Removal of Pb2+ and Cd2+ from aqueous solution using chars from pyrolysis and microwave-assisted hydrothermal carbonization of Prosopis africana shell

Selective Capacitive Removal of Pb2+ from Wastewater over Biochar Electrodes by Zinc Regulation

Biochar materials have shown great potential for broad catalytic application. However, using these materials in the capacitive deionization technology (CDI) system for heavy metal removal still faces a significant challenge due to their low specific capacity and removal capability. Here, a comprehensive regulation on the interfacial/bulk electrochemistry of biochar by Zn doping is reported, which suggests a high renewable capacity (20 mg g-1) and outstanding selective capacitive removal ability (SCR) of Pb2+ from leachate. The SCR efficiency of Pb2+ is as high as 99% compared to K+ (8%), Na+ (13%), and Cd2+ (37%). This work proves that the doped Zn on the biochar can combine with OH- generated by water splitting to form M─OH bonds, which is beneficial for improving the specific capacity. Significantly, the relationship between double-layer capacitance and pseudo-capacitance can also be optimized by regulating the content of Zn, leading to different removal abilities of heavy metals. Therefore, this work offers insights into charge-storage kinetics, which provide valuable guidelines for designing and optimizing the biochar electrode for broader environmental applications.

Application of machine learning in prediction of Pb2+ adsorption of biochar prepared by tube furnace and fluidized bed

Data mining by machine learning (ML) has recently come into application in heavy metals purification from wastewater, especially in exploring lead removal by biochar that prepared using tube furnace (TF-C) and fluidized bed (FB-C) pyrolysis methods. In this study, six ML models including Random Forest Regression (RFR), Gradient Boosting Regression (GBR), Support Vector Regression (SVR), Kernel Ridge Regression (KRR), Extreme Gradient Boosting (XGB), and Light Gradient Boosting Machine (LGBM) were employed to predict lead adsorption based on a dataset of 1012 adsorption experiments, comprising 422 TF-C groups from our experiments and 590 FB-C groups from literatures. The XGB model showed superior accuracy and predictive performance for adsorption, achieving R2 values for TF-C (0.992) and FB-C (0.981), respectively. Contrasting inferior results were observed in other models, including RF (0.962 and 0.961), GBR (0.987 and 0.975), SVR (0.839 and 0.763), KRR (0.817 and 0.881), and LGBM (0.975 and 0.868). Additionally, a hybrid dataset combining both biochars in Pb adsorption also indicated high accuracy (0.972) as obtained from XGB model. The investigation revealed that the influence of char characteristics and adsorption conditions on Pb adsorption differs between the two biochar. Specific char characteristics, particularly nitrogen content, significantly influence lead adsorption in both biochar. Interestingly, the influence of pyrolysis temperature (PT) on lead adsorption is found to be greater for TF-C than for FB-C. Consequently, careful consideration of PT is crucial when preparing TF-C biochar. These findings offer practical guidance for optimizing biochar preparation conditions during heavy metal removal from wastewater.

Fabrication of two novel amino-functionalized and starch-coated CuFe2O4-modified magnetic biochar composites and their application in removing Pb2+ and Cd2+ from wastewater

Novel magnetic biochar composites (SFeCu@SBCO and FeCu@SBCO-NH2) were fabricated by modifying oxidized sawdust biochar (SBCO) with Fe/Cu loading, starch-coating/amination, characterized (FTIR, XRD, BET, SEM-EDS and XPS) and applied in capturing Pb2+ and Cd2+ from wastewater. Adsorption experiments revealed that SFeCu@SBCO and FeCu@SBCO-NH2 exhibited extraordinary adsorption performance toward Pb2+/Cd2+ with the maximum adsorption capacity reaching 184.26/173.35 mg g-1 and 201.43/190.81 mg g-1, respectively, which were >5 times higher than those of SBC. The great increase in adsorption capacity of the two adsorbents was ascribed to the introduction of CuFe2O4 and starch/amino groups. Pb2+ and Cd2+ adsorption was an endothermic reaction controlled by monolayer chemisorption. Complexation and electrostatic attraction were the two predominant mechanisms. Besides, ion exchange together with physical adsorption also occurred during the adsorption. Additionally, the both adsorbents displayed favorable stability and reusability as well as desirable anti-interfering ability to other metal cations. Taken together, the both adsorbents could be utilized as reusable magnetic adsorbents with promising prospect in the effective remediation of Pb2+/Cd2+ contaminated water. The study not only contributed to the better understanding of biochar modification strategy and the application of modified biochar in heavy metals pollutants removal, but also realized resource utilization of biomass waste.

Adsorption isotherms and kinetics for Pb(ii) ion removal from aqueous solutions with biogenic metal oxide nanoparticles

This study investigates the sorption removal of lead(ii) ions using zinc oxide (ZnO) and copper(ii) oxide (CuO) nanoparticles synthesized through a wet burning method with the aid of plant extract from Serratula coronata L. The effect of plant collection time on polyphenol content was investigated and optimal conditions were determined. The structural and chemical properties of the nanoparticles were studied by scanning electron microscopy, energy dispersive analysis, X-ray phase analysis, and X-ray photoelectron spectroscopy. A comparative analysis of lead ion sorption on the surface of synthesized nanoparticles was conducted. The kinetic study revealed that the sorption process follows a pseudo-second-order mechanism, and the Freundlich sorption model provides a better fit for the experimental data. ZnO and CuO nanoparticles exhibited significant sorption capacities, with values of 163.6 and 153.8 mg g-1, respectively.

Adsorption of lead ions and methylene blue on acrylate-modified hydrochars

Hydrochars are promising sorbents for wastewater treatment. Herein, two acrylate-modified hydrochars (AMHC₁ and AMHC₂) were obtained by grafting acrylic acid on the surface of two hydrochars (MHC₁ and MHC₂ hydrothermally carbonized in water and acidic medium respectively) with free radical polymerization. Characterizations show that MHC₂ is more prone to free radical polymerization than MHC₁ does, and has higher carboxylate content after modification. The adsorption amounts of AMHC₂ over methylene blue (MB) and Pb(II) are much higher than those of AMHC₁. Pseudo-second-order kinetic and Langmuir isotherm equations well fit the Pb(II) and MB sorption data of AMHC₂. The Pb(II) adsorptive mechanism is mainly inner-surface complexation accompanied by ion exchange and cation-π interaction. MB adsorption involves ion exchange, electrostatic interaction, H-bonding and π-π interaction. Hence, the one-step modification method of free radical polymerization under alkaline condition has great potential for preparing carboxylate-modified hydrochars to adsorb cationic pollutants.

Eco-Friendly Electroless Template Synthesis of Cu-Based Composite Track-Etched Membranes for Sorption Removal of Lead(II) Ions

This paper reports the synthesis of composite track-etched membranes (TeMs) modified with electrolessly deposited copper microtubules using copper deposition baths based on environmentally friendly and non-toxic reducing agents (ascorbic acid (Asc), glyoxylic acid (Gly), and dimethylamine borane (DMAB)), and comparative testing of their lead(II) ion removal capacity via batch adsorption experiments. The structure and composition of the composites were investigated by X-ray diffraction technique and scanning electron and atomic force microscopies. The optimal conditions for copper electroless plating were determined. The adsorption kinetics followed a pseudo-second-order kinetic model, which indicates that adsorption is controlled by the chemisorption process. A comparative study was conducted on the applicability of the Langmuir, Freundlich, and Dubinin-Radushkevich adsorption models to define the equilibrium isotherms and the isotherm constants for the prepared composite TeMs. Based on the regression coefficients R², it has been shown that the Freundlich model better describes the experimental data of the composite TeMs on the adsorption of lead(II) ions.

