Recent advances in nanoscale-metal assisted biochar derived from waste biomass used for heavy metals removal

Plant biomass-based nanoparticles for remediation of contaminants from water ecosystems: Recent trends, challenges, and future perspectives

Green nanomaterials can mitigate ecological concerns by minimizing the impact of toxic contaminants on human and environmental health. Biosynthesis seems to be drawing unequivocal attention as the traditional methods of producing nanoparticles through chemical and physical routes are not sustainable. In order to utilize plant biomass, the current review outlines a sustainable method for producing non-toxic plant biomass-based nanoparticles and discusses their applications as well as recent trends involved in the remediation of contaminants, like organic/inorganic pollutants, pharmaceuticals, and radioactive pollutants from aquatic ecosystems. Plant biomass-based nanoparticles have been synthesized using various vegetal components, such as leaves, roots, flowers, stems, seeds, tuber, and bark, for applications in water purification. Phyto-mediated green nanoparticles are effectively utilized to treat contaminated water and reduce harmful substances. Effectiveness of adsorption has also been studied using variable parameters, e.g., pH, initial contaminant concentration, contact time, adsorbent dose, and temperature. Removal of environmental contaminants through reduction, photocatalytic degradation, and surface adsorption mechanisms, such as physical adsorption, precipitation, complexation, and ion exchange, primarily due to varying pH solutions and complex functional groups. In the case of organic pollutants, most of contaminants have been treated by catalytic reduction and photodegradation involving the formation of NaBH4, H2O2, or both. Whereas electrostatic interaction, metal complexation, H-bonding, π- π associations, and chelation along with reduction have played a major role in the adsorption of heavy metals, pharmaceuticals, radioactive and other inorganic pollutants. This review also highlights several challenges, like particle size, toxicity, stability, functional groups, cost of nanoparticle production, nanomaterial dynamics, and biological interactions, along with renewability and recycling of nanoparticles. Lastly, this review concluded that plant-biomass-based nanoparticles provide a sustainable, eco-friendly remediation method, utilizing the unique properties of nanomaterials and minimizing chemical synthesis risks.

Preparation of highly adsorptive biochar by sequential iron impregnation under refluxing and pyrolysis at low temperature for removal of tetracycline

Iron-doping modification is a prevailing approach for improving adsorption capability of biochar with environmental friendliness, but usually requires high temperature and suffers from iron aggregation. Herein, a highly adsorptive biochar was manufactured via sequential disperse impregnation of iron by refluxing and pyrolysis at low temperature for eliminating tetracycline (TC) from aqueous solution. Iron oxides and hydroxides were impregnated and stably dispersed on the carbon matrix as pyrolyzed at 200 °C, meanwhile abundant oxygen and nitrogen functional groups were generated on surface. The iron-doped biochar exhibited up to 891.37 mg/g adsorption capacity at pH 5, and could be recycled with high adsorption capability. The adsorption of TC should be mostly contributed to the hydrogen bonding of N/O functional groups and the hydrogen bonding/coordination of iron oxides/hydroxides. This would provide a valuable guide for dispersedly doping iron and conserving functional groups on biochar, and a super iron-doped biochar was prepared with superior recyclability.

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.

Nanomaterials in biochar: Review of their effectiveness in remediating heavy metal-contaminated soils

Biochar can be used for soil remediation in environmentally beneficial manner, especially when combined with nanomaterials. After a decade of research, still, no comprehensive review was conducted on the effectiveness of biochar-based nanocomposites in controlling heavy metal immobilization at soil interfaces. In this paper, the recent progress in immobilizing heavy metals using biochar-based nanocomposite materials were reviewed and compared their efficacy against that of biochar alone. In details, an overview of results on the immobilization of Pb, Cd, Cu, Zn, Cr, and As was presented by different nanocomposites made by various biochars derived from kenaf bar, green tea, residual bark, cornstalk, wheat straw, sawdust, palm fiber, and bagasse. Biochar nanocomposite was found to be most effective when combined with metallic nanoparticles (Fe₃O₄ and FeS) and carbonaceous nanomaterials (graphene oxide and chitosan). This study also devoted special consideration to different remediation mechanisms by which the nanomaterials affect the effectiveness of the immobilization process. The effects of nanocomposites on soil characteristics related to pollution migration, phytotoxicity, and soil microbial composition were assessed. A future perspective on nanocomposites' use in contaminated soils was presented.

Qualitative and quantitative analysis for Cd2+ removal mechanisms by biochar composites from co-pyrolysis of corn straw and fly ash

Removal of heavy metals (e.g., Cd) from contaminated water using waste-converted adsorbents is promising, but the efficiency still needs to be improved. Here, we prepared a functional biochar composite as novel Cd adsorbents by co-pyrolysis of two typical solid wastes, i.e., agricultural corn straw and industrial fly ash. The adsorption behavior and mechanism were investigated using batch and column adsorption experiments and modern characterization techniques. Results showed that alkali-modified fly ash (AMFA) was loaded onto the surface of the corn straw biochar as some fine particle forms, with quartz (SiO₂) and silicate being the main mineral phases on the surface. The maximum sorption capacity fitted by Langmuir model for functionalized biochar composite (FBC700) was up to 137.1 mg g^-1, which was 7.7 times higher than that of the original corn straw biochar (BC700). Spectroscopic analysis revealed that adsorption mechanisms of Cd onto the FBC700 included mainly precipitation and ion exchange, with complexation and Cd-π interaction also contributing. The AMFA could effectively improve the mineral precipitation with Cd. The adsorption columns filled with FBC700 exhibited a longer breakthrough time than that filled with BC700. The adsorption capacity calculated by Thomas model for FBC700 was also approximately 6.0 times higher than that for BC700, showing that FBC700 was more suited to practical applications. This study provided a novel perspective for recycling solid wastes and treating Cd-contaminated water.

Designed synthesis of multifunctional lignin-based adsorbent for efficient heavy metal ions removal and electromagnetic wave absorption

Multifunctional lignin-based adsorbents, which have shown great application prospect, have attracted widespread attention. Herein, a series of multifunctional lignin-based magnetic recyclable adsorbents were prepared from carboxymethylated lignin (CL), which was rich in carboxyl group (-COOH). After optimizing the mass ratio of CL to Fe₃O₄, the prepared CL/Fe₃O₄ (3:1) adsorbent showed efficient adsorption capacities for heavy metal ions. The kinetic and isotherm nonlinear fitting studies revealed that the adsorption process followed the second-order kinetic and Langmuir models, and the maximum adsorption capacities (Q_max) of CL/Fe₃O₄ (3:1) magnetic recyclable adsorbent for Pb²⁺, Cu²⁺ and Ni²⁺ ions reached 189.85, 124.43 and 106.97 mg/g, respectively. Meanwhile, after 6 cycles, the adsorption capacities of CL/Fe₃O₄ (3:1) for Pb²⁺, Cu²⁺ and Ni²⁺ ions could keep at 87.4 %, 83.4 % and 82.3 %, respectively. In addition, CL/Fe₃O₄ (3:1) also exhibited excellent electromagnetic wave absorption (EMWA) performance with a reflection loss (RL) of -28.65 dB at 6.96 GHz under the thickness of 4.5 mm, and its effective absorption bandwidth (EAB) achieved 2.24 GHz (6.08-8.32 GHz). In short, the prepared multifunctional CL/Fe₃O₄ (3:1) magnetic recyclable adsorbent with outstanding adsorption capacity for heavy metal ions and superior EMWA capability opens a new avenue for the diversified utilization of lignin and lignin-based adsorbent.

