Adsorption characteristics and mechanism of Pb(II) by agricultural waste-derived biochars produced from a pilot-scale pyrolysis system

Adsorption of heavy metals by biochar in aqueous solution: A review

Heavy metal pollution (e.g., Cd, Hg, Pb, Cu, Ni, Zn, As and Cr) has become a crucial issue worldwide. Among various remediation strategies, adsorption is widely recognized for its environmental sustainability, cost-effectiveness, and operational simplicity. In this context, biochar has gained significant attention due to its promising adsorption performance. To systematically support adsorption studies, this review compiled essential models for adsorption experiments, including commonly used adsorption kinetics models, isotherm models, and thermodynamic analysis methods. Moreover, we systematically analyzed key factors affecting heavy metal adsorption by biochar, such as its physicochemical properties, environmental pH, temperature, initial concentration, dosage, and the presence of coexisting ions, to identify the conditions that govern adsorption capacity. In addition, the adsorption performance of biochar toward eight significant heavy metals is reviewed in detail, with a focus on elucidating the underlying mechanisms, including complexation, ion exchange, cation-π bonding, electrostatic interactions, and precipitation. Finally, based on identified research gaps and critical challenges, we discuss emerging research tools, including machine learning and advanced surface modifications, to guide the targeted design of biochar materials for enhanced adsorption capacity.

Synthesis of magnetic chitosan-composite biochar and its removal of copper ions (Cu2+) and methylene blue (MB) dye from aqueous solutions

This study presents the synthesis and evaluation of a magnetic chitosan-modified biochar (M-BC-CS) composite, developed from waste maize straw, for the efficient removal of copper ions (Cu2+) and methylene blue (MB) dye from aqueous solutions. The composite was characterized using advanced techniques such as SEM, BET, FTIR, XPS, and XRD, confirming its enhanced surface area, porosity, and magnetic properties. The study is aimed at investigating the optimal conditions for adsorption of Cu2+ and MB by M-BC-CS through analysis of the influence of diverse adsorbent dosages, pH levels, reaction times, and initial solution concentrations. The findings demonstrated that the equilibrium duration for the adsorption of Cu2+ and MB by M-BC-CS was 60 min, resulting in corresponding equilibrium adsorption quantities of 54.42 mg/g and 67.23 mg/g, respectively. To elucidate the adsorption mechanism, the present investigation applied the pseudo-second-order kinetic model and the Langmuir isotherm. The outcomes suggested that the adsorption process is attributable to single molecular layer chemisorption. XPS and FTIR analysis determined that ion exchange and electrostatic interactions are the predominant mechanisms responsible for the simultaneous adsorption of Cu2+ and MB, and a competitive relationship exists between these mechanisms. In addition, M-BC-CS exhibited exceptional magnetic separation performance, enabling effortless and effective separation when exposed to an external magnetic field. Furthermore, the results demonstrated that M-BC-CS has good reusability and high adsorption capacity also in real wastewater, thus emphasizing its potential as a promising adsorbent for the elimination of Cu2+ and MB from aqueous solutions.

Adsorptive removal of oxytetracycline hydrochloride using bagasse-based biochar powder and beads

Oxytetracycline Hydrochloride (OTC), a common antibiotic used to treat specific illnesses in humans and animals, is characterized by poor absorption into cells, low volatility, and high hydrophilicity. It is a potent contaminant that poses a serious threat to the ecosystem, particularly the aquatic sources. Adsorption onto natural adsorbents is one of the most successful, economical, and ecologically friendly ways to remove antibiotics from waste water. The present work focuses on the adsorption of OTC utilizing alginate biochar beads (AlBCB) and biochar powder (BC) derived from bagasse. The influence of several factors were studies and optimized through batch studies employing BC and AlBCB. After 50 min BC displayed a removal of 97%, at an initial concentration of 10 ppm. The experimental data was discovered to follow PFO kinetics and fit with the Freundlich isotherm adsorption model. AlBCB, after a contact time of 40 min, indicated a maximum percentage removal of 86% for initial concentration of 10 ppm OTC. Al-biochar beads showed the maximum percentage removal at pH 10. 0.5 g of adsorbent was used to carry out all batch experiments at room temperature. The adsorption fitted Freundlich adsorption isotherm and intraparticle diffusion kinetics.

