Sharif Digital Repository

Nonporous and mesoporous silica-coated magnetite cluster nanocomposites particles were fabricated with various silica structures in order to develop a desired carrier for the lipase immobilization and subsequent biodiesel production. Lipase from Pseudomonas cepacia was covalently bound to the amino-functionalized particles using glutaraldehyde as a coupling agent. The hybrid systems that were obtained exhibited high stability and easy recovery regardless of the silica structure, following the application of an external magnetic field. The immobilized lipases were then used as the recoverable biocatalyst in a transesterification reaction to convert the soybean oil to biodiesel with methanol.... 

Uniformly sized superparamagnetic single-shell nonporous (S1) and double-shell mesoporous silica nanocomposite particles with ∼130 nm magnetite cluster cores are synthesised in this study. Mesoporous particles are prepared with two BJH pore sizes (2.44 and 3.76 nm, designated as S2 and S3 particles, respectively). Once the lipase was immobilised on particles, our results showed that the enzyme loading capacities of mesoporous structures, i.e. S2 and S3, are higher than that for nonporous particles (S1). Hydrolytic activity tests reveal that immobilised lipases retain about 90% of the free enzyme's activity. Furthermore, comparing to the free enzyme, the thermal stability of immobilised... 

In the present work, the mechanical properties, in particular, the Poisson's ratio of four two-dimensional silica structures, called here α,β,γ and δ are studied by means of molecular dynamics simulations. The α structure has been synthesized experimentally and the others have been reported as the most stable low-energy structures that reveal in-plane negative Poisson's ratio based on the first principles calculations. Among these structures, β-silica exhibits the largest in-plane negative Poisson's ratio which is 2–4 times higher than penta-graphene. Our results illustrate that the classical molecular dynamics simulation reproduces results in agreement with those of the first principles...