Construction of Cu7 S4 @CuCo2 O4 Yolk-Shell Microspheres Composite and Elucidation of Its Enhanced Photocatalytic Activity, Mechanism, and Pathway for Carbamazepine Degradation.

Water pollution caused by the massive use of medicines has caused significant environmental problems. This work first reports the synthesis and characterization of the Cu7 S4 /CuCo2 O4 (CS/CCO) yolk-shell microspheres via hydrothermal and annealing methods, and then investigates their photocatalytic performance in removing organic water pollutants. The 10-CS/CCO composite with yolk-shell microspheres exhibits the highest photodegradation rate of carbamazepine (CBZ), reaching 96.3% within 2 h. The 10-CS/CCO also demonstrates more than two times higher photodegradation rates than the pure (Cu7 S4 ) CS and (CuCo2 O4 ) CCO. This outstanding photocatalytic performance can be attributed to the unique yolk-shell structure and the Z-scheme charge transfer pathway, reducing multiple reflections of the acting light. These factors enhance the light absorption efficiency and efficiently transfer photoexcited charge carriers. In-depth, photocatalytic degradation pathways of CBZ are systematically evaluated via the identification of degradation intermediates with Fukui index calculation. The insights gained from this work can serve as a guideline for developing low-cost and efficient Z-scheme photocatalyst composites with the yolk-shell structure.

Complete mineralization of a humic acid by SO4 ·- generated on CoMoO4/gC3N4 under visible-light irradiation.

The sulfate radical ([Formula: see text]), almost a most active species, is believed to be the best oxidant in the elimination of aquatic organics in advanced oxidation processes. However, acquiring their steady-state generation with high concentration is still challenging work. In this report, we focused on designing a novel composite, in which uniform and rod-like CoMoO4 was fabricated on gC3N4 through Co-N coordination. In this way, the composite acquired an immobilization of Co (II) in its refraining from leaking, and synchronically, a dense heterojunction between CoMoO4 and gC3N4. Over the heterojunctions, photogenerated electrons gained a prolonged lifetime through their efficient separation from holes. The life-prolonged electrons, together with Co (II) in CoMoO4, effectively activated the persulfate, and a concentration of steady-state [Formula: see text] as high as 1.8 × 10-14 mol · l-1 was obtained. With [Formula: see text] fast and complete mineralization of a humic acid was achieved.

Unraveling the pyridinic nitrogen vacancy in carbon nitride for photo-self Fenton-like purification of organic contaminants.

This work reports a carbon nitride with pyridinic nitrogen-vacancy (N2CV-CN), which purifies organic contaminants via an in-situ photo-self Fenton-like reaction. Experiments and calculations demonstrated that the nitrogen-vacancy induces lone-paired (LP) and symmetry-unpaired electrons, promoting the formation of low-energy LP-π hybridized orbitals and helping to overcome the pairing energy required for oxygen to accept electrons. Furthermore, the nitrogen-vacancy accelerates film and intra-particle diffusion rates of organic contaminants on N2CV-CN, creating beneficial conditions for reactive oxide species to mineralize organic contaminants. Under sunlight and atmospheric oxygen, a photo-self Fenton-like reaction involving proton-coupled electron transfer occurred on the surface of N2CV-CN. Furthermore, by integrating photocatalysis with flocculation, about 99.1 % suspended substance, 45.5 % chemical oxygen demand, and 38.4 % biological oxygen demand were reduced from polluted river-water. Constructing N2CV-CN and understanding its crucial role offer theoretical and methodological insights into the in-situ purification of contaminated water bodies.

[Synthesis and properties of nano-rutile TiO2 photocatalysts].