Performance and mechanism of Pb2+ and Cd2+ ions’ adsorption via modified antibiotic residue-based hydrochar

This study investigated the hydrochar-based porous carbon prepared by combining the technical route of hydrothermal carbonization (HTC) + chemical activation. The hydrochar morphology was adjusted by changing the activation reaction conditions and adding metal salts. Experiments showed that the activation of KHCO₃ significantly increased the specific surface area and pore size of the hydrochar. Besides, oxygen-rich groups on the surface of the activated hydrochar interacted with heavy metal ions to achieve efficient adsorption. The activated hydrothermal carbon adsorption capacity for Pb²⁺ and Cd²⁺ ions reached 289 and 186 mg/g, respectively. The adsorption mechanism study indicated that the adsorption of Pb²⁺ and Cd²⁺ was related to electrostatic attraction, ion exchange, and complexation reactions. The "HTC + chemical activation" technology was environmentally friendly and effectively implemented antibiotic residues. Carbon materials with high adsorption capacity can be prepared so that biomass resources can be utilized with excessive value, as a consequence presenting technical assistance for the comprehensive disposal of organic waste in the pharmaceutical industry and establishing a green and clean production system.

Solvent-Free Synthesis of Magnetic Sewage Sludge-Derived Biochar for Heavy Metal Removal from Wastewater

The commonly used two-step and one-pot synthesis methods for producing biochar require the use of iron salt solutions, resulting in the undesirable consequences of energy consumption for dewatering and potential pollution risks. To address this drawback, a magnetic sewage sludge-derived biochar (MSBC-2) was synthesized by a solvent-free method in this study. The pseudo-second-order kinetic model and Langmuir model provided the best fit to the experimental data, implying a monolayered chemisorption process of Pb2+, Cd2+and Cu2+ onto MSBC-2. As the reaction temperature increased from 25 °C to 45 °C, the maximum adsorption capacities increased from 113.64 mg·g−1 to 151.52 mg·g−1 for Pb2+, from 101.01 mg·g−1 to 109.89 mg·g−1 for Cd2+ and from 57.80 mg·g−1 to 74.07 mg·g−1 for Cu2+, respectively. Thermodynamic parameters (ΔG0 < 0, ΔS0 > 0, ΔH0 > 0) revealed that the adsorption processes of all three metals by MSBC-2 were favourable, spontaneous and endothermic. Surface complexation, cation-π interaction, ion exchange and electrostatic attraction mechanisms were involved in the adsorption of Pb2+, Cd2+ and Cu2+ onto MSBC-2. Overall, this study will provide a new perspective for the synthesis of magnetic biochar and MSBC-2 shows great potential as an adsorbent for heavy metal removal.

Calcium-pyro-hydrochar derived from the spent mushroom substrate as a functional sorbent of Pb2+ and Cd2+ from aqueous solutions

A calcium-pyro-hydrochar (Ca-PHC) can be distinguished as a novel sorbent of Pb²⁺ and Cd²⁺ from an aqueous solution. It was obtained using hydrothermal treatment of the spent mushroom substrate (SMS), followed by a CaCl₂·5H₂O activation and pyrolysis. The characterisation of chars before and after modifications was done by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) and Fourier transform infrared (FTIR). Batch experiments were performed to examine Ca-PHC's sorption properties and binding mechanisms to selected metal ions. The maximum sorption capacities of Ca-PHC for Pb²⁺ and Cd²⁺ were 297 mg g^-1, and 131 mg g^-1, respectively. The obtained results demonstrated that the sorption of Pb²⁺ and Cd²⁺ by Ca-PHC follows a pseudo-second kinetic model and Freundlich isotherm. The binding of the selected metals onto Ca-PHC was enabled by the ion-exchange mechanism, surface complexation, mineral precipitation and cation-π interaction. Thermodynamic parameters indicate that metal ions binding by Ca-PHC are spontaneous and endothermic. Due to the high adsorption capacities, the obtained Ca-PHC has good potential for application in industrial wastewater treatment. In addition, the demonstrated use of SMS highlights another possibility of applying this specific biomass relevant to sustainable and economical waste management in the growing mushroom industry.

Comparative Study of Biochar Modified with Different Functional Groups for Efficient Removal of Pb(II) and Ni(II)

The potential application of biochar in water treatment is attracting interest due to its sustainability and low production cost. In the present study, H₃PO₄-modified porous biochar (H-PBC), ethylenediaminetetraacetic acid-modified porous biochar (E-PBC), and NaOH-modified porous biochar (O-PBC) were prepared for Ni(II) and Pb(II) adsorption in an aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller analysis (BET), and Fourier-transform infrared (FT-IR) spectroscopy were employed to characterize the as-obtained samples, and their capacities for Ni(II) and Pb(II) adsorption were determined. SEM showed that H-PBC retained the hierarchical porous structure of pristine biochar. FT-IR showed that H-PBC possessed abundant oxygen-containing and phosphorus-containing functional groups on the surface. BET analysis demonstrated that the surface areas of H-PBC (344.17 m²/g) was higher than O-PBC (3.66 m²/g), and E-PBC (1.64 m²/g), respectively. H-PBC, E-PBC, and O-PBC all exhibited excellent performance at Ni(II) and Pb(II) adsorption with maximum adsorption capacity of 64.94 mg/g, 47.17 mg/g, and 60.24 mg/g, and 243.90 mg/g, 156.25 mg/g, and 192.31 mg/g, respectively, which were significantly higher than the adsorption capacity (19.80 mg/g and 38.31 mg/g) of porous biochar (PBC). Pseudo-second order models suggested that the adsorption process was controlled by chemical adsorption. After three regeneration cycles, the Ni(II) and Pb(II) removal efficiency with H-PBC were still 49.8% and 56.3%. The results obtained in this study suggest that H-PBC is a promising adsorbent for the removal of heavy metals from aqueous solutions.

A comparative study on adsorption of cadmium and lead by hydrochars and biochars derived from rice husk and Zizania latifolia straw

In this study, hydrochars and biochars were prepared from rice husk (RH) and Zizania latifolia straw (ZL) at various pyrolysis temperatures as absorbents, for removing toxic ions from single and competitive solutions of cadmium (Cd) and/or lead (Pb). The adsorption efficiencies of Cd and Pb in both hydrochars and biochars were lower in the competitive solution than in the single solution, and the absorbents had a stronger affinity for Pb than for Cd. Compared to hydrochars, biochars showed more favorable Cd and Pb adsorption capacities in the single or competitive solutions, and the ZL biochars had the maximum adsorption capacity among them. The SEM and FTIR analyses suggest that the predominant adsorption mechanisms of biochars and hydrochars are surfaces monolayer adsorption, precipitation, complexation, and coordination with π electrons. However, hydrochars derived from ZL exhibited an optimal additional Pb adsorption capacity in the high-level (5 ~ 10 mg L^-1 Cd and Pb) competitive solution. This extra Pb adsorption of hydrochars was likely attributed to the Si-O-Si groups and more bumpy structure. Zizania latifolia straw biochar had a huge potential removal of Cd or/and Pb, and applying hydrochars as absorbents was beneficial to the removal of Cd and Pb in polluted solutions.

