Sorption of mercury (II) and atrazine by biochar, modified biochars and biochar based activated carbon in aqueous solution

Enhancing soil health, microbial count, and hydrophilic methomyl and hydrophobic lambda-cyhalothrin remediation with biochar and nano-biochar

Pesticide contamination and soil degradation present significant challenges in agricultural ecosystems, driving extensive exploration of biochar (BC) and nano-biochar (NBC) as potential solutions. This study examines their effects on soil properties, microbial communities, and the fate of two key pesticides: the hydrophilic methomyl (MET) and the hydrophobic lambda-cyhalothrin (LCT), at different concentrations (1%, 3%, and 5% w w-1) in agricultural soil. Through a carefully designed seven-week black bean pot experiment, the results indicated that the addition of BC/NBC significantly influenced soil dynamics. Soil pH and moisture content (MC) notably increased, accompanied by a general rise in soil organic carbon (SOC) content. However, in BC5/NBC5 treatments, SOC declined after the 2nd or 3rd week. Microbial populations, including total plate count (TPC), phosphate-solubilizing bacteria (PSB), and nitrogen-fixing bacteria (NFB), showed dynamic responses to BC/NBC applications. BC1/NBC1 and BC3/NBC3 applications led to a significant increase in microbial populations, whereas BC5/NBC5 treatments experienced a decline after the initial surge. Furthermore, the removal efficiency of both MET and LCT increased with higher BC/NBC concentrations, with NBC demonstrating greater efficacy than BC. Degradation kinetics, modeled by a first-order equation, revealed that MET degraded faster than LCT. These findings underscore the profound impact of BC/NBC on pesticide dynamics and microbial communities, highlighting their potential to transform sustainable agricultural practices.

Potential of GTL biosolids in a circular economy: investigating blending, pyrolysis, activation, and characterisation

Qatar's population has been rapidly increasing in recent years, and the country's long-term vision, QNV 2030, aims to sustain this growth by transforming the country into a sustainable state. One aspect of this vision is to convert waste into value-added products, which will reduce the environmental and spatial burden associated with waste in Qatar, while contributing to a circular economy. This study describes methods for producing biochar and activated carbon (AC) from gas-to-liquids derived biosolids, cardboard waste and mixed samples using pyrolysis and activation techniques. The characterisation of products revealed that the yield of biochar samples was higher than AC, and that the pH of the biochar samples was more alkaline than the feed samples due to metals after pyrolysis and reduced acid surface functional groups. Proximate analysis of samples showed lowered moisture and enhanced ash in feeds upon pyrolysis and activation due to increased temperature with reduced volatile content. AC application to water treatment is considered a potential benefit due to the increased surface area, pore volume and magnetic properties based on the Brunauer-Emmett-Teller (BET) and X-ray Powder Diffraction (XRD) analysis. The X-ray photoelectron spectroscopy (XPS) analysis also showed increased -CO3/O-C = O and potassium in the ACs as a result of potassium carbonate activation. The study proposes various applications that can support a circular economy, but future studies should investigate actual applications and potential health and environmental effects and evaluate the feasibility and environmental impact of production methods.

Physicochemical properties and performance of non-woody derived biochars for the sustainable removal of aquatic pollutants: A systematic review

Biochar is a carbon-rich material produced from the partial combustion of different biomass residues. It can be used as a promising material for adsorbing pollutants from soil and water and promoting environmental sustainability. Extensive research has been conducted on biochars prepared from different feedstocks used for pollutant removal. However, a comprehensive review of biochar derived from non-woody feedstocks (NWF) and its physiochemical attributes, adsorption capacities, and performance in removing heavy metals, antibiotics, and organic pollutants from water systems needs to be included. This review revealed that the biochars derived from NWF and their adsorption efficiency varied greatly according to pyrolysis temperatures. However, biochars (NWF) pyrolyzed at higher temperatures (400-800 °C) manifested excellent physiochemical and structural attributes as well as significant removal effectiveness against antibiotics, heavy metals, and organic compounds from contaminated water. This review further highlighted why biochars prepared from NWF are most valuable/beneficial for water treatment. What preparatory conditions (pyrolysis temperature, residence time, heating rate, and gas flow rate) are necessary to design a desirable biochar containing superior physiochemical and structural properties, and adsorption efficiency for aquatic pollutants? The findings of this review will provide new research directions in the field of water decontamination through the application of NWF-derived adsorbents.

The boom era of emerging contaminants: A review of remediating agricultural soils by biochar

Emerging contaminants (ECs) are widely sourced persistent pollutants that pose a significant threat to the environment and human health. Their footprint spans global ecosystems, making their remediation highly challenging. In recent years, a significant amount of literature has focused on the use of biochar for remediation of heavy metals and organic pollutants in soil and water environments. However, the use of biochar for the remediation of ECs in agricultural soils has not received as much attention, and as a result, there are limited reviews available on this topic. Thus, this review aims to provide an overview of the primary types, sources, and hazards of ECs in farmland, as well as the structure, functions, and preparation types of biochar. Furthermore, this paper emphasizes the importance and prospects of three remediation strategies for ECs in cropland: (i) employing activated, modified, and composite biochar for remediation, which exhibit superior pollutant removal compared to pure biochar; (ii) exploring the potential synergistic efficiency between biochar and compost, enhancing their effectiveness in soil improvement and pollution remediation; (iii) utilizing biochar as a shelter and nutrient source for microorganisms in biochar-mediated microbial remediation, positively impacting soil properties and microbial community structure. Given the increasing global prevalence of ECs, the remediation strategies provided in this paper aim to serve as a valuable reference for future remediation of ECs-contaminated agricultural lands.

Low-cost materials as vehicles for pesticides in aquatic media: a review of the current status of different biosorbents employed, optimization by RSM approach

Water contamination by pesticides is increasing dramatically due to population growth and the extensive use of pesticides in agriculture, leading to grave environmental and health concerns. Thus, efficient processes and the design and development of effective treatment technologies are required due to the enormous demand for fresh water. The adsorption approach has been widely used to remove organic contaminants such as pesticides because of its performance, less expense, high selectivity, and simplicity of operation compared to other treatment technologies. Among alternative adsorbents, biomaterials abundantly available for pesticide sorption from water resources have attracted the attention of researchers worldwide. The main objective of this review article is to (i) present studies on a wide range of raw or chemically modified biomaterials potentially effective in removing pesticides from aqueous media; (ii) indicating the effectiveness of biosorbents as green and low-cost materials for removing pesticides from wastewater; and (iii) furthermore, report the application of response surface methodology (RSM) for modeling and optimizing adsorption.

Fabrication of engineered biochar for remediation of toxic contaminants in soil matrices and soil valorization

Biochar has emerged as an efficacious green material for remediation of a wide spectrum of environmental pollutants. Biochar has excellent characteristics and can be used to reduce the bioavailability and leachability of emerging pollutants in soil through adsorption and other physico-chemical reactions. This paper systematically reviewed previous researches on application of biochar/engineered biochar for removal of soil contaminants, and underlying adsorption mechanism. Engineered biochar are derivatives of pristine biochar that are modified by various physico-chemical and biological procedures to improve their adsorption capacities for contaminants. This review will promote the possibility to expand the application of biochar for restoration of degraded lands in the industrial area or saline soil, and further increase the useable area. This review shows that application of biochar is a win-win strategy for recycling and utilization of waste biomass and environmental remediation. Application of biochar for remediation of contaminated soils may provide a new solution to the problem of soil pollution. However, these studies were performed mainly in a laboratory or a small scale, hence, further investigations are required to fill the research gaps and to check real-time applicability of engineered biochar on the industrial contaminated sites for its large-scale application.

