Effects of the biochar aromaticity and molecular structures of the chlorinated organic compounds on the adsorption characteristics

Agri-food waste biosorbents for volatile organic compounds removal from air and industrial gases - A review

Approximately 1.3 billion metric tons of agricultural and food waste is produced annually, highlighting the need for appropriate processing and management strategies. This paper provides an exhaustive overview of the utilization of agri-food waste as a biosorbents for the elimination of volatile organic compounds (VOCs) from gaseous streams. The review paper underscores the critical role of waste management in the context of a circular economy, wherein waste is not viewed as a final product, but rather as a valuable resource for innovative processes. This perspective is consistent with the principles of resource efficiency and sustainability. Various types of waste have been described as effective biosorbents, and methods for biosorbents preparation have been discussed, including thermal treatment, surface activation, and doping with nitrogen, phosphorus, and sulfur atoms. This review further investigates the applications of these biosorbents in adsorbing VOCs from gaseous streams and elucidates the primary mechanisms governing the adsorption process. Additionally, this study sheds light on methods of biosorbents regeneration, which is a key aspect of practical applications. The paper concludes with a critical commentary and discussion of future perspectives in this field, emphasizing the need for more research and innovation in waste management to fully realize the potential of a circular economy. This review serves as a valuable resource for researchers and practitioners interested in the potential use of agri-food waste biosorbents for VOCs removal, marking a significant first step toward considering these aspects together.

Application of Artificial Neural Network (ANN) as a predictive tool for the removal of pharmaceutical from wastewater streams using biochar: a multifunctional technology for environment sustainability

This study investigates biochar as an attractive option for removing pharmaceuticals from wastewater streams utilizing data from various literature sources and also explores the sensitivity of the characteristics and implementation of biochar. ANN 1 was designed to determine the optimal biochar characteristics (Surface Area, Pore Volume) to achieve the maximum percentage removal of pharmaceuticals in wastewater streams. ANN 2 was developed to identify the optimal biomass feedstock composition, pyrolysis conditions (temperature and time), and chemical activation (acid or base) to produce the optimal biochar from ANN 1. ANN 3 was developed to investigate the effectiveness of the biochar produced in ANN 1 and 2 in removing dye from water. Biomass feedstock with a high lignin content and high volatile matter at a high pyrolysis temperature, whether using an acid or base, achieves a high mesopore volume and high surface area. The biochar with the highest surface area and mesopore volume achieved the highest removal percentage. Regardless of hydrophobicity conditions, at low dosages (0.2), a high surface area and pore volume are required for a high percent removal. And with a higher dosage, a lower surface area and pore volume is necessary to achieve a high percent removal.

Experimental and DFT insights into the adsorption mechanism of methylene blue by alkali-modified corn straw biochar

As an efficient and cost-effective adsorbent, biochar has been widely used in the adsorption and removal of dyes. In this study, a simple NaOH-modified biochar with the pyrolysis temperature of 300 °C (NaCBC300) was synthesized, characterized, and investigated for the adsorption performances and mechanisms of methylene blue (MB). NaCBC300 exhibited excellent MB adsorption performance with maximum removal efficiency and adsorption capacity of 99.98% and 290.71 mg g-1, which were three and four times higher than biochar without modification, respectively. This might be attributed to the increased content of -OH and the formation of irregular flakes after NaOH modification. The Freundlich isotherm suggested multilayer adsorption between NaCBC300 and MB. Spectroscopic characterizations demonstrated that multiple mechanisms including π-π interaction, H-bonding, and pore-filling were involved in the adsorption. According to density functional theory (DFT) calculations, electrostatic interaction between NaCBC300 and MB was verified. The highest possibility of the attraction between NaCBC300 and MB was between -COOH in NaCBC300 and R-N(CH3)2 in MB. This work improved our understanding of the mechanism for MB adsorption by modified biochar and provided practical and theoretical guidance for adsorbent preparation with high adsorption ability for dyes.

