Photochemical deposition of SnS2 on graphitic carbon nitride for photocatalytic aqueous Cr(VI) reduction

Synthesis and Characterization of Composite WO3 Fibers/g-C3N4 Photocatalysts for the Removal of the Insecticide Clothianidin in Aquatic Media

Photocatalysis is a prominent alternative wastewater treatment technique that has the potential to completely degrade pesticides as well as other persistent organic pollutants, leading to detoxification of wastewater and thus paving the way for its efficient reuse. In addition to the more conventional photocatalysts (e.g., TiO2, ZnO, etc.) that utilize only UV light for activation, the interest of the scientific community has recently focused on the development and application of visible light-activated photocatalysts like g-C3N4. However, some disadvantages of g-C3N4, such as the high recombination rate of photogenerated charges, limit its utility. In this light, the present study focuses on the synthesis of WO3 fibers/g-C3N4 Z-scheme heterojunctions to improve the efficiency of g-C3N4 towards the photocatalytic removal of the widely used insecticide clothianidin. The effect of two different g-C3N4 precursors (urea and thiourea) and of WO3 fiber content on the properties of the synthesized composite materials was also investigated. All aforementioned materials were characterized by a number of techniques (XRD, SEM-EDS, ATR-FTIR, Raman spectroscopy, DRS, etc.). According to the results, mixing 6.5% W/W WO3 fibers with either urea or thiourea derived g-C3N4 significantly increased the photocatalytic activity of the resulting composites compared to the precursor materials. In order to further elucidate the effect of the most efficient composite photocatalyst in the degradation of clothianidin, the generated transformation products were tentatively identified through UHPLC tandem high-resolution mass spectroscopy. Finally, the detoxification effect of the most efficient process was also assessed by combining the results of an in-vitro methodology and the predictions of two in-silico tools.

A novel tungsten diselenide nanoparticles for enhanced photocatalytic performance of Cr (VI) reduction and ciprofloxacin (CIP)

Nanoparticles (NPs) fabrication is a significant approach to enhance the visible light response of photocatalysts, to realize inexpensive and more harmful compound removal, at larger scale. The poor electrons and holes separation capability and low light activity of bulk materials can be notably enhanced through developing NPs. From photocatalytic investigation, better performance was received in the tungsten diselenide (WSe2) NPs than that in bare WSe2, exhibiting the action of restrained recombination of charge carriers in the NPs. The photocatalytic Cr(VI) reduction efficiency of WSe2 NPs is 2.7 folds greater than that by bare WSe2. On the other hand, the photocatalytic efficiency follows the order of nano WSe2-3 > nano WSe2-2 > nano WSe2-1 > bare WSe2, nano WSe2-3 is nearly 2.7 folds greater than that of bare WSe2. The results imply the fabrication of WSe2 NPs and it possesses improved visible light utilization. The proposed WSe2 NPs have merged with the three aspects of photocatalytic capability including the visible light activity, the valid separation of photo-response charge carriers and enough surface active sites owing to the nanoscale formed. This research endows conduct on the potential style of NPs for photo-response water environmental remediation.

Ni2P-Modified P-Doped Graphitic Carbon Nitride Hetero-Nanostructures for Efficient Photocatalytic Aqueous Cr(VI) Reduction

Targeting heterostructures with modulated electronic structures and efficient charge carrier separation and mobility is an effective strategy to improve photocatalytic performance. In this study, we report the synthesis of 2D/3D hybrid heterostructures comprising P-doped graphitic carbon nitride (g-C3N4) nanosheets (ca. 50–60 nm in lateral size) and small-sized Ni2P nanoparticles (ca. 10–12 nm in diameter) and demonstrate their prominent activity in the photocatalytic reduction of Cr(VI). Utilizing a combination of spectroscopic and electrochemical characterization techniques, we unveil the reasons behind the distinct photochemical performance of these materials. We show that Ni2P modification and P doping of the g-C3N4 effectively improve the charge-carrier transportation and spatial separation through the interface of Ni2P/P-doped g-C3N4 junctions. As a result, the catalyst containing 15 wt.% Ni2P exhibits superior photocatalytic activity in the detoxification of Cr(VI)-contaminated effluents under UV-visible light illumination, presenting an apparent quantum yield (QY) of 12.5% at 410 nm, notably without the use of sacrificial additives. This study marks a forward step in understanding and fabricating cost-effective photocatalysts for photochemical applications.

