A review on thermal and catalytic pyrolysis of plastic solid waste (PSW)

Plastic plays an important role in our daily lives due to its versatility, light weight and low production cost. Plastics became essential in many sectors such as construction, medical, engineering applications, automotive, aerospace, etc. In addition, economic growth and development also increased our demand and dependency on plastics which leads to its accumulation in landfills imposing risk on human health, animals and cause environmental pollution problems such as ground water contamination, sanitary related issues, etc. Hence, a sustainable and an efficient plastic waste treatment is essential to avoid such issues. Pyrolysis is a thermo-chemical plastic waste treatment technique which can solve such pollution problems, as well as, recover valuable energy and products such as oil and gas. Pyrolysis of plastic solid waste (PSW) has gained importance due to having better advantages towards environmental pollution and reduction of carbon footprint of plastic products by minimizing the emissions of carbon monoxide and carbon dioxide compared to combustion and gasification. This paper presents the existing techniques of pyrolysis, the parameters which affect the products yield and selectivity and identify major research gaps in this technology. The influence of different catalysts on the process as well as review and comparative assessment of pyrolysis with other thermal and catalytic plastic treatment methods, is also presented.

Recent progress on deep eutectic solvents in biocatalysis

Deep eutectic solvents (DESs) are eutectic mixtures of salts and hydrogen bond donors with melting points low enough to be used as solvents. DESs have proved to be a good alternative to traditional organic solvents and ionic liquids (ILs) in many biocatalytic processes. Apart from the benign characteristics similar to those of ILs (e.g., low volatility, low inflammability and low melting point), DESs have their unique merits of easy preparation and low cost owing to their renewable and available raw materials. To better apply such solvents in green and sustainable chemistry, this review firstly describes some basic properties, mainly the toxicity and biodegradability of DESs. Secondly, it presents several valuable applications of DES as solvent/co-solvent in biocatalytic reactions, such as lipase-catalyzed transesterification and ester hydrolysis reactions. The roles, serving as extractive reagent for an enzymatic product and pretreatment solvent of enzymatic biomass hydrolysis, are also discussed. Further understanding how DESs affect biocatalytic reaction will facilitate the design of novel solvents and contribute to the discovery of new reactions in these solvents.

Energy storage materials derived from Prussian blue analogues

Prussian blue analogues (PBAs) with open frameworks have drawn much attention in energy storage fields due to their tridimensional ionic diffusion path, easy preparation, and low cost. This review summarizes the recent progress of using PBAs and their derivatives as energy storage materials in alkali ions, multi-valent ions, and metal-air batteries. The key factors to improve the electrochemical performance of PBAs as cathode materials in rechargeable batteries were firstly discussed. Several approaches for performance enhancement such as controlling the amounts of vacancies and coordinated water, optimizing morphologies, and depositing carbon coating are described in details. Then, we highlighted the significance of their diverse architectures and morphologies in anode materials for lithium/sodium ion batteries. Finally, the applications of Prussian blue derivatives as catalysts in metal-air batteries are also reviewed, providing insights into the origin of favorable morphologies and structures of catalyst for the optimal performance.

One-step synthesis of hollow porous gold nanoparticles with tunable particle size for the reduction of 4-nitrophenol

Hollow porous gold nanoparticles (HPGNPs) were synthesized via a one-step solution phase method at ambient temperature. The particle size, ranging from 80nm to 350nm, was easily controlled by changing the concentration of HAuCl4. The morphology and the structure of the as-prepared HPGNPs were investigated by SEM, TEM, HRTEM and XPS. Langmuir isotherm analysis yielded values of 8973m(2)/g for the outer surface area and 58724m(2)/g for the inner surface area for the 80nm HPGNPs. Due to a special hollow porous nanostructure, the HPGNPs exhibited superior catalytic activity and stability for the reduction of 4-nitrophenol (4-NP). No significant inactivation of the 80nm HPGNPs was observed, even after recycling for six cycles or storing for more than 1 month. Due to these excellent properties, it is expected that HPGNPs can be used in such applications as water pollutant removal and environmental remediation.