Efficient Remediation of p-chloroaniline Contaminated Soil by Activated Persulfate Using Ball Milling Nanosized Zero Valent Iron/Biochar Composite: Performance and Mechanisms

In this study, efficient remediation of p-chloroaniline (PCA)-contaminated soil by activated persulfate (PS) using nanosized zero-valent iron/biochar (B-nZVI/BC) through the ball milling method was conducted. Under the conditions of 4.8 g kg^-1 B-nZVI/BC and 42.0 mmol L^-1 PS with pH 7.49, the concentration of PCA in soil was dramatically decreased from 3.64 mg kg^-1 to 1.33 mg kg^-1, which was much lower than the remediation target value of 1.96 mg kg^-1. Further increasing B-nZVI/BC dosage and PS concentration to 14.4 g kg^-1 and 126.0 mmol L^-1, the concentration of PCA was as low as 0.15 mg kg^-1, corresponding to a degradation efficiency of 95.9%. Electron paramagnetic resonance (EPR) signals indicated SO₄•^-, •OH, and O₂•^- radicals were generated and accounted for PCA degradation with the effect of low-valence iron and through the electron transfer process of the sp² hybridized carbon structure of biochar. 1-chlorobutane and glycine were formed and subsequently decomposed into butanol, butyric acid, ethylene glycol, and glycolic acid, and the degradation pathway of PCA in the B-nZVI/BC-PS system was proposed accordingly. The findings provide a significant implication for cost-effective and environmentally friendly remediation of PCA-contaminated soil using a facile ball milling preparation of B-nZVI/BC and PS.

Significant roles of surface functional groups and Fe/Co redox reactions on peroxymonosulfate activation by hydrochar-supported cobalt ferrite for simultaneous degradation of monochlorobenzene and p-chloroaniline

CoFe₂O₄/hydrochar composites (FeCo@HC) were synthesized via a facile one-step hydrothermal method and utilized to activate peroxymonosulfate (PMS) for simultaneous degradation of monochlorobenzene (MCB) and p-chloroaniline (PCA). Additionally, the effects of humic acid, Cl^-, HCO₃^-, H₂PO₄^-, HPO₄^2- and water matrices were investigated and degradation pathways of MCB and PCA were proposed. The removal efficiencies of MCB and PCA were higher in FeCo@HC140-10/PMS system obtained under hydrothermal temperature of 140 °C than FeCo@HC180-10/PMS and FeCo@HC220-10/PMS systems obtained under higher temperatures. Radical species (i.e., SO₄^•-, •OH) and nonradical pathways (i.e., ¹O₂, Fe (IV)/Co (IV) and electron transfer through surface FeCo@HC140-10/PMS* complex) co-occurred in the FeCo@HC140-10/PMS system, while radical and nonradical pathways were dominant in degrading MCB and PCA respectively. The surface functional groups (i.e., C-OH and CO) and Fe/Co redox cycles played crucial roles in the PMS activation. MCB degradation was significantly inhibited in the mixed MCB/PCA solution over that in the single MCB solution, whereas PCA degradation was slightly promoted in the mixed MCB/PCA solution. These findings are significant for the provision of a low-cost and environmentally-benign synthesis of bimetal-hydrochar composites and more detailed understanding of the related mechanisms on PMS activation for simultaneous removal of the mixed contaminants in groundwater.

Hydrothermally assisted synthesis of nano zero-valent iron encapsulated in biomass-derived carbon for peroxymonosulfate activation: The performance and mechanisms for efficient degradation of monochlorobenzene

A facile, green and easily-scalable method of synthesizing stable and effective nano zero-valent iron (nZVI)‑carbon composites for peroxymonosulfate (PMS) activation was highly desirable for in-situ groundwater remediation. This study developed a two-step hydrothermally assisted carbothermal reduction method to prepare nZVI-encapsulated carbon composite (Fe@C) using rice straw and ferric nitrate as precursors. The hydrothermal reactions were conducive to iron loading, and carbothermal temperature was crucial for the aromatization and graphitization of hydrothermal carbonaceous products, the reductive transformation of iron oxides into nZVI and the development of porous structure in composites. At carbothermal temperature of 800 °C following hydrothermal reactions, the stable Fe@C800 with nZVI encapsulated in the spherical carbon shell was obtained and exhibited the best catalytic performance for PMS activation and the degradation of monochlorobenzene (MCB) in a wide range of pH values (3-11) with removal efficiency after 120 min reaction and first-order kinetic rate constant (k₁) of 98.7% and 0.087 min^-1 respectively under the optimum conditions of 10 mM PMS and 0.2 g·L^-1 Fe@C800. The inhibiting effects of common co-existed anions (i.e., Cl^-, HCO₃^- and H₂PO₄^-) and humic acid in groundwater on the removal of MCB in Fe@C800/PMS system was also investigated. Both OH-dominated radical processes and nonradical pathways involving ¹O₂ and surface electron transfers were accounted for PMS activation and MCB removal. The inner nZVI was protected by the carbon shell, endowing Fe@C800 with high reactivity and good reusability. Additionally, 81.2% and 73.5% of MCB removal rates were achieved in tap water and actual contaminated groundwater respectively. This study not only provided a novel strategy to synthesize highly effective and stable nZVI‑carbon composites using the agricultural biomass waste for PMS induced oxidation of organic contaminants in groundwater, but also enhanced the understanding on the activation mechanism of iron‑carbon based catalysts towards PMS.

