Adsorption of Cd(II) from aqueous solutions by rape straw biochar derived from different modification processes

Impact of different amendments on biochemical responses of sesame (Sesamum indicum L.) plants grown in lead-cadmium contaminated soil

Soil co-contamination with lead (Pb) and cadmium (Cd) is a tenacious risk to crop production globally. The current experiment observed the roles of amendments [biochar (BC), slag (SL), and ferrous manganese ore (FMO)] for enhancing Pb and Cd tolerance in sesame (Sesamum indicum L.). Our results revealed that application of amendments significantly enhanced the nutrient level of sesame seedlings developed under extreme Pb and Cd conditions. The higher Pb and Cd-tolerance in sesame encouraged by amendments might be credited to its capability to restrict Pb and Cd uptake and decreased oxidative damage induced by Pb and Cd that is also demonstrated by lesser production of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and reduced electrolyte leakage (EL) in plant biomass. The added amendments relieved Pb and Cd toxicity and improved photosynthetic pigments, soluble protein, and proline content. Not only this amendments also decreased the antioxidant bulk, such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in sesame plants compared to control when exposed to Pb and Cd. Moreover, the added amendments = down-regulated the genes expression which regulate the SOD, POD, and CAT activity in sesame under Pb and Cd-stress. Furthermore, supplementation of amendments to the soil, reduced the bio accessibility (SBET), leachability (TCLP), and mobility (CaCl₂) of Pb and Cd. Collectively, our findings conclude that the application of amendments enhanced sesame tolerance to Pb and Cd stress by restricting Pb and Cd accumulation, maintained photosynthetic presentation and dropped oxidative loss through enhanced antioxidant system, thus signifying amendments as an operational stress regulators in modifying Pb and Cd-toxicity that is highly important economically in all crops including sesame.

Nitric acid-anionic surfactant modified activated carbon to enhance cadmium(II) removal from wastewater: preparation conditions and physicochemical properties

The authors used a nitric acid (HNO₃)-sodium dodecyl benzene sulfonate (SDBS) method to modify a lignite-based activated carbon. These modified carbons were appraised for their removal of Cd(II) from aqueous solutions. Response surface methodology was employed to optimize the preparation factors including nitric acid concentration C_N, temperature T and SDBS concentration C_S. Statistical analysis indicated that the interaction of C_N and C_S incurred the most effect on the maximum cadmium adsorption capacity (Q_m). The optimal Q_m appeared at C_N = 3.29 mol/L, T = 76 °C and C_S=30,700 mg/L. The optimal protocol achieved 44.21 mg/g Q_m for Cd(II) which was about 7 times larger than for this pristine lignite activated carbon (LAC) (6.78 mg/g). The physical-chemical properties of the modified activated carbons following each synthesis step were characterized relative to their surface area, oxygen functionality, and external surface charge. It was confirmed that the developed surface area, functional groups and negative charges were mainly responsible for the higher adsorption capacity for the LAC that have been more favorably tailored by this HNO₃-SDBS protocol.

Magnetic biochar-based manganese oxide composite for enhanced fluoroquinolone antibiotic removal from water

Magnetic biochar-based manganese oxide composite (MMB) and raw biochar (BC) were synthesized via pyrolysis at a temperature of 500 °C under anoxic conditions of potato stems and leaves, characterized, and successfully used for the removal of norfloxacin (NOR), ciprofloxacin (CIP), and enrofloxacin (ENR) as representative compounds of fluoroquinolone antibiotics (FQs). Characterization results suggested that Fe₃O₄ and MnO_x are the dominant crystals in MMB. MMB possessed large surface area and pore volume than BC. Batch adsorption experiments showed that the maximum adsorption abilities of MMB for norfloxacin (NOR), ciprofloxacin (CIP), and enrofloxacin (ENR) were 6.94, 8.37, and 7.19 mg g^-1. In comparison to BC, the adsorption abilities of MMB increased 1.2, 1.5, and 1.6 times for NOR, CIP, and ENR, respectively. The pseudo-second-order kinetic model and the Langmuir model correlated satisfactorily to the experimental data. Thermodynamic studies revealed that the adsorption processes were spontaneous and endothermic. The adsorption capacity of MMB decreased with increasing solution pH (between 3.0 and 10.0) and increasing ionic strength (0.001-0.1). The MMB with high FQ removal efficiency, easy separation, and desirable regeneration ability may have promising environmental applications for the removal of fluoroquinolone antibiotics from water environment.