Heterogeneous catalytic ozonation of biologically pretreated Lurgi coal gasification wastewater using sewage sludge based activated carbon supported manganese and ferric oxides as catalysts

Sewage sludge of biological wastewater treatment plant was converted into sewage sludge based activated carbon (SBAC) with ZnCl₂ as activation agent, which supported manganese and ferric oxides as catalysts (including SBAC) to improve the performance of ozonation of real biologically pretreated Lurgi coal gasification wastewater. The results indicated catalytic ozonation with the prepared catalysts significantly enhanced performance of pollutants removal and the treated wastewater was more biodegradable and less toxic than that in ozonation alone. On the basis of positive effect of higher pH and significant inhibition of radical scavengers in catalytic ozonation, it was deduced that the enhancement of catalytic activity was responsible for generating hydroxyl radicals and the possible reaction pathway was proposed. Moreover, the prepared catalysts showed superior stability and most of toxic and refractory compounds were eliminated at successive catalytic ozonation runs. Thus, the process with economical, efficient and sustainable advantages was beneficial to engineering application.

Perovskite synthesis, properties and their related biochemical and industrial application

The perovskite structure is shown to be the single most versatile ceramic host. Inorganic perovskite type oxides are attractive compounds for varied applications due to its large number of compounds, they exhibit both physical and biochemical characteristics and their Nano-formulation have been utilized as catalysts in many reaction due to their sensitivity, unique long-term stability and anti-interference ability. Some perovskites materials are very hopeful applicants for the improvement of effective anodic catalysts performance. Depending Perovskite-phase metal oxides distinct variety of properties they became useful for various applications they are newly used in electrochemical sensing of alcohols, glucose, hydrogen peroxide, gases, and neurotransmitters. Perovskite organometallic halide showed efficient essential properties for photovoltaic solar cells. This review presents a full coverage of the structure, progress of perovskites and their related applications. Stress is focused particularly to different methods of perovskites properties and there related application.

Preparation of magnetic biochar and its application in catalytic degradation of organic pollutants: A review

In recent years, magnetic biochar (MBC) has been greatly concerned because of its magnetic separation characteristics, and has been successfully used as a catalyst in the catalytic degradation of organic pollutants. However, there is currently a lack of a more systematic summary of MBC preparation methods, and no detailed overview of the catalytic mechanism of MBC catalysts for the degradation of organic pollutants. Therefore, we carry out this work to fill the above gaps. At first, we summarize the raw materials, preparation methods, and types of MBC in detail, and emphasize the MBC prepared by iron-containing sludge. Then, the catalytic mechanisms of MBC in peroxydisulfate, peroxymonosulfate, Fenton-like, photocatalysis, and NaBH₄ systems are carefully summarized, highlighting the contribution of various parts of MBC in catalysis. The degradation efficiency of organic pollutants in the above systems is evaluated. Finally, the stability and reusability of MBC catalysts are evaluated. In conclusion, this review contributes a meager force to the future development of MBC.

2D Layered Double Hydroxide Nanosheets and Their Derivatives Toward Efficient Oxygen Evolution Reaction

Layered double hydroxides (LDHs) have attracted tremendous research interest in widely spreading applications. Most notably, transition-metal-bearing LDHs are expected to serve as highly active electrocatalysts for oxygen evolution reaction (OER) due to their layered structure combined with versatile compositions. Furthermore, reducing the thickness of platelet LDH crystals to nanometer or even molecular scale via cleavage or delamination provides an important clue to enhance the activity. In this review, recent progresses on rational design of LDH nanosheets are reviewed, including direct synthesis via traditional coprecipitation, homogeneous precipitation, and newly developed topochemical oxidation as well as chemical exfoliation of parent LDH crystals. In addition, diverse strategies are introduced to modulate their electrochemical activity by tuning the composition of host metal cations and intercalated counter-anions, and incorporating dopants, cavities, and single atoms. In particular, hybridizing LDHs with conductive components or in situ growing them on conductive substrates to produce freestanding electrodes can further enhance their intrinsic catalytic activity. A brief discussion on future research directions and prospects is also summarized.

