Starvation Process Would Induce Different Bacterial Mobilities and Attachment Performances in Porous Media without and with Nutrients on Surfaces.

The influence and mechanisms of starvation on the bacterial mobile performance in porous media with different nutrition conditions are not well understood. The present study systematically investigated the impacts of starvation on the mobility and attachment of both Gram-negative and Gram-positive strains in porous media without and with nutrients on surfaces in both simulated and real water samples. We found that regardless of strain types and water chemistries, starvation would greatly inhibit bacterial attachment onto bare porous media without nutrients yet could significantly enhance cell attachment onto porous media with nutrients on their surfaces. The mechanisms driving the opposite transport behaviors induced by starvation in porous media without and with nutrients were totally different. We found that the starvation process decreased cell motility and increased repulsive force between bacteria and porous media via decreasing cell sizes and zeta potentials, reducing EPS secretion and cell hydrophobicity, thus increasing transport/inhibiting attachment of bacteria in porous media without nutrients on sand surfaces. In contrast, through strengthening the positive chemotactic response of bacteria to nutrients, the starvation process greatly enhanced bacterial attachment onto porous media with nutrients on sand surfaces. Clearly, via modification of the nutrient conditions in porous media, the mobility/attachment performance of bacteria could be regulated.

Simultaneous inactivation of Microcystis aeruginosa and degradation of microcystin-LR in water by activation of periodate with sunlight.

Harmful algal blooms pose tremendous threats to ecological safety and human health. In this study, simulated solar light (SSL) irradiation was used to activate periodate (PI) for the inactivation of Microcystis aeruginosa and degradation of microcystin-LR (MC-LR). We found that PI-SSL system could effectively inactivate 5 × 106 cells·mL-1 algal cells below the limit of detection within 180 min. ·OH and iodine (IO3· and IO4·) radicals generated in PI-SSL system could rupture cell membranes, releasing intracellular substances including MC-LR into the reaction system. However, the released MC-LR could be degraded into non-toxic small molecules via hydroxylation and ring cleavage processes in PI-SSL system, reducing their environmental risks. High algae inactivation performance of PI-SSL system in solution with a wide pH range (3-9), with the coexisting anions (Cl-, NO3- and SO42-) and the copresence of natural organic matters (humic acid and fulvic acid), real water (lake water and river water), as well as in continuous-flow reactor (14 h) were also achieved. In addition, under natural sunlight irradiation, effective algae inactivation could also be achieved in an enlarged reactor (1 L). Overall, our study showed that PI-SSL system could avoid the inference by the background substances and could be employed as a feasible technique to treat algal bloom water.

Elimination of representative antibiotic-resistant bacteria, antibiotic resistance genes and ciprofloxacin from water via photoactivation of periodate using FeS2.

The propagation of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) induced by the release of antibiotics poses great threats to ecological safety and human health. In this study, periodate (PI)/FeS2/simulated sunlight (SSL) system was employed to remove representative ARB, ARGs and antibiotics in water. 1 × 107 CFU mL-1 of gentamycin-resistant Escherichia coli was effectively disinfected below limit of detection in PI/FeS2/SSL system under different water matrix and in real water samples. Sulfadiazine-resistant Pseudomonas and Gram-positive Bacillus subtilis could also be efficiently sterilized. Theoretical calculation showed that (110) facet was the most reactive facet on FeS2 to activate PI for the generation of reactive species (·OH, ·O2-, h+ and Fe(IV)=O) to damage cell membrane and intracellular enzyme defense system. Both intracellular and extracellular ARGs could be degraded and the expression levels of multidrug resistance-related genes were downregulated during the disinfection process. Thus, horizontal gene transfer (HGT) of ARB was inhibited. Moreover, PI/FeS2/SSL system could disinfect ARB in a continuous flow reactor and in an enlarged reactor under natural sunlight irradiation. PI/FeS2/SSL system could also effectively degrade the HGT-promoting antibiotic (ciprofloxacin) via hydroxylation and ring cleavage process. Overall, PI/FeS2/SSL exhibited great promise for the elimination of antibiotic resistance from water.