Nano-rutile TiO2 photocatalysts with bigger specific surface area were prepared by a hydrolysis method at 323 K, and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), ultraviolet-visible diffuse reflection spectroscopy (UV-Vis DRS), infrared spectroscopy (IR) and photoelectrochemical (PEC). The ultraviolet (UV) and visible light photocatalytic activities of as-prepared rutile and anatase TiO2 nano-photocatalysts with almost same specific surface areas were evaluated by methyl orange (MO) as mode compound to photocatalytic reaction. The results of the photocatalytic experiment shows that when rutile and anatase have the similar specific surface area of approximately 95 m2.g-1, the UV light photocatalytic activity of rutile is comparable to that of anatase, while rutile shows significantly higher visible light photocatalytic activities than anatase. The photoelectrochemical experiment shows that the order of photocurrent densities of the catalysts from weak to strong is in accordance with the order of UV light photocatalytic activities of the catalysts from low to high under UV light irradiation.

A novel scheme to improve the photo-Fenton performance of iron oxychloride by carbon: Three existent states and roles of carbon in the degradation of tetracycline in water.

The photo-Fenton process is promising for sincerely treating contaminated water. In this work, carbon-decorated iron oxychloride (C-FeOCl) is synthesized as a photo-Fenton catalyst for removing tetracycline (TC) from water. Three actual states of carbon are identified and their different roles in enhancing photo-Fenton performance are revealed. All carbon on/in FeOCl, including graphite carbon, carbon dots and lattice carbon, enhance visible light adsorption. More importantly, a homogeneous graphite carbon on the outer surface of FeOCl accelerates the transportation-separation of photo-excited electrons along the horizontal direction of FeOCl. Meanwhile, the interlayered carbon dots offer a FeOC bridge in helping the transportation-separation of photo-excited electrons along the vertical direction of FeOCl. In this way, C-FeOCl acquires isotropy in conduction electrons to ensure an efficient Fe(II)/Fe(III) cycle. These interlayered carbon dots extend the layer spacing (d) of FeOCl to about 1.10 nm, exposing the internal iron centers. The lattice carbon significantly increases the amounts of coordinatively unsaturated iron sites (CUISs) in activating hydrogen peroxide (H2O2) to hydroxyl radical (OH). Density functional theory (DFT) calculations confirm this activation on inner and external CUISs with a significantly low activation energy of about 0.33 eV.

Role of humic acid in the transformation of hexavalent chromium in a sulfidated ferrihydrite system.

Ferrihydrite (Fh) often coexists with organic matter (i.e., humic acid (HA)) in the environment; however, its impacts on the transformation of hexavalent chromium (Cr(VI)) is poorly understood during the sulfidation of Fh. Upon exposed to 2 mM sulfide for 12 h, the total amount of Fe(II) (Fe(II)tot, 0.78 mM) in treatments with HA (300 mg HA/L) was higher than that (0.67 mM) in treatments without HA, since HA could enhance the solubility of Fe(II). After then, the Cr(VI) was reduced by sulfidated Fh. Aqueous Cr(VI) concentration (Cr(VI)aq) declined from 0.67 to 0.43 mM with the increase of HA concentration from 0 to 400 mg/L, which was partly ascribed to the inhibition of surface passivation by HA. Moreover, the increase in Fe(II) during the sulfidation of Fh also exerted a strong impact on the transformation of Cr(VI) subsequently. In addition of HA, batch experiments suggested that EDTA could also promote the formation of Fe(II) (Fe(II)tot, 0.80 mM), rendering a lower Cr(VI)aq (0.59 mM) in EDTA-300 treatments. This study further demonstrated that HA played an important role in the transformation of Cr(VI), hence providing a theoretical basis for in-situ remediation of Cr(VI) in the future.

Regulating Lewis acidity and local electron density of iron-based metal organic frameworks via cerium doping for efficient photo-Fenton process.

