Effective photodegradation of antibiotics by guest-host synergy between photosensitizer and bismuth vanadate: Underlying mechanism and toxicity assessment.

The removal of antibiotics in wastewater has attracted increasing attention. Herein, a superior photosensitized photocatalytic system was developed with acetophenone (ACP) as the guest photosensitizer, bismuth vanadate (BiVO4) as the host catalyst and poly dimethyl diallyl ammonium chloride (PDDA) as the bridging complex, and used for the removal of sulfamerazine (SMR), sulfadiazine (SDZ) and sulfamethazine (SMZ) in water under simulated visible light (λ > 420 nm). The obtained ACP-PDDA-BiVO4 nanoplates attained a removal efficiency of 88.9%-98.2% for SMR, SDZ and SMZ after 60 min reaction and achieved kinetic rate constant approximately 10, 4.7 and 13 times of BiVO4, PDDA-BiVO4 and ACP-BiVO4, respectively, for SMZ degradation. In the guest-host photocatalytic system, ACP photosensitizer was found to have a great superiority in enhancing the light absorption, promoting the surface charge separation-transfer and efficient generation of holes (h+) and superoxide radical (·O2-), greatly contributing to the photoactivity. The SMZ degradation pathways were proposed based on the identified degradation intermediates, involving three main pathways of rearrangement, desulfonation and oxidation. The toxicity of intermediates was evaluated and the results demonstrated that the overall toxicity was reduced compared with parent SMZ. This catalyst maintained 92% photocatalytic oxidation performance after five cyclic experiments and displayed a co-photodegradation ability to others antibiotics (e.g., roxithromycin, ciprofloxacin et al.) in effluent water. Therefore, this work provides a facile photosensitized strategy for developing guest-host photocatalysts, which enabling the simultaneous antibiotics removal and effectively reduce the ecological risks in wastewater.

Electrochemical Advanced Oxidation of Perfluorooctanoic Acid: Mechanisms and Process Optimization with Kinetic Modeling.

Electrochemical advanced oxidation processes (EAOPs) are promising technologies for perfluorooctanoic acid (PFOA) degradation, but the mechanisms and preferred pathways for PFOA mineralization remain unknown. Herein, we proposed a plausible primary pathway for electrochemical PFOA mineralization using density functional theory (DFT) simulations and experiments. We neglected the unique effects of the anode surface and treated anodes as electron sinks only to acquire a general pathway. This was the essential first step toward fully revealing the primary pathway applicable to all anodes. Systematically exploring the roles of valence band holes (h+), hydroxyl radicals (HO•), and H2O, we found that h+, whose contribution was previously underestimated, dominated PFOA mineralization. Notably, the primary pathway did not generate short-chain perfluoroalkyl carboxylic acids (PFCAs), which were previously thought to be the main degradation intermediates, but generated other polyfluorinated alkyl substances (PFASs) that were rapidly degraded upon formation. Also, we developed a simplified kinetic model, which considered all of the main processes (mass transfer with electromigration included, surface adsorption/desorption, and oxidation on the anode surface), to simulate PFOA degradation in EAOPs. Our model can predict PFOA concentration profiles under various current densities, initial PFOA concentrations, and flow velocities.

Novel sphere-like copper bismuth oxide fabricated via ethylene glycol-introduced solvothermal method with improved adsorptive and photocatalytic performance in sulfamethazine removal.

In this research, ethylene glycol-introduced solvothermal method was employed to fabricate a novel sphere-like CuBi2O4 material to improve the adsorptive and photocatalytic performance of conventional CuBi2O4. A series of characterization has been applied to investigate properties of the obtained CuBi2O4 (CBO-EG3). Compared with conventional rod-like CuBi2O4 (CBO), the synthesized sphere-like CBO-EG3 exhibited rough surface, larger specific surface area, and more effective separation of photo-generated carriers, which overcome main shortcomings of CuBi2O4. The removal efficiency of typical antibiotic sulfamethazine (SMZ) reached almost 100% under the optimal experimental conditions. About 70% of SMZ could be adsorbed in 180-min dark reaction, with residual being photodegraded in 30 min. CBO-EG3 showed much higher photocatalytic efficiency than pure CBO, attributing to its highly effective photo-induced electron and hole separation. Meanwhile, substantial adsorption of pollutant on CBO-EG3 contributed vastly to removal of SMZ, photo-generated electrons and holes inclined to react with adsorbed SMZ directly, and photocatalytic process was mainly led by non-radical reaction. Elimination of SMZ in actual water samples and recycling experiment were also performed to evaluate CBO-EG3's practical application potential. This study delivered a method to promote CuBi2O4's adsorptive and photocatalytic ability, which could expand the application of CuBi2O4 in wastewater treatment.

Use mechanochemical activation to enhance interfacial contaminant removal: A review of recent developments and mainstream techniques.

