A critical review of the production and advanced utilization of biochar via selective pyrolysis of lignocellulosic biomass

Predicting Cd(II) adsorption capacity of biochar materials using typical machine learning models for effective remediation of aquatic environments

The screening and design of "green" biochar materials with high adsorption capacity play a pivotal role in promoting the sustainable treatment of Cd(II)-containing wastewater. In this study, six typical machine learning (ML) models, namely Linear Regression, Random Forest, Gradient Boosting Decision Tree, CatBoost, K-Nearest Neighbors, and Backpropagation Neural Network, were employed to accurately predict the adsorption capacity of Cd(II) onto biochars. A large dataset with 1051 data points was generated using 21 input variables obtained from batch adsorption experiments, including preparation conditions for biochar (2 features), physical properties of biochar (4 features), chemical composition of biochar (9 features), and adsorption experiment conditions (6 features). The rigorous evaluation and comparison of the ML models revealed that the CatBoost model exhibited the highest test R2 value (0.971) and the lowest RMSE (20.54 mg/g), significantly outperforming all other models. The feature importance analysis using Shapley Additive Explanations (SHAP) indicated that biochar chemical compositions had the greatest impact on model predictions of adsorption capacity (42.2 %), followed by adsorption conditions (37.57 %), biochar physical characteristics (12.38 %), and preparation conditions (7.85 %). The optimal experimental conditions optimized by partial dependence plots (PDP) are as follows: as high Cd(II) concentration as possible, C(%) of 33 %, N(%) of 0.3 %, adsorption time of 600 min, pyrolysis time of 50 min, biochar dosage of less than 2 g/L, O(%) of 42 %, biochar pH value of 11.2, and DBE of 1.15. This study unveils novel insights into the adsorption of Cd(II) and provides a comprehensive reference for the sustainable engineering of biochars in Cd(II) wastewater treatment.

Metal-doped biochar for selective recovery and reuse of phosphate from water: Modification design, removal mechanism, and reutilization strategy

Phosphorus (P) plays a crucial role in plant growth, which can provide nutrients for plants. Nonetheless, excessive phosphate can cause eutrophication of water, deterioration of aquatic environment, and even harm for human health. Therefore, adopting feasible adsorption technology to remove phosphate from water is necessary. Biochar (BC) has received wide attention for its low cost and environment-friendly properties. However, undeveloped pore structure and limited surface groups of primary BC result in poor uptake performance. Consequently, this work introduced the synthesis of pristine BC, parameters influencing phosphate removal, and corresponding mechanisms. Moreover, multifarious metal-doped BCs were summarized with related design principles. Meanwhile, mechanisms of selective phosphate adsorption by metal-doped BC were investigated deeply, and the recovery of phosphate from water, and the utilization of phosphate-loaded adsorbents in soil were critically presented. Finally, challenges and prospects for widespread applications of selective phosphate adsorption were proposed in the future.

Synergistic effect of adsorption and photolysis on methylene blue removal by magnetic biochar derived from lignocellulosic biomass

In this study, magnetic biochar was synthesized by doping Fe3O4 onto the biochar surface followed by analysis of its properties. The efficiency of methylene blue (MB) removal through the combined processes of adsorption and photolysis was assessed. The presence of Fe3O4 on the biochar surface was confirmed using Raman spectroscopy and X-ray photoelectron spectroscopy. The magnetic biochar, after MB adsorption, showed a magnetism of 39.50 emu/g leading to a 97.07 % recovery rate. The specific surface area of biochar was higher (380.68 m2/g) than that of magnetic biochar (234.46 m2/g), and the maximum adsorption capacity of MB was higher in the biochar (0.03 mg/g) than that in magnetic biochar (0.02 mg/g) under the optimal conditions for MB adsorption. The MB adsorption experiments using biochar or magnetic biochar were optimally conducted under 10-20 mg/L MB concentration, 1 g biochar dosage, pH 12, 200 rpm rotation speed, 25 °C temperature, and 30 min duration. Under dark conditions, biochar had a higher MB removal rate, at 83.91 %, compared to magnetic biochar, at 78.30 %. Under visible light (λ > 425 nm), magnetic biochar effectively removed MB within 10 min, highlighting the synergistic effect of adsorption and photolysis. MB is physically and chemically adsorbed by the monolayer on the surface of EB and EMB according to adsorption behavior.

Heat-resistant boron-nitrogen doped lignin-derived adsorbent-catalyst for gaseous aromatic pollutants removal

Lignin-based carbon material can be utilized as carbonaceous adsorbents for the removal of toxic gaseous organic pollutants, while the poor heat-resistance limited its widely application. Here in, B-N co-doped lignin carbon (BN-C) with high thermal stability was synthesized, and the optimized BN-C (1:2) exhibited notably improved heat resistance with the decomposition temperature up to 505 °C, and excellent adsorption capacity for o-dichlorobenzene (o-DCB) (1510.0 mg/g) and toluene (947.3 mg/g), together with good cyclic stability over 10 cycles for o-dichlorobenzene. The existence of abundant hexagonal boron nitride (h-BN) with good thermal conductivity contributed to the superior heat-resistance of BN-C (1:2), and the high specific surface area (1764.5 m2/g), enriched hydroxyl functional groups and improved graphitization degree contributed to its enhanced adsorption performance. More importantly, BN-C (1:2) supported Ru could effectively remove o-DCB and toluene at wide temperature range (50-300 °C). The present work guided the development of heat-resistant lignin-derived adsorbent-catalyst for gaseous aromatic pollutants removal, which benefits both environmental protection and resource utilization.

Coconut shell-based biochars produced by an innovative thermochemical process for obtaining improved lignocellulose-based adsorbents

The urgent need for a simple and cost-effective thermochemical process to produce biochar has prompted this study. The aim was to develop a straightforward thermochemical process under O2-limited conditions for the production of coconut-based biochar (CBB) and to assess its ability to remove methylene blue (MB) through adsorption, comparing it with CBB produced by slow pyrolysis. CBBs were obtained under different atmospheric conditions (O2-limited, muffle furnace biochar (MFB); and inert, pyrolytic reactor biochar (PRB)), at 350, 500, and 700 °C, and for 30 and 90'. MFB and PRB were characterized using FTIR, RAMAN, SEM, EDS, and XRD analyses. Adsorption tests were conducted using 1.0 g L-1 of MFB and PRB, 10 mg L-1 of MB at 25 °C for 48 h. Characterization revealed that atmospheric conditions significantly influenced the yield and structural features of the materials. PRB exhibited higher yields and larger cavities than MFB, but quite similar spectral features. Adsorption tests indicated that MFB and PRB had qt values of 33.1 and 9.2 mg g-1, respectively, which were obtained at 700 °C and 90', and 700 °C and 30', respectively. This alternative method produced an innovative and promising lignocellulose-based material with great potential to be used as a biosorbent.

Potent Anthelmintic Activity of Chalcones Synthesized by an Effective Green Approach

There is currently an urgent need for new anthelmintic agents due to increasing resistance to the limited available drugs. The chalcone scaffold is a privileged structure for developing new drugs and has been shown to exhibit potential antiparasitic properties. We synthesized a series of chalcones via Claisen-Schmidt condensation, introducing a novel recoverable catalyst derived from biochar obtained from the pyrolysis of tree pruning waste. Employing microwave irradiation and a green solvent, this approach demonstrated significantly reduced reaction times and excellent compatibility with various functional groups. The result was the generation of a library of functionalized chalcones, exhibiting exclusive (E)-selectivity and high to excellent yields. The chalcone derivatives were evaluated on the free-living nematode Caenorhabditis elegans. The chalcone scaffold, along with two derivatives incorporating a methoxy substituent in either ring, caused a concentration-dependent decrease of worm motility, revealing potent anthelmintic activity and spastic paralysis not mediated by the nematode levamisole-sensitive nicotinic receptor. The combination of both methoxy groups in the chalcone scaffold resulted in a less potent compound causing worm hypermotility at the short term, indicating a distinct molecular mechanism. Through the identification of promising drug candidates, this work addresses the demand for new anthelmintic drugs while promoting sustainable chemistry.