A functional lignin for heavy metal ions adsorption and wound care dressing

Recently, the application of lignin activation by demethylation to improve reactivity and enrich multiple functions has intensively attracted attention. However, it is still challenge up to now due to the low reactivity and complexity of lignin structure. Here, an effective demethylation way was explored by microwave-assisted method for substantially enhancing the hydroxyl (-OH) content and retaining the structure of lignin. Then, the optimum demethylated lignin was used to removal heavy metal ions and promote wound healing, respectively. In detail, for microwave-assisted demethylated poplar lignin (M-DPOL), the contents of phenolic (Ar-OH) and total hydroxyl (Tot-OH) groups reached the maximum for 60 min at 90 °C in DMF with 7.38 and 9.13 mmol/g, respectively. After demethylation, with this M-DPOL as lignin-based adsorbent, the maximum adsorption capacity (Q_max) for Pb²⁺ ions reached 104.16 mg/g. Based on the isotherm, kinetic and thermodynamic models analyses, the chemisorption occurred in monolayer on the surface of M-DPOL, and all adsorption processes were endothermic and spontaneous. Meanwhile, M-DPOL as a wound dressing had excellent antioxidant property, outstanding bactericidal activity and remarkable biocompatibility, suggesting that it did not interfere with cell proliferation. Besides, the wounded rats treated with M-DPOL significantly promoted its formation of re-epithelialization and wound healing of full-thickness skin defects. Overall, microwave-assisted method of demethylated lignin can offer great advantages for heavy metal ions removal and wound care dressing, which facilitates high value application of lignin.

Effects of different concentrations of biochar amendments and Pb toxicity on rhizosphere soil characteristics and bacterial community of red clover (Trifolium pretense L.)

Amending soil with biochar can reduce the toxic effects of heavy metals (HM) on plants and the soil. However, the effects of different concentrations of biochar on the properties and microbial activities in lead (Pb)-contaminated soils are unclear. In this study, two Pb concentrations were set (low, 1000 mg/kg; high, 5000 mg/kg), and five corn straw biochar (CSB) concentrations (0, 2.5, 5, 10 and 15%) were used to determine the response of the growth and rhizosphere of red clover (Trifolium pretense L.) (in terms of soil properties and bacteria) to CSB and Pb application. The results showed that 5% CSB better alleviated the toxicity of Pb on the shoot length of red clover, the biomass increased by 74.55 and 197.76% respectively and reduced the enrichment factor (BCF) and transport factor (TF) of red clover. Pb toxicity reduced soil nutrients, catalase (CAT), acid phosphatase (ACP) and urease activity, while the addition of CSB increased soil pH, soil organic matter (SOM) content and soil enzyme activity. 16S rDNA amplicon sequencing analysis showed that Pb toxicity reduced the diversity of rhizosphere bacteria in red clover and reduced the relative abundance of plant growth-promoting rhizobacteria such as Gemmatimonas, Devosia and Bryobacter. Spearman correlation analysis showed that the addition of alkaline CSB restored the relative abundance of rhizobacteria positively correlated with pH, such as Chitinophaga, Sphingomonas, Devosia and Pseudomonas, and thus restored the rhizosphere soil environment. This study demonstrates that 5% CSB can better alleviate the toxicity of Pb to red clover and soil. We also provide a theoretical basis for the subsequent use of beneficial bacteria to regulate the repair efficiency of red clover.

Nitrogen-doped biochar (N-doped BC) and iron/nitrogen co-doped biochar (Fe/N co-doped BC) for removal of refractory organic pollutants

The presence of refractory organic pollutants (ROPs) in the ecosystem is a serious concern because of their impact on environmental constituents as well as their known or suspected ecotoxicity and adverse health effects. According to previous studies, carbonaceous materials, such as biochar (BC), have been widely used to remove pollutants from ecosystems owing to their desirable features, such as relative stability, tunable porosity, and abundant functionalities. Nitrogen (N)-doping and iron/nitrogen (Fe/N) co-doping can tailor BC properties and provide supplementary functional groups as well as extensive active sites on the N-doped and Fe/N co-doped BC surface, which is advantageous for interaction with and removal of ROPs. This review investigates the impact of N-doped and Fe/N co-doped BC on the removal of ROPs through adsorption, activation oxidation, and catalytic reduction due to the synergistic Fe, N, and BC features that modify the physicochemical properties, surface functional groups, and persistent free radicals of BC to aid in the degradation of ROPs. Owing to the attractive properties of N-doped and Fe/N co-doped BCs for the removal of ROPs, this review focuses and evaluates previous experimental investigations on the manufacturing (including precursors and influencing parameters during manufacturing) and characterizations of N-doped and Fe/N co-doped BCs. Additionally, the effective applications and mechanisms of N-doped and Fe/N co-doped BCs in adsorption, activation oxidation, and reductive remediation of ROPs are investigated herein. Moreover, the application of N-doped and Fe/N co-doped BC for progressive environmental remediation based on their effectiveness against co-pollutants, regeneration, stability, affordability, and future research prospects are discussed.

Effect of montmorillonite biochar composite amendment on thallium bioavailability in contaminated agricultural soils and its mitigated health risk

Little information is available on the effect of clay minerals and biochar composite on the remediation and bioavailability of thallium in agricultural soils. This study thus investigated the influence of montmorillonite biochar composite (Mnt-BC) amendment on the remediation of agricultural soil contaminated artificially by Tl and its potential health risks. Herein, bok choi was cultured to estimate the efficiency of soil Mnt-BC amendments through the bioavailability of Tl of the vegetable. Results showed that Tl bioavailability was significantly reduced in Mnt-BC-amended soils, mainly ascribed to the elevated soil pH and other improved soil properties of high functional groups (-OH, -COOH), negative charges, and exchangeable cations after amendment. Specifically, the highest immobilization efficiency of Tl in soils was observed in 2.5% treated soils with 79.11%, while in plant leaves the highest reduction of Tl was estimated to be 75.1% compared to the control treatment. Hence, the amendment dosage improved the immobilization of Tl in soil and subsequently reduced Tl uptake by the vegetable. Furthermore, from target hazard quotient (THQ) estimation, Mnt-BC amendment can lower the potential health risk while consuming such cultured bok choi in Tl-contaminated soils. Considering the environmental friendliness and high efficiency of Mnt-BC, it could be used as a potential soil amendment to remediate agricultural soils contaminated by Tl.

