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.     

Quantitative evaluation of relationships between adsorption and partition of atrazine in biochar-amended soils with biochar characteristics

Atrazine (ATZ) adsorption in two natural soils amended with biochars produced from different feedstocks at 300, 500, and 700 °C were investigated; further, the relationships between the surface and partition adsorption capacities of ATZ in biochar-amended soils with biochar characteristics were quantitatively evaluated. The results revealed that high aromaticity, hydrophobicity, and low polarity of biochar facilitated ATZ adsorption. The addition of selected biochars significantly increased the adsorption of ATZ on paddy soil (PS) and black soil (BS) by 5.2–7.5 times and 2.3–4.2 times, respectively. On the contrary, the degree of increase in surface adsorption was much higher than that in partition adsorption, mainly due to the role of the specific adsorption of ATZ on biochar. Meanwhile, the respective contributions of surface and partition adsorptions to the total ATZ adsorption on biochar-amended soil changed with different addition amounts of biochar. The multiple nonlinear regression analysis demonstrated the linear dependence of H/C ratio, (O + N)/C ratio, and specific surface area (SSA) of biochar on the surface adsorption capacity of biochar-amended PS and BS, as well as the linear dependence of organic carbon and ash contents on the partition adsorption capacity of biochar-amended PS and the linear dependence of the H/C ratio and SSA on the partition adsorption capacity of biochar-amended BS. In biochar-amended soil systems, interactions between biochar and soil could affect ATZ adsorption, and organic matter in biochar might compensate for the role of soil organic matter in the competition for adsorption sites with a decrease in the biochar pyrolysis temperature.

Adsorption of atrazine (ATZ) in two natural soils amended with different biochars was investigated, and the relationships of adsorption capacity of biochar-amended soils with biochar characteristics were also quantitatively evaluated.     

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.     

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.     

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.     

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.     

Adsorption–desorption of CO2 on zeolite-Y-templated carbon at various temperatures

This study aims to investigate the adsorption–desorption of CO₂ on a micro-mesoporous zeolite-Y-templated carbon (ZTC) at various temperatures. ZTC was synthesized via sucrose impregnation, carbonization, and template removal. The adsorption–desorption of CO₂ on ZTC was performed using the gravimetric method. Results showed that the CO₂ adsorption capacity was 9.51 wt%, 5.60 wt%, and 3.47 wt%, and desorbed up to 59.83%, 69.70%, 77.5% for temperatures of 30 °C, 40 °C, and 50 °C, respectively. The adsorption process of CO₂ at temperatures of 30 °C and 40 °C follow the pseudo-second order, while at 50 °C follows intra-particle diffusion. The thermodynamic analyses indicate that the adsorption was due to physisorption.

A micro-mesoporous structure of ZTC was synthesized via an impregnation method, and the structure assisted in a faster CO₂ adsorption–desorption equilibrium.     

Bioremediation of petroleum hydrocarbon-contaminated soil by petroleum-degrading bacteria immobilized on biochar

Biochar is investigated experimentally as a new highly effective amendment to remediate contaminated soil. A crucial consideration is the influence of biochar on the bioremediation of soil polluted with total petroleum hydrocarbons (TPHs), and in particular, the use of biochar as a bacteria immobilization carrier with a synergistic effect of absorption and degradation. Therefore, we studied the ability of petroleum-degrading bacteria immobilized on biochar, free bacteria, and biochar alone on the removal of TPHs in soil using gravimetric analysis and gas chromatography-mass spectrometry. After 60 days of remediation, the strategy involving immobilized bacteria on biochar was more effective than other treatments in reducing the contents of TPHs and n-alkanes with C_12–18, which showed the shortest half-life and highest biodegradation efficiency; variations in the features of enzymatic activities and microbial respiration indicated that the biochar treatment improved not only the soil fertilizer and carbon storage, but the immobilization greatly affected both the physicochemical properties of soil and bacterial activities. Moreover, the bacterial population diversity and bioavailability of hydrocarbons were promoted by the inputs of the combination of biochar and petroleum-degrading bacteria. Overall, our results highlight the potential of applying immobilized microorganisms on biochar for accelerating the biodegradation of petroleum and maintaining the balance of the soil ecosystem, which may be ascribed to the synergistic effect of biostimulation and bioaugmentation.

The immobilization of bacteria on biochar was effective in reducing TPHs, n-alkanes with C_12–18 and maintaining the balance of the soil ecosystem.     

