Langmuir-Hinshelwood Kinetic Model Research Articles

Harnessing the potential of Type-II heterostructures: NiO/TiO2/ZnO fibers for enhanced photocatalytic and electrochemical performance in asymmetric supercapacitors

A novel two-step approach, electrospinning followed by wet chemical route, was used for the synthesis of NiO/TiO2/ZnO heterostructure fibers. Structural, morphological, and elemental analyses confirmed the single-phase formation with a unique, one-dimensional furry insect-like morphology, free of impurities. BET analysis revealed a significant increase in the specific surface area from 12.64 to 54.50 m2/g for NiO/TiO2/ZnO heterostructure fibers, indicating the existence of more active sites for catalytic and redox activities. Optical studies demonstrated a reduction in the band gap of NiO in the presence of TiO2 and ZnO, enhancing the photocatalytic properties. The Langmuir-Hinshelwood kinetic model was employed to measure the reaction rate constant, showing improved photocatalytic performance of NiO by enhancing the separation rate of photo-generated electrons and holes on its surface. Furthermore, the electrochemical performance of the prepared fibers-based asymmetric supercapacitors (ASCs) showed a low polarization, attributed to low charge transfer resistance. The NiO/TiO2/ZnO fibers-based ASCs exhibited higher specific capacitance (108 F/g), with a maximum specific energy density of 9.6 Wh/kg at a specific power density of 2000 W/kg indicating excellent performance suitable for finding potential uses in energy storage applications. Various practical and physical tests further certified the efficient performance of the prepared NiO/TiO2/ZnO heterostructure fibers-based asymmetric supercapacitors. The contribution of NiO and TiO2 to the inner surface were ∼52.02 and ∼47.08 %, respectively. In contrast, the NiO/TiO2/ZnO fibers showed a notable difference, with ZnO-NWs contributing ∼4.99 % to the overall surface. This increase in the inner surface contribution to around 95.01 % indicates that the growth of ZnO-NWs provides additional channels for electrochemical reactions during redox processes and enhances adhesion between the ZnO-NWs and NiO/TiO2 heterostructure, facilitating OH− ions transportation.

Micro-nano bubbles in action: AC/TiO2 hybrid photocatalysts for efficient organic pollutant degradation and antibacterial activity

Developing highly active and sustainable photocatalysts is crucial for environmental remediation. This work focuses on the enhanced photocatalytic degradation efficiency of synthetic dyes using TiO2-coated AC hybrid photocatalysts under MNB aeration. The TiO2-coated AC hybrid photocatalyst (HP) was synthesized via a sol-gel method and characterized using XRD, FTIR, SEM, EDS, HR-TEM, and DRS. The study investigated the photocatalytic degradation of three dyes indigo carmine (IC), reactive black 5 (RB5), and methylene blue (MB) in wastewater, with initial dye concentrations ranging from 10 to 100 μM. Under UVA irradiation, the hybrid photocatalyst with MNB aeration (HP + UVA + MNB) achieved the highest degradation efficiencies of 69.09%, 60.06%, and 55.19% for IC, MB, and RB5, respectively. Further analysis showed that the chromophores and complex structures of these dyes were broken into intermediate products. The Langmuir-Hinshelwood kinetic model was used to describe the reaction mechanisms. The HP + UVA + MNB system demonstrated superior photocatalytic degradation activity, making it suitable for operational and environmental applications in dye wastewater treatment. Additionally, the antibacterial properties of AC and HP were tested at 100 μg/mL, showing effectiveness against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli.

