Currently, owing to the valorization of carbon dioxide through CCU (carbon capture and utilization) processes, it is possible to mitigate the impact of greenhouse gases and decrease the use of fossil fuels by reducing the amount of CO₂ through the use of solar fuels . In this work, the valorisation of CO₂ into CO and CH₄ was investigated using a hybrid catalytic approach as the photothermocatalysis and unconventional photocatalysts, i.e., modified commercial phyllosilicates, which was achieved using the montmorillonite K30. The modification of K30 with Ni and Ce was carried out using the hydrothermal method. The coatings with Mn and Cu oxides were created by means of the precipitation method. The catalytic tests were conducted in a cylindrical batch reactor at 120°C using a solar lamp for 5h of irradiation. The analysis of the reaction products was performed with GC-TCD/FID, and the samples were characterized by means of SEM, FT-IR, UV-DRS, Raman, CO₂-TPD, and N₂- physisorption. The best performance was obtained by K30-Ni/Ce@MnCuO_x, with 76.7% of the CO₂ being converted and 13.9 and 4.9 mmol/gcat•h CO and CH₄, respectively. With this latter sample, we also conducted stability tests using a treatment in a H₂ flow for the reactivation of the sample. The coating using noncritical mixed metal oxides improved the performance of the bare K30 and K30 that was modified with Ni and Ce. The photothermocatalysis also represents a greener strategy for mitigating the impact of CO₂. The performance of this catalyst was also compared to “artificial clays”, such as MXenes. These compounds were modified with the addition of CeO₂, TiO₂, and SiO₂ to further improve their photothermocatalytic activity due to their photothermal properties.

Acknowledgements: SAMOTHRACE CUP-E63C22000900006. R.F. thanks the CO2@photothermocat project PRIN 2022 PNRR CUP E53D23015700001

The large amount of interest in methanol as a pioneering hydrogen source for fuel cell applications is related to its high energy density, easy storage/transportation and environmental safeguarding compared to conventional fuels. In fact, CH3OH production from biomass and other renewable feedstocks benefits sustainable technologies available for its conversion to hydrogen¹. Methanol and steam, at moderate temperatures and under the assistance of a catalyst, can generate H₂ and CO₂. In particular, to enhance hydrogen selectivity and reduce CO formation, the identification of highly active, selective and stable catalysts is crucial. Sintering is one of the main drawbacks of Cu-based catalysts commonly selected for methanol steam reforming, and the addition of CeO₂ is expected to improve active-phase dispersion as well as metal–support interactions².

In this work, a series of non-noble (Ni, Cu and Zn) metal-based bimetallic and trimetallic catalysts were prepared by the sequential wet impregnation of the active species on the CeO₂-Al₂O₃ support (30 wt% of ceria) and tested for methanol steam reforming (MSR). After the catalysts' reduction in situ (at 800°C; heating rate of 10°C·min^-1), MSR was performed under a 10%CH₃OH-15%H₂O-75%Ar stream at atmospheric pressure from 600 to 200°C; the Weight Hourly Space Velocity was fixed at 2 h^-1. For the non-noble metal-based catalysts, methanol was completely converted up to 300°C. Moreover, the trimetallic Zn-Ni-Cu sample showed a methanol conversion rate of around 40% at 200°C. However, at low temperatures, CO formation became stable. The lowest carbon monoxide selectivity was recorded for the 20 wt%Cu/CeO₂-Al₂O₃ catalyst.

This study explores the catalytic oxidation of phenol using an iron-supported natural illite clay catalyst, focusing on optimizing operational parameters to enhance degradation efficiency while minimizing environmental impact. The effects of pH, temperature, catalyst dosage, initial phenol concentration, and H₂O₂ concentration were systematically examined. Optimal conditions were found at pH 3 and 50°C, which promoted hydroxyl radical formation and improved reaction kinetics. Under these conditions, the catalyst achieved a 99% phenol degradation rate and an 83% reduction in chemical oxygen demand (COD), with no detectable metal leaching, ensuring catalyst stability. The catalyst's characterization was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), BET surface area analysis, and laser granulometry, confirming its structural integrity and stability. Additionally, the H₂O₂ concentration was optimized at 8.7 mM to enhance the oxidation process while minimizing reagent excess. An analysis of intermediate by-products revealed stepwise degradation, highlighting efficient oxidation pathways. Environmental impact assessments demonstrated that the catalyst, with its low metal leaching and high stability, had minimal toxicity to aquatic life, particularly fish, confirming its safe use in wastewater treatment applications. This study underscores the potential of iron-impregnated natural clays as stable, non-leaching, cost-effective catalysts for the treatment of phenolic pollutants, with reduced environmental risks.