Effects of arsenic on the transport and attachment of microplastics in porous media.

Understanding the impact of arsenic (As(III), inorganic pollutant widely present in natural environments) on microplastics (MPs, one type of emerging contaminants) mobility is essential to predict MPs fate and distribution in soil-groundwater systems, yet relevant research is lacking. This study explored the effects of As(III) copresent in suspensions (0.05, 0.5, and 5 mg/L) on MPs transport/attachment behaviors in porous media containing varied water contents (θ = 100 %, 90 %, and 60 %) under different ionic strengths (5, 10, and 50 mM NaCl) and flow rates (2, 4, and 8 m/day). Despite solution ionic strengths, flow rates, porous media water contents, sizes, and surface charges of MPs, with coexisting humic acid, and in actual water samples, As(III) of three concentrations increased MPs transport in quartz sand and natural sandy soil. The increased electrostatic repulsion between MPs and sand caused by the altered MPs surface charge via the adsorption of As(III) together with steric repulsion from As(III) in solution contributed to the promoted MPs mobility in porous media. The occupying attachment sites by As(III) partially contributed to the increased mobility of MPs with negative surface charge in porous media. Clearly, As(III) coexisting in suspensions would enhance MPs transport in porous media, increasing MPs environment risks.

Transport and release behaviors of PFOA in saturated and unsaturated porous media with biochar amendment.

The widespread usage of perfluorooctanoic acid (PFOA) in daily consumer products and its high mobility in porous media have resulted in ubiquitous contamination of PFOA in the natural environment. Developing techniques to immobilize and inhibit the transport of PFOA thus is critical to reduce its potential risks. In present study, biochar, one type of environmental-friendly material produced from cellulose, was utilized in porous media to test its addition on inhibiting the transport and release of PFOA before and after aging process. We found that although PFOA had high mobility in saturated/unsaturated porous media, biochar addition could significantly inhibit PFOA transport in porous media with different saturations due to its high adsorption capacity towards PFOA. The inhibited transport of PFOA by biochar also held true in solution with copresence of natural organic matter and in actual river water. Moreover, we found that negligible PFOA was released from porous media with biochar amendment even after exposure to freeze-thaw/dry-wet treatment. PFOA adsorbed onto biochar could be completely desorbed and the biochar could be reused for subsequent cycles after desorption. Clearly, amendment of porous media with biochar would be a feasible and cost-effective method to immobilize PFOA in natural environment and reduce its environmental risks.

Is crystalline chromium phosphate environmentally stable? A study on the formation, dissolution and oxidation risk of CrPO4·6H2O.

Hexavalent chromium (Cr(VI)) contamination in soil and groundwater is usually remediated via reduction techniques. The formation of crystalline chromium phosphate (CrPO4·6 H2O) occurs as a byproduct during Cr(VI) remediation processes in the presence of phosphate, yet its stability in the environment has received limited attention. In this study, the formation conditions, structure, properties, and risks associated with the dissolution and oxidation of CrPO4·6 H2O were comprehensively assessed. Results showed that crystalline CrPO4·6 H2O was formed under pH 5 - 7 at room temperature. CrPO4·6 H2O exhibits higher dissolution risk compared to Cr(OH)3·3 H2O due to a long Cr-P bond (4.2 Å). H+ and OH- increased the risk of dissolution at pH 5 and 11, respectively, owing to the formation of CrH2PO42+ and Cr(OH)4-. In addition, under faintly acidic conditions, the high solubility of CrPO4·6 H2O increases the risk of oxidation; under neutral and weakly alkaline conditions, the presence of positively charged Cr(H2O)63+ structures on the surface elevates its susceptibility to contact and oxidation by δ-MnO2 compared to Cr(OH)3·3 H2O. Specifically, at pH 11, the conversion of CrPO4·6 H2O to Cr(OH)3·3 H2O results in similar oxidation risks for both Cr(III) precipitates.

