Efficient removal of formaldehyde using metal-biochar derived from acid mine drainage sludge and spent coffee waste.

A novel metal-biochar (Biochar/AMDS) composite were fabricated by co-pyrolysis of spent coffee waste (SCW)/acid mine drainage sludge (AMDS), and their effective application in adsorptive removal of air pollutants such as formaldehyde in indoor environments was evaluated. The physicochemical characteristics of Biochar/AMDS were analyzed using SEM/EDS, XRF, XRD, BET, and FTIR. The characterization results illustrated that Biochar/AMDS had the highly porous structure, carbonaceous layers, and heterogeneous Fe phases (hematite, metallic Fe, and magnetite). The fixed-bed column test showed that the removal of formaldehyde by Biochar/AMDS was 18.4-fold higher than that by metal-free biochar (i.e., SCW-derived biochar). Changing the ratio of AMDS from 1:6 to 1:1 significantly increased the adsorption capacity for formaldehyde from 1008 to 1811 mg/g. In addition, thermal treatment of used adsorbent at 100 °C effectively restored the adsorptive function exhausted during the column test. These results provide new insights into the fabrication of practical, low-cost and ecofriendly sorbent for formaldehyde.

Adsorption of As(V) and Ni(II) by Fe-Biochar composite fabricated by co-pyrolysis of orange peel and red mud.

This study aimed to compare the adsorption performance of Fe-biochar composites (Fe-C-N2 and Fe-C-CO2), fabricated by co-pyrolysis of red mud and orange peel in N2 and CO2, for As(V) and Ni(II). By the syngas production comparison test, it was confirmed that CO2 was more advantageous than N2 as a pyrolytic medium gas to produce more CO. The resulting Fe-biochar composite showed the aggregate morphology consisting of different Fe phases (magnetite or metal Fe) from the inherent hematite phase in red mud and carbonized carbon matrix, and there was no distinct difference between the structural shapes of two Fe-biochar composites. Adsorption experiments showed that the adsorption capacities for As(V) and Ni(II) in single mode were almost similar with 7.5 and 16.2 mg g-1 for Fe-C-N2 and 5.6 and 15.1 mg g-1 for Fe-C-CO2, respectively. The adsorption ability of Fe-C-CO2 for both As(V) and Ni(II) was further enhanced in binary adsorption mode (As(V): 13.4 mg g-1, Ni(II):17.6 mg g-1) through additional removal of those ions by Ni(II)-As(V) complexation. The overall results demonstrated CO2-assisted pyrolysis can provide a viable platform to convert waste materials into fuel gases and environmental media for co-adsorption of cationic and anionic heavy metals.

Preparation of nitrogen-doped Cu-biochar and its application into catalytic reduction of p-nitrophenol.

Nitrogen-doped copper-biochar (N-Cu-biochar) was synthesized via pyrolysis of glucose in the presence of copper and melamine and used as a catalyst in the reduction of p-nitrophenol by NaBH4. N-Cu-biochar was characterized by field emission scanning electron microscopy/energy-dispersive spectroscopy, Raman spectroscopy, X-ray Diffraction, and Brunauer-Emmett-Teller surface analyzer. The catalytic performance of N-Cu-biochar was evaluated under varying conditions of NaBH4 concentration, biochar dosage, and initial p-nitrophenol concentration. N-Cu-biochar was composed of ~83% C, ~9% O, and ~8% Cu, with Cu/Cu2O phases evenly dispersed on graphitic carbon aggregates possessing both macro- and meso-pores. N-Cu-biochar showed superior catalytic ability in mediating p-nitrophenol reduction as compared to Cu-biochar and N-doped biochar, achieving complete reduction of 0.35 mM p-nitrophenol within 30 min at a dose of 0.25 g L-1. Reduction of p-nitrophenol catalyzed by N-Cu-biochar followed pseudo-first-order kinetics, and the reaction rate was dependent upon NaBH4 concentration. The overall results indicate that biochar can be a suitable candidate as a support for catalyst synthesis, and N-doped Cu-biochar can be a promising catalyst for the reduction of p-nitrophenol.

Evaluation of pyrite/sodium hypochlorite for activating purification of arsenic from fractured-bedrock groundwater.

