Application of biochar for the removal of pollutants from aqueous solutions

Assessing the effect of pyrolysis temperature on the molecular properties and copper sorption capacity of a halophyte biochar

The capacity of biochar to take up heavy metals from contaminated soil and water is influenced by the pyrolysis temperature. We have prepared three biochar samples from Jerusalem artichoke stalks (JAS) by pyrolysis at 300, 500 and 700 °C, denoted as JAS300, JAS500, and JAS700, respectively. A variety of synchrotron-based techniques were used to assess the effect of pyrolysis temperature on the molecular properties and copper (Cu) sorption capacity of the samples. The content of oxygen-containing functional groups in the biochar samples decreased, while that of aromatic structures and alkaline mineral components increased, with a rise in pyrolysis temperature. Scanning transmission X-ray microscopy indicated that sorbed Cu(II) was partially reduced to Cu(I), but this process was more evident with JAS300 and JAS700 than with JAS500. Carbon K-edge X-ray absorption near edge structure spectroscopy indicated that Cu(II) cations were sorbed to biochar via complexation and Cu-π bonding. With rising pyrolysis temperature, Cu(II)-complexation weakened while Cu-π bonding was enhanced. In addition, the relatively high ash content and pH of JAS500 and JAS700 facilitated Cu precipitation and the formation of langite on the surface of biochar. The results of this investigation will aid the conversion of halophyte waste to useable biochar for the effective remediation of Cu-contaminated soil and water.

Recovery of Cr(III) by using chars from the co-gasification of agriculture and forestry wastes

The aim of the present work was to assess the efficiency of biochars obtained from the co-gasification of blends of rice husk + corn cob (biochar 50CC) and rice husk + eucalyptus stumps (biochar 50ES), as potential renewable low-cost adsorbents for Cr(III) recovery from wastewaters. The two gasification biochars presented a weak porous structure (A_BET = 63-144 m² g^-1), but a strong alkaline character, promoted by a high content of mineral matter (59.8% w/w of ashes for 50CC biochar and 81.9% w/w for 50ES biochar). The biochars were used for Cr(III) recovery from synthetic solutions by varying the initial pH value (3, 4, and 5), liquid/solid (L/S) ratio (100-500 mL g^-1), contact time (1-120 h), and initial Cr(III) concentration (10-150 mg L^-1). High Cr(III) removal percentages (around 100%) were obtained for both biochars, due to Cr precipitation, at low L/S ratios (100 and 200 mL g^-1), for the initial pH 5 and initial Cr concentration of 50 mg L^-1. Under the experimental conditions in which other removal mechanisms rather than precipitation occurred, a higher removal percentage (49.9%) and the highest uptake capacity (6.87 mg g^-1) were registered for 50CC biochar. In the equilibrium, 50ES biochar presented a Cr(III) removal percentage of 27% with a maximum uptake capacity of 2.58 mg g^-1. The better performance on Cr(III) recovery for the biochar 50CC was attributed to its better textural properties, as well as its higher cation exchange capacity.

Potential of Punica granatum biochar to adsorb Cu(II) in soil

Biochar as a promising adsorbent to remove heavy metals has attracted much attention globally. One of the potential adsorbents is biochar derived from punica granatum peels, a growing but often wasted resource in tropical countries. However, the immobilization capacity of punica granatum peel biochar is not known. This study investigated the physicochemical properties of punica granatum peel boichars pyrolyzed at 300 °C and 600 °C (referred as BC300 and BC600), and the efficiency and mechanisms of Cu(II) adsorption of five types of material treatments: BC300, BC600, soil only, and soils with biochar amendment BC300 and BC600, respectively, at the rate of 1% of the soil by weight. The results show that BC300 had higher yield, volatile matter content and organic carbon content, and larger pore diameter, but less ash content, surface area, pH, and cation exchange capacity than BC600. The Cu(II) adsorption capacity onto biochars and soils with biochar were greatly influenced by initial ion concentration and contact time. The Cu(II) adsorption capacity of biochar, independent of pyrolysis temperature, was around 52 mg g⁻¹. The adsorption capacity of the soil amended with biochar nearly doubled (29.85 mg g⁻¹) compared to that of the original soil (14.99 mg g⁻¹), indicating superb synergetic adsorption capacity of the biochar-amended soils. The adsorption isotherms showed monolayer adsorption of Cu(II) on biochar, and co-existence of monolayer and multilayer adsorption in soils with or without biochar amendment. Results also suggest that the adsorption process is spontaneous and endothermic, and the rate-limiting phase of the sorption process is primarily chemical. This study demonstrates punica granatum peel biochar has a great potential as an adsorbent for Cu(II) removal in soil.

Mineral elements uptake and physiological response of Amaranthus mangostanus (L.) as affected by biochar

Amaranthus mangostanus L. (amaranth) was hydroponically grown in different concentrations of biochar amended nutrient solution to investigate the mineral elements migration and physiological response of amaranth as affected by biochar. Our results showed that exposure to 26.6 g/L of biochar greatly increased the root and shoot K, Na and Al content, while 2.6 g/L of biochar greatly increased the root Ca and Mg content. The uptake of K and Al notably altered other elements' accumulation in shoots and roots upon the biochar exposure. The ratio of Ca: K in shoots and Mg: K in roots were negatively correlated to the biochar concentrations, while the ratio of Al: Ca and Al: Mg in roots were positively related to the biochar concentrations. The Al: Fe ratio was also polynomial correlated to the concentrations of biochar. The addition of biochar beyond 2.6 g/L resulted in the cell membrane and DNA damages in roots. The activity of SOD and CAT in 6.7 g/L biochar treated roots was significantly elevated as compared to the ones in other biochar treatments and was almost 2-fold of the control. The photosynthetic F_v/F_m intensity and subcellular structure in leaves were also compromised upon exposure to 26.6 g/L biochar. Taken together, biochar could significantly alter the mineral migration in amaranth and physiologically damage in the plants. It is essential to study the effect of biochar within appropriate concentrations on plants prior to wide application in agriculture.

