Search Results (80)

This research focuses on the synthesis, characterization, and photocatalytic performance of Cu-based polyoxometalate (Cu-POM) as an effective catalyst for the degradation of organic dyes, specifically Congo Red (CR) and Phenol Red (PR). The main goals are to synthesize Cu-POM using a controlled self-assembly technique, characterize its optical and structural characteristics using FTIR, XRD, SEM, TGA, and UV-Vis spectroscopy, and estimate its photocatalytic activity when exposed to UV light. The outcomes confirm the successful formation of Cu-POM with well-defined nanostructures and a crystalline polyoxometalate framework. The determined optical bandgap of 3.65 eV indicates its strong UV-light responsiveness. The photocatalytic degradation experiments demonstrated high removal efficiencies of 58.1% for CR and 64.6% for PR under UV irradiation, corresponding kinetic rate constants of 0.00484 min⁻¹ and 0.00579 min⁻¹, respectively. The superior photocatalytic activity is attributed to the efficient charge carrier separation and high surface area of Cu-POM. These findings highlight the potential of Cu-POM as a promising heterogeneous photocatalyst for sustainable wastewater treatment and environmental remediation. Full article

Water pollution by persistent organic and inorganic contaminants constitutes a significant problem for ecosystems and public health. Organic substances such as dyes, pharmaceutical residues, pesticides, and phenolic compounds are increasingly detected in water due to industrial and agricultural activities. Alongside these, toxic heavy metals contribute to the complexity of water treatment challenges. Conventional remediation methods often fall short due to high operational costs or limited efficiency. In this context, photocatalysis has emerged as a promising approach for pollutant degradation in water under light irradiation. In this sense, covalent organic frameworks (COFs), a class of porous, crystalline materials formed by the covalent linkage of organic units, offer great advantages as photocatalysts. Their tunable electronic properties, structural diversity, and high stability under aqueous conditions make them ideal for visible light-driven processes. This review explores the structural features that govern the photocatalytic activity of COFs, including conjugation, bandgap modulation, and donor–acceptor structures. Mechanistic insights into photocatalytic degradation are also discussed. Finally, examples of pre-designed COFs are presented with their application in the photodegradation of water pollutants, and their main reactive oxygen species (ROS) involved in the photodegradation mechanism. Overall, this review aims to provide a foundation for the rational design of COFs in advanced water treatment technologies. Full article

Ferrous oxalate dihydrate (α-FOD) was synthesized from Ecuadorian black sands for phenol removal from aqueous solutions. Visible light-driven photodegradation kinetics were studied by varying the initial pollutant concentration, solution pH, and α-FOD dosage and by adding peroxydisulfate (PDS), including quenching tests. A representative model of phenol photodegradation was obtained by the Langmuir–Hinshelwood mechanism over a large range of concentrations (apparent kinetic constant, k = 0.524 h⁻¹). Almost complete removal was reached within 1 h under dark + 9 h under visible irradiation. The degradation rate was slightly affected by pH in the range of 3 to 9, with a significant improvement at pH 11 (k = 1.41-fold higher). The optimal α-FOD dosage was ~0.5 g/L. Two regimes were observed when using PDS: first, a heterogeneous Fenton-like process during the first few minutes after PDS addition; second, pure photocatalysis to completely remove the phenol. When comparing the two systems, without and with PDS, the half-life time for pure photocatalysis was 2.5 h (after the lamp was switched on). When adding PDS (1.0 mM), the half-life time was reduced to a few minutes (5 min after PDS addition, phenol removal was 66%). The photocatalyst presented remarkable degradation efficiency up to five repeated cycles. Full article

WO₃ nanoflowers were synthesized via anodization and subsequently calcined in air at different temperatures (200–700 °C) to evaluate their photocatalytic activity. The samples were characterized in terms of their morphological, crystallite, and optical properties. Anodization produced WO₃ hydrate with a layer thickness of ~1.2 µm, which was transformed into WO₃ after heating. All samples exhibited monoclinic phase, with Raman shift intensity increasing with the calcination temperature. Some residual WO₃·H₂O was detected at certain temperatures. The calculated bandgap energy ranged from 2.49 to 2.67 eV, with higher calcination temperatures leading to lower absorbance in the UV region. The photodegradation of phenol under UV-Vis radiation reached 35% in 60 min for WO₃_700 °C, where the photocatalyst suffered a morphological transformation from a nanoflower to nanogranular structure, accompanied by increased crystallinity. Under visible light, the phenol abatement was limited, achieving 1–3% degradation. The WO₃ surface is likely negatively charged at the solution’s pH (5.6), which may explain the low phenol adsorption (~1%). Full article

