Biochar最新文献

Important properties of biochar as an effective soil amendment are its high water-holding capacity (WHC) and inhibition of water evaporation. However, the mechanism and the importance of biochar properties in controlling its own WHC and bound water evaporation remain little known. In this study, wheat straw and pine sawdust biochars were pyrolyzed in N₂-flow, CO₂-flow, and air-limitation environments at 300–750 ℃, and a series of the produced biochars’ properties were characterized to explore the dominant controlling factors of their WHC and bound water evaporation. The results have shown that with the increasing contents of hydrogen, nitrogen, and oxygen as well as such ratios as H/C, and (O + N)/C, WHC of the biochars was also increasing while the evaporation of biochar-bound water was decreasing. With an increase in the other studied factors, such as carbon content, pH, and specific surface area (SSA), WHC of the biochars was decreasing, and the evaporation of biochar-bound water was increasing. That was connected with the fact that biochar-nitrogen was mainly in pyridinic and pyrrolic forms, while oxygen was in the form of C = O and C–O bonds. These forms of nitrogen and oxygen could be the receptors of hydrogen bonds to link to H₂O molecules. Aliphatic hydrogen with a weak positive charge could be a donor of hydrogen bonds to link to H₂O molecules. However, high carbon content, as well as high SSA, indicated more exposed aromatic carbon (hydrophobic sites) that could suppress the binding of H₂O molecules. Additionally, high pH indicated that H₂O molecules were dominated by OH^–, which generated strong electrostatic repulsion with the negatively charged nitrogen- and oxygen-containing groups of biochar. It was also shown that the nitrogen-containing groups played a more important role (importance – 0.31) in WHC of the biochar than other parameters, including carbon, oxygen, hydrogen, ash contents, pH, SSA (importance from 0.02 to 0.09). Nitrogen, oxygen, and carbon contents had the most important influence on the evaporation of biochar-bound water in all studied factors. Furthermore, wheat straw biochar produced at low pyrolysis temperatures in N₂ atmosphere (with high nitrogen and oxygen contents) had the highest WHC and the lowest evaporation of biochar-bound water. Consequently, it can be suggested that biochar rich in nitrogen can be an effective water retention agent and can improve agricultural soil moisture.

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Arsenic (As) detoxification in polluted soils by iron-based materials can be mediated by the endogenous soil organic matter (SOM), nevertheless the mechanisms remain unclear. Herein, endogenous SOM in a paddy soil was substantially removed to understand its roles on As immobilization by biochar-supported zero-valent iron (ZVI/BC). The results demonstrated that ZVI/BC application significantly decreased As bioavailability by 64.2% compared with the control soil under the anaerobic condition. XPS and HR-TEM suggested As immobilization by ZVI/BC mainly invoked the formation of ternary complexes (i.e., As-Fe-SOM). However, SOM depletion compromised the efficacy of ZVI/BC for As immobilization by 289.8%. This is likely because SOM depletion increased the fulvic acid and OH⁻ contents in soils. Besides, ZVI/BC increased the proportion of As(III) in available As fraction, but SOM depletion altered the mechanisms associated with As(V) reduction. That is, As(V) reduction resulted from the reductive capacity of ZVI in the pristine soil, but the As(V)-reducing bacteria contributed greater to As(V) reduction in the SOM-depleted soil. Additionally, SOM depletion boosted the abundances of Fe(III)- and As(V)-reducing bacteria such as Bacillus and Ammoniphilus in soils, which enhanced the dissimilatory arsenate reduction. Thus, this work highlighted the importance of SOM in the remediation of As-contaminated soils by ZVI/BC.

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Abstract

The swift advancement of sustainable energy technologies, coupled with the urgent need to address environmental challenges, has generated considerable interest in the multifaceted applications of biochar materials to promote energy, water, and environmental sustainability. This comprehensive review examines recent advancements in the production and applications of functionalized biochar materials, emphasizing their pivotal roles in energy conversion and storage, wastewater treatment, CO₂ reduction, soil amelioration, and the promotion of carbon neutrality within a circular economy framework. The functionalization of biochar materials involves surface chemistry and porosity modifications, achieved through techniques like templating, chemical activation, metal impregnation, or heteroatom doping. These modifications substantially enhance the catalytic activity, energy storage capacity, and cycling stability of biochar materials, making them particularly effective in diverse energy applications such as water splitting, fuel cells, and supercapacitors. Additionally, functionalized biochar materials demonstrate remarkable efficacy as catalysts and adsorbents in wastewater treatment, proficiently removing pollutants like heavy metals, organic contaminants, and nutrients, thereby facilitating resource recovery from wastewater. The review also underscores the potential of functionalized biochar materials in CO₂ capture and conversion, exploring innovative strategies to augment their CO₂ adsorption capacity and state-of-the-art catalytic processes for transforming captured CO₂ into valuable fuels and chemicals. In summary, this review offers valuable insights into the recent advancements in biochar research, underscoring its substantial commercial potential as a versatile material contributing to a cleaner and more sustainable future.

