Conversion Of Waste Biomass Research Articles

Improved Method for Preparing Nanospheres from Pomelo Peel to Achieve High Graphitization at a Low Temperature

Biomass waste is a valuable resource that can be recovered, reused, and is renewable. However, converting biomass waste to a high degree of order is a bigger challenge, and graphitization at low temperatures is even more difficult. This paper proposes an improved method (Ni element catalysis) for highly graphitizing pomelo peel at low temperatures (750 –900 °C). In this paper, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and high-resolution transmission electron microscopy (HRTEM) were used to study the method and the effect of temperature on structural changes during graphitization. Under the improved method, pomelo peel was transformed into nano-spherical graphitized material. The degree of graphitization reached 80.23% at 900 °C, which was 31.39% higher than that of the traditional method. Furthermore, through HRTEM, the lattice fringe spacing was observed to be 0.337 nm, which is between pure graphite (0.3354 nm) and amorphous graphite (0.3440 nm). In this paper, the improved method can obtain highly graphitized nanospheres at low temperatures, thus reducing energy consumption, reducing environmental pollution, and promoting sustainable development.

Comprehensive resource utilization of peony seeds shell: Extraction of active ingredients, preparation and application of activated carbon

In this paper, a new high value-added biomass conversion route was proposed. Oligostilbenes in peony seeds shell (PSS) were extracted by ethanol, and high-performance activated carbon (ACPSR) was prepared by peony seeds shell residue (PSR). The content of the main oligostilbenes in the extract was determined by HPLC, and the biological activity of the extract was also evaluated. ACPSR was systematically characterized, and the adsorption performance of phenol was optimized by response surface methodology (RSM), and the adsorption mechanism was also studied. The results showed that the ethanol extract of PSS was rich in oligostilbenes, which had strong antioxidant, antibacterial and antitumor activities. ACPSR had a high specific surface area (1499.5 m2.g−1)and a highly developed pore structure(1.49 cm3.g−1). ACPSR could effectively remove phenol pollutants in solution, and when the dosage of adsorbent was 0.33 g.L−1, the initial concentration was 71.5 mg.L−1, the pH value was 5.1 and the ultrasonic time was 3.0 min, the optimal adsorption efficiency of ACPSR was 93.11%. As an economical and environmentally friendly biomass precursor, PSS had great potential in the development of food additives and drugs with good biological activities, as well as efficient adsorbents for the remediation of water pollution. This study provided useful reference for the high value-added conversion of waste biomass, and opened up a broad prospect for the application of the conversion products.

A Review of Biomass Resources and Thermochemical Conversion Technologies

AbstractWaste biomass has the potential to produce renewable fuels and fine chemicals. Biofuels derived from agricultural, forestry, and energy crop systems are promising resources to address climate change and minimize greenhouse gas emissions. The recent advances in various thermochemical technologies for the conversion of waste biomass to value‐added biofuel products are discussed. A summarized outline of thermochemical technologies such as torrefaction, liquefaction, pyrolysis, and gasification is provided. An overview of different types and sources of biomass as well as their physicochemical properties is presented. The thermochemical conversion products and their environmental benefits are considered as well.

Biomass Waste‐Derived Electrocatalyst Constructed with g‐C3N4 as a Multifunctional Template for Efficient Oxygen Reduction Reaction

AbstractExploring an effective way to convert biomass waste into highly active oxygen reduction reaction (ORR) electrocatalysts will not only benefit alleviating environmental management pressure, but also open up new ways for the development of alternatives to Pt‐based catalysts. Although the traditional pyrolysis conversion method has been proved to be stable and feasible, the low electrocatalytic activity of the product and the cumbersome post‐treatment process make it difficult to be popularized. Here, we report an effective method to overcome the mentioned drawbacks: the introduction of g‐C3N4. The experimental results confirm that g‐C3N4 can be used as a multifunctional template for adjusting the morphology and providing N source. More importantly, it will decompose at 700 °C and avoid post‐treatment of residues. The pyrolysis products assisted by g‐C3N4 exhibit similar ORR performances to commercial Pt/C, including onset potential of 0.963 V (vs. RHE), half‐wave potential of 0.835 V (vs. RHE) and limiting current density of 6.35 mA ⋅ cm−2. Impressively, the product displayed outstanding performance on output power density (107 mW ⋅ cm−2) and discharge performance at different current densities as the air electrode of zinc‐air battery, which even superior to that of commercial Pt/C. This study elucidated the functional role of g‐C3N4 in reaction system and facilitated the development of more efficient biomass waste‐based ORR electrocatalysts.

