Catalytic reduction of 4-nitrophenol and methylene blue pollutants in water by copper and nickel nanoparticles decorated polymer sponges

Reduction-immobilizing strategy of polymer-embedded sub-2 nm Cu nanoparticles with uniform size and distribution responsible for robust catalytic reactions

Polymer-embedded metal nanoparticles are in great demand owing to their unique features, leading to their use in various important applications, including catalysis reactions. However, particle sintering and aggregation are serious drawbacks, resulting in a drastic loss of catalytic activity and recyclability. Herein, a reduction-immobilizing strategy of polymer-embedded sub-2 nm Cu nanoparticles offered highly controlled distribution and nanoparticle size within polymer structures with high fidelity. This work sheds light on the high catalytic performance of nanoparticles that rely on their ultrasmall size and uniform distribution in polymer structures, generating more active sites that result in high efficiency reduction of organic compounds. A catalysis study was carried out for the hydrogenation of nitro compounds, achieving nearly 100% reduction in an extremely short time and remaining stable after 15 consecutive cycles. Furthermore, the catalytic mechanism was demonstrated by density functional theory (DFT) calculations. Notably, the discovery of this facile strategy may enable the remarkable cutting-edge design of catalyst materials with promising performance and stability.

Green NiO nanoparticle-integrated PVA-alginate hydrogel: potent nanocatalyst for efficient reduction of anthropogenic water pollutants

Hydrogel nanocatalyst composed of nickel oxide (NiO) nanoparticles embedded in PVA-alginate hydrogels were potentially explored toward the reduction of anthropogenic water pollutants. The NiO nanoparticles was accomplished via green method using waste pineapple peel extract. The formation of the nanoparticles was affirmed from different analytical techniques such as UV-Vis, FTIR, XRD, TGA, FESEM, and EDS. Spherical NiO nanoparticles were obtained having an average size of 11.5 nm. The nano NiO were then integrated into PVA-alginate hydrogel matrix forming a nanocomposite hydrogel (PVALg@ NiO). The integration of nano NiO rendered an improved thermal stability to the parent hydrogel. The PVALg@ NiO hydrogel was utilized as a catalyst in the reduction of 4-nitrophenol (4-NP), potassium hexacyanoferrate (III), rhodamine B (RhB), methyl orange (MO), and malachite green (MG) in the presence of a reducing agent, i.e., NaBH4. Under optimized conditions, the reduction reactions were completed by 4.0 min and 3.0 min for 4-NP and potassium hexacyanoferrate (III), respectively, and the rate constant was estimated to be 1.14 min-1 and 2.15 min-1. The rate of reduction was found to be faster for the dyes and the respective rate constants were be 0.17 s-1 for RhB, MG and 0.05 s-1 for MO. The PVALg@ NiO hydrogel nanocatalyst demonstrated a recyclability of four runs without any perceptible diminution in its catalytic mettle. The efficacy of the PVALg@ NiO hydrogel nanocatalyst was further examined for the reduction of dyes in real water samples collected from different sources and the results affirm its high catalytic potential. Thus, this study paves the path for the development of a sustainable hydrogel nanocatalyst for reduction of hazardous pollutants in wastewater treatment.

Chitosan-sunflower meal biochar hydrogel incorporated with green synthesized NiO nanoparticles for enhanced catalytic reduction of anthropogenic water pollutants

Anthropogenic activities have been one of the crucial driving factors for water pollution globally, thereby warranting a sustainable strategy for its redressal. In this study, we have developed a hydrogel-biochar nanocomposite for catalytic reduction of water pollutants. To begin with, green synthesis of nickel oxide nanoparticles (NiO NPs) was accomplished from waste kinnow peel extract via the environmentally benign microwave method. The formation of NiO NPs was affirmed from different analytical techniques namely ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS). The FESEM images revealed spherical nature of NiO NPs. The average particle size was found to be 15.61 nm from XRD data. A novel hydrogel-biochar nanocomposite comprising the green NiO NPs, sunflower meal biochar and chitosan was prepared (Cs-biochar@ NiO) and explored as a nanocatalyst towards catalytic reduction of pollutants such as 4-nitrophenol, potassium hexacyanoferrate (III) and organic dyes methyl orange (MO), Congo red (CR), methylene blue (MB) in the presence of a reducing agent, i.e. NaBH4. Under optimized conditions, the reduction reactions were completed by 120 s and 60 s for 4-NP and potassium hexacyanoferrate (III) respectively and the rate constants were estimated to be 0.044 s-1 and 0.110 s-1. The rate of reduction was found to be faster for the dyes and the respective rate constants were 0.213 s-1 for MO, 0.213 s-1 for CR and 0.135 s-1 for MB. The assessment of the nanocatalyst in the reduction of binary dye systems depicted its selectivity towards the anionic dyes CR and MO. The nanocatalyst displayed effective reduction of dyes in real-water samples collected from different sources. Taken altogether, this study validates the design of sustainable hydrogel-biochar nanocatalyst for the efficient reduction of hazardous anthropogenic water pollutants.