In this work, the effectiveness of pyrite/sodium hypochlorite (FeS2/NaClO) treatment to eliminate arsenic (As) from fractured-bedrock groundwater via oxidative adsorption was evaluated. The As concentration in the tested reactors decreased sharply during the initial 5 min, as the addition of NaClO effectively increased the As removal efficiency, attaining 98.6% removal within 60 min in the presence of 0.05 M NaClO. There was no coexisting anion effect (Cl-, CO3-, HCO3-, NO3-, and F-) on the As removal capacity of FeS2/NaClO, except for the PO43- which resulted in less removal of As. X-ray spectroscopy analysis of As(III)-sorbed FeS2 surfaces revealed that a portion of As(III) was oxidized into As(V) during the adsorption process. Scanning electron microscopy-energy-dispersive spectrometer results of FeS2 exhibited the distribution of adsorbed As on the newly formed iron (oxy) hydroxide surfaces, with an As element ratio of 1.27%. A continuous flow-bed column study further demonstrated the efficiency of FeS2/NaClO treatment to lower the contamination level of As at the removal rates of 0.66-3.02 mg/L·day for 160 h. These results suggest that FeS2/NaClO treatment can be considered an effective strategy for removing As in groundwater of bedrock aquifers.

Practical approach of As(V) adsorption by fabricating biochar with low basicity from FeCl3 and lignin.

One of the main challenges of biochar application for environmental cleanup is rise of pH in water or soil due to high ash and alkali metal contents in the biochar. While this intrinsic property of biochar is advantageous in alleviating soil and water acidity, it severely impairs the affinity of biochar toward anionic contaminants such as arsenic. This study explored a technical approach that can reduce the basicity of lignin-based biochar by utilizing FeCl3 during production of biochar. Three types of biochar were produced by co-pyrolyzing feedstock composed of different combinations of lignin, red mud (RM), and FeCl3, and the produced biochar samples were applied to adsorption of As(V). The biochar samples commonly possessed porous carbon structure embedded with magnetite (Fe3O4) particles. The addition of FeCl3 in the pyrolysis feedstock had a notable effect on reducing basicity of the biochar to yield significantly lower solution pH values than the biochar produced without FeCl3 addition. The extent of As(V) removal was also closely related to the final solution pH and the greatest As(V) removal (>77.6%) was observed for the biochar produced from co-pyrolysis of lignin, RM, and FeCl3. The results of adsorption kinetics and isotherm experiments, along with x-ray spectroscopy (XPS), strongly suggested adsorption of As(V) occurred via specific chemical reaction (chemisorption) between As(V) and Fe-O functional groups on magnetite. Thus, the overall results suggest the use of FeCl3 is a feasible practical approach to control the intrinsic pH of biochar and impart additional functionality that enables effective treatment of As(V).

Carbon dioxide-assisted thermochemical conversion of magnetically harvested harmful algae into syngas and metal biochar.

With rising of harmful algae blooming and toxin exposure, practical utilization of harmful algae has been developed. This work aimed to magnetically harvest Microcystis aeruginosa (MA) using iron oxides and investigate the feasibility of algae/iron oxides mixture as feedstock in pyrolytic platform to produce syngas and metal biochar. Carbon dioxide (CO2) was used as a feeding gas to enhance the production efficiency of syngas and also functioned pH controller for better MA harvesting and toxin removal. CO2 support brought multiple benefits: magnetite (Fe3O4) and maghemite (γ-Fe2O3) recovered MA in a relatively short period of time (∼1 min), the recovered biomass generated 34-fold increased carbon monoxide, and metal biochar adsorbed higher amount of toxin from MA (2.8-fold). Pyrolytic utilization of harmful algae supported by CO2 and iron oxides could be one of promising techniques for evolution of metal biochar to remove toxin, while efficiently recover biomass and enhance syngas production.

Adsorption of potentially harmful elements by metal-biochar prepared via Co-pyrolysis of coffee grounds and Nano Fe(III) oxides.

Nano Fe(III) oxide (FO) was used as an amendment material in CO2-assisted pyrolysis of spent coffee grounds (SCG) and its impacts on the syngas (H2 & CO) generation and biochar adsorptive properties were investigated. Amendment of FO led to 153 and 682% increase of H2 and CO in pyrolytic process of SCG, respectively, which is deemed to arise from enhanced thermal cracking of hydrocarbons and oxygen transfer reaction mediated by FO. Incorporation of FO successfully created porous structure in the produced biochar. The adsorption tests revealed that the biochar exhibited bi-functional capability to remove both positively charged Cd(II) and Ni(II), and negatively charged Sb(V). The adsorption of Cd(II) and Ni(II) was hardly deteriorated in the multiple adsorption cycles, and the adsorption of Sb(V) was further enhanced through formation of surface ternary complexes. The overall results demonstrated nano Fe(III) oxide is a promising amendment material in CO2-assisted pyrolysis of lignocellulosic biomass for enhancing syngas generation and producing functional biochar.