The photo-Fenton performance of Fe-based metal organic frameworks (Fe-MOFs) largely depends on the amount and the local electron density of metal coordinately unsaturated sites (M CUSs). However, a majority of Fe active sites are fully bound by organic ligands leading to decreased Fe CUSs. Additionally, the symmetrical electronic distribution of iron-oxo (Fe-O) clusters and the fast electron-hole recombination are unbeneficial for the directional electron transfer and the following electron accumulation on Fe CUSs. Herein, the structure of Fe-O clusters onto the framework of MIL-88B was controllably regulated via change of Ce doping amount, among which Fe0.8Ce0.2-MIL-88B exhibited highest removal efficiency of tetracycline (TC). That was mainly ascribed to the following two points: for one, the induced ligand missing defects ameliorated the pore structures and generated more M CUSs; for another, the lower electronegativity of Ce than Fe and the role of ligand missing defects as electron trap state collectively increased the local electron density at Fe CUSs. As a result, the increased M CUSs provided more active sites for H2O2 coordination and the highly concentrated electrons density at Fe CUSs afforded the substantial electron donation towards robust H2O2 dissociation into ∙OH. Furthermore, the increased mesoporous size favored highly-efficient utilization of ∙OH. This work provides a facile strategy to improve photo-Fenton performance of Fe-MOFs.

Triisobutyl phosphate biodegradation by enriched activated sludge consortia: Degradation mechanism and bioaugmentation potential.

This study investigated the ability of activated sludge (AS) to biodegrade triisobutyl phosphate (TiBP) after acclimation in an AS bioreactor by adding 50 mg/L TiBP. The bioreactor significantly increased the biotransformation rate of TiBP (2.15-12.7 d-1) over two months of acclimation. Seven transformation products (TPs) of TiBP were identified by high-resolution mass spectrometry, and hydrolysis, hydroxylation and dehydrogenation were the major biodegradation pathways of TiBP. TiBP degradation solutions at 0, 3, 7, and 10 h showed significantly toxic effects on zebrafish embryos, while the toxicity of TiBP degradation solutions at 24 h significantly decreased. Pseudomonas was inferred to be a specific bacterial population in the TiBP metabolic microbial consortium (TMMC) that degrades TiBP (p < 0.001). When TMMC (0.5, 1, and 2 gss/L) was introduced into AS, the TiBP biotransformation rates (1.97, 2.05, and 2.26 d-1 at 1.0 mg/L TiBP, and 0.09, 0.11, and 0.83 d-1 at 30.0 mg/L TiBP) were significantly enhanced compared to the control (0.31 and 0.07 d-1) without TMMC inoculation. In general, this study provides new insights into the key species populations that accelerate TiBP degradation and promote the development of TiBP reduction biotechnology in WWTPs.

Mechanistic insight into the charge carrier separation and molecular oxygen activation of manganese doping BiOBr hollow microspheres.

High-efficiency separation of photogenerated charges and molecular oxygen activation is very important for photocatalytic removal of organic pollutants. However, the current understanding of the effect mechanism of metal substitution for the separation of photo-generated charges and molecular oxygen activation is still poor. Herein, efficient manganese (Mn)-doped BiOBr hollow microspheres synthesis, systematic characterizations, and theoretical calculation discovered that Mn-doping could not only induce produce oxygen vacancies (OVs), but also can act as active sites for catalytic reactions. The induced production of OVs and Mn2+/Mn3+ by Mn optimal doping introduced into BiOBr can synergistic promote the separation of photogenerated charges and molecular oxygen activation leads to significantly enhances degradation of crystal violet (CV). Upon analysis, Mn-doping introducing unsaturated d-orbital with bridging O2- formation π-donation accelerated the separation of photo-generated charges. Meanwhile, the larger overlap of Mn-3d orbitals with O2-2p orbitals forms a π-donation bond with charge transfer from metal to O2 leading to the oxygen-oxygen (OO) bond length and molecular oxygen activation. Finally, we proposed a possible mechanism to explain the highly efficient photocatalytic degradation performance of the acquired photocatalysts. This study provides not only a novel strategy for the rational design of highly active photocatalysts, but also in-depth insights into the separation of photo-generated charges and molecular oxygen activation.

Aerobic degradation of parent triisobutyl phosphate and its metabolite diisobutyl phosphate in activated sludge: Degradation pathways and degrading bacteria.

