Utilization of biochar produced from invasive plant species to efficiently adsorb Cd (II) and Pb (II)

Adsorption of Pb, Cu, and Ni Ions on Activated Carbon Prepared from Oak Cupules: Kinetics and Thermodynamics Studies

Agricultural residue-activated carbon and biochar, inexpensive and environmentally friendly adsorbent materials, have recently received significant research attention. This study investigated the potential use of oak cupules in activated carbon form to remove widespread heavy metals (Pb2+, Cu2+, and Ni2+) from wastewater. The oak-activated carbon was prepared from oak cupules and activated with phosphoric acid. Oak-activated carbon was characterized using FTIR, BET analysis, energy-dispersive X-ray spectrometry (EDS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Freundlich, Langmuir, and Temkin isotherm models were used to assess the equilibrium data. The impact of various parameters, including pH effect, temperature, adsorbent dose, and contact time, was estimated. The Freundlich model was the most agreeable with Pb2+ adsorption by oak-based activated carbon, and Langmuir was more compatible with Cu2+ and Ni2+. Under optimum conditions, the average maximum removal was 63% Pb2+, 60% Cu2+, and 54% Ni2+ when every ion was alone in the aqueous solution. The removal was enhanced to 98% Pb2+, 72% Cu2+, and 60% Ni2+ when found as a mixture. The thermodynamic model revealed that the adsorption of ions by oak-based activated carbon is endothermic. The pseudo-second-order kinetic best describes the adsorption mechanism in this study; it verifies chemical sorption as the rate-limiting step in adsorption mechanisms. The oak-activated carbon was effective in removing Pb2+, Cu2+, and Ni2+ from wastewater and aqueous solutions.

Effect of pyrolysis temperature and molecular weight on characterization of biochar derived dissolved organic matter from invasive plant and binding behavior with the selected pharmaceuticals

A comprehensive understanding of the characteristics of biochar released-dissolved organic matter (BDOM) derived from an invasive plant and its impact on the binding behavior of pharmaceuticals is essential for the application of biochar, yet has received less attention. In this study, the binding behavior of BDOM pyrolyzed at 300-700 °C with sulfathiazole, acetaminophen, chloramphenicol (CAP), and carbamazepine (CMZ) was investigated based on a multi-analytical approach. Generally, the pyrolysis temperature exhibited a more significant impact on the spectral properties of BDOM and pharmaceutical binding behavior than those of the molecular weight. With increased pyrolysis temperature, the dissolved organic carbon decreased while the proportion of the protein-like substance increased. The highest binding capacity towards the drugs was observed for the BDOM pyrolyzed at 500 °C with the molecular weight larger than 0.3 kDa. Moreover, the protein-like substance exhibited higher susceptive and released preferentially during the dialysis process and also showed more sensitivity and bound precedingly with the pharmaceuticals. The active binding points were the aliphatic C-OH, amide II N-H, carboxyl CO, and phenolic-OH on the tryptophan-like substance. Furthermore, the binding affinity of the BDOM pyrolyzed at 500 °C was relatively high with the stability constant (logKM) of 4.51 ± 0.52.

Optimization of hydrothermal synthesis conditions of Bidens pilosa-derived NiFe2O4@AC for dye adsorption using response surface methodology and Box-Behnken design

The presence of stable and hazardous organic dyes in industrial effluents poses significant risks to both public health and the environment. Activated carbons and biochars are widely used adsorbents for removal of these pollutants, but they often have several disadvantages such as poor recoverability and inseparability from water in the post-adsorption process. Incorporating a magnetic component into activated carbons can address these drawbacks. This study aims to optimizing the production of NiFe2O4-loaded activated carbon (NiFe2O4@AC) derived from a Bidens pilosa biomass source through a hydrothermal method for the adsorption of Rhodamine B (RhB), methyl orange (MO), and methyl red (MR) dyes. Response surface methodology (RSM) and Box-Behnken design (BBD) were applied to analyze the key synthesis factors such as NiFe2O4 loading percentage (10-50%), hydrothermal temperature (120-180 °C), and reaction time (6-18 h). The optimized condition was found at a NiFe2O4 loading of 19.93%, a temperature of 135.55 °C, and a reaction time of 16.54 h. The optimum NiFe2O4@AC demonstrated excellent sorption efficiencies of higher than 92.98-97.10% against all three dyes. This adsorbent was characterized, exhibiting a well-developed porous structure with a high surface area of 973.5 m2 g-1. Kinetic and isotherm were studied with the best fit of pseudo-second-order, and Freundlich or Temkin. Qmax values were determined to be 204.07, 266.16, and 177.70 mg g-1 for RhB, MO, and MR, respectively. By selecting HCl as an elution, NiFe2O4@AC could be efficiently reused for at least 4 cycles. Thus, the Bidens pilosa-derived NiFe2O4@AC can be a promising material for effective and recyclable removal of dye pollutants from wastewater.

Effects of BC on metal uptake by crops (availability) and the vertical migration behavior in soil: A 3-year field experiments of crop rotation

Biochar (BC) has been substantiated to effectively reduce the available content of heavy metals (HMs) in soil-plant system; however, the risk of biochar (BC)derived dissolved organic matter (DOM) induced metal vertical migration has not been well documented, especially in the long-term field conditions. Therefore, this study investigated HM vertical migration ecological risks and the long-term effectiveness of the amendment of biochar in the three successive years of field trials during the rotation system. The results revealed that biochar application could increase soil pH and DOM with a decrease in soil CaCl2 extractable pool for Pb, Cu, and Cd. Furthermore, the results indicated a significant decrease in acid phosphatase activities and an increase in urease and catalase activities in the soil. Cucumber was shown to be safe during a three-year rotation system in the field. These results suggest that BC has the potential to enhance soil environment and crop yields. BC derived DOM-specific substances were identified using parallel factor analysis of excitation-emission matrix in deep soil (0-60 cm). The study incorporated HM concentration fluctuations in deep soils, providing an additional interpretation of DOM and co-migration of HMs.The environmental risk associated with the increase in DOM hydrophobicity should not be ignored by employing BC for soil HM remediation applications. The study enhances understanding of biochar-derived DOM's migration and stabilization mechanisms on heavy metals, providing guidelines for its use as a soil amendment.

