Lead (Pb) pollution in natural water bodies is an environmental concern due to toxic effects on aquatic ecosystems and human health, while adsorption is an effective approach to remove Pb from the water. Surface interactions between adsorbents and adsorbates play a dominant role in the adsorption process, and properly engineering a material’s surface property is critical to the improvement of adsorption performance. In this study, the magnesium oxide (MgO) nanoparticles stabilized on the N-doped biochar (MgO@N-biochar) were synthesized by one-pot fast pyrolysis of an MgCl2-loaded N-enriched hydrophyte biomass as a way to increase the exchangeable ions and N-containing functional groups and facilitate the adsorption of Pb2+. The as-synthesized MgO@N-biochar has a high performance with Pb in an aqueous solution with a large adsorption capacity (893 mg/g), a very short equilibrium time (<10 min), and a large throughput (∼4450 BV). Results show that this excellent adsorption performance can be maintained with various environmentally relevant interferences including pH, natural organic matter, and other metal ions, suggesting that the material may be suitable for the treatment of wastewater, natural bodies of water, and even drinking water. In addition, MgO@N-biochar quickly and efficiently removed Cd2+ and tetracycline. Multiple characterizations and comparative tests have been performed to demonstrate the surface adsorption and ion exchange contributed to partial Pb adsorption, and it can be inferred from these results that the high performance of MgO@N-biochar is mainly due to the surface coordination of Pb2+ and C═O or O═C–O, pyridinic, pyridonic, and pyrrolic N. This work suggests that engineering surface functional groups of biochar may be crucial for the development of high performance heavy metal adsorbents.

Biomass is increasingly perceived as a renewable resource rather than as an organic solid waste today, as it can be converted to various chemicals, biofuels, and solid biochar using modern processes. In the past few years, pyrolysis has attracted growing interest as a promising versatile platform to convert biomass into valuable resources. However, an efficient and selective conversion process is still difficult to be realized due to the complex nature of biomass, which usually makes the products complicated. Furthermore, various contaminants and inorganic elements (e.g., heavy metals, nitrogen, phosphorus, sulfur, and chlorine) embodied in biomass may be transferred into pyrolysis products or released into the environment, arousing environmental pollution concerns. Understanding their behaviors in biomass pyrolysis is essential to optimizing the pyrolysis process for efficient resource recovery and less environmental pollution. However, there is no comprehensive review so far about the fates of chemical elements in biomass during its pyrolysis. Here, we provide a critical review about the fates of main chemical elements (C, H, O, N, P, Cl, S, and metals) in biomass during its pyrolysis. We overview the research advances about the emission, transformation, and distribution of elements in biomass pyrolysis, discuss the present challenges for resource-oriented conversion and pollution abatement, highlight the importance and significance of understanding the fate of elements during pyrolysis, and outlook the future development directions for process control. The review provides useful information for developing sustainable biomass pyrolysis processes with an improved efficiency and selectivity as well as minimized environmental impacts, and encourages more research efforts from the scientific communities of chemistry, the environment, and energy.

Although biochar has been intensively studied as an inexpensive adsorbent for diverse organic pollutants in aqueous solution, synchronously achieving high adsorption capacity, separability, and stability is still a challenge. Herein, we partially addressed this issue via an integrated activation and pyrolytic magnetization of sawdust hydrochar, during which the surface area of magnetic activated sawdust hydrochar (M-SDHA) increases from 1.7 to 1710 m2 g–1, and the weight loss decreases from 70 to 5% at 700 °C. Correspondingly, the maxmium adsorption capacity of M-SDHA toward tetracycline (TC) reaches 423.7 mg g–1 and remains constant at pH 5–9. Multiple characterizations show that the fine pore structure and surface functional groups of M-SDHA were maintained during the pyrolysis magnetization process, which is responsible for the high adsorption capacity. In the pyrolysis magnetization process, the FeCl3 was reduced to Fe3O4 which endowed M-SDHA with magnetism and may simultaneously improve the thermostability of M-SDHA. In addition, acidic–basic stability of M-SDHA may be responsible for the stable adsorption toward TC at different pHs based on Fourier transform infrared spectroscopic results. These results along with the column adsorption experiment show that M-SDHA is an effective and practical adsorbent for TC removal.