Simultaneous adsorption of toxic metals in binary systems using peanut and sheanut shells biochars

Converting peanut and sheanut shells into biochar is a smart strategy for recycling agricultural waste. Biochar was produced from peanut and sheanut shells at temperatures of 350 ± 5 °C and 700 ± 5 °C. The adsorption capacities for lead (Pb²⁺), cadmium (Cd²⁺) and mercury (Hg²⁺) in the binary systems were evaluated. In the binary systems with concentrations of 5 : 5 mg/L, 10 : 10 mg/L, 25 : 25 mg/L and 50 : 50 mg/L the removal efficiencies of GB350, SB350, GS350, GB700, SB700 and GS700 were 100% for Pb²⁺ and 88.70%–99.46% for Cd²⁺, 98.20%–100% for Pb²⁺ and 100% for Hg²⁺, 79.30%–100% for Cd²⁺ and 99.96%–100% for Hg²⁺. The higher adsorption percentages of Pb²⁺, Cd²⁺ and Hg²⁺ by the biochar in the binary systems indicated that the pH values of the solutions were good and suitable for adsorption. The biochar from peanut and sheanut shells showed excellent capacity to remove Pb, Cd and Hg in the binary systems. The Langmuir model (0.3351 ≤ R² ≤ 0.9901) was more suitable than the Freundlich model (0.0014 ≤ R² ≤ 0.9994) for the adsorption of toxic metal ions onto the biochar in the binary systems. The interactive effects of the binary mixtures in the aqueous solution of Pb²⁺, Cd²⁺, and Hg²⁺ were found to be either antagonistic or synergistic. Peanut and sheanut shell biochar were rich in calcium, potassium, magnesium, and sodium, and phosphates affected the mechanisms of Pb and Cd adsorption. The high sulphur content might have influenced the mechanism of Hg adsorption in the aqueous solutions on peanut and sheanut shell biochar. These results suggest that peanut and sheanut shell biochar have enormous potential and are suitable for adsorption of Pb²⁺, Cd²⁺ and Hg²⁺ in wastewater and polluted soil. Therefore, their effectiveness should be further tested in an actual water polluted environment.

Utilization of Waste Amine-Oxime (WAO) Resin to Generate Carbon by Microwave and Its Removal of Pb(II) in Water

Utilising waste amine-oxime (WAO) resin through microwave semi-carbonization, a carbon adsorbent (CA) was obtained to remove Pb(II). After microwave treatment, the pore size of the skeleton structure, three-dimensional porous network, and lamellar pore structure of WAO was improved. The distribution coefficient (Kd) of Pb(II) onto CA is 620 mL/g, and the maximum adsorption capacity of Pb(II) is 82.67 mg/g after 20 min of WAO microwave treatment. The adsorption kinetics and adsorption isotherms conform to the quasi-second-order kinetic equation and Langmuir adsorption isotherm model, respectively. The surface of MT-WAO is negatively charged and the adsorption mechanism is mainly electrostatic interaction. Pb(II) elution in hydrochloric acid solution is more than 98%, and its recovery is high at 318 K and for 1 h.

Synthesis of polyaminophosphonated-functionalized hydrochar for efficient sorption of Pb(II)

Surface modification can effectively improve the ability of hydrochar to capture pollutants from wastewater. In this work, polyaminophosphonated-functionalized hydrochar (PAP-HC) was successfully synthesized by a chemical grafting approach and applied efficiently to adsorb aqueous Pb(II). Properties of PAP-HC were characterized by ICP, FTIR, XPS, SEM-EDS, elemental analysis, zeta potential, and BET. The Pb(II) adsorbing behavior of PAP-HC was tested by batch adsorbing assays, including the pH impact, uptake kinetics, sorption isotherms, sorption thermodynamics, and PAP-HC recycling. Sorption isotherms were better illustrated by a Langmuir equation, while the kinetic profile was modeled by a pseudo-second-order equation. Adsorption of Pb(II) onto PAP-HC mainly relied on chelating Pb(II) with aminophosphonate groups of PAP-HC by XPS and FTIR analyses. The actual adsorbed amount of PAP-HC maximized to 179.92 mg·g^-1 at 298 K, which showed high adsorption ability. Nitric acid and hydroxide solutions were suitable for desorption of adsorbed Pb(II) and activated PAP-HC, respectively. PAP-HC can be reused for at least five cycles without obvious change in adsorption performance. The results suggest PAP-HC is a prospective adsorbent to capture Pb(II) from wastewater.

Preparation of the Carbonized Zif−8@PAN Nanofiber Membrane for Cadmium Ion Adsorption

The zeolitic imidazolate framework (ZIF−8)@polyacrylonitrile (PAN) nanofiber membrane was prepared and carbonized for heavy metal cadmium ion (Cd²⁺) adsorption in aqueous medium. Zinc oxide (ZnO) was first sputtered onto the surface of the PAN electrospun nanofiber membrane to provide a metal ion source. Then, the ZIF−8@PAN nanofiber membrane was prepared via in situ solvothermal reaction and carbonized in a tube furnace at 900 °C under a N₂ atmosphere to enhance adsorption performance. The synthesized ZIF−8 particles with polyhedral structure were uniformly immobilized on the surface of the PAN electrospun nanofiber membrane. After being heated at 900 °C, the polygonal ZIF−8 shrank, and the carbonized ZIF−8@PAN nanofiber membrane was obtained. Compared with the nanofiber membrane without being carbonized, the adsorption capacity of the carbonized ZIF−8@PAN nanofiber membrane reached 102 mg L⁻¹, and its Cd²⁺ adsorption efficiency could be more than 90% under the adsorption temperature of 35 °C and solution of pH = 7.5 conditions. According to the adsorption thermodynamics analysis, the Cd²⁺ adsorption process of the carbonized ZIF−8@PAN nanofiber membrane was spontaneous. The whole Cd²⁺ adsorption process was more suitably described by the pseudo second-order adsorption kinetics model, indicating that there exists a chemical adsorption mechanism besides physical adsorption.

The efficiency of potato peel biochar for the adsorption and immobilization of heavy metals in contaminated soil

We investigated the potential application of potato peel biochar (PPB) for the adsorption and immobilization of heavy metals (Cd, Pb, and Ni) in contaminated acidic soil. The addition of PPB to the soil, especially at the application rate of 8%, increased soil pH, cation exchange capacity (CEC), and organic carbon (OC). The maximum adsorption capacity of Cd, Pb, and Ni in the soil amended with PPB at the application rate of 8% was 3215.9, 4418.67, and 3508.51 mg kg^-1, respectively. Compared to the control, the addition of 8% PPB to the soil decreased the soluble and exchangeable fraction of Cd, Pb, and Ni to 84.3, 90.6, and 79.1 mg kg^-1, respectively. In contrast, the addition of 8% PPB to the soil increased the organically-bound and residual fractions of metals in the following order: Pb > Cd > Ni, and Cd > Pb > Ni, respectively. The results of this study showed that potato peel biochar has the potential to stabilize and reduce the bioavailability of heavy metals in contaminated acidic soil. Therefore, potato peel biochar can serve as an eco-friendly, low-cost, and efficient adsorbent to immobilization of heavy metals in contaminated acidic soils.NOVELTY STATEMENTEffect of biochar produced from potato peel on the adsorption of the heavy metals in contaminated acidic soil.Immobilization of heavy metals in contaminated acidic soil amended with potato peel biochar.Improving the chemical properties of soil amended with potato peel biochar.