Fabrication of aluminum beads derived from selectively recovered Al-rich precipitates and their application into defluoridation.

This work introduced a new way of fabricating a granular material with the supply of Al-rich precipitates selectively obtained from acid mine drainage (AMD), and its potential as a promising adsorbent for fluoride (F) was evaluated. Through the selective sequential precipitation (SP) process in the field, Al-rich precipitates with high purity (>81%) were collected at the high recovery rate (>99.8%) as a raw material for adsorbent fabrication. The granular adsorbent (ALB) was synthesized through encapsulation of precipitate powders by chemically inducing polymeric bead formation. The characterization results revealed that ALB possessed a highly porous structure and embedded a large number of nanoparticles of amorphous Al hydroxides inside its framework. Less adsorption of F occurred at an alkaline pH condition due to the competitive effect of hydroxyl ions. The adsorption process can be divided into fast adsorption by the outer surface and slow diffusion in the inner phase. The maximum adsorption capacity of ALB for F was calculated to be 17.7 mg g-1 in the Langmuir isotherm model fitting results. By the repetitive adsorption/desorption and XPS results, it turned out that both chemisorption and physisorption gave a contribution in the removal of F, and the regeneration of adsorbent using NaOH was effective to restore the adsorption capability but accompanied the loss of adsorption sites. As a result, it can be concluded that a granule-type material fabricated using Al-rich precipitates selectively recovered from AMD neutralization can be considered as a promising adsorbent for F removal in aqueous solution.

Valorization of plastics and paper mill sludge into carbon composite and its catalytic performance for acarbon material consisted of the multi-layerzo dye oxidation.

In this work, polyvinyl chloride (PVC) and paper mill sludge (PMS) were co-pyrolyzed under two environments of N2 and CO2. The pyrolysis process was assessed by conducting thermogravimetric analysis (TGA) and monitoring the evolution of gaseous products. The resulting solid composites were characterized using XRD, XPS, BET, and Raman analyzers, and their ability to catalytically activate persulfate (S2O82-) was tested by conducting methyl orange (MO) degradation experiments. Co-pyrolysis of PVC and PMS at the same mass ratio (1:1) in CO2 resulted in the highest production of H2 and CO (0.36 mol % H2 at 480 °C & 1.53 mol % CO at 700 °C). The characterization results revealed that the composite consisted of Fe3O4, highly graphitic carbon, and mesoporous structure. In MO oxidation experiments, the co-pyrolyzed composite actively generated OH and SO4- by activating S2O82- to achieve complete removal of 5 mg L-1 of MO during 100 min at acidic-neutral pH condition. The composite was also able to complete 3 successive cycles of MO oxidation without deactivation. Consequently, the feasibility of achieving the simultaneous production of energy resources and catalyst via industrial wastes utilization in pyrolytic process was demonstrated.

Zirconia-Assisted Pyrolysis of Coffee Waste in CO2 Environment for the Simultaneous Production of Fuel Gas and Composite Adsorbent.

This work newly employed monoclinic zirconia (ZrO2) as a promoter to improve CO2 pyrolysis of coffee waste (CW). The CO2 pyrolysis of CW presented the high level of CO production (14.3 mol%) during two stages of non-isothermal (280 to 700 °C) and isothermal pyrolysis (kept at 700 °C). At the same condition, the incorporation of ZrO2 improved the CO generation up to about twice that of CW (29.5 mol%) by possibly inducing more conversion of pyrolytic oil into gas. The characterization results exhibited that ZrO2-impregnated biochar (ZrB) possessed the distinctive surface morphology that highly graphitic- and porous carbon layers were covered by ZrO2 nanoparticle clusters. In a series of adsorption experiments, ZrB composite showed pH-dependent As(V) adsorption and pH neutralization ability. The adsorption proceeded relatively rapid with 95% removal during 120 min in the early stage, followed by 5% removal in the remaining 240 min. The maximum adsorption capacity was found to be 25.2 mg g-1 at final pH 8. The reusability and stability of ZrB were demonstrated in the 6 consecutive cycles of adsorption/desorption. As a result, ZrO2-assisted CO2 pyrolysis can potentially produce fuel gas with high CO fraction and composite adsorbent suitable for As(V) removal in acidic wastewater.