Although organophosphate esters (OPEs) degradation has been widely studied, the degradation of their metabolites is always ignored. Triisobutyl phosphate (TiBP), a typical alkyl-OPEs, is of emerging concern because of its potential ecotoxicity in the environment. This study provides comprehensive understanding about the degradation of TiBP and one of its metabolites, diisobutyl phosphate (DiBP) using activated sludge (AS). The results showed that TiBP and DiBP were degraded mainly through hydrolysis, dehydrogenation, and hydroxylation. The degradation kinetics indicated that DiBP had similar transformation rates to its parent TiBP in AS, highlighting the importance of metabolite DiBP study. Dehydrogenase, hydroxylase, phosphotriesterase, phosphodiesterase, and phosphomonoesterase played an important role in contributing to TiBP and its metabolites degradation via enzyme activity analysis. Besides, the expression of genes encoding these enzymes in bacteria and the relative abundance change of bacterial populations indicated that Sphingomonas and Pseudomonas may be the degrading bacteria of TiBP and Pseudomonas may be the main degrading bacteria of DiBP. This study provides new perspectives for metabolite DiBP and its parent TiBP degradation. It highlights that the formation and degradation of metabolites must be considered into the future researches.

Insight into the existent state of nitrogen-doped carbon dots in titanate nanotubes and their roles played toward simultaneous removal of coexisted Cu2+ and norfloxacin in water.

In this work, nitrogen-doped carbon dots (NCDs) were introduced in different existent sites of titanate nanotubes (TNTs) by a facile synthesis, and their effects on surface potential, photoelectrochemical properties and simultaneous removal of coexisted Cu2+ and norfloxacin (NOR) performance in water were systematically investigated. Constructed NCDs-TNTs composite displayed superior performance towards the adsorption (ion exchange/coordination) of Cu2+ and adsorption-oxidization of NOR over the two individuals, mainly benefiting from the collaboration of NCDs in different existent states. The existence of TiNH chemical linkage was identified between TNTs and NCDs-OT (NCDs on the outer surface of TNTs), which not only modulates the surface potential to favor the external diffusion of Cu2+ or NOR+ from aqueous solution to the negatively charged NCDs-TNTs, but also facilitates the intraparticle transfer of contaminants to the reactive sites. In addition, the up-conversion light property of NCDs-OT and the interstitial NCDs-IT (NCDs on the inner surface of TNTs) doping in TNTs interact together to enable NCDs-IT-TNTs to fully absorb and utilize all visible light. The photoexcited electrons were further trapped by NCDs-OT to promote the photogenerated carrier separation. Adsorbed Cu2+ could also improve the performance of NCDs-TNTs toward NOR oxidization, mainly owing to the self-synchronous doping of adsorbed Cu2+ broadening light absorption area and acting as mediators for delivering electrons. This work provides unique insights into the structural design of composite materials for such combined contamination remediation in water.

Highly dispersed of Ag/AgCl nanoparticles on exfoliated FeOCl nanosheets as photo-Fenton catalysts for pollutants degradation via accelerating Fe(II)/Fe(III) cycle.

In this work, Ag/AgCl/FeOCl (Ag-Fe) catalysts were successfully prepared via multistep routes in which Ag was uniformly anchored to the enriched Cl sites provided by exfoliated FeOCl nanosheets. Among these Ag-Fe catalysts, 5% Ag-Fe exhibited the highest pseudo first-order kinetic constant 0.1056 min-1 for photo-Fenton degradation of Rhodamine B (RhB), which was 11 times higher than that of FeOCl (0.0096 min-1). Ag-Fe catalysts exposed more coordinatively unsaturated Fe active sites to coordinate with H2O2 due to the cleavage of Fe-Cl bond. The exposed coordinatively unsaturated Fe(III) active sites could capture the photoinduced electrons and reduce them to Fe(II), which boosted the separation efficiency of photogenerated charge carriers. Meanwhile, the photogenerated electrons of Ag0 transferred to the FeOCl, promoting the reduction of Fe(III) to Fe(II). In addition, the intensified visible light adsorption (SPR effect) was achieved after introducing Ag/AgCl nanoparticles on exfoliated FeOCl. Hydroxyl radicals (·OH) and holes (h+) were determined as the main reactive oxidative species (ROS) in the photo-Fenton degradation process.

