Structure Of Biochar Research Articles

New approaches for regulation of structure and adsorption properties of biochar based on freshwater sediments (sapropels)

Biochar based on sapropel have been synthesized and the effect of chemical modification on their textural characteristics, acid-base and adsorption properties has been studied. It was found that preliminary treatment of raw sapropel with a weakly concentrated solution of alkali increases the fraction of micropores: from 0.006 cm3 g−1 (for BС-N) to 0.021 cm3 g−1 (for КОН-BC), and additional treatment with hydrofluoric acid leads to an increase in the fraction of micropores up 0.047 cm3 g−1 (for КОН-BC-HF) and also of specific surface area up to 211 m2 g−1 at a considerable decrease in the fraction of mineral part due to leaching of silicon-containing phases. The proposed chemical modification makes it possible not only to change the ratio of mineral and carbon parts and the pore space, but also to vary the surface properties of biochar: рНPZC, concentration and features of oxygen-containing groups. It is shown that the total content of acidic groups increases in the series BС-N (0.3290 mmol g−1) < КОН-BC (0.5567 mmol g−1) < КОН-BC-HF (1.3046 mmol g−1). Simultaneously the type of treatment affects the nature of oxygen-containing groups: the maximum amount of phenolic groups (0.4845 mmol g−1) in sample КОН-BC, the surface acidity of КОН-BC-HF is contented by the presence of a considerable amount of carboxyl groups (0.9198 mmol g−1). The analysis of the data obtained shows that the total content of acidic groups increases in the series The adsorption of Cu(II) ions from an aqueous solution on the synthesized samples of biochar was studied for the first time. Biochar obtained using the sapropel pretreated with alkali showed the maximum adsorption capacity toward copper ions of 27.9 mg g−1. Conceptual model identifying the mechanisms of adsorption copper (II) ions on biosorbent from sapropels was shown. The experimentally obtained isotherms were approximated using the Freundlich and Langmuir models. It was found that the adsorption of copper on the tested samples can be described quite adequately by the Langmuir monomolecular adsorption model (R2 ≥0.98).

Raw Rice Husk Biochar as a Potential Valuable Industrial Byproduct for the Removal of Rhodamine B from Water

In this work, raw rice husk biochar (RRHB) was investigated for its potential as a valuable industrial byproduct for the decontamination of water using rhodamine B (RB) as a model pollutant. Specific functional chemical groups that were identified in the structure of the biochar using Fourier transform infrared (FTIR) spectra were determined to be responsible for the interaction between the biochar and the pollutant, explaining the sorption process. The interaction between the pollutant and biochar was also explained by the porosity of the sorbent, as demonstrated by scanning electron microscopy (SEM), and the specific surface area (Brunauer–Emmett–Teller analysis, BET). The ionic charge of the biochar structure was determined based on the point of zero charge (pHPCZ). The best kinetic fit for the sorption of the dye on/in the biochar was obtained with the nonlinear pseudo-second-order and Elovich models. The nonlinear Freundlich isotherm had the best fit to the experimental data, and it was determined that the maximum sorption capacity was ~40 mg g−1. The thermodynamic parameters indicated that the sorption of the RB on/in the RRHB was spontaneous. Overall, RRHB was demonstrated to be a potential biosorbent for cationic dyes such as RB. Finally, it is possible to recover the biosorbent, aggregating value to the byproduct and showing it to be an excellent option for use in water purification filters.

