Low Metal Leaching Research Articles

The effect of biopolymer stabilisation on biostimulated or bioaugmented mine residue for potential technosol production

Mine waste can be transformed into technosol as an ecological strategy. Despite its importance to soil functions, biological activity is often overlooked. Biopolymers can serve as innovative tools for bioremediation, facilitating chemical reactions and creating networks to encapsulate contaminants. This work aims to assess the use of bioleached and stabilised residues from a tungsten mine for technosol production. The first objective was to evaluate mine tailings for their bioleaching potential by biostimulation or bioaugmentation with strain Diaphorobacter polyhydroxybutyrativorans B2A2W2. The second was to evaluate the effect of Portland cement or biopolymers such as Carboxymethyl Cellulose (CMC) or Xanthan Gum (XG) on the stabilisation of bioleached residues. The impact of biopolymers on residues’ characteristics, such as metal leaching, number of cultivable microorganisms, compression strength and ecotoxicity was evaluated using flow systems. Over time, bioleached metallic elements decreased, except for iron (Fe). Biostimulated and stabilised residues exhibited similar trends; both CMC and cement showed low leaching rates and viable microorganisms in the same order (106 CFU × ml−1). However, bioaugmented residue stabilised with XG showed 106 CFU × ml−1 viable microorganisms and increased 2.2-fold Fe leaching than BA_Control. CMC addition to bioaugmented residue reduced 5.9-fold Fe leaching and increased 100-fold viable microorganisms. By utilising both biological and engineering approaches to characterise the technosol, this study contributes to advancing knowledge of technosol production. The residues biostimulated and stabilised with CMC produced a material useful for bio-applications, with low toxicity and metal leaching, useful for bio-applications. XG was the best stabiliser for geotechnical engineering applications, with improved compression strength. In conclusion, the study demonstrates the usefulness of biopolymer treatment for residues and emphasises the importance of selecting the appropriate biopolymer for the intended function of technosols.

Hydrodeoxygenation of Isoeugenol-derived Model Compound over Carbon-supported Pt and Pt-SnS Catalysts for the Production of Sustainable Jet Fuel.

This study focuses on the sustainable production of bio-jet fuel through the catalytic hydrodeoxygenation (HDO) of isoeugenol (IE). Properties of two spraying synthesis methods (in situ and ex situ metal doping) with different platinum (Pt) loading percentages. The catalyst was characterised using various techniques such as XAS, X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis. The HRTEM and FESEM results show the successful preparation of a spherical nanoparticle doped over activated carbon, and Pt was dispersed on the outer shell of the particles. The catalytic HDO of IE showed a high yield and conversion as follows: IE conversion of 100%, liquid-phase mass balance of 95.92%, dihydroeugenol conversion of 99.32%, propylcyclohexane yield of 88.94% and HYD yield of 76.19%. Moreover, the catalyst exhibited high reusability with low metal leaching and high coke resistance for 10 cycles. The catalyst was evaluated in a continuous flow reactor for 100 h at different reaction temperatures, and interestingly, the catalyst showed low deactivation with a high half-time.

Efficient peroxydisulfate activation with γ-Al2O3-C-MIL-100(Fe) framework for sulfamethazine degradation: Enhanced oxidant utilization and reduced metal leaching

Low degradation efficiency and significant transition metal leaching are two challenges in persulfate activation systems based on metal-organic frameworks (MOFs) for organic pollutant degradation. Here, the challenges were solved by designing and synthesizing a micron-sized core-shell material, γ-Al2O3-C-MIL-100(Fe) (γACM), by coating the γ-Al2O3 core with carbon (γ-Al2O3-C) and futher modifying with MIL-100(Fe). Testing γACM with sulfamethazine (SMZ) demonstrated its outstanding peroxydisulfate (PDS) activation, achieving 92.5 % SMZ removal within 20 min at a low oxidant/pollutant ratio. Fe leaching from γACM was effectively inhibited, with only 3.59 % Fe lost after three recycles. The system showed adaptability across a wide pH range, and usability in sewage effluent, indicating promise for practical application. The hydrophobicity of γ-Al2O3-C, the coordinatively unsaturated sites in MIL-100(Fe), and the strong bounding of MIL-100(Fe) on γ-Al2O3-C ensured the effective SMZ gather, PDS activation, and Fe stability respectively, which led to the excellent performances of γACM.

