Gamma-radiated biochar carbon for improved supercapacitor performance

Biochar carbon YP-50 exposed to gamma radiation at 50 kGy, 100 kGy, and 150 kGy was used as an electrode for an electric double-layer capacitor. The gamma radiation affected the pore structure and pore volume of the biochar electrodes. The optimized surface morphology, pore structure, and pore volume of the biochar with an irradiation dose of 100 kGy showed outstanding specific capacitance of 246.2 F g⁻¹ compared to the untreated biochar (115.3 F g⁻¹). The irradiation dose of 100 kGy exhibited higher specific power and specific energy of 0.1 kW kg⁻¹ and 34.2 W h kg⁻¹ respectively, with a capacity retention of above 96% after 10 000 cycles at a current density of 2 A g⁻¹. This improvement can be attributed to the decrease in average particle size, an increase in the porosity of biochar carbon. Besides, the charge transfer resistance of supercapacitor is significantly reduced from 21.7 Ω to 7.4 Ω after treating the biochar carbon with 100 kGy gamma radiation, which implies an increase in conductivity. This gamma radiation strategy to pretreat the carbon material for improving the properties of carbon materials can be promising for the development of high-performance supercapacitors for large-scale applications.

(a) Schematic of the biochar carbon YP-50 exposed to gamma radiation. (b) Cyclic Voltammetry of supercapacitor with untreated biochar and biochar treated with 50 kGy, 100 kGy, and 150 kGy gamma-radiation.     

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.     

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

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

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

Preparation of high-yield N-doped biochar from nitrogen-containing phosphate and its effective adsorption for toluene

Novel biochar was prepared from plant-based biomass by the addition of nitrogen-containing phosphates (NCPs), including ammonia phosphate (AP), ammonia polyphosphate (APP) and urea phosphate (UP). The results demonstrated that with the addition of NCPs, the yield of biochar could be significantly increased from about 30% to up to about 60%. The pore structure of the biochar was significantly improved, and the AP-prepared biochar obtained a higher S_BET and V_tot of 798 m² g⁻¹ and 0.464 cm³ g⁻¹, respectively. Moreover, the surface chemistry of the NCP-prepared biochar was affected, and N heteroatoms could be successfully doped on the surface of biochar, up to 4.16%. Furthermore, through TG-FTIR and XPS analysis, some possible interactions between plant-based biomass and NCPs during the pyrolysis process were proposed to explore the mechanisms of the preparation process, including the P route and N route, in which the H₃PO₄ and NH₃ gradually generated during the heating process played the dominant roles for the high yield N-doped biochar. All the NCP-prepared biochar presented good toluene adsorption capacities from 175.9 to 496.2 mg g⁻¹, which were significantly higher than that of blank char (6.5 mg g⁻¹).

Novel biochar was prepared from plant-based biomass by the addition of nitrogen-containing phosphates (NCPs), including ammonia phosphate (AP), ammonia polyphosphate (APP) and urea phosphate (UP).     

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.     

Single-component and competitive adsorption of tetracycline and Zn(ii) on an NH4Cl-induced magnetic ultra-fine buckwheat peel powder biochar from water: studies on the kinetics,isotherms, and mechanism

Single-component and competitive adsorption of tetracycline (TC) and Zn(ii) on an NH₄Cl-induced magnetic ultra-fine buckwheat peel powder biochar (NH₄Cl-BHP-char/Fe₃O₄) was investigated in batch experiments. NH₄Cl-BHP-char/Fe₃O₄ exhibited a large surface area of 1119.097 m² g⁻¹ and a total pore volume of 0.139 cm³ g⁻¹ and was easily separated from aqueous solution using a magnet. Also, adsorption was endothermic, spontaneous, and highly pH-dependent. The optimum pH of the single-component adsorption of TC and Zn(ii) was 4.0 and 6.5, respectively, and the optimum pH of co-adsorption was 6.0. The kinetics studies showed the prepared biochar could be rapidly adsorbed within 60 min, and chemical adsorption was dominant. For single-component adsorption, the maximum adsorption capacities of TC and Zn(ii) were 106.38 and 151.52 mg g⁻¹, respectively, and they underwent monolayer adsorption on the biochar surface. Moreover, for competitive adsorption, maximum TC and Zn(ii) adsorption capacities of 126.58 and 357.14 mg g⁻¹ were achieved. Both film diffusion and intra-particle diffusion were found to be significant processes to facilitate adsorption. TC and Zn(ii) promoted the adsorption of each other. The proposed biochar could be used repeatedly for at least four cycles. All these results demonstrated that developed NH₄Cl-BHP-char/Fe₃O₄ was regarded as a low-cost alternative adsorbent to remove the heavy metal ions and antibiotic pollutants from water or wastewater.