Porous Fe-doped graphitized biochar: An innovative approach for co-removing per-/polyfluoroalkyl substances with different chain lengths from natural waters and wastewater

Legacy long-chain per-/polyfluoroalkyl substances (PFAS) are being replaced by short-chain homologs, which have been widely detected in the environment. To achieve the co-removal of different chain length PFAS, this study systematically explored the single and synergistic effects of FeCl3-impregnation, wet ball-milling and different carbonization temperatures on the surface chemistry and pore structures of different biochars as well as sorption performances and mechanisms towards long-chain perfluorooctanoic acid (PFOA) and short-chain perfluorobutyric acid (PFBA). As a consequence, we presented a new method to synthesize magnetic sorbents by wet ball-milling with FeCl3 solution and high-temperature carbonization. Through this process, we tailored a magnetic porous Fe-doped graphitized biochar (named Fe-M−BC900) that contains abundant dispersed positive iron sites with stable Fe0/Fe3C, multi-stage pore structure, highly hydrophobic graphite-like carbon, and O-containing functional groups. Fe-M−BC900 exhibited a high sorption capacity of 10.1 mg PFBA/g and 39.1 mg PFOA/g. PFAS sorption on Fe-M−BC900 was mainly governed by pore-filling, electrostatic interaction, and hydrophobic partitioning. The sorption of PFBA on Fe-doped biochars depends more on electrostatic interaction and is less affected by hydrophobic partitioning compared to PFOA. Finally, we demonstrated that Fe-M−BC900 performed high co-removal rates (>96 %) for a wide range of legacy and emerging PFAS with different chain lengths and functional groups in natural waters (∑PFAS: 142 ∼ 265 μg/L) and simulated wastewater (∑PFAS: 600 μg/L), with a high relative sorption capacity of > 91 %, even after four consecutive recycling processes. This new adsorbent could help water facilities comply with upcoming PFAS regulations if tested on a larger scale.

Surface oxidation modification of nitrogen doping biochar for enhancing CO2 adsorption

The purpose of this paper is to demonstrate a surface oxidation modification strategy of nitrogen doping biochar for enhancing CO2 adsorption. The porous structure and surface group distribution of nitrogen doping biochars before and after modification (remarked as TF and OTFs) were characterized. Then the thermodynamic and kinetic characteristics of CO2 adsorption such as adsorption capacity, selectivity and activation energy were systematically investigated. The results indicated that the modified biochars OTFs exhibited high adsorption capacity of CO2 between 5 and 8 mmol·g-1 at 100 kPa and 273 K. The oxidation modification affected CO2 adsorption behaviors by the ways of adjusting surface pore size and surface group distributions. The former decreased the mass transfer diffusion resistance of CO2 from gas phase to biochar surface by transforming some micropores to the mesopores. And the later improved the adsorption selectivity of CO2 to the other gases such as N2 based on the interaction difference enhancement by those oxygen-containing (OFGs) and nitrogen-containing functional groups (NFGs). When the molar ratios of CO2/N2 in gas mixture were 1:1 and 15:85, the modified biochar OTF-10 exhibited the better selectivity, and the maximum selectivities of CO2 to N2 at 273 K were 44.7 and 69.4, respectively. Furthermore, the behavior of CO2 adsorption on the biochars well conformed to the quasi-first-order dynamical model, accompanied by the higher adsorption rate of CO2 and activation energy. The obtained activation energies for TF and OTF-10 were 12.98 and 16.62 kJ·mol-1, respectively. The higher activation energy for OTF-10 meant that the adsorption temperature had a stronger effect on adsorption rate of CO2.

Influence of plasticity and porewater salinity on shrinkage and water retention characteristics of biochar‐engineered clays

AbstractClay‐engineered barriers might be subjected to soil salinization issues under climate change. A recently emerged desalinization method is achieved by modifying clays using biochar. However, unsaturated soil responses of biochar‐engineered clays in saline environments under drought conditions remain unknown. This study aims to investigate soil shrinkage and water retention characteristics of biochar‐amended kaolin and bentonite under saline conditions. Soil shrinkage and water retention tests were conducted on clays (with and without biochar addition) with various porewater salinity (i.e., 0%–10%). Physiochemical properties (including zeta potential and porewater pH) were measured to interpret particle–fluid interactions. Shrinkage characteristics of kaolin and bentonite exhibited sensitivity and insensitivity to the porewater salinity, respectively. This phenomenon was explained by hydrogen‐sodium ion exchange and deprotonation phenomenon occurring on kaolin and bentonite, respectively. Biochar significantly alleviated the salinity‐induced shrinkage of clays by increasing the shrinkage limit of kaolin and bentonite by 6%–14% and 50%–107%, respectively (p &lt; 0.05). This was attributed to the porous structure and hydrophilic functionality of biochar that immobilized sodium ions through ion exchange and protonation reactions. The air entry value of clays significantly increased with porewater salinity and biochar addition due to the reduction of void ratio and enhanced capillarity, respectively. An empirical equation was proposed to predict the shrinkage limit of clay in various saline conditions. It highlighted that the application of biochar‐engineered clays could contribute to the desalination and the improvement of resistance to shrinkage damage in hydro‐chemical barriers.

