Insight into biomass feedstock on formation of biochar-bound environmentally persistent free radicals under different pyrolysis temperatures

Environmentally persistent free radicals (EPFRs) in biochars have the ability of catalytic formation of reactive oxygen species, which may pose potential oxidative stresses to eco-environment and human health. Therefore, comprehending the formation and characteristics of EPFRs in biochars is important for their further applications. In this study, the woody lignocellulosic biomass (wood chips, pine needle and barks), non-woody lignocellulosic biomass (rice husk, corn stover, and duckweed), and non-lignocellulosic biomass (anaerobically digested sludge) were selected as biomass feedstock to prepare biochars under different pyrolysis temperatures (200–700 °C). The impact of biomass feedstock on formation of biochar-bound EPFRs was systematically compared. Elemental compositions and atomic ratios of H/C and O/C varied greatly among different biomass feedstocks and the subsequently resulting biochars. EPFRs in biochars derived from the studied lignocellulosic biomass have similar levels of spin concentrations (10¹⁸–10¹⁹ spins per g) except for lower EPFRs in biochars under 200 and 700 °C; however, sludge-based biochars, a typical non-lignocellulosic-biomass-based biochar, have much lower EPFRs (10¹⁶ spins per g) than lignocellulosic-biomass-based biochars under all the studied pyrolysis temperatures. Values of g factors ranged from 2.0025 to 2.0042 and line width was in the range of 2.15–11.3 for EPFRs in the resulting biochars. Spin concentrations of biochar-bound EPFRs increased with the increasing pyrolysis temperatures from 200 to 500 °C, and then decreased rapidly from 500 to 700 °C and oxygen-centered radicals shifted to carbon-centered radicals with the increasing pyrolysis temperatures from 200 to 700 °C for all the studied biomass feedstock. 300–500 °C was the appropriate pyrolysis temperature range for higher levels of spin concentrations of biochar-bound EPFRs. Moreover, EPFRs'' concentrations had significantly positive correlation with C contents and weak or none correlation with contents of transition metals. Overall, different types of biomass feedstock have significant impact on the formation of EPFRs in the resulting biochars.

Environmentally persistent free radicals (EPFRs) in biochars have the ability of catalytic formation of reactive oxygen species, which may pose potential oxidative stresses to eco-environment and human health.     

Investigation of element migration characteristics and product properties during biomass pyrolysis: a case study of pine cones rich in nitrogen

To further understand the element migration characteristics and product properties during biomass pyrolysis, herein, pine cone (PC) cellulose and PC lignin were prepared, and their pyrolysis behavior was determined using thermogravimetric analysis (TGA). Subsequently, the PC was pyrolyzed in a vertical fixed bed reactor system at 400–700 °C for 60 min. The characteristics of element migration and the physicochemical properties of the pyrolysis products were analyzed and discussed. In the pyrolysis temperature range from 200 °C to 500 °C, there were two distinct weight loss peaks for PC. During the pyrolysis process, the C element was primarily retained in the biochar, while the O element mainly migrated into liquid and gaseous products in the form of compounds such as CO₂, CO, and H₂O. Besides, 28.42–76.01% of the N element in PC migrated into biochar. Of the three-phase products, the gases endow the lowest energy yield, while the energy of the biochar dominates the pyrolysis of the PC. Additionally, the N content and specific surface area for the PC-derived biochar obtained at 400 °C in a N₂ atmosphere were higher than those of the biochar derived from fiberboard.

To further understand the element migration characteristics and product properties during biomass pyrolysis, herein, pine cone (PC) cellulose and PC lignin were prepared, and their pyrolysis behavior was determined using thermogravimetric analysis (TGA).     