Co-sorption/co-desorption mechanism of the mixed chlorobenzenes by fresh bulk and aged residual biochar

Since little is known about the sorption/desorption behaviors of the mixed chlorobenzenes (CBs) on fresh and aged biochar, this study evaluated the co-sorption/co-desorption mechanism of the mixed monochlorobenzene (MCB), 1,2-dichlorobenzene (1,2-DCB) and 1,2,4-tirchlorobenzene (1,2,4-TCB) on the fresh bulk biochar derived from pinewood sawdust and corn straw under the heat treatment temperature (HTT) of 300 and 500 °C, and elucidated the aging-induced changes in the sorption/desorption of mixed CBs by biochar. The distinct sorption capacities of MCB< 1,2-DCB< 1,2,4-TCB were observed on all the tested biochar with the differences being further enhanced following the rise of HTT, as the main sorption mechanism was converted from phase partitioning to π-π interaction between graphitized biochar moieties and more hydrophobic aromatic chemicals. In comparison to the fresh biochar, the sorption suppression of the mixed CBs on the aged biochar was likely attributable to the reduction in accessibility to the aromatic carbon in biochar by introducing O-containing polar moieties on the biochar surfaces. Intriguingly, the kinetics of desorption was decreased with the aging of biochar may be caused by the increase in surface steric hindrance. These findings can provide new insights on understanding the co-sorption/co-desorption mechanism of the mixed CBs and help assess and manage the application of biochar on the treatment of contaminated soil and groundwater under field conditions.

Carbon stability and mobility of ball milled lignin- and cellulose-rich biochar colloids

Numerous studies have explored the transport mechanism of biochar colloids in porous medium. However, the effect of feedstock biopolymer compositions and pyrolytic temperature on carbon stability and mobility of biochar colloids is limited. This study prepared four ball milled biochar colloids pyrolyzed from lignin-rich pinewoods and cellulose-rich corn stalks under 300 °C and 500 °C (termed as PW300, PW500, CS300, CS500) and analyzed their differences in the chemical stability and transport behaviors. The results indicated that high contents of lignin in biomass and pyrolytic temperature could enhance the compact aromatic structures of biochar colloids characterized by the elemental composition, FTIR, ¹³C NMR and XRD analyses. Therefore, PW500 with the strongest chemical stabilities (least C loss of 13%), electronegativity (-44.9 mV vs. -41.6-28.3 mV) and smallest hydrodynamic diameter (608.7 nm vs. 622-997.2 nm) was obtained under ball milling. Moreover, both the critical coagulation concentrations (CCC) and the maximum relative effluent concentration (C/C₀) with the NaCl ionic strength of 1 mM were demonstrated to be in the increase order of CS300 (76.1 mM, 70%) < PW300 (183.1 mM, 78%) < CS500 (363.9 mM, 89%) < PW500 (563.1 mM, 95%), which suggested stronger colloidal stability and mobility of PW biochar colloids than those of CS biochar colloids. In addition, the C/C₀ for CS300, PW300 and CS500 were about 7.3%-36% lower than that for PW500 with the NaCl ionic strength increasing to 50 mM indicated the notable superiority in the mobility of PW500. These findings can provide new insights toward understanding the transformation and migration, and evaluating the environmental risk of biochar colloids.