Bio-derived carbon-based materials for sustainable environmental remediation and wastewater treatment

Biosynthesized nanocomposites, particularly those incorporating carbon-based materials, exhibit exceptional tunability and multifunctionality, surpassing the capabilities of conventional materials in these aspects. Developing practical solutions is critical to address environmental toxins from pharmaceuticals, heavy metals, pesticides, and dyes. Biomass waste is a readily available carbon source, which emerges as a promising material for producing biochar due to its inherent advantages: abundance, low cost, and environmentally friendly nature. This distribution mainly uses carbon-based materials (CBMs) and biomass waste in wastewater treatment. This review paper investigates several CBM types, including carbon aerogels, nanotubes, graphene, and activated carbon. The development of bio-derived carbon-based nanomaterials are discussed, along with the properties and composition of carbon materials derived from biomass waste and various cycles, such as photodegradation, adsorption, and high-level oxidation processes for natural remediation. In conclusion, this review examines the challenges associated with biochar utilization, including cost, recovery, and practical implementation.

Efficient degradation of tetracycline via peroxymonosulfate activation by phosphorus-doped biochar loaded with cobalt nanoparticles

The accumulation of tetracycline hydrochloride (TCH) threatens human health because of its potential biological toxicity. Carbon -based materials with easy isolation and excellent performance that can activate peroxymonosulfate (PMS) to generate reactive oxygen species for TCH degradation are essential, but the development of such materials remains a significant challenge. In this study, based on the idea of treating waste, tricobalt tetraoxide loaded P-doped biochar (Co NP-PBC) was synthesised to activate PMS for the degradation of TCH. Possible degradation pathways and intermediate products of TCH were identified using High performance liquid chromatography tandem mass spectrometry (HPLC-MS) detection and density functional theory analysis. Toxicity analysis software was used to predict the toxicity of the intermediate products. Compared to catalysts loaded with Fe and Mn and other Co-based catalysts, Co NP-PBC exhibited an optimal performance (with a kinetic constant of 0.157 min-1 for TCH degradation), and over 99.0% of TCH can be degraded within 20 min. This mechanism demonstrates that the non-free radical oxidation of 1O2 plays a major role in the degradation of TCH. This study provides insights into the purification of wastewater using BC-based catalysts.

Synergistic interactions and reaction mechanisms of biochar surface functionalities in antibiotics removal from industrial wastewater

Biochar, a carbon-rich material with a unique surface chemistry (high abundance of surface functional groups, large surface area, and well-distributed), has shown great potential as a sustainable solution for industrial wastewater treatment as compared to conventional industrial wastewater treatment techniques demand substantial energy consumption and generate detrimental byproducts. This critical review emphasizes the surface functionalities formation and development in biochar to enhance its physiochemical properties, for utilization in antibiotics removal. Factors affecting the formation of functionalities, including carbonization processes, feedstock materials, operating parameters, and the influence of pre-post treatments, are thoroughly highlighted to understand the crucial role of factors influencing biochar properties for optimal antibiotics removal. Furthermore, the research explores the removal mechanisms and interactions of biochar-based surface functionalities, hydrogen bonding, encompassing electrostatic interactions, hydrophobic interactions, π-π interactions, and electron donor and acceptor interactions, to provide insights into the adsorption/removal behavior of antibiotics on biochar surfaces. The review also explains the mechanism of factors influencing the removal of antibiotics in industrial wastewater treatment, including particle size and pore structure, nature and types of surface functional groups, pH and surface charge, temperature, surface modification strategies, hydrophobicity/hydrophilicity, biochar dose, pollutant concentration, contact time, and the presence of coexisting ions and other substances. Finally, the study offers reusability and regeneration, challenges and future perspectives on the development of biochar-based adsorbents and their applications in addressing antibiotics. It concludes by summarizing the key findings and emphasizing the significance of biochar as a sustainable and effective solution for mitigating antibiotics contamination in industrial wastewater.

Properties and Possibilities of Using Biochar Composites Made on the Basis of Biomass and Waste Residues Ferryferrohydrosol Sorbent

Biochar enriched with metals has an increased potential for sorption of organic and inorganic pollutants. The aim of the research was to identify the possibility of using biochar composites produced on the basis of waste plant biomass and waste FFH (ferryferrohydrosol) containing iron atoms, after CO2 capture. The composites were produced in a one-stage or two-stage pyrolysis process. Their selected properties were determined as follows: pH, ash content, C, H, N, O, specific surface area, microstructure and the presence of surface functional groups. The produced biochar and composites had different properties resulting from the production method and the additive used. The results of experiments on the removal of methylene blue (MB) from solutions allowed us to rank the adsorbents used according to the maximum dye removal value achieved as follows: BC1 (94.99%), B (84.61%), BC2 (84.09%), BC3 (83.23%) and BC4 (83.23%). In terms of maximum amoxicillin removal efficiency, the ranking is as follows: BC1 (55.49%), BC3 (23.51%), BC2 (18.13%), B (13.50%) and BC4 (5.98%). The maximum efficiency of diclofenac removal was demonstrated by adsorbents BC1 (98.71), BC3 (87.08%), BC4 (74.20%), B (36.70%) and BC2 (30.40%). The most effective removal of metals Zn, Pb and Cd from the solution was demonstrated by BC1 and BC3 composites. The final concentration of the tested metals after sorption using these composites was less than 1% of the initial concentration. The highest increase in biomass on prepared substrates was recorded for the BC5 composite. It was higher by 90% and 54% (for doses of 30 g and 15 g, respectively) in relation to the biomass growth in the soil without additives. The BC1 composite can be used in pollutant sorption processes. However, BC5 has great potential as a soil additive in crop yield and plant growth.

Lignocellulosic biomass fertilizers: Production, characterization, and agri-applications

The growing focus on sustainable agriculture and optimal resource utilization has spurred investigations into lignocellulosic biomass as a potential source for producing environmentally friendly fertilizers. This paper reviews recent advancements in the production and application of innovative fertilizers derived from lignocellulose. It highlights potential in enhancing agricultural productivity and reducing environmental impacts such as carbon footprint and water pollution. The paper outlines various methods for conversion, highlighting the unique advantages of chemical, enzymatic, and microbiological processes, for converting lignocellulosic biomass into nutrient-rich fertilizers. The study compares the efficacy of lignocellulosic fertilizers to traditional fertilizers in promoting crop growth, enhancing soil health, and reducing nutrient losses. The results demonstrate the potential of lignocellulosic biomass-derived fertilizers in promoting resource efficiency and sustainable agriculture. While this research significantly contributes to the existing body of knowledge, further studies on long-term impacts and scalability are recommended for the development of innovative and sustainable agricultural practices.

Cooperative production of monophenolic chemicals and carbon adsorption materials from cascade pyrolysis of acid hydrolysis lignin

A novel cascade pyrolysis upgrading process for acid hydrolysis lignin (AHL), consisting of pyrolysis, catalytic upgrading of pyrolysis vapors, and pyrolysis char, was developed to improve the yield of value-added products (monophenolic chemicals and carbon materials). Pyrolysis of AHL at 450 °C and subsequent catalytic upgrading of pyrolysis vapors over Ni/H-ZSM-5 boosted the concentration of monophenolic chemicals in pyrolysis liquids by 58%. The carbon material prepared from pyrolysis char using KOH as activating agent exhibited a large specific surface area of 2902.5 m2/g and a large total pore volume of 1.45 cm3/g, thus affording good adsorption capacity for methylene blue (824.87 mg/g) and iodine (2333.17 mg/g). Moreover, the cascade pyrolysis upgrading of AHL achieved a yield of 68.52% desired products, which was much higher than the reported results (single production of monophenols and pyrolysis char). In summary, this work provides a potential reference for efficient utilization of lignin in large-scale applications.

