A microkinetic study of CO2 hydrogenation to methanol on Pd1-Cu(111) and Pd1-Ag(111) catalysts: a DFT analysis

The thermochemical conversion of CO2 into methanol, a process known for its selectivity, often encounters a significant obstacle: the reverse water gas reaction. This problem emerges due to the demanding high temperatures and pressures, causing instability in catalytic performance. Recent endeavours have focused on innovatively designing catalysts capable of withstanding such conditions. Given the costliness of experimental approaches, a theoretical framework has emerged as a promising avenue for addressing the challenges in methanol production. It has been reported that transition metals, especially Pd, provide ideal binding sites for CO2 molecules and hydrogen atoms, facilitating their interactions and subsequent conversion to methanol. In the geometric single-atom form, their surface enables precise control over the reaction pathways and enhances the selectivity towards methanol. In our study, we employed density functional theory (DFT) to explore the conversion of CO2 to CH3OH on Pd1-Cu(111) and Pd1-Ag(111) single-atom alloy (SAA) catalysts. Our investigation involved mapping out the complex reaction pathways of CO2 hydrogenation to CH3OH using microkinetic reaction modelling and mechanisms. We examined three distinct pathways: the COOH* formation pathway, the HCOO* formation pathway, and the dissociation of CO2* to CO* pathway. This comprehensive analysis encompassed the determination of adsorption energies for all reactants, transition states, and resultant products. Additionally, we investigated the thermodynamic and kinetic profiles of individual reaction steps. Our findings emphasised the essential role of the Pd single atom in enhancing the activation of CO2, highlighting the key mechanism underlying this catalytic process. The favoured route for methanol generation on the Pd1-Ag(111) single-atom alloy (SAA) surface unfolds as follows: CO2* progresses through a series of transformations, transitioning successively into HCOO*, HCOOH*, H2COOH*, CH2O*, and CH2OH*, terminating in the formation of CH3OH*, due to lower activation energies and higher rate constants.

Technological trends in nanosilica synthesis and utilization in advanced treatment of water and wastewater

Water and wastewater treatment applications stand to benefit immensely from the design and development of new materials based on silica nanoparticles and their derivatives. Nanosilica possesses unique properties, including low toxicity, chemical inertness, and excellent biocompatibility, and can be developed from a variety of sustainable precursor materials. Herein, we provide an account of the recent advances in the synthesis and utilization of nanosilica for wastewater treatment. This review covers key physicochemical aspects of several nanosilica materials and a variety of nanotechnology-enabled wastewater treatment techniques such as adsorption, separation membranes, and antimicrobial applications. It also discusses the prospective design and tuning options for nanosilica production, such as size control, morphological tuning, and surface functionalization. Informative discussions on nanosilica production from agricultural wastes have been offered, with a focus on the synthesis methodologies and pretreatment requirements for biomass precursors. The characterization of the different physicochemical features of nanosilica materials using critical surface analysis methods is discussed. Bio-hybrid nanosilica materials have also been highlighted to emphasize the critical relevance of environmental sustainability in wastewater treatment. To guarantee the thoroughness of the review, insights into nanosilica regeneration and reuse are provided. Overall, it is envisaged that this work's insights and views will inspire unique and efficient nanosilica material design and development with robust properties for water and wastewater treatment applications.

Enhanced light olefins production via n-pentane cracking using modified MFI catalysts

