Catalytic innovations: Improving wastewater treatment and hydrogen generation technologies

The effective reduction of hazardous organic pollutants in wastewater is a pressing global concern, necessitating the development of advanced treatment technologies. Pollutants such as nitrophenols and dyes, which pose significant risks to both human and aquatic health, making their reduction particularly crucial. Despite the existence of various methods to eliminate these pollutants, they are not without limitations. The utilization of nanomaterials as catalysts for chemical reduction exhibits a promising alternative owing to their distinguished catalytic activity and substantial surface area. For catalytically reducing the pollutants NaBH4 has been utilized as a useful source for it because it reduces the pollutants quiet efficiently and it also releases hydrogen gas as well which can be used as a source of energy. This paper provides a comprehensive review of recent research on different types of nanomaterials that function as catalysts to reduce organic pollutants and also generating hydrogen from NaBH4 methanolysis while also evaluating the positive and negative aspects of nanocatalyst. Additionally, this paper examines the features effecting the process and the mechanism of catalysis. The comparison of different catalysts is based on size of catalyst, reaction time, rate of reaction, hydrogen generation rate, activation energy, and durability. The information obtained from this paper can be used to steer the development of new catalysts for reducing organic pollutants and generation hydrogen by NaBH4 methanolysis.

Elimination of toxic azo dye using a calcium alginate beads impregnated with NiO/activated carbon: Preparation, characterization and RSM optimization

Nickel oxide nanoparticles supported activated carbon (AC-NiO) was fabricated using thermal activation. Then, AC-NiO composite was immobilized on alginate beads to obtain 3-dimensional network structure ALG@AC-NiO nanocomposite beads for catalytic reduction of Congo red (CR) dye. The resulting nanocomposite beads were identified by various physical techniques. The crystalline nature and dispersion of NiO nanoparticles was defined by the XRD and EDS techniques, respectively. ALG@AC-NiO beads have a Ni element content of 4.65 wt% with an average NiO particle diameter of 23 nm. The statistical approach mathematically describes the catalytic reduction of the CR dye as a function of the NaBH₄ concentration, the catalyst dose and the concentration of the CR dye modeled by a BBD-RSM. According to the statistical modeling and the optimization process, the catalytic optimum conditions were obtained for NaBH₄ concentration of 0.05 M, catalyst dose of 11 mg and CR dye concentration of 80 ppm who permit meet 99.67 % of CR dye conversion. The adjusted coefficient of determination (R² = 0.9957) indicates that the considered model was quite suitable with a good correlation between the experiment and predicted.

Role of polyaniline in accomplishing a sustainable environment: recent trends in polyaniline for eradicating hazardous pollutants

Attaining a sustainable environment has become a prime area of research interest, as it is an utmost necessity for a healthy life. Hence, ample studies have been carried out in adopting different processes and utilizing various materials to attain the goal. Herein, we present an exclusive discussion on one such material, i.e., polyaniline (PANI) and its derivatives. Being an intrinsic conducting type, it has grabbed more attention due to its durability in different doped/un-doped states, promptness in structural alteration, and solution processability. This review presents an exhaustive discussion on published reports showing utilization of PANI and its derivative in various forms like pure and composites, for cleaning the environment through adsorption, photodegradation, etc., and the various methods adopted in order to achieve an optimum operating condition to obtain the maximum outcome. In addition to these merits and demerits, various technical challenges faced with materials have been also presented. Therefore, it is expected that this piece of work, presenting the exhaustive discussion on PANI and; its derivatives would help to develop a better understanding of this excellent conducting polymer PANI and provide a state of art on the role of this material for attaining sustainable surroundings for the living beings.

Catalytic behavior and antibacterial/antifungal activities of new MNPs/zeolite@alginate composite beads

In this paper, a new family of composite materials was prepared based on calcium alginate and metal nanoparticle-loaded zeolite omega. Different types of metal nanoparticles (MNPs), namely Cu, Co and Fe, were loaded onto zeolite omega to test the performance of the resulting metal/zeolite@alginate composites towards the catalytic reduction of methylene blue dye. To examine their application field as broadly as possible, these composite beads were also tested as antibacterial and antifungal agents against several types of bacteria. Several techniques such as XRD, XRF, FTIR, XPS, SEM and TGA were used to characterize the samples. The obtained results showed that all the composite bead samples were effective in the reduction of MB dye. The composite Co/Zeolite@ALG with relatively low Co nanoparticle (NP) content was selected as the best performing catalyst due to its reduction of MB dye being completely achieved in 3 min with a rate constant of 1.4 min-1, which was attributed to its highly porous structure. The reuse tests conducted on the best-performing catalyst showed good results which persisted through five successive cycles. For antibacterial and antifungal activities, the Cu/Zeolite@ALG and Fe/Zeolite@ALG composites showed good activity with significant inhibition zones.

