Green mechanochemical activation of solid persulfate to remove PAHs in soil: Performance and mechanism.

Due to the high biotoxicity and persistence of polycyclic aromatic hydrocarbons (PAHs), the remediation of PAHs-contaminated soil becomes an intractable problem. Persulfate-based advanced oxidation processes are widely used to degrade PAHs in aquatic environment. However, they are not convenient for used in soil due to the heterogeneity and complexity of soil matrix. In this study, a green and convenient ball milling process is introduced to activate persulfate for the remediation of PAHs-contaminated soil. About 82.5% PAHs were removed with 10% wt. Na2S2O8 (PS) addition and ball-milling for 2 h under 500 r/min. The degradation of PAHs is attributed to the attack of radicals (SO4·- and·OH) generated from the activation of PS by mechanochemistry. Moreover, stable Si-O bonds were disrupted during ball-milling process, and formed free electron on the surface of soil particles. This facilitates the electron transfer from oxidants to contaminants. The particle size, surface element composition, functional group, and thermogravimetric analysis confirmed the slight disturbance of ball-milling-assisted PS process on the physical and chemical properties of soil. Therefore, ball-milling assisted PS approach would be a promising technology for the remediation of PAHs-contaminated soil.

Space-confined manganese oxides nanosheets for efficient catalytic decomposition of ozone.

Ground-level ozone has long posed a substantial menace to human well-being and the ecological milieu. The widely reported manganese-based catalysts for ozone decomposition still facing the persisting issues encompass inefficiency and instability. To surmount these challenges, we developed a mesoporous silica thin films with perpendicular nanochannels (SBA(⊥)) confined Mn3O4 catalyst (Mn3O4@SBA(⊥)). Under a weight hourly space velocity (WHSV) of 500,000 mL g-1 h-1, the Mn3O4@SBA(⊥) catalyst exhibited 100% ozone decomposition efficiency in 5 h and stability across a wide humidity range, which exceed the performance of bulk Mn3O4 and Mn3O4 confine in commonly reported SBA-15. Rapidly decompose 20 ppm O3 to a safety level below 100 µg m-3 in the presence of dust in smog chamber (60 × 60 × 60 cm) was also realized. This prominent catalytic performance can be attributed to the unique confined structure engenders the highly exposed active sites, facilitate the reactant-active sites contact and impeded the water accumulation on the active sites. This work offers new insights into the design of confined structure catalysts for air purification.

Single Atom Catalyst in Persulfate Oxidation Reaction: From Atom Species to Substance.

With maximum utilization of active metal sites, more and more researchers have reported using single atom catalysts (SACs) to activate persulfate (PS) for organic pollutants removal. In SACs, single metal atoms (Fe, Co, Cu, Mn, etc.) and different substrates (porous carbon, biochar, graphene oxide, carbon nitride, MOF, MoS2 , and others) are the basic structural. Metal single atoms, substances, and connected chemical bonds all have a great influence on the electronic structures that directly affect the activation process of PS and degradation efficiency to organic pollutants. However, there are few relevant reviews about the interaction between metal single atoms and substances during PS activation process. In this review, the SACs with different metal species and substrates are summarized to investigate the metal-support interaction and evaluate their effects on PS oxidation reaction process. Furthermore, how metal atoms and substrates affect the reactive species and degradation pathways are also discussed. Finally, the challenges and prospects of SACs in PS-AOPs are proposed.

Internal Electric Field Facilitates Facet-Dependent Photocatalytic Cl- Utilization on BiOCl in High-Salinity Wastewater for Ammonium Removal.