Valorisation of agricultural waste derived biochars in aquaculture to remove organic micropollutants from water - experimental study and molecular dynamics simulations

In this work, we evaluated the valorisation of agricultural waste materials by transforming coconut husks and shells, corncobs and rice straw into biochar for water treatment in aquaculture. We compared the biochars' suitability for removal of organic micropollutants (acetaminophen, oxytetracycline, tetracycline, enrofloxacin, atrazine, diuron and diclofenac) from surface water needed for aquaculture. The biochars were prepared by three methods ranging from inexpensive drum kilns (200 °C) to pyrolysis with biogasfication (350-750 °C). Overall, antibiotics tetracycline and enrofloxacin were the most strongly sorbed micropollutants, and coconut husk biochar prepared at 750 °C was the best sorbent material. Molecular Dynamics simulations indicated that the major sorption mechanism is via π-π stacking interactions and there is a possibility of multilayer sorption for some of the micropollutants. We observed, a strong impact of ionic strength (salinity), which is an important consideration in coastal aquaculture applications. High salinity decreased the sorption for antibiotics oxytetracycline, tetracycline and enrofloxacin but increased diclofenac, atrazine and diuron sorption. We considered coconut husk biochar produced in drum kilns the most practical option for biochar applications in small-scale coastal aquacultures in South Asia. Pilot trials of canal water filtration at an aquaculture farm revealed that micropollutant sorption by coconut husk biochar under real-world conditions might be 10-500 times less than observed in the laboratory studies. Even so, biochar amendment of sand enhanced the micropollutant retention, which may facilitate subsequent biodegradation and improve the quality of brackish surface water used for food production in coastal aquaculture.

Applying Cassava Stems Biochar Produced from Agronomical Waste to Enhance the Yield and Productivity of Maize in Unfertile Soil

Many agronomical wastes are produced annually in significant amounts after cultivation, especially in agricultural countries. This study applied biochar produced from the pyrolysis of cassava stems to improve soil with low fertility for maize cultivation. The effect of soil biochar incorporation on maize yield and productivity was also investigated. Eight experimental plots, each with four replicates, were applied with cassava stem biochar (CSB) at different rates of 0.5 kg/m2 (TB0.5), 2.5 kg/m2 (TB2.5) and 3.0 kg/m2 (TB3.0), fertilizer at 0.56 kg/m2 (TM), fertilizer at 0.56 kg/m2 mixed with CSB at 0.5 kg/m2 (TMB0.5), 2.5 kg/m2 (TMB2.5), 3.0 kg/m2 (TMB3.0) and untreated soil (TC). Pyrolysis of cassava stems at 450–500 °C produced strongly alkaline CSB with pH 9.6 and increased nutrient contents. Specific surface area and total pore volume increased, and pores were classified as mesoporous, while average pore diameter decreased. CSB had a highly stable carbon content of 58.46%, with high aromaticity and polarity obtained from O/C and H/C ratios. Results indicated that CSB enhanced and supported maize growth by improving soil physicochemical properties to suit cultivation. Applying CSB into the soil gave higher maize yield and productivity than cultivation using fertilizer. The highest yield and nutrition contents were obtained in seed from cultivation using fertilizer mixed with biochar at 3.0 kg/m2. Biochar production from cassava stems generated a useful commodity from waste material.

Sustainable carbonaceous biochar adsorbents derived from agro-wastes and invasive plants for cation dye adsorption from water

This study investigated methyl orange (MO) dye adsorption using three biochars produced from agro-waste and invasive plants; the latter consisted of wattle bark (BA), mimosa (BM), and coffee husks (BC). BC had the lowest specific surface area (2.62 m²/g) compared to BA (393.15 m²/g) and BM (285.53 m²/g). The adsorption efficiency of MO was stable at pH 2-7 (95%-96%), whilst it had reduced stability at pH 7-12. Between 0 and 30 min, MO adsorption efficiency was >82%, and at 120 min, representative adsorption equilibrium had occurred. The maximum adsorption capacity of the biochars was 12.3 mg/g. The underlying adsorption mechanisms of the three biochars were governed by electrostatic adsorption and pore diffusion. There was an abundance of active sites for adsorption in BA and BM, while chemical adsorption appeared to be more vital for BC, as it contained more functional groups on its surface. The highest MO adsorption efficiency occurred with BM. BC was not recommended for MO removal, as it was observed to stain the water when a dose exceeding 5.0 g/L was utilized.

