Biochar-supported nanomaterials for environmental applications

Characteristics and life cycle carbon emission reduction potential of waste recycling after implementing new waste classification policy in China: From case study to national perspective

Under the background of resource shortage and global warming, it is of great significance to explore the status, influencing factors and carbon emission reduction effect of waste recycling in China after the implementation of new waste classification policy for guiding waste classification and carbon emission accounting. In this research, the temporal and spatial changes and influencing factors of waste recycling were studied from subdistrict level, life-cycle carbon emission reduction was predicted and policy suggestions for waste recycling were proposed. The results showed that after the implementation of new waste classification policy, the amount of recycled waste and the proportion of low-value recycled waste increased by 420.93 t and 2.29 % per month on average, respectively. The district center has the largest amount of recycled waste. Income was the main factors affecting waste recycling, and online shopping and takeout could become important sources of recyclable waste. Accounting cradle-to-grave life cycle carbon footprint, waste plastics takes up the most contribution, accounting for 39.11 %, and nearly 391.68 Mt CO2eq would be reduced by waste recycling in China by 2030. Therefore, in the process of waste classification, refining waste classification to increase the amount of low-value recyclables, and rationally deploying collection and transportation vehicles to ensure efficient waste recycling are of great significance to achieve the goal of "carbon peaking and carbon neutrality".

Advances in waste-derived functional materials for PFAS remediation

Per- and polyfluoroalkyl substances (PFAS) are synthetic organofluoride compounds, widely used in industries since the 1950s for their hydrophobic properties. PFAS contamination of soil and water poses significant environmental and public health risks due to their persistence, chemical stability, and resistance to degradation. The Chemical Abstracts Service catalogs approximately 4300 PFAS globally. Research in various regions such as North America, Asia, Europe, and remote polar zones has revealed the accumulation of perfluorooctane sulfonate (PFOS) in the tissues of various animal species, with concentrations reaching up to 1900 ng/g in aquatic species like dolphins and whales. Researchers have employed various remediation techniques such as solvent extraction, ion exchange, precipitation, adsorption, and membrane filtration, each of which has its drawbacks. Adsorption, particularly using waste-derived functional materials like biochar, is emerging as a promising method for PFAS remediation due to its cost-effectiveness and sustainability. For example, waste timber-derived biochar exhibits adsorption efficiency comparable to commercial activated carbon. This review highlights advancements in using agricultural, industrial, and biological waste-derived materials for sustainable PFAS remediation. We discuss innovative modification techniques like hydrothermal synthesis, pyrolysis, calcination, co-precipitation, the sol-gel method, and ball milling. The study also examines adsorption mechanisms, factors affecting adsorption efficiency, and the technological challenges in scaling up waste-derived material use. It aims to explore developments, challenges, and future directions for using these materials for efficient PFAS remediation and contributing to sustainable environmental cleanup solutions.

Remediation of chromium contaminated water and soil by nitrogen and iron doped biochars

Chromium (Cr) is a toxic and redox-sensitive contaminant that has accumulated in water and soil systems, becoming a serious issue worldwide. Producing novel remedial materials with enhanced removal efficiency from plentiful available sources is a pleasing aspect for Cr removal. This review explores valuable insights into the production of nitrogen doped biochar (N/BC), iron doped biochar (Fe/BC), and iron‑nitrogen doped biochar (Fe-N/BC) and their application for Cr (trivalent (Cr(III)) and hexavalent (Cr(VI)) removal. Specifically, this review focuses on conferring knowledge about producing environmentally friendly N and Fe doped BCs with enhanced surface functionalities, physicochemical properties, and holding capacities for removing Cr(VI) through adsorption and reduction. Affecting factors for Cr(VI) removal by N/BC, Fe/BC, and Fe-N/BC through reviewing the literature on the reaction system pH, mass transfer driving forces, effect of coexisting ions, BC production conditions, and redox potential are overviewed. Notably, isotherm and kinetic models and removal mechanisms of Cr(VI) by N/BC, Fe/BC, and Fe-N/BC with the assistance of characterization analyses, experimental results, and computational modeling methods are explored. Finally, the regeneration, cost evaluation, and environmental implications, as well as the real-world applications and environmental risks of N/BC, Fe/BC, and Fe-N/BC are discussed. This review shows that N and Fe doped BCs are remedial materials that can potentially remediate Cr(VI) contaminated water and soil.

Green Synthesis of Fe2O3 Nanoparticles Using Eucalyptus globulus Leaf Extract on Pinus radiata Sawdust for Cationic Dye Adsorption

The present study reports the synthesis of Fe2O3 nanoparticles on Pinus radiata sawdust (Fe2O3@PS) using a Eucalyptus globulus leaf extract. The morphology and structure of Fe2O3@PS were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis diffuse reflectance. The adsorption capacity of the system was evaluated by testing its ability to remove the Rhodamine B (RhB) dye. The optimization of the system was carried out using the Plackett-Burman design (PBD) and the response surface methodology (steepest ascent and the Box-Behnken design), which provided information on the main parameters affecting the adsorption process. The PBD results showed that the most important parameters for the removal of RhB using Fe2O3@PS were the removal time, the RhB concentration, and the initial pH of the system. The reusability of Fe2O3@PS under optimal conditions was tested and it was found to maintain its efficiency after five cycles of use. The efficiency and rate of RhB removal observed at pH values near 7.0 were found to be predominantly influenced by electrostatic interactions. In contrast, the analyses conducted at pH values near 8.3 exhibited reduced influence from electrostatic attractions, with π-π interactions and hydrogen bonds emerging as dominant forces. At pH values exceeding 8.3, all potential interactions between RhB and Fe2O3@PS exhibited diminished strength. This research provides valuable information on the formation of eco-friendly nanoparticles immobilized on a forest residue such as sawdust, which can effectively remove organic pollutants like RhB. This contributes to the valorization of resources and the search for solutions to water pollution.

Biochar Meets Single-Atom: A Catalyst for Efficient Utilization in Environmental Protection Applications and Energy Conversion

Single-atom catalysts (SACs), combining the advantages of multiphase and homogeneous catalysis, have been increasingly investigated in various catalytic applications. Carbon-based SACs have attracted much attention due to their large specific surface area, high porosity, particular electronic structure, and excellent stability. As a cheap and readily available carbon material, biochar has begun to be used as an alternative to carbon nanotubes, graphene, and other such expensive carbon matrices to prepare SACs. However, a review of biochar-based SACs for environmental pollutant removal and energy conversion and storage is lacking. This review focuses on strategies for synthesizing biochar-based SACs, such as pre-treatment of organisms with metal salts, insertion of metal elements into biochar, or pyrolysis of metal-rich biomass, which are more simplistic ways of synthesizing SACs. Meanwhile, this paper attempts to 1) demonstrate their applications in environmental remediation based on advanced oxidation technology and energy conversion and storage based on electrocatalysis; 2) reveal the catalytic oxidation mechanism in different catalytic systems; 3) discuss the stability of biochar-based SACs; and 4) present the future developments and challenges regarding biochar-based SACs.