Efficient As(III) removal from water by ZrO2 modified covalent organic framework under visible light irradiation.

Adsorption-oxidation is a promising technique to decontaminate As(III) polluted water. In present study, ZrO2-modified covalent organic framework (ZrO2-COF) was fabricated and used to remove arsenic from water under visible light irradiation. The results showed that ZrO2-COF (0.2 g/L) could efficiently capture As(III) (5 mg/L) from water and then oxidize the adsorbed As(III) into less toxic As(V) under visible light irradiation (60 min), achieving the complete decontamination of As(III) polluted water. Based on characterization results and theoretical calculations, we found that in ZrO2-COF composite, ZrO2 served as sites for adsorption of As(III)/the latter transformed As(V), while COF worked as photocatalytic center for As(III) oxidation. Effective As(III) removal could also be achieved by ZrO2-COF under visible light irradiation in complex water chemistry conditions including wide solution pH range (3-11), broad solution ion strength range (1-100 mM), the copresence of natural organic matter (0.1-1 mg/L humic acid) and various coexisting ions in solutions, as well as in real water samples. In addition, we found that ZrO2-COF had excellent reuse performance in 4 consecutive cycles. Our results showed that under visible light irradiation, ZrO2-COF composites could be a promising technique for efficient As(III) removal from water.

Efficient Photosynthesis of Hydrogen Peroxide by Cyano-Containing Covalent Organic Frameworks from Water, Air and Sunlight.

The insufficient exciton (e- -h+ pair) separation/transfer and sluggish two-electron water oxidation are two main factors limiting the H2 O2 photosynthetic efficiency of covalent organic frameworks (COFs) photocatalysts. Herein, we present an alternative strategy to simultaneously facilitate exciton separation/transfer and reduce the energy barrier of two-electron water oxidation in COFs via a dicyano functionalization. The in situ characterization and theoretical calculations reveal that the dicyano functionalization improves the amount of charge transfer channels between donor and acceptor units from two in COF-0CN without cyano functionalization to three in COF-1CN with mono-cyano functionalization and four in COF-2CN with dicyano functionalization, leading to the highest separation/transfer efficiency in COF-2CN. More importantly, the dicyano group activates the neighbouring C atom to produce the key *OH intermediate for effectively reducing the energy barrier of rate-determining two-electron water oxidation in H2 O2 photosynthesis. The simultaneously enhanced exciton separation/transfer and two-electron water oxidation in COF-2CN result in high H2 O2 yield (1601 µmol g-1 h-1 ) from water and oxygen without using sacrificial reagent under visible-light irradiation. COF-2CN can effectively yield H2 O2 in water with wide pH range, in different real water samples, in scaled-up reactor under natural sunlight irradiation, and in continuous-flow reactor for consecutively producing H2 O2 solution for water decontamination.

Sulfite Poses a Risk of Hexavalent Chromium Rebound in Vadose Zone: A Challenge of the Stability of CrxFe1-x(OH)3.

Cr(VI) rebound is the primary risk associated with the reduction remediation of Cr(VI)-contaminated soil. The potential impact of sulfites, which can be produced by microbial activities or originate from sulfur-containing remediation agents, on the Cr(VI) rebound in the vadose zone has been overlooked. When sulfites are present, the stability of CrxFe1-x(OH)3 is compromised and significantly inferior to that of Cr(OH)3, as demonstrated in this paper. First, Fe acts as a catalyst for the conversion of adsorbed sulfite to SO4·-, which subsequently triggers the oxidation of Cr(III) and results in the rebound of Cr(VI). The heterogeneous catalysis by Fe on the surface of CrxFe1-x(OH)3 plays a predominant role, contributing to 78% of the actual oxidation of Cr(III) among all employed catalytic processes. The presence of ambient Cl- can exacerbate the rebound effect of Cr(VI) by promoting the generation of HOCl. Furthermore, a portion of released Cr(VI) was reduced to Cr(III) by dissolved sulfite in the presence of dissolved Fe as a catalyst, thereby increasing the dissolution and migration risk associated with CrxFe1-x(OH)3. Hence, the presence of sulfites results in a significant increase in the Cr(VI) rebound and Cr(III) release from CrxFe1-x(OH)3. This challenges the conventional understanding of the stability of CrxFe1-x(OH)3.

