Aerosol-Assisted Self-Assembly of Reticulated N-Doped Carbonaceous Submicron Spheres for Effective Removal of Hexavalent Chromium

Tuning active sites on biochars for remediation of mercury-contaminated soil: A comprehensive review

Mercury (Hg) contamination is acknowledged as a global issue and has generated concerns globally due to its toxicity and persistence. Tunable surface-active sites (SASs) are one of the key features of efficient BCs for Hg remediation, and detailed documentation of their interactions with metal ions in soil medium is essential to support the applications of functionalized BC for Hg remediation. Although a specific active site exhibits identical behavior during the adsorption process, a systematic documentation of their syntheses and interactions with various metal ions in soil medium is crucial to promote the applications of functionalized biochars in Hg remediation. Hence, we summarized the BC's impact on Hg mobility in soils and discussed the potential mechanisms and role of various SASs of BC for Hg remediation, including oxygen-, nitrogen-, sulfur-, and X (chlorine, bromine, iodine)- functional groups (FGs), surface area, pores and pH. The review also categorized synthesis routes to introduce oxygen, nitrogen, and sulfur to BC surfaces to enhance their Hg adsorptive properties. Last but not the least, the direct mechanisms (e.g., Hg- BC binding) and indirect mechanisms (i.e., BC has a significant impact on the cycling of sulfur and thus the Hg-soil binding) that can be used to explain the adverse effects of BC on plants and microorganisms, as well as other related consequences and risk reduction strategies were highlighted. The future perspective will focus on functional BC for multiple heavy metal remediation and other potential applications; hence, future work should focus on designing intelligent/artificial BC for multiple purposes.

Preparation of N-doped porous biochar with high specific surface area and its efficient adsorption for mercury ion from aqueous solution

Herein, a new type of super active nitrogen-doped biochar sheet (SNBC) was prepared by two-step pyrolysis and KOH chemical activation with melamine and cherry kernel powder as precursors of nitrogen and carbon source for removing Hg2+ from wastewater. The N2 adsorption/desorption and scanning electron microscope characterization revealed that the resulted SNBC under 600 °C calcination owned huge specific surface area of 2828 m2/g and plenty of well-developed micropores, and X-ray photoelectron spectroscopy and Fourier transform-infrared spectroscopy analysis testified the existence of functional groups containing N and O, which could provide adsorption sites for Hg2+. The SNBC-600 showed high adsorption capacity for Hg2+ even at low pH, and interfering cations had little effect on the adsorption. The adsorption process was rapid and dynamic data fit the pseudo-second-order dynamic model well. The maximum adsorption capacity of Hg2+ on SNBC-600 calculated by Langmuir model was 230 mg/g. After six times of reuse, the adsorption capacity still exceeded 200 mg/g, exhibiting good reusability. The designed microfiltration membrane device base on SNBC-600 could remove low concentration of Hg2+ effectively from solution. This study provided a simple and environment-friendly method for manufacturing nitrogen-doped biochar sheet, which was of great significance in the practical application of Hg2+ pollution treatment.

CO2 Adsorption on N-Doped Porous Biocarbon Synthesized from Biomass Corncobs in Simulated Flue Gas

This study was to develop a low-cost N-doped porous biocarbon adsorbent that can directly adsorb CO₂ in high-temperature flue gas from fossil fuel combustion. The porous biocarbon was prepared by nitrogen doping and nitrogen-oxygen codoping through K₂CO₃ activation. Results showed that these samples exhibited a high specific surface area of 1209-2307 m²/g with a pore volume of 0.492-0.868 cm³/g and a nitrogen content of 0.41-3.3 wt %. The optimized sample CNNK-1 exhibited a high adsorption capacity of 1.30 and 0.27 mmol/g in the simulated flue gas (14.4 vol % CO₂ + 85.6 vol % N₂) and a high CO₂/N₂ selectivity of 80 and 20 at 25 and 100 °C and 1 bar, respectively. Studies revealed that too many microporous pores could hinder CO₂ diffusion and adsorption due to the decrease of CO₂ partial pressure and thermodynamic driving force in the simulated flue gas. The CO₂ adsorption of the samples was mainly chemical adsorption at 100 °C, which depended on the surface nitrogen functional groups. Nitrogen functional groups (pyridinic-N and primary and secondary amines) reacted chemically with CO₂ to produce graphitic-N, pyrrolic-like structures, and carboxyl functional groups (-N-COOH). Nitrogen and oxygen codoping increased the amount of nitrogen doping content in the sample, but acidic oxygen functional groups (carboxyl groups, lactones, and phenols) were introduced, which weakened the acid-base interactions between the sample and CO₂ molecules. It was demonstrated that SO₂ and water vapor had inhibition effects on CO₂ adsorption, while NO nearly has no effect on the complex flue gas. Cyclic regenerative adsorption showed that CNNK-1 possessed excellent regeneration and stabilization ability in complex flue gases, indicating that corncob-derived biocarbon had excellent CO₂ adsorption in high-temperature flue gas.