Water pollution, resulting from industrial effluents, agricultural runoff, and pharmaceutical residues, poses serious threats to ecosystems and human health, highlighting the need for innovative approaches to effective remediation, particularly for non-biodegradable emerging pollutants. This research work explores the influence of shape-controlled nanocrystalline titanium dioxide (TiO₂ NC), synthesized by a simple hydrothermal method, on the photodegradation efficiency of three different classes of emerging environmental pollutants: phenol, pesticides (methomyl), and drugs (sodium diclofenac). Experiments were conducted to assess the influence of the water matrix on treatment efficiency by using ultrapure water and stormwater (basic) collected from an urban drainage system as matrices. The size and shape of the nano-cuboids were accurately controlled during synthesis to assess their impact on photoactivity and selectivity. Regarding total organic carbon removal using TiO₂ nano-cuboids in basic environments, the results were particularly remarkable. TiO₂ nano-cuboids and truncated bipyramids synthesized in the 200–250 °C temperature range showed an enhanced photocatalytic efficiency when compared to alternative formulations. Diclofenac, methomyl, and phenol were fully mineralized from ultrapure water and basic stormwater. The TiO₂ nano-cuboids/nano-bipyramids demonstrated better selectivity and photoactivity in comparison to irregular TiO₂ nanoparticles. The differences in photoactivity and selectivity are explained in terms of charge carrier separation and trapping on the different crystal facets. Their performance demonstrates their potential as sustainable materials for the photodegradation of emerging pollutants in various water matrices. Full article

Accelerated photooxidation of salicylic acid (SA) was performed using UV radiation and hydrogen peroxide. HPLC-MS analysis showed that the primary intermediates are 2,5-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid, pyrocatechol, and phenol. Deeper oxidation leads to low molecular weight aliphatic acids, such as maleic, fumaric, and glyoxylic. The photooxidation of the main intermediates was carried out in the same conditions. The degradation of SA and its main intermediates follows first-order reaction kinetics. In the case of UV irradiation alone, photodegradation of 2,5-dihydroxybenzoic acid is slightly faster (reaction rate constant is 0.007 min⁻¹) compared to SA (0.0052 min⁻¹). Other products degrade more slowly than SA. Hydrogen peroxide, in concentrations of 1.8–8.8 mM, accelerates the photodegradation of salicylic acid and intermediate products. An ecotoxicological evaluation of SA and the main products was performed using the EPI Suite^TM software. The overall persistence (P_OV) and long-range transport potential (LRTP) of all transformation products were assessed using OECD P_OV and the LRTP screening tool. Salicylic acid and its transformation products have low toxicity. Due to their high solubility, these contaminants can travel considerable distances in the aquatic environment. SA and phenol have LRTP values of 156–190 km. Other products can travel shorter distances (less than 100 km). Full article

The concept of using polyaniline/titanium dioxide heterostructures as efficient photocatalysts is based on the synergistic effect of conducting polymer and metal oxide semiconductors. Due to inconclusive literature reports, the effect of different polyaniline/TiO₂ ratios on photocatalytic activity under UV and visible light was investigated. In most papers, non-recommended dyes are used as model compounds to evaluate visible light activity. Therefore, colorless phenol was used instead of dyes in this study to clarify the real visible light-induced photocatalytic activity of polyaniline/TiO₂ composites. This publication also includes a discussion of whether materials derived from bulk (non-nanostructured) polyaniline and TiO₂ by the standard in situ oxidative polymerization method are suitable candidates for promising photocatalytic materials. The evaluation of photocatalytic activity was performed in both UV and visible light systems. X-ray diffraction and UV-Vis diffuse reflectance spectroscopy methods were applied to characterize the obtained samples. Obtained polyaniline (pure and in composites) was identified as emeraldine salt. In the UV system, none of the prepared samples with different polyaniline–titania ratios had activity better than reference P25 titania. It has been observed that the presence of polyaniline adversely affects the photocatalytic properties, as the polyaniline layer covering the titania surface can shield the UV light transmission by blocking the contact between the TiO₂ surface and organic molecules. In the case of using visible light, no synergies have been observed between polyaniline and titania either. The photodegradation efficiencies of the most active samples were similar to those of pure polyaniline. In conclusion, in order to obtain efficient polyaniline/titania photocatalysts active in UV and/or visible light, it is necessary to take into account the morphological and surface properties of both components. Full article