Nanotechnology- A ray of hope for heavy metals removal

Environmental effects of heavy metal pollution are considered as a widespread problem throughout the world, as it jeopardizes human health and also reduces the sustainability of a cleaner environment. Removal of such noxious pollutants from wastewater is pivotal because it provides a propitious solution for a cleaner environment and water scarcity. Adsorption treatment plays a significant role in water remediation due to its potent treatment and low cost of adsorbents. In the last two decades, researchers have been highly focused on the modification of adsorption treatment by functionalized and surface-modified nanomaterials which has spurred intense research. The characteristics of nano adsorbents attract global scientists as it is also economically viable. This review shines its light on the functionalized nanomaterials application for heavy metals removal from wastewater and also highlights the importance of regeneration of nanomaterials in the view of visualizing the economic aspects along with a cleaner environment. The review also focused on the proper disposal of nanomaterials with crucial issues that persist in the adsorption process and also emphasize future research modification at a large-scale application in industries.

Nano Modifications of Biochar to Enhance Heavy Metal Adsorption from Wastewaters: A Review

Biochar (BC) is a carbon-rich material that can be obtained by thermal decomposition of agricultural solid waste under oxygen-limited conditions. It has received increasing attention as a cost-effective sorbent to treat metal-contaminated water due to attributes such as high porosity and the presence of various functional groups. The heavy metal (HM) sorption and removal capacity of BC can be enhanced by developing novel biochar nanohybrids (BNHs) that can be produced via surface modification of BC with nanomaterials. Loading of nanomaterials on the biochar surface can improve its physicochemical properties through alterations in the functional group profile, porosity, and availability of active sites on the BC surface which can enhance the HM adsorption ability. This manuscript provides information on preparation of nano-based biochar hybrids emanating from the type of modifying agent for the removal of different HM ions from wastewaters, and the underlying mechanisms have been discussed. Further, this compilation discusses published literature depicting the influence of different processes of preparation on the physicochemical properties and adsorption capacity of nanobiochar hybrids. The potential risks of BNHs have been reviewed to effectively avoid the possible harmful impacts on the environment, and future research directions have been proposed.

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.

Efficient removal of aqueous Cr(VI) with ferrous sulfide/N-doped biochar composites: Facile, in-situ preparation and Cr(VI) uptake performance and mechanism

FeS nanoparticles loaded on nitrogen-doped biochar (FeS/BNC) were fabricated by pyrolyzing coffee husks pretreated with Mohr's salt. The nitrogen doping and FeS loading of biochar are simultaneously achieved in one-pot pyrolysis. The elemental analysis, SEM, TEM, XRD, XPS, Raman, FTIR and N₂ adsorption-desorption technologies were used to characterize the composition and structure of FeS/NBC. The appraisement for removing aqueous Cr(VI) testified that FeS/NBC offered a synergistic scavenging effect of Cr(VI) by FeS and NBC. The effect of crucial experimental conditions (FeS/NBC dosage, foreign ions, initial pH and concentration of Cr(VI) solution) were investigated. The Cr(VI) removal capacity was as high as 211.3 ± 26 mg g^-1 under the optimized condition. The practicability of FeS/NBC was examined by using simulated actual samples from tap water and lake water. The mechanism examination showed that surface adsorption/reduction and solution reduction were implicated in the removal of Cr(VI). The current work introduces a novel FeS/NBC composite prepared by an in situ pyrolysis method with excellent potential for chromium pollution remediation.

Phytofabrication of bimetallic silver-copper/biochar nanocomposite for environmental and medical applications

In the current study, a novel, green, low-cost, and sustainable path for the phyto-fabrication of Ag-Cu biochar nanocomposite (Ag-Cu/biochar) by Atriplex halimus biomass and aqueous extract is described. Surface plasmon resonance peaks were detected at 450 nm and 580 nm signifying the formation of both silver and copper nanoparticles, respectively on the biochar surface. XRD analysis confirmed the crystal structure of the phytosynthesized Ag-Cu/biochar whereas FT-IR, SEM, EDX, and XPS analyses confirmed the successful phytofabrication of the composite. Ag and Cu nanoparticles loaded on the biochar surface were almost spherically-shaped with a particle size ranging from 25 nm to 45 nm. Zeta potential of -25.5 mV showed the stability of Ag-Cu/biochar. The potential of this novel nanocomposite in the removal of doxycycline (DOX) was evident under different conditions as it reached nearly 100% under the optimum reaction conditions (DOX concentration; 50 ppm, pH; 9, a dose of Ag-Cu/biochar; 0.01 g, temperature; 25 °C, and H₂O₂ concentration; 100 mM). The promising regeneration of Ag-Cu/biochar was evident as the removal efficiency was 81% after 6 consecutive cycles. Ag-Cu/biochar was also shown an excellent antimicrobial activity against gram-negative bacteria as well a promising antioxidant activity.

Surface Modification of Biochar for Dye Removal from Wastewater

Nowadays, biochar is being studied to a great degree because of its potential for carbon sequestration, soil improvement, climate change mitigation, catalysis, wastewater treatment, energy storage, and waste management. The present review emphasizes on the utilization of biochar and biochar-based nanocomposites to play a key role in decontaminating dyes from wastewater. Numerous trials are underway to synthesize functionalized, surface engineered biochar-based nanocomposites that can sufficiently remove dye-contaminated wastewater. The removal of dyes from wastewater via natural and modified biochar follows numerous mechanisms such as precipitation, surface complexation, ion exchange, cation–π interactions, and electrostatic attraction. Further, biochar production and modification promote good adsorption capacity for dye removal owing to the properties tailored from the production stage and linked with specific adsorption mechanisms such as hydrophobic and electrostatic interactions. Meanwhile, a framework for artificial neural networking and machine learning to model the dye removal efficiency of biochar from wastewater is proposed even though such studies are still in their infancy stage. The present review article recommends that smart technologies for modelling and forecasting the potential of such modification of biochar should be included for their proper applications.