Aqueous carbofuran removal using slow pyrolyzed sugarcane bagasse biochar: equilibrium and fixed-bed studies

Herein, biochar was produced by the slow pyrolysis of sugarcane bagasse at 500 °C in absence of oxygen. The resulting sugarcane bagasse biochar (SB500) was characterized and used for aqueous carbofuran sorptive removal. Batch carbofuran sorption studies were accomplished to ascertain the influence of solution pH, contact time, temperature (25, 35 and 45 °C) and adsorbate/adsorbent concentration. SB500 adsorbed more carbofuran at low pH values and less carbofuran at high pH values. The necessary sorption equilibrium, kinetic and thermodynamic parameters were determined. The equilibrium isotherm data were fitted to the Freundlich, Langmuir and Temkin models. The Langmuir equation best fitted the experimental sorption data. The maximum Langmuir adsorption capacity of 18.9 mg g⁻¹ was obtained at pH 6.0 and 45 °C. The enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy (ΔG°) were evaluated. The fixed-bed carbofuran sorption studies were carried out using the optimum parameters determined via the batch studies. The necessary fixed-bed design parameters were obtained. Carbofuran desorption and SB500 regeneration were successfully achieved. About 96% of the total carbofuran was successfully desorbed from the exhausted biochar using 20 mL ethanol in 10 mL increments. Moreover, a possible carbofuran adsorption mechanism has been proposed. A number of interactions including (1) hydrogen bonding of the protonated and neutral carbofuran to biochar, (2) carbofuran sorption onto biochar via π–π electron donor–acceptor interactions and (3) carbofuran diffusion into the biochar pores were considered to explain the sorption mechanism. The batch and fixed-bed sorption results demonstrate that the sugarcane bagasse biochar (SB500) can be effectively used for the sustainable removal and recovery of carbofuran from water.

Sugarcane bagasse biochar was prepared, characterized and used for aqueous carbofuran removal. Sorption equilibrium and dynamics studies were carried out. An adsorption capacity of 19 mg g⁻¹ was obtained at 45 °C. Carbofuran adsorption mechanism has been proposed.     

Environmental risk assessment in livestock manure derived biochars

Livestock-manure-derived biochar is one of major products obtained from the pyrolysis of livestock manure. This study quantitatively assesses the pollution level and ecological risks associated with heavy metals in livestock manure and the biochar produced by its pyrolysis. The geo-accumulation index (GAI) values of heavy metals in livestock manure were significantly decreased (P < 0.05) and indicated to be at the grade of uncontaminated expected for Zn in pig-manure-derived biochar (PMB, 0.94, 800 °C) via pyrolysis. Therefore, Zn should be paid more attention in PMB. The risk factors (E_rⁱ) result shows that heavy metals in biochars were significantly decreased (P < 0.05) with increasing pyrolysis temperature. Potential ecological risk index values revealed that the integrated risks from the heavy metals were significantly decreased (P < 0.05) after pyrolysis. Similarly, the risk assessment code values indicated that the risks from the heavy metals in livestock-manure-derived biochars were significantly decreased (P < 0.05) after pyrolysis. In summary, pyrolysis represents an effective treatment method for livestock manure and can provide an effective method to reduce the risks of environmental pollution.

Livestock-manure-derived biochar is one of major products obtained from the pyrolysis of livestock manure. This study quantitatively assesses the pollution level and ecological risks associated with heavy metals in livestock manure and the biochar produced by its pyrolysis.     

Biochar preparation from Solidago canadensis and its alleviation of the inhibition of tomato seed germination by allelochemicals

Solidago canadensis is a malignant invasive plant widely distributed in China. In this study, it was used as a biomass source to prepare biochar via an oxygen-limited pyrolysis method. The effect of temperature, heating rate and pyrolysis time on the yield and surface characteristics of the biochar was identified. The adsorption properties for dimethyl phthalate (DMP), a typical allelochemical of Solidago canadensis, of the biochar were explored. In addition, a pot experiment was conducted to reveal the effect of the biochar on tomato seed germination in the presence of allelochemicals. The maximum yield of the biochar was observed when Solidago canadensis was pyrolyzed at 300 °C for 2 h, with a heating rate of 8 °C min⁻¹. Variation of pyrolysis conditions had little influence on the surface characteristics of the biochar. The adsorption of DMP on the biochar could be well described by the Langmuir model, with a maximum adsorption capacity of 59.37 mg kg⁻¹. The addition of biochar to the soil could promote tomato seed germination in the presence of allelochemicals. Therefore, the biochar prepared from Solidago canadensis can be used for soil amendment for invaded sites.