Iron-modified biochar inhibiting Cd uptake in rice by Cd co-deposition with Fe oxides in the rice rhizosphere

Fe-enriched biochar has proven to be effective in reducing Cd uptake in rice plants by enhancing iron plaque formation. However, the effect of Fe on biochar, especially the biochar with high S content, for Cd immobilization in rice rhizosphere was not fully understood. To obtain eco-friendly Fe-loaded biochar at a low cost, garlic straw, bean straw, and rape straw were chosen as the feedstocks for Fe-enhanced biochar production by co-pyrolysis with Fe2O3. The resulting biochars and Fe-loaded biochars were GBC, BBC, BRE, GBC-Fe, BBC-Fe, and BRE-Fe, respectively. XRD and FTIR analyses showed that Fe was successfully loaded onto the biochar. The pristine and Fe-containing biochars were applied at rates of 0% (BC0) and 0.1% in pot experiments. Results suggested that BBC-Fe caused the highest reduction in Cd content of rice grain, and the reductions were 67.9% and 31.4%, compared with BC0 and BBC, respectively. Compared to BBC, BBC-Fe effectively reduced Cd uptake in rice roots by 47.5%. The exchangeable and acid-soluble fraction of Cd (F1-Cd) in soil with BBC-Fe treatment was 37.6% and 63.7% lower than that of BC0 and BBC, respectively. Compared to BC0, soil pH was increased by 0.53 units with BBC-Fe treatment. BBC-Fe significantly increased Fe oxides (free Fe oxides, amorphous Fe oxides, and complex Fe oxides) content in the soil as well. DGT study demonstrated that BBC-Fe could enhance the mobility of sulfate in the rhizosphere, which might be beneficial for Cd fixation in the rhizosphere. Moreover, BBC-Fe increased the relative abundance of Bacteroidota, Firmicutes, and Clostridia, which might be beneficial for Cd immobilization in the rhizosphere. This work highlights the synergistic effect of loaded Fe and biochar on Cd immobilization by enhancing Cd deposited with Fe oxides.

Applications and synergistic degradation mechanisms of nZVI-modified biochar for the remediation of organic polluted soil and water: A review

Increasing organic pollution in soil and water has garnered considerable attention in recent years. Nano zero-valent iron-modified biochar (nZVI/BC) has been proven to remediate the contaminated environment effectively due to its abundant active sites and unique reducing properties. This paper provides a comprehensive overview of the application of nZVI/BC in organic polluted environmental remediation and its mechanisms. Firstly, the review introduced primary synthetic methods of nZVI/BC, including in-situ synthesis (carbothermal reduction and green synthesis) and post-modification (liquid-phase reduction and ball milling). Secondly, the application effects of nZVI/BC were discussed in remediating soil and water polluted by antibiotics, pesticides, polycyclic aromatic hydrocarbons (PAHs), and dyes. Thirdly, this review explored the mechanisms of the adsorption and chemical degradation of nZVI/BC, and synergistic degradation mechanisms of nZVI/BC-AOPs and nZVI/BC-Microbial interactions. Fourth, the factors that influence the removal of organic pollutants using nZVI/BC were summarized, encompassing synthesis conditions (raw materials, pyrolysis temperature and aging of nZVI/BC) and external factors (reagent dosage, pH, and coexisting substances). Finally, this review proposed future challenges for the application of nZVI/BC in environmental remediation. This review offers valuable insights for advancing technology in the degradation of organic pollutants using nZVI/BC and promoting its on-site application.

Biochar obtained from alkaline earth metal-treated mushroom residue: Thermal behavior and methyl orange adsorption capability

To achieve the resource utilization of edible fungi residue and obtain efficient adsorbents for treating dyeing wastewater, biochars were prepared from mushroom residue (MR) with the introduction of alkaline-earth metals (AEMs) and used for methyl orange (MO) wastewater treatment. The thermal behavior of the AEM-treated MR was analyzed using thermogravimetric analysis. The physicochemical properties of the biochars obtained from AEM-treated MR (MRCs) were characterized using Fourier transform infrared spectroscopy, laser particle size analyzer, N2 adsorption/desorption, and scanning electron microscopy. The adsorption performance of MRCs on MO was also investigated. The involvement of AEMs was found to obviously move the main pyrolysis zone of MR to a low temperature region and reduce the temperature corresponding to the maximum weight loss rate and activation energy, which is highly dependent on the concentration of AEMs, the anion and cationic species of the AEMs. Moreover, the addition of AEMs resulted in a decrease in oxygen-containing functional groups (-OH, CO, or C-O), a weakening of surface negative charges, an enhancement in aromatic functional groups, and an increase in specific surface area of the MRCs. The adsorption performance of MO on MRCs was significantly improved with the introduction of AEMs as well. Among them, MR pre-treated with 5 mmol/g MgCl2 (MR-MgCl2-5) shows the lowest temperature corresponding to the maximum weight loss rate and the lowest activation energy of 278.52 °C and 4.28 kJ/mol, respectively. The biochar prepared from MR-MgCl2-5 under 400 °C (MR-MgCl2-5-400C) has the weakest surface negative charge and the highest adsorption capacity for MO. The adsorption isotherms, adsorption kinetics, and thermodynamic analysis results showed that the adsorption of MO on MR-MgCl2-5-400C was a spontaneous, chemically dominant monolayer adsorption, with a theoretical maximum adsorption capacity of 81.30 mg/g. This study suggests that AEMs treatment, especially with 5 mmol/g MgCl2, can readily transform edible fungi residue into a low-cost, high-efficient dyeing wastewater adsorbent.

Performance and mechanism of benzene adsorption on ZnCl2 one-step modified corn cob biochar

Utilizing cost-effective corn cob, zinc chloride-modified biochar was synthesized through one-step method for benzene adsorption from air. Study on impregnation ratio impact showed optimal benzene adsorption at ZnCl2:CC ratio of 1.5:1, with capacity reaching 170.53 mg g-1. Characterization using BET, SEM, FTIR, and XPS was conducted. BET results indicated specific surface area of Zn1.5BC at 1260.63 m2 g-1 and maximum pore volume of 0.546 m3 g-1. SEM analysis revealed microporous-mesoporous structure in Zn1.5BC, marking significant improvement over original biomass. DFT pore size distribution and FTIR analysis suggested post-modification dehydration and elimination reactions, leading to volatile compound release, functional group reduction, and pore widening. XPS analysis showed decrease in O = C-OH content with increased impregnation ratio, enhancing biochar's π-π electron diffusion for benzene. Langmuir isotherm and pseudo-second-order kinetic models effectively described experimental data, indicating multilayer benzene adsorption on biochar controlled by complex physicochemical adsorption and pore diffusion. Adsorption condition assessment, including adsorption temperature (20-120 ℃) and benzene concentration in inlet phase (159.73-383.36 mg L-1), was performed. Yoon-Nelson model fitting indicated adsorption site loss at higher temperatures and reduced capture ability due to increased adsorbate molecule kinetic energy. Higher adsorbate concentrations aided adsorption molecule diffusion to biochar surface and internal pores, increasing adsorption rate and shortening equilibrium time. Overall, zinc chloride-modified biochar facilitates benzene adsorption through pore filling and π-π interactions, with pore filling as primary mechanism. Produced biochar shows excellent regeneration properties and reusability.

