Well-ordered mesoporous silica nanoparticles (MSNs) feature a great number of important characteristics including large surface area and pore volume, tunable pore diameter, uniform particle size, and good biocompatibility. The feasibility of selective functionalization on the exterior and interior surface of MSNs makes them applicable in areas as diverse as sorption, separation, sensing, drug delivery, and catalysis.

Poly(L-lysine) was immobilized onto the outer surface of amine functionalized MSN via ring-opening polymerization. The poly(L-lysine) coated MSN (PLL-MSN) could be internalized by human cervical cancer (HeLa) cells with extremely high efficiency, which made the delivery of a large amount of drugs into cells possible. The release of the drugs was regulated by the degradation of poly(L-lysine). Trypsin, an enzyme abundant in the intestine where most molecules are absorbed by human body, could digest poly(L-lysine) and open the pore channels of PLL-MSN. On the other hand, pepsin, an enzyme that accumulates in the stomach, had no impact on poly(L-lysine) and therefore the loaded drugs could be kept inside the pore channels and protected from acid-induced hydrolysis. We envision that PLL-MSN has great potential as an oral drug delivery vehicle.

MSNs were also used as catalyst supports in cellulose degradation reactions. We have synthesized a series of platinum nanoparticle immobilized mesoporous silica nanoparticles (Pt NP-MSNs) by using N-(2-aminoethyl)-3-aminopropyl (AAP) and 3-[2-(2-aminoethylamino)ethylamino]propyl (AEP) functionalized MSNs as solid supports. Platinum nanoparticles were anchored on the MSNs by complexation between the Pt precursor and surface amine groups followed by hydrogen reduction. Pt NP-MSNs successfully catalyzed the conversion of cellulose into valuable polyols: sorbitol and mannitol and could be recycled at least three times under optimized reaction conditions.

In order to expand the applications of MSN, a series of organofunctionalized large pore mesoporous silica nanoparticles (LPMSNs) were synthesized via the co-condensation method under acidic conditions using a triblock copolymer (P104) as the structure-directing agent. The hydrothermal temperature, the amount of organosilanes, and the sequence of reagent additions were optimized to yield functionalized LPMSN with large pore size and well-controlled particle morphology. The sulfonic acid functionalized silica synthesized under optimum conditions showed better catalytic performance than traditional sulfonic acid functionalized SBA-15 in esterification reactions.

A mesoporous aluminum silicate (Al-MS) material has been synthesized via co-condensation by using NaAlO2 as aluminum source under basic conditions. The aluminum was tetrahedrally coordinated throughout Al-MS and, for the first time, the quantity of the surface aluminum sites was determined by solid-state NMR studies. The silicon to aluminum atomic ratios at the surface and in the bulk were around 100 and 60, respectively; indicating less chemically accessible aluminum sites on the surface. Despite the low surface concentration of aluminum. Al-MS showed excellent catalytic reactivity for the Claisen rearrangement of allyl phenyl ether.