Mechanistic insight into the removal of aqueous Cd using an immobilized ZIF-8 and microflora cooperative composite

Biotechnology and metal-organic-frameworks (MOFs) materials have been investigated intensively for the removal of heavy metal from wastewater. However, the cooperative effect of bacteria and MOFs on heavy metal adsorption was less reported. Considering this, this study has screened out microflora with cadmium (Cd) adsorption ability. Furthermore, it was combined with zeolitic imidazolate framework-8 (ZIF-8) to form a ZIF-8 and microflora complex (ZMC). Moreover, ZMC was further immobilized to improve its Cd adsorption effect and reusability. Results revealed that the immobilized ZMC exhibited 99.91% and 78.83% Cd adsorption rate for 20 mg L^-1 and 300 mg L^-1 Cd, respectively. Meanwhile, the immobilized ZMC maintained a relatively stable adsorption effect under varied external pH. The reaction mechanism was summarized as covalent binding accompanied with a small amount of electrostatic attraction. Microflora could enhance the surface electronegativity of ZIF-8. ZIF-8 could strengthen the response of antioxidant activity of microflora and augmented the affinity of microflora secretions for Cd. This proposed method may provide a new insight for the removal of heavy metal contaminants in water.

Simultaneous co-hydrothermal carbonization and chemical activation of food wastes to develop hydrochar for aquatic environmental remediation

Locally generated food wastes, such as Arabic coffee ground (ACG) and olive oil cake (OOC) were converted to N-ACG: OOC - 3 hydrochar (HC) through simultaneous co-hydrothermal carbonization (Co-HTC) and chemical activation. The optimized ACG: OOC mass ratio (g: g) and chemical activation agent used were 1.2: 0.8 and 0.1 M HNO₃, respectively. Spectroscopic analyses confirmed the dominance of oxygen-containing functionalities, whereas the X-ray diffraction pattern displayed peaks for both sucrose and cellulose on N-ACG: OOC - 3. The developed HC was tested for methylene blue (MB) and crystal violet (CV) adsorption in aqueous systems. Batch scale adsorption studies showed pH, initial concentration (C_o), time (t), and temperature (T) dependent dye uptake. Maximum dye uptake was observed at pH 7, with 50 - 70% and 76 - 90 % CV and MB removal achieved within 15 min at varied C_o: 50 - 200 mg/L. Adsorption was governed by multiple mechanisms, including hydrogen bonding, electrostatic interactions, π-π interactions, and n-π interactions. Dye elution was higher in ethanol (EtOH: C₂H₅OH), and CV elution (50.8%) was more significant than MB elution (14.8%).

Characterization of Waste Amidoxime Chelating Resin and Its Reutilization Performance in Adsorption of Pb(II), Cu(II), Cd(II) and Zn(II) Ions

The continuous expansion of the market demand and scale of commercial amidoxime chelating resins has caused large amounts of resin to be discarded around the world. In this study, the waste amidoxime chelating resin was reutilized as an adsorbent for the removal and recovery of Pb(II), Cu(II), Cd(II) and Zn(II) ions from aqueous solutions. The physical morphology and chemical composition of the waste amidoxime chelating resin (WAC-resin) from the factory was characterized by the elemental analyzer, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The influence of the initial metal ions concentration, contact time, temperature and the solution pH on the adsorption performance of the metal ions was explored by batch experiments. It was shown that the optimal pH was 4. Kinetic studies revealed that adsorption process corresponded with the pseudo-second-order kinetic model and the adsorption isotherm was consistent with the Langmuir model. At room temperature, the adsorption capacities of WAC-resin for Pb2+, Cu2+, Zn2+ and Cd2+ reached 114.6, 93.4, 24.4 and 20.7 mg/g, respectively.

Characterization of Bio-Adsorbents Produced by Hydrothermal Carbonization of Corn Stover: Application on the Adsorption of Acetic Acid from Aqueous Solutions

In this work, the influence of temperature on textural, morphological, and crystalline characterization of bio-adsorbents produced by hydrothermal carbonization (HTC) of corn stover was systematically investigated. HTC was conducted at 175, 200, 225, and 250 °C, 240 min, heating rate of 2.0 °C/min, and biomass-to-H2O proportion of 1:10, using a reactor of 18.927 L. The textural, morphological, crystalline, and elemental characterization of hydro-chars was analyzed by TG/DTG/DTA, SEM, EDX, XRD, BET, and elemental analysis. With increasing process temperature, the carbon content increased and that of oxygen and hydrogen diminished, as indicated by elemental analysis (C, N, H, and S). TG/DTG analysis showed that higher temperatures favor the thermal stability of hydro-chars. The hydro-char obtained at 250 °C presented the highest thermal stability. SEM images of hydro-chars obtained at 175 and 200 °C indicated a rigid and well-organized fiber structure, demonstrating that temperature had almost no effect on the biomass structure. On the other hand, SEM images of hydro-chars obtained at 225 and 250 °C indicated that hydro-char structure consists of agglomerated micro-spheres and heterogeneous structures with nonuniform geometry (fragmentation), indicating that cellulose and hemi-cellulose were decomposed. EDX analysis showed that carbon content of hydro-chars increases and that of oxygen diminish, as process temperature increases. The diffractograms (XRD) identified the occurrence of peaks of higher intensity of graphite (C) as the temperature increased, as well as a decrease of peaks intensity for crystalline cellulose, demonstrating that higher temperatures favor the formation of crystalline-phase graphite (C). The BET analysis showed 4.35 m2/g surface area, pore volume of 0.0186 cm3/g, and average pore width of 17.08 μm. The solid phase product (bio-adsorbent) obtained by hydrothermal processing of corn stover at 250 °C, 240 min, and biomass/H2O proportion of 1:10, was activated chemically with 2.0 M NaOH and 2.0 M HCl solutions to investigate the adsorption of CH3COOH. The influence of initial acetic acid concentrations (1.0, 2.0, 3.0, and 4.0 mg/mL) was investigated. The kinetics of adsorption were investigated at different times (30, 60, 120, 240, 480, and 960 s). The adsorption isotherms showed that chemically activated hydro-chars were able to recover acetic acid from aqueous solutions. In addition, activation of hydro-char with NaOH was more effective than that with HCl.

