Removal of Cyanobacteria and Cyanotoxins in Waters

Harmful cyanobacterial algal blooms and cyanotoxins currently pose a major threat to global society, one that exceeds local and national interests due to their extremely destructive effects on the environment and human health. In the near future, the formation of harmful cyanobacterial algal blooms and, in turn, cyanotoxins is expected to become widespread, driven by eutrophication and anthropogenic causes such as water pollution and promoted by escalating global temperatures. Such trends, studied since the late 1990s, have attracted increased interest due to (i) the high environmental impact of cyanobacterial blooms and cyanotoxins worldwide, (ii) the ineffective removal of those pollutants by conventional water treatment processes, (iii) the transformational capacity to completely destroy those organic toxins via alternative treatments such as advanced oxidation processes,and (iv) engineering challenges when transitioning toward the treatment of large volumes of water. The global context of this threat thus urges the innovation of simple, sustainable, low-cost strategies and technologies for water decontamination that can be readily implemented worldwide

Bioinspired ZnO-based solar photocatalysts for the efficient decontamination of persistent organic pollutants and hexavalent chromium in wastewater

Biomimetic/bioinspired engineering and sulfidation processes are effective strategies for improving the visible light-driven photocatalytic performance of ZnO photocatalysts. A facile electrodeposition process in high oxygen-flux conditions was used to synthesize well-defined fractal micro/nanoferns, consequently increasing the photocatalyst's light-trapping capability and accessible active surface. Next, a simple sulfidation process was used to form a thin layer of ZnS, producing ZnO@ZnS core@shell micro/nanoferns and thereby tuning the optoelectronic properties and extending the photoresponse to the visible region. The ZnO@ZnS micro/nanoferns exhibited clear superiority over other ZnO photocatalyts in the photooxidation of persistent organic pollutants (POPs) and the photoreduction of Cr(VI). Their excellent photocatalytic performance allowed the photodegradation under UV-filtered sunlight of nearly 97% of methylene blue after 60 min; the mineralization of >98% of a mixture of methylene blue, 4-nitrophenol, and rhodamine-B after 210 min; and the removal of nearly 65% of Cr(VI) after 180 min. In addition, the ZnO@ZnS micro/nanoferns demonstrated good ability to decontaminate an inorganic-organic bipollutant system, with promising potential to leverage synergistic effects. Finally, these micro/nanoferns presented great recyclability and reusability for both photooxidation and photoremediation processes. These findings support that sulfidation and biomimetic engineering can be a superior route for designing efficient sunlight-driven ZnO-photocatalysts for water decontamination

Enhanced photocatalytic removal of cyanotoxins by Al-doped ZnO nanoparticles with visible-LED irradiation

The ZnO-based visible-LED photocatalytic degradation and mineralization of two typical cyanotoxins, microcystin-LR (MC-LR) and anatoxin-A, were examined. Al-doped ZnO nanoparticle photocatalysts, in Al:Zn ratios between 0 and 5 at.%, were prepared via sol-gel method and exhaustively characterized by X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and nitrogen adsorption-desorption isotherms. With both cyanotoxins, increasing the Al content enhances the degradation kinetics, hence the use of nanoparticles with 5 at.% Al content (A5ZO). The dosage affected both cyanotoxins similarly, and the photocatalytic degradation kinetics improved with photocatalyst concentrations between 0.5 and 1.0 g L-1. Nevertheless, pH study revealed that the chemical state of a species decisively facilitates the mutual interaction of cyanotoxin and photocatalysts. A5ZO nanoparticles achieved better outcomes than other photocatalysts to date, and after 180 min, the mineralization of anatoxin-A was virtually complete in weak alkaline medium, whereas only 45% of MC-LR was in neutral conditions. Moreover, photocatalyst reusability is clear for anatoxin-A, but it is adversely affected for MC-LR

Electrodeposition of nanostructured Bi2MoO6@Bi2MoO6-x homojunction films for the enhanced visible-light-driven photocatalytic degradation of antibiotics

Complex tunable visible-light-driven Aurivillius-phase-based micro- and nanostructured photocatalysts were fabricated following a novel, scalable, easily implemented sequential process based on electrochemical deposition and thermal treatment. Regarding its novelty, electrochemistry was the primary tool for synthesis, one that constitutes a viable alternative to other complex chemical and physical processes. The parameters of electrodeposition and thermal conditions promoted different nanostructured Bi2MoO6 and Bi2MoO6@Bi2MoO6-x films. The nanostructured homojunction Bi2MoO6@Bi2MoO6-x films obtained after 3 h of calcination showing micro- and nanowire morphology emerged as the most effective photocatalyst for degrading and mineralizing the mono- and multiantibiotic solutions (i.e., tetracycline, ciprofloxacin, and/or levofloxacin), which achieved near-total degradation and exceptionally high mineralization values (>95%) after 180 min of radiation. The materials' proven reusability, low photocorrosion activity, and excellent photocatalytic performance in mineralizing antibiotics can support the implementation of Bi2MoO6@Bi2MoO6-x homojunctions as efficient visible-light photocatalysts under solar radiation

Facile cost-effective fabrication of Cu@Cu2O@CuO-microalgae photocatalyst with enhanced visible light degradation of tetracycline

The widespread use and negative environmental effects of antibiotics have made their removal from aqueous media essential in terms of wastewater treatment. Accordingly, a hybrid helical Cu@Cu2O@CuO-microalgae photocatalyst for antibiotic photodegradation was synthesized in this study by a simple, inexpensive, and scalable process based on electroless Cu deposition and soft thermal treatment. The hybrid photocatalyst was more competitive for the photocatalytic degradation of tetracycline, especially in terms of mineralization and energy consumption, than state-of-the-art photocatalysts. The excellent photocatalytic performance is attributable to the effective formation of onion-like Cu@Cu2O@CuO heterojunctions, which synergistically lower the electron-hole recombination rate, promote the utilization of light and photogeneration of charge carriers, and decrease the photocorrosion activity. All these effects result in the enhanced photocatalytic degradation and mineralization of tetracycline. The high photocatalytic performance of the Cu@Cu2O@CuO-microalgae hybrids under LED irradiation resulted in a significantly lower electrical energy per order¿i.e., the electrical energy required to diminish the tetracycline concentration by one order of magnitude in a unit of volume¿of 57 kW h m−3 order-1. Importantly, the Cu@Cu2O@CuO-microalgae hybrids can easily be recycled after reaching their effective lifetime to fabricate competitive microalgal pellets, then integrated into a circular process in an environment-energy nexus to minimize the generation of residues

Photocatalytic treatment of natural waters. Reality or hype? The case of cyanotoxins remediation

This review compiles recent advances and challenges in the photocatalytic treatment of natural water by analyzing the remediation of cyanotoxins. The review frames the treatment need based on the occurrence, geographical distribution, and legislation of cyanotoxins in drinking water while highlighting the underestimated global risk of cyanotoxins. Next, the fundamental principles of photocatalytic treatment for remediating cyanotoxins and the complex degradation pathway for the most widespread cyanotoxins are presented. The state-of-the-art and recent advances on photocatalytic treatment processes are critically discussed, especially the modification strategies involving TiO2 and the primary operational conditions that determine the scalability and integration of photocatalytic reactors. The relevance of light sources and light delivery strategies are shown, with emphasis on novel biomimicry materials design. Thereafter, the seldomly-addressed role of water-matrix components is thoroughly and critically explored by including natural organic matter and inorganic species to provide future directions in designing highly efficient strategies and scalable reactors

Electrodeposited Ni-rich Ni-Pt mesoporous nanowires for selective and efficient formic acid-assisted hydrogenation of levulinic acid to γ-valerolactone

In pursuit of friendlier conditions for the preparation of high-value biochemicals, we developed a catalytic synthesis of -valerolactone by levulinic acid hydrogenation with formic acid as the hydrogen source. Both levulinic and formic acid are intermediate products in the biomass transformation processes. The objective of the work is two-fold; development of a novel approach for milder synthesis conditions to produce -valerolactone and the reduction of the economic cost of the catalyst. Ni-rich Ni-Pt mesoporous nanowires were synthesized in an aqueous medium using a combined hard-soft template-assisted electrodeposition method, in which porous polycarbonate membranes controlled the shape, and the pluronic P-123 copolymer served as the porogen agent. The electrodeposition conditions selected favored nickel deposition and generated nanowires with nickel percentages above the 75 at. %. The increase in deposition potential favored nickel deposition. However, it was detrimental for the porous diameter, because the mesoporous structure is promoted by the presence of the platinum-rich micelles near the substrate, which is not favored at the more negative potentials. The prepared catalysts promoted the complete transformation to -valerolactone in a yield of around 99% and proceeded with the absence of by-products. The couple temperature and reaction time were optimized considering the energy cost. The threshold operational temperature was established at 140 ºC, at which, 120 minutes were sufficient for attaining the complete transformation. Working temperatures below 140 ºC rendered the reaction completion difficult. The Ni78Pt22 nanowires exhibited excellent reusability, with minimal nickel leaching into the reaction mixture, whereas those with higher nickel contents showed corrosion

Electrodeposited manganese oxides as efficient photocatalyst for the degradation of tetracycline antibiotics pollutant

One of the important environmental challenges of the 21st century is the effective removal of pollutants from the aquatic environment. In this study, electrodeposited manganese oxides (MnyOx) films were applied as visible-light-driven photocatalyst for the removal and mineralization of Tetracycline (TC) antibiotics. The photocatalytic activity of as-deposited and annealed MnyOx was tested at different pH values using LED visible illumination, resulting in 92.4 % of TC mineralization efficiency after 180 min for the best performing manganese oxide. Quenching experiments showed that hydroxyl radicals (radical dotOH) are the main active species responsible for the TC degradation. The photocorrosion of MnyOx has been studied by quantifying the concentration of the dissolved manganese cations during the photocatalytic experiments. By comparing the catalyst mass loss with the % of TC mineralization, we revealed that the degradation of the oxide surface structure is the factor that, more than the photocorrosion, is limiting the photocatalytic activity of MnyOx films. Finally, the photocatalytic mechanism of TC mineralization is proposed based on the detection of the intermediates species of the mineralization process by High-Performance Liquid Chromatography Mass-Spectroscopy. The facile synthesis process and the superior mineralization rate can open up a new approach for the possible large-scale utilization of electrodeposited MnyOx films as an effective visible light photocatalyst

Electrodeposition of mesoporous Ni-rich Ni-Pt films for highly efficient methanol oxidation

The use of soft templates for the electrosynthesis of mesoporous materials has shown tremendous potential in energy and environmental domains. Among all the approaches that have been featured in the literature, block copolymer-templated electrodeposition had robustness and a simple method, but it practically cannot be used for the synthesis of mesoporous materials not based on Pt or Au. Nonetheless, extending and understanding the possibilities and limitations of block copolymer-templated electrodeposition to other materials and substrates is still challenging. Herein, a critical analysis of the role of the solution's primary electroactive components and the applied potential were performed in order to understand their influences on the mesostructure of Ni-rich Ni-Pt mesoporous films. Among all the components, tetrahydrofuran and a platinum (IV) complex were shown to be crucial for the formation of a truly 3D mesoporous network. The electrosynthesized well-ordered mesoporous Ni-rich Ni-Pt deposits exhibit excellent electrocatalytic performance for methanol oxidation in alkaline conditions, improved stability and durability after 1000 cycles, and minimal CO poisoning

Self-assembled oil palm biomass-derived modified graphene oxide anode: An efficient medium for energy transportation and bioremediating Cd (II) via microbial fuel cells

Although microbial fuel cells (MFCs) rank among the most promising bioelectrochemical approaches for generating energy while removing pollutants from wastewater, their relatively poor performance, largely due to electrode material that hinder their applicability, has limited their commercial viability. Thus, in our study, self-assembled modified graphene oxide (GO) anodes were developed from oil palm (Elaeis guineensis) biomass, and several techniques were applied to assess the physiochemical properties of material synthesized with waste material. Ultimately, the waste material was an excellent source for generating energy in the form of anodes in MFCs. The bioinspired modified GO anodes demonstrated greater energy output (135.96 mA/m2) of more than eight times the unmodified GO anodes (15.65 mA/m2), even though the source of inoculation was synthetic wastewater with 100 ppm of Cd (II) solution. To our knowledge, no work has reported removing Cd (II) from synthetic wastewater by using waste-derived anodes via MFCs. This paper reports on the utilization of waste-derived organic waste (oil palm trunk sap) as an organic substrate which is a healthy source of nutrients for bacteria in an inoculated media. Along with evidence of their electrochemical and biological character, the primary result achieved (i.e., 90% removal efficiency) supports using MFCs on an industrial scale