In-situ active formation of carbides coated with NPTiO2 nanoparticles for efficient adsorption-photocatalytic inactivation of harmful algae in eutrophic water

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.

Recent progress and prospect of graphitic carbon nitride-based photocatalytic materials for inactivation of Microcystis aeruginosa

The proliferation of harmful algal blooms is a global concern due to the risk they pose to the environment and human health. Algal toxins which are hazardous compounds produced by dangerous algae, can potentially kill humans. Researchers have been drawn to photocatalysis because of its clean and energy-saving properties. Graphite carbon nitride (g-C3N4) photocatalysts have been extensively studied for their ability to eliminate algae. These photocatalysts have attracted notice because of their cost-effectiveness, appropriate electronic structure, and exceptional chemical stability. This paper reviews the progress of photocatalytic inactivation of harmful algae by g-C3N4-based materials in recent years. A brief overview is given of a number of the modification techniques on g-C3N4-based photocatalytic materials, as well as the process of inactivating algal cells and destroying their toxins. Additionally, it provides a theoretical framework for future research on the eradication of algae using g-C3N4-based photocatalytic materials.

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.

Nanoparticles, an Emerging Control Method for Harmful Algal Blooms: Current Technologies, Challenges, and Perspectives

Harmful algal blooms (HABs) are a global concern because they harm aquatic ecosystems and pose a risk to human health. Various physical, chemical, and biological approaches have been explored to control HABs. However, these methods have limitations in terms of cost, environmental impact, and effectiveness, particularly for large water bodies. Recently, the use of nanoparticles has emerged as a promising strategy for controlling HABs. Briefly, nanoparticles can act as anti-algae agents via several mechanisms, including photocatalysis, flocculation, oxidation, adsorption, and nutrient recovery. Compared with traditional methods, nanoparticle-based approaches offer advantages in terms of environmental friendliness, effectiveness, and specificity. However, the challenges and risks associated with nanoparticles, such as their toxicity and ecological impact, must be considered. In this review, we summarize recent research progress concerning the use of nanoparticles to control HABs, compare the advantages and disadvantages of different types of nanoparticles, discuss the factors influencing their effectiveness and environmental impact, and suggest future directions for research and development in this field. Additionally, we explore the causes of algal blooms, their harmful effects, and various treatment methods, including restricting eutrophication, biological control, and disrupting living conditions. The potential of photocatalysis for generating reactive oxygen species and nutrient control methods using nanomaterials are also discussed in detail. Moreover, the application of flocculants/coagulants for algal removal is highlighted, along with the challenges and potential solutions associated with their use. This comprehensive overview aims to contribute to the development of efficient and sustainable strategies for controlling HAB control.

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.

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.

Efficient photocatalytic inactivation of Microcystis aeruginosa by a novel Z-scheme heterojunction tubular photocatalyst under visible light irradiation

The design of a photocatalyst for efficient algal inactivation under visible light is essential for the application of photocatalysis to the control of harmful algal blooms. In this study, a novel Z-scheme heterojunction tubular photocatalyst, Ag₂O@PG, was synthesized by chemically depositing silver oxide compounded with P-doped hollow tubular graphitic carbon nitride for the photocatalytic inactivation of Microcystis aeruginosa (M. aeruginosa). The photocatalytic algal inactivation experiments showed that the photocatalytic activity of Ag₂O@PG was influenced by the ratio of the composition of the obtained materials. The optimal algal inactivation efficiency was observed when using Ag₂O@PG-0.4 at a dosage of 0.2 g/L. It was able to achieve a 99.1 % M. aeruginosa inactivation at an initial concentration of 4.5 × 10⁶ cells/mL following 5 h' visible light irradiation. During the process, the cell membrane permeability and cell morphology changed. Furthermore, under the constant attack of superoxide radicals and holes caused by Ag₂O@PG, the superoxide dismutase, glutathione and malondialdehyde of algae cells increased during the experiments to alleviate oxidative damage. Eventually, the antioxidant system of algae cells was destroyed. To further validate the potential application of Ag₂O@PG-0.4 in real algal bloom environment, an experiment in real water samples was carried out. Overall, the Ag₂O@PG-0.4 as an efficient photocatalyst has a promising potential for emergency treatment measures to alleviate algal blooms.

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.

