A multiple Kirkendall strategy for converting nanosized zero-valent iron to highly active Fenton-like catalyst for organics degradation

Electron transfer tuning for persulfate activation via the radical and non-radical pathways with biochar mediator

Electron mediator-based in-situ chemical oxidation (ISCO) offers a novel strategy for groundwater remediation due to diverse reaction pathways. However, distinguishing and further tuning the reaction pathway remains challenging. Herein, biochar as an electron mediator targeted active peroxysulphate (PDS) via the radical or non-radical pathway. Exemplified by the triazin pesticides removal, the complex radical (•OH and SO4•-) and non-radical active species (electron transfer oxidation) were generated and identified in different biochar/PDS systems. The electron transfer process between biochar and PDS was significantly distinguished via an innovatively in-situ visualization of radical pathway, and the electron transfer oxidation non-radical pathway is directly unveiled via a galvanic cell experiment combined with LC-MS analyses. The electron transfer mechanism was revealed via establishing the quantitative structure-activity relationships between biochar and ln kobs. The redox capacity of biochar was assessed as a key for tuning the atrazine degradation by non-radical pathway, and the surface carbon-centered persistent free radicals (PFRs) were identified as key electron donors for triggering the radical pathway. This study gives new insights into the electron transfer mechanism during tuning radical and non-radical activation pathways and the enhanced utilization of oxidants in ISCO technology.

Nitrogen-doped porous hydrochar for enhanced chromium(VI) and bisphenol A scavenging: Synergistic effect of chemical activation and hydrothermal doping

Nitrogen-doped porous hydrochar (NPHC) was successfully synthesized by hydrothermal carbonization and activation with KHCO3, which was employed for scavenging hexavalent chromium (Cr(VI)) and bisphenol A (BPA) in contaminated water. N doping increased the unique active sites such as amino and molecular N in NPHC for adsorbing contaminants, and enhanced the activation effect. Compared to original (HC) and N-doped hydrochar (NHC), the SBET of material improved from 3.99 m2/g and 4.71 m2/g to 1176.77 m2/g. Meanwhile, NPHC exhibited more superior adsorption capacity for Cr(VI) (323.25 mg/g) and BPA (545.34 mg/g) than that of porous hydrochar (213.17 and 343.67 mg/g). Moreover, NPHC possessed pH-dependence and presented more excellent tolerance for interfering ions and regeneration performance. Notably, the Cr(VI) capture by NPHC was dominated via pore filling, electrostatic interaction, reduction, and complexation, while π-π stacking, H-bond interaction, and hydrophobic action were relevant to the binding mechanism of BPA. Overall, the proposed functionalization strategy for biochar was conducive to enhance the remediation of water bodies.

Hydroxylamine hydrochloride-driven activation of NiFe2O4 for the degradation of phenol via peroxymonosulfate

In this study, hydroxylamine hydrochloride (HA) was employed to enhance the activation of NiFe2O4 towards peroxymonosulfate (PMS) for the effective degradation of phenol. NiFe2O4 particles were synthesized via a simple hydrothermal method, followed by characterization of their surface morphology, and microstructure. Upon the addition of HA to the system of NiFe2O4/PMS, the degradation activity is significantly enhanced. The degradation efficiency of phenol reached 98.5% after 60 min using 0.6 g/L NiFe2O4, 3 mmol/L PMS, 2 mmol/L HA at pH 7, which increased by 4.76 times compared to the system without HA. The study further explored the activation mechanism of the NiFe2O4/HA/PMS system, revealing that HA significantly enhanced the conversion of Fe3+/Fe2+ and the leaching of metal ions, thereby accelerating the reaction rate. In addition, the NiFe2O4/HA/PMS system proved effective across a broad range of pH values. This study provides new insights and perspectives into enhancing peroxymonosulfate activation coupled with metal oxides catalysts through the use of reducing agents.

Effective removal of Cr(VI) from water by ball milling sulfur-modified micron zero-valent iron：Influencing factors and removal mechanism

To address the issues of ZVI's susceptibility to oxidation and aggregation, ball milling and Na2S·9H2O modification were employed on ZVI to enhance its efficiency in removing Cr(VI) from effluent. The characterization results expressed that S-mZVIbm had mesoporous and macroporous structures, enabling successful capture of Cr(VI). Moreover, S-mZVIbm had the highest adsorption capacity for Cr(VI) (350.04 mg/g) at pH = 2.00 and reached kinetic equilibrium within 420 min. Furthermore, the adsorption of Cr(VI) by S-mZVIbm conformed to the Avrami-fractional-order model, demonstrated that the adsorption process indicated a complex multi-adsorption process. Meanwhile, the adsorption also fit to Langmuir and Sips models, suggesting monolayer-level adsorption with heterogeneous sites located on S-mZVIbm. The S-mZVIbm could enhance Cr(VI) adsorption through various synergistic mechanisms, such as electrostatic interaction, chemical precipitation, surface complexation, and reduction. Overall, this research presented an innovative perspective for the modification of ZVI, and S-mZVIbm could be widely applied in the practical remediation of wastewater containing Cr(VI).