Exploring nanomaterial-modified biochar for environmental remediation applications

Environmental pollution, particularly from heavy metals and toxic elements, poses a significant threat to both human health and ecological systems. While various remediation technologies exist, there is an urgent need for cost-effective and sustainable solutions. Biochar, a carbon-rich product derived from the pyrolysis of organic matter, has emerged as a promising material for environmental remediation. However, its pristine form has limitations, such as low adsorption capacities, a relatively narrow range of pH adaptability which can limit its effectiveness in diverse environmental conditions, and a tendency to lose adsorption capacity rapidly in the presence of competing ions or organic matters. This review aims to explore the burgeoning field of nanomaterial-modified biochar, which seeks to overcome the limitations of pristine biochar. By incorporating nanomaterials, the adsorptive and reactive properties of biochar can be significantly enhanced. Such modifications, especially biochar supported with metal nanoparticles (biochar-MNPs), have shown promise in various applications, including the removal of heavy metals, organic contaminants, and other inorganic pollutants from aqueous environments, soil, and air. This review provides a comprehensive overview of the synthesis techniques, characterization methods, and applications of biochar-MNPs, as well as discusses their underlying mechanisms for contaminant removal. It also offers insights into the advantages and challenges of using nanomaterial-modified biochar for environmental remediation and suggests directions for future research.

A comprehensive review of the "black gold catalysts" in wastewater treatment: Properties, applications and bibliometric analysis

A significant amount of effort has been devoted to the utilization of biochar-based catalysts in the treatment of wastewater. By virtue of its abundant functional groups and high specific surface area, biochar holds significant promise as a catalyst. This article presents a comprehensive systematic review and bibliometric analysis covering the period from 2009 to 2024, focusing on the restoration of wastewater through biochar catalysis. The production, activation, and functionalization techniques employed for biochar are thoroughly examined. In addition, the application of advanced technologies such as advanced oxidation processes (AOPs), catalytic reduction reactions, and biochemically driven processes based on biochar are discussed, with a focus on elucidating the underlying mechanisms and how surface functionalities influence the catalytic performance of biochar. Furthermore, the potential drawbacks of utilizing biochar are also brought to light. To emphasize the progress being made in this research field and provide valuable insights for future researchers, a scientometric analysis was conducted using CiteSpace and VOSviewer software on 595 articles. Hopefully, this review will enhance understanding of the catalytic performance and mechanisms pertaining to biochar-based catalysts in pollutant treatment while providing a perspective and guidelines for future research and development efforts in this area.

An overview of biochar production techniques and application in iron and steel industries

Integrating innovation and environmental responsibility has become important in pursuing sustainable industrial practices in the contemporary world. These twin imperatives have stimulated research into developing methods that optimize industrial processes, enhancing efficiency and effectiveness while mitigating undesirable ecological impacts. This objective is exemplified by the emergence of biochar derived from the thermo-chemical transformation of biomass. This review examines biochar production methods and their potential applications across various aspects of the iron and steel industries (ISI). The technical, economic, and sustainable implications of integrating biochar into the ISI were explored. Slow pyrolysis and hydrothermal carbonization are the most efficient methods for higher biochar yield (25-90%). Biochar has several advantages- higher heating value (30-32 MJ/kg), more porosity (58.22%), and significantly larger surface area (113 m2/g) compared to coal and coke. However, the presence of biochar often reduces fluidity in a coal-biochar mixture. The findings highlighted that biochar production and implementation in ISI often come with higher costs, primarily due to the higher expense of substitute fuels compared to traditional fossil fuels. The economic viability and societal desirability of biochar are highly uncertain and vary significantly based on factors such as location, feedstock type, production scale, and biochar pricing, among others. Furthermore, biomass and biochar supply chain is another important factor which determines its large scale implementation. Despite these challenges, there are opportunities to reduce emissions from BF-BOF operations by utilizing biochar technologies. Overall, the present study explored integrating diverse biochar production methods into the ISI aiming to contribute to the ongoing research on sustainable manufacturing practices, underscoring their significance in shaping a more environmentally conscious future.

The potential and prospects of modified biochar for comprehensive management of salt-affected soils and plants: A critical review

Soil salinization has become a global problem that threatens farmland health and restricts crop production. Salt-affected soils seriously restrict the development of agricultural, mainly because of sodium ion (Na+) toxicity, nutrient deficiency, and structural changes in the soil. Biochar is a carbon (C)-based substance produced by heating typical biomass waste at high temperatures in anaerobic circumstances. It has high cation exchange capacity (CEC), adsorption capacity, and C content, which is often used as a soil amendment. Biochar generally reduces the concentration of Na+ in soil colloids through its strong adsorption, or uses the calcium (Ca) or magnesium (Mg) rich on its surface to exchange sodium ions (Ex-Na) from soil colloids through cation exchange to accelerate salt leaching during irrigation. Nowadays, biochar is widely used for acidic soils improvement due to its alkaline properties. Although the fact that biochar has gained increasing attention for its significant role in saline alkali soil remediation, there is currently a lack of systematic research on biochar improvers and their potential mechanisms for identifying physical, chemical, and biological indicators of soil eco-environment assessment and plant growth conditions affected by salt stress. This paper reviews the preparation, modification, and activation of biochar, the effects of biochar and its combination with beneficial salt-tolerant strains on salt-affected soils and plant growth. Finally, the limitations, benefits, and future needs of biochar-based soil health assessment technology in salt-affected soils and plant were discussed. This article elaborates on the future opportunities and challenges of biochar in the treatment of saline land, and a green method was provided for the integrate control to salt-affected soils.

Tuning active sites on biochars for remediation of mercury-contaminated soil: A comprehensive review

Mercury (Hg) contamination is acknowledged as a global issue and has generated concerns globally due to its toxicity and persistence. Tunable surface-active sites (SASs) are one of the key features of efficient BCs for Hg remediation, and detailed documentation of their interactions with metal ions in soil medium is essential to support the applications of functionalized BC for Hg remediation. Although a specific active site exhibits identical behavior during the adsorption process, a systematic documentation of their syntheses and interactions with various metal ions in soil medium is crucial to promote the applications of functionalized biochars in Hg remediation. Hence, we summarized the BC's impact on Hg mobility in soils and discussed the potential mechanisms and role of various SASs of BC for Hg remediation, including oxygen-, nitrogen-, sulfur-, and X (chlorine, bromine, iodine)- functional groups (FGs), surface area, pores and pH. The review also categorized synthesis routes to introduce oxygen, nitrogen, and sulfur to BC surfaces to enhance their Hg adsorptive properties. Last but not the least, the direct mechanisms (e.g., Hg- BC binding) and indirect mechanisms (i.e., BC has a significant impact on the cycling of sulfur and thus the Hg-soil binding) that can be used to explain the adverse effects of BC on plants and microorganisms, as well as other related consequences and risk reduction strategies were highlighted. The future perspective will focus on functional BC for multiple heavy metal remediation and other potential applications; hence, future work should focus on designing intelligent/artificial BC for multiple purposes.