Effects of dairy manure biochar on adsorption of sulfate onto light sierozem and its mechanisms

The adsorption of nitrogen and phosphorous nutrients on biochar and even biochar–soil mixtures was investigated. However, the situation of sulfur was not very clear. Here, sulfate (SO₄²⁻) adsorption onto dairy manure biochar obtained at 700 °C (DMBC700), soil (light sierozem) and a 1 : 9 (w/w) biochar–soil mixture (DMBC700-soil) was investigated using batch experiments. The contact time, sulfate concentration, and solution pH value were chosen as the main factors; their effects on sulfate adsorption were tested, and the kinetics and isotherms were also investigated. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopies were used to characterize DMBC700 and soil before and after adsorbing sulfate, respectively, and to analyze the mechanisms of adsorption. The results showed that the adsorption kinetics were well described by the pseudo-second-order model, whereas the Langmuir and Freundlich models fitted well with the equilibrium data. DMBC700 modification did not increase the adsorption capacity of light sierozem for sulfate. When the pH values of the initial solution were increased, all the adsorption capacities of sulfate onto DMBC700, light sierozem and light sierozem with DMBC700 decreased. The electrostatic interaction was the main force for the adsorption of sulfate onto DMBC700, whereas both electrostatic interaction and formation of poorly soluble CaSO₄ were the main forces for adsorption of sulfate onto light sierozem. DMBC700 was found to have negative effect on sulfate adsorption onto light sierozem.

Amendment of dairy manure biochar exhibits negative effect on sulfate adsorption onto light sierozem.     

Characterization of biochars derived from different materials and their effects on microbial dechlorination of pentachlorophenol in a consortium

The properties of biochars derived from different raw materials (rice husk, bamboo, caragana, and garbage) and their effects on the microbial reductive dechlorination of pentachlorophenol (PCP) were investigated to understand how biochars influence the biotransformation of environmental pollutants. The results indicated that only caragana-derived biochar showed stable electron transfer activity for PCP dechlorination. Electro(chemical) analyses revealed that caragana biochar had the highest electrical conductivity (EC) (2.22 × 10⁶ μS cm⁻¹), while those of the other biochars were <1500 μS cm⁻¹. The electron transfer capacities were within the ranges of 61.63–155.83 μmol e⁻ g⁻¹. Cyclic voltammetry analysis suggested that there were no obvious redox peaks for the biochars, while the Fourier transform infrared analysis showed similar transmission spectra with variable absorption intensity; this suggested that all biochars possessed similar structures and functional group classes and the enhancement of PCP dechlorination was not attributable to the redox reaction. Overall, the beneficial effects of caragana biochar on PCP dechlorination depended on the EC rather than the redox functional groups, possibly because high EC values enabled the highest electron transfer, and thus resulted in the greatest promotion of reductive dechlorination activity.

The properties of four biochars and their effects on the microbial reductive dechlorination of PCP were investigated.     

Functional utilization of biochar derived from Tenebrio molitor feces for CO2 capture and supercapacitor applications

Biochar has attracted great interest in both CO₂ capture and supercapacitor applications due to its unique physicochemical properties and low cost. Fabrication of eco-friendly and cost-effective biochar from high potential biomass Tenebrio molitor feces can not only realize the functional application of waste, but also a potential way of future carbon capture and energy storage technology. In this study, a novel KOH activation waste-fed Tenebrio molitor feces biochar (TMFB) was developed and investigated in terms of CO₂ capture and electrochemical performance. When activated at 700 °C for 1 h, the specific surface area of the feces biochar (TMFB-700A) increased significantly from 232.1 to 2081.8 m² g⁻¹. In addition, well-developed pore distribution facilitates CO₂ capture and electrolyte diffusion. TMFB-700A can quickly adsorb a large amount of CO₂ (3.05 mol kg⁻¹) with excellent recycling performance. TMFB-700A also exhibited promising electrochemical performance (335.8 F g⁻¹ at 0.5 A g⁻¹) and was used as electrode material in a symmetrical supercapacitor. It provided a high energy density of 33.97 W h kg⁻¹ at a power density of 0.25 kW kg⁻¹ with 90.47% capacitance retention after 10 000 charge–discharge cycles. All the results demonstrated that TMFB could be a potential bifunctional material and provided valuable new insights for Tenebrio molitor feces high-value utilization.

Biochar has attracted great interest in both CO₂ capture and supercapacitor applications due to its unique physicochemical properties and low cost.     