Iron-cobalt loading carbon nitride bimetallic catalyst activates peroxymonosulfate for bisphenol A degradation

In order to reduce metal leaching loss and carbon emissions, an active Peroxymonosulfate (PMS) catalyst (Fe/Co–CN) was prepared using a one-step thermal polycondensation method for the efficient treatment of wastewater containing bisphenol A (BPA). Fe/Co–CN has a low metal leaching (＜1 mg/L) and has good catalytic degradation performance for BPA. The degradation efficiency was 90.7% in 5 min and ∼100% in 10 min, which is much higher than single metal-loaded Fe–CN (77.2%) and Co–CN (73.2%). Nonradical species dominated by 1O2 and high-valent species were the main reactive oxygen species that degraded BPA in the Fe/Co–CN/PMS system. By strictly controlling the energy consumption during the synthesis and application of Fe/Co–CN, lower carbon emissions have been achieved than most catalysts reported. This achievement is of great significance for applying advanced oxidation methods to treat organic micro-pollutants and provides reference for the calculation of PMS catalysts carbon emissions.

Introducing and Boosting Oxygen Vacancies within CoMn2O4 by Loading on Planar Clay Minerals for Efficient Peroxymonosulfate Activation.

CoMn2O4 (CMO) has been recognized as an effective peroxymonosulfate (PMS) activator; however, it still shows disadvantages such as limited reactive sites and metal leakage. Herein, an effective and environmentally friendly composite catalyst, CMO/Kln, was synthesized by anchoring CMO on kaolinite (Kln), a natural clay mineral with a special lamellar structure, to activate peroxymonosulfate (PMS) for the degradation of residue pharmaceuticals in water. The abundant hydroxyl groups located on the surface of Kln helped induce rich oxygen vacancies (OVs) into composite CMO/Kln, which not only acted as additional active sites but also accelerated working efficiency. In addition, compared with bare CMO, CMO/Kln showed lower crystallinity, and the adoption of the Kln substrate contributed to its structural stability with lower metal leaching after three rounds of reaction. The universal applicability of CMO/Kln was also verified by using three other pharmaceuticals as probes. This work shed light on the adoption of natural clay minerals in modifying CMO catalysts with promoted catalytic activity for the efficient and eco-friendly remediation of pharmaceuticals in wastewater.

Enhanced Fenton-like catalysis via interfacial regulation of g-C3N4 for efficient aromatic organic pollutant degradation

For the efficient degradation of organic pollutants with the goal of reducing the water environment pollution, we employed an alkaline hydrothermal treatment on primeval g-C3N4 to synthesize a hydroxyl-grafted g-C3N4 (CN-0.5) material, from which we engineered a novel Fenton-like catalyst, known as Cu–CN-0.5. The introduction of numerous hydroxyl functional groups allowed the CN-0.5 substrate to stably fix active copper oxide particles through surface complexation, resulting in a low Cu leaching rate during a Cu–CN-0.5 Fenton-like process. A sequence of characterization techniques and theoretical calculations uncovered that interfacial complexation induced charge redistribution on the Cu–CN-0.5 surface. Specifically, some of the π electrons in the tris-s-triazine units were transferred to the copper oxide particles along the newly formed chemical bonds (C(π)-O-Cu), forming a π-deficient area on the tris-s-triazine plane near the complexation site. In a typical Cu–CN-0.5 Fenton-like process, a stable π-π interaction was established due to the favorable positive-negative match of electrostatic potential between the aromatic pollutants and π-deficient areas, leading to a significant improvement in Cu–CN-0.5's adsorption capacity for aromatic pollutants. Furthermore, pollutants also delivered electrons to the Cu–CN-0.5 Fenton-like system via a “through-space” approach, which suppressed the futile oxidation of H2O2 in reducing the high-valent Cu2+ and significantly improved the generation efficiency of •OH with high oxidative capacity. As expected, Cu–CN-0.5 not only exhibited an efficient Fenton degradation for several typical aromatic organic pollutants, but also demonstrated both a low metal leaching rate (0.12 mg/L) and a H2O2 utilization rate exceeding 80%. The distinctive Fenton degradation mechanism substantiated the potential of the as-prepared material for effective wastewater treatment applications.