Cost-Effective Biochar Produced from Agricultural Residues and Its Application for Preparation of High Performance Form-Stable Phase Change Material via Simple Method

A new form-stable composite phase change material (PEG/ASB) composed of almond shell biochar (ASB) and polyethylene glycol (PEG) was produced via a simple and easy vacuum impregnation method. The supporting material ASB, which was cost effective, environmentally friendly, renewable and rich in appropriate pore structures, was produced from agricultural residues of almond shells by a simple pyrolysis method, and it was firstly used as the matrix of PEG. Different analysis techniques were applied to investigate the characteristics of PEG/ASB, including structural and thermal properties, and the interaction mechanism between ASB and PEG was studied. The thermogravimetric analysis (TGA) and thermal cycle tests demonstrated that PEG/ASB possessed favorable thermal stability. The differential scanning calorimetry (DSC) curves demonstrated that the capacities for latent heat storage of PEG/ASB were enhanced with increasing PEG weight percentage. Additionally, PEG/ASB had an excellent thermal conductivity of 0.402 W/mK, which was approximately 1.6 times higher than that of the pure PEG due to the addition of ASB. All the study results indicated that PEG/ASB had favorable phase change properties, which could be used for thermal energy storage.

Chemical activation of biochar for energy and environmental applications: a comprehensive review

Biochar (BC) generated from thermal and hydrothermal cracking of biomass is a carbon-rich product with the microporous structure. The graphene-like structure of BC contains different chemical functional groups (e.g. phenolic, carboxylic, carbonylic, etc.), making it a very attractive tool for wastewater treatment, CO2 capture, toxic gas adsorption, soil amendment, supercapacitors, catalytic applications, etc. However, the carbonaceous and mineral structure of BC has a potential to accept more favorable functional groups and discard undesirable groups through different chemical processes. The current review aims at providing a comprehensive overview on different chemical modification mechanisms and exploring their effects on BC physicochemical properties, functionalities, and applications. To reach these objectives, the processes of oxidation (using either acidic or alkaline oxidizing agents), amination, sulfonation, metal oxide impregnation, and magnetization are investigated and compared. The nature of precursor materials, modification preparatory/conditions, and post-modification processes as the key factors which influence the final product properties are considered in detail; however, the focus is dedicated to the most common methods and those with technological importance.

Efficient removal of Cd2+ and Pb2+ from aqueous solution with amino- and thiol-functionalized activated carbon: Isotherm and kinetics modeling