Migration characteristics of chlorine during pyrolysis of municipal solid waste pellets

The migration process of chlorine during municipal solid waste (MSW) pellets pyrolysis was studied in a fixed bed reactor. Distribution and speciation changes of chlorine at different pyrolysis temperatures were determined by ion chromatography (IC) and X-ray photoelectron spectroscopy (XPS) analyses. Results showed that chlorine was mainly distributed in pyrolysis char (42.36-65.29 %) and gas (26.66-35.03 %) after MSW pellets pyrolysis. With the temperature increasing, chlorine in char and tar was enriched due to the increase of chlorine release and the decrease of product yields, with chlorine concentration increasing to 3498 ppm and 1415 ppm at 800 °C, respectively. Results of chlorine forms analysis indicated that most of the organic-Cl in MSW was released into the volatiles during pyrolysis due to the dissociation of CCl. Inorganic-Cl became the dominant form of chlorine in char after pyrolysis, with the proportion increasing from 46.69 % (raw) to 61.22 % (500 °C), which also suggested that part of organic-Cl was converted into the inorganic-Cl. Notably, the proportions of inorganic-Cl decreased at >600 °C due to the migration of inorganic. In addition, the pyrolysis release behavior of chlorine was affected by the pore structure of char, which could be inhibited by the unprosperous pores in char, especially at low temperatures (<600 °C). These findings provided a reference for the chlorine regulation of MSW pyrolytic products.

Application of Selected Methods to Modify Pyrolyzed Biochar for the Immobilization of Metals in Soil: A Review

Soil contamination through heavy metals (HMs) is a serious environmental problem that needs to be addressed. One of the methods of remediating soils contaminated with HMs and reducing the environmental risks associated with them is to immobilize these HMs in the soil using specific amendment(s). The use of biochar as an organic amendment can be an environmentally friendly and practically feasible option, as (i) different types of biomass can be used for biochar production, which contributes to environmental sustainability, and (ii) the functionality of biochar can be improved, enabling efficient immobilization of HMs. Effective use of biochar to immobilize HMs in soil often requires modification of pristine biochar. There are various physical, chemical, and biological methods for modifying biochar that can be used at different stages of pyrolysis, i.e., before pyrolysis, during pyrolysis, and after pyrolysis. Such methods are still being intensively developed by testing different modification approaches in single or hybrid systems and investigating their effects on the immobilization of HMs in the soil and on the properties of the remediated soil. In general, there is more information on biochar modification and its performance in HM immobilization with physical and chemical methods than with microbial methods. This review provides an overview of the main biochar modification strategies related to the pyrolysis process. In addition, recent advances in biochar modification using physical and chemical methods, biochar-based composites, and biochar modified with HM-tolerant microorganisms are presented, including the effects of these methods on biochar properties and the immobilization of HMs in soil. Since modified biochar can have some negative effects, these issues are also addressed. Finally, future directions for modified biochar research are suggested in terms of scope, scale, timeframe, and risk assessment. This review aims to popularize the in situ immobilization of HMs with modified biochar.

Cr(VI) removal from wastewater using nano zero-valent iron and chromium-reducing bacteria

Significant global efforts are currently underway to alleviate the presence of toxic metals in water bodies, aiming to encourage a sustainable environment. Nevertheless, the scientific community has yet to methodically inspect the performance and mechanisms underlying the interaction between nanomaterials and microorganisms in this context. Therefore, this study seeks to address this knowledge gap by developing a novel system that integrates nano zero-valent iron (nZVI) with chromium-reducing bacteria (CrRB) to efficiently remove Cr(VI) from water sources. The combined use of RBC600 and CrRB resulted in a Cr(VI) removal rate of 77.73%, displaying a substantial improvement of 17.61% compared to the use of CrRB alone. The efficacy of Cr(VI) elimination was observed to be affected by several factors within the system, such as the pH value, the quantity of nZVI added, the degree of CrRB inoculation, and the initial concentration of Cr(VI) at the onset of the experiment. When the pH was adjusted to 5, the complete removal of 200 mg/L Cr(VI) was achieved within 36 h. Increasing the dosage of nZVI to above 2 g/L resulted in the complete elimination of Cr(VI) from the solution within 72 h. This can be attributed to the availability of more reaction sites for the reduction of Cr(VI), facilitated by the higher nZVI dose. Additionally, the increased dose of nZVI allowed for the dissolution of more reactive Fe(II) ions. The characterization analysis, high-throughput sequencing, and fluorescence quantitative PCR results have established that CrRB and its extracellular polymer effectively reduce and complex Cr(VI). This process facilitated the dissolution of the passivated layer on the surface of nZVI, thus significantly enhancing the efficiency of nZVI in responding to Cr(VI). Additionally, the presence of nZVI created a favorable living environment for CrRB, resulting in increased richness and diversity within the CrRB community. These findings provide valuable preliminary insights into the mechanism underlying Cr(VI) elimination by the synergistic interaction between nZVI and CrRB. Therefore, this study establishes a solid theoretical foundations for the application of nano-bio synergy in the remediation of Cr(VI).

Spinel ferrite nanoparticles as potential materials in chlorophenol removal from wastewater

Persistent organic pollutants (POPs) including chlorophenols (CPs) are increasing in water effluents, creating serious problems for both aquatic and terrestrial lives. Several research attempts have considered the removal of CPs by functionalised nanomaterials as adsorbents and catalysts. Besides the unique crystal structure, spinel ferrite nanomaterials (SFNs) own interesting optical and magnetic properties that give them the potential to be utilised in the removal of different types of CPs. In this review, we highlighted the recent research work that focused on the application of SFNs in the removal of different CP substances based on the number of chlorine atom attached to the phenolic compound. We have also discussed the structure and properties of SFN along with their numerous characterisation tools. We demonstrated the importance of identifying the structure, surface area, porosity, optical properties, etc. in the efficiency of the SFN during the CP removal process. The reviewed research efforts applied photocatalysis, wet peroxide oxidation (WPO), persulfate activated oxidation and adsorption. The studies presented different paths of enhancing the SFN ability to remove the CPs including doping (ion substitution), oxide composite structure and polymer composite structure. Experimental parameters such as temperature, dosage of CPs and SFN structure have shown to have a major effect in the CP removal efficiency. More attention is needed to investigate the different properties of SFN that can be tailored through different techniques and expected to have major role in the removal mechanism of CPs.

Palladium Nanoparticles Grafted onto Phytochemical Functionalized Biochar: A Sustainable Nanozyme for Colorimetric Sensing of Glucose and Glutathione

The devising and development of numerous enzyme mimics, particularly nanoparticles and nanomaterials (nanozymes), have been sparked by the inherent limitations imposed by natural enzymes. Peroxidase is one of the enzymes that is extensively utilized in commercial, medical, and biological applications because of its outstanding substrate selectivity. Herein, we present palladium nanoparticles grafted on Artocarpus heterophyllus (jackfruit) seed-derived biochar (BC-AHE@Pd) as a novel nanozyme to imitate peroxidase activity en route to the rapid and colorimetric detection of H2O2, exploiting o-phenylenediamine as a peroxidase substrate. The biogenically generated BC-AHE@Pd nanocatalyst was synthesized utilizing Artocarpus heterophyllus seed extract as the reducing agent for nanoparticle formation, while the residue became the source for biochar. Various analytical techniques like FT-IR, GC-MS, FE-SEM, EDS, TEM, SAED pattern, p-XRD, and ICP-OES, were used to characterize the BC-AHE@Pd nanocatalyst. The intrinsic peroxidase-like activity of the BC-AHE@Pd nanocatalyst was extended as a prospective nanosensor for the estimation of the biomolecules glucose and glutathione. Moreover, the BC-AHE@Pd nanocatalyst showed recyclability up to three recycles without any significant loss in activity.

