Search Results (42)

This study investigates the photocatalytic degradation of methylene blue (MB) using strontium-doped SnO₂ nanofibers synthesized via electrospinning. The 1% Sr-doped SnO₂ nanofibers exhibited remarkable photocatalytic activity, achieving 84.74% MB degradation under visible light irradiation, substantially outperforming both undoped SnO₂ nanofibers (61%) and the same catalyst under UV light (69%) under identical experimental conditions. Comprehensive electrochemical investigations revealed that Sr doping fundamentally transformed interfacial charge transfer kinetics, with 1% Sr-doped nanofibers exhibiting a remarkable three-fold decrease in charge transfer resistance (404 Ω compared to 1350 Ω for undoped samples), a dramatic enhancement in charge carrier density (5.17 × 10²² versus 9.24 × 10¹⁹ for undoped samples), and an approximately eight-fold increase in diffusion coefficient (8.78 × 10⁻¹⁰ versus 1.13 × 10⁻¹⁰ cm²s⁻¹). These electrochemical improvements were corroborated by comprehensive structural characterization, which demonstrated that strategic Sr incorporation induced beneficial oxygen vacancies, reduced crystallite size, increased microstrain, and enhanced dislocation density, collectively contributing to superior surface reactivity and accelerated photocatalytic mechanisms. This work establishes a quantitative correlation between electrochemical characteristics and photocatalytic activity in Sr-doped SnO₂ nanofibers, revealing the fundamental mechanisms that transform the SnO₂ nanostructure from UV-dependent to efficient visible light-driven catalysts for organic pollutant degradation. Full article

The current environmental pollution and energy crises are global concerns that must be addressed. Considering this background, three perovskites (YMnO₃, Co-doped YMnO₃, and Sn-doped YMnO₃) were synthesized via a sol–gel method and characterized by XRD, SEM, and EDX. Their water-splitting electrocatalytic activity was evaluated in a strongly alkaline medium. The highest activity was observed during hydrogen evolution reaction (HER) experiments on a glassy carbon electrode coated with a catalyst ink containing the Co-doped material. Initially, the HER overpotential value at −10 mA/cm² was 0.59 V, and the Tafel slope was 115 mV/dec. Following a chronoamperometric stability test, the overpotential became 0.46 V and the Tafel slope 119 mV/dec. The higher HER activity of the modified electrode is ascribed to a higher number of catalytic sites exposed to the electrolyte solution and the presence of Carbon Black. The photocatalytic activity of the perovskites was investigated as well, using different experimental conditions and simulated solar irradiation. The results show that the photocatalytic activity can be improved by doping, and the highest removal efficiency is achieved in the presence of the Co-doped YMnO₃ when ~60% of 17α-ethynylestradiol is degraded. Furthermore, the initial pH has no favorable effect on the degradation efficiency. The reusability of Co-doped YMnO₃ was also tested and minimal activity loss was found after three photocatalytic cycles. Full article

Sn-doped TiO₂–carbon composites were identified as promising multifunctional supports for Pt electrocatalysts, in which the oxide component enhances resistance against corrosion and strong metal–support interactions at the Pt-oxide boundary ensure high stability for the Pt nanoparticles. This work is devoted to the study of the influence of preliminary functionalization of the carbon on the properties of Pt/Ti_0.9Sn_0.1O₂–C catalysts. The structural, compositional and morphological differences between the samples prepared using functionalized or unmodified carbon, as well as the effect of carbon pre-modification on the electrocatalytic behavior of the synthesized Pt catalysts, were investigated using TEM, XRD, XPS, nitrogen adsorption and electrochemical measurements. The presence of oxygen-containing functional groups on carbon treated with HNO₃ and glucose leads to the formation of a homogeneous coating of the carbon with dispersed crystallites of mixed oxide. Elemental mapping revealed the proximity of Sn species with highly dispersed (2–3 nm) Pt particles. Notably, the electrochemical results indicated enhanced activity in CO electrooxidation for both functionalized and unmodified carbon-containing catalysts. An improvement in the 10,000-cycle long-term stability of the catalyst prepared using functionalized carbon was evident compared to the catalyst with untreated carbon or reference Pt/C. Full article