Effects of different types of inorganic potassium in biomass on volatile-char interactions for co-pyrolysis of coal and biomass

Co-gasification of biomass and coal has many advantages. However, the volatile-char interaction during co-pyrolysis, which is the first step of co-gasification, significantly changes the properties and the structure of biochar, thus affecting gasification. The present work investigated the effect of the interaction between the volatile from a coal and the biochar of K-salt-doped (K2CO3, K2SO4 and KCl) pine wood in a lab-scale, fixed-bed reactor at 600, 700 and 800 °C to understand how the occurrence mode of inorganic K in biomass alters the volatile-char interaction during co-pyrolysis. The volatile-char interaction has insignificant effects on the biochar of pine wood without the doping of K salts while it has significant effects on the biochar of K-salt-doped pine wood, especially for K2CO3 and K2SO4. The volatile-char interaction significantly increases the formation of C-O-K bonds, the content of oxygen containing compounds and the aromaticity of the biochar for K2CO3-doped and K2SO4-doped pine wood. In contrast, the evident presence of C-O-K bonds can only be found for KCl-doped pine wood at 800 °C after the volatile-char interaction. The increase in the pyrolysis temperature and the presence of the volatile-char interaction make the carbon structure of the biochar of K2SO4-doped and KCl-doped pine wood less ordered and generate more active sites. However, although the char order is lower and the number of active sites is higher for the biochar of K2CO3-doped pine wood than for that of K2SO4-doped and KCl-doped pine wood, the volatile-char interaction has insignificant effects on improving the activity of its biochar. Lastly, the volatile-char interaction causes insignificant additional release of K from the biochar. This may indicate that significant amounts of stable C-O-K bonds have been formed in the biochar to retain K.

Formation and evolution mechanism of persistent free radicals in biochar during biomass pyrolysis: Insights from biochar’s element composition and chemical structure

The persistent free radicals (PFRs) in biochar can play a crucial role during biochar’s utilization, but the formation and evolution mechanism of PFRs in biochar are poorly understood because of biochars’ element specificity and chemical structure complexity. In order to further understand the formation and evolution mechanism of PFRs, the PFRs characteristics, chemical structure and element composition of six types of biomasses were investigated. The results revealed that the changing trend of the PFRs types, concentration and line width with pyrolysis temperature is similar for all six feedstocks. The difference in the feedstocks’ properties just affects the absolute value of PFRs’ characteristic parameters. The arrangement and combination of elements and carbon skeleton structure in biochar determine the evolution of PFRs in the pyrolysis process. Additionally, the (H + O)/C atomic ratio of the biomass feedstock and the content of substitutional groups on aromatic rings were found to influence the types of PFRs in biochar. When biochar has a similar O/C atom ratio, a higher H content can reduce the carbon-centered PFRs in biochar. Besides, the reduction in O element content contributes to a decrease in line width due to the reduction in the effect of heteroatoms. The good correlation between O/C atomic ratio, H/C atomic ratio, chemical structure and PFRs characteristics can be used to predict the PFRs characteristics. Combining the changing characteristics in PFRs concentration and carbon skeleton structure of biochar, a three-stage model of PFRs formation and evolution was constructed.

