Characterization And Adsorption Properties Of Citric Acid Modified Biochar

Water hyacinth(Eichornia crassipes),as one of the worst aquatic plant and the most aggressive invasive species in the world,has been a serious problem around the world,due to its rapid spread and uncontrolled growth.The conversion of the biomass of this invasive species into biochar for adsorbing pollutants in water could be a feasible and sustainable strategy for management of water hyacinth.Methylene blue(MB)is accepted as a model compound for determining adsorption capacity of contaminants,particularly organic dyes onto various adsorbents in liquid-phase adsorption.Citric acid(CA)has never been used as a surface modification agent impregnated on the surface of biochar to enhance its adsorption capacity of contaminants by improving the quantity and composition of functional groups.In this work,a novel potential adsorbent,citric acid modified biochar,named as CAWB,was obtained from water hyacinth biomass by slow pyrolysis in a N2 environment at 300?.The CA modification focused on enhancing the contaminants adsorption capacity of biochar pyrolyzed at relatively low temperature.Over 90%of the total MB could be removed at the first 60 min by CAWB,and the maximum MB adsorption capacity could reach to 395 mg/g.The physicochemical properties of CAWB was examined by FTIR,XPS,SEM and BET analysis.The results indicated that the additional carboxyl groups were introduced to the surface of CAWB via the esterification reaction with CA,which played a significant role in the adsorption of MB.Batch adsorption studies showed that the initial MB concentration,solution pH,background ionic strength,and temperature could affect the removal efficiency obviously.The adsorption process could be well described by the pseudo-second-order kinetic model and Langmuir isotherm.Thermodynamic analysis revealed that the MB adsorption onto CAWB was an endothermic and spontaneous process.The regeneration study revealed that CAWB still exhibited an excellent regeneration and adsorption performance after multiple cycle adsorptions.It is our overarching objective of this work to explore a new highly efficient and cost-effective adsorbent with high adsorption capacity,less energy consumption and low production cost.In order to achieve this goal,the following four aspects should be controlled:1.Choose water hyacinth as raw material for biochar.The water hyacinth is everywhere and low cost,can reduce its environmental side effects and achieve its resource utilization when used as biochar raw materials.2.Select a lower biochar preparation temperature.Biochar preparation temperature is mostly controlled at 600 ? and above,higher temperature need to consume more energy and increase the cost of preparation.300?,which is recognized as the lowest preparation temperature,was chosen to be used as the preparation temperature to produce the biochar,can cause less energy consumption and preparation cost.3.Modified with citric acid.The properties of porosity,specific surface area and cation exchange capacity of the relatively low temperature prepared biochar is not good as the high-temperature prepared biochar,but retained more oxygen-containing functional groups on its surface.The use of citric acid can further increase the species and number of oxygen-containing functional groups on the surface of biochar,so as to improve its adsorption capacity to organic dyes such as methylene blue.In addition,the citric acid reagent itself is low in cost and can be used in large quantities.4.Recycling.The citric acid modified water hyacinth biochar adsorbed with methylene blue can be recycled and desorbed by HCl,and can be used repeatedly to further reduce costs and improve the efficiency of adsorbent utilization.Unlike most other studies,this study not only can greatly improve the adsorption efficiency of adsorbents to organic dyes,but also at the same time,focus on the multi-link,whole process control to reduce the cost and improve the viability of the utilization of modified biochar to organic wastewater,and provide basic research to large-scale environmental applications of citric acid modified biochar.