Simultaneous removal of harmful algal cells and toxins by a Ag2CO3-N:GO photocatalyst coating under visible light

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.

Magnetically recyclable Cu2+ doped Fe3O4@biochar for in-situ inactivation of Microcystis aeruginosa: Performance and reusability

Harmful cyanobacterial blooms in eutrophic water bodies have frequently occurred worldwide and become a major environmental concern. Therefore, it is imperative to develop a stable and efficient algaecide to solve this issue. In this study, our purpose was to investigate the efficacy and mechanism of a newly developed Cu2+ doped Fe3O4@Biochar magnetic composite (Cu-Mag-BC) in in-situ inactivation of Microcystis aeruginosa (M. aeruginosa). We successfully synthesized the Cu-Mag-BC by coating Cu2+ onto Fe3O4@Biochar. Cu-Mag-BC exhibited superparamagnetic behavior and was uniformly impregnated by Cu2+. Cu-Mag-BC (5 mg/L), rapidly inactivated chlorophyll-a (Chl-a) in M. aeruginosa with low Fe and Cu leaching, during which time the OD264 value and malondialdehyde (MDA) content increased, while the activities of superoxide dismutase (SOD) and catalase (CAT) first increased and then decreased, due to oxidative stress induced by over-generated reactive oxygen species (ROS). Quantitative results showed that ·O2- and ·OH were the main ROS species produced from Cu-Mag-BC. Inactivation efficiency was maintained at approximately 80 % after three consecutive runs and total Chl-a removal efficiency reached 2.84 g/g, indicating good reusability and stability. A possible inactivation mechanism is proposed; amino groups and adipose chain were the primary oxidation sites. Thus, Cu-Mag-BC shows potential as a candidate for simultaneously inactivating harmful cyanobacteria and preventing secondary pollution.

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.

Designing a cercosporin-bioinspired bifunctional algicide with flocculation and photocatalysis for efficiently controlling harmful cyanobacterial blooms

Harmful cyanobacterial blooms (HCBs) are spreading in freshwater ecosystems worldwide, adversely affecting drinking water supplies, aquatic production, recreational and tourism activities. Therefore, the efficient and environmentally friendly method is still of interest to be developed to effectively control HCBs. Inspired by the excellent algicidal activity of cercosporin (CP), a novel metal-free algaecide SiO2@EDU@CP (EDU, N-ethyl-N'-(3-dimethylaminopropyl)urea) with flocculation and photoremoval functions, was successfully designed and prepared in one-step to simultaneously introduce CP and EDU on SiO2 nanoparticles. It could rapidly form algae flocs in 20 min with 97.1% flocculation rate, and remove Microcystis aeruginosa within 12 h with 91.0% algicidal rate under 23 W compact fluorescent light irradiation without any leaked CP detected. Additionally, odorant β-cyclocitral and toxin microcystin-LR were both photodegraded after treatment of SiO2@EDU@CP. Further mechanistic studies showed that the introduction of EDU significantly reversed the zeta potential of SiO2-COOH to achieve the flocculation through neutral charge, and the photophysical characterization of SiO2@EDU@CP revealed the improved charge separation ability to generate reactive oxygen species. More importantly, the utility of SiO2@EDU@CP was well demonstrated by its effectiveness for algae from Taihu Lake under natural sunlight and inability to regrow after treatment. This study not only establishes a bifunctional algicide SiO2@EDU@CP to efficiently control HCBs, but also provides design possibilities to develop more novel and efficient algicides for the better control of practical HCBs.

Metabolomic analysis and pathway profiling of paramylon production in Euglena gracilis grown on different carbon sources

Paramylon (β-1,3-glucan) produced by Euglena gracilis displays antioxidant, antitumor, and hypolipidaemic functions. The biological properties of paramylon production by E. gracilis can be understood by elucidating the metabolic changes within the algae. In this study, the carbon sources in AF-6 medium were replaced with glucose, sodium acetate, glycerol, or ethanol, and the paramylon yield was measured. Adding 0.1260 g/L glucose to the culture medium resulted in the highest paramylon yield of 70.48 %. The changes in metabolic pathways in E. gracilis grown on glucose were assessed via non-targeted metabolomics analysis using ultra-high-performance liquid chromatography coupled to high-resolution quadrupole-Orbitrap mass spectrometry. We found that glucose, as a carbon source, regulated some differentially expressed metabolites, including l-glutamic acid, γ-aminobutyric acid (GABA), and l-aspartic acid. Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes further showed that glucose regulated the carbon and nitrogen balance through the GABA shunt, which enhanced photosynthesis, regulated the flux of carbon and nitrogen into the tricarboxylic acid cycle, promoted glucose uptake, and increased the accumulation of paramylon. This study provides new insights into E. gracilis metabolism during paramylon synthesis.