In order to address the increasingly severe pollution issue caused by heavy metals, activated carbon-based absorbents have gained considerable attention. Herein, two novel adsorbents, amino-functionalized activated carbon (N-AC) and thiol-functionalized activated carbon (S-AC), were successfully synthesized by stepwise modification with tetraethylenepentamine (TEPA), cyanuric chloride (CC) and sodium sulfide. The pristine and synthesized materials were characterized by BET analysis, SEM, FTIR spectroscopy, elemental analysis and zeta-potential analyzer. Meanwhile, their adsorption properties for Cd²⁺ and Pb²⁺ and the effects of various variables on the adsorption processes were systematically investigated. The findings confirmed that amino-groups and thiol-groups endowed the AC with a strong affinity for metal ions and that the pH of solution affected the uptake efficiencies of the adsorbents by influencing their surface charges. Furthermore, six isotherm models (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Sips and Redlich-Peterson) and four kinetic models (pseudo-first-order, pseudo-second-order, Intra-particle diffusion and Elovich) were applied to interpret the adsorption process at three different temperatures (288 K, 298 K and 308 K). The results indicated that temperature played an important role and that the rate-limiting step was chemosorption. A better fit for all adsorption systems was obtained with Langmuir model, with the maximum adsorption capacities at 298 K of 79.20 mg Cd²⁺/g and 142.03 mg Pb²⁺/g for N-AC, 130.05 mg Cd²⁺/g and 232.02 mg Pb²⁺/g for S-AC, respectively. Subsequently, the thermodynamic parameters revealed the nature of the adsorption was endothermic and spontaneous under the experimental condition. The possible adsorption procedures and the underlying mechanisms comprising physical and chemical interactions were proposed. Moreover, the as-synthesized adsorbents exhibited excellent regeneration performance after five adsorption/desorption cycles. The overall results demonstrated that both N-AC and S-AC could be the promising efficient candidates for removing Cd²⁺ and Pb²⁺ from contaminated water.

The environmental characteristics and applications of biochar

The environmental deterioration is in a grave situation, and it is urgent to restore the environment. Biochar is a carbon-rich pyrolysis product of feedstock, which has aroused extensive concern due to its broad application potential for getting rid of pollutants and rehabilitating environment. This review generalizes three aspects on biochar, including production and properties, applications and mechanisms, and its modifications. Firstly, the production and characteristics have been summarized, because the practical applications of biochar are highly related to the special characteristics of biochar. Secondly, this paper outlines the latest applications of biochar for environmental remediation, and further provides a critical review on the application mechanisms in environmental restoration. Thirdly, the modification methods and applications of modified biochar are summarized, and all of the ways can be classified into two types: pretreatment of feedstock and modification of primitive biochar. Furthermore, the possible improvements and outlooks of applying biochar in environmental remediation are proposed. This review provides useful information for the application of biochar in environmental restoration.

Preparation of rice straw-derived biochar for efficient cadmium removal by modification of oxygen-containing functional groups

In order to enhance the adsorption capacity of cadmium (Cd) ion from aqueous solution, the rice straw-derived biochar (BC800) was modified by a mixture of HNO₃ and H₂O₂ (MHH) with equal volume. Several elemental, chemical and structural characterization methods were used to determine the characteristics of biochars. Batch adsorption experiments were carried out concerning the influences of contact time, initial pH value, and initial concentration. The results indicated that the modified biochar (BCM) was more effective in removing Cd²⁺ from water than BC800. For 550mgL^-1 Cd²⁺ concentration solution, the adsorption capacity of 93.2mgg^-1 was observed for BCM, which was much higher than that of BC800 (69.3mgg^-1). The BCM had a significant increase of acidic functional groups with a rate of 101.6% and the component carboxyl, lacton and phenol groups increased by 124.1%, 29.3% and 111.3% respectively, while the specific surface area increased about 22.0%, compared with BC800. The pseudo-second-order model provided high correlation coefficients for BCM, speculating chemisorption of the Cd²⁺ onto biochars. Therefore, the rice straw-based biochar treated by MHH is considered to be an efficient adsorbent for Cd²⁺ removal from aqueous solution, especially for high concentrations of cadmium solution.

Iron and manganese oxides modified maize straw to remove tylosin from aqueous solutions

Maize straw modified by iron and manganese oxides was synthesized via a simple and environmentally friendly method. Three maize straw materials, the original maize straw, maize straw modified by manganese oxides and maize straw modified by iron and manganese oxides, were detected by SEM, BET, XPS, XRD and FTIR. The results showed that maize straw was successfully modified and maize straw modified by iron and manganese oxides has a larger surface area than MS. According to the experimental data, the sorption trend could conform to the pseudo-second-order kinetic model well, and the sorption ability of tylosin on sorbents followed the order of original maize straw < maize straw modified by manganese oxides < maize straw modified by iron and manganese oxides. The study indicated that manganese oxides and iron-manganese oxides could significantly enhance the sorption capacity of original maize straw. The sorption isotherm data of tylosin on original maize straw fit a linear model well, while Freundlich models were more suitable for maize straw modified by manganese oxides and maize straw modified by iron and manganese oxides. The pH, ionic strength and temperature can affect the sorption process. The sorption mechanisms of tylosin on iron and manganese oxides modified maize straw were attribute to the surface complexes, electrostatic interactions, H bonding and hydrophobic interactions.