Performance of various catalysts on treatment of refractory pollutants in industrial wastewater by catalytic wet air oxidation: A review

The tremendous increase of industrialization and urbanization worldwide causes the depletion of natural resources such as water and air which urges the necessity to follow the environmental sustainability across the globe. This requires eco-friendly and economical technologies for depollution of wastewater and gases or zero emission approach. Therefore, in this context the treatment and reuse of wastewater is an environmental friendly approach due to shortage of fresh water. Catalytic wet air oxidation (CWAO) is a promising technology for the treatment of toxic and non-biodegradable organic pollutants in the wastewater generated from various industries. Various heterogeneous catalysts have been extensively used for treatment of various model pollutants such as phenols, carboxylic acids, nitrogenous compounds and different types of industrial effluents. The present review focuses on the literature published on the performances of various noble and non-noble metal catalysts for the treatment of various pollutants by CWAO. Reports on biodegradability enhancement of industrial wastewater containing toxic contaminants by CWAO are reviewed. Detailed discussion is made on catalyst deactivation and their mitigation study and also on the various factors which affects the CWAO reaction.

A critical review on metal complexes removal from water using methods based on Fenton-like reactions: Analysis and comparison of methods and mechanisms

Metals mainly exist in the form of complexes in urban wastewater, fresh water and even drinking water, which are difficult to remove and further harm human health. Fenton-like reaction has been used for the removal of metal complexes. Effective removal of metal complexes using Fenton-like reaction requires the removal of both metals and organic ligands, meanwhile, the fate of metals and organic pollutions must be clearly understood. Thus, this review summarizes the relevant research on metal complex removal from using Fenton-like reactions in the past ten years, with the detailed removal approaches and mechanisms analyzed. Electro-, photo-, microwave/ultrasound-Fenton reactions or the synergistic Fenton reaction have been shown to exhibit excellent metal complex treatment capabilities. Furthermore, various catalysts, such as transition metals, bimetals and metal-free catalytic systems can expand the potential applications of Fenton-like reactions. Novel Fenton reaction methods without the addition of metals or H₂O₂, with construction of a dual active center catalyst, or with the introduction of other free radicals, are all worthy of further investigation. Due to increasing levels of environmental metal and organic pollutions remediation requirements, more research is required for the development of economical and efficient novel Fenton-like processes.

Influence of catalysts on co-combustion of sewage sludge and water hyacinth blends as determined by TG-MS analysis

Effects of the three metal carbonates (K₂CO₃, Na₂CO₃, and MgCO₃) were quantified on catalytic co-combustion of the sewage sludge and water hyacinth (SW) blend using a thermogravimetric-mass spectrometric (TG-MS) analysis and kinetics modeling. The main dominating steps of the catalysts were the organic volatile matter release and combustion stage. Weighted mean values of activation energy (E_m) were estimated at 181.18KJ·mol^-1, 199.76KJ·mol^-1, 138.76KJ·mol^-1, and 177.88KJ·mol^-1 for SW, SW+5% K₂CO₃, SW+5% Na₂CO₃, and SW+5% MgCO₃, respectively. The lowest E_m occurred with SW+5% Na₂CO₃. Overall, catalyst effect on co-combustion appeared to be negligible as indicated by Gibbs free energy (ΔG). The normalized intensities of SW+MgCO₃ were strongest. The addition of Na₂CO₃ and MgCO₃ to SW increased flue gases emissions (CO₂, NO₂, SO₂, HCN, and NH₃) of SW, whereas the addition of K₂CO₃ to SW reduced flue gases emissions from the entire combustion process.