Low-molecular-weight aromatic acids mediated the adsorption of Cd2+ onto biochars: effects and mechanisms

Low-molecular-weight aromatic acids (LWMAAs), a ubiquitous organic substance in natural systems, are important in controlling the environmental fate of potentially toxic metals. However, little is known about the effects of LWMAAs on the interactions between biochars and potentially toxic metals. Herein, the influences of three aromatic acids, including benzoic acid (BA), p-hydroxy benzoic acid (PHBA), and syringic acid (SA), on the adsorption of Cd2+ onto biochars generated at three different pyrolysis temperatures under acidic and neutral conditions were examined. Generally, the adsorption ability of biochars for Cd2+ improved with the increase of pyrolysis temperature, which was ascribed to the increased inorganic element contents (e.g., P, S, and Si) and aromaticity, increasing the complexation between mineral anions and metal ions, and the enhanced cation-π interaction. Interestingly, aromatic acids considerably inhibited the adsorption of Cd2+ onto biochars, which was mainly ascribed to multi-mechanisms, including competition of LWMAA molecules and metal ions for adsorption sites, the pore blocking effect, the weakened interaction between mineral anions and Cd2+ induced by the adsorbed aromatic acids, and the formation of water-soluble metal-aromatic acid complexes. Furthermore, the inhibitory effects of LWMAAs on Cd2+ adsorption intensively depended on the aromatic acid type and followed the order of SA > PHBA > BA. This trend was related to the differences in the physicochemical features (e.g., the octanol/water partition coefficient (log Kow) and molecular size) of diverse LMWAAs. The results of this study demonstrate that the effects of coexisting LMWAAs should not be ignored when biochars are applied in soil remediation and wastewater treatment.

Novel pretreatment with hydrogen peroxide enhanced microwave biochar for heavy metals adsorption: Characterization and adsorption performance

Hydrogen peroxide (HP) was used to pretreat wheat straw (WS) for microwave biochar production at 100-600 W, the physicochemical properties of pretreated WS and biochar products as well as heavy metals adsorption performance were investigated. Results showed that HP enhanced specific surface area (SSA) and pore volume (PV) of WS, and the largest SSA (190.35 m2 g-1) and PV (0.1493 cm3 g-1) of biochar were obtained at microwave powers of 600 W (HPWS600) and 500 W (HPWS500), respectively. HPWS500 showed maximum adsorption capacities, which were 57.56, 190.21, and 65.16 mg g-1 for Cd2+, Pb2+, and Cu2+, respectively. Solution pH values and cation concentrations exhibited significant effects on adsorption capacities of biochar. The pseudo-second-order kinetic and Langmuir isotherm models fitted better for metal adsorption process. The FTIR results suggested that chemisorption mechanisms including precipitation with carbonate and complexation with oxygen-containing functional groups might be predominant adsorption mechanisms. These results suggest that HP pretreatment has excellent potential for biochar production.

Efficient removal of Cd(II) and Pb(II) from aqueous solution using biochars derived from food waste

Massive amount of food waste has been generated annually, posing a threat to ecological sustainability and the social economy due to current disposal methods. Urgent action is needed worldwide to convert the traditional pathway for treating food waste into a sustainable bioeconomy, as this will significantly benefit food chain management. This study explores the use of pyrolysis to produce different types of food waste biochars and investigates their adsorption capabilities for removing Cd2+ and Pb2+ in aqueous solution. The results indicated that co-pyrolysis biochar from fresh food waste and rice husk (FWRB) exhibited superior adsorption performance for Cd2+ (61.84 mg·g-1) and Pb2+ (245.52 mg·g-1), respectively. Pseudo-second-order kinetics (0.74 ≤ R2 ≤ 0.98) and Langmuir isotherms (0.87 ≤ R2 ≤ 0.98) indicated that the immobilized Cd2+ and Pb2+ on biochars were mainly attributed to the chemisorption, including precipitation with minerals (e.g., carbonates, silicates, and phosphate), complexation with functional groups (-OH), cation exchange (-COO-), and coordination with π-electrons. Furthermore, FWRB demonstrated reduced EC and Na content in comparison to food waste digestate biochar (FWDB) and food waste digestate co-pyrolysis with sawdust biochar (FWSB), with levels of Cd and Pb falling below China's current guideline thresholds. These findings suggested that co-pyrolysis of fresh food waste with rice husk could be applicable to the recycling of food waste into biochar products for heavy metal stabilization in contaminated water and soils.

Biochar may alter plant communities when remediating the cadmium-contaminated soil in the saline-alkaline wetland

It is thought remediating cadmium pollution with biochar can affect plant traits. However, the potential impact of this practice on plant communities is poorly understood. Here, we established natural-germinated plant communities using soil seed bank from a saline-alkaline wetland and applied a biochar treatment in Cd-polluted wetland soil. The outcomes illustrated that Juglans regia biochar (JBC), Spartina alterniflora biochar (SBC), and Flaveria bidentis biochar (FBC) promoted exchangeable Cd transform into FeMn oxide bound Cd. Additionally, most biochar addition reduced species abundance, root-shoot ratio, biomass, diversity, and community stability, yet enhanced community height. Among all treatments, the 5 % SBC demonstrated the most significant reduction in species abundance, biomass, species richness and functional richness. Specifically, it resulted in a reduction of 92.80 % in species abundance, 73.80 % in biomass, 66.67 % in species richness, and 95.14 % in functional richness compared to the CK. We also observed changes in root morphological traits and community structure after biochar addition. Soil pH, salinity, and nutrients played a dominant role in shaping plant community. These findings have implications for biodiversity conservation, and the use of biochar for the remediation of heavy metals like cadmium should be approached with caution due to its potential negative impacts on plant communities.