Article Highlights

• The current status of biochar research is comprehensively reviewed.

• The potential of biochar in energy, water, and environmental fields is critically examined.

• Technology readiness levels (TRLs) of various biochar-based technologies are evaluated.

The global environmental issue of soil contamination with antibiotic-resistance genes has garnered increased attention in recent years due to its impact on ecosystems and human health. Despite this recognition, researchers face challenges in comprehensively understanding the mechanisms underlying the production and dissemination of soil resistance genes, particularly in relation to their implications for human health. This lack of understanding poses a barrier to the development of effective and precise control strategies. Biochar, a sustainable material, exhibits favorable adsorption properties characterized by its large pores and specific surface area. Therefore, we propose to explore the potential application of biochar addition in soil resistance gene management. In order to establish a solid research foundation in this area, in this paper we review the mechanisms underlying the generation and accumulation of soil resistance genes over the last decade, along with their transmission pathways and interfacial interactions. Biochar may help repair soil resistance genes by affecting factors like antibiotic levels, environmental conditions, enzymatic activity, and gene migration mechanisms, opening up new research possibilities.

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Anaerobic digestion (AD) was initially evaluated as a potential preprocessing method for preparing biomass-based carbon electrocatalysts in this study. The AD pretreatment succeeded in the structural depolymerization and nitrogen enrichment of Hybrid Pennisetum, which provided favorable conditions to achieve efficient and homogeneous nitrogen introduction due to microorganism community enrichment and provided a porous structure by degradation of the biodegradable components. The resulted biochar exhibited improved physiochemical properties including higher specific surface areas, nitrogen content and graphitization degree than that obtained from pyrolyzing raw biomass. These improvements were positively correlated with the AD time and showed to have enhanced the performance in oxygen reduction reaction and practical microbial fuel cell applications. Amongst the investigated samples, the obtained biochar pretreated by AD for 15 days exhibited the most excellent performance with an onset potential of 0.17 V (VS. saturated calomel electrode) and the maximal power density of 543.2 mW cm⁻² assembled in microbial fuel cells. This study suggested applying AD as a new biological pretreatment in the preparation of biomass-based electrocatalysts, and provided a unique pathway for fabricating high-performance biochar-based catalysts by structure optimization and N-containing active sites construction via gentle biological method, thereby providing a cost-effective method to fabricate metal-free catalysts for oxygen reduction reaction.

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Bamboo biochar was modified by lignin impregnation and microwave irradiation to enhance its performance for CO₂ capture. The pore structure of lignin-impregnated biochar was significantly affected by the impregnation ratio. The maximum specific surface area of 377.32 m² g⁻¹ and micropore volume of 0.163 cm³ g⁻¹ were observed on the biochar with an impregnation ratio of 1:20 (mass ratio of lignin to biochar). Lignin impregnation increased the CO₂ adsorption capacity of biochar up to 134.46 mg g⁻¹. Correlation analysis confirmed the crucial role of biochar’s pore structure in adsorption. The Avrami model fitted the CO₂ capture curves well. The calculation of adsorption activation energy suggested that the adsorption process was dominated by physical mechanism assisted with partial chemical mechanism. Meanwhile, Langmuir isotherm analysis indicated that lignin impregnation transformed the larger pores of biochar into more uniform micropores, thereby making the adsorption process closer to monolayer adsorption. Both the high reusability (89.79–99.06%) after 10 successive cycles and the excellent CO₂ selectivity in competitive adsorption confirmed that lignin-impregnated biochar is an outstanding adsorbent for CO₂ capture.

