Pore Structure Of Biochar Research Articles

Experiment and multiscale molecular simulations on the Cu absorption by biochar-modified asphalt: An insight into removal capability and mechanism of heavy metals from stormwater runoff

Asphalt has been the primary material for pavements and other building components such as roof shingles and waterproofing systems, which can be the path for stormwater runoff pollutants such as heavy metals (HMs). In this study, the capability and mechanism of asphalt and biochar-modified asphalt (BMA) to remove Cu as the typical HM found in the road dust and surface runoff were fundamentally explored for the first time. Experiment and multiscale molecular simulations were performed. Molecular dynamics (MD) simulations showed the Cu absorption into the asphalts. Monte Carlo (MC) and density functional theory (DFT) revealed the detailed mechanism of Cu absorption. Biochar (BC) presence modified the spatial distribution of maltene and asphaltene fractions in asphalt and enhanced the absorption. Maltenes were absorbed into the porous structure of BC, leaving more asphaltenes in the asphalt part of BMA. Asphaltenes were the Cu adsorbing preference sites ascribed to the cation-π interaction between Cu and the aromatic plane. The DFT simulations also suggested favourable adsorption of other commonly found metals (e.g., Cr, Pb, Ni, Cd, and Zn) onto asphaltenes. The present study found the capability and mechanism of BMA and asphalt to remove HMs at the molecular scales, providing a path for designing asphalts with value-added functionality in minimizing environmental pollution.

A new strategy of preparing high-value products by co-pyrolysis of bamboo and ZIF-8

To improve the pore structure of biochar, the H2 yield of gas, and the quality of bio-oil in biomass pyrolysis, a new pyrolysis strategy of co-pyrolyzing bamboo and Zeolitic Imidazolate Frameworks (ZIF-8) at different temperatures and mixing ratios was proposed. Results showed that ZIF-8 blending improved the quality of pyrolytic products. For biochar, the specific surface area was increased tenfold from 49.63 m2/g for raw bamboo to 557.37 m2/g with a 4:1 mass ratio of bamboo to ZIF-8 at 900 °C. And hierarchical porous biochars were formed. For gas, the H2 yield was increased significantly from 4.35 mmol/g (32.84 vol%) for raw bamboo to 7.87 mmol/g (43.73 vol%) with a 4:1 mass ratio of bamboo to ZIF-8 at 900 °C. For bio-oil, ZIF-8 blending promoted the conversion of bamboo to acetic acids, furans, and cyclopentanones, while inhibiting the formation of polyaromatic compounds, showing that ZIF-8 could enhance the secondary cracking of volatiles and promote the branch chain fracture, dehydrogenation, ring-opening and decarbonylation of bamboo. These results indicated that ZIF-8 had excellent effects on bamboo pyrolysis to produce high-value products, and it was enlightening for biomass thermal conversion utilization.

Simultaneous adsorption of Cd(II) and degradation of OTC by activated biochar with ferrate: Efficiency and mechanism

Biochar-supported zero-valent iron nanocomposites have received much attention due to their application potential in environmental pollution remediation. However, in many occasions, zero-valent iron loading improves the electron transfer efficiency and catalytic oxidation capacity of biochar while blocking the original pore structure of biochar, limiting its application potential. In this study, a zero-valent iron composites with large SSA (865.86 m2/g) was prepared in one step using pre-pyrolysis of biochar powder and K2FeO4 grinding for co-pyrolysis. The processes of ZVI generation and SSA expansion during the pyrolysis were investigated. The factors affecting the removal process of Cd and OTC in water by the composites were investigated. The mechanisms of Cd fixation and OTC degradation by the composites were explored by experiments, characterization, and DFT calculations. The OTC degradation pathway was proposed by theoretical predication and LC-MS spectrometry. The results indicate that ion exchange, complexation with oxygen-containing functional groups, electrostatic attraction, and interaction with π-electrons are the main mechanisms of Cd immobilization. The degradation pathways of OTC mainly include dehydroxylation, deamination and dealkylation.