Preparation of Biomass Carbon Composites MgO@ZnO@BC and Its Adsorption and Removal of Cu(II) and Pb(II) in Wastewater

The ternary composite MgO@ZnO@BC was synthesized and characterized for the adsorption of Cu2+, Pb2+ heavy metal ions from wastewater. The results show that the addition of the MgO@ZnO@BC composite results in higher adsorption properties for Cu2+ and Pb2+, with a molar ratio of 5% 0.1 g, and maximum adsorption capacity (50.63 mg/g for Cu2+ and 61.46 mg/g for Pb2+). The Langmuir adsorption isotherm of the adsorption complex and the kinetics of adsorption are secondary kinetics. The adsorption of Cu2+ and Pb2+ was mainly chemisorption, accompanied by physical adsorption. This adsorption method fully conforms to the concepts of clean production and efficient waste utilization, providing a reference for the removal of heavy metal ions from wastewater and waste recycling using ternary composite materials.

Heavy metal pollution in the aquatic environment: efficient and low-cost removal approaches to eliminate their toxicity: a review

Heavy metal contamination of water sources has emerged as a major global environmental concern, threatening both aquatic ecosystems and human health. Heavy metal pollution in the aquatic environment is on the rise due to industrialization, climate change, and urbanization. Sources of pollution include mining waste, landfill leachates, municipal and industrial wastewater, urban runoff, and natural phenomena such as volcanic eruptions, weathering, and rock abrasion. Heavy metal ions are toxic, potentially carcinogenic, and can bioaccumulate in biological systems. Heavy metals can cause harm to various organs, including the neurological system, liver, lungs, kidneys, stomach, skin, and reproductive systems, even at low exposure levels. Efforts to find efficient methods to remove heavy metals from wastewater have increased in recent years. Although some approaches can effectively remove heavy metal contaminants, their high preparation and usage costs may limit their practical applications. Many review articles have been published on the toxicity and treatment methods for removing heavy metals from wastewater. This review focuses on the main sources of heavy metal pollution, their biological and chemical transformation, toxicological impacts on the environment, and harmful effects on the ecosystem. It also examines recent advances in cost-effective and efficient techniques for removing heavy metals from wastewater, such as physicochemical adsorption using biochar and natural zeolite ion exchangers, as well as decomposition of heavy metal complexes through advanced oxidation processes (AOPs). Finally, the advantages, practical applications, and future potential of these techniques are discussed, along with any challenges and limitations that must be considered.

Removal Performance of KOH-Modified Biochar from Tropical Biomass on Tetracycline and Cr(VI)

Biochar can be used to address the excessive use of tetracycline and micronutrient chromium (Cr) in wastewater that potentially threatens human health. However, there is little information about how the biochar, made from different tropical biomass, facilitates tetracycline and hexavalent chromium (Cr(VI)) removal from aqueous solution. In this study, biochar was prepared from cassava stalk, rubber wood and sugarcane bagasse, then further modified with KOH to remove tetracycline and Cr(VI). Results showed that pore characteristics and redox capacity of biochar were improved after modification. KOH-modified rubber wood biochar had the highest removal of tetracycline and Cr(VI), 1.85 times and 6 times higher than unmodified biochar. Tetracycline and Cr(VI) can be removed by electrostatic adsorption, reduction reaction, π-π stacking interaction, hydrogen bonding, pore filling effect and surface complexation. These observations will improve the understanding of the simultaneous removal of tetracycline and anionic heavy metals from wastewater.

Preparation and Characterization of an Invasive Plant-Derived Biochar-Supported Nano-Sized Lanthanum Composite and Its Application in Phosphate Capture from Aqueous Media

Invasive plants pose a great threat to natural ecosystems owing to their rapid propagation and spreading ability in nature. Herein, a typical invasive plant, Solidago canadensis, was chosen as a novel feedstock for the preparation of nano-sized lanthanum-loaded S. canadensis-derived biochar (SCBC-La), and its adsorption performance for phosphate removal was evaluated by batch adsorption experiment. The composite was characterized by multiple techniques. Effects of parameters, such as the initial concentration of phosphate, time, pH, coexisting ions, and ionic strength, were studied on the phosphate removal. Adsorption kinetics and isotherms showed that SCBC-La shows a faster adsorption rate at a low concentration and SCBC-La exhibits good La utilization efficiency than some of the reported La-modified adsorbents. Phosphate can be effectively removed over a relatively wide pH of 3-9 because of the high pH _pzc of SCBC-La. Furthermore, the SCBC-La shows a strong anti-interference capability in terms of pH value, coexisting ions, and ionic strength, exhibiting a highly selective capacity for phosphate removal. Additionally, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements reveal that hydroxyl groups on the surface of SCBC-La were replaced by phosphate and manifest the reversible transformation between La(OH)₃ and LaPO₄. Considering its high adsorption capacity and excellent selectivity, SCBC-La is a promising material for preventing eutrophication. This work gives a new method of pollution control with waste treatment since the invasive plant (S. canadensis) is converted into biochar-based nanocomposite for effective removal of phosphate to mitigate eutrophication.

Multicomponent adsorption of heavy metals onto biogenic hydroxyapatite: Surface functional groups and inorganic mineral facilitating stable adsorption of Pb(Ⅱ)

Due to the coexistence of various heavy metals in the contaminated environment, it is essential to comprehensively study the multicomponent adsorption of heavy metals in order to tackle these combined pollutants. Herein, the adsorption processes of Pb(Ⅱ), Cu(Ⅱ) and Cd(Ⅱ) by biogenic hydroxyapatite (BHAp) were investigated in single and multicomponent systems. The maximum adsorption capacity for Pb(Ⅱ), Cu(Ⅱ) and Cd(Ⅱ) by BHAp in single system reached 311.16, 82.05 and 92.54 mg g^-1, respectively, while adsorption capacity for Cu(Ⅱ) and Cd(Ⅱ) in multicomponent system decreased more obviously than that of Pb(Ⅱ). Furthermore, the stability of Cu(Ⅱ) and Cd(Ⅱ) adsorbed on BHAp was indeed influenced in multicomponent system. By means of the characterization analysis, it was found that ion exchange was more instrumental in the adsorption processes of Cu(Ⅱ) and Cd(Ⅱ) in single system than in multicomponent system. Significantly, it was observed that the proportion of generally stable Pb(II) adsorbed on BHAp exceeded 95% in both single and multicomponent systems. This result might be due to the in-site growth of stable crystals of Pb_xCa_10-x(PO₄)₆(OH)₂, which was synergistically induced by surface functional groups and inorganic mineral of BHAp, and was unaffected by the coexistence of Cu(Ⅱ) and Cd(Ⅱ).