For safe disposal and environmentally benign recycling, lignocellulosic biomass wastes are increasingly studied for use as precursors for the preparation of value-added porous carbon materials. However, conventional chemical vapor deposition is time consuming and difficult to perform on a large scale. Herein, we obtained nitrogen-doped porous carbon materials (NPCMs) with high supercapacitor performance by one-pot copyrolysis of a carbon precursor (wheat straw), nitrogen precursor (melamine), and salt templating (mixed salt of KCl/ZnCl2 at 51:49). The NPCM with 7.78% nitrogen content exhibited an excellent gravimetric capacitance of 223.9 F g–1, which is mainly attributed to the increase in surface area by the activation of salt templating and the decrease in ion-transport resistance by N doping of the NPCM. The removal of silicon in pyrolysis products efficiently enhanced the capacitance of materials, but there was a negative effect on capacitance if the silicon was removed from feedstocks before pyrolysis. The post-removal of the silicon greatly increased the cycle stability of NPCMs and maintained 91.4% of capacitance after 10,000 CV tests. BET and XPS analyses indicate that the silicon can improve the pore structure and facilitate the formation of reactive nitrogen species (N-5 and N-6) by hard template and catalysis functions during pyrolysis, which is mainly responsible for the high performance of as-prepared NPCM. This study provides a facile method for synthesizing biomass-based NPCMs, especially to utilize biomass waste that contains high silicon content.Keywords: Melamine; One-pot; Pyrolysis; Salt templating; Silicon; Supercapacitor material; Wheat straw;

CuO nanoparticles (NPs) have been widely used, and the inevitable release of Cu species into agricultural soil would bring potential toxicity to edible plants. Soil remediation may be the last barrier to block the entrance of Cu into the food chain of human beings. In this study, we experimentally demonstrated a new application of biochar which can significantly reduce the biotoxicity of CuO NPs on seed germination and growth of wheat (Triticum aestivum L.). The results showed that the 3% wt addition of biochar to a hydroponic culture system can completely eliminate the inhibition effect of CuO NPs on plant growth even with concentrations of CuO NPs up to 500 mg L−1, based on the comparison of germination rate, growth, and fresh and dry weight of wheat. The Cu content of shoots and roots decreased by 3.7–7.8 and 3.3–4.9 times in the presence of biochar, respectively. Further exploration indicated that both the adsorption of Cu2+ and space shield by biochar significantly suppress the entrance of Cu2+ and CuO NPs into plant cells and consequently reduce the biotoxicity of CuO NPs. These findings are of particular significance to increasing the production of crops while preventing the accumulation of metallic NPs in the food chain.

Fast pyrolysis of biomass wastes which is usually finished in a few seconds for the preparation of porous carbonaceous materials (PCMs) is much faster and more energy-efficient than the conventional hydrothermal carbonization (HTC) method and does not require the use of solvents. In this study, PCMs were prepared using corn gluten meal (CGM) waste by fast pyrolysis combined with chemical activation by KOH, and the capacitance performance of the resulting PCMs was investigated. The specific capacitance of PCMP500 (fast pyrolysis at 500 °C) was 488 F g−1 at a current density of 0.5 A g−1, which is better than those of PCMs obtained at other pyrolytic temperatures (PCMP300 and PCMP400). Under the same conditions, the PCMs prepared by the HTC process exhibited relatively lower supercapacitance performance, i.e., PCMH250 (HTC at 250 °C) is 433 F g−1. The high performance of PCMP500 was mainly attributed to the high specific surface area and pore structure, which depends on the thermal treatment methods. This work demonstrates that fast pyrolysis may be a promising technology for massive production of high performance PCMs from biomass wastes.

•A new antifouling application of biochar in MBR was proposed.•The modified biochars significantly decreased the trans-membrane pressure.•The hydrophilicity of the biochar improved the settling performance of the sludge.•The abundant functional groups of the biochar increased the adsorption of EPS.Biochar is a low-cost by-product of biomass pyrolysis to obtain renewable energy, and is composed of carbon skeleton, oxygen-containing functional groups, and minerals. Herein a new environmental application of biochar is detailed, namely, alleviating membrane fouling in a membrane bioreactor (MBR) process by dosing the bioreactor with quantities of various modified biochars (alkali washed (AW-BC), hydrophobic (HB-BC), hydrophilic (HL-BC), and activated biochars (AC-BC)). Results of trans-membrane pressure (TMP) tests showed that with the exception of HB-BC, all the other modified biochars exhibited robust antifouling capability and the TMP was decreased by as much as 36.8% and 31.4% at 24 h and 10 d respectively for AW-BC (most easily prepared) compared to a control. This was comparable to the results obtained in the use of expensive activated carbon (AC). Instead of dealing with the large surface area and scouring effects of AC, it was found that the indirect effects of biochar on sludge may be the basis for the antifouling mechanism, where the hydrophilicity of the biochar improved the settling of sludge. In addition, it was speculated that the abundant functional groups of the biochar increased the adsorption of Extracellular polymeric substance (EPS) based on the characterizations of N2-adsorption-desorption, fourier transform infrared spectroscopy (FTIR), X–ray photoelectron spectroscopy (XPS), Raman, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). Compared to traditional antifouling materials, the results of this study may offer a low-cost alternate for alleviating membrane fouling in MBRs.

