Palladium Supported on Porous Chitosan-Graphene Oxide Aerogels as Highly Efficient Catalysts for Hydrogen Generation from Formate

Bimetallic NiPt nanoparticles-enhanced catalyst supported on alginate-based biohydrogels for sustainable hydrogen production

Alginate hydrogel beads were loaded with bimetallic NiPt nanoparticles by in situ reduction of the respective polymer matrix containing precursor metallic ions using a NaBH₄ aqueous solution. The alginate hydrogel beads loaded with NiPt nanoparticles were characterized by TEM, AAS, FT-IR, TGA, XPS, and oscillatory rheometry. The prepared hybrid hydrogels were proven to be effective as catalytic materials for the hydrolysis of ammonia borane (AB) for quantitative hydrogen generation using catalytic loadings of 0.1 mol%. In addition, the reaction mechanism of the hydrolytic reaction using NiPt loaded alginate hydrogel beads was determined by Langmuir-Hinshelwood model. The experimental results showed that the reaction mechanism consisted of an initial fast adsorption of reactants at the surface of the nanoparticles, followed by a rate-limiting surface reaction. The NiPt nanoalloys exhibited an enhanced behavior for hydrogen generation with a maximum TOF of 84.1 min^-1, almost 71 % higher compared to monometallic platinum atoms, and likely related to a synergistic interaction between both metals. Finally, the hydrogel matrix enabled the material to be easily recovered from the reaction medium and reused in further catalytic cycles without desorption of active nanoparticles from the material.

Phosphorus-Rich Ruthenium Phosphide Embedded on a 3D Porous Dual-Doped Graphitic Carbon for Hydrogen Evolution Reaction

Metal phosphides have recently emerged as promising electrocatalysts for hydrogen evolution reaction (HER). Herein, we report the synthesis of ruthenium diphosphide embedded on a dual-doped graphitic carbon by pyrolyzing chitosan beads impregnated with ruthenium chloride and phosphorus pentoxide. The as-synthesized RuP₂@N-P-C displays a good electrocatalytic activity in acidic, neutral and alkaline media. We show that the HER activity of the electrocatalyst can be tuned by varying the concentration of Li⁺ cations. Co-diffusion effects on H⁺ exerted by Li⁺ on HER in the porous carbon matrix have been observed.

An Update on Graphene Oxide: Applications and Toxicity

Graphene oxide (GO) has attracted much attention in the past few years because of its interesting and promising electrical, thermal, mechanical, and structural properties. These properties can be altered, as GO can be readily functionalized. Brodie synthesized the GO in 1859 by reacting graphite with KClO3 in the presence of fuming HNO3; the reaction took 3-4 days to complete at 333 K. Since then, various schemes have been developed to reduce the reaction time, increase the yield, and minimize the release of toxic byproducts (NO2 and N2O4). The modified Hummers method has been widely accepted to produce GO in bulk. Due to its versatile characteristics, GO has a wide range of applications in different fields like tissue engineering, photocatalysis, catalysis, and biomedical applications. Its porous structure is considered appropriate for tissue and organ regeneration. Various branches of tissue engineering are being extensively explored, such as bone, neural, dentistry, cartilage, and skin tissue engineering. The band gap of GO can be easily tuned, and therefore it has a wide range of photocatalytic applications as well: the degradation of organic contaminants, hydrogen generation, and CO2 reduction, etc. GO could be a potential nanocarrier in drug delivery systems, gene delivery, biological sensing, and antibacterial nanocomposites due to its large surface area and high density, as it is highly functionalized with oxygen-containing functional groups. GO or its composites are found to be toxic to various biological species and as also discussed in this review. It has been observed that superoxide dismutase (SOD) and reactive oxygen species (ROS) levels gradually increase over a period after GO is introduced in the biological systems. Hence, GO at specific concentrations is toxic for various species like earthworms, Chironomus riparius, Zebrafish, etc.

The solvent-free mechano-chemical grinding of a bifunctional P25-graphene oxide adsorbent-photocatalyst and its configuration as porous beads

Owing to their use in water-cleaning technology, titanium-dioxide-based nanomaterials have dominated the photocatalysis scene, with so-called Degussa (P25) being the most promising under UV light. However, this is not the case under visible light, where it is necessary to combine titanium dioxide with other photosensitising nanomaterials. Unfortunately, most of the strategies aimed in this direction are chemically non-facile, energy-intensive, economically expensive, and not suitable for large-scale production. We herein describe a straightforward solvent-free approach for accessing visible-light-activated titanium-dioxide-based photocatalysts via the mechanochemical grinding of Degussa P25 with a second solid partner. Upon comparing several solid-material benchmarks, P25-graphene oxide is the best combination. The resulting material showed efficient performance for the adsorption and photodegradation of different dye pollutants, namely methylene blue, malachite green, Congo red, and methyl orange. The recorded performance was nearly comparable to that reached using sol-gel materials, with the ultimate advantage of being more sustainable and industrially scalable. The recyclability can be improved through a porous-bead configuration using biomass waste chitosan hydrogel, an approach that can further fulfill the requirement for more sustainable photocatalyst designs.