Recent developments in hydrogels containing copper and palladium for the catalytic reduction/degradation of organic pollutants

The elimination of toxic and hazardous contaminants from different environmental media has become a global challenge, causing researchers to focus on the treatment of pollutants. Accordingly, the elimination of inorganic and organic pollutants using sustainable, effective, and low-cost heterogeneous catalysts is considered as one of the most essential routes for this aim. Thus, many efforts have been devoted to the synthesis of novel compounds and improving their catalytic performance. Recently, palladium- and copper-based hydrogels have been used as catalysts for reduction, degradation, and decomposition reactions because they have significant features such as high mechanical strength, thermal stability, and high surface area. Herein, we summarize the progress achieved in this field, including the various methods for the synthesis of copper- and palladium-based hydrogel catalysts and their applications for environmental remediation. Moreover, palladium- and copper-based hydrogel catalysts, which have certain advantages, including high catalytic ability, reusability, easy work-up, and simple synthesis, are proposed as a new group of effective catalysts.

The elimination of toxic and hazardous contaminants from different environmental media has become a global challenge, causing researchers to focus on the treatment of pollutants.

Facile synthesis of superparamagnetic Fe3O4@noble metal core-shell nanoparticles by thermal decomposition and hydrothermal methods: comparative study and catalytic applications

Herein, we report on developing a facile synthetic route for reusable nanocatalysts based on a combination of the supermagnetic properties of magnetite with the unique optical and catalytic properties of noble metal hybrid nanomaterials. We compare two different synthetic methods, to find out which is best from synthetic and application points of view, for the synthesis of Fe₃O₄ and Fe₃O₄@M (M = Ag or Au) core-shell hybrid nanostructures. The two different single-step synthetic methods are: thermal decomposition and hydrothermal. The structural, morphological and magnetic properties of the obtained Fe₃O₄ and Fe₃O₄@M nanoparticles were characterized by various techniques. XRD of the Fe₃O₄ nanoparticles exhibited sharp and strong diffraction peaks, confirming the highly crystalline structure of the Fe₃O₄ particles synthesized by the hydrothermal method, while broad and weak peaks were observed on using the thermal decomposition method. Both Fe₃O₄@Ag and Fe₃O₄@Au core-shells obtained by the hydrothermal method showed the reflection planes of Fe₃O₄ and additional planes of Ag or Au. But on the formation of Fe₃O₄@Ag/Au by the thermal decomposition method the peak for Fe₃O₄ disappeared and only the diffraction peaks of Ag or Au appeared. According to TEM analysis there was a broad particle-size distribution, random near-spherical shapes and slight particle agglomeration for Fe₃O₄ synthesized by the thermal decomposition method. However, there was a moderate size distribution, spherical shapes and well-dispersed particles without large aggregations for the hydrothermal method. TEM images of the synthesized nanoparticles by the two methods used showed a pronounced difference in both size and morphological shape. The catalytic performance of the synthesized nanoparticles was examined for the reduction of Congo red dye in the presence of NaBH₄. The Fe₃O₄ nanocatalyst maintained its catalytic activity for only one cycle. In the cases of Fe₃O₄@Au and Fe₃O₄@Ag, the catalytic activity was conserved for four and ten successive cycles, respectively. Based on the obtained results, it was concluded that the hydrothermal synthesis of Fe₃O₄, Fe₃O₄@Ag and Fe₃O₄@Au nanostructures is highly recommended due to their selectivity and merits.

Enzymatic degradation and detoxification of azo dye Congo red by a new laccase from Oudemansiella canarii

A single laccase with molecular weight of 41 kDa was produced by the white-rot fungus Oudemansiella canarii cultured on solid state fermentation using a mixture of sugarcane bagasse-wheat bran as substrate. The enzyme (5 U) was able to decolourize 80% of 50 mg/L Congo red within 24 h at 30 °C and pH 5.5. The relationship between the decolorization rate and dye concentration obeyed Michaelis-Menten kinetics, with K_M and V_max values of 46.180 ± 6.245 µM and 1.840 ± 0.101 µmol/min, respectively. Fourier transform infrared spectroscopy (FTIR) and mass spectrometry allowed to conclude that the laccase acts not only on the dye chromophore group, but also that it cleaves different covalent bonds, causing an effective fragmentation of the molecule. The action of the laccase caused a significant reduction in toxicity, as indicated by the Microtox test. In conclusion, O. canarii laccase could be useful in future biological strategies aiming at degrading azo dyes.