Customizable Three-Dimensional Printed Zerovalent Iron: An Efficient and Reusable Fenton-like Reagent for Florfenicol Degradation

Zerovalent iron (Fe0)-based Fenton-like technology has great potential for treating recalcitrant organic pollutants (ROPs) in wastewater. However, rapidly and precisely manufacturing Fe0-based materials with the desired geometries is challenging. Herein, novel three-dimensional printed Fe0 (3DP-Fe0) and bimetallic 3DP-Ni/Fe0 were customized by 3D printing for efficient Fenton-like degradation of florfenicol (FLO), a typical antibiotic in wastewater. 3DP-Ni/Fe0 with hydrogen peroxide (H2O2) exhibited superior reactivity toward FLO than 3DP-Fe0, generating hydroxyl radicals (·OH) and atomic hydrogen to achieve >90% dehalogenation and >70% total organic carbon removal within 10 min. The resulting degradation intermediates possessed lower antibacterial activity than FLO and did not cause resistance gene proliferation in activated sludge. The Fenton-like activity of 3DP-Ni/Fe0 was similar across different shapes but increased with increasing porosity and size. Compared with powdered Ni/Fe0, 3DP-Ni/Fe0 exhibited faster electron transfer during Fe(II)/Fe(III) cycling, which increased the utilization efficiency of dissolved Fe2+ and H2O2 for ·OH production. Moreover, 3DP-Ni/Fe0 could be reused >150 times, 5-fold more than powdered Ni/Fe0, owing to its lower metal ion release and Fe0 depletion. 3DP-Ni/Fe0 with H2O2 can also efficiently remove chemical oxygen demand from real wastewater and other ROPs (e.g., acetaminophen, carbamazepine, thiamphenicol, and tetrabromobisphenol A).

Bio-inspired Cu2O cathode for O2 capturing and oxidation boosting in electro-Fenton for sulfathiazole decay

A hydrophobic Cu2O cathode (CuxO-L) was designed to solve the challenge of low oxidation ability in electro-Fenton (EF) for treating emerging pollutants. This fabrication process involved forming Cu(OH)2 nanorods by oxidizing copper foam (Cu-F) with (NH4)2S2O8, followed by coating them with glucose via hydrothermal treatment. Finally, a self-assembled monolayer of 1-octadecanethiol was introduced to create a low-surface-energy, functionalized CuxO-L cathode. Results exhibited an approximately 7.9-fold increase in hydroxyl radical (·OH) generation compared to the initial Cu-F. This enhancement was attributed to two key factors: (Ⅰ) the superior O2-capturing ability of CuxO-L cathode, which led to high H2O2 production due to a 2 nm thick hydrophobic gas layer facilitated O2-capturing; (Ⅱ) a relative high concentration of Cu+ at the CuxO-L cathode promoted the activation of H2O2 into·OH. In addition, the performance of EF with the CuxO-L cathode using sulfathiazole (STZ) as a model pollutant was evaluated. This study offers valuable insights into the design of O2-capturing cathodes in EF processes, particularly for treating emerging organic pollutants.

Acid-modified hydrochar for higher biodegradation rate of atrazine in various conditions by Paenarthrobacter sp. KN0901: Higher cell viability and bacterial number

Microbial remediation is a viable and eco-friendly approach for decontaminating pollution. However, its effectiveness can be limited by the microorganisms' survival and growth in changing environments. Hydrochar materials have been utilized in this study to increase the growth and atrazine degradation capabilities of Paenarthrobacter sp. KN0901, a strain capable of atrazine biodegradation. Acid-modified hydrochars exhibited a higher carbonation rate, specific surface area, and number of defect sites compared to raw hydrochar. Following three days of incubation at 15 °C, the atrazine degradation rate increased from 90.7 % to 98.2 % when utilizing H3PO4-modified hydrochar (PHC). Additionally, the addition of PHC resulted in an increase in both bacterial concentration and cell viability of strain KN0901, by 1.6 and 1.4 times, respectively. Under various conditions, including temperatures of 4 ºC and 35 ºC, as well as pH levels of 5 and 9, and dd·H2O media, PHC exhibited a significant enhancement in atrazine degradation and cell viability of strain KN0901. Furthermore, PHC demonstrated the ability to sustain high proliferation and viability of strain KN0901 over five cycles, indicating its remarkable stability and biocompatibility. This study offers a new perspective on the development and application of bioremediation approaches in restoring atrazine-polluted environments, even under challenging conditions.

A Nanoconfined FeCo2O4-Embedded Ceramic Membrane Regulates Electron Transfer in Peroxymonosulfate Activation to Selectively Generate Singlet Oxygen for Water Decontamination

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs), as a promising technology for water decontamination, are constrained by low reaction kinetics due to limited reaction selectivity and mass transfer. Herein, we designed a nanoconfined FeCo2O4-embedded ceramic membrane (FeCo2O4-CM) under flow-through pattern for PMS activation. Confining PMS and FeCo2O4 within nanochannels (3.0-4.7 nm) enhanced adsorption interactions (-7.84 eV vs -2.20 eV), thus boosting mass transfer. Nanoconfinement effect regulated electron transfer pathways from PMS to FeCo2O4-CM by modulating the active site transformation to ≡Co(III) in nanoconfined FeCo2O4-CM, enabling selectively generating 1O2. The primary role of 1O2 in the nanoconfined system was confirmed by kinetic solvent isotope experiments and indicative anthracene endoperoxide (DPAO2). The system enabled 100% removal of atrazine (ATZ) within a hydraulic retention time of 2.124 ms, demonstrating a rate constant over 5 orders of magnitude higher than the nonconfined system (3.50 × 103 s-1 vs 0.42 min-1). It also exhibited strong resilience to pH variations (3.3-9.0) and coexisting substances, demonstrating excellent stability indicated by consistent 100% ATZ removal for 14 days. This study sheds light on regulating electron transfer pathways to selectively generate 1O2 through the nanoconfinement effect, boosting the practical application of PMS-based AOPs in environmental remediation and potentially applying them to various other AOPs.