Temperature influence on layered double hydroxide tailored corncob biochar and its application for fluoride removal in aqueous media

Exposure to excess fluoride is a controversial public health concern as it can cause dental/skeletal fluorosis as well as renal toxicity. The study intended to evaluate the synergistic interaction of clay intercalation and thermochemical modification on corncob biochar to remove fluoride from aqueous solutions. Layered double hydroxide was assorted with thermally activated (torrefaction and pyrolysis) corncob biochar at 1:1 (w/w) ratio to obtain composites called LDH-CCBC250 and LDH-CCBC500. Physicochemically characterized adsorbents were assessed against the pH (3–9), reaction time (up to 12 h) and initial fluoride concentration (0.5–10 mg L−1) for defluoridation. The porous structure of biochar was found to be richer compared to biocharcoal. The adsorption performance of LDH-CCBC500 was 6-fold higher compared to LDH-CCBC250 signifying the pronounced effect of thermal activation. Fluoride adsorption was pH dependent, and the best pH was in the range of pH 3.5–5.0 and there was no ionic strength dependency. Fluoride uptake by LDH-CCBC500 follows pseudo-second order and Elovich kinetic models, which suggests a chemisorption process followed by physisorption. The most expected way to eliminate fluoride by LDH-CCBC500, which had a maximum adsorption capacity of 7.24 mg g−1, was cooperative chemical adsorption upon the Langmuir and Hills isotherm (r2 = 0.99) parameters. Layered double hydroxide intercalated corncob biochar derived from slow pyrolysis is best performing in acidic waters.

Effect of Aging on Stabilization of Cd2+ Through Biochar Use in Alkaline Soil of Bayan Obo Mining Area

Although biochar has been widely used in the remediation of heavy metal pollution in acidic and neutral soils, less attention has been paid to whether biochar will alter its structural properties and the ability to retain heavy metals after different degrees of aging in alkaline soils. In this study, two artificial accelerated aging methods (freeze-thaw cycle and dry-wet cycle) and a short-term natural aging method were used to simulate the aging process of biochar prepared from corn stalk. We investigated the changes in the soil pH and bioavailability, total content, and transformation of Cd2+ before and after aging treatments. Biochar was separated from the soil for characterization to explore the effect of aging on the passivation of Cd2+ by biochar in the alkaline soil of the mining area. The results showed that adding biochar to alkaline soil in the Bayan Obo mining area had no significant liming effect, and pH decreased after the freeze-thaw and dry-wet accelerated aging treatments. Compared with that in the control, the CaCl2-extractable contents of Cd2+ decreased by 19.32%-30.67%, and the total contents of Cd2+ decreased by 5.02%-7.18%. Aging did not significantly change the transformation of Cd2+ but reduced the distribution of acid-soluble and reducible fractions, indicating that biochar could immobilize Cd2+ for a long time after aging, which was related to the increase in oxygen-containing functional groups and the pore structure of biochar. These results are important for evaluating its long-term application prospects in the mining environment.

Effect of nano-Fe3O4 biochar on anaerobic digestion of chicken manure under high ammonia nitrogen concentration

In order to improve the stability and CH4 production efficiency of the anaerobic digestion (AD) system under high ammonia nitrogen (AN) concentration, this study investigated the effect of biochar loaded with nano-Fe3O4 particles to generate nano-Fe3O4 biochar on AD of chicken manure (CM). The results showed that biochar can be used as an excellent carrier for nano-Fe3O4 particles, solving the problem of easy agglomeration and loss. The inhibition of the AD system caused by high concentrations of AN was greatly mitigated after loading nano-Fe3O4 particles on biochar, and the CH4 yield was substantially increased. The highest CH4 yield was achieved when the amount of nano-Fe3O4 biochar was 15%, which was 62.61% higher compared to the control group. Microbial community analysis showed that the porous structure of biochar was capable of immobilizing and enriching microorganisms, and the relative abundance of Firmicutes and Methanobacterium increased by 28.67–54.44% and 52.62–87.70%, respectively. Firmicutes acted as an important acetate bacterium, contributing to syntrophic acetate oxidation (SAO) with hydrotropic methanogenesis. SAO was an effective alternative pathway for acetate degradation under ammonia stress involving the syntrophic activities of SAO bacteria and hydrogenotrophic archaea. The load of nano-Fe3O4 particles increased the relative abundance of Chloroflexi from 0.52% to 3.51% and the Methanosarcina from 27.50% to 49.30%. Chloroflexi and Methanosarcina could act as potential direct electron transfer (DIET) partners for facilitating methane production by promoting the SAO pathway.

Is biochar a reliable catalyst for activating peroxydisulfate? Damage of biochar during catalytic process.