Fabrication, application, and mechanism of metal and heteroatom co-doped biochar composites (MHBCs) for the removal of contaminants in water: A review

The potential risk of various contaminants in water has recently attracted public attention. Biochars and modified biochars have been widely developed for environmental remediation. Metal and heteroatom co-doped biochar composites (MHBCs) quickly caught the interest of researchers with more active sites and higher affinity for contaminants compared to single-doped biochar by metal or heteroatoms. This study provides a comprehensive review of MHBCs in wastewater decontamination. Firstly, the main fabrication methods of MHBCs were external doping and internal doping, with external doping being the most common. Secondly, the applications of MHBCs as adsorbents and catalysts in water treatment were introduced emphatically, which mainly included the removal of metals, antibiotics, dyes, pesticides, phenols, and other organic contaminants. Thirdly, the removal mechanisms of contaminants by MHBCs were deeply discussed in adsorption, oxidation and reduction, and degradation. Furthermore, the influencing factors for the removal of contaminants by MHBCs were also summarized, including the physicochemical properties of MHBCs, and environmental variables of pH and co-existing substance. Finally, futural challenges of MHBCs are proposed in the leaching toxicity of metal from MHBCs, the choice of heteroatoms on the fabrication for MHBCs, and the application in the composite system and soil remediation.

Green synthesis of bimetallic Ag/ZnO@Biohar nanocomposite for photocatalytic degradation of tetracycline, antibacterial and antioxidant activities

In this work, a simple and green synthesis procedure for phytofabrication Zinc oxide-silver supported biochar nanocomposite (Ag/ZnO@BC) via Persicaria salicifolia biomass is investigated for the first time to uphold numerous green chemistry such as less hazardous chemical syntheses. XRD technique showed the crystal structure of the phytosynthesized Ag/ZnO@BC, whereas UV-visible spectroscopy, FT-IR, SEM, EDX, TEM, and XPS analyses indicated the successful biosynthesis of the nanocomposite. Testing the photocatalytic potential of this novel nanocomposite in the removal of TC under different conditions unraveled its powerful photodegradation efficiency that reached 70.3% under the optimum reaction conditions: TC concentration; 50 ppm, pH; 6, a dose of Ag/ZnO@BC; 0.01 g, temperature; 25 °C, and H₂O₂ concentration; 100 mM. The reusability of Ag/ZnO@BC was evident as it reached 53% after six cycles of regeneration. Ag/ZnO@BC was also shown to be a potent antimicrobial agent against Klebsiella pneumonia as well as a promising antioxidant material. Therefore, the current work presented a novel nanocomposite that could be efficiently employed in various environmental and medical applications.

Emerging application of biochar as a renewable and superior filler in polymer composites

Biochar is conventionally and widely used for soil amendment or as an adsorbent for water treatment. Nevertheless, the need for transition to renewable materials has resulted in an expansion of biochar for use as a filler for polymer composites. The aim is to enhance the physical, chemical, mechanical and rheological properties of the polymer composite. The reinforcement of biochar into a polymer matrix however is still new, and limited reports are focusing on the effects of biochar towards polymer composite properties. Hence, this review highlights the unique properties of biochar and its effect on the crystallization, thermal, flammability, electrical conductivity, and mechanical properties of polymer composites. This review does not solely summarize recent studies on biochar-polymer-based composites, but also offers insights into a new direction of biochar as a renewable and superior polymer filler in the future.

Efficient removal of Cd(II) by phosphate-modified biochars derived from apple tree branches: Processes, mechanisms, and application

Phosphate (P)-modified biochar is a good material for cadmium (Cd) immobilization, and the pore-forming effect of potassium ions (K⁺) can favor the P loading on biochar. However, few studies have been done specifically on Cd(II) removal by composites of potassium phosphates with biochar, and the removal potential and mechanisms are not clear. Herein, apple tree branches, a major agricultural waste suitable for the development of porous materials, were pyrolyzed individually or together with KH₂PO₄, K₂HPO₄·3H₂O, or K₃PO₄·3H₂O to obtain biochars to remove Cd(II), denoted as pristine BC, BC-1, BC-2, and BC-3, respectively. The results showed that the orthophosphates containing more K⁺ enlarged the specific surface area, total pore volume and phosphorus loading of biochar. Co-pyrolysis of apple tree branches and P promoted the thermochemical transformation of P species. Only weak signal of orthophosphate was observed in the pristine BC, while the presence of orthophosphate, pyrophosphate and metaphosphate were detected in BC-1, and BC-2 and BC-3 showed the presence of orthophosphate and pyrophosphate. The maximum Cd(II) adsorption capacities of pristine BC, BC-1, BC-2 and BC-3 were 10.4, 88.5, 95.8, and 116 mg·g^-1, respectively. Orthophosphate modification enhanced the Cd(II) adsorption capacity due to the formation of Cd-P-precipitates, namely Cd₅(PO₄)₃Cl, Cd₅(PO₄)₃OH, Cd₃(PO₄)₂, Cd₂P₂O₇, and Cd(PO₃)₂. Furthermore, higher cation exchange efficiencies between Cd(II) and K⁺ in P-modified biochars also contributed to their high Cd(II) adsorption capacity. Cd(II) removal by BC-3 from artificially polluted water bodies showed more than 99.98% removal rates. Application of BC-3 also reduced the diethylene triamine pentaacetic acid-extracted Cd(II) in soil by 69.1%. The co-pyrolysis of apple tree branches and potassium phosphates shows great prospect in Cd(II) wastewater/soil treatment and provide a promising solution for agricultural waste utilization and carbon sequestration.

Biochar can mitigate co-selection and control antibiotic resistant genes (ARGs) in compost and soil

Heavy metals (HMs) contamination raises the expression of antibiotic resistance (AR) in bacteria through co-selection. Biochar application in composting improves the effectiveness of composting and the quality of compost. This improvement includes the elimination and reduction of antibiotic resistant genes (ARGs). The use of biochar in contaminated soils reduces the bioaccessibility and bioavailability of the contaminants hence reducing the biological and environmental toxicity. This decrease in contaminant bioavailability reduces contaminants induced co-selection pressure. Conditions which favour reduction in HMs bioavailable fraction (BF) appear to favour reduction in ARGs in compost and soil. Biochar can prevent horizontal gene transfer (HGT) and can eliminate ARGs carried by mobile genetic elements (MGEs). This effect reduces maintenance and propagation of ARGs. Firmicutes, Proteobacteria, and Actinobacteria are the major bacteria phyla identified to be responsible for dissipation, maintenance, and propagation of ARGs. Biochar application rate at 2-10% is the best for the elimination of ARGs. This review provides insight into the usefulness of biochar in the prevention of co-selection and reduction of AR, including challenges of biochar application and future research prospects.