Pristine Bi₂WO₆ and different concentrations of aluminum-doped Bi₂WO₆ nanoparticles were synthesized using a simple hydrothermal method for a comparative study of the decolorization of aqueous organic pollutants. The synthesized nanoparticles were characterized using X-ray diffraction (XRD), UV–visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Brunauer–Emmett–Teller (BET), Zeta potential, field-emission scanning electron microscopy (FE-SEM), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS). The XRD pattern revealed the formation of an orthorhombic structure for pure and Al-doped Bi₂WO₆. Aluminum doping decreased the crystallite size. The formation of 3D flower-like nanostructures that were composed of 2D nanosheets was observed through FE-SEM. The band gap increased because of the doping aluminum, which revealed the blue shift of the band gap. We performed both photocatalytic and adsorption experiments for 20 ppm aqueous Methylene Blue (MB) and Rhodamine B (RhB) for all synthesized catalysts. The aluminum-doped Bi₂WO₆ catalysts showed enhanced decolorizing efficiency, and 0.15Al-Bi₂WO₆ exhibited the best performance for adsorption. The results were analyzed using various models such as second-order kinetics, the BMG model, and the intraparticle Weber and Morris diffusion model. We found taht 97.02% and 95.61% of MB and RhB dye solutions decolorized in 20 and 30 min using 0.15Al-Bi₂WO₆, with second-order rate constants of 0.566 Lmg^-1min^-1 and 0.225Lmg^-1min^-1, respectively.

The photocatalytic reduction of hexavalent chromium (Cr(VI)) is an advanced method for remediating toxic chromium pollution in water. Cr(VI) is highly poisonous, carcinogenic, and water-soluble, making it a significant environmental and health concern. Photocatalysis offers a sustainable approach to reducing Cr(VI) to its less toxic and insoluble trivalent state (Cr(III)) using light energy and a photocatalyst. Titanium dioxide (TiO₂) is one of the most widely used photocatalysts due to its high catalytic efficiency, non-toxicity, chemical stability, resistance to photo corrosion, abundance, and cost-effectiveness properties. However, due to its wide bandgap (~3.2 eV), it can adequately work under UV light only and exhibit relatively less quantum efficiency. To overcome these limitations, black TiO₂ (BT) with oxygen vacancies, Ti³⁺ sites, enlarged surface area, and active sites may be considered as potential alternatives. Herein, BT was synthesized via chemical reduction using NaBH₄ as a reducing agent. In total, 40 mg photocatalytic efficiently reduced 60 ppm of Cr(VI) within 60 min of visible light (450 nm ) illumination at room temperature using EDTA-2Na (500 ppm) as a hole scavenger. The 1,5-Diphenylcarbazide (DPC) colorimetric method was utilized to detect the reduction of Cr(VI) to Cr(III). From UV-vis DRS spectra, a clear red shift was observed for BT compared to TiO₂, suggesting the improved light absorption capability and Tauc plot disclosed reduced energy bandgap (~1.5–2.5 eV), which further accelerated the transition of photo-generated electrons from the valance band to the conduction band.

Background: Acacia arabica tree is a moderate-sized, short-trunked, and almost evergreen tree mostly found in drier areas. The aqueous stem bark extract of this plant contains phenolic, condensed tannin which acts as a reducing and capping agent in green synthesized ZnO NPs, making it the least toxic semiconductor photocatalyst for the treatments of wastewater containing dye effluents, with moderate bandgap energy.