Global trends of pyrolysis research: a bibliometric analysis

Pyrolysis has become an interesting waste valorization method leading to an increasing number of research studies in this field in the last decade. The present study aims to provide a comprehensive knowledge map of scientific production in pyrolysis, discuss the current state of research, and identify the main research hotspots and trends in recent years. The systematic review, supported by analysis of countries and institutions, keyword co-occurrence analysis, analysis of keyword trends, journal analysis, and article impact, was carried out on 6234 journal articles from the Science Citation Index Expanded database of the Web of Science Core Collection. As a result, four main research hotspots were identified: 1) characterization techniques and pyrolysis kinetic models, 2) biochar production and its main applications, 3) bio-oil production and catalytic pyrolysis, and 4) co-pyrolysis, which has become a consolidated research hotspot since 2018. Additionally, the main challenges and opportunities for future research have been identified, such as 1) the development of multi-step kinetic models for studying complex wastes, 2) the integration of biochar into other valorization processes, such as anaerobic digestion, and 3) the development of catalytic hydropyrolysis for the valorization of organic waste. This bibliometric analysis provides a visualization of the current context and future trends in pyrolysis, facilitating future collaborative research and knowledge exchange.

Stability and ecological risk assessment of nickel (Ni) in phytoremediation-derived biochar

Improper treatment of heavy metal-enriched biomass generated after phytoremediation might cause secondary pollution in soil and water. At present, the pyrolysis process is an effective method for the treatment of phytoremediation residue. In this study, Ni-enriched biomass was prepared using hydroponics method and further pyrolyzed at different temperatures (300-700 °C). At low pyrolysis temperatures (below 500 °C), carbonate precipitation was the main reason of Ni stabilization in biochar. Nevertheless, the formed phosphate and aluminosilicate were important factors for immobilizing Ni in biochar at high pyrolysis temperatures (above 500 °C). Moreover, the oxidizable (F3) and residual (F4) components of Ni in biochar increased with increasing pyrolysis temperature, which indicated that higher pyrolysis temperature could effectively reduce the bioavailability of Ni in biochar. The results of deionized water, acidification, oxidation, and toxic characteristic leaching procedure (TCLP) experiments showed that pyrolysis temperature was the dominant factor for Ni stabilization in biochar. The ecological risk assessments further proved that pyrolyzed Ni-enriched biochar could reduce the environmental toxicity and potential ecological risks of Ni. In the soil simulated experiment, the soil microenvironment gradually promoted the transformation of Ni in BCNiX from bioavailable fraction to stable fraction. Overall, this study would expose more reasonable reference for the long-term storage of phytoremediation residues.

Agrowaste-generated biochar for the sustainable remediation of refractory pollutants

The rapid growth of various industries has led to a significant, alarming increase in recalcitrant pollutants in the environment. Hazardous dyes, heavy metals, pesticides, pharmaceutical products, and other associated polycyclic aromatic hydrocarbons (such as acenaphthene, fluorene, fluoranthene, phenanthrene, and pyrene) have posed a significant threat to the surroundings due to their refractory nature. Although activated carbon has been reported to be an adsorbent for removing contaminants from wastewater, it has its limitations. Hence, this review provides an elaborate account of converting agricultural waste into biochar with nanotextured surfaces that can serve as low-cost adsorbents with promising pollutant-removing properties. A detailed mechanism rationalized that this strategy involves the conversion of agrowaste to promising adsorbents that can be reduced, reused, and recycled. The potential of biowaste-derived biochar can be exploited for developing biofuel for renewable energy and also for improving soil fertility. This strategy can provide a solution to control greenhouse gas emissions by preventing the open burning of agricultural residues in fields. Furthermore, this serves a dual purpose for environmental remediation as well as effective management of agricultural waste rich in both organic and inorganic components that are generated during various agricultural operations. In this manner, this review provides recent advances in the use of agrowaste-generated biochar for cleaning the environment.

Enhancing sorption of layered double hydroxide-based magnetic biochar for arsenic and cadmium through optimized preparation protocols

The impact of multiple preparation protocols on properties and performance of modified biochar remains unclear. This study prepared layered double hydroxide (LDH)-based magnetic biochars (LMBCs) with different LDH loading rates (LLR), pyrolysis temperatures, and biomass sources to explore their performance-characterization relationships toward As(III) and Cd(II). Higher LLR and pyrolysis temperature enhanced LMBCs᾿ adsorption capacities by increasing specific surface area (SSA) and metal/O-containing groups. Hence, LMBC produced at 2:1 LLR (LDH: magnetic biochar) and 800 ℃ pyrolysis exhibited maximum adsorption over 2 times that of LMBC with 0.5:1 LLR and 400 ℃ pyrolysis. Bamboo-sourced LMBC demonstrated superior adsorption than sewage sludge and garlic-sourced LMBCs due to its increased SSA, enabling a higher loading of nano-LDH. Adsorption of As(III) and Cd(II) onto LMBCs was governed by metal-mineral and metal-containing group through co-precipitation and complexation. This study provides a reference for adjusting the preparation protocols to improve sorption performance of modified biochar toward multiple heavy metals.

Unlocking the potential of Dongting Lake-grown Miscanthus lutarioriparius biomass: A comprehensive quality analysis and bioproduct application study

Miscanthus lutarioriparius grown in Dongting Lake has an annual biomass yield potential of 1 million tons. However, with the shutdown of its previous utilization for paper-making, abandoning this huge amount of biomass has caused serious economic, ecological, and social problems. Constructing an industrial cluster to continuously convert biomass into various bioproducts is a win-win measure to address this dilemma. With the increasing confirmation of the importance of biomass quality affecting the conservation process, fully understanding the biomass characteristics of Dongting Lake-grown M. lutarioriparius is crucial for building a scientific industrial cluster. The present work is designed to explore the variation in biomass quality across the entire Dongting Lake area. Results show that the biomass contented with Cd, Mn, Zn, and Cr has significant geographical differences, with a general trend of Southern Dongting Lake-grown biomass having a higher concentration than that from Eastern and Western Dongting Lake areas. Moreover, significant differences are found in terms of biomass ash content, lignin content, and the degree of polymerization of cellulose (DP). The biomass with low ash content is generally from the entire Eastern Dongting Lake area and the northern part of the Western Dongting Lake area. Virtually all Western Dongting Lake-grown biomass has a low lignin content (approximately 18 %). Regarding the spatial variation of DP, Eastern Dongting Lake-grown biomass has a higher DP (average at 585.33) than that in Southern (575.15) and then Western Dongting Lake (529.16). Based on these quality indicators, the biomass production potentials for bioethanol, biochar, and xylo-oligosaccharide were calculated and visualized. Results show that biomass from almost the entire Western and Eastern Dongting Lake area is suitable for bioethanol and xylo-oligosaccharide production, while biomass from the Southern Dongting Lake area for biochar production. These results provide scientific guidance for the future utilization of Dongting Lake-grown M. lutarioriparius biomass.

Conversion of agricultural biomass into valuable biochar and their competence on soil fertility enrichment

Globally several nations generates a large amount of biomass waste. Thus, this review focuses on the potential for converting plant biomass into nutritionally enriched useful biochar with promising properties. The use of biochar on farmland acts as both a soil fertility enhancer, improving both the physical as well as chemical characteristics of soil. The biochar availability in soil can retain minerals and water as well as considerably enhanced the soil fertility by their optimistic characteristics. Thus, this review also discuss about how biochar enhances the quality of agriculture soil and polluted soil. Since, the biochar derived from the plant residues might contain most valuable nutritional properties, which can enhance the physicochemical properties of soil and that can support the growth of plant along with the increased biomolecule content. Since, the healthy plantation can support the production of nutritionally enriched crop yield. Agriculture biochar amalgamated soil significantly improved soil beneficial microbial diversity. Beneficial microbial activity increased soil fertility and balanced the soil's physicochemical properties significantly. Such balanced soil physicochemical properties significantly enhanced plantation growth, as well as disease resistance and higher yield potential than any other fertiliser supplements for soil fertility and plant growth.

