Preparation Of Super-wetting Cotton-based Composites By SI-ATRP And Its Application In Water Treatment

Due to the increase of human activities and the limited sustainable cleaning strategy,water pollution has become one of the main environmental problems in today's society.Special wettable surface materials are used to remove pollutants in water due to their multifunctional properties.Low cost and biodegradable cotton fiber has a large number of hydroxyl groups on the surface,which is easy to modify and adjust the surface wettability of cotton based composites.Through the design of multifunctional cotton based surface materials,the problem of water pollution faced by modern society can be solved.Researchers have tried various modification methods to improve the adsorption performance of cotton based surface materials,but there are still some defects such as low adsorption capacity,poor durability and low reuse rate.In this paper,cotton-based composites with special wettability were prepared by surface polymer grafting process,and their oil-water separation and heavy metal adsorption properties were improved by using functional polymer brushes.The main research contents are as follows:(1)The second chapter of the paper reports the facile fabrication of robust and durable superhydrophobic and superoleophilic cotton for highly efficient oil/water separation based on the combination of hydrophobic octadecanoyl chain bonding and polymer grafting via surface-initiated atom transfer radical polymerization(SI-ATRP).Octadecanoyl chain tethered and polymer grafted superhydrophobic cotton was obtained by simultaneous treatment with stearoyl chloride and?-bromoisobutyryl bromide to generate hydrophobic cotton bearing initiating sites for ATRP(C18-Cotton-Br),followed by SI-ATRP of acrylonitrile and styrene to obtain polymer grafted cotton(C18-Cotton-g-PSAN).The surface morphology,chemical composition and structure of modified cotton were studied by scanning electron microscopy(SEM),FT-IR,X-ray photoelectron spectroscopy(XPS),and nitrogen physical adsorption experiments.The water contact angle(WCA),oil-water separation,oil absorption and mechanical properties of cotton were systematically evaluated.The results showed that octadecanoyl and?-bromoisobutyryl groups were successfully bonded on pristine cotton to exhibit hydrophobicity and further polymer grafting of PSAN was realized with high grafting density of about 0.47 nm^-2.Compared with C18-Cotton-Br,after polymer grafting C18-Cotton-g-PSAN displayed enhanced superhydrophobicity with the WCA increasing from 154°to 159°due to the increased surface roughness.C18-Cotton-g-PSAN exhibited a highly efficient oil/water separation achieving 99.2%,excellent absorption capacity of 26 g/g for toluene with easily recovering performance,and the adsorbed toluene can be easily removed from the superhydrophobic C18-Cotton-g-PSAN by simple squeezing process.The octadecanoyl groups bonded and PSAN grafted cotton microfibers including those deeply imbedded inside endowed C18-Cotton-g-PSAN with high abrasion resistance.The biodegradable and recyclable C18-Cotton-g-PSAN demonstrated high selectivity for absorbing of oil and is expected to become sustainable and highly effective materials for oil-spill cleanup and the oily wastewater treatment from households and industries.Endowed with the robust superhydrophobic durability,the superhydrophobic and superoleophilic cotton can be further weaved into cotton fabric to demonstrate their versatilities.(2)The third chapter of this paper,a preparation method of solid particle-free polymer grafted biodegradable cotton fabrics without auxiliary of fluorine and silicon was proposed for sequential separation of oil/water mixture and removal of heavy metal ions.Superhydrophobic poly(acrylonitrile-co-styrene)grafted cotton fabrics(CF-g-PSAN)designed for oil/water separation were fabricated by successive initiator tethering and polymer grafting via SI-ATRP.Further amination of CF-g-PSAN with tetraethylenepentamine(TEPA)led to the formation of CF-g-APSAN,which converted C?N groups of tethered PSAN into amino group(N-C=N).The hydrophilic cotton fabric(CF-g-APSAN)can be used to adsorb heavy metal ions.The obtained CF-g-PSAN exhibited superhydrophobicity with WCA achieving 150odue to the combination of surface tethered hydrophobic PSAN and increased surface roughness.In the sequential treatments of oil/water separation and heavy metal ion removal,the polymer grafted cotton fabrics achieved a high oil/water separation efficiency exceeding 97.8%and demonstrated as excellent adsorbent towards heavy metal ions with record-high uptake capacity of about 682.5,375.8,438.3,535.7 mg/g for Pb²⁺?Cu²⁺?Zn²⁺and Ni²⁺,respectively.The adsorption capacity was significantly higher than that previously reported.Since high grafting density of hydrophilic CF-g-APSAN enabled heavy metal ions free access towards APSAN brushes in aqueous medium and maximized the number of accessible chelating sites towards heavy metal ions originating from the high affinity of pendent amino diethylenepentamine groups.Furthermore,CF-g-APSAN showed rapid and efficient capture ability for trace heavy metal ions(5 ppm)under dynamic flow conditions with high removal rates of 91,89,89,and 87%for Pb(II),Cu(II),Zn(II),and Ni(II),respectively.After five cycles,the removal rate remained above 86%,showing significant cycle stability.The above shows that the recyclable CF-g-PSAN and CF-g-APSAN demonstrated combined high separation efficiency and record-high adsorption capacity,which are expected to find industrial applications in oily wastewater treatment as sustainable and highly effective materials.