Investigating the adsorption behavior and the relative distribution of Cd2+ sorption mechanisms on biochars by different feedstock

The objective of this study was to investigate the adsorption behavior and the relative distribution of Cd²⁺ sorption mechanisms on biochars by different feedstock. Bamboo biochars (BBCs), corn straw biochars (CBCs) and pig manure biochars (PBCs) were prepared at 300-700 °C. Adsorption results showed PBCs have the best adsorption capacity for Cd²⁺, the extra adsorption capacity of PBCs mainly attributed to the precipitation or cation exchange, which played an important role in the removal of Cd²⁺ by PBCs. The contribution of involved Cd²⁺ removal mechanism varied with feedstock due to the different components and oxygen-containing functional groups. Cd²⁺-π interaction was the predominant mechanism for Cd²⁺ removal on biochars and the contribution proportion significantly decreased from 82.17% to 61.83% as the ash content increased from 9.40% to 58.08%. Results from this study may suggest that the application of PBC is a feasible strategy for removing metal contaminants from aqueous solutions.

A novel modification of lignin on corncob-based biochar to enhance removal of cadmium from water

In order to improve the adsorption capacities of corncob-based biochars for heavy metal, the different pyrolysis temperature (350 °C, 450 °C and 550 °C) of corncob-based biochars were modified with the acrylonitrile, and adsorption capacities of Cadmium from solution by biochars were studied. The results showed that only at 350 °C the biochar can be successfully modified. The Cd adsorption capacity (85.65 mg/g) by the biosorbent was higher than other methods of modifying biochars previously reported. SEM-EDS and FTIR confirmed that the CN group was grafted on the biochar at low pyrolysis temperature. Batch adsorption experiment including pH-dependence, adsorption kinetics, and isotherms and XPS results showed that the removal mechanism of Cd(II) by the modified biochar was ion exchange and adsorption-complexation. This research not only obtained a novel method to modify biochar but also furthered research into the lignin of biochar composition, and provided an efficient sorbent for heavy metal.

AMOchar: Amorphous manganese oxide coating of biochar improves its efficiency at removing metal(loid)s from aqueous solutions

A novel sorbent made from biochar modified with an amorphous Mn oxide (AMOchar) was compared with pure biochar, pure AMO, AMO+biochar mixtures and biochar+birnessite composite for the removal of various metal(loid)s from aqueous solutions using adsorption and solid-state analyses. In comparison with the pristine biochar, both Mn oxide-biochar composites were able to remove significantly greater quantities of various metal(loid)s from the aqueous solutions, especially at a ratio 2:1 (AMO:biochar). The AMOchar proved most efficient, removing almost 99, 91 and 51% of Pb, As and Cd, respectively. Additionally, AMOchar and AMO+biochar mixture exhibited reduced Mn leaching, compared to pure AMO. Therefore, it is concluded that the synthesis of AMO and biochar is able to produce a double acting sorbent ('dorbent') of enhanced efficiency, compared with the individual deployment of their component materials.

