Sodium Alginate-based Adsorption And Filtration Materials For Water Contaminants Removal

Nowadays,common water pollutants(e.g.,organic molecules,oil contamination,or heavy metal ions)discharged from industry to the ecosystem has become a top environmental issue.When contaminated water enters into soil or groundwater,it has jeopardized animals,plants and human health owing to its highly toxic or non-biodegradable ingredients.Therefore,it is urgent to develop advanced materials or versatile technologies for environmental remediation.Recently,due to high specific surface area or controllable surface chemical properties,nanomaterials have become a rising star in environmental pollution remediation.Notably,powdery materials may be inconvenient to be utilized in water purification when they are directly applied as water remediation materials.After removing water contaminants,filtration or centrifugation technologies are usually used to separate powdery nanocomposites for next use from water medium,so it actually becomes extremely difficult and time-consuming to recover and separate nanocomposites in real applications.Additionally,traditional powder-form materials may also block filters due to fine size,and cause secondary harmful pollutants associated with its leakage,especially in flowing liquids.These aforementioned drawbacks have severely hindered their applications in large scale.In order to solve above problems,a series of adsorption and filtration materials were designed,and their separation performance was carefully investigated.First,a millimeter-sized porous sodium alginate/attapulgite adsorbent material was prepared by a freeze-drying method.This kind of synthetic method has some significant advantages,and the resulting cubic sponges would exert the capacity of both components,and reduce the cost of adsorbents when attapulgite was introduced into sodium alginate polymer matrix.This porous adsorbent material is floatable,easy to collect and recycle many times.Next,hydrophobic modification of sodium alginate sponges via a simple freeze-drying and post cross-linking method induced by zirconium(Zr)ions was developed.It is worth noting that Zr ions mainly caused the hydrophobic sodium alginate composite sponges while Ca ions assisted sodium alginate composite sponges with more porous structure.Finally,superhydrophilic and underwater superhydrophobic calcium alginate hydrogel-coated meshes were prepared via a green dip-coating and a layer-by-layer self-assembly method.This separation process was spontaneous and only driven by gravity.Allowing for recyclable and safe applications,those materials exhibited more predominant performance than traditional nanosized materials.The main studies of this thesis are as follows:(1)Floatable and porous adsorbents constructed by encapsulating attapulgite in sodium alginate were fabricated via a freeze-drying and post cross-linking method,and both attapulgite and sodium alginate possessed adsorptive sites.These adsorbents were characterized by X-ray diffraction(XRD),Fourier transform infrared spectra(FTIR),and Scanning electron microscopy(SEM)to investigate their crystal structures,surface properties,size and morphology.In the adsorption tests,the adsorption capacity was derived from the Langmuir isotherm model,and the maximal adsorption capacity of as-prepared adsorbents was 119.0mg/g for Cu(II)and 160.0 mg/g for Cd(II),respectively.In addition,these adsorbents presented strong chemical stability and were readily recyclable because of their floatability in water solution.These aforementioned advantages highlight that the alginate-encapsulated attapulgite sponges are potential scalable adsorbents for heavy metal ions removal from polluted water,and such a structure design could intrigue the development of novel adsorptive materials.(2)Hydrophobic modification of sodium alginate sponges via a simple freeze-drying and post cross-linking method induced by Zr ions was developed.SEM,FTIR and X-ray photoelectron spectroscopy(XPS)results demonstrated that Zr ions not only constructed surface microstructure but also lowered surface energy of sponges,leading to the hydrophobic character.Hydrophobic and oleophilic sponges showed excellent adsorption capacities for different oils and organic solvents(11.2-25.9 g/g).Furthermore,sodium alginate solution can be also coated on porous substrates,such as melamine sponges and nylon strainers,to give hydrophobic modification by Zr ion crosslinking.These excellent performances made them a promise for oil adsorption and cleanup.(3)Superhydrophilic and underwater superhydrophobic calcium alginate hydrogel-coated meshes were prepared via a green dip-coating and a layer-by-layer self-assembly method.All results proved that calcium alginate was introduced to generate both hydrophilic chemical compositions and rough structures onto resultant mesh surfaces.The obtained meshes,which possessed a underwater oil contact angle of~154.3~o and low oil sliding angle of~7~o,could separate various oil/water mixtures with efficiency above 99%and maximum water flux up to28108.9 L/m~2/h.This separation process was spontaneous and only driven by gravity.Furthermore,as-prepared meshes still maintained high stability under corrosive organic solvents.These outstanding performances made it a promise for oil/water separation in the future.In short,this thesis aims to design and prepare some separation materials which are easy to separate and recycle.These materials possess their own attractive characters,(i)floatable and millimeter-sized characteristics make it easy to separate and recycle in practical applications,(ii)the durability and stability of materials under harsh environments make it reused many times,(iii)simple,green and low-cost preparation methods are practically suitable for large-scale productions.