Single-component and competitive adsorption of tetracycline (TC) and Zn(ii) on an NH₄Cl-induced magnetic ultra-fine buckwheat peel powder biochar (NH₄Cl-BHP-char/Fe₃O₄) was investigated in batch experiments.     

Superb adsorption capacity of biochar derived from leather shavings for Congo red

Research on biochar for removal of dyes has been a hot topic because of its excellent eco-friendly and economical properties. In this study, leather shavings biochar (LSB) with high adsorption capacity was prepared and tested with Congo red as a model dye for adsorption. The research results show that the as-prepared biochar exhibits a porous structure, with a high specific surface area (2365 m² g⁻¹), and it would be beneficial for removing Congo red from effluents. More interestingly, adsorption capacity of LSB for Congo red was enhanced by chromium compounds on the surface of biochar through chelation and electrostatic interactions. Chelation occured between the chromium compounds and amino groups of Congo red. Adsorption data for Congo red on the biochar were successfully described by Langmuir isotherm and the pseudo-second order kinetics model. Langmuir maximum adsorption capacity of LSB at 30 °C reached 1916 mg g⁻¹, which is much higher than that of conventional activated carbon (AC). Recycling experiment shows that LSB has a potential market for removing Congo red.

Leather shavings biochar can achieve high adsorption performance for Congo red through physical and chemical interactions.     

Adsorption and regeneration of leaf-based biochar for p-nitrophenol adsorption from aqueous solution

As an environmentally friendly and low-cost adsorbent, biochar has great potential in wastewater treatment. This study investigated biochar derived from Platanus orientalis L. leaves (PLB) activated by KOH in terms of its capacity and reusability to adsorb p-nitrophenol (PNP). PLB had a large specific surface area and total pore volume, and exhibits good PNP removal with a maximal adsorption capacity of 622.73 mg g⁻¹ at 298 K. Batch experiments showed that PLB had a high PNP adsorption capacity under acidic conditions. Experimental results were well described by the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model. The thermodynamic study showed that PNP adsorption was a spontaneously exothermic process, and increasing temperature was not conducive to adsorption. In addition, PNP adsorption was mainly attributed to hydrophobic interaction. The regeneration experiment showed that PLB had good reusability. After the fifth regeneration, the adsorption capacity of PLB still reached 557.05 mg g⁻¹. The deactivation of oxygen-containing functional groups and pore blockage were the causes for the decrease in adsorption capacity of the recycled PLB. Moreover, the biochar showed good adsorption efficiency and reusability, thereby suggesting its potential to serve as an efficient PNP adsorbent for wastewater treatment.

As an environmentally friendly and low-cost adsorbent, biochar has great potential in wastewater treatment.     

Chitin derived biochar for efficient capacitive deionization performance

The selection and preparation of an electrode material is the core of capacitive deionization. In order to obtain a material with a good deionization properties, we have designed an environmentally-friendly and simple way of preparing biochar. In this work, biochar was prepared by a thermal-deposition method and after chemical modification it was characterized with a scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The specific surface area of biochar modified by KOH is as high as 833.76 m² g⁻¹, but the specific surface area of the unmodified electrode material is only 126.43 m² g⁻¹. The electrochemical analysis (CV and EIS) of the biochar indicates that HC-800 has a lower charge transfer resistance and a higher specific capacitance, where the specific capacity of HC-800 reaches 120 F g⁻¹. A CDI property analysis of HC-800 shows a better electrosorption capacity of 11.52 mg g⁻¹ and better regeneration and cycling stability than CS-800. The desalination amount remains 87.23% after several cycles.

Schematic illustration of the fabrication of chitin derived biochar and KOH-activated chitin derived biochar electrodes for capacitive deionization.     

A novel,recyclable magnetic biochar modified by chitosan–EDTA for the effective removal of Pb(ii) from aqueous solution