Adsorptive removal of dimethyl phthalate using peanut shell-derived biochar from aqueous solutions: equilibrium, kinetics, and mechanistic studies

Rise in polymer industry and extensive use of their products leads to leaching of phthalate esters and distributed into the different matrices of the environment. This chemical group has the potential to hamper the life of living organisms and ecosystem. Thus, it is essential to develop cost-effective adsorbents capable of removing these harmful compounds from the environment. In this work, peanut hull-derived biochar was taken as the adsorbent, and DMP was selected as the model pollutant or adsorbates. The biochars of different properties were produced at three pyrolysis temperatures (i.e., 450, 550, and 650 °C) to check how temperature affected the adsorbent properties and adsorption performance. Consequently, the performance of biochars for DMP adsorption was thoroughly studied by the combination of experiments and compared with commercial activated carbon (CAC). All the adsorbents are meticulously characterized using various analytical techniques and used for adsorption DMP from aqueous solutions. The results suggested that adsorption was favoring chemisorption with multi-layered adsorption as adsorption kinetics and isotherm are in good alignment with pseudo-second-order kinetics and Freundlich isotherm, respectively. Further, thermodynamic study revealed DMP adsorption on adsorbent is physically spontaneous and endothermic. The removal efficiency order of four adsorbent was as follows: BC650 > CAC > BC550 > BC450 with maximum efficiency of 98.8% for BC650 followed by 98.6% for CAC at optimum conditions. And as it is a short carbon chain PAE, dominant mechanisms of adsorption for DMP onto porous biochar were H-bonding, π-π EDA interactions, and diffusion within the pore spaces. Therefore, this study can provide strategies for the synthesis of biochar for effectively removing DMP from aqueous solution.

Preparation, Modification, and Application of Biochar in the Printing Field: A Review

Biochar is a solid material enriched with carbon produced by the thermal transformation of organic raw materials under anoxic or anaerobic conditions. It not only has various environmental benefits including reducing greenhouse gas emissions, improving soil fertility, and sequestering atmospheric carbon, but also has the advantages of abundant precursors, low cost, and wide potential applications, thus gaining widespread attention. In recent years, researchers have been exploring new biomass precursors, improving and developing new preparation methods, and searching for more high-value and meaningful applications. Biochar has been extensively researched and utilized in many fields, and recently, it has also shown good industrial application prospects and potential application value in the printing field. In such a context, this article summarizes the typical preparation and modification methods of biochar, and also reviews its application in the printing field, to provide a reference for future work.

Efficient mitigation of emerging antibiotics residues from water matrix: Integrated approaches and sustainable technologies

The prevalence of antibiotic traces in the aquatic matrices is a concern due to the emanation of antibiotic resistance which requires a multifaceted approach. One of the potential sources is the wastewater treatment plants with a lack of advance infrastructure leading to the dissemination of contaminants. Continuous advancements in economic globalization have facilitated the application of several conventional, advanced, and hybrid techniques for the mitigation of rising antibiotic traces in the aquatic matrices that have been thoroughly scrutinized in the current paper. Although the implementation of existing mitigation techniques is associated with several limiting factors and barriers which require further research to enhance their removal efficiency. The review further summarizes the application of the microbial processes to combat antibiotic persistence in wastewater establishing a sustainable approach. However, hybrid technologies are considered as most efficient and environmental-benign due to their higher removal efficacy, energy-efficiency, and cost-effectiveness. A brief elucidation has been provided for the mechanism responsible for lowering antibiotic concentration in wastewater through biodegradation and biotransformation. Overall, the current review presents a comprehensive approach for antibiotic mitigation using existing methods however, policies and measures should be implemented for continuous monitoring and surveillance of antibiotic persistence in aquatic matrices to reduce their potential risk to humans and the environment.

Efficient Removal of Tetracycline and Bisphenol A from Water with a New Hybrid Clay/TiO2 Composite

New TiO₂ hybrid composites were prepared from kaolin clay, predried and carbonized biomass, and titanium tetraisopropoxide and explored for tetracycline (TET) and bisphenol A (BPA) removal from water. Overall, the removal rate is 84% for TET and 51% for BPA. The maximum adsorption capacities (q_m) are 30 and 23 mg/g for TET and BPA, respectively. These capacities are far greater than those obtained for unmodified TiO₂. Increasing the ionic strength of the solution does not change the adsorption capacity of the adsorbent. pH changes only slightly change BPA adsorption, while a pH > 7 significantly reduces the adsorption of TET on the material. The Brouers-Sotolongo fractal model best describes the kinetic data for both TET and BPA adsorption, predicting that the adsorption process occurs via a complex mechanism involving various forces of attraction. Temkin and Freundlich isotherms, which best fit the equilibrium adsorption data for TET and BPA, respectively, suggest that adsorption sites are heterogeneous in nature. Overall, the composite materials are much more effective for TET removal from aqueous solution than for BPA. This phenomenon is assigned to a difference in the TET/adsorbent interactions vs the BPA/adsorbent interactions: the decisive factor appears to be favorable electrostatic interactions for TET yielding a more effective TET removal.

Biochar preparation and evaluation of its effect in composting mechanism: A review

This article provides an overview of biochar application for organic waste co-composting and its biochemical transformation mechanism. As a composting amendment, biochar work in the adsorption of nutrients, the retention of oxygen and water, and the promotion of electron transfer. These functions serve the micro-organisms (physical support of niche) and determine changes in community structure beyond the succession of composing primary microorganisms. Biochar mediates resistance genes, mobile gene elements, and biochemical metabolic activities of organic matter degrading. The participation of biochar enriched the α-diversity of microbial communities at all stages of composting, and ultimately reflects the high γ-diversity. Finally, easy and convincing biochar preparation methods and characteristic need to be explored, in turn, the mechanism of biochar on composting microbes at the microscopic level can be studied in depth.

Low temperature pyrolytic biochar is a preferred choice for sulfonamide-Cu(II) contaminated soil remediation in tropical climate region

Biochar is getting increasing consideration for eco-friendly soil amendment and environmental remediation. Once added to the soil, biochar would undergo the natural ageing process, affecting its physicochemical properties and, as a result, the adsorption and immobilization of pollutants in the water and soil. To evaluate the high/low temperature pyrolyzed biochar performance on complex contaminants and the effect of climate ageing, the batch experiments were conducted on the adsorption of the pollutants of antibiotics sulfapyridine (SPY) and a typical coexisting heavy metal Cu²⁺ as one or binary system on low/high pyrolytic temperature biochars before and after the simulated tropical climate and frigid climate region ageing treatment. The results showed that high-temperature ageing could enhance the SPY adsorption in biochar-amended soil. The SPY sorption mechanism was fully elucidated, and the result confirmed that H-bonding was the dominant role in biochar-amended soil, and π-π electron-donor-acceptor (EDA) interaction and micro-pore filling was another factor for SPY adsorption. This study could lead to the conclusion that low-temperature pyrolytic biochar is a better option for sulfonamide-Cu(II) contaminated soil remediation in tropical regions.

