Efficient integration of plasmonic Ag/AgCl with perovskite-type LaFeO3: Enhanced visible-light photocatalytic activity for removal of harmful algae

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.

Novel Ag3PO4/ZnWO4-modified graphite felt electrode for photoelectrocatalytic removal of harmful algae: Performance and mechanism

A novel Ag3PO4/ZnWO4-modified graphite felt electrode (AZW@GF) was prepared by drop coating method and applied to photoelectrocatalytic removal of harmful algae. Results showed that approximately 99.21% of chlorophyll a and 91.57% of Microcystin-LR (MCLR) were degraded by the AZW@GF-Pt photoelectrocatalytic system under the optimal operating conditions with a rate constant of 0.02617 min-1 and 0.01416 min-1, respectively. The calculated synergistic coefficient of photoelectrocatalytic algal removal and MC-LR degradation by the AZW@GF-Pt system was both larger than 1.9. In addition, the experiments of quenching experiments and electron spin resonance (ESR) revealed that the photoelectrocatalytic reaction mainly generated •OH and •O2- for algal removal and MC-LR degradation. Furthermore, the potential pathway for photoelectrocatalytic degradation of MC-LR was proposed. Finally, the photoelectrocatalytic cycle algae removal experiments were carried out on AZW@GF electrode, which was found to maintain the algae removal efficiency at about 91% after three cycles of use, indicating that the photoelectrocatalysis of AZW@GF electrode is an effective emergency algae removal technology.

The secondary outbreak risk and mechanisms of Microcystis aeruginosa after H2O2 treatment

The secondary outbreak of cyanobacteria after algicide treatment has been a serious problem to water ecosystems. Hydrogen peroxide (H2O2) is an algaecide widely used in practice, but similar re-bloom problems are inevitably encountered. Our work found that Microcystis aeruginosa (M. aeruginosa) temporarily hibernates after H2O2 treatment, but there is still a risk of secondary outbreaks. Interestingly, the dormant period was as long as 20 and 28 days in 5 mg L-1 and 20 mg L-1 H2O2 treatment groups, respectively, but the photosynthetic activity was both restored much earlier (within 14 days). Subsequently, a quantitative imaging flow cytometry-based method was constructed and confirmed that the re-bloom had undergone two stages including first recovery and then re-division. The expression of ftsZ and fabZ genes showed that M. aeruginosa had active transcription processes related to cell division protein and fatty acid synthesis during the dormancy stat. Furthermore, metabolomics suggested that the recovery of M. aeruginosa was mainly by activating folate and salicylic acid synthesis pathways, which promoted environmental stress resistance, DNA synthesis, and cell membrane repair. This study reported the comprehensive mechanisms of secondary outbreak of M. aeruginosa after H2O2 treatment. The findings suggest that optimizing the dosage and frequency of H2O2, as well as exploring the potential use of salicylic acid and folic acid inhibitors, could be promising directions for future algal control strategies.

Recent advances in visible light driven inactivation of bloom forming blue-green algae using novel nano-composites: Mechanism, efficiency and fabrication approaches

Over the years, algae have proved to be a water pollutant due to global warming, climate change, and the unregulated addition of organic compounds in water bodies from diffused resources. Harmful algal blooms (HABs) are severely affecting the health of humans and aquatic ecosystems. Among available anti-blooming technologies, semiconductor photocatalysis has come forth as an effective alternative. In the recent past, literature has been modified extensively with a decisive knowledge regarding algal invasion, desired preparation of nanomaterials with enhanced visible light absorption capacity and mechanisms for algal cell denaturation. The motivation behind this review article was to gather algal inactivation data in a systematic way based on various research studies, including the construction of nanoparticles and purposely to test their anti-algal activities under visible irradiation. Additionally, this article mentions variety of starting materials employed for preparation of various nano-powders with focus on their synthesis routes, analytical techniques as well as proposed mechanisms for lost cellular integrity in context of reduced chlorophyll' a' level, cell rapture, cell leakage and damages to other physiological constituents; credited to oxidative damage initiated by reactive oxidation species (ROS). Various floating and recyclable composited catalysts Ag2CO3-N: GO, Ag/AgCl@ZIF-8, Ag2CrO4-g-C3N4-TiO2/mEP proved to be game-changers owing to their enhanced VL absorption, adsorption, stability, separation and reusability. An outlook for the generalized limitations of published reports, cost estimations for practical implementation, issues and challenges faced by nano-photocatalysts and possible opportunities for future studies are also proposed. This review will be able to provide vast insights for coherent fabrication of catalysts, breakthroughs in experimental methodologies and help in elaboration of damage mechanisms.