Effects and mechanism on cadmium adsorption removal by CaCl2-modified biochar from selenium-rich straw

As every-one knows, cadmium contamination poses a significant and permanent threat to people and aquatic life. Therefore, research on how to remove cadmium from wastewater is essential to protect the natural environment. In this study, agricultural and forestry waste straw sprayed with selenium-enriched foliar fertilizer was prepared as biochar, which was altered by calcium chloride (CaCl₂) to remove Cd²⁺ from water. The outcomes demonstrated that biochar generated by pyrolysis at 700 °C (BC700) had the best adsorption effect. Secondly, pseudo-second-order kinetics and Langmuir adsorption models were used to predict the Cd²⁺ adsorption. Finally, electrostatic adsorption, ion exchange, and complexation of oxygen functional groups (OFGs) were demonstratedto be the main adsorption mechanisms. These conclusions indicate that selenium-rich straw biochar is a novel adsorbent for agroforestry waste recovery. Meanwhile, this work will offer a promising strategy for the overall utilization of rice straw.

Decreased in vitro bioaccessibility of Cd and Pb in an acidic Ultisol through incorporation of crop straw-derived biochar

Studies analyzing the in vitro bioaccessibility (BAc) of heavy metals in biochar-amended soils are currently lacking. The present study aimed to assess the metal BAc in Cd- and Pb-spiked acidic Ultisol samples treated individually with 2% (w/w) maize, rice, wheat, soybean, and pea straw-derived biochar. The results indicate that the Cd-BAc simulated in gastric phase (GP) decreased from 78.4% to 66.5-72.3% and the Pb-BAC decreased from 74.3% to 67.2-69.2%; however, the Cd-BAc in the intestinal phase (IP) decreased from 35.6% to 27.9-33.5% and the Pb-BAc decreased from 34.7% to 29.7-32.9% after 120 d of incubation with biochar application compared to the un-amended Ultisol. The Cd- and Pb-BAc in both GP and IP were significantly negatively correlated with soil pH, CEC, and organic carbon (P < 0.05), which increased after biochar application. The soybean straw-derived biochar amendment has the greatest potential to decrease the BAc of Cd and Pb in the GP and IP, owing to the highest level of CEC, SOC, TC and TN among all soil samples. Moreover, the BAc was positively correlated with the exchangeable, and exchangeable + carbonate-bound Cd and Pb fractions (P < 0.05), indicating these fractions had a dominant influence on the BAc of cationic heavy metals. Therefore, crop straw-derived biochar amendment can decrease the BAc of Cd and Pb in acidic Ultisol, and thus mitigate the health risks posed by these metals from incidental ingestion.

Microwave biochar produced with activated carbon catalyst: Characterization and adsorption of heavy metals

Novel microwave biochar derived from wheat straw (WS) using a range of power levels, with activated carbon catalyst as microwave absorber, was produced, characterized and tested as adsorbent of three heavy metals (Pb²⁺, Cd²⁺, and Cu²⁺). The microwave biochar with the greatest specific surface area (156.09 m² g^-1) and total pore volume (0.0790 cm³ g^-1) were produced at 600 W (WS600) and 500 W (WS500) power level, respectively. Maximum adsorption capacities of WS500 to Pb²⁺, Cd²⁺ and Cu²⁺ were 139.44 mg g^-1, 52.92 mg g^-1, and 31.25 mg g^-1, respectively. Optimal pH value for heavy metal removal was at range of 5-6, and Pb²⁺ showed the strongest affinity in competitive adsorption experiments. The adsorption data were fitted better by pseudo-second-order model and Langmuir isotherm, indicating that adsorption process was mainly explained by monolayer adsorption, and chemical adsorption occupied important role. The predominant adsorption mechanisms of heavy metals on microwave pyrolysis biochar included complexation with oxygen-containing functional groups (i.e., carboxylic acid CO and -OH) and precipitation with carbonate. In addition, reused WS600 maintained 76.17% and 96.07% of their initial adsorption capacity for Cu²⁺ and Cd²⁺, respectively. These results suggest that microwave biochar produced with activated carbon catalyst has excellent potential for efficient use in the removal of heavy metals from waste water.

Global perspectives for biochar application in the remediation of heavy metal-contaminated soil: a bibliometric analysis over the past three decades

Herein, 7,308 relevant documents on biochar application for the remediation of heavy metal (HM)-contaminated soil (BARHMCS) from 1991 to 2020 were extracted from the Web of Science Core Collection and subjected to bibliometric and knowledge mapping analyses to provide a global perspective. The results showed that (1) the number of publications increased over time and could be divided into two subperiods, i.e., the slow growth period (SGP) and rapid growth period (RGP), according to whether the annual publication number was ≥300. (2) A total of 126 countries, 741 institutions, and 1,021 scholars have contributed to this field. (3) These studies are mainly published in Science of the Total Environment, Chemosphere, etc., and are mainly based on the categories of environmental science, soil science, and environmental engineering. (4) The top five keyword clusters for the SGP were biochar, biochar, sorption, charcoal, and HMs, and those for the RGP were adsorption, black carbon, nitrous oxide, cadmium, and pyrolysis. (5) The main knowledge domains and the most cited references during the SGP and RGP were discussed. (6) Future directions are related to biochar application for plant remediation, the mitigation of climate change through increased carbon sequestration, biochar modification, and biochar for HMs and multiple organic pollutants.

