Biomass TiO₂/alginate Composite Aerogels:Fabrication And Their Applications In Water Treatment

With the discharge of oil-bearing sewage and the frequent occurrence of oil leakage,oily wastewater has become one of the most urgent problems to be solved.Oil/water separation is an issue involving interface science of filter material.Inspired by nature,the super-wettability?e.g.,superhydrophobicity,superhydrophilicity-underwater superoleophobicity?materials are attracting extensive attention.Among these super-wettability materials,the superhydrophilic-underwater superhydrophobic aerogels with three-dimensional porous network have become the focus of research.However,some shortcomings such as complex preparation process,short service life and poor service performance still impede the widely applications of superhydrophilic-underwater superhydrophobic aerogels.In this work,using low-cost and environmentally friendly polysaccharides as raw materials,inorganic nanoparticles and carbon materials as heterogeneous reinforcements,a series of polysaccharide-based aerogels have been successfully fabricated and their performances in oil/water separation are also studied.1.Using sodium alginate as matrix material and TiO₂nanoparticles as functional additives,TiO₂/alginate composite aerogels are successfully prepared by a facile combined freeze-drying and ionic cross-linking method.The as-prepared aerogels have well developed three-dimensional porous network and interconnected pore structure.The introduction of TiO₂ nanoparticles can build nanoscale microstructure on aerogel surface,leading to a much rougher surface.Under the synergistic effect of surface nanostructure and the abundant hydrophilic functional groups of alginate,the TiO₂/alginate composite aerogels show an excellent underwater oleophobicity for various oils,and the underwater contact angle with kerosene can reach 147o.2.The TiO₂/alginate composite aerogel is further applied in the separation of oil/water mixture.The results show that the separation efficiencies of TiO₂/alginate composite aerogel for various oil/water mixture are all over 98.7%.For the soybean oil/water mixture,the separation efficiency of TiO₂/alginate composite aerogel can reach99.7%,and this value can remains>99.2%even after 60 times reuses.More importantly,the firmly attached TiO₂ photocatalyst can also endow the aerogel with better UV-aging resistance,photoinduced self-cleaning and environmental remediation performance.When the addition amount of TiO₂ is 0.1g,the TiO₂/alginate composite aerogel shows a excellent photocatalytic performance for methyl orange?MO?degradation?⁹7.6%under 150 min irradiation?,and the degradation efficiency could still be maintained at>87%after 6times repeated use.3.Graphene oxide?GO?nanosheets,which act as heterogeneous reinforcements,are further introduced into the aerogels to enhance the underwater oleophobic,mechanical and photocatalytic performances.By photoreduction with TiO₂,GO nanosheets is reduced and the RGO/TiO₂composites can be obtained.Then,the RGO/TiO₂/alginate composite aerogels are prepared by incorporating RGO/TiO₂ composites with alginate matrix through a facile freeze-drying and ionic cross-linking method.It is found that RGO can enhance the mechanical properties of composite aerogels and play a role as reaming agent to enlarge the pore sizes.Additionally,the RGO/TiO₂ composites can also improve the surface roughness of aerogel,which is an important factor for underwater oleophobicity of the aerogels.The as-prepared TRGA-1 composite aerogel exhibits underwater superoleophobicity for various oil,and the underwater contact angle of kerosene is as high as 165°.The results of oil/water separation experiments indicate that TRGA-1 composite aerogel possessesanexcellentseparationperformance(separation efficiency>98.9%,and water flux⁹.76 L·m^-2·s^-1)for various oil/water mixtures.4.Furthermore,RGO/TiO₂ composites can also endow TRGA aerogels with excellent light-driven self-cleaning ability.the deteriorate oil/water separation performance?caused by the accumulation of oil pollution?of the composite aerogels can be effectively renewed by short-time light irradiation.The results of oil/water separation circulation experiments prove that combined with twice light treatments during the120 cycles,the oil/water separation performance of TRGA-1 composite aerogels can be maintained very well,the final separation efficiency is>99.3%and the water flux is about 10.96 L·m^-2·s^-1.In addition,the as-prepared TRGA-1 aerogel also exhibits underwater superoleophobicity in harsh environment?acid,alkali and salt solutions?,indicating that the composite aerogel has good mechanical stability and chemical corrosion resistance.In summary,the“green”facile fabrication process,excellent oil/water separation,photoinduced self-cleaning and reusable performances,make the as-prepared composite aerogels promising for practical sewage treatments.