Lanthanum and cerium functionalised forestry waste biochar for phosphate removal: Mechanisms and real-world applications

Phosphorus as a diminishing finite resource, yet is an essential element for the growth of biota. However, elevated concentrations in water can imbalance ecosystems and cause eutrophication. To address both problems, two highly efficient biochars, namely La-OB and CeLa-OB were synthesised by lanthanum and cerium doping. The performance of La-OB and CeLa-OB were evaluated in both batch and dynamic regimes with synthetic phosphate (PO43--P) solutions and eutrophic lake water. PO43--P adsorption mechanisms were investigated in terms of pH, kinetics, isotherms, activation energy, thermodynamics and using in-depth characterisation (XPS, FTIR, XRD, BET, pHpzc and SEM-EDX). The feasibility of using such biochar in ‘real life’ situations was studied with column filtration of lake water with low and high PO43--P concentrations. Reusability/desorption and toxicity in the water environment was also considered. The mechanistic study showed that both biochars predominantly had inner-sphere complexes with La and Ce ligands (as a monolayer), while outer-sphere complexation was less common. The exothermic adsorption process followed the Elovich kinetic and Langmuir isotherm models, with a maximum adsorption capacity of 112 mg/g for La-OB and 40 mg/g for CeLa-OB. In column filtration trials the adsorption capacity reached 78 mg/g, while low metal leaching (0.08 mg/L) and low toxicity to Lepidium sativum germination were detected. The results indicated that these biochars, especially La-OB, could be used in circular economy-based water treatment.

Electro-controlled membrane coupling heterogeneous electro-Fenton (EM-HEF) in treating acetaminophen: performance, mechanism, DFT calculation, and application

The utilization of hybrid electro-Fenton (EF) processes has gained considerable attention, which can combine the advantages of two or more treatment methods resulting in efficient removal of refractory pollutants from water. Here, an electro-controlled membrane coupling heterogeneous EF (EM-HEF) system was constructed for the degradation of acetaminophen (APAP) in water. In the EM-HEF system, a bifunctional ACF/CC-FeOCl-Cu cathode material was synthesized to enhance the HEF reaction, while a tubular Ti microfiltration membrane was used as both cathode and membrane. Degradation experiments indicated the EM-HEF system exhibited remarkable removal efficiency (97.0 %) towards APAP within 30 min under the conditions of flow rate at 60 mL min−1, initial pH at 7.1, and current density at 3 mA cm−2. Notably, the cathode materials showed low metal leaching rate and high APAP removal rate in the 10 cyclic experiments. The common inorganic anions (Cl−, HCO3−, HPO42−, and NO3−) did not inhibit the removal of APAP significantly, whereas humic acid exhibited a more pronounced inhibitory effect only at concentrations exceeding 10 mg L−1. Quenching experiments and electron spin resonance (ESR) tests confirmed the pivotal role of hydroxyl radicals in the decomposition of APAP. Combining density functional theory (DFT) and LC-MS results, three pathways were proposed. The overall toxicity of intermediates was relieved during EM-HEF degradation of APAP. Furthermore, it also achieved good performance in the treatment of landfill leachate, with increasing BOD5/COD ratio from 0.11 to 0.34. This work provides an efficient strategy for the removal of refractory pollutants in water.

Immobilizing cobalt-iron bimetal on Al2O3 by electroless plating-calcination for peroxymonosulfate activation: Performance, mechanistic and practicality