•Summarized the post-modification methods of biochar.•Reviewed the applications of biochar as electrode and supercapacitor materials.•Provided some guidance for future study on post-modification of biochar.•Envisaged some potential usages of modified biochar.Biochar is a common byproduct from thermochemical conversion of biomass to produce bioenergy. However, the biochar features, such as morphology, porosity and surface chemistry, cannot be well controlled in conventional conversion approaches, limiting the wide application of raw biochar. Aiming to meet the specific requirements, post-modification of raw biochar was frequently conducted to improve the quality. In this review, recent developments regarding post-modification methods of biochar are presented and discussed. Progresses on the applications of post modified biochar as electrode materials for supercapacitors are intensively summarized. This review aims to reveal the key factors that affecting the performance of biochar-based supercapacitors, and provide guidance for rationalizing the modification methods to expand the applications of biochar-based functional materials in supercapacitors.Download high-res image (187KB)Download full-size image

•Summarized the characteristics of non-lignocellulosic biomass and biochar.•Reviewed the thermochemical behaviors of main components in NLBC.•Summarized the updated characterization methods for NLBC and conversion process.•Provided some guidance for future study on NLBC.Biochar obtained from non-lignocellulosic biomass (NLBM) has attracted wide interests in various fields like pollutants removal, catalysis, and energy storage. However, the thermochemical conversion processes from NLBM to non-lignocellulosic biochar (NLBC) have not been well summarized until now. To fill the knowledge gap, this review presents a systematical summary of NLBM characteristics, thermochemical behaviors of main components (e.g., C, O, N, P and metals), characterization methods for NLBC and conversion process, and the main applications of NLBC. Moreover, the vacancy and limitations of the current researches are pointed out to provide some guidance for future study. This review would contribute to deepen the understanding of NLBC, meanwhile optimize the efficient disposal and value-added utilization of NLBM wastes via thermochemical conversion.Download high-res image (85KB)Download full-size image

Biochar is a solid material obtained from thermochemical conversion of biomass in an oxygen-limited environment. It is widely used as a soil remediator and carbon sequestrator. However, its biotoxicity to the ecosystem remains unclear. In this study, we assess the toxic effects of three fast pyrolytic biochar extract solutions (rice husk, saw dust, Acorus calamus) on a miocroorganism (Pseudomonas aeruginosa), a plant (Triticum spp.), and an animal (Caenorhabditis elegans). Systematic toxicity tests indicate that the biotoxicity of biochars varies with their biomass sources. Biochars derived from rice husk and sawdust have negligible toxic effects on all the tested organisms, suggesting that biochars obtained from agricultural waste are safe for soil application. By contrast, biochar derived from Acorus calamus shows significant toxicity on all tested organisms at relative high dosage, indicating that risk assessment is necessary before its environmental use. Furthermore, this study found that use of the UV254 value is more practical than the SUV254 value for evaluation of biochar biotoxicity. Finally, gel permeation chromatography (GPC) suggests that certain small aromatic molecules may be responsible for the toxicity of biochar derived from Acorus calamus.Keywords: Biotoxicity; Caenorhabditis elegans; Gel permeation chromatography; Pseudomonas aeruginosa; Pyrolytic biochar; Triticum spp.; UV254 value;

Catalytic hydrogenation of lignin to produce chemical commodities can significantly decrease the consumption of fossil fuels. However, the conversion efficiency, cost, and product selectivity using conventional catalysts are still unsatisfactory. In this study, we expediently prepared a mesoporous carbon supported Ni–Mo2C catalyst by one-pot fast pyrolysis of Ni–Mo preloaded sawdust and demonstrated its catalytic performance for hydrogenation of lignin. The as-prepared catalyst exhibited excellent catalytic performance in highly efficient and selective hydrogenation of lignin in the presence of H2 and isopropanol. Under mild reaction conditions (temperature of 250 °C, 2 h and 2.0 MPa initial H2 pressure), 61.3 wt% of lignin can be catalytically converted to liquid products, 80 wt% of which are phenols, guaiacols, and trimethoxybenzenes. The conversion rate of lignin remained at around 60% after recycling five times, indicating the good stability and reusability of the Ni–Mo2C/C catalyst. The high catalytic performance of Ni–Mo2C/C toward lignin hydrogenation may be attributed to the synergistic effect of the graphitized biochar matrix and the Ni–Mo2C nanoparticles which facilitates electron transfer.

