Rapid synthesis of homogeneous titania-silica composite with high-BET surface area

We rapidly synthesized a homogeneous titania-silica composite with properties desired by the paper and paint industries by the sol-gel method in a controlled manner. The composite was synthesized by impregnating TiOCl₂ (titania precursor) into preformed silica networks (SiO₂ trimers). The first step before the formation of high molecular weight polymers in this rapid, versatile, and reproducible method involves the generation of trimers of SiO₂ after the rapid condensation of silicic acid monomers. The latter were formed as a product of the reaction of aqueous sodium silicate solution (SiO₂/Na₂O = 3.24) with 2 N HCl. In the second step, TiOCl₂ was added to the SiO₂ trimers at 50 °C. The structure of the composite was characterized by FE-SEM, EDS, TEM, XRD, FTIR, and nitrogen physisorption studies. The results demonstrated the homogeneous incorporation of titania into silica, which is normally difficult to perform because of the significant differences between the hydrolysis rates of the precursors. The maximum BET surface area, average diameter of the pores, and the maximum pore volume obtained were 739 m²/g, 27.4 Å, and 0.29 cm³/g respectively. The composite has superior oil absorption (240 ml/100 g) compared to that of the conventional pure TiO₂ (100 ml/100 g) filler. It also shows significant photocatalytic ability. The materials prepared via the proposed method are potential candidates for large scale commercial production.     

Titania-silica composites with less aggregated particles

Less aggregated titania-silica composite was developed by a versatile and reproducible method using relatively cheap precursors. The final product has more suitable properties than the conventional materials. The composite was synthesized by using sodium silicate, as a silica precursor, and freshly prepared TiOCl₂ as a titania source. The final product was obtained after subsequent calcination for 5 h at 300 to 1000 °C. The primary particles of the composite, as examined by SEM technique, are generally less aggregated. The XRD patterns for the calcined samples indicate the presence of TiO₂ and there is a significant increase of peak intensity as the calcination temperature increases. EDS and XPS analyses confirmed the formation of pure composite rich in Ti, Si, and O. Nitrogen physisorption studies reveal that the composite is mesoporous and have large BET surface area (~ 375 m²/g). A simple experiment of photoreduction of methyl orange under solar radiation was attempted to demonstrate the reliability and improvement of titania-silica composite in practice. It was found out that its efficiency is high as compared to P-25 TiO₂ under solar light. The results demonstrate that composite with desirable properties for various applications can be obtained via the present route.     

Preparation of amino-functionalized silica for copper removal from an aqueous solution

In the present research, amino-functionalized silica materials were synthesized to develop absorbents for removing copper (II) ions from water. Three kinds of silica with various BET surface areas and pore volumes (331.4 m²/g, 460.1 m²/g, 717.7 m²/g and 1.38 cm³/g, 1.06 cm³/g, 0.57 cm³/g, respectively) were used to determine an optimum material. 3-Aminopropyltrimethoxysilane (3-APTMS) and N-[3-(trimethoxysilyl)propyl]-ethylenediamine (MSDA) are two amino-functional moieties grafted onto silica surfaces. A maximum copper absorption of 33.45 mg/g was confirmed using the amino-functionalized material at an initial 3-APTMS concentration of 2.52 mmol/g. Silica with a BET surface of 331 m²/g and a pore volume of 1.38 cm³/g demonstrated a good copper absorption capacity. Interference species such as pH, NH₃ and EDTA were also studied in this work.     

Synthesis of light weight recron fiber-reinforced sodium silicate based silica aerogel blankets at an ambient pressure for thermal protection

Journal of Porous Materials - In this work, for the sake of improving the performance of homogeneous and flexible silica aerogel blankets in practical applications, lightweight recron fibers were...     

Mesoporous titania–silica composite from sodium silicate and titanium oxychloride. Part II: one-pot co-condensation method

Mesoporous titania–silica composite with large primary particles and homogeneous dispersion of Ti in the silica matrix were synthesized by the sol–gel method via a one-pot co-condensation method using cetyltrimethylammonium bromide (CTAB) as a structure-directing agent. Freshly prepared titanium oxychloride (TiOCl₂, titania precursor that is relatively stable) and sodium silicate were used as titania and silica precursors (at the initial ratio of Ti:Si = 1), respectively. The final products were obtained after removing the template by calcination and had overall ratio of Ti:Si = 2:3 (based on EDS and XRF analyses). Other characterization techniques employed include FE-SEM, TEM, FT-IR, DTGA, and nitrogen physisorption studies. The textural properties of the products were highly influenced by the molar concentration of CTAB. Materials with large primary particles (submicrometer-scale dimensions) were obtained at higher concentrations of CTAB (1.7 wt%). The porosities of the templated material were highly reduced compared to that of the untemplated material, emphasizing the influence of Ti loading in the silica matrix. Both pore size and surface area increased at a calcination temperature of 550 °C. The DTGA result showed that the composites exhibited elevated thermal stability (up to 900 °C). In summary, mesoporous titania–silica composite with desirable properties were developed via the proposed method using a relatively inexpensive silica precursor.     