Dual-catalyst catalytic pyrolysis of poplar sawdust: A systematic study on first-layered catalysts

• A systematic study was conducted on the dual-catalyst CFP of poplar sawdust. • Totally 18 catalysts belonging to three types were tested as first-layered catalysts. • Effects of the 18 first-layered catalysts on the bio-oil production were evaluated. • Synergistic effects between the dual-layered catalysts were studied and compared. • Porous materials + ZSM-5 provided the highest bio-oil yield and quality. Dual-catalyst catalytic fast pyrolysis (CFP) technology is effective in converting biomass waste into hydrocarbon-rich bio-oils. However, systematic studies on dual-catalyst biomass CFP are limited, especially with respect to the best-performed dual catalyst design. In this context, dual-catalyst CFP of poplar sawdust was conducted with 18 in-situ first-layered catalysts, including 6 inorganic salts (NaCl, KCl, MgCl 2 , ZnCl 2 , K 3 PO 4 , and K 2 HPO 4 ), 7 metal oxides (SiO 2 , Al 2 O 3 , CaO, MgO, ZnO, Fe 2 O 3 , and CuO), and 5 porous materials (SBA-15, MCM-41, Y zeolite, Beta zeolite, and SAPO-34), while the ZSM-5 zeolite was fixed as an ex-situ second-layered catalyst. The effects of the 18 first-layered catalysts on bio-oil production were investigated and compared. Applying the porous materials as the first-layered catalysts increased the bio-oil yields compared to the inorganic salts and metal oxides. In particular, mesoporous SBA-15 combined with ZSM-5 led to the highest bio-oil yield of 19.4 wt% and a satisfactory hydrocarbon selectivity of 30.5 area%. The synergistic effects of the dual-layered catalysts were also studied. The first-layered catalysts cracked the primary biomass volatiles into smaller oxygenates, while the second-layered ZSM-5 deoxidized these molecules to hydrocarbons. In addition, the porous materials exhibited better synergy with ZSM-5 by simultaneously deoxygenating all the oxygenate types. The dual catalysts configured by Beta + ZSM-5 converted the most oxygenates into hydrocarbons, and the hydrocarbon selectivity (41.4 area%) was twice that in the blank experiment ( Thermal/ZSM-5 ). Therefore, combining the porous materials and ZSM-5 delivers a promising catalyst for dual-catalyst biomass CFP.

A study on torrefaction of spent coffee ground to improve its fuel properties

Excessive use of fossil fuels has contributed significantly to global warming and the impending energy crisis, necessitating the promotion and development of alternative energy sources to achieve green energy or energy neutrality. Converting waste biomass into energy has a significance impact in solid waste management. Spent coffee grounds (SCG) are the primary residue from the coffee industry generated during the coffee brewing process. This study, therefore, aims to improve the fuel properties of SCG via torrefaction and investigates the characteristics of torrefied products. A horizontal tubular reactor, at temperatures ranging from 250 °C to 350 °C at 20 °C intervals, and residence times ranging from 0 to 30 min with 10-min intervals, were utilized for torrefaction. The associated physical and chemical transformations in SCG torrefaction were investigated using proximate and ultimate analysis, gas composition, thermogravimetric and derivative analyses along with Fourier Transform Infrared Spectroscopy (FTIR). The mass and energy yields decreased while the higher heating value increased with the increase in torrefaction temperature. Additionally, the decrease in the oxygen content and increase in the fixed carbon content helped to improve the fuel properties of the SCG. A torrefaction temperature of 290 °C and a residence time of 10 min was found to be the optimal conditions for SCG torrefaction.