Combustion behaviors and kinetics of sewage sludge blended with pulverized coal: With and without catalysts

The combustion behaviors of sewage sludge (SS), pulverized coal (PC), and their blends were studied using a thermogravimetric analyzer. The effect of the mass ratio of SS to PC on the co-combustion characteristics was analyzed. The experiments showed that the ignition performance of the blends improved significantly as the mass percentage of SS increased, but its combustion intensity decreased. The burnout temperature (T_b) and comprehensive combustibility index (S) of the blends were almost unchanged when the mass percentage of SS was less than 10%. However, a high mass percentage of SS (>10%) resulted in a great increase in T_b and a notable decrease in S. Subsequently, the effects of different catalysts (CaO, CeO₂, MnO₂, and Fe₂O₃) on the combustion characteristics and activation energy of the SS/PC blend were investigated. The four catalysts promoted the release and combustion of volatile matters in the blended fuels and shifted their combustion profiles to a low temperature. In addition, their peak separating tendencies were obvious at 350-550 C, resulting in high peak widths. All the catalysts improved combustion activity of the blended fuel and accelerated fixed carbon combustion, which decreased the ignition temperature and burnout temperature of the fuels. CeO₂ had the best catalytic effects in terms of the comprehensive combustion performance and activation energy, followed closely by Fe₂O₃. However, the rare-earth compounds are expensive to be applied in the catalytic combustion process of SS/PC blend at present. Based on both catalytic effects and economy, Fe₂O₃ was potentially an optimal option for catalytic combustion among the tested catalysts.

Catalytic hydrotreatment of kraft lignin into aromatic alcohols over nickel-rhenium supported on niobium oxide catalyst

Direct hydrogenolysis of Kraft lignin was catalyzed over a series of supported Ni or Re catalysts in ethanol solvent. The best results showed that the oil yield of 96.70 wt% was obtained with less char formation at 330 °C for 3 h over 5Ni-5Re/Nb₂O₅ catalyst. Product analysis demonstrated that the monomer yield of 35.41 wt% was given under mild condition, and low-molecular-weight aromatic alcohols were the main component in the liquid products. Ethanol was found to be more effective in H₂ production and facilitated the transformation of phenolic monomers to aromatic chemicals. The results confirmed that the optimal 5Ni-5Re/Nb₂O₅ catalyst had superior oxophilicity and appropriate acid sites, which improved the ability to directly remove the methoxyl and hydroxyl groups of lignin-derived phenolic compounds without aromatic ring hydrogenation. In addition, the temperature, time and solvent effects on the lignin depolymerization were also investigated.

Review on the treatment of organic wastewater by discharge plasma combined with oxidants and catalysts

Discharge plasma technology is a new advanced oxidation technology for water treatment, which includes the effects of free radical oxidation, high energy electron radiation, ultraviolet light hydrolysis, and pyrolysis. In order to improve the energy efficiency in the plasma discharge processes, many efforts have been made to combine catalysts with discharge plasma technology. Some heterogeneous catalysts (e.g., activated carbon, zeolite, TiO₂) and homogeneous catalysts (e.g., Fe²⁺/Fe³⁺, etc.) have been used to enhance the removal of pollutants by discharge plasma. In addition, some reagents of in situ chemical oxidation (ISCO) such as persulfate and percarbonate are also discussed. This article introduces the research progress of the combined systems of discharge plasma and catalysts/oxidants, and explains the different reaction mechanisms. In addition, physical and chemical changes in the plasma catalytic oxidation system, such as the effect of the discharge process on the catalyst, and the changes in the discharge state and solution conditions caused by the catalysts/oxidants, were also investigated. At the same time, the potential advantages of this system in the treatment of different organic wastewater were briefly reviewed, covering the degradation of phenolic pollutants, dyes, and pharmaceuticals and personal care products. Finally, some suggestions for future water treatment technology of discharge plasma are put forward. This review aims to provide researchers with a deeper understanding of plasma catalytic oxidation system and looks forward to further development of its application in water treatment.