Preparation of magnesium Ferrite-Doped magnetic biochar using potassium ferrate and seawater mineral at low temperature for removal of cationic pollutants

Magnetic biochar has captured a great interest for remediation of environment as an easily separable carbonous adsorbent. Herein, a highly adsorptive magnetic biochar was manufactured through seawater mineral and K₂FeO₄ co-promoted pyrolysis of jackfruit peel at 300 °C for removal of different cationic pollutants, and characterized by element analysis, FTIR, SEM-EDS, XRD, XPS and so on. MgFe₂O₄ was generated without external base and a 19.42 emu/g saturation magnetization was achieved. Simultaneously, iron oxides and oxygen containing groups were introduced. The magnetic biochar exhibited 61.30 mg/g, 129.61 mg/g, and 1238.30 mg/g adsorption capacities for Cu²⁺, methylene blue (MB), and malachite green (MG) at 25 °C, respectively, and remarkably surpassed the corresponding pristine biochar. The adsorption of MB and MG was mainly realized by electrostatic interaction, hydrogen bonding, complexation, and π-π electron-donor-acceptor interaction, and that of Cu²⁺ was attributed to electrostatic interaction, hydrogen bonding, and complexation.

Migration and Transformation of Multiple Heavy Metals in the Soil–Plant System of E-Waste Dismantling Site

E-waste generation has become a major environmental issue worldwide. Heavy metals (HMs) in e-waste can be released during inappropriate recycling processes. While their pollution characteristics have been studied, the migration and transformation of different multi-metal fractions in soil–plant system of e-waste dismantling sites is still unclear. In this study, pot experiments were conducted to investigate the migration and transformation of different multi-metal fractions (Cu, Pb, Zn and Al) in the soil–plant system using two Chinese cabbage cultivars (heavy metals low-accumulated variety of Z1 and non-low-accumulated Z2) treated with or without biochar. The result showed that the acid-soluble fraction of Cu, Pb, Zn and Al in soil decreased by 5.5%, 55.7%, 7.8% and 21.3%, but the residual fraction (ResF) of them increased by 48.5%, 1.8%, 30.9% and 43.1%, respectively, when treated with biochar and plants, compared to that of the blank soil (CK). In addition, Pb mainly existed as a reducible fraction, whereas Cu existed as an oxidisable fraction. Biochar combined with plants significantly increased the ResF of multi-metals, which reduced the migration ability of Pb among all other metals. The relative amount of labelled ¹³C in the soil of Z1 was higher than that of Z2 (25.4 fold); among them, the Gram-negative bacteria (18-1ω9c, 18-1ω7c) and fungi (18-2ω6c) were significantly labelled in the Z1-treated soil, and have high correlation with HM migration and transformation. In addition, Gemmatimonadete were significantly positive in the acid-soluble fraction of HMs, whereas Ascomycota mostly contributed to the immobilisation of HMs. Therefore, the distribution of fractions rather than the heavy metal type plays an important role in the HM migration in the soil–plant system of e-waste dismantling sites.

Removed heavy metal ions from wastewater reuse for chemiluminescence: Successive application of lignin-based composite hydrogels

The novel sulfomethylated lignin-grafted-polyacrylic acid (SL-g-PAA) hydrogel was fabricated in this work via a facile and green synthetic strategy for the efficient removal of heavy metal ions from wastewater, and then successively reused for chemiluminescence (CL). The sulfomethylation of lignin was first performed to improve its water solubility and introduce numerous active sites for adsorption of heavy metal ions. The as-synthesized SL-g-PAA hydrogel with high content of lignin exhibited the highly efficient and rapid removal of various metal ions from simulated wastewater. More importantly, the spent hydrogel (M²⁺@SL-g-PAA) after adsorption was reused for the first time to develop a new CL system by an ingenious strategy, in which these metal ions adsorbed on M²⁺@SL-g-PAA act as heterogeneous catalytic sites to catalyze the CL reaction between N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and H₂O₂. The resultant CL system displayed high CL intensity and long duration time, which could be observed by naked eye in the dark and lasted for > 24 h. The combination of facile fabrication process, renewable raw materials, and ingenious strategy for successive application in adsorption and CL endows this lignin-based composite hydrogel with a great potential for application in wastewater treatment, biological imaging and cold light sources.

Artificial intelligence (AI) applications in adsorption of heavy metals using modified biochar

The process of removal of heavy metals is important due to their toxic effects on living organisms and undesirable anthropogenic effects. Conventional methods possess many irreconcilable disadvantages pertaining to cost and efficiency. As a result, the usage of biochar, which is produced as a by-product of biomass pyrolysis, has gained sizable traction in recent times for the removal of heavy metals. This review elucidates some widely recognized harmful heavy metals and their removal using biochar. It also highlights and compares the variety of feedstock available for preparation of biochar, pyrolysis variables involved and efficiency of biochar. Various adsorption kinetics and isotherms are also discussed along with the process of desorption to recycle biochar for reuse as adsorbent. Furthermore, this review elucidates the advancements in remediation of heavy metals using biochar by emphasizing the importance and advantages in the usage of machine learning (ML) and artificial intelligence (AI) for the optimization of adsorption variables and biochar feedstock properties. The usage of AI and ML is cost and time-effective and allows an interdisciplinary approach to remove heavy metals by biochar.

Low-cost biochar adsorbents prepared from date and delonix regia seeds for heavy metal sorption

In this study, low-cost biochar as bio-adsorbents derived from locally accessible delonix regia seed and date seeds were explored for heavy metal environmental cleaning. These prepared biochars were characterized by proximate and elemental analyses, CHNS/O analysis, Fourier-transformed infrared spectroscopy and thermo-gravitational methods. Bio-sorbent's ability to adsorb arsenic ions in synthetic wastewater was studied and optimized at varying solution pH, adsorbent dose, and starting metal concentrations. Experimentation and optimization studies were also carried out with the help of Design-software 6.0.8. The trials were designed by using response-surface methods, which includes three components and stages of Box-Behnken design. Date seeds derived-biochars eliminated 95% of arsenic from synthetic wastewater, whereas Delonix regia seeds removed 93.8%. The kinetics, isotherms and mechanism of As adsorption were also postulated. This study proposes that these seed's biochars might be employed as an effective, low-cost, and environmentally friendly adsorbent to remove heavy metals from the environment.

