Environmental Catalysis: Present and Future

Downshift of the Ni d band center over Ni nanoparticles in situ confined within an amorphous silicon nitride matrix

Herein, nanocomposites made of Ni nanoparticles in situ distributed in an amorphous silicon nitride (Ni/a-Si3N4) matrix, on the one hand, and within an amorphous silicon dioxide (Ni/a-SiO2) matrix, on the other hand, were synthesized from the same Ni-modified polysilazane precursor. In both compounds, the Ni/Si atomic ratio (0.06-0.07), average Ni nanocrystallite size (7.0-7.6 nm) and micro/mesoporosity of the matrix were rigorously fixed. Hydrogen (H2)-temperature-programmed desorption (TPD) profile analysis revealed that the activation energy for H2 desorption at about 100-130 °C evaluated for the Ni/a-Si3N4 sample (47.4 kJ mol-1) was lower than that for the Ni/a-SiO2 sample (68.0 kJ mol-1). Mechanistic study with X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations revealed that, at Ni nanoparticle/matrix heterointerfaces, Ni becomes more covalently bonded to N atoms in the a-Si3N4 matrix compared to O atoms in the a-SiO2 matrix. Therefore, based on experimental and theoretical studies, we elucidated that nickel-nitrogen (Ni-N) interactions at the heterointerface lead to remarkable Ni d band broadening and downshifting of the d band center relative to those generated by Ni-oxygen (Ni-O) interactions at the heterointerface. This facilitates H2 desorption, as experimentally observed in the Ni/a-Si3N4 sample.

Fabrication and characterization of novel, cost-effective graphitic carbon nitride/Fe coated textile nanocomposites for effective degradation of dyes and biohazards

Textile-based photocatalysts are the new materials that can be utilized as an effective sustainable solution for biochemical hazards. Hence, we aimed to develop a sustainable, cost-effective, and facile approach for the fabrication of photocatalytic fabric using graphitic carbon nitride (g-C3N4) and ferric-based multifunctional nanocomposite. Bulk g-C3N4 was prepared from urea by heating it at 500 °C for 2 h. The structure of ball-milled g-C3N4 was engineered by doping with various amounts of iron (III) chloride hexahydrate solution (0.006 mol/L) and sintered at 90 °C for 24 h to prepare g-C3N4-nanosheets/α-Fe2O3 composites. These nanocomposites have potential avenues towards rational designing of g-C3N4 for improved photocatalytic, antibacterial, and antiviral behavior. The prepared nanocomposite was characterized for its surface morphology, chemical composition, crystal structure, catalytic, antibacterial, and antiviral behavior. The fabrication of ferric doped g-C3N4 nanocomposites was characterized by SEM, EDX, FTIR, and XRD analysis. The coated fabric nanocomposite was characterized for methylene blue dye degradation under visible light, antibacterial and antiviral behavior. The developed textile-based photocatalyst has been found with very good recyclability with photocatalytic degradation of dye up to 99.9 % when compared to conventional g-C3N4 powder-based photocatalyst.

Synthesis and Crystal Structures of Bis(diallydithiocarbamato)zinc(II) and Silver(I) Complexes: Precursors for Zinc Sulfide and Silver Sulfide Nanophotocatalysts

We report the preparation and crystal structures of bis(diallydithiocarbamato)zinc(II) and silver(I) complexes. The compounds were used as single-source precursors to prepare zinc sulfide and silver sulfide nanophotocatalysts. The molecular structure of bis(diallydithiocarbamato)zinc(II) consists of a dimeric complex in which each zinc(II) ion asymmetrically coordinates with two diallydithiocarbamato anions in a bidentate chelating mode, and the centrosymmetrically related molecule is bridged through the S-atom that is chelated to the adjacent zinc(II) ion to form a distorted trigonal bipyramidal geometry around the zinc(II) ions. The molecular structure of bis(diallydithiocarbamato)silver(I) formed a cluster complex consisting of a trimetric Ag₃S₃ molecule in which the diallydithiocarbamato ligand is coordinated to all the Ag(I) ions. The complexes were thermolyzed in dodecylamine, hexadecylamine, and octadecylamine (ODA) to prepare zinc sulfide and silver sulfide nanoparticles. The powder X-ray diffraction patterns of the zinc sulfide nanoparticles correspond to the hexagonal wurtzite while silver sulfide is in the acanthite crystalline phase. The high-resolution transmission electron microscopy images show that quantum dot zinc sulfide nanoparticles are obtained with particle sizes ranging between 1.98 and 5.49 nm, whereas slightly bigger silver sulfide nanoparticles are obtained with particle sizes of 2.70-13.69 nm. The surface morphologies of the ZnS and AgS nanoparticles capped with the same capping agent are very similar. Optical studies revealed that the absorption band edges of the as-prepared zinc sulfide and silver sulfide nanoparticles were blue-shifted with respect to their bulk materials with some surface defects. The zinc sulfide and silver sulfide nanoparticles were used as nanophotocatalysts for the degradation of bromothymol blue (BTB) and bromophenol blue (BPB). ODA-capped zinc sulfide is the most efficient photocatalyst and degraded 87% of BTB and 91% of BPB.