The feasibility of amending the soil of Solidago canadensis invaded sites with biochar produced from Solidago canadensis was explored.     

Waste eggshell membrane-templated synthesis of functional Cu2+–Cu+/biochar for an ultrasensitive electrochemical enzyme-free glucose sensor

A fast and sensitive test of blood glucose levels is very important for monitoring and reducing diabetic complications. Herein, a simple and sensitive non-enzymatic glucose sensing platform was fabricated by employing Cu²⁺–Cu⁺/biochar as the catalyst. The Cu²⁺–Cu⁺/biochar was synthesized through a bio-inspired synthesis, in which waste eggshell membrane (ESM) was introduced as a template to absorb Cu²⁺, then converting it into Cu²⁺–Cu⁺ biochar via a rapid pyrolysis. The structure and properties of the as-prepared Cu²⁺–Cu⁺ biochar were determined by scanning electron microscopy (SEM), FT-IR spectroscopy, Raman spectroscopy and cyclic voltammetry (CV). Due to great advantages of Cu²⁺–Cu⁺/biochar, such as high electrical conductivity, unique three-dimensional porous network and large electrochemically active surface area, the as-prepared Cu²⁺–Cu⁺ biochar modified electrode showed high catalytic activity towards glucose oxidization. The fabricated enzyme-free glucose sensor showed excellent performance for glucose determination with a linear range of 12.5–670 μM, and a limit of detection (LOD) of 1.04 μM. Moreover, the as-fabricated sensor has good anti-interference ability and stability. Finally, the proposed senor has been successfully applied to detect glucose in clinical samples (human serum). Owing to the green synthesis method, using biowaste ESM as a template, and the superior catalytic performance and low cost of Cu²⁺–Cu⁺/biochar, the developed sensor shows great potential in clinical applications for direct sensing of glucose.

The fabrication process of the nonenzyme glucose sensing based Cu²⁺–Cu⁺/biochar.     

The effects of different factors on the removal mechanism of Pb(ii) by biochar-supported carbon nanotube composites

Herein, biochar-supported nanomaterials were synthesized using a mixture of chestnut shells and carbon nanotubes via slow pyrolysis at 600 °C for 1 h. Then, the adsorption ability of chestnut shell-carbon nanotubes (CS-CNTs) towards the removal of aqueous Pb(ii) was tested. The removal capacity of Pb(ii) by CS-CNT was 1641 mg g⁻¹, which was significantly higher than that by the biochar of chestnut shells (CSs) (1568 mg g⁻¹), which demonstrated that the sorption capacity could be improved by the carbon nanotubes. The factors studied here indicated that the adsorption was rapid in the initial 15 min under the conditions of the Pb(ii) concentration of 50 mg L⁻¹ and the pH value of 5, and the values reached 1417 mg g⁻¹ and 1584 mg g⁻¹. The adsorption rate and capacity increased on increasing the concentration of NaCl. The sorption reaction was consistent with the Langmuir model, indicating a mono-layer adsorption behavior. The adsorption process can also be defined via the pseudo-second-order model, suggesting that the adsorption of Pb(ii) might be controlled by chemisorption. After carrying out four cycles of adsorption–desorption experiments, the adsorption rates of CS and CS-CNT remained at 82.92% and 88.91%, respectively, indicating that the biochar samples had stable and excellent sorption ability for heavy metals and huge application value. Thus, this study would provide a promising sorbent for the treatment and remediation of metal contaminants.

