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.

Investigation on characterization, antifouling and cytotoxic properties of zinc oxide nanoparticles biosynthesized by a mangrove-associated actinobacterium Streptomyces olivaceus (MSU3)

The present study was undertaken to biosynthesize zinc oxide nanoparticles (ZnONPs) using a mangrove-associated actinobacterium Streptomyces olivaceus (MSU3) under in vitro conditions. The synthesized ZnONPs were structurally characterized through UV, FT-IR, TG-DTA, XRD, SEM and EDX analysis. Analysis of biosynthesized ZnONPs in UV-Vis spectroscopy showed presence of functional groups between the wavelengths 325 and 380 nm. FT-IR analysis showed the functional groups, such as halo bromide (C-Br), alkyne (C≡C), carboxylic acid (O-H), nitro (N-O), fluoro (C-F), alkene (C=C) and aromatic (R-C-H) groups, respectively, within the wave numbers between 614.30 and 3074.41 cm^-1. The crystalline poly-dispersed quasi spherical nature of ZnONPs expressed the average particle size of 37.9 nm with the 2θ values of 11.802-37.885°. Antibacterial activity of ZnONPs showed pronounced inhibitory zone (25 mm) and least MIC and MBC values (125 and 250 µg ml^-1) against Escherchia sp. In the antifouling study, ZnONPs strongly inhibited byssal thread formation in mussel Perna indica and recorded LC₅₀ value of 424.47 µg ml^-1. Mollusc foot adherence assay inferred that the ZnONPs effectively inhibited settlement of limpet Patella vulgata and showed minimal fouling (26.43%) at 350 µg ml^-1 and recorded LC₅₀ value of 218.77 µg ml^-1. Results of anticrustacean assay depicted that, ZnONPs had registered LC₅₀ value of 676.08 µg ml^-1 against Artemia salina nauplii. From this study, it could be concluded that an eco-friendly approach could be used to open a new avenue for biosynthesis of ZnONPs from a mangrove associated actinobacterium S. olivaceus (MSU3) in antifouling studies.

Microwave-Assisted Synthesis and Characterization of Solar-Light-Active Copper–Vanadium Oxide: Evaluation of Antialgal and Dye Degradation Activity

In this work, solar-light-active copper–vanadium oxide (Cu-VO) was synthesized by a simple microwave method and characterized by FESEM, EDS, XRD, XPS, UV–Vis/near-infrared (NIR), and FT-IR spectroscopy. Antialgal and dye degradation activities of Cu-VO were investigated against Microcystis aeruginosa and methylene blue dye (MB), respectively. The mechanism of action of Cu-VO was examined regarding the production of hydroxyl radical (·OH) in the medium and intracellular reactive oxygen species (ROS) in M. aeruginosa. FESEM and XRD analyses of Cu-VO disclosed the formation of monoclinic crystals with an average diameter of 132 nm. EDX and XPS analyses showed the presence of Cu, V, and O atoms on the surface of Cu-VO. Furthermore, FT-IR analysis of Cu-VO exposed the presence of tetrahedral VO4 and octahedral CuO6. Cu-VO effectively reduced the algal growth and degraded methylene blue under solar light. A total of 4 mg/L of Cu-VO was found to be effective for antialgal activity. Cu-VO degraded 93% of MB. The investigation of the mechanism of action of Cu-VO showed that ·OH mediated antialgal and dye degradation of M. aeruginosa and MB. Cu-VO also triggered the production of intracellular ROS in M. aeruginosa, leading to cell death. Thus, Cu-VO could be an effective catalyst for wastewater treatment.