Pd immobilized on hybrid of magnetic graphene quantum dots and cyclodextrin decorated chitosan: An efficient hydrogenation catalyst

Fabrication of uniform Pd nanoparticles immobilized on crosslinked ionic chitosan support as a super-active catalyst toward regioselective synthesis of pyrazole-fused heterocycles

Selection of biodegradable chitosan as a raw material is a smart technique due to its easy modifiability and high renewability. Herein, taking advantage of these functional characteristics, an ionic biopolymer support is produced from copolymerization of allylated chitosan (with 48 % degree of substitution) and polymerizable ionic liquid ([MEVIm]Br). Next, palladium nanoparticles are successfully stabilized in this designed support through a facile manner based on interconnected porous network, ionic nature and rich functional groups. Then, the Pd@CS-PIL structure was utilized as a heterogeneous catalyst for regioselective synthesis of pyrazole-fused heterocycles. The as-synthesized Pd@CS-PIL was characterized by various techniques such as XRD, EDX, FESEM, elemental mapping, TEM, BET, ICP, TGA, and FT-IR to better determine the structure, morphology, purity and physical properties. The obtained results revealed that the proposed nanostructure provides favorable porosity with significant specific surface area (139.2 m2.g-1), Pd nanoparticles with high dispersion (mean diameter ∼ 22.8 nm) and crosslinked nature with good thermal stability (50 % weight loss about 600 °C). Therefore, Pd@CS-PIL nanostructure showed the key features of a super-active catalyst, and pharmaceutical pyrazole-fused scaffolds were produced in favorable yields (86-96 %) under ultrasound conditions.

A critical review on selenium removal capacity from water using emerging non-conventional biosorbents

Anthropogenic-driven selenium (Se) contamination of natural waters has emerged as severe health and environmental concern. Lowering Se levels to safe limits of 40 μg-L-1 (recommended by WHO) presents a critical challenge for the scientific community, necessitating reliable and effective methods for Se removal. The primary obectives of this review are to evaluate the efficiency of different biosorbents in removing Se, understand the mechanism of adsorption, and identify the factors influencing the biosorption process. A comprehensive literature review is conducted to analyze various studies that have explored the use of modified biochars, iron oxides, and other non-conventional biosorbents for selenium removal. The assessed biosorbents include biomass, microalgae-based, alginate compounds, peats, chitosan, and biochar/modified biochar-based adsorbents. Quantitative data from the selected studies analyzed Se adsorption capacities of biosorbents, were collected considering pH, temperature, and environmental conditions, while highlighting advantages and limitations. The role of iron impregnation in enhancing the biosorption efficiency is investigated, and the mechanisms of Se adsorption on these biosorbents at different pH levels are discussed. A critical literature assessment reveals a robust understanding of the current state of Se biosorption and the effectiveness of non-conventional biosorbents for Se removal, providing crucial information for further research and practical applications in water treatment processes. By understanding the strengths and limitations of various biosorbents, this review is expected to scale-up targeted research on Se removal, promoting the development of innovative and cost-effective adsorbents, efficient and sustainable approaches for Se removal from water.

Palladated Cyclodextrin Nanosponge-Alginate Dual Bead as an Efficient Catalyst for Hydrogenation of Nitroarenes in Aqueous Solution

In this study, we present a novel composite material consisting of β-cyclodextrin nanosponge and sodium alginate, used as a support for the immobilization of palladium (Pd) nanoparticles. The composite alginate-cyclodextrin nanosponge beads were prepared, taking advantage of the 3D polymeric network and β-cyclodextrin cavity of the nanosponge. These beads exhibited excellent encapsulation capabilities for hydrophobic substrates, allowing their transfer in aqueous media. The cyclodextrin nanosponge served as a stabilizer for Pd nanoparticles and facilitated phase transfer. Additionally, the sodium alginate bead contributed to the robustness of the structure and improved the recovery and recyclability of the composite material. Comparative studies with control catalysts confirmed the beneficial effect of incorporating cyclodextrin nanosponge within alginate beads, particularly for more hydrophobic substrates. Optimization of reaction conditions revealed that employing 0.03 g of catalyst per mmol of nitroarene at 45 °C resulted in the maximum yield within 90 min. Evaluation of the substrate scope demonstrated the hydrogenation capability of various substrates with different electronic properties under the developed protocol. Notably, the nitro group was selectively reduced in substrates featuring competing functionalities. Furthermore, the recyclability and stability of the composite catalyst were confirmed, making it a promising candidate for sustainable catalysis.