Mussel-inspired immobilization of Au on bare and graphene-wrapped Ni nanoparticles toward highly efficient and easily recyclable catalysts

Bimetallic nanocatalysts have been gaining huge research attention in the heterogeneous catalysis community recently owing to their tunable properties and multifunctional characteristics. In this work, we fabricated a bimetallic core-shell nanocomposite catalyst by employing a mussel-inspired strategy for immobilizing gold nanoparticles (AuNP) on the surface of nickel nanoparticles (NiNP). NiNPs obtained from the reduction of Ni(ii) were first coated with polydopamine to provide the anchoring sites towards the robust immobilization of AuNPs. The as-synthesized nanocomposite (Ni-PD-Au) exhibited outstanding catalytic activity while reducing methylene blue (MB) and 4-nitrophenol (4-NP) yielding rate constants 13.11 min-1 and 4.21 min-1, respectively, outperforming the catalytic efficiency of its monometallic counterparts and other similar reported catalysts by large margins. The superior catalytic efficiency of the Ni-PD-Au was attributed to the well-known synergistic effect, which was experimentally investigated and compared with prior reports. Similar bio-inspired immobilization of AuNPs was also applied on graphene-wrapped NiNPs (Ni-G) instead of bare NiNPs to synthesize another composite catalyst (Ni-G-PD-Au), which yet again exhibited synergistic catalytic activity. A comparative study between the two nanocomposites suggested that Ni-PD-Au excelled in catalytic activity but Ni-G-PD-Au provided noteworthy stability showing ∼100% efficiency over 17 repeated cycles. However, along with excellent synergistic performance, both nanocomposites demonstrated high magnetization and thermal stability up to 350 °C ascertaining their easy separation and sustainability for high-temperature applications, respectively.

Highly effective bromate reduction by liquid phase catalytic hydrogenation over Pd catalysts supported on core-shell structured magnetites: Impact of shell properties

Liquid phase catalytic reduction of bromate with supported noble metals as the catalysts is a promising method to remove bromate in water. Magnetic supports provide a feasible way to recover catalysts whose surface properties also strongly influence the catalytic efficiency. In this study, Pd nanoparticles supported on core-shell structured magnetites with varied shells (e.g., carbon, SiO₂, polypyrrole, polyaniline, polydopamine and chitosan) were prepared and catalytic reduction of bromate on the catalysts was investigated. The results showed that in comparison with other catalysts Pd/(Fe₃O₄@polyaniline) exhibited a higher catalytic efficiency due to its higher point of zero charge and surface hydrophilicity. In parallel, bromate reduction on Pd/(Fe₃O₄@polyaniline) followed the Langmuir-Hinshelwood model, confirming the crucial role of bromate adsorption. At pH 5.6 and a catalyst dosage of 0.05 g/L, 0.4 mM bromate could be completely reduced into bromide within 120 min. Furthermore, the magnetic catalysts could be effectively separated and recovered under an external magnetic field within 3 min. The results of catalyst reuse showed that after five consecutive catalytic reduction cycles Pd/(Fe₃O₄@polyaniline) retained 87% of its fresh catalyst activity. The present findings indicate that Pd/(Fe₃O₄@polyaniline) with polyaniline as the shell is a highly active, stable and recyclable catalyst for liquid phase catalytic hydrogenation of pollutants in water.

Biosynthesis of Au nanoparticles supported on Fe3O4@polyaniline as a heterogeneous and reusable magnetic nanocatalyst for reduction of the azo dyes at ambient temperature

In this research Au nanoparticles, supported on Fe₃O₄@polyaniline as a magnetic nanocatalyst, was synthesized and its performance has been evaluated to reduce Methylene Blue (MB) and Methyl Orange (MO) from aqueous solutions. Gold nanoparticles, as a nanocatalyst with excellent activity, were prepared through the reduction of Au³⁺ using a wild herbal extract (Allium Sp) without any toxic chemical compounds and harmful materials. The synthesized Fe₃O₄@PANI-Au magnetic nanocatalyst was characterized by different instruments. To investigate the effect of nanocatalyst concentration on the degradation rate of azo dyes, two different catalyst concentrations were used at ambient temperature. According to the carried out calculations, degradation reaction of azo dyes with NaBH₄ in presence of the nanocatalyst is 10³ to 10⁴ times faster than degradation without using the catalyst.

Fabrication of Fe3O4-based ternary magnetic microsphere catalysts based on supramolecular chemistry and their catalytic performance

In this paper, magnetic catalysts were successfully synthesized using host–guest chemistry and a self-assembly strategy.