Improving bifunctional catalytic activity of biochar via in-situ growth of nickel-iron hydroxide as cathodic catalyst for zinc-air batteries

Expanding the application scenarios of wood-derived biochar guided by the conversion of traditional energy to new energy shows great promise as a field. As thrilling energy conversion apparatus, zinc-air batteries (ZABs) require cathode catalysts with high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities and stability. Herein, two-dimensional nickel-iron hydroxide nanosheets were creatively assembled in N-doped wood-derived biochar (NiFe-LDH@NC) by an in-situ growth method. The categorized porous organization in wood-derived biochar facilitates the rapid seepage of electrolytes and rapid diffusion of reaction gases. The unique interfacial structure of biochar and NiFe-LDH accelerates electron transfer during oxygen electrocatalysis, and endows NiFe-LDH@NC with first-class catalytic activity and durability for ORR and OER. The ZAB derived from NiFe-LDH@NC showed elevated discharge productivity and cycle endurance, making it promising for viable applications. This work provided a convenient way for the conversion of wood-derived biochar to high-value added electrocatalysts.Graphical

Importance of oxygen-containing functionalities and pore structures of biochar in catalyzing pyrolysis of homologous poplar

Biochar and bio-oil are produced simultaneously in one pyrolysis process, and they inevitably contact and may interact, influencing the composition of bio-oil and modifying the structure of biochar. In this sense, biochar is an inherent catalyst for pyrolysis. In this study, in order to investigate the influence of functionalities and pore structures of biochar on its capability for catalyzing the conversion of homologous volatiles in bio-oil, three char catalysts (600C, 800C, and 800AC) produced via pyrolysis of poplar wood at 600 or 800 °C or activated at 800 °C, were used for catalyzing pyrolysis of homologous poplar wood at 600 °C, respectively. The results indicated that the 600C catalyst was more active than 800C and 800AC for catalyzing cracking of volatiles to form more gas (yield increase by 40.2%) and aromatization of volatiles to form more light or heavy phenolics, due to its abundant oxygen-containing functionalities acting as active sites. The developed pores of the 800AC showed no such catalytic effect but could trap some volatiles and allow their further conversion via sufficient aromatization. Nevertheless, the interaction with the volatiles consumed oxygen on 600C (decrease by 50%), enhancing the aromatic degree and increasing thermal stability. The dominance of deposition of carbonaceous material of a very aromatic nature over 800C and 800AC resulted in net weight gain and blocked micropores but formed additional macropores. The in situ diffuse reflectance infrared Fourier transform spectroscopy characterization of the catalytic pyrolysis indicated superior activity of 600C for removal of –OH, while conversion of the intermediates bearing CO was enhanced over all the char catalysts.

Biochar supported nano core-shell (TiO2/CoFe2O4) for wastewater treatment

The porous structure of biochar, its large surface area, and its anti-oxidant properties are extensively used for pollutant removal strategies. The literature to date has reported that the biochar assisted metal-oxide core-shells have a dominating degradation ability under solar irradiation. Therefore, this study is significantly focused on cinnamon biochar as an active anti-oxidant agent incorporated in titania-cobalt ferrite nanocore-shell (Biochar/TiO2/CoFe2O4) structures for the first time in wastewater treatment against chlorophenol pollutants. Pure materials, core-shells, and biochar aided composites were synthesized by chemical methods, and their characteristics were analyzed using various instrumentation techniques. The diffraction outcomes of Biochar/TiO2/CoFe2O4 showed the mixed phases containing biochar, TiO2, and CoFe2O4. The morphological characteristics revealed that the biochar creates porosity and a peripheral layer covering the core-shell. Meanwhile, absorption studies of TiO2/CoFe2O4 core-shell and Biochar/TiO2/CoFe2O4 samples achieved 65% and 92% degradation efficiencies when exposed to visible light against chlorophenol pollutants, respectively. All these results confirm the presence of distinct functional groups as well as the combined synergistic effects that activated the charge separation, resulting in the successful destruction of water pollutants. In addition, the highly efficient Biochar/TiO2/CoFe2O4 sample was recycled, and the efficiency was maintained stable for five repeated degradation processes. Thus, Biochar/TiO2/CoFe2O4 will be utilized to expand the possibilities for biofuel generation and energy storage devices.

