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Nowadays, the soil arsenic pollution is considered as a serious environmental issue, and the high toxicity of arsenic can seriously affect the quality and safety of agricultural products and human health. Biochar, as a solidifying/passivating agent, has been widely used in the treatment of soil heavy metal pollution. Pine biochar (BC) was used as a carrier in this study, and biochar-loaded nano-zirconia (N-ZrO2-BC) was synthesized to investigate its adsorption and fixation characteristics on As (V) in soil and water. The adsorption experiment showed that the second-order kinetic equation had a good fitting effect on the adsorption curve of As (V) on the N-ZrO2-BC surface, which indicated that chemical adsorption was the main factor controlling the reaction rate. FTIR and SEM results showed that ion exchange and surface complexation were the main mechanisms of As (V) adsorption by N-ZrO2-BC. Soil culture experiments showed that the stabilization efficiency of arsenic in soil with 2% N-ZrO2-BC reached 99.30% after 60 days, and the extractable arsenic content was reduced to 3.07 μg·L-1, which reached the quality standard of class III groundwater (<0.01 mg·L-1, GB/T 14848-2017). Comparing with the control, the content of acid extractable arsenic in soil decreased by 90.57%, and the residual arsenic increased by 51.46%, indicating that the addition of N-ZrO2-BC could effectively promote the transformation of active arsenic to stable arsenic in soil. [ABSTRACT FROM AUTHOR]

In order to solve the problem that the traditional biochar(BC) has insufficient removal ability of enrofloxacin and TiO2 is difficult to recycle. In this study, TiO2-modified biochar composites were prepared by impregnation method. Through characterization analysis, The BET specific surface area results indicated that after loading TiO2, the specific surface area of TiO2-biochar(Ti-BC), TiO2-ironized biochar(Ti-FBC) and TiO2-alkaline biochar(Ti-KBC) increased by 4.34, 10.43 and 11.52 times, respectively. The analysis results of SEM, EDS, FT-IR, XRD and XPS showed that TiO2 was supported on biochar in the anatase state. The UV-vis DRS measurement showed that the band width of Ti-KBC was the smallest and the best catalytic activity. Under 15 W UV lamp (254 nm) irradiation, the photocatalytic degradation process of enrofloxacin by different biochar accords with the first-order kinetic equation. Ti-KBC showed best degradation effect under different initial concentrations of enrofloxacin. When the pH of the solution was 5.0 and the dosage of Ti-KBC was at 2.5 g·L−1, the enrofloxacin degradation rate of 100 mg·L−1 reached 85.25%. The quenching test confirmed that the active substance O2•— played a major role in the photocatalytic degradation process. After five cycles of the test, the degradation rate of Ti-KBC for enrofloxacin was 77.14%, which was still better than that of BC, Ti-BC and Ti-FBC. [ABSTRACT FROM AUTHOR]

The levels of enrofloxacin have exceeded acceptable standards in the water environment of many global regions, and the problem of pollution caused by enrofloxacin needs to be solved urgently. In this study, phosphoric acid and potassium hydroxide were used to modify corn stalk biochar. The properties and structure of the modified biochar were studied by scanning electron microscopy, infrared spectrometer, X-ray diffraction spectroscopy, and other analytical methods. Other factors influencing enrofloxacin adsorption were assessed using the equilibrium adsorption method. The surface area of the acid- and alkali-modified biochar was found to increase 10- and 14-fold, respectively. The equilibrium adsorption capacity of enrofloxacin on the acid- and alkali-modified biomass carbon increased by 27.80% and 54.08%, respectively. The quasi-second-order kinetic equation and Langmuir equation described the adsorption process of the biochars accurately. At pH = 5.0, the biochars had the highest levels of enrofloxacin adsorption. The adsorption of enrofloxacin onto the biochars negatively correlated with the concentration of Ca2+ in the background solution. [ABSTRACT FROM AUTHOR]

Biochar plays an important role in the behaviors of organic pollutants in the soil environment. The role of humic acid (HA) and metal cations on the adsorption affinity of polychlorinated biphenyls (PCBs) to the biochars in an aqueous medium and an extracted solution from a PCBs-contaminated soil was studied using batch experiments. Biochars were produced with pine needles and wheat straw at 350 °C and 550 °C under anaerobic condition. The results showed that the biochars had high adsorption affinity for PCBs. Pine needle chars adsorbed less nonplanar PCBs than planar ones due to dispersive interactions and separation. Coexistence of HA and metal cations increased PCBs sorption on the biochars accounted for HA adsorption and cation complexation. The results will aid in a better understanding of biochar sorption mechanism of contaminants in the environment. [Copyright &y& Elsevier]