Globalization has increased production in various industries, including textiles, food, and pharmaceuticals. These industries employ different dyes in production, leading to undesired discharge, which conventional treatment fails to remove from the water. The present study aims to synthesize, characterize, and use different pure catalysts (TiO₂ and Zn₂SnO₄) and their compounds doped with CoFe₂O₄ together with ozone (O₃) for the degradation of the azo dye yellow tartrazine (TZ), evaluating the process. For this characterization, N₂ porosimeter, zeta potential, X-ray diffraction, SEM-EDS, and diffuse reflectance spectra were used. Specific surface areas (m² g⁻¹) of 109, 106, 65, and 83 were used for TiO₂, CoFe₂O₄/TiO₂, Zn₂SnO₄, and CoFe₂O₄/Zn₂SnO₄, respectively. Both compounds are characterized as nanocatalysts as they have a band gap of 2.75 and 2.83 eV and average particle size of 98 and 85 nm for CoFe₂O₄/TiO₂ and Zn₂SnO₄, respectively. We employed a reactional model, which was able to describe the catalytic ozonation for all cases, with a low R² of 0.9731. The combination of processes increased TZ degradation from 57% to 74% compared to O₃ alone, achieving a maximum degradation of 98.5% within 50 min of catalysis at a low ozone flow rate. This highlights the potential of the produced catalysts for energy-efficient effluent treatment. Full article

Developing new nanomaterials and performing functionalization to increase their photocatalytic capacity are essential in developing low-cost, eco-friendly, and multipurpose-capacity catalysts. In this research, SnO₂/Se-doped quantum dots (QDs) covered with glycerol (SnO₂/Se-GLY) were synthesized using microwave irradiation. Then, their cover was replaced with glutaraldehyde through a ligand exchange procedure (SnO₂/Se-GLUT). The XRD analyses confirmed a tetragonal rutile structure of SnO₂. The HR-TEM analysis confirmed the generation of QDs with a size around 8 nm, and the optical analysis evidenced low bandgap energies of 3.25 and 3.26 eV for the SnO₂/Se-GLY and SnO₂/Se-GLUT QDs, respectively. Zeta-sizer analysis showed that the hydrodynamic sizes for both nanoparticles were around 230 nm (50 mg/L), and the zeta potential confirmed that SnO₂/Se-GLUT QDs were more stable than SnO₂/Se-GLY QDs. The cover-modified QDs (SnO₂/Se-GLUT) showed a higher and faster adsorption capacity, followed by a slower photocatalytic process than the original QDs (SnO₂/Se-GLY). The QTOF-LC-MS analysis confirmed MB degradation through the identification of intermediates such as azure A, azure B, azure C, and phenothiazine. Adsorption isotherm analysis indicated Langmuir model compliance, supporting the high monolayer adsorption capacity and efficiency of these QDs as adsorbent/photocatalytic agents for organic pollutant removal. This dual capability for adsorption and photodegradation, along with the demonstrated reusability, highlights the potential of SnO₂/Se QDs in wastewater treatment and environmental remediation. Full article

Autothermal oxidative coupling of methane (OCM) is a highly attractive approach for methane utilization. If platinum-based catalysts are operated in short-contact-time reactors with high space velocities, high methane conversion can be achieved. Using a 1 wt.% Pt/Al₂O₃ catalyst as a benchmark, the present study elucidates how different dopants, namely Ni, Sn, and V₂O₅, affect the OCM reaction. Kinetic catalyst tests reveal that acetylene (C₂H₂) is the predominant C₂ product, irrespective of the catalyst formulation or operation conditions. Furthermore, the use of bimetallic catalysts allows either for the maintenance or even the improvement of the C₂ selectivity during OCM, which is attributed to synergistic effects that occur when expensive Pt is partially replaced by cheaper dopants. In particular, the 1 wt.% Pt/Al₂O₃ reference catalyst yielded a maximum C₂ selectivity of 8.2%, whereas the best-performing doped sample 0.25 wt.% Pt 0.75 wt.% V₂O₅/Al₂O₃ yielded a total C₂ selectivity of 11.3%. Full article