Breaking the Crowther limit: combining depth-sectioning and tilt tomography for high-resolution, wide-field 3D reconstructions

To date, high-resolution (<1 nm) imaging of extended objects in three-dimensions (3D) has not been possible. A restriction known as the Crowther criterion forces a tradeoff between object size and resolution for 3D reconstructions by tomography. Further, the sub-Angstrom resolution of aberration-corrected electron microscopes is accompanied by a greatly diminished depth of field, causing regions of larger specimens (>6 nm) to appear blurred or missing. Here we demonstrate a three-dimensional imaging method that overcomes both these limits by combining through-focal depth sectioning and traditional tilt-series tomography to reconstruct extended objects, with high-resolution, in all three dimensions. The large convergence angle in aberration corrected instruments now becomes a benefit and not a hindrance to higher quality reconstructions. A through-focal reconstruction over a 390 nm 3D carbon support containing over 100 dealloyed and nanoporous PtCu catalyst particles revealed with sub-nanometer detail the extensive and connected interior pore structure that is created by the dealloying instability.

A Review of In-Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions

Electrocatalytic oxygen reduction reaction (ORR) is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal-O2/air batteries, etc. However, the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process, and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction. This makes them difficult to be accurately captured, making the identification of ORR active sites and the elucidation of ORR mechanisms difficult. Thus, it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR. This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts. Specifically, the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized, such as phase, valence, electronic transfer, coordination, and spin states varies. In-situ revelation of intermediate adsorption/desorption behavior, and the real-time monitoring of the product nucleation, growth, and reconstruction evolution are equally emphasized in the discussion. Other interference factors, as well as in-situ signal assignment with the aid of theoretical calculations, are also covered. Finally, some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed.

Hydrothermal liquefaction of de-oiled Jatropha curcas cake using Deep Eutectic Solvents (DESs) as catalysts and co-solvents

Biomass liquefaction using ionic liquids (ILs) as catalysts has received appreciable attention, in renewable fuels and chemicals production, recently. However, issues associated with the production cost, long reaction time and use of volatile solvents are undeniably challenging. Thus, Deep Eutectic Solvents (DESs) emerged as promising and potential ILs substitutes. The hydrothermal liquefaction of de-oiled Jatropha curcas cake was catalyzed by four synthesized DESs as catalysts and co-solvents for selective extraction. Proximate and ultimate analyses including ash, moisture and carbon contents of bio-crude produced varied slightly. The higher heating values found ranges from 21.15 ± 0.82 MJ/kg to 24.30 ± 0.98 MJ/kg. The bio-crude yields obtained using ChCl-KOH DES was 43.53 wt% and ChCl-p-TsOH DES was 38.31 wt%. Bio-crude yield using ChCl-FeCl3 DES was 30.80 wt%. It is suggested that, the selectivity of bio-crude could be improved, by using DESs as catalyst and co-solvent in HTL of biomass such as de-oiled J. curcas cake.

Generation and identification of 1O2 in catalysts/peroxymonosulfate systems for water purification

Catalysts for peroxymonosulfate (PMS) activation are appealing in the purification of organic wastewater. Singlet oxygen (1O2) is widely recognized as a crucial reactive species for degrading organic contaminants in catalysts/PMS systems due to its adamant resistance to inorganic anions, high selectivity, and broad pH applicability. With the rapid growth of studies on 1O2 in catalysts/PMS systems, it becomes necessary to provide a comprehensive review of its current state. This review highlights recent advancements concerning 1O2 in catalysts/PMS systems, with a primary focus on generation pathways and identification methods. The generation pathways of 1O2 are summarized based on whether (distinguished by the geometric structures of metal species) or not (distinguished by the active sites) the metal element is included in the catalysts. Furthermore, this review thoroughly discusses the influence of metal valence states and metal species with different geometric structures on 1O2 generation. Various potential strategies are explored to regulate the generation of 1O2 from the perspective of catalyst design. Identification methods of 1O2 primarily include electron paramagnetic resonance (EPR), quenching experiments, reaction in D2O solution, and chemical probe tests in catalysts/PMS systems. The principles and applications of these methods are presented comprehensively along with their applicability, possible disagreements, and corresponding solutions. Besides, an identifying procedure on the combination of main identification methods is provided to evaluate the role of 1O2 in catalysts/PMS systems. Lastly, several perspectives for further studies are proposed to facilitate developments of 1O2 in catalysts/PMS systems.