High Cl- concentration in saline wastewater (e.g., landfill leachate) limits wastewater purification. Catalytic Cl- conversion into reactive chlorine species (RCS) arises as a sustainable strategy, making the salinity profitable for efficient wastewater treatment. Herein, aiming to reveal the structure-property relationship in Cl- utilization, bismuth oxychloride (BiOCl) photocatalysts with coexposed {001} and {110} facets are synthesized. With an increasing {001} ratio, the RCS production efficiency increases from 75.64 to 96.89 µg L-1 min-1. Mechanism investigation demonstrates the fast release of lattice Cl- as an RCS and the compensation of ambient Cl-. Correlation analysis between the internal electric field (IEF, parallel to [001]) and normalized efficiency on {110} (kRCS/S{110}, perpendicular to [001]) displays a coefficient of 0.86, validating that the promoted carrier dynamics eventually affects Cl- conversion on the open layered structure. The BiOCl photocatalyst is well behaved in ammonium (NH4+-N) degradation ranging from 20 to 800 mg N L-1 with different chlorinity (3-12 g L-1 NaCl). The sustainable Cl- conversion into RCS also realizes 85.4% of NH4+-N removal in the treatment of realistic landfill leachate (662 mg of N L-1 NH4+-N). The structure-property relationship provides insights into the design of efficient catalysts for environment remediation using ambient Cl-.

Confining Bismuth-Halide Perovskite in Mesochannels of Silica Nanomembranes for Exceptional Photocatalytic Abatement of Air Pollutants.

Spatially confined photocatalysis has emerged as a viable strategy for the intensification of various redox reactions, but the influence of confined structure on reaction behavior is always overlooked in gas-solid reactions. Herein, we report a nanomembrane with confining Cs3 Bi2 Br9 nanocrystals inside vertical channels of porous insulated silica thin sheets (CBB@SBA(⊥)) for photocatalytic nitric oxide (NO) abatement. The ordered one-dimensional (1D) pore channels with mere 70 nm channel length provide a highly accessible confined space for catalytic reactions. A record-breaking NO conversion efficiency of 98.2 % under a weight hourly space velocity (WHSV) of 3.0×106  mL g-1 h-1 , as well as exceptionally high stability over 14 h and durability over a wide humidity range (RH=15-90 %) was realized over SBA(⊥) confined Cs3 Bi2 Br9 , well beyond its nonconfined analogue and the Cs3 Bi2 Br9 confine in Santa Barbara Amorphous (SBA-15). Mechanism studies suggested that the insulated pore channels of SBA(⊥) in CBB@SBA(⊥) endow concentrated electron field and enhanced mass transfer that render high exposure of reactive species and lower reaction barrier needs for ⋅O2 - formation and NO oxidation, as well as prevents structural degradation of Cs3 Bi2 Br9 . This work expands an innovative strategy for designing efficient photocatalysts for air pollution remediation.

Oxidant-mediated radical reactions of the azole fungicide TEB in aquatic media: Degradation mechanism and toxicity evolution.

The degradation of tebuconazole (TEB) by UV/H2O2, UV/NaClO, and ozonation was investigated in this research. The experimental findings unveiled that under the specified conditions, the degradation percentages of TEB were raised to 99% within 40 s, 5 min, and 3 min for UV/H2O2, UV/NaClO and ozonation, respectively. The mineralization percentages within 1 h were 59%, 31% and 8% for the three AOPs. UV/H2O2 and UV/NaClO technologies mainly acted through OH·, while O3 treatment primarily relied on the free radicals such as 1O2 and O2·-. UV-based AOPs achieved almost complete dechlorination within 1 h, whereas O3 treatment had a less effective dechlorination, reaching only 27.61%. Notably, UV alone achieved a dechlorination percentage of 43.07%. By identifying the TPs, we found that the three AOPs shared three similar degradation pathways. The degradation mechanism of TEB mainly entailed the removal of the benzene ring, tert-butyl group and triazolyl group. Toxicity assessment revealed an initial increase followed by a gradual decrease in toxicity for UV/NaClO and O3 treatments, whereas UV/H2O2 treatment exhibited a sustained decrease. This was due to the presence of TP278 and TP303 by UV/NaClO and TP168 and TP153 by ozonation. After estimating the costs of the three AOPs, UV/H2O2 standed out as the best choice for achieving a 90% degradation percentage and exhibiting lower toxicity performance, while O3 treatment was favored for low TOC demands. These research findings provided valuable reference for understanding the degradation mechanism and developing a new technology of the removal of TEB.

Deep Oxidation of Chlorinated VOCs by Efficient Catalytic Peroxide Activation over Nanoconfined Co@NCNT Catalysts.

