Theoretical Study On Persulfate Activation By Carbon Materials For Removing Organic Pollutants

Water and air are essential environmental factors for human life.Owing to the rapid development of industrialization and urbanization in the past decades,a large number of organic pollutants have been discharged into the water body and the atmosphere.Organic pollutants of toxity are the induced factors of a series of lesions,including cancer and even death.On the other hand,organic pollutants discharged into the environment can cause catastrophic damage to ecosystems,such as the black odor caused by eutrophication of water bodies and optical chemical fumes caused by hydrocarbon organic gases.Therefore,there is an urgent-need for an efficient and economical pollution control technology.The persulphate-based advanced oxidation technology?P-AOPs?with carbon material as the catalyst is believed to be one of promising technologies for organic pollutants abatement because of its high-strength of decontamination and low cost.However,there are still some issues desired to be addressed before its comercialization.Among those issues,the intrinsic nature of carbon matrix for persulfate activation,the mechanism of nonradical pathway are the crucial factors which ditermine the efficiency of organic pollutants removal.Solving the above problems is essential to for the pratical application of persulfate based advanced oxidation technology.Therefore,we conduct a systematic and in-depth study on above issues using DFT calculations,and the results are the following:?1?The atomic-level descriptors of adsorption energy(E_ads),the length of O-O bond(l_O-O)and S-O bond(l_S-O)in persulfate can hardly provide a reliable evaluation for the active states of ROSs in non-radical pathway of PDS.Therefore,we take the B,N doped nano-carbon catalyzed PDS system as an example,to develop a new desciptor to evaluate the relationship between the active site and the activity of ROSs.All possible configurations of B,N doped nanocarbons were considered for PDS adsorption behavior.The local electronic affinity index???was calculated to evaluate the oxidative capacity of the S₂O₈^2-adsorbed on catalyst surface.We found that the catalytic activity of PDS in B-N-C materials depends on the position of B and N rather than the content of doping component.?2?The good conductivity of carbon nanotubes?CNTs?is beneficial to the electrons transfer bwtween the activated PDS and organic pollutants in non-radical system.Utilizeing CNTs as the electrode of capacitor can further enhance its catalytic efficiency,and the anode is found to be significantly higher than the cathode in experiment study.For a depth insight into the mechanism of PDS activation on CNT electrodes,we study the adsorption behavior of PDS on CNTs in different electric field direction and intensity,We found that carbon nanotubes of anode and cathode have different effects on PDS activation.Negative polarization of CNTs on cathode induces the stretching of O-O bond of PDS,while positive polarization of CNTs on anode elongates the S-O bond of PDS.Due to the electrostatic attraction of carbon nanotubes,positive electrode polarization is more conducive to S₂O₈^2-adsorption on the CNT anode.The S-O bond in the S₂O₈^2-on anode is stretched by the positive charge on the CNT surface,making S₂O₈^2-activated.and the activated S₂O₈^2-has a much higher oxidation capacity than the those of PDS on the cathode and pristine CNTs.The critical factor for PDS activation on different electrodes is the evolution of electronic structure of different bonds in the PDS molecule.?3?In view of the excellent performance of carbon materials in adsorption of organic matter and activation of peroxygen sulfates,the P-AOPS with single-wall carbon nanotubes?SWCNT?as peroxymonosulfate?PMS?avtivator was extended to treat volatile organic pollutants?VOCs?by spraying sulfate solutions.The factors of VOCs adsorption and PMS activation by SWCNT were investigated using theoretical calculations.We found that the adsorption VOCs on SWCNTs depends on the polarizability of VOCs.Further,the?electrons of bulk carbon atoms on SWCNT was identified to attributed to the degeneration of O-O in PMS,resulting the geneation of·OH.In the subsequent degradation investigation,we found that formaldehyde has ultra-fast degradation rate and diffusion rate on carbon nanotubes with no CO byproducts.In addition,the critical obstacles mainly encountered by other technologies in dealing with VOC can be avoids in this SWCNT/P-AOPs,indicating that it is a very promising technology for VOCs abatement.