A thorough investigation into the adsorption behavior of sophorolipid-modified fly ash towards compound pollution of lead and tetracycline

Heavy metal ions and antibiotics were simultaneously detected in authentic water systems. This research, for the first time, employed synthesized sophorolipid-modified fly ash(SFA) to eliminate tetracycline(TC) and lead(Pb2+) from wastewater. Various characterization techniques, including SEM-EDS, FTIR, XPS, BET, and Zeta, were employed to investigate the properties of the SFA. The results showed that the sophorolipid modification significantly improved the fly ash's adsorption capacities for the target pollutants. The static adsorption experiments elucidated the adsorption behaviors of SFA towards TC and Pb2+ in single and binary systems, highlighting the effects of different Environmental factors on the adsorption behavior in both types of systems. In single systems, SFA exhibited a maximum adsorption capacity of 128.96 mg/g for Pb2+ and 55.57 mg/g for TC. The adsorption of Pb2+ and TC followed pseudo-second-order kinetics and Freundlich isotherm models. The adsorption reactions are endothermic and occur spontaneously. SFA demonstrates varying adsorption mechanisms for two different types of pollutants. In the case of Pb2+, the primary mechanisms include ion exchange, electrostatic interaction, cation-π interaction, and complexation, while TC primarily engages in hydrogen bonding, π-π interaction, and complexation. The interaction between Pb2+ and TC has been shown to improve adsorption efficiency at low concentrations. Additionally, adsorption-desorption experiments confirm the reliable cycling performance of modified fly ash, highlighting its potential as a cost-effective and efficient adsorbent for antibiotics and heavy metals.

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.

Effective adsorption of Pb(II) ion from aqueous solution onto ZSM-5 zeolite synthesized from Vietnamese bentonite clay

ZSM-5 zeolite was successfully synthesized from bentonite clay sourced from Lam Dong Province, Vietnam, using the hydrothermal method at 170 °C for 18 h. The synthesized ZSM-5 (SiO2/Al2O3 ratio ~ 34) exhibited a single phase with high crystallinity (91.8%), and a clear and uniform shape. In a detailed examination of the synthesized material's Pb(II) adsorptive capacity, various factors were taken into account, including pH, interaction time, ionic strength, and the amount of adsorbent. Isotherms and kinetics were examined to elucidate the uptake behavior. Study results suggested that Pb(II) ion uptake by ZSM-5 was most appropriately described by the Sips isotherm and intraparticle diffusion kinetic models. The calculated maximum monolayer adsorption capacity according to the Langmuir isotherm model was 48.36 mg/g. Furthermore, the adsorption mechanisms of Pb(II) on ZSM-5 involving electrostatic interactions, ion exchange, and diffusion into pores were demonstrated using the analytical techniques before and after Pb(II) adsorption. These findings demonstrate that ZSM-5 synthesized from bentonite clay exhibits an excellent adsorption capacity for Pb(II), resulting in promising applications for treating drinking water or aqueous industrial waste containing Pb(II) ions.

Advanced Materials Design for Adsorption of Toxic Substances in Cigarette Smoke

Cigarettes, despite being economically important legal consumer products, are highly addictive and harmful, particularly to the respiratory system. Tobacco smoke is a complex mixture containing over 7000 chemical compounds, 86 of which are identified to have "sufficient evidence of carcinogenicity" in either animal or human tests. Thus, tobacco smoke poses a significant health risk to humans. This article focuses on materials that help reduce the levels of major carcinogens in cigarette smoke; these include nicotine, polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines, hydrogen cyanide, carbon monoxide, and formaldehyde. Specifically, the research progress on adsorption effects and mechanisms of advanced materials such as cellulose, zeolite, activated carbon, graphene, and molecularly imprinted polymers are highlighted. The future trends and prospects in this field are also discussed. Notably, with advancements in supramolecular chemistry and materials engineering, the design of functionally oriented materials has become increasingly multidisciplinary. Certainly, several advanced materials can play a critical role in reducing the harmful effects of cigarette smoke. This review aims to serve as an insightful reference for the design of hybrid and functionally oriented advanced materials.

Enhanced Chromium (VI) Adsorption onto Waste Pomegranate-Peel-Derived Biochar for Wastewater Treatment: Performance and Mechanism

Surface chemical modification allows for the rational construction of biochar with desirable structures and functionalities for environment purification. Fruit-peel-derived adsorbing material has been well studied in the adsorption of heavy-metal removal due to its abundance and non-toxicity, but its precise mechanism in removing chromium-containing pollutants remains unclear. Herein, we explored the potential application of engineered biochar prepared from fruit waste via chemical modification to remove chromium (Cr) from an aqueous solution. By synthesizing two types of agricultural residue-derived adsorbents, including pomegranate peel adsorbent (PG) and its modified product, pomegranate-peel-derived biochar (PG-B), via chemical and thermal decomposition methods, we elucidated the adsorption property of Cr(VI) on the studied materials and identified the cation retention mechanism of the adsorption process. Batch experiments and varied characterizations demonstrated that superior activity was exhibited in PG-B, which can contribute to the porous surfaces caused by pyrolysis and effective active sites resulting from alkalization. The highest Cr(VI) adsorption capacity is obtained at pH 4, a dosage of 6.25 g L^-1, and a contact time of 30 min. The maximum adsorption efficiency of 90.50% in a short period (30 min) was obtained on PG-B, while PG reached a removal performance of 78.01% at 60 min. The results from kinetic and isotherm models suggested that monolayer chemisorption dominated the adsorption process. The Langmuir maximum adsorption capacity is 16.23 mg g^-1. This study shortened the adsorption equilibrium time of pomegranate-based biosorbents and presents positive significance in designing and optimizing waste fruit-peel-derived adsorption materials for water purification.