Biochar integrated reactive filtration of wastewater for P removal and recovery, micropollutant catalytic oxidation, and negative CO2 e: Process operation and mechanism

Biochar (BC) use in water treatment is a promising approach that can simultaneously help address societal needs of clean water, food security, and climate change mitigation. However, novel BC water treatment technology approaches require operational testing in field pilot-scale scenarios to advance their technology readiness assessment. Therefore, the objective of this study is to evaluate the system performance of BC integrated into hydrous ferric oxide reactive filtration (Fe-BC-RF) with and without catalytic ozonation (CatOx) process in laboratory and field pilot-scale scenarios. For this investigation, Fe-BC-RF and Fe-CatOx-BC-RF pilot-scale trials were conducted on synthetic lake water variants and at three municipal water resource recovery facilities (WRRFs) at process flows of 0.05 and 0.6 L/s, respectively. Three native and two iron-modified BCs were used in these studies. The commercially available reactive filtration process (Fe-RF without BC) had 96%-98% total phosphorus (TP) removal from 0.075- and 0.22-mg/L TP, as orthophosphate process influent in these trials. With BC integration, phosphorus removal yielded 94%-98% with the same process-influent conditions. In WRRF field pilot-scale studies, the Fe-CatOx-BC-RF process removed 84%-99% of influent total phosphorus concentrations that varied from 0.12 to 8.1 mg/L. Nutrient analysis on BC showed that the recovered BC used in the pilot-scale studies had an increase in TP from its native concentration, with the Fe-amended BC showing better P recovery at 110% than its unmodified state, which was 16%. Lastly, the field WRRF Fe-CatOx-BC-RF process studies showed successful destructive removals at >90% for more than 20 detected micropollutants, thus addressing a critical human health and environmental water quality concern. The research demonstrated that integration of BC into Fe-CatOx-RF for micropollutant removal, disinfection, and nutrient recovery is an encouraging tertiary water treatment technology that can address sustainable phosphorus recycling needs and the potential for carbon-negative operation. PRACTITIONER POINTS: A pilot-scale hydrous ferric oxide reactive sand filtration process integrating biochar injection typically yields >90% total phosphorus removal to ultralow levels. Biochar, modified with iron, recovers phosphorus from wastewater, creating a P/N nutrient upcycled soil amendment. Addition of ozone to the process stream enables biochar-iron-ozone catalytic oxidation demonstrating typically excellent (>90%) micropollutant destructive removals for the compounds tested. A companion paper to this work explores life cycle assessment (LCA) and techno-economic analysis (TEA) to explore biochar water treatment integrated reactive filtration impacts, costs, and readiness. Biochar use can aid in long-term carbon sequestration by reducing the carbon footprint of advanced water treatment in a dose-dependent manner, including enabling an overall carbon-negative process.

Adsorption of antibiotic, heavy metal and antibiotic plasmid by a wet-state silicon-rich biochar/ferrihydrite composite to inhibit antibiotic resistance gene proliferation/transformation

Decreasing bioaccessible antibiotics, heavy metals, and antibiotic resistance genes (ARGs) in soil by adsorption is an attractive, but unrealized, approach for ARG risk reduction. This approach has the potential to reduce the (co)selection pressure from antibiotics and heavy metals on bacteria and ARG horizontal gene transformation to pathogens. Here, a wet-state silicon-rich biochar/ferrihydrite composite (SiC-Fe(W)) synthesized by loading ferrihydrite onto rice straw-derived biochar was examined for i) adsorption of oxytetracycline and Cu²⁺ to reduce (co)selection pressure and ii) adsorption of extracellular antibiotic resistance plasmid pBR322 (containing tetA and bla_TEM-1) to inhibit ARG transformation. SiC-Fe(W) gained the adsorption priority of biochar (for Cu²⁺) and wet-state ferrihydrite (for oxytetracycline and pBR322) and showed adsorptive enhancement (for Cu²⁺ and oxytetracycline) from a more wrinkled and exposed surface from biochar silica-dispersed ferrihydrite and a more negatively charged biochar, and the adsorption capacity for SiC-Fe(W) was 17-135 times that of soil. Correspondingly, 10 g/kg SiC-Fe(W) amendment increased the soil adsorption coefficient K_d by 31%-1417% and reduced the selection pressure from dissolved oxytetracycline, co-selection pressure from dissolved Cu²⁺, and transformation frequency of pBR322 (assessed with Escherichia coli). The development of Fe-O-Si bonds on silicon-rich biochar in alkaline enhanced ferrihydrite stability and adsorption capacity (for oxytetracycline), presenting a new potential strategy of biochar/ferrihydrite composite synthesis for adsorptive inhibition of ARG proliferation and transformation in ARG pollution control.

Biochar and nano-ferric oxide synergistically alleviate cadmium toxicity of muskmelon

Cadmium is toxic to plants. The accumulation of cadmium in edible plants such as muskmelon may affect the safe production of crops and result in human health problem. Thus effective measures are urgently needed for soil remediation. This work aims to investigate the effects of nano-ferric oxide and biochar alone or mixture on muskmelon under cadmium stress. The results of growth and physiological indexes showed that compared with the application of cadmium alone, the composite treatment (biochar and nano-ferric oxide) decreased malondialdehyde content by 59.12% and ascorbate peroxidase activity increased by 276.6%. Their addition can increase the stress resistance of plants. The results of soil analysis and cadmium content determination in plants showed that the composite treatment was beneficial to reduce the cadmium content in various parts of muskmelon. In the presence of high concentration of cadmium, the Target Hazard Quotient value of peel and flesh of muskmelon in the composite treatment was less than 1, which means the edible risk was greatly reduced. Furthermore, the addition of composite treatment increased the content of effective components; the contents of polyphenols, flavonoids, and saponins in the flesh of the compound treatment were increased by 99.73%, 143.07%, and 18.78% compared with the cadmium treatment. The results provide a technical reference for the further application of biochar combined with nano-ferric oxide in the field of soil heavy metal remediation, and provide a theoretical basis for further research on reducing the toxicity of cadmium to plants and improving the edible quality of crops.

Cornstalk biochar-TiO2 composites as alternative photocatalyst for degrading methyl orange

Dye wastewater is one of the most harmful wastewater types generated during industrial processes. Effectively treating dye wastewater is essential. This study used TiO₂ and cornstalk biochar to prepare biochar-TiO₂ composites in order to treat methyl orange (MO) in the water. It is found that composites prepared using biochar generated at 700 ℃ and TiO₂/biochar mass ratio values of 0.75/1 showed the best performance on decolorization efficiency and mineralization efficiency of MO while low pH, low initial MO concentration, and 1 g/L of composite amount added can enhance MO degradation efficiency. Additionally, it is also noted that biochar-TiO₂ composites were easier to separate from water compared to pure TiO₂. This benefits the recycling of biochar-TiO₂ composites after application. Furthermore, the study indicated that the biochar-TiO₂ composites degrade MO by a combination of adsorption and photocatalysis while photoelectron (e^-) and ·O₂^- are the key species participating in photocatalytic degradation of MO. These research outcomes suggest that cornstalk biochar and TiO₂ can be used to prepare composites, which can be seen as an alternative photocatalyst for dye wastewater treatment. However, further investigations related to their long-term applications and in real scale projects are recommended.