Lead (Pb) is one of the most widespread toxic heavy metals in water distribution systems and surface water, and how to quickly and completely remove Pb from the water has received global concern. Here we designed and synthesized a 3D nitrogen doped carbon hydrogel/FeMg layered double hydroxide (NC–FeMg LDH) nanocomposite through a one-pot solvothermal process and investigated the Pb removal efficiency and underlying mechanism. Multiple characterization methods including XRD, FTIR, and TEM confirmed that the 3D NC–FeMg LDH is formed by incorporating 2D FeMg-LDH nanosheets with the nitrogen doped carbon hydrogel which is in situ formed in the solvothermal carbonization of glucosamine. The as-synthesized 3D NC–FeMg LDH shows favorable performance in the removal of Pb from aqueous solution with very short equilibrium time (2 min) and large adsorption capacity (344.8 mg g−1). The excellent removal performance toward Pb is demonstrated to be a structure-dependent multiplex surface chemical process between Pb and LDH involving Mg2+/Pb2+ ion exchange, Pb/CO or OC–O, and Pb/pyrrolic N surface complexation. This work may provide an idea for designing hybrid functional materials for selective and high-efficiency removal of other heavy metals from polluted water.

Massively produced sewage sludge brings a serious problem to environment. Pyrolysis is a promising and bifunctional technology to dispose the sewage sludge and recover energy, in which a large amount of pyrolytic sludge char is also produced. In this study, we proposed a value-added utilization of sludge char. We prepared an adsorbent with ultrahigh capacity for hydrophobic organic pollutant (1-naphthol) by pyrolysis of sludge and removal of the ash moiety from the sludge char. The adsorptive behavior of the adsorbent is strongly dependent on the pyrolytic temperature of sludge, and the maximum adsorption capacity of 666 mg g–1 was achieved at 800 °C, which is comparable to deliberately modified graphene. Further exploration indicated that the robust adsorption to 1-naphthol is attributed to the catalytic effect of ash in sludge which facilitated the formation of more orderly graphitic structures and aromaticity at high pyrolytic temperatures.

The optimal strategy for the safe disposal of large amounts of hydrophyte biomass with enriched levels of N and P is challenging. In this study, we proposed and illustrated a facile pyrolysis approach to prepare an N, P-dually doped porous carbon (NPC) material with robust energy storage performance using a thermochemical self-doping process and a widely distributed hydrophyte biomass (Typha angustifolia). As a supercapacitor electrode material for electrochemical energy storage, the NPC shows a maximum capacitance of 257 F g–1 and energy density of 19.0 Wh kg–1 and only 3% capacitance loss after 6000 times of cyclic use, which places the NPC among the best porous carbon supercapacitors known previously. Multiple characterizations (BET, SEM, XPS, and Raman) provide evidence that NPC’s excellent energy storage performance involves a pseudocapacitive contribution due to the Faradaic redox reactions of the N and P functional groupsand a capacitive contribution from the formation of the electrical double layer. The external nitrogen resource cannot improve the supercapacitor performance of NPC, suggesting a role for the assimilated nitrogenof plants. In contrast, an external phosphorus resource can significantly increase the specific capacitance from 257 to 375 F g–1 of NPC. These findings provide useful information for effective energy storage utilization of biomass wastes with differentconcentrations of N and P by fast pyrolysis and activation processes.

As a low-cost and readily available adsorbent for removal of pollutants, biochar has been intensively studied for adsorption performance and its mechanism. However, it is still far from its practical applications due to difficulties of separation after adsorbing pollutants. In this study, we significantly improved mechanical stability and adsorption performance of biochar by fast co-pyrolysis of a mixture of sawdust, FeCl3, and kaolin. Results indicated that dosing FeCl3 during biomass pyrolysis can drastically increase the yield of biochar, and also increase the strength of granular biochar (GBC). The GBC prepared at 650 °C with 5 mmol g−1 of FeCl3 dosage (Fe5-GBC650) exhibited a 4-chlorophenol adsorption capacity of 35.71 mg g−1, which was twice the adsorption capacity without FeCl3 (Fe0-GBC650), although pure biochars in both Fe0-GBC650 and Fe5-GBC650 have a maximum 4-CP adsorption capacity of 250 mg g−1. The compressive strength of Fe5-GBC650 was 4.86 MPa, which was four times higher than that of Fe0-GBC650 (1.12 MPa). Moreover, the scatter ratio of Fe5-GBC650 was only 2.58%, which was significantly lower than that of Fe0-GBC650 (45.61%). Multiple characterization techniques including SEM, FTIR, XPS, and scanning acoustic microscope imaging were conducted to explain the underlying mechanism. The preferable adsorption capacity of Fe5-GBC650 may be attributed to catalytic decomposition of the biomass and the reductive deposition of carbon (e.g., CH4, C2H4, and C2H2) by FeCl3 that increases the yield of biochar and the specific surface area of GBC. The high stability may have resulted from the binding interaction of FeCl3 products. This work may facilitate the replacement of granular activated carbon by low cost biochar.

