Study On Reductive Transformation Of Chloronitrobenzenes By Zero-valent Iron And QSAR

Chloronitrobenzenes, as important building blocks for synthesis of industrial chemicals, are quite recalcitrant and toxic. They have been declared to be the priority persistent toxic substances(PTS) by the EPA of USA, EEC and China, and great interest is taken in the remediation technique. Over the past decade, Zero-valent iron(ZVI) has attracted considerable attention as a effective reductant, which is capable of reducing a variety of important organic pollutants, such as chlorinated hydrocarbons and nitroaromatic compounds(NACs). Based on its successful application in the situ reactive barriers as well as in above-ground treatment systems, we investigated the reductive transformation characterization of chloronitrobenzenes by ZVI in anaerobic, NaHC03-HAc buffered batch systems, to (1)gain insight into the reductive transformation mechanism, influencing factors and kinetics of 4-chloronitrobenzene(4-CNB), (2)further our understanding of the reductive transformation activity of NACs, including 2-chloronitrobenzene (2-CNB), 3,4-dichloronitrobenzene(3,4-DCN), nitrobenzene(NB), 4-nitrophenol(4-NP) and 4-nitroaniline(4-NA), and (3)set up the correlation between reductive transforming rates of NACs and molecular connectivity indexs(MCl). The following results were achieved:1. In anaerobic, pH5 NaHCO₃-HAc solution, NACs were reduced by ZVI to amine aromatic compounds. Reductive reactions were followed by pseudo-first-order kinetics. 4-CNB was reduced to 4-CA by ZVI without dechlorination product AN, and the reductive transformation pathway was proposed depending on the GC/MS analysis. Compared to ZVI, Pd/ZVI(Pd loading of 10^-6and 2×10^-6) showed 40% and 66% dechlorination efficiency with the product of 4-CA and AN, but Pd/ZVI meant no significance to enhance the reductive transformation rate.2. The reductive transformation rate was affected by various factors including acid pretreatment, ZVI dosage and surface area, initial concentration of 4-CNB, and the buffer pH. And in the presence of ultrasound, the rate was enhanced.3. Based on Langmuir-Hinshelwood model, related model and first-order deactivatingmodel, a new modeling approach was developed which could fit the observed values well. The constants in ZVI system: reductive transformation rate of 4-CNB k₁ ( 8.04±0.52 ) h^-1, appearance rate of 4-CA k₂ (2.06±0.32) h^-1, ZVI deactivating rate k_d1 (0.29±0.06) h^-1. And the constants in Pd/ZVI system: reductive transformation rate of 4-CNB k₁ (4.27±0.04) h^-1, appearance rate of 4-CA k₂ (1.06±0.09) h^-1, appearance rate of AN k₃ (0.27±0.03) h^-1, ZVI deactivating rate k_d2 (0.09±0.01) h^-1。4. Competition experiments with binary mixtures of 4-CNB and each one of other NACs revealed the effect of different substituent groups on relative affinities for ZVI surface, and the activity order was 3,4-DCN>2-CNB>4-NA>4-NP>4-CNB>NB.5. There was significant quantitative structure—activity relationship(QSAR) between the first-order connectivity index ¹X^v, the forth-order connectivity index ⁴X_pc^v. non-dispersion forces factor Ax and the reductive transforming rate constants. The QSAR models were k_x-nb=16.993 · ⁴X_pc^v- 0.397 · ¹X^v+ 14.624 · â–³x - 15.275 (R²=0.934) and Q=1.327 ·⁴X_pc^v + 0.087 · ¹X^v+ 0.345 · â–³x-0.492(R²=0.862)。...