Experimental and modeling studies on char combustion under pressurized O2/H2O conditions

The desorption kinetic parameters for pressurized combustion and gasification reactions were determined based on a C++ program coupled with the Langmuir-Hinshelwood (L-H) kinetic model developed and experimental data from pressurized char combustion, and the established L-H kinetic model for pressurized char-O2/H2O combustion was refined in the current paper. The activation energy for desorption in reactions involving pressurized char-O2 and char-H2O was determined to be 250.8 kJ/mol, accompanied by a pre-exponential factor of 5.42×1010 g/(m2 s). Using this foundation, the current research conducted simulations to investigate the impacts of temperature, pressure, and H2O concentration on the oxidation adsorption rate (Rads,oxi), desorption rate (Rdes), gasification adsorption rate (Rads,gas), and the competitive influences of kinetics and diffusion processes within the pressurized char-O2/H2O combustion. The simulation results indicate a gradual increase in Rdes and Rads,gas with char conversion to reach a peak, followed by a gradual decline. Conversely, the Rads,oxi varies smoothly throughout the char conversion process. At 1673 K/1.0 MPa, the char-O2/H2O reaction rate is primarily constrained by Rads,oxi and Rads,gas, with the adsorption reaction serving as the rate-controlling step. Moreover, it was noted that a rise in pressure resulted in a linear increase in Rads,oxi, Rdes, and Rads,gas. At elevated temperatures, the impact of pressure on them becomes more noticeable. However, the introduction of H2O mitigates this effect. Elevated temperature and pressure facilitate the competition on the kinetics of char-O2 combustion for O2 diffusion, resulting in the conversion of char being more susceptible to O2 diffusion rate limitation. With the addition of 20% H2O, the competition effect was weakened. In the case of pressurized combustion involving char and O2/H2O, the char conversion is primarily constrained by the O2 diffusion rate and is scarcely influenced by the H2O diffusion rate.

Application of Ce2(WO4)3–ZnO–CuO nanocomposite as active photocatalyst for removal of ciprofloxacin from wastewater

In this study, the synthesis of Ce2(WO4)3/ZnO/CuO nanocomposite (NCs) was carried out using Co-precipitation method. The structural, morphological and spectral confirmation was achieved through X-ray diffraction (XRD), Scanning electron microscopy (SEM), Differential reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR) analysis. The degradation efficiency for photocatalytic degradation of Ciprofloxacin (CF) and band gap value of prepared Ce2(WO4)3/ZnO/CuO nanocomposite was determined by using UV–Visible and DRS analysis. Band gap value for Ce2(WO4)3/ZnO/CuO was found to be 1.39 eV. Effects of different parameters such as contact time, pH, and effect of concentration of catalyst were investigated to optimize degradation conditions. This prepared nanocomposite was used for the degradation of CF and about 91 % degradation efficiency of CF has been achieved at pH 5 within 70 min by irradiation under sunlight and 60 mg concentration of photocatalyst. The EDTA and IPA scavenged photo-generated holes and hydroxyl ions respectively, the decrease in photocatalytic degradation indicates that holes and hydroxyl ions are reactive species in photocatalytic degradation of CF. The value of R2 = 0.99 confirms the validity of Pseudo first order and Langmuir-Hinshelwood kinetic model for the degradation of CF. These results showed a novel method for the preparation of nanocomposite and the efficient degradation of antibiotics and can be applied to industrial manufacture.

Efficient photocatalysis activation for reactive red 195 degradation by magnetic MIL-53(Fe)/Fe3O4@TiO2 hybrid nanocomposite

The study investigated the performance of a novel magnetic hybrid MIL-53(Fe)/Fe3O4@TiO2 composite for removing reactive red 195 (RR195) dye from water using UVc light. Various analytical techniques were used to characterize the nanocomposite materials. X-ray diffraction analysis confirmed the presence of MIL-53(Fe) and TiO2 in the composite. FT-IR analysis identified carboxyl and Ti-O-Ti groups in the photocatalyst structure. The study evaluated the effects of pH, dye concentration, photocatalyst dosage, and temperature on RR195 photodegradation. The Langmuir-Hinshelwood kinetic model provided the best fit for the reaction rate. Optimal conditions for an 84 % dye degradation were found at a photocatalyst dose of 15 mg/100 mL, pH 3, dye concentration of 100 mg/L, and 35 °C after 120 minutes of UVc light exposure. Thermodynamic analysis indicated an endothermic reaction with positive values for Δ#H and negative values for Δ#S. The MIL-53(Fe)/Fe3O4@TiO2 composite demonstrated excellent stability and achieved over 90 % dye degradation after five cycles. Overall, the composite shows promise for treating wastewater with dyes.