The unsatisfactory reuse performance of biochar in the catalytic system has become an important factor limiting its application. Damage of biochar in the catalytic systems has been reported, but the mechanism of damage is still unclear. In this study, cotton stalk and walnut shell biochar were used to activate peroxydisulfate (PDS) for sulfamethazine degradation, and multiple characterization methods were used to determine the damage of biochar. The comparative experiments of biochar, recycled biochar, and the biochar treated by PDS in catalytic reaction showed that the performance of biochars decreased by 37.5%-65.3%. After the catalytic reaction, the unstable carbon in biochar was lost, and the biochar surface was oxidized, which reduced its affinity to organic matter. CO2 physisorption showed that the pore structure of biochars barely changed. However, for walnut shell biochar, its adsorption capacity of nitrogen decreased obviously. Moreover, the electrochemical tests showed that the conductivity of walnut shell biochar decreased, which would lead to the reduction of its catalytic performance through the electron transfer path. Overall, the effects of catalytic process on the performance of biochar cannot be ignored. Therefore, more efforts are needed to improve the stability and homogeneity of biochar as an efficient and sustainable PDS activator.

Phosphoric acid surface modified Moringa oleifera leaves biochar for the sequestration of methyl orange from aqueous solution: Characterizations, isotherm, and kinetics analysis

AbstractBiochar is a promising engineering material to sequestrate organic pollutants from wastewater. In the current study, several surface‐modified Moringa (M.) oleifera leaf biochars were prepared and utilized for the sorption of methyl orange (MO) dye from an aqueous solution. Raw biochar was produced by the carbonization of M. oleifera leaves at 350°C in a muffle furnace for 2 h. The surface‐modified M. oleifera biochars were prepared at 400°C, 500°C, and 600°C using phosphoric acid (H3PO4) at different combinations to improve the biochar pore structure, surface functional groups, and biochar stability. The highest surface area (267.15 ± 42.40 m2/g) of the modified biochar was achieved at 500°C with H3PO4 to raw biochar ratio of 1.5. Surface morphological results revealed the formation of pores, troughs, and channels with the increasing activation temperature. The carbon (C) content (wt%) was maximum (79.61%) for activated biochar at 500°C. The presence of enhanced functional groups, e.g., hydroxyl, aliphatic carbon‐hydrogen, carbonyl, ester, and phenol structures in surface‐modified biochars was observed from FT‐IR results. The Langmuir isotherm model was fitted to better describe the adsorption phenomenon for both surface‐modified biochars and raw biochar compared to the Freundlich isotherm model. The highest adsorption capacity was 175 mg MO dye/g of activated biochar prepared at 500°C with an H3PO4 impregnation ratio of 1.5. Pseudo‐1st order model fitted the best for raw biochars whereas pseudo‐2nd order and intraparticle diffusion models better describe the sorption of MO onto activated biochar. The results anticipated M. oleifera leaf‐activated biochar as an efficient tool for the treatment of MO contaminated wastewater.

Tetracycline Removal by Hercynite-Biochar from the Co-Pyrolysis of Red Mud-Steel Slag-Sludge.

The sludge-derived biochar is considered an effective emerging contaminants adsorbent for wastewater treatment. In this paper, red mud and steel slag (RMSS) was used for improving sludge dewaterability and enhancing the sludge-derived biochar adsorption capacity. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and a scanning electron microscope (SEM) were employed to comprehensively characterize the mineral composition, functional group, and morphology of the adsorbent. RMSS was able to improve the sludge dewatering performance by providing a skeleton structure to promote drainage and Fe(III) to decrease the Zeta potential. The dosage of 20 mg/g RMSS was able to reduce the specific resistance to filtration (SRF) and the Zeta potential of sludge from 1.57 × 1013 m/kg and −19.56 mV to 0.79 × 1013 m/kg and −9.10 mV, respectively. The co-pyrolysis of RMSS and sludge (2:8) induced the formation of biochar containing FeAl2O4 (PS80). The PS80 exhibited a large surface area (46.40 m2/g) and high tetracycline (TC) removal capacity (98.87 mg/g) when combined with H2O2 (PS80-H2O2). The adsorption process of TC onto PS80 and PS80-H2O2 was well described by the pseudo-first-order and pseudo-second-order kinetic model, indicating physisorption and chemisorption behavior. The results indicated that co-pyrolysis of RMSS sludge PS80-H2O2 could enhance the biochar adsorption capacity of TC, attributable to the degradation by ·OH generated by the heterogeneous Fenton reaction of FeAl2O4 and H2O2, the release of adsorbed sites, and the improvement of the biochar pore structure. This study proposed a novel method for the use of RMSS to dewater sludge as well as to induce the formation of FeAl2O4 in biochar with effective TC removal by providing a Fe and Al source, achieving a waste-to-resource strategy for the integrated management of industrial solid waste and sewage sludge.