A critical review on biochar-assisted free radicals mediated redox reactions influencing transformation of potentially toxic metals: Occurrence, formation, and environmental applications

Potentially toxic metals have become a viable threat to the ecosystem due to their carcinogenic nature. Biochar has gained substantial interest due to its redox-mediated processes and redox-active metals. Biochar has the capacity to directly adsorb the pollutants from contaminated environments through several mechanisms such as coprecipitation, complexation, ion exchange, and electrostatic interaction. Biochar's electron-mediating potential may be influenced by the cyclic transition of surface moieties and conjugated carbon structures. Thus, pyrolysis configuration, biomass material, retention time, oxygen flow, and heating time also affect biochar's redox properties. Generally, reactive oxygen species (ROS) exist as free radicals (FRs) in radical and non-radical forms, i.e., hydroxyl radical, superoxide, nitric oxide, hydrogen peroxide, and singlet oxygen. Heavy metals are involved in the production of FRs during redox-mediated reactions, which may contribute to ROS formation. This review aims to critically evaluate the redox-mediated characteristics of biochar produced from various biomass feedstocks under different pyrolysis conditions. In addition, we assessed the impact of biochar-assisted FRs redox-mediated processes on heavy metal immobilization and mobility. We also revealed new insights into the function of FRs in biochar and its potential uses for environment-friendly remediation and reducing the dependency on fossil-based materials, utilizing local residual biomass as a raw material in terms of sustainability.

Immobilized Nanomaterials for Environmental Applications

Nanomaterials (NMs) have been extensively used in several environmental applications; however, their widespread dissemination at full scale is hindered by difficulties keeping them active in engineered systems. Thus, several strategies to immobilize NMs for their environmental utilization have been established and are described in the present review, emphasizing their role in the production of renewable energies, the removal of priority pollutants, as well as greenhouse gases, from industrial streams, by both biological and physicochemical processes. The challenges to optimize the application of immobilized NMs and the relevant research topics to consider in future research are also presented to encourage the scientific community to respond to current needs.

Recent advances in waste-derived functional materials for wastewater remediation

Water pollution is a major concern for public health and a sustainable future. It is urgent to purify wastewater with effective methods to ensure a clean water supply. Most wastewater remediation techniques rely heavily on functional materials, and cost-effective materials are thus highly favorable. Of great environmental and economic significance, developing waste-derived materials for wastewater remediation has undergone explosive growth recently. Herein, the applications of waste (e.g., biowastes, electronic wastes, and industrial wastes)-derived materials for wastewater purification are comprehensively reviewed. Sophisticated strategies for turning wastes into functional materials are firstly summarized, including pyrolysis and combustion, hydrothermal synthesis, sol-gel method, co-precipitation, and ball milling. Moreover, critical experimental parameters within different design strategies are discussed. Afterward, recent applications of waste-derived functional materials in adsorption, photocatalytic degradation, electrochemical treatment, and advanced oxidation processes (AOPs) are analyzed. We mainly focus on the development of efficient functional materials via regulating the internal and external characteristics of waste-derived materials, and the material's property-performance correlation is also emphasized. Finally, the key future perspectives in the field of waste-derived materials-driven water remediation are highlighted.

Effects of Biochar on Biointensive Horticultural Crops and Its Economic Viability in the Mediterranean Climate

The effects of biochar on different horticultural crops (lettuce, tomato, sweet pepper, and radish) were evaluated in the Mediterranean climate. Biochar was produced by pyrolysis of Pinus pinaster wood chips at 550 °C and used at 1 (B1) and 2 (B2) kg/m2 application rates on six 3.5 m2 plots in each treatment, with two control plots (B0). No fertilizer was used. Treatment B1 led to a significant increase (p < 0.01) of 35.4%, 98.1%, 28.4%, and 35.2% in the mean fresh weight of radishes, lettuce, tomatoes, and sweet peppers, respectively. Treatment B2 resulted in an improvement of 70.7% in radishes, 126.1% in lettuce, 38.4% in tomatoes, and 95.0% in sweet peppers (p < 0.01). Significant differences between treatments B1 and B2 were observed in the radish, tomato, and sweet pepper crops but not in lettuce. The profitability of biochar application to these crops was studied by considering a biochar price of 800 EUR/t and applying a CO2 fixation subsidy, assuming the updated February 2022 price (90 EUR/t). In lettuce, tomato, and sweet pepper crops, the investment payback period was approximately one year. Application of biochar generated economic benefit either from the first harvest or in the second year. In radish, this period was longer than two years; however, an increase in the annual frequency of cultivation should be studied to optimize the benefit. The dose that provided the greatest benefit was B1 (for all crops, except for sweet pepper). Biochar considerably improved fruit and vegetable yield under the Mediterranean climate; however, further studies are needed to assess the effects of biochar on soil properties and yield to estimate long-term environmental and economic benefits.

Biosorption of heavy metals: Transferability between batch and column studies

The design of an industrial water treatment system using sorption is based on laboratory column tests. To verify the applicability of a column sorption system at industrial scale, it is necessary to determine the system's breakthrough time (BT) in a laboratory setting. In a laboratory column set-up, BT is referred to as the time taken by the adsorbate to appear at column outlet for the first time. This is when the mass transfer zone (MTZ), where the equilibrium sorption occurs, reaches the end of the sorbent bed. However, such laboratory set-up requires significant resources including laboratory space, time and multiple trials, which is the opposite to the batch experimental approach that is commonly used to assess efficiency of sorbents. This study identified batch sorption parameters that can be used to determine BT for a column sorption setting for three toxic heavy metals commonly found in industrial wastewater, namely, Pb²⁺, Cd²⁺ and Cu²⁺. The study conducted a comprehensive evaluation of the relationships between column BT and its key influential factors, namely, equilibrium sorption capacity (q_e), pseudo second-order kinetic rate constant (k₂) and initial sorption rate (h). The results revealed that BT can be better estimated using h compared to q_e and k₂. As such, a batch experiment which is more resource efficient could be undertaken for an initial estimation of the experimental BT of a column system. Moreover, a simulation model developed to replicate column sorption could demonstrate the behaviour of the breakthrough curve, which is a key to the selection and assessment of the performance of a sorbent in an adsorbent column. The estimation errors in q_e and k₂ were found to influence the simulation outcomes. Hence, it is necessary to further investigate the other factors that can potentially influence sorption behaviour.

Integrating Tank Model and adsorption/desorption characteristics of filter media to simulate outflow water quantity and quality of a bioretention basin: A case study of biochar-based bioretention basin

Reliable approaches for accurately assessing the performance of stormwater treatment systems is essential for their effective design, including filter media selection which can be a significant constituent in stormwater treatment systems. This study presents an innovative modelling approach integrating the Tank Model with the adsorption-desorption characteristics of the filter media. The resulting modelling approach was applied to simulate a field-scale bioretention basin where biochar was used as filter media with over ten years of rainfall records. The resulting outflow and overflow volumes were compared with observed data for calibration. The Stormwater Treatment Tank Model (STTM) was validated using the Leave-One-Out-Cross-Validation (LOOCV) method. The simulation outcomes include water outflow and overflow (quantity) from the bioretention basin as well as outflow water quality represented by three heavy metals (Pb, Cu, and Zn). The modelling approach developed was found to be capable of accurately simulating outflow and overflow volumes, with outlet water quantity being significantly influenced by the total rainfall depth. The modeling results also suggested that a sole treatment system would not be adequate, particularly for large rainfall events (>100 mm) and a treatment train would be more effective. Simulating long-term (over ten years) pollutant removal performance in the bioretention basin indicated that heavy metals outflow event mean concentration (EMCs) values calculated using simulated results of 30% biochar application rate generated the best pollutant removal with consistent values (2.7 μg/L, 3.0 μg/L, 17.2 μg/L for Pb, Cu, and Zn, respectively). These results confirm that the modelling approach is reliable for assessing long-term treatment performance, as well as a robust tool able to contribute to more effective treatment system design, particularly filter media selection and evaluation.