Dispersion of ZnO or TiO2 nanoparticles onto P. australis stem-derived biochar for highly efficient photocatalytic removal of doxycycline antibiotic under visible light irradiation

Abstract Biochar (BC) derived from reed stems was prepared by high-temperature pyrolysis, and two types of ZnO/biochar (ZBC) and TiO2/biochar (TBC) composite materials were synthesized via a simple hydrolysis method. These composites, compared to pure ZnO and TiO2, exhibit not only improved but significantly enhanced crystalline structures and larger specific surface areas. This enhancement in the physical and chemical properties of ZBC and TBC composites is a crucial aspect of our research, as it leads to a distinct red-shifted absorption edge and excellent visible-light absorption characteristics. The photocatalytic degradation efficiency of ZBC and TBC composite materials, a key finding of our study, was evaluated using doxycycline antibiotic as a simulated pollutant under visible-light irradiation. The results demonstrate a 6.0-fold and 7.3-fold increase in photocatalytic degradation efficiency of ZBC and TBC composites compared to pure ZnO and TiO2, respectively, further underscoring the significance of these enhanced properties. Furthermore, active species trapping experiments reveal that ·OH radicals are the dominant reactive species in the photocatalytic degradation process of doxycycline. A Langmuir–Hinshelwood kinetic model accurately represents this degradation process. Kinetic data indicate that the degradation rate constants (k) of ZBC and TBC catalysts are 4.314 × 10−2 min−1 and 3.416 × 10−2 min−1, respectively. The photocatalysts exhibit no significant decrease in degradation efficiency for ZBC and TBC even after the fourth cycle, indicating their relatively high reusability. These results suggest that ZBC and TBC materials can be used as stable, efficient, cost-effective, and sustainable photocatalytic composite materials for antibiotic-contaminated wastewater treatment.

Synthesis and characterization of CuCoFe2O4@GA/AC as a bio-based matrix magnetic nano-heterogeneous photocatalyst for ceftriaxone degradation from aqueous media

Emerging contaminants such as ceftriaxone are a significant issue in the environment. They have led to a series of ecological, environmental, and health issues, and it is urgent to find a green and secure method to remove antibiotics from water effectively. In this research, the CuCoFe2O4@Gum Arabic (GA)/Activated Carbon (AC) as an innovative bio-based matrix magnetic nanocatalyst was synthesized for the efficient degradation of ceftriaxone from aqueous media. The structure of CuCoFe2O4@GA/AC was characterized via FESEM, EDS, Mapping, XRD, FTIR, VSM, and DRS analyses. The structural analysis of the catalyst revealed its synthesis at the nanometer scale (40–50 nm), exhibiting high magnetic strength (Ms: 5.38 emu/g) and favorable optical properties with a bandgap of 3.6 eV. Under optimized conditions, including a pH of 5, 60 min of irradiation time, 0.24 g/L photocatalyst dose, and ceftriaxone concentration of 5 mg/L, the removal efficiency from synthetic and real samples was 94.43% and 62.5%, respectively. The photocatalytic degradation process of ceftriaxone followed pseudo-first-order and Langmuir–Hinshelwood kinetic models. Furthermore, analysis of the process mechanism indicated a prominent role of the superoxide radical. The catalyst had a high recovery capability and chemical stability. The photocatalytic degradation of ceftriaxone by CuCoFe2O4@GA/AC showcased remarkable efficiency, indicating its potential utility in the treatment of wastewater contaminated with antibiotics.