Enhanced removal of tetracycline by vitamin C-modified cow manure biochar in water

Vitamin C (VC), due to its chemical properties, can provide more oxygen-containing functional groups such as hydroxyl groups for biochar (BC), which promotes the adsorption of tetracycline on biochar. Therefore, in this study, cow dung biochar (CDBC) was modified with VC and VC-modified CDBC (CDBC-VC) was synthesized. The modified biochar was characterized and related factors, adsorption kinetics, isotherms and adsorption mechanisms were investigated. Adsorption kinetics indicate a fast rate of adsorption. The adsorption isotherms showed that the maximum adsorption capacity was 31.72 mg/g (CDBC) and 50.90 mg/g (CDBC-VC), respectively, and the adsorption process was inhomogeneous with multiple molecular layers and the adsorbent has a higher affinity. Mechanistic studies showed that hydrogen bonding interactions, π-π electron donor-acceptor interactions, hydrophobic interactions, and electrostatic interactions were the key to the adsorption process. The analysis of adsorbent regeneration showed that CDBC-VC had good adsorption performance. CDBC and CDBC-VC showed the best performance in simulated industrial wastewater with removal rates of 78.81% and 93.69%. The adsorption mechanism was comprehensively analyzed using six machine learning models. The extreme gradient boosting model gave the best fit. Analysis of the weights of the input variables for predicting adsorption efficiency showed that the ratio of initial TC concentration to BC dosage (29.8%), specific surface area (23%), isoelectric point (8.8%), and ash content (7.7%) had a significant effect on the predicted results.

Multifunctional biomolecular corona-inspired nanoremediation of antibiotic residues

Facing complex and variable emerging antibiotic pollutants, the traditional development of functional materials is a "trial-and-error" process based on physicochemical principles, where laborious steps and long timescales make it difficult to accelerate technical breakthroughs. Notably, natural biomolecular coronas derived from highly tolerant organisms under significant contamination scenarios can be used in conjunction with nanotechnology to tackling emerging contaminants of concern. Here, super worms (Tubifex tubifex) with high pollutant tolerance were integrated with nano-zero valent iron (nZVI) to effectively reduce the content of 17 antibiotics in wastewater within 7 d. Inspired by the synergistic remediation, nZVI-augmented worms were constructed as biological nanocomposites. Neither nZVI (0.3 to 3 g/L) nor worms (104 to 105 per liter) alone efficiently degraded florfenicol (FF, as a representative antibiotic), while their composite removed 87% of FF (3 μmol/L). Under antibiotic exposure, biomolecules secreted by worms formed a corona on and modified the nZVI particle surface, enabling the nano-bio interface greater functionality, including responsiveness, enrichment, and reduction. Mechanistically, FF exposure activated glucose-alanine cycle pathways that synthesize organic acids and amines as major metabolites, which were assembled into vesicles and secreted, thereby interacting with nZVI in a biologically response design strategy. Lactic acid and urea formed hydrogen bonds with FF, enriched analyte presence at the heterogeneous interface. Succinic and lactic acids corroded the nZVI passivation layer and promoted electron transfer through surface conjugation. This unique strategy highlights biomolecular coronas as a complex resource to augment nano-enabled technologies and will provide shortcuts for rational manipulation of nanomaterial surfaces with coordinated multifunctionalities.

Metal-doped biochar for selective recovery and reuse of phosphate from water: Modification design, removal mechanism, and reutilization strategy

Phosphorus (P) plays a crucial role in plant growth, which can provide nutrients for plants. Nonetheless, excessive phosphate can cause eutrophication of water, deterioration of aquatic environment, and even harm for human health. Therefore, adopting feasible adsorption technology to remove phosphate from water is necessary. Biochar (BC) has received wide attention for its low cost and environment-friendly properties. However, undeveloped pore structure and limited surface groups of primary BC result in poor uptake performance. Consequently, this work introduced the synthesis of pristine BC, parameters influencing phosphate removal, and corresponding mechanisms. Moreover, multifarious metal-doped BCs were summarized with related design principles. Meanwhile, mechanisms of selective phosphate adsorption by metal-doped BC were investigated deeply, and the recovery of phosphate from water, and the utilization of phosphate-loaded adsorbents in soil were critically presented. Finally, challenges and prospects for widespread applications of selective phosphate adsorption were proposed in the future.