Chemical immobilization of heavy metals is a simple, low-cost, and environment-friendly technology for remediation of heavy metals contaminated soils. However, changes in environmental conditions, such as water management, acid deposition, temperature fluctuation, etc., might result in release of metal ions from the fixation sites, and the long-term stability of immobilization remediation is unclear. This study attempted to investigate the impact of water management strategies (wetting-drying cycle and dry cycle) on the stability of heavy metal immobilization by one-time application of biochar during 3 consecutive years of rice-wheat crop in Cu/Cd-contaminated soil. The transformation and accumulation of Cd and Cu in soil-crop system and the morphololgy and composition of biochar were analyzed. The results revealed that wetting-drying cycle and drying treatments reduced the contents of available Cd and Cu in soil by 15.9%–17.7% and 23.9%–31.5% and by 19.8%–62.7% and 16.1%–65.0%, as well as increased soil pH by 0.11–0.31 and 0.17–0.56, respectively. In the wetting-drying cycle treatment, biochar was more favorable for decrease in Cd and Cu accumulation in crop, when compared with that in dry treatment; however, the differences were insignificant in the subsequent years. Although the different water management strategies had no obvious effect on the soil total C, physicochemical analysis of the biochar collected after pot experiments indicated that the obvious structural decomposition of biochar in the drying treatment may have resulted in the release of heavy metals immobilized in biochar. These findings help in better understanding of the long-term immobilization mechanism of biochar in soil-plant system. • Biochar immobilized more Cd and Cu under wetting-drying cycle than under drying. • The aging degree of biochar under drying was stronger than wetting-drying cycle. • The Cd and Cu immobilization stability by biochar decreased with time. [ABSTRACT FROM AUTHOR]

In this study, the photogeneration of reactive oxygen species (ROS) from biochar suspension was investigated. The characterizations of biochar particles before and after photochemical reactions were analyzed by using FTIR, Raman, XPS and electron paramagnetic resonance (EPR) techniques. It was found that the model pollutant diethyl phthalate (DEP) was efficiently degraded and partially mineralized under UV and simulated solar lights in biochar suspension, with hydroxyl radicals ( OH) and singlet oxygen ( 1 O 2 ) as the dominant ROS. EPR coupled with chemical probe methods and free radical quenching studies were used to quantify and elucidate the formation mechanism of OH and 1 O 2 . The results indicated that biochar carbon matrix (BCM) accounted for 63.6%–74.6% of OH and 10%–44.7% of 1 O 2 formation, while dissolved organic matter (DOM) derived from biochar generated 46.7%–86.3% of 1 O 2 and 3.7%–12.5% of OH. BCM-bound persistent free radicals (BCM-PFRs) and quinone-like structure of BCM (BCM-Q) were the predominant factors affecting OH and 1 O 2 formation from BCM under light. Detailed ROS generation pathways are proposed as: (i) DOM from biochar particles contributes to OH and 1 O 2 formation via light-induced energy and electron transfer processes; (ii) BCM-Q forms excited triplet states ( 3 [BCM-Q]*) under light irradiation and induces the formation 1 O 2 ; (iii) UV promotes the formation of BCM-PFRs, which transfer electrons to oxygen to form superoxide anion radical (O 2 − ), further yielding H 2 O 2 ; and (iv) H 2 O 2 -dependent pathways including BCM-PFRs activation and photo-Fenton reaction are primarily responsible for OH production. Furthermore, BCM exhibits the excellent reusability towards DEP degradation during the three cycles under light. [ABSTRACT FROM AUTHOR]