Toxic effects and action mechanism of metal-organic framework UiO-66-NH2 in Microcystisaeruginosa

The zirconium metal-organic framework UiO-66-NH2 has garnered considerable attention for their potentials of removing environmental contaminants from water. The production and application of UiO-66-NH2 make their releases into the aquatic environment inevitable. Nevertheless, little information is available regarding its potential risk to the environment and aquatic organisms, thus limiting the evaluation of its safe and sustainable use. In this study, the ecotoxicity of UiO-66-NH2 was evaluated, specifically its impacts on growth, extracellular organic matter release, and metabolomic changes of the model phytoplankton Microcystis aeruginosa (M. aeruginosa). UiO-66-NH2 exhibited moderate effects on algal physiology including growth, viability, and photosynthetic system. At concentrations below 20 mg/L, UiO-66-NH2 induced negligible inhibition of algal growth, algal viability, and photosynthesis. In contrast, UiO-66-NH2 boosted the release of extracellular organic matter even at concentration as low as 0.02 mg/L. These findings indicated that, while no evident damage to algal cells was observed, UiO-66-NH2 was hazardous to the aquatic environment as it stimulated the release of algal toxins. Moreover, UiO-66-NH2 entered algal cells rather than adhering to the surface of M. aeruginosa as observed by the fluorescence imaging. Based on metabolic analysis, UiO-66-NH2 influenced the cyanobacteria mainly through interference with purine metabolism and ABC transporter. This study sheds light on the potential threat UiO-66-NH2 posing to microalgae, and has potential implications for its safe utilization in the environmental field.

The effects of water, substrate, and intermediate adsorption on the photocatalytic decomposition of air pollutants over nano-TiO2 photocatalysts

The photocatalytic performance of nano-TiO2 photocatalysts in air pollutant degradation greatly depends on the adsorption of water, substrates, and intermediates. Especially under excessive humidity, substrate concentration, and intermediate concentration, the competitive adsorption of water, substrates, and intermediates can seriously inhibit the photocatalytic performance. In the past few years, extensive studies have been performed to investigate the influence of humidity, substrate concentration, and intermediates on the photocatalytic performance of TiO2, and significant advances have been made in the area. However, to the best of our knowledge, there is no review focusing on the effects of water, substrate, and intermediate adsorption to date. A comprehensive understanding of their mechanisms is key to overcoming the limited application of nano-TiO2 photocatalysts in the photocatalytic decomposition of air pollutants. In this review, the progress in experimental and theoretical fields, including a recent combination of photocatalytic experiments and adsorption and photocatalytic simulations by density functional theory (DFT), to explore the impact of adsorption of various reaction components on nano-TiO2 photocatalysts is comprehensively summarized. Additionally, the mechanism and broad perspective of the impact of their adsorption on the photocatalytic activity of TiO2 in air treatment are also critically discussed. Finally, several solutions are proposed to resolve the current problems related to environmental factors. In general, this review contributes a comprehensive perspective of water, substrate, and intermediate adsorption toward boosting the photocatalytic application of TiO2 nanomaterials.

Advanced oxidation processes for synchronizing harmful microcystis blooms control with algal metabolites removal: From the laboratory to practical applications

Harmful algal blooms (HABs) in freshwater systems have become a global epidemic, leading to a series of problems related to cyanobacterial outbreaks and toxicity. Studies are needed to improve the technology used for the simultaneous removal of harmful cyanobacteria and algal metabolites. In this review, widely reported advanced oxidation processes (AOPs) strategies for removing major species Microcystis aeruginosa (M. aeruginosa) and microcystins (MCs) were screened through bibliometrics, such as photocatalysis, activated persulfate, H2O2, Ozone oxidation, ultrasonic oxidation, and electrochemical oxidation, etc. AOPs generate kinds of reactive oxygen species (ROS) to inactivate cyanobacteria and degrade cyanotoxins. A series of responses occurs in algal cells to resist the damaging effects of ROS generated by AOPs. Specifically, we reviewed laboratory research, mechanisms, practical applications, and challenges of HABs treatments in AOPs. Problems common to these technologies include the impact of algal response and metabolites, and environmental factors. This information provides guidance for future research on the removal of harmful cyanobacteria and treatment of algal metabolites using AOPs.