The organic pollutants discharged from industrial wastewater have caused serious harm to human health. The efficient photocatalytic degradation of organic pollutants under sunlight shows promise for industrial applications and energy utilization. In this study, a modified TiO₂ photocatalyst doped with bismuth (Bi) and fluorine (F) and composited with SnO₂ and SiO₂ was prepared, and its performance for the degradation of Rhodamine B (RhB) under simulated sunlight was evaluated. Through the optimization of the doping levels of Bi and F, as well as the ratio of SnO₂ and SiO₂ to TiO₂, the optimal catalyst reached degradation efficiency of 100% for RhB within 20 min under simulated sunlight, with a first-order reaction rate constant of 0.291 min⁻¹. This value was 15, 41, 6.5, and 3.3 times higher than those of TiO₂/SnO₂, Bi/TiO₂, Bi-TiO₂/SnO₂, and F/Bi-TiO₂/SnO₂, respectively. The active species detection showed that h⁺ was the most crucial active species in the process. The role of Bi and F addition and SnO₂-SiO₂ compositing was investigated by characterization. Bi formed a chemical bonding with TiO₂ by doping into TiO₂. The absorbance intensity in the UV and visible light regions was improved by SnO₂ and F modification. Composite with SiO₂ led to a larger surface area that allowed for more RhB adsorption sites. These beneficial modifications greatly enhanced the photocatalytic activity of the catalyst. Full article

Proton-exchange-membrane hydrogen fuel cells (PEMFCs) are an important energy device for achieving a sustainable hydrogen society. Carbon-based catalysts used in PEMFCs’ cathode can degrade significantly during operation-voltage shifts due to the carbon deterioration. The longer lifetime of the system is necessary for the further wide commercialization of PEMFCs. Therefore, carbon-free catalysts are required for PEMFCs. In this study, highly crystallized conducting Sb-doped SnO₂ (Sb-SnO₂) nanoparticles (smaller than 7 nm in size) were synthesized using an ozone-assisted hydrothermal synthesis. Pt nanoparticles were loaded on Sb-SnO₂ supporting particles by polyol method to be “Pt/Sb-SnO₂ catalyst”. The Pt/Sb-SnO₂ catalyst showed a high oxygen reduction reaction (ORR) mass activity (178.3 A g_-Pt⁻¹ @ 0.9 V), compared to Pt/C (149.3 A g_-Pt⁻¹ @ 0.9 V). In addition, the retention ratio from the initial value of electrochemical surface area (ECSA) during 100,000-voltage cycles tests between 1.0 V and 1.5 V, Pt/SnO₂ and Pt/Sb-SnO₂ catalyst exhibited higher stability (90% and 80%), respectively, than that of Pt/C catalyst (47%). Therefore, the SnO₂ and Sb-SnO₂ nanoparticles synthesized using this new ozone-assisted hydrothermal method are promising as carbon-free catalyst supports for PEMFCs. Full article

Biomass valorization is an essential strategy for converting organic resources into valuable energy and chemicals, contributing to the circular economy, and reducing carbon footprints. Glycerol, a byproduct of biodiesel production, can be used as a feedstock for a variety of high-value products and can contribute to reducing the carbon footprint. This study examines the impact of surface-level modifications of Mg, Cu, and Sn on Ni-Ce-Zr catalysts for the hydrogenolysis of glycerol, with in situ generated hydrogen. The aim of this approach is to enhance the efficiency and sustainability of the biomass valorization process. However, the surface modification resulted in a decrease in the global conversion of glycerol due to the reduced availability of metal sites. The study found that valuable products, such as H₂ and CH₄ in the gas phase, and 1,2-PG in the liquid phase, were obtained. The majority of the liquid fraction was observed, particularly for Cu- and Sn-doped catalysts, which was attributed to their increased acidity. The primary selectivity was towards the cleavage of the C–O bond. Post-reaction characterizations revealed that the primary causes of deactivation was leaching, which was reduced by the inclusion of Cu and Sn. These findings demonstrate the potential of Cu- and Sn-modified Ni-Ce-Zr catalysts to provide a sustainable pathway for converting glycerol into value-added chemicals. Full article

