The effects of in-situ immobilization of heavy metals by applying natural and chitosan-introduced zeolite, bentonite, and activated carbon (AC) were systematically studied to remediate cadmium (Cd)-contaminated soils in a pot experiment using Brassica juncea as the indicator plant. The results show that zeolite, bentonite, and its chitosan composites can increase soil pH and reduce the biological effectiveness of heavy metals. The Brassica juncea dry weight increased with increasing of amendment dosage. Highest values were found for CS-AC, followed by CS-bentonite, CS-zeolite, AC, bentonite, and zeolite. With an amendment dosage of 75 g per pot, Brassica juncea dry weight increased by 41.91%, 39.00%, 27.64%, 35.93%, 23.78%, and 23.58%, respectively, for CS-AC, CS-bentonite, CS-zeolite, AC, bentonite, and zeolite, compared to the control. Cadmium uptake by Brassica juncea was lowest for this dosage. With a dosage of 75 g, 50 g, 75 g, 75 g, 50 g, and 75 g per pot for CS-AC, CS-bentonite, CS-zeolite, AC, bentonite, and zeolite, respectively, Cd uptake decreased by 21.89%, 19.88%, 19.48%, 18.67%, 17.47%, and 13.85%, respectively. Similarly, bioavailable Cd content decreased by 27.38%, 19.29%, 22.83%, 23.22%, 15.74%, and 8.66%, respectively, compared to the control.

A composite combination of nano-zero valent iron (nZVI) and granular activated carbon (GAC) was introduced to achieve nitrate transformation into nitrogen with minimum byproducts via chemical reduction. The results showed that nitrate removal was significantly intensified and GAC was an excellent partner of nZVI chemical reduction. Both the dispersion and long-term reactivity of nZVI were improved, and more than 80% of nitrate was removed at 10 g/L nZVI/GAC composite within 90 min in steady state. The byproducts of nitrite and ammonium formed in reduction process were below 0.008 and 0.04 mg/L, respectively, and nitrogen was the main end product, which was confirmed by X-ray photoelectron spectroscopy analysis. Moreover, the kinetic model of nitrate reduction by nZVI/GAC composite can be described well by pseudo-first-order reaction kinetic (R² = 0.984). The intensification is closely related to the dispersion effect of GAC matrix to nZVI and the promotion effect to electrons transfer between nZVI and nitrate pollutant of internal iron–carbon microelectrolysis existing in such a composite. Therefore, the findings are very beneficial to develop an efficient and low-cost chemical remediation method for nitrate-contaminated groundwater.

In this study, the synergetic effects in a Fenton-like system catalyzed by nano zero-valent iron (nZVI Fenton-like system) were studied using nitrobenzene (NB) as a model contaminant. The results showed that homogeneous and heterogeneous Fenton processes existed simultaneously in the nZVI Fenton-like system, and a synergetic removal effect between these processes played a considerable role in NB removal. Through quantitative analysis, 36.5% of NB degradation was attributed to the synergetic degradation effect, which was caused by a synergetic catalytic effect between nZVI and dissolved iron ions (Fe3+ and Fe2+). In the bulk solution, the Fe3+/Fe2+ redox rate was accelerated by nZVI, resulting in the efficiency improvement of homogeneous catalysis; in the surface of nZVI, these dissolved iron ions promoted the electrons transfer from nZVI core to shell, enhancing the efficiency of heterogeneous catalysis. The synergetic catalytic effect also improved the utilization-rate of H2O2 by reducing the decomposition caused by Fe3+/Fe2+ redox compared to that in the homogeneous Fenton system. Based on these results, a possible mechanism of synergetic effects in the nZVI Fenton-like system was proposed. These results could provide insight into an nZVI Fenton-like system.