Water defluorination using granular composite synthesized via hydrothermal treatment of polyaluminum chloride (PAC) sludge.

In this work, we newly synthesized granular composite (GASA) via hydrothermal treatment of polyaluminum chloride (PAC) and subsequently granulation pelleting with starch gel as an organic binder. The resulting composite was characterized with analytic instruments, and the feasibility of utilizing GASA as adsorbent for the removal of fluoride (F-) was tested in the batch and column experiments. The characterization results revealed that GASA possessed a spherical/porous framework consisting of aluminosilicate (i.e., ordered albite, NaAlSiO3O8). The results of final pH effect experiments and XRD/XPS analyses showed the dominant adsorption mechanisms of F- on GASA were electrostatic attraction by protonated surface Al-OH, ligand exchange between surface hydroxyl groups and F ions, and surface precipitation (i.e., cryolite formation). Based on the results of adsorption kinetics and adsorption isotherm, granulation resulted in the relatively slow kinetics of F adsorption compared to the powder type, but was preferred to retain good adsorption capacity. The regeneration possibility of GASA was also proven with the adsorption/desorption cyclic test. In the column study, 15-cm length of the GASA layer and the flow rate less than 0.85 mL min-1 were proposed to keep the satisfactory level of F in water. The experimental results offer a potential of PAC sludge-derived composite as adsorbent for the removal of F from water.

Fabrication and environmental applications of multifunctional mixed metal-biochar composites (MMBC) from red mud and lignin wastes.

This study fabricated a new and multifunctional mixed metal-biochar composites (MMBC) using the mixture of two abundant industrial wastes, red mud (RM) and lignin, via pyrolysis under N2 atmosphere, and its ability to treat wastewater containing various contaminants was comprehensively evaluated. A porous structure (BET surface area = 100.8 m2 g-1) was created and metallic Fe was formed in the MMBC owing to reduction of Fe oxides present in RM by lignin decomposition products during pyrolysis at 700 °C, which was closely associated with the transformation of liquid to gaseous pyrogenic products. The potential application of the MMBC was investigated for the removal of heavy metals (Pb(II) and Ni(II)), oxyanions (As(V) and Cr(VI)), dye (methylene blue), and pharmaceutical/personal care products (para-nitrophenol and pCBA). The aluminosilicate mineral, metallic Fe, and porous carbon matrix derived from the incorporation of RM and lignin contributed to the multifunctionality (i.e., adsorption, chemical reduction, and catalytic reaction) of the MMBC. Thus, engineered biochar composites synthesized from selected industrial wastes can be a potential candidate for environmental applications.

Concurrent adsorption and micro-electrolysis of Cr(VI) by nanoscale zerovalent iron/biochar/Ca-alginate composite.

This study introduced a new approach for simultaneously enhancing Cr(VI) removal performance and mitigating release of dissolved Fe during nanoscale zero-valent iron (nZVI)-mediated reactions. After entrapping nZVI-impregnated biochar (BC) in the matrix of calcium-alginate (CA) bead, the physicochemical characterization of nZVI/BC/CA composites revealed that nZVI/BC particles were embedded inside CA having a spherical shape and several cracks on its outer layer. The multi-functionality of nZVI/BC/CA composites consisting of reductant (nZVI), porous adsorbent (BC), and external screening layer (CA) enhanced the removal of Cr(VI) with the maximum adsorption capacity of 86.4 mg/g (based on the Langmuir isotherm) and little release of dissolved Fe. With the XPS analysis and fitting results of kinetics (pseudo second order) and isotherms (Redlich-Peterson model), plausible removal mechanisms of Cr(VI) were simultaneous adsorption and micro-electrolysis reactions by nZVI/BC/CA composites. The practical applicability of nZVI/BC/CA composites was further demonstrated through the fixed-bed column experiments. These results provide new insights into the design of high-performance engineered biochar for wastewater treatment.

Porous biochar composite assembled with ternary needle-like iron-manganese-sulphur hybrids for high-efficiency lead removal.