Comparison of cadmium adsorption by hydrochar and pyrochar derived from Napier grass

Biochar (e.g. pyrochar and hydrochar) is considered a promising adsorbent for Cd removal from aqueous solution. Considering the vastly different physicochemical properties between pyrochar and hydrochar, the Cd²⁺ sorption capacity and mechanisms of pyrochars and hydrochars should be comparatively determined to guide the production and application of biochar. In this study, the hydrochars and pyrochars were prepared from Napier grass by hydrothermal carbonization (200 and 240 °C) and pyrolysis (300 and 500 °C), respectively, and the physicochemical properties and Cd²⁺ sorption performances of biochars were systematically determined. The pyrochars had higher pH and ash content as well as better stability, while the hydrochars showed more oxygen-containing functional groups (OFGs) and greater energy density. The pseudo second order kinetic model best fitted the Cd²⁺ sorption kinetics data of biochars, and the isotherm data of pyrochar and hydrochar were well described by Langmuir and Freundlich models, respectively. In comparison with hydrochar, the pyrochar exhibited better Cd²⁺ sorption capacity (up to 71.47 mg/g). With increasing production temperature, the Cd²⁺ sorption capacity of pyrochar elevated, while the reduction was found for hydrochar. The mineral interaction, complexation with surface OFGs, and coordination with π electron were considered the main mechanisms of Cd²⁺ removal by biochars. The minerals interaction and the complexation with OFGs was the dominant mechanism of Cd²⁺ removal by pyrochars and hydrochars, respectively. Therefore, the preparation technique and temperature have significant impacts on the sorption capacity and mechanisms of biochar, and pyrochar has better potential for Cd²⁺ removal than the congenetic hydrochar.

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.

Toxicological effect assessment of aged biochar on Escherichia coli

Biochar (BC) is a biomass material that has a wide range of applications on the remediating heavy metals. In this experiment, we prepared BC (300 ºC, 500 ºC, and 700 ºC) and applied them to adsorb lead ions (Pb²⁺) to simulate BC treatment of Pb²⁺-contaminated soil. The retention capacity of BC for heavy metals was altered by means of bacterial culture, and the heavy metals released by BC can have toxicological effects on bacteria. This approach was used to assess the effects of long-term application of BC in heavily contaminated land with heavy metals on soil microorganisms. The results show that Escherichia coli survived in the medium containing lower doses of Pb²⁺-aged BC prepared at 300 ºC and 500 ºC (25 mg/L and 50 mg/L), depending on its ability of tolerating a certain amount of Pb²⁺. The addition of 100 mg/L Pb²⁺-aged BC prepared at 700 ºC not only significantly inhibited the growth of E. coli, but also promoted the release of citric acid from E. coli, which in turn triggered BC releasing more Pb²⁺. It is hoped that this will provide foundation to support the long-term application of BC in the remediation of heavy metal contaminated soils.

Manganese oxide-modified biochar derived from discarded mushroom-stick for the removal of Sb(III) from aqueous solution

In this study, discarded mushroom-stick, which is widely available, was selected as a precursor to prepare MnO₂-modified biochar (MBC) for Sb(III) removal. Several characterisation methods (SEM, BET, XPS, FT-IR, and XRD) were used to explore the mechanisms of antimony adsorption onto MBC. The results showed that MBC is a mesoporous material with a fluffy structure and a higher specific surface area (23.56 and 32.09 m²·g^-1) than PBC600 (13.62 m²·g^-1), exhibiting superior and stable adsorption capacities for Sb(III) (50.30 mg·g^-1 for 1/30MBC600 and 64·12 mg·g^-1 for 1/20MBC600) across a wide pH range (pH 4-8). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy analyses indicated that the main oxides and functional groups involved in the adsorption were manganese oxides and hydroxyl groups. Forty-four per cent of the adsorbed Sb(III) was oxidised to Sb(V) by manganese oxides or hydroxyl groups both on the surface of biochar and in solution. According to adsorption kinetics and isotherms, the adsorption process of Sb(III) is chemisorption, which includes monolayer and multilayer heterogeneous chemisorption processes. To sum up, MBC is an excellent adsorbent for the capture of Sb(III) from contaminated water with strong potential for future application.

A Mesoporous Faujasite Prepared by Space-Confined Method for Highly Effective Selectivity of Copper Ions

The discharge of copper ion (Cu(II)) into natural waters can lead to serious environmental and health problems; however, an abundantly porous hierarchical adsorbent, such as faujasite (FAU), can rapidly remove unwanted Cu(II). In this research, a hierarchically structured, abundantly mesoporous faujasite (FAU) was fabricated from industrial-waste lithium-silicon powder (LSP), with the addition of biochar and graphene oxide (GO) via hydrothermal synthesis without high-temperature calcination. The results demonstrated that just a small amount of biochar or GO can significantly improve the mesopore volume (0.14 cm³/g) and the Cu(II) adsorption capacity (115.65 mg/g) of composite FAU. In particular, careful examination of the properties of the composite FAU showed that the biochar and GO had favorably affected the growth of the zeolite crystals, thus promoting the formation of the FAU skeleton structure, ion-exchange sites and Si-OH. The composite FAU exhibited superior adsorption capacities and highly effective Cu(II) selectivity. Thus, the findings of this study provide a novel and cost-effective avenue for the synthesis of composite FAU with high copper-selective removal capacity.

Advances on tailored biochar for bioremediation of antibiotics, pesticides and polycyclic aromatic hydrocarbon pollutants from aqueous and solid phases

Biochar is gaining incredible importance for remediation applications due to their attractive removal properties. Moreover, it is becoming ecofriendly, cost-effective and sustainable bioadsorbents towards replacing expensive activated carbons. Studies reveal biochar effectiveness for removal of important and potentially severe organic pollutants such as antibiotics and pesticides. Recent research advancements on biochar modification (physical, chemical and biological) opens greater opportunity to form tailored biochar with improved surface properties than their native forms for offering better removal efficiencies. Further attentions paid towards emergent new modification methods to cover broad-spectrum pollutants using tailored biochar. Current review aims to summarize recent updates upon biochar tailoring, comparative account of tailored biochars removal efficiencies with respect to their native forms and to provide in-depth discussion covering specific interactions of tailored biochars with antibiotics, polycyclic aromatic hydrocarbons (PAHs) and pesticides for their effective removals and degradation from polluted environments. Application of inducer compounds e.g., peroxymonosulfate and sodium percarbonate further improved the biochar role towards degradation of toxic organic pollutants into their less or nontoxic forms. Biochar engineered with specific metals enable them for the same role without inducer compounds. Moreover, microbial interactions with biochar not only improve the bioremediation level further but also degrade the pollutants from the environment and open up better environmental and socio-economic prospects. Application of green, cost-effective and sustainable biochar for remediation of environmentally potential organic pollutants offers economical treatment methods as well as safe environment. These benefits are inline with global trends towards developing a sustainable process for biocircular economy.

