Manufacture of chitosan microbeads using centrifugally driven flow of gel-forming solutions through a polymeric micronozzle

A centrifugally driven pulse-free flow has been used for generation of tripolyphosphate (TPP)-gelated chitosan beads with tunable diameters ranging from 148 to 257 lm. The production process requires a single motor as the sole actively actuated component. The 2% (w/w) chitosan solution was extruded through a polymeric nozzle with an inner diameter of 127 lm in the centrifugal field ranging from 93 to 452g and the drops were collected in an Eppendorf tube containing 10% (w/w) TPP solution at pH 4.0. The reproducibility of the bead diameters out of different nozzles was very good with overall CVs of the bead diameters down to 15% and the production rate was 45 beads per second per nozzle at 44 Hz rotor frequency. The production rate was proportional to the sixth power of the rotor frequency, which was explained by the non-Newtonian behaviour of the chitosan solution with a flow behaviour index of 0.466. An analytical model for the bead diameter and production rate has been presented and validated by the experimental data. The shrinkage of chitosan drops during gelation was estimated from the observations and the theoretical model

Chromophoric Dyads for the Light-Driven Generation of Hydrogen: Investigation of Factors in the Design of Multicomponent Photosensitizers for Proton Reduction

Two new dyads have been synthesized and studied as photosensitizers for the light-driven generation of H₂ from aqueous protons. One of the dyads, <b>Dy-1</b>, consists of a strongly absorbing Bodipy (dipyrromethene-BF₂) dye and a platinum diimine benzenedithiolate (bdt) charge transfer (CT) chromophore, denoted as PtN₂S₂. The two components are connected through an amide linkage on the bdt side of the PtN₂S₂ complex. The second dyad, <b>Dy-2</b>, contains a diketopyrrolopyrrole dye that is linked directly to the acetylide ligands of a Pt diimine bis­(arylacetylide) CT chromophore. The two dyads, as well as the Pt diimine bis­(arylacetylide) CT chromophore, were attached to platinized TiO₂ via phosphonate groups on the diimine through sonication of the corresponding esters, and each system was examined for photosensitizer effectiveness in photochemical generation of H₂ from aqueous protons and electrons supplied by ascorbic acid. Of the three photosensitizers, <b>Dy-1</b> is the most active under 530 nm radiation with an initial turnover frequency of 260 h^–1 and a total of 6770 turnovers over 60 h of irradiation. When a “white” LED light source is used, samples with <b>Dy-2</b> and the Pt diimine bis­(arylacetylide) chromophore, while not as effective as <b>Dy-1</b>, perform relatively better. A key conclusion is that the presence of a strongly absorbing organic dye increases dyad photosensitizer effectiveness only if the energy of the CT excited state lies below that of the organic dye’s lowest excited state; if not, the organic dye does not improve the effectiveness of the CT chromophore for promoting electron transfer and the light-driven generation of H₂. The nature of the spacer between the organic dye and the charge transfer chromophore also plays a role in the effectiveness of using dyads to improve light-driven energy-storing reactions