The Preparation And Nitration Reductive Modification Of Diffierent Mesoporous Carbon For Enhanced Adsorption Mechanism Of Cu(?)

Biochar has wide application because of its wide sources,low cost,simple preparation and cleanness.However,since biochar has rich micropore structure,it is difficult for macromolecules such as heavy metal ions to enter the pore channel,which limits the adsorption capacity.While mesoporous carbon can make best use of advantages and bypass the disadvantages.The key for an adsorbent to adsorb heavy metal ions is the amount of functional groups on the active sites.Therefore,adsorbents with functional groups are more valuable.We prepared amino functional groups carbon modified from mesopore biochar and mesoporous carbon,and used it to remove the Cu(?)from wastewater.The adsorption kinetics,thermodynamics and other impact factor were evaluated in order to understand the copper ion adsorption mechanism.Several main conclusions of this research are as follows:Three different species biochar with high mesoporosity were prepared from bagasse and cotton stalk by phosphoric acid-microwave(or muffle)method.According to the N2 adsorption-desorption isotherms,three kinds of biochars all have well-developed porous structure,large specific surface area and the mesoporosity porosity of bagasse biochars reached 89.5%.And then amino-functionalized mesoporous biochar prepared from nitration substitution and reduction reactions has abundant mesoporous pore and more surface functional groups.FTIR results show that nitrogen content increased from 0.3%to 4.41%.The adsorption experimental results showed that after modification,adsorption capacity for heavy metal ions Cu(?)was largely enhanced,exhibiting a superior comprehensive performance compared with other relevant adsorbents.The most effective is MB which prepared from bagasse by phosphoric acid-muffle.Under the same experimental conditions,the adsorption quantity of modified MB-N is up to 15.49 mg/g,nearly four times than pristine MB.The modified MB-N appears quick adsorption property,suggesting the effect of nitration substitution and reduction reactions on adsorption capacity.Mesopore carbon(MC)with high specific surface area was synthesized in the preparation of neutral conditions by use of triblock copolymers F108 as template agent and phenol/formaldehyde as carbon source,and the MC was further treated to gain amino modified mesopore carbon(MC-N).Characterization results show that both MC and MC-N with respectively,surface area 1387.3 m2/g and 1077.6 m2/g and pore volume 0.955 cm3/g and 0.699 cm3/g,have vermicular channel structure,large specific surface area and high mesoporosity.FTIR and TEM indicate that MC-N was successful to graft amino functional groups.Compared with biochars,mesopore carbon has well-developed pore structure and rich functional groups,which shows significant advantage in adsorption and diffusion to benefit the adsorption and transportation of the molecule.What's more,mesopore carbon also shows the strong ability to remove Cu(?)form wastewater and the adsorption quantity of MC-N was up to 218.34mg/g,which was more than 14 times of MB-N.Adsorption experiments showed that the adsorption of MB-N,MC and MC-N basically reached equilibrium in sixty minutes.MC and MC-N after nitration substitution and reduction modification showed higher Cu(?)remove rate than MB-N.The pseudo-second rate equation can be used to describe the adsorption process,which highlighted the chemisorption rate-controlling mechanism.In addition,the results also further proved that the carbon reacted with Cu(?)during the adsorption.Adsorption thermodynamics conformed to Langmuir model with perfect fitness,suggesting that copper sorption on amino modified carbon materials is monolayer coverage.The adsorption isotherm of MB-N,MC and MC-N to Cu(?)is the optimal adsorption isotherm,which indicated that the increase of temperature benefited to the adsorption to some extent.Solution pH is an important parameter affecting the properties of sorbent surface and metal speciation in solution,further affecting the combined form of Cu(?)during the adsorption.The capacity is stable in the range of pH 5.0-6.0 because Cu ions are in free state.Thus,carbon will reach the best adsorption capacity by controlling solution pH.Further study of competitive adsorption found that the Cu(?)combined with sorbent through complexation reaction,which enable it with the ion selectivity.The interactive mechanism of nitration reductive modified carbon and Cu(?)was worked out by ATR-FTIR and XPS analysis.-NH2 included in the MB-N took complexing action with Cu(?)to benefit the adsorption,thus appearing much improved adsorption capacity than MB.However,except the complexation of-NH2 with Cu(?),mesoporous carbon itself contains a large number of unsaturated alkenes,alkynes and aromatic hydrocarbon molecules,which as ligands have stronger complexation with metal ions in this process.Cu(?)provide an empty track to combined nitrogen,oxygen and other atoms of MC and MC-N into ligands,thus forming a more stable chelate,appearing more efficient adsorption ability and the high pH stability and ion selectivity.