Search

Graphical abstract Highlights • A facile approach to prepare N-doped carbon materials was developed. • N-doped biochar was synthesized by simply ball milling pristine biochar with NH 3 ·H 2 O. • NH 2 and C N were loaded on biochar through the dehydration of COOH and OH. • N-doped biochar showed enhanced sorption for CO 2 and reactive red in comparison to N-free biochar. Abstract 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 CO 2 uptake and reactive red removal were evaluated. Most of N introduced to biochar was loaded on its surface in forms of NH 2 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 CO 2 and anionic reactive red. For example, the CO 2 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • H 2 O 2 -modified ball-milled biochar were synthesized to adsorb methylene blue (MB). • H 2 O 2 modification increased the oxygen-containing functional groups of biochar. • H 2 O 2 modification improved the adsorption capacity of biochar to MB. In this work, hickory chip biochars developed at distinctive pyrolysis temperatures were ball milled (BMHC) and then post-modified with a 10% hydrogen peroxide (H 2 O 2) solution to obtain a set of novel sorbents (BMHC-H 2 O 2). The specific surface area (SSA) was dramatically increased after ball-milling while the hydroxyl and carboxyl groups on the surface of the biochars were further increased through H 2 O 2 modification. Additionally, thermal stability of the biochar treated with ball-milling was not greatly reduced by H 2 O 2 modification and hydrodynamic radius was decreased. Ball milling enhanced the adsorption efficiency to methylene blue (MB) by the biochar, and this ability was further increased by H 2 O 2 modification, because of the increasing in oxygen-containing functional groups (OCFG) to interact with MB. The rate of MB adsorption to BMHC-H 2 O 2 was faster than that of BMHC, reaching equilibrium after about 6 h. Among adsorbents tested, the 450 °C BMHC-H 2 O 2 had the greatest MB adsorption capacity (310 mg g−1). [ABSTRACT FROM AUTHOR]

A facile ball-milling method was developed to synthesize MgO/biochar nanocomposites as a dual-functional adsorbent. The physicochemical properties of the synthesized nanocomposites indicated that the composites achieved nano-scaled morphologies and mesoporous structure with MgO nanoparticles, which is approximate 20 nm and dispersed uniformly on the surface of the biochar matrix. Batch sorption experiments yielded 62.9% removal of phosphate, an anion, and 87.5% removal of methylene blue, a cationic organic dye, at low adsorbent dosages of 1.0 g L−1 and 0.2 g L−1, respectively. This work indicates that ball milling, as a facile and promising method for synthesis of carbon-metal oxide nanocomposites, lends the advantage of operational flexibility and chemical adjustability for targeted remediation of diverse environmental pollutants. Image 1 • Solvent-free synthesis of MgO/biochar nanocomposites was achieved through ball milling. • MgO nanoparticles (20 nm) dispersed uniformly on the surface of the biochar matrix. • MgO/biochar nanocomposites showed dual functions to effectively adsorb cationic dye and anionic phosphate. • Ball milling method has the advantage of operational flexibility and chemical adjustability. [ABSTRACT FROM AUTHOR]

In this paper, bismuth oxybromide (BiOBr)/biochar composites were synthesized by a facile ball milling method for synergistic adsorption and photodegradation of Reactive red 120 (RR120). The characterizations show that ball milling changed the degree of crystallization, increased the surface area, and promoted the charge transfer ability of biochar. The 70% BiOBr/BC composite showed the best removal efficiency for RR120 removal with or without light illumination, which proves its enhanced removal ability by adsorption and photodegradation. The biochar is served as a support of BiOBr for preventing its aggregation and a transporter of charges for promoting the separation of photo-induced carriers in composites. BiOBr can release the adsorption sites on the surface of composites by degradation, which facilitated the RR120 removal and regenerated the photocatalyst for reusing. The strong interactions between BiOBr and biochar in composites resulted from ball milling were beneficial for the charge transfer and synergistic removal of adsorption and degradation. Findings of this work indicate that ball milling method is an effective method to prepare highly efficient biochar-based composites for RR120 removal through synergistic adsorption and photodegradation. [Display omitted] • BiOBr/biochar composites were firstly synthesized by ball milling method. • Biochar increased the surface area and promoted charge transfer in composites. • There were strong interactions between BiOBr and biochar after ball milling. • Synergy between adsorption and photodegradation in BiOBr/biochar is elucidated. [ABSTRACT FROM AUTHOR]