Quantitative recovery of high purity nanoporous silica from waste products of the phosphate fertilizer industry

This study reports on the quantitative recovery of high purity nanoporous silica from wastes material (H₂SiF₆) of the phosphate fertilizer industry and Na₂O·SiO₂. The silica recovered from the wastes was compared with silica from the reaction of H₂SO₄ and Na₂O·SiO₂ because H₂SO₄ is commonly used. The product recovered from the wastes material and H₂SO₄ were 99.3% and 99.1% pure, respectively. The quantity recovered were 22.30 g and 20.11 g, respectively. The product had superior properties suitable for applications such as chromatography, reinforcing material for rubber and plastics. The process may significantly reduce the release of SiF₄ gas into the environment.     

Silver-doped silica powder with antibacterial properties

In this study a simple and reproducible method was used to develop silver-doped silica powder with antibacterial properties. Silica matrices were synthesized via a sol–gel route which allows one to easily tailor textural and chemical properties. A wide range of silica-materials/products was obtained via the present route. These are: pure silver nanoparticles (Ag⁰), silver in ionic state (Ag⁺), AgCl nanoparticles, and the mixture of Ag⁰ and AgCl. The efficacy of these products were tested against Escherichia coli and the results demonstrate that materials that are suitable for antibacterial applications were obtained by this newly developed technique while utilizing sodium silicate, which is relatively inexpensive, as a silica precursor. This may significantly boost the industrial production of the inexpensive silver-doped silica products for various applications. A project on other innovative industrial applications of our products is in progress.     

Mesoporous titania–silica composite from sodium silicate and titanium oxychloride. Part I: grafting method

In this study, we report a versatile method for designing a titania–silica composite using relatively inexpensive precursors. The composite was synthesized by grafting (impregnating) a precursor of a guest component into the preformed host’s solid network. The latter was prepared using sodium silicate as a silica precursor in the presence of cetyltrimethylammonium bromide (CTAB). A freshly prepared solution of titanium oxychloride (TiOCl₂, titania precursor that is relatively stable) was introduced into the host’s network to develop a titania–silica composite with initial ratio of Ti:Si = 1. The final product has the overall ratio of Ti:Si = 7:3 and was obtained after calcination for 5 h at 600–1000 °C. The XRD patterns for the calcined samples indicate the presence of TiO₂, and there was a significant increase in peak intensity as the calcination temperature increased. EDS, XRF, and FT-IR analyses indicated the formation of a highly pure composite rich in Ti, Si, and O. A Si–O–Ti band at 954 cm⁻¹ was observed, confirming the formation of a titania–silica composite. A composite with optimum properties (homogenous dispersion of the composite and less individual oxide phase separation) was obtained at 600 °C. A similar experiment was also conducted in the absence of CTAB. In this case, the final product was microporous, rendering it unsuitable for some applications.     

Structure‐property relationship in polyurethane elastomers containing starch as a crosslinker

Polyurethane elastomers were synthesized using polypropylene glycol (PPG 2000) as the polyol and starch as the multifunctional crosslinker in varying concentrations. Thermal and mechanical properties were measured by DSC, DMA and tensile tests. The morphology was examined by SEM. The swelling behavior of the polyurethanes in various solvents was investigated and the solubility parameter was determined. All these properties were compared with those of polyurethanes containing 1,1,1 ‐trimethylol propane (TMP) as the crosslinker. Starch‐based polyurethanes exhibited better mechanical properties. The effect of varying the starch:TMP ratio on the mechanical strength was also studied. With increasing starch content, the tensile strength and elongation increased. The starch‐based PUs exhibited two glass transitions, whereas TMP‐based PUs exhibited one T_g. No significant difference in the T_gs of the two PUs was observed. The activation energy of St‐PU calculated from DMA was 69 kcal/mol. Soil degradation tests indicated greater biodegradability in polyurethanes containing starch than in those containing TMP.     

Preparation of hydrophobic mesoporous silica powder with a high specific surface area by surface modification of a wet-gel slurry and spray-drying

A hydrophobic mesoporous silica powder was prepared by surface modification of a sodium silicate-based wet-gel slurry. The effects of the volume percentage (%V) of trimethylchlorosilane (TMCS), used as surface-modifying agent, on the physicochemical properties of the silica powder were investigated. We observed that as the %V of TMCS in the simultaneous solvent exchange and surface modification process increased, so did the specific surface area and cumulative pore volume of the resulting silica powder. Hydrophobic silica powder with low tapping density (0.27 g/cm³), high specific surface area (870 m²/g), and a large cumulative pore volume (2.2 cm³/g) was obtained at 10%V TMCS. Surface silanol groups of the wet-gel slurry were replaced by non-hydrolysable methyl groups (-CH₃), resulting in a hydrophobic silica powder as confirmed by FT-IR spectroscopy and contact angle measurements. We also employed FE-SEM, EDS, TG-DTA, and nitrogen physisorption studies to characterize the silica powders produced and to compare the properties of modified and unmodified silica powders. Moreover, we used a spray-dying technique in the present study, which significantly reduced the overall processing time, making our method suitable for economic and large-scale industrial production of silica powder.