Adsorption mechanisms, kinetics and photoactivities of green synthesized hydroxyapatite supported ZnO and La–ZnO catalysts

In this study, hydroxyapatite (HAP) is synthesized by a co-precipitation method from the waste eggshell, utilized as a support for ZnO (ZnO-HAP) and La–ZnO (La–ZnO-HAP) and employed to degrade methyl orange (MO) and methylene blue (MB) dyes under UV irradiation. Water vapor adsorption as relative humidity (84 % RH) on the HAP structure and the as-prepared catalysts are also examined. The characteristic ZnO and HAP reflections are detected in X-ray diffraction (XRD) analysis of ZnO-HAP, La–ZnO-HAP and humidified samples. ZnO and La–ZnO existence is also verified by scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, UV–Vis diffuse reflectance (UV–Vis DRS) spectra and X-ray photoelectron spectra (XPS). ZnO and La–ZnO loading on the HAP induce the formation of mesoporous structures with high surface areas. Dark adsorption capacities and photoactivities of the as-prepared samples are explored regarding electrostatic interactions, Lewis acid-base interactions and hydrogen bonding for both MO and MB. In particular, La–ZnO-HAP 500 °C and La–ZnO-HAP 500 °C (RH) exhibit improved adsorption abilities and photoactivities. The pseudo-second order model describes the kinetic behavior of all samples under dark conditions. Unhumidified samples follow Langmuir isotherm while Freundlich isotherm better fits humidified ones. Under irradiation, the Langmuir-Hinshelwood kinetic model describes the photoactivities of all samples. The four recycling tests confirm the stabilities of HAP 100 °C, HAP 500 °C, ZnO-HAP 500 °C and La–ZnO-HAP 500 °C. This study suggests that the ZnO or La–ZnO loaded HAP catalysts prepared in the presence and absence of humid conditions are considered promising materials for environmental remediation.

Macroporous p-SnO/n-SnO2 heterojunction photocatalysts via dealloying and thermal oxidation of immiscible Sn30Zn70 precursors to boost photodegradation

Controlled synthesis of macroporous tin photocatalyst with a SnOx surface layer (SnOx@P-Sn) was achieved via chemical dealloying then thermal oxidation. The microstructure of macroporous Sn was inherited from the immiscible Sn30Zn70 precursor. The chemical composition of surface SnOx and the concentration of oxygen vacancies on the Sn ligaments is dependent on the thermal oxidation temperature, with p-SnO/n-SnO2 heterojunctions being formed at 500°C. The obtained SnOx@P-Sn@500°C p-n heterojunction surface layer achieved an outstanding degradation efficiency of 96.7 % when used to catalyze the photodegradation of methyl orange azo dyes (MO). The Langmuir-Hinshelwood Kinetics model was modified to describe the photodegradation process with higher coefficient of determination. The reason for the superior degradation reaction rates of SnOx@P-Sn@500°C p-n heterojunction photocatalyst includes: large specific surface area of the Sn substrates, appropriate band gap formed via thermal oxidation, higher oxygen vacancies, and efficient separation of electron/hole pairs in the p-SnO/n-SnO2 heterojunction.

The Conundrum of "Pair Sites" in Langmuir-Hinshelwood Reaction Kinetics in Heterogeneous Catalysis.

Understanding reaction kinetics is crucial for designing and applying heterogeneous catalytic processes in chemical and energy conversion. Here, we revisit the Langmuir-Hinshelwood (L-H) kinetic model for bimolecular surface reactions, originally formulated for metal catalysts, assuming immobile adsorbates on neighboring pair sites, with the rate varying linearly with the density of surface sites (sites per unit area); r ∝ [*]o 1. Supported metal oxide catalysts, however, offer systematic control over [*]o through variation of the active two-dimensional metal oxide loading in the submonolayer region. Various reactions catalyzed by supported metal oxides are analyzed, such as supported VO x catalysts, including methanol oxidation, oxidative dehydrogenation of propane and ethane, SO2 oxidation to SO3, propene oxidation to acrolein, n-butane oxidation to maleic anhydride, and selective catalytic reduction of nitric oxide with ammonia. The analysis reveals diverse dependencies of reaction rate on [*]o for these surface reactions, with r ∝ [*]o n , where n equals 1 for reactions with a unimolecular rate-determining step and 2 for those with a bimolecular rate-limiting step or exchange of more than 2 electrons. We propose refraining from a priori assumptions about the nature and density of surface sites or adsorbate behavior, advocating instead for data-driven elucidation of kinetics based on the density of surface sites, adsorbate coverage, etc. Additionally, recent studies on catalytic surface mechanisms have shed light on nonadjacent catalytic sites catalyzing surface reactions in contrast to the traditional requirement of adjacent/pair sites. These findings underscore the need for a more nuanced approach in modeling heterogeneous catalysis, especially supported metal oxide catalysts, encouraging reliance on experimental data over idealized assumptions that are often difficult to justify.