Applications of engineered biochar in remediation of heavy metal(loid)s pollution from wastewater: Current perspectives toward sustainable development goals

Environmental pollution of heavy metal(loid)s (HMs) caused adverse impacts, has become one of the emerging concerns and challenges worldwide. Metal(loid)s can pose significant threats to living organisms even when present in trace levels within environmental matrices. Extended exposure to these substances can lead to adverse health consequences in humans. Removing HM-contaminated water and moving toward sustainable development goals (SDGs) is critical. In this mission, biochar has recently gained attention in the environmental sector as a green and alternative material for wastewater removal. This work provides a comprehensive analysis of the remediation of typical HMs by biochars, associated with an understanding of remediation mechanisms, and gives practical solutions for ecologically sustainable. Applying engineered biochar in various fields, especially with nanoscale biochar-aided wastewater treatment approaches, can eliminate hazardous metal(loid) contaminants, highlighting an environmentally friendly and low-cost method. Surface modification of engineered biochar with nanomaterials is a potential strategy that positively influences its sorption capacity to remove contaminants. The research findings highlighted the biochars' ability to adsorb HM ions based on increased specific surface area (SSA), heightened porosity, and forming inner-sphere complexes with oxygen-rich groups. Utilizing biochar modification emerged as a viable approach for addressing lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and chromium (Cr) pollution in aqueous environments. Most biochars investigated demonstrated a removal efficiency >90 % (Cd, As, Hg) and can reach an impressive 99 % (Pb and Cr). Furthermore, biochar and advanced engineered applications are also considered alternative solutions based on the circular economy.

Adsorption characteristics of S-Metolachlor onto the sawdust biochar derived from Acacia auriculiformis

The adsorption mechanism of S-Metolachlor in an aqueous solution by sawdust biochar derived from Acacia auriculiformis (SAB) was studied. SAB was manufactured at 500 °C for 4 h under oxygen-limited conditions and characterized for SEM, EDS, pHpzc, BET, and FTIR. The adsorption kinetics, isotherm, and diffusion studies of S-Metolachlor and SAB were further explored. Moreover, the effects of the solution pH were examined on the adsorption of S-Metolachlor by SAB. The BET analysis of SAB was achieved at 106.74 m2.g-1 and the solution pH did not significantly influence the S-Metolachlor adsorption. The adsorption data were fitted into a Langmuir isotherm and the PSO model. The film diffusion coefficient Df (4.93 × 10-11 to 8.17 × 10-11 m2.s-1) and the particle diffusion coefficient Dp (1.68 × 10-11 to 2.65 × 10-11 m2.s-1) were determined and the rate-limiting step of S-Metolachlor adsorption and SAB was governed by liquid film diffusion. The S-Metolachlor adsorption process onto SAB was controlled by multiple mechanisms, including pore filling, H-bonding, hydrophobic interaction, and π-π EDA interactions. H-bonding is the main interaction for the adsorption of S-Metolachlor and SAB. Conclusively, the study illustrates that biochar produced from Acacia auriculiformis sawdust possessed effective adsorption properties for S-Metolachlor herbicide.

Boosted simultaneous removal of chlortetracycline and Cu (II) by Litchi Leaves Biochar: Influence of pH, ionic strength, and background electrolyte ions

The coexistence of heavy metals and antibiotics in the environment always results in greater toxicity compared to the individual precursors. Therefore, efficient and economic technology for the simultaneous removal of antibiotics and heavy metals is essential. Herein, litchi leaves biochar carbonized at 550 °C (L550) demonstrated high efficiency in co-removal of CTC (1838.1 mmol/kg) and Cu (II) (1212.9 mmol/kg) within wide range of pH (pH 4-7). Ionic strength obviously enhanced the Cu (II) removal but showed no significant effect on CTC removal. Although Al3+ and HPO42- decreased the adsorption capacities of CTC and Cu (II) on L550, the coexistence of Na+, K+, Mg2+, Cl-, NO3-, CO32- and SO42- showed a negligible effect on the simultaneous removal of CTC and Cu (II). Moreover, the adsorption capacities of CTC and Cu (II) on L550 were excellent in the river water, tap water, and lake water. In addition to electrostatic interactions, ion exchange governed Cu (II) adsorption, while surface complexation played a key role in CTC adsorption on L550. Our results demonstrated that litchi leaves biochar could be a promising adsorbent for remediating multi-contaminated environments.

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.

Capacitive removal of Pb ions via electrosorption on novel willow biochar-manganese dioxide composites

Biochar derived from lignocellulosic biomass has been used as a low-cost adsorbent in wastewater treatment applications. Due to its rich porous structure and good electrical conductivity, biochar can be used as a cost-effective electrode material for capacitive deionization of water. In this work, willow biochar was prepared through carbonization of shrub willow chips, activated with potassium hydroxide, and loaded with manganese dioxide (WBC-K-MnO2 nanocomposite). The prepared materials were used to electrochemically adsorb Pb2+ from aqueous solutions. Under the applied potential of 1.0 V, the WBC-K-MnO2 electrode exhibited a high Pb2+ specific electrosorption capacity (23.3 mg/g) as compared to raw willow biochar (4.0 mg/g) and activated willow biochar (9.2 mg/g). KOH activation followed by MnO2 loading on the surface of raw biochar enhanced its BET surface area (178.7 m2/g) and mesoporous volume ratio (42.1%). Moreover, the WBC-K-MnO2 nanocomposite exhibited the highest specific capacitance value of 234.3 F/g at a scan rate of 5 mV/s. The electrosorption isotherms and kinetic data were well explained by the Freundlich and pseudo-second order models, respectively. The WBC-K-MnO2 electrode demonstrated excellent reusability with a Pb2+ electrosorption efficiency of 76.3% after 15 cycles. Thus, the WBC-K-MnO2 nanocomposite can serve as a promising candidate for capacitive deionization of heavy metal contaminated water.

Effective reducing the mobility and health risk of mercury in soil under thiol-modified biochar amendment

Soil mercury contamination poses health risks. However, effective immobilization techniques are lacking with challenges including low efficiency, limited long-term stability, susceptibility to multi-medium interference, and difficulty in controlling health risks. This study confirmed the feasibility of thiol-modified biochar, and elucidated the underlying mechanisms. Within 32 days of treatment, the leachable mercury decreased from 184.7 μg/L to below the hazardous waste threshold (100 μg/L, HJ/T299-2007, China). After 198 days of treatment, the soil achieved a safe ecological state with a mercury immobilization rate of 79.8-98.2% and a 50% reduction in available methylmercury. Thiol-modified biochar facilitated the conversion of active mercury species (exchangeable, carbonate, and oxide) into stable forms (organic and residual) through complexation and precipitation (e.g., HgS). Soil quality improvements were observed, including enhanced cation exchange capacity, available nitrogen, and total organic carbon. Thiol-modified biochar exhibits long-term effectiveness. After one and two years of treatment, the leachable mercury remained within acceptable health risk limit (hazard quotient < 1) for adults and children, respectively. After three years, the leachable mercury met the Level III groundwater quality standard (< 1 μg/L, GB 14848-2017, China). This study demonstrates an effective strategy for long-term diminishing mercury mobility and health risks in soil.