A novel Ca/Mn-modified biochar recycles P from solution: mechanisms and phosphate efficiency

The excessive use of phosphate leads to severe environmental issues, such as a shortage of phosphorus resources and water eutrophication. In this study, a novel Ca-Mn-impregnated biochar (CMBC) composite was synthesized by co-pyrolysis at 600 °C for P recovery from solution. The efficiency of P-sorbed CMBC as a fertilizer was assessed via pot experiments. Kinetic experiments exhibited a higher phosphate sorption efficiency for the CM₁BC and CM₂BC composites. Pot experiments revealed that P-sorbed CMBC treatment significantly improved plant growth and yield. Compared with those of the control, the dry weight, fresh weight, and P content of rape leaf (root) P₅₀-CMBC_1.0% treatment increased by 108.6% (350%), 88.7% (396%), and 132.8% (109.3%), respectively. This may be due to the porous surface structures that develop during the treatment and Ca-P precipitation on P-sorbed biochar partly dissolved in the slightly acidic soil (pH: 6.25). The maximum P adsorption values fitted by the Langmuir isotherm model were up to 9.15, 3.19, 15.58, and 20.84 mg g^-1 for CBC, MBC, CM₁BC, and CM₂BC, respectively. The mechanism of phosphate recovery mainly includes electrostatic attraction, surface precipitation, and the formation of inner-sphere complexes with hydroxyl groups that were assessed using BET, zeta potential, SEM-EDS, FTIR, and XPS analyses. These mechanisms suggest that phosphate may be desorbed from the P-laden sorbent, which was consistent with the results of the pot experiments and desorption experiments in aqueous media. These results imply that P-sorbed modified biochar has the potential to be a promising P fertilizer in soil.

Banana stem and leaf biochar as an effective adsorbent for cadmium and lead in aqueous solution

Lead (Pb) and cadmium (Cd) are toxic heavy metals commonly found in aqueous environments. Biochar as a green adsorbent generated from biomass feedstock may be used for effective removal of these heavy metals. This study investigated the adsorption kinetics and isotherms of Pb²⁺ and Cd²⁺ in aqueous solutions at different pH by biochar prepared from banana stem and leaf (BSL-BC) at 400 °C. Characterizations using scanning electron microscope, X-ray diffraction, and Fourier-transform infrared spectroscopy showed that the synthesized BSL-BC had rough surface, porous structure, and oxygen-containing functional groups. The adsorption of Pb²⁺ and Cd²⁺ onto BSL-BC reached equilibrium in 8 h and 200 min, respectively, with faster adsorption attained at higher pH and the optimum pH occurred at 5 (Pb²⁺) and 8 (Cd²⁺). All adsorption kinetic data followed the pseudo-second-order rate model. The adsorption isotherm data of Pb²⁺ and Cd²⁺ could be well-described by the Langmuir and Freundlich models, respectively, whereas neither the Temkin or Dubinin-Radushkevich models provided satisfactory fitting results. The maximum adsorption capacities for Pb²⁺ and Cd²⁺ were 302.20 and 32.03 mg/g, respectively. The calculated mechanism contributions showed that complexation with oxygen-containing functional groups, ion exchange, mineral precipitation, and Pb²⁺/Cd²⁺-π coordination accounted for 0.1%, 8.4%, 88.8%, and 2.6% to Pb²⁺ adsorption, and 0.4%, 6.3%, 83.0%, and 10.4% to Cd²⁺ adsorption, respectively. Therefore, mineral precipitation was likely the major mechanism responsible for adsorption of both Pb²⁺ and Cd²⁺ by BSL-BC. The results suggest that the synthesized BSL-BC has great potential for adsorption of Pb²⁺ and Cd²⁺ from aqueous solutions.

Invasive plants as biosorbents for environmental remediation: a review

Water contamination is an environmental burden for the next generations, calling for advanced methods such as adsorption to remove pollutants. For instance, unwanted biowaste and invasive plants can be converted into biosorbents for environmental remediation. This would partly solve the negative effects of invasive plants, estimated at 120 billion dollars in the USA. Here we review the distribution, impact, and use of invasive plants for water treatment, with emphasis on the preparation of biosorbents and removal of pollutants such as cadmium, lead, copper, zinc, nickel, mercury, chromate, synthetic dyes, and fossil fuels. Those biosorbents can remove 90-99% heavy metals from aqueous solutions. High adsorption capacities of 476.190 mg/g for synthetic dyes and 211 g/g for diesel oils have been observed. We also discuss the regeneration of these biosorbents.

High-efficiency removal of lead/cadmium from wastewater by MgO modified biochar derived from crofton weed

The adsorption performance and mechanisms of Pb²⁺ and Cd²⁺ in wastewater using MgO modified biochar derived from crofton weed (MBCW600) are investigated. The Pb²⁺ and Cd²⁺ adsorption capacities of MBCW600 by the Hill model reach 384.08 mg/g and 207.02 mg/g, respectively, which is larger than that of original biochar. Pb²⁺ could be more easily captured by MBCW600 compared to Cd²⁺ in the multimetal system. Mg²⁺ contributes to Pb²⁺ and Cd²⁺ adsorption among coexisting cations. The exhausted MBCW600 could be well regenerated by simple method after use. The adsorption mechanism study indicates that Pb²⁺ and Cd²⁺ removal are primary contributed to mineral precipitation and ion exchange. The effective treatment volumes of Pb²⁺ and Cd²⁺ wastewater achieve 3050 mL and 2150 mL in the fixed-bed column experiment, respectively. Therefore, MBCW600 presents remarkable adsorption capability, excellent recoverability and large throughput, which shows the potential application in future treatment of wastewater containing heavy metal.