Removal of copper ions from aqueous solution using low temperature biochar derived from the pyrolysis of municipal solid waste

Sustainable methods to produce filter materials are needed to remove a variety of pollutants found in water including organic compounds, heavy metals, and other harmful inorganic and biological contaminants. This study focuses on the removal of Cu(II) from copper aqueous solutions using non-activated char derived from the pyrolysis of mixed municipal discarded materials (MMDM) using a new heat pipe-based pyrolysis reactor. Adsorption experiments were conducted by adding the char to copper solutions of varying concentration (50-250 mg/L) at a constant temperature of 30 °C. The effect of pH on copper adsorption onto the char was also investigated in the range of pH 3 to 6. Copper removal using the char was found to be heavily dependent on pH, adsorption was observed to decrease below a pH of 4.5. However, the initial copper concentration had a little effect on the sorption of copper at high concentration solutions (above 100 mg/L). Overall, the biochar showed an effective copper adsorption capacity (4-5 mg/g) when using copper solutions with a concentration below100 mg/L and pH >4.5. Copper removal using the char tended to follow the pseudo second order kinetic model. Langmuir isothermal model was shown to be the closest fitting isotherm using the linearized Langmuir equation. However, the variety of feedstock used to produce the char led to a variation in results compared to other studies of more specific feedstocks.

Comparison of biochars derived from different types of feedstock and their potential for heavy metal removal in multiple-metal solutions

Three different types of feedstocks and their biochars were used to remove Cr(III), Cd(II), Cu(II) and Pb(II) ions from a mixture of multiple heavy metals. The effect of the initial concentration of heavy metals in solution has been analysed, and kinetics modelling and a comparison of the adsorption capacity of such materials have been performed to elucidate the possible adsorption mechanisms. The results show that the adsorption capacity is dependent on the type of feedstock and on the pyrolysis conditions. The adsorption capacity of the biomass types is ranked as follows: FO (from sewage sludge)>> LO > ZO (both from agriculture biomass waste)>> CO (from wood biomass waste). Biochars, which are the product of the pyrolysis of feedstocks, clearly improve the adsorption efficiency in the case of those derived from wood and agricultural biomasses. Complexation and cation exchange have been found to be the two main adsorption mechanisms in systems containing multiple heavy metals, with cation exchange being the most significant. The pore structure of biomass/biochar cannot be neglected when investigating the adsorption mechanism of each material. All the disposal biomasses presented here are good alternatives for heavy metal removal from wastewaters.

Interactive effects of rice straw biochar and γ-Al2O3 on immobilization of Zn

Biochar system technology has been proved as a sustainable remediation method for metal contaminated soils. However, little attention has been paid to the interaction between biochar and oxide minerals and their influence on metal immobilization in soils. In this study, batch-type Zn sorption experiments were conducted using the mixture of γ-Al₂O₃ and rice straw biochar as a model binary geosorbent systems. In addition, advanced spectroscopic technics such as EXAFS, FTIR and XRD were performed to reveal the mechanism. EXAFS spectroscopy revealed that 62% of Zn existed as Zn-Al layered double hydroxide (LDH) on γ-Al₂O₃ at pH 7.5 (for 2 mM Zn loading) within 24 h, which was 19% in the mixture. The Zn in biochar samples mainly existed as Zn-OM (53%-76%) and Zn₂SiO₄ (21%-47%), while the proportion of Zn₂SiO₄ (0-6%) was negligible compared with Zn-Al silicate (26-48%) in the mixtures. The overall findings confirmed that Al released from γ-Al₂O₃ was sorbed in parallel with Zn on biochar to form Zn-Al silicate, rather than Zn-Al LDH on the γ-Al₂O₃ surface. These results unveiled the dynamic interactions between amended biochar and soil oxide minerals which can significantly affect the immobilization pathways of metals in contaminated soils.

The relative importance of different carbon structures in biochars to carbamazepine and bisphenol A sorption

Biochar, a carbon-rich material, has attracted immense attention owing to its applications in soil remediation. However, the mechanisms by which heterogeneous carbon structures of biochars immobilize organic contaminants are not yet fully understood. In this study, the noncondensed aromatic components in biochars were selectively removed through bleaching. Different techniques, such as ¹³C nuclear magnetic resonance, were applied to characterize the biochar compositions, and thus the role of the different carbon structures in organic contaminant sorption was discussed. The aromatic carbon structures in biochars were gradually developed and evolved from noncondensed to condensed structure with increasing pyrolytic temperatures from 300 to 700 °C. Based on elemental analysis, the carbon removed by bleaching decreased from 43.9% to 5.92% with increasing temperatures. After the surface area normalization of the apparent sorption, bleaching increased the sorption of carbamazepine and bisphenol A on biochars produced at 500 °C, but not for those produced at 300 and 700 °C. Bleaching removed noncondensed aromatics and enriched condensed aromatics, which resulted in increased sorption. However, bleaching also resulted in the blockage of micropores in biochars with abundant condensed aromatics, causing decreased sorption. The apparent sorption was determined by the balancing of these two opposite effects.

Graphene and graphene-based nanocomposites used for antibiotics removal in water treatment: A review

Due to their extensive application in human and veterinary medicine, antibiotics have been found worldwide and studied as new pollutants in the aquatic environment. In order to remove such pollutants, adsorption and photocatalysis have attracted tremendous attention because of their great potential in antibiotics removal from aqueous solutions. Graphene, as a novel two-dimensional nanomaterial, possesses unique structure and physicochemical properties, which can be used to efficiently adsorb and photodegrade antibiotics. This review provides an overview of the adsorptive and catalytic properties of graphene, and recent advances in adsorption and photodegradation of antibiotics by graphene and its derivatives. The factors that affect the adsorption and photodegradation of antibiotics are reviewed and discussed. Furthermore, the underlying mechanisms of adsorption and photodegradation are summarized and analyzed. Meanwhile, statistical analysis is conducted based on the number of papers and the maximum adsorption and photodegradation ability on various antibiotics removal. Finally, some unsolved problems together with major challenges that exist in the fabrication and application of graphene-based nanocomposites and the development for antibiotics removal is also proposed. This work provides theoretical guidance for subsequent research in the field of adsorption and photocatalytic removal of antibiotics from aqueous solution, especially on influence factors and mechanisms aspects.