Obtaining lignocellulosic biomass-based catalysts and their catalytic activity in cellobiose hydrolysis and acetic acid esterification reactions

Global challenges prompt the world to modify its strategies and shift from a fossil-fuel-based economy to a bio-resource-based one with the production of renewable biomass chemicals. Different processes exist that allow the transformation of raw biomass into desirable bio-based products and/or energy. In this work different biochars that were obtained as a by-product from birch chip fast pyrolysis and carbonization were used as is or chemically/physically treated. These sulfonated carbon catalysts were compared to a commercially available sulfonated styrene-divinylbenzene macroreticular resin (Dowex 50W X8). Characterisation (water content and pH value, FTIR, base titration, element analysis and N₂ desorption) was done to evaluate the obtained sulfonated biocarbon catalysts. Catalytic activity was tested using cellobiose (CB) hydrolysis and acetic acid esterification. For the catalytic CB hydrolysis, we tested the reaction temperature, time and CB and catalyst mass ratios. The determined optimal conditions were 120 °C and 24 h, with CB and catalyst mass ratio 1 : 5. The highest glucose yield was observed for biochar obtained from the birch chip fast pyrolysis process (BC_Py-H₂SO₄) – 92% within 24 h for 120 °C. Comparably high glucose yield was observed for biochar that was obtained in birch chip carbonization (BC_Carbon-H₂SO₄) – 86% within 24 h for 120 °C.

In this work different biochars that were obtained as a by-product from birch chip fast pyrolysis and carbonization were used as is or chemically/physically treated. The characterisation was done using CB hydrolysis and acetic acid esterification.     

Removal of acenaphthene from water by Triton X-100-facilitated biochar-immobilized Pseudomonas aeruginosa

By adding the nonionic surfactant Triton X-100 and using biochar as an immobilization carrier, a Triton X-100-facilitated biochar-immobilized Pseudomonas aeruginosa (TFBIP) material was prepared using the sorption method and was used to treat acenaphthene in water. The results showed that a low concentration of Triton X-100 simultaneously promoted the sorption capacity of the biochar and the degradation activity of P. aeruginosa, thereby significantly enhancing the removal of acenaphthene from water by the immobilized P. aeruginosa material. Compared with the control without Triton X-100, a low concentration of Triton X-100 significantly increased the acenaphthene removal rate by 20–50%. The optimal conditions for preparing the TFBIP were a loading time of 24 h, the use of a bacterial suspension with a concentration of OD₆₀₀ = 0.2, and a Triton X-100 concentration of 10 mg L⁻¹. The optimized TFBIP material could efficiently remove acenaphthene from water at temperatures of 10–50 °C, pH values of 4.5–10.5, and NaCl concentrations of up to 0.2 mol L⁻¹. The new TFBIP material can be used for the treatment of wastewater and may also be directly used for the remediation of soils contaminated with organic pollutants.

A new efficient PAH-degrading bacterial material was produced by using biochar as an immobilization carrier and adding nonionic surfactant.     

Lead and uranium sorptive removal from aqueous solution using magnetic and nonmagnetic fast pyrolysis rice husk biochars

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars. The porosity, specific surface area, hydrophobility, and reusability of biochar were effectively improved (1–2 times) after magnetic modification. The optimum adsorption conditions were as follows: biochar loading was 0.4 g L⁻¹, pH value was 7.0, and anion strength of NO₃⁻ and PO₄³⁻ were 0.01 mol L⁻¹ for Pb(ii) and 0.04 mol L⁻¹ for U(vi) respectively. Compared with U(vi), Pb(ii) had the faster adsorption rate and higher adsorption capacity on magnetic biochar (MBC). The adsorption experimental data were well fitted by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of Pb(ii) and U(vi) on MBC was 129 and 118 mg g⁻¹ at 328 K respectively, which was significantly higher than that of other sources biochars. Pb(ii) was mainly bonded to biochar by physisorption but the adsorption of U(vi) on biochar was mostly chemisorption. Fe oxides in MBC noticeably improved the ion exchange and complexation action between biochar and metal ion especially for U(vi). The experimental results confirmed MBC material can be used as a cost-effective adsorbent for the removal of Pb(ii) and U(vi) and can be separated easily from aqueous solution when application.

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars.     