Okara and okara modified and functionalized with iron oxide nanoparticles for the removal of Microcystis aeruginosa and cyanotoxin

Eutrophicating compounds promote the growth of cyanobacteria, which has the potential of releasing toxic compounds. Alternative raw materials, such as residues, have been used in efficient adsorption systems in water treatment. The aim of the present study was to apply the residue Okara in its original form and modified by hydrolysis with immobilization of magnetic nanoparticles as an adsorbent. For the removal, the cyanobacteria Microcystis aeruginosa was chosen, as well as its secondary metabolites, L-amino acids leucine and arginine (MC-LR microcystin), from aqueous solutions. The adsorbents presented a negative surface charge, and the x-ray diffraction (DRX) outcomes successfully demonstrated the immobilization of iron oxide nanoparticles on the adsorbents. The adsorbent with the best result was the Okara hydrolyzed and functionalized with iron oxide, which showed a 47% (qe = 804.166 cel/g) and 85% (qe = 116.94 µg/L) removal for the cyanobacteria cells and chlorophyll-a, respectively. The kinetics study demonstrated a pseudo-first-order adsorption with maximal adsorption in 480 minutes, removing 761 µg/L of chlorophyll-a. In this trial, a low organic material removal has occurred, with a removal rate of 5% (qe = 0.024 mg/g) in the analysis of compounds in absorbance by ultraviolet light (UV) monitored by optical density determination in 254 nm (OD254). Nevertheless, the reaction system with the presence of organic material removed 53,28% of the MC-LR toxin, with adsorption capacities of 2.84 µg/L in a preliminary trial conducted for two hours, arising as a potential and alternative adsorbent with a capacity of removing cyanobacteria and cyanotoxin cells simultaneously.

Recyclable self-floating A-GUN-coated foam as effective visible-light-driven photocatalyst for inactivation of Microcystis aeruginosa

In this work, a recyclable self-floating A-GUN-coated (Ag/AgCl@g-C₃N₄@UIO-66(NH₂)-coated) foam was fabricated for effective inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. The floating photocatalyst was able to inactivate 98% of M. aeruginosa within 180 min under the visible-light irrigation, and the floating photocatalyst exhibited a stable performance in various conditions. Moreover, the inactivation efficiency can still maintain nearly 92% after five times recycle experiments, showing excellent photocatalytic stability. Furthermore, effects of A-GUN/SMF floating catalyst on the physiological properties, cellular organics, and algal functional groups of M. aeruginosa were studied. The floating photocatalyst can not only make full use of excellent photocatalytic activities of A-GUN nanocomposite, but also promote contact between catalyst and algae, and realize the effective recovery of the photocatalyst. Finally, possible photocatalytic inactivation mechanisms of algae were obtained, which provides references for removing cyanobacteria blooms in real water bodies.

In-situ responses of phytoplankton to graphene photocatalysis in the eutrophic lake Xingyun, southwestern China

Graphene photocatalysis is receiving increased attention for its potential to be used as a novel green technology for mitigating harmful algae in highly eutrophic waters. However, graphene is seldom applied to in situ aquatic ecosystems for environmental applications. Here, the impacts of graphene photocatalysis on phytoplankton and environmental conditions were evaluated through an in situ macrocosm experiment in the eutrophic Lake Xingyun, southwestern China. The graphene photocatalysis treated area had significantly reduced conductivity, total nitrogen (TN), total phosphorus (TP) and dissolved phosphorus concentrations, as well as increased dissolved oxygen (DO) concentrations. The abundances of all species of the genus Microcystis were significantly reduced in the graphene photocatalysis-treated area; in contrast, the abundances of all species of the diazotrophic genera, including Anabaena and Aphanizomenon, greatly increased after treatment with graphene photocatalysis. Eukaryotic algae, especially Chlorophyta, Euglenophyta and Pyrrophyta, as well as Cryptophyta, had significantly higher abundances in the graphene photocatalysis-treated area, whereas most of the eutrophic diatom species had lower abundances in the treated area. These observed differences in eukaryotic algae between the two groups might be related to their sensitivity to graphene photocatalysis and their tolerance of nutrients. Generally, graphene photocatalysis can make a great contribution to the improvement of eutrophic water, as evidenced by the reduction in cyanobacteria abundance and phosphorus concentration, as well as the increase in species richness and the dissolved oxygen concentration in the treated area. However, the mechanisms underlying these differences in phytoplankton community structure and environmental conditions require further study.