Mechanistic insights into aerobic oxidative cleavage of glycol catalyzed by an Anderson-type polyoxometalate [IMo6O24]5

A computational investigation of the aerobic oxidative C-C bond cleavage reaction of glycol catalyzed by an Anderson-type heteropolyanion HPA [IMo₆O₂₄]^5- in the presence of acetonitrile as solvent has been performed at the WB97XD/6-31G(d,p)/lanl2dz level. Two reaction pathways have been identified. The catalytic cycle of each pathway consists of three steps: oxidation cleavage of a glycol molecule by the HPA, oxidation of the HPA by one dioxygen molecule, and, finally, oxidation of a second glycol and regeneration of the catalyst. These reaction pathways have been thoroughly investigated in terms of energetic, natural bond orbital (NBO), natural charges, and geometrical parameters. It is found that (i) even though the top oxygen atoms of the Anderson heteropolyanion are not the most negatively charged ones, they are more likely to react with the diol hydroxyl groups, (ii) a direct relationship between the presence of the iodine ion I(VII) and the studied oxidation reaction could not be identified, and (iii) in terms of energy, the transfer of the two hydrogen atoms is the most energetic step.

Azide-Alkyne Cycloaddition Catalyzed by Copper(I) Coordination Polymers in PPM Levels Using Deep Eutectic Solvents as Reusable Reaction Media: A Waste-Minimized Sustainable Approach

Two air-stable copper(I)-halide coordination polymers 1 and 2 with NNS and NNO ligand frameworks were synthesized and successfully utilized as efficient catalysts in an important organic reaction, namely, copper-catalyzed azide-alkyne cycloaddition, which is generally conducted in a mixture of water and organic solvents. The azide-alkyne "click" reaction was successfully conducted in pure water at r.t. under aerobic conditions. Other green solvents, including ethanol and glycerol, were also effectively used. Finally, deep eutectic solvents as green and sustainable reaction media were successfully utilized. In deep eutectic solvents, complete conversion with excellent isolated yield was achieved in a short period of time (1 h) with low catalyst loading (1 mol %) at r.t. Full conversion could also be achieved within 24 h with ppm-level (50 ppm) catalyst loading at 70 °C. Optimized reaction conditions were used for the syntheses of a large number of 1,4-disubstituted 1,2,3-triazoles with various functionalities. Triazole products were easily isolated by simple filtration. The reaction media, such as water and deep eutectic solvents, were recovered and recycled in three consecutive runs. The limited waste production is reflected in a very low E-factor (0.3-2.8). Finally, the CHEM21 green metrics toolkit was employed to evaluate the sustainability credentials of different optimized protocols in various green solvents such as water, ethanol, glycerol, and deep eutectic solvents.

Chitin-Derived Nanocatalysts for Reductive Amination Reactions

Chitin, the second most abundant biopolymer in the planet after cellulose, represents a renewable carbon and nitrogen source. A thrilling opportunity for the valorization of chitin is focused on the preparation of biomass-derived N-doped carbonaceous materials. In this contribution, chitin-derived N-doped carbons were successfully prepared and functionalized with palladium metal nanoparticles. The physicochemical properties of these nanocomposites were investigated following a multi-technique strategy and their catalytic activity in reductive amination reactions was explored. In particular, a biomass-derived platform molecule, namely furfural, was upgraded to valuable bi-cyclic compounds under continuous flow conditions.