Capacity and potential mechanisms of Cd(II) adsorption from aqueous solution by blue algae-derived biochars

The removal of potentially toxic metals by biochars is currently a popular and salutary method. In this study, we combined the advantages of blue algae (Microcystic) and pyrolysis technology to produce a late-model biochar. Moreover, the adsorption capacity and potential mechanisms of blue algae-derived biochars for the removal of cadmium (Cd) from aqueous solution were evaluated in comparison with the adsorption capacity and potential mechanisms of corn straw-derived biochar (CSBC) and rice husk-derived biochar (RHBC). Batch adsorption experiments were used to explore the adsorption performance of biochars, and a wide range of characterization techniques were employed: scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and zeta potential analysis. The results showed that the adsorption isotherms could be described well by the Langmuir model and that the pseudo-second-order model fit the Cd(II) adsorption kinetics best, indicating that the process was monolayer and controlled by chemisorption. Moreover, the Cd(II) removal capacity of optimal blue algae-derived biochar (BC600-2) (135.7 mg g^-1) was 85.9% and 66.9% higher than the removal capacity of CSBC and RHBC, respectively. In addition, the results of the characterization methods showed that precipitation with minerals was the primary mechanism, accounting for 68.7-89.5% of the capacity. Overall, blue algae-derived biochars, as a product from freshwater biowaste, may be a novel and potentially valuable adsorbent for Cd(II) removal.

Effect of biochar aging and co-existence of diethyl phthalate on the mono-sorption of cadmium and zinc to biochar-treated soils

In this study, the influence of the aging process of pig-(PB) and P. orientalis-(POB) derived biochars on the sorption capacity of the biochar-treated soils for cadmium (Cd) and zinc (Zn) with and without the co-existence of diethyl phthalate (DEP) was investigated. Additionally, the surface and internal characteristics of biochars were determined before and after their aging in soils. The PB-treated soil had a higher sorption capacity for Cd²⁺ and Zn²⁺ than the POB-treated soil. The sorption capacity of the biochar-treated soils for Cd²⁺ and Zn²⁺ increased with biochar application rates. After aging, the abundance of oxygen-containing functional groups on the biochar surface, and the pH and organic carbon content of the biochar-treated soils significantly increased, thereby improving the sorption capacity for Cd²⁺ and Zn²⁺. The sorption capacities of biochar-treated soils for Cd²⁺ and Zn²⁺ followed the order of 1-month aging > 6-month aging > fresh. The co-existence of DEP enhanced the sorption capacity of the fresh biochar-treated soils for Cd²⁺ and Zn²⁺, whereas this enhancing effect disappeared for the aged biochar treatments. Our findings provide insights into the interactions between mixed contaminants in biochar-amended soils and the long-term efficacy of biochar treatments on metal sorption to soils.

Effects of feedstock biopolymer compositions on the physiochemical characteristics of dissolved black carbon from lignocellulose-based biochar

Dissolved black carbon (DBC) is becoming increasingly concerned by researchers due to its unique environmental behavior. However, understanding of the influence mechanism of biopolymer compositions of cellulose (CEL), hemicellulose (HEM) and lignin (LIG) on the formation and physiochemical characteristics of DBC from lignocellulose-based biochar is limited. This study therefore examined the formation of DBCs derived from the biopolymer compositions, corn straw (CS), corncob (CC), bamboo sawdust (BS) and pinewood sawdust (PS) under the heat treatment temperatures (HTTs) of 300-500 °C. Zeta potential and hydrodynamic diameters (D_h) of DBCs produced under 300 °C were further investigated. DBC formation may be closely associated with the HTT-dependent heterogeneities of biopolymer compositions, in which significant effects of CEL and HEM charring on physiochemical properties of DBCs were identified under the HTT of 300 and 400 °C, while the formation of DBCs was closely related to LIG and its proportions in biomass under high HTT (>500 °C). On the rise of the HTT, the carbonaceous structures of biopolymer compositions were reorganized and converted to graphitic structures in biochar accompanied by the large decomposition or carbonization of CEL and HEM, leading to the reduced carbon content, surface functional groups, aromaticity and molecular weight of DBCs, as well as the decrease of protein-like and relative increase of fulvic-like fluorescent substances in most DBCs. LIG in biomass may facilitate the migration of DBCs due to abundant surface negative charges and the formation of low D_h. This study offered new insights into our understanding of influencing mechanisms of biopolymer compositions on the characteristic of DBCs under different HTTs.