Bimetallic (Ta/Ti, V, Co, Nb) mesoporous MCM-41 nanoparticles were obtained by direct synthesis and hydrothermal treatment. The obtained mesoporous materials were characterized by XRD, XRF, N₂ adsorption/desorption, SEM, TEM, XPS, Raman, UV-Vis, and PL spectroscopy. A more significant effect was observed on the mesoporous structure, typically for MCM-41, and on optic properties if the second metal (Ti, Co) did not belong to the same Vb group with Ta as V and Nb. The XPS showed for the TaTi-MCM-41 sample that framework titanium is the major component. The new nanoparticles obtained were used as catalysts for oxidation with hydrogen peroxide of olefinic compounds (1,4 cyclohexadiene, cyclohexene, styrene) and photodegradation of organic pollutants (phenol, methyl orange) from water. The results showed improvementsin activity and selectivity in oxidation reactions by the addition of the second metal to the Ta-MCM-41 catalyst. The slow addition of H₂O₂ was also beneficial for the selectivity of epoxide products and the stability of the catalysts. The band gap energy values decreased in the presence of the second metal, and the band edge diagram evidenced positive potential for all the conduction bands of the bimetallic samples. The highestlevels of photocatalytic degradation were obtained for the samples with TaTi and TaV. Full article

Coffea arabica, Centella asiatica, and Curcuma longa extracts have demonstrated significant antioxidant and anti-aging activities. However, research on combining these three extracts in specific proportions to enhance their antioxidant and anti-hyaluronidase effects remains limited. Therefore, this study aimed to determine the optimal proportions of C. arabica, C. asiatica, and C. longa extracts to maximize their combined antioxidant and anti-hyaluronidase activities. A two-level full factorial design was used to identify the optimal concentration ratios of the mixed extracts. The results indicated that all extracts influenced antioxidant activity, with the optimal proportions of C. arabica, C. asiatica, and C. longa extracts being 0.5:6:2 mg/mL, respectively. In addition, all factors affected hyaluronidase enzyme inhibition, with the optimal proportions for C. arabica, C. asiatica, and C. longa extracts being 10:10:5 mg/mL to achieve the best inhibition. In a photostability study on individual extracts, mixed extracts, and mixed extracts combined with sodium metabisulfite and bis-ethylhexyloxyphenol methoxyphenyl triazine, it was observed that preparing the mixed extracts and adding an antioxidant and a sunscreen agent helped reduce the photodegradation of phenolic compounds in the mixed extracts. Consequently, the stabilized mixed extracts could serve as raw materials in cosmetic products. Full article

Ilex paraguariensis (IP) extract was added to prepare edible films using a central rotational composite design (CCRD) 2² with IP extract and sorbitol concentrations as variables. The IP extract was characterized by color parameters, total phenolic content, caffeine, flavonoids, and chlorophyll content, and antioxidant activity and the edible films were assessed for the same analysis and thickness, water vapor permeability (WVP), solubility in water, fluorescence, photodegradation and UV/Vis light barrier, FT-IR, thermogravimetry, and differential exploratory colorimetry. Sorbitol increased thickness and WVP, while the extract influenced the concentration of phenolic compounds in the films. The optimum concentrations of extract and sorbitol were 10% and 15%, respectively. Films presented thermal resistance (until 230 °C) and an excellent barrier to UV light. Furthermore, these films could carry compounds originally in IP, showing good functional properties concerning the water vapor barrier (showing a great variation scale due to the possibility to increase sorbitol or not, between 3.33 and 5.27 g mm/m² day KPa). The films showed great potential to replace conventional primary packaging, and if consumed with food, as a bullet paper, they can add nutritional value to the packaged product. Full article

Extractives, which naturally evolve as fundamental defense mechanisms in wood against environmental stresses, hold an essential place in the field of wood conservation science. Despite their low content in woody substrates, extractives are chemically complex and can be extracted accurately by solvents with different polarities, covering key components such as aliphatic, terpenoid, and phenolic compounds. The application of solvent extraction allows for the effective recovery of these extracts from forestry waste, thereby creating new opportunities for their reuse in wood modification and enhancing the economic value and potential applications of forestry waste. In the wood industry, extractives not only act as efficient preservatives and photo-stabilizers, significantly improving the decay resistance and photodegradation resistance of wood, but also serve as ideal dyes for fast-growing wood due to their abundant natural colors, which lend the product a distinct aesthetic appeal. The aim of this paper is to provide a comprehensive review of the origin and distribution characteristics of wood extractives and to examine the impact of solvent selection on extraction efficiency. At the same time, the mechanism of extractives in enhancing wood decay resistance and slowing down photodegradation is deeply analyzed. In addition, specific examples are presented to illustrate their wide utilization in the wood industry. This is intended to provide references for research and practice in related fields. Full article

The highly crystalline ZnAl layered double hydroxides (ZnAl-NO₃-LDHs) are utilized for the potential transformation into mixed metal oxides (MMOs) through thermal decomposition and used further for the photodegradation of phenol to assess the influence of calcination on ZnAl-LDHs with enhanced photoactivity. The structure, composition, and morphological evolution of ZnAl-LDHs to ZnO-based MMO nanocomposites, which are composed of ZnO and ZnAl₂O₄, after calcination at different temperatures (400–600 °C), are all thoroughly examined in this work. The final ZnO and ZnAl₂O₄-based nanocomposites showed enhanced photocatalytic activity. The findings demonstrated that calcining ZnAl-LDHs from 400 to 600 °C increased the specific surface area and also enhanced the interlayer spacing of d₀₀₃ while the transformation of LDHs into ZnO/ZnAl₂O₄ nanocomposites through calcining the ZnAl-LDH precursor at 600 °C showed significant photocatalytic properties, leading to complete mineralization of phenol under UV irradiation. Full article