Ion-in-Conjugation: A Promising Concept for Multifunctional Organic Semiconductors

Most organic semiconductors (OSCs) consist of conjugated skeletons with flexible peripheral chains. Their weak intermolecular interactions from dispersion and induction forces result in environmental susceptibilities and are unsuitable for many multifunctional applications where direct exposure to external environments is unavoidable, such as gas absorption, chemical sensing, and catalysis. To exploit the advantages of inorganic semiconductors in OSCs, ion-in-conjugation (IIC) materials are proposed. An IIC material refers to any conjugated material (molecules, polymers, and crystals) in Kekule's structural formula containing stoichiometric ionic states in its conjugated backbone in the electronic ground state. In this review, the definitions, structures, synthesis, properties, and applications of IIC materials are described briefly. Four types of IIC material, including zwitterionic conjugated molecules/polymers, conjugated ionic dyes, π-d conjugated molecules and polymers, and coordinatively doped polymers, are reported. Their applications in gas sensing, humidity sensing, resistive memory devices, and thermal/photo-/electro-catalysis are demonstrated. The challenges and opportunities for future research are also discussed. It is expected that this work will inspire the design of new organic electronic information materials.

CeFeO3-CeO2-Fe2O3 Systems: Synthesis by Solution Combustion Method and Catalytic Performance in CO2 Hydrogenation

Rare-earth orthoferrites have found wide application in thermocatalytic reduction-oxidation processes. Much less attention has been paid, however, to the production of CeFeO₃, as well as to the study of its physicochemical and catalytic properties, in particular, in the promising process of CO₂ utilization by hydrogenation to CO and hydrocarbons. This study presents the results of a study on the synthesis of CeFeO₃ by solution combustion synthesis (SCS) using various fuels, fuel-to-oxidizer ratios, and additives. The SCS products were characterized by XRD, FTIR, N₂-physisorption, SEM, DTA-TGA, and H₂-TPR. It has been established that glycine provides the best yield of CeFeO₃, while the addition of NH₄NO₃ promotes an increase in the amount of CeFeO₃ by 7-12 wt%. In addition, the synthesis of CeFeO₃ with the participation of NH₄NO₃ makes it possible to surpass the activity of the CeO₂-Fe₂O₃ system at low temperatures (300-400 °C), as well as to increase selectivity to hydrocarbons. The observed effects are due to the increased gas evolution and ejection of reactive FeO_x nanoparticles on the surface of crystallites, and an increase in the surface defects. CeFeO₃ obtained in this study allows for achieving higher CO₂ conversion compared to LaFeO₃ at 600 °C.

Metal-Free N-Doped Carbons for Solvent-Less CO2 Fixation Reactions: A Shrimp Shell Valorization Opportunity

High anthropogenic CO₂ emissions are among the main causes of climate change. Herein, we investigate the use of CO₂ for the synthesis of organic cyclic carbonates on metal-free nitrogen-doped carbon catalysts obtained from chitosan, chitin, and shrimp shell wastes, both in batch and in continuous flow (CF). The catalysts were characterized by N₂ physisorption, CO₂-temperature-programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and CNHS elemental analysis, and all reactivity tests were run in the absence of solvents. Under batch conditions, the catalyst obtained by calcination of chitin exhibited excellent performance in the conversion of epichlorohydrin (selected as a model epoxide), resulting in the corresponding cyclic carbonate with 96% selectivity at complete conversion, at 150 °C and 30 bar CO₂, for 4 h. On the other hand, in a CF regime, a quantitative conversion and a carbonate selectivity >99% were achieved at 150 °C, by using the catalyst obtained from shrimp waste. Remarkably, the material displayed an outstanding stability over a reaction run time of 180 min. The robustness of the synthetized catalysts was confirmed by their good operational stability and reusability: ca. (75 ± 3)% of the initial conversion was achieved/retained by all systems, after six recycles. Also, additional batch experiments proved that the catalysts were successful on different terminal and internal epoxides.

Noncovalent Assembly and Catalytic Activity of Hybrid Materials Based on Pd Complexes Adsorbed on Multiwalled Carbon Nanotubes, Graphene, and Graphene Nanoplatelets