Distribution, risk assessment of heavy metals in sediments, and their potential risk on water supply safety of a drinking water reservoir, middle China

Heavy metals in reservoir sediments were analyzed to assess the pollution level and to understand the potential risk on water supply safety. Heavy metals in sediments will enter the biological chain through bio-enrichment and bio-amplification in water and eventually pose a threat to the safety of drinking water supply. Analysis of eight sampling sites in JG (Jian gang) drinking water reservoir of the sediments showed that from Feb 2018 to Aug 2019 heavy metals including Pb, Ni, Cu, Zn, Mo, and Cr increased by 1.09-17.2%. Vertical distributions of heavy metals indicated that the concentrations increased gradually by 9.6-35.8%. Risk assessment code analysis indicated that Pb, Zn, and Mo were of high risk in the main reservoir area. What is more, enrichment factors of Ni and Mo were 2.76-3.81 and 5.86-9.41, respectively, showing the characteristics of exogenous input. The continuous monitoring results of the bottom water showed that the concentration of heavy metals in the bottom water exceeded the environmental quality standard value of surface water in China, and exceeded the standard by 1.76 times (Pb), 1.43 times (Zn), and 2.04 times (Mo), respectively. Heavy metals in the sediments of JG Reservoir, especially in the main reservoir area, have a potential risk of release from the sediment to the overlying water. Water supply reservoir as a source of drinking water, its quality is directly related to human health and production activities. Therefore, this first study on JG Reservoir is of great significance for the protection of drinking water safety and human health.

Visible light-driven photocatalytic degradation of Microcystin-LR by Bi2WO6/Reduced graphene oxide heterojunctions: Mechanistic insight, DFT calculation and degradation pathways

Developing heterostructure photocatalysts for removing Microcystin-LR (MC-LR) under visible light was of positive significance to control the risk of Microcystins and ensure the safety of water quality. Herein, the Bi₂WO₆/Reduced graphene oxide (RGO) nanocomposites were prepared via a simple one-spot hydrothermal method for the first time to degrade MC-LR. The optimized Bi₂WO₆/RGO (Bi₂WO₆/RGO_3%) achieved a removal efficiency of 82.3% toward MC-LR, with 1.9-fold higher efficiencies than Bi₂WO₆, and it showed superior reusability and high stability after 5 cycles. The degradation efficiency of MC-LR demonstrated a negative trend with the initial concentration of MC-LR, fulvic acid, and initial algal density increased, while MC-LR removal rate for the presence of anions was in the order of Cl^- > CO₃^-2 > NO₃^- > H₂PO₄^-. The degradation efficiency of MC-LR could reach up to 82.3% within 180 min in the neutral condition. The active species detection experiments and EPR measurements demonstrated that the holes (h⁺), hydroxide radicals (∙OH), and superoxide radicals (∙O₂^-) participated in the degradation of MC-LR. The DFT calculations showed that 0.56 of electron transferred from Bi₂WO₆ to RGO, indicating RGO introduction could prevent the recombination of photoelectrons and holes and was beneficial for MC-LR degradation. Finally, the possible intermediate products and degradation pathways were also proposed by the LC-MS/MS analysis.

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.

Photocatalytic degradation effect and mechanism of Karenia mikimotoi by non-noble metal modified TiO2 loading onto copper metal organic framework (SNP-TiO2@Cu-MOF) under visible light

In this study, the SNP-TiO₂@Cu-MOF composite was prepared successfully by loading non-noble metal modified TiO₂ (SNP-TiO₂) on the surface of copper metal organic skeleton (Cu-MOF), and compared the inactivation efficiency of different photocatalysts to Karenia mikimotoi (K. mikimotoi) under visible light. The obtained photocatalyst had the characteristic crystal faces of Cu-MOF and SNP- TiO₂, and contained functional groups such as Cu-O, -COOH, N-O, P-O, etc., which indicated the structural stability of the photocatalyst. The band gap of SNP-TiO₂@Cu-MOF composite was 2.82 eV, and it had great light absorption ability in visible light region. It was proved to be a mesoporous adsorption material, which had a huge specific surface area (245 m²/g). Compared with other photocatalysts, SNP-TiO₂@Cu-MOF composite showed the strongest photocatalytic activity. When the concentration of composite material was set to 100 mg/L and the exposure time was 6 h, the visible light photocatalytic inactivation efficiency of K. mikimotoi was 93.75 %. By measuring various metabolic indexes of K. mikimotoi under the action of different photocatalysts for 1 h, it was confirmed that cell inactivation was due to the increased membrane permeability and degradation of photosynthetic pigments and main life proteins. This research showed that SNP-TiO₂@Cu-MOF composite material was full of great potential and application prospect in controlling the outbreak of eutrophication.