Green Hydrogel-Biochar Composite for Enhanced Adsorption of Uranium

Uranium is the backbone of the nuclear fuel used for energy production but is still a hazardous environmental contaminant; thus, its removal and recovery are important for energy security and environmental protection. So far, the development of biocompatible, efficient, economical, and reusable adsorbents for uranium is still a challenge. In this work, a new orange peel biochar-based hydrogel composite was prepared by graft polymerization using guar gum and acrylamide. The composite's structural, morphological, and thermal characteristics were investigated via Fourier transform infrared (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. The composite's water absorption properties were investigated in different media. The performance of the prepared composite in adsorbing uranium (VI) ions from aqueous media was systematically investigated under varying conditions including solution's acidity and temperature, composite dose, contact time, and starting amount of uranium. The adsorption efficiency increased with solution pH from 2 to 5.5 and composite dose from 15 to 50 mg. The adsorption kinetics, isotherms, and thermodynamics parameters were analyzed to get insights into the process's feasibility and viability. The equilibrium data were better described through a pseudo-second-order mechanism and a Langmuir isotherm model, indicating a homogeneous composite surface with the maximum uranium (VI) adsorption capacity of 263.2 mg/g. The calculated thermodynamic parameters suggested that a spontaneous and endothermic process prevailed. Interference studies showed high selectivity toward uranium (VI) against other competing cations. Desorption and recyclability studies indicated the good recycling performance of the prepared composite. The adsorption mechanism was discussed in view of the kinetics and thermodynamics data. Based on the results, the prepared hydrogel composite can be applied as a promising, cost-effective, eco-friendly, and efficient material for uranium (VI) decontamination.

Emerging materials and technologies for landfill leachate treatment: A critical review

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Humulus scandens-Derived Biochars for the Effective Removal of Heavy Metal Ions: Isotherm/Kinetic Study, Column Adsorption and Mechanism Investigation

Humulus scandens was first adopted as a biomass precursor to prepare biochars by means of a facile molten salt method. The optimized biochar exhibits a high specific surface area of ~450 m²/g, a rich porous structure and abundant oxygen functional groups, which demonstrate excellent adsorption performance for heavy metal ions. The isotherm curves fit well with the Langmuir models, indicating that the process is governed by the chemical adsorption, and that the maximum adsorption capacity can reach 748 and 221 mg/g for Pb²⁺ and Cu²⁺, respectively. In addition, the optimized biochar demonstrates good anti-interference ability and outstanding removal efficiency for Cu²⁺ and Pb²⁺ in simulated wastewater. The mechanism investigation and DFT calculation suggest that the oxygen functional groups play dominant roles in the adsorption process by enhancing the binding energy towards the heavy metal ions. Meanwhile, ion exchange also serves as the main reason for the effective removal.

Recent Advancements in the Nanomaterial Application in Concrete and Its Ecological Impact

At present, nanotechnology is a significant research area in different countries, owing to its immense ability along with its economic impact. Nanotechnology is the scientific study, development, manufacturing, and processing of structures and materials on a nanoscale level. It has tremendous application in different industries such as construction. This study discusses the various progressive uses of nanomaterials in concrete, as well as their related health risks and environmental impacts. Nanomaterials such as nanosilica, nano-TiO₂, carbon nanotubes (CNTs), ferric oxides, polycarboxylates, and nanocellulose have the capability to increase the durability of buildings by improving their mechanical and thermal properties. This could cause an indirect reduction in energy usage and total expenses in the concrete industry. However, due to the uncertainties and irregularities in size, shape, and chemical compositions, some nanosized materials might have harmful effects on the environment and human health. Acknowledgement of the possible beneficial impacts and inadvertent dangers of these nanosized materials to the environment will be extremely important when pursuing progress in the upcoming years. This research paper is expected to bring proper attention to the probable effects of construction waste, together with the importance of proper regulations, on the final disposal of the construction waste.

Biochar Modified by Nano-manganese Dioxide as Adsorbent and Oxidant for Oxytetracycline

Biochar has limited capacity to adsorb oxytetracycline (OTC). Here we have used bamboo willow biochar (BC) as a carrier to produce nMnO₂-loaded biochars (MBC) by a co-precipitation method. Their chemical compositions, morphological features, specific surface area, and surface functional groups were observed or determined. Batch experiments were conducted to assess the effects of reaction time, initial OTC concentrations, pH, salt concentrations, and natural organic matter (NOM) on OTC removal. Kinetics and isotherms indicated that OTC was mainly adsorbed via chemical interactions, and mono- and multi-layer adsorption occurred on the surface. MBC removed 19-25 times more OTC than BC, and the removal was highest at near-neutral pH, not influenced by NaCl (2, 10 mM), slighted reduced by NOM (0-20 mg L^-1), and enhanced by NaHCO₃ (2, 10 mM). Besides being an adsorbent, MBC acted as an oxidant and degraded 58.5% of OTC at 24 h.

Nano-Fe3O4-modified biochar promotes the formation of iron plaque and cadmium immobilization in rice root

Rice as a paddy field crops, iron-containing materials application could induce its iron plaque formation, thereby affecting cadmium (Cd) transportation in the rhizosphere and its uptake in root. In this study, a hydroponic experiment was conducted to investigate the effects of three exogenous iron materials, namely nano-Fe₃O₄-modified biochar (BC-Fe), chelated iron (EDTA-Fe), and ferrous sulfate (FeSO₄), on the iron plaque formation on the surface of rice root, and to investigate the effects of formed iron plaque on the absorption, migration, and transportation of Cd and Fe in rice plant. The results showed that yellow-brown and brown iron plaque was formed on surface cells of the Fe-treated rice root, and some black particles were embedded in the iron plaque formed by BC-Fe. The proportion of crystallized iron plaque (31.8%-35.9%) formed by BC-Fe was much higher than that formed by EDTA-Fe and FeSO₄. The Cd concentrations in the crystallized iron plaque formed by BC-Fe were 7.64-13.0 mg·kg^-1, and increased with the increasing of Fe concentrations in the plaque. The Cd translocation factor from root to stem (TF_r-s) and the Cd translocation factor from stem to leaf (TF_s-l) with BC-Fe treatment decreased by 84.7% and 80.0%, respectively. The results demonstrated that application BC-Fe promoted the formation of iron plaque and enhanced the sequestration of Cd and Fe in roots, thus reduced the transportation and accumulation of Cd in aerial rice tissues.

