Reduction Of 4-chloronitrobenzene Research Articles

Anisotropic oxidative growth of goethite-coated sand particles in column reactors during 4-chloronitrobenzene reduction by Fe(ii)/goethite

Goethite nanoparticles attached to sand grains in column reactors increase grown in length when exposed to ferrous iron and 4-chloronitrobenzene.

Effect of nonreactive kaolinite on 4-chloronitrobenzene reduction by Fe(ii) in goethite–kaolinite heterogeneous suspensions

This work demonstrates that even nonreactive clays may influence outcomes of natural attenuation in contaminated groundwater by iron oxide nanoparticles.

The reduction of 4-chloronitrobenzene by Fe(II)-Fe(III) oxide systems - correlations with reduction potential and inhibition by silicate

Recent studies have demonstrated that the rate at which Fe(II)-Fe(III) oxyhydroxide systems catalyze the reduction of reducible contaminants, such as 4-chloronitrobenzene, is well correlated to their thermodynamic reduction potential. Here we confirm this effect in the presence of Fe(III) oxyhydroxide phases not previously assessed, namely ferrihydrite and nano-goethite, as well as Fe(III) oxyhydroxide phases previously examined. In addition, silicate is found to decrease the extent of Fe(II) sorption to the Fe(III) oxyhydroxide surface, increasing the reduction potential of the Fe(II)-Fe(III) oxyhydroxide suspension and, accordingly, decreasing the rate of 4-chloronitrobenzene reduction. A linear relationship between the reduction potential of the Fe(II)-Fe(III) oxyhydroxide suspensions and the reduction rate of 4-chloronitrobenzene (normalized to surface area and concentration of sorbed Fe(II)) was obtained in the presence and absence of silicate. However, when ferrihydrite was doped with Si (through co-precipitation) the reduction of 4-chloronitrobenzene was much slower than predicted from its reduction potential. The results obtained have significant implications to the likely effectiveness of naturally occurring contaminant degradation processes involving Fe(II) and Fe(III) oxyhydroxides in groundwater environments containing high concentrations of silicate, or other species which compete with Fe(II) for sorption sites.

Reduction of 4-chloronitrobenzene in a bioelectrochemical reactor with biocathode at ambient temperature for a long-term operation

In this study, the enhancement on 4-chloronitrobenzene (4-CNB) reduction was investigated in a dual-bioelectrochemical system with the cathode seeded by enriched 4-CNB degradation inoculums. We demonstrated that the biocathode had the ability to promote 4-CNB reduction and avoid more reluctant byproducts production. At room temperature, when initial 4-CNB concentration was 20mg/L with 0.5V external voltage, the 4-CNB removal efficiency reached 93.7%, while in the abiotic reactor and anaerobic bioreactor reduction rate were 62.9% and 88.4%, respectively. The 4-CNB was mainly converted to 4-CAN (para-chloroaniline). Some of the 4-CAN could be dechlorinated and form aniline (AN), which was more degradable by microorganism. The biodiversity was richer based on the result of scanning electron microscope. Results also showed that the present used reactor was feasible to simplify pollutant transformation and improve transformation efficiency compared with the single abiotic cathode and anaerobic reactor. The bioelectrochemical reactor cathode provided a promising condition for pollutants reduction.

Goethite nanoparticle aggregation: effects of buffers, metal ions, and 4-chloronitrobenzene reduction

The rates at which highly oxidized species are reduced by Fe(ii) sorbed onto iron mineral surfaces can change dramatically with small changes in solution conditions, mainly through changes in nanoparticle aggregation state.

Development and Assessment of a Rate Equation for Chemical Transformations in Reactive Porous Media

With increasing interest in reactive porous media for groundwater remediation, such as granular iron, kinetic rate equations based on the Langmuir-Hinshelwood (L-H) assumptions have proven useful. Three parameters describe L-H kinetics: the two Langmuir sorption parameters, J and Cmax, and the first order rate constant, k. Unfortunately, the Cmax and k are lumped in the L-H equation, making it impossible to estimate their individual magnitudes. A re-examination of the theory underlying the L-H rate equation showed that L-H kinetics are not necessarily appropriate for packed reactive porous media experiments in columns or in the field. A more general rate equation was derived by accounting for changes in sorbed concentrations over time. The equation contains the Langmuir sorption parameter Cmax not lumped with the reaction rate constant, k, so it is possible to obtain unique estimates of J and Cmax and the rate constant, k. A sensitivity analysis suggested that this separation of variables can be achieved over a finite range of conditions applicable to granular iron media. The equation was demonstrated to be applicable, and the separation of variables possible, using the reduction of 4-chloronitrobenzene with Connelly granular iron as a test case.

ABIOTIC REDUCTION OF NITROAROMATIC CONTAMINANTS BY IRON(II) COMPLEXES WITH ORGANOTHIOL LIGANDS

Complexation of Fe(II) by dissolved and surface-bound ligands can significantly modify the metal's redox reactivity, and recent work reveals that Fe(II) complexes with selected classes of organic ligands are potent reductants that may contribute to the natural attenuation of subsurface contaminants. In the present study, we investigated the reactivity of Fe(II)-organothiol ligand complexes with nitroaromatic contaminants (NACs; ArNO(2)). Experimental results show that NACs are unreactive in Fe(2+)-only and ligand-only solutions but are reduced to the corresponding aniline compounds (ArNH(2)) in solutions containing both Fe(II) and a number of organothiol ligands. Observed reaction rates are highly dependent on the structure of the Fe(II)-complexing ligand, solution composition, Fe(II) speciation, and NAC structure. For two model ligands, cysteine and thioglycolic acid, observed pseudo-first order rate constants for 4-chloronitrobenzene reduction (k(obs); 1/s) are linearly correlated with the concentration of the respective 1:2 Fe(II)- organothiol complexes (FeL(2)(2-)), and k(obs) measurements are accurately predicted by k(obs) = k(FeL(2-)(2))[FeL(2-)(2)], where k(FeL(2-)(2)) = 1.70 (+/-0.59) 1/M/s and 26.0 (+/-4.8) 1/M/s for cysteine and thioglycolic acid, respectively. The high reactivity of these Fe(II) complexes is attributed to a lowering of the standard one-electron reduction potential of the Fe(III)/Fe(II) redox couple on complexation by organothiol ligands. The relative reactivity of a series of substituted NACs with individual Fe(II) complexes can be described by linear free-energy relationships with the apparent one-electron reduction potentials of the NACs. Tests also show that organothiol ligands can further promote NAC reduction indirectly by re-reducing the Fe(III) that forms when Fe(II) complexes are oxidized by reactions with the NACs.

Minimizing Mass Transfer Effects in Granular Iron Batch Tests Using GEM Reactors

The glass encased magnet (GEM) batch reactor was designed to permit reactivity studies of granular iron with good mixing, and minimal abrasion. This study compared the GEM reactor with two conventional batch test designs (for granular iron studies). In the GEM reactor experiments, the reduction of 4-chloronitrobenzene with Connelly granular iron was found to proceed at about twice the maximum rate of the reaction mixed by orbital shaking or rolling, indicating that mass transfer was minimized in the GEM tests. In addition, the reproducibility of GEM tests was superior, possibly due to abrasion or other variations to the grain surfaces that occurred in the other types of tests. The biases and uncertainties in kinetic parameters estimated from the shaker and roller experiments were shown to be significant compared to the GEM derived parameters.