of bagasse ash for mesoporous silica production with its excellent adsorptive capacity that makes it beneficial as an environmental solution.     

Growth of silicon carbide nanorods from the hybrid of lignin and polysiloxane using sol-gel process and polymer blend technique

We report here the formation of silicon carbide (SiC) nanorods from organic-inorganic hybrid of the commercially available lignin and sol-gel derived nanosized silica. The SiC nanorods were identified by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface morphology shows the formation of continuous nanorods of diameter in the range of 50-200 nm. The X-ray diffraction (XRD) pattern show peaks at 2θ = 35.5° and 60.2° indicate the formation of β-SiC and a sharp peak at 2θ = 22.1° suggests the presence of unreacted crystalline silica (crystoballite). The characteristic vibration of SiC at 791 cm^− 1 in Fourier transform infrared spectroscopy (FTIR) was also observed.     

Study of annealing-induced changes in CdS thin films using X-ray diffraction and Raman spectroscopy

We have investigated as grown and annealed (300 °C, 400 °C and 500 °C) thin films of CdS grown on GaAs (001) by chemical bath deposition. X-ray diffraction (XRD) shows that the as grown CdS film is polycrystalline and predominantly cubic. A residual compressive stress of the order of 1.45% in the as grown film relaxes on annealing the film at 300 °C. Furthermore, CdS film undergoes a structural phase transition from the metastable cubic phase to the stable hexagonal phase, when, annealed at 500 °C. This is accompanied by significant improvement in crystalline quality of the film. Line shape analysis of the asymmetry of the longitudinal optical phonon shows a disorder-activated mode, which correlates well with the crystalline quality estimated from XRD and photoluminescence measurements. The additional features observed in the Raman spectra ∼ 254 cm^− 1 and 309 cm^− 1 are investigated using temperature dependent Raman spectroscopy and identified as superposition of transverse optical: E₁ (TO) and E₂ phonons at q = 0 and combination mode (two zone-edge E₂ phonons) respectively.     

Post deposition annealing of aluminum oxide deposited by atomic layer deposition using tris(diethylamino)aluminum and water vapor on Si(100)

Thin stoichiometric aluminum oxide films were deposited using tris(diethylamino)aluminum precursor and water. Changes in aluminum oxide film and interfacial regions were studied after post deposition annealing under inert ambience at 600, 800 and 1000 °C using Fourier Transform InfraRed (FTIR) spectroscopy, X-ray Photoelectron Spectroscopy, and Scanning Transmission Electron Microscopy (STEM)/Electron Energy Loss spectroscopy (EELS) techniques. STEM/EELS analyses were also done on samples annealed in situ, i.e., inside the electron microscope at temperatures as high as 800 °C. Up to an annealing temperature of 600 °C, the atomic layer deposited alumina film was thermally stable and remained amorphous with no interfacial silica growth observed. After annealing at 800 °C for 5 min, the only change observed was a small increase in the interfacial layer thickness which was found to be mainly silicon oxide without any significant silicate content. Annealing at 1000 °C induced a significant increase in the interfacial layer thickness which consisted of a mixture of silicon oxide and aluminum silicate. The composition of the interfacial layer was found to change with depth, with silicate concentration decreasing with distance from the Si substrate. Also, the FTIR spectra exhibited strong absorption features due to Al-O stretching in condensed AlO₆ octahedra which indicate crystallization of the alumina film after annealing at 1000 °C for 5 min.     

Deposition of WNxCy thin films for diffusion barrier application using the dimethylhydrazido (2) tungsten complex (CH3CN)Cl4W(NNMe2)

Tungsten nitride carbide (WN_xC_y) thin films were deposited by chemical vapor deposition using the dimethylhydrazido (2⁻) tungsten complex (CH₃CN)Cl₄W(NNMe₂) (1) in benzonitrile with H₂ as a co-reactant in the temperature range 300 to 700 °C. Films were characterized using X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy and four-point probe to determine film crystallinity, composition, atomic bonding, and electrical resistivity, respectively. The lowest temperature at which growth was observed from 1 was 300 °C. For deposition between 300 and 650 °C, AES measurements indicated the presence of W, C, N, and O in the deposited film. The films deposited below 550 °C were amorphous, while those deposited at and above 550 °C were nano-crystalline (average grain size < 70 Å). The films exhibited their lowest resistivity of 840 µΩ-cm for deposition at 300 °C. WN_xC_y films were tested for diffusion barrier quality by sputter coating the film with Cu, annealing the Cu/WN_xC_y/Si stack in vacuum, and performing AES depth profile and XRD measurement to detect evidence of copper diffusion. Films deposited at 350 and 400 °C (50 and 60 nm thickness, respectively) were able to prevent bulk Cu transport after vacuum annealing at 500 °C for 30 min.     

Synthesis and characterization of mesoporous silica thin films as a catalyst support on a titanium substrate

Mesoporous silica films with a thickness of 500-900 nm were synthesized on a titanium substrate by the evaporation-induced self-assembly method (with 900-1200 rpm for 90 s) using cetyltrimethylammonium bromide (CTAB) as structure-directing agent and tetraethyl orthosilicate as the silica source. Prior to coating deposition, the titanium substrate was oxidized to increase the surface roughness up to 500 nm and to produce a thin titania layer. Just before the synthesis, the titania layer was made super hydrophilic by an UV treatment for 2 h to provide a better adhesion of the silica film to the substrate. Films with hexagonal and cubic mesostructures with a uniform pore size of 2.8 nm and a surface area of 1080 m²/g were obtained and characterized by different methods. An alternative approach for surfactant removal by gradual heating up to 250 °C in vacuum was applied. Complete removal of CTAB from the as-synthesized silica films was confirmed by infrared spectroscopy.