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.     

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.     

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.     

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.     

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.     

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.     

SO2 enhanced desorption from basic aluminum sulfate desulphurization–regeneration solution by falling-film evaporation

To find the optimal structure of the converging–diverging tube and develop a high-efficiency falling-film evaporator, the heat and mass transfer performances of falling-film evaporation with converging–diverging tubes of different dimensions were studied. The optimal converging–diverging tube was used in falling-film evaporation desorption of the basic aluminum sulfate desulphurization–regeneration solution, and different influential factors on the desorption effect were analyzed. It was found that converging–diverging tubes with large falling-film flow rate performed well in the heat and mass transfer of falling-film evaporation, and their rib height largely affected the heat and mass transfer performances. At the same rib height and rib pitch, the longer the converging segment of the converging–diverging tube was, the better the heat transfer performance was. The evaporation heat transfer coefficient and evaporation mass transfer rate in the optimal converging–diverging tube were 1.6 and 1.38 times larger than the smooth tube, respectively. The optimal converging–diverging tube was used in falling-film evaporation desorption of basic aluminum sulfate desulphurization–regeneration solution, at a perimeter flow rate of 0.114–0.222 kg m⁻¹ s⁻¹, the desorption efficiency inside the tube was up to 94.2%, which was 10.3–10.5% higher than that of the smooth tube. At the inlet sulfur concentration of 0.02–0.1 kmol m⁻³, the desorption efficiency was up to 94.1%, which was 12.0–16.3% larger than that of the smooth tube. At the heating temperature of 371.15–386.15 K, the desorption efficiency was up to 93.4%, which was 6.7–11.5% larger than that of the smooth tube. Smaller falling-film flow rate, higher sulfur concentration, or higher heating temperature was more constructive to SO₂ desorption. Correlations were obtained to predict the mass transfer coefficient and SO₂ desorption efficiency. This study develops a new type of falling-film evaporator for SO₂ desorption from basic aluminum sulfate desulphurization–regeneration solution and provides a basis for process design and industrial application.

The heat and mass transfer performances of falling-film evaporation with converging–diverging tubes of different dimensions were studied.     

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.     

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.     

Rice husk biochar modified-CuCo2O4 as an efficient peroxymonosulfate activator for non-radical degradation of organic pollutants from aqueous environment

A series of rice husk biochar (RHBC) modified bimetallic oxides were prepared using a simple pyrolysis method to activate peroxymonosulfate (PMS) for the degradation of acid orange G (OG). The results demonstrated that 50 mg L⁻¹ OG was completely decomposed by 1 mM PMS activated with 100 mg L⁻¹ RHBC–CuCo₂O₄ within 15 min at initial pH 3.4. The OG degradation rate constant k of RHBC–CuCo₂O₄/PMS (0.95 × 10⁻¹ min⁻¹) was five times greater than that of CuCo₂O₄/PMS (0.19 × 10⁻¹ min⁻¹), suggesting that the introduction of RHBC significantly improved the activity of bimetallic oxides. The effects of the initial pH, catalyst dosage, PMS concentration and reaction temperature on OG removal were also studied. The degradation products of OG were analysed using a gas chromatography-mass spectrometer (GC-MS). Electron paramagnetic resonance (EPR) and quenching experiments showed that singlet oxygen (¹O₂) was the main active species. The RHBC–CuCo₂O₄/PMS oxidation system is not only unaffected by inorganic anions (Cl⁻, NO₃⁻, HCO₃⁻) and humic acid (HA), but also could remove other typical pollutants of acetaminophen (ACT), sulfathiazole (STZ), rhodamine B (RhB), and bisphenol A (BPA). These findings show that RHBC–CuCo₂O₄ has great potential for practical applications in the removal of typical organic pollutants.

A series of rice husk biochar (RHBC) modified bimetallic oxides were prepared using a simple pyrolysis method to activate peroxymonosulfate (PMS) for the degradation of acid orange G (OG).     

Redox properties of nano-sized biochar derived from wheat straw biochar

Nano-sized biochar (NBC) has received increasing attention due to its unique physicochemical characteristics and environmental behaviour, but an understanding of its redox properties is limited. Herein, the redox properties of NBC derived from wheat straw were investigated at two pyrolysis temperatures (400 and 700 °C). These NBC materials were prepared from bulk-biochar by grinding, ultrasonication and separation treatments. The resulting NBC had average particle sizes of 78.8 ± 1.9 and 122.0 ± 2.1 nm after 400 and 700 °C treatments, respectively. The physicochemical measurements demonstrated that both the NBC prepared at 400 °C (NBC-400) and the NBC prepared at 700 °C (NBC-700) were enriched in carboxyl and phenolic oxygen-content groups. Electrochemical analyses showed that both NBC-400 and NBC-700 were redox active and had an electron transfer capacity (ETC) of 196.57 μmol⁻¹ g_C⁻¹ and 363.47 μmol⁻¹ g_C⁻¹, respectively. On the basis of its redox activity of NBC, the NBC was capable of mediating the reduction of iron and manganese minerals as well as the degradation of methyl orange (MO) by sulfide. The NBC-700 could stimulate these reactions better than the NBC-400 due to its higher redox activity. Meanwhile, the NBC was more active in stimulating these reactions than bulk-biochar. Our results highlight the importance of size in evaluating the redox reactivity of biochar and related environmental processes and improve our understanding of the redox properties of biochar.

NBC exhibit significant efficiency in mediating MO or minerals reduction by accelerating electron transfer. NBC-700 has higher SSA, ETC and stronger redox property than NBC-400.     