In this study, biochar and biochar-supported nanocomposites were prepared through the slow pyrolysis of chestnut shells pre-treated with CNTs, and the effects of different factors on the sorption of Pb(ii) on biochar samples were investigated.     

Synthesis and application of tuneable carbon–silica composites from the microwave pyrolysis of waste paper for selective recovery of gold from acidic solutions

Microwave pyrolysis bio-oil from waste paper and K60 silica gel has successfully been utilised to synthesise mesoporous carbon–silica composites with uniquely tuneable surface properties, where functionality and structural characteristics can be altered and even enhanced by curing at different temperatures. This temperature-dependence resulted in composites ranging from highly oxygenated polymerised bio-oil composites at 300 °C to aromatic carbonaceous materials covering the silica surface at 800 °C, making them attractive materials for gold recovery from mining wastewater. The composite materials exhibit exceptional ability and selectivity to recover gold from dilute solutions. Metal adsorption on the surface of these composites proceeded via both chemisorption and physisorption leading to the reduction of Au(iii) to Au(0), resulting in high recovery capacities for gold. Composite material prepared at 500 °C demonstrated the optimum combination of surface functionality and porosity, allowing for an adsorption capacity of 320 mg g⁻¹ of gold and with 99.5% removal being achieved at concentrations mimicking those of real-life mine tailing wastes. All materials pioneered in this research display great potential as selective adsorbents for the recovery of gold from acidic media.

Microwave pyrolysis bio-oil from waste paper and K60 silica gel have been utilised to synthesise mesoporous carbon–silica composites with uniquely tuneable surface properties for the selective recovery of gold from acidic solutions.     

Conversion of woody oil into bio-oil in a downdraft reactor using a novel silicon carbide foam supported MCM41 composite catalyst

This study reports the synthesis of a SiC-MCM41 composite catalyst by a microwave-assisted hydrothermal process and the composite catalyst had the characteristics of MCM41 and SiC, and the surface of SiC grew evenly with a layer of MCM41 after characterization of the catalysts by various means (X-ray diffraction, Brunauer–Emmett–Teller, scanning electron microscopy). The catalyst was applied in the pyrolysis of waste oil to investigate how it influences the bio-oil component proportion compared with no catalyst, only SiC, only MCM41 catalysis and the catalytic effect was also investigated at different temperatures and different catalyst to feed ratios. In a downdraft system with a pyrolysis temperature of 550 °C, a catalyst to feed ratio of 1 : 2, and a catalytic temperature of 400 °C, 32.43% C₅–C₁₂ hydrocarbons and 41.10% mono-aromatics were obtained. The composite catalyst combined the catalytic effect of SiC and MCM41 because it increased the amount of C₅–C₁₂ hydrocarbons and decreased the amount of oxygen-containing compounds in bio-oil. After repeated uses, the composite catalyst still retained the catalytic properties.

Main flow chart of the pyrolysis process using SiC-MCM41 catalyst.     

Corncob biochar combined with Bacillus subtilis to reduce Cd availability in low Cd-contaminated soil