Green catalysts with excellent performance in Cu-free Sonogashira coupling reactions can be prepared by the supramolecular decoration of graphene surfaces with Pd(II) complexes. Here we report the synthesis, characterization, and catalytic properties of new catalysts obtained by the surface decoration of multiwalled carbon nanotubes (MWCNTs), graphene (G), and graphene nanoplatelets (GNPTs) with Pd(II) complexes of tetraaza-macrocyclic ligands bearing one or two anchor functionalities. The decoration of these carbon surfaces takes place under environmentally friendly conditions (water, room temperature, aerobic) in two steps: (i) π–π stacking attachment of the ligand via electron-poor anchor group 6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxo-pyrimidine and (ii) Pd(II) coordination from PdCl₄^2–. Ligands are more efficiently adsorbed on the flat surfaces of G and GNPTs than on the curved surfaces of MWCNTs. All catalysts work very efficiently under mild conditions (50 °C, aerobic, 7 h), giving a similar high yield (90% or greater) in the coupling of iodobenzene with phenylacetylene to form diphenylacetylene in one catalytic cycle, but catalysts based on G and GNPTs (especially on GNPTs) provide greater catalytic efficiency in reuse (four cycles). The study also revealed that the active centers of the ligand-Pd type decorating the support surfaces are much more efficient than the Pd(0) and PdCl₄^2– centers sharing the same surfaces. All of the results allow a better understanding of the structural factors to be controlled in order to obtain an optimal efficiency from similar catalysts based on graphene supports.

Green catalysts with high efficiency in the Cu-free Sonogashira C−C coupling reactions can be prepared by the supramolecular functionalization of carbon materials.

Soybean Oil Epoxidation Catalyzed by a Functionalized Metal–Organic Framework with Active Dioxo-Molybdenum (VI) Centers

In this work, a functionalized gallium metal–organic framework with active dioxo-molybdenum (VI) centers was evaluated as a catalyst in the epoxidation of soybean oil using tert-butyl-hydroperoxide as an oxidizing agent. The influence of the reaction time, temperature, and concentration of the oxidizing agent was studied, and it was demonstrated that the highest epoxide selectivity was obtained at 110 °C after 4 h of reaction (29% conversion and 91% selectivity) using a soybean oil/oxidizing agent ratio of 1/2. The stability of the metal–organic framework was confirmed by infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy EDS. The stability tests demonstrated that the catalyst could be reused in the catalytic process for the recovery of vegetable oils.

Graphical Abstract

Photocatalytic Materials Obtained from E-Waste Recycling: Review, Techniques, Critique, and Update

Waste-derived materials obtained from the recovery and recycling of electronic waste (e-waste) such as batteries and printed circuit boards have attracted enormous attention from academia and industry in recent years, especially due to their eco-friendly nature and the massive increment in e-waste due to technological development. Several investigations in the literature have covered the advances achieved so far. Meanwhile, photocatalytic applications are especially of interest since they maintain mutual benefits and can be used for H2 production from solar water splitting based on semiconductor processing as a proper environmentally friendly technique for solar energy conversion. In addition, they can be utilized to degrade a variety of organic and non-organic contaminations. Nonetheless, to the best of the authors’ knowledge, there has not been any comprehensive review that has specifically been focused on e-waste-derived photocatalytic materials. In this regard, the present work is dedicated to thoroughly discussing the related mechanisms, strategies, and methods, as well as the various possible photocatalysts synthesized from e-wastes with some critiques in this field. This brief overview can introduce modern technologies and promising possibilities for e-waste valorization, photocatalytic processes, and new photocatalytic degradation methods of eco-friendly nature. This paper discusses various e-waste-obtained photocatalytic materials, synthesis procedures, and applications, as well as several types of e-waste, derived materials such as TiO2, ZnO, indium tin oxide, and a variety of sulfide- and ferrite-based photocatalytic materials.

Continuous Flow Glycolipid Synthesis Using a Packed Bed Reactor

Glycolipids are a class of biodegradable biosurfactants that are non-toxic and based on renewables, making them a sustainable alternative to petrochemical surfactants. Enzymatic synthesis allows a tailor-made production of these versatile compounds using sugar and fatty acid building blocks with rationalized structures for targeted applications. Therefore, glycolipids can be comprehensively designed to outcompete conventional surfactants regarding their physicochemical properties. However, enzymatic glycolipid processes are struggling with both sugars and fatty acid solubilities in reaction media. Thus, continuous flow processes represent a powerful tool in designing efficient syntheses of sugar esters. In this study, a continuous enzymatic glycolipid production catalyzed by Novozyme 435® is presented as an unprecedented concept. A biphasic aqueous–organic system was investigated, allowing for the simultaneous solubilization of sugars and fatty acids. Owing to phase separation, the remaining non-acylated glucose was easily separated from the product stream and was refed to the reactor forming a closed-loop system. Productivity in the continuous process was higher compared to a batch one, with space–time yields of up to 1228 ± 65 µmol/L/h. A temperature of 70 °C resulted in the highest glucose-6-O-decanoate concentration in the Packed Bed Reactor (PBR). Consequently, the design of a continuous biocatalytic production is a step towards a more competitive glycolipid synthesis in the aim for industrialization.