Preparation and application of Fe/biochar (Fe-BC) catalysts in wastewater treatment: A review

The removal of organic pollutants from water environments is a challenging problem. Fe-based BC (Fe-BC) composites are promising catalysts for generating reactive oxygen species (ROS) for environmental remediation considering their low costs and excellent physicochemical surface characteristics. The synthesis methods, properties, applications, and the mechanism of Fe-BC for removing pollutants are reviewed. Various methods have been used to prepare Fe-BC composites, and the synthetic methods and conditions used affect the properties of the Fe-BC material, thereby influencing its pollutant removal performance. The mechanisms of pollutant removal by Fe-BC are intricate and include adsorption, degradation and reduction. Fe loading on BC could improve the performance of BC by affecting its surface area, surface functional groups and electron transfer rate. Moreover, research gaps and uncertainties that exist in the use of Fe-BC were identified. Finally, the problems that need to be solved to make Fe-BC suitable for future applications are described.

Preparation and bacteriostatic research of porous polyvinyl alcohol / biochar / nanosilver polymer gel for drinking water treatment

Microbial contamination in drinking water has become an important threat to human health. There is thus an urgent need to develop antibacterial materials to treat drinking water. Here, porous silver-loaded biochar (C–Ag) was prepared using corn straw as the substrate and silver as the antibacterial agent. C–Ag was then uniformly distributed in polyvinyl alcohol gel beads of eluted calcium carbonate to prepare p-PVA/C–Ag antibacterial composite. The polymer composites were tested by FT-IR, XRD, SEM and TG-DSC. The results showed that C–Ag was more evenly distributed in the PVA gel spheres. Antibacterial experiments showed that p-PVA/C–Ag greatly inhibited Escherichia coli. Practical application tests revealed that p-PVA/C–Ag showed high and sustained bactericidal inhibition and reusability. Generally, p-PVA/C–Ag composite shows high potential to be applied to drinking water treatment.

Burgeoning prospects of biochar and its composite in persulfate-advanced oxidation process

In the last decade, more and more refractory organic contaminants with severe health risks have been detected in the aquatic ecosystem. Sulfate radical (SO₄^·-)-based advanced oxidation process (SR-AOP) is recognized as an efficient approach for the removal of organic contaminants. Biochar (BC) and its composites (BCs) have been applied into SR-AOP for the double advantages of adsorption and catalytic ability. This paper gives systematic emphasis to the development and progress of biochar and its composites as catalyst in persulfate-advanced oxidation process. Synthetic techniques including the directed pyrolysis of mixed materials and post-immersed method are discussed. The physicochemical properties of biochar (such as surface area, surface functional groups, defect structure and persistent free radicals, etc.) that affect persulfate activation are provided. Then, emphasis is placed on the crucial role of biochar in affecting the catalytic property of BCs including stabilizing nanoparticles, expanding the surface area, increasing active sites and regulating electron transfer reactions. Integrating mechanistic insights and different biochar-based catalysts highlight the understanding of persulfate activation and catalytic degradation. Possible challenges are finally proposed in the fundamental research and practically scaled-up application.

Recent Developments in Understanding Biochar’s Physical–Chemistry

Biochar is a porous material obtained by biomass thermal degradation in oxygen-starved conditions. It is nowadays applied in many fields. For instance, it is used to synthesize new materials for environmental remediation, catalysis, animal feeding, adsorbent for smells, etc. In the last decades, biochar has been applied also to soils due to its beneficial effects on soil structure, pH, soil organic carbon content, and stability, and, therefore, soil fertility. In addition, this carbonaceous material shows high chemical stability. Once applied to soil it maintains its nature for centuries. Consequently, it can be considered a sink to store atmospheric carbon dioxide in soils, thereby mitigating the effects of global climatic changes. The literature contains plenty of papers dealing with biochar’s environmental effects. However, a discrepancy exists between studies dealing with biochar applications and those dealing with the physical-chemistry behind biochar behavior. On the one hand, the impression is that most of the papers where biochar is tested in soils are based on trial-and-error procedures. Sometimes these give positive results, sometimes not. Consequently, it appears that the scientific world is divided into two factions: either supporters or detractors. On the other hand, studies dealing with biochar’s physical-chemistry do not appear helpful in settling the factions’ problem. This review paper aims at collecting all the information on physical-chemistry of biochar and to use it to explain biochar’s role in different fields of application.

Synthesis, characterization and application of novel MnO and CuO impregnated biochar composites to sequester arsenic (As) from water: Modeling, thermodynamics and reusability

The present study aimed at enhancing the adsorption potential of novel nanocomposites of Sesbania bispinosa biochar (SBC) with copper oxide (SBC/CuO) and manganese oxide nanoparticles (SBC/MnO) for the efficient and inexpensive removal of environmentally concerned contaminant arsenic (As) from contaminated water at batch scale. The scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray (EDX), X-ray diffraction (XRD) and point of zero charge (PZC) analyses proved successful impregnation of the metallic nanoparticles on SBC surface. The results revealed the maximum As removal (96 %) and adsorption (12.47 mg/g) by SBC/CuO composite at 10 mg As/L, optimum pH-4, dose 1.0 g/L and ambient temperature (25 ± 1.5 °C) as compared with SBC (7.33 mg/g) and SBC/MnO (7.34 mg/g). Among four types of adsorption isotherms, Freundlich isotherm demonstrated best fit with R² > 0.997. While pseudo second-order kinetic model revealed better agreement with kinetic experimental data as matched with other kinetic models. The thermodynamic results depicted that As adsorption on the as-synthesized adsorbents was endothermic and spontaneous in nature with increased randomness. The SBC/CuO displayed excellent reusability and stability over four adsorption/desorption cycles and proved that the as-synthesized SBC/CuO composite may be the efficient adsorbent for practical removal of As from contaminated water.

Applying modified biochar with nZVI/nFe3O4 to immobilize Pb in contaminated soil

Lead (Pb) pollution in soil has become one of the most serious environmental problems, and it is more urgent in areas where acid rain is prevalent. Curing agents to solidify heavy metals in soil are efficiently applied to remediate Pb-contaminated soil. In this study, we prepared biochar, biochar loaded with nano-zero-valent iron (BC-nZVI), and biochar loaded with nano-ferroferric oxide (BC-nFe₃O₄), and investigated the Pb-immobilizing efficiency in contaminated soil in the condition of acid rain by them. The results showed that 8 g/kg is the best added dosage of curing agents for immobilizing Pb, which of the immobilizing efficiency of Pb were 19% (biochar), 42% (BC-nZVI), and 23% (BC-nFe₃O₄), respectively. Besides, the curing agents had positive effects on immobilizing Pb under acid rain condition, which could significantly reduce the content of acid extractable Pb, especially BC-nZVI (1.5%). And the immobilization efficiency of modified biochar was better than biochar, especially BC-nZVI (66%). BC-nZVI showed a more ideal effect on decreasing the leaching amount of Pb in the condition of acid rain. The results highlighted that biochar-loaded nano-iron-based materials, especially BC-nZVI, was promising and environmentally friendly materials for remediating Pb-contaminated soils, which provided scientific reference and theoretical basis for the treatment of Pb-contaminated soils around industrial sites particularly in acid rain area.