Methodology: At the initial stage, a 40 mL aqueous leaf extract of Acacia arabica wascombined with 460 mL of 4.36M (CH₃COO)₂Zn.2H₂O and heated at 60°C while stirring, after which the obtained precipitate was filtered. Next, 30 mL of NH₄OH solution was added dropwise to 500 mL of the filtrate obtained from the initial reaction stage with constant stirring for 20 minutes at room temperature, and then stirred at 60°C for 4 h. The resulting chemo-green ZnO NPs were filtered and washed with ethyl alcohol, followed by calcination at 450⁰C for 2.5 h, then again washed with ethyl alcohol and dried in an oven at 100⁰C. XRD, zeta potential, and FTIR and DRS, measurements were carried out to examine the crystallinity, surface charge, and optical properties of chemo-green synthesized ZnO NPs. For photocatalytic testing, a 10 mg/L aqueous solution of malachite green dyes and 1 g/L ZnO NPs was stirred in the dark, followed by irradiation in sunlight.

Results and Discussion: Here, chemo-green synthesized ZnO NPs have direct band gap energies equivalent to ZnO NPs from the chemical and green method; they had negatively charged surfaces and good dye degradation in 160 minutes, which suggests the reutilization of unused filtrate obtained from the green method for further high-yield synthesis of ZnO NPs with scant use of ammonium hydroxide, stimulating sustainability and lightening the economic burden; they can be used for the demineralization of dyes coming from wastewater from the textile industry.

In recent decades, the release of drugs into aquatic ecosystems has heightened human apprehension. The literature includes multiple studies that have recorded Ciprofloxacin (CIP) levels in diverse sources, such as wastewater treatment facilities, untreated drinking water, hospital effluent, lakes, and discharge from pharmaceutical manufacturers. This literature review indicates that semiconductor-based AOPs can be used to effectively remove pharmaceuticals from wastewater. In order to facilitate the water splitting reaction, it is necessary to use catalysts that are highly active, stable, low-cost, and abundant.

The synthesis of molybdenum diselenide and the doping of zinc metal (X= weight percentages, 2.5%,5%, 7.5%,10%) into it have been conducted in this study. Using techniques such as FESEM, EDX, XRD, Raman, FTIR, and XPS, extensive investigations have been conducted which indicate the catalyst's efficient production. FESEM confirms the nanoflower structure with a size range of 30-50 nm. UV-VIS DRS analysis has been carried out to assess the synthesized sample's optical characteristics; it also helps to identify the band gap that promotes effective visible light absorption. The semiconductor type, charge transfer kinetics, and charge separation and transfer inside the on and off zones have been investigated using the Mott--Schottky plot, an Electrochemical Impedance Spectroscopy (EIS) study, and photocurrent investigation, respectively. An appropriate photochemical reactor was used to break down ciprofloxacin (CIP), and the reaction rate constant was measured. Under optimal conditions, the residual concentration of the antibiotic decreased to a point where it was no longer detectable after 45 minutes.

Further, the 5% doping of Zinc metal over molybdenum diselenide allowed for maximum photocatalytic efficiency due to the Se vacancy creation in the MoSe₂ structure under visible light illumination. Also, Zinc doping reduces the residence time to achieve faster reaction rates.

Introduction: Nanopowders with different compositions, purities, sizes, and dimensional distributions can be created using the sol--gel method [1,2]. The metal precursors were added either during synthesis (in a single step) or by post-synthesis impregnation to the sol--gel method used for obtaining the powder photocatalysts.

Methods: The materials used include ethanol, TiO₂, and Pt/TiO₂ powders (obtained by the sol--gel method). Characterization methods such as thermal analysis (DTA), infrared spectroscopy (IR), X-ray diffraction (XRD), and X-ray fluorescence (XRF), and the determination of the specific BET surface area and pore distribution, are complementary and necessary.

Results: As a result of the post-synthesis heat treatment, oxide compounds were obtained in the form of white (TiO₂) and gray (Pt-modified TiO₂) crystallized powder. The photocatalytic activity of titanium dioxide synthesized by the sol--gel route was compared to that of pristine and platinum doped photocatalysts, both during synthesis and by post-synthesis impregnation. As a result of the post-synthesis heat treatment, oxide compounds were obtained in the form of white (TiO₂) and gray (Pt-modified TiO₂) crystallized powder. The photocatalytic activity of titanium dioxide synthesized by the sol-gel route was compared to that of pristine and platinum-doped photocatalysts, both during synthesis and by post-synthesis impregnation. The samples were tested as photocatalysts in the oxidative degradation of ethanol in the gaseous phase and under solar simulated light irradiation. The folliwing is an increasing order of powder reactivity in the photocatalytic tests: TiO₂, TiO₂-Pt in-situ, and TiO₂-Pt by post-synthesis impregnation (with the highest conversion being 72,24%).

