A Robust Pyro-phototronic Route to Markedly Enhanced Photocatalytic Disinfection.

Photocatalysis offers a direct, yet robust, approach to eradicate pathogenic bacteria. However, the practical implementation of photocatalytic disinfection faces a significant challenge due to low-efficiency photogenerated carrier separation and transfer. Here, we present an effective approach to improve photocatalytic disinfection performance by exploiting the pyro-phototronic effect through a synergistic combination of pyroelectric properties and photocatalytic processes. A set of comprehensive studies reveals that the temperature fluctuation-induced pyroelectric field promotes photoexcited carrier separation and transfer and thus facilitates the generation of reactive oxygen species and ultimately enhances photocatalytic disinfection performance. It is worth highlighting that the constructed film demonstrated an exceptional antibacterial efficiency exceeding 95% against pathogenic bacteria under temperature fluctuations and light irradiation. Moreover, the versatile modulation role of the pyro-phototronic effect in boosting photocatalytic disinfection was corroborated. This work paves the way for improving photocatalytic disinfection efficiency by harnessing the synergistic potential of various inherent material properties.

Reinvestigation on High-Valent Cobalt for the Degradation of Micropollutants in the Co(II)/Peroxymonosulfate System: Roles of Co(III).

Recently, reactive cobalt (Co) species, including Co(IV)-oxo and Co(II)-OOSO3- complexes, were proposed to be the primary intermediates formed during the process of activating peroxymonosulfate (PMS) by Co(II), mainly based on the observation that the methyl phenyl sulfoxide (MPSO) probe was transformed to methyl phenyl sulfone (MPSO2) in this process. However, in this work, we rationalized the results of the MPSO probe assay based on the chemistry of aqueous Co(III), an alternative reactive Co species. Moreover, 18O-labeled water experiments and Raman spectroscopy analysis clearly proved the Co(III) formation in the Co(II)/PMS system. In parallel, sulfate radicals (SO4•-) and hydroxyl radicals (HO•) were also involved in this system. Further, the relative contribution of Co(III) to the abatement of carbamazepine (CBZ), a representative micropollutant, in the Co(II)/PMS system was significantly increased by increasing the Co(II) dosage but was dramatically decreased by improving the PMS dosage and increasing the pH from 3 to 7. Additionally, the degradation pathway of CBZ by Co(III) and the Co(II)/PMS system was comparatively explored, confirming that Co(III) participated in the hydroxylation, carbonylation, deacetylation, and ring reduction of CBZ by the Co(II)/PMS system. Our work addresses the controversy regarding the reactive Co species involved in the Co(II)/PMS system with evidence of Co(III) as the chief one, which highlights the significance of re-evaluating the relative contribution of Co(III) in relevant environmental decontamination processes.

Enhancing the Abatement of Permanganate-inert Micropollutants: Multiple Roles of Nascent Manganese Dioxide in Permanganate Oxidation.

Permanganate (Mn(VII)) is widely used as an oxidant in water treatment and usually reduced to nascent manganese dioxide (MnO2), which could promote Mn(VII) oxidation for the Mn(VII)-reactive compounds such as phenols and anilines. However, the removal of micropollutants containing diverse functional groups and the underlying mechanisms remain largely unexplored. This study reveals that Mn(VII)/nascent MnO2 was effective for the degradation of Mn(VII)-inert micropollutants, including sulfonamide antibiotics, ß-blockers and trimethoprim, with observed first-order rate constants (k'obs) of 0.126 ∼ 9 min-1 at pH 4.0. The synergetic effect of Mn(VII) and nascent MnO2 on the degradation of Mn(VII)-inert micropollutants decreased significantly when pH increased from 4.0 to 9.5. MnO2 played multiple roles in micropollutant degradation, which acted as a catalyst to promote the Mn(VII) oxidation of trimethoprim and propranolol, as well as an oxidant in propranolol degradation. Besides, Mn(III) oxidation accounted for 58% of the overall degradation of propranolol, but was not important for trimethoprim oxidation. Hydroxylated products were common products formed in Mn(VII)/MnO2. Differently, trimethoprim tended to form single-ring products via MnO2-catalyzed Mn(VII) oxidation, while propranolol preferentially formed dimers via in situ formed MnO2 oxidation. This study is the first to report that MnO2 enhances the abatement of Mn(VII)-inert micropollutants during Mn(VII)-based water treatment and unravels the multiple roles of MnO2 in micropollutant degradation by Mn(VII)/MnO2.