Degradation of 2,4-DCP by immobilized laccase on modified biochar carrier.

Rape straw was used as the raw material for the biochar in this study, which was then changed using acid, alkali, and magnetic techniques. The laccase was attached using the adsorptions-crosslinking process, and the three modified biochars served as the carriers. The ideal circumstances for laccase immobilization were explored, and both biochar and immobilized laccase's characteristics were examined. The removal of 2,4-dichlorophenol (2,4-DCP) by immobilized laccase from modified biochar and its degradation products were researched. The main conclusions are as follows: the optimal concentration of glutaraldehyde (GLU) was 4%, and the pH was four, and the enzyme dosage was 1.75mg/mL for the immobilized laccase of acid-modified biochar (SBC@LAC). The optimal concentration of GLU was 5%; the pH was four, and the enzyme dosage was 2mg/mL for immobilized laccase from alkali-modified biochar (JBC@LAC). The optimal concentration of GLU was 5%; the pH was four, and the enzyme dosage was 1.75mg/mL for immobilized laccase from magnetically modified biochar (CBC@LAC). SEM images could show the changes in the surface morphology of biochar caused by three modification methods. The BET results demonstrated that acid and magnetic modification increased the specific surface area of biochar, and alkali modification mainly expanded the pore size of biochar. FT-IR and XRD showed that modification and laccase loading had little effect on the structure of biochar. The stability of immobilized laccase was better than that of free laccase in acid-base, heat, and storage. Among the three modified biochar immobilized laccases, JBC@LAC showed the best acid-base stability and thermal stability, and the relative enzyme activity changed the least when pH and temperature conditions changed. The storage stability of SBC@LAC is the best. After 30days of storage, the relative enzyme activity is still 83%. The removal rates of 2,4-DCP were 57, 99, and 63%, respectively, by SBC@LAC, JBC@LAC, and CBC@LAC. After five reuses, the removal rates of 2,4-DCP by SBC@LAC, JBC@LAC and CBC@LAC were 26, 42, and 27%, respectively. The intermediate products of 2,4-DCP degradation by immobilized laccase were p-phenol, p-benzoquinone and maleic acid.

Activation of peroxymonosulfate by food waste digestate derived biochar for sulfamethoxazole degradation: Performance and mechanism

Digested derived biochar-based peroxymonosulfate (PMS) systems are promising for degrading antibiotics from water. Identifying the reactive sites on biochar and understanding the relationship between biochar structure and reactive oxygen species (ROS) generation are crucial for design and application of biochar-based catalysts. Herein, food waste digested was selected for the biochar preparation (FWDB). In a FWDB/PMS system, sulfamethoxazole (SMX) was degraded primarily by non-radicals rather than free radicals based on the contribution calculation. Correlation of catalytic sites on FWDB surface to ROS production was revealed. Defects exhibited a strong positive correlation with 1O2 contribution. The C = O, C-O, pyrrolic N, pyridinic N contents showed a moderate positive correlation with 1O2 contribution. Besides, the designed granular FWDB was loaded in a continuous flow reactor, achieving efficient and stable removal of contaminants from secondary effluent in a municipal wastewater plant. Findings from this study might offer novel perspectives for the development and design of biochar catalysts, promoting the actual application of biochar in a complicated aqueous matrix.