Heterogeneity of humic/fulvic acids derived from composts explains the differences in accelerating soil Cd-hyperaccumulation by Sedum alfredii

The hyperaccumulating mechanism concerning heavy metal activation or passivation and plant response triggered by fulvic acid (FA) and humic acid (HA) recruitments are investigated herein. We carefully examine the Cd activation effect by various FA and HA, tracing from pig, goat, and duck manure composts to straw compost and commercial materials (i.e., PC, GC, DC, SC, and CM), as well as their roles in plant growth promotion and Cd uptake. Our results indicate that due to the decrease of soil pH and their multiple functional groups, the contents of available Cd (AE-Cd) increased by 4.3-4.8% and 3.6-6.3% when all FA and HA sources were applied for 30 days. A 13.1-19.9% increase in AE-Cd was observed when CFA, DFA, and PFA were applied for five days, and a 9.5% increment was found when PHA was applied for 10 days. In the pot experiment, the Cd accumulation in plants increased by 2.78 and 2.17 folds with PFA and PHA applications, respectively, compared to the blank control group. This result can be attributed to the stimulative effects of the simultaneous Sedum alfredii growth and Cd phytoavailability. Notably, the Cd accumulation increased by 2.26 times with the SFA amendment due to the predominant stimulation effect to the phytoavailable Cd rather than plant growth. However, slight inhibitory effects were observed upon plant growth or Cd uptake, which led to the reduction of the Cd accumulation with DHA, SHA, and CHA employments. Consistently, the corresponding soil Cd removal efficiencies were 43.5% and 34.6% with PFA and PHA, respectively, which hold abundant O- and N-containing groups. Our research aims to gain insights into the ternary interaction in the presence of heavy metal, humic substances, and S. alfredii to simultaneously accelerate Cd activation and hyperaccumulation.

Effect of nickel salts on the production of biochar derived from alkali lignin: properties and applications

The massive generation of alkali lignin, has aroused the attention of all walks of life, and an eco-friendly utilization approach needs to be exploited. Herein, a simple pretreatment method with nickel salts was developed for the valorisation of alkali lignin through slow pyrolysis. The pretreatment of nickel salts improved the foaming or swelling behaviors of alkali lignin upon heating, and the specific surface area and total pore size of biochars increased about thirteenfold and eighteenfold, respectively. Additionally, Ni⁰ particles were generated and embedded in the carbon matrix of biochars. The biochar from Ni(NO₃)₂ pretreated lignin catalyzed the selective hydrogenation of nitrobenzene, yielding 80.5% of aniline; and that from (CH₃COO)₂Ni pretreated lignin showed adsorption capacity of lead around 87.1 mg/g. Moreover, the NiCl₂ pretreatment contributed to the formation of 1,2-dihydroxybenzene, while Ni(SO₄)₂ was conducive to the production of 4-methylguaiacol.

Engineering conversion of Asteraceae plants into biochars for exploring potential applications: A review

Asteraceae presents one of the most globally prevalent, cultivated, and fundamental plant families. However, a large amount of agricultural wastes has been yearly released from Asteraceae crops, causing adverse impacts on the environment. The objective of this work is to have insights into their biomass potentials and technical possibility of conversion into biochars. Physicochemical properties are systematically articulated to orientate environmental application, soil amendment, and other utilizations. Utilizations of Asteraceae biochars in wastewater treatment can be categorized by heavy metal ions, organic dyes, antibiotics, persistent organic pollutants (POPs), and explosive compounds. Some efforts were made to analyze the production cost, as well as the challenges and prospects of Asteraceae-based biochars.

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

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

Quantitative analysis on the mechanism of Cd2+ removal by MgCl2-modified biochar in aqueous solutions

In this study, a pristine biochar (BC) and MgCl₂-modified biochar (MBC) were prepared using Pennisetum sp. straw for removing Cd²⁺ from aqueous solutions. Scanning electron microscope (SEM) imaging combined with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), as well as the surface area and porosity analyses were used to reveal the physico-chemical characteristics of the pristine and modified adsorbents. Results suggested that MgCl₂ impregnation during the synthesis had enhanced the specific surface area and pore volume of the biochar. Batch adsorption experiments indicated that the Cd²⁺ adsorption data of MBC fitted the Langmuir isothermal and pseudo-second order kinetic models, indicating a chemical adsorption was undergoing in the system. The maximum adsorption capacity of Cd²⁺ on MBC was 763.12 mg/g, which was 11.15 times higher than that of the pristine BC. The Cd²⁺ removal by MBC was mainly attributed to the mechanisms in an order: Cd(OH)₂ precipitation (73.43%) > ion exchange (22.67%) > Cd²⁺-π interaction (3.88%), with negligible contributions from functional group complexation, electrostatic attraction and physical adsorption. The MBC could thus be used as a promising adsorbent for Cd²⁺ removal from aqueous solutions.

Biochar-amended coastal wetland soil enhances growth of Suaeda salsa and alters rhizosphere soil nutrients and microbial communities

Biochar has the potential to improve soil properties and increase plant productivity. However, due to the different types of soil, plants, and environmental factors, the impact of biochar is likely to vary. We explored the impacts of biochar prepared from an invasive plant Spartina alterniflora on plant performance and soil characteristics in a simulated coastal wetland ecosystem. We investigated the impact of three application ratios (control, 1%, and 5%; weight ratio) of biochar on the germination and growth of a native plant Suaeda salsa, the nutrient content and microbial community characteristics of the rhizosphere soil under three flooding treatments (no flooding, episodic flooding, and continuous flooding). Biochar application had no impact on seed germination of S. salsa, but promoted its seedling growth (biomass, height, root length) and nitrogen content. Biochar application also enhanced soil nutrient content and affected soil microbial community characteristics. Seed germination and seedling growth of S. salsa were sensitive to flooding and were the best under episodic flooding. Notably, flooding inhibited the impact of biochar on S. salsa and rhizosphere soil. In conclusion, biochar can positively affect the growth of S. salsa and improve the quality of rhizosphere soil, especially under no flooding. Our findings highlight the possibility of applying biochar for the restoration of S. salsa in coastal wetlands.