Chitosan-supported metal nanocatalysts for the reduction of nitroaromatics

The second most abundant natural polymer in the earth's crust is chitosan (CS). The unique physical, chemical, structural, and mechanical features of this natural polymer have led to its increased application in a variety of fields such as medicine, catalysis, removal of pollutants, etc. To eliminate various pollutants, it is preferable to employ natural compounds as their use aids the removal of contaminants from the environment. Consequently, employing CS to eliminate contaminants is a viable choice. For this aim, CS can be applied as a template and support for metal nanoparticles (MNPs) and prevent the accumulation of MNPs as well as a reducing and stabilizing agent for the fabrication of MNPs. Among the pollutants present in nature, nitro compounds are an important and wide category of biological pollutants. 4-Nitrophenol (4-NP) is one of the nitro pollutants. There are different ways for the removal of 4-NP, but the best and most effective method for this purpose is the application of a metallic catalyst and a reducing agent. In this review, we report the recent developments regarding CS-supported metallic (nano)catalysts for the reduction of nitroaromatics such as nitrophenols, nitroaniline compounds, nitrobenzene, etc. in the presence of reducing agents. The metals investigated in this study include Ag, Au, Ni, Cu, Ru, Pt, Pd, etc.

Fabrication and application of chitosan-based biomass composites with fire safety, water treatment and antibacterial properties

In this work, a biomass composite material (CS@NC@PA-Na) was prepared from chitosan (CS), nano-cellulose (NC) and sodium phytate (PA-Na). The prepared products were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrometry (XPS) and X-ray diffraction (XRD). The fire/water safety and antimicrobial properties of the CS@NC@PA-Na were fully studied. The results indicated CS@NC@PA-Na (50 mg) could effectively reduce the concentration of methyl orange by 85 % under 30 min adsorption. Meanwhile, only 5 wt% CS@NC@PA-Na could increase the limiting oxygen index (LOI) value of epoxy resin composite from 24.5 to 30.1 %, and decrease the peak heat/smoke release rate by 29.5 and 33.3 %, respectively. Moreover, CS@NC@PA-Na also exhibited excellent antibacterial effect. This work provides an efficient, feasible and eco-friendly route for large-scale production of multi-functional CS-based biomass materials that could be used in the fields of fire safety and environmental conservation.

Preparation, Characterization, and Staphylococcus aureus Biofilm Elimination Effect of Baicalein-Loaded β-Cyclodextrin-Grafted Chitosan Nanoparticles

BACKGROUND AND PURPOSE

Infections caused by Staphylococcus aureus (S. aureus) colonization in medical implants are resistant to antibiotics due to the formation of bacterial biofilm internal. Baicalein (BA) has been confirmed as an inhibitor of bacterial biofilm with less pronounced effects owing to its poor solubility and absorption. Studies have found that β-cyclodextrin-grafted chitosan (CD-CS) can improve drug efficiency as a drug carrier. Therefore, this research aims to prepare BA-loaded CD-CS nanoparticles (CD-CS-BA-NPs) for S. aureus biofilm elimination enhancement.

METHODS

CD-CS-BA-NPs were prepared via the ultrasonic method. The NPs were characterized using the X-ray diffraction (XRD), Thermo gravimetric analyzer (TGA), Transmission electron microscopy (TEM) and Malvern Instrument. The minimum inhibitory concentration (MIC) of the NPs were investigated. The biofilm models in vivo and in vitro were constructed to assess the S. aureus biofilm elimination ability of the NPs. The Confocal laser method (CLSM) and the Live/Dead kit were employed to explore the mechanism of the NPs in promoting biofilm elimination.

RESULTS

CD-CS-BA-NPs have an average particle size of 424.5 ± 5.16 nm, a PDI of 0.2 ± 0.02, and a Zeta potential of 46.13 ± 1.62 mV. TEM images revealed that the NPs were spherical with uniform distribution. XRD and TGA analysis verified the formation and the thermal stability of the NPs. The NPs with a MIC of 12.5 ug/mL exhibited a better elimination effect on S. aureus biofilm both in vivo and in vitro. The mechanism study demonstrated that the NPs may permeate into the biofilm more easily, thereby improving the biofilm elimination effect of BA.

CONCLUSION

CD-CS-BA-NPs were successfully prepared with enhanced elimination of S. aureus biofilm, which may serve as a reference for future development of anti-biofilm agents.

