To understand the feasibility of its application to the in situ remediation of contaminated groundwater,the dechlori-nation of 2,4-dichlorophenol (2,4-DCP) by Ni/Fe nanoparticles in the presence of humic acid (HA) was investigated.We found that,as high performance liquid chromatography (HPLC) was used,the 2,4-DCP was first quickly reduced to o-chlorophenol (o-CP) and p-chlorophenol (p-CP),and then reduced to phenol as the final product.Our experimental results indicated that HA had an adverse effect on the dechlorination of 2,4-DCP by Ni/Fe nanoparticles,as the HA concentration increased,the removal rate decreased evidently.It also demonstrated that 2,4-DCP was reduced more easily to o-CP than to p-CP,and that the sequence of the tendency in dechlorination of intermediates was p-CP>o-CP.Transmission electron microscope (TEM) showed that HA could act as an adsorbate to compete reactive sites on the surface of Ni/Fe nanoparticles to decrease the dechlorination rate.Also we con-cluded that the dechlorination reaction of 2,4-DCP over Ni/Fe nanoparticles progressed through catalytic reductive dechlorination.
Batch experiments were conducted to investigate the adsorption of 2,4-dichlorophenol (2,4-DCP) onto microwave modified activated carbon (AC) at three different temperatures (303 K, 313 K and 323 K). Adsorption isotherms, kinetics, and thermodynamics of the adsorption process were explored. Equilibrium data were fitted into Langmuir and Freundlich equations, and the result reveals that the Freundlich isotherm model fits better than the Langmuir model. Three simplified kinetic models: pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations were adopted to examine the mechanism of the adsorption process, and the pseudo-second-order kinetic model proved to be the best in describing the adsorption data. The thermodynamic parameters of the adsorption process were estimated, showing that the adsorption of 2,4-DCP was exothermic and spontaneous, and the adsorption studied in this paper can be assigned to a physisorption mechanism.
The kinetics of Cr(VI)reduction to Cr(III)by metallic iron(Fe0)was studied in batch reactors for a range of reactant concentrations,pH and temperatures.Nearly 86.8%removal efficiency for Cr(VI)was achieved when Fe0 concentration was 6 g/L(using commercial iron powder(<200 mesh)in 120 min).The reduction of hexavalent chro-mium took place on the surface of the iron particles following pseudo-first order kinetics.The rate of Cr(VI)reduction increased with increasing Fe0 addition and temperature but inversely with initial pH.The pseudo-first-order rate coeffi-cients(kobs)were determined as 0.0024,0.010,0.0268 and 0.0628 min−1 when iron powder dosages were 2,6,10 and 14 g/L at 25°C and pH 5.5,respectively.According to the Arrehenius equation,the apparent activation energy of 26.5 kJ/mol and pre-exponential factor of 3330 min−1 were obtained at the temperature range of 288−308 K.Different Fe0 types were compared in this study.The reactivity was in the order starch-stabilized Fe0 nanoparticles>Fe0 nano-particles>Fe0 powder>Fe0 filings.Electrochemical analysis of the reaction process showed that Cr(III)and Fe(III)hydroxides should be the dominant final products.
Over Pd/Fe bimetallic catalyst, o-nitrochlorobenzene(o-NCB), at a concentration of 20 mg/L in aqueous solutions, is rapidly converted to o-chloroaniline(o-CAN) first, and then quickly dechlorinated to aniline(AN) and Cl^-, without other intermediate reaction products. The aminated and dechlorinated reactions are believed to take place on the surface site of the Pd/Fe. The o-NCB removal efficiency and the next dechlorination rate increase with an increase of bulk loading of palladium and catalysts addition due to the increase of both the surface loading of palladium and the total surface area. These results indicate that reduction, amination and dechlorination of o-NCB by palladium-catalyzed Fe^0 particles, can be designed for remediation of contaminated groundwater.