Hierarchical porous biochar derived from corn straw containing ternary needle-like iron-manganese-sulphur composites (Fe-Mn-S@HCS) are fabricated, and their physicochemical characteristics and performance for Pb removal were examined in detail. Introduction of Mn (transition metal) into Fe-biochar composites can effectively alter the chemical state of Fe; simultaneous doping with S can enhance cation exchange for Pb removal. High uptake of Pb by Fe-Mn-S@HCS in a short time period was observed with the adsorption capacity of 181.5 mg g-1 and the pseudo-second-order rate constant of 0.075 g mg-1 h-1. Complexation, reduction, and precipitation were found to be involved in the Pb removal by Fe-Mn-S@HCS based on the results of HRTEM, XPS, and XRD analyses. This study demonstrated the feasibility of Fe-Mn-S biochar composites for high-efficiency Pb removal from aqueous solution.

Engineered biochar composite fabricated from red mud and lipid waste and synthesis of biodiesel using the composite.

Co-pyrolysis of lipid waste and red mud was investigated to achieve valorization of red mud by fabricating biochar composite. For the further sustainable approach, this study intentionally employed carbon dioxide (CO2) as reaction medium in the co-pyrolysis process. The use of CO2 on co-pyrolysis of lipid waste and red mud enabled manipulation of the carbon distributions between pyrogenic products. CO2 expedited the thermal cracking of lipid waste and further reacted with lipid waste during the thermolysis. These mechanistic roles of CO2 were catalytically enhanced by the presence of mineral phases (Fe2O3) in red mud, thereby resulting in the enhanced formation of CO (40 times more at 550 °C). However, CO2 suppressed dehydrogenation of lipid waste (∼ 50%), which resulted in the different pathway for reducing iron oxide in red mud. Moreover, as an aspect of valorization of red mud, catalytic capability of biochar composite was evaluated. As a case study, biodiesel (FAMEs) were synthesized, and all experimental findings suggested that biochar composite could be an effective catalyst for biodiesel synthesis. As compare to biodiesel synthesis using silica (92% yield at 360 °C), the equivalent biodiesel yield was achieved with the biochar at much lower temperature (130 °C).

Green remediation of As and Pb contaminated soil using cement-free clay-based stabilization/solidification.

Stabilization/solidification (S/S) is a low-cost and high-efficiency remediation method for contaminated soils, however, conventional cement-based S/S method has environmental constraints and sustainability concerns. This study proposes a low-carbon, cement-free, clay-based approach for simultaneous S/S of As and Pb in the contaminated soil, and accordingly elucidates the chemical interactions between alkali-activated clay binders and potentially toxic elements. Quantitative X-ray diffraction and 27Al nuclear magnetic resonance analyses indicated that the addition of lime effectively activated the hydration of kaolinite clay, and the presence of limestone further enhanced the polymerization of hydrates. X-ray photoelectron spectroscopy showed that approximately 19% of As[III] was oxidized to As[V] in the alkali-activated clay system, which reduced toxicity and facilitated immobilization of As. During the cement-free S/S process, As and Pb consumed Ca(OH)2 and precipitated as Ca3(AsO4)2·4H2O and Pb3(NO3)(OH)5, respectively, accounting for the low leachability of As (7.0%) and Pb (5.4%). However, the reduced amount of Ca(OH)2 decreased the degree of hydration of clay minerals, and the pH buffering capacity of the contaminated soil hindered the pH increase. Sufficient dosage of lime was required for ensuring satisfactory solidification and contaminant immobilization of the clay-based S/S products. The leachability of As and Pb in high-Ca S/S treated soil samples was reduced by 96.2% and 98.8%, respectively. This is the first study developing a green and cement-free S/S of As- and Pb-contaminated soil using clay minerals as an environmentally compatible binding material.

Novel synergy of Si-rich minerals and reactive MgO for stabilisation/solidification of contaminated sediment.

Disposal of significant amounts of dredged contaminated sediment poses an economic and environmental problem worldwide. Transforming contaminated sediment into value-added construction materials using low-carbon MgO cement is a sustainable option; however, the weak mechanical strength and unreliable water-solubility of MgO cement restrict its practical engineering applications. This study elucidates the potential role of industrial Si-rich minerals in the performance enhancement of MgO-based products via the promotion of magnesium silicate hydrate (M-S-H) gel formation. Quantitative X-ray diffraction and 29Si nuclear magnetic resonance analyses indicated that compositions and crystallinities of the Si-rich minerals significantly influence the formation and polymerisation of the M-S-H gel. Pulverised fly ash was found to be a promising Si-rich mineral for generating polymeric M-S-H gel, whereas incinerated sewage sludge ash samples demonstrated a low degree of polymerisation, and the use of glass powder samples gave a low yield of M-S-H. The formation of M-S-H gel enhanced the compressive strength and water resistance (strength retention after water immersion). Further experiments demonstrated that Si-modified MgO cement can transform dredged sediment into fill materials with satisfactory mechanical properties and contaminant immobilisation. Therefore, the synergy between reactive MgO and Si-rich industrial waste is a novel option for sustainable remediation and environmental applications.