Synthesis of a novel magnetic Caragana korshinskii biochar/Mg–Al layered double hydroxide composite and its strong adsorption of phosphate in aqueous solutions

Phosphate pollution of aquatic ecosystems is of great concern and requires the development of high-performance materials for effective pollution treatment. To realize efficient phosphate removal from aqueous solution, an easily separable magnetic (Fe₃O₄) Caragana korshinskii biochar/Mg–Al layered double hydroxide composite (denoted as FCB/MAC) was synthesized via two-step electro-assisted modification for the first time. Subsequently, the physical and chemical properties of FCB/MAC were characterized. Furthermore, the sorption mechanism for phosphate removal was investigated in detail. The results indicated that Fe₃O₄ and the Mg–Al layered double hydroxide were successfully embedded in the biochar matrix. Moreover, FCB/MAC exhibited a high phosphate adsorption capacity and excellent magnetic properties for easy recovery. The maximum phosphate sorption capacity of FCB/MAC was 252.88 mg g⁻¹, which is much higher than the capacities of most magnetic phosphate adsorbents. In addition, the adsorption kinetics and isotherms indicated that phosphate adsorption by FCB/MAC was controlled by the pseudo-second-order kinetic model and the Langmuir–Freundlich isotherm model. The phosphate adsorption mechanism involves anion exchange, electrostatic attraction, and ligand exchange. After five adsorption–desorption cycles, the phosphate adsorption capacity of FCB/MAC was 25.71 mg g⁻¹ with 51.43% removal efficiency and high recyclability. Thus, the composite prepared in this study is a promising adsorbent for phosphate removal from aqueous solution, and this work provides an excellent reference for constructing novel biochar-based phosphate adsorbents.

This study describes an optimized two-step electro-assisted modification process for the preparation of biochar modified with Fe₃O₄ and Mg–Al layered double hydroxide.     

Impacts of different biochar types on the anaerobic digestion of sewage sludge

In this study, the effect of nine types of biochar generated from three different feedstocks on the anaerobic digestion (AD) of sewage sludge was investigated. The obtained results indicated that methane production could be significantly enhanced by all types of biochar used in the test. The maximum cumulative methane yield of 218.45 L per kg VS was obtained for the culture with corn straws pyrolyzed at 600 °C which also exhibited the largest specific surface area. Adding an appropriate amount of biochar was beneficial to improve the cumulative methane yield, while excessive addition could inhibit the AD process. Biochar could also enhance AD process stability by increasing buffering capacity, releasing volatile fatty acid accumulation and alleviating ammonia inhibition. Simultaneously, microbial community analysis revealed that biochar addition was able to improve the diversity of archaeal community and adjust the microbial communities. It was notable that biochar treatment facilitated the aceticlastic methanogens (Methanosarcina) compared to the hydrogenotrophic methanogens. Overall, biochar addition could be an ideal approach that is not only expected to successfully improve the performance of AD, but also lay a new path for future biomass energy utilization.

Pyrolysis temperature and feedstock types had a pronounced effect on biochar properties, and biochar could facilitate the anaerobic digestion process.     

Removal of copper ions by functionalized biochar based on a multicomponent Ugi reaction

Copper is widely present in the natural environment and inevitably poses a risk to both human health and the natural environment. Biochar is an inexpensive, clean and sustainable sorbent material that can be used as a resource for copper removal, and there is interest in new ways to chemically treat biochar to tune its unique properties and modify its atomic structure. In this study, biochar was oxidized, and then polyethyleneimine (PEI) modified chitosan and carboxylated biochar were economically compounded through a multicomponent Ugi reaction to effectively remove Cu(ii). PEI enhances the adsorption of Cu(ii) within an optimum solution pH range of 3.5–5.5. The adsorption process follows a pseudo-second-order kinetic model. When the dosage of BC-NH2 was 4 g L⁻¹ and the temperature was 303 K, the maximum adsorption capacity calculated by the Langmuir model was 26.67 mg g⁻¹. The adsorption process of Cu(ii) on BC-NH2 was heat-trapping and spontaneous. BC-NH2 showed good selectivity for K⁺ and Mg²⁺, and BC-NH2 desorbed by NaOH showed better adsorption performance than H₂SO₄ in the adsorption–desorption cycle. Characterization by SEM, EDS, BET, FTIR, TGA and XPS showed successful coupling and that the amide group of BC-NH2 had chelated with Cu(ii). This atomically economical multicomponent Ugi reaction provides a new option for preparing composite materials that effectively remove heavy metals.

Polyethyleneimine-modified chitosan and carboxylated biochar were economically compounded by a multicomponent Ugi reaction to produce products rich in amide functional groups.     