Tuning active sites on biochars for remediation of mercury-contaminated soil: A comprehensive review

Mercury (Hg) contamination is acknowledged as a global issue and has generated concerns globally due to its toxicity and persistence. Tunable surface-active sites (SASs) are one of the key features of efficient BCs for Hg remediation, and detailed documentation of their interactions with metal ions in soil medium is essential to support the applications of functionalized BC for Hg remediation. Although a specific active site exhibits identical behavior during the adsorption process, a systematic documentation of their syntheses and interactions with various metal ions in soil medium is crucial to promote the applications of functionalized biochars in Hg remediation. Hence, we summarized the BC's impact on Hg mobility in soils and discussed the potential mechanisms and role of various SASs of BC for Hg remediation, including oxygen-, nitrogen-, sulfur-, and X (chlorine, bromine, iodine)- functional groups (FGs), surface area, pores and pH. The review also categorized synthesis routes to introduce oxygen, nitrogen, and sulfur to BC surfaces to enhance their Hg adsorptive properties. Last but not the least, the direct mechanisms (e.g., Hg- BC binding) and indirect mechanisms (i.e., BC has a significant impact on the cycling of sulfur and thus the Hg-soil binding) that can be used to explain the adverse effects of BC on plants and microorganisms, as well as other related consequences and risk reduction strategies were highlighted. The future perspective will focus on functional BC for multiple heavy metal remediation and other potential applications; hence, future work should focus on designing intelligent/artificial BC for multiple purposes.

Waste biomass derived highly-porous carbon material for toxic metal removal: Optimisation, mechanisms and environmental implications

Toxic elements, lead, and copper are often found in wastewater discharged from industries such as mining. The discharge of untreated effluent poses severe environmental challenges and sorption methods using agricultural waste materials are proposed as an efficient and cost-effective solution. For this research, activated sunflower material (ASM) was prepared from abundantly available agricultural sunflower waste residues and utilised to remove Pb2+ and Cu2+ ions from an aqueous medium. To begin, we examine variables that may have an impact on the adsorption process, such as pH, contact time, adsorbent dose, and initial concentration using Box-Behnken Design (BBD) to find optimal conditions. Maximum removal efficiency was found at a pH of 5, contact time of 180 min, and initial concentration of 50 mg/L for Pb2+ and 150 mg/L for Cu2+. Additionally, adsorbent dose differed by element, for Cu2+ it was 200 mg, whilst for Pb2+ it was 124 mg. Features of activated carbon such as morphology, elemental composition, textural properties, and surface functionalities were characterised using SEM-EDS, BET, FTIR, and XPS. The adsorption equilibrium data were analysed by Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. It was found that the obtained results for Pb2+ adsorption were better described with the Freundlich isotherm model. Maximum adsorption capacities for Pb2+ and Cu2+ were 91.8 mg/g and 20.5 mg/g, respectively. Furthermore, kinetic studies confirmed that the adsorption process followed a pseudo-first-order kinetic model for Pb2+, but for Cu2+ all applied kinetic models fitted experimental data with the same values of the correlation coefficient (R2 = 0.99). After comprehensive analysis using the methods mentioned above, ASM was tested for the removal of Cu2+ from mining wastewater sample, and the obtained removal efficiency was 98.6% ± 2.0%. The results of desorption experiments conducted, confirm that ASM has good potential to be reused for the purpose of removing Cu2+ from wastewater.

A review of the next-generation biochar production from waste biomass for material applications

The development of carbonaceous materials such as biochar has triggered a hot spot in materials application. Carbon material derived from biomass could be a vital platform for energy storage and conversion. Biochar-based materials deliver a novel approach to deal with the current energy-related challenges. To design and utilize the maximum potential of biochar for environmentally sustainable applications, it is crucial to understand the recent progress and advancement in molecular structures of biochar to discover a new possible field to simplify structural application networks. However, most of the studies demonstrated the application of biochar in the form of soil enhancers and bio-adsorbents, reducing soil emissions of greenhouse gases and as fertilizers. The present review on biochar highlighted the application of biochar-based materials in various energy storage and conversion sectors, comprising different types of conversion technologies, biochar formation mechanisms, modification techniques on biochar surface chemistry and its functionality, catalysts, biochar application in energy storage gadgets such as supercapacitors and nanotubes, bio-based composite materials and inorganic based composites materials. Finally, this review addressed some vital outlooks on the prospect of the functionalization and best utilization of biochar-supported materials in numerous energy storage and conversion fields. After reviewing the literature, it was directed that advanced and in-depth research is essential for structural analysis and separation, considering the macroscopic and microscopic evidence of the formed structural design of biochar for specific applications.

Low-temperature biochar production from torrefaction for wastewater treatment: A review

Biochar, a carbon-rich and por ous material derived from waste biomass resources, has demonstrated tremendous potential in wastewater treatment. Torrefaction technology offers a favorable low-temperature biochar production method, and torrefied biochar can be used not only as a solid biofuel but also as a pollutant adsorbent. This review compares torrefaction technology with other thermochemical processes and discusses recent advancements in torrefaction techniques. Additionally, the applications of torrefied biochar in wastewater treatment (dyes, oil spills, heavy metals, and emerging pollutants) are comprehensively explored. Many studies have shown that high productivity, high survival of oxygen-containing functional groups, low temperature, and low energy consumption of dried biochar production make it attractive as an adsorbent for wastewater treatment. Moreover, used biochar's treatment, reuse, and safe disposal are introduced, providing valuable insights and contributions to developing sustainable environmental remediation strategies by biochar.

A review on adsorption of heavy metals from wastewater using carbon nanotube and graphene-based nanomaterials

The rampant rise in world population, industrialization, and urbanization expedite the contamination of water sources. The presence of the non-biodegradable character of heavy metals in waterways badly affects the ecological balance. In this modern era, the unavailability of getting clear water as well as the downturn in water quality is a major concern. Therefore, the effective removal of heavy metals has become much more important than before. In recent years, the attention to better wastewater remediation was directed towards adsorption techniques with novel adsorbents such as carbon nanomaterials. This review paper primarily emphasizes the fundamental concepts, structures, and unique surface properties of novel adsorbents, the harmful effects of various heavy metals, and the adsorption mechanism. This review will give an insight into the current status of research in the realm of sustainable wastewater treatment, applications of carbon nanomaterials, different types of functionalized carbon nanotubes, graphene, graphene oxide, and their adsorption capacity. The importance of MD simulations and density functional theory (DFT) in the elimination of heavy metals from aqueous media is also discussed. In addition to that, the effect of factors on heavy metal adsorption such as electric field and pressure is addressed.