Waste to energy: A review of biochar production with emphasis on mathematical modelling and its applications

United Nations charter to build a sustainable future has paved the way for the introduction of the Sustainability Development Goals (SDGs) at a global forum. In particular, SDG 11 is aligned with the idea of developing cities and communities that provide quality human life, by attaining net-zero discharge and self-sustainability. In line with the efforts of the global community, biochar has emerged as a viable solution due to its ability to convert waste into value. Finding applications in a spectrum of domains, biochar is being studied for use as an adsorbent, a co-catalyst to promote industrial-grade reactions and as a feed for fuel cells. Moreover, the inclusion of biochar as a soil enhancement material advocates the implementation of closed-loop nutrient cycles. Hence, it is imperative to have a proper understanding of the biomass characteristics, the hydrothermal treatment and the process parameters to be adopted for the production of char in order to identify biomass feedstock based on the application. The current work provides insight into the key factors and conditions employed for the production of biochar based on the plethora of applications. In order build a basic framework to aid in the production of char, the development of a statistical correlation was undertaken to determine the feed and optimum process parameters for the production of biochar based on its applications.

Pb(II) bioremediation using fresh algal-bacterial aerobic granular sludge and its underlying mechanisms highlighting the role of extracellular polymeric substances

Lead (Pb) discharged from rural industries poses a significant threat to the environment and human health. Algal-bacterial aerobic granular sludge (A-B AGS) is a promising alternative for sewage treatment with high efficiency and good settleability. In this study, Pb(II) biosorption using fresh A-B AGS was investigated for the first time. The important role of extracellular polymeric substances (EPS) was revealed with the involved mechanisms being clarified. The desorbents for Pb recovery from Pb-loaded A-B AGS were also screened. Results showed that A-B AGS has an excellent maximum Pb adsorption capacity of 72.4 mg·g^-1 at pH 6.0. EPS plays an important role in keeping microbial activity, Pb bonding, and providing metal ions (Ca, Na and Mg) for Pb ion exchanges. Electrostatic interaction, ion exchange, and bonding to functional groups may occur orderly in the Pb biosorption process and the formation of pyromorphite (Pb₅(PO₄)₃Cl) contributes to Pb biosorption. About 66 % of the adsorbed Pb was accumulated in the A-B AGS microbial cells. Na₂EDTA (0.05 M) can recover 60.3 % of the loaded Pb with the highest microbial activity of granules being remained. All the findings will provide the theoretical basis for the large-scale application of A-B AGS to bioremediate Pb(II)-containing wastewater.

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.

Facile Synthesis of ZnS/1T-2H MoS2nanocomposite for Boosted adsorption/photocatalytic degradation of methylene blue under visiblelight

Facile solvothermal techniques were used to manufacture ZnS/1T-2H MoS₂ nanocomposite (ZMS) with outstanding adsorption-photocatalytic activity. The formed catalyst was characterized by different tools; XRD, HR-TEM, EDX, FTIR, Raman, N₂adsorprion/desorption, Zeta potential, PL,and XPS. The analysis provided the formation on mixed phase of metallic 1Tand 2H phases. ZMS has a high porosity and large specific surface area, and it has a high synergistic adsorption-photocatalytic degradation effect for MB, with a removal efficiency of ≈100% in 45 minutes under visible light irradiation. The extraordinary MB removal efficiency of ZMS was attributed not only to the high specific surface area (49.15 m²/g) and precious reactive sites generated by ZMS, but also to the formation of 1T and 2H phases if compared to pristine MoS₂ (MS). The best adsorption affinity was induced by the existance of 1T phase. The remarkably enhanced photocatalytic activity of ZMS nanocomposite can be ascribed to the 2D heterostructure which enhances the adsorption for pollutants, provides abundant reaction active sites, extends the photoresponse to visible light region.

Alginate-modified biochar derived from rice husk waste for improvement uptake performance of lead in wastewater

In this work, alginate-modified biochar derived from rice husk waste was synthesized using a simple process. The modified biochar (MBC) and rice husk biochar (RhBC) were investigated for removing Pb (II) ions in wastewater. The BET result displayed significantly improved specific surface area of MBC up to 120 m²/g along with a total pore volume of 0.653 cm³/g. FTIR spectrums presented the higher oxygen-contained functional groups of MBC as compared to RhBC, resulting in increasing adsorption capacity of Pb (II). MBC had higher adsorption capacity (112.3 mg/g) and faster removal rate (0.0081 g mg^-1 min^-1) than those of RhBC (41.2 mg/g and 0.00025 g mg^-1 min^-1). Modified RhBC can remove more than 99% of Pb (II) from wastewater and it could be utilized for three cycles with a removal performance of over 90%. In addition, the Pb adsorption mechanism by using MBC was proposed and the practical application of MBC for the treatment of wastewater in Vietnam was discussed.

