Photocatalytic degradation of 4-nitrophenol using TiO2 + Fe2O3 and TiO2/Fe2O3-supported bentonite as heterogeneous catalysts

Catalyst-On-Hotspot Nanoarchitecture: Plasmonic Focusing of Light onto Co-Photocatalyst for Efficient Light-To-Chemical Transformation

Plasmon-mediated catalysis utilizing hybrid photocatalytic ensembles promises effective light-to-chemical transformation, but current approaches suffer from weak electromagnetic field enhancements from polycrystalline and isotropic plasmonic nanoparticles as well as poor utilization of precious co-catalyst. Here, efficient plasmon-mediated catalysis is achieved by introducing a unique catalyst-on-hotspot nanoarchitecture obtained through the strategic positioning of co-photocatalyst onto plasmonic hotspots to concentrate light energy directly at the point-of-reaction. Using environmental remediation as a proof-of-concept application, the catalyst-on-hotspot design (edge-AgOcta@Cu2O) enhances photocatalytic advanced oxidation processes to achieve superior organic-pollutant degradation at ≈81% albeit having lesser Cu2O co-photocatalyst than the fully deposited design (full-AgOcta@Cu2O). Mass-normalized rate constants of edge-AgOcta@Cu2O reveal up to 20-fold and 3-fold more efficient utilization of Cu2O and Ag nanoparticles, respectively, compared to full-AgOcta@Cu2O and standalone catalysts. Moreover, this design also exhibits catalytic performance >4-fold better than emerging hybrid photocatalytic platforms. Mechanistic studies unveil that the light-concentrating effect facilitated by the dense electromagnetic hotspots is crucial to promote the generation and utilization of energetic photocarriers for enhanced catalysis. By enabling the plasmonic focusing of light onto co-photocatalyst at the single-particle level, the unprecedented design offers valuable insights in enhancing light-driven chemical reactions and realizing efficient energy/catalyst utilizations for diverse chemical, environmental, and energy applications.

Synthesis and Characterization of New Catalysts Grains Based on Iron(Oxy)Hydroxides supported on Zirconium for the Degradation of 4-Nitrophenol in Aqueous Solution

This study reports the preparation of catalyst grains based on oxyhydroxides of iron and zirconium via the coprecipitation method and their application in the degradation of 4-nitrophenol. The morphology, microstructure, and surface composition of these catalysts were characterized by scanning electron microscopy, X-ray diffraction, nitrogen physisorption, and Fourier transform infrared spectroscopy. The catalytic activity of the grains was assessed in the degradation of 4-nitrophenol in a heterogeneous system at different operating conditions. Degradation rates up to 93% were obtained after 4 h of contact time where the catalytic activity of tested materials was higher at pH 7 than in acidic and basic conditions. Amorphous iron hydroxide with a ratio of 75% Zr+25%Fe showed the best catalytic properties. These novel materials are an interesting alternative for facing the water pollution caused by organic compounds.

Facile synthesis of a novel BaSnO3/MXene nanocomposite by electrostatic self-assembly for efficient photodegradation of 4-nitrophenol

Photocatalysis is regarded as one of the most effective strategies for the removal of the toxic organic pollutants from aqueous solutions. However, a lack of the efficient photocatalysts prevents the widespread practical application. Herein, the electrostatic self-assembly method has been designed for facile synthesis of a novel BaSnO₃/PDDA/MXene (BSO/P/MX) nanocomposite as high efficient photocatalyst. In this nanocomposite, the BaSnO₃ (BSO), poly (dimethyl-diallylammonium chloride) (PDDA) and MXene (Ti₃C₂T_x) act as the active species, structure stabilizer and efficient electron transfer medium, respectively. Due to the strong synergy of the nanocomposite, the electron-transferring ability as well as the charge separation efficiency is boosted and thus high catalytic activity achieves towards the photodegradation of 4-nitrophenol. The superior degradation rate of 98.8% and a rate constant K of 0.09113 min^-1 have been realized within 75 min of ultraviolet (UV) light irradiation over the BSO/P/MX-8% catalyst. This as-prepared nanocomposite with the excellent catalytic activity can be employed as a promising photocatalyst for treating the organic pollutants from aqueous solutions.