Nitric acid-modified hydrochar enhance Cd2+ sorption capacity and reduce the Cd2+ accumulation in rice

Remediating the agricultural soil polluted by cadmium (Cd) is a serious issue in China. Hydrochar showed its potential to purify Cd-contaminated water and improve Cd-contaminated soil due to its vast amounts of macro- and microporous structures. In this study, three concentration gradients of nitric acid (HNO₃, mass fraction: 5%, 10%, 15%) were implemented to age pristine wheat straw hydrochar (N0-HC) aiming to improve surface physiochemical properties. Four HNO₃-aging hydrochars named N0-HC, N5-HC, N10-HC, N15-HC were used to both remove Cd²⁺ from aqueous solution and improve soil properties. Results showed that HNO₃-aging significantly improved the Cd²⁺ adsorption capacity by 1.9-9.9 folds compared to crude hydrochar due to the increased specific surface area (by 1.5-6.5 folds) and oxygen-containing functional group abundance (by 4.5-22.1%). Besides, initial solution pH of 8 or environmental temperature of 318.15 K performed the best Cd²⁺ adsorption capacity. Furthermore, the process of Cd²⁺ adsorption was fitted best to pseudo-second-order (R² = 0.95) and Langmuir models (R² = 0.98), respectively. Nanjing 46 (Oryza sativa L) and HNO₃-aging hydrochars were furtherly applied into Cd-contaminated paddy soil to investigate the mitigation of Cd translation from soil to rice. N15-HC-1% (w/w) performed the best effect on reducing cadmium accumulation in various parts of rice plants. Overall, this research provided an approach to improve hydrochar capacity to remove Cd²⁺ from aqueous solution and mitigate Cd translation from soil to rice.

Optimized production, Pb(II) adsorption and characterization of alkali modified hydrochar from sugarcane bagasse

Today, sugarcane bagasse (SB) is used for bioethanol and biodiesel production, energy generation, and adsorbent synthesis. The goal of this project is to determine the optimized conditions for producing adsorbent from sugarcane bagasse using hydrothermal carbonization (HTC) and KOH activation. To optimize process parameters such as reaction temperature, residence time, ZnCl2/SB mixing ratios, and water/SB mixing ratios, response surface methodology was used. The results revealed that the optimum modified adsorption occurred at 180 °C, 11.5 h, a water to biomass ratio of (5:1), and a ZnCl2 to precursor ratio of (3.5:1). The physicochemical features of optimum activated hydrochar were investigated, as well as batch adsorption experiments. The pseudo-second-order kinetic model and the Langmuir isotherm model were found to fit the experimental results in batch adsorption studies [[Formula: see text] (mg/g)]. Thermodynamic experiments further confirmed the spontaneous and exothermic adsorption mechanism.

Adsorptive removal of Pb(II) ions onto surface modified adsorbents derived from Cassia fistula seeds: Optimization and modelling study

Cassia fistula seeds has been utilized for the abstraction of Pb(II) ions from the aqueous environment. Raw Cassia fistula seeds (RCF) and three different surface modified (physically treated - PMCF and chemically treated - HMCF and SMCF) adsorbent material were taken for investigation. The adsorption properties of these materials and their contact amongst the Pb(II) ion and sorbent materials were characterized by FTIR and SEM analysis. The parameters influencing the adsorption capacity of varied adsorbents were evaluated: maximum solution pH for Pb(II) is 5.0; interactive time is 30 min; dosage is 8.0 g/L for RCF, 4.0 g/L for HMCF, 2.5 g/L for PMCF and 1.0 g/L for SMCF. The modelling study reveals that Freundlich isotherm and Pseudo first order kinetics fits well and the utmost adsorption measurements for the varied adsorbents were found to be 13.22, 28.28, 48.66 and 129.3 mg/g, respectively.

Waste-to-wealth application of wastewater treatment algae-derived hydrochar for Pb(II) adsorption

Hydrochar, as an energy-lean solid waste, is generated from an advanced biofuel conversion technique hydrothermal liquefaction (HTL) and always leads to environmental pollution without appropriate disposal. In this study, HTL-derived hydrochar is recycled and prepared as adsorbent used for Pb(Ⅱ) removal from wastewater. As the original porous structure of hydrochar is masked by oily volatiles remained after HTL, two types of oil-removal pretreatment (Soxhlet extraction and CO₂ activation) are explored. The result shows that CO₂ activation significantly enhances the adsorption capacity of Pb(Ⅱ), and the maximum adsorption capacity is 12.88 mg g⁻¹, as evaluated using Langmuir adsorption model. Further, apart from oily volatiles, most inorganic compounds derived from wastewater-grown algae is enriched in hydrochar, causing a smaller surface area of hydrochar. An ash-removal alkali treatment following CO₂ activation is introduced to dramatically increase the adsorption capacity to 25.00 mg g⁻¹ with an extremely low Pb(II) equilibrium concentration of 5.1×10^-4 mg L⁻¹, which is much lower than the maximum level of Pb concentration in drinking water (set by World Health Organization). This work introduces an approach to reuse HTL-hydrochar as an inexpensive adsorbent in Pb-contaminated water treatment, which not only provides another possible renewable adsorbent candidate applied in the field of lead adsorption, but also finds an alternative route to reduce solid waste effluent from HTL process.

Malachite green adsorption from aqueous solutions onto biochar derived from sheep manure: adsorption kinetics, isotherm, thermodynamic, and mechanism

The adsorption of Malachite Green (MG) from aqueous solution was achieved using biochar derived from sheep manure pyrolyzed at 450 °C. Sheep manure biochar was characterized before and after adsorption of MG by SEM and FTIR. In addition, surface area measurement was performed by BET surface area and pore analyzer. The influence of contact time, pH, dose, temperature, and initial MG concentrations on the adsorption of MG onto sheep manure biochar (SMB) was investigated in experiments. Langmuir, Freundlich, Temkin, and Dubinin-Raduskevich isotherm models were used to analyze the data. Results assumed best fitting model is Langmuir isotherm model (R² value 0.99). Mean free adsorption energy (E) was obtained 94.71 kJ mol^-1, R_L value was between 0.013 and 0.14. That indicates monolayer, favorable, and physisorption adsorption, as well as an endothermic adsorption process. Maximum uptake value from Langmuir model obtained 208.33 mg g^-1. Surface area of SM biochar was 11.731 m² g^-1.NOVELTY STATEMENTThis study is the first study on the adsorption of malachite green dye substance on sheep manure derived biochar.A natural and cheap adsorbent with high dye removal, such as 208,33 mg g^-1.A guiding study for the conversion of agricultural waste into products with highly added value.

Lead(II) adsorption on microwave-pyrolyzed biochars and hydrochars depends on feedstock type and production temperature

Adsorption of lead(II) using carbon-rich chars is an environmentally sustainable approach to remediate lead(II) pollution in industrial wastewater. We studied mechanisms for lead(II) adsorption from synthetic wastewater by biochars produced by microwave-assisted pyrolysis and hydrochars by hydrothermal carbonization at three temperatures using four feedstocks. Lead(II) adsorption was highest (165 mg g^-1) for canola straw biochar produced at 500 °C. Except for chars derived from sawdust, biochars outperformed hydrochars for lead(II) adsorption due to changes in solution pH driven by char pH. As char production temperature increased, lead(II) adsorption decreased in hydrochar mainly due to interaction with aromatic carbon but increased in biochar due to precipitation as hydrocerussite and lead oxide phosphate. Lead(II) adsorption also occurred via surface complexation and cation-ᴨ interaction, as the data fitted well to Freundlich, Langmuir and Temkin models, and the pseudo-first and pseudo-second order kinetic models, depending on feedstock type and production temperature. More than 80% of lead(II) adsorption occurred in the first 3 h for both types of chars; with a few exceptions, adsorption continued for almost 24 h. We conclude that production method, production temperature and feedstock type are crucial factors to consider in designing chars as adsorbents for removing lead(II) from wastewater.