In heterogeneous electro-Fenton process, the design of electrocatalysts for in-situ generation of H 2 O 2 and efficient conversion to •OH remains a challenge. Herein, a simple one-step pyrolysis strategy has been developed to synthesize green and stable dual-functional electro-catalysts from agricultural wastes. The biochar of soybean roots (RSBC) with ample -COOH and C-O-C functional groups exhibited considerable capacity for H 2 O 2 production (21.6 mM at −0.4 V vs RHE), and the dual-functional electron-catalyst exhibits an excellent catalytic reaction for antibiotics removal (100 % cloroquine phosphate with k obs =0.035 min−1). The ultra-small MnO nanoclusters (<2 nm) in the biochar of Phytolacca americana leaves (LPBC) were the active center via the transfer of electrons between adsorbed H 2 O 2 and Mn atoms to produce reactive •OH, as identified by operando X-ray absorption fine structure (XAFS) spectroscopy and density functional theory calculations. This work provides a new direction in the design of dual-functional carbon cathode catalysts for environmental remediation. [Display omitted] • A Cost effective strategy to fabricate GDE derived from agricultural wastes for H 2 O 2 synthesis via 2e ORR. • Facile pyrolysis treatment for the synthesis of ultra-small MnOx cluster derived from Phytolacca americana leaves. • The ultra-small MnOx cluster (<2 nm) can efficiently convert H 2 O 2 into •OH in HEF system. • Extraordinary activity and stability of the dual-functional cathode for organic pollutant degradation. [ABSTRACT FROM AUTHOR]

• The positively charged γ-Al 2 O 3 neutralized the negative surface charge of biochar. • Sorption experiments showed that at pH 7.5 the Zn sorption capacity followed the order: γ-Al 2 O 3 >mixture>biochar, which was reversed at pH 5.5. • Biochar depressed Zn-Al LDH precipitation in a mixture of biochar + γ-Al 2 O 3. • Al released from γ-Al 2 O 3 was sorbed in parallel with Zn on biochar to form Zn-Al silicate, rather than forming Zn-Al LDH on the γ-Al 2 O 3 surface. Biochar system technology has been proved as a sustainable remediation method for metal contaminated soils. However, little attention has been paid to the interaction between biochar and oxide minerals and their influence on metal immobilization in soils. In this study, batch-type Zn sorption experiments were conducted using the mixture of γ-Al 2 O 3 and rice straw biochar as a model binary geosorbent systems. In addition, advanced spectroscopic technics such as EXAFS, FTIR and XRD were performed to reveal the mechanism. EXAFS spectroscopy revealed that 62% of Zn existed as Zn-Al layered double hydroxide (LDH) on γ-Al 2 O 3 at pH 7.5 (for 2 mM Zn loading) within 24 h, which was 19% in the mixture. The Zn in biochar samples mainly existed as Zn-OM (53%–76%) and Zn 2 SiO 4 (21%–47%), while the proportion of Zn 2 SiO 4 (0–6%) was negligible compared with Zn-Al silicate (26–48%) in the mixtures. The overall findings confirmed that Al released from γ-Al 2 O 3 was sorbed in parallel with Zn on biochar to form Zn-Al silicate, rather than Zn-Al LDH on the γ-Al 2 O 3 surface. These results unveiled the dynamic interactions between amended biochar and soil oxide minerals which can significantly affect the immobilization pathways of metals in contaminated soils. [ABSTRACT FROM AUTHOR]

Engineered biochar represents a promising material for green remediation practices. In this paper, we present an innovative approach to produce MnO x -loaded biochars by pyrolyzing the biomass of a Mn-hyperaccumulator species (Phytolacca americana). Batch sorption and stirred-flow kinetic experiments were combined with spectroscopic techniques to elucidate the mechanisms behind the Cd sorption onto those biochars, named here as PABCs. The incorporation of MnO x into the PABCs increased their surface densities of oxygen-containing functional groups. The average Mn leaching (< 9%) from PABCs was lower than that measured for the non-pyrolyzed biomass of P. americana (30–43%). PABCs pyrolyzed at 500 °C had Cd sorption capacities as high as 212–337 mg/g, which achieved by far the best performance reported for biochar materials. The stirred-flow experiments showed that MnO x loading was instrumental in increasing both the Cd sorption onto PABCs as well as its irreversibility. Extended X-ray absorption fine structure spectroscopy revealed that the Cd immobilization occurred mainly through its association with organic matter (Cd-OM) and, to a lesser extent, with carbonate (CdCO 3) and MnO x (Cd-MnO x). In short, MnO x -loaded biochar prepared from the biomass of a Mn-hyperaccumulator species proved to be an effective, sustainable, and eco-friendly material for remediating Cd-contaminated waters. [Display omitted] • Engineered biochars were prepared from Mn hyperaccumulator (PABC). • Carbonization increased the stability of Mn in PABCs. • PABCs pyrolyzed at 500 °C were high-efficient sorbents for Cd. • The presence of MnO x increased the sorption and decreased the desorption of Cd. [ABSTRACT FROM AUTHOR]

