Daixiong Zhang,Xueming Li,Bo Qin,Xiaolin Li,Xiaogang Guo,Chuan Lai
Chromium (III) oxide has been widely used as a coating material for corrosion resistance. In this study, electrophoretic deposition (EPD) of nano chromium (III) oxide (Cr 2 O 3 ) particle (60 nm) was investigated to develop coatings with potential applications of anticorrosive material. The stable suspension of Nano-Cr 2 O 3 particles were obtained in the mixture of acetylacetone and ethanol containing 0.00025 M nitric acid. The coating growth rate was studied with using different deposition times in the range of 1–30 min at voltages of 50–150 V with various concentrations of suspension. The electrophoretic Cr 2 O 3 coating was sintered at 1000°C and 1200°C for 2 h. The micro-morphology of coating was qualitatively characterized by focused ion beam scanning electron microscopy (FIB/SEM). The SEM micrographs obviously showed that the electrophoretic Cr 2 O 3 coating has formed a uniform and dense ultrathin layer after sintering at 1200°C. We demonstrated that nano-Cr 2 O 3 coating could be easily obtained by EPD for the surface modification of metallic materials for potential interest in hard wear-resistant and/or low-friction coatings.
Chemical oxidation processes are widely used for the remediation of organically contaminated soils, but their potential impact on variable-valence and toxic metals such as chromium (Cr) is often overlooked. In this study, we investigated the risk of Cr(Ⅲ) oxidation in soils during the remediation of 2-chlorophenol (2-CP) contaminated soils using four different processes: Potassium permanganate (KMnO 4 ), Modified Fenton (Fe 2+ /H 2 O 2 ), Alkali-activated persulfate (S 2 O 8 2− /OH − ), and Fe 2+ -activated persulfate (S 2 O 8 2− /Fe 2+ ). Our results indicated that the KMnO 4 , Fe 2+ /H 2 O 2 , and S 2 O 8 2− /Fe 2+ processes progressively oxidized Cr(III) to Cr(Ⅵ) during the 2-CP degradation. The KMnO 4 process likely involved direct electron transfer , while the Fe 2+ /H 2 O 2 and S 2 O 8 2− /Fe 2+ processes primarily relied on HO• and/or SO 4 • - for the Cr(III) oxidation. Notably, after 4 h of 2-CP degradation, the Cr(VI) content in the KMnO 4 process surpassed China's 3.0 mg kg −1 risk screening threshold for Class I construction sites, and further exceeded the 5.7 mg kg −1 limit for Class II construction sites after 8 h. Conversely, the S 2 O 8 2− /OH − process exhibited negligible oxidation of Cr(III), maintaining a low oxidation ratio of 0.13%, as highly alkaline conditions induced Cr(III) precipitation, reducing its exposure to free radicals . Cr(III) oxidation ratio was directly proportional to oxidant dosage, whereas the Fe 2+ /H 2 O 2 process showed a different trend, influenced by the concentration of reductants. This study provides insights into the selection and optimization of chemical oxidation processes for soil remediation , emphasizing the imperative for thorough risk evaluation of Cr(III) oxidation before their application.
Liu Huan-Huan,Yang Lei,Li Xiao-Tong,Shi Hui,Guo Lin-Kai,Tu Li-Xin,Wang Jia,Li Yan-Li
Extensive application of nanomaterials enlarges its concentrations in the aquatic environments and poses a threat to algae. This study comprehensively analyzed the physiological and transcriptional responses of Chlorella sp. after being exposed to chromium (III) oxide nanoparticles (nCr 2 O 3 ). The nCr 2 O 3 at 0–100 mg/L presented adverse effects on cell growth (96 h EC 50 = 16.3 mg/L), decreasing the photosynthetic pigment concentrations and photosynthetic activity. Moreover, more extracellular polymeric substances (EPS), especially polysaccharides in soluble EPS, were produced in algae cell, which mitigated the damage of nCr 2 O 3 to cells. However, with the increase of nCr 2 O 3 doses, the EPS protective responses were exhausted, accompanied by toxicity in the form of organelle damage and metabolic disturbance. The enhanced acute toxicity was closely related to the physical contact of nCr 2 O 3 with cells, oxidative stress, and genotoxicity. Firstly, large amounts of nCr 2 O 3 aggregated around and were attached to cells, causing physical damage. Then, the intracellular reactive oxygen species and malondialdehyde levels were significantly increased that led to lipid peroxidation, especially at 50–100 mg/L nCr 2 O 3 . Finally, the transcriptomic analysis further revealed that the transcription of ribosome, glutamine, and thiamine metabolism-related genes were impaired under 20 mg/L nCr 2 O 3 , suggesting nCr 2 O 3 inhibited algal cell growth through metabolism, cell defense, and repair, etc. Graphical Abstract
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