Disposal of heavy metal-contaminated biomass obtained from phytoremediation or biosorption by using environmentally benign methods is a big challenge. In this study, we proposed a win–win strategy to recycle Ag-contaminated biomass by fast pyrolysis to obtain renewable bio-oil and achieve the catalytic reduction of Cr(VI) with the Ag-embedded biochar. We herein focused on the one-pot synthesis of a Ag nanoparticle-embedded biochar hybrid material (Ag@biochar) by fast pyrolysis of the Ag preloaded biomass and its catalytic effect on Cr(VI) reduction. The results show that Ag@biochar can completely catalytically reduce Cr(VI) in aqueous solution within 20 min using formic acid as a reducing agent at 323 K. The particle size of Ag NPs on the biochar was found to be pyrolysis temperature dependent and played an important role in the reduction of Cr(VI). We found that the reduction of Cr(VI) catalyzed by Ag@biochar follows a CO (produced from HCOOH decomposition) reduction mechanism which is quite different from the H2 reduction mechanism with catalysis of some noble metal based catalysts (e.g. Pd and Pt). This study offers a sustainable approach for simultaneous disposal of the biomass waste and synthesis of functional materials and might be expanded in the recycling of other metal-contaminated biomass (e.g. Cu, Ni, Co, Zn, and Fe).

Ni–NiFe2O4/carbon nanofiber (Ni–NiFe2O4/CNF) composite materials were synthesized by fast pyrolysis of the FeCl3 and NiCl2 preloaded biomass. The as-synthesized materials showed a favourable catalytic performance in the hydrogenation of aromatic nitro compounds with high yield and selectivity. The catalyst can be easily separated using a magnet and its catalytic activity remains almost unchanged after 7-time reuse.

Lignin valorization is considered an important part of the modern biorefinery scheme. The unique structure and composition of lignin may offer many effective routes to produce several bulk chemicals and functional materials. Thermochemical conversion of lignin to synthesize value-added functional materials has recently attracted a lot of attention. In this review, we have presented currently available approaches and strategies for the thermochemical conversion of lignin to functional carbon materials. The transformation behavior and mechanism of lignin during the thermochemical process (e.g., pyrolysis and hydrothermal carbonization) are illuminated. The characteristics (structure and surface chemistry) of lignin-based functional carbon materials are summarized systematically. The advances in the functionalization of lignin-based carbon materials (surface functionality tuning and porosity tailoring) and the applications of lignin-based functional carbon materials in the fields of catalysis, energy storage, and pollutant removal are reviewed. Perspectives on how lignin-based functional materials would develop and, especially, in which fields the use of these functionalized materials could be expanded are discussed. This review clearly shows that a rational design of the functionalized lignin-based materials will lead to a rich family of hybrid functional carbon materials with various applications toward a green and sustainable future.

Lead (Pb) is a ubiquitous heavy metal pollutant, and its removal and immobilization from the environment have attracted considerable attention. In this study, we prepared amino-functionalized hydrochar (AFHC) from waste biomass and investigated its adsorption and immobilization activity toward Pb(II). The results showed that AFHC exhibits high performance in Pb removal, achieving over 1000 mg g−1 removal capacity within the first 5 min of reaction, and high selectivity toward this metal ion. Notably, AFHC can efficiently remove low concentrations of Pb from aqueous solution, suggesting that it has potential utility in treatment of drinking water, especially in point-of-use water treatment in underdeveloped areas. Further investigations indicated that the robust performance of the hydrochar may be attributed to the formation of rod-like Pb5(PO4)3(OH) crystals on its surface, where amino groups function as bridges and hydrolyze to provide basic groups.

A Ag/C3N4 nanocomposite with optimum Ag content is an efficient and green photocatalyst for pollutant degradation under visible light irradiation. In this study, we synthesized Ag NPs using NaBH4 and the squeezed out liquid (SOL) of plant biomass. The Ag NPs thus obtained have been loaded to C3N4 to form Ag/C3N4 nanocomposites that show superior photocatalytic performance toward Rhodamine B (RhB) under visible light irradiation. The photocatalytic activity of both biogenic and chemogenic Ag/C3N4 nanocomposites with different Ag contents is compared. Results show that the biogenically synthesized Ag/C3N4 exhibits better photocatalytic performance than the chemosynthetic composite. Of all the different nanocomposites prepared in this study, Ag48/C3N4 (0.048% of Ag content) exhibits excellent photoreactivity, with a reaction rate constant (k) 7-fold higher that the chemosynthetic Ag/C3N4. The observed improvement in the photoreactivity is mainly attributed to the high dispersion of Ag NPs on C3N4, facilitated by the organic compounds in SOLs. Besides, these organic compounds also enhance the photoreactivity of the catalyst by providing adsorption sited for RhB molecules and by shifting the Fermi level to more negative potential.Keywords: Ag NPs; Graphitic carbon nitride; Nanocomposite; Photoreactivity; Pollutants

In the present study, a value-added Cu NP anchored magnetic carbon (Cu&Fe3O4-mC) material was obtained directly by fast pyrolysis of heavy metal polluted biomass (derived from a biosorption process using fir sawdust to remove Cu(II) from synthetic wastewater). The composition and structure of the Cu&Fe3O4-mC were characterized by various physicochemical techniques, which indicated that the Cu NPs were monodispersed on the mesoporous carbon support with an average particle size of 21.2 nm. The material shows favorable activity and separability on the catalytic reduction of 4-nitrophenol, and can be reused several times without a decrease in the catalytic activity. The maximum release concentration of Cu during the recycling process is 0.7 mg L−1, which is below the limit of the Cu concentration in the surface water. This study would provide a green and sustainable pathway for simultaneous disposal of the biomass waste, removal of the heavy metal pollution, and pretreatment of 4-nitrophenol.

The utilization of phosphorus (P) in activated sludge discharged from wastewater treatment plants is an important part of the global phosphorus circulation. Thermal treatment of excess sludge would become a promising method for their disposal throughout the world. Herein, we investigated the transformation and migration of P in sewage sludge during different thermal treatment conditions. The results indicate that the temperature can significantly influence the species and content of P in the sewage sludge char or ash (SSC/A), while the atmosphere of thermal treatment has a slight effect on the fate of P. 31P NMR and XRD analysis indicated that P migrated mainly to the medium-term plant available P pool (poolNaOH) on treating the sewage sludge at a low temperature (673–873 K), while it was prone to migration to the long-term plant available P pool (poolHCl) when treated at a high temperature (873–1073 K).Keywords: Char; Phosphorus; Sewage sludge; Temperature and atmosphere; Thermal treatment

Disposal and recycling of the large scale biomass waste is of great concern. Themochemically converting the waste biomass to functional carbon nanomaterials and bio-oil is an environmentally friendly apporach by reducing greenhouse gas emissions and air pollution caused by open burning. In this work, we reported a scalable, “green” method for the synthesis of the nanofibers/mesoporous carbon composites through pyrolysis of the Fe(III)-preloaded biomass, which is controllable by adjustment of temperature and additive of catalyst. It is found that the coupled catalytic action of both Fe and Cl species is able to effectively catalyze the growth of the carbon nanofibers on the mesoporous carbon and form magnetic nanofibers/mesoporous carbon composites (M-NMCCs). The mechanism for the growth of the nanofibers is proposed as an in situ vapor deposition process, and confirmed by the XRD and SEM results. M-NMCCs can be directly used as electrode materials for electrochemical energy storage without further separation, and exhibit favorable energy storage performance with high EDLC capacitance, good retention capability, and excellent stability and durability (more than 98% capacitance retention after 10 000 cycles). Considering that biomass is a naturally abundant and renewable resource (over billions tons biomass produced every year globally) and pyrolysis is a proven technique, M-NMCCs can be easily produced at large scale and become a sustainable and reliable resource for clean energy storage.

Co-pyrolysis of plastic waste and wood biomass to recover valuable chemicals is a cost-effective waste-recycling technology. However, widely used organophosphate ester additives in plastic, such as tris(2-butoxyethyl) phosphate (TBEP), can form diverse phosphorus (P)-containing species. These P-containing compounds can pose new environmental challenges when the biochar is reused. In this study, a mixture of TBEP and lignin was used to simulate the feedstock of plastic waste and wood biomass, and the thermochemical behavior of TBEP in slow pyrolysis (20 K min–1) and fast pyrolysis at 400–600 °C was investigated. The results show that low temperature in fast pyrolysis favors the enrichment of P in char. Up to 76.6% of initial P in the feedstock is retained in the char resulting from 400 °C, while only 51% is retained in the char from 600 °C. Slow pyrolysis favors the formation of stable P species regardless of the temperature; only 7% of the P retained in the char is extractable from char from slow pyrolysis, while 20–40% of P can be extracted from char resulting from fast pyrolysis. The addition of CaCl2 and MgCl2 can significantly increase the fraction of P retained in the char by the formation of Ca, Mg—P compounds. Online TG-FTIR-MS analysis suggests that TBEP undergoes decomposition through different temperature-dependent pathways. The P-containing radicals react with the aromatic rings produced by the pyrolysis of lignin to form Ar—P species, which is an important factor influencing the distribution and stabilization of P in char.

Pyrolysis is an emerging technology for the disposal of huge amounts of sewage sludge. However, the thermochemical decomposition mechanism of organic compounds in sludge is still unclear. We adopt a novel online TG-FTIR-MS technology to investigate the pyrolysis of sludge. The sludge samples were pyrolyzed from 150 to 800 °C with heating rates of 10, 50, and 200 K min–1. We found for the first time that the heating rate of pyrolysis can significantly change the species of liquid organic compounds produced, but cannot change the gaseous species produced under the same conditions. The contents of produced gas and liquid compounds, most of which were produced at 293–383 °C, are influenced by both the heating rate and temperature of pyrolysis. The results also showed that heterocyclic-N, amine-N, and nitrile-N compounds are obtained from the decomposition of N-compounds in sludge, such as pyrrolic-N, protein-N, amine-N, and pyridinic-N. Heterocyclic-N compounds are the dominant N-containing products, which can be due to the thermochemical decomposition of pyridine-N and pyrrole-N, whereas fewer amine-N compounds are produced during the pyrolysis. A mechanism for the decomposition of N-containing compounds in sludge is proposed based on the obtained data.

Environmental dredging is an efficient means to counteract the eutrophication of water bodies caused by endogenous release of nitrogen and/or phosphorus from polluted sediments. The huge operational cost and subsequent disposal cost of the dredged polluted sediments, as well as the adverse effect on the benthic environment caused by excessive dredging, make the currently adopted dredging methods unfavorable. Precise dredging, i.e., determining the dredging depth based on the pollution level, not only significantly decreases the costs but also leaves a uniform favorable environment for benthos. However, there is still no feasible process to make this promising method executable. Taking a river heavily polluted by organic compounds as an example, we proposed an executable precise dredging process, including sediment survey, model establishment, data interpolation, and calculation of dredging amount. Compared with the traditional dredging method, the precise one would save 16 to 45 % of cost according to different pollutant removal demands. This precise dredging method was adopted by the National Water Project of China to treat the endogenous pollution of Nanfei River in 2010. This research provides a universal scientific and engineering basis for sediment dredging projects.

Anthropogenic CO2 emission makes significant contribution to global climate change and CO2 capture and storage is a currently a preferred technology to change the trajectory toward irreversible global warming. In this work, we reported a new strategy that the inexhaustible MgCl2 in seawater and the abundantly available biomass waste can be utilized to prepare mesoporous carbon stabilized MgO nanoparticles (mPC-MgO) for CO2 capture. The mPC-MgO showed excellent performance in the CO2 capture process with the maximum capacity of 5.45 mol kg–1, much higher than many other MgO based CO2 trappers. The CO2 capture capacity of the mPC-MgO material kept almost unchanged in 19-run cyclic reuse, and can be regenerated at low temperature. The mechanism for the CO2 capture by the mPC-MgO was investigated by FTIR and XPS, and the results indicated that the high CO2 capture capacity and the favorable selectivity of the as-prepared materials were mainly attributed to their special structure (i.e., surface area, functional groups, and the MgO NPs). This work would open up a new pathway to slow down global warming as well as resolve the pollution of waste biomass.

As a liquid product from the fast pyrolysis of renewable biomass, bio-oil has a great potential use as a fuel or high-value chemicals resource, but it is accompanied by inherent drawbacks, such as strong corrosiveness and chemical instability. A facile method for bio-oil upgrading by zero valent metals (Al, Fe, Mg, and Zn) at ambient temperature and pressure was reported for the first time in this work. The chemical features of the raw and upgraded bio-oils were analyzed by Nuclear Magnetic Resonance (NMR) and GC-MS. The results show that the zero valent Zn favorably demonstrated improvement of the quality of bio-oil. In the upgraded bio-oil, the CO compounds are reduced from 9.8 to 3.1 mol%, and the pH value was elevated from 3.53 to 4.85, which significantly increased the chemical stability and decreased the corrosiveness of bio-oil. The possible formation mechanism of 13 newly formed compounds in the upgraded bio-oil was explored, and most of them were found to be derived from hydrogenation of CO compounds. This work provides an economical and environmentally friendly approach for bio-oil upgrading.

Heavy-metal-polluted biomass derived from phytoremediation or biosorption is widespread and difficult to be disposed of. In this work, simultaneous conversion of the waste woody biomass into bio-oil and recovery of Cu in a fast pyrolysis reactor were investigated. The results show that Cu can effectively catalyze the thermo-decomposition of biomass. Both the yield and high heating value (HHV) of the Cu-polluted fir sawdust biomass (Cu-FSD) derived bio-oil are significantly improved compared with those of the fir sawdust (FSD) derived bio-oil. The results of UV–vis and 1H NMR spectra of bio-oil indicate pyrolytic lignin is further decomposed into small-molecular aromatic compounds by the catalysis of Cu, which is in agreement with the GC-MS results that the fractions of C7–C10 compounds in the bio-oil significantly increase. Inductively coupled plasma-atomic emission spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy analyses of the migration and transformation of Cu in the fast pyrolysis process show that more than 91% of the total Cu in the Cu-FSD is enriched in the char in the form of zerovalent Cu with a face-centered cubic crystalline phase. This study gives insight into catalytic fast pyrolysis of heavy metals, and demonstrates the technical feasibility of an eco-friendly process for disposal of heavy-metal-polluted biomass.