Effective photocatalytic inactivation of Microcystis aeruginosa by Ag3VO4/BiVO4 heterojunction under visible light

In recent years, photocatalytic technology has been increasingly used for the treatment of algal blooms in water bodies due to its high efficiency and environmental advantages. However, conventional semiconductor materials suffer from high electron-hole recombination rate, low carrier mobility and weak surface adsorption ability, which made their photocatalytic performance limited. Therefore, the photocatalytic performance of the composites can be improved by coupling another semiconductor material to form a heterojunction to accelerate electron transfer. In this study, a novel composite Ag3VO4/BiVO4 (ABV) photocatalyst was successfully prepared by in-situ deposition method for the photocatalytic inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. The photocatalyst showed excellent photocatalytic activity, and the degradation rate of M. aeruginosa chlorophyll a was up to 99.8% within 4 h under visible light. During the photocatalytic degradation, the morphology of algae cells, the permeability of cell membrane, the organic matter inside and outside the cells, the antioxidant system and the soluble protein were seriously damaged. Moreover, three cycle experiments showed that the prepared ABV photocatalyst had high reusability. Finally, a possible mechanism of M. aeruginosa inactivation was proposed. In general, the synthesized ABV photocatalyst can effectively inactivate cyanobacteria under visible light and provided a new method for M. aeruginosa removal in water.

Synthesis of Cu2+ doped biochar and its inactivation performance of Microcystis aeruginosa: Significance of synergetic effect

The harmful cyanobacteria bloom is frequently occurring in the aquatic environment and poses a tremendous threat to both aquatic organisms and ecological function. In this study, a series of Cu2+ doped biochar (BC) composites (Cu-BCs) with different loading ratios (0.1 %-5 wt %) (Cu-BC-0.1/0.5/1/2.5/5) was successfully fabricated through a one-step adsorption method for in-situ inactivation of Microcystis aeruginosa and simultaneous removal of microcystin-LR (MC-LR). Compared with the single BC/CuSO4 and other Cu-BCs composites, the Cu-BC-2.5 exhibited the best algae inactivation performance with the lowest 72 h medium effective concentration (EC50) value of 0.34 mg/L and highest chlorophyll α degradation efficiency of 8.31 g/g. Notably, the as-prepared Cu-BC-2.5 maintained good inactivation performance in the near-neutral pH (6.5-8.5), and the presence of humic acid and salts such as Na2CO3 and NaCl. The outstanding inhibitory effect of the Cu-BC-2.5 could be explained by the synergetic effect between biochar and Cu2+, which greatly elevated reactive oxygen species (ROS) intensity and in turn led to severe membrane damage and collapse of the antioxidant system. Additionally, the Cu-BC-2.5 could simultaneously remove the released microcystin-LR (MC-LR) throughout the inactivation process and prevent secondary pollution, thus offering a new insight into the alleviation of harmful cyanobacteria in aquatic environment.

Magnetic-field-induced simultaneous charge separation and oxygen transfer in photocatalytic oxygen activation for algae inactivation

Photocatalytic oxygen activation is an excellent strategy for algae control in water. However, the fast recombination of photogenerated charge and slow rate of oxygen transfer limit the reactive oxygen species generation efficiency for algae inactivation. Herein, to solve above issues, magnetic field was introduced to the BiO_2-x/Bi₃NbO₇ system to effectively covert oxygen into reactive radicals. The electrochemical experiment and DFT calculation results indicated the charge separation could be accelerated by the Lorentz force generated by the magnetic field, resulting in increase of electron concentration. Meanwhile, the value of volumetric gas-liquid mass transfer coefficient was increased by 59.79 % with magnetic field, thus more oxygen could be reduced to superoxide radical. Photocatalytic algae inactivation rate by BiO_2-x/Bi₃NbO₇ with magnetic field could be increased by 2.07 times than that without magnet filed. This work further extends the strategy of using magnetic field to simultaneously facilitate the charge separation and oxygen transfer rate.