n-pentane catalytic cracking was studied over a series of MFI zeolites with varying SiO₂/Al₂O₃ ratios (30, 80, 280, 500, and 1500) using a fixed-bed reactor operated at temperature 550–650 °C. Other MFI zeolites (SiO₂/Al₂O₃ = 280) with various crystal morphology and size (such as large crystal and nano size) were also synthesized and tested for n-pentane cracking. The effects of MFI zeolite modification with ammonia and phosphorus on its physiochemical properties and catalytic activity were investigated. Among the parent MFI zeolites, MFI (280) demonstrated high selectivity (51%) towards light olefins (C₃⁼/C₂⁼ = 0.7) at 650 °C with undesired C₁–C₄ alkanes (38%). Surface modified MFI (280) zeolites of different crystal size and morphology showed improvement towards propylene selectivity by suppressing undesired reactions. Phosphorous-modified MFI zeolite with a large crystal size was found to improve light olefin selectivity (52.2%) with C₃⁼/C₂⁼ = ∼1.3 and reduce undesired C₁–C₄ alkanes (8%) formation due to suppressed strong acidic sites. The characterization and evaluation results for the modified MFI (280) revealed that the incorporation of phosphorous created moderate acidic sites, which were stabilized by some non-framework aluminum species, thereby leading to suppressing the formation of undesired C₁–C₄ alkanes with improved light olefins selectivity.

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n-pentane cracking over MFI zeolites with various Si₂O₃/Al₂O₃ ratios (30, 80, 280, 500, and 1500) was investigated.

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MFI (280) zeolite at 650 °C showed 51% selectivity for light olefins (C₃⁼/C₂⁼ = 0.7) with 23.8% undesirable C₂-C₄ alkanes.

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Phosphorous-modified large crystal MFI catalyst with moderate acid sites inhibited hydrogen transfer reaction.

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P/HZ280-LC provide improved light olefins production (selectivity 52.2%, C₃⁼/C₂⁼ = 1.3).

PEGylated green halloysite/spinel ferrite nanocomposites for pH sensitive delivery of dexamethasone: A potential pulmonary drug delivery treatment option for COVID-19

Dexamethasone (Dex) is used in drug regimen for treatment of Coronavirus disease (COVID-19). Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) fusion and entry into the cell occurs at pH 5.5. In our present study, we have identified a green, cheap clay based halloysite (Hal) nanoformulation with release capability of Dex at such interactive pH condition. 30%ZnFe₂O₄/Hal and 30%NiFe₂O₄/Hal were prepared by one-pot synthesis technique. Dex (5% wt/wt) was functionalized over both nanocomposites. Finally, polyethylene glycol (PEG) was coated over ZnFe₂O₄/Hal/Dex and NiFe₂O₄/Hal/Dex nanocomposite using lyophilization technique (0.08 μl/mg of nanocarrier). The release ability of Dex was studied under pulmonary infection and normal pH conditions (pH = 5.6 and 7.4). The characterization study using X-ray diffraction (XRD) and UV-visible diffuse reflectance (DRS) spectra confirmed the presence of spinel ferrites over Hal. Nitrogen adsorption isotherm showed the surface area of ZnFe₂O₄/Hal (75 m²/g), pore volume (0.27 cm³/g) with average pore size (14.5 nm). Scanning electron microscope/Energy dispersive spectroscopy (SEM-EDS) and Transmission electron microscopy analysis revealed a textural change in halloysite tubular type indicating drug adsorption and PEG adhesion. DRS spectra indicated an intergrowth of zinc ferrite nanoparticles on the halloysite nanotubes. Interestingly, ZnFe₂O₄/Hal/Dex/PEG exhibited a high Dex release ability (17.5%, 168 h) at pH = 5.6 relevant to SARS-CoV-2 fusion entry into the cell pH condition of 5.5. Comparatively, the nanocomposite showed a less Dex release (<5%) release for 168 h at neutral pH = 7.4. The drug release kinetics were studied and the obtained data were fitted for the release constant and release exponent, using the Korsmeyer-Peppas model. To test the compatibility of our nanocomposites, we performed the cell viability assay (MTT) using HEK293 cells. Our results showed that at 0.3 mg/ml, Dex-loaded nanocomposite had a statistically significant improvement in cell viability compared to Dex alone. These results suggest that our nanocomposite has prevented the toxic effect of Dex and has huge potential to act as pulmonary drug delivery system for targeted lung infection therapeutics.