Rational synthesis of porous zirconia particles with hierarchical pore size and pore architectureSupports based on zirconia, particles with high density and excellent thermal and chemical stability, can offer increased flexibility relative to silica and polymeric phases when designing separations. However the widespread applicability of zirconia particles in chromatography is precluded by the unavailability of varying particle and pore sizes. Our work has documented the spray-drying technique to produce 25-40 um zirconia particles with a pore size of 22 nm, from a 100 nm colloid suspension [Clausen et al., J.Chrom-A, 831, 63-72, 1999]. Further, the utility of EDTPA-modified zirconia particles in the purification of immunoglobulins from cell culture supernatant and serum has also been demonstrated [Subramanian et al., J.Chrom-A, 890, 15-23, 2000 and Subramanian et al., J.Liq.Chrom., 29(4), 471-484, 2006].
An analysis of the mass transport fluxes governing the transport of hIgG in the first generation of zirconia particles (particle diameter 22-35μm and pore size 22 nm) suggests that pore diffusion is the rate-limiting transport mechanism in the EDTPA-modified zirconia particles [Sarkar and Subramanian,J.Chrom-B, 821, 124-131, 2005]. Based on our results, the next logical step was then to produce zirconia supports with particle diameters in the range of 50 to 200 μm and with pore sizes in the range of 35 to 100 nm. We have successfully used the method of polymer induced colloid aggregation (PICA) process, both in the presence and absence of porogens wherein a porogen was first embedded during the particle synthesis, followed by its removal in a subsequent step to prepare particle aggregates that were 7 to 45 μm in diameter with BET surface areas between 21 and 54 m2/g and pores ranging from 18 to 120 nm in diameter.
The nitrogen sorptometry and mercury porosimetry data of these support particles were modeled to calculate surface fractal dimension, pore accessibility parameters, pore network and pore geometry [Pattanaik and Subramanian, International Journal of Applied Ceramic Technology, 2009, DOI:10,1111/j.1744-7402.2009.02410.x]. Further, we have also combined polymer induced colloid aggregation (PICA) process and the oil emulsion method (OE) to produce macro- and giga-porous zirconia supports (50-250 microns) (see Figure 1). The pore and throat size distributions showed narrow bi-modal distributions over two distinct size scales: 10-100 nm and 600-3000 nm, respectively [Pattanaik and Subramanian, Powder Technology, 192, 359-366]. In future, transport properties of these matrices will be evaluated.