Study On Qsar Of Nonradical Oxidation Of Aromatic Organic Contaminants In Water

Refractory organic cotaminants in water may pose a threat to human health and ecosystem.Compared with traditional advanced oxidation processes,nonradical-based oxidation technology has great potential for water treatment because of its mild redox potential,high selectivity,wide pH feasibility,and resistance to complex water matrices.However,the nonradical reaction processes are complicated and the mechanisms are not clear.In this study,the nonradical-based homogeneous and heterogeneous oxidation systems were studied in deep via kinetic models and quantitative structure-activity relationship（QSAR）,aiming at deepening the understanding of nonradical reaction mechanisms and providing theoretical support for practical application.（1）In homogeneous systems,tetra-amido macrocyclic ligand（TAML）activator can activate H₂O₂ to form high valence iron-oxo complexes,which selectively oxidize aromatic organic contaminants（ACs）.The QSAR models were developed based on measured pseudo first-order kinetic constants（6）_obs)of 29 ACs including monosubstituted phenols and drugs at pH 7 and pH 10.The results inferred that the energies of the highest occupied molecular orbital(E_HOMO)of ACs is the predominant factor affecting the TAML/H₂O₂ oxidation,indicating that the rate limiting step is single-electron transfer（SET）.At pH 7,the6)_obs is also affected by propensity for electrophilic attack（1）^-₈4)9)))and the most positive atomic charge on hydrogen atoms（qH⁺）.At pH 10,TAML/H₂O₂ reacts faster towards ACs with a lower hydrogen to carbon atoms ratio（#H:C）,indicating the importance of the hydrogen abstraction reaction.In addition,the oxidation reaction rates and pathways of ACs are highly sensitive to pH.These QSAR models are statistically robust,which help predict the relative reaction rate and mechanism of TAML/H₂O₂ systems.（2）In heterogeneous systems,carbon nanotubes/persulfate systems can oxidize organic contaminants effectively via nonradical process but the mechanisms are not well understood.Herein,we determined the initial degradation rates of 15 phenolic compounds（ArOH）under various concentration oxidized by commercial multiwalled carbon nanotubes（MWCNTs）and peroxydisulfate（PDS）,and found they obeyed binary Langmuir-Hinshelwood kinetics.Polyparameter linear free energy relationships（pp-LFERs）and QSAR were developed for the equilibrium adsorption constant（K）and the apparent rate constants（k_r）to gain a mechanistic insight in phenolic compounds oxidation by MWCNTs/PDS systems.pp-LFERs using Abraham descriptors suggested that affinity interactions between phenols and MWCNTs were mainly related toπ-π（64–95%of contribution）and H-bonding（5–36%of contribution）interactions.QSAR indicated that substituent effects（Hammettσ^-andσ⁺）,hydrogen atom transfer（HAT）ability（O–H bond dissociation energies（BDE））,and descriptors related to SET pathway(E_HOMO,ionization potential（IP）,and one-electron oxidation potentials(E_ox))are predominant factors affecting the reactivity of phenols towards MWCNTs/PDS.Additionally,nonradical reactions occur between adsorbed ArOH and adsorbed PDS,indicating that surface reaction processes of MWCNTs determine the overall reaction rates.