Resource utilization of rice straw to prepare biochar as peroxymonosulfate activator for naphthalene removal: Performances, mechanisms, environmental impact and applicability in groundwater

Herein, biochar was prepared using rice straw, and it served as the peroxymonosulfate (PMS) activator to degrade naphthalene (NAP). The results showed that pyrolysis temperature has played an important role in regulating biochar structure and properties. The biochar prepared at 900°C (BC900) had the best activation capacity and could remove NAP in a wide range of initial pH (5-11). In the system of BC900/PMS, multi-reactive species were produced, in which 1O2 and electron transfer mainly contributed to NAP degradation. In addition, the interference of complex groundwater components on the NAP removal rate must get attention. Cl− had a significant promotional effect but risked the formation of chlorinated disinfection by-products. HCO3−, CO32−, and humic acid (HA) had an inhibitory effect; surfactants had compatibility problems with the BC900/PMS system, which could lead to unproductive consumption of PMS. Significantly, the BC900/PMS system showed satisfactory remediation performance in spiked natural groundwater and soil, and it could solve the problem of persistent groundwater contamination caused by NAP desorption from the soil. Besides, the degradation pathway of NAP was proposed, and the BC900/PMS system could degrade NAP into low or nontoxic products. These suggest that the BC900/PMS system has promising applications in in-situ groundwater remediation.

Feasibility of nitrate adsorption from aqueous solution by nitrogen and oxygen-modified pine bark biochar: experimental and computational approach

Efficient and economical wastewater treatment has presented itself as a global challenge. In this context, adsorption is one of the most effective methods to remove contaminants from wastewater. The present study evaluated the feasibility of chemically modified pine bark biochar’s nitrate adsorption ability. Pine bark biochar was modified with urea and sulfuric acid to remove nitrate from an aqueous solution. The physicochemical properties of the biochar samples, such as pH, pH at point of zero charges, surface atomic composition, surface morphology, and surface area, were evaluated. The equilibrium adsorption data were fitted to the Langmuir and Freundlich isotherm models. The kinetic data were fitted to different kinetic models (pseudo-first order, pseudo-second order, intraparticle diffusion, and Elovich). The adsorption data fitted well with the Langmuir and pseudo-first order models. The maximum nitrate adsorption capacity was found to be 1.548 mg g−1. Mass transfer studies were conducted to identify the rate-limiting step, values of the external mass transfer coefficient, and diffusion coefficient in the nitrate adsorption process by the modified biochar. The external mass transfer coefficients were in the range of 2.2 × 10–11–2.86 × 10–10 m s−1. The intraparticle diffusion coefficient ranged from 6.53 × 10–10 to 1.78 × 10–9 m2 s−1. The Biot number value less than 100 indicated that the adsorption was controlled by film diffusion. Interaction energies between nitrate ions and model biochar structures were calculated DFT-based quantum chemical software (Gaussian). The positive interaction energy values (2.3485–2.485 eV) suggested nitrate adsorption on model biochar structures was thermodynamically not feasible.Graphical

Heteroatoms intra-actions and oxidant-pollutant competition over BC2O sites in N, S, B-tri-doped biochar for the nonradical activation of peroxymonosulfate

Tri-doping effect on the catalytic activity of biochar remains limitedly explored. In this study, N, S, B-tri-doped biochar was fabricated via a one-pot calcination technique. The effects of calcination temperature and boric acid (BA):thiourea (heteroatom precursors) ratio on the surface properties and catalytic performance of the biochar were systemically investigated to elucidate the heteroatoms intra-actions during the doping process. Increasing the calcination temperature from 500 to 800 °C significantly increased the BC2O content, reduced atomic percent (at.%) of S by over 95 %, and had minimal effect on graphitic N content. Increasing the BA:thiourea ratio had a generally positive effect on BC2O content and promoted pyrrolic and pyridinic N formation. Furthermore, BCO2 groups vigorously competed against S over doping sites in the biochar structure. The catalytic performance of the tri-doped biochar as peroxymonosulfate (PMS) activator was studied using tetracycline (TC) as the model pollutant. A more effective catalytic activity can be obtained at higher calcination temperature and BA:thiourea ratio. The catalytic performance was found to withstand different water matrixes and conditions. The chemical scavenger studies and electrochemical analysis stipulated a major contribution of nonradical activation pathway with a competitive behavior between PMS and TC over adsorption and activation on the catalyst surface, with BC2O playing a decisive role in PMS activation. Lastly, based on the identified TC degradation intermediates, the TC degradation pathways were proposed, and the toxicity of these intermediates was evaluated. Overall, the results of this study show that tri-doping can potentially produce an effective PMS activator for practical applications.