There are challenges in developing multifunctional materials that can not only effectively adsorb but also completely eliminate organic contaminants in water. In this work, novel ZnO/biochar nanocomposites were synthesized using a facile ball-milling method. A series of characterization results showed that the ZnO nanoparticles dispersed uniformly on carbon surface within the biochar matrix. Ball milling increased the mesopores and macropores of the nanocomposites by breaking biochar and squeezing ZnO. The addition of appropriate amount of ZnO into biochar enhanced both the adsorption capacity and photocatalytic ability of the nanocomposites for methylene blue (MB) removal. When the initial concentration of MB was 160 mg/g, the nanocomposites exhibited high MB removal efficiency (up to 95.19%) under visible light through the combination of adsorption and photocatalysis. This work provides a feasible synthesis of metal oxide/biochar nanocomposites with excellent adsorption and photocatalysis properties for the treatment of organic dye wastewater. [Display omitted] • ZnO/biochar nanocomposites were fabricated through simple ball milling. • Varied sized ZnO nanoparticles dispersed uniformly in the biochar matrix. • Ball milling increased the mesopores and macropores of nanocomposites. • Adsorption and photocatalytic activity were enhanced with proper ZnO addition. • BZ-X exhibited efficient MB removal by combining adsorption and photocatalysis. [ABSTRACT FROM AUTHOR]

As the first of its kind, a novel biochar/iron oxide composite (BM-Fe-HC) was successfully prepared by simply ball milling iron-laden biochar (Fe-HC). The performance and mechanisms of Cr(VI) removal by BM-Fe-HC were investigated. Ball milling effectively reduced particle size, increased specific surface area, more importantly, enhanced the distribution and increased the exposure of iron oxides on biochar surface. As a result, Cr(VI) removal by BM-Fe-HC showed fast kinetics and large adsorption capacity with the Langmuir maximum capacity of 48.1 mg/g, higher than that of other biochar/iron composites reported in the literature. Acidic pH promoted Cr(VI) removal while competition ions (Cl-, SO 4 2- and PO 4 3-) inhibited Cr(VI) removal by BM-Fe-HC. Comparison of pre- and post-adsorption samples revealed that iron oxides of the BM-Fe-HC played the dominant role in the adsorption and reduction of Cr(VI) during the removal. After adsorption, part of adsorbed Cr(VI) was reduced by Fe(II) and then stabilized by Fe(III) in the form of amorphous Cr x Fe 1−x (OH) 3 on the composite surface. All the results demonstrate that novel ball-milled biochar/iron oxide composites can be used as an effective adsorbent to remove Cr(VI) from water. [Display omitted] • Ball milling iron-laden biochars produced novel biochar/iron oxide composites • Ball milling increased the exposure of iron oxides on biochar surface • Ball-milled biochar/iron oxide composites showed enhanced removal of Cr(VI) • Iron oxides of the composites are the main sites that can adsorb and reduce Cr(VI) [ABSTRACT FROM AUTHOR]

Pristine and ball milled wheat stalk biochars pyrolysed at 300 °C, 450 °C, 600 °C were studied for tetracycline hydrochloride (TCH) adsorption from aqueous solution. Surface characteristics of ball milled biochar (BM-biochar) were significantly enhanced over their pristine counterparts. TCH adsorption occurred largely on external surface and by filling pores of biochars as evidenced by strong positive correlation between adsorption and external specific surface area (SSA), total pore volume, or mesoporous volume. A two-stage intra-particle diffusion model, limited by the TCH diffusion through the boundary liquid layer, well described TCH adsorption. Maximum TCH adsorption occurred at about pH = 6–8. While solution cations including Na+, K+ and Mg2+ subdued TCH adsorption as they competed for adsorption sites, Ca2+ promoted TCH adsorption due to formation of tetracycline-Ca2+ complexes. The best performing BM-biochar was the one pyrolysed at 600 °C with TCH adsorption amount of 84.54 mg/g. Therefore, this BM-biochar has the potential for TCH removal from aqueous solutions. And the research shed light on the management of organic contaminants in real wastewater by BM-biochar. Image 1 • Ball milling enhanced external specific surface area and mesoporous volume of biochar. • Ball milling increased sorption ability of biochars to TCH. • TCH adsorption by BM-biochars was controlled by surface adsorption and pore filling. • TCH adsorption on BM-biochars was affected by pH and cation in solution. [ABSTRACT FROM AUTHOR]