Preparation of floating BiOCl0.6I0.4/ZnO photocatalyst and its inactivation of Microcystis aeruginosa under visible light

Frequent occurrence of harmful algal blooms has already threatened aquatic life and human health. In the present study, floating BiOCl_0.6I_0.4/ZnO photocatalyst was synthesized in situ by water bath method, and and applied in inactivation of Microcystis aeruginosa under visible light. The composition, morphology, chemical states, optical properties of the photocatalyst were also characterized. The results showed that BiOCl_0.6I_0.4 exhibited laminated nanosheet structure with regular shape, and the light response range of the composite BZ/EP-3 (BiOCl_0.6I_0.4/ZnO/EP-3) was tuned from 582 to 638 nm. The results of photocatalytic experiments indicated that BZ/EP-3 composite had stronger photocatalytic activity than a single BiOCl_0.6I_0.4 and ZnO, and the removal rate of chlorophyll a was 89.28% after 6 hr of photocatalytic reaction. The photosynthetic system was destroyed and cell membrane of algae ruptured under photocatalysis, resulting in the decrease of phycobiliprotein components and the release of a large number of ions (K⁺, Ca²⁺ and Mg²⁺). Furthermore, active species trapping experiment determined that holes (h⁺) and superoxide radicals (·O₂^-) were the main active substance for the inactivation of algae, and the p-n mechanism of photocatalyst was proposed. Overall, BZ/EP-3 showed excellent algal removal ability under visible light, providing fundamental theories for practical algae pollution control.

Inactivation of algae by visible-light-driven modified photocatalysts: A review

Harmful algal blooms have raised great concerns due to their adverse effects on aquatic ecosystems and human health. Recently, visible light-driven (VLD) photocatalysis has attracted attention for algae inactivation owing to its unique characteristics of low cost, mechanical stability, and excellent removal efficiency. However, the low utilization of visible light and the high complexation rate of electron-hole (e^--h⁺) pairs are essential drawbacks of conventional photocatalysts. Scientific efforts have been devoted to modifying VLD photocatalysts to enhance their antialgal activity. This review concisely summarizes the anti-algae performance of the latest modified VLD photocatalysts. The summary of the mechanisms in VLD photocatalytic inactivation demonstrates that reactive oxygen species (ROS) can induce oxidative damage to algal cells and photocatalytic degradation of released organic matter. In addition, the factors, such as photocatalyst dosage, algal concentration and species, and the physicochemical properties of different water matrices, such as pH, natural organic matter, and inorganic ions, affecting the efficacy of VLD catalytic oxidation for algae removal are briefly outlined. Thereafter, this review compiles perspectives on the emerging field of VLD photocatalytic inactivation.

Removal of harmful algae in natural water by semiconductor photocatalysis- A critical review

Harmful Algal Blooms (HABs) have turned out to be a global occurrence owing to the detrimental phenomenon like eutrophication and global climate change caused by human activities. This newly emergent threat imposes a severe hazardous to public health, ecosystems and fishery-based economies. Rapid and exponential growth of certain delirious and toxic algal species shall be held causative to the formation of HABs. The potential disadvantages they pose, make it necessary the identification of efficient treatment methodologies. Photocatalysis has been identified as the most promising solution amongst all the identified and investigated methods, for the environmental and economic benefits beheld. Different treatment methodologies were evaluated and light has been thrown on the advantages beheld by photocatalysis over the other methods. Focus has been given to the different photocatalysts that have been so far put to use towards photocatalytic disinfection of HABs and algal toxins. This present study provides useful information on the application of the traditional and photocatalysis process for removal of HABs in water bodies. Moreover, the results revealed that photocatalysis method could cause potent inhibitory effect on growth of algae species and disrupted algal cells membranes to some extent. Finally, the conventional treatment techniques have been recognized to be insufficient for removal of HABs. However, the photocatalyst technology have been utilized mostly for the mineralization and neutralization of the algal pollutants without any harmful secondary pollutants.