Preparation of hierarchical porous carbon by pyrolyzing sargassum under microwave: The internal connection between structure−oriented regulation and performance optimization of supercapacitors

To find an effective correlation between the preparation process and the application performance of symmetric supercapacitors, the relationship between the structural characteristics of biomass porous carbon and the electrochemical performances of supercapacitors was studied. Based on a response surface experimental design, the pore structure of biochar produced by the microwave pyrolysis of sargassum was adjusted through the collaborative optimization of key parameters, and graded sargassum porous carbon (SPC) with different pore characteristics was successfully prepared. Three representative samples, SPC−1, SPC−2, and SPC−3, were selected by systematically exploring the effects of the specific surface area (SSA), pore volume (Vtotal), and pore size distribution on the electrochemical performances. The SSA and Vtotal values of SPC−1 were 1500.50 m2 g−1 and 1.0513 cm3 g−1, respectively. The large number of micropores provided space for electronic storage, allowing it to have an excellent electronic storage capacity. The SSA of SPC−2 was 2019.90 m2 g−1, and Vtotal was 1.2241 cm3 g−1. The rich micropores resulted in a good charge–discharge rate. The SSA of SPC−3 was as high as 2103.20 m2 g−1, and Vtotal was 1.4756 cm3 g−1. The micron−level mesopores between the SPC−3 carbon skeletons acted as ion buffer reservoirs to shorten the ion diffusion distance and produce excellent rate performances. Subsequently, the morphology and surface properties of porous carbon samples were characterized. The study revealed that hierarchical porous carbon materials with excellent properties must achieve a balance of the microstructure and surface properties and their influence on the electrochemistry. A higher degree of graphitization could bring about a high pore regularity, thereby optimizing the ion transport kinetics. Heteroatoms could increase redox active surface sites and provide additional pseudocapacitance, but the resulting defect structure formed a large number of pores with high edge roughness in the carbon material, which had a certain negative impact on the capacity properties of the materials. The above findings can provide technical support and a theoretical basis for controlling the pore networks and directionally optimizing the performances of supercapacitors by adjusting the pore structure of biochar.

Preparation and evaluation of fine-tuned micropore biochar by lignin impregnation for CO2 and VOCs adsorption

The pore structure of adsorbent plays a critical role during the CO2 and volatile organic compounds (VOCs) adsorption. To improve the adsorption performance, fine-tuned micropore biochar was prepared by impregnation using sodium lignosulfonate as precursor. And the impregnated biochar was characterized and used as adsorbent to adsorb CO2 and VOCs (benzene and acetone). The results showed that the specific surface area (SSA) and micropore volume (Vmicropore) of impregnated biochar increased 3.27 and 5.02 times, which enhanced the CO2 adsorption amount obviously (77.02–102.88 mg/g). The pore structure of biochar was critical to CO2 capture, and high SSA, large Vmicropore and narrow aperture were benefits for the adsorption. Both Avrami fractional model and Freundlich model fitted the adsorption better, indicating the CO2 adsorption on impregnated biochar was multilayer adsorption and determined by both physical and chemical mechanisms. The adsorption was overwhelming exothermic process, thus increasing the temperature from 0 ℃ to 65 ℃ would decrease the adsorption amount by 74.22%-79.40%. High reusability (93.98%-98.21%) after 10 times adsorption-desorption cycles acknowledged the biochar was promising CO2 adsorbents. In addition, the impregnated biochar exhibited excellent VOCs adsorption performance, with the adsorption amount being 31.35–61.14 mg/g and 44.67–80.99 mg/g for benzene and acetone, respectively. All the results showed lignin impregnated biochar is a promising adsorbent for CO2 capture and pollution adsorption.