Soil contamination by heavy metals such as Cd can pose a risk to the environment and human health. However, Cd is difficult to immobilize at low concentration levels in soil. Individually, Bacillus subtilis and biochar have been shown to be inefficient at immobilizing Cd in soil. In this study, corncob biochar was generated at different pyrolysis temperatures (300 °C-550 °C), and the Cd immobilization efficiency and performance of corncob biochar loaded with B. subtilis (CB@B) and corncob biochar alone (CB) were evaluated in solutions and in soil. The characterization (SEM and FTIR) of CB generated at different pyrolysis temperatures and CB generated at different pyrolysis temperatures in CB@B (300 °C-550 °C) indicated that a superior pore structure and abundant O-functional groups were obtained at a pyrolysis temperature of 400 °C for both CB@B and CB. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that the formation of Cd compounds was associated with the positive combined biosorption effect of the bacteria and biochar, electronic adsorption, activity of the O-functional groups (C O, COOH, OH, and Si–O–Si), and complexation between extracellular substances and Cd²⁺. Adsorption experiments were conducted in a solution to assess the effects of various operating parameters such as the time, pH, and adsorbent dose. The 400 °C-CB@B and 400 °C-CB samples achieved the largest reductions in the Cd concentration at 81.21% and 5.70%, respectively. Then, CaCl₂ extraction experiments were conducted in soil, and using 0.25%-CB@B, a 55.21% decrease was realized in the Cd concentration after 56 days and a 16.71% increase was realized in soil pH to 8.38. No significant difference was observed in the CB-treated groups, among which 1.0%-CB achieved the largest reduction of 26.08% after 56 days and a 3.20% increase in the soil pH to 7.41. The Tessier sequential extraction method obtained similar trends. Overall, 400 °C-CB@B demonstrated outstanding immobilization efficiency and durability, indicating that it provided a safe and nutrient-rich habitat for B. subtilis to realize a synergistic effect for Cd immobilization.

There were multiple mechanisms worked during 400 °C CB@B immobilized Cd in soil, and reduction of availability Cd reached 69%.     

Upgrading biochar via co-pyrolyzation of agricultural biomass and polyethylene terephthalate wastes

Spent polyethylene terephthalate (PETE) bottles were collected and co-pyrolyzed with rice straw (RS) to examine the characteristics and performance of biochar as a sorbent for various types of U.S. EPA priority pollutants, including 2,4-dinitrotoluene (DNT), 2,4-dichlorophenol (DCP), Pb, chromate (CrO₄²⁻), and selenate (SeO₄²⁻). During sorption of contaminants to PETE/RS-derived biochar, PETE residues from pyrolysis, pH, and pyrolysis temperature greatly affected the sorption process. Depending on the types of contaminants and experimental conditions, co-pyrolysis of PETE and RS may enhance the sorption of contaminants through different sorption mechanisms, including hydrophobicity, electrostatic force, ion exchange, surface complexation, and surface precipitation. Unlike other contaminants, selenate was reductively transformed by delocalized electrons from the graphitic structure in biochar. Our results strongly suggest that co-pyrolysis of PETE and agricultural wastes may be favorable to enhance the properties of biochar. In addition to syn-gas and bio-oil from co-pyrolysis, biochar may be a valuable by-product for commercial use.

Spent polyethylene terephthalate (PETE) bottles were co-pyrolyzed with rice straw to examine the performance of biochar as a sorbent for various types of pollutants, including 2,4-dinitrotoluene, 2,4-dichlorophenol, Pb, chromate, and selenate.     

Adsorption–desorption behavior of carbendazim by sewage sludge-derived biochar and its possible mechanism

Biochar application in agricultural soil for environmental remediation has received increasing attention, however, few studies are focused on sewage sludge based biochar. The present study evaluated the effect of raw sewage sludge and sewage sludge based biochars produced at different pyrolysis temperatures (100–700 °C) on the adsorption–desorption of carbendazim in soil. Sewage sludge derived biochar significantly enhanced the sorption affinity and limited the desorption capacity of the soil for carbendazim. A maximum removal efficiency of 98.9% and a greatest value of 144.05 ± 0.32 μg g⁻¹ sorption capacity occurred in soil amended with biochar pyrolyzed at 700 °C (BC700). As the pyrolysis temperature and the amendment rate of biochars increased, the sorption of carbendazim was promoted and desorption was further inhibited. The adsorption–desorption hysteresis index of carbendazim was consistently higher in soils amended with biochars (>0.85) than in the unamended soil (0.42–0.68), implying that carbendazim could be immobilized in soil amended with sewage sludge derived biochars. The partition effect was dominant in the sorption process for carbendazim in the biochar–soil mixtures. This study will be helpful for the disposal of sewage sludge and its utilization, and it is the first report for the study the sorption–desorption process of carbendazim in soil amended with sewage sludge derived biochar. Furthermore, these findings may be also useful for understanding the distribution and transport of carbendazim in the environment and will be of great significance in remediation strategies for contaminated soil.