Synergistic effect in simultaneous removal of cationic and anionic heavy metals by nitrogen heteroatom doped hydrochar from aqueous solutions

Industrial wastewater typically contains both cationic and anionic heavy metals; therefore, their simultaneous removal must be considered to ensure environmental sustainability. Herein, nitrogen heteroatom (N) doped hydrochar derived from corncob was prepared via facile NH₄Cl-aided hydrothermal carbonization and used for the simultaneous adsorption of divalent copper (Cu(II)) and hexavalent chromium (Cr(VI)) in aqueous solutions. During hydrothermal carbonization, NH₄Cl played a vital role as the porogen and N dopant, which contributed to the efficient adsorption affinity toward coexisting Cu(II) and Cr(VI). The theoretical maximum adsorption capacities of the N-doped hydrochar were determined to be 1.223 mmol/g for Cu(II) and 1.995 mmol/g for Cr(VI), which were much better than those of the pristine hydrochar. Furthermore, in the binary-component system, the synergistic effect between Cu(II) and Cr(VI) significantly promoted the adsorption affinity of N-doped hydrochar, resulting in adsorption capacities for Cu(II) and Cr(VI) 9.48 and 1.92 times higher than those of the single-component system, respectively. A series of adsorption experiments and spectroscopic analyses demonstrated that multiple mechanisms, including electrostatic shielding, cation bridging, and redox reactions, mutually contributed to the synergistic effect in the adsorption of coexisting Cu(II) and Cr(VI). Overall, the N-doped hydrochar proved to be effective in simultaneously removing both cationic and anionic heavy metal pollutants.

Effect of Bamboo biochar on strength and water retention properties of low plastic clay and silty sand

Biochar is a carbon-rich stable product derived from the thermochemical decomposition of biomass. The properties of biochar vary with types of feedstock, heating rate, pyrolysis temperature, etc. Consequently, the mechanical and hydrological properties of biochar amended soil (BAS) also differ with types of biochar and soils. However, the effect of bamboo biochar (BB) amendment on soil strength and water retention properties is missing in the previous literature. Bamboo biomass was pyrolysed at 600 °C to produce biochar. BB and soils (low plastic clay (CL) and silty sand (SM)) were mixed to prepare BAS. The samples were prepared by mixing BB in five ratios, i.e., 0%, 1%, 2%, 3.5% and 5% of dry soil weight. The biochar application has increased optimum moisture content, alkalinity (pH) and Atterberg limits, whereas, reduced maximum dry density and specific gravity of both the soils (CL and SM). The unconfined compressive strength (UCS) of CL soil was noted to increase by 10.5% with 2% biochar content and decreased after that, whereas the UCS of SM soil was found to decrease continuously with the biochar content increment. Therefore, the unconfined compressive strength (UCS) result showed that biochar application has contrary effects on both soils. The measured gravimetric water content (GWC) of BAS was increased with biochar increment in both soils. However, GWC increased more in CL than in SM soil at the same biochar content. The microstructural analysis showed that the biochar amendment filled the pore space of the soil matrix, resulting in an increase in UCS and GWC values. The increased water retention capacity and strength (UCS) of biochar amended CL soil provides evidence that it could be used as a landfill cover material.

The activation of peroxymonosulfate by biochar derived from anaerobic and aerobic iron-containing excess sludge

The excess sludge from municipal sewage treatment plants is rich in Fe (III) due to chemical dephosphorization. The activation of peroxymonosulfate (PMS) by biochar derived from anaerobic and aerobic iron-containing excess sludge was studied systematically in this research. Fe (III)-containing excess sludge was cultured in an anaerobic environment for conversion of partial Fe (III) to Fe (II), which was further carbonized to prepare biochar labeled AnSx@Fe. Meanwhile, aerobic sludge with different Fe (III) content was directly carbonized to produce biochar labeled AeS@Fe. For biochar (AnS20@Fe-15%) prepared from 15% Fe(III)-containing anaerobic cultured 20 days sludge, the relative contents of Fe (III) and Fe (II) were 21.26% and 78.74%, which were 31.03% and 68.97% for biochar (AeS@Fe-10%) prepared from 10% Fe (III)-containing aerobic sludge. Fe (III) can be reduced to Fe (II) by both anaerobic culture and carbonization. Their removal rates of tetracycline (TC) through 60 min PMS activation were 97% and 98%, with TOC (Total organic carbon) removal of 61.8% and 53.4% respectively. The reactive species including sulfate radical [Formula: see text], hydroxyl radical (·OH) and singlet oxygen (¹O₂) were produced during PMS activation. After O₂-aeration treatment of both AeS@Fe and AnSx@Fe, the relative content of Fe (II) was decreased and group C = O was disappeared, which resulted in reduction of [Formula: see text], ·OH and ¹O₂. The generation of [Formula: see text] and ·OH was dominated by the Fe (II) activation and the ¹O₂ generation was originated from graphite type N and C = O. Direct carbonization of aerobic and anaerobic sludge is a feasible method to produce biochar for PMS activation.

Bamboo for producing charcoal and biochar for versatile applications

Bamboo, the fastest-growing plant, has several unique characteristics that make it appropriate for diverse applications. It is low-cost, high-tensile, lightweight, flexible, durable, and capable of proliferating even in ineffectual areas (e.g., incline). This review discusses the unique properties of bamboo for making charcoal and biochar for diverse applications. To produce bamboo charcoal and biochar, this study reports on the pyrolysis process for the thermal degradation of organic materials in an oxygen-depleted atmosphere under a specific temperature. This is an alternative method for turning waste biomass into products with additional value, such as biochar. Due to various advantages, bamboo charcoal is preferred over regular charcoal as it has four times the absorption rate and ten times more surface area reported. According to the reports, the charcoal yield ranges from 24.60 to 74.27%. Bamboo chopsticks were the most useful source for producing charcoal, with a high yield of 74.27% at 300 °C in nitrogen, but the thorny bamboo species have a tremendous amount of minimal charcoal, i.e., 24.60%. The reported biochar from bamboo yield ranges from 32 to 80%. The most extensive biochar production is produced by the bamboo D. giganteus, which yields 80% biochar at 300 °C. Dry bamboo stalks at 400 °C produced 32% biochar. One of the sections highlights biochar as a sustainable solution for plastic trash management produced during the COVID-19 pandemic. Another section is dedicated to the knowledge enhancement about the broad application spectrum of the charcoal and biochar. The last section highlights the conclusions, future perspectives, and recommendations on the charcoal and biochar derived from bamboo.

Graphical Abstract

Facile Synthesis of Metal-Impregnated Sugarcane-Derived Catalytic Biochar for Ozone Removal at Ambient Temperature

This study presents the first attempt at employing catalytic biochar to remove ground-level ozone at ambient temperature. With the increase in human activity, ozone has become a critical inorganic pollutant that needs to be addressed, using more sustainable methods. Fe- and Mn-impregnated catalytic biochars were prepared from a sugarcane feedstock via the wet impregnation method and pyrolysis at various temperatures, where the optimum value was determined to be 550 °C. The metal-impregnated biochar samples demonstrated enhanced surface areas and pore volumes compared with the pristine biochar (SCB550), resulting in improved ozone-adsorption capacity. SCB550-Fe exhibited an ozone-adsorption capacity of 52.1 mg/g at 20 ppm, which was approximately four times higher than that of SCB550. SCB550-Fe demonstrated superior ozone-removal performance compared to SCB550-Mn; 122 mg/g capacity as opposed to 116.2 mg/g at 80 ppm, respectively. Isothermal and kinetic modeling are also presented to suggest a plausible mechanism of ozone removal by catalytic biochar. This includes physical adsorption, complexation, electrostatic interaction, and electron transfer during the redox reaction between ozone and metals. Overall, this study should provide preliminary insights into ozone removal using biochar and promote further research regarding material optimization and kinetic studies.

Review of biochar production via crop residue pyrolysis: Development and perspectives

Worldwide surge in crop residue generation has necessitated developing strategies for their sustainable disposal. Pyrolysis has been widely adopted to convert crop residue into biochar with bio-oil and gas being two co-products. The review adopts a whole system philosophy and systematically summarises up-to-date knowledge of crop residue pyrolysis processes, influential factors, and biochar applications. Essential process design tools for biochar production e.g., cost-benefit analysis, life cycle assessment, and machine learning methods are also reviewed, which has often been overlooked in prior reviews. Important aspects include (a) correlating techno-economics of biochar production with crop residue compositions, (b) process operating conditions and management strategies, (c) biochar applications including soil amendment, fuel displacement, catalytic usage, etc., (d) data-driven modelling techniques, (e) properties of biochar, and (f) climate change mitigation. Overall, the review will support the development of application-oriented process pipelines for crop residue-based biochar.