Interfacial processes, including adsorption and catalysis, play crucial roles in environmental contaminant removal. Mechanochemical activation (MCA) emerges as a competitive method to improve the performance of adsorbents and catalysts. The development and application of MCA in the last decades are thereby systematically reviewed, particularly highlighting its contribution to interfacial process modulation. Two typical apparatuses for MCA are ball milling (BaM) and bead milling (BeM). Compared to BaM, BeM is able to yield a much higher MCA intensity, because it could pulverize bulk solid particles to nearly 100 nm. Since MCA intensity on the adsorbents and catalysts is directly responsible for the contaminant removal afterwards, quantitative and qualitative determination methods for valid MCA intensity are introduced. MCA benefits both the adsorption kinetics and capacity of powdered activated carbon by increasing the specific surface area. Carbon oxidation should be given an additional attention, but potentially favors the adsorption of heavy metals. MCA favors the catalyst performance by providing abundant surface functional group and increasing the free energy in the near-surface region. Finally, the future research needs are identified.

Hydrochars from pinewood for adsorption and nonradical catalysis of bisphenols.

In the present study, hydrochars (HCs) were prepared from pinewood biomass by high-temperature pyrolysis and applied as environmental-friendly adsorbents and catalysts in the removal of bisphenol F (BPF) and bisphenol S (BPS) from water. It was found that the structural oxygen defects on hydrochars not only enhance the specific surface area for adsorption of the bisphenols, but also function as an electron conductor for molecular oxygen activation in nonradical pathways. The hydrochar pyrolyzed at 800 °C (HC-800) showed the superior adsorption and catalytic performances toward BPS and BPF removals in a wide pH range, and the removal efficiencies were hardly inhibited by the coexistent inorganic anions and humic acid. Particularly, the nonradical reaction is the dominated catalytic oxidation process in a H2O2-HC-800 system, different from the traditional radical-based process with persistent free radicals on hydrochars derived from low-temperature pyrolysis. This study provides a novel route toward the efficient removal of endocrine disrupting compounds via the synergistic adsorption and nonradical catalysis.

Targeted modulation of g-C3N4 photocatalytic performance for pharmaceutical pollutants in water using ZnFe-LDH derived mixed metal oxides: Structure-activity and mechanism.

Pharmaceuticals have been frequently detected in various water bodies, posing potential threat to human health and ecological environment. In this work, ZnFe-LDH derived mixed metal oxides (ZnO/ZnFe2O4, ZnFeMMO) were innovatively adopted to modulate the g-C3N4 photocatalytic performance for the enhanced degradation of ibuprofen (IBF) and sulfadiazine (SDZ) as targeted pollutants. Characterization analyses indicated that the g-C3N4/ZnFeMMO composites were in the feature of rationally-designed microarchitecture, increased specific surface area, improved light absorbance and efficient charge separation, thereby resulting in promoted photocatalytic activities. Furthermore, the ratio of g-C3N4 to ZnFeMMO in the composites was found to exert significant effects on the resulted microstructures and properties. The results showed that the composite with low g-C3N4 content of 1.0 wt% or high g-C3N4 content of 90 wt% exhibited the optimum catalytic activity for the degradation of IBF or SDZ, respectively. Such distinct structure-activities can be attributed to the different dominated reactive species in two cases: h+ for IBF degradation but OH for SDZ degradation. A Z-scheme mechanism was proposed for the charge separation, together with ZnFe2O4 as a light sensitizer. Degradation pathways for IBF and SDZ were established by ESI-QToF-MS technology. This work provided a new perspective to develop rationally-architectured g-C3N4 based photocatalysts for the decontamination of water polluted by pharmaceuticals.

Visible-light degradation of sulfonamides by Z-scheme ZnO/g-C3N4 heterojunctions with amorphous Fe2O3 as electron mediator.

ZnO grafted amorphous Fe2O3 matrix (ZnO/Fe2O3) was coupled with g-C3N4 to synthesize heterojunction photocatalysts with a loosened multilayered structure. The ZnO/Fe2O3/g-C3N4 exhibited enhanced photocatalytic performance in the degradation of sulfamethazine under visible-light irradiation (λ > 420 nm), with an optimum photocatalytic degradation rate approximately 3.0, 2.4 times that of pure g-C3N4 and binary ZnO/g-C3N4. Moreover, the target sulfonamides spiked in actual surface water samples could be efficiently photodegraded by ZnO/Fe2O3/g-C3N4 after 8 h of irradiation, demonstrating its practical potential. An amorphous Fe2O3-mediated Z-scheme mechanism was proposed for the charge transfer at the heterojunction surface, which involved a Fe(III)/Fe(II) oxidation-reduction center that favored the retarded charge recombination and improved photocatalytic activity. Such a mechanism was well supported by the direct detection of surface generated O2- and OH reactive species. Finally, detailed transformation pathways were proposed based on the photodegradation products identified by QToF-MS analyses. This work provides an illustrative strategy for developing efficient Z-scheme photocatalysts for water purification, by taking advantage of amorphous Fe-based oxides in the semiconductor lattice matching.