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One strategy to reduce CO₂ emissions from cement production is to reduce the amount of Portland cement produced by replacing it with supplementary cementitious materials (SCMs). Biochar is a potential SCM that is an eco-friendly and stable porous pyrolytic material. However, the effects of biochar addition on the performances of Portland cement composites are not fully understood. This meta-analysis investigated the impact of biochar addition on the 7- and 28-day compressive strength of Portland cement composites based on 606 paired observations. Biochar feedstock type, pyrolysis conditions, pre-treatments and modifications, biochar dosage, and curing type all influenced the compressive strength of Portland cement composites. Biochars obtained from plant-based feedstocks (except rice and hardwood) improved the 28-day compressive strength of Portland cement composites by 3–13%. Biochars produced at pyrolysis temperatures higher than 450 °C, with a heating rate of around 10 C min^-1, increased the 28-day compressive strength more effectively. Furthermore, the addition of biochar with small particle sizes increased the compressive strength of Portland cement composites by 2–7% compared to those without biochar addition. Biochar dosage of < 2.5% of the binder weight enhanced both compressive strengths, and common curing methods maintained the effect of biochar addition. However, when mixing the cement, adding fine and coarse aggregates such as sand and gravel affects the concrete and mortar's compressive strength, diminishing the effect of biochar addition and making the biochar effect nonsignificant. We concluded that appropriate biochar addition could maintain or enhance the mechanical performance of Portland cement composites, and future research should explore the mechanisms of biochar effects on the performance of cement composites.

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The Boudouard reaction presents promising application prospects as a straightforward and efficient method for CO₂ conversion. However, its advancement is hindered primarily by elevated activation energy and a diminished conversion rate. This study employed a microwave reactor with a variable frequency as the initial approach to catalyze the CO₂ Boudouard reaction over biochar, with the primary objective of producing renewable CO. The study systematically investigated the influence of various variables, including the heating source, microwave frequency, microwave power, gas hourly space velocity (GHSV), and carrier gas, on the conversion of CO₂ and the selectivity towards CO. The experimental findings indicate that under static conditions, with a fixed microwave frequency set at 2450 MHz and 100 W microwave power, the Boudouard reaction did not initiate. Conversely, a CO₂ conversion rate of 8.8% was achieved when utilizing a microwave frequency of 4225 MHz. Under this unique frequency, further elevating the microwave power to 275 W leads to the complete conversion of CO₂. Furthermore, a comparative analysis between microwave and electrical heating revealed that the CO production rate was 37.7 μmol kJ⁻¹ for microwave heating, in stark contrast to the considerably lower rate of 0.2 μmol kJ⁻¹ observed for electric heating. Following the reaction, the biochar retained its robust 3D skeleton structure and abundant pore configuration. Notably, the dielectric constant increased by a factor of 1.8 compared to its initial state, rendering it a promising microwave-absorbing material.

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Soil contamination by uranium presents a burgeoning global environmental concern, exerting detrimental effects on both agricultural production and soil health. Biochar, a carbonaceous material derived from biomass pyrolysis, exhibits considerable potential for remediating uranium-contaminated soils. However, a comprehensive review of the effects of biochar on the fate and accumulation of uranium in soil–plant systems remains conspicuously absent. In this paper, uranium sources and contamination are reviewed, and the impact of biochar on uranium immobilization and detoxification in soil–plant systems is analyzed. We reviewed the status of uranium contamination in soils globally and found that mining activities are currently the main sources. Further meta-analysis revealed that biochar addition significantly reduced the soil uranium bioavailability and shoot uranium accumulation, and their effect value is 58.9% (40.8–76.8%) and 39.7% (15.7–63.8%), respectively. Additionally, biochar enhances the soil microenvironment, providing favourable conditions for promoting plant growth and reducing uranium mobility. We focused on the mechanisms governing the interaction between biochar and uranium, emphasising the considerable roles played by surface complexation, reduction, ion exchange, and physical adsorption. The modification of biochar by intensifying these mechanisms can promote uranium immobilisation in soils. Finally, biochar alleviates oxidative stress and reduces uranium accumulation in plant tissues, thereby mitigating the adverse effects of uranium on plant growth and development. Overall, our review highlights the capacity of biochar to remediate uranium contamination in soil–plant systems through diverse mechanisms, providing valuable insights for sustainable environmental remediation.

Highlights

• Biochar reduces uranium mobility through a variety of mechanisms, including surface complexation, reduction, ion exchange, and physical adsorption.

• Biochar significantly reduces uranium bioavailability in soil and limits its accumulation in plants.

• Modified biochar has been shown to enhance its effectiveness in immobilising uranium.

• Biochar application to soil not only promotes uranium remediation but also improves soil quality.

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