NaCl-Assisted Ultrasmall Mo2C Nanocrystals Confined in N, S Double-Doped Hierarchical Porous Carbon for Efficient Hydrogen Generation

Refining the size of nonprecious metal-based catalysts and restricting them in multiheteroatom-doped hierarchical porous carbon can achieve efficient electrical energy conversion. In this study, ultrasmall Mo2C nanocrystals with an average size of 4.9 nm are fitted to N and S double-doped hierarchical porous carbon (us-Mo2C/N,S-HPC) through a template strategy and used for efficient hydrogen production. First, the metal molybdenum salt is captured and fixed by natural bamboo leaf fibers which are pulverized by a ball mill. Meanwhile, the soluble sodium salt is largely filled in the bamboo leaf tissue. Subsequently, Mo2C nanocrystals formed by high-temperature reduction are uniformly anchored on the bamboo-derived N, S double-doped hierarchical porous carbon. As a result, the prepared us-Mo2C/N,S-HPC requires 150, 197, and 148 mV overpotential to drive a current density of 10 mA cm–1 at pH = 0, 7, and 14, respectively. This improvement is attributed to the synergistic effects of size controllable Mo2C, multidoped heteroatoms, and multiscale assembly structures. Significantly, this study is conducive to the construction of ultrafine nanocrystals and the high-value conversion of waste biomass.

Modeling of thermochemical conversion of waste biomass – a comprehensive review

Thermochemical processes, which include pyrolysis, torrefaction, gasification, combustion, and hydrothermal conversions, are perceived to be more efficient in converting waste biomass to energy and value-added products than biochemical processes. From the chemical point of view, thermochemical processes are highly complex and sensitive to numerous physicochemical properties, thus making reactor and process modeling more challenging. Nevertheless, the successful commercialization of these processes is contingent upon optimized reactor and process designs, which can be effectively achieved via modeling and simulation. Models of various scales with numerous simplifying assumptions have been developed for specific applications of thermochemical conversion of waste biomass. However, there is a research gap that needs to be explored to elaborate the scale of applicability, limitations, accuracy, validity, and special features of each model. This review study investigates all above mentioned important aspects and features of the existing models for all established industrial thermochemical conversion processes with emphasis on waste biomass, thus addressing the research gap mentioned above and presenting commercial-scale applicability in terms of reactor designing, process control and optimization, and potential ways to upgrade existing models for higher accuracy.

A 3D-macroporous pomelo peel foam based on anti-shrinkage properties of MnOx for solar water purification

The conversion of biomass waste into photothermal materials is a promising solution. However, the carbonization process always leads to structural collapse and blocks vapor diffusion channels of biomass-derived carbon materials, resulting in poor evaporation performance. Herein, by utilizing a cheap and abundant biowaste of pomelo peels (denoted PP) as a porous structure precursor, a 3D-macroporous evaporator (denoted MPP) was formed through a one-pot pyrolysis method in the presence of MnCO3 (filler agent). The pyrolysis of MnCO3 generated gas and MnOx anchored on the skeleton of PP, confining its shrinkage, in turn obtaining MPP with larger pore volume. As a result, the 3D-macroporous structure facilitates the fast water vapor diffusion and MnOx improves the photothermal conversion capability of the direct carbonized pomelo peel (denoted CPP). The surface temperature of MPP reaches 92.2 ℃ under one sun irradiation, which is ~ 10 ℃ higher than CPP. And the evaporation rate of MPP (1.43 kg m−2 h−1) increased significantly by 50% compared to that of CPP (0.95 kg m−2 h−1). Moreover, its performance can be further enhanced up to 1.805 kg m−2 h−1 by being fabricated into a hierarchical mimetic tree-like solar vapor system, due to the reduced heat loss from MPP to bulk water and enhanced thermal concentration at the MPP surface. Furthermore, this system performed the excellent self-desalting performance without salt crystals on the surface of the MPP even in 20% brine during 8 h desalination and showed the high removal efficiency of metallic ion and dye (over 99.9%) in wastewater disposal.

Peroxymonosulfate activation by recycling of discarded cigarette filters: Selective degradation of contaminants