Preparation of Si-Mn/biochar composite and discussions about characterizations, advances in application and adsorption mechanisms

A novel Si-Mn binary modified biochar composite material (SMBC) was prepared after being sintered 450 °C for 2 h. The crystal structure, surface functional groups, surface morphology and element composition, specific surface area and pore structure were characterized by XRD, FTIR, XPS, SEM + EDS and BET etc. The results showed that the surface of SMBC was rough and loose, and the specific surface area increased to 35.4284 m²/g. Si and Mn were uniformly attached to the surface of biochar in the form of SiO₂, MnO_x, MnSiO₃. Batch adsorption experiments showed that SMBC had a higher removal efficiency (139.06 mg/g, above 98%) for Cu(II) when the dosage was 2 g/L and pH = 6. The cycle experiments showed that SMBC had good reusability, and its regeneration efficiency still reached 80.24%. The leaching amount of Mn (0.65 mg/L) was greatly reduced and avoid second-pollution resulted from ion exchange, which was attributed to the existence of Si-O-Mn bonds, and they could help Mn adhere to the surface of biochar more stable. The adsorption process was dominated by single-layer chemical adsorption and mainly occurred in the membrane diffusion stage. Cu(II) mainly formed -COOCu, -OCu, Cu(OH)₂, Cu(OH)₂CO₃, Si-O-Cu, Mn-O-Cu by the mechanisms such as precipitation (4.74%), ion exchange (13.81%), complexation and physical adsorption (total 81.45% of the two mechanisms). Among them, complexation was dominant in the adsorption process.

Effect of Sonochemical Treatment on Thermal Stability, Elemental Mercury (Hg0) Removal, and Regenerable Performance of Magnetic Tea Biochar

Elemental mercury (Hg⁰) removal from a hot gas is still challenging since high temperature influences the Hg⁰ removal and regenerable performance of the sorbent. In this work, a facile yet innovative sonochemical method was developed to synthesize a thermally stable magnetic tea biochar to capture the Hg⁰ from syngas. A sonochemically synthesized magnetic sorbent (TUF_0.46) exhibited a more prodigious surface area with developed pore structures, ultra-paramagnetic properties, and high dispersion of Fe₃O₄/γ-Fe₂O₃ particles than a simply synthesized magnetic sorbent (TF_0.46). The results showed that TUF_0.46 demonstrated strong thermostability and attained a high Hg⁰ removal performance (∼98.6%) at 200 °C. After the 10th adsorption/regeneration cycle, the Hg⁰ removal efficiency of TUF_0.46 was 19% higher than that of TF_0.46. Besides, at 23.1% Hg⁰ breakthrough, TUF_0.46 achieved an average Hg⁰ adsorption capacity of 16.58 mg/g within 24 h under complex syngas (20% CO, 20% H₂, 5% H₂O, and 400 ppm H₂S). In addition, XPS results revealed that surface-active components (Fe⁺, O^2-, O*, C=O) were the key factor for high Hg⁰ removal performance over TUF_0.46 from syngas. Hence, sonochemistry is a promising practical tool for improving the surface morphology, thermal resistance, renewability, and Hg⁰ removal efficiency of a sorbent.

Iron-carbon microelectrolysis for wastewater remediation: Preparation, performance and interaction mechanisms

Rapid industrialization and urbanization have produced a lot of hazardous substances in water and wastewater, which has turned into a crucial issue to the environment and the public health. Recently, iron carbon microelectrolysis (IC-ME) has attracted extensive attention in environmental remediation due to its low costs and excellent performance. Nevertheless, there is still a lack of a more systematic review on IC-ME preparation methods, their performance, and the interaction mechanisms of IC-ME in the remediation of wastewater. Herein, this work summarizes the synthetic methods, application of IC-ME materials, and the mechanism of pollutant removal by IC-ME. A variety approaches have been applied to prepare IC-ME materials, and the preparation methods and conditions have a certain influence on the properties of IC-ME materials, thus affecting the performance of pollutant removal. The mechanisms of IC-ME for contaminants removal are very complex, including adsorption, coprecipitation, reduction, surface complexation, and oxidation. Moreover, research vacant fields and problems that existed in the application of IC-ME are proposed. At last, the problems to be addressed to adapt IC to future applications are introduced. This paper reviews and prospects IC-ME wastewater remediation technology, which provides a reference for further scientific research and engineering applications.

Coating magnetite alters the mechanisms and site energy for sulfonamide antibiotic sorption on biochar

Magnetite-coating biochar (MBC) is a promising remediator for antibiotic contamination. Accurate models describing the sorption affinity are required to better understand the role of minerals. In this study, the presence of magnetite led to the improvements of oxygen-containing groups (i.e. C˭O) and regulation of π-systems within BC. Based on Dubinin-Ashtakhov (DA) model, the differences of site energy (E_m) and sorption heterogeneity (σ_e*) led to the variances between sorption capacities of sulfonamides (SAs). The positive correlations between E_m and the oxygen content or pore volume of MBCs indicated that π-π interactions, H-bonding, and pore-filling may act as the high energy sites. Moreover, σ_e* was related to the distribution of magnetite on BC and their porosities. These results suggested that compared to BCs, the coating minerals improved the π-interaction assisted H-bonding and proton configuration of antibiotic when sorbing on MBC. The negative correlations between the E_m of different SAs with their molecular sizes and solubilities resulted from steric effects and competition with water, which further confirmed the proposed high energy sites on MBCs. This study provided the insightful information of site energy distribution and understanding of fate and transport of organic pollutants on BC when the iron minerals were embedded or coated.

Biochar as a tool for effective management of drought and heavy metal toxicity

Drought and heavy metal stress undesirably disturb soil fertility and plant growth. Heavy metals pose severe biological toxic effects. Biochar, a carbon rich source application ameliorates this stress by increasing the plant growth, biomass, nutrient uptake and improves gaseous exchange in drought stress. Application of biochar reduces drought stress by increasing water holding capacity of soil through modification of soil physio-chemical properties that in turn increases water availability to plants and also enhances mineral uptake and regulation of stomatal conductance. Biochar mediates the retention of moisture, nutrients, inhibits harmful bacteria, absorbs heavy metals, pesticides, prevents soil erosion, increases soil pH, improves cationic exchange and boosts soil fertility. Drought and heavy metal stress often lead to production of reactive oxygen species. However, biochar significantly modifies the Reactive Oxygen Species (ROS) scavenging enzymes and provides an efficient electron transferring mechanism to tackle the toxic effects of ROS in plants. Biochar is regarded as a tool for the effective management of agricultural productivity and various environmental issues. This review provides insights on the potential role of biochar in ameliorating drought and heavy metal stress.