Biocatalysis as Key to Sustainable Industrial Chemistry

The role and power of biocatalysis in sustainable chemistry has been continuously brought forward step by step to its present outstanding position. The problem-solving capabilities of biocatalysis have been realized by numerous substantial achievements in biology, chemistry and engineering. Advances and breakthroughs in the life sciences and interdisciplinary cooperation with chemistry have clearly accelerated the implementation of biocatalytic synthesis in modern chemistry. Resource-efficient biocatalytic manufacturing processes have already provided numerous benefits to sustainable chemistry as well as customer-centric value creation in the pharmaceutical, food, flavor, fragrance, vitamin, agrochemical, polymer, specialty, and fine chemical industries. Biocatalysis can make significant contributions not only to manufacturing processes, but also to the design of completely new value-creation chains. Biocatalysis can now be considered as a key enabling technology to implement sustainable chemistry.

Glycerol Valorization towards a Benzoxazine Derivative through a Milling and Microwave Sequential Strategy

Glycerol and aminophenol intermolecular condensation has been investigated through a milling and microwave-assisted sequential strategy, towards the synthesis of a benzoxaxine derivative. Mechanochemical activation prior to the microwave-assisted process could improve the probability of contact between the reagents, and greatly favors the higher conversion of aminophenol. At the same time, following a mechanochemical-microwave sequential approach could tune the selectivity towards the formation of a benzoxazine derivative, which could find application in a wide range of biomedical areas.

Pd Doped on TCH@SBA-15 Nanocomposites: Fabrication and Application as a New Organometallic Catalyst in the Three-Component Synthesis of N-Benzo-imidazo- or -thiazole-1,3-thiazolidinones

In this study, Pd(II)/TCH@SBA-15 nanocomposites were synthesized by the grafting of 3-chloropropyltriethoxysilane and thiocarbohydrazide on SBA-15 and subsequent deposition of palladium acetates through the ligand-metal coordination method. The structure and morphology of this nanoporous nanocomposite was thoroughly identified by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, atomic absorption spectroscopy, and Brunauer-Emmett-Teller instrumental analyses. Furthermore, the catalytic activity of this nanocomposite was investigated in the three-component synthesis of 3-benzimidazolyl or benzothiazoleyl-1,3-thiazolidin-4-ones via a reaction of 2-aminobenzimidazole or 2-aminobenzothiazole, aromatic aldehydes, and thioglycolic acid in an acetone-H2O mixture under green conditions. The Pd/TCH@SBA-15 nanocatalyst is demonstrated to exhibit a high catalyzing activity in the three-component reaction of the synthesis of N-heterocyclic thiazolidinones with good to excellent yields. One of the advantages of the suggested method is the direct application of the thiocarbohydrazide ligand to stabilize Pd nanoparticles through formation of a stable ring complex without creating an additional Schiff base step. Moreover, this organometallic nanocatalyst can be recycled several times with no notable leaching or loss of performance.

A Waste-Minimized Approach to Cassar-Heck Reaction Based on POLITAG-Pd0 Heterogeneous Catalyst and Recoverable Acetonitrile Azeotrope

Three different Pd0 -based heterogeneous catalysts were developed and tested in the Cassar-Heck reaction (i. e., copper-free Sonogashira reaction) aiming at the definition of a waste minimized protocol. The cross-linked polymeric supports used in this investigation were designed to be adequate for different reaction media and were decorated with different pincer-type ionic ligands having the role of stabilizing the formation and dimension of palladium nanoparticles. Among the ionic tags tested, bis-imidazolium showed the best performances in terms of efficiency and durability of the metal catalytic system. Eventually, aqueous acetonitrile azeotrope was selected as the reaction medium as it allowed the best catalytic efficiency combined with easy recovery and reuse. Finally, the synergy between the selected catalyst and reaction medium allowed to obtain highly satisfactory isolated yields of a variety of substrates while using a low amount of metal catalyst. The high performance of the designed POLymeric Ionic TAG (POLITAG)-Pd0 , along with its good selectivity achieved in a copper-free process, also led to a simplified purification procedure allowing the minimization of the waste generated as also proven by the very low E-factor values (1.4-5) associated.

Heterogeneous Photocatalysis

Heterogeneous photocatalysis is a subtype of catalysis that refers to chemical processes catalysed by a semiconductor solid under proper illumination conditions [...]

