Adsorption Behavior And Mechanism For Static And Dynamic Adsorption Of Dye Solution Onto Modified Plant Fiber

Discharging untreated or partially organic wastewater,especially organic dye wastewater,to bodies of water can pose a great threat to aquatic plants,animals,and the eventually humansat the top of the food chain in the environment.Dye wastewater treatment is an urgent imperative.The biosorption which is characterized as abundant resource,non-toxic,and biodegradabilityhas drawn much academic attraction these years.However,natural plant fiber,namely,fallen tree leaves has low adsorption capacity of dye solution and bad adsorption performance.Herein,the efficient and effective modified biosorbents for cationic and anionic dye are prepared by fallen phoenix tree leaves.This thesis focuses on the static and dynamic adsorption of basic magenta,methylene blue,and Congo red in single and binary systems by these biosorbents.The main works are summarized as follows:Pyromellitic dianhydride(PMDA)modified plant fiberwas prepared by a simple method.The effect of initial concentration,contact time,pH and ion concentration on the adsorption of basic magenta was evaluated from batch experiments.The breakthrough curves were obtained from dynamic experiments.Results showed thatthe adsorption capacity ofplant fiberincreased from190.92 mg/g to 362.24 mg/g after the modification.The Langmuir model fitted the equilibrium data well and the adsorption process was observed to be monolayer adsorption.Good correlations by pseudo-second-order and intra-particle diffusion models indicated that the adsorption kinetics was not only controlled by the intra-particle diffusion mechanism,but also by the film diffusion mechanism.The removal efficiency of basic magenta was positively dependent on pH,maximum adsorption occurred at a pH of 8.Ion concentration showed slight effect in adsorption.The presence of divalent ions had more obvious effects than monovalent ions.The inlet concentrations had an influence on the dynamic adsorption uptake,which were 187.7,213.2 mg/g,at inlet concentrations of 0.3 and 0.5 mmol/L,respectively,calculated by S shaped breakthrough curves.The Yoon-Nelson model showed a better fit to the dynamic adsorption data and can be employed to evaluate the breakthrough time.Adsorption isotherms and kinetics of methylene blue by PMDA modified plant fiberwere analysed in batch experiments.Results showed thatthe adsorption capacity of methylene blueincreased dramatically from 88.6 mg/g to443.5 mg/g after modification.The adsorption rate was controlled by the amount of active sites and the initial concentration of methylene blue.Dynamic results indicated that the adsorption uptakes by fixed-bed were 447.50,444.62,414.69 mg/g at inlet concentration of 0.3,0.5,0.8 mmol/L,respectively.The adsorption uptakes by fixed-bed were 450.54,437.01 mg/g at particle size 0.075~0.150 mm and 0.150~0.250 mm,respectively.The adsorption uptakes by fixed-bed were 414.14,446.07,427.26mg/g with adsorbent dosage 1g,2g,3g,respectively.It can be concluded that the inlet concentration,particle size and adsorbent dosage has little effect on the dynamic adsorption performance.Furthermore,PMDA modified plant fiber fixed-bed holds good regeneration ability and ease for practical application when desorbed by 0.1 mol/L HCl.TEPA modified plant fiber were prepared by the crosslinked method.The effect of initial dye concentration,contact time,and ion concentration of the solution on the removal of Congo redwere investigated from batch experiments,the breakthrough curves was obtained by the dynamicexperiments.Results showed the adsorption capacity of Congo red increased remarkably from 17.74 mg/g to 259.82 mg/g after modification.The Langmuir isotherm model yielded the best fit to the equilibrium data.High value of correlation coefficient obtained by pseudo-first-order and intra-particle diffusion models suggested that intra-particle diffusion along with external transport were part of the adsorption mechanism.Moreover,the addition of salt contributed to the adsorption of anionic dye on positive charged TEPA modified plant fiber.Dynamic experimental results showed that the plant fiber adsorption capacity increased with the increase of inlet dye concentration,achieving up to 240.52 mg/g,and the Adams-Bohart and Yoon-Nelsonmodels gave the best fit to the experimental data.The adsorption potential of modified plant fiber based phoenix tree leaves to remove basic magenta and Congo red simultaneously from aqueous solution was explored by using fixed-beds in series.It was found that a single PMDA modified plant fiber fixed-bed,which is negatively charged,showed high affinity towards cationic dye molecules,basic magenta.A single TEPA modified plant fiber fixed-bed exhibited good Congo red adsorption performance.Furthermore,fixed-beds in series combined the advantage of each fixed-bed,showed synergisticbehavior by the mixture solution,and achieved the simultaneous removal of cationic dye and anionic dye in aqueous solution.Series fixed-beds performed a good adsorption uptake for Congo red and basic magenta,attaining 205.87 and 60.64 mg/g adsorption capacity respectively.The research above indicates that fallen phoenix tree leaves with surface modifications can be employed as an effective dye pollutant adsorbent.The ability to repurpose refuse for wastewater treatment represents both an environmentally friendly and economically attractive opportunity.