A review of the next-generation biochar production from waste biomass for material applications

The development of carbonaceous materials such as biochar has triggered a hot spot in materials application. Carbon material derived from biomass could be a vital platform for energy storage and conversion. Biochar-based materials deliver a novel approach to deal with the current energy-related challenges. To design and utilize the maximum potential of biochar for environmentally sustainable applications, it is crucial to understand the recent progress and advancement in molecular structures of biochar to discover a new possible field to simplify structural application networks. However, most of the studies demonstrated the application of biochar in the form of soil enhancers and bio-adsorbents, reducing soil emissions of greenhouse gases and as fertilizers. The present review on biochar highlighted the application of biochar-based materials in various energy storage and conversion sectors, comprising different types of conversion technologies, biochar formation mechanisms, modification techniques on biochar surface chemistry and its functionality, catalysts, biochar application in energy storage gadgets such as supercapacitors and nanotubes, bio-based composite materials and inorganic based composites materials. Finally, this review addressed some vital outlooks on the prospect of the functionalization and best utilization of biochar-supported materials in numerous energy storage and conversion fields. After reviewing the literature, it was directed that advanced and in-depth research is essential for structural analysis and separation, considering the macroscopic and microscopic evidence of the formed structural design of biochar for specific applications.

Synthesis and pharmacological properties of polysubstituted 2-amino-4H-pyran-3-carbonitrile derivatives

2-Amino-3-cyano-4H-chromenes are structural core motifs that received increasing attention in the last years due to their interesting potential pharmacological properties. In this review, the synthetic methods for these compounds are classified based on the type of catalyst in the pertinent reactions. In addition, the wide range of pharmacological properties of these compounds is covered in a separate section.

Comparison of real waste (MSW and MPW) pyrolysis in batch reactor over different catalysts. Part II: contaminants, char and pyrolysis oil properties

Pyrolysis of real wastes (MPW and MSW) has been investigated at 500°C, 550°C and 600°C using Y-zeolite, β-zeolite, equilibrium FCC, MoO3, Ni-Mo-catalyst, HZSM-5 and Al(OH)3 as catalysts. The viscosity of pyrolysis oils could be decreased by the using of catalysts, especially by β-zeolite and MoO3. Both carbon frame and double bound isomerization was found in case of thermo-catalytic pyrolysis. Char morphology and texture analysis showed more coke deposits on the catalyst surface using MSW raw material. Pyrolysis oils had K, S, P Cl, Ca, Zn, Fe, Cr, Br and Sb as contaminants; and the concentrations of K, S, P, Cl and Br could be decreased by the using of catalysts.

Synthesis of novel palladium(0) nanocatalysts by microorganisms from heavy-metal-influenced high-alpine sites for dehalogenation of polychlorinated dioxins

In a search for new aqueous-phase systems for catalyzing reactions of environmental and industrial importance, we prepared novel biogenerated palladium (Pd) nanocatalysts using a "green" approach based on microorganisms isolated from high-alpine sites naturally impacted by heavy metals. Bacteria and fungi were enriched and isolated from serpentinite-influenced ponds (Totalp region, Parsenn, near Davos, Graubünden, Switzerland). Effects on growth dynamics were monitored using an automated assay in 96-well microtiter plates, which allowed for simultaneous cultivation and on-line analysis of Pd(II)- and Ni(II)-mediated growth inhibition. Microorganisms from Totalp ponds tolerated up to 3mM Pd(II) and bacterial isolates were selected for cultivation and reductive synthesis of Pd(0) nanocatalysts at microbial interfaces. During reduction of Pd(II) with formate as the electron donor, Pd(0) nanoparticles were formed and deposited in the cell envelope. The Pd(0) catalysts produced in the presence of Pd(II)-tolerant Alpine Pseudomonas species were catalytically active in the reductive dehalogenation of model polychlorinated dioxin congeners. This is the first report which shows that Pd(0) synthesized in the presence of microorganisms catalyzes the reductive dechlorination of polychlorinated dibenzo-p-dioxins (PCDDs). Because the "bioPd(0)" catalyzed the dechlorination reactions preferably via non-lateral chlorinated intermediates, such a pathway could potentially detoxify PCDDs via a "safe route". It remains to be determined whether the microbial formation of catalytically active metal catalysts (e.g., Zn, Ni, Fe) occurs in situ and whether processes involving such catalysts can alter the fate and transport of persistent organic pollutants (POPs) in Alpine habitats.