We report here the preparation process of a recyclable magnetic biochar functionalized with chitosan and ethylenediaminetetraacetic acid (E-CMBC). This prepared biochar was then evaluated regarding its adsorption performance for Pb(ii) from an aqueous solution along with the potential adsorption mechanisms behind this process. XRD and SEM analyses showed that the magnetite particles were successfully embedded into biochar and the subsequent surface coating of chitosan and ethylenediaminetetraacetic acid modification were also successful. The effects of the adsorbent dosage, ionic strength, initial solution pH, and contact time, on adsorption kinetics, adsorption isotherms, adsorption thermodynamics and regeneration performance were investigated. The removal of Pb(ii) was dramatically improved to 156.68 mg g⁻¹ compared with that by unmodified pristine biochar (10.90 mg g⁻¹) at pH 3.0. In the range of pH 2.0–5.0, the adsorption performance of Pb(ii) by E-CMBC remained above 152.50 mg g⁻¹, which suggested that the adsorption capacity of the novel sorbent was not impacted by the competing adsorption of hydrogen cations under acidic conditions. The adsorption process could be well described by the Avrami fractional-order and Langmuir models. Thermodynamic analysis proved that the adsorption process was spontaneous and endothermic. The magnetic strength of E-CMBC was measured as 3.1 emu g⁻¹, suggesting that the consumed E-CMBC could be separated from water by an external magnet. A regeneration study showed that after three cycles of adsorption–desorption, 78.60% of the sorbent was recovered and 97.26% of the adsorption capacity was retained. The adsorption mechanism investigation indicated that Pb(ii) adsorption was mainly due to the presence of functional amides and carboxyl groups of E-CMBC forming strong chemical complexation. In conclusion, E-CMBC is a novel, recyclable, and highly efficient adsorbent for removal of Pb(ii) from aqueous solution.

EDTA modified magnetic chitosan biochar was synthesized and used as an adsorbent for adsorption of Pb(ii).     

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.     

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.     

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.     

Hierarchically porous SiO2/C hollow microspheres: a highly efficient adsorbent for Congo Red removal

Hierarchically porous SiO₂/C hollow microspheres (HPSCHMs) were synthesized by a hydrothermal and NaOH-etching combined route. The adsorption performance of the prepared HPSCHMs was investigated to remove Congo Red (CR) in aqueous solution. The results show that the synthesized composite possesses a hollow microspherical structure with hierarchical pores and a diameter of about 100–200 nm, and its surface area is up to 1154 m² g⁻¹. This material exhibits a remarkable adsorption performance for CR in solution, and its maximum adsorption amount for CR can reach up to 2512 mg g⁻¹. It shows faster adsorption and much higher adsorption capacity than the commercial AC and γ-Al₂O₃ samples under the same conditions. The studies of the kinetics and thermodynamics indicate that the adsorption of CR on the PHSCHM sample obeys the pseudo-second order model well and belongs to physisorption. The adsorption activation energy is about 7.72 kJ mol⁻¹. In view of the hierarchically meso–macroporous structure, large surface area and pore volume, the HPSCHM material could be a promising adsorbent for removal of pollutants, and it could also be used as a catalyst support.

Hierarchically porous SiO₂/C hollow microspheres (HPSCHMs) were synthesized. Its surface area is up to 1154 m² g^–1. Hierarchically porous structure facilitates diffusion of adsorbate. Its maximum adsorption amount for Congo Red is up to 2512 mg g^–1.     

Facile and green preparation of solid carbon nanoonions via catalytic co-pyrolysis of lignin and polyethylene and their adsorption capability towards Cu(ii)

Carbon nanomaterials, such as carbon nanoonions (CNOs), possess promising applications in various fields. There are urgent demands to synthesize carbon nanomaterials from a green and renewable carbon source. In this study, solid CNOs with relatively uniform size distribution (with diameters of about 30–50 nm), abundant structure defects and oxygen-containing surface functional groups (such as –OH and –COOH) are developed from co-pyrolysis of lignin (LG) and polyethylene (PE) in the presence of Ni-based catalysts. The type of catalyst, the concentration of catalyst and catalytic co-pyrolysis temperature play important roles in the morphologies and properties of CNOs as confirmed by TEM and SEM. Furthermore, the produced CNOs can act as a low-cost and highly-efficient adsorbent to remove Cu(ii) from aqueous solution according to a homogeneous monolayer, chemical action-dominated, endothermic and spontaneous process. The theoretical maximum adsorption capacity of CNOs calculated from the Langmuir model is 100.00 mg g⁻¹. Surface deposition, complexation, π electron–cation interaction and electrostatic interaction are responsible for the adsorption of Cu(ii) using the prepared CNOs.

Solid carbon nanoonions with relatively uniform size distribution, abundant structure defects and oxygen-containing surface functional groups can be prepared from lignin with the introduction of polyethylene and Ni-based catalysts.     