Remediation competence of nanoparticles amalgamated biochar (nanobiochar/nanocomposite) on pollutants: A review

Advanced biochar blended nanoparticles substances, such as nano biochar or nanocomposites, have provided long-term solutions to a wide range of modern-day problems. Biochar blended nano-composites can be created to create better composite materials that combine the benefits of biochar and nanoparticles. Such materials have been typically improved with active functional groups, porous structure, active surface area, catalytic deterioration ability, as well as easy recovery or separation of pollutants. Such biochar-basednanocomposites have good adsorption properties for a variety of pollutants in various form of polluted medium (soil and water contamination). Catalytic nanoparticle encapsulated biochar, can perform concurrently the adsorption (by biochar) as well as catalytic degradation (nanoparticles) functions for pollutants removal from polluted sites. In this review, the advanced and practically feasible techniques involved in the biochar blended nanoparticles-based nanocomposites have been discussed with environmental applications. Furthermore, the mechanisms involved in this composite material in remediation, as well as the advantages and disadvantages of biochar blended nanoparticles-based nanocomposites, were discussed, and future directions for study in this field were suggested.

Bio-oil and biochar from the pyrolytic conversion of biomass: A current and future perspective on the trade-off between economic, environmental, and technical indicators

Over the years, the transformation of biomass into a plethora of renewable value-added products has been identified as a promising strategy to fulfil high energy demands, lower greenhouse gas emissions, and exploit under-utilized resources. Techno-economic analysis (TEA) and life-cycle assessment (LCA) are essential to scale up this process while lowering the conversion cost. In this study, trade-offs are made between economic, environmental, and technical indicators produced from these methodologies to better evaluate the commercialization potential of biomass pyrolysis. This research emphasizes the necessity of combining LCA and TEA variables to assess the performance of the early-stage technology and associated constraints. The important findings based on the LCA analysis imply that most of the studies reported in literature focussed on the global warming potentials (GWP) under environmental category by considering greenhouse gases (GHGs) as evaluation parameter, neglecting many other important environmental indices. In addition, the upstream and downstream processes play an important role in understanding the life cycle impacts of a biomass based biorefinery. Under upstream conditions, the use of a specific type of feedstock may influence the LCA conclusions and technical priority. Under downstream conditions, the product utilization as fuels in different energy backgrounds is crucial to the overall impact potentials of the pyrolysis systems. In view of the TEA analysis, investigations towards maximizing the yield of valuable co-products would play an important role in the commercialization of pyrolysis process. However, comprehensive research to compare the conventional, advanced, and emerging approaches of biomass pyrolysis from the economic perspective is currently not available in the literature.

Recent progress on production technologies of food waste-based biochar and its fabrication method as electrode materials in energy storage application

The abundance of food waste across the globe has called for the mitigation and reduction of these discarded wastes. Herein, the potential of biochar derived from food waste is unquestionable as it provides a sustainable way of utilizing the abundance of available biomass, as well as an effective way of preserving the ecosystem through the reduction of concerning environmental issues. This review focuses on the food waste-based biochar as advanced electrode materials in the energy storage devices. Efforts have been made to present and discuss the current exploration of the food waste utilization, along with the biochar production technologies through thermochemical conversion, including combustion, gasification, and pyrolysis method. Finding its limitation in literatures, discussion on the food waste-based biochar fabrication method as the electrode materials is elaborated, alongside the current food waste-based biochar that has been explored in the energy application thus far. Towards the end, the outlook and perspective on the further development of food waste-based biochar have been outlined.

Preparation of magnetic biochar and its catalytic role in degradation of Cu-EDTA by heterogeneous Fenton reaction

In this study, magnetic biochar (Fe-BC) was synthesized from phoenix tree leaves and FeSO₄·7H₂O by impregnation-pyrolysis method, and was used to activate H₂O₂ to degrade Cu-EDTA. The effects of preparation parameters on the degradation of Cu-EDTA by Fe-BC/H₂O₂ system were investigated by degradation experiments and characterization methods (SEM, BET, FTIR, XRD and XPS). The results showed that the magnetic biochar prepared under the pyrolysis temperature of 400 °C, pyrolysis time of 3 h and iron content of 3 wt% had the best catalytic activity. Within 120 min, the breaking efficiency of Cu-EDTA binding, precipitation efficiency of Cu²⁺ and removal efficiency of TOC could reach 78.48, 71.65 and 46.54% at the conditions of adding 1.0 g/L magnetic biochar and 25 mM H₂O₂ and the iron dissolution was only 0.32 mg/L. The characterization results and comparison experiments demonstrated that the catalytic effect of magnetic biochar not only depends on the transfer of electrons to H₂O₂ by the loaded iron oxides, but also the active oxygen functional groups (OFGs) and persistent free radicals (PFRs) contained on the surface can transfer electrons to H₂O₂ or even dissolved oxygen to produce an amount of hydroxyl radicals (^·OH) and superoxide anion radicals (O₂^·-).

MOF@biomass hybrids: Trends on advanced functional materials for adsorption

This contribution aims to demonstrate the scope of new hybrids between biomass and metal-organic frameworks (MOF@biomass) used in the adsorption process of pollutants. After a brief presentation of the use of the main series of MOFs as efficient adsorbents for different types of pollutants, the limitations of these structures related to particle size and hydrodynamic problems during their application are highlighted. Lignocellulosic biomasses are also recognized as an alternative adsorbent, mainly due to their high natural abundance and their low environmental impact during and after their application. The limited capacity of bioadsorbents becomes important in this research. Consequently, the largest amount of information existing in the last ten years on MOF-Biomass functionalization as a hybrid and improvement technology for adsorption processes is compiled, analyzed, compared and contrasted. So far, there is no evidence of works that exploit the concept of functionalization of adsorbents of different nature to give rise to new hybrid materials. Through this review it was found that the hybrids obtained show a higher adsorption capacity (Qe) compared to their precursors, due to the increase of organic functional groups provided by the biomass. Thus, for heavy metals, dyes, Arsenium anions and other organic and pharmaceutical compounds, there are increases in Qe of about 100 mg g^-1. The possibility of the new hybrid being studied for desorption and reuse processes is also raised, resulting in a new line of research that is attractive for the industry from an economic and environmental point of view. The functionalization methods and techniques used in the studies cited in this article are outlined. In conclusion, this research brings a new horizon of study in the field of adsorption and mentions the main future challenges related to new sustainable applications.

Removal of cadmium in aqueous solutions using a ball milling-assisted one-pot pyrolyzed iron-biochar composite derived from cotton husk

A novel iron-biochar composite adsorbent was produced via ball milling-assisted one-pot pyrolyzed BM-nZVI-BC 800. Characterization proved that nano zero valent iron was successfully embedded in the newly produced biochar, and the nZVI payload was higher than that of traditional one-pot pyrolyzed methods. BM-nZVI-BC 800 provided a high adsorption performance of cadmium reaching 96.40 mg·g^-1 during batch testing. Alkaline conditions were beneficial for cadmium removal of BM-nZVI-BC 800. The pseudo-second-order kinetic model and Langmuir isotherm fitted better, demonstrating that the Cd adsorption on the BM-nZVI-BC 800 was a chemical and surface process. The intraparticle diffusion controlled the adsorption of BM-nZVI-BC 800. The physisorption dominated by high specific surface area and mesoporous structure was the primary mechanism in the removal of cadmium, though electrostatic attraction and complexation also played a secondary role in cadmium adsorption. Compared to adsorbents prepared by more traditional methods, the efficiencies of the ball milling-assisted one-pot pyrolyzed method appears superior.