Decontamination of lead and tetracycline from aqueous solution by a promising carbonaceous nanocomposite: Interaction and mechanisms insight

Innovative carbonaceous nano-chlorapatites (CNClAPs) which originated from the pyrolyzation of the mixture of bamboo residues and chlorapatites varying from 400 °C to 600 °C were used to investigate the decontamination efficacy of lead (Pb²⁺) and tetracycline (TC) from wastewater. Rising pyrolytic temperature can highly improve the decontamination efficacy, of which CNClAP600 exhibited the most remarkable effects for Pb²⁺ and TC decontamination (90.37% for Pb²⁺ and 86.58% for TC at pH = 7). The kinetic, isotherm and characterization analysis demonstrated that the inner mechanisms for the decontamination of Pb²⁺ and TC involved precipitation, electrostatic interaction, hydrogen bonding, π-π interaction and pore filling. Experiment indicated that the enhancement and competitive adsorption resulted from the interaction between Pb²⁺ and TC could facilitate their joint decontamination under low concentrations. This research shed light on the management of coexisting heavy metals and organic matters contamination in wastewater by CNClAPs under different temperatures.

A novel sorbent Ulva lactuca-derived biochar for remediation of Remazol Brilliant Orange 3R in packed column

An up-flow fixed column study was conducted to remediate Remazol Brilliant Orange 3R (RBO3R) from contaminated solutions using biochar derived from Ulva lactuca biomass. The influences of column parameters on dye sorption were studied in detail, which include initial RBO3R concentration, bed depth, and flow rate. Optimization experiments indicated that maximum RBO3R column uptake of 0.114 mmol/g was observed at 0.25 mmol/L (initial RBO3R concentration), 0.3 L/hr (flow rate), and 25 cm (U. lactuca bed depth). Modeling of column sorption data was performed using the Yoon-Nelson, modified dose-response and Thomas models. The spent biochar was desorbed and rejuvenated using 0.01 M NaOH. The elutant (0.01 M NaOH) exhibited 99.7% efficiency, and the process was completed in 115 min with high overall concentration factor of 8.4. PRACTITIONER POINTS: This study explores the impact of column parameters on the dye removal potential of U. lactuca-derived biochar. At optimized condition, the biochar bed exhibited highest Remazol Brilliant Orange 3R uptake capacity of 0.114 mmol/g. The regeneration and desorption of U. lactuca-derived biochar bed was possible with NaOH (0.01 M) as elutant.

Comparative assessment of metribuzin sorption efficiency of biochar, hydrochar and vermicompost

In this study, we used two biochars (BC) produced from grapevine pruning residues (BCgv) and red spruce wood (BCrs), two hydrochars (HC) from urban pruning residues (HCup) and the organic fraction of municipal solid wastes (HCuw), and two vermicomposts (VC) obtained vermicomposting digestates from buffalo manure (VCbm) and mixed feedstock (VCmf). Adsorption kinetics and isotherms of metribuzin onto these materials were performed. Sorption kinetics followed preferentially a pseudo-second-order model, thus indicating the occurrence of chemical interactions between the sorbate and the adsorbents. Adsorption constants were calculated using the Freundlich and Langmuir models. Metribuzin sorption data on BCgv and both HC fitted preferentially the Freundlich equation, whereas on the other materials data fitted both isotherms well (r > 0.95). Metribuzin sorption capacity of the materials followed the trend BC > HC > VC. Sorption constants of metribuzin normalised per organic carbon content (K_OC) on BCgv, BCrs, HCup, HCuw, VCbm and VCmf were 561, 383, 251, 214, 102 and 84 L kg^-1, respectively. A significant positive correlation (P = 0.016) was calculated between distribution coefficients (K_d) of all materials and the corresponding organic carbon contents, thus indicating a prominent role of the organic fraction of these materials in the adsorption of metribuzin.

The effect of biochar mild air oxidation on the optimization of lead(II) adsorption from wastewater

In the present study, the effects of mild air oxidation of a biochar produced by the Pyrovac Inc. pyrolysis process, on the adsorption of lead(II) from synthetic wastewater under batch experimental conditions have been investigated. The adsorption experiments were performed under several conditions suggested by the response surface methodology, which allowed finding the optimal conditions, in order to maximize the adsorption capacity (Q(mgg^-1)), as well as the extraction efficiency (E (%)). The optimal conditions of lead ions adsorption were as follows: pH = 5, agitation time = 300 min, adsorbent mass = 0.5 g (per 50 cm³ of solution), and lead initial concentration = 100gm^-3, resulted in an adsorption capacity of 7.9 mg g^-1. Equilibrium adsorption was then obtained by keeping pH and adsorbent mass at the optimal values and changing the lead initial concentration for a sufficient agitation time. Results showed that mild air oxidation increased the equilibrium adsorption capacity of biochar from 2.5 to 44 mg g^-1. Oxidized biochar after equilibrium adsorption was submitted to SEM/EDX and XPS analysis. From SEM it was found that lead particles were distributed heterogeneously after adsorption. From XPS analysis, it was revealed that the external surface of oxidized biochar particles becomes saturated for the initial point of equilibrium diagram, obtained at lead initial concentration of 100gm^-3, suggesting that for a higher concentration, the internal surfaces of particles participate in the cations adsorption. The participation of surface functional groups in the adsorption process showed that carbonyl, carboxylic, and aromatic rings of oxidized biochar were involved in the adsorption. This work suggests that the very simple process of mild air oxidation can be used instead of the usual costly chemical activation, in order to improve biochar cation exchange capacity.

Biochar versus bone char for a sustainable inorganic arsenic mitigation in water: What needs to be done in future research?

Arsenic (As) is an emerging contaminant on a global scale posing threat to environmental and human health. The relatively brief history of the applications of biochar and bone char has mapped the endeavors to remove As from water to a considerable extent. This critical review attempts to provide a comprehensive overview for the first time on the potential of bio- and bone-char in the immobilization of inorganic As in water. It seeks to offer a rational assessment of what is existing and what needs to be done in future research as an implication for As toxicity of human health risks through acute and chronic exposure to As contaminated water. Bio- and bone-char are recognized as promising alternatives to activated carbon due to their lower production and activation cost. The surface modification via chemical methods has been adopted to improve the adsorption capacity for anionic As species. Surface complexation, ion exchange, precipitation and electrostatic interactions are the main mechanisms involved in the adsorption of As onto the char surface. However, arsenic-bio-bone char interactions along with their chemical bonding for the removal of As in aqueous solution is still a subject of debate. Hence, the proposed mechanisms need to be scrutinized further using advanced analytical techniques such as synchrotron-based X-ray. Moving this technology from laboratory phase to field scale applications is an urgent necessity in order to establish a sustainable As mitigation in drinking water on a global scale.