Overlooked Roles and Transformation of Carbon-Centered Radicals Produced from Natural Organic Matter in a Thermally Activated Persulfate System

The presence and induced secondary reactions of natural organic matter (NOM) significantly affect the remediation efficacy of in situ chemical oxidation (ISCO) systems. However, it remains unclear how this process relates to organic radicals generated from reactions between the NOM and oxidants. The study, for the first time, reported the vital roles and transformation pathways of carbon-centered radicals (CCR•) derived from NOM in activated persulfate (PS) systems. Results showed that both typical terrestrial/aquatic NOM isolates and collected NOM samples produced CCR• by scavenging activated PS and greatly enhanced the dehalogenation performance under anoxic conditions. Under oxic conditions, newly formed CCR• could be oxidized by O2 and generate organic peroxide intermediates (ROO•) to catalytically yield additional •OH without the involvement of PS. Nuclear magnetic resonance (NMR) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) results indicated that CCR• predominantly formed from carboxyl and aliphatic structures instead of aromatics within NOM through hydrogen abstraction and decarboxylation reactions by SO4•- or •OH. Specific anoxic reactions (i.e., dehalogenation and intramolecular cross-coupling reactions) further promoted the transformation of CCR• to more unsaturated and polymerized/condensed compounds. In contrast, oxic propagation of ROO• enhanced bond breakage/ring cleavage and degradation of CCR• due to the presence of additional •OH and self-decomposition. This study provides novel insights into the role of NOM and O2 in ISCO and the development of engineered strategies for creating organic radicals capable of enhancing the remediation of specific contaminants and recovering organic carbon.

Ball-milled biochar-modified zero-valent aluminum activates peroxodisulfate for phenol degradation: Enhancement of catalysis by membrane-breaking effect

Zero-valent aluminum (ZVAl) is a potential activator for peroxodisulfate (PDS), yet the dense oxide film on its surface hampers electron transfer for the O-O bond cleavage of PDS. We synthesized zero-valent aluminum-biochar (BM-ZVAl@BC) composites through ball milling, which effectively disrupted the native oxide layer on BM-ZVAl@BC. Within the BM-ZVAl@BC/PDS system, biochar (BC) not only suppressed the rapid oxidation of BM-ZVAl@BC but also enhanced the dispersion and electron transfer rate of ZVAl, thereby improving the overall catalytic efficiency. Consequently, the phenol removal efficacy in the BM-ZVAl@BC/PDS system was notably improved. Optimal catalytic performance of the prepared BM-ZVAl@BC was achieved at a charcoal-to‑aluminum mass ratio of 2:1, resulting in 95.7 % phenol removal after 180 min. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that both free radicals (SO4•-, •OH, and O2•-) and non-radical species (1O2) contributed to phenol degradation, with SO4•- and •OH playing predominant roles. In summary, the BM-ZVAl@BC/PDS system represented an effective and promising technology for the remediation of phenolic water pollutants.

Ferruginous components of particulate matters in subway environments, α-Fe2O3 or Fe3O4, exacerbates allergies

The respiratory effects of particulate matter (PM) in subway station platforms or tunnels have attracted considerable research attention. However, no studies have characterized the effects of subway PM on allergic immune responses. In this study, iron oxide (α-Fe2O3 and Fe3O4) particles-the main components of subway PM-were intratracheally administered to BALB/c mice where ovalbumin (OVA) induced allergic pulmonary inflammation. Iron oxide particles enhanced OVA-induced eosinophil recruitment around the bronchi and mucus production from airway epithelium. The concentrations of type 2 cytokines, namely, interleukin (IL)-5 and IL-13, in bronchial alveolar lavage fluids were increased by iron oxide particles. Iron oxide particles also increased the number of type 2 innate lymphoid cells and CD86+ cells in the lung. Moreover, phagocytosis of particles in lung cells was confirmed by Raman spectroscopy. In a subsequent in vitro study, bone marrow-derived antigen-presenting cells (APCs) isolated from NC/Nga mice were exposed to iron oxide particles and OVA. They were also exposed to outdoor ambient PM: Vehicle Exhaust Particulates (VEP) and Urban Aerosols (UA) as references. Iron oxide particles promoted the release of lactate dehydrogenase, C-X-C motif chemokine ligand 1 and IL-1α from APCs, which tended to be stronger than those of VEP. These results suggest that iron oxide particles enhance antigen presentation in the lungs, promoting allergic immune response in mice; iron oxide particles-induced death and inflammatory response of APCs can contribute to allergy exacerbation. Although iron oxide particles do not contain various compounds like VEP, iron oxide alone may have sufficient influence.

Arsenic redistribution associated with Fe(II)-induced jarosite transformation in the presence of polygalacturonic acid

Jarosite exists widely in acid-sulfate soil and acid mine drainage polluted areas and acts as an important host mineral for As(V). As a metastable Fe(III)-oxyhydoxysulfate mineral, its dissolution and transformation have a significant impact on the biogeochemical cycle of As. Under reducing conditions, the trajectory and degree of abiotic Fe(II)-induced jarosite transformation may be greatly influenced by coexisting dissolved organic matter (DOM), and in turn influencing the fate of As. Here, we explored the impact of polygalacturonic acid (PGA) (0-200 mg·L-1) on As(V)-coprecipitated jarosite transformation in the presence of Fe(II) (1 mM) at pH 5.5, and investigated the repartitioning of As between aqueous and solid phase. The results demonstrated that in the system without both PGA and Fe(II), jarosite gradually dissolved, and lepidocrocite was the main transformation product by 30 d; in Fe(II)-only system, lepidocrocite appeared by 1 d and also was the mainly final product; in PGA-only systems, PGA retarded jarosite dissolution and transformation, jarosite might be directly converted into goethite; in Fe(II)-PGA systems, the presence of PGA retarded Fe(II)-induced jarosite dissolution and transformation but did not alter the pathway of mineral transformation, the final product mainly still was lepidocrocite. The retarding effect on jarosite dissolution enhanced with the increase of PGA content. The impact of PGA on Fe(II)-induced jarosite transformation mainly was related to the complexation of carboxyl groups of PGA with Fe(II). The dissolution and transformation of jarosite drove pre-incorporated As transferred into the phosphate-extractable phase, the presence of PGA retarded jarosite dissolution and maintained pre-incorporated As stable in jarosite. The released As promoted by PGA was retarded again and almost no As was released into the solution by the end of reactions in all systems. In systems with Fe(II), no As(III) was detected and As(V) was still the dominant redox species.