The catalytic removal of chlorinated VOCs (CVOCs) in gas-solid reactions usually suffers from chlorine-containing byproduct formation and catalyst deactivation. AOP wet scrubber has recently attracted ever-increasing interest in VOC treatment due to its advantages of high efficiency and no gaseous byproduct emission. Herein, the low-valence Co nanoparticles (NPs) confined in a N-doped carbon nanotube (Co@NCNT) were studied to activate peroxymonosulfate (PMS) for efficient CVOC removal in a wet scrubber. Co@NCNT exhibited unprecedented catalytic activity, recyclability, and low Co ion leakage (0.19 mg L-1) for chlorobenzene degradation in a very wide pH range (3-11). The chlorobenzene removal efficiency was kept stable above 90% over Co@NCNT, much higher than that of nonconfined Co@NCNS (45%). The low-valence Co NPs achieved a continuous electron redox cycling (Co0/Co2+ → Co3+ → Co0/Co2+) and greatly promoted the O-O bond dissociation of PMS with the least energy (0.83 eV) inside the channel of Co@NCNT to form abundant HO• and SO4•-. Thus, the deep oxidation of chlorobenzene was achieved without any biphenyl byproducts from the coupling reaction. This study provided a new avenue for designing novel nanoconfined catalysts with outstanding activity, paving the way for the deep oxidation of CVOC waste gas via AOP wet scrubber.

Selective electrocatalytic transformation of highly toxic phenols in wastewater to para-benzoquinone at ambient conditions.

The selective transformation of organics from wastewater to value-added chemicals is considered an upcycling process beneficial for carbon neutrality. Herein, we present an innovative electrocatalytic oxidation (ECO) system aimed at achieving the selective conversion of phenols in wastewater to para-benzoquinone (p-BQ), a valuable chemical widely utilized in the manufacturing and chemical industries. Notably, 96.4% of phenol abatement and 78.9% of p-BQ yield are synchronously obtained over a preferred carbon cloth-supported ruthenium nanoparticles (Ru/C) anode. Such unprecedented results stem from the weak Ru-O bond between the Ru active sites and generated p-BQ, which facilitates the desorption of p-BQ from the anode surface. This property not only prevents the excessive oxidation of the generated p-BQ but also reinstates the Ru active sites essential for the rapid ECO of phenol. Furthermore, this ECO system operates at ambient conditions and obviates the need for potent chemical oxidants, establishing a sustainable avenue for p-BQ production. Importantly, the system efficacy can be adaptable in actual phenol-containing coking wastewater, highlighting its potential practical application prospect. As a proof of concept, we construct an electrified Ru/C membrane for ECO of phenol, attaining phenol removal of 95.8% coupled with p-BQ selectivity of 73.1%, which demonstrates the feasibility of the ECO system in a scalable flow-through operation mode. This work provides a promising ECO strategy for realizing both phenols removal and valuable organics recovery from phenolic wastewater.

Molecular understanding on ultraviolet photolytic degradation of cyano liquid crystal monomers.

Cyano liquid crystal monomers (LCMs) are proposed as emerging chemical pollutants with persistent, bioaccumulative, and toxic properties. Herein, five cyano LCMs, including 4-cyano-4'-ethylbiphenyl (2CB), 4-Butyl-4'-cyanobiphenyl (4CB), 4-cyano-4'-ethoxybiphenyl (2OCB), 4-(trans-4-Ethylcyclohexyl)benzonitrile (2CHB) and 4-(trans-4-Vinylcyclohexyl)benzonitrile (2eCHB), were selected to investigate the reaction kinetics and excited state characteristic variations with their molecular structures by ultraviolet (UV) photolysis. Theoretical calculations reveal that the benzene ring, ethoxy and double bond can deeply alter the electron distribution of cyano LCMs. This will affect the exciton separation ability, excitation properties and active sites to electrophilic attack, causing the distinction in photolysis efficiency. Due to the effective charge separation during local excitation (LE) process and the property of being most susceptible to electrophilic attack by 1O2 and O2•-, 2eCHB with double bond exhibits the largest degradation rate. Conversely, the weakest exciton separation of 2OCB with ethoxy during charge transfer (CT) process limits its subsequent sensitized photolysis process. The molecular orbital and fragment contributions to holes and electrons further deepen the understanding of the excited states charge transfer. This study confirmed that the intrinsic molecular structure, chemical nature and existing sites directly defined the excitation and decomposition activity in the UV photolysis of cyano LCMs.