Preparation of novel N-doped biochar and its high adsorption capacity for atrazine based on π-π electron donor-acceptor interaction

Novel nitrogen (N)-doped cellulose biochar (NC1000-10) with large adsorption capacity (103.59 mg g^-1) for atrazine (ATZ) was synthesized through the one-pot method. It has the best adsorption efficiency than N-doped biochars prepared from hemicellulose and lignin. The adsorption behaviors of ATZ by N-doped biochars with different N doping ratios (NC1000-5, NC1000-10, NC1000-20 and NC1000-30) were significantly different, which was attributed to the difference of sp² conjugate C (I_D/I_G = 0.99-1.18) and doped heteroatom N (pyridinic N, pyrrolic N and graphitic N). Adsorption performance of ATZ on NC1000-10 conformed to the pseudo-second-order kinetic and Langmuir adsorption isotherm model. Thermodynamic calculations showed that adsorption performance was favorable. Besides, wide pH adaptability (pH = 2-10), good resistance to ionic strength and excellent recycling efficiency make it have extensive practical application potential. Further material characterizations and the density functional theory (DFT) calculations indicated that good adsorption performance of NC1000-10 for ATZ mainly depended on chemisorption, and π-π electron donor-acceptor (EDA) interaction contributed the most due to high graphitization degree. Specifically, pyridinic N and graphitic N further promoted adsorption performance by hydrophobic effect and π-π EDA interaction between ATZ and NC1000-10, respectively. Pyrrolic N and other surface functional groups (-COOH, -OH) facilitated the hydrogen bond effect.

Facile Synthesis of Magnetic Biochar Derived from Burley Tobacco Stems towards Enhanced Cr (VI) Removal: Performance and Mechanism

In this study, ferric-loaded magnetic burley tobacco stem biochar (MBTS) was synthesized via pyrolysis to improve the removal of Cr(VI). The results showed that MBTS had an adsorption capacity of 54.92 mg Cr(VI)/g, which was about 14 times higher than raw burley tobacco stem biochar (i.e., 3.84 mg/g). According to the findings obtained, a three-step mechanism of Cr(VI) removal by MBTS was further put forward, i.e., (1) Cr(VI) exchanged with hydroxyl groups on MBTS, (2) the reduction in Cr(VI) to Cr(III) mediated by oxygen-containing groups, and (3) the chelation of produced Cr(III) with the amino groups on MBTS. FTIR spectra further revealed that C-N, C-H, and C=C groups played an important role in Cr(VI) removal. Furthermore, the adsorption equilibrium and kinetics of Cr(VI) on MBTS could better be described by the Langmuir equation and pseudo-second-order rate equation. This study clearly demonstrated that ferric-loaded biochar derived from burley tobacco stems could serve as a cost-effective magnetic adsorbent for the high-efficiency removal of soluble Cr(VI) from wastewater. Tobacco stem-adsorbed Cr(VI) realized a green path for treating waste by waste.

Recyclable Functionalized Material for Sensitive Detection and Exceptional Sorption of Hexavalent Chromium and Permanganate Ions with Biosensing Applications

Environmental remediation with a single platform for selective sensing and removal of toxic analytes with recyclability of the material has always been a desirable system for sustainability. However, materials comprising all the abovementioned advantages are rarely known for oxoanions. We herein developed a fluorogenic napthalimide-based functionalized mesoporous silica material (SiO₂@NBDBIA) as a signaling and remediation system for oxoanions (CrO₄^2-, Cr₂O₇^2-, and MnO₄^-) from a pool of several anions. The fluorescence quenching of the SiO₂@NBDBIA material in the presence of CrO₄^2-, Cr₂O₇^2-, and MnO₄^- ions gives the limit of detection (LOD) values of 6.23, 25.2, and 20.32 ppb, respectively, which are well below the maximum contaminant level demarcated by the United States Environmental Protection Agency. The maximum adsorption capacities of the material for the abovementioned oxoanions are found to be 352, 363, and 330 mg/g, respectively, which are well above those mentioned in the literature reports. Contrary to the literature-dominated irreversible ion-exchange mechanism, the reversible hydrogen-bonded binding of the material with the oxoanions leads to the recyclability of the material easily, which is very rare in the literature. The DFT calculations were performed to examine the interactions between the material and oxoanions. For real applications, this material was also used as a fluorescence probe to detect these oxoanions in the actual water samples, and more interestingly, used as a biosensing probe for these oxoanions in the living organism Artemia salina through fluorescence imaging. Thus, the SiO₂@NBDBIA material is a unique example of recyclable material for detecting and remediating oxoanions.

