Jie-Bin Pang

Synthesis and characterization of mesoporous titania and silica-titania materials by urea templated sol-gel reactions

Abstract Mesoporous titania and mesoporous silica–titania materials have been successfully synthesized by using organic compound urea as template (or pore-forming agent) via sol–gel reactions of tetrabutyl titanate alone and with tetraethyl orthosilicate, respectively, followed by removing the urea by extraction with water. The pore parameters and morphology were characterized by N 2 adsorption–desorption measurement, powder X-ray diffraction and transmission electron microscopy. The pore diameters of synthesized titania, up to 5.5 nm, were larger than those mesoporous titania materials prepared by other nonsurfactant compounds reported previously by us. The pore diameters of silica–titania materials decreased with the increase of Si/Ti ratio from 1/100 to 2/1 under the same template concentration.

Preparation of mesoporous silica materials with non-surfactant hydroxy-carboxylic acid compounds as templates via sol–gel process

Abstract Mesoporous silica materials with pore sizes of 2–6 nm have been prepared through the sol–gel reactions of tetraethyl orthosilicate (TEOS) in the presence of hydroxy-carboxylic acid compounds, including citric acid (CA), malic acid (MA), tartaric acid (TA) and lactic acid (LA), as templates or pore-forming agents, followed by extraction with ethanol to remove the template molecules. The materials are characterized by infrared spectroscopy, nitrogen adsorption–desorption tests, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the materials prepared at template concentrations of 40–60 wt% have large surface areas (ca. 900 m 2 /g) and pore volumes (ca. 1.0 cm 3 /g). The mesoporosity arises from interconnecting channels and pores with, however, disordered channel arrangements. The pore diameters and pore volumes increase as the template concentration is increased. The mesoporous materials retain high surface areas and pore volumes with a little change in pore diameters upon calcination at 773 K for 6 h.

Synthesis of Mesoporous Silica Materials via Nonsurfactant Templated Sol-Gel Route by Using Mixture of Organic Compounds as Template

Mesoporous silica materials have been successfully prepared by employing a mixture of β-cyclodextrin and urea as a template in a HCl-catalyzed sol-gel process, followed by extraction with water. The obtained materials are characterized by nitrogen adsorption-desorption measurements, powder X-ray diffraction patterns and transmission electron microscopy. The changes of the pore parameters depend on both the weight ratio of β-cyclodextrin and urea and the template content in the final silica composite. The effects of the mixture as template (or pore-forming agent) on the physicochemical properties of the two synthesized systems, with different weight ratio and same template content, as well as varied template content and fixed weight ratio, were investigated in this paper. The results show that the hydrogen bonding interactions between β-cyclodextrin and urea molecules or urea aggregates, the urea-holding β-cyclodextrin molecules themselves as well as inorganic species are the driving force in the formation of mesoporous silica materials.

Synthesis of Mesoporous Silica Materials via Nonsurfactant Urea-Templated Sol-Gel Reactions

Mesoporous silica materials with pore diameters of 2 to 6 nm have been prepared using urea as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate, followed by removing the urea molecules by extraction with methanol or water. Characterization results from nitrogen sorption isotherm, powder X-ray diffraction, and transmission electron microscopy indicate that the materials have large specific surface areas (e.g., 600 m2/g) and pore volumes (e.g., 0.8 cm3/g) as well as narrow pore size distributions. The mesoporosity is arisen from interconnecting wormlike channels and pores of regular diameters. As the urea concentration is increased, the nitrogen sorption isotherms of the silica matrices transform from the reversible type I to the type IV form with type H2 hysteresis, along with increases in the diameter and volume of the pores.

A novel nonsurfactant pathway to hydrothermally stable mesoporous silica materials

Abstract A novel way is described to tune the pore diameters of the hydroxy-carboxylic acid templated mesoporous silica materials by adding different amount of aluminum chloride to the synthesis mixture for the sol–gel reactions, and these silica materials obtained have higher hydrothermal stability than those prepared without AlCl 3 .

Synthesis of Mesoporous Silica Materials with Hydroxyacetic Acid Derivatives as Templates via a Sol-Gel Process

A series of mesoporous silica materials were synthesized via HCl-catalyzed sol-gel process of tetraethyl orthosilicate at 60°C in the presence of nonsurfactant compounds such as hydroxyacetic acid (HA), lactic acid (LAC), 2-hydroxyisobutyric acid (HIBA) and diphenylglycolic acid (DPGA) as templates or pore-forming agents. After the removal of the nonsurfactant template compounds from the template-containing SiO2 composite, mesoporous silica materials were obtained. Results from Brunauer–Emmett–Teller (BET), powder X-ray diffraction (XRD), and transmission electron microscopy (TEM) experiments identified the formation of mesopores. Nitrogen adsorption-desorption isotherms showed that pore parameters increased with the template concentration except for the DPGA system. However, the pore parameters did not simply increase with the size of the template molecules. These results revealed that the molecular structure, molecular affinity, number of hydrophobic groups and steric hindrance played a significant role on the pore size of the final materials.

A facile preparation of transparent and monolithic mesoporous silica materials

Monolithic mesoporous silica samples of ca. 2 × 2 × 1 mm in dimension with large surface areas (>900 m2 g−1) and pore volumes (>0.80 cm3 g−1) have been readily prepared via a sol–gel process in the presence of hydroxy-carboxylic acid compounds as non-surfactant templates, and their pore structure was observed directly by means of atomic force microscopy (AFM).