Activation of peroxymonosulfate with ZIF-67-derived Co/N-doped porous carbon nanocubes for the degradation of Congo red dye

In this study, porous carbon nanocubes encapsulated magnetic metallic Co nanoparticles (denoted as Co@N-PCNC) was prepared via pyrolyzing ZIF-67 nanocubes precursor at 600 °C and characterized by various technologies. It was used to activate peroxymonosulfate (PMS) to degrade Congo red (CR) dye efficiently. Over 98.45% of 50 mg L−1 CR was degraded using 0.033 mM PMS activated by 75 mg L−1 Co@N-PCNC within 12 min. The free radical quenching experiments were performed to reveal the nature of the reactive oxygen species radicals generated throughout the catalytic oxidation of CR. The effects of common inorganic anions and the water matrix on CR removal were studied. Moreover, the results of the kinetic study revealed the suitability of the pseudo-first-order and Langmuir–Hinshelwood kinetic models for illustrating CR degradation using the Co@N-PCNC/PMS system. Ultimately, the Co@N-PCNC displayed good operational stability, and after five cycles, the CR removal rate can still maintain over 90% after 12 min.

Reaction mechanism and kinetics for Pt/C and Au/C catalyzed aqueous phase glycerol oxidation to various carboxylic acids

Fundamental understanding of heterogeneously catalytic aerobic oxidation of polyol is highly desirable for sustainable and efficient chemical synthesis. Herein, based on the purpose of exploring the selectivity of various carboxylic acids on Pt-Au catalysts with different ratios, we conducted a comprehensive investigation into the reaction pathways of glycerol oxidation over pristine Pt/C and Au/C catalysts via experiments, kinetics analysis and DFT calculations. Structural characterizations revealed that Pt/C exhibits a higher metallic state and more d electrons, thus tending to strongly adsorb OH– and promote oxygen activation. Conversely, the weak oxygen activation of Au/C could be attributed to fewer cationic high valence state and d electrons. Furthermore, the Langmuir-Hinshelwood kinetic model and DFT calculations indicate both catalysts exhibit obvious differences in product distribution. Specifically, Pt demonstrated higher selectivity towards lactic acid by facilitating dehydration of C-OH in glyceraldehyde and promoting timely desorption of lactic acid species. In contrast, Au displayed more glycolic acid products caused by strengthening oxidative cleavage of C-C bond in glyceric acid. Expanding to bimetallic catalysts, it was observed that catalysts with higher Au content exhibit enhanced selectivity towards the oxidation of glyceric acid to glycolic acid, while those with a higher Pt ratio demonstrate increased selectivity for the oxidation of glycerol to lactic acid. These findings provide valuable insights for guiding the design and optimization of this catalytic process to achieve targeted product generation.

