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Herein, we reported the synthesis of nanoscale zero-valent iron particles stabilized by sulfur/nitrogen dual-doped r-GO (nZVIPs@SN-G) and their applications as the heterogeneous catalysts to the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by combining H2O2 under varying pHs, temperatures, catalyst dosages and H2O2 concentrations, as well as in the presence of radical scavengers. The experimental results showed that this heterogeneous Fenton-like catalytic system remained effective up to 90 min of reaction time, and could reach at least 98% degradation efficiency at the optimal conditions, especially when the initial pH values were below 4.5. And the scavenging experiments revealed that 2,4-D was mainly decomposed by the attack of surface-bounded hydroxyl radicals ( OH). The structure and properties of the nZVIPs@SN-G catalyst was characterized by X-ray diffraction (XRD), scanning elctron microscopy (SEM), surface area analysis (BET), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). The SEM images indicated that nanoscale zero-valent iron particles (nZVIPs) with size of about 10–50 nm were uniformly stabilized on the surface of sulfur/nitrogen dual-doped r-GO (SN-G), and had good combination with the multilayer matrix. Additionally, the catalyst at the optimum pH could maintain effective degradation even after five cycles, and achieved 91% degradation efficiency of 2,4-D, which was indicative of a good stability. More importantly, the possible reaction mechanism and dechlorination pathway of 2,4-D by the nZVIPs@SN-G/H2O2 heterogeneous catalytic system was also illustrated in this study.

Herein, Pd/Fe bimetallic nanoparticles (Pd/FePs) were uniformly distributed on the surface of graphene sheet structure, and had good combination with the multilayer substrate. The nanocomposites could maintain high reactivity even after five times degradation reactions of carbon tetrachloride (CT) in succession, indicating that the modified technology had a positive effect on achieving high surface activity and prolonging the longevity. The structure evolution and compositional changes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photo-electron spectroscopy (XPS). Also, humic acid (HA) as non-reactive adsorbate could preferentially occupy surface active sites of Pd/FePs to mediate the predominant radical species in the degradation process, which caused a 53% decrease in dechlorination rate of CT. These findings provided an important understanding of the stability and reactive mechanism involved in Pd/Fe bimetallic system toward CT degradation. Moreover, batch experiments were conducted to investigate the actual catalytic activity in view of the effects of common inorganic anions in aqueous solution. The results revealed that the presence of Cl−, HCO3−, and HPO42− was beneficial to the CT degradation while SO42- and NO3− exerted the negative effects. Based on the detection results by means of gas chromatography (GC) and ion chromatography (IC), a possible degradation pathway was propose.

Herein, we reported a study on using the catalytic performance of nanoscale palladized zero-valent iron@ graphene composites (PFGC) synthesized by using coprecipitation method to significantly enhance carbon tetrachloride (CT) dechlorination in the laboratory, and then the nanocomposite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunner-Emmet-Teler (BET), and X-ray photoelectron spectroscopy (XPS). The catalytic activity was investigated in consideration of several operation parameters including the initial pH, temperature, the dosage of nanocatalyst and the optimal content of palladium metal. The results showed that 50.4% and 93.5% CT (C initial = 3 mg L −1 ) were removed from aqueous solution by nZVI (Nanoscale zero-valent iron, 0.5 g L −1 ) and PFGC (Nanoscale palladized zero-valent iron@ graphene composites, using Fe/GO = 2:1 and Pd/Fe = 0.75%, 0.5 g L −1 ), respectively. The degradation kinetics of CT in all experiments followed pseudo first-order reaction kinetics. Moreover, it has been found that palladium metal (Pd 0 ) accelerated hydrogen formation and activation to generate atomic hydrogen (·H) which in turn behaved as the reducing agents responsible for the dechlorination reactions as presented in the conceptual model. And the activation energies reduced from 44.42 to 30.18 kJ/mol. However, it was very easy to agglomerate and form large-sized particles due to the high specific surface energy, hence, graphene as the supporting matrix graphically depicted in the SEM images increased specific surface areas to improve the dispersibility of bimetallic nanoparticles. After five successive runs, there was no significant reduction in the removal efficiency indicating a good reusability and stability of PFGC.