Insight into mass transfer mechanism and equilibrium modeling of heavy metals adsorption on hierarchically porous biochar

One-step pyrolysis of biomass/zinc salts composites was investigated to clarify the effects of zinc salts on the pore structure of biochar and its performance for removing heavy metals from wastewater. The characterization results indicated that zinc salts not only promoted the pyrolysis of biomass but also decomposed to generate volatile gas and thermally removable pores templates in situ that established the hierarchical porous biochar (HPBC). More specifically, HPBC exhibited a significantly increased pore volume compared with pristine biochar (by a factor of up to 80) and large specific surface areas ranging from 769.91 to 1192.37 m2/g. To connect these improved properties with the heavy metals removal performance, the pore volume and surface diffusion model (PVSDM) was used to numerically simulate the adsorption process and investigate the diffusion and mass transfer mechanism. Notably, the fitted pore volume diffusion coefficient of HPBCs (DpHPBC) was at least three orders of magnitude larger than their surface diffusion coefficient (DSHPBC), whereas these two parameters (DpBC&DSBC) for pristine biochar (BC) were of the same order of magnitude but were much smaller in value than those obtained by HPBCs. These results suggested that the improved biochar pore structure by co-pyrolyzing with zinc salts mainly enhanced the pore volume diffusion of heavy metals during their adsorption. The adsorption process of Pb2+ on HPBCs was controlled by the intra-particle diffusion mechanism, while the adsorption process of Cd2+ was controlled by external and internal mass transfer.

Volatile-char interactions during biomass pyrolysis: Reactor design toward product control

This paper proposes a novel reactor featuring controllable adjustment of volatile-char interactions to investigate the pyrolysis of poplar wood and corresponding products. Controllable adjustment of volatile-char interactions enables the selective production of pyrolysis products. The oxygen content in biochar nearly disappears with the reduction of volatile-char interactions and the pore structure of biochar is improved after the interactions being intensified. Moreover, as the interactions reduce, the bio-oil yield increases by 1.23 times, and the outputs of acetic acid and phenols in the bio-oil exhibit decreasing trends, while that of levoglucosan is improved by nearly 4.5 times. Furthermore, the average molecular weight of bio-oil decreases from 786 to 322 g/mol with the continuous intensification of volatile-char interactions. It concludes that the controllable adjustment of volatile-char interactions plays a vital role in regulating the distribution of pyrolysis products and is of great importance to the production of light oil.

The potential use of straw-derived biochar as the adsorbent for La(III) and Nd(III) removal in aqueous solutions.

Recent attention on the lanthanides (Ln) contaminant such as lanthanum (La) and neodymium (Nd) extensively used in industry has aroused the great desire for the effective adsorbent. Biochar, relying on its high selectivity and optional ease, is regarded as a promising adsorbent for lanthanides removal although the evaluation of the efficiency and mechanism of La(III) and Nd(III) adsorption on biochar still lags. Here, we investigated the aqueous adsorption processes through SEM, TEM, EDS, FTIR and Raman spectra, XPS, and batch experiments. The porous structure of biochar and the complex functional groups on its surface contributed to the La(III) and Nd(III) removal processes. The kinetic of La(III) and Nd(III) adsorption agreed well with the pseudo-second-order kinetic model. The adsorption capacity showed a strong positive correlation with pH value. However, it was only slightly altered and robust in La(III) and Nd(III) adsorption respectively. The isotherm results reflected significant fitting to the Sips model as well as Langmuir and Freundlich model. Thermodynamic demonstrated the spontaneity, endothermic nature, and temperature favor of the adsorptions on biochar surface (La: ΔH0=35.39 (kJ/Mol), ΔS0=104.71(J*Mol-1*K-1) and ΔG0<0; Nd: ΔH0=16.71(KJ/mol), ΔS0=119.41(J*Mol-1*K-1) and ΔG0<0). Both the La(III) and Nd(III) removal processes combined physical and chemical adsorptions. Therefore, biochar could be a potential green material for the lanthanum and neodymium adsorption with high efficiency.