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.     

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.     

Microwave assisted green synthesis of Fe2O3/biochar for ultrasonic removal of nonsteroidal anti-inflammatory pharmaceuticals

Iron oxide/biochar (Fe₂O₃/biochar) was prepared by green synthesis via a microwave to evaluate ultrasound-assisted adsorption capacity of Nonsteroidal Anti-inflammatory Drugs (NSAIDs) (salicylic acid, naproxen, and ketoprofen) from the water. Several techniques of characterization, including, Fourier transform infrared spectrometry, scanning electron microscopy, EDS analysis, N₂ adsorption–desorption, X-ray diffraction, and Raman spectrometry were applied. The adsorption of NSAIDs onto Fe₂O₃/biochar was performed using an ultrasonic bath. The effects of batch adsorption under various experimental parameters such as contact time (0–120 min), initial concentration (10–500 mg L⁻¹) and pH (2–12) were tested. The obtained Fe₂O₃/biochar specific surface area, mesopore volume/micropore volume, and pores size were equal to 786 m² g⁻¹, 0.409 cm³ g⁻¹, and 1.534 cm³ g⁻¹, respectively. The pseudo-second-order model could describe better all NSAID adsorptions onto Fe₂O₃/biochar. The Langmuir model agreed well with the NSAID adsorptions and the maximum adsorption capacities reached 683 mg g⁻¹, 533 mg g⁻¹ and 444 mg g⁻¹ for salicylic acid, naproxen, and ketoprofen, respectively. Fe₂O₃/biochar can be used as an excellent adsorbent for the treatment of NSAIDs in water.

Here, we have developed a simple and green microwave synthesis of iron oxide/biochar for the removal of new emergent pharmaceutical pollutants.     

Ultradispersed titanium dioxide nanoparticles embedded in a three-dimensional graphene aerogel for high performance sulfur cathodes

Lithium–sulfur (Li–S) batteries are regarded as one of the most promising energy storage technologies, however, their practical application is greatly limited by a series of sulfur cathode challenges such as the notorious “shuttle effect”, low conductivity and large volume change. Here, we develop a facile hydrothermal method for the large scale synthesis of sulfur hosts consisting of three-dimensional graphene aerogel with tiny TiO₂ nanoparticles (5–10 nm) uniformly dispersed on the graphene sheet (GA–TiO₂). The obtained GA–TiO₂ composites have a high surface area of ∼360 m² g⁻¹ and a hierarchical porous structure, which facilitates the encapsulation of sulfur in the carbon matrix. The resultant GA–TiO₂/S composites exhibit a high initial discharge capacity of 810 mA h g⁻¹ with an ultralow capacity fading of 0.054% per cycle over 700 cycles at 2C, and a high rate (5C) performance (396 mA h g⁻¹). Such architecture design paves a new way to synthesize well-defined sulfur hosts to tackle the challenges for high performance Li–S batteries.

GA–TiO₂ composites as a cathode material realize an excellent electrochemical performance in Li–S batteries.     

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.     

Antibiotic removal by agricultural waste biochars with different forms of iron oxide

Pollution by antibiotics has become a serious threat to public health. In this study, agricultural waste, corn husk, in the form of biochar, was utilized for antibiotic removal from wastewater. Two kinds of iron-loaded biochars, impregnation–pyrolysis biochar (IP) and pyrolysis–impregnation biochar (PI), were synthesized to adsorb the typical antibiotics tetracycline (TC) and levofloxacin (LEV). PI contained amorphous hydrated iron oxide, whereas the major component of IP was γ-Fe₂O₃. Compared with IP, PI had a much higher adsorption capacity for both TC and LEV. This was because PI could provide more –OH, especially –OH_ads, to serve as the adsorption sites. In comparison with TC, –OH was prone to combine with LEV. FT-IR and XPS results indicated that the mechanisms of LEV adsorption included hydrogen bonding, F-replacement, electrostatic attraction and bridging bidentate complexation. TC adsorption may involve complexation, hydrogen bonding and electrostatic attraction.

The possible adsorption mechanisms.     

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.     

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.     

A mitochondrion-targeted dual-site fluorescent probe for the discriminative detection of SO32− and HSO3− in living HepG-2 cells

Sulfur dioxide, known as an environmental pollutant, produced during industrial productions is also a common food additive that is permitted worldwide. In living organisms, sulfur dioxide forms hydrates of sulfite (SO₂·H₂O), bisulfite (HSO₃⁻) and sulfite (SO₃²⁻) under physiological pH conditions; these three exist in a dynamic balance and play a role in maintaining redox balance, further participating in a wide range of physiological and pathological processes. On the basis of the differences in nucleophilicity between SO₃²⁻ and HSO₃⁻, for the first time, we built a mitochondrion-targeted dual-site fluorescent probe (Mito-CDTH-CHO) based on benzopyran for the highly specific detection of SO₃²⁻ and HSO₃⁻ with two diverse emission channels. Mito-CDTH-CHO can discriminatively respond to the levels of HSO₃⁻ and SO₃²⁻. Besides, its advantages of low cytotoxicity, superior biocompatibility and excellent mitochondrial enrichment ability contribute to the detection and observation of the distribution of sulfur dioxide derivatives in living organisms as well as allowing further studies on the physiological functions of sulfur dioxide.

Rational design and sensing mechanism of a dual-site fluorescence probe for HSO₃⁻ and SO₃²⁻.