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.

Molecular structure on the detoxification of fluorinated liquid crystal monomers with reactive oxidation species in the photocatalytic process.

Fluorinated liquid crystal monomers (LCMs) are begun to emerge as new persistent organic pollutants. Herein, the structure-reactivity relationships of fluorinated LCMs 1,2,3-trifluoro-5-[3-(3-propylcyclohexyl)cyclohexyl]benzene (TPrCB), 1,2-difluoro-4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzene (DPrCB), 4-[(trans,trans)-4'-(3-Buten-1-yl)[1,1'-bicyclohexyl]-4-yl]-1,2-difluoro-benzene (BBDB) and 1-[4-(4-ethylcyclohexyl)cyclohexyl]-4(trifluoromethoxy)benzene (ECTB) subject to photocatalysis-generated oxidation species were investigated. The degradation rate constant of BBDB was 3.0, 2.6, and 6.8 times higher than DPrCB, TPrCB and ECTB, respectively. The results reveal that BBDB, DPrCB and TPrCB had mainly negative electrostatic potential (ESP) regions which were vulnerable to electrophilic attack by h+, •OH and •O2 -, while ECTB was composed of mainly positive ESP regions which were vulnerable to nucleophilic attack by •OH and •O2 -. The detoxification processes of BBDB, DPrCB and TPrCB included carbon bond cleavage and benzene ring opening. However, the methoxy group of ECTB reduced the nucleophilic reactivity on the benzene ring, leading to slower detoxification efficiency. These findings may help to develop LCMs treatment technologies based on structure-reactivity relationships.

Structure-dependent degradation of nitroimidazoles by cobalt-manganese layered double hydroxide catalyzed peroxymonosulfate process.

The increasing concentration of nitroimidazoles antibiotics (NIs) in the water environment has great threat to human and ecosystem security. Herein, the degradation rates of four NIs were found to vary with their molecular structures using Co3Mn-layered double hydroxide (LDH) catalyzed peroxymonosulfate oxidation process. Specifically, the degradation efficiency of secnidazole (SNZ) was determined to be the highest with a reaction rate of 0.24 min-1, which was 3.6, 2.3 and 1.8 times to that of menidazole (MZ), metronidazole (MTZ) and ornidazole (ONZ), respectively. During the reaction, 8.3% of Co2+ and 8.4% of Mn3+ transformed to Co3+ and Mn4+ after reaction, respectively. The conversion of bimetallic valence in Co3Mn-LDH donated electrons (e-) for PMS activation, resulting in the production of 1O2, OH, SO4- and O2-. Density functional theory (DFT) calculation showed that the presence of electron-donating groups (-CH3 and -OH) and the absence of electron-withdrawing atom (Cl) leaded to the richest active sites in the molecular structure of SNZ, which thus contributed to the highest degradation efficiency of SNZ. By deducing the structure-dependent degradation pathways of four NIs, the carbon chain of SNZ was found to be more easily attacked to form MTZ and MZ because of its unique active sites, resulting in the faster degradation rate of SNZ than MTZ and MZ. This study may provide a valuable insight into the effects of molecular structures on the degradation rates and transformation pathways of NIs.

Near-infrared light to heat conversion in peroxydisulfate activation with MoS2: A new photo-activation process for water treatment.

The advantage of light-to-heat conversion can be employed as an optical alternative for environmental remediation. As a proof of concept, for the first time we introduce the light-to-heat conversion application in peroxydisulfate (PDS) activation by molybdenum disulphide (MoS2) under near infrared (NIR) light irradiation. Theoretical kinetics analysis suggests that the reaction rates of PDS activation is increased up to 9.2 times when increasing from room temperature to 50 °C. MoS2 has the capability to quickly convert NIR light to heat energy (~45°C), thereby being able to activate PDS to generate hydroxyl and sulfate radicals. The observed reaction rate of carbamazepine degradation by NIR/MoS2/PDS process is 6.5 times of that in MoS2/PDS and even 2.6 times higher than the sum of those in NIR/MoS2, MoS2/PDS and NIR/PDS processes. Combining with theoretical calculation and oxidation species analysis, a new photo-activation PDS mechanism is proposed, in which MoS2 absorbs the energy of light to generate heat energy for overcoming the energy barrier of PDS activation. By loading MoS2 on carbon cloths, a flexible photothermal membrane is designed for practical application of sunlight-to-heat conversion to activate PDS with high efficiency, stability, and recycling. The present results demonstrate the potential of applying light-to-heat conversion in Fenton-like processes in pollution control, which opens new avenues towards utilization of inexhaustible solar energy and novel approaches for environmental remediation.