Preparation and characterization of chitosan/polyvinyl porous alcohol aerogel microspheres with stable physicochemical properties

Chitosan/polyvinyl alcohol (CS/PVA) porous aerogel microspheres with stable physicochemical properties were obtained by gelation and freeze-drying process, and modified by adding different content of polyvinyl alcohol (PVA) into the microspheres. The physicochemical properties of porous aerogel microspheres, including porosity, swelling degree, acid-base resistance and compression performance were compared with chitosan (CS) microspheres. The microspheres were characterized by scanning electronic microscopy, Fourier transform infrared spectra, X-ray diffraction and compression test. The results showed that the structure of hybrid aerogel microspheres could be controlled by adjusting the content of PVA. The increase of PVA content reduced the pore size of CS/PVA porous aerogel microspheres, promoted the roughness of the surface and formed more orderly pore distribution. The higher PVA content was, the greater the swelling degree of the CS/PVA porous microspheres was. Adding proper amount of PVA into the CS/PVA microspheres could improve their acid resistance, but reduce their alkali resistance. Furthermore, the porosity of CS/PVA microspheres containing 33.3% PVA was the highest (78.3%) and the best compression strength (0.0505 MPa) when compression depth was 60% of the maximum height.

Formate-Bicarbonate Cycle as a Vehicle for Hydrogen and Energy Storage

In recent years, hydrogen has been considered a promising energy carrier for a sustainable energy economy in the future. An easy solution for the safer storage of hydrogen is challenging and efficient methods are still being explored in this direction. Despite having some progress in this area, no cost-effective and easily applicable solutions that fulfill the requirements of industry are yet to be claimed. Currently, the storage of hydrogen is largely limited to high-pressure compression and liquefaction or in the form of metal hydrides. Formic acid is a good source of hydrogen that also generates CO₂ along with hydrogen on decomposition. Moreover, the hydrogenation of CO₂ is thermodynamically unfavorable and requires high energy input. Alkali metal formates are alternative mild and noncorrosive sources of hydrogen. On decomposition, these metal formates release hydrogen and generate bicarbonates. The generated bicarbonates can be catalytically charged back to alkali formates under optimized hydrogen pressure. Hence, the formate-bicarbonate-based systems being carbon neutral at ambient condition has certain advantages over formic acid. The formate-bicarbonate cycle can be considered as a vehicle for hydrogen and energy storage. The whole process is carbon-neutral, reversible, and sustainable. This Review emphasizes the various catalytic systems employed for reversible formate-bicarbonate conversion. Moreover, a mechanistic investigation, the effect of temperature, pH, kinetics of reversible formate-bicarbonate conversion, and new insights in the field are also discussed in detail.

Catalysis by Hybrid Nanomaterials

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Preparation of aerogel beads and microspheres based on chitosan and cellulose for drug delivery: A review

Spherical aerogels are not easily broken during use and are easier to transport and store which can be used as templates for drug delivery. This review summarizes the possible approaches for the preparation of aerogel beads and microspheres based on chitosan and cellulose, an overview to the methods of manufacturing droplets is presented, afterwards, the transition mechanisms from sol to a spherical gel are reviewed in detail followed by different drying processes to obtain spherical aerogels with porous structures. Additionally, a specific focus is given to aerogel beads and microspheres to be regarded as drug delivery carriers. Furthermore, a core/shell architecture of aerogel beads and microspheres for controlled drug release is described and subjected to inspire readers to create novel drug release system. Finally, the conclusions and outlooks of aerogel beads and microspheres for drug delivery are summarized.

Biorefinery Approach for Aerogels

According to the International Energy Agency, biorefinery is "the sustainable processing of biomass into a spectrum of marketable bio-based products (chemicals, materials) and bioenergy (fuels, power, heat)". In this review, we survey how the biorefinery approach can be applied to highly porous and nanostructured materials, namely aerogels. Historically, aerogels were first developed using inorganic matter. Subsequently, synthetic polymers were also employed. At the beginning of the 21st century, new aerogels were created based on biomass. Which sources of biomass can be used to make aerogels and how? This review answers these questions, paying special attention to bio-aerogels' environmental and biomedical applications. The article is a result of fruitful exchanges in the frame of the European project COST Action "CA 18125 AERoGELS: Advanced Engineering and Research of aeroGels for Environment and Life Sciences".

Biomass: A Renewable Source of Fuels, Chemicals and Carbon Materials

Fossil fuels have been long used as a source of carbon for synthetizing the fuels, chemicals, and carbon-based materials we use on a daily basis [...].

Nanopore-Supported Metal Nanocatalysts for Efficient Hydrogen Generation from Liquid-Phase Chemical Hydrogen Storage Materials

Hydrogen has emerged as an environmentally attractive fuel and a promising energy carrier for future applications to meet the ever-increasing energy challenges. The safe and efficient storage and release of hydrogen remain a bottleneck for realizing the upcoming hydrogen economy. Hydrogen storage based on liquid-phase chemical hydrogen storage materials is one of the most promising hydrogen storage techniques, which offers considerable potential for large-scale practical applications for its excellent safety, great convenience, and high efficiency. Recently, nanopore-supported metal nanocatalysts have stood out remarkably in boosting the field of liquid-phase chemical hydrogen storage. Herein, the latest research progress in catalytic hydrogen production is summarized, from liquid-phase chemical hydrogen storage materials, such as formic acid, ammonia borane, hydrous hydrazine, and sodium borohydride, by using metal nanocatalysts confined within diverse nanoporous materials, such as metal-organic frameworks, porous carbons, zeolites, mesoporous silica, and porous organic polymers. The state-of-the-art synthetic strategies and advanced characterizations for these nanocatalysts, as well as their catalytic performances in hydrogen generation, are presented. The limitation of each hydrogen storage system and future challenges and opportunities on this subject are also discussed. References in related fields are provided, and more developments and applications to achieve hydrogen energy will be inspired.