Adsorption of Co(II) from aqueous solution using municipal sludge biochar modified by HNO3

Here adsorption studies were proposed on a carboxylated sludge biochar (CSB) material modified by HNO₃ to assess its capacity in the removal of cobalt from aqueous solution. The as-prepared sludge biochar material was characterized by Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The isotherm process could be well described by the Langmuir isotherm model. The adsorption kinetics indicated that cobalt adsorption followed a pseudo-second-order kinetics model. The mechanism between Co(II) and biochar involved electrostatic interaction, ion exchange, surface complexation and physical function. The adsorption capacity on CSB was as high as 72.27 mg·g^-1, surpassing original sludge biochar (SB) as CSB had abundant oxygen-containing functional groups and many hydroxyls, plus the BET surface areas increased when SB was modified by HNO₃, which stimulated adsorption effect. Therefore, this work shows that CSB could be used as an efficient adsorbent to remove Co(II) in wastewater.

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

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

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

Nonlinear regression analysis and response surface modeling of Cr (VI) removal from synthetic wastewater by an agro-waste Cocos Nucifera: Box-Behnken Design (BBD)

In this study mixture of coconut shell and coir was used for Cr (VI) removal from synthetic wastewater and statistical tool Response Surface Modeling (RSM) was applied to optimize process parameters. The solution pH (2-6), reaction time (20-100 minutes) and adsorbent quantity (0.03-0.2 g) was optimized to find the maximum response of Cr (VI) removal using statistical Box-Behnken design (BBD) software. The equilibrium data obtained by the batch experiment were analyzed by ANOVA and found fitted in a second-order polynomial equation through multiple regression analysis. The optimum value of pH, adsorbent quantity and reaction time for 99% of Cr(VI) was found as 2, 0.1 g and 100 minutes, respectively. By using non-linear regression method it was found that Freundlich isotherm and Pseudo-second-order kinetic with high correlation coefficient (R²), low Chi-square (χ²) and root mean squares errors (RMSE), best describe the adsorption of Cr (VI) on mixture of coconut shell and coir (MCSC) surface. Positive enthalpy (ΔH°) and negative Gibbs free energy (ΔG^o) values confirm the endothermic and spontaneous nature of adsorption process. Pre and post adsorption phenomenon was confirmed by characterization of adsorbent using AFM, FTIR, SEM, and EDX analysis. The adsorbent MCSC has regenerative property and can be reused 3-4 times after treating with alkaline medium (0.2 N NaOH) and offered more than 60% removal of Cr (VI) at the fourth cycle. It can be inferred based on this study that MCSC is an effective adsorbent for Cr (VI) removal and can be used on an industrial scale for social and environmental benefit. Novelty statement An agriculture waste mixture of coconut shell and coir (MCSC) without the addition of any chemical reagent, was used for Cr(VI) removal. As per literature survey and best of our knowledge, the adsorbent MCSC has not been reported for Cr (VI) removal. In the previous study, authors reported either coconut coir pith or coconut shell or coconut charcoal as adsorbent for Cr (VI) removal. The adsorbent MCSC is efficient even at very low doses (0.1 g) as compared to the reported adsorbent.