Effects of fine fractions of soil organic, semi-organic, and inorganic amendments on the mitigation of heavy metal(loid)s leaching and bioavailability in a post-mining area

This study investigated the effects of soil amendments including biomasses (rice husk, RRH and maple leaf, RML), biochar (rice husk biochar, RHB and maple leaf biochar, MLB), and industrial by-products (red mud, RM and steel slag, SS), at two application rates (0, 1, and 2% w/w) on leaching and bioavailability of heavy metal(loid)s (HMs) (As, Cd, Cu, Pb, and Zn) in the presence of an Asteraceae (i.e., lettuce). Physicochemical properties of the soil (i.e., pH, EC, CEC, and HMs leaching) and plants were examined before and after amending. The addition of amendments significantly (p < 0.05) increased soil EC (from 100 to 180 μScm^-1) and CEC (from 7.6 to 15 meq100 g^-1). Soil pH from 6.7 ± 0.05 increased about 2 units with increasing in the application rate of MLB, RM, and SS, while it decreased about 0.8 units in RML amended soil. Soil amendments reduced the easily leachable fractions (exchangeable and carbonate) of HMs in the order of MLB > SS > RM > RHB. The average concentration of Cd, Cu, Pb, and Zn in plant roots and shoots decreased >30 wt% in biochars and industrial by-products amended soils, while biomasses mitigated As uptake in lettuce. Results demonstrated that adding maple-derived biochar combined with revegetation effectively immobilized HMs in a post-mining area beside an induce in plant growth parameters.

Sorption mechanisms of antibiotic sulfamethazine (SMT) on magnetite-coated biochar: pH-dependence and redox transformation

Sorption of sulfonamides (SAs) on magnetite-coated biochar (MBC) is a promising approach for the remediation of antibiotic contaminants, due to its extended adsorption capacity and irreversibility. However, the actual sorption mechanisms of SAs on MBC remain unclear and the gap in knowledge hinders understanding of the fate of SAs in soils or sediments. In this study, various MBCs were prepared under different pyrolysis temperatures, with batch sorption experiments conducted using SMT as the model pollutant. Results of a two-compartment kinetic model demonstrated that aromatic components of MBCs dominated slow-sorption mechanisms, whereas the embedded magnetite further accelerated fast-sorption due to H-bonding. Modification of BC with magnetite improved the distribution coefficient (K_d) and isotherm linearity of SMT. Multi-parameter model results indicated that the pH-dependence of SMT sorption on BCs and MBCs occurred via a dominant mechanism of π-bond assisted H-bonding. Compared to pristine BCs, the change in pH-dependent sorption characteristics of SMT on MBC results from the regulation of π-bonding and proton configuration. Simultaneous transformation of SMT to sulfate ions on BCs or MBCs was also observed. The degradation of SMT occurred because of persistent free radicals (PFRs) on BCs or the inherent redox of iron minerals on MBCs. However, the small fraction of SMT transformed on BCs or MBCs was not found to result in overestimation of SMT sorption. This study presents the critical mechanisms of SMT sorption on pyrochars and provides novel understanding of the fate of SMT on carbonaceous materials during practical remediation applications.

One-step synthesis of cake-like biosorbents from plant biomass for the effective removal and recovery heavy metals: Effect of plant species and roles of xanthation

The continuous production of plant wastes and heavy metal pollution of waters have become widespread unavoidable challenges. Reutilization of plant wastes to treat toxic metal-contaminated water is an eco-friendly way to simultaneously solve these problems. Herein, three cake-like biosorbents were synthesized from tea waste, trimmed lawn grass and Nephrolepis cordifolia leaves through a one-step xanthation modification method combined with lyophilization, respectively. The plant species affected the appearance, structure and mechanical strength of the biosorbents due to the different contents of hydrocarbons and inorganic substances, which influenced the gel-like degree and thus the ability of the particles to pack between water molecules. The maximum adsorption capacities of the modified materials for Pb(II), Cu(II) and Cd(II) were 247.20, 85.80 and 265.31 mg/g, respectively, far higher than those of the original wastes, and the adsorption was selective. These results were mainly attributed to newly introduced -(CS)-S-Na groups, which triggered ion exchange, complexation and microprecipitation between heavy metal ions and functional groups. As-prepared biosorbents owned an excellent regenerability, which contributed to recovery heavy metals. The physicochemical properties and adsorption performances of the modified materials indicated that xanthation is a universal modification method suited to different plant biomasses with great potential to purify heavy metal-contaminated water. These biosorbents with excellent separability and regenerability might be promising for continuous-flow sewage treatment.

Self-assembly preparation of lignin-graphene oxide composite nanospheres for highly efficient Cr(vi) removal

Recently, research interest in the application of lignin is growing, especially as adsorbent material. However, single lignin shows unsatisfactory adsorption performance, and thus, construction of lignin-based nanocomposites is worth considering. Herein, we introduced graphene oxide (GO) into lignin to form lignin/GO (LGNs) composite nanospheres by a self-assembly method. FTIR and 1H NMR spectroscopy illustrated that lignin and GO are tightly connected by hydrogen bonds. The LGNs as an environmental friendly material, also exhibit excellent performance for Cr(vi) removal. The maximum sorption capacity of LGNs is 368.78 mg g-1, and the sorption efficiency is 1.5 times than that of lignin nanospheres (LNs). The removal process of Cr(vi) via LGNs mainly relies on electrostatic interaction, and it also involves the reduction of Cr(vi) to Cr(iii). Moreover, LGNs still have high adsorption performance after repeating five times with the sorption capacity of 150.4 mg g-1 in 200 mg g-1 Cr(vi) solution. Therefore, the prepared lignin-GO composite nanospheres have enormous potential as a low-cost, high-absorbent and recyclable adsorbent, and can be used in wastewater treatment.

Hydrochar and pyrochar for sorption of pollutants in wastewater and exhaust gas: A critical review

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

High efficiency removal of Pb(ii) in aqueous solution by a biochar-supported nanoscale ferrous sulfide composite

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution. The experimental results of SEM, EDS, XRD, and FT-IR spectroscopy clearly implied that the biochar was successfully modified with nanoscale ferrous sulfide composite. The maximum adsorption capacity of Pb(ii) ions by FeS@biochar reached 88.06 mg g⁻¹. Compared with other reported adsorbents, the removal rate of Pb(ii) ions by FeS@biochar was higher. The pseudo-second-order kinetic model and Langmuir isotherm model could better fit the experimental adsorption results. The removal rate of Pb(ii) ions by FeS@biochar was controlled by the chemical reaction and monolayer adsorption on the surface of FeS@biochar. The mechanisms of Pb(ii) removal from aqueous solutions by biochar involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange, and chemical precipitation. Additionally, the chemical stability and reusability of FeS@biochar were good. It is also an environment-friendly material for low-cost wastewater treatment.

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution.