Modified sludge biochar, recognized for its notable economic and environmental benefits, demonstrates potential as an effective catalyst for peroxydisulfate (PDS) activation. Nevertheless, the specific mechanisms underlying its catalytic performance require more comprehensive investigation. In this study, a modified biochar (TSBC) doped with oxygen (O) and nitrogen (N) atoms was synthesized from sewage sludge and tannin extract, which significantly enhanced the activation of PDS for the degradation of sulfamethoxazole (SMX). The TSBC/PDS system demonstrated robust performance for SMX degradation, achieving over 90% efficiency over a wide pH range (3–10). Subsequent quenching experiments demonstrated that TSBC predominantly catalyzed PDS to generate $\mathrm{O}_2^1$, which effectively degraded SMX via a non-radical pathway. The O- and N-containing functional groups in TSBC were identified as the primary catalytic sites. Besides, density functional theory (DFT) calculations revealed that the incorporation of graphitic N significantly improved the adsorption capacity of PDS on the TSBC surface. Furthermore, based on the identification of intermediates and theoretical calculations, SMX was degraded mainly by two different pathways: S-N cleavage and $\mathrm{O}_2^1$ oxidation. This study offers a foundational framework for the targeted modification of sludge biochar, thereby expanding its applications. Full article

Silver oxide-doped tin oxide (SnAg₂O₃) nanoparticles were synthesized and different spectroscopic techniques were used to structurally identify SnAg₂O₃ nanoparticles. The reduction of 4-nitrophenol (4-NP), congo red (CR), methylene blue (MB), and methyl orange (MO) was studied using SnAg₂O₃ as a catalyst. Only 1.0 min was required to reduce 95% MO; thus, SnAg₂O₃ was found to be effective with a rate constant of 3.0412 min⁻¹. Being a powder, SnAg₂O₃ is difficult to recover and recycle multiple times. For this reason, SnAg₂O₃ was coated on adhesive tape (AT) to make it recyclable for large-scale usage. SnAg₂O₃@AT catalyst was assessed toward MO reduction under various conditions. The amount of SnAg₂O₃@AT, NaBH₄, and MO was optimized for best possible reduction conditions. The catalyst had a positive effect since it speed up the reduction of MO by adding more SnAg₂O₃@AT and NaBH₄ as well as lowering the MO concentration. SnAg₂O₃@AT totally reduced MO (98%) in 3.0 min with a rate constant of 1.3669 min⁻¹. These findings confirmed that SnAg₂O₃@AT is an effective and useful catalyst for MO reduction that can even be utilized on a large scale for industrial purposes. Full article

This work addresses the global sustainable development concerns by investigating the enhancement of piezo-photocatalytic efficiency in bismuth ferrite-based thin films synthesized using reactive high-power impulse magnetron sputtering. The influence of substrate type and Cr addition on structural, optical and ferroelectric properties of bismuth ferrite (BFO) based thin films was investigated. X-ray diffraction measurements showed the formation of different phases depending on the substrate used for sample growth. Compared to the BFO film deposited on FTO (F-SnO₂), the Cr-doped BFO (BFCO) sample on SrTiO₃ (STO) exhibits higher photodegradation efficiency (52.3% vs. 27.8%). The enhanced photocatalytic activity of BFCO is associated with a lower energy band gap (1.62 eV vs. 1.77 eV). The application of ultrasonic-wave vibrations simultaneously with visible light improved 2.85 times and 1.86 times the photocatalytic degradation efficiencies of BFO/FTO and BFCO/STO catalysts, respectively. The piezoresponse force microscopy (PFM) measurements showed that both catalysts exhibit ferroelectric behavior, but a higher piezoelectric potential was evidenced in the case of the BFO/FTO thin film. The enhancement of piezo-photodegradation efficiency was mainly attributed to the piezoelectric-driven separation and transport of photo-generated carriers toward the surface of the photocatalyst. Full article

