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To improve the regeneration efficiency of methylene blue (MB) saturated biochar in H2O2 system, biochar was modified by Fe‐doped by using FeSO4 and Fe(NO3)3 as iron sources. The effects of Fe‐doped on its microstructure were characterized by XRD, SEM, and BET. The adsorption and regeneration performance of biochar before and after Fe‐doped were compared through adsorption and regeneration experiments. X‐ray photoelectron spectroscopy, electron spin resonance, and quenching experiments were used to explore the regeneration mechanism. The results show that Fe‐doped biochar (SP‐GBC) prepared from FeSO4 maintains a high specific surface area of 1205.9 m2/g and a high adsorption capacity of 375.43 mg·g−1 for MB. After adsorption, the MB‐saturated SP‐GBC exhibits excellent regeneration performance in the H2O2 system, in which the regeneration efficiencies for five consecutive cycles are 85.76%, 83.92%, 94.01%, 99.24%, and 100.79%, respectively. The synergistic effect of H2O2 desorption and degradation is the main regeneration mechanism for MB‐saturated SP‐GBC. The zero valent iron and Fe (II) on the surface of SP‐GBC are the main active sites for H2O2 activation, while 1O2 and HO· are the main oxidation species. In summary, this work provides a simple and feasible method for the design and synthesis of adsorbents with highly efficient regeneration performance. [ABSTRACT FROM AUTHOR]

In this study, a new sludge-based biochar loaded with Fe species (Fe/SSBC) was prepared by a two-step process involving hydrothermal treatment and low-temperature air calcination, and used to degrade tetracycline (TC) by activating peroxymonosulfate (PMS). After 30 min reaction, more than 98 % TC (50 mg/L) could be removed by optimized Fe/SSBC/PMS system (k = 0.166 min−1), which was 2.18 times compared with individual hydrothermal treatment (k = 0.076 min−1). Besides, it also exhibited good stabilization. Detailed characterizations revealed the effect of hydrothermal treatment on the Fe–O coordination of the biochar surface and the change of the Fe valence state by air calcination. The electron paramagnetic resonance (EPR), electrochemical analysis and quenching experiments confirmed that singlet oxygen (1O2) was the main active substance. We further elucidated the influence of grafting Fe–O on the surface electron distribution of biochar by DFT calculations. Moreover, two possible pathways were proposed based on LC-MS analysis. In this study, a method of preparing high catalytic performance sludge-based carbon materials under low energy consumption has been proposed, which provides a new strategy for sludge recycling.

Eichhornia crassipes is a hyperaccumulator of metals and has been widely used to remove metal pollutants from water, but disposal of contaminated plants is problematic. Biochar prepared from plants is commonly used to remediate soils and sequester carbon. Here, the catalytic activity of biochar prepared from plants enriched with iron was investigated as a potentially beneficial use of metal-contaminated plants. In a 30-day hydroponic experiment, E. crassipes was exposed to different concentrations of Fe(III) (0, 4, 8, 16, 32 and 64 mg/L), and Fe-biochar (Fe-BC) was prepared by pyrolysis of the plant roots. The biochar was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Brunauer–Emmett–Teller (BET) analysis, X-ray photoelectron spectroscopy (XPS) and atomic absorption spectrometry (AAS). The original root morphology was visible and iron was present as γ-Fe 2 O 3 and Fe 3 O 4. The biochar enriched with Fe(III) at 8 mg/L (8-Fe-BC) had the smallest specific surface area (SSA, 13.54 m2/g) and the highest Fe content (27.9 mg/g). Fe-BC catalytic activity was tested in the electrocatalytic reduction of H 2 O 2 using cyclic voltammetry (CV). The largest reduction current (1.82 mA/cm2) was displayed by 8-Fe-BC, indicating the highest potential catalytic activity. We report here, for the first time, on the catalytic activity of biochar made from iron-enriched plants and demonstrate the potential for reusing metal-contaminated plants to produce a biochar catalyst. Unlabelled Image [ABSTRACT FROM AUTHOR]

High-content Cr(VI)-contaminated soils are challenging to remediate using a single remediation technique. This study combined soil washing and immobilization to remediate high-content (3440 mg kg−1) Cr(VI)-contaminated soil, which investigated the effects of operating time, temperature, and liquid-solid ratio (LSR) on the Cr(VI) removal efficiency of soil washing and evaluated the potential of Fe-doped biochar (FeBC) in soluble Cr(VI) removal from the washing wastewater and residual Cr(VI) immobilization in the washed soil. The Cr(VI) removal efficiency of soil washing increased with the operating time, temperature, and LSR, but still cannot remove Cr(VI) to achieve the safety content (<100 mg kg−1). FeBC showed satisfactory potential in both Cr(VI) removal and immobilization from wastewater and soil, in which the main mechanisms involve ion exchange, redox, and coprecipitation. These results demonstrate applying soil washing & immobilization to remediate high-content Cr(VI)-contaminated soil is a promising alternative method. [Display omitted] • Single-time soil washing cannot completely remove Cr from heavily Cr(VI) polluted soil. • Washing-immobilization successfully remediated high-content Cr(VI) polluted soil. • FeBC can be both a scavenger and immobilization agent in soil washing-immobilization. • Fe(II) plays a critical role in Cr(VI) remediation in wastewater and soil. [ABSTRACT FROM AUTHOR]

The disposal and management of waste sludge is a considerable challenge for environmental protection and resource utilization. Herein, sludge-based biochar material loaded with nano-Fe 3 O 4 (xS@Fe-y) was fabricated via hydrothermal carbonization process and employed as catalyst to activate peroxymonosulfate (PMS) for degrading organic dyes in wastewater. Benefiting from the proper iron content, porous structure and the good dispersibility of iron on the catalyst surface, the proposed 5S@Fe-500 catalyst not only exhibited excellent catalytic activity and durability in the activation of PMS to degrade Rhodamine B (RhB), which was almost completely removed in 10 min (50 mL 50 mg L−1), but also performed broad application prospects in pollutant degradation. More importantly, the free radical quenching test and electron spin-resonance spectroscopy (ESR) detection demonstrated that O 2 •-, SO 4 •-, OH and 1O 2 were generated during the process of catalyst activation of PMS. Based on this, a possible reaction pathway for degrading RhB with the aid of 5S@Fe-500 was put forward. It is believed that this work offers a promising reuse method of converting the waste sludge to a high efficiency and low-cost nano magnetic catalyst to activate PMS for degrading refractory organic pollutants in aquatic surroundings. Waste sludge was transformed into Fe-doped biochar catalyst via green hydrothermal carbonization for organic dye degradation in wastewater. Image 1 • Waste sludge was transformed into Fe-doped biochar for organic dye degradation. • Active species in sludge biochar and doped magnetic iron exhibited synergistic effect. • Mechanism of RhB degradation by 5S@Fe-500 was coaction of O 2 -, SO 4 -, OH and 1O 2. [ABSTRACT FROM AUTHOR]