Application of perovskite oxides and their composites for degrading organic pollutants from wastewater using advanced oxidation processes: Review of the recent progress

In the recent years, perovskite oxides are gaining an increasing amount of attention owing to their unique traits such as tunable electronic structures, flexible composition, and eco-friendly properties. In contrast, their catalytic performance is not satisfactory, which hinders real wastewater remediation. To overcome this shortcoming, various strategies are developed to design new perovskite oxide-based materials to enhance their catalytic activities in advanced oxidation process (AOPs). This review article is to provide overview of basic principle and different methods of AOPs, while the strategies to design novel perovskite oxide-based composites for enhancing the catalytic activities in AOPs have been highlighted. Moreover, the recent progress of their synthesis and applications in wastewater remediation (pertaining to the period 2016-2022) was described, and the related mechanisms were thoroughly discussed. This review article helps scientists to have a clear outlook on the selection and design of new effective perovskite oxide-based materials for the application of AOPs. At the end of the review, perspective on the challenges and future research directions are discussed.

Green Synthesis and Characterization of Antimicrobial Synergistic AgCl/BAC Nanocolloids

All over the world, one of the major challenges is the green synthesis of potential materials against antimicrobial resistance and viruses. This study demonstrates a simple method like chemistry lab titration to synthesize green, facile, scalable, reproducible, and stable synergistic silver chloride/benzyldimethylhexadecyl-ammonium chloride (AgCl/BAC) colloidal Nanoantimicrobials (NAMs). Nanocolloidal dispersions of AgCl in an aqueous medium are prepared by using silver nitrate (AgNO3) as precursor and BAC as both sources of chloride and stabilizer, holding an asymmetric molecular structure. The synthetic approach is scalable and green. Both the morphology and stability of AgCl/BAC nanocolloids (NCs) were investigated as a function of different molar fractions of the reagents. AgCl/BAC NCs were characterized by transmission electron microscopy (TEM) and X-ray photoelectron and UV-vis spectroscopies. Zeta potential measurements revealed increasing positive potential values at every stage of the synthesis. Size distribution and hydrodynamic diameter of the particles were measured by dynamic light scattering (DLS), which predicted the formation of BAC layered structures associated with the AgCl nanoparticles (NPs). Small-angle X-ray scattering (SAXS) experiments verify the thickness of the BAC bilayer around AgCl. The produced AgCl/BAC NCs probably have synergistic antimicrobial properties from the AgCl core and the biocide BAC shell. AgCl/BAC NCs stability over months was investigated. The experimental evidence supports the morphological stability of the AgCl/BAC NCs, while higher positive zeta potential values anticipate a long-term antimicrobial effect: a higher surface charge causes NPs to be potentially more lethal to bacteria. AgCl/BAC antimicrobial aqueous colloidal suspensions will be used as additives for the industrial production of antimicrobial coatings.

Photocatalytic Remediation of Harmful Alexandrium minutum Bloom Using Hybrid Chitosan-Modified TiO2 Films in Seawater: A Lab-Based Study

The uncontrolled growth of harmful algal blooms (HABs) can negatively impact the environment and pose threats to human health and aquatic ecosystems. Titanium dioxide (TiO2) is known to be effective in killing harmful algae through flocculation and sedimentation. However, TiO2 in a dispersed form can harm other non-target marine organisms, which has raised concerns by environmentalists and scientists. This research seeks to explore the utility of immobilized titanium oxide as a photocatalyst for mitigation of HABs, where the Alexandrium minutum bloom was used as a model system herein. Chitosan was modified with 0.2 wt.% TiO2 (Chi/TiO2 (x mL; x = 1, 3 and 5 mL) and the corresponding films were prepared via solvent casting method. Scanning electron microscope (SEM) images of the films reveal a highly uneven surface. X-ray diffraction (XRD) analysis indicates the reduction in chitosan crystallinity, where the presence of TiO2 was negligible, in accordance with its dispersion within the chitosan matrix. The photocatalytic mitigation of A.minutum was carried out via a physical approach in a laboratory-scale setting. The negative surface charge of the films was observed to repel the negatively charged A.minutum causing fluctuation in the removal efficiency (RE). The highest RE (76.1 ± 13.8%) was obtained when Chi/TiO2 (1 mL) was used at 72 h, where the hydroxyl radicals generated were inferred to contribute to the deactivation of the algae cells by causing oxidative stress. An outcome of this study indicates that such hybrid films have the potential to replace the non-immobilized (dispersed) TiO2 for HAB mitigation. However, further investigation is required to deploy these films for field applications at a larger scale.