The composites of transition metal-doped titania and carbon have emerged as promising supports for Pt electrocatalysts in PEM fuel cells. In these multifunctional supports, the oxide component stabilizes the Pt particles, while the dopant provides a co-catalytic function. Among other elements, Sn is a valuable additive. Stong metal-support interaction (SMSI), i.e., the migration of a partially reduced oxide species from the support to the surface of Pt during reductive treatment is a general feature of TiO₂-supported Pt catalysts. In order to explore the influence of SMSI on the stability and performance of Pt/Ti_0.8Sn_0.2O₂-C catalysts, the structural and catalytic properties of the as prepared samples measured using XRD, TEM, XPS and electrochemical investigations were compared to those obtained from catalysts reduced in hydrogen at elevated temperatures. According to the observations, the uniform oxide coverage of the carbon backbone facilitated the formation of Pt–oxide–C triple junctions at a high density. The electrocatalytic behavior of the as prepared catalysts was determined by the atomic closeness of Sn to Pt, while even a low temperature reductive treatment resulted in Sn–Pt alloying. The segregation of tin oxide on the surface of the alloy particles, a characteristic material transport process in Sn–Pt alloys after oxygen exposure, contributed to a better stability of the reduced catalysts. Full article

The Baeyer-Villiger Oxidation (BVO) of ketones and aldehydes produce lactones and formates, while aerobic carboxylation of aldehydes manufactures carboxylic acids, both having high added value. This work prepared a series of Al-containing silicates modified with organic ligands and SnO₂ nanoparticles, which were then employed as catalyst in BVO and carboxylation. Characterizations revealed the morphology of the synthesized catalyst was changed from micron-sized thin sheets to smaller blocks, and then to uniform nanoparticles (size of 50 nm) having the doped SnO₂ nanoparticles with a size of 29 nm. All catalysts showed high BET surface areas featuring silt-like mesopores. In determining the priority of BVO and carboxylation, an influence evaluation of the parameters showed the order to be substrate > oxidant > solvent > catalyst. Cyclic aliphatic ketones were suitable for BVO, but linear aliphatic and aromatic aldehydes for carboxylation. Coordination of (S)-binaphthol or doping of Sn into catalyst showed little influence on BVO under m-CPBA, but the Sn-doped catalyst largely increased BVO under (NH₄)₂S₂O₈ and H₂O₂. Calculations revealed that the catalyst containing both Al and Sn could give BVO intermediates lower energies than the Sn-beta zeolite model. The present system exhibited merits including wider substrate scope, innocuous catalytic metal, greener oxidant, as well as lower catalyst cost. Full article

This study primarily addresses the development of dynamic, selective and economical metal–acid (bifunctional) catalysts for one-pot menthol production by citral hydrogenation. Specifically, various metals such as Pd, Pt, Ni, Cs and Sn were doped over alumina support. Additionally, bifunctional composite catalysts were also prepared with the impregnation of heteropoly acids and Pd precursors over alumina support. Analytical techniques (e.g., BET, PXRD, FT-IR, pyridine adsorption and amine titration methods) were applied for characterization of the most efficient and selective catalysts (e.g., Al₂O₃ and PTA-Cat-I). Similarly, most of the essential operational variables (e.g., loading rate of metal precursor, type of heteropoly acid, temperature, gas pressure and reaction time) were examined during this study. The experimental data shows that the bifunctional catalyst (PTA-Cat-I) produced 45% menthol at full citral substrate conversion (r = 0.038 mmoles.min⁻¹) in liquid-phase citral hydrogenation (at optimized operating conditions: 70 °C, 0.5 MPa and 8 h). However, the heteropoly acid-supported bifunctional catalysts (e.g., PTA-Cat-I, PMA-Cat-I, SMA-Cat-I and STA-Cat-I) resulted in cracking and the dehydration of isopulegol/menthol by the generation of side products (e.g., 4-isopropyl-1-methyl, cyclohex-1-ane/ene); therefore, menthol yield was extensively diminished. On the other hand, non-acidic catalysts (e.g., Cat-I, Cat-II, Cat-III, Cat-IV and Cat-V) readily promoted hydrogenation reactions. The optimum menthol yield occurred due to the presence of strong Lewis and weak Bronsted acid sites. Mass transfer and reaction rate were substantially diminished due to acidity strength, heteropoly acid type and blockage of pores by the applied bifunctional catalysts. Full article