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Low-cost biochar adsorbent owning great potential for environmental remediation faces a bottleneck in application for its unsatisfied adsorption performance. Compared to the efforts on increasing adsorption capacity, improving adsorption speed which is important for treatment efficiency is often neglected. Herein, a hierarchical porous biochar (HPB) derived from shrimp shell was prepared and exhibited good adsorption capacity (Q m >300 mg/g) and fast adsorptive equilibrium (≤10 min) towards three typical aromatic organics, whose adsorption universality was further proved by two-way ANOVA analysis. Whereafter, model analysis demonstrated that, the adsorptive forms (mono- and multi-layers) on HPB depended on whether the contaminant is charged. Compared to the benzene-ring site of organics, the charged site contributed 5.13 times to adsorption promotion in monolayer but -0.49 times in inhibition for multilayers forms. Simultaneously, functional group sites contributed relatively weak (0.023 to 0.342 times only). Following structural control revealed that, hierarchical pore structure of HPB was the key for the fast adsorption speed, and highly graphitic structure was important for the high adsorption capacity. This study aims to provide an advanced biochar adsorbent, not only in adsorption capacity but also in adsorptive speed, and reveal the relationship between the structure and adsorption performance of biochar. [ABSTRACT FROM AUTHOR]

Highlights • MS-biochar exhibited better catalytic ability than GP, GO and MWCNT. • ASS was the most important contributor for MS-400/600 while CM dominated MS-800. • ASS was effective for SO 4 − formation and CM was primarily committed to OH. • Iron compounds, doped-nitrogen and graphitic carbon were proved as catalytic sites. • Two internal electron transfer paths among MS-biochar's CM were proposed. Abstract Persulfate-based advanced oxidation process is a powerful countermeasure for water remediation, where effective and low-cost catalysts are still needed. Herein, a one-pot synthetic method for magnetic nitrogen-doped sludge biochar (MS-biochar) was presented, which exhibited better catalytic property with PDS for tetracycline degradation than typical graphitic carbon (graphite powder, graphene oxide and multiwalled carbon nanotubes) and two other types biochars. EDAX manifested the uniform dispersion of elements in MS-biochar. Similar to "top-down", a research thought from whole to part of MS-biochar for contribution measurement was presented, where acid-soluble substance (ASS) was the most important contributor for MS-400/600 while carbon matrix (CM) was dominant for MS-800. Quenching and EPR demonstrated a free-radicals pathway in MS-biochar/PDS, where ASS mainly assumed to be effective for SO 4 − and CM was primarily committed to OH generation. EDAX, XPS and Raman studies proved three kinds of catalytic sites, namely the iron compounds, doped nitrogen and graphitic carbon. And their activating mechanism were discussed where one internal electron migration path (from sp3 to nanocrystalline sp2 carbon) has been first proposed. Reusability, metal leaching detection and pharmaceutical wastewater application indicated the potential of MS-biochar. This work not only presents a potential resource-based disposal of sewage sludge, a novel research thought from whole to part for materials performance measurement, but also provides guidance for carbon materials' design for persulfate activation, especially for sp2 and sp3 co-hybridized carbons. [ABSTRACT FROM AUTHOR]

Municipal sewage sludge (MS)-derived biochar shows low-cost superiority as a potential adsorbent in organic contaminants removal, but limited by its poor adsorption capacity and heavy metal leaking risk. Herein, a novel and effective alkali-acid combined method was proposed for its modification and applied to tetracycline adsorption. The associative facilitation between the alkali and acid modifications was explored, and the influences of pyrolysis temperatures on MS-biochar’s properties were investigated. The successfully preserved γ-Fe 2 O 3 vested SNMS-800 with magnetism. It turned out that SNMS-800 exhibited optimum performance for tetracycline removal with adsorption capacity up to 286.913 mg/g, where all goodness-of-fit indexes of isothermal models were measured by MPSD model. The strong adsorption mechanisms were dominated by two considerable interactions, including strong π-π stacking interaction and pore-filling effect due to the significantly enhanced porosity which was proved by density functional theory model calculations. It manifested that appropriate multiple relation (1.7–6 times) between adsorbent’s pore size and adsorbate size closely related to the adsorption strength. The remarkably improved and stable adsorption capacity, extremely low-cost, easy magnetic preparation, and good reusability in natural water samples entrusted SNMS-800 with good potential for actual aqueous contaminant removal on a large scale. Meanwhile, it provides a clue for materials modification starting with its specific components, and supplies a cost-effective way for municipal sewage sludge’s resource disposal. [ABSTRACT FROM AUTHOR]