Biochar application in agricultural soil for environmental remediation has received increasing attention, however, few studies are focused on sewage sludge based biochar.     

Structural and adsorption characteristics of potassium carbonate activated biochar

Potassium carbonate activated biochar (450 °C, 600 °C and 750 °C) and nonactivated biochar (600 °C) were prepared by using corn stalk as the raw material. These biochar samples were labeled as KBC450, KBC600, KBC750 and BC600. The physical and chemical properties of the biochar were strongly influenced by the activation of potassium carbonate. After activation with potassium carbonate, the aromatic, hydrophobic and non-polar properties of the biochar were enhanced to form an aromatized non-polar surface, and the aromatic properties were enhanced with the increase of the pyrolysis temperature. The outside surface of the activated biochar was similar to that of porous sponge with a mesoporous–microporous composite structure inside. The specific surface area of KBC600 was 5 times that of BC600, and KBC750 had a maximum surface area of 815 m² g⁻¹. Batch adsorption experiments showed that the adsorption capacity of KBC for naphthalene increased with the increase of pyrolysis temperature. The adsorption capacity of the biochar for naphthalene showed a significant positive correlation with O/C and (O + N)/C. KBC750 with the strongest surface hydrophobicity and the largest specific surface area had the largest adsorption capacity of 130.7 mg g⁻¹. Physical adsorption and π–π EDA were the main adsorption mechanisms.

The structure activation of K₂CO₃ enriches the surface pores of biochar and increases the specific surface area nearly 10 times. The changes of pore structure and surface properties significantly affect the adsorption process of naphthalene.     

Characterization of biofuel production from hydrothermal treatment of hyperaccumulator waste (Pteris vittata L.) in sub- and supercritical water

In this study, hyperaccumulator waste, i.e., Pteris vittata L. was converted into bio-oil, biogas and biochar via sub- and supercritical hydrothermal liquefaction processes. These products were characterized in terms of EI/MS, FTIR, TGA and GC to understand their chemical composition, thermal decomposition, structural properties and high biofuel reactivity. Characterization results revealed that the dominant chemical components in the heavy bio-oil were esters (40.22%), phenols (20.02%), alcohols (10.16%), organic acids (9.07%), nitrogenous compounds (8.83%) and ketones/aldehydes (6.42%), while the light oil was rich with a higher fraction of phenols (54.13%) and nitrogenous compounds (27.04%). Particularly, bio-oils obtained from supercritical conditions contained increased phenolic compounds and reduced oxygenated chemicals such as alcohols, aliphatic acid, ketones and aldehydes, suggesting the improved quality of bio-oil due to the reduction in oxygen contents. Meanwhile, H₂-rich syngas production with the H₂ yield of 38.87% was obtained at 535 °C for 20 min, and higher reaction temperature presented a positive influence on H₂ production during Pteris vittata L. liquefaction. Moreover, the remaining biochar product was analyzed to determine whether it could be used as a direct solid fuel or auxiliary fuel. This study provided full exploitation of this feedstock waste in energy and valuable chemical complexes.

This study evaluated the utilization of HTL to handle hyperaccumulator waste, i.e., Pteris vittata L. in both sub and supercritical water for the production of biofuels as a partial substitute for fossil fuels and valuable chemicals.     