BackgroundThe conversion of waste biomass into multi-hole carbon materials is an effective way in recent years. A new type of biochar was prepared by one-step calcination method by utilizing used cigarette filter (UCF) as raw material. In addition, we investigated the catalytic degradation properties of UCF, as well as the degradation mechanism. MethodsThe catalytic degradation properties of the material were verified by degradation experiments. The morphology of the material, and the microstructural state, were analyzed by SEM (Scanning Electron Microscope) and HRTEM (High Resolution Transmission Electron Microscopy). Using Raman, XRD (X-ray diffraction), BET, XPS (X-ray photoelectron spectroscopy) studied the structure and chemical composition of the material. The degradation mechanism was analyzed by quenching experiments and EPR (Electron Paramagnetic Resonance), XPS. Significant findingsThe first, UCF completely removed 0.01 g L−1 Rhodamine B within 80 min. And, degradation rate of Rhodamine B is as high as 95% within 20 min. Some defects were observed, and the dominant microporous structures and high specific surface area were present. The heteroatom in the UCF effectively activated the sp2-hybridized carbon crystal lattice, leading to the creation of more activation sites in UCF. Different carbide temperatures also affected the degree of material graphitization, and UCF (700 °C) had rich defects and larger porous structures. Besides, Electron paramagnetic resonance and quenching experiments showed that UCF degradation systems acted via free and non-radical pathways. The mechanism of catalytic degradation and the reasonable source of heterogeneous atoms at the catalytic site were also proposed. The use of the discarded cigarette filter as a low-cost catalyst for persulfate has great potential.

Efficient catalytic system for converting N-acetyl-d-glucosamine into valuable chemical 3-acetylamino-5-acetylfuran

This paper briefs the emerging strategies for the designing of catalytic systems, which direct conversion of chitin biomass monomer N-acetyl-d-glucosamine (NAG) to 3-acetylamino-5-acetylfuran was studied systemically. Twelve catalysts were investigated, and pyrazine hydrochloride ([Pyz]Cl) ionic liquid exhibited the good performance-achieving 3A5AF with yields of 36.94% from NAG. Further adding boric acid and CaCl2, treating at 190 °C for 60 min, the conversion rate of NAG is 100%, and the yield of 3A5AF can be increased to 69.54% in DMA. Furthermore, functional group changes before and after the reaction have been characterized by FTIR, HPLC-MS and 13C NMR were applied to monitor the reaction process with [Pyz]Cl as the catalyst. The reactive intermediate was clearly detected by these techniques. Accordingly, a possible reaction pathway was proposed. The results of this experiment provide a mild and efficient reaction route for the degradation of biomass, and enrich the theoretical research of quaternary amine catalysts in the conversion of biomass waste into high value-added chemicals.

Novel cattail fiber composites: converting waste biomass into reinforcement for composites

Vacuum-assisted resin transfer molding (VARTM), used in manufacturing medium to large-sized composites for transportation industries, requires non-woven mats. While non-woven glass mats used in these applications are optimized for resin impregnation and properties, such optimized mats for natural fibers are not available. In the current research, cattail fibers were extracted from plants (18–30% yield) using alkali retting and non-woven cattail fiber mat was manufactured. The extracted fibers exhibited a normal distribution in diameter (davg. = 32.1 µm); the modulus and strength varied inversely with diameter, and their average values were 19.1 GPa and 172.3 MPa, respectively. The cattail fiber composites were manufactured using non-woven mats, Stypol polyester resin, VARTM pressure (101 kPa) and compression molding pressures (260 and 560 kPa) and tested. Out-of-plane permeability changed with the fiber volume fraction (Vf) of the mats, which was influenced by areal density, thickness, and fiber packing in the mat. The cattail fibers reinforced the Stypol resin significantly. The modulus and the strength increased with consolidation pressures due to the increase in Vf, with maximum values of 7.4 GPa and 48 MPa, respectively, demonstrating the utility of cattail fibers from waste biomass as reinforcements.

Rice husk hydrochars from metal chloride-assisted hydrothermal carbonization as biosorbents of organics from aqueous solution

Hydrochar a carbon-rich material resulting from hydrothermal carbonization of biomass, has received substantial attention because of its potential application in various areas such as carbon sequestration, bioenergy production and environmental amelioration. A series of hydrochars were prepared by metal chloride-assisted hydrothermal carbonization of rice husk and characterized by elemental analysis, zeta potential, X-ray diffraction, Brunauer–Emmett–Teller measurements, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The results reveal that the prepared hydrochars have carbon contents ranging from 45.01 to 58.71%, BET specific areas between 13.23 and 45.97 m2/g, and rich O-containing functional groups on the surfaces. The metal chlorides added in the feedwater could improve the degree of carbonization and show significant effects on the physical, chemical and adsorption properties of the hydrochars. The adsorption of the selected organics on the hydrochars is a spontaneous and physisorption-dominated process. The hydrochars possess larger adsorption capacities for 2-naphthol than for berberine hydrochloride and Congo red, and the modeling maximum adsorption capacities of 2-naphthol are in the range of 170.1–2680 mg/g. The adsorption equilibrium could be accomplished in 10, 40 and 30 min for 2-naphthol, berberine hydrochloride and Congo red, respectively. These results suggest metal chloride-assisted hydrothermal carbonization a promising method for converting biomass waste into effective adsorbents for wastewater treatment.