Enhanced Pb immobilization via the combination of biochar and phosphate solubilizing bacteria

Application of biochar in heavy metal remediation suffers from lack of long-term stability. Phosphate-solubilizing bacteria (PSB) are able to elevate P release and the subsequent reaction with Pb to form stable pyromorphite. This study investigated the feasibility of applying PSB modified biochar to enhance immobilization of Pb²⁺. An alkaline biochar produced from rice husk (RB) and a slightly acidic biochar produced from sludge (SB) were selected. It showed that the biochars can effectively remove Pb²⁺ via adsorption, i.e., aqueous Pb concentrations after RB and SB addition were reduced by 18.61 and 53.89% respectively. The addition of PSB increased the Pb²⁺ removal for both biochars (to 24.11 and 60.85%, respectively). In particular, PSB significantly enhanced the formation of stable pyromorphite on surface of SB. This is due to that the evenly distributed PSB enhanced P release and regulated pH on the biochar surface. Moreover, small particles (<0.074 mm) showed their higher ability to induce the formation of pyromorphite, for both RB and SB. Nevertheless, SB demonstrated higher capability of sorption, together with its more abundant P content, which provided a more suitable platform to attract PSB to immobilize heavy metals. Therefore, the combination of biochar and PSB is a promising candidate material for heavy metal remediation. However, the types and particle size distribution of biochar should be addressed.

Zr4+ ions embedded chitosan-soya bean husk activated bio-char composite beads for the recovery of nitrate and phosphate ions from aqueous solution

Removal of nitrate and phosphate ions using Zr4+ ions embedded chitosan-soya bean husk activated bio-char composite beads (Zr-CS-SAC) was carried out by batch mode to overcome the environmental problems due to eutrophication. The adsorbent was well characterized by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) analysis with energy dispersive X-ray analyzer (EDX), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller surface analyzer (BET), thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) etc. The adsorption equilibrium models of Langmuir, Freundlich and D-R isotherms were evaluated and the results described that the Freundlich model was the best for both the adsorbates of nitrate and phosphates ions with respective capacities of 90.09 and 131.29 mg g-1 at 30 °C. Studies on thermodynamic parameters revealed the endothermic and spontaneous nature of the adsorption. Different kinetic models were studied and found that pseudo-second-order kinetic data were well fitted for adsorption process. These results suggested that Zr-CS-SAC composite beads as a promising adsorbent for the removal of nitrate and phosphate ions from water with good removal efficiency, adsorbability, recyclability and non- toxicity.

Immobilized laccase on bentonite-derived mesoporous materials for removal of tetracycline

Bentonite is a natural and environmentally clay mineral, and bentonite-derived mesoporous materials (BDMMs) were obtained conveniently from the alkali and acid treatment of bentonite. In the present study, BDMMs were explored for immobilization of laccase obtained from Trametes versicolor. As a result, bentonite-derived mesoporous materials-Laccase (BDMMs-Lac) was developed for the removal of tetracycline (TC). The enzyme immobilization process was carried out through physical adsorption contact (ion exchange adsorption, hydrogen bond adsorption, and Van der waals adsorption) between the BDMMs and laccase. The process of immobilization remarkably increased its operating temperature. The BDMMs-Lac exhibited over 60% removal efficiency for TC within 3 h in the presence of 1-hydroxybenzotriazole (HBT). In conclusion, BDMMs-Lac showed more promising potential than free laccase for practical continuous applications.

Adsorption behavior of engineered carbons and carbon nanomaterials for metal endocrine disruptors: Experiments and theoretical calculation

Adsorption behaviors and mechanisms of metal endocrine disruptors (Pb²⁺, Cd²⁺, and Hg²⁺) by pyrogenic carbonaceous materials including engineered carbons (biochar and activated carbon) and carbon nanomaterials (multi-walled carbon nanotubes and graphene oxide) have been investigated by experimental and density functional theory (DFT) studies. The adsorption isotherms of metal endocrine disruptors on carbonaceous materials were better fitted by Langmuir models. The adsorption capacities were in the order as follows: GO > BC600 > BC300 > CNT > AC for Pb²⁺, GO > BC300 > AC > BC600 > CNT for Cd²⁺, and GO > BC300 ≥ AC > CNT > BC600 for Hg²⁺, respectively. The DFT-computed binding energy (kcal/mol) of different oxygen-containing functional groups with metal endocrine disruptors followed the orders: (ⅰ) CMCOCPb (-136.70) > CM-COO^--Pb (-91.58) > CMCOPb (-33.57) > CMOHPb (-4.69), (ⅱ) CM-COO^--Cd (-45.91) > CMCOCCd (-4.49) > CMOHCd (-3.68) > CMCOCd (1.08), (ⅲ) CM-COO^--Hg (-25.51) > CMCOCHg (-3.58) > CMOHHg (-0.63) > CMCOHg (0.23). And COC has the highest binding energy for Pb²⁺, whereas COC has much lower binding energy for Cd²⁺ and Hg²⁺. Comprehensively considering DFT calculations, competitive adsorption results and the cost analysis, this work may provide insights into the design of selective adsorbent for specific contaminant.

Adsorptive behaviour of palm oil mill sludge biochar pyrolyzed at low temperature for copper and cadmium removal

In this work, the influence of pyrolysis temperature on the physicochemical properties of palm oil mill sludge biochar (POSB) and its adsorption properties towards cadmium (Cd) and copper (Cu) was investigated. Characterization experiments suggested that POSBs' surface functional groups play the major role in the adsorption process. POSB pyrolyzed at 400 °C showed the best characteristics for Cu and Cd removal. Adsorption study indicated that contact time and shaking speed enhances the adsorption capacity of POSB. It was affirmed that pH adjustment is not necessary for POSB to adsorb Cu and Cd. Mechanism studies fitted well with Langmuir and Pseudo-Second Order model. Thermodynamic parameters indicated that the adsorption was spontaneous, endothermic and correspond to chemical adsorption. The highest uptakes of Cu and Cd were recorded at 48.8 mg/g and 46.2 mg/g respectively. This work verifies that the temperature used for palm oil mill sludge (POS) pyrolysis and adsorption condition played the most prominent role in Cu and Cd removal from aqueous solutions.