In situ photoreduction of structural Fe(III) in a metal-organic framework for peroxydisulfate activation and efficient removal of antibiotics in real wastewater.

Structural Fe(III) is widely found in various coordination complexes and inorganic compounds. In this work, a typical Fe-based metal organic framework (MOF) (viz. MIL-100(Fe)) was chosen as an example in the activation of peroxydisulfate (PDS) for the removal of antibiotic pollutants. Interestingly, an auto-acceleration effect was observed in the process of MIL-100(Fe) activating PDS aided by visible light irradiation. Compared to the processes with MIL-100(Fe)-activated PDS alone and the photo-activated PDS alone, the degradation efficiency of sulfamethoxazole (SMX) obtained in the visible light assisted PDS activation by MIL-100(Fe) process was enhanced by 2.1 and 5.6 times, respectively. Therein, the photogenerated electrons from MIL-100(Fe) carried out an in situ reduction of the surface structural Fe(III) to form Fe(II), which in turn significantly improved the PDS activation efficiency in the generation of ·OH and O2-· radicals for the removal of SMX. The degradation pathways of SMX were deduced based on the experimental results and theoretical calculations. Acute toxicity estimation indicated the formation of less toxic products after the treatment of SMX. Additionally, degradation of five antibiotics in the real wastewater were investigated to further confirm the advantages of such in situ photoreduced structural Fe(III) in MOFs to activate the PDS process.

The effect of peroxymonosulfate in WS2 nanosheets for the removal of diclofenac: Information exposure and degradation pathway.

The search for a suitable heterogeneous catalyst in peroxymonosulfate (PMS) activation holds tremendous promise for the degradation of organic pollutants. Two-dimensional (2D) transition metal dichalcogenides such as WS2 exhibit broad applications in heterogeneous catalysis, and we first extended its application in PMS activation in this work. It was found that WS2 could efficiently activate PMS resulting in the degradation of diclofenac (DCF). The results show that the PMS offers direct oxidation, and WS2 could initiate PMS to produce singlet oxygen (1O2) and superoxide radical (·O2-). This resulted in the improved removal of DCF in the WS2/PMS system. Furthermore, the degradation pathway of DCF was proposed according to the detected intermediates/products and density functional theory (DFT) calculation. Degradation intermediates and the evaluation of product toxicity indicated that the developed WS2/PMS system was a safe and detoxifying process while also offering efficient DCF removal. This study offers more insight into the development of suitable materials for the activation of PMS and gives clear direction for the degradation of DCF and its toxic intermediates.

Determination of polycyclic aromatic hydrocarbons in dungeness crabs (Cancer magister) near an aluminum smelter in Kitimat Arm, British Columbia, Canada.

An aluminum smelter situated at the head of Kitimat Arm (BC, Canada) has discharged polycyclic aromatic hydrocarbons (PAHs) into the receiving waters since 1954. The purpose of the present study was to examine the distribution of PAHs contaminants in dungeness crabs (Cancer magister) collected in Kitimat Arm and Douglas Channel (BC, Canada) by determining the concentrations of PAHs in the hepatopancreas and muscle tissues of crabs by using gas chromatography-mass spectrometry. Crabs were collected at specific sites down the Arm from the smelter on four separate occasions over a three-year period. Hepatopancreas and muscle tissues of the crabs were analyzed for 10 of the 16 PAH priority pollutants recommended by the U.S. Environmental Protection Agency. Results of the studies showed that the crabs had detectable levels of PAHs in hepatopancreas and muscle tissues. The highest concentrations of PAHs in the tissues were found at a site near the aluminum smelter, the alleged point source of PAH discharge. The concentrations of PAH analytes were high in crabs collected close to the smelter and at lower levels in crabs collected throughout Douglas Channel. These results show that PAHs discharged by the smelter were bioavailable to the crabs. The concentration of each PAH analyte in the hepatopancreas was found to be strongly related to its water solubility. However, the PAH analyte concentrations in the hepatopancreas and muscle did not appear to correlate highly with each other.