Highly efficient reduction of 4-nitrophenolate to 4-aminophenolate by Au/γ-Fe2O3@HAP magnetic composites

In this article, the catalyst Au/γ-Fe₂O₃@hydroxyapatite (Au/γ-Fe₂O₃@HAP) consisting of Au nanoparticles supported on the core–shell structure γ-Fe₂O₃@HAP was prepared through a deposition–precipitation method. The catalyst was characterized by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, N₂ adsorption–desorption and atomic absorption spectrometry. The as-prepared Au/γ-Fe₂O₃@HAP exhibited excellent performance for the reduction of 4-nitrophenolate (4-NP) to 4-aminophenolate (4-AP) in the presence of NaBH₄ at room temperature. Thermodynamic and kinetic data on the reduction of 4-NP to 4-AP catalyzed by the as-prepared catalyst were studied. The as-prepared catalyst could be easily separated by a magnet and recycled 6 times with over 92% conversion of 4-NP to 4-AP. In addition, the as-prepared catalyst showed excellent catalytic performance on other nitrophenolates. The TOF value of this work on the reduction of 4-NP to 4-AP was 241.3 h⁻¹. Au/γ-Fe₂O₃@HAP might have a promising potential application on the production of 4-AP and its derivatives.

In this article, the catalyst Au/γ-Fe₂O₃@hydroxyapatite (Au/γ-Fe₂O₃@HAP) consisting of Au nanoparticles supported on the core–shell structure γ-Fe₂O₃@HAP was prepared through a deposition–precipitation method.

Hierarchically Grown NiO-Decorated Polyaniline-Reduced Graphene Oxide Composite for Ultrafast Sunlight-Driven Photocatalysis

Polymers and transition-metal oxides have gained great interest as a photocatalyst in environmental remediation. They could be modified with each other in order to improve their activity. Here, a sunlight-responsive hierarchically structured ternary composite of nickel oxide, polyaniline, and reduced graphene oxide (NiO@PANI/RGO) has been synthesized and employed as a catalyst for dye [methylene blue (MB)] degradation. PANI/GO synthesized by interfacial polymerization acts as a matrix for the growth of NiO using a microemulsion solvothermal method, ensuing an in situ reduction of graphene oxide during the formation of a hierarchical NiO@PANI/RGO composite. Morphological studies of the as-synthesized NiO@PANI/RGO composite reveal fine NiO (10 nm) nanoparticles intercalated between the uniformly grown PANI spines (50-60 nm) over the RGO surface. The optical band gap of ∼1.9 eV calculated from the UV-vis spectrum illustrates the extended light absorption range for the NiO@PANI/RGO photocatalyst. The efficiency of 98% MB degradation within 11 min with the degradation rate constant 0.086 min-1 for NiO@PANI/RGO has surpassed any other report on metal oxide/graphene-based ternary composites. Overall, this work could pave the way for the fabrication of futuristic hierarchical structured ternary nanocomposites as an efficient photocatalyst and facilitate their application in the environmental protection issues.

Recent progress in layered double hydroxide based materials for electrochemical capacitors: design, synthesis and performance

As representative two-dimensional (2D) materials, layered double hydroxides (LDHs) have received increasing attention in electrochemical energy storage and conversion because of the facile tunability between their composition and morphology. The high dispersion of active species in layered arrays, the simple exfoliation into monolayer nanosheets and chemical modification offer the LDHs an opportunity as active electrode materials in electrochemical capacitors (ECs). LDHs are favourable in providing large specific surface areas, good transport features as well as attractive physicochemical properties. In this review, our purpose is to provide a detailed summary of recent developments in the synthesis and electrochemical performance of the LDHs. Their composites with carbon (carbon quantum dots, carbon black, carbon nanotubes/nanofibers, graphene/graphene oxides), metals (nickel, platinum, silver), metal oxides (TiO₂, Co₃O₄, CuO, MnO₂, Fe₃O₄), metal sulfides/phosphides (CoS, NiCo₂S₄, NiP), MOFs (MOF derivatives) and polymers (PEDOT:PSS, PPy (polypyrrole), P(NIPAM-co-SPMA) and PET) are also discussed in this review. The relationship between structures and electrochemical properties as well as the associated charge-storage mechanisms is discussed. Moreover, challenges and prospects of the LDHs for high-performance ECs are presented. This review sheds light on the sustainable development of ECs with LDH based electrode materials.

Ice-templating synthesis of macroporous noble metal/3D-graphene nanocomposites: their fluorescence lifetimes and catalytic study

Porous architectures of 3D-graphene assembled with noble metal (Au, Pd and Pt) nanoparticles were successfully fabricated through a one-step green route using a low-cost freeze-casting method.

Robust and economic reduction protocol employing immensely stable and leach-proof magnetically separable nanocomposites

Metals stabilized over modified magnetic ferrite nanoparticles (M@Dop@CoFe₂O₄) have been established as very stable, magnetically recyclable and leach-proof competent catalysts for the reduction of nitroarenes.

Tin-based nanomaterials for electrochemical energy storage

A summary of the synthesis, modification, and electrochemical performance of Sn-based nanomaterials; lithium/sodium ion batteries and supercapacitors are carefully discussed.