Alleviation of cadmium accumulation in maize (Zea mays L.) by foliar spray of zinc oxide nanoparticles and biochar to contaminated soil

Due to the increase in area of cadmium (Cd)-contaminated soils worldwide, effective measures are necessary to minimize the Cd accumulation in cereals including maize (Zea mays L.) plant. A study was therefore performed to explore the effectiveness of foliar spray of zinc oxide (ZnO) nanoparticle (NPs) alone (0, 50, 75, 100 mg/L) or combined with soil application of biochar (1.0% w/w) on biomass, antioxidant enzyme activity and Cd concentrations in maize plants grown on a Cd-contaminated soil. The results depicted that ZnO NPs alone or in combination with biochar improved the height of maize plants, number of leaves, shoot and roots dry biomass, chlorophyll concentrations and gas exchange attributes. All the amendments reduced the electrolyte leakage, malondialdehyde, and hydrogen peroxide contents while improved the activities of antioxidant enzymes in leaf and roots of maize over the control. The application of 50, 75 and 100 mg/L ZnO NPs reduced the Cd contents in shoots by about 12%, 23, and 61%, and in roots by 18%, 33%, and 53%, respectively, over the control. The Cd concentrations in shoot decreased by 15%, 28%, and 68% and in roots by 14%, 35, and 55% after biochar combined with foliar spray of 50, 75 and 100 mg/L ZnO NPs, respectively. All the amendments improved the Zn concentrations in maize shoots and roots whereas reduced the soil bioavailable Cd. Overall, biochar combined with foliar spray of ZnO NPs could be recommended for safely growing the crops on Cd-contaminated soils.

The adsorption, regeneration and engineering applications of biochar for removal organic pollutants: A review

In recent years, with the continuous development of industry and agriculture, the content of organic pollutants in the environment has been increasing, which has caused serious pollution to the environment. Adsorption has proven to be an effective and economically viable method of removing organic contaminants. Since biochar has many advantages such as various types of raw materials, low cost, and recyclability, it can achieve the effect of turning waste into treasure when used for environmental treatment. This paper summarizes the source and production of biochar, points out its research status in the removal of organic pollutants, expounds its adsorption mechanism on organic pollutants, introduces the relevant adsorption parameters, summarizes its regeneration methods, studies its application of engineering, and finally analyses of benefits and describes the development prospects.

Influence of humic substances on the toxic effects of cadmium and SDBS to the green alga Scenedesmus obliquus

The joint toxicity of chemicals mixture in the aquatic environment was still not well clear. To clarify the joint toxicity of the mixtures of metals and organic pollutants, as well as the influence of dissolved organic matter (DOM) in field water-body on their toxic effects, we conducted the toxicity tests with cadmium (Cd) and sodium dodecyl benzene sulfonate (SDBS) on Scenedesmus obliquus (S. obliquus) with or without the presence of fulvic acid (FA), a typical of DOM. Our results showed Cd was more toxic to S. obliquus than SDBS, and the effects of fulvic acid on SDBS were greater than Cd. The joint toxicity of Cd and SDBS expressed a synergistic effect on S. obliquus, which was observed to be increased with the presence of FA. Our results gave an example for the joint toxicity investigations of organics and metals, aiding to understanding the toxicity of pollutant mixtures in field water bodies containing DOM.

Preferable phosphate removal by nano-La(III) hydroxides modified mesoporous rice husk biochars: Role of the host pore structure and point of zero charge

Immobilizing La(OH)₃ nanoparticles (NPs) to porous hosts has been widely applied to inhibiting their inherent aggregation as well as the subsequent low utilization efficiency of La. In this study, a series of rice husk biochars (RHBCs) with high mesoporous rates were prepared and the effects of host pore structure and point of zero charge (pH_pzc) on phosphate adsorption by La-modified RHBCs was particularly focused. Characterization results confirmed that La(OH)₃ NPs were both confined in the pore channel and external surface of RHBCs. Adsorption kinetics and isotherms showed that La-modified RHBCs with higher mesoporous rates of the host showed a faster adsorption rate and La-modified RHBCs exhibited superior La utilization efficiency than many reported La-incorporated adsorbents. Phosphate could be effectively captured over a wide pH of 3-10 due to the high pH_pzc of La-modified RHBCs. Moreover, the La-modified RHBCs showed satisfactory affinity towards phosphate in the presence of coexisting anions and the phosphate adsorption by La-RHBC₉ was enhanced in the presence of Ca²⁺, while it was inhibited in the presence of Mg²⁺. The mesoporous structure of RHBCs strengthened the stability of La-modified RHBCs and weakened the inhibition of coexisting humic substances on phosphate adsorption through the "shielding effect".

Removal of 17β-Estradiol from water by adsorption onto montmorillonite-carbon hybrids derived from pyrolysis carbonization of carboxymethyl cellulose

In this work, we demonstrated the preparation of the carbonized montmorillonite/carboxymethyl cellulose (MMT/CMC) hybrids and their application as an adsorbent for efficient removal of 17β-Estradiol (βE2). X-ray diffractometer (XRD) results showed that CMC intercalation reached saturation at a CMC to MMT weight ratio of 1; transmission electron microscope (TEM) measurements clearly revealed that carbonization caused graphenes distribute on the MMT surfaces; pyrolysis temperature at 600 °C yielded novel MMT/CMC sample of high surface areas as reflected by Brunauer-Emmett-Teller (BET) surface area. The adsorbed amount of βE2 under various conditions decreased in the order MMT/CMC_1:1(600) > MMT/CMC_1:1(450) > MMT/CMC_1:1(300) ∼ MMT/CMC_2:1(600) ∼ MMT > MMT/CMC_5:1(600). The removal of βE2 by MMT/CMC_1:1(600) occurred very quickly, and the adsorption kinetics could be well fitted by the Ritchie nth-order kinetic model; the best-fit adsorption isotherm model was Freundlich model. The MMT/CMC_1:1(600) also exhibited good regeneration performance after five adsorption/desorption cycles. The experimental results also showed that the adsorption of βE2 on the MMT/CMC_1:1(600) composite could contribute to hydrophobic partitioning, π-π staking interaction, H-bond interaction, pore-filling effect and simple van der Waals interaction. This highly effective and novel adsorbent can be easily synthesized and regenerated, indicating its great potential in drinking and wastewater purification for endocrine disruptor compounds.