Degradation of antibiotics by modified vacuum-UV based processes: Mechanistic consequences of H2O2 and K2S2O8 in the presence of halide ions.

In this work, the degradation of cefalexin, norfloxacin, and ofloxacin was examined via various advanced oxidation processes (AOPs). Direct photolysis by ultraviolet (UV) and vacuum ultra violet (VUV) was less effective for the degradation of fluoroquinolone antibiotics such as norfloxacin and ofloxacin than that of cefalexin. Both hydrogen peroxide (H2O2) and potassium persulfate (K2S2O8) assisted UV/VUV process remarkably enhanced fluoroquinolone degradation. The addition of K2S2O8 was superior to H2O2 under VUV irradiation, with the best removal efficiency of norfloxacin and ofloxacin being almost 100% within 3 min in the presence of VUV/K2S2O8. The ofloxacin degradation rate was accelerated as concentrations of H2O2 and K2S2O8 was increased to 3 mM, but the degradation rate was slightly decreased with excess H2O2 (>3 mM). The performance of modified VUV processes (i.e., VUV/H2O2 and VUV/K2S2O8) was inhibited at highly alkaline condition (pH 11). The co-existence of halides (Cl- and Br-) enhanced antibiotics degradation via the modified VUV processes, but the reaction was almost unaffected in the presence of single halides. This study demonstrated that modified VUV processes (especially VUV/K2S2O8) are efficient for eliminating fluoroquinolone antibiotics from water, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.

Microwave-assisted low-temperature hydrothermal treatment of red seaweed (Gracilaria lemaneiformis) for production of levulinic acid and algae hydrochar.

In this study, red seaweed (Gracilaria lemaneiformis) food waste with high carbohydrate content was valorized into levulinic acid (LA) and algae hydrochar through microwave-assisted low-temperature hydrothermal treatment in dilute acid solution. Various parameters including treatment temperature (160-200 °C), reaction time (1-40 min), acid concentration (0-0.6 M), and biomass-to-liquid ratio (1%-10%, w/v) were examined. The energy efficiency and carbon recovery of the proposed process were investigated. Under the experimental conditions of 5% (w/v) biomass loading, 0.2 M H2SO4, 180 °C, and 20 min, the highest levulinic acid yield of 16.3 wt% was produced. The resulting hydrochar showed approximately 45-55% energy yield and higher heating values of 19-25 MJ kg-1. The energy efficiency of the present study (1.31 × 10-6 g LA/J) was comparable to those of the conventional hydrothermal treatment of lignocellulosic biomass, while the reaction time (20 min) was much shorter with a high carbon recovery (73.3%).

Synthesis of cobalt-impregnated carbon composite derived from a renewable resource: Characterization and catalytic performance evaluation.

A novel nitrogen-doped biochar embedded with cobalt (Co-NB) was fabricated via pyrolysis of glucose pretreated with melamine (N donor) and Co(II). The Co-NB showed high catalytic capability by converting p-nitrophenol (PNP) into p-aminophenol (PAP) by NaBH4. The analyses of FE-SEM, TEM, BET, XRD, Raman, and X-ray photoelectron spectroscopy XPS of the Co-NB showed hierarchical porous structure (BET 326.5m2g-1 and pore volume: 0.2403cm3g-1) with well-dispersed Co nanoparticles (20-60nm) on the N-doped graphitic biochar surface. The Co-NB showed higher PNP reduction capability compared to the Co-biochar without N-doping, achieving 94.3% removal within 4min at 0.24gL-1 catalyst dose and initial concentration of 0.35mM PNP. Further conversion experiments under varying environmental conditions (e.g., NaBH4 concentration (7.5-30mM), biochar dosage (0.12-1.0gL-1), initial PNP concentration (0.08-0.17mM)) were conducted in batch mode. The reusability of Co-NB was validated by the repetitive conversion experiments (5cycles). The overall results demonstrated biochar potential as catalysts for environmental applications if properly designed.