Impacts of anions on activated persulfate oxidation of Fe(II) - Rich potassium doped magnetic biochar

A critical review on biochar for the removal of toxic pollutants from water environment

As an effort to tackle some of the most pressing ecological issues we are currently experiencing, there has been an increasing interest in employing biomass-derived char products in various disciplines. Thermal combustion of biomass results in biochar production, which is a remarkably rich source of carbon. Not only does the biochar obtained by the thermochemical breakdown of biomass lower the quantity of carbon released into the environment, but it also serves as an eco-friendly substitute for activated carbon (AC) and further carbon-containing products. An overview of using biochar to remove toxic pollutants is the main subject of this article. Several techniques for producing biochar have been explored. The most popular processes for producing biochar are hydrothermal carbonization, gasification and pyrolysis. Carbonaceous materials, alkali, acid and steam are all capable of altering biochar. Depending on the environmental domains of applications, several modification techniques are chosen. The current findings on characterization and potential applications of biochar are compiled in this survey. Comprehensive discussion is given on the fundamentals regarding the formation of biochar. Process variables influencing the yield of biochar have been summarized. Several biochars' adsorption capabilities for expulsion pollutants under various operating circumstances are compiled. In the domain of developing biochar, a few suggestions for future study have been given.

Efficient Cr(VI) removal by pyrite/porous biochar: Critical role of potassium salt and sulphur

The excessive accumulation of hexavalent chromium (Cr(VI)) in the environment poses a risk to environment and human health. In the present study, a potassium bicarbonate-modified pyrite/porous biochar composite (PKBC) was prepared in a one-step process and applied for the efficient removal of Cr(VI) in wastewater. The results showed that PKBC can significantly remove Cr(VI) within 4 h over a wide range of pH (2-11). Meanwhile, the PKBC demonstrated remarkable resistance towards interference from complex ions. The addition of potassium bicarbonate increased the pore structure of the material and promoted the release of Fe2+. The reduction of Cr(VI) in aqueous solution was primarily attributed to the Fe(II)/Fe(III) redox cycle. The sulphur species achieved Fe(II)/Fe(III) cycle through electron transfer with iron, thus ensuring the continuous reduction capacity of PKBC. Besides, the removal rate was also maintained at more than 85% in the actual water samples treatment process. This work provides a new way to remove hexavalent chromium from wastewater and demonstrates the potential critical role of potassium bicarbonate and sulphur.

Lanthanum-doped magnetic biochar activating persulfate in the degradation of florfenicol

In this study, lanthanum-doped magnetic biochar (LaMBC) was synthesized from bagasse by co-doping iron salt and lanthanum salt, and it was characterized for its application in the activation of persulfate (PS) in the degradation of Florfenicol (FLO). The results indicated that the LaMBC/PS system consistently achieved a degradation efficiency of over 99.5 %, with a reaction rate constant 4.71 times as that of MBC. The mechanism of FLO degradation suggested that O2•- and •OH played dominant roles, contributing 40.92 % and 36.96 %, respectively, during FLO degradation. Through physicochemical characterization and quenching experiments, it can be concluded that the key reasons for the enhancement of MBC activation performance are as follows: (1) Lanthanum doping in magnetized biochar increased the Fe(II) content in MBC. (2) Lanthanum doping significantly improved the adsorption capacity of LaMBC, increased the concentration of pollutants on the catalyst surface and effectively enhancing the reaction rate. (3) Lanthanum doping effectively increased the surface Fe(II) content during the reaction process in LaMBC, promoted the generation of active oxygen species in PS. This study delves into synthesizing and applying LaMBC for PS activation and FLO removal. The emphasis is on comprehensively characterizing and experimenting to elucidate the mechanism, proposing an innovative approach for efficiently degrading antibiotic wastewater.