Synthesis and application of starch-stablized Fe-Mn/biochar composites for the removal of lead from water and soil

Starch-stablized and Fe/Mn bimetals modified biochar derived from corn straw (SFM@CBC and SFM@CBC-350) were firstly prepared, characterized (FTIR, XRD, SEM, EDS, BET and XPS), and applied in Pb removal from water and soil. SFM@CBC and SFM@CBC-350 displayed highly effective adsorption performance of Pb²⁺ from wastewater with the maximum adsorption capacity of 170.91 mg g^-1 and 190.17 mg g^-1, respectively, which were much greater than that of FM@CBC (149.25 mg g^-1) and CBC (101.10 mg g^-1). Studies of adsorption kinetics, isotherms and thermodynamics indicated that the absorption of Pb²⁺ by SFM@CBC and SFM@CBC-350 was spontaneous and endothermic reaction, and it was controlled by monolayer chemisorption. The mechanism studies indicated that Pb²⁺ removal involved with multiple mechanism, including complexation (dominant process confirmed by XPS analysis), physical adsorption, electrostatic attraction, and cation exchange. The reusability test demonstrated that SFM@CBC and SFM@CBC-350 had very good stability and reusability. In addition, in order to further explore Pb removal performance of the modified biochar, SFM@CBC-350 was used in soil-ryegrass pot systems. Compared with the controls, the addition of SFM@CBC-350 reduced Pb content in soil and ryegrass, increased the biomass and total chlorophyll content, reduced the activity of antioxidant enzymes (CAT, SOD, MDA and POD) and ROS fluorescence intensity of ryegrass, thus alleviating Pb stress of ryegrass. Besides, the addition of SFM@CBC-350 could increase the richness and diversity of soil microorganisms, which was beneficial to the growth of ryegrass. Hence, SFM@CBC-350 has the potential of being used as a green, efficient and promising adsorbent in Pb removal from wastewater and soil.

Lead removal from aqueous solutions by olive mill wastes derived biochar: Batch experiments and geochemical modelling

In this study, lead removal from aqueous solutions using biochar derived from olive mill solid and liquid wastes has been investigated by applying batch experiments and geochemical modelling. The batch adsorption experiments included the assessment of several key parameters such as the contact time (kinetic), initial concentration (isotherm), pH, adsorbent dose, and the presence of competitive cations, whilst the geochemical modelling focused on the involved adsorption mechanisms using the PHREEQC code. The kinetic studies showed that lead adsorption is a relatively fast process, where intraparticle diffusion is the rate-limiting step. Biochar dose, solution pH and the presence of competitive ions significantly affected the Pb adsorption effectiveness by the biochar. Especially the higher Pb removal percentages were observed in mono-elemental solutions with high biochar dose at mildly acidic solution pH values. The maximum Pb adsorption capacity of biochar was estimated as 40.8 mg g^-1 which is higher than various biochars derived from sludge, lignocellulosic and animal biomasses. On the other hand, the geochemical modelling employing the PHREEQC code showed that ion exchange and Pb precipitation are the main reactions controlling its removal from aqueous solutions, whilst surface complexation is insignificant, mainly due to the low surface functional groups on the used biochar.

Remediation of heavy metal polluted waters using activated carbon from lignocellulosic biomass: An update of recent trends

The use of a cheap and effective adsorption approach based on biomass-activated carbon (AC) to remediate heavy metal contamination is clearly desirable for developing countries that are economically disadvantaged yet have abundant biomass. Therefore, this review provides an update of recent works utilizing biomass waste-AC to adsorb commonly-encountered adsorbates like Cr, Pb, Cu, Cd, Hg, and As. Various biomass wastes were employed in synthesizing AC via two-steps processing; oxygen-free carbonization followed by activation. In recent works related to the activation step, the microwave technique is growing in popularity compared to the more conventional physical/chemical activation method because the microwave technique can ensure a more uniform energy distribution in the solid adsorbent, resulting in enhanced surface area. Nonetheless, chemical activation is still generally preferred for its ease of operation, lower cost, and shorter preparation time. Several mechanisms related to heavy metal adsorption on biomass wastes-AC were also discussed in detail, such as (i) - physical adsorption/deposition of metals, (ii) - ion-exchange between protonated oxygen-containing functional groups (-OH, -COOH) and divalent metal cations (M²⁺), (iii) - electrostatic interaction between oppositely-charged ions, (iv) - surface complexation between functional groups (-OH, O^2-, -CO-NH-, and -COOH) and heavy metal ions/complexes, and (v) - precipitation/co-precipitation technique. Additionally, key parameters affecting the adsorption performance were scrutinized. In general, this review offers a comprehensive insight into the production of AC from lignocellulosic biomass and its application in treating heavy metals-polluted water, showing that biomass-originated AC could bring great benefits to the environment, economy, and sustainability.

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.