Covalent organic frameworks for direct photosynthesis of hydrogen peroxide from water, air and sunlight.

Solar-driven photosynthesis is a sustainable process for the production of hydrogen peroxide, the efficiency of which is plagued by side reactions. Metal-free covalent organic frameworks (COFs) that can form suitable intermediates and inhibit side reactions show great promise to photo-synthesize H2O2. However, the insufficient formation and separation/transfer of photogenerated charges in such materials restricts the efficiency of H2O2 production. Herein, we provide a strategy for the design of donor-acceptor COFs to greatly boost H2O2 photosynthesis. We demonstrate that the optimal intramolecular polarity of COFs, achieved by using suitable amounts of phenyl groups as electron donors, can maximize the free charge generation, which leads to high H2O2 yield rates (605 µmol g-1 h-1) from water, oxygen and visible light without sacrificial agents. Combining in-situ characterization with computational calculations, we describe how the triazine N-sites with optimal N 2p states play a crucial role in H2O activation and selective oxidation into H2O2. We further experimentally demonstrate that H2O2 can be efficiently produced in tap, river or sea water with natural sunlight and air for water decontamination.

Boosting Exciton Dissociation and Charge Transfer in Triazole-Based Covalent Organic Frameworks by Increasing the Donor Unit from One to Two for the Efficient Photocatalytic Elimination of Emerging Contaminants.

As novel photocatalysts, covalent organic frameworks (COFs) have potential for water purification. Insufficient exciton dissociation and low charge mobility in COFs yet restricted their photocatalytic activity. Excitonic dissociation and charge transfer in COFs could be optimized via regulating the donor-acceptor (D-A) interactions through adjusting the number of donor units within COFs, yet relevant research is lacking. By integrating the 1,2,4-triazole or bis-1,2,4-triazole unit with quinone, we fabricated COF-DT (with a single donor unit) and COF-DBT (with double donor units) via a facile sonochemical method and used to decontaminate emerging contaminants. Due to the stronger D-A interactions than COF-DT, the exciton binding energy was lower for COF-DBT, facilitating the intermolecular charge transfer process. The degradation kinetics of tetracycline (model contaminant) by COF-DBT (k = (12.21 ± 1.29) × 10-2 min-1) was higher than that by COF-DT (k = (5.11 ± 0.59) × 10-2 min-1) under visible-light irradiation. COF-DBT could efficiently photodegrade tetracycline under complex water chemistry conditions and four real water samples. Moreover, six other emerging contaminants, both Gram-negative and Gram-positive strains, could also be effectively eliminated by COF-DBT. High tetracycline degradation performance achieved in a continuous-flow system and in five reused cycles in both laboratory and outdoor experiments with sunlight irradiation showed the stability and the potential for the practical application of COF-DBT.

Effects of Antibiotic Resistance Genes and Antibiotics on the Transport and Deposition Behaviors of Bacteria in Porous Media.

Antibiotics present in the natural environment would induce the generation of antibiotic-resistant bacteria (ARB), causing great environmental risks. The effects of antibiotic resistance genes (ARGs) and antibiotics on bacterial transport/deposition in porous media yet are unclear. By using E. coli without ARGs as antibiotic-susceptible bacteria (ASB) and their corresponding isogenic mutants with ARGs in plasmids as ARB, the effects of ARGs and antibiotics on bacterial transport in porous media were examined under different conditions (1-4 m/d flow rates and 5-100 mM NaCl solutions). The transport behaviors of ARB were comparable with those of ASB under antibiotic-free conditions, indicating that ARGs present within cells had negligible influence on bacterial transport in antibiotic-free solutions. Interestingly, antibiotics (5-1000 µg/L gentamicin) present in solutions increased the transport of both ARB and ASB with more significant enhancement for ASB. This changed bacterial transport induced by antibiotics held true in solution with humic acid, in river water and groundwater samples. Antibiotics enhanced the transport of ARB and ASB in porous media via different mechanisms (ARB: competition of deposition sites; ASB: enhanced motility and chemotaxis effects). Clearly, since ASB are likely to escape sites containing antibiotics, these locations are more likely to accumulate ARB and their environmental risks would increase.