Despite many studies on single doping (especially N, S) to improve the catalytic performance of biochar in persulfate-based oxidation process (PS-AOP), the investigations of co-doping with multiple heteroatoms for biochar are relatively few. Herein, choosing shrimp shell biochar (NSC-bio, natural N,S co-doped) as research object with exogenous P/S doping, N,S co-doped and N,S,P co-doped biochars were prepared and applied in PS-AOP, respectively. Exogenous S doping (NSC–S-bio) showed a negative effect with the decreased removal efficiency from 88.7% to 45.7%. Quantitative structure-activity relationships analysis showed that, the decreased k obs (0.0692–0.0171 min−1) of NSC-S-bio was linearly related to the decreased Qe (229.0–158.7 mg/g), where the increased electrostatic repulsion during the key catalytic zone by S doping was the key factor. As for NSC-P-bio, a positive effect could be observed (98.9% removal). The increased k obs (0.0692–0.1299 min−1) showed high linear fitting toward P content and specific surface area (449.4–971.6 m2/g) but low fitting degree toward Qe. Further electrochemical characterization revealed that, the increased surface catalytic sites and enhanced electronic conductivity endowed NSC-P-bio improved catalytic performance, which achieved rapid activation of PDS via non-radical electron transfer path and showed selectively toward substrate with electron-donating groups. This study provides new insight for the construction of efficient co-doped biochar catalysts in PS-AOP. [Display omitted] [ABSTRACT FROM AUTHOR]

Finding a low cost and effective alternative to noble metal based catalyst has long been concerned in wastewater treatment and organic transformation. This work developed a highly efficient sewage sludge-based catalyst via a simple one-step pyrolysis method, and for the first time, applied it in the catalytic reduction of nitrophenols. Due to the higher content of graphitic nitrogen, abundant defect sites and low electron transfer resistance, sewage sludge derived biochar obtained at 800 °C (SSBC-800) exhibits the best catalytic performance, with the reaction rate of 0.48 min−1 and turnover frequency for 4-nitrophenol calculated to be 1.25 × 10−4 mmol•mg−1 min−1, which is comparable to or even superior than some reported noble metal-based catalyst. Moreover, SSBC-800 showed good recyclability of 90% 4-nitrophenol removal within 8 min after 4 runs, and maintained high catalytic activity in reduction of other substituent nitrophenols, such as 2-nitrophenol (0.54 min−1), 3-nitrophenol (0.61 min−1) and 2,4-dinitrophenol (0.18 min−1), and in real water samples, indicating its practical applicability. The electron paramagnetic resonance spectra and electrochemical characterization demonstrate that SSBC-800 accelerates the dissociation of BH 4 − to form active hydrogen, which is the main species responsible for 4-nitrophenol reduction, while electron transfer reaction involving the surface bound hydride derived from the intimate contact between BH 4 − and SSBC-800 plays an important role in this process. This research not only provides a novel valorization pathway for sewage sludge, but also sheds new light on further designing of carbon-based catalyst for nitrophenol reduction. [Display omitted] [ABSTRACT FROM AUTHOR]