Peroxymonosulfate (PMS) based advanced oxidation processes are promising technologies for emerging contaminants removal and exploring catalysts with high catalytic activity and low metal leaching for PMS activation gets a lot of attention. Herein, Co-Fe/Al2O3 was synthesized by electroless plating-calcination method. Characterizations indicated that Co and Fe were uniformly dispersed on the surface of Al2O3. Results demonstrated that Co-Fe/Al2O3-PMS system could achieve 100 % sulfamethoxazole (SMX) removal with kobs of 0.0552 min−1 under optimal conditions of [PMS] = 0.20 mM, [Co-Fe/Al2O3] = 50.0 mg/L, pH = 6.4. Compared with Co/Al2O3-PMS, Fe/Al2O3-PMS, Co-Fe/Al2O3 alone, and PMS alone, the developed Co-Fe/Al2O3-PMS system achieved a combination of high decontamination efficiency, efficient PMS utilization and insignificant Co leaching. The electrochemistry tests proved the electron transfer speed of Co-Fe/Al2O3 is much higher than that of Co/Al2O3 and Fe/Al2O3, suggesting the synergistic effect of Co and Fe to enhance catalytic activity. The catalytic mechanisms were proposed that both CoII and FeII could react with PMS to initiate activation with SO4•- formation as the major active species and the coexistence of Fe and Co on Al2O3 promoted the heterogeneous redox cycle of CoII/CoIII with CoII involving in PMS activation again. Furthermore, Cl− and H2PO4- facilitated SMX removal, while HCO3− and HA inhibited SMX removal. Co-Fe/Al2O3-PMS system could retain more than 80 % SMX removal within five cycles, indicating good stability and reusability of Co-Fe/Al2O3 for PMS activation. Aniline ring oxidation and isoxazole ring oxidation were proposed as dominant degradation pathways according to the detected intermediates of SMX degradation. This research was instructive to the development of PMS activation induced by supported bimetallic catalysts for wastewater treatment.

Catalytic activation of peroxymonosulfate by intrinsic defects in amorphous carbon: Enhanced electronic transfer and oxygen-functional groups

Inherent defects in carbon material serve as an important way to enhance peroxymonosulfate (PMS) activity, however, the mechanism that activates PMS has always been ambiguous. Herein, the pyrolysis of straw with Prussian blue nanoparticles to prepare CoFe2O4/C (Carbon) was applied to analyze the mechanism of defective amorphous-C catalyzed activation of PMS. Amorphous-C structural defects increased the specific surface area of CoFe2O4/C (from 44.19 to 108.73 m2/g) with triggered electronic rearrangement, resulting in more PMS adsorption. CoFe2O4/C ensured the supply of low-valent metals (≡Co2+ and ≡Fe2+) simultaneously introduced a large number of surface oxygen-containing functional groups, which facilitated free radical generation. The structural defects enhanced electron transfer contributing to the direct oxidative degradation of BPA. Thus, 100 % removal of 450 µM BPA was achieved within 40 min attributed to the combined effect of catalyst-mediated ∙OH, 1O2, and electron transfer. Furthermore, the CoFe2O4/C/PMS system for BPA degradation exhibited universal pH suitability (4 ∼ 10) and low metal leaching (452.10 and 19.53 μg/L for Co and Fe, respectively). This study constructs systematic support for proposing the catalytic mechanism of carbon intrinsic defects activated PMS.

Cobalt nanoparticles embedded in carbon nanotubes with high specific surface area activate peroxymonosulfate to degrade ciprofloxacin

Advanced oxidation method based on sulfate radical (SO4−) are increasingly used to degrade organic pollutants. However, high-efficient and stable catalysts are still needed at this stage. In this study, nitrogen-doped carbon nanotubes coated cobalt nanoparticles (Co@NCNTs) were prepared by a simple and rapid pyrolysis method and employed as a high performance peroxymonosulfate (PMS) activator for degradation of the antibiotic ciprofloxacin (CIP). The Co@NCNTs/PMS system achieved 100 % removal of CIP in 40 min with low metal leaching. The effects of Co@NCNTs on PMS activation under different experimental conditions were investigated. The catalyst maintained excellent catalytic activity in the presence of different anions and humic acids and in a wide pH range (4–9). SO4– was identified as the active substance primarily responsible for removing CIP. The possible degradation pathway of CIP was proposed by analyzing the degradation intermediates of CIP. This work provides a high-performance catalyst to activate PMS for the removal of antibiotic with low metal leaching.

Ce/Fe bimetallic MOF derivatives in situ modified bulk carbon aerogel composite cathode for efficient heterogeneous electro-fenton degradation of chloramphenicol

