Autofluorescence of hydrogels without a fluorophore.

Fluorescent hydrogels have recently attracted great attention for medical diagnostics, bioimaging and environmental monitoring. However, additional phosphors or fluorophores are always required to label the hydrogels, and they suffer from marker bleaching, signal drifts, or information misrepresentation. Here we report autofluorescence that universally exists in carbonyl-containing hydrogels without any traditional fluorophore. The fluorescence is successfully employed to self-monitor the gelation process since the fluorescence signal is closely related to the internal structural change of the gels. The crosslinked structure is beneficial to the fluorescence efficiency. Specifically, the fluorescence intensity is amplified with decreasing water content of the gels. The system realizes aggregation-induced emission in a water-deficient environment. The fluorescence is quenched by the addition of some specific metal ions, which can realize the successfully erasure and rewriting of information under visible light and ultraviolet light respectively. We believe that the spontaneous fluorescence of a gel provides the most reliable basis for the detection of a gel structure and opens new prospects in the application of hydrogels.

Recycling waste thermosetting unsaturated polyester resins into oligomers for preparing amphiphilic aerogels.

The styrene-maleic acid copolymer (SMC) was obtained by selective and complete cleavage of ester groups from waste thermosetting unsaturated polyester resins (WTUPR). The degradation was performed in glycol at 180 °C for 5 h with potassium carbonate as a catalyst and the resultant potassium salt of SMC (SMC-K) can be very easily separated by precipitation using ethanol with a yield of 63.8%. The SMC-K was integrated with polyvinyl alcohol to form amphiphilic aerogels via freeze-thaw and freeze-drying processes. The aerogel exhibits a low density of 0.024 g·mL-1 due to hierarchical pore structures with a size range from nanometer to micrometer scale. Besides, the good compressibility and resilience of the aerogel are demonstrated. The amphiphilic aerogel displayed high absorption of both water and oily liquids (over 30 g.g-1 and 20 g.g-1 for water and dichloromethane respectively), together with a good recycle adsorption efficiency (>90% after 10 cycles). This work provides a new strategy on upcycling of WTUPR.

Fast microwave-assisted hydrolysis of unsaturated polyester resin into column packing for rapid purifying of dye wastewater.

Microwave-assisted selective degradation successfully converts thermosetting unsaturated polyester resins into a low-swelling (below 10 g g-1) gel material (GM) with a high yield (58-65%) in water at 100°C for only 1 h. The obtained GM possesses rough and porous structure while the content of carboxylate group obtained by cleavage of partial ester groups is more than 10%, varying with the concentration of the catalyst. It is suitable for use as packing of adsorption column to rapidly purify sewage. Super high filtering rates of 18582-27002 L h-1 m-3 without external pressure and high removal efficiency of more than 99.8% were achieved, promoting practical application for rapid removal of organic pollutants.

Removal of phenol by powdered activated carbon prepared from coal gasification tar residue.

Coal gasification tar residue (CGTR) is a kind of environmentally hazardous byproduct generated in fixed-bed coal gasification process. The CGTR extracted by ethyl acetate was used to prepare powdered activated carbon (PAC), which is applied later for adsorption of phenol. The results showed that the PAC prepared under optimum conditions had enormous mesoporous structure, and the iodine number reached 2030.11 mg/g, with a specific surface area of 1981 m2/g and a total pore volume of 0.92 ml/g. Especially, without loading other substances, the PAC, having a strong magnetism, can be easily separated after it adsorbs phenol. The adsorption of phenol by PAC was studied as functions of contact time, temperature, PAC dosage, solution concentration and pH. The results showed a fast adsorption speed and a high adsorption capacity of PAC. The adsorption process was exothermic and conformed to the Freundlich models. The adsorption kinetics fitted better to the pseudo-second-order model. These results show that CGTR can be used as a potential adsorbent of phenols in wastewater.

Rapid Recovery Hydrogel Actuators in Air with Bionic Large-Ranged Gradient Structure.

Fast recovery in a nonaqueous environment is a big challenge for hydrogel actuators. In this work, a temperature-responsive hydrogel actuator with outstandingly rapid recovery in air was reported. The hydrogel with bionic large-ranged gradient structure was fabricated by copolymerization of hydrophilic monomer hydroxyethyl acrylate (HEA) and N-isopropylacrylamide in the dispersion of Laponite utilizing a facile electrophoretic method. The deformation degree and time can be regulated by varying the concentration of HEA to change the lower critical solution temperature (LCST) and swelling of the hydrogel. A dynamic equilibrium between the water into and out of the hydrogel was observed, and the hydrogel showed no shrink above LCST. The synthesized hydrogels showed fast response in hot water and rapid recovery in air. Such nonshrink characteristics and excellent reversibility made it possible for these hydrogels to be used as temperature-controlled microfluidic switches. This work provided an approach to design fast recovery hydrogel actuators by the incorporation of hydrophilic monomers and extend the application of the hydrogel actuators into fields such as soft robots, micromanipulation, microfluidics and artificial muscles in various environments.