Sandwich-like Nanosystem for Simultaneous Removal of Cr(VI) and Cd(II) from Water and Soil

In this work, a novel nanosystem with a sandwich-like structure was synthesized via face-to-face combination of two pieces of waste cotton fabrics (CFs) carrying ferrous sulfide (FeS) and carboxyl-functionalized ferroferric oxide microsphere (CFFM), respectively, and the obtained nanosystem was named as FeS/CFFM/CF. Therein, FeS has high reduction and adsorption capabilities for hexavalent chromium (Cr(VI)), CFFM possesses a high adsorption ability on cadmium ion (Cd(II)) through electrostatic attraction and chelation, and CF displays high immobilization ability for FeS and CFFM and adsorption performance on Cd(II). FeS/CFFM/CF could simultaneously remove Cr(VI) and Cd(II) from water and inhibit the uptake of Cr and Cd by fish and water spinach, ensuring the food safety. Besides, this technology could efficiently control the migration of Cr(VI) and Cd(II) in the sand-soil mixture, which was favorable to prevent their wide diffusion. Importantly, FeS/CFFM/CF possessed a high flexibility and could be conveniently produced with needed scale and shape and easily separated from water and soil, displaying a promising approach to remediate Cr(VI)-/Cd(II)-contaminated water and soil and a huge application potential.

Maize straw decorated with sulfide for tylosin removal from the water

MS-ZnS and MS-ZnS:Mn complexes were synthesized via a simple method. The results showed that sulfide was successfully loaded on the maize straw. The results of fitting the experimental data showed that the sorption conforms to the pseudo-second-order kinetics, and the TYL sorption on MS fit the Henry model well, but the Freundlich model was more suited to MS-ZnS and MS-ZnS:Mn. In addition, the k_f values of MS-ZnS (206.0(mg/kg)/(mg/L)ⁿ) and MS-ZnS:Mn (382.5(mg/kg)/(mg/L)ⁿ) were significantly greater than that of MS (72.2(mg/kg)/(mg/L)ⁿ), indicating that ZnS and ZnS:Mn could improve the sorption capacity of TYL on MS. The pH, ionic strength and temperature influence the sorption process, and the sorption ability of TYL on MS-ZnS and MS-ZnS:Mn showed little change when the solution pH was > 5; the amount of TYL sorption on the adsorbents gradually decreased with the increasing concentration of KNO₃. Electrostatic interactions, H bonding and hydrophobic interactions are involved in the sorption of TYL on MS, MS-ZnS and MS-ZnS:Mn, and compared with MS, the main mechanism is surface complexation. This research can provide technical support for the utilization of biomass and the restoration of water polluted by antibiotics.

Investigating the sorption behavior of cadmium from aqueous solution by potassium permanganate-modified biochar: quantify mechanism and evaluate the modification method

In this work, a KMnO₄-modified-biochar-based composite material with manganese oxide produced at 600 °C was fabricated to investigate the sorption mechanism of Cd(II) and to comprehensively evaluate the effect of the modification on biochar properties. Cd(II) adsorption mechanisms were mainly controlled by interaction with minerals, complexation with oxygen-containing functional groups, and cation-π interaction. The sorption capacity was significantly reduced after a deash treatment of biochar, almost shrunk by 3 and 3.5 times for pristine biochar (PBC) and modified biochar (MBC). For deashed PBC, oxygen-containing functional groups were the main contributor toward Cd(II) adsorption while interaction with minerals was significantly compromised and became negligible. The sorption capacity was also apparently decreased after the deash treatment of MBC; however, for deashed MBC, interaction with minerals still was the main contributor to the sorption ability, which could be attributed to the mechanism of interaction of Cd(II) with loaded MnO_x on biochar. Cation-π interaction in MBC was notably enhanced compared to PBC due to the oxidation of KMnO₄ on biomass. Also, sorption performance by oxygen-containing functional groups was also enhanced. Hence, the modification by KMnO₄ has a significant effect on the Cd(II) sorption performance of biochar.