Sodium salt promoted the generation of nano zero valent iron by carbothermal reduction: For activating peroxydisulfate to degrade antibiotic

Carbothermal reduction is a promising method for the industrial preparation of nano-zero-valent iron. Preparing it also involves very high pyrolysis temperatures, which leads to a significant amount of energy consumption. The temperature required for the preparation of nano-zero-valent iron by carbothermal reduction was reduced by 200 °C by the addition of sodium salt. Carbon-loaded nano zero-valent iron (Fe0/CB-Na) was prepared by carbothermal reduction through the addition of sodium salt. The results showed that Fe0/CB-Na@700 had the same activation performance as Fe0/CB@900 and the newly prepared nano-zero-valent iron. The addition of sodium salt promoted the transfer of oxygen from the iron oxide to the carbon structure during the roasting process so that the iron oxide was reduced to as much Fe0 as possible. Thus, sodium salts were optimized for the preparation of nano-zero-valent iron by carbothermal reduction through interfacial amorphization and oxygen transfer, thus reducing the preparation cost.

Enhanced thermal desorption of chlorinated hydrocarbons by nanoscale zero-valent iron: the effect of in situ dechlorination

Thermal desorption provides an efficient solution to remediate soil contaminated with chlorinated organic pollutants. However, enhanced desorption efficiency is desired to facilitate easier and less costly remediation. Hence, nanoscale zero-valent iron (nZVI) was combined with thermal desorption to remove trichloroethene (TCE) and trichlorobenzene (TCB) from soil in a laboratory-scale study. The addition of nZVI greatly improved the desorption efficiency, especially at low temperature with 99.6% of TCE and 98.8% of TCB removed at 300 °C for 2 h. Characterization results revealed that the addition of nZVI loosened the structure of soil, preventing the soil from agglomerating during the thermal treatment. Besides, the analyses of dechlorination intermediates and the variation of Fe species proved the in situ dechlorination effect of nZVI and the redox cycle of Fe was revealed. Moreover, the influences of nZVI dosage and treatment time on thermal treatment were assessed. This study not only offers new perspectives for contaminated soil remediation, but also provides mechanistic insights into the dechlorination effect of nZVI in the thermal desorption.

Ultrafast and highly efficient Cd(II) and Pb(II) removal by magnetic adsorbents derived from gypsum and corncob: Performances and mechanisms

The utilization of gypsum and biomass in environmental remediation has become a novel approach to promote waste recycling. Generally, raw waste materials exhibit limited adsorption capacity for heavy metal ions (HMIs) and often result in poor solid-liquid separation. In this study, through co-pyrolysis with corncob waste, titanium gypsum (TiG) was transformed into magnetic adsorbents (GCx, where x denotes the proportion of corncob in the gypsum-corncob mixture) for the removal of Cd(II) and Pb(II). GC10, the optimal adsorbent, which was composed primarily of anhydrite, calcium sulfide, and magnetic Fe3O4, exhibited significantly faster adsorption kinetics (rate constant k1 was 218 times and 9 times of raw TiG for Cd(II) and Pb(II)) and higher adsorption capacity (Qe exceeded 200 mg/g for Cd(II) and 400 mg/g for Pb(II)) than raw TiG and previous adsorbents. Cd(II) removal was more profoundly inhibited in a Cd(II) + Pb(II) binary system, suggesting that GC10 showed better selectivity for Pb(II). Moreover, GC10 could be easily separated from purified water for further recovery, due to its high saturation magnetization value (6.3 emu/g). The superior removal capabilities of GC10 were due to adsorption and surface precipitation of metal sulfides and metal sulfates on the adsorbent surface. Overall, these waste-derived magnetic adsorbents provide a novel and sustainable approach to waste recycling and the deep purification of multiple HMIs.

Photocatalysis Meets Piezoelectricity in a Type-I Oxygen Vacancy-Rich BaTiO3/BiOBr Heterojunction: Mechanism Insights from Characterizations to DFT Calculations

It is a challenging task to design a piezoelectric photocatalyst with excellent performance under mechanical agitation instead of ultrasonic irradiation. Integrating vacancy defects into a heterojunction seems to be an effective strategy for synergistically increasing its piezo-photocatalytic performance. For this goal, a two-step hydrothermal method was adopted to architect a type-I oxygen-vacancy-rich BaTiO3/BiOBr heterojunction to surge the degradation of Rhodamine B (RhB) under the combined action of simulated sunlight irradiation and mechanical agitation. Various instrumental techniques demonstrated the formation of a BaTiO3/BiOBr heterojunction with high crystallinity. The existence of surface oxygen vacancies was confirmed by XPS and EPR tests. PFM results manifested that this heterojunction had excellent piezoelectric properties, with a piezoelectric response value of 30.31 pm V-1. Comparative experiments indicated that RhB degradation efficiency under piezo-photocatalysis over this heterojunction largely exceeded the total sum of those under piezocatalysis and photocatalysis. h+, ·O2-, and 1O2 were the dominant reactive species for RhB degradation. The improved separation efficiency of photogenerated charges was verified by electrochemical measurements. DFT calculations indicated that the polarization of BaTiO3 could affect the electronic band structure of BiOBr. This work will provide comprehensive insights into piezo-photocatalytic mechanism at a microcosmic level and help to develop new-styled piezoelectric photocatalysts.

