Fabrication Of Biochar And Graphene Oxide Based Composites And Their Removal Properties For Water Pollutants

Biochar and graphene oxide are enormously significant among carbon based materials and are continuously performing a leading role in practical applications to improve quality of life and environment.Both biochar and graphene possess exceptional properties in terms of mechanical,chemical,physical,and thermal properties,surface area(SA),and high aspect ratio owing to nanoscale geometry.Both the biochar(porous carbon rich)and graphene(sp2 bonded aromatic carbon structure)has been applied extensively as adsorbents and in membranes for water treatment and purification,and continue to attract further research interest due to their fascinating properties.A large number of research results have been reported based on biochar and graphene due to their novel properties,feasibility and felicity among others.Given that,the majority of research progress demonstrates considerable efforts in synthesis,modification,fabrication,and integration with each other or functional polymers for practical applications.However,despite continuous research efforts and progress,safe and efficient applications of biochar and graphene remain challenging keeping in view structural properties of adsorbents and membranes,modification methods,and practical applications to improve efficacy in environmental remediation.Research progress regarding biochar modification in adsorption affinity and selectivity towards organic pollutants remains unclear.The ordered graphene sheets in biochar were only found at above 600 ? temperature,thus the structural change and properties of biochar and graphene composites remains unclear.In addition,the practical applications of biochar are still in the form of solid particle,which results easy loss or release in natural environments,and may put possible difficulties during recycling or recovery process.Considering graphene oxide(GO)research progress,the negatively charged functional groups on GO causes repulsion in aqueous solution,which results disintegration,destabilization,and decrease the selectivity of GO membranes.However,the functional moieties of GO could be used for membrane surface modification,while ensuring simultaneous removal and recycling.Therefore,the processing and scale-up of stable GO membranes remains limited in practice and somewhat counterintuitive.In this thesis,the key challenges of biochar and graphene oxide were solved for experimental realization as adsorbents and membranes.The structural properties of biochar and graphene(and composites)as adsorbents and membranes,and their performance in water treatment were investigated.The work detailed in this thesis contains four different parts.First,biochar and graphene composites were synthesized and adsorption capability and performance of biochar-graphene(BG)composites for phthalic acid esters(PAEs)were studied experimentally with structural properties and relationship.Second,biochar was fabricated in membrane matrix to assure organic pollutant removal via membrane adsorption and sieving simultaneously,by structural characteristics and synergistic mechanisms,while assuring antibiofouling,recovery and reuse.Third,porous polyvinylidene fluoride and GO(PVdF/GO)nanofibrous membranes(NFMs)were prepared for selective separation and recycling of charged organic dyes.Finally,GO membranes were prepared with controlled interlayer spacing and thickness for practical stability and ions rejections.The structural modification of biochar and graphene introduce new properties,which not only enhance physical,chemical and structural properties,but are also promising for use in practical water purification and treatment.The summarized results and conclusions are as following.(1)BG composites were prepared by one step facile dip coating method following thermal route at three different temperatures(300,500,700 ?),in addition to biochars.It was found that graphene nanosheets(GNS?1?m,0.1%mass)could ensure relatively higher SA(N2 and CO2),porous structure and thermal stability within BG composites.BG composites portrayed the existence of graphene bearing cavities.The adsorption capacity of biochars and BG composites towards dimethyl phthalate(DMP),diethyl phthalate(DEP),and dibutyl phthalate(DBP)as model PAEs were examined.The aromatic sheets of biochars and GNS on biochars dominated the ?-? EDA(electron donor-acceptor)interaction for ring structure of DMP molecule,whereas adsorption of DBP was attributed to hydrophobicity.The BG composites exhibited the increased adsorption capacity comparatively to biochars,thus could be considered as promising adsorbents.(2)Biochar composite membranes were fabricated for the first time with wood biochars(at 300 and 700 ?)blending with polyvinylidene fluoride(PVdF)through thermal phase inversion process.The biochar composite membranes possess high mechanical strength,water flux,and porous structure with uniform distribution of biochar particles throughout the membrane surface and cross-section.The biochar composite membranes indicate promising adsorption capacity(47 to 187 mg g-1)for RB dye and high retention(74 to 93%)for E.coli bacterial suspensions through filtration.After simple physical washing,both the adsorption and sieving capability of biochar composite membranes could be recovered effectively.The multifunctional biochar composite membranes not only prevent the problems caused by direct application of biochar particle as adsorbent,but also assure effective recovery and recycling for practical applications.(3)A versatile porous structured PVdF-GO NFMs were prepared by using simple and straightforward electrospinning approach for selective separation,filtration,and recycling of industrial organic dyes.The PVdF-GO NFMs possesses high mechanical strength and SFE,consequently resulting high permeation and filtration efficiency as compared to PVdF NFM.The selectivity towards positively charged dyes(99%)based on electrostatic attraction,while maintaining rejection(100%)for negatively charged dye from mixed solutions highlight the role of GO in PVdF-GO NFM,owing to uniform pores and negatively charged surface.The actual efficiency of NFMs could be recovered easily up to three consecutive filtration cycles by regeneration,thereby assuring high stability.The filtration efficiency is promising for use in practical water purification,particularly for selective filtration and recycling of dyes.(4)Despite considerable research efforts,however,GO laminates are known to be unstable in water.Nonetheless,GO dispersions can be processed easily to form a continuous and uniform GO film with scalability while being highly ordered.The interlayer spacing and thickness of GO membranes was controlled with cations intercalation.The interlayer spacing and thickness was correlated with hydrated radius of cations and GOM with Li+ and Na+ were not stable enough after immersion in water,whereas K+,Mg2+,Ca2+ and Ba2+ stabilize GO membranes effectively.Moreover,GOM with Ca2+ and after reduction was further investigated in water,acidic and alkaline solutions to assure stability and practical application.The high permeation,filtration efficiency,and good stability of GO membranes are promising for use in practical water purification and applications,particularly for environmental and industrial filtration.