Recycle of Fenton sludge through one-step synthesis of aminated magnetic hydrochar for Pb2+ removal from wastewater

In order to achieve proper disposal of Fenton sludge, a new recycle method for preparing adsorbents based on one-step hydrothermal carbonization synthesis of aminated hydrochar from Fenton sludge (AHFS) was developed. It was found that AHFS prepared at 340 °C for 60 min showed Pb²⁺ adsorption capacity as high as 359.83 mg g^-1. Adsorption kinetics and thermodynamics results indicated that chemical interaction, intra-particle diffusion and monolayer homogeneous surface of AHFS dominated in adsorption process. The contribution proportion of different mechanisms, including cation-exchange (43.15%), acidic groups complexation (28.17%) and amino groups complexation (24.06%) to overall Pb²⁺ adsorption, demonstrated that complexation of surface functional groups played the dominated role in the adsorption process. Especially, the addition of amino was conducive to the increased adsorption capacity of hydrochar. In addition, according to the regeneration test, the magnetic AHFS exhibited a satisfactory reproducibility and recyclability. These findings illustrated that the synthesis of aminated magnetic hydrochar not only provided an innovative and efficient heavy metal adsorbent to remove Pb²⁺ from wastewater, but also explored a new method for the resource utilization of Fenton sludge.

Facile modification of hydrochar derived from cotton straw with excellent sorption performance for antibiotics: Coupling DFT simulations with experiments

This study aimed to investigate the sorption of tetracycline (TC) and norfloxacin (NOR) by modified cotton straw hydrochars (CSHC), which would enable the agricultural waste to be processed and recycled. Three kinds of hydrochars were prepared by H₂SO₄, KOH and KMnO₄ modification, showed obvious differences in structures and surface functional groups. The sorption processes contain film diffusion, intraparticle diffusion, and equilibrium. The interaction mechanism between hydrochar and antibiotics include π-π stacking, hydrogen bond, and electrostatic interaction. KMnO₄-modified hydrochar had the largest sorption capacity for TC (58.09 mg/g), while H₂SO₄-modified hydrochar had the largest sorption capacity for NOR (49.64 mg/g). Density functional calculations (DFT) results confirmed that the sorption capacity between hydrochar (HC) and TC was larger than that between HC and NOR. During the sorption process, the TC and NOR were regarded as electron acceptor and electron donor. Generally, CSHC-KMnO₄ and CSHC-H₂SO₄ may be simply prepared and have the potential to eliminate antibiotics from water.

Adsorption characteristics and mechanisms of Pb2+ and Cd2+ by a new agricultural waste-Caragana korshinskii biomass derived biochar

In order to explore the comprehensive utilisation and recycling technology of Caragana korshinskii resources, a new agricultural biomass waste, 15 kinds of Caragana korshinskii biochar (CB) were prepared by controlling the pyrolysis temperature and time at the anaerobic environment. Moreover, we pay more attention to deriving the adsorption mechanisms and exploring the difference in adsorption characteristics of Pb²⁺ and Cd²⁺. The optimal preparation conditions and the batch adsorption experiments were evaluated, and the adsorption characteristics and mechanisms were discussed using 8 theoretical adsorption models and multiple characterisation methods. The results showed that the CB prepared at 650 °C for 3 h presented the best performance. The Langmuir and Freundlich models can well simulate the isotherm adsorption process of CB for Pb²⁺ and Cd²⁺, respectively. The adsorption kinetics of CB for Pb²⁺ and Cd²⁺ were best fitted by the pseudo-second-order model. The adsorption equilibrium for Pb²⁺ and Cd²⁺ was reached within 3 h, and their maximum adsorption capacity reached 220.94 mg g^-1 and 42.43 mg g^-1, respectively. In addition, the best addition amount was 3 g L^-1 and 2.2 g L^-1 for Pb²⁺ and Cd²⁺, respectively. The optimum pH range was 3-6 for Pb²⁺ and 6-7.5 for Cd²⁺. The adsorption mechanisms of CB for Pb²⁺ and Cd²⁺ were physicochemical composite adsorption processes, mainly including physical sorption on surface sites, intraparticle diffusion, electrostatic adsorption, ion/ligand exchange, cationic-π interactions, surface complexation and precipitation. Furthermore, the ash of CB also presented a positive effect on the adsorption of Pb²⁺. Compared with other cellulose- and lignin-based biomass materials, CB showed low cost and efficient performance without complicated modification conditions. Therefore, this study demonstrates that CB is a promising raw material in water pollution control to immobilise heavy metals.

Synthesis of metal–organic frameworks (MOFs) MIL-100(Fe) functionalized with thioglycolic acid and ethylenediamine for removal of eosin B dye from aqueous solution

The interaction of eosin B dye from aqueous solution with MIL-100(Fe) and functionalized MIL-100(Fe) metal–organic frameworks (MOFs) is reported in this study. MIL-100(Fe) was prepared and functionalized with thioglycolic acid (TH) and ethylenediammine (ED) separately by incorporating the thiol (–SH) and the amine (–NH2) group of the functionalizing agents into the open metal sites of the MIL-100(Fe) to obtain the acidic (TH-MIL-100) and basic (ED-MIL-100) forms of the MOF respectively. Characterization of the MOFs was done by melting point analysis, elemental analysis, spectroscopic techniques, scanning electron microscopy (SEM), and powdered X-ray diffraction (PXRD) analysis. The adsorption experiments were carried out at different conditions such as pH, adsorbent dosage, contact time, temperature, and initial concentration of the dye to estimate the optimum conditions and the maximum adsorption capacities. Adsorption capacities were observed to increase in the order of ED-MIL-100 < MIL-100 < TH-MIL-100, while the TH-MIL-100 was the most effective in the removal process due to acid–base interaction between the acidic thiol group (–SH) and the alkaline medium of eosin B dye solution. The Langmuir Isotherm was seen to fit well to adsorption data obtained for all three adsorbent materials studied, and adsorption processes followed the pseudo-second order kinetics. This study, therefore, indicates the suitability of functionalization of MIL-100(Fe) towards improving its adsorption capacity.

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.

Lead ion adsorption on functionalized sugarcane bagasse prepared by concerted oxidation and deprotonation

Targeting the removal of Pb²⁺ in wastewater, sugarcane bagasse was treated with nitric acid and an alkaline solution to prepare adsorbents. On a typical adsorbent, the adsorption isotherms agreed well with the Langmuir expression, and the maximum adsorption capacity reached 200.3 mg/g. In the presence of 150 ppm Ca²⁺, a common cation in natural water, the Pb²⁺ adsorption capacity slightly declined. In contrast, Mg²⁺ obviously prohibited the adsorption for Pb²⁺. The spent adsorbent could be regenerated at least five times through elution with an EDTA solution. EDS and XPS results demonstrated that nitric acid functioned as an oxidant instead of nitrification agent in the treatment of bagasse. The adsorption process was consistent with quasi-second-order kinetics. Based on thermodynamic studies, the changes in enthalpy and Gibbs free energy were calculated to be - 33.3 and ca. - 18 kJ/mol, indicating that the adsorption process was exothermic and spontaneous. The equilibrium Pb²⁺ adsorption amounts were proportional to the numbers of carboxylate groups on different adsorbents. The binding energies of Pd 4f_5/2 and Pd 4f_7/2 XPS spectra of Pb²⁺ adsorbed were 0.6-0.7 eV lower than those of free Pb(NO₃)₂, indicating the transfer of electrons during adsorption. The conversion of hydroxymethyl groups in sugarcane bagasse into carboxylate groups, as well as the chelation between Pb²⁺ ions and carboxylate groups, was validated in this work, which is beneficial for the treatment of wastewater polluted by lead ions.

