The Preparation Of Hybrid Gels Used For Skin Health Monitoring And Modification Of Multi-dimensional Structure

Recently,photocatalytic technology based on visible light has received extensive attention and rapid development because of the potential applications in water splitting for hydrogen（H₂）evolution and dye degradation.As an inorganic non-metallic photocatalytic reagent,g-C₃N₄ can accomplish the photocatalytic reaction by visible light radiation due to its suitable semiconducting band gap（2.7 e V）.However,g-C₃N₄has the limitations of difficult recovery,easy aggregation and poor dispersion in various solvents.The agglomeration of photocatalysts greatly lowers its specific surface area,which also greatly affects its own photocatalytic reaction efficiency.Overcoming the agglomeration of photocatalysts and improving the photocatalytic performance are crucial for the photocatalysts used for the degradation of dyeing wastewater.The thermo-responsive hydrogels with lower critical solution temperature（LCST）,as a typical type of stimuli-responsive polymers,have received extensive attentions and applications.They have been extensively used for drug release,cell tissue engineering,photocatalysis,composite material carriers,thin film detectors and smart textiles due to their rapid response to the external change of temperature.They also possess the characteristics of water absorption,moisture retention,high swelling capability,large specific surface area and fast response ability,which can be used as an excellent carrier in hybrid materials.Thus,thermo-responsive gels can be used as a carrier to construct a new type of hybrid material containing the photocatalyst g-C₃N₄.The obtained hybrid gels have an important practical significance and research value for solving the limitations of photocatalytic materials,improving the light utilization and enhancing the photocatalytic performance of new hybrid materials.Based on the above discussions,in order to solve the aggregation and recovery of photocatalyst（g-C₃N₄）,synthesis of photoinitiated polymerization to prepare hybrid IPN hydrogels was optimised by utilizing light-responsive characteristics of g-C₃N₄ and mechanism of photo-initiated polymerization.By characterization of swelling behaviors,pore structure and thermo-responsive property,the effect of porous structure on photocatalytic perfomance of thermo-responsive hydrogels is investigated.To further enlarge the specific surface area and photocatalytic performance,g-C₃N₄nanosheets are loaded on thermo-responsive microgels with sub-micron scale to obtain hybrid microgels.Due to the fact that the chance of suffering skin cancer is significantly increases during the outdoor activities,a skin health monitor is designed by preparation of hybrid gels with micro-nano structure.In favor of the absorption and degradation of dyes by the g-C₃N₄ nanosheets in the hyrbids gels,the skin health monitoring can be successfully installed.The specific research contents and results are as follows:（1）Based on photocatalystic property of g-C₃N₄,the amine（triethylamine）with multiple electronic structure was introduced to the reaction to obtain stable and effective photoinitiation system.The g-C₃N₄ nanosheets were applied to photo-initiate the polymerization of monomer poly（ethylene glycol）methyl ether methacrylate(OEGMA₃₀₀)and N-isopropylacrymide（NIPAM）under UV light radiation.In order to enhance mechanical strengths of thermo-responsive hydrogels,alginate-Ca²⁺was introduced to reaction system to prepare hybrid alginate-Ca²⁺/P(NIPAM-co-OEGMA₃₀₀)/g-C₃N₄ hydrogels with interpenetrating polymeric network（IPN）structure.The morphology characterization of surfaces and cross-sections from hybrid IPN hydrogels photo-initiated by g-C₃N₄ and triethylamine demonstrates that no aggregation of g-C₃N₄ existed in hydrogels.A large number of regular honeycomb pore structures with a diameter of about 10μm can be observed in the SEM images of cross sections.The g-C₃N₄ nanosheets show uniform distribution in the hybrid IPN hydrogels from the TEM images.The photocatalytic degradation measurement（200 m L of MB solution with a concentration of 10 mg/L）at 50°C showed that the photodegradation of 4 h under visible light can realize the full degradation of the dyes.Its photodegradation efficiency is twice than that of the hybrid IPN hydrogels initiated by ammonium persulfate（APS）and N,N,N’,N’-tetramethylethylenediamine（TEMED）.The reason can be attributed to the less aggregation of g-C₃N₄ in the hydrogels initiated by g-C₃N₄.（2）Due to the existence of the thermo-responsive polymer with lower critical solution temperature（LCST）in the as-prepared hybrid IPN hydrogels,it maintains the thermo-responsive properity.The switching from the hydrophility to the hydrophobicity of the IPN hydrogels further enhances the porosity in the hydrogels.By adjusting the molar ratio of NIPAM and OEGMA₃₀₀,a series of hybrid IPN hydrogels with different LCST can be abtained.For instance,the trasition temperature（TT）of as-prepared hybrid IPN hydrogels is 50°C when NIPAM∶OEGMA300=1∶1.When the ambient temperature is above TT,the thermo-responsive NIPAM-co-OEGMA₃₀₀network collapses,whereas the alginate-Ca²⁺network remains unchanged.Thus a more porous structure is realized in hydrogels.It can directly enhance the adsorption and diffusion of MB.Moreover,photodegradation efficiency of hybrid IPN hydrogels for dye can be also significantly improved.The photocatalytic degradation measurements under different temperatures illustrate that the hybrid IPN hydrogels can achieve complete degradation in 4 h when the temperature is above TT.However,the complete degradation requires 8 h when the temperature is below TT.（3）For IPN hydrogels,its mechanical strength can be significantly improved because of the introduction of alginate-Ca²⁺and better dispersion of g-C₃N₄ in hydrogels.Compressive strength measurements demonstrate that mechanical strength of hybrid IPN hydrogels initiated by g-C₃N₄ and triethylamine increases 10%.The hybrid IPN hydrogels initiated by g-C₃N₄ and triethylamine present stable mechanical strength by 10 cycles of compression measurement.Thus,the as-prepared IPN hydrogels possess good recycling performance in practical application.（4）Thermo-responsive microgels with sub-micron scale possess the advantages of large specific surface area and rapid response,and can be used as an excellent carrier of photocatalysts.As-prepared thermo-responsive microgels cantaining g-C₃N₄ present more efficient photodegradation efficiency above TT.The photocatalytic degradation measurement under visible light radiation showed that its photodegradation efficiency is twice than that of the hybrid IPN hydrogels photo-initiated by g-C₃N₄ and triethylamine under the identical experimental conditions.（5）Based on the efficient photodegradation efficiency of hybrid IPN hydrogels photo-initiated by g-C₃N₄ and triethylamine to MB,the bracelet monitoring skin health is prepared by simply immersing the hybrid IPN hydrogels into the MB solution（15min,30 min and 45 min,respectively）and then wrapping with PET foil.The g-C₃N₄nanosheets in hybrid IPN hydrogels degrade MB and realize visualized discoloration of the bracele under solar ultraviolet radiation.Comparing the time required for the full photodegradation under xenon lamp radiation and solar radiation,the results confirm that photodegradation of wearable bracelets for skin health management is stable.Thus,sensitive indication of solar ultraviolet intensity can be realized by visualized discoloration of the bracelet,which can be applied to prevent skin diseases such as erythema,sunburn and even skin cancer caused by excessive solar radiation.