Strategic use of crop residue biochars for removal of hazardous compounds in wastewater

Crop residues are affordable lignocellulosic waste in the world, and a large portion of the waste has been burned, releasing toxic pollutants into the environment. Since the crop residue is a carbon and ingredient rich material, it can be strategically used as a sorptive material for (in)organic pollutants in the wastewater after thermo-chemical valorization (i.e., biochar production). In this review, applications of crop residue biochars to adsorption of non-degradable synthetic dyes, antibiotics, herbicides, and inorganic heavy metals in wastewater were discussed. Properties (porosity, functional groups, heteroatom, and metal(oxide)s, etc.) and adsorption capacity relationships were comprehensively reviewed. The current challenges of crop residue biochars and guidelines for development of efficient adsorbents were also provided. In the last part, the future research directions for practical applications of the crop residue biochars in wastewater treatment plants have been suggested.

Remediation of pesticides contaminated water using biowastes-derived carbon rich biochar

The competition impact and feedstock type on the removal of water pesticides using biochar have not yet been sufficiently investigated. Therefore, here we investigated the potentiality of three different biochars (BCs) derived from rice husk (RHB), date pit (DPB), and sugarcane bagasse (SBB) biowastes for the simultaneous removal of ten pesticides from water in a competitive adsorption system. The BCs structural characterization and morphology were investigated by XRD, FTIR spectroscopy and SEM analysis. The potential adsorption mechanisms have been investigated using various isothermal and kinetic models. RHB showed the highest removal percentages (61% for atrazine/dimethoate and 97.6% for diuron/chlorfenvinphos) followed by DPB (56% for atrazine/dimethoate and 95.4% for diuron/chlorpyrifos) and then SBB (60.8% for atrazine/dimethoate and 90.8% for chlorpyrifos/malathion). The higher adsorption capacity of RHB and DPB than SBB can be due to their high total pore volume and specific surface area (SSA). Langmuir model described well the sorption data (R2 = 0.99). Adsorption equilibrium was achieved after 60 min for RHB, and 120 min for both DPB and SBB. The optimum adsorbent dose (g/L) was 10 for RHB and 4 for DPB and SBB. The removal efficiency of pesticides was enhanced by decreasing pH from 9 to 5 by RHB and to 3 by DPB and SBB. XRD and FTIR spectroscopy confirmed that BCs contain some active adsorption groups and metal oxides such as MgO, SiO, Al2O3, CaO, and TiO2 that can play an effective role in the pesticides sorption. BET-N2 adsorption analysis demonstrated that the BC pore size contributes significantly to pesticide adsorption. These findings indicate that RHB, DPB, and SBB have ability for adsorption of water pesticides even under acidic conditions. Therefore, the rice husk, date pit, and sugarcane bagasse biowastes could be pyrolyzed and reused as effective and low-cost sorbents for elimination of hazardous substances such as pesticides in the aqueous environments.

Experimental and Theoretical Estimations of Atrazine's Adsorption in Mangosteen-Peel-Derived Nanoporous Carbons

Nanoporous carbons were prepared via chemical and physical activation from mangosteen-peel-derived chars. The removal of atrazine was studied due to the bifunctionality of the N groups. Pseudo-first-order, pseudo-second-order, and intraparticle pore diffusion kinetic models were analyzed. Adsorption isotherms were also analyzed according to the Langmuir and Freundlich models. The obtained results were compared against two commercially activated carbons with comparable surface chemistry and porosimetry. The highest uptake was found for carbons with higher content of basic surface groups. The role of the oxygen-containing groups in the removal of atrazine was estimated experimentally using the surface density. The results were compared with the adsorption energy of atrazine theoretically estimated on pristine and functionalized graphene with different oxygen groups using periodic DFT methods. The energy of adsorption followed the same trend observed experimentally, namely the more basic the pH, the more favored the adsorption of atrazine. Micropores played an important role in the uptake of atrazine at low concentrations, but the presence of mesoporous was also required to inhibit the pore mass diffusion limitations. The present work contributes to the understanding of the interactions between triazine-based pollutants and the surface functional groups on nanoporous carbons in the liquid-solid interface.

Synthesizing sulfhydryl-functionalized biochar for effectively removing mercury ions from contaminated water

Biochar is regarded as an effective adsorbent for heavy metal pollution treatment, and functional optimization is still needed to improve its performance. We created raw biochar (BC and BP) from corn straw and pine sawdust, which were modified to produce sulfhydryl-modified biochar (MBC and MBP). Isothermal adsorption experiments and adsorption kinetics experiments as well as the related model fitting were performed to evaluate the adsorption performance of biochar on Hg(II). According to the results of the Langmuir model fitting, the maximum adsorption capacities of sulfhydryl-modified biochar were 193.05 mg/g (MBC) and 178.04 mg/g (MBP), respectively, which were approximately 1.6 times higher than the raw biochar. The results showed that adding sulfhydryl groups to biochar can improve its adsorption performance. The prompt effect resulted from the sulfhydryl modification providing additional functional groups and enhanced chemisorption and physical adsorption properties.

Adsorption kinetics and mechanism of atrazine on iron-modified algal residue biochar in the presence of soil

Atrazine has been widely used as an herbicide, and its harm has attracted more and more attention. In this study, magnetic algal residue biochar (MARB) was prepared from algae residue, a by-product of aquaculture, by ball milling it with ferric oxide to study the adsorption and removal of the triazine herbicide atrazine in a soil medium. The adsorption kinetics and isotherm results showed that atrazine removal by MARB reached 95.5% within 8 h at a concentration of 10 mg·L^-1, but the removal rate dropped to 78.4% in the soil medium. The pseudo-first- and pseudo-second-order kinetics and Langmuir isotherms best described atrazine adsorption on MARB. It is estimated that the maximum adsorption capacity of MARB can reach 10.63 mg·g^-1. The effects of pH, humic acids, and cations on the adsorption performance of MARB for atrazine were also studied. When pH was 3, the adsorption capacity of MARB was twice that of other pHs. Only in the presence of 50 mg·L^-1 HA and 0.1 mol·L^-1 NH₄⁺, Na, and K, the adsorption capacity of MARB to AT decreased by 8% and 13%, respectively. The results showed that MARB had a stable removal profile over a wide range of conditions. The adsorption mechanisms involved multiple interaction forms, among which the introduction of iron oxide promoted hydrogen bonding formation and π-π interactions by enriching -OH and -COO on the surface of MARB. Overall, the magnetic biochar prepared in this study can be used as an effective adsorbent to remove atrazine in complex environments and is ideal for algal biomass waste treatment and environmental governance.^+.