The application of P-modified biochar in wastewater remediation: A state-of-the-art review

Phosphorus modified biochar (P-BC) is an effective adsorbent for wastewater remediation, which has attracted widespread attention due to its low cost, vast source, unique surface structure, and abundant functional groups. However, there is currently no comprehensive analysis and review of P-BC in wastewater remediation. In this study, a detailed introduction is given to the synthesis method of P-BC, as well as the effects of pyrolysis temperature and residence time on physical and chemical properties and adsorption performance of the material. Meanwhile, a comprehensive investigation and evaluation were conducted on the different biomass types and phosphorus sources used to synthesize P-BC. This article also systematically compared the adsorption efficiency differences between P-BC and raw biochar, and summarized the adsorption mechanism of P-BC in removing pollutants from wastewater. In addition, the effects of P-BC composite with other materials (element co-doping, polysaccharide stabilizers, microbial loading, etc.) on physical and chemical properties and pollutant adsorption capacity of the materials were investigated. Some emerging applications of P-BC were also introduced, including supercapacitors, CO2 adsorbents, carbon sequestration, soil heavy metal remediation, and soil fertility improvement. Finally, some valuable suggestions and prospects were proposed for the future research direction of P-BC to achieve the goal of multiple utilization.

Adsorption interactions between typical microplastics and enrofloxacin: Relevant contributions to the mechanism

Microplastics (MPs) are increasingly contaminating the environment and they can combine with antibiotics as carriers to form complex contaminants. In this study, we systematically investigated the interactions between the antibiotic enrofloxacin (ENR) and MPs comprising polyethylene (PE), polyvinyl chloride (PVC), and polystyrene (PS). Characterization was performed by using conventional techniques and the mechanisms involved in interactions were initially explored based on adsorption kinetics, isotherms, and resolution experiments, and the adsorption capacities of the MPs were determined. In addition, the extended Derjaguin-Landau-Verwey-Overbeek theory was used to investigate the interaction mechanisms. The results showed that the interactions were weaker in strong acidic and alkaline environments, and the interactions were also inhibited at higher salt ion concentrations. The saturation adsorption amounts of ENR on PVC, PE, and PS were 74.63 μg/g, 103.09 μg/g, and 142.86 μg/g, respectively. The interactions between MPs and ENR were dominated by hydrophobic interactions, followed by van der Waals forces and acid-base forces. This study provides new insights into the adsorption behavior of ENR by MPs.

Adsorption behavior of lead, cadmium, and arsenic on manganese-modified biochar: competition and promotion

Biochar adsorption of heavy metals has been a research hotspot, yet there has been limited reports on the effect of heavy metal interactions on adsorption efficiency in complex systems. In this study, the adsorbent was prepared by pyrolysis of rice straw loaded with manganese (BC-Mn). The interactions of Pb, Cd and As adsorption on BC-Mn were systematically studied. The results of the adsorption isotherms for the binary metal system revealed a competitive adsorption between Pb and Cd, resulting in decreased Pb (from 214.38 mg/g to 148.20 mg/g) and Cd (from 165.73 mg/g to 92.11 mg/g). A notable promotion occurred between As and Cd, showing an increase from 234.93 mg/g to 305.00 mg/g for As and 165.73 mg/g to 313.94 mg/g for Cd. In the ternary metal system, Pb inhibition did not counteract the promotion of Cd and As. Furthermore, the Langmuir isotherm effectively described BC-Mn's adsorption process in monometallic, binary, and ternary metal systems (R2 > 0.9294). Zeta and FTIR analyses revealed simultaneous competition between Pb and Cd for adsorption on BC-Mn's -OH sites. XPS analysis revealed that As adsorption by BC-Mn facilitated the conversion of MnO2 and MnO to MnOOH, resulting in increased hydroxyl radical production on BC-Mn's surface. Simultaneously, Cd combined with the adsorbed As to form ternary Cd-As-Mn complexes, which expedited the removal of Cd. These results help to provide theoretical support as well as technical support for the treatment of Pb-Cd-As contaminated wastewater.

Two-step pyrolytic preparation of biochar for the adsorption study of tetracycline in water

In this study, cow dung biomass was converted into biochar (BC). BC900 was obtained through one-step pyrolysis at 900 °C, while BC700-900 and BC900-700 were obtained via two-step pyrolysis at temperature ranges of 700-900 °C and 900-700 °C, respectively. The primary objective was to investigate the adsorption performance and application value of BCs for tetracycline (TC) in water. The samples underwent characterization using scanning electron microscopy and mapping analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. Subsequently, the effects of reaction time, adsorbent dosage, temperature, pH, and ionic strength were analyzed. Based on the fitting results of adsorption kinetics, the pyrolytic BCs exhibited a better fit with the pseudo-secondary kinetic model. The adsorption isotherm indicated monolayer adsorption on the surface of the adsorbents, with maximum adsorption capacities of 158.93 mg/g for BC900-700, 150.15 mg/g for BC700-900, and 142.56 mg/g for BC900, respectively. Furthermore, results from simulated wastewater and regeneration experiments demonstrated that BC900-700 exhibited not only excellent adsorption performance in wastewater but also remarkable regeneration capabilities. The two-step pyrolysis BCs in this study displayed a higher adsorption capacity compared to the one-step pyrolysis BCs in practical applications. These findings provide insights for further exploring the adsorption mechanism and optimizing the process.