Conclusions: The topic of this paper focuses on the development of the photocatalytic activity of simple and noble metal-modified TiO₂ used for the degradation of contaminants in the gas phase and ambient conditions.

References:

• Sakka, Sol-gel process and applications, Handbook of Advances Ceramics, Elsevier, 883–910 (2013).
• Savolainen et all, Nanotechnologies, engineered nanomaterials and occupational health and safety, Safety Science, 48 (8), 957–963 (2010).

The degradation of organic pollutants using photocatalysis is a more environmentally friendly method because it uses solar energy. Covalent organic frameworks (COFs) are photocatalysts that are composed of covalent bonds of light elements and do not contain harmful metals. COFs have been studied in various fields, but their use in removing organic pollutants has not been fully investigated. In this study, the photocatalyst TpPa-COF-Cl₂ was made into a membrane and its activity against dyes was examined. TpPa-COF-Cl₂ slightly decolorized methyl orange.

-Synthesis of catalyst

①Mesitylene (4.5 mL), 1,4-dioxane (4.5 mL), acetic acid (3M, 1.5 mL), 1,3,5-triformylphloroglucinol (Tp), and 2,5-dichloro-p-phenylenediamine (Pa) (molar ratio Tp:Pa=1:1.5) were added, heated, and stirred to obtain TpPa-COF-Cl₂ powder.

②A mixture of 20 mg of TpPa-COF-Cl₂ powder, sodium alginate, and 1.7 mL of water was heated and stirred, spread on a glass plate, and immersed in a CaCl₂ solution (3 wt%) for 24 hours to synthesize 5 to 6 TpPa-COF-Cl₂ films.

-Dye degradation

One membrane was placed in 5 ppm methyl orange (MO) and left in the dark for 30 minutes to reach adsorption equilibrium, after which it was irradiated with a 450 nm LED lamp for 60 minutes and its absorbance was measured every 10 minutes.

-Result, Conclusion

SEM and TEM revealed that the powdered TpPa-COF-Cl₂ had a layered structure. In addition, an absorption edge at 600 nm was confirmed by DRS.

The TpPa-COF-Cl₂ membrane formed by the cross-linking reaction of alginic acid and calcium ions maintained its structure even after the photocatalytic reaction. The TpPa-COF-Cl₂ membrane decolorized approximately 5% of MO. Although the decolorization efficiency was inferior to that of the powder form, it was easier to remove the catalyst.

In recent years, there has been a consensus in the scientific community to seek more sustainable technologies that minimize environmental impact while providing social benefits. Among the most common pollutants being addressed in natural and wastewater, dyes stand out as a significant concern. Advanced Oxidative Processes (APOs) stand out as one of the most widely used methodologies for environmental remediation. These methods employ catalysts to generate reactive oxidative species, such as hydrogen peroxide (H₂O₂), which produces hydroxyl radicals and water as products after a catalytic reaction [1]. However, controlling the amount of peroxide involved in the reaction, as well as the excess released into the environment, is essential. Thus, photocatalysis has emerged as a more efficient strategy and as an alternative to commonly used AOPs. This approach requires only a semiconductor material and sunlight as an energy source to drive the reduction reactions. Among semiconductor materials, Quantum Dots (QDs) are particularly notable due their unique optical properties, which arise from quantum confinement, as well as their low production costs. Additionally, these nanocrystals can catalyze the decomposition of H₂O₂, leading to the generation of anionic radicals [2]. In this study, copper-based QDs were prepared by colloidal synthesis in an aqueous medium. A 10 ppm solution of methyl orange (MO) dye was brought into contact with the QD suspension, both in the presence and absence of H₂O₂, and exposed to a full-spectrum solar lamp, simulating sunlight. The photodegradation process of the dye was characterized using UV/Vis spectroscopy. The preliminary results showed a significant decrease in MO concentration in the presence of QDs and light irradiation. These results represent a promising advancement in photodegradation technology while reinforcing a commitment to environmental sustainability.

[1] Bi, W. et al. 2024. 10.17159/wsa/2024.v50.i2.4078.

[2] Shen, H. et al. 2022. 10.3390/nano12183130.