The mechanism of cadmium sorption by sulphur-modified wheat straw biochar and its application cadmium-contaminated soil

Cadmium (Cd) pollution in soils has received considerable research attention globally, and sulphur-modified biochar (SBC) could combine the advantages of biochar and the sulphur element for Cd remediation. Biochar from agricultural waste is feasible, which has a low preparation cost. However, there are few studies regarding the effects of the sulphur modification of biochar on the Cd immobilization mechanism. This study aimed to research the Cd immobilization mechanism of pristine wheat straw biochar (BC) and sulphur-modified biochar (SBC), and the Cd immobilization effects of BC and SBC in Cd-contaminated soils. Elemental and SEM analysis confirmed that sulphur was successfully loaded on the pristine biochar. XPS analysis confirmed that there was a considerable discrepancy between adsorption mechanisms of Cd on BC and SBC. In particular, cadmium sorption on BC was due to Cd(OH)₂ and CdCO₃ precipitation formation and interaction with carbonyl and carboxyl groups, whereas on SBC, sorption was mainly due to CdS and CdHS⁺ formation and interaction with organic sulphide. In the incubation experiment, SBC and BC additions increased pH value and also reduced the available Cd concentrations in the soil. Compared with the control, the contents of available Cd in soil were significantly decreased by 15.86% ~ 22.10% and 22.72% ~ 27.90%, following treatments with BC and SBC, respectively.

Effect of sulfamethazine on surface characteristics of biochar colloids and its implications for transport in porous media

Antibiotics are contaminants of emerging concern due to their potential effect on antibiotic resistance and human health. Antibiotics tend to sorb strongly to organic materials, and biochar, a high efficient agent for adsorbing and immobilizing pollutants, can thus be used for remediation of antibiotic-contaminated soil and water. The effect of ionizable antibiotics on surface characteristics and transport of biochar colloids (BC) in the environment is poorly studied. Column experiments of BC were conducted in 1 mM NaCl solution under three pH (5, 7, and 10) conditions in the presence of sulfamethazine (SMT). Additionally, the adsorption of SMT by BC and the zeta potential of BC were also studied. The experimental results showed that SMT sorption to BC was enhanced at pH 5 and 7, but reduced at pH 10. SMT sorption reduced the surface charge of BC at pH 5 and 7 due to charge shielding, but increased surface charge at pH 10 due to adsorption of the negatively charged SMT species. The mobility of BC was inhibited by SMT under acidic or neutral conditions, while enhanced by SMT under alkaline conditions, which can be well explained by the change of electrostatic repulsion between BC and sand grains. These findings imply that pH conditions played a crucial role in deciding whether the transport of BC would be promoted by SMT or not. Biochar for antibiotics remediation will be more effective under acidic and neutral soil conditions, and the mobility of BC will be less than in alkaline soils.

Multifunctional Pd/Fe-biochar composites for the complete removal of trichlorobenzene and its degradation products

To elucidate the effect of structure and property of biochar on the structure-activity relationship among the composites of biochar supported Pd/Fe and 1,2,4-trichlorobenzene (1,2,4-TCB) and its dechlorination products, biochar supported Pd/Fe nanoparticles with different mass ratios were investigated for the enhanced removal of 1,2,4-TCB (52 μmol/L) and its dechlorination products. 1,2,4-TCB was removed through the electrochemical dechlorination by Pd/Fe and adsorption by biochar simultaneously. As the mass ratio of CS700 to Pd/Fe was 0.1:1, biochar within the Pd/Fe-CS700_0.1 system played a significant role in the adsorption of 1,2,4-TCB. However, there is little adsorption to biochar for dechlorination products due to strong competition by 1,2,4-TCB. As the mass ratio of CS700 to Pd/Fe was increased to 5:1, 1,2,4-TCB was completely removed from the solution by the composites within 0.5 h. The dechlorination products (1,2-DCB, MCB, benzene and trace 1,3-DCB) were completely sequestered on solid phase but absent in aqueous solution. However, the excessive biochar increased the inaccessibility of 1,2,4-TCB or decreased the reactive sites of Pd/Fe leading to the less dechlorination of 1,2,4-TCB. The alkaline biochar did not influence the chemical reactivity of Pd/Fe in the composites and buffered the acid and alkaline solutions with pH being maintained at neutral conditions under initial pH ranging from 3.07 to 10.03. The highly hydrophobicity of biochar could maintain the affinity of the composite for the chlorinated compounds even if the concentration of 1,2,4-TCB was up to 80.9% of its aqueous solubility. This study provides efficient synergistic removal support for the treatment of TCB affected groundwater.