Sorption of tetracycline on biochar derived from rice straw and swine manure

Biochar is an efficient and cost-effective sorbent for removing contaminants from aqueous environments. In this study, biochar samples derived from rice straw (R) and swine manure (M) pyrolyzed at 400 °C (R400 and M400) and 600 °C (R600 and M600) were used to adsorb tetracycline from an aqueous solution. The adsorption of tetracycline on both types of biochar included multi-step adsorption processes that were well described by the pseudo-second-order kinetics model (R² > 0.99). The adsorption equilibrium of tetracycline on rice straw and swine manure derived biochar was reached after 24 h and 36 h respectively. The solution pH affected the adsorption processes by changing the surface charges of tetracycline and biochar. Adsorption isotherms fitted both the Langmuir and Freundlich models well. The adsorption capacity was higher in biochar derived from rice straw than in biochar derived from swine manure, and increased with increasing pyrolysis temperature. Thermodynamic analysis revealed a spontaneous and endothermic tetracycline adsorption process. The values of the adsorption coefficient (K_d) were on the order of 10³ for R600 and 10²–10³ for the other three types of biochar. These experiments indicate that R600 can be used as an inexpensive adsorbent to remove tetracycline from aqueous solutions, but swine manure derived biochar needs more improvement to be a suitable adsorbent.

Comparing the adsorption ability of biochar from swine manure and rice straw on tetracycline and investigating the relative mechanisms involved in the process.     

Characterization of pruned tea branch biochar and the mechanisms underlying its adsorption for cadmium in aqueous solution

In the present study, discarded pruned tea branch was used to prepare a new biochar, and the physicochemical properties and adsorption characteristics were investigated by characterization and batch experiments. With increasing pyrolysis temperature from 400 to 800 °C, the yield, specific surface area, and acidic functional groups had significant differences. The optimum adsorption conditions were determined as pH = 6 and dosage of 2 g L⁻¹. The pseudo-second-order kinetic and Langmuir isothermal model could fit well to the adsorption data, which showed that the adsorption process was dominated by monolayer chemical adsorption. The highest adsorption property (74.04 mg g⁻¹) was obtained by the pyrolysis of tea branch biochar (TBB) at 700 °C owing to the adsorption mechanisms, including surface complexation, precipitation, metal ion exchange, and Cd²⁺–π interaction. After five cycles of desorption, biochar still showed superior adsorption (80%). Hence, the TBB acted as a regenerable adsorbent for treating Cd²⁺-containing wastewater.

In the present study, discarded pruned tea branch was used to prepare a new biochar, and the physicochemical properties and adsorption characteristics were investigated by characterization and batch experiments.     

Effect of pyrolysis temperature on sulfur content,extractable fraction and release of sulfate in corn straw biochar

The contents and release of the nutrient elements N, P and K in biochars have been investigated. Sulfur is an indispensable element for plants, but its content and release in biochar are still unclear. The effect of pyrolysis temperature (300, 500 and 700 °C) on the sulfur content, extractable fraction and release of sulfate in corn straw biochars (CS300, CS500 and CS700) was investigated. The biochars were characterized using element analysis, BET, FTIR, and XRD. It was shown that the contents of sulfur in biochars decreased significantly with increasing pyrolysis temperature. The extraction results indicated that the percentages of water extractable-sulfate (W–SO₄²⁻) and organosulfur in biochars decreased while those of HCl- and NaH₂PO₄-extractable sulfate (HCl–SO₄²⁻, NaH₂PO₄–SO₄²⁻) increased with pyrolysis temperature. Batch release experiments were conducted to test the effect of contact time and addition of Hoagland nutrient solution (HNS) on the release of sulfate from biochars. The release kinetics fitted well with a pseudo-second-order model. Approximately 10.7 mg g⁻¹ of sulfate was released from CS300 during the initial 2 h, whereas 6.32 and 3.93 mg g⁻¹ were released from CS500 and CS700, respectively. Increasing the amounts of HNS led to negative effects on sulfate release. The results indicate that low-temperatures might be optimal for producing biochar from corn straw to improve the sulfur fertilization.

Low pyrolysis temperature is optimal for biochar to release sulfate and the release kinetics fitted well with a pseudo-second-order model.     