In this study, we utilized a Ce-modified iron-based metal-organic framework derivative to in situ modify bulk CA (Ce/Fe@C-CA) as a bifunctional composite cathode to degrade chloramphenicol (CAP) in the heterogeneous electro-Fenton (EF) process. The composite cathode exhibited satisfactory CAP degradation efficiency, wide pH adaptability (2–9) and low metal leaching. Under the appropriate conditions (pH = 5, current density = 6 mA/cm2), 94.89% of CAP degradation efficiency was obtained within 60 min. The introduction of Ce increased the oxygen vacancy content, enhanced the cathodic electrochemical activity, promoted the production of a variety of reactive oxygen species and participates in the degradation of CAP, of which ·OH and 1O2 were dominant. Meanwhile, the electron transfer and synergistic catalysis between Ce and Fe promoted the regeneration of the metal active site, which was beneficial to improve the reuse stability of the Ce/Fe@C-CA cathode. The degradation pathway of CAP was obtained by DFT calculations and UPLC-MS/MS detection. This study not only proposed a novel bifunctional electro-Fenton cathode, but also provided a effective strategy for the treatment of actual pharmaceutical wastewater.

Superior performance of oxygen vacancy-enriched Cu-Co3O4/urushiol-rGO/peroxymonosulfate for hypophosphite and phosphite removal by enhancing singlet oxygen

The treatment of wastewater containing hypophosphite [P(I)] and phosphite [P(III)] is challenged by limitations of traditional Fenton oxidation such as low efficiency, secondary pollution and high costs. This study introduced a facile solvent-thermal method to synthesize Cu-Co3O4 nanoparticles uniformly loaded on graphene (Cu-Co3O4/U-rGO) through the reduction and coordination effects of urushiol (U). As prepared Cu-Co3O4/U-rGO exhibited excellent activity in activating peroxymonosulfate (PMS) for the oxidation of P(I)/P(III) to phosphate [P(V)] (0.229 min−1), along with high stability and reusability (91.5 % after 6 cycles), low metal leaching rate (Co: 0.2 mg/L, Cu: 0.05 mg/L), insensitivity to common anions in water and a wide pH range (3–11). The activation mechanism involved the synergistic effects from both urushiol and graphene, which promoted redox of Cu+/Cu2+ and Co2+/Co3+ and induced abundant oxygen vacancies for PMS activation to produce singlet oxygen. Furthermore, the Cu-Co3O4/U-rGO/PMS was also excellent in the oxidative removal of organic phosphorus. This study is expected to advance strategies for the treatment of P(I)/P(III)-rich wastewater and provide new insights for the development of low-cost, highly efficient heterogeneous catalysts with abundant oxygen vacancies.

Insight on the degradation of P-chlorophenol based on the Co-g-C3N4/diatomite composite photo-Fenton process

The non-metallic photocatalyst g-C3N4 is characterized by non-toxicity and straightforward preparation. Still, the drawbacks of low specific surface area and fast carrier complexation rate limit its practical application in photocatalysis. In this work, Co-doped g-C3N4 was prepared on the surface of diatomite (DE) through a simple one-step calcination method and used to degrade 4-chlorophenol (4-CP). Photocatalytic experiments showed that Co-g-C3N4/DE removed up to 98.7% of 4-CP. The doping of Co could capture the photogenerated electrons, thereby reducing the recombination of photocarriers and accelerating the oxidation–reduction reaction of Co3+/Co2+ and H2O2, promoting the generation of OH. Introducing DE improved the aggregation of g-C3N4 and expanded its surface area. Moreover, the Co-g-C3N4/DE composite material exhibited a low metal leaching rate and good reusability throughout the experiments. In addition, based on DFT calculations, the ROS attack mechanism of 4-CP degradation was speculated and calculated. The final product of 4-CP was found to pose a more minor environmental threat, according to the T.E.S.T. In short, the prepared Co-g-C3N4/DE composite realized the capture of photogenerated electrons and the acceleration of photocatalytic reactions, which are expected to solve the challenges in wastewater treatment.

Fe-nanocluster embedded biomass-derived carbon for efficient photo-Fenton-like activity in water purification