Nitrogen and sulfur codoped micro-mesoporous carbon sheets derived from natural biomass for synergistic removal of chromium(VI): adsorption behavior and computing mechanism

We reported the effective removal of chromium(VI) (Cr(VI)) from wastewater with nitrogen and sulfur codoped micro-mesoporous carbon sheets (N,S-MMCSs), which were fabricated by pyrolysis of natural biomass (luffa sponge) followed by chemical activation and hydrothermal treatment. N,S-MMCSs possessed a hierarchical micro-mesoporous sheet-like framework, large specific surface area (1525.45 m² g^-1), high pore volume (1.21 cm³ g^-1), and appropriate N (1.81 wt%) and S (1.01 wt%) co-doping. Batch adsorption experiments suggested that Cr(VI) adsorption by the N,S-MMCSs increased with increase the solution acidity, adsorbent dosage, Cr(VI) concentration, temperature, and time. The Cr(VI) adsorption was mainly controlled by the chemisorptions and could be well interpreted by the Langmuir isotherm and pseudo-second-order kinetic models. The maximum adsorption capacities of Cr(VI) were 217.39, 277.78, and 312.50 mg g^-1 at 298, 308, and 318 K, respectively. The Cr(VI) adsorption procedure was spontaneous, endothermic, and randomness. The Cr(VI) adsorption mechanism followed the physical adsorption, electrostatic attraction, in situ reduction, and surface chelation. Besides, the density functional theory (DFT) calculation demonstrated that the N and S co-doping could decrease the adsorption energy and enhance the attractive interaction between N,S-MMCSs and Cr(VI) through the synergistic effect, and thus significantly improve the Cr(VI) adsorption property.

Effective removal of Cd(II) from aqueous solution based on multifunctional nanoporous silicon derived from solar kerf loss waste

Recycling of kerf-loss slurry waste has become a meaningful and urgent issue in recent years. In this study, a novel hybrid material was prepared by Ag-assisted chemical etching kerf loss silicon waste and subsequently functionalized by a facile three-step graft process of 3-aminopropyltrimethoxy-silane, maleic anhydride, and ethylenediamine, named as EDA-MAH-APTES-NPSi, which could work as an effective adsorbent for removal of Cd(Ⅱ) from aqueous solution. The effect of initial pH, absorption duration, and metal ion concentrations on absorption performance were investigated. The adsorption equilibrium achieved after 120 min, the maximum adsorption capacity reached up to 210.01 mg/g and pH was at 5.5. The adsorption kinetic was fitted in the pseudo-second-order model and the Freundlich equation provided an accurate description for adsorption behavior. The XPS and FT-IR analysis manifested that Cd(Ⅱ) removal might be ascribed to the adsorption on the surface organic functional group by chemical chelating reaction and the ion exchange reaction. The EDA-MAH-APTES-NPSi maintained excellent adsorption capacity which decreased approximately 15.3 % (from 40.5-34.3 mg/g) after five successive regenerated cycles. The work confirms the potential of Cd(Ⅱ) removal from aqueous solution based on the modified NPSi and opens up a new way for recycling silicon cutting waste.

A novel composite of almandine supported humboldtine nanospheres, in situ synthesized from natural almandine, possesses high removal efficiency of Cr(Ⅵ) over a wide pH range

Preparing a cost-effective material which can been applied in a wide pH range is very crucial for the remediation of Cr(Ⅵ) polluted water. In this study, a novel material, almandine/humboldtine nanospheres (AHN) composites, was synthesized directly from almandine by one-pot method. Characterizations of XRD and SEM/TEM showed that the structure changes of almandine to nano-humboldtine leaded to significant increase of Cr(Ⅵ) removal capacities. And 96.45% of Cr(Ⅵ) was removed by AHN-24 composite at pH value of 3, initial Cr(Ⅵ) concentration of 20 mg/L, temperature of 298.15 K and dosage of 0.6 g/L. Furthermore, Cr(Ⅵ) removal capacity was only decreased from 48.23 mg/g to 34.33 mg/g when the initial pH value increased from 3 to 11, which demonstrated that the synthesized composite had a wide pH application range in Cr(Ⅵ) removal. The thermodynamic parameters (ΔG⁰ < 0, ΔH⁰ > 0 and ΔS⁰ > 0) illustrated that Cr(VI) removal process was spontaneous and endothermic. FTIR and XPS revealed that the Cr(Ⅵ) removal mechanisms included reduction-precipitation and reduction-complexation. Combined with cost analysis, all of results implied that the synthesized composites were a high efficient and low cost material for Cr(Ⅵ) pollution remediation in a wide pH range.