Efficient peroxymonosulfate activation by magnetic MoS2@Fe3O4 for rapid degradation of free DNA bases and antibiotic resistance genes.

Antibiotic resistance genes (ARGs) have become as emerging contaminant with great concerns worldwide due to their threats to human health. It is thus urgent to develop techniques to degrade ARGs in water. In this study, MoS2@Fe3O4 (MF) particles were fabricated and used to activate peroxymonosulfate (PMS) for the degradation of four types of free DNA bases (T, A, C, and G, major components of ARGs) and ARGs. We found that MF/PMS system could effectively degrade all four DNA bases (T within 10 min, A within 30 min, C within 5 min, and G within 5 min) in very short time. During the reaction process, MF could activate PMS to form the reactive radicals such as ·OH, SO4·-, O2·-, and 1O2, contributing to the degradation of DNA bases. Due to the low adsorption energy, high charge transfer, and great capability for PMS cleavage, MF exhibited excellent PMS adsorption and activation performances. MoS2 in MF could enhance the cycle of Fe(III)/Fe(II), improving the catalytic performance. Excellent catalytic performances of MF/PMS system were achieved in complex water matrix (including different solution pH, coexisting of anions and natural organic matter) as well as in real water samples (including tap water, river water, sea water, and sewage) especially under high salinity conditions due to the generation of Cl· radicals and HClO species. MF/PMS system could also efficiently degrade ARGs (chromosomal kanR and plasmid gmrA) and DNA extracted from antibiotic resistant bacteria (ARB) in super-short time. Moreover, complete disinfection of two types of model ARB (E. coli K-12 MG 1655 and E. coli S17-1) could also be achieved in MF/PMS system. The high degradation performances of MF/PMS system achieved in the reused experiments and the 14-day continuous flow reactor experiments indicated the stability of MF particles. Due to the magnetic property, it would be convenient to separate MF particles from water after use via using magnet, facilitating their reuse of MF and avoiding potential water contamination by catalysts. Overall, this study not only provided a deep insight on Fe/Mo-triggered PMS activation process, but also provided an effective and reliable approach for the treatment of DNA bases, ARGs, DNA, and ARB in water.

Cotransport of different electrically charged microplastics with PFOA in saturated porous media.

The fate and transport behavior of microplastics (MPs), emerging colloidal contaminant ubiquitous in natural environments, would be greatly affected by other copresent pollutants. PFOA (emerging surfactant pollutant) would interact with MPs after encounter with them in natural environments, which could alter the transport behavior of both pollutants. Relevant knowledge is still lacking, affecting accurate prediction the fate and distribution of these two emerging contaminants in natural porous media. The cotransport behavior of different surface charged MPs (negatively/positively charged, CMPs/AMPs) with PFOA (three concentrations ranging from 0.1 to 10 mg/L) in porous media in both 10 and 50 mM NaCl solutions thus was investigated in the present study. We found PFOA inhibited CMPs transport in porous media, while enhanced AMPs transport. The mechanisms leading to the altered transport of CMPs/AMPs caused by PFOA were found to be different. The decreased electrostatic repulsion between CMPs-sand induced by the decreased CMPs negative zeta potentials via the adsorption of PFOA led to the inhibited transport of CMPs in CMPs-PFOA suspension. The enhanced electrostatic repulsion between AMPs-sand due to the decreased positive charge of AMPs via the adsorption of PFOA together with steric repulsion induced by suspended PFOA resulted in the increased transport of AMPs in AMPs-PFOA suspension. Meanwhile, we found that the adsorption onto MPs surfaces also impacted the transport of PFOA. Due to the lower mobility of MPs than PFOA, the presence of MPs despite their surface charge decreased the transport of PFOA of all examined concentrations in quartz sand columns. This study demonstrates that when MPs and PFOA are co-existing in environments, their interaction with each other will alter the fate and transport behavior of both pollutants in porous media and the alteration is highly correlated with the amount of PFOA adsorbed onto MPs and original surface properties of MPs.