Single-atom catalysts (SACs) as photo-Fenton-like catalysts have attracted widespread attention in water purification. However, the development of SACs with renewability, cleanliness, high mass loading, and raw material abundance is a formidable challenge to achieve efficient pollutant removal. In this study, we fabricated high-performance Fe-nanocluster embedded biomass-derived carbon (Fe/Bio-C) from Ficus altissima wastes for quinolone antibiotics degradation. The high-angle annular dark-field scanning transmission electron microscopy with aberration correction (AC-HAADF-STEM) and X-ray absorption fine structure spectroscopy (XAFS) revealed that the Fe/Bio-C exhibited a porous structure with abundant Fe-N4 active sites. The Fe/Bio-C catalysts achieved an exceptional efficiency of 98.6 % for the removal of the representative quinolone antibiotic, namely lomefloxacin (LOM), within 30 min. Furthermore, an in-depth exploration was conducted to assess the influence of reaction parameters on degradation performance, kinetics, toxicity, and mechanism. The free radical quenching experiments and electron paramagnetic resonance (EPR) spectra demonstrated the existence of ·O2−, 1O2, ·OH, SO4·− in the reaction system and the ·O2− radicals played a relatively important role in the degradation progress. This work broaden the avenue for constructing metal-nanocluster photocatalysts with the high reactivity, low metal leaching, and universality to various pollutants.

Enhanced Degradation of Levofloxacin through Visible-Light-Driven Peroxymonosulfate Activation over CuInS2/g-C3N4 Heterojunctions.

In this work, the heterojunctions of CuInS2 embedded in the g-C3N4 materials (xCuInS2/g-C3N4, abbreviated as xCIS/GCN) was successfully prepared for peroxymonosulfate (PMS) activation under visible light. The catalysts are characterized by different techniques, such as XRD, FTIR, SEM, TEM, and UV-vis. The unique heterojunction composites can suppress the recombination of photogenerated pairs. The catalytic results showed that the 3CIS/GCN exhibited excellent catalytic levofloxacin (LVF) degradation efficiency, while more than 98.9% of LVF was removed in 60 min over a wide pH range. SO4•-, O2•-, OH•, and 1O2 were verified as the main reactive species for LVF degradation via the quenching experiments and electron paramagnetic resonance technology (EPR). The synergetic effect of xCIS/GCN, PMS, and visible light irradiation was discussed. The possible LVF degradation pathway was proposed through byproducts analysis (LC-MS). Moreover, the 3CIS/GCN/vis-PMS system has very low metal leaching. Owing to xCIS/GCN having good properties for PMS activation, it has potential applications for LVF or other hazardous pollutants degradation.

Synthesis of magnetic biochar-supported Fe-Cu bimetallic catalyst from pulp and paper mill wastes for the Fenton-like removal of rhodamine B dye

Treating the wastes generated from pulp and paper mills, such as black liquor and Fenton sludge is challenging. In this study, the biochar-supported Fe-Cu bimetallic catalysts were synthesized by a one-step pyrolysis method using Fenton sludge as iron source, acid-precipitated black liquor (APBL) as carbon source and copper nitrate as copper source. The catalysts were used to remove rhodamine B (RhB) dye from aqueous solution by Fenton-like reaction. The optimal catalyst (FeCu@BC600-2) was pyrolyzed at 600 °C with an Fe/Cu mixing ratio of 2 and consisted of mesoporous biochar supported nanoscale Fe3O4 and Cu0. It had a specific surface area of 104.6 m2·g−1 and a saturation magnetization of 33.3 emu·g−1. In the FeCu@BC600-2/H2O2 system, RhB dye (10 mg·L-1) was completely removed within 60 min at acidic pH (initial pH 3, 0.2 g·L-1 catalyst, 1 mM H2O2) or 6 h at neutral pH (initial pH 7, 0.25 g·L-1 catalyst, 25 mM H2O2) at 30 °C. Moreover, the FeCu@BC600-2 exhibited good magnetic separation ability, low metal leaching, excellent reusability and broad applicability to other synthetic dyes. The dye removal mechanism involved the synergistic effect of adsorption and catalytic oxidation (especially heterogeneous catalytic oxidation). At acidic pH, RhB degradation was due to •OH radical, which was generated from the activation of H2O2 by ≡Cu(I) or Cu(I) oxidized from Cu0 and ≡Fe(II) in Fe3O4. At neutral pH, RhB degradation was mainly due to •OH and 1O2 with the former being produced by ≡Cu(I) and ≡Fe(II). Furthermore, Cu(I) oxidized from Cu0 and the active functional groups (such as sp2 C = C) in the biochar facilitated the reduction of Fe(III) to Fe(II), resulting in a high catalytic oxidation efficiency.

