Display omitted
•Light-driven oxidation technologies for removing microcystin-LR from water were reviewed.•Factors affecting the microcystin-LR degradation were probed.•Microcystin-LR was removed ...using photocatalysis/oxidation under real scenarios.•Conjugated dienes, double bonds, free carboxyl groups, and peptide ring were toxicity-induced structures.•Several new pathways of attacking peptide ring of microcystin-LR were introduced.
Cyanobacterial algal blooms are ubiquitous around the globe and lead to severe cyanotoxin pollution, which poses a severe threat to the safety of drinking water. Microcystins (MCs), the monocyclic heptapeptides, are the most commonly occurring cyanotoxin, which consist of five D-amino acids and two variable L-amino acids. There exist over 100 MC variants, and microcystin-leucine arginine (MC-LR) is one of the most hazardous and prevalent variants. This review comprehensively discussed the status quo of investigations light-driven oxidation technology for degradation of MC-LR, including photolysis, heterogenous photocatalysis and homogeneous oxidation that are driven by UV, visible light and solar light (main information of homogeneous oxidation are shown in Supplementary materials). The effects of key parameters on these systems are critically clarified, including light wavelength, photocatalyst/oxidant concentration, initial MC-LR concentration, pH values, and coexisting organic or inorganic matter. An increasing number of studies are conducted on real water matrix at toxin concentrations and pH values that are similar to water contaminated by cyanobacterial algal blooms. However, very few studies have investigated the mineralization and detoxification of treated water, and little is known about the fragments of MC-LR that are responsible for its toxicity. Thereafter, reaction mechanism, ecotoxicological effects and operational costs of the MC-LR photodegradation process in all systems are also comprehensively elucidated. This paper will help to better understand the MC-LR decomposition process and provide improved perspectives for future research in this field.
In this study, sludges generated from Ti-based flocculation of dye wastewater were used to retrieve photoactive titania (S–TiO2). It was heterojunctioned with graphitic carbon nitride (g-CN) to ...augment photoactivity under UV/visible light irradiance. Later the as-prepared samples were utilized to remove nitrogen oxides (NOx) in the atmospheric condition through photocatalysis. Heterojunction between S–TiO2 and g-CN was prepared through facile calcination (@550 °C) of S–TiO2 and melamine mix. Advanced sample characterization was carried out and documented extensively. Successful heterojunction was confirmed from the assessment of morphological and optical attributes of the samples. Finally, the prepared samples’ level of photoactivity was assessed through photooxidation of NOx under both UV and visible light irradiance. Enhanced photoactivity was observed in the prepared samples irrespective of the light types. After 1 h of UV/visible light-based photooxidation, the best sample STC4 was found to remove 15.18% and 9.16% of atmospheric NO, respectively. In STC4, the mixing ratio of S–TiO2, to melamine was maintained as 1:3. Moreover, the optical bandgap of STC4 was found as 2.65 eV, where for S–TiO2, it was 2.83 eV. Hence, the restrained rate of photogenerated charge recombination and tailored energy bandgap of the as-prepared samples were the primary factors for enhancing photoactivity.
Display omitted
•Successful heterojunction of sludge generated TiO2 and g-CN.•Effective NOx removal has been observed under UV/visible light.•Heterojunction caused optical bandgap narrowing and reduced charge recombination.•NOx removal mechanism was explained using advanced characterizations.
•Co-doped TiO2 and ZnO materials were synthetized by solvent and hydrothermal method.•Effect of Co-doping amount was investigated on photocatalytic efficiency.•Doped materials were tested on ...ketoprofen degradation in real wastewater.
The effect of cobalt doping on semiconductors materials synthesized via solution and hydrothermal methods was investigated by testing its photocatalytic efficiency on pollutants abatement. X Ray Diffraction technique was used to evaluate samples crystallographic phases allowing to identify different species due to the introduction of the dopants. Diffuse Reflectance UV–vis Spectroscopy was employed to determine the bandgap as well as the absorption corresponding to d-d transitions for cobalt doped systems. Finally, Electron Paramagnetic Resonance Spectroscopy was adopted to perform a pre-screening of the photoactivity of the prepared samples.
The Co-doped TiO2 and ZnO materials photoactivity was assessed on phenol degradation, selected as pollutant probe, under UVA irradiation. Doping TiO2 with cobalt in low amounts (0.25% and 0.5%) prepared by hydrothermal method leads to an enhancement on phenol degradation. Also, the presence of Co-doped ZnO obtained by hydrothermal process if prepared with defined cobalt amount (0.5 or 1%) promote an increasing on phenol abatement. Ketoprofen was used to evaluate the doping effect, being the Co-doped ZnO material more efficient on ketoprofen mineralization comparing with bare material. The ketoprofen and its transformation products were easily abated and, in wastewater, they were completely eliminated within 1 h, endorsing that inserting cobalt can improve the ZnO photocatalysis efficiency for water remediation.
Polymers have emerged as a new group of photoactive materials owing to their excellent optical and electronic properties. In this work, we report the synthesis and application of novel conjugated ...polymer for photocatalytic water remediation. The photoactive polymer was fabricated via the heat polymerization of Tris(4-carbazoyl-9-ylphenyl)amine (TCTA) into the Polyvinylpyrrolidone (PVP) host polymer (with mass ratio of 98%). TCTA is an electron rich with high lying LUMO and band gap of Eg = 3.4 eV, however, its polymerization with PVP results in higher visible light response until 900 nm. Two conjugated polymer samples were prepared with low and high TCTA contains, namely CP1 and CP2, respectively. The as-prepared photoactive samples were used as photoredox catalysts for the photocatalytic reduction of Cr(VI) and oxidation of MB under visible light (420 nm). CP2 showed higher visible light response, better electrochemical activity and excellent photocatalytic activity compared to CP1. In terms of Cr(VI) photoreduction, CP2 (0.25 g/L) can totally reduce Cr(VI) (20 ppm) at pH ranging from 3 to 8 under visible light. A total reduction of 40 ppm of Cr(VI) was found within 60 min using 0.75 g/L of CP2. 98% of MB was oxidized within 90 min using 0.25 g/L of CP2 under visible light. The photoactive polymer was supported into lignocellulosic biomass for higher surface area and better stability. As a result, this latter composite showed an enhanced adsorption capacity and photocatalytic efficiency towards Cr(VI) and MB compared to bare photoactive polymer. The main compounds used to fabricate this composite including PVP and natural biomass are eco-friendly, safe and low-cost which make it economically feasible photocatalyst for water remediation or other photoredox systems.