Modification of a Brazilian natural clay and catalytic activity in heterogeneous photo-Fenton process

The catalytic activity of a Brazilian natural clay modified with the immobilization of iron oxide was applied in the heterogeneous Fenton process for the degradation of the antibiotic sulfathiazole (STZ). The clay without any treatment indicated a lamellar type material with mesoporous distribution that presents a heterogeneous mixture of phases (type 1:1 and 2:1 structures), with a predominance of quartz, montmorillonite, gibbsite and kaolinite, and with SiO₂, Al₂O₃, Fe₂O₃, K₂O, TiO₂, MgO as major oxides. Its high absorption in the UV-Vis ranges with a bandgap energy of 1.9 eV was attributed to the presence of hematite. It was observed that the effects of the addition of starch before heat treatment, and impregnation with iron, modified the clay surface. F rom the X-ray photoelectron spectroscopy analysis it was concluded that a structural reorganization is related to the conversion of the various iron oxide phases into hematite, as well as promoting an increase in Fe²⁺/ Fe³⁺ redox reactions allowing rapid degradation of STZ. The catalyst impregnated with iron and treated at 600 °C showed to be an economical and versatile catalyst with high catalytic efficiency (>97% STZ degradation after 60 min), with small differences according to the type of LED device used. Furthermore, it presented high stability and reusability reaching 93% degradation of STZ after four cycles of reuse with low consumption of H₂O₂.

Geochemical and Physicochemical Characteristics of Clay Materials from Congo with Photocatalytic Activity on 4-Nitrophenol in Aqueous Solutions

This study investigated the geochemical and physicochemical characteristics of natural clay collected in the Democratic Republic of Congo. The optical properties of the sample collected in Golf (GOL) were tested in the removal of 4-nitrophenol in aqueous solution. The geochemical analysis depicted that all the samples are plotted within the shale quadrant. Furthermore, the Chemical Index of Alteration (CIA) indicated that the samples are extremely weathered. The particle size distribution ranged from 0.41 to 418.6 μm, while the pore diameters for all the samples were under 100 Å. A flake-like surface morphology was observed in all the samples. SiO₂, Al₂O₃, Fe₂O₃, K₂O, and TiO₂ were the major chemical compounds found in all the samples, while the XRD analysis showed the presence of quartz, kaolinite, magnetite, and illite. The presence of metal oxides (i.e., TiO₂ and Fe₂O₃) indicated that these natural clays can be used for photocatalytic oxidation of pollutants. The sample collected in Katuba (KAT) displayed the higher reflectance percentages for the selected wavelengths except at 200 nm. Interestingly, the GOL sample exhibited lower energy band gaps (2.68 and 3.94 eV) necessary for photocatalysis. The untreated GOL clay sample removed 99.13% of 4-nitrophenol from aqueous solution through the photodegradation process. The usage of the untreated GOL clay could be a cost-effective solution in the removal of 4-nitrophenol in wastewater.

Palladium Nanoparticles on a Creatine-Modified Bentonite Support: An Efficient and Sustainable Catalyst for Nitroarene Reduction

Creatine as the nitrogen-rich, green and cheap compound is used for modification of natural bentonite and the resulting material is employed for the stabilization of Palladium nanoparticles having an average diameter of 3 nm. This new material bento-crt@Pd is characterized using different techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), solid state UV-vis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and energy-dispersive X-ray spectroscopy (EDX). This green catalyst promotes efficient reduction of aromatic nitro compounds in aqueous media. By using this catalyst nitroarenes having electron donating as well as electron withdrawing groups were reduced efficiently to their corresponding amines at room temperature. The catalyst can be recycled seven times and the reused catalyst was characterized by TEM and XPS.