Efficient elimination of the pollutants in eutrophicated water with carbon strengthened expanded graphite based photocatalysts: Unveiling the synergistic role of metal sites

Metal sites (Ni, Bi or Ag) were introduced into carbon strengthened expanded graphite (CEG) based photocatalysts, and performed as a novel strategy to enhance the elimination of Microcystis aeruginosa and microcystin-LR from water. Results show that metal doping can efficiently improve the adsorption of harmful algae and enhance the photocatalytic activities in inactivation of harmful algae and degradation of MC-LR. Among the CEG catalysts, Ni-CEG can achieve the highest removal rate up to 90.6% for algal cells with 5 h visible light irradiation, while Bi-CEG catalyst provides the best performance for MC-LR degradation with the removal rate of 80.9% in 6 h visible light irradiation. In general, considering the coexistence of algal cells and microcystin-LR, Bi-CEG is proved to be an excellent candidate for the remediation of eutrophicated waters since it can achieve the efficient removal of both harmful algae and MC-LR. DFT calculations indicate that metal doping can transform the photocatalysts into n-type semiconductor, and provide the mid-gap state. In addition, the partial charge density distribution near Fermi level was mainly composed by the metal dopants, which can enhance the interaction with harmful algae and MC-LR.

Anti-algal activity of a fluorine-doped titanium oxide photocatalyst against Microcystis aeruginosa and its photocatalytic degradation

Fluorine-doped TiO2 was successfully synthesised and applied as algaecide. Studies on algae removal efficiencies and mechanisms illustrated that F-TiO2 was suitable for algae elimination in natural water bodies.

One-Step Synthesis of b-N-TiO2/C Nanocomposites with High Visible Light Photocatalytic Activity to Degrade Microcystis aeruginosa

Black TiO2 with doped nitrogen and modified carbon (b-N-TiO2/C) were successfully prepared by sol-gel method in the presence of urea as a source of nitrogen and carbon. The photocatalysts were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, electron paramagnetic resonance (EPR), and UV-vis diffuse reflectance spectra (DRS). The doped nitrogen, introduced defects, and modified carbon played a synergistic role in enhancing photocatalytic activity of b-N-TiO2/C for the degradation of chlorophyll-a in algae cells. The sample, with a proper amount of phase composition and oxygen vacancies, showed the highest efficiency to degrade chlorophyll-a, and the addition of H2O2 promoted this photocatalysis degradation. Based on the trapping experiments and electron spin resonance (ESR) signals, a photocatalytic mechanism of b-N-TiO2/C was proposed. In the photocatalytic degradation of chlorophyll-a, the major reactive species were identified as OH and O2−. This research may provide new insights into the photocatalytic inactivation of algae cells by composite photocatalysts.

Surface-Induced ARGET ATRP for Silicon Nanoparticles with Fluorescent Polymer Brushes

Well-defined polymer brushes attached to nanoparticles offer an elegant opportunity for surface modification because of their excellent mechanical stability, functional versatility, high graft density as well as controllability of surface properties. This study aimed to prepare hybrid materials with good dispersion in different solvents, and to endow this material with certain fluorescence characteristics. Well-defined diblock copolymers poly (styrene)-b-poly (hydroxyethyl methyl acrylate)-co-poly (hydroxyethyl methyl acrylate- rhodamine B) grafted silica nanoparticles (SNPs-g-PS-b-PHEMA-co-PHEMA-RhB) hybrid materials were synthesized via surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). The SNPs surfaces were modified by 3-aminopropyltriethoxysilane (KH-550) firstly, then the initiators 2-Bromoisobutyryl bromide (BIBB) was attached to SNPs surfaces through the esterification of acyl bromide groups and amidogen groups. The synthetic initiators (SNPs-Br) were further used for the SI-ARGET ATRP of styrene (St), hydroxyethyl methyl acrylate (HEMA) and hydroxyethyl methyl acrylate-rhodamine B (HEMA-RhB). The results indicated that the SI-ARGET ATRP initiator had been immobilized onto SNPs surfaces, the Br atom have located at the end of the main polymer chains, and the polymerization process possessed the characteristic of controlled/"living" polymerization. The SNPs-g-PS-b-PHEMA-co-PHEMA-RhB hybrid materials show good fluorescence performance and good dispersion in water and EtOH but aggregated in THF. This study demonstrates that the SI-ARGET ATRP provided a unique way to tune the polymer brushes structure on silica nanoparticles surface and further broaden the application of SI-ARGET ATRP.