Nitrogen containing functional groups of biochar: An overview

Biochar is a carbonaceous material produced by thermal treatment, e.g., pyrolysis, of biomass in oxygen-deficient or oxygen-free environment. Nitrogen containing functional groups of biochar have a wide range of applications, such as adsorption of pollutants, catalysis, and energy storage. To date, many methods have been developed and used to strengthen the function of N-containing biochar to promote its application and commercialization. However, there is no review available specifically on the development of biochar technologies concerning nitrogen-containing functional groups. This paper aims to present a review on fractionation, analysis, formation, engineering, and application of N-functional groups of biochar. The effect of influencing factors on biochar N-functional groups, including biomass feedstock, pyrolysis parameters (e.g., temperature), and additional treatment (e.g., N-doping) were discussed in detail to reveal the formation mechanisms and performance of the N-functional groups. Future prospective investigation directions on the analysis and engineering of biochar N-functional groups were also proposed.

Colloidal Template Synthesis of Nanomaterials by Using Microporous Organic Nanoparticles: The Case of C@MoS2 Nanoadsorbents

The so-called colloidal template synthesis has been applied to the preparation of surface-engineered nanoadsorbents. Colloidal microporous organic network nanotemplates (C-MONs), which showed a high surface area (611 m²  g^-1 ) and enhanced microporosity, were prepared through the networking of organic building blocks in the presence of poly(vinylpyrrolidone) (PVP). Owing to entrapment of the PVP in networks, the C-MONs showed good colloidal dispersion in EtOH. MoS₂ precursors were incorporated into the C-MONs and heat treatment afforded core-shell-type C@MoS₂ nanoparticles with a diameter of 80 nm, a negative zeta potential (-39.5 mV), a high surface area (508 m²  g^-1 ), and excellent adsorption performance towards cationic dyes (q_max =343.6 and 421.9 mg g^-1 for methylene blue and rhodamine B, respectively).

A novel superparamagnetic micro-nano-bio-adsorbent PDA/Fe3O4/BC for removal of hexavalent chromium ions from simulated and electroplating wastewater

In order to improve the adsorption efficiency of the adsorbent and solve the problem of separation difficulty, a novel superparamagnetic micro-nano-bio-adsorbent (PDA/Fe₃O₄/BC) was prepared by in situ self-assembly of polydopamine (PDA). The results of scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), X-ray photoelectron spectrometer (XPS), and vibrating sample magnetometer (VSM) characterization showed that the size of bio-adsorbent was about 200 nm. PDA and Fe₃O₄ modifications increased the specific surface area of adsorbent, changed the surface functional group of biochar (BC), and made the adsorbent have super-high magnetization (294.76 emu g^-1). PDA/Fe₃O₄/BC was applied to treat Cr wastewater. The results show that the adsorption of Cr by PDA/Fe₃O₄/BC includes single-layer and multilayer adsorption. The adsorption follows the pseudo-second-order kinetic model. The adsorption is spontaneous and endothermic, and its maximum adsorption capacity and activation energy are 25.25 mg g^-1 at 318 K and 23.108 kJ mol^-1, respectively. After adsorption treatment, PDA/Fe₃O₄/BC still possesses high magnetization (233.04 emu g^-1). PDA/Fe₃O₄/BC can treat actual electroplating wastewater with Cr(VI) concentration from 20 mg L^-1 to less than 0.2 mg L^-1, which met the PRC discharge standard (GB/21900-2008) of electroplating pollutants. Graphical abstract.

Skeleton Carbonylation of Conjugated Microporous Polymers by Osmium Catalysis for Amine-Rich Functionalization

This work introduces a new efficient method for the postsynthetic modification of conjugated microporous polymers (CMPs). Osmium catalysis of hollow CMP (H-CMP) in the presence of NaClO₃ resulted in the conversion of alkynes in the skeleton of CMPs to dicarbonyl groups to form H-CMP-DC. Through controlling the reaction time, the carbonylation degree of H-CMP could be managed, maintaining hollow morphology. We verified the benefits of carbonyl groups in H-CMP-DC in the removal of Cr(VI) from water. Imination of H-CMP-DC resulted in amine-rich H-CMP (H-CMP-A), which showed enhanced adsorption performance toward Cr(VI) in water with q_max up to 73 mg/g, compared with the H-CMP and H-CMP-DC. The H-CMP-A could be recycled at least five times, maintaining its original adsorption ability.