Efficient recovery of Cr(vi) from electroplating wastewater by iron-modified sludge-based hollow-structured porous carbon: coexistence effects and competition for adsorption

In the present work, porous carbon was made from sewage sludge and hybrid liriodendron leaves, and modified with iron ions (Fe@LS-BC) carried out on Cr(vi) in aqueous solution from a single-component system and in competitive biosorption with methyl orange (MO) from a binary-component system. The iron ion-modified porous carbon (Fe@LS-BC) showed higher efficiency in the removal of Cr(vi) compared to porous carbon prepared by the co-pyrolysis of sludge and hybrid liriodendron leaves. The incorporation of the Fe element improved the ability of the material to redox Cr(vi), while imparting magnetic characteristics to the porous carbon and improving the reusability of the porous carbon. On the other hand, Fe@LS-BC exhibited a better pore volume, facilitating the contact of the material with Cr(vi) ions. The highest adsorption capacity was 0.33 mmol g⁻¹, and the adsorption experimental results for the single-component and binary-component systems of Cr(vi) matched well with the Langmuir–Freundlich models. When the concentration of MO was 0.2 and 0.8 mmol L⁻¹, respectively, the highest adsorption capacity of Cr(vi) was 0.35 and 0.46 mmol g⁻¹ in the binary system. The positively charged N–CH₃⁺ on the MO molecule promoted the electrostatic adsorption between HCrO₄⁻, CrO₄²⁻, and Fe@LS-BC, and increased the adsorption potential of Cr(vi).

Mechanism for the adsorption of hexavalent chromium and methyl orange in a binary system.     

Fast removal of methylene blue from aqueous solution using coal-based activated carbon

Coal-based activated carbons (CACs) were prepared from three long flame coals with different ash and volatile matter content. CACs prepared by coal with high ash (6.74%) and volatile matter content (34.31%) showed better adsorption efficiency towards MB (547.35 mg g⁻¹) due to higher surface area and pore volume. The effect of coal to activating agent ratio (CAR) was also investigated in a batch reactor. The porosity development is closely related to the CAR. The calculated monolayer adsorption amount (714.29 mg g⁻¹) was found on YLC-AC-3 with a surface area of 1212.50 m² g⁻¹. The equilibrium data were favorably described by the Langmuir and Freundlich isotherm models, and adsorption kinetics fitted well to the pseudo-second order model. The removal efficiency remains at 98.21% after five runs. The results of the present study suggest that CACs are potential and effective adsorbents in fast removal of dyes from aqueous solution.

A monolayer adsorption amount of MB (714.29 mg g⁻¹) was found on a coal-based activated carbon prepared by a simple method.     

Rapid microwave activation of waste palm into hierarchical porous carbons for supercapacitors using biochars from different carbonization temperatures as catalysts

A rapid, simple and cost-effective approach to prepare hierarchical porous carbons (PCs) for supercapacitors is reported by microwave activation of abundant and low-cost waste palm, biochar (BC) and KOH. BCs from waste palm at different carbonization temperatures (300–700 °C), as catalysts and microwave receptors, were used here for the first time to facilitate the conversion of waste palm into hierarchical PCs. As a result, the high-graphitization PC obtained at a BC carbonization temperature of 300 °C (PC-300) possessed a high surface area (1755 m² g⁻¹), a high pore volume (0.942 cm³ g⁻¹) and a moderate mesoporosity (37.79%). Besides their high-graphitization and hierarchical porous structure, the oxygen doping in PC-300 can also promote the rapid transport of electrolyte ions. The symmetric supercapacitor based on the PC-300 even in PVA/LiCl gel electrolyte exhibited a high specific capacitance of 164.8 F g⁻¹ at a current density of 0.5 A g⁻¹ and retained a specific capacitance of 121.3 F g⁻¹ at 10 A g⁻¹, demonstrating a superior rate capacity of 73.6%. Additionally, the PC-300 supercapacitor delivered a high energy density of 14.6 W h kg⁻¹ at a power density of 398.9 W kg⁻¹ and maintained an energy density of 10.8 W h kg⁻¹ at a high power density of 8016.5 W kg⁻¹, as well as an excellent cycling stability after 2000 cycles with a capacitance retention of 92.06%.

A rapid, simple and cost-effective approach to prepare hierarchical porous carbons (PCs) for supercapacitors is reported by microwave activation of abundant and low-cost waste palm, biochar (BC) and KOH.     

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.     

Porous carbon from tobacco stalk for removal of organic dyes from water

Tobacco stalk, a kind of agricultural residue, will cause environmental pollution because it contains some harmful substances such as nicotine. To realize the high-value utilization of this agricultural residue, we prepared porous carbon (TS-C) by high temperature carbonization using tobacco stalk as a precursor. It was found that TS-C displays a hierarchical pore structure and high Brunauer–Emmett–Teller (BET) surface area of 1416 m² g⁻¹. Moreover, TS-C has excellent performance in organic dye adsorption at room temperature, especially for Gentian violet (GV), with the maximum adsorption capacity of 926 mg g⁻¹.

Harmful organic dyes in water can be removed by porous carbon from hazardous tobacco stalk.