Surface-Modified Biochar with Polydentate Binding Sites for the Removal of Cadmium

In this study, a surface chemical-modified rice husk biochar with abundant amino groups and disulfide bonds for the removal of cadmium was prepared using cystamine dihydrochloride as a modification ligand and glutaraldehyde as a crosslinker. The biochars were characterized by Fourier transform infrared spectrometry (FTIR), elemental analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermogravimetry analysis (TGA), and nitrogen sorption (BET) before and after modification. The adsorption properties of the modified biochars for Cd (II) were investigated in detail via adsorption isotherm models, adsorption kinetics models, and selective adsorption experiments. The surfaces of the cystamine-modified biochars with granular nanopolymers of sufficient functional groups of primary amine and disulfide linkage rendered the biochar surface more conducive to electrostatic attraction and surface complexation. The theoretical maximum adsorption capacity of the modified biochars (81.02 mg g^-1) was almost 10-fold greater than that of the raw biochars (8.347 mg g^-1) for Cd (II). Besides, the cystamine-modified biochars had a better affinity for Cd (II) compared to other heavy metals (Zn, As, Cd, Co, Ni, Cr), showing six-fold greater affinity for Cd (II) than Zn²⁺. The results of this study indicate that the modification of biochars derived from rice husks shows great potential in the removal of Cd (II) from contaminated water.

Accelerated Microbial Reduction of Azo Dye by Using Biochar from Iron-Rich-Biomass Pyrolysis

Biochar is widely used in the environmental-protection field. This study presents the first investigation of the mechanism of biochar prepared using iron (Fe)-rich biomass and its impact on the reductive removals of Orange G dye by Shewanella oneidensis MR-1. The results show that biochars significantly accelerated electron transfer from cells to Orange G and thus stimulated reductive removal rate to 72–97%. Both the conductive domains and the charging and discharging of surface functional groups in biochars played crucial roles in the microbial reduction of Orange G to aniline. A high Fe content of the precursor significantly enhanced the conductor performance of the produced biochar and thus enabled the biochar to have a higher reductive removal rate of Orange G (97%) compared to the biochar prepared using low-Fe precursor (75%), but did not promote the charging and discharging capacity of the produced biochar. This study can prompt the search for natural biomass with high Fe content to confer the produced biochar with wide-ranging applications in stimulating the microbial reduction of redox-active pollutants.

Enhanced removal of Cr(VI) by biochar with Fe as electron shuttles

Biochar is extensively used as an effective soil amendment for environmental remediation. In addition to its strong contaminant sorption capability, biochar also plays an important role in chemical transformation of contaminant due to its inherent redox-active moieties. However, the transformation efficiency of inorganic contaminants is generally very limited when the direct adsorption of contaminants on biochar is inefficient. The present study demonstrates the role of Fe ion as an electron shuttle to enhance Cr(VI) reduction by biochars. Batch experiments were conducted to examine the effects of Fe(III) levels, pyrolysis temperature of biochar, initial solution pH, and biochar dosage on the efficiency of Cr(VI) removal. Results showed a significant enhancement in Cr(VI) reduction with an increase in Fe(III) concentration and a decrease of initial pH. Biochar produced at higher pyrolysis temperatures (e.g., 700°C) favored Cr(VI) removal, especially in the presence of Fe(III), while a higher biochar dosage proved unfavorable likely due to the agglomeration or precipitation of biochar. Speciation analysis of Fe and Cr elements on the surface of biochar and in the solution further confirmed the role of Fe ion as an electron shuttle between biochar and Cr(VI). The present findings provide a potential strategy for the advanced treatment of Cr(VI) at low concentrations as well as an insight into the environmental fate of Cr(VI) and other micro-pollutants in soil or aqueous compartments containing Fe and natural or engineered carbonaceous materials.

High-performance porous biochar from the pyrolysis of natural and renewable seaweed (Gelidiella acerosa) and its application for the adsorption of methylene blue

A high-performance porous biochar adsorbent prepared by facile thermal pyrolysis of seaweed (Gelidiella acerosa) is reported. The textural characteristics of the prepared seaweed biochar (SWBC) and the performance in the adsorption of methylene blue (MB) dye were evaluated. The batch experiment for the adsorption of MB was conducted under different parameters, such as temperature, pH, and initial concentration of MB in the range of 25-400 mg/L. The developed SWBC exhibited a relatively high surface area, average pore size, and pore volume of 926.39 m²/g, 2.45 nm, and 0.57 cm³/g, respectively. The high surface area and pristine mineral constituents of the biochar promoted a high adsorption capacity of 512.67 mg/g of MB at 30 °C. The adsorption isotherm and kinetics data best fitted the Langmuir and pseudo-second-order equations. The results indicate that SWBC is efficient for MB adsorption and could be a potential adsorbent for wastewater treatment.

Biochar as a Multifunctional Component of the Environment—A Review

The growing demand for electricity, caused by dynamic economic growth, leads to a decrease in the available non-renewable energy resources constituting the foundation of global power generation. A search for alternative sources of energy that can support conventional energy technologies utilizing fossil fuels is not only of key significance for the power industry but is also important from the point of view of environmental conservation and sustainable development. Plant biomass, with its specific chemical structure and high calorific value, is a promising renewable source of energy which can be utilized in numerous conversion processes, enabling the production of solid, liquid, and gaseous fuels. Methods of thermal biomass conversion include pyrolysis, i.e., a process allowing one to obtain a multifunctional product known as biochar. The article presents a review of information related to the broad uses of carbonization products. It also discusses the legal aspects and quality standards applicable to these materials. The paper draws attention to the lack of uniform legal and quality conditions, which would allow for a much better use of biochar. The review also aims to highlight the high potential for a use of biochar in different environments. The presented text attempts to emphasize the importance of biochar as an alternative to classic products used for energy, environmental and agricultural purposes.

Influence of immobilization on phenanthrene degradation by Bacillus sp. P1 in the presence of Cd(II)

Suspended microbes gradually lost advantages in practical applications of PAHs and heavy metals bioremediation. Therefore this study investigated the effect of immobilization on phenanthrene degradation by Bacillus sp. P1 in the presence of different Cd(II) concentrations. Condensed Bacillus sp. P1 was immobilized with polyvinyl alcohol and sodium alginate and PVA-SA-cell cryogel beads were prepared. The results indicated that the use of gel beads increased the number of adsorption sites thus accelerating phenanthrene degradation. In addition, changes in detoxification indices, including superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH), were determined to elucidate the immobilization mechanisms related to cells protection from Cd(II) when degrading phenanthrene. By protecting the gel membrane, oxidative damage was minimized, while SOD activity increased from 55.72 to 81.33 U/mgprot as Cd(II) increased from 0 to 200 mg/L but later dropped to 44.29 U/mgprot as Cd(II) increased to 300 mg/L for the non-immobilized system. On the other hand, the SOD activity kept increasing from 52.23 to 473.35 U/mgprot for the immobilized system exposed to Cd(II) concentration between 0 and 300 mg/L. For CAT and GSH, immobilization only slowed down the depletion process without any change on the variation trends. The changes in surface properties and physiological responses of microbes caused the differences of immobilization effect on phenanthrene biodegradation in the presence of Cd(II), which is a novel finding.