XPS and NMR analyze the combined forms of Pb in Cladophora rupestris subcells and its detoxification

In this study, the combined forms of Pb in Cladophora rupestris (L.) (C. rupestris) were investigated via X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), different Pb concentrations (0, 0.5, and 5.0 mg/L), and C. rupestris subcells were explored. Results showed that combined forms of Pb mainly account for Pb-polysaccharides (Pb-OH of carbohydrates) in the cell wall, Pb-protein (Pb-N= and (C-N-)₂Pb) in the organelle, and Pb-organic acid (Pb-sulfates, (CO)₂-Pb and (COO)₂-Pb) in the soluble fraction. Pb-S-containing group (Pb-C-S) could formed in subcelluar when C. rupestris was subjected to high Pb stress. Meanwhile, Pb²⁺ could penetrate the C. rupestris cells via the formed chelate between GSH/MT and -OH functional groups. Results could help understand the role of subcellular fraction in the algae remediation and detoxification to heavy metal.

Co-Pyrolysis of Cotton Stalks and Low-Density Polyethylene to Synthesize Biochar and Its Application in Pb(II) Removal

It is inevitable that reclaimed cotton stalks will contain a certain amount of plastic film due to the wide application of plastic mulching during the process of cotton cultivation, and this makes it inappropriate to return it to the field or for it to be processed into silage. In this study, biochars were prepared by the co-pyrolysis of cotton stalk with low-density polyethylene (LDPE) in the proportions of 1:0, 3:1, 2:1, and 1:1 (w/w) at 400 °C, 450 °C, and 500 °C and maintaining them for 1 h. The effects of the co-pyrolysis of cotton stalk with LDPE on the properties of biochars (e.g., pH, yield, elemental analysis, specific surface area, etc.) and the Pb(II) removal capacity were analyzed. Co-pyrolysis cotton stalks with LDPE could delay the decomposition of LDPE but could promote the decomposition of cotton stalk. At 400 °C and 450 °C, the addition of LDPE decreased the H/C ratio, while no significant difference was found between the pristine biochar and the blended biochar pyrolyzed at 500 °C. An FTIR analysis indicated that the surface functional groups of biochar were not affected by the addition of LDPE, except for CH₃ and CH₂. The results of the SEM showed that LDPE could cover the surface of biochar when pyrolyzed at 400 °C, while many macropores were found in the blended biochar that was pyrolyzed at 450 °C and 500 °C, thus increasing its surface area. The blended biochar that was pyrolyzed at 500 °C was more effective in the removal of Pb(II) than the cotton-stalk-derived biochar, which was dominated by monolayer adsorption with a maximum adsorption capacity of approximately 200 mg·g⁻¹. These results suggested that the co-pyrolysis of cotton stalks and LDPE may be used to produce biochar, which is a cost-effective adsorbent for heavy metal removal from aqueous solutions.

Mesoporous Magnetic Cysteine Functionalized Chitosan Nanocomposite for Selective Uranyl Ions Sorption: Experimental, Structural Characterization, and Mechanistic Studies

Nuclear power facilities are being expanded to satisfy expanding worldwide energy demand. Thus, uranium recovery from secondary resources has become a hot topic in terms of environmental protection and nuclear fuel conservation. Herein, a mesoporous biosorbent of a hybrid magnetic–chitosan nanocomposite functionalized with cysteine (Cys) was synthesized via subsequent heterogeneous nucleation for selectively enhanced uranyl ion (UO₂²⁺) sorption. Various analytical tools were used to confirm the mesoporous nanocomposite structural characteristics and confirm the synthetic route. The characteristics of the synthesized nanocomposite were as follows: superparamagnetic with saturation magnetization (M_S: 25.81 emu/g), a specific surface area (S_BET: 42.56 m²/g) with a unipore mesoporous structure, an amine content of ~2.43 mmol N/g, and a density of ~17.19/nm². The experimental results showed that the sorption was highly efficient: for the isotherm fitted by the Langmuir equation, the maximum capacity was about 0.575 mmol U/g at pH range 3.5–5.0, and Temperature (25 ± 1 °C); further, there was excellent selectivity for UO₂²⁺, likely due to the chemical valent difference. The sorption process was fast (~50 min), simulated with the pseudo-second-order equation, and the sorption half-time (t_1/2) was 3.86 min. The sophisticated spectroscopic studies (FTIR and XPS) revealed that the sorption mechanism was linked to complexation and ion exchange by interaction with S/N/O multiple functional groups. The sorption was exothermic, spontaneous, and governed by entropy change. Desorption and regeneration were carried out using an acidified urea solution (0.25 M) that was recycled for a minimum of six cycles, resulting in a sorption and desorption efficiency of over 91%. The as-synthesized nanocomposite’s high stability, durability, and chemical resistivity were confirmed over multiple cycles using FTIR and leachability. Finally, the sorbent was efficiently tested for selective uranium sorption from multicomponent acidic simulated nuclear solution. Owing to such excellent performance, the Cys nanocomposite is greatly promising in the uranium recovery field.