An exhaustive exploration of Zn0.15Sn0.85(Se0.95S0.05)2 crystal-based photodetector and its potential application as a photocatalytic material

The research pioneers the exploration of synthesized quaternary Zn0.15Sn0.85(Se0.95S0.05)2 (ZSSS) crystals, demonstrating remarkable efficacy as optoelectronic switching devices and potent photocatalysts. The ZSSS photodetector recorded a stable photoresponse with remarkable rapid rise and decay times. The Langmuir-Hinshelwood kinetic model was used to look at the photocatalytic activity at different methylene blue concentrations. The researchers grew highly pure ZSSS crystals using the direct vapour transport (DVT) method. Field effect scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) images reveal the layer growth mechanism in the grown crystals. The structural analyses of the grown crystals were carried out using an X-ray diffraction (XRD) pattern and temperature-dependent Raman spectroscopy. The Lorentzian function was fitted to experimental data to carry out the temperature-dependent Raman analysis. The grown crystals exhibit a direct optical bandgap of 1.69 eV. The electrical analyses explain the semiconducting nature of the crystals.

Efficient photocatalytic reduction of Cr(VI) and degradation of tetracycline by Bi2Se3@ZnIn2S4 binary heterostructures enriched with sulfur vacancies: Mechanism and mineralization analysis

Constructing a sulfur-vacancy-enriched heterostructure offers advantages in enhancing photocatalytic performance due to the synergy between the vacancy’s electron-trapping and the internal electric field (IEF) features. In this study, a series of IEF-modulated type-I heterostructures containing sulfur vacancies-rich ZnIn2S4 (SV-ZIS) and Bi2Se3 (BSe) was rationally developed by hydrothermal and reduction methods. The optimized BSe@SV-ZIS catalyst shows an outstanding photocatalytic Cr(VI) reduction and tetracycline degradation rates, which are ∼ 2.1 and ∼ 1.5 times higher than that of pure SV-ZIS and BSe, respectively. Notably, the enhanced catalytic performance of binary samples could be linked to efficient absorption of the full spectrum of light, heterojunction formation and larger contact area to enhance the charge carriers movement at their interface and exceptional photo-stability. By assisting DRS, VB-XPS, and UPS analyses, details of the energy band position, charge carriers transport route, and preliminary photocatalytic mechanism were systematically explored. Furthermore, radical scavenging and electron paramagnetic resonance experiments were conducted to provide evidence of the participation of the reactive species during photocatalysis over BSe@SV-ZIS. Kinetic analysis revealed that the rate of photocatalytic process adheres to the Langmuir–Hinshelwood kinetic model. These results demonstrated that the heterostructuring approach holds significant potential as an effective avenue for developing photocatalysts that can harness both visible and NIR light, offering promising solutions to contemporary challenges in the realms of environmental decontamination and energy.

Facile green synthesis of a novel NiO and its catalytic effect on methylene blue photocatalytic reduction and sodium borohydride hydrolysis

NiO nanoparticles were synthesized from pine cone extract by green synthesis method, which is a simple, cost-effective, environmentally friendly and sustainable method. The particle size of NiO nanoparticles was determined to be in the range of 10–25 nm by X-diffraction differential and transmission electron microscope analysis, and the bandgap energy of NiO nanoparticles was determined to be 2.66 eV. The catalytic effect of NiO nanoparticles in both microwave-assisted sodium borohydride hydrolysis and photocatalytic reduction of methylene blue was examined and it was determined that they had a high catalytic effect in both applications. It was determined that the hydrogen production rate in sodium borohydride hydrolysis was 1135 mL/g/min. The activation energy of sodium borohydride hydrolysis is 29.69 kJ/mol and 29.59 kJ/mol for the nth-order and Langmuir Hinshelwood kinetic models, respectively. In the photocatalytic reduction of methylene blue with NaBH4, it was determined that the reduction did not occur in the absence of a catalyst, but in the presence of the catalyst, the reduction occurred 98% in 3 min. It was determined that NiO nanoparticles were used five times in the photocatalytic reduction of methylene blue and the reduction efficiency for the fifth time was 93%. It was determined that the photocatalytic reduction of methylene blue was pseudo-first order and the rate constant was 1.63 s−1. It was determined that NiO nanoparticles synthesized by the environmentally friendly green synthesis method can be used as catalysts for two different applications.

