Dopamine-modified poly(acrylic acid) (PAA-dopa) and poly(vinylpyrrolidone) (PVPON) was layer-by-layer (LbL) assembled to prepare thin film based on hydrogen bonding. The carboxylic group of acrylic acid and the phenolic hydroxyl group of dopamine can both act as hydrogen bond donors. The critical assembly and the critical disintegration pH values of PVPON/PAA-dopa film are enhanced compared with PVPON/PAA film. The hydrogen-bonded PVPON/PAA-dopa thin film can be cross-linked via catechol chemistry of dopamine. After cross-linking, the film can be exfoliated from the substrate in alkaline solution to get a free-standing film. Moreover, by tuning the pH value, deprotonation and protonation of PAA will make the hydrogen bond in the film break and reconstruct, which induces that the free-standing film has a reversible swelling-shrinking behavior.
The
photocatalytic conversion of CO2 to valuable fuels
or chemicals has displayed the promise to solve urgent energy and
environmental problems. Photocatalytic systems for CO2 reduction
in water usually suffer from low efficiency and selectivity due to
competitive proton reduction and relatively low CO2 concentration.
In this work, we report a CoII–ZnII heterometallic
dinuclear complex [CoZn(bpbp)(CH3COO)2](CH3COO) (CoZn), which shows high photocatalytic
activity and selectivity for CO2-to-CO conversion in a
water/acetonitrile solution. The values of TONCO and CO
selectivity reach as high as 6680 and 98%, respectively. It was found
that CoZn exhibits much higher activity than the corresponding
CoII–CoII homometallic dinuclear complex
[Co2(bpbp)(CH3COO)2](CH3COO) (CoCo) under the same conditions. The electrochemical
properties and DFT calculations indicated that the improved photocatalytic
activity of CoZn in comparison to CoCo is
attributed to the smaller energy barrier of the rate-limiting CO2 coordination step for photocatalytic CO2-to-CO
conversion via the synergistic effect between the two different metal
centers.
Abstract:The hydrogen-bonded polymer complex thin film of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA) was fabricated with layer-by-layer (LbL) assembly. The film shows exponential growth at early stage and transfers to linear growth after 10 assembling cycles, and the stable thickness increment per assembling cycle in the linear region could be higher than 100 nm. The film growth should be related with polymer chain diffusion during LbL assembly. The effects of assembling time, rinsing time, temperature, pH value, concentration and molecular weight on the thin film growth were investigated. Increasing the assembly time, the temperature and the concentration is favorable to produce the thick film. Prolonging rinsing time is good for preparing smooth film. The film can be constructed below pH 4.5 while the prepared film will not completely dissolve until pH value elevates to 7.0. Molecular weight has a subtle effect on the PEOX/PAA film growth. The PEOX-PAA pair that has a big molecular weight contrast shows fast film growth in the linear region.
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