Efficient Prevention of Aspergillus flavus Spores Spread in Air Using Plasmonic Ag-AgCl/α-Fe2O3 under Visible Light Irradiation

Aspergillus flavus is a kind of widespread fungi that can produce carcinogenic, teratogenic, and mutagenic secondary metabolites known as aflatoxins. Aspergillus flavus mainly spread through the means of fungal spores in air, thus preventing the spores spread is an effective strategy to control aflatoxins contamination from source. Herein, a rapid and efficient control way to prevent the spread of Aspergillus flavus spores in air was demonstrated. Ag-AgCl nanoparticles were combined with tetrahedral α-Fe₂O₃ to form plasmonic composites that presented 93.65 ± 1.53% prevention rate of Aspergillus flavus spores under 50 min visible light irradiation. The efficient activity was attributed to the synergy effect of Ag including intrinsic disinfection, electron sink, and localized surface plasmon resonance effect, which were proven by photoelectric characterization, density functional theory, and finite difference time domain methods. The calculated work functions of α-Fe₂O₃, Ag, and AgCl were 3.71, 4.52, and 5.38 eV, respectively, which could accelerate photoinduced carrier transfer through Ag during photoreaction. Moreover, it was found that the intrinsic disinfection of Ag and hydroxyl radical from photocatalytic reaction were the main factors to the prevention of Aspergillus flavus spores, which resulted in the destruction of spore structure and the leakage of intracellular protein with 62.15 ± 2.63 μg mL^-1. Most important, it was proven that the composites also showed high activity (90.52 ± 1.26%) to prevent Aspergillus flavus spore spread in the storage process of peanuts. These findings not only provided useful information for an efficient and potential strategy to prevent Aspergillus flavus contamination but also could be as a reference in toxic fungi control.

Reducing the risk of exposure of airborne antibiotic resistant bacteria and antibiotic resistance genes by dynamic continuous flow photocatalytic reactor

In this study, based on the dynamic photocatalytic reactor constructed by the new photocatalyst TiO₂/MXene, the purification process of different biological particles in aerosol was systematically studied. Multidrug resistant bacteria were easier to inactivate than common bacteria of the same kind, whether under UV conditions or photocatalysis. Photocatalyst was loaded on porous polyurethane sponge filler so that the combined effect of adsorption and advanced oxidation significantly improved the antibiotic resistant bacteria (ARB) disinfection effect. The inactivation efficiency of two ARBs under UV254 increased by 1.2 lg and 2.1 lg. In addition, it was found that the microorganisms treated by UV had slight self-repair phenomenon in a short time, while the microbial activity decreased continuously after photocatalysis. With the addition of photocatalyst, the particle size distribution of airborne Escherichia coli decreased and the micro morphology of cells was more seriously damaged. Antibiotic resistance genes (ARGs) carried by ARB can be dissociated into the environment after cell destruction, but it can be removed at a high level (sul2 can achieve 2.11 lg) in the continuous reactor at the same time. While avoiding secondary pollution, it also provides a powerful solution for airborne ARGs control.

Exploring the photocatalytic inactivation mechanism of Microcystis aeruginosa under visible light using Ag3PO4/g-C3N4

In this work, a series of Ag₃PO₄/g-C₃N₄ (AG) photocatalysts were synthesized. After characterizing the properties, the effects of mass ratio, light intensity, and material dosages on photodegradation were investigated. The material with a 1/2 mass ratio of Ag₃PO₄/g-C₃N₄ showed the highest photocatalytic activity under visible light, and the removal efficiency reached 90.22% for an initial suspended algae concentration of 2.7 × 10⁶ cells/mL, 0.1 g of AG, and 3 h of irradiation. These results showed that the conductivity was increased while the total protein and COD contents of the algae suspension were declined rapidly. In contrast, the variations in the malondialdehyde (MDA) level suggested that the algae cell wall was severely damaged and that selective permeability of the membrane was significantly affected. A possible photocatalytic mechanism was proposed and •O₂^- was shown to be the major reactive oxygen species in the photocatalysis. In summary, during the visible light photocatalytic process, the cell structure was destroyed, which caused the leakage of electrolyte, the inactivation of protein, and the inhibition of photosynthesis; finally, the cells died. This study provides a reference for photodegradation of algae pollution in water bodies.