Characterization and Use of Char Produced from Pyrolysis of Post-Consumer Mixed Plastic Waste

In this work, the pyrolysis of post-consumer mixed plastic waste (polypropylene (PP), polystyrene (PS) and polyethylene film (PE)) is carried out. The solid product of the pyrolysis is characterized and tested for its use as adsorbent of lead present in aqueous media. The pyrolysis temperature has a great influence on the solid product yield, decreasing when the temperature increases. The highest yield to solid product obtained is from the pyrolysis of film at lower temperature (450 °C), reaching almost 14%. The results of product solid characterization reveal that the carbon, hydrogen and nitrogen content decreases with increasing pyrolysis temperature. Furthermore, both the ash and the volatile content are related to the pyrolysis temperature. The ash content is higher when the pyrolysis temperature is higher, while when the temperature increases, a solid product with lower volatile content is obtained. In respect to specific surface area, a higher pyrolysis temperature improves the properties of the solid product as an adsorbent. The adsorption capacity increases as the pyrolysis temperature increases, with the highest value of 7.91 mg/g for the solid obtained in the pyrolysis at 550 °C. In addition, adsorption capacity increases as the initial concentration of lead rises, reaching a maximum value close to 26 mg/g for an initial concentration of 40 mg/L. The Sips model is the one that best reproduces the experimental results of the adsorption process equilibrium study.

Synthesis, characterization and advanced sustainable applications of titanium dioxide nanoparticles: A review

Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields. Among nanoparticles (NPs), titanium dioxide (TiO₂) NPs have been widely used in daily life and can be synthesized through various physical, chemical, and green methods. Green synthesis is a non-toxic, cost-effective, and eco-friendly route for the synthesis of NPs. Plenty of work has been reported on the green, chemical, physical and biological synthesis of TiO₂ NPs and these NPs can be characterized through high tech. instruments. In the present review, dense data have been presented on the comparative synthesis of TiO₂ NPs with different characteristics and their wide range of applications. Among the TiO₂ NPs synthesis techniques, the green methods have been proven to be efficient than chemical synthesis methods because of the less use of precursors, time-effectiveness, and energy-efficiency during the green synthesis procedures. Moreover, this review describes the types of plants (shrubs, herbs and trees), microorganisms (bacteria, fungi and algae), biological derivatives (proteins, peptides, and starches) employed for the synthesis of TiO₂ NPs. The TiO₂ NPs can be effectively used for the treatment of polluted water and positively affected the plant physiology especially under abiotic stresses but the response varied with types, size, shapes, doses, duration of exposure, metal species along with other factors. This review also highlights the regulating features and future standpoints for the measurable enrichment in TiO₂ NPs product and perspectives of TiO₂ NPs reliable application.

Characterization and utilization of biochars derived from five invasive plant species Bidens pilosa L., Praxelis clematidea, Ipomoea cairica, Mikania micrantha and Lantana camara L. for Cd2+ and Cu2+ removal

Exotic invasive plants endanger the integrity of agricultural and natural systems throughout the world. Thus, the development of cost-effective and economic application of invasive plants is warranted. Here, we characterized fifteen biochars derived from five invasive plants at different temperatures (300, 500, and 700 °C) by determining their yield, ash content, pH, CEC, surface area, elementary composition, functional groups, and mineral composition. We conducted batch adsorption experiments to investigate the adsorption capacity and efficiency for Cd²⁺ and Cu²⁺ in wastewater. Our results suggest that all invasive plants are appropriate for biochar production, temperature and plant species had interacting effects on biochar properties, and the biochars pyrolyzed at 500 and 700 °C exhibited high metal adsorption capacity in neutral (pH = 7) solutions. The adsorption kinetics can be explained adequately by a pseudo-second-order model. BBC500 (Bidens pilosa L. derived biochar at 500 °C) and MBC500 (Mikania micrantha) exhibited higher metal equilibrium adsorption capacities (38.10 and 38.02 mg g^-1 for Cd²⁺, 20.01 and 20.10 mg g^-1 for Cu²⁺) and buffer abilities to pH than other biochars pyrolyzed at 500 °C. The Langmuir model was a better fit for IBC500 (Ipomoea cairica), MBC500, and LBC500 (Lantana camara L.) compared to the Freundlich model, whereas the opposite was true for BBC500 and PBC500 (Praxelis clematidea). These results suggest that the adsorption of metals by IBC500, MBC500, and LBC500 was mainly monolayer adsorption, while that by BBC500 and PBC500 was mainly chemical adsorption. Our results are important for the utilization and control of invasive plants as well as the decontamination of aqueous pollution.

Industrial alkali lignin-derived biochar as highly efficient and low-cost adsorption material for Pb(II) from aquatic environment

Developing a cost-effective and high-efficiency biochar is critical in various environmental applications. Lignin-based materials are natural and abundant adsorbents to heavy metals benefited from their special polyphenol structure and physicochemical properties. In this study, adsorption capacities to Pb(II) by alkali lignin (AL) and its biochar derivative (ALB) were comparatively discussed, and the latter exhibited superior adsorption performance, with a maximum adsorption capacity almost twice that of the former, and a much faster absorption rate. The q_m value of ALB was significantly superior to that of other reported biochar materials. Pb(II) was mainly adsorbed into ALB in three forms: mineral precipitation, ion exchange, and surface complexation, with complexation and mineral precipitation being the dominant mechanisms of adsorption. This study demonstrates that alkali-lignin derived biochar is a promising material for the remediation of polluted by Pb(II).

Improved Glucose Recovery from Sicyos angulatus by NaOH Pretreatment and Application to Bioethanol Production

As greenhouse gases and environmental pollution become serious, the demand for alternative energy such as bioethanol has rapidly increased, and a large supply of biomass is required for bioenergy production. Lignocellulosic biomass is the most abundant on the planet and a large part of it, the second-generation biomass, has the advantage of not being a food resource. In this study, Sicyos angulatus, known as an invasive plant (harmful) species, was used as a raw material for bioethanol production. In order to improve enzymatic hydrolysis, S. angulatus was pretreated with different NaOH concentration at 121 °C for 10 min. The optimal NaOH concentration for the pretreatment was determined to be 2% (w/w), and the glucan content (GC) and enzymatic digestibility (ED) were 46.7% and 55.3%, respectively. Through NaOH pretreatment, the GC and ED of S. angulatus were improved by 2.4-fold and 2.5-fold, respectively, compared to the control (untreated S. angulatus). The hydrolysates from S. angulatus were applied to a medium for bioethanol fermentation of Saccharomyces cerevisiae K35. Finally, the maximum ethanol production was found to be 41.3 g based on 1000 g S. angulatus, which was 2.4-fold improved than the control group.