Environmental Materials Of Nanofibrillar Polysaccharides And Their Biochars

Chitin,chitosan and cellulose are polysaccharides in nature with several advantages of extensive sources,green-nature,non-toxic,naturally renewable as well as biodegradability.These materials have many active groups making them useful as effective adsorbents.Besides,these polysaccharide nanofibrils have the advantages of high elastic modulus and rigidity thus they been predominantly seen as favorable reinforcing materials.Biochar,a solid material with more hydrogen and oxygen components than activated carbon obtained from the thermochemical conversion of biomass in an oxygen-limited environment,is a stable and high aromatized porous carbon material.Biochar have shown good prospects in dealing with water pollution due to its rich oxygenic groups and flourishing hollow structure.Similarly,starch foams have often displayed good mechanical properties,however,its low and bad expansion rate prevents it from broad utilization.Therefore,the main objective of this work was to study the application of polysaccharides and microfibrillar polysaccharidic biochars in solving water pollution problems.Meanwhile,greater emphasis was placed on how positively the properties of these materials could be enhanced for the most efficient application.In this thesis,chitin,chitosan and cellulose nanofibrils were defibrillated through wet-grinding and homogenizing processes.The starch(STA)/chitin nonofibril(CTF)and starch(STA)/chitosan nanofibril(CSF)composite foams were fabricated by freeze-drying method.The morphology,structure and mechanical property of composite foams were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),Fourier transform infrared spectrogram(FTIR)and compression testing.The results revealed that the porosity of the composite foams increased with an increasing nanofibril content.However,the ultimate moisture contents decreased compared with STA foam.The SCT40 and SCS30 had the highest compressive stress of 64 kPa and 72 kPa,respectively.Secondly,the as-prepared nanofibril suspension was freeze-dried into fibrillar foams and the cellulose nanofibril was labeled as CLF.Meanwhile,the as-fabricated microfibrillar polysaccharide foams were packaged in foil and subsequently subjected to pyrolysis under nitrogen atmosphere.Using FE-SEM,XPS,elemental analysis and BET analysis the as-prepared biochars were characterized.Furthermore,the batch of adsorption experiments were investigated to study the removal efficiency of sodium benzoate(SB).Particularly,the effect parameters such as pH,temperature,contact time and initial concentration of SB were duly studied.FE-SEM shows that all the biochars exhibited micro-scaled fibril morphs and microstructure network.XPS and elemental analysis revealed the presence of much amorphous surface carbon in microfibrillar biochars with amino and cyanide in FCTB and FCSB.During the batch of adsorption experiments,the spontaneous and endothermic nature of SB sorption by the three microfibrillar biochars was achieved.The results showed that the adsorption process was highly pH-dependent with the optimal adsorption obtained at pH 7.0.Adsorption kinetic studies carried out onto SB indicated that the pseudo-second order model could best fit the data.Also,the adsorption equilibrium studies revealed that FCTB and FCLB best fitted the Langmuir isotherm while the adsorption behavior onto FCSB fitted Freundlich isotherm better.Tailoring the chemical composition,sorption behavior and sorption mechanism constituted a possible strat to achieve adequate structure-effects of this novel biochar for potential application in environmental treatment.Chitosan is known to effectively gather heavy metals in water due to the presence of amino and hydroxyl.Nonetheless,this often times is suppressed since chitosan easily dissolves in acidic solutions.Hydrolyzing chitosan with trivalent chromium ion leaves the suspension acidic and this can greatly affect the adsorption capacity of chitosan.In this final part of the work,the solution after adsorption was freeze-dried and later placed in ethyl alcohol to dissolve the non-adsorbed Cr(?)ions.The concentration of Cr(?)in ethyl alcohol was tested via atomic absorption spectrophotometer(AAS).The results indicated that the adsorption capacity of Cr(?)onto chitosan was found to be 69.51mg/g.Also,the adsorption capacities of Cr(?)onto chitosan and CSF were found to be 16.19 and 24.26mg/g,respectively.Furthermore,the adsorption kinetic studies carried out on Cr(?)revealed that the pseudo-second order model could best fit the adsorption process of chitosan and CSF.Moreover,the adsorption equilibrium studies showed Freundlich isotherm was best fit for both chitosan and CNSF.