Development,modification, and application of low-cost and available biochar derived from corn straw for the removal of vanadium(v) from aqueous solution and real contaminated groundwater

In this work, a low-cost and available material for use as a permeable reactive barrier (PRB) to prevent vanadium in groundwater from leaking into river water was developed. Three modified biochars were prepared from available corn straw pretreated with CsCl, Zn(ii), and Zr(iv) to enhance ion exchange capacity (IEC) and specific surface area, and were designated as Cs-BC, Zn-BC, and Zr-BC, respectively. These materials were characterized via IEC, N₂ adsorption–desorption, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. The Langmuir isotherm model could be applied for the best fit for the adsorption data of Cs-BC and Zr-BC, indicating that vanadium(v) sorption occurred in a monolayer. The vanadium(v) adsorption capacities of Cs-BC, Zn-BC, and Zr-BC were 41.07, 28.46, and 23.84 mg g⁻¹, respectively, which were 3.22–5.55 times higher than that of commercial activated carbon (AC) (7.40 mg g⁻¹), probably because of their higher IECs and specific surface areas after modification. In addition, no heavy metal leaching was found from the modified biochars during the adsorption processes when pH > 2. According to the FTIR and XRD patterns, the adsorption mechanism of Cs-BC and Zr-BC was ion exchange, whereas for Zn-BC, it was mainly surface precipitation and electrostatic attraction. The adsorption of vanadium(v) onto the modified biochars was independent of pH in the range of 4.0 to 8.0. Furthermore, the removal efficiency of the vanadium(v) in real contaminated groundwater from the catchment of the Chaobei River by Zn-BC reached 100% at a dose of 4 g L⁻¹. Hence, modified biochars are promising PRB filling materials for removing vanadium(v) from contaminated groundwater.

In this work, a low-cost and available material for use as a permeable reactive barrier (PRB) to prevent vanadium in groundwater from leaking into river water was developed.     

In-depth study of bio-oil and biochar production from macroalgae Sargassum sp. via slow pyrolysis

Sargassum is undoubtedly one of the most predominant brown macroalgae, posing a significant disposal problem for coastal areas worldwide. The effective valorization of Sargassum sp. would be beneficial not only for environmental mitigation but also for producing high-value chemicals. However, the valorization of Sargassum sp. for bio-oil and biochar production via slow pyrolysis has not been well studied yet. Hence, this study aimed to conduct a comprehensive investigation into bio-oil and biochar production from Sargassum sp. via slow pyrolysis to provide valuable data for further valorization. A batch reactor was employed, and the pyrolysis of Sargassum sp. was conducted in a temperature range of 400–600 °C and with retention times of 10–50 min. The results showed significant compounds could be identified in bio-oil from Sargassum sp., including carboxylic acids, furan derivatives, aliphatic hydrocarbons, and N-aromatic compounds. Based on the ultimate analysis, the H/C and O/C atomic ratios of biochar were lower than the feedstock, reflecting the occurrence of dehydration and decarboxylation reactions throughout the pyrolysis. Biochar exhibited calorific values in the range of 23.12–25.89 MJ kg⁻¹, indicating it has more potential to be used as a solid fuel than low-ranked coals. Surface morphological analysis was performed by scanning electron microscopy (SEM) and showed a larger surface area in biochar than in the algal feedstock. Furthermore, a reaction model was deduced, and it was confirmed that the pyrolysis reaction obeyed the Arrhenius behaviour. Overall, the slow pyrolysis of Sargassum sp. provides an opportunity to obtain value-added chemicals and biochars, which could be further utilized for other applications.

Slow pyrolysis of brown macroalgae (Sargassum sp.) for bio-oil and biochar production.     

FeS–biochar and Zn(0)–biochar for remediation of redox-reactive contaminants

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis. These biochars significantly promoted the removal of 2,4-dichlorophenol (DCP) by means of sorption and reduction. Compared to direct reduction with FeS and Zn(0), the formation of reduction intermediates and product was enhanced from 21% and 22% of initial DCP concentration to 41% and 52%, respectively. 2,4-Dinitrotoluene (DNT), chromate (CrO₄²⁻) and selenate (SeO₄²⁻) were also reductively transformed to reduction products (e.g., 2,4-diaminotoluene [DAT], Cr³⁺, and selenite [SeO₃²⁻]) after they sorbed onto the biochars including FeS and Zn(0). Mass recovery as DAT, Cr³⁺ and selenite was 4–20%, 1–3%, and 10–30% under the given conditions. Electrochemical and X-ray analyses confirmed the reduction capability of the biochars including FeS and Zn(0). Fe and S in the FeS–biochar did not effectively promote the reductive transformation of the contaminants. Contrastingly, the stronger reducer Zn(0) yielded faster reductive transformation of contaminants over the Zn(0)-containing biochar, while not releasing high concentrations of Zn²⁺ into the aqueous phase. Our results suggest that biochars including Zn(0) may be suitable as dual sorbents/reductants to remediate redox-reactive contaminants in natural environments.

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis.