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Doping of nitrogen (N) on carbon materials often requires complicated synthetic steps or specific machinery. In this study, N-doped biochar was successfully synthesized by simply ball milling pristine biochar with ammonium hydroxide. The content and species of N in the resulting N-doped biochars were carefully characterized, the formation mechanisms of N-related groups were illustrated, and their applications in CO2 uptake and reactive red removal were evaluated. Most of N introduced to biochar was loaded on its surface in forms of NH2 and C N, resulting from the dehydration of COOH and OH. Biochars produced at 450 °C were doped with more N on the surface (XPS, 2.41%–2.65%) than those produced at 600 °C (XPS, 1.18%–1.82%) because the content of O-containing functional groups in biochar decreases with increasing pyrolysis temperature. The basic properties of N-related groups enhanced the sorption performance of biochar to both acidic CO2 and anionic reactive red. For example, the CO2 uptake of the N-doped, 450 °C hickory biochar was 31.6%–55.2% higher than the corresponding pristine and ball-milled biochars. The maximum sorption capacity of the N-doped, 600 °C bagasse biochar to reactive red was about 3.66–16.2 times of the corresponding biochars without N doping. This paper provides an alternative and facile approach to prepare N-doped biochar that can be extended to other carbon materials to meet the specific needs in different applications, especially adsorption.

Carbon-based adsorbents such as graphene and its derivatives, carbon nanotubes, activated carbon, and biochar are often used to remove heavy metals from aqueous solutions. One of the important aspects of effective carbon adsorbents for heavy metals is their tunable surface functional groups. To promote the applications of functionalized carbon adsorbents in heavy metal removal, a systematic documentation of their syntheses and interactions with metals in aqueous solution is crucial. This work provides a comprehensive review of recent research on various carbon adsorbents in terms of their surface functional groups and the associated removal behaviors and performances to heavy metals in aqueous solutions. The governing removal mechanisms of carbon adsorbents to aqueous heavy metals are first outlined with a special focus on the roles of surface functional groups. It then summarizes and categorizes various synthesis methods that are commonly used to introduce heteroatoms, primarily oxygen, nitrogen, and sulfur, onto carbon surfaces for enhanced surface functionalities and sorptive properties to heavy metals in aqueous solutions. After that, the effects of various functional groups on adsorption behaviors of heavy metals onto the functionalized carbon adsorbents are elucidated. A perspective of future work on functional carbon adsorbents for heavy metal removal as well as other potential applications is also presented at the end.

Phosphorus (P), a vital growth-limiting nutrient, is often lost in wastewater discharge, which may not only deteriorate water quality but also accelerate P depletion. In this study, laboratory experiments were conducted to investigate the reclamation and reuse of P from secondary treated wastewater (STWW) by engineered biochar loaded with aluminum oxyhydroxides (AlOOH). Biochar loaded with colloidal and nanosized AlOOH crystalline flakes was successfully produced through direct pyrolysis of hickory wood chips pretreated with aluminum salt. STWW samples were collected from a local wastewater treatment plant to evaluate the P sorption ability of the engineered biochar. The real wastewater was used in batch sorption experiments and the results showed that the engineered biochar effectively removed P from the STWW with relatively fast kinetics (

High photocatalytic hole-electron pairs separation efficiency and the wide use of inexpensive and earth-abundant materials as cocatalysts in most semiconductor-based photocatalytic systems are desired for improving the photocatalytic activity and practical application. Herein, we report a facile one-pot solvothermal approach of integrating stable metallic nonmetal materials 1T-MoS2 nanosheets with MIL-53(Fe) to form needle-shaped 1T-MoS2@MIL-53(Fe) (TSMF) composites. Interestingly, the introduction of 1T-MoS2 turns nonspecial-structured MIL-53(Fe) into needle-like structure and the BET analysis reveals that the optimal TSMF composites possess abundant coexistence of micropores and mesopores with a large surface area of 337 m2 g−1, which is about 16 folds higher than that of the pure MOFs. Meanwhile, it is remarkable that the photocatalytic rate of ibuprofen (IBP) by optimal TSMF nanocomposites has improved 7.5 and 9.4 times compared to the pristine MIL-53(Fe) and 1T-MoS2, respectively. The photocatalytic efficiency of TSMF composites enhances due to the emerging micropores, which can provide more adsorption and reaction sites. In addition, the formed compact and uniform interface contact between 1T-MoS2 sheets and MOF may dramatically accelerate the separation of the photo-induced charges, thus enhance the photocatalytic activity. We also study the photocatalytic mechanism combined the corresponding electrochemical testing and the photo-degradation intermediates identified by ion chromatography (IC) and LC–MS-MS, indicating that superoxide radicals ( O2–), hydroxyl radical ( OH) and electrons (e−) are the main active radicals in IBP photocatalysis and decarboxylation and hydroxylation are the main degradation pathways of IBP.

Understanding the transport behavior of N-doped graphene (NG) in porous media is critical to assess its environmental impact. In this work, sand column experiments were conducted to compare the transport and retention of NG and graphene oxide (GO) and to investigate the effects of temperature (4 and 25 °C), solution ionic strength (1 and 5 mM) and sand grain size (0.3–0.4 and 0.5–0.6 mm) on the transport and retention of NG in saturated porous media. The retention of NG in the column was larger than GO. The transport of NG was sensitive to solution ionic strength, and it was more mobile under lower ionic strength. The transport of NG increased with the increasing of sand grain size, and the results can be expounded by the colloid filtration theory. The transport of NG was larger at the lower temperature tested because of the reduction of repulsively electrostatic forces between sand and NG as temperature increased. Advection-dispersion equation was applied to simulate the transport and retention of GO and NG in saturated porous media and model simulations fitted the experimental data very well. Findings of this study are of great importance for exploring the transport and fate of NG in the natural environment.

Sustainable bio-based coated fertilizers not only reduce nonpoint-source pollution, but also shift dependence away from petroleum-based materials. In this paper, a bio-based polyurethane (BPU) was derived from liquefied cotton straw (LCS) and was used to coat urea prills for a BPU-coated fertilizer (BPCF). Siloxane was incorporated into the BPU for the synthesis of a siloxane modified BPCF (SBPCF). In addition, both siloxane and polyether were used to modify the BPU to prepare a dual-modified BPCF (DBPCF). Various analytical and characterization tools were used to determine the properties (e.g., composition, structure, and morphology) of the BPU and the coating shells. Nutrient release experiments were also conducted to evaluate the nitrogen (N) release characteristics of the coated fertilizers. Structure and morphology analyses and measurements of the water contact angle and water adsorption revealed that the siloxane modification enhanced the hydrophobicity of the coatings of SBPCF and DBPCF to repel water entrance and thus improved the N release characteristics. As evidenced by the composition, structure and morphology analyses, further polyether modification created an interpenetrating polymer network (IPN) with the DBPCF coating to fix some of the inactive components that mitigated the rising of micropore number and size in the coating during nutrient release. As a result, the DBPCF showed the best properties and release characteristics. Findings of this work suggest that BPU-coated fertilizers, particularly DBPCF, present promising opportunities to the sustainable development of modern agriculture.

Novel adsorbents were produced through the grinding of biochars of different feedstock and pyrolysis temperature in a planetary ball mill. The removal effectiveness and mechanisms of aqueous methylene blue by these adsorbents were examined. Ball milled sugarcane bagasse biomass pyrolyzed at 450 °C (BMBG450) had the highest methylene blue sorption capacity thus was chosen for further study. Compared to unmilled bagasse biochar (BG450), BMBG450 had greater specific surface area, larger pore volume, smaller hydrodynamic radius, stronger negative zeta potential (about 1.6-fold increase), and more oxygen-containing functional groups (1.05 mmol/g increase). These characteristics resulted in much greater methylene blue removal capacity (354 mg/g Langmuir maximum adsorption capacity vs. 17.2 mg/g of original BG450). The increased in BM–biochar’s external and internal surface areas exposed its graphitic structure and oxygen-containing functional groups, thus enhancing methylene blue adsorption via π–π interaction and electrostatic attraction. Experimental and modeling results suggest external mass transfer as the rate-limiting adsorption step for BG450 and surface diffusion as the rate-limiting adsorption step for BMBG450. BM–biochars had a lower equilibrium dosage and shorter reactor detention time when applied in a completely mixed flow reactor (CMFR).

Discovering sustainable materials that can efficiently capture and store CO2 is a crucial step towards mitigating anthropogenic greenhouse gas emissions. The current materials used in post-combustion scenarios have significant drawbacks, including high cost and resulting hazardous byproducts. This study developed a simple and cost-effective method of producing activated MgO nanoparticles that have high CO2 capture efficiency. To optimize CO2 capture, we incorporate biomass during the production to ensure complete and dispersed MgO nanoparticle formation from the decomposition of MgCl2 hydrate. Materials are characterized by SEM, XRD, BET/DFT, ICP, and TGA analysis. Resulting carbon-supported activated MgO nanoparticles efficiently captured CO2 at low temperature, by physisorption and magnesium carbonate formation. Without the incorporation of biomass, MgCl2 hydrate decomposed via low temperature pyrolysis, is still capable of CO2 capture; however, the efficiency is enhanced with the addition of biomass, as this helps support the formation and distribution of MgO nanoparticles. The carbon-supported MgO nanoparticles produced with a 5:2.5 (w/w MgCl2:biomass) ratio was capable of greatest CO2 capture capacity on both a g−1 material (up to 235 mg g−1) and g−1 magnesium (733 mg g−1) basis after 3 h. The carbon-supported MgO nanoparticles have potential to be applied in inexpensive large-scale CO2 capture, as the production can be adjusted based on capacity, resource, or energy constraints.

Microplastic (MP) pollution has raised public concerns in recent decades globally due to its wide global spreading and potential toxicity. Most of existing studies have focused on MP pollution in marine, freshwater, and sediment systems. However, much less research attention has been paid to soil, which is a major sink of MPs. Furthermore, research interest in MPs in groundwater is even lower than that in soils. There is a critical need to digest and summarize the existing knowledge and the latest advancements to promote research on MP pollution in soils and groundwater. As the first of its kind, this work provides a systematical review of the newest knowledge on occurrences, sources, analytical methods, and impacts of MPs in both soils and groundwater. It first outlines the characteristics (global occurrences, sources, and pathways) of MP pollution in soils and groundwater. Commonly used analytical methods including sample collection (sites, tools, depth, points, and quantity), sample preparation (drying and sieving), extraction (separation, digestion, etc.), identification (visual sorting, chromatography, and vibration spectroscopy), and quality assurance/quality control are then systematically reviewed. Furthermore, the risks and impacts of MPs on soil properties, plants, animals, and antibiotic resistance genes (ARGs) between microorganisms and humans are discussed. At the end, this review also identifies the knowledge gaps and points out potential directions for future research.

Ischemic injury is mostly caused by insufficient blood supply, excessive inflammation and increased oxidative stress. Pro-angiogenic gene delivery can foster vascular remodeling and increase blood perfusion, but the adverse ischemia microenvironment leads to inadequate therapy effect and high recurrence rate. A novel combination strategy should be developed for the effective therapy of ischemic injury via remediating microenvironment and accelerating revascularization simultaneously. Carbon monoxide (CO) exhibits multiple bio-functions, especially anti-inflammation and anti-oxidant effects, suggesting that it might be an attractive candidate for ischemia therapy. Herein, for the first time, “controlled CO release” was introduced to treat limb ischemia. We developed the controlled CO delivery nanoplatform (PR@CORM) via encapsulating CO-releasing molecule-401 by the stimulus-responsive and ECs-adhesive peptide functionalized nanocarrier. In response to oxidants, PR@CORM can intelligently release therapeutic CO gas to remediate the microenvironment, but the pro-angiogenic effect is still disappointing. We thereby combined “CO therapy” and “pro-angiogenic gene therapy” to achieve the cooperative effects for ischemia therapy. This strategy exhibits superiority in the treatment of ischemic injury through extensively normalizing the microenvironment and accelerating revascularization. The “controlled CO release” serves as a scavenger of inflammation and reactive oxygen species, and pro-angiogenic gene holds potential for ischemia therapy.

Gene-engineered vascular endothelial cells have acquired satisfactory ischemia therapy in animal models. However, its clinical process is still severely limited by the hurdle of transfection-structure-toxicity and single therapeutic pathway. To this end, inspired by green process, we innovatively introduced “green” concept into gene delivery. “Green” means fully utilizing carrier and gene via simple, economic and nontoxic process. Herein, the combined strategy of “bioactive carrier” and “CO2-modification” was proposed. On the basis of the cascaded expression from ZNF580 to endothelial nitric oxide synthase (eNOS), we designed cationic peptide based on L-arginine as bioactive carrier to deliver pZNF580. Furthermore, CO2-bubbling was performed to endow bioactive carrier with pH-sensitive nanobomb effect. The carrier dramatically enhanced endo/lysosomal escape via nanobomb effect for high pZNF580 delivery and expression. In turn, carrier changed “enhanced vehicle” identity into NO substrate after completing gene delivery and further was catalyzed by transfection-triggered eNOS overexpression, which greatly amplified NO generation via their synergistic promotion. This simple design obtained dual-high results of ZNF580 (to mediate angiogenesis) and NO (to mediate angiogenesis and anti-inflammation) level. In critical hind limb ischemia (CLI) mice, the strategy simultaneously promoted angiogenesis and mitigated inflammation, which co-worked to recover blood flow and rescue limb. Besides, it was nontoxic to muscle tissue. The multi-pathways achieved significant CLI treatment. Taken together, we established a positive feedback between CO2-enhanced bioactive carrier and target-gene expression via green design and process. This can maximize and expand the output of gene therapy through simplifying the input of gene complexes, thus guaranteeing high transfection, simple structure and low toxicity. We believe that this green strategy will provide a novel viewpoint for gene delivery.

Hydrogen bonded metal–organic supramolecules are a new family of cocatalysts for high-efficiency water oxidation photoanodes owing to their suitable electrical conductivity. We herein designed a calix [4] resorcinarene-based metal–organic supramolecular system with rich hydrogen bonds, namely [Cu2L(H2O)2]∙3DMF (L = calix [4] resorcinarene-based ligand and DMF = N,N’-dimethylformamide) or Cu2L. Then, the hydrogen bonded metal–organic supramolecular system was applied as a cocatalyst in BiVO4 nanoplate photoanode for water oxidation reaction. Photoelectrochemical and electrochemical analysis demonstrated that the obtained Cu2L-modified BiVO4 photoanode showed greatly enhanced water oxidation efficiency, which was about three times higher than bare BiVO4 nanoplates. In addition, photoelectrochemical activity was well maintained within three hours. Cu2L as an efficient cocatalyst can promote the holes on the surface of the photoanode to participate in the oxygen evolution reaction, thus improving the performance of the photoanode. This work presents a feasible strategy by using the hydrogen bonded metal–organic supramolecular system to functionalize photoanodes for enhanced water oxidation efficiency.

As a green solvent-free process, ball milling has attracted considerable attention in fabricating nanocomposites. Herein, we synthesized novel Z-scheme heterojunction CeO2/g-C3N4 nanocomposites by simply direct ball milling CeO2 and g-C3N4 at three different mass ratios (3:7, 7:3, and 9:1). In comparison to individual CeO2 and g-C3N4, the ball-milled nanocomposites showed stronger UV light response, higher charge carrier separation efficiency, greater photodegradation potential, higher photocurrent intensity, and faster electron transfer, indicating much better photocatalytic activity. When used as photocatalysts to remove methylene blue (MB) under UV light irradiation, 70% CeO2/g-C3N4 exhibited the highest removal rate (90.1%), much better than that of CeO2 (6.2%) or g-C3N4 (45.7%). The synergistic interact between adsorption and photodegradation of the CeO2/g-C3N4 nanocomposites was simulated by kinetic models, and a strong positive correlation (r = 0.834 and rs = 0.777) between adsorption and photocatalysis was identified. The results indicate that adsorption can promote photodegradation by accelerating the kinetics, while photodegradation can regenerate adsorption sites. This work provides not only a facile synthesis of Z-scheme heterojunction photocatalysts but also a novel perspective for better understanding the synergy between adsorption and photocatalysis.

In this study, biochars were ball milled in a planetary mill to investigate the effect of atmosphere (air, N2, and vacuum) on physicochemical properties and pollutant removal capacities of resulted ball-milled biochars. Ball milling turned granular biochars into nanosized particles and increased their surface area (SA) from 2.60-343 m2 g−1 to 300–452 m2 g−1. Oxygen-limited atmosphere (N2 and vacuum) was more favorable for reducing biochar size than air atmosphere. Decrease of particle size increased external surface area of biochar produced at 450 °C (HC450), so SA of ball-milled biochars produced in N2 (BMHC450-N) and vacuum (BMHC450-V) was higher than that produced in air (BMHC450-A). However, for biochar produced at 600 °C (HC600), smaller particle size also caused severe agglomeration, thus BMHC600-N and BMHC600-V had smaller SA than BMHC600-A. Apart from morphology, atmosphere also affected the formation of surface functional groups. N2 and vacuum inhibited the introduction of O-moieties to HC450 during milling process with the decrease of C O to 2.78–3.02%. Ball milling increased the removal capacity of biochars to reactive red from 1.70–3.60 mg g−1 to 9.20–34.8 mg g−1. Compared to air atmosphere, N2 and vacuum were superior for the enhanced removal due to higher external SA and less negative charge, facilitating the external diffusion of reactive red. Overall, both morphology and surface functional groups of ball-milled biochars were strongly affected by milling atmosphere, influencing their ability to remove contaminants.

In order to improve the recycling of waste paper and metallic ions in waste water, waste art paper with high contents of fillers/adhesives was carbonized at 300, 450, and 600 °C and the resulting engineered biochars were used to recycle the aqueous Pb(II). The waste-art-paper biochars obtained at higher temperature showed extraordinary removal of aqueous Pb(II) with the Langmuir maximum sorption capacity of 1555 mg g −1 , significantly higher than that of other carbon sorbents in literatures. Comparison of Pb(II) sorption onto biochar’s deashing component and ash suggested the important role of minerals in Pb(II) sorption. The pH changes and the releases of Ca 2+ after Pb(II) sorption further suggested the reactions between calcite minerals of the biochars with the lead ion during Pb(II) sorption. Characterizations of pristine and post-sorption biochars with scanning electron microscope equipped with an energy dispersive spectrometer, Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron analyses confirmed the precipitation of Pb(II) with CO 3 2− to form PbCO 3 and Pb 2 (OH) 2 CO 3 crystals on the biochar surfaces. As a result, acid extraction (1.0 mol L −1 HNO 3 ) effectively recycled all the sorbed lead. Furthermore, incineration of Pb(II)-laden biochar under 350 °C not only successfully recovered the lead but also turned it into high purity (>96%) PbO nanoparticles. Findings from this work indicated that recycle waste art paper for biochar production can be a promising environmentally friendly and cost-effective technology because of the extraordinary sorption ability of waste-art-paper biochar and the effective recovery of sorbed Pb(II) into value-added nanoparticles from exhausted biochar.

Innovative and cost-effective methods are needed to capture and store CO2 to reduce anthropogenic impact on global warming. This work produced and characterized aluminum hydroxide, magnesium hydroxide, and iron oxide–biochar composites, and evaluated their ability to capture CO2 at room temperature and atmospheric pressure. Biomass feedstocks were treated with metal ions of a variety of concentrations, and were then pyrolyzed at 600 °C. Characterization experiments showed that the process not only turned the biomass into biochar, but also converted the metal ions into metal oxyhydroxide nanoparticles onto the carbon surfaces with the biochar matrix. As a result, the composites, particularly the ones with optimal metal to biomass ratios, had higher CO2 capture capacity than the unmodified biochar. All the composites had relatively large surface area and captured CO2 mainly through physical adsorption. Although Fe2O3–biochar composites had the highest surface area, the AlOOH–biochar composite showed the largest sorption. Thus, both the characteristics of the metal oxyhydroxides and the surface area contributed to the CO2 capture capacity. The maximum adsorption capacity (71 mg g−1 at 25 °C) by AlOOH–biochar is comparable to commercial adsorbents. The samples had between 90% and 99% desorption at 120 °C, so they required low cost regeneration. All these results suggested that biochar-based composites could be a high efficiency and cost-effective adsorbent for CO2 capture.

High efficiency and cost-effective remediation technologies are needed to remove tetrachloroethylene (PCE) from the source zones in soil and groundwater systems. This work evaluated the ability of a biodegradable surfactant (Tween 80) coupled with an effective oxidant (Fe 2+ (activation agent)–citrate (chelating agent) activated persulfate (PS, oxidant)) to remove PCE from porous media. Batch experiments were used to optimize the oxidant by testing the effects of PS, citrate, and Fe 2+ concentrations on the PCE degradation. The optimal molar ratio of PS/citrate/Fe 2+ /PCE was 15:15:5:1 for PCE degradation in presence of the surfactant. Four sandbox experiments were performed to compare the effectiveness of the surfactant and the combination of the surfactant with the optimized oxidant in the removal of PCE from homogeneous and heterogeneous porous media. PCE saturation distributions in the sandboxes were quantified using a light transmission system. In addition, the PCE, PS, and Cl − concentrations in the effluents were also monitored during the experiments. While the Tween 80 solution removed about 52% and 67% of PCE from the homogeneous and heterogeneous porous media; the combination solution was more effective with removal rates of 80% and 84%, respectively. The enhanced PCE removal was due to the combined effects of the surfactant solubilization and PS oxidation: (1) Tween 80-enhanced solubilization resulted in an enlarged effective contact and reaction between PCE and PS; and (2) PS degraded the PCE from the soluble phase and thus facilitated its dissolution from the source zone, resulting in more efficient use of Tween 80. Findings from this work indicate that the combination of surfactant and oxidant can provide an effective way for the remediation of PCE in soils and groundwater.

Solid waste containing heavy metals, halogens and other hazardous substances can cause harm to humans and environment. It is a central issue that how to treat solid waste effectively and harmlessly. Hydrothermal technology is a prominent method to treat solid waste and has attracting worldwide attentions. In the hydrothermal reaction, water acts as a reaction medium, which is clean and environmentally friendly. The high temperature and high pressure environment prompt various reactions occurring quickly and efficiently. The closed environment of the hydrothermal reactor is conducive to avoid secondary pollution. In this paper, the concept and principle of hydrothermal technology are introduced, and the applications on the treatment of solid waste are summarized from three angles of reduction, detoxification, and recycling. At the end of the paper, we look forward to the future development of the hydrothermal technology applied on the solid waste treatment.

Porous carrier supported metal oxide composites possess significant potential for sequestration of heavy metals from various waters. However, slow diffusion of targeted metal ions within the micropores of the porous carriers is a key technical barrier limiting practical application of these hybrid adsorbents, particularly in high flow systems. In this study, we first synthesized a biochar with enlarged pore channel (namely K-BC) by adding KHCO3 during the biochar pyrolysis process and then employed the K-BC as a supporter to fabricate a new manganese oxide-based composite (namely HMO-K-BC). It is striking that the effective intra-particle diffusion coefficient D of Pb(II) inside the K-BC is comparable to that in aqueous solution (1.5 × 10−6 v.s. 2.1 × 10−6 cm2 s−1). Although the D value of Pb(II) inside the HMO-K-BC was reduced to 1.8 × 10−7 cm2 s−1, it is still 1–2 orders of magnitude higher than that of conventional adsorbents such as activated carbon, ion exchanger and biochar. As a result, the HMO-K-BC can rapidly sequestrate Pb(II) and Cd(II) within 7.5 min. The HMO-K-BC can also selectively remove Pb(II) and Cd(II) in the presence of high level Ca(II) and humic acid. Column tests further showed that HMO-K-BC was able to effectively treat simulated and real Pb(II)- and Cd(II)-polluted wastewater in a high-flow system with superficial liquid velocity of 0.53 m h−1 (20 BV h−1). All the results manifest that expanding pores of biochar is a promising measure for promoting the practical application of biochar supported composites in wastewater treatment.

Hickory wood was pyrolyzed at 300 °C, 450 °C, and 600 °C to produce biochars, which were then modified by ball milling. The pristine and ball-milled biochars were used to remove volatile organic compounds (VOCs) including acetone, ethanol, chloroform, cyclohexane, and toluene. Compared with the corresponding pristine one, each ball-milled biochar showed significantly improved structural characteristics. Their specific surface area (SSA) increased by 1.4–29.1 times, average pore size (APS) decreased slightly, and the hydrophilicity and polarity were also enhanced according to the elemental analysis. The adsorption of VOCs by ball-milled biochar increased by 1.3–13.0 folds, and the maximum adsorption capacity of acetone was up to 103.4 mg/g. The adsorption of polar VOCs (acetone, ethanol, and chloroform) onto ball-milled biochars was mainly controlled by surface adsorption process, which was affected by the SSA, APS, and volatile organic matter of the biochars, as well as the properties of the VOCs. The adsorbed VOCs were completely desorbed from the ball-milled biochars at relatively low temperature (≤115.2 °C). Reusability experiments with five adsorption-desorption cycles showed that ball-milled biochar had an excellent reusability for all VOCs. Ball-milled biochars can therefore be used as an effective and regenerable adsorbent for the removal of VOCs.

Despite its importance, chemical process has been often overlooked in CO2 sorption on carbon based oxyhydroxide composites. In this study, pristine and ball-milled biochar/Fe oxyhydroxide composites were fabricated for CO2 sorption at 25 °C. The composites, particularly the ones with high Fe content, were effective sorbents for CO2 with the capacities of up to 160 mg g−1. The primary mechanism of CO2 sorption on biochar composites with low Fe content was physical adsorption. When the Fe content increased, biochar/Fe oxyhydroxide composites showed enhanced CO2 sorption capacities, but the sorption kinetics became slower. This is because the governing CO2 sorption mechanism was shifted from physical adsorption to chemical reaction between Fe oxyhydroxides and CO2. The formed (oxy)hydroxycarbonate could be decomposed at a temperature between 50 and 125 °C. Furthermore, ball milling could speed up CO2 mineralization rate on the composites, especially for those with high Fe content, to favor the relative significance of chemical sorption. Both physical and chemical CO2 sorption mechanisms were verified by different characterization methods including in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Findings of this study not only demonstrate the importance of chemical sorption, but also provide new insights on CO2 capture by low-cost and environmentally benign biochar/Fe oxyhydroxide composites. Besides, the low regeneration temperature of chemically-sorbed CO2 gives biochar/Fe oxyhydroxide composite a competitive edge over other CO2 sorbents, which often need a high regeneration temperature or are not regenerable.

The synergy between adsorption and photocatalysis has been well recognized in contaminant photodegradation; however, the governing mechanism is still not clear. The main objective of this work is to understand the kinetic processes of synergic adsorption-photocatalysis of graphitic carbon nitrate (g-C3N4), a visible light responsive photocatalyst with a planar graphitic-like structure, in organic contaminant removal. An anionic dye Reactive Red 120 (RR120), which has six sulphonate groups and a complex aromatic molecular structure, was selected as a model contaminant compound. A range of experiments were conducted to determine the kinetics of adsorption, photodegradation, and the integrated process. Various kinetic models were used to simulate and interpret the experimental data and thus to unveil the governing mechanisms. The integrated adsorption and photodegradation of the dye by g-C3N4 was mainly controlled by: 1) adsorption of dye onto g-C3N4 surface, 2) photodegradation of dye in bulk solution, and 3) photodegradation of adsorbed dye on g-C3N4 surface. Both experimental and modeling results showed that the adsorption kinetic rate (3.37 min−1) was faster than the photodegradation kinetic rates. In addition, the surface photodegradation kinetic rate of adsorbed dye (0.149 min−1) was faster than that in solution (0.005 min−1). Adsorption process thus can promote the photodegradation of contaminants by g-C3N4. On the other hand, photodegradation of dye-laden g-C3N4 regenerated its adsorption capacity for multiple times, suggesting photocatalysis process can also promote the adsorption of contaminates on g-C3N4.

Hydrothermally carbonized biomass (hydrochar) has received increased attention recently as a potential agent for contaminant remediation and soil improvement. There is a need to understand how the properties of hydrochar vary with production conditions. In this work, sugarcane bagasse, hickory, and peanut hull were converted into hydrochars at three different temperatures (200 °C, 250 °C, and 300 °C). Basic physicochemical properties of the nine hydrochars were determined and batch aqueous sorption experiments were conducted to measure ability of the hydrochars to sorb methylene blue, lead, and phosphate. The yield, surface area, and pore volume of the hydrochars decreased with increasing conversion temperatures. Among all the hydrochars, the ones made at the lowest temperature (200 °C) were the best for sorption of methylene blue and lead. However, none of the hydrochars were able to remove significant amounts of phosphate from solution. In addition, the hydrochars did not significantly affect seed germination rate, though some did have a significant effect on root development of seedlings. Findings from this work suggest that lower temperature hydrochars may be optimal for contaminant remediation because of their higher sorption ability and absence of negative effect on plants.

Knowledge of the fate and transport of graphene (GR) nanosheets in porous media is essential to understand their environmental impacts. In this work, sand column experiments were conducted to investigate the retention and transport of surfactant-dispersed GR nanoparticles under various conditions. An anionic surfactant, sodium dodecylbenzene sulfonate (SDBS) and a cationic surfactant, cetyltrimethylammonium bromide (CTAB) were used to disperse and stabilize GR in aqueous solutions. Both surfactants were effective in stabilizing the GR particles, even at low concentration (0.004% w:v) because the surfactant coating introduced negative (SDBS) or positive (CTAB) charges on the GR surfaces. As a result, the SDBS- and CTAB-GR showed different retention and transport behaviors in the saturated porous media. At low surfactant concentration, the transport of SDBS-GR was much higher than that of the CTAB-GR, which was almost immobile in the sand columns with mass recovery rate only about 4%. When the surfactant concentration increased from 0.004% to 0.4%, it reduced the transport of SDBS-GR and dramatically enhanced the mobility of the CTAB-GR (with mass recovery rate of 91%). It is suggested that the presence of ‘free’ SDBS ions may reduce the electrosteric repulsions between SDBS-GR and sand surfaces by compressing the electrical double layer. The ‘free’ CTAB ions, however, may compete with the CTAB-GR for adsorption sites on the sand surfaces. Findings from this study indicated that the dispersion method plays an important role in affecting the environmental fate and transport of GR particles.

A fixed-bed sand column with graphene oxide (GO) layer was used to remove heavy metals (Cu(II) and Pb(II)) from an aqueous solution injected under steady flow. Due to the time constrained kinetic process of heavy metal sorption to GO, removal efficiency was affected by the injection flow rate. When injection flow rate changed from 1 to 5 mL min−1, the removal efficiency of the two metals decreased from 15.3% to 10.3% and from 26.7% to 19.0% for Cu(II) and Pb(II), respectively. Provided a fixed concentration of heavy metals in the injected flow, an increase in GO in column from 10 to 30 mg resulted in an sharp increase in the removal efficiency of Pb(II) from 26.7% to 40.5%. When Cu(II) and Pb(II) were applied simultaneously, the removal efficiency of the two metals was lower than when applied by individually. GO-sand column performance was much better for the removal of Pb(II) than for Cu(II) in each corresponding treatment. When breakthrough curve (BTC) data were simulated by the convection-dispersion-reaction (CDER) model, the fittings for Cu in every treatment were better than that of Pb in corresponding treatment. Considering the small amount of GO used to enable the sand columns that resulted in a great increase in k value, compared to the GO-free sand columns, the authors propose GO as an effective adsorption media in filters and reactive barriers to remove Pb(II) from flowing water.

A slow-release fertilizer was developed by encapsulating KNO3 pellets with graphene oxide (GO) films. The material was then subjected to heat treatment, where adjacent GO sheets were soldered and reduced to reduced graphene oxide (re-GO) sheets by potassium. After the re-GO shell formed on KNO3 pellets, the slow-release characteristics of the fertilizer dramatically improved. The process of releasing fertilizer was prolonged to 8 h in water. We believe that this new coating technology could hold great promise for the development of environmentally-benign controlled-release fertilizer for crop production.

Anthropogenic CO2 emissions continue to climb due to increases in global energy demand. Because power plants are the largest stationary source of anthropogenic CO2, developing effective and affordable post combustion CO2 capture technology has attracted substantial research attention. This study assessed the adsorption of CO2 onto biochar, a low-cost adsorbent that can be produced from waste biomass through low-temperature pyrolysis. Sugarcane bagasse (BG) and hickory wood (HW) feedstock converted into biochar at 300, 450, and 600 °C. Sorption of CO2 on each of the resulted biochar was measured by monitoring its weight changes in CO2 at 25 or 75 °C. The biochar was found to be effective for CO2 capture and the adsorption process could be described by the second-order kinetics model. In general, the biochars produced at higher temperature had better CO2 capture performance. The BG biochar produced at 600 °C showed the most adsorption of CO2 (73.55 mg g−1 at 25 °C). However, even when the feedstock was exposed to only 300 °C pyrolysis, the biochar was still able to capture more than 35 mg g−1 CO2 at 25 °C. Experimental results suggest that CO2 weakly bound to the surface of the biochar through physisorption, so surface area was a significant determinant of CO2 adsorption (Pearson’s r = 0.82); nevertheless, the presence of nitrogenous groups also played a role, when the surface area was sufficient. Biochar’s porous structure and unique surface properties enable it to be an efficient CO2 adsorbent, while being sustainable and inexpensive.

A novel engineered biochar with clay particles distributed on carbon surfaces within the biochar matrix has been successfully developed as a low-cost adsorbent for environmental applications. Three biomass feedstocks were pretreated with montmorillonite or kaolinite suspensions and then pyrolyzed at 600 °C for 1 h in a N2 environment. Physicochemical characterizations including microscopy and X-ray analyses confirmed clay particles were present on the surface of biochar during the annealing process. Laboratory adsorption experiments indicated that the presence of clay particles on carbon surfaces had dramatically increased (about 5 times) the biochars’ adsorption ability to methylene blue (MB). In addition, the clay–biochar composites could be recycled and reused after dye adsorption with a stable capacity of around 7.90 mg g−1. The experimental results also showed that the sorption of MB on the clay–biochar composites is mainly controlled by the ion exchange (with clay) and electrostatic attraction (with biochar) mechanisms. Findings from this work indicate that engineered biochar, prepared from two low-cost materials (clay and biochar), is a valuable adsorbent for removing contaminants from aqueous solutions.

This work explored the effect of temperature, production method, and feedstock type on the physicochemical and biological properties of biochars and hydrochars. Biochars and hydrochars made at lower temperatures had higher production rates. Higher pyrolysis temperatures not only increased carbon content of biochars but also produced higher thermal stability biochars that did not start to decompose in air after 400–450 °C. The production method showed strong effect on biochar properties. Compared to the dry-pyrolysis biochars derived from the same feedstocks, the hydrochars had more acidic pH values and lower carbon contents. The results showed that feedstock types could also influence characteristics of the biochars. None of the chars showed statistically significant effects on plant seed germination and seedling growth and thus could be used as soil amendments. Our findings indicated that biochars with different properties could be developed by changing production conditions to better satisfy their environmental applications.

Innovative technologies incorporating engineered nanoparticles into biochar production systems could improve the functions of biochar for many applications including soil fertility enhancement, carbon sequestration and wastewater treatment. In this study, hybrid multi-walled carbon nanotube (CNT)-coated biochars were synthesized by dip-coating biomass in varying concentrations of carboxyl-functionalized CNT solutions (0.01% and 1% by weight) prior to slow pyrolysis. Untreated hickory and bagasse biochars (HC and BC, respectively) and CNT–biochar composites (HC–CNT and BC–CNT, respectively) were characterized, and the methylene blue (MB) sorption ability of the resulting chars was evaluated in batch sorption experiments. The addition of CNTs significantly enhanced the physiochemical properties of the biochars with HC–CNT-1% and BC–CNT-1% exhibiting the greatest thermal stabilities, surface areas (351 and 390 m2 g−1, respectively), and pore volumes (0.14 and 0.22 cc g−1, respectively). Sorption kinetic and isotherm data showed that, among the biochars examined, BC–CNT-1% had the highest MB sorption capacity (6.2 mg g−1). While increased pH (up to ∼7), promoted the uptake of MB by all the biochars, whether coated or not, increasing ionic strength decreased the uptake of MB by all biochars tested. These findings suggest that electrostatic attraction was the dominant mechanisms for the sorption of MB onto the chars, though diffusion controlled its rate. Hybridized CNT–biochar nanocomposite can thus be considered a promising, inexpensive sorbent material for removing dyes and organic pollutants from aqueous systems.

In this work, chitosan-modified biochars were synthesized in efforts to produce a low-cost adsorbent for heavy metal environmental remediation. Characterization results showed that the coating of chitosan on biochar surfaces could improve its performance as a soil amendment or an adsorbent. Batch sorption experiments showed that, compared to the unmodified biochars, almost all the chitosan-modified biochars showed enhanced removal of three metals (i.e., Pb2+, Cu2+, and Cd2+) from solution. Further investigations of lead sorption on chitosan-modified bamboo biochar (i.e., BB-C) indicated that, although sorption kinetics were slow, BB-C had a relatively high Langmuir lead sorption capacity of 14.3 mg/g biochar (71.5 mg/g chitosan). Sorption of lead on the chitosan-modified biochar greatly reduced its metal toxicity. Both seed germination rate and seedling growth of the Pb-laden BB-C were similar to that of control groups without lead. In addition, uptake of lead by plants was reduced about 60% when lead was sorbed onto the chitosan-modified biochar. This work suggests that chitosan-modified biochars may be used as an effective, low-cost, and environmental-friendly adsorbent to remediate heavy metal contamination in the environment.

In this work, cotton fibers and pyrene-dispersed graphene sheets were used to produce graphene-coated pyrogenic carbon as an anode material for lithium battery. The graphene sheets were wrapped around the cotton fibers by simply dipping the fabric in a graphene/pyrene-derivative suspension. And then the cotton/graphene textile was annealed at 700 °C in a quartz tube furnace under Ar flow conditions. During the annealing process, the gaps between separated graphene sheets were “soldered” by “glue” molecules (aromatic molecular surfactant) to form graphene-coated pyrogenic carbon. Because of the unique electric properties of the graphene “skin” on the pyrogenic carbon, the flexible graphene-coated pyrogenic carbon showed relatively large storage capacity to lithium. Galvanostatic charge–discharge experiments also showed that the graphene-coated pyrogenic carbon electrode provided a reversible discharge capacity as high as 288 mA h g−1 even after 50 cycles and thus can be used an anode material in lithium battery.

In this work, sand and bubble column experiments were conducted to explore the deposition mechanisms of graphene oxide (GO) particles in porous media with various combinations of moisture content and ionic strength. Sand column experimental results indicated that retention and transport of GO in porous media were strongly dependent on solution ionic strength. Particularly, GO showed high mobility under low ionic strength conditions in both saturated and unsaturated porous media. Increasing ionic strength dramatically increased the retention of GO particles in porous media, mainly through secondary-minimum deposition as indicated in the XDLVO interaction energy profiles. Recovery rates of GO in unsaturated sand columns were lower than that in saturated columns under the same ionic strength conditions, suggesting moisture content also played an important role in the retention of GO in porous media. Findings from the bubble column experiments showed that the GO did not attach to the air–water interface, which is consistent with the XDLVO predictions. Additional retention mechanisms, such as film straining, thus could be responsible to the reduced mobility of GO in unsaturated porous media. The experimental data of GO transport through saturated and unsaturated porous media could be accurately simulated by an advection–dispersion-reaction model.

In this work, a biochar based composite material with AlOOH nano-flakes was fabricated from AlCl 3 pretreated biomass through slow pyrolysis in a N 2 environment at 600 °C. Physicochemical properties of the biochar/AlOOH nanocomposite were studied systematically with several commonly used material characterization instruments, including electron microscopes and X-ray techniques. Structure and morphology analysis of the sample showed that the AlOOH particles/flakes are nanosized and uniformly grow on the carbon surface within the pores of the biochar. Laboratory batch sorption experiments were conducted to evaluate the sorption ability of the biochar/AlOOH nanocomposite to three representative aqueous contaminants: arsenic, methylene blue, and phosphate. The adsorption isotherm and adsorption kinetics data suggested that the biochar/AlOOH nanocomposite is an excellent multifunctional adsorbent that can effectively remove all these contaminants from aqueous solutions.

Porous core–shell microcapsules were obtained by assembling graphene layers on zeolite surfaces during amorphization process. When fused onto the surface, the self-assembled graphene layers played a role as ‘isolation bubbles’ that prevented the vapor releasing from bulk zeolites. The self-steaming of vapor served as the foaming agent of bringing the porous structure inside zeolites but also created an expansive force to form microcapsules. Due to their porous structures, the as-produced microcapsules showed excellent slow-release characteristics. The release of potassium from the microcapsules reaches equilibrium after 27 days, much slower than that from zeolites (2 days). We believe that the new microcapsules can be used as controlled-release agent for delivery of chemical compounds (e.g., fertilizers) as well as be used as microreactors, micro-devices, sensors, and catalysts. In addition, it is anticipated that the new synthesis route, especially using graphene layers to mediate amorphization, may be extended to other reactions.

Widespread applications of engineered nanoparticles (ENPs) have raised concerns over their occurrences in the environment. In this work, laboratory experiments and mathematical modeling were conducted to determine whether carbon materials could be used to remove 3 ENPs: silver nanoparticles (AgNPs), carbon nanotubes (CNTs), and titanium dioxide (NTiO2) from water. Hickory chips biochar (HC) and activated carbon (AC) were used and the two carbons were modified with iron impregnation to enhance their affiliation to the ENPs. Results from batch sorption experiments showed that all the carbon sorbents could sorb the ENPs in aqueous solutions and the iron modification improved their sorption ability. When the carbons were packed in sand columns, however, the unmodified carbon showed little removal efficiency to the ENPs, no better than the sand media. Similarly, the columns enabled with iron-modified carbons had better filtration ability to the ENPs, particularly to NTiO2 and AgNP. Among all the carbons, the iron-modified biochar was the best in filtering all the ENPs. Simulations from a model based on the advection-dispersion equation matched the filtration and transport of ENPs in the columns well. The DLVO theory also accurately described the interaction between the ENPs and the carbon materials. Findings from this study indicate that biochar, particularly after modification, can be used as a low-cost filter material to remove ENPs from water.

A new synthesis was developed to create highly porous nanocomposite material consisting of MgO nano-flakes within a biochar matrix that has high sorption ability for ionic contaminations. The synthesis method was used in laboratory to produce MgO-biochar nanocomposites from a variety of carbon-rich biomass. Physical and chemical properties of the synthesized nanocomposites were studied systematically with X-ray powder diffraction, thermogravimetric analysis, scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray analysis. In addition, batch sorption experiment was conducted to determine the sorption ability of the MgO-biochar nanocomposites to aqueous phosphate and nitrate. The results showed that the MgO nano-flakes have uniform morphologies and disperse uniformly on the surface of the biochar matrix. HR-TEM indicated that the biochar matrix is mesoporous with average pore size of 50 nm and the MgO nano-flakes have spacing between 2 and 4 nm, which can serve as adsorption sites for anions. As a result, all the tested MgO-biochar nanocomposites showed excellent removal efficiencies to phosphate and nitrate in water. Nanocomposites made from sugar beet tailings and peanut shells had the best performances with Langmuir adsorption capacities as high as 835 mg g −1 for phosphate and 95 mg g −1 for nitrate, respectively, much higher than the reported values of other adsorbents.

Although carbon nanotubes (CNTs) are well known to have a strong affinity to various heavy metals in aqueous solution, little research has been dedicated to exploit their use in fixed-bed water treatment systems (e.g., trickling filters). In this work, batch sorption and fixed-bed experiments were conducted to examine the ability of functionalized multi-walled CNTs as filter media to remove two heavy metal ions (Pb2+ and Cu2+) from infiltrating water. Batch sorption experiments confirmed the strong sorption affinity of the CNTs for Pb2+ and Cu2+ in both single and dual metal solution systems. In addition, sonication-promoted dispersion of the CNT particles enhanced their heavy metal sorption capacity by 23.9–32.2%. For column experiments, laboratory-scale fixed-bed columns were packed with CNTs and natural quartz sand by three different packing: layered, mixed, and deposited. While all the three packing methods enhanced the fixed-bed filtering efficiency of Pb2+ and Cu2+ from single and dual metal systems, the CNT-deposited packing method was superior. Although the amount of the CNTs added into the fixed-bed columns was only 0.006% (w/w) of the sand, they significantly improved the fixed-bed’s filtering efficiency of Pb2+ and Cu2+ by 55–75% and 31–57%, respectively. Findings from this study demonstrate that functionalized multi-walled CNTs, together with natural sand, can be used to effectively and safely remove heavy metals from water.

Biochar converted from agricultural residues can be used as an alternative adsorbent for removal of aqueous heavy metals. In this work, experimental and modeling investigations were conducted to examine the effect of H2O2 treatment on hydrothermally produced biochar (hydrochar) from peanut hull to remove aqueous heavy metals. Characterization measurements showed that H2O2 modification increased the oxygen-containing functional groups, particularly carboxyl groups, on the hydrochar surfaces. As a result, the modified hydrochar showed enhanced lead sorption ability with a sorption capacity of 22.82 mg g−1, which was comparable to that of commercial activated carbon and was more than 20 times of that of untreated hydrochar (0.88 mg g−1). When used as filter media in a packed column, the modified hydrochar was also much more effective in filtering lead than the unmodified one. The lead removal capacity of the modified hydrochar packed column was about 20 times of that containing untreated hydrochar. In a multi-metal system, the modified hydrochar column still effectively removed lead, as well as other heavy metals (i.e., Cu2+, Ni2+, and Cd2+) from water flow. Model results indicated that the heavy metal removal ability of the modified hydrochar follows the order of Pb2+ > Cu2+ > Cd2+ > Ni2+. Findings from this work suggest that H2O2-modified hydrochar may be an effective, less costly, and environmentally sustainable adsorbent for many environmental applications, particularly with respect to metal immobilization.