Birch sap consists of a natural water-based solution with valuable compounds such as minerals, sugars, organic acids and phenolic compounds that can be used advantageously in the preparation of edible films. In this study, gelatine- and casein-based films were prepared using birch sap as biopolymer solvent and source of bioactive compounds with the aim of developing new bioactive materials for food packaging. The physical, mechanical, barrier, antioxidant and iron-chelating properties of the obtained films were investigated. Birch sap enhanced the mechanical properties of the films by increasing puncture strength and flexibility, as well as their ultraviolet–visible light barrier properties. In addition, the presence of bioactive compounds endowed the birch sap films with an antioxidant capacity of almost 90% and an iron-chelating capacity of 40–50% with respect to the control films. Finally, to test these films as food packaging material, a photosensitive curcumin solution was packed and exposed to ultraviolet light. Tested films were able to protect curcumin against photodegradation, and the presence of bioactive compounds inside the birch-sap-enriched materials offered an additional 10% photoprotective effect compared to control films. Results showed the potential of birch sap as an environmentally friendly biopolymer solvent and plasticizer that can improve the mechanical and photoprotective properties of the prepared materials. Full article

Palladium@mesoporous titania core@shell nanoparticles with uniform and narrow particle size distribution were synthesised using a four component ‘‘water in oil’’ microemulsion system. The prepared materials were well characterised using N₂ adsorption–desorption measurements, temperature program oxidation, X-ray diffraction, ICP-OES, DRS UV-Vis, PL, TGA and transmission electron microscopy techniques. The core@shell nanoparticles showed very good absorption in both the UV and visible regions and a low bandgap, indicating that the prepared materials are visible-light-active, unlike the pristine TiO₂ P25. The activity of the prepared materials was evaluated in the photodegradation of phenol using both UV and visible light, in batch and continuous flow trickle-bed and Taylor flow photoreactors. The prepared 2%Pd@mTiO₂ core@shell nanoparticles showed better photocatalytic performance for phenol degradation in visible light in comparison to pristine TiO₂ P25 and conventional 0.5%Pd/TiO₂ P25 catalysts. The TiO₂ P25 and conventional 0.5%Pd/TiO₂ P25 catalysts showed gradual catalyst deactivation due to photocorrosion, the deposition of intermediates and Pd metal leaching. In comparison, the 2%Pd@mTiO₂ catalyst showed higher catalyst stability and reusability. The 2%Pd@mTiO₂ catalysts showed very high and stable phenol degradation (97% conversion) in continuous flow over 52 h. The results showed the feasibility of utilising the developed continuous Taylor flow photoreactor for phenol degradation or as a wastewater treatment plant. Full article

Organic pollutants found in industrial effluents contribute to significant environmental risks. Degradation of these pollutants, particularly through photocatalysis, is a promising strategy ensuring water purification and supporting wastewater treatment. Thus, photodegradation of rhodamine B and phenol under visible-light irradiation using TiO₂/SiO₂ composite nanoparticles was within the main scopes of this study. The nanocomposite was synthesized through a wet impregnation method using TiO₂ and SiO₂ nanopowders previously prepared via a facile sol–gel approach and was fully characterized. The obtained results indicated a pure anatase phase, coupled with increased crystallinity (85.22%) and a relative smaller crystallite size (1.82 nm) in relation to pure TiO₂ and SiO₂ and an enhanced specific surface area (50 m²/g) and a reduced energy band gap (3.18 eV). Photodegradation of rhodamine B upon visible-light irradiation was studied, showing that the TiO₂/SiO₂ composite reached total (100%) degradation within 210 min compared to pure TiO₂ and SiO₂ analogues, which achieved a ≈45% and ≈43% degradation rate, respectively. Similarly, the composite catalyst presented enhanced photocatalytic performance under the same irradiation conditions towards the degradation of phenol, leading to 43.19% degradation within 210 min and verifying the composite catalyst’s selectivity towards degradation of rhodamine B dye as well as its enhanced photocatalytic efficiency towards both organic compounds compared to pure TiO₂ and SiO₂. Additionally, based on the acquired experimental results, ●O₂⁻, h⁺ and e⁻ were found to be the major reactive oxygen species involved in rhodamine B’s photocatalytic degradation, while ●OH radicals were pivotal in the photodegradation of phenol under visible irradiation. Finally, after the TiO₂/SiO₂ composite catalyst was reused five times, it indicated negligible photodegradation efficiency decrease towards both organic compounds. Full article