Removal Of Ciprofloxacin From Aqueous Solution By Biochar-based Materiais Efficiency And Its Mechanism Analysis

Extensive production and use of different pharmaceuticals especially ciprofloxacin,because of their fatality,has pose serious threats to the environment.It is because of their incomplete metabolization,which results in addition of large amount of pharmaceuticals to the aquatic environment.Therefore,it has gained the attention of scientific community.There are different materials being used to treat water e.g.graphene,biochar,carbon nanotubes,clay minerals and montmorillonite etc.Biochar,obtained from waste biomass,plays an essential role in altered environmental remediations such as enhancing soil fertility,mitigating climate change and water treatment,etc.To access the versatility of biochar,this Ph.D.dissertation investigated the applications of different biochar-based materials,produced by pyrolysis at a temperature of 450℃,to remove ciprofloxacin from water by applying different techniques such as adsorption,sonocatalytic degradation and membrane filtration.For adsorption,two biochar-based adsorbents were used to remove ciprofloxacin and their sorption capacities were measured by performing different adsorption experiments at different conditions such as at different pH levels,with different initial concentrations of ciprofloxacin,at different temperatures,at different intervals of time and in the presence of different electrolytes.Hence,different kinetic and adsorption isotherm models and adsorption mechanism were assessed.For sonocatalytic degradation of ciprofloxacin,ultrasonic irradiations were applied to a novel biochar based sonocatalyst,which was also applied for adsorption purpose.To confirm the successful degradation,reactive oxygen species(ROS),responsible for degrading the organics,were detected along with intermediate products.As membrane filtration has several advantages over other techniques of water purification.That’s why,versatile biochar was also constructed in membrane of polymeric network.Prepared membranes,after different characterization analyses,were proved to be of good quality and showed good results of ciprofloxacin removal with least fouling.Finally,all the biochar-based materials were successfully regenerated and showed good results for repeated removal of ciprofloxacin.Main conclusions of the study are listed below.Biochar,being in powder form,is very hard to retrieve from aqueous solutions after adsorption.To overcome this problem,it was encapsulated in chitosan,a polymeric network,to mold it in the form of beads,which were easy to separate and reuse after regeneration.Moreover,biochar was also incorporated with humic acid to enhance its adsorptive capacity by adding functional groups of humic acid before being encapsulated in chitosan.Characterization of both adsorbents,before and after adsorption,was performed by different instrumentation techniques such as Scanning electronic microscopy(SEM),X-ray photoelectronic spectroscopy(XPS),Fourier transform infrared(FTIR)etc.In both cases,adsorption pursued pseudo secondary order kinetic model and Langmuir adsorption isothermal model.Moreover,different electrolytes,such as NaCl,Na2SO4,NaNO3 and Na3PO4,were added to the adsorption system and they showed similar effect on adsorption in both cases.Adsorption mechanism was also similar in both cases including bonding of hydrogen,hydrophobic interfaces,and π-π electrons acceptor donor(EAD)interactions.Whereas,adsorption was more prominent and faster with the beads made from humic acid incorporated biochar(155.26 mg/g)as compared to that of beads made from only biochar(36.72 mg/g),encapsulated separately in chitosan.Both adsorbents were easy to regenerate and showed good adsorption behavior for ciprofloxacin in repeated cycles,hence showing the potential for long term efficient application.For sonocatalytic degradation,titanium dioxide(TiO2)was incorporated on surface of biochar using a well-known sol-gel method before being encapsulated in chitosan to prepare a catalyst,titanium-biochar/chitosan hydrogel beads(TBCB),for the degradation of ciprofloxacin using ultrasonic waves.Different characterization analyses for instance SEM,Energy Dispersive X-ray spectroscopy(EDX)and FTIR verified efficacious production of sonocatalyst.Generation of different intermediate products during degradation were monitored by LC-MS.XPS analysis also confirmed the successful degradation of ciprofloxacin by showing a new peak,which indicated the reduction of Ti+3 to Ti+2.Reactive oxygen species(ROS)generation like Superoxide Radicals(·O2-),holes(h+)and hydroxyl radical(·OH),responsible for degradation of ciprofloxacin,was monitored by adding quenchers such as benzoquinone(BQ),triethanolamine(TEA)and isopropyl alcohol(IPA).These quenchers captured above ROS,hence resulted in a decrease of degradation efficiency(DE)from 85.23%to 81.50%(BQ),74.27%(TEA),and 61.77%(IPA)within 25 minutes,respectively.Hence,above discussion proved the successful generation of sonocatalyst and its capability to degrade ciprofloxacin.Efficiency of degradation was also measured at different ultrasonic power and in presence of different electrolytes and at varied intervals of time.Degradation efficiency was found to be maximum at 150 W with initial concentration of 10 ppm(85.23%).Moreover,this catalyst proved itself to be a good adsorbent for ciprofloxacin too,and adsorption abide by pseudo first order kinetic model and Langmuir adsorption isothermal model.To further explore the versatility of biochar,it was also used in manufacturing the membranes by constructing it in polyether sulfone(PES)and Polyvinylpyrrolidone(PVP)at different ratio,for separation of ciprofloxacin from water.When biochar ratio was increased,the separation efficiency for ciprofloxacin was increased.Different characterization tests such as SEM,FTIR,Atomic Force Microscopy(AFM),XPS and contact angle measurement supported the fact that quality of membrane was enhanced by increasing ratio of biochar,hence increased separation efficiency.M11,the membrane with equal ratio of biochar and PES,showed maximum results of different parameters such as water flux(790.37 L/m’h),ciprofloxacin flux(595.54 L/m2h),porosity(68.9%),pore radius(266.96 nm)and removal efficiency for ciprofloxacin(95.19%),than three other prepared membranes of different biochar to PES ratio.M11 also showed good results for three other antibiotics too and it was also easily regenerable for sustainable use.