Pd on cyclotriphosphazen-hexa imine decorated boehmite as an efficient catalyst for hydrogenation of nitro arenes under mild reaction condition

Cyclotriphosphazen-hexa imine ligand was prepared through successive reactions of phosphonitrilchloride trimer with 4-hydroxybenzaldehyde and (3-aminopropyl) triethoxy silane. The as-prepared ligand was then covalently grafted on boehmite to furnish an efficient support for the immobilization of Pd nanoparticles and synthesis of a novel heterogeneous catalyst for hydrogenation of nitro arenes. The catalytic tests revealed that the catalyst had excellent catalytic activity for hydrogenation of various nitro arenes with different steric and electronic features under mild reaction condition in aqueous media. Noteworthy, the catalyst was highly selective and in the substrates with ketone or aldehyde functionalities, reduction of nitro group was only observed. The catalyst was also recyclable and only slight loss of activity was detected after each recycling run. Hot filtration test also approved true heterogeneous nature of catalysis.

Pd on thermo-responsive composite of silica-coated carbon nanotube and 1-vinyl-3-butylimidazolium-based ionic liquid copolymers as an efficient catalyst for hydrogenation of nitro compounds

In this work, an ionic liquid-containing thermo-responsive heterogeneous catalyst with utility for promoting hydrogenation of nitro-compounds in aqueous media is developed. To prepare the catalyst, silica-coated carbon nanotubes were synthesized and vinyl-functionalized. The resulted compound was then polymerized with 1-viny-3-butylimidazolium bromide and N-isopropylacrylamide. The obtained ionic liquid-containing thermo-responsive composite was palladated via wet-impregnation method to give the final catalyst. Study of the performance of the catalyst confirmed high catalytic activity of the catalyst at temperature above the lower critical solution temperature. Furthermore, the catalyst was highly recyclable and showed negligible Pd leaching upon recycling. Broad substrate scope and selectivity of the catalyst towards reduction of nitro functionality were also confirmed. Furthermore, hot filtration test implied the heterogeneous nature of the catalysis. The comparison of the activity of Pd/CNT-P with some control catalysts approved the importance of hybridization of P and CNT and the presence of ionic liquid for the catalytic activity.

Functionalized hybrid magnetic catalytic systems on micro- and nanoscale utilized in organic synthesis and degradation of dyes

Herein, a concise review of the latest developments in catalytic processes involving organic reactions is presented, focusing on magnetic catalytic systems (MCSs). In recent years, various micro- and nanoscale magnetic catalysts have been prepared through different methods based on optimized reaction conditions and utilized in complex organic synthesis or degradation reactions of pharmaceutical compounds. These biodegradable, biocompatible and eco-benign MCSs have achieved the principles of green chemistry, and thus their usage is highly advocated. In addition, MCSs can shorten the reaction time, effectively accelerate reactions, and significantly upgrade both pharmaceutical synthesis and degradation mechanisms by preventing unwanted side reactions. Moreover, the other significant benefits of MCSs include their convenient magnetic separation, high stability and reusability, inexpensive raw materials, facile preparation routes, and surface functionalization. In this review, our aim is to present at the recent improvements in the structure of versatile MCSs and their characteristics, i.e., magnetization, recyclability, structural stability, turnover number (TON), and turnover frequency (TOF). Concisely, different hybrid and multifunctional MCSs are discussed. Additionally, the applications of MCSs for the synthesis of different pharmaceutical ingredients and degradation of organic wastewater contaminants such as toxic dyes and drugs are demonstrated.

Functionalized cotton charcoal/chitosan biomass-based hydrogel for capturing Pb2+, Cu2+ and MB

In this work, a porous multi-functional biomass carbon was prepared by acid-base modification method, which realized the reuse of waste cotton material. Then, the modified biochar was combined with the acrylic-based hydrogel by radical polymerization, and the biochar acrylic-based hydrogel (CS/EDTA/CBC) composite with chitosan and ethylenediamine tetraacetic acid was successfully prepared. This not only increases the adsorption performance of the adsorbent but also improves the stability of hydrogel. These characteristics provide high-efficiency adsorption capacity for pollutants (1105.78 mg g^-1 for Pb²⁺, 678.04 mg g^-1 for Cu²⁺, and 590.72 mg g^-1 for methylene blue (MB)), which is far superior to most reported adsorbents. Meanwhile, the adsorbent would have a strong chemical interaction with Pb²⁺ and Cu²⁺, can form a stable chelating structure, and showed stronger selective adsorption. The adsorption process is more suitable for the Langmuir isotherm and follows a pseudo-second-order kinetic model, which indicates that the adsorption is a single-layer adsorption, and the rate-limiting step is a chemical chelation reaction. XPS results confirmed that surface complexation and electrostatic attraction are the main mechanisms of the adsorption reaction. After five cycles, the adsorption capacity of the adsorbent and the recovery of heavy metal ions remained at a high level.