Adjusting Surface Oxidized Layer of CoTe on PCN via In Situ N-Doping Strategy to Promote Charge Separation of Z-Scheme Heterojunction for Propelling Photocatalytic CO2 Reduction.

It has been a challenging issue to profoundly actuate the transfer and separation of photoinduced charge carriers by controlling the interface structure inside the heterojunction, owing to the molecular/subnanometric level interface region. Herein, a unique one-dimensional/two-dimensional (1D/2D) CoTe/PCN Z-scheme heterojunction is fabricated through the self-assembly of CoTe nanorods on the surface of polymeric carbon nitride (PCN) nanosheets. Significantly, in situ N-doping in the molecular/subnanometric surface oxidized layer of CoTe nanorods is achieved, effectively adjusting its chemical structure and element chemical states. Moreover, this N-doped surface oxidized layer can serve as a recombination region of photogenerated electrons from PCN and photogenerated holes from CoTe to increase the overall carrier separation efficiency in the Z-scheme heterojunction actuated by the built-in electric field. As a result, the photocatalytic CO2 reduction (CO2R) performance is enhanced dramatically, in which the yield of CO generated over the optimal 1D/2D CoTe/PCN heterojunction reaches up to triple than that over PCN. This unique contribution provides an emblematic paradigm for adjusting the interfacial structure of heterojunction and has a profound insight into the interfacial adjusting mechanism to improve the charge separation efficiency in the photocatalytic reaction.

Construction of highly dispersed iron active sites for efficient catalytic ozonation of bisphenol A.

The essential factor of catalytic ozonation technology relies on an efficient and stable catalyst. The construction of highly dispersed active sites on heterogeneous catalysts is an ideal strategy to combine the merits of homogeneous and heterogeneous catalysis with high activity and stability. Herein, an iron-containing mesoporous silica material (Fe-SBA15) with sufficient iron site exposure and enhanced intrinsic activity of active sites was employed to activate ozone for bisphenol A (BPA) degradation. Approximately 100% of BPA and 36.6% of total organic carbon (TOC) removal were realized by the Fe-SBA15 catalytic ozonation strategy with a reaction constant of 0.076 min-1, well beyond the performance of FeOx/SBA15 mixture and Fe2O3. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that the hydroxyl radicals (HO•) and superoxide radicals (O2•-) played an important role in the degradation process. The iron sites with recyclable Fe(III)/Fe(II) pairs act as both the electron donors and active sites for catalytic ozonation. The mesoporous framework of SBA15 in Fe-SBA15 stabilizes the iron sites that enhance its stability. With high catalytic performance and high reusability for catalytic ozonation of BPA, the Fe-SBA15 is expected to be a promising catalyst in catalytic ozonation for wastewater treatment.

Dipole field in nitrogen-enriched carbon nitride with external forces to boost the artificial photosynthesis of hydrogen peroxide.

Artificial photosynthesis is a promising strategy for efficient hydrogen peroxide production, but the poor directional charge transfer from bulk to active sites restricts the overall photocatalytic efficiency. To address this, a new process of dipole field-driven spontaneous polarization in nitrogen-rich triazole-based carbon nitride (C3N5) to harness photogenerated charge kinetics for hydrogen peroxide production is constructed. Here, C3N5 achieves a hydrogen peroxide photosynthesis rate of 3809.5 µmol g-1 h-1 and a 2e- transfer selectivity of 92% under simulated sunlight and ultrasonic forces. This high performance is attributed to the introduction of rich nitrogen active sites of the triazole ring in C3N5, which brings a dipole field. This dipole field induces a spontaneous polarization field to accelerate a rapid directional electron transfer process to nitrogen active sites and therefore induces Pauling-type adsorption of oxygen through an indirect 2e- transfer pathway to form hydrogen peroxide. This innovative concept using a dipole field to harness the migration and transport of photogenerated carriers provides a new route to improve photosynthesis efficiency via structural engineering.

Photocatalytic fuel cell based on integrated silicon nanowire arrays/zinc oxide heterojunction anode for simultaneous wastewater treatment and electricity production.