Activation methods increase biochar's potential for heavy-metal adsorption and environmental remediation: A global meta-analysis

Removal of heavy metals (HMs) by adsorption on biochar's surface has shown promising results in the remediation of contaminated soil and water. The adsorption capacity of biochar can be altered by pre- or post-pyrolysis activation; however, the effect of activation methods on biochar's adsorption capacity varies widely. Here, we conducted a meta-analysis to identify the most effective methods for activation to enhance HM removal by biochar using 321 paired observations from 50 published articles. Activation of biochar significantly improves the adsorption capacity and removal efficiency of HMs by 136 and 80 %, respectively. This study also attempts to find suitable feedstocks, pyrolysis conditions, and physicochemical properties of biochar for maximizing the effect of activation of biochar for HMs adsorption. Activation of agricultural wastes and under pyrolysis temperatures of 350-550 °C produces biochars that are the most effective for HM adsorption. Activation of biochars with a moderate particle size (0.25-0.80 mm), low N/C (<0.01) and H/C ratios (<0.03), and high surface area (> 100 m² g^-1) and pore volume (> 0.1 cm³ g^-1) are the most desirable characteristics for enhancing HM adsorption. We conclude that pre-pyrolysis activation with metal salts/oxides was the most effective method of enhancing biochar's potential for adsorption and removal of a wide range of HMs. The results obtained from this study can be helpful in choosing appropriate methods of activations and the suitable choice of feedstocks and pyrolysis conditions. This will maximize HM adsorption on biochar surfaces, ultimately benefiting the remediation of contaminated environments.

Na4P2O7-Modified Biochar Derived from Sewage Sludge: Effective Cu(II)-Adsorption Removal from Aqueous Solution

With the rapid development of industrialization, the amount of copper-containing wastewater is increasing, thereby posing a threat to the aquatic ecological environment and human health. Sludge biochar has received extensive concern in recent years due to its advantages of low cost and sustainability for the treatment of heavy-metal-containing wastewater. However, the heavy-metal-adsorption capacity of sludge biochar is limited. This study prepared a sodium pyrophosphate- (Na4P2O7-) modified municipal sludge-based biochar (SP-SBC) and evaluated its adsorption performance for Cu(II). Results showed that SP-SBC had higher yield, ash content, pH, Na and P content, and surface roughness than original sewage sludge biochar (SBC). The Cu(II)-adsorption capacity of SP-SBC was 4.55 times than that of SBC at room temperature. For Cu(II) adsorption by SP-SBC, the kinetics and isotherms conformed to the pseudo-second-order model and the Langmuir–Freundlich model, respectively. The maximum adsorption capacity of SP-SBC was 38.49 mg·g−1 at 35°C. Cu(II) adsorption by SP-SBC primarily involved ion exchange, electrostatic attraction, and precipitation. The desired adsorption performance for Cu(II) in the fixed-bed column experiment indicated that SP-SBC can be reused and had good application potential to treat copper-containing wastewater. Overall, this study provided a desirable sorbent (SP-SBC) for Cu(II) removal, as well as a new simple chemical-modification method for SBC to enhance Cu(II)-adsorption capacity.

Biochar for the Removal of Emerging Pollutants from Aquatic Systems: A Review

Water contaminated with emerging pollutants has become a serious environmental issue globally. Biochar is a porous and carbon-rich material produced from biomass pyrolysis and has the potential to be used as an integrated adsorptive material. Many studies have shown that biochar is capable to adsorb emerging pollutants from aquatic systems and could be used to solve the water pollution problem. Here, we provided a dual perspective on removing emerging pollutants from aquatic systems using biochar and analyzed the emerging pollutant removal efficiency from the aspects of biochar types, pollutant types and coexistence with heavy metals, as well as the associated mechanisms. The potential risks and future research directions of biochar utilization are also presented. This review aims to assist researchers interested in using biochar for emerging pollutants remediation in aquatic systems and facilitate research on emerging pollutants removal, thereby reducing their environmental risk.

Insight into atrazine removal by fallen leaf biochar prepared at different pyrolysis temperatures: Batch experiments, column adsorption and DFT calculations

The environmental pollution caused by atrazine in the agricultural production cannot be ignored. In this study, the fallen leaf biochar (LBC) was prepared at three different temperatures (500 °C, 600 °C, and 700 °C) using a simple pyrolysis method (500 LBC, 600 LBC, and 700 LBC) for atrazine adsorption. Batch experiments showed that the performance of LBC in atrazine adsorption improved with rising pyrolysis temperature, and the highest adsorption amount of 700 LBC reached 84.32 mg g^-1. Kinetic and isotherm models showed that the adsorption behaviors were both monolayer and multilayer chemisorption. The findings of the characterizations (Elemental analysis, BET, XRD, Raman, FT-IR, and XPS) confirmed that the degree of aromatization determined the adsorption capacity of LBC to atrazine, and π-π electron donor-acceptor interaction was the main adsorption mechanism. Density functional theory (DFT) calculations showed that the highly aromatized biochar was more effective for atrazine adsorption, manifested as smaller molecular distances, higher adsorption energies, more stable complex structures, and stronger π-electron conjugation. In the column adsorption experiments, reducing the inlet flow rate or increasing the bed height extended the breakthrough time and exhaustion time of the breakthrough curves, and 700 LBC still showed good adsorption performance after five cycles. Overall, fallen leaf biochar as a reuse product of resource showed good potential for application in atrazine adsorption, which can be used for atrazine-contaminated water remediation.

Biochar-plant interaction and detoxification strategies under abiotic stresses for achieving agricultural resilience: A critical review

The unpredictable climatic perturbations, the expanding industrial and mining sectors, excessive agrochemicals, greater reliance on wastewater usage in cultivation, and landfill leachates, are collectively causing land degradation and affecting cultivation, thereby reducing food production globally. Biochar can generally mitigate the unfavourable effects brought about by climatic perturbations (drought, waterlogging) and degraded soils to sustain crop production. It can also reduce the bioavailability and phytotoxicity of pollutants in contaminated soils via the immobilization of inorganic and/or organic contaminants, commonly through surface complexation, electrostatic attraction, ion exchange, adsorption, and co-precipitation. When biochar is applied to soil, it typically neutralizes soil acidity, enhances cation exchange capacity, water holding capacity, soil aeration, and microbial activity. Thus, biochar has been was widely used as an amendment to ameliorate crop abiotic/biotic stress. This review discusses the effects of biochar addition under certain unfavourable conditions (salinity, drought, flooding and heavy metal stress) to improve plant resilience undergoing these perturbations. Biochar applied with other stimulants like compost, humic acid, phytohormones, microbes and nanoparticles could be synergistic in some situation to enhance plant resilience and survivorship in especially saline, waterlogged and arid conditions. Overall, biochar can provide an effective and low-cost solution, especially in nutrient-poor and highly degraded soils to sustain plant cultivation.

Biochar application for remediation of organic toxic pollutants in contaminated soils; An update

Bioremediation of organic contaminants has become a major environmental concern in the last few years, due to its bio-resistance and potential to accumulate in the environment. The use of diverse technologies, involving chemical and physical principles, and passive uptake utilizing sorption using ecofriendly substrates have drawn a lot of interest. Biochar has got attention mainly due to its simplicity of manufacturing, treatment, and disposal, as it is a less expensive and more efficient material, and has a lot of potential for the remediation of organic contaminants. This review highlighted the adverse impact of persistent organic pollutants on the environment and soil biota. The utilization of biochar to remediate soil and contaminated compounds i.e., pesticides, polycyclic aromatic hydrocarbons, antibiotics, and organic dyes has also been discussed. The soil application of biochar has a significant impact on the biodegradation, leaching, and sorption/desorption of organic contaminants. The sorption/desorption of organic contaminants is influenced by chemical composition and structure, porosity, surface area, pH, and elemental ratios, and surface functional groups of biochar. All the above biochar characteristics depend on the type of feedstock and pyrolysis conditions. However, the concentration and nature of organic pollutants significantly alters the sorption capability of biochar. Therefore, the physicochemical properties of biochar and soils/wastewater, and the nature of organic contaminants, should be evaluated before biochar application to soil and wastewater. Future initiatives, however, are needed to develop biochars with better adsorption capacity, and long-term sustainability for use in the xenobiotic/organic contaminant remediation strategy.

