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The excessive consumption of petroleum resources leads to global warming, fast depletion of petroleum reserves, as well as price instability of gasoline. Thus, there is a strong need for alternative renewable fuels to replace petroleum-derived fuels. The striking features of an alternative fuel include the low carbon footprints, renewability and affordability at manageable prices. Biodiesel, made from waste oils, animal fats, vegetal oils, is a totally renewable and non-toxic liquid fuel which has gained significant attraction in the world. Due to technological advancements in catalytic chemistry, biodiesel can be produced from a variety of feedstock employing a variety of catalysts and recovery technologies. Recently, several ground-breaking advancements have been made in nano-catalyst technology which showed the symmetrical correlation with cost competitive biodiesel production. Nanocatalysts have unique properties such as their selective reactivity, high activation energy and controlled rate of reaction, easy recovery and recyclability. Here, we present an overview of various feedstock used for biodiesel production, their composition and characteristics. The major focus of this review is to appraise the characterization of nanocatalysts, their effect on biodiesel production and methodologies of biodiesel production.

The excessive utilization of petroleum resources leads to global warming, crude oil price fluctuations, and the fast depletion of petroleum reserves. Biodiesel has gained importance over the last few years as a clean, sustainable, and renewable energy source. This review provides knowledge of biodiesel production via transesterification/esterification using different catalysts, their prospects, and their challenges. The intensive research on homogeneous chemical catalysts points to the challenges in using high free fatty acids containing oils, such as waste cooking oils and animal fats. The problems faced are soap formation and the difficulty in product separation. On the other hand, heterogeneous catalysts are more preferable in biodiesel synthesis due to their ease of separation and reusability. However, in-depth studies show the limited activity and selectivity issues. Using biomass waste-based catalysts can reduce the biodiesel production cost as the materials are readily available and cheap. The use of an enzymatic approach has gained precedence in recent times. Additionally, immobilization of these enzymes has also improved the statistics because of their excellent functional properties like easy separation and reusability. However, free/liquid lipases are also growing faster due to better mass transfer with reactants. Biocatalysts are exceptional in good selectivity and mild operational conditions, but attractive features are veiled with the operational costs. Nanocatalysts play a vital role in heterogeneous catalysis and lipase immobilization due to their excellent selectivity, reactivity, faster reaction rates owing to their higher surface area, and easy recovery from the products and reuse for several cycles.

This study focused on generating biodiesel from waste cooking oil (WCO) employing an αFe₂O₃/CuO nanocatalyst synthesized via a co-precipitation method. Several characterization techniques, including FTIR, XRD, SEM-EDX, BET, and TEM analyses, were applied to scrutinize the features of the fabricated nanocatalyst. The results confirmed the successful incorporation of CuO into the αFe₂O₃ structure. BET analysis further revealed that the addition of CuO nanoparticles significantly enhanced the catalyst’s surface properties, increasing the number of active sites available for transesterification reactions. Besides, the αFe₂O₃/CuO nanocatalyst exhibited a specific surface area of 334 m²/g, highlighting its high surface availability for catalytic activity. The process was statistically optimized using response surface methodology (RSM) with a Box-Behnken design (BBD) to assess the influence of critical reaction parameters. Vital parameters evaluated included temperature (50–70 °C), methanol/WCO molar ratio (8–14 mol/mol), and catalyst loading (1–3 wt%). Moreover, ANOVA results indicated that the methanol/WCO molar proportion had the most remarkable effect on biodiesel production efficiency, with an F-value of 337.11. Under optimal conditions reaction time of 3 h, methanol/WCO molar ratio of 11, αFe₂O₃/CuO dosage of 2 wt%, and temperature of 60 °C a highest biodiesel yield of 94.27% was achieved. Additionally, the reusability assessment of the αFe₂O₃/CuO nanocatalyst demonstrated notable stability, with only a 12% reduction in efficiency observed over seven cycles. This research demonstrates that αFe₂O₃/CuO nanocatalysts, owing to their unique properties, have the potential to serve as highly effective heterogeneous catalysts for transesterification.

In this paper, we shown that copper(II) complex supported on the surface of magnetic nanoparticles modified with 2-methoxy-1-phenylethan-1-imine (Fe3O4@SiO2-MPI-Cu(II) nanocatalyst) is an efficient nanocatalyst for synthesis of propargylamines and diaryl sulfides. The copper-nanomagnetic catalyst was fully characterized by FT-IR spectroscopy, SEM, TEM, BET, EDX, TGA, XRD, VSM, ICP-OES spectroscopic techniques. The Fe3O4@SiO2-MPI-Cu(II) nanocomposite exhibited high catalytic activity in the synthesis of propargyl amines and diaryl sulfides. The Fe3O4@SiO2-MPI-Cu(II) nanocatalyst was readily recovered by simple magnetic decantation and can be reused seven cycles without considerable loss in catalytic activity.