Fe/N co-doped magnetic porous hydrochar for chromium(VI) removal in water: Adsorption performance and mechanism investigation

Four kinds of Fe/N co-doped porous hydrochar were prepared by one/two-step N-doping schemes using microwave/traditional pyrolysis methods for removing Cr(VI) from aqueous phase. Heterocyclic-N was introduced through CO(NH2)2-based hydrothermal carbonization process, which could adjust the electronic structure of the hydrochar framework. Furthermore, Fe0 and Fe3O4 were embedded into hydrochar via carbothermal reduction reaction using FeCl3 as the precursor, which improved the reducibility and magnetism of the material. The modified hydrochar exhibited pH-dependency and rapid kinetic equilibrium, and the maximal adsorption amount of magnetic porous hydrochar obtained by microwave-assisted one-step N-doping (MP1HCMW) reached 274.34 mg/g. Meanwhile, the modified hydrochar had a high tolerance to multiple co-existing ions and the removal efficiency maintained above 73.91 % during five regeneration cycles. Additionally, MP1HCMW efficiently removed Cr(VI) via pore filling, electrostatic attraction, ion exchange, reduction, complexation, and precipitation. Summarily, Fe/N co-doped porous hydrochar was a feasible adsorbent with outstanding remediation potential for Cr(VI)-contaminated water.

Phosphoric acid activation of cow dung biochar for adsorbing enrofloxacin in water: Icing on the cake

In this study, we used different concentrations of H3PO4 to activate pristine biochar (BC) derived from cow dung (BC and BC modified with phosphoric acid at concentrations of 10% (10P-BC), 30% (30P-BC), and 50% (50P-BC)) in order to obtain cheap, high-performance adsorbents. Brunauer-Emmett-Teller analysis, scanning electron microscopy, X-ray diffraction, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, organic element composition determination, and other analyses showed that activation with H3PO4 increased the porosity and hydrophilicity compared with the original BC, thereby enhancing the adsorption properties. The Langmuir isotherm model obtained the best fit and the maximum capacities for adsorbing enrofloxacin by BCs were 12.66 mg/g for BC, 51.90 mg/g for 10P-BC, 63.61 mg/g for 30P-BC, and 26.79 mg/g for 50P-BC. The main mechanisms responsible for antibiotic loading on BC were hydrogen bonding, π-π electron donor-acceptor interactions, pore filling, and electrostatic interactions. Calculations of fixed carbon retention before and after pyrolysis, and adsorption showed that activated BC had a good carbon fixation capacity and it was more capable of adsorbing enrofloxacin compared with the original BC, thereby providing a new method for removing organic pollutants from the environment and reducing carbon emissions. The cost efficiency was analyzed using the improved fuzzy comprehensive evaluation model based on the entropy method. Removal efficiency and utilization efficiency indicators were calculated for the different phosphoric acid activated BCs. The pollutant removal efficiencies were better for 10P-BC and 30P-BC, and the optimal removal efficiency was determined for 30P-BC. Given the current global climate change situation, using 10P-BC and 30P-BC could also help to meet China's carbon neutrality goals by reducing emissions of pollutants containing carbon.

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.

Carbon and hydrogen isotopic evidence for atrazine degradation by electro-activated persulfate: Radical contributions and comparisons with heat-activated persulfate

The activation ways of persulfate (PS) were dominate for pollutant degradation and energy consumption. For the first time, this research compared electro-activated PS and heat-activated PS from the perspective of isotope fractionation, in order to "fingerprinted" and precisely interpretate reaction contributions and degradation pathways. As results, PS can be electrochemically activated with atrazine (ATZ) removal rates of 84.8% and 88.8% at pH 4 and 7. The two-dimensional isotope plots (ɅC/H) values were 6.20 at pH 4 and 7.46 at pH 7, rather different from that of SO4·- -dominated process with ɅC/H value of -4.80 at pH 4 and -23.0 at pH 7, suggesting the weak contribution of SO4·-. ATZ degradation by electro-activated PS was controlled by direct electron transfer (DET) and ·OH radical, and ·OHPS (derived from PS activation) played the crucial role with contributing rate of 63.2%-69.1%, while DET and ·OHBDD (derived from electrolysis of H2O) contributed to 4.5-7.9% and 23.0%-30.8%, respectively. This was different from heat activation of PS, of which the latter was dominated by SO4·- with contributions of 83.9%-100%. The discrepant dominating reactive oxygen species should be responsible for their different degradation capabilities and pathways. This research provided isotopic interpretations for differences of PS activation mode, and further efforts can be made to realize the selective degradation by enhancing the specific reaction process.