Phosphogypsum/titanium gypsum coupling for enhanced biochar immobilization of lead: Mineralization reaction behavior and electron transfer effect

The hazards caused by Pb pollution have received worldwide attention. Phosphogypsum (PG) and titanium gypsum (TG) have the disadvantage of limited adsorption capacity and poor dispersion when used as heavy metal adsorbents on their own. The excellent pore and electron transfer capacity of biochar makes it possible to combine with PG and TG to solidify/stabilize Pb2+. In this study, the mechanism of Pb2+ adsorption/immobilization by rice husk biochar (BC) combined with PG/TG was investigated in terms of both mineral formation and electron transfer rate. The removal rate of Pb2+ by BC composite PG (BC/PG-Pb) or TG (BC/TG-Pb) was as high as 97%–98%, an increase of 120.9% and 122.5% over BC. Adsorption kinetics and mineral precipitation results indicate that the main removal of Pb2+ from BC/PG-Pb and BC/TG-Pb is achieved by PG/TG induced Pb-sulfate and Pb-phosphate formation. The addition of PG/TG significantly enhances the formation of stable Pb-minerals on the biochar surface, with the proportion of non-bioaccessible forms exceeding 50%. The four-step extraction results confirm that P and F in PG/TG are key in facilitating the conversion of Pb minerals to pyromorphite. The rich pore structure of biochar not only disperses the easily agglomerated PG/TG onto the biochar surface, but also attracts Pb2+ for uniformly dispersed precipitation. Furthermore, the excellent electrical conductivity and smooth electron transfer channels of biochar facilitate the reaction rate of Pb2+ mineralization. Overall, the use of biochar in combination with PG/TG is a promising technology for the combination of solid waste resourceisation and Pb remediation.

Sustainable catalytic graphitization of biomass to graphitic porous carbon by constructing permeation network with organic ligands

Common strategies for catalytic graphitization of biochar into graphitic porous carbon (GPC) still face great challenges, such as the realization of simple procedures, energy conservation, and green processes. Controlling over the graphitization degree and pore structure of biochar is the key to its structural diversification. Herein, a clean and energy-efficient method is developed to synthesize adjustable graphitic degree and structure porosity GPC from rice husk-based carbon (RHC) at a relatively low temperature of 800–1000 °C with environment-benign organometallic catalyst ethylenediaminetetraacetic acid ferric sodium salt (EDTA-iron) and the recovery ratio of catalyst is as high as 97%. The formed by the organic ligands of EDTA-iron facilitates the etching of RHC surface and pore by iron, resulting in highly graphitized and developed porous GPCs. The pore structure and graphitization degree of GPCs can be adjusted by altering the catalyst loading, temperature, and holding time. The catalyst EDTA-iron with a lower concentration mainly plays the role of etching, which promotes the formation of porous carbon with larger surface area (SBET = 1187.2 m2·g−1). The catalyst with higher concentration mainly plays the role of catalyzing graphitization and promotes the obtaining of graphitic carbon with high graphitization degree (ID/IG = 0.19). The mechanism of EDTA-iron catalyzed graphitization of RHC is explored by the comprehensive analysis of BET, XRD, Raman, TEM and TGA. This research not only provides an efficient method for the preparation of high-quality biomass-based graphite carbon, but also provides a feasible method for the preparation of biomass-based porous carbon.