Recovery/Reuse of Heterogeneous Supported Spent Catalysts

The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.

The design and synthesis of heterogeneous catalysts for environmental applications

With the rapid advancements in synthetic strategies, the field of heterogeneous catalysis has expanded enormously over the last few decades, and today it is one of the foremost areas in energy and environmental research. Various templating and non-templating routes for designing porous nanomaterial-based catalysts starting from precursor building blocks are highlighted here. CO₂ and biomass are two major abundant resources that can be utilized as feedstocks for various heterogeneous catalytic processes. These are described in brief, together with environmental clean-up applications and future perspectives for addressing environmental issues.

CO2 hydrogenation over functional nanoporous polymers and metal-organic frameworks

CO₂ is one of the major environmental pollutants and its mitigation is attracting huge attention over the years due to continuous increase in this greenhouse gas emission in the atmosphere. Being environmentally hazardous and plentiful presence in nature, CO₂ utilization as C1 resource into fuels and feedstock is very demanding from the green chemistry perspectives. To accomplish this CO₂ utilization issue, functional organic materials like porous organic polymers (POPs), covalent organic frameworks (COFs) as well as organic-inorganic hybrid materials like metal-organic frameworks (MOFs), having characteristics of large surface area, high thermal stability and tunability in the porous nanostructures play significant role in designing the suitable catalyst for the CO₂ hydrogenation reactions. Although CO₂ hydrogenation is a widely studied and emerging area of research, till date review exclusively focused on designing POPs, COFs and MOFs bearing reactive functional groups is very limited. A thorough literature review on this matter will enrich our knowledge over the CO₂ hydrogenation processes and the catalytic sites responsible for carrying out these chemical transformations. We emphasize recent state-of-the art developments in POPs/COFs/MOFs having unique functionalities and topologies in stabilizing metallic NPs and molecular complexes for the CO₂ reduction reactions. The major differences between MOFs and porous organics are critically summarized in the outlook section with the aim of the future benefit in mitigating CO₂ emission from ambient air.

In situandoperandoelectron microscopy in heterogeneous catalysis-insights into multi-scale chemical dynamics

This review features state-of-the-artin situandoperandoelectron microscopy (EM) studies of heterogeneous catalysts in gas and liquid environments during reaction. Heterogeneous catalysts are important materials for the efficient production of chemicals/fuels on an industrial scale and for energy conversion applications. They also play a central role in various emerging technologies that are needed to ensure a sustainable future for our society. Currently, the rational design of catalysts has largely been hampered by our lack of insight into the working structures that exist during reaction and their associated properties. However, elucidating the working state of catalysts is not trivial, because catalysts are metastable functional materials that adapt dynamically to a specific reaction condition. The structural or morphological alterations induced by chemical reactions can also vary locally. A complete description of their morphologies requires that the microscopic studies undertaken span several length scales. EMs, especially transmission electron microscopes, are powerful tools for studying the structure of catalysts at the nanoscale because of their high spatial resolution, relatively high temporal resolution, and complementary capabilities for chemical analysis. Furthermore, recent advances have enabled the direct observation of catalysts under realistic environmental conditions using specialized reaction cells. Here, we will critically discuss the importance of spatially-resolvedoperandomeasurements and the available experimental setups that enable (1) correlated studies where EM observations are complemented by separate measurements of reaction kinetics or spectroscopic analysis of chemical species during reaction or (2) real-time studies where the dynamics of catalysts are followed with EM and the catalytic performance is extracted directly from the reaction cell that is within the EM column or chamber. Examples of current research in this field will be presented. Challenges in the experimental application of these techniques and our perspectives on the field's future directions will also be discussed.

Recent catalytic routes for the preparation and the upgrading of biomass derived furfural and 5-hydroxymethylfurfural

Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are generally obtained from cellulose and hemicellulose fractions of biomass via the acid-catalyzed dehydration of their relative C6-C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.