A comprehensive review on the photocatalytic inactivation of Microcystis aeruginosa: Performance, development, and mechanisms

Harmful algae blooms (HABs), caused by severe eutrophication and extreme weather, have spread all over the world, posing adverse effects on eco-environment and human health. Microcystis aeruginosa is the dominant harmful cyanobacterial species when HABs occur, and the toxic metabolites produced by it, microcystins, are even fatal to humans. Photocatalytic technology has received wide attention from researchers for its clean and energy-efficient features, while the basic mechanisms and modification methods of photocatalysts have also been widely reported. In recent years, photocatalytic technology has shown great promise in the inhibition of HABs. In this article, we systematically reviewed the progress in photocatalytic performance and algae removal efficiency, discuss the damage mechanisms of photocatalysts for algae removal, including physical damage and various oxidative stresses, and also explore the degradation rates and possible pathways of microcystins. It can be concluded that during the photocatalytic process, the cytoarchitectural integrity of algae cells was damaged, a variety of important protein and enzyme systems were disrupted, and the antioxidant systems collapsed due to the continuous attack of ROS, which adversely affected the normal physiological activities and growth, resulting in the inactivation of algae cells. Moreover, photocatalysts have a degrading effect on microcystins, thus reducing the adverse effects of HAB. Finally, a brief summary of future research priorities regarding the photocatalytic degradation of algae cells is presented. This study helps to enhance the understanding of the destruction mechanism of Microcystis aeruginosa during the photocatalytic process, and provides a reference for the photodegradation of HAB in water bodies.

Immobilization of photocatalytic materials for (waste)water treatment using 3D printing technology - advances and challenges

Photocatalysis has been considered a promising technology for the elimination of a wide range of pollutants in water. Various types of photocatalysts (i.e., homojunction, heterojunction, dual Z-scheme photocatalyst) have been developed in recent years to address the drawbacks of conventional photocatalysts, such as the large energy band gap and rapid recombination rate of photogenerated electrons and holes. However, there are still challenges in the design of photocatalytic reactors that limit their wider application for real (waste)water treatment, such as difficulties in their recovery and reuse from treated (waste)waters. 3D printing technologies have been introduced very recently for the immobilization of materials in novel photocatalytic reactor designs. The present review aims to summarize and discuss the advances and challenges in the application of various 3D printing technologies (i.e., stereolithography, inkjet printing, and direct ink writing) for the fabrication of stable photocatalytic materials for (waste)water treatment purposes. Furthermore, the limitations in the implementation of these technologies to design future generations of photocatalytic reactors have been critically discussed, and recommendations for future studies have been presented.

Fabrication of g-C3N4@Bi2MoO6@AgI floating sponge for photocatalytic inactivation of Microcystis aeruginosa under visible light

In this work, a floating photocatalyst was constructed by loading g-C₃N₄@Bi₂MoO₆@AgI (GBA) nanocomposite on a modified polyurethane sponge via a simple dip-coating method and applied for the inactivation of Microcystis aeruginosa under visible light. GBA ternary photocatalyst was fabricated successfully and the morphology, structure, chemical state, and optical properties were characterized systematically. The floating catalyst achieved near 100% removal efficiency of algae cells under 6 h visible light irradiation and also could be retrieved and used at least three times repeatedly. The influences of various conditions on photocatalytic performance such as loading content of nanoparticles, algae density, and concentration of natural organic matters were also studied, which revealed that the GBA floating catalyst exhibited excellent photocatalytic performance of algae removal under different conditions. Furthermore, the physiological characteristics of algae cells during the photocatalytic process, including cell morphology, membrane permeability, Zeta potential, photosynthetic system, antioxidant system, and the metabolic activity were investigated. Results confirmed that the algae cells were severely damaged during the photocatalytic inactivation and the normal physiological functions were significantly affected, which resulted in the death of algae cells at last. Finally, a possible photocatalytic inactivation mechanism of algae cells was proposed. In summary, GBA floating catalyst can effectively inactivate Microcystis aeruginosa under visible light, which confirmed the high efficiency of the novel photocatalytic algae removal technology. Meanwhile, the recyclable floating material also makes the practical application in eutrophic waters of the algae removal technology possible.