Analysis of The Impact of Biochar Application on Soil Fertility and Productivity

The increase agricultural production through intensification and extensification programs does not only provide solutions to food security, but it raises several challenges in sustainable production. In addition to increasing greenhouse emissions which have an impact on global warming, increased production also escalate the production of biomass waste. Although biomass waste is more environmentally friendly than oil-based waste, without proper treatment, this solid waste will have a negative impact on the environment and the sustainability of agricultural production. The conversion of biomass waste into new technology must be adapted to the characteristics of the biomass. Several studies have shown that biomass waste has the potential to be converted into products of higher value such as biochar. Biochar is a material converted from organic waste or agricultural / plantation waste that is rich in carbon, used to increase soil productivity . The long-term advantage of biochar application for the availability of plant nutrients is related to the high stability of organic carbon. The effectiveness of biochar application depends on the biochar production process, the amount of biochar that applied, the soil characteristic, the type of crop being cultivated.

Microbial conversion of waste biomass into bioethanol: current challenges and future prospects

Microbial conversion of waste biomass into bioethanol: current challenges and future prospects

Modeling of a hybrid externally fired gas turbine applied to a landfill and green waste management facility

This work discusses the integration of an externally-fired-gas-turbine power plant in a waste disposal facility where municipal solid waste is disposed in a landfill while green waste is pre-treated and selected to be sold as fuel for biomass power plants. The advantages deriving from the in situ green waste biomass conversion using the externally-fired-gas-turbine power plant is simulated using a thermodynamic model implemented in Matlab Simulink. Two different configurations are simulated: a Standard-Externally-Fired-Gas-Turbine (S-EFGT) power plant fuelled with green-waste-derived wood chips and a Hybrid-Externally-Fired-Gas-Turbine (H-EFGT) power plant fuelled with the previous biomass together with landfill gas. Power plant subsystems are modelled through a black box approach. Inputs and outputs of each box are interconnected together to create the overall models. Preliminary simulations were performed for each configuration at the same working fluid flow rate to compare the electrical and thermal efficiency of both power plants. Full scale simulations, considering an existing case study, are then developed. First, energy fluxes and the resulting efficiencies of each configuration are evaluated. Then the techno-economical comparison between the proposed solutions is discussed. Results show a net electrical energy production of 9392 MWh/year with an electrical efficiency of 14.03% for the S-EFGT using about 18,294 ton/year of wood biomass; the H-EFGT energy yield is 25,392 MWh/year with an electrical efficiency of 17.89% using the same biomass consumption and an average flow rate of 1200 Nm3/h of landfill gas. The economic analysis is completed considering the wood biomass sale, the Net Present Value (NPV) analysis showed a payback time of 7 years for the S-EFGT investment and 5.5 years for the H-EFGT one, the NPV value is 1.310.600,00 € and 6.655.792,00 € for the S-EFGT and H-EFGT configuration, respectively.

Integrating strategies for sustainable conversion of waste biomass into dark-fermentative hydrogen and value-added products

Inefficient waste management and associated environmental pollution are exhausting societies’ precious renewable resources. Moreover, their effects on human health adversely affect the global economic scenario. These adverse effects are a constant cause of concern for environmental and health management. This review presents alternatives to uneconomical and non-eco-friendly methods for waste management and treatment. The multistep microbial anaerobic digestion (AD) process has the potential to metabolize up to 95% of organic matter to energy-rich methane (CH4) and carbon dioxide. The intermediates of AD can be transformed into value-added products, such as hydrogen (H2), polyhydroxyalkanoates (PHAs), and CH4. The unique feature of these value-added products is their eco-friendly nature (non-polluting and biodegradable). The use of biowaste as feed makes the process economical. A few limiting factors that must be circumvented include (i) the slow metabolic rates of methanogens, (ii) high susceptibility to oxygen concentrations, and (iii) the complexity of biowaste. Here, we focus on using biowaste as a feed for integrating dark-fermentative H2 production processes with those of i) photo-fermentative H2, ii) PHAs, and (iii) CH4. This strategy could encourage a transition to an economy based on sustainable waste management and energy generation.