A recent global review of hazardous chlorpyrifos pesticide in fruit and vegetables: Prevalence, remediation and actions needed

Pollution with pesticides is a widespread global problem and biomonitoring of the environment and human populations is necessary to assess potential harmful biological effects. One of the pesticides that are showing up in vegetables and fruit is chlorpyrifos (CPS). CPS is a nerve-poisoning organophosphorus insecticide, which is in up to 1/3 of all conventionally produced citrus fruits. Our review shows that CPS is a hazardous material that poses risks to human health and also pollutes the environment. There is numerous risk assessment of CPS reported, however, the assessment is easily affected by factors such as climate change, exposure period and CPS concentration. Therefore, rigorous update of the hazardous level of CPS is needed to determine the threshold level safe for humans and animals. There is a need for remediation using for example photoreactive nanoparticle methods and microbial degeneration possessing high degradation efficiency (73-97%). In addition, stringent biomonitoring of food, environment and human exposure should occur to avoid exposure to chemicals via citrus fruits and vegetables. This is necessary to assess health risks and socioeconomic impacts which also require collaboration between private and public sectors to facilitate the growth, sale and manufacturing of biopesticides.

Green synthesis of a novel Mn-Zn ferrite/biochar composite from waste batteries and pine sawdust for Pb2+ removal

Magnetic ferrite/biochar composites are a kind of promising adsorbents due to their high adsorption efficiency and facile magnetic separation; however, their synthesis is associated with high cost and secondary environmental impacts. In this study, a novel Mn-Zn ferrite/biochar composite (MZF-BC) is synthesized via a green two-step biocheaching and hydrothermal method using waste batteries and pine sawdust. Characterization results indicate that the introduced Mn-Zn ferrite particles are successfully embedded and coated on biochar (BC), and synthesized MZF-BC₅₀ with 50% BC content exhibits best performance with a specific surface area of 138.5 m² g^-1, the saturation magnetization of 27.5 emu g^-1 and CEC value of 53.2 mmol 100 g^-1. The maximum adsorption capacity of Pb²⁺ is 99.5 mg g^-1 based on the Langmuir sorption isotherm study at 298 K, and pseudo-second-order model accurately describes the adsorption process. Regeneration test suggests that MZF-BC₅₀ can be efficiently reused for 6 cycles. In addition, it exhibits a good selective Pb²⁺ and Cd²⁺ removal performance in lead-acid battery wastewater. The results illustrate that this newly developed material has low cost and rapid remediation of Pb²⁺ as good application potential.

Nitrate removal from aqueous solutions by adsorption onto hydrogel-rice husk biochar composite

In the present study, we investigated the performance of hydrogel-rice husk biochar composites, as low-cost, alternative, and biocompatible adsorbents for separating nitrate ions from aqueous solutions. Hydrogel-biochar composite was synthesized at dosages of 2.5%, 3.6%, 4.8%, and 9.6% weight ratios of biochar. The composite was characterized by several common methods including FTIR, SEM, TEM, TGA, and DSC. In addition, the effect of contact time, initial concentration of nitrate ions, and solution pH were considered. The maximum removal of nitrate was about 34.3% at acidic pH (pH = 3) using 0.02 g of adsorbent in 25 ml of nitrate solution with the initial concentration (20 mg/L) and temperature of 25°C for 60 min. Based on the findings, 5% biochar in the composite was the optimal dosage. Adsorption kinetic study revealed that this process followed the first-order kinetic model. The experimental equilibrium adsorption data were tested by the Temkin isotherm model with R²  > 0.97. Based on the thermodynamic studies, the adsorption process was endothermic and spontaneous. Overall, the results suggested that the obtained composite can be specifically employed for removal of contaminations from aqueous solutions. PRACTITIONER POINTS: Hydrogel-biochar composite provides a biocompatible and cost-effective adsorbent. Hydrogel-biochar composite was applied to eliminate nitrate from aqueous solutions. Nitrate removal increased in the synthesized composite upon elevation of the weight ratio of biochar to 0.2 g.

Enhanced removal of 1,2,4-trichlorobenzene by modified biochar supported nanoscale zero-valent iron and palladium

Biochar pyrolysed at 300 °C, 500 °C, 700 °C was modified by hydrochloric acid (HCl), hydrofluoric acid (HF), sodium hydroxide (NaOH), hydrogen peroxide (H₂O₂), nitric acid (HNO₃) and potassium permanganate (KMnO₄), and subsequently evaluated for removal efficiency of 1,2,4-trichlorobenzene (1,2,4-TCB) by biochar supported nanoscale zero-valent iron (nZVI) and palladium (Pd) composites. Under the initial 1,2,4-TCB concentration of 10 mg L^-1 and the solid-liquid ratio of 0.16 g L^-1, the synthesized composites of nZVI-Pd with BC700 modified by HF (FBC700-nZVI-Pd) and nZVI-Pd with BC300 modified by NaOH (SBC300-nZVI-Pd) demonstrated significantly enhanced removal efficiencies for 1,2,4-TCB achieving 98.8% and 94.7% after 48 h, respectively. The physicochemical properties of biochar including specific surface area, aromaticity and hydrophobicity after the modification by HF and NaOH were improved. Increased the supporting sites for Fe/Pd nanoparticles and the contact between composites and 1,2,4-TCB were mainly responsible for enhanced removal efficiency for 1,2,4-TCB. Both the adsorption by biochar and reduction by Fe/Pd nanoparticles effectively contributed to the removal of 1,2,4-TCB. It is estimated that the proportion of reduction was about twice that of adsorption in the first 12 h, which produced 1,2-DCB, benzene and other degradation products. Therefore, biochar treated with HF and NaOH and supported Fe/Pd nanoparticles could be effective functional materials for remediation of groundwater contaminated by 1,2,4-TCB.

Effects of electromagnetic induction on migration and speciation of heavy metals in drying sewage sludge: Mechanistic insights

Novel and efficient drying method based on electromagnetic induction plate (EMI-P) heating was used to treat sewage sludge (SS). This work focused on the effects of EMI-P action on heavy metals (HMs) in dried SS. Surface functional groups, surface chemistry and microstructures of SS treated were investigated and compared to provide insights into the transformation mechanisms of HMs during EMI-P drying process. The results show that the EMI-P-dried SS showed undesirably total concentrations of Cd and Zn and leaching concentrations of HMs (Cr, Ni, Zn, Cd and As) exceeded the Chinese ground water standard (GB/T14848-2017). Ni, Zn, and As in the EMI-P-dried SS still exhibited high mobility, the leaching percent of Ni, Zn, and As (under 300 V and 500 V) can reach up to 28.56%/10.36%, 26.96%/26.61% and 30.64%/23.14%, respectively. Compared with conventional thermal drying, the EMI-P method can effectively reduce the eco-toxicity derived from HMs by 28.06% under 500 V condition. The stabilization effect of the EMI-P action can be attributed to the following: (1) EMI-P action promoted the generation of surface complexes with HMs, (2) HMs adsorption by silicate minerals was enhanced under high-frequency magnetic fields and (3) honeycomb structures of EMI-P dried SS with micropores provided abundant active sites to bond with HMs.

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.