Internal dry reforming of methane in solid oxide fuel cells

In the context of global efforts to reduce greenhouse gas emissions and combat extreme global warming, the direct dry reforming of methane reaction in solid oxide fuel cells presents a promising avenue for clean energy production. This study delves into the influence of temperature, gas composition, and current density on the kinetics of dry methane reforming in solid oxide fuel cells. Power Law and Langmuir-Hinshelwood kinetic models were proposed to highlight the impact of operating conditions on dry methane reforming reactions. Results revealed that the feed gas composition strongly affects methane conversion, with higher methane contents resulting in lower conversions. Increasing the CH4/CO2 ratio increases reaction rates, and the effect decreases at a ratio of 1.25. The changes in methane concentration on dry methane reforming reaction rate are more significant than those for carbon dioxide. However, increasing carbon dioxide concentration enhances methane conversion. The exothermic nature of CO2 adsorption suggests that the adsorption process is thermodynamically favourable in dry reforming, and the elevated temperatures generally improve reaction rates and methane conversion by removing carbon deposits and providing the energy needed to break down the chemical bonds in methane which facilitating its transformation. A higher current density significantly enhances the CO2 adsorption equilibrium constant and further increases methane conversion, highlighting the positive role of electrochemical reactions on dry methane reforming. This study aims to fill the knowledge gap regarding the influence of electrochemical reactions on dry methane reforming behaviours in solid oxide fuel cells, offering critical insights for advancing anode design, thus contributing to the development of solid oxide fuel cell technologies to address global warming and reduce greenhouse gas emissions.

Synergistic bifunctionality of ZnO nanowalls: Antibacterial activity and photocatalysis through integrated in silico and in vitro approaches

This research investigation delves into the versatile attributes of ZnO nanowalls, specifically probing into their dual functionality encompassing antibacterial and photocatalytic properties. The synthesis of ZnO was achieved by employing a microwave-mediated co-precipitation technique. The resulting sample underwent thorough characterization through diverse analytical methodologies. X-ray diffraction analysis disclosed the prevalence of the hexagonal wurtzite phase, as confirmed by JCPDS card No. 36–1451, with an average crystallite size determined as 23.48 nm. Tauc plot extrapolation method was applied to the UV absorption spectrum to ascertain the bandgap energy. The ZnO nanostructure morphology, featuring multi-directional nano-walls, was unveiled through scanning electron microscopy (SEM). The BET nitrogen adsorption technique quantified the surface area of the ZnO sample as 6.69 m2/g. In antibacterial evaluation, the in vitro (disk diffusion) method showcased the remarkable efficacy of ZnO against both gram-positive Staphylococcus sp. and gram-negative E. coli bacteria. Complementing these experimental findings, in silico molecular docking studies exposed both nano ZnO ligands with standard and corrected lattice parameter values exhibiting favorable binding energy. Moreover, the synthesized ZnO nanoparticles exhibited remarkable photocatalytic activity, particularly demonstrated in the decolorisation of Azure A and Azure B dyes, following the first-order Langmuir–Hinshelwood kinetic model. The collective findings underscored a synergistic effect within the fabricated ZnO nanoparticles, showcasing their dual prowess in both antibacterial and photocatalytic activities. The observed phenomenon can be chiefly ascribed to the presence of lattice strain and dislocation density. This intriguing dual functionality positions them as promising candidates for potential applications in wastewater treatment.

Microstructures, Optical, magnetic Properties, and photocatalytic activity of magnetically separable and reusable ZnO-Doped Fe3O4/rGO nanocomposite synthesized via green route