Fishbone is a major by-product of fishing processing and how to deal with the increasingly generated fishbone has been a big challenge. In an effort to convert the low-value waste into valuable material, this research explores the valorization of fishbone biowaste, which can be transformed into biochar as a persulfate activator for phenol removal. The fishbone derived biochar (FBBC) was prepared by one-step pyrolysis without additional template. The catalytic efficiency of FBBC increases with pyrolysis temperature, with FBBC-800 (pyrolyzed at 800 °C) exhibiting the best performance of 100% phenol (20 mg/L) removal within 60 min at the catalyst dosage of 0.1 g/L, which is comparable to other recently reported carbon-based catalysts but with the advantage of easy preparation, low cost and wastes valorization. The high efficacy of FBBC-800 is related to its large surface area (758.44 m2/g), carbonyl group and defective structure. In the FBBC-800/peroxydisulfate/phenol system, both radical and non-radical pathways are involved, among which hydroxyl radical is more important in radical pathway while singlet oxygen dominates in non-radical pathway. Electron transfer plays a key role in this process through electron capture experiment and electrochemical characterization. This study proposes a new strategy for the valorization of fishbone, and provides the guidance for the structure design of carbon-based catalyst for persulfate activation. Image 1 • A new strategy for fishbone valorization was developed. • The fishbone derived biochar is cost effective and easy to prepare. • High surface area, carbonyl group and defective structure contribute to the catalytic activity. • SO 4 · −, · OH, O 2 · − and 1O 2 were identified in the catalytic reaction. • Electron transfer mechanism for pollutant degradation was proposed. [ABSTRACT FROM AUTHOR]

• An efficient and low-cost catalyst (Ca/BS-800-KOH) was successfully prepared. • Ca/BS-800-KOH showed good phenol removal rate with relatively low dose (0.066 g/L). • The mechanism of PS activation by Ca/BS-800-KOH was addressed. • Free and non-free radical pathways were proposed, where 1O 2 plays a key role. • Ca/BS-800-KOH/PS had a good application potential in organic wastewater treatment. Carbon-based catalysis for green and sustainable degradation of phenol in water and soil has attracted extensive concern. In this study, mesoporous biochar produced by bagasse calcination with KOH and CaCl 2 modified activation (Ca/BS-800-KOH) was used to stimulate persulfate (PS) for the surface oxidation degradation of phenol, which exhibited excellent removal rate of 90% in 60 min (k = 0.0404 min−1) with a relatively low dosage (0.066 g/L). Compared with untreated materials (BS-800, 27% removal rate in 180 min), after KOH and CaCl 2 treatment, the functional groups (C OH), increased porosity, defective structure and the more efficient electron transfer of Ca/BS-800-KOH were probably responsible for its good adsorptive and catalytic performance, which also closely related to the inactivation of Ca/BS-800-KOH. In the (Ca/BS-800-KOH)/PS/phenol system, PS was successfully activated in the presence of catalyst, and radical and non-radical reaction pathways were firstly found, in which the non-radical pathway like 1O 2 accelerated quickly the oxidative degradation of phenol. While in radical pathway involving SO 4 ·− and ·OH, ·OH was the main oxidative species and also played an irreplaceable role in the degradation of phenol. The Ca/BS-800-KOH as a medium promotes the electron transfer between phenol (electron donor) and PS (electron acceptor), in which Ca accelerates the electron transfer rate on the surface of Ca/BS-800-KOH, thereby causing oxidative degradation of phenol. The superior removal efficiencies of common environmental pollutants (all more than 93%) and phenol in water (100%) and soil samples were found. This research proposed an insightful mechanism of the low cost and feasible carbon-material-based PS-AOPs in degrading organic pollutants. [ABSTRACT FROM AUTHOR]

• Prepared biochar (PSS-800) owned hierarchical pore structure. • Adsorption was the key step for the catalytic process. • PSS-800 was dominated by a novel two-electron transfer path. • Porosity and carbon configuration were two crucial impact factors of biochar. Herein, hierarchical porous biochar from shrimp shell (PSS-bio) was prepared and applied for persulfate activation for 2,4-dichlorophenol removal. The pyrolysis temperature was found to play an important role in carbon structure and property modulation, where PSS-bio obtained at 800 °C (PSS-800) exhibited the fastest adsorption capacity and the best catalytic activity with the degradation rates 29 times higher than that of PSS-bio obtained at 400 °C (PSS-400). Further analysis demonstrated that hierarchical pores and carbon configuration were two key impact factors of biochar in AOP. Interestingly, the original free-radical dominated pathway in PSS-400 also changed into a non-radical one (direct two-electron transfer path) in PSS-800, whose efficiency could be somewhat disturbed by pH values, humic acid and anions regardless of their concentrations as low as 5 mM or as high as 500 mM, demonstrating its application potential for the treatment of both highly saline water and organic-rich water. [ABSTRACT FROM AUTHOR]