Insights into photocatalytic degradation of phthalate esters over MSnO3 perovskites (M = Mg, Ca): Experiments and density functional theory

In this study, the physicochemical and photocatalytic properties of two kinds of stannate perovskite oxides (MgSnO₃ and CaSnO₃) were investigated under simulated sunlight, where dimethyl phthalate (DMP) and diethyl phthalate (DEP) were selected as the probe pollutants. The results of photochemical characterization showed that MgSnO₃ perovskite exhibited better photocatalytic performance than CaSnO₃ perovskite. MgSnO₃ perovskite could effectively degrade 75% of DMP and 79% of DEP through pseudo-first-order reaction kinetics, which remained good in pH 3.0 to 9.0. Quenching experiments and electron paramagnetic resonance (EPR) characterization indicated that photogenerated holes (h⁺), superoxide (O₂^-), and hydroxyl radicals (OH) worked in the photo-degradation, while O₂^- played the most important role. Furthermore, intermediates identification and density functional theory (DFT) calculations were used to explore the degradation mechanism. For both DMP and DEP, the reactive oxygen species (ROS, including O₂^- and OH) were responsible for the hydroxylation of benzene ring and the breaking of the aliphatic chain, while h⁺ was prone to break the aliphatic chain. This work is expected to provide new insights on the photocatalytic mechanism of stannate perovskites for environmental remediation.

Plasmonic Ag nanoparticles decorated copper-phenylacetylide polymer for visible-light-driven photocatalytic reduction of Cr(VI) and degradation of PPCPs: Performance, kinetics, and mechanism

The development of efficacious photocatalysts for the elimination of contaminants in water remains a challenge. Herein, a promising Ag nanoparticles-decorated copper-phenylacetylide (Ag/PhC₂Cu) plasmonic photocatalyst was fabricated for the reduction of hexavalent chromium (Cr(VI)) and degradation of pharmaceutical and personal care products (PPCPs). Typically, the optimized 5Ag/PhC₂Cu could rapidly reduce Cr(VI) (98.1% within 12 min), and degrade norfloxacin (NOR) (100% within 40 min) with a 56.2% mineralization rate under visible light. The superior photocatalytic activity of Ag/PhC₂Cu was attributed to the synergistic effects of the highly reducing photoinduced electrons conferred by the PhC₂Cu (-1.98 eV), and Ag nanoparticles in promoting photocarrier separation and enhancing solar-energy-conversion efficiencies. Subsequently, the photocatalytic reaction mechanism of Ag/PhC₂Cu was investigated. It was found that e^- and O₂^•- were the main reactive species for Cr(VI) reduction, while O₂^•- and h⁺ were primarily responsible for the degradation of NOR. Of note, the Ag/PhC₂Cu system could effectively generate H₂O₂ and partially decomposed it to •OH, which might be involved in NOR mineralization. This study not only demonstrates a highly active photocatalytic system for the remediation of environmental pollution and sustainable solar-to-chemical energy conversion, but contributes to the future exploration of multifunctional plasmonic photocatalysts.

Hybrid Plasmonic Nanomaterials for Hydrogen Generation and Carbon Dioxide Reduction

The successful development of artificial photosynthesis requires finding new materials able to efficiently harvest sunlight and catalyze hydrogen generation and carbon dioxide reduction reactions. Plasmonic nanoparticles are promising candidates for these tasks, due to their ability to confine solar energy into molecular regions. Here, we review recent developments in hybrid plasmonic photocatalysis, including the combination of plasmonic nanomaterials with catalytic metals, semiconductors, perovskites, 2D materials, metal-organic frameworks, and electrochemical cells. We perform a quantitative comparison of the demonstrated activity and selectivity of these materials for solar fuel generation in the liquid phase. In this way, we critically assess the state-of-the-art of hybrid plasmonic photocatalysts for solar fuel production, allowing its benchmarking against other existing heterogeneous catalysts. Our analysis allows the identification of the best performing plasmonic systems, useful to design a new generation of plasmonic catalysts.