We have developed an innovative mesoporous nanocatalyst by carefully attaching a 2-aminothiophenol-Cu complex onto functionalized MCM-41. This straightforward synthesis process has yielded a versatile nanocatalyst known for its outstanding efficiency, recyclability, and enhanced stability. The structural integrity of the nanocatalyst was comprehensively analyzed using an array of techniques, including BET (Brunauer-Emmett-Teller) for surface area measurement, ICP (Inductively Coupled Plasma) for metal content determination, EDS (Energy-Dispersive X-ray Spectroscopy) for elemental mapping, XRD (X-ray Diffraction) for crystalline structure elucidation, SEM (Scanning Electron Microscopy), EMA (Elemental Mapping Analysis), TEM (Transmission Electron Microscopy), TGA (Thermogravimetric Analysis), FT-IR (Fourier Transform Infrared Spectroscopy), AFM (Atomic Force Microscopy), and CV (cyclic voltammetry). Subsequently, the catalytic properties of the newly developed MCM-41-CPTEO-2-aminothiophenol-Cu catalyst was evaluated in the synthesis of biphenyls, demonstrating outstanding yields through a Suzuki coupling reaction between phenylboronic acid and aryl halides. Importantly, this reaction was conducted in an environmentally friendly medium. Note the remarkable recyclability of the catalyst, proving its sustainability over six cycles with minimal loss in activity additionally hot filtration test was prepared to examine the stability of this nanocatalyst. This outstanding feature emphasizes the catalyst's potential for long-term, environmentally conscious catalytic applications.

In recent years, several physicochemical methods have been proposed for decolourising textile dyes; however, few have been adopted by the textile industry because of factors such as high cost, low efficiency, and limited applicability to a wide range of dyes. The current study focuses on synthesising algae-mediated Cu and CuO nanocatalysts (Alg-Cu and Alg-CuO) using natural waste materials from green algae. The synthesised Alg-CuO nanocatalyst was characterised and confirmed using SEM, TEM, UV, FT-IR, XRD, XPS, GC-MS, and TGA. An innovative and efficient technique for decolourising dyes through aerobic oxidation was implemented in industrial wastewater treatment. Various hydroxylamine substrates were successfully transformed into the desired aldehydes using an Alg-CuO nanocatalyst. In the process of aerobic oxidation, 2-(2-amino-ethyl)-aminoethanol can be converted into 2-(2-amino-ethyl)acetaldehyde, resulting in 96% product conversion within 4 min. In addition, the synthesised Alg-CuO nanocatalyst was used to investigate the dye decolourisation process using CBB G250 dye. The Alg-CuO nanocatalyst exhibited excellent decolourisation properties; for 20 min, 85% decolourisation of the CBB G250 dye was achieved. As a result, green synthesis is a viable medium for producing Alg-CuO nanocatalysts with high bond energies for dye decolourisation. Finally, the dye and Alg-CuO nanocatalyst was separated and reused for the following process. This method has been used for industrial wastewater treatment.

Materials at the nanoscale show exciting and different properties. In this review, the applications of nanomaterials for modifying the main components of microbial fuel cell (MFC) systems (i.e., electrodes and membranes) and their effect on cell performance are reviewed and critically discussed. Carbon and metal-based nanoparticles and conductive polymers could contribute to the growth of thick anodic and cathodic microbial biofilms, leading to enhanced electron transfer between the electrodes and the biofilm. Extending active surface area, increasing conductivity, and biocompatibility are among the significant attributes of promising nanomaterials used in MFC modifications. The application of nanomaterials in fabricating cathode catalysts (catalyzing oxygen reduction reaction) is also reviewed herein. Among the various nanocatalysts used on the cathode side, metal-based nanocatalysts such as metal oxides and metal-organic frameworks (MOFs) are regarded as inexpensive and high-performance alternatives to the conventionally used high-cost Pt. In addition, polymeric membranes modified with hydrophilic and antibacterial nanoparticles could lead to higher proton conductivity and mitigated biofouling compared to the conventionally used and expensive Nafion. These improvements could lead to more promising cell performance in power generation, wastewater treatment, and nanobiosensing. Future research efforts should also take into account decreasing the production cost of the nanomaterials and the environmental safety aspects of these compounds.

In the last decades, photocatalysis has arisen as a solution to degrade emerging pollutants such as antibiotics. However, the reduced photoactivation of TiO2 under visible radiation constitutes a major drawback because 95% of sunlight radiation is not being used in this process. Thus, it is critical to modify TiO2 nanoparticles to improve the ability to absorb visible radiation from sunlight. This work reports on the synthesis of TiO2 nanoparticles decorated with gold (Au) nanoparticles by deposition-precipitation method for enhanced photocatalytic activity. The produced nanocomposites absorb 40% to 55% more radiation in the visible range than pristine TiO2, the best results being obtained for the synthesis performed at 25 °C and with Au loading of 0.05 to 0.1 wt. %. Experimental tests yielded a higher photocatalytic degradation of 91% and 49% of ciprofloxacin (5 mg/L) under UV and visible radiation, correspondingly. Computational modeling supports the experimental results, showing the ability of Au to bind TiO2 anatase surfaces, the relevant role of Au transferring electrons, and the high affinity of ciprofloxacin to both Au and TiO2 surfaces. Hence, the present work represents a reliable approach to produce efficient photocatalytic materials and an overall contribution in the development of high-performance Au/TiO2 photocatalytic nanostructures through the optimization of the synthesis parameters, photocatalytic conditions, and computational modeling.

Synthesis and characterization of new magnetically recoverable and high-performance nanocatalysts of Pd and Pt Schiff base complexes on magnetite nanoparticles were considered. Catalytic activity of these nanocatalysts was explored in Suzuki and Heck cross coupling reactions. The catalysts can be easily reused fourth consecutive runs without significant loss of catalytic efficiency. Graphical Abstract