Pd on the Composite of Perlite and Allylamine-N-isopropylacrylamide Copolymer: A Thermo-Responsive Catalyst for Hydrogenation of Nitroarenes under Mild Reaction Condition

A novel thermo-responsive catalyst for the hydrogenation of nitroarenes under mild reaction condition was devised. To prepare the catalyst, a thermo-responsive polymer was first synthesized through the co-polymerization of N-isopropylacrylamide and allylamine and then covalently grafted on the Cl-functionalized perlite. The resulting composite was subsequently utilized as a support for the stabilization of Pd nanoparticles. Investigation of the catalytic activity of the catalyst approved its high catalytic activity at a temperature above the lower critical solution temperature. More precisely, 0.03 g of the catalyst can promote the reaction of 1 mmol of nitro-compounds in H2O/EtOH (1:1) at 45 °C to furnish the corresponding products in 70–100% yields. This issue was assigned to the collapse of the polymeric component and formation of a hydrophobic environment that was beneficial for the mass-transfer of the hydrophobic nitroarenes. Notably, the catalytic activity of the catalyst was higher than that of palladated perlite and thermos-responsive polymer due to the synergistic effects between the perlite and polymeric moiety. Furthermore, the study of the substrate scope confirmed that a wide range of substrates with different steric and electronic properties could tolerate hydrogenation reaction. Moreover, the catalyst was highly selective toward hydrogenation of the nitro group and could be recycled up to seven runs with insignificant Pd leaching and loss of catalytic activity. The hot filtration test also confirmed the heterogeneous nature of the catalysis.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

Outstanding Graphene Quantum Dots from Carbon Source for Biomedical and Corrosion Inhibition Applications: A Review

Graphene quantum dots (GQD) is an efficient nanomaterial composed of one or more layers of graphene with unique properties that combine both graphene and carbon dots (CDs). It can be synthesized using carbon-rich materials as precursors, such as graphite, macromolecules polysaccharides, and fullerene. This contribution emphasizes the utilization of GQD-based materials in the fields of sensing, bioimaging, energy storage, and corrosion inhibitors. Inspired by these numerous applications, various synthetic approaches have been developed to design and fabricate GQD, particularly bottom-up and top-down processes. In this context, the prime goal of this review is to emphasize possible eco-friendly and sustainable methodologies that have been successfully employed in the fabrication of GQDs. Furthermore, the fundamental and experimental aspects associated with GQDs such as possible mechanisms, the impact of size, surface alteration, and doping with other elements, together with their technological and industrial applications have been envisaged. Till now, understanding simple photo luminance (PL) operations in GQDs is very critical as well as there are various methods derived from the optical properties of manufactured GQDs can differ. Lack of determining exact size and morphology is highly required without loss of their optical features. Finally, GQDs are promising candidates in the after-mentioned application fields.

Fabrication of a metal free catalyst for chemical reactions through decoration of chitosan with ionic liquid terminated dendritic moiety

In attempt to develop a biocompatible metal-free catalyst, a dendritic moiety was grown on chitosan through successive reactions with 2,4,6-trichloro-1,3,5-triazine and ethylenediamine. Subsequently, the terminal functional groups of the dendron were decorated with 1-methylimidazolium chloride. The catalyst was characterized with SEM, EDS, TGA, FTIR, XRD and mapping analysis. Then, the catalytic activity of the resultant composite was scrutinized for catalyzing Knoevenagel condensation and synthesis of xanthene derivatives in aqueous media under mild reaction condition. The results confirmed high activity of the catalyst, superior to ionic liquid free counterpart and bare chitosan. This observation was ascribed to the instinct catalytic activity of ionic liquid. Moreover, using control catalysts, it was confirmed that the presence of the dendritic moiety that could increase the content of ionic liquid on the backbone of the catalyst enhanced the catalytic activity.

Fabrication of CS/GA/RGO/Pd composite hydrogels for highly efficient catalytic reduction of organic pollutants

In this study, natural polymer material chitosan (CS) and graphene oxide (GO) with large specific surface area were used to prepare a new CS/RGO-based composite hydrogel by using glutaraldehyde (GA) as cross-linking agent. In addition, a CS/GA/RGO/Pd composite hydrogel was prepared by loading palladium nanoparticles (Pd NPs). The morphologies and microstructures of the prepared hydrogels were characterized by SEM, TEM, XRD, TG, and BET. The catalytic performance of the CS/GA/RGO/Pd composite hydrogel was analyzed, and the experimental results showed that the CS/GA/RGO/Pd composite hydrogel had good catalytic performance for degradation of p-nitrophenol (4-NP) and o-nitroaniline (2-NA). Therefore, this study has potential application prospect in wastewater treatment and provides new information for composite hydrogel design.

New functional CS/GA/RGO/Pd composite hydrogels are prepared via a self-assembly process, demonstrating potential applications in catalysis as well as composite materials.