Preparation of biochar by mango peel and its adsorption characteristics of Cd(ii) in solution

Biochars were prepared by pyrolyzing mango peel waste at 300, 400, 500, 600 and 700 °C. Various characterizations were carried out to explore the effect of pyrolysis temperature on the biochars. The data indicated that the physical and chemical properties of biochar such as pH, element ratio, specific surface area and functional groups changed with the increase of pyrolysis temperature. The yield and contents of hydrogen, nitrogen and oxygen decreased, while contents of the ash and carbon, pH and specific surface area of the biochars increased. In addition, the molar ratios of H/C, O/C and (O + N)/C decreased. In this study, batch adsorption experiments for Cd(ii) adsorption were performed with initial Cd(ii) concentrations of 10–300 mg L⁻¹, contact times of 0–2880 min, various pH (2–8) and biochar dose (1–20 g L⁻¹). Langmuir isotherm and pseudo-second-order kinetics models were better fits than other models, suggesting the dominant adsorption of mango peel biochars is via monolayer adsorption. Biochar derived at 500 °C was found to have the highest adsorption capacity of 13.28 mg g⁻¹ among all biochars and the adsorption efficiency was still 67.7% of the initial adsorption capacity after desorption for 4 times. Based on adsorption kinetics and isotherm analysis in combination with EDS, FTIR and XRD analysis, it was concluded that cation exchange, complexation with surface functional groups and precipitation with minerals were the dominant mechanisms responsible for Cd adsorption by mango peel biochar. The study suggested that mango peel can be recycled to biochars and can be used as a low-cost adsorbent for Cd(ii) removal from wastewater.

Biochars were prepared by pyrolyzing mango peel waste at 300, 400, 500, 600 and 700 °C.     

Co-production of fully renewable medium chain α-olefins and bio-oil via hydrothermal liquefaction of biomass containing polyhydroxyalkanoic acid

Medium chain-length linear α-olefins (mcl-LAO) are versatile precursors to commodity products such as synthetic lubricants and biodegradable detergents, and have been traditionally produced from ethylene oligomerization and Fischer–Tropsch synthesis. Medium chain-length polyhydroxyalkanoic acid (mcl-PHA) can be produced by some microorganisms as an energy storage. In this study, Pseudomonas putida biomass that contained mcl-PHA was used in HTL at 300 °C for 30 min, and up to 65 mol% of mcl-PHA was converted into mcl-LAO. The yield and quality of the bio-oil co-produced in the HTL was remarkably improved with the biomass rich in mcl-PHA. Experiments with extracted mcl-PHA revealed the degradation mechanism of mcl-PHA in HTL. Overall, this work demonstrates a novel process to co-produce mcl-LAO and bio-oil from renewable biomass.

Co-production of fully renewable medium chain α-olefins and bio-oil by hydrothermal liquefaction.     

Study on the hydrothermal liquefaction of antibiotic residues with molecular sieve catalysts in the ethanol–water system: focus on product distribution and characterization

In this study, the antibiotic residue was used as a raw material to catalyze hydrothermal liquefaction (HTL) in an ethanol–water system to prepare bio-oil. The study explored the effects of ethanol–water ratio and three kinds of molecular sieve catalysts (HZSM-5, MCM-41, and γ-Al₂O₃) on the yield and characterization of bio-oil. The experimental results showed that the highest bio-oil yield was obtained at the ethanol–water ratio of 1 : 1 and the three kinds of molecular sieve catalysts of 15%. GC-MS, ¹H NMR, TGA, and CHNS were used for the characterization of bio-oil. Higher carbon (up to 71.44%), hydrogen (up to 9.376%), and a high heating value (HHV, 34.714 MJ kg⁻¹) were observed for catalytically liquefied bio-oil compared to non-catalytically liquefied bio-oil. The analysis of aqueous phase products indicated the existence of valuable nutrients. Besides, the reusability of three kinds of molecular sieve catalysts indicated that catalysts could be successfully reused several times and continuously exhibited the catalyst effect.

In this study, the antibiotic residue was used as a raw material to catalyze hydrothermal liquefaction (HTL) in an ethanol–water system to prepare bio-oil.