State-of-the-Art of Eggshell Waste in Materials Science: Recent Advances in Catalysis, Pharmaceutical Applications, and Mechanochemistry

Eggshell waste is among the most abundant waste materials coming from food processing technologies. Despite the unique properties that both its components (eggshell, ES, and eggshell membrane, ESM) possess, it is very often discarded without further use. This review article aims to summarize the recent reports utilizing eggshell waste for very diverse purposes, stressing the need to use a mechanochemical approach to broaden its applications. The most studied field with regards to the potential use of eggshell waste is catalysis. Upon proper treatment, it can be used for turning waste oils into biodiesel and moreover, the catalytic effect of eggshell-based material in organic synthesis is also very beneficial. In inorganic chemistry, the eggshell membrane is very often used as a templating agent for nanoparticles production. Such composites are suitable for application in photocatalysis. These bionanocomposites are also capable of heavy metal ions reduction and can be also used for the ozonation process. The eggshell and its membrane are applicable in electrochemistry as well. Due to the high protein content and the presence of functional groups on the surface, ESM can be easily converted to a high-performance electrode material. Finally, both ES and ESM are suitable for medical applications, as the former can be used as an inexpensive Ca2+ source for the development of medications, particles for drug delivery, organic matrix/mineral nanocomposites as potential tissue scaffolds, food supplements and the latter for the treatment of joint diseases, in reparative medicine and vascular graft producing. For the majority of the above-mentioned applications, the pretreatment of the eggshell waste is necessary. Among other options, the mechanochemical pretreatment has found an inevitable place. Since the publication of the last review paper devoted to the mechanochemical treatment of eggshell waste, a few new works have appeared, which are reviewed here to underline the sustainable character of the proposed methodology. The mechanochemical treatment of eggshell is capable of producing the nanoscale material which can be further used for bioceramics synthesis, dehalogenation processes, wastewater treatment, preparation of hydrophobic filters, lithium-ion batteries, dental materials, and in the building industry as cement.

C-F Activation for C(sp2)-C(sp3) Cross-Coupling by a Secondary Phosphine Oxide (SPO)-Nickel Complex

A secondary phosphine oxide (SPO)-nickel catalyst allowed the activation of otherwise inert C-F bonds of unactivated arenes in terms of challenging couplings with primary and secondary alkyl Grignard reagents. The C-F activation is characterized by mild reaction conditions and high levels of branched selectivity. Electron-rich and electron-deficient arenes were suitable electrophiles for this transformation. In addition, this strategy also proved suitable to heterocycles and for the activation of C-O bonds under slightly modified conditions.

Ru and Ni—Privileged Metal Combination for Environmental Nanocatalysis

Privileged structures is a term that is used in drug design to indicate a fragment that is popular in the population of drugs or drug candidates that are in the application or investigation phases, respectively. Privileged structures are popular motifs because they generate efficient drugs. Similarly, some elements appear to be more efficient and more popular in catalyst design and development. To indicate this fact, we use here a term privileged metal combination. In particular, Ru-based catalysts have paved a bumpy road in a variety of commercial applications from ammonia synthesis to carbon (di)oxide methanation. Here, we review Ru/Ni combinations in order to specifically find applications in environmental nanocatalysis and more specifically in carbon (di)oxide methanation. Synergy, ensemble and the ligand effect are theoretical foundations that are used to explain the advantages of multicomponent catalysis. The economic effect is another important issue in blending metal combinations. Low temperature and photocatalytic processes can be indicated as new tendencies in carbon (di)oxide methanation. However, due to economics, future industrial developments of this reaction are still questionable.

Iron-Catalyzed C-H Functionalizations under Triazole-Assistance

3d transition metals-catalyzed C-H bond functionalizations represent nowadays an important tool in organic synthesis, appearing as the most promising alternative to cross-coupling reactions. Among 3d transition metals, iron found widespread application due to its availability and benign nature, and it was established as an efficient catalyst in organic synthesis. In this context, the use of ortho-orientating directing groups (DGs) turned out to be necessary for promoting selective iron-catalyzed C-H functionalization reactions. Very recently, triazoles DGs were demonstrated to be more than an excellent alternative to the commonly employed 8-aminoquinoline (AQ) DG, as a result of their modular synthesis as well as the mild reaction conditions applied for their removal. In addition, their tunable geometry and electronics allowed for new unprecedented reactivities in iron-catalyzed C-H activation methodologies that will be summarized within this review.