Quantitative analysis of feedstock structural properties can help to produce willow biochar with homogenous pore system

Novel bioeconomic approaches call for increasingly faster production of lignocellulosic biomass and its better-tailored use for higher added value. The high-yield capacity and structural properties of willows (Salix spp.) suggest their excellent potential for the production of designed biochar for use in agronomic, electronic and technical applications. All these applications rely on the internal pore structure of biochar. However, we lack an in-depth quantitative understanding of the interlinkages between the feedstock properties and the physical quality of the biochar produced. We studied quantitatively how the clonal and within-plant properties of five different willow clones (hybrids of Salix schwerinii E.L. Wolf) affected the micrometre-scale pore properties of the produced biochars (pyrolyzed at + 462 °C). The porosity and pore size distribution were analysed before and after slow pyrolysis by X-ray microtomography and image analysis. We also studied the potential of conventional low-cost fibre analysis techniques to be used to predict biochar pore properties directly from fresh feedstock. The total porosity (0.55–0.62) and the pore size distribution of willow wood and derived biochars varied between clones. Approximately two-thirds of the biochar total porosity was associated with pores formed by wood fibres. Pyrolysis levelled off the structural variation detected between and within the clones. Pyrolysis-induced shrinkage reduced the pore sizes and narrowed the pore size distribution. The results suggest that conventional fibre analysis techniques could be utilized to predict biochar homogeneity. Short rotation coppice willows are suitable feedstock to produce homogenous biochar precursor for production of bio-based carbon materials to be used in high value-added technical applications. The structural homogeneity of the feedstock and produced biochar can be enhanced by selecting proper harvesting strategy and clones used in plantations. From the industrial perspective, comprehensive understanding of feedstock properties helps to control quality of the produced biochar.

Insights into the mechanism of tar reforming using biochar as a catalyst

Biochar is an efficient catalyst for tar removal from syngas during biomass gasification. The aim of this research is to investigate the mechanism of tar reforming using biochar as a catalyst. A series of in situ steam tar reforming experiments were carried out using a two-stage fluidized-bed/fixed-bed reactor at 800 °C. Mallee wood biochar (106–250 μm) was activated in 15 vol% H2O balanced with Ar for different times (0–50 min) and then used as a catalyst for tar reforming. The on-line gas composition, light tar composition and the pore structure of biochar were analysed using mass spectrometer (MS), GC–MS and synchrotron small angle X-ray scattering (SAXS) respectively. An increased ratio of H2/CO was observed after reforming with biochar compared to reforming without biochar. The destruction of light tar compounds, especially the non-oxygen-containing compounds, was significantly enhanced when activated biochars were used. Steam activation increased the specific surface area (SSA), micro- and mesopore volumes in biochar while the values stayed almost unchanged during tar reforming. Results indicate that the micro- and mesopores in biochar promote the diffusion of both small and large tar molecules into the internal surface of biochar. However, the catalytic activity of biochar for tar reforming mainly depends on the content of O-containing functional groups in biochar. The O-containing functional groups facilitate the dissociation of tar molecules to form tar radicals, giving rise to the enhanced tar removal efficiency. Moreover, the formation of tar radicals over O-containing functional groups appears as the rate-limiting step in the process of catalytic reforming of tar over biochar catalysts.

A SAXS study of the pore structure evolution in biochar during gasification in H2O, CO2 and H2O/CO2

Gasification of biomass allows for its efficient utilisation as a renewable fuel through syngas production. This work presents the different effects of gasifying agents (H2O, CO2 and H2O/CO2) on the pore structure evolution in biochar during gasification. The effects of temperature (700, 800 and 900 °C) and biomass particle size (up to 5.6 mm) were also studied. The pore structure of biochar was characterized using synchrotron small angle X-ray scattering (SAXS). The pore development in biochar during gasification in H2O/CO2 was close to that in H2O. Carbon removal is more selective in CO2 than H2O and the derived biochar displayed pore fractal features, whereas the biochars gasified in H2O and H2O/CO2 exhibited a surface fractal network due to the less selective carbon removal in the presence of H2O. The pore structure development produced by various gasifying agents was paralleled by the evolution of the aromatic structures characterized by Raman spectroscopy. The different pore structure features result from the different reactivity of carbon sites with H2O and CO2, which can be attributed to the different amounts of O-containing groups in biochar, as well as the different reactivity of H2O and CO2. Increasing temperature reduced the differences in pore structure between biochars gasified in H2O and CO2. Biomass particle size had little impact on the pore structure of biochar.

