The development of new, efficient, and low-cost OER electrocatalysts with advanced structures is of great significance for hydrogen production by electrolysis of water. A Ni-doped ferrous oxalate nanorod electrocatalyst (Ni-FeC 2 O 4 ) was synthesized using a one-step solvothermal method, which showed an outstanding OER activity with a low overpotential of 296 mV at 10 mA cm −2 . The Ni-FeC 2 O 4 electrocatalyst exhibited excellent OER stability in the 300 mV constant potential test, which was mainly attributed to the fact that Ni doping can increase the electrochemical active surface areas and the interfacial charge transfer abilities of the FeC 2 O 4 electrocatalyst, optimize the electronic structure of the real active species ferric hydroxide, promote the formation of the decisive step *OOH of ferric hydroxide, and improve its intrinsic activity.
Lei Zhou,Yongqing Zhang,Lijin Zhang,Xuefeng Wu,Ran Jiang,Lu Wang
A significant amount of iron from the waste nickel-cadmium (Ni-Cd) battery sulfuric acid leachate seriously hinders the separation and recovery of nickel and cadmium. Therefore, an efficient and economical way to remove iron from this leachate is desired. This paper demonstrated the efficient iron extraction from a simulated Ni-Cd battery sulfuric acid leachate with saponified Di (2-ethylhexyl) phosphoric acid (D2EHPA). The iron-loaded D2EHPA was then stripped with oxalic acid and the iron was recovered in the form of iron oxalate. This process realizes the efficient separation and high-value recovery of iron. The results showed that the saponification of the D2EHPA greatly promoted the extraction of iron from the Ni-Cd battery sulfuric acid leachate. Under suitable conditions, the iron’s single-stage extraction rate was more than 95%, and the iron’s single-stage stripping rate was more than 85%. Moreover, the iron’s extraction rate was more than 99% after two theoretical extraction stages, and the stripping rate was 95.6% after two theoretical stripping stages. The slope analysis determines that five molecules of D2EHPA were combined with one molecule of Fe3+in the extraction process. The FT-IR analysis shows that the extraction mechanism of Fe3+using the saponified D2EHPA is a cation exchange. These results can help guide the industrial separation and recovery of iron from the waste Ni-Cd battery sulfuric acid leachate.
Yuhang Zhang,Hao Zhang,Nuanqin Zhang,Biao Zhou,Falong Jia,Lizhi Zhang,Zhihui Ai,Xiao Liu
Cadmium (Cd) contamination is highly toxic to human health, and the complexed Cd in wastewater is tricky to remove owing to its stable chelating structure. In this study, industrial zero-valent iron (ZVI) was modified by ball-milling with tiny formic acid (FA), and the as-prepared sample (FA-ZVI bm ) was attempted in the treatment of Cd II -ethylenediaminetetraacetic acid (Cd II -EDTA). Little FA addition to ball-milling could dramatically improve the performance of FA-ZVI bm towards Cd II -EDTA elimination and raise the elimination rate constant by more than 200 times. Results ascertained that the (HCOO) 2 Fe II shell formed on FA-ZVI bm promoted Cd II -EDTA decomplexation and activation of dissolved O 2 to reactive oxygen species (ROS) for oxidative degradation of EDTA ligands. Cd II -EDTA was instantly decomplexation by Fe 3+ replacement, and the decomplexed Cd 2+ was rapidly captured by FA-ZVI bm . At the same time, the EDTA ligands underwent oxidative degradation, avoiding the re-chelation ecological hazard. Interestingly, we found that replacement decomplexation has a synergistic mechanism for activating dissolved O 2 to ROS , facilitating oxidative destruction of EDTA ligands. Furthermore, the FA-ZVI bm fixed-bed reactor could remediate Cd II -EDTA contaminated environmental water one-stop, and the effluent stably meets the emission standards. This study demonstrated that FA-ZVI bm could be a viable approach for Cd II -EDTA decontamination and clarified the remediation mechanism.
Zero-valent iron (ZVI), with high reduction capacity and cost effectiveness, has been widely used as an activator for persulfate in remediation of organic pollutants. However, the existence of inherent iron oxide shell blocked the transfer of proton and further reduced its reactivity. In present study, a novel persulfate (PS) activator BZVI@OA was synthesized via ball milling ZVI with oxalic acid dihydrate. Scanning electron microscope , X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry and Time-of-flight secondary ion mass spectroscopy confirmed the original low proton conductive oxidation shell was replaced by a high proton conductive FeC 2 O 4 shell. The generated shell significantly improved persulfate activated capacity, through which degradation rates of various contaminants were enhanced for 1.64 to 2.33 times. Dissolved oxalate was proved to form complexes with iron ions, dramatically reduced the potential difference and relieved the blocked cyclic conversion. Electron paramagnetic resonance and quenching experiments confirmed an inner sphere adsorption of PS on FeC 2 O 4 ·2H 2 O shell which facilitated the peroxide bonds cleavage, leading high efficiency of ROS generation. The accelerated proton transition was confirmed with AC impedance method, resulting in fast and elevated surface bound Fe 2+ for persulfate decomposition into active species. Furthermore, BZVI@OA/PS system demonstrated high tolerance over wide initial pH range and promising reusability within 6 cycles. This work clarifies an effective strategy for developing efficient modified ZVI as a PS activator for organic pollutant degradation in water.
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