A comprehensive review on physical activation of biochar for energy and environmental applications

Biochar is a solid by-product of thermochemical conversion of biomass to bio-oil and syngas. It has a carbonaceous skeleton, a small amount of heteroatom functional groups, mineral matter, and water. Biochar’s unique physicochemical structures lead to many valuable properties of important technological applications, including its sorption capacity. Indeed, biochar’s wide range of applications include carbon sequestration, reduction in greenhouse gas emissions, waste management, renewable energy generation, soil amendment, and environmental remediation. Aside from these applications, new scientific insights and technological concepts have continued to emerge in the last decade. Consequently, a systematic update of current knowledge regarding the complex nature of biochar, the scientific and technological impacts, and operational costs of different activation strategies are highly desirable for transforming biochar applications into industrial scales. This communication presents a comprehensive review of physical activation/modification strategies and their effects on the physicochemical properties of biochar and its applications in environment-related fields. Physical activation applied to the activation of biochar is discussed under three different categories: I) gaseous modification by steam, carbon dioxide, air, or ozone; II) thermal modification by conventional heating and microwave irradiation; and III) recently developed modification methods using ultrasound waves, plasma, and electrochemical methods. The activation results are discussed in terms of different physicochemical properties of biochar, such as surface area; micropore, mesopore, and total pore volume; surface functionality; burn-off; ash content; organic compound content; polarity; and aromaticity index. Due to the rapid increase in the application of biochar as adsorbents, the synergistic and antagonistic effects of activation processes on the desired application are also covered.

The relative importance of different carbon structures in biochars to carbamazepine and bisphenol A sorption

Biochar, a carbon-rich material, has attracted immense attention owing to its applications in soil remediation. However, the mechanisms by which heterogeneous carbon structures of biochars immobilize organic contaminants are not yet fully understood. In this study, the noncondensed aromatic components in biochars were selectively removed through bleaching. Different techniques, such as ¹³C nuclear magnetic resonance, were applied to characterize the biochar compositions, and thus the role of the different carbon structures in organic contaminant sorption was discussed. The aromatic carbon structures in biochars were gradually developed and evolved from noncondensed to condensed structure with increasing pyrolytic temperatures from 300 to 700 °C. Based on elemental analysis, the carbon removed by bleaching decreased from 43.9% to 5.92% with increasing temperatures. After the surface area normalization of the apparent sorption, bleaching increased the sorption of carbamazepine and bisphenol A on biochars produced at 500 °C, but not for those produced at 300 and 700 °C. Bleaching removed noncondensed aromatics and enriched condensed aromatics, which resulted in increased sorption. However, bleaching also resulted in the blockage of micropores in biochars with abundant condensed aromatics, causing decreased sorption. The apparent sorption was determined by the balancing of these two opposite effects.

Sorption of chlorinated hydrocarbons to biochars in aqueous environment: Effects of the amorphous carbon structure of biochars and the molecular properties of adsorbates

Currently, the role of amorphous carbon structure (ACS) in sorption of chlorinated hydrocarbons (CHs) to biochars remains little known. Therefore, three CHs (1,1,2,2-tetrachloroethane, 1,3,5-trichlorobenzene and γ-hexachlorocyclohexane) with different molecular properties were selected as model adsorbates to investigate the effect of ACS on sorption of CHs to biochars produced at seven different pyrolysis temperatures (300-900 °C). There were two main mechanisms for ACS controlling the sorption of CHs. First, the polar sites on ACS are hydrophilic, CHs with greater polarity could strongly compete with the water molecule for the hydrophilic sites. Second, ACS of low temperature (300-400 °C) produced biochars possessing the natural organic matter (NOM)-like structure occupied some hydrophobic sites on condensed graphitic structure (CGS) of biochars. CHs with great hydrophobicity possibly seized the hydrophobic sorption sites on CGS from the NOM-like structure. Therefore, ACS of biochar was more benefit for sorption of strong polar CHs (1,1,2,2-tetrachloroethane: π^∗ = 0.95; LogK_ow = 2.39) or strong hydrophobic CHs (1,3,5-trichlorobenzene: π^∗ = 0.70; LogK_ow = 4.19) than CHs (γ-hexachlorocyclohexane: π^∗ = 0.68; LogK_ow = 3.72) with relatively low polarity and hydrophobicity. The result reflects that the interaction between NOM and natural black carbon/biochars in soil and water environment possibly plays the similar role in controlling the environmental behavior of various polar or hydrophobic organic pollutants. Moreover, with increasing concentration of adsorbate (C_e), the first mechanism enhanced, while the second mechanism weakened. This study gives a deep insight into the roles of ACS of biochars in controlling the fate and availability of CHs with different molecular properties in environment.