Freeze-thaw treatment of bacteria significantly affects bacterial transport behaviors in both saturated and unsaturated porous media: Deep investigation the roles of flagella and extracellular polymeric substances.

The effects of freeze-thaw (FT) treatment and mechanisms on bacteria transport/retention in porous media with different moisture contents remain unclear. The transport/retention behaviors of bacteria with different FT treatment cycles (0, 1, and 3) in sand columns with different moisture contents (100 %, 90 %, 60 %, and 30 %) in NaCl solutions (10 and 100 mM) thus were investigated. Regardless of moisture content and solution chemistry, FT treatment increased bacteria deposition in sand columns, consistent with the results of QCM-D and visible parallel plate flow chamber (PPFC) systems. Via deep investigation of the contribution of flagella through using genetic-modified bacteria strain without flagella and that of extracellular polymeric substances (EPS) through analyzing its overall quantity, composition as well as the secondary structure of its two major components (proteins and polysaccharides), the mechanisms of FT treatment controlling bacterial transport/deposition were revealed. Although FT treatment induced flagella loss, it was not the major contributor to driving to the enhanced FT-treated cell deposition. Instead, FT treatment stimulated EPS secretion and increased its hydrophobicity (via increasing hydrophobicity of both proteins and polysaccharides), mainly contributing to the enhanced bacterial deposition. Even with copresent humic acid, FT treatment still enhanced bacterial deposition in sand columns with different moisture contents.

The overlooked role of UV185 induced high-energy excited states in the dephosphorization of organophosphorus pesticide by VUV/persulfate.

Vacuum ultraviolet (VUV) based advanced oxidation processes (AOPs) recently attracted widespread interests. However, the role of UV185 in VUV is only considered to be generating a series of active species, while the effect of photoexcitation has long been overlooked. In this work, the role of UV185 induced high-energy excited state for the dephosphorization of organophosphorus pesticides was studied using malathion as a model. Results showed malathion degradation was highly related to radical yield, while its dephosphorization was not. It was UV185 rather than UV254 or radical yield that was responsible for malathion dephosphorization by VUV/persulfate. DFT calculation results demonstrated that the polarity of P-S bond was further increased during UV185 excitation, favoring dephosphorization while UV254 did not. The conclusion was further supported by degradation path identification. Moreover, despite the fact that anions (Cl-, SO42- and NO3-) considerably affected radical yield, only Cl- and NO3- with high molar extinction coefficient at 185 nm significantly affected dephosphorization. This study shed light on the crucial role of excited states in VUV based AOPs and provided a new idea for the development of mineralization technology of organophosphorus pesticides.

Influence of flagella and their property on the initial attachment behaviors of bacteria onto plastics.

Flagella and their property would influence the initial attachment of bacteria onto plastics, yet their impacts have not been investigated. In present study, four types of E. coli with or without flagella as well as with normal or sticky flagella were utilized to investigate the effects of flagella and their property on the initial attachment behaviors of bacteria onto six types of plastics in freshwater systems. We found that E. coli with flagella exhibited better initial attachment performance onto all six types of plastics than strain without flagella. Flagella could help bacteria swim near to plastics, pierce the energy barrier, and subsequently attach onto plastics. With stronger adhesive force, sticky flagella could further facilitate bacterial attachment onto plastics. Moreover, flagella especially sticky flagella could help bacteria form more rigid attachment layer on plastics. Even with humic acid in suspensions or in river water, flagellar E. coli showed greater attachment onto plastics than E. coli without flagella. Humic acid might adsorb onto sticky flagella and thus decreased the attachment of bacteria with sticky flagella onto plastics. Obviously, flagella as well as their property would impact the initial attachment of bacteria onto plastics and the subsequent formation of plastisphere in freshwater.