We report magnetically-separable, reusable, green-synthesized Fe3O4/rGO/ZnO, as heterogeneous catalyst for photo-Fenton degradation of organic pollutants in aqueous solution under certain treatments. Fe3O4 nanoparticles was green-synthesized using Moringa oleifera leaf extract, while rGO was synthesized utilizing Amaranthus viridis leaf extract. Fe3O4/rGO was composited under sonication treatment. Afterwards, Fe3O4/rGO was doped with ZnO with various concentration of ZnO. X-ray diffraction and selected area electron diffraction showed that Fe3O4 and ZnO had spinel cubic and hexagonal structure, respectively; another phase appeared as Fe2O3 spinel cubic structure. Crystallite size was decreased as the ZnO concentration increased. Morphology image showed almost spherical, non-uniform, and slightly dispersed particle under agglomerated condition, attaching to rGO sheets. The particle size of Fe3O4, Fe3O4/rGO, and Fe3O4/rGO/ZnO is 14.3; 14.1; and 10.4 nm, respectively. Fourier-transform infrared spectra showed metallic functional groups, such as Fe-O and Zn–O at 562–589 and 462–478 cm−1 also suggests nanocomposite formation. However, blue-shift absorption and band gap widening were observed with ZnO addition. Raman spectroscopy revealed the formation as-synthesized GO and rGO. Vibrating sample magnetometer showed that green-synthesized Fe3O4/rGO/ZnO exhibited superparamagnetic properties. Removal efficiency of photodegradation methylene blue was optimal for green-synthesized Fe3O4/rGO/ZnO under sonication treatment, reached 100 % degradation within 180 min for uptake every 30 min. Photodegradation was also analyzed using Langmuir-Hinshelwood kinetic model, resulting rate constant of 24.7 × 10−3 min−1 and half-life time of 28.1 min at optimum treatment. Reusability of photocatalytic activity after 3 cycles showed only a tiny drop in catalytic efficiency. Meanwhile, it possesses high stability in catalytic activity and structure. The green-synthesized Fe3O4/rGO/ZnO potential as an environmentally friendly reusable photocatalyst for wastewater degradation.

Hexavalent Chromium Reduction Mediated by Interfacial Electron Transfer over the Co@NC Nanosheet-Assembled Microflowers.

The reductive transformation of Cr(VI) into Cr(III) mediated by formic acid with efficient, stable, and cost-effective catalysts is a promising strategy for remediating Cr(VI) contamination. Herein, we report the facile construction of uniform Co@NC nanosheet-assembled microflowers for the reduction of Cr(VI). Both experimental results and density functional theory (DFT) calculations reveal the vital role of the intensive interfacial electronic interaction between Co nanoparticles and the N-doped carbon layer in facilitating the anchoring and dispersion of Co nanoparticles within the carbon framework. The interfacial electron transfer from Co to NC contributes to the interaction with Cr2O72- ions, promoting the subsequent H-transfer reaction. A Langmuir-Hinshelwood kinetic model has been established for the Cr(VI) reduction catalyzed by the CNCF2 (pyrolyzed at 700 °C), which shows a superior reaction performance. This study provides a facile strategy to delicately design well-assembled heterostructures with rich interfaces and strong interfacial interactions for a series of applications in environmental/thermal catalysis.

Structure–activity relationships over Ru/NiAl2O4 catalysts in anisole demethoxylation: spectroscopic and kinetic studies

Demethoxylation was kinetically and spectroscopically studied over three catalysts with different Ru0/Ruδ+ ratios. In-situ spectroscopic tests demonstrated that the synergy between Ru0 and Ruδ+ was crucial, and Ru0 was in charge of H2 activation and adsorption of aromatic ring while Ruδ+ adsorbed with O in methoxyl. A Langmuir–Hinshelwood kinetic model was proposed, and ratio of Ru0/Ruδ+ was the key in deciding the rate-determining step (RDS): i) desorption of toluene was RDS over catalyst with high Ru0 ratio; ii) dissociation of H2 was RDS over Ruδ+ enriched catalyst; iii) demethoxylation was rate-determined by CO water–gas shift (WGS) when Ru0/Ruδ+ approached ~ 1. The best performance was obtained over Ru/NiAl2O4-200, which effectively enabled both C-O bond activation and rapid recovery of adsorption sites for aromatic rings. Finally, in-situ DRIFT studies on methoxy decomposition and CO-WGS unraveled that the electronic composition of Ru was more stable in Ru/NiAl2O4-200 which contributes to its excellence.