Superior reduction and immobilization of Cr(VI) in soil utilizing sulfide nanoscale zero-valent iron supported by phosphoric acid-modified biochar: Efficiency and mechanism investigation

A novel strategy was proposed to remediate Cr(VI)-contaminated soil via phosphoric acid-modified biochar supported sulfide nanoscale zero-valent iron (SnZVI@PBC). Results of characterizations revealed that FeSX shell existed in outer layer of nZVI to prevent its oxidation after sulfidation modification, and SnZVI was effectively dispersed owing to the support of PBC, accelerating the electron transport for Cr(VI) reduction. The SnZVI@PBC presented pH-dependence and fast capture for Cr(VI) with outstanding binding amount of 335.55 mg/g. More importantly, the Cr(VI) content declined from 1300.75 to 223.30 mg/kg with conversion into stable Cr(III) in soil after 42 d of remediation with 2.0 % SnZVI@PBC under 60 % moisture content. Furthermore, leaching experiments showed that SnZVI@PBC could effectively immobilize Cr(VI), decreasing its migration and harmful risks to plants and human. Particularly, the fractions of exchangeable and carbonate-bound Cr decreased by 96.77 % and 83.60 %, which transformed to relatively stable fractions. Interestingly, the presence of humic acid, and the freezing-thawing/wetting-drying process promoted the immobilization performance of SnZVI@PBC for Cr(VI). SnZVI@PBC could alleviate the migration and poisonousness of Cr(VI) in soil primarily via reduction, co-precipitation, pore filling, and electrostatic attraction. Overall, SnZVI@PBC could be considered as a feasible amendment with superior reducing capacity and immobilization performance for Cr(VI)-contaminated soil.

Exploring the mechanism of norfloxacin removal and active species evolution by coupling persulfate activation with biochar hybridized Fe3O4 composites

In situ growth of dispersed active sites on substrates is a strategy for designing highly efficient catalysts for sulfate radical (SO4•-)-based advanced oxidation processes (SR-AOPs). Here, magnetic biochar composite (Fe3O4/BC) was fabricated as an activator to trigger PDS (peroxydisulfate) for norfloxacin (NOR) removal, achieving reliable NOR removal efficiency (>90%) within 10 min. Based on the synergistic effect between Fe3O4 and BC, the removal rate increases to 0.0265 L mg-1 min-1. Fe3O4/BC exhibited decent adaptability, stability, and recyclability toward affecting factors variation during PDS activation, attributed to the synergistic effect between Fe3O4 and BC. The electron transfer of magnetic Fe3O4 coupled with the adsorption and conduction function of carbon skeleton, which overcomes typical problems as crystal agglomeration, metal leaching, and catalysts recovery etc. The electron-rich Fe(II) sites promote the radical pathway by generating reactive oxygen species (ROS, •OH, SO4•- and O2•-), and radicals evolution contributing to the form of 1O2 in non-radical pathway. Under the effect of multipath in NOR degradation, HPLC-QTOF-MS spectroscopy and DFT calculation revealed the possible degradation pathway of NOR. In addition, according to toxicity prediction, the overall NOR contamination toxicity of NOR was effectively alleviated by Fe3O4/BC + PDS system. Overall, this study presents a promising composite in PDS activation and views the active species evolution in the NOR removal system, which is crucial for mechanism study in relevant research in the future.

Thermodynamic restrictions determine ammonia tolerance of functional floras during anaerobic digestion

Ammonia inhibition is a major challenge in anaerobic digestion processes, affecting the activity and performance of functional floras, including syntrophic butyrate oxidation (FSBO), syntrophic propionate oxidation (FSPO), acetoclastic methanogenesis (FAMs), and hydrogenotrophic methanogenesis (FHMs). FHMs was more tolerant to ammonia, with a half maximal inhibitory concentration (IC50) of 18.80 g/L, followed by FSBO (IC50 = 14.26 g/L) and FSPO (IC50 = 10.47 g/L), and FAMs was the most sensitive to ammonia with the lowest IC50 (1.74 g/L). The order of ammonia tolerance (IC50) was found to be correlated with the Gibbs free energy of metabolic reactions in each functional flora. The results suggested the functional flora with higher energy availability (exergonic capacity) exhibited enhanced ammonia resistance ability. These findings provide insights into the thermodynamic restrictions and ammonia tolerance mechanisms of functional floras, which can guide the optimization and operation of anaerobic digestion systems for efficient methane production.

Microwave-assisted one-pot preparation of magnetic cactus-derived hydrochar for efficient removal of lead(Ⅱ) and phenol from water: Performance and mechanism exploration

A novel magnetic hydrochar derived from cactus cladode (MW-MHC) was successfully synthesized through one-pot microwave-assisted process for efficiently removing lead(Pb)(Ⅱ) and phenol. From batch adsorption experiments, MW-MHC possessed the highest uptake amounts for Pb(Ⅱ) and phenol of 139.34 and 175.32 mg/g within 20 and 60 min, respectively. Moreover, the removal of Pb(Ⅱ) and phenol by MW-MHC remained essentially stable under the interference of different co-existing cations, presenting the excellent adaptability of MW-MHC. After three cycles of regeneration experiments, MW-MHC still had preferable adsorption performance and could be easily recycled, indicating its excellent reusability. Significantly, the uptake mechanisms of Pb(Ⅱ) on MW-MHC were regarded as chemical complexation, pore filling, precipitation, and electrostatic attraction. Meanwhile, the phenol uptake might be dominated by π-π interaction and hydrogen bonding. The above consequences revealed that MW-MHC with high removal performance was a promising adsorbent for remediating wastewater containing heavy metals and organics.