Polar organic compounds (POCs) are one of the main categories of pollutants in wastewater, and their effective removal is highly desirable. In this work a novel hyper-cross-linked polyphosphamide resin (HPR) with flexible structure and functional groups for POCs adsorption was synthesized and characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Phenol, a typical POC, was used to test its adsorption amount. The experimental results showed that the polymer exhibited an excellent phenol adsorptive capacity of 516 mg g–1 in phenol aqueous solution, though its surface area was 14.5 m2 g–1 only. The influences of pH, contact time, and the zero point charges of adsorption were investigated. This research provides a new and effective approach to separate and recover phenols, especially at a high concentration, from wastewater.

Removal of heavy metals from wastewater by biosorption is an attractive approach. In this work, the interactions between lead and Typha angustifolia biomass, a cost-effective biosorbent, were investigated. It was found that the interactions between lead and T. angustifolia biomass were complex, and the solution pH was a key factor governing such interactions. The FTIR characterization and the results of blocking experiment indicate the amino, hydroxyl, and carboxyl are the main functional groups contributing to these interactions. A synergistic mechanism involving ion exchange, complexation, and hydrogen binding was elucidated. According to this mechanism, the dominant interactions between the biomass and lead altered with the variation of pH, which was consistent with the experimental results. Additionally, a simple method was explored to estimate the contributions of different interactions between the biomass and lead.

Disposal of heavy metal-contaminated biomass obtained from phytoremediation or biosorption by using environmentally benign methods is a big challenge. In this study, we proposed a win–win strategy to recycle Ag-contaminated biomass by fast pyrolysis to obtain renewable bio-oil and achieve the catalytic reduction of Cr(VI) with the Ag-embedded biochar. We herein focused on the one-pot synthesis of a Ag nanoparticle-embedded biochar hybrid material (Ag@biochar) by fast pyrolysis of the Ag preloaded biomass and its catalytic effect on Cr(VI) reduction. The results show that Ag@biochar can completely catalytically reduce Cr(VI) in aqueous solution within 20 min using formic acid as a reducing agent at 323 K. The particle size of Ag NPs on the biochar was found to be pyrolysis temperature dependent and played an important role in the reduction of Cr(VI). We found that the reduction of Cr(VI) catalyzed by Ag@biochar follows a CO (produced from HCOOH decomposition) reduction mechanism which is quite different from the H2 reduction mechanism with catalysis of some noble metal based catalysts (e.g. Pd and Pt). This study offers a sustainable approach for simultaneous disposal of the biomass waste and synthesis of functional materials and might be expanded in the recycling of other metal-contaminated biomass (e.g. Cu, Ni, Co, Zn, and Fe).

Lead (Pb) is one of the most widespread toxic heavy metals in water distribution systems and surface water, and how to quickly and completely remove Pb from the water has received global concern. Here we designed and synthesized a 3D nitrogen doped carbon hydrogel/FeMg layered double hydroxide (NC–FeMg LDH) nanocomposite through a one-pot solvothermal process and investigated the Pb removal efficiency and underlying mechanism. Multiple characterization methods including XRD, FTIR, and TEM confirmed that the 3D NC–FeMg LDH is formed by incorporating 2D FeMg-LDH nanosheets with the nitrogen doped carbon hydrogel which is in situ formed in the solvothermal carbonization of glucosamine. The as-synthesized 3D NC–FeMg LDH shows favorable performance in the removal of Pb from aqueous solution with very short equilibrium time (2 min) and large adsorption capacity (344.8 mg g−1). The excellent removal performance toward Pb is demonstrated to be a structure-dependent multiplex surface chemical process between Pb and LDH involving Mg2+/Pb2+ ion exchange, Pb/CO or OC–O, and Pb/pyrrolic N surface complexation. This work may provide an idea for designing hybrid functional materials for selective and high-efficiency removal of other heavy metals from polluted water.

Lead (Pb) is a ubiquitous heavy metal pollutant, and its removal and immobilization from the environment have attracted considerable attention. In this study, we prepared amino-functionalized hydrochar (AFHC) from waste biomass and investigated its adsorption and immobilization activity toward Pb(II). The results showed that AFHC exhibits high performance in Pb removal, achieving over 1000 mg g−1 removal capacity within the first 5 min of reaction, and high selectivity toward this metal ion. Notably, AFHC can efficiently remove low concentrations of Pb from aqueous solution, suggesting that it has potential utility in treatment of drinking water, especially in point-of-use water treatment in underdeveloped areas. Further investigations indicated that the robust performance of the hydrochar may be attributed to the formation of rod-like Pb5(PO4)3(OH) crystals on its surface, where amino groups function as bridges and hydrolyze to provide basic groups.