Designer biochar with enhanced functionality for efficient removal of radioactive cesium and strontium from water

Radioactive elements released into the environment by accidental discharge constitute serious health hazards to humans and other organisms. In this study, three gasified biochars prepared from feedstock mixtures of wood, chicken manure, and food waste, and a KOH-activated biochar (40% food waste + 60% wood biochar (WFWK)) were used to remove cesium (Cs⁺) and strontium (Sr²⁺) ions from water. The physicochemical properties of the biochars before and after adsorbing Cs⁺ and Sr²⁺ were determined using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, extended X-Ray absorption fine structure (EXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). The WFWK exhibited the highest adsorption capacity for Cs⁺ (62.7 mg/g) and Sr²⁺ (43.0 mg/g) among the biochars tested herein. The removal of radioactive ¹³⁷Cs and ⁹⁰Sr exceeded 80% and 47%, respectively, in the presence of competing ions like Na⁺ and Ca²⁺. The functional groups present in biochar, including -OH, -NH₂, and -COOH, facilitated the adsorption of Cs⁺ and Sr²⁺. The Cs K-edge EXAFS spectra revealed that a single coordination shell was assigned to the Cs-O bonding at 3.11 Å, corresponding to an outer-sphere complex formed between Cs and the biochar. The designer biochar WFWK may be used as an effective adsorbent to treat radioactive ¹³⁷Cs- and ⁹⁰Sr-contaminated water generated during the operation of nuclear power plants and/or unintentional release, owing to the enrichment effect of the functional groups in biochar via alkaline activation.

Impact of sulfur-impregnated biochar amendment on microbial communities and mercury methylation in contaminated sediment

S-impregnation of biochar through elemental S streaming is known to increase its sorption performance against Hg and methyl mercury (MeHg). However, the effects of %S-loading on biochar's mechanism and sorption capacities for MeHg, and its consequent impact when used as an amendment material for Hg-contaminated sediments, are poorly understood, and thus, were investigated in this work. Our results showed that a minimum sulfur loading of 1% was the most effective in reducing MeHg levels in sediments. At higher %S-loading (3-20%), the reduction in surface area, pore blockage due to unreacted sulfur particles, and presence of poorly bound sulfur species resulted in lowered effectiveness for MeHg control. Increasing S-functionalization during impregnation shifted the sorption process of MeHg from Hg-O to Hg-S in S-impregnated biochar (BCS). Our 60-day slurry experiment showed a significant reduction in pore water THg (40-70%) and MeHg (30-55%), as well as sediment MeHg (50-60%) in biochar-amended sediments. The reduction in the bioavailable Hg resulted in lowered Hg methylation, as supported by the suppression of both the Fe- and SO₄^2--reduction activities in the amended sediments. The microbial community structure in BCS-amended sediments showed a shift towards sulfur-consuming, iron-reducing, thiosulfate-oxidizing, and sulfate-reducing bacterial populations. At the genus level, the overall relative abundance of principal Hg methylators was also lower in the BCS treatment than in the unamended sediments. This study highlights the application of BCS as a promising strategy for remediation of Hg-contaminated sediments.

Nanoporous biochar with high specific surface area based on rice straw digestion residue for efficient adsorption of mercury ion from water

The unreasonable disposal of residue after anaerobic digestion seriously affects the stability of the ecosystem, and the preparation of adsorbent is an effective way to value-added utilization of the residue. In this study, a high adsorption capacity (209.65 mg/g) biochar-based adsorbent was prepared by hydrothermal carbonization and alkali modification using rice straw biogas residue. The lignocellulosic structure was destroyed after anaerobic digestion, forming porous biochar with larger specific surface area (2372.51 m²/g) and richer pore structure. Besides, the mercury ion complexed on the adsorbent surface in monovalent and divalent forms and possessed favorable selectivity in the presence of other examples of interference. The adsorption process is consistent with pseudo second-order kinetics and the Langmuir isotherm, indicating a predominance of chemisorption. This study provides a methodology for use of rice straw biogas residue and treatment of mercury containing wastewater, which offers a fresh direction for resource utilization of biogas residue.

Reclaimable MoS2 Sponge Absorbent for Drinking Water Purification Driven by Solar Energy

With the fast development of modern industries, scarcity of freshwater resources caused by heavy metal pollution (i.e., Hg²⁺) has become a severe issue for human beings. Herein, a 3D-MoS₂ sponge as an excellent absorbent is fabricated for mercury removal due to its multidimensional adsorption pathways, which decreases the biomagnification effect of methylmercury in water bodies. Furthermore, a secondary water purification strategy is employed to harvest drinkable water with the exhausted adsorbents, thus alleviating the crisis of drinking water shortage. Compared to the conventional landfill treatment, the exhausted MoS₂ sponge absorbents are further functionalized with a poly(ethylene glycol) (PEG) layer to prevent the heavy metals from leaking and enhance the hydrophilicity for photothermal conversion. The fabricated evaporator displays excellent evaporation rates of ∼1.45 kg m^-2 h^-1 under sunlight irradiation and produces freshwater with Hg²⁺ under the WHO drinking water standard at 0.001 mg L^-1. These results not only assist in avoiding the biodeposition effect of mercury in water but also provide an environment-friendly strategy to recycle hazardous adsorbents for water purification.

Mercury Removal from Contaminated Water by Wood-Based Biochar Depends on Natural Organic Matter and Ionic Composition

Biochars can remove potentially toxic elements, such as inorganic mercury [Hg(II)] from contaminated waters. However, their performance in complex water matrices is rarely investigated, and the combined roles of natural organic matter (NOM) and ionic composition in the removal of Hg(II) by biochar remain unclear. Here, we investigate the influence of NOM and major ions such as chloride (Cl^-), nitrate (NO₃^-), calcium (Ca²⁺), and sodium (Na⁺) on Hg(II) removal by a wood-based biochar (SWP700). Multiple sorption sites containing sulfur (S) were located within the porous SWP700. In the absence of NOM, Hg(II) removal was driven by these sites. Ca²⁺ bridging was important in enhancing removal of negatively charged Hg(II)-chloro complexes. In the presence of NOM, formation of soluble Hg-NOM complexes (as seen from speciation calculations), which have limited access to biochar pores, suppressed Hg(II) removal, but Cl^- and Ca²⁺ could still facilitate it. The ability of Ca²⁺ to aggregate NOM, including Hg-NOM complexes, promoted Hg(II) removal from the dissolved fraction (<0.45 μm). Hg(II) removal in the presence of Cl^- followed a stepwise mechanism. Weakly bound oxygen functional groups in NOM were outcompeted by Cl^-, forming smaller-sized Hg(II)-chloro complexes, which could access additional intraparticle sorption sites. Therein, Cl^- was outcompeted by S, which finally immobilized Hg(II) in SWP700 as confirmed by extended X-ray absorption fine structure spectroscopy. We conclude that in NOM containing oxic waters, with relatively high molar ratios of Cl^-: NOM and Ca²⁺: NOM, Hg(II) removal can still be effective with SWP700.