Steady release-activation of hydrogen peroxide and molecular oxygen towards the removal of ciprofloxacin in the FeOCl/CaO2 system.

Difficult storage of hydrogen peroxide (H2O2), low production of reactive oxygen species (ROS), and inefficient Fe(II)/Fe(III) recycling limit the application of the Fenton-like process. Calcium peroxide (CaO2) based iron oxychloride (FeOCl) system was developed for solving these deficiencies, and ciprofloxacin (CIP) was effectively degraded within 20 min treatment. 0.33 mmol/L H2O2 and 2.4 mg/L dissolved oxygen (DO) were produced via CaO2. Quenching experiments and electron paramagnetic resonance results confirmed that hydroxyl radicals (·OH) and superoxide anion (·O2-) worked as the main ROS. Density functional theory (DFT) calculations and experimental results suggested that H atoms of H2O2 adsorbed on FeOCl favored the activation of H2O2 into ·OH and DO into ·O2-, and electrophilic Cl and O coordination in FeOCl contributed to the cycle of Fe(II)/Fe(III). ·OH and·O2- were responsible for CIP degradation, and toxicity assessments demonstrated that the developed system reduced the hazard of treated solution. Clarity of FeOCl/CaO2 system triple roles, including H2O2 and O2 production, activation into ROS, and Fe(II)/Fe(III) recycling, facilitates the efficient utilization of O2 in Fenton-like system.

Novel scheme towards interfacial charge transfer between ZnIn2S4 and BiOBr for efficient photocatalytic removal of organics and chromium (VI) from water.

Construction of Z-scheme heterostructure is an effective strategy to enhance the charge carriers' separation. However, successfully achieving this on the defect heterojunction to improve the photocatalytic activity remains challenging. This work successfully obtained sulfur vacancy in the ZnIn2S4/BiOBr (SZIS/BOB) heterojunction composites with S-O covalent bonding using a hydrothermal method. As a result, they exhibited superior photocatalytic and stability performance. The optimized SZIS/BOB-10 exhibited excellent rhodamine B degradation (95.2%) and chromium (VI) reduction (97.8%) within 100 min under visible light. The enhanced composites with S-vacancies, S-O bond, and internal electric field induced the Z-scheme charge transfer mechanism. We had verified this mechanism based on the surface photovoltage spectra, electron spin response spectra, and density functional theory calculations. This work not only provides valuable insights into designing photocatalysts with a direct Z scheme heterostructure but also delineates a promising strategy for developing efficient photocatalysts to degrade organic pollutants.

A review on organophosphate flame retardants in the environment: Occurrence, accumulation, metabolism and toxicity.

Organophosphate flame retardants (OPFRs), as a substitute for brominated flame retardants (BFRs), are widely used in industrial production and life. The presence of OPFRs in the environment has an adverse effect on the ecological environment system. This review provides comprehensive data for the occurrence of OPFRs and their diester metabolites (OP diesters) in wastewater treatment plants, surface water, drinking water, sediment, soil, air and dust in the environment. In particular, the accumulation and metabolism of OPFRs in organisms and the types of metabolites and metabolic pathways are discussed for animals and plants. In addition, the toxicity of OP triesters and OP diesters in organisms is discussed. Although research on OPFRs has gradually increased in recent years, there are still many gaps to be filled, especially for metabolic and toxicity mechanisms that need in-depth study. This review also highlights the shortcomings of current research and provides suggestions for a basis for future research on OPFRs.

Efficient photoreduction of Cr(VI) on TiO2/functionalized activated carbon (TiO2/AC-AEMP): improved adsorption of Cr(VI) and induced transfer of electrons.