Evaluating the Aqueous Phase From Hydrothermal Carbonization of Cow Manure Digestate as Possible Fertilizer Solution for Plant Growth

Improving the agronomic use of recycled nutrients derived from organic waste is one of the priorities within the measures adopted by the European community to reduce environmental issues but remains an unexplored area of research. This study focused on investigating the possibility of using innovative fertilizer solutions in hydroponic systems for the growth of agricultural plants. To this purpose, a liquid fraction [aqueous hydrothermal carbonization (HTC) liquid (AHL)] derived from HTC of cow manure digestate was chemically characterized (pH, electrical conductivity, mineral elements, and organic compounds such as phytotoxins), diluted with distilled water (1:30, 1:60, and 1:90, v/v) to reduce its potential phytotoxicity, and used to grow hydroponic maize (Zea mays L.) plants instead of the classical full-strength nutrient solution. The results indicated that the dilution ratio 1:30 of the AHL solution maintained a high level of toxicity for the plants (phytotoxic substances, especially Na and alkalinity), inducing the arrest of their growth. Differently, the two other dilution ratios (i.e., 1:60 and 1:90) seemed to considerably limit the levels of toxicity, since they allowed the plants to develop. However, these dilution ratios were poor in nutrient elements, inducing alteration in photosynthesis and an onset of deficiency symptoms such as pronounced leaf chlorosis. In view of an eco-friendly approach, future studies are, therefore, needed to identify the correct species-specific dilution ratio to supply both low levels of phytotoxins and adequate content of essential nutrients for appropriate plant growth and development. Furthermore, in order to lower specific Na phytotoxicity, treatments are of utmost importance before using AHL as a fertilizer solution.

Efficient Removal of Cu(II), Zn(II), and Cd(II) from Aqueous Solutions by a Mineral-Rich Biochar Derived from a Spent Mushroom (Agaricus bisporus) Substrate

This study evaluated the novel application of a mineral-rich biochar derived from a spent Agaricus bisporus substrate (SAS). Biochars with various pyrolysis temperatures (350–750 °C) were used to remove Cu(II), Zn(II), and Cd(II) from aqueous solutions. The adsorption characteristics and removal mechanisms of the biochars were investigated. The adsorption kinetics and isotherm data were fitted well by pseudo-second-order and Freundlich models. The Langmuir maximum removal capacity (Q_max) values of Cu(II), Zn(II), and Cd(II) were ordered as SAS750 > SAS350 > SAS550, and the Q_max values of SAS750 were 68.1, 55.2, and 64.8 mg·g⁻¹, respectively. Overall, the removal mechanisms of biochar at a low production temperature (350 °C) to Cu(II), Zn(II), and Cd(II) were mainly via ion exchange (54.0, 56.0, and 43.0%), and at a moderate production temperature (550 °C), removal mechanisms were mainly via coordination with π electrons (38.3, 45.9, and 55.0%), while mineral precipitation (65.2, 44.4, and 76.3%, respectively) was the dominant mechanism at a high produced temperature (750 °C). The variation of the mutual effect of minerals and heavy metals was the predominant factor in the sorption mechanism of mineral precipitation and ion exchange. The results demonstrated that spent Agaricus bisporus substrate biochar is a potential candidate for the efficient removal of heavy metals, which provides a utilization route for spent mushroom substrates.

Novel oxone treated hydrochar for the removal of Pb(II) and methylene blue (MB) dye from aqueous solutions

This study represents the first ever work on a novel oxone treated hydrochar as an adsorbent for the efficient removal of different contaminants from aqueous solutions. Pine wood hydrochar (HC) was prepared by hydrothermal treatment at 300 °C and oxidized with oxone to produce oxidized pine wood hydrochar (OHC). Different analytical tools such as elemental analysis, FTIR, TGA, FE-SEM, and BET were used for the characterization of the OHC. Conductometric titration of OHC showed a substantial increase from 22 μmol/g to 600 μmol/g in the hydrochar carboxylic content. The OHC sorption performance was assessed by using Pb(II) ions and methylene blue (MB) dye as two models of contaminants. Sorption benchmarks were performed by varying the contaminant initial concentration, time, and temperatures. Sorption kinetic data was fitted well to the pseudo-second order kinetic model with high correlation coefficients (R² > 0.99) and isothermal data was fitted to the Langmuir model. The highest adsorption capacities for MB and Pb(II) were 86.7 mg/g and 46.7 mg/g, respectively. This study proves that oxone treatment could be a potential sustainable oxidation method to tune the hydrochar surface to increase selectivity towards heavy metal ions and dye sorption.

Enhanced adsorption of Pb(II) by nitrogen and phosphorus co-doped biochar derived from Camellia oleifera shells

We describe the synthesis of a series of novel nitrogen- and phosphorus-enriched biochar (activated carbon, AC) nanocomposites via the co-pyrolysis of Camellia oleifera shells (COSs) with different weight ratios of ammonium polyphosphate (APP) (w_APP: w_COSs = 1-3:1). The physicochemical characteristics of these nanocomposites (APP@ACs) were investigated via X-ray diffraction (XRD), Raman spectroscopy, N₂ adsorption/desorption analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results revealed that the APP@ACs exhibited richer N- and P-containing functional groups than unmodified AC. In addition, the removal performance of APP@AC-3 with respect to Pb(II) (723.6 mg g^-1) was greatly improved relative to unmodified AC (264.2 mg g^-1). Kinetic and equilibrium data followed the pseudo-second-order kinetic model and Langmuir model, respectively. The removal mechanism could be attributed to partial physisorption and predominant chemisorption. The N₂ adsorption/desorption isotherms demonstrated that pore-volume properties could be an effective physical trap for Pb(II). Furthermore, the XPS and FTIR analysis revealed that the chemical removal mechanism of the APP@ACs is surface complexation via N-containing and P-containing functional groups. These findings indicate that the co-pyrolysis of COSs and APP leads to the formation of nitrogen- and phosphorus-containing functional groups that facilitate excellent activated carbon-based (biochar) adsorption performance.