A Mild Method for Preparation of Highly Selective Magnetic Biochar Microspheres

We report the use of biochar and Fe₃O₄ nanoparticles as co-stabilizers for oil-in-water (o/w) Pickering emulsion. The emulsion is subsequently used to prepare magnetic tetracycline-imprinted biochar composite microspheres (MMIPMs) with good uniformity and high selectivity. The MMIPMs were characterized by scanning electron microscopy (SEM), Brunner-Emmet-Teller (BET) measurements, Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and thermogravimetry analysis (TGA). The adsorption properties of tetracycline to the MMIPMs were investigated using different adsorption experiments including adsorption kinetic experiment, equilibrium binding experiment, selectivity evaluation and competitive adsorption tests. The theoretical maximum adsorption capacity of the MMIPMs (15.45 mg g⁻¹) was greater than that of the raw biochar (2.10 mg g⁻¹) and non-imprinted biochar composite microspheres (3.39 mg g⁻¹) for tetracycline. Further, the MMIPMs were used as adsorbent for magnetic solid phase extraction (SPE) for the extraction of tetracycline present in drinking water, milk, fish and chicken samples. Under optimal conditions, the results showed good recovery yield ranging from 88.41% to 106.29% with a relative standard deviation (RSD) ranging from 0.35% to 6.83%, respectively.

Biochar/iron (BC/Fe) composites for soil and groundwater remediation: Synthesis, applications, and mechanisms

Biochar/iron (BC/Fe) composites, such as nano zero-valent iron (nZVI)/BC, iron sulfide/BC, and iron oxide/BC, have been developed and applied to deal with various contaminants owing to their excellent physicochemical properties. This work summarizes the progress in the preparation of BC/Fe composites, the properties and applications of BC/Fe, and the mechanism of the synergistic effect between Fe and BC in the composites. Various methods, including pyrolysis, hydrothermal carbonization, fractional precipitation, and ball milling, have been used to synthesize BC/Fe composites. In addition, the introduction of stabilizers, such as carboxymethyl cellulose (CMC), in the fractional precipitation process further prevents the agglomeration of Fe particles, which enhances the stability and fluidity of the resultant composites to facilitate the application of the composites in soil and water remediation. The application of BC/Fe composites in water and soil remediation is discussed in three aspects based on the interaction mechanisms, namely adsorption, reduction, and oxidation. Overall, the composites showed the synergistic effect of BC and Fe owing to the combination of the specific properties of Fe, such as reduction, catalysis, and magnetism, which can enhance the properties of BC with a larger surface area, abundant functional groups, and increased electron transfer efficiency. This review systemically summarizes the recent developments in BC/Fe composites to maximize the efficiency of BC/Fe application in soil and groundwater remediation. Key challenges and further research needs are also suggested.

Preparation, environmental application and prospect of biochar-supported metal nanoparticles: A review

Biochar is a low-cost, porous, and carbon-rich material and it exhibits a great potential as an adsorbent and a supporting matrix due to its high surface activity, high specific surface area, and high ion exchange capacity. Metal nanomaterials are nanometer-sized solid particles which have high reactivity, high surface area, and high surface energy. Owing to their aggregation and passivation, metal nanomaterials will lose excellent physiochemical properties. Carbon-enriched biochar can be applied to overcome these drawbacks of metal nanomaterials. Combining the advantages of biochar and metal nanomaterials, supporting metal nanomaterials on porous and stable biochar creates a new biochar-supported metal nanoparticles (MNPs@BC). Therefore, MNPs@BC can be used to design the properties of metal nanoparticles, stabilize the anchored metal nanoparticles, and facilitate the catalytic/redox reactions at the biochar-metal interfaces, which maximizes the efficiency of biochar and metal nanoparticles in environmental application. This work detailedly reviews the synthesis methods of MNPs@BC and the effects of preparation conditions on the properties of MNPs@BC during the preparation processes. The characterization methods of MNPs@BC, the removal/remediation performance of MNPs@BC for organic contaminants, heavy metals and other inorganic contaminants in water and soil, and the effect of MNPs@BC properties on the remediation efficiency were discussed. In addition, this paper summarizes the effect of various parameters on the removal of contaminants from water, the effect of MNPs@BC remediation on soil properties, and the removal/remediation mechanisms of the contaminants by MNPs@BC in water and soil. Moreover, the potential directions for future research and development of MNPs@BC have also been discussed.

Facile Ball-Milling Synthesis of CuO/Biochar Nanocomposites for Efficient Removal of Reactive Red 120

With the goal of improving the removal of anionic contaminants, copper oxide (CuO)-modified biochar (BC) nanocomposites were successfully prepared through simply ball milling CuO particles with BC. The physicochemical properties of the fabricated CuO/BC nanocomposites were systematically characterized by a series of techniques; their adsorption performances were assessed, and the main adsorption mechanism was revealed. X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses of the nanocomposites showed the strong interaction between CuO and BC and confirmed the success of the ball-milling syntheses. Because of strong electrostatic attraction between the embedded CuO nanoparticles and reactive red (RR120), the composited adsorbents exhibited excellent RR120 removal. The 10%-CuO/BC nanocomposite achieved the best RR120 removal efficiency (46%), which is much higher than that of pristine BC (20%). In addition, the adsorption was insensitive to the change of solution initial pH (4-10). The 10%-CuO/BC also showed fast adsorption kinetics (equilibrium time < 3 h) and extremely high adsorption capacity (Langmuir maximum capacity of 1399 mg g^-1) to RR120 in aqueous solutions. Findings from this study demonstrate not only the strong feasibility of ball-milling synthesis of BC-based nanocomposites but also the promising potential of the CuO/BC nanocomposites to remove aqueous anionic contaminants.

Nanomaterials in speciation analysis of metals and metalloids

Nanomaterials have draw extensive attention from the scientists in recent years mainly due to their unique and attractive thermal, mechanical and electronic properties, as well as high surface to volume ratio and the possibility for surface functionalization. Whereas mono functional nanomaterials providing a single function, the preparation of core/shell nanoparticles allows different properties to be combined in one material. Their properties have been extensively exploited in different extraction techniques to improve the efficiency of separation and preconcentration, analytical selectivity and method reliability. The aim of this paper is to provide an updated revision of the most important features and application of nanomaterials (metallic, silica, polymeric and carbon-based) for solid phase extraction and microextraction techniques in speciation analysis of some metals and metalloids (As, Cr, Sb, Se). Emphasis will be placed on the presentation of the most representative works published in the last five years (2015-2019).

Influence of feedstocks and modification methods on biochar's capacity to activate hydrogen peroxide for tetracycline removal

Three types of raw biochar (i.e. CBC, OBC, PBC produced from cornstalk, orange peel and peanut hull, respectively) and the modified ones (i.e., KMnO₄-, KOH- and H₃PO₄-treatment) were employed to activate H₂O₂ for the removal of tetracycline (TC). The effects of pyrolysis temperatures, H₂O₂ concentration and initial pH were examined. TC removal by raw biochars w/o H₂O₂ was dependent on the feedstock and pyrolysis temperature of biochar, but the removal efficiency was still quite low under optimum conditions. The KMnO₄-treatment significantly enhanced the adsorption of TC on all three biochars, but only enhanced the TC removal by CBC + H₂O₂. The KOH-treatment had insignificant effect on the adsorption of TC on biochar, but improved the performance of CBC/PBC + H₂O₂. The H₃PO₄-treatment had a negative impact on TC removal by biochar w/o H₂O₂. Overall, H₂O₂ could either enhance or decrease the TC removal by biochar, depending on biochar type, H₂O₂ concentration and solution pH.