Sonochemical water splitting in the presence of powdered metal oxides

Kinetics of hydrogen formation was explored as a new chemical dosimeter allowing probing the sonochemical activity of argon-saturated water in the presence of micro- and nano-sized metal oxide particles exhibiting catalytic properties (ThO2, ZrO2, and TiO2). It was shown that the conventional sonochemical dosimeter based on H2O2 formation is hardly applicable in such systems due to catalytic degradation of H2O2 at oxide surface. The study of H2 generation revealed that at low-frequency ultrasound (20 kHz) the sonochemical water splitting is greatly improved for all studied metal oxides. The highest efficiency is observed for relatively large micrometric particles of ThO2 which is assigned to ultrasonically-driven particle fragmentation accompanied by mechanochemical water molecule splitting. The nanosized metal oxides do not exhibit particle size reduction under ultrasonic treatment but nevertheless yield higher quantities of H2. The enhancement of sonochemical water splitting in this case is most probably resulting from better bubble nucleation in heterogeneous systems. At high-frequency ultrasound (362 kHz), the effect of metal oxide particles results in a combination of nucleation and ultrasound attenuation. In contrast to 20 kHz, micrometric particles slowdown the sonolysis of water at 362 kHz due to stronger attenuation of ultrasonic waves while smaller particles show a relatively weak and various directional effects.

Ultrasound-assisted synthesis of pyrimidines and their fused derivatives: A review

The pyrimidine scaffold is present in many bioactive drugs; therefore, efficient synthetic routes that provide shorter reaction times, higher yields, and site-selective reactions are constantly being sought. Ultrasound (US) irradiation has emerged as an alternative energy source in the synthesis of these heterocyclic scaffolds, and over the last ten years there has been a significant increase in the number of publications mentioning US in either the construction or derivatization of the pyrimidine core. This review presents a detailed summary (with 140 references) of the effects of US (synergic or not) on the construction and derivatization of the pyrimidine core through classical reactions (e.g., multicomponent, cyclocondensation, cycloaddition, and alkylation reactions). The main points that were taken into consideration are as follows: chemo- and regioselectivity issues, and the results of conventional heating methods compared to US and mechanistic insights that are also presented and discussed for key reactions.

Green in situ immobilization of gold and silver nanoparticles on bacterial nanocellulose film using Punica granatum peels extract and their application as reusable catalysts

In this study, Punica granatum peels extract induced in situ deposition was applied to prepare Au and Ag nanoparticles on bacterial nanocellulose film. Bacterial nanocellulose provided as an eco-friendly and excellent support for the interaction of P. granatum peel biomolecules and further reduction of Au and Ag ions. Meanwhile, a possible in situ growth mechanism of Au and Ag on bacterial cellulose by P. granatum peel extract biomolecules was presented. Further, the metal nanoparticles incorporated bacterial cellulose films were used to catalyze the reduction of 4-nitrophenol. The results of the present study indicated excellent catalytic reduction properties of Au and Ag nanocellulose films for 4 consecutive cycles. In addition, Au and Ag incorporated cellulose nanofiber films exhibited superior antioxidant activity and improved mechanical properties compared to pristine cellulose nanofiber film. The findings of this study may provide new insights and broad application of bacterial cellulose and green synthesis method for the development of various metal-cellulose composites.