Machine learning in the evaluation and prediction models of biochar application: A review

This article reviews recent studies applying machine learning (ML) approaches to biochar applications. We first briefly introduce the general biochar production process. Various aspects are contained, including the biochar application in the elimination of heavy metals and/or organic compounds and the biochar application in environmental and economic scopes, for instance, food security, energy, and carbon emission. The utilization of ML methods, including ANN, RF, and NN, plays a vital role in evaluating and predicting the efficiency of biochar absorption. It has been proved that ML methods can validly predict the adsorption effectiveness of biochar for water heavy metals with higher accuracy. Moreover, the literature proposed a comprehensive data-driven model to forecast biochar yield and compositions under various biomass input feedstock and different pyrolysis criteria. They said a 12.7% improvement in prediction accuracy compared to the existing literature. However, it might need further optimization in this direction. In summary, this review concludes increasing studies that a well-trained ML method can sufficiently reduce the number of experiment trials and working times associated with higher prediction accuracy. Moreover, further studies on ML applications are needed to optimize the trade-off between biochar yield and its composition.

Coconut shell and husk biochar: A review of production and activation technology, economic, financial aspect and application

The coconut industry generates a relatively large amount of coconut shell and husk biomass, which can be utilized for industrial and environmental purposes. Immense potential for added value when coconut shell and husk biomass are turned into biochar and limited studies are available, making this review paper significant. This paper specifically presents the production and activation technology, economic and financial aspect and application of biochar from coconut shell and husk biomass. Pyrolysis, gasification and self-sustained carbonization are among the production technology discussed to convert this biomass into carbon-rich materials with distinctive characteristics. The surface characteristics of coconut-based biochar, that is, Brunauer-Emmett-Teller (BET) surface area (S_BET), pore volume (V_p), pore diameter (d_p) and surface functional group can be enhanced by physical and chemical activation and metal impregnation. Due to their favourable characteristics, coconut shell and husk-activated biochar exhibit their potential as valuable adsorption materials for industrial and environmental application including biodiesel production, capacitive deionization, soil amendment, water treatment and carbon sequestration. With the knowledge of the potential, the coconut industry can contribute to both the local and global biocircular economy by producing coconut shell and husk biochar for economic development and environmental remediation. The capital and operating cost for production and activation processes must be taken into account to ensure bioeconomy sustainability, hence coconut shell and husk biomass have a great potential for income generation.

Biochar application for greenhouse gas mitigation, contaminants immobilization and soil fertility enhancement: A state-of-the-art review

Rising global temperature, pollution load, and energy crises are serious problems, recently facing the world. Scientists around the world are ambitious to find eco-friendly and cost-effective routes for resolving these problems. Biochar has emerged as an agent for environmental remediation and has proven to be the effective sorbent to inorganic and organic pollutants in water and soil. Endowed with unique attributes such as porous structure, larger specific surface area (SSA), abundant surface functional groups, better cation exchange capacity (CEC), strong adsorption capacity, high environmental stability, embedded minerals, and micronutrients, biochar is presented as a promising material for environmental management, reduction in greenhouse gases (GHGs) emissions, soil management, and soil fertility enhancement. Therefore, the current review covers the influence of key factors (pyrolysis temperature, retention time, gas flow rate, and reactor design) on the production yield and property of biochar. Furthermore, this review emphasizes the diverse application of biochar such as waste management, construction material, adsorptive removal of petroleum and oil from aqueous media, immobilization of contaminants, carbon sequestration, and their role in climate change mitigation, soil conditioner, along with opportunities and challenges. Finally, this review discusses the evaluation of biochar standardization by different international agencies and their economic perspective.

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.

Catalytic pyrolysis for upgrading silver grass (Miscanthus sinensis) and carbon dioxide into flammable gases

This study proposes a sustainable hydrogen production platform using a fast-growing and inedible biomass waste, silver grass (Miscanthus sinensis). Pyrolysis of silver grass waste (SGW) was investigated using CO₂ as a co-feedstock, focusing on the distribution of hydrogen in different products. When the catalyst was absent, hydrogen element distribution to H₂ gas during pyrolysis of SGW at 800 °C reached 10 wt%. During pyrolysis with the Ni/SiO₂ catalyst, 60.3 wt% of hydrogen was converted into H₂ gas, and 7.3 wt% of hydrogen was distributed in gaseous hydrocarbons at 600 °C. Owing to the addition of CO₂, CO production was promoted by the catalytic conversion of CO₂ and volatile matter. Notably, CO₂ has been proven to be a useful reactant for producing value-added CO. Thus, catalytic pyrolysis in the presence of CO₂ can be considered as a renewable approach to produce flammable gases with the mitigation of CO₂ emissions.

Current Challenges and Perspectives for the Catalytic Pyrolysis of Lignocellulosic Biomass to High-Value Products

Lignocellulosic biomass is an excellent alternative of fossil source because it is low-cost, plentiful and environmentally friendly, and it can be transformed into biogas, bio-oil and biochar through pyrolysis; thereby, the three types of pyrolytic products can be upgraded or improved to satisfy the standard of biofuel, chemicals and energy materials for industries. The bio-oil derived from direct pyrolysis shows some disadvantages: high contents of oxygenates, water and acids, easy-aging and so forth, which restrict the large-scale application and commercialization of bio-oil. Catalytic pyrolysis favors the refinement of bio-oil through deoxygenation, cracking, decarboxylation, decarbonylation reactions and so on, which could occur on the specified reaction sites. Therefore, the catalytic pyrolysis of lignocellulosic biomass is a promising approach for the production of high quality and renewable biofuels. This review gives information about the factors which might determine the catalytic pyrolysis output, including the properties of biomass, operational parameters of catalytic pyrolysis and different types of pyrolysis equipment. Catalysts used in recent research studies aiming to explore the catalytic pyrolysis conversion of biomass to high quality bio-oil or chemicals are discussed, and the current challenges and future perspectives for biomass catalytic pyrolysis are highlighted for further comprehension.

Effect of biochar amendment on metal mobility, phytotoxicity, soil enzymes, and metal-uptakes by wheat (Triticum aestivum) in contaminated soils

The use of low-cost substances such as biochar could be a sustainable approach to reduce the mobility, accumulation, and toxic impact of heavy metals in crop systems. This study investigates the effect of biochar amendment on heavy metal (Cr, Cd, Cu, Pb, Ni, Zn, Mg and Fe) mobility, bioaccumulation factor (BAF), plant (wheat) metal-uptake, plant oxidative stress, and soil enzymatic profile in contaminated industrial soil. Biochar was obtained from slow pyrolysis of Lantana (LBC), and Parthenium (PBC) biomass, and applied at 3% rates in contaminated soils for wheat crop study under a greenhouse experimental setup. Results show in comparison with control setups, low mobility of Cr (14.15-16.35%), Cd (7.17-15.24%), Cu (9.81-12.97%), Pb (7.99-15.23%), Ni (1.52-2.38%), Zn (10.47-14.42%), Mg (48.85-52.89%), and Fe (19.13-19.90%) contents in soils. The heavy metal uptake rates were 63.08% (Cr), 78.07% (Cd), 74.61% (Cu), 78.11% (Pb), 75.73% (Ni), 69.71% (Zn), 28.78% (Mg), and 49.26% (Fe) lower in biochar amendments, compared with the control treatments. Similarly, the biochar amended treatments exhibited low oxidative stress in wheat plants than control setups. In addition, soil enzymes (dehydrogenase, β-glucosidase, alkaline phosphatase, and urease) alleviated in biochar amended soils indicating reduced toxicity of metals in experimental soils. In summary, this study indicates that biochar amendment in contaminated soils not only improves plant growth but also lowers the rates of soil and plant toxicity and metal bioavailability as well.