Cr(VI) removal from aqueous solution using biochar modified with Mg/Al-layered double hydroxide intercalated with ethylenediaminetetraacetic acid

In this study, the bamboo biomass loaded with ethylenediaminetetraacetic acid (EDTA) intercalated Mg/Al-layered double hydroxides (LDH) was calcined to obtain a novel nano-adsorbent (BC@EDTA-LDH), and BC@EDTA-LDH was used to remove hexavalent chromium (Cr(VI)) in aqueous solutions. The results showed that the interaction between LDH and Cr(VI) on biochar played a dominant part in adsorption. The LDH of Cr(VI) intercalation was successfully reconstructed after adsorption. Fourier transform infrared spectra and X-ray diffraction results confirmed the reconstruction of Mg/Al-LDH. LDH had sustained release effect on the solution. As the pH values increased, the electrostatic repulsion between Cr₂O₇^2- and OH^- increased, and there existed competition for adsorption sites. The maximum adsorption capacity of Cr(VI) was 38 mg/g. The data was well-fitted with pseudo second-order model and Langmuir-Freundlich model. BC@EDTA-LDH showed a high adsorption capacity and was potentially suitable for removing heavy metals in wastewater.

Adsorption mechanism of dichlorvos onto coconut fibre biochar: the significant dependence of H-bonding and the pore-filling mechanism

The adsorption mechanism of dichlorvos onto coconut fibre biochar (CFB) was investigated by the batch adsorption technique. Coconut fibre waste material was synthesised at 600 °C for 4 h under oxygen-limited conditions. The biochar was modified by HCl acid to enhance the specific surface area and porosity. The characteristics of the biochar were analysed by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area, and Fourier transform-infrared (FT-IR). The results showed that the BET specific surface area of biochar was 402.4 m²/g. Experimental data presented a good fit to Langmuir isotherm and the pseudo-second-order model. Langmuir isotherm illustrated that monolayer adsorption of dichlorvos occurred on the surface of CFB, with a maximum adsorption capacity of 90.9 mg/g. The diffusion model confirmed that the liquid film diffusion was the rate-limiting step, and the major diffusion mechanism of dichlorvos onto biochar. The BET result after dichlorvos adsorption demonstrated that pore-filling occurred and occupied 58.27%. The pore-filling and chemical interactions, performed important roles in the adsorption of dichlorvos onto CFB. Chemical adsorption is comprised of two interactions, which are hydrophobic and H-bonding, but the prime is H-bonding. CFB is a very potential material for the removal of dichlorvos and environmental pollutants.

Enhanced adsorption for Pb(II) and Cd(II) of magnetic rice husk biochar by KMnO4 modification

Novel KMnO₄-treated magnetic biochar (FMBC) was successfully synthesized by addition of Fe(NO₃)₃ during carbonization and KMnO₄ treatment following for Pb(II) and Cd(II) adsorption. SEM-EDS, XPS, and ICP-AES were used to evaluate the FMBC and magnetic biochar (FBC) on surface morphology, surface chemistry characteristics, surface functional groups, and Pb(II) and Cd(II) adsorption behavior. Results showed that the Langmuir maximum adsorption quantity of FMBC reached 148 mg/g for Pb(II) and 79 mg/g for Cd(II), nearly 7 times of that of FBC. The enhancement of FMBC for heavy metal adsorption was due to the successful load of manganese oxides and the increased oxygen functional groups consistent with XPS and FTIR results. The adsorption capacities of FMBC were maintained over 95% when the pH value was higher than 2.5 and 3.5 for Pb(II) and Cd(II), respectively. The adsorption performances of both heavy metals by FMBC were hardly influenced by ionic strength and humid acid. The adsorption capacities of FMBC could maintain over 50% and 87% after four cycles for Pb(II) and Cd(II), respectively. The saturation magnetization of FMBC was about 11.5 emu/g, which did not change after adsorption. This work proposed a new method to fabricate a magnetic biochar with high adsorption capacities of heavy metals Pb(II) and Cd(II).

Biochar seeding promotes struvite formation, but accelerates heavy metal accumulation

This study investigated the effects of biochar seeding (wheat straw biochar and rice husk biochar) on nutrient recovery via struvite formation, and improvements in the particle size of precipitated struvite from anaerobic digestate supernatant. Simultaneously, the influence of biochar seeding on heavy metal accumulation and elimination of pathogens (total coliforms and Escherichia coli) was evaluated under various operational factors, e.g., pH, supersaturation, reaction time, and seeding rates. Compared to the non-seeding process (maximum recovery efficiency of phosphate and ammonium 91% and 83%, respectively, with a particle size of 70 μm) and the struvite-seeding process (maximum recovery efficiency of phosphate and ammonium 97% and 94%, respectively, with a particle size of 100 μm), the process of biochar seeding improved nutrient recovery up to 7% and 11% for phosphate and ammonium, respectively, and increased struvite particle size by 43%, regardless of biochar type. XRD diffraction and FTIR analysis confirmed the prevalence of orthorhombic characteristics and an inner crystalline structure of the struvite formed by biochar seeding. About 75% of total coliforms and 70% of Escherichia coli were removed from the digestate supernatant through seeded struvite precipitation, regardless of the seeding materials. However, the biochar seeding process led to an accumulation of heavy metals in the acquired struvite product than that with non-seeded precipitation process. The concentrations of these metals were still well below permissible limits for application on agricultural land. It can be concluded that the inclusion of biochar as a seeding material might be a sustainable strategy to enhance struvite formation, intensify nutrient recovery, and yield high-quality struvite fertilizer with increased particle sizes.