Slow and random transfer of pollutants and photo-induced carriers on photocatalysts causes loss of efficiency in photodegradation of contaminants. Enhancing and directing mass transfer of them are considered as two major methods for improving the photodegradation of pollutants over photocatalysts. Here in this work, we focused on the design of a novel photocatalyst which not only accelerated the transfer rate of Cr(VI) and electrons but also provided specific transfer routes for them. By careful characterizations, it is indicated that 2-((2-(2-aminoethylamino)ethylimino)methyl)phenol (AEMP) was covalently attached onto activated carbon (AC), which enhanced Cr(VI) transfer from bulk solution to AC through electrostatic or coordinative interactions. The external mass transfer coefficient (Kf) of Cr(VI) over TiO2/AC-AEMP was estimated as 1.75 × 10-6 m s-1, which was ~ 12.79 and ~ 5.96 times that of TiO2 and TiO2/AC, respectively. Dense and homogeneous heterojunctions between AC and TiO2 were acquired synchronically by forming Ti-O-C linkages, which increased traveling of electrons from TiO2 to AC. Accordingly, Cr(VI) can capture photo-induced electrons on the surface of AC via concrete routes and then be reduced efficiently. The results showed that the photoreduction rate of Cr(VI) on TiO2/AC-AEMP reached to ~ 92.7%, and the overall photocatalytic activity of this well-designed TiO2/AC-AEMP has been enhanced significantly by 5.5 times compared to TiO2/AC. The enhanced photocatalytic activity of TiO2/AC-AEMP was mainly attributed to an improved synergetic process of mass transfer-induced adsorption-photoreduction by forming specific transfer routes for accelerative motion of Cr(VI) and electrons. This work provides a feasible strategy to improve the photoactivity of photocatalysts for the degradation of pollutants by effective mass transfer. Graphical abstract.

Araneose Ti3+ self-doping TiO2/SiO2 nanowires membrane for removal of aqueous MB under visible light irradiation.

Araneose Ti3+ self-doped TiO2/SiO2 nanowires (RTiO2/SiO2) were prepared and anchored onto a polyethersulfone (PES) membrane. Careful characterizations and measurements indicated a covalent grafting of SiO2 onto reduced TiO2 (RTiO2) through Ti-O-Si linkages, acquiring uniformed RTiO2/SiO2 nanowires of almost complete anatase and benign hydrophilicity. The RTiO2/SiO2-based PES membrane showed a significantly enhanced visible light-driven degradation rate of methylene blue (MB) (90.7%), compared with that on bare PES (11.1%) and PES-RTiO2 (59.6%) membranes. The residual MB in filtered water was less than 5% after reusing three times. The normalized permeate flux of the modified membrane was 0.83, and the transmembrane pressure only increased by 0.4 MPa under irradiation of visible light. The improved performance of the PES-RTiO2/SiO2 was attributed to efficient intercept of MB molecular, light harvesting of visible light, and separation of charge carriers on araneose RTiO2/SiO2 nanowires.

Versatility of CoPcS in CoPcS/TiO2 for MB degradation: photosensitization, charge separation and oxygen activation.

In this report, a composite photocatalyst consisting of cobalt phthalocyanine sulfate (CoPcS) and TiO2 was prepared by a facile synthesis. Careful characterizations and measurements indicate a covalent grafting of CoPcS onto TiO2 through Ti-O-S linkages, acquiring an intimate heterojunction between TiO2 and CoPcS. The obtained composite was evaluated for its photocatalytic activity toward the degradation of methyl blue (MB) under visible light irradiation. The evaluation showed a significantly enhanced degradation rate of MB by CoPcS/TiO2. The improved photocatalytic performance of CoPcS/TiO2 was attributed to the photosensitization of TiO2 by CoPcS, charge separation by electron transfer at the interface of the heterojunction formed between CoPcS and TiO2, and oxygen activation via CoPcS. A synergetic mechanism in improving the photocatalytic performance of TiO2 by CoPcS was investigated.