Improving the surface properties of municipal solid waste-derived pyrolysis biochar by chemical and thermal activation: Optimization of process parameters and environmental application

Biochar produced from the slow pyrolysis of municipal solid waste was activated with KOH and thermal treatments to enhance its surface and adsorptive properties. The effects of KOH concentration, activation temperature and time on the specific surface area (SSA) of the activated biochar were evaluated and optimized using central composite design (CCD) of the response surface methodology (RSM). Results showed that the activation of biochar enhanced its SSA from 402.8 ± 12.5 to 662.4 ± 28.6 m² g^-1. The adsorptive capacities of the pristine biochar (PBC) and activated biochar (ABC) were compared using methylene blue (MB) dye as model compound. For MB concentrations up to 25 mg L^-1, more than 99% dye removal was achieved with ABC, while only a maximum of 51% was obtained with PBC. Results of the isotherm study showed that the Langmuir model best described MB adsorption on ABC with adsorption capacity of 37.0-41.2 mg g^-1.

Degradation of Orange G by Fenton-like reaction with Fe-impregnated biochar catalyst

This study was conducted to evaluate the catalytic activity of Fe-impregnated sugarcane biochar (FSB) for removing azo dye Orange G (OG) from solution under various Fenton-like oxidation conditions. The optimum molar Fe concentration for impregnation to achieve maximum catalytic activity of FSB in Fenton-like reaction with acceptable effluent Fe release was 0.25 M (163.4 Fe mg/g in FSB). High removal efficiency of 99.7% was achieved within 2 h of reaction at optimum conditions of 0.075 g/L H₂O₂, 0.5 g/L FSB for 0.1 g/L OG at initial pH 5.5 under 25 °C. For every 10 °C increase, the time for maximum OG degradation efficiency decreased by 0.5 h. The OG removal by FSB exhibited a slow induction reaction followed by fast OG decomposition. FSB can be used successively for at least 4 runs with >89.3% OG removal. The FSB was more economical, efficient, and recyclable than other conventional Fenton oxidation catalysts.

Adsorption characteristics of Cd(ii) in aqueous solutions using spent mushroom substrate biochars produced at different pyrolysis temperatures

To effectively remove Cd from water, biochars were produced by pyrolyzing surplus agricultural wastes of spent mushroom substrate (SMS) at 300, 500, and 700 °C. The biochars were characterized, and their Cd(ii) removal ratios and adsorption capacities in aqueous solutions were evaluated. The physical and chemical properties of the biochars were significantly affected by increasing the pyrolysis temperature; the data indicated that the ash content, pH and specific surface area of the biochars increased, whereas the yield and contents of carbon, hydrogen, nitrogen and oxygen decreased. In addition, the molar ratios of H/C, O/C and (O + N)/C decreased, which implied that the biochars became more aromatic and carbonaceous with a lower polarity and fewer oxygen-based functional groups. The pseudo-second-order kinetics model and Langmuir and Temkin isotherm models described the Cd(ii) adsorption better than the other tested models. The biochars derived at higher pyrolysis temperatures had higher adsorption capacities, and the maximum adsorption capacities for PC700 and SC700 were 71.49 and 46.87 mg g⁻¹, respectively. The Q_m values in our study were equivalent to or even higher than those for other modified biochars. This result shows that the biochars in this study are effective adsorbents for Cd(ii) removal from wastewater.

To effectively remove Cd from water, biochars were produced by pyrolyzing SMS. And the adsorption characteristics of Cd(ii) using SMS biochars was studied.

Challenges and recent advances in biochar as low-cost biosorbent: From batch assays to continuous-flow systems

Over the past few years, the increasing amount of pollutants and their diversity demand to develop versatile low-cost adsorption systems. The use of biomass feedstock such as agricultural residues, wood chips, manure or municipal solid wastes as source to produce low-cost biosorbent, and the new advances in their synthesis have encouraged remarkable efforts towards the development of biochar "on demand" in which their characteristics can be improved. This new trend opens the potential of biochar application in the removal of pollutants from wastewater, however, its use in environmental management requires the development of full-scale biosorption in engineered systems. Thus, this paper provides a brief review of recent progress in the research and practical application of biochar with a special emphasis on its potential to reduce the pollutants present in wastewater or to render them harmless. Furthermore, research gaps and uncertainties detected in their scale-up in continuous-flow systems are highlighted.