Recent advances in waste-derived functional materials for wastewater remediation

Water pollution is a major concern for public health and a sustainable future. It is urgent to purify wastewater with effective methods to ensure a clean water supply. Most wastewater remediation techniques rely heavily on functional materials, and cost-effective materials are thus highly favorable. Of great environmental and economic significance, developing waste-derived materials for wastewater remediation has undergone explosive growth recently. Herein, the applications of waste (e.g., biowastes, electronic wastes, and industrial wastes)-derived materials for wastewater purification are comprehensively reviewed. Sophisticated strategies for turning wastes into functional materials are firstly summarized, including pyrolysis and combustion, hydrothermal synthesis, sol-gel method, co-precipitation, and ball milling. Moreover, critical experimental parameters within different design strategies are discussed. Afterward, recent applications of waste-derived functional materials in adsorption, photocatalytic degradation, electrochemical treatment, and advanced oxidation processes (AOPs) are analyzed. We mainly focus on the development of efficient functional materials via regulating the internal and external characteristics of waste-derived materials, and the material's property-performance correlation is also emphasized. Finally, the key future perspectives in the field of waste-derived materials-driven water remediation are highlighted.

Insights into the highly efficient treatment of dyeing wastewater using algal bloom derived activated carbon with wide-range adaptability to solution pH and temperature

Here, a low-cost acid-base and temperature tolerant algal bloom derived activated carbon (ABAC) was successfully prepared to remove rhodamine B (RhB) from water. The ABAC exhibited maximum adsorption capacity of RhB (1101 ± 11 mg/g), higher than that of laboratory-prepared rape straw activated carbon (176 ± 5 mg/g) and commercial activated carbon (489 ± 5 mg/g). It is attributed to larger surface area and mesoporous structure of the ABAC. Furthermore, the effective adsorption of RhB by using ABAC was achieved at a wide range of solution pH (3.2-10.8) and temperature(25-50 °C). The mass transfer resistance of RhB adsorption process well depicted by Langmuir model was controlled by external mass transfer. The adsorption process involved both secondly chemisorption (H-bonds and π-π interaction) and dominated physisorption. Four dyes in river water were efficiently removed. This work provides a promising approach for developing high-absorption biomass materials for actual dye wastewater treatment.

Enhanced adsorption of metal ions onto Vetiveria zizanioides biochar via batch and fixed bed studies

The study highlights the potential of Vetiveria Zizanioides derived biochar for heavy metal removal in multicomponent systems. Biochar efficiency varies with pH, metal ion concentration and residence time. Maximum removal efficiency was found to be 66.34, 67.23, 46.54, 69.92, 68.23 and 63.34% for Arsenic, Copper, Nickel, Cadmium, Lead and Chromium at 90 min respectively. Ternary system revealed that Copper ions have inhibitory effect on Lead ions and have lower adsorption capacity than binary system. Multicomponent isotherm model was used to analyse simultaneous adsorption of metal ions and shows a good fit with modified Langmuir model for binary and ternary systems. Fixed-bed column was tested for scale-up feasibility and maximum adsorption capacity of 139, 130, and 123 mg/g for Lead, Copper, and Nickel ions were obtained at 1.5 L/h and a bed height of 12 cm. In fixed bed column, multicomponent sequence provides more protection against premature exhaustion of biochar.

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.

Content and morphology of lead remediated by activated carbon and biochar: A spectral induced polarization study

Soil and groundwater contamination with lead (Pb) poses serious challenges for the environment. Activated carbon (AC) and biochar have huge potential application in the in-situ remediation processes through permeable reactive barriers (PRB). Spectral induced polarization (SIP) technique recently showed promises in nondestructively monitoring the spatio-temporal characteristics of physical, chemical and biological processes in porous media. In this study SIP technique was used for monitoring Pb remediation by AC and biochar in column scale. The calculated characteristic grain/pore size evolutions from SIP signals on AC, agreed well with the size of precipitates measured by SEM and mercury intrusion porosimetry (MIP) methods. The content increment process of the retained Pb on AC was also recorded via the magnitude increment of the imaginary conductivity. The mechanisms of Pb-AC and Pb-biochar interactions were investigated using SEM-EDS, TEM, FTIR, XRD, and XPS measurements. It showed that AC immobilizes through physical adsorption and precipitation, whereas complexation with functional groups is the remediation mechanism for biochar. Furthermore, the observed SIP responses of both AC and biochar are two orders of magnitude higher than those of typical natural soils or silica materials. This distinct difference is an additional advantage for the field application of SIP technique in PRB scenarios.