Synthesis of ZnO immobilized on recycled polyethylene terephtalate for sonocatalytic removal of Cr(VI) from synthetic, drinking waters and electroplating wastewater

In this study, Cr(VI) was removed sonocatalytically by the zinc oxide nanoparticle coated with polyethylene terephthalate (PET) fabricated through a facile co-precipitation method. The crystal structure, functional groups on the surface, morphology, surface composition and oxidation states of the nanomaterials were investigated by XRD, FTIR, SEM, EDX and XPS techniques. Environmental parameters including solution pH, catalyst dose, hexavalent chromium concentration, H₂O₂ content, purging gases, organic compounds and type and anions strength on the sonotocatalytic removal of Cr(VI) were also investigated. Additionally, the contribution of each process, reusability, Cr(VI) reduction from actual water and electroplating wastewater were evaluated. Under the optimal conditions, [Cr(VI)]₀=20 mg/L, nanocomposite loading=1.6 g/L and pH=5, 99.92% of Cr(VI) was removed within 60 min. By increaing, Cr(VI) concentration (5-50 mg/L), k_obs decreased to values between 0.1498 and 0.0063 min^-1 and the calculated electrical energy per order (E_Eo) increased from 148.68 to 3535.24 kWh.m^-3, respectively. The presence of purging gases, organic compounds and ionic strength negatively affected Cr(VI) reduction. Examination of radical scavengers showed that the most active radicals in Cr(VI) removal were O₂^•- and h⁺. The removal of the Cr(VI) using the US/ZnO-PET method (99.92%) was higher than that of the US/ZnO method (70.78%). The catalyst activity was well maintained up to eight consecutive cycles. In addition, the removal efficiency was approximately 72.23 and 68.55% for drinking water and real electroplating wastewater samples, respectively. The results of toxicity in the sonotocatalytic removal of Cr(VI) by Daphnia magna showed LC₅₀ and toxicity unit (TU) 48 h, which was equal to 81.46 and 1.227 vol percent.

Comparison of Cr(VI) adsorption and photocatalytic reduction efficiency using leonardite powder

It is very important to treat Cr(VI) from the aquatic environment due to its toxic and harmful effects. Conventional treatment methodology involving biological pathways is generally ineffective for wastewater containing Cr(VI). Therefore, it is necessary to develop environmentally friendly and economical methods to remove Cr(VI) from the aquatic environment. In this study, leonardite, which is a natural mineral that has no harmful effects on the environment, was used for Cr(VI) removal. Leonardite was used in both adsorption and photocatalytic treatment systems by only pulverizing without any chemical treatment. Characterizations of leonardite were obtained using X-ray fluorescence (XRF), fouirer transform infrared spektrofotometre (FTIR), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) analyses methods. The effects of solution pH (2-10), particle size (45-300 μm), adsorbent dose (0.25-3 g/L), and initial concentration (10-30 mg/L) on Cr(VI) removal efficiency were investigated in both adsorption and photocatalytic experiments. In the adsorption process, a complete removal efficiency (100%) was obtained for 3 g/L of adsorbent dose with an initial Cr(VI) concentration of 10 mg/L at pH 2 for 2 h. In the photocatalytic process, 100% removal efficiency of Cr(VI) was obtained when four times less adsorbent dosage was used under the same conditions. In addition, the reuse of leonardite powder was also investigated under optimum experimental conditions. Leonardite powder preserved approximately 70% of its activity in the photocatalytic process while it lost 50% of its activity after 5 reuses in adsorption process.