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.

The effect of graphene photocatalysis on microbial communities in Lake Xingyun, southwestern China

Graphene photocatalysis is a new method for harmful algae and water pollution control. However, microbial communities undergoing graphene photocatalysis treatment in freshwater lakes have been poorly studied. Here, using 16S rRNA and 18S rRNA gene high-throughput sequencing, the responses of microbial communities to graphene photocatalysis were analyzed in the eutrophic lake, Lake Xinyun, southwestern China. For microeukaryotes, we found that Arthropoda was dominant in summer, while its abundant level declined in spring under natural conditions. The evident reduction of Arthropods was observed after graphene photocatalysis treatment in summer and then reached a relatively stable level. For bacteria, Cyanobacteria decreased in summer due to the graphene photocatalysis-mediated inactivation. However, Cyanobacteria was higher in the treated group in spring with a genera group-shift. Functional analysis revealed that microeukaryotes showed higher potential for fatty acid oxidation and TCA cycle in the treated group in summer, but they were more abundant in control in spring. Pathways of starch and sucrose metabolism and galactose metabolism were more abundant in control in summer, while they were enriched in the treated group in spring for bacteria. This study offers insights into the effects of graphene photocatalysis on microbial communities and their functional potential in eutrophic lake.

Removal of microcystins from water and primary treatment technologies - A comprehensive understanding based on bibliometric and content analysis, 1991-2020

Microcystins are a group of heptapeptide hepatotoxins produced by a variety of algae and are frequently detected in aquatic ecosystems, posing a global threat to ecological stability and human health. However, it is difficult to eliminate them completely and innocuously from water by conventional water treatment processes. This study comprehensively evaluated a total of 821 original articles retrieved from the Web of Science (1991-2020) about the removal of microcystins using bibliometric and content analysis to provide a qualitative and quantitative research landscape and a global view of research hotspots and future research directions. Furthermore, the primary and promising treatment technologies for microcystin pollution were also summarized and discussed. The results indicated an urgent practical demand to remediate microcystin pollution according to the increasing number of publications since 2005. China had the highest number of publications, whereas the United States was the core country in the international collaboration network. The Chinese Academy of Sciences and University of Cincinnati showed their leading positions considering article amounts and academic cooperation. Dionysiou DD contributed the most articles, and Carmichael WW had the highest number of co-citations. Three treatment technologies, including biodegradation, chemical oxidation and adsorption, were the major strategies to remediate the pollution of microcystins in water. In addition, the toxicity of toxins/their metabolites, degradation kinetics, and elimination mechanism were also important research contents. Bacterial degradation, photocatalytic degradation, and multiple-technologies approach have been identified with great potential and should be given more attention in future studies. This work summarizes the current research status on microcystin management, provides a valuable reference for researchers to identify potential opportunities for collaboration in related fields, and guides future research directions to inter-disciplinary and multi-perspective approaches.

Effects and behaviors of Microcystis aeruginosa in defluorination by two Al-based coagulants, AlCl3 and Al13

The complexity of natural water made it difficult to remove fluoride. Based on the environmental problems found in the investigation, the fluoride removal research in the water containing algal cells was carried out. In this study, AlCl₃ and [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ (Al₁₃) were used to remove fluoride. Additionally, the role of aluminum speciation in fluoride removal and the effect of Microcystis aeruginosa on the fluoride removal by different aluminum species coagulants were elucidated. The results showed that AlCl₃ mainly removed fluoride by physical interactions, surface adsorption and enmeshment. When algal cells were added to the system, the fluoride removal rate increased from 22.75 % to 72.99 % at a dosage of 40.0 mg/L. This was because algal cells greatly increased the distribution of Al(OH)₃ in the flocs. In particular, the specific surface area of the flocs containing algal cells reached 160.77 m²/g, which allowed more fluoride to be adsorbed. However, excessive Al³⁺ led to serious damage to algal cells and release of intracellular organic matter (IOM), worsening the effect of defluoridation. F^- and Al³⁺ formed AlF²⁺ and AlF₂⁺ via complexation in water. These compounds were not conducive to defluoridation. Al₁₃ removed fluorine mainly through ion exchange, substitution and hydrogen bonding. Algal cells had an inhibitory effect on defluorination, which was observed in the process of coagulation by different Al dosages. Al₁₃ achieved agglomeration of algal cells and generated small and dense flocs through charge neutralization and electrostatic patch mechanism. Once Al₁₃ combined with algal cells and algae organic matter (AOM), the reaction between Al₁₃ and fluoride would be weakened. Al₁₃ not only maintained the defluoridation performance, but also did not damage the integrity of algal cells, even at high dosages.