The stabilization of heavy metals adsorbed in the spent biochar remains a challenge, and the risk of secondary pollution under environmental changes will rise under inadequate post-treatment. Moreover, the safe and sufficient re-utilization of the spent biochar with heavy metals loaded have attracted extensive attention. In this research, the performance and mechanism of rice straw biochar (RSBC) pyrolyzed at different temperature for nickel and cobalt adsorption were investigated, and the stabilization of the adsorbed heavy metals was achieved via a simple two-step strategy: the adsorption of metal ions and the hydrothermal process to form the stable layered double hydroxides (LDH) on biochar, with a leaching rate below 0.005% evaluated by EPA toxicity characteristic leaching procedure (TCLP). Meanwhile, the stabilized RSBC-LDH can be reused as an excellent catalyst in the activation of peroxymonosulfate (PMS) to degrade organic pollutants efficiently. This work eliminated the risk of heavy metal desorption from the spent biochar, and enabled a new strategy for the optimized utilization of biochar in environmental remediation. [Display omitted] • Co2+ and Ni2+ adsorbed in biochar are stabilized to form stable LDH. • TCLP leaching rate decrease from 60% to 0.005% after stabilization. • RSBC-LDH can be reused as an activator for PMS to degrade organic pollutants. • The risk of secondary pollution from the spent biochar was eliminated. [ABSTRACT FROM AUTHOR]

Microbial remediation is an inherently eco-friendly and promising approach, if it can be implemented properly. One important approach advancing microbial remediation is the immobilization technology with carbonaceous materials (CMs), i.e., biochar, activated carbon, carbon nanotubes, graphene, and its derivatives as carriers. Carbonaceous carriers for functional microbes pyramid the advantages of highly-efficient physiochemical sorption and microbial metabolisms. This review focuses on the synthesis of microorganisms (e.g., metal-resistant microorganisms and organic pollutant-degraders)-CMs immobilized complexes (McMICs) and their potential applications in environmental pollution control. Among different CMs, biochar and activated carbon have been popularly utilized for cell immobilization due to their low toxicity and abundant feedstock. Immobilized cells normally exhibit higher removal efficiency for a variety of pollutants than CMs alone or free cells. The immobilization of metal-tolerant microorganisms on CMs could directly enhance metals removal efficiencies or indirectly ameliorate soil contamination by promoting the phytoremediation effect. Particularly, immobilized cells have been extensively applied in the treatment of organic pollutants. The removal efficiency of McMICs could be enhanced more than 8-fold synergistically by physiochemical sorption and microbial degradation as reported. Studies have also placed an emphasis on the roles of key determining factors like temperature and pH in the relevant bioremediation processes. Importantly, McMICs possessed higher stability than free cells and excellent reusability in bioremediation processes. Future challenges in this area include the selection of novel, effective and low-cost carbonaceous carriers and expansion of McMICs's environmental applications. Overall, this work improves our understanding of engineering pathways to the industrial applications of McMICs. [Display omitted] • Biochar and activated carbon were widely utilized for cell immobilization. • Immobilized cells normally exhibited higher removal efficiency for various pollutants than CMs alone or free cells. • Immobilized cells possessed higher stability and excellent reusability than free cells. [ABSTRACT FROM AUTHOR]

• New toxicant disclosed in biochar from biomass with high alkali salt. • Theoretical calculation confirms metal cyanide (MCN) formation. • A model for prediction of MCN within biochar is developed. • Alkali carbonate in biomass greatly promotes MCN formation. • Metal chloride in biomass significantly inhibits MCN formation. With the aim to develop optimized biochar with minimal contaminants, it is important significance to broaden the understanding of biochar. Here, we disclose for the first time, a highly toxic substance (metal cyanide, MCN, such as KCN or NaCN) in biochar. The cyanide ion (CN−) content in biochar can be up to 85,870 mg/kg, which is determined by the inherent metal content and type in the biomass with K and Na increasing and Ca, Mg and Fe decreasing its formation. Density functional theory (DFT) analysis shows that unstable alkali oxygen-containing metal salts such as K 2 CO 3 can induce an N rearrangement reaction to produce for example, KOCN. The strong reducing character of the carbon matrix further converts KOCN to KCN, thus resulting biochar with high risk. However, the stable Mg, Ca and Fe salts in biomass cannot induce an N rearrangement reaction due to their high binding energies. We therefore propose that high valent metal chloride salts such as FeCl 3 and MgCl 2 could be used to inhibit the production of cyanide via metal interactive reaction. These findings open a new point of view on the potential risk of biochar and provide a mitigation solution for biochar's sustainable application. [ABSTRACT FROM AUTHOR]