Synthetic strategies and application of gold-based nanocatalysts for nitroaromatics reduction

With the increasing requirement of efficient organic transformations on the basic concept of Green Sustainable Chemistry, the development of highly efficient catalytic reaction system is greatly desired. In this case, gold (Au)-based nanocatalysts are promising candidates for catalytic reaction, especially for the reduction of nitroaromatics. They have attracted wide attention and well developed in the application of nitroaromatics reduction because of the unique properties compared with that of other conventional metal-based catalysts. With this respect, this review proposes recent trends in the application of Au nanocatalysts for efficient reduction process of nitroaromatics. Some typical approaches are compared and discussed to guide the synthesis of highly efficient Au nanocatalysts. The mechanism on the use of H₂ and NaBH₄ solution as the source of hydrogen is compared, and that proposed under light irradiation is discussed. The high and unique catalytic activity of some carriers, such as oxides and carbons-based materials, based on different sizes, structures, and shapes of supported Au nanocatalysts for nitroaromatics reduction are described. The catalytic performance of Au combining with other metal nanoparticles by alloy or doping, like multi-metal nanoparticles system, is further discussed. Finally, a short discussion is introduced to compare the catalysis with other metallic nanocatalysts.

Factors affecting the sorption of halogenated phenols onto polymer/biomass-derived biochar: Effects of pH, hydrophobicity, and deprotonation

High-performance biochar synthesized via co-pyrolysis of a polymer and rice straw (RS) was evaluated as a sorbent for ionizable halogenated phenols. Compared with RS-derived biochar, the sorption of 2,4-dichlorophenol (DCP), 2,4-dibromophenol (DBP), and 2,4-difluorophenol (DFP) onto polymer/RS-derived biochar was significantly enhanced by the properties of biochar changing due to polymer residues. According to Langmuir sorption isotherm model maximum sorption capacities for DCP, DBP, and DFP were 25.5-27.8, 22.1-26.5, and 11.5-13.3 mg/g, respectively, 3-5 times higher than those of RS-derived biochar. The removal of the polymer residues and increasing aromaticity of polymer/RS-derived biochar at elevated pyrolysis temperatures affected the sorption capacity of halogenated phenols. The surface charge of biochar and deprotonation of the halogenated phenols according to the solution pH were other factors responsible for sorption onto polymer/RS-derived biochar. Competition with other halogenated phenols, Zn²⁺, and Cu²⁺ implied that similar sorption mechanisms existed and that surface complexation and electron donor-acceptor interactions were involved in sorption onto polymer/RS-derived biochar. Our results suggest that co-disposal of thermoplastic and biomass wastes through pyrolysis may be an effective option to produce high-performance upgraded biochar as a sorbent for various types of contaminants.

Effects of biochar on 2, 2', 4, 4', 5, 5'-hexabrominated diphenyl ether (BDE-153) fate in Amaranthus mangostanus L.: Accumulation, metabolite formation, and physiological response

The accumulation and metabolism of 2, 2', 4, 4', 5, 5'-hexabrominated diphenyl ether (BDE-153) in Amaranthus mangostanus L. (amaranth) as affected by different concentrations of biochar (1.3 to 26.6 g/L) under hydroponic conditions exposed to 10 μg/L BDE-153 after 10 days were investigated. Biochar significantly reduced BDE-153 shoot and root content by 27.5-61.6% and 73-95.3%, respectively. In general, BDE-153 migration from solution to amaranth decreased with increasing the doses of biochar. BDE-153 metabolites altered with doses of biochar. The ratio of de-BDEs to BDE-153 in root was polynomial correlated to biochar dose (R² = 0.9356**). Root and shoot Fe content was positively correlated with the BDE-153 amounts (R² = 0.948** and 0.822*, respectively). Though the higher biochar dose could obviously control BDE-153 uptake by the vegetable, the toxicity was caused more significantly. For instances, the high concentration of biochar at 26.6 g/L reduced pigment content, increased total ROS, and elevated antioxidant enzyme activity. At the same time, the O₂^- intensity was linearly positively correlated with de-BDEs in root (R² = 0.7324*) while photosynthetic parameter F_v/fm intensity was polynomial correlated to BDEs in shoot (R² = 0.9366*). Transmission electron microscopy (TEM) confirmed that exposure to BDE-153 and high concentration biochar at 26.6 g/L severely altered the chloroplasts in terms of the organelle shape and the presence of starch granules in the chloroplast. Taken together, biochar as a soil amendment could significantly control BDE-153 uptake and enhance BDE-153 metabolism in vegetables, but considering the dose of biochar to avoid its toxicity with higher dose.

Magnetic nanoferromanganese oxides modified biochar derived from pine sawdust for adsorption of tetracycline hydrochloride

In this study, a new type of composite material, namely modified biochar (MBC), was synthesized by loading the magnetic ferromanganese oxide nanoparticles on pine biochar. BET, SEM, and FTIR were employed to analyze the surface properties and pore structures of MBC. In addition, XRD was adopted to examine the crystal structure of MBC. Characterization results showed that the surface area and porosity of MBC have been greatly improved, and the functional groups have been introduced by ferromanganese oxides. Adsorption experiments of tetracycline hydrochloride (TC) including kinetics, isotherms, thermodynamics as well as the influence of pH, salt ion strength, and the environmental risk of MBC, were evaluated. The results revealed that the experimental data conformed to the pseudo-second-order kinetic model and the Freundlich isotherm model. In the adsorption process, MBC showed excellent adsorption ability (maximum capacity for TC 100.74 mg g^-1) to BC (33.76 mg g^-1). In isotherm experiments, the maximum adsorption capacity of TC by MBC reached 177.71 mg g^-1. Toxicity studies showed that the MBC had no harm to the environment. To conclude, MBC has great potential for applications in removing TC from water.

Insight into interaction between biochar and soil minerals in changing biochar properties and adsorption capacities for sulfamethoxazole

Biochars produced from wheat straw at 400 °C (BC400) and 700 °C (BC700) were treated with three typical soil minerals to examine the effects of soil minerals on biochar properties and adsorption capacity for sulfamethoxazole (SMX). Mineral treatment enlarged the surface area and pore size of biochar, and the electron donating capacity (EDC) of the mineral-treated biochars also increased due to the increased phenolic group in BC400 and the enhanced conjugated π-electron system in BC700, respectively, which in turn affected the adsorption capacity of biochars for SMX. The adsorption of SMX on BC700 was increased after mineral treatment due to the facilitating effect of π-π electron donor-acceptor interaction as indicated by the positive correlation of surface adsorption amount (Q_A) of SMX with EDC of biochars (R² = 0.92-0.96). In contrast, mineral treatment decreased SMX adsorption on BC400, which could be attributed to the potential association of organic matter with minerals via coprecipitation and adsorption, in addition to the weak adsorption capacities of soil minerals for SMX. These results can provide a new insight for better understanding the interaction between biochar and soil minerals and its effect on adsorption capacity of biochar for organic pollutants.