Efficient removal of Cd(II) from aqueous solution by pinecone biochar: Sorption performance and governing mechanisms

Cadmium (Cd) is one of the most harmful and widespread environmental pollutants. Despite decades-long research efforts, the remediation of water contaminated by Cd has remained a significant challenge. A novel carbon material, pinecone biochar, was previously hypothesized to be a promising adsorbent for Cd, while so far, it has received little attention. This study evaluated the sorption capacity of pinecone biochar through isotherm experiments. Based on Langmuir model, the adsorption maximum for Cd(II) was up to 92.7 mg g^-1. The mechanism of Cd(II) adsorption on pinecone biochar was also explored through both thermodynamic and kinetics adsorption experiments, as well as both solution and solid-phase microstructure characterization. The solid-solution partitioning behaviour of Cd(II) fitted best with the Tόth model while the adsorption process followed a pseudo-second-order rate, suggesting that the Cd(II) adsorption on the pinecone biochar was mainly a chemisorption process. Microstructure characteristics and mechanism analysis further suggested that coprecipitation and surface complexation were the main mechanisms of Cd adsorption by biochar. Coprecipitation occurred mainly through the forms of Cd(OH)₂ and CdCO₃. Our results demonstrated that pinecone biochar was an efficient adsorbent which holds a huge potential for Cd(II) removal from aqueous solution.

Review of Biochar Properties and Remediation of Metal Pollution of Water and Soil

BACKGROUND

Mining, waste disposal, and agrochemical residues have contributed to pollution of water and soil with toxic metals in most low- and middle-income countries, raising concerns of ecological safety and public health. This has prompted many studies into the production and utilization of biochars to adsorb toxic metal contaminants from soil and water.

OBJECTIVE

The present study presents a review of biochar properties, the mechanisms of toxic metal adsorption onto biochar, and sorption of toxic metal contaminants in water and soil in small scale applications and laboratory experiments.

METHODS

A total of 305 articles were collected, and after screening for relevance, a final of 164 articles from both high- and low- and middle-income countries were used in this review paper.

DISCUSSION

Biochar for sorption has proven effective and its raw materials are readily available, cost effective, environmentally stable and a good form of waste management.

CONCLUSIONS

Different techniques of biochar production influence the properties of biochar and adsorption of toxic metals from water and soil.

COMPETING INTERESTS

The authors declare no competing financial interests.

Effect of temperature and duration of pyrolysis on spent tea leaves biochar: physiochemical properties and Cd(II) adsorption capacity

We analyzed the effects of pyrolysis temperature and duration on the physiochemical properties and Cd(II) adsorption capacity of spent tea leaves (STL) biochar. The STL biochar was produced by pyrolysis at 300, 400, 500 and 600 °C for 1 and 2 h. The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S_BET), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios. Furthermore, the surface porosity of STL biochar increased, the density of oxygen-containing functional groups decreased, and the formation of aromatic structures was enhanced at higher pyrolysis temperatures. The adsorption of Cd(II) onto STL biochar fitted with the pseudo-second-order kinetics and Langmuir isotherms model. The STL biochar produced at 600 °C for 2 h showed the maximum Cd(II) adsorption capacity of 97.415 mg/g. In addition, Cd(II) adsorption was mainly physical and occurred in monolayers. Thus, STL biochar is a suitable low-cost adsorbent for wastewater treatment.

Biochar for Wastewater Treatment—Conversion Technologies and Applications

Biochar as a stable carbon-rich material shows incredible potential to handle water/wastewater contaminants. Its application is gaining increasing interest due to the availability of feedstock, the simplicity of the preparation methods, and their enhanced physico-chemical properties. The efficacy of biochar to remove organic and inorganic pollutants depends on its surface area, pore size distribution, surface functional groups, and the size of the molecules to be removed, while the physical architecture and surface properties of biochar depend on the nature of feedstock and the preparation method/conditions. For instance, pyrolysis at high temperatures generally produces hydrophobic biochars with higher surface area and micropore volume, allowing it to be more suitable for organic contaminants sorption, whereas biochars produced at low temperatures own smaller pore size, lower surface area, and higher oxygen-containing functional groups and are more suitable to remove inorganic contaminants. In the field of water/wastewater treatment, biochar can have extensive application prospects. Biochar have been widely used as an additive/support media during anaerobic digestion and as filter media for the removal of suspended matter, heavy metals and pathogens. Biochar was also tested for its efficiency as a support-based catalyst for the degradation of dyes and recalcitrant contaminants. The current review discusses on the different methods for biochar production and provides an overview of current applications of biochar in wastewater treatment.

Waste shrimp shell-derived hydrochar as an emergent material for methyl orange removal in aqueous solutions

Shrimp processing and consumption generate large amounts of waste shrimp shell (WSS) rich in chitin and protein. Herein, we successfully synthesized WSS-based hydrochar (WSH) adsorbent through deproteinization and deacetylation followed by hydrothermal carbonization (HTC) and acid washing. For comparison, another hydrochar (CCH) adsorbent was synthesized from HTC of commercial chitosan under identical conditions. Specifically, WSH contained rich nitrogen-containing functional groups with a long aliphatic chains structure. Acid etching of calcium carbonate in WSS led to a higher specific surface area of WSH (12.65 m²/g) which was nearly 6 times higher than that of CCH (2.13 m²/g). The lower deacetylation degree of WSH was responsible for higher amide I and amino groups retained therein. Under an optimal initial solution pH of 4.0, WSH could rapidly achieve a superb adsorption capacity of 755.08 mg/g for methyl orange molecule. Moreover, the adsorption process followed a pseudo-second-order kinetics model and was well described by a monolayer adsorption pattern based on the Langmuir isotherm model with correlation coefficients higher than 0.9989. Prominent adsorption performance of WSH for methyl orange was mainly attributed to electrostatic interactions, while steric hindrance effect had a detrimental impact on the adsorption capacity of CCH. Superb adsorption capacity and excellent regeneration performance suggest WSH could be a promising and affordable adsorbent candidate for anionic dye removal.

Effect of thiourea-modified biochar on adsorption and fractionation of cadmium and lead in contaminated acidic soil

Biochar was obtained through pyrolysis of carrot pulp (CP) and then further modified with thiourea (CH₄N₂S). We investigated the effect of carrot pulp biochar (CPB) and modified CPB (MCPB) for adsorption and chemical fractionation of cadmium (Cd) and lead (Pb) in contaminated acidic soil. Application of modified biochar significantly (p < 0.05) increased the pH, soil organic carbon (SOC), and cation exchange capacity (CEC) of the soil, especially at the 8% application rate. The adsorption equilibrium data showed that the adsorption behavior of Cd and Pb could be described more reasonably by the pseudo-second-order kinetic model and the Langmuir isotherm model more accurately fitted the experimental data than Freundlich and Temkin isotherm models. The maximum adsorption capacity of soil treated with MCPB at the 8% application rate for Cd and Pb were 4122.7 and 5219.6 mg kg^-1, respectively. Sequential chemical extractions revealed that incorporation soil with MCPB induced the transformation of the acid-soluble fraction of Cd to oxidizable and residual fractions, and the acid-soluble fraction of Pb to reducible, oxidizable, and residual fractions. The results demonstrated that the application of MCPB could effectively immobilize Cd and Pb, thereby reducing their mobility in contaminated acidic soil.

Comments on "Enhanced removal of Cr(VӀ) from aqueous solution by supported ZnO nanoparticles on biochar derived from waste water hyacinth"

A mistake of using pseudo-first-order kinetic equation for testing kinetic parameters of adsorption has been pointed out, as well as inappropriate citations for the adsorption kinetic models. Further, this discussion gives a correct pseudo-first-order kinetic equation and makes a suggestion for citing the original papers for the pseudo-second-order and intra-particle diffusion kinetic equations.