Enhanced Cr(VI) removal from acidic solutions using biochar modified by Fe3O4@SiO2-NH2 particles

Fe₃O₄@SiO₂-NH₂ magnetic particles with core-shell structure were attached on carboxylated biochar derived from phoenix tree leaves to synthesize a novel magnetic biochar for removing Cr(VI) ions from acidic solutions. FSEM, FTEM, XRD characterizations of the synthesized magnetic biochar revealed that the Fe₃O₄@SiO₂-NH₂ magnetic particles distributed uniformly on the surface or macrospores of carboxylated biochar by strong chemical bonding. The Cr(VI) ions adsorption capacity of magnetic biochar was 27.2mg·g^-1, surpassing original carboxylated biochar (18.2mg·g^-1). VSM and XPS characterizations demonstrated that the attached Fe₃O₄@SiO₂-NH₂ magnetic particles not only endowed biochar with perfect magnetic property (23emu·g^-1) but also provided complexing sites for binding Cr(III) cations reduced from Cr(VI) anions. The Cr(VI) ions removal by magnetic biochar contained three steps: (1) adsorption of Cr(VI) anions by protonated functional groups; (2) reduction of Cr(VI) anions to Cr(III) cations by electron-donor groups; and (3) chelation of Cr(III) cations by amine groups. The adsorption recycling test showed that magnetic biochar kept 85% of its initial Cr(VI) adsorption capacity at the sixth cycle, and the Fe leakage under pH1.0 was smaller than 0.25mg·L^-1. The results indicated that this novel magnetic biochar was applicable for the practical treatment of Cr(VI)-containing wastewater.

Enhanced removal of hexavalent chromium from aqueous media using a highly stable and magnetically separable rosin-biochar-coated TiO2@C nanocomposite

Recently, nanosized metal-oxides have been extensively investigated for their ability to remove metal ions from aqueous media. However, the activity and capacity of these nanosized metal-oxides for removing metal ions decrease owing to their agglomeration in aqueous media. Herein, we synthesized a highly stable and magnetically separable rosin-biochar-coated (RBC) TiO₂@C nanocomposite through a facile and environment-friendly wet chemical coating process, followed by a one-step heating route (pyrolysis) for efficient removal of Cr(vi) from aqueous solution. An array of techniques, namely, TEM, HRTEM, TEM-EDS, XRD, FTIR, VSM, BET and TGA, were used to characterize the prepared nanocomposite. The pyrolysis of rosin into biochar and the fabrication of Fe onto the RBC-TiO₂@C nanocomposite were confirmed by FTIR and XRD examination, respectively. Moreover, TEM and HRTEM images and elemental mapping using TEM-EDS showed good dispersion of iron and carbon on the surface of the RBC-TiO₂@C nanocomposite. Sorption of Cr(vi) ions on the surface of the RBC-TiO₂@C nanocomposite was very fast and efficient, having a removal efficiency of ∼95% within the 1^st minute of reaction. Furthermore, thermodynamic analysis showed negative values of Gibb's free energy at all five temperatures, indicating that the adsorption of Cr(vi) ions on the RBC-TiO₂@C nanocomposite was favorable and spontaneous. Conclusively, our results indicate that the RBC-TiO₂@C nanocomposite can be used for efficient removal of Cr(vi) from aqueous media due to its novel synthesis and extraordinary adsorption efficacy during a short time period.

A biochar-coated RBC-TiO₂@C nanocomposite was synthesized using a wet chemical coating followed by a one-step heating route (pyrolysis) for the efficient removal of Cr(vi).

Nitrogen-functionalization biochars derived from wheat straws via molten salt synthesis: An efficient adsorbent for atrazine removal

N-doped porous carbon sheets (NPCS) resulted from wheat straws are fabricated through using molten salts via the carbonization-functionalization progress, which show unique hierarchical structure, large pore volume and high surface area with affluent micropores. Results indicate that there exist many hierarchical pores consisting of the single carbon sheet with ultrathin nature, owing to the template role of molten salt mixtures at high temperature. Such superior structure can bring about desired performance of adsorption capacity of 82.8mg/g and quick adsorption rate of 1.43L/(gh) with an initial concentration of 35mg/L at 25°C. Langmuir and Freundlich models are adopted to interpret the adsorption behavior of atrazine and modified Freundlich and intraparticle diffusion (IPD) models are employed to characterize the dynamics of adsorption. Furthermore, nitrogen-functionalization biochars via molten salt synthesis should be further developed as a one-pot methodology to produce N-doped carbons, opening up a feasible approach for resource utilization of crop straws and other biomass wastes.

Highly efficient removal of hexavalent chromium in aqueous solutionsviachemical reduction of plate-like micro/nanostructured zero valent iron

The plate-like micro/nanostructured zero valent iron has exhibited the significantly enhanced ability to remove Cr(vi) from the real electroplating wastewater compared with the commercial zero valent iron.