Experimental investigations of bio-syngas production using microwave pyrolysis of UAE’S palm date seed pits

Energy has been essential for the human society, and since the 1700s, the growing need for energy has outstripped the available sources owing to social development and increased use of machines. Biomass as a renewable resource of energy has attracted current research interest. Thermochemical conversion of waste biomass into bio-syngas supports energy needs and provides a better solution for waste management as the economic appraisal of any nation depends on the available energy. In this paper, microwave pyrolysis of the most abundant agricultural waste found in UAE, the Allig date seed pits, is evaluated for bio-syngas production. A full factorial parametric study was performed based on different particle sizes, microwave powers and moisture contents. The syngas yield and the pyrolysis temperature were experimentally analyzed. The experimental result revealed that the maximum bio-syngas was attained at a1000W microwave power, 467 μm particle size and a dry sample, which were producing CH4 and CO bio-gas yield with 21 vol% and 15 vol% respectively. Hence, Allig date seed pits as a biomass in the microwave pyrolysis process may be a promising source of sustainable power for industrial and consumer applications.

Lignosulfonate for improving electrochemical performance of chitin derived carbon materials as a superior anode for lithium-ion batteries

Lignosulfonate, a by-product spent sulfite pulping liquor from the paper and pulping industry, was a suitable natural sulfur dopant for improving electrochemical performance of chitin derived carbon materials. Herein, a cost-effective method of possible large-scale production was reported to fabricate heteroatoms-doped porous carbon (CLs) as advanced electrode materials for lithium-ion batteries applications. After a simple pyrolysis process of chitin mixed with lignosulfonate, generated CLsequipped with abundant defect structures. Remarkably, although portion of lignosulfonate (1/3 of chitin) was introduced, the specific surface area (SSA) of CLs enhanced to 411.64 m2g−1 (CL800). In addition, its capacitive characteristic improved, effectively, delivering high a reversible specific capacity of up to 644.5 mA h g−1 at current density of 50 mA g−1. After 300 cycles at the current density of 100 mA g−1, it still remained a specific capacity of 350.7 mA g−1. Such anode material presented excellent electrochemical performance, good rate capability and cycling stability, attributed to containing abundant N and S elements, providing a green avenue for converting biomass waste to high electrochemical performance heteroatoms-doped carbon materials, having promising application in the energy storage field.

Pyrolysis temperature-dependent carbon retention and stability of biochar with participation of calcium: Implications to carbon sequestration

Converting biomass waste into biochar by slow pyrolysis with subsequent soil amendment is a prospective approach with multiple environmental benefits including soil contamination remediation, soil amelioration and carbon sequestration. This study selected cow manure as precursor to produce biochar under 300 °C, 400 °C, 500 °C and 600 °C, and a remarkable promotion of carbon (C) retention in biochar by incorporation of exogenous Ca was achieved at all investigated pyrolysis temperatures. The C retention was elevated from 49.2 to 68.3% of pristine biochars to 66.1–79.7% of Ca-composite biochars. It was interesting that extent of this improvement increased gradually with rising of pyrolysis temperature, i.e., doping Ca in biomass promoted pyrolytic C retention in biochar by 16.6%, 23.4%, 29.1% and 31.1% for 300 °C, 400 °C, 500 °C and 600 °C, respectively. Thermogravimetric-mass spectrometer (TG-MS) and X-ray photoelectron spectroscopy (XPS) showed that Ca catalyzed thermal-chemical reactions and simultaneously suppressed the release of small organic molecular substances (C2–C7) via physical blocking (CaO, CaCO3, and CaClOH) and chemical bonding (CO and OC–O). The catalyzation mainly occurred at 200–400 °C, while the suppression was more prominent at higher temperatures. Raman spectra and 2D FTIR analysis on biochar microstructure showed that presence of Ca had negative influence on carbon aromatization and thus weakened biochar's stability, while increasing pyrolysis temperature enhanced the stability of carbon structure. Finally, with integrating “C retention” during pyrolysis and “C stability” in biochar, the maximum C sequestration (56.3%) was achieved at 600 °C with the participation of Ca. The study highlights the importance of both Ca and pyrolysis temperature in enhancing biochar's capacity of sequestrating C.