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.

A novel, efficient and economical alternative for the removal of toxic organic, inorganic and pathogenic water pollutants using GO-modified PU granular composite

Multicomponent wastewater treatment utilising simple and cost-effective materials and methods is an important research topic. This study has reported the fabrication and utilisation of graphene oxide (GO) embedded granular Polyurethane (PU) (GOPU) adsorbent for the treatment of lead ion (Lead ion (Pb(II)), Methylene blue (MB), and E. coli. PU granules were wrapped with GO flakes to improve hydrophilicity, interaction with polluted water, cation-exchange reaction, and binding of pollutants on its surface. Synthesised GOPU granules were characterised by X-Ray Diffraction (XRD), Raman, Fourier transform infrared (FTIR) spectroscopy, and Scanning electron microscopy (SEM) analysis to ensure the successful synthesis of GO and fabrication of GOPU granules. Further, batch and continuous adsorption processes were studied in different operating conditions to evaluate the performance of GOPU granules in practical applications. The kinetic and isotherm analyses revealed that the adsorption of Lead (Pb(II)) ion and Methylene Blue (MB) dye followed the Freundlich and Langmuir isotherm models, respectively, and they showed good agreement with the Pseudo-second-order kinetic model. The adsorption capacities of GOPU granules for the elimination of Pb(II) and MB dye were about 842 mg/g and 899 mg/g, respectively. Additionally, investigations into the fixed bed column revealed that the adsorption column performed best at a flow rate of 5 mL/min and a bed height of 6 cm. Pb(II) adsorption had a bed uptake capacity (q_bed) of 88 mg/g and percentage removal efficiency (%R) of 76%. Similarly, MB adsorption had a bed uptake capacity of 202 mg/g and a percentage removal efficiency of 71%. A systematic invention on antibacterial activity toward E. coli showed that The GOPU granules have a removal efficiency of about 100% at an exposure of 24 h. These findings indicated the possible use of GOPU granules as promising adsorbents for various water pollutants.

Magnetic alginate-carboxymethyl cellulose to immobilize copper nanoparticles as a green and sustainable catalyst for 4-nitrophenol reduction

In the present work, sustainable green catalysts with high activity, and excellent stability were prepared and thoroughly characterized by XRD, FT-IR, BET, VSM, SEM, EDX, HR-TEM, and TGA techniques. The combined sodium alginate (SA) and carboxymethyl cellulose (CMC) biopolymers were functionalized with Fe₃O₄ nanoparticles to immobilize copper nanoparticles to form Fe₃O₄@SA-CMC-CuNP nanocomposites in batch experiments. Furthermore, the Fe₃O₄@SA-CMC-CuNP nanocomposites were utilized as the heterogeneous catalyst for 4-nitrophenol (4-NP) reduction to 4-aminophenol (4-AP) in the presence of NaBH₄, and the progress of the catalytic reaction was monitored using UV-visible spectrophotometry. The Fe₃O₄@SA-CMC-CuNP nanocomposite exhibited much higher catalytic activity for the 4-nitrophenol reduction reaction than individual components Fe₃O₄ and Fe₃O₄@SA-CMC. The effect of parameters such as the amount of catalyst was evaluated and 30 mg of the catalyst amount with a 95.0% reduction of 4-nitrophenol for 1.5 min was obtained. The effect of reaction temperature was also investigated to find out the activation energy. The analyses of kinetics and thermodynamics were carried out to understand the catalytic behavior. Furthermore, the catalyst can be separated from the reaction system through the usage of a magnet and recycled up to five times without any loss of activity. Therefore, the development of sustainable green catalyst biopolymer-based nanocomposites is promising for new catalysts in the future for treating organic wastewater.

Integrating thermodynamics towards bulk level synthesis of nano Ni catalysts: a green mediated sol–gel auto combustion method

Novel strategy for the environmentally benign bulk level synthesis of nickel nanoparticles.

Gum Hydrocolloids Reinforced Silver Nanoparticle Sponge for Catalytic Degradation of Water Pollutants

The accumulation of organic contaminants including dyes in aquatic systems is of significant environmental concern, necessitating the development of affordable and sustainable materials for the treatment/elimination of these hazardous pollutants. Here, a green synthesis strategy has been used to develop a self-assembled gum kondagogu-sodium alginate bioconjugate sponge adorned with silver nanoparticles, for the first time. The properties of the nanocomposite sponge were then analyzed using FTIR, TGA, SEM, and MicroCT. The ensued biobased sponge exhibited hierarchical microstructure, open cellular pores, good shape memory, and mechanical properties. It merges the attributes of an open cellular porous structure with metal nanoparticles and are envisaged to be deployed as a sustainable catalytic system for reducing contaminants in the aqueous environment. This nanocomposite sponge showed enhanced catalytic effectiveness (k_m values up to 37 min⁻¹ g⁻¹ and 44 min⁻¹ g⁻¹ for methylene blue and 4-nitrophenol, respectively), antibacterial properties, reusability, and biodegradability (65% biodegradation in 28 days).