Shape stability control of a 3D-printed clay/biochar-based monolith to support Fe catalyst for continuous levofloxacin degradation with low metal leaching

Disposing of wet solid waste sludge has become a prominent issue because it has high environmental risks. Herein, a clay/biochar-based monolith (CBM) is prepared using a three-dimensional (3D) printing design method. The CBM is loaded with iron (Fe) and used as a catalyst (Fe/CBM) to activate peroxymonosulfate (PMS) for degrading levofloxacin (LVF) in an aqueous solution. The monolith preparation process is inexpensive, and the monolith has designable flow paths that facilitate improved mass transport and material recycling. ZnCl2, as a chemical activator, is added to the 3D-printed slurry to improve the catalytic performance of Fe/CBM. Oscillatory stress sweep and frequency sweep tests prove that incorporating ZnCl2-containing sludge in the slurry effectively increases the elastic modulus and critical stress, improving structural stability and constructability. The slurry containing 10% sludge (S10%-Zn with 1 M ZnCl2), exhibits 30% higher static yield stress than the slurry containing only clay and water (S0%). Fe/CBM is prepared by loading Fe active sites onto the surface of CBM via an impregnation method, and it leaches very low amounts of Fe (<0.2 mg/L) and other heavy metals (e.g., Cd, and Pd, etc). Fe/CBM-S10%-Zn/PMS with 10% mass fraction of sludge exhibits much higher (∼80% at 20 min) degradation efficiency than Fe/CBM-S0%/PMS (∼15% at 20 min) and Fe/CBM-S10%/PMS (∼43% at 20 min). Combining with XPS results, when ZnCl2 is added to the slurry, the content of Fe2+ in the catalytic material increases, improving the catalytic performance. The PMS activation mechanism of Fe/CBM-S10%-Zn for LVF degradation is also discussed, which is ascribed to the radical and nonradical pathways. This provides new insights on how to recycle solid waste and make high-performance clay/biochar-based monolith catalysts for the continuous wastewater treatment.

Peroxymonosulfate activation by Co@TiO2 for high-efficiency organic removals

Here we demonstrated that the Co doped anatase titanium dioxide (Co@TiO2) prepared by a facile wet chemical method could activate peroxymonosulfate (PMS) for efficiently degrading a wide range of refractory organic pollutants. The characterization results demonstrated that the doped Co replaced partial Ti while did not bring obvious structural change. The Co@TiO2/PMS system can efficiently remove about 100 % chlortetracycline (CTC) within 40 min and 100 % Rhodamine B (RhB) within 15 min. The Co@TiO2/PMS/CTC system maintained a good catalytic performance over a wide pH range from 3 to 11 and the removal efficiency of CTC improved with increasing pH. The Co@TiO2/PMS system had a good anti-interference ability, which was free from interference by inorganic ions (such as H2PO42-, NO3- and SO42-, etc.) and HA, and also in the different real water matrixes and refractory organic pollutants. Quenching experiments and electron spin resonance (EPR) measurements confirmed that the system had a typical radical process as hydroxyl radical (•OH), sulfate radical (SO4•−) and superoxide radical (O2•−) were the main reactive species for the degradation of CTC. Furthermore, the Co@TiO2 also showed excellent stability and low metal leaching during long-term use because of the excellent chemical and physical stability of TiO2.

Accelerating peroxymonosulfate-based Fenton-like reaction via Mott-Schottky heterojunction

A Mott-Schottky heterojunction is reported to boost the peroxymonosulfate (PMS) activation in Fenton-like reaction through a non-radical path. The heterojunction with Co nanoparticles encapsulated by nitrogen-doped graphitized carbon (N-GC) shell was synthesized via pyrolysis of ZIF67 @ZIF8 and subsequent acidic treatment. Benefiting from Mott-Schottky effect, the electrons were transferred from Co nanoparticles to the N-GC shell, leading to the rearranged electron density on N-GC surface and improvement of the PMS activation. The PMS activation efficiency of heterojunction (86.0%) was much higher than the reference catalyst without Mott-Schottky effect (35.3%), and even comparable to Co2+ (86.2%). 85.0% of tetracycline (TC) removal efficiency was realized after only 10.0 s. Moreover, the intrinsic advantages of non-radical path were well inherited by Mott-Schottky heterojunction, including high anti-interfere property toward various anions, cations and organics, high catalytic activity in a wide pH range, low metal leaching, and high magnetic recyclability.