Biochar pyrolyzed with concentrated solar radiation for enhanced nitrate adsorption

Biochar has been recognized as an effective soil amendment for reducing nitrogen leaching in agriculture, but its large-scale implementation is impeded by the costly production process due to high energy requirements for thermal decomposition of feedstock. This study aimed to develop a novel pyrolysis system utilizing concentrated solar radiation to produce biochar and explore the potential of solar-pyrolyzed biochar for nitrate adsorption. Results showed that the solar-pyrolyzed biochar exhibited a maximum adsorption capacity of 35.59 mg/g for nitrate, significantly higher than two out of the three commercially available biochars in America that are selected for comparison. The Fourier-transform infrared (FTIR) analysis suggested a variety of oxygen-containing polar functional groups present in the solar-pyrolysis biochar, which enhances its affinity for nitrate and other hydrophilic ions. The X-ray diffraction (XRD) analysis revealed that the solar pyrolysis biochar was an amorphous material with a poorly crystalline, carbon-rich phase, indicating a high degree of carbonization and recalcitrance, as confirmed by Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) analysis. The porous structure of the solar-pyrolysis biochar suggested a larger specific surface area, which could benefit adsorption. Although further experiments are required to determine the stability and cost-effectiveness of a scaled-up solar-pyrolysis apparatus, these findings provide hope for a more sustainable and high-performing biochar production process in the future.

Antibacterial Effect of Polyvinyl Alcohol/Biochar–Nano Silver/Sodium Alginate Gel Beads

To date, biochar bacteriostatic material has attracted much attention from researchers. The compact porous structure of fish-scale biochar provides good application prospects. In this study, silver-carrying biochar–polyvinyl alcohol–alginate gel beads (C/PVA/SA) were designed for suppressing bacteria. The biochar was loaded with nano silver particles as the filler, alginate as the substrate, and polyvinyl alcohol (PVA) as the additive to enhance the mechanical properties. The composite gel beads were characterized using Fourier-transform infrared spectrometry (FT-IR). The results indicated that adjusting the PVA concentration could retain the bacteriostatic performance of the gel beads in different pH value solutions. It was found that C/PVA/SA gel beads had a strong inhibitory effect on Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. After ten consecutive antibacterial tests, the antibacterial rate remained high (above 99%) for 15 days. The adhesive effect of SA and PVA resulted in a tight spatial structure of the gel beads. The C/PVA/SA gel composition could effectively prevent water loss and enhance the shrinkage ability of the gel beads. The good degradation performance of C/PVA/SA was also in line with the concept of environmental protection. In general, the C/PVA/SA gel beads showed high potential for application in the treatment of microbial contamination and environmental protection.

CO2 and H2O as sweep gases elevated carbon stability and decreased phytotoxicity of biochars

As a crucial pyrolysis factor for biochar production, the mechanistically effect of different sweep gases on the inherent multi-level chemical structure of biochars is poorly understood, impeding the widespread use of biochars as sustainable carbon-negative materials. This study investigated the effect of CO2 and H2O as sweep gases relative to N2 on the physic-chemical properties of biochars derived from sawdust (SBC-N/C/H) and pig manure (PBC-N/C/H) at 300–700 °C. Meanwhile, carbon sequestration potential and potential environmental risks of SBC-N/C/H and PBC-N/C/H were comprehensively evaluated. Unlike N2, CO2 showed a superior effect on biochar (especially SBCs with more carbonaceous substances), decreased the oxygenated-functional groups content in SBC-C (14.6%–28.1%) relative to SBC-N (25.5%–37.4%) via cracking reaction. Besides, CO2 stimulated the formation of pore structure in biochar (surface area increased from 15.2 m2/g in SBC700-N to 24.1 m2/g in SBC700-C) by boudouard reaction. H2O exhibited a similar but less pronounced effect with CO2, leading to a lower H/C ratio in biochar by aggravated demethylation of methoxyl groups and facilitating a more developed pore structure with water–gas reaction. Both CO2 and H2O enhanced the carbon stability of biochar and carbon sequestration potential in SBC500-C (30.1%) and SBC500-H (28.7%) was higher than SBC500-N (25.6%). Moreover, CO2 and H2O exhibited excellent performance in mitigating phytotoxicity of biochars (especially for PBCs) to radish and cucumber seeds via the reduced release of polycyclic aromatic hydrocarbons and heavy metals. These results proposed an effective approach to improve long-term carbon sequestration and environmental safety of biochars.