Performance of wild plants-derived biochar in the remediation of water contaminated with lead: sorption optimization, kinetics, equilibrium, thermodynamics and reusability studies

This study aims to investigate the sorptive performance of Pb(II) from water of a novel biochar (WPC) produced by fast pyrolysis under anoxic conditions of wild plants (WP). The maximum Pb(II) sorption capacity of WPC is 50.25 mg/g under determined optimum conditions, which are solution pH 5.0, WPC dose 50 mg, contact time 180 min and solution temperature 50 °C. The sorption kinetics and isotherm data were observed to fit well with the Ho-McKay and Langmuir models, respectively. The thermodynamic parameters (ΔG^o, ΔH^o and ΔS^o) calculated for the WPC-Pb(II) sorption system showed that the process was spontaneous and endothermic. The Pb(II) desorption and regeneration studies of WPC with different desorbent agents was also performed. The findings in this study showed that WP can be used as an abundant precursor in the production of very low cost and eco-friendly biochar, and also that its biochar can be used as an environmentally-friendly sorbent in wastewater treatment. Novelty statementWith increasing population and developing industry in the world, agriculture and industrial wastes are increasing. These wastes create environmental and water pollution and adversely affect the health of living things. Efforts to eliminate these negativities have a negative impact on the world economy. For this purpose, various improvement methods are applied. However, the adsorption method is widely used due to its ease of application, efficiency and economic. In order to make this method more economical, many researchers have carried out researches on the preparation of low-cost adsorbents, especially from vegetable wastes.The novelty of this study is the first reporting to use wild plants as a sustainable precursor to produce a low-cost biochar using the traditional pyrolysis method and to examine its adsorption performance for Pb(II) ion removal from water. I believe that if this study is published, it will create a paradigm in environmental improvement studies on wild plants evaluation.

Hydrous manganese dioxide modified poly(sodium acrylate) hydrogel composite as a novel adsorbent for enhanced removal of tetracycline and lead from water

In this study, hydrous manganese dioxide (HMO) modified poly(sodium acrylate) (PSA) hydrogel was produced for the first time to remove tetracycline(TC) and lead(Pb(II)) from water. The as-prepared composite was characterized using various techniques, such as SEM-EDS, FTIR, XRD, BET, and XPS, to elucidate the successful loading of HMO and analyze subsequent sorption mechanisms. Different influencing parameters such as adsorbent dose, initial concentration of adsorbates, reaction time, solution pH, and temperature were also investigated. The adsorption kinetic studies of both TC and Pb(II) removal indicated that equilibrium was achieved within 12 h, with respective removal rates of 91.9 and 99.5%, and the corresponding adsorption data were fitted to the second-order kinetics model. According to the adsorption isotherm studies, the sorption data of TC best fitted to the Langmuir isotherm model while the adsorption data of Pb(II) were explained by the Freundlich isotherm model. The maximum adsorption capacities of both TC and Pb(II) were found to be 475.8 and 288.7 mg/g, respectively, demonstrating excellent performances of the adsorbent. The uptake capacity of PSA-HMO was significantly influenced by the level of solution pH, in which optimum adsorption amount was realized at pH 4.0 in the TC and Pb(II) systems, respectively. Thermodynamic studies showed the process of TC and Pb(II) adsorptions were endothermic and spontaneous. Overall this study elucidated that PSA-HMO composite can be a promising candidate for antibiotics and heavy metal removal in water treatment applications.

Effects and mechanism of pyrolysis temperature on physicochemical properties of corn stalk pellet biochar based on combined characterization approach of microcomputed tomography and chemical analysis

To further explain effects of pyrolysis temperature on physicochemical properties of corn stalk pellet biochar from a new perspective, various lab physicochemical analysis methods combining microcomputed tomography were used to characterize biochar in this study. The results showed that at pyrolysis temperatures from 300 °C to 800 °C, yield of biochar decreased logarithmically with increasing pyrolysis temperature (T); changes of proximate and elemental compositions all showed significant differences, but the change rules were not consistent; high temperature pyrolysis biochar had high stability, high hardness and was convenient for storage and transportation; the proportions of hydroxyl group and amino group were highest in BC800 and BC600, respectively, contributing to the adsorption and removal of pollutants; BC400 had the best combustion performance; X-ray mean attenuation coefficient (XMAC) showed the following correlations, namely, XMAC = 0.003*ln(T-285.329) + 0.011 (R² = 0.904) and XMAC = -0.031*(VM/100) + 0.021*(Ash/100) + 0.027 (R² = 0.915). Above results provide important basic data support for development of corn stalk pellet biochar.

Study on arsenic, selenium, and lead produced in coal combustion: bibliometric method

The literature on trace element pollutants (arsenic, selenium, lead) produced during coal burning from 2007 to 2020 was summarized by the bibliometric method, and the characteristics of published articles and research trends were analyzed. Taking 2007 as the starting point for statistics on articles in this research direction, there was a process of rapid growth in the total number of published articles by 2015, and it was increased over time. In the last 5 years of statistics, it is found that the number of articles published in China is the largest, accounting for almost half of the total. Most of the articles are published in the fields of energy, environmental protection, etc. Among them, the research on arsenic, selenium, and lead is mainly related to the use of adsorbents. At the same time, the effects of temperature, catalyst, material, and other conditions on the removal efficiency of arsenic, selenium, and lead in coal were considered. Application of photocatalysis, preparation of new adsorption materials, and mining of the properties of existing materials under different experimental conditions are a good development prospect.

