Molecular Dynamics Simulation Of Adsorption Characteristics Of Organic Molecules On Coal Surface

At present,the discharge of coal chemical wastewater is large and involves a wide range,which is harmful to the environment.Coal,carbon and graphene oxide are good adsorbents for organic pollutants in coal chemical wastewater.They are often used as adsorbents to remove harmful substances from wastewater.The oxygenic functional groups on the surface of adsorbents have a significant impact on the adsorption of organic pollutants in wastewater.The surface oxygenic functional groups of most adsorbents are complex and diverse,and the adsorption mechanism of oxygenic functional groups on organic pollutants is not clear.At the same time,the preparation of coal water slurry from coal chemical wastewater is an economical and feasible method of wastewater resource utilization.It can not only solve the problem of pollution control of coal chemical wastewater,but also not reduce the use value of the coal powder,and does not involve the regeneration of absorbent.When coal chemical wastewater is used to make coal water slurry,the substances that contained in the wastewater will cause different effects on the adsorption of additives on the coal surface,then may affect the slurry forming ability of coal water slurry.In view of the above situation,this thesis is divided into two parts.(1)Due to the high content of phenols in coal chemical wastewater.In this study,the graphene substrates were used as models of coal and carbon adsorbents,and the carboxyl,hydroxyl and carbonyl groups were used to modify the substrates.The adsorption processes of phenol on the four different adsorbent substrates were studied by molecular dynamics simulation.The effects of different oxygenic functional groups on the adsorption of phenol were discussed from the aspects of van der Waals interaction,electrostatic interaction,?-? interaction,hydrogen bond interaction and interaction energy.(2)Combined with experiments and molecular dynamics simulation methods,reference to the deionized water environment,the effects of four representative substances(quinoline,phenol,acetic acid and 5-hydroxymethylfurfural)on the adsorption of additives on the surface of coal were analyzed,and the slurry mechanism of coal chemical industry coal water slurry was analyzed.The results show that:(1)The van der Waals interaction,electrostatic interaction,?-? interaction and hydrogen bonding between the substrates and phenol were affected by the modification of the substrates with three oxygenic functional groups.It was found that van der Waals interaction and ?-? interaction was the main factors affecting the adsorption of phenol on the substrates,while electrostatic interaction and hydrogen bonding were the secondary factors.Two different effects,which are promoting and hindering,on the adsorption of phenol were generated depending on the position of hydrogen bonding.The hydrogen bond between phenol and oxygenic functional groups on the substrate promoted the adsorption of phenol,whereas the hydrogen bond between water molecules and water molecules or between water molecules and phenol hindered the migration of phenol in solution.The interaction energy reflected the spontaneity of the adsorption process and the stability of the adsorption system with an equilibrium state.A large absolute value of interaction energy meant a stable adsorption equilibrium system.Carboxyl group showed a strong effect in enhancing the adsorbing stability of phenol to adsorbent substrate.The hydrophilicity of the substrates can be enhanced to varying degrees by modifying the substrates with different oxygenic functional groups.Specially,the carboxyl group had the strongest effect followed by the hydroxyl group,whereas the carbonyl group hardly increased the hydrophilicity of the substrate.(2)The adsorption capacity of additives on the coal surface is different in deionized water,quinoline,phenol,acetic acid and 5-hydroxymethylfurfural solution.The presence of the quinoline will increase the equilibrium adsorption of additives on the coal surface,while the presence of the phenol,the acetic acid and the 5-hydroxymethylfurfural will reduce the equilibrium adsorption of additives on the coal surface.The Gibbs free energy that adsorbed by additives on coal surface in different water environment is negative,indicating that the adsorption is spontaneous.The adsorption process,the density distribution,the interaction energy and the mobility of coal additives in different water environments were calculated by molecular dynamics simulation.In five kinds of water environment,the adsorption process of the additive shows a similar rule,that is,the additive adsorbs on the aromatic ring structure of the coal surface through its aromatic ring structure,while the hydrophilic sulfonic acid group is far away from the coal surface and extends into the water phase,but in different water environment,the amount,form and degree of combination of the additive adsorbed on the coal surface are different.In this thesis,by comparing the density distribution,interaction energy and mobility between coal and additives,it was found that quinoline can increase the adsorption capacity of coal to additives,weaken the mobility of additives near the coal surface,and increase the adsorption capacity of additives on the coal surface.However,the phenol,the acetic acid and the 5-hydroxymethylfurfural weaken the adsorption of additives on the coal surface and increase the mobility of additives on the coal surface,which is not conducive to the adsorption of additives on the coal surface.