Adsorption Characteristics and Mechanisms of Fe-Mn Oxide Modified Biochar for Pb(II) in Wastewater

This study prepared iron-manganese oxide-modified biochar (FM-BC) by impregnating rice straw biochar (BC) with a mixed solution of ferric nitrate and potassium permanganate. The effects of pH, FM-BC dosage, interference of coexisting ions, adsorption time, incipient Pb(II) concentration, and temperature on the adsorption of Pb(II) by FM-BC were investigated. Moreover, the Pb(II) adsorption mechanism of FM-BC was analyzed using a series of characterization techniques. The results showed that the Fe-Mn oxide composite modification significantly promoted the physical and chemical functions of the biochar surface and the adsorption capacity of Pb(II). The specific surface area of FM-BC was 18.20 times larger than that of BC, and the maximum Pb(II) adsorption capacity reached 165.88 mg/g. Adsorption kinetic tests showed that the adsorption of Pb(II) by FM-BC was based on the pseudo-second-order kinetic model, which indicated that the adsorption process was mainly governed by chemical adsorption. The isothermal adsorption of Pb(II) by FM-BC conformed to the Langmuir model, indicating that the adsorption process was spontaneous and endothermic. Characterization analyses (Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy) showed that the adsorption mechanism of Pb(II) by FM-BC was mainly via electrostatic adsorption, chemical precipitation, complexation, ion exchange, and the transformation of Mn₂O₃ into MnO₂. Therefore, FM-BC is a promising adsorbent for Pb(II) removal from wastewater.

Biochars and activated carbons as adsorbents of inorganic and organic compounds from multicomponent systems - A review

Biochars are obtained by biomass pyrolysis, whereas activated carbon is a biochar that has undergone chemical or physical activation. Owing to the large surface area and easy surface modification both solids are widely applied as adsorbents. They are low-costs materials, they could be regenerated and their disposal is not troublesome. Adsorption of heavy metals, dyes, pharmaceuticals on the surface of biochars and activated carbons, from simple systems of adsorbate containing only one compound, are described extensively in the literature. The present paper provides an overview of reports on adsorption of inorganic and organic compounds onto these two types of adsorbents from the mixed adsorbate systems. The described adsorbate systems have been divided into those consisting of: two or more inorganic ions, two or more organic compounds and both of them (inorganic and organic ones). The research of this type is carried out much less frequently due to the more complicated description of interactions in the mixed adsorbate systems.

Preparation of biochar from constructed wetland plant and its adsorption performance towards Cu2

In order to solve problems in the treatment and disposal of huge production of artificial wetland plants and heavy metal pollution, two constructed wetland plants of reed and gladiolus were selected as raw materials to prepare biochar for adsorbing heavy metals from aqueous solutions. The experimental results showed that reed biochar prepared at 600℃ and activated by KOH with an impregnation ratio of 1:3 (KRAC-3) exhibited relatively high adsorption ability towards Cu²⁺. The optimal results analyzed by Design-Expert software showed that the maximum adsorption rate of KRAC-3 towards Cu²⁺ was obtained under the optimal conditions of adsorbent dosage of 1.2 g/L, pH of 4.96, and reaction time of 137.43 min. The adsorption of Cu²⁺ followed pseudo-second-order kinetics and the Langmuir adsorption model. The theoretical maximum adsorption capacity of KRAC-3 calculated from the Langmuir isotherm model was 148.08 mg/g. Microscopic tests with the help of SEM, EDS, and XRD revealed that physical adsorption, ion exchange, electrostatic adsorption, surface complexation, and precipitation were the main adsorption mechanism of Cu²⁺ loading onto KRAC-3. This study will provide a theoretical basis for the application of biochar prepared from constructed wetland plants and the treatment of heavy metal-containing wastewater.

Mercury Removal from Water Using a Novel Composite of Polyacrylate-Modified Carbon

The contamination of groundwater by mercury (Hg) is a serious global threat, and its removal is of great importance. Activated carbon (AC) is considered a very promising adsorbent to remove Hg from water systems. However, specific functional groups can be added to AC to enhance its adsorption efficiency. In this work, AC was synthesized from palm shells and grafted with a copolymer of acrylamide and methacrylic acid to produce a polyacrylate-modified carbon (PAMC) composite. The synthesized adsorbent (PAMC) was characterized by Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), electron dispersive X-ray (EDX) spectroscopy, and Brunauer-Emmett-Teller (BET) analysis. PAMC was then evaluated for Hg removal from aqueous solutions, and the adsorption efficiency was optimized under several parameters (pH, contact time, and PAMC dosage). Kinetic, isotherm, and thermodynamic investigations were performed to gain a further understanding of the adsorption properties. The adsorption data were best fitted by pseudo-second-order and Redlich-Peterson models. Also, the thermodynamic investigation confirmed the spontaneity and the endothermic nature of the Hg adsorption process over PAMC. The maximum adsorption capacity (q _m) of PAMC was found to be 76.3 mg/g ,which is relatively higher than some activated carbon-based adsorbents. Therefore, PAMC offers a potential promise for wastewater treatment due to its fast and high uptake removal capacity in addition to the cheap and environmentally friendly activated carbon source.

Effective removal of Hg(II) and MeHg from aqueous environment by ball milling aided thiol-modification of biochars: Effect of different pyrolysis temperatures

In order to synthesize biochar with the enhanced adsorption of inorganic mercury (Hg(II)) and organic mercury (Methylmercury, MeHg), biochars pyrolyzed at different pyrolysis temperatures (300, 500, and 700 °C) were ball milled with 3-trimethoxysilylpropanethiol (3-MPTS). Characterization results showed that 3-MPTS acted as an activator which further enlarged pores in biochars and ball-milling increased surface area of biochars. During ball milling, oxygen-containing functional groups increased which facilitated the loading of -SH group. The maximum adsorption capacities for Hg(II) adsorption in ball mill sulfhydryl modified biochars of 300, 500, and 700 °C were 401.8, 379.6 and 270.6 mg/g, respectively; simultaneously, the maximum adsorption capacity of MeHg was 108.16, 85.27 and 39.14 mg/g, respectively, which showed preferential increasing of 5.54 times on MeHg compared to the non-thiol modified biochar at low pyrolysis temperature of 300 °C. Results of kinetic adsorption experiments suggested that sorption data fitted well with Pseudo-second-order kinetic model, which proved that the mainly rate-limiting adsorption step was surface diffusion. Langmuir isotherm model fitting result showed that ligand exchange, surface complexation, surface adsorption and electrostatic attraction are dominant removal mechanisms. The 3-MPTS content and ball milling time are crucial during ball milling, and 2% 3-MPTS and 30 h of ball milling were found to be the most suitable conditions for both Hg(II) and MeHg adsorption. The result suggests that ball milling aided thiol-modification has great potential in synthesis of -SH modified biochar with prioritized MeHg adsorption.