Biochar engineering and ageing influence the spatiotemporal dynamics of soil pH in the charosphere

The charosphere, the interface microzone between biochar and soil, plays a vital role in biochemical processes following biochar application to soil. However, the development of the charosphere over time, and the pH dynamics within and around it, remain poorly understood as biochar ages. In this study, two kinds of biochars with distinct characteristics, a pristine biochar (BCSE) and a hydroxyapatite engineered biochar (BCHA), were subjected to artificial physicochemical ageing treatment. The localized impact of the fresh and aged biochars on soil pH were quantified, and spatiotemporal changes at the microscale visualized, using the planar optode technique. Association between the biochar characteristics and their charospheres was assessed using correlation and redundancy analyses to identify controls on charosphere properties.Significant localized effects on soil pH were induced by biochar application, with pH gradients around biochar particles forming gradually over 24 h. Fresh biochars generated charospheres with radii ranging from 1.13 mm to 1.63 mm. However, ageing treatment slightly narrowed the charosphere radius to 1.08–1.12 mm. The spatiotemporal variations of pH in the charosphere were closely related to biochar characteristics. Ageing treatment resulted in large increases in the oxygen (91%–349%) and available phosphorus (670%–1094%) contents of biochar, but decreases in ash content (42%–45%), as well as pH (26%–54%) and electrical conductivity (EC) (17%–64%) values. The pore structure of biochar was altered and minerals were lost during the ageing process, so that aged biochars had much smaller specific surface area compared to the fresh biochars. Correlation and redundancy analyses revealed that the biochar EC value was the main factor determining the charosphere radius and pH within it. This study is the first to visualize and compare the charosphere derived from different fresh and aged biochars at a high resolution. The results provide new insight into the pH dynamics of the charosphere and the availability of elements as biochar ages following application to soil, which are important for understanding nutrient availability to plants and mobility of soil contaminants.

Effect of temperature on pyrolysis of sewage sludge: biochar properties and environmental risks from heavy metals

Biochars were prepared via the pyrolysis of sewage sludge at temperatures ranging from 350–550 °C. The properties and behaviors of heavy metals in the biochars were investigated. The results indicated that the pH values and ash contents of the biochars increased, while biochar yield and C, H, and N contents decreased with the increasing temperature. A high pyrolysis temperature contributed to a developed biochar pore structure. The specific surface area and pore volume of the biochars increased, while the average pore width decreased, with the increasing temperature. Heavy metals in the biochars were further enriched with the increasing temperature. TCLP tests demonstrated that the leaching potential of heavy metals from the biochars significantly decreased with the increasing temperature, indicating the decrease of potential ecological risks of heavy metals to the environment. Additionally, BCR tests confirmed the transformation of heavy metals from mobile fractions (F1 and F2) to stable fractions (F3 and F4). The evaluation results showed that a high pyrolysis temperature can effectively inhibit the ecological risks of heavy metals in the biochars. Thus, the conversion of sewage sludge into biochar via pyrolysis is a promising method for the safe disposal of sewage sludge.

Effect of carbonization methods on the properties of tea waste biochars and their application in tetracycline removal from aqueous solutions

The properties of biochars and their adsorption performance are highly dependent on the carbonation methods. In this study, five carbonation methods, namely, hydrothermal treatment (HT), direct carbonization (BC), carbonization of hydrochar (HBC), KHCO3 activation carbonation (KBC), and KHCO3 activation carbonation of hydrochar (KHBC), were adopted to prepare tea waste biochars. Adsorption behaviors and mechanisms toward tetracycline (TC) by biochar in the aquatic environment were investigated. The results showed that carbonation methods significantly influence the morphology, carbon structure, chemical composition, and functional groups of the biochars based on the characterization of surface area and pore volume analysis, Fourier Transform Infrared Spectroscopy, Raman spectrum, Scanning Electron Microscope, Transmission Electron Microscope, X-ray photoelectron spectroscopy, X-Ray Diffraction, and elemental analysis. Combination of hydrothermal treatment with KHCO3 activation can significantly increase the surface area and enlarge the pore structure of biochar (KHBC and KBC). The BET of KHCO3-activated BCs nearly increased 280 times (KHBC: 1350.80 m2 g−1; KBC: 1405.06 m2 g−1). BET, total pore volume and micropores volume of biochar has a positive influence on TC adsorption capacity. In addition, all adsorption processes can be well fitted by Langmuir and pseudo-second-order kinetic models. The maximum adsorption capacity of KHCO3-activated BCs nearly increased approximately 40 times (KHBC: 451.45 mg g−1; KBC: 425.17 mg g−1). The dominant mechanisms of biochar-adsorbed TC were pore-filling effect and π–π interactions, followed by hydrogen bonds and electrostatic interactions. Therefore, KHBC has the potential to act as sorbents for TC removal from aquatic environment.