A comparative study of Cu-anchored 0D and 1D ZnO nanostructures for the reduction of organic pollutants in water

In this work, Cu NPs were loaded at a fixed percentage (5 wt%) on 1D, (1D + 0D) and 0D ZnO nanostructures to investigate the effect of the support morphology on the reduction of organic pollutants in water. The synthesized materials were characterized by high-resolution transmission electron microscopy (HR-TEM), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS). The results reveal that the loading of Cu NPs decreases the optical band gap, and a slight change in the crystallite sizes increases the specific surface area value of the nanocomposites. The TEM images reveal that 1D ZnO has an average width of 44.7 nm and an average length of 211 nm, while 0D ZnO has an average diameter of 54.5 nm. The HR-TEM and XPS data confirm the loading of metallic Cu NPs on the surface of the ZnO nanostructures. The pure ZnO and nanocomposites were tested for 4-nitrophenol (4-NP) reduction in the presence of NaBH4 at room temperature. The obtained results show that pure ZnO nanostructures have no catalytic performance, while the nanocomposites showed good catalytic activities. The catalytic reduction efficiency of 4-NP was found to follow the order of Cu/0DZnO > Cu/(1D + 0D)ZnO > Cu/1DZnO. The complete reduction of 4-NP has been observed to be achievable within 60 s using the Cu/0DZnO nanocomposite, with a k app value of 8.42 min-1 and good recyclability of up to five cycles. This nanocomposite was then applied in the reduction of organic dyes in water; it was found that the reduction rate constants for the methylene blue, Congo red, and acriflavine hydrochloride dyes were 1.4 min-1, 1.2 min-1, and 3.81 min-1, respectively. The high catalytic performance of this nanocomposite may be due to the small particle size, high specific surface area, and the high dispersion of Cu NPs on the surface of ZnO.

Nanoarchitectured Cu based catalysts supported on alginate/glycyl leucine hybrid beads for tainted water treatment

Water pollution reached worrying point due to different dye pollutants which demands an instant solution. One of the best ways to manage water pollutants is their reduction and decolorization to less-toxic and useful compounds. However, reduction process requires an effective, stable, and recyclable catalyst to reduce such pollutants more effectively. Metal nanoparticles (M⁰) are highly effective catalysts but separation of nanoparticles after reaction is difficult and requires a high-speed centrifugation. If loaded on polymer-beads, they can be easily separated from the reaction-mixture. Hearin, alginate/glycyl leucine (AGL) hybrid-beads were prepared, and copper nanoparticles (Cu⁰) were grown on it by simple process. M⁰/AGL bead catalysts were tested toward reducing various toxic compounds. Among all developed composite-beads, the catalytic performance of Cu⁰/AGL was highest in terms of reduction kinetics. After initial screening for different pollutants, Cu⁰/AGL was much more effective for MO reduction, thus, all optimized different parameters i.e., catalyst dosage, stability, amount of reducing-agent and recyclability were experimentally determined. The Cu⁰/AGL showed high-rate constants (k_app) of 0.7566 and 2.9506 min^-1 depending on beads content. The reusability of the Cu⁰/AGL catalysts up to the 7^th cycle has been checked. With the use of AGL as support for the Cu nanoparticles, not only the catalytic activity was retained for longer times during reusability, but it helped in their easy separation.

Carbon Microsphere-Supported Metallic Nickel Nanoparticles as Novel Heterogeneous Catalysts and Their Application for the Reduction of Nitrophenol

Nickel nanoparticles are gaining increasing attention in catalysis due to their versatile catalytic action. A novel, low-cost and facile method was developed in this work to synthesize carbon microsphere-supported metallic nickel nanoparticles (Ni-NP/C) for heterogeneous catalysis. The synthesis was based on carbonizing a polystyrene-based cation exchange resin loaded with nickel ions at temperatures between 500 and 1000 °C. The decomposition of the nickel-organic framework resulted in both Ni-NP and carbon microsphere formation. The phase composition, morphology and surface area of these Ni-NP/C microspheres were characterized by powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy and BET analysis. Elemental nickel was found to be the only metal containing phase; fcc-Ni coexisted with hcp-Ni at carbonization temperatures between 500 and 700 °C, and fcc-Ni was the only metallic phase at 800–1000 °C. Graphitization and carbon nanotube formation were observed at high temperatures. The catalytic activity of Ni-NP/C was tested in the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride, and Ni-NP/C was proved to be an efficient catalyst in this reaction. The relatively easy and scalable synthetic method, as well as the easy separation and catalytic activity of Ni-NP/C, provide a viable alternative to existing nickel nanocatalysts in future applications.