Sorption mechanisms of chlorinated hydrocarbons on biochar produced from different feedstocks: Conclusions from single- and bi-solute experiments

Biochar is increasingly deemed a potential sorbent for contaminants in soil and water remediation. We tested three biochars from different feedstocks (cattle manure, grain husk, and wood chips) produced at relatively low pyrolysis temperature (450 °C), for their sorption behavior towards trichloroethylene (TCE) and tetrachloroethylene (PCE) in single- and bi-solute systems. In single-solute experiments, all biochars show stronger sorption for TCE (about 50% based on solubility-normalized Freundlich coefficients). The lower sorption of PCE is attributed to steric effects, e.g. size exclusion in small micropores and specific interactions. Plant-derived, carbon-rich biochars with high specific surface area and microporosity predominantly sorb via pore-filling, as also observed in activated carbon. Biochar produced from manure, with higher ash content and polarity, and smaller total pore volume (PV_tot), shows significant contribution of partitioning. These findings also apply to bi-solute systems. TCE and PCE show different competition behavior depending on biochar properties. Plant-based biochars are pore-filling-dominated and show strong competition. However, competition behavior in microporous biochars depends on the concentration range. Manure biochar with high polarity and low PV_tot shows significant partitioning and therefore less competition. Compared to the plant-based chars competition in manure biochar is not concentration-dependent. These results indicate that biochars with a large fraction of non-carbonized phase facilitate non-competitive sorption and might be a valuable sorbent in mixed contaminant systems.

Role of membrane pore polymerization conditions for pH responsive behavior, catalytic metal nanoparticle synthesis, and PCB degradation

This article describes the effects of changing monomer and cross-linker concentrations on the mass gain, water permeability, Pd-Fe nanoparticle (NP) loading, and the rate of degradation of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) of pore functionalized polyvinylidene fluoride (PVDF) membranes. In this study, monomer (acrylic acid (AA)) and cross-linker (N, N'- methylene-bis (acrylamide)) concentrations were varied from 10 to 20 wt% of polymer solution and 0.5-2 mol% of monomer concentration, respectively. Results showed that responsive behavior of membrane could be tuned in terms of water permeability over a range of 270-1 L m-2 h-1 bar-1, which is a function of water pH. The NP size on the membrane surface was found in the range of 16-23 nm. With increasing cross-linker density the percentage of smaller NPs (< 10 nm) increases due to smaller mesh size formation during in-situ polymerization of membrane. NP loading was found to vary from 0.21 to 0.94 mg per cm2 of membrane area depending on the variation of available carboxyl groups in membrane pore domain. The NPs functionalized membranes were then tested for use as a platform for the degradation of PCB 126. The observed batch reaction rate (Kobs) for PCB 126 degradation for per mg of catalyst loading was found 0.08-0.1 h-1. Degradation study in convective flow mode shows 98.6% PCB 126 is degraded at a residence time of 46.2 s. The corresponding surface area normalized reaction rate (K sa ) is found about two times higher than K sa of batch degradation; suggesting elimination of the effect of diffusion resistance for degradation of PCB 126 in convective flow mode operation. These Pd-Fe-PAA-PVDF membranes and nanoparticles are characterized by TGA, contact angle measurement, surface zeta potential, XRD, SEM, XPS, FIB, TEM and other techniques reveal the details about the membrane surface, pores and nanoparticles size, shape and size-distribution. Statistical analysis based on experimental results allows us to depict responsive behavior of functionalized membrane. In our best knowledge this paper first time reports detail study on responsive behavior of pore functionalized membrane in terms of permeability, NPs size, metal loading and its effect on PCB 126 degradation in a quantified approach.