Efficiently catalytic degradation of tetracycline via persulfate activation with plant-based biochars: Insight into endogenous mineral self-template effect and pyrolysis catalysis

Endogenous mineral of plant such as potassium, calcium and iron may play a crucial role in boosting the physicochemical structure and catalytic activity of high temperature pyrolyzed plant-based biochar while it is often neglected owing to its relative less content. Herein, self-template pyrolyzed plant-based biochars were prepared from two different ash-contained agricultural wastes of peanut hull (PH, 3.2% ash) and cotton straw (CS, 0.8% ash), and aimed at investigating the relationship among the endogenous mineral fractions of plant-based biomass, physicochemical active structure and persulfate (PS) catalytic degradation activity for tetracycline (TC). The results of energy/spectral characterization showed that under the self-template effect and pyrolysis catalysis of endogenous minerals, PH biochar (PBC) possessed much more specific surface area, conjugated graphite domain, C=O and pyrrolic-N surface active functional sites than CS biochar (CBC), enhancing TC removal rate of PBC/PS to 88.37%, twice that of CBC/PS (44.16%). Meanwhile, reactive oxygen quenching and electrochemical experiments showed that electrons transfer and non-free radical pathways based on singlet oxygen contributed 92% of TC removal in PBC/PS system. Remarkably, by comparing the differences in structure and TC removal performance of pre-deashing and non-deashing prepared plant-based biochars, a possible mechanism for endogenous mineral components' self-template effect and pyrolysis catalysis role of plant-based biomass was proposed. This study provides a new insight for revealing the intrinsic mechanism of mineral elements enhancing the active surface structures and catalytic properties of plant-based biochars derived from distinct feedstocks.

Effect of Mn-based magnetic biochar /PS reaction system on oxidation of metronidazole

In order to fully exploit the potential of magnetic biochar-based persulfate (PS) systems, Mn was utilized to modify the magnetic biochar-based catalysts through impregnation-pyrolysis method. Taking metronidazole (MNZ), a typical antifungal drug, as the target contaminant, the reactivity of the synthesized magnetic biochar (MMBC) catalyst was evaluated. The degradation efficiency of MNZ in MMBC/persulfate system was 95.6%, which was 13.0 times higher than that in MBC/PS system. The characterization experiments confirmed the degradation of metronidazole by surface binding free radicals, the ·OH and 1O2 played the key role in remove of MNZ in the system of MMBC/PS. Physicochemical characterization, Fe(II) semi-quantitative analysis and masking experiments confirmed that the doping of MBC with Mn increased its Fe(II) content (43.0 mg/g), approximately 7.8 times higher than that of pristine MBC. The increase of Fe(II) content in MBC is the key reason to improve the optimization of MBC modified with Mn. Simultaneously, both Fe(II) and Mn(II) were the key components of PS activation by magnetic biochar. This paper presents a method to optimize the high efficiency of PS activation by magnetic biochar.

Peroxymonosulfate activation by CuFe-prussian blue analogues for the degradation of bisphenol S: Effect, mechanism, and pathway

The fenton-like process based on peroxymonosulfate (PMS) activation is considered as a promising strategy for the removal of organic pollutants. However, the development of efficient photocatalysts for PMS activation remains challenging. Herein, copper-iron prussian blue analogue (Cu_nFe₁-PBA, n = 1, 2, 3, 4) nanomaterials were first fabricated through a simple combination of co-precipitation and calcination processes. The as-synthesized Cu_nFe₁-PBA composite catalyst was used to activate PMS for the degradation of endocrine disruptor bisphenol S (BPS). As the result, Cu₃Fe₁-PBA calcined at 300 °C (Cu₃Fe₁-PBA*300 °C) mainly composed of CuFe₂O₄ and CuO showed a higher catalytic activity for activating PMS for BPS degradation than those of Cu_nFe₁-PBA composite. Additionally, Cu₃Fe₁-PBA*300 °C/PMS system was suitable for degradation of BPS at 400 mg/L catalyst or PMS and wide pH ranges from 3 to 11 while coexisting inorganic anions (SO₄^2-, NO₃^-, and HCO₃^-) and humic acid all inhibited the reaction. Radical trapping experiment, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) proved that Cu and Fe could regulate the charge balance through changes of valence state, and active PMS to produce free radicals effectively, especially the production of ¹O₂. Furthermore, the analysis of the BPS intermediates of degradation was carried out by ultra-performance liquid chromatography-mass spectrometry, and two degradation pathways of BPS were proposed. In summary, this work provides a facile avenue to design efficient catalysts to activate PMS for the degradation of emerging organic pollutants in water remediation.