Carbon Nanotubes in Biomedicine

Nowadays, biomaterials have become a crucial element in numerous biomedical, preclinical, and clinical applications. The use of nanoparticles entails a great potential in these fields mainly because of the high ratio of surface atoms that modify the physicochemical properties and increases the chemical reactivity. Among them, carbon nanotubes (CNTs) have emerged as a powerful tool to improve biomedical approaches in the management of numerous diseases. CNTs have an excellent ability to penetrate cell membranes, and the sp² hybridization of all carbons enables their functionalization with almost every biomolecule or compound, allowing them to target cells and deliver drugs under the appropriate environmental stimuli. Besides, in the new promising field of artificial biomaterial generation, nanotubes are studied as the load in nanocomposite materials, improving their mechanical and electrical properties, or even for direct use as scaffolds in body tissue manufacturing. Nevertheless, despite their beneficial contributions, some major concerns need to be solved to boost the clinical development of CNTs, including poor solubility in water, low biodegradability and dispersivity, and toxicity problems associated with CNTs' interaction with biomolecules in tissues and organs, including the possible effects in the proteome and genome. This review performs a wide literature analysis to present the main and latest advances in the optimal design and characterization of carbon nanotubes with biomedical applications, and their capacities in different areas of preclinical research.

Gold, Silver and Iron Oxide Nanoparticles: Synthesis and Bionanoconjugation Strategies Aimed at Electrochemical Applications

Nanomaterials have revolutionized the sensing and biosensing fields, with the development of more sensitive and selective devices for multiple applications. Gold, silver and iron oxide nanoparticles have played a particularly major role in this development. In this review, we provide a general overview of the synthesis and characteristics of gold, silver and iron oxide nanoparticles, along with the main strategies for their surface functionalization with ligands and biomolecules. Finally, different architectures suitable for electrochemical applications are reviewed, as well as their main fabrication procedures. We conclude with some considerations from the authors' perspective regarding the promising use of these materials and the challenges to be faced in the near future.

Sustainability in Catalytic Cyclohexane Oxidation: The Contribution of Porous Support Materials

The development of green and sustainable protocols for synthetic routes is a growing area of research in chemistry worldwide. The development of sustainable processes and products through innovative catalytic materials and technologies, that allow a better use of resources, is undoubtedly a very important issue facing research chemists today. Environmentally and economically advanced catalytic processes for selective alkane oxidations reactions, as is the case of cyclohexane oxidation, are now focused on catalysts’ stability and their reuse, intending to overcome the drawbacks posed by current homogeneous systems. The aim of this short review is to highlight recent contributions in heterogeneous catalysis regarding porous support materials to be applied to cyclohexane oxidation reaction. Different classes of porous materials are covered, from carbon nanomaterials to zeolites, mesoporous silicas, and metal organic frameworks. The role performed by the materials to be used as supports towards an enhancement of the activity/selectivity of the catalytic materials and the ability of recycling and reuse in consecutive catalytic cycles is highlighted.

Waste-derived Materials: Opportunities in Photocatalysis

Waste-derived materials have been gaining increased attention in recent years due to their great potential and environmentally friendly nature. Several contributions in the literature have covered the advances achieved so far in this area. Nonetheless, to the best of our knowledge, no review has been dedicated specifically to waste-derived or templated photocatalytic materials. Both photocatalysis and (bio)waste-inspired design yield materials of a remarkably green nature. Therefore, the partnership between them may open promising possibilities for both waste valorization and photocatalytic processes, which in turn will lead to sustainable development globally, with the potential for full utilization of renewable energy sources such as biomass and sunlight. Several photocatalytic waste-derived materials, synthetic procedures, and applications will be described throughout this work, including waste-derived/templated TiO₂, ZnO, and metal sulfide materials. Special attention will be given to biomass-inspired carbonaceous materials, including carbon quantum dots and graphitic carbon nitride (g-C₃N₄).

Mechanochemically Synthesized Supported Magnetic Fe-Nanoparticles as Catalysts for Efficient Vanillin Production

Magnetically separable nanocatalysts were synthesized by incorporating ironnanoparticles on a mesoporous aluminosilicate (Al-SBA-15) through a mechanochemical grindingpathway in a single step. Noticeably, magnetic features were achieved by employing biomass wasteas a carbon source, which additionally may confer high oxygen functionalities to the resultingmaterial. The resulting catalysts were characterized using X-ray diffraction, X-ray photoelectronspectroscopy, transmission electron microscopy, scanning electron microscopy, porosimetry, andmagnetic susceptibility. The magnetic nanocatalysts were tested in the selective oxidative cleavagereaction of isoeugenol and vanillyl alcohol to vanillin. As a result, the magnetic nanocatalystsdemonstrated high catalytic activity, chemical stability, and enormous separation/reusabilityqualities. The origin of catalytic properties and its relationship with the iron oxide precursor wereanalyzed in terms of the chemical, morphological, and structural properties of the samples. Suchanalysis allows, thus, to highlight the superficial concentration of the iron entities and the interactionwith Al as key factors to obtain a good catalytic response.