Cysteine chemical modification for surface regulation of biochar and its application for polymetallic adsorption from aqueous solutions

Biochar (BC) has been widely used to remove heavy metals from wastewater. However, due to the hydrophobicity of BC and the lack of its surface functional groups, the effect of metal ions adsorption onto BC is limited. In order to improve the adsorption efficiency, L-cysteine was used to modify biochar derived from pomelo peel (PP) to regulate surface structure. The characteristics of BC and cysteine/biochar composite (cys/BC) were analyzed by various characterization methods. Results showed that the hydrophilicity of biochar was enhanced, and the number of surface functional groups was increased, resulting to strong adsorption ability of Ag(I) (618.9 mg/g), Pb(II) (274.5 mg/g), and As(V) (34.7 mg/g) for cys/BC, which increased approximately by 15%, 35%, and 29% compared with that of BC, respectively. The adsorption process of Pb(II) onto cys/BC was fitted better by the Freundlich isotherm model and for Ag(I) and As(V) by the Langmuir isotherm model. Moreover, the adsorption kinetics followed pseudo-second-order equation and the adsorption process was controlled by the intraparticle diffusion for Ag(I), Pb(II), and As(V) adsorption onto cys/BC. In addition, the adsorption capacities of cys/BC for Ag(I), Pb(II), and As(V) decreased slightly after five adsorption/desorption cycles. Finally, the multiple adsorption mechanisms including functional groups, pore adsorption, surface complexation, and cations-π were analyzed. The paper demonstrated that the cys/BC composite could be reused as effective adsorbents for removing contaminants in the environment.

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.

Biochar from Agricultural by-Products for the Removal of Lead and Cadmium from Drinking Water

This study reports the adsorption capacity of lead Pb2+ and cadmium Cd2+ of biochar obtained from: peanut shell (BCM), “chonta” pulp (BCH) and corn cob (BZM) calcined at 500, 600 and 700 °C, respectively. The optimal adsorbent dose, pH, maximum adsorption capacity and adsorption kinetics were evaluated. The biochar with the highest Pb2+ and Cd2+ removal capacity is obtained from the peanut shell (BCM) calcined at 565 °C in 45 min. The optimal experimental conditions were: 14 g L−1 (dose of sorbent) and pH between 5 and 7. The sorption experimental data were best fitted to the Freundlich isotherm model. High removal rates were obtained: 95.96% for Pb2+ and 99.05. for Cd2+. The BCH and BZM revealed lower efficiency of Pb2+ and Cd2+ removal than BCM biochar. The results suggest that biochar may be useful for the removal of heavy metals (Pb2+ and Cd2+) from drinking water.

Adsorption behaviors on trace Pb2+ from water of biochar adsorbents from konjac starch

Biochar adsorbents used to treat different heavy metals in water are efficient and low-cost. Appropriate raw materials, excellent selectivity and detailed adsorption mechanism are of important for research on biochar adsorbents. In this work, konjac starch was dispersed in polyvinylpyrrolidone (PVP) solution to prepare different sizes hydrophilic carbon spheres (HCSs) by hydrothermal synthesis method. Adsorption kinetics of the HCSs towards Pb2+ is described perfectly by the pseudo-second-order equation. With the temperature increasing, adsorption thermodynamics are more consistent with the Freundlich model. The calculated ΔG, ΔH and ΔS shows the adsorption of the HCSs towards Pb2+ is a spontaneous, endothermic and entropy increase process. In addition, HCSs have excellent selectivity for the adsorption of Pb2+ and Cu2+. HCSs prepared from konjac starch make full use of natural biomass resources, they can be used as a potential adsorbent material in treatment on heavy metal ion from water field.

Evaluation of biochar pyrolyzed from kitchen waste, corn straw, and peanut hulls on immobilization of Pb and Cd in contaminated soil

Biochar has a wide range of feedstocks, and different feedstocks often resulted in different properties, such as element distribution and heavy metal immobilization performance. In this work, batch experiments were conducted to assess the effectiveness of biochar pyrolyzed from kitchen waste (KWB), corn straw (CSB), and peanut hulls (PHB) on immobilization of Cd and Pb in contaminated soil by planting swamp cabbage (Ipomoea aquatica Forsk.) with a combination of toxicological and physiological tests. The results showed that biochar could all enhance the soil pH, and reduce extractable Pb and Cd in soil by 22.61%-71.01% (KWB), 18.54%-64.35% (CSB), and 3.28%-60.25% (PHB), respectively. The biochar led to a drop in Cd and Pb accumulation in roots, stems, and leaves by 45.43%-97.68%, 59.13%-96.64%, and 63.90%-99.28% at the dosage of 60.00 mg/kg, respectively. The root length and fresh weight of swamp cabbage were promoted, while superoxide dismutase (SOD) and peroxidase (POD) decreased after biochar treatment. The distribution of heavy metal fractions before and after biochar treatment indicated that biochar could transform Cd and Pb into a state of lower bioavailability, thus inhibiting Cd and Pb uptake by swamp cabbage. Biochar with different feedstocks could be ranked by the following order according to immobilization performance: KWB > CSB > PHB.