Adsorbent selection for pesticides removal from drinking water

Pesticides present in water resources can cause adverse health effects even in low concentrations, due to their bio-accumulative character. Therefore, the challenge for drinking water production increases, due to the limitations of conventional water treatment technologies in the removal of small molecular weight dissolved compounds. This work aimed to provide technical and scientific support for the selection of pulverized activated carbon - PACs, granular activated carbon - GACs, and carbon nanotubes - CNT concerning atrazine - ATZ, simazine - SMZ, and diuron - DIU adsorption for application in water treatment plants, considering two forms of application commercial product - CP and analytical standard - SD. These forms of application were tested aiming to verify the influence of the purity of the products used in experiments on the adsorption efficiency. It was possible to verify the adsorption efficiencies were not guided only by the characteristics of the adsorptive materials used, and that the selection should not be carried out only based on the, specific superficial area - BET size and distribution of specific pore volume. The isotherms demonstrated that the parameter Kf associated with the results of the selection experiment can be considered an alternative technical tool of simple application and sufficient for this purpose. Also, the capacity of activated carbons - ACs and nanomaterials - NMs were affected by the application of the compounds, highlighting the importance of using commercial product - CP in scientific research and technical investigations.Hightlights The pesticides efficiency removal was affected due to the forms of application, SD and CP;The parameters IN and MBI were not decisive in the selection of the activated carbon;The main adsorption mechanism in all the materials was chemical;GAC was the most efficient adsorbent in the removal of the pesticides;An adequate adsorbent selection is crucial for satisfactory removal of pesticides in water.

Biomass Carbon Magnetic Adsorbent Constructed by One-Step Activation Method for the Removal of Hg0 in Flue Gas

Elemental mercury (Hg⁰) emission from industrial boilers equipped in factories such as coal-fired power plants poses serious hazards to the environment and human health. Herein, an iron-modified biomass carbon (Fe/BC) magnetic adsorbent was prepared by a one-step method using pepper straw waste as raw material and potassium oxalate and ferric nitrate as activator and catalyst precursor, respectively. A fixed-bed reactor was used to evaluate the Hg⁰ removal performance of the Fe/BC adsorbent. The synthesized adsorbent showed a wide temperature window for Hg⁰ removal. In a N₂ + O₂ atmosphere, the removal efficiency toward Hg⁰ was 97.6% at 150 °C. Further, O₂ or SO₂ could promote the removal of Hg⁰, while NO could inhibit the conversion of Hg⁰ over the Fe/BC adsorbent. The consequence of XPS and Hg-TPD showed that lattice oxygen in Fe₂O₃ and chemisorbed oxygen were the main active sites for Hg⁰ removal, and HgO was the main mercury species on used Fe/BC. Moreover, Fe/BC adsorbent showed a good regeneration and magnetization performance, which was conducive to the cost reduction of actual industrial application. This study provides a facile approach for efficient removal of Hg⁰ using biomass-derived carbon material.

Does biochar application in heavy metal-contaminated soils affect soil micronutrient dynamics?

Biochar has been practically used as a soil conditioner in degraded or contaminated soils. Whether biochar would simultaneously affect soil micronutrient bioavailability in heavy metal-contaminated soils warrants research. A 90-d incubation of rice straw biochar with either Pb- or Cd-contaminated soils was conducted to investigate the biochar effect on Fe, Mn, Cu and Zn bioavailability. Biochar amendment decreased the DTPA-extractable, acid extractable and reducible Pb and Cd but increased the oxidizable and residual Pb and Cd. It decreased the DTPA-extractable Fe by 73.8% and 23.1% but increased the DTPA-extractable Mn by 9.8% and 44.3% in the neutral and acidic soil, respectively. The lower Fe availability was attributed to the liming effect and the increased numbers of oxygen-containing groups and organic-mineral phases of biochar over time. Biochar amendment increased soil bacterial richness and diversity in both soils. Rice straw biochar can effectively immobilize heavy metals and reduce soil Fe bioavailability but increase Mn bioavailability, which would potentially affect soil micronutrient fertility and productivity.

Triazine-Based Functionalized Activated Carbon Prepared from Water Hyacinth for the Removal of Hg2+, Pb2+, and Cd2+ Ions from Water

A novel chelating adsorbent, based on the functionalization of activated carbon (AC) derived from water hyacinth (WH) with melamine thiourea (MT) to form melamine thiourea-modified activated carbon (MT-MAC), is used for the effective removal of Hg2+, Pb2+, and Cd2+ from aqueous solution. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) theory confirm the successful functionalization of AC with the melamine thiourea chelating ligand through the amidation reaction between the carboxyl groups of oxidized activated carbon (OAC) and the amino groups of melamine thiourea (MT) in the presence of dicyclohexylcarbodiimide (DCC) as a coupling agent. The prepared MT-MAC exhibited extensive potential for the adsorption of the toxic metal ions Hg2+, Pb2+, and Cd2+ from wastewater. The MT-MAC showed high capacities for the adsorption of Hg2+ (292.6 mg·g-1), Pb2+ (237.4 mg·g-1), and Cd2+ (97.9 mg·g-1) from aqueous solution. Additionally, 100% removal efficiency of Hg2+ at pH 5.5 was observed at very low initial concentrations (25-1000 ppb).The experimental sorption data could be fitted well with the Langmuir isotherm model, suggesting a monolayer adsorption behavior. The kinetic data of the chemisorption mechanism realized by the melamine thiourea groups grafted onto the activated carbon surface have a perfect match with the pseudo-second-order (PSO) kinetic model. In a mixed solution of metal ions containing 50 ppm of each ion, MT-MAC showed a removal of 97.0% Hg2+, 68% Pb2+, 45.0% Cd2+, 17.0% Cu2+, 7.0% Ni2+, and 5.0% Zn2+. Consequently, MT-MAC has exceptional selectivity for Hg2+ ions from the mixed metal ion solutions. The MT-MAC adsorbent showed high stability even after three adsorption-desorption cycles. According to the results obtained, the use of the MT-MAC adsorbent for the adsorption of Pb2+, Hg2+, and Cd2+ metal ions from polluted water is promising.

Modification of naturally abundant resources for remediation of potentially toxic elements: A review

Water and soil contamination due to potentially toxic elements (PTEs) represents a critical threat to the global ecosystem and human health. Naturally abundant resources have significant advantages as adsorbent materials for environmental remediation over manufactured materials such as nanostructured materials and activated carbons. These advantages include cost-effectiveness, eco-friendliness, sustainability, and nontoxicity. In this review, we firstly compare the characteristics of representative adsorbent materials including bentonite, zeolite, biochar, biomass, and effective modification methods that are frequently used to enhance their adsorption capacity and kinetics. Following this, the adsorption pathways and sites are outlined at an atomic level, and an in-depth understanding of the structure-property relationships are provided based on surface functional groups. Finally, the challenges and perspectives of some emerging naturally abundant resources such as lignite are examined. Although both unamended and modified naturally abundant resources face challenges associated with their adsorption performance, cost performance, energy consumption, and secondary pollution, these can be tackled by using advanced techniques such as tailored modification, formulated mixing and reorganization of these materials. Recent studies on adsorbent materials provide a strong foundation for the remediation of PTEs in soil and water. We speculate that the pursuit of effective modification strategies will generate remediation processes of PTEs better suited to a wider variety of practical application conditions.