Mustafa K. Bayazit

Linker-controlled polymeric photocatalyst for highly efficient hydrogen evolution from water

Polymeric photocatalysts have been identified as promising materials for H2 production from water due to their comparative low cost and facile modification of the electronic structure. However, the majority only respond to a limited wavelength region (λ 420 nm), with an apparent quantum yield (AQY) of 10.3% at 420 nm and 2.1% at 500 nm, measured under ambient conditions, which is closer to the real environment (instead of vacuum conditions). The strategy used here thus paves a new avenue to dramatically tune both the light absorption and charge separation to increase the activity of polymeric photocatalysts.

A microwave promoted continuous flow approach to self-assembled hierarchical hematite superstructures

In this work, a microwave promoted flow (MWPF) system to reproducibly synthesize self-assembled hierarchical hematite superstructures (Hem-SSs) using the sole precursor (Fe(NO3)3·9H2O) and single mode microwave under aqueous conditions was developed. The functional characterisation by XRD, (HR)TEM, XPS, UV-vis and Raman spectroscopy proved that highly crystalline ellipsoid Hem-SSs (∼180 nm × 140 nm) were produced, built from primary hematite nanoparticles, 5–10 nm in size using 0.05 mol L−1 precursor concentration, 1 mL min−1 flow rate and short reaction time (about 6 min). Particles produced via conventional heating (CH) at 120 and 140 °C in the same flow reactor under similar experimental conditions were found to consist of mixtures of goethite and hematite. The effects of precursor concentration (0.1 and 0.2 mol L−1) and flow rate (2 and 5 mL min−1) were further investigated and the synthesis mechanism was also discussed. This novel method opens a window for continuous fabrication of metal or metal oxide nanoparticles/superstructures by a green approach.

Tailoring degree of esterification and branching of poly(glycerol sebacate) by energy efficient microwave irradiation

Poly(glycerol sebacate) (PGS) is known as an exciting biomaterial owing to its tunable mechanical properties and controllable degradation rate. However, it is always challenging to control these properties. In this study, we have proposed a solvent-based system to provide a better control of reaction temperature in a microwave cavity, which can minimize evaporation of monomers, and water was collected to analyse the degree of esterification. Pre-PGSs with varied degrees of esterification were prepared using both single mode and multimode microwave cavity irradiation (MI) in this solvent-based reaction system. For a similar degree of esterification of pre-PGSs, the reaction time was almost halved with a better control on mechanical properties by single mode MI compared to multimode MI. Furthermore, the single mode MI approach was compared with the conventional heating (CH) approach. The mechanical properties and degradation rate of PGSs can be controlled readily by using the single mode MI approach compared to CH, which are crucial for their application as a biomaterial. It has been found that the single mode MI not only accelerates the pre-polymerisation process rate by six times, but also speeds up the curing time to the same extent. The Youngs modulus of PGSs prepared by single mode MI is increased from 0.77 to 3.14 MPa when the degree of esterification is 66.82%, which is 50% higher than that reported in the literature. Furthermore, PGS using a highly branched pre-PGS prepared by the single mode MI method has a large degree of flexibility. It can achieve a much higher Youngs modulus than that obtained by CH with a short curing time (<10 hours). In addition, the residual mass of PGSs prepared by single mode MI is varied from 78.54% to 92.96% compared to the CH method that ranges from 84.24% to 93.31%. Thus, these highly branched PGSs produced by single mode MI also show a wider degradation window (approximately 59% higher degree of flexibility than the CH method), which is found to be highly dependent on the degree of esterification and curing time of the pre-polymer, and controlled by branching.

Synthesis and characterization of branched fullerene-terminated poly(ethylene glycol)s

Poly(ethylene glycol) [1, PEG∼4(OH)2, Mn ∼ 200], glycerol ethoxylate [2, PEG∼21(OH)3, Mn ∼ 1000] and pentaerythritol ethoxylate [3, PEG∼15(OH)4, Mn ∼ 797] react directly with phenyl-C61-butyric acid methyl ester (PCBM), in the presence of dibutyltinoxide (DBTO) catalyst at 140 °C, to give a mixture of fullerene [C60] end-capped PEGs via transesterification. Among these PEG linkers, only PEG∼4(OPCB)2 (4a) (OPCB: ester oxygen linked phenyl-C61-butyryl group) was successfully isolated from the crude product mixture in the fully end-capped form. Fully acylated PEG∼21(OPCB)3 (5) and PEG∼15(OPCB)4 (6) could not be separated chromatographically from incompletely reacted species due to the polydispersity in branch lengths. This purification challenge was overcome by using a monodisperse branched core, 1,3,5-tris(octagoloxymethyl)benzene [7, PEG24(OH)3] to give a monodisperse tris-fullerene homostar, PEG24(OPCB)3 (8). The structures of the bis- and tris-fullerene products were confirmed by MALDI-TOF mass spectrometry and 1H NMR spectroscopy with supporting FTIR and UV-vis spectroscopic analysis.