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.

Mussel-Inspired Immobilization of Photocatalysts with Synergistic Photocatalytic-Photothermal Performance for Water Remediation

The serious problem of pharmaceutical and personal care product pollution places great pressure on aquatic environments and human health. Herein, a novel coating photocatalyst was synthesized by adhering Ag-AgCl/WO₃/g-C₃N₄ (AWC) nanoparticles on a polydopamine (PDA)-modified melamine sponge (MS) through a facile layer-by-layer assembly method to degrade trimethoprim (TMP). The formed PDA coating was used for the anchoring of nanoparticles, photothermal conversion, and hydrophilic modification. TMP (99.9%; 4 mg/L) was removed in 90 min by the photocatalyst coating (AWC/PDA/MS) under visible light via a synergistic photocatalytic-photothermal performance route. The stability and reusability of the AWC/PDA/MS have been proved by cyclic experiments, in which the removal efficiency of TMP was still more than 90% after five consecutive cycles with a very little mass loss. Quantitative structure-activity relationship analysis revealed that the ecotoxicities of the generated intermediates were lower than those of TMP. Furthermore, the solution matrix effects on the photocatalytic removal efficiency were investigated, and the results revealed that the AWC/PDA/MS still maintained excellent photocatalytic degradation efficiency in several actual water and simulated water matrices. This work develops recyclable photocatalysts for the potential application in the field of water remediation.

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

A novel plasmonic Ag/AgCl@LaFeO₃ (ALFO) photocatalyst was successfully synthesized by a simple in-situ synthesis method with enhanced photocatalytic activity under visible light for harmful algal blooms (HABs) control. The structure, morphology, chemical states, optical and electrochemical properties of the photocatalyst were systematically investigated using a series of characterization methods. Compared with pure LaFeO₃ and Ag/AgCl, ALFO-20% owned a higher light absorption capacity and lower electron-hole recombined rate. Therefore, ALFO-20% had higher photocatalytic activity with a near 100% removal rate of chlorophyll a within 150 min, whose kinetic constant was 15.36 and 9.61 times faster than those of LaFeO₃ and Ag/AgCl. In addition, the changes of zeta potential, cell membrane permeability, cell morphology, organic matter, total soluble protein, photosynthetic system and antioxidant enzyme system in Microcystis aeruginosa (M. aeruginosa) were studied to explore the mechanism of M. aeruginosa photocatalytic inactivation. The results showed that ALFO-20% could change the permeability and morphology of the algae cell membrane, as well as destroy the photosynthesis system and antioxidant system of M. aeruginosa. What's more, ALFO could further degrade the organic matters flowed out after algae rupture and die, reducing the secondary pollution and avoiding the recurrence of HABs. Finally, the species of reactive oxygen species (ROS) (mainly •O₂^- and •OH) produced by ALFO were determined through quenching experiments, and a possible photocatalytic mechanism was proposed. Overall, ALFO can efficiently remove the harmful algae under the visible light, providing a promising method for controlling HABs.

In situ synthesis of Ag3PO4/C3N5Z-scheme heterojunctions with enhanced visible-light-responsive photocatalytic performance for antibiotics removal

Environmental pollution caused by antibiotics-containing wastewater has attracted increasing attention. Considering the superior photocatalytic performance and the issue of photo-corrosion over silver-based photocatalysts, it is desirable to construct silver-based photocatalysts with high photostability. Herein, a serious of Ag₃PO₄/C₃N₅ nanocomposites with Z-scheme band alignment were rationally designed and fabricated for tetracycline hydrochloride (TCH) removal. A variety of characterizations were employed to systematically study the phase structure, morphology and microstructure, optical properties, surface chemical states, and photocatalytic performance of the as-fabricated photocatalysts. The as-prepared Ag₃PO₄/C₃N₅ nanocomposites exhibited superior photocatalytic activity and photochemical stability than a single component toward TCH removal, meanwhile, the photocatalytic performance was not increased with the increasing amount of Ag₃PO₄. The possible photocatalytic mechanism (Z-scheme mechanism) was investigated and verified. The Z-scheme heterojunctions formed between Ag₃PO₄ and C₃N₅ is the main reason for the enhanced photocatalytic activities.