Construction of perylene diimide/CuS supramolecular heterojunction for the highly efficient visible light-driven environmental remediation

Developing photocatalysts that are inexpensive and efficient in degrading pollutants are essential for environmental remediation. Herein, a novel system of perylene diimide (PDI)/CuS p-n heterojunction was synthesized by a two-step self-assembly strategy for removal of tetracycline in waste water. Results showed that PDI/CuS-10% exhibited highest photocatalytic behavior. The apparent rate constants for tetracycline (TC) degradation for the blend were 5.27 and 2.68 times higher than that of CuS or PDI, respectively. The enhancement of photocatalytic activity was mainly attributed to the π-π stacking and p-n junction, which can accelerate the separation of the photo-generated h⁺-e^- pairs. Besides, the light absorption of PDI/CuS from 800 to 200 nm was significantly enhanced and the absorption edge even reached the near-infrared region, which also played an important role in providing desired photocatalytic properties. Surprisingly, PDI/CuS could maintain high catalytic activity even after 5 cycles under simulated conditions, indicating that the composite had high potential for practical applications. Owing to high efficiency, low cost and wide application range, the PDI/CuS nanocomposites are promising candidates for environmental remediation.

Magnetically separable ZnFe2O4/Ag3PO4/g-C3N4 photocatalyst for inactivation of Microcystis aeruginosa: Characterization, performance and mechanism

Water eutrophication leads to increasingly serious harmful algal blooms (HABs), which poses tremendous threats on aquatic environment and human health. In this work, a novel magnetically separable ZnFe₂O₄/Ag₃PO₄/g-C₃N₄ (ZFO/AP/CN) photocatalyst with double Z-scheme was constructed for Microcystis aeruginosa (M. aeruginosa) inactivation and Microcystin-LR (MC-LR) degradation under visible light. The photocatalyst was characterized by XRD, SEM, EDS, TEM, XPS, FTIR, UV-vis, PL, and VSM. Approximately 96.33% of chlorophyll a was degraded by ZFO/AP/CN (100 mg/L) after 3 h of visible light irradiation. During the photocatalytic process, the malondialdehyde (MDA) of M. aeruginosa increased, the activities of superoxide dismutase (SOD) and catalase (CAT) increased initially and decreased afterwards. Furthermore, the photocatalytic removal efficiency of M. aeruginosa (OD₆₈₀ ≈0.732) and MC-LR (0.2 mg/L) reached 94.31% and 76.92%, respectively, in the simultaneous removal of algae and algal toxin experiment. Reactive species scavenging experiments demonstrated that·O₂^- and·OH played key roles in inactivating M. aeruginosa and degrading MC-LR. The excellent recoverability and stability of ZFO/AP/CN were proved by cycling photocatalytic experiment which using magnetic recovery method. In summary, the synthesized magnetically separable ZFO/AP/CN photocatalyst has remarkable photocatalytic activity under visible light and shows promising potential for practical application of alleviating HABs.

Self-floating photocatalytic hydrogel for efficient removal of Microcystis aeruginosa and degradation of microcystins-LR

Cyanobacterial harmful algal blooms (CyanoHABs) and the release of cyanotoxins have posed adverse impacts to aquatic system and human health. In this study, a novel self-floating Ag/AgCl@LaFeO₃ (ALFO) photocatalytic hydrogel was prepared via freeze-thaw method for removal of Microcystis aeruginosa (M. aeruginosa). The ALFO hydrogel performed an excellent photocatalytic activity with a 99.4% removal efficiency of chlorophyll a within 4 h. It can still remove above 95% chlorophyll a after six consecutive recycles. Besides it has also shown excellent mechanical strength and elasticity, which can ensure its use in practical applications. The mechanisms of M. aeruginosa inactivation are attributed to •O₂^- and •OH generated by the ALFO hydrogel under visible light radiation. In addition, •O₂^- and •OH can further oxidative degrade and even mineralize the leaked algae organic matter, avoiding the recurrence of CyanoHABs. What's more, the ALFO hydrogel owns good photocatalytic degradation performance for microcystins-LR (MC-LR) with a 97% removal efficiency within 90 min. A possible photocatalytic degradation pathway of MC-LR was proposed through the identification of the intermediate products during the photocatalytic reaction, which confirmed the reduction of MC-LR toxicity. This work develops recyclable a self-floating ALFO hydrogel to simultaneously inactivate M. aeruginosa and degrade MC-LR, providing a prospective method for governing and controlling CyanoHABs in practical application.

Self-photoreduced Ag0-doped Ag(i)–organic frameworks with efficient visible-light-driven photocatalytic performance

A series of Ag0-doped Ag(i)organic frameworks have been constructed via a facile self-photoreduction strategy and can be applied as efficient photocatalysts for the photocatalytic degradation of methyl orange.