Periodate activation by pyrite for the disinfection of antibiotic-resistant bacteria: Performance and mechanisms.

The propagation of antibiotic-resistant bacteria (ARB) greatly endangers the ecological safety and human health. This study employed pyrite (FeS2, naturally abundant mineral) for periodate (PI) activation to disinfect ARB. FeS2/PI system could disinfect 1 × 107 CFU mL-1 of kanamycin-resistant E.coli below the limit of detection in 20 min. Efficient ARB inactivation performance was achieved in pH from 3 to 9, ionic strength from 0 to 300 mM, with HA (0.1-10 mg L-1) in suspension, and in real water samples including tap water, river water and sewage. FeS2/PI system could also efficiently disinfect gentamycin-resistant E.coli and Gram-positive B. subtilis. The generated reactive species including Fe(IV), ·O2- and ·OH would attack cell membrane and overwhelmed intracellular defense system. The intracellular kanamycin resistance genes in cells would be released and then degraded in FeS2/PI system. PI preferred to be adsorbed on Fe site of FeS2 (with lower adsorption energy, more occupancy of bonding state and stronger bonding strength). The subsequent transfer of electron cloud from Fe site to PI would cleave IO bond to generate reactive species. Moreover, FeS2/PI system could also combine with sand filtration system to efficiently capture and disinfect ARB. Therefore, FeS2/PI system is a promising approach to inactivate ARB in different scenarios.

Non-radical degradation of organic pharmaceuticals by g-C3N4 under visible light irradiation: The overlooked role of excitonic energy transfer.

In this work, an excitonic energy transfer (EET) based non-radical mechanism was proposed for the degradation of organic pharmaceuticals by graphitic carbon nitride (g-C3N4) under visible light irradiation. Using diclofenac (DCF) as a model molecule, the competition between single electron transfer (SET) and EET was studied through modulating the exciton binding energy of g-C3N4. The different mechanisms of SET and EET for DCF degradation were predicted by DFT calculation, and further confirmed by their different degradation pathways. When EET played an important role, the rationality of some very popular radical scavengers, such as p-BQ, TEMPOL and furfuryl alcohol must be reconsidered. In addition, humic acid (HA) had a distinct effect on EET and SET. Specifically, HA enhanced the EET process through photosensitization, but suppressed SET through radical quenching effect. The effect of HA on DCF degradation depended on the contribution ratio of SET and ET.

The degradation of municipal solid waste incineration leachate by UV/persulfate and UV/H2O2 processes: The different selectivity of SO4•- and •OH.

In this work, the different selectivity of SO4•- and •OH towards municipal solid waste incineration leachates (MSWILs) was studied by a comparative study of UV/persulfate (PS) and UV/H2O2. Results showed SO4•- preferentially mineralized carbon atoms of higher average oxidation state, while •OH showed a two-stage mechanism of partial oxidation and mineralization successively. Electron spin resonance (ESR) analysis showed SO4•- had superior selectivity towards MSWILs than •OH, and Fe(II) would significantly affect the selectivity via forming Fe-MSWILs complex. As the consequence, Fe(II) showed slightly negative effect on UV/PS, but greatly enhanced the performance of UV/H2O2/Fe(II). High concentration of Cl- affected the degradation of non-fluorescent substances by UV/PS, while SO42- and NO3- showed no effect. In contrast, anions showed no effect on UV/H2O2. In addition, •OH preferentially attacked large molecules, but SO4•- showed no selectivity. This study further revealed the selectivity of SO4•- and •OH in the treatment of hypersaline wastewater, and provided theoretical support for the development of targeted technology.