Research On Preparation And Adsorption Performance Of Biochar Modified Adsorption Material

Water pollution has become one of the key problems facing the world.Heavy metal wastewater,organic dye wastewater and pharmaceutical wastewater have become typical representatives of water pollution.In recent years,biochar had replaced activated carbon as a novel adsorbent due to the advantages of low cost,excellent adsorption performance and wide source of raw materials.At the same time,membrane separation technology had also been developed to a certain extent.The study found that the adsorption performance of raw straw biochar needed to be improved.Therefore,multiple modification methods were adopted to promote its development in pollutant adsorption,and biochar/membrane composite materials were developed to enhance its application in the field of wastewater treatment.1.In this paper,a noval Si-Mn binary modified biochar composite（SMBC）was prepared by co-precipitation method using corn straw as the raw material.The modification mechanism of SMBC was explored by various characterization methods.Batch adsorption experiments were used to study the adsorption behavior of Cu（II）on SMBC,and the adsorption mechanism and contribution rate were analyzed.The main conclusions were as follows:（1）Si-Mn loading accelerated the decomposition of organic matter in biomass and improved the thermal stability of biochar.Si and Mn were uniformly loaded on the surface of SMBC mainly in the form of Si O₂,Mn O_xand Mn Si O₃,which made the surface of the final prepared SMBC more loose and rough.（2）When the dosage was 2 g/L and the solution p H was 2-6,the removal rate of50 mg/L Cu（II）solution by SMBC reached more than 95%.The adsorption process conformed to Langmuir and pseudo-second-order kinetic model,and is controlled by liquid film diffusion and intra-particle diffusion,belonging to monolayer chemisorption.After 5 cycles,the removal rate of Cu（II）by SMBC could still reach80.24%.（3）The adsorption mechanisms of Cu（II）on SMBC were precipitation,ion exchange,surface complexation and pore filling.The contribution rates of precipitation and ion exchange were 4.74%and 13.71%,respectively.The joint contribution rates of surface complexation and pore filling were 84.55%,and surface complexation was the main adsorption mechanism.The presence of Si-O-Mn and Mn Si O₃could greatly reduce the leaching of Mn²⁺caused by ion exchange,stabilize the attachment of Mn to SMBC,and reduce the risk of secondary pollution.2.Nano-silica modified biochar（NSBC）was synthesized by a combination of ball milling,pyrolysis and alkali activation to remove methylene blue（MB）and tetracycline（TC）in wastewater.The removal of MB and TC at concentrations of 50 to500 mg/L by NSBC was evaluated.SEM,EDS,BET,FTIR,XRD,XPS and other techniques were used to characterize the properties of modified biochar in order to explore the modification mechanism of NSBC and the possible adsorption mechanism.The main conclusions are as follows:（1）Nano-Si O₂was combined with biochar through the formation of Si-C and Si-O-C bonds,which changed the original C arrangement.The rough surface and well-developed mesoporous structure（the average pore size of NBC-30 and NBC-40were 4.7840 nm and 4.2229 nm,respectively）facilitate the adhesion of pollutants on biochar.Si O₂,trace Ca O and Ca₂Si O₄,abundant functional groups such as-OH and-COOH attached to the surface of NSBC provide a large number of effective active sites for the adsorption of pollutants.（2）When the ratio of nano-Si O₂and straw was 1:7,the milling time were 40 min or 30 min,the biochar prepared were suitable for MB or TC adsorption,respectively.The best dosage of NSBC-40 for MB was 1g/L,and the best dosage of NSBC-30 for TC was 3g/L.p H had obvious influence on the adsorption process.Langmuir model and pseudo-second-order kinetic model could better describe the adsorption process,which belonged to monolayer chemical adsorption.Combined with Webber-Morris model fitting results,it was found that the adsorption process was controlled by both liquid film diffusion and intra particle diffusion.The Langmuir model calculated that the maximum adsorption capacity of MB and TC were 247.22 mg/g and 86.95 mg/g,respectively.After five adsorption-desorption cycles,NSBC still had good adsorption capacity,with adsorption capacity of MB and TC reaching 99.30 mg/g and 19.89 mg/g,respectively.（3）The possible adsorption mechanisms of MB and TC on NSBC included intermolecular hydrogen bonding,surface complexation,electrostatic attraction,n-π/π-πconjugation and pore filling.3.NSBC/PSf-M was prepared by blending biochar modified by nanometer silica and polysulfone,and used for the separation of MB in wastewater.The results showed that:（1）When the polysulfone content was 16 wt%and NSBC content was 0.6 wt%,the removal amount of MB（21.384 g/m~2·h）of NSBC/PSf-M prepared at the initial flow rate of 0.5 m L/min was significantly higher than that of mixed membrane materials prepared under other conditions.（2）The surface of NSBC/PSf-M was relatively smooth,and the internal pore structure was significantly improved.The crystal structure and surface functional group types did not change due to the mixing of NSBC.The increase of-OH and-COOH content significantly reduced the water contact angle,and the hydrophilic ability was enhanced.（3）After 5 filtration and adsorption cycles,the removal of MB by NSBC/PSf-M could still reach 15.684 g/m~2,and the efficiency remained at the initial 73.3%.It showed that NSBC/PSf-M had good reuse performance.