Photocatalytic fuel cells (PFCs) convert organic waste into electricity, thereby providing a potential solution for remediating environmental pollution and solving energy crises. Most PFCs for energy generation applications use powder photocatalysts, which have poor mechanical stability, high internal resistance, and may detach from the substrate during reactions, leading to unstable performance. Integrated photoelectrodes can overcome the drawbacks of powder catalysts. In this study, an integrated photoanode was prepared based on a silicon nanowire arrays/zinc oxide (Si NWs/ZnO) heterojunction by combining metal-assisted chemical etching (MACE) and hydrothermal methods. The resulting photoanode was used to assemble a PFC for simultaneous electricity generation and Rhodamine (RhB) dye wastewater degradation. This PFC showed excellent cell performance under irradiation, with a short-circuit current density of 0.183 Am-2, an open-circuit voltage (OCV) of 0.72 V, and a maximum power density of 0.87 W m-2. It could also be used continuously 20 times while degrading > 90% of RhB. This performance was ascribed to the three-dimensional (3D) structure and large surface area of Si NWs, as well as the matched band structure of ZnO, which facilitated the efficient separation and transport of photogenerated carriers in Si NWs/ZnO. The integrated structure also shortened the carrier transport pathways and suppressed carrier recombination. This research provides a foundation for the development of efficient, stable, low-cost, small-scale PFCs.

Roles of Activated Carbon in UV/Chlorine/Activated Carbon-TiO2 Process for Micropollutant Abatement and DBP Control.

The ultraviolet (UV)/chlorine process has attracted increasing attention for micropollutant abatement. However, the limited hydroxyl radical (HO•) generation and the formation of undesired disinfection byproducts (DBPs) are the two major issues in this process. This study investigated the roles of activated carbon (AC) in the UV/chlorine/AC-TiO2 process for micropollutant abatement and DBP control. The degradation rate constant of metronidazole by UV/chlorine/AC-TiO2 was 3.44, 2.45, and 1.58 times higher than those by UV/AC-TiO2, UV/chlorine, and UV/chlorine/TiO2, respectively. AC acted as an electron conductor and dissolved oxygen (DO) adsorbent, resulting in the steady-state concentration of HO• that was ∼2.5 times that of UV/chlorine. Compared with UV/chlorine, the formation of total organic chlorine (TOCl) and known DBPs in UV/chlorine/AC-TiO2 was reduced by 62.3 and 75.7%, respectively. DBP could be controlled via adsorption on AC, and the increased HO• and decreased chlorine radical (Cl•) and chlorine exposure reduced DBP formation. UV/chlorine/AC-TiO2 efficiently abated 16 structurally different micropollutants under environmentally relevant conditions owing to the enhanced generation of HO•. This study provides a new strategy for designing catalysts with photocatalytic and adsorption properties for UV/chlorine to promote micropollutant abatement and DBP control.

Efficient carbamazepine degradation with Fe3+ doped 1T/2H hybrid molybdenum disulfide as peroxymonosulfate activator under high salinity wastewater.

Drawing on the robust activation activity and affinity that transition metal ions and MoS2 exhibit towards peroxymonosulfate (PMS), 1T/2H hybrid molybdenum disulfide doped with Fe3+ (Fe3+/N-MoS2) was synthesized to activate PMS for the treatment of organic wastewater. The ultrathin sheet morphology and 1T/2H hybrid nature of Fe3+/N-MoS2 were confirmed by characterization. The (Fe3+/N-MoS2 + PMS) system demonstrated excellent performance in the degradation of carbamazepine (CBZ) above 90% within 10 min even under high salinity conditions. By electron paramagnetic resonance and active species scavenging experiments, it was inferred that SO4•─ palyed a dominant role in the treatment process. The strong synergistic interactions between 1T/2H MoS2 and Fe3+ efficiently promoted PMS activation and generated active species. Additionally, the (Fe3+/N-MoS2 + PMS) system was found to be capable of high activity for CBZ removal in high salinity natural water, and Fe3+/N-MoS2 exhibited high stability during recycle tests. This new strategy of Fe3+ doped 1T/2H hybrid MoS2 for more efficient PMS activation provides valuable insights for the removal of pollutants from high salinity wastewater.

Piezoelectric-channels in MoS2-embedded polyvinylidene fluoride membrane to activate peroxymonosulfate in membrane filtration for wastewater reuse.

The conjugation of membrane filtration (MF) with advanced oxidation process (AOPs) is being considered as an alternative advanced treatment process for the potable reuse of wastewater. Beyond conventional MF/AOPs conjugation, a new downstream MF process with piezoelectric-channels induced piezo-activated peroxymonosulfate (PMS) is herein constructed to deal with antiepileptic carbamazepine (CBZ) pollutants through polyvinylidene fluoride (PVDF) membrane (PVDF-M10). Through a MF process, ca. 93.8% CBZ pollutants can be removed under an ultrasonic-assisted piezo-activation PMS, whereas only 18.3% and 60.2% CBZ can be removed by using pure PVDF membrane under the same condition and PVDF-M10 membrane without ultrasonic-assisted piezo-activation. Even after 9-cycles, CBZ removal efficiency was maintained at 56.4% under this MF process. These superior performances are attributed to the piezoelectric exfoliated-MoS2 nanosheets (E-MoS2) embedded PVDF nanofibers in PVDF-M10 membrane, which lead to rich piezoelectric-channels in the membrane. These piezoelectric-channels not only produced more charges to activate PMS to boost the yield of reactive oxide species (ROS) but also provided an ideal platform for the rapid reaction between CBZ and ROS during MF process. This investigation develops a new MF technique to conjugate piezo-activation of PMS-AOPs for the efficient removal of emerging pollutants for the potable reuse of wastewater.

Double-Confined Ultrafine Cobalt Clusters for Efficient Peroxide Activation.

The construction of highly active catalysts presents great prospects, while it is a challenge for peroxide activation in advanced oxidation processes (AOPs). Herein, we facilely developed ultrafine Co clusters confined in mesoporous silica nanospheres containing N-doped carbon (NC) dots (termed as Co/NC@mSiO2) via a double-confinement strategy. Compared with the unconfined counterpart, Co/NC@mSiO2 exhibited unprecedented catalytic activity and durability for removal of various organic pollutants even in extremely acidic and alkaline environments (pH from 2 to 11) with very low Co ion leaching. Experiments and density functional theory (DFT) calculations proved that Co/NC@mSiO2 possessed strong peroxymonosulphate (PMS) adsorption and charge transfer capability, enabling the efficient O-O bond dissociation of PMS to HO• and SO4•- radicals. The strong interaction between Co clusters and mSiO2 containing NC dots contributed to excellent pollutant degradation performances by optimizing the electronic structures of Co clusters. This work represents a fundamental breakthrough in the design and understanding of the double-confined catalysts for peroxide activation.

Modulating the metal center in MIL-101 for the piezoelectric catalytic synthesis of hydrogen peroxide.

Modulation of metal centers is a promising strategy to boost catalytic performance. Two structurally identical MOFs with different metal centers, namely MIL-101(Cr) and MIL-101(Fe), were synthesized. MIL-101(Cr) exhibits superior H2O2 yield due to Cr's electron-donating ability. This work helps in developing the rational design and optimization of MOF catalysts for catalytic reactions.

Proton Transfer Dynamics-Mediated CO2 Electroreduction.

Electrochemical CO2 reduction reaction (CO2 RR) is crucial to addressing environmental crises and producing chemicals. Proton activation and transfer are essential in CO2 RR. To date, few research reviews have focused on this process and its effect on catalytic performance. Recent studies have demonstrated ways to improve CO2 RR by regulating proton transfer dynamics. This Concept highlights the use of regulating proton transfer dynamics to enhance CO2 RR for the target product and discusses modulation strategies for proton transfer dynamics and operative mechanisms in typical systems, including single-atom catalysts, molecular catalysts, metal heterointerfaces, and organic-ligand modified metal catalysts. Characterization methods for proton transfer dynamics during CO2 RR are also discussed, providing powerful tools for the hydrogen-involving electrochemical study. This Concept offers new insights into the CO2 RR mechanism and guides the design of efficient CO2 RR systems.