Display omitted
•Fabrication of novel lignocellulosic biomass supported photoactive redox polymer.•Tris(4-carbazoyl-9-ylphenyl)amine band gap was narrowed via polymerization with PVP.•The prepared composite showed an extended visible light response up to 900 nm.•The composite showed excellent photocatalytic Cr(VI) reduction and dye oxidation.
A novel and efficient approach for the synthesis of α, β‐unsaturated sulfones through heterogeneous photocatalyzed C−S coupling reactions have been developed. The use of molten‐salt method derived ...carbon nitride (MCN), a transition metal‐free polymeric photocatalyst, combined with enhanced crystallinity and potassium iodide as an additive, effectively modulates photogenerated reactive redox species, markedly increasing the overall reaction selectivity. This method achieves the shortest reaction time (2 h) with high yield (up to 95 %) among the reported heterogeneous catalytic C−S bond formation reactions, matching the efficiency of the homogeneous photocatalysts. Furthermore, the application to challenging alkyne substrates has been demonstrated, underscoring the potential for a broad range of applications in pharmaceutical research and synthetic chemistry.
A transition metal‐free heterogeneous photocatalytic C−S coupling reaction has been developed. Through optimizing the crystallinity of photocatalyst and incorporating potassium iodide, the distribution of photogenerated redox species are effectively modulated to enhance the formation of the sulfonyl radical and (iodoethynyl)benzene. This method thus achieves high yields of up to 95 % in a significantly reduced reaction time of 2 hours.
In the present study treatability of persistent organic compounds from the flow back water after hydrauling fracturing was investigated. The combination of TiO2 photocatalyst and magnetic oxide ...nanoparticles enhance the separation and recoverable property of nanosized TiO2 photocatalyst. Fe3O4/TiO2 and Fe3O4@SiO2/TiO2 nanocomposites were prepared by heteroagglomeration. The photocatalysts’ characteristics by X-ray diffractometry (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) showed that sample with the mass ratio of Fe3O4 to TiO2 equal 1:4 and molar ratio of TEOS:Fe3O4 = 8:1 and NH4OH:TEOS = 16:1 obtained by deposition TiO2 P25 (Evonik) on magnetite core had about 124 m2 g−1 specific surface area and superparamagnetic properties. The prepared composites contained TiO2 and Fe3O4 crystal phases. The photocatalytic activity was estimated by measuring the decomposition rate of three model pollutants identified in the flow back water from one of the Baltic Shale Basin. Regarding flow back water treatment after shale gas exploration, the progress of photocatalytic degradation of organic compounds was measured by chemical oxygen demand (COD) concentration. The Fe3O4@SiO2/TiO2_P25 composite nanoparticles were recovered and re-used without significant reduction of efficiency.
Display omitted
•Photocatalytic treatment of organic compounds present in flow back water was studied.•The effect of TiO2 type on structural, magnetic and photocatalytic properties was reported.•Most active sample was obtained by deposition of commercial titania P25 on Fe3O4/SiO2 nanocomposite surface.
The present study evaluated the main factors that influence the photocatalytic activity of titanium dioxide (TiO2) films grown by metalorganic chemical vapor deposition (MOCVD) at 400 and 500 °C, in ...different growth times. The photocatalytic behavior was analyzed by measuring the methyl orange dye degradation at different pH values. Structural and morphological characteristics, and the recyclability of the catalysts for several cycles were also investigated. Anatase phase was identified in all films. The higher photodegradation performances were obtained at acidic pH. The results demonstrated that the photocatalyst thickness is an important parameter in heterogenous photocatalysis. The best photocatalytic result occurred for the 395 nm-thick TiO2 film grown at 400 °C, which presented 65.3% of the dye degradation under UV light. The recyclability experiments demonstrated that the TiO2 films grown by MOCVD present a great stability after several photocatalytic cycles, which allows their practical application for water treatment with high efficiency.
ZnO nanomaterials are grown in-situ on graphene oxide (GO) materials by a facile hydrothermal method at a temperature of 100°C. These ZnO–graphene composite materials display a strong and broad ...absorption in the visible region besides an intense UV absorption peak. The enhanced fluorescent quenching observed for the graphene hybrids compared to ZnO, indicates the photoinduced electron transfer between ZnO and graphene layers, which in-turn reduces the recombination of charge carriers. In order to understand the mechanism of improved photocatalytic properties, reagents such as a radical scavenger t-BuOH and a hole scavenger EDTA-2Na were employed. The addition of t-BuOH did not show any appreciable changes in the photo-degradation properties of the ZnO–graphene hybrids. However, the addition of EDTA-2Na significantly reduced the photocatalytic activities of the ZnO–graphene hybrids indicated that photo-generated holes are the main reactive oxidative species responsible for the photocatalytic reaction. It